强电场作用下反铁电锆钛酸铅的介电行为研究

采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示，锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化，在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处，最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中，小信号介电常数εc减小；在电场降低铁电回复成反铁电过程中，小信号介电常数εc增大，小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电 关键词： 锆钛酸铅反铁电陶瓷 介电行为 强电场条件     

Symmetry breaking and gravitational interaction

A scalar field Lagrangian is considered in the curved space-time to which a Hamiltonian determining nonzero vacuum field value is added. The initial Lagrangian can be expressed as a sum of Lagrangians for the constant scalar field component and perturbation. The first Lagrangian can be considered as a Lagrangian for the Einstein gravitational field in vacuum. The problem of renormalization of the constant scalar field component is investigated. It is demonstrated that in the case of conformal relation of the scalar field to the space-time curvature, there exists a unique value of the scalar space curvature for which the field can be considered constant (field perturbations do not result in renormalization of the constant component). This curvature value determines the unique value of the equilibrium nuclide density. A correlation of the examined Lagrangian parameters with the integral parameters of the Solar system is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 18–34, July, 2006.     

Physical implications of the cosmological constant

The contribution of the quantum vacuum to the energy-momentum stress tensor in Einstein's field equations is very large. The observed cosmos is not in agreement with such a large term; thus, we require the presence of a cosmological constant to cancel this term. We discuss why this constant cannot originate from a quantum field or the gravitational field. We propose that this constant is physical evidence of the structure of space. The physical structure of space gives space an existence independent of the existence of matter and radiation.     

Energy Spectrum of Simply Constant Chromoelectric Flux Tubes

In this article we obtain the energy spectrum of colored, spinor particles in chromoelectric flux tubes. The chromoelectric field of the flux tubes considered here comes from simply constant gauge potentials rather than from covariantly constant gauge potential, as is usually the case. The energy spectrum of the simply constant flux tubes is different than that of the covariantly constant flux tubes. The spectrum is discrete due to the walls of the tube and with a plus/minus constant shift depending on the magnitude of the constant chromoelectric background. This goes against the classical intuition where one would expect a charged particle in a uniform “electric” field to accelerate with ever increasing velocity/energy i.e. there would be no constant energy eigenvalue.     

Field Equations due to a Constant Modification in General Relativity

In this article, by adding a constant to Einstein-Hilbert action, we derive field equations for a non-vacuum space. Also we derive a general solution for these field equations, considering a de Sitter like initial geometric constraint. It is shown that how this additional constant can affect usual gravitational field equations, which are derived from general relativity.     

Effect of variation of dielectric constant on the magnetic field modulation of exciplex luminescence

The effect of variation of dielectric constant on the relative magnetic field effect in singlet luminescence has been studied using a typical exciplex system at a saturating field. The study indicates strong specificity in the perturbation of the magnetic field effect by alcoholic solvents. In contrast to alcohols where relative singlet magnetic field effect is of the order of 2% only, the magnetic field effect in non-alcoholic medium reaches as high as 9%. Moreover, dielectric constant variation in alcohols yields curves which are distinctly different from those in non-alcoholic media. It turns out that this dependence of magnetic field effect on dielectric constant is similar in all non-alcoholic solvent mixtures. An analytical study based on Hong and Noolandi’s solution of Smoluchowski equation has been made. Derived expressions can interpret experimental curves reasonably well.     

Bohlin transformation for a two-dimensional singular oscillator in a constant magnetic field

Bohlin transformation for a circular singular oscillator in a constant magnetic field is considered. It is shown that this transformation leads to a two-dimensional Kepler problem with an additional centrifugal potential from the constant magnetic field whose strength decreases inversely proportional to the distance from the center of attraction of the system. The energy spectrum of the considered system is obtained.     

Tunneling from a 3-dimensional quantum well in an electric field: an analytic solution

We derive the stationary tunneling solution for charged particles moving in a spherical, 3-dimensional zero-range potential plus a constant electric field. From the analytic expression for the wave function we calculate the distribution of the current inside and outside the vacuum barrier. At low field strengths there is a constant spreading of the tunnel current orthogonal to the direction of the applied field. At intermediate field strengths the exact results for the current distribution behave different from the semiclassical predictions.     

