We study domain walls that are topological solitons in one dimension. We present an existence theory for the solutions of the basic governing equations of some extended geometrically constrained domain-wall models. When the cross-section and potential density are both even, we establish the existence of an odd domain-wall solution realizing the phase-transition process between two adjacent domain phases. When the cross-section satisfies a certain integrability condition, we prove that a domain-wall solution always exists that links two arbitrarily designated domain phases.

We define and study families of conjugate and reflected curve congruences associated to a self-adjoint operator on a smooth and oriented surface M endowed with a Lorentzian metric g. These families trace parts of the pencil joining the equations of the -asymptotic and the -principal curves, and the pencil joining the -characteristic and the -principal curves, respectively. The binary differential equations (BDEs) of these curves can be viewed as points in the projective plane. Using the polar lines of various BDEs with respect to the conic of degenerate quadratic forms, we obtain geometric results on the above pencils and their relation with the metric g, on the type of solutions of a given BDE, of its -conjugate equation and on BDEs with orthogonal roots.

This paper is concerned with the limit of the vanishing ratio of the electron mass to the ion mass in the hydrodynamic models for plasmas in critical Besov spaces. We give a new construction of approximation solutions and show that periodic initial-value problems of certain scaled hydrodynamic models have smooth solutions in a (finite) time interval where the Euler solution is known to exist. Furthermore, it is justified that, as the electron mass tends to zero, the smooth solutions converge rigorously to solutions of the incompressible Euler equations, and the definite convergence orders are also obtained.

By using the symmetric mountain pass theorem, we establish some new existence criteria to guarantee that the second-order Hamiltonian systems ü(t) − L(t)u(t) + ∇W(t,u(t)) = 0 have infinitely many homoclinic orbits, where t ∈ ℝ, u ∈ ℝN, L ∈ C(ℝ, ℝN × N) and W ∈ C1(ℝ × ℝN, ℝ) are not periodic in t. Our results generalize and improve some existing results in the literature by relaxing the conditions on the potential function W(t, x).

Irregular mappings that are weak solutions of the energy–momentum equations are presented. One example is discontinuous at a countable number of points while the other is C1, but not C2. These mappings are not solutions of the usual Euler–Lagrange equations.

We study (p, q)-inequalities of Ulyanov type for moduli of smoothness of fractional order in the Lp and the Lp(ℝn) setting, p ≥ 1. In particular, we obtain estimates for the modulus of smoothness of a generalized Liouville derivative of a function via the modulus of smoothness of the function itself. We give examples showing the sharpness of these inequalities.