Effect of ion polarization drift on shielding and dynamical potentials in magnetized plasmas

The role of an external magnetic field via the ion polarization drift effect has been investigated theoretically on the dust-Coulomb crystal formation in a dusty plasma in the presence of continuous ion flows from the bulk plasma to the sheath. The effects of the ions polarization drift on the strength and the effective lengths of the static Debye shielding potential and the oscillatory dynamical potential are clearly demonstrated.     

Stability and fluctuations in the external source problem of QCD2 with massless quarks

We discuss the stability of the static field and polarization charge produced by an abelian static external source in two-dimensional QCD with massless quarks. This is done in a previously proposed scheme allowing an approximate treatment of polarization effects. The discussion is based on linear fluctuation equations obtained from the equations of motion written in an appropriate moving gauge frame. We establish that the static configuration is stable in the sense that there are no initially small fluctuations which grow in time. However, in contrast with QED₂, there are fluctuations which are localized near the external source and whose amplitudes do not decay in time. These modes are studied in detail in the case of a single external point source.     

Massive gauge field in source theory. II

In an earlier source theory investigation it was shown that the vacuum polarization of a massive gauge field is finite, provided that the conservation of current is imposed everywhere, including the interior of the sources. It is shown in the present paper that radiative corrections to a vertex function (two-particle production by an external source) are also finite if the same requirement about current conservation is imposed. In other words one-loop corrections turn out to be finite in both calculations. The cancellations leading to convergence may be understood in terms of Ward identities. The three form factors that appear are not only shown to be finite but are also explicity found.     

Real-time observation of liquid crystal molecular directions based on a snapshot polarimeter

The polarization state of transmitted light is linked to liquid crystal(LC) molecular distribution. The dynamic behavior of a twisted nematic LC molecule is measured with a home-built 10 k Hz snapshot polarimeter. Only the transient molecule rotations are observed when the external voltage changes, and the molecules return to their original orientations quickly even when high voltage is applied. Our observations cannot be attributed to the traditional electro-optic effect. The invalidation of the static external field indicates the shielding effect of redistributing impurity ions in an LC cell.     

Infrared problem and boson suppression in massless Abelian gauge theory

The vacuum polarization effects lead to a complete shielding of the charge and to a suppression of real boson excitations in massless Abelian gauge theory. Nevertheless, fermions interact by means of neutral vector currents. It is concluded that charged massless fermions cannot exist.     

On the possibility of detecting superheavy quasimolecules

The formation of superheavy electronic quasimolecules leads to measurable deviations from the Rutherford cross section in heavy ion collisions. For the system ²³⁸₉₂U-²³⁵₉₂U with E_c.m. = 800 MeV we find an average correction of 1.5% for the scattering cross section in forward directions. Additional background contributions like electronic shielding of the nucleus, vacuum polarization, nuclear Coulomb excitation and static deformations of the nuclei are taken into account.     

String dust solutions of the Einstein field equations with spherical or static cylindrical symmetry

The Einstein field equations are solved assuming spherical or static cylindrical symmetry and a string dust source. All solutions which may be matched onr =a to an external vacuum solution having the same symmetry are found.     

Gravitational Shielding Effect in Gauge Theory of Gravity

In 1992, E.E. Podkletnov and R. Nieminen found that under certain conditions, ceramic superconductor with composite structure reveals weak shielding properties against gravitational force. In classical Newton's theory of gravity and even in Einstein's general theory of gravity, there are no grounds of gravitational shielding effects. But in quantum gauge theory of gravity, the gravitational shielding effects can be explained in a simple and natural way. In quantum gauge theory of gravity, gravitational gauge interactions of complex scalar field can be formulated based on gauge principle. After spontaneous symmetry breaking, if the vacuum of the complex scalar field is not stable and uniform, there will be a mass term of gravitational gauge field. When gravitational gauge field propagates in this unstable vacuum of the complex scalar field, it will decays exponentially, which is the nature of gravitational shielding effects. The mechanism of gravitational shielding effects is studied in this paper, and some main properties of gravitational shielding effects are discussed.     

微带线电路板端口对入射电磁波的电压响应

 在考虑电磁波与电子设备的耦合时,屏蔽腔中电路板端口对入射电磁波的电压响应是一个重要的参数。分别计算了微带线电路板端口在自由空间和在屏蔽腔内这两种不同情况下的电压响应,以及屏蔽腔内耦合系数的变化。对所得结果进行了比较分析,结果表明,在自由空间时,响应电压频谱为连续的变化,而在屏蔽腔内时,只有在本征模的频率处才会激励起端口电压,频谱分布变为分立的。当屏蔽腔上开有窄缝时,窄缝方向和入射场极化方向对激励起来的端口电压都有影响,而电场极化方向和微带线方向之间的关系,是决定端口激励电压大小的关键因素。     

铁电材料光催化活性的研究进展

光催化技术被认为是最有前景的环境污染处理技术,这就使得光催化剂材料备受瞩目.近年来,铁电材料作为新型光催化剂材料受到人们越来越多的关注,其原因在于铁电材料特有的自发极化有望解决催化反应过程中的电子-空穴对复合问题,进而提高光催化活性.本文从两个方面对铁电极化如何影响光催化进行综述:一方面,从铁电极化入手归纳总结其对电子-空穴对分离的影响,进而更深入地从极化引发的退极化场和能带弯曲两个部分来阐述具体的影响机理;另一方面,为了消除静电屏蔽,分别从温度、应力(应变)、电场三个外场因素调控极化入手,归纳总结外场调控极化对电子-空穴对分离的影响,进而影响光催化活性.最后对该领域今后的发展前景进行了展望.     

