A structural and thermal packaging approach for power processing units for 30-cm ion thrusters

Solar Electric Propulsion (SEP) is currently being studied for possible use in a number of near earth and planetary missions. The thruster subsystem for these missions would consist of 30 centimeter ion thrusters with Power Processor Units (PPU) clustered in assemblies of from two to ten units. A preliminary design study of the electronic packaging of the PPU has been completed at Lewis Research Center of NASA. This study evaluates designs meeting the competing requirements of low system weight and overall mission flexibility. These requirements are evaluated regarding structural and thermal design, electrical efficiency, and integration of the electrical circuits into a functional PPU layout

Academic boredom, engagement and the achievement of undergraduate students at university: a review and synthesis of relevant literature

This review and synthesis of relevant literature considers the nature of boredom and boredom proneness in general terms before focusing on how the academic boredom experienced by undergraduates at university is sufficiently different from other known types to warrant a unique and important field of study. Derived from within the literature itself, academic boredom is commonly presented as a largely negative and deactivating achievement-related emotion known to impact usually adversely on student engagement and performance. Tracing traditional as well as contemporary views from psychology, which has tended to dominate the field, findings that remain largely quantitative and highly statistical in nature are exemplified alongside the more exploratory but mixed-methods and educational work recently conducted in the UK. A comparison of the questionnaire-based self-report instruments frequently used in data collection is also included. Rooted within Control-Value Theory, the implications associated with academic boredom are far from trivial, particularly with respect to understanding sites and triggers, how students respond and cope and how the overall quality of the student experience might be improved. Limitations in the work undertaken to date draw attention to opportunities for further educational and interdisciplinary research

Mass study for modular approaches to a solar electric propulsion module

The propulsion module comprises six to eight 30-cm thruster and power processing units, a mercury propellant storage and distribution system, a solar array ranging in power from 18 to 25 kW, and the thermal and structure systems required to support the thrust and power subsystems. Launch and on-orbit configurations are presented for both modular approaches. The propulsion module satisfies the thermal design requirements of a multimission set including: Mercury, Saturn, and Jupiter orbiters, a 1-AU solar observatory, and comet and asteroid rendezvous. A detailed mass breakdown and a mass equation relating the total mass to the number of thrusters and solar array power requirement is given for both approaches

The effect of competition on the control of invading plant pathogens

1. New invading pathogen strains must compete with endemic pathogen strains to emerge and spread. As disease control measures are often non-specific, i.e. they do not distinguish between strains, applying control not only affects the invading pathogen strain but the endemic as well. We hypothesise that the control of the invasive strain could be compromised due to the non-specific nature of the control. 2. A spatially-explicit model, describing the East African cassava mosaic virus-Uganda strain (EACMV-UG) outbreak, is used to evaluate methods of controlling both disease incidence and spread of invading pathogen strains in pathosystems with and without an endemic pathogen strain present. 3. We find that while many newly introduced or intensified control measures (such as resistant cultivars or roguing) decrease the expected incidence, they have the unintended consequence of increasing, or at least not reducing, the speed with which the invasive pathogen spreads geographically. We identify which controls cause this effect and methods in which these controls may be applied to prevent it. 4. We found that the spatial spread of the invading strain is chiefly governed by the incidence at the wave front. Control can therefore be applied, or intensified, once the wave front has passed without increasing the pathogen’s rate of spread. 5. When trade of planting material occurs, it is possible that the planting material is already infected. The only forms of control in this study that reduces the speed of geographic spread, regardless of the presence of an endemic strain, are those that reduce the amount of trade and the distance over which trade takes place. 6. Synthesis and applications. Imposing trade restrictions before the epidemic has reached a given area and increasing other control methods only once the wave front has passed is the most effective way of both slowing down spread and controlling incidence when the presence of an endemic strain is unknow

The biomechanical role of the chondrocranium and sutures in a lizard cranium

The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard Salvator merianae. We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite element model to examine strain magnitude and distribution. We find that strains within the chondrocraniumare greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocraniumunless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending

Modular thrust subsystem approaches to solar electric propulsion module design

Three approaches are presented for packaging the elements of a 30 cm ion thruster subsystem into a modular thrust subsystem. The individual modules, when integrated into a conceptual solar electric propulsion module are applicable to a multimission set of interplanetary flights with the space shuttle interim upper stage as the launch vehicle. The emphasis is on the structural and thermal integration of the components into the modular thrust subsystems. Thermal control for the power processing units is either by direct radiation through louvers in combination with heat pipes or an all heat pipe system. The propellant storage and feed system and thruster gimbal system concepts are presented. The three approaches are compared on the basis of mass, cost, testing, interfaces, simplicity, reliability, and maintainability

Metamorphic Conditions of an Archean Core Complex in the Northern Wind River Range, Wyoming

