STRESS INTENSITY FACTORS AND WEIGHT FUNCTIONS FOR SEMI-ELLIPTICAL SURFACE CRACKS IN FINITE-THICKNESS PLATES UNDER TWO-DIMENSIONAL STRESS DISTRIBUTION

Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%.     

Triple check for antigen specificity of B cells during germinal centre reactions

Somatic hypermutation of the immunoglobulin variable genes during germinal reactions might permit the expansion of B-cell clones with unwanted (e.g. autoreactive) specificity. Here, Ernst Lindhout and colleagues propose three antigen-specific checkpoints that ensure the appropriate antigen specificity of activated B cells is maintained by regulating the activation, selection and further differentiation of B cells.     

Proving termination of GHC programs

A transformational approach for proving termination of parallel logic programs such as GHC programs is proposed. A transformation from GHC programs to term rewriting systems is developed; it exploits the fact that unifications in GHC-resolution correspond to matchings. The termination of a GHC program for a class of queries is implied by the termination of the resulting rewrite system. This approach facilitates the applicability of a wide range of termination techniques developed for rewrite systems in proving termination of GHC programs. The method consists of three steps: (a) deriving moding information from a given GHC program, (b) transforming the GHC program into a term rewriting system using the moding information, and finally (c) proving termination of the resulting rewrite system. Using this method, the termination of many benchmark GHC programs such as quick-sort, merge-sort, merge, split, fair-split and append, etc., can be proved. This is a revised and extended version of Ref. 12). The work was partially supported by the NSF Indo-US grant INT-9416687 Kapur was partially supported by NSF Grant nos. CCR-8906678 and INT-9014074. M. R. K. Krishna Rao, Ph.D.: He currently works as a senior research fellow at Griffith University, Brisbane, Australia. His current interests are in the areas of logic programming, modular aspects and noncopying implementations of term rewriting, learning logic programs from examples and conuterexamples and dynamics of mental states in rational agent architectures. He received his Ph.D in computer science from Tata Institute of Fundamental Research (TIFR), Bombay in 1993 and worked at TIFR and Max Planck Institut für Informatik, Saarbrücken until January 1997. Deepak Kapur, Ph.D.: He currently works as a professor at the State University of New York at Albany. His research interests are in the areas of automated reasoning, term rewriting, constraint solving, algebraic and geometric reasoning and its applications in computer vision, symbolic computation, formal methods, specification and verification. He obtained his Ph.D. in Computer Science from MIT in 1980. He worked at General Electric Corporate Research and Development until 1987. Prof. Kapur is the editor-in-chief of the Journal of Automated Reasoning. He also serves on the editorial boards of Journal of Logic Programming, Journal on Constraints, and Journal of Applicable Algebra in Engineering, Communication and Computer Science. R. K. Shyamasundar, Ph.D.: He currently works as a professor at Tata Institute of Fundamental Research (TIFR), Bombay. His current intersts are in the areas of logic programming, reactive and real time programming, constraint solving, formal methods, specification and verification. He received his Ph.D in computer science from Indian Institute of Science, Bangalore in 1975 and has been a faculty member at Tata Institute of Fundamental Research since then. He has been a visiting/regular faculty member at Technological University of Eindhoven, University of Utrecht, IBM TJ Watson Research Centre, Pennsylvania State University, University of Illinois at Urbana-Champaign, INRIA and ENSMP, France. He has served on (and chaired) Program Committees of many International Conferences and has been on the Editorial Committees.     

Automatic tuning of decentralized PID controllers for MIMO processes

An automatic tuning algorithm for decentralized PID control in multiple-input multiple-output (MIMO) plants is presented. This algorithm generalizes the authors' recent auto-tuner for two-input two-output systems to any number of inputs and outputs. The algorithm consists of two stages. In the first, the desired critical point, which consists of the critical gains of all the loops and a critical frequency, is identified. The auto-tuner identifies the desired critical point with almost no a priori information about the process. During the identification phase all controllers are replaced by relays, thus generating limit cycles with the same period in all loops. It is shown that each limit cycle corresponds to a single critical point of the process. By varying the relays parameters different points can be determined. The auto-tuner contains a procedure which converges rapidly to the desired critical point while maintaining the amplitudes of the process variables as well as of the manipulated variables within prespecified ranges. In the second stage, the data of the desired critical point is used to tune the PID controllers by the Ziegler-Nichols rules or their modifications. This paper focuses on the first stage. The steady-state process gains, which are required for the appropriate choice of the desired critical point, are determined by the auto-tuner in closed-loop fashion simultaneously with the identification of the critical point. The identification of the process gains is achieved at no extra plant time. Based upon a large number of simulated cases, the proposed auto-tuner seems to be efficient and robust. The paper discusses the underlying principles of the auto-tuner and its properties and capabilities are demonstrated via examples.     

Review of Constructing the subject: Historical origins of psychological research.

Reviews the book, Constructing the subject: Historical origins of psychological research by Kurt Danziger (1990). Kurt Danziger's Constructing the Subject: Historical Origins of Psychological Research is a book of singular importance because it provides such a penetrating analysis, and does so in a manner that is cause for considerable reflection. In brief, Danziger provides a history lesson that not only situates the names and the projects of experimental psychology in the first part of this century, but also aims to clarify the project of knowledge generation both past and present. Indeed, shades of Quine, Kuhn, and Hesse permeate this book in a way that demands psychologists examine their own investigative practices and logics of justification. Through Wundt, through Galton, through Ebbinghaus and others, Danziger illuminates the development of experimental psychology along with the historical and philosophical vicissitudes that have given rise to numerous psychological knowledge claims. If it is true that we must understand our history in order to understand our present, then Danziger's book should be required reading in all research laboratories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In Situ ceramic particle-reinforced aluminum matrix composites fabricated by reaction pressing in the TiO2 (Ti)-Al-B (B2O3) systems

Particulate TiB₂ reinforced aluminum-based metal matrix composites (MMCs) were successfully fabricated by means of the reaction processing method. TiB₂ particulates were formed in situ through the reaction of Ti and B in Ti-Al-B, TiO₂ and B in TiO₂-Al-B, and TiO₂ and B₂O₃ in TiO₂-Al-B₂O₃ systems. The results showed that in situ TiB₂ particulates formed in the Ti-Al-B system had a size of 5 μm and they exhibited block and rodlike structures. Moreover, coarse Al₃Ti blocks several tens of micrometers in size were also formed simultaneously. On the other hand, equiaxed Al₂O₃ and TiB₂ particulates with a size of less than 2 μm were formed in situ in the TiO₂-Al-B and TiO₂-Al-B₂O₃ systems. The Al₃Ti phase was completely eliminated in the TiO₂-Al-B system with increasing B content. Tensile tests revealed that the Al₂O₃ · TiB₂/Al composite fabricated from the TiO₂-Al-B system exhibits excellent mechanical properties. The yield strength of the Al₂O₃ · TiB₂/Al composite appeared to increase with increasing TiB₂ content. The yield strength of the Al₂O₃ · TiB₂/Al composite could be further increased by introducing CuO into the TiO₂-Al-B system. Such an increment in mechanical strength arose from the strengthening effect caused by the Al₂Cu precipitates. The incorporation of CuO had no effect on the in situ reaction process of the TiO₂-Al-B system. Finally, the effect of SiC addition on the microstructure and mechanical properties of the composites fabricated from the TiO₂-Al-B and TiO₂-Al-B-CuO systems was also investigated.