Counting signals from radioactivity-measurement systems

The original time-interval distribution of Poisson events, as for instance those originating from the decay of a radioactive source, is modified by the finite width of the electrical pulses. For the simple case of assumed rectangular pulses it is found that the available counting signals can be subdivided into single pulses and pile-up pulses (of a given order). The probability for observing a counting signal of order i is derived in a simple way and expressions for mean width and count rate are given. Confirmation has been obtained both by simulation and by experiments with a random-pulse generator.     

Potential parameterization from proxy systems

We give an analysis and critique of a procedure for sequential multi-scale parameterization of so-called ab initio potentials. Such potentials are based upon a small selection of reference data generated at relatively low levels refinement of quantum mechanical (QM) methodology. Two closely related potentials for silica, BKS and TTAM, are explored in some depth because both have found frequent use in the literature of molecular dynamics simulation. The use of a single small molecular cluster as a proxy for the behavior of larger silica structures is shown to be perilous. Choices of ionic charge, basis set size, inclusion of electron correlation at some prescribed level of approximation, and parameterization data are each shown to have a substantial impact on the final potential parameterization. The analysis and critique provide the logical foundation for the different approach to the problem of parameterization and use of classical potentials that is treated in detail elsewhere in this collection. The use of extended model systems, force data calculated from QM methods, and a focused (limited) range of application are shown to be essential for a consistent (and ultimately, predictive) embedding approach to concurrent multi-scale materials simulation.     

基于三视图的实体重建技术研究

基于三视图的三维实体重建技术是根据已有二维视图中的几何信息和拓扑信息,生成相应的三维实体模型。以AutoCAD绘制的三视图及DXF格式的文件信息为基础,提出并实现了一种由三视图重建三维实体的算法。通过对三视图的规则处理,由计算机自动实现实体重建,对三视图分别进行平移、旋转、拉伸操作,然后作相应的布尔运算即可反求出该视图所对应的三维实体。     

Image restoration from vibrating photographic systems

Many photographic systems are located on moving platforms. Because of mechanical vibrations that exist on those platforms, the photographed image is distorted. To avoid those distortions requires that very complicated mechanical attenuators be used. We suggest an optoelectronic image-processing algorithm to overcome the distortions caused by such vibrations. The algorithm for different types of vibration is reformulated in an exact manner, as opposed to the reformulations of previously known calculations. Furthermore, new types of vibration are explored. The algorithm is fully computerized and thus avoids the need for attenuating devices.     

基于海藻制备超级电容器用三维多孔石墨烯

以海藻作为固相碳源,利用海藻对金属离子具有吸附性能的特点,在未进行生物质材料改性的条件下,实现海藻生物质材料对催化剂金属离子的均匀吸附.本文结合原位高温金属催化和化学活化的方法制备三维多孔石墨烯,并研究了其作为超级电容器电极材料的电化学性能.通过扫描电镜、透射电镜、X射线衍射、拉曼光谱、氮气吸附等手段对三维多孔石墨烯的形貌与结构进行表征分析.研究结果表明,制备的三维多孔石墨烯具有片层状三维网络结构,且片层较薄,并具有较高的石墨化程度,其比表面积达到1 700 m~2/g,孔径分布主要在2~10 nm.以该三维多孔石墨烯材料作为超级电容器电极材料,进行电化学性能表征,发现在较低的电压扫速下得到的比电容量为90 F/g,同时,该材料还具有较高的能量密度和功率密度.以海藻为固相碳源制备得到的三维多孔石墨烯材料在超级电容器领域具有一定的应用前景.     

Three dimensional hierarchy structures from self-assembly of quantum dots

We have reported first example of 3D hierarchy structure from self-assembly of water-soluble QDs followed by chemical reaction control. After addition of ethylenediaminetetraacetic acid, dipotassium salt dehydrate (EDTA) into L-cysteine-stabilized CdTe QD solution, the color of solution was observed to become lighter and shallower, and finally white precipitates appeared. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results confirm that the morphology transformation from zero dimensional (0D) QDs via two-dimensional (2D) nanoflakes to 3D microflowers occurs among those QD assemblies. Meanwhile, EDX results demonstrate that the as-formed QD-assemblies are not CdTe but CdS. The turnover of chemistry nature from CdTe to CdS after addition of EDTA is mainly due to the oxidation of Te followed by a series of chemical reactions. The photoluminescence (PL) spectroscopy and confocal laser scanning microscopy (CLSM) results reveal that such 3D hierarchy structure of CdS QDs have good optical property.     

