The Hugoniot equation of state of the fluid He+D2 mixtures

The fluid variational theory and effective one-component model have been used to calculate the Hugoniot equation of state (EOS) of fluid He, D2, and He+D2 mixtures with different He:D2 compositions under high pressures and temperatures. An examination of the confidence of above computation is performed by comparing experiment and calculation, in which the similar calculation procedure used for He+D2 is adopted, of He and D2 each, since no experimental data are available to conduct this kind of comparison. Good agreement in both comparisons is found. This fact may be looked as if an indirect positive verification of calculation procedure used here at least in the pressure and temperature domain covered by the experimental data of He and D2 used for comparison, numerically nearly up to 35 GPa and 105K.     

Effect of He pre-plating on third sound in superfluid He

We recently reported observation of third sound resonances in superfluid films of pure ³He on a disk-shaped polished copper substrate. From the observed spectra of resonant modes, the third sound speed, the average superfluid density, and information on dissipation were obtained. The film thicknesses studied were larger than or comparable to the superfluid coherence length, which is near 100 nm. We describe preliminary results from efforts aimed at using third sound in thinner films on a substrate which has been coated with a few atomic layers of ⁴He.     

Critical velocities and two mechanisms of transition in superfluid liquid He

Two mechanisms of transition of the superfluid liquid ⁴He to quantum turbulence regimes are proposed for the case when the influence of the normal fluid on superfluid flow is suppressed by introducing superleaks at the ends of the capillary. Using dimensional analysis it is found that in the roton mechanism the critical velocity depends on channel size as vc∝d−1/4, matching the experiments. For the second, super-flow mechanism, the analysis of independent parameters relevant for this phenomena leads to critical velocity depending on d as vc∝d−1. It is shown that turbulence for super-flow mechanism arises when a “quantum Reynolds number” exceeds some critical value which is about 10³ for 1D geometry. The dimensional analysis of the equation for critical velocity of superfluid flow without superleaks at the ends of the capillary is also presented.     

Spatial evolution of pulses of low-energy phonons in liquid He

The system of equations that describes the temporal and spatial evolution of low-energy phonons (l-phonons) is obtained for the cases of plane and axial symmetry. From the solutions of these equations, we discuss the time-resolved measurements of the angular distribution of l-phonons. These show a rather unusual mesa shape with a flat top in the direction normal to the heater. We consider that the flat top is due to the creation of high-energy phonons (h-phonons).     

Experimental evidence against zero temperature spin-wave damping in He

We have discovered unexpected features in the NMR signal of the ³He– ⁴He mixture inside the mixing chamber of a ⁴He circulating dilution refrigerator. The dilution process not only cools the liquid in the mixing chamber to 12–15 mK but also enhances the nuclear spin polarization of the concentrated as well as the dilute phase to nearly four times the equilibrium value in a magnetic field of 9.36 T. The NMR features are ascribed to standing spin waves trapped by falling dilute phase droplets. The temperature and polarization dependence of the quality factor of the spin-wave modes contradicts evidence from previous work that favored zero temperature spin-wave damping in moderately polarized degenerate Fermi liquids.     

3He的低温物理特性及其应用

随着低温技术研究的不断发展和日益深入 ,3He已经作为一种有潜力的工质在科学研究中得到应用。采用 3He作制冷工质 ,可获得比 4 He更低的制冷温度和更大的制冷量。文中将介绍 3He的基本物理性质 ,总结 3He在低温下的特性表现、获取方法以及应用情况 ,以供参考     

Remnant magmatic activity in the Coastal Range of East Taiwan after arc–continent collision: fission-track data and He/He ratio evidence

The magma activity of the North Luzon Arc is considered to have ceased, due to collision with the Asian continental margin, since late Miocene. New fission track dates of zircons taken from dike swarms in the central Coastal Range of East Taiwan show very young ages of 0.5 Ma. Furthermore, the high ³He/⁴He ratios (2.5 R_A; R_A is the air ratio) of hot spring gases near the same area indicate that more than 30% of a mantle-derived source component is necessary to account for the helium composition. These results suggest the existence of later remnant magmatic activity (more than 4 Ma) in the central Coastal Range. Therefore, arc magmatism may survive longer than the previously expected after collision.     

