开孔矩形腔体电磁泄漏特性的解析研究

本文提出了一种用于计算开孔矩形腔体电磁泄漏场的解析理论模型.该理论模型先基于模式展开法求解封闭腔场,进而依据Bethe小孔耦合理论将泄漏场与封闭腔场用等效偶极子关联.该模型可以考虑波频率、场源位置、开孔位置及场强观测点位置等因素的影响,计算结果与全波仿真结果一致.本文计算分析了相关因素对电磁屏蔽效能的影响规律,并给出了物理解释.结果表明近场屏蔽效能小于远场屏蔽效能,且近场区电场屏蔽效能与磁场屏蔽效能并不相同.     

像偶极子法计算导体颗粒簇团的偶极矩

计算均匀电场中颗粒簇团的偶极矩通常是困难的,这是因为颗粒间的相互耦合较难处理.这种相互耦合使颗粒的极化依赖于簇团的结构和大小.利用像偶极子法对这种耦合加以分析.首先,分别考虑了置于纵向和横向电场中的任意间距的等径导体球对,确定了各球上的像偶极子和像电荷及其分布.之后,计算了由4个置于正方形顶点和8个置于立方体顶点的导体球构成的簇团的偶极矩,并给出紧凑表达式.与先前的结果进行了比较,获得了很好的一致性. 关键词： 偶极矩 颗粒簇团 像偶极子法 分形     

Structure of the magnetic field perturbations of a low-frequency dipole by a metallic sphere

The potentials of the magnetic field of a low-frequency magnetic dipole reflected by a sphere are analyzed. It is shown that for short ranges between the dipole and the sphere this field can be described by one potential, where the field is equivalent to the field of a system of dipoles and charges.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 73–77, March, 1976.     

The electrical conduction variation in stained carbon nanotubes

Carbon nanotubes become stained from coupling with foreign molecules, especially from adsorbing gas molecules. The charge exchange, which is due to the orbital hybridization, occurred in the stained carbon nanotube induces electrical dipoles that consequently vary the electrical conduction of the nanotube. We propose a microscopic model to evaluate the electrical current variation produced by the induced electrical dipoles in a stained zigzag carbon nanotube. It is found that stronger orbital hybridization strengths and larger orbital energy differences between the carbon nanotube and the gas molecules help increasing the induced electrical dipole moment. Compared with the stain-free carbon nanotube, the induced electrical dipoles suppress the current in the nanotube. In the carbon nanotubes with induced dipoles the current increases as a result of increasing orbital energy dispersion via stronger hybridization couplings. In particular, at a fixed hybridization coupling, the current increases with the bond length for the donor-carbon nanotube but reversely for the acceptor-carbon nanotube.     

The physics of amorphous and nanocrystalline hard magnetic materials

The magnetic properties of amorphous and nanocrystalline hard magnetic materials are summarized. The reduction of the “effective” anisotropy field due to exchange coupling in nanocrystalline materials is demonstrated. This leads experimentally as well as theoretically to a remanence enhancement and to a reduced coercivity. Also the domain structure shows the effect of exchange coupling. Nd–Fe–Al is taken as an example of a new “amorphous” hard magnetic material. For magnetostrictive materials the possibility of reducing the anisotropy in nanocrystalline samples without loosening the high magnetostriction is discussed.     

Optical Super-Resonances in Mesoscale Dielectric Cenosphere: Giant Magnetic Field Generations

Resonant light scattering by mesoscale dielectric spheres has received enormous attention and found many interesting applications. The recently emerged field of Mesotronics provides novel opportunities for wavelength-scaled optics and new fundamental aspects are still being uncovered. It has recently been demonstrated that high-order Mie resonances can be excited in homogeneous low-dissipation mesoscale dielectric spheres, leading to the generation of intense magnetic fields. This article describes a simple and effective way to drastically enhance the superresonance effect. Proof-of-principle results for the first time show that yet one more novel phenomenon of increasing the intensity of the magnetic field without changing the resonant Mie size parameter of the sphere by introducing an air cavity. In such a dielectric cenosphere (from two Greek words “kenos”-hollow and “sphaira”-sphere), by correct choice of the air cavity size, it is possible to increase the intensity of the electromagnetic fields at the poles of the sphere by an order of magnitude due to increasing of the amplitude of resonant partial wave coefficient.     

