Aerothermodynamic Assessment of Corrugated Panel Thermal Protection Systems

The feasibility of using corrugated panels as a thermal protection system for an advanced space transportation vehicle was investigated. The study consisted of two major tasks: development of improved correlations for wind tunnel heat transfer and pressure data to yield design techniques, and application of the design techniques to determine if corrugated panels have application future aerospace vehicles. A single-stage-to-orbit vehicle was used to assess advantages and aerothermodynamic penalties associated with use of such panels. In the correlation task, experimental turbulent heat transfer and pressure data obtained on corrugation roughened surfaces during wind tunnel testing were analyzed and compared with flat plate data. The correlations and data comparisons included the effects of a large range of geometric, inviscid flow, internal boundary layer, and bulk boundary layer parameters in supersonic and hypersonic flow

Analysis of Historical Distribution of Submerged Aquatic Vegetation (SAV) in the York and Rappahannock Rivers as Evidence of Historical Water Quality Conditions

Historical black and white format photographs at scales of approximately 1:20,000, dating from 1952 to 1956 were used to delineate the maximum coverage of SAV in the study region. Coverage of photography from decades before and after this period were found to generally to be of poorer quality and show less SAV presence. Photo-interpretation of the aerial photographs was accomplished using a head-up, on-screen digitizing system at fixed image scale of 1:12,000 and followed as closely as possible the methods currently used to delineate SAV beds throughout the Chesapeake Bay as well as the delineation of historical SAV coverage for other region. A total of 16,340 hectares of sub-tidal bottom in the western shore bay region between the James and Potomac Rivers including all of the York and Rappahannock Rivers were found to display SAV signatures. Of this total approximately 11,260 ha, or 69%, were determined to be growing at depths shallower than 1 m MLW (Mean Low Water), 4,200 ha or 26% between 1 m and 2 m MLW, and 884 ha or 5% at depths below 2 m MLW. Comparison of the historical depths of growth with that of photography taken in 1999 reveal a general decrease in maximum depth of growth of approximately 0.5m in many areas. The most upriver areas of the York and Rappahannock, where SAV no longer are found, had SAV bed signatures to 1 m MLW, while downriver areas and regions along the Chesapeake Bay had maximum depths or 2 m or more in some areas. Losses of vegetation have been much more extensive in the Rappahannock than the York. In 1999, in the lower York River (YRKPH) approximately 23% of the historical SAV coverage remained while only 1% remained in the lower Rappahannock (RPPMH). Areas along the bay shoreline had the highest proportion of remaining beds with bay segments CB6PH and MOBPH exceeding 50% of historical coverage

Analysis of Histocial Distribution of SAV in the Eastern Shore Coastal Basins and Mid-Bay Island Complexes as Evidence of Historical Water Quality Conditions and a Restored Bay Ecosystem

Historical black and white format photographs at scales of approximately 1:20,000, dating from 1952 to 1956 were used to delineate the maximum coverage of SAV in the study region. Coverage of photography from decades before and after this period were found to generally to be of poorer quality and show less SAV presence. Photo-interpretation of the aerial photographs was accomplished using a head-up, on-screen digitizing system at fixed image scale of 1:12,000 and followed as closely as possible the methods currently used to delineate SAV beds throughout the Chesapeake Bay as well as the delineation of historical SAV coverage for other region. A total of 13,046 hectares of sub-tidal bottom in the Eastern Shore bay region between the tip of Fisherman’s Island to the Virginia-Maryland border, including the mid-bay island complex, were found to display SAV signatures. Of this historical total, approximately 10,451 ha, or 80%, were determined to be growing at depths shallower than 1 m MLW (Mean Low Water), 2,511 ha or 19% between 1 m and 2 m MLW, and 84 ha o

Radio sources in the Chandra Galactic Bulge Survey

We discuss radio sources in the Chandra Galactic Bulge Survey region. By cross-matching the X-ray sources in this field with the NRAO VLA Sky Survey archival data, we find 12 candidate matches. We present a classification scheme for radio/X-ray matches in surveys taken in or near the Galactic plane, taking into account other multiwavelength data. We show that none of the matches found here is likely to be due to coronal activity from normal stars because the radio to X-ray flux ratios are systematically too high. We show that one of the source could be a radio pulsar, and that one could be a planetary nebula, but that the bulk of the sources are likely to be background active galactic nuclei (AGN), with many confirmed through a variety of approaches. Several of the AGN are bright enough in the near-infrared (and presumably in the optical) to use as probes of the interstellar medium in the inner Galaxy

Identity and function of an essential nitrogen ligand of the nitrogenase cofactor biosynthesis protein NifB.

