一种恶劣环境下高协同度信号产生方法及其FPGA实现

鉴于高温恶劣环境下不同晶振搭建的信号源间的频率差不能保持恒定的问题,论述了一种基于FPGA技术使用直接数字频率合成技术(DDS)和锁相环技术(PLL)设计工作在恶劣环境下的高协同度信号源的方法。详细阐述了系统的整体结构,系统级性能优化方案和模块级性能优化方案。模拟实际工作环境进行了实验,实验结果验证了设计的正确性。     

Quasi-cyclic LDPC code construction for implementation of parallel joint row-column decoding

针对普通低密度校验(LDPC)码制约行列联合(JRC)译码算法并行度提高的问题,基于块渐进边增长(BPEG)算法,提出了一种用于并行JRC译码的LDPC码构造方法.该方法构造的准循环LDPC码(QC-LDPC)基矩阵由含r(r为大于1的整数)行的行组构成,允许一个行组内的r行进行并行JRC运算.仿真结果表明,用上述构造方法构造的LDPC码与BPEG码的误码性能相当.硬件实现表明,用此构造码的并行译码器的速率能达到典型传统准循环译码器的3倍以上,为面向译码器的LDPC码构造提供了范例.     

A mechanically fastened composite laminate joint and progressive failure analysis

A comprehensive procedure for a mechanically fastened composite laminate joint (ASTM D5961 Proc. A, B) is demonstrated from fixture design to analysis of test results. The ASTM tests are applied to evaluate the standard laminate properties and the composite joints. Composite laminate mechanical joints were analyzed using the finite element method (FEM), and the results were compared to test results. A progressive failure analysis (PFA) was applied to the FEM to predict the overall failure behavior of the test specimens. Three laminate failure theories – maximum stress, maximum strain, and Tsai–Wu – were applied to the PFA to predict the test failure load, displacement and strength. The PFA method was suitable to predict the initial test range of test and maximum test load except for the excessive failure area.     

ISM analysis of CPFR implementation barriers

Collaborative planning, forecasting and replenishment (CPFR) as an interconnection scheme between organisations have been shown to have significant benefits. Since its inception in the 1990s, its uptake has been lower than originally predicted. This paper identifies the major barriers and their interrelationships in CPFR implementations with a focus on high-tech industries. Interpretive Structural Modelling is used with a group of CPFR experts from industry/academia and Matrice d’Impacts Croisés Multiplication Appliquée àun Classement analysis to identify the driving and dependence powers. The paper identified 45 CPFR barriers and classifies them into four categories based on expert opinion, with only 13 of these determined to be significant. The results indicate that in terms of categories, managerial barriers are a significant root cause for both process and cultural barriers and CPFR implementation difficulties. It also indicates that although the importance of information technology to launch collaborative schemes has been addressed by many scholars, technology alone is not the complete solution for successful CPFR implementation. The paper has significant practical implications for organisations as it identifies the main CPFR barriers and their causal relationships. This will help firms in the process of CPFR strategy development particularly for mitigation strategies for dominant barriers.     

Optical implementation of cellular neural networks based on bias and joint correlation

A new bias method for the optical implementation of cellular neural networks is proposed to reduce electronic precalculation and increase processing speed. A multiple-object joint transform correlator is then used to realize the summation of multiple correlations resulting from the bias method. Compared with other optical systems for cellular neural networks, the proposed method offers the advantages of higher processing speed, easy implementation, and robustness. Computer simulations of the optical cellular neural networks for edge detection and corner and horizontal line extraction are also presented.     

Fatigue analysis of railway coupling joint

A new type of railway coupling joint, developed by a leading international railway manufacturer, has shown limited fatigue lives in service, in a preliminary service assessment of fatigue life. To get more data about this problem a detailed study was carried out of the fatigue design of the component including stress analysis and fatigue life evaluation.The main objective of this paper consisted in getting accurate information concerning the level of operational reliability of the fatigue behaviour of this new type of coupling used in carriages for passenger transportation in suburban lines.The strains in service were obtained with strain gauge rosettes in a typical line. Values of the cumulative fatigue damage were obtained in this service conditions. Linear damage accumulation laws were used.A numerical stress analysis using FE methods were performed. Detailed stress distributions were obtained in the component. Hot spot areas of stress were obtained and also the values of critical fatigue damage in these critical points of stress distributions. The extrapolation method to the hot spot points, was used to obtain the critical values of fatigue damage.The results of fatigue damage gave an infinite value of fatigue life for the coupling.     

