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61.
Mean grain sizes and specific surface areas (SSAs) of ice substrates formed by vapor deposition at low temperatures are of importance in simulating external surfaces of icy satellites in the solar system. Environmental scanning electron microscopy (ESEM) was used to obtain granule sizes and to observe the phase of ice granules prepared on borosilicate, silicon, and metallic plates. Ices prepared at a temperature lower than 140 K appear to be amorphous, and their granule sizes are typically submicrometer. At slightly warmer temperatures, near 180-200 K, ice films are composed of either hexagonal or cubic granules with sizes up to a few micrometers. When briefly annealed to even warmer temperatures, ice granule sizes approach approximately 10 microm. SSAs of ice substrates were determined from BET (Brunauer, Emmett, and Teller) analysis of gas adsorption isotherms in the temperature range from 83.5 to 261 K. SSAs decrease drastically from 102 m2/g at 83.5 K to 0.87 m2/g at 150 K and further decrease slowly to 0.22 m2/g at 261 K, suggesting that the transition from amorphous to crystalline forms occurs at approximately 150 K. The overall decrease in SSAs is primarily due to metamorphism and sintering. These results are comparable to recent field and laboratory measurements. Possible implications for theoretical models of icy satellites of outer planets using remote sensing techniques are also discussed. 相似文献
62.
Poly methyl methacrylate (PMMA)‐ethylene vinyl acetate (EVA)‐organoclay nanocomposites were prepared with and without in situ crosslinking using tetrapropoxysilane (TPOS) as a crosslinking agent and dibutyl tin oxide (DBTO) as a catalyst. Brabender Plasticorder experimental results suggest that in situ crosslinking transforms the EVA from a liquid to a viscoelastic solid. Transmission electron micrographs analysis indicates that most of the organoclay was clustered in the crosslinked EVA phase. X‐ray diffraction and morphology indicate that the PMMA‐EVA‐organoclay nanocomposites were intercalated and incompatible. Dynamic mechanical analysis (DMA) results indicate some interaction between PMMA‐EVA‐clay nanocomposites. The in situ crosslinked of EVA and the addition of organoclay increased the modulus properties of PMMA. However, in situ crosslinking slightly reduced the barrier properties of PMMA‐EVA‐organoclay nanocomposites. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
63.
Twenty-six known compounds and two new compounds, including a new lignan, (7S*,8R*,7'R*,8'S*)-icariol A?-9-O-β-xylopyranoside (1), and a new indole alkaloid, hygarine (2), were isolated from the extracts of Hygroryza aristata (Gramineae). The structures of all compounds were elucidated on the basis of NMR spectral analysis. The compounds (-)-epigallocatechin-3-O-gallate (4) and (-)-epicatechin-3-O-gallate (5) possess free radical scavenging activities and compound 1 could inhibit superoxide anion generation and elastase release by fMLP/CB-induced human neutrophils with IC?? values of 19.33 ± 0.86 and 24.14 ± 1.59 μM, respectively. 相似文献
64.
In the present study, the chemical investigation of the bioactive fractions of the rhizomes of Zingiber officinale has resulted in the identification of twenty-nine compounds including one new compound, O-methyldehydrogingerol (1). Some of the isolates were subjected into the evaluation of their antiplatelet aggregation and vasorelaxing bioactivities. Among the tested compounds, [6]-gingerol (13) and [6]-shogaol (17) exhibited potent anti-platelet aggregation bioactivity. In addition, [10]-gingerol (15) inhibited the Ca2+-dependent contractions in high K+ medium. According to the results in the present research, the bioactivity of ginger could be related to the anti-platelet aggregation and vasorelaxing mechanism. 相似文献
65.
Lan YH Peng YT Thang TD Hwang TL Dai DN Leu YL Lai WC Wu YC 《Chemical & pharmaceutical bulletin》2012,60(2):280-282
Further investigation of the methanolic extract of Fissistigma latifolium resulted in two new compounds whose structures were assigned as 2,5,6,7-tetramethoxyflavan (1) and 2'-hydroxy-4',5',6'-trimethoxybenzil (2). These two compounds were determined on the basis of chemical and spectroscopic evidences. Compound 2 is the first report of benzil from Fissistigma species. 2,5,6,7-Tetramethoxyflavan (1) showed a potent inhibitory effect on superoxide anion production in formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)/cytochalasin B (CB)-activated human neutrophils. 相似文献
66.
Dustiness test of nanopowders using a standard rotating drum with a modified sampling train 总被引:2,自引:1,他引:1
Chuen-Jinn Tsai Chien-Hsien Wu Ming-Long Leu Sheng-Chieh Chen Cheng-Yu Huang Perng-Jy Tsai Fu-Hsiang Ko 《Journal of nanoparticle research》2009,11(1):121-131
The standard rotating drum tester was used to determine the dustiness of two nanopowders, nano-TiO2 and fine ZnO, in standard 1-min tests. Then, the sampling train was modified to determine the number and mass distributions
of the generated particles in the respirable size range using a Scanning Mobility Particle Sizer (SMPS), an Aerodynamic Particle
Sizer (APS) and a Multi-orifice Uniform Deposit Impactor (MOUDI) in the 30-min tests. It was found that very few particles
below 100 nm were generated and the released rate of particles decreased with increasing rotation time for both nanopowders
in the 30-min tests. Due to the fluffy structure of the released TiO2 agglomerated particles, the mass distributions measured by the MOUDI showed large differences with those determined by the
APS assuming the apparent bulk densities of the powders. The differences were small for the ZnO agglomerates, which were more
compact than the TiO2 agglomerates. 相似文献
67.
Growth characteristics of ultra long double-ended acicular ZnO synthesized by a hydrothermal process
Double-ended acicular ZnO structure can be synthesized via a hydrothermal process with tetramethylammonium hydroxide and zinc acetate as precursors and polyvinyl alcohol (PVA) as a structure-directing agent. The as-prepared ZnO products show the well crystalline wurtzite structure with growth direction along [0 0 0 1]. For the first time, PVA is found to be employed as a reservoir of Zn2+ ions in the present study, and can control the concentration of Zn2+ in reaction solution, and the acicular morphology can be formed at the two ends of the 1-D ZnO structure, due to the effect of secondary growth that occurs as the sufficient concentration of Zn2+ ions chelated by PVA releasing to the reaction solution. Furthermore, the size of the 1-D ZnO structure can be tuned by different amounts of PVA addition. 相似文献
68.
69.
The rate constant for the reaction Br + O3 → BrO + O2 has been measured over the temperature range 224 to 422 K in a discharge flow system using a mass spectrometer as a detector. Results, expressed in the form k1 = (3.34 ± 0.40) × 10?11 X exp[?(978 ± 36)/T] cm3 s?1, are compared with previous measurements. 相似文献
70.
In this paper, we propose a non-Gaussion state space model to apply in software reliability. This model assumes an exponential distribution for the failure time in every test-debugging stage, conditionally on the state parameter — the number of faults in the program. It is a generalized JM model which can be applied to the imperfect debugging situation as well as in evolving programs. By examining a set of data on evolving program failures, the effect of evolving program model is amply proved. 相似文献