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SUMMARYIn recent years, there has been a considerable expansion of deployments of portable seismic stations across Australia, which have been analysed by receiver function or autocorrelation methods to extract estimates of Moho depth. An ongoing program of full-crustal reflection profiles has now provided more than 25 000 km of reflection transects that have been interpreted for Moho structure. The Moho data set is further augmented by extensive marine reflection results. These new data sources have been combined with earlier refraction and receiver function results to provide full continental coverage, though some desert areas remain with limited sampling. The dense sampling of the Moho indicates the presence of rapid changes in Moho depth, and so, the Moho surface has been constructed using an approach that allows different weighting and spatial influence depending on the nature of the estimate. The inclusion of Moho results from continental-wide gravity inversion with low weighting helps to resolve the continent-ocean transition and to provide additional control in the least sampled zones. The refined distribution indicates the presence of widespread smaller-scale variations in Moho structure. Strong lateral contrasts in crustal thickness remain, but some have become more subdued with improved sampling of critical areas. The main differences from earlier results lie in previously poorly sampled regions around the Lake Eyre Basin, where additional passive seismic results indicate somewhat thicker crust though still with a strong contrast in crustal thickness to the cratonic zone to the west.

UV light, more specifically UV-C light at a wavelength of 254 nm, is often used to disinfect surfaces, air, and liquids. In early 2020, at the cusp of the COVID-19 pandemic, UV light was identified as an efficient means of eliminating coronaviruses; however, the variability in published sensitivity data is evidence of the need for experimental rigor to accurately quantify the effectiveness of this technique. In the current study, reliable and reproducible UV techniques have been adopted, including accurate measurement of light intensity, consideration of fluid UV absorbance, and confirmation of uniform dose delivery, including dose verification using an established biological target (T1UV bacteriophage) and a resistant recombinant virus (baculovirus). The experimental results establish the UV sensitivity of SARS-CoV-2, HCoV-229E, HCoV-OC43, and mouse hepatitis virus (MHV) and highlight the potential for surrogate viruses for disinfection studies. All four coronaviruses were found to be easily inactivated by 254 nm irradiation, with UV sensitivities of 1.7, 1.8, 1.7, and 1.2 mJ/cm2/log10 reduction for SARS-CoV-2, HCoV-229E, HCoV-OC43, and MHV, respectively. Similar UV sensitivities for these species demonstrate the capacity for HCoV-OC43, HCoV-229E, and MHV to be considered surrogates for SARS-CoV-2 in UV-inactivation studies, greatly reducing hazards and simplifying procedures for future experimental studies. IMPORTANCE Disinfection of SARS-CoV-2 is of particular importance due to the global COVID-19 pandemic. UV-C irradiation is a compelling disinfection technique because it can be applied to surfaces, air, and water and is commonly used in drinking water and wastewater treatment facilities. UV inactivation depends on the dose received by an organism, regardless of the intensity of the light source or the optical properties of the medium in which it is suspended. The 254 nm irradiation sensitivity was accurately determined using benchmark methodology and a collimated beam apparatus for four coronaviruses (SARS-CoV-2, HCoV-229E, HCoV-OC43, and MHV), a surrogate indicator organism (T1UV), and a resistant recombinant virus (baculovirus vector). Considering the light distribution across the sample surface, the attenuation of light intensity with fluid depth, the optical absorbance of the fluid, and the sample uniformity due to mixing enable accurate measurement of the fundamental inactivation kinetics and UV sensitivity.

Zusammenfassung Gegenstand und Ziel: Gegenstand der vorliegenden Studie war die Frage, ob sich die Akute-Phase-Proteine Serum-Amyloid A, Haptoglobin und Fibrinogen nicht nur für die Entzündungsdiagnostik eignen, sondern auch eine Aussage über das Ausmaß einer Entzündung und den postoperativen Heilungsverlauf zulassen. Material und Methoden: Es wurden zwei Gruppen von Hengsten verglichen, die alle einer bedeckten Kastration in Allgemeinanästhesie unterzogen wurden. Pferde in Gruppe 1 (n = 13, mittleres Alter drei Jahre) zeigten postoperativ keine bis geringgradige Wundheilungsstörungen. Dagegen traten bei Pferden der Gruppe 2 (n = 12, durchschnittliches Alter zwei Jahre) mittel- bis hochgradige Wundheilungsstörungen auf (geschwollener, vermehrt warmer Wundbereich, Exsudation, teilweise eitrig, Schmerzhaftigkeit, Lahmheit). Die Probanden wurden unmittelbar vor und sechs, 12, 24, 48 und 72 Stunden sowie sieben Tage nach der Operation untersucht. Ergebnisse: Die Körperinnentemperatur differierte ebenso wie die Gesamtleukozytenzahl zwischen den Gruppen deutlich. Die Konzentration von Serum-Amyloid A stieg bei allen Pferden innerhalb von 24 Stunden nach der Kastration signifikant an. Alle Probanden wiesen 48 Stunden nach dem Eingriff einen Anstieg der Fibrinogenkonzentration im Plasma auf. Die Haptoglobinmessung ergab eine Erhöhung im Plasma innerhalb von 48 Stunden in Gruppe 1 und innerhalb von 72 Stunden in Gruppe 2. Schlussfolgerung: Sowohl die Verlaufskontrolle der klinischen Parameter als auch der ausgewählten Akute- Phase-Proteine zeigte als Reaktion auf die Operation und eine nachfolgende Entzündung deutlich ansteigende Werte. Klinische Relevanz: Während bei der Kastration die Bestimmung der klinischen Parameter ausreichend erscheint, bietet sich eine kombinierte Messung von Serum-Amyloid A und Haptoglobin oder Fibrinogen zur Einstufung von unbekannten Entzündungsherden und -symptomen an.

