One method of calculating Cerenkov losses of spatially extended charged systems

In this article, we shall study the Cerenkov radiation of spatially extended uniformly charged systems (in particular, systems whose charge is distributed over the volume of an ellipsoid of revolution, over the surface of a sphere, and over an infinitely thin ring) and volume currents moving at constant velocity along the optical axis of a uniaxial transparent ferrodielectric.The authors express their appreciation to Professor A. A. Sokolov for his discussion of the results.     

Influence of charge relaxation on the capillary disintegration of a jet of a viscous dielectric liquid placed in an electrostatic field collinear with the axis of the jet

A dispersion relation is derived for capillary waves with an arbitrary symmetry on the surface of a charged jet of a finite-conductivity viscous liquid placed in an electric field collinear with the axis of the jet. Analytical calculations are carried out in an approximation that is linear in dimensionless wave amplitude. In the case of axisymmetric waves, the instability of which causes disintegration of the jet into drops, the finiteness of the potential equalization rate has a noticeable effect only for jets of poorly conducting liquids. The charge relaxation shows up in that “purely relaxation” periodic and aperiodic liquid flows arise. When the conductivity of the liquid declines, the instability growth rates for unstable waves increase and their spectrum extends toward short waves. A charge present on the surface of the jet enhances its instability. An increase in the charge surface diffusion coefficient variously influences the capillary and relaxation branches of the solution: the damping ratio increases in the former case and decreases in the latter. As the diffusion coefficient rises, relaxation flows may become unstable.     

High Pressure as a Tool for Characterizing Charge Carriers in a Conducting Polymer

A characteristic feature of conducting polymers is the existence of localized charge carriers. The localization process is closely related to the charge carrier-phonon interaction, which is a function of local molecular properties of the polymer chain on which the carriers are localized. Depending on this interaction in conducting polymers with a non-degenerate ground state singly charged polarons or doubly charged bipolarons may exist. It will be shown that high pressure is a useful tool for studying charge carrier properties by influencing the local molecular conformation. A transition between both types of charge carriers is observed in polypyrrole.     

Nonlinear analytical asymptotic investigation of oscillations of nonaxisymmetric modes of a charged jet of an ideal liquid

Technical Physics - A jet of an ideal incompressible conducting liquid with a uniformly charged surface is considered. The jet moves at a constant velocity along the symmetry axis of its...     

均匀带电细圆环电场的级数解

根据点电荷场强公式和电场叠加原理,导出了均匀带电细圆环电场的级数表达式,进而讨论了均匀带电细圆环平面内、中心轴线上和远区的电场.     

A wire trap for neutral atoms

We present new ways of trapping a neutral atom with static electric and magnetic fields. We discuss the interaction of a neutral atom with the magnetic field of a current carrying wire and the electric field of a charged wire. Atoms can be trapped by the 1/r magnetic field of a current-carrying wire in a two-dimensional trap. The atoms move in Kepler-like orbits around the wire and angular momentum prevents them from being absorbed at the wire. Trapping was demonstrated in an experiment by guiding atoms along a 1 m long current-carrying wire. Stable traps using the interaction of a polarizable atom with the electric field of a charged wire alone are not possible because of the 1/r ² form of the interaction potential. Nevertheless, we show that one can build a microscopic trap with a combination of a magnetic field generated by a current in a straight wire and the static electric field generated by a concentric charged ring which provides the longitudinal confinement. In all of these traps, the neutral atoms are trapped in a region of maximal field, in theirhigh-field seeking state.Dedicated to H. Walther on the occasion of his 60th birthday     

Effect of targets on plasma focus dynamics

Shadowgraphs were taken of a 3-kJ plasma focus in the presence of a flat disc target placed downstream of the anode and a 1-mm wire target inserted along the axis at the anode. It was found that: (i) the flat disc target does not affect the dynamics of the focus proper when it is placed downstream at a distance greater than the anode radius; (ii) the current sheet moves over the disc and forms a pinch beyond it as though the disc had become a new anode; and (iii) the plasma focuses strongly onto a 1-mm wire on-axis. These observations may be used to design beam-target experiments in a plasma focus machine. They indicate the possibility of focus-fiber experiments, and also raise the possibility of and indicate the guidelines for designing a sequential focus device     

Electrostatic interaction of a spherical particle in the vicinity of a circular orifice

The electrostatic interaction of a charged spherical particle in the vicinity of an orifice plane has been investigated in this paper.The particle can creep along the axis of the orifice and is immersed in a bulk electrolyte.By solving the Poisson-Boltzmann problem,we have obtained the effective electrostatic interaction for several values of reduced orifice radius h,including the cases of h > 1,h = 1 and h < 1.Two kinds of boundary conditions of the orifice plane are considered.One is the constant potential model corresponding to a conducting plane,the other is the constant charge model.In the constant potential model,there is an electrostatic attraction between the particle and the orifice plane when they get close to each other,while there is a pure electrostatic repulsion in the constant charge model.The interactions in both boundary models are sensitive to the parameters of the reduced orifice radius,the reduced particle-orifice distance,surface charge densities of the particle and orifice plane,and the reduced Debye screen constant corresponding to the salt-ion concentration and ion valence.     

