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Characterizations of Some Combinatorial Geometries

Description: We give several characterizations of partition lattices and projective geometries. Most of these characterizations use characteristic polynomials. A geometry is non—splitting if it cannot be expressed as the union of two of its proper flats. A geometry G is upper homogeneous if for all k, k = 1, 2, ... , r(G), and for every pair x, y of flats of rank k, the contraction G/x is isomorphic to the contraction G/y. Given a signed graph, we define a corresponding signed—graphic geometry. We give a characterization of supersolvable signed graphs. Finally, we give the following characterization of non—splitting supersolvable signed-graphic geometries : If a non-splitting supersolvable ternary geometry does not contain the Reid geometry as a subgeometry, then it is signed—graphic.
Date: August 1992
Creator: Yoon, Young-jin
Partner: UNT Libraries

TEM Studies of Carbon Coated LiFePO4 after Charge DischargeCycling

Description: Carbon coating has proven to be a successful approach toimprove the rate capability of LiFePO4 used in rechargeable Li-ionbatteries. Investigations of the microstructure of carbon coated LiFePO4after charge discharge cycling shows that the carbon surface layerremains intact over 100 cycles. We find micro cracks in the cycledmaterial that extend parallel to low indexed lattice planes. Ourobservations differ from observations made by other authors. However thedifferences between the orientations of crack surfaces in both studiescan be reconciled considering the location of weak bonds in the unit celland specimen geometry as well as elastic stress fields ofdislocation.
Date: November 30, 2006
Creator: Gabrisch, H.; Wilcox, J. & Doeff, M.
Partner: UNT Libraries Government Documents Department


Description: The atomic positions of the Rh(111) + ({radical}3 x {radical}3)R30{sup o} CO and CO{sub 2} surfaces are analyzed by dynamical LEED. The Rh(111) + ({radical}3 x {radical}3)R30{sup o} CO and CO{sub 2} systems produce identical I-V curves, confirming the dissociation of CO{sub 2} to CO on this surface. The adsorbed CO is found to stand perpendicular to the surface with the carbon end down at an atop site (that is, terminally bonded). The CO overlayer spacings are d{sub RhC} = 1.95 {+-} 0.1 {angstrom} and d{sub CD} = 1.07 {+-} 0.1 {angstrom}. This geometry yields a Zanazzi-Jona R-factor of 0.40 and a Pendry R-factor of 0.50.
Date: September 1, 1980
Creator: Koestner, R.J.; Van Hove, M.A. & Somorjai, G.A.
Partner: UNT Libraries Government Documents Department

Designing the Ideal Uranyl Ligand: a Sterically-Induced Speciation Change in Complexes with Thiophene-Bridged Bis(3-hydroxy-N-methylpyridin-2-one)

Description: Structural characterization of a mononuclear uranyl complex with a tetradentate, thiophene-linked bis(3-hydroxy-N-methylpyridin-2-one) ligand reveals the most planar coordination geometry yet observed with this ligand class. The introduction of ethylsulfanyl groups onto the thiophene linker disrupts this planar, conjugated ligand arrangement, resulting in the formation of dimeric (UO{sub 2}){sub 2}L{sub 2} species in which each ligand spans two uranyl centers. Relative energy calculations reveal that this tendency toward dimer formation is the result of steric interference between ethylsulfanyl substituents and linking amides.
Date: September 11, 2009
Creator: Szigethy, Geza & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Predictions of Elliptic flow and nuclear modification factor from 200 GeV U+U collisions at RHIC

Description: Predictions of elliptic flow (v{sub 2}) and nuclear modification factor (R{sub AA}) are provided as a function of centrality in U + U collisions at {radical}s{sub NN} = 200 GeV. Since the {sup 238}U nucleus is naturally deformed, one could adjust the properties of the fireball, density and duration of the hot and dense system, for example, in high energy nuclear collisions by carefully selecting the colliding geometry. Within our Monte Carlo Glauber based approach, the v{sub 2} with respect to the reaction plane v{sub 2}{sup RP} in U + U collisions is consistent with that in Au + Au collisions, while the v{sub 2} with respect to the participant plane v{sub 2}{sup PP} increases {approx}30-60% at top 10% centrality which is attributed to the larger participant eccentricity at most central U + U collisions. The suppression of R{sub AA} increases and reaches {approx}0.1 at most central U + U collisions that is by a factor of 2 more suppression compared to the central Au + Au collisions due to large size and deformation of Uranium nucleus.
Date: July 7, 2010
Creator: Masui, Hiroshi; Mohanty, Bedangadas & Xu, Nu
Partner: UNT Libraries Government Documents Department