This paper addresses the packaging, power, and cooling of the IBM eServerTM BladeCenter® compact server infrastructure consisting of 14 servers in a 7U (1U = 44.45 mm) vertical space for installation in an industry-standard rack. A typical rack is 42U tall. Therefore, six BladeCenter systems will fit in a rack, for a total of 84 servers. The density of a BladeCenter system (servers/ U) is double that of previous 1U rack-optimized servers. To build such a dense server system required overcoming a multitude of challenges in packaging, power, and cooling design. Our approach to these challenges is described, but in the broader context of not only increasing the density, but setting a new server standard for a highly available redundant infrastructure with integrated systems management and network switching that uses less power and is simple to maintain on site or remotely, even by nonspecialized personnel. Server processors, memory, storage, and input/output devices were combined in a single compact server unit called a processor blade, while the support infrastructure, such as systems management, network connectivity, optical media, power, and cooling, was consolidated in a single structure and shared among many servers. The result is a package architecture that lends itself well to standardization. Custom server blades and input/output devices may be designed in accordance with BladeCenter base specifications and be effectively integrated into the blade server system.

One-year old, bare-root, loblolly pine (Pinus taeda L.) seedlings grown in an early successional plant community, were exposed to four ozone treatments, 12 h day(-1) (09:00-21:59 h CST), 7 day week(-1) in east-central Alabama for 2 years (1994-1995). Treatments included AA=ambient air (open plot; no chamber), CF = carbon-filtered air (approximately 0.5xAA), 1X = non-filtered air, and 2X = twice ambient (AA) air. Pine height and diameter were measured monthly for 2 years and total above-ground biomass determined at termination of the experiment. In addition, height, diameter and volume (d2h) growth was modeled for the 2-year study. Trees growing in the CF chambers exhibited the least growth for any variable measured. The predicted height growth rate (r) was the least for the CF- and 2X-treated pines when compared with the AA and 1X treatments. In addition, percent total vegetative cover was significantly negatively correlated with height. diameter and volume growth in 1994, but not 1995. Our findings regarding the trees growing in the CF treatments, are contrary to previous reports regarding ozone impacts to loblolly pine grown without competition from other vegetation.

A dense phase of GaAs wires forms a corrugated surface in the early stages of strained growth on GaP, assembling from elongated Stranski–Krastanow islands. For a series of samples, the evolution of shape and whisker periodicity has been followed as a function of deposition time. This has been done with the help of atomic-force microscopy together with autocorrelation measurements. Transmission electron microscopy measurements support the results. The lateral wire period and long shapes are not predicted by published models, though we conclude that the island orientation is picked out by facet energy inequivalencies.

We have investigated individual InAs quantum dots embedded in GaAs using photoluminescence spectroscopy as a function of temperature and excitation power density. We also present $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ calculations including both direct and exchange interactions for systems with up to three excitons in the dot. From these calculations we are able to assign some of the many peaks observed to various few-particle states. A rate-equation model has also been developed which allows simulations of the peak intensities with excitation power density to be made and compared with experiment.

This study compared simulated values of surface runoff and erosion from two current erosion prediction technologies (WEPP and GLEAMS) to observed data for two grazing pressures on three pasture vegetation types (switchgrass, bermudagrass, and tall fescue) in the Tennessee Valley region of Alabama. Based on the results of statistical analysis for each forage type and grazing pressure, GLEAMS performed better than WEPP, although either model did not predict sediment loss within an acceptable level. Because it was determined that grazing pressure had no significant impact on runoff and erosion from the experiment plots, the data for each forage were pooled over the same grazing pressure and the correlation between observed and simulated data were analyzed. This analysis showed that overall, predicted runoff values for both WEPP and GLEAMS had linear relationship to observed data. When sediment loss was analyzed, GLEAMS predicted value showed significant correlation with observed data, while WEPP pre...