Field-induced magnetic transition in a mixed rare-earth aluminum garnet Er<Subscript>2</Subscript>HoAl<Subscript>5</Subscript>O<Subscript>12</Subscript>

The temperature dependence of the ac magnetic susceptibility of a single-crystal mixed rare-earth garnet Er₂HoAl₅O₁₂ has been investigated within the range from 1.8 to 300 K in a zero constant field and in applied bias fields of up to 9 T. In the absence of a constant magnetic field the magnetic susceptibility followed the Curie–Weiss law. The application of a constant magnetic field caused a magnetic phase transition, the temperature of which increased with increasing magnetic field. The temperature of the maximum of the ac magnetic susceptibility, which is a characteristic of the phase transition, did not show a noticeable dependence on the frequency of the alternating magnetic field.     

A family of Jordan-Brans-Dicke Kerr solutions

A family of solutions of the vacuum Jordan-Brans-Dicke or scalar-tensor gravitational field equations is given. This family reduces to the Kerr rotating solution of the vacuum Einstein equations when the scalar field is constant. The family does not have spherical symmetry when the rotation is zero and the scalar field is not constant. The method used to generate the new solutions can also be used to obtain vacuum Jordan-Brans-Dicke solutions from any given vacuum stationary, axisymmetric solution.     

Ferromagnetic resonance of nonstoichiometric zinc ferrite and cobalt-doped zinc ferrite nanoparticles

Ferromagnetic resonance spectra of zinc ferrite and cobalt doped zinc ferrite nanoparticles, measured at various temperatures, exhibit an invariant point at a given field. This makes it possible to determine the equation relating the resonance field shift to the peak-to-peak linewidth. When particles are frozen in a matrix in a magnetic field, the anisotropy constant of the material can be derived from the angular variation of the resonance field. This procedure is useful to determine the thermal dependence of the anisotropy constant, but is shown to require various freezing temperatures experiments to estimate the accuracy of the deduced anisotropy constant values. It is also shown that the angular dependence of the resonance field is similar for a uniaxial (zinc ferrite) and cubic (zinc ferrite containing 40% cobalt ions) anisotropy. This unexpected result is explained by the weakness of the texturation, leading to a distribution in easy axes directions.     

Automatic evaluation of photoelastic fringe constant by the nonlinear least-squares method

A nonlinear least-squares method was applied to determine the photoelastic fringe constant from isochromatic phase field obtained by digital phase-shifting photoelasticity. To perform automatic evaluation, not only the photoelastic fringe constant but the center coordinates of a disk under diametral compression are also determined simultaneously using the nonlinear least-squares method. A set of over-determined nonlinear equations is obtained to estimate the unknown parameters by an iterative procedure based on Newton–Raphson method. Simulation and experimental results show that the parameters are evaluated accurately from the isochromatic phase field obtained from the phase-shifting photoelasticity. The photoelastic fringe constant and the disk center coordinates can be evaluated easily, simply and automatically by the technique.     

Spatial dependence of the local field enhancement in dielectric shell coated silver nanospheres

The dependence of the local field factor around dielectric shell coated silver nanospheres was investigated by theoretical calculation as a function of the spatial distance. The local field factors in the dielectric shell are sensitive to the distance from particle center and shell thickness. When the shell dielectric constant is greater than that of surrounding medium, the maximum of local field factor at inner surface of the shell red shift and increases nonlinearly with increasing the shell thickness. On the contrary, when shell dielectric constant is less than that of surrounding medium, increasing the shell thickness leads the maximum of local field factor at inner surface blue shifts and decreases nonlinearly. However, with increasing the shell thickness, the maximum of local field factor at exterior surface of the shell always decrease nonlinearly. Furthermore, with increasing shell thickness, all these variations get gentle approach to a constant value when the shell thickness is two times of the core radius. When the core and shell diameter have fixed values, the local field factors in dielectric shell decrease with increasing the distance from particle center, but the peak position is not sensitive to the distance.     

