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1

Implementation and Verification of a Nodally-Integrated Tetrahedral Element in FEBio  

E-print Network

Implementation and Verification of a Nodally-Integrated Tetrahedral Element in FEBio Steve A. Maas Abstract: Finite element simulations in computational biomechanics commonly require the discretization. To overcome these problems we have implemented a stabilized, nodally-integrated tetrahedral element

Utah, University of

2

A Family of Uniform Strain Tetrahedral Elements and a Method for Connecting Dissimilar Finite Element Meshes  

SciTech Connect

This report documents a collection of papers on a family of uniform strain tetrahedral finite elements and their connection to different element types. Also included in the report are two papers which address the general problem of connecting dissimilar meshes in two and three dimensions. Much of the work presented here was motivated by the development of the tetrahedral element described in the report "A Suitable Low-Order, Eight-Node Tetrahedral Finite Element For Solids," by S. W. Key {ital et al.}, SAND98-0756, March 1998. Two basic issues addressed by the papers are: (1) the performance of alternative tetrahedral elements with uniform strain and enhanced uniform strain formulations, and (2) the proper connection of tetrahedral and other element types when two meshes are "tied" together to represent a single continuous domain.

Dohrmann, C.R.; Heinstein, M.W.; Jung, J.; Key, S.W.

1999-01-01

3

A computational study of nodal-based tetrahedral element behavior.  

SciTech Connect

This report explores the behavior of nodal-based tetrahedral elements on six sample problems, and compares their solution to that of a corresponding hexahedral mesh. The problems demonstrate that while certain aspects of the solution field for the nodal-based tetrahedrons provide good quality results, the pressure field tends to be of poor quality. Results appear to be strongly affected by the connectivity of the tetrahedral elements. Simulations that rely on the pressure field, such as those which use material models that are dependent on the pressure (e.g. equation-of-state models), can generate erroneous results. Remeshing can also be strongly affected by these issues. The nodal-based test elements as they currently stand need to be used with caution to ensure that their numerical deficiencies do not adversely affect critical values of interest.

Gullerud, Arne S.

2010-09-01

4

A finite element boundary integral formulation for radiation and scattering by cavity antennas using tetrahedral elements  

NASA Technical Reports Server (NTRS)

A hybrid finite element boundary integral formulation is developed using tetrahedral and/or triangular elements for discretizing the cavity and/or aperture of microstrip antenna arrays. The tetrahedral elements with edge based linear expansion functions are chosen for modeling the volume region and triangular elements are used for discretizing the aperture. The edge based expansion functions are divergenceless thus removing the requirement to introduce a penalty term and the tetrahedral elements permit greater geometrical adaptability than the rectangular bricks. The underlying theory and resulting expressions are discussed in detail together with some numerical scattering examples for comparison and demonstration.

Gong, J.; Volakis, J. L.; Chatterjee, A.; Jin, J. M.

1992-01-01

5

Tetrahedral hpFinite Elements: Algorithms and Flow Simulations  

NASA Astrophysics Data System (ADS)

We present a new discretisation for the incompressible Navier-Stokes equations that extends spectral methods to three-dimensional complex domains consisting of tetrahedral subdomains. The algorithm is based on standard concepts of hpfinite elements as well as tensorial spectral elements. This new formulation employs a hierarchical/modal basis constructed from a new apex co-ordinate system which retains a generalised tensor product. These properties enable the development of computationally efficienct algorithms for use on standard finite volume unstructured meshes. A detailed analysis is presented that documents the stability and exponential convergence of the method and several flow cases are simulated and compared with analytical and experimental results

Sherwin, S. J.; Karniadakis, G. E.

1996-03-01

6

A suitable low-order, eight-node tetrahedral finite element for solids  

Microsoft Academic Search

To use the all-tetrahedral mesh generation existing today, the authors have explored the creation of a computationally efficient eight-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four mid-face nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping, and the element`s performance in applications are presented. In particular they examine the

S. W. Key; M. S. Heinstein; C. M. Stone; F. J. Mello; M. L. Blanford; K. G. Budge

1998-01-01

7

A suitable low-order, eight-node tetrahedral finite element for solids  

SciTech Connect

To use the all-tetrahedral mesh generation existing today, the authors have explored the creation of a computationally efficient eight-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four mid-face nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping, and the element`s performance in applications are presented. In particular they examine the eight-node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element samples only constant strain states and, therefore, has 12 hour-glass modes. In this regard it bears similarities to the eight-node, mean-quadrature hexahedral finite element. Comparisons with the results obtained from the mean-quadrature eight-node hexahedral finite element and the four-node tetrahedral finite element are included. Given automatic all-tetrahedral meshing, the eight-node, constant-strain tetrahedral finite element is a suitable replacement for the eight-node hexahedral finite element in those cases where mesh generation requires an inordinate amount of user intervention and direction to obtain acceptable mesh properties.

Key, S.W.; Heinstein, M.S.; Stone, C.M.; Mello, F.J.; Blanford, M.L.; Budge, K.G.

1998-03-01

8

A Diffusion-Split Method To Deal With Thermal Shocks Using Standard Linear Tetrahedral Finite Elements  

E-print Network

A Diffusion-Split Method To Deal With Thermal Shocks Using Standard Linear Tetrahedral Finite. INTRODUCTION The Galerkin (standard) version of the finite element method (FEM) applied to diffusion problems of thermal shocks is not longer necessary. But in many important applications processes, such as welding, hot

Paris-Sud XI, Université de

9

Uniform Strain Elements for Three-Node Triangular and Four-Node Tetrahedral Meshes  

SciTech Connect

A family of uniform strain elements is presented for three-node triangular and four-node tetrahedral meshes. The elements use the linear interpolation functions of the original mesh, but each element is associated with a single node. As a result, a favorable constraint ratio for the volumetric response is obtained for problems in solid mechanics. The uniform strain elements do not require the introduction of additional degrees of freedom and their performance is shown to be significantly better than that of three-node triangular or four-node tetrahedral elements. In addition, nodes inside the boundary of the mesh are observed to exhibit superconvergent behavior for a set of example problems.

Dohrmann, C.R.; Heinstein, M.W.; Jung, J.; Key, S.W.; Witkowski, W.R.

1999-03-02

10

A discontinuity capturing SUPG formulation using quadratic element  

NASA Astrophysics Data System (ADS)

The purpose of the present study is to add the discontinuity capturing term into the quadratic streamline upwind Petrov-Galerkin (SUPG) finite element formulation for predicting high resolution solution in a flowfield containing possible discontinuities. Both good stability and high-order accuracy can be achieved in solving the linear one-dimensional Burgers' equation containing three profiles of different characters and nonlinear Burgers' equation. The extension to the two dimensional analysis is also attempted in this study in the context of quadratic element formulation.

Sheu, Tony W. H.; Husang, Philip G. Y.; Wang, Morten M. T.

1992-12-01

11

Geometrically nonlinear analysis of hyperelastic solids by high-order tetrahedral finite elements  

NASA Astrophysics Data System (ADS)

The purpose of this study is to develop a computer code for accurate prediction of the mechanical behavior of hyperelastic solids under large deformation and finite strains. It is used, in the present work, the Lagrangian positional version of the Finite Element Method, in which the degrees of freedom are current positions instead of displacements. The main mechanical variables are the Green-Lagrange strain and the second Piola-Kirchhoff stress tensors. Isoparametric tetrahedral solid finite element of any approximation degree is employed with full integration in order to obtain accuracy. In order to be general, it is developed a numerical strategy to determine the shape functions coefficients of any order, following tetrahedral basis. The solid equilibrium is achieved at the current position by means of the Minimal Potential Energy Principle regarding positions and is solved by the Newton-Raphson iterative scheme. It is important to mention that the adopted constitutive laws are nonlinear, isotropic and homogeneous hyperelastic, normally used in mechanical analysis of elastomers, with the near compressibility assumption. It is applied the Flory decomposition, i.e., the multiplicative split of the deformation gradient into a volumetric and an isochoric part. A parallel processing strategy is used to increase the simulation speed and memory capacity, justifying the use of high order elements for solid analysis. Results confirm that the developed computer code is capable of predicting the static behavior of complex problems, such as Cook's membrane and partially loaded block. The shape functions generator code exhibits simplicity and, thus, it may be easily implemented in other finite elements. The increase in the order of approximation and the mesh refinement improve accuracy and, therefore, the proposed methodology together with parallel computing indicate a safe way for further developments in plasticity and damage mechanics for large strain and deformations.

Pascon, João P.; Coda, Humberto B.

2010-06-01

12

Bivariate C^1 quadratic finite elements and vertex splines  

NASA Astrophysics Data System (ADS)

Following work of Heindl and of Powell and Sabin, each triangle of an arbitrary (regular) triangulation ? of a polygonal region ? in {R^2} is subdivided into twelve triangles, using the three medians, yielding the refinement hat ? of ? , so that {C^1} quadratic finite elements can be constructed. In this paper, we derive the Bezier nets of these elements in terms of the parameters that describe function and first partial derivative values at the vertices and values of the normal derivatives at the midpoints of the edges of ? . Consequently, bivariate {C^1} quadratic (generalized) vertex splines on ? have an explicit formulation. Here, a generalized vertex spline is one which is a piecewise polynomial on the refined grid partition hat ? and has support that contains at most one vertex of the original partition ? in its interior. The collection of all {C^1} quadratic generalized vertex splines on ? so constructed is shown to form a basis of S_2^1(hat ? ) , the vector space of all functions on {C^1}(? ) whose restrictions to each triangular cell of the partition hat ? are quadratic polynomials. A subspace with the basis given by appropriately chosen generalized vertex splines with exactly one vertex of ? in the interior of their supports, that reproduces all quadratic polynomials, is identified, and hence, has approximation order three. Quasi-interpolation formulas using this subspace are obtained. In addition, a constructive procedure that yields a locally supported basis of yet another subspace with dimension given by the number of vertices of ? , that has approximation order three, is given.

