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Quinine induces changes in the motion of the cupula in the lateral line canal of the African knife-fish in response to sinusoidal water movements. Two different phases in the action of quinine on the cupular frequency response can be discerned. In the first phase the best frequency, i.e., the frequency at which the cupular vibratory displacement is maximal in response to constant-amplitude sinusoidal canal fluid displacement, shifts toward higher frequencies. During this phase, lasting about 70-100 min, the best frequency increases by a factor between 1.3 and 1.5. In the second phase, during roughly the following 90 min, the best frequency decreases gradually to a value 0.3-0.5 times that observed before the application of quinine. 相似文献
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CA Peh SR Burrows M Barnden R Khanna P Cresswell DJ Moss J McCluskey 《Canadian Metallurgical Quarterly》1998,8(5):531-542
Tapasin is a resident ER protein believed to be critical for antigen presentation by HLA class I molecules. We demonstrate that allelic variation in MHC class I molecules influences their dependence on tapasin for peptide loading and antigen presentation. HLA-B*2705 molecules achieve high levels of surface expression and present specific viral peptides in the absence of tapasin. In contrast, HLA-B*4402 molecules are highly dependent upon human tapasin for these functions, while HLA-B8 molecules are intermediate in this regard. Significantly, HLA-B*2705 like HLA-B*4402, requires tapasin to associate efficiently with TAP (transporters associated with antigen processing). The unusual ability of HLA-B*2705 to form peptide complexes without associating with TAP or tapasin confers flexibility in the repertoire of peptides presented by this molecule. We speculate that these properties might contribute to the role of HLA-B27 in conferring susceptibility to inflammatory spondyloarthropathies. 相似文献
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Triblock copolymers of hexamethyl cyclotrisiloxane (D3) and styrene were synthesized by first preparing “living” species of polystyrene dianion followed by polymerization of D3. The chain lenght of polymeric blocks could be controlled in a predictable fashion leading to a central hard block of polystyrene and the two end segments of amorphous polydimethylsiloxane having narrow molecular weight distribution, were characterized by gel permeation chromatography. The chemical composition of block copolymers was determined by silicon analysis and infrared and nuclear magnetic resonance spectra. Thermal aging of block copolymers at 150, 200, and 300°C was also discussed. 相似文献
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Polymer blends with varying amounts of poly(vinyl chloride) (PVC), acrylonitrile-butadiene-styrene (ABS) and polyester have been developed to produce parts with highly flexible, good impact strength, and flame retardant hinge properties. In the present work, the rheological and dynamic mechanical properties are balanced by changing the blend formulations. It is shown that blends morphology and rheology have greater impact on the dimensional stability and delamination at the surface of the molded hinge parts. 相似文献
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A conceptual pore level model (Chem. Eng. Sci. 57 (2002) 3401) of spreading of liquid over internally wet porous particles is applied to explain reported rector level enhancement in wetting of trickle bed reactor (Ind. Eng. Chem. Res. 36 (1997) 5133). It is confirmed that a symbiotic relationship exists between internal and external wetting of porous particles whereby each enhances the other. Further, it is illustrated that liquid spreading in porous solids is driven more by porosity than by contact angle. A major implication of this phenomena is that liquid will spread more on less wettable (but porous) surfaces in comparison to more wettable (but nonporus) surfaces and a reinterpretation of experiments involving spreading of liquid over porous solids is required. On a large scenario, it is hoped that present exercise will be in important step towards explaining the complex reactor level macro phenomena by simple and conceptual pore level micro models. 相似文献
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K. M. N. Prasanna A. S. Khanna Ramesh Chandra W. J. Quadakkers 《Oxidation of Metals》1996,46(5-6):465-480
Alumina-forming ODS superalloys are excellent oxidation-resistant materials. Their resistance relies upon the establishment of a stable, slow-growing, and adherent -alumina. In the present investigation, these alloys exhibited unstable and relatively less adherent -alumina phase, which increased the oxidation rate in the transient stage and converted into -alumina in the later part of the exposure. The oxide-growth process was found to depend upon various parameters such as temperature, time, and presence of an active elecment in the superalloy. Characterization carried out by XRD, SEM/EDAX, and AES on oxidized ODS and non-ODS alloys demonstrated a significant influence of the active element, Y, on the transformation of - to -alumina. SIMS analysis of two-stage oxidation at 900°C for two different durations evidently showed that the change in the transport process is due to -to--alumina transformation. On the basis of these results, a new and consistent mechanism is proposed to explain the influence of -alumina and its transformation on growth kinetics and the effect of yttrium on the transformation leading to good scale adherence and oxidation resistance. 相似文献
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This paper presents the design, fabrication and reliability testing of a double spiral platinum-based MEMS hotplate for gas sensing applications. The structure of MEMS hotplate consists of a 0.7 µm-thick thermally grown SiO2 membrane of size 120 µm × 120 µm over which a double spiral platinum resistor is laid out. The hotplate membrane is supported by its four arms connected to the Si-substrate. The design and simulation of the hotplate structure was carried out using MEMS-CAD Tool COVENTORWARE. Based on the design, a double spiral platinum resistor of 103 Ω is fabricated on SiO2 membrane using lift-off technique. The platinum deposition is carried out using DC sputtering technique. Bulk micromachining of Si is done from front side of the structure to create the suspended SiO2 membrane. The temperature coefficient of resistance (TCR) of platinum is measured and found to be 2.19 × 10?3/ °C. The TCR value is used for temperature estimation of the hotplate. The test results show that the microhotplate consumes only 20 mW power when heated up to 500 °C. For reliability testing of fabricated structure, the hotplate is continuously operated at 300 °C for 1.8 h. Also, it can sustain at least 61 cycles pulse-mode operation at 530 °C with ultra-low resistance and temperature drifts. The structure can sustain a maximum temperature and current of 611 °C and 11.55 mA respectively without any damage. 相似文献
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