Thermal helium clusters at 3.2 Kelvin in classical and semiclassical simulations

The thermodynamic stability of⁴He_4–13 at 3.2 K is investigated with the classical Monte Carlo method, with the semiclassical path-integral Monte Carlo (PIMC) method, and with the semiclassical all-order many-body method. In the all-order many-body simulation the dipole-dipole approximation including short-range correction is used. The resulting stability plots are discussed and related to recent TOF experiments by Stephens and King. It is found that with classical Monte Carlo of course the characteristics of the measured mass spectrum cannot be resolved. With PIMC, switching on more and more quantum mechanics. by raising the number of virtual time steps results in more structure in the stability plot, but this did not lead to sufficient agreement with the TOF experiment. Only the all-order many-body method resolved the characteristic structures of the measured mass spectrum, including magic numbers. The result shows the influence of quantum statistics and quantum mechanics on the stability of small neutral helium clusters.     

LaB6在低压强氮气和氦气中的放电特性

 研究了LaB₆在1~10 Pa氮气和氦气中的直流和脉冲放电特性以及放电过程对电极的影响。结果表明，电极直径为5 mm的LaB6氦气放电管在脉冲工作状态下可以长期稳定放电。在脉冲电压为2.2 kV、脉冲宽度10 ms、频率13.3 Hz下，脉冲峰值放电电流超过120 A。氦气放电管在放电过程中，阴极表面有离子的清洗和活化作用，可以使电极的表面逸出功降低，提高放电管的发射能力和稳定性。LaB₆作为气体放电电极具有寿命长、延迟时间短、放电电流大等优点，可用于重复强流脉冲气体放电的高压高速开关器件。     

Fermi and Coulomb correlations in the 21 S state of the helium isoelectronic sequence

The Fermi and Coulomb holes of the 2¹ S state of the helium isoelectronic sequence are investigated. Several interesting differences between the results obtained and those which might be expected on the basis of the corresponding 2³ S state are pointed out and discussed.     

Hydrogen analysis in solid samples by utilizing He metastable atoms induced by TEA CO2 laser plasma in He gas at 1 atm

A TEA CO₂ laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO₂ laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected H emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO₂ laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO₂ laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens.     

Medium-size Gaussian basis sets for hydrogen through argon

Summary Medium-sized Gaussian basis sets are reoptimized for the ground states of the atoms from hydrogen through argon. The composition of these basis sets is (4s), (5s), and (6s) for H and He, (9s5p) and (12s7p) for the atoms Li to Ne, and (12s8p) and (12s9p) for the atoms Na to Ar. Basis sets for the² P states of Li and Na, and the³ P states of Be and Mg are also constructed since they are useful in molecular calculations. In all cases, our energies are lower than those obtained previously with Gaussian basis sets of the same size.     

非低温法的稀有气体纯化技术概述

稀有气体广泛应用于工业生产中,如离子刻蚀、检漏等。但是它们在地球上的含量比较少,属于稀有资源,因此需要对它们进行纯化以循环再利用。首先介绍了不同气体纯化的原理,然后以实际生产中的不同稀有气体使用范围为例,说明纯化装置的设计方法和需要考虑的问题。为以后气体纯化装置的设计提供借鉴。     

氦气提纯技术发展现状与应用分析

为实现氦气资源的循环利用,有必要对氦气进行回收纯化。文中对目前国内外氦气的提纯技术发展现状进行了分析介绍,并综合分析比较了这些方法的应用原理、优缺点及发展趋势,针对各自的使用特点,给出了几种详细的提纯工艺实现方法,为促进我国氦气提纯技术的发展提供了新的思路。     

Chemical characterization and ultrastructure study of pulp fibers

Understanding the ultrastructure and chemical characterization of pulp fibers is highly important in utilizing wood as a raw material in a wide scope of applications, such as forest biomass-based biorefineries and low-cost renewable materials. The observation of the ultrastructure is not possible without advanced microscopy and spectroscopy techniques. Therefore, this study focuses on exploring the ultrastructure of pulp fibers with helium ion microscopy (HIM) and scanning electron microscopy (SEM). For the analysis of chemical characterization in the pulp fibers, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were performed. For these studies, the pulp fiber samples were obtained mainly from three different wood species, i.e. spruce, birch and eucalyptus. They were received in the never dried state and dried with a critical point drier (CPD) to minimize pore collapse. The spectroscopy results showed a strong signal from crystalline cellulose and confirmed the absence of lignin after Kraft pulping and bleaching. However, with XPS about 2% of lignin was detected in eucalyptus pulp. The results obtained with the microscopy techniques are compared and indicating the nanofibril size, shape, surface roughness as well as their orientation in pulp fibers. To our knowledge, this is the first time that HIM is applied to study the ultrastructure of pulp fibers and compared against more conventional microscopy and spectroscopy techniques. The main differences between HIM and SEM were found to be related to the focusing and magnification. The individual nano- and microfibrils as well as their bundles were more easily visible with HIM than with SEM. Also, with HIM it was possible to get the total area in focus at once which was not the case with SEM. The increased understanding of the ultrastructure and chemical composition of wood pulp enhance the development of novel wood-based products and processes for their manufacture.     

不同气体工质对激光推力器冲量耦合系数的影响

通过冲击摆实验,测量了激光推力器在不同气体工质(氩气,氦气)、不同工作压力条件下的冲量耦合系数,比较了不同气体对激光推力器冲量耦合系数的影响.实验结果表明:冲量耦合系数随着环境压力的下降而下降,并且下降趋势越来越快;在氩气中测量的冲量耦合系数比氦气的高;实验产生误差的主要因素是摆角的测量误差.     

TCH-600氧、氮、氢分析仪在唐钢的应用

通过TCH-600氧、氮、氢分析仪在唐钢的实际应用,重点介绍了助熔剂、坩埚、样品熔解及空白和校正过程中应注意的问题,钢铁样品分析条件的选择.