239 Matching Results

Search Results

Results: 1 - 24 next
open access

THz radiation as a bunch diagnostic forlaser-wakefield-accelerated electron bunches

Description: Experimental results are reported from two measurementtechniques (semiconductor switching and electro-optic sampling) thatallow temporal characterization of electron bunches produced by alaser-driven plasma-based accelerator. As femtosecond electron bunchesexit the plasma-vacuum interface, coherent transition radiation (at THzfrequencies) is emitted. Measuring the properties of this radiationallows characterization of the electron bunches. Theoretical work on theemission mechanism is represente… more
Date: February 15, 2006
Creator: van Tilborg, J.; Schroeder, C. B.; Filip, C. V.; Toth, Cs.; Geddes, C. G. R.; Fubiani, G. et al.
Partner: UNT Libraries Government Documents Department
open access

Beyond Boltzmann-Gibbs statistics: Maximum entropy hyperensemblesout-of-equilibrium

Description: What is the best description that we can construct of athermodynamic system that is not in equilibrium, given only one, or afew, extra parameters over and above those needed for a description ofthe same system at equilibrium? Here, we argue the most appropriateadditional parameter is the non-equilibrium entropy of the system, andthat we should not attempt to estimate the probability distribution ofthe system, but rather the metaprobability (or hyperensemble) that thesystem is described by a par… more
Date: February 23, 2006
Creator: Crooks, Gavin E.
Partner: UNT Libraries Government Documents Department
open access

In Vivo Enhancer Analysis Chromosome 16 Conserved NoncodingSequences

Description: The identification of enhancers with predicted specificitiesin vertebrate genomes remains a significant challenge that is hampered bya lack of experimentally validated training sets. In this study, weleveraged extreme evolutionary sequence conservation as a filter toidentify putative gene regulatory elements and characterized the in vivoenhancer activity of human-fish conserved and ultraconserved1 noncodingelements on human chromosome 16 as well as such elements from elsewherein the genome. We … more
Date: February 1, 2006
Creator: Pennacchio, Len A.; Ahituv, Nadav; Moses, Alan M.; Nobrega,Marcelo; Prabhakar, Shyam; Shoukry, Malak et al.
Partner: UNT Libraries Government Documents Department
open access

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
open access

Reversible expansion of gallium-stabilized (delta)-plutonium

Description: It is shown that the transient expansion of plutonium-gallium alloys observed both in the lattice parameter as well as in the dimension of a sample held at ambient temperature can be explained by assuming incipient precipitation of Pu{sub 3}Ga. However, this ordered {zeta}-phase is also subject to radiation-induced disordering. As a result, the gallium-stabilized {delta}-phase, being metastable at ambient temperature, is driven towards thermodynamic equilibrium by radiation-enhanced diffusion o… more
Date: February 27, 2006
Creator: Wolfer, W G; Oudot, B & Baclet, N
Partner: UNT Libraries Government Documents Department
open access

Proceedings of RIKIN BNL Research Center Workshop - Volume 79

Description: Since the earliest days of ultra-relativistic heavy ion physics, there has been interest in strange particle production. Originally, an anomalously large strangeness production was believed to be a signature of the Quark Gluon Plasma. Now the flavor composition of the plasma as reflected in the ratios of abundances of strange and non-strange particles is believed by advocates to tell us the temperature and baryon number density of the Quark Gluon Plasma at decoupling. In addition, there are arg… more
Date: February 16, 2006
Creator: Samios, N.
Partner: UNT Libraries Government Documents Department
open access

Effect of salt identity on the phase diagram for a globularprotein in aqueous electrolyte solution

Description: Monte Carlo simulations are used to establish the potential of mean force between two globular proteins in an aqueous electrolyte solution. This potential includes nonelectrostatic contributions arising from dispersion forces first, between the globular proteins, and second, between ions in solution and between each ion and the globular protein. These latter contributions are missing from standard models. The potential of mean force, obtained from simulation, is fitted to an analytic equation. … more
Date: February 22, 2006
Creator: Bostrom, Mathias; Tavares, Frederico W.; Ninham, Barry W. & Prausnitz, John M.
Partner: UNT Libraries Government Documents Department
open access

The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-masswhite dwarf star

Description: The acceleration of the expansion of the universe, and theneed for Dark Energy, were inferred from the observations of Type Iasupernovae (SNe Ia) 1;2. There is consensus that SNeIa are thermonuclearexplosions that destroy carbon-oxygen white dwarf stars that accretematter from a companion star3, although the nature of this companionremains uncertain. SNe Ia are thought to be reliable distance indicatorsbecause they have a standard amount of fuel and a uniform trigger theyare predicted to explod… more
Date: February 1, 2006
Creator: Howell, D.Andrew; Sullivan, Mark; Nugent, Peter E.; Ellis,Richard S.; Conley, Alexander J.; Le Borgne, Damien et al.
Partner: UNT Libraries Government Documents Department
open access

