Field and Poynting vectors of homogeneous waves in uniaxial and absorbing dielectric media

The propagation of a homogeneous plane wave in uniaxial and absorbing dielectric media is described in detail. Complete expressions for electric displacement field, electric field, magnetic field and Poynting vector are derived using a new formalism that simplifies the interpretation of polarization. These expressions are analysed and verified in some particular situations. Whilst absorption is directly determined by the absorption coeffcient k, the field geometry depends exclusively on the absorption index X for given ordinary and extraordinary refractive indices. When ordinary and extraordinary absorption indices are equal, the field geometry coincides with the field geometry in a transparent medium with the same refractive index as the absorbing medium.     

Deterministic Magnetization Switching Using Lateral Spin–Orbit Torque

Current-induced magnetization switching by spin–orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin–orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, deterministic current-induced SOT full magnetization switching by lateral spin–orbit torque in zero external magnetic field is reported. The Pt/Co/Pt magnetic structure is locally annealed by a laser track along the in-plane current direction, resulting in a lateral Pt gradient within the ferromagnetic layer, as confirmed by microstructure and chemical composition analysis. In zero magnetic field, the direction of the deterministic current-induced magnetization switching depends on the location of the laser track, but shows no dependence on the net polarization of external out-of-plane spin currents. From the behavior under external magnetic fields, two independent mechanisms giving rise to SOT are identified, i.e., the lateral Pt–Co asymmetry as well as out-of-plane injected spin currents, where the polarization and the magnitude of the SOT in the former case depends on the relative location and the laser power of the annealing track.     

Near-field thermal transport in a nanotip under laser irradiation

We report on a systematic study of highly enhanced optical field and its induced thermal transport in nanotips under laser irradiation. The effects on electric field distribution caused by curvature radius, tip aspect ratio, and polarization angle of the incident laser are studied. Our Poynting vectors' study clearly shows that when a laser interacts with a metal tip, it is bent around the tip and concentrated under the apex, where extremely high field enhancement appears. This phenomenon is more like a liquid flow being forced/squeezed to go through a narrow channel. As the tip-substrate distance increases, the peak field enhancement decreases exponentially. A shift of field peak position away from the tip axis is observed. For the incident light, only its component along the tip axis direction has a contribution to the electric field enhancement under the tip apex. The optimum tip apex radius for field enhancement is about 9 nm when the half taper angle is 10°. For a tip with a fixed radius of 30 nm, field enhancement increases with the half taper angle when it is less than 25°. The thermal transport inside the nanoscale tungsten tips due to absorption of incident laser light is explored using the finite element method. A small fraction of light penetrates into the tip. As the polarization angle or apex radius increases, the peak apex temperature decreases. The peak apex temperature goes down as the half taper angle increases, even though the mean laser intensity inside the tip increases, revealing a very strong effect of the taper angle on thermal transport.     

Refractive index of polymethylmethacrylate oriented by fluid temperature under electrical field

We prepared micron and submicron polymethylmethacrylate (PMMA) layers by the spin-coating method. We investigated the possibility to orientate polymer dipoles in electric field in the glass transition area (T _g) and the fluid temperature of PMMA with the aim to increase its refractive index (n) after the layer is cooled below T _g. We have studied the effect of electric field (up to 12 kV cm⁻¹) on change of surface morphology of the layer, dependence of n and contact angle (surface wettability) on the field and dependence of layers orientation on orientation of electric field. The surface morphology was examined using atomic force microscopy (AFM), contact angles were measured by goniometer, film thickness was measured by profilometer, refractive index of films was determined using refractometer. The change of refractive index as dependent on the PMMA layer orientation in electric field depends on temperature and electric field. The highest change in n was found for electric field 11 kV cm⁻¹. The change in contact angle (wettability) on surface of an orientated PMMA layer confirms the dipoles orientation in electric field unambiguously. The orientation of layers causes a “slight” change in their morphology and a “slight” increase of surface roughness only for one direction of field effect. Change in colour for oriented layers does not depend on orientation of electric field.     

