A Model of Gas-Phase Transport During the Initial Stages of Sintering of Silicon Carbide

New Jersey 08854 Carbon, which is often used as an additive to silicon carbide powder, is thought to facilitate densification during sintering by aiding the removal of the native SiO 2 layer, which is present on the starting SiC powder. The mechanism is the reduction of SiO 2 to SiC with the formation of primarily CO gas, which diffuses out from the porous compact at a temperature below the normal sintering temperature. It has been found beneficial to hold the compact at an intermediate temperature to allow time for the CO and other gases to diffuse out before the pores close. We investigate this process using a computational model based on codiffusion of multiple gas species, which enables prediction of the gas and condensed phase compositions as a function of time and position in the specimen. The results are used to determine the optimum holding time for complete SiO 2 removal as a function of key parameters, such as specimen thickness, particle size, temperature, etc., as well as the necessary amount of C additive. The results of the modeling are consistent with the experimentally observed spatial variation of density and composition in SiC compacts

The obstructed kidney

Urinary obstruction is a common cause of acute and chronic renal failure. The symptoms and signs of an obstructed kidney may vary from asymptomatic to severe acute pain. The diagnosis and management of a hydronephrotic kidney is not very difficult with ultrasonography, IVU, and diuretic renography. The approach to manage such patients has been rationalized after the advent of diuretic renography. The obstructed kidney should be decompressed as early as possible because of progressive loss of renal function with prolonged obstruction. Nephrectomy may be required for a non-functioning kidney. Further advancements are being made as the molecular mechanisms involved in the pathophysiology of the obstructed kidney become known to us

Structural biology of Mycobacterium tuberculosis proteins: the Indian efforts

Among the many different objectives of large scale structural genomics projects are expanding the protein fold space, enhancing understanding of a model or disease-related organism, and providing foundations for structure-based drug discovery. Systematic analysis of protein structures of Mycobacterium tuberculosis has been ongoing towards meeting some of these objectives. Indian participation in these efforts has been enthusiastic and substantial. The proteins of M. tuberculosis chosen for structural analysis by the Indian groups span almost all the functional categories. The structures determined by the Indian groups have led to significant improvement in the biochemical knowledge on these proteins and consequently have started providing useful insights into the biology of M. tuberculosis. Moreover, these structures form starting points for inhibitor design studies, early results of which are encouraging. The progress made by Indian structural biologists in determining structures of M. tuberculosis proteins is highlighted in this review