http://dspace.nbuv.gov.ua:80/handle/123456789/117855 2026-04-11T19:20:40Z 2026-04-11T19:20:40Z Shikin, V.B. Nazin, S.S. http://dspace.nbuv.gov.ua:80/handle/123456789/121800 2017-06-17T00:02:47Z 2007-01-01T00:00:00Z

Energy of a single electron in gaseous media Shikin, V.B.; Nazin, S.S. The so-called «optical» approximation in the theory of electron energy spectrum in the presence of scattering centers with positive scattering length randomly distributed with the average density ng is considered for a number of inert gases. The average minimal energy W of a single electron calculated beyond the optical approximation reveals a behavior qualitatively different from that of the same quantity W₀ derived within the optical approximation. Results of calculations are in qualitative agreement with experimental data available for theW(ng) dependence for different cryogenic gases.

2007-01-01T00:00:00Z Antsygina, T.N. Poltavskaya, M.I. Poltavsky, I.I. Chishko, K.A. http://dspace.nbuv.gov.ua:80/handle/123456789/121799 2017-06-17T00:03:18Z 2007-01-01T00:00:00Z

Heat capacity and spin susceptibility of two-dimensional t–J model Antsygina, T.N.; Poltavskaya, M.I.; Poltavsky, I.I.; Chishko, K.A. Thermodynamic properties of the t–J model on square and triangular lattices near half-filling are investigated theoretically within an analytical approach based on the Kondo and Yamaji’s Green function decoupling scheme. The temperature dependences of the heat capacity and spin susceptibility are calculated in the wide temperature range for the case when the exchange constant J is greater than the hopping amplitude t. It was found, that with the increase of doping from the half-filling, the maximum of the spin susceptibility increases and its position shifts to lower temperatures for both types of lattices. Such behavior is in agreement with the qualitative predictions [E. Dagotto, Rev. Mod. Phys. 66, 763 (1994)]. Heat capacity demonstrates a double peak shape. The high temperature peak associated with the «spin wave-like» excitations shifts to lower temperatures with doping. The low temperature peak appears due to the holes and its height and position depend on both the doping and the ratio t / J .

2007-01-01T00:00:00Z Kokshenev, V.B. http://dspace.nbuv.gov.ua:80/handle/123456789/121798 2017-06-17T00:03:10Z 2007-01-01T00:00:00Z

Cluster relaxation dynamics in liquids and solids near the glass-transformation temperature Kokshenev, V.B. The structural relaxation in glass forming materials is studied near the glass transformation temperature Tg indicated by the heat capacity maximum. The late-time asymptote of the Kohlrausch–Williams–Watts form of the relaxation function is rationalized via the mesoscopic-scale correlated regions in terms of the Debye-type clusters following the dynamic scaling law. It is repeatedly shown that regardless of underlying microscopic realizations in glass formers with site disorder the structural relaxation is driven by local random fields, described via the directed random walks model. The relaxation space dimension ds = 3 at Tg is suggested for relaxing units of fractal dimension d f = 5/2 for quadrupolar-glass clusters in ortho–para hydrogen mixtures, that is compared with entangled-chain clusters in polymers (d f = 1) and solid-like clusters relaxing in supercooled molecular liquids (with ds = 6 and d f = 3). The relaxation dynamics of orientational-glass clusters in plastic crystals is attributed to the model of continuos time random walks in space ds = 6. As a by-product, the expansivity in polymers, molecular liquids and networks is predicted.

2007-01-01T00:00:00Z Krivchikov, A.I. Korolyuk, O.A. Romantsova, O.O. http://dspace.nbuv.gov.ua:80/handle/123456789/121797 2017-06-17T00:02:59Z 2007-01-01T00:00:00Z

Heat transfer in crystalline clathrate hydrates at low temperatures Krivchikov, A.I.; Korolyuk, O.A.; Romantsova, O.O. The experimental results on the thermal conductivity k(T) of crystalline Xe, CH₄, and THF clathrate hydrates have been analyzed. In a wide region of temperatures above 2 K, k(T) exhibits a behavior typical of disordered solids, which depends weakly on their chemical composition, crystalline structure and microstructure. The results are discussed in the context of phenomenological models of phonon scattering by local modes. It has been found that the Xe clathrate has a feature unusual for glasses, namely, k(T) decreases almost two-fold as the temperature increases from 50–100 K. The behavior of k(T) is presumably determined mainly by the strong phonon scattering on water molecules.

2007-01-01T00:00:00Z