Orion Entry, Descent, and Landing Performance and Mission Design

The Orion Vehicle is the next spacecraft to take humans into space and will include missions to ISS as well as missions to the Moon. As part of that challenge, the vehicle will have to accommodate multiple mission design concepts, since return from Low Earth Orbit and return from the Moon can be quite different. Commonality between the different missions as it relates to vehicle systems, guidance capability, and operations concepts is the goal. Several unique mission design concepts include the specification of multiple land-based landing sites for a vehicle with closed-loop direct and skip entry guidance, followed by a parachute descent and landing attenuation system. This includes the ability of the vehicle to accurately target and land at a designated landing site, including site location aspects, landing site size, and landing opportunities assessments. Analyses associated with these mission design and flight performance challenges and constraints will be discussed as well as potential operational concepts to provide feasibility and/or mission commonality

Natural selection favoring more transmissible HIV detected in United States molecular transmission network.

HIV molecular epidemiology can identify clusters of individuals with elevated rates of HIV transmission. These variable transmission rates are primarily driven by host risk behavior; however, the effect of viral traits on variable transmission rates is poorly understood. Viral load, the concentration of HIV in blood, is a heritable viral trait that influences HIV infectiousness and disease progression. Here, we reconstruct HIV genetic transmission clusters using data from the United States National HIV Surveillance System and report that viruses in clusters, inferred to be frequently transmitted, have higher viral loads at diagnosis. Further, viral load is higher in people in larger clusters and with increased network connectivity, suggesting that HIV in the United States is experiencing natural selection to be more infectious and virulent. We also observe a concurrent increase in viral load at diagnosis over the last decade. This evolutionary trajectory may be slowed by prevention strategies prioritized toward rapidly growing transmission clusters

Effects of an E-Learning Module on Students’ Attitudes in an Electronics Class

Research has shown that students exhibit negative attitudes towards Electronics especially when they are taught using the conventional method. This is in addition to poor instructional methods that do not promote individualization of instruction or make learning interesting. The purpose of this study was to design an e-learning module in “Transistors” – a topic in the Electronics course - and determine its effects on students’ attitudes in Kenyan Polytechnics. The Solomon-three quasi-experimental, non-equivalent control group research design was used for the study. A sample consisting of 103 first year Electronic Engineering students from three Polytechnics were randomly assigned to three groups; one experimental, E and two controls; C1 and C2. A self-administered Students’ Attitude Questionnaire (SAQ) with a calculated Cronbach-alpha reliability coefficient of 0.88 was used for data collection. The data was analysed using t-tests and the analysis of covariance (ANCOVA) statistical test at an alpha level of significance of 0.05. The results of the t-test revealed that the differences in gain from pre-test to post-test between groups E and C1 were significant in favour of group E. Further results using ANCOVA revealed that there were statistically significant differences in post-test scores for students’ attitudes between groups E and C2 in favour of group E. This showed that the presence of a pre-test had a significant effect on students’ attitude towards the topic being taught irrespective of whether they were taught using the e-learning module or the conventional method. The findings of the study shall be useful to Electronics students and lecturers, curriculum developers, e-learning practitioners and educational policy makers in Kenya. Keywords: e-learning, conventional method, attitudes, electronics, transistors, studen

Composite Accretion Disk and White Dwarf Photosphere Analyses of the FUSE and HST Observations of EY Cygni

We explore the origin of FUSE and HST STIS far UV spectra of the dwarf nova, EY Cyg, during its quiescence using \emph{combined} high gravity photosphere and accretion disk models as well as model accretion belts. The best-fitting single temperature white dwarf model to the FUSE plus HST STIS spectrum of EY Cygni has T$_{eff} = 24,000$K, log $g = 9.0$, with an Si abundance of 0.1 x solar and C abundance of 0.2 x solar but the distance is only 301 pc. The best-fitting composite model consists of white dwarf with T$_{eff} = 22,000$K, log $g = 9$, plus an accretion belt with T$_{belt} = 36,000$K covering 27% of the white dwarf surface with V$_{belt} sin i = 2000$ km/s. The accretion belt contributes 63% of the FUV light and the cooler white dwarf latitudes contribute 37%. This fit yields a distance of 351 pc which is within 100 pc of our adopted distance of 450 pc. EY Cyg has very weak C {\sc iv} emission and very strong N {\sc v} emission, which is atypical of the majority of dwarf novae in quiescence. We also conducted a morphological study of the surroundings of EY Cyg using direct imaging in narrow nebular filters from ground-based telescopes. We report the possible detection of nebular material^M associated with EY Cygni. Possible origins of the apparently large N {\scv}/C {\sc iv} emission ratio are discussed in the context of nova explosions, contamination of the secondary star and accretion of nova abundance-enriched matter back to the white dwarf via the accretion disk or as a descendant of a precursor binary that survived thermal timescale mass transfer. The scenario involving pollution of the secondary by past novae may be supported by the possible presence of a nova remnant-like nebula around EY Cyg.Comment: To appear in AJ, Oct. 2004. 5 figures, including 2 color ones (2D pictures

