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 Defence and Evacuation of the Kuban Bridgehead, January – October 1943

This thesis examines German and Soviet operations in the Kuban area of southern Russia during January – October 1943. As the bulk of German Army Group A withdrew from the Caucasus in early 1943 to avoid encirclement following the Soviet counter-offensive at Stalingrad, Seventeenth Army was ordered to hold a bridgehead on the Kuban Peninsula as a jumping-off point for a future resumption of the German offensive into the Caucasus. In early February, the Soviets attempted to eliminate the German bridgehead through a combined amphibious and ground operation. The ground operation did not achieve any significant gain, and the main amphibious landing operation was a catastrophic failure, but a secondary landing succeeded in gaining a foothold in the southern suburbs of the port city of Novorossiysk that was quickly expanded and became known as Malaya Zemlya (The Small Land). Early April saw the launch of Operation Neptune, a German effort to eliminate the Malaya Zemlya beachhead. This failed utterly due to the weakness of the German assault groups and the tenacious Soviet defence. The Soviets then launched a series of attempts through the spring and summer to break the German line, with minimal success. The final phase of operations in the Kuban was the withdrawal of Seventeenth Army by sea and air across the Kerch Strait to the Crimea. Almost a quarter of a million men and the bulk of their equipment were successfully evacuated, with very light losses. The thesis examines some factors that contributed to the success or failure of these operations and also considers why a region that was of key strategic interest in both German and Soviet planning in the first period of the war quickly diminished in importance and has been largely neglected in the published history of the war

Part I: Cyclic Poly-Ynes. Part II: Addition of Dinitrogen Tetroxide to Unsaturated Acids

This thesis is in two distinct parts. Part I describes an investigation of the oxidative coupling of ethynyl compounds, and the syntheses of certain cyclic conjugated alpha-diynes. Part II describes the investigation of the addition of dinitrogen tetroxide to long-chain unsaturated acids. Part I is subdivided into three sections. Section I describes the preliminary investigation of the oxidative coupling reaction of ethynyl compounds, and its successful extension to reaction in homogeneous organic medium. Section II describes the use of a high-dilution modification of the conditions to provide the first cyclic poly-ynes, the properties and reactions of which are discussed. Section III discusses the possible syntheses of novel conjugated macrocycles by the oxidative coupling reaction, and describes one such macrocycle, from o-diethynylbenzene, and an investigation of its properties and reactions. Part II describes an investigation of the addition products of the addition of dinitrogen tetroxide to long-chain unsaturated acids, in an attempt to confirm the reported findings, and to investigate the uses of the products

A processing system for Argos meteorological data

Upper Ocean Processes Group meteorological data is transmitted from surface buoys via Argos satellite and processed in an automatic mode on a UNIX workstation. Data is extracted from input files based on instrument type and experiment, processed as appropriate, and plotted, without user intervention. While the processing system normally runs automatically, it is designed so that modules can also be run directly from a terminal when necessary. The Argos processing system allows us to monitor the meteorological data being collected in the field, and provides early information about problems with sensors, instruments, or buoys, when they occur. The automatic process allows more information to be viewed with less effort, and increases the usefulness of the Argos data.Funding was provided by the Office of Naval Research through Grant No. N000I4-94-1-0161

Efficient algorithms for pairing-based cryptosystems

We describe fast new algorithms to implement recent cryptosystems based on the Tate pairing. In particular, our techniques improve pairing evaluation speed by a factor of about 55 compared to previously known methods in characteristic 3, and attain performance comparable to that of RSA in larger characteristics.We also propose faster algorithms for scalar multiplication in characteristic 3 and square root extraction over Fpm, the latter technique being also useful in contexts other than that of pairing-based cryptography

ADCP measurements from the ICESHELF 94 experiment

The ICESHELF 94 Experiment was conducted during April of 1994 from an ice camp in the Lincoln Sea at approximately 84 degrees N, 63 degrees W. An Acoustic Doppler Current Profiler (ADCP) was operated at the camp from 8 to 24 April. This report describes the ADCP configuration and presents the raw data recorded by the ADCP. Processing steps involved in computing horizontal velocities in geographic coordinates from the raw data are described, and time series and spectra of the resulting data are presented. Horizontal velocities with precision of about 1 cm/s were obtained between 27.7 m and 137.0 m depth with 7.8 m resolution. Data were obtained at five minute intervals, but averaged to 1 hr during processing to suppress instrument noise. Spectra show the velocity field to be dominated by variance at semi-siurnal frequency, with a maximum in energy between 50 and 110m depth. Maximum amplitudes of 8 to 10 cm/s were seen near 80 m depth. Velocities from an InterOcean S4 current meter deployed at the same site were compared to those from the ADCP. The largest differences were associated with peaks in the semi-diurnal oscilations, with the S4 underspeeding relative to the ADCP.Funding was provided by the Office of Naval Research through Contract No. N00014-90-J-1359

Pressure, temperature, salinity and dissolved-oxygen profile data from R/V Atlantis II cruise 107 : leg X

This report summarizes in graphical and tabular form the continuous conductivity-temperature-pressure-dissolved-oxygen (CTD02) data collected during the R/V ATLANTIS II Cruise 107, Leg X. These data were collected in the .austral winter of 1980 as part of the International Southern Ocean Studies (ISOS) to evaluate and test various Antarctic Intermediate Water formation and circulation mechanisms.Prepared for the National Science Foundation - Office of International Decade of Ocean Exploration under Grant OCE-78-22223

The Horn, Polkemmet: Experimental Assessment of the Aerodynamic Response Characteristics. G.U. Aero Report 9609

A qualitative assessment of the aerodynamic response characteristics of the Horn, planned for Polkemmet Country Park, West Lothian, is presented. The assessment is based on scale model experiments conducted in the smoke flow visualisation wind tunnel in the Department of Aerospace Engineering, University of Glasgow for a range of flow conditions compatible with the expected wind environment. A number of adverse unsteady aerodynamic phenomena are identified which are highly dependent on wind direction. These include a dominant transient vortex system emanating from the mouth of the Horn, periodic vortex shedding from the neck and support mast, conical vortices generated on the Horn surface, and a general bluff body wake in the lee of the Horn. It is anticipated that the aerodynamic behaviour identified in the model tests persists, at least qualitatively, under full scale conditions. As a result, the potential exists for both aerodynamically induced transient and periodic structural excitation of the Horn. Means of alleviating the adverse aerodynamic characteristics are available. However, any assessment of the effectiveness of such measures requires further experimental investigation