Equivalent electrical network of the DNA molecule

The variation of current density with bias or temperature is examined for DNA molecules of different configuration. To this end, the DNA molecule is represented as an equivalent electrical network whose behavior is then simulated with PSPICE. The results are found to be in close agreement with ones obtained within a physical model. It is established that the electrical response of a DNA molecule to an applied electric field depends on the boundary conditions and the potential profile along the molecule. This finding should contribute to the creation of a complete library of DNA-molecule configurations with prescribed electrical properties.     

Creep and stress-rupture strength of rolled sheet and welded joints of niobium alloy of the system Nb-W-Mo-Zr at high temperatures

High-temperature strength characteristics of rolled sheet, welded joints, and weld metal of niobium alloy 5VMTs of the system Nb-W-Mo-Zr at 1520–2020 K and stresses comprising 0.4–1.0 of the material ultimate strength are given. It is shown that welded joints and cast weld metal under high-temperature prolonged loading conditions are the same as the basic metal, and in a number of cases they surpass it in high-temperature strength characteristics. Empirical dependences are obtained connecting the short-term material strength with its creep resistance characteristics and stress-rupture strength at temperatures above the start of dynamic recrystallization.Translated from Problemy Prochnosti, No. 12, pp. 24–32, December, 1993.     

Improvement in the accuracy of determining shear moduli for orthotropic bars with twisting

A method is described for improving the accuracy of measuring shear moduli under twisting conditions taking account of the compliance of elements by testing an additional specimen.Translated from Problemy Prochnosti, No. 3, pp. 60–62, March, 1994.     

Effect of vitamins A, E and K on the indices of the glutathione antiperoxide system in gingival tissues in periodontosis

Glutathione reductase is activated and the content of glutathione sulfhydryl groups is increased in the gingival tissue of patients afficted with parodontosis. The degree of alterations depends on the degree of the development and character of the disease. Application of antioxidant vitamin therapy (vitamins A, E and K) locally and per os normalizes the parameters under study and improves the status of the parodontium.     

Self-ignition ahead of the flame front in piston spark-ignition engines

The hypothesis that engine knock is a result of competition of two types of chemical reaction—frontal frontal and volumetric—is put forward. A mathematical model for mixture self-ignition ahead of the flame front in an internal-combustion spark-ignition engine is constructed. The operation process was calculated numerically with variation of the ignition angle, the degree of compression, and the rotation frequency of the crankshaft. A critical condition for the occurrence of engine knock is obtained by approximate analytical solution of the problem. Comparison of theoretical results for ten engine parameters and operation with experimental data of different authors confirms the validity of the proposed hypothesis on the occurrence of engine knock. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 6, pp. 3–13, November–December, 1997.     

Hierarchy of processing equipment configuration design problems for multiproduct chemical plants

A procedure for performing one stage of designing multiproduct chemical plant—definition of the processing equipment configuration is proposed. At this stage, a three-level hierarchical structure of problems is formed—at the upper level, the parameters of the operational mode of the chemical engineering system that ensures the desired output of each product are found; at the middle level, the size and number of equipment units and methods of product processing for all processing stages are chosen; at the lower level, technological and mechanical design of individual pieces of equipment (machines) are performed. The decomposition of the processing equipment design problem into three problems described above reduces the original mixed integer nonlinear programming problem to one nonlinear programming problem and a set of integer programming problems, where the number of integer programming problems is equal to the number of processing stages. The reduced problems can be solved using available optimization methods, which considerably reduces the solution time and improves the quality of design solutions. Basic information links between the problems of different hierarchical levels are determined, general problem statements and an algorithm for the simultaneous solution of the upper and middle level problems is proposed. By way of example, the problem of selection and design of a mechanical agitator for a vertical bulk-capacity storage is considered.     

Sol–Gel Synthesis of Doped Vitreous Materials with the Use of Modified Aerosils

A novel variant of the sol–gel synthesis of silica glasses and optical composites containing transition-metal ions and nanoparticles is developed. Xerogels and glasses containing 10- to 46-nm particles are prepared with the use of aerosils modified by chromium oxide. The structural and physicochemical properties of chromium oxide–modified silica samples are investigated by X-ray powder diffraction, differential thermal analysis, thermal gravimetric analysis, and IR spectroscopy. The optical properties of transparent samples are examined using the transmission spectra and the refractive index distribution over the cross section of the xerogel preform. Xerogels and glasses containing nanoparticles of metallic copper and Cu _x Se are formed in the tetraethoxysilane–aerosil–copper nitrate system. An analysis of the optical properties of the nanocomposites demonstrates that SiO₂ : Cu _x Se nanocomposites can be used as passive Q switches.     

Forming conditions for Au-Sb and Ag-Sb ore according to thermodynamic modeling data

Ore forming conditions for Au-Sb and Ag-Sb deposits have been estimated using thermodynamic modeling. PTX-parameters of ore-forming fluids obtained by fluid inclusion study in the minerals were used as original data for modeling. Analysis of composition of fluid inclusion solutions in the minerals of Au-Sb deposits together with mineralogical and geochemical data show that Au-Sb deposits were formed by two types of solutions: neutral–weak alkaline (C_Cl < 5 wt % NaCl-eq.), and acid high concentrated chloride solution (up to 30 wt% NaCl-eq.), containing FeCl₂ and CaCl₂ besides NaCl. In low concentrated chloride solution Sb is transported as sulfide and hydroxide complexes, and Au and Ag as bihydrosulfide species. In acid high chloride solution of late superimposed stage, which contains Cu, Ag, Pb, and Zn, predominating Au and Ag species are chloride complexes, and for Sb chloride and hydroxy-complexes. The main factors determining geochemical specialization of Ag-Sb ore are high chloride concentration and pH = 3.5–4, determining low Au-bearing capacity of the solution. Unsaturated in Ag low concentrated chloride solutions took part in Au-Sb deposit forming that determines their specific composition.