Structure of “bis(methoxymagnesium)diselenide”: A reagent for the introduction of selenium into organic molecules

The reaction of magnesium and selenium in dry methanol has been reported to yield a reagent tentatively identified as bis(methoxymagnesium) diselenide. The dark red-brown solution obtained from this reaction yielded red crystals that crystallized in the monoclinic space group C2/c, a=17.391(4) ?, b=15.823(3) ?, c=21.626(4) ?, β=110.71(3)°, V=5566.5(19) ?³, Z=4, R=0.0350, wR₂=0.0850 for 4930 reflections. X-ray crystallographic analysis of this reagent showed it to be dodecamethanol-tetramethoxy-di(μ₄-hydroxy)tetra(μ₃-methoxy)hexamagnesium hexaselenide, Mg₆(μ₄-OH)₂(μ₃-OCH₃)₄(OCH₃)₄(CH₃OH)₁₂]Se₆·2CH₃OH (1), not the bis(methoxymagnesium) diselenide as previously described. The structure of 1 is composed of six magnesium ions and six bridging oxygen-containing ligands in a face-sharing cubic arrangement.     

ESP: a method to predict toxicity and pharmacological properties of chemicals using multiple MCASE databases

We describe here the development of a computer program which uses a new method called Expert System Prediction (ESP), to predict toxic end points and pharmacological properties of chemicals based on multiple modules created by the MCASE artificial intelligence system. The modules are generally based on different biological models measuring related end points. The purpose is to improve the decision making process regarding the overall activity or inactivity of the chemicals and also to enable rapid in silico screening. ESP evaluates the significance of the biophores from a different viewpoint and uses this information for predicting the activity of new chemicals. We have used a unique encoding system to represent relevant features of a chemical in the form of a pattern vector and a genetic artificial neural network (GA-ANN) to gain knowledge of the relationship between these patterns and the overall pharmacological property. The effectiveness of ESP is illustrated in the prediction of general carcinogenicity of a diverse set of chemicals using MCASE male/female rats and mice carcinogenicity modules.     

An automated ac-magnetic susceptibility apparatus

We report here both hardware and software for an ac susceptibility measurement system, namely the design and construction of the cryostat, coil system, sample rod assembly and also the automation of the sample rod movement, bridge control and nulling etc with the help of an inexpensive Z-80A microprocessor via a home-made IEEE-488 interface. The variable parameters are temperature, magnitude of the rms field and frequency. An entirely new dynamic bridge nulling algorithm with continuous sample movement, which eliminates to a large extent problems related to time-dependent drifts, has been developed. We also present some experimental data collected with this system.     

Determination of the diffusivity-mobility ratio in highly degenerate semiconductors at low temperatures from measurements of wavelength shift with cavityQ in junction lasers

The diffusivity-mobility ratio of the electrons in highly degenerate semiconductors in which prominent band tails are formed, at low temperatures when the tail states are mostly occupied, is expressed in terms of the characteristic energy of the tail. A method is then shown for directly determining the ratio from measurements of wavelength shift with cavityQ in junction lasers.The authors are indebted to Professor J. N.Bhar for his keen interest in the work.     

Stiffly stable second derivative multistep methods with higher order and improved stability regions

New stiffly stable second derivative multistep formulas with better stability regions and higher order are presented. These formulas of order as high as thirteen and with optimized stability regions are developed by using arbitrary parameters suitably implanted into the formulas. The stability properties of the formulas suggest their use especially for problems with Jacobians possessing eigenvalues close to the imaginary axis. The high order formulas will be specially useful when the accuracy requirement is stringent.     

Effective operators with potentials from meson theory

We have studied the effective charge and interaction in the (sd) shell with the Bonn-Jülich and Paris potentials. Incorporating essentially all the low-energy correlations of known importance, we find that the former potential gives quite a good account of the data when allowance is made for the effect of low-lying particle-hole states. The Paris potential gives somewhat less core polarization and a less attractive bare T=0 spectrum due to weaker T=0 matrix elements.     

Influence of alloy composition on the dependence of the diffusivity-mobility ratio in ternary semiconductors on a quantizing magnetic field

An expression is derived for the diffusivity-mobility ratio in degenerate narrow-gap ternary semiconductors in the presence of a quantizing magnetic field. With the help of this expression, the diffusivity-mobility ratio is shown, taking n-Hg_1–xCd_xTe as an example, to have an oscillatory dependence on a quantizing magnetic field. The influence of alloy composition on such dependence is also investigated.