NifB is a radical S-adenosyl-L-methionine (SAM) enzyme that is essential for nitrogenase cofactor assembly. Previously, a nitrogen ligand was shown to be involved in coupling a pair of [Fe4S4] clusters (designated K1 and K2) concomitant with carbide insertion into an [Fe8S9C] cofactor core (designated L) on NifB. However, the identity and function of this ligand remain elusive. Here, we use combined mutagenesis and pulse electron paramagnetic resonance analyses to establish histidine-43 of Methanosarcina acetivorans NifB (MaNifB) as the nitrogen ligand for K1. Biochemical and continuous wave electron paramagnetic resonance data demonstrate the inability of MaNifB to serve as a source for cofactor maturation upon substitution of histidine-43 with alanine; whereas x-ray absorption spectroscopy/extended x-ray fine structure experiments further suggest formation of an intermediate that lacks the cofactor core arrangement in this MaNifB variant. These results point to dual functions of histidine-43 in structurally assisting the proper coupling between K1 and K2 and concurrently facilitating carbide formation via deprotonation of the initial carbon radical

3D-Laser-Scanning Technique Applied to Bulk Density Measurements of Apollo Lunar Samples

In order to better interpret gravimetric data from orbiters such as GRAIL and LRO to understand the subsurface composition and structure of the lunar crust, it is import to have a reliable database of the density and porosity of lunar materials. To this end, we have been surveying these physical properties in both lunar meteorites and Apollo lunar samples. To measure porosity, both grain density and bulk density are required. For bulk density, our group has historically utilized sub-mm bead immersion techniques extensively, though several factors have made this technique problematic for our work with Apollo samples. Samples allocated for measurement are often smaller than optimal for the technique, leading to large error bars. Also, for some samples we were required to use pure alumina beads instead of our usual glass beads. The alumina beads were subject to undesirable static effects, producing unreliable results. Other investigators have tested the use of 3d laser scanners on meteorites for measuring bulk volumes. Early work, though promising, was plagued with difficulties including poor response on dark or reflective surfaces, difficulty reproducing sharp edges, and large processing time for producing shape models. Due to progress in technology, however, laser scanners have improved considerably in recent years. We tested this technique on 27 lunar samples in the Apollo collection using a scanner at NASA Johnson Space Center. We found it to be reliable and more precise than beads, with the added benefit that it involves no direct contact with the sample, enabling the study of particularly friable samples for which bead immersion is not possibl

Systematics of Fission Barriers in Superheavy Elements

We investigate the systematics of fission barriers in superheavy elements in the range Z = 108-120 and N = 166-182. Results from two self-consistent models for nuclear structure, the relativistic mean-field (RMF) model as well as the non-relativistic Skyrme-Hartree-Fock approach are compared and discussed. We restrict ourselves to axially symmetric shapes, which provides an upper bound on static fission barriers. We benchmark the predictive power of the models examining the barriers and fission isomers of selected heavy actinide nuclei for which data are available. For both actinides and superheavy nuclei, the RMF model systematically predicts lower barriers than most Skyrme interactions. In particular the fission isomers are predicted too low by the RMF, which casts some doubt on recent predictions about superdeformed ground states of some superheavy nuclei. For the superheavy nuclei under investigation, fission barriers drop to small values around Z = 110, N = 180 and increase again for heavier systems. For most of the forces, there is no fission isomer for superheavy nuclei, as superdeformed states are in most cases found to be unstable with respect to octupole distortions.Comment: 17 pages REVTEX, 12 embedded eps figures. corrected abstrac

Passive sorting of asteroid material using solar radiation pressure

Understanding dust dynamics in asteroid environments is key for future science missions to asteroids and, in the long-term, also for asteroid exploitation. This paper proposes a novel way of manipulating asteroid material by means of solar radiation pressure (SRP). We envisage a method for passively sorting material as a function of its grain size where SRP is used as a passive in-situ ‘mass spec-trometer’. The analysis shows that this novel method allows an effective sorting of regolith material. This has immediate applications for sample return, and in-situ resource utilisation to separate different regolith particle sizes

Discovery of a high state AM CVn binary in the Galactic Bulge Survey

We report on the discovery of a hydrogen-deficient compact binary (CXOGBS J175107.6-294037) belonging to the AM CVn class in the Galactic Bulge Survey. Deep archival X-ray observations constrain the X-ray positional uncertainty of the source to 0.57 arcsec, and allow us to uniquely identify the optical and UV counterpart. Optical spectroscopic observations reveal the presence of broad, shallow He i absorption lines while no sign of hydrogen is present, consistent with a high state system. We present the optical lightcurve from Optical Gravitational Lensing Experiment monitoring, spanning 15 years. It shows no evidence for outbursts; variability is present at the 0.2 mag level on timescales ranging from hours to weeks. A modulation on a timescale of years is also observed. A Lomb-Scargle analysis of the optical lightcurves shows two significant periodicities at 22.90 and 23.22 min. Although the physical interpretation is uncertain, such timescales are in line with expectations for the orbital and superhump periods. We estimate the distance to the source to be between 0.5 - 1.1 kpc. Spectroscopic follow-up observations are required to establish the orbital period, and to determine whether this source can serve as a verification binary for the eLISA gravitational wave mission.Comment: Accepted for publication in MNRAS Letter