Study of single silicon quantum dots' band gap and single-electron charging energies by room temperature scanning tunneling microscopy

Scanning tunneling spectroscopy in the shell-filling regime was carried out at room temperature to investigate the size dependence of the band gap and single-electron charging energy of single Si quantum dots (QDs). The results are compared with model calculation. A 12-fold multiple staircase structure was observed for a QD of about 4.3 nm diameter, reflecting the degeneracy of the first energy level, as expected from theoretical calculations. The systematic broadening of the tunneling spectroscopy peaks with decreasing dot diameter is attributed to the reduced barrier height for smaller dot sizes and to the splitting of the first energy level.     

Least-squares design of higher order nonrecursive differentiators

A method is described that can be used to design non-recursive linear-phase higher order differentiators that can perform differentiation over any frequency range. The method is based on formulating the absolute mean-square error between the amplitude responses of the practical and ideal differentiator as a quadratic function. The coefficients of the differentiators are obtained by solving a set of linear equations. This method leads to a lower mean-square error and is computationally more efficient than both the eigenfilter method and the method based on the Remez exchange algorithm. Design of differentiators based on minimization of the relative mean-square error is also carried out. Finally, the method is extended to the design of frequency selective higher order differentiators     

Assessment of iodine deficiency in selected blocks of east and west Champaran districts of Bihar

OBJECTIVE: A survey conducted in 1964 reported a goitre prevalence of 40.3% in East and West Champaran districts of Bihar. No recent survey has been documented on the prevalence of iodine deficiency in these districts. The present study was therefore undertaken (i) to assess the prevalence of IDD in these districts, and (ii) to estimate the iodine content of salt consumed by population. METHODOLOGY: In each district, one block was selected. In each block more than 630 children in the age group of 6-12 years were included in the study and were clinically examined. Urine samples were collected from 261 children and were analyzed using standard laboratory procedures. A total of 456 salt samples were collected from children and 35 from traders from the two districts and analyzed using the standard iodometric titration method. RESULTS: The total goiter prevalence was 11.6%. The percentage of children with < 2, 2.0-4.9, 5.0-9.9 and > or = 10 mcg/dl of urinary iodine excretion level were 12.3, 13.4, 23.4 and 51.0, respectively. The median urinary iodine excretion of the children was 10.0 mcg/dl. None of the families were consuming salt with a nil iodine content and about 29.3%, were consuming salt with less than 15 ppm of iodine. Of the 35 salt samples collected from traders, all had iodine and about 17% had less than 15 ppm of iodine. CONCLUSION: The study stresses the need for strengthening the existing system of monitoring of quality of salt being provided in the East and West Champaran districts by Government of Bihar.     

DNA sequence analysis of spontaneous mutagenesis in Saccharomyces cerevisiae

To help elucidate the mechanisms involved in spontaneous mutagenesis, DNA sequencing has been applied to characterize the types of mutation whose rates are increased or decreased in mutator or antimutator strains, respectively. Increased spontaneous mutation rates point to malfunctions in genes that normally act to reduce spontaneous mutation, whereas decreased rates are associated with defects in genes whose products are necessary for spontaneous mutagenesis. In this article, we survey and discuss the mutational specificities conferred by mutator and antimutator genes in the budding yeast Saccharomyces cerevisiae. The implications of selected aspects of the data are considered with respect to the mechanisms of spontaneous mutagenesis.     

Potent non-peptidyl inhibitors of protein tyrosine phosphatase 1B

The development of inhibitors of protein tyrosine phosphatases (PTPs) has recently been the subject of intensive investigation due to their potential as chemotherapeutics and as tools for studying signal transduction pathways. Here we report the evaluation of a variety of small molecule, non-peptidyl inhibitors of protein tyrosine phosphatase 1B (PTP1B), bearing the alpha, alpha-difluoromethylenephosphonic acid (DFMP) group, a non-hydrolyzable phosphate mimetic. A series of phenyl derivatives bearing a single DFMP group were initially surveyed. In general, these were not significantly more potent inhibitors than the parent compound, alpha, alpha-difluorobenzylphosphonic acid, with the exception being the meta-phenyl substituted species which decreased the IC50 by approximately 17-fold relative to alpha, alpha-difluorobenzylphosphonic acid. However, certain compounds bearing two DFMP moieties were very potent inhibitors. Some of these are among the most potent small molecule inhibitors of any PTP reported to date with the best one exhibiting a Ki of 1.5 microM. The structural basis for these results are discussed. One of the bis-DFMP inhibitors was examined in detail and it was found that the fluorines were essential for potent inhibition. Inhibition was independent of pH between pH 5.5-7.2 suggesting that both the mono and dianionic forms of the individual DFMP groups bind equally well. The trends observed in the inhibitory potency of these compounds with PTP1B were very similar to the trends observed by other workers on the K(m)'s of the analogous phenylphosphate substrates with rat PTP1. This indicates that studies of non-peptidyl substrates with rat PTP1 can be used as a guide for the development of human PTP1B inhibitors.     

The Effect of Acoustic Field on the Thermal Conductivity of composite propellants

A study is conducted to determine the effect of acoustic field on the thermal conductivity of composite propellants based on poly- butadiene and polyurethane binders. The thermal conductivity of the propellant is determined by a specially designed equipment. The thermal conductivity measurements are made in steady state conditions and in an acoustic field of constant amplitude at various frequencies ranging from 1 kHz to 6 kHz and at different temperatures ranging from 30°C to 50°C. The results indicate that the thermal conductivities of the composite propellants increase when they are subjected to an acoustic field. The data obtained are presented in the paper. Since the burning behaviour of solid propellants is influenced also by its thermal conductivity, the present work may be of direct relevance in improving upon some of the existing burning rate and combustion models.