Development of Accurate Constitutive Models for Simulation of Superplastic Forming

Superplastic forming (SPF) has been considered a process for improving the formability of aluminum alloys for the production of automotive body panels. In order to accurately simulate the SPF process, elevated temperature, uniaxial tension tests are used to develop the material flow model. Due to the high temperature and large degree of deformation in these tests, strain is typically calculated using crosshead displacement rather than with an extensometer. This approach requires the assumption of a constant material volume in the gage section to calculate the uniform strain. It has been observed that a significant amount of material flows from the grips into the gage section during testing which results in inaccuracies in the material model. This article presents a numerical tool that accounts for material flow from the grips and produces a more accurate constitutive equation. Experimental and numerical validations of the results of the developed tool are presented. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

Far-Infrared Optics Design & Verification

Compact quasi-optics are difficult to design with any confidence using techniques developed for visible wavelengths. In this paper we investigate the performance of existing software design tools (ASAP, CODE V, GLAD) as well as a Gaussian beam mode analysis technique not yet available as commercial software. We have devised a set of test cases and used these to study the underlying methodologies and physics of these packages and we probe their suitability for the analysis of submillimetre-wave systems and components. We have used the physical optics package GRASP as our benchmark software.     

Alu-Alu recombination results in a duplication of seven exons in the lysyl hydroxylase gene in a patient with the type VI variant of Ehlers-Danlos syndrome

The type VI variant of the Ehlers-Danlos syndrome (EDS) is a recessively inherited connective-tissue disorder. The characteristic features of the variant are muscular hypotonia, kyphoscoliosis, ocular manifestations, joint hypermobility, skin fragility and hyperextensibility, and other signs of connective-tissue involvement. The biochemical defect in most but not all patients is a deficiency in lysyl hydroxylase activity. Lysyl hydroxylase is an enzyme that catalyzes the formation of hydroxylysine in collagens and other proteins with collagen-like amino acid sequences. We have recently reported an apparently homozygous large-duplication rearrangement in the gene for lysyl hydroxylase, leading to the type VI variant of EDS in two siblings. We now report an identical, apparently homozygous large duplication in an unrelated 49-year-old female originally analyzed by Sussman et al. Our simple-sequence-repeat-polymorphism analysis does not support uniparental isodisomy inheritance for either of the two duplications. Furthermore, we indicate in this study that the duplication in the lysyl hydroxylase gene is caused by an Alu-Alu recombination in both families. Cloning of the junction fragment of the duplication has allowed synthesis of appropriate primers for rapid screening for this rearrangement in other families with the type VI variant of EDS.     

Light-induced enhancement of quantum dot photovoltaic devices with nitrogen doped titanium oxide capping layers

For the first time it is reported that nitrogen-doped titanium oxide with light annealing can improve the device performance by 300% when acting as an interfacial layer between CdSe quantum dot/poly-3-hexylthiophene and the cathode in the photovoltaic devices. Substitutional N doping with a concentration of 1.2 at.% was found by X-ray photoelectron spectroscopy which was responsible for 0.1 eV band gap reduction of TiO_x. Photoluminescence and the external quantum efficiency spectrum confirmed the enhanced charge collection and association rate after light annealing. Three-dimensional atomic force microscopy results agreed with the series resistance measurements, confirming that a good contact was achieved. The topography study also indicated that the active layer morphology changed upon light annealing. Improved stability and longer lifetime were also found with TiO_xN_y capped devices, which were optimized with light annealing. TiO_x capped devices were also evaluated for comparison in this study.     

Medial-based deformable models in nonconvex shape-spaces for medical image segmentation

We explore the application of genetic algorithms (GA) to deformable models through the proposition of a novel method for medical image segmentation that combines GA with nonconvex, localized, medial-based shape statistics. We replace the more typical gradient descent optimizer used in deformable models with GA, and the convex, implicit, global shape statistics with nonconvex, explicit, localized ones. Specifically, we propose GA to reduce typical deformable model weaknesses pertaining to model initialization, pose estimation and local minima, through the simultaneous evolution of a large number of models. Furthermore, we constrain the evolution, and thus reduce the size of the search-space, by using statistically-based deformable models whose deformations are intuitive (stretch, bulge, bend) and are driven in terms of localized principal modes of variation, instead of modes of variation across the entire shape that often fail to capture localized shape changes. Although GA are not guaranteed to achieve the global optima, our method compares favorably to the prevalent optimization techniques, convex/nonconvex gradient-based optimizers and to globally optimal graph-theoretic combinatorial optimization techniques, when applied to the task of corpus callosum segmentation in 50 mid-sagittal brain magnetic resonance images.     

Analyzing the power coupled between partially coherent waveguide fields in different states of coherence

A procedure is described for calculating the power coupled between partially coherent waveguide fields that are in different states of coherence. The method becomes important when it is necessary to calculate the power transferred from a distributed source S to a distributed load L through a length of multimode metallic, or dielectric, waveguide. It is shown that if the correlations between the transverse components of the electric and magnetic fields of S and L are described by coherence matrices M and M', respectively, then the normalized average power coupled between them is (eta) = Tr[MM']/Tr[M]Tr[M'], where Tr denotes the trace. When the modal impedances are equal, this expression for the coupled power reduces to an equation derived in a previous paper [J. Opt. Soc. Am. A 18, 3061 (2001)], by use of thermodynamic arguments, for the power coupled between partially coherent free-space beams.     

Post-buckling behaviour of structures using a finite element–nonlinear eigenvalue technique

A series of finite element algorithms for the calculation of the post-buckling behaviour of structures are proposed. The algorithms represent a finite element implementation of a variational principle for nonlinear eigenvalue problems. Incremental amplitude solution schemes are defined. Numerical results are presented for the post-buckling behaviour of specific structures with linear and nonlinear pre-buckling states.     

Community psychology: Boundary problems, psychological perspectives, and an empirical overview of the field.

Argues that L. D. Goodstein and I. Sandler's (see record 1979-22507-001) conceptual analysis of the role of community psychology (CP) exacerbates the boundary problem between CP and allied fields and loses sight of the part of CP that is psychological in nature. A content analysis of published literature on CP reveals overlaps between CP and community mental health, as well as between CP and public policy, organizational, and applied psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)