MO／PVA薄膜材料在Ar^＋激光488.0nm线预辐照下的红光多重全息存贮

报道了甲基橙偶氮染料掺杂的聚乙烯醇薄膜材料在Ａｒ＾＋激光４８８．０ｎｍ线辐照下，用正交线偏振的６３２．８ｎｍ光作为写入光，通过旋转样品，在同一光斑内形成多个取向不同的相位光栅，实现了多重全息存贮的实验结果。在三重图象的存贮中，通过控制每次的写入时间、得到了三个均匀明亮的衍射图像，其平均衍射效率为０．１％。     

Types of likelihood maxima in mixture models and their implication on the performance of tests

In two-component mixtures of exponential distributions, different strategies for starting the likelihood maximization algorithm converge to different types of maxima. The power of an LR test of homogeneity against such a mixture strongly depends on the considered strategy, and global maximization need not result in the largest power. An explanation is given on basis of a systematic investigation of the likelihood function in a large number of simulations, using a variety of diagnostic tools. Thereby, we also gain a deeper insight into the properties of the samples that generate particular types of solutions of the likelihood equation. In particular, “spurious solutions” often occur; these are mainly responsible for the fact that global maximization may not result in a statistically meaningful estimator. Removing the smallest elements of a sample may drastically increase the power of previously inferior strategies. This research has been supported by a grant from the Deutsche Forschungsgemeinschaft.     

Multiple-prism near-grazing-incidence grating solid-state dye-laser oscillator

Solid-state multiple-prism near grazing-incidence grating dye lasers have been configured in cavities as short as 73 mm using dye-doped modified PMMA gain media. Single-longitudinal-mode emission, in near-Gaussian temporal pulses of 6-7 ns (FWHM) duration, has been achieved. Measured laser linewidths are in the 375 MHz range, and beam divergence is 2.3 mrad, at 3%-4% conversion efficiencies.     

Experimental results and basic considerations concerning injection and transport of electrons in the dye-sensitized colloidal sponge-type anatase TiO2 electrode

Electron transfer over the reaction distance corresponding to three saturated bonds occurs within 70 fs from the excited singlet state of anchored perylene chromophores to empty electronic levels in a sponge-type anatase TiO₂ electrode. Injected electrons can be consumed in three different types of recombination processes at the interface with the electrolytic contact. Electron transport through the electrode follows a potential gradient that is set-up in the dark, corresponding to the difference between the Fermi levels of the two contact materials. It is dominated by multiple trapping and trap filling processes.     

高频CO2激光脉冲写入的长周期光纤光栅传感器的特性研究

报道了一种用高频CO₂激光脉冲写入的新型长周期光纤光栅（LPFG）.发现该LPF G具有独特的应变、温度、弯曲、扭曲和横向负载特性.分析表明这些特性与单侧CO₂激光 加热导致光 栅横截面折射率分布不均匀有关.基于这些独特的特性提出了几种新型的LPFG传感器：1)能 彻底解决弯曲与其他参量之间交叉敏感问题的弯曲不敏感的传感器；2) 不仅能绝对测量扭 曲率而且能判断扭曲方向的扭曲传感器；3)单个LPFG实现温度和横向负载同时测量的传感器 .这些新型的传感器具有方法简 关键词： 长周期光纤光栅 光纤传感器 应变传感器 温度传感器 弯曲传感器 扭曲传感器     

SARS疫情分析及对北京疫情走势的预测

在考虑每个SARS病人每日平均传染概率和他的直接传染的平均期限的基础上，建立了一个统计分析模型．分析表明，每个病人可以造成直接感染他人的期限平均在20天左右，这个值在不同地区和不同疫情阶段似乎变化不大．病人的平均每天感染率与社会状况有关，在疫情爆发期较大，在疫情控制期要小很多．北京后期如果控制在香港后期的感染率水平上，则有望在6月上中旬下降到日增几例．然后再经过约一个月，即7月上中旬达到日增0病例，而累积总病例数将达到3100多．但如果北京的新病例下降速度与广东类似的话，则要再多花至少一个月，才能达到上述的效果，且累积总病例数会达到3800左右．     

SOLUTION OF A CLASS INTEGRALEQUATIONS

1TwoTheoremsonmultipleintegrationTheorem1.1Supposethatf(t)isarbitrarycontinuousfunctiondefinedonRandh(fl,'')fi)isarbitrarycontinuousfunctiondefinedonm(1Sp0}ProofWeshallproveitbymathematicalinduction…     

Periodic load balancing

Multiprocessor load balancing aims to improve performance by moving jobs from highly loaded processors to more lightly loaded processors. Some schemes allow only migration of new jobs upon arrival, while other schemes allow migration of jobs in progress. A difficulty with all these schemes, however, is that they require continuously maintaining detailed state information. In this paper we consider the alternative of periodic load balancing, in which the loads are balanced only at each T time units for some appropriate T. With periodic load balancing, state information is only needed at the balancing times. Moreover, it is often possible to use slightly stale information collected during the interval between balancing times. In this paper we study the performance of periodic load balancing. We consider multiple queues in parallel with unlimited waiting space to which jobs come either in separate independent streams or by assignment (either random or cyclic) from a single stream. Resource sharing is achieved by periodically redistributing the jobs or the work in the system among the queues. The performance of these systems of queues coupled by periodic load balancing depends on the transient behavior of a single queue. We focus on useful approximations obtained by considering a large number of homogeneous queues and a heavy load. When the number of queues is sufficiently large, the number of jobs or quantity of work at each queue immediately after redistribution tends to evolve deterministically, by the law of large numbers. The steady-state (limiting) value of this deterministic sequence is obtained as the solution of a fixed point equation, where the initial value is equal to the expected transient value over the interval between successive redistributions conditional on the initial value. A refined approximation based on the central limit theorem is a normal distribution, where the mean and variance are obtained by solving a pair of fixed-point equations. With higher loads, which is natural to consider when load balancing is performed, a heavy-traffic limit theorem shows that one-dimensional reflected Brownian motion can be used to approximately describe system performance, even with general arrival and service processes. With these approximations, we show how performance depends on the assumed arrival pattern of jobs and the model parameters. We do numerical calculations and conduct simulation experiments to show the accuracy of the approximations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Thermodynamic-Controlled Gas Phase Process for the Synthesis of Nickel Nanoparticles of Adjustable Size and Morphology

Gas phase processes are a successful route for the synthesis of nano materials. Nickel particles are used in applications ranging from catalysis to nano electronics and energy storage. The application field defines the required particle size, morphology, crystallinity and purity. Nickel tetracarbonyl is the most promising precursor for the synthesis of high purity nickel particles. Due to the toxicity of this precursor and to obtain an optimal process control we developed a two-step flow type process. Nickel carbonyl and nickel particles are synthesized in a sequence of reactions. The particles are formed in a hot wall reactor at temperatures below 400°C in different gas compositions. Varying the process conditions enables the adjustment of the particle size in a range from 3 to 140 nm. The controllable crystalline habits are polycrystalline, single crystals or multiple twinned particles (MTP). Spectroscopic investigations show an excellent purity. We report about the process and first investigations of the properties of the synthesized nickel nanomaterial.     

客观赋权法指导下的部分权重信息多属性决策方法研究

提出了一种客观赋权法指导下的部分权重信息的多属性决策方法 ,该方法将决策者主观给出的部分权重信息和客观实际相结合 ,既充分利用了客观信息 ,又以最小偏差的形式尽可能满足决策者的主观愿望 ,达到两者的统一 .最后通过具体的应用实例验证了该模型的可行性 .