SOAR (Support Office for Aerogeophysical Research) Annual Report 1994/1995

The Support Office for Aerogeophysical Research (SOAR) was a facility of the National Science Foundation's Office of Polar Programs whose mission is to make airborne geophysical observations available to the broad research community of geology, glaciology and other sciences. The central office of the SOAR facility is located in Austin, Texas within the University of Texas Institute for Geophysics. Other institutions with significant responsibilities are the Lamont­ Doherty Earth Observatory of Columbia University and the Geophysics Branch of the U.S . Geological Survey. This report summarizes the goals and accomplishments of the SOAR facility during 1994/1995 and plans for the next year.National Science Foundation's Office of Polar ProgramsInstitute for Geophysic

Ensuring Payload Safety in Missions with Special Partnerships

The National Aeronautics and Space Administration (NASA) Expendable Launch Vehicle (ELV) payload space flight missions involve cooperative work between NASA and partners including spacecraft (or payload) contractors, universities, nonprofit research centers, Agency payload organization, Range Safety organization, Agency launch service organizations, and launch vehicle contractors. The role of NASA's Safety and Mission Assurance (SMA) Directorate is typically fairly straightforward, but when a mission's partnerships become more complex, to realize cost and science benefits (e.g., multi-agency payload(s) or cooperative international missions), the task of ensuring payload safety becomes much more challenging. This paper discusses lessons learned from NASA safety professionals working multiple-agency missions and offers suggestions to help fellow safety professionals working multiple-agency missions

Imaging bedrock topography and geological controls on ice streams flowing in the Wilkes Subglacial Basin sector of East Antarctica

The northern Wilkes Subglacial Basin (NWSB) in East Antarctica underlies the catchments of the Matusevich, Cook, Ninnis and Mertz Glaciers, which are largely marine-based and hence particularly sensitive to past and future ocean and climate warming. Here we use airborne radar, aeromagnetic and airborne gravity data to image bedrock topography, subglacial geology and deeper crustal structure and assess its influence on ice sheet dynamics in the NWSB. The previously identified Central Basins extend beneath the fast flowing Cook ice streams, indicating that potential ocean-induced changes could propagate further into the interior of the ice sheet. By analogy with the better exposed Rennick Graben in northern Victoria Land, these deep subglacial basins are interpreted here as grabens that steer fast glacial flow. With the aid of depth to source estimates and forward magnetic and gravity models, we image the 3D variability in geological basal boundary conditions, including Beacon sediments and Jurassic basaltic rocks and uplifted basement blocks within and along the flanks of these grabens. A remarkable contrast in magnetic anomaly signatures is observed over the coastal and inland segments of the Cook ice stream catchment. We model several km thick early Cambrian to late Neoproterozoic sedimentary basins in the basement of the coastal region, in contrast to a prominent Proterozoic basement high at the onset of fast glacial flow further inland. We further hypothesise that this difference affects geothermal heat flux at the base of the ice sheet, which could in turn influence basal melting and subglacial hydrology

Topology and energy transport in networks of interacting photosynthetic complexes

We address the role of topology in the energy transport process that occurs in networks of photosynthetic complexes. We take inspiration from light harvesting networks present in purple bacteria and simulate an incoherent dissipative energy transport process on more general and abstract networks, considering both regular structures (Cayley trees and hyperbranched fractals) and randomly-generated ones. We focus on the the two primary light harvesting complexes of purple bacteria, i.e., the LH1 and LH2, and we use network-theoretical centrality measures in order to select different LH1 arrangements. We show that different choices cause significant differences in the transport efficiencies, and that for regular networks centrality measures allow to identify arrangements that ensure transport efficiencies which are better than those obtained with a random disposition of the complexes. The optimal arrangements strongly depend on the dissipative nature of the dynamics and on the topological properties of the networks considered, and depending on the latter they are achieved by using global vs. local centrality measures. For randomly-generated networks a random arrangement of the complexes already provides efficient transport, and this suggests the process is strong with respect to limited amount of control in the structure design and to the disorder inherent in the construction of randomly-assembled structures. Finally, we compare the networks considered with the real biological networks and find that the latter have in general better performances, due to their higher connectivity, but the former with optimal arrangements can mimic the real networks' behaviour for a specific range of transport parameters. These results show that the use of network-theoretical concepts can be crucial for the characterization and design of efficient artificial energy transport networks.Comment: 14 pages, 16 figures, revised versio

