Obliquely propagating ion-acoustic shock waves in a degenerate quantum plasma

A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars.     

Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Effect of Epinephrine and Insulin on Glucose Metabolism in Isolated Fat Cells

Since epinephrine and insulin are known to counteract each other in several metabolic respects, it was found of interest to evaluate the interaction of these hormones on glucose metabolism in isolated fat cells. Results indicate that in spite of reduced lipolysis, insulin potentiates the conversion of glucose to glyceride-glycerol. This means that a certain degree of esterification of fatty acids must take place. So the low rate of lipolysis is sufficient to provide fatty acids for this esterification.     

The electrochemical reduction of some fused ring systems

The electrochemical reduction of some fused ring systems containing four carbonyl moieties has been studied in alcoholic aqueous media. A mechanism has been proposed and clarified in which one carbonyl is reduced to a methylene group via an uptake of four electrons.     

FROM A SYSTEMIC APPROACH IN TEACHING AND LEARNING CHEMISTRY（SATLC）TO BENIGN ANALYSIS

The Systemic Approach in Teaching and Learning Chemistry (SATLC)was established in 1997^[1-3].Our interest in developing the SATL strategy arose from the recognition of the increasing globalization of a wide specturm of human activities such as economics,media,politics,and entertainment,Systemics is our attempt to provide the student with a global view of his/her studies of chemistry.     

Modeling and simulation of butanol separation from aqueous solutions using pervaporation

A study was conducted to separate butanol from an aqueous solution using pervaporation. A specially designed and manufactured cell was used to separate the butanol from butanol/water solutions of different butanol concentrations (6-8-11-16-20-50) g/l. A 250 cm³ butanol mixture at 33 °C was used to feed the cell, while the pressure of permeation side was about 0 bar. Results revealed that butanol concentration changes non-linearly during the first 3 h, and then proceeds linearly. The percentage of butanol removal increases with increasing feed concentration. The permeability of the used membrane was determined experimentally. A resistance in series model was used to simulate the pervaporation step. The butanol concentration in the feed during the pervaporation step was predicted by using the developed model. There is a fair agreement between butanol concentration in feeding tank of pervaporation cell both experimentally and predicted from the developed model.     

Activated nitriles in heterocyclic synthesis: Synthesis of several new coumarin derivatives

Several new benzopyran and benzopyranopyridine derivatives were synthesized via condensation of 2-amino-1,1,3-tricyanopropene (1) and diethyl 2-amino-1-cyanopropene-1,3-dicarboxylate (2) with salicylaldehyde and treatment of the resulted products with active methylene regents. The spectroscopic data of the synthesized compounds are reported and discussed.

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Aktivierte Nitrile in der Heterocyclen-Synthese: Darstellung einiger neuer Cumarinderivate

Zusammenfassung Einige neue Benzopyran- und Benzopyranopyridin-derivate wurden durch Kondensation von 2-Amino-1,1,3-tricyanopropen (1) und 2-Amino-1-cyanopropen-1,3-dicarbonsäuredimethylester (2) mit Salicylaldehyd und Behandlung der Reaktionsprodukte mit aktiven Methylenreagenzien dargestellt. Die spektroskopischen Daten der neuen Verbindungen werden diskutiert.