Analysis of the Effects of Compositional and Configurational Assumptions on Product Costs for the Thermochemical Conversion of Lignocellulosic Biomass to Mixed Alcohols -- FY 2007 Progress Report (open access)

Analysis of the Effects of Compositional and Configurational Assumptions on Product Costs for the Thermochemical Conversion of Lignocellulosic Biomass to Mixed Alcohols -- FY 2007 Progress Report

The purpose of this study was to examine alternative biomass-to-ethanol conversion process assumptions and configuration options to determine their relative effects on overall process economics. A process-flow-sheet computer model was used to determine the heat and material balance for each configuration that was studied. The heat and material balance was then fed to a costing spreadsheet to determine the impact on the ethanol selling price. By examining a number of operational and configuration alternatives and comparing the results to the base flow sheet, alternatives having the greatest impact the performance and cost of the overall system were identified and used to make decisions on research priorities.
Date: December 5, 2008
Creator: Zhu, Yunhua; Gerber, Mark A.; Jones, Susanne B. & Stevens, Don J.
Object Type: Report
System: The UNT Digital Library
Anthropogenically-Induced Climate Change: Final Report (open access)

Anthropogenically-Induced Climate Change: Final Report

Paper number 1 addresses the fact that the procedure used in the Earth Radiation Budget Experiment for identifying the presence of clouds over snow/ice surfaces is known to have shortcomings, and this is corroborated through use of surface insolation measurements at the South Pole as an independent means of identifying clouds. These surface insolation measurements are then used to validate the more detailed cloud identification scheme used in the follow-up Clouds and the Earth's Radiant Energy System (CERES), and this validation is extended to the polar night through use of CERES measurements of the outgoing longwave radiation. General circulation models (GCMs) are highly sophisticated computer tools for modeling climate change, and they incorporate a large number of physical processes and variables. One of the most important challenges is to properly account for water vapor (clouds and humidity) in climate warming. In this Perspective, Cess discusses results reported in the same issue by Soden et al. in which water vapor feedback effects are tested by studying moistening trends in the upper troposphere. Satellite observations of atmospheric water vapor are found to agree well with moisture predictions generated by one of the key GCMs, showing that these feedback effects are being properly …
Date: December 5, 2008
Creator: Cess, Robert D.
Object Type: Report
System: The UNT Digital Library
Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons (open access)

Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons

The reactions of the methylidyne radical (CH) with ethylene, acetylene, allene, and methylacetylene are studied at room temperature using tunable vacuum ultraviolet (VUV) photoionization and time-resolved mass spectrometry. The CH radicals are prepared by 248 nm multiphoton photolysis of CHBr3 at 298 K and react with the selected hydrocarbon in a helium gas flow. Analysis of photoionization efficiency versus VUV photon wavelength permits isomer-specific detection of the reaction products and allows estimation of the reaction product branching ratios. The reactions proceed by either CH insertion or addition followed by H atom elimination from the intermediate adduct. In the CH + C2H4 reaction the C3H5 intermediate decays by H atom loss to yield 70(+-8)percent allene, 30(+-8)percent methylacetylene and less than 10percent cyclopropene, in agreement with previous RRKM results. In the CH + acetylene reaction, detection of mainly the cyclic C3H2 isomer is contrary to a previous RRKM calculation that predicted linear triplet propargylene to be 90percent of the total H-atom co-products. High-level CBS-APNO quantum calculations and RRKM calculation for the CH + C2H2 reaction presented in this manuscript predict a higher contribution of the cyclic C3H2 (27.0percent) versus triplet propargylene (63.5percent) than these earlier predictions. Extensive calculations on the C3H3 and …
Date: December 5, 2008
Creator: Goulay, Fabien; Trevitt, Adam J.; Meloni, Giovanni; Selby, Talitha M.; Osborn, David L.; Taatjes, Craig A. et al.
Object Type: Article
System: The UNT Digital Library
Evaluation of the Reproductive Success of Wild and Hatchery Steelhead in Hatchery and Natural and Hatchery Environments : Annual Report for 2008. (open access)

Evaluation of the Reproductive Success of Wild and Hatchery Steelhead in Hatchery and Natural and Hatchery Environments : Annual Report for 2008.

