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Stability of Galactic Gaseous Disks and the Formation of Massive Clusters

Description: We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can… more
Date: August 21, 2008
Creator: Escala, Andres & Larson, Richard B.
Partner: UNT Libraries Government Documents Department
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Test of weak and strong factorization in nucleus-nucleuscollisions atseveral hundred MeV/nucleon

Description: Total and partial charge-changing cross sections have been measured for argon projectiles at 400 MeV/nucleon in carbon, aluminum, copper, tin and lead targets; cross sections for hydrogen were also obtained, using a polyethylene target. The validity of weak and strong factorization properties has been investigated for partial charge-changing cross sections; preliminary cross section values obtained for carbon, neon and silicon at 290 and 400 MeV/nucleon and iron at 400 MeV/nucleon, in carbon, a… more
Date: June 21, 2006
Creator: La Tessa, Chiara; Sihver, Lembit; Zeitlin, Cary; Miller, Jack; Guetersloh, Stephen; Heilbronn, Lawrence et al.
Partner: UNT Libraries Government Documents Department
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Fluorine for Hydrogen Exchange in the Hydrofluorobenzene Derivatives C6HxF(6-x), where x = 2, 3, 4 and 5 by Monomeric [1,2,4-(Me3C)3C5H2]2CeH; The Solid State Isomerization of [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,5-C6HF4) to [1,2,4-(Me3C)3C5H2]2Ce(2,3,4,6-C6HF4)

Description: The reaction between monomeric bis(1,2,4-tri-t-butylcyclopentadienyl)cerium hydride, Cp'2CeH, and several hydrofluorobenzene derivatives is described. The aryl derivatives that are the primary products, Cp'2Ce(C6H5-xFx) where x = 1,2,3,4, are thermally stable enough to be isolated in only two cases, since all of them decompose at different rates to Cp'2CeF and a fluorobenzyne; the latter is trapped by either solvent when C6D6 is used or by a Cp'H ring when C6D12 is the solvent. … more
Date: April 21, 2008
Creator: Andersen, Richard; Werkema, Evan L. & Andersen, Richard A.
Partner: UNT Libraries Government Documents Department
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Effects of vibrational motion on core-level spectra of prototype organic molecules

Description: A computational approach is presented for prediction and interpretation of core-level spectra of complex molecules. Applications are presented for several isolated organic molecules, sampling a range of chemical bonding and structural motifs. Comparison with gas phase measurements indicate that spectral lineshapes are accurately reproduced both above and below the ionization potential, without resort to ad hoc broadening. Agreement with experiment is significantly improved upon inclusion of vib… more
Date: August 21, 2008
Creator: Uejio, Janel S.; Schwartz, Craig P.; Saykally, Richard J. & Prendergast, David
Partner: UNT Libraries Government Documents Department
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Bacillus atrophaeus Outer Spore Coat Assembly and Ultrastructure

Description: Our previous atomic force microscopy (AFM) studies successfully visualized native Bacillus atrophaeus spore coat ultrastructure and surface morphology. We have shown that the outer spore coat surface is formed by a crystalline array of {approx}11 nm thick rodlets, having a periodicity of {approx}8 nm. We present here further AFM ultrastructural investigations of air-dried and fully hydrated spore surface architecture. In the rodlet layer, planar and point defects, as well as domain boundaries, … more
Date: November 21, 2005
Creator: Plomp, M; Leighton, T J; Wheeler, K E; Pitesky, M E & Malkin, A J
Partner: UNT Libraries Government Documents Department
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Scaling, Microstructure and Dynamic Fracture

Description: The relationship between pullback velocity and impact velocity is studied for different microstructures in Cu. A size distribution of potential nucleation sites is derived under the conditions of an applied stochastic stress field. The size distribution depends on flow stress leading to a connection between the plastic flow appropriate to a given microstructure and nucleation rate. The pullback velocity in turn depends on the nucleation rate resulting in a prediction for the relationship betwee… more
Date: December 21, 2005
Creator: Minich, R W; Kumar, M; Schwarz, A & Cazamias, J
Partner: UNT Libraries Government Documents Department
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SOLVING THE STAND-OFF PROBLEM FOR MAGNETIZED TARGET FUSION: PLASMA STREAMS AS DISPOSABLE ELECTRODES, PLUS A LOCAL SPHERICAL BLANKET

