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《Current Applied Physics》2014,14(1):122-126
The molecular dynamics of the homogeneously aligned nematic liquid crystal mixture E7 subject to a magnetic field has been studied. The dielectric spectra study has revealed a low bias magnetic field effect on the evolution of dielectric relaxation spectra occurred at lower (∼kHz) (δ-relaxation) and higher (∼MHz) (α-relaxation) frequency regions. The complex electric modulus, which converted from experimental dielectric spectra, has been analyzed with theoretical model of Debye relaxation. The obtained fitting parameters of relaxation time and strength of dielectric components are shown to vary systematically with the strength of applied magnetic field. A microscopic molecular dynamic model has been proposed to describe the two-step variation of E7 molecular under the bias magnetic field. The results provide implication for magneto-modulation of liquid crystal molecular dynamics under the bias magnetic field. 相似文献
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利用闭合轨道理论, 研究了变化的磁场和不同电介质表面对氢负离子光剥离截面的影响, 并推导出了该体系下的光剥离截面公式. 结果发现, 氢负离子的光剥离截面不仅与磁场的强度有关, 而且还与电介质常数有关. 当氢负离子到电介质表面的距离和电介质常数一定时, 体系的光剥离截面中的振荡随磁场的变化而明显变化. 随着磁场强度的 增大, 体系的闭合轨道数目增多, 光剥离截面的振荡越来越复杂. 当氢负离子到电介质表面的距离和磁场强度一定时, 电介质常数的变化对光剥离截面的影响也很重要, 随着电介质常数的增大, 体系的闭合轨道数目增多, 光剥离截面的振荡也变得越来越复杂. 因此, 可以通过改变磁场强度和电解质常数来调整负离子的光剥离截面. 此结果 对于研究负离子体系在表面附近和外场中的光剥离问题具有一定的参考价值. 相似文献
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利用自编1D3V PIC程序,数值研究了不同外加磁场方式对次级电子倍增抑制的物理过程,给出了次级电子数目、平均能量、密度、运动轨迹、渡越时间、介质表面静电场及沉积功率等物理量时空分布关系。模拟结果表明:不同方向外加磁场抑制次级电子倍增的机理有所不同。轴向外加磁场利用电子回旋运动干扰微波电场对电子加速过程,使其碰壁能量降低以达到抑制二次电子倍增的效果;横向外加磁场利用电子回旋漂移过程中,电子半个周期被推离介质表面(不发生次级电子倍增),半个周期被推回介质表面(降低电子碰撞能量)的作用机理,达到抑制二次电子倍增的效果。讨论了横向磁场在回旋共振下,电子回旋同步加速导致回旋半径增大,电子能量持续增加的特殊过程。两种外加磁场方式都可以通过增加磁场达到进一步抑制次级电子倍增的目的。轴向外加磁场加载容易,但对磁场要求较高;横向外加磁场需要磁场较低,但加载较为困难。 相似文献
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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. 相似文献
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Photodetachment microscopy of H~- in the magnetic field near different dielectric surfaces
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《中国物理 B》2015,(6)
We study the photo-detachment interference patterns of a hydrogen negative ion in the magnetic field near different dielectric surfaces with a semi-classical open orbit theory.We give a clear physical picture describing the photo-detachment of H-in this case.The electron flux distributions are calculated at various dielectric surfaces with unchanged magnetic field strength.It is found that the electron flux distributions of H-are very different in a magnetic field near different dielectric surfaces,namely the dielectric surface has a great influence on the photo-detachment interference pattern of the negative ion.Therefore,the interference pattern in the detached-electron flux distribution can be controlled by changing the dielectric constant.We hope that our studies may guide the future experimental research in photo-detachment microscopy. 相似文献
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《Journal of magnetic resonance. Series B》1996,110(2):117-123
Electromagnetic resonators consisting of low-loss dielectric material and/or metallic boundaries are widely used in microwave technologies. These dielectric resonators usually have high Q factors and well-defined field distributions. Magnetic resonance imaging was shown as a way of visualizing the magnetic field distribution of the resonant modes of these resonators, if the dielectric body contains NMR sensitive nuclei. Dielectric resonators have also been proposed as RF coils for magnetic resonance experiments. The feasibility of this idea in high-field MR is discussed here. Specifically, the dielectric resonances of cylindrical water columns were characterized at 170.7 MHz (4 T1H Larmor frequency), and evaluated as NMR transmit and receive coils. The dielectric resonance of a cylindrical volume of D2O was used to image a hand at 170.7 MHz. This study demonstrated that MRI is an effective way of visualizing the magnetic field in dielectric structures such as a water cylinder, and can potentially be generalized to solid-state dielectric devices. The possible applications of dielectric resonators other than simple cylindrical volumes in MRI and MR solution spectroscopy at high field strengths are also discussed. 相似文献
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The effect of a constant magnetic field on the dielectric properties of triglycine sulfate crystals has been investigated. It has been shown that, after the magnetic treatment of the crystal (2 T, 20 min), the hysteresis loop becomes narrower; i.e., the coercive field decreases, and the dielectric permittivity changes in the region of the phase transition. It has been found that the observed effect is anisotropic with respect to the orientation of the crystal in a magnetic field and occurs when the vector of magnetic induction is perpendicular to the polar axis of the crystal. The relative orientation of the magnetic field and the domain structure determines its sign. The doping of the crystal with chromium makes the effect more pronounced and leads to a change in the kinetics of the magnetically stimulated increase in the dielectric permittivity. 相似文献
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E. A. Petrzhik E. S. Ivanova V. I. Alshits 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(10):1052-1057
Changes are found in the microhardness and dielectric permittivity of triglycine sulfate (TGS) crystals after magnetic treatment in a permanent magnetic field or in the scheme of electron paramagnetic resonance (EPR) using the Earth’s magnetic field. The temporal kinetics of microhardness reduction and the rise in dielectric permittivity (as along with their recovery) are nearly identical. The effects disappear when the crystal’s axis of symmetry is parallel to the static magnetic field in both variants of exposure. 相似文献
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《Waves in Random and Complex Media》2013,23(4):459-474