Analytic solutions to Maxwell–London equations and levitation force for a general magnetic source in the presence of a long type-II superconducting cylinder

The interaction between a general magnetic source and a long type-II superconducting cylinder in the Meissner or mixed state is studied within the London theory. We first study the Meissner state and solve the Maxwell–London equations when the source is a magnetic monopole located at an arbitrary position. Then the field and supercurrent for a more complicated magnetic charge distribution can be obtained by superposition. A magnetic point dipole with arbitrary direction is studied in detail. It turns out that the levitation force on the dipole contains in general an angular as well as a radial component. By integration we obtain the field and supercurrent when the source is a two-dimensional monopole (a magnetically charged long thread along the axial direction), from which the results for a two-dimensional point dipole easily follow. In the latter case the levitation force points in the radial direction regardless of the orientation of the dipole. The case for a current carrying long straight wire parallel to the cylindrical axis is solved separately. The limit of ideal Meissner state is discussed in most cases. The case of mixed state is discussed briefly. It turns out that vortex lines along the axial direction and vortex rings concentric with the cylinder have no effect outside the cylinder and the levitation forces remain the same as in the case of the Meissner state.     

Ground state energies of neutral and negatively charged donors in nanowire superlattice

Using the Bastard-type trial function for the neutral donor and the Hylleraas-type trial function for the negatively charged donor, we investigate the effect of donor positions inside the cylindrical GaAs/Ga(Al)As nanowire superlattice on their ground state energies. Results of calculation, presented in the form of contour plots of the energies corresponding to different donor positions along a cross section through symmetry axis, show a close relationship between the energies of the neutral and negatively charged donors and the charge distributions in one- and two-electron nanowire superlattices, respectively, at the point of their locations. The higher the charge density resulting from the unbound electron at a point in the heterostructure, the lower are the ground state energies of the neutral and negatively charged donors located at this point.     

导电箔对于相对论环形束的约束作用分析及其对束流群聚过程影响的初步实验结果

分析导电箔上的镜像电荷对环形束的约束作用,给出了可用于设计选择聚焦环形束的导电箔几何尺寸的计算结果。利用已有的X波段相对论速调管(RKA)进行了初步的镜像电荷聚焦RKA的实验。虽然实验中的导电箔对电子束的通过率只有0.88,但结果表明导电箔对RKA的束流有一定聚焦作用,不影响束流群聚过程。     

Heat transport over nonmagnetic lithium chains in LiCuVO<Subscript>4</Subscript>, a new one-dimensional superionic conductor

The thermal conductivity of three single-crystal samples of the quasi-one-dimensional spin system of LiCuVO₄ with different concentrations of defects (primarily, vacancies on the lithium sublattice) was measured along the crystallographic a axis (along the nonmagnetic lithium chains) in the temperature interval 5–300 K. An increase in thermal conductivity from that of the crystal lattice was revealed for T>150–200 K. This increase can be accounted for only by assuming LiCuVO₄ to be a superionic conductor. This assumption was confirmed by measuring its electrical conductivity in the temperature interval 300–500 K. Li⁺ ions move over vacancies on the lithium sublattice (conducting channels) and act as charge carriers in LiCuVO₄. It is shown that LiCuVO₄ is a fairly good superionic conductor with application potential.     

磁环中非晶丝的阻抗效应分析

依据Landau-Lifshitz阻尼项和Gilbert阻尼项的磁矩转动方程,提出统一形式的磁化率张量表达式.基于等效磁导率将非晶丝中各向异性的电磁场求解问题转化为等效的各向同性问题,进而分析了套在绝缘磁环或导电磁环中非晶丝的阻抗.采用基于有限元的数值方法仿真磁环中非晶丝的阻抗,仿真结果验证了理论分析结论.理论分析和仿真实验均表明,外磁体的附加阻抗将严重降低阻抗变化率,破坏巨磁阻抗特性.为此,提出采用回路形式降低附加阻抗的方法,并基于仿真实验验证了该方法的有效性. 关键词： 巨磁阻抗效应 非晶材料 Maxwell方程 有限元     

The Method of Images applied to the grounded sphere: The problem of the ground wire

The Method of Images poses an important difficulty when used to solve the problem of a charge in the presence of a grounded conducting sphere. This arises from the fact that the sum of the inducing charge and the image charge is different from zero. As a consequence, there is a monopole field far from the system, and any ground wire physically connected to the sphere will carry an electric current, changing the initial balance of charges until a new equilibrium is reached. The approach taken in this paper assumed an infinite straight wire connecting the sphere to ground. The charge distribution over the surface of the conductors was calculated, and the results analyzed. It was shown that the thinner the wire, the lower will be its total charge, and the closer will be the calculated charge density at the surface of the sphere to the conventional solution by the Method of Images.     

