63 Matching Results

Results open in a new window/tab.

AdS/CFT and QCD (open access)

AdS/CFT and QCD

The AdS/CFT correspondence between string theory in AdS space and conformal .eld theories in physical spacetime leads to an analytic, semi-classical model for strongly-coupled QCD which has scale invariance and dimensional counting at short distances and color confinement at large distances. Although QCD is not conformally invariant, one can nevertheless use the mathematical representation of the conformal group in five-dimensional anti-de Sitter space to construct a first approximation to the theory. The AdS/CFT correspondence also provides insights into the inherently non-perturbative aspects of QCD, such as the orbital and radial spectra of hadrons and the form of hadronic wavefunctions. In particular, we show that there is an exact correspondence between the fifth-dimensional coordinate of AdS space z and a specific impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron in ordinary space-time. This connection allows one to compute the analytic form of the frame-independent light-front wavefunctions, the fundamental entities which encode hadron properties and allow the computation of decay constants, form factors, and other exclusive scattering amplitudes. New relativistic lightfront equations in ordinary space-time are found which reproduce the results obtained using the 5-dimensional theory. The effective light-front equations possess remarkable algebraic structures …
Date: February 21, 2007
Creator: Brodsky, Stanley J. & de Teramond, Guy F.
System: The UNT Digital Library
Diagnostics for the Combustion Science Workbench (open access)

Diagnostics for the Combustion Science Workbench

As the cost of computers declines relative to outfitting andmaintaining laser spectroscopy laboratories, computers will account foran increasing proportion of the research conducted in fundamentalcombustion science. W.C. Gardiner foresaw that progress will be limitedby the ability to understand the implications of what has been computedand to draw inferences about the elementary components of the combustionmodels. Yet the diagnostics that are routinely applied to computerexperiments have changed little from the sensitivity analyses includedwith the original chemkin software distribution. This paper describessome diagnostics capabilities that may be found on the virtual combustionscience workbench of the future. These diagnostics are illustrated bysome new results concerning which of the hydrogen/oxygen chain branchingreactions actually occur in flames, the increased formation of NOx inwrinkled flames versus flat flames, and the adequacy oftheoreticalpredictions of the effects of stretch. Several areas are identified wherework is needed, including the areas of combustion chemistry and laserdiagnostics, to make the virtual laboratory a reality.
Date: February 21, 2007
Creator: Grcar, J. F.; Day, M. S. & Bell, J. B.
System: The UNT Digital Library
ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN (open access)

ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN

The model assumes that an 'initiating event' results in positive ions on the surface near the anode and reverses the direction of the normal component of electric field so that electrons in vacuum are attracted to the dielectric locally. A sequence of surface electron avalanches progresses in steps from the anode to the cathode. For 200 kV across 1 cm, the spacing of avalanches is predicted to be about 13 microns. The time for avalanches to step from the anode to the cathode is predicted to be about a ns.
Date: February 21, 2007
Creator: Lauer, E J
System: The UNT Digital Library
HEND: A Database for High Energy Nuclear Data (open access)

HEND: A Database for High Energy Nuclear Data

We propose to develop a high-energy heavy-ion experimental database and make it accessible to the scientific community through an on-line interface. The database will be searchable and cross-indexed with relevant publications, including published detector descriptions. It should eventually contain all published data from older heavy-ion programs such as the Bevalac, AGS, SPS and FNAL fixed-target programs, as well as published data from current programs at RHIC and new facilities at GSI (FAIR), KEK/Tsukuba and the LHC collider. This data includes all proton-proton, proton-nucleus to nucleus-nucleus collisions as well as other relevant systems and all measured observables. Such a database would have tremendous scientific payoff as it makes systematic studies easier and allows simpler benchmarking of theoretical models to a broad range of experiments. To enhance the utility of the database, we propose periodic data evaluations and topical reviews. These reviews would provide an alternative and impartial mechanism to resolve discrepancies between published data from rival experiments and between theory and experiment. Since this database will be a community resource, it requires the high-energy nuclear physics community's financial and manpower support.
Date: February 21, 2007
Creator: Brown, David & Vogt, Ramona
System: The UNT Digital Library
Nanotechnology in Science and Art (open access)