Many researchers have reported on individual plant responses to O{sub 3}, but few have investigated the effects of this pollutant on ecosystem function. This investigation examined the influence of O{sub 3} on short-term (Phase 1) litter decomposition of blackberry (Rubus cuneifolus Pursh.) and broomsedge bluestem (Andropogon virginicus L.), two plant species native to early successional forest communities in the southern US. Mixed blackberry/broomsedge litter (1:1) collected from plants exposed to different levels of O{sub 3} for one growing season was placed in open-top chambers and exposed to different O{sub 3} levels of treatments for 24 weeks. Litter also was incubated in microcosms in the laboratory t 25 or 30 C to determine the effects of climate change on O{sub 3}-treated litter. Initial C and N concentrations of the collected foliage did not differ significantly among treatments for either species. Blackberry litter had approximately twice as much N as broomsedge, and when collected from 2X O{sub 3} chambers, had significantly greater permanganate lignin than the other treatments. Initial permanganate lignin concentration of blackberry, over all O{sub 3} treatments, correlated significantly with remaining mass of the litter mixture after 24 wk exposure. Litter decomposed more slowly in the 2X chambers than inmore » the other treatment chambers, regardless of litter source. Elevated O{sub 3}-exposed litter (2X) decomposed the slowest regardless of treatment applied. There were significant temperature and time effects observed with litter decomposition: litter incubated at 30 C decomposed faster than at 25 C. The data suggest O{sub 3} may influence substrate quality and microbial activity, thus reducing the rate of litter decomposition in early successional forest communities.« less

The evolution of the initial GaAs islands that form on flat (0 0 1) GaP during chemical beam epitaxy has been studied for layer thicknesses below 10 GaAs monolayers. Reflection high-energy electron diffraction and atomic force microscopy were used to characterize island formation in reciprocal and direct space, respectively. Both methods clearly show the anisotropic growth behavior, beginning with growth of isolated elongated islands which at thicker deposition evolve into a corrugated surface of densely packed GaAs quantum wires. Intensity-versus-time measurements were made for island-related diffraction features which allowed distinctions to be made between the different morphological growth regimes.

An understanding of the basic mechanisms responsible for the pathogenesis of liver neoplasms is needed in order to develop better therapeutic strategies. The present study utilized a pharmacogenetic mouse model to assess the role of cytochrome P4501A1 (Cyp1a1) in modulating genetic damage to oncogenic and tumor suppressor loci following in utero exposure to the polycyclic aromatic hydrocarbon, 3-methylcholanthrene (MC). Analysis of the Ha-ras, Kiras, INK4a and p53 genes was carried out with lysates from paraffin-embedded liver tissue from transplacentallytreated mice. The lysates were subjected to DNA amplification by the PCR technique followed by allele-specific oligonucleotide hybridization screening and SSCP analysis. All of the 26 neoplasms screened (23 hepatocellular carcinomas, two hepatocellular adenomas and one sarcoma) exhibited a GGC→CGC (GLY 13 →ARG 13 ) transversion at the Ki-ras gene locus. None of the tumors had Ki-ras mutations at codon 12 of exon 1. Approximately 12% (3/ 26) of the liver tumors exhibited point mutations in exon 1o f theINK4a gene, with each of the three tumors exhibiting two point mutations. Analysis of exon 2 of the INK4a gene showed the presence of a CCG→CTG (PRO 73 →LEU 73 ) transition in two of the 26 neoplasms. No mutations were found in exons 1 or 2 of the Ha-ras gene, or in exons 5‐8 of the p53 gene. Analysis of tumor RNAs showed overexpression of Ha-ras, cip1 and c-jun in ~38% of the liver tumor samples. The results of this study suggest that mutagenic damage to oncogenes and tumor suppressor genes may be critical factors in mediating transplacentallyinduced liver tumorigenesis. The fact that Ki-ras mutations were found in all of the tumors suggests that mutation at this gene locus may be an early event in liver tumor pathogenesis, while mutation in tumor suppressor genes may occur later during tumor progression. These combined results are consistent with the pathogenesis of cancer in humans. *Abbreviations: ASO, allele-specific oligonucleotide hybridization; cdk, cyclin-dependent kinase; Cyp1a1, cytochrome P4501A1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; MC, 3-methylcholanthrene; PAH, polycyclic aromatic hydrocarbon; PCR, polymerase chain reaction; Rb, retinoblastoma; SSCP, single strand conformation polymorphism; SDS, sodium dodecylsulfate; 13 SSC, 0.15 M NaCl/0.015 M sodium citrate (pH 7.0); BPB, bromophenol blue; 13 TBE, 100 mM Tris‐HCL/90 mM boric acid/ 1 mM EDTA.

We studied the formation of InAs islands in holes defined by electron-beam lithography on GaAs substrates. The islands grew selectively in the holes, with one to nine islands per hole. The number of islands depends simply on the hole diameter, filling the holes at a constant effective two-dimensional density. We define the ratio of this effective density to the density on an unpatterned control sample to be the selectivity ratio, and we find a selectivity ratio of greater than 1000 for the present samples. We estimated the lateral conduction-band coupling for closely spaced islands and conclude them to be plausible candidates for weakly coupled device building blocks.

