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The frequency and damping of ion acoustic waves in collisional and collisionless two-species plasma
The dispersion properties of ion acoustic waves (IAW) are sensitive to the strength of ion-ion collisions in multi-species plasma in which the different species usually have differing charge-to-mass ratios. The modification of the frequency and damping of the fast and slow acoustic modes in a plasma composed of light (low Z) and heavy (high Z) ions is considered. In the fluid limit where the light ion scattering mean free path, {lambda}{sub th} is smaller than the acoustic wavelength, {lambda} = 2{pi}/k, the interspecies friction and heat flow carried by the light ions scattering from the heavy ions causes the damping. In the collisionless limit, k{lambda}{sub lh} >> 1, Landau damping by the light ions provides the dissipation. In the intermediate regime when k{lambda}{sub lh} {approx} 1, the damping is at least as large as the sum of the collisional and Landau damping.
Date:
July 15, 2004
Creator:
Berger, R L & Valeo, E J
Object Type:
Article
System:
The UNT Digital Library
Ground Truth Collection for Mining Explosions in Northern Fennoscandia and Russia
Analysis of data from our deployments and ground truth collection in northern Fennoscandia and northwestern Russia shows systematic variations in the P/S ratios of different types of explosions. The fact that this fundamental discriminant varies with firing practice is not in itself surprising - such variations probably contribute to the spread in P/S ratios normally observed for ripple-fired explosions. However, the nature of the variations is sometimes counterintuitive. Last year [Harris, 2003] we found that the P/S ratios of small compact underground explosions in mines of the Khibiny Massif are systematically lower than the P/S ratios of large ripple-fired surface explosions. We had anticipated that smaller underground shots would be more like single well-coupled explosions, thus having higher P/S ratios than large ripple-fired explosions. We now are performing a more extensive analysis of the data including compact and large ripple-fired explosions at additional mines and different types of explosions: small surface shots and large ripple-fired underground explosions. Our data are more complete as a result of an additional year of collection and allow a more complete sampling of the signals in range from the source. As of this writing we have measured Pn/Lg ratios on a larger number of explosions …
Date:
July 15, 2004
Creator:
Harris, D.; Ringdal, F.; Kremenetskaya, E.; Mykkeltveit, S.; Rock, D. E.; Schweitzer, J. et al.
Object Type:
Article
System:
The UNT Digital Library
Employing Thin HPGe Detectors for Gamma-Ray Imaging
We have evaluated a collimator-less gamma-ray imaging system, which is based on thin layers of double-sided strip HPGe detectors. The position of individual gamma-ray interactions will be deduced by the strip addresses and the Ge layers which fired. Therefore, high bandwidth pulse processing is not required as in thick Ge detectors. While the drawback of such a device is the increased number of electronics channels to be read out and processed, there are several advantages, which are particularly important for remote applications: the operational voltage can be greatly reduced to fully deplete the detector and no high bandwidth signal processing electronics is required to determine positions. Only a charge sensitive preamplifier, a slow pulse shaping amplifier, and a fast discriminator are required on a per channel basis in order to determine photon energy and interaction position in three dimensions. Therefore, the power consumption and circuit board real estate can be minimized. More importantly, since the high bandwidth signal shapes are not used to determine the depth position, lower energy signals can be processed. The processing of these lower energy signals increases the efficiency for the recovery of small angle scattering. Currently, we are studying systems consisting of up to ten …
Date:
April 15, 2002
Creator:
Vetter, K; Mihailescu, L; Ziock, K; Burks, M; Hull, E; Madden, N et al.
Object Type:
Article
System:
The UNT Digital Library
Simulations of Fluid Nitromethane Under Extreme Conditions
We report density functional molecular dynamics simulations to determine the early chemical events of hot (T = 3000 K) and dense (1.97 g/cm{sup 3}, V/V{sub 0} = 0.68) nitromethane (CH{sub 3}NO{sub 2}). The first step in the decomposition process is an intermolecular proton abstraction mechanism that leads to the formation of CH{sub 3}NO{sub 2}H and the aci ion H{sub 2}CNO{sub 2}{sup -}, in support of evidence from static high-pressure and shock experiments. An intramolecular hydrogen transfer that transforms nitromethane into the aci acid form, CH{sub 2}NO{sub 2}H, accompanies this event. This is the first confirmation of chemical reactivity with bond selectivity for an energetic material near the condition of fully reacted specimen. We also report the decomposition mechanism followed up to the formation of H{sub 2}O as the first stable product.
