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排序方式: 共有353条查询结果,搜索用时 26 毫秒
31.
M.-F. Vallat D. J. Plazek B. Bhushan 《Journal of Polymer Science.Polymer Physics》1986,24(9):2123-2134
Two distinguishable effects of thermal exposure of biaxially oriented poly(ethylene terephthalate) (PET) have been observed in the temperature range from room temperature to 140°C. Upon heating above the glass transition temperature Tg of the film an irreversible shrinkage of a few percent occurred with a concomitant decrease in the rate of creep. Some loss of orientation in the noncrystalline phase with an attendant slight increase in density is believed to be responsible. Since the film was anisotropic in its plane, different amounts and rates of shrinkage were observed along with differing thermal expansion coefficients in various directions relative to the primary optic axis. Upon cooling the 50% crystalline PET from above Tg to lower temperatures, reversible “physical aging” was observed. Creep rates were found to decrease with the residence time below Tg. As with purely amorphous polymers, the effects of the aging are removed by heating the specimen above Tg where the density of the amorphous phase achieves equilibrium values. 相似文献
32.
JPC – Journal of Planar Chromatography – Modern TLC - A simple and rapid method has been established for indirect separation of the enantiomers of (R,S)-metoprolol and (R,S)-carvedilol... 相似文献
33.
Chiral assay of enantiomers of fluoxetine was achieved in pharmaceutical formulations using direct and indirect methods. L-tartaric acid was used as a mobile phase additive in thin-layer chromatography; the enantiomers were separated and isolated and were used to determine the elution order in HPLC. (R,S)-flouxetine was derivatized with (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester [(S)-NIFE], Marfey's reagent and 1-fluoro-2,4-dinitrophenyl-L-methionine amide (FDNP-L-Met-NH?. The diastereomers were separated using RP-HPLC. The effect of flow rate and TFA concentration on resolution was studied. The diastereomers obtained by derivatization with FDNP-L-Met-NH? were also separated by RP-TLC. 相似文献
34.
B. Bhushan A. Basumallick N.Y. Vasanthacharya S. Kumar D. Das 《Solid State Sciences》2010,12(7):1063-1069
Multiferroic nanoparticles of Bi1?xSrxFeO3 (x = 0, 0.01, 0.03, 0.05 and 0.07) were prepared by a facile sol–gel route and the variation of their structural, optical, dielectric and magnetic properties on strontium concentration has been studied. XRD and TEM results confirm the phase purity of the samples having high degree of crystallinity and monodispersity. The average particle size shows an exponential decline with increase in Sr concentration. A shape transformation from a multifaceted polygon to a spherical one has been observed as Sr concentration in the sample increases to 5%. In the second derivative FTIR spectra, the intensity of vibration peak at ~593 cm?1 that is characteristic of rhombohedral BiFeO3 is seen to decrease after Sr doping. All the samples showed typical M–H behavior of a ferromagnet with saturation magnetization achieved within an applied magnetic field of 10 kOe. The sample with 3% Sr substitution displayed saturation and remanent magnetization values 1.37 emu/g and 0.32 emu/g respectively that are highest among all the samples studied. Presence of exchange coupling produced due to interaction between the antiferromagnetic core and ferromagnetic shell is also observed in all Bi1?xSrxFeO3 nanoparticles. 相似文献
35.
Atenolol and propranolol (the β-blocking agents) and salbutamol (broncho- and vasodilator) were resolved into their enantiomers by adopting different modes of loading/impregnating the Cu(II) complexes of l-proline (l-Pro), l-phenylalanine (l-Phe), l-histidine (l-His), N,N-dimethyl-l-phenylalanine (N,N-Me2-l-Phe), and l-tryptophan (l-Trp) on commercial precoated normal phase plates. The three different approaches were (A) using the Cu(II)-l-amino acid complex as chiral mobile phase additive, (B) ascending development of plain commercial plates in the solutions of Cu complex, and (C) using a solution of Cu(II) acetate as mobile phase additive for the commercial TLC plates impregnated with ascending development of plates in the solutions of amino acid. Spots were located using iodine vapour. The results obtained for the three methods have been compared for their efficiency and the issue of involvement of the Cu(II) cation for the best performance of the three methods has been discussed with respect to the same mobile phase. The detection limit is 0.18 μg for each enantiomer. 相似文献
36.
Eleven chiral derivatizing reagents (CDRs) were used for preparation of diastereomers of (R,S)‐mexiletine containing a primary amino group in close proximity to the stereogenic center. One anhydride, namely [(S,S)‐O,O'‐di‐p‐toluoyl tartaric acid anhydride] was synthesized and (S)‐naproxen was used as such as the chiral derivatizing reagent. The other nine CDRs were synthesized by substituting one of the fluorine atoms in 1,5‐difluoro‐2,4‐dinitrobenzene with six amino acid amides and three amino acids. The diastereomers were separated by reversed‐phase high‐performance liquid chromatography. The method was validated for linearity, accuracy, limit of detection and limit of quantification. The limit of detection was found in the range of 10–30 pmol. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
37.
Usama Zaghloul George Papaioannou Bharat Bhushan Fabio Coccetti Patrick Pons Robert Plana 《Microelectronics Reliability》2011,51(9-11):1810-1818
This paper reviews the state of the art knowledge related to critical failure mechanisms in electrostatic micro- and nano-electromechanical systems (MEMS and NEMS) which are the dielectric charging and stiction. It describes also the recent employed nanoscale characterization techniques for these phenomena based on Kelvin probe force microscopy (KPFM) and force–distance curve measurements. The influence of relative humidity and dielectric deposition conditions on the charging/discharging processes is discussed. Moreover, different stiction mechanisms induced by electrostatic force and/or meniscus formation are analyzed. Finally, novel characterization methods are presented and used to correlate between the results from MEMS devices and metal–insulator–metal (MIM) capacitors. These methods are employed in view of application in electrostatic capacitive MEMS switches and could be easily extended to explore other NEMS/MEMS devices. The study provides an accurate understanding of the charging and stiction related failure mechanisms, presents guidelines for a proper packaging environment, and reveals precise explanations for the literature reported device level measurements of electrostatic MEMS devices. 相似文献
38.
JPC – Journal of Planar Chromatography – Modern TLC - The normal-phase (NP) and reversed-phase (RP) thin-layer chromatographic separations of aminoglycosides (streptomycin, kanamycin,... 相似文献
39.
Bhushan Sopori 《Journal of Electronic Materials》2005,34(5):564-570
Thin films of many dielectric materials have been used in the past for fabrication of solar cells and as a part of their device
structure. However, current efforts to reduce solar cell costs in commercial production have led to simplification of cell
design and fabrication. Use of self-aligning techniques has obviated the need for photolithography and conventional masking
with dielectric films for cell fabrication. Currently, the most favored dielectric material in Si solar cell production is
SiN:H, deposited by the plasma-enhanced chemical vapor deposition (PECVD) process. The SiN:H layer and its processing play
multiple roles of serving as an antireflection coating, a surface passivating layer, a buffer layer through which metal is
fired, and a means of transporting hydrogen into the bulk of the solar cell. In order to optimize the solar cell performance,
the SiN:H layer must meet some conflicting demands. The various applications of the SiN:H layer in solar cell fabrication
are described here. 相似文献
40.