You may contact a Proposer directly about a specific project or contact the Postgraduate Admissions Secretary with general enquiries.

Title LOT Groups
Group(s) Algebra and Analysis
Proposer(s) Dr Martin Edjvet
Description

A labelled oriented graph is a connected, finite, directed graph in which each edge is labelled by a vertex. A labelled oriented graph gives rise to a group presentation whose generating set is the vertex set and whose defining relations say that the initial vertex of an edge is conjugated to its terminal vertex by its label. A group G is a LOG group if it has such a presentation. A LOT group is a LOG group for which the graph is a tree. Every classical knot group is a LOT group. In fact LOT groups are characterised as the fundamental groups of ribbon n-discs in Dn+2.The most significant outstanding question on the topology of ribbon discs is: are they aspherical? The expected answer is yes. Howie has shown that it is sufficient to prove that LOT groups are locally indicable. An interesting research project would be to study the following two questions: is every LOT group locally indicable; is every LOT group an HNN extension of a finitely presented group?

Relevant Publications
  • J. Howie, On the asphericity of ribbon disc complements, Trans Amer Math Soc, 289, 281-302, 1985
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Title Equations over groups
Group(s) Algebra and Analysis
Proposer(s) Dr Martin Edjvet
Description

Let G be a group. An expression of the form g1 t … gk t=1 where each gi is an element of G and the unknown t is distinct from G is called an equation over G. The equation is said to have a solution if G embeds in a group H containing an element h for which the equation holds. There are two unsettled conjectures here. The first states that if G is torsion-free then any equation over G has a solution. The second due to Kervaire and Laudenbach states that if the sum of the exponents of t is non-zero then the equation has a solution. There have been many papers published in this area. The methods are geometric making use of diagrams over groups and curvature. This subject is related to questions of asphericity of groups which could also be studied.

Relevant Publications
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Title Quadratic forms and forms of higher degree, nonassociative algebras
Group(s) Algebra and Analysis
Proposer(s) Dr Susanne Pumpluen
Description

Dr. Pumplün currently studies forms of higher degree over fields, i.e. homogeneous polynomials of degree d greater than two (mostly over fields of characteristic zero or greater than d). The theory of these forms is much more complex than the theory of homogeneous polynomials of degree two (also called quadratic forms). Partly this can be explained by the fact that not every form of degree greater than two can be “diagonalized”, as it is the case for quadratic forms over fields of characteristic not two. (Every quadratic form over a field of characteristic not two can be represented by a matrix which only has non-zero entries on its diagonal, i.e. is diagonal.)

A modern uniform theory for these forms like it exists for quadratic and symmetric bilinear forms (cf. the standard reference books by Scharlau or Lam) seems to be missing, or only exists to some extent. Many questions which have been settled for quadratic forms quite some time ago are still open as as soon as one looks at forms of higher degree. It would be desirable to obtain a better understanding of the behaviour of these forms. First results have been obtained. Another related problem would be if one can describe forms of higher degree over algebraic varieties, for instance over curves of genus zero or one.

Dr. Pumplün is also studying nonassociative algebras over rings, fields, or algebraic varieties. Over rings, as modules these algebras are finitely generated over the base ring. Their algebra structure, i.e. the multiplication, is given by any bilinear map, such that the distributive laws are satisfied. In other words, the multiplication is not required to be associative any more, as it is usually the case when one talks about algebras. Her techniques for investigating certain classes of nonassociative algebras (e.g. octonion algebras) include elementary algebraic geometry. One of her next projects will be the investigation of octonion algebras and of exceptional simple Jordan algebras (also called Albert algebras) over curves of genus zero or one. Results on these algebras would also imply new insights on certain algebraic groups related to them.

Another interesting area is the study of quadratic or bilinear forms over algebraic varieties. There are only few varieties of dimension greater than one where the Witt ring is known. One well-known result is due to Arason (1980). It says that the Witt ring of projective space is always isomorphic to the Witt ring of the base field.

If you want to investigate algebras or forms over algebraic varieties, this will always involve the study of vector bundles of that variety. However, even for algebraically closed base fields it is usually very rare to have an explicit classification of the vector bundles. Hence, most known results on quadratic (or symmetric bilinear) forms are about the Witt ring of quadratic forms, e.g. the Witt ring of affine space, the projective space, of elliptic or hyperelliptic curves. An explicit classification of symmetric bilinear spaces is in general impossible because it would involve an explicit classification of the corresponding vector bundles (which admit a form). There are still lots of interesting open problems in this area, both easier and very difficult ones.

Relevant Publications
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Title Cohomology Theories for Algebraic Varieties
Group(s) Algebra and Analysis
Proposer(s) Dr Alexander Vishik
Description

After the groundbreaking works of V. Voevodsky, it became possible to work with algebraic varieties by completely topological methods. An important role in this context is played by the so-called Generalized Cohomology Theories. This includes classical algebraic K-theory, but also a rather modern (and more universal) Algebraic Cobordism theory. The study of such theories and cohomological operations on them is a fascinating subject. It has many applications to the classical questions from algebraic geometry, quadratic form theory, and other areas. One can mention, for example: the Rost degree formula, the problem of smoothing algebraic cycles, and u-invariants of fields. This is a new and rapidly developing area that offers many promising directions of research.

Relevant Publications
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Title Quadratic Forms: Interaction of Algebra, Geometry and Topology
Group(s) Algebra and Analysis
Proposer(s) Dr Alexander Vishik
Description

From the beginning of the 20th century it was observed that quadratic forms over a given field carry a lot of information about that field. This led to the creation of rich and beautiful Algebraic Theory of Quadratic Forms that gave rise to many interesting problems. But it became apparent that quite a few of these problems can hardly be approached by means of the theory itself. In many cases, solutions were obtained by invoking arguments of a geometric nature. It was observed that one of the central questions on which quadratic form theory depends is the so-called "Milnor Conjecture". This conjecture, as we now understand it, relates quadratic forms over a field to the so-called motivic cohomology of this field. Once proven, this would provide a lot of information about quadratic forms and about motives (algebro-geometric analogues of topological objects) as well. The Milnor Conjecture was finally settled affirmatively by V. Voevodsky in 1996 by means of creating a completely new world, where one can work with algebraic varieties with the same flexibility as with topological spaces. Later, this was enhanced by F. Morel, and now we know that quadratic forms compute not just the cohomology of a point in the "algebro geometric homotopic world", but also the so-called stable homotopy groups of spheres as well. It is thus no wonder that these objects indeed have nice properties.

Therefore, by studying quadratic forms, one actually studies the stable homotopy groups of spheres, which should shed light on the classical problem of computing such groups (one of the central questions in mathematics as a whole). So it is fair to say that the modern theory of quadratic forms relies heavily on the application of motivic topological methods. On the other hand, the Algebraic Theory of Quadratic Forms provides a possibility to view and approach the motivic world from a rather elementary point of view, and to test the new techniques developed there. This makes quadratic form theory an invaluable and easy access point to the forefront of modern mathematics.

Relevant Publications
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Title Regularity conditions for Banach function algebras
Group(s) Algebra and Analysis
Proposer(s) Dr Joel Feinstein
Description

Banach function algebras are complete normed algebras of bounded, continuous, complex-valued functions defined on topological spaces. There are very many different examples with a huge variety of properties. Two contrasting examples are the algebra of all continuous complex-valued functions on the closed unit disc, and the subalgebra of this algebra consisting of those functions which are continuous on the closed disc and analytic on the interior of the disc. In the second of these algebras, any function which is zero throughout some non-empty open set must be constantly zero. This is very much not the case in the bigger algebra: indeed Urysohn’s lemma shows that for any two disjoint closed subsets of the closed disc, there is a continuous, complex-valued function defined on the disc which is constantly 0 on one closed set and constantly 1 on the other (algebras of this type are called regular algebras).

Most Banach function algebras have some features in common with one or the other of these two algebras. The aim of this project is to investigate a variety of conditions, especially regularity conditions, for Banach function algebras, and to relate these conditions to each other, and to other important conditions that Banach function algebras may satisfy.

Regularity conditions have important applications in several areas of functional analysis, including automatic continuity theory and the theory of Wedderburn decompositions. There is also a close connection between regularity and the theory of decomposable operators on Banach spaces.

Relevant Publications
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Title Properties of Banach function algebras and their extensions
Group(s) Algebra and Analysis
Proposer(s) Dr Joel Feinstein
Description

Banach function algebras are complete normed algebras of bounded continuous, complex-valued functions defined on topological spaces. There are very many different examples with a huge variety of properties. Two contrasting examples are the algebra of all continuous complex-valued functions on the closed unit disc, and the subalgebra of this algebra consisting of those functions which are continuous on the closed disc and analytic on the interior of the disc. In the second of these algebras, any function which is zero throughout some non-empty open set must be constantly zero. This is very much not the case in the bigger algebra: indeed Urysohn’s lemma shows that for any two disjoint closed subsets of the closed disc, there is a continuous, complex-valued function defined on the disc which is constantly 0 on one closed set and constantly 1 on the other (algebras of this type are called regular algebras).

Most Banach function algebras have some features in common with one or the other of these two algebras. The aim of this project is to investigate a variety of conditions (including regularity conditions) for Banach function algebras, to relate these conditions to each other, and to other important conditions that Banach function algebras may satisfy, and to investigate the preservation or introduction of these conditions when you form various types of extension of the algebras (especially ‘algebraic’ extensions such as Arens-Hoffman or Cole extensions).

Relevant Publications
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Title Meromorphic Function Theory
Group(s) Algebra and Analysis
Proposer(s) Prof James Langley
Description

A meromorphic function is basically one convergent power series divided by another: such functions arise in many branches of pure and applied mathematics. Professor Langley has supervised ten PhD students to date, and specific areas covered by his research include the following.

  • Zeros of derivatives. There is a long history of work on these questions which can be viewed as natural generalizations of the classical Picard theorem to the effect that an entire function which omits two values is a constant. Langley’s best known result is probably his 1993 proof of Hayman’s 1959 conjecture on the zeros of a meromorphic function and its second derivative. More recently, Langley, Bergweiler and Eremenko  settled the last outstanding case of a conjecture of Wiman from 1911 concerning the derivatives of real entire functions, and Langley has extended much of this work to meromorphic functions.
  • Differential equations in the complex domain, in particular the growth and oscillation of solutions of linear differential equations. This has been an active area in recent years and there are potential applications.
  • Properties of compositions of entire functions. This area has connections to complex dynamics, in which the famous Julia and Mandelbrot sets arise, and which has been a very successful field of research in recent years.
  • Critical points of potentials associated with distributions of charged points and wires, and zeros of related meromorphic functions. This research was awarded an EPSRC Project Studentship in 2003-4.
Relevant Publications
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Title Compensated convex transforms and their applications
Group(s) Algebra and Analysis
Proposer(s) Prof Kewei Zhang
Description

This aim of the project is to further develop the theory and numerical methods for compensated convex transforms introduced by the proposer and to apply these tools to approximations, interpolations, reconstructions, image processing and singularity extraction problems arising from applied sciences and engineering.

Relevant Publications
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Title Endomorphisms of Banach algebras
Group(s) Algebra and Analysis
Proposer(s) Dr Joel Feinstein
Description

Compact endomorphisms of commutative, semisimple Banach algebras have been extensively studied since the seminal work of Kamowitz dating back to 1978. More recently the theory has expanded to include power compact, Riesz and quasicompact endomorphisms of commutative, semiprime Banach algebras.

This project concerns the classification of the various types of endomorphism for specific algebras, with the aid of the general theory. The algebras studied will include algebras of differentiable functions on compact plane sets, and related algebras such as Lipschitz algebras. 

Relevant Publications
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Title Iteration of quasiregular mappings
Group(s) Algebra and Analysis
Proposer(s) Dr Daniel Nicks
Description

Complex dynamics is the study of iteration of analytic functions on the complex plane. A rich mathematical structure is seen to emerge amidst the chaotic behaviour. Its appeal is enhanced by the intricate nature of the Julia sets that arise, and fascinating images of these fractal sets are widely admired.

Quasiregular mappings of n-dimensional real space generalise analytic functions on the complex plane. Roughly, a mapping is called quasiregular if it locally distorts space by only a bounded amount, so that small spheres are mapped to small ellipsoids. This is more flexible than the situation with analytic functions, where the Cauchy-Riemann equations tell us that infinitesimally small circles are mapped to small circles.

There are many similarities between the behaviour of analytic functions and quasiregular mappings. One can therefore attempt to develop a theory of quasiregular iteration parallel to the results of complex dynamics. Such a theory is just beginning to emerge, lying between the well-studied analytic case (where many powerful tools from complex analysis are available) and general iteration in several real variables, which is much less well-understood.

The problems studied will be inspired and guided by existing results in complex dynamics. For example, we can ask questions about the ‘escaping set’ of a function – this is the set of all starting points from which the sequence of iterates tends to infinity. One of the challenges we encounter is that as we increase the number of iterations of a quasiregular mapping, the amount of local distortion may become increasingly large.

This is very much a pure mathematics project and will appeal to someone who enjoys topics such as real analysis, complex analysis, metric spaces or discrete dynamical systems.

Relevant Publications
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Title Hydrodynamic limit of Ginzburg-Landau vortices
Group(s) Algebra and Analysis
Proposer(s) Dr Matthias Kurzke
Description

Many quantum physical systems (for example superconductors, superfluids, Bose-Einstein condensates) exhibit vortex states that can be described by Ginzburg-Landau type functionals. For various equations of motion for the physical systems, the dynamical behaviour of finite numbers of vortices has been rigorously established. We are interested in studying systems with many vortices (this is the typical situation in a superconductor). In the hydrodynamic limit, one obtains an evolution equation for the vortex density. Typically, these equations are relatives of the Euler equations of incompressible fluids: for the Gross-Pitaevskii equation (a nonlinear Schrödinger equation), one obtains Euler, for the time-dependent Ginzburg-Landau equation (a nonlinear parabolic equation), one obtains a dissipative variant of the Euler equations.

There are at least two interesting directions to pursue here. One is to extend recent analytical progress for the Euler equation to the dissipative case. Another one is to obtain hydrodynamic limits for other motion laws (for example, mixed or wave-type motions).

This is a project mostly about analysis of PDEs, possibly with some numerical simulation involved.

Relevant Publications
  • M Kurzke, D Spirn: Vortex liquids and the Ginzburg-Landau equation. arXiv:1105.4781
  • R Jerrard, D Spirn: Hydrodynamic limit of the Gross-Pitaevskii equation. arXiv:1310.4558
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Title Dynamics of boundary singularities
Group(s) Algebra and Analysis
Proposer(s) Dr Matthias Kurzke
Description

Some physical problems can be modelled by a function or vector field with a near discontinuity at a point. Specific examples include boundary vortices in thin magnetic films, and some types of dislocations in crystals. Typical static configurations can be found by minimizing certain energy functionals. As the core size of the singularity tends to zero, these energy functionals are usually well described by a limiting functional defined on point singularities.

This project investigates how to obtain dynamical laws for singularities (typically in the form of ordinary differential equations) from the partial differential equations that describe the evolution of the vector field. For some such problems, results for interior singularities are known, but their boundary counterparts are still lacking.

This project requires some background in the calculus of variations and the theory of partial differential equations.

Relevant Publications
  • M Kurzke: The gradient flow motion of boundary vortices Ann. Inst. H. Poincaré Anal. Non Linéaire. 24(1), 91-112
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Title Where graphs and partial differential equations meet
Group(s) Algebra and Analysis
Proposer(s) Dr Yves van Gennip
Description

Many problems in image analysis and data analysis can be represented mathematically as a network based
problems. Examples are image segmentation and data clustering. Traditionally these kind of graph based
problems have been tackled by combinatorial algorithms, but in recent years interest has grown in
applying ideas from variational methods and nonlinear partial differential equations (PDEs) to such
problems.

This has lead to an interesting mix of theoretical questions (what is the dynamics on the network induced
by these methods? which correspondences between PDE quantities and graph quantities can we find, e.g.
total variation, graph cut, curvature...?) and practical applications.

This project will investigate graph curvature and related quantities and make links to established
results in PDE theory.

Relevant Publications
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Title Graph limits for faster computations
Group(s) Algebra and Analysis
Proposer(s) Dr Yves van Gennip
Description

Many problems in image analysis and data analysis, such as image segmentation or data clustering, require
the computation of pairwise similarity scores between nodes of a network. When the image or data set is
large, the computational cost is very prohibitive. One way to deal with this problem is to compute only a
subset of all the pairwise comparisons and use those to approximate the others.

Recent developments in the theory of (dynamics on) graph limits offer the hope that this subset can be
chosen in such a way that the resulting dynamics of the segmentation or clustering algorithm is a very
good approximation of the dynamics on the full graph.

This project will investigate this possibility and can be taken in a theoretical and/or application
oriented direction.

Relevant Publications
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Title Vectorial Calculus of Variations, Material Microstructure, Forward-Backward Diffusion Equations and Coercivity Problems
Group(s) Algebra and Analysis, Algebra and Analysis
Proposer(s) Prof Kewei Zhang
Description

This aim of the project is to solve problems in vectorial calculus of variations, forward-backward diffusion equations, partial differential inclusions and coercivity problems for elliptic systems. These problems are motivated from the variational models for material microstructure, image processing and elasticity theory. Methods involve quasiconvex functions, quasiconvex envelope, quasiconvex hull, Young measure, weak convergence in Sobolev spaces, elliptic and parabolic partial differential equations, and other analytic and geometric tools.

Relevant Publications
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Title Mathematical image analysis of 4D X-ray microtomography data for crack propagation in aluminium wire bonds in power electronics
Group(s) Algebra and Analysis, Industrial and Applied Mathematics
Proposer(s) Dr Yves van Gennip
Description

Supervised by Dr Yves van Gennip and Dr Pearl Agyakwa

 

In this project we will develop mathematical image processing methods for the analysis of 4D (3d+time) X-ray microtomography data of wire bonds [1].

 

Wire bonds are an essential but life-limiting component of most power electronic modules, which are critical for energy conversion in applications like renewable energy generation and transport.

 

The key issue we will examine is how we can use mathematical image processing and image analysis techniques to study how defects in wire bonds arise and evolve under operating conditions; this will facilitate more accurate lifetime prediction.

Relevant Publications
  • [1] Agyakwa et al., “A non-destructive study of crack development during thermal cycling of Al wire bonds using x-ray computed tomography
  • [2] Brune C., “4D imaging in tomography and optical nanoscopy”, PhD thesis, University of Münster (2010)
  • [3] van Gennip, Y., Athavale, P., Gilles, J. and Choksi, R., 2015, "A Regularization Approach to Blind Deblurring and Denoising of QR Barcodes”, IEEE Transactions on Image Processing, 24(9), 2864-2873
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3D X-ray microtomography provides non-destructive observations of defect growth, which allows the same wire bond to be evaluated over its lifetime, affording invaluable new insights into a still insufficiently understood process. 

 

Analysis and full exploitation of the useful information contained within these large datasets is nontrivial and requires advanced mathematical techniques [2,3]. A major challenge is the ability to subsample compressible information without losing informative data features, to improve temporal accuracy.

