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An overview is presented of experiments on ballistic electrical transport in inhomogeneous superconducting systems which are controlled by the process of Andreev reflection. The initial experiments based on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The point contacts have recently evolved towards the atomic scale owing to the use of mechanical break-junctions, revealing a very detailed dependence of Andreev reflection on the macroscopic phase of the superconducting state. In present-day research, the superconducting in homogeneity is constructed by clean room technology and combines superconducting materials, for example, with low-dimensional materials and topological insulators. Alternatively, the superconductor is combined with nano-objects, such as graphene, carbon nanotubes, or semiconducting nanowires. Each of these 'inhomogeneous systems' provides a very interesting range of properties, all rooted in some manifestation of Andreev reflection. [ABSTRACT FROM AUTHOR]

We consider explicit solutions to the problem of ballistic aggregation of dustlike matter whose particles stick together absolutely inelastically upon collisions—a description of the formation of a large-scale structure in cosmology in terms of the adhesion model, which is a generalization of the Zel’dovich approximation. The two previously suggested different representations of the solutions for a plane-symmetric 1D flow are shown to be equivalent. Explicit representations of the solutions in cylindrical and spherical symmetries are constructed. We provide explicit examples showing that the two representations under consideration cannot be generalized to a multidimensional nonsymmetric flow. [ABSTRACT FROM AUTHOR]

The behavior of an acoustoelectric current through a three-dimensional quantum microconstriction placed in a longitudinal uniform magnetic field is studied theoretically in the ballistic transport regime. The oscillation periods of the acoustoelectric current are studied in detail as functions of the chemical potential and the magnetic field induction. The temperature effect is taken into account. It is shown that the acoustoelectric current as a function of the chemical potential can exhibit a steplike behavior. The limits for the existence of a steplike structure are determined. [ABSTRACT FROM AUTHOR]

The electric current induced by an ultrasonic phonon flux in a ballistic quasi-two-dimensional quantum channel is investigated theoretically. Two types of confining potential are considered. An analytic expression for the acoustoelectric current is derived, and its dependence on the chemical potential and on the magnitude of the longitudinal magnetic field is investigated. It is shown that the dependence of the acoustoelectric current on the chemical potential may be of the experimentally observed step type. The oscillatory dependence of the acoustoelectric current on the magnetic field is considered for the cases of weak and strong magnetic quantization. [ABSTRACT FROM AUTHOR]

The effect of the temperature on the kinetic coefficients of a mesoscopic sample in contact with two electron reservoirs is considered for the case in which the electron transmission coefficient of the sample undergoes oscillations near the Fermi energy. [ABSTRACT FROM AUTHOR]