The dielectric permittivity tensor elements of a rotating cold collisionless plasma spheroid in an external magnetic field with toroidal and axial components are obtained. The effects of inhomogeneity in the densities of charged particles and the initial toroidal velocity on the dielectric permittivity tensor and field equations are investigated. The field components in terms of their toroidal components are calculated and it is shown that the toroidal components of the electric and magnetic fields are coupled by two differential equations. The influence of thermal and collisional effects on the dielectric tensor and field equations in the rotating plasma spheroid are also investigated. In the limiting spherical case, the dielectric tensor of a stationary magnetized collisionless cold plasma sphere is presented. 相似文献
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Kelvin J. A. Ooi 《Contemporary Physics》2013,54(2):197-198
When a conductor is in a magnetic field and radiation propagates in the direction of the field, the complex dielectric constant may be usefully represented on an Argand diagram so that the variation with magnetic field of the real and imaginary parts of the dielectric constant may be readily appreciated. 相似文献
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The drag force on ions moving in a magnetized electron plasma is calculated in dielectric linear response. Various representations of the dielectric function ε(k, ω) are investigated for their suitability to display the limits for an infinite and a vanishing magnetic field. While the influence of the magnetic field is negligible in certain regions of k-space, it introduces in other regions a strong oscillatory structure in the dielectric function. This requires a careful treatment of the multidimensional integrations necessary for the drag force. The contributions from oscillatory integrands are treated by the saddle point method. Explicit results are obtained for the dependence of the drag force on the magnetic field, the direction of motion of the ion relative to the magnetic field, the shielding in the electron plasma, its density and the anisotropy of the electron temperature. The importance of the collective response of the electrons is investigated for limiting cases of the magnetic field. The validity of the linearization of the dielectric theory is checked by comparison with results obtained by numerical simulation of the nonlinear Vlasov-Poisson equation. For strong magnetic fields and low ion velocities, the simulations rather agree with the complementary binary collision model than with linear response. 相似文献
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The dielectric response in a magnetic field is routinely used to probe the existence of coupled magnetic and elastic order in the multiferroics. However, here we demonstrate that magnetism is not necessary to produce a magnetocapacitance when the material is inhomogeneous. By considering a two-dimensional, two-component composite medium, we find a characteristic dielectric resonance that depends on magnetic field. We propose this as a possible signature of inhomogeneities and we argue that this behavior has already been observed in nanoporous silicon and some manganites. 相似文献
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All-dielectric left-handed metamaterial based on dielectric resonator: design, simulation and experiment
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Dipoles with Lorentz-type resonant electromagnetic responses can realise negative effective parameters in their negative resonant region. The electric dipole and magnetic dipole can realise, respectively, negative permittivity and negative permeability, so both the field distribution forms of electric and magnetic dipoles are fundamentals in designing left-handed metamaterial. Based on this principle, this paper studies the field distribution in high-permittivity dielectric materials. The field distributions at different resonant modes are analysed based on the dielectric resonator theory. The origination and influence factors of the electric and magnetic dipoles are confirmed. Numerical simulations indicate that by combining dielectric cubes with different sizes, the electric resonance frequency and magnetic resonance frequency can be superposed. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial composed by this means. 相似文献
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《Current Applied Physics》2007,7(1):34-38
We explore the dielectric relaxation properties of NiFe nanowires in a nanoporous silicon template. Dielectric data of the NiFe–silicon structure show a strong relaxation resonance near 30 K. This system shows Arrhenius type of behavior in the temperature dependence of dissipation peaks vs. frequency. We report magnetic field dependence of dipolar relaxation rate and the appearance of structure in the dielectric spectrum related to multiple relaxation rates. A magnetic field affects both the exponential prefactor in the Arrhenius formula and the activation energy. From this field dependence we derive a simple exponential field dependence for the prefactor and linear field approximation for the activation energy which describes the data. We find a significant angular dependence of the dielectric relaxation spectrum for regular silicon and nanostructured silicon vs. magnetic field direction, and describe a simple sum rule that describes this dependence. We find that although similar behavior is observed in both template and nanostructured materials, the NiFe–silicon shows a more complex, magnetic field dependent relaxation spectrum. 相似文献
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V. V. Braguta S. N. Valgushev O. V. Pavlovsky M. I. Polikarpov M. V. Ulybyshev 《JETP Letters》2013,97(9):517-519
Monte Carlo simulation of graphene in an external magnetic field perpendicular to the plane of graphene has been reported. The calculations have been performed using the effective quantum field theory with a noncompact (3 + 1)-dimensional Abelian gauge field and (2 + 1)-dimensional Kogut-Susskind fermions. It has been revealed that the external magnetic field shifts the semimetal-insulator phase transition point toward higher dielectric constants of the substrate. The phase diagram of the semimetal-insulator phase transition has been plotted in the (dielectric constant of the substrate-magnetic field) plane. 相似文献