 

Our goal is to construct new mathematical imaging and data analysis methods for evaluating 2D and 3D tomography data for the same wire bond specimen at various stages of wear-out during its lifetime, to better understand the degradation mechanism(s). This will include methods for denoising of data, detection and segmentation of the wires and their defects in the tomography images, and image registration to quantify the wire deformations that occur over time.

Title Crystallisation in polymers
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Richard Graham
Description

Polymers are very long chain molecules and many of their unique properties depend upon their long chain nature. Like simple fluids many polymer fluids crystallise when cooled. However, the crystallisation process is complicated by the way the constituent chains are connected, leading to many curious and unexplained phenomena. Furthermore, if a polymer fluid is placed under flow, this strongly affects both the ease with which the polymer crystallises and the arrangement of the polymer chains within the resulting crystal. This project will develop and solve models for polymer dynamics and phase transitions using a range of analytical, numerical and stochastic techniques, with the ultimate aim of improving our understanding of polymer crystallisation. The project offers the opportunity to collaborate with a wide range of scientists working in the field, including several world-leading experimental groups.

Relevant Publications
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Title Dynamics of entangled polymers
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Richard Graham
Description

Polymers are extraordinarily long molecules, made out of chains of simpler molecules. They occur everywhere in our everyday lives, including in the DNA chains that make up our genetics, in many high-tech consumer products and in the simple plastic bag. Often these applications depend crucially on the way that the polymer chains move. This is especially true in concentrated polymer liquids, where the chain dynamics are controlled by how the chains become entangled with each other. A powerful mathematical framework for describing these entangled systems has been under development for some time now, but the ideas have yet to be fully developed, tested and exploited in practical applications. Working on this PhD project will give the opportunity to train in a wide range of mathematical techniques including analytical work, numerical computations and stochastic simulation and to apply these to problems of real practical impact. This lively research field involves mathematicians, scientists and engineers and a keenness to learn from and co-operate with researchers from a range of backgrounds would be a real asset in this project.

Relevant Publications
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Title Instabilities of fronts
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Cox, Dr Paul Matthews
Description

Chemical reactions often start at a point and spread through a reactant, much as a fire spreads through combustible material. The advancing zone in which the reactions take place is called a reaction front. In the simplest cases, the reaction front is smooth (flat, cylindrical or spherical), but it may develop irregularities due to instability. Sometimes the instability is so strong that it destroys the front itself; in other cases, it just results in a slight modulation to the front shape. This project involves studying a partial differential equation, the Nikolaevskiy equation, that describes the nonlinear development of the instability of a front. Numerical simulations of the Nikolaevskiy equation show highly complicated, chaotic solutions. This project will involve a mix of numerical simulations and analytical work to understand the behaviour of the Nikolaevskiy equation and of front instabilities in general.

Relevant Publications
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Title Power converters
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Cox, Dr Stephen Creagh
Description

In a wide range of applications, it is necessary to convert one electrical power supply to another, of different voltage or frequency. Power converters are devices which achieve this, but they often suffer highly undesirable instabilities, which significantly compromise their operation. The goal of this project is to develop mathematical models for existing power converter technologies and to use these to provide a detailed description of their operation and a thorough understanding of the instability. Through mathematical modelling, it may prove possible to improve existing power converter designs to reduce or eliminate the stability problems! This project will be theoretical in nature, relying largely on analytical and numerical techniques for differential equations, and will involve significant interaction with the Power Electronics Group in the Department of Electrical and Electronic Engineering.

Relevant Publications
  • S M Cox and J C Clare Nonlinear development of matrix-converter instabilities. Journal of Engineering Mathematics 67 (2010) 241-259.
  • S M Cox and S C Creagh Voltage and current spectra for matrix power converters. SIAM Journal on Applied Mathematics 69 (2009) 1415-1437.
  • S M Cox Voltage and current spectra for a single-phase voltage-source inverter. IMA Journal of Applied Mathematics 74 (2009) 782-805.
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Title Class-D audio amplifiers
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Cox, Dr Stephen Creagh
Description

The holy grail for an audiophile is distortion-free reproduction of sound by amplifier and loudspeaker. This project concerns the mathematical modelling and analysis of class-D audio amplifiers, which are highly efficient and capable of very low distortion. Designs for such amplifiers have been known for over 50 years, but only much more recently have electronic components been up to the job, making class-D amplifiers a reality. (Class-D amplifiers rely on very high frequency – around 1MHz – sampling of the input signal, and so test their components to the limit.) Unfortunately, while the standard class-D design offers zero distortion, it has poor noise characteristics; when the design is modified by adding negative feedback to reduce the noise, the amplifier distorts. By a further modification to the design it is possible to eliminate (most of) the distortion. This project involves modelling various class-D designs and determining their distortion characteristics, with the aim of reducing the distortion. The project will be largely analytical, applying asymptotic methods and computer algebra to solve the mathematical models. Simulations in matlab or maple will be used to test the predictions of the mathematical models. 

Relevant Publications
  • J Yu, M T Tan, S M Cox and W L Goh Time-domain analysis of intermodulation distortion of closed-loop Class D amplifiers. IEEE Transactions on Power Electronics 27 (2012) 2453-2461.
  • S M Cox, C K Lam and M T Tan A second-order PWM-in/PWM-out class-D audio amplifier. IMA Journal of Applied Mathematics (2011).
  • S M Cox, M T Tan and J Yu A second-order class-D audio amplifier. SIAM Journal on Applied Mathematics 71 (2011) 270-287.
  • S M Cox and B H Candy Class-D audio amplifiers with negative feedback. SIAM Journal on Applied Mathematics 66 (2005) 468-488.
  • S M Cox and S C Creagh Voltage and current spectra for matrix power converters. SIAM Journal on Applied Mathematics 69 (2009) 1415-1437.
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Title Mathematical modelling and analysis of composite materials and structures
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Konstantinos Soldatos
Description

Nottingham has established and maintained, for more than half a century, world-wide research leadership in developing the Continuum Theory of fibre-reinforced materials and structures. Namely, a theoretical mechanics research subject with traditional interests to engineering and, more recently, to biological material applications. The subject covers extensive research areas of mathematical modelling and analysis which are of indissoluble adherence to basic understanding and prediction of the elastic, plastic, visco-elastic or even viscous (fluid-type) behaviour observed during either manufacturing or real life performance of anisotropic, composite materials and structural components.

Typical research projects available in this as well as in other relevant research subjects are related with the following interconnected areas:

  • Linearly and non-linearly elastic, static and dynamic analysis of homogeneous and inhomogeneous, anisotropic, solid structures and structural components;
  • Forming flow (process modelling) of fibre-reinforced viscous resins;
  • Plastic behaviour modelling as well as study of failure mechanisms/modes of fibrous-composites;
  • Mass-growth modelling of soft and hard tissue, such as human nail and hair.  
  • Mathematical modelling and analysis of the behaviour of thin walled, anisotropic structures in terms of high-order, linear or non-linear, ordinary and partial differential equations;
  • Development and/or use of various analytical, semi-analytical and/or numerical mathematical methods suitable for solving the sets of differential equations which emerge in the above research areas.

The large variety of topics and relevant problems emerging in these subjects of Theoretical Mechanics and Applied Mathematics allow considerable flexibility in the formation of PhD projects. A particular PhD project may accordingly be formed/designed around the strong subjects of knowledge of a potential post-graduate student. The candidate’s relevant co-operation is accordingly desirable and, as such, will be appreciated at the initial, but also at later stages of tentative research collaboration. 

Relevant Publications
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Title Dynamics of coupled nonlinear oscillators
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Paul Matthews
Description

Coupled oscillators arise in many branches of science and technology and also have applications to biological systems. One spectacular example is swarms of fireflies that flash in synchrony. This research field is an expanding area in applied mathematics because of the many applications within physics and biology and because of the variety of behaviour which such systems can exhibit. Recent work on coupled oscillators has revealed some interesting novel results: nonlinear oscillators can synchronise to a common oscillation frequency even if they have different natural frequencies, provided the coupling is above some threshold; the breakdown of synchronisation as the coupling strength decreases involves periodic behaviour and chaos. The project involves extending and improving this work in two ways. First, the oscillator model used in earlier work was simple and idealised; the model will be refined to make it more realistic.

Second, most earlier work used a simple linear global coupling so that each oscillator is equally coupled to all of the others. In most practical examples this is not the case and a coupling law over a two- or three-dimensional lattice would be more appropriate, with stronger coupling between nearer pairs of oscillators. The research will be carried out using a combination of numerical and analytical techniques.

Relevant Publications
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Title Dynamo action in convection
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Paul Matthews
Description

The magnetic fields of the Earth and Sun are maintained by dynamo action. Fluid motions are generated by thermal convection. The kinetic energy of these fluid motions is then converted to magnetic energy, in a manner similar to that of a bicycle dynamo. Dynamo theory studies how this conversion takes place. It is known that in order for a dynamo to work efficiently, the fluid flow must exhibit chaos.

This project will investigate dynamo action in convection, using 3D numerical simulation of the equations for the fluid motion and the magnetic field. An existing computer program will be used to study the dynamo problem. A sequence of numerical simulations will be carried out to determine

  1. the conditions under which convection is able to generate a magnetic field,
  2. whether rotation is necessary or advantageous for dynamo action,
  3. the underlying topological stretching mechanism responsible for the magnetic field generation.

The project is also suitable for analytical work, either based on an asymptotic analysis of the equations, or in investigating or proving 'anti-dynamo' theorems.

Relevant Publications
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Title Nonlinear penetrative convection
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Paul Matthews
Description

The phenomenon of convection, in which heat is transferred by fluid motion, occurs very commonly in nature. Examples include in the Earth's atmosphere, the interior of the Sun, the Earth's liquid outer core, lakes and oceans. The most commonly used mathematical model for convection assumes that a layer of fluid is bounded above and below by boundaries that are maintained at a fixed temperature. This is not a good model for most of the environmental applications, where typically part of the fluid layer is thermally unstable and part is stable. Convection in the unstable layer overshoots and penetrates into the stable layer. This phenomenon, known as 'penetrative convection', has received relatively little investigation. The research project will study penetrative convection in the nonlinear regime. An existing computer program will be adapted to investigate penetrative convection numerically, and analytical work will be carried out using asymptotic methods and methods of bifurcation theory. In particular, the extent of penetration into the stable layer and the possibility of instability to a mean flow will be explored.

Relevant Publications
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Title Coupling between optical components
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Creagh
Description

Evanescent coupling between different optical components is a very important process in optical communications. In this effect, light travelling along an optical fibre effectively spills out a little bit into the region of space immediately surrounding the fibre itself and can then leak into and become captured by other, nearby optical components. Among other uses, this mechanism forms a basis for optical switches, which transfer light from one fibre to another, and for wavelength filters, which selectively transmit or redirect light in only certain frequency ranges.

This project will investigate the coupling between cylindrical and spherical optical components in two and three dimensions using the geometry of the underlying ray solutions. The aim will be to exploit and generalise approximations which have been developed in the context of quantum waves but which should be equally applicable to the optics problem.

Relevant Publications
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Title Is Periodic Behaviour an Emergent Phenomenon?
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Keith Hopcraft
Description

Periodic behaviours can be described with great power and economy using the rather simple mathematical machinery associated with wave phenomena. However periodic effects can also be ‘observed’ in collections of discrete objects, be they individuals sending emails, fire-flies signaling to attract mates, synapses firing in the brain or photons emerging from a cavity. The manifestation of periodicity requires both a dynamical process and a ‘medium’ in which it operates and the project will seek to identify the essential properties of the dynamics and the structure of the medium required to do this without invoking the ideas of the continuum, determinism or reversibility.

A very simple but surprisingly rich model has been constructed, that involves purely random dynamics acting on a graph, which nevertheless exhibits amorphous, coherent and collapsed states as a single control parameter is changed. The coherent states indeed do exhibit periodic behaviours, and the criteria for this emergence to occur have been identified. Periodicity requires a minimum of three nodes in the graph, for there to be a bias in the direction for flow of information around the network and for the control parameter to exceed a threshold. It also requires the concept of ‘action at a distance’, which is familiar to any field theory. The project will investigate some of the other emergent properties this model possesses, before seeing whether the assumption of a field can be relaxed by considering the self-interaction of a node’s dynamics.

Relevant Publications
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Title Modeling acoustic emission energy propagation
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Creagh, Prof Gregor Tanner
Description

This project will develop modelling techniques to predict acoustic emissions radiated from a water jet hitting a target object and subsequently reverberating within the structure. The approach taken will be to exploit dynamical systems and ray-propagation approaches developed in the context of wave and quantum chaos. The source is complex and statistically characterized in this scenario, so ray-tracing techniques must be adapted to predict features such as average intensities and correlations rather than the field amplitude itself.

The motivation for this project is provided by manufacturing processes in which such water jets are used to create deformation or attrition on the target object, and will be undertaken in collaboration with Dr Amir Rabani of the School of Mechanical, Materials and Manufacturing Engineering. In the experiments, high-energy fluid jet milling where a multi phase media is used as the source of attrition is an example of such processes. These deformations or attritions are primarily due to the mechanical energy applied to the target object. This mechanical energy propagates within the target object in the shape of high frequency elastic and plastic waves that can be picked up using acoustic emission sensors [1]. 

Modeling the propagation of the mechanical energy of the propagating waves and their attenuation can provide valuable information about the applied energy to the target object by the source. This information can potentially provide means to monitor/control the deformation or attrition process of the target object. The applications of the acoustic emission energy propagation model can go beyond the manufacturing arena and can be used in condition monitoring to diagnose the causes of deformations and attritions. This provides measures to take fail preventative actions that other methods such as non-destructive evaluation (NDE) methods fail to provide.  

 

References:

[1] Rabani, A., Marinescu, I., & Axinte, D. (2012). Acoustic emission energy transfer rate: a method for monitoring abrasive waterjet milling. International journal of machine tools and Manufacture, 61, 80-89.

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Title Solitons in higher dimensions
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Jonathan Wattis
Description

The localisation of energy and its transport is of great physical interest in many applications. The mechanisms by which this occurs have been widely studied in one-dimensional systems; however, in two- and three-dimensional systems a greater variety of waves and wave phenomena can be observed; for example, waves can be localised in one or both directions.

This project will start with an analysis of the nonlinear Schrodinger equation (NLS) in higher space dimensions, and with more general nonlinearities (that is, not just $\gamma=1$). Current interest in the Bose-Einstein Condensates which are being investigated in the School of Physics and Astronomy at Nottingham makes this topic particularly timely and relevant.

The NLS equation also arises in the study of astrophysical gas clouds, and in the reduction of other nonlinear wave equations using small amplitude asymptotic expansions. For example, the reduction of the equations of motion for atoms in a crystal lattice; this application is particularly intriguing since the lattice structure defines special directions, which numerical simulations show are favoured by travelling waves. Also the motion of a wave through a hexagonal arrangement of atoms will differ from that through a square array of atoms. The project will involve a combination of theoretical and numerical techniques to the study such systems.

Relevant Publications
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Title Modelling the vibro-acoustic response of complex structures
Group(s) Industrial and Applied Mathematics
Proposer(s) Prof Gregor Tanner
Description

The vibro-acoustic response of mechanical structures (cars, airplanes, ...) can in general be well approximated in terms of linear wave equations. Standard numerical solution methods comprise the finite or boundary element method (FEM, BEM) in the low frequency regime and so-called Statistical Energy Analysis (SEA) in the high-frequency limit. Major computational challenges are posed by so-called mid-frequency problems - that is, composite structures where the local wave length may vary by orders of magnitude across the components.

Recently, I propsed a set of new methods based on ideas from wave chaos (also known as quantum chaos) theory.  Starting from the phase space flow of the underlying - generally chaotic - ray dynamics, the new method called Dynamical Energy Analysis (DEA) interpolates between SEA and ray tracing containing both these methods as limiting cases. Within the new theory SEA is identified as a low resolution ray tracing algorithm and typical SEA assumptions can be quantified in terms of the properties of the ray dynamics. I have furthermore developed a hybrid SEA/FEM method based on random wave model assumptions for the short-wavelength components. This makes it possible to tackle mid-frequency problems under certain constraints on the geometry of the structure.

The PhD project wil deal with extending these techniques towards a DEA/FEM hybrid method as well as  considering FEM formulations of the method. The work will comprise a mix of analytic and numerical skills and will be conducted in close collaboration with our industrial partners inuTech GmbH, Nurenberg, Germany and Jaguar/landrover, Gaydon, UK.

Relevant Publications
  • Wave chaos in acoustics and elasticity, G. Tanner and N. Soendergaard, J. Phys. A 40, R443 - R509 (2007).
  • Dynamical Energy Analysis - determining wave energy distributions in complex vibro-acoustical structures, G. Tanner, Journal of Sound and Vibration 320, 1023 (2009).
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Title Ruin, Disaster, Shame!
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Keith Hopcraft
Description

Naturally occurring disasters, such as a freak wave that inundates a ship, a bear market that plunges an economy into recession, or those caused by extremes in weather resulting from ‘global warming’, cannot be avoided. But they can be planned for so that their devastating effects can be ameliorated. This project will study the mathematical properties extremal events that are caused by a stochastic process exceeding a threshold. It forms part of a larger programme that will generate data from an optical analogue of extremal events – the generation of caustics, and from analyses of financial and climate data. The project will investigate the extrema produced by a non-gaussian stochastic process that is represented mathematically by the nonlinear filtering of a signal, and will determine such useful quantities as the fluctuations in number of extremal events, and the time of occurrence to the next event. The project will involve modelling of stochastic processes, asymptotic analysis, simulation and data processing. Direct involvement with the experimental programme will also be encouraged. A Case Award supplement may be available for a suitably qualified candidate.

Relevant Publications
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Title Projects in the mechanics of crystals
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Gareth Parry
Description

The aim is to understand different aspects of plastic behaviour in complex defective crystals. It is not surprising that methods of traditional continuum mechanics play a role in this area of materials science, but it is perhaps unexpected that classical ideas of differential geometry are central to an appreciation of the issues involved. A student of traditional background in either pure or applied mathematics will be guided, first of all, in reading and in other preparatory exercises, in such a way as to strengthen his or her knowledge appropriately. Possible research projects in this area are the following.