Nanotechnology in Science and Art

The burgeoning field of nanotechnology opens windows between science and art. Exploration of this interplay encourages interaction between scientists, artists and educators alike. The image below serves as an example of the fertile ground for exchange. The substrate that this image captures is made of silicon, the material from which computer chips are made. A thin ({approx}1 nm thick) chemical coating was applied homogeneously to the silicon. Specific regions of the coating, 600 nm wide (approximately 150 times smaller than the diameter of a human hair), were then locally removed from the silicon via photocatalytic nanolithography (PCNL(Bearinger, Hiddessen et al. 2005)). PCNL engages light, such as from a light emitting diode or an ultraviolet source, to activate molecules that are attached to a transparent mask above the silicon substrate. These molecules can be compounds similar to chlorophyll, the photoactive material that aids plants in photosynthesis, or may be semiconductor materials, such as TiO{sub 2}. Once these molecules are activated, chemical reactions result in local destruction of the coating on the silicon. Thus, only regions of the coated silicon in close contact with mask are affected. A non-fouling polymer hydrogel ({approx}10 nm thick) was then grafted to the retained coating. Hydrogels …
Date: February 21, 2007
Creator: Bearinger, J.
System: The UNT Digital Library
Recent Developments in the Site-Specific Immobilization of Proteins onto Solid Supports (open access)

Recent Developments in the Site-Specific Immobilization of Proteins onto Solid Supports

Immobilization of proteins onto surfaces is of great importance in numerous applications, including protein analysis, drug screening, and medical diagnostics, among others. The success of all these technologies relies on the immobilization technique employed to attach a protein to the corresponding surface. Non-specific physical adsorption or chemical cross-linking with appropriate surfaces results in the immobilization of the protein in random orientations. Site-specific covalent attachment, on the other hand, leads to molecules being arranged in a definite, orderly fashion and allows the use of spacers and linkers to help minimize steric hindrances between the protein and the surface. The present work reviews the latest chemical and biochemical developments for the site-specific covalent attachment of proteins onto solid supports.
Date: February 21, 2007
Creator: Camarero, J A
System: The UNT Digital Library
Short sequence motifs, overrepresented in mammalian conservednon-coding sequences (open access)

Short sequence motifs, overrepresented in mammalian conservednon-coding sequences

Background: A substantial fraction of non-coding DNAsequences of multicellular eukaryotes is under selective constraint. Inparticular, ~;5 percent of the human genome consists of conservednon-coding sequences (CNSs). CNSs differ from other genomic sequences intheir nucleotide composition and must play important functional roles,which mostly remain obscure.Results: We investigated relative abundancesof short sequence motifs in all human CNSs present in the human/mousewhole-genome alignments vs. three background sets of sequences: (i)weakly conserved or unconserved non-coding sequences (non-CNSs); (ii)near-promoter sequences (located between nucleotides -500 and -1500,relative to a start of transcription); and (iii) random sequences withthe same nucleotide composition as that of CNSs. When compared tonon-CNSs and near-promoter sequences, CNSs possess an excess of AT-richmotifs, often containing runs of identical nucleotides. In contrast, whencompared to random sequences, CNSs contain an excess of GC-rich motifswhich, however, lack CpG dinucleotides. Thus, abundance of short sequencemotifs in human CNSs, taken as a whole, is mostly determined by theiroverall compositional properties and not by overrepresentation of anyspecific short motifs. These properties are: (i) high AT-content of CNSs,(ii) a tendency, probably due to context-dependent mutation, of A's andT's to clump, (iii) presence of short GC-rich regions, and (iv) avoidanceof CpG contexts, due to their hypermutability. Only a small number ofshort …
Date: February 21, 2007
Creator: Minovitsky, Simon; Stegmaier, Philip; Kel, Alexander; Kondrashov,Alexey S. & Dubchak, Inna
System: The UNT Digital Library
TYPE B RADIOACTIVE MATERIAL PACKAGE FAILURE MODES AND CONTENTS COMPLIANCE (open access)