Date:
July 15, 2003
Creator:
Fried, L E; Reed, E J & Manaa, M R
Object Type:
Article
System:
The UNT Digital Library
Status of Models for Land Surface Spills of Nonaqueous Liquids
This report discusses models for describing the behavior of nonaqueous phase liquids (NAPLs) spilled over a land surface. This study addresses NAPLs that are not highly volatile and as such would not tend to exhibit a large evaporative mass loss before being mainly absorbed into the land. The study devises a NAPL spill model that can estimate the spreading area, which possibly would determine the liquid's detectability by remote sensing. The size of the surface region wetted by a particular NAPL spill clearly determines the opportunity for detecting it by remote sensing technology. Therefore, the main attribute of a model for treating NAPL spills on a land surface is the capability to predict spreading behavior. Clearly, how rapidly a spilled liquid disappears into the subsurface determines how far it may spread on the land surface. Thus, the modeling of both liquid spreading and infiltration into the subsurface are equally important to determining the extent of a spill.
Date:
August 15, 2003
Creator:
Simmons, Carver S. & Knell, Jason M.
Object Type:
Report
System:
The UNT Digital Library
LER Data Mining Pilot Study Final Report
LERs consist of a one page standard form with a standard header and free text data, followed by additional continuation pages of free text data. Currently this LER data is analyzed by first inputting the heading and text data manually into a categorical relational database. The data is then evaluated by enumeration of data in various categories and supplemented by review of individual LERs. This is labor intensive and makes it difficult to relate specific descriptive text to enumerated results. State of the art data mining and visualization technology exists that can eliminate the need for manual categorization, maintain the text relationships within each report, produce the same enumerated results currently available, and provide a tool to support potentially useful additional analysis of the informational content of LERs in a more timely and cost effective manner.
Date:
October 15, 2004
Creator:
Young, Jonathan; Zentner, Michael D. & McQuerry, Dennis L.
Object Type:
Report
System:
The UNT Digital Library
High-Pressure, Solid-State Experiments for NIF
In this report, we summarize our plan for using NIF for measuring solid-state deformation physics at very high pressures, P >> 1 Mbar. There are several key uncertainties, the strength and phase being two of them. The deformation mechanisms at high pressure and high strain rate are also uncertain. The state, as well as strength, of a material that has first been melted, then dynamically refrozen by high-pressure compression is very uncertain. There is no single facility that can address all of these issues at all parameter regimes of interest. Rather, a coordinated plan involving multiple laboratories and universities and multiple facilities will ultimately be needed. We present here our first thoughts for the NIF component of this effort. In Sec. I, we motivate the physics of this regime, and point out the uncertainties, then describe in Sec. II the development work that we have done over the last 5 years in this area. In Sec. III, we describe several NIF designs we have developed to probe solid-state deformation physics at very high pressures.
Date:
February 15, 2001
Creator:
Remington, B.; Belak, J.; Colvin, J.; Edwards, J.; Kalantar, D.; Lasinski, B. et al.
Object Type:
Report
System:
The UNT Digital Library
DYNAMIC APERTURE OPTIMIZATION FOR LOW EMITTANCE LIGHT SOURCES.
State of the art low emittance light source lattices, require small bend angle dipole magnets and strong quadrupoles. This in turn creates large chromaticity and small value of dispersion in the lattice. To counter the high linear chromaticity, strong sextupoles are required which limit the dynamic aperture. Traditional methods for expanding the dynamic aperture use harmonic sextupoles to counter the tune shift with amplitude. This has been successful up to now, but is non-deterministic and limited as the sextupole strength increases, driving higher order nonlinearities. We have taken a different approach that makes use of the tune flexibility of a TBA lattice to minimize the lowest order nonlinearities, freeing the harmonic sextupoles to counter the higher order nonlinearities. This procedure is being used to improve the nonlinear dynamics of the NSLS-II lattice.
