Regular Electric Field in Electromagnetic Coupled to a Scalar Field

In the framework of an electromagnetic field coupled nonminimally with a scalar field in flat spacetime, the existence of a non-singular electric field is proved for a point electric charge or electric monopole. In analogy with the Maxwell-dilaton system introduced by Gibbons and Wells, first, a Maxwell-anti-dilaton system is constructed where the radial electric field of a static electric monopole is coupled to an anti-dilaton. The field equations are solved analytically for the electric and dilaton fields and observe the nonsingular electric field. Also, the self-energy of the electric monopole is found to be finite. Furthermore, the formalism to a Maxwell-scalar field is generalized where a mechanism is introduced upon which the coupled regular-electric field and scalar field is obtained. The formalism shows that for a given regular electric field there are two supersymmetric coupling functions corresponding to a scalar and a phantom field.     

Finite temperature field from stochastic mechanics

Stochastic mechanics of Nelson when generalized to positive temperature for a scalar field, gives rise to a stochastic field which appears to be a hybrid of euclidean and minkowskian field if the usual value of the diffusion parameter is taken. The stochastic process associated with it is a gaussian non-Markov process. The thermal expectations of this stochastic field fails to satisfy the KMS periodic condition. If the diffusion parameter is allowed to continue analytically to a purely imaginary value, the resulting field can be identified with the usual finite temperature quantum field in minkowskian space-time. The relation of this field with that of thermo field dynamics is discussed.     

超导磁体剩余磁场对软磁材料测试的影响

超导磁体体积小,能够获得强磁场,磁场稳定度、均匀度很高,因此,在磁学测量设备中应用很广泛.美国Quantum Design公司的高精度磁学测量系统采用的就是超导磁体,最高磁场能够达到7 T.由于超导磁体材料本身缺陷的钉扎作用,在磁体退磁后,磁体内部有剩余磁场,有时能够大于30 Oe.由此产生的磁场误差将导致测试的矫顽力、剩磁等数据不准确,甚至导致反向的磁滞回线.设置的磁场初始值不同,剩余磁场的大小也不同;初始磁场越大,剩余磁场越大.这种剩余磁场效应在软磁材料测试过程中表现得尤为明显,产生的测试误差不可忽略,必须进行磁场误差修正才能得到正确的结果.本文阐明了超导磁体产生剩余磁场的原因、影响因素和规律,详述了测试软磁材料可能遇到的问题,并给出解决方法.     

Magnetic field driven domain-wall propagation in magnetic nanowires

The mechanism of magnetic field induced magnetic domain-wall (DW) propagation in a nanowire is revealed: A static DW cannot exist in a homogeneous magnetic nanowire when an external magnetic field is applied. Thus, a DW must vary with time under a static magnetic field. A moving DW must dissipate energy due to the Gilbert damping. As a result, the wire has to release its Zeeman energy through the DW propagation along the field direction. The DW propagation speed is proportional to the energy dissipation rate that is determined by the DW structure. The negative differential mobility in the intermediate field is due to the transition from high energy dissipation at low field to low energy dissipation at high field. For the field larger than the so-called Walker breakdown field, DW plane precesses around the wire, leading to the propagation speed oscillation.     

采用分布式球形阵列的球谐波域声场分离方法

为从测得的混合声场信号中提取出需要的目标声场,提出一种基于分布式球形传声器阵列的声场分离方法。该方法依据声场的球谐波分解,利用阵列各传声器采集到的声场声压信号,获得目标声场与干扰声场的球谐波展开系数,进而估计目标声场。该方法利用声场以不同中心展开的球谐波系数之间的变换关系,直接建立传声器测量声压信号与整体坐标系下声场展开系数的方程,与传统的分布式球形阵列声场分离方法,即先求解局部坐标系下声场展开系数,再变换为整体展开系数的方法,进行比较。分别通过数值仿真和实验说明了提出方法的有效性。结果表明:该方法能够从混合声场中较准确地估计出目标声场,并且在干扰声场能量增大时,保持了较小的声场估计误差,相比于传统方法误差增加更少。     

Evolution of the Photon-number Probability Distribution in the System of a Three Level Atom with an Added Kerr-like Medium

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高速飞行器磁控阻力特性

采用低磁雷诺数磁流体数学模型,对外加磁场下的高超声速半球体流场进行数值模拟.选取三种简单理想磁场(轴向、径向、周向均布磁场),分析了不同磁场类型对流场结构、气动阻力与洛伦兹阻力的影响及作用机理.研究发现,轴向磁场径向"挤压"效应使得激波外形凸出,且壁面静压存在"饱和现象";径向磁场存在轴向"外推"效应,较大的磁场强度会导致肩部形成高温区;周向磁场下感应电场的存在导致增阻效果很差.进而对比了两种相同驻点磁感应强度特殊分布磁场(偶极子磁场、螺线管磁场)下的流场,发现了不同于理想磁场的径向"扩张"效应.按增阻效果从大到小依次为径向磁场、螺线管磁场、轴向磁场、偶极子磁场、周向磁场.     

