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Geometric metastability, quivers and holography

Description: We use large N duality to study brane/anti-brane configurations on a class of Calabi-Yau manifolds. With only branes present, the Calabi-Yau manifolds in question give rise to N=2 ADE quiver theories deformed by superpotential terms. We show that the large N duality conjecture of hep-th/0610249 reproduces correctly the known qualitative features of the brane/anti-brane physics. In the supersymmetric case, the gauge theories have Seiberg dualities which are represented as flops in the geometry. Moreover, the holographic dual geometry encodes the whole RG flow of the gauge theory. In the non-supersymmetric case, the large N duality predicts that the brane/anti-brane theories also enjoy such dualities, and allows one to pick out the good description at a given energy scale.
Date: September 6, 2007
Creator: Aganagic, Mina; Aganagic, Mina; Beem, Christopher & Freivogel, Ben
Partner: UNT Libraries Government Documents Department

FY2012 summary of tasks completed on PROTEUS-thermal work.

Description: PROTEUS is a suite of the neutronics codes, both old and new, that can be used within the SHARP codes being developed under the NEAMS program. Discussion here is focused on updates and verification and validation activities of the SHARP neutronics code, DeCART, for application to thermal reactor analysis. As part of the development of SHARP tools, the different versions of the DeCART code created for PWR, BWR, and VHTR analysis were integrated. Verification and validation tests for the integrated version were started, and the generation of cross section libraries based on the subgroup method was revisited for the targeted reactor types. The DeCART code has been reorganized in preparation for an efficient integration of the different versions for PWR, BWR, and VHTR analysis. In DeCART, the old-fashioned common blocks and header files have been replaced by advanced memory structures. However, the changing of variable names was minimized in order to limit problems with the code integration. Since the remaining stability problems of DeCART were mostly caused by the CMFD methodology and modules, significant work was performed to determine whether they could be replaced by more stable methods and routines. The cross section library is a key element to obtain accurate solutions. Thus, the procedure for generating cross section libraries was revisited to provide libraries tailored for the targeted reactor types. To improve accuracy in the cross section library, an attempt was made to replace the CENTRM code by the MCNP Monte Carlo code as a tool obtaining reference resonance integrals. The use of the Monte Carlo code allows us to minimize problems or approximations that CENTRM introduces since the accuracy of the subgroup data is limited by that of the reference solutions. The use of MCNP requires an additional set of libraries without resonance cross sections so that reference ...
Date: June 6, 2012
Creator: Lee, C.H. & Smith, M.A. (Nuclear Engineering Division)
Partner: UNT Libraries Government Documents Department

Higher Order Modes Damping Analysis for the SPX Deflecting Cavity Cyromodule

Description: A single-cell superconducting deflecting cavity operating at 2.815 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source (APS) upgrade. A cryomodule of 4 such cavities will be needed to produce the required 2-MV deflecting voltage. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. The damping of the LOM/HOM below the beampipe cutoff has been analyzed in the single cavity geometry and shown to meet the design requirements. The HOM above the beampipe cutoff in the 4-cavity cyromodule, however, may result in cross coupling which may affect the HOM damping and potentially be trapped between the cavities which could produce RF heating to the beamline bellows. We have evaluated the HOM damping in the 4-cavity cryomodule using the parallel finite element EM code suite ACE3P developed at SLAC. We will present the results of the cryomodule analysis in this paper.
Date: June 6, 2012
Creator: Xiao, L; Li, Z.; Ng, C.; /SLAC; Nassiri, A.; Waldschmidt, G. et al.
Partner: UNT Libraries Government Documents Department

