Amplification of terahertz/infrared field at the nodes of Ranvier for myelinated nerve

The myelination of axons was the last major evolution in the vertebrate nervous system. Myelin promotes the speed of action potential by two orders, and modulates the conduction of neurons, important for learning new skills. However, the intrinsic mechanism for high-speed information propagation in myelin in the nervous systems is still unclear. We propose that myelinated nerve fibres serve as dielectric waveguides for the high-frequency electromagnetic information in a certain mid-infrared to terahertz spectral range. Based on the structure characteristics of myelinated nerve composed of periodic nodes of Ranvier and myelin sheath, the energy for the signal propagation is supplied and amplified when crossing the nodes of Ranvier via a periodic relay. In this work, we exploit the quasi-quantum model of amplification for neural terahertz/infrared information at the nodes of Ranvier, and prove the existence of biomolecular ensemble for three-energy-level amplification, revealing the essential mechanism of high-speed electromagnetic information transmitting in myelinated nerves.     

一种传播速度可以是任意值的特殊"电磁波"

通过对一个具体事例的求解--一种特殊静磁场的坐标变换,得出了一种特殊的"电磁波",它的传播速度可以是任意值.指出了这种特殊的"电磁波"与传统意义上的电磁波的本质区别,并对一般意义的电磁波与传统意义上的电磁波的概念进行了厘清.本文对于深刻理解和认识电磁场、电磁场的坐标变换和电磁波具有一定意义.     

电磁脉冲在实验室等离子体中传播时间的实验研究

利用矢量网络分析仪，对频域9—11 GHz的电磁脉冲在实验室稳态无磁场等离子体中传播时间的问题进行了实验研究.实验发现当等离子体密度在0.65—1.43×10¹¹ cm^-3范围内时，电磁脉冲通过该等离子体传播的时间将会小于该电磁脉冲在真空中传播同样距离所需要的时间，在密度约为1.10×10¹¹ cm^-3时，这两个时间差会出现一个极值.进一步的研究表明在此密度范围内，非磁化Xe等离子体中的电磁波色散关系将不再成立. 关键词： 电磁脉冲 脉冲传播时间 等离子体密度 色散关系     

On Anomalous Propagation in Transversely Uniaxial Bianisotropic Mediums

We consider the propagation of a plane electromagnetic wave in transversely uniaxial bianisotropic mediums (TUBMS). Anomalous propagation takes place when a certain condition is fulfilled by the constitutive parameters of the medium. A detailed field analysis for this anomalous behaviour is provided.     

基于二维特异材料波导的表面电磁波的慢波实验研究

本文在理论分析的基础上,实验研究了二维MNG/DPS/MNG(磁单负材料/双正材料/磁单负材料)表面波波导中的慢波效应.该波导的色散曲线随着电路参数(单元电容)的改变而改变,而且在色散曲线的截止频率点,电磁波的群速度理论上等于零.因此可以通过改变MNG区域的电路参数,得到在不同截止频率的慢波特性.另外,本文还通过改变MNG区域的电路参数实现在某一固定频率下波速度渐变的慢波效应.实验结果与仿真结果相一致.     

Extinction theorem and propagation of electromagnetic waves between two anisotropic materials

We systematically investigate the reflection and refraction of an electromagnetic wave between two semi-infinite anisotropic magnetoelectric materials. Using the integral formulation of Hertz vectors and the principle of superposition, we generalize the extinction theorem and derive the propagation characteristics of wave. Applying the results obtained, we find a general origin of Brewster effect. We also show that, through choosing appropriate material parameters, oblique or omnidirectional total transmission can occur to TE and TM waves. Compared to the traditional method, the method used here discloses the underlying mechanism of wave propagation between two arbitrary anisotropic materials and can be applied to other problems of propagation.     

基于数字地图的二维电波传播问题仿真

为快速预测二维地理环境下的电磁环境特性,应用二维抛物方程模型对电磁环境进行仿真。为了得到真实有效的地形数据,研究了从GeoTiff中抽取网格点上地理信息的方法,并利用双线性插值法计算了任意位置处的高程值。同时研究了地球表面两点之间计算距离的方法,将该方法的计算结果与GIS软件结果进行对比,验证了该方法的可靠性。在标准大气环境下,利用二维抛物方程模型仿真分析了不同距离处不同高度的电波传播传播因子的变化情况,为预测真实地理环境中的电波传播特性提供了一种有效的方法。     

