Modeling of Cold Compressor Pump Down Process

The Facility for Rare Isotope Beams (FRIB) will use a sub-atmospheric helium refrigeration process operating at 2 K (31 mbar) to support the superconducting radio frequency (SRF) Niobium structures (known as cavities), which are housed within ‘cryo-modules’. The cryomodules are large containers whose exterior forms a vacuum chamber that serves as a thermal shield. The cryo-modules, and the superconducting devices contained within, are used to accelerate charged particles. The accelerator at FRIB is comprised of three separate linear segments, separately or collectively, called a linear accelerator or ‘LINAC’. The helium used as the working fluid to cool the SRF Niobium cavities is supplied from a 4.5 K refrigerator, but the sub-atmospheric condition will be produced by ‘pumping-down’ the LINAC using cryogenic (cold) centrifugal compressors to remove mass, thus reducing the pressure within the SRF Niobium cavities. The initial condition of liquid helium before starting a ‘pump-down’ can range from a 2 K sub-cooled liquid to a saturated liquid at around 1 bar. These initial condition extremes will result in pump-down processes that are different. This variability of initial conditions increase the complexity of the overall process. As such, a process model can provide considerable insight into the best approach to use for a particular pump-down. This research has developed a simplified model of sub-atmospheric components downstream of the 4.5 K cold box. The initial condition of the helium within the SRF Niobium cavity is assumed to be a saturated mixture at near atmospheric pressure and remain a saturated mixture as the pump-down proceeds. The prime mover in this study is a single radial centrifugal cold compressor removing mass from the Niobium SRF cavities. A model for the return transfer line is incorporated to simulate pressure drop, heat in-leak, and mass accumulation of the sub-atmospheric helium returning from the LINAC back to the cold compressor. A counter flow heat exchanger is also a part of the model. This heat exchanger uses the sub-atmospheric helium stream leaving the SRF cavity to the cool the supply stream from the 4.5 K cold box. The model accounts for the non-constant thermal capacity rates present in this heat exchanger. The sum of the SRF cavities are modeled as a single dewar process, with a non-flowing two-phase mixture. The dewar process involves heat transfer to the liquid, and mass and energy depletion. The model is used to study the time to achieve a desired final within the dewar for a given set of system parameters. The component models are individually validated. The overall process can be extended and validated and compared to the FRIB process after such commissioning is complete. This model serves as the foundation for further process studies

Klauder's coherent states for the radial Coulomb problem in a uniformly curved space and their flat-space limits

First a set of coherent states a la Klauder is formally constructed for the Coulomb problem in a curved space of constant curvature. Then the flat-space limit is taken to reduce the set for the radial Coulomb problem to a set of hydrogen atom coherent states corresponding to both the discrete and the continuous portions of the spectrum for a fixed \ell sector.Comment: 10 pages, no figure

Using Remote Sensing and Inclined Drilling to Locate High-Yield Water Wells in the Eastern Kentucky Coal Field

The Kentucky Geological Survey has developed a method using lineament analysis in conjunction with inclinced exploration boreholes to identify subsurface fractures in the Eastern Kentucky Coal Field. Wells are then drilled to intersect these fractures, with the hope that the wells will be high yielding (greater than 30 gal/min). Lineaments were selected from Landsat TM imagery, side-looking airborne radar (SLAR) imagery, and two enhanced Landsat TM images for over 6,400 square miles of eastern Kentucky. Lineaments were replotted on 7.5-minute topographic quadrangle maps, and field reconnaissance identified locations where lineaments correlated with straight-line topographic features and fracture zones. Subsquent application of an inclined drilling technique at six sites has resulted in four production wells with yields ranging from 47 to 72 gal/min. All production wells intersected fractured rock. According to data from the Kentucky Groundwater Data Repository through October 2002, the yields of these four production wells are greater than the yields of 95 percent of the wells drilled in the Eastern Kentucky Coal Field. This study suggests that to minimize the chances of encountering salty groundwater, the best sites for high-yield wells are in first- or second-order stream valleys with fracture zones

Effects of Longwall Mining on Hydrogeology, Leslie County, Kentucky Part 1: Pre-Mining Conditions

An investigation of the hydrologic effects of longwall coal mining is in progress in the Eastern Kentucky Coal Field. The study area is located in a first-order watershed in southern Leslie County over Shamrock Coal Company\u27s Beech Fork Mine (Edd Fork Basin on the Helton 7.5-minute quadrangle). Longwall panels approximately 700 feet wide are separated by three-entry gateways 200 feet wide. The mine is operating in the Fire Clay coal (Hazard No. 4); overburden thickness ranges from 300 to 1,000 feet. Mining in the watershed began in late summer 1993. Undermining of the instrumented panel (panel 7) is anticipated for summer 1994. This report documents pre-mining hydrogeologic conditions. Three sites over panel 7 (ridge-top, valley-side, and valley-bottom settings) were selected for intensive monitoring. An NX core hole was drilled at each site to provide stratigraphic control for well installation, to evaluate fractures, to conduct pressure-injection tests, and to provide a borehole for installation of time domain reflectometry cables. A rain gage and flume were installed in the basin in summer 1992. Twenty-four monitoring wells, completed in July 1992, provide water-level and water-quality data on individual stratigraphic zones represented by the three well locations. Interpretation of pre-mining conditions was used to develop a conceptual model of ground-water flow in the study basin. Three ground-water zones were identified on the basis of hydraulic properties. The shallow-fracture zone, a highly conductive region parallel to the ground surface, extends to a depth of 60 to 70 feet. The elevation-head zone includes the ridge interior, mostly above drainage, where total head consists of elevation head only. The pressure head zone, largely below drainage, is the region where total head is the sum of elevation head and pressure head. Two fresh-water geochemical facies are also present. Shallow ground water is a calcium-magnesium-bicarbonatesulfate type, whereas ground water in the deeper regional system is sodium-bicarbonate type. Anticipated effects from longwall mining include a decrease in water levels in the pressure-head zone. Temporary decreases are expected in the shallow-fracture zone as newly created void spaces subsequently fill. The elevation-head zone should not be greatly affected because it is predicted to be in the aquiclude zone

