Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Effect of substituents on the properties of 2-(o-hydroxystyryl) benzimidazolium salts

The results of a calculation of the benzimidazolium cation and its 5(6)-substituted derivatives by the Hückel MO method show that the ±I effects of substituents have a considerably lesser influence on the magnitude of the charge on the C₍₂₎ atom than ±M effects. Replacement of C₍₅₎ by a positively charged nitrogen atom (imidazo[4,5-c]pyridinium dication) increases the charge on C₍₂₎ to the same extent as the introduction of a substituent with a vacant p_Z orbital into the 5 position. In accordance with this, the methyl group in the 2 position of the 1,2,3,5-tetramethylimidazolio[4,5-c]pyridinium ion condenses with salicylaldehyde, but the merocyanine cannot be isolated from the 1,3,5-trimethyl-2-(o-hydroxystyryl) imidazolio[4,5-c]pyridinium diperchlorate because of the irreversible degradation of the latter.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 683–686, May, 1972.     

Permanently oriented antibody immobilization for digoxin determination with a flow-through fluoroimmunosensor

This paper reports a new flow-through fluoroimmunosensor, the function of which is based on antibodies immobilized on an inmunoreactor of controlled-pore glass (CPG), for determination of digoxin, used in the treatment of congestive heart failure and artery disease. The immunosensor has a detection limit of 1.20 microg L(-1) and provides high reproducibility (RSD=4.5% for a concentration of 0.0025 mg L(-1), and RSD=6.7% for 0.01 mg L(-1)). The optimum working concentration range was found to be 1.2 x 10(-3)-4.0 x 10(-2) mg L(-1). The lifetime of the immunosensor was about 50 immunoassays; if stored unused its lifetime can be extended to three months. A sample speed of about 10-12 samples per hour can be attained. Possible interference from substances with structures similar to digoxin (morphine, heroin, tebaine, codeine, pentazocine and narcotine) was investigated. No cross-reactivity was seen at the highest digoxin: interferent ratio studied (1:100). The proposed fluoroimmunosensor was successfully used to determine digoxin concentrations in human serum samples.     

Kinetics of the gas-phase thermal chlorination of methane

Based on information concerning the rate constants of elementary steps corrected with consideration for experimental data obtained under laboratory, pilot-plant, and industrial conditions, the kinetics of the gas-phase process of thermal chlorination of methane was considered. The form of the rate equation of the process depends on the mode of chain termination. Of four possible variants, cross termination with the participation of a chlorine atom and a hydrocarbon radical and quadratic-law termination on hydrocarbon radicals are significant under industrial conditions. The fractions of the participation of either of these variants at various degrees of chlorine conversion were determined. Rate equations were found to describe the chlorination of methane, methyl chloride, methylene chloride, and chloroform with cross and quadratic-law chain terminations. The overall kinetic order of these equations with respect to reactants was 1.5. Combined equations that imply the simultaneous occurrence of cross and quadratic-law chain terminations were proposed.     

New Trends in the Development of Methods for Catalyst Preparation for the Processes of Organochlorine Synthesis

The formation of heterogeneous mercury-, zinc-, and copper-containing catalytic systems obtained by supporting salt components (SCs) without a solvent is studied. It is shown that due to strong interaction between SC and support, the size of salt clusters on the surface and their relative contribution decrease. That is, the concentration of excess salt phases decreases. The dispersity increases up to molecular distribution. When surface-linked two-dimensional disordered structures are formed, the state of salt phases in the compositions of catalytic systems changes. The surface mobility of salt clusters during the contact with the reaction medium is found. Compared to the systems obtained by impregnation with aqueous solutions, the proposed systems are 2–3 times more thermally stable, their surface is enriched in defect structures that are active in catalysis, and the processes of organochlorine synthesis become more efficient.     

Flat cyclic modules

Necessary and sufficient conditions are established for cyclic -modules to be flat, and rings over which any flat cyclic -module is free are investigated.Translated from Matematicheskie Zametki, Vol. 8, No. 2, pp. 245–250, August, 1970.The author wishes to thank L. A. Skornyakov for his advice and suggestions for improving this article.     

Peroxiredoxin-1 from the Human Hookworm Ancylostoma ceylanicum Forms a Stable Oxidized Decamer and Is Covalently Inhibited by Conoidin A

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