各向异性不同含量羟基铁粉颗粒/磁性聚氨酯泡沫的可控力学和声学性能

聚氨酯泡沫(PUFs)被广泛应用于飞机、车辆和许多其他设施中的噪声控制。本文研究的磁性聚氨酯泡沫(MPUFs)是一种新型智能泡沫,其力学和声学特性可通过磁场控制。采用一步全水法制备了添加羟基铁粉颗粒的磁性聚氨酯泡沫(CIPs/MPUFs),在发泡过程中施加一定强度的磁场,磁颗粒沿着外加磁场方向排列成链状有序结构,得到各向异性磁性泡沫。在外加磁场作用下,CIPs/MPUFs内部磁性颗粒发生迁移,材料的力学和声学性能发生改变。实验研究了外加磁场对CIPs/MPUFs力学性能和吸声性能的影响。实验结果表明:在外加磁场条件下,CIPs/MPUFs的储能模量和损耗模量随磁性颗粒含量的增加而增加;CIPs/MPUFs的平均吸声系数变化幅度在1%~7%之间,当颗粒含量为5wt%、制备磁场为200 mT、测试施加1.5 A电流时,CIPs/MPUFs的平均吸声系数增加幅度最大,为6.5%。      

Lasing without or with inversion in an open four-level system with a phase-fluctuation driving field

The effect of exit rate and the ratio of atomic injection rate on gain behaviour has been investigated, and the effects of phase fluctuation on absorption, dispersion and population difference in an open four-level system have been analysed by using numerical simulation from the steady linear, analytical solution. The variation of the linewidth, Rabi frequency of the driving field, the exit rate or the ratio of atomic injection rate can change the lasing properties in the open system. The presence of finite linewidth due to driving-field phase fluctuation prevents the open four-level atomic system from obtaining a high refractive index along with zero absorption.     

Electronic Structure and Physical Characteristics of Dioxin Under External Electric Field

Dioxin is a highly toxic and caustic substance, which widely existed in the atmosphere, soil and water with tiny particles. Dioxin pollution has become a major problem that concerns the survival of mankind, which must be strictly controlled. The bond length, bond angle, energy, dipole moment, orbital energy level distribution of dioxin under the external field are investigated using DFT (density functional theory) on basis set level of B3LYP/6-31G (d, p). The results indicate that with the increase of the electric field, the length of one Carbon-Oxygen bond increases while another Carbon-Oxygen bond decreases. The energy gradually decreases with the electric field, while the change of the dipole moment has an opposite trend. In the infrared spectra, the vibration frequency decreases with the electric field increasing and shows an obvious red shift. Moreover, the ultraviolet-visible absorption spectra under different electric fields are analyzed with TD-DFT (time-dependent density functional theory) method. The wavelength of the strongest absorption peak increases and occurs red shift with the increase of the electric field. All the above results can provide reference for further research on the properties of dioxin under different external electric field.     

Quantum oscillations in magnetoacoustic attenuation of degenerate piezoelectric semiconductors

Effects of parabolic and nonparabolic band structures on ultrasonic waves propagating at an angle relative to the direction of a dc magnetic fieldB in a degenerate semiconductor such as n-type InSb are investigated by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The interaction of conduction electrons with ultrasonic waves is via deformation-potential and piezoelectric couplings. It is found that the absorption coefficient and change in sound velocity oscillate with the dc magnetic field when ultrasonic waves propagate along the dc magnetic field for both parabolic and nonparabolic band structures. However, when the angle is different from zero, the absorption coefficient and change in sound velocity for the parabolic band structure do not oscillate with the magnetic field, due to the reduction of the component of the sound wave vector along the magnetic field, and those for the nonparabolic band structure will still oscillate with the magnetic field, due to the nonlinear effect of the energy eigenvalue equation.Partially supported by National Council of China in Taiwan.     

