Devonian Sandstone Lithostratigraphy, Northern Arkansas

Two areas of Devonian sandstone development may be recognized in northern Arkansas. In northwestern Arkansas, the Clifty Formation comprises a massively bedded, super mature quartz arenite of Middle Devonian age overlain by thinner bedded, phosphatic quartz arenite and chert breccia of the Sylamore Sandstone Member, Chattanooga Shale (Upper Devonian). This sequence overlies Ordovician strata (Powell or Everton) and is succeeded by the Chattanooga Shale and strata of Lower Mississippian age. In north-central Arkansas, the Clifty Formation is absent and the Chattanooga Shale may develop sandstone at its base and top. Occasionally the Chattanooga Shale is absent and the entire interval may be Upper Devonian sandstone. These Upper Devonian sandstones are phosphatic, mature quartz arenites referred to the Sylamore Member except where they overlie the Chattanooga Shale. In these cases, the sandstone is recognized as an informal upper member of the Chattanooga. Reports of Lower Mississippian Sylamore Sandstone in north-central Arkansas are regarded as misidentification of the Bachelor Formation (Middle Kinderhookian

A Simple Model for Finite Chemical Kinetics Analysis of Supersonic Turbulent Shear Layer Combustion

A simple flow/thermodynamic model is proposed to describe finite chemical kinetic rate combustion in a turbulent supersonic shear layer for the purposes of assessing Damköhler number effects in such flows. Sample calculations and comparisons for the H_2/NO/F_2 chemical system and the H_2/air system are described for a set of initial flow and thermodynamic conditions of the entrained reactants

Overview of a Proposed Flight Validation of Aerocapture System Technology for Planetary Missions

Aerocapture System Technology for Planetary Missions is being proposed to NASA's New Millennium Program for flight aboard the Space Technology 9 (ST9) flight opportunity. The proposed ST9 aerocapture mission is a system-level flight validation of the aerocapture maneuver as performed by an instrumented, high-fidelity flight vehicle within a true in-space and atmospheric environment. Successful validation of the aerocapture maneuver will be enabled through the flight validation of an advanced guidance, navigation, and control system as developed by Ball Aerospace and two advanced Thermal Protection System (TPS) materials, Silicon Refined Ablative Material-20 (SRAM-20) and SRAM-14, as developed by Applied Research Associates (ARA) Ablatives Laboratory. The ST9 aerocapture flight validation will be sufficient for immediate infusion of these technologies into NASA science missions being proposed for flight to a variety of Solar System destinations possessing a significant planetary atmosphere

Exploring Venus with Balloons - Science Objectives and Mission Architectures for Small and Medium-Class Missions

This presentation was part of the session : Current Planetary Probe Science and TechnologySixth International Planetary Probe WorkshopFollowing the trailblazing flights of the 1985 twin Soviet VEGA balloons, missions to fly in the skies of Venus have been proposed to both NASA's Discovery Program and ESA's Cosmic Visions amd are currently being planned for NASA's next Frontiers Mission opportunity. Such missions will answer fundamental science issues highlighted in a variety of high-level NASA-authorized science documents in recent years, including the Decadal Study, various NASA roadmaps, and recommendations coming out of the Venus Exploration Analysis Group (VEXAG). Such missions would in particular address key questions of Venus's origin, evolution, and current state, including detailed measurements of (1) trace gases associated with Venus's active photo- and thermo-chemistry and (2) measurements of vertical motions and local temperature which characterize convective and wave processes. As an example of what can be done with small and medium class missions (less than $900M and$500M, respectively), the Venus Aerostatic-Lift Observatories for in-situ Research (VALOR) Discovery and New Frontiers mission concepts will be discussed. Floating in Venus's rapid windstream near an altitude of 55 km, VALOR's twin balloon-borne aerostats will sample rare gases and trace chemicals and measure vertical and horizontal motions and cloud aerosols within Venus's dynamic middle cloud layer. Each balloon will explore a distinctive dynamical/meteorological region within Venus's energetic atmosphere as each circles the globe for over a week, with one drifting in the cloudy north polar region and the other flying in the less-cloudy but more convective temperate region. The New Frontiers concept would carry several drop sondes that would provide vertical profiles from 55 km down to the surface of temperature, pressure, winds, and the abundances of key reactive gases including SO2, CO, and H2O. In addition, each drop sonde would obtain stereoscopic images and spectra of the surface. Each of these VALOR missions would test a variety of scenarios for the origin, formation, and evolution of Venus by sampling all the noble gases and their isotopes, especially the heaviest elements never reliably measured previously, xenon and krypton. Riding the gravity and planetary waves of Venus a la the VEGA balloons in 1985, the VALOR balloons would sample in particular the chemistry and dynamics of Venus's sulfur-cloud meteorology. Tracked by an array of Earth-based telescopes, zonal, meridional, and vertical winds would be measured with unprecedented precision. Such measurements will help in developing our fundamental understanding of (1) the circulation of Venus, including the role of waves in powering the planet's poorly-understood super-rotation, (2) the nature of Venus's sulfur cycle, key to Venus's current climate, and (3) how Earth's neighbor formed and evolved over the aeons.NAS

Overview of a Proposed Flight Validation of Aerocapture System Technology

Aerocapture is a very useful capability for NASA that can be used across a wide range of planetary mission sizes and destinations. A substantial mass advantage may be realized through aerocapture maneuver implementation. The mass advantage is enabling for certain outer planet mission profiles. Aerocapture technology provides corollary benefits to the related applications of atmospheric entry and precision landing on worlds with atmospheres through aero/aerothermodynamic model validation, hypersonic guided flight, tps materials, and performance model validation. The ST9 Aerocapture flight validation will be sufficient to immediately infuse aerocapture technology into future NASA science missions. The advanced technologies being flight validated will enable the system level goal of performing an aerocapture maneuver. The advanced technologies include: The GN&C System, TPS materials, plus Advanced recession and heat flux sensors

