Latest content added for UNT Digital Library Partner: UNT Libraries Government Documents Departmenthttp://digital.library.unt.edu/explore/partners/UNTGD/browse/?start=40&display=list2016-09-27T01:39:22-05:00UNT LibrariesThis is a custom feed for browsing UNT Digital Library Partner: UNT Libraries Government Documents Department0.351 micron Laser Beam propagation in High-temperature Plasmas2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc897677/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc897677/"><img alt="0.351 micron Laser Beam propagation in High-temperature Plasmas" title="0.351 micron Laser Beam propagation in High-temperature Plasmas" src="http://digital.library.unt.edu/ark:/67531/metadc897677/small/"/></a></p><p>A study of the laser-plasma interaction processes have been performed in plasmas that are created to emulate the plasma conditions in indirect drive inertial confinement fusion targets. The plasma emulator is produced in a gas-filled hohlraum; a blue 351-nm laser beam propagates along the axis of the hohlraum interacting with a high-temperature (T{sub e} = 3.5 keV), dense (n{sub e} = 5 x 10{sup 20}cm{sup -3}), long-scale length (L {approx} 2 mm) plasma. Experiments at these conditions have demonstrated that the interaction beam produces less than 1% total backscatter resulting in transmission greater than 90% for laser intensities less than I < 2 x 10{sup 15} W-cm{sup -2}. The bulk plasma conditions have been independently characterized using Thomson scattering where the peak electron temperatures are shown to scale with the hohlraum heater beam energy in the range from 2 keV to 3.5 keV. This feature has allowed us to determine the thresholds for both backscattering and filamentation instabilities; the former measured with absolutely calibrated full aperture backscatter and near backscatter diagnostics and the latter with a transmitted beam diagnostics. A plasma length scaling is also investigated extending our measurements to 4-mm long high-temperature plasmas. At intensities I < 5 x 10{sup 14} W-cm{sup -2}, greater than 80% of the energy in the laser is transmitted through a 5-mm long, high-temperature (T{sub e} > 2.5 keV) high-density (n{sub e} = 5 x 10{sup 20} w-cm{sup -3}) plasma. Comparing the experimental results with detailed gain calculations for the onset of significant laser scattering processes shows a stimulated Brillouin scattering threshold (R=10%) for a linear gain of 15; these high temperature, low density experiments produce plasma conditions comparable to those along the outer beams in ignition hohlraum designs. By increasing the gas fill density (n{sub e} = 10{sup 21} cm{sup -3}) in these targets, the inner beam ignition hohlraum conditions are accessed. In this case, stimulated Raman scattering dominates the backscattering processes and we show that scattering is small for gains less than 20 which can be achieved through proper choice of the laser beam intensity. The first three-dimensional (3D) simulations of a high power 0.351 {micro}m laser beam propagating through a high-temperature hohlraum plasma are also reported. We show that 3D linear kinetic modeling of Stimulated Brillouin scattering reproduces quantitatively the experimental measurements, provided it is coupled to detailed hydrodynamics simulation and a realistic description of the laser beam from its millimeter-size envelop down to the micron scale speckles. These simulations accurately predict the strong reduction of SBS measured when polarization smoothing is used.</p>Calibration and Characterization of Single Photon Counting Cameras for Short-Pulse Laser Experiments2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc900813/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc900813/"><img alt="Calibration and Characterization of Single Photon Counting Cameras for Short-Pulse Laser Experiments" title="Calibration and Characterization of Single Photon Counting Cameras for Short-Pulse Laser Experiments" src="http://digital.library.unt.edu/ark:/67531/metadc900813/small/"/></a></p><p>The photon counting efficiency of various CCD based cameras was studied as a function of x-ray energy and exposure. A pair of Spectral Instruments Model 800 CCD cameras fitted with 16 {micro}m thick back-illuminated CCDs were calibrated at low x-ray energy using two well established histogram methods, a standard pixel for pixel histogram and the single pixel event histogram method. In addition, two new thick substrate CCDs were evaluated for use at high energy. One was a commercially available Princeton Instruments LCX1300 deep depletion CCD camera while the other was a custom designed 650 {micro}m thick partially depleted CCD fitted to a SI 800 camera body. It is shown that at high x-ray energy, only a pixel-summing algorithm was able to derive spectral data due to the spreading of x-ray events over many pixels in the thicker substrate CCDs. This paper will describe the different algorithms used to extract spectra and the absolute detection efficiencies using these algorithms. These detectors will be very useful to detect high-energy x-ray photons from high-intensity short pulse laser interactions.