TYPE B RADIOACTIVE MATERIAL PACKAGE FAILURE MODES AND CONTENTS COMPLIANCE

Type B radioactive material package failures can occur due to any one of the following: inadequate design, manufacture, and maintenance of packages, load conditions beyond those anticipated in the regulations, and improper package loading and operation. The rigorous package design evaluations performed in the certification process, robust package manufacture quality assurance programs, and demanding load conditions prescribed in the regulations are all well established. This paper focuses on the operational aspects of Type B package loading with respect to an overbatch which may cause a package failure.
Date: February 21, 2007
Creator: Watkins, R; Steve Hensel, S & Allen Smith, A
System: The UNT Digital Library
2006 Sensory Transduction in Microorganisms Gordon Conference - January 22-27 (open access)

2006 Sensory Transduction in Microorganisms Gordon Conference - January 22-27

This Report is Description of Sensory Transduction in Microorganisms at Gordon Conference.
Date: March 21, 2007
Creator: Borkovich, Katherine
System: The UNT Digital Library
Active RF Pulse Compression Using Electrically Controlled Semiconductor Switches (open access)

Active RF Pulse Compression Using Electrically Controlled Semiconductor Switches

In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer and has achieved a switching time of 300ns. The wafer is inserted into a cylindrical waveguide operating in the TE01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. The RF energy is stored in a room-temperature, high-Q 375 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has achieved a gain of 8, which is the ratio between output and input power.
Date: March 21, 2007
Creator: Guo, J. & Tantawi, S.
System: The UNT Digital Library
Linac Coherent Light Source (LCLS) Bunch-Length Monitor using Coherent Radiation (open access)

Linac Coherent Light Source (LCLS) Bunch-Length Monitor using Coherent Radiation

The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) based on the final kilometer of the Stanford Linear Accelerator. One of the most critical diagnostic devices is the bunch length monitor (BLM), which is to be installed right after each compressor utilizing coherent radiation from the last bending magnet. We describe the components and the optical layout of such a BLM. Based on the setup geometry, we discuss some issues about the coherent radiation signal.
Date: March 21, 2007
Creator: Wu, Juhao & Emma, P.
System: The UNT Digital Library
The Linac Cooherent Light Source (LCLS) Accelerator (open access)

The Linac Cooherent Light Source (LCLS) Accelerator

The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) based on the final kilometer of the Stanford Linear Accelerator. Such an FEL requires a high energy, high brightness electron beam to drive the FEL instability to saturation. When fed by an RF-photocathode gun, and modified to include two bunch compressor chicanes, the SLAC linac will provide such a high quality beam at 14 GeV and 1-{micro}m normalized emittance. In this paper, we report on recent linac studies, including beam stability and tolerances, longitudinal and transverse feedback systems, conventional and time-resolved diagnostics, and beam collimation systems. Construction and installation of the injector through first bunch compressor will be completed by December 2006, and electron commissioning is scheduled to begin in January of 2007.
Date: March 21, 2007
Creator: Wu, Juhao & Emma, P.
System: The UNT Digital Library
The Long-Term Corrosion Test Facility at the Lawrence Livermore National Laboratory (open access)

The Long-Term Corrosion Test Facility at the Lawrence Livermore National Laboratory

The long-term corrosion test facility (LTCTF) at the Lawrence Livermore National Laboratory (LLNL) consisted of 22 vessels that housed more than 7,000 corrosion test specimens from carbon steels to highly corrosion resistant materials such Alloy 22 and Ti Grade 7. The specimens from LTCTF range from standard weight-loss coupons to U-bend specimens for testing susceptibility to environmentally assisted cracking. Each vessel contained approximately 1000 liters of concentrated brines at 60 C or 90 C. The LTCTF started its operations in late 1996. The thousands of specimens from the LTCTF were removed in August-September 2006. The specimens are being catalogued and stored for future characterization. Previously removed specimens (e.g. 1 and 5 years) are also archived for further studies.
Date: March 21, 2007
Creator: Fix, D V & Rebak, R B
System: The UNT Digital Library
Multiple Synthesis Routes to Transparent Ceramic Lutetium Aluminum Garnet (open access)

Multiple Synthesis Routes to Transparent Ceramic Lutetium Aluminum Garnet

None
Date: March 21, 2007
Creator: Kuntz, J. D.; Roberts, J. J.; Hough, M. E. & Cherepy, N. J.
System: The UNT Digital Library
Production and Decay of Omega_c^0 (open access)

