X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

Cooperativity and substrate specificity of an alkaline amylase and neopullulanase complex of Micrococcus halobius OR-1

The saccharifying alkaline amylase and neopullulanase complex of Micrococcus halobius OR-1 hydrolyzes both α-(1,4)- and α-(1,6)-glycosidic linkages of different linear and branched polysaccharides. The following observations were made concerning the analysis of the coexpressed amylase and neopullulanase enzymes. Even though the enzymes were subjected to a rigorous purification protocol, the activities could not be separated, because both the enzymes were found to migrate in a single peak. By contrast, two independent bands of amylolytic activity at 70 kDa and pullulanolytic activity at 53 kDa were evident by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), reducing and nonreducing PAGE, and zymographic analysis on different polysaccharides. Preferential chemical modification of the enzyme and concomitant high-performance thin-layer chromatographic analyses of the saccharides liberated showed that amylase is sensitive to 1-(dimethylamino-propyl)-3-ethyl carbodiimide-HCl and cleaved α-(1,4) linkages of starch, amylose, and amylopectin producing predominantly maltotriose. On the other hand, formalin-sensitive neopullulanase acts on both α-(1,4) and α-(1,6) linkages of pullulan and starch with maltotriose and panose as major products. It is understood that neopullulanase exhibits dual activity and acts in synergy with amylase toward the hydrolysis of α-(1,4) linkages, thereby increasing the overall reaction rate; however, such a synergism is not seen in zymograms, in which the enzymes are physically separated during electrophoresis. It is presumed that SDS-protein intercalation dissociated the enzyme complex, without altering the individual active site architecture, with only the synergism lost. The optimum temperature and pH of amylase and neopullulanase were 60°C and 8.0, respectively. The enzymes were found stable in high alkaline pH for 24 h. Therefore, the saccharifying alkaline amylase and neopullulanase of M. halobius OR-1 evolved from tapioca cultivar shows a highly active and unique enzyme complex with several valuable biochemical features.     

Exotic decay in cerium isotopes

Half life for the emission of exotic clusters like ⁸Be, ¹²C, ¹⁶O, ²⁰Ne, ²⁴Mg and ²⁸Si are computed taking Coulomb and proximity potentials as interacting barrier and many of these are found well within the present upper limit of measurement. These results lie very close to those values reported by Shanmugam et al using their cubic plus Yukawa plus exponential model (CYEM). It is found that ¹²C and ¹⁶O emissions from ¹¹⁶Ce and ¹⁶O from ¹¹⁸Ce are most favorable for measurement (T _1/2<10¹⁰ s). Lowest half life time for ¹⁶O emission from ¹¹⁶Ce stress the role of doubly magic ¹⁰⁰Sn daughter in exotic decay. Geiger-Nuttall plots were studied for different clusters and are found to be linear. Inclusion of proximity potential will not produce much deviation to linear nature of Geiger-Nuttall plots. It is observed that neutron excess in the parent nuclei slow down the exotic decay process. These findings support the earlier observations of Gupta and collaborators using their preformed cluster model (PCM).     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.