Optical and Morphological Studies of Thermally Vacuum Evaporated ZnSe Thin Films

Zinc selenide (ZnSe) thin films were deposited on optical glass substrates using thermal vacuum evaporation, by sublimation of zinc selenide powder from a single quartz crucible heated at 600 degrees C. The substrates temperatures were maintained constant during deposition at 220 degrees C. All the samples were subjected to post - deposition thermal treatments in the same deposition chamber, at 250 degrees C for 20 minutes. AFM and SEM studies confirmed that post - deposition annealing improved the grains growth and their distribution over the entire surface of the film. Optical constants (refraction indices and extinction coefficients) of semiconducting ZnSe thin films were measured by spectroscopic ellipsometry in the range of 190 nm to 500 nm. Optical measurements were completed with the spectral dependencies of transmission and absorption using a double beam UV - VIS spectrophotometer. The values for optical bandgaps calculated from the absorption spectra were found to be around 2.7 eV. All these results lead to the conclusion, that ZnSe thin films are good candidates to replace the conventional CdS thin films used as n-type window layers in the thin film heterojunction solar cells

A two step algorithm for learning from unspecific reinforcement

We study a simple learning model based on the Hebb rule to cope with "delayed", unspecific reinforcement. In spite of the unspecific nature of the information-feedback, convergence to asymptotically perfect generalization is observed, with a rate depending, however, in a non- universal way on learning parameters. Asymptotic convergence can be as fast as that of Hebbian learning, but may be slower. Moreover, for a certain range of parameter settings, it depends on initial conditions whether the system can reach the regime of asymptotically perfect generalization, or rather approaches a stationary state of poor generalization.Comment: 13 pages LaTeX, 4 figures, note on biologically motivated stochastic variant of the algorithm adde

Interplay between Symmetric Exchange Anisotropy, Uniform Dzyaloshinskii-Moriya Interaction and Magnetic Fields in the Phase Diagram of Quantum Magnets and Superconductors

We theoretically study the joint influence of uniform Dzyaloshinskii-Moriya (DM) interactions, symmetric exchange anisotropy (with its axis parallel to the DM vector) and arbitrarily oriented magnetic fields on one-dimensional spin 1/2 antiferromagnets. We show that the zero-temperature phase diagram contains three competing phases: (i) an antiferromagnet with Neel vector in the plane spanned by the DM vector and the magnetic field, (ii) a {\em dimerized} antiferromagnet with Neel vector perpendicular to both the DM vector and the magnetic field, and (iii) a gapless Luttinger liquid. Phase (i) is destroyed by a small magnetic field component along the DM vector and is furthermore unstable beyond a critical value of easy-plane anisotropy, which we estimate using Abelian and non-Abelian bosonization along with perturbative renormalization group. We propose a mathematical equivalent of the spin model in a one-dimensional Josephson junction (JJ) array located in proximity to a bulk superconductor. We discuss the analogues of the magnetic phases in the superconducting context and comment on their experimental viability.Comment: 20 pages, 16 figures; submitted to Phys. Rev.

Issue 1: “It’s Better Late Than Never”: A Community-Based HIV Research and Training Response to Supporting Mothers Living with HIV Who Have Child Welfare Involvement (Part I)

Grounded in community-based research (CBR) principles and an anti-oppression framework, the Positive Parenting Pilot Project (P4) aimed to develop, implement, and evaluate an HIV education and training module to enhance the provision of support for families affected by HIV and who are at risk of or already involved with child protection services. We set out to strengthen the ability of Children’s Aid Societies (CAS) in Ontario to provide anti-oppressive services to families affected by HIV from diverse communities by increasing the capacity of social workers who support these families. Applying the principles of CBR, we increased communication and forged new collaborative relationships within and between CAS agencies, the HIV service sector, parents living with HIV, and researchers in order to better address family needs at societal and structural levels. The goal of this project was to develop, provide, and evaluate a framework for an anti-oppressive education and training module related to the multiple layers of oppression that are experienced by families living with HIV including HIV-related stigma and discrimination, racism, sexism, violence and poverty. This paper presents the qualitative analysis of pre- and post- focus groups with CAS workers who participated in P4 and the emerging practice implications for working with families living with and affected by HIV

Bicrossed products for finite groups

We investigate one question regarding bicrossed products of finite groups which we believe has the potential of being approachable for other classes of algebraic objects (algebras, Hopf algebras). The problem is to classify the groups that can be written as bicrossed products between groups of fixed isomorphism types. The groups obtained as bicrossed products of two finite cyclic groups, one being of prime order, are described.Comment: Final version: to appear in Algebras and Representation Theor

Optical, morphological and electrical studies of thermally vacuum evaporated CdTe thin films for photovoltaic applications

Cadmium telluride (CdTe) semiconductor thin films were obtained by thermal vacuum evaporation (TVE) on optical glass substrates. The optical characterizations of CdTe thin films were made by spectroscopic ellipsometry (SE) and optical spectrophotometry. The optical constants (refractive indices and extinction coefficients) were obtained for CdTe thin films of different thicknesses. High absorption coefficients of order 105 cm−1 and suitable optical bandgaps values of 1.5 eV were obtained. The surface morphology of the obtained films was investigated by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) techniques. The influences of post-deposition thermal treatment on CdTe morphological properties were discussed. The current–voltage characteristics of CdTe films were recorded at temperatures in the range 150–280 K. An electrical analysis of the conduction mechanisms specific for different voltage ranges was also employed