On the work distribution for the adiabatic compression of a diluteclassical gas

Description: We consider the adiabatic and quasi-static compression of adilute classical gas, confined in a piston and initially equilibratedwith a heat bath. We find that the work performed during this process isdescribed statistically by a gamma distribution. We use this result toshow that the model satisfies the non-equilibrium work and fluctuationtheorems, but not the fluctation-dissipation relation. We discuss therare but dominant realizations that contribute most to the exponentialaverage of the work,… more
Date: February 23, 2006
Creator: Crooks, Gavin E. & Jarzynski, Christopher
Partner: UNT Libraries Government Documents Department
open access

EUV multilayer coatings for the Atmospheric Imaging Assembly instrument aboard the Solar Dynamics Observatory

Description: Multilayer coatings for the 7 EUV channels of the AIA have been developed and completed successfully on all AIA flight mirrors. Mo/Si coatings (131, 171, 193.5, 211 {angstrom}) were deposited at Lawrence Livermore National Laboratory (LLNL). Mg/SiC (304, 335 {angstrom}) and Mo/Y (94 {angstrom}) coatings were deposited at Columbia University. EUV reflectance of the 131/335 {angstrom}, 171 {angstrom}, 193.5/211 {angstrom} primary and secondary flight mirrors and the 94/304 {angstrom} secondary fl… more
Date: February 9, 2006
Creator: Soufli, R.; Windt, D. L.; Robinson, J. C.; Baker, S. L.; Spiller, E.; Dollar, F. J. et al.
Partner: UNT Libraries Government Documents Department
open access

Time-Resolved FT-IR Spectroscopy of CO Hydrogenation overSupported Ru Catalyst at 700K

Description: Time-resolved FT-IR spectra of carbon monoxide hydrogenation over alumina-supported ruthenium were recorded on the millisecond timescale at 703 K using various H{sub 2} concentrations (1 atm total pressure). Adsorbed carbon monoxide was detected along with gas phase products methane (3016 and 1306 cm{sup -1}), water (sharp bands from 1900 - 1300 cm{sup -1}), and carbon dioxide (2348 cm{sup -1}). No other surface species were detected other than adsorbed carbon monoxide. The rate of formation of… more
Date: February 13, 2006
Creator: Wasylenko, Walter & Frei, Heinz
Partner: UNT Libraries Government Documents Department
open access

Seismic Waves in Rocks with Fluids and Fractures

Description: Seismic wave propagation through the earth is often strongly affected by the presence of fractures. When these fractures are filled with fluids (oil, gas, water, CO{sub 2}, etc.), the type and state of the fluid (liquid or gas) can make a large difference in the response of the seismic waves. This paper will summarize some early work of the author on methods of deconstructing the effects of fractures, and any fluids within these fractures, on seismic wave propagation as observed in reflection s… more
Date: February 6, 2006
Creator: Berger, E. L.
Partner: UNT Libraries Government Documents Department
open access

Longitudinal Density Modulation and Energy Conversion in Intense Beams

Description: Density modulation of charged particle beams may occur as a consequence of deliberate action, or may occur inadvertently because of imperfections in the particle source or acceleration method. In the case of intense beams, where space charge and external focusing govern the beam dynamics, density modulation may under some circumstances be converted to velocity modulation, with a corresponding conversion of potential energy to kinetic energy. Whether this will occur depends on the properties of … more
Date: February 17, 2006
Creator: Harris, J; Neumann, J; Tian, K & O'Shea, P
Partner: UNT Libraries Government Documents Department
open access

WRN Exonuclease Structure, Molecular Mechanism, and DNA EndProcessing Role

Description: WRN is unique among the five human RecQ DNA helicases by having a functional exonuclease domain (WRN-exo) and being defective in the premature aging and cancer-related disorder Werner syndrome. Here, we characterize WRN-exo crystal structures, biochemical activity and participation in DNA end-joining. Metal ion complex structures, active site mutations and activity assays reveal a two-metal-ion mediated nuclease mechanism. The DNA end-binding Ku70/80 complex specifically stimulates WRN-exo acti… more
Date: February 15, 2006
Creator: Perry, J. Jefferson P.; Yannone, Steven M.; Holden, Lauren G.; Hitomi, Chiharu; Asaithamby, Aroumougame; Han, Seungil et al.
Partner: UNT Libraries Government Documents Department
open access

Genomes of three facultatively symbiotic Frankia sp. strainsreflect host plant biogeography

