Continuum Model for Electronic Polarization Based on a Novel Dielectric Response Function

基于连续介质模型推导了一个普适的描述电介质介电弛豫过程的响应函数. 该介电响应函数依赖于电介质的介电谱. 基于该函数推导得到了以前特殊情况下用于描述溶剂弛豫的响应函数一致的表达式.结合三种典型极性溶剂,水、甲醇和乙腈的介电谱,研究了三种溶剂在外加电场线性变化时的电子极化过程. 结果表明,溶剂的电子极化伴随着电子跃迁同步发生,没有时滞.     

Calculation of Dielectric Function of a Quark-Gluon Plasma

With the hard thermal loop （HTL） resummation technique, we calculate the dielectric function excited by hard gluon in quark-gluon plasma （QCP）. We find that in a section of the space-like region po/p ∈ [0.78, 0.95], there are two extremum structures on the dielectric function curve, while the dielectric function in the HTL approximation decreases monotonously without these properties. Through the analyses of the imaginary part of the dielectric function, we conclude that the character of the dielectric function in this region reflects effects of the Landau damping.     

The Polarization Response Function and Electrostatic Modes of Focused Beams

It is shown that the method of percussion for obtaining the spatial-temporal representation of the polarization response function directly [1] can also be used to study stability problems in nonuniform plasmas, thus providing a physical and mathematical alternative to the traditional approach. As an example, the stability analysis of particle beams is given, focused with cylindrical symmetry through an axis. The integral equation for electrostatic modes is set up with the polarization response, and solved with a technique that provides both the characteristic values and an integral representation for the field. The instability of this model, which is the cylindrical counterpart of the plane symmetric counterstreaming configuration, is then discussed.     

Quantum Theory of Solid State Plasma Dielectric Response

We review the quantum mechanical derivation of the random phase approximation (RPA) for solid state plasmas, starting from the Hamilton equations for canonically paired “second quantized” creation and annhilation field operators of interacting quantum many‐body systems. Discussing variational differentiation, the coupled equations of motion for the quantum field operators are derived. The concept of Green's functions is reviewed and interpreted, first for retarded Green's functions, and their equations of motion are developed from the equations of motion for the field operators. Thermodynamic Green's functions are discussed, and their periodicity/antiperiodicity properties in imaginary time are carefully examined with discussion of Matsubara Fourier series and representation in terms of a spectral weight function. The analytic continuation from imaginary time to real time is treated. Finally, we define nonequilibrium Green's functions and discuss the linearized timedependent Hartree approximation leading to the random phase approximation. An interesting application to the case of Graphene in a perpendicular magnetic field is discussed in detail, along with applications to normal systems, in terms of attendant phenomenology involving electron‐hole pair excitations and plasmons (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Complex Response Function of Whispering Gallery Dielectric Resonators

A whispering gallery resonator coupled to a dielectric waveguide is experimentally investigated around 86 GHz using a vectorial network analyzer. The resulting complex response function is compared with a theoretical model, simplified assuming negligible stationary waves; indeed their presence can be effectively compensated by a proper normalization procedure, made possible by a suitable analysis in the complex field. It is demonstrated that the proposed approach well reproduce the experimental results in a wide range of coupling conditions. Moreover, some outcomes of the model concerning the power flowing into the resonator are briefly discussed.     

Orientational Ordering of Tree Elements in the Dielectric Permittivity Model of a Forest Stand

Russian Physics Journal - The dielectric characteristics of trees are studied for a dielectric permittivity model of a forest stand of L1 band signals of navigation satellites. The contribution of...     

Ab Initio Simulation of Complex Dielectric Function for Dense Aluminum Plasma

We present calculations of frequency‐dependent complex dielectric function of dense aluminum plasma by quantum molecular dynamics method for temperatures up to 20 kK. Analysis shows that the dependencies for real and imaginary parts can be interpolated by the Drude formula with two effective parameters: the mean charge of ions and the effective frequency of collisions. The rise of these parameters with temperature deviates from simple theoretical predictions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Extended Mermin‐like Dielectric Function for a Two‐Component Plasma

The Mermin dielectric function is extended by including energy conservation. Within the framework of the relaxation time ansatz, the Zubarev approach to linear response theory is used which allows to incorporate the exact Hamiltonian dynamics of the relevant degrees of freedom. Analytical expressions for the dielectric function in the entire (k, w)‐plane are given for a two‐component plasma.     

Coupling of NRD-Guide Filled with Low Permittivity Dielectric Between Waveguides

A new version of NRD-guide coupling structure is proposed in which a low permittivity dielectric is filled between the coupling waveguides. It takes full advantage of the common NRD-guide with more flexibility. The choice of different dielectric materials can optimize the required performance. The corresponding coupling characteristics are analyzed. Some examples are given to show the new coupling characteristics. An important feature is the enhanced coupling between the waveguides and increased attenuation in the transverse direction, and this implies a size reduction and enhanced EMC capability. Furthermore, the filling of the low dielectric material between the coupling waveguides makes the structure an integrated unit and especially suitable for realization by micro-electromechanical system (MEMS) or by microwave integrated circuits.     