Date:
May 15, 2005
Creator:
KRAMER, S. & BENGTSSON, J.
Object Type:
Article
System:
The UNT Digital Library
User's guide to fete: From ENDF/B-VI To ENDL
None
Date:
September 15, 2004
Creator:
Brown, D. A.; Hedstrom, G. & Hill, T.
Object Type:
Text
System:
The UNT Digital Library
Astrometry with the MACHO Data Archive
We present the preliminary results of our astrometric study of stellar motions along the lines of sight of the Magellanic Clouds and the Galactic bulge. We find that we are able to select stars with proper motions as small as 0.03 inch/yr from five years of PSF photometry due to the characteristic nature of the shapes the light curves of HFM stars. This shape arises from the proper motion of the object relative to the initial fixed centroid location where all photometry of the object is performed. By selecting such light curves and performing astrometry on candidate HPM stars we have discovered 154 new high proper motion (HPM) stars in 50{sup {open_square}}{sup o} from amongst the {approx} 55 million of stars observed by the MACHO project in these fields. These objects have proper motions as high as 0.5 inch/yr, luminosities ranging from V {approx} 13 to V {approx} 19, and V-R colours between 0.3 and 1.45.
Date:
October 15, 2000
Creator:
Drake, A. J.; Alcock, C.; Allsman, R.; Alves, D. R.; Axelrod, T. S.; Becker, A. C. et al.
Object Type:
Article
System:
The UNT Digital Library
Solution Sythesis Of Geranium Nanocrystals: Success And Open Challenges
We present a two-steps synthesis route that yields nanometer size crystalline germanium in the form of a black powder. It relies on high temperature decomposition of tetraethylgermane (TEG) in organic solvents. The presence of pure germanium with diamond structure is unambiguously attested by powder XRD measurements. Low resolution TEM indicates that the particles are between {approx}5 to 30 nm in size depending on the synthesis conditions. The as-synthesized Ge powders can be stored in air for months and no oxidation occurs. The Ge powders are sparingly soluble in conventional solvents because Ge nanocrystals are likely embedded in a matrix, composed mainly of C=C, C-C, and C-H bonds. The presence of residual organic by-products impedes probing of the optical properties of the dots. Also, we discuss drawbacks and open challenges in high temperature solution synthesis of Ge nanocrystals that could also be faced in the synthesis of Si nanocrystals. Overall, our results call for a cautious interpretation of reported optical properties of Ge and Si nanocrystals obtained by high temperature solution methods.
Date:
December 15, 2003
Creator:
Casula, M; Galli, G; Saw, C; Zaitseva, N; Gerion, D; van Buuren, T et al.
Object Type:
Article
System:
The UNT Digital Library
First Results of Reaction Propagation Rates in HMX at High Pressure
The authors have measured the reaction propagation rate (RPR) in weapons-grade, ultrafine octahydro-1,3,57-tetranitro-1,3,5,7-tetrazocine (HMX) powder in a diamond anvil cell over the pressure range 0.7-35 GPa. In order to have a cross-comparison of their experiments, they carried out a series of experiments on nitromethane (NM) up to 15 GPa. The results on NM are indistinguishable from previous measurements of Rice and Folz. In comparison to high-pressure, NM, the burn process for solid HMX is not spatially uniform.
