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Species doubling and effective Lagrangians

Description: Coupling gauge fields to the chiral currents from an effective Lagrangian for pseudoscalar mesons naturally gives rise to a species doubling phenomenon similar to that seen with fermionic fields in lattice gauge theory. 17 refs.
Date: September 1, 1996
Creator: Creutz, M. & Tytgat, M.
Partner: UNT Libraries Government Documents Department


Description: Vortex breakdown is simulated by a three dimensional Lagrangian method using vortex filaments. The filaments are approximated by vortex elements and their velocity is computed by a Biot-Savart type law of interaction. The numerical calculations show the development of an axisymmetric bubble with a recirculation zone and resemble in many respects the results obtained in the physical experiments on vortex breakdown.
Date: October 1, 1978
Creator: Prete, Vincenza Del
Partner: UNT Libraries Government Documents Department

1-D Van der Waals Foams Heated by Ion Beam Energy Deposition

Description: One dimensional simulations of various initial average density aluminum foams (modeled as slabs of solid metal separated by low density regions) heated by volumetric energy deposition are conducted with a Lagrangian hydrodynamics code using a van der Waals equation of tate (EOS). The resulting behavior is studied to facilitate the design of future warm dense matter (WDM) experiments at LBNL. In the simulations the energy deposition ranges from 10 to 30 kJ/g and from 0.075 to 4.0 ns total pulse length, resulting in temperatures from approximately 1 o 4 eV. We study peak pressures and temperatures in the foams, expansion velocity, and the phase evolution. Five relevant time scales in the problem are identified. Additionally, we present a method for characterizing the level of inhomogeneity in a foam target as it is heated and the time it takes for a foam to homogenize.
Date: December 23, 2009
Creator: Zylstra, A. B.; Barnard, J. J. & More, R. M.
Partner: UNT Libraries Government Documents Department


Description: A method is proposed for the treatment of concave cells in staggered-grid Lagrangian hydrodynamics. The method is general enough to be applied to two- and three-dimensional unstructured cells. Instead of defining a cell-point as the geometric average of its nodes (a cell-center), the cell-point is that which equalizes the triangular/tetrahedral area/volume in two/three dimensions. Examples are given.
Date: December 1, 2000
Creator: ROUSCULP, C. & BURTON, D.
Partner: UNT Libraries Government Documents Department

Curved mesh generation and mesh refinement using Lagrangian solid mechanics

Description: We propose a method for generating well-shaped curved unstructured meshes using a nonlinear elasticity analogy. The geometry of the domain to be meshed is represented as an elastic solid. The undeformed geometry is the initial mesh of linear triangular or tetrahedral elements. The external loading results from prescribing a boundary displacement to be that of the curved geometry, and the final configuration is determined by solving for the equilibrium configuration. The deformations are represented using piecewise polynomials within each element of the original mesh. When the mesh is sufficiently fine to resolve the solid deformation, this method guarantees non-intersecting elements even for highly distorted or anisotropic initial meshes. We describe the method and the solution procedures, and we show a number of examples of two and three dimensional simplex meshes with curved boundaries. We also demonstrate how to use the technique for local refinement of non-curved meshes in the presence of curved boundaries.
Date: December 31, 2008
Creator: Persson, P.-O. & Peraire, J.
Partner: UNT Libraries Government Documents Department

SPH and Material Failure: Progress Report

Description: Smoothed Particle Hydrodynamics (SPH) is a meshless Lagrangian technique for modeling hydrodynamics, and as such offers some unique advantages when applied to problems of material failure and breakup. The two most important of these advantages are: (1) SPH is Lagrangian and robust--i.e., it is never necessary to advect or remap. Damage models typically involve a number of complex history variables (such as the damage associated with the Lagrangian mass, crack orientations, etc.), and advecting these quantities as is required in a mesh based algorithm is a very challenging problem. (2) SPH allows the Lagrangian points to move about, reconnect, or separate as dictated by the material flow. This naturally allows for the points to move apart as distinct fragments of material form, resulting in gaps or cracks between the fragments. Typically mesh based algorithms represent the ''cracks'' between fragments as zones of failed material, which is quite different than allowing voids devoid of material to form.
Date: April 12, 2005
Creator: Owen, J M
Partner: UNT Libraries Government Documents Department

