Method to evaluate the invariant J-integral in finite-element models of prismatic bodies

A new method to evaluate the J-integral in finite-element models is developed and implemented. It is shown that in contrast to well-known approaches, this method ensures the invariance of the J-integral in finite-element solution of linear and nonlinear problems Translated from Prikladnaya Mekhanika, Vol. 44, No. 12, pp. 70–82, December 2008.     

The formation of primary galactic nuclei during phase transitions in the early universe

A new mechanism describing the formation of protogalaxies is proposed, based on the second-order phase transition in the inflation stage and the domain wall formation upon the end of inflation. The presence of closed domain walls with the size markedly exceeding the cosmological horizon at the instant of their formation and the wall collapse in the postinflation epoch (when the wall size becomes comparable with the cosmological horizon) lead to the formation of massive black hole clusters that can serve as nuclei for the future galaxies. The black hole mass distributions obtained do not contradict the available experimental data. The number of black holes with M ～ 100 solar masses (M _⊙) and above is comparable with the number of galaxies in the visible Universe. Development of the proposed approach gives grounds for a principally new scenario of galaxy formation in the model of a hot Universe.     

Initial stages of the growth of barium strontium titanate films on a semi-isolating silicon carbide substrate

The initial stages of the growth of ferroelectric barium strontium titanate films on single-crystal silicon carbide substrates have been studied for the first time. The choice of a substrate with high thermal conductivity has been due to the possibility of applying these structures in powerful microwave devices. The temperature ranges separating the mechanism of the surface diffusion of deposited atoms from the diffusion via a gaseous phase during the growth of multicomponent films have been determined. The studies show that the mass transfer by means of surface diffusion leads to the formation of small-height nuclei that cover a large area of the substrate, whereas the mass transfer via a gaseous phase leads to the formation of a “columnar” islandtype structure with small percentage of covering the substrate and larger island heights.     

HF-plasmatron experiment and numerical simulation of heat transfer in underexpanded dissociated-nitrogen jets

Experiments on heat transfer in underexpanded supersonic jets of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency plasmatron at a pressure of 10.4 GPa in a compression chamber. At gas flow rates of 2.4 and 3.6 g/s and HF generator powers of 45 and 64 kW the heat fluxes to the copper, stainless steel, MPG-7 graphite, and quartz surfaces are measured at the stagnation point of a water-cooled cylindrical, flat-ended model, 20 mm in diameter. In the same regimes the stagnation pressures are measured. The effect of the surface catalyticity with respect to nitrogen atom recombination on the heat flux is demonstrated and the qualitative catalyticity scale of the studied materials is established. In the supersonic regimes nonequilibrium nitrogen plasma flow in the discharge channel of the plasmatron and the underexpanded jet flow past the model are numerically simulated for the experimental conditions. The experimental and calculated data on the stagnation pressures and the heat fluxes to cooled surfaces of the metals, graphite, and quartz are compared.     

Distribution of radiant heat fluxes over the surface of three-dimensional and axisymmetric bodies in a supersonic ideal-gas flow

Numerous studies have been devoted to the calculation of supersonic radiating flow past bodies (see the bibliography in [1, 2]). In almost all these studies the gas flows investigated are plane or axisymmetric. Three-dimensional flows, however, have received little attention. The flow of air past three-dimensional bodies was considered in [3], where the chief object was to investigate the accuracy with which a real radiating volume can be simulated by the widely used plane-layer approximation. In [4] the flow of a hydrogen-helium mixture past three-dimensional bodies was investigated in the hypersonic approximation in the neighborhood of the stagnation point and in two planes of symmetry with allowance for the screening of the radiation of vaporized material.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 92–97, January–February, 1986.The authors wish to thank V. V. Lunev for his useful observations and advice.     

Field-emission diodes based on semiconductor—polycrystalline diamond heterojunctions

A complex of electrophysical and technological studies of solid-state field-emission diodes is carried out. Emission comes from an array of nanometer objects near the semiconductor—polycrystalline diamond interface. The process route of the diode heterostructures includes the fabrication of nanometer masks and nanometer cone (tip) arrays, as well as plasma-assisted growth of polycrystalline diamond films on the surface of structures with nanometer cone arrays. In field-emission diodes thus formed, a current density as high as 20 A/cm² is achieved at a threshold of field emission from the nanotip arrays into the diamond of about 0.5 V.     

