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1.
Sandip P. Trivedi 《Pramana》2004,63(4):777-783
We discuss a recent proposal to construct de Sitter vacua in string theory. It is based on flux compactifications in string
theory where all the moduli are stabilised and supersymmetry is broken with control. The resulting picture is that of a complicated
landscape with many vacua of widely varying values for the cosmological constant. 相似文献
2.
Recent X-ray diffraction studies on α-quartz (SiO2) by Kingmaet al [1], have shown the occurrence of a reversible, crystalline-to-crystalline, phase transition just prior to amorphization
at ≈ 21 GPa. This precursor transition has also been confirmed by our recent molecular dynamics simulation study [2]. In order
to investigate the possibility of a similar behaviour in other isostructural compounds, which also undergo pressure induced
amorphization, α-GeO2 and α-AlPO4 (berlinite form) were studied using energy dispersive X-ray diffraction. In either of these materials, no such phase transition
is detected prior to amorphization. The onset of amorphization and its reversal is found to be time dependent in GeO2. 相似文献
3.
Abstract —Thymine starvation prior to 254 nm ultraviolet light (UV) exposures has been found to decrease the level of maximum photoreactivation in Escherichia coli B s-1 . The dark equilibrium level of photoreactivating enzyme-substrate complexes was determined from the levels of photoreactivation obtained with exposures to single flashes of high-intensity light. The kinetics indicate that photoreactivating enzyme concentration does not decrease as a result of thymine starvation. The UV sensitivities of normal and thymine-starved cells are found to be the same. Photoreactivation by sequential flashes shows a lesser number of total photorepairable lesions in starved cells. It is concluded that thymine starvation renders a portion of the dimers inaccessible to the photoreactivating enzyme, thus lowering the level of maximum photoreactivation. 相似文献
4.
Disc type ceramic aluminium oxide membrane has been prepared by tape casting technique. Thickness of this single layer membrane is in the range 200–300 μm. Porosity and pore size distribution have been determined by mercury porosimetry. Polymeric binder content of the green tape and the firing temperature are found to have strong influence on the average pore size, pore size distribution and overall porosity. Higher binder content promotes agglomeration of the ceramic particles, which on firing leads to wider pore size distribution and formation of closed pores. Pore coarsening is observed with increasing firing temperature. 相似文献
5.
Dyer JA Trivedi P Sanders SJ Scrivner NC Sparks DL 《Journal of colloid and interface science》2004,270(1):66-76
Previous studies demonstrated the environmental and economic benefits of treating lead(II)-contaminated water streams with ferrihydrite in multiple equilibrium sorption stages. In this work, multistage ferrihydrite sorption systems were evaluated for their effectiveness in reducing single-solute zinc(II) (Zn(II)) concentrations in contaminated water streams to very low levels. As for lead(II) (Pb(II)), experimental data and modeling results indicate that a multistage sorption system can significantly reduce Zn(II) effluent concentrations for the same total amount of sorbent or, alternatively, dramatically lower total sorbent consumption for the same effluent Zn(II) concentration. Compared to Pb(II), however, Zn(II) removal requires on the order of 10 times more sorbent to achieve the same target effluent concentration for the same pH and number of stages. Model predictions were made using a steady-state, multistage, equilibrium adsorber model that was previously developed for and integrated into OLI Systems' Environmental Simulation Program (ESP). The modified triple-layer model was used to simulate Zn(II) surface-liquid equilibria within the adsorber model. Engineering screening evaluations again indicate that a 2- to 3-stage sorption process can provide significant economic savings when compared to a 1-stage process operating with the same target effluent Zn(II) concentration. Additional equilibrium stages beyond 2 or 3 provide diminishing economic returns. The major economic driver for multiple contacting stages is reduced capital investment and operating costs for sludge handling, dewatering, and disposal. 相似文献
6.
A method is described to impart flexibility and mechanical strength to conducting polyaniline by polymerizing aniline on fabrics and on cellulose papers. The study indicates that these conducting fabrics offer 16–18 dB of shielding effectiveness for the control of electromagnetic interference (EMI) up to a frequency of 103 MHz. 相似文献
7.
8.
A low-cost lead-acid battery with high specific-energy 总被引:1,自引:0,他引:1
S. K. Martha B. Hariprakash S. A. Gaffoor D. C. Trivedi A. K. Shukla 《Journal of Chemical Sciences》2006,118(1):93-98
Lightweight grids for lead-acid battery grids have been prepared from acrylonitrile butadiene styrene (ABS) copolymer followed
by coating with lead. Subsequently, the grids have been electrochemically coated with a conductive and corrosion-resistant
layer of polyaniline. These grids are about 75% lighter than those employed in conventional lead-acid batteries. Commercial-grade
6V/3.5Ah (C20-rate) lead-acid batteries have been assembled and characterized employing positive and negative plates constituting these
grids. The specific energy of such a lead-acid battery is about 50 Wh/kg. The batteries can withstand fast charge-discharge
duty cycles.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
9.
10.
Differential pulse polarographic methods for the determination of selenium(IV) and tellurium(IV) in nitric acid medium are described. The peak current is maximal when 0.25M nitric acid medium is used, the DPP peaks for Se(IV) and Te(IV) being at -0.54 and -0.8 V vs. Ag/AgCl respectively. The peak current is a linear function of selenium concentration over three ranges, 5.1 x 10(-6)-1.3 x 10(-5), 1.27 x 10(-5)-1.27 x 10(-4) and 1.27 x 10(-4)-7.60 x 10(-4)M Se(IV), with different slopes. The plot for Te(IV) is linear over the range 0.78 x 10(-6)-9.40 x 10(-5)M. 相似文献