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361.
Micro-mechanical theories have recently been developed to model the propagation of force through a granular material based on single grain interactions. We describe here an experimental technique, developed to validate such theories, that is able to measure the individual contact forces between the grains and the wall of the containing vessel, thereby avoiding the spatial averaging effect of conventional pressure transducers. The method involves measuring interferometrically the deflection of an interface within a triple-layer elastic substrate consisting of epoxy, silicone rubber, and glass. A thin coating of gold between the epoxy and rubber acts as a reflective film, with the reference wave provided by the glass/air interface. Phase shifting is carried out by means of a tunable laser. Phase difference maps are calculated using a 15-frame phase-shifting formula based on a Hanning window. The resulting displacement resolution of order 1 nm allows the wall stiffness to be increased by some two orders of magnitude compared to previously described methods in the literature. 相似文献
362.
For aerodynamic force measurement in shock tunnels and similar short duration aerodynamic testing facilities we have developed a novel measurement technique. Its key feature is a mounting support, which releases the test model and grips it again after a free flight duration of about 10 milliseconds. The model is equipped with small accelerometers and may contain additional installations. The short free flight allows the use of thin wires because the model travels only a few millimeters during this time. Validation experiments with a cone-cylinder of known drag coefficient show good accuracy with a response time of about half a millisecond. Pitot pressure measurement and suitable data processing allow for direct evaluation of aerodynamic coefficients in slowly changing flow.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
363.
364.
M. J. Szab R. K. Szilgyi C. Unaleroglu L. Bencze 《Journal of Molecular Structure》1999,490(1-3):219-232
Harmonic DTMM and COSMIC molecular mechanical force fields were extended to cover aliphatic silanes. Structures of the thirty-five molecules were examined and they generally fit approximately within experimental error. For these, root mean square deviations between the calculated and the experimentally determined geometrical data were found to be less than 0.05 Å and 1.7 deg. for bond lengths and bond angles, respectively. The accuracy of these force fields was also verified in comparison with the other force fields (MM2, MM3), semi-empirical (PM3), ab initio (HF,MP2) and density functional (B3LYP, BP86) quantum chemical methods. The relative stability of the seventeen conformations of seven simple molecules was investigated and the limitations of the DTMM software is discussed. 相似文献
365.
GaGa and AlFe Multiple Bonds? An Attempt of Interpretation on the Basis of Force Constants Comparison of force constant values given by DFT frequency calculations shows that GaGa‐bonds in Ga2H42– and Ga2H22– are only slightly strengthened with respect to the GaGa‐single bond in Ga2H62–. On the other hand FeAl bonds in compounds like CpAlFe(CO)4 are interpreted as double bonds. 相似文献
366.
Several new results are derived upon gas density as well as upon velocity and force fields relative to a gasdynamic laser within a supersonic nozzle. Evolution equations, including the continuity equation, are employed to obtain the above results. In particular, the continuity equation is used to determine the shape of the nozzle so that its cross-sectional area is calculated as a function of distance. This function is one of the ingredients to get our results relative to gas density, velocity, and force. In addition, the time-dependent power associated with the vibrational non-equilibrium expansion in the nozzle of hot gas at high pressure is evaluated. 相似文献
367.
人口老龄化对经济的直接影响体现为劳动力老化对劳动生产率的影响.本文在基于标准C-D生产函数的计量经济模型框架下,采用省级面板数据和固定效应估计方法,深入探究全国以及不同区域劳动力老化对劳动生产率的影响.实证结果显示,我国劳动力老化对劳动生产率有显著的消极影响,且沿海地区劳动力老化对劳动生产率的消极影响比非沿海地区更强烈.要缓解劳动力力老化对劳动生产率的消极影响,可以从以下三个方面入手:首先,稳定低生育水平,适当放宽人口政策;其次,大力发展教育事业,特别是对老年劳动力的教育和培训;第三,合理引导人口流动,实现地区间劳动力年龄结构的优势互补. 相似文献
368.
In this paper, we propose an alternative approach for forecasting mortality for multiple populations jointly. Our contribution is developed upon the generalized linear models introduced by Renshaw et al., (1996) and Sithole et al., (2000), in which mortality forecasts are generated within the model structure, without the need of additional stochastic processes. To ensure that the resulting forecasts are coherent, a modified time-transformation is developed to stipulate the expected mortality differential between two populations to remain constant when the long-run equilibrium is attained. The model is then further extended to incorporate a structural change, an important property that is observed in the historical mortality data of many national populations. The proposed modeling methods are illustrated with data from two different pairs of populations: (1) Swedish and Danish males; (2) English and Welsh males and U.K. male insured lives. 相似文献
369.
对于年金的定价问题的研究,传统精算理论假定利率是恒定不变的.但事实上,由于受到多种因素的影响,利率往往具有不确定性.因此,本文采用可逆MA(1)模型来刻画利率期限机构,在此基础上,研究了期末付倒平顶虹式年金的各阶矩问题,推导出了其年金现值的期望和方差的简洁公式.通过数值模拟分析了此年金面临的利率风险,其结论对年金定价有一定的参考价值. 相似文献
370.
cndo/Force method is used to evaluate the redundancy free internal valence force fields for two conformers of nitromethane. The
initial force field is set up by taking the interaction and bending force constants from this method and transferring the
stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining
the initial force field using vibrational frequencies of isotopic speciesviz CH3NO2, CD3NO2, CH3
15NO2 and CH3N18O2. The final force field thus obtained is reasonable on the basis of frequency fit and potential energy distribution. The barrier
to internal rotation is found to be 0.048 kcal mol−1. 相似文献