Black Hole Entropy, Marginal Stability and Mirror Symmetry

Description: We consider the superconformal quantum mechanics associated to BPS black holes in type IIB Calabi-Yau compactifications. This quantum mechanics describes the dynamics of D-branes in the near-horizon attractor geometry of the black hole. In many cases, the black hole entropy can be found by counting the number of chiral primaries in this quantum mechanics. Both the attractor mechanism and notions of marginal stability play important roles in generating the large number of microstates required to explain this entropy. We compute the microscopic entropy explicitly in a few different cases, where the theory reduces to quantum mechanics on the moduli space of special Lagrangians. Under certain assumptions, the problem may be solved by implementing mirror symmetry as three T-dualities: this is essentially the mirror of a calculation by Gaiotto, Strominger and Yin. In some simple cases, the calculation may be done in greater generality without resorting to conjectures about mirror symmetry. For example, the K3 x T{sub 2} case may be studied precisely using the Fourier-Mukai transform.
Date: October 6, 2006
Creator: Aspinwall, Paul S.; Maloney, Alexander & Simons, Aaron
Partner: UNT Libraries Government Documents Department

Precise Calculation of Traveling-Wave Periodic Structure

Description: The effects of the round edge beam hole on the frequency and wake field are studied using variational method, which allows for rounded iris disk hole without any approximation in shape treatment. The frequency and wake field of accelerating mode and dipole mode are studied for different edge radius cases, including the flat edge shape that is often used to approximately represent the actual structure geometry. The edge hole shape has weak effect on the frequency, but much effect on the wake field. Our study shows that the amounts of wake fields are not precise enough with the assumption of the flat edge beam hole instead of round edge.
Date: July 6, 2007
Creator: Wang, L.; Li, Z.; Seryi, A. & /SLAC
Partner: UNT Libraries Government Documents Department

Monte Carlo Particle Transport Capability for Inertial Confinement Fusion Applications

Description: A time-dependent massively-parallel Monte Carlo particle transport calculational module (ParticleMC) for inertial confinement fusion (ICF) applications is described. The ParticleMC package is designed with the long-term goal of transporting neutrons, charged particles, and gamma rays created during the simulation of ICF targets and surrounding materials, although currently the package treats neutrons and gamma rays. Neutrons created during thermonuclear burn provide a source of neutrons to the ParticleMC package. Other user-defined sources of particles are also available. The module is used within the context of a hydrodynamics client code, and the particle tracking is performed on the same computational mesh as used in the broader simulation. The module uses domain-decomposition and the MPI message passing interface to achieve parallel scaling for large numbers of computational cells. The Doppler effects of bulk hydrodynamic motion and the thermal effects due to the high temperatures encountered in ICF plasmas are directly included in the simulation. Numerical results for a three-dimensional benchmark test problem are presented in 3D XYZ geometry as a verification of the basic transport capability. In the full paper, additional numerical results including a prototype ICF simulation will be presented.
Date: November 6, 2006
Creator: Brantley, P S & Stuart, L M
Partner: UNT Libraries Government Documents Department

FY05 LDRD Final ReportNanomaterials for Radiation Detection

Description: We have demonstrated that it is possible to enhance current radiation detection capability by manipulating the materials at the nano level. Fabrication of three-dimensional (3-D) nanomaterial composite for radiation detection has great potential benefits over current semiconductor- and scintillation-based technologies because of the precise control of material-radiation interaction and modulation of signal output. It is also a significant leap beyond current 2-D nanotechnology. Moreover, since we are building the materials using a combination of top-down and bottom-up approaches, this strategy to make radiation detection materials can provide significant improvement to radiation-detection technologies, which are currently based on difficult-to-control bulk crystal growth techniques. We are applying this strategy to tackle two important areas in radiation detection: gamma-rays and neutrons. In gamma-ray detection, our first goal is to employ nanomaterials in the form of quantum-dot-based mixed matrices or nanoporous semiconductors to achieve scintillation output several times over that from NaI(Tl) crystals. In neutron detection, we are constructing a 3-D structure using a doped nanowire ''forest'' supported by a boron matrix and evaluating the detection efficiency of different device geometry with simulation.
Date: February 6, 2006
Creator: Wang, T F; Letant, S E; Nikolic, R J & Chueng, C L
Partner: UNT Libraries Government Documents Department

