Materials selection for long life in LEO: A critical evaluation of atomic oxygen testing with thermal atom systems

The use of thermal atom test methods as a materials selection and screening technique for low-Earth orbit (LEO) spacecraft is critically evaluated. The chemistry and physics of thermal atom environments are compared with the LEO environment. The relative reactivities of a number of materials determined to be in thermal atom environments are compared to those observed in LEO and in high quality LEO simulations. Reaction efficiencies measured in a new type of thermal atom apparatus are one-hundredth to one-thousandth those observed in LEO, and many materials showing nearly identical reactivities in LEO show relative reactivities differing by as much as a factor of 8 in thermal atom systems. A simple phenomenological kinetic model for the reaction of oxygen atoms with organic materials can be used to explain the differences in reactivity in different environments. Certain specific thermal test environments can be used as reliable materials screening tools. Using thermal atom methods to predict material lifetime in LEO requires direct calibration of the method against LEO data or high quality simulation data for each material

International photovoltaic program. Volume 2: Appendices

The results of analyses conducted in preparation of an international photovoltaic marketing plan are summarized. Included are compilations of relevant statutes and existing Federal programs; strategies designed to expand the use of photovoltaics abroad; information on the domestic photovoltaic plan and its impact on the proposed international plan; perspectives on foreign competition; industry views on the international photovoltaic market and ideas about the how US government actions could affect this market;international financing issues; and information on issues affecting foreign policy and developing countries

Local forest structure variability increases resilience to wildfire in dry western U.S. coniferous forests.

A 'resilient' forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine-scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long-lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire-induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability

Disseminated Mycobacterium genavense Infection in Two Patients with AIDS

Mycobacterium genavense is a recently defined fastidious organism that has been identified as a cause of disseminated infection in patients with AIDS. We report the cases of two patients who had advanced AIDS and a clinical syndrome of fever, anorexia, abdominal pain, diarrhea, and weight loss. In addition, splenomegaly and lymphadenopathy were prominent in both cases, and in one patient's case radiographic findings were suggestive of splenic abscesses. Mycobacteria isolated from specimens of blood and bone marrow grew in liquid media but not on solid media. The results of DNA probe tests for Mycobacterium tuberculosis and Mycobacterium avium complex were false-positive for both patients. After treatment of the broth cultures to lyse red blood cells, the results of DNA probe tests were negative for these pathogens. Amplification and sequencing of 16S rRNA with use of the polymerase chain reaction indicated that the mycobacterial isolates from both patients had sequences identical to those previously reported for M. genavense. One patient survived 5 months after diagnosis, the other 2 months after diagnosis; only one patient responded (transiently) to antimycobacterial chemotherap

Reliability-Based Electronics Shielding Design Tools

Shielding design on large human-rated systems allows minimization of radiation impact on electronic systems. Shielding design tools require adequate methods for evaluation of design layouts, guiding qualification testing, and adequate follow-up on final design evaluation

Electronics Shielding and Reliability Design Tools

It is well known that electronics placement in large-scale human-rated systems provides opportunity to optimize electronics shielding through materials choice and geometric arrangement. For example, several hundred single event upsets (SEUs) occur within the Shuttle avionic computers during a typical mission. An order of magnitude larger SEU rate would occur without careful placement in the Shuttle design. These results used basic physics models (linear energy transfer (LET), track structure, Auger recombination) combined with limited SEU cross section measurements allowing accurate evaluation of target fragment contributions to Shuttle avionics memory upsets. Electronics shielding design on human-rated systems provides opportunity to minimize radiation impact on critical and non-critical electronic systems. Implementation of shielding design tools requires adequate methods for evaluation of design layouts, guiding qualification testing, and an adequate follow-up on final design evaluation including results from a systems/device testing program tailored to meet design requirements

Validation of ISS Floating Potential Measurement Unit Electron Densities and Temperatures

Validation of the Floating Potential Measurement Unit (FPMU) electron density and temperature measurements is an important step in the process of evaluating International Space Station spacecraft charging issues .including vehicle arcing and hazards to crew during extravehicular activities. The highest potentials observed on Space Station are due to the combined VxB effects on a large spacecraft and the collection of ionospheric electron and ion currents by the 160 V US solar array modules. Ionospheric electron environments are needed for input to the ISS spacecraft charging models used to predict the severity and frequency of occurrence of ISS charging hazards. Validation of these charging models requires comparing their predictions with measured FPMU values. Of course, the FPMU measurements themselves must also be validated independently for use in manned flight safety work. This presentation compares electron density and temperatures derived from the FPMU Langmuir probes and Plasma Impedance Probe against the independent density and temperature measurements from ultraviolet imagers, ground based incoherent scatter radar, and ionosonde sites

The Grizzly, April 6, 1984

Loyalty Fund Phon-a-thon, Successful • Parsons Re-elected VP of Historical Society • Nagy\u27s Stellar Lecture • McQuaid Presents Views on Candidates • Letters to the Editor: Fraternities Help to Combat Apathy; Bubble World ; UC Social Life Needs Help; Pledging Not Destructive; Pledging Enhances Development; To Ban Pledging not a Positive Aspect; In Memory of Zeta Chi; Pledging to Expand Socially • Patrol Pattern Changed, Woman is Assaulted • The Limerick Syndrome: What Would UC do? • Mardi Gras Ball Declared Success • Changing Picture of Health in \u2780\u27s • Ride for Your Life! • Two Views on the Bussing Situation • Women\u27s Tennis Splits in Opening Matches • Softball Undefeated at 6-0 • Tennis Team Nets Two Victories • Denning Captures Fencing Title • Strizke, Rosenberg Qualify for Gymnastics Championship • Men\u27s Track Kicks off \u2784 Season • Men\u27s Lacrosse Thumps Bloomsburg • Hot Hitting Leads Bears Batsmen to Victories • Baseball Team Raises Record to 6-3 • Women\u27s Track Promisinghttps://digitalcommons.ursinus.edu/grizzlynews/1116/thumbnail.jp

Cross-scale interaction of host tree size and climatic water deficit governs bark beetle-induced tree mortality

The recent Californian hot drought (2012&ndash;2016) precipitated unprecedented ponderosa pine (Pinus ponderosa) mortality, largely attributable to the western pine beetle (Dendroctonus brevicomis; WPB). Broad-scale climate conditions can directly shape tree mortality patterns, but mortality rates respond non-linearly to climate when local-scale forest characteristics influence the behavior of tree-killing bark beetles (e.g., WPB). To test for these cross-scale interactions, we conduct aerial drone surveys at 32 sites along a gradient of climatic water deficit (CWD) spanning 350&thinsp;km of latitude and 1000&thinsp;m of elevation in WPB-impacted Sierra Nevada forests. We map, measure, and classify over 450,000 trees within 9 km2, validating measurements with coincident field plots. We find greater size, proportion, and density of ponderosa pine (the WPB host) increase host mortality rates, as does greater CWD. Critically, we find a CWD/host size interaction such that larger trees amplify host mortality rates in hot/dry sites. Management strategies for climate change adaptation should consider how bark beetle disturbances can depend on cross-scale interactions, which challenge our ability to predict and understand patterns of tree mortality. The 2012&ndash;2016 drought and western pine beetle outbreaks caused unprecedented mortality of ponderosa pine in the Sierra Nevada, California. Here, the authors analyse drone-based data from almost half a million trees and find an interaction between host size and climatic water deficit, with higher mortality for large trees in dry, warm conditions but not in cooler or wetter conditions.</p