Airborne gravity and precise positioning for geologic applications

Airborne gravimetry has become an important geophysical tool primarily because of advancements in methodology and instrumentation made in the past decade. Airborne gravity is especially useful when measured in conjunction with other geophysical data, such as magnetics, radar, and laser altimetry. The aerogeophysical survey over the West Antarctic ice sheet described in this paper is one such interdisciplinary study. This paper outlines in detail the instrumentation, survey and data processing methodology employed to perform airborne gravimetry from the multiinstrumented Twin Otter aircraft. Precise positioning from carrier-phase Global Positioning System (GPS) observations are combined with measurements of acceleration made by the gravity meter in the aircraft to obtain the free-air gravity anomaly measurement at aircraft altitude. GPS data are processed using the Kinematic and Rapid Static (KARS) software program, and aircraft vertical acceleration and corrections for gravity data reduction are calculated from the GPS position solution. Accuracies for the free-air anomaly are determined from crossover analysis after significant editing (2.98 mGal rms) and from a repeat track (1.39 mGal rms). The aerogeophysical survey covered a 300,000 km2 region in West Antarctica over the course of five field seasons. The gravity data from the West Antarctic survey reveal the major geologic structures of the West Antarctic rift system, including the Whitmore Mountains, the Byrd Subglacial Basin, the Sinuous Ridge, the Ross Embayment, and Siple Dome. These measurements, in conjunction with magnetics and ice-penetrating radar, provide the information required to reveal the tectonic fabric and history of this important region

God\u27s Church Is Just: A Specific Discussion Of Some Cases of Church Discipline

https://digitalcommons.acu.edu/crs_books/1364/thumbnail.jp

Airborne radar sounding evidence for deformable sediments and outcropping bedrock beneath Thwaites Glacier, West Antarctica

The geologic and morphologic records of prior ice sheet configurations show evidence of rapid, back-stepping, meltwater intensive retreats. However, the potential for such a retreat in a contemporary glacier depends on the lithology of the current ice sheet bed, which lies beneath kilometers of ice, making its physical properties difficult to constrain. We use radar sounding and marine bathymetry data to compare the bed configuration of Thwaites Glacier to the bed of paleo-Pine Island Glacier. Using observed and modeled radar scattering, we show that the tributaries and upper trunk of Thwaites Glacier are underlain by ice flow-aligned bedforms consistent with deformable sediment and that the lower trunk is grounded on a region of high bed roughness consistent with outcropping bedrock. This is the same configuration as paleo-Pine Island Glacier during its retreat across the inner continental shelf

Constant amplitude and post-overload fatigue crack growth behavior in PM aluminum alloy AA 8009

A recently developed, rapidly solidified, powder metallurgy, dispersion strengthened aluminum alloy, AA 8009, was fatigue tested at room temperature in lab air. Constant amplitude/constant delta kappa and single spike overload conditions were examined. High fatigue crack growth rates and low crack closure levels compared to typical ingot metallurgy aluminum alloys were observed. It was proposed that minimal crack roughness, crack path deflection, and limited slip reversibility, resulting from ultra-fine microstructure, were responsible for the relatively poor da/dN-delta kappa performance of AA 8009 as compared to that of typical IM aluminum alloys

Spectral signatures of photosynthesis I: Review of Earth organisms

Why do plants reflect in the green and have a 'red edge' in the red, and should extrasolar photosynthesis be the same? We provide: 1) a brief review of how photosynthesis works; 2) an overview of the diversity of photosynthetic organisms, their light harvesting systems, and environmental ranges; 3) a synthesis of photosynthetic surface spectral signatures; 4) evolutionary rationales for photosynthetic surface reflectance spectra with regard to utilization of photon energy and the planetary light environment. Given the surface incident photon flux density spectrum and resonance transfer in light harvesting, we propose some rules with regard to where photosynthetic pigments will peak in absorbance: a) the wavelength of peak incident photon flux; b) the longest available wavelength for core antenna or reaction center pigments; and c) the shortest wavelengths within an atmospheric window for accessory pigments. That plants absorb less green light may not be an inefficient legacy of evolutionary history, but may actually satisfy the above criteria.Comment: 69 pages, 7 figures, forthcoming in Astrobiology March 200