Spectrum of relativistic radiation from electric charges and dipoles as they fall freely into a black hole

The motion of electric charges and dipoles falling radially and freely into a Schwarzschild black hole is considered. The inverse effect of the electromagnetic fields on the black hole is neglected. Since the dipole is assumed to be a point particle, the deformation due to the action of tidal forces on it is neglected. According to the theorem stating that “black holes have no hair”, the multipole electromagnetic fields should be completely radiated as a multipole falls into a black hole. The electromagnetic radiation power spectrum for these multipoles (a monopole and a dipole) has been found. Differences have been found in the spectra for different orientations of the falling dipole. A general method has been developed to find the radiated multipole electromagnetic fields for multipoles (including higher-order multipoles—quadrupoles, etc.) falling freely into a black hole. The calculated electromagnetic spectra can be compared with observational data from stellar-mass and smaller black holes.     

Very Low Frequency Far-Infrared Spectra of Mixtures of Dioxan with the Halogens and Related Molecules

Abstract

There has been considerable interest recently in the study of the submillimetre (or very far-infrared) absorption shown by both polar^1–4 and non-polar molecules.^2,5–8 Such absorption, in the ～5–100 cm^?1 region, for non-polar molecules is thought^2,6 to be caused by fluctuating dipoles associated with classical quadrupole-induced dipole interactions (in general multipole-induced dipole interactions). These effects are said to be “collision-induced” and can be thought of as being due to “collision” complexes in the liquid phase. For polar molecules the absorption is now thought^1–4 to be due to libration of the dipole in a “cage” of surrounding molecules (either molecules of the same species or of solvent). This so-called Poley-Hill model^9,10 is not inconsistent with the idea^1,2 of a residual rotation of the molecular dipole in the liquid phase. This similarity is underlined by the fact that some simple polar molecules^11,12 have a liquid phase Poley-Hill absorption the general shape and position of which follow quite closely that of the pressure broadened, gas phase spectrum. Our interest in the far-infrared region stems from our studies on halogen complexes with various n and bπ donors.^13,14 The pyridine-I₂ system (in cyclohexane) for example shows two bands in the far in frared not present in either component. The band at -183 cm is thought to be the stretching mode of the iodine, perturbed in the complex. The band at ～96 cm to the v(1-I) band, has so far been interpreted molecular″ stretching modebetween donor and acceptor, v(D-A).     

Dynamic magnetic susceptibility of a two-layer film in a strong magnetic field

A theoretical study is reported of the effect of interlayer exchange coupling on the resonance properties of a two-layer magnetic film with “easy-axis” and “easy-plane” anisotropic layers in a strong tilted magnetic field. The dependence of the resonance fields on the tilting angle of the external magnetic field to the film has been obtained, the tensor of integrated high-frequency film susceptibility has been found, and its dependence on the strength and orientation of the external field, as well as on layer thickness, has been analyzed. The results obtained agree with the available experimental data.     

均匀电场中颗粒簇偶极矩的确定

置于均匀电场中的一簇球形颗粒,由于其内部的相互作用而耦合在一起．这致使簇的感应偶极矩与簇的几何结构,大小以及颗粒的介电常数等参量有关．试图通过已知的链的偶极矩确定任意大小长方结构的簇的偶极矩．假定颗粒链可以被具有同样偶极矩的一个等效介质球代替,并将具有空间结构的颗粒簇处理成面结构簇,再将面结构简化成一个颗粒链,从而确定簇的偶极矩．在这一过程中,通过不断增加等效球的尺寸,将颗粒间的相互作用包含在簇的偶极矩中．数值分析了立方结构簇的偶极矩,结果是可接受的. 关键词：     

Spin-wave resonance spectra of films with a uniform gradient of anisotropy field

It has been shown that the number of high-intensity spin-wave modes in the spin-wave resonance spectrum of films with a uniform gradient of the effective anisotropy field depends on the thickness of the film and on the exchange stiffness. It has been established that there is a “critical” thickness of the film which depends on the exchange stiffness and the anisotropy field gradient. When the thickness of the film is less than the “critical” value, only one high-intensity mode is excited in the resonance absorption spectrum.     

