从静止宇宙向膨胀宇宙的发展

 当夜幕降临的时候,漫天灿烂的星斗,浩瀚无际的天空,为人们提供了巨大的想象空间(图1).可这巨大的空间是无限的还是有限的呢？宇宙是一直在演化着的,还是总是保持这个样子呢？关于这些问题,从古至今的人们一直就在研究着、争论着,构成了一部不断发展着的天文学和宇宙学的发展史.     

3D影像技术中的光学应用

 近年来,3D 开始进入人们眼帘,在我们生活的周围到处充斥着着3D 广告、图书、电影等,原本是平淡无奇的平面为什么会展示出栩栩如生的神奇立体世界？魔术？还是幻觉？其实道理很简单,以下我们从光学的角度出发探讨一下这神奇世界背后的奥秘.     

试析这张照片的拍摄时间

人教版高中物理选修第7页“科学漫步”栏目提出一个有趣的问题：教材中的照片是在黄昏拍摄的还是在黎明拍摄的（图1）？     

先有手性均一性还是先有生命？

先有手性均一性还是先有生命？民间谚语说：“万物都在转、转、转”．但这要通过什么途径？为什么？这是科学之谜，１９９５年２月１５－１７日美国洛杉矶召开了“生命中手性起源”问题的国际讨论会［１］，来自世界各地的２４位物理学家、化学家和天文学家出席了会议。会...     

如何正确理解氢原子的能量──折合质量的物理意义

当考虑原子核的运动，引进折合质量μ以后，氢原子的能量Ｅ＝μｖ２＋Ｕ（ｒ）表示电子相对于原子核运动的能量呢？还是表示氢原子在其质心参考系 中的能量？这显然是一个重要的问题，然而却存在不少混淆．本文证明：上式是整个氢原子在其质心参考系中的能量，并非电子相对于原子核运动的能量．一．三种不同的相对运动的能量     

对静电场中导体表面的电场强度的研究

在研究导体在外电场中感应产生感应电荷达到静电平衡状态时，导体表面的电荷分布与表面曲率和外电场分布情况有关，然而导体表面上的电场强度究竟由什么决定?是同导体内的电场强度即为零还是等于导体外周围附近的电场强度即为σ/ε0？还是既不等于零也不等于σ/ε0，而是由其他因素决定。     

浅谈哲学与自然科学的关系

 哲学是关于宇宙观和人生观的学问,是人们对自然知识和社会知识的概括和总结．因此,哲学与自然科学和社会科学有着密切的联系．这里,以粒子物理学为例,谈谈哲学与自然科学的关系．千百年来,哲学家和自然科学家一直在探索这样的问题：我们周围的物质,从天上的星星到海边的沙粒,究竟是由什么组成的？如果人们尝试把它们一次又一次不断地分割下去,将会出现什么情况？是无限可分,还是存在最小成分？若是后者,物质的最小成分究竟是什么？不同的哲学家对这个问题作出了不同的回答．希腊哲学家德谟克利特认为,物质是由许多微小的、不可分割的单个颗粒组成的,这种颗粒称为“原子”．     

小谈广义相对论--"从低速到高速"之五

我们已介绍过狭义相对论；在那里爱因斯坦把牛顿的相对性原理推广到包括电磁现象，但还是指惯性系说的；各个参考系是相对做匀速运动的惯性参考系．对加速参考系又该如何呢？爱因斯坦在马赫思想的影响下提出：物理规律对所有参考系，不管是惯性系还是加速系，都应该是一样的．这个进一步推广了的相对性原理叫“广义相对性原理”．它是爱因斯坦广义相对论的一个基本原理．     

SWITRIM程序的研制和使用概况

第一个计算氚投料量在FEB聚变堆各个子系统中的分布及其随时间变化行为的数值模拟程序包SWITRIM研制成功。近5年来的使用情况表明其合理性得到国外同行的充分认可。取得了一些有创新性的成果。例如，我们在国际上首次指出聚变堆起动过程中的一种“氚坑深度和氚坑时间”新现象，它有些类似裂变堆中的“碘坑深度和碘坑时间”现象，但又是非常不同的问题。作者不但提出而且通过数值模拟解释了这种“氚坑深度和氚坑时间”新现象。以FEB设计为例子求解出FEB堆的氚坑深度为317g，氚坑时间为240d，氚储备子系统中低谷时间为起动后第10天。这意味着我们能预测聚变堆起动过程中的最少氚储备量是多少？氚储备子系统中何时是最少氚储备的时刻？实现氚的得失相当的有效运行时间要多长？     

准晶的前世今生：2011年度诺贝尔化学奖述评

2011年10月5日，诺贝尔奖委员会宣布将今年的化学奖授予以色列材料科学家Dan Shechtman（图1）．虽然获奖理由只有淡淡的一句话“因为准晶的发现（for the discovery of quasicrystal）”，但是Shechtman的获奖还是引起了同此前许多其他奖项可比拟的热烈讨论．那么，什么是准晶？何以准晶的发现会被授予诺贝尔奖？此项发现的价值何在，其背后的故事对科学发展和科学工作者有什么启发性的意义？本文试图对上述问题给出一些粗浅的讨论．     

The time dependent Dirac-Frenkel-McLachlan variation of parameters: an NMR application

The time dependent variation of parameters solution to the time dependent Schr?dinger equation pioneered by Dirac, Frenkel, and McLachlan is described in terms useful for immediate application to complex time dependent problems in magnetic resonance. A benchmark comparison of the theory to one dimensional images and spin echo envelope signals in simple spatially varying magnetic fields with molecular diffusion is provided.     