The Archean granulite-facies rocks of the northern Wind River Range consist of extensive granitic orthogneisses and migmatites hosting banded iron formations, amphibolites, metapelites, metabasites, ultramafites and quartzites. Quantitative pressure and temperature estimates from inclusions within garnet porphyroblasts are 815±5O%C and 8±1 kb using equilibria buffered by the assemblages spinel-quartz-garnet-sillimanite and garnet-rutile-ilmenite-sillimanite-quartz. Pressure-temperature estimates from the groundmass core assemblages of the banded iron formations and hornblende granulites are 750 ±50 %C and 5·5 ± 1 kb using garnet-clinopyroxene, garnet-orthopyroxene, and two-pyroxene thermometry, and geobarometers based on the assemblages garnet-quartz-plagioclase-orthopyroxene and orthopyroxene-olivine-quartz. Rim compositions of the matrix minerals indicate nearly isobaric cooling from the conditions of 750 %C and 5-5 kb to < 600%C at 5 kb. Taken together, the P-T estimates from both the garnet inclusions and matrix assemblages are consistent with a clockwise P-T-t path for this terrane. Temperature estimates based on oxygen isotope thermometry in the banded iron formations vary systematically with the degree of visible late-stage deformation. There is no correlation between the isotopic temperature estimates and those from cation-based thermometers. The highest pressures and temperatures for the Wind River terrane are preserved by the inclusions in garnet porphyroblasts. The ability of these inclusions to preserve chemistries corresponding to higher pressures and temperatures is attributed to the combined effects of inclusion isolation and fixed inclusion volume within the garnet porphyroblasts. Cation-based thermometers in the groundmass preserve lower temperatures as a result of diffusional partial resetting. Isotopic thermometry will yield the lowest temperatures if there is even minor retrograde deformation. Geothermobarometry for the northern Wind River Archean terrane is consistent with a tectonic regime of doubly thickened crust. Peak metamorphic conditions preserved in the cores of the garnets are compatible with deep burial during the early stages of tectonism. Rapid to intermediate uplift due to erosion of the upper plate could explain the nearly isothermal decompression from 8·0 to 5-5 kb. The later, nearly isobaric, cooling path indicated by the rim compositions of the matrix minerals is consistent with relaxation of the elevated geother

Liver Transplantation for Advanced Liver Disease with Alpha-1antitrypsin Deficiency

ALPHA-1-antitrypsin deficiency associated with chronic obstructive airway disease was recognized in 1963 by Laurell and Ericksson.1 In 1969, Sharp2 described the first cases of alpha-1-antitrypsin-deficiency disease in children with cirrhosis. Since then, this inborn error has been recognized as one of the more common factors in cirrhosis of infancy and childhood,3 including “neonatal hepatitis.”4 Alpha-1-antitrypsin is a glycoprotein that accounts for a major portion of the alpha-1 globulin fraction of the serum.5 It is responsible for approximately 90 per cent of the antitrypsin activity6 of the serum, and it also inhibits several other plasma enzymes, including plasmin,7 elastase,8 collagenase,9 and. © 1980, Massachusetts Medical Society. All rights reserved

A discrete time-dependent method for metastable atoms in intense fields

The full-dimensional time-dependent Schrodinger equation for the electronic dynamics of single-electron systems in intense external fields is solved directly using a discrete method. Our approach combines the finite-difference and Lagrange mesh methods. The method is applied to calculate the quasienergies and ionization probabilities of atomic and molecular systems in intense static and dynamic electric fields. The gauge invariance and accuracy of the method is established. Applications to multiphoton ionization of positronium and hydrogen atoms and molecules are presented. At very high intensity above saturation threshold, we extend the method using a scaling technique to estimate the quasienergies of metastable states of the hydrogen molecular ion. The results are in good agreement with recent experiments.Comment: 10 pages, 9 figure, 4 table

Risk factors for failure of outpatient parenteral antibiotic therapy (OPAT) in infective endocarditis

Objectives: To identify risk factors for failure of outpatient antibiotic therapy (OPAT) in infective endocarditis (IE). Patients and methods: We identified IE cases managed at a single centre over 12 years from a prospectively maintained database. ‘OPAT failure’ was defined as unplanned readmission or antibiotic switch due to adverse drug reaction or antibiotic resistance. We analysed patient and disease-related risk factors for OPAT failure by univariate and multivariate logistic regression. We also retrospectively collected follow-up data on adverse disease outcome (defined as IE-related death or relapse) and performed Kaplan–Meier survival analysis up to 36 months following OPAT. Results: We identified 80 episodes of OPAT in IE. Failure occurred in 25/80 episodes (31.3%). On multivariate analysis, cardiac or renal failure [pooled OR 7.39 (95% CI 1.84–29.66), P = 0.005] and teicoplanin therapy [OR 8.69 (95% CI 2.01–37.47), P = 0.004] were independently associated with increased OPAT failure. OPAT failure with teicoplanin occurred despite therapeutic plasma levels. OPAT failure predicted adverse disease outcome up to 36 months (P = 0.016 log-rank test). Conclusions: These data caution against selecting patients with endocarditis for OPAT in the presence of cardiac or renal failure and suggest teicoplanin therapy may be associated with suboptimal OPAT outcomes. Alternative regimens to teicoplanin in the OPAT setting should be further investigated