We have studied the balance between growth and desorption at a (001) GaAs surface in a chemical beam epitaxy chamber using reflection high energy electron diffraction. We found the growth rate to be proportional to the flux of our precursors tertiarybutylarsine and triethylgallium (TEG). The growth rates and desorption rates were found to be nearly constant in large temperature regions. The surface cracking of TEG limited the growth rate for low temperatures, and the desorption of Ga and As limited the high temperature growth rates. For high temperatures we show that through the application of the law of mass action the heat of evaporation for Ga can be determined to be 4.2±0.2 eV. This is very close to the values measured in molecular beam epitaxy. We thus conclude that the high temperature behavior is not determined by precursor desorption or chemistry and that the hydrogen and other chemical reaction products do not appreciably alter the GaAs phase diagram at chemical beam epitaxy growth conditions.

An early successional plant community was exposed to various ozone concentrations for two growing seasons (1994–1995) in open-top chambers in Auburn, Alabama, USA. The ozone treatments were: AA, ambient air (open plots); CF, carbon-filtered air (c. 0·5×ambient air), 1×, non-filtered air, and 2×, twice ambient air. Vegetative canopy cover exhibited a pattern of accumulation in the spring, with maximum canopy cover attained in summer, then senescence of foliage in the autumn 1994. This pattern was not observed in 1995 as a result of a drought during the spring and summer. Varying ozone exposures caused shifts in the competitive interactions between plants, thereby altering community structure. Higher canopy cover, vertical canopy density (layers of foliage), species richness, diversity, and evenness existed in the CF treatments than in the other treatments. In addition, winged sumac (Rhus copallina L.) became a major component of the CF treatments only during 1995. Surprisingly, blackberry (Rubus cuneifolius Pursh.), a species considered ozone-sensitive, based on visible injury, dominated canopy cover within the 2× treatments, 41 and 33% of total canopy cover in 1994 and 1995, respectively. From these results it is concluded that plant communities existing in areas where lower ozone concentrations are prevalent might be more complex and diverse than those existing in areas with higher ozone concentrations.

The bulk dielectric function, the surface reflectance anisotropy, and the surface dielectric anisotropy of InP(001) were determined from room temperature up to 875 K. Measurements were performed in-situ on as-grown samples in both a metal-organic vapour phase epitaxy and a chemical beam epitaxy (CBE) system using a rotating analyser type ellipsometer (SE) and a reflectance anisotropy spectrometer (RAS). The temperature dependence of the bulk critical points was deduced by performing a direct line shape analysis of the SE spectra. A high-temperature bulk dielectric function database for optical in-situ studies was established by applying a combined cubic spline/harmonic oscillator interpolation scheme to the measured data. Three InP(001) surface reconstructions were found by reflection high-energy electron diffraction (RHEED) measurements in the CBE system: (2 x 1) and c(4 x 4) under phosphorus-rich conditions and a (2 x 4) reconstruction under reduced phosphorus supply. Characteristic RAS spectra are assigned to these reconstructions. The temperature shift of the main features of the surface dielectric anisotropy spectra are compared to those of the bulk critical points.

We demonstrate the manipulation of InAs island size through growth on patterned GaAs substrates. Using chemical beam epitaxy, we deposited islands on patterns consisting of concentric circular trenches. One sample was left uncapped for atomic force microscopy, and another was capped with GaAs for micro-photoluminescence. Luminescence images taken at particular energies show that at different orientations along the circular arcs, the islands have different luminescence energies and thus different sizes. In correlating the island distributions found by atomic force microscopy images with the luminescence, we conclude that the InAs islands that form in high-density one-dimensional chains are smaller than those that are not in chains.

With chemical beam epitaxy we stacked small InAs islands, separated by thin GaAs layers. Reflection electron diffraction during growth showed that after a seed‐layer growth, subsequent depositions require less InAs to form the islands. At 5 K the stacks have narrower luminescence peaks at lower energies than single island layers, and the stacks luminesce at room temperature. For 4‐nm‐high pyramidal islands with 20‐nm‐wide bases, we observed vertical periods down to 5.4 nm, small enough to couple quantum mechanically. The electronic structures possible for this class of objects should be sufficient for designing and observing room temperature quantum mechanical phenomena.

Strained, coherent InAs islands were grown in the Stranski-Krastanov growth mode on patterned GaAs by chemical beam epitaxy. The present work represents initial steps in quantitatively understanding the placement and growth of islands in patterns. The trade-offs between regular pattern features and better island nucleation are demonstrated by a deposition on a pattern of concentric circles. InAs mass transport is also measured, where material is seen to move on the order of a micron to and from different local orientations. An important practical result is that the pattern definition for island alignment need not be finer than 0.25 μm, within the reach of present-day optical lithography.

