夫兰克-赫兹实验教学的发展与完善

根据不同时期对夫兰克-赫兹实验仪的改进及对实验内容的改革扩充,阐述了该实验教学的不断发展与完善.重点介绍了对第一代夫兰克-赫兹实验的改造,增加了数据采集、电脑显示及数据处理等功能,实现集模拟与数字化为一体的实验装置.     

Molecular fusion of fullerenes

New experimental data is reported for the absolute cross sections for the fusion reaction channel in single gas-phase collisions between fullerenes. The experimental data is compared with the results of quantum mechanical and classical molecular dynamics simulations as well as with simple models. Quantum molecular dynamics simulations are in very good quantitative agreement with the experimental data. The overall dynamical behaviour can be well-described qualitatively in the framework of simple models. Received 2 October 2000     

20 MeV以下65Cu(n,p)65Ni 反应截面及其协方差数据的评价

为满足核工程对核数据的需求,对20 MeV以下65Cu(n, p)65Ni 反应截面的实验数据进行了分析和评价,包括实验数据的收集、修正、选取、归一、误差调整和数据处理,在分析实验误差特别是关联误差的基础上构造了每家数据的协方差矩阵,最后利用样条拟合程序SPCC给出了评价截面数据和实验数据的协方差矩阵。评价不仅考虑了实验数据的误差,还考虑了数据间的相关性。To meet the needs for nuclear data engineering, the experimental data of the 65Cu(n, p)65Ni cross section below 20 MeV were analyzed and evaluated.The evaluation procedure includes the experimental data collection, correction, selection, normalization, error adjustment and data processing, especially the covariance matrix for each experimental data is constructed with the information on experimental errors and correlation errors. The evaluation cross section data and the corresponding covariance matrices were given using the spline fitting procedure SPCC. The evaluation work was done with the consideration of not only the experimental errors but also the correlation of data.     

利用GEANT4和TALYS研究中子与铁作用的次级中子双微分截面

铁的次级中子双微分截面对核装置的设计、运行与维护具有重要作用。相关实验数据缺乏,且评价数据不完善,需要使用可靠的核理论模型进行计算。本工作利用GEANT4程序结合不同的中子评价数据计算了8.17, 11.5, 14.1和18 MeV等入射能量下中子轰击薄铁靶不同出射角度的次级中子双微分截面;同时利用TALYS程序和GEANT4程序结合BIC、BERT和INCLXX模型计算了25.7, 65, 100和150 MeV等入射能量下中子轰击薄铁靶不同出射角度的次级中子双微分截面,并与实验数据进行对比。研究表明,在20 MeV以下能区,ENDF/B-VIII.0库的计算结果与实验数据符合较好,BROND-3.1、CENDL-3.1、JENDL-4.0u和JEFF-3.3库的计算结果与实验数据存在差异。在20~150 MeV能区,GEANT4程序的BERT模型和TALYS程序的计算结果与实验数据符合较好,INCLXX模型和BIC模型的计算结果与实验数据存在分歧。整体来看,需要对铁的中子评价数据和核反应理论模型做进一步研究。     

基于MATLAB编程的弗兰克-赫兹实验数据处理方法探讨

弗兰克-赫兹实验是理工科近代物理实验教学中的一个重要实验,由于弗兰克-赫兹实验手动测量数据时,所得数据量大而且精度不高,学生人工处理数据的过程中往往面临繁、难等问题.本文提出运用MATLAB GUI的可视化,通过自动读取人工测量实验数据,进行图像拟合,进而使用逐差法和最小二乘法进行数据处理.教学实践表明,该方法不仅能够有效地解决实验数据处理中的繁琐、困难等问题,还能够充分发挥学生的主动性,使学生对实验原理的本质和实验数据的处理有更加深刻的理解和思考,提高物理实验教学的有效性.在教学实践中,使用该方法,不仅有了更多的时间综合训练学生的实验操作能力,同时也提高了实验教学的有效性,创新了传统实验教学的复杂数据处理过程,实验教学效果较佳.     

Calculation of Neutron Resonance Spacing with Microscopic Theory

Nuclear level spacings calculated with a microscopic theory are compared with spacings determined fromneutron resonance experiment. The gross features of the experimental data due to nuclear shells are reproduced with themicroscopic theory. The experimental data for nuclei with statistically deformed nuclei have also been tested with leveldensity formula including low energy rotational levels. The experimental data for the actinide nuclei and the lanthanidenuclei are found to be consistent with the theory which includes collective rotational levels.     

