导电介质中电磁波相移常数与振幅衰减常数的方向关系的讨论

对文献上给出的非均匀电磁波在同一均匀导电介质中传播时,电磁波的相移常数和振幅衰减常数方向之间满足定量关系的结论,重新进行了分析和推导,利用电磁波在导电介质界面的边界条件,给出了两种情况下的相移常数和振幅衰减常数的表达式,以及它们与界面法线的夹角正弦的表达式.结果表明,在同一均匀导电介质中,非均匀电磁波的相移常数的方向和振幅衰减常数的方向之间一般不满足定量关系.     

光在吸收介质中传播的折射定律

光波在均匀非吸收介质中传播时振幅不衰减,在两种非吸收介质界面处产生折射现象,由几何光学中实数形式的光折射定律定量描述.而光波在均匀吸收介质中传播时,其振幅沿传播方向衰减,且其等振幅面与等相位面会发生分离.考虑吸收对光波传播特性的影响,本文回顾了复折射率的概念和复数形式的折射定律,据此对光波由吸收介质入射到吸收介质和光波由非吸收介质入射到吸收介质的两种情况进行了讨论,阐明了复数折射定律在具体问题讨论中的必要性和便利性,同时分析了实数形式和复数形式折射定律的关系.     

多层光变防伪膜的非均匀垂直偏振光反射特性

基于非均匀光波在导电介质中传播时其相移传播方向和振幅衰减方向的不一致性,利用光波动方程的解由电磁场边界条件导出非均匀垂直偏振光在多层超薄金属膜与透明介质膜组合膜系中光波的传输递推公式.为验证方法的可靠性,给出了不同厚度金属膜防伪光变膜系的能量反射率算例,并与现有算法进行对比,结果表明:两种算法得到的能量反射曲线的分布特征具有很好的相似性,但本文算法表现出金属膜具有强的吸收特性和窄带反射效应.     

电磁波在磁化等离子体中传播的时域有限差分模拟

基于Z变换形式的时域有限差分法计算公式,模拟了传播方向垂直于磁化磁场的电磁波在磁化等离子体层中的传播.通过离散傅立叶变换,给出了电磁波通过均匀和非均匀磁化等离子体后的反射系数和透射系数随频率的变化关系.还给出了电磁波经过均匀磁化等离子体层后的反射和透射系数和理论值的对比.     

论菲涅耳公式对半波损失的解释

本文对一般教科书中直接用菲涅耳公式解释电磁波的半波损失问题提出质疑,认为平行于入射面的反射波、折射波与入射波的电矢量振动的振幅一般不在同一直线上,由菲涅耳公式给出的反射波、折射波与入射波电矢量振动的振幅之比,只能描述其相应振幅之比的大小随入射角和折射角变化的关系,而不能反映其相应振幅间的位相随入射角和折射角变化的关系.笔者认为若将平行于入射面的电矢量振动的振幅分解为平行于界面法线和垂直于界面法线的两个坐标分量,然后根据边界条件导出相应振幅坐标分量之比随入射角和折射角变化的关系。便可以较为严格地解释电磁波在界面反射中发生半波损失的物理实质。 关于电磁波的半波损失在其有关学术领域中一直是一个众说纷纭的问题,近年来,在国内举行的有关学术讨论会中,对该问题的争论重新激烈起来,其争论的焦点在于如何用菲涅耳公式解释电磁波传播至两不同介质的界面时,发生半波损失现象的物理实质。 所谓半波损失,其实质是位相突变π,即电磁波经界面反射后,反射波的电矢量振动的振幅与入射波的振幅反向,亦有π的位相差。反射波位相的改变取决于具体问题的边界条件。振幅反向即位相差为π。对应半波长(λ/2)的光程改变。并非反射过程中真实失去λ/2的光程。 经典电磁理论认为,     

对"关于‘电磁波在非均匀等离子体中的吸收''的评论"的回复

在张海峰等的评文 (以下简称评文 )中提到 ,总出射波振幅应等于每层等离子体反射与透射振幅的矢量和 ,而在我们文章中认为总出射功率等于每层等离子体反射与透射功率之和。我们认为在对空间取平均后 ,这两种观点是一致的。与我们原来文章的假定一样 ,我们设非均匀等离子体层的厚度为ｄ。电磁波由等离子体的一侧入射 ,另一面为金属反射面。电磁波电场的极化方向如图 1所示。取ｚ轴垂直于等离子体层 ,平衡等离子体密度在ｚ方向具有非均匀性。Ｅ′ｉ 为电磁波在第ｉ层与第ｉ + 1层界面反射后 ,最后射出等离子体层的出射电场矢量为 :Ｅ′ｉ =-Ｅ…     

电磁波在非均匀等离子体中的吸收

研究了电磁波在非均匀碰撞等离子体中的传播和吸收,提出了一种计算电磁波在非均匀等离子体层中反射和透射功率的模型。对几种典型的非均匀密度剖面,计算了在不同的碰撞频率和层边缘密度下电磁波衰减率与电磁波频率的关系,结果表明,对于给定的密度剖面和有效吸收频宽,存在一个最佳的磁撞频率。     

电磁波在一维非均匀介质中的透射

推导了一维非均匀介质中透射电磁波的电场振幅与介质表面入射电磁波电场振幅之间的关系式 关键词：     

离子对电磁波传播特性的影响

对等离子体中电磁波传播的平板几何模型进行了修正, 讨论了离子对电磁波在大气压均匀非磁化弱电离等离子体中的反射、吸收和透射等传播特性的影响。数值分析的结果表明: 大气条件下, 离子对电磁波在均匀非磁化弱电离等离子体中传播特性的影响是显著的, 同时给出等离子体对电磁波的最大吸收值和吸收宽带。     