Investigation on the escaped and trapped emission in organic light-emitting devices

The escaped and trapped emission of small molecule based bottom emission organic light-emitting diodes was investigated by using an integrating sphere and a fiber spectrometer and a glass hemisphere. It was found that the maximum external coupling ratio r_ext, namely the ratio of escaped emission to the emission of escaped and trapped in the substrate, is 56%. We also extended the “half-space” dipole model by taking dipole radiation pattern into account, which agreed well with our experiments. Our experimental and theoretical results will benefit the optimization of device structures for the higher out-coupling efficiency.     

Zur Streuung langwelliger Magnonen an Gitterfehlern

The scattering of ferromagnetic magnons by point defects is calculated within the framework of a phenomenological theory. This theory essentially takes account of the magnetic dipole interaction, and the magnetoelastic interaction, which are usually neglected. The scattering is due to an effective magnetic field, which is produced by the longrange strains of the lattice. For small wavenumbers this effective field is more important than the local disturbance of the exchange coupling in the vicinity of the defect, which hitherto has been considered almost exclusively, within the Heisenberg model. Due to the magnetic dipole interaction, the scattered wave and the differential cross section depend on the angle in a rather complicated manner: For each direction of scattering there are up to three groups of scattered waves, running away from the defect with different velocities. The differences between the classical and the quantum mechanical calculation are worked out.     

OH− dipole reorientability in hydroxyapatites: Effect of tunnel size

A study of calcium phosphate hydroxyapatite with the thermally stimulated currents methods (TSC) has led to the conclusion that the reorientable dipoles responsible for the dielectric properties measured are the structural OH⁻ ions in the “tunnels”. The co-operative motions along chains of these dipoles have been followed by the identification and determination of compensation phenomena at T_c = 212°C and 356°C. These phenomena correspond to physical events characterized by co-operative motions, such as the monoclinic-to-hexagonal phase transition observed in several apatites. Even in a material in which the higher temperature phase is frozen in at a lower temperature (e.g. by defects or by quenching), the TSC method can reveal the onset of those co-operative dipole reorientations which would otherwise produce a phase transition.An effect of the “tunnel” size and environment of OH⁻ dipole reorientation movements has been investigated with two additional hydroxyapatites, strontium phosphate hydroxyapatite, Sr₁₀(PO₄)₆OH₂, and calcium arsenate hydroxyapatite, Ca₁₀(AsO₄)₆OH₂. “Tunnel size” is here defined as the distance from the center (6, axis) to the ion center less the ion radius. The larger tunnel sizes led to lower compensation temperatures.     

Modeling of the dolphin’s clicking sound source: The influence of the critical parameters

A physical and a mathematical models of the dolphin’s source of echolocation clicks have been recently proposed. The physical model includes a bottle of pressurized air connected to the atmosphere with an underwater rubber tube. A compressing rubber ring is placed on the underwater portion of the tube. The ring blocks the air jet passing through the tube from the bottle. This ring can be brought into self-oscillation by the air jet. In the simplest case, the ring displacement follows a repeated triangular waveform. Because the acoustic pressure gradient is proportional to the second time derivative of the displacement, clicks arise at the bends of the displacement waveform. The mathematical model describes the dipole oscillations of a sphere “frozen” in the ring and calculates the waveform and the sound pressure of the generated clicks. The critical parameters of the mathematical model are the radius of the sphere and the peak value and duration of the triangular displacement curve. This model allows one to solve both the forward (deriving the properties of acoustic clicks from the known source parameters) and the inverse (calculating the source parameters from the acoustic data) problems. Data from click records of Odontocetes were used to derive both the displacement waveforms and the size of the “frozen sphere” or a structure functionally similar to it. The mathematical model predicts a maximum source level of up to 235 dB re 1 μPa at 1-m range when using a 5-cm radius of the “frozen” sphere and a 4-mm maximal displacement. The predicted sound pressure level is similar to that of the clicks produced by Odontocetest.     

