冲击加载下金属铝中氦泡演化行为的相场模拟

氦泡等缺陷对金属材料动态强度的影响一直是动态强度研究关注的重点。将相场方法引入冲击加载下氦泡演化行为研究中,通过与晶体塑性理论耦合,建立了可描述冲击下氦泡早期演化行为的介观模拟技术。应用该方法,针对含氦泡的金属铝材料,从介观尺度对氦泡的演化行为及其对位错集体演化行为的影响进行了研究。结果表明:氦泡结构的非均匀性导致局域应力集中和塑性变形集中,局域塑性变形集中会导致沿冲击波传播方向发射稀疏波;从能量守恒角度上看,在材料变形过程中氦泡生长与塑性变形呈竞争关系,塑性耗散的快慢直接影响氦泡的生长速率,使其发生改变。研究结果可为解读含氦泡材料的宏观屈服强度和层裂行为提供理论支撑。     

Ultrasonic reflection properties of planar defects within austenitic welds

Reflection of ultrasonic beams from the faces of planar weld defects is affected by the anisotropic nature of the weld material. The simple laws of geometrical reflection no longer hold and energy may be strongly reflected into unexpected directions. This has important consequences for ultrasonic inspection techniques relying on specular signals for defect detection. In this Paper a ray tracing approach is used to study, theoretically, the expected patterns of defect reflection behaviour for several weld types and several defect locations and orientations. In general we find that when the ultrasonic beam is generated in the austenitic weld material without first passing through the base metal then the strongly reflected specular signal travels in very unexpected directions. If, however, the ultrasonic beam travels into the weld metal via the base metal then reflected signals usually occur close to the expected directions, except for vertically polarized shear waves. Furthermore, for a given weld type it is obviously useful to minimize ultrasonic ray paths within the weld material, to minimize both attenuation and curvature of ray paths.     

Field ionization within the forbidden zone

Mass spectra of helium and neon obtained by field ionization in the presence of hydrogen or another low ionization potential gas contain lines indicating noble gas ions with energies exceeding those of the ordinary field ions by 16 or 13 eV, respectively. These ions originate from the apex-adsorbed state within the forbidden zone following excitation by impinging electrons from free-space ionization of the auxiliary gas.     

Asymmetric Oscillation and Acoustic Response from an Encapsulated Microbubble Bound within a Small Vessel

Understanding the dynamics of ultrasonic excited microbubbles bound within microvessels is of significance for novel ultrasonic imaging, drug delivery and therapeutic biomedicad applications. A finite element model （FEM） considering acoustic nonlinearity is developed to describe the asymmetric oscillation and acoustic response from mn encapsulated microbubble bound within a small vessel. Numerical simulation is performed for a 2 μm encapsulated microbubble bound within 8-20μm vessels using 2 MHz ultrasound excitation. The oscillation of the bound microbubble becomes more asymmetric under larger ultrasound pressure or within the smaller vessel. The normalized difference between the major and minor axes of epllipse is estimated to be 2.16%for the 8 μm vessel at an acoustic pressure of 0.5 MPa. In addition, the fundamental component of the acoustic scattering from the bound microbubble is enhanced by 6 dB while the second harmonic component is decreased by approximately 29 dB compared with the free microbubble.     

Bubbles and the odd-state force

We show that the formation of bubbles in spherical Hartree-Fock calculations on ³⁶A depends sensitively on the odd-state effective interaction, being strongly favoured, like alpha clustering, when this is repulsive     

Interaction of Two Nearly Contacting Gas Bubbles Pulsating in a Liquid in an Alternating Pressure Field

JETP Letters - The conditions for the coalescence of two pulsating spherical bubbles in a liquid in a weak low-frequency acoustic pressure field, as well as the conditions for absence of such a...     

Acousto-Optic Diffraction in an Ultrasonic Field of a Width-Profiled Transducer

Acoustical Physics - Acousto-optical diffraction in an ultrasonic field of a slow acoustic mode in paratellurite excited by a hexagonal-shaped piezoelectric transducer has been simulated in a...     

Application of Discrete Huygens Method for Diffraction of Transient Ultrasonic Field

Several time-domain methods have been widely used to predict impulse response in acoustics. Despite its great potential, Discrete Huygens Method (DHM) has not been as widely used in the domain of ultrasonic diffraction as in other fields. In fact, little can be found in literature about the application of the DHM to diffraction phenomenon that can be described in terms of direct and edge waves, a concept suggested by Young since 1802. In this paper, a simple axisymmetric DHM-model has been used to simulate the transient ultrasonic field radiation of a baffled transducer and its diffraction by a target located on axis. The results are validated by impulse response based calculations. They indicate the capability of DHM to simulate diffraction occurring at transducer and target edges and to predict the complicated transient field in pulse mode.     