On a biphononic origin of the 1125 cm^(-1) absorption band in cuprous oxide

We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1}) and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the cuprous oxide. A detailed analysis based on a comparison of the temperature dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active fundamental vibrations results in assignment of the former to a biphonon.Comment: 5 pages, 5 figures (to appear in Phys.Lett. A

Influence of deformation axis onto the length free path of screw dislocations in pure fcc materials

In this paper the influence of crystal's deformation axis orientation on formation of long, strong dislocation junctions which can be barriers that limit the shear zone has been studied. The probability of strong junctions formation has been obtained on the basis of interdislocation contact interactions model. The length of free path of screw dislocations has been defined for different orientations of crystal's deformation axis

Characterization of body weight and composition changes during the sophomore year of college

<p>Abstract</p> <p>Background</p> <p>Years spent in college represents a critical time for obesity development though little information is known regarding how body weight and composition changes beyond the first year of college. The aim of this study was to investigate changes in body weight and composition and the factors influencing those changes among sophomore females.</p> <p>Methods</p> <p>Body composition by dual energy X-ray absorptiometry was obtained in participants beginning during their freshman year and continued through their sophomore year.</p> <p>Results</p> <p>No difference was observed between sophomore year fall and spring visits for body weight (60.4 versus 60.6 kg) or fat mass (19.3 versus 18.7 kg). However, a significant (<it>P </it>≤ 0.05) decrease was observed for body fat (31.9 versus 30.9 %fat) and a significant increase was observed for fat-free mass (37.7 versus 38.4 kg). Participants living off campus significantly (<it>P </it>≤ 0.05) declined in body fat (33.0 versus 31.0 %fat) and fat mass (19.4 versus 18.2 kg) and increased in fat-free mass (36.1 versus 37.2 kg) with no differences in those living on campus.</p> <p>Conclusion</p> <p>No change in body weight was observed in females during their sophomore year. However, an increase in fat-free mass accompanied with a decrease in fat mass resulted in a decrease in body fat. Participants living off campus had favorable changes in their body composition by means of decreasing %fat and fat mass while increasing fat-free mass. Participants living on campus did not demonstrate these favorable changes.</p

Optical properties of (AlxGa1-x)(0.52)In0.48P at the crossover from a direct-gap to an indirect-gap semiconductor

The optical properties and the dynamics of excitons and the electron-hole plasma have been studied in disordered (AlxGa1−x)0.52In0.48P near to the direct-to-indirect band gap crossover. In particular we have investigated three epitaxial layers grown by solid-source molecular beam epitaxy with varying Al content x. Two of them have compositions in the immediate vicinity of the crossover point, the other is assigned to the indirect-gap regime. Both direct and indirect recombination processes contribute to the photon emission from the material. Since the relative importance of the different recombination processes depends strongly on temperature, excitation intensity, and excitation pulse duration, the processes can be identified by changing these parameters. As a result, we can determine the relative alignment of the conduction band minima and the distribution of the electrons among them. At high excitation levels the two crossover samples show stimulated emission at a photon energy of ∼2.29 eV, i.e., in the green spectral range. Using the variable stripe length method, we find an optical gain of up to ∼600 cm−1 at excitation levels of ∼350 kW/cm2.Stimulated emission involves direct recombination. This conclusion is reached from the experiments and from line-shape modeling, including a self-consistent treatment of populations and renormalization of the conduction band minima

Hydrogeology and Ground-Water Monitoring of Coal-Ash Disposal Sites in a Karst Terrane near Burnside, South-Central Kentucky

The effects of two coal-ash disposal facilities on ground-water quality at the John Sherman Cooper Power Plant, located in a karst region of south-central Kentucky, were evaluated using dye traces in springs. Springs were used for monitoring rather than wells, because in a karst terrane wells are unlikely to intercept individual conduits. A closed-out ash pond located over a conduit-flow system discharges to three springs in the upper Salem and Warsaw Formations along Lake Cumberland. Water discharging from these downgradient springs is similar to springs unaffected by ash-disposal facilities and is a calcium-bicarbonate type. No constituent concentrations found in this flow system exceeded maximum contaminant levels (MCL’s) or secondary maximum contaminant levels (SMCL’s) defined by the U.S. Environmental Protection Agency. An active ash pond is situated over another conduit-flow system that discharges to springs in the lower St. Louis Limestone. Water discharging from these downgradient springs is intermediate between the calciumbicarbonate type of the unaffected springs and the calcium-sulfate type of the active ash pond. No constituent concentrations found in this flow system exceeded MCL’s or SMCL’s. A third flow system associated with a coal stockpile adjacent to the plant is delineated by springs in the St. Louis Limestone and the Salem and Warsaw Formations that discharge calcium-sulfate type water. Chromium and cadmium concentrations exceeded MCL’s in at least one sample from this flow system. Iron, manganese, sulfate, and total dissolved solid concentrations exceeded SMCL’s in at least one sample. The closed-out ash pond appears to have no adverse impact on the water quality, nor does the active ash pond. In general, the coal stockpile has a more adverse impact on ground-water quality in the study area than the ash-disposal facilities