Radiation of an electron in an electric field

By the methods of classical theory, the motion of an electron in the field of a longitudinal electric wave is analyzed. This field may be taken as a model of the accelerating field at the axis of a linear accelerator. It was shown that the radiation of electrons in this field is analogous to the radiation in a constant homogeneous electric field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 96–99, May, 1976.The authors are sincerely grateful to Prof. V. A. Bagrov for formulating the problem and for his constant interest in the work.     

On the variation of the effective cosmological term

In the framework of classical field theory, we try to explain why the effective cosmological constant is so small. The basis of the attempt is a Higgs field that shall determine the global structure of the universe. Einstein's theory of gravitation does not allow one to realize the idea. But we are successful if we start from some variant of the scalar-tensor theory of gravitation, choosing for the parameters that enter the Lagrangean of the Higgs field the Compton length of a proton and Eddington's number as self-coupling constant.     

双光子过程耦合腔系统中光场的量子特性

本文研究了双光子过程原子与耦合腔相互作用系统中腔场的压缩效应和反聚束效应.考虑系统总激发数等于2的情况,利用数值计算方法讨论了腔场间的耦合强度变化和原子与腔场间耦合强度变化对反聚束效应的影响.研究结果表明:腔场不呈现出压缩效应;腔场的反聚束效应与原子与腔场的耦合系数之间,以及与腔场间的耦合系数之间都存在着非线性关系.     

Symmetric Variations of the Metric and Extrema of the Action for Pure Gravity

Symmetries of generalized gravitational actions, yielding field equations which typically involve at most second-order derivatives of the metric, are considered. The field equations for several different higher-derivative theories in the first-order formalism are derived, and variations of a generic set of higher-order curvature terms appearing in string effective actions are studied. It is shown that there often exists a particular set of solutions to the field equations of pure gravity theories, consisting of different combinations of curvature tensors, which satisfies the vacuum equations with cosmological constant. Implications of generalized symmetries of the field equations derived from the superstring effective action for the cosmological constant problem are discussed.     

Conformally coupled scalar field solutions and the cosmological constant

Solutions are presented for a scalar field coupled conformally to Einstein gravity with a nonvanishing cosmological constant, in the case that the spacetime metric is spatially homogeneous and isotropic. Since the cosmological constant destroys the conformal invariance of the action, these solutions cannot be obtained by solving the flat space wave equation for the scalar field. It turns out that the metric is determined entirely by the cosmological constant, while the scalar field acquires an apparent mass squared which is proportional to the cosmological constant. It is conjectured that the cosmological constant in the universe at present may thus be disguised as the mass of some scalar field.     

Dilation analyticity in constant electric field

We extend the analysis of Paper I from two body dilation analytic systems in constant electric field toN-body systems in constant electric field. Particular attention is paid to what happens to isolated eigenvalues of an atomic or molecular system in zero field when the field is turned on. We prove that the corresponding eigenvalue of the complex scaled Hamiltonian is stable and becomes a resonance. We study analyticity properties of the levels as a function of the field and also Borel summability.Research partially supported by USNSF grant MCS 78-00101Research partially supported by USNSF grant MCS 78-01885     

Dilatons and the dynamical collapse of charged scalar field

We studied the influence of dilaton field on the dynamical collapse of a charged scalar one. Different values of the initial amplitude of dilaton field as well as the altered values of the dilatonic coupling constant were considered. We described structures of spacetimes and properties of black holes emerging from the collapse of electrically charged scalar field in dilaton gravity. Moreover, we provided a meaningful comparison of the collapse in question with the one in Einstein gravity, when dilaton field is absent and its coupling with the scalar field is equal to zero. The course and results of the dynamical collapse process seem to be very sensitive to the amplitude of dilaton field and to the value of the coupling constant in the underlying theory.