We have begun to compile a list of the surface reconstructions for (001) InAs, GaAs and InP. The symmetries that we have observed include 1 × 1, 2 × 1, 2 × 4, 4 × 6, 3 × 4, 4 × 3, 2 × 3, 3 × 3, 1 × 3, 3 × 1, 4 × 2, 4 × 1 and 8 × 2. These reconstructions were observed during various growth and non-growth conditions in order to make up phase diagrams that depend on the group V and III fluxes and the temperature. Some of the phase boundaries can serve as temperature reference points in our epitaxy machine. A comparison of the different semiconductor surfaces is made and the growth properties of these surfaces are discussed.

Digestion-resistant tissues found in C 4 grasses may allow soluble protein to escape rumen degradation. The objective of this study was to use immunofluorescent localization to follow loss of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCase) from switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman) parenchyma bundle sheath cells (BSC) during rumen degradation. Fluorescent signal was observed from switchgrass and big bluestem BSC through 24 and 16 h in situ digestion, respectively, and from BSC associated with both intact tissue fragments, and isolated vascular bundles in omasal digesta and focal material from steers (Bos tarus L.) grazing switchgrass. Immunofluorescent localization demonstrated that in certain C 4 grasses (i) parenchyma BSC can protect RuBPCase from degradation through 24-h in situ incubation, (ii) BSC containing RuBPCase can exit the rumen prior to degradation, and (iii) protein protected by BSC can escape degradation in the whole gastrointestinal tract and be excreted.

We report on coherently strained InAs quantum-dots grown by chemical beam epitaxy on GaAs. The morphological phase transition of the InAs layer from two-dimensional to three-dimensional was characterized with reflection high-energy electron diffraction. The transition is found to be quasi-equilibrium in the slow deposition regime studied, to be approximately linear in InAs thickness, and to be suppressed both by higher temperature and As pressure. Patterned substrates were used to assemble the dots in specific locations. Conditions were found to align dots in chains of several-μm length, to place small numbers of dots in holes, and to grow dots only within patterns but not on adjoining flat surfaces. When capped with GaAs, the islands are optically active.

We report characterization and modeling of serpentine superlattice nanowire-array lasers. These samples were grown by molecular beam epitaxy on (100) n/sup +/-GaAs vicinal substrates. In-plane ridge-waveguide lasers with ridge stripes either parallel or perpendicular to the nanowire arrays have been characterized at low temperatures. The measured net gain spectra at 1.4 K showed strong optical gain anisotropy such that the TM mode gain became greater than the TE mode gain when the optical cavity was placed along the nanowire direction. This provides strong evidence that the lateral quantum confinement in the serpentine superlattice is stronger than the vertical quantum confinement. Optical gain spectra in the serpentine superlattice are calculated with consideration of coupling between wires and homogeneous line broadening. A good fit to the measured polarization-dependent gain spectra is achieved when the lateral Al segregation and the homogeneous line broadening are chosen to be 8% and 7 meV, respectively. This small but finite Al segregation in the serpentine superlattice provides lateral quantum confinement for holes, which results in significant anisotropy in the relation between net gain and injection current density,. >

We have measured photoluminescence excitation (PLE) spectra and radiative lifetimes as functions of temperature for serpentine superlattice quantum-wire arrays. The (Al, Ga)As arrays have lateral periods near 10 nm, and lateral confining potentials of 120 meV in the conduction band. At low temperature the excitons are strongly localized within potential fluctuations along the wires. The radiative lifetime of these localized states is 340 ps at 2 K. The degree of exciton localization decreases with increasing temperature, from which we estimate the strongly-localizing potential fluctuations to be approximately 10 meV deep. Above 80 K the excitons have sufficient thermal energy for motion along the wires. The radiative lifetimes increase with temperature, to 20 ns for free carriers at 325 K. The lateral potential barriers inhibit diffusion to non-radiative recombination sites.

NASA’s extra-vehicular activities (EVAs) involve exposure to high energy photons while breathing 100% oxygen. Using previously verified mouse models, our laboratory is studying whether low dose irradiation under these hyperoxic conditions could lead to an increase in carcinogenic potential. To simulate the environment astronauts encounter during an EVA, enclosed chambers were constructed that allowed for mouse movement, controlled gas conditions, and uniform radiation dose delivery. Custom-built gas chambers with input/output gas valves and dividers that allowed for uniform gas flow were used to keep 6 unanesthetized mice separated while they were irradiated. The chambers were supplied with 100% oxygen or air using ball valves linked together with T-splitters. A calibrated ion chamber was used to verify the radiation dose distribution across an entire chamber. Mice were placed in the gas environments for 0.5 h, irradiated with a 10 or 18 MV photon beam from a medical linear accelerator, and left in their gas environment for 2 h post-irradiation. We irradiated 200 mice (5 different doses between 0–1000 mGy) under normoxic or 100% oxygen conditions. For the next step of this research, these mice will be euthanized 9 months post-irradiation, and lung tumors will be counted and sized to determine if hyperoxia increases the carcinogenic effect for this model.