Rapid magnetization reversal in magnetic small particles induced by non-static bias field

Magnetization reversal processes by a switching field in single-domain nano-sized magnetic particles in the presence of a small transverse non-static bias field are studied. Applying an oscillating bias field instead of a static field, the reversal time becomes much shorter when the switching field is slightly stronger than the effective anisotropy field. A pulsed bias field of a suitably chosen duration in the nanosecond scale is found to induce a rapid switching, even when the switching field is smaller than the anisotropy field. The dependence of the reversal time on the frequency of an oscillating bias field and the duration of a pulsed bias field are studied. The present work thus complement the earlier studies on switching in the presence of a static bias field.     

An ampere-like law for displacement vector field and near-field optical microscopy

We make up a novel and simple theory for near field and near-field optical microscopy (NOM). Our theory is composed of two parts. The first is a formulation to calculate the scattered near field of light by a small dielectric. We state that a wavenumber-vector-independent picture appears in the theory of the near field, and we find that this is expressed by an Ampere-like law for the displacement vector field. The second part is a formulation of field intensity for far field observation and near field observation from a unified point of view. We suggest a theoretical formula for the field intensity corresponding to the NOM image and demonstrate how to understand the relation between the near field and this image.     

Induced field of an electromagnetic vibrator above a conducting screen placed in a microwave beam

The induced field of a cylindrical electromagnetic vibrator with spherically rounded ends is calculated. The vibrator is above a flat screen placed in a linearly polarized quasi-optical microwave beam. The plane of the screen is perpendicular to the Poynting vector of the radiation. The axis of the vibrator is aligned with the vector of the exciting field electrical component. In calculation, the length of the vibrator and the vibrator-screen distance were varied, while its diameter and the initial field were kept constant. It is found that the induced field of the vibrator with a length close to the half-wavelength of the field is maximal at the ends of the vibrator and the field strength resonantly depends on the length of the vibrator. The shortening of the “half-wavelength” vibrator that provides a maximal induced field is determined. The result of numerical simulation is to an extent intriguing. It is revealed that the induced field of a resonance half-wavelength vibrator rises considerably when the vibrator-screen distance becomes shorter than the quarter-wavelength of the field. The Q factor of an equivalent electromagnetic oscillating circuit characterizing the vibrator also grows, and the induced field more and more concentrates between the screen and the surface of the vibrator’s ends facing the screen. Full-scale experiments qualitatively support theoretical predictions. The results allow researchers to considerably extend the application area of vibrators as initiators of breakdown in high-pressure gases to ignite microwave discharges in quasi-optical beams with a low initial field.     

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.     

光电子发射引起的系统电磁脉冲模拟研究?

基于给定光电子的时间、能量谱,分析研究了从有界平面金属向自由空间发射的光电子所引起的系统电磁脉冲效应;采用2.5维全电磁粒子模拟(PIC)程序模拟研究了光电子在空间的运动及分布规律、空间电磁场的组成成分及各组分场的特性。模拟与分析表明:系统电磁脉冲的空间电磁场由直流本底场和辐射场两部分组成。直流场是径向场,随距离的增大迅速衰减;而辐射场又由两部分组成,一是电子从金属平板发射过程中产生的超辐射,二是电子在空间运动过程中产生的辐射场。对两种辐射场特性进行了深入的分析和研究。     

基于磁通门和时域数字鉴频的磁场锁定系统

永磁型磁共振仪器的磁体易受温度和其他环境磁场干扰,造成主磁场波动,进而影响仪器测量的重复性和准确性．本文讨论了两种解决磁场波动的锁定方法：一方面,通过磁通门传感器对环境波动引起的瞬态磁场进行高灵敏探测,然后采用现场可编程门阵列进行实时处理并计算磁场补偿量;另一方面,针对环境温度变化引起的缓慢磁场偏移,则采用时域数字鉴频锁场方法,在对锁样品进行射频激发后,将磁共振信号通过混频变换到较低的频率范围,再转换为方波,然后直接送入现场可编程门阵列进行周期测量,并计算磁场补偿量．将两种方法获得的磁场补偿量叠加后,再转换为电流信号驱动安装在磁体上的B₀补偿线圈,并研制了一套磁场锁定系统,以实现对磁场的锁定.在0.5 T食品快检磁共振分析仪上进行测试验证,结果显示当受到瞬态干扰时,可将磁场稳定在±4 Hz(对应磁场为±0.093 9μT)范围内,同时也可以精准测量温度造成的磁场偏移,该结果验证了本文磁场锁定方法的可行性．     