Velocity field of wave-induced local fluid flow in double-porosity media

Under the excitation of elastic waves,local fluid flow in a complex porous medium is a major cause for wave dispersion and attenuation.When the local fluid flow process is simulated with wave propagation equations in the double-porosity medium,two porous skeletons are usually assumed,namely,host and inclusions.Of them,the volume ratio of inclusion skeletons is low.All previous studies have ignored the consideration of local fluid flow velocity field in inclusions,and therefore they can not completely describe the physical process of local flow oscillation and should not be applied to the situation where the fluid kinetic energy in inclusions cannot be neglected.In this paper,we analyze the local fluid flow velocity fields inside and outside the inclusion,rewrite the kinetic energy function and dissipation function based on the double-porosity medium model containing spherical inclusions,and derive the reformulated Biot-Rayleigh(BR)equations of elastic wave propagation based on Hamilton’s principle.We present simulation examples with different rock and fluid types.Comparisons between BR equations and reformulated BR equations show that there are significant differences in wave response characteristics.Finally,we compare the reformulated BR equations with the previous theories and experimental data,and the results show that the theoretical results of this paper are correct and effective.     

旋光媒质中光波传播的物理光学理论

由麦克斯韦电磁理论,结合旋光媒质的本构关系,研究旋光媒质中光波的传播,给出均匀媒质中光波的色散关系、媒质界面上光波的反射和折射规律以及旋光性的结果.     

Ephaptic coupling of myelinated nerve fibers

Numerical predictions of a simple myelinated nerve fiber model are compared with theoretical results in the continuum and discrete limits, clarifying the nature of the conduction process on an isolated nerve axon. Since myelinated nerve fibers are often arranged in bundles, this model is used to study ephaptic (nonsynaptic) interactions between impulses on parallel fibers, which may play a functional role in neural processing.     

信号在时变等离子体中的传播特性

高速飞行器等离子鞘套由于飞行姿态调整、湍流、非均匀烧蚀等因素的影响,使其等离子体参数存在时变特性,针对这种传输介质的快速时变特性引起的电波幅度、相位上的寄生调制效应,本文利用大面积辉光放电等离子体产生装置,搭建了等离子体中信号传输实验系统,进行了S频段的单频信号与调制信号传输实验,观测验证了调制效应的存在,且其调制频率与等离子体变化频率具有一致性,进一步分析了等离子参数与寄生调制效应的关系,理论和实验结果表明:即使当载波频率大于等离子频率时,时变等离子引起的寄生调制效应也会使传输信号的星座图发生旋转,造成其判决容差裕度变小,通信可靠性下降,并且载波频率越接近等离子频率时,其寄生调制效应越强烈。     

THz电磁波在时变非磁化等离子体中的传播特性研究

本文建立了时变非磁化等离子体平板的一维模型,并采用时域有限差分(FDTD)方法对太赫兹(THz)电磁波在时变等离子体中传播时的反射、透射系数及吸收率进行了计算.然后根据计算结果分析了时变等离子体的上升时间、电子密度、温度以及等离子体平板厚度等参数对不同频段THz波在等离子体中传播特性的影响.分析结果表明:THz波在时变等离子体中传播时,其反射系数受等离子体电子密度和上升时间的影响较大;而吸收率则随着上升时间的减小、电子密度及平板厚度的增加而增大;此外,THz电磁波能够穿透量级为1020m-3的高密度等离子体层,可以作为再入段飞行器通信以及高密度等离子体诊断的理想工具.     

Theory of electromagnetic wave propagation in a longitudinally periodic cylinder

Thinking of photonic crystals, we investigate the theory of electromagnetic wave propagation in a perfectly conducting semi-cylinder endowed with a periodic permittivity along its axis while its circular base is illuminated by an harmonic Bessel beam, symmetric around the cylinder axis. We prove that the Floquet-Bessel expansions of electromagnetic fields whose Floquet parts are solutions of a Mathieu equation. is a suitable tool to handle this kind of problems.     

Pseudo-Hermiticity and electromagnetic wave propagation: The case of anisotropic and lossy media

Pseudo-Hermitian operators can be used in modeling electromagnetic wave propagation in stationary lossless media. We extend this method to a class of non-dispersive anisotropic media that may display loss or gain. We explore three concrete models to demonstrate the utility of our general results and reveal the physical meaning of pseudo-Hermiticity and quasi-Hermiticity of the relevant wave operator. In particular, we consider a uniaxial model where this operator is not diagonalizable. This implies left-handedness of the medium in the sense that only clockwise circularly polarized plane-wave solutions are bounded functions of time.     