A High Resolution Monolithic Crystal, DOI, MR Compatible, PET Detector

Description: The principle objective of this proposal is to develop a positron emission tomography (PET) detector with depth-of-interaction (DOI) positioning capability that will achieve state of the art spatial resolution and sensitivity performance for small animal PET imaging. When arranged in a ring or box detector geometry, the proposed detector module will support <1 mm3 image resolution and >15% absolute detection efficiency. The detector will also be compatible with operation in a MR scanner to support simultaneous multi-modality imaging. The detector design will utilize a thick, monolithic crystal scintillator readout by a two-dimensional array of silicon photomultiplier (SiPM) devices using a novel sensor on the entrance surface (SES) design. Our hypothesis is that our single-ended readout SES design will provide an effective DOI positioning performance equivalent to more expensive dual-ended readout techniques and at a significantly lower cost. Our monolithic crystal design will also lead to a significantly lower cost system. It is our goal to design a detector with state of the art performance but at a price point that is affordable so the technology can be disseminated to many laboratories. A second hypothesis is that using SiPM arrays, the detector will be able to operate in a MR scanner without any degradation in performance to support simultaneous PET/MR imaging. Having a co-registered MR image will assist in radiotracer localization and may also be used for partial volume corrections to improve radiotracer uptake quantitation. The far reaching goal of this research is to develop technology for medical research that will lead to improvements in human health care.
Date: March 6, 2012
Creator: Miyaoka, Robert S
Partner: UNT Libraries Government Documents Department

Angularly Adaptive P1--Double P0 Diffusion Solutions of Non-Equilibrium Grey Radiative Transfer Problems in Planar Geometry

Description: The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. The standard P{sub 1} angular approximation represents the angular dependence of the radiation specific intensity using a linear function in the angular domain -1 {le} {mu} {le} 1. In contrast, the DP{sub 0} angular approximation represents the angular dependence as isotropic in each half angular range -1 {le} {mu} < 0 and 0 < {mu} {le} 1. Neglecting the time derivative of the radiation flux, both the P{sub 1} and DP{sub 0} equations can be written as a single diffusion equation for the radiation energy density. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near the non-equilibrium wave front. We develop an adaptive angular technique that locally uses either the DP{sub 0} or the P{sub 1} diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for a test problem due to Su and Olson for which a semi-analytic transport solution exists. The numerical results demonstrate that the adaptive P{sub 1}-DP{sub 0} diffusion approximation can yield improvements in accuracy over the standard P{sub 1} diffusion approximation for non-equilibrium grey radiative transfer.
Date: June 6, 2005
Creator: Brantley, P S
Partner: UNT Libraries Government Documents Department

Two-dimensional Fully Kinetic Simulations Of Driven Magnetic Reconnection With Boundary Conditions Relevant To The Magnetic Reconnection Experimen

Description: Two-dimensional fully kinetic simulations are performed using global boundary conditions relevant to model the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys Plasmas 4, 1936 (1997)]. The geometry is scaled in terms of the ion kinetic scales in the experiment, and a reconnection layer is created by reducing the toroidal current in the flux cores in a manner similar to the actual experiment. The ion-scale features in these kinetic simulations are in remarkable agreement with those observed in MRX, including the reconnection inflow rate and quadrupole field structure. In contrast, there are significant discrepancies in the simulated structure of the electron layer that remain unexplained. In particular, the measured thickness of the electron layers is 3�5 times thicker in MRX than in the kinetic simulations. The layer length is highly sensitive to downstream boundary conditions as well as the time over which the simulation is driven. However, for a fixed set of chosen boundary conditions, an extrapolation of the scaling with the ion to electron mass ratio implies that at realistic mass ratio both the length and width will be too small compared to the experiment. This discrepancy implies that the basic electron layer physics may differ significantly between MRX and the two-dimensional, collisionless simulations. The two leading possibilities to explain the discrepancy are weak Coulomb collisions and three-dimensional effects that are present in the experiment but not included in the simulation model.
Date: November 6, 2008
Creator: S. Dorfman, W. Daughton, V. Roytershteyn, H. Ji, Y. Ren, and M. Yamada
Partner: UNT Libraries Government Documents Department

