Nuclear spin conversion in CH F induced by an alternating electric field

The nuclear spin conversion in CH₃F molecules subjected to an alternating electric field was investigated experimentally. The conversion rate was found to be almost unaffected by low electric fields ( V/cm) but sharply increased tenfold when the electric field amplitude exceeds the values ( V/cm) sufficiently high to produce crossings of the ortho and para states of the molecule. A theoretical model for the molecular conversion in alternating electric field was developed. The results of the experiment were found to be in a good agreement with the theory. Received 23 July 1999 and Received in final form 7 September 1999     

Modulation of structure and dynamics of water under alternating electric field and the role of hydrogen bonding

Using Molecular Dynamics simulations, we investigate the effect of alternating (AC) electric field on static and dynamic properties of water. The central question we address is how hydrogen bonds respond to perpetual field-induced dipole reorientations. We assess structural perturbations of water network and changes of hydrogen bond dynamics in a range of alternating electric field strengths and frequencies using a non-polarisable water model, SPC/E, and two distinct polarisable models: SWM4-NDP and BK3. We confirm that AC field causes only moderate structural perturbations. Dynamic properties, including the rates of bond breaking, switching of hydrogen-bonding partners, and diffusion, accelerate with the strength of AC fields. All models reveal a nonmonotonic frequency dependence with fastest dynamics at frequencies around 200?GHz where the period of the field oscillation is commensurate with the average time it takes a typical proton to switch from one acceptor to another. Higher frequencies result in smaller amplitudes of angle oscillations and in reduced probability to complete the switch to another acceptor before the field reversal restores the original configuration. As frequency increases, these effects gradually weaken the influence of the field on the kinetics of hydrogen bonding and the associated rates of translational and rotational diffusion in water.     

Degenerate plasma in a half-space under an external alternating electric field near resonance

The behavior of the electric field near the surface of a half-space filled with a degenerate electron gas in an external ac electric field is studied. The resonance case is considered in which the frequency of the external field is close to that of plasma oscillations. The special features of the behavior of the screened field are analyzed for diffuse reflection of electrons from the boundary. It is shown that there are two layers adjoining the surface in which the behavior of the screened field differs significantly.     

Efficient unstationary holographic recording in photorefractive crystals under an external alternating electric field

The theoretical analysis of unstationary holographic recording in photorefractive crystals under an external alternating electric field is presented. In particular, a step-like ac field resulting in a shifted phase hologram with an amplitude exceeding that of a hologram recorded under an external dc field is shown to be most efficient. The experimental curves for the gain factor Γ obtained in Bi₁₂TiO₂₀ (λ = 0.63μm) under an ac step-like field illustrate the field and spatial frequency dependencies of the hologram amplitude characteristics of the unstationary mechanisms of holographic recording.     

通过磁光效应研究磁性液体在外场下的颗粒成链现象

在对磁性液体的磁光效应的理论分析与实验测量的基础上讨论了其在磁场下的各向异性现象.首先,通过电磁理论对成链的各向异性介质模型的介电张量形式进行了一般性的分析,然后,基于磁性液体的微观理论模型讨论了磁性液体在外加磁场下出现凝聚成链的行为.基于上面的结果,我们将实验可观测量——两种传输模式的折射率差和不同颗粒数的链(长度不同的链)的比例以及磁场强度建立联系.最后,在实验上探测了磁性液体薄膜的透射光偏振状态变化随外磁场的变化,并对测得的数据进行计算机拟合分析,验证了不同长度的链的数目之间的比例关系.     

Efficiency of particle charging by an alternating electric field charger

Alternating electric field charger is a device in which the particles are charged by ionic current and periodically deflected by alternating electric field during their flow through the charger. The oscillatory motion of small amplitude reduces the particle loss within the charger. The results of measurements of mean charge of the particles at the outlet and their penetration through the charger are presented in the paper.     

On the motion of charged particles in an alternating nonuniform electric field

The equations of motion for a charged particle in an electric field featuring a stationary and an oscillating component are considered for the case where the force of friction is linear in the particle velocity. The averaging of these equations over the period of field oscillations is legitimate under some specific conditions. The most general expression for an additional stationary force acting on the particle under these conditions is derived, and the limiting values of this force are found. Applications of the results obtained in the present study are considered. Such applications include the use of pulsed currents in the electrochemical dimensional treatment of materials.     