Induced-dipole-electric-field contribution of atomic chains and atomic planes to the refractive index and birefringence of nanoscale crystalline dielectrics

The induced-dipole-electric-field contribution to the refractive index at any location within a nanometer-scale dielectric is quantified by summing the electronic dipole contributions due to all the surrounding atoms in the dielectric. Using a tetragonal lattice and varying the ratio of lattice constants illustrates the important limiting chainlike and planelike behaviors. Strong polarizing effects and thus high refractive indices occur for an electric field applied along the length of a chain of atoms or applied in a planar direction to a plane of atoms. In contrast, a strong depolarizing effect and thus low refractive indices occur for an electric field applied normal to a chain of atoms or applied normal to a plane of atoms. Birefringence is increased or decreased by the simultaneous presence or absence of polarizing and depolarizing effects.     

Photodetachment of negative hydrogen ion in circularly polarized monochromatic and bichromatic laser fields

We theoretically have investigated the detachment of negative hydrogen ion in circularly polarized monochromatic and bichromatic laser fields by calculating the photoelectron momentum distributions (PMDs). We find that the PMDs are controlled by the electric field of laser pulse. For circularly polarized monochromatic laser fields, the PMDs are perfect and isotropic rings, and the photodetachment rates in random direction are same. For this case, the photoelectron momentum spectra directly reflect the electronic distributions of negative hydrogen ion. For circularly polarized bichromatic laser field, the PMDs are inversion asymmetric, but symmetric about a certain axis. The emission directions of the photoelectrons vary with the electric field shape, that is to say that the emission directions of the photoelectrons vary with the carrier-envelope (CE) phases, which decide the electric field of laser pulse. The maximal photodetachment rates and the spectra shape, however, are same for the different CE phases.     

Radiation from a current sheet at the interface between a conventional medium and anisotropic negative refractive medium

In this paper we investigate the radiation from a current sheet at the interface between semiinfinite isotropic positive refractive medium and anisotropic negative refractive medium. The distribution of the electric and magnetic fields in two regions and Poynting vectors associated with propagating and evanescent waves are calculated. The reasons for the singularity of the electric or magnetic field are briefly provided if the waves are evanescent in two media.     

Ni/PSt/TiO2多层芯-壳结构电磁响应

制得了粒径均匀、兼有电磁响应的镍／聚苯乙烯／二氧化钛(Ni／PSt／TiO2)三层核-壳结构的复合微球．用红外光谱、X射线衍射及透射电镜对微球进行了表征，研究了包覆前后微粒的沉降性、导电性、耐蚀性、热稳定性以及在电、磁场作用下的运动．结果表明，所制得的镍／聚苯乙烯／二氧化钛(Ni／PSt／TiO2)复合微球对电磁场有良好的响应性，在相互垂直的电场与磁场作用下排列形成了一种网状花样结构，为利用电、磁场调控排列粒子成三维有序结构提供基础．     

磁性液体纳米磁性颗粒磁场诱导链状结构研究

研究了磁性液体在有、无外加磁场作用时磁性液体中纳米磁性颗粒的微观排列结构, 发现无外加磁场作用时磁性颗粒随机均匀分布在载液中, 有外加均匀磁场作用时, 磁性颗粒沿磁场方向排列成均匀链状结构。当外加均匀磁场强度为11.1 kA/m, TEM照片清晰显示磁性颗粒排列成一条链状结构, 随着外加均匀磁场强度逐渐增强到28.6 kA/m, 更多磁性颗粒沿磁场方向紧密排列成链状结构。在外加梯度磁场作用下, 铁芯中心处磁场强度为28.7 kA/m时, 大量磁性颗粒聚集于线圈中心轴附近形成复杂链状团簇结构; 沿r轴方向磁场强度较弱的地方, 较少磁性颗粒排列成链状结构。当磁场梯度从1.73 kA/m²逐渐增加到5.11 kA/m²时, 磁场梯度轴线上的磁性颗粒团簇结构由稀疏逐渐变成为密集。磁场诱导磁性颗粒链状排列结构的研究对磁性液体在机械工程、生物工程、热力工程等领域的应用有重要意义。     

