恒定流速场与静电场、静磁场的类比

本文将“物理类比法”引入大学物理电磁学部分的教学,将恒定流速场与静电场和静磁场在特征量、场的分布及其描述等方面进行了类比,使学生对电磁场有一个较清晰和全面的认识,对电磁学的理论有一个较深刻的理解和掌握,收到了较理想的教学效果.     

Antiferromagnets in a field and ferromagnets in a random field

A new mean field approach for antiferromagnets in a field is shown to be equivalent to a mean field treatment of ferromagnets in a random field. Phase diagrams of the two systems are analogous.     

When is a field theory a generalized free field?

We show within a scalar relativistic quantum field theory that if either some even truncatedn-point-function vanishes or some multiple commutator of the field operators is a c-number then the field is necessarily a generalized free field.     

External field of a localized charge in unified field theory

The possibility of the existence of localized charged distribution giving rise to a special axially symmetric electrostatic field has been explored in Einstein's unified field theory [2]. The field equations have been studied in two particular cases. In one case the field equations have a solution representing flat space-time along with an electrostatic field which is constant in the direction of the axis of symmetry. For the other case the solution is non-existent.     

Phase field simulation of single bubble behavior under an electric field

Based on the Cahn-Hilliard phase field model, a three-dimensional multiple-field coupling model for simulating the motion characteristics of a rising bubble in a liquid is established in a gas-liquid two-phase flow. The gas-liquid interface motion is simulated by using a phase-field method, and the effect of the electric field intensity on bubble dynamics is studied without electric field, or with vertical electric field or horizontal electric field. Through the coupling effect of electric field and flow field, the deformation of a single rising bubble and the formation of wake vortices under the action of gravity and electric field force are studied in detail. The correctness of the results is verified by mass conservation, and the influences of different electric field directions and different voltages on the movement of bubbles in liquid are considered. The results show that the ratio of the length to axis is proportional to the strength of the electric field when the air bubble is stretched into an ellipsoid along the electric field line under the action of electrostatic gravity and surface tension. In addition, the bubble rising speed is affected by the electric field, the vertical electric field accelerates the bubble rise, and the horizontal direction slows it down.     

On weyl's gauge field in a non-local field

In this paper, a non-local field (i.e. the (x, ψ)-field) is constructed by regarding the spinor (ψ) as the internal freedom attached to each point (x). Since this field is likened to a unified field between the (x)- and (ψ)-fields, the metric is given bydσψ=gλ dx ^λψ. Concerning this, some conformally equivalent relations are considered. Next, Weyl's gauge field is introduced into the concept of connection in order to consider the gauge invariance. Finally, some essential features underlying our non-local field are grasped by formulating some fundamental equations of the spin curvature tensors.     

Phase field simulation of spinodal decomposition under external magnetic field

A computational model was developed to simulate the spinodal decomposition process of ferromagnetic alloys under an external magnetic field. In this model, the temporal evolution of the modulated structure was described by a phase field method, and the magnetic configuration was solved by using a micromagnetic method. The spinodal decomposition and coarsening processes of a single magnetic particle and an A-B hypothetical system under an external magnetic field were simulated using the proposed model. The simulation results show that the precipitated particles were elongated along the direction of the external magnetic field. The dependence of the modulated structure of an A-B hypothetic system on external magnetic field is much more sensitive than that of the single particle structure. The simulation results also demonstrate that the modulation of the external magnetic field is effective even if the spinodal decomposition has been completed and a stable modulated structure was formed.     

Magnetic field tomography

Neutral atoms may be trapped via the interaction of their magnetic dipole moment with magnetic field gradients. One of the possible schemes is the cloverleaf trap. It is often desirable to have at hand a fast and precise technique for measuring the magnetic field distribution. We use for instantaneous imaging the equipotential lines of the magnetic field a diagnostic tool which is based on spatially resolved observation of the fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of resonant laser light within the magnetic field region to be investigated. The inhomogeneous magnetic field spatially modulates the resonance condition between the Zeeman-shifted hyperfine sublevels and the laser light and therefore the amount of scattered photons. We apply this technique for mapping the field of our cloverleaf trap in three dimensions under various conditions. Received 20 March 2001 and Received in final form 12 May 2001     

A new electrostatic field measurement method: The coherent-notch field mill

Conventional electric field mill designs are not able to measure quasi-static atmospheric electric fields in the vicinity of high-voltage power systems. The electric fields generated by such power systems produce severe perturbations to the quasi-static background electric field. Filtering of these perturbations by the field mill circuitry seems to be easy because of their periodically alternating character. However, the operation of a field mill involves an effective signal filtering method, as presented in this paper. Because field mill operation gives rise to amplitude modulation of the incident electric field under measurement, a new technique based on coherent demodulation and notch filtering is proposed. Simulation and experimental results validate the excellent performance of the proposed method for measuring sudden step functions in electric field in presence of a severely perturbed ambient.     

