Normal halogen dependence of 13C NMR chemical shifts of halogenomethanes revisited at the four‐component relativistic level

The ‘Normal Halogen Dependence’ of ¹³C NMR chemical shifts in the series of halogenomethanes is revisited at the four‐component relativistic level. Calculations of ¹³C NMR chemical shifts of 70 halogenomethanes have been carried out at the density functional theory (DFT) and MP2 levels with taking into account relativistic effects using the four‐component relativistic theory of Dirac‐Coulomb within the different computational methods (4RPA, 4OPW91) and hybrid computational schemes (MP2 + 4RPA, MP2 + 4OPW91). The most efficient computational protocols are derived for practical purposes. Relativistic shielding effect reaches as much as several hundreds of ppm for heavy halogenomethanes, and to account for this effect in comparison with experiment at the qualitative level, relativistic Dyall's basis sets of triple‐zeta quality or higher are to be used within the framework of the four‐component relativistic theory taking into account solvent effects. Relativistic geometrical optimization (as compared with the non‐relativistic level) is essential for the molecules containing at least two iodines at one carbon atom. Copyright © 2016 John Wiley & Sons, Ltd.     

Li-defect interactions in electron-irradiated n-type silicon by EPR measurements

Single crystal silicon, both with and without oxygen, has been diffused with lithium to concentrations ～10¹⁷/cm², irradiated with 1 to 1.5 MeV electrons, and the ensuing defects studies by EPR measurements. The presence of oxygen strongly affects the properties of these defects. Measurements have indicated the presence of two new defects which involve Li-one in O-containing material and one in O-free material. The defects are observed in their electron-filled state, and indicate a net electron spinof ½. The defect spectra disappear (with time) at room temperature, and can be explained by the formation of other Li-involved defects which lie deeper in the energy bandgap and are not visible by EPR. Electron irradiation at 40 °K followed by annealing at higher temperatures show that both EPR defects described above begin to form at about 200 °K and begin to decrease at about 275 °K-just as does the 250 °K reverse annealing observed generally for n-type Si. Based on these data, and the work of others, it is suggested that both defects form as a result of the motion of Si interstitials which produce a (Li-O-interstitial) complex in O-containing Si, and a (Li-interstitial) complex in O-free Si.     

Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations

The technique of applying form-invariant, spatial coordinate transformations of Maxwell’s equations can facilitate the design of structures with unique electromagnetic or optical functionality. Here, we illustrate the transformation-optical approach in the designs of a square electromagnetic cloak and an omni-directional electromagnetic field concentrator. The transformation equations are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations. The two devices presented demonstrate that the transformation optic approach leads to the specification of complex, anisotropic and inhomogeneous materials with well directed and distinct electromagnetic behavior.     

New localized Superluminal solutions to the wave equations with finite total energies and arbitrary frequencies

By a generalized bidirectional decomposition method, we obtain new Superluminal localized solutions to the wave equation (for the electromagnetic case, in particular) which are suitable for arbitrary frequency bands; several of them being endowed with finite total energy. We construct, among the others, an infinite family of generalizations of the so-called “X-shaped" waves. Results of this kind may find application in the other fields in which an essential role is played by a wave-equation (like acoustics, seismology, geophysics, gravitation, elementary particle physics, etc.). Received 23 June 2002 Published online 24 September 2002 RID="a" ID="a"Work partially supported by MIUR and INFN (Italy), and by FAPESP (Brazil). This paper did first appear as e-print physics/0109062 [and as preprint INFN/FM-01/02 (I.N.F.N.; Frascati, 2001)]. RID="b" ID="b"e-mail: recami@mi.infn.it     

空气中声波对电磁波的定向反射

以电磁波折射率具有周期性变化的层状结构来模拟空气中两个相距较远的相干声源干涉形成的中心区域,研究了结构对电磁波定向反射的特性。理论研究结果表明:尽管声波在空气中引起的电磁波折射率的振荡幅度非常小,但是在一定的条件下,声波的存在会对电磁波造成非常强烈的定向反射。文中给出了发生强烈定向反射时,声波波长、电磁波波长和入射角等应该满足的条件,并且计算了反射峰的宽度。     

有限差分法解电磁场方程的共轭梯度法三角阵预处理器

通过考察电磁场微分方程经非均匀网格离散后的有限差分方程组矩阵,建立了函数偏微分运算与离散向量矩阵相乘运算的对应关系,给出了差分方程组矩阵对应于微分算子的分解式,并据此提出了共轭梯度法的三角阵预处理器。此外,还提出了对不同的边界条件、求解域内部边界、介质分界面和时谐场方程的处理技术以便应用该预处理器。数值计算结果验证了本文算法的正确性,展示了其十分明显的加速收敛效果,表明了本文算法有线性的存储复杂度和几乎线性的计算复杂度,可有较广泛的应用。本文中将算子细节和矩阵细节对应的基本思想对构造其它高效预处理器具有借鉴作用。     

基于高斯积分的平面波谱法分析天线罩电性能

将平面波谱表面积分法与高斯积分相结合分析天线罩的电特性。在计算了口径天线的差波谱以求解带罩天线差方向图的基础上,将高斯积分应用到由罩外表面切向场求远场方向图中,提高了平面波谱法的计算精度。最后通过具体算例表明了本文方法的有效性。     

变频器在变压器绕线机系统中的应用

本文介绍了如何使用普传PI7100变频器的主板端子功能、制动功能及保护功能实现变压器绕线机系统的自动调速控制的工艺要求。着重介绍控制系统如何设计及其工作过程，变频器常见故障及排除措施。     

变频调速应用技术（十一）——第六讲经济效益赞变频（上）

本文分析了节能问题的几个方面。主要有：负载需求与节能的关系，调速方法与节能的关系，以及大马拉小车的节能问题等。     

屏蔽与接地技术中值得注意的几个问题

屏蔽线信号传输线路被广泛应用在计算机网络系统和有线电视系统中,它既可防止被干扰,也可以防止对外辐射造成干扰。本文通过对几种不同的“屏蔽接地”形式的比较,说明干扰电压的形成及解决方法。