</p>Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc902752/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc902752/"><img alt="Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments" title="Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments" src="http://digital.library.unt.edu/ark:/67531/metadc902752/small/"/></a></p><p>Establishing safe handling limits for explosives in elevated temperature environments is a difficult problem that often requires extensive simulation. The largest influence on predicting thermal cookoff safety lies in the chemical kinetic model used in these simulations, and these kinetic model reaction sequences often contain multiple steps. Several small-scale cookoff experiments, notably Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), One-Dimensional Time-to-Explosion (ODTX), and the Scaled Thermal Explosion (STEX) have been performed on various explosives to aid in cookoff behavior determination. Past work has used a single test from this group to create a cookoff model, which does not guarantee agreement with the other experiments. In this study, we update the kinetic parameters of an existing model for the common explosive 2,4,6-Trinitrotoluene (TNT) using DSC and ODTX experimental data at the same time by minimizing a global Figure of Merit based on hydrodynamic simulated data. We then show that the new kinetic model maintains STEX agreement, reduces DSC agreement, and improves ODTX and TGA agreement when compared to the original model. In addition, we describe a means to use implicit hydrodynamic simulations of DSC experiments to develop a reaction model for TNT melting.</p>Calibration of symmetric and non-symmetric errors for interferometry of ultra-precise imaging systems2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc901358/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc901358/"><img alt="Calibration of symmetric and non-symmetric errors for interferometry of ultra-precise imaging systems" title="Calibration of symmetric and non-symmetric errors for interferometry of ultra-precise imaging systems" src="http://digital.library.unt.edu/ark:/67531/metadc901358/small/"/></a></p><p>The azimuthal Zernike coefficients for shells of Zernike functions with shell numbers n<N may be determined by making measurements at N equally spaced rotational positions. However, these measurements do not determine the coefficients of any of the purely radial Zernike functions. Label the circle that the azimuthal Zernikes are measured in as circle A. Suppose that the azimuthal Zernike coefficients for n<N are also measured in a smaller circle B which is inside circle A but offset so that it is tangent to circle A and so that it has the center of circle A just inside its circular boundary. The diameter of circle B is thus only slightly larger than half the diameter of circle A. From these two sets of measurements, all the Zernike coefficients may be determined for n<N. However, there are usually unknown small rigid body motions of the optic between measurements. Then all the Zernike coefficients for n<N except for piston, tilts, and focus may be determined. We describe the exact mathematical algorithm that does this and describe an interferometer which measures the complete wavefront from pinholes in pinhole aligners. These pinhole aligners are self-contained units which include a fiber optic, focusing optics, and a 'pinhole mirror'. These pinhole aligners can then be used in another interferometer so that its errors would then be known. Physically, the measurements in circles A and B are accomplished by rotating each pinhole aligner about an aligned axis, then about an oblique axis. Absolute measurement accuracies better than 0.2 nm were achieved.</p>CAMS/LLNL Ion Source Efficiency Revisited2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc895016/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc895016/"><img alt="CAMS/LLNL Ion Source Efficiency Revisited" title="CAMS/LLNL Ion Source Efficiency Revisited" src="http://digital.library.unt.edu/ark:/67531/metadc895016/small/"/></a></p><p>Abstract not provided</p>Cancellation of spin and orbital magnetic moments in (delta)-Pu: theory2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc895687/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc895687/"><img alt="Cancellation of spin and orbital magnetic moments in (delta)-Pu: theory" title="Cancellation of spin and orbital magnetic moments in (delta)-Pu: theory" src="http://digital.library.unt.edu/ark:/67531/metadc895687/small/"/></a></p><p>Density functional theory (DFT), in conjunction with the fixed-spin-moment (FSM) method, spin-orbit coupling (SO), and orbital polarization (OP), is shown to retain key features of the conventional DFT treatment of {delta}-Pu while at the same time not producing the substantial net magnetic moments commonly predicted by this theory. It is shown that when a small adjustment of the spin moment (less than 20%) is allowed, a complete spin- and orbital-moment cancellation occurs which results in a zero net magnetic moment in {delta}-Pu. This minor modification, accomplished by the FSM method, is shown to have a very small effect on the calculated total energy as well as the electron density-of-states (DOS). The photoemission spectra (PES), obtained from the DOS of the present model, compares equal or better to measured spectra, than that of two other recent non-magnetic models for {delta}-Pu.