Algorithm for solving the inverse problem of ballistics in the case of an asymmetric object

An algorithm to identify the aerodynamic characteristics of an asymmetric object from its trajectory data obtained in a ballistic experiment is developed based on the technique for estimating the nonlinear system’s parameters. Using the method of successive approximations, the coefficients of the aerodynamic function polynomial representation are found that best describe measuring data. The essence of the algorithm is the solution of the direct problem of the symmetric object’s dynamics using the complete set of Euler dynamic equations. The variation of the desired parameters is statistically estimated during calculations. The algorithm allows for jointly processing data of a series of experiments with similar models. Thereby, the volume of processed data is augmented and the final result becomes more accurate.     

Aerosol deposition of detonation nanodiamonds used as nucleation centers for the growth of nanocrystalline diamond films and isolated particles

The aerosol deposition of detonation nanodiamonds (DNDs) on a silicon substrate is comprehensively studied, and the possibility of subsequent growth of nanocrystalline diamond films and isolated particles on substrates coated with DNDs is demonstrated. It is shown that a change in the deposition time and the weight concentration of DNDs in a suspension in the range 0.001–1% results in a change in the shape of DND agglomerates and their number per unit substrate surface area N _s from 10⁸ to 10¹¹ cm⁻². Submicron isolated diamond particles are grown on a substrate coated with DND agglomerates at N _s ≈ 108 cm⁻² using microwave plasma-enhanced chemical vapor deposition. At N _s ≈ 10¹⁰ cm⁻², thin (∼100 nm) nanodiamond films with a root-mean-square surface roughness less than 15 nm are grown.     

Synthesis and properties of fluorosilicon compounds for protection of cultural monuments from harmful environmental exposure

Methods for the synthesis of perfluorocarboxylic acid derivatives with reactive trialkoxysilyl groups soluble in organic and organofluorine (1,1,2-trichlorotrif1uoroethane, etc.) solvents have been developed. The contact angles of water and decalin, water absorption, resistance to freezing, and salt-resistance of limestone and plaster samples treated with these compounds were determined. Fluorosilicon organic compounds impart more hydro- and oleophobic properties to the protected surfaces than known organosilicon agents and reliably protect sculptures and architectural monuments from mold and algae deposition.     

Heterometallic derivatives of dicarbonylcyclopentadienylrhenium disulfide containing chromium pentacarbonyl and bis(triphenylphosphine)platinum

The reaction of Cp′Re(CO)₂THF (Cp′ = C₅H₄Me), THF is tetrahydrofuran) with sulfur affords Cp′Re(CO)₂S₂(I) and [Cp′Re(CO)₂]₂S (II). The synthesized compounds are isolated chromatographically and characterized by X-ray diffraction analysis. The adduct Cp′Re(CO)₂S₂Cr(CO)₅ (III) is synthesized by the reaction of compound I with Cr(CO)₅(THF). The adduct CpRe(CO)₂S₂Cr(CO)₅ (IV) is obtained similarly from known CpRe(CO)₂S₂ and Cr(CO)₅(THF). The reaction of compound I with (PPh₃)₂Pt(C₂Ph₂) results in the removal of Ph₂C₂ and one sulfur atom to form Cp′Re(CO)₂SPt(PPh₃)₂ (V). The structures of compounds I–V are determined by X-ray diffraction analysis (CIF files CCDC nos. 984554 (I), 984555 (II), 984556 (III), 984557 (IV), and 984558 (V)). Compound I contains the three-membered cycle ReS₂ with the ordinary S-S bond (2.044(4) Å) and shortened Re-S bonds (average 2.434(3) Å). The three-membered cycle Re₂S containing the ordinary Re-Re bond (2.932(1) Å) and shortened Re-S bonds (2.371(1) Å) is observed in compound II. In compounds III and IV, the formation of the ordinary S-Cr(CO)₅ bond (2.406(1) Å) with one of the sulfur atoms almost does not change the geometry of the ReS₂ fragment. The thermal decomposition of compound III proceeds with the elimination of six CO ligands in the range 110–160°C and then with the loss of CO and Cp′ in the range 160–430°C and the formation of the inorganic residue ReCrS₂. Compound V contains the triangular framework ReSPt with the ordinary Pt-Re bond (2.7882(3) Å) and substantially shortened bonds Re-S (2.3984(9) Å) and Pt-S (2.2724(8) Å). It is assumed that compounds II and V can be presented as products of the π-coordination of the double bonds in Cp′(CO)₂Re=S with the Cp′Re(CO)₂ or Pt(PPh₃)₂ groups, respectively.