Chui, Charles K.; He, Tian Xiao

1990-01-01

13

Quadratic Finite Element Method for 1D Deterministic Neutron Transport  

SciTech Connect

We focus on improving the angular discretization of the angular flux for the one-dimensional (1D) spherical geometry neutron transport equation. Unlike the conventional SN method, we model the angular dependence of the flux with a Petrov-Galerkin finite element approximation for the differencing of the angular variable in developing the 1D spherical geometry S{sub N} equations. That is, we use both a piecewise bi-linear and a quadratic function in each angular bin to approximate the angular dependence of the flux. This new algorithm that we have developed shows faster convergence with angular resolution than conventional SN algorithms. (U)

Tolar, Jr., D R; Ferguson, J M

2004-11-24

14

The quarter-point quadratic isoparametric element as a singular element for crack problems  

NASA Technical Reports Server (NTRS)

The quadratic isoparametric elements which embody the inverse square root singularity are used for calculating the stress intensity factors at tips of cracks. The strain singularity at a point or an edge is obtained in a simple manner by placing the mid-side nodes at quarter points in the vicinity of the crack tip or an edge. These elements are implemented in NASTRAN as dummy elements. The method eliminates the use of special crack tip elements and in addition, these elements satisfy the constant strain and rigid body modes required for convergence.

Hussain, M. A.; Lorensen, W. E.; Pflegel, G.

1976-01-01

15

Quadratic Finite Element Method for 1D Deterministic Transport  

SciTech Connect

In the discrete ordinates, or SN, numerical solution of the transport equation, both the spatial ({und r}) and angular ({und {Omega}}) dependences on the angular flux {psi}{und r},{und {Omega}}are modeled discretely. While significant effort has been devoted toward improving the spatial discretization of the angular flux, we focus on improving the angular discretization of {psi}{und r},{und {Omega}}. Specifically, we employ a Petrov-Galerkin quadratic finite element approximation for the differencing of the angular variable ({mu}) in developing the one-dimensional (1D) spherical geometry S{sub N} equations. We develop an algorithm that shows faster convergence with angular resolution than conventional S{sub N} algorithms.

Tolar, Jr., D R; Ferguson, J M

2004-01-06

16

Quadratic  

NSDL National Science Digital Library

Shows how the roots of a quadratic change as the b term in the equation changes. The equation was chosen to illustrate the fact that only real roots are seen as points where the curve crosses the x-axis. This can lead to a useful discussion of what is meant by a physically meaningful solution.

17

Parallel Anisotropic Tetrahedral Adaptation  

NASA Technical Reports Server (NTRS)

An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.

Park, Michael A.; Darmofal, David L.

2008-01-01

18

Building Tetrahedral Kites  

NSDL National Science Digital Library

Working in teams of four, students build tetrahedral kites following specific instructions and using specific materials. They use the basic processes of manufacturing systems â cutting, shaping, forming, conditioning, assembling, joining, finishing, and quality control â to manufacture complete tetrahedral kites within a given time frame. Project evaluation takes into account team efficiency and the quality of the finished product.

Center For Engineering Educational Outreach

19

Building Tetrahedral Kites  

NSDL National Science Digital Library

Working in teams of four, learners build tetrahedral kites following specific instructions and using specific materials. They use the basic processes of manufacturing systems--cutting, shaping, forming, conditioning, assembling, joining, finishing, and quality control--to manufacture complete tetrahedral kites within a given time frame. Investigating questions encourage learners to reflect about the engineering and manufacturing process. Activity contains recommended resources about the history of kites and their construction.

Tufts University

2013-01-01

20

Tetrahedral SnS DOI: 10.1002/smll.200500460  

E-print Network

. Solvothermal methods, using a combination of tin chloride and thiourea or elemental Sn and S, have produced 0DTetrahedral SnS DOI: 10.1002/smll.200500460 Tetrahedral Zinc Blende Tin Sulfide Nano, seedless solution route to zinc blende (ZB) tin sulfide (SnS) nano- and micro- crystals with tetrahedral

Odom, Teri W.

21

Quadratic formula  

NSDL National Science Digital Library

The quadratic formula is easy to solve, yet sufficiently sophisticated that it provides insight into oscillations of masses connected by springs, as well as insight into chemical bonds between atoms. The purpose of this video is to illustrate what it means to find the "zeros" or "roots" of the quadratic equation, both using a graphical description, as well as by analytically completing the square to obtain the famous quadratic formula.

2013-06-21

22

Feature-Sensitive Tetrahedral Mesh Generation with Guaranteed Quality  

PubMed Central

Tetrahedral meshes are being extensively used in finite element methods (FEM). This paper proposes an algorithm to generate feature-sensitive and high-quality tetrahedral meshes from an arbitrary surface mesh model. A top-down octree subdivision is conducted on the surface mesh and a set of tetrahedra are constructed using adaptive body-centered cubic (BCC) lattices. Special treatments are given to the tetrahedra near the surface such that the quality of the resulting tetrahedral mesh is provably guaranteed: the smallest dihedral angle is always greater than 5.71°. The meshes generated by our method are not only adaptive from the interior to the boundary, but also feature-sensitive on the surface with denser elements in high-curvature regions where geometric feature most likely reside. A variety of experimental results are presented to demonstrate the effectiveness and robustness of this algorithm. PMID:22328787

Wang, Jun; Yu, Zeyun

2012-01-01

23

The quadratic Fock functor  

NASA Astrophysics Data System (ADS)

We construct the quadratic analog of the boson Fock functor. While in the first order (linear) case all contractions on the 1-particle space can be second quantized, the semigroup of contractions that admit a quadratic second quantization is much smaller due to the nonlinearity. The encouraging fact is that it contains, as proper subgroups (i.e., the contractions), all the gauge transformations of second kind and all the a.e. invertible maps of Rd into itself leaving the Lebesgue measure quasi-invariant (in particular, all diffeomorphism of Rd). This allows quadratic two-dimensional quantization of gauge theories, of representations of the Witt group (in fact it continuous analog), of the Zamolodchikov hierarchy, and much more. Within this semigroup we characterize the unitary and the isometric elements and we single out a class of natural contractions.

Accardi, Luigi; Dhahri, Ameur

2010-02-01

24

Tetrahedral Rovers: The Next Generation  

NASA Astrophysics Data System (ADS)

Addressable, reconfigurable rover architectures capable of real time transformation in size, shape, and gait will be essential for accessing those `hard to reach’ places where evidence for activity, geological or biological, might be hiding on planetary surfaces. We have designed and field tested simple tetrahedral rovers and are about to finish our third generation prototype, a human-sized 12tetrahedral rover capable of rolling, crawling, and climbing gaits. Our first prototype (1tet) walked a steep, slaggy slope at meteor crater. The performance of the new prototype will be evaluated in a variety of field environments using metrics which will allow comparison to wheeled rover performance in analogous terrains. Extreme mobililty is based on the capability for rapid reconfiguation of addressable struts interconnected at nodes (forming the space-filling tetrahedra) combined with rapid and low bandwidth position determination, communication and navigation/maneuvering systems. These latter capabilities are already under development elsewhere. We are designing a payload node which will allow lightweight sensors to remain upright for operation. Power generation requiring peak power for locomotion will be via a tetrahedrally deployable solar cell/rechargeable battery system. A variety of electrostatic dust control methods are being investigated. Basic gaits, developed for prevailing terrain conditions, are adjustable with movement across terrain approaching `real time’ for a human explorer.`Falling’ (except over a cliff) is not possible. Such a rover provides complimentary capabilities to a wheeled rover, which has the most efficient locomotion on terrain relatively smooth and flat on the scale of the wheels, and is thus capable of acting as an equipment base. The tetrahedral rover, acting as a scout, could provide reconnaissance, surveying, in situ sensing/sampling, and monitoring on what would be `slippery slopes’ for wheels.

Clark, Pamela E.; Curtis, S. A.; Rilee, M. L.; Wesenberg, R.; Cheug, C. Y.; Dorband, J.; Brown, G.; Sams, J.

2006-09-01

25

Towards Real Earth Models --Computational Geophysics on Unstructured Tetrahedral Meshes?  

E-print Network

Towards Real Earth Models -- Computational Geophysics on Unstructured Tetrahedral Meshes? Colin tetrahedral meshes. EM geophysics on unstructured tetrahedral meshes. Disadvantages, difficulties, challenges. Conclusions. #12;Outline: Geological models! Advantages of unstructured tetrahedral meshes. EM geophysics

Farquharson, Colin G.

26

CONVEC: A computer program for transient incompressible fluid flow based on quadratic finite elements. Part 1: Theoretical aspects  

Microsoft Academic Search

The theoretical and numerical aspects of the finite element computer code CONVEC designed for the transient analysis of two-dimensional plane or three-dimensional axisymmetric incompressible flows including the effects of heat transfer are described. The governing equations are the time-dependent incompressible Navier-Stokes equations and the thermal energy equation. The finite element method (FEM) is employed as a basic spatial discretization technique.

