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61.
A novel catalytic application of titanosilicate molecular sieves (TS-1 and TiMCM-41), in the synthesis of polycarbonate precursors like cyclic carbonates and dimethyl and diphenyl carbonates, avoiding toxic chemicals like phosgene or CO, is reported. Cyclic carbonates were prepared, over TS-1 and TiMCM-41, in high yields, by cycloaddition of CO2 to epoxides, like epichlorohydrin, propylene oxide and styrene oxide, at low temperatures and pressures. Further, transesterification of the cyclic carbonates with methanol and phenol, over TiMCM-41, yielded other polycarbonate precursors like dimethyl carbonate (DMC) and diphenyl carbonate (DPC). The cyclic carbonates could also be synthesized from the olefins in the same reactor by reacting the olefins, in the presence of TiMCM-41, with a mixture of an epoxidizing agent (like H2O2 or tert-butyl hydroperoxide) and CO2. 相似文献
62.
This paper looks at heat and mass transfer effects on an unsteady MHD flow of a couple‐stress fluid in a horizontal wavy porous space with travelling thermal waves in the presence of a heat source and viscous dissipation. Initially the temperatures of the walls are maintained at different constant temperatures. The analytical expressions for velocity, temperature, and concentration field are obtained by the regular perturbation technique. The results are presented graphically for various values of emerging dimensionless parameters of the problem and are discussed to show interesting aspects of the solution. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21040 PACS: 44.15.+a, 44.30.+f, 44.27.nd, 47.50.Cd 相似文献
63.
64.
Saptarshi Sasmal K. Ramanjaneyulu Balthasar Novák V. Srinivas K. Saravana Kumar Christian Korkowski Constanze Roehm N. Lakshmanan Nagesh R. Iyer 《Construction and Building Materials》2011,25(1):175-182
The paper discusses the aspects of repair and retrofitting technique adopted for a damaged reinforced concrete beam-column joint specimen under cyclic loading. A specimen designed based on Indian Standard specifications with consideration of seismic load but without adopting ductile detailing (NonDuctile) was investigated under reverse cyclic loading. Then, the damaged nonductile specimen was repaired with epoxy mortar and grouted using low viscous polymer, and retrofitted using fiber reinforced plastic (FRP) wrapping in beam and column components and steel plate jacketing in joint region. The experimental results showed that the retrofitted specimen not only regained its original strength and stiffness but also has overcome the deficiencies of nonductile detailing. The present study shows that a proper repair and adequate retrofitting technique can be used for strengthening and improvement of damaged regions in reinforced concrete structures. 相似文献
65.
In our earlier work we have shown the relevance of stability theory in understanding the sustenance of turbulence in turbulent
boundary layers. Here we adopt the same model to study the evolution of organised disturbances in turbulent channel flow.
Since the dominant modes are wall modes we find that the stability characteristics in the two flows are nearly identical although
the boundary conditions (at the edge of the boundary layer and at the centre of the channel) are different. Comparisons with
the experiments of Hussain and Reynolds are also presented. 相似文献
66.
67.
The results of a study performed on crosslinked polyethylene (XLPE) insulated cables tested in the laboratory under accelerated conditions are described. URD-type cables rated at 15 kV were aged at 60 Hz, 6 kV/mm, (150 V/mil) and load cycled daily to 90°C conductor, with water inside the pipe and outside of the samples, for periods of up to 3 years. DC testing was performed before and during the aging. An anticipated significant reduction in the AC breakdown strength is observed in control cables (not DC tested), from 44 kV/mm (1100 V/mil) for unaged cables, to 10 kV/mm (250 V/mil), for aged cables. However, there was no further reduction in the AC breakdown strength of cables subjected to DC testing as compared to those that are not tested with DC. It is concluded that AC breakdown strength is not an effective diagnostic tool for determining the effect of DC testing of URD cables aged under the conditions described 相似文献
68.
NR Srinivas WC Shyu J Lee DS Greene RH Barbhaiya 《Canadian Metallurgical Quarterly》1997,18(7):585-593
An annual atmospheric pollen survey was performed for 14 consecutive years in the autumn at Sakado city, Saitama prefecture. The survey was performed on the transition of pollen dispersion of major allergen plants: ragweed (Ambrosia spp.), Humulus japonicus, Artemisia spp. and Gramineae. 1. Annual total pollen count of ragweed showed marked increases beginning from 1991. Total pollen count in 1991 was 8.8 times and that in 1996 was 18.6 times that in 1983. This increase is probably caused by marked proliferation of giant ragweed which is left without mowing as it is on a dry riverbed, and consequently produces much more pollen than short ragweed. 2. Annual increases in total pollen counts of other major plants which disperse their pollen in the same season as ragweed were 0.95 times in 1991 and 0.5 times in 1996 that in 1983 for Humulus japonicus, 0.68 times in 1991 and 1.5 times in 1996 that in 1983 for Artemisia spp. and 1.3 times in 1991 and 1.4 times in 1996 that in 1983 for Gramineae. None of these species showed a marked increase of pollen dispersion although they showed some annual variation. The above findings suggest that changes in the proliferous state of various allergenic plants due to environmental change should be considered with respect to characteristics of pollen allergy. 相似文献
69.
70.
Salkalachen S. Krishnan N.H. Krishnan S. Satyamurthy H.B. Srinivas K.S. 《Semiconductor Manufacturing, IEEE Transactions on》1990,3(1):12-17
Factors governing long-term stability of silicon power devices are discussed with particular reference to a major failure mechanism observed in a thyristor device. The device failure was due to electrical instability during an electrical and thermal stability storage test, wherein it was observed that the reverse blocking voltage deteriorated under applied bias at the rated maximum junction temperature. The major cause of this failure was identified as lack of exhaust during the edge passivation and curing process due to which excessive chemical deposits are retained in the bevel region of the silicon element. This contributes to surface leakage current and, hence, a rapid degradation of the off-state characteristics. An orthogonal array experiment was employed to optimize the process factors and levels. The manufacturing process was then modified by incorporating an effective exhaust system in the passivant curing oven. This resulted in marked improvements in the electrical stability and manufacturing yield of this device 相似文献