A finite element procedure for the stress analysis of tubular joint connections

Ahmad's superparametric thick shell element with reduced integration, a transition element type having variable degrees-of-freedom per node and a three-dimensional incompatible element have been used to calculate the stress distribution at the intersection region of T- and Y-joint connections. To minimize the numerical effort, a transfinite blending function interpolation approach has been applied for the automatic mesh generation and the resulting system of linear equations has been solved using the front width method. Comparison of the computed solutions with some very carefully conducted experimental results has shown very good agreement.     

A joint econometric analysis of seat belt use and crash-related injury severity

This paper formulates a comprehensive econometric structure that recognizes two important issues in crash-related injury severity analysis. First, the impact of a factor on injury severity may be moderated by various observed and unobserved variables specific to an individual or to a crash. Second, seat belt use is likely to be endogenous to injury severity. That is, it is possible that intrinsically unsafe drivers do not wear seat belts and are the ones likely to be involved in high injury severity crashes because of their unsafe driving habits. The preceding issues are considered in the current research effort through the development of a comprehensive model of seat belt use and injury severity that takes the form of a joint correlated random coefficients binary-ordered response system. To our knowledge, this is the first instance of such a model formulation and application not only in the safety analysis literature, but in the econometrics literature in general. The empirical analysis is based on the 2003 General Estimates System (GES) data base. Several types of variables are considered to explain seat belt use and injury severity levels, including driver characteristics, vehicle characteristics, roadway design attributes, environmental factors, and crash characteristics. The results, in addition to confirming the effects of various explanatory variables, also highlight the importance of (a) considering the moderating effects of unobserved individual/crash-related factors on the determinants of injury severity and (b) seat belt use endogeneity. From a policy standpoint, the results suggest that seat belt non-users, when apprehended in the act, should perhaps be subjected to both a fine (to increase the chances that they wear seat belts) as well as mandatory enrollment in a defensive driving course (to attempt to change their aggressive driving behaviors).     

SRLU算法的设计分析与实现

本文提出了一种对非2次幂求余的SRLU算法，并基于该算法出了具体的设计和实现方案，测试表明该方法具有良好的稳定性和快速的收敛性。     

初相未知信号联合检测与估计的序贯实现

在未知参数的充分统计量和再生概率密度函数的基础上，引入了联合检测与估计的序贯算法，给出了算法的实现框图，并将该算法应用于高斯噪声中初相位未知信号的联合检测与估计当中，仿真实验表明，新算法较传统算法有一定的性能改善。     

A structural stress definition and numerical implementation for fatigue analysis of welded joints

A mesh-size insensitive structural stress definition is presented in this paper. The structural stress definition is consistent with elementary structural mechanics theory and provides an effective measure of a stress state that pertains to fatigue behavior of welded joints in the form of both membrane and bending components. Numerical procedures for both solid models and shell or plate element models are presented to demonstrate the mesh-size insensitivity in extracting the structural stress parameter. Conventional finite element models can be directly used with the structural stress calculation as a post-processing procedure. To further illustrate the effectiveness of the present structural stress procedures, a collection of existing weld S-N data for various joint types were processed using the current structural stress procedures. The results strongly suggests that weld classification based S-N curves can be significantly reduced into possibly a single master S-N curve, in which the slope of the S-N curve is determined by the relative composition of the membrane and bending components of the structural stress parameter. The effects of membrane and bending on S-N behaviors can be addressed by introducing an equivalent stress intensity factor based parameter using the structural stress components. Among other things, the two major implications are: (a) structural stresses pertaining to weld fatigue behavior can be consistently calculated in a mesh-insensitive manner regardless of types of finite element models; (b) transferability of weld S-N test data, regardless of welded joint types and loading modes, can be established using the structural stress based parameters.     

