Calculation of the molten pool depth in vacuum arc remelting of alloy Vt3-1

This paper is devoted to a simple heat model of vacuum arc remelting (VAR) including the solution of a nonlinear heat conduction equation with nonlinear boundary conditions typical for VAR. A finite-difference analog of the model’s initial equation is obtained by the finite-volume method. The system obtained is solved by a two-cyclic scheme of component-wise splitting. A simplified model neglecting the magnetohydrodynamic phenomena in the molten pool is tested by comparison of the results of numerical calculations of the pool depth in remelting of the Russian titanium alloy Vt3-1 (Ti-6.5Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) with the results of radiographic experiments. It has been shown that the model fits the experimental data well under various remelting conditions (the ingot diameter and operating current intensity).     

Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconductivity

We report ab initio linear-response calculations 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 agree well with the experiment. Factors accounting for the relatively low critical temperatures T _c in transition metal compounds with light elements are considered and the possible ways of increasing T _c are discussed. The text was submitted by the author in English.     

Acoustic Signals Induced in a Copper Target under Irradiation by a Low-Energy High-Current Electron Beam

Russian Physics Journal - Results of investigations of acoustic signals induced in a copper plate irradiated with a microsecond lowenergy high-current electron beam (LEHCEB) are presented. The...     

Dynamics of complex-shape traveling pulses in a fitz hugh-nagumo system with modulated parameters

The dynamics of traveling-pulse solutions is studied for a Fitz Hugh-Nagumo model with modulated parameters. The boundaries of the modulation depth of the system parameters where these solutions still exist are found by numerical simulation. The compensation effect of the parameter modulation acting on the stability of such solutions is obtained. This work was presented at the Summer Workshop “Dynamic Days” (Nizhny Novgorod, June 30–July 2, (998). Lobachevsky State University of Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 12, pp. 1586–1592, December, 1998.     

Magnetic phase transitions in nanostructures induced by shear stress under high pressure

Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range.     

Transition from two-to three-dimensional behavior in anisotropic polymer layers

Two types of anisotropic polymer systems were studied in the spherical approximation used in the classical theory of ferromagnetism. These were a three-dimensional system composed of weakly interacting layers with isotropic interactions between chain segments in the layer planes and thin quasi-two-dimensional polymer films possessing intra-and interchain interaction anisotropy, whose behavior is close to that of two-dimensional systems. Laws that govern a change in the temperature T _cr of phase transition from the long-range order state to a disordered state depending on the magnitude of anisotropy and the size of the layers were established. For systems of the former type in which interlayer interactions is weakened, T _cr tends to zero, being inversely proportional to lng, where g is the ratio of the interaction constant between the layers to that of inplane interaction in a layer. For systems of the latter type, the transition temperature T _cr → 0 according to the T _cr ～ √? law, where ? is the parameter that characterizes the anisotropy of intra-and interchain interactions. The number of layers required for the systems to be considered three-dimensional was estimated. Regardless of the type of boundary conditions for finite systems, the number of layers increases with enhancement of interaction anisotropy (a decrease in g and ?) and an increase in the number of chains in the layers, especially for systems of the former type. Transverse orientational correlations of chain segments with respect to the arrangement of the layers decrease according to a power law, as in the case of infinite two-dimensional systems. There are fluctuations of three-dimensional long-range orientation order in the plane of the layers, the fluctuations are enhanced with an increase in the anisotropy of interactions in the system.     

Specific features of interaction between formic acid and oxygen adsorbed on smooth polycrystalline platinum: Transients of the open-circuit potential

Transients of the open-circuit potential, which are observed when formic acid is interacting wit adsorbed oxygen (O_ads) preliminarily accumulated on polycrystalline “smooth” platinum (pcPt), are measure in an aqueous solution of sulfuric acid. It is shown that, as with platinized platinum (Pt/Pt), at large coverage by adsorbed oxygen (θ_O = 1?0.8), adsorbed oxygen interacts directly with molecules of formic acid from solution. In the region of medium coverages (θ_O = 0.8?0.2), on the other hand, a mechanism of “conjugated reactions” is realized. It is established that, in the case of pcPt, the direct interaction of O_ads with molecules of HCOOH from solution proceeds slower by nearly three times and the interaction via the mechanism of “conjugated reactions,” faster by about three times, as compared with Pt/Pt.     

Plasma-assisted oxidative degradation of organic dyes in solution by the joint action of underwater discharge and ozone

Data on the degradation kinetics of two organic dyes in a mixture by the action of electrical underwater discharges and ozone are presented. It has been found that the rate of degradation by the to combined treatment of the both dyes with face discharge and ozone is five times the sum of degradation rates expected on the assumption of the additive effect of each of these factors.     

Dimeric stilbenes of the wood of Maackia amurensis

Dimeric stilbenes have been isolated from the wood of Amur maackia for the first time. Two of them have been identified as the known scirpusins A and B. The structure of a new dimeric stilbene with a dioxane linkage, which has been called maackinin, has been established. The PMR and¹³C NMR spectra of the substances isolated have been studied in detail.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, Russian Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 468–476, September–October, 1992.