  • Locking mechanisms in defective crystals: The traditional view regarding the propagation of defects such as dislocations is that they move under the influence of stress until they encounter some imperfection or other inhomogeneity. The aim of the project is to quantify this idea in the context of a mathematical model of defective crystals.
  • Slip in complex crystals: Existing work details the types of slip that are allowed in a continuum theory of crystals for which the appropriate "state" is given by prescribing three linearly independent vector fields at each point of the region occupied by the crystal. Many crystals do not fit into this scheme, since more than three vector fields are required in the model. The project will extend the existing work to encompass these more complex cases.
  • Geometrical structure of defective crystals: In some cases, the geometrical structure of defective crystals derives from the structure of certain three-dimensional Lie groups. This connection has not been exploited at all in the past, and the project will begin the cross-fertilization of mathematics and mechanics in this context.
  • Constitutive functionals for defective crystals: Specifying relationships between stress and strain, subject to certain invariance requirements, is a classic and well-developed procedure in traditional continuum mechanics. In the presence of defects, the procedure is not so clear cut first of all one has to decide on appropriate measures of changes in geometry (like strain) and then decide if ideas like stored energy and stress are realistic. Finally, symmetry requirements deriving from microscopic considerations have to be derived. The project thus provides an essential prerequisite for any study of the continuum mechanics of this type of crystal.
  • Variational problems: In the classical calculus of variations formulation of the theory of elasticity, the task is to find the infimum of the "stored energy" functional, sometimes accomplished by choosing a function (representing the elastic deformation) which actually provides a minimum of the functional. In defective crystals, the corresponding task is to find the infimum of an appropriate functional by choosing two functions representing (i) the elastic deformation (ii) the rearrangement (or slip) of the crystal. The project will consist of the study of mathematical problems of this type.
  • Thermodynamics of defective crystals: It is accepted in the materials science community that friction and energy dissipation are involved in the slip of one crystal lattice plane over another and that temperature effects are important in the mechanics of crystals allowed to deform by slip. The task is to incorporate modern thermodynamic ideas into a theory of the mechanics of such processes.
Relevant Publications
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Title The frequency of catastrophes
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Keith Hopcraft
Description

We have recently developed analytical stochastic models that are capable of describing the frequency of discrete events that have (essentially) an arbitrary distribution, including such extreme cases as when the mean does not exist. Such models can be used to investigate the frequency of rare or extremal events, and can be used to quantify the size of fluctuations that are generated by systems that are close to a critical point, where correlations have a dominating role. The current interest on global climate change provides an interesting and important area with which to apply these models. Climate records provide a detailed source of data from which one can deduce extremal events, such as the number of times the temperature or precipitation exceeds the mean during a period and the models then provide the capacity to estimate the future frequency of such occurrences. The work will involve time-series analysis of climate records, stochastic model building and solution of those models using analytical and numerical techniques.

Relevant Publications
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Title Caustics: optical paradigms of complex systems
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Keith Hopcraft
Description

A complex system is multi-component and heterogeneous in character, the interactions between its component parts leading to collective, correlated and self-organising behaviours. Manifestations of these behaviours are diverse and can range from descriptions of matter near a critical point, through turbulence, to the organising structures that emerge in societies. The interactions which generate these behaviours are always nonlinear and often triggered by the system crossing a threshold, the frequency of crossing this barrier provides an important characteristic of the system under consideration. The pattern of caustics observed on the bottom of a swimming pool is one commonly experienced manifestation of such a threshold phenomenon, the caustics being caused by the stationary points of the water's surface. This illustrates how a continuous fluctuation- i.e. the water's surface, leads to the occurrence of a discrete the number of events — the caustics. The project will investigate the how the number of caustics depends on the properties of the surface and propagation distance (i.e. the depth of the swimming pool). The work will be mainly analytical in nature, involving elements of stochastic model building and their solution, with some simulation. There is a possibility of comparing models with experimental data of light propagation through 'model swimming-pools' and entrained fluids.

Relevant Publications
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Title The discrete random phasor
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Keith Hopcraft
Description

In 1965 Richard Feynman wrote ‘I think I can safely say that nobody understands quantum mechanics’, and that situation has not changed in the intervening years despite its continued predictive capacity. One of the many paradoxes that the theory presents is wave-particle duality – for example an electric field behaves as a continuous wave disturbance according to Maxwell’s theory, but also presents phenomenology associated with discrete photons at microscopic scale-sizes. In the first instance this project will investigate how a very simple representation of electric field behaviour, a phasor of constant amplitude but random phase, has real and imaginary parts that can be represented by a population of classically interacting particles (photons). The project will proceed by seeking a generalization to this population model with characteristic that can be interpreted as being the addition of two random phasors, each of constant amplitude but independent phase. Such a model leads  to interference effects. No prior knowledge of quantum mechanics is required.

Relevant Publications
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Title Machine learning for first-principles calculation of physical properties.
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Richard Graham
Description

The physical properties of all substances are determined by the interactions between the molecules that make up the substance. The energy surface corresponding to these interactions can be calculated from first-principles, in theory allowing physical properties to be derived ab-initio from a molecular simulation; that is by theory alone and without the need for any experiments. Recently we have focussed on applying these techniques to model carbon dioxide properties, such as density and phase separation, for applications in Carbon Capture and Storage. However, there is enormous potential to exploit this approach in a huge range of applications. A significant barrier is the computational cost of calculating the energy surface quickly and repeatedly, as a simulation requires. In collaboration with the School of Chemistry we have recently developed a machine-learning technique that, by using a small number of precomputed ab-initio calculations as training data, can efficiently calculate the entire energy surface. This project will involve extending the approach to more complicated molecules and testing its ability to predict macroscopic physical properties.

This project will be jointly supervised by Dr Richard Wheatley in the School of Chemistry.

Relevant Publications
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Title Modelling Thermal Effects within Thin-Film Flows
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Hibberd
Description

A number of technologies in aerospace gas turbine transmission systems must maintain appropriate cooling of component surfaces and mitigate contact by the use of thin fluid films. In many cases the operating requirements for these components include high rotation speeds, high pressures and high temperatures. Modern design processes for aeroengine components depend increasingly on high quality modelling tools to guide the creation of new products to obtain a comprehensive understanding of the underlying flow characteristics. This project aims to develop detailed understanding of heat transfer in highly sheared thin-film flows through the creation of sophisticated modelling approaches and numerical tools. Using this capability there will be an opportunity to perform detailed analysis of several engine-relevant configurations.

 

The classical theory of thin-film flow is associated with solutions typically for low fluid speeds (Reynolds equation). For higher speed flow an important physical process, often neglected from many current thin-film flow models, is the generation, transfer and effect of heat within the film and from the surrounding structures. Advanced modelling requires the careful development of fully representative equations and the specification of appropriate boundary conditions. A new model to incorporate non-isothermal effects relevant to a bearing chamber context is provided by

This multi-disciplinary project will be undertaken by a graduate student in mathematics, engineering or related degree with a strong applied mathematics background and with an interest in fluid mechanics, mathematical and numerical methods.

Relevant Publications
  • • Kay, E. D, Hibberd, S. and Power, H., (2014); A depth-averaged model for non-isothermal thin-film rimming flow. Int Jnl. Heat and Mass Transfer,70, 1003-1015. doi 10.1016/j.ijheatmasstansfer.2013.11.040
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The supervision team will include include Prof H Power, Faculty of Engineering and a project partner at Rolls-Royce plc.

 

This project is eligible as an EPSRC Industrial CASE award supported by Rolls –Royce plc that includes an additional stipend and a period of experience working locally at Rolls-Royce plc.

Title On mathematical models for high speed non-isothermal air bearings
Group(s) Industrial and Applied Mathematics
Proposer(s) Dr Stephen Hibberd
Description

There are a number of technologies that must maintain appropriate cooling of component surfaces and may include resisting contact by the use of thin fluid films. Modern design processes increasingly on high quality numerical modelling tools to guide the creation of new products and identify operating requirements that include high rotation speeds, high pressures and high temperatures. These demanding operating conditions make a comprehensive understanding of the underlying flow characteristics essential.

 

Advanced modelling requires the careful development of representative equations for all thermal effects, coupling with an appropriate (film) Reynolds equation and the specification of appropriate boundary conditions. Further, implementation of appropriate numerical methods and analysis is required in these demanding model systems.

 

High speed gas film bearing bearings (and seals), as proposed for future aero-engines, are designed to work with no contact and very small gaps and applicable to a wide range of industrial applications. Air-riding bearings have inherent dynamic advantages in making use of local structural features to maintain sufficient gap between the rotating parts but these may lead to significant instabilities as a result of the dynamic behaviour of the gas film and potential thermal and mechanical distortions. 

 

Building on recent PhD studies this project aims to develop detailed understanding of heat transfer in highly sheared thin-film flows through the creation of sophisticated and numerical and modelling approaches.

 

Relevant Publications
  • BAILEY, N.Y., CLIFFE, K.A., HIBBERD, S. and POWER, H., 2014. Dynamics of a parallel high speed fluid lubricated bearing with Navier slip boundary conditions. IMA Journal of Applied Mathematics, doi:10.1093/immat/hxu053, 1-22.
  • VOSPER, H., CLIFFE, K.A., HIBBERD, S. and POWER, H., 2013. On thin film flow in hydrodynamic bearings with a radial step at finite Reynolds number. Journal of Engineering Mathematics. DOI 10.1007/s10665-013-9627-8, 1-22
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The supervision team will include Prof H Power, Faculty of Engineering

Title Classical and quantum Chaos in 3-body Coulomb problems
Group(s) Industrial and Applied Mathematics, Mathematical Physics
Proposer(s) Prof Gregor Tanner
Description

The realisation that the dynamics of 2 particles interacting via central forces is fundamentally different from the dynamics of three particles can be seen as the birth of modern dynamical system theory. The motion of two particles (for example the earth-moon problem neglecting the sun and other planets) is regular and thus easy to predict. This is not the case for three or more particles (especially if the forces between all these particles are of comparable size) and the resulting dynamics is in general chaotic, a fact first spelt out be Poincaré at the end of the 19th century. An important source for chaos in the three-body problem is the possibility of triple collisions, that is, events where all three particles collide simultaneously. Triple collisions form essential singularities in the equation of motions, that is, trajectories can not be smoothly continued through triple collision events. This is related to the fact, that the dynamics at the triple collision point itself takes place on a collision manifold of non-trivial topology.

During the project, the student will be introduced to scaling techniques which allow to study the dynamics at the triple collision point. We will in particular consider three-body Coulomb problems, such as two-electron atoms, and study the influence of the triple-collision on the total dynamics of the problem. As a long term goal, we will try to uncover the origin of approximate invariants of the dynamics whose existence is predicted by experimental and numerical quantum spectra of two-electron atoms such as the helium atom.

Relevant Publications
  • The semiclassical helium atom, G. Tanner and K Richter, www.scholarpedia.org/article/Semiclassical_theory_of_helium_atom
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Title Electromagnetic compatibility in complex environments: predicting the propagation of electromagnetic waves using wave-chaos theory
Group(s) Industrial and Applied Mathematics, Mathematical Physics
Proposer(s) Dr Stephen Creagh, Prof Gregor Tanner
Description

The focus of this project is the development of a mathematical framework to understand the propagation of electromagnetic fields within complicated environments – a challenging task especially in the high frequency limit. Modern technology is typically stuffed with electronic componentry. Devices ranging from a mobile phone to a pc to an Airbus A380 will have many internal electronic components operating at high frequencies and therefore radiating electromagnetic waves. If the waves radiated from one component are strong enough, they can interfere with the functioning of another component somewhere else in the unit. The field of Electromagnetic Compatibility (EMC) aims to mitigate these effects by better understanding the emitted radiation.

The outcome of the research will help to design electronic devices, which are protected from interference from other EM sources within buildings, pc enclosures or even planes. The innovative idea in the proposed approach rests on combining EM-field propagation with ideas of chaos theory and nonlinear dynamics. In particular, the representation of waves emitted from a complex source is described in terms of their ray-dynamics in phase space using the so-called Wigner distribution function (WDF) formalism.  It allows us to replace the wave propagation problem with one of propagating classical densities within phase space. 

 

Relevant Publications
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Title Wave propagation in complex built-up structures – tackling quasi-periodicity and inhomogeneity
Group(s) Industrial and Applied Mathematics, Mathematical Physics
Proposer(s) Prof Gregor Tanner, Dr Stephen Creagh
Description

Computing the dynamic response of modern aerospace, automotive and civil structures can be a computationally challenging task. Characterising the structural dynamics in terms of waves in a uniform or periodic medium is often an important first step in understanding the principal propagating wave modes. 

Real mechanical structures are rarely fully periodic or homogeneous – variations in shape or thickness, boundaries and intersections as well as curvature destroy the perfect symmetry. The aim of the project is to extend periodic structure theory to wave propagation in quasi-periodic and inhomogeneous media such as stiffened structures. The modelling of waves can then be recast in terms of Bloch theory, which will be modified by using appropriate energy or flux conservation assumptions. The information about the propagating modes will then be implemented into modern high-frequency wave methods – such as the so-called Dynamical Energy Analysis developed in Nottingham - making it possible to compute the vibrational response of structures with arbitrary complexity at large frequencies.



 

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Title Network performance subject to agent-based dynamical processes
Group(s) Industrial and Applied Mathematics, Statistics and Probability
Proposer(s) Dr Keith Hopcraft, Dr Simon Preston
Description

Networks – systems of interconnected elements – form structures through which information or matter is conveyed from one part of an entity to another, and between autonomous units. The form, function and evolution of such systems are affected by interactions between their constituent parts, and perturbations from an external environment. The challenge in all application areas is to model effectively these interactions which occur on different spatial- and time-scales, and to discover how

i)     the micro-dynamics of the components influence the evolutionary structure of the network, and

ii)    the network is affected by the external environment(s) in which it is embedded.

Activity in non-evolving networks is well characterized as having diffusive properties if the network is isolated from the outside world, or ballistic qualities if influenced by the external environment. However, the robustness of these characteristics in evolving networks is not as well understood. The projects will investigate the circumstances in which memory can affect the structural evolution of a network and its consequent ability to function.

Agents in a network will be assigned an adaptive profile of goal- and cost-related criteria that govern their response to ambitions and stimuli. An agent then has a memory of its past behaviour and can thereby form a strategy for future actions and reactions. This presents an ability to generate ‘lumpiness’ or granularity in a network’s spatial structure and ‘burstiness’ in its time evolution, and these will affect its ability to react effectively to external shocks to the system. The ability of externally introduced activists to change a network’s structure and function - or agonists to test its resilience to attack - will be investigated using the models. The project will use data of real agent’s behaviour.

Relevant Publications
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Title Fluctuation Driven Network Evolution
Group(s) Industrial and Applied Mathematics, Statistics and Probability
Proposer(s) Dr Keith Hopcraft, Dr Simon Preston
Description

A network’s growth and reorganisation affects its functioning and is contingent upon the relative time-scales of the dynamics that occur on it. Dynamical time-scales that are short compared with those characterizing the network’s evolution enable collectives to form since each element remains connected with others in spite of external or internally generated ‘shocks’ or fluctuations. This can lead to manifestations such as synchronicity or epidemics. When the network topology and dynamics evolve on similar time-scales, a ‘plastic’ state can emerge where form and function become entwined. The interplay between fluctuation, form and function will be investigated with an aim to disentangle the effects of structural change from other dynamics and identify robust characteristics.

Relevant Publications
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Title Excitability in biology - the role of noisy thresholds
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Ruediger Thul, Prof Stephen Coombes
Description

Excitability is ubiquitous in biology. Two important examples are the membrane potential of neurons or the dynamics of the intracellular calcium concentration. What characterises excitable systems is the presence of a threshold. For instance, neurons only fire when the membrane potential crosses a critical value. Importantly, the dynamics of excitable systems is often driven by fluctuations such as the opening of ion channels or the binding of hormones to a receptor. A mathematically and computationally appealing approach is to represent this biological noise by a random excitability threshold. This concept has already provided great insights into the dynamics of neurons that process sounds [1]. In this project, we will investigate the role of correlations of the noisy threshold in shaping cellular responses. Our applications will come from neuroscience in the form of single cell and neural field models as well as from cell signalling when we investigate travelling calcium waves. This will help us to understand the emergence of unusual firing patterns in the brain as well as of the wide variety of travelling calcium waves observed in numerous cell types.

Relevant Publications
  • Coombes, S, R Thul, J Laudanski, A R Palmer, and C J Sumner. 2011. “Neuronal Spike-Train Responses in the Presence of Threshold Noise.” Frontiers in Life Science 5: 91–105.
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Title Spatio-temporal patterns with piecewise-linear regulatory networks
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Etienne Farcot
Description

A number of fascinating and important biological processes involve
various kinds of spatial patterns: spatial patterns on animal skins, or
the very regular organ arrangements found in plants (called phyllotaxis)
for instance. These patterns often originate at very small scales, and
their onset can only be seen using very recent microscope and image
analysis techniques.
Among several families of models for biological patterning, one of the
simplest is based on the idea that mobile substances (called morphogens)
are acting upstream of their targets, which respond locally to a globally
defined  gradient pattern.
In this project one will consider models where targets are themselves
mobile morphogens, potentially regulating their own input. One will
study the effect of such spatial feedback on patterning. To do so, one will rely
on a class of models which are biologically relevant, tractable analytically,
and not much studied yet in a context with spatial interactions. A class of
models which meet all this criteria is provided by piecewise-linear differential
equations.

Relevant Publications
  • L.G. Morelli et al. Computational Approaches to Developmental Patterning. Science 336, 187 (2012).
  • L. Glass, S.A. Kauffman. The logical analysis of continuous, nonlinear biochemical control networks. Journal of Theoretical Biology 39, 103-129 (1973).
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Title Spine morphogenesis and plasticity
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Stephen Coombes, Dr Ruediger Thul
Description

Mathematical Neuroscience is increasingly being recognised as a powerful tool to complement neurobiology to understand aspects of the human central nervous system.  The research activity in our group is concerned with developing a sound mathematical description of sub-cellular processes in synapses and dendritic trees.  In particular we are interested in models of dendritic spines [1], which are typically the synaptic contact point for excitatory synapses.  Previous work in our group has focused on voltage dynamics of spine-heads [2].  We are now keen to broaden the scope of this work to include developmental models for spine growth and maintenance, as well as models for synaptic plasticity [3].  Aberrations in spine morphology and density are well known to underly certain brain disorders, including Fragile X syndrome (which can lead to attention deficit and developmental delay) and depression [4].  Computational modelling is an ideal method to do in-silico studies of drug treatments for brain disorders, by modelling their action on spine development and plasticity.  This is an important complementary tool for drug discovery in an area which is struggling to make headway with classical experimental pharmaceutical tools.

The mathematical tools relevant for this project will be drawn from dynamical systems theory, biophysical modelling, statistical physics, and scientific computation.

Relevant Publications
  • [1] Rafael Yuste, 2010, Dendritic spines, MIT Press
  • [2] Y Timofeeva, G J Lord and S Coombes 2006 Spatio-temporal filtering properties of a dendritic cable with active spines, Journal of Computational Neuroscience, Vol 21, 293-306
  • [3] Cian O'Donnell, Matthew F. Nolan, and Mark C. W. van Rossum, 2012, Dendritic Spine Dynamics Regulate the Long-Term Stability of Synaptic Plasticity, The Journal of Neuroscience, 9 November 2011, 31(45):16142-16156
  • [4] R M Henig, 2012, Lifting the black cloud, Scientific American, Mar, p 60-65
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Title Rare event modelling for the progression of cancer
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Richard Graham, Prof Markus Owen
Description

Purpose

This project will apply cutting-edge mathematical modelling techniques to solve computational and modelling issues in predicting the evolution of cancerous tumours. The project will combine rare event modelling from the physical sciences and cellular-level models from mathematical biology. The aim is to produce new cancer models with improved biological detail that can be solved on clinically relevant timescales, which can be decades.

 

Background

A wide-spread problem in treating cancer is to distinguish indolent (benign) tumours from metastatic-capable primary tumours (tumours that can spread to other parts of the body). Although therapies for metastatic disease exist, metastatic disease is a significant cause of death in cancer patients.  This problem can lead to misdiagnosis, unnecessary treatment and a lack of clarity on which treatments are most effective.