Modification of the defect structure and electrophysical properties in zinc selenide crystals under the action of an alternating electric field

Modifications in the structure and electrophysical properties of ZnSe crystals subjected to a high alternating electric field of industrial frequency are investigated. It is established that such an action changes their defect structure and dielectric parameters. The latter exhibit different dependences on temperature and photoexcitation wavelength. The modifications are caused by ionic conduction, which is associated with local anomalies in the electric and elastic subsystems of the crystals.     

Dielectric properties of pyridine N-oxide aqueous solution under the static electric field and microwave field

Molecular dynamics simulations of the pyridine N-oxide aqueous solution have been performed in the canonical ensemble macroscopic canonical ensemble (NVT) both in the absence and presence of an external electromagnetic field. It extracts the radial distribution function for each concentration solution, dielectric constant and other information on dielectric properties. Analysing the microscopic dielectric information of the aqueous solution under the static electric field (0–3×10⁹ V/m) and microwave frequencies (2.45G, 0–3×10⁹ V/m), and comparing the dielectric information between the different concentrations and different field strengths, we can get the dielectric properties of two kinds of polar aqueous solution under microwave irradiation. Thus, this project can provide the data of the sample to other correlation studies.     

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.     

Generation of high harmonics by an alternating electric field in superlattices based on graphene

The conductivity of a superlattice based on graphene in an alternating electric field with a vector of intensity directed along the axis of the superlattice is described. The electronic system is described in terms of the kinetic Boltzmann equation in approximation of a constant time of relaxation. Nonlinear responses to the applied harmonic field are calculated and analyzed.     

Undulation instability of lipid membranes under an electric field

The influence of an external electric field on a poorly conductive membrane such as a lipid bilayer is studied theoretically. The unbalanced electric stress created by an ionic current across a non-perfectly flat membrane gives rise to a destabilizing surface energy enhancing undulations. The deformation of a membrane attached to a frame is derived and the electrohydrodynamic instability of a free floating membrane is studied. We find a most unstable mode of undulation, of wavelength in the microm range, connected to the crossover between membrane and solvent dominated dissipations.     

Phase diagram of water under an applied electric field

Simulations are used to investigate for the first time the anisotropy of the dielectric response and the effects of an applied electric field E(ex) on the phase diagram of water. In the presence of electric fields ice II disappears from the phase diagram. When E(ex) is applied in the direction perpendicular to the ac crystallographic plane the melting temperatures of ices III and V increase whereas that of ice Ih is hardly affected. Ice III also disappears as a stable phase when E(ex) is applied in the direction perpendicular to the ab plane. E(ex) increases by a small amount the critical temperature and reduces slightly the temperature of the maximum density of liquid water. The presence E(ex) modifies all phase transitions of water but its effect on solid-solid and solid-fluid transitions seems to be more important and different depending on the direction of E(ex).     

Quasi-2D Monte Carlo simulations of a colloidal dispersion composed of magnetic plate-like particles with magnetic moment normal to the particle axis

We have investigated aggregation phenomena of a colloidal dispersion composed of magnetic plate-like particles by means of Monte Carlo simulations. Such plate-like particles have been modelled as disk-like particles with magnetic moment normal to the particle axis at the particle centre, with the section shape of a spherocylinder. The main objective of the present study is to clarify the influences of the magnetic field strength and magnetic interactions between particles on particle aggregation phenomena. We have concentrated our attention on a quasi-2D system from an application point of view such as the development of surface quality changing technology using such magnetic plate-like particles. A magnetic field is applied along the direction perpendicular to the plane of the monolayer. Internal structures of particle aggregates are discussed quantitatively in terms of radial distribution and orientational pair correlation functions. For the case of strong magnetic interactions between particles, particles form long column-like clusters with their magnetic moments alternating in direction between the neighbouring particles. These tendencies appear under circumstances of a weak applied magnetic field. However, as the magnetic field strength increases, particles incline towards the magnetic field direction, so that particles do not form such clusters.     

