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排序方式: 共有896条查询结果,搜索用时 62 毫秒
71.
声波测井仪器中的发射换能器发射的声功率越大,声波测井波形的幅度就越大,测井资料的质量就越有保证。从这个意义上说,最有效地激发声功率是提高声波测井仪器性能或测井资料质量的一个重要的技术手段。用在线测量的声波测井仪器的导纳圆参数可以分析发射电路与换能器的匹配情况。文章首先给出了一个动态试验结果.用小的感性负载串联到换能器的回路后,换能器发射声波的能量提高了近一倍。然后用单频的电路阻抗模型简单地分析了提高发射声功率的原因。最后通过一个计算例子指出,在某些频率,由于有相位因素的影响,加在换能器上的电压的模可以比电源电压还大。 相似文献
72.
R. E. Taylor 《International Journal of Thermophysics》1998,19(3):931-939
There is an intense and growing demand for knowledge of the thermal transport properties and contact conductances of coatings, thin films, and interfaces. The laser flash technique is uniquely suited for many of the measurements. The usefulness and limitations of this technique for coatings, greases, and joining techniques are described in some detail. Several alternate techniques, namely, step heating, multiproperty, and photoacoustic techniques, are briefly examined. 相似文献
73.
A compact Ids model with physical drain-conductance (gds) modeling for deep-submicron MOSFETs is formulated based on first-principle momentum-/energy-balance equations, which simultaneously includes the hot-electron and thermoelectric effects in a unified compact form with two fitting parameters and one-step extraction. The model has been verified with 0.18-μm experimental data with good gds prediction. 相似文献
74.
通过仿真模拟分析光伏电池特性,针对传统的变步长电导增量(INC)法存在无法同时满足跟踪速率和减少振荡的问题,提出了一种基于改变步长比例因子的变步长最大功率算法,实时判断工作点的状态来选择不同的步长比例因子,从而解决MPPT控制过程中动态响应和稳态波动的这一矛盾关系。仿真结果表明:改进的算法和传统的变步长INC相比,跟踪过程更快速,跟踪结果更精确,系统输出功率在最大功率点处的振荡得以有效降低,动态性能和稳态性能都更优异。 相似文献
75.
Cheng Du Li Chen Haijun Zhang Zhongchao Wang Wenchao Liu Xiaodong Xie Manjiang Xie 《International journal of molecular sciences》2014,15(11):20706-20722
Increasing evidence suggests that caveolin-1 and large conductance Ca2+-activated potassium (BKCa) channels are implicated in the carcinogenesis processes, including cell proliferation and invasion. These two proteins have been proven to interact with each other in vascular endothelial and smooth muscle cells and modulate vascular contractility. In this study, we investigated the probable interaction between caveolin-1 and BKCa in MCF-7 breast cancer cells. We identified that caveolin-1 and BKCa were co-localized and could be reciprocally co-immunoprecipitated in human breast cancer MCF-7 cells. siRNA mediated caveolin-1 knockdown resulted in activation and increased surface expression of BKCa channel, and subsequently promoted the proliferation and invasiveness of breast cancer cells. These effects were attenuated in the presence of BKCa-siRNA. Conversely, up-regulated caveolin-1 suppressed function and surface expression of BKCa channel and exerted negative effects on breast cancer cell proliferation and invasion. Similarly, these opposing effects were abrogated by BKCa up-regulation. Collectively, our findings suggest that BKCa is a critical target for suppression by caveolin-1 in suppressing proliferation and invasion of breast cancer cells. The functional complex of caveolin-1 and BKCa in the membrane microdomain may be served as a potential therapeutic target in breast cancer. 相似文献
76.
Satoshi Kaneko 《Fullerenes, Nanotubes and Carbon Nanostructures》2014,22(1-3):166-172
A pyrazine molecular junction was investigated using mechanically controllable break junction (MCBJ) technique at 10 K. The conductance measurements revealed the single pyrazine molecular junctions showed two distinct conductance values of 0.27 ± 0.04 and 1.0 ± 0.2 G 0 (2e 2/h). The conductance value of the single pyrazine molecular junction was comparable with that of the metal atomic junction. The interface between pyrazine molecule and Pt surface was investigated by near edge X-ray absorption fine structure (NEXAFS). The broadening of the π* peak in N K-edge NEXAFS spectra suggested that the pyrazine molecule connected to Pt surface via a nitrogen atom. Based on the measurements of the conductance and NEXAFS, we could propose the structural models of two distinct conductance states for the single pyrazine molecular junction. 相似文献
77.