 

A predictive mathematical model of cancer development could assist with the above issues. However, as the progression of cancer to metastasis is a rare event, in a direct simulation, virtually all of the computational time is consumed in simulating the quasi-stable behaviour of the indolent tumour, revealing no information about progression. This generic problem of rare events is common in the physical sciences, where modern techniques have enabled rare events to be simulated and understood. This project will extend these techniques to cancer modelling. The project will build on a state-of-the-art spatiotemporal cancer model, which models individual cancer cells in a host tissue, vascular networks and angiogenesis. In this model cells can divide, migrate or die, in response to their microenvironment of cell crowding and cell signalling. To this framework the project will add transitions between cell types, driven by random mutation events and intravasation events.

 

The project will use a rare event algorithm, forward flux sampling (FFS), to create a statistical map of the transition from indolent cancer to metastatic cancer. In a typical rare event transition the system spends the overwhelming majority of the time close to the start. Consequently, the sampling of the trajectory space is very uneven. Thus, despite a very long simulation the statistical resolution of the mechanism and crossing rate are very poor. FFS solves this problem by dividing the phase space into a series of interfaces that represent sequential advancement towards the rare event. The algorithm logs forward crossings of these interfaces and a series of trajectories are begun at these crossing points. This produces a far more even sampling of the trajectory space and so better statistics of the whole mechanism from a shorter simulation.

 

Relevant Publications
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Title Stochastic Neural Network Modelling
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Stephen Coombes, Dr Ruediger Thul
Description

Large scale studies of spiking neural networks are a key part of modern approaches to understanding the dynamics of biological neural tissue. One approach in computational neuroscience has been to consider the detailed electrophysiological properties of neurons and build vast computational compartmental models. An alternative has been to develop minimal models of spiking neurons with a reduction in the dimensionality of both parameter and variable space that facilitates more effective simulation studies. In this latter case the single neuron model of choice is often a variant of the classic integrate-and-fire model, which is described by a non-smooth dynamical system with a threshold [1]. It has recently been shown [2] that one way to model the variability of neuronal firing is to introduce noise at the threshold level. This project will develop the analysis of networks of synaptically coupled noisy neurons. Importantly it will go beyond standard phase oscillator approaches to treat strong coupling and non-Gaussian noise. One of the main mathematical challenges will be to extend the Master-Stability framework for networks of deterministic limit cycle oscillators to the noisy non-smooth case that is relevant to neural modelling. This work will determine the effect of network dynamics and topology on synchronisation, with potential application to psychiatric and neurological disorders. These are increasingly being understood as disruptions of optimal integration of mental processes sub-served by distributed brain networks [3].

Relevant Publications
  • [1] S Coombes, R Thul and K C A Wedgwood 2012 Nonsmooth dynamics in spiking neuron models, Physica D, DOI: 10.1016/j.physd.2011.05.012
  • [2] S Coombes, R Thul, J Laudanski, A R Palmer and C J Sumner 2011 Neuronal spike-train responses in the presence of threshold noise, Frontiers in Life Science, DOI: 10.1080/21553769.2011.556016
  • [3] J Hlinka and S Coombes 2012 Using computational models to relate structural and functional brain connectivity, European Journal of Neuroscience, to appear
Other information
Title Cell signalling
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof John King
Description

Cell signalling effects have crucial roles to play in a vast range of biological processes, such as in controlling the virulence of bacterial infections or in determining the efficacy of treatments of many diseases. Moreover, they operate over a wide range of scales, from subcellular (e.g. in determining how a particular drug affects a specific type of cell) to organ or population (such as through the quorum sensing systems by which many bacteria determine whether or not to become virulent). There is therefore an urgent need to gain greater quantitative understanding of these highly complex systems, which are well-suited to mathematical study. Experience with the study of nonlinear dynamical systems would provide helpful background for such a project.

Relevant Publications
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Title Modelling DNA Chain Dynamics
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Jonathan Wattis
Description

Whilst the dynamics of the DNA double helix are extremely complicated, a number of well-defined modes of vibration, such as twisting and bending, have been identified. At present the only accurate models of DNA dynamics involve large-scale simulations of molecular dynamics. Such approaches suffer two major drawbacks: they are only able to simulate short strands of DNA and only for extremely short periods (nanoseconds). the aim of this project is to develop simpler models that describe vibrations of the DNA double helix. The resulting systems of equations will be used to simulate the dynamics of longer chains of DNA over long timescales and, hence, allow larger-scale dynamics, such as the unzipping of the double helix, to be studied.

Relevant Publications
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Title Multiscale modelling of vascularised tissue
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Markus Owen
Description

Most human tissues are perfused by an evolving network of blood vessels which supply nutrients to (and remove waste products from) the cells. The growth of this network (via vasculogenesis and angiogenesis) is crucial for normal embryonic and postnatal development, and its maintenance is essential throughout our lives (e.g. wound healing requires the repair of damaged vessels). However, abnormal remodelling of the vasculature is associated with several pathological conditions including diabetic retinopathy, rheumatoid arthritis and tumour growth.

The phenomena underlying tissue vascularisation operate over a wide range of time and length scales. These features include blood flow in the existing vascular network, transport within the tissue of blood-borne nutrients, cell division and death, and the expression by cells of growth factors such as VEGF, a potent angiogenic factor. We have developed a multiscale model framework for studying such systems, based on a hybrid cellular automaton which couples cellular and subcellular dynamics with tissue-level features such as blood flow and the transport of growth factors. This project will extend and specialise our existing model to focus on particular applications in one of the following areas: wound healing, retinal angiogenesis, placental development, and corpus luteum growth. This work would require a significant element of modelling, numerical simulation and computer programming.

Relevant Publications
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Title Self-similarity in a nanoscale island-growth
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Jonathan Wattis
Description

Molecular Beam Epitaxy is a process by which single atoms are slowly deposited on a surface. These atoms diffuse around the surface until they collide with a cluster or another atom and become part of a cluster. Clusters remain stationary. The distribution of cluster sizes can be measured, and is observed to exhibit self-similarity. Various systems of equations have been proposed to explain the scaling behaviour observed. The purpose of this project is to analyse the systems of differential equations to verify the scalings laws observed and predict the shape of the size-distribution. The relationship of equations with other models of deposition, such as reactions on catalytic surfaces and polymer adsorption onto DNA, will also be explored.

Relevant Publications
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Title Sequential adsorption processes
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Jonathan Wattis
Description

The random deposition of particles onto a surface is a process which arises in many subject areas, and determining its efficiency in terms of the coverage attained is a difficult problem.

In one-dimension the problem can be viewed as how many cars can be parked along a road of a certain length; this problem is similar to a problem in administering gene therapy in which polymers need to be designed to package and deliver DNA into cells.

Here one wishes to know the coverage obtained when one uses a variety of polymer lengths to bind to strands of DNA.

The project will involve the solution of recurrence relations, and differential equations, by a mixture of asymptotic techniques and stochastic simulations.

Relevant Publications
Other information
Title Robustness of biochemical network dynamics with respect to mathematical representation
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Etienne Farcot
Description

In the recent years, a lot of multi-disciplinary efforts have been
devoted to improving our understanding of the dynamics of interactions
between the many types of molecules present in biological cells. This
has led to a widespread viewpoint where networks of genes, proteins and
other biochemical species are considered at once, as complex dynamical
systems from which the global state of cells emerge.
Several mathematical formalisms are used to represent these systems,
from discrete or boolean models to differential equations. One striking
fact, especially regarding models of developmental processes, is that a
number of relevant properties of these networks can be captured
similarly by all these formalisms, like for instance the property of
bistability.
One possible interpretation of this independence with respect to
formalism is that biological regulatory systems are most often extremely
robust.
The project will start by developing parallel models – using different
formalisms – of actual biological networks whose behaviour is known.
Elaborating on these examples the theoretical and practical implications
of this notion of robustness will be explored.

Relevant Publications
Other information
Title Neurocomputational models of hippocampus-dependent place learning and navigation
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Stephen Coombes
Description

This project will be based at the University of Nottingham in the School of Mathematical Sciences and the School of Psychology.  

Humans and other animals can readily remember significant places and associated events and return to these places as appropriate. From an experimental point of view, studies of the neuro-psychological mechanisms underlying place learning and navigation offer unique opportunities, because similar tests can be used in rodent models and human participants. Studies in rodent models have led to a detailed understanding of the neuro-psychological mechanisms of place memory, and the importance of the hippocampus for place learning and navigation in humans and other animals is well-established. In this project, we aim to develop quantitative models describing how neurons in the hippocampus and associated brain areas give rise to place learning and navigation, and construct an in silico model for testing ideas about functional mechanisms. The project brings together behavioural neuroscience expertise on hippocampal function and place learning (Bast, Psychology) with expertise in mathematical and computational neuroscience (Coombes, Mathematical Sciences) to understand rapid place learning. A particular emphasis will be on the hippocampal learning-behaviour translation: how place information (as encoded, for example, by hippocampal place cells) is related to decision making processes and, ultimately, translated into motor behaviour (for example, by way of interactions with prefrontal and subcortical circuits). From a mathematical perspective the project will develop new neurocomputational models of hippocampus-dependent place learning and navigation using tools from stochastic optimal control, reinforcement learning theory, dynamical systems and computational neuroscience.

Relevant Publications
Other information
Eligibility/Entry Requirements:  
We require an enthusiastic graduate with a 1st class degree in Mathematics (or other highly mathematical field such as Physics or Chemistry), preferably at MMath/MSc level, or an equivalent overseas degree (in exceptional circumstances a 2:1 class degree, or equivalent, can be considered).  

Apply:  
This studentship is available to start from September 2017 and remain open until it is filled. To apply please visit the University Of Nottingham application page: http://www.nottingham.ac.uk/pgstudy/apply/apply-online.aspx 

Funding Notes

Summary: UK/EU students - Tuition Fees paid, and full Stipend at the RCUK rate, which is £14,296 per annum for 2016/17. There will also be some support available for you to claim for limited conference attendance. The scholarship length will be 3 or 3.5, depending on the qualifications and training needs of the successful applicant.

Title Spirals and auto-soliton scattering: interface analysis in a neural field model
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Stephen Coombes, Dr Daniele Avitabile
Description

Neural field models describe the coarse grained activity of populations of interacting neurons. Because of the laminar structure of real cortical tissue they are often studied in 2D, where they are well known to generate rich patterns of spatio-temporal activity. Typical patterns include localised solutions in the form of travelling spots as well as spiral waves [1]. These patterns are naturally defined by the interface between low and high states of neural activity. This project will derive the dimensionally reduced equations of motion for such interfaces from the full nonlinear integro-differential equation defining the neural field.  Numerical codes for the evolution of the interface will be developed, and embedded in a continuation framework for performing a systematic bifurcation analysis.  Weakly nonlinear theory will be developed to understand the scattering of multiple spots that behave as auto-solitons, whilst strong scattering solutions will be investigated using the scattor theory that has previously been developed for multi-component reaction diffusion systems [2].

Relevant Publications
  • [1] C R Laing 2005 Spiral waves in nonlocal equations, SIAM J. Appl. Dyn. Sys., Vol 4, 588-606.
  • [2] Y Nishiura, T Teramoto, and K-I Ueda. Scattering of traveling spots in dissipative systems. Chaos, 15:047509(1–10), 2005.
Other information

S Coombes, H Schmidt and I Bojak 2012 Interface dynamics in planar neural field models, Journal of Mathematical Neuroscience, 2:9

Title Modelling signal processing and sexual recognition in mosquitoes: neural computations in insect hearing systems
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Daniele Avitabile, Prof Stephen Coombes
Description

Insects have evolved diverse and delicate morphological structures in order to
capture the inherently low energy of a propagating sound wave. In mosquitoes, the
capture of acoustic energy, and its transduction into neuronal signals, is assisted
by the active mechanical participation of actuators called scolopidia.

When a sound wave reaches the head of a mosquito, the antenna oscillates under the
action of the external pressure field (passive component) and of the force provided by
the mechanical actuators (active component). The latter is particularly
relevant for sexual recognition: when a male mosquito hear the flyby of a female, his
antennal oscillation are greatly amplified by the scolopidia. In other words, the
antenna of a male is tuned very sharply around the frequency and intensity of a
female flyby.

Recent studies have shown that mosquitoes of either sex use both their antenna and
their wing beat to select a partner: understanding how their hearing system works
could help us controlling the population of species that carry viral diseases.

Even though some models of mosquitoes hearing systems have been proposed in the past,
a number of key questions remain unanswered. Where do the mechanical actuators get
their energy? How do they twitch? How is the mechanical motion of the antenna
transformed into an electric signal? Do neurones control the mechanical motion? How
does the brain of a mosquito process the neural information and distinguish various
sources of sound? Is the sexual recognition entirely based on sound perception, or is
it also influenced by olfactory signals? Is the antenna sensitive to sounds from
different directions?

Relevant Publications
  • AVITABILE, D, HOMER, M, CHAMPNEYS, AR, JACKSON, JC and ROBERT, D, 2010. Mathematical Modelling Of The Active Hearing Process In Mosquitoes Journal Of The Royal Society Interface. 7(42), 105-122
  • CHAMPNEYS, AR, AVITABILE, D, HOMER, M and SZALAI, R, 2011. The Mechanics Of Hearing: A Comparative Case Study In Bio-Mathematical Modelling Anziam Journal. 52(3), 225-249
Other information
Title Mechanistic models of airway smooth muscle cells - application to asthma
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Bindi Brook
Description

Lung inflammation and airway hyperresponsiveness (AHR) are hallmarks of asthma, but their interrelationship is unclear. Excessive shortening of airway smooth muscle (ASM) in response to bronchoconstrictors is likely an important determinant of AHR. Hypercontractility of ASM could stem from a change in the intrinsic properties of the muscle, or it could be due to extrinsic factors such as chronic exposure of the muscle to inflammatory mediators in the airways with the latter being a possible link between lung inflammation and AHR. The aim of this project will be to investigate the influence of chronic exposure to a contractile agonist on the force-generating capacity of ASM via a cell-level model of an ASM cell. Previous experimental studies have suggested that the muscle adapts to basal tone in response to application of agonist and is able to regain its contractile ability in response to a second stimulus  over time. This is thought to be due to a transformation in the  cytoskeletal components of the cell enabling it to bear force, thus freeing up subcellular contractile machinery to generate more force. Force adaptation in ASM as a consequence of prolonged exposure to the many spasmogens found in asthmatic airways could be a mechanism contributing to AHR seen in asthma. We will develop and use a cell model in an attempt to either confirm this hypothesis or determine other mechanisms that may give rise to the observed phenomenon of force adaptation.

Relevant Publications
  • Adaptation of airway smooth muscle to basal tone relevance to airway hyperresponsiveness, Bosse et al, American Journal of Respiratory Cell Molecular Biology,Vol 40. pp 13–18, 2009
  • The role of contractile unit reorganization in force generation in airway smooth muscle, B S Brook and O E Jensen, Mathematical Medicine and Biology, 2013. doi:10.1093/imammb/dqs031
Other information
Title Synchronisation and propagation in human cortical networks
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Reuben O'Dea
Description

Around 25% of the 50million epilepsy sufferers worldwide are not responsive to antiepileptic medication; improved understanding of this disorder has the potential to improve diagnosis, treatment and patient outcomes. The idea of modelling the brain as a complex network is now well established. However, the emergence of pathological brain states via the interaction of large interconnected neuronal populations remains poorly understood. Current theoretical study of epileptic seizures is flawed by dynamical simulation on inadequate network models, and by the absence of customised network measures that capture pathological connectivity patterns.

This project aims to address these deficiencies via improved computational models with which to investigate thoroughly the influence of the geometry and connectivity of the human brain on epileptic seizure progression and initiation, and the development of novel network measures with which to characterise epileptic brains. Such investigations will be informed by exhaustive patient datasets (such as recordings of neural activity in epilepsy patients and age-matched controls), and will be used to study (i) improved diagnostic strategies, (ii) the influence of treatment strategies on seizure progression and initiation, and (iii) the identification of key sites of epilepsy initiation.

Relevant Publications
Other information
Title Patterns of synchrony in discrete models of gene networks
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Etienne Farcot
Description

One of the greatest challenges of biology is to decipher the relation between genotype and
phenotype. One core difficulty in this task is that this relation is not a map; the proteins which
are produced thanks to the information contained in the genome are themselves used to
control which parts of the genome are being used in a given situation. To understand the effect
of this feedback between genes and their product it is crucial to consider the dynamics of this
process.
The term 'gene network' refers to a set of genes which regulate each other; understanding
the dynamics of gene networks is thus crucial to decipher the genotype-phenotype relation. Mathematical
models of gene networks have been proposed since the 1960's, among which the class of Boolean
models has proved very successful. Because of the discrete nature of these models, the effect of time
is often described using representations inspired by manufactured computing device, where the
genes are updated in parallel, or in series. However, the updating scheme of genes could in principle
be much more general. In this project, one will investigate the effect of such a generalization. One
will consider arbitrary update schemes, both deterministic and stochastic, notably in relation to
the dynamics of continuous models of gene networks.

Relevant Publications
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Title Cell cycle desynchronization in growing tissues
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Etienne Farcot
Description

A very general phenomenon is the fact that coupled oscillators tend to naturally
synchronize [1]. This simple fact takes many forms observable in real life:
synchronization of applause after a concert, of neural cells, of flashing fireflies, and
many other. A complete understanding of this phenomenon, depending on the particular
dynamics of individual oscillators or the nature of their coupling, is still an on-going
topic of mathematical research.
However general, the synchronization of coupled oscillators is not a universal rule. In this
project, one will study a situation where it indeed does not seem to occur: the division cycles
of cells in a growing tissue does not seem to be synchronized, as observed in recent
data form plant tissues. A plausible explanation is that the divisions of cell induce a change in
the coupling between cells, which is mostly due to physical or chemical exchanges between
neighbouring cells. Relying on simplified representations, one will consider the effect of growth,
whereby the coupling structure of a system changes in time, on synchronization in populations
of oscillators.

Relevant Publications
  • [1] S.H. Strogatz and I. Stewart. Coupled oscillators and biological synchronization. Scientific American 269 (6) 102-109 (1993).
Other information
Title Bottom-up development of multi-scale models of airway remodelling in asthma: from cell to tissue.
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Bindi Brook, Dr Reuben O'Dea
Description

Airway remodelling in asthma has until recently been associated almost exclusively with inflammation over long time-scales. Current experimental evidence suggests that broncho-constriction (as a result of airway smooth muscle contraction) itself triggers activation of pro-remodelling growth factors that causes airway smooth muscle growth over much shorter time-scales. This project will involve the coupling of sub-cellular mechano-transduction signalling pathways to biomechanical models of airway smooth muscle cells and extra-cellular matrix proteins with the aim of developing a tissue-level biomechanical description of the resultant growth in airway smooth muscle. 

The mechano-transduction pathways and biomechanics of airway smooth muscle contraction are extremely complex. The cytoskeleton and contractile machinery within the cell and ECM proteins surrounding it are thought to rearrange dynamically (order of seconds). The cell is thought to adapt its length (over 10s of seconds). To account for all these processes from the bottom-up and generate a tissue level description of biological growth will require the combination of agent-based models to biomechanical models governed by PDEs. The challenge will be to come up with suitably reduced models with elegant mathematical descriptions that are still able to reproduce observed experimental data on cell and tissue scales, as well as the different time-scales present.