H. Laval

1981-01-01

27

CONVEC: A computer program for transient incompressible fluid flow based on quadratic finite elements. Part 2: User's manual  

Microsoft Academic Search

The computer code CONVEC is a general computer program designed for the solution of transient two-dimensional incompressible fluid flow problems. The solution procedure is based on the finite element method. The class of problems treated by the present version of CONVEC are those described by the time-dependent, two-dimensional (plane or axisymmetric) form of the Navier-Stokes equations. The flow field is

H. Laval

1981-01-01

28

TETRAHEDRAL MESH GENERATION FROM VOLUMETRIC BINARY AND GRAY SCALE IMAGES  

Microsoft Academic Search

We report a general purpose mesh generator for creating finite-element surface or volumetric mesh from 3D binary or gray-scale medical images. This toolbox incorporates a number of existing free mesh processing utilities and enables researchers to perform a range of mesh processing tasks for image-based mesh generation, including raw image processing, surface mesh extraction, surface re-sampling, and multi-scale\\/adaptive tetrahedral mesh

Qianqian Fang; David A. Boas

2009-01-01

29

Tetrahedral Mesh Generation from Volumetric Binary and Grayscale Images  

Microsoft Academic Search

We report a general purpose mesh generator for creating finite-element surface or volumetric mesh from 3D binary or gray-scale medical images. This toolbox incorporates a number of existing free mesh processing utilities and enables researchers to perform a range of mesh processing tasks for image-based mesh generation, including raw image processing, surface mesh extraction, surface re-sampling, and multi-scale\\/adaptive tetrahedral mesh

Qianqian Fang; David A. Boas

2009-01-01

30

Building Tetrahedral Kites. Grades 6-8.  

ERIC Educational Resources Information Center

Working in teams of four, students build a tetrahedral kite following a specific set of directions and using specific provided materials. Students use basic processes of manufacturing systems-- cutting, shaping, forming, conditioning, assembling, joining, finishing, and quality control--to manufacture a complete tetrahedral kite within a given…

Rushton, Erik; Ryan, Emily; Swift, Charles

31

Solving quadratic Introduction  

E-print Network

Solving quadratic equations 3.2 Introduction A quadratic equation is one which can be written. In this section we describe several ways in which quadratic equations can be solved. ' & $ % Prerequisites Before completing this Section you should be able to . . . recognise a quadratic equation solve a quadratic

Vickers, James

32

Au40: A Large Tetrahedral Magic Cluster  

SciTech Connect

40 is a magic number for tetrahedral symmetry predicted in both nuclear physics and the electronic jellium model. We show that Au{sub 40} could be such a magic cluster from density functional theory-based basin hopping for global minimization. The putative global minimum found for Au{sub 40} has a twisted pyramid structure, reminiscent of the famous tetrahedral Au{sub 20}, and a sizable HOMO-LUMO gap of 0.69 eV, indicating its molecular nature. Analysis of the electronic states reveals that the gap is related to shell closings of the metallic electrons in a tetrahedrally distorted effective potential.

Jiang, Deen [ORNL; Walter, Michael [University of Freiburg, Germany

2011-01-01

33

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for high Reynolds number laminar flows  

NASA Technical Reports Server (NTRS)

A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables were interpolated using complete quadratic shape functions and the pressure was interpolated using linear shape functions. For the two dimensional case, the pressure is defined on a triangular element which is contained inside the complete biquadratic element for velocity variables; and for the three dimensional case, the pressure is defined on a tetrahedral element which is again contained inside the complete tri-quadratic element. Thus the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow for Reynolds number of 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorable with those of the finite difference methods as well as experimental data available. A finite elememt computer program for incompressible, laminar flows is presented.

Kim, Sang-Wook

1988-01-01

34

Substructure Topology Preserving Simplification of Tetrahedral Meshes  

E-print Network

the power of our system with real world scientific datasets from electromagnetism simulations. 1. Our system combines this topological validity test with simple geometric and numeric error measuresSubstructure Topology Preserving Simplification of Tetrahedral Meshes Fabien Vivodtzev1, Georges

Boyer, Edmond

35

Soluble Zintl phases A14ZnGe16 (A = K, Rb) featuring [(?3-Ge4)Zn(?2-Ge4)]6- and [Ge4]4- clusters and the isolation of [(MesCu)2(?3,?3-Ge4)]4-: the missing link in the solution chemistry of tetrahedral group 14 element Zintl clusters.  

PubMed

The number of Zintl phases containing polyhedral clusters of tetrel elements that are accessible for chemical reactions of the main-group element clusters is rather limited. The synthesis and structural characterization of two novel ternary intermetallic phases A(14)ZnGe(16) (A = K, Rb) are presented, and their chemical reactivity is investigated. The compounds can be rationalized as Zintl phases with 14 alkali metal cations A(+) (A = K, Rb), two tetrahedral [Ge(4)](4-) Zintl anions, and one anionic heterometallic [(Ge(4))Zn(Ge(4))](6-) cluster per formula unit. The Zn-Ge cluster comprises two (Ge(4)) tetrahedra which are linked by a Zn atom, with one (Ge(4)) tetrahedron coordinating with a triangular face (?(3)) and the other one with an edge (?(2)). [(?(3)-Ge(4))Zn(?(2)-Ge(4))](6-) is a new isomer of the [(Ge(4))Zn(Ge(4))](6-) anion in Cs(6)ZnGe(8). The phases dissolve in liquid ammonia and thus represent rare examples of soluble Zintl compounds with deltahedral units of group 14 element atoms. Compounds with tetrahedral [E(4)](4-) species have previously been isolated from solution for E = Si, Sn, and Pb, and the current investigation provides the "missing link" for E = Ge. Reaction of an ammonia solution of K(14)ZnGe(16) with MesCu (Mes = 2,4,6-(CH(3))(3)C(6)H(2)) in the presence of [18]-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) yielded crystals of the salt [K([18]-crown-6)](2)K(2)[(MesCu)(2)Ge(4)](NH(3))(7.5) with the polyanion [(MesCu)(2)Ge(4)](4-). This MesCu-stabilized tetrahedral [Ge(4)](4-) cluster also completes the series of [(MesCu)(2)Si(4-x)Ge(x)](4-) clusters, which have previously been isolated from solution for x = 0 and 0.7, as the end member with x = 4. The electronic structures of [(Ge(4))Zn(Ge(4))](6-) and [(MesCu)(2)Ge(4)](4-) were investigated in terms of a molecular orbital description and analyses of the electron localization functions. The results are compared with band structure calculations for the A(14)ZnGe(16) phases (A = K, Rb). PMID:22867109

Stegmaier, Saskia; Waibel, Markus; Henze, Alexander; Jantke, Laura-Alice; Karttunen, Antti J; Fässler, Thomas F

2012-09-01

36

The NASA Tetrahedral Unstructured Software System (TETRUSS)  

NASA Technical Reports Server (NTRS)

The NASA Tetrahedral Unstructured Software System (TetrUSS) was developed during the 1990's to provide a rapid aerodynamic analysis and design capability to applied aerodynamicists. The system is comprised of loosely integrated, user-friendly software that enables the application of advanced Euler and Navier-Stokes tetrahedral finite volume technology to complex aerodynamic problems. TetrUSS has matured well because of the generous feedback from many willing users representing a broad cross-section of background and skill levels. This paper presents an overview of the current capabilities of the TetrUSS system along with some representative results from selected applications.

Frink, Neal T.; Pirzadeh, Shahyar Z.; Parikh, Paresh C.; Pandya, Mohagna J.; Bhat, M. K.

2000-01-01

37

Automatic finite element mesh generation for maxillary second premolar.  

PubMed

Developing three dimensional finite element mesh models for irregular geometric objects requires a large amount of manual efforts, hence limiting the three dimensional approach for dental structure analyses. An automatic procedure which can be used to generate a three dimensional finite element mesh for the maxillary second premolar was developed in this study. Firstly, a embedded second premolar was sliced and scanned parallel to the occlusal surface. A self-developed image processing system was employed to detect the boundaries of different materials within each section. An automatic mesh generation program was used on these boundaries to create tetrahedral elements based on moving nodes of uniform cube approach. Six mesh models of the second premolar with different element sizes using linear and quadratic elements were analyzed. Strain energy and von Mises stresses were reviewed for convergence in the crown regions. PMID:10386768

Lin, C L; Chang, C H; Cheng, C S; Wang, C H; Lee, H E

1999-06-01

38

Graphing Quadratic Equations  

NSDL National Science Digital Library

This is an introductory lesson to graphing quadratic equations. This lesson uses graphing technology to illustrate the differences between quadratic equations and linear equations. In addition, it allows students to identify important parts of the quadratic equation and how each piece changes the look of the graph.

Lengacher, Robert

2012-07-05

39

Lesson 14: Quadratic Formula  

NSDL National Science Digital Library

Completing the square is applied to the general quadratic to derive the quadratic formula. Before an area application example is given there is a quick review of the four methods that have been presented for solving quadratic equations. Complex numbers are introduced before the discriminant is presented.

