The Kirkwood correlation factor of dense methanol as a function of temperature and pressure under isochoric conditions and its statistical mechanical treatment

Experimental data of dielectric susceptibilities of methanol available in the literature over a wide range of temperature and pressure have been used for constructing a state function of the Kirkwood correlation factor g _K of methanol applicable in the homogeneous fluid region between 298 and 580?K and up to 350?MPa. Results of three isochores at 786.32, 820 and 850 kg m^?3 of this state function have been compared with predictions made by a statistical mechanical theory developed in previous work. The theory is based on an association model of alcohols accounting for the correlation of effective dipole moments of chains of all length as well as ringlike cluster formations. Most of the parameters such as association constants and association enthalpies have been obtained from quantum mechanical ab initio calculations of methanol clusters up to six members, reducing the numbers of adjustable parameters to three association constants and an averaged value of the angle between dipoles. The theory which has turned out to provide excellent results for alcohol + hydrocarbon and alcohol +?CCl₄ liquid mixtures at ambient pressure is also able to predict isochoric values of pure methanol up to a pressure of 350?MPa and temperatures of 570?K without adjusting further parameters in satisfying agreement with experimental data.     

温度对应变式位移传感系统灵敏系数的影响

应变式位移传感系统的工作原理是基于电阻应变效应,该系统具有精度高﹑稳定性好等优点,但温度尤其是极端低温环境将影响该系统的灵敏系数,进而影响其测量精度.本文介绍了一种可用于低温环境的应变式位移传感系统,理论分析和实验研究了温度对该系统灵敏系数的影响,研究结果为其在低温环境中的应用提供了一定基础。     

非共轴激光雷达几何因子分析与测量

介绍了非共轴激光雷达几何因子的物理意义,分别通过理论分析和试验测量给出了求解几何因子的方法。结合自行研制的CSY-1便携式能见度激光雷达,将两种方法得到的几何因子进行对比,讨论了系统参数对几何因子的影响,从而实现了对激光雷达系统优化设计的可能性。     

White and some colored marbles as alternative radiation shielding materials for applications

ABSTRACT

In this paper, the radiation shielding parameters such as linear attenuation coefficients (LAC, µ), mass attenuation coefficients (MAC, µ/ρ), effective atomic numbers (Z_eff), effective electron densities (N_eff), half value of layers (HVL), mean free paths (MFP) and buildup factors (exposure (EBF) and energy absorption (EABF)) were investigated for cream (M1), pink (M2), white (M3), maroon (M4) and green (M5) marbles. Attenuation coefficients were measured in the energy region 31.18–661.66 keV photon energies. The values of Z_eff and N_eff were then calculated using these coefficients with logarithmic interpolation method, and HVLs and MFPs were calculated using the values of LAC of marble samples at the same photon energies. The experimental results were compared with the theoretical values obtained from WinXCom program, and good agreements were observed between the experimental and theoretical results. HVLs and MFPs of all marble samples were compared with those of some concretes, glasses and commercial radiation shielding glasses (SCHOTT Co.). The studied marbles were better radiation shielding materials than standard shielding concretes due to lower HVL and MFP values lower than the ordinary concrete. Finally, EBFs and EABFs of the marbles were calculated in the energy region 0.015–1?MeV up to penetration depths of 40 mfps by Geometric Progression method (G-P), and the results were discussed in terms of photon energies and chemical compositions of the marbles.     

Ba2MgGe2O7:Cr4+晶体中荷移激发态对g因子贡献的研究

文章建立了立方四面体3d2络合物g因子的完全高阶微扰公式.在这个公式中,除了与d-d跃迁光谱(晶场激发态)有关的晶场(CF)机制的贡献(包括近年发展的双旋-轨耦合参量模型)外,与电荷转移光谱(荷移激发态)有关的荷移(CT)机制的贡献也被考虑.将这个公式应用于Ba2MgGe2O7:Cr4 晶体平均g因子的计算,发现理论计算值与实验值很好的一致,同时,荷移机制对g移动△g(=g-2.002 3)的贡献△gCT在符号上与晶场机制的贡献△gCF相反,而在大小上约为晶场机制贡献的38%.因此,在对高价态过渡金属离子络合物的g因子计算时应考虑CF机制和CT机制的贡献.     