Crustal processes sustain Arctic abiotic gas hydrate and fluid flow systems

The Svyatogor Ridge and surroundings, located on the sediment-covered western flank of the Northern Knipovich Ridge, host extensive gas hydrate and related fluid flow systems. The fluid flow system here manifests in the upper sedimentary sequence as gas hydrates and free gas, indicated by bottom simulating reflections (BSRs) and amplitude anomalies. Using 2D seismic lines and bathymetric data, we map tectonic features such as faults, crustal highs, and indicators of fluid flow processes. Results indicate a strong correlation between crustal faults, crustal highs and fluid accumulations in the overlying sediments, as well as an increase in geothermal gradient over crustal faults. We conclude here that gas generated during the serpentinization of exhumed mantle rocks drive the extensive occurrence of gas hydrate and fluid flow systems in the region and transform faults act as an additional major pathway for fluid circulation

Large-area epitaxial growth of curvature-stabilized ABC trilayer graphene.

The properties of van der Waals (vdW) materials often vary dramatically with the atomic stacking order between layers, but this order can be difficult to control. Trilayer graphene (TLG) stacks in either a semimetallic ABA or a semiconducting ABC configuration with a gate-tunable band gap, but the latter has only been produced by exfoliation. Here we present a chemical vapor deposition approach to TLG growth that yields greatly enhanced fraction and size of ABC domains. The key insight is that substrate curvature can stabilize ABC domains. Controllable ABC yields ~59% were achieved by tailoring substrate curvature levels. ABC fractions remained high after transfer to device substrates, as confirmed by transport measurements revealing the expected tunable ABC band gap. Substrate topography engineering provides a path to large-scale synthesis of epitaxial ABC-TLG and other vdW materials

Ultrasonic Method for Deployment Mechanism Bolt Element Preload Verification

Deployment mechanisms play a pivotal role in mission success. These mechanisms often incorporate bolt elements for which a preload within a specified range is essential for proper operation. A common practice is to torque these bolt elements to a specified value during installation. The resulting preload, however, can vary significantly with applied torque for a number of reasons. The goal of this effort was to investigate ultrasonic methods as an alternative for bolt preload verification in such deployment mechanisms. A family of non-explosive release mechanisms widely used by satellite manufacturers was chosen for the work. A willing contractor permitted measurements on a sampling of bolt elements for these release mechanisms that were installed by a technician following a standard practice. A variation of approximately 50% (+/- 25%) in the resultant preloads was observed. An alternative ultrasonic method to set the preloads was then developed and calibration data was accumulated. The method was demonstrated on bolt elements installed in a fixture instrumented with a calibrated load cell and designed to mimic production practice. The ultrasonic method yielded results within +/- 3% of the load cell reading. The contractor has since adopted the alternative method for its future production. Introductio

Oral Transmissibility of Prion Disease Is Enhanced by Binding to Soil Particles

Soil may serve as an environmental reservoir for prion infectivity and contribute to the horizontal transmission of prion diseases (transmissible spongiform encephalopathies [TSEs]) of sheep, deer, and elk. TSE infectivity can persist in soil for years, and we previously demonstrated that the disease-associated form of the prion protein binds to soil particles and prions adsorbed to the common soil mineral montmorillonite (Mte) retain infectivity following intracerebral inoculation. Here, we assess the oral infectivity of Mte- and soil-bound prions. We establish that prions bound to Mte are orally bioavailable, and that, unexpectedly, binding to Mte significantly enhances disease penetrance and reduces the incubation period relative to unbound agent. Cox proportional hazards modeling revealed that across the doses of TSE agent tested, Mte increased the effective infectious titer by a factor of 680 relative to unbound agent. Oral exposure to Mte-associated prions led to TSE development in experimental animals even at doses too low to produce clinical symptoms in the absence of the mineral. We tested the oral infectivity of prions bound to three whole soils differing in texture, mineralogy, and organic carbon content and found soil-bound prions to be orally infectious. Two of the three soils increased oral transmission of disease, and the infectivity of agent bound to the third organic carbon-rich soil was equivalent to that of unbound agent. Enhanced transmissibility of soil-bound prions may explain the environmental spread of some TSEs despite the presumably low levels shed into the environment. Association of prions with inorganic microparticles represents a novel means by which their oral transmission is enhanced relative to unbound agent