Sampling of fluid from power hydraulic systems

The demand for higher efficiencies from hydraulic machinery has produced equipment and methods to predict and ensure reliability. Here the author discusses the monitor method of sampling and its development as a fluid assessment technique. Argument for this technique as an aid to understanding filtration controls is given by the study of case histories..     

Analysis of grouped data from field-failure reporting systems

Observed reliability data from fielded systems is highly desirable because they implicitly account for all actual usage and environmental stresses. Many companies and large organizations have instituted automated field-failure reporting systems to organize and disseminate these data. Despite these advantages, field data must be used with caution because they often lack sufficient detail. Specifically, the precise times-to-failure are often not recorded and only cumulative failure quantities and operating times are available. When only data of this type are available, it is difficult to determine whether component or system hazard function varies with time or is constant (i.e., exponential distribution). Analysts often use the exponential distribution to model time-to-failure because the distribution parameter can be estimated with just the merged data. However, this can be dangerous if the exponential distribution is not appropriate. An approach is presented in this paper for Type II censored data, with and without replacement, to evaluate this assumption even when individual times-to-failure are not available. A hypothesis test is presented to test the suitability of the exponential distribution for a particular data set composed of multiple merged data records. Two examples are presented to demonstrate the approach. The hypothesis test readily rejects an exponential distribution assumption when the data originate from a Weibull distribution. This is a very important result because it has generally been assumed that time-to-failure data were always required to evaluate the suitability of specific time-to-failure distributions.     

Phase reconstruction from intensity measurements in linear systems

The phase of a signal at a plane is reconstructed from the intensity profiles at two close parallel screens connected by a small abcd canonical transform; this applies to propagation along harmonic and repulsive fibers and in free media. We analyze the relationship between the local spatial frequency (the signal phase derivative) and the derivative of the squared modulus of the signal under a one-parameter canonical transform with respect to the parameter. We thus generalize to all linear systems the results that have been obtained separately for Fresnel and fractional Fourier transforms.     

Geometric method of reconstructing systems from experimental data

A method of reconstructing model dynamic evolution equations reduced to the central invariant manifold is described, which is based on an analysis of experimental data from controlled objects. The proposed method takes into account the group transformations of phase trajectories, which retain the topological equivalence of local regions.     

Time-dependent linear systems derivable from a variational principle

This paper presents a study of time-varying linear systems of second order ordinary differential equations, which can be derived from a Lagrangian after multiplication by a suitable matrix. It concerns a generalization of previous studies on systems with constant coefficients. After a simplification of the Helmholtz conditions, it is shown that the problem is reduced to a purely algebraic one, provided one can solve a matrix differential equation which produces the transformation to canonical form of the given system. This further leads to a theoretical characterization of all systems admitting a multiplier. Various algebraic relations are derived, involving constant matrices only, which can help to detect, prior to any integration procedure, whether or not: a multiplier exists. They are referred to as the generalized commutativity conditions. The first of these, which is sufficient for the existence of a Lagrangian, is shown to allow also a simple construction of a quadratic first integral, and to have some other interesting features. The paper ends with an example.     

利用三条谱线计算频率紧邻的两个成分的参数

对频率间隔小于2个FFT分辨率的两个成分，直接使用比值校正法精度较差。就双频率模型(DFM)而言，利用谱峰附近三点的频谱可建立一个非线性复约束的DFM方程，它表现为一个复行列式等于零。给出了牛顿法求解该约束的具体格式，讨论了迭代的相关细节。研究结果表明：这种方法对初值要求比较苛刻；通过设置容许区间和随机重置初值等措施，可减弱对初值的要求；除了一些奇异点外，若初值选择合适。经过大约10次迭代，两个频率可收敛到准确值；当两个频率计算准确之后，幅值和相位可由另外一组线性关系解出。     

Recovery of Characteristics of Non-Stationary Dynamic Systems from Three Test Signals

Measurement Techniques - Non-stationary continuous and discrete dynamical systems are modeled, respectively, by Volterra integral equations of the first kind and their discrete analogues....