Probing the Geometry of Warped String Compactifications at the LHC

Description: Warped string compactifications, characterized by the nonsingular behavior of the metric in the infrared (IR), feature departures from the usual anti?de Sitter warped extra dimensions. We study the implications of the smooth IR cutoff for Randall-Sundrum- (RS-)type models. We find that the phenomenology of the Kaluza-Klein gravitons (including their masses and couplings) depends sensitively on the precise shape of the warp factor in the IR. In particular, we analyze the warped deformed conifold, find that the spectrum differs significantly from that of RS, and present a simple prescription (a mass-gap ansatz) that can be used to study the phenomenology of IR modifications to 5D warped extra dimensions.
Date: May 28, 2007
Creator: Walker, Devin; Shiu, Gary; Underwood, Bret; Zurek, Kathryn M. & Walker, Devin G. E.
Partner: UNT Libraries Government Documents Department

Surprising Coordination Geometry Differences in Ce(IV)- and Pu(IV)-Maltol Complexes

Description: As part of a study to characterize the detailed coordination behavior of Pu(IV), single crystal X-ray diffraction structures have been determined for Pu(IV) and Ce(IV) complexes with the naturally-occurring ligand maltol (3-hydroxy-2-methyl-pyran-4-one) and its derivative bromomaltol (5-bromo-3-hydroxy-2-methyl-pyran-4-one). Although Ce(IV) is generally accepted as a structural analog for Pu(IV), and the maltol complexes of these two metals are isostructural, the corresponding bromomaltol complexes are strikingly different with respect to ligand orientation about the metal ion: All complexes exhibit trigonal dodecahedral coordination geometry but the Ce(IV)-bromomaltol complex displays an uncommon ligand arrangement not mirrored in the Pu(IV) complex, although the two metal species are generally accepted to be structural analogs.
Date: February 12, 2008
Creator: Laboratory, Lawrence Berkeley National; Raymond, Kenneth; Szigethy, Geza; Xu, Jide; Gorden, Anne E.V.; Teat, Simon J. et al.
Partner: UNT Libraries Government Documents Department

Mapping the geometry of the E6 group

Description: In this paper we present a construction for the compact form of the exceptional Lie group E{sub 6} by exponentiating the corresponding Lie algebra e{sub 6}, which we realize as the sum of f{sub 4}, the derivations of the exceptional Jordan algebra J{sub 3} of dimension 3 with octonionic entries, and the right multiplication by the elements of J{sub 3} with vanishing trace. Our parameterization is a generalization of the Euler angles for SU(2) and it is based on the fibration of E{sub 6} via a F{sub 4} subgroup as the fiber. It makes use of a similar construction we have performed in a previous article for F{sub 4}. An interesting first application of these results lies in the fact that we are able to determine an explicit expression for the Haar invariant measure on the E{sub 6} group manifold.
Date: October 1, 2007
Creator: Cerchiai , Bianca; Bernardoni, Fabio; Cacciatori, Sergio L.; Cerchiai, Bianca L. & Scotti, Antonio
Partner: UNT Libraries Government Documents Department

TEM Study of Fracturing in Spherical and Plate-like LiFePO4Particles

Description: An investigation of fracturing in LiFePO{sub 4} particles as a function of the particle morphology and history is presented. Two types of samples, one subjected to electrochemical cycling and another to chemical delithiation are compared. We observe the formation of micro fractures parallel to low indexed lattice planes in both samples. The fracture surfaces are predominantly parallel to (100) planes in the chemically delithiated powder and (100) and (010) planes in the electrochemically cycled powder. A consideration of the threshold stresses for dislocation glide shows that particle geometry plays an important role in the observed behavior.
Date: December 20, 2007
Creator: Gabrisch, H.; Wilcox, J. & Doeff, M.M.
Partner: UNT Libraries Government Documents Department