Date:
June 15, 2001
Creator:
Farber, D L; Esposito, A; Zaug, J M & Aracne-Ruddle, C
Object Type:
Article
System:
The UNT Digital Library
2003 Initial Assessments of Closure for the C Tank Farm Field Investigation Report (FIR):Numerical Simulations
In support of CH2M HILL Hanford Group, Inc.'s (CHG) preparation of a Field Investigative Report (FIR) for the closure of the Hanford Site Single-Shell Tank (SST) Waste Management Area (WMA) tank farms, a set of numerical simulations of flow and solute transport was executed to predict the performance of surface barriers for reducing long-term risks from potential groundwater contamination at the C Farm WMA. This report documents the simulation of 14 cases (and two verification cases) involving two-dimensional cross sections through the C Farm WMA tanks C-103 – C-112. Utilizing a unit release scenario at Tank C-112, four different types of leaks were simulated. These simulations assessed the impact of leakage during retrieval, past leaks, and tank residual wastes and tank ancillary equipment following closure activities. . Two transported solutes were considered: uranium-238 (U-238) and technetium-99 (Tc-99). To evaluate the impact of sorption to the subsurface materials, six different retardation coefficients were simulated for U-238. Overall, simulations results for the C Farm WMA showed that only a small fraction of the U-238 with retardation factors greater than 0.6 migrated from the vadose zone in all of the cases. For the conservative solute, Tc-99, results showed that the simulations investigating leakages …
Date:
July 15, 2003
Creator:
Zhang, Z. F.; Freedman, Vicky L. & White, Mark D.
Object Type:
Report
System:
The UNT Digital Library
Vibrational and intruder structures in 116Cd: a conundrum
Decay properties of multiphonon quadropole vibrational states and intruder structures in {sup 116}Cd have been examined with the (n,n'{gamma}) reaction. Gamma-ray excitation functions, angular distributions and {gamma}-{gamma} coincidences have been measured. Lifetimes of many levels were determined with the Doppler-shift attenuation method, exposing the degree of collectivity of the intruder structure and the three-phonon states. In combination with other recent results, this new information reveals that the intruder picture is well supported in the Cd nuclei. However, a conundrum not present in the lighter cadmium nuclei emerges in {sup 116}Cd; strong configuration mixing between intruder and multiphonon vibrational excitations cannot describe the observed decays of the lowest 0{sup +} excited states.
Date:
October 15, 2003
Creator:
M., K; N, W; PE, G; J, J & SW, Y
Object Type:
Article
System:
The UNT Digital Library
Ground Motion Simulations To Investigate The Feasibility Of Space-Based Seismometry
This report describes elastic finite-difference simulations of ground motion resulting from explosions and earthquakes for use in a Laboratory Directed Research and Development Feasibility Study (LDRD-FS). The results will be used to as input into further simulations of various spaced-based remote-sensing techniques, such as laser ranging and radar systems. The ground motion calculations involve two types of sources: shallow fully-coupled explosions at relatively shallow depth (1 km) and strike-slip earthquakes at 5 km depth. The event sizes vary from M{sub W} 3.3 to 5.5 to capture a broad range of possible surface motion. The simulations are presented as densely sampled full-field images of ground velocity and displacement as well as peak ground motion versus distance from the event. The resulting peak displacements in the near source region (0-40 km) range from centimeters (10{sup -2} m) for the largest events at short ranges to microns (10{sup -6} m) for the smallest events at longer ranges. Peak velocities range from centimeters/second (10{sup -2} m/s) to micron/second (10{sup -6} m/s).
Date:
September 15, 2004
Creator:
Rodgers, A
Object Type:
Report
System:
The UNT Digital Library
RF photoinjector development for a short-pulse, hard x-ray Thomson scattering source
An important motivation in the development of the next generation x-ray light sources is to achieve picosecond and sub-ps pulses of hard x-rays for dynamic studies of a variety of physical, chemical and biological processes. Present hard x-ray sources are either pulse-width or intensity limited, which allows ps-scale temporal resolution only for signal averaging of highly repetitive processes. A much faster and brighter hard x-ray source is being developed at LLNL, based on Thomson scattering of fs-laser pulses by a relativistic electron beam, which will enable x-ray characterization of the transient structure of a sample in a single shot. Experimental and diagnostic techniques relevant to the development of next generation sources including the Linac Coherent Light Source can be tested with the Thomson scattering hard x-ray source. This source will combine an RF photoinjector with a 100 MeV S-band linac. The photoinjector and linac also provide an ideal test-bed for examining space-charge induced emittance growth effects. A program of beam dynamics and diagnostic experiments are planned in parallel with Thomson source development. Our experimental progress and future plans will be discussed.