2011-01-01

40

Self-Replicating Quadratics  

ERIC Educational Resources Information Center

We show that there are exactly four quadratic polynomials, Q(x) = x [superscript 2] + ax + b, such that (x[superscript 2] + ax + b) (x[superscript 2] - ax + b) = (x[superscript 4] + ax[superscript 2] + b). For n = 1, 2, ..., these quadratic polynomials can be written as the product of N = 2[superscript n] quadratic polynomials in x[superscript…

Withers, Christopher S.; Nadarajah, Saralees

2012-01-01

41

Substructure Topology Preserving Simplification of Tetrahedral Meshes  

E-print Network

the power of our system with real world scientific datasets from electromagnetism simulations. 1 the topology of the mesh and of its substructures. Our system combines this topological validity testSubstructure Topology Preserving Simplification of Tetrahedral Meshes Fabien Vivodtzev1, Georges

Hahmann, Stefanie

42

On a combined adaptive tetrahedral tracing and edge diffraction model  

NASA Astrophysics Data System (ADS)

A major challenge in architectural acoustics is the unification of diffraction models and geometric acoustics. For example, geometric acoustics is insufficient to quantify the scattering characteristics of acoustic diffusors. Typically the time-independent boundary element method (BEM) is the method of choice. In contrast, time-domain computations are of interest for characterizing both the spatial and temporal scattering characteristics of acoustic diffusors. Hence, a method is sought that predicts acoustic scattering in the time-domain. A prediction method, which combines an advanced image source method and an edge diffraction model, is investigated for the prediction of time-domain scattering. Adaptive tetrahedral tracing is an advanced image source method that generates image sources through an adaptive process. Propagating tetrahedral beams adapt to ensonified geometry mapping the geometric sound field in space and along boundaries. The edge diffraction model interfaces with the adaptive tetrahedral tracing process by the transfer of edge geometry and visibility information. Scattering is quantified as the contribution of secondary sources along a single or multiple interacting edges. Accounting for a finite number of diffraction permutations approximates the scattered sound field. Superposition of the geometric and scattered sound fields results in a synthesized impulse response between a source and a receiver. Evaluation of the prediction technique involves numerical verification and numerical validation. Numerical verification is based upon a comparison with analytic and numerical (BEM) solutions for scattering geometries. Good agreement is shown for the selected scattering geometries. Numerical validation is based upon experimentally determined scattered impulse responses of acoustic diffusors. Experimental data suggests that the predictive model is appropriate for high-frequency predictions. For the experimental determination of the scattered impulse response the merits of a maximum length sequence (MLS) versus a logarithmic swept-sine (LSS) are compared and contrasted. It is shown that a LSS is an appropriate stimuli for testing acoustic diffusors by comparing against scattered relative levels measured by a MLS signal.

Hart, Carl R.

43

Lattice Cleaving: Conforming Tetrahedral Meshes of Multimaterial Domains with Bounded Quality  

PubMed Central

Summary We introduce a new algorithm for generating tetrahedral meshes that conform to physical boundaries in volumetric domains consisting of multiple materials. The proposed method allows for an arbitrary number of materials, produces high-quality tetrahedral meshes with upper and lower bounds on dihedral angles, and guarantees geometric fidelity. Moreover, the method is combinatoric so its implementation enables rapid mesh construction. These meshes are structured in a way that also allows grading, in order to reduce element counts in regions of homogeneity. PMID:25309969

Bronson, Jonathan R.; Levine, Joshua A.; Whitaker, Ross T.

2013-01-01

44

A Quadratic Programming Bibliography - Optimization Online  

E-print Network

Feb 27, 2001 ... of the global optimum, computational experience on a number of nonconvex .... Elastic-plastic plane stress finite element analysis of a disk rolling on a .... A decomposition algorithm for a dual angular type quadratic ...... satisfaction of all kinematic boundary conditions and inter-element continuity conditions.

2001-02-27

45

Tetrahedrally coordinated carbonates in Earth's lower mantle.  

PubMed

Carbonates are the main species that bring carbon deep into our planet through subduction. They are an important rock-forming mineral group, fundamentally distinct from silicates in the Earth's crust in that carbon binds to three oxygen atoms, while silicon is bonded to four oxygens. Here we present experimental evidence that under the sufficiently high pressures and high temperatures existing in the lower mantle, ferromagnesian carbonates transform to a phase with tetrahedrally coordinated carbons. Above 80?GPa, in situ synchrotron infrared experiments show the unequivocal spectroscopic signature of the high-pressure phase of (Mg,Fe)CO3. Using ab-initio calculations, we assign the new infrared signature to C-O bands associated with tetrahedrally coordinated carbon with asymmetric C-O bonds. Tetrahedrally coordinated carbonates are expected to exhibit substantially different reactivity than low-pressure threefold coordinated carbonates, as well as different chemical properties in the liquid state. Hence, this may have significant implications for carbon reservoirs and fluxes, and the global geodynamic carbon cycle. PMID:25692448

Boulard, Eglantine; Pan, Ding; Galli, Giulia; Liu, Zhenxian; Mao, Wendy L

2015-01-01

46

Quadratic eigenvalue problems.  

SciTech Connect

In this report we will describe some nonlinear eigenvalue problems that arise in the areas of solid mechanics, acoustics, and coupled structural acoustics. We will focus mostly on quadratic eigenvalue problems, which are a special case of nonlinear eigenvalue problems. Algorithms for solving the quadratic eigenvalue problem will be presented, along with some example calculations.

Walsh, Timothy Francis; Day, David Minot

2007-04-01

47

Small Power Technology for Tetrahedral Rovers  

NASA Astrophysics Data System (ADS)

The Small Power Technology (SPOT) being studied at GSFC has the potential to be an efficient and compact radioisotope based electrical power system. Such a system would provide power for innovative tetrahedral robotic arms and walkers to support the lunar exploration initiative within the next decade. Presently, NASA has designated two flight qualified Radioisotope Power Supplies (RPS): the Multi-Mission RTG (MMRTG) which uses thermocouple technology and the more efficient but more massive Stirling RTG (SRTG) which uses a mechanical heat (Stirling) engine technology. With SPOT, thermal output from a radioisotope source is converted to electrical power using a combination of shape memory material and piezoelectric crystals. The SPOT combined energy conversion technologies are potentially more efficient than thermocouples and do not require moving parts, thus keeping efficiency high with an excellent mass to power ratio. Applications of particular interest are highly modular, addressable, reconfigurable arrays of tetrahedral structural components designed to be arms or rovers with high mobility in rough terrain. Such prototypes are currently being built at GSFC. Missions requiring long-lived operation in unilluminated environments preclude the use of solar cells as the main power source and must rely on the use of RPS technology. The design concept calls for a small motor and battery assembly for each strut, and thus a distributed power system. We estimate, based on performance of our current tetrahedral prototypes and power scaling for small motors, that such devices require tens of watts of power output per kilogram of power supply. For these reasons, SPOT is a good candidate for the ART (addressable Reconfigurable Technology) baseline power system.

Clark, P. E.; Floyd, S. R.; Butler, C. D.; Flom, Y.

2006-01-01

48

Extreme Mobility: Next Generation Tetrahedral Rovers  

NASA Astrophysics Data System (ADS)

This paper describes the development and testing of a patented rover concept called Tetrahedral Explorer Technologies (TET), designed to provide extreme mobility and plug-and-play utility through reconfigurable addressable architecture. Here, we present the results of preliminary lab and field tests of Prototype III. Reconfigurable architecture is essential in exploration because reaching features of the great potential interest will require crossing a wide range of terrains largely inaccessible to permanently appendaged vehicles. One surface might be relatively flat and navigable, while another could be rough, variably sloping, broken, or dominated by unconsolidated debris. To be totally functional, structures must form pseudo-appendages varying in size, rate, and manner of deployment (gait) and moving at a speed approaching that of a human in rugged terrain. TET architecture is based on the tetrahedron, the basic space-filling shape, as building block. Tetrahedra are interconnected, their apices acting as nodes from which struts reversibly deploy. The tetrahedral framework acts as a simple skeletal muscular structure. Two simple robotic walker prototypes have already been developed from a single reconfigurable tetrahedron capable of tumbling. This paper presents the results of our attempts to simulate motions, improve the hardware, and develop gaits for a more evolved 12Tetrahedral Walker (Prototype 3) which high degrees of freedom locomotion commandable through a user friendly interface. Our rover is an early level mission concept, realized as an electromechanical system at present, which would allow autonomous in situ exploration of lunar sites when we return to the Moon. Such a rover could carry into inaccessible terrain an in situ analysis payload designed to provide not only details of composition of traversed terrain, but the identification of sites with resources useful for permanent bases, including water and high Ti glass.

Clark, P. E.; Curtis, S. A.; Rilee, M. L.; Cheung, C. Y.; Wesenberg, R.; Brown, G.; Cooperrider, C.

2007-01-01

49

Theory of prospective tetrahedral perovskite ferroelectrics  

E-print Network

Using first-principles methods, we predict the energy landscape and ferroelectric states of double perovskites of the form AA$'$BB$'$O$_6$ in which the atoms on both the A and B sites are arranged in rock-salt order. While we are not aware of compounds that occur naturally in this structure, we argue that they might be realizable by directed synthesis. The high-symmetry structure formed by this arrangement belongs to the tetrahedral $F\\bar{4}3m$ space group. If a ferroelectric instability occurs, the energy landscape will tend to have minima with the polarization along tetrahedral directions, leading to a rhombohedral phase, or along Cartesian directions, leading to an orthorhombic phase. We find that the latter scenario applies to CaBaTiZrO$_6$ and KCaZrNbO$_6$, which are weakly ferroelectric, and the former one applies to PbSnTiZrO$_6$, which is strongly ferroelectric. The results are modeled with a fourth- or fifth-order Landau-Devonshire expansion, providing good agreement with the first-principles calcul...

Roy, Anindya

2010-01-01

50

Quadratic Liénard Equations with Quadratic Damping  

Microsoft Academic Search

In this paper we study the generalized Liénard equations x+f(x)x+g(x)=0 with quadratic polynomialsfandg. We prove that these kind of equations can have at most one limit cycle, and we give the complete bifurcation diagram and classification of the phase portraits. The paper also contains a shorter proof for the result in A. Lins, W. de Melo, and C. C. Pugh,

Freddy Dumortier; Chengzhi Li

1997-01-01

51

Main graphs: Quadratic equation  

E-print Network

a>0 OR OR OR x x x xxx x x x y y y Quadratic equation: The general solution of a quadratic equation equations: Equation dN dt = kN has the solution: N(t) = N0ekt; N0 is an (arbitrary) initial value of N. Systems of linear differential equations: For system dx dt = ax+by dy dt = cx+dy , the characteristic

Utrecht, Universiteit

52

A bicontinuous tetrahedral structure in a liquid-crystalline lipid  

NASA Astrophysics Data System (ADS)

The structure of most lipid-water phases can be visualized as an ordered distribution of two liquid media, water and hydrocarbons, separated by a continuous surface covered by the polar groups of the lipid molecules1. In the cubic phases in particular, rod-like elements are linked into three-dimensional networks1,2. Two of these phases (space groups Ia3d and Pn3m) contain two such three-dimensional networks mutually inter-woven and unconnected. Under the constraints of energy minimization3, the interface between the components in certain of these `porous fluids' may well resemble one of the periodic minimal surface structures of the type described mathematically by Schwarz4,5. A structure of this sort has been proposed for the viscous isotropic (cubic) form of glycerol monooleate (GMO) by Larsson et al.6 who suggested that the X-ray diagrams of Lindblom et al.7 indicated a body-centred crystal structure in which lipid bilayers might be arranged as in Schwarz's octahedral surface4. We have now found that at high water contents, a primitive cubic lattice better fits the X-ray evidence with the material in the crystal arranged in a tetrahedral way. The lipid appears to form a single bilayer, continuous in three dimensions, separating two continuous interlinked networks of water. Each of the water networks has the symmetry of the diamond crystal structure and the bilayer lies in the space between them following a surface resembling Schwarz's tetrahedral surface4.

