Photon emission induced by elastic exciton--carrier scattering in semiconductor quantum wells

We present a study of the elastic exciton--electron ($X-e^-$) and exciton--hole ($X-h$) scattering processes in semiconductor quantum wells, including fermion exchange effects. The balance between the exciton and the free carrier populations within the electron-hole plasma is discussed in terms of ionization degree in the nondegenerate regime. Assuming a two-dimensional Coulomb potential statically screened by the free carrier gas, we apply the variable phase method to obtain the excitonic wavefunctions, which we use to calculate the 1$s$ exciton--free carrier matrix elements that describe the scattering of excitons into the light cone where they can radiatively recombine. The photon emission rates due to the carrier-assisted exciton recombination in semiconductor quantum-wells (QWs) at room temperature and in a low density regime are obtained from Fermi's golden rule, and studied for mid-gap and wide-gap materials. The quantitative comparison of the direct and exchange terms of the scattering matrix elements shows that fermion exchange is the dominant mechanism of the exciton--carrier scattering process. This is confirmed by our analysis of the rates of photon emission induced by electron-assisted and hole-assisted exciton recombinations.Comment: Thoroughly revised version of previous work. Weak and incorrect assumptions have been removed from the paper, and its scope has evolved: see abstract. This is the final version, i.e. as accepted for publication in the European Physical Journal

The American School of Oboe Playing: Robert Bloom, John de Lancie, John Mack, and the Influence of Marcel Tabuteau

The American school of oboe playing is a distinct national style that evolved during the twentieth century. It is characterized by a darker tone than other national schools and a phrasing style that emphasizes long, connected lines with nuances in tonal intensity. The style was developed by Marcel Tabuteau, and is distinguished by his modified long scrape reed as well as the numerical system he used to teach musical phrasing. Even today, his ideas continue to disseminate, and most American oboists can trace their pedagogical roots back to Tabuteau. Yet despite the school\u27s evolution from one person, diversity exists. This project researches three of Tabuteau students: Robert Bloom, John de Lancie, and John Mack, chosen for their influence as both performers and as pedagogues, and the focus of the research is on their approach to tone production and musicianship. Because reed making is interconnected with tone production, reed styles are also compared. Research reveals that variations exist within the American school; however from a global perspective, the similarities still suggest a unified style

Transferrin Binding to Peripheral Blood Lymphocytes Activated by Phytohemagglutinin Involves a Specific Receptor: Ligand Interaction

Immunohistological studies have indicated that membrane sites binding transferrin are present upon activated human peripheral blood lymphocytes. In this study, we have investigated transferrin uptake in human lymphocytes exposed to phytohemagglutinin (PHA), by quantitative radiobinding and immunofluorescence in parallel. In stimulated lymphocytes, binding was maximal after a 30-min incubation, being greatest at 37°C, and greater at 22°C than at 4°C. Although some shedding and endocytosis of transferrin occurred at 22° and 37°C, these factors, and resulting synthesis of new sites, did not affect measurement of binding which was found to be saturable, reversible, and specific for transferrin (Ka 0.5-2.5 x 10^8 M-1). Binding was greater after a 48-h exposure to PHA than after 24 h, and was maximal at 66 h. Sequential Scatchard analysis revealed no significant elevation in affinity of interaction. However, although the total number of receptors increased, the proportion of cells in which binding of ligand was detected immunohistologically increased in parallel, and after appropriate correction, the cellular density of receptors remained relatively constant throughout (60,000-80,000 sites/cell). Increments in binding during the culture period were thus due predominantly to expansion of a population of cells bearing receptors. Similar differences in binding were apparent upon comparison of cells cultured in different doses of PHA, and in unstimulated cells binding was negligible. Transferrin receptors appear, therefore, to be readily detectable only upon lymphocytes that have been activated

Modelling of Unsteady, Incompressible Separation on an Aerofoil Using an Inviscid Flow Algorithm. G.U. Aero Report 8412

Presented in this report is a new method for the prediction of unsteady, incompressible separated flow over a two-dimensional aerofoil. The algorithm was developed from an existing unsteady potential flow model and makes use of an inviscid formulation for the flowfield. The aerofoil is represented by vortex panels of linearly varying strength which are piecewise continuous at the corners. Discrete vortices with finite cores are used to model the separating shear layers. Following a brief summary of unsteady separation modelling, the theoretical framework is presented and the subsequent numerical implementation is discussed in detail. Results are given for flows which tend asymptotically to the steady state and conclusions are drawn regarding the usefulness of the method