A Search for Pentaquarks

Description: Recently observed hadrons that do not fit into the ''normal'' spectroscopic order should have been produced in old experiments. Are these claims supported by the legacy data? Fermilab Experiment 690 collected a 5 x 10{sup 9} event sample of p+p{yields} p{sub f}+X events at a beam momentum of 800 GeV/c ({radical}s = 38.8 GeV) at Lab G in the Neutrino-East beam line in the Tevatron 1991 fixed target run. The detector was an open geometry magnetic spectrometer with large geometric acceptance and extremely good momentum resolution.
Date: September 6, 2005
Creator: Hartouni, E
Partner: UNT Libraries Government Documents Department

Proposed Few-optical Cycle Laser-driven ParticleAccelerator Structure

Description: We describe a transparent dielectric grating accelerator structure that is designed for ultra-short laser pulse operation. The structure is based on the principle of periodic field reversal to achieve phase synchronicity for relativistic particles, however to preserve ultra-short pulse operation it does not resonate the laser field in the vacuum channel. The geometry of the structure appears well suited for application with high average power lasers and high thermal loading. Finally, it shows potential for an unloaded gradient of 10 GeV/m with 10 fsec laser pulses and the possibility to accelerate 10{sup 6} electrons per bunch at an efficiency of 8%. The fabrication procedure and a proposed near term experiment with this accelerator structure are presented.
Date: October 6, 2006
Creator: Plettner, T.; Lu, P.; Byer, R.L. & /Stanford U., Ginzton Lab.
Partner: UNT Libraries Government Documents Department

Multi-Grained Level of Detail for Rendering Complex Meshes Using a Hierarchical Seamless Texture Atlas

Description: Previous algorithms for view-dependent level of detail provide local mesh refinements either at the finest granularity or at a fixed, coarse granularity. The former provides triangle-level adaptation, often at the expense of heavy CPU usage and low triangle rendering throughput; the latter improves CPU usage and rendering throughput by operating on groups of triangles. We present a new multiresolution hierarchy and associated algorithms that provide adaptive granularity. This multi-grained hierarchy allows independent control of the number of hierarchy nodes processed on the CPU and the number of triangles to be rendered on the GPU. We employ a seamless texture atlas style of geometry image as a GPU-friendly data organization, enabling efficient rendering and GPU-based stitching of patch borders. We demonstrate our approach on both large triangle meshes and terrains with up to billions of vertices.
Date: November 6, 2006
Creator: Niski, K; Purnomo, B & Cohen, J
Partner: UNT Libraries Government Documents Department

Update on the Development and Validation of MERCURY: A Modern, Monte Carlo Particle Transport Code

Description: An update on the development and validation of the MERCURY Monte Carlo particle transport code is presented. MERCURY is a modern, parallel, general-purpose Monte Carlo code being developed at the Lawrence Livermore National Laboratory. During the past year, several major algorithm enhancements have been completed. These include the addition of particle trackers for 3-D combinatorial geometry (CG), 1-D radial meshes, 2-D quadrilateral unstructured meshes, as well as a feature known as templates for defining recursive, repeated structures in CG. New physics capabilities include an elastic-scattering neutron thermalization model, support for continuous energy cross sections and S ({alpha}, {beta}) molecular bound scattering. Each of these new physics features has been validated through code-to-code comparisons with another Monte Carlo transport code. Several important computer science features have been developed, including an extensible input-parameter parser based upon the XML data description language, and a dynamic load-balance methodology for efficient parallel calculations. This paper discusses the recent work in each of these areas, and describes a plan for future extensions that are required to meet the needs of our ever expanding user base.
Date: June 6, 2005
Creator: Procassini, R J; Taylor, J M; McKinley, M S; Greenman, G M; Cullen, D E; O'Brien, M J et al.
Partner: UNT Libraries Government Documents Department

