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71.
72.
The crystal structure of Zr3N4 is shown to crystallize in the centrosymmetric space group Pnam rather than in the noncentrosymmetric space group Pna21. 相似文献
73.
Ar—Kr溶液扩散系数的分子动力学模拟及其与温度的关系 总被引:2,自引:1,他引:2
用分子动力学模拟方法研究确定Ar-Kr溶液的自扩散系数D1、D2和互扩散系数D12以及它们随温度变化的规律。结果表明,分别用Green-Kubo法和Einstein法得到的扩散系数在数值上一致;该溶液的3种扩散系数均满足D=D0e^E/RT关系。 相似文献
74.
J.J. Camacho L. DíazM. Santos J.M.L. Poyato 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(1):57-66
Laser-induced breakdown spectroscopy of helium plasma, initially at room temperature and pressures ranging from 12 to 101 kPa was investigated using a transverse excitation atmospheric CO2 pulsed laser (λ = 9.621 and 10.591 μm, a full width at half maximum of 64 ns, and an intensity from 1.5 to 5.36 GW cm−2). The helium breakdown spectrum is mainly due to electronic relaxation of excited He, He+ and H. Plasma characteristics were examined in detail on the emission lines of He and He+ by the time-integrated and time-resolved optical emission spectroscopy technique. Optical breakdown threshold intensities, ionization degree and plasma temperatures were obtained. An auxiliary metal mesh target was used to analyze the temporal evolution of the species in the plasma. The results show a faster decay of the continuum emission and He+ species than in the case of neutral He atoms. The velocity and kinetic energy distributions for He and He+ species were obtained from time-of-flight measurements. Electron density in the laser-induced plasma was estimated from the analysis of spectral data at various times from the laser pulse incidence. Temporal evolution of electron density has been used for the estimation of the three-body electron-ion recombination rate constant. 相似文献
75.
Summary Linear velocity in capillary SFC is commonly controlled by restricting capillaries. In this paper, a model is described that quantitatively predicts the linear velocity of a supercritical fluid in SFC using tapered or ceramic frittype restrictors. In this model, the flow from the restricting capillary is assumed to be an isentropic expansion. The variation of the linear velocity as a function of pressure, temperature and cross-sectional area of the restricting aperture was predicted by this model. This predictive capability is important to the use of gradient programming in capillary SFC. Finally, the ideal variable restrictor for gradient programming was found to be one that could reversibly increase or decrease the linear velocity independent of the pressure, temperature, and/or density conditions used to create the gradient. 相似文献
76.
The loss of pulmonary artery (PA) compliance has significant pathophysiological effect on the right ventricle. Noninvasive and reliable assessment of PA wall stiffness would be an essential determiner of right heart load and a clinically useful factor to assess cardiovascular risk. Two MRI techniques have been proposed for assessing PA stiffness by measuring pulse wave velocity (PWV): transit time (TT) and flow area (QA). However, no data are available that compares the two techniques and evaluates their performance, especially over a wide range of PWV values or at 3.0-T, which is the purpose of the present study. Thirty-three patients with different heart conditions were imaged using optimized high-temporal resolution and high-spatial resolution velocity-encoding MRI sequences. Statistical analysis was conducted to study intermethod, interobserver and intraobserver variabilities. The PWV measurements using TT and QA techniques showed good agreement (P>0.1). The Bland-Altman analysis showed negligible differences between the two methods (mean±S.D.=0.11±0.35 m/s, correlation coefficient r=0.94). The repeated measurements showed low interobserver and intraobserver variabilities, although the S.D. of the differences was larger in the QA technique. The mean±S.D. of the TT/QA measurement differences were −0.05±0.2/0.0±0.36 m/s and 0.02±0.26/0.02±0.39 m/s for the interobserver and intraobserver differences, respectively. In conclusion, each technique has its own advantages and disadvantages. The two techniques result in similar measurements, although the QA method is more subjective due to its dependency on operator intervention. 相似文献
77.
78.
The influence of Free-Stream Turbulence (FST) on the space–time dynamics of a conical vortex developing along a A-pillar is studied experimentally. Measurements of unsteady wall pressure and velocity by High Speed-Stereo PIV highlight the important effects of turbulence on the mean and instantaneous properties of the vortex. Very significant increases in Reynolds stresses into the vortex region and in wall fluctuating pressure are observed in the presence of FST. In smooth flow, the frequency content of the pressure and velocity fields is very rich with low and high frequency contributions due to the meandering of the vortex and instabilities in the vortex core. Meandering shows, for the different integral length scales and intensities of turbulence tested, a great receptivity to the presence of a FST and we observe a global motion of the vortex structure at low frequency. This frequency is modulated by the value of the integral length scale of the FST. We show that the mean conical structure is a wave guide for the perturbations of the core but that, with FST, the spatio-temporal evolution of the envelope overwhelms the intrinsic instability of the vortex core observed in smooth flow. 相似文献
79.
有限元离散一类速度追踪问题后得到具有鞍点结构的线性系统,针对该鞍点系统,本文提出了一种新的分裂迭代技术.证明了新的分裂迭代方法的无条件收敛性,详细分析了新的分裂预条件子对应的预处理矩阵的谱性质.数值结果验证了对于大范围的网格参数和正则参数,新的分裂预条件子在求解有限元离散速度追踪问题得到的鞍点系统时的可行性和有效性. 相似文献
80.
模糊度搜索空间的大小是影响模糊度解算效率的关键因素之一.针对传统确定模糊度搜索空间的方法较为保守,致使搜索空间过大,提出了一种基于最小二乘模糊度降相关平差法(LAMBDA)的改进方法.首先对目前模糊度搜索空间确定方法给予了介绍和深入的分析比较,评价了这些经典方法的优缺点.在此基础上,定义了搜索空间的一个影响因子η,并结合LAMBDA方提出了确定模糊度搜索空间的修正公式.基于仿真和实测数据对修正方法进行实验,结果表明方法在保证获得期望模糊度组数的前提下,其确定的模糊度搜索空间包含的整数点个数更小,可保证90%以上实际模糊度组数接近于期望值. 相似文献