We report on aerosol particles formed by bubbling a carrier gas through bubblers in metalorganic vapor phase epitaxy (MOVPE). A triethylgallium bubbler was investigated in a MOVPE set-up regarding the generation of aerosol. We measured particle number concentrations with an ultrafine condensation particle counter, which can detect submicrometer aerosol particles larger than 3 nm in diameter. We found that a standard triethylgallium bubbler used in a conventional way produces aerosol particles. The number of particles is a function of the carrier gas flow through the bubbler and correlates with the number of bubbles. The aerosol size distributions were analyzed with a differential mobility particle sizer and found to range from 10 to 600 nm, with maxima between 150 and 200 nm. Size distribution as well as total number of aerosol particles depend on evaporation processes during transport in undersaturated gas flows. While the number of particles reaching the reactor is not negligible, the precursor is predominantly transported as gas molecules. Particles can in principle, though, reach the substrate and create defects on the surface.

InGaAs quantum wells (QWs) were grown in a chemical beam epitaxy (CBE) machine with trimethylindium (TMI), triethylgallium (TEG) and tertiarybutylarsine (TBA) as precursors. Growth was monitored in-situ by reflectance difference (RD) and reflection high energy electron diffraction (RHEED), on both flat and vicinal (2° off in the 〈111〉 A direction) (001)GaAs substrates. The RD was monitored at 632.8 nm. At this wavelength the RD signal from a GaAs surface is primarily related to the absorption by Ga dimers. When InGaAs had been grown, both the average RD signal and the amplitude of the RD oscillations for the subsequent growth of GaAs increased significantly, compared to GaAs growth on GaAs. This In influence was found to persist even after the growth of 20–30 ML of pure GaAs. As a result we were able to monitor growth oscillations with RD and RHEED simultaneously during growth of quantum wells of InGaAs in GaAs. As a conclusion to these observations we suggest that the group III dimer bond concentration, detected in the RD signal, increases.

An experimental technique to measure simultaneously the thermal diffusivity and thermal conductivity of small specimens of thermal‐insulator materials is described. Experimental conditions are developed which approach the mathematical idealization of a one‐dimensional, infinite, two‐component, composite solid whose planar interface is subjected to a step‐function heat flux. The heat flux is generated by resistive heating of a thin metallic foil. Although this principle has been exploited previously, the present technique permits specimens with volumes two orders of magnitude smaller than prior work based on the same idealization. A number of difficulties related to small specimen volume are identified and overcome. Another improvement over past efforts is the use of the nonlinear least‐squares analysis to determine the optimum values for diffusivity and conductivity. A comparison of measurements of these properties for acrylic and Pyrex glass with literature values suggests that the technique affords accuracies of about 5% for materials in this range.

Serpentine superlattices with a built-in quantum-wire array have been grown on vicinal (100) GaAs substrates by molecular-beam epitaxy. The quantum wires have parabolic cross sections with confinement dimensions on the order of 100 \AA{}. The goal of this paper is to make a comprehensive optical study of two different serpentine-superlattice samples. The serpentine structures have been characterized by low-temperature cathodoluminescence, photoluminescence, and photoluminescence-excitation measurements. In photoluminescence, a rather sharp peak (typically 7 meV full width at half maximum) is attributed to excitonic recombination in the built-in quantum-wire array. The linear polarization dependence of the serpentine-superlattice emission has been measured with a photoelastic modulation technique, showing a pronounced polarization anisotropy in both photoluminescence and photoluminescence excitation. The serpentine-superlattice photoluminescence emission normal to the vicinal surface shows a linear polarization along the wires of up to about 30% due to the lateral confinement. The carrier confinement has been further characterized by measuring the linear polarization dependence of the photoluminescence normal to the cleaved edges. The measured polarization anisotropy has been compared with the calculated polarization dependence as a function of intermixing between the lateral barriers and wells. It is found that there is a substantial intermixing between the barriers and wells, with at least 30% of the Al intended for the barrier ending up in the well.This results in hole states confined to one dimension, while the electron states are two dimensional due to coupling through the lateral barriers. Linearly polarized photoluminescence excitation has been used to reveal the laterally induced heavy-hole--light-hole splitting. Photoluminescence decay-time measurements of the serpentine-superlattice emission (390 ps) show a longer radiative decay time at low temperature than for a reference alloy-well structure (260 ps), indicating a reduced recombination rate in the serpentine structure. The linear polarization of the photoluminescence is found to be rather constant over large areas of the wafer even though the growth rate varies by a few percent. This indicates that uniform quantum-wire-like states are formed and demonstrates the intended advantage of the serpentine superlattice, which avoids the tilt sensitivity of the tilted superlattice.