Analytical and Experimental Investigation of Mixing in Large Passive Containment Volumes

Description: This final report details results from the past three years of the three-year UC Berkeley NEER investigation of mixing phenomena in large-scale passive reactor containments. We have completed all of our three-year deliverables specified in our proposal, as summarized for each deliverable in the body of this report, except for the experiments of steam condensation in the presence of noncondensable gas. We have particularly exiting results from the experiments studying the mixing in large insulated containment with a vertical cooling plate. These experiments now have shown why augmentation has been observed in wall-condensation experiments due to the momentum of the steam break-flow entering large volumes. More importantly, we also have shown that the forced-jet augmentation can be predicted using relatively simple correlations, and that it is independent of the break diameter and depends only on the break flow orientation, location, and momentum. This suggests that we will now be able to take credit for this augmentation in reactor safety analysis, improving safety margins for containment structures. We have finished the version 1 of 1-D Lagrangian flow and heat transfer code BMIX++. This version has ability to solve many complex stratified problems, such as multi-components problems, multi-enclosures problems (two enclosures connected by one connection for the current version), incompressible and compressible problems, multi jets, plumes, sinks in one enclosure problems, problems with wall conduction, and the combinations of the above problems. We believe the BMIX++ code is a very powerful computation tool to study stratified enclosures mixing problems.
Date: October 17, 2002
Creator: Peterson, Per F.
Partner: UNT Libraries Government Documents Department

Paraxial expansion of a static magnetic field in a ring accelerator

Description: In the paraxial approximation, trajectories of beam particles in a ring accelerator are computed expanded in powers of lateral displacements and slopes from a closed reference orbit. To do this, one needs first the expanded expressions of the magnetic field and potentials producing the particle motion. This is derived here in a most general form.
Date: June 1, 1995
Creator: Teng, L.C.
Partner: UNT Libraries Government Documents Department

Strong WW scattering chiral lagrangians, unitarity and resonances

Description: Chiral lagrangians provide a model independent description of the strongly interacting symmetry breaking sector. In this work, first we review the LHC sensitivity to the chiral parameters (in the hardest case of non-resonant low-energy WW scattering). Later we show how to reproduce or predict the resonance spectrum by means of dispersion theory and the inverse amplitude method. We present a parameter space scan that covers many different strong WW scattering scenarios.
Date: August 1, 1996
Creator: Pelaez, J.R.
Partner: UNT Libraries Government Documents Department

Duality in supersymmetric Yang-Mills theory

Description: These lectures provide an introduction to the behavior of strongly-coupled supersymmetric gauge theories. After a discussion of the effective Lagrangian in nonsupersymmetric and supersymmetric field theories, the author analyzes the qualitative behavior of the simplest illustrative models. These include supersymmetric QCD for N{sub f} < N{sub c}, in which the superpotential is generated nonperturbatively, N = 2 SU(2) Yang-Mills theory (the Seiberg-Witten model), in which the nonperturbative behavior of the effect coupling is described geometrically, and supersymmetric QCD for N{sub f} large, in which the theory illustrates a non-Abelian generalization of electric-magnetic duality. 75 refs., 12 figs.
Date: February 1, 1997
Creator: Peskin, M.E.
Partner: UNT Libraries Government Documents Department

Use of an operational model evaluation system for model intercomparison

Description: The Atmospheric Release Advisory Capability (ARAC) is a centralized emergency response system used to assess the impact from atmospheric releases of hazardous materials. As part of an on- going development program, new three-dimensional diagnostic windfield and Lagrangian particle dispersion models will soon replace ARAC`s current operational windfield and dispersion codes. A prototype model performance evaluation system has been implemented to facilitate the study of the capabilities and performance of early development versions of these new models relative to ARAC`s current operational codes. This system provides tools for both objective statistical analysis using common performance measures and for more subjective visualization of the temporal and spatial relationships of model results relative to field measurements. Supporting this system is a database of processed field experiment data (source terms and meteorological and tracer measurements) from over 100 individual tracer releases.
Date: March 1, 1998
Creator: Foster, K. T., LLNL
Partner: UNT Libraries Government Documents Department

