Anisotropy of structural response of single crystal austenitic stainless steel to friction stir welding

The structural response of an austenitic stainless steel single crystal to friction stir welding (FSW) was examined. The microstructural changes induced by FSW were found to essentially vary around the rotating tool. This effect was attributed to variable orientation of the shear plane and shear direction inherent to the FSW process, which significantly influenced slip activity of the single crystal.     

Effect of electrodynamic phenomena in arc furnaces on the meniscus formation in a liquid metal

The main laws of the electrodynamic action of an electric arc on the surface of the liquid metal bath in electric arc furnaces of various types are considered.     

Local environment of Eu3+ and Tb3+ ions in fluorophosphate glasses of the Ba(PO3)2-MgCaSrBaAl2F14 system

The induced optical absorption and EPR absorption spectra of fluorophosphate glasses of the compositions 40Ba(PO₃)₂ · 60MgCaSrBaAl₂F₁₄ and 5Ba(PO₃)₂ · 95MgCaSrBaAl₂F₁₄ doped with Tb³⁺ and Eu³⁺ ions are investigated within the model of the effective capture volume of free carriers. The concentration dependences of the relative number of radiation centers on the dopant concentration in fluorophosphate glasses are analyzed. It is established that the character of the distribution of dopant ions in glasses depends on the dopant concentration and the structure of the glass. The critical concentrations at which the oxygen local environment of Eu³⁺ or Tb³⁺ ions in the structure of fluorophosphate glasses transforms into a mixed local environment are determined for glasses of the compositions under investigation.     

The Kiss-and-Run Model of Intra-Golgi Transport

The Golgi apparatus (GA) is the main station along the secretory pathway. Mechanisms of intra-Golgi transport remain unresolved. Three models compete with each other for the right to be defined as the paradigm. The vesicular model cannot explain the following: (1) lipid droplets and aggregates of procollagen that are larger than coatomer I (COPI)-dependent vesicles are transported across the GA; and (2) most anterograde cargoes are depleted in COPI vesicles. The compartment progression/maturation model has the following problems: (1) most Golgi-resident proteins are depleted in COPI vesicles; (2) there are no COPI vesicles for the recycling of the resident proteins in the trans-most-Golgi cisterna; and (3) different proteins have different rates of intra-Golgi transport. The diffusion model based on permanent inter-cisternal connections cannot explain the existence of lipid, ionic and protein gradients across the Golgi stacks. In contrast, the kiss-and-run model has the potential to explain most of the experimental observations. The kiss-and-run model can be symmetric when fusion and then fission occurs in the same place, and asymmetric when fusion takes place in one location, whereas fission takes place in another. The asymmetric kiss-and-run model resembles the carrier maturation mechanism, and it can be used to explain the transport of large cargo aggregates.     

Composition of the Products of Thermolysis of Heavy Oil with the Addition of Light Hydrocracked Naphtha

Abstract

A series of experiments has been carried out on the thermolysis of heavy oil using 2.5–10.0% light hydrocarbon naphtha additive of vacuum gasoil prepared from conventional oil. It has been shown that the employment of the additive increases the conversion of heavy oil, avoids coke formation in the products of thermolysis as compared to the basic process without additive, and does not prevent the decrease in the viscosity of the products during thermolysis. It has been revealed on the example of the heavy oil of Ashal’chinskoe deposit (Russia) that the thermolysis with the addition of light naphtha gives a liquid product with the yield higher than 97% and the viscosity of less than 80?mm²/s.     

Development of grain structure during friction stir welding of pure titanium

The microstructure evolution during friction stir welding of commercial purity titanium was studied. Material flow was found to be close to the simple-shear deformation and arose mainly from the prism slip. The grain structure evolution was shown to be a complex process including several stages. Far from the welding tool, the microstructural evolution was found to be governed by geometrical effects of strain and limited discontinuous recrystallization. In the stir zone, formation of a strong texture was shown to lead to texture-induced grain convergence, and the grain structure development was thus closely related to the texture evolution.     

Rapid biofabrication of tubular tissue constructs by centrifugal casting in a decellularized natural scaffold with laser-machined micropores

Centrifugal casting allows rapid biofabrication of tubular tissue constructs by suspending living cells in an in situ cross-linkable hydrogel. We hypothesize that introduction of laser-machined micropores into a decellularized natural scaffold will facilitate cell seeding by centrifugal casting and increase hydrogel retention, without compromising the biomechanical properties of the scaffold. Micropores with diameters of 50, 100, and 200 mum were machined at different linear densities in decellularized small intestine submucosa (SIS) planar sheets and tubular SIS scaffolds using an argon laser. The ultimate stress and ultimate strain values for SIS sheets with laser-machined micropores with diameter 50 mum and distance between holes as low as 714 mum were not significantly different from unmachined control SIS specimens. Centrifugal casting of GFP-labeled cells suspended in an in situ cross-linkable hyaluronan-based hydrogel resulted in scaffold recellularization with a high density of viable cells inside the laser-machined micropores. Perfusion tests demonstrated the retention of the cells encapsulated within the HA hydrogel in the microholes. Thus, an SIS scaffold with appropriately sized microholes can be loaded with hydrogel encapsulated cells by centrifugal casting to give a mechanically robust construct that retains the cell-seeded hydrogel, permitting rapid biofabrication of tubular tissue construct in a "bioreactor-free" fashion.     

Studying gold nanoclusters within the Hubbard model

The approximation of static fluctuations in the Hubbard model is used to calculate the anticommutator Green’s functions, the thermodynamic averages characterizing the possibilities of electron hopping from site to site, the correlation functions which characterize the probability of finding two electrons on one site of a nanosystem, and the energies of the ground state for the closed atomic structures consisting of three, four, and sixteen gold atoms. Original Russian Text ? G.I. Mironov, 2008, published in Fizika Metallov i Metallovedenie, 2008, Vol. 105, No. 4, pp. 355–365.     

Burning of hydrogenous mixtures in the model of an internal-combustion-engine chamber

The integral characteristics of burning of stoichiometric and lean hydrogenous mixtures in a cylindrical chamber at initial pressures of 0.024 to 1 MPa have been investigated. The propagation of the flame has been visualized and the distributions of its velocity and the running parameters of burning have been obtained. It has been shown that in synthesis-gas-based mixtures, the flame front has a "cellular structure;" its characteristic dimension grows with propagation of the flame. A method for determining the shape factor, which makes it possible to explain certain experimental regularities of burning, has been proposed. The results of the work can be used in selecting the parameters of mixtures and combustion chambers of heat engines operating on modified fuels.     

High-output thermionic converter based on a metal-oxygen system on the collector

The results of comprehensive experimental investigations of thermionic converters with collectors containing oxygen in an adsorbed near-surface layer and capable of decreasing the barrier index below 2 eV are presented. A vanadium-doped alloy based on chromium, which was investigated in a converter in a pair with different emitters consisting of platinum and single crystal tungsten oriented along the (110) face, was examined as an example of an efficient metal-oxygen system on the collector. The emission-adsorption properties of electrodes and the output electrical characteristics, obtained under working conditions of the converter, as well as surface characteristics of the collector, such as the elemental composition temperature, and others, are described. 6 figures, 21 references. State Science Center of the Russian Federation—A. I. Leipunskii Physics and Power-Engineering Institute. Translated from Atomnaya énergiya, Vol. 89, No. 1, pp. 39–48, July, 2000.