Description: In a fusion reactor based on the Magnetized Target Fusion approach, the permanent power supply has to deliver currents up to a few mega-amperes to the target dropped into the reaction chamber. All the structures situated around the target will be destroyed after every pulse and have to be replaced at a frequency of 1 to 10 Hz. In this paper, an approach based on the use of spherical blanket surrounding the target, and pulsed plasma electrodes connecting the target to the power supply, is discus… more
Date: March 21, 2006
Creator: Ryutov, D. D. & Thio, Y. F.
Partner: UNT Libraries Government Documents Department
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Synthesis and magnetic properties of cerium macrocyclic complexeswith tmtaaH2, tetramethyldibenzotetraaza[14]-annulene

Description: The complexes [Ce(tmtaa)2], [Ce(tmtaa)(tmtaaH)]and[Ce2(tmtaa)3(thf)2]are obtained from Ce[N(SiMe3)2]3 and tmtaaH2, themacrocyclic ligand 6,8,15,17-tetramethyldibenzotetraaza[14]-annulene,depending on the stoichiometry, solvent and temperature. The crystalstructure of Ce(tmtaa)2 is isostructural with Zr(tmtaa)2, howevermagnetic susceptibility measurements in the range 5-300 K show thatCe(tmtaa)2 is not diamagnetic, but is a temperature-independentparamagnet (TIP), similar to Ce(cot)2, cerocene.
Date: February 21, 2006
Creator: Walter, Marc D.; Fandos, Rosa & Andersen, Richard A.
Partner: UNT Libraries Government Documents Department
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X-ray survival characteristics and genetic analysis for nineSaccharomyces deletion mutants that affect radiation sensitivity

Description: We examine ionizing radiation (IR) sensitivity and epistasisrelationships of several Saccharomyces mutants affectingpost-translational modifications of histones H2B and H3. Mutantsbre1delta, lge1delta, and rtf1delta, defective in histone H2B lysine 123ubiquitination, show IR sensitivity equivalent to that of the dot1deltamutant that we reported on earlier, consistent with published findingsthat Dot1p requires H2B K123 ubiquitination to fully methylate histone H3K79. This implicates progressive … more
Date: July 21, 2006
Creator: Game, John C.; Williamson, Marsha S. & Baccari, Clelia
Partner: UNT Libraries Government Documents Department
open access

Microscopic Approaches to Nuclear Structure: Configuration Interaction

Description: The configuration interaction (CI) approach to solving the nuclear many-body problem, also known as the interacting shell model, has proven to be powerful tool in understanding the structure of nuclei. The principal criticism of past applications of the shell model is the reliance on empirical tuning to interaction matrix elements. If an accurate description of nuclei far from the valley of stability, where little or no data is available, a more fundamental approach is needed. This starts with … more
Date: September 21, 2007
Creator: Ormand, W E
Partner: UNT Libraries Government Documents Department
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Negative Transconductance in Apertured Electron Guns

Description: Passing an electron beam through an aperture can serve to reduce the beam current or change the transverse beam profile. For a sufficiently intense beam, space charge will drive a radial expansion of the beam, which may cause the current passing through the aperture to increase even though the current arriving at the aperture is decreasing. When a gridded electron gun is used, this may be expressed by stating that the transconductance of the apertured gun is negative. Here we explain this effec… more
Date: September 21, 2007
Creator: Harris, J R & O'Shea, P G
Partner: UNT Libraries Government Documents Department
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IMPACT OF ALUMINATE IONS ON THE PROPERTIES OF SALTSTONE GROUT MIXES

Description: It is important to identify and control the operational and compositional variables that impact the important processing and performance properties of Saltstone grout mixes. The grout that is produced at the Saltstone Production Facility (SPF) is referred to as Saltstone and is a waste form that immobilizes low concentrations of radionuclides as well as certain toxic metals. The Saltstone will be disposed of in vaults at Savannah River Site (SRS). An effort referred to as the Saltstone Variabil… more
Date: February 21, 2008
Creator: Harbour, J; Tommy Edwards, T; Erich Hansen, E & Vickie Williams, V
Partner: UNT Libraries Government Documents Department
open access

