能带理论的进展

引言一、能带的形成 1.周期性势场中电子的波函数 2.电子的加速度与速度二、能带计算的主要方法 1.紧束缚法 2.原胞法 3.正交化平面波法三、和能带结构有关的物理性质 1.回旋共振 a.半导体的迴旋共振 b.金属的迴旋共振 2.电流磁效应 a.n型锗和硅 b.p型锗和硅 3.磁化率 a.晶体中电子的磁化率 b.半导体的磁化率 c.底哈斯,凡阿尔芬效应 4.反常的趋肤效应参考文献     

水的汽化热实验装置的改进

水的汽化热实验是高校普物实验中的一个传统实验.目前国内高校测水的汽化热误差较大,效果不佳.经过反复实验,我们制成一套测定水的汽化热的仪器.此仪器结构简单、成本低、测量方便、误差小. 如图所示:被橡皮塞2紧密固定盖住的球形烧瓶1中装有水.加热器3的引出线和管4穿过塞子.管4使排出的蒸汽通过冷凝器5成冷却水.当水沸腾时,形成的蒸汽通     

内耗研究的历史评述

通过介绍几位在内耗领域的先驱研究者:C.Zener,葛庭燧,P.G.Bordoni ,J.L.Snoek,评述了内耗研究的进展.也介绍了日本研究者的相关工作.     

反作用力的演示

材料: 1.容量为80c.c.的试管一个。2.软木塞一个。软木塞的大小与试管口的大小相同。此软木塞中央有一小孔。3.长约5厘米的玻璃管一根,其直径与软木塞中央的小孔一样。4.碳酸钙(CaCO_3)约10克。5.浓度为35—37%的盐酸(HC1)约20克     

高均匀度的NMR超导磁体的设计计算

本文给出了高均匀度的NMR超导磁体的设计方法.给出了体积极小的六阶补偿线圈的各个参数. 讨论了几何尺寸误差带来的影响.给出了补偿绕组位置可调磁体的计算结果.     

邮票上的物理学史——原子论的确立

原子论最早是由古希腊哲学家德谟克利特 (邮票见本专栏第一篇“古希腊时期”)提出的 .他认为 ,万事万物都由原子和虚空组成 .原子既不可分 ,也不会变 ,并且没有内部组成 .不同元素的原子不同 .它们以机械的嵌合方式结合 ,构成万物 .各种物体及其属性的差别归结为组成它们的原子的数量不同 .这个理论带有朴素唯物论的色彩 .伊壁鸠鲁继承和发展了德谟克利特的原子论 ,他的原子可以有内部组成 ,但仍是不可分的 .罗马的卢克莱修的长诗《论物性》系统地阐述和宣扬了伊壁鸠鲁的原子论 .文艺复兴后 ,原子论也得到恢复 .对早期原子论做出重要贡献的…     

从阴极射线的争议到电子的发现

一、从“暗区”到“阴极射线” 法拉第在1838年研究真空放电时发现真空管中出现一道暗环,它把紫色的阴极电辉和粉红色的阳极电辉分开.随着气压降低,阳极辉光就变成了数条彩带.后来这个暗环便命名为“法拉第暗区”. 二十一年过去了.德国物理学家J.Pluck重新研究法拉第暗区时偶然发现,在阴极附近的管壁上有一片荧光,磁铁可以改变它的位置.Pluck直觉认为,荧光很可能是由阴极抛射出的某种带电粒子流撞击管壁产生的.但是,他又觉得这种解释与法拉第把电当作“力态”的思想相违,遂不敢坚持己见[1], 又过了十年,Pliuck的学生J.W.Hittorf实验证明…     

简易动画机的制作

青少年都非常喜欢动画片,为了使他们了解电影、电视中动画的视觉暂留原理,并且能够自己动手制作简易动画机,自行设计创作各种动画,进而培养学生的创新精神和实践能力.因此,开发研制了一种主要利用可乐瓶制作的“科教简易动画机”.1　原理结构科教简易动画机主要根据人眼对图象可以停留0.1s的视觉暂留原理和巧妙的顶针式转动机构设计研制的.该作品由转桶部分、底座部分、动画部分构成.具体结构如图1所示.图1　简易动画机的结构示意图1.长条孔带2.竖直条形动画3.水平圆形动画4.圆盘5.粘接剂6.底板7.瓶底8.顶针轴9.车条帽10.转桶1.1　转桶部分…     

关于B.W.Lee的公式ΓΓ=0的推广

本文将B.W.Lee的公式Γ*Γ=0推广为Γ^AF=0^[1,2], 只要命B.W.Lee公式中的dλ=ζ₁ζ₂ζ₀即可, 而不需要B.W.Lee式的二次变化变化等于零的限制. 从而, 该公式不仅包含了B.W.Lee的公式, 而且能直接解决其他一些问题.     

邮票上的物理学史⒂--光谱学的建立

光的波动说确立之后,人们知道光谱中的不同成分对应于不同的频率(波长),并且测量了不同色光的波长.整个可见光光谱的宽度,从红光到紫光,大约一个倍频程.图1为西班牙1969年发行的纪念在马德里召开的第15次国际光谱学会议的邮票,画面是可见光谱.发现天王星的英国天文学家W.赫舍尔首先指出光谱超出可见光的范围,1800年,他用水银温度计做接收器,证明了红外线的存在.图2是英国1970年发行的纪念皇家天文学会成立150周年的邮票,左边手中拿星图的是W.赫舍尔,他是皇家天文学会的创始人和第一任会长,右边是他的儿子J.赫舍尔,中间是F.Baily,都是著名的天文学家.紫外线则是1803年J.Ritter发现的.     