Measurement of Thermal Dependencies of PBG Fiber Properties

Description: Photonic crystal fibers (PCFs) represent a class of optical fibers which have a wide spectrum of applications in the telecom and sensing industries. Currently, the Advanced Accelerator Research Department at SLAC is developing photonic bandgap particle accelerators, which are photonic crystal structures with a central defect used to accelerate electrons and achieve high longitudinal electric fields. Extremely compact and less costly than the traditional accelerators, these structures can support higher accelerating gradients and will open a new era in high energy physics as well as other fields of science. Based on direct laser acceleration in dielectric materials, the so called photonic band gap accelerators will benefit from mature laser and semiconductor industries. One of the key elements to direct laser acceleration in hollow core PCFs, is maintaining thermal and structural stability. Previous simulations demonstrate that accelerating modes are sensitive to the geometry of the defect region and the variations in the effective index. Unlike the telecom modes (for which over 95% of the energy propagates in the hollow core) most of the power of these modes is located in the glass at the periphery of the central hole which has a higher thermal constant than air ({gamma}{sub SiO{sub 2}} = 1.19 x 10{sup -6} 1/K, {gamma}{sub air} = -9 x 10{sup -7} 1/K with {gamma} = dn/dT). To fully control laser driven acceleration, we need to evaluate the thermal and structural consequences of such modes on the PCFs. We are conducting series of interferometric tests to quantify the dependencies of the HC-633-02 (NKT Photonics) propagation constant (k{sub z}) on temperature, vibration amplitude, stress and electric field strength. In this paper we will present the theoretical principles characterizing the thermal behavior of a PCF, the measurements realized for the fundamental telecom mode (TE{sub 00}), and the experimental demonstration of TM-like mode ...
Date: July 6, 2011
Creator: Laouar, Rachik
Partner: UNT Libraries Government Documents Department

D-Branes in Curved Space

Description: This thesis is a study of D-branes in string compactifications. In this context, D-branes are relevant as an important component of the nonperturbative spectrum, as an incisive probe of these backgrounds, and as a natural stringy tool for localizing gauge interactions. In the first part of the thesis, we discuss half-BPS D-branes in compactifications of type II string theory on Calabi-Yau threefolds. The results we describe for these objects are pertinent both in their role as stringy brane-worlds, and in their role as solitonic objects. In particular, we determine couplings of these branes to the moduli determining the closed-string geometry, both perturbatively and non-perturbatively in the worldsheet expansion. We provide a local model for transitions in moduli space where the BPS spectrum jumps, and discuss the extension of mirror symmetry between Calabi-Yau manifolds to the case when D-branes are present. The next section is an interlude which provides some applications of D-branes to other curved backgrounds of string theory. In particular, we discuss a surprising phenomenon in which fundamental strings moving through background Ramond-Ramond fields dissolve into large spherical D3-branes. This mechanism is used to explain a previously-mysterious fact discovered via the AdS-CFT correspondence. Next, we make a connection between type IIA string vacua of the type discussed in the first section and M-theory compactifications on manifolds of G{sub 2} holonomy. Finally we discuss constructions of string vacua which do not have large radius limits. In the final part of the thesis, we develop techniques for studying the worldsheets of open strings ending on the curved D-branes studied in the first section. More precisely, we formulate a large class of massive two-dimensional gauge theories coupled to boundary matter, which flow in the infrared to the relevant boundary conformal field theories. Along with many other applications, these techniques are used to ...
Date: July 6, 2005
Creator: McGreevy, John Austen
Partner: UNT Libraries Government Documents Department

Validation and Comparison of KENO V.a and KENO-VI

Description: This report documents the validation and comparison of KENO V.a and KENO-VI using the SCALE 27-group ENDF/B-IV and 238-group ENDF/B-V cross-section libraries against critical experiments. Experiments considered were primarily high- or low-enriched uranium systems. The results indicate that KENO V.a and KENO-VI Monte Carlo Criticality Programs accurately calculate a broad range of critical experiments. A number of the calculations showed a positive or negative bias in excess of 1 1/2% in k-effective (k{sub eff}). Classes of criticals that show a bias include 3% enriched green blocks, highly-enriched uranyl fluoride slab arrays, and highly-enriched uranyl nitrate arrays. If these biases are properly taken into account, KENO V.a and KENO-VI can be used with confidence for the design and criticality safety analysis of uranium-containing systems. KENO V.a and KENO-VI calculate the same k{sub eff} for a system within statistics and thus may be used interchangeably as long as the geometry of the problem can be modeled.
Date: May 6, 2002
Creator: Fox, P.B.
Partner: UNT Libraries Government Documents Department