We report low-temperature studies of microwave-induced cyclotron resonance of photo-generated carriers in (A1,Ga)As serpentine superlattice quantum-wire arrays. The geometric size of the parabolic-crescent cross-section of the quantum wires was of the order of 100 A x 50 A, depending on the angle of the vicinal substrate and the amount of parabolic curvature. Comparing the obtained spectra, we estimate the relative degree of carrier confinement in the ordered AlGaAs structure.

(Al,Ga)As serpentine superlattices (SSLs) with a built-in quantum wire array have been grown on vicinal GaAs substrates by molecular beam epitaxy. The geometric size of the parabolic-crescent cross section of the quantum wires is on the order of 160 A × 50 A, depending on the angle of the vicinal substrate and the amount of parabolic curvature. The low-temperature magneto-luminescence properties of these quantum wire arrays have been studied in magnetic fields up to 13 T. The diamagnetic shift from the serpentine structure was found to be smaller than from a reference alloy-well sample, indicating an increased binding energy of the exciton due to the lateral confinement in the serpentine structure. A diamagnetic shift anisotropy is observed when the magnetic field is applied in the three principal perpendicular directions of the wire. In particular we see a difference when the magnetic field is applied parallel to the the wire and perpendicular to the wire, in qualitative agreement with theoretical calculations. This is a direct observation of the one-dimensional properties of the excitonic wave function. The linewidth is found to increase with the applied magnetic field, with the amount of the increase critically dependent on the direction of the magnetic field. This is explained by the way the exciton volume is probing the potential variations in the ordered SSL structure.

The detailed optical design of the Solar Maximum Mission-Ultraviolet Spectrometer and Polarimeter is discussed in conjunction with the scientific objectives that led to the design. The instrument consists of a 1.8-m effective focal length aplanatic Gregorian telescope followed by a 1-m Ebert spectrometer. The design of the Stokes polarimeter is also discussed.

Polarization modulation is used to investigate the polarization dependencies in the low‐temperature photoluminescence (PL) and the photoluminescence excitation (PLE) of GaAs/AlGaAs quantum wire arrays. The modulation technique employing a photoelastic modulator is described and its implementation in the experimental setup of the PL and PLE experiments is presented. In the PL experiment the technique is used to analyze the emitted light with respect to its polarization, whereas for the PLE experiment the polarization of the exciting light is modulated, probing the polarization dependence of the absorption of the light. Since the modulation of the light is restricted to the polarization, the polarization dependence can be measured simultaneously with the PL or PLE intensity. The versatility and the sensitivity of the technique is exemplified by presenting results of polarized PL and PLE obtained on quantum wire samples grown on the vicinal (100) surface of GaAs by molecular‐beam epitaxy that show a considerable anisotropy in the linear polarization for both the PL and PLE.Polarization modulation is used to investigate the polarization dependencies in the low‐temperature photoluminescence (PL) and the photoluminescence excitation (PLE) of GaAs/AlGaAs quantum wire arrays. The modulation technique employing a photoelastic modulator is described and its implementation in the experimental setup of the PL and PLE experiments is presented. In the PL experiment the technique is used to analyze the emitted light with respect to its polarization, whereas for the PLE experiment the polarization of the exciting light is modulated, probing the polarization dependence of the absorption of the light. Since the modulation of the light is restricted to the polarization, the polarization dependence can be measured simultaneously with the PL or PLE intensity. The versatility and the sensitivity of the technique is exemplified by presenting results of polarized PL and PLE obtained on quantum wire samples grown on the vicinal (100) surface of GaAs by molecular‐beam epitaxy that show a consider...

Quantized conductance is observed in a split gate structure at temperatures up to 30K and with bias voltages of up to 12mV. This work addresses the limited temperature range and signal levels of ballistic constrictions by a comprehensive design strategy employing two dimensional self consistent Poisson-Schrodinger simulations to design a structure giving large energy subband separations. The large signal level of 700nA, made possible by a 10meV separation, allows measurements to be made without a lock-in amplifier.

A prototype, direct nozzle injection (DNI) spray boom was designed, constructed, and tested. The DNI design developed for this study consisted of 10 spray nozzles on a conventional boom, with simulated chemical injected immediately upstream of each nozzle through small metering orifices. A variable differential pressure across the metering orifices was used to establish varying spray nozzle discharge concentrations. The uniformity of the resulting spray was evaluated on a nozzle-to-nozzle basis (to gauge overall boom performance) and across an individual nozzle’s spray pattern (to gauge mixing characteristics).