On possible light–torsion mixing in background magnetic field

The interaction of the light with propagating axial torsion fields in the presence of an external magnetic field has been investigated. Axial torsion fields appearing in higher derivative quantum gravity possess two states, with spin one and zero, with different masses. The torsion field with spin-0 state is a ghost that can be removed if its mass is infinite. We investigate the possibility when the light mixes with the torsion fields resulting in the effect of vacuum birefringence and dichroism. The expressions for ellipticity and the rotation of light polarization axis depending on the coupling constant and the external magnetic field have been obtained.     

Photon polarization tensor in a magnetized plasma system

We investigate the photon polarization tensor at finite temperatures in the presence of a static and homogeneous external magnetic field. In our scheme, the summing of the Matsubara frequency is performed after Poisson resummation, which is easily completed and converges quickly. Moreover, the behaviors of finite Landau levels are presented explicitly. It shows a convergence while summing infinite Landau levels. Consequently, there is no necessity to truncate the Landau level in a numerical estimation. At zero temperature, the lowest Landau level (LLL) approximation is analytically satisfied for the vacuum photon polarization tensor. However, we examine that the LLL approximation is not enough for the thermal polarization tensor. The thermal tensor obtains non-trivial contributions from the finite-n Landau levels. And, photon spectra gains a large imaginary contribution in thermal medium, which is the so-called Landau damping. Finally, it is argued that the summation of Matsubara frequency is not commuted with Landau level ones, such conjecture is excluded in our calculations.     

Exact two-loop vacuum polarization correction to the Lamb shift in hydrogenlike ions

We present a calculation scheme for the two-loop vacuum polarization correction of order to the Lamb shift of hydrogenlike high-Z atoms. The interaction with the external Coulomb field is taken into account to all orders in . By means of a modified potential approach the problem is reduced to the evaluation of effective one-loop vacuum polarization potentials. An expression for the energy shift is deduced within the framework of partial wave decomposition performing appropriate subtractions. Exact results for the two-loop vacuum polarization contribution to the Lamb shift of K- and L-shell electron states in hydrogenlike Lead and Uranium are presented. Received: 10 August 1997 / Revised: 31 October 1997 / Accepted: 18 November 1997     

Multipactor discharge on a dielectric surface in the field of circularly polarized plane waves

The secondary-emission discharge (multipactor) on a dielectric surface irradiated by a plane TEM wave of circular polarization is analyzed theoretically. It is shown that interaction of electrons with the electromagnetic wave field can provide their return to the emission surface, which makes a multipactor possible even without any external static fields. Multipactor conditions for different reflection coefficients of the incident wave are found. The obtained results are used to estimate the throughput of the output window of a high-power vacuum microwave device. Specifically, it is established that decreasing the high-frequency field amplitude on the window surface when the mode of a partially standing wave is realized in the vicinity of the window does not always help raise its electric strength.     

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.     

On quantum radiation in curved spacetime

In the context of quantum field theories in curved spacetime, we compute the effective action of the transition amplitude from vacuum to vacuum in the presence of an external gravitational field. The imaginary part of the resulted effective action determines the probability of vacuum decay via a quantum tunneling process, giving the rate and spectrum of particle creations. We show that (i) the gravitational field polarizes the vacuum and discretizes its spectrum; (ii) vacuum gains gravitational energy by such a polarization. On the basis of gravitational vacuum polarization, we discuss the quantum origin of vacuum decay in curved spacetime as pair-creations of particles and anti-particles. The thermal spectrum of particle creations is attributed to (i) the CPT invariance of pair-creations (annihilations) from (into) vacuum and (ii) vacuum acts as a reserve with the temperature determined by gravitational energy-gain.     

Passive magnetic shielded spin polarized electron source with optical electron polarimeter

A new GaAs(100) spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel--iron--molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5×10^-7,T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95cm distance through an 1mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8\pm3.5% measured with a He optical polarimeter.     

CIRCE: a dedicated storage ring for coherent THz synchrotron radiation

We present the concepts for an electron storage ring dedicated to and optimized for the production of stable coherent synchrotron radiation (CSR) over the far-infrared terahertz wavelength range from 200 μm to about 1 cm. CIRCE (Coherent InfraRed CEnter) will be a 66 m circumference ring located on top of the ALS booster synchrotron shielding tunnel and using the existing ALS injector. This location provides enough floor space for both the CIRCE ring, its required shielding, and numerous beamlines. We briefly outline a model for CSR emission in which a static bunch distortion induced by the synchrotron radiation field is used to significantly extend the stable CSR emission towards higher frequencies. This model has been verified with experimental CSR results. We present the calculated CIRCE photon flux where a gain of 6–9 orders of magnitude is shown compared to existing far-IR sources. Additionally, the particular design of the dipole vacuum chamber has been optimized to allow an excellent transmission of these far-infrared wavelengths. We believe that the CIRCE source can be constructed for a modest cost.     

Vacuum birefringence in strong magnetic fields: (I) Photon polarization tensor with all the Landau levels

Photons propagating in strong magnetic fields are subject to a phenomenon called the “vacuum birefringence” where refractive indices of two physical modes both deviate from unity and are different from each other. We compute the vacuum polarization tensor of a photon in a static and homogeneous magnetic field by utilizing Schwinger’s proper-time method, and obtain a series representation as a result of double integrals analytically performed with respect to proper-time variables. The outcome is expressed in terms of an infinite sum of known functions which is plausibly interpreted as summation over all the Landau levels of fermions. Each contribution from infinitely many Landau levels yields a kinematical condition above which the contribution has an imaginary part. This indicates decay of a sufficiently energetic photon into a fermion–antifermion pair with corresponding Landau level indices. Since we do not resort to any approximation, our result is applicable to the calculation of refractive indices in the whole kinematical region of a photon momentum and in any magnitude of the external magnetic field.