52 research outputs found

    High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

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    A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

    Thermoviscosimetric characteristics of borosilicate glasses with regard to the promising area of low-melting compositions currently being developed for the removable small-scale melter designed by Mayak Production Association

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    Relevance. The need to obtain experimental data on dependence of thermoviscosimetric properties of the examined borosilicate glasses on temperature, in order to solve the problem of developing a low-melting composition of borosilicate glass for a small-scale melter designed by Mayak Production Association. Aim. To get the most complete characterization of the glasses under study using thermoviscometric measurements. Methods. Mathematical modelling, simplex-lattice design. Results and conclusions. One of the most effective methods of experiment planning, which allows, with a relatively small number of experiments, obtaining a mathematical model reflecting the dependence of the studied property of the mixture on the content of components in it, is the simplex experiment planning method. To simplify the solution of such a task, a group or groups of components are usually distinguished, in which the ratio of the mass fraction of the components does not change. In this article, three groups of components are taken – simulators of high-level radioactive waste, sodium and boron oxides, and glass frit. The authors have identified the most promising area, where the mass fraction of glass frit is from 67.5 to 75%, the mass fraction of sodium and boron is from 25 to 32.5% and the mass fraction of high-level waste components is from 0 to 20%. The paper presents the results of thermoviscometric measurements of 15 melts of low-melting borosilicate glasses of different compositions at temperatures ranging from 700 to 1,200°C. Using simplex-based mathematical models of experiment planning, domains of dependence of thermoviscosimetric characteristics of glass melts on their compositions were created. The authors identified the compositions of glass melts that are found within the viscosity limits determined as allowable for glass melt discharge during operation of the removable small-scale melter of Mayak Production Association design

    On Effect of Equilibrium Fluctuations on Superfluid Density in Layered Superconductors

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    We calculate suppression of inter- and intralayer superconducting currents due to equilibrium phase fluctuations and find that, in contrast to a recent prediction, the effect of thermal fluctuations cannot account for linear temperature dependence of the superfluid density in high-Tc superconductors at low temperatures. Quantum fluctuations are found to dominate over thermal fluctuations at low temperatures due to hardening of their spectrum caused by the Josephson plasma resonance. Near Tc sizeable thermal fluctuations are found to suppress the critical current in the stack direction stronger, than in the direction along the layers. Fluctuations of quasiparticle branch imbalance make the spectral density of voltage fluctuations at small frequencies non zero, in contrast to what may be expected from a naive interpretation of Nyquist formula.Comment: 5 pages, LaTeX, RevTeX, Submitted to PR
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