Molecular conformation and interactions in oligomeric mixtures of polystyrene with polybutadiene: a small-angle neutron scattering study

In this preliminary study we report values of the interaction parameter determined from small angle neutron measurements at two temperatures and three concentrations for two blends of oligomeric polystyrene with polybutadiene. One blend contained labelled (deuterated) polystyrene with hydrogenous polybutadiene and the other deuterated polybutadiene with hydrogenous polystyrene. The results from the latter are compared with predicted values.     

基于K线及布林线的房地产市场趋势预测

以K线和布林线为基本工具,提出了直观形象判断和预测房地产市场的周期波动的机理;并以月为基本周期绘制厦门市整体区域和分区房地产市场K线图,结合厦门市宏观经济形势、房地产市场发展状况以及宏观政策,判断和预测厦门市房地产周期波动及价格趋势。实验结果证明,K线与布林线组合的房地产周期波动分析及价格趋势预测是一种有效的研究手段,能够反映房地产周期波动的特征及趋势,是一种值得推广的研究方法。     

Oscillations in gas-fluidized beds: Ultra-fast magnetic resonance imaging and pressure sensor measurements

Ultra-fast Magnetic Resonance Imaging (MRI) and pressure sensor measurements have been applied to study: (i) pressure fluctuations, (ii) the eruption of bubbles at the top of a bed and (iii) the formation of bubbles in a gas-fluidized bed. Ultra-fast MRI has been applied for the first time to study the formation and eruption of bubbles; the technique is non-intrusive and provides measurements with good temporal and spatial resolutions. The MRI measurements revealed that bubbles are formed periodically, rather than randomly at a distributor, which in this case was a perforated plate. The frequency at which bubbles erupted from the top of the bed matched the frequency of the pressure fluctuations measured just above the distributor, where the measured pressure is predicted very well for the case of slug flow by Kehoe and Davidson's [P.W.K. Kehoe, J.F. Davidson, Pressure fluctuations in slugging fluidized beds, AIChE Symp. Ser. 128 (69) (1973) 34-40] correlation, originally developed for locations high up a bed. Both findings lead to the conclusion that the passage and eruption of bubbles at the top of a bed are the dominant cause of the pressure fluctuations, which are subsequently propagated downwards through the bed. Two new correlations are proposed for predicting the frequency of pressure fluctuations in a bubbling bed; both correlations agree well with experimental measurements. A modification of Baeyens and Geldart's [J. Baeyens, D. Geldart, An investigation into slugging fluidized beds, Chem. Eng. Sci. 29 (1974) 255-265] correlation predicts the frequency of pressure fluctuations when slugs are formed, but are not fully developed. The frequency of bubble formation, as measured by MRI, is equal to or higher than both the frequency of bubble eruption at the top of the bed and the frequency of pressure fluctuations, depending on the depth of the bed. The frequency of bubble formation is significantly lower than predicted by Davidson and Schüler's [J.F. Davidson, B.O.G. Schüler, Bubble formation at an orifice in an inviscid liquid, Trans. Inst. Chem. Eng. 38 (1960) 335-342] equation, originally developed for gas-liquid systems.     

Evaluation of the elastic constants of nanoparticles from atomistic simulations

We present an approach to estimate the elastic constants of molecules and nanoparticles, based on the analysis of thermal fluctuations from Monte Carlo (MC) or molecular-dynamics (MD) atomistic simulations. The method and the force-field used for these calculations have been tested by the calculation of Young's modulus of a graphite sample along the basal plane; the calculated value was found to be 1.07 TPa, in very good agreement with the experimentally determined one of 1.02 TPa.The results on a carbon-based nanotube indicate that for the longitudinal direction of the particle, the value of the elastic constant is on the order of 400 GPa. The elastic constant of the considered nanotube in the radial direction is significantly lower, the predicted values being in the range 4-7 GPa.The method was also applied to the elastic constants of a type of siloxane-based nanostructure, whose longitudinal elastic constant (30 GPa) is an order of magnitude lower than the corresponding value for the carbon-based nanotube.     

Probing Inhomogeneities in Type II Superconductors by Means of Thermal Fluctuations, Magnetic Fields, and Isotope Effects

Type II superconductors, consisting of superconducting domains embedded in a normal or insulating matrix, undergo a rounded phase transition. Indeed, the correlation length cannot grow beyond the spatial extent of the domains. Accordingly, the thermodynamic properties will exhibit a finite size effect. It is shown that the specific heat and penetration depth data of a variety of type II superconductors, including cuprates, exhibit the characteristic properties of a finite size effect, arising from domains with nanoscale extent. The finite size scaling analysis reveals essential features of the mechanism. Transition temperature and superfluidity increase with reduced domain size. The combined finite size and isotope effects uncover the relevance of local lattice distortions.     

Flow-Induced Instabilities in Pump-Turbines in China

The stability of pump-turbines is of great importance to the operation of pumped storage power (PSP) stations. Both hydraulic instabilities and operational instabilities have been reported in PSP stations in China. In order to provide a reference to the engineers and scientists working on pump-turbines, this paper summarizes the hydraulic instabilities and performance characteristics that promote the operational instabilities encountered in pump-turbine operations in China. Definitions, analytical methods, numerical and experimental studies, and main results are clarified. Precautions and countermeasures are also provided based on a literature review. The gaps between present studies and the need for engineering practice are pointed out.     

带有指令滤波的电力弹簧系统反步控制

针对新能源发电系统因间接性和不确定性导致的电压波动问题,本文提出一种带有指令滤波的电力弹簧(Electrical springs,ES)反步控制策略。根据ES的数学模型利用反步法设计控制器,并加入指令滤波器,以解决ES反步控制中的计算膨胀问题,同时设计了误差补偿信号,并利用Lyapunov稳定性理论验证了系统稳定性。通过仿真模拟新能源发电系统网侧电压发生波动时,ES对关键负载电压稳定的效果,验证出本文所提出的策略具有响应速度快、谐波含量低、抗干扰能力强的优势。     

流道喷涂对双吸离心泵压力脉动特性影响研究

流道喷涂技术能有效提高水泵过流部件抗磨损能力并降低水力损失,但其对压力脉动特性的影响并不明确。本文采用试验的方法,对一双吸离心泵流道喷涂前后的压力脉动进行同台测试,并分析了混频幅值和频谱特性。结果表明:流道喷涂处理降低了流道粗糙度,减小了水力损失,提高了效率,但同时也改变了水泵固有的压力脉动特性。对于吸水室,喷涂处理缩小了压力脉动稳定区的范围,使小流量工况区的压力脉动峰峰值达到喷涂处理前的2.8倍,加剧了水泵在小流量工况下运行的不稳定性。对于压水室,喷涂处理使靠近隔舌区域在小流量区的压力脉动明显增加,使远离隔舌区域在大流量区的压力脉动增加。而在设计流量区域,喷涂对各个位置压力脉动影响不明显。为了使喷涂技术发挥综合效果,保证水泵运行稳定,应该尽量避免喷涂后的水泵在偏离设计流量工况运行,特别是严格避免水泵在低于0.75倍设计流量工况运行。     

Analytic expression of the error in a linear estimator of discrepancies between time scales

An analytic dependence of the error of a linear estimator of the nonstationary random process of discrepancies between time scales in filtration, extrapolation, interpolation, and approximation from the values of the characteristics of the frequency stability of standards, the precision characteristics of instruments used in the measurement of discrepancies between time scales, the number of measurements, and algorithms used to process the results of these measurements are obtained. Translated from Izmeritel’naya Tekhnika, No. 1, pp. 28–31, January, 2009.