基于自由响应数据的时变系统物理参数识别

提出了一种基于自由响应信号识别时变系统物理参数的子空间方法.该方法以任意组合的位移、速度、加速度响应信号为测量信息,通过对仅利用一组响应信号组成的Hankel矩阵做奇异值分解,识别出等效状态的系统矩阵,然后运用推导出来的通用时变系统的转换矩阵,将等效状态系统矩阵转换成为实际物理状态下的系统矩阵,从而识别出实际系统的刚度、阻尼矩阵.以二自由度弹簧-质量-阻尼模型为算例,研究了突变、线性变化和周期变化三种变化形式下物理参数的识别,并讨论了不同信噪比下噪声对识别结果的影响,仿真算例验证了该方法的正确性和有效性.     

Amplitude distribution acoustic emission signatures of unidirectional fibre composite hybrid materials

The failure processes in fibre-reinforced materials can be arranged in order of ascending energies as matrix crazing, interfacial delamination and fibre fracture. In glass fibre-reinforced plastics, delamination plays a significant part in the failure process. In carbon fibre-reinforced plastics, failure normally occurs by catastrophic fibre fracture with very little acoustic activity before the event. When two composites are combined within a single matrix to produce a fibre composite hybrid material, it is expected that a mixture of failure modes will occur, although this will be dependent on stress and strain levels. Acoustic emissions are the sounds generated by materials under stress: in practice, the amplitude of the acoustic emission signal is most commonly used as a measure of energy. Thus if a histogram of the number of acoustic events within a specific range of energies is formed, then a characteristic series of ‘signatures’ can be expected for each type of composite. The results of amplitude distribution acoustic emission tests are reported in this paper for unidirectional carbon fibre with glass fibre hybrid reinforced plastics, tested to failure in bending.     

Information terminological system for inorganic materials science (exemplified by concrete science)

Using concrete science as an example, we discuss priority issues in and principles and methodology of creating information terminological systems for inorganic materials science. The development of such systems builds on a typological approach, terminological field indexing methods, etc.     

The determination of nuclear reaction yields by means of an isotope-separator-on-line (ISOL) system

The present report describes a method to extract nuclear reaction yield data from activities measured in a sample after isotope separation. The contribution from the formation of a reaction product, i.e. corresponding to the independent yield of this product, is evaluated as are the contributions from parents and grandparents. The analysis takes into account the delay between production and sample collection of the three elements involved.     

Composite organic-inorganic nanoparticles (COINs) with chemically encoded optical signatures

To obtain a coding system for multiplex detection, we have developed a method to synthesize a new type of nanomaterial called composite organic-inorganic nanoparticles (COINs). The method allows the incorporation of a broad range of organic compounds into COINs to produce surface enhanced Raman scattering (SERS)-like spectra that are richer in variety than fluorescence-based signatures. Preliminary data suggest that COINs can be used as Raman tags for multiplex and ultrasensitive detection of biomolecules.     

First-principles DFT modeling of nuclear fuel materials

We review the state of first-principles density functional theory (DFT) modeling of nuclear fuel materials. DFT-based first-principles modeling has emerged as a quantitatively rigorous method that has been widely used to study these materials. The main challenge in DFT modeling of nuclear fuels lies in the f electron nature of actinide materials. DFT + U methods along with regular DFT methods including both non-spin-polarized and spin-polarized treatments are discussed. The review topics include bulk and intrinsic defects properties, stability of fission products, modeling of fission gas (xenon) transport, and non-equilibrium behavior of fission products in uranium dioxide and surrogate materials. In addition, DFT modeling activity in alternative fuel forms including uranium nitride, uranium carbide, and metal fuels is reviewed. Some of the limitations of empirical potential calculations addressed by DFT are also discussed.     