Abelian Higgs model with a Chern-Simons term in 3-dimensional gravitation

We consider the Abelian Higgs model with a Chern-Simons term coupled to the Einstein theory of gravitation in 3-dimensional space-time. We seek a finite solution, regular everywhere, having a stationary, cylindrically symmetric metric. We analyze these field equations and we suggest that such a solution exists. We find that the asymptotic metric of this solution corresponds to that which describes gravitationally a massive particle with spin. We obtain explicitly the expression of the spin. We give only the expression of the mass in the first order with respect to the gravitational coupling constant.     

Resistive Plates Carrying a Steady Current: Electric Potential and Surface Charges Close to the Battery

We treat the problem of two resistive plates carrying a steady current in the same direction. We consider a linear battery orthogonal to the direction of the current in the middle of the plates. We study the behavior of the surface charges close to the battery. We calculate the potential and electric field in the space outside the plates. We also consider the case of a single resistive plate carrying a steady current.     

Quantum phase analysis of 1D superconducting quantum dot lattice using extended Bose-Hubbard model

We have obtained the quantum phase diagram of a one-dimensional superconducting quantum dot lattice using the extended Bose-Hubbard model for different commensurabilities. We describe the nature of different quantum phases at the charge degeneracy point. We find a direct phase transition from the Mott insulating phase to the superconducting phase for integer band fillings of Cooper pairs. We predict explicitly the presence of two kinds of repulsive Luttinger liquid phases, besides the charge density wave and superconducting phases for half-integer band fillings. We also predict that extended range interactions are necessary to obtain the correct phase boundary of a one-dimensional interacting Cooper system. We have used the density matrix renormalization group method and Abelian bosonization to study our system.     

Multiplexing encryption technique by combining random amplitude and phase masks

We propose and demonstrate an encryption-selectable undercover multiplexing. We encrypt and multiplex images for storage by means of a random phase mask common to every image, covered with random amplitude masks different for each image. In order to get a correct decryption of the encoded information, we have to use the appropriate random amplitude mask; otherwise fake information is recovered. We employ a phase conjugation scheme to generate the recovering wavefronts. We analyze and compare the different alternatives and degrees of complexity this combination of masks brings to enhance the security of optical encrypting techniques. We also include an analysis on the advantages and disadvantages this undercover multiplexing protocol offers. We present digital simulations to demonstrate the soundness of the proposal.     

Diffusion controlled multiplicative process: typical versus average behaviour

We investigate the dynamics of the number of particles diffusing in a multiplicative medium. We show that the typical behaviour of the growth process is different from the average. We develop a new formalism to study the average growth process and extend it to the calculation of higher moments and finally of the probability distribution. We show that the fluctuations of the growth process increase exponentially with time. We describe the interesting features of the distribution.     

Stability of closed timelike curves in the Gödel universe

We study, in some detail, the linear stability of closed timelike curves in the Gödel universe. We show that these curves are stable. We present a simple extension (deformation) of the Gödel metric that contains a class of closed timelike curves similar to the ones associated to the original metric. This extension correspond to the addition of matter whose energy-momentum tensor is analyzed. We find the conditions to have matter that satisfies the usual energy conditions. We study the stability of closed timelike curves in the presence of usual matter as well as in the presence of exotic matter (matter that does satisfy the above mentioned conditions). We find that the closed timelike curves in the Gödel universe with or without the inclusion of regular or exotic matter are stable under linear perturbations. We also find a sort of structural stability.     

Flavor changing neutral currents and a Z′

We consider a non-universal Z′ that affects primarily the third generation fermions as an example of new physics associated with the top-quark. We first discuss constraints on the mass and coupling strength of such a Z′. We then turn our attention to the flavor changing neutral currents (FCNC) present in the model. We discuss the experimental constraints and their implications. We propose an ansatz to understand the smallness of the FCNC in terms of the CKM matrix.     

Controlling soliton explosions

We investigate the dynamics of solitons in generalized Klein–Gordon equations in the presence of nonlinear damping and spatiotemporal perturbations. We will present different mechanisms for soliton explosions. We show (both analytically and numerically) that some space-dependent perturbations or nonlinear damping can make the soliton internal mode unstable leading to soliton explosion. We will show that, in some cases, while some conditions are satisfied, the soliton explodes becoming a permanent, extremely complex, spatiotemporal dynamics. We believe these mechanisms can explain some of the phenomena that recently have been reported to occur in excitable media. We present a method for controlling soliton explosions.     

The Renormalization Group and Its Finite Lattice Approximations

We investigate finite lattice approximations to the Wilson renormalization group in models of unconstrained spins. We discuss first the properties of the renormalization group transformation (RGT) that control the accuracy of this type of approximation and explain different methods and techniques to practically identify them. We also discuss how to determine the anomalous dimension of the field. We apply our considerations to a linear sigma model in two dimensions in the domain of attraction of the Ising fixed point using a Bell–Wilson RGT. We are able to identify optimal RGTs which allow accurate computations of quantities such as critical exponents, fixed-point couplings and eigenvectors with modest statistics. We finally discuss the advantages and limitations of this type of approach.