Topics in N = 1 supergravity in four dimensions and superstring effective field theories beyond tree-level

Description: In this thesis, the author presents some works in the direction of studying quantum effects in locally supersymmetric effective field theories that appear in the low energy limit of superstring theory. After reviewing the Kaehler covariant formulation of supergravity, he shows the calculation of the divergent one-loop contribution to the effective boson Lagrangian for supergravity, including the Yang-Mills sector and the helicity-odd operators that arise from integration over fermion fields. The only restriction is on the Yang-Mills kinetic energy normalization function, which is taken diagonal in gauge indices, as in models obtained from superstrings. He then presents the full result for the divergent one-loop contribution to the effective boson Lagrangian for supergravity coupled to chiral and Yang-Mills supermultiplets. He also considers the specific case of dilaton couplings in effective supergravity Lagrangians from superstrings, for which the one-loop result is considerably simplified. He studies gaugino condensation in the presence of an intermediate mass scale in the hidden sector. S-duality is imposed as an approximate symmetry of the effective supergravity theory. Furthermore, the author includes in the Kaehler potential the renormalization of the gauge coupling and the one-loop threshold corrections at the intermediate scale. It is shown that confinement is indeed achieved. Furthermore, a new running behavior of the dilaton arises which he attributes to S-duality. He also discusses the effects of the intermediate scale, and possible phenomenological implications of this model.
Date: May 1, 1997
Creator: Saririan, K.
Partner: UNT Libraries Government Documents Department

QCD scales and chiral symmetry in finite nuclei

Description: The authors report on this progress in the calculation of nuclear ground-state properties using effective Lagrangians whose construction is constrained by QCD scales and chiral symmetry. Good evidence is found that QCD and chiral symmetry apply to finite nuclei.
Date: October 1, 1997
Creator: Madland, D.G.
Partner: UNT Libraries Government Documents Department

Lagrangian with off-shell vertices and field redefinitions

Description: Meson exchange diagrams following from a lagrangian with off-shell meson-nucleon couplings are compared with those generated from conventional dynamics. The off-shell interactions can be transformed away with the help of a nucleon field redefinition. Contributions to the NN- and 3N-potentials and nonminimal contact e.m. meson-exchange currents are discussed, mostly for an important case of scalar meson exchange.
Date: August 1, 1997
Creator: Adam, J.; Gross, Franz & Orden, J.W. Van
Partner: UNT Libraries Government Documents Department

A Hybrid Vortex Method for Two-Dimensional Flow Over Tube Bundles

Description: A hybrid vortex method is presented for computing flows about objects that accurately resolves the boundary layer details while keeping the number of free vortices at a reasonable level. The method uses a wall layer model close to the body surface and discrete vortex blobs in the free wake. Details of the wall layer implementation are presented, and results of sample calculations are compared with known analytical solutions and with calculations from other vortex codes. These results show that the computed boundary layer details are accurate to approximately 0.3 percent of analytical solutions while using three orders of magnitude fewer vortices than other vortex simulations.
Date: November 13, 1998
Creator: Strickland, J.H. & Wolfe, W.P.
Partner: UNT Libraries Government Documents Department