多组份流动质量分数保极值原理算法

对基于质量分数的Mie-Gruneisen状态方程多流体组份模型提出了新的数值方法.该模型保持混合流体的质量、动量、和能量守恒,保持各组份分质量守恒,在多流体组份界面处保持压力和速度一致.该模型是拟守恒型方程系统.对该模型系统的离散采用波传播算法.与直接对模型中所有守恒方程采用相同算法不同的是,在处理分介质质量守恒方程时,对波传播算法进行了修正,使之满足质量分数保极值原理.而不作修改的算法则不能保证质量分数在[0,1]范围.数值实验验证了该方法有效.     

各向异性渗流条件下弹性波的传播特征

研究了弹性波在非均匀裂纹孔隙介质中的传播特性,建立了各向异性喷射流模型.当弹性波通过裂纹孔隙介质时,由于波的扰动及裂纹和孔隙几何结构的不一致,导致在裂纹内部及裂纹与周边孔隙之间同时存在着流体压力梯度.此时的弹性波波动响应中包含着裂纹内连通性特征和背景孔隙渗透率信息.流体的动态流动过程使得介质的等效弹性参数为复数(非完全弹性),并且具有频率依赖性.当弹性波为低频和高频极限时,介质为完全弹性;当处于中间频段时,波有衰减和频率依赖.裂纹孔隙介质的各向异性连通性(渗透率)对应着各向异性特征频率(当渗流长度等于非均匀尺度时的弹性波频率),波的传播受到裂纹内连通性的影响.在一定频段内,随着裂纹厚度的增加,将出现第二峰值,峰值大小同时受到裂纹厚度和半径的影响.     

Towards dispersion relations for tapered core dielectric elliptical fibers

The paper presents an analytical investigation of the electromagnetic wave propagation in a tapered core dielectric elliptical step-index fiber. Implementing Maxwell's equations in elliptical coordinates, field components are deduced that essentially incorporate Mathieu and the modified Mathieu functions. Finally, the characteristic dispersion equations are developed for even and odd modes supported by the fiber.     

Electroseismic waves excited by vertical magnetic dipole in borenole

Acoustic and electromagnetic fields are coupled in a fluid saturated porous medium due to seismoelectric effect. Seismoelectric well logging method has been proposed to detect deep target formation utilizing such effect. Because of uncoupling of SH waves with P-SV waves, a simple and forthright way to get shear waves information is possible, especially for soft or slow formation whose shear wave velocity is lower than the velocity of borehole fluid. We consider the wave fields excited by a vertical magnetic dipole (VMD) source. Two methods are used to simulate, one is the coupled method based on Pride model and the other is the uncoupled method. For two methods, the frequency wavenumber domain representations of the acoustic field and associated seismoelectric field are formulated. The full waveforms of acoustic waves and electromagnetic wave induced SH waves excited by VMD source in the time domain propagation in borehole are simulated and analyzed.     

强流环形电子束在同轴永磁Halbach结构磁路中传输的初步分析

利用有限元程序SUPERFISH计算求解了同轴永磁Halbach结构磁路的磁场, 并推导出该磁场位形磁感应强度各分量的近似表达式. 利用流体模型分析了作用在电子束上的力并导出了改进马丢方程形式的径向力平衡方程, 给出了平衡条件; 利用2.5维全电磁粒子模拟程序研究了强流环形电子束在该周期系统中传输的物理过程. 计算得出强流相对论电子束的稳定传输与电子束电流, 电子束厚度, 磁场强度, 电子束入射角度等因素有关. 分析认为利用同轴永磁Halbach结构磁路导引数KA的环形电子束, 并使之稳定传输是可能的. 同时该磁场聚焦形式也为Ubitron中的束--波相互作用提供了一个作用机制.     

Wave propagation in axion electrodynamics

In this paper, the axion contribution to the electromagnetic wave propagation is studied. First we show how the axion electrodynamics model can be embedded into a premetric formalism of Maxwell electrodynamics. In this formalism, the axion field is not an arbitrary added Chern–Simon term of the Lagrangian, but emerges in a natural way as an irreducible part of a general constitutive tensor. We show that in order to represent the axion contribution to the wave propagation it is necessary to go beyond the geometric approximation, which is usually used in the premetric formalism. We derive a covariant dispersion relation for the axion modified electrodynamics. The wave propagation in this model is studied for an axion field with timelike, spacelike and null derivative covectors. The birefringence effect emerges in all these classes as a signal of Lorentz violation. This effect is however completely different from the ordinary birefringence appearing in classical optics and in premetric electrodynamics. The axion field does not simple double the ordinary light cone structure. In fact, it modifies the global topological structure of light cones surfaces. In CFJ-electrodynamics, such a modification results in violation of causality. In addition, the optical metrics in axion electrodynamics are not pseudo-Riemannian. In fact, for all types of the axion field, they are even non-Finslerian.