NASA space materials research

The effect of the space environment on: (1) thermal control coatings and thin polymer films; (2) radiation stability of 250 F and 350 F cured graphite/epoxy composites; and (3) the thermal mechanical stability of graphite/epoxy, graphite/glass composites are considered. Degradation in mechanical properties due to combined radiation and thermal cycling is highlighted. Damage mechanisms are presented and chemistry modifications to improve stability are suggested. The dimensional instabilities in graphite/epoxy composites associated with microcracking during thermal cycling is examined as well as the thermal strain hysteresis found in metal-matrix composites

Robust degradation and enhancement of robot mission behaviour in unpredictable environments

© 2015 ACM.Temporal logic based approaches that automatically generate controllers have been shown to be useful for mission level planning of motion, surveillance and navigation, among others. These approaches critically rely on the validity of the environment models used for synthesis. Yet simplifying assumptions are inevitable to reduce complexity and provide mission-level guarantees; no plan can guarantee results in a model of a world in which everything can go wrong. In this paper, we show how our approach, which reduces reliance on a single model by introducing a stack of models, can endow systems with incremental guarantees based on increasingly strengthened assumptions, supporting graceful degradation when the environment does not behave as expected, and progressive enhancement when it does

A survey of debris trails from short-period comets

We observed 34 comets using the 24 micron camera on the Spitzer Space Telescope. Each image contains the nucleus and covers at least 10^6 km of each comet's orbit. Debris trails due to mm-sized or larger particles were found along the orbits of 27 comets; 4 comets had small-particle dust tails and a viewing geometry that made debris trails impossible to distinguish; and only 3 had no debris trail despite favorable observing conditions. There are now 30 Jupiter-family comets with known debris trails, of which 22 are reported in this paper for the first time. The detection rate is >80%, indicating that debris trails are a generic feature of short-period comets. By comparison to orbital calculations for particles of a range of sizes ejected over 2 yr prior to observation, we find that particles comprising 4 debris trails are typically mm-sized while the remainder of the debris trails require particles larger than this. The lower-limit masses of the debris trails are typically 10^11 g, and the median mass loss rate is 2 kg/s. The mass-loss rate in trail particles is comparable to that inferred from OH production rates and larger than that inferred from visible-light scattering in comae.Comment: accepted by Icarus; figures compressed for astro-p

Critical health literacy: conceptualization and settings-based development

Background Health literacy is conceptualized as a continuum of social practices spanning functional, interactive and critical domains. Critical health literacy enables individuals and communities to reflect on the wider health determinants and engage in social and political processes towards health equity. This project introduces the Oxford Bibliographies (OB) entry and illustrates through an empirical case study of critical health literacy in a community-based setting. Methods The OB entry provides a literature review of critical health literacy conceptualization, measurement and interventions. An institutional ethnography of critical health literacy in libraries, models a settings-based approach to critical health literacy development in children. Results Barriers to critical health literacy development include the lack of validated instruments and evaluation of interventions. Common settings for development with children are schools, but institutional settings face challenges in developing the political action element of critical health literacy. There is a need to move beyond single settings to consider multiple settings working in partnership where children can learn, live, and play. A coordinated supersetting approach leverages the strengths of different settings to promote critical health literacy. A model proposes four antecedents to a supersetting in which sub-settings collectively support (1) a determinants-based perspective, (2) open access to information and resources, (3) involvement of community stakeholders and (4) informed action on health. Conclusions Although conceptualized over two decades ago, it is only recently that research on critical health literacy has normalized the consolidation of both its cognitive and social dimensions into a joint strategy of critical thinking and empowerment. A supersetting approach can combine community-based and school-based support to embed critical health literacy development opportunities early in the life course

The effects of space radiation on a chemically modified graphite-epoxy composite material

The effects of the space environment on the engineering properties and chemistry of a chemically modified T300/934 graphite-epoxy composite system are characterized. The material was subjected to 1.0 x 10 to the 10th power rads of 1.0 MeV electron irradiation under vacuum to simulate 30 years in geosynchronous earth orbit. Monotonic tension tests were performed at room temperature (75 F/24 C) and elevated temperature (250 F/121 C) on 4-ply unidirectional laminates. From these tests, inplane engineering and strength properties (E sub 1, E sub 2, Nu sub 12, G sub 12, X sub T, Y sub T) were determined. Cyclic tests were also performed to characterize energy dissipation changes due to irradiation and elevated temperature. Large diameter graphite fibers were tested to determine the effects of radiation on their stiffness and strength. No significant changes were observed. Dynamic-mechanical analysis demonstrated that the glass transition temperature was reduced by 50 F(28 C) after irradiation. Thermomechanical analysis showed the occurrence of volatile products generated upon heating of the irradiated material. The chemical modification of the epoxy did not aid in producing a material which was more radiation resistant than the standard T300/934 graphite-epoxy system. Irradiation was found to cause crosslinking and chain scission in the polymer. The latter produced low molecular weight products which plasticize the material at elevated temperatures and cause apparent material stiffening at low stresses at room temperature

Independence v. Accountability: Finding a Balance Amidst the Changing Politics of State-Court Judicial Selection

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Marquette University Law School Hooding Ceremony

Non

Independence v. Accountability: Finding a Balance Amidst the Changing Politics of State-Court Judicial Selection

Non