Phenomenological aspects of heterotic orbifold models at one loop

Description: We provide a detailed study of the phenomenology of orbifold compactifications of the heterotic string within the context of supergravity effective theories. Our investigation focuses on those models where the soft Lagrangian is dominated by loop contributions to the various soft supersymmetry breaking parameters. Such models typically predict non-universal soft masses and are thus significantly different from minimal supergravity and other universal models. We consider the pattern of masses that are governed by these soft terms and investigate the implications of certain indirect constraints on supersymmetric models, such as flavor-changing neutral currents, the anomalous magnetic moment of the muon and the density of thermal relic neutralinos. These string-motivated models show novel behavior that interpolates between the phenomenology of unified supergravity models and models dominated by the superconformal anomaly.
Date: August 5, 2003
Creator: Birkedal-Hansen, A.; Binetruy, P.; Mambrini, Y. & Nelson, B.
Partner: UNT Libraries Government Documents Department

Magnetic field generation from Self-Consistent collective neutrino-plasma interactions

Description: A new Lagrangian formalism for self-consistent collective neutrino-plasma interactions is presented in which each neutrino species is described as a classical ideal fluid. The neutrino-plasma fluid equations are derived from a covariant relativistic variational principle in which finite-temperature effects are retained. This new formalism is then used to investigate the generation of magnetic fields and the production of magnetic helicity as a result of collective neutrino-plasma interactions.
Date: November 24, 1999
Creator: Brizard, A.J.; H., Murayama & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Potential motion for Thomas-Fermi non-topological solitons

Description: In the Thomas-Fermi approximation to theories of coupled fermions and scalars, the equations for spherically-symmetric non-topological solitons have the form of potential motion. This gives a straightforward method for proving the existence of non-topological solitons in a given theory and for finding the constant-density, saturating solutions.
Date: April 1, 1992
Creator: Bahcall, S. & Lynn, B.W.
Partner: UNT Libraries Government Documents Department

DOLIB: Distributed Object Library

Description: This report describes the use and implementation of DOLIB (Distributed Object Library), a library of routines that emulates global or virtual shared memory on Intel multiprocessor systems. Access to a distributed global array is through explicit calls to gather and scatter. Advantages of using DOLIB include: dynamic allocation and freeing of huge (gigabyte) distributed arrays, both C and FORTRAN callable interfaces, and the ability to mix shared-memory and message-passing programming models for ease of use and optimal performance. DOLIB is independent of language and compiler extensions and requires no special operating system support. DOLIB also supports automatic caching of read-only data for high performance. The virtual shared memory support provided in DOLIB is well suited for implementing Lagrangian particle tracking techniques. We have also used DOLIB to create DONIO (Distributed Object Network I/O Library), which obtains over a 10-fold improvement in disk I/O performance on the Intel Paragon.
Date: January 1, 1994
Creator: D'Azevedo, E.F.
Partner: UNT Libraries Government Documents Department


Description: Using state-of-the-art flow/particle visualization and animation techniques, the time-dependent statistical distributions of charged-particle swarms exposed to external fields (both electrostatic and flow) are analyzed. We found that interparticle interaction and drag forces mainly influenced swarm dispersion in a Lagrangian reference frame, whereas the ''average'' particle trajectory was affected primarily by the external electric field.
Date: July 12, 2001
Creator: Jhon, Myung S.
Partner: UNT Libraries Government Documents Department

Numerical simulations of turbulent dispersion around buildings via a lagrangian stochastic particle model

Description: This paper describes a numerical modeling approach that can be used to provide estimates of air concentrations due to emissions at industrial sites or other sites where buildings may have an important impact on the dispersion patterns. The procedure consists of two sequential steps: (i) Prediction of mean flow and turbulence fields via a turbulent flow model; and, (ii) Employment of the calculated flow and Turbulence fields to drive a Lagrangian Stochastic Particle Model. Two flow scenarios in which the approaching mean wind is assumed to be at 90{degrees} and 30{degrees} to the building complex are used as input to the Lagrangian model. The first calculation is based on an earlier transport and diffusion simulation that employed an existing particle-in-cell flux-gradient dispersion model. The second simulation is used to demonstrate the strong spatial variations that the concentration field exhibit within the highly complex separation zones of building wakes. The relationship between concentration levels and toxic load are discussed for the case of a chemical spill.
Date: July 1, 1995
Creator: Lee, R.L. & Naeslund, E.
Partner: UNT Libraries Government Documents Department