# Analysis of Nonlinear Partial Differential Equations

Lead Research Organisation: University of Oxford
Department Name: Mathematical Institute

### Abstract

Partial differential equations (PDEs) are equations that relate the partial derivatives, usually with respect to space and time coordinates, of unknown quantities. They are ubiquitous in almost all applications of mathematics, where they provide a natural mathematical description of phenomena in the physical, natural and social sciences, often arising from fundamental conservation laws such as for mass, momentum and energy. Significant application areas include geophysics, the bio-sciences, engineering, materials science, physics and chemistry, economics and finance. Length-scales of natural phenomena modelled by PDEs range from sub-atomic to astronomical, and time-scales may range from nanoseconds to millennia. The behaviour of every material object can be modelled either by PDEs, usually at various different length- or time-scales, or by other equations for which similar techniques of analysis and computation apply. A striking example of such an object is Planet Earth itself.Linear PDEs are ones for which linear combinations of solutions are also solutions. For example, the linear wave equation models electromagnetic waves, which can be decomposed into sums of elementary waves of different frequencies, each of these elementary waves also being solutions. However, most of the PDEs that accurately model nature are nonlinear and, in general, there is no way of writing their solutions explicitly. Indeed, whether the equations have solutions, what their properties are, and how they may be computed numerically are difficult questions that can be approached only by methods of mathematical analysis. These involve, among other things, precisely specifying what is meant by a solution and the classes of functions in which solutions are sought, and establishing ways in which approximate solutions can be constructed which can be rigorously shown to converge to actual solutions. The analysis of nonlinear PDEs is thus a crucial ingredient in the understanding of the world about us.As recognized by the recent International Review of Mathematics, the analysis of nonlinear PDEs is an area of mathematics in which the UK, despite some notable experts, lags significantly behind our scientific competitors, both in quantity and overall quality. This has a serious detrimental effect on mathematics as a whole, on the scientific and other disciplines which depend on an understanding of PDEs, and on the knowledge-based economy, which in particular makes increasing use of simulations of PDEs instead of more costly or impractical alternatives such as laboratory testing.The proposal responds to the national need in this crucial research area through the formation of a forward-looking world-class research centre in Oxford, in order to provide a sharper focus for fundamental research in the field in the UK and raise the potential of its successful and durable impact within and outside mathematics. The centre will involve the whole UK research community having interests in nonlinear PDEs, for example through the formation of a national steering committee that will organize nationwide activities such as conferences and workshops.Oxford is an ideal location for such a research centre on account of an existing nucleus of high quality researchers in the field, and very strong research groups both in related areas of mathematics and across the range of disciplines that depend on the understanding of nonlinear PDEs. In addition, two-way knowledge transfer with industry will be achieved using the expertise and facilities of the internationally renowned mathematical modelling group based in OCIAM which, through successful Study Groups with Industry, has a track-record of forging strong links to numerous branches of science, industry, engineering and commerce. The university is committed to the formation of the centre and will provide a significant financial contribution, in particular upgrading one of the EPSRC-funded lectureships to a Chair

### Publications

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Acharya A (2017) Fluids, Elasticity, Geometry, and the Existence of Wrinkled Solutions in Archive for Rational Mechanics and Analysis

Ammari H (2010) Progress on the strong Eshelby's conjecture and extremal structures for the elastic moment tensor in Journal de Mathématiques Pures et Appliquées

Ammari H (2008) Electrical Impedance Tomography by Elastic Deformation in SIAM Journal on Applied Mathematics

Ammari H (2011) Microwave Imaging by Elastic Deformation in SIAM Journal on Applied Mathematics

AMMARI H (2009) Mathematical models and reconstruction methods in magneto-acoustic imaging in European Journal of Applied Mathematics

Ammari H (2010) Enhanced Resolution in Structured Media in SIAM Journal on Applied Mathematics

Ball J (2017) Partial regularity and smooth topology-preserving approximations of rough domains in Calculus of Variations and Partial Differential Equations

Description This was a broad grant designed to help consolidate research on nonlinear partial differential equations in the UK. In particular the Oxford Centre for Nonlinear PDE was founded as a result of the grant and is now a leading international centre. As regards specific research advances, these were in various areas of applications of PDE, for example to fluid and solid mechnaics, liquid crystals, electromagnetism, and relativity.
Exploitation Route Through publications and consultation with current and former members of OxPDE.
Sectors Aerospace, Defence and Marine,Chemicals,Construction,Electronics,Energy,Environment

URL https://www0.maths.ox.ac.uk/groups/oxpde

Description This broad research grant helped to consolidate research on nonlinear partial differential equations in the UK. The Oxford Centre for Nonlinear PDE (OxPDE) was founded as a result of the grant and is now a leading international centre. OxPDE played a central role in establishing "Oxford Solid Mechanics", an initiative to promote interaction between researchers throughout the University of Oxford who work on solid mechanics, and it ran the EPSRC-funded centre for doctoral training "Partial Differential Equations: Analysis in Applications", which, through its five cohorts, produced highly trained, outstanding mathematicians with deep expertise and interdisciplinary skills in the analysis and applications of partial differential equations and related areas of core mathematics and its interfaces. Thus the effect of the grant on society and industry was mainly indirect, and the result of training of highly qualified young researchers, who, for example, have taken up jobs in software engineering, machine learning, investment analysis and fuel trading. More direct impacts were on the design of new (low hysteresis) alloys and the understanding of the behaviour of liquid crystals.
First Year Of Impact 2014
Sector Digital/Communication/Information Technologies (including Software),Energy,Financial Services, and Management Consultancy,Other
Impact Types Societal,Economic