Longley, William; McIntosh, Thomas J.

1983-06-01

53

Convex combination maps over triangulations, tilings, and tetrahedral meshes  

E-print Network

Convex combination maps over triangulations, tilings, and tetrahedral meshes Michael S. Floater with arbitrary tilings. We also give a simple counterexample to show that convex combination mappings over, Secondary: 65D17, 58E20. Key words: triangulation, tiling, tetrahedral mesh, convex combination, discrete

Floater, Michael S.

54

Updates to Multi-Dimensional Flux Reconstruction for Hypersonic Simulations on Tetrahedral Grids  

NASA Technical Reports Server (NTRS)

The quality of simulated hypersonic stagnation region heating with tetrahedral meshes is investigated by using an updated three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. An earlier implementation of this algorithm provided improved symmetry characteristics on tetrahedral grids compared to conventional reconstruction methods. The original formulation however displayed quantitative differences in heating and shear that were as large as 25% compared to a benchmark, structured-grid solution. The primary cause of this discrepancy is found to be an inherent inconsistency in the formulation of the flux limiter. The inconsistency is removed by employing a Green-Gauss formulation of primitive gradients at nodes to replace the previous Gram-Schmidt algorithm. Current results are now in good agreement with benchmark solutions for two challenge problems: (1) hypersonic flow over a three-dimensional cylindrical section with special attention to the uniformity of the solution in the spanwise direction and (2) hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problems provide a sensitive indicator for algorithmic effects on heating. Additional simulations on a sharp, double cone and the shuttle orbiter are then presented to demonstrate the capabilities of the new algorithm on more geometrically complex flows with tetrahedral grids. These results provide the first indication that pure tetrahedral elements utilizing the updated, three-dimensional, upwind reconstruction algorithm may be used for the simulation of heating and shear in hypersonic flows in upwind, finite volume formulations.

Gnoffo, Peter A.

2010-01-01

55

A Parallel Quadratic Programming Method for Dynamic Optimization ...  

E-print Network

A Parallel Quadratic Programming Method for Dynamic. Optimization ..... finite number of disjoint active sets further induces a subdivision of the dual ? space: ..... Cholesky factorization, the latter only regularizes those diagonal elements for.

2013-11-29

56

Quadratic exponential vectors  

SciTech Connect

We give a necessary and sufficient condition for the existence of a quadratic exponential vector with test function in L{sup 2}(R{sup d}) intersection L{sup {infinity}}(R{sup d}). We prove the linear independence and totality, in the quadratic Fock space, of these vectors. Using a technique different from the one used by Accardi et al. [Quantum Probability and Infinite Dimensional Analysis, Vol. 25, p. 262, (2009)], we also extend, to a more general class of test functions, the explicit form of the scalar product between two such vectors.

Accardi, Luigi; Dhahri, Ameur [Volterra Center, University of Roma Tor Vergata, Via Columbia 2, 00133 Roma (Italy)

2009-12-15

57

A tetrahedral modeling method for electromagnetic scattering by arbitrarily shaped inhomogeneous dielectric bodies  

NASA Astrophysics Data System (ADS)

A method for calculating the electromagnetic scattering from and internal field distribution of arbitrarily shaped, inhomogeneous, dielectric bodies is presented. A volume integral equation is formulated and solved by using the method of moments. Tetrahedral volume elements are used to model a scattering body in which the electrical parameters are assumed constant in each tetrahedron. Special basis functions are defined within the tetrahedral volume elements to insure that the normal electric field satisfies the correct jump condition at interfaces between different dielectric media. An approximate Galerkin testing procedure is used, with special care taken to correctly treat the derivation in the scalar potential term. Calculated internal field distributions and scattering cross sections of dielectric spheres and rods are compared to and found in agreement with other calculations. The accuracy of the fields calculated by using the tetrahedral cell method is found to be comparable to that of cubical cell methods presently used for modeling arbitrarily shaped bodies, while the modeling flexibility is considerably greater.

Schaubert, D. H.; Wilton, D. R.; Glisson, A. W.

1984-01-01

58

Artificial intelligence approach to planning the robotic assembly of large tetrahedral truss structures  

NASA Technical Reports Server (NTRS)

An assembly planner for tetrahedral truss structures is presented. To overcome the difficulties due to the large number of parts, the planner exploits the simplicity and uniformity of the shapes of the parts and the regularity of their interconnection. The planning automation is based on the computational formalism known as production system. The global data base consists of a hexagonal grid representation of the truss structure. This representation captures the regularity of tetrahedral truss structures and their multiple hierarchies. It maps into quadratic grids and can be implemented in a computer by using a two-dimensional array data structure. By maintaining the multiple hierarchies explicitly in the model, the choice of a particular hierarchy is only made when needed, thus allowing a more informed decision. Furthermore, testing the preconditions of the production rules is simple because the patterned way in which the struts are interconnected is incorporated into the topology of the hexagonal grid. A directed graph representation of assembly sequences allows the use of both graph search and backtracking control strategies.

Homemdemello, Luiz S.

1992-01-01

59

Why Quadratic Mean Diameter?  

Microsoft Academic Search

Quadratic mean diameter is the measure of average tree diameter conventionally used in forestry, rather than arithmetic mean diameter. The historical and practical reasons for this convention are reviewed. West. J. Appl. For. 15(3):137-139. Average diameter is a widely used stand statistic that appears in virtually all yield tables, simulator outputs, stand summaries, and much inventory data. To most people,

Robert O. Curtis; David D. Marshall

60

Generalized quadratic Liénard equations  

Microsoft Academic Search

In this article we give explicit formulae for the Liapunov quantities of generalized Liénard systems with either quadratic damping or restoring coefficients. These quantities provide necessary conditions in order for the origin to be a centre. Recent results are also presented for these systems.

S. Lynch

1998-01-01

61

A reduced Sequential Quadratic Programming method for large systems exploiting existing simulators  

E-print Network

illustrative realistic applications using the state-of-the-art massively parallel finite element code MPSALSAA reduced Sequential Quadratic Programming method for large systems exploiting existing simulators

Gorban, Alexander N.

62

Streaming Compression of Tetrahedral Volume Meshes  

SciTech Connect

Geometry processing algorithms have traditionally assumed that the input data is entirely in main memory and available for random access. This assumption does not scale to large data sets, as exhausting the physical memory typically leads to IO-inefficient thrashing. Recent works advocate processing geometry in a 'streaming' manner, where computation and output begin as soon as possible. Streaming is suitable for tasks that require only local neighbor information and batch process an entire data set. We describe a streaming compression scheme for tetrahedral volume meshes that encodes vertices and tetrahedra in the order they are written. To keep the memory footprint low, the compressor is informed when vertices are referenced for the last time (i.e. are finalized). The compression achieved depends on how coherent the input order is and how many tetrahedra are buffered for local reordering. For reasonably coherent orderings and a buffer of 10,000 tetrahedra, we achieve compression rates that are only 25 to 40 percent above the state-of-the-art, while requiring drastically less memory resources and less than half the processing time.

Isenburg, M; Lindstrom, P; Gumhold, S; Shewchuk, J

2005-11-21

63

More About the Tetrahedral Unstructured Software System  

NASA Technical Reports Server (NTRS)

TetrUSS is a comprehensive suite of computational fluid dynamics (CFD) programs that won the Software of the Year award in 1996 and has found increasing use in government, academia, and industry for solving realistic flow problems (especially in aerodynamics and aeroelastics of aircraft having complex shapes). TetrUSS includes not only programs for solving basic equations of flow but also programs that afford capabilities for efficient generation and utilization of computational grids and for graphical representation of computed flows (see figure). The 2004 version of the Tetrahedral Unstructured Software System (TetrUSS), which is one of two software systems reported in "NASA s 2004 Software of the Year," NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 18, has been improved greatly since 1996. These improvements include (1) capabilities to simulate viscous flow by solving the Navier-Stokes equations on unstructured grids, (2) portability to personal computers from diverse manufacturers, (3) advanced models of turbulence, (4) a parallel-processing version of one of the unstructured-grid Navier-Stokes-equation-solving programs, and (5) advanced programs for generating unstructured grids.

Abdol-Hamid, Khaled S.; Frink, Neal T.; Hunter, Craig A.; Parikh, Paresh C.; Pizadeh, Shalyar Z.; Samareh, Jamshid A.; Bhat, Maharaj K.; Pandya, Mohagna J.; Grismer, Matthew J.

2006-01-01

64

Unidirectional Formation of Tetrahedral Voids in Irradiated Silicon Carbide  

SciTech Connect

After high-dose, high temperature fast neutron irradiation, near-tetrahedral voids bounded with {111} surfaces were observed in beta-SiC. This was unexpected as the surface-to-volume ratio is larger than {111} octahedral voids common in both metals and ceramics. To obtain additional insight, three-dimensional structure of the tetrahedral voids was studied by transmission electron microscopy. Interestingly, only one half of {111} family planes in the zinc blende structure were permitted as void surfaces. The result is that the tetrahedral voids were oriented in only one of two possible directions, indicating that all void faces are either Si- or C-terminated polar surfaces.

