The inaction approach to gauge theories

The inaction approach introduced previously for φ⁴ [1] is generalized to gauge theories. It combines the advantages of the effective field theory and causal approaches to quantum fields. Also, it suggests ways to generalizing gauge theories.     

Photoconductivity and photoemission studies of diamond irradiated by ultrashort VUV pulses

We investigated relaxation of free charge carriers in pure crystalline diamond exposed to VUV irradiation of high order harmonics of femtosecond Ti:Sa laser in the spectral range 17–32 eV. Electron–hole pairs, possessing a significant kinetic energy, are generated in the material via direct interband transitions, relaxation of which is monitored by means of induced conductivity in the bulk and photoemission from the surface of the material. The experimental data provided by these complementary techniques are compared and discussed in terms of the competition between ionization and conductivity looking for evidences of multiplication of free charge carriers due to impact ionization. PACS 42.65.Re; 72.20.Jv; 72.40.+w; 79.60.-i     

Influence of Heterogeneity of Ion-Exchange Membranes on the Limiting Current and Current–Voltage Curves

A heterogeneous-membrane model is employed to demonstrate that, following a decrease in the ionite fraction in membranes, true values of limiting currents in electrolytes of different nature are not lower than in a pure ionite, while relative (measured) values drop by 2–5 times, which is explained by a decrease in the conducting surface areas of membranes. The formation of a limiting state on a heterogeneous surface is described qualitatively with allowance made for the morphology of membranes. The region of inflection in experimental and calculated current–voltage curves, which corresponds to a limiting state, is shown to degenerate with a decrease in the ionite fraction in membranes, which is due to the effect the membrane structure has on the polarization. The activation energy of the limiting state is determined.     

Energy filtration of charge carriers in a nanostructured material based on bismuth telluride

The dependences of the electrical conductivity and thermopower on the size of grains in a nanocrystalline material based on Bi₂Te₃-Sb₂Te₃ solid solutions of the p type have been investigated theoretically and experimentally. The relaxation time in the case of hole scattering by nanograin boundaries in an isotropic polycrystal has been calculated taking into account the energy dependence of the probability of tunneling of charge carriers and the dependence of the scattering intensity on the nanograin size L _n . A decrease in the probability of boundary scattering with an increase in the energy of charge carriers leads to an increase in the thermopower. The dependences of the thermopower and electrical conductivity on the nanograin size, which have been obtained taking into account the boundary scattering and scattering by acoustic phonons, are in good agreement with experimental data. For the material under consideration, the thermopower coefficient increases by 10–20% compared to the initial solid solution at L _n = 20–30 nm. This can lead to an increase in the thermoelectric figure of merit by 20–40%, provided that the decrease in the electrical conductivity and the decrease in the lattice thermal conductivity compensate each other. Despite the absence of a complete compensation, it has been possible to increase the thermoelectric figure of merit for the samples under investigation to ZT = 1.10–1.12.     

A central limit theorem for projections of the cube

We prove a central limit theorem for the volume of projections of the cube \([-1,1]^N\) onto a random subspace of dimension \(n\) , when \(n\) is fixed and \(N\rightarrow \infty \) . Randomness in this case is with respect to the Haar measure on the Grassmannian manifold.     

Quantum features of reflection of relativistic particles by a crystal surface

A new mechanism of reflection of relativistic particles by a crystal surface at grazing angles is considered. The reflection takes place when the “transverse” energy value (connected with the particle motion perpendicular to the surface) lies in the forbidden band of the energy spectrum in a one-dimensional periodic potential which is the sum of continuous potentials of crystallographic planes being parallel to the surface.