Low-Temperature Heat Capacity of $$^{}$$He Films on Graphite

Heat capacities of \(^{4}\)He films have been measured at rather low temperatures between 2 and 80 mK and at areal densities between 2 and 24 \(\hbox {nm}^{-2}\). These areal densities correspond to a monolayer fluid and third-layer fluid. For monolayer films, the results do not contradict previous measurements carried out at high temperatures. On the other hand, at some areal densities, small and broad but definite bumps, whose origin has not yet been understood, have been observed around 15 mK. Between 13 and 24 \(\hbox {nm}^{-2}\), the measured heat capacities above 40 mK are proportional to \(T^{2}\) and hardly change with areal density. These behaviors suggest that the second atomic layer does not solidify before the third-layer promotion, at least not into a commensurate solid, such as the so-called 4/7 phase.     

The Condensate Wave Function of a Trapped Atomic Gas

We discuss various properties of the ground state of a Bose-condensed dilute gas confined by an external potential. We devote particular attention to the role played by the interaction in determining the kinetic energy of the system and the aspect ratio of the velocity distribution. The structure of the wave function near the classical turning point is discussed and the drawback of the Thomas-Fermi approximation is explicitly pointed out. We consider also states with quantized vorticity and calculate the critical angular velocity for the production of vortices. The presence of vortex states is found to increases the stability of the condensate in the case of attractive interactions.     

$$^1S_0$$ Pairing in Neutron Matter

We report calculations of the superfluid pairing gap in neutron matter for the \(^1S_0\) components of the Reid soft-core \(V_6\) and the Argonne \(V_{4}'\) two-nucleon interactions. Ground-state calculations have been carried out using the central part of the operator-basis representation of these interactions to determine optimal Jastrow–Feenberg correlations and corresponding effective pairing interactions within the correlated basis formalism, the required matrix elements in the correlated basis being evaluated by Fermi hypernetted-chain (FHNC) techniques. Different implementations of the Fermi hypernetted-chain Euler–Lagrange (FHNC-EL) method agree at the percent level up to nuclear matter saturation density. For the assumed interactions, which are realistic within the low density range involved in \(^1S_0\) neutron pairing, we did not find a dimerization instability arising from divergence of the in-medium scattering length, as was reported recently for simple square-well and Lennard–Jones potential models (Fan et al. in Phys Rev A 92:023640, 2015).     

The AB Transition in Superfluid $$^3$$ 3 He

Journal of Low Temperature Physics - The discovery of superfluidity in $$^3$$ He in 1971, published in 1972, [1, 2] has influenced a wide range of investigations that extend well beyond fermionic...     

Regularization and Wave Approach to Dynamic Measurements

Asymmetric formulas for wavelet transformation are established making it possible to include regularization in the general scheme of wavelet processing. A new class of filtering functions is constructed for direct and inverse wavelet transformations.     

基于子空间聚类的供应商分类方法研究

根据动态交易行为对供应商分类,更好地为供应商提供服务,是大型企业供应商关系管理的核心问题之一.针对供应商行为的交易数据最大、表达复杂的特点,提出基于k-均值子空间聚类算法对供应商分类的数据挖掘方法,解决高维和稀疏数据的分析问题,并通过实例验证该方法的准确性和高效性.结果表明该方法是优化供应商关系,提高企业能力的有效方法.     

Flow Expansion behind a Shock Wave Discharged from a Channel

The results are given of experimental and numerical investigations of the structure of flow behind a shock wave discharged from open ends of round and square channels. It is demonstrated that the expansion regions arising in a flow behind a diffracted wave are characterized by a larger volume and a higher expansion ratio than those arising in a stationary underexpanded jet with the same value of the Mach number of flow at the channel exit section.     

浸没的圆柱壳在冲击波作用下动响应的Galerkin解法

研究了无粘、无旋和不可压缩流体中两端简支圆柱壳在给定冲击波作用下的动响应。圆柱壳的运动方程中考虑了流体动压力和冲击波压力的共同作用，通过将冲击波压力分布函数表示为Ｆｏｕｒｉｅｒ级数有限项形式，并利用Ｇａｌｅｒｋｉｎ方法对耦合方程进行数值求解，得到了圆柱壳在冲击波作用下的位移响应特性     

Dynamics of Laser Ablation in Superfluid $$^4\hbox {He}$$

Pulsed laser ablation of metal targets immersed in superfluid \(^4\hbox {He}\) is visualized by time-resolved shadowgraph photography and the products are analyzed by post-experiment atomic force microscopy (AFM) measurements. The expansion dynamics of the gaseous ablation half-bubble on the target surface appears underdamped and follows the predicted behavior for the thermally induced bubble growth mechanism. An inherent instability of the ablation bubble appears near its maximum radius and no tightly focused cavity collapse or rebound events are observed. During the ablation bubble retreat phase, the presence of sharp edges in the target introduces flow patterns that lead to the creation of large classical vortex rings. Furthermore, on the nanometer scale, AFM data reveal that the metal nanoparticles created by laser ablation are trapped in spherical vortex tangles and quantized vortex rings present in the non-equilibrium liquid.     

