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...     

Classification of Adversarial Attacks Using Ensemble Clustering Approach

As more business transactions and information services have been implemented via communication networks, both personal and organization assets encounter a higher risk of attacks. To safeguard these, a perimeter defence like NIDS (network-based intrusion detection system) can be effective for known intrusions. There has been a great deal of attention within the joint community of security and data science to improve machine-learning based NIDS such that it becomes more accurate for adversarial attacks, where obfuscation techniques are applied to disguise patterns of intrusive traffics. The current research focuses on non-payload connections at the TCP (transmission control protocol) stack level that is applicable to different network applications. In contrary to the wrapper method introduced with the benchmark dataset, three new filter models are proposed to transform the feature space without knowledge of class labels. These ECT (ensemble clustering based transformation) techniques, i.e., ECT-Subspace, ECT-Noise and ECT-Combined, are developed using the concept of ensemble clustering and three different ensemble generation strategies, i.e., random feature subspace, feature noise injection and their combinations. Based on the empirical study with published dataset and four classification algorithms, new models usually outperform that original wrapper and other filter alternatives found in the literature. This is similarly summarized from the first experiment with basic classification of legitimate and direct attacks, and the second that focuses on recognizing obfuscated intrusions. In addition, analysis of algorithmic parameters, i.e., ensemble size and level of noise, is provided as a guideline for a practical use.     

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.     

A Guided Wave Approach to Defect Detection in Switch Rail

An approach to detect switch rail defect based on ultrasonic guided wave technology is studied. Eight typical cross-sections are chosen from the switch rail, and each cross-section's theoretical dispersion curves and wave structures are derived using the semianalytical finite-element method. The dispersion curve of eight sections has 262 modes at 60 kHz. Based on k-means clustering analysis algorithm, 25 kinds of classification results are obtained from 262 modes. According to the mean and variance of energy, an optimal set of modes with uniform amplitude over the entire section of the switch rail is selected. The optimal excitation point is determined based on the vibration energy. The defect echo signal is obtained by excitation of these guided wave modes. Field experiment results show that by comparing the sum of the differences between the collected and basic data and setting a certain threshold, the internal defect detection of the switch guide rail can be realized. The research results herein are valuable for analyzing the dispersion characteristics and realizing the nondestructive testing of the variable cross-section waveguide.     

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.     

Intelligent Approach for Clustering Mutations’ Nature of COVID-19 Genome

In December 2019, a group of people in Wuhan city of Hubei province of China were found to be affected by an infection called dark etiology pneumonia. The outbreak of this pneumonia infection was declared a deadly disease by the China Center for Disease Control and Prevention on January 9, 2020, named Novel Coronavirus 2019 (nCoV-2019). This nCoV-2019 is now known as COVID-19. There is a big list of infections of this coronavirus which is present in the form of a big family. This virus can cause several diseases that usually develop with a serious problem. According to the World Health Organization (WHO), 2019-nCoV has been placed as the modern generation of Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) coronaviruses, so COVID-19 can repeatedly change its internal genome structure to extend its existence. Understanding and accurately predicting the mutational properties of the genome structure of COVID-19 can form a good leadership role in preventing and fighting against coronavirus. In this research paper, an analytical approach has been presented which is based on the k-means cluster technique of machine learning to find the clusters over the mutational properties of the COVID-19 viruses’ complete genome. This method would be able to act as a promising tool to monitor and track pathogenic infections in their stable and local genetics/hereditary varieties. This paper identifies five main clusters of mutations with as best in most cases in the coronavirus that could help scientists and researchers develop disease control vaccines for the transformation of coronaviruses.     

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     

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.     

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.     

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...     

4He Shadow Wave Function with an Inverse Seventh Power Particle–Particle Correlation Function

Many ground state studies of ⁴He using a shadow wave function with an inverse fifth power McMillan particle–particle correlation function have yielded radial distribution functions with misplaced peaks. It has been conjectured that this is due to the specific choice of the McMillan correlation function. However, beyond the use of fully optimized two-particle correlation functions, there has been little study of simple alternatives that can correct this defect. In this work we show that the remedy is surprisingly simple. When a shadow wave function with an inverse seventh power particle–particle correlation function is used to study ⁴He, it gives a correctly peaked radial distribution function, lowers the energy at all liquid and solid densities, and produces an excellent equation of state.     

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.     

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.     

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。