Ethylene glycol retention method for estimating specific surface area of adsorbent carbons

Ethylene glycol retention method, standardised by Dyal and Hendricks for clays and soils, has been used for determining specific surface areas of a large variety of adsorbent carbons differing widely in the extent as well as chemical nature of their surfaces. The proposed method yields values comparable with those obtained by the gaseous adsorption methods, irrespective of the oxygen contents of the carbons. A small amount of oxygen, probably within 0.2%, is essential to bring about proper wetting of the carbon by glycol.     

Electrochemical behaviour of cobalt and nickel complexes with ϵ-caprolactam at dropping mercury electrode

The kinetics of polarographic reduction of Co(II) and Ni(II) has been investigated in the presence of increasing concentration of complex forming agent viz ?-caprolactam at pH 6.2 under constant ionic strength. In both the cases the waves were found to be diffusion controlled and irreversible. The values of the kinetic parameters αn_a and k⁰_{f, h} have been calculated as a function of the ligand concentration. The polarographic wave was precisely proportional to the concentration up to 3.5 mM of the metal ions. Hence the straight line is useful as a calibration curve in quantitative analysis of these two metal ions. The error does not exceed more than ± 0.2% in any case.     

Phospholipase A2: its role in ADP- and thrombin-induced platelet activation mechanisms

ADP and thrombin are two of the most important agonists of platelet aggregation--a cellular response that is critical for maintaining normal hemostasis. However, aberrant platelet aggregation induced by these agonists plays a central role in the pathogenesis of cardiovascular and cerebrovascular diseases. Agonist-induced primary or secondary activation of phospholipases leads to generation of the second messengers that participate in biochemical reactions essential to a number of platelet responses elicited by ADP and thrombin. Phospholipase A2 (PLA2) has been linked to cardiovascular diseases. However, the mechanism(s) of activation of PLA2 in platelets stimulated by ADP and thrombin has remained less well defined and much less appreciated. The purpose of this review is to examine and compare the molecular mechanisms of activation of PLA2 in platelets stimulated by ADP and thrombin.     

A BDD SAT solver for satisfiability testing: An industrial case study

The satisfiability problem (SAT) is a fundamental problem in mathematical logic, constraint satisfaction, VLSI engineering, and computing theory. Methods to solve the satisfiability problem play an important role in the development of computing theory and systems. In this paper, we give a BDD (Binary Decision Diagrams) SAT solver for practical asynchronous circuit design. The BDD SAT solver consists of a structural SAT formula preprocessor and a complete, incremental SAT algorithm that is able to find an optimal solution. The preprocessor compresses a large size SAT formula representing the circuit into a number of smaller SAT formulas. This avoids the problem of solving very large SAT formulas. Each small size SAT formula is solved by the BDD SAT algorithm efficiently. Eventually, the results of these subproblems are integrated together that contribute to the solution of the original problem. According to recent industrial assessments, this BDD SAT solver provides solutions to the practical, industrial asynchronous circuit design problems.This research is supported in part by the 1993 ACM/IEEE Design Automation Award, by the Alberta Microelectronics Graduate Scholarship, by the NSERC research grant OGP0046423, and was supported in part by the NSERC strategic grant MEF0045793.Presently, Jun Gu is on leave with the Department of Computer Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.     

Diakoptic theory for multielement antennas

A theory is presented for the analysis of multielement antennas which consist of interconnected, conductive structure elements of electrically small dimensions. The theory is based on the retarded electromagnetic potentials which permit a diakoptic approach to the problem. The antenna is broken up into its individual structure elements. Each element is assumed to be excited by currents which are impressed at its terminals, i.e., junctions with adjacent elements (current coupling) and by the electric fields of the currents and charges on all the other elements (fieid coupling). Both excitations are treated independently. Each impressed current produces a "dominant" current distribution, a characteristic of the element, which can be readily computed. Current coupling is formulated by "intrinsic" impedance matrices which relate the scaler potentials at the terminals of an element, caused by its dominant current distributions, to the impressed currents of the element. Field coupling produces "scatter" currents on all the elements and is formulated by a "fieid-coupling" matrix which relates the scalar potentials at the terminals, caused by field coupling, to the impressed currents at all the terminals. Intrinsic and "field-coupling" matrices are combined to form the "complete" impedance matrix of the diakopted antenna. Enforcing continuity of the currents and equality of the scalar potentials at all the interconnections between the elements yields a system of linear equations for the junction currents and the input impedance of the antenna. Current coupling dominates field coupling. Fieid coupling is primarily affected by the dominant current distributions of the elements, and in general the scatter currents have negligible effect on it. Although detailed numerical investigations will be presented in another paper, a simple example is included here to demonstrate that the diakoptic theory yields very good results even if greatly simplified assumptions are made.     

Partial purification and characterisation of potato pectinesterase

Pectinesterase (EC 3.1.1.11) was extracted from potato (Solanum tuberosum var. Russet Burbank) tissue and purified 9.6-fold by ammonium sulphate precipitation and chromatography on Sephadex G-100. The enzyme preparation thus obtained has a molecular weight of 25,000, an apparent K_m of 0.09% for citrus pectin and a pH optimum of 7.5. NaCl is a positive modulator of the enzyme. The energy of activation of the enzyme is 6200 calories. A Q₁₀ of 1.33 is observed in the temperature range of 25 to 45°C, and the optimum temperature for the enzyme is 55°C.     

Application of carbon nanomaterial as a microwave absorber

Microwave absorption (8 GHz to 12 GHz) studies have been made with carbon nanomaterials for the first time. Carbon nanomaterials are synthesized by the pyrolysis of camphor. It is observed that film of carbon prepared under certain synthetic condition, can absorb microwave of either some specific wavelengths e.g., 9.5 GHz and 11.5 GHz or full range from 8-12 GHz to the extent of 20 dB depending upon their preparation condition. Carbon nanobeads seems to absorb the microwave in the range of 8-12 GHz.     

Modeling and analysis of white layer depth in a wire-cut EDM process through response surface methodology

A white layer is considered a major flaw on a workpiece surface machined with wire-cut electrical discharge machining (WEDM). In this paper, an attempt has been made to model the white layer depth through response surface methodology (RSM) in a WEDM process comprising a rough cut followed by a trim cut. An experimental plan for rotatable central composite design of second order involving four variables with five levels has been employed to carry out the experimental investigation and subsequently to establish the mathematical model correlating the input process parameters with the response. Pulse on time during rough cutting, pulse on time, wire tool offset, and constant cutting speed during trim cutting are considered the dominant input process parameters whilst the white layer depth is the response. An insignificant lack of fit term indicated a curve with a good fit. Also, an extensive analysis of the influences of all the individual input parameters on the response has been carried out and presented in this research study.