SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS

High quality epitaxial YBa₂Cu₃O_7-x thin films have been succcessfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO₃, LaAlO₃ and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a J_c (at 77 K, H=0) over 10⁶A/cm². It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by X-ray diffraction. Rutherford backscattering and channeling spectroscopy, X-ray double-crystal diffraction and transmission election microscopy. The experimental results demonstrated that the epitaxial YBa₂Cu₃O_7-x films had excellent superconducting properties and quite perfect structure.     

GaAs-Based Metamorphic Long-Wavelength InAs Quantum Dots Grown by Molecular Beam Epitaxy

A bilayer stacked InAs/GaAs quantum dot structure grown by molecular beam epitaxy on an In0.05Ga0.95As metamorphic buffer is investigated. By introducing a InGaAs：Sb cover layer on the upper InAs quantum dots （QDs） layers, the emission wavelength of the QDs is extended successfully to 1.533 μm at room temperature, and the density of the QDs is in the range of 4× 10^9-8 ×10^9cm^-2. Strong photoluminescence （PL） intensity with a full width at half maximum of 28.6meV of the PL spectrum shows good optical quality of the bilayer QDs. The growth of bilayer QDs on metamorphic buffers offers a useful way to extend the wavelengths of GaAs-based materials for potential applications in optoeleetronic and quantum functional devices.     

单种群反馈控制生态系统的持久性

利用[1～3]所给的方法研究一类单种群生态系统,得到这类单种群生态系统的持久性的一个新的充分条件.     

强混合的保测变换引起的混沌

研究强混合的保测变换所引起的混沌现象,证明了以下结论:如果X是一个满足第二可数性公理的拓扑空间,m是其上的一个外测度,满足条件:(1)X的每一个非空开集都是m-可测的并且有正的m-测度;(2)m在X的Borelσ-代数B(X)上的限制是一个概率测度:(3)对于任何Y(?)M存在一个 Borel集B∈(?)(X)使得B(?)Y和m(B)=m(Y),则对于概率空间(X,(?)(X),m)的任何一个强混合的保测变换f: X→X,和由正整数构成的任何一个严格递增的序列 {m_i},存在着一个集合C(?)X使得m(C)=1并且C是有限型混沌的,即对于C的任何一个有限子集A和任何一个映射F:A→X,序列{m_i}有一个子序列{r_i}使得lim_i→∞f^r_i(a)=F(a)对于任何a∈A成立.给出了一维映射上的某些应用.     

凸体形状匹配的参考点

本文研究了在平移变换下凸体形状的匹配．通过估计凸体形心与凸体内可测子集形心之间的距离的方法，得到了形心之间距离的不等式和形心是凸体在形状匹配下的参考点的结论．     

Power flow in the coupled dynamic system of machinery and building floor

I.IntroductinnWithmoreandmoremulthetoreyworkshopsandmultifunctinnaltallbuildingsarebeingconstructednowadays,thereshowsanincreasingtrendformachinesandequlpmentstobemoulltedonupperlloors.Inthesituationofmachinesrunningonupperfloors,thetraditionaltheoryisnotValidbecausetheflooritselfisaflewhlestructure.Therefore,itisinagreatdemandtostudyonthedynaInicillteractionofmachinescoupledwithflekiblefoundationsalldtoproposearesonableandeffectiveapproachtocontrolvibrationandtosuppressnoise.Formachineryonu…     

一种基于带权CAT的DDoS分布式检测方法

针对DCD(distributed change-point detection)方案存在受害端开销大、检测率低等问题,提出了一种基于带权CAT(change aggregation trees)的检测方案.采用分布式分级体系结构,将检测任务分布到互联网源端、中间网络和受害端,实现攻击的早期检测;利用CUSUM算法对微小变化的敏感性,在源端主机和中间网络的路由器处进行基于到达目标数据包数量的检测以及基于超级流聚合变化的检测;受害端进行基于域树权重的榆测.实验和分析表明,CAT方案对UDP攻击的检测率从DCD的最高0.72提高到0.94,TCP攻击检测率也略有提高;网络的通信开销和受害端的存储丌销从o(mnk)降为o(mk),受害端的计算开销从o(mn)降为o(m).系统在实现检测的同时,获得了攻击路径和攻击的准确位置,实现了DDoS攻击的分布式追踪.     

固体介质电偶极子等温衰减电流与激活能分布

从经典的单一弛豫时间Debye方程着手,考虑各个弛豫时间的电偶极子对弛豫过程贡献的物理意义后,近似地获得了以任意激活能分布的电偶极子数与等温衰减电流的基本关系,即电偶极子激活能分布密度与电流I和衰减时间t的乘积成正比.数值计算结果检验该理论时表明:无论以分立或连续分布形式存在的电偶极子,精确的与近似的It-logt关系符合得相当好.该理论解决了长期以来电介质中弛豫时间分布非常难得的问题,应用于介电频谱时得到了Hamon早年提出的广泛应用的经验公式的相似结果.     

数码相机在研究阻尼振动中的应用

介绍一种采用数码相机来研究阻尼振动的特性参数及其运动规律的方法.     

Chaos in a topologically transitive system

The chaotic phenomena have been studied in a topologically transitive system and it has been shown that the erratic time dependence of orbits in such a topologically transitive system is more complicated than what described by the well-known technology "Li-Yorke chaos". The concept "sensitive dependency on initial conditions" has been generalized, and the chaotic phenomena has been discussed for transitive systems with the generalized sensitive dependency property.