Supergravity Analysis of Hybrid Inflation Model from D3--D7 System

Description: The slow-roll inflation is a beautiful paradigm, yet the inflaton potential can hardly be sufficiently flat when unknown gravitational effects are taken into account. However, the hybrid inflation models constructed in D = 4 N = 1 supergravity can be consistent with N = 2 supersymmetry, and can be naturally embedded into string theory. This article discusses the gravitational effects carefully in the string model, using D = 4 supergravity description. We adopt the D3--D7 system of Type IIB string theory compactified on K3 x T^2/Z_2 orientifold for definiteness. It turns out that the slow-roll parameter can be sufficiently small despite the non-minimal Kahler potential of the model. The conditions for this to happen are clarified in terms of string vacua. We also find that the geometry obtained by blowing up singularity, which is necessary for the positive vacuum energy, is stabilized by introducing certain 3-form fluxes.
Date: November 20, 2003
Creator: Koyama, Fumikazu; Tachikawa, Yuji & Watari, Taizan
Partner: UNT Libraries Government Documents Department

On complexity of the mixed volume of parallelograms

Description: Let K = (K{sub 1}...K{sub n}) be a n-tuple of convex compact subsets in the Euclidean space R{sup n}, and let V({center_dot}) be the Euclidean volume in R{sup n}. It is well known Herman Minkowski result (see for instance 5), that the value of the V{sub K}({gamma}{sub 1}K{sub 1} + ... {gamma}{sub n}K{sub n}) is a homogeneous polynomial of degree n, called the Minkowski polynomial, in nonnegative variables {gamma}{sub 1}...{gamma}{sub n1}, where '+' denotes Minkowski sum, and {gamma}K denotes the dilatation of K with coefficient {gamma}. The coefficient V(K{sub 1}...K{sub n}) of {gamma}{sub 1}{center_dot}{gamma}{sub 2}...{center_dot}{gamma}{sub n} is called the mixed volume of K{sub 1}...K{sub n}. Alternatively, V(K{sub 1}...K{sub n}) = ({partial_derivative}{sup n} / {partial_derivative}{gamma}{sub 1}...{partial_derivative}{gamma}{sub n})V{sub K}({gamma}{sub 1}K{sub 1}+...{gamma}{sub n}K{sub n}).
Date: January 1, 2009
Creator: Gurvits, Leonid
Partner: UNT Libraries Government Documents Department

The verdict geometric quality library.

Description: Verdict is a collection of subroutines for evaluating the geometric qualities of triangles, quadrilaterals, tetrahedra, and hexahedra using a variety of metrics. A metric is a real number assigned to one of these shapes depending on its particular vertex coordinates. These metrics are used to evaluate the input to finite element, finite volume, boundary element, and other types of solvers that approximate the solution to partial differential equations defined over regions of space. The geometric qualities of these regions is usually strongly tied to the accuracy these solvers are able to obtain in their approximations. The subroutines are written in C++ and have a simple C interface. Each metric may be evaluated individually or in combination. When multiple metrics are evaluated at once, they share common calculations to lower the cost of the evaluation.
Date: March 1, 2006
Creator: Knupp, Patrick Michael; Ernst, C.D. (Elemental Technologies, Inc., American Fork, UT); Thompson, David C. (Sandia National Laboratories, Livermore, CA); Stimpson, C.J. (Elemental Technologies, Inc., American Fork, UT) & Pebay, Philippe Pierre
Partner: UNT Libraries Government Documents Department

Toward Interoperable Mesh, Geometry and Field Components for PDE Simulation Development

Description: Mesh-based PDE simulation codes are becoming increasingly sophisticated and rely on advanced meshing and discretization tools. Unfortunately, it is still difficult to interchange or interoperate tools developed by different communities to experiment with various technologies or to develop new capabilities. To address these difficulties, we have developed component interfaces designed to support the information flow of mesh-based PDE simulations. We describe this information flow and discuss typical roles and services provided by the geometry, mesh, and field components of the simulation. Based on this delineation for the roles of each component, we give a high-level description of the abstract data model and set of interfaces developed by the Department of Energy's Interoperable Tools for Advanced Petascale Simulation (ITAPS) center. These common interfaces are critical to our interoperability goal, and we give examples of several services based upon these interfaces including mesh adaptation and mesh improvement.
Date: July 11, 2005
Creator: Chand, K K; Diachin, L F; Li, X; Ollivier-Gooch, C; Seol, E S; Shephard, M et al.
Partner: UNT Libraries Government Documents Department