Metal-insulator transition in one-dimensional lattices with chaotic energy sequences

We study electronic transport through a one-dimensional array of sites by using a tight binding Hamiltonian, whose site-energies are drawn from a chaotic sequence. The correlation degree between these energies is controlled by a parameter regulating the dynamic Lyapunov exponent measuring the degree of chaos. We observe the effect of chaotic sequences on the localization length, conductance, conductance distribution and wave function, finding evidence of a Metal-Insulator Transition (MIT) at a critical degree of chaos. The one-dimensional metallic phase is characterized by a Gaussian conductance distribution and exhibits a peculiar non-selfaveraging.Comment: 5 pages, 5 figures (one figure replaced). Includes new results and a few additional references. Improved style for publication. Accepted in Physics Letters

Understanding the Relationship between Activity and Neighbourhoods (URBAN) Study: research design and methodology

<p>Abstract</p> <p>Background</p> <p>Built environment attributes are recognized as being important contributors to physical activity (PA) engagement and body size in adults and children. However, much of the existing research in this emergent public health field is hindered by methodological limitations, including: population and site homogeneity, reliance on self-report measures, aggregated measures of PA, and inadequate statistical modeling. As an integral component of multi-country collaborative research, the Understanding the Relationship between Activity and Neighbourhoods (URBAN) Study seeks to overcome these limitations by determining the strengths of association between detailed measures of the neighborhood built environment with PA levels across multiple domains and body size measures in adults and children. This article outlines the research protocol developed for the URBAN Study.</p> <p>Methods and design</p> <p>The URBAN Study is a multi-centered, stratified, cross-sectional research design, collecting data across four New Zealand cities. Within each city, 12 neighborhoods were identified and selected for investigation based on higher or lower walkability and Māori demographic attributes. Neighborhoods were selected to ensure equal representation of these characteristics. Within each selected neighborhood, 42 households are being randomly selected and an adult and child (where possible) recruited into the study. Data collection includes: objective and self-reported PA engagement, neighborhood perceptions, demographics, and body size measures. The study was designed to recruit approximately 2,000 adults and 250 children into the project. Other aspects of the study include photovoice, which is a qualitative assessment of built environment features associated with PA engagement, an audit of the neighborhood streetscape environment, and an individualized neighborhood walkability profile centered on each participant's residential address. Multilevel modeling will be used to examine the individual-level and neighborhood-level relationships with PA engagement and body size.</p> <p>Discussion</p> <p>The URBAN Study is applying a novel scientifically robust research design to provide urgently needed epidemiological information regarding the associations between the built environment and health outcomes. The findings will contribute to a larger, international initiative in which similar neighborhood selection and PA measurement procedures are utilized across eight countries. Accordingly, this study directly addresses the international priority issues of increasing PA engagement and decreasing obesity levels.</p

Renewing social work practice through a postmodern perspective

Postmodernism is one of the most recent significant developments within the social sciences. This paper reviews the movement toward a postmodern perspective beginning in the late 19th century in the field of sociology. The evolution toward a postmodern perspective in the social sciences has important implications for the profession of social work. The authors suggest that the postmodern perspective has the potential to renew the profession of social work

Reduced T-cell receptor CD3ζ-chain protein and sustained CD3ε expression at the site of mycobacterial infection

Control of mycobacterial infection by the cellular immune system relies both on antigen-presenting cells and on T lymphocytes. The quality of an effective cellular immune response is dependent on functional signal transduction residing in the cytoplasmic tails of the T-cell receptor CD3 components. In order to investigate potential effects of mycobacteria on T-cell receptor signalling, we examined the protein expression of T-cell signal transduction molecules (CD3ζ, ZAP-70, p59(fyn), p56(l ck)). In Western blots of peripheral blood mononuclear cells of Mycobacterium tuberculosis infected patients, only the CD3ζ-chain showed a marked reduction in protein expression. To investigate the situation in situ, immunoenzymatic and immunofluorescence stainings for CD3ε and CD3ζ expression were performed on sections of normal lymphoid tissue, M. leprae infected and sarcoid tissue. CD3ε and CD3ζ expression were similar with respect to intensity, localization and the number of cells stained in normal lymphoid tissue and in sarcoid granulomas. In contrast, the granulomas of M. leprae infected tissues showed a significantly reduced expression of CD3ζ compared to CD3ε. Using double immunofluorescence analysis, virtually no CD3ζ expression could be detected in comparison to the CD3ε expression in the lesions. Apparently, mycobacteria are capable of significantly reducing CD3ζ-chain expression, which may be restored by cytokines. IL-2-enhanced ζ-chain expression and T-cell effector functions, defined by interferon-γ release, in M. tuberculosis-specific and human leucocyte antigen-DR restricted CD4(+) T cells isolated from granuloma lesions from patients with pulmonary tuberculosis. Because CD3ζ is essential for CD3 signalling and for eliciting T-cell effector functions, reduced CD3ζ protein expression could result in altered signal transduction and inefficient T-cell effector functions. Alternatively, reduced CD3ζ-chain expression may protect T cells from repetitive TCR stimulation associated with anergy or apoptosis