Date:
August 15, 2000
Creator:
Le Sage, G P; Anderson, S G; Cowan, T E; Crane, J K; Ditmire, T & Rosenzweig, J B
Object Type:
Article
System:
The UNT Digital Library
Computational Flow Modeling of a Simplified Integrated Tractor-Trailer Geometry
For several years, Sandia National Laboratories and Lawrence Livermore National Laboratory have been part of a consortium funded by the Department of Energy to improve fuel efficiency of heavy vehicles such as Class 8 trucks through aerodynamic drag reduction. The objective of this work is to demonstrate the feasibility of using the steady Reynolds-Averaged Navier-Stokes (RANS) approach to predict the flow field around heavy vehicles, with special emphasis on the base region of the trailer, and to compute the aerodynamic forces. In particular, Sandia's computational fluid dynamics code, SACCARA, was used to simulate the flow on a simplified model of a tractor-trailer vehicle. The results are presented and compared with NASA Ames experimental data to assess the predictive capability of RANS to model the flow field and predict the aerodynamic forces.
Date:
September 15, 2003
Creator:
Salari, K & McWherter-Payne, M
Object Type:
Report
System:
The UNT Digital Library
Transmutation of radioactive nuclear waste
Lack of a safe disposal method for radioactive nuclear waste (RNW) is a problem of staggering proportion and impact. A typical LWR fission reactor will produce the following RNW in one year: minor actinides (i.e. {sup 237}Np, {sup 242-243}Am, {sup 243-245}Cm) {approx}40 kg, long-lived fission products (i.e, {sup 99}Tc, {sup 93}Zr, {sup 129}I, {sup 135}Cs) {approx}80 kg, short lived fission products (e.g. {sup 137}Cs, {sup 90}Sr) {approx}50kg and plutonium {approx}280 kg. The total RNW produced by France and Canada amounts to hundreds of metric tonnes per year. Obtaining a uniform policy dealing with RNW has been blocked by the desire on one hand to harvest the energy stored in plutonium to benefit society and on the other hand the need to assure that the stockpile of plutonium will not be channeled into future nuclear weapons. In the meantime, the quantity and handling of these materials represents a potential health hazard to the world's population and particularly to people in the vicinity of temporary storage facilities. In the U.S., societal awareness of the hazards associated with RNW has effectively delayed development of U.S. nuclear fission reactors during the past decade. As a result the U.S. does not benefit from the large …
Date:
March 15, 2000
Creator:
Toor, A & Buck, R
Object Type:
Report
System:
The UNT Digital Library
Gas Lasers for Strong-Field Applications.
Atomic-, molecular- and excimer-gas lasers employ variety of pumping schemes including electric discharge, optical, or chemical reactions and cover a broad spectral range from UV to far-IR. Several types of gas lasers can produce multi-kilojoule pulses and kilowatts of average power. Among them, excimer- and high-pressure molecular lasers have sufficient bandwidth for generating pico- and femtosecond pulses. Projects are underway and prospects are opening up to bring ultrafast gas laser technology to the front lines of advanced accelerator applications.
Date:
September 15, 2004
Creator:
Pogorelsky, I. V.
Object Type:
Article
System:
The UNT Digital Library
First Quarter Hanford Seismic Report for Fiscal year 2003
This reports earthqaukes that occurred during the first quarter of FY03.
Date:
January 15, 2003
Creator:
Hartshorn, Donald C.; Reidel, Steve P. & Rohay, Alan C.
Object Type:
Report
System:
The UNT Digital Library
IMPACTS OF SOURCE TERM HETEROGENEITIES ON WATER PATHWAY DOSE.