This report summarizes the field, laboratory, and analytical work from December 2007 through November 2008 on a research project that investigates interactions and comparative reproductive success of wild and hatchery origin steelhead (Oncorhynchus mykiss) trout in Forks Creek, a tributary of the Willapa River in southwest Washington. First, we continued to successfully sample hatchery and wild (i.e., naturally spawned) adult and wild smolt steelhead at Forks Creek. Second, we revealed microsatellite genotype data for adults and smolts through brood year 2008. Finally, four formal scientific manuscripts were published in 2008 and two are in press, one is in revision and two are in preparations.
Date: December 5, 2008
Creator: Quinn, Thomas P.; Seamons, todd; Hauser, Lorenz & Naish, Kerry
Object Type: Report
System: The UNT Digital Library
Imaging with Mass Spectrometry: A SIMS and VUV-Photoionization Study of Ion-Sputtered Atoms and Clusters from GaAs and Au (open access)

Imaging with Mass Spectrometry: A SIMS and VUV-Photoionization Study of Ion-Sputtered Atoms and Clusters from GaAs and Au

A new mass spectrometry surface imaging method is presented in which ion-sputtered neutrals are postionized by wavelength-tunable vacuum ultraviolet (VUV) light from a synchrotron source. Mass spectra and signal counts of the photoionized neutrals from GaAs (100) and Au are compared to those of the secondary ions. While clusters larger than dimers are more efficiently detected as secondary ions, certain species, such as As2, Au and Au2, are more efficiently detected through the neutral channel. Continuously tuning the photon wavelength allows photoionization efficiency (PIE) curves to be obtained for sputtered Asm (m=1,2) and Aun (n=1-4). From the observed ionization thresholds, sputtered neutral As and Au show no clear evidence of electronic excitation, while neutral clusters have photoionization onsets shifted to lower energies by ~;;0.3 eV. These shifts are attributed to unresolved vibrational and rotational excitations. High-spatial resolution chemical imaging with synchrotron VUV postionization is demonstrated at two different photon energies using a copper TEM grid embedded in indium. The resulting images are used to illustrate the use of tunable VUV light for verifying mass peak assignments by exploiting the unique wavelength-dependent PIE of each sputtered neutral species. This capability is valuable for identifying compounds when imaging chemically complex systems with …
Date: December 5, 2008
Creator: Takahashi, Lynelle; Zhou, Jia; Wilson, Kevin R.; Leone, Stephen R. & Ahmed, Musahid
Object Type: Article
System: The UNT Digital Library
Laser Tracker Calibration - Testing the Angle Measurement System - (open access)

Laser Tracker Calibration - Testing the Angle Measurement System -

Physics experiments at the SLAC National Accelerator Laboratory (SLAC) usually require high accuracy positioning, e. g. 100 {micro}m over a distance of 150 m or 25 {micro}m in a 10 x 10 x 3 meter volume. Laser tracker measurement systems have become one of the most important tools for achieving these accuracies when mapping components. The accuracy of these measurements is related to the manufacturing tolerances of various individual components, the resolutions of measurement systems, the overall precision of the assembly, and how well imperfections can be modeled. As with theodolites and total stations, one can remove the effects of most assembly and calibration errors by measuring targets in both direct and reverse positions and computing the mean to obtain the result. However, this approach does not compensate for errors originating from the encoder system. In order to improve and gain a better understanding of laser tracker angle measurement tolerances we extended our laboratory's capabilities with the addition of a horizontal angle calibration test stand. This setup is based on the use of a high precision rotary table providing an angular accuracy of better than 0.2 arcsec. Presently, our setup permits only tests of the horizontal angle measurement system. A …
Date: December 5, 2008
Creator: Gassner, Georg & Ruland, Robert
Object Type: Article
System: The UNT Digital Library
Local Two-Photon Couplings and the J=0 Fixed Pole in Real and Virtual Compton Scattering (open access)

