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Element Types (element + type)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

Effect of screw element type in degradation of polypropylene upon multiple extrusions

ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2002
Sebastião V. Canevarolo
Abstract The screw profile of a twin-screw extruder can be designed to contain kneading and conveying elements inducing different levels of degradation in the polymer melt. In this work, the level of degradation in polypropylene has been measured after multiple extrusions,for various screw profiles,using size exclusion chromatography and IR spectroscopy. The average molecular weight and the polydispersity have been reduced and the carbonyl and unsaturation indexes increase as the number of extrusions and the aggressivity of the screw profile increase. The kneading element with 90° caused the greater level of degradation. On the other hand, the addition of left-hand conveying elements reduces the level of degradation because of the extra volume of molten polymer held in the screw, reducing the viability of oxygen inside the barrel. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 243,249, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10028 [source]

DNA Preservation in Skeletal Elements from the World Trade Center Disaster: Recommendations for Mass Fatality Management,

JOURNAL OF FORENSIC SCIENCES, Issue 4 2009
Amy Z. Mundorff M.A.
Abstract:, The World Trade Center (WTC) victim identification effort highlights taphonomic influences on the degradation of DNA from victims of mass fatality incidents. This study uses a subset of the WTC-Human Remains Database to evaluate differential preservation of DNA by skeletal element. Recovery location, sex, and victim type (civilian, firefighter, or plane passenger) do not appear to influence DNA preservation. Results indicate that more intact elements, as well as elements encased in soft tissue, produced slightly higher identification rates than more fragmented remains. DNA identification rates by element type conform to previous findings, with higher rates generally found in denser, weight-bearing bones. However, smaller bones including patellae, metatarsals, and foot phalanges yielded rates comparable to both femora and tibiae. These elements can be easily sampled with a disposable scalpel, and thus reduce potential DNA contamination. These findings have implications for DNA sampling guidelines in future mass fatality incidents. [source]

Interface handling for three-dimensional higher-order XFEM-computations in fluid,structure interaction

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2009
Ursula M. Mayer
Abstract Three-dimensional higher-order eXtended finite element method (XFEM)-computations still pose challenging computational geometry problems especially for moving interfaces. This paper provides a method for the localization of a higher-order interface finite element (FE) mesh in an underlying three-dimensional higher-order FE mesh. Additionally, it demonstrates, how a subtetrahedralization of an intersected element can be obtained, which preserves the possibly curved interface and allows therefore exact numerical integration. The proposed interface algorithm collects initially a set of possibly intersecting elements by comparing their ,eXtended axis-aligned bounding boxes'. The intersection method is applied to a highly reduced number of intersection candidates. The resulting linearized interface is used as input for an elementwise constrained Delaunay tetrahedralization, which computes an appropriate subdivision for each intersected element. The curved interface is recovered from the linearized interface in the last step. The output comprises triangular integration cells representing the interface and tetrahedral integration cells for each intersected element. Application of the interface algorithm currently concentrates on fluid,structure interaction problems on low-order and higher-order FE meshes, which may be composed of any arbitrary element types such as hexahedra, tetrahedra, wedges, etc. Nevertheless, other XFEM-problems with explicitly given interfaces or discontinuities may be tackled in addition. Multiple structures and interfaces per intersected element can be handled without any additional difficulties. Several parallelization strategies exist depending on the desired domain decomposition approach. Numerical test cases including various geometrical exceptions demonstrate the accuracy, robustness and efficiency of the interface handling. Copyright © 2009 John Wiley & Sons, Ltd. [source]

On evaluation of shape sensitivities of non-linear critical loads

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2003
E. Parente Jr.
Abstract The present paper focuses on the evaluation of the shape sensitivities of the limit and bifurcation loads of geometrically non-linear structures. The analytical approach is applied for isoparametric elements, leading to exact results for a given mesh. Since this approach is difficult to apply to other element types, the semi-analytical method has been widely used for shape sensitivity computation. This method combines ease of implementation with computational efficiency, but presents severe accuracy problems. Thus, a general procedure to improve the semi-analytical sensitivities of the non-linear critical loads is presented. The numerical examples show that this procedure leads to sensitivities with sufficient accuracy for shape optimization applications. Copyright © 2002 John Wiley & Sons, Ltd. [source]

A vertex-based finite volume method applied to non-linear material problems in computational solid mechanics

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2003
G. A. Taylor
Abstract A vertex-based finite volume (FV) method is presented for the computational solution of quasi-static solid mechanics problems involving material non-linearity and infinitesimal strains. The problems are analysed numerically with fully unstructured meshes that consist of a variety of two- and three-dimensional element types. A detailed comparison between the vertex-based FV and the standard Galerkin FE methods is provided with regard to discretization, solution accuracy and computational efficiency. For some problem classes a direct equivalence of the two methods is demonstrated, both theoretically and numerically. However, for other problems some interesting advantages and disadvantages of the FV formulation over the Galerkin FE method are highlighted. Copyright © 2002 John Wiley & Sons, Ltd. [source]