Microstructure and strength of metals processed by severe plastic deformation

The microstructure of f.c.c. metals (Al, Cu, Ni) and alloys (Al-Mg) processed by severe plastic deformation (SPD) methods is studied by X-ray diffraction line profile analysis. It is shown that the crystallite size and the dislocation density saturate with increasing strain. Furthermore, the Mg addition promotes efficiently a reduction of the crystallite size and an increase of the dislocation density in Al during the SPD process. The yield strength correlates well with that calculated from the dislocation density using the Taylor equation, thereby indicating that the main strengthening mechanism in both pure metals and alloys is the interaction between dislocations

Evolving DNA motifs to predict GeneChip probe performance

Background: Affymetrix High Density Oligonuclotide Arrays (HDONA) simultaneously measure expression of thousands of genes using millions of probes. We use correlations between measurements for the same gene across 6685 human tissue samples from NCBI's GEO database to indicated the quality of individual HG-U133A probes. Low correlation indicates a poor probe. Results: Regular expressions can be automatically created from a Backus-Naur form (BNF) context-free grammar using strongly typed genetic programming. Conclusion: The automatically produced motif is better at predicting poor DNA sequences than an existing human generated RE, suggesting runs of Cytosine and Guanine and mixtures should all be avoided. © 2009 Langdon and Harrison; licensee BioMed Central Ltd

Simple Max-Min Ant Systems and the Optimization of Linear Pseudo-Boolean Functions

With this paper, we contribute to the understanding of ant colony optimization (ACO) algorithms by formally analyzing their runtime behavior. We study simple MAX-MIN ant systems on the class of linear pseudo-Boolean functions defined on binary strings of length 'n'. Our investigations point out how the progress according to function values is stored in pheromone. We provide a general upper bound of O((n^3 \log n)/ \rho) for two ACO variants on all linear functions, where (\rho) determines the pheromone update strength. Furthermore, we show improved bounds for two well-known linear pseudo-Boolean functions called OneMax and BinVal and give additional insights using an experimental study.Comment: 19 pages, 2 figure

FACTORS INFLUENCING THE STRESS-STRAIN BEHAVIOR OF CERAMIC MATERIALS.

The stress-strain behavior of ceramic materials is greatly influenced by microstructural features ranging from the presence of point defects in single crystals to the size and location of pores and nature of grain boundaries in polycrystals. Several factors may affect the behavior at anyone time, and the analysis of experimental data, particularly for polycrystals, is thus extremely difficult. This review examines the interpretation of mechanical behavior in materials having the rock salt structure, with particular emphasis on the role of impurities, the significance of grain boundary and/or intragranular porosity, and the problems associated with the intersection of slip bands. <br/

A high-wavenumber boundary-element method for an acoustic scattering problem

In this paper we show stability and convergence for a novel Galerkin boundary element method approach to the impedance boundary value problem for the Helmholtz equation in a half-plane with piecewise constant boundary data. This problem models, for example, outdoor sound propagation over inhomogeneous flat terrain. To achieve a good approximation with a relatively low number of degrees of freedom we employ a graded mesh with smaller elements adjacent to discontinuities in impedance, and a special set of basis functions for the Galerkin method so that, on each element, the approximation space consists of polynomials (of degree $\nu$) multiplied by traces of plane waves on the boundary. In the case where the impedance is constant outside an interval $[a,b]$, which only requires the discretization of $[a,b]$, we show theoretically and experimentally that the $L_2$ error in computing the acoustic field on $[a,b]$ is ${\cal O}(\log^{\nu+3/2}|k(b-a)| M^{-(\nu+1)})$, where $M$ is the number of degrees of freedom and $k$ is the wavenumber. This indicates that the proposed method is especially commendable for large intervals or a high wavenumber. In a final section we sketch how the same methodology extends to more general scattering problems

A Galerkin boundary element method for high frequency scattering by convex polygons

In this paper we consider the problem of time-harmonic acoustic scattering in two dimensions by convex polygons. Standard boundary or finite element methods for acoustic scattering problems have a computational cost that grows at least linearly as a function of the frequency of the incident wave. Here we present a novel Galerkin boundary element method, which uses an approximation space consisting of the products of plane waves with piecewise polynomials supported on a graded mesh, with smaller elements closer to the corners of the polygon. We prove that the best approximation from the approximation space requires a number of degrees of freedom to achieve a prescribed level of accuracy that grows only logarithmically as a function of the frequency. Numerical results demonstrate the same logarithmic dependence on the frequency for the Galerkin method solution. Our boundary element method is a discretization of a well-known second kind combined-layer-potential integral equation. We provide a proof that this equation and its adjoint are well-posed and equivalent to the boundary value problem in a Sobolev space setting for general Lipschitz domains

Using Photovoice in PETE Programs to Initiate Positive Change

The purpose of this presentation will be to provide teacher educators with an overview of the Photovoice methodology and its potential utility in curricular change. The National Association for Sport and Physical Education’s ([NASPE], 2008) PETE standards state educators should allow diversity to drive instructional related decision-making. Photovoice, a participatory action research methodology, is a tool teacher educators can use to be responsive to the continuously changing contexts of public schools

HIV risk among Australian men travelling overseas: networks and context matter

Increasing international mobility presents a risk for communicable disease transmissions. Overseas-acquired HIV infections have been increasingly observed across Australian jurisdictions. This includes a mix of men emigrating from countries with high HIV prevalence and men travelling abroad. There is currently little research exploring international mobility and HIV risk and as a consequence the increase of men acquiring HIV while travelling overseas is poorly understood. This article draws on data from a qualitative study exploring the risk perspectives and experiences of 14 Australian men who acquired HIV while travelling overseas in the years between 2000-2009. Participants articulated a strong desire to distance themselves from the identity of a tourist. Social networks were highlighted as important entry points to engage with other foreign travellers and expatriates. These networks were highly influential and were understood by the participants to provide guidance on how they should negotiate the local scene, including where to meet sex partners. Limited discussion of safe sex and HIV was mentioned in these contexts. The findings suggest that prevalent social norms and social networks play an influential role in how participants negotiate sex and social relations in overseas settings. These networks could potentially provide sites for effective HIV prevention programs. Keywords: male tourists; HIV transmission; social networks; behaviour; sexual risk; HIV preventio

Influence of inhomogeneity on mechanical properties of commercially pure titanium processed by HPT

Already for fifteen years many researchers have been trying to discover metallic materials with unusual combinations of strength and ductility: with high strength and enhanced ductility . This combination may be achieved through different ways: alloying, nanostructuring, etc. This report is an attempt to analyze the influence of inhomogeneity of different types (structural, phase and space) on mechanical properties of commercially pure ti tanium (bulk and powder) subjected to high- pressure torsion. Experimental results for HPT bulk and powder titanium have demonstrated that mechanical behavior of CP titanium strongly depends on phase inhomogeneity (alpha + omega phases), structural inhomoge neity (bimodal grain size distribution) and space inhomogeneity (retained porosity) in case of cold consolidated Ti powder. High strength in HPT bulk titanium due to the formation of hard omega phase during HPT processing at room temperature was detected. The strong omega phase transforms back to nanograined alpha phase domains during short annealing at elevated temperature. HPT consolidation of titanium powder leads to the formation of brittle specimens showing high strength but almost zero plasticityPeer ReviewedPostprint (author's final draft