A branching process model for sand avalanches

An analytically solvable model for sand avalanches of noninteracting grains of sand, based on the Chapman-Kolmogorov equations, is presented. For a single avalanche, distributions of lifetimes, sizes of overflows and avalanches, and correlation functions are calculated. Some of these are exponentials, some are power laws. Spatially homogeneous distributions of avalanches are also studied. Computer simulations of avalanches of interacting grains of sand are compared to the solutions to the Chapman-Kolmogorov equations. We find that within the range of parameters explored in the simulation, the approximation of noninteracting grains of sand is a good one.     

Asymptotic behavior of fluctuations for the 1D Ising model in zero-temperature limit

Fluctuation of the average spin for one-dimensional Ising spins with nearest neighbor interactions are studied. The distribution function for the average spin is calculated for a finite volume, finite temperature, and finite magnetic field. As the volume increases and the temperature diminishes at zero magnetic field, there are two limits in which the probability distribution shows quite different behaviors: in the thermodynamic limit as the volume goes to infinity for finite temperature, small deviations of the fluctuations are described by a Gaussian distribution, and in the limit as the temperature vanishes for a finite volume, the ground states are realized with probability one. The crossover between these limits is analyzed via a ratio of the correlation length to the volume. The helix-coil transition in a polypeptide is discussed as an application.     

高压下Al0.77Mn0.19Yb0.04合金准晶T相的形成及结构

利用静高压(4.2GPa)熔态(1300℃)淬火(10~2℃/S)方法,对含稀土的铝锰合金Al_(0.77)Mn_(0.10)Yb_(0.04)进行了研究。首次发现了准晶T相的形成。利用选区透射电子衍射技术,对合金中准晶态的结构对称性进行了观察和分析。根据X射线和电子衍射对其衍射峰进行了指标化。使用扫描电镜和能谱技术进行了成份分析。     

Amplification of spontaneous emission in Nd~(3 )-doped fiber pumped by Ti: Al_2O_3 tunable laser

Amplification of spontaneous emission(ASE) in 4m Nd~(3 )-doped fiber pumped by Ti : Al~2O_3 tunable laser is studied theoretically and experimentally. The output of 2.64mW from ASE source pumped at 833 nm is obtained and the experimental results of ASE source are compared with that of Nd~(3 )-doped fiber ring laser.     

HCl氧化物MOS结构质子辐照诱导的界面陷阱效应

用微分电容法研究质子辐照HCl氧化物铝栅MOS结构诱导的界面陷阱,栅氧化层在1 160℃很干燥的、含0～10％HCl的气氛中热生长而成,质子辐照能量为120～300keV,注入总剂量范围为8×10~(13)～1×10~(16)p/cm~2。结果表明,辐照诱导的界面陷阱能级密度随质子能量、剂量增加而增加。然而,氧化层中掺入6％HCl时,辐照诱导的界面陷阱明显减少。这样,已能有效地改变MOS器件的抗辐照性能。实验结果可用H~+二级过程解释。     

激光化学反应法制备CaO超精细粉末及激光多相催化1—庚烯异构化的研究

采用激光固相热解反应法，以ＣＷＣＯ２激光作为辐照光源，成功地合成了ＣａＯ超精细粉末。实验结果表明：本法生成的粉末呈球状结构，粒径在２０～５０ｎｍ之间。激光多相催化１－庚烯反应使１－度烯异构化的转化率升高。并且使得顺式的相对含量大于反式的相对含量。     

Co-Ni-Sr-O系低温热敏陶瓷材料研究

着重研究了工作温度范围为20~77K的低温热敏电阻器的生产工艺参数。利用先进的半导体陶瓷工艺,合成了新的低温NTC热敏陶瓷材料SrCoO3-δ,并用不同量的Ni取代Co对其掺杂改性,得到了不同阻值、不同B值的陶瓷材料,同时研究了烧结温度和恒温时间对Co-Ni-Sr-O系NTC热敏材料参数的影响。在材料粉体合成中,采用固相烧结、共沉淀法、溶胶凝胶法、Pechini法等不同方法制备,讨论了不同方法的基本原理与特点,并对一些具体制备方法进行了比较。     

利用El Gamal密码体制解决安全多方多数据排序问题

基于E1Gamal同态密码体制给出了一个解决百万富翁问题的扩展问题的协议——安全多方多数据排序协议。并使用安全多方计算的对安全性的定义，在半诚实模型下，对协议的正确性和安全性进行了理论证明。该协议为保密电子投标和拍卖、保密在线交易等新型电子交易奠定了基础。     

BER Analysis of Equalized OFDM Systems in Nakagami, <Emphasis Type="Italic">m</Emphasis> < 1 Fading

The orthogonal frequency division multiplexing (OFDM) transmission scheme is currently experiencing increased popularity due to advances in very large scale integration technology. It is used for a variety of broadband systems such as asymmetric digital subscriber lines, very-high-speed digital subscriber lines, digital video, and audio broadcasting, and wide local area network standards such as IEEE 802.11a, IEEE 802.11 g, and ETSI Hiperlan/2. However, propagation impairments can cause severe degradation in bit error rates (BER) for coherent detection. We derive a semi-analytical method to evaluate BER of a quadrature phase shift keying (QPSK)-OFDM system in Nakagami, m < 1 fading and additive noise where pilot-assisted linear channel estimation and channel equalization are used. This allows modeling of more severe fading environments than can be depicted by a Rayleigh distribution. Numerical simulations are used to validate the proposed methods. The techniques developed can be applied to other channel estimation techniques, modulation schemes and the performance evaluation of equalized single carrier narrowband systems.     

不同剂量C离子注入Si单晶中Si1-xCx合金的形成及其特征

室温下在单晶Si中注入(0.6—1.5)%的C原子,利用高温退火固相外延了Si_1-xC_x合金,研究了不同注入剂量下Si_1-xC_x合金的形成及其特征.如果注入C原子的浓度小于0.6%,在850—950℃退火过程中,C原子容易与注入产生的损伤缺陷结合,难于形成Si_1-xC_x合金相.随注入C原子含量的增加,C原子几乎全部进入晶格位置形成Si_1-xC_{x 关键词： 1-x}C_x合金')" href="#">Si_1-xC_x合金 离子注入 固相外延