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Statistical Stability and Time-Reversal Imgaing in Random Media

Description: Localization of targets imbedded in a heterogeneous background medium is a common problem in seismic, ultrasonic, and electromagnetic imaging problems. The best imaging techniques make direct use of the eigenfunctions and eigenvalues of the array response matrix, as recent work on time-reversal acoustics has shown. Of the various imaging functionals studied, one that is representative of a preferred class is a time-domain generalization of MUSIC (MUltiple Signal Classification), which is a well… more
Date: February 5, 2002
Creator: Berryman, J; Borcea, L; Papanicolaou, G & Tsogka, C
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Partner: UNT Libraries Government Documents Department
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The Godunov-Inverse Iteration: A Fast and Accurate Solution to the Symmetric Tridiagonal Eigenvalue Problem.

Description: We present a new hybrid algorithm based on Godunov's method for computing eigenvectors of symmetric tridiagonal matrices and Inverse Iteration, which we call the Godunov-Inverse Iteration Algorithm. We use eigenvectors computed according to Godunov's method as starting vectors in the Inverse Iteration, replacing any nonnumeric elements of the Godunov eigenvectors with random uniform numbers. We use the right-hand bounds of the Ritz intervals found by the bisection method as Inverse Iteration sh… more
Date: November 27, 2002
Creator: Matsekh, Anna M.
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Partner: UNT Libraries Government Documents Department
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Critical masses of uranium diluted with matrix material

Description: Critical masses of square-prisms of highly enriched uranium diluted in various X/235U ratios with matrix material and polyethylene were measured. The Configuration cores were 22.86-cm and 45.72-cm square and were reflected with 8.1 3-cm and 10.1 6-cm thick side polyethylene reflectors, respectively. The configurations had 10.1 6-cm thick top and bottom polyethylene reflectors. For some configurations, the Rossi-a, which is an eigenvalue value characteristic for a particular configuration, was m… more
Date: January 1, 2002
Creator: Sanchez, R. G. (Rene G.); Loaiza, D. J. (David J.) & Kimpland, R. H. (Robert H.)
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Partner: UNT Libraries Government Documents Department
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Krylov subspace iterations for the calculation of K-Eigenvalues with sn transport codes

Description: We apply the Implicitly Restarted Arnoldi Method (IRAM), a Krylov subspace iterative method, to the calculation of k-eigenvalues for criticality problems. We show that the method can be implemented with only modest changes to existing power iteration schemes in an SN transport code. Numerical results on three dimensional unstructured tetrahedral meshes are shown. Although we only compare the IRAM to unaccelerated power iteration, the results indicate that the IRAM is a potentially efficient and… more
Date: January 1, 2002
Creator: Warsa, J. S. (James S.); Wareing, T. A. (Todd A.); Morel, J. E.; McGhee, J. M. (John M.) & Lehoucq, R. B. (Richard B.)
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Partner: UNT Libraries Government Documents Department
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Stationarity and source convergence in monte carlo criticality calculation.

Description: In Monte Carlo (MC) criticality calculations, source error propagation through the stationary cycles and source convergcnce in the settling (inactive) cycles are both dominated by the dominance ratio (DR) of fission kernels, Le., the ratio of the second largest to largest eigenvalues. For symmetric two fissile component systems with DR close to unity, the extinction of fission source sites can occur in one of the components even when the initial source is symmetric and the number of histories p… more
Date: January 1, 2002
Creator: Ueki, T. (Taro) & Brown, F. B. (Forrest B.)
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Partner: UNT Libraries Government Documents Department
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Operational measure of entanglement based on experimental consequences.

Description: The maximum eigenvalue of the real part of the density matrix expressed in a maximally entangled basis with a particular phase relationship can be used as an operational measure of entanglement. This measure is related to the fidelity, maximized with a local unitary operating on either subsystem, of a standard dense coding, teleportation, or entanglement swapping protocol.
Date: January 1, 2002
Creator: Grondalski, J. P. (John P.) & James, D. F. (Daniel F.)
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Partner: UNT Libraries Government Documents Department
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Resolution depths for some transmitter receiverconfigurations

Description: Away from a conductive body, secondary magnetic fields due to currents induced in the body by a time varying external magnetic field are approximated by (equivalent) magnetic dipole fields. Approximating the external magnetic field by its value at the location of the equivalent magnetic dipoles, the equivalent magnetic dipoles' strengths are linearly proportional to the external magnetic field, for a given time dependence of external magnetic field, and are given by the equivalent dipole polari… more
Date: August 28, 2002
Creator: Smith, J. Torquil; Morrison, H. Frank & Becker, Alex
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Partner: UNT Libraries Government Documents Department
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Status of the VIM Monte Carlo neutron/photon transport code.