Kondo, Sosuke [ORNL; Katoh, Yutai [ORNL; Snead, Lance Lewis [ORNL

2008-01-01

65

Hoop/column and tetrahedral truss electromagnetic tests  

NASA Technical Reports Server (NTRS)

The distortion of antennas was measured with a metric camera system at discrete target locations on the surface. Given are surface distortion for hoop column reflector antennas, for tetrahedral truss reflector antennas, and distortion contours for the tetrahedral truss reflector. Radiation patterns at 2.27-GHz, 4.26-GHz, 7.73-GHz and 11.6-GHz are given for the hoop column antenna. Also given are radiation patterns at 4.26-GHz and 7.73-GHz for the tetrahedral truss antenna.

Bailey, M. C.

1987-01-01

66

Analytical and Photogrammetric Characterization of a Planar Tetrahedral Truss  

NASA Technical Reports Server (NTRS)

Future space science missions are likely to require near-optical quality reflectors which are supported by a stiff truss structure. This support truss should conform closely with its intended shape to minimize its contribution to the overall surface error of the reflector. The current investigation was conducted to evaluate the planar surface accuracy of a regular tetrahedral truss structure by comparing the results of predicted and measured node locations. The truss is a 2-ring hexagonal structure composed of 102 equal-length truss members. Each truss member is nominally 2 meters in length between node centers and is comprised of a graphite/epoxy tube with aluminum nodes and joints. The axial stiffness and the length variation of the truss components were determined experimentally and incorporated into a static finite element analysis of the truss. From this analysis, the root mean square (RMS) surface error of the truss was predicted to be 0.11 mm (0004 in). Photogrammetry tests were performed on the assembled truss to measure the normal displacements of the upper surface nodes and to determine if the truss would maintain its intended shape when subjected to repeated assembly. Considering the variation in the truss component lengths, the measures rms error of 0.14 mm (0.006 in) in the assembled truss is relatively small. The test results also indicate that a repeatable truss surface is achievable. Several potential sources of error were identified and discussed.

Wu, K. Chauncey; Adams, Richard R.; Rhodes, Marvin D.

1990-01-01

67

The group theory of trigonal and tetrahedral molecule rotations in trigonal and tetrahedral crystal fields  

NASA Astrophysics Data System (ADS)

The permutation symmetry groups introduced by Longuet-Higgins are employed to solve the group theory for molecules of C3v and Td symmetry rotating in crystal fields of C3v and Td symmetry. The qualitative appearances of the energy level diagrams for the groups (C3v, &(C)macr;3v), (C3v, &(T)macr;d) and (Td, &(C)macr;3v) are deduced for the range of barrier heights from the free-rotor limits to the pinned limits, for the ground state multiplet only. The correlations between the groups derived here and the group (Td, &(T)macr;d) treated by Miller and Decius are considered and the alteration in the ground state splitting pattern in going from a tetrahedral molecule in a tetrahedral field through to a trigonal molecule in a trigonal field is illustrated. The group (C3v, &(C)macr;3v) is treated in detail and applied to the tunnelling states of monodeuteromethane adsorbed on the surface of graphite. The rotational Hamiltonian matrix is constructed in the pocket state formalism and diagonalized using the character table for (C3v, &(C)macr;3v). The quantitative appearance of the energy level diagram for the ground librational state of CH3D on graphite is shown.

Smalley, M. V.; Ball, P. C.

68

Main graphs: Quadratic equation  

E-print Network

Main graphs: Quadratic equation: Equation A2 +B+C = 0, has solutions given by the following 'abc equations: Equation dN dt = kN has the solution: N(t) = N0ekt; N0 is an (arbitrary) initial value of N. Characteristic time of change is = 1/k. Systems of linear differential equations: For system dx dt = ax+by dy dt

Utrecht, Universiteit

69

Inhibitors of angiotensin-converting enzyme containing a tetrahedral arsenic atom.  

PubMed Central

A series of tetrahedral oxo acids of Group VA and VIA elements and of silicon and boron were examined as inhibitors of angiotensin-converting enzyme. Arsenate is a competitive inhibitor with a Ki of 27 +/- 1 mM, at least 10-fold more potent than phosphate. Dimethylarsinate is a competitive inhibitor with a Ki of 70 +/- 9 mM, 2-fold more potent than dimethylphosphinate. Oxo acids of boron, silicon, antimony, sulphur and selenium are not inhibitors. On the basis of these results and the strong inhibition of this zinc metallopeptidase by substrate analogues containing a tetrahedral phosphorus atom, two substrate analogues containing a tetrahedral arsenic atom were prepared. 2-Arsonoacetyl-L-proline is a competitive inhibitor with a Ki of 18 +/- 7 mM, more than 2000-fold weaker than that of its phosphorus analogue 2-phosphonoacetyl-L-proline. 4-Arsono-2-benzylbutanoic acid is a mixed inhibitor with a Ki of 0.5 +/- 0.2 mM, indistinguishable in potency from its phosphorus analogue 2-benzyl-4-phosphonobutanoic acid. PMID:2986596

Galardy, R E; Kortylewicz, Z P

1985-01-01

70

Enriching low-order finite elements by interpolation covers  

E-print Network

This dissertation presents an enriched finite element procedure based on the use of interpolation cover functions for low-order finite elements, namely, the 3-node triangular and 4- node tetrahedral elements. The standard ...

Kim, Jae Hyung, Ph. D. Massachusetts Institute of Technology

2013-01-01

71

Lesson 17: Quadratic Inequalities  

NSDL National Science Digital Library

The lesson begins with using graphs to solve quadratic inequalities. AN equation modeling the height of a rocket is graphed along with a second equation that represents the minimum height at which the rocket can legally and safely be exploded. The intersections of the graphs provide the solution interval. A second method is then presented where the inequality is put into standard form and then solved for its x-intercepts. Interval notation and union of sets is reviewed before a purely algebraic procedure for solving the inequalities is presented. The lesson concludes with an application problem.

2011-01-01

72

Solving quadratic equations using reduced unimodular quadratic forms  

Microsoft Academic Search

Let Q be an n × n symmetric matrix with integral entries and with detQ ?= 0, but not necesarily positive definite. We describe a generalized LLL algorithm to reduce this quadratic form. This algorithm either reduces the quadratic form or stops with some isotropic vector. It is proved to run in polynomial time. We also describe an algorithm for

Denis Simon

2005-01-01

73

Unidirectional formation of tetrahedral voids in irradiated silicon carbide  

SciTech Connect

The (111) tetrahedral voids induced by neutron irradiation in 3C-SiC were found to be spatially oriented in only one of two possible directions. The tetrahedral shape was unexpected as the surface-to-volume ratio is larger than the alternative (111) octahedral void common in both metals and ceramics. From a geometric viewpoint, all faces of the observed voids are either Si- or C-terminated surfaces. By comparing the surface area with the octahedral void (composed of the both Si- and C-surfaces) of the same volume, the considerable difference in surface energy between the Si(111) and C(111) was implicated.

Kondo, S.; Katoh, Y.; Snead, L. L. [Materials Science and Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6138 (United States)

2008-10-20

74

Mixed-integer quadratic programming  

Microsoft Academic Search

This paper considers mixed-integer quadratic programs in which the objective function is quadratic in the integer and in the continuous variables, and the constraints are linear in the variables of both types. The generalized Benders' decomposition is a suitable approach for solving such programs. However, the program does not become more tractable if this method is used, since Benders' cuts

Rafael Lazimy

1982-01-01

75

Inertial Confinement Fusion with Tetrahedral Hohlraums at OMEGA  

Microsoft Academic Search

Indirect-drive inertial confinement fusion will require for ignition a highly symmetric x-ray flux around the capsule. To this end, the ``tetrahedral hohlraum,'' spherical in shape with four laser entrance holes located at the vertices of a tetrahedron, has been proposed. The first experimental test of this concept, using the OMEGA laser, is reported here. Drive symmetry was probed using capsule

J. M. Wallace; T. J. Murphy; N. D. Delamater; K. A. Klare; J. A. Oertel; G. R. Magelssen; E. L. Lindman; A. A. Hauer; P. Gobby; J. D. Schnittman; R. S. Craxton; W. Seka; R. Kremens; D. Bradley; S. M. Pollaine; R. E. Turner; O. L. Landen; D. Drake; J. J. Macfarlane

1999-01-01

76

Pre-integrated Flow Illustration for Tetrahedral Meshes  

Microsoft Academic Search

Previous work has demonstrated the clarity and usefulness of illustrative techniques for visualizing flow data. However, previous systems were limited to applying these techniques to uniform grids. Since unstructured grids have emerged as a common basis for computing flow simulations, we present a method to apply and extend the flow illustration approach to tetrahedral meshes using pre-integrated GPU-accelerated raycasting. Our

N. A. Svakhine; D. Ebert; E. Tejada; T. Ertl; K. Gaither

77

Hardware-Based Ray Casting for Tetrahedral Meshes  

Microsoft Academic Search

We present the first implementation of a volume ray casting algorithm for tetrahedral meshes running on off-the-shelf programmable graphics hardware. Our implementation avoids the memory transfer bottleneck of the graphics bus since the complete mesh data is stored in the local memory of the graphics adapter and all computations, in particular ray traversal and ray integration, are performed by the

Manfred Weiler; Martin Kraus; Markus Merz; Thomas Ertl

2003-01-01

78

Linear?quadratic optimal control with integral quadratic constraints  

Microsoft Academic Search

SUMMARY We derive closed-form solutions for the linear-quadratic (LQ) optimal control problem subject to integral quadratic constraints. The optimal control is a non-linear function of the current state and the initial state. Furthermore, the optimal control is easily calculated by solving an unconstrained LQ control problem together with an optimal parameter selection problem. Gradient formulae for the cost functional of

A. E. B. Lim; Y. Q. Liu; K. L. Teo; J. B. Moore

1999-01-01

79

Quadratics, polynomial form in y  

NSDL National Science Digital Library

Explore the graph of a quadratic of the form x = ay2 + by + c. Vary the coefficients of the equation and examine how the graph changes in response. Calculate the location of the vertex and y-intercepts.