Methods of estimation of equilibrium charge distribution of ions in solid and gaseous media

The new version of theoretical estimation of equilibrium charge distribution of ions passing through the matter is proposed. This estimation is based on the correction of charge exchange cross sections for gases taking into account the density effect. The results of calculations are compared with experimental data and with empirical estimation based on the averaging of experimental data for charge distributions of ions in gases and solids. The theoretical method describes the experimental oscillations of width of the charge distribution in contrast to the empirical method.     

Ag Raman modes of RBCO (R = Gd, Pr) by density functional theory approach

Ab initio total energy calculations have been performed for superconducting GdBa₂Cu₃O₇ and insulating PrBa₂Cu₃O₇ using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated unit cell volume and lattice parameters with the experimental data indicates the improvement of these parameters in the GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about 6% smaller and 1.25% larger than the experimental data, respectively for both systems. Thus frozen phonon calculations have been performed to determine the eigenvalues and eigenvectors of the k=0 A_g modes of the two systems in equilibrium structure have been obtained in GGA. The calculated frequencies in the GGA are in good agreement with the other LDA calculations for similar systems. Comparison of computational data with experimental data indicates that calculations determine the frequencies about ten percent below the experimental data. Even by improving LDA to GGA in these calculations, the calculated phonon frequencies have remained almost ten percent below the experimental data, even though the calculated unit cell volumes are nearly equal to the experimental data. So, applying GGA has not considerably decreased the difference between the computational and experimental data. The effect of Pr doping on the eigenvalues and eigenvectors have also been investigated.     

UPS and EELS study of zirconium oxidation

The electronic structures of metallic zirconium, zirconium oxide, and zirconium surfaces with intermediate degrees of oxidation have been studied by photoemission spectroscopy using synchrotron radiation and by electron energy loss spectroscopy. Both methods are used to analyze the same samples in one experimental cycle. Some specific features of the electronic structures that had not been detected earlier are revealed. The experimental data obtained are explained using the first-principles calculations of the electronic states of hcp metallic zirconium and cubic or monoclinic zirconia. The dielectric function and the electron-energy-loss function are calculated for comparison with the experimental data. Despite certain quantitative differences, the experimental and calculated data on the electronic structures of zirconium and its oxide are in good qualitative agreement.     

On the static polarizability of small metal particles

The size-dependent static polarizability of small sodium particles is calculated within a non-self-consistent spherical jellium model. The results are compared both with recent experimental data and with recent theoretical work based on a completely self-consistent jellium model. The non-self-consistently obtained polarizabilities agree better with the experimental values than those obtained in a completely self-consistent way. The reasons for this are discussed and it is outlined how lattice effects could improve the agreement between the results of a self-consistent theory and the experimental data.     

Adaptive nonlinear prediction of ocean reverberation

An adaptive nonlinear prediction algorithm is proposed to predict ocean reverberation based on the phase space reconstruction of nonlinear dynamic system. The prediction algorithm is tested by experimental reverberation data measured in two areas, and the one-step forward prediction results are in good agreement with the experimental data. If the errors between the predicted and experimental data are chosen as the variable to detect the target in the reverberation series, the reverberation is suppressed and the signal-to-reverberation ratio is improved.     

Al、Cu、Ta高压熔化曲线的理论计算

由位错熔化理论和不同的静高压实验数据优化的体模量(B0)、剪切模量(G0)及它们对压力的一阶偏导数(B′0、G′0)值计算了Al、Cu、Ta的高压熔化曲线.理论计算的Al、Cu高压熔化曲线与静、动高压实验值较为吻合,Ta的理论高压熔化曲线与动高压实验结果一致,但与静高压实验结果相差较大.     

关于密立根油滴实验数据处理的新探讨

密立根油滴实验是大学物理的经典实验,通过处理实验测量数据即可得出基本电荷量.各高校开展实验的方法基本相同,但处理实验数据的方法却各式各样.为了减小因数据处理带来的误差,提出多种方法结合处理数据,即在作图法的基础上增加分组法和最小二乘法处理数据,结果显示误差明显减小.通过5个教学班的试验教学,验证了文中观点的可行性,并取...     