Local Two-Photon Couplings and the J=0 Fixed Pole in Real and Virtual Compton Scattering

The local coupling of two photons to the fundamental quark currents of a hadron gives an energy-independent contribution to the Compton amplitude proportional to the charge squared of the struck quark, a contribution which has no analog in hadron scattering reactions. We show that this local contribution has a real phase and is universal, giving the same contribution for real or virtual Compton scattering for any photon virtuality and skewness at fixed momentum transfer squared t. The t-dependence of this J = 0 fixed Regge pole is parameterized by a yet unmeasured even charge-conjugation form factor of the target nucleon. The t = 0 limit gives an important constraint on the dependence of the nucleon mass on the quark mass through the Weisberger relation. We discuss how this 1=x form factor can be extracted from high energy deeply virtual Compton scattering and examine predictions given by models of the H generalized parton distribution.
Date: December 5, 2008
Creator: Brodsky, Stanley J.; Llanes-Estrada, Felipe J. & Szczepaniak, Adam P.
Object Type: Article
System: The UNT Digital Library
Metrics for the National SCADA Test Bed Program (open access)

Metrics for the National SCADA Test Bed Program

The U.S. Department of Energy Office of Electricity Delivery and Energy Reliability (DOE-OE) National SCADA Test Bed (NSTB) Program is providing valuable inputs into the electric industry by performing topical research and development (R&D) to secure next generation and legacy control systems. In addition, the program conducts vulnerability and risk analysis, develops tools, and performs industry liaison, outreach and awareness activities. These activities will enhance the secure and reliable delivery of energy for the United States. This report will describe metrics that could be utilized to provide feedback to help enhance the effectiveness of the NSTB Program.
Date: December 5, 2008
Creator: Craig, Philip A.; Mortensen, J. & Dagle, Jeffery E.
Object Type: Report
System: The UNT Digital Library
Modern Scientific Visualization is more than Just Pretty Pictures (open access)

Modern Scientific Visualization is more than Just Pretty Pictures

While the primary product of scientific visualization is images and movies, its primary objective is really scientific insight. Too often, the focus of visualization research is on the product, not the mission. This paper presents two case studies, both that appear in previous publications, that focus on using visualization technology to produce insight. The first applies"Query-Driven Visualization" concepts to laser wakefield simulation data to help identify and analyze the process of beam formation. The second uses topological analysis to provide a quantitative basis for (i) understanding the mixing process in hydrodynamic simulations, and (ii) performing comparative analysis of data from two different types of simulations that model hydrodynamic instability.
Date: December 5, 2008
Creator: Bethel, E Wes; Rubel, Oliver; Wu, Kesheng; Weber, Gunther; Pascucci, Valerio; Childs, Hank et al.
Object Type: Article
System: The UNT Digital Library
Rapid Response Small Machining NNR Project 703025 (open access)

Rapid Response Small Machining NNR Project 703025

This project was an effort to develop a machining area for small sized parts that is capable of delivering product with a quick response time. This entailed focusing efforts on leaning out specific work cells that would result in overall improvement to the entire machining area. This effort involved securing the most efficient available technologies for these areas. In the end, this incorporated preparing the small machining area for transformation to a new facility.
Date: December 5, 2008
Creator: Kanies, Tim
Object Type: Report
System: The UNT Digital Library
Structures and Functions of Oligosaccharins: The Role of Endoglycanases (open access)