While this study will be aimed specifically at airway remodelling, the methodology developed will have application in multi-scale models of vascular remodelling and tissue growth in artificially engineered tissues. Initially models will be informed by data from on-going experiments in Dr Amanda Tatler's lab in Respiratory Medicine but there will also be the opportunity to design new experiments based on model results.

Relevant Publications
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Title Multiscale modelling of cell signalling and mechanics in tissue development and cancer
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof John King, Dr Reuben O'Dea
Description

Cells respond to their physical environment through mechanotransduction, the translation of mechanical forces into biochemical signals; evoked cell phenotypic changes can lead to an altered cell microenvironment, creating a developmental  feedback. Interplay between such mechanosentive pathways and other inter- and intra-cellular signalling mechanisms determines cell differentiation and, ultimately, tissue development. Such developmental mechanisms have key relevance to the initiation and development of cancer, a disease of such inherent complexity (involving the interaction of a variety of processes across disparate spatio-temporal scales, from intracellular signalling cascades to tissue-level mechanics) that, despite a wealth of theoretical and experimental studies, it remains a leading cause of mortality and morbidity: in the UK, more than one in three people will develop some form of cancer. There is therefore an urgent need to gain greater quantitative understanding of these highly complex systems, which are well-suited to mathematical study.

This project will develop a predictive framework, coupling key signalling pathways to cell- and tissue-level mechanics, to elucidate key developmental mechanisms and their interaction. Investigations will include both multiscale computational approaches, and asymptotic methods for model reduction and analysis. Importantly, model development, analysis and experimental validation will be enabled via close collaboration with Dr Robert Jenkins (Francis Crick Institute, a multidisciplinary biomedical discovery institute dedicated to understanding the scientific mechanisms of living things), thereby ensuring the relevance of the investigations undertaken.

Experience of mathematical/numerical techniques for ODEs and PDEs, the study of nonlinear dynamical systems, or mathematical biology more generally would be an advantage; prior knowledge of the relevant biology is not required.

Relevant Publications
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Title From molecular dynamics to intracellular calcium waves
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Ruediger Thul, Prof Stephen Coombes
Description

Intracellular calcium waves are at the centre of a multitude of cellular processes. Examples include the generation of a heartbeat or the beginning of life when egg cells are fertilised. A key driver of intracellular calcium waves are ion channels, which are large molecules that control the passage of calcium ions across a cell. Importantly, these ion channels display stochastic behaviour such as random opening and closing. A key challenge in mathematical physiology and computational biology is to link this molecular stochasticity to travelling calcium waves.

In this project, we will use a fire-diffuse-fire (FDF) model of intracellular calcium waves and couple it to Markov chains of ion channels. Traditionally, simulating large numbers of Markov chains is computationally expensive. Our goal is to derive an effective description for the stochastic ion channel dynamics. This will allow us to incorporate the molecular fluctuations from the ion channels into the FDF model without having to evolve Markov chains. This will put us in an ideal position to answer current questions in cardiac dynamics (How does an irregular heart beat emerge, leading to a potentially life-threatening condition?) as well as to elucidate fundamental concepts in cell signalling.

 

Relevant Publications
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Title Waves on a folded brain
Group(s) Mathematical Medicine and Biology
Proposer(s) Dr Daniele Avitabile, Prof Stephen Coombes
Description

The human brain has a wonderfully folded cortex with regions of both negative and positive curvature at gyri and sulci respectively.  As the state of the brain changes waves of electrical activity spread and scatter through this complicated surface geometry.  This project will focus on the mathematical modelling of realistic cortical tissue and the analysis of wave propagation and scattering using techniques from dynamical systems theory and scientific computation.

In more detail the project will consider models of neural activity represented by non-local integro-differential equations posed on both idealised and human realistic cortical structures.  The former will allow the development of analytical tools to understand the role of tissue heterogeneity and disorder in sculpting wave dynamics, such as the recently developed interface approach [1].  The latter will extend this so-called neural field approach [2] using cortical meshes from human connectome databases, making extensive use of spectral and finite element methods.  

This applied mathematical project will be facilitated by interaction with colleagues from the Sir Peter Mansfield Imaging Centre. As well as exposing the PhD student to rich neuroimaging data-sets collected locally using cutting edge magnetoencephalography techniques, the project will contribute to our understanding of cortical waves in the functioning of the human brain.

Relevant Publications
  • [1] S Coombes, H Schmidt and I Bojak 2012 Interface dynamics in planar neural field models, Journal of Mathematical Neuroscience, 2:9.
  • [2] S Coombes, H Schmidt and D Avitabile 2014 Spots: Breathing, drifting and scattering in a neural field model, Neural Fields, Ed. S Coombes, P beam Graben, R Pottiest and J J Wright, Springer Verlag
Other information
Title Modelling macrophage extravasation and phenotype selection
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Markus Owen
Description

Macrophages are a type of white blood cell, a vital component of the immune system, and play a complex role in tumour growth and other diseases. Macrophage precursors, called monocytes, are produced in the bone marrow and enter the blood, before leaving the bloodstream (extravasating). Monocyte extravasation requires adhesion to, and active movement through, the blood vessel wall, both of which are highly regulated processes. Once in the tissue, monocytes begin to differentiate into macrophages, and it has become clear that the tissue micro-environment is a crucial determinant of macrophage function [1]. A spectrum of phenotypes have been identified: at one end, macrophages produce a variety of signals that are beneficial to a tumour, including those that promote the formation of new blood vessels and suppress inflammation. At the other end of the scale, inflammation is promoted and appropriately stimulated macrophages can kill tumour cells.

This project will consider in some detail the mechanisms that regulate monocyte extravasation and macrophage phenotype selection. Initially, mathematical models will be formulated as systems of ordinary differential equations describing transitions between monocyte subpopulations (for example, those fully adherent to the vessel wall, and those that are actively moving through the wall), regulated by various signalling and adhesion molecules. Research on phenotype selection will determine whether the dynamics can be manipulated by subsequent external intervention. For example, if the system is bistable, it may be possible to force a switch from a deleterious to a beneficial phenotype. Relevant signal transduction pathways will be modelled in detail, and the law of mass-action will be used to derive systems of ODEs. Where possible, model reductions based on a separation of timescales will be used to simplify the system, and analytical and numerical approaches will be used to characterise steady state structure and bifurcations as tissue conditions vary.

Relevant Publications
  • A Mantovani, S Sozzani, M Locati, P Allavena, and A Sica: Macrophage polarization: tumor-associated macrophages as a paradigm for polarized M2 mononuclear phagocytes. Trends Immunol., 23:549--555, (2002).
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Title Neuronal dynamics of perceptual inference
Group(s) Mathematical Medicine and Biology
Proposer(s) Prof Stephen Coombes
Description

Inference of the world around us is made by processing sensory signals in the brain and relating them to memories of previous experience.  The study of this process has generated a number of candidate frameworks, with perhaps the most popular being ‘Bayesian cognition'.  This powerful statistical description posits that the central nervous system of animals is capable of integrating prior probabilities with new sensory data in an optimal way to make perceptual decisions1.  How this process could be realised in dynamic circuits of neurons is as yet unclear2. Additionally, while there are some spectacular experimental data on the capability of humans to accomplish such Bayes-optimal computations, strong evidence only comes from a limited set of experiments3, other evidence often assuming Bayesian algorithms a priori4 and there is an influential literature demonstrating the failures of human information processing to incorporate prior probabilities5. This project will probe the mechanisms involved in perceptual inference in a multi-disciplinary way mixing techniques from cognitive psychology and neuroimaging with those from mathematical neuroscience.  

A PhD student will approach this question on two frontiers: Phenomenologically, they will use advanced psychophysical techniques and mathematical modelling 6 to study how humans integrate prior probabilities and sensory information more generally (i.e. investigate the parameter space where the Bayesian observer model applies) and measure neuronal activity during such processes noninvasively7. Computationally, they will then investigate a new class of forward models for the generation of brain rhythms based on mean-field reductions of synaptically interacting nonlinear integrate-and-fire systems8.  These are ideally suited for studying the phase-amplitude coupling of brain rhythms in hierarchical cortical networks that have been reported in human and animal studies on the integration of prior information9,10.  The implementation of a Bayesian machine in this architecture will shed light on the debate about how higher frequency 'gamma oscillations' can communicate sensory feed-forward information, whilst top-down feedback is mediated by lower frequency 'alpha-' or 'beta-' band oscillations11.  The PhD student will be actively involved not only in model development and delivery but the acquisition of psychophysical data.  Initial experiments will be used to validate the model, progressing through to the design of new experiments to test model-generated hypotheses about the breakdown of computation in mental illness.  In particular the project will explore the role of NMDA vs. AMPA glutamatergic receptors in subserving neurodynamics for Bayesian cognition and their disturbance in schizophrenia12.

The project will be jointly supervised by Dr Markus Bauer (School of Psychology) and Professor Stephen Coombes (School of Mathematical Sciences).

 

1) Knill, D.C. & Pouget, A. The Bayesian brain: the role of uncertainty in neural coding and computation. Trends Neurosci 27, 712-719, (2004). 2) Pouget, A., Beck, J.M., Ma, W. J. & Latham, P. E. Probabilistic brains: knowns and unknowns. Nat Neurosci 16, 1170-1178, (2013).

3) Ernst, M.O. & Banks, M.S. Humans integrate visual and haptic information in a statistically optimal fashion. Nature 415, 429-433, doi:10.1038/415429a (2002).

4) Vossel, S., Bauer, M. et al. Cholinergic stimulation enhances bayesian belief updating in the deployment of spatial attention. J Neurosci 34, 15735-15742, (2014).

5) Kahneman, D. & Tversky, A. On the study of statistical intuitions. Cognition 11, 123-141 (1982).

6) Coombes, S. Large-scale neural dynamics: simple and complex. Neuroimage 52, 731-739, (2010).

7) Wenzlaff, H., Bauer, M., Maess, B. & Heekeren, H.R. Neural characterization of the speed-accuracy tradeoff in a perceptual decision-making task. J Neurosci 31, 1254-1266, (2011).

8) Coombes, S., Thul, R. & Wedgwood, K.C.A. Nonsmooth dynamics in spiking neuron models. Physica D 241, 2042-2057, (2012).

9) Bastos, A.M. et al. Canonical microcircuits for predictive coding. Neuron 76, 695-711, (2012).

10) Friston, K.J. et al. LFP and oscillations-what do they tell us? Curr Opin Neurobiol 31, 1-6, (2015).

11) Bauer, M., et al.. Attentional modulation of alpha/beta and gamma oscillations reflect functionally distinct processes. J Neurosci 34, 16117-16125, (2014).

12) Adams, R.A., et al. The computational anatomy of psychosis

Relevant Publications
Other information
Title Critical random matrix ensembles
Group(s) Mathematical Physics
Proposer(s) Dr Alexander Ossipov
Description

In Random Matrix Theory (RMT) one deals with matrices whose entries are given by random variables. RMT has a great number of applications in physics, mathematics, engineering, finance etc. In this project, a particular class of random matrix ensembles --- critical random matrix models will be studied. These models describe statistical properties of disordered systems at a point of the quantum phase transition. Using RMT one can compute various critical exponents, correlation functions and other physically important quantities.


In the language of RMT, the criticality implies very special properties of eigenvalues and eigenvectors of random matrices. One can show, for example, that eigenvectors in critical models are fractal. For certain models fractality of eigenvectors can be investigated with the help of rather simple random matrices, such as two by two matrices in the simplest case. In other cases, much more sophisticated methods, such as supersymmetry, should be employed.  Some steps in this direction have been taken recently, but very few general results are available at the moment. The aim of the project is to close this gap.

Relevant Publications
  • Y. V. Fyodorov, A. Ossipov, and A. Rodriguez, Anderson localization transition and eigenfunction multifractality in ensemble of ultrametric random matrices, J. Stat. Mech., L12001 (2009).
  • V.E. Kravtsov, A. Ossipov, O.M. Yevtushenko, E. Cuevas, Dynamical scaling for critical states: is Chalker's ansatz valid for strong fractality?, Phys. Rev. B 82, 161102(R) (2010).
  • A. Ossipov, I. Rushkin, and E. Cuevas, Level number variance and spectral compressibility in a critical two-dimensional random matrix model, Phys. Rev. E 85, 021127 (2012).
  • A. Ossipov, Virial expansion of the non-linear sigma model in the strong coupling limit, J. Phys. A: Math. Theor. 45, 335002 (2012).
  • A. Ossipov, Anderson localization on a simplex, http://arxiv.org/abs/1211.2643
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Title Models of Quantum Geometry
Group(s) Mathematical Physics
Proposer(s) Prof John Barrett
Description

There are a number of projects investigating aspects of quantum geometry models and related mathematics. This study is based on the approach to non-commutative geometry pioneered by Alain Connes. It also uses techniques from topology, algebra, category theory and geometry, as well as numerical computations. The motivation is to study models that include gravity, working towards solving the problem of quantum gravity, and to study implications for particle physics. For the latest information on this research, please see my homepage https://johnwbarrett.wordpress.com/

Relevant Publications
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Title Hydrodynamic simulations of rotating black holes
Group(s) Mathematical Physics
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Description

We are currently carrying out an experiment to study the effects occurring around effective horizons in an analogue gravity system. In particular, the scientific goals are to explore superradiant scattering and the black hole evaporation process. To address this issue experimentally, we utilize the analogy between waves on the surface of a stationary draining fluid/superfluid flows and the behavior of classical and quantum field excitations in the vicinity of rotating black. 

This project will be based at the University of Nottingham at the School of Mathematical Sciences. The two external collaborators are Prof. Josef Niemela (ICTP, Trieste in Italy) and Prof. Stefano Liberati (SISSA, Trieste in Italy). The external consultant for the experiment is Prof. Bill Unruh, who will be a regular visitor. 

The PhD student will be involved in all aspects of the experiments theoretical as well experimental. We require an enthusiastic graduate with a 1st class degree in Mathematics/Physics/Engineering (in exceptional circumstances a 2(i) class degree  can be considered), preferably of the MMath/MSc level. Candidates would need to be keen to work in an interdisciplinary environment and interested in learning about quantum field theory in curved spacetimes, fluid dynamics, analogue gravity, and experimental techniques such as flow visualisation (i.g. Particle Imaging or Laser Doppler Velocimetry) and surface measurements (i.g. profilometry methods). 

Relevant Publications
  • Carlos Barceló and Stefano Liberati and Matt Visser, "Analogue Gravity", Living Rev. Relativity 14, (2011), 3. URL: http://www.livingreviews.org/lrr-2011-3
  • W. G. Unruh, “Experimental Black-Hole Evaporation?” Phys. Rev. Lett. 46, 1351 – Published 25 May 1981.
  • Silke Weinfurtner, Edmund W. Tedford, Matthew C. J. Penrice, William G. Unruh, and Gregory A. Lawrence, “Measurement of Stimulated Hawking Emission in an Analogue System”, Phys. Rev. Lett. 106, 021302 – Published 10 January 2011
  • Mauricio Richartz, Silke Weinfurtner, A. J. Penner, W. G. Unruh, “Generalised superradiant scattering”, Phys. Rev. D80:124016,2009
  • Mauricio Richartz, Angus Prain, Stefano Liberati, Silke Weinfurtner, "Rotating black holes in a draining bathtub: superradiant scattering of gravity waves ", arXiv:1411.1662 [gr-qc]
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Title Gravity as a theory of connections
Group(s) Mathematical Physics
Proposer(s) Prof Kirill Krasnov
Description

General Relativity is normally described as a dynamical theory of spacetime metrics. However, GR is a rather complicated theory - think about the rather non-trivial exercise of deriving Schwarzschild solution, with its computation of Christoffel symbols, then the curvature tensor, then Ricci tensor. At the same time, it has been appreciated for a long time that one can simplify the GR formalism by using differential forms. Indeed, the exercise leading to Schwarzschild solution does become simpler if one uses tetrads and the spin connection instead of the metric and the affine connection. Also in 3 spacetime dimensions General Relativity is best thought of as a theory of flat Poincare connections, with the action describing the dynamics being that of Chern-Simons theory. A point of view on 3D gravity as a theory of connections has been extremely successful both classically (in describing the space of all possible solutions of 3D GR) and quantum mechanically (in quantising the space of solutions and obtaining an explicit description of the arising Hilbert space). 

This PhD project will concern itself with developing a similar language for 4D GR. Thus, it turns out to be possible to describe 4D GR as a dynamical theory of connections rather than metrics. The metric appears as a derived notion, and is constructed in a certain way from the curvature of the connection. There are many possible projects within this general area of development. One can either explore how some concrete solutions of GR are obtained in this way, or study the quantum mechanics of gravity (i.e. perturbative quantum gravity) in this language. The language of connections is simpler in many aspects than the usual metric formalism for GR, and the hope is that this simplicity will lead to qualitatively new understanding of what gravity really is.

Relevant Publications
  • http://arXiv.org/abs/arXiv:1202.6183
  • http://arxiv.org/abs/1312.2831
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Title Acceleration, black holes and thermality in quantum field theory
Group(s) Mathematical Physics
Proposer(s) Dr Jorma Louko
Description

Hawking's 1974 prediction of black hole radiation continues to inspire the search for novel quantum phenomena associated with global properties of spacetime and with motion of observers in spacetime, as well as the search for laboratory systems that exhibit similar phenomena. At a fundamental level, a study of these phenomena provides guidance for developing theories of the quantum mechanical structure of spacetime, including the puzzle of the microphysical origin of black hole entropy. At a more practical level, a theoretical control of the phenomena may have applications in quantum information processing in situations where gravity and relative motion are significant, such as quantum communication via satellites.

Specific areas for a PhD project could include:

Model particle detectors as a tool for probing nonstationary quantum phenomena in spacetime, such as the onset of Hawking radiation during gravitational collapse. See arXiv:1406.2574 and references therein.

Black hole structure behind the horizons as revealed by quantum field observations outside the horizons. See arXiv:1001.0124 and references therein.

Quantum fields in accelerated cavities. See arXiv:1210.6772 and arXiv:1411.2948 and references therein.

Relevant Publications
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Title Scattering in disordered systems with absorption: beyond the universality
Group(s) Mathematical Physics
Proposer(s) Dr Alexander Ossipov
Description

The study of wave scattering in quantum systems with disorder or underlying classical chaotic dynamics is essential for an understanding of many different physical systems. These include, for example, light propagation in random media, transport of electrons in quantum dots, transmission of microwaves in waveguides and cavities, and many others.

An important feature of any real experiment on scattering is the presence of absorption. As the result, not all the incoming flux is either reflected or transmitted through system, but part of it is irreversibly lost in the environment.

In recent years, considerable progress has been made in the study of scattering in disordered or chaotic quantum systems in the presence of absorption, see e.g Fyodorov, Savin & Sommers, (2005). However almost all results known so far are restricted by the so called "universal limit" described by the conventional Random Matrix Theory. The idea of the suggested project is to go beyond the "universal limit" and to investigate properties of the scattering matrix in lossy systems for the case of a quasi-one-dimensional disordered waveguide. This model describes for example electron dynamics in a thick disordered wire or propagation of light or microwave radiation in a slab geometry. There are two recent advances making an analytical treatment of this problem feasible. The first one is a discovery of a kind of fluctuation dissipation relation between the properties of an open system in the presence of absorption and a certain correlation function of its closed counterpart. This can be exploited, for example, to relate statistics of scattering characteristics to eigenfunction fluctuations in closed systems (Ossipov & Fyodorov, 2005). The second one is a new analytical insight into properties of quasi-one-dimensional disordered conductors, see Skvortsov & Ostrovsky, (2006).

