Study of the secondary structures of filled rubbers

It is shown that the secondary structure of rubbers filled with carbon blacks can be expressed in terms of the volume of the relaxation kinetic element (V), calculated from the stress relaxation curves. The effect of the type and concentration of carbon black and the extension of the specimen on the quantity V has been investigated. The volume of the kinetic element decreases with increase in the concentration and dispersity of the carbon black. This is associated with an increase in the rubber-filler contact area, which causes the orientation of groups of molecular chains and reduces the size of the deformation unit. As the degree of extension of the specimen increases, V decreases.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1066–1069, 1967     

Controlled Formation of β-Si3N4 on Native Oxidized Silicon Wafers in Ammonia Flow

Crystallography Reports - The formation of β-Si3N4 for subsequent growth of AlGaN and GaN heterostructures of silicon wafers has been studied. It is established that the native oxide layer...     

High-Quality AlN Layers Grown on Si(111) Substrates by Metalorganic Chemical Vapor Deposition

Crystallography Reports - The effect of trimethylaluminum preflow time on the crystalline quality of AlN films grown by metalorganic chemical vapor deposition on Si(111) substrates has been...     

3-Fluoroalkyl (CF3, CHF2, CH2F) Cyclobutane-Derived Building Blocks for Medicinal Chemistry: Synthesis and Physicochemical Properties

Synthesis and physicochemical characterization of all possible cis- and trans-1,3-disubstituted cyclobutane-derived amines and carboxylic acids bearing mono-, di- and trifluoromethyl groups at the C-3 position is disclosed. Tetramethylammonium fluoride (TMAF)- or morpholinosulfur trifluoride (Morph-DAST)-mediated nucleophilic fluorination of appropriate cis- and trans-diastereomeric substrates was used as the key step for the preparation of CH₂F- and CHF₂-substituted derivatives. To obtain the corresponding cis- and trans-isomeric CF₃-substituted derivatives, resolution of known 3-(trifluoromethyl)cyclobutanecarboxylic acid (obtained as a mixture of diastereomers) was applied. The proposed procedures were suitable for the preparation of corresponding fluoroalkyl-substituted cyclobutane-derived amines and carboxylic acids on up to 50 g scale. All 12 building blocks obtained were characterized by measuring dissociation constants (pK_a) and lipophilicities (LogP, for model derivatives) to evaluate the effect of the fluoroalkyl substituents on their physicochemical properties relevant to further drug discovery applications.     

Numerical models of a far turbulent wake of an elongated body of revolution

The work presents a comparison of numerical models of a far turbulent wake of a towed elongated body of revolution in a homogeneous fluid: model based on the direct numerical simulation, and two semi-empirical models involving the equation of the turbulence energy balance. Computational results demonstrate the self-similarity of the decay and agree with known experimental data.     

Electron microscopy study of the microstructure of Ni–W substrate surface

The surface microstructure of Ni–W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni₉₅W₅ tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO₄ precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950°С is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing in a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.     

Self-similar decay of a momentumless swirling turbulent wake

Numerical simulation of the decay of a momentumless swirling turbulent wake of a body of revolution has been carried out. It has been shown that beginning with the distances of the order of 1000 body diameters, the flow passes to the self-similar regime. Using the results of the numerical analysis of the flow, simplified mathematical models of far wake have been constructed.     

On numerical modeling of the dynamics of turbulent wake behind a towed body in linearly stratified medium

Two numerical models of the dynamics of a turbulent wake behind a towed body in a linearly stratified medium are compared, namely, the model based on direct numerical integration of Navier-Stokes equations in the Oberbeck-Boussinesq approximation and the mathematical model with applying a semiempirical turbulence model of the second order. The calculation results of the two models are similar to the known experimental data and are in good agreement.     

Numerical modeling of a turbulent flow behind a heated grid

A numerical model of the dynamics of turbulence and temperature fluctuations behind a heated grid located in a wind tunnel is constructed on the basis of closed Kármán-Howarth and Corrsin equations. Results calculated by this model are in reasonable agreement with available experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 118–126, May–June, 2009.