Aerial Deployment and Inflation System for Mars Helium Balloons

A method is examined for safely deploying and inflating helium balloons for missions at Mars. The key for making it possible to deploy balloons that are light enough to be buoyant in the thin, Martian atmosphere is to mitigate the transient forces on the balloon that might tear it. A fully inflated Mars balloon has a diameter of 10 m, so it must be folded up for the trip to Mars, unfolded upon arrival, and then inflated with helium gas in the atmosphere. Safe entry into the Martian atmosphere requires the use of an aeroshell vehicle, which protects against severe heating and pressure loads associated with the hypersonic entry flight. Drag decelerates the aeroshell to supersonic speeds, then two parachutes deploy to slow the vehicle down to the needed safe speed of 25 to 35 m/s for balloon deployment. The parachute system descent dynamic pressure must be approximately 5 Pa or lower at an altitude of 4 km or more above the surface

Transmembrane helix dynamics of bacterial chemoreceptors supports a piston model of signalling.

Transmembrane α-helices play a key role in many receptors, transmitting a signal from one side to the other of the lipid bilayer membrane. Bacterial chemoreceptors are one of the best studied such systems, with a wealth of biophysical and mutational data indicating a key role for the TM2 helix in signalling. In particular, aromatic (Trp and Tyr) and basic (Arg) residues help to lock α-helices into a membrane. Mutants in TM2 of E. coli Tar and related chemoreceptors involving these residues implicate changes in helix location and/or orientation in signalling. We have investigated the detailed structural basis of this via high throughput coarse-grained molecular dynamics (CG-MD) of Tar TM2 and its mutants in lipid bilayers. We focus on the position (shift) and orientation (tilt, rotation) of TM2 relative to the bilayer and how these are perturbed in mutants relative to the wildtype. The simulations reveal a clear correlation between small (ca. 1.5 Å) shift in position of TM2 along the bilayer normal and downstream changes in signalling activity. Weaker correlations are seen with helix tilt, and little/none between signalling and helix twist. This analysis of relatively subtle changes was only possible because the high throughput simulation method allowed us to run large (n = 100) ensembles for substantial numbers of different helix sequences, amounting to ca. 2000 simulations in total. Overall, this analysis supports a swinging-piston model of transmembrane signalling by Tar and related chemoreceptors

Waterfowl recently infected with low pathogenic avian influenza exhibit reduced local movement and delayed migration

Understanding relationships between infection and wildlife movement patterns is important for predicting pathogen spread, especially for multispecies pathogens and those that can spread to humans and domestic animals, such as avian influenza viruses (AIVs). Although infection with low pathogenic AIVs is generally considered asymptomatic in wild birds, prior work has shown that influenza-infected birds occasionally delay migration and/or reduce local movements relative to their uninfected counterparts. However, most observational research to date has focused on a few species in northern Europe; given that influenza viruses are widespread globally and outbreaks of highly pathogenic strains are increasingly common, it is important to explore influenza–movement relationships across more species and regions. Here, we used telemetry data to investigate relationships between influenza infection and movement behavior in 165 individuals from four species of North American waterfowl that overwinter in California, USA. We studied both large-scale migratory and local overwintering movements and found that relationships between influenza infection and movement patterns varied among species. Northern pintails (Anas acuta) with antibodies to avian influenza, indicating prior infection, made migratory stopovers that averaged 12 days longer than those with no influenza antibodies. In contrast, greater white-fronted geese (Anser albifrons) with antibodies to avian influenza made migratory stopovers that averaged 15 days shorter than those with no antibodies. Canvasbacks (Aythya valisineria) that were actively infected with influenza upon capture in the winter delayed spring migration by an average of 28 days relative to birds that were uninfected at the time of capture. At the local scale, northern pintails and canvasbacks that were actively infected with influenza used areas that were 7.6 and 4.9 times smaller than those of uninfected ducks, respectively, during the period of presumed active influenza infection. We found no evidence for an influence of active influenza infection on local movements of mallards (Anas platyrhynchos). These results suggest that avian influenza can influence waterfowl movements and illustrate that the relationships between avian influenza infection and wild bird movements are context- and species-dependent. More generally, understanding and predicting the spread of multihost pathogens requires studying multiple taxa across space and time

Aerocapture Systems Analysis for a Neptune Mission

A Systems Analysis was completed to determine the feasibility, benefit and risk of an aeroshell aerocapture system for Neptune and to identify technology gaps and technology performance goals. The systems analysis includes the following disciplines: science; mission design; aeroshell configuration; interplanetary navigation analyses; atmosphere modeling; computational fluid dynamics for aerodynamic performance and aeroheating environment; stability analyses; guidance development; atmospheric flight simulation; thermal protection system design; mass properties; structures; spacecraft design and packaging; and mass sensitivities. Results show that aerocapture is feasible and performance is adequate for the Neptune mission. Aerocapture can deliver 1.4 times more mass to Neptune orbit than an all-propulsive system for the same launch vehicle and results in a 3-4 year reduction in trip time compared to all-propulsive systems. Enabling technologies for this mission include TPS manufacturing; and aerothermodynamic methods for determining coupled 3-D convection, radiation and ablation aeroheating rates and loads