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排序方式: 共有385条查询结果,搜索用时 15 毫秒
131.
《应用陶瓷进展》2013,112(7):408-414
AbstractA comparative study is carried out between the non-humidity sensitive Li vanadates, LiMnVO4 and LiCuVO4, from 25 to 500°C at frequencies from 42 Hz to 1 MHz. The mobile ion hopping rate of LiMnVO4 is found to be higher than that of LiCuVO4 due to the lower LiMnVO4 bulk and grain boundary activation energy values. Dielectric constant values from 25 to 500°C at frequencies from 42 Hz to 1 MHz revealed the presence of all types of polarisation. At the plots of LiCuVO4 tan?δ (dielectric loss) versus frequency, tan?δ displays a peak at a frequency that shifts to higher values with temperature. At 400°C, the maximum losses appear at 1 kHz and at 500°C at 10 kHz. The modulus master curves of LiCuVO4 and LiMnVO4 suggested the presence of conduction processes with the same activation energy at different frequencies. 相似文献
132.
This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion. 相似文献
133.
An optical interferometric technique has been used to investigate fluid film thickness in sliding, isoviscous elastohydrodynamic contacts (I-EHL). Monochromatic two-beam interferometry has been employed to map lubricant film thickness across a range of applied loads and entrainment speeds. The contact was formed between an elastomer sphere and plain glass disc, illuminated under red light, λ= 630 nm. Experimental work has employed sunflower oil and glycerol/water solutions as the test lubricants, due to their similar refractive indices and varying viscosity. A black-and-white-image-intensified camera has been employed to capture interference images and a computer processing technique used to analyse these images, pixel by pixel, and create film thickness maps based on their gray-scale intensity representations. Comparison of film thickness results to theoretical models shows reasonable qualitative agreement. Experimental results show both a reduced horseshoe, which is limited to the rear of the contact, and wedge-shaped film thickness profile within the Hertzian contact region. This is unlike conventional hard EHL contacts where the horseshoe-shaped pressure constriction extends around the contact toward the inlet. Experimental results suggest that film thickness profiles take on a convergent wedge shape similar to that used in many hydrodynamic bearings. It is likely that this wedge is largely responsible for generating fluid pressure and therefore the load-carrying capacity of the contact. 相似文献
134.
介绍了在改造搓丝机实现小模数花键冷搓加工过程中遇到的一个问题,即花键的错齿现象,分析了错齿产生的原因,提出了解决冷搓过程中花键错齿的措施. 相似文献
135.
结合西安集装箱中心站工程的湿陷性黄土不良地质,分析了重型振动碾压技术的工作原理,通过重型振动碾压技术的应用,表明该技术可有效消除黄土的湿陷性,可使压实度、承载力、压缩模量达到设计要求。 相似文献
136.
137.
DuJiang PengQicong 《电子科学学刊(英文版)》2004,21(6):441-448
This paper investigates the blind algorithm for channel estimation of Orthogonal Frequency Division Multiplexing-Multiple Input Multiple Output (OFDM-MIMO) wireless communication system using the subspace decomposition of the channel received complex baseband signals and proposes a new two-stage blind algorithm. Exploited the second-order cyclostationarity inherent in OFDM with cyclic prefix and the characteristics of the phased antenna, the practical HIPERLAN/2 standard based OFDM-MIMO simulator is established with the sufficient consideration of statistical correlations between the multiple antenna channels under wireless wideband multipath fading environment, and a new two-stage blind algorithm is formulated using rank reduced subspace channel matrix approximation and adaptive Constant Modulus (CM) criterion. Simulation results confirm the theoretical analysis and illustrate that the proposed algorithm is capable of tracking matrix channel variations with fast convergence rate and improving acceptable overall system performance over various common wireless and mobile communication links. 相似文献
138.
基于小波变换的信号相关技术在电力电缆故障测距中的应用 总被引:10,自引:5,他引:5
提出了一种基于小波分解的信号相关技术.针对以往应用冲闪法的电力电缆故障测距技术普遍存在故障时刻检测不准确的问题,提出将小波分解与信号相关技术相结合,先对采集到的信号进行多层小波分解,去掉低频信号中的高频分量,应用信号相关技术计算出粗略的奇异点,然后运用搜索模极大值线的方法找到高频分量中的奇异点,从而得到精确的脉冲到达时刻.数字仿真结果验证了该方法的有效性. 相似文献
139.
The present work aims to investigate the influence of the main process parameters (pressure and temperature) and biomass characteristics (moisture content and particle size) on some mechanical properties (density and durability) of olive tree pruning residues pellets. By means of a lab scale pellet press, able to control process parameters, the biomass, ground with three different hammer mill screen sizes (1, 2 and 4 mm) and conditioned at different moisture contents (5, 10, 15 and 20% w.b.), was pelletized at various process temperatures (60, 90, 120 and 150 °C) and pressures (71, 106, 141 and 176 MPa). Compressed sample dimensions and mass were measured in order to calculate pellet density, while compressive strength tests were carried out to estimate the durability of the final biofuel. The relationships between the factor settings and the responses (density, compression strength and modulus of elasticity) were examined by univariate and multivariate statistical analysis.Temperature resulted the most important variable influencing pellet mechanical properties, followed by the initial moisture content and the particle size of the raw material. In particular, high process temperature, low moisture contents and reduced particle sizes allowed obtaining good quality pellets. The effect of compression force resulted scarcely relevant. 相似文献
140.
H.L. Sun Z.X. Song D.G. Guo F. Ma K.W. Xu State Key Laboratory for Mechanical Behavior of Materials School of Materials Science Engineering Xi an Jiaotong University Xi'an China 《材料科学技术学报》2010,26(1):87-92
Tungsten (W) thin films were prepared by magnetron sputtering onto Si (100) substrates. Their microstructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The hardness and modulus were evaluated by nanoindentation. It is found that a 30 nm Cr sticking layer induces structure changes of deposited W film from β-W to α-W structure. In addition, remarkable hardness enhancement both for the deposited and annealed W... 相似文献