Thermoelastic stresses in ribbons and tubes grown from the melt by the Stepanov method

Ribbons and tubes grown from the melt by the Stepanov technique have a wide range of technical applications. Sapphire ribbons are used as substrates in microelectronics and sapphire tubes are used as gas-discharge balloons in laser engineering, fine chemical technology and high-vacuum equipment. Practice has shown that misorientation angles of small-angle boundaries in sapphire crystals should not exceed several degrees because an increase in the misorientation angles between blocks drastically lowers the strength and worsens the dielectric properties of these crystals. One of the main mechanisms of formation of the block structure of melt-grown crystals, including shaped sapphire crystals, is dislocation polygonization that begins when the dislocation density exceeds a certain critical value. In turn, dislocations are formed under deformations due to thermal stresses. Calculations of thermal fields in crystals and the corresponding thermoelastic stress fields can be used as an input to improve and optimize the growth process. The dependence of thermoelastic stresses in ribbons and tubes on the technological parameters has been calculated.Nomenclature ₁ Thermal diffusivity of the melt - ₂ Thermal diffusivity of the crystal - k ₁ Thermal conductivity of the melt - k ₂ Thermal conductivity of the crystal - V ₁ Velocity vector of the melt - V ₂ Velocity vector of the growing crystal - V ₀ Crystal pulling rate - H _f Latent heat of fusion - ₁ Density of the melt - ₂ Density of the crystal - in Interface normal vector - Crystal-melt interface normal vector - t Interface tangential vector - s Sided crystal-melt tangential vector - T _m Melting temperature - T _e Ambient temperature - T ₁ ⁰ Temperature at the bottom of the meniscus - T ₂ ⁰ Crystal temperature at the top of the meniscus - Normal vector at lateral surfaces of the crystal and meniscus - Stefan-Boltzmann constant - ₁ Emissivity of the meniscus lateral surface - ₂ Emissivity of the crystal lateral surface - g Acceleration due to gravity - _LG Melt-gas surface tension - a Die half dimension - ₀ Angle of growth - _t Thermal expansion coefficient - h ₁ Heat transfer coefficient of the melt - h ₂ Heat transfer coefficient of the crystal - C s Heat capacity - E Young's modulus - Poisson's coefficient - Melt kinematic viscosity - P Pressure in the melt     

Conductivity of Bismuth Nanowires at Low Temperatures in Transverse Magnetic Field

We investigate theoretically and experimentally the conductivity of bismuth nanowires at low temperatures in a uniform magnetic field directed perpendicularly to the wire axis. Using the Kubo formula, we calculate the conductivity for the cases of systems with degenerate and nondegenerate carrier gas with elastic acoustic-phonon scattering of carriers. Size, temperature, and field dependence of the conductivity of a Bi quantum wire are discussed in detail. For a nanowire with nondegenerate carrier gas, the conductivity depends exponentially on a combination of field, temperature, and wire diameter. For a semimetallic Bi quantum wire can be observed the negative magnetoresistance.     

Electron Spin Resonance in a Multilayer Graphene Synthesized with Polystyrene

Technical Physics Letters - Electron spin resonance in a multilayer graphene–polystyrene composite has been studied as dependent on the temperature and magnetic field. The observed g-factor...     

The action of amino acid di[2-haloethyl]hydrazides on DNA synthesis in normal and tumor cells and on the cell cycle kinetics in mice with melanoma B-16

A comparative study was carried out with two alkylating agents IMB-MM and IMB-97 which are di-(2-halogenoethyl) hydrazides of amino acid derivatives. They have been found to exert a high activity towards wide spectrum of experimental tumours. Both agents caused inhibition of incorporation of 3H-thymidine into DNA of melanoma B16, marrow, intestinal mucosa, spleen and liver cells of mice with tumours. A maximal inhibition of DNA synthesis in all tissues was observed 24 h after the single doses of drugs. However 96 h later this effect was removed excluding the tumour cells. The cytofluorimetric study have shown that IMB-MM, like sarcolysine, caused an accumulation of tumour cells in G2/M phase of cell cycle, while IMB-97 increased accumulation of S-phase cells. The difference in phase sensitivity of tumour cells towards IMB-MM and IMB-97 is due to the differences in aminoacid carriers of di-(2-halogenethyl) hydrazide groups.     

One-Step Synthesis of the Polyaniline–Single-Walled Carbon Tubes Nanocomposite in Formic Acid and Its Electrochemical Properties

A one-step synthesis of a stable dispersion of nanocomposite consisting of polyaniline (PANI) and single-walled carbon nanotubes (SWCNTs) was carried out by the oxidative polymerization of aniline with benzoyl peroxide (PB) in concentrated formic acid (FA). Electrically conductive film coatings were obtained by direct application of this dispersion to an electrode. The coatings have high specific electrochemical capacitance and stability during prolonged cycling in an aprotic electrolyte (1 M LiBF₄ in γ-butyrolactone).     

Corrosivity of atmosphere toward structural metals and mapping the continental Russian territory

ABSTRACT

The corrosivity of atmosphere in the continental territory of Russia toward carbon steel, zinc, copper and aluminium was determined and estimated. The atmosphere corrosivity was determined from experimental data on first-year corrosion losses in representative test locations. The atmosphere corrosivity was estimated using first-year corrosion losses of structural materials calculated by means of dose–response functions: new ones (DRF^N) and those presented in ISO 9223 (DRF^S). Estimation of atmosphere corrosivity in the Russian Federation (RF) territory was performed using the data bank of the Institute of physical chemistry and electrochemistry of the Russian Academy of Sciences containing long-term annual average meteorological atmosphere parameters. The mapping of RF continental territory by categories of atmosphere corrosivity is presented. The atmosphere corrosivities estimated by DRF^N and DRF^S for each metal are compared. It has been shown that DRF^N provides more reliable atmosphere corrosivity estimates.     

Refractories with malinovetskoe kaolins in the binder

Technological tests of Malinovetskoe kaolins have shown that mixtures with these kaolins in the binder give chamotte refractories with a porosity of 19–24%. Denser articles can be produced with the addition of sintering clays such as Novoraiskoe or Nizhne-Uvel’skoe, by the method of joint milling, or with an additive of finely milled chamotte