Optical properties of the polarized Dirac vacuum

An investigation is made of the propagation of laser radiation through the Dirac vacuum polarized by a strong electric field. Calculations are made of the refractive index of the vacuum and the angle of rotation of the plane of polarization of the radiation. The possibility of measuring strong electric fields is assessed. Pis’ma Zh. Tekh. Fiz. 24, 45–47 (July 26, 1998)     

Thick film resistors in low-temperature resistance thermometry in high magnetic fields

Thick film resistors exhibit a strong dependence on temperature in the cryogenic range below 20 K. In this range the temperature coefficient of resistance is estimated to be comparable to that of commonly used resistance thermometers.The resistance change by the action of the magnetic field is observed to be only small and independent of magnetic field direction. By using these resistors in cryogenic resistance thermometry in intense magnetic field the temperature error due to the magnetoresistance is shown to be only small in comparison with frequently used sensors.According to these results thick film resistors are reported to offer an interesting alternative in cryogenic resistance thermometry within intense magnetic fields.     

Optical phase contrast measurement of ultrasonic fields

This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (λ_l = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180° about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields)     

Oscillations in longitudinal magnetoresistance in single-crystal films of bismuth

Theoretically, it has been shown by Erukhimov and Tavger that, when the magnetic and electric fields are in the same direction and parallel to the film surface, a change in the film thickness or the magnetic field leads to oscillations in conductivity for experimentally attainable conditions. We report small amplitude oscillations in the longitudinal magnetoresistance of single-crystal bismuth films in weak magnetic fields at liquid nitrogen temperature, due to the influence of the magnetic field on size quantization.     

The experimental observation and investigation of defects in glass forming substances with selenium as an example by viscosimetry in magnetic and electric fields

The effect of magnetic and electric fields influence on selenium viscosity is got. The effect dependence on temperature, field strenght and direction are investigated. Using quasidefects notion the qualitative explanation of the effect is given.     

Optimizing band width and resolution in micro-free flow electrophoresis

The broadening mechanisms for micro-free flow electrophoresis (micro-FFE) have been investigated using a van Deemter analysis. Separation power, the product of electric field and residence time, is presented as a parameter for predicting the position of sample streams and for comparing separations under different conditions. Band broadening in micro-FFE is governed by diffusion at lower linear velocities and a migration distance-dependent mechanism at higher linear velocities. At higher linear velocities, the parabolic flow profile is elongated, generating a distribution of analyte residence times in the separation channel. This distribution of residence times gives rise to a distribution of migration distances in the lateral direction since analytes spend different amounts of time in the electric field. Equations were derived to predict the effect of electric field and buffer flow rate on broadening. Experimental data were collected to determine whether the derived equations were useful in explaining broadening caused by diffusion and hydrodynamic flow at different linear velocities and electric fields. Overall there was an excellent correlation between the predicted and experimentally observed values allowing linear velocity and electric field to be optimized. Suppression of electroosmotic flow is proposed as a means of reducing micro-FFE band broadening due to hydrodynamic effects and maximizing resolution and peak capacity.     

The strip dielectric breakdown model

This paper reports on the analysis of the strip dielectric breakdown (DB) model for an electrically impermeable crack in a piezoelectric medium based on the general linear constitutive equations. The DB model assumes that the electric field in a strip ahead of the crack tip is equal to the dielectric breakdown strength, which is in analogy with the classical Dugdale model for plastic yielding. Using the Stroh formalism and the dislocation modeling of a crack, we derived the relationship between the DB strip size and applied mechanical and electrical loads, the intensity factors of stresses and electric displacement, and the local energy release rate. Based on the results, we discussed the effect of electric fields on fracture of a transversely isotropic piezoelectric ceramic by applying the local energy release rate as a failure criterion. It is shown that for an impermeable crack perpendicular to the poling direction, a positive electric field will assist an applied mechanical stress to propagate the crack, while a negative electric field will retard crack propagation. However, for an impermeable crack parallel to the poling direction, it is found that the applied electric field does not change the mode I stress intensity factor and the local energy release rate, i.e., the applied electric field has no effect on the crack growth.