Production and Decay of Omega_c^0

We present an analysis of inclusive {Omega}{sub c}{sup 0} baryon production and decays in 230.5 fb{sup -1} of data recorded with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} collider at the Stanford Linear Accelerator Center. {Omega}{sub c}{sup 0} baryons are reconstructed in four final states ({Omega}{sup -}{pi}{sup +}, {Omega}{sup -}{pi}{sup +}{pi}{sup 0}, {Omega}{sup -}{pi}{sup +}{pi}{sup +}{pi}{sup -}, {Xi}{sup -}K{sup -}{pi}{sup +}{pi}{sup +}) and the ratios of branching fractions for these final states are measured. We also measure the momentum spectrum of the {Omega}{sub c}{sup 0} baryons in the e{sup +}e{sup -} center-of-mass frame. From the spectrum, they observe {Omega}{sub c}{sup 0} production from B decays and in c{bar c} events, and extract the two rates of production.
Date: March 21, 2007
Creator: Aubert, B.
System: The UNT Digital Library
Proposed RF Breakdown Studies at the AWA (open access)

Proposed RF Breakdown Studies at the AWA

A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. We plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV) to determine the role of explosive electron emission in the breakdown process. Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector [1] that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after the breakdown can shed some light on a number of observations such as the crater formation process.
Date: March 21, 2007
Creator: Antipov, S.; Conde, M.; Gai, W.; Power, J. G.; Spentzouris, L.; Yusof, Z. et al.
System: The UNT Digital Library
Segue between Favorable and Unfavorable Solvation (open access)

Segue between Favorable and Unfavorable Solvation

Solvation of small and large clusters are studied by simulation, considering a range of solvent-solute attractive energy strengths. Over a wide range of conditions, both for solvation in the Lennard-Jones liquid and in the SPC model of water, it is shown that the mean solvent density varies linearly with changes in solvent-solute adhesion or attractive energy strength. This behavior is understood from the perspective of Weeks theory of solvation [Ann. Rev. Phys. Chem. 2002, 53, 533] and supports theories based upon that perspective.
Date: March 21, 2007
Creator: Maibaum, Lutz & Chandler, David
System: The UNT Digital Library
Chiral perturbation theory with tensor sources (open access)

Chiral perturbation theory with tensor sources

We construct the most general chirally-invariant Lagrangian for mesons in the presence of external sources coupled to the tensor current \bar psi sigma_mu nu psi. In order to have only even terms in the chiral expansion, we consider the new source of O(p2). With this choice, we build the even-parity effective Lagrangian up to the p6-order (NLO). While there are only 4 new terms at the p4-order, at p6-order we find 78 terms for n_f=2 and 113 terms for n_f=3. We provide a detailed discussion on the different mechanisms that ensure that our final set of operators is complete and non-redundant. We also examine the odd-parity sector, to conclude that the first operators appear at the p8-order (NNLO).
Date: May 21, 2007
Creator: Cata, Oscar; Cata, Oscar & Mateu, Vicent
System: The UNT Digital Library
The Community Environmental Monitoring Program: Reducing Public Perception of Risk through Stakeholder Involvement (open access)

The Community Environmental Monitoring Program: Reducing Public Perception of Risk through Stakeholder Involvement

The Community Environmental Monitoring Program (CEMP) has promoted stakeholder involvement, awareness, and understanding of radiological surveillance in communities surrounding the Nevada Test Site (NTS) since 1981. It involves stakeholders in the operation, data collection, and dissemination of information obtained from a network of 29 stations across a wide area of Nevada, Utah and California. It is sponsored by the U.S. Department of Energy, National Nuclear Security Administration’s Nevada Site Office (NNSA/NSO) and administered by the Desert Research Institute (DRI) of the Nevada System of Higher Education. Integration of a near real-time communications system, a public web site, training workshops for involved stakeholders, and educational programs all help to alleviate public perception of risk of health effects from past activities conducted at the NTS.
Date: May 21, 2007
Creator: Hartwell, William T.
System: The UNT Digital Library
DISPOSAL OF REACTOR DEIONIZER VESSELS HIGHLY CONTAMINATED WITH 14 CARBON IN THE INTERMEDIATE LEVEL VAULT FACILITY AT SRS (open access)