</p>A Cartesian embedded boundary method for hyperbolic conservation laws2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc902656/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc902656/"><img alt="A Cartesian embedded boundary method for hyperbolic conservation laws" title="A Cartesian embedded boundary method for hyperbolic conservation laws" src="http://digital.library.unt.edu/ark:/67531/metadc902656/small/"/></a></p><p>The authors develop an embedded boundary finite difference technique for solving the compressible two- or three-dimensional Euler equations in complex geometries on a Cartesian grid. The method is second order accurate with an explicit time step determined by the grid size away from the boundary. Slope limiters are used on the embedded boundary to avoid non-physical oscillations near shock waves. They show computed examples of supersonic flow past a cylinder and compare with results computed on a body fitted grid. Furthermore, they discuss the implementation of the method for thin geometries, and show computed examples of transonic flow past an airfoil.</p>Ce-doped single crystal and ceramic garnets for �y ray detection2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc900252/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc900252/"><img alt="Ce-doped single crystal and ceramic garnets for �y ray detection" title="Ce-doped single crystal and ceramic garnets for �y ray detection" src="http://digital.library.unt.edu/ark:/67531/metadc900252/small/"/></a></p><p>Ceramic and single crystal Lutetium Aluminum Garnet scintillators exhibit energy resolution with bialkali photomultiplier tube detection as good as 8.6% at 662 keV. Ceramic fabrication allows production of garnets that cannot easily be grown as single crystals, such as Gadolinium Aluminum Garnet and Terbium Aluminum Garnet. Measured scintillation light yields of Cerium-doped ceramic garnets indicate prospects for high energy resolution.</p>A Cell-Based Approach for the Biosynthesis/Screening of Cyclic Peptide Libraries against Bacterial Toxins2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc893994/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc893994/"><img alt="A Cell-Based Approach for the Biosynthesis/Screening of Cyclic Peptide Libraries against Bacterial Toxins" title="A Cell-Based Approach for the Biosynthesis/Screening of Cyclic Peptide Libraries against Bacterial Toxins" src="http://digital.library.unt.edu/ark:/67531/metadc893994/small/"/></a></p><p>Available methods for developing and screening small drug-like molecules able to knockout toxins or pathogenic microorganisms have some limitations. In order to be useful, these new methods must provide high-throughput analysis and identify specific binders in a short period of time. To meet this need, we are developing an approach that uses living cells to generate libraries of small biomolecules, which are then screened inside the cell for activity. Our group is using this new, combined approach to find highly specific ligands capable of disabling anthrax Lethal Factor (LF) as proof of principle. Key to our approach is the development of a method for the biosynthesis of libraries of cyclic peptides, and an efficient screening process that can be carried out inside the cell.</p>The Challenges to Coupling Dynamic Geospatial Models2016-09-27T01:39:22-05:00http://digital.library.unt.edu/ark:/67531/metadc896439/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc896439/"><img alt="The Challenges to Coupling Dynamic Geospatial Models" title="The Challenges to Coupling Dynamic Geospatial Models" src="http://digital.library.unt.edu/ark:/67531/metadc896439/small/"/></a></p><p>Many applications of modeling spatial dynamic systems focus on a single system and a single process, ignoring the geographic and systemic context of the processes being modeled. A solution to this problem is the coupled modeling of spatial dynamic systems. Coupled modeling is challenging for both technical reasons, as well as conceptual reasons. This paper explores the benefits and challenges to coupling or linking spatial dynamic models, from loose coupling, where information transfer between models is done by hand, to tight coupling, where two (or more) models are merged as one. To illustrate the challenges, a coupled model of Urbanization and Wildfire Risk is presented. This model, called Vesta, was applied to the Santa Barbara, California region (using real geospatial data), where Urbanization and Wildfires occur and recur, respectively. The preliminary results of the model coupling illustrate that coupled modeling can lead to insight into the consequences of processes acting on their own.</p>