Partial field decomposition of multi-source cyclostationary sound field

The cyclostationary sound field is a kind of special non-stationary field which has obvious modulation phenomena. Conventional planar near-field acoustic holography (PNAH) technique cannot exactly reflect its modulation characteristics. If the cyclic spectral density (CSD) instead of the complex sound pressure is adopted as the reconstruction variable, the modulating wave and carrier wave components of the cyclostationary sound field can be extracted effectively. A new technique called cyclostationary PNAH utilizing the CSD is proposed in this paper. Based on this technique, the problem of partial field decomposition by singular value decomposition (SVD) of multiple incoherent cyclostationary sound sources is researched. The results of numerical simulation and experiments show that the CPNAH technique and SVD decomposition method are effective.     

Magnetic response to applied electrostatic field in external magnetic field

We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.     

磁多极场场参数的理论计算与分析

根据磁多极场的对称性，首先导出了磁多极场磁场分量的泰勒级数展开式，定义了磁多极场的场参数，然后根据毕奥-萨伐尔定律，导出了马鞍型磁多极场线圈的场参数理论计算公式.对各个场参数数量级的大小进行了分析，找出了场参数的递推规律，给出了场参数高阶导数的计算方法，从而能够准确计算整个空间的磁场值.还从简单单根导线计算结果过渡到多根导线或具有某种连续分布的情况. 这对于磁二极场、磁四极场、磁六极场等的应用提供了可靠的理论依据. 关键词： 磁多极场 场参数 马鞍型线圈     

声场与电场作用下空化泡的动力学特性

以液体为工作介质, 利用空化泡的RP控制方程, 模拟分析了无量纲化的电场频率、场强的幅值以及无量纲化的声波频率、 声压幅值的变化对空化泡运动特性的影响. 结果表明: 声场和电场联合作用时, 空化泡运动处于混沌区域范围远高于两者单独作用下空化泡的混沌区域范围. 这不仅对声空化的进一步研究具有重要的理论意义, 而且对于提高和改进空化降解有机污染物的技术也具有指导意义.     

On Weyl's gauge field

A new scalar field, called a measure field, is proposed which plays a rôle of measure assigned to each world point. By measuring all the quantities with a standard given by the above mentioned measure field, it is shown to be possible to write all the field equations in a manifestly gauge-invariant manner. Weyl's gauge field, when it is written in this fashion, is proved to have a negative energy density and has a tachyon-like property inside material particles. It is shown, however, that such a strange field can not come out of the matter.     

耗散系统中原子和场的熵交换与纠缠

研究耗散腔中,二能级原子与单模辐射场在相互作用过程中熵关联的情况。结果表明：原子与场之间存在熵交换现象,更重要的是证明了它们之间的熵交换需要满足一定的条件。同时也计算了原子与场之间的纠缠,发现两子系统间熵交换与纠缠的关系。     

耗散系统中原子和场的熵交换与纠缠

研究耗散腔中, 二能级原子与单模辐射场在相互作用过程中熵关联的情况. 结果表明：原子与场之间存在熵交换现象, 更重要的是证明了它们之间的熵交换需要满足一定的条件. 同时也计算了原子与场之间的纠缠, 发现两子系统间熵交换与纠缠的关系.     

Gravitational anomalies: Antisymmetric tensor gauge field versus bispinor field

It is shown perturbatively that the gravitational anomaly of the chiral bispinor field is twice as large as that of the self-dual antisymmetric tensor gauge field; in the previous literature they were supposed to agree with each other. This implies that a naive application of Fujikawa's path integral method leads to a wrong result for the anomaly of the self-dual antisymmetric tensor gauge field.     

Calculations of field ionization in the field ion microscope

The ionization of a gas atom as it occurs in the field ion microscope is discussed. A wide range of values for the electric field intensity at the metal surface are considered in calculating the ionization occurring both far away from and close to the tip. Ionization distribution curves are calculated and electric fields strengths are determined at points where the distributions peak. Calculations of ionization zone widths and best image conditions are made and a new interpretation of best image conditions is considered. A new field calibration method is suggested.     

Adaptive wave field synthesis for active sound field reproduction: experimental results

Sound field reproduction has applications in music reproduction, spatial audio, sound environment reproduction, and experimental acoustics. Sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. The room response thus reduces the quality of the physical sound field reproduction by WFS. In recent research papers, adaptive wave field synthesis (AWFS) was defined as a potential solution to compensate for these quality reductions from which WFS objective performance suffers. In this paper, AWFS is experimentally investigated as an active sound field reproduction system with a limited number of reproduction error sensors to compensate for the response of the listening environment. Two digital signal processing algorithms for AWFS are used for comparison purposes, one of which is based on independent radiation mode control. AWFS performed propagating sound field reproduction better than WFS in three tested reproduction spaces (hemianechoic chamber, standard laboratory space, and reverberation chamber).     

Modeling spatio-temporal field evolution

Prediction of spatio-temporal field evolution is based on the extraction of a physical law from joint experimental data. This extraction is usually described by a set of differential equations. If the only source of information is a field record, a method of field generators based on nonparametric modeling by conditional average can successfully replace differential equations. In this article we apply the method of field generators to a two-dimensional chaotic field record that describes the asynchronous motion of high-amplitude striations. We show how to choose the model structure in order to optimize the quality of the prediction process.