电偶极子源定位问题的研究

首先得到了封闭形式的电偶极子处于任意位置时电场分布的公式，它是一个线性变换，称其变换矩阵为传递矩阵.并给出了传递矩阵的具体表达式和许多有用的性质，得到了传递矩阵的逆矩阵，导出了利用电场分布来确定单个或者多个偶极子源位置矢量和电偶极矩矢量的公式.对单个偶极子源的计算表明，如果测得两点的电场分布相同，就可以确定偶极子处于它们连线的中点上. 关键词： 电偶极子 传递矩阵 电场分布 定位问题     

Electrodynamic coupling of electric dipole emitters to a fluctuating mode density within a nanocavity

We investigate the impact of rotational diffusion on the electrodynamic coupling of fluorescent dye molecules (oscillating electric dipoles) to a tunable planar metallic nanocavity. Fast rotational diffusion of the molecules leads to a rapidly fluctuating mode density of the electromagnetic field along the molecules' dipole axis, which significantly changes their coupling to the field as compared to the opposite limit of fixed dipole orientation. We derive a theoretical treatment of the problem and present experimental results for rhodamine 6G molecules in cavities filled with low and high viscosity liquids. The derived theory and presented experimental method is a powerful tool for determining absolute quantum yield values of fluorescence.     

Split interstitials in computer models of single-crystal and amorphous copper

The effect of interstitial atoms in a dumbbell configuration on elastic moduli of single crystal copper has been investigated using molecular dynamics simulation. It has been shown that shear components of the dipole tensor and λ-tensor increase when the concentration of split interstitials exceeds 0.6–0.7%. This is associated with their interaction responsible for a significant change in the distribution of orientations of split interstitials and, hence, for a change in the type of the induced local symmetry breakings of the face-centered cubic structure. It has been found that, in the model of amorphous copper, there are “defects” (elastic dipoles) with properties similar to those of split interstitials in the single crystal. The deviatoric component of their λ-tensor is more than an order of magnitude greater than the dilatation component and is responsible for the decreased value of the shear modulus and thermal effects in noncrystalline metallic materials.     

Nonlocal excitonic–mechanical interaction in a nanosystem

The dynamics of a nanoparticle during its dipole interaction with an excitonic excitation in an extended quasi-one-dimensional polarizable medium is investigated. Bundles of J-aggregates of dye molecules are considered as an example of the latter. The nonlocal excitonic–mechanical interaction between the field of an amplifying or absorbing nanoparticle and excitons in a bundle has been simulated numerically. It has been found that the interaction between the field of the induced nanoparticle dipole and the fields of the molecular dipoles in an aggregate can lead to a change in the particle trajectory and excitonic pulse shape. The possibility of controlling the nanoparticle by excitonic pulses and the reverse effect of the nanoparticle field on the dynamics of excitons due to the nonlocal excitonic–mechanical interaction has been demonstrated.     

Brownian dynamics simulation of electrostatically interacting proteins

Brownian dynamics simulation software has been developed to study the dynamics of proteins as a whole in solution. The proteins were modelled as spheres with point dipoles embedded in the centre of sphere. A set of Brownian dynamics simulations at different values of the dipole moments, protein concentration and translational diffusion coefficient was performed to investigate the influence of interprotein electrostatic interactions on dynamic protein behaviour in solution. It was shown that these interactions led to the slowing down of protein rotation and a complex non-exponential shape of the rotational correlation function. Analysis of the correlation functions was performed within the frame of the model of electrostatic interprotein interactions advanced earlier on the basis of NMR and dielectric spectroscopy data. This model assumes that, due to electrostatic interactions, protein Brownian rotation becomes anisotropic. The lifetime of this anisotropy is controlled mainly by translational diffusion of proteins. Thus, the correlation function can be decomposed into two components corresponding to anisotropic Brownian rotation and an isotropic motion of an external electric field vector produced by the surrounding proteins.