Structures and Functions of Oligosaccharins: The Role of Endoglycanases

The research proposed will investigate two projects that involve studies of the chemistry and biology of protein/protein and protein/carbohydrate interactions involved in host/pathogen interactions. Specifically, the projects involve (i) the interactions between fungal endopolygalacturonases and plant polygalacturonase-inhibiting proteins and (ii) the interactions between fungal endoxylanases and plant arabinoxylans. During pathogenesis fungi secrete families of endoglycanases that fragment the cell wall polysaccharides of the plant host. The result of endoglycanase action on cell wall polysaccharides can include weakening of the wall, penetration of host cells by the pathogen, solubilization of carbohydrate nutrients, and formation of oligosaccharins (oligosaccharides with regulatory function) that can stimulate plant defenses. We have made significant advances during the last funding period to support the hypothesis that the outcome of attempted pathogenesis can be influenced by protein/protein and protein/carbohydrate interactions in the extracellular matrices of the host and pathogen. We plan to expand on those successes by further exploring the mechanism of action of the endoglycanases and their plant-derived inhibitors, the expression of the various members of the endoglycanase families at various stages of infection and their role in the release of oligosaccharins and in pathogenicity, as well as the role played by the polysaccharide substrates in both …
Date: December 5, 2008
Creator: Bergmann, Carl W.
Object Type: Report
System: The UNT Digital Library
Thermodynamic Characterization of Mexico City Aerosol during MILAGRO 2006 (open access)

Thermodynamic Characterization of Mexico City Aerosol during MILAGRO 2006

Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM{sub 2.5} is insensitive to changes in ammonia but is to acidic semivolatile species. For particle sizes up to 1 {micro}m diameter, semi-volatile partitioning requires 30-60 min to equilibrate; longer time is typically required during the night and early morning hours. When the aerosol sulfate-to-nitrate molar ratio is less than unity, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as 'equivalent sodium' (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatically. This suggests that explicitly considering crustals in the thermodynamic calculations is required to accurately predict the partitioning and phase state of aerosols.
Date: December 5, 2008
Creator: Fountoukis, C.; Nenes, A.; Sullivan, A.; Weber, R.; VanReken, T.; Fischer, M. et al.
Object Type: Article
System: The UNT Digital Library
Time-resolved Studies of Phase Transition Dynamics in Strongly Correlated Manganites (open access)

Time-resolved Studies of Phase Transition Dynamics in Strongly Correlated Manganites

Ultrafast light pulses can be used to control electronic, magnetic and structural phases of complex solids. Here, we investigate the dynamics of insulator-metal phase transitions in colossal magnetoresistive (CMR) manganites by a combination of femtosecond visible-to-midinfrared pump-probe techniques and transport measurements. We show that an insulator-metal transition can be stimulated in CMR manganites by both above bandgap excitation and selective excitation of individual vibrational degrees of freedom. These two approaches rely on the ultrafast manipulation of parameters controlling the electronic filling and the electronic bandwidth respectively, extending the concepts of filling and bandwidth control to the ultrafast timescale. The ultrafast vibrational control of correlated-electron phases may provide new insights into the role played by lattice vibrations in determining the electronic properties of complex solids.
Date: December 5, 2008
Creator: Rini, M.; Tobey, R.; Dean, N.; Wall, S.; Ehrke, H.; Zhu, Y. et al.
Object Type: Article
System: The UNT Digital Library
Universal Entanglement Entropy in 2D Conformal Quantum Critical Points (open access)

Universal Entanglement Entropy in 2D Conformal Quantum Critical Points

We study the scaling behavior of the entanglement entropy of two dimensional conformal quantum critical systems, i.e. systems with scale invariant wave functions. They include two-dimensional generalized quantum dimer models on bipartite lattices and quantum loop models, as well as the quantum Lifshitz model and related gauge theories. We show that, under quite general conditions, the entanglement entropy of a large and simply connected sub-system of an infinite system with a smooth boundary has a universal finite contribution, as well as scale-invariant terms for special geometries. The universal finite contribution to the entanglement entropy is computable in terms of the properties of the conformal structure of the wave function of these quantum critical systems. The calculation of the universal term reduces to a problem in boundary conformal field theory.
Date: December 5, 2008
Creator: Hsu, Benjamin; Mulligan, Michael; Fradkin, Eduardo & Kim, Eun-Ah
Object Type: Article
System: The UNT Digital Library
A VUV photoionization measurement and ab-initio calculation of the ionization energy of gas phase SiO2 (open access)

