Exponential stability of states close to resonance in infinite-dimensional Hamiltonian systems

We develop canonical perturbation theory for a physically interesting class of infinite-dimensional systems. We prove stability up to exponentially large times for dynamical situations characterized by a finite number of frequencies. An application to two model problems is also made. For an arbitrarily large FPU-like system with alternate light and heavy masses we prove that the exchange of energy between the optical and the acoustical modes is frozen up to exponentially large times, provided the total energy is small enough. For an infinite chain of weakly coupled rotators we prove exponential stability for two kinds of initial data: (a) states with a finite number of excited rotators, and (b) states with the left part of the chain uniformly excited and the right part at rest.     

微纳世界的音乐之声——用低维纳米机电器件探索微观世界

纳米机电器件是具有机械运动自由度的纳米电子器件。特别有趣的是,纳米机电器件同时也构成了微纳世界的各种乐器,能够演奏出独特的音乐之声。如同宏观世界中的乐器各有各的特色,这类微纳器件在研究低维及纳米尺度的物理现象时,也展现出一些独到的潜力和优势,例如研究低维体系中的独特相变过程以及纳米材料中的力学各向异性效应等。在这些工作中,通过精密测量低维纳米材料的机械振动,即仔细倾听这些乐器所奏出的音乐之声,能够帮助研究者们观察到一些原来不易被测量的现象,进而探索新的低维物理过程和材料体系,带来新的科学发现。     

Monte Carlo方法模拟低能电子在Al中的散射

基于文献[1]的工作,电子在固体中的弹性散射用Mott微分截面计算;非弹性散射分为单电子激发和等离子激发并由Streitwolf、Gryzinski及Quinn的截面描述.模拟了低能电子在Al块样及薄膜中的散射过程,对不同能量低能电子作用下Al的背散射系统、能谱又透射系数作了计算,结果与实验符合较好.也对背散射电子、低能损背散射电子表面分布作了计算,结果表明低能损背散射电子具有较好的空间分辨率.     

Interference between resonance and potential scattering of high energy electrons from crystal surfaces

A solution of the tight-binding model of resonance diffraction of high-energy electrons from a crystal surface is found which describes the behaviour of the reflectivity in the vicinity of the intersection of a resonace parabola and a horizontal Kikuchi line. A simple analytical formula is obtained which makes it possible to evaluate the wave function for the case where both resonance and potential contributions to the reflectivity are of the same order of magnitude. The intensity of the specular reflection is shown to be directly related to the effective displacement Δ of the beam in the direction parallel to the surface, and a general formula suitable for evaluation of Δ from calculated RHEED rocking curves is derived.     

用X射线衍射仪验证康普顿效应的实验研究

充分利用多晶X射线衍射仪的衍射、单转、定时计数、叠扫等功能测量数据,采用3种实验测量方法验证了康普顿散射波长的位移公式,分析了不同测量方法对实验结果的影响.     

用X射线衍射仪测量康普顿散射的波长改变

详细阐述了利用多晶X射线衍射仪测量康普顿散射射线波长的实验方法和实验结果.     

Diffuse scattering of modulated structures and quasicrystals

The method of Fourier transforms is applied to the calculation of sharp (coherent) and diffuse (incoherent) scattering of modulated structures and quasicrystals. It is shown that the fundamental difference between both may best be described by introducing different distribution functions of atoms, before applying modulations of the structure.     

A new experimental technique for measuring the local birefringence and molecular orientation in liquid crystals

A new experimental technique is described for the measurement of local birefringence and molecular orientation in liquid crystals. This technique consists in analyzing the local channeled spectra obtained by optical polarising microscopy.     

Electron resonances in VLEED from Cu(111)

The sensitivity of the VLEED I–V curves to the shape and the position of the barrier is shown for the image- type surface barriers. For demonstration and comparison with experimental data the intensities of specularly reflected electron beams from Cu(111) are computed by dynamical theory of electron diffraction. Image plane position changes and modifications of the saturation shape of the surface barrier induce pronounced changes in the I–V curves calculated with the image-type barrier. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.