Thomas J. Bridges – författare

Nonlinear waves are pervasive in nature, but are often elusive when they are modelled and analysed. This book develops a natural approach to the problem based on phase modulation. It is both an elaboration of the use of phase modulation for the study of nonlinear waves and a compendium of background results in mathematics, such as Hamiltonian systems, symplectic geometry, conservation laws, Noether theory, Lagrangian field theory and analysis, all of which combine to generate the new theory of phase modulation. While the build-up of theory can be intensive, the resulting emergent partial differential equations are relatively simple. A key outcome of the theory is that the coefficients in the emergent modulation equations are universal and easy to calculate. This book gives several examples of the implications in the theory of fluid mechanics and points to a wide range of new applications.

In the summer of 2014 leading experts in the theory of water waves gathered at the Newton Institute for Mathematical Sciences in Cambridge for four weeks of research interaction. A cross-section of those experts was invited to give introductory-level talks on active topics. This book is a compilation of those talks and illustrates the diversity, intensity, and progress of current research in this area. The key themes that emerge are numerical methods for analysis, stability and simulation of water waves, transform methods, rigorous analysis of model equations, three-dimensionality of water waves, variational principles, shallow water hydrodynamics, the role of deterministic and random bottom topography, and modulation equations. This book is an ideal introduction for PhD students and researchers looking for a research project. It may also be used as a supplementary text for advanced courses in mathematics or fluid dynamics.

Nonlinear waves are pervasive in nature, but are often elusive when they are modelled and analysed. This book develops a natural approach to the problem based on phase modulation. It is both an elaboration of the use of phase modulation for the study of nonlinear waves and a compendium of background results in mathematics, such as Hamiltonian systems, symplectic geometry, conservation laws, Noether theory, Lagrangian field theory and analysis, all of which combine to generate the new theory of phase modulation. While the build-up of theory can be intensive, the resulting emergent partial differential equations are relatively simple. A key outcome of the theory is that the coefficients in the emergent modulation equations are universal and easy to calculate. This book gives several examples of the implications in the theory of fluid mechanics and points to a wide range of new applications.

"In this dark, when we all talk at once, some of us must learn to whistle."In this comprehensive collection of his work, Craig Keen''s voice emerges as that of a theologian who has indeed learned to whistle. In a day when much of what passes for academic "theology" is careful to maintain a safe distance from any determinate act of faith or work of praise, Keen evinces a single-minded determination to think and to speak, to write and to live doxologically. And whether writing or lecturing, teaching or conversing, Keen understands theology to be nothing less than an invitation to work out one''s faith with fear and trembling.Throughout this volume Keen argues that the life, death, and resurrection of Jesus disrupt all metaphysical attempts to determine the reality of "God," and suggests instead that theology is to be done liturgically and eucharistically--as the work of a people whose labor is carried out with open hands, free from all attempts to grasp and control. Keen discusses doctrinal issues--the Trinity, incarnation, creation--as well as a number of critical theological concerns--church and culture, justice, holiness, Christian education--in this light. The result is a profound set of reflections on the ways in which the word of the cross simultaneously transgresses our constructions of "God" and gives us to live transgressively in love.

The monograph is a study of the local bifurcations ofmultiparameter symplectic maps of arbitrary dimension in theneighborhood of a fixed point.The problem is reduced to astudy of critical points of an equivariant gradientbifurcation problem, using the correspondence between orbitsofa symplectic map and critical points of an actionfunctional. New results onsingularity theory forequivariant gradient bifurcation problems are obtained andthen used to classify singularities of bifurcating period-qpoints. Of particular interest is that a general frameworkfor analyzing group-theoretic aspects and singularities ofsymplectic maps (particularly period-q points) is presented.Topics include: bifurcations when the symplectic map hasspatial symmetry and a theory for the collision ofmultipliers near rational points with and without spatialsymmetry. The monograph also includes 11 self-containedappendices each with a basic result on symplectic maps. Themonograph will appeal to researchers and graduate studentsin the areas of symplectic maps, Hamiltonian systems,singularity theory and equivariant bifurcation theory.

The monograph is a study of the local bifurcations ofmultiparameter symplectic maps of arbitrary dimension in theneighborhood of a fixed point.The problem is reduced to astudy of critical points of an equivariant gradientbifurcation problem, using the correspondence between orbitsofa symplectic map and critical points of an actionfunctional. New results onsingularity theory forequivariant gradient bifurcation problems are obtained andthen used to classify singularities of bifurcating period-qpoints. Of particular interest is that a general frameworkfor analyzing group-theoretic aspects and singularities ofsymplectic maps (particularly period-q points) is presented.Topics include: bifurcations when the symplectic map hasspatial symmetry and a theory for the collision ofmultipliers near rational points with and without spatialsymmetry. The monograph also includes 11 self-containedappendices each with a basic result on symplectic maps. Themonograph will appeal to researchers and graduate studentsin the areas of symplectic maps, Hamiltonian systems,singularity theory and equivariant bifurcation theory.

This book presents a wide-ranging geometric approach to the stability of solitary wave solutions of Hamiltonian partial differential equations (PDEs). It blends original research with background material and a review of the literature. The overarching aim is to integrate geometry, algebra, and analysis into a theoretical framework for the spectral problem associated with the transverse instability of line solitary wave solutions—waves that travel uniformly in a horizontal plane and are embedded in two spatial dimensions. Rather than focusing on individual PDEs, the book develops an abstract class of Hamiltonian PDEs in two spatial dimensions and time, based on multisymplectic Dirac operators and their generalizations. This class models a broad range of nonlinear wave equations and benefits from a distinct symplectic structure associated with each spatial dimension and time. These structures inform both the existence theory (via variational principles, the Maslov index, and transversality conditions) and the linear stability analysis (through a multisymplectic partition of the Evans function). The spectral problem arising from linearization about a solitary wave is formulated as a dynamical system, with three symplectic structures contributing to the analysis. A two-parameter Evans function—depending on the spectral parameter and transverse wavenumber—is constructed from this system. This structure enables new results concerning the Evans function and the linear transverse instability of solitary waves. A key result is an abstract derivative formula for the Evans function in the regime of small stability exponents and transverse wavenumbers. To illustrate the theory, the book introduces a class of vector-valued nonlinear wave equations in 2+1 dimensions that are multisymplectic and admit explicit solitary wave solutions. In this example, the stable and unstable subspaces involved in the Evans function construction are each four-dimensional and can be explicitly computed. The example is used to demonstrate the geometric instability condition and to explore the inner workings of the theory in detail.