Enhanced Group Analysis and Exact Solutions of Variable Coefficient Semilinear Diffusion Equations with a Power Source

A new approach to group classification problems and more general investigations on transformational properties of classes of differential equations is proposed. It is based on mappings between classes of differential equations, generated by families of point transformations. A class of variable coefficient (1+1)-dimensional semilinear reaction-diffusion equations of the general form $f(x)u_t=(g(x)u_x)_x+h(x)u^m$ ($m\ne0,1$) is studied from the symmetry point of view in the framework of the approach proposed. The singular subclass of the equations with $m=2$ is singled out. The group classifications of the entire class, the singular subclass and their images are performed with respect to both the corresponding (generalized extended) equivalence groups and all point transformations. The set of admissible transformations of the imaged class is exhaustively described in the general case $m\ne2$. The procedure of classification of nonclassical symmetries, which involves mappings between classes of differential equations, is discussed. Wide families of new exact solutions are also constructed for equations from the classes under consideration by the classical method of Lie reductions and by generation of new solutions from known ones for other equations with point transformations of different kinds (such as additional equivalence transformations and mappings between classes of equations).Comment: 40 pages, this is version published in Acta Applicanda Mathematica

Reduction of the self-dual Yang-Mills equations. I. The Poincaré group

For the vector potential of the Yang-Mills field, we give a complete description of ansatzes invariant under three-parameterP (1, 3) -inequivalent subgroups of the Poincaré group. By using these ansatzes, we reduce the self-dual Yang-Mills equations to a system of ordinary differential equations.Для вектор-потенціалу поля Янга - Міллса побудовано повний набір інваріантних відносно Р(1,3)- нееквівалентних підгруп групи Пуанкаре анзаців, з використанням яких проведено редукцію самодуальних рівнянь Янга - Мілса до систем звичайних диференціальних рівнянь

Nonlinear Hyperbolic Equations and Linear Heat Conduction with Memory

The model of a rigid heat conductor with memory is considered. Specifically, in the one-dimensional case, a connection, via Cole-Hopf Transformation, between the linear integro-differential evolution equation which describes heat conduction with memory and a nonlinear partial integro-differential equation of hyperbolic type is established. Notably, when the heat conductor is homogeneous, as well as when the homogeneity hypothesis is removed, the differential operator of the transformed nonlinear partial differential equation is of hyperbolic type