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

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

Material fragmentation as dissipative process of micro rotation sequence formation: Hybrid model of excitable cellular automata

The authors have developed a multi-level model of energy propagation along interfaces between the various structural elements of a solid with taking into account mutual energy transformations of various kinds. They have also designed a computer simulation tool based on the excitable cellular automaton (ECA) method. An algorithm for calculating the local moments of forces has been developed for the case of material rotation and torsion. The relationship for the accumulated elastic energy is supplemented with a dissipation term. Numerical experiments have been carried out on high-energy impact on polycrystalline copper specimens with different grain sizes. The paper shows that during the nanostructuring of material surface layer, the dissipation of elastic energy gives rise to the rotation of structural elements. This makes it possible to prevent the occurrence of stress concentrators with peak values typical of coarse-grained specimens and reducing their mechanical properties

HISTORY AND RESULTS OF THE INTRODUCTION OF PALMS (ARECACEAE C.H. SCHULTZ) ON THE SOUTHERN COAST OF THE CRIMEA

The results of the introduction of palms have been summarized, and the assortment, opportunities and conditions of their cultivation on  the Southern Coast of the Crimea (SCC) defined. Long-term  observations on the experimental plants with an assessment of their  prospects according to a frosting scale during severe winters and  biometric measurements of their habit by instrumental methods  have been conducted. The article describes the history and results of the palms' introduction beginning from 1814 up to the present  moment. It was established that growth and development of palms  in the NBG's arboretum depend not only on their winter resistance  but also on the growing conditions and cultivation practices. The  results of the palms' introduction over a 30-year span of the  research (1984-2014) through the example of their growth and  development in the NBG's arboretum have been summed up. The  data about the characteristic habits and reproductive capabilities for  the year 1984 have been provided and compared with the same  parameters obtained in 2014 on the same experimental trees. A  picture of actual damages of various palm species during severe  winters has been shown, and the degree of their tolerance to  extreme negative temperatures determined. A promising assortment of palms tested in the NBG's arboretum has been identified, and the  conditions of their cultivation on the SCC shown. The environmental  and biological criteria influencing growth and development of 12  species of palms have been defined. Recommendations as to  agricultural practices, protection in winter, and rational utilization of palms in ornamental gardening have been provided