Experimental analysis of surgically corrected knee joint

Holographic interferometry, speckle photography and photoelasticity have been employed in the experimental investigations of the knee joint in four conditions - anatomically normal joint, varus joint, joint after Coventry popliteal osteotomy and joint after correction made using a new variety of the Coventry procedure¹. The studies included the investigations of the displacements of the bone in the sagittal plane, the displacements of points on the bone's surface in the frontal plane and the three dimensional state of stress. The obtained results show to what degree changes in the lower limb geometry affect the knee joint and in particular, its stability, functionality and the way in which it carries loads.     

Filter implementation technique for multicriteria characterization of coding domains in the joint transform correlator

An improved method for implementing correlation filters in the joint transform correlator architecture is proposed. We derived the method from computer-generated holography techniques. It allows us to use any correlation filters, especially ones that provide an optimal trade-off between noise robustness, peak sharpness, and optical efficiency, with any spatial light modulator (SLM). This method also allows for an objective comparison of the performance of the coding domains of various SLM's.     

A synergistic fracture mechanics approach to fatigue life evaluation

A technique for modeling synergistic effects in fatigue crack propagation (FCP) is presented. First, a mission (load/temperature history) is segregated into elemental damage events. A simple three parameter model is then used to describe these events. The model coefficients are seen to be interrelated linear functions of FCP rate controlling variables such as frequency, temperature, stress ratio (σ_min/σ_max), dwell, overload ratio ($\text{P}{}_{\mathrm{overload}}$/$\text{P}{}_{\max }$) and cycles between overload. Finally, integrating event-by-event crack advance gives the expected component crack propagation life under mission cycling. Results of this procedure applied to gas turbine disk materials IN100 and Waspaloy are discussed to examine the accuracy of the model.     

Crack deflection at an interface of alumina/metal joint: A numerical analysis

Deflection of a crack at the bimaterial interface is the initial mechanism required for obtaining enhanced toughness in bimaterial system. In this paper, a criterion is presented to predict the competition between crack deflection and penetration at the interface, using an energy release rate criterion. The finite element methods are used to calculate the strain energy release rates at the crack tip of alumina–metal bimaterial that either deflect or penetrate at the interface as a function of elastic mismatch and length of the deflected or penetrated crack. The effects of the elastic properties of two bonded materials were highlighted in order to evaluate the conditions for the crack deflection by the interface as well as the distance between the crack tip and the interface.     

A hardware implementation of pure ESTEREL

esterel is a synchronous concurrent programming language dedicated to reactive systems (controllers, protocols, man-machine interfaces etc.). esterel has an efficient standard software implementation based on well-defined mathematical semantics. We present a new hardware implementation of the pure synchronization subset of the language. Each program generates a specific circuit that responds to any input in one clock cycle. When the source program satisfies some statically checkable dynamic properties, the circuit is shown to be semantically equivalent to the source program. The hardware translation has been effectively implemented on the programmable active memory perle0 developed by J Vuillemin and his group at Digital Equipment.     

Rapid implementation of material models within finite element analysis

This paper presents a simple procedure for obtaining a numerical approximation to the consistent tangent matrix, together with a straightforward implicit (Euler backward) integration algorithm. The combined algorithm is used to incorporate four models into the commercial finite element package ABAQUS/Standard; illustrating how it can be used to rapidly implement material models within finite element analysis. The models have been chosen, not only because they help to illuminate the structure of the algorithm, but also because they illustrate its wide ranging applicability and permit the procedure to be tested against analytical results and an existing, well established, model.     

网络入侵防御系统设计与测试

该文主要研究云计算网络环境下的入侵检测与防御技术,在总结传统入侵检测技术的基础上,对云计算环境中的入侵检测系统进行比较全面的研究,开发以神经网络技术为基础的网络入侵防御系统。对于入侵检测模块,重点对数据捕获、行为规则匹配以及神经网络判别模块进行分析,并通过具体的测试检验其实现结果。