Relevant Publications
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Title Quantum learning for large dimensional quantum systems
Group(s) Mathematical Physics
Proposer(s) Dr Madalin Guta
Description

This project stems from the ongoing collaboration with Theo Kypraios and Ian Dryden (Statistics group, Nottingham), Cristina Butucea (Univesite Paris Est) and Thomas Monz and Philipp Schindler (Rainer Blatt trapped ions experimental group, University of Innsbruck). The aim is to explore and investigate new methods for learning quantum states of large dimensional quantum systems. The efficient statistical reconstruction of such states is a crucial enabling tool for current quantum engineering experiments in which multiple qubits can be controlled and prepared in exotic entangled states. However, standard estimation methods such as maximum likelihood become practically unfeasible for systems of merely 10 qubits, due to the exponential growth of the Hilbert space with the number of qubits. Therefore new methods are needed which are able to "learn" the structure of the quantum state by making use of prior information encoded in physically relevant low dimensioanal models.

In [1] we investigated the use of model selection methods for state estimation, in particular the Akaike information criterion and  the Bayesian information criterion.  The general principle is to find the simplest, or most parsimonious explanation of the data, by fitting different models and choosing the estimator with the best trade-off between likelihood fit and model complexity, the latter being given by the rank of the density matrix. Another rank selection technique was considered in [2] and its performance under compressed sensing [3,4] measurements is currently analysed from a statistical viewpoint.

The goal of the project is to compare the efficiency of the different methods, and explore new, possibly hybrid estimators which are both accurate and computationally efficient. Possible directions to be explored include models bases on matrix product states, optimal design of experiments, quantum pattern recognition, asymptotical structure of the statistical models. The project will involve both theoretical and computational work at the overlap between quantum information theory and modern statistical inference.

Relevant Publications
  • [1] M. Guta, T. Kypraios and I. Dryden, Rank based model selection for multiple ions quantum tomography New Journal of Physics, 14, 105002 (2012), Arxiv: 1206.4032
  • [2] C. Butucea, M. Guta, T. Kypraios, Spectral thresholding quantum tomography for low rank states, New Journal of Physics, 17 113050 (2015), ArXiv:1504.08295
  • [3] D. Gross, Y. K. Liu, S. Flammia, S. Becker and J. Eisert, Physical Review Letters 105 150401 (2010) Arxiv:0909.3304
  • [4] S. Flammia, D. Gross, Y.K. Liu and J. Eisert Quantum Tomography via Compressed Sensing: Error Bounds, Sample Complexity, and Efficient Estimators New Journal of Physics 14, 095022 (2012) ArXiv:1205.2300
Other information

Click here to  find more information on this topic and some illustrations of different types of estimators. For more about my reasearch interests you can visit my homepage.

Title Feedback control of quantum dynamical systems and applications in metrology
Group(s) Mathematical Physics
Proposer(s) Dr Madalin Guta
Description

 

The ability to manipulate, control and measure quantum systems is a central issue in Quantum Technology applications such as quantum computation, cryptography, and high precision metrology [1].
Most realistic systems interact with an environment and it is important to understand how this affects the performance of quantum protocols and how it can be used to improve it.
The input-output theory of quantum open systems [2] offers a clear conceptual understanding of quantum dynamical systems and continuous-time measurements, and has been used extensively at interpreting experimental data in quantum optics.
Mathematically, we deal with an extension of the classical filtering theory used in control engineering at estimating an unobservable signal of interest from some available noisy data [3].
 

This projects aims at investigating the identification and control of quantum dynamical systems in the framework of the input-output formalism. As an example, consider a quantum system (atom) interacting with an incoming "quantum noise" (electromagnetic field); the output fields (emitted photons) emerging from the interaction can be measured, in order to learn about the system's dynamical parameters (e.g. its hamiltonian). The goal is to find optimal system identification strategies which may involve input state preparation, output measurement design, and quantum feedback control. An interesting related question is to understand the information-disturbance trade-off which in the context of quantum dynamical systems becomes identification-control trade-off.

The first steps in this direction were made in [4] which introduce the concept of asymptotic quantum Fisher information for "non-linear" quantum Markov processes, and [5] which investigates system identification for linear quantum systems, using transfer functions techniques from control theory. A furhter goal is to develop genearal Central Limit theory for quantum output processes as a probablistic underpinning of the asymptotic estimation theory. Another direction is the recently found connection between dynamical phase transitions in many-body open systems and high precision metrology for dynamical parameters (see arXiv:1411.3914).

 

 

Relevant Publications
  • [1] M. A. Nielsen, I. L. Chuang, Quantum Computation and Quantum Information, Cambridge Universtiy Press (2000)
  • [2] C. Gardiner, P. Zoller, Quantum Noise: A Handbook of Markovian and Non-Markovian Quantum Stochastic Methods with Applications to Quantum Optics, Springer (2004)
  • [3] K. Zhou, J.C. Doyle and K. Glover, Robust and Optimal Control, Prentice Hall, (1995)
  • [4] M. Guta, Quantum information Fisher information and asymptotic normality in system identification for quantum Markov chains, Physical Review A, 83, 062324 (2011) Arxiv:1007.0434; M. Guta, J. Kiukas, Equivalence classes and local asymptotic normality in system identification for quantum Markov chains, Commun. Math. Phys. 335, 1397–1428 (2014)
  • [5] M. Guta and N. Yamamoto, System identification for linear passive quantum systems Short version of the archive paper appeared in Proc. 52 IEEE CDC Conference Florence 2013 arXiv:1303.3771v2
Other information

Click here to  find more information on this topic and some illustrations of different types of estimators. For more about my reasearch interests you can visit my homepage.

Title Quantum correlations in many-body systems
Group(s) Mathematical Physics
Proposer(s) Prof Gerardo Adesso
Description

The behaviour of physical systems at the microscopic scale obeys the laws of quantum mechanics. Quantum systems can share a form of quantum correlations known as entanglement, which is nowadays acknowledged as a resource for enhanced information processing. However, there are more general types of quantum correlations, beyond entanglement, that can be present in separable quantum states.

This project deals with the characterisation of the nonclassicality of correlations in multipartite quantum systems. Interesting aspects of this project are the elucidation of the relationship between these more general forms of quantum correlations, as quantified e.g. by the "quantum discord", and entanglement in mixed multipartite quantum states. Another theme will be the identification of experimentally friendly schemes to engineer quantum correlations, and detect them in practical demonstrations, as well as rigorously assessing the usefulness of quantum correlations beyond entanglement as resources for next-generation quantum information protocols.

Relevant Publications
  • C. Rodo', G. Adesso, A. Sanpera; Operational Quantification of Continuous-Variable Correlations; Phys. Rev. Lett. 100, 110505 (2008)
  • G. Adesso, A. Datta; Quantum versus classical correlations in Gaussian states; Phys. Rev. Lett. 105, 030501 (2010)
  • D. Girolami, M. Paternostro, G. Adesso; Non-classicality indicators and extremal quantum correlations in two-qubit states; arXiv:1008.4136
Other information

http://www.maths.nottingham.ac.uk/personal/ga

Title Quantum aspects of frustration in spin lattices
Group(s) Mathematical Physics
Proposer(s) Prof Gerardo Adesso
Description

Recently, a number of tools developed in the framework of quantum information theory have proven useful to tackle founding open questions in condensed matter physics, such as the characterization of quantum phase transitions and the scaling of correlations at critical points.  Our contribution to the field dealt  with a method, based on quantum informational concepts, to identify analytically factorized (unentangled) ground states in many-body spin models, which constitute an exact solution to generally non-exactly solvable models for specific values of the Hamiltonian parameters. In presence of frustration, ground state factorization is suppressed. Therefore the factorizability provides a qualitative handle on the degree of quantum frustration.

This project will build on these premises and will seek for genuine signatures of quantum versus classical frustration in spin systems, a topic of great relevance for condensed matter. Frustrated quantum models may play a key role for high-temperature superconductivity and for certain biological processes. The relationship between frustration, disorder and entanglement is yet largely unexplored.

Relevant Publications
  • S. M. Giampaolo, G. Adesso, F. Illuminati; Theory of Ground State Factorization in Quantum Cooperative Systems; Phys. Rev. Lett. 100, 197201 (2008)
  • S. M. Giampaolo, G. Adesso, F. Illuminati; Separability and ground-state factorization in quantum spin systems; Phys. Rev. B 79, 224434 (2009)
  • S. M. Giampaolo, G. Adesso, F. Illuminati; Probing Quantum Frustrated Systems via Factorization of the Ground State; Phys. Rev. Lett. 104, 207202 (2010)
Other information

http://www.maths.nottingham.ac.uk/personal/ga

Title Quantum information with non-Gaussian states
Group(s) Mathematical Physics
Proposer(s) Prof Gerardo Adesso
Description

Quantum information with continuous variable systems is a burgeoning area of research which has recorded astonishing theoretical and experimental successes, mainly thanks to the manipulation and exploitation of Gaussian states of light and matter. However, quite recently a number of tasks have been individuated which can not be perfectly implemented by using Gaussian states and operations only, and another set of processes is being explored where some non-Gaussianity has been recognised as an advantageous ingredient to sharply improve performances of quantum communication.

In this project the student will investigate the limitations of the Gaussian scenario in different contexts such as quantum communication, computation and estimation and, more generally, quantum technology. This is paralleled by recent progresses in the experimental generation of non-Gaussian states, which further motivate their application in quantum information science. Special emphasis will be put on devising efficient methods to quantify the entanglement in selected classes of non-Gaussian states, using techniques whose complexity is not exceedingly large compared to the usual tools (quadrature measurements, homodyne detection) which are effective for Gaussian states.

Relevant Publications
  • G. Adesso, F. Illuminati; Entanglement in continuous-variable systems: recent advances and current perspectives; J. Phys. A 40, 7821 (2007)
  • G. Adesso; Experimentally friendly bounds on non-Gaussian entanglement from second moments; Phys. Rev. A 79, 022315 (2009)
  • G. Adesso, F. Dell'Anno, S. De Siena, F. Illuminati, L. A. M. Souza; Optimal estimation of losses at the ultimate quantum limit with non-Gaussian states; Phys. Rev. A 79, 040305(R) (2009)
Other information

http://www.maths.nottingham.ac.uk/personal/ga

Title Developing new relativistic quantum technologies
Group(s) Mathematical Physics
Proposer(s) Prof Ivette Fuentes
Description

Relativistic quantum information is an emerging field which studies how to process information using quantum systems taking into account the relativistic nature of spacetime. The main aim of this PhD project is to find ways to exploit relativity to improve quantum information tasks such as teleportation and to develop new relativistic quantum technologies.

Moving cavities and Unruh-Dewitt type detectors promise to be suitable systems for quantum information processing [1,2]. Interestingly, motion and gravity have observable effects on the quantum properties of these systems [2,3]. In this project we will find ways to implement quantum information protocols using localized systems such as cavities and detectors. We will focus on understanding how the protocols are affected by taking into account the non-trivial structure of spacetime. We will look for new protocols which exploit not only quantum but also relativistic resources for example, the non-local quantum correlations present in relativistic quantum fields.

Relevant Publications
  • T. Downes, I. Fuentes, & T. C. Ralph Entangling moving cavities in non-inertial frames Physics Review Letters, 106, 210502 (2011)
  • D. E. Bruschi, I. Fuentes, & J. Louko Voyage to Alpha Centauri: Entanglement degradation of cavity modes due to motion accepted in Physical Review D Rapid Communications
  • N. Friis, D. E. Bruschi, J. Louko & I. Fuentes Motion generates entanglement Submitted to Physical Review D
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Title Many-body localization in quantum spin chains and Anderson localization
Group(s) Mathematical Physics
Proposer(s) Dr Alexander Ossipov
Description

Properties of wave functions in many-body systems is very active topic of research in modern condensed matter theory. Quantum spin chains are very useful models for studying quantum many-body physics. They are known to exhibit complex physical behaviour such as quantum phase transitions. Recently, they have been studied intensively in the context  of many-body localization.
 
The key idea of this project is to explore the similarity between Hamiltonians of the spin chain models and the Anderson models on d-dimensional hypercube. In such models, single particle wave functions can be localized in space due to the famous phenomenon of the Anderson localization.

Understanding of the relation between many-body localization and Anderson localization, quantum phase transitions in spin chains and the Anderson metal-insulator transition will be the main topic of this project.

Relevant Publications
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Title Entanglement of non-interacting fermions at criticality
Group(s) Mathematical Physics
Proposer(s) Dr Alexander Ossipov
Description

Entanglement of the ground state of many-particle systems has recently attracted a lot of attention. For non-interacting fermions, the ground state entanglement can be calculated from the eigenvalues of the correlation matrix of the single particle wavefunctions. For this reason, the nature of the single particle wavefunctions is crucially important for understanding of the entanglement properties of a many-body system.

The ground state entanglement is well understood now for free fermions, whose wavefuctions are simple plane waves. However, there are almost no analytical results available in the case where wavefuctions are non-trivial.

This project will explore the ground state entanglement at the quantum critical point of the metal-insulator transition, where single particle wavefunctions are known to have self-similar fluctuations, characterised by non-trivial fractal dimensions.

Relevant Publications
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Title Gravity at all scales
Group(s) Mathematical Physics
Proposer(s) Dr Thomas Sotiriou
Description

Various projects are available on the interplay between any of the following areas: quantum gravity, alternative theories of gravity, strong gravity and black holes.

The description of phenomena for which gravity is important and also are in the realm of quantum physics requires a quantum gravity theory. Developing candidate theories to the extent that they can be confronted with observations is a very challenging task. In their classical limit these theories are mostly expected to deviate from General Relativity. In this sense, classical alternative gravity theories can be the interface between quantum gravity theory and classical phenomenology.

The gravitational interaction is much less explored in regimes where gravity is strong, such as in the vicinity of black holes or veer compact stars. These system can be thought of as natural laboratories for gravity.

The overall scope is to follow a synthetic approach which will combine results about the behavior of gravity at all different scales - from the quantum to astrophysical and cosmological system - in order to provide new insights.

See also http://thomassotiriou.wix.com/challenginggr for further info

Relevant Publications
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Title Topological Resonances on Graphs
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

If a light wave in a resonator between two almost perfect mirrors shows resonance if the wavelength is commensurate with the distance between the two mirrors. If this condition is satisfied it will decay much slower than at other wavelengths which are not commensurate. This is one of the simplest mechanisms for a resonace in a wave system. There are other weill known mechanisms that rely on complexity and disorder. It has recently been observed that a netork of wire may have a further mechanism that leads to resonances. This mechanism relies on cycles in the network and leads to various signatures which cannot be explained using other well-known mechanisms for resonances. In this project these signatures will be analysed in detail.

Relevant Publications
  • GNUTZMANN, S., SMILANSKY, U. and DEREVYANKO, S., 2011. Stationary scattering from a nonlinear network Physical Review A. 83, 033831
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Title Quantum Chaos in Combinatorial Graphs
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

Graphs consist of V vertices connected by B bonds (or edges). They are used in many branches of science as simple models for complex structures. In mathematics and physics one is strongly interested in the eigenvalues of the V x V connectivity matrix C of a graph. The matrix element C_ij of the latter is defined to be the number of bonds that connect the i'th vertex to the j'th vertex.

In this PhD project the statistical properties of the connectivity spectra in (generally large) graph structures will be analysed using methods known from quantum chaos. These methods have only recently been extended to combinatorial graphs (Smilansky, 2007) and allow to represent the density of states and similar spectral functions of a graph as a sum over periodic orbits. The same methods have been applied successfully to metric graphs and quantum systems in the semiclassical regime for more than two decades.

Relevant Publications
  • Idan Oren, Amit Godel and Uzy Smilansky Trace formulae and spectral statistic for discrete Laplacians on regular graphs (I) J. Phys. A: Math. Theor. 42 (2009) 415101
  • Idan Oren, Amit Godel and Uzy Smilansky Trace formulae and spectral statistic for discrete Laplacians on regular graphs (II) J. Phys. A: Math. Theor. 43 (2010) 225205
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Title Supersymmetric field theories on quantum graphs and their application to quantum chaos
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

Quantum graphs are a paradigm model for quantum chaos. They consist of a system of wires along which waves can propagate. Many properties of the excitation spectrum and the spatial distribution of standing waves can be mapped exactly onto a supersymmetric field theory on the network. In a mean-field approximation one may derive various universal properties for large quantum graphs. In this project we will focus on deviations from universal behaviour for finite quantum graphs with the field-theoretic approach.

Relevant Publications
  • GNUTZMANN, S, KEATING, J.P. and PIOTET, F., 2010. Eigenfunction statistics on quantum graphs Annals of Physics. 325(12), 2595-2640
  • GNUTZMANN, S., KEATING, J.P. and PIOTET, F., 2008. Quantum Ergodicity on Graphs PHYSICAL REVIEW LETTERS. VOL 101(NUMB 26), 264102
  • GNUTZMANN, S. and SMILANSKY, U., 2006. Quantum graphs: applications to quantum chaos and universal spectral statistics Advances in Physics. 55(5-6), 527-625
  • GNUTZMANN, S. and ALTLAND, A., 2005. Spectral correlations of individual quantum graphs. Physical Review E. 72, 056215
  • GNUTZMANN, S. and ALTLAND, A., 2004. Universal spectral statistics in quantum graphs. Physical Review Letters. 93(19), 194101
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Title Pseudo-orbit expansions in quantum graphs and their application
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

Quantum graphs are a paradigm model to understand and analyse the effect of complexity on wave propagation and excitations in a network of wires. They have also been used as a paradigm model to understand topics in quantum and wave chaos where the complexity has a different origin while the mathematical framework is to a large extent analogous.

Many properties of the waves that propagate through such a network can be described in terms of trajectories of a point particle that propagates through the network. The ideas is to write a property of interest as a sum over amplitudes (complex numbers) connected to all possible trajectories of the point particle. These sums remain challenging objects for explicit evaluations. Recently a numer of advanced methods for their summation have been introduced. The latter are built on so-called pseudo-orbits. In this project these methods will be develloped further and applied to questions related to quantum chaos and random-matrix theory.