A VUV photoionization measurement and ab-initio calculation of the ionization energy of gas phase SiO2

In this work we report on the detection and vacuum-ultraviolet (VUV) photoionization of gas phase SiO2 generated in situ via laser ablation of silicon in a CO2 molecular beam. The resulting species are investigated by single photon ionization with tunable VUV synchrotron radiation and mass analyzed using reflectron mass spectrometry. Photoionization efficiency (PIE) curves are recorded for SiO and SiO2 and ionization energy estimates are revealed from such measurements. A state-to-state ionizationenergy of 12.60 (+-0.05) eV is recorded by fitting two prominent peaks in the PIE curve for the following process: 1SUM O-Si-O --> 2PRODg [O-Si-O]+. Electronic structure calculations aid in the interpretation of the photoionization process and allow for identification of the symmetric stretch of 2PRODg [O-Si-O]+ which is observed in the PIE spectrum to be 0.11 eV (890 cm-1) above the ground state of the cation and agrees with the 892 cm-1 symmetric stretch frequency calculated at the CCSD(T)/aug-cc-pVTZ level.
Date: December 5, 2008
Creator: Kostko, Oleg; Ahmed, Musahid & Metz, Ricardo B.
Object Type: Article
System: The UNT Digital Library
Catalytic epoxidation of propene with H2O-O2 reactants on Au/TiO2 (open access)

Catalytic epoxidation of propene with H2O-O2 reactants on Au/TiO2

Au/TiO{sub 2} catalysts form hydroperoxy species from H{sub 2}O-O{sub 2} mixtures at near-ambient temperatures. These species can be used in the selective epoxidation of propene to propylene oxide.
Date: November 5, 2008
Creator: Ojeda, Manuel & Iglesia, Enrique
Object Type: Article
System: The UNT Digital Library
Contraints on New Physics in MFV models: a model-independent analysis of \DeltaF=1 processes (open access)

Contraints on New Physics in MFV models: a model-independent analysis of \DeltaF=1 processes

We analyze the constraints on dimension-six {Delta}F = 1 effective operators in models respecting the MFV hypothesis, both in the one-Higgs doublet case and in the two-Higgs doublet scenario with large tan {beta}. The constraints are derived mainly from the b {yields} s inclusive observables measured at the B factories. The implications of these bounds in view of improved measurements in exclusive and inclusive observables in b {yields} s{ell}{sup +}{ell}{sup -} and s {yields} d{nu}{bar {nu}} transitions are discussed.
Date: November 5, 2008
Creator: Hurth, Tobias; /SLAC, /CERN; Isidori, Gino; /Pisa, Scuola Normale Superiore /INFN, Pisa /Frascati; Kamenik, Jernej F.; /Frascati /Stefan Inst., Ljubljana et al.
Object Type: Article
System: The UNT Digital Library
Evidence for B Semileptonic Decays into the Lambda_c Charm Baryon (open access)

Evidence for B Semileptonic Decays into the Lambda_c Charm Baryon

We present the first evidence for B semileptonic decays into the charmed baryon {Lambda}{sub c}{sup +} based on 420 fb{sup -1} of data collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II e{sup +}e{sup -} storage rings. Events are tagged by fully reconstructing one of the B mesons in a hadronic decay mode. We measure the relative branching fraction {Beta}({bar B} {yields} {Lambda}{sub c}{sup +} X{ell}{sup -}{bar {nu}}{sub {ell}})/{Beta}({bar B} {yields} {Lambda}{sub c}{sup +}/{bar {Lambda}}{sub c}{sup -}X) = (3.2 {+-} 0.9{sub stat.} {+-} 0.9{sub syst.})%. The significance of the signal including the systematic uncertainty is 4.9 standard deviations.
Date: November 5, 2008
Creator: Aubert, Bernard; Bona, M.; Karyotakis, Y.; Lees, J. P.; Poireau, V.; Prencipe, E. et al.
Object Type: Article
System: The UNT Digital Library
F-AREA PUMP TANK 1 MIXING ANALYSIS (open access)