Radioactive sealed sources are used extensively throughout the world in different field and various activities such as medicine, agriculture, industry, research, education military applications, as well as nuclear facilities. The International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation sources [1] defines a sealed source as ''radioactive material that is (a) permanently sealed in capsule or (b) closely bounded and in a solid form. The capsule or material of sealed source shall be strong enough to maintain remain leak free under the conditions of use and wear for which the source was designed, also under foreseeable mishaps''. When a radioactive sealed source is no longer needed, or becomes unfit for the intended application it is considered spent. A spent sealed source is not necessarily a waste because it can be used in other applications. If for any technical or economic reason (decay, obsolete equipment and technique, worn out equipment) no further use is foreseen, the spent sealed source is considered spent and becomes radioactive waste [2] [3]. In addition, a source may be taken out of service temporarily or indefinitely. In this case the source is out of used (''disused'') but not considered spent …
Date:
September 15, 2004
Creator:
SULLIVAN, T.; GUSKOV, A.; POSKAS, P.; RUPERTI, N.; HANUSIK, V. & AL., ET
Object Type:
Report
System:
The UNT Digital Library
STRUCTURE FUNCTION ANALYSIS OF LONG-TERM QUASAR VARIABILITY
In our second paper on long-term quasar variability, we employ a much larger database of quasars than in de Vries, Becker & White. This expanded sample, containing 35,165 quasars from the Sloan Digital Sky Survey Data Release 2, and 6,413 additional quasars in the same area of the sky taken from the 2dF QSO Redshift Survey, allows us to significantly improve on our earlier conclusions. As before, all the historic quasar photometry has been calibrated onto the SDSS scale by using large numbers of calibration stars around each quasar position. We find the following: (1) the outbursts have an asymmetric light-curve profile, with a fast-rise, slow-decline shape; this argues against a scenario in which micro-lensing events along the line-of-sight to the quasars are dominating the long-term variations in quasars; (2) there is no turnover in the Structure Function of the quasars up to time-scales of {approx}40 years, and the increase in variability with increasing time-lags is monotonic and constant; and consequently, (3) there is not a single preferred characteristic outburst time-scale for the quasars, but most likely a continuum of outburst time-scales, (4) the magnitude of the quasar variability is a function of wavelength: variability increases toward the blue part …
Date:
November 15, 2004
Creator:
de Vries, W; Becker, R; White, R & Loomis, C
Object Type:
Article
System:
The UNT Digital Library
Convex Crystal X-ray Spectrometer for Laser Plasma Experiments
Measuring time and space-resolved spectra is important for understanding Hohlraum and Halfraum plasmas. Experiments at the OMEGA laser have used the Nova TSPEC which was not optimized for the OMEGA diagnostic space envelope or for the needed spectroscopic coverage and resolution. An improved multipurpose spectrometer snout, the MSPEC, has been constructed and fielded on OMEGA. The MSPEC provides the maximal internal volume for mounting crystals without any beam interferences at either 2x or 3x magnification. The RAP crystal is in a convex mounting geometry bent to a 20 cm radius of curvature. The spectral resolution, E/dE, is about 200 at 2.5 keV. The spectral coverage is 2 to 4.5 keV. The MSPEC can record four separate spectra on the framing camera at time intervals of up to several ns. The spectrometer design and initial field-test performance will be presented and compared to that of the TSPEC. Work supported by U. S. DoE/UC LLNL contract W-7405-ENG-48
Date:
April 15, 2004
Creator:
May, M.; Heeter, R. & Emig, J.
Object Type:
Article
System:
The UNT Digital Library
Summary of Synthetic Lap Polishing Experiments at LLNL, FY95
The purpose of this research was to support the optics finishing development work for the NIF, the National Ignition Facility. One of the major expenses for the construction of NIF is the cost of finishing of the large aperture optics. One way to significantly reduce the cost of the project is to develop processes to reduce the amount of time necessary to polish the more than 3,000 amplifier slabs. These slabs are rectangular with an aspect ratio of more than twenty to one and are made of a very temperature sensitive glass, Nd doped phosphate laser glass. As a result of this effort, we could potentially reduce the time necessary to polish each surface of an amplifier from 20-30 hours of run time to under an hour to achieve the same removal and still maintain a flatness of between one to three waves concave figure. We also feel confident that we can polish rectangular thermally sensitive glass flat by use of temperature control of the polishing platen, pad curvature, slurry concentration with temperature control, pad rotation, and pressure; although further, larger scale experiments are necessary to gain sufficient confidence that such a procedure could be successfully fielded.
Date:
October 15, 2001
Creator:
Nichols, M A
Object Type:
Article
System:
The UNT Digital Library