Relevant Publications
  • Daniel Waltner, Sven Gnutzmann, Gregor Tanner, Klaus Richter, A sub-determinant approach for pseudo-orbit expansions of spectral determinants, arXiv:1209.3131 [nlin.CD]
  • Ram Band, Jonathan M. Harrison, Christopher H. Joyner, Finite pseudo orbit expansions for spectral quantities of quantum graphs, arXiv:1205.4214 [math-ph]
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Title The ten-fold way of symmetries in quantum mechanics. An approach using coupled spin operators.
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

About 50 years ago Wigner and Dyson proposed a three-fold symmetry classification for quantum mechanical systems -- these symmetry classes consisted of time-reversal invariant systems with integer spin which can be described by real symmetric matrices, time-reversal invariant systems with half-integer spin which can be described by real quaternion matrices, and systems without any time-reversal symmetry which are described by complex hermitian matrices. These three symmetry classes had their immediate application in the three classical Gaussian ensembles of random-matrix theory: the Gaussian orthogonal ensemble GOE, the Gaussian symplectic ensemble GSE, and the Gaussian unitary ensemble GUE. In the 1990's this classification was extended by adding charge conjugation symmetries -- symmetries which relate the positive and negative part of a spectrum and which are described by anti-commutators.
The classification was completed by Altland and Zirnbauer who have shown that there are essentially only seven further symmetry classes on top of the Wigner-Dyson classes leading to what is now known as the 'ten-fold way'. All symmetry classes have applications in physics. The new symmetry classes are realised by various cases of the Dirac equation and the Bogoliubov-de Gennes equation. For a long time people have thought of these symmetries only in the context of many-body physics or quantum field theory. However there are simple quantum mechanical realisations of all ten symmetry classes which in terms of two coupled spins where the classification follows from properties of the coupling parameters and of the irreducible SU(2) representations on which the spin operators act. This project will explore these simple representations in the quantum mechanical and semiclassical context. One goal will be to understand the implications of the quantum mechanical symmetries for the corresponding classical dynamics which appears in the semiclassical limit of large spins.

Relevant Publications
  • M.R. Zirnbauer, Riemannian symmetric superspaces and their origin in random matrix theory, J. Math. Phys. 37, 4986 (1996)
  • A. Altland, M.R. Zirnbauer, Non-standard symmetry classes in mesoscopic normal-/superconducting hybrid structures, Phys. Rev. B 55, 1142 (1997)
  • S. Gnutzmann and B. Seif, Universal spectral statistics in Wigner-Dyson, chiral, and Andreev star graphs. I. Construction and numerical results, Physical Review E 69, 056219 (2004)
  • S. Gnutzmann and B. Seif, Universal spectral statistics in Wigner-Dyson, chiral, and Andreev star graphs. II. Semiclassical approach. Physical Review E 69, 056220 (2004)
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Title Nonlinear waves in waveguide networks
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

Many wave guides (such as optical fibres) show a Kerr-type effect that leads to nonlinear wave propagation. If th wave guides are coupled at junctions then there is an additional element of complexity due to the non-trivial connectivity of wave guides. In this project the impact of the structure and topology of the network on wave propagation will be studied starting from simple geometries such as a Y-junctions (three waveguides coupled at one junction), a star (many waveguides at one junction), or a lasso (a waveguide that forms a loop and is connected at one point to a second waveguide).

Relevant Publications
  • Sven Gnutzmann, Uzy Smilansky, and Stanislav Derevyanko, Stationary scattering from a nonlinear network, Phys. Rev. A 83, 033831 (2011)
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Title The statistics of nodal sets in wavefunctions
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

If a membrane vibrates at one of its resonance frequencies there are certain parts of the membrane that remain still. These are called nodal points and the collection of nodal points forms the nodal set. Building on earlier work this project will look at the statistical properties of the nodal set -- e.g. for 3-dimensional waves the nodal set consists of a coillection of surfaces and one may ask questions about how the area of the nodal set is distributed for an ensemble of membranes or for an ensemble of different resonances of the same membrane. This project will involve a strong numerical component as wavefunctions of irregular membranes need to be found and analysed on the computer. Effective algorithms to find the area of the nodal set, or the number of domain in which the sign does not change (nodal domains) will need to be developed andimplemented.

Relevant Publications
  • Galya Blum, Sven Gnutzmann, Uzy Smilansky, Nodal domains statistics- a criterion for quantum chaos, Phys. Rev. Lett. 88, 114101 (2002)
  • Alejandro G. Monastra, Uzy Smilansky and Sven Gnutzmann, Avoided intersections of nodal lines, J. Phys. A. 36, 1845-1853 (2003)
  • G. Foltin, S. Gnutzmann and U. Smilansky, The morphology of nodal lines- random waves vs percolation, J. Phys. A 37, 11363 (2004)
  • Yehonatan Elon, Sven Gnutzmann, Christian Joas and Uzy Smilansky, Geometric characterization of nodal domains: the area-to-perimeter ratio, J. Phys. A 40, 2689 (2007)
  • S. Gnutzmann, P. D. Karageorge and U Smilansky, Can one count the shape of a drum?, Phys. Rev. Lett. 97, 090201 (2006)
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Title Coherent states, nonhermitian Quantum Mechanics and PT-symmetry
Group(s) Mathematical Physics, Industrial and Applied Mathematics
Proposer(s) Dr Sven Gnutzmann
Description

Heisenberg's uncertainty principle states that momentum and position cannot be sharp at the same time because there is a lower bound for the product of the uncertaincies. Coherent states can be defined as the states that minimize the uncertainty -- in this sense they are as close as quantum mechanics allows to describe a classical point particle. When a quantum system starts in a coherent states it's expectation values follow the classical equations of motion while the shape of the wave function often changes only very slowly. Coherent states are an important tool to understand the corresp[ondence between quantum and classical dynamics.

In this project this correspondence will be analysed for a generalized quantum dynamics where the Hamilton operator is not required to be Hermitian. Such dynamics can arise in practice as an effective description for an open quantum system with eitehr decay or gain. Accordingly the energy eigenvalues may have an imaginary part that describes the loss or gain. Recently there have also be suggestions that non-hermitian Hamilton operators could play a fundamental role in quantum mechanics if the Hamilton operator remains symmetric with respect to a combined operatyion of parity P and time reversal T. Such PT-symmetric dynamics have a balance between gain and loss which can lead to real energy eigenvalues. Classical to quantum correspondence for such systems remains an open research topic and this project will aim at getting a clear understanding of the underlying classical dynamics using coherent states as the main tool.

Relevant Publications
  • S.Gnutzmann, M Kus, Coherent states and the classical limit on irreducible SU3 representations, J. Phys. A 31, 9871 (1998)
  • E.-M. Graefe, M. Höning, H.J. Korsch, Classical limit of non-Hermitian quantum dynamic - a generalized canonical structure, J. Phys A 43, 075306 (2010)
  • E.-M. Graefe, R. Schubert, Complexified coherent states and quantum evolution with non-Hermitian Hamiltonians, J. Phys. A 45, 244033 (2012)
  • C.M. Bender, M. DeKieviet, S.P. Klevansky, PT Quantum Mechanics, Philosophical Transactions of the Royal Society A 371, 20120523 (2013)
Other information
Title Geometry and analysis of Schubert varieties
Group(s) Number Theory and Geometry
Proposer(s) Dr Sergey Oblezin
Description

Schubert varieties is a basic tool of classical algebraic and enumerative geometry. In modern mathematics these geometric object arise widely in representation theory, theory of automorphic forms and in harmonic analysis. In particular, it appears that the classical geometric structures can be naturally extended to infinite-dimensional setting (loop groups and, more generally, Kac-Moody groups), and such generalizations provide new constructions in infinite-dimensional geometry. Moreover, many of the arising constructions are supported by (hidden) symmetries and dualities of quantum (inverse) scattering theory and quantum integrability. Possible PhD projects will be devoted to extensive development of harmonic analysis on Schubert varieties with further applications to automorphic forms, arithmetic goemetry and number theory.

Relevant Publications
  • A.Gerasimov; D.Lebedev; S.Oblezin, Parabolic Whittaker functions and topological field theories I. Commun. Number Theory Phys. 5 (2011), no. 1, 135–201
Other information
Title Orthogonal polynomials in probability, representation theory and number theory
Group(s) Number Theory and Geometry
Proposer(s) Dr Sergey Oblezin
Description

Orthogonal ensembles play a crucial role in many areas including random matrix theory, probability and harmonic analysis. In the recent decades a new striking connections with the theory of automorphic forms and number theory appeared. However, there is a definite lack of general results and implementations at present. Possible PhD projects will be aiming at developing these recent interactions among the group theory, harmonic analysis and number theory.

Relevant Publications
  • I.G. Macdonald, Symmetric functions and Hall polynomials. Second edition.
  • I.G.Macdonald, Affine Hecke algebras and orthogonal polynomials.
  • A.Gerasimov; D.Lebedev; S.Oblezin, Baxter operator formalism for Macdonald polynomials. Lett. Math. Phys. 104 (2014), no. 2, 115–139
Other information
Title Number theory in a broad context
Group(s) Number Theory and Geometry
Proposer(s) Prof Ivan Fesenko
Description

Ivan Fesenko studies zeta functions in number theory using zeta integrals. These integrals are better to operate with than the zeta functions, they translate various properties of zeta functions into properties of adelic objects. This is a very powerful tool to understand and prove fundamental properties of zeta functions in number theory. In the case of elliptic curves over global fields, associated zeta functions are those of regular models of the curve, i.e. the zeta function of a two dimensional object. Most of the classical work has studied arithmetic of elliptic curves over number fields treating them as one dimensional objects and working with with generally noncommutative Galois groups over the number field, such as the one generated by all torsion points of the curve. The zeta integral gadget works with adelic objects associated to the two dimensional field of functions of the curve over a global field and using commutative Galois groups. The latter has already been investigated in two dimensional abelian class field theory and it is this theory which supplies adelic objects on which the zeta integral lives. For example, Fourier duality on adelic spaces associated to the model of the curve explains the functional equation of the zeta function (and of the L-function of the curve).  

The theory uses many parts of mathematics: class field theory, higher local fields and several different adelic structures, translation invariant measure and integration on higher local fields (arithmetic loop spaces), functional analysis and harmonic analysis on such large spaces, groups endowed with sequential topologies, parts of algebraic K-theory, algebraic geometry. This results in a beautiful conceptual theory. 

There are many associated research problems and directions at various levels of difficulty and opportunities to discover new objects, structures and laws.

Relevant Publications
Other information
Title Computational methods for elliptic curves and modular forms
Group(s) Number Theory and Geometry
Proposer(s) Dr Christian Wuthrich
Description

Computational Number Theory is a fairly recent part of pure mathematics even if computations in number theory are a very old subject. But over the last few decades this has changed dramatically with the modern, powerful and cheap computers. In the area of explicit computations on elliptic curves, there are two subjects that underwent a great development recently: elliptic curves over finite fields (which are used for cryptography) and 'descent' methods on elliptic curves over global fields, such as the field of rational numbers.

It is a difficult question for a given elliptic curve over a number field to decide if there are infinitely many solutions over this field, and if so, to determine the rank of the Mordell-Weil group. Currently, there are only two algorithms implemented for finding this rank, one is the descent method that goes back to Mordell, Selmer, Cassels,... and the other is based on the work of Gross, Zagier, Kolyvagin... using the link of elliptic curves to modular forms. While the first approach works very well over number fields of small degree, it becomes almost impossible to determine the rank of elliptic curves over number fields of larger degree. The second method unfortunately is not always applicable, especially the field must be either the field of rational numbers or a quadratic extension thereof.

There is another way of exploiting the relation between elliptic curves and modular forms by using the p-adic theory of modular forms and the so-called Iwasawa theory for elliptic curves. Results by Kato, Urban, Skinner give us a completely new algorithm for computing the rank and other invariants of the elliptic curve, but not much of this has actually been implemented. Possible PhD projects could concern the further development of these new methods and their implementation.

Relevant Publications
Other information
Title Variants of automorphic forms and their L-functions
Group(s) Number Theory and Geometry
Proposer(s) Dr Nikolaos Diamantis
Description

Classical automorphic forms are a powerful tool for handling difficult number theoretic problems. They provide links between analytic, algebraic and geometric aspects of the study of arithmetic problems and, as such, they are at the heart of the major research programmes in Number Theory, e.g. Langlands programme. Crucial for these links are certain functions associated to automorphic forms, called L-functions, which are the subject of some of the most important conjectures of Mathematics.

In recent years, investigations into the theory of automorphic forms have led into the study of variants of automorphic forms and of their L-functions, such as quasi-modular forms, harmonic Maass forms, mock modular forms, higher order modular forms and multiple Dirichlet series. In most cases, the motivation for introducing these objects was not just to generalize the classical automorphic forms and their L-functions, but to obtain novel tools to address already stated number theoretic problems. The techniques associated with these new objects in turn raise new interesting questions  and highlight connections beyond the original motivating problems. For example, the theory of harmonic Maass forms and modular forms has been used to resolve problems in partitions of numbers, and higher order modular forms have been applied to Percolation Theory problems in Physics.

As these techniques have only recently been discovered, they lead to a number of very interesting open questions, e.g. how to construct mock modular forms encoding specific partition functions, how to determine the arithmetic nature of high-order forms or how to use the theory of multiple Dirichlet series to bound moments of the Riemann zeta function. Questions of this type, are highly relevant both for the outstanding problems in classical automorphic forms and for the further development of the new subjects themselves. Therefore, many of these questions are very appropriate for a PhD project.
 

Relevant Publications
Other information
Title Foundations of adaptive finite element methods for PDEs
Group(s) Scientific Computation, Algebra and Analysis
Proposer(s) Dr Kris van der Zee
Description

Foundations of adaptive finite element methods for PDEs
(Or- Why do adaptive methods work so well?) 

Adaptive finite element methods allow the computation of solutions to partial differential equations (PDEs) in the most optimal manner that is possible. In particular, these methods require the least amount of degrees-of-freedom to obtain a solution up to a desired accuracy! In recent years a theory has emerged that explains this behaviour. It relies on classical a posteriori error estimation, Banach contraction, and nonlinear approximation theory. Unfortunately, the theory so far applies only to specific model problems.

Challenges for students:
* How can the theory be extended to, for example, nonsymmetric problems, nonlinear problems, or time-dependent problems?
* What about nonstandard discretisation techniques such as, discontinuous Galerkin, isogeometric analysis, or virtual element methods? 

Depending on the interest of the student, several of these issues (or others) can be addressed.
Also, the student is encouraged to suggest a second supervisor, possibly from another group! 

Relevant Publications
  • J.M. Cascon, C. Kreuzer, R.H. Nochetto, and K.G. Siebert, Quasi-optimal convergence rate for an adaptive finite element method, SIAM J. Numer. Anal. 26 (2008), pp. 2524-2550
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Title Partitioned-domain concurrent multiscale modelling
Group(s) Scientific Computation, Mathematical Medicine and Biology
Proposer(s) Dr Kris van der Zee
Description

Partitioned-domain concurrent multiscale modelling
(Or- How does one get cheap, but accurate, models?)

Multiscale modeling is an active area of research in all scientific disciplines. The main aim is to address problems involving phenomena at disparate length and/or time scales that span several orders of magnitude! An important multiscale-modeling type is known as partitioned-domain concurrent modelling. This type addresses problems that require a fine-scale model in only a small part of the domain, while a coarse model is employed in the remainder of the domain. By doing this, significant computational savings are obtained compared to a full fine-scale model. Unfortunately, it is far from trivial to develop a working multiscale model for a particular problem.

Challenges for students:
* How can one couple, e.g., discrete (particle) systems with continuum (PDE) models?
* Or a fine-scale PDE with a coarse-scale PDE?
* How can one decide on the size and location of the fine-scale domain?
* Is it possible to proof the numerically observed efficiency of concurrent multiscale models? 
* Can the multiscale methodology be applied to biological growth phenomena (e.g., tumours) where one couples cell-based (agent-based) models with continuum PDE models?

Depending on the interest of the student, several of these issues (or others) can be addressed.
Also, the student is encouraged to suggest a second supervisor, possibly from another group!

Relevant Publications
  • J.T. Oden, S. Prudhomme, A. Romkes, and P.T. Bauman, Multiscale modeling of physical phenomena: Adaptive control of models, SIAM J. Sci. Comput. 28 (2006), pp. 2359-2389
Other information
Title Phase-field modelling of evolving interfaces
Group(s) Scientific Computation, Mathematical Medicine and Biology
Proposer(s) Dr Kris van der Zee
Description

Phase-field modelling of evolving interfaces
(Or – How does one effectively model and simulate interfacial phenomena?)

Evolving interfaces are ubiquitous in nature, think of the melting of the polar ice caps, the separation of oil and water, or the growth of cancerous tumours. Two mathematical descriptions exist to model evolving interfaces: those with sharp-interface descriptions, such as parametric and level-set methods, and those with diffuse-interface descriptions, commonly referred to as phase-field models.

Challenges for students:
* Can one develop a phase-field model for a particular interfacial phenomenon?
* What are the foundational laws underpinning phase-field models?
* What is the connection between sharp-interface models and phase-field models?
* Can one design stable time-stepping schemes for phase-field models?
* Or efficient adaptive spatial discretisation methods?

Depending on the interest of the student, one of these issues (or others) can be addressed.
Also, the student is encouraged to suggest a second supervisor, possibly from another group! 

Relevant Publications
  • H. GOMEZ, K.G. VAN DER ZEE, Computational Phase-Field Modeling, in Encyclopedia of Computational Mechanics, Second Edition, E. Stein, R. de Borst and T.J.R. Hughes, eds., to appear
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Title Numerical methods for stochastic partial differential equations
Group(s) Scientific Computation, Statistics and Probability
Proposer(s) Prof Michael Tretyakov
Description

Numerics for stochastic partial differential equations (SPDEs) is one of the central topics in modern numerical analysis. It is motivated both by applications and theoretical study. SPDEs essentially originated from the filtering theory and now they are also widely used in modelling spatially distributed systems from physics, chemistry, biology and finance acting in the presence of fluctuations. The primary objectives of this project include construction, analysis and testing of new numerical methods for SPDEs.

 

Relevant Publications
Other information

Web-page http://www.maths.nott.ac.uk/personal/pmzmt

Title Property Prediction of Composite Components Prior to Production
Group(s) Scientific Computation, Statistics and Probability
Proposer(s) Prof Michael Tretyakov, Prof Frank Ball
Description

Property Prediction of Composite Components Prior to Production

Supervisors: Dr Frank Gommer1*, Prof Michael Tretyakov2*, Prof Frank Ball2 , Dr Louise P. Brown1

University of Nottingham, University Park, Nottingham NG7 2RD, UK

1 Polymer Composites Group, Faculty of Engineering

2 School of Mathematical Sciences

* Contact: F.Gommer@nottingham.ac.uk or Michael.Tretyakov@nottingham.ac.uk

 

This is an exciting opportunity for a postgraduate student to join a vibrant inter-disciplinary team and to work in the modern area of Uncertainty Quantification.

Fibre reinforced composites are increasingly used in the transport industry to decrease the structural weight of a vehicle and thus increase its fuel efficiency. The importance of the UK composite sector is reflected in the current growth rate of 17% pa for high performance composite components and the expected gross value of £2 billion in 2015 [1]. However, due to the large number of production steps and the necessary saturation of the fibre preform with a resin matrix, a significant amount of waste is produced, which may range between 2% and 20% of the production volume [2]. A major cause of rejecting parts is variability in the reinforcement, such as varying yarn spacing and yarn path waviness, which can significantly influence subsequent properties. For example, these variabilities can affect resin flow and may cause dry spots or reduce mechanical properties. This PhD project will enable the successful candidate to work at the forefront of material science, combining engineering standards, applied mathematics and statistics, with a potential of making an impact on the way of manufacturing composite parts in the future.