Borehole Seismic Monitoring of Injected CO2 at the Frio Site

Description: As part of a small scale sequestration test (about 1500 tonsof CO2) in a saline aquifer, time-lapse borehole seismic surveys wereconducted to aid in characterization of subsurface CO2 distribution andmaterial property changes induced by the injected CO2. A VSP surveydemonstrated a large increase (about 75 percent) in seismic reflectivitydue to CO2 injection and allowed estimation of the spatial extent of CO2induced changes. A crosswell survey imaged a large seismic velocitydecrease (up to 500 m… more
Date: April 21, 2006
Creator: Daley, Thomas M.; Myer, Larry R.; Hoversten, G.M.; Peterson, JohnE. & Korneev, Valeri A.
Partner: UNT Libraries Government Documents Department
open access

Object Classification at the Nearby Supernova Factory

Description: We present the results of applying new object classification techniques to the supernova search of the Nearby Supernova Factory. In comparison to simple threshold cuts, more sophisticated methods such as boosted decision trees, random forests, and support vector machines provide dramatically better object discrimination: we reduced the number of nonsupernova candidates by a factor of 10 while increasing our supernova identification efficiency. Methods such as these will be crucial for maintaini… more
Date: December 21, 2007
Creator: Aragon, Cecilia R.; Bailey, Stephen; Aragon, Cecilia R.; Romano, Raquel; Thomas, Rollin C.; Weaver, B. A. et al.
Partner: UNT Libraries Government Documents Department
open access

Using Perturbed QR Factorizations To Solve Linear Least-Squares Problems

Description: We propose and analyze a new tool to help solve sparse linear least-squares problems min{sub x} {parallel}Ax-b{parallel}{sub 2}. Our method is based on a sparse QR factorization of a low-rank perturbation {cflx A} of A. More precisely, we show that the R factor of {cflx A} is an effective preconditioner for the least-squares problem min{sub x} {parallel}Ax-b{parallel}{sub 2}, when solved using LSQR. We propose applications for the new technique. When A is rank deficient we can add rows to ensur… more
Date: March 21, 2008
Creator: Avron, Haim; Ng, Esmond G. & Toledo, Sivan
Partner: UNT Libraries Government Documents Department
open access

Kinetic Effects in the Self-Assembly of Pure and Mixed Tetradecyland Octadecylamine Molecules on Mica

Description: The self-assembly of tetradecylamine (C14) and of mixtures of tetradecyl and octadecylamine (C18) molecules from chloroform solutions on mica has been studied using atomic force microscopy(AFM). For pure components self-assembly proceeds more slowly for C14 than for C18. In both cases after equilibrium is reached islands of tilted molecules cover a similar fraction of the surface. Images of films formed by mixtures of molecules acquired before equilibrium is reached (short ripening time at room… more
Date: September 21, 2005
Creator: Benitez, J. J. & Salmeron, M.
Partner: UNT Libraries Government Documents Department
open access

Comparison of Cluster Lensing Profiles with Lambda CDM Predictions

Description: We derive lens distortion and magnification profiles of four well known clusters observed with Subaru. Each cluster is very well fitted by the general form predicted for Cold Dark Matter (CDM) dominated halos, with good consistency found between the independent distortion and magnification measurements. The inferred level of mass concentration is surprisingly high, 8 < c{sub vir} < 15 (<c{sub vir}> = 10.39 {+-} 0.91), compared to the relatively shallow profiles predicted by the {Lam… more
Date: May 21, 2008
Creator: Broadhurst, Tom; U., /Tel Aviv; Umetsu, Keiichi; /Taipei, Inst. Astron. Astrophys.; Medezinski, Elinor; U., /Tel Aviv et al.
Partner: UNT Libraries Government Documents Department
open access

A Beamline for High Pressure Studies at the Advanced Light Source With a Superconducting Bending Magnet as the Source

Description: A new facility for high-pressure diffraction and spectroscopy using diamond anvil high-pressure cells has been built at the Advanced Light Source on Beamline 12.2.2. This beamline benefits from the hard X-radiation generated by a 6 Tesla superconducting bending magnet (superbend). Useful x-ray flux is available between 5 keV and 35 keV. The radiation is transferred from the superbend to the experimental enclosure by the brightness preserving optics of the beamline. These optics are comprised of… more
Date: April 21, 2005
Creator: Kunz, M.; MacDowell, A. A.; Caldwell, W. A.; Cambie, D.; Celestre, R. S.; Domning, E. E. et al.
Partner: UNT Libraries Government Documents Department
open access

