811 research outputs found
Vibrational and rotational analysis of the emission spectra of the arc jet flow
Applying atomic and molecular physics to the analysis of the radiation emitted from the arc jet flow provides a means for determining the species and excitation temperature of the constituents of the flow. A rotational and vibrational analysis of the spectra obtained from the radiation emitted in the shock layer and in the free stream of the jet flow was performed, specifically, in the shock layer bands of the First Negative Group of ionized molecular nitrogen and in the free stream of the gamma-system of nitric oxide
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Solar-powered alkali metal vapor lasers
The emission spectrum of the A(1 Sigma u +) - X(1 Sigma g +) band of Na2 has been recorded following excitation by monochromatic radiation in the region of X-A and X-B absorption. The spectral profile has been investigated as a function of excitation wavelength, sodium vapor temperature and buffer gas pressure. Additionally, gain measurements were made for the satellite of the A-X band as a function of the sodium vapor temperature and buffer gas pressure
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Alternate Site Selection Process for the Falls City, Texas, Umtra Project
This evaluation of possible alternate disposal sites for the Falls City Uranium Mill Tailings Remediation Act (UMTRA) site in southeastern Texas (fig. 1) was undertaken in response to the requirements promulgated by the U.S. Department of Energy (DOE) for the remediation of UMTRA sites in accordance with the Uranium Mill Tailings Radiation Control Act of 1978. Primary objectives of this report are to (1) describe the general geology and hydrology of the areas that have been identified as containing potential alternate tailings sites and (2) describe the systematic process utilized to identify those areas that may contain potential alternate tailings disposal sites.
The alternate site selection process employed for the Falls City site generally follows the format established in the 1988 UMTRA-DOE/AL Document 200129.0007 R-4 titled "Alternate Site Selection Process for UMTRA Project Sites." Implementation of the final step of the alternate site selection process as described in the 1988 UMTRA-DOE document would, however, require the collection of detailed, site-specific lithologic and hydrologic data, and this is beyond the scope of the present study.
The site selection process used in the current study comprises three distinct phases: (1) designation of the search region and identification of the geologic formations exposed within this region; (2) screening of geologic units within the search region based upon broad geologic characteristics; and (3) application of geologic, hydrologic, environmental, and engineering criteria to the formation(s) not excluded by phase two of the process in order to identify the less favorable outcrop areas within these formations.
Implementation of this three-phase process reduced the original 7,850 mi2 alternate site search region to a final region of interest of less than 30 mi2. The geologic and hydrologic characteristics of the final region of interest suggest that it may contain one or more alternate tailings storage sites.Bureau of Economic Geolog
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Hydrogeology and Hydrochemistry of the Falls City Uranium Mine Tailings Remedial Action Project, Karnes County, Texas
Oxidized uranium ore deposits were discovered in the Deweesville sandstone (also referred to as the Stones Switch; Bunker and MacKallor [1973]) in the Falls City region in the 1950s. Uranium was mined and milled in the small community of Deweesville by Susquehanna-Western, Inc. (SWI) from April 1961 to August 1973. Tailings composed of sediment residue from the sulfuric acid milling process and residual sulfuric acid solutions were disposed of in six ponds on the outcrop of the Deweesville, within the mined-out uranium pits in the Deweesville, and on the outcrop of the Conquista, creating a set of large tailings impoundments (figs. 1.1 and 1.2). From 1978 to 1982 Solution Engineering, Inc. (SEI) conducted a secondary recovery of the remaining uranium in the tailings piles by in situ leaching. In 1984, the ponds on top of two of the tailings piles were spray evaporated and a clay cap was placed over the piles to prevent additional percolation of water through the piles and into the underlying aquifers. Acidic tailings solutions have been recharging the underlying aquifers since initial tailings disposal and may still be leaking into these aquifers.