Calculation of thermodynamic properties of dense neon using statistical mechanical perturbation theory

Abstract

Thermodynamic properties of fluid neon were calculated between 73 and 348 K and up to the melting line, using Ross’ variational perturbation theory. Parameter values for the EXP-6 potential were determined from experimental sound velocity data in the range 100–300 K, 0.1–1 GPa. Calculations with this and several pure pair potentials (XC, HFD), with and without more body interactions, were compared with experimental pVT and sound velocity data. The EXP-6 potential describes the experimental data up to 1 GPa with an accuracy of almost the experimental error. An equation of state is presented in the range from 98 to 348 K and from 0.6 to 6 GPa.     

Molecular dynamics simulations of the surface tension of n-hexane,n-decane and n-hexadecane

Molecular dynamics simulations have been used to compute the surface tension of linear alkanes. The OPLS force field has been compared with the SKS force field for alkanes (n-hexane, n-decane and n-hexadecane) over two ranges of temperature: high temperatures where no experimental data are available for surface tension and lower temperatures where comparisons may be made with experiments. At high temperatures, for a given coexistence density, these two models predict a similar surface tension. For a given temperature the two models yield different surface tensions. However, these deviations can be attributed to differences in the prediction of the coexistence curves. For the SKS model the computed coexistence properties have been compared with experimental data. The simulation data are in reasonable agreement with the experimental data.     

Identification and updating of loading in frameworks using dynamic measurements

This paper is concerned with the effect of structural loading on dynamic performance. This topic is recognised as being of importance when validating finite element (FE) models with experimental data. A strategy for including axial load effects in a model updating procedure is developed. The method can be used to identify loading in structural frameworks using measured dynamic data.The effectiveness of the new method is demonstrated by means of case studies involving both simulated and experimental data. The theoretical study allows aspects of the sensitivity of the method to realistic levels of experimental noise to be studied as well as the way in which dynamic load identification can be enhanced with static measurements. The experimental case study proves the practical success of the technique. Updated axial load parameters are compared with static measurements of the same quantities.     

Theoretical Analysis and New Formulae for Half-Lives of Proton Emission

The proton radioactivity hMf-lives of spherical proton emitters are calculated by the cluster model with the con- tribution of a centrifugal potential barrier considered separately. The results are compared with the experimental data and other theoretical data, and good agreement is found for most nuclei. In addition, two formulae are pro- posed for the proton decay half-life of spherical proton emitters through the least squares fit to the experimental data available, and could reproduce the experimental half-lives successfully.     

The evidence of the existing and the parameters of the second region of water dipole relaxation

In order to explain experimental data of dielectric properties of water in the microwave region at temperature from 0 up to 90 °C and at frequencies from 9.5 to 75.4 GHz, we propose a new method. This method is based on normalizing all considered experimental data and presenting them in a sole Cole–Cole plot. The normalizing relation is derived with supposition that there exists a sole Debye dispersion region. As the result of this normalization, we present the data of various experimental groups made at various temperatures and frequencies, and, hence, we get the possibility to process at the same time various experimental data. The analysis carried out in wide frequency range from ωτ1 to ωτ≈10 showed that dielectric permittivity of water cannot be completely explained in the model of a sole Debye relaxation region. It was shown that it is enough to suppose two relaxation Debye regions. The processing of experimental data allowed us to determine the parameters of these regions.     

Total cross section prediction of the collisions of positrons and electrons with alkali atoms using Gradient Tree Boosting

A relatively new computational technique, namely gradient tree boosting (GTB), is presented for modeling the total cross sections of the scattering of positrons and electrons by alkali atoms in the low and intermediate energy regions. The calculations have been performed in the framework of gradient tree boosting (GTB). The GTB has been running based on the experimental data of the total collisional cross sections to produce the total cross sections for each alkali atom as a function of the incident energy of the projectile as well as the atomic number and the static dipole polarizability of the atom. Moreover our GTB model is used to predict the experimental data for total collisional cross sections that are not used in the training session. The calculated and predicted total collisional cross sections are compared with the experimental data. We find that the GTB technique shows a good match to the experimental data. To our knowledge, this is the first application of the GTB technique to the data of positron and electron collisions with alkali atoms at low and intermediate energies.     

MgO声子散射曲线和热力学特性的第一原理研究

利用从头算场论结合局域密度近似和Troullier-Martins赝势,计算了MgO的声子散射曲线和热力学特性.计算结果和所有的有效实验值进行了比较,发现理论计算结果和实验结果吻合的很好.