An experimentally validated thermo-mechanical model for the prediction of thermal contact conductance 总被引:1,自引:0,他引:1
Vishal Singhal Paul J. Litke Anthony F. Black Suresh V. Garimella 《International Journal of Heat and Mass Transfer》2005,48(25-26):5446-5459
A predictive model for estimating thermal contact conductance between two nominally flat metallic rough surfaces has been developed and experimentally validated. The predictive model consists of two complementary parts, the first of which is a surface deformation analysis to calculate the actual area of contact for each contact spot, while the second accounts for the effects of constriction resistance and gas gap conductance between the contacting surfaces. A surface characterization technique is developed which generates an equivalent 3-D surface profile from multiple 2-D profiles and determines the unique wavelengths of importance for the surface deformation and constriction resistance models. For given surface profiles and material properties of two contacting surfaces, and a specified contact pressure, the surface characterization technique filters out non-essential wavelengths on the surface, after which the surface deformation analysis calculates the deformation and contact area of each contacting asperity by considering three different modes of deformation, namely, elastic, elastic–plastic, and plastic. The constriction resistance model is then used to calculate the constriction resistance for each contacting asperity based on the area of contact and radius of curvature of the asperity. The constriction resistance values for all the contacting asperities are then used to calculate the total thermal contact conductance. An experimental facility has also been constructed to measure thermal contact conductance of interfaces to verify the results of the predictive model. Good agreement has been found between the model predictions and experimental measurements, validating the modeling approach. 相似文献
78.
太阳能电池阵列输出特性具有强烈的非线性,为了提高系统的整体效率,一个重要的途径就是实时调整光伏电池的工作点,进行最大功率点跟踪(maximum power pointtracker,MPPT),使之始终工作在最大功率点附近。最大功率点跟踪方法是一个提高光伏组件效率的很有效的方法。 相似文献
79.
Yang Liu Zhiyong Zhang Xianlong Wei Quan Li Lian‐Mao Peng 《Advanced functional materials》2011,21(20):3900-3906
The thermoelectric parameters, in particular the thermal conductivity and dimensionless figure of merit ZT, of ZnO nanowires, are estimated via two terminal current–voltage measurements. The measurements are carried out in situ in a transmission electron microscope and negative differential conductance is observed on individually suspended ZnO nanowires. From the low bias region of the current–voltage curve, the electrical parameters, including carrier concentration and mobility, are obtained by fitting the experimental data using a metal–semiconductor–metal model. The thermal conductivity is extracted from the high bias region of the same current–voltage curve using a self‐consistent method, which combines the self‐heating thermal conduction and electrical transport properties of ZnO nanowires. It is shown that the thermal conductivity of ZnO nanowires is suppressed significantly in comparison with that of bulk ZnO, which is attributed to the strong surface scattering of phonons. The thermal conductivity is also found to decrease more steeply than the expected $ {1 \mathord{\left/{\vphantom {1 T}} \right.} T} $ trend, but does obey a $ {1 \mathord{\left/{\vphantom {1 {\left({\alpha T + \beta T^2} \right)}}} \right. } {\left({\alpha T + \beta T^2} \right)}} $ relation; this is shown to result from four‐phonon processes at high temperatures. The dimensionless figure of merit ZT is determined to be about 0.1 at 970 K. Finally, the thermoelectric properties of individual ZnO nanowires are also discussed, indicating that ZnO nanowires are promising high temperature thermoelectric materials. 相似文献
80.
The authors examined the incremental validity of the reaction time (RT) measure beyond that of skin conductance response (SCR) in the detection of concealed information. Participants performed a Stroop-like task in which they named the color of critical and neutral words. Results show that the SCR highly differentiated between the relevant and neutral words. However, the RT demonstrated a significant differentiation only when the critical words denoted personally significant items (e.g., one's own name) and not when they denoted crime-relevant items related to a simulated crime. In both cases, combining the 2 measures yielded no advantage over the use of SCR alone. Thus, although behavioral measures may differentiate between relevant and neutral information in some cases, their practical use is questionable. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献