F-AREA PUMP TANK 1 MIXING ANALYSIS

The F-area pump tanks are used to transfer supernate, sludge, and other materials. In any transfer, the solution must stay well mixed without allowing particulate matter to settle out of the liquid and, thus, accumulate in the bottom of the pump tank. Recently, the pulse jet mixing in F-area Pump Tank 1 (FPT1) has been decommissioned. An analysis of the liquid transfer through FPT1 has been performed using computational fluid dynamics (CFD) methods to assess whether or not the velocities throughout the tank will remain high enough to keep all particulate suspended using only transfer and recirculation pumps. The following paragraph is an abbreviated synopsis of the transfer procedure for FPT1 [1, 2]. Prior to a transfer, FPT1 begins to be filled with inhibited water through the inlet transfer line (TI). When the tank liquid level reaches 52.5 inches above the absolute tank bottom, the recirculation pump (RI and RO) is activated. At a tank liquid level of 72.5 inches above the absolute tank bottom, the outlet transfer line (TO) is activated to reduce the liquid level in FPT1 and transfer inhibited water to H-area Pump Tank 7 (HPT7). The liquid level is reduced down to 39.5 inches, with an …
Date: November 5, 2008
Creator: Tamburello, D; Richard Dimenna, R & Si Lee, S
Object Type: Report
System: The UNT Digital Library
Far-from-equilibrium measurements of thermodynamic length (open access)

Far-from-equilibrium measurements of thermodynamic length

Thermodynamic length is a path function that generalizes the notion of length to the surface of thermodynamic states. Here, we show how to measure thermodynamic length in far-from-equilibrium experiments using the work fluctuation relations. For these microscopic systems, it proves necessary to define the thermodynamic length in terms of the Fisher information. Consequently, the thermodynamic length can be directly related to the magnitude of fluctuations about equilibrium. The work fluctuation relations link the work and the free energy change during an external perturbation on a system. We use this result to determine equilibrium averages at intermediate points of the protocol in which the system is out-of-equilibrium. This allows us to extend Bennett's method to determine the potential of mean force, as well as the thermodynamic length, in single molecule experiments.
Date: November 5, 2008
Creator: Feng, Edward H. & Crooks, Gavin E.
Object Type: Article
System: The UNT Digital Library
Full Fuel-Cycle Comparison of Forklift Propulsion Systems.A (open access)

Full Fuel-Cycle Comparison of Forklift Propulsion Systems.A

Hydrogen has received considerable attention as an alternative to fossil fuels. The U.S. Department of Energy (DOE) investigates the technical and economic feasibility of promising new technologies, such as hydrogen fuel cells. A recent report for DOE identified three near-term markets for fuel cells: (1) Emergency power for state and local emergency response agencies, (2) Forklifts in warehousing and distribution centers, and (3) Airport ground support equipment markets. This report examines forklift propulsion systems and addresses the potential energy and environmental implications of substituting fuel-cell propulsion for existing technologies based on batteries and fossil fuels. Industry data and the Argonne Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model are used to estimate full fuel-cycle emissions and use of primary energy sources, back to the primary feedstocks for fuel production. Also considered are other environmental concerns at work locations. The benefits derived from using fuel-cell propulsion are determined by the sources of electricity and hydrogen. In particular, fuel-cell forklifts using hydrogen made from the reforming of natural gas had lower impacts than those using hydrogen from electrolysis.
Date: November 5, 2008
Creator: Gaines, L. L.; Elgowainy, A.; Wang, M. Q. & Systems, Energy
Object Type: Report
System: The UNT Digital Library
Fundamental Investigations of Nanoscale Phenomena in Beam-Assisted Nucleation, Growth and Surface Smoothing, Using in situ LEEM (open access)

