Short-time critical dynamics of the three-dimensional systems with long-range correlated disorder

Monte Carlo simulations of the short-time dynamic behavior are reported for three-dimensional Ising and XY models with long-range correlated disorder at criticality, in the case corresponding to linear defects. The static and dynamic critical exponents are determined for systems starting separately from ordered and disordered initial states. The obtained values of the exponents are in a good agreement with results of the field-theoretic description of the critical behavior of these models in the two-loop approximation and with our results of Monte Carlo simulations of three-dimensional Ising model in equilibrium state.Comment: 24 RevTeX pages, 12 figure

Noncommutative Novikov algebras

The class of Novikov algebras is a popular object of study among classical nonassociative algebras. The generic example of a Novikov algebra may be obtained from a differential associative and commutative algebra. We consider a more general class of linear algebras which may be obtained in the same way from not necessarily commutative associative algebras with a derivation.Comment: 18 page

Interface states in junctions of two semiconductors with intersecting dispersion curves

A novel type of shallow interface state in junctions of two semiconductors without band inversion is identified within the envelope function approximation, using the two-band model. It occurs in abrupt junctions when the interband velocity matrix elements of the two semiconductors differ and the bulk dispersion curves intersect. The in-plane dispersion of the interface state is found to be confined to a finite range of momenta centered around the point of intersection. These states turn out to exist also in graded junctions, with essentially the same properties as in the abrupt case.Comment: 1 figur

Epoxy Polymer Gasification under Combustion

The processes taking place in the preflame zone at flame spread over the surface of epoxy polymer have been investigated in the present work. It has been shown that heating of yet unignited polymer ahead of flame spreading over the thermally thick samples is done mainly by the heat conduction through condensed phase. The compositions of highly- and hardly-volatile products of gasification are determined in conditions of the preflame zone. It is shown that the main combustible product of gasification is CO (ca. 85 %). The mass rates of gasification and the linear velocities of an injection of gasification products into gas phase of preflame zone have been determined. The complicated aerodynamic structure of the preflame zone with a vortex formation is shown to exist. As a result oxygen gets a free access to a polymer surface and can participate in gasification processes. Experimental simulation of the epoxy polymer gasification processes was carried out in the oxygen-18 enriched atmosphere. The main oxygen-containing product of gasification is shown to be generated both as a result of pyrolysis, and a result of thermooxidation. More than 75% of carbon dioxide is formed only due to thermooxidative destruction, and 75 - 90% of carbon oxide is formed only due to pyrolysis. It has been shown that in a course of epoxy polymer gasification in preflame zone the main mass of combustible products is generated by pyrolysis, but an energy for this is mostly supplied by simultaneously occurred exothermal processes of thermooxidation of the near-surface layers of epoxy  polymer

Rapidly rotating neutron star progenitors

Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, $\tau_c$. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 $M_\odot$ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value $\tau_c \simeq 5 \times 10^5$ years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being $\sim 0.1-1\%$ of the total core collapses, depending on the common envelope efficiency.Comment: 10 pages, 4 figures, accepted for publication in MNRA

Constrained flow around a magnetic obstacle

Many practical applications exploit an external local magnetic field -- magnetic obstacle -- as an essential part of their constructions. Recently, it has been demonstrated that the flow of an electrically conducting fluid influenced by an external field can show several kinds of recirculation. The present paper reports a 3D numerical study whose some results are compared with an experiment about such a flow in a rectangular duct.Comment: accepted to JFM, 26 pages, 14 figure