Magnetic Field Effect on the Cathodic Potential Oscillation of Zinc Electrode in Alkaline Solution

The magnetic field effect (0?C0.47?T) on cathodic potential oscillation of a zinc cathode in an alkaline solution was studied. By applying a magnetic field, the oscillation interval increased. The oscillation was quenched at 0.47?T. In situ bore-scope observation of the cathode during electrolysis in magnetic fields revealed that the solution convection induced by the Lorentz force causes the observed effect.     

LETTER: Some Remarks on the Neutrino Oscillation Phase in a Gravitational Field

The weak gravitational field expansion method to account for the gravitationally induced neutrino oscillation effect is critically examined, then it is shown that the splitting of the neutrino phase into a "kinematic" and a "gravitational" phase is not always possible because the relativistic factor modifies the particle interference phase splitting condition in a gravitational field.     

超强激光作用下相对论电子振荡所导致的谐波辐射

研究发现，在超强激光作用下电子运动的相对论效应可导致高次谐波辐射，采用单电子模型计算分析了不同偏振微光作用下的高次谐波发射，表明圆偏振激光较线偏振激光更有利于高次谐波产生。     

Monopole and Coulomb Field as Duals within the Unifying Reissner-NordstrSm Geometry

We are going to prove that the Monopole and the Coulomb fields are duals within the unifying structure provided by the Reissner-Nordstrom spacetime. This is accomplished when noticing that in order to produce the tetrad that locally and covariantly diagonalizes the stress-energy tensor, both the Monopole and the Coulomb fields are necessary in the construction. Without any of them it would be impossible to express the tetrad vectors that locally and covariantly diagonalize the stress-energy tensor. Then, both electromagnetic fields are an integral part of the same structure, the Reissner-Nordstrom geometry.     

Levitation and Control for an Ordered Group of Particles and Rectilinear Structures in an Ultrasonic Field

Acoustical Physics - A method of control for an ordered group of particles that levitate in an ultrasonic field and structures of rectilinear segments is proposed. An ultrasonic field in air at a...     

The Transverse Oscillation of Coaxial Multiple Beams Propagating along a Magnetic Field in a Vacuum Tube

A fluid Maxwell theory has been derived to study a system of multibeams propagating parallel to an applied axial magnetic field in an evacuated conducting drift tube. The stability analysis is performed for a rigid-rotor and cold-laminar flow equilibria. It is assumed that the particle beams are tenuous and the guiding field is very strong. As a result, the perturbation theory is derived under the condition that the plasma frequency is much smaller than the cyclotron frequency for each beam particle. A dispersion relation is obtained for a special case of sharp-boundary density profiles. The stability properties of infinitely long beams are illustrated in detail for different geometries and various beam parameters. The results agree with those obtained by Uhm [8] in a special case where a solid electron beam propagates through an annular electron beam. The finite geometry effect of the accelerator is discussed briefly. It might have a substantial influence on the behavior of a real device.     

B型超声诊断仪声场参数的测量与计算的一种简化方法

本文概述了B型超声诊断仪声场特性的基本测量和计算方法，提出了一系列典型声压波形的瞬时声压平方函数的时间积分解析表达式，可用来近似计算脉冲声强积分和各种脉冲声强参数．对三种典型超声诊断仪的输出声压波形函数，分别进行数值积分和解析计算，两者的计算结果偏离值均小于±7．0％，表明利用这些公式可使测量过程中的数据采集和计算程序大为简化，在实际应用中具有推广价值．     

Bubbles, shocks and elementary technical trading strategies

In this paper we provide a unifying framework for a set of seemingly disparate models for bubbles, shocks and elementary technical trading strategies in financial markets. Markets operate by balancing intrinsic levels of risk and return. This seemingly simple observation is commonly over-looked by academics and practitioners alike. Our model shares its origins in statistical physics with others. However, under our approach, changes in market regime can be explicitly shown to represent a phase transition from random to deterministic behaviour in prices. This structure leads to an improved physical and econometric model. We develop models for bubbles, shocks and elementary technical trading strategies. The list of empirical applications is both interesting and topical and includes real-estate bubbles and the on-going Eurozone crisis. We close by comparing the results of our model with purely qualitative findings from the finance literature.