ExploreMath.com

2001-01-01

80

An Investigation on Quadratic Equations.  

ERIC Educational Resources Information Center

Argues that exploring a familiar topic or examination question in a novel manner is a useful way to find topics for mathematical investigation in the classroom. The example used to illustrate the premise is a quadratic equation. (PK)

Hirst, Keith

1988-01-01

81

ATTILA: A three-dimensional, unstructured tetrahedral mesh discrete ordinates transport code  

SciTech Connect

Many applications of radiation transport require the accurate modeling of complex three-dimensional geometries. Historically, Monte Carlo codes have been used for such applications. Existing deterministic transport codes were not applied to such problems because of the difficulties of modeling complex three-dimensional geometries with rectangular meshes. The authors have developed a three-dimensional discrete ordinates (S{sub n}) code, ATTILA, which uses linear-discontinuous finite element spatial differencing in conjunction with diffusion-synthetic acceleration (DSA) on an unstructured tetrahedral mesh. This tetrahedral mesh capability enables the authors to efficiently model complex three-dimensional geometries. One interesting and challenging application of neutron and/or gamma-ray transport is nuclear well-logging applications. Nuclear well-logging problems usually involve a complex geometry with fixed sources and one or more detectors. Detector responses must generally be accurate to within {approx}1%. The combination of complex three-dimensional geometries and high accuracy requirements makes it difficult to perform logging problems with traditional S{sub n} differencing schemes and rectangular meshes. Hence, it is not surprising that deterministic S{sub n} codes have seen limited use in nuclear well-logging applications. The geometric modeling capabilities and the advanced spatial differencing of ATTILA give it a significant advantage, relative to traditional S{sub n} codes, for performing nuclear well-logging calculations.

Wareing, T.A.; McGhee, J.M.; Morel, J.E. [Los Alamos National Lab., NM (United States)

1996-12-31

82

Quality Tetrahedral Mesh Smoothing via Boundary-Optimized Delaunay Triangulation  

PubMed Central

Despite its great success in improving the quality of a tetrahedral mesh, the original optimal Delaunay triangulation (ODT) is designed to move only inner vertices and thus cannot handle input meshes containing “bad” triangles on boundaries. In the current work, we present an integrated approach called boundary-optimized Delaunay triangulation (B-ODT) to smooth (improve) a tetrahedral mesh. In our method, both inner and boundary vertices are repositioned by analytically minimizing the error between a paraboloid function and its piecewise linear interpolation over the neighborhood of each vertex. In addition to the guaranteed volume-preserving property, the proposed algorithm can be readily adapted to preserve sharp features in the original mesh. A number of experiments are included to demonstrate the performance of our method. PMID:23144522

Gao, Zhanheng; Yu, Zeyun; Holst, Michael

2012-01-01

83

Supercritical ordered trajectories with quadratically irrational winding number  

Microsoft Academic Search

The dynamics of the circle map is studied in the supercritical regime where the map is not invertible and thus the trajectory elements are clustered on the circle. Existence of a simple ordering structure is established for trajectories with arbitrary irrational winding number. A previously developed formalism is then generalized to predict the trajectories when the winding number is quadratically

Subir Kumar Sarkar

1984-01-01

84

Parallel Interior Point Solver for Structured Quadratic Programs ...  

E-print Network

Parallel Interior-Point Solver for Structured Quadratic Programs: Application to ... ?1 and X and S are diagonal matrices in Rn×n with elements of vectors x and ..... at times t = 0,... ,T; each of the ?t has only a finite number of possible outcomes.

1910-30-82

85

A Generalized Method for Constructing Sub-quadratic Complexity ) Multipliers  

E-print Network

-parallel multipliers, finite fields, Winograd convolution 1 Introduction Finite fields have numerous applications representation of the field elements (and hence the operands). It is customary to view a finite field as a vectorA Generalized Method for Constructing Sub-quadratic Complexity GF(2k ) Multipliers Draft Copy B

86

The statistical mechanics of ion-dipole-tetrahedral quadrupole mixtures  

NASA Astrophysics Data System (ADS)

We examine the solution of the Ornstein-Zernike equations for the correlation functions of a fluid mixture in which the molecular interactions consist of a hard sphere plus a multipolar potential that contains coulombic, dipolar as well as quadrupolar terms. In particular we consider the case in which the molecule has a dipole moment in the z direction of the molecular axis system and a non-linear tetrahedral quadrupole tensor of the form ?xx = - ?yy, ?zz = 0 = ???, ? ? ? in the molecular frame. This model is a good representation of the dipolar and quadrupolar properties of water and our analysis will form the basis for constructing a Civilized Model electrolyte in which ions are dissolved in a solvent whose molecules possess water-like multipole moments. One of our main results is that for any theory which retains only the subset of rotational invariants that either appear in the interaction potentials or are generated by angular convolution from those appearing in the interaction potentials, e.g. the linearized hypernetted chain (LHNC) or mean spherical approximations (MSA), the equations for an ion-dipole-tetrahedral quadrupolar mixture only differ from those for an ion-dipole-linear quadrupole mixture (?xx = ?yy = - 1/2?zz, ??? = 0, ? ? ?) in minor details. We have investigated the thermodynamic properties of a fluid of hard spheres with the dipole and tetrahedral moments of water using thermodynamic perturbation theory. We find that contributions to the thermodynamic properties from dipole-quadrupole interaction are very important. For a pure hard sphere tetrahedral quadrupolar fluid there is considerable difference between the results from perturbation theory and from the MSA, for which we have obtained an analytic solution.

Carnie, Steven L.; Chan, Derek Y. C.; Walker, Glen R.

87

Multiple arrival tracking within irregular triangular or tetrahedral cell model  

NASA Astrophysics Data System (ADS)

The focus of this research is to introduce a triangular shortest-path method incorporating a multistage scheme for tracking multiple arrivals composed of any kind of combinations of transmissions, conversions and reflections in complex 2D or 3D layered media, in which a triangular (2D) or a tetrahedral (3D) cell is used to parameterize the velocity model. The basic principle is to divide a layered model into several different computational domains using irregular triangular (or tetrahedral) cells in model parameterization, and then to apply the multistage technique to trace the multiple arrivals. Meanwhile, a second level of forward star technique (where a forward star represents a geometric arrangement of network connections, or possible ray branching points into adjacent nodes), previously defined in gridded model, is first introduced into the triangular (or tetrahedral) cell model. The results show that using irregular triangular (or tetrahedral) cells can effectively approximate the undulated subsurface and velocity discontinuity, easily define the velocity distribution across the irregular subsurface interface, and hence greatly improve the computational accuracy. Several examples (including the Marmousi model) are used to demonstrate the viability and versatility of the multistage triangular shortest-path method in heterogeneous media, even in the presence of high-velocity contrasts involving interfaces of relatively high curvature. With the introduction of the second level of the forward star scheme, the total number of nodes is reduced sufficiently (normally by half), and therefore the computer memory required is less. Most important is that the computing accuracy with the second level forward star scheme can be greatly improved (say, 2-3 times in general) over those with the first level of forward star scheme applied.

Bai, Chao-ying; Li, Xiao-ling; Wang, Qing-lin; Peng, Jian-bing

2012-02-01

88

Linear state feedback, quadratic weights, and closed loop eigenstructures. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Results are given on the relationships between closed loop eigenstructures, state feedback gain matrices of the linear state feedback problem, and quadratic weights of the linear quadratic regulator. Equations are derived for the angles of general multivariable root loci and linear quadratic optimal root loci, including angles of departure and approach. The generalized eigenvalue problem is used for the first time to compute angles of approach. Equations are also derived to find the sensitivity of closed loop eigenvalues and the directional derivatives of closed loop eigenvectors (with respect to a scalar multiplying the feedback gain matrix or the quadratic control weight). An equivalence class of quadratic weights that produce the same asymptotic eigenstructure is defined, sufficient conditions to be in it are given, a canonical element is defined, and an algorithm to find it is given. The behavior of the optimal root locus in the nonasymptotic region is shown to be different for quadratic weights with the same asymptotic properties.

Thompson, P. M.

1979-01-01

89

A stabilized mixed finite element method for shear-rate dependent non-Newtonian fluids: 3D benchmark problems and application to blood flow in bifurcating arteries  

NASA Astrophysics Data System (ADS)

This paper presents a stabilized mixed finite element method for shear-rate dependent fluids. The nonlinear viscosity field is a function of the shear-rate and varies uniformly in space and in time. The stabilized form is developed via application of Variational Multiscale (VMS) framework to the underlying generalized Navier-Stokes equation. Linear and quadratic tetrahedral and hexahedral elements are employed with equal-order interpolations for the velocity and pressure fields. A variety of benchmark problems are solved to assess the stability and accuracy properties of the resulting method. The method is then applied to non-Newtonian shear-rate dependent flows in bifurcating artery geometry, and significant non-Newtonian fluid effects are observed. A comparative study of the proposed method shows that the additional computational costs due to the nonlinear shear-rate dependent viscosity are only ten percent more than the computational cost for a Newtonian model.