This proposed doctoral study aims to demonstrate that properties of light-weight fibre reinforced plastics can be predicted in real time before a part is actually manufactured. Data gained from images taken of each layer of a composite during the stacking process are used to determine local geometries and variabilities, within and in-between individual layers [3]. For example, based on the measured textile geometries it will be possible to predict the resin flow within a preform during a liquid composite moulding (LCM) process considering individual variabilities before injection. These specific flow predictions will allow adjustments of the process parameters during the impregnation process to ensure full saturation of the entire preform with a liquid resin matrix. This will be especially useful when a number of inlet and outlet ports are present such as in the case of complex or large parts. The formation of dry spots will be avoided, which will reduce immediate wastage. For these predictions, faster solutions than currently available are necessary. To find such solutions, appropriate advanced statistical techniques and stochastic modelling for quantifying uncertainties in composites production will be developed in the course of the PhD project.

In addition, the developed techniques will also allow virtual testing of a finished component with its specific inherent reinforcement variability. This will make it feasible to customise predictions for every fabricated component. In combination with continuous health monitoring of a structure, it may be possible to estimate the influence of loading conditions, load cycles and damage evaluation. This will also make it possible to predict an individual life expectancy of a part in service. These data can then be used to determine customised inspection intervals for each component.

We require an enthusiastic graduate with a 1st class degree in Mathematics or Engineering, preferably of the MMath/MSc level, with good programming skills and willing to work as a part of an interdisciplinary team. A candidate with a solid background in statistics will have an advantage.

References

[1] CompositesUK. www.compositesuk.co.uk/Information/FAQs/UKMarketValues.aspx.

[2] A. C. Long, Design and Manufacture of Textile Composites: Woodhead Publ, 2005.

[3] F. Gommer, L. P. Brown, and R. Brooks, “Quantification of meso-scale variability and geometrical reconstruction of a textile”, submitted to Compos Part A-Appl S, 2015.

Relevant Publications
Other information

This project is supported by  EPSRC DTG Centre in Complex Systems and Processes, see elligibility and how to apply at http://www.nottingham.ac.uk/complex-systems/index.aspx

Title Index policies for stochastic optimal control
Group(s) Statistics and Probability
Proposer(s) Dr David Hodge
Description

Since the discovery of Gittins indices in the 1970s for solving multi-armed bandit processes the pursuit of optimal policies for this very wide class of stochastic decision processes has been seen in a new light. Particular interest exists in the study of multi-armed bandits as problems of optimal allocation of resources (e.g. trucks, manpower, money) to be shared between competing projects. Another area of interest would be the theoretical analysis of computational methods (for example, approximative dynamic programming) which are coming to the fore with ever advancing computer power.


Potential project topics could include optimal decision making in the areas of queueing theory, inventory management, machine maintenance and communication networks.

Relevant Publications
Other information

Keywords: multi-armed bandits, dynamic programming, Markov decision processes

Title Semi-Parametric Time Series Modelling Using Latent Branching Trees
Group(s) Statistics and Probability
Proposer(s) Dr Theodore Kypraios
Description

A class of semi-parametric discrete time series models of infinite order where we are be able to specify the marginal distribution of the observations in advance and then build their dependence structure around them can be constructed via an artificial process, termed as Latent Branching Tree (LBT). Such a class of models can be very useful in cases where data are collected over long period and it might be relatively easy to indicate their marginal distribution but much harder to infer about their correlation structure. The project is concerned with the development of such models in continuous-time as well as developing efficient methods for making Bayesian inference for the latent structure as well as the model parameters. Moreover, the application of such models to real data would be also of great interest.

Relevant Publications
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Title Ion channel modelling
Group(s) Statistics and Probability
Proposer(s) Prof Frank Ball
Description

The 1991 Nobel Prize for Medicine was awarded to Sakmann and Neher for developing a method of recording the current flowing across a single ion channel. Ion channels are protein molecules that span cell membranes. In certain conformations they form pores allowing current to pass across the membrane. They are a fundamental part of the nervous system. Mathematically, a single channel is usually modelled by a continuous time Markov chain. The complete process is unobservable but rather the state space is partitioned into two classes, corresponding to the receptor channel being open or closed, and it is only possible to observe which class of state the process is in. The aim of single channel analysis is to draw inferences about the underlying process from the observed aggregated process. Further complications include (a) the failure to detect brief events and (b) the presence of (possibly interacting) multiple channels. Possible projects include the development and implementation of Markov chain Monte Carlo methods for inferences for ion channel data, Laplace transform based inference for ion channel data and the development and analysis of models for interacting multiple channels.

Relevant Publications
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Title Optimal control in yield management
Group(s) Statistics and Probability
Proposer(s) Dr David Hodge
Description

Serious mathematics studying the maximization of revenue from the control of price and availability of products has been a lucrative area in the airline industry since the 1960s. It is particularly visible nowadays in the seemingly incomprehensible price fluctuations of airline tickets. Many multinational companies selling perishable assets to mass markets now have large Operations Research departments in-house for this very purpose. This project would be working studying possible innovations and existing practices in areas such as: customer acceptance control, dynamic pricing control and choice-based revenue management. Applications to social welfare maximization, away from pure monetary objectives, and the resulting game theoretic problems are also topical in home energy consumption and mass online interactions.

Relevant Publications
Other information
Title Stochastic Processes on Manifolds
Group(s) Statistics and Probability
Proposer(s) Prof Huiling Le
Description

As well as having a wide range of direct applications to physics, economics, etc, diffusion theory is a valuable tool for the study of the existence and characterisation of solutions of partial differential equations and for some major theoretical results in differential geometry, such as the 'Index Theorem', previously proved by totally different means. The problems which arise in all these subjects require the study of processes not only on flat spaces but also on curved spaces or manifolds. This project will investigate the interaction between the geometric structure of manifolds and the behaviour of stochastic processes, such as diffusions and martingales, upon them.

Relevant Publications
Other information
Title Statistical Theory of Shape
Group(s) Statistics and Probability
Proposer(s) Prof Huiling Le
Description

Devising a natural measure between any two fossil specimens of a particular genus, assessing the significance of observed 'collinearities' of standing stones and matching the observed systems of cosmic 'voids' with the cells of given tessellations of 3-spaces are all questions about shape.

It is not appropriate however to think of 'shapes' as points on a line or even in a euclidean space. They lie in their own particular spaces, most of which have not arisen before in any context. PhD projects in this area will study these spaces and related probabilistic issues and develop for them a revised version of multidimensional statistics which takes into account their peculiar properties. This is a multi-disciplinary area of research which has only become very active recently. Nottingham is one of only a handful of departments at which it is active.

Relevant Publications
Other information
Title Automated tracking and behaviour analysis
Group(s) Statistics and Probability
Proposer(s) Dr Christopher Brignell
Description

In collaboration with the Schools of Computer and Veterinary Science we are developing an automated visual surveillance system capable of identifying, tracking and recording the exact movements of multiple animals or people.  The resulting data can be analysed and used as an early warning system in order to detect illness or abnormal behaviour.  The three-dimensional targets are, however, viewed in a two dimensional image and statistical shape analysis techniques need to be adapted to improve the identification of an individual's location and orientation and to develop automatic tests for detecting specific events or individuals not following normal behaviour patterns.

Relevant Publications
Other information
Title Asymptotic techniques in Statistics
Group(s) Statistics and Probability
Proposer(s) Prof Andrew Wood
Description

Asymptotic approximations are very widely used in statistical practice. For example, the large-sample likelihood ratio test is an asymptotic approximation based on the central limit theorem. In general, asymptotic techniques play two main roles in statistics: (i) to improve understanding of the practical performance of statistics procedures, and to provide insight into why some proceedures perform better than others; and (ii) to motive new and improved approximations. Some possible topics for a Ph.D. are

  • Saddlepoint and related approximations
  • Relative error analysis
  • Approximate conditional inference
  • Asymptotic methods in parametric and nonparametric Bayesian Inference
Relevant Publications
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Title Statistical Inference for Ordinary Differential Equations
Group(s) Statistics and Probability
Proposer(s) Dr Theodore Kypraios, Dr Simon Preston, Prof Andrew Wood
Description

Ordinary differential equations (ODE) models are widely used in a variety of scientific fields, such as physics, chemistry and biology.  For ODE models, an important question is how best to estimate the  model parameters given experimental data.  The common (non-linear  least squares) approach is to search parameter space for parameter values that minimise the sum of squared differences between the model solution and the experimental data. However, this requires repeated numerical solution of the ODEs and thus is computationally expensive; furthermore, the optimisation's objective function is often highly multi-modal making it difficult to find the global optimum.  In this project we will develop computationally less demanding  likelihood-based methods, specifically by using spline regression  techniques that will reduce (or eliminate entirely) the need to solve numerically the ODEs.

Relevant Publications
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Title Statistical shape analysis with applications in structural bioinformatics
Group(s) Statistics and Probability
Proposer(s) Dr Christopher Fallaize
Description

In statistical shape analysis, objects are often represented by a configuration of landmarks, and in order to compare the shapes of objects, their configurations must first be aligned as closely as possible. When the landmarks are unlabelled (that is, the correspondence between landmarks on different objects is unknown) the problem becomes much more challenging, since both the correspondence and alignment parameters need to be inferred simultaneously.

An example of the unlabelled problem comes from the area of structural bioinformatics, when we wish to compare the 3-d shapes of protein molecules. This is important, since the shape of a protein is vital to its biological function. The landmarks could be, for example, the locations of particular atoms, and the correspondence between atoms on different proteins is unknown. This project will explore methods for unlabelled shape alignment, motivated by the problem of protein structure alignment. Possible topics include development of:
i) efficient MCMC methods to explore complicated, high-dimensional distributions, which may be highly multimodal when considering large proteins;
ii) fast methods for pairwise alignment, needed when a large database of structures is to be searched for matches to a query structure;
iii) methods for the alignment of multiple structures simultaneously, which greatly exacerbates the difficult problems faced in pairwise alignment.   

Relevant Publications
  • Green, P.J. and Mardia, K.V. (2006) Bayesian alignment using hierarchical models, with applications in protein bioinformatics. Biometrika, 93(2), 235-254.
  • Mardia, K.V., Nyirongo, V.B., Fallaize, C.J., Barber, S. and Jackson, R.M. (2011). Hierarchical Bayesian modeling of pharmacophores in bioinformatics. Biometrics, 67(2), 611-619.
Other information
Title High-dimensional molecular shape analysis
Group(s) Statistics and Probability
Proposer(s) Prof Ian Dryden
Description

In many application areas it is of interest to compare objects
and to describe the variability in shape as an object evolves over time.
For example in molecular shape analysis it is common to have several thousand
atoms and a million time points. It is of great interest to reduce the
dimension to a relatively small number of dimensions, and to describe
the variability in shape and coverage properties over time. Techniques
from manifold learning will be explored, to investigate if the variability can
be effectively described by a low dimensional manifold. A recent method for
shapes and planar shapes called principal nested spheres will be adapted for
3D shape and surfaces. Also, other non-linear dimension reduction techniques such as
multidimensional scaling will be explored, which approximate the geometry
of the higher dimensional manifold. The project will involve collaboration
with Dr Charlie Laughton of the School of Pharmacy.

Relevant Publications
  • Jung, S., Dryden, I.L. and Marron, J.S. (2012). Analysis of principal nested spheres. Biometrika, 99, 551–568.
Other information
Title Statistical analysis of neuroimaging data
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Dr Christopher Brignell
Description

The activity of neurons within the brain can be detected by function magnetic resonance imaging (fMRI) and magnetoencephalography (MEG).   The techniques record observations up to 1000 times a second on a 3D grid of points separated by 1-10 millimetres.  The data is therefore high-dimensional and highly correlated in space and time.  The challenge is to infer the location, direction and strength of significant underlying brain activity amongst confounding effects from movement and background noise levels.  Further, we need to identify neural activity that are statistically significant across individuals which is problematic because the number of subjects tested in neuroimaging studies is typically quite small and the inter-subject variability in anatomical and functional brain structures is quite large.

Relevant Publications
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Title Identifying fibrosis in lung images
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Dr Christopher Brignell
Description

Many forms of lung disease are characterised by excess fibrous tissue developing in the lungs.  Fibrosis is currently diagnosed by human inspection of CT scans of the affected lung regions.  This project will develop statistical techniques for objectively assessing the presence and extent of lung fibrosis, with the aim of identifying key factors which determine long-term prognosis.  The project will involve developing statistical models of lung shape, to perform object recognition, and lung texture, to classify healthy and abnormal tissue.  Clinical support and data for this project will be provided by the School of Community Health Sciences.

Relevant Publications
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Title Modelling hospital superbugs
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Prof Philip O'Neill, Dr Theodore Kypraios
Description

The spread of so-called superbugs such as MRSA within healthcare settings provides one of the major challenges to patient welfare within the UK. However, many basic questions regarding the transmission and control of such pathogens remain unanswered. This project involves stochastic modelling and data analysis using highly detailed data sets from studies carried out in hospital, addressing issues such as the effectiveness of patient isolation, the impact of different antibiotics, the way in which different strains interact with each other, and the information contained in data on high-resolution data (e.g. whole genome sequences).

Relevant Publications
  • Kypraios, T., O'Neill, P. D., Huang, S. S., Rifas-Shiman, S. L. and Cooper, B. S. (2010) Assessing the role of undetected colonization and isolation precautions in reducing Methicillin-Resistant Staphylococcus aureus transmission in intensive care units. BMC Infectious Diseases 10(29).
  • Worby, C., Jeyaratnam, D., Robotham, J. V., Kypraios, T., O.Neill, P. D., De Angelis, D., French, G. and Cooper, B. S. (2013) Estimating the effectiveness of isolation and decolonization measures in reducing transmission of methicillin-resistant Staphylococcus aureus in hospital general wards. American Journal of Epidemiology 177 (11), 1306-1313.
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Title Modelling of Emerging Diseases
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Prof Frank Ball
Description

When new infections emerge in populations (e.g. SARS; new strains of influenza), no vaccine is available and other control measures must be adopted. This project is concerned with addressing questions of interest in this context, e.g. What are the most effective control measures? How can they be assessed? The project involves the development and analysis of new classes of stochastic models, including intervention models, appropriate for the early stages of an emerging disease.

Relevant Publications
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Title Structured-Population Epidemic Models
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Prof Frank Ball
Description

The structure of the underlying population usually has a considerable impact on the spread of the disease in question. In recent years the Nottingham group has given particular attention to this issue by developing, analysing and using various models appropriate for certain kinds of diseases. For example, considerable progress has been made in the understanding of epidemics that are propogated among populations made up of households, in which individuals are typcially more likely to pass on a disease to those in their household than those elsewhere. Other examples of structured populations include those with spatial features (e.g. farm animals placed in pens; school children in classrooms; trees planted in certain configurations), and those with random social structure (e.g. using random graphs to describe an individual's contacts). Projects in this area are concerned with novel advances in the area, including developing and analysing appropriate new models, and methods for statistical inference (e.g. using pseudo-likelihood and Markov chain Monte Carlo methods).

Relevant Publications
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Title Bayesian Inference for Complex Epidemic Models
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Prof Philip O'Neill, Dr Theodore Kypraios
Description

Data-analysis for real-life epidemics offers many challenges; one of the key issues is that infectious disease data are usually only partially observed. For example, although numbers of cases of a disease may be available, the actual pattern of spread between individuals is rarely known. This project is concerned with the development and application of methods for dealing with these problems, and involves using the latest methods in computational statistics (e.g. Markov Chain Monte Carlo (MCMC) methods, Approximate Bayesian Computation, Sequential Monte Carlo methods etc).

Relevant Publications
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Title Bayesian model choice assessment for epidemic models
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Prof Philip O'Neill, Dr Theodore Kypraios
Description

During the last decade there has been a significant progress in the area of parameter estimation for stochastic epidemic models. However, far less attention has been given to the issue of model adequacy and assessment, i.e. the question of how well a model fits the data. This project is concerned with the development of methods to assess the goodness-of-fit of epidemic models to data, and methods for comparing different models.

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Title Epidemics on random networks
Group(s) Statistics and Probability, Mathematical Medicine and Biology
Proposer(s) Prof Frank Ball
Description

There has been considerable interest recently in models for epidemics on networks describing social contacts.  In these models one first constructs an undirected random graph, which gives the network of possible contacts, and then spreads a stochastic epidemic on that network.  Topics of interest include: modelling clustering and degree correlation in the network and analysing their effect on disease dynamics; development and analysis of vaccination strategies, including contact tracing; and the effect of also allowing for casual contacts, i.e. between individuals unconnected in the network.  Projects in this area will address some or all of these issues.

Relevant Publications
  • Ball F G and Neal P J (2008) Network epidemic models with two levels of mixing. Math Biosci 212, 69-87.
  • Ball F G, Sirl D and Trapman P (2009) Threshold behaviour and final outcome of an epidemic on a random network with household structure. Adv Appl Prob 41, 765-796.
  • Ball F G, Sirl D and Trapman P (2010) Analysis of a stochastic SIR epidemic on a random network incorporating household structure. Math Biosci 224, 53-73.
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Title Statistical analysis of fibre variability in composites manufacture
Group(s) Statistics and Probability, Scientific Computation
Proposer(s) Prof Frank Ball, Prof Michael Tretyakov
Description

Multidisciplinary collaborations are a critical feature of material science research enabling integration of data collection with computational and/or mathematical modelling. This PhD study provides an exciting opportunity for an individual to participate in a project spanning research into composite manufacturing, stochastic modelling, statistical analysis and scientific computing. The project is integrated into the EPSRC Centre for Innovative Manufacturing in Composites, which isled by the University of Nottingham and delivers a co-ordinated programme of research in composites manufacturing.

This project focuses on the development of a manufacturing route for composite materials capable of producing complex components in a single process chain based on advancements in the knowledge, measurement and prediction of uncertainty in processing. The outcome of this work will enable a step change in the capabilities of composite manufacturing technologies to be made, overcoming limitations related to part thickness, component robustness and manufacturability as part of a single process chain, whilst yielding significant developments in mathematics and statistics with generic application in the fields of stochastic modelling and inverse problems.

The specific aims of this project are: (i) statistical analysis of fibber placements based on textile and composite material data sets; (ii) statistical analysis and stochastic modelling of permeability of textiles and composites; (iii) efficient sampling techniques of stochastic permeability. A student will obtain an excellent grasp of various statistical and stochastic techniques (e.g., spatial statistical methods, use of random fields, Monte Carlo methods), how to apply them, how to work with real data and how to do related modelling and simulation. This knowledge and especially experience are transferable to other applications of statistics and probability.

The PhD programme contains a training element, the exact nature of which will be mutually agreed by the student and their supervisors.

We require an enthusiastic graduate with a 1st class honours in Mathematics (in exceptional circumstances a 2(i) class degree can be considered), preferably at the MMath/MSc level, with good programming skills and williness to work as a part of an interdisciplinary team. A candidate with a solid background in statistics and stochastic processes will have an advantage.

The studentship is available for a period of three and a half years from September/October 2015 and provides a stipend and full payment of Home/EU Tuition Fees. Students must meet the EPSRC eligibility criteria.

Informal enquiries should be addressed to Prof. Michael Tretyakov, email: michael.tretyakov@nottingham.ac.uk.

To apply, please access: https://my.nottingham.ac.uk/pgapps/welcome/. Please ensure you quote ref: SCI/1262x1. This studentship is open until filled. Early application is strongly encouraged.

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