ETEKOS experimental ecological system

The problem of changes in the ecology resulting, for example, in increases in water temperature because of discharges from large thermal power plants is considered. An experiment creating a model of such an ecological system is described

Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-Tc

Ab initio linear-response calculations are reported of the phonon spectra and the electron-phonon interaction for several transition metal carbides and nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and superconducting properties are calculated in detail at various pressures and the normal-pressure results are found to well agree with the experiment. Factors accounting for the relatively low critical temperatures Tc in transition metal compounds with light elements are considered and the possible ways of increasing Tc are discussed.Comment: 19 pages, 7 figure

Critical temperature and giant isotope effect in presence of paramagnons

We reconsider the long-standing problem of the effect of spin fluctuations on the critical temperature and isotope effect in a phonon-mediated superconductor. Although the general physics of the interplay between phonons and paramagnons had been rather well understood, the existing approximate formulas fail to describe the correct behavior of $$ for general phonon and paramagnon spectra. Using a controllable approximation, we derive an analytical formula for $T_{c}$ which agrees well with exact numerical solutions of the Eliashberg equations for a broad range of parameters. Based on both numerical and analytical results, we predict a strong enhancement of the isotope effect when the frequencies of spin fluctuation and phonons are of the same order. This effect may have important consequences for near-magnetic superconductors such as MgCNi$_{3}$Comment: 5 pages, 2 figure

Stationary striations in plasma, created by a short microwave pulse in a waveguide filled with a neutral gas

It was observed experimentally that after crossing a waveguide filled with a neutral gas, a short powerful microwave pulse leaves a periodic glow of plasma along the waveguide, persisting several tens of nanoseconds. A theoretical model is presented which in combination with numerical simulations proposes a possible explanation of this phenomenon.Comment: 15 pages, 9 figure

Some Algorithms for the Dynamic Reconstruction of Inputs

For some classes of systems described by ordinary differential equations, a survey of algorithms for the dynamic reconstruction of inputs is presented. The algorithms described in the paper are stable with respect to information noises and computation errors; they are based on methods from the theory of ill-posed problems as well as on appropriate modifications of N. N. Krasovskii's principle of extremal aiming, which is known in the theory of guaranteed control. © 2011 Pleiades Publishing, Ltd.This work was supported by the Russian Foundation for Basic Research (project no. 09-01-00378), by the Program for Fundamental Research of the Presidium of the Russian Academy of Sciences “Mathematical Theory of Control” (project no. 09-P-1-1014), by the Program for State Support of Leading Scientific Schools of the Russian Federation (project no. NSh-65590.2010.1), and by the Ural–Siberian Integration Project no. 09-S-1-1010

Manifestation of impurity induced s_{+-} -> s_{++} transition: multiband model for dynamical response functions

We investigate effects of disorder on the density of states, the single particle response function and optical conductivity in multiband superconductors with s_{+-} symmetry of the order parameter, where s_{+-} -> s_{++} transition may take place. In the vicinity of the transition the superconductive gapless regime is realized. It manifests itself in anomalies in the above mentioned properties. As a result, intrinsically phase-insensitive experimental methods like ARPES, tunneling and terahertz spectroscopy may be used for revealing of information about the underlying order parameter symmetry.Comment: 14 pages, 6 figure

Geometrical edge barriers and magnetization in superconducting strips with slits

We theoretically investigate the magnetic-field and current distributions for coplanar superconducting strips with slits in an applied magnetic field H_a. We consider ideal strips with no bulk pinning and calculate the hysteretic behavior of the magnetic moment m_y as a function of H_a due solely to geometrical edge barriers. We find that the m_y-H_a curves are strongly affected by the slits. In an ascending field, the m_y-H_a curves exhibit kink or peak structures, because the slits prevent penetration of magnetic flux. In a descending field, m_y becomes positive, because magnetic flux is trapped in the slits, in contrast to the behavior of a single strip without slits, for which m_y =0.Comment: 11 pages, 5 figures, revtex

Use of Nanocomposite Material Based on Graphene Oxide and Silver Nanoparticles in Research of Blood Erythrocytes in Various Diseases

The electrical and structural properties of a nanocomposite material based on silver nanoparticles and graphene oxide were investigated. Using electron and atomic force microscopy it was shown that the nanoparticles formed predominantly have sizes from 60 to 100 nm. Measurements of the current-voltage characteristics showed electrical conductivity values significantly exceeding the parameters of the initial graphene oxide. The prepared nanocomposites were used for scanning by electron microscopy (SEM) of blood samples of sick children with hematuria syndrome and patients of the radiological department of an oncologic dispensary diagnosed with cervical cancer. The formation of nanosize objects on the surface of erythrocytes is revealed. The size of these volumes is comparable to the size of the viruses. Results of these studies can indirectly confirm an assumption of authors about possible transportation of viruses by erythrocytes to various organs and viral etiology of renal diseases with the hematuria syndrome and cervical cancer. Keywords: graphene, graphene oxide, silver nanoparticles, structural and electrical properties, nephropathy, diagnostics

Structure stability in the simple element sodium under pressure

The simple alkali metal Na, that crystallizes in a body-centred cubic structure at ambient pressure, exhibits a wealth of complex phases at extreme conditions as found by experimental studies. The analysis of the mechanism of stabilization of some of these phases, namely, the low-temperature Sm-type phase and the high-pressure cI16 and oP8 phases, shows that they satisfy the criteria for the Hume-Rothery mechanism. These phases appear to be stabilized due to a formation of numerous planes in a Brillouin-Jones zone in the vicinity of the Fermi sphere of Na, which leads to the reduction of the overall electronic energy. For the oP8 phase, this mechanism seems to be working if one assumes that Na becomes divalent metal at this density. The oP8 phase of Na is analysed in comparison with the MnP-type oP8 phases known in binary compounds, as well as in relation to the hP4 structure of the NiAs-type

Multiband model for tunneling in MgB2 junctions

A theoretical model for quasiparticle and Josephson tunneling in multiband superconductors is developed and applied to MgB2-based junctions. The gap functions in different bands in MgB2 are obtained from an extended Eliashberg formalism, using the results of band structure calculations. The temperature and angle dependencies of MgB2 tunneling spectra and the Josephson critical current are calculated. The conditions for observing one or two gaps are given. We argue that the model may help to settle the current debate concerning two-band superconductivity in MgB2.Comment: minor corrections, published in Phys. Rev. B 65, 180517(R) (2002