Supersonic Inviscid Corner Flows with Regular and Irregular Shock Interaction

The results of a numerical and analytical investigation of steady-state supersonic inviscid flows in corners formed by intersecting compression wedges are presented. The flows considered are symmetric about the corner bisector. The distinctive features of flow pattern formation related with the reflection of wedge-generated shocks from the bisector plane are studied. The wedge angles at which transition from regular to irregular shock reflection occurs are determined both numerically and analytically using the criteria available for plane flows; the data thus obtained are found to be in agreement. Flow patterns with irregular shock reflection, namely, single, transitional, and double Mach, as well as von Neumann reflection, are identified; they are similar to the known types of reflection for plane quasi-steady-state flows. Varieties of these types not observed in the plane flows are found to exist. The effects of the angle of inclination of the plane surfaces of the corner to the freestream direction, the sweep angle of the leading edges, and the dihedral angle are investigated. Some previously unknown parameters of corner configurations for which transition may occur in accordance with the von Neumann criterion are determined.     

Lateral ordering during self-organization of statistical multiblock copolymers

The self-organization of statistical multiblock and Bernoulli AB copolymers is studied. The initial ensemble is generated via the polymer-analogous reaction A→B that proceeds with the accelerating effect of neighboring B units. In a two-dimensional model, the reaction is performed in a rectangle composed of stretched chains. Then, the rectangle is closed into a cylinder, so that ring chains are located on its side surface. The self-organization of the ensemble is simulated via the successive rotation of each upper ring over the lower ring until arrangement with the maximum (in modulus) energy of attraction between chains is attained. Self-organization by energy is accompanied by lateral ordering: the sizes of clusters—accumulations of the one-type units—and mean heights H _A (H _B) of stems—columns consisting of A or B units perpendicular to chains—increase. The ratio between the values of H _A, as well as H _B, for ordered and initial ensembles is independent of the average composition of the system and as a rule increases as the length of blocks increases and the length of chains decreases. Features of generation of the ensemble of short chains and their ordering are revealed. It is shown that, during ordering of multiblock copolymers, the probabilistic properties (the stochastic behavior) of the ensemble are disturbed. The self-organization of statistical multiblock copolymers in a three-dimensional model is investigated via rotation of rings in the torus of the rectangular cross-section. The effects of various factors on self-organization by energy and local ordering in 2D and 3D models are similar; however, the efficiency of ordering in the three-dimensional system is always lower because, in this case, arrangements with the maximum energy of attraction simultaneously to two neighboring chains, rather than to one, are implemented for the majority of chains.     

Simulation of heterogeneous end-coupling reactions in polydisperse polymer blends

The influence of polydispersity on the interfacial kinetics of end-coupling and microstructure formation in the melt of immiscible polymers was studied using dissipative particle dynamics simulations. The irreversible reaction started at a flat interface between two layers, each of which contained polymer chains of two different lengths with functionalized or unreactive end groups. As in the case of fully functionalized monodisperse reactants [A. V. Berezkin and Y. V. Kudryavtsev, Macromolecules 44, 112 (2011)], four kinetic regimes were observed: linear (mean field coupling at the initial interface), saturation (decreasing the reaction rate due to the copolymer brush formation or reactant depletion near the interface), autocatalytic (loss of the initial interface stability and formation of a lamellar microstructure), and terminal (microstructure ripening under diffusion control). The interfacial instability is caused by overcrowding the interface with the reaction product, and it can be kinetically suppressed by increasing chain length of the reactants. Main effects of polydispersity are as follows: (i) the overall end-coupling rate is dominated by the shortest reactive chains; (ii) the copolymer concentration at the interface causing its instability can be not the same as in the lamellas formed afterwards; (iii) mean length of the copolymer product considerably changes with conversion passing through a minimum when a microstructure is just formed.     

Design of small-molecule thrombin inhibitors based on the <Emphasis Type="Italic">cis</Emphasis>-5-phenylproline scaffold

The design of novel organic compounds containing no strongly basic amidine or guanidine functional groups typical of serine protease inhibitors was performed to develop an oral anticoagulant drug. A three-dimensional computational model for thrombin active site was constructed and optimized for docking of small-molecule organic compounds and calculating the energies of inhibitor-enzyme interactions. Novel racemic derivatives of 1-[2-(4-chlorophenylthio)acetyl]-5-phenylpyrrolidine-2,4-dicarboxylic acids were synthesized for which Cl-π interactions between the inhibitors and the S1 pocket of thrombin active site are predicted by modeling. The compounds synthesized deactivate thrombin in vitro and the inhibition properties show good correlations with the results of calculations.     

New carbazole-containing chalcones and pyrimidines based thereon: Synthesis and electrochemical study

Condensations of aromatic carbo- and heterocyclic ketones and aldehydes in methanol gave new chalcones containing carbazole fragments, 1,3-diaryl(9-R-9H-carbazol-3-yl)prop-2-en-1-ones. Some of the synthesized chalcones reacted with guanidine sulfate to produce 2-amino-4,6-diarylpyrimidines that are promising materials for the design of light emitting diodes. Study on electrochemical polymerization of both chalcones and pyrimidines derived therefrom showed that almost all the examined substrates give rise to stable colored conjugated polymer films on the surface of working electrode under conditions of cyclic voltammetry.     

Modeling learning process

We consider the problems of creating computer-based learning systems and teaching environments on the basis of discrete models based on automata. We estimate the perspectives of using computer models of learning for improving the quality of education.     

On the Nonlocal Darboux Transformation for Time-Independent Axially Symmetric Schrödinger and Helmholtz Equations

JETP Letters - The nonlocal Darboux transformation for the time-independent axially symmetric Schrödinger and Helmholtz equations has been considered. New examples of two-dimensional...     

Phase Diagrams of Semicrystalline Polymer–Crystalline Substances: Polyolefins–1,2,4,5-Tetrachlorobenzene

The full phase diagrams of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and isotactic polypropylene (i-PP) mixtures with 1,2,4,5-tetrachlorobenzene (TeCB), including the solubility curve of TeCB in a solid polymer, were constructed by an optical method. The diagrams contain a eutectic point that corresponds to the situation when the crystallization of TeCB out of its solution in a polyolefin is accompanied by the crystallization of monomer units of the macromolecules. As a result, the polymer acquires a gel structure with crystallites as crosslinks and amorphous regions saturated with TeCB. It is demonstrated that the eutectic point position on the phase diagram can be used for ranking polymers with respect to their thermodynamic affinity to a solvent. For the studied systems, the affinity to TeCB was decreased in the order i-PP, HDPE, and LDPE. Direct experimental evidence was obtained that TeCB crystals can be dissolved in a solid polymer via a vapor phase mechanism, which leads to the polymer amorphization.     

Magnetic and magnetoelastic properties of Fe64Co21B15 and Fe73Co12B15 amorphous metal strips

The effect of magnetic annealing on the magnetic and magnetoelastic properties of FeCoB amorphous metal strips in the temperature range from 290 to 380°C has been investigated. With the method of photostimulated exoelectronic emission it has been found that in this temperature range there occurs crystallization of the surface of the test strips. It has been shown that the minima of the coercive force, residual induction, and differential magnetic permeability and the maximum absolute values of the negative Δ-effect are attained at magnetic annealing temperatures close to the temperatures corresponding to the maxima of the intensity of photostimulated exoelectronic emission. An explanation of the results obtained has been proposed which is based on the notions about the effect of internal stresses on the induced magnetic anisotropy of the test strips. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 59–65, August, 2006.