Novel pitch-based carbons with bimodal distribution of uniform mesopores

A new method is proposed for the synthesis of pitch-based carbons with bimodal distribution of uniform mesopores formed by co-imprinting of spherical silica colloids and hexagonally ordered mesoporous particles of SBA-15 into mesophase pitch particles and subsequent silica dissolution.     

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.     

Molecular transient effects in K-band spectroscopy

The time dependence of microwave transient absorption and emission was measured forJ=2←1 of the OCS molecule under on- and off-resonant conditions by the technique of Stark switching. The results are analyzed with the theory of a coherent electromagnetic wave interacting with a two-level quantum system through the electric dipole interaction to obtain the pressure dependence of the relaxation timesT ₂ and in consequence the pressure broadening parameterC _w=26.7±0.9 (μs·mTorr)^?1 has been obtained.     

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).     

Graphitized pitch-based carbons with ordered nanopores synthesized by using colloidal crystals as templates

A highly graphitized ordered nanoporous carbon (ONC) was synthesized by using commercial mesophase pitch as carbon precursor and siliceous colloidal crystal as template. Since silica colloids of different sizes (above 6 nm) and narrow particle size distribution are commercially available, the pore size tailoring in the resulting ONCs is possible.     

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.     

Adsorption and structural properties of ordered mesoporous carbons synthesized by using various carbon precursors and ordered siliceous P6mm and Ia3d mesostructures as templates

Adsorption and structural properties of inverse carbon replicas of two ordered siliceous P6mm and Ia3d mesostructures have been studied by nitrogen adsorption, powder X-ray diffraction, and transmission electron microscopy. These carbon replicas were prepared by filling the pores of SBA-15 and KIT-6 siliceous templates with various carbon precursors followed by carbonization and silica dissolution. Sucrose, furfuryl alcohol, acenaphthene, mesophase pitch, and petroleum pitch were used to obtain inverse carbon replicas of SBA-15 and KIT-6. While structural properties of the resulting ordered mesoporous carbons are mainly determined by the hard template used, their adsorption properties depend on the type of the carbon precursor.     

Carbons with extremely large volume of uniform mesopores synthesized by carbonization of phenolic resin film formed on colloidal silica template

Mesoporous carbons with extremely large pore volume ( approximately 6 cm3/g) and narrow bimodal pore size distribution were synthesized by using 24 nm silica colloids as template.