H_2+He流体混合物在部分离解区的物态方程

H2+He流体混合物在高温高压下由于氢的离解化学反应形成由H2,H,He三种粒子构成的混合体系,此时粒子间的相互作用较为复杂,离解能也会由于粒子间的这种复杂相互作用而降低.本文利用自洽流体变分理论来研究部分离解区H2+He流体混合物的高温高压物态方程,模型考虑了各种粒子间的相互作用及由温致和压致效应引起的离解能降低的自洽变分修正,并通过自洽流体变分过程对非理想的离解平衡方程求解得到粒子数密度分布,进而对自由能求导获得体系的热力学状态参量.计算结果与已有的冲击波实验数据、蒙特卡罗模拟及其他理论计算进行了比较.     

Simulation of the scattering in an atomic beam evaporated from a He film

We have simulated the scattering in a pulsed atomic beam evaporated from a superfluid ⁴He film. Assuming that the atoms leaving the surface of the film have an equilibrium Maxwellian distribution, we find that the experimentally observed deviations from Lambert's law are explained by scattering of the atoms after evaporation.     

Decay of quantized vorticity in superfluid He at mK temperatures

An experimental investigation of the free decay of quantized turbulence in isotopically pure superfluid ⁴He at mK temperatures is discussed. Vortices are created by a vibrating grid, and detected by their trapping of negative ions. Preliminary results suggest the existence of a temperature-independent vortex decay mechanism below T70 mK.     

Effective interactions in dilute mixtures of3He in4He

Nonlocal pseudopotentials which describe the effective interaction between³He quasiparticles, and between these quasiparticles and the background⁴He liquid, are obtained as a function of concentration and pressure by generalizing the Aldrich-Pines pseudopotentials for pure³He and⁴He to dilute mixtures. The hierarchy of physical effects which determine these pseudopotentials is established. Interaction-induced short-range correlations are the dominant physical feature; next in order of importance is the greater zero point motion associated with the replacement of a⁴He atom by a³He atom, while spin-induced Pauli principle correlations play a significantly smaller, albeit still important role. We find a consistent trend in the change of the effective direct quasiparticle interactions with increasing concentration, and show how the Aldrich-Pines pseudopotentials for pure³He quasiparticles represent a natural extension of our results for dilute mixtures. Our calculated nonlocal pseudopotential for³He quasiparticles is qualitatively similar to that proposed by Bardeen, Baym, and Pines; it changes sign at somewhat lower momentum transfers than the BBP result, varies little with concentration, and provides a physical basis for understanding the BBP result. The effective interaction between quasiparticles of parallel spin, here determined for the first time, is essentially repulsive in the very dilute limit; as the concentration increases, it becomes increasingly attractive at low momentum transfers, and resembles closely that between antiparallel spin quasiparticles at 5% concentration. The concentration-dependent transport properties calculated from these pseudopotentials (which involve only one phenomenological parameter) are in good agreement with experiment at saturated vapor pressure (SVP), 10 atm, and 20 atm. Maxima in the thermal conductivity and spin diffusion are predicted to occur at concetrations somewhat less than 4%. Because the effective quasiparticle interactions are somewhat more repulsive than those previously proposed, we find the transition of the³He quasiparticles to the superfluid state takes place at significantly lower temperatures than many previous estimates; our predicted maximum superfluid transition temperature is 2×10^–8 K (for a 0.6% mixture at 20 atm).     

