Stark ladders as tunable far-infrared emitters

A superlattice of GaAs/Ga(1 – x)Al(x)As quantum wells forms a Stark ladder under the influence of a perpendicular electric field. A two level incoherent emitter system, formed by radiative intersubband transitions between adjacent wells, is investigated as a tunable far-infrared radiation source. Intersubband transition rates are calculated at 4, 77, and 300 K for applied fields from 0 to 40 kV cm(–1). It is shown that the quantum efficiency of the radiative emission reaches a maximum at low temperatures for a field of 32 kV cm(–1). Under these conditions the emission wavelength is 38 µm with an estimated power output of 1.1 mW. © 1998 American Institute of Physics

Defect chemistry and characterization Hg(1-x)Cd(x)Te

Iodine doped single crystal samples of mercury cadmium telluride were annealed at temperatures varying from 450 C to 600 C in Hg vapor and quenched to room temperature. Hall effect measurements at 77 K on the crystals cooled to room temperature indicate the samples to be n-type after anneals at high Hg pressures whereas they turn p-type after anneals at low Hg pressures; the electron concentration increases with increase in Hg pressure. The results are explained on the basis that the crystals are saturated with (Hg,Cd)I2, with a fraction of the iodine being present as donor occupying tellurium lattice sites and a fraction being present as acceptors resulting from the iodine on tellurium lattice sites pairing with the doubly ionized native acceptor defects. The solubility of the donor species increases with increase in Hg pressure, whereas that of the acceptor species increases with decrease in Hg pressure. Equilibrium constants for the incorporation of the iodine species as well as the pairing reaction were established

Integrated gasifier combined cycle polygeneration system to produce liquid hydrogen

An integrated gasifier combined cycle (IGCC) system which simultaneously produces electricity, process steam, and liquid hydrogen was evaluated and compared to IGCC systems which cogenerate electricity and process steam. A number of IGCC plants, all employing a 15 MWe has turbine and producing from 0 to 20 tons per day of liquid hydrogen and from 0 to 20 MWt of process steam were considered. The annual revenue required to own and operate such plants was estimated to be significantly lower than the potential market value of the products. The results indicate a significant potential economic benefit to configuring IGCC systems to produce a clean fuel in addition to electricity and process steam in relatively small industrial applications

Low-temperture electrostatic silicon-to-silicon seals using sputtered borosilicate glass

Silicon members are hermetically sealed to each other. Process produces no measurable deformation of silicon surfaces and is compatible with package designs of tight tolerance. Seals have been made with glass coatings in 10-mm to 20-mm thickness range without any prior annealing of coated silicon substrates

The development of radiation resistant insulating layers for planar silicon technology, 29 May 1968 - 28 June 1969

Ion implantation method for improving radiation resistance of thermal oxides on silico

Development of single-cell protectors for sealed silver-zinc cells

Three design approaches to cell-level protection were developed, fabricated, and tested. These systems are referred to as the single-cell protector (SCP), multiplexed-cell protector(MCP). To evaluate the systems 18-cell battery packs without cell level control were subjected to cycle life test. A total of five batteries were subjected to simulate synchronous orbit cycling at 40% depth of discharge at 22C. Batteries without cell-level protection failed between 345 and 255 cycles. Cell failure in the cell level protected batteries occurred between 412 and 540. It was determined that the cell-level monitoring and protection is necessary to attain the long cycle life of a AgZn battery. The best method of providing control and protection of the AgZn cells depends on the specific application and capability of the user

Mass spectrometry analysis of contaminants of emerging concern: Nanoparticles, algal toxins, and cyanotoxins in natural waters and their potential health impacts

“The analysis of contaminants of emerging concern is critical to protecting environmental health. In the presented dissertation, two groups of contaminants of emerging concern were assessed using mass spectrometry methods: nanoparticles and algal and cyanotoxins. Analysis of metal oxide nanoparticles in environmental matrices has been a challenging issue, as most traditional methods require complicated sample preparation methods or that can alter or destroy the nanoparticles in the system. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) methods were used to detect metal oxide nanoparticles in surface waters and their removal through drinking water treatment simulations while retaining all information regarding primary particles. Methods were developed to monitor titanium dioxide, cerium dioxide, zinc oxide, citrate-coated silver, and citrated-coated gold nanoparticles directly in surface water and water treated by multiple drinking water treatment methods. Results from these studies indicate that removal depends on the starting water quality, the surface of the nanoparticles, and the type of treatment employed. Cyanotoxins, produced by freshwater cyanobacteria, are a group of contaminants of emerging concern at the freshwater-marine water continuum. Cyanotoxins and several marine algal toxins were analyzed by a direct injection liquid chromatography tandem mass spectrometry (LC/MS/MS) in estuary samples from the contiguous United States. Anatoxin-a, cylindrospermopsin, domoic acid, and microcystins were detected in U.S. estuaries, indicating that cyanotoxins are transported to or produced in estuary systems”--Abstract, page iv

The Influence of Measurement Scale and Uncertainty on Interpretations of River Migration

Environmental scientists increasingly use remotely-sensed images to measure how rivers develop over time and respond to upstream changes in environmental drivers such as land use, urbanization, deforestation and agricultural practices. These measurements are subject to uncertainty that can bias conclusions. The first step towards accurate interpretation of river channel change is properly quantifying and accounting for uncertainty involved in measuring changes in river morphology. In Chapter 2 we develop a comprehensive framework for quantifying uncertainty in measurements of river change derived from aerial images. The framework builds upon previous uncertainty research by describing best practices and context-specific strategies, comparing each approach and outlining how to best handle measurements that fall below the minimum level of detection. We use this framework in subsequent chapters to reduce the impact of erroneous measurements. Chapter 3 evaluates how the time interval between aerial images influences the rates at which river channels appear to laterally migrate across their floodplains. Multiple lines of evidence indicate that river migration measurements obtained over longer time intervals (20+ years) will underestimate the ‘true’ rate because the river channel is more likely to have reversed the direction of migration, which erases part of the record of gross erosion as seen from aerial images. If the images don’t capture channel reversals and periodic episodes of fast erosion, the river appears to have migrated a shorter distance (which corresponds to a slower rate) than reality. Obtaining multiple measurements over shorter time intervals (\u3c 5 years) and limiting direct comparisons to similar time intervals can reduce bias when inferring how river migration rates may have changed over time. Chapter 4 explores the physical processes governing the relationship between river curvature and the rate of river migration along a series of meander bends. We used fine-scale empirical measurements and geospatial analyses to confirm theory and models indicating that migration and curvature exhibit a monotonic relationship. The results will improve models seeking to emulate river meander migration patterns

A study of references cited in senior high school economics textbooks

Thesis (M.A.)--Boston University, 1948. This item was digitized by the Internet Archive