Hexahedron, wedge, tetrahedron, and pyramid diffusion operator discretization

Description: The diffusion equation, {phi}({rvec x}), is solved by finding the extrema of the functional, {Gamma}[{phi}] = {integral}({1/2}D{rvec {nabla}}{phi}{center_dot}{rvec {nabla}}{phi} + {1/2}{sigma}{sub a}{phi}{sup 2} - {ital Q}{phi}){ital d}{sup 3}{ital x}. A matrix is derived that is investigated for hexahedron, wedge, tetrahedron, and pyramid cells. The first term of the diffusion integration was concentrated and the others dropped; these dropped terms are also considered. Results are presented for hexahedral meshes and three weighting methods.
Date: August 6, 1996
Creator: Roberts, R. M.
Partner: UNT Libraries Government Documents Department

Estimates of error introduced when one-dimensional inverse heat transfer techniques are applied to multi-dimensional problems

Description: A study of the errors introduced when one-dimensional inverse heat conduction techniques are applied to problems involving two-dimensional heat transfer effects was performed. The geometry used for the study was a cylinder with similar dimensions as a typical container used for the transportation of radioactive materials. The finite element analysis code MSC P/Thermal was used to generate synthetic test data that was then used as input for an inverse heat conduction code. Four different problems were considered including one with uniform flux around the outer surface of the cylinder and three with non-uniform flux applied over 360{degree}, 180{degree}, and 90{degree} sections of the outer surface of the cylinder. The Sandia One-Dimensional Direct and Inverse Thermal (SODDIT) code was used to estimate the surface heat flux of all four cases. The error analysis was performed by comparing the results from SODDIT and the heat flux calculated based on the temperature results obtained from P/Thermal. Results showed an increase in error of the surface heat flux estimates as the applied heat became more localized. For the uniform case, SODDIT provided heat flux estimates with a maximum error of 0.5% whereas for the non-uniform cases, the maximum errors were found to be about 3%, 7%, and 18% for the 360{degree}, 180{degree}, and 90{degree} cases, respectively.
Date: January 6, 2000
Creator: Lopez, C.; Koski, J.A. & Razani, A.
Partner: UNT Libraries Government Documents Department

Circulating Fluid-Bed Technology for Advanced Power Systems

Description: Circulating fluid bed technology offers the advantages of a plug flow, yet well-mixed, and high throughput reactor for power plant applications. The ability to effectively scale these systems in size, geometry, and operating conditions is limited because of the extensive deviation from ideal dilute gas-solids flow behavior (Monazam et al., 2001; Li, 1994). Two fluid computations show promise of accurately simulating the hydrodynamics in the riser circulating fluid bed; however, validation tests for large vessels with materials of interest to the power industry are lacking (Guenther et al., 2002). There is little available data in reactors large enough so that geometry (i.e. entrance, exit, and wall) effects do not dominate the hydrodynamics, yet with sufficiently large particle sizes to allow sufficiently large grid sizes to allow accurate and timely hydrodynamic simulations. To meet this need experimental tests were undertaken with relatively large particles of narrow size distribution in a large enough unit to reduce the contributions of wall effects and light enough to avoid geometry effects. While computational fluid dynamic calculations are capable of generating detailed velocity and density profiles, it is believed that the validation and model development begins with the ability to simulate the global flow regime transitions. The purpose of this research is to generate well-defined test data for model validation and to identify and measure critical parameters needed for these simulations.
Date: November 6, 2001
Creator: Shadle, Lawrence J.; Ludlow, J. Christopher; Mei, Joseph S. & Guenther, Christopher
Partner: UNT Libraries Government Documents Department

Effect of channel geometry on the quenching of laminar flames

Description: Report presenting the effect of channel geometry on flame quenching, as calculated on the basis of average active particle chain lengths, is related among six different geometries: plane parallel plates of infinite extent, cylindrical tubes, rectangular slots, cylindrical annuli, and tubes of elliptical and equilaterally triangular shape. The results indicated that the observed variation of flame quenching as a function of quenching geometry may be successfully predicted for a range of pressures and for rich as well as lean propane-air flames.
Date: May 6, 1954
Creator: Berlad, A. L. & Potter, A. E., Jr.
Partner: UNT Libraries Government Documents Department