Stability of a charged drop near a conductor wall

The effect of conductor boundaries on the deformation and stability of a charged drop is presented. The motivation for such a study is the occurrence of a charged conductor drop near a conductor wall in experiments (Millikan-like set-up in studies on Rayleigh break-up) and applications (such as electrospraying, ink-jet printing and ion mass spectroscopy). In the present work, analytical (linear stability analysis (LSA)) and numerical methods (boundary element method (BEM)) are used to understand the instability. Two kinds of boundaries are studied: a spherical, conducting, grounded enclosure (similar to a spherical capacitor) and a planar conducting wall. The LSA of a charged drop placed at the center of a spherical cavity shows that the Rayleigh critical charge (corresponding to the most unstable l = 2 Legendre mode) is reduced as the non-dimensional distance ?d = (b - a)/a decreases, where a and b are the radii of the drop and spherical cavity, respectively. The critical charge is independent of the assumptions of constant charge or constant potential conditions. The trans-critical bifurcation diagram, constructed using BEM, shows that the prolate shapes are subcritically unstable over a much wider range of charge as [Formula: see text] decreases. The study is then extended to the stability of a charged conductor drop near a flat conductor wall. Analytical theory for this case is difficult and the stability as well as the bifurcation diagram are constructed using BEM. Moreover, the induced charges in the conductor wall lead to attraction of the drop to the wall, thereby making it difficult to conduct a systematic analysis. The drop is therefore assumed to be held at its position by an external force such as the electric field. The case when the applied field is much smaller than the field due to inherent charge on the drop ((a(3)ρg)/(3ε(0)Ψ(2)) ? 1 is considered. The wall breaks the fore-aft symmetry in the problem, and equilibrium, predominantly prolate shapes corresponding to the legendre mode, l = 2 , are observed. The deformation increases with increasing charge on the drop. The breakup of the prolate equilibrium shapes is independent of the legendre modes of the initial perturbations. The prolate perturbations are subcritically unstable. Since the equilibrium prolate shapes cannot continuously exchange instability with equilibrium oblate shapes, an imperfect transcritical bifurcation is observed. A variety of highly deformed equilibrium oblate shapes are predicted by the BEM calculations.     

Axial magnetostatics of a ring current in a Kerr field

The electromagnetic fields generated by a ring current around a Kerr black hole have been found. The acceleration of a charged particle by a force electric field along the rotation axis is investigated in the constructed model, as applied to the astrophysics of quasars.     

Molecules on kepler orbits: An experimental study

We have demonstrated experimentally that polar molecules revolve around the inner electrode of a charged cylindrical capacitor in helical trajectories that result from a superposition of a translational motion along and an orbital motion around the cylinder axis. In this way molecular beams can be guided over any given distance. The results have been obtained for nozzle beams of NaCl, NaBr, and NaI seeded in Kr. The capacitor bent into a toroid may be used as a storage ring for polar molecules in high field seeking rotational states.     

Magnetoresistance of the quasi-one-dimensional conductor NbSe<Subscript>3</Subscript> with a charge density wave in magnetic fields of different orientations

The magnetoresistance of NbSe₃ single crystals is measured as a function of magnetic field for different field orientations. A possibility of studying the Fermi surface by using the dependence of the Shubnikov-de Haas oscillation phase on the rotation angle of the magnetic field is demonstrated. The results of the study show that the quasi-momenta of carriers that are not condensed in the charge density wave are predominantly oriented along the conducting chains.     

On the absence of charge symmetry in electrostatic interaction between charged drops and hard particles

It is shown that the analytical expressions for the energy and force of electrostatic interaction between charged conducting particles (drops), a point charge, and a finite-size particle, as well as between a particle (a drop or a point charge) and a conducting plane, are asymmetric with respect to the sign of one of the charges. This is because the polarization interaction is always attractive irrespective of the signs of interacting particles. The absence of this symmetry leads to the self-constriction of charged aerodispersed systems containing a condensed phase, for example, plasma or liquid-droplet systems.     

Electromagnetic field perturbation by an internal void in a conducting cylinder excited by a wire loop

A thin prolate spheroidal void in an infinite conducting circular cylinder is used to model an internal flaw in a wire rope. The rope is excited by an electric ring current which is a model for a thin solenoid or multi-turn wire loop. The anomalous external fields are computed from the induced electric and magnetic dipole moments of the void. For this type of excitation, the induced axial magnetic dipole moment is the dominant contributor to the scattered field. The results have application to nondestructive testing of wire ropes.