O型契伦柯夫器件慢波结构高频特性

理论推导了电磁波在半无限长直波导和均匀慢波结构交界面上的反射系数表达式,得到反射系数模值和相位随电磁波的纵向相移常数和慢波结构末端相位的变化关系。运用传输线理论以及反射系数的理论计算结果,得到了有限长慢波结构的纵向谐振条件,可以分析各种情况下有限长慢波结构的纵向谐振特性。计算了一种有限长慢波结构的纵向谐振频率,理论预测与数值仿真结果基本一致。对于一种非均匀慢波结构的数值计算结果表明,其纵向谐振模式对应的频率、场分布与相应的均匀慢波结构接近,因此仍可根据提出的纵向谐振条件对非均匀慢波结构进行分析。     

Determination of the gravitational constant G

A precise knowledge of the Newtonian gravitational constant G has an important role in physics and is of considerable meteorological interest. Although G was the first physical constant to be introduced and measured in the history of science, it is still the least precisely determined of all the fundamental constants of nature. The 2002 CODATA recommended value for G, G = (6.6742 ± 0.0010) × 10⁻¹¹m³ · kg⁻¹ · s⁻², has an uncertainty of 150 parts per million (ppm), much larger than that of all other fundamental constants. Reviewed here is the status of our knowledge of the absolute value of G, methods for determining G, and recent high precision experiments for determining G.     

Stress-energy connection and cosmological constant problem

We study gravitational properties of vacuum energy by erecting a geometry on the stress-energy tensor of vacuum, matter and radiation. Postulating that the gravitational effects of matter and radiation can be formulated by an appropriate modification of the spacetime connection, we obtain varied geometrodynamical equations which properly comprise the usual gravitational field equations with, however, Planck-suppressed, non-local, higher-dimensional additional terms. The prime novelty brought about by the formalism is that, the vacuum energy does act not as the cosmological constant but as the source of the gravitational constant. The formalism thus deafens the cosmological constant problem by channeling vacuum energy to gravitational constant. Nevertheless, quantum gravitational effects, if any, restore the problem via the graviton and graviton-matter loops, and the mechanism proposed here falls short of taming such contributions to cosmological constant.     

恒温恒湿空调三种工况下自动控制研究

针对恒温恒湿空调在夏季、冬季和过渡季节三种典型工况下的自动控制,详细分析了三种工况下空气处理过程,对温度和湿度的控制进行了分解、给出了实现框图并分析了控制系统本身造成的控制精度问题,为恒温恒湿空调的控制改进提供参考。     

Wormhole with varying cosmological constant

It has been suggested that the cosmological constant is a variable dynamical quantity. A class of solution has been presented for the spherically symmetric space time describing wormholes by assuming the erstwhile cosmological constant Λ to be a space variable scalar, viz., Λ = Λ (r) . It is shown that the averaged null energy condition (ANEC) violating exotic matter can be made arbitrarily small.     

测量光栅常量的一种简便方法

介绍了用普通日光灯作光源测量光栅常量的简便方法。     

相对介电常量实验研究

利用冰作介质，在低频范围内研究了相对介电常量随频率变化的规律。     

利用常脉冲扰动实现混沌控制

提出一种通过常脉冲对非线性系统中的变量进行扰动实现混沌控制的方法。以单模激光混沌系统为例 ,进行了数值研究。结果表明 :该方法能有效地控制非线性系统中的混沌行为 ,并获得了一系列稳定的周期轨道。     

Colossal dielectric constant in high entropy oxides

Entropic contributions to the stability of solids are very well understood and the mixing entropy has been used for forming various solids, for instance such as inverse spinels, see Nawrotsky et al., J. Inorg. Nucl. Chem. 29 , 2701 (1967) [1]. A particular development was related to high entropy alloys by Yeh et al., Adv. Eng. Mater. 6 , 299 (2004) [2] and Cantor et al., Mater. Sci. Eng. A 375–377 , 213 (2004) [3] (for recent reviews see Zhang et al., Prog. Mater. Sci. 61 , 1 (2014) [4] and Tsai et al., Mater. Res. Lett. 2 , 107 (2014) [5]) in which the configurational disorder is responsible for forming simple solid solutions and which are thoroughly studied for various applications especially due to their mechanical properties, e.g. Gludovatz et al., Science 345 , 1153 (2014) [6] and Lu et al., Sci. Rep. 4 , 6200 (2014) [7], but also electrical properties, Kozelj et al., Phys. Rev. Lett. 113 , 107001 (2014) [8], hydrogen storage, Kao et al., Int. J. Hydrogen Energy 35 , 9046 (2010) [9], magnetic properties, Zhang et al., Sci. Rep. 3 , 1455 (2013) [10]. Many unexplored compositions and properties still remain for this class of materials due to their large phase space. In a recent report it has been shown that the configurational disorder can be used for stabilizing simple solid solutions of oxides, which should normally not form solid solutions, see Rost et al., Nature Commun. 6 , 8485 (2015) [11] these new materials were called ”entropy‐stabilized oxides”. In this pioneering report, it was shown that mixing five equimolar binary oxides yielded, after heating at high temperature and quenching, an unexpected rock salt structure compound with statistical distribution of the cations in a face centered cubic lattice. Following this seminal study, we show here that these high entropy oxides (named HEOx hereafter) can be substituted by aliovalent elements with a charge compensation mechanism. This possibility largely increases the potential development of new materials by widening their (already complex) phase space. As a first example, we report here that at least one HEOx composition exhibits colossal dielectric constants, which could make it very promising for applications as large‐k dielectric materials. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)