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Complicated Problem (complicated + problem)
Selected AbstractsTensile and compressive damage coupling for fully-reversed bending fatigue of fibre-reinforced compositesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2002W. Van Paepegem ABSTRACT Due to their high specific stiffness and strength, fibre-reinforced composite materials are winning through in a wide range of applications in automotive, naval and aerospace industry. Their design for fatigue is a complicated problem and a large research effort is being spent on it today. However there is still a need for extensive experimental testing or large safety factors to be adopted, because numerical simulations of the fatigue damage behaviour of fibre-reinforced composites are often found to be unreliable. This is due to the limited applicability of the theoretical models developed so far, compared to the complex multi-axial fatigue loadings that composite components often have to sustain in in-service loading conditions. In this paper a new phenomenological fatigue model is presented. It is basically a residual stiffness model, but through an appropriate choice of the stress measure, the residual strength and thus final failure can be predicted as well. Two coupled growth rate equations for tensile and compressive damage describe the damage growth under tension,compression loading conditions and provide a much more general approach than the use of the stress ratio R. The model has been applied to fully-reversed bending of plain woven glass/epoxy specimens. Stress redistributions and the three stages of stiffness degradation (sharp initial decline , gradual deterioration , final failure) could be simulated satisfactorily. [source] Eigenvalue analysis of temperature distribution in composite wallsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2001Galip Oturanē Abstract The transient heat conduction problem in two-layer composite wall is solved analytically using spectral analysis. Eigenvalues and corresponding eigenfunctions of the spectral problem for the temperature distribution in composite walls are analysed using the Rouche Theorem. The number of eigenvalues is obtained and the temperature distribution of this complicated problem is given by a formula with calculated eigenvalues. The analytical solution obtained is in explicit form and provides easy determination of temperature rise in heating and thawing applications of composite materials. Copyright © 2001 John Wiley & Sons, Ltd. [source] Limb salvage of infected diabetic foot ulcers with free deep inferior epigastric perforator flaps ,MICROSURGERY, Issue 2 2006Masayoshi Ohta M.D. Soft-tissue reconstruction of the feet in diabetic patients with angiopathy, sensorial neuropathy, and immunopathy is a complicated problem. Until the mid-1980s, chronic foot ulcers in diabetic patients were treated conservatively, because flap surgery was regarded as too risky. However, in recent years, early debridement and flap coverage have become popular reconstructive methods for diabetic foot wounds. Several flap donor sites are available, depending on the nature of the defect. The deep inferior epigastric artery perforator (DIEP) flap is a relatively new flap that developed as a modification of the transverse rectus abdominis muscle (TRAM) flap. It provides a large amount of skin and subcutaneous tissue, without the donor-site morbidity of the ordinary TRAM flap. Furthermore, using the DIEP flap avoids the loss of major vessels. In this study, we report on the successful use of the DIEP flap in four cases of diabetic foot ulceration. © 2006 Wiley-Liss, Inc. Microsurgery 26: 87,92, 2006. [source] Electron gyration modified in the magnetic field tilted to the symmetry species of a crystalline metalPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006S. Olszewski Abstract When a crystal electron is gyrating in the magnetic field being normal to the crystallographic plane, the calculation of the gyration frequency represents a relatively easy task. The paper approaches a more complicated problem of the gyration frequency in the case when the magnetic field is tilted to the crystallographic axes. The tightly-bound s-electrons in crystal lattices of cubic symmetry are considered as examples. Another problem concerns a metal plate for which the changes of the electron gyration frequency are examined as a function of the inclination angle of the magnetic field with respect to the planar boundaries of that plate. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A MATLAB toolbox for solving acid-base chemistry problems in environmental engineering applicationsCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2005Chetan T. Goudar Abstract A MATLAB toolbox incorporating several computer programs has been developed in an attempt to automate laborious calculations in acid-base chemistry. Such calculations are routinely used in several environmental engineering applications including the design of wastewater treatment systems and for predicting contaminant fate and transport in the subsurface. The computer programs presented in this study do not replace student thinking involved in formulating the problem solving strategy but are merely tools that simplify the actual problem solving process. They encompass a wide variety of acid-base chemistry topics including equilibrium constant calculations, construction of distribution diagrams for mono and multiprotic systems, ionic strength and activity coefficient calculations, and buffer index calculations. All programs are characterized by an intuitive graphical user interface where the user supplies input information. Program outputs are either numerical or graphical depending upon the nature of the problem. The application of this approach to solving actual acid-base chemistry problems is illustrated by computing the pH and equilibrium composition of a 0.1 M Na2CO3 system at 30°C using several programs in the toolbox. As these programs simplify lengthy computations such as ionization fraction and activity coefficient calculations, it is hoped they will help bring more complicated problems to the environmental engineering classroom and enhance student understanding of important concepts that are applicable to real-world systems. The programs are available free of charge for academic use from the authors. © 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 257,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20051 [source] New and old trends in chemometrics.JOURNAL OF CHEMOMETRICS, Issue 8-10 2002How to deal with the increasing data volumes in R&D&P (research, development, process modeling, production), with examples from pharmaceutical research Abstract Chemometrics was started around 30 years ago to cope with and utilize the rapidly increasing volumes of data produced in chemical laboratories. The methods of early chemometrics were mainly focused on the analysis of data, but slowly we came to realize that it is equally important to make the data contain reliable information, and methods for design of experiments (DOE) were added to the chemometrics toolbox. This toolbox is now fairly adequate for solving most R&D problems of today in both academia and industry, as will be illustrated with a few examples. However, with the further increase in the size of our data sets, we start to see inadequacies in our multivariate methods, both in their efficiency and interpretability. Drift and non-linearities occur with time or in other directions in data space, and models with masses of coefficients become increasingly difficult to interpret and use. Starting from a few examples of some very complicated problems confronting chemical researchers today, possible extensions and generalizations of the existing chemometrics methods, as well as more appropriate preprocessing of the data before the analysis, will be discussed. Criteria such as scalability of methods to increasing size of problems and data, increasing sophistication in the handling of noise and non-linearities, interpretability of results, and relative simplicity of use will be held as important. The discussion will be made from a perspective of the evolution of the scientific methodology as driven by new technology, e.g. computers, and constrained by the limitations of the human brain, i.e. our ability to understand and interpret scientific and data analytical results. Quilt-PCA and Quilt-PLS presented here address and offer a possible solution to these problems. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||