A Method for Predicting Unsteady Potential Flow About an Aerofoil. G.U. Aero Report 8401

Summary: A new model is presented for the calculation of the incompressible, inviscid flow around an arbitrary aerofoil undergoing unsteady motion. The technique was developed from the steady flow algorithm of Leishman and Galbraith (1) in which use was made of a linear distribution of panel vorticity. The procedure is in the same class as that of Basu and Hancock (2) but, because of the particular approach to the manner of specifying the shed vorticity, only a set of linear simultaneous equations needs be solved, unlike the method of reference (2), complicated by the necessary solution of a quadratic. A brief history of unsteady flow modelling is given in the introduction, followed by the mathematical details of the current method. Results are presented and discussed for a number of cases which clearly illustrate relevant characteristics of unsteady flow

Miniature mobile sensor platforms for condition monitoring of structures

In this paper, a wireless, multisensor inspection system for nondestructive evaluation (NDE) of materials is described. The sensor configuration enables two inspection modes-magnetic (flux leakage and eddy current) and noncontact ultrasound. Each is designed to function in a complementary manner, maximizing the potential for detection of both surface and internal defects. Particular emphasis is placed on the generic architecture of a novel, intelligent sensor platform, and its positioning on the structure under test. The sensor units are capable of wireless communication with a remote host computer, which controls manipulation and data interpretation. Results are presented in the form of automatic scans with different NDE sensors in a series of experiments on thin plate structures. To highlight the advantage of utilizing multiple inspection modalities, data fusion approaches are employed to combine data collected by complementary sensor systems. Fusion of data is shown to demonstrate the potential for improved inspection reliability

Tuning biexciton binding and anti-binding in core/shell quantum dots

We use a path integral quantum Monte Carlo method to simulate excitons and biexcitons in core shell nanocrystals with Type-I, II and quasi-Type II band alignments. Quantum Monte Carlo techniques allow for all quantum correlations to be included when determining the thermal ground state, thus producing accurate predictions of biexciton binding. These subtle quantum correlations are found to cause the biexciton to be binding with Type-I carrier localization and strongly anti-binding with Type-II carrier localization, in agreement with experiment for both core shell nanocrystals and dot in rod nanocrystal structures. Simple treatments based on perturbative approaches are shown to miss this important transition in the biexciton binding. Understanding these correlations offers prospects to engineer strong biexciton anti-binding which is crucial to the design of nanocrystals for single exciton lasing applications.Comment: 10 pages, 11 figure

Wind Tunnel Investigations into the Air Flow around the Existing and Proposed Bridges at Kingston. G.U. Aero Report 9316

This report presents the results obtained from a series of flow visualisation and flow measurement wind tunnel tests, carried out at Glasgow University, on models of the existing and proposed Kingston bridges. The background to the tests, commissioned by Strathclyde Regional Council after discussions with staff from the Department of Aerospace Engineering, is provided in the Introduction. Details of the facilities employed and bridge representation are included also. The important experimental consideration of Similarity is addressed in some detail, with particular reference to the use of appropriate scaling parameters for flow frequencies and velocities in the vicinity of the bridges. Test results are presented firstly in the form of still photographs of the illuminated smoke traces, with the main features illustrated by the provision of flow diagrams for each test. Secondly, the more quantitative measurements are presented as graphs of velocity versus time at a variety of measuring stations. In addition, selected video records have been made and are available on an accompanying, indexed VHS cassette. A detailed discussion of the results is presented, and five main conclusions are made concerning the structure of the flow around the existing and proposed bridges

A Review of the Susceptibility of the Scalpay Bridge to Aerodynamic Effects. G.U. Aero Report 9512.

An independent review is presented of the procedures employed by Crouch, Hogg & Waterman (CHW) in their assessment of the likely aerodynamic effects on the proposed Scalpay Bridge. The review identifies the principal design criteria relevant to the aerodynamic and structural dynamic performance of the Scalpay Bridge as prescribed in BD 49/93. On the basis of data and information supplied by CHW, an assessment is made of the degree to which these criteria are satisfied. It is concluded that there are several sensitive areas in the design analyses undertaken by CHW that should be reconsidered in view of the apparent susceptibility of the bridge to aerodynamic effects. In particular, it is recommended that the response of the bridge to vortex excitation and turbulence, and the narrow stability margin against galloping, be investigated furthe