Description: Recent work on the VIM Monte Carlo code has aimed at advanced data libraries, ease of use, availability to users outside of Argonne, and fission source convergence algorithms in eigenvalue calculations. VIM is one of three US Monte Carlo codes in the USDOE Nuclear Criticality Safety Program, and is available through RSICC and the NEA Data Bank.
Date: January 22, 2002
Creator: Blomquist, R.N.
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Partner: UNT Libraries Government Documents Department
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Moments for general quadratic densities in n dimensions

Description: We present the calculation of the generating functions and the rth-order correlations for densities of the form {rho}(x) {proportional_to} where g(s) is a non-negative function of the quadratic ''action'' s(x)={summation}{sub i,j}H{sub ij}x{sub i}x{sub j}, where x = (x{sub 1},x{sub 2}...,x{sub n}) is a real n-dimensional vector and H is a real, symmetric n x n matrix whose eigenvalues are strictly positive. In particular, we find the connection between the (r+2)th-order and rth-order correlatio… more
Date: March 20, 2002
Creator: Furman, Miguel A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Response Matrix Solution Using Boundary Condition Perturbation Theory for the Diffusion Approximation

Description: A second-order response matrix method is developed for solving the diffusion equation in a coarse-mesh grid. In this method, the problem domain is divided into a grid of coarse meshes (nodes) of the size of a fuel assembly. Then, by using the fact that all nodes have the same eigenvalue, an equation is developed for the node interface current to flux ratio. The fine-mesh solution in the domain is then obtained by evaluating perturbation expressions for the core eigenvalue and the flux with the … more
Date: June 26, 2002
Creator: McKinley, M.S. & Rahnema, F.
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Partner: UNT Libraries Government Documents Department
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Transiting Topological Sectors With the Overlap

Description: The overlap operator provides an elegant definition for the winding number of lattice gauge field configurations. Only for a set of configurations of measure zero is this procedure undefined. Without restrictions on the lattice fields, however, the space of gauge fields is simply connected. I present a simple low dimensional illustration of how the eigenvalues of a truncated overlap operator flow as one travels between different topological sectors.
Date: June 29, 2002
Creator: Creutz, M.
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Partner: UNT Libraries Government Documents Department
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Bursting Frequency Predictions for Compressible Turbulent Boundary Layers

Description: A computational method for the prediction of the bursting frequency associated with the coherent streamwise structures in high-speed compressible turbulent boundary layers is presented. The structures are described as wavelike disturbances of the turbulent mean flow. A direct resonance theory is used to determine the frequency of bursting. The resulting hydrodynamic linear stability equations are discretized by using a Chebyshev collocation method. A global numerical method capable of resolving… more
Date: October 1, 2002
Creator: LIOU, WILLIAM W. & FANG, YICHUAN
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Alternative implementations of the Monte Carlo power method.

Description: We compare nominal efficiencies, i.e. variances in power shapes for equal running time, of different versions of the Monte Carlo eigenvalue computation, as applied to criticality safety analysis calculations. The two main methods considered here are ''conventional'' Monte Carlo and the superhistory method, and both are used in criticality safety codes. Within each of these major methods, different variants are available for the main steps of the basic Monte Carlo algorithm. Thus, for example, d… more
Date: March 18, 2002
Creator: Blomquist, R.N. & Gelbard, E.M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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SCALIScaling and Modeling Studies of High-Bootstrap Fraction Tokamaks

Description: OAK A271 SCALING AND MODELING STUDIES OF HIGH-BOOTSTRAP FRACTION TOKAMAKS. A theoretical framework is developed to generate tokamak equilibrium configurations for which, on one hand, the current results entirely from the bootstrap current source driven by the pressure gradient while, on the other hand, the pressure gradient is determined from the thermal conduction equation with a thermal diffusivity constructed to have properties observed in confinement experiments: gyroBohm confinement, gradi… more
Date: November 1, 2002
Creator: Perkins, F. W.; Casper, T. A. & Politzer, P. A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Simulating Photons and Plasmons in a Three-dimensional Lattice

Description: Three-dimensional metallic photonic structures are studied using a newly developed mixed finite element-finite difference (FE-FD) code, Curly3d. The code solves the vector Helmholtz equation as an eigenvalue problem in the unit cell of a triply periodic lattice composed of conductors and/or dielectrics. The mixed FE-FD discretization scheme ensures rapid numerical convergence of the eigenvalue and allows the code to run at low resolution. Plasmon and photonic band structure calculations are pre… more
Date: September 3, 2002
Creator: Pletzer, A. & Shvets, G.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Reactor whole core transport calculations without fuel assembly homogenization

Description: The variational nodal method is generalized by dividing each spatial node into a number of triangular finite elements designated as subelements. The finite subelement trail functions allow for explicit geometry representations within each node, thus eliminating the need for nodal homogenization. The method is implemented within the Argonne National Laboratory code VARIANT and applied to two-dimensional multigroup problems. Eigenvalue and pin-power results are presented for a four-assembly OECD/… more
Date: October 18, 2002
Creator: Tsoulfanidis, Nicholas; Lewis, Elmer; Smith, M. A.; Palmiotti, G. & Taiwo, T. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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