Diagnostic system for identification of accident scenarios in nuclear power plants using artificial neural networks

This paper presents the work carried out towards developing a diagnostic system for the identification of accident scenarios in 220 MWe Indian PHWRs. The objective of this study is to develop a methodology based on artificial neural networks (ANNs), which assists in identifying a transient quickly and suggests the operator to initiate the corrective actions during abnormal operations of the reactor. An operator support system, known as symptom-based diagnostic system (SBDS), has been developed using ANN that diagnoses the transients based on reactor process parameters, and continuously displays the status of the reactor. As a pilot study, the large break loss of coolant accident (LOCA) with and without the emergency core cooling system (ECCS) in reactor headers has been considered. Several break scenarios of large break LOCA have been analyzed. The time-dependent transient data have been generated using the RELAP5 thermal hydraulic code assuming an equilibrium core, which conforms to a realistic estimation. The diagnostic results obtained from the ANN study are satisfactory. These results have been incorporated in the SBDS software for operator assistance. A few important outputs of the SBDS have been discussed in this paper.     

Generalized formulation for the description of hysteresis in softmagnetic materials

Presents a phenomenological formulation that broadens the range of applicability of the Basso-Bertotti hysteresis model to include soft magnetic materials with very gradual saturation, such as commercial manganese-zinc (MnZn) power ferrites. The formulation also enables the Basso-Bertotti model to better characterize both the major loop and the minor loops of these soft magnetic materials. The formulation introduces a model parameter m_t that defines the transition between low fleld/minor loops and high field/major loop. An explicit expression for magnetization in term of domain-wall position was synthesized to make the hysteresis model numerically attractive. The formulation was verified by experimental data of commercial MnZn ferrites     

红外隐身材料的性能特征述评

简述了红外隐身材料的工作原理 ,分析了不同类型红外隐身材料的性能特征 ,并综述了国内外红外隐身材料的研究现状     

Self-propagating high-temperature (combustion) synthesis (SHS) of powder-compacted materials

Self-propagating high-temperature synthesis (SHS) of powder compacts is a novel processing technique currently being developed as a route for the production of engineering ceramics and other advanced materials. The process, which is also referred to as combustion synthesis, provides energy- and cost-saving advantages over the more conventional processing routes for these materials. At the same time, the rapid heating and cooling rates provide a potential for the production of metastable materials with new and, perhaps, unique properties. This paper reviews the research that has been, and is being, undertaken in this exciting new processing route for high-technology materials and examines the underlying theoretical explanations which will, eventually, lead to improved control over processing parameters and product quality.     

System of x-ray identification of substantially multiphase materials

The information storage and retrieval system of x-ray phase identification (ISRS PI) targeted to determination of a substantial phase composition of complex and substantially multicomponent polycrystalline materials by their x-ray diffraction spectra is described. A base element of the system is a problem-oriented operator language of search queries for phase identification (PI). The identification procedure is performed with the use of a graphical interface that provides processing of x-ray powder diffraction patterns, self-programming and fulfillment of queries for PI hidden from the user, and construction of model spectra. The identification possibilities of ISRS PI (Retrieve QQPA) are discussed on the basis of data on the Search-Match Round Robin-2002 Internet competition carried out by the CPD Commission of the International Union of Crystallographers.     

Optimization of pre-metal Dielectric (PMD) materials

It is very important to select superior interlayer pre-metal dielectric (PMD) materials that can act as a penetration barrier to various impurities created by the chemical mechanical polishing (CMP) process. In this paper, hot carrier degradation and device characteristics were studied on various materials of PMD-1 layers, which included low-pressure tetra-ethyl-ortho-silicate glass (LP-TEOS), Si-rich (SR)-oxide, plasma-enhanced (PE)-oxynitride, PE-nitride and PE-TEOS films. Pressure cooker test (PCT) analysis was used to obtain the electrical characteristics of devices, such as the shifts in threshold voltage and transconductance as a function of stress time, junction leakage current and breakdown voltage of field transistors with variation of these PMD-1 materials. Also, the most effective PMD-1 materials which can prevent degradation effects due to hot carrier stress were investigated. From experimental results, it is clearly shown that silicon oxide turned out to be a better PMD-1 material than both PE-oxynitride and PE-nitride. From the results, it is suggested that LP-TEOS film is the best PMD-1 material among the silicon oxide samples. © 2001 Kluwer Academic Publishers