Fundamental Investigations of Nanoscale Phenomena in Beam-Assisted Nucleation, Growth and Surface Smoothing, Using in situ LEEM

The purposes for which this grant was provided were specifically (1) to construct a tandem instrument that combined a low energy electron microscope (LEEM) with an ion beam source capably of irradiating a sample during observation of the surface using LEEM; and (2) to employ the new machine to whatever degree possible to observe the evolution of clean crystal surfaces during ion beam irradiation. A principal motivation was to investigate the fundamental behavior of radiation damage under circumstances for which the damage can be observed directly in real time as it occurs. A second main motivation was to create tunable perturbations of the defect (adatom and advacancy) equilibrium on clean crystal planes and in this way explore the fundamental kinetics of surface behavior that enters into numerous phenomena of interest to DOE including surface erosion, catalysis, and the damage to crystals caused by impacts of energetic particles. The funding has been employed to successfully pursue all the original goals, and additional opportunities that developed as a result of discoveries made in this research.
Date: November 5, 2008
Creator: Flynn, Colin P.
Object Type: Text
System: The UNT Digital Library
Gravity Duals of Lifshitz-Like Fixed Points (open access)

Gravity Duals of Lifshitz-Like Fixed Points

We find candidate macroscopic gravity duals for scale-invariant but non-Lorentz invariant fixed points, which do not have particle number as a conserved quantity. We compute two-point correlation functions which exhibit novel behavior relative to their AdS counterparts, and find holographic renormalization group flows to conformal field theories. Our theories are characterized by a dynamical critical exponent z, which governs the anisotropy between spatial and temporal scaling t {yields} {lambda}{sup z}t, x {yields} {lambda}x; we focus on the case with z = 2. Such theories describe multicritical points in certain magnetic materials and liquid crystals, and have been shown to arise at quantum critical points in toy models of the cuprate superconductors. This work can be considered a small step towards making useful dual descriptions of such critical points.
Date: November 5, 2008
Creator: Kachru, Shamit; /Stanford U., Phys. Dept. /SLAC; Liu, Xiao; Phys., /Perimeter Inst. Theor.; Mulligan, Michael & /Stanford U., Phys. Dept. /SLAC
Object Type: Article
System: The UNT Digital Library
Holographic Systematics of D-brane Inflation (open access)

Holographic Systematics of D-brane Inflation

We provide a systematic treatment of possible corrections to the inflaton potential for D-brane inflation in the warped deformed conifold. We consider the D3-brane potential in the presence of the most general possible corrections to the throat geometry sourced by coupling to the bulk of a compact Calabi-Yau space. This corresponds to the potential on the Coulomb branch of the dual gauge theory, in the presence of arbitrary perturbations of the Lagrangian. The leading contributions arise from perturbations by the most relevant operators that do not destroy the throat geometry. We find a generic contribution from a non-chiral operator of dimension {Delta} = 2 associated with a global symmetry current, resulting in a negative contribution to the inflaton mass-squared. If the Calabi-Yau preserves certain discrete symmetries, this is the dominant correction to the inflaton potential, and fine-tuning of the inflaton mass is possible. In the absence of such discrete symmetries, the dominant contribution comes from a chiral operator with {Delta} = 3/2, corresponding to a {phi}{sup 3/2} term in the inflaton potential. The resulting inflationary models are phenomenologically identical to the inflection point scenarios arising from specific D7-brane embeddings, but occur under far more general circumstances. Our strategy extends immediately …
Date: November 5, 2008
Creator: Baumann, Daniel; /Harvard U., Phys. Dept. /Princeton U.; Dymarsky, Anatoly; /Stanford U., Phys. Dept.; Kachru, Shamit; /Stanford U., Phys. Dept. /SLAC et al.
Object Type: Article
System: The UNT Digital Library