Several hydrogeologic investigations have been conducted to assess whether there has been groundwater contamination from the tailings. Early studies were conducted by Turk, Kehle and Associates (1976), and Ford, Bacon & Davis Utah (1978, 1981). Each of these studies included only minor investigations of the hydrogeology and hydrochemistry of the site and, in general, underestimated the extent of contamination from the site. Investigations conducted by the U.S. Department of Energy (DOE) from 1985 to 1991 have since revealed the true extent of contamination (U.S. Department of Energy, 1991).Bureau of Economic Geolog
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The Effects on 3D Printed Molds on Metal Castings
Additive manufacture of sand molds via binder jetting enables the casting of complex metal
geometries. Various material systems have been created for 3D printing of sand molds;
however, a formal study of the materials’ effects on cast products has not yet been conducted. In
this paper the authors investigate potential differences in material properties (microstructure,
porosity, mechanical strength) of A356 – T6 castings resulting from two different commercially
available 3D printing media. In addition, the material properties of cast products from traditional
“no-bake” silica sand is used as a basis for comparison of castings produced by the 3D printed
molds.Mechanical Engineerin
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Preliminary Evaluation of the Eagle Flat Region Hudspeth County, Texas
Preliminary evaluation of the Eagle Flat region, as designated by the Texas Legislature, indicates several areas that may have geologic and hydrologic conditions favorable for further evaluation as potential siting areas for the Texas low-level radioactive waste repository. This determination is based on a review of available data regarding surface drainage, thickness and character of alluvial fill, depth to groundwater, and apparent presence or absence of such features as late Cenozoic faults, fissures, known natural resources, and evidence of erosion. Some general siting areas have been identified that contain several sections that appear to have favorable characteristics. Examples of apparently favorable general siting areas are east of Yucca Mesa, south of Eagle Flat Mountain, and north of Little Hills. Our preliminary assessment is that, of the three areas cited above, the Yucca Mesa location should be given priority consideration. Initial flooding and drainage analysis indicates that the Yucca Mesa site includes sufficient surface areas unaffected by flooding. There are no known fissures or late Cenozoic faults. Depth to groundwater may be in excess of 500 ft, and the water quality may be poor. Shallow alluvium may be somewhat finer grained than at other settings, and the surface appears to be relatively stable and devoid of major incision by existing drainages. Although each of these characteristics needs to be investigated by further work, the most critical unanswered question is the thickness of alluvial fill. Available gravity data, including recent work by The University of Texas at El Paso, indicates that 100 ft or more of alluvial fill may be present in the area. Other areas may be present that are of equal or similar merit, but the preliminary analysis and available information suggest that the Yucca Mesa location apparently has the most favorable characteristics of those general siting areas identified currently. Smaller potential siting areas, generally about 400 to 800 acres in size, also may exist locally throughout the region where alluvial fill may be of sufficient thickness and drainage characteristics may be appropriate. These smaller potential siting areas would require additional site-specific evaluation of surface drainage characteristics before drill testing could be recommended. Any potential siting area is unique and would require site-specific evaluation activities to assess its suitability for characterization.Bureau of Economic Geolog
Novel Riboswitch Ligand Analogs as Selective Inhibitors of Guanine-Related Metabolic Pathways
Riboswitches are regulatory elements modulating gene expression in response to specific metabolite binding. It has been recently reported that riboswitch agonists may exhibit antimicrobial properties by binding to the riboswitch domain. Guanine riboswitches are involved in the regulation of transport and biosynthesis of purine metabolites, which are critical for the nucleotides cellular pool. Upon guanine binding, these riboswitches stabilize a 5′-untranslated mRNA structure that causes transcription attenuation of the downstream open reading frame. In principle, any agonistic compound targeting a guanine riboswitch could cause gene repression even when the cell is starved for guanine. Antibiotics binding to riboswitches provide novel antimicrobial compounds that can be rationally designed from riboswitch crystal structures. Using this, we have identified a pyrimidine compound (PC1) binding guanine riboswitches that shows bactericidal activity against a subgroup of bacterial species including well-known nosocomial pathogens. This selective bacterial killing is only achieved when guaA, a gene coding for a GMP synthetase, is under the control of the riboswitch. Among the bacterial strains tested, several clinical strains exhibiting multiple drug resistance were inhibited suggesting that PC1 targets a different metabolic pathway. As a proof of principle, we have used a mouse model to show a direct correlation between the administration of PC1 and the reduction of Staphylococcus aureus infection in mammary glands. This work establishes the possibility of using existing structural knowledge to design novel guanine riboswitch-targeting antibiotics as powerful and selective antimicrobial compounds. Particularly, the finding of this new guanine riboswitch target is crucial as community-acquired bacterial infections have recently started to emerge
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