两种外磁场形式对介质面次级电子倍增的抑制

利用自编1D3V PIC程序,数值研究了不同外加磁场方式对次级电子倍增抑制的物理过程,给出了次级电子数目、平均能量、密度、运动轨迹、渡越时间、介质表面静电场及沉积功率等物理量时空分布关系。模拟结果表明:不同方向外加磁场抑制次级电子倍增的机理有所不同。轴向外加磁场利用电子回旋运动干扰微波电场对电子加速过程,使其碰壁能量降低以达到抑制二次电子倍增的效果;横向外加磁场利用电子回旋漂移过程中,电子半个周期被推离介质表面（不发生次级电子倍增）,半个周期被推回介质表面（降低电子碰撞能量）的作用机理,达到抑制二次电子倍增的效果。讨论了横向磁场在回旋共振下,电子回旋同步加速导致回旋半径增大,电子能量持续增加的特殊过程。两种外加磁场方式都可以通过增加磁场达到进一步抑制次级电子倍增的目的。轴向外加磁场加载容易,但对磁场要求较高;横向外加磁场需要磁场较低,但加载较为困难。     

脉冲电场测试中的激光供电技术

为解决脉冲电场测试系统中的供电问题，设计了一套激光光纤供电系统，该系统由激光器、多模光纤及光电池构成。重点研究了激光器与光纤的耦合问题，设计了透镜系统对激光器输出光束进行准直和压缩。通过MOCVD法研制了GaAs光电池，并制作了椭球形"光伏眼"来提高光电转换效率。仿真和实验表明:采用透镜耦合时，激光器与光纤的耦合效率可达80%以上，远远高于直接耦合时的16%，改进后的"光伏眼"耦合效率相比直接耦合时提高了54.5%，激光供电系统的转化效率在40%以上。该系统的研制为解决脉冲电场的供电问题提供了一种方案。     

涡流型切割磁铁的理论分析和模拟计算

从理论上推导了涡流型切割磁铁的漏场变化规律.以上海同步辐射装置(SSRF)用涡流型切割磁铁为例,进行了分析性计算和讨论,并与OPERA程序模拟计算的结果进行了比较.在此基础上,提出了降低漏场的方法和措施.     

Turbulent diamagnetism in flowing liquid sodium

The nature of Ohm's law is examined in a turbulent flow of liquid sodium. A magnetic field is applied to the flowing sodium, and the resulting magnetic field is measured. The mean velocity field of the sodium is also measured in an identical-scale water model of the experiment. These two fields are used to determine the terms in Ohm's law, indicating the presence of currents driven by a turbulent electromotive force. These currents result in a diamagnetic effect, generating magnetic field in opposition to the dominant fields of the experiment. The magnitude of the fluctuation-driven magnetic field is comparable to that of the field induced by the sodium's mean flow.     

Effect of radio frequency field on toroidal plasma parameters

Low temperature plasma parameters in a toroidal magnetic field are measured. The effect of an externally applied perpendicular electric field on the plasma parameters is studied. The lifetime of the plasma is measured in the presence and absence of the RF electric field. Decrease in the plasma lifetime in the presence of RF field is attributed to detrapping of the primary electrons to a larger volume. Plasma lifetime increases when a small vertical magnetic field is added to the toroidal magnetic field.     

Interaction of a magnetic vortex with the probe field of a magnetic force microscope

The interaction of a magnetic vortex in a circular ferromagnetic nanoparticle with the probe field of a magnetic force microscope (MFM) is theoretically investigated. In the calculations, the probe field is approximated by the point dipole field. The rigid magnetic vortex model is used to describe the vortex state of magnetization. It is found that the effect of the probe field on the rigid magnetic vortex shell is similar to the effect of a uniform magnetic field parallel to the particle plane. The effect of the Z component of the probe field on the core of the vortex results in mutual probe-vortex attraction or repulsion. It is shown that the magnetization direction of the core of the vortex in the MFM probe field can be changed without a change in the shell vorticity direction.     

外加交变电场对光折变基频空间电荷场瞬态特性的影响

利用“跳跃模型”讨论外加交变电场（包括正弦和方波电场）对光折变基频空间电荷建立的影响,给出了空间电荷场基频分量随时间、外加交流电场振幅频率等变化的通解表达式。发现基频空间电荷场虎部和实部的振荡频率分别是外加交流电场振荡频率的两倍和一倍。当外加交变电场频率较大时光折变光栅是相移型的。这和基于“带导模型”给出的数值结果相符。