Piezoelectric resonators with mechanical damping and resistance in current conduction

A novel design method for high Q piezoelectric resonators was presented and proposed using the 3-D equations of linear piezoelectricity with quasi-electrostatic approximation which include losses attributed to mechanical damping in solid and resistance in current conduction. There is currently no finite element sofware for estimating the Q of a resonator without apriori assumptions of the resonator impedance or damping. There is a necessity for better and more realistic modeling of resonators and filters due to miniaturization and the rapid advances in frequency ranges in telecommunication. We presented new three-dimensional finite element models of quartz and barium titanate resonators with mechanical damping and resistance in current conduction. Lee, Liu and Ballato’s 3-D equations of linear piezoelectricity with quasi-electrostatic approximation which include losses attributed to mechanical damping in solid and resistance in current conduction were formulated in a weak form and implemented in COMSOL. The resulting finite element model could predict the Q and other electrical parameters for any piezoelectric resonator without apriori assumptions of damping or resistance. Forced and free vibration analyses were performed and the results for the Q and other electrical parameters were obtained. Comparisons of the Q and other electrical parameters obtained from the free vibration analysis with their corresponding values from the forced vibration analysis were found to be in excellent agreement. Hence, the frequency spectra obtained from the free vibration analysis could be used for designing high Q resonators. Results for quartz thickness shear AT-cut and SC-cut resonators and thickness stretch poled barium titanate resonators were presented. An unexpected benefit of the model was the prediction of resonator Q with energy losses via the mounting supports.     

Exchange charge model and analysis of the microscopic crystal field effects in KAl(MoO4)2:Cr

In the present paper, we report on consistent crystal field calculations of the Cr³⁺ ions energy levels in KAl(MoO₄)₂ using actual D_3d site symmetry of the Cr³⁺ position and employing the exchange charge model (ECM) of the crystal field. In addition to the energy level calculations, the Huang-Rhys factor S=5.7 and effective phonon energy ?ω=268 cm^-1 were evaluated in the single configurational coordinate model. Detailed treatment of the microscopic crystal field effects in the ECM framework allowed to obtain analytical dependence of the crystal field strength 10Dq on the Cr-O interionic distance and extracting from it the values of some parameters of the electron-vibrational interaction (EVI) in the KAl(MoO₄)₂:Cr³⁺ system. All obtained results are compared with experimental data and discussed; agreement between the calculated and experimental parameters is good.     

Year Discrimination of Mild Aroma Chinese Liquors Using Three-Dimensional Fluorescence Spectroscopy Combined with Parallel Factor and Neural NetworkSCIEI北大核心CSCD

Three-dimensional fluorescence spectroscopy coupled with parallel factor analysis and neural network was applied to the year discrimination of mild aroma Chinese liquors. The excitation-emission fluorescence matrices (EEMs) of 120 samples with various years were measured by FLS920 fluorescence spectrometer. The trilinear decomposition of the data array was performed and the loading scores of and the excitation-emission profiles of four components were also obtained. The scores were employed as the inputs of the BP neural networks and the PARAFAC-BP identification model was constructed. 10 samples were collected from 10, 20 and 30 years of liquors respectively, and 30 samples were selected as the test sets. The remaining 90 samples were used as the training sets to build the training model. The year prediction of unknown samples was also carried out, and the prediction accuracy was 90%, 100% and 100%, respectively. Meanwhile, the discrimination analysis method and the multi way partial least squares discriminant analysis were compared, namely PARAFAC-BP and NPLS-DA. The results indicated that parallel factor combined with the neural network (PARAFAC-BP) has higher prediction accuracy. The proposed method can effectively extract the spectral characteristics, and also reduce the dimension of the input variables of neural network. A good year discrimination result was finally achieved.     

A New Statistical Aspect of the Cluster Variation Method for Lattice Systems

This paper presents an alternative statistical way to derive the cluster variation method (CVM) for lattice systems. The formulation is developed for a series of different clusters, each of which is the largest overlap cluster between two clusters of the next larger type. We arrive at the CVM expression of the lattice configuration factor by deriving the number of different ways of distributing clusters of a selected type in the lattice so that they overlap each other at the largest overlap clusters in a physically correct manner. The essential assumption employed is that individual overlapping events are statistically independent of each other. This reveals a new statistical aspect of the CVM: The CVM is based on a Bethe tree of clusters of the selected type.