DISPOSAL OF REACTOR DEIONIZER VESSELS HIGHLY CONTAMINATED WITH 14 CARBON IN THE INTERMEDIATE LEVEL VAULT FACILITY AT SRS

At the Savannah River Site (SRS), nuclear production reactors used deionizers to control the chemistry of the reactor moderator during their operation to produce nuclear materials primarily for the weapons program. These deionizers were removed from the reactors and stored as a legacy waste with no path to disposal due to the relatively high {sup 14}C contamination (i.e., on the order of 20 curies per deionizer for 48-50 deionizers) and the low disposal limit of 4.2 Ci previously established for the Intermediate Level Vault (ILV). The ILV is considered most appropriate facility within which to dispose these items due to the method of solidifying waste items with cementitious material inside concrete vaults. In previous analyses the {sup 14}C ILV disposal limit was established at 4.2 Ci resulting from the use of a very conservative method to analyze the dose received from atmospheric releases of gaseous {sup 14}C. This investigation implemented a more rigorous evaluation of the physical and chemical processes influencing the release and migration of gaseous {sup 14}C (as CO{sub 2}) to obtain a more realistic estimate of atmospheric dose and to determine new ILV disposal limits.
Date: May 21, 2007
Creator: Hiergesell, R. & Daniel Kaplan, D.
System: The UNT Digital Library
Parton Distributions and Spin-Orbital Correlations (open access)

Parton Distributions and Spin-Orbital Correlations

In this talk, the author summarizes a recent study showing that the large-x parton distributions contain important information on the quark orbital angular momentum of nucleon. This contribution could explain the conflict between the experimental data and the theory predictions for the polarized quark distributions. Future experiments at JLAB shall provide further test for our predictions.
Date: May 21, 2007
Creator: Feng, Y.
System: The UNT Digital Library
Quarkonium shadowing in pPb and Pb+Pb collisions (open access)

Quarkonium shadowing in pPb and Pb+Pb collisions

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 included since the SPS x range is in the antishadowing region. The d+Au RHIC data support smaller absorption, {sigma}{sup J/{psi}}{sub abs} {approx} 0-2 mb. Thus our predictions for J/{psi} and {Upsilon} production in pPb and Pb+Pb interactions at the LHC are shown for initial-state shadowing alone with no absorption or dense matter effects. We note that including absorption would only move the calculated ratios down in proportion to the absorption survival probability since, at LHC energies, any rapidity dependence of absorption is at very large |y|, outside the detector acceptance.
Date: May 21, 2007
Creator: Vogt, R
System: The UNT Digital Library
The Tritium Underflow Study at the Savannah River Site (open access)

The Tritium Underflow Study at the Savannah River Site

An issue of concern at the Savannah River Site (SRS) over the past 20 years is whether tritiated groundwater originating at SRS might be the cause of low levels of tritium measured in certain domestic wells in Georgia. Tritium activity levels in several domestic wells have been observed to occur at levels comparable to what is measured in rainfall in areas surrounding SRS. Since 1988, there has been speculation that tritiated groundwater from SRS could flow under the river and find its way into Georgia wells. A considerable effort was directed at assessing the likelihood of trans-river flow, and 44 wells have been drilled by the USGS and the Georgia Department of Natural Resources. Also, as part of the data collection and analysis, the USGS developed a numerical model during 1997-98 (Ref. 1) to assess the possibility for such trans-river flow to occur. The model represented the regional groundwater flow system surrounding the Savannah River Site (SRS) in seven layers corresponding to the underlying hydrostratigraphic units, which was regarded as sufficiently detailed to evaluate whether groundwater originating at SRS could possibly flow beneath the Savannah River into Georgia. The model was calibrated against a large database of water-level measurements obtained …
Date: May 21, 2007
Creator: Hiergesell, Robert A. & Kaplan, D.
System: The UNT Digital Library
Absolute Measurement of Electron Cloud Density (open access)

Absolute Measurement of Electron Cloud Density

Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 {micro}s duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.
Date: June 21, 2007
Creator: Covo, M K; Molvik, A W; Cohen, R H; Friedman, A; Seidl, P A; Logan, G et al.
System: The UNT Digital Library