采用常规状态方程计算氦-3热力性质的可行性研究

3He作为一种特殊的工质在低温工程、基础物理学和空间技术等领域获得重要应用,这些应用需要可靠的3He热力学性质数据。但是目前没有适用于3He的宽范围状态方程。不仅如此,而且有关的热物性实验数据也十分稀缺,这给应用3He的研究人员带来了困难。本文基于全面收集和整理有关3He的各类数据,通过编写计算机程序,考察了五种常用的状态方程(理想气体状态方程,范德瓦尔方程,RK方程,RKS方程和PR方程)用于计算3He在4K~100K温区定压下比容-温度关系的可行性,并将计算结果与实验数据进行了比较。这些比较结果将为3He状态方程的研究提供有价值的参考。     

He离子注入单晶Si纳米气泡形成生长及其应用探讨

首先简述了He离子注入单晶Si引起的气泡形成、生长以及其它缺陷对其生长的影响,介绍了Si中He气泡生长的可能微观机制以及它们在现代半导体技术中潜在的应用前景,提出了该领域研究有待解决的关键问题.He ion implantation induced bubbles or cavities in silicon have been paid more and more attentions due to their potential applications in modern semiconductor technology. In this paper, He ion implantation induced formation and growth of bubbles in silicon together with their interactions with other defects were first briefly reviewed. Then the possible growth mechanisms of He bubbles in silicon and their potential applications in modern semiconductor technology were described. Finally, we presented the ke...     

Nuclear magnetism of sub-monolayer solid He on graphite

Nuclear magnetization has been measured with NMR down to temperatures around 0.1 mK for sub-monolayer solid ³He formed on graphite preplated with two layers of HD. The data for the commensurate phase show no evidence of a magnetic transition and a rather slow increase of the magnetization even at ultra-low temperature (0.15 mK), much lower than the antiferromagnetic exchange interaction of −6.3 mK.     

关于Young-Laplace公式和Kelvin公式的对话

讨论了Young-Laplace公式及Kelvin公式证明和应用中的一些问题.     

温度对bcc铁中He行为影响的模拟研究

温度对bcc铁中的He行为有重要的影响,基于bcc晶格的晶格动力学蒙特卡罗（Lattice Kinetic Monte Carlo,LKMC）方法,模拟研究了298—1298 K范围内温度对bcc铁中He行为的影响.结果表明：温度对bcc铁中He行为的影响可以分为4个阶段：（1）298—598 K,（2）598—798 K,（3）798—998 K,（4）998—1298 K.第一阶段随着温度的增加,晶粒内He原子浓度略有降低,但He泡中平均He原子个数迅速增加;第二阶段随着温度的增加,晶粒内的He原子浓度迅速降低,但He泡中平均He原子个数几乎不变;第三阶段随着温度的增加,晶粒内的He原子浓度和He泡中平均He原子个数均迅速减少;第四阶段随着温度的增加,晶粒内He原子浓度以及He泡中平均He原子个数均有所增加,到1298 K时,晶粒内He原子浓度与室温时相近,几乎没有He原子从铁晶粒内逃逸出.模拟结果与文献正电子湮灭实验结果有很好的吻合. 关键词： bcc铁 He 晶格动力学蒙特卡罗 温度     

Critical Behavior of Liquid 3He

We investigate the liquid–gas second-order phase transition in liquid ³He using the variational calculations based on the cluster expansion of the energy functional. We also compute the critical point exponents of liquid ³He that are in agreement with experimental data.     

Investigation of the electronic structure of Be2+He and Be+He,and static dipole polarisabilities of the helium atom

The potential energy and spectroscopic constants of the ground and many excited states of the Be⁺He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be²⁺ core and the electron-He interactions by effective potentials. Furthermore, the core–core interactions are incorporated. This permits the reduction of the number of active electrons of the Be⁺He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin–orbit interaction. The core–core interaction for Be²⁺He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be⁺He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole moment has been determined for a large and dense grid of internuclear distances including the spin orbit effect. In addition, a vibrational spacing analysis for the Be²⁺He and Be⁺He ground states is performed to extract the He atomic polarisability.     

用组态相互作用理论研究He原子的非谐振光致电离

本文用组态相互作用理论研究Ｈｅ原子的非谐振光致电离。本文详细分析双重激发自电离态，考察第一电离阈值附近的非谐振谱，计算非谐振区的ｅ－Ｈｅ＋，１，３Ｐ散射位相移动及来自ｌｓｎｓ１，３Ｓ的光致电离截面，本文计算结果与实验观测值及现有的理论结果相比较，相当符合。