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排序方式: 共有1604条查询结果,搜索用时 15 毫秒
101.
G S Cha D Liu M E Meyerhoff H C Cantor A R Midgley H D Goldberg R B Brown 《Analytical chemistry》1991,63(17):1666-1672
Ammonium and potassium ion-selective membranes formulated with PVC/hydroxylated PVC, polyurethane/hydroxylated PVC, and moisture-curable silicone rubber matrices are studied in an effort to extend the lifetime of solid-state ion sensors through improved membrane adhesion. The PVC/membranes exhibit electrochemical performance equivalent to that of conventional PVC membranes in terms of slope, detection limit, and selectivity. The polyurethane- and silicone-rubber-based membranes have better adhesion to silicon nitride than do PVC or hydroxylated PVC matrices. Incorporating a silanizing reagent (silicon tetrachloride) significantly improves the adhesion of the polyurethane matrix. The use of silicon tetrachloride in membrane matrices also enhances the electrochemical stability of the interfacial potential between ion-selective polymer-matrix membranes and silver epoxy inner reference electrodes of solid-state sensors. The biocompatibility of the polymer matrices is examined via radiotracer protein adsorption studies and whole blood clotting time measurements. The polyurethane- and silicone-rubber-based membranes exhibit less overall nonspecific protein adsorption than the PVC or hydroxylated PVC matrices. 相似文献
102.
Electrolyte design for Li ion batteries was approached by means of comparison of faradaic and non-faradaic currents. The faradaic
current by the movement of Li+ ions was dependent on the composition of the electrolyte and was related to the battery capacity; the higher the capacity,
the greater the current by the faradaic reaction. The open circuit potential of the electrode with a greater faradaic current
decreased at a slower rate than that of the electrode with a smaller faradaic current. This analysis method can be used to
prepare an optimal electrolyte of an actual Li ion battery, especially when developing batteries with excellent high-rate
discharge capabilities and low temperature discharge properties. 相似文献
103.
SW Kim SS Cha HS Cho JS Kim NC Ha MJ Cho S Joo KK Kim KY Choi BH Oh 《Canadian Metallurgical Quarterly》1997,36(46):14030-14036
Bacterial Delta5-3-ketosteroid isomerase (KSI) catalyzes a stereospecific isomerization of steroid substrates at an extremely fast rate, overcoming a large disparity of pKa values between a catalytic residue and its target. The crystal structures of KSI from Pseudomonas putida and of the enzyme in complex with equilenin, an analogue of the reaction intermediate, have been determined at 1.9 and 2.5 A resolution, respectively. The structures reveal that the side chains of Tyr14 and Asp99 (a newly identified catalytic residue) form hydrogen bonds directly with the oxyanion of the bound inhibitor in a completely apolar milieu of the active site. No water molecule is found at the active site, and the access of bulk solvent is blocked by a layer of apolar residues. Asp99 is surrounded by six apolar residues, and consequently, its pKa appears to be elevated as high as 9.5 to be consistent with early studies. No interaction was found between the bound inhibitor and the residue 101 (phenylalanine in Pseudomonas testosteroni and methionine in P. putida KSI) which was suggested to contribute significantly to the rate enhancement based on mutational analysis. This observation excludes the residue 101 as a potential catalytic residue and requires that the rate enhancement should be explained solely by Tyr14 and Asp99. Kinetic analyses of Y14F and D99L mutant enzymes demonstrate that Tyr14 contributes much more significantly to the rate enhancement than Asp99. Previous studies and the structural analysis strongly suggest that the low-barrier hydrogen bond of Tyr14 (>7.1 kcal/mol), along with a moderate strength hydrogen bond of Asp99 ( approximately 4 kcal/mol), accounts for the required energy of 11 kcal/mol for the transition-state stabilization. 相似文献
104.
Cher Liang Cha Eng Fong Chor Hao Gong An Qing Zhang Lap Chan 《Semiconductor Manufacturing, IEEE Transactions on》2000,13(3):386-389
The breakdown time of flash memory oxide/nitride/oxide (ONO) layer tbd under positive constant current stressing has been found to be closely related to the cumulative extent of (over)etch of the tungsten silicide, control polysilicon, and ONO layers, i.e., Σ(ΛOE). An empirical first-order relation between tbd and Σ(ΛOE) has been derived to facilitate the plasma etch recipe optimization. This has led to a four-fold increase in the average tbd across a 200-mm wafer to 208 s. More importantly, the spread in tbd has been tightened to ~5%, which is down from ~54% 相似文献
105.