Description: Filamentous actinobacteria from the genus Frankia anddiverse woody trees and shrubs together form N2-fixing actinorhizal rootnodule symbioses that are a major source of new soil nitrogen in widelydiverse biomes 1. Three major clades of Frankia sp. strains are defined;each clade is associated with a defined subset of plants from among theeight actinorhizal plant families 2,3. The evolution arytrajectoriesfollowed by the ancestors of both symbionts leading to current patternsof symbiont compatibi… more
Date: February 1, 2006
Creator: Normand, Philippe; Lapierre, Pascal; Tisa, Louis S.; Gogarten, J. Peter; Alloisio, Nicole; Bagnarol, Emilie et al.
Partner: UNT Libraries Government Documents Department
open access

A New Stabilized Nodal Integration Approach

Description: A new stabilized nodal integration scheme is proposed and implemented. In this work, focus is on the natural neighbor meshless interpolation schemes. The approach is a modification of the stabilized conforming nodal integration (SCNI) scheme and is shown to perform well in several benchmark problems.
Date: February 8, 2006
Creator: Puso, M; Zywicz, E & Chen, J S
Partner: UNT Libraries Government Documents Department
open access

Multiscale Modeling with Carbon Nanotubes

Description: Technologically important nanomaterials come in all shapes and sizes. They can range from small molecules to complex composites and mixtures. Depending upon the spatial dimensions of the system and properties under investigation computer modeling of such materials can range from equilibrium and nonequilibrium Quantum Mechanics, to force-field-based Molecular Mechanics and kinetic Monte Carlo, to Mesoscale simulation of evolving morphology, to Finite-Element computation of physical properties. T… more
Date: February 21, 2006
Creator: Maiti, A
Partner: UNT Libraries Government Documents Department
open access

An Implementation and Evaluation of the AMLS Method for SparseEigenvalue Problems

Description: We describe an efficient implementation and present aperformance study of an algebraic multilevel sub-structuring (AMLS)method for sparse eigenvalue problems. We assess the time and memoryrequirements associated with the key steps of the algorithm, and compareitwith the shift-and-invert Lanczos algorithm in computational cost. Oureigenvalue problems come from two very different application areas: theaccelerator cavity design and the normal mode vibrational analysis of thepolyethylene particles.… more
Date: February 14, 2006
Creator: Gao, Weiguo; Li, Xiaoye S.; Yang, Chao & Bai, Zhaojun
Partner: UNT Libraries Government Documents Department
open access

The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain

Description: This paper investigates the impact of proposed repositorythermal-loading on mountain-scale flow and heat transfer in theunsaturated fractured rock of Yucca Mountain, Nevada. In this context, amodel has been developed to study the coupled thermal-hydrological (TH)processes at the scale of the entire Yucca Mountain. This mountain-scaleTH model implements the current geological framework and hydrogeologicalconceptual models, and incorporates the latest rock thermal andhydrological properties. The … more
Date: February 28, 2006
Creator: Wu, Y.-S.; Mukhopadhyay, Sumit; Zhang, Keni & Bodvarsson, G.S.
Partner: UNT Libraries Government Documents Department
open access

Why every national deep-geological-isolation program needs a long-term science & technology component

Description: The objective of this paper is to set down the rationale for a separate Science & Technology (S&T) Program within every national deep-geological-isolation program. The fundamental rationale for such a Program is to provide a dedicated focus for longer-term science and technology activities that ultimately will benefit the whole repository mission. Such a Program, separately funded and with a dedicated staff (separate from the ''mainline'' activities to develop the repository, the surface fa… more
Date: February 10, 2006
Creator: Budnitz, R J
Partner: UNT Libraries Government Documents Department
open access

A 3D Model for Ion Beam Formation and Transport Simulation

Description: In this paper, we present a three-dimensional model forself-consistently modeling ion beam formation from plasma ion sources andtransporting in low energy beam transport systems. A multi-sectionoverlapped computational domain has been used to break the originaltransport system into a number of weakly coupled subsystems. Within eachsubsystem, macro-particle tracking is used to obtain the charge densitydistribution in this subdomain. The three-dimensional Poisson equation issolved within the subd… more
Date: February 7, 2006
Creator: Qiang, J.; Todd, D. & Leitner, D.
Partner: UNT Libraries Government Documents Department
open access

Metal inhibition of human alkylpurine-DNA-N-glycosylase activityin base excision repair

Description: Cadmium (Cd{sup 2+}), nickel (Ni{sup 2+}) and cobalt (Co{sup 2+}) are human and/or animal carcinogens. Zinc (Zn{sup 2+}) is not categorized as a carcinogen, and rather an essential element to humans. Metals were recently shown to inhibit DNA repair proteins that use metals for their function and/or structure. Here we report that the divalent ions Cd{sup 2+}, Ni{sup 2+}, and Zn{sup 2+} can inhibit the activity of a recombinant human N-methylpurine-DNA glycosylase (MPG) toward a deoxyoligonucleot… more
Date: February 28, 2006
Creator: Wang, Ping; Guliaev, Anton B. & Hang, Bo
Partner: UNT Libraries Government Documents Department
Back to Top of Screen