K-alpha conversion efficiency measurments for x-ray scattering in inertial confinement fusion plasmas

Description: The conversion efficiency of ultra short-pulse laser radiation to K-{alpha} x-rays has been measured for various chlorine-containing targets to be used as x-ray scattering probes of dense plasmas. The spectral and temporal properties of these sources will allow spectrally-resolved x-ray scattering probing with picosecond temporal resolution required for measuring the plasma conditions in inertial confinement fusion experiments. Simulations of x-ray scattering spectra from these plasmas show tha… more
Date: November 21, 2006
Creator: Kritcher, A L; Neumayer, P; Urry, M K; Robey, H; Niemann, C; Landen, O L et al.
Partner: UNT Libraries Government Documents Department
open access

OXYGEN ISOTOPIC COMPOSITIONS OF THE ALLENDE TYPE C CAIs: EVIDENCE FOR ISOTOPIC EXCHANGE DURING NEBULAR MELTING AND ASTEROIDAL THERMAL METAMORPHISM

Description: Based on the mineralogy and petrography, coarse-grained, igneous, anorthite-rich (Type C) calcium-aluminum-rich inclusions (CAIs) in the CV3 carbonaceous chondrite Allende have been recently divided into three groups: (i) CAIs with melilite and Al,Ti-diopside of massive and lacy textures (coarse grains with numerous rounded inclusions of anorthite) in a fine-grained anorthite groundmass (6-1-72, 100, 160), (ii) CAI CG5 with massive melilite, Al,Ti-diopside and anorthite, and (iii) CAIs associat… more
Date: February 21, 2008
Creator: Krot, A N; Chaussidon, M; Yurimoto, H; Sakamoto, N; Nagashima, K; Hutcheon, I D et al.
Partner: UNT Libraries Government Documents Department
open access

A table-top femtosecond time-resolved soft x-ray transient absorption spectrometer

Description: A laser-based, table-top instrument is constructed to perform femtosecond soft x-ray transient absorption spectroscopy. Ultrashort soft x-ray pulses produced via high-order harmonic generation of the amplified output of a femtosecond Ti:sapphire laser system are used to probe atomic core-level transient absorptions in atoms and molecules. The results provide chemically specific, time-resolved dynamics with sub-50-fs time resolution. In this setup, high-order harmonics generated in a Ne-filled c… more
Date: May 21, 2008
Creator: Leone, Stephen; Loh, Zhi-Heng; Khalil, Munira; Correa, Raoul E. & Leone, Stephen R.
Partner: UNT Libraries Government Documents Department
open access

Lithographically-directed self-assembly of nanostructures

Description: The combination of lithography and self-assembly provides apowerful means of organizing solution-synthesized nanostructures for awide variety of applications. We have developed a fluidic assembly methodthat relies on the local pinning of a moving liquid contact line bylithographically produced topographic features to concentratenanoparticles at those features. The final stages of the assembly processare controlled first by long-range immersion capillary forces and then bythe short-range electro… more
Date: September 21, 2004
Creator: Liddle, J. Alexander; Cui, Yi & Alivisatos, Paul
Partner: UNT Libraries Government Documents Department
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Undulator Background in the Final Focus Test Beam Experiment with Polarized Positrons

Description: In the proposed E-166 experiment at SLAC, 50 GeV electrons pass through a helical undulator, and produce circularly polarized photons, which interact with a tungsten target and generate longitudinally polarized positrons. The background is an important issue for an experiment under consideration. To address this issue, simulations were performed with the code GEANT3 to model the production of secondary particles from high-energy electrons hitting an undulator. The energy density of photons gene… more
Date: September 21, 2006
Creator: Batygin, Yuri K.
Partner: UNT Libraries Government Documents Department
open access

Quarkonium shadowing in pPb and Pb+Pb collisions

Description: The d+Au data from RHIC, including the pA results from the fixed-target CERN SPS pA data, suggest increased importance of initial-state shadowing and decreasing nuclear absorption with increasing energy. This is not surprising since smaller x is probed at higher energy while absorption due to multiple scattering is predicted to decrease with energy. The CERN SPS data suggest a J/{psi} absorption cross section of about 4 mb without shadowing, and a larger absorption cross section if it is includ… more
Date: May 21, 2007
Creator: Vogt, R
Partner: UNT Libraries Government Documents Department
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