R. Gerling F.P. Schimansky A. Stark A. Bartels H. Kestler L. Cha C. Scheu H. Clemens 《Intermetallics》2008,16(5):689-697
The possible application of gamma titanium aluminides in aerospace industry requires a detailed understanding of the microstructure–property relationship of sheets made from this material. This paper reports the mechanical properties of sheets up to 1000 °C, based on alloy concepts with high Nb concentrations and small additions of C. Sheets were manufactured by rolling powder metallurgical compacts with compositions Ti 45Al 5Nb and Ti 45Al 5Nb 0.5C. The microstructures of both sheets are “near gamma” and consist of γ-TiAl and 2-Ti3Al phases. The texture of both phases is very weak. The strengths levels are very high and that of the C-containing sheet exceeds that of the C-free material at RT by 200 MPa. The mechanical properties of Ti 45Al 5Nb are independent of the direction in the sheet, in the whole temperature range from RT to 1000 °C. However, for the C-containing sheet this is true only in the upper temperature range. 相似文献
106.
107.
W Schmidt-Lorenz T Bischofberger S K Cha 《International journal of food microbiology》1990,10(2):157-176
Comparative determination of the specific growth kinetics in mineral water and low and higher concentrated broths at 20 degrees C of 25 selected Gram-negative bacteria isolated from natural non-carbonated mineral water yielded three groups: (1) facultative oligocarbotolerants--with faster growth in normal broth (In g l-1: yeast extract 2.5; casein peptone 5.0; glucose 1.0); (2) obligate oligocarbotolerants--with equal rates of growth in normal and 1:10 diluted broth; and (3) oligocarbophiles--with faster growth in 1:10 diluted broth and in mineral water. In addition, three nutrient types, 'eu-, meso- and oligotrophic' could be distinguished on the basis of full, weak and no growth in brain-heart infusion broth. Further characterization was made between slow and very slow growth types in 1:10 diluted broth. All 25 isolates were psychrotrophic with a minimum growth temperature below 0 degree C. The optimum and maximum temperatures of growth in 1:10 diluted broth, as determined in a temperature gradient incubator were between 20 and 32, and between 29 and 34 degrees C with an average of 26 and 31 degrees C, respectively. Based on these results a very simple nutrient-tolerance test was proposed. After inoculation of the three media, 1:10 diluted broth, normal broth and brain-heart infusion, it is only necessary to check whether or when visible turbidity occurs during 2 weeks incubation at 20 degrees C. This allows additional characterization of bacteria from natural mineral water, which are often difficult to identify, on the basis of growth characteristics in various types of nutrient media. 相似文献
108.
1.5 mu m band travelling-wave semiconductor optical amplifiers (TWAs), characterised by their window facet structure and symmetrised active waveguide, have been developed. 1.5 dB spectral gain ripple and 1.3 dB TE-TM mode gain difference at 22 dB signal gain were achieved simultaneously. An average facet reflectivity as low as 0.06% was estimated.<> 相似文献
109.
Young Chul Choi Ho-Young Cha Eastman L.F. Spencer M.G. 《Electron Devices, IEEE Transactions on》2005,52(9):1940-1948
A novel silicon carbide (SiC) normally off lateral channel vertical junction field-effect transistor (LC-VJFET), namely a source-inserted double-gate structure with a supplementary highly doped region (SHDR), was proposed for achieving extremely low power losses in high-power switching applications. The proposed architecture was based on the combination of an additional source electrode inserted between two adjacent surface gate electrodes and a unique SHDR in the vertical channel region. Two-dimensional numerical simulations for the static and resistive switching characteristics were performed to analyze and optimize the SiC LC-VJFET structures for this purpose. Based on the simulation results, the excellent performance of the proposed structure was compared with optimized conventional structures with regard to total power losses. Finally, the proposed structure showed about a 20% reduction in on-state loss (P/sub on/) compared to the conventional structures, due to the effective suppression of the JFET effect. Furthermore, the switching loss (P/sub sw/) of the proposed structure was found to be much lower than the results of the conventional structures, about a 75% /spl sim/ 95% reduction, by significantly reducing both input capacitance (C/sub iss/) and reverse transfer capacitance (C/sub rss/) of the device. 相似文献
110.
Hyo Jin Yoo Jeong Hyun Seo Dong Gyun Kang Hyung Joon Cha 《Korean Journal of Chemical Engineering》2007,24(1):99-101
Monitoring of biological activity for target enzyme is important for its production in recombinant expression systems. Previously,
we demonstrated that green fluorescent protein (GFP) as a fusion partner is successfully tooled for facile, in vivo, and non-invasive
quantification of target enzyme levels based on a linear relationship between GFP fluorescence and enzyme (chloramphenicol
acetyltransferase; CAT) activity. Here, we investigated the effects of culture environmental variations (initial glucose amount,
surface aeration, and inducer concentration) on correlation between GFP fluorescence and CAT activity, and established a general
linear correlation as a unique criterion for quantitative monitoring of CAT biological activity. This general correlation
for GFP fusion strategy can be applied for non-invasive and on-line monitoring of recombinant enzyme production under various
culture conditions without further experimental calibrations. 相似文献