Design and simulation of an all-optical photonic crystal AND gate using nonlinear Kerr effect

A photonic crystal optical limiter with a sharp input-output characteristic curve is initially designed in this paper. Thereafter; using an optimized Y-junction, a new topology for an all-optical photonic crystal AND gate is proposed. The mentioned gate has a transition time less than 1?ps, a delay time less than 0.4?ps and occupies an area less than 100?μm². The 1,550?nm input lasers should have a power equal to 10W to be able to trigger the switching mechanism. The photonic crystal used for this purpose is a two dimensional triangular lattice of holes in a GaAs substrate. PWE and FDTD methods are used to simulate the proposed structure. Time domain simulations confirm the switching mechanism of the proposed AND gate.     

Energy and Momentum of Higher Dimensional Black Holes

In this paper, we devote to investigate the energy-momentum problem of higher dimensional black holes in the general theory of relativity. The energy and momentum complex of M?ller has been used for the calculations. Also, total energy and total momentum of some special cases for higher dimensional black holes such as Schwarzschild-like black holes, Reissner-Nordstr?m-like charged black holes, AdS-like black holes, topological black holes, BTZ-like and charged BTZ-like black holes were obtained. It is invented that the momentum of black holes vanishes everywhere while the energy of black holes are not equal to zero in higher dimension. Also the results agree with Yang and Radinschi or Vagenas results in three and four dimensional black holes, respectively (Jang and Radinschi in AIP Conf. Proc. 895, 325, 2007; Vagenas in Mod. Phys. Lett. A 21, 1947, 2006).     

An exactly solvable non-linear Boltzmann equation

The initial value problem for a model Boltzmann equation of a two dimensional gas with a continuous or discrete energy distribution function and a transition probability δ(? - ?') is solved exactly; ? and ?' are the total energies before and after collision.     

Induced explode-decay dromions in the (2 + 1) dimensional nonisospectral nonlinear Schrödinger (NLS) equation

In this paper, we have identified a novel method of inducing localized solutions in the (2+1) dimensional nonisospectral nonlinear Schr?dinger (NLS) equation by utilising the freedom in the system. The new class of localized solutions includes induced dromions, lump dromions, dipole dromions etc. The amplitude of the localized solutions generated is found to explode or decay with time. We have also brought out the interaction of induced dromions.     

KAM for the Quantum Harmonic Oscillator

In this paper we prove an abstract KAM theorem for infinite dimensional Hamiltonians systems. This result extends previous works of S.B. Kuksin and J. P?schel and uses recent techniques of H. Eliasson and S.B. Kuksin. As an application we show that some 1D nonlinear Schr?dinger equations with harmonic potential admits many quasi-periodic solutions. In a second application we prove the reducibility of the 1D Schr?dinger equations with the harmonic potential and a quasi periodic in time potential.     

The linear response of a one-dimensional electron gas

A not widely used method is employed to calculate the static dielectric function of an electron gas. A specific calculation is presented for a one- dimensional electron system surrounded by a medium of dielectric constant ?₀. The asymptotic, oscillatory, two-body interaction decays more slowly than in the three-dimensional case.     

Effective field theory of a topological insulator and the Foldy–Wouthuysen transformation

Employing the Foldy–Wouthuysen transformation, it is demonstrated straightforwardly that the first and second Chern numbers are equal to the coefficients of the 2+1 and 4+1 dimensional Chern–Simons actions which are generated by the massive Dirac fermions coupled to the Abelian gauge fields. A topological insulator model in 2+1 dimensions is discussed and by means of a dimensional reduction approach the 1+1 dimensional descendant of the 2+1 dimensional Chern–Simons theory is presented. Field strength of the Berry gauge field corresponding to the 4+1 dimensional Dirac theory is explicitly derived through the Foldy–Wouthuysen transformation. Acquainted with it, the second Chern numbers are calculated for specific choices of the integration domain. A method is proposed to obtain 3+1 and 2+1 dimensional descendants of the effective field theory of the 4+1 dimensional time reversal invariant topological insulator theory. Inspired by the spin Hall effect in graphene, a hypothetical model of the time reversal invariant spin Hall insulator in 3+1 dimensions is proposed.     

Fast parallel optical digital multiplication

A parallel optical binary multiplication scheme is proposed in which parallel convolution preprocessing is performed using a parallel-input optical outer-product processor together with a one dimensional either space or time integrator. Using a thetamodulation based optical A/D converter and a carry look-ahead adder array, the resulting mixed-binary partial product can be reduced to the final binary multiplication result.     

Some Propagation Properties of the Iwatsuka Model

In this paper we study a two dimensional magnetic field Schr?dinger Hamiltonian introduced in [7]. This model has some interesting propagation properties, as conjectured in [2] and at the same time is a special case of the class of analytically decomposable Hamiltonians [5]. Our aim is to start from a conjugate operator, intimately related to the band structure of the Hamiltonian and to prove existence of an asymptotic velocity in one spatial direction and a theorem giving minimal and maximal velocity bounds for the propagation associated to the Hamiltonian. A simple example of this model, with a very simple conjugate operator, has been given in [9]. At the same time, by using the Virial Theorem, we obtain a generalisation of the hypothesis in [7]. Received: 12 February 1997 / Accepted: 26 February 1997