A cursory study of error quantification was conducted to develop a general error term to be applied to the performance of chemical applicators. The term developed is capable of taking into consideration the time delays associated with direct boom injection applicators. The term was then applied to the cases of diluted mix and direct boom injection applicators for the case of a sinusoidally varying ground speed to compare error on a nozzle-by-nozzle basis. The magnitudes and temporal occurrence of errors associated with boom injection sprayers typically depends on the lateral location of a given nozzle. Errors associated with tank-mix sprayers are a function of ground speed only if no mixing errors occur.

Sputter deposited FeRhN films with unique microstructural characteristics are presented. They consist of fine α-Fe and γ-Fe4N grains with slightly expanded lattice parameters, which result in soft magnetic properties of the film. The significant amount of face-centered-cubic Fe4N phase gives rise to higher resistivity and therefore improved high frequency permeability than conventional FeRhN films.

A unique optical design consisting of a compound parabolic concentrator and an elliptical concentrator joined at their throats is discussed. The optic has a number of advantages over conventional infrared telescopes for applications in interferometry and photometry. Ray-tracing results are presented.

The effect of magnetic layer deposition rate on longitudinal media’s magnetic, crystalline, and recording properties was studied. Slower deposition rates were found to produce a systematic reduction in media transition noise. X‐ray diffraction and torque magnetometer data indicated that as the deposition rate was slowed, the out‐of‐plane anisotropy component of the media increased. Slower deposition rates were also found to increase media saturation magnetization. Increased media signal‐to‐noise ratios were observed when higher process temperatures were used in conjunction with slower rates. These results are discussed in terms of recent theories which have linked phase segregation and out‐of‐plane crystalline anisotropy with media magnetic and recording properties.

The vicinal surface ordering required for the TSL deposition has been studied as a function of temperature and composition for Ga x Al 1−x As, GaSb and AlSb surfaces. The interface sharpness observed during the Al-Ga co-deposition and self-organization on a vicinal surface has been modeled using a stochastic kinetics method. The modeling reproduces well the observations. To avoid critical effects of the tilt parameter variations, a novel structure, the serpentine superlattice, has been proposed. This structure has a “build in” two-dimensional confinement and yields uniform luminescence properties over large wafer areas. Finally, the TSL concept has been demonstrated for a novel system, the GaSb-AlSb system.

We present an epitaxial growth technique for vicinal substrates which avoids the geometric tilt sensitivity inherent to the cyclic growth of such structures as tilted superlattices. This cyclical deposition and growth technique produces a serpentine superlattice (SSL) (M.S. Miller et al., in: Proc. 20th Intern. Conf. on Physics of Semiconductors, Thessaloniki, August 1990). Purposefully varying the per-cycle growth rate produces a lateral superlattice with a variable, meandering tilt, with 1 D, microscopically confined electronic states formed where the superlattice bends over. The quantum wire electronic confinement is principally determined by the SSL shape near these widest regions, near places with a vertical tangent. This shape is accurately established through the smooth adjustment of the fractional monolayer growth rates. If a large enough range of growth rates is spanned, then a particular confinement structure is guaranteed: With a SSL, quantum wire arrays with particular energy levels may be precisely realized. Not only is this true at a particular place on the substrate, but the growth rate variations across a substrate are automatically accommodated and uniform wires are realized over the entire wafer. Calculations of the two-dimensional subband structure were performed for (Ga,Al)As SSLs to confirm the 1D electronic states, determine optimal structure parameters and explain experimental results. Such (Ga,Al)As SSLs have been prepared by MBE and characterized with photoluminescence. We find emitted light in several samples that is polarized parallel to the direction of the vicinal substrate's steps, which we interpret to be consistent with quasi-1D confinement.

Spin–valve films with the structure Ta/NiFe/FeCo/Cu(18–30 A)/FeCo/FeMn–70 A/Ta were deposited using a Veeco ion beam deposition (IBD) system, model IBD-350. The physical properties of these spin–valve films as a function of primary ion beam energy have been studied in a primary ion beam energy range of 600–1500 eV. Xe was used as the working gas. The optimal ion beam energy range for the best spin-valve performance has been found to be around 600 eV. Giant magnetoresistance (GMR) values of ΔR/R∼8% have been measured for the spin–valve films deposited in this energy range. A strong dependence on beam energy of magnetic properties for these spin–valve films has been observed in the energy range from 600 to 1500 eV. ΔR/R for spin–valve films with a Cu layer thickness of 22 A decreases from 7.5% at 600 eV monotonically to 6.1% at 1500 eV with increasing ion beam energy. Interlayer coupling field increases from 20 Oe at 600 eV to 37 Oe at 1500 eV. Further reduction in the interlayer coupling field to 13 Oe and...

The CoZrCr alloy has been developed for high speed write heads. This sputter deposited alloy exhibits soft magnetic properties and high resistivity which is suitable for high data rate write head applications. Resistivity of these sputtered films is about 90 μΩ cm, saturation magnetization is 13.6 kG, anisotropy field (Hk) is 15 Oe in as deposited state, which could be reduced to 5 Oe by annealing. Easy and hard axis coercivities are