Post-deposition dynamics of multiple cluster aggregation on liquid surfaces

A comprehensive simulation model---deposition, diffusion, rotation and aggregation---is presented to demonstrate the post-deposition phenomena of multiple cluster growth on liquid surfaces, such as post-deposition nucleation, post-deposition growth and post-deposition coalescence. Emphasis is placed on the relaxations of monomer density, dimer density and cluster density as well as combined cluster-plus-monomer density with time after deposition ending. It is shown that post-deposition coalescence largely takes place after deposition due to the large mobility of clusters on liquid surfaces, while the post-deposition nucleation is only possible before the saturation cluster density is reached at the end of the deposition. The deposition flux and the moment of deposition ending play important roles in the post-deposition dynamics.     

Transient dynamics of a one‐dimensional Holstein polaron under the influence of an external electric field

Following the Dirac‐Frenkel time‐dependent variational principle, transient dynamics of a one‐dimensional Holstein polaron with diagonal and off‐diagonal exciton‐phonon coupling in an external electric field is studied by employing the multi‐D₂ Ansatz, also known as a superposition of the usual Davydov D₂ trial states. Resultant polaron dynamics has significantly enhanced accuracy, and is in perfect agreement with that derived from the hierarchy equations of motion method. Starting from an initial broad wave packet, the exciton undergoes typical Bloch oscillations. Adding weak exciton‐phonon coupling leads to a broadened exciton wave packet and a reduced current amplitude. Using a narrow wave packet as the initial state, the bare exciton oscillates in a symmetric breathing mode, but the symmetry is easily broken by weak coupling to phonons, resulting in a non‐zero exciton current. For both scenarios, temporal periodicity is unchanged by exciton‐phonon coupling. In particular, at variance with the case of an infinite linear chain, no steady state is found in a finite‐sized ring within the anti‐adiabatic regime. For strong diagonal coupling, the multi‐ Anstaz is found to be highly accurate, and the phonon confinement gives rise to exciton localization and decay of the Bloch oscillations.

     

外电场作用下ZnO分子的结构特性研究

本文以6-311++g(d,p)为基组, 采用密度泛函理论的B3P86方法优化得到了ZnO分子的基态稳定构型, 并计算了不同外电场(-0.05–0.05a.u.)下ZnO基态分子的稳定电子结构, 研究外电场对ZnO基态分子键长、总能量、电荷分布、能级分布、能隙及红外光谱的影响. 结果表明: 外加电场的大小和方向对分子结构和电子特性均有明显影响. 随着正向外加电场的增加, ZnO基态分子的平衡键长先减小后增加, 而分子总能量、振动频率和红外光谱的强度均先增加后减小. 分子的最高占据轨道能量E_H、最低未占据轨道能量E_L和能隙E_g始终处于减小趋势, 因而占据轨道的电子更容易被激发至空轨道. 这一结果可为ZnO分子的电致发光机理研究提供一定的理论参考. 关键词： ZnO 外电场 结构参数 激发     

电场作用下C60富勒烯分子的几何构形与电子结构

采用分子动力学与半经验量子力学相结合的方法,对不同强度电场作用下C60富勒烯分子的体积、形变、电荷分布、偶极矩、系统能量、分子轨道能级等进行了计算,分析了外加电场对C60富勒烯分子几何构形、电子结构的影响.研究结果表明:①在电场作用下,C60富勒烯发生极化,分子沿电场方向伸长,沿垂直电场的方向缩短,体积膨胀.当电场强度增至0.102 a.u.时,C60分子构形破坏.②随着外加电场强度的增加,C60分子的偶极矩增大,系统能量、LUMO,HOMO能级减小,但LUMD,HOMO之间的能隙却先是减小,然后增大.     

On the observation of anomalous electron emission from a thin film under the influence of an outside electric field

Summary It is established that accelerated secondary electrons with very low energies emitted from a thin surface layer where M?ssbauer absorption and normal photoeffect are taking place show two distinctly separated energy lines. The maximum of the first line corresponds to the applied accelerating voltage while that of the second one corresponds to about 30% higher energy. The investigations are performed with a magnetic beta-spectrometer and with an electrostatic analyser. It is found that the intensity of the second, ?anomalous? line depends on the nature of the emitting layer. A number of experiments confirming the reality of the observed effects are reported. This authors of this paper have agreed to not receive the proofs for correction.