Wave propagation from a spherical cavity imbedded in an elasto-plastic medium

Summary The problem of an impulsively applied pressure acting on the surface of a spherical cavity imbedded in an elasto-plastic medium governed by a bilinear stress-strain law is considered. The problem is solved by using a certain iterative finite difference scheme which prevents almost all the numerical oscillations which usually occur in the region behind the discontinuity at the elastic-plastic boundary, when a standard finite difference scheme is applied.     

Hot Electron Relaxation in Ferromagnetic Metals: Memory Function Approach

Journal of Superconductivity and Novel Magnetism - This study leads to the investigation of the non-equilibrium electron relaxation in ferromagnetic metals. Here we consider the relaxation of...     

Anomalous Reflection of a Longitudinal Ultrasonic Wave from a Strongly Dissipative Medium

Normal reflection of a longitudinal acoustic wave from the plane interface between a solid acoustic line and a strongly dissipative medium (an epoxide resin compound in the process of solidification) has been experimentally investigated. A 14fold change in the reflection coefficient of pulsed signals and a decrease in their duration have been detected and the point of phase transmission has been reliably determined by the minimum of the reflection coefficient. The coefficient of reflection of continuous acoustic waves with frequencies of 1–10 MHz from the interface between a plexiglas (or aluminum) and an epoxide resin compound in the process of solidification has been measured. The influence of the amplitudefrequency characteristic of an ultrasonic piezoelectric transducer on the measurement data obtained has been analyzed. The change in the viscosity coefficient of an epoxide resin compound in the process of its solidification has been calculated by the spectral transform method with the use of computer programs and experimental data on the reflection coefficient dynamics.     

可测速的智能超声波液位仪

利用一对超声波传感器，一个安置在封闭罐外的底部，用来测量罐内液体的液位，一个安置在罐外的侧壁上，用来测定罐内液体中超声波的传播速度，这样对任何液体且不论温度如何变化，都能准确测出超声波在液体中的传播速度，并根据这一速度准确测出液位的高度。由于是直接测速方式，提高了测量精度，避免了采用热敏电阻测温补偿方式带来的滞后现象。     

Wave effects in a two-phase medium

A wave equation derived in the article is used to obtain a relation for the propagation velocity of small perturbations in a two-phase medium. This relation is confirmed indirectly by a computer analysis of a wet-steam nozzle, as well as experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 1, pp. 92–99, July, 1971.     

Influence of $$^$$He Coverage on Resonance Properties of a Quartz Tuning Fork Immersed in Liquid $$^3$$3He

Nowadays quartz tuning forks are commonly used for temperature measurements in experiments with liquid (both normal and superfluid) \(^3\)He. In most of the experiments pure \(^3\)He is used, but in some cases \(^4\)He is added in order to cover surfaces by a few monolayers of \(^4\)He. We report here measurements of influence of different \(^4\)He coverages on the fork resonance properties at different pressures. We have found that the presence of even small amounts of paramagnetic \(^3\)He on the fork surface may essentially change the temperature calibration.     

Wave Theory for a Converging Spherical Incident Wave in an Infinite-aperture System

Abstract

Weyl's formula describes the decomposition of a monochromatic spherical wave into an angular spectrum of plane waves. In this paper, explicit formulae for the separate contributions of homogeneous and inhomogeneous plane waves are given, and the results used to obtain an exact solution to the half-space boundary-value problem for the focusing of a converging spherical incident wave in an infinite-aperture system.     

Wave Scattering from a Slightly Wavy Interface Between two Anisotropic Media

Wave scattcring from a periodic interface separating two anisotropic layers in a thick elastic plate is studied in the two-dimensional case. The problem is solved by replacing the exact boundary conditions, i.e. continuous displacement and traction on the wavy interface, by approximate first order conditions on a flat reference surface. Numerical results are presented for a number of cases and compared to the exact solution obtained by the null field approach. The conclusion is that the approximate method gives reasonably accurate results as long as the slope of the surface is small and the amplitude of the wavy surface is not too large compared to the wavelength of the incident wave.