Negative Capacity of a Dielectric as a Result of the Development of Relaxation Polarization

The reasons for the emergence of negative capacitance in matter are discussed. The relaxation polarization in matter, accompanied by the creation of an electric field of the inverse directivity, is named one of the possible reasons for the emergence of a negative capacitance. This field can appear in local areas of a substance after development of the polarization of ionic displacement. Calculated dielectric spectra of matter characteristic of such relaxation polarization are presented.     

Dielectric and Polarization Studies of KNO3 Thin Layers

Ultrapure and homogeneous KNO₃ thin layers are subjected to dielectric and polarization measurements over a wide temperature range. The dielectric results obtained are discussed on the assumption of probable formation and migration of vacancies. The variation of polarization with the applied field was found to be nonlinear and the polarization reversal occurs at a critical value of the applied field of strength 11 kV/cm. This value is in good agreement with the value of the coercive field determined previously by the ferroelectric hysteresis loops.     

Forward and Backward Acoustic Waves in Crystals with High Piezoactivity and Dielectric Permittivity

Results are presented from studying the characteristics of acoustic waves of different types in plates of ceramic materials with high piezoactivity and dielectric permittivity (e.g., 0.95(Na_0.5Bi_0.5)TiO₃–0.05BaTiO₃, (K,Na)(Nb,Ta)O₃, and Ba(Zr_0.2Ti_0.8)O₃–50(Ba_0.7Ca_0.3)TiO₃). The dependences of the phase velocities and electromechanical coupling coefficients of these waves on parameter hf (where h is the thickness of a plate, and f is the frequency of a wave) are calculated for directions XY and YX of propagation. It is found that the investigated materials are characterized by frequency ranges of the existence of backward acoustic waves whose phase and group velocities are oriented in different directions. The existence of extremely broad frequency ranges that depend very weakly on a change in the electrical boundary conditions on the surface of a plate is established for waves with negative group velocity in the case of a 0.95(Na_0.5Bi_0.5)TiO₃–0.05BaTiO₃ single crystal. It is shown that the electromechanical coupling coefficient of acoustic waves in the investigated materials is greatest for an SH₁-wave in YX Ba(Zr_0.2Ti_0.8)O₃–50(Ba_0.7Ca_0.3)TiO₃, and can be as high as 7?30% in the range hf = 1330–2000 m/s.     

Rotation Part of the Dielectric Permittivity of Water Vapor for Different Spectral Line Profiles

We estimate the possible influence of spectral line profile (Lorentz profile, Van Vleck–Weisskopf profile, and profile obtained by solving kinetic equation) on the rotation part of the dielectric permittivity of water-vapor monomers. Spectral regions corresponding to long-wavelength (static) and high-frequency (optical) limiting cases as well as regions in close proximity to resonances of various intensities are considered. The studied effects are compared with the corresponding effects on water-vapor absorption coefficient, which are related to factors determining the line-shape structure.     

Radiation Polarization Distribution Function of a Dye Laser

The Fokker–Planck equation for the distribution function of the intensity of an individual component has been solved in the approximation of the Ornstein–Uhlenbeck process within the framework of the formalism of the method of polarization components. Based on this solution, we have constructed the distribution functions of the degree of lasing radiation polarization, analyzed experimental data for a certain geometry of laser pumping, and determined the values of the distribution parameters, including the loss coefficients for the polarization component.     

Measuring the Dielectric Permittivity of Sapphire at Temperatures 93–343 K

We consider a method for measuring the elements of the dielectric-permittivity tensor of a slightly lossy uniaxial anisotropic dielectric using the spectrum of resonance frequencies of a metal-dielectric resonator in the form of an axially anisotropic cylindrical specimen with endface metal mirrors. Measurements of both elements of the dielectric-permittivity tensor of sapphire at temperatures 93–343 K are performed using the spectrum of symmetric E modes. To avoid the influence of the residual gaps between the specimen and the mirrors, the endface surfaces of the specimen are metallized. We performed independent measurements of the axial and transverse elements of the permittivity tensor at room temperature from the spectra of azimuthal E modes and symmetric H modes. The values of the axial and transverse elements of the dielectric-permittivity tensor of sapphire in the range 93–343 K are presented with a spacing of 10 K.     

Development of a Polarization Jet and Plasma Drifts in the Ionospheric F Region

Radiophysics and Quantum Electronics - We consider Doppler measurements at the Yakutsk subauroral ionospheric station in the periods of the formation and development of a polarization jet above the...     

木条演示电介质在静电场中的极化现象

介绍了用木条演示电介质在静电场中的极化现象的实验方法,指出了实验时要注意的问题