Kwack, JaeHyuk; Masud, Arif

2014-04-01

90

An assessment of the adaptive unstructured tetrahedral grid, Euler Flow Solver Code FELISA  

NASA Technical Reports Server (NTRS)

A three-dimensional solution-adaptive Euler flow solver for unstructured tetrahedral meshes is assessed, and the accuracy and efficiency of the method for predicting sonic boom pressure signatures about simple generic models are demonstrated. Comparison of computational and wind tunnel data and enhancement of numerical solutions by means of grid adaptivity are discussed. The mesh generation is based on the advancing front technique. The FELISA code consists of two solvers, the Taylor-Galerkin and the Runge-Kutta-Galerkin schemes, both of which are spacially discretized by the usual Galerkin weighted residual finite-element methods but with different explicit time-marching schemes to steady state. The solution-adaptive grid procedure is based on either remeshing or mesh refinement techniques. An alternative geometry adaptive procedure is also incorporated.

Djomehri, M. Jahed; Erickson, Larry L.

1994-01-01

91

Tetrahedral coordination of Zn ions in molten zinc halides  

NASA Astrophysics Data System (ADS)

Measurements of the scattering of thermal neutrons from natural samples of molten ZnCl2, ZnBr2, and ZnI2 are reported. The experiments were undertaken on the liquids and amorphous materials diffractometer of the ISIS spallation source at the Rutherford-Appleton laboratory. The data reveal some shortcomings in earlier studies of ZnCl2 but confirm a structural model in which the small Zn2+ ions occupy tetrahedrally coordinated sites in a closely packed anion structure, with strong intermediate range ordering. Features arising from changes in the anion species are identified and temperature-dependent effects are resolved in ZnCl2.

Allen, D. A.; Howe, R. A.; Wood, N. D.; Howells, W. S.

1991-04-01

92

Inertial Confinement Fusion with Tetrahedral Hohlraums at OMEGA  

SciTech Connect

Indirect-drive inertial confinement fusion will require for ignition a highly symmetric x-ray flux around the capsule. To this end, the {open_quotes}tetrahedral hohlraum,{close_quotes} spherical in shape with four laser entrance holes located at the vertices of a tetrahedron, has been proposed. The first experimental test of this concept, using the OMEGA laser, is reported here. Drive symmetry was probed using capsule implosion symmetries, which varied qualitatively as expected with hohlraum dimensions. Modeling of the experiments gives time-averaged flux asymmetries as low as 1{percent} rms over a 2.2-ns laser pulse. {copyright} {ital 1999} {ital The American Physical Society}

Wallace, J.M.; Murphy, T.J.; Delamater, N.D.; Klare, K.A.; Oertel, J.A.; Magelssen, G.R.; Lindman, E.L.; Hauer, A.A.; Gobby, P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Schnittman, J.D.; Craxton, R.S.; Seka, W.; Kremens, R.; Bradley, D. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299 (United States)] [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299 (United States); Pollaine, S.M.; Turner, R.E.; Landen, O.L. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Drake, D. [InterScience, Germantown, Maryland 20875-0659 (United States)] [InterScience, Germantown, Maryland 20875-0659 (United States); MacFarlane, J.J. [University of Wisconsin, Madison, Wisconsin 53706 (United States)] [University of Wisconsin, Madison, Wisconsin 53706 (United States)

1999-05-01

93

Inertial Confinement Fusion with Tetrahedral Hohlraums at OMEGA  

NASA Astrophysics Data System (ADS)

Indirect-drive inertial confinement fusion will require for ignition a highly symmetric x-ray flux around the capsule. To this end, the ``tetrahedral hohlraum,'' spherical in shape with four laser entrance holes located at the vertices of a tetrahedron, has been proposed. The first experimental test of this concept, using the OMEGA laser, is reported here. Drive symmetry was probed using capsule implosion symmetries, which varied qualitatively as expected with hohlraum dimensions. Modeling of the experiments gives time-averaged flux asymmetries as low as 1% rms over a 2.2-ns laser pulse.

Wallace, J. M.; Murphy, T. J.; Delamater, N. D.; Klare, K. A.; Oertel, J. A.; Magelssen, G. R.; Lindman, E. L.; Hauer, A. A.; Gobby, P.; Schnittman, J. D.; Craxton, R. S.; Seka, W.; Kremens, R.; Bradley, D.; Pollaine, S. M.; Turner, R. E.; Landen, O. L.; Drake, D.; Macfarlane, J. J.

1999-05-01

94

Novel biomedical tetrahedral mesh methods: algorithms and applications  

NASA Astrophysics Data System (ADS)

Tetrahedral mesh generation algorithm, as a prerequisite of many soft tissue simulation methods, becomes very important in the virtual surgery programs because of the real-time requirement. Aiming to speed up the computation in the simulation, we propose a revised Delaunay algorithm which makes a good balance of quality of tetrahedra, boundary preservation and time complexity, with many improved methods. Another mesh algorithm named Space-Disassembling is also presented in this paper, and a comparison of Space-Disassembling, traditional Delaunay algorithm and the revised Delaunay algorithm is processed based on clinical soft-tissue simulation projects, including craniofacial plastic surgery and breast reconstruction plastic surgery.

Yu, Xiao; Jin, Yanfeng; Chen, Weitao; Huang, Pengfei; Gu, Lixu

2007-12-01

95

Practical implementation of tetrahedral mesh reconstruction in emission tomography.  

PubMed

This paper presents a practical implementation of image reconstruction on tetrahedral meshes optimized for emission computed tomography with parallel beam geometry. Tetrahedral mesh built on a point cloud is a convenient image representation method, intrinsically three-dimensional and with a multi-level resolution property. Image intensities are defined at the mesh nodes and linearly interpolated inside each tetrahedron. For the given mesh geometry, the intensities can be computed directly from tomographic projections using iterative reconstruction algorithms with a system matrix calculated using an exact analytical formula. The mesh geometry is optimized for a specific patient using a two stage process. First, a noisy image is reconstructed on a finely-spaced uniform cloud. Then, the geometry of the representation is adaptively transformed through boundary-preserving node motion and elimination. Nodes are removed in constant intensity regions, merged along the boundaries, and moved in the direction of the mean local intensity gradient in order to provide higher node density in the boundary regions. Attenuation correction and detector geometric response are included in the system matrix. Once the mesh geometry is optimized, it is used to generate the final system matrix for ML-EM reconstruction of node intensities and for visualization of the reconstructed images. In dynamic PET or SPECT imaging, the system matrix generation procedure is performed using a quasi-static sinogram, generated by summing projection data from multiple time frames. This system matrix is then used to reconstruct the individual time frame projections. Performance of the new method is evaluated by reconstructing simulated projections of the NCAT phantom and the method is then applied to dynamic SPECT phantom and patient studies and to a dynamic microPET rat study. Tetrahedral mesh-based images are compared to the standard voxel-based reconstruction for both high and low signal-to-noise ratio projection datasets. The results demonstrate that the reconstructed images represented as tetrahedral meshes based on point clouds offer image quality comparable to that achievable using a standard voxel grid while allowing substantial reduction in the number of unknown intensities to be reconstructed and reducing the noise. PMID:23588373

Boutchko, R; Sitek, A; Gullberg, G T

2013-05-01

96

Ligands effects on the magnetic anisotropy of tetrahedral cobalt complexes.  

PubMed

The effect of ligands with heavy donor atoms on the magnetic anisotropy of the pseudo-tetrahedral cobalt complexes, Co(quinoline)2I2 (1) and Co(EPh3)2I2 (2-3) (E = P, As) has been investigated. The axial zero-field splitting parameter D was found to vary from +9.2 cm(-1) in 1 to -36.9 cm(-1) in 2 and -74.7 cm(-1) in 3. Compounds 2 and 3 exhibit slow relaxation of the magnetization up to 4 K under an applied dc field, indicating SMM behavior. PMID:25183324

Saber, Mohamed R; Dunbar, Kim R

2014-10-21

97

Solving Quadratic Equations by Factoring  

NSDL National Science Digital Library

This video explains how to solve quadratic equations with the factoring method. In 4 minutes 23 seconds, the two narrators explain in detail the steps required. Additionally, how these equations relate to objects and events in the real world such as roller coasters is covered.

2012-08-06

98

Distributed Control with Integral Quadratic Constraints  

E-print Network

Distributed Control with Integral Quadratic Constraints Hui Fang, Panos J. Antsaklis Department Integral Quadratic Constraints (IQC) on the interconnections are derived. These results take the form in control theory, namely control under communication constraints. In particular, researchers have considered

Antsaklis, Panos

99

Distributed Control with Integral Quadratic Constraints  

E-print Network

1 Distributed Control with Integral Quadratic Constraints Hui Fang and Panos J. Antsaklis Abstract, and the multipliers are specified by the underlying integral quadratic constraints to model interconnections between. Antsaklis, "Distributed Control with Integral Quadratic Constraints," ISIS Technical Report ISIS-2007

Antsaklis, Panos

100

Quadratic bosonic and free white noises  

E-print Network

We discuss the meaning of renormalization used for deriving quadratic bosonic commutation relations introduced by Accardi and find a representation of these relations on an interacting Fock space. Also, we investigate classical stochastic processes which can be constructed from noncommutative quadratic white noise. We postulate quadratic free white noise commutation relations and find their representation on an interacting Fock space.

Piotr Sniady

2003-03-20

101

Quadratic Residues a is a quadratic residue mod m if x2  

E-print Network

if the following equation has a solution: x2 = a (mod m) . Otherwise, a is a quadratic nonresidue mod m. Example. 8 a quadratic equation mod p has at most two solutions (Prove it!), there are exactly two. Example. x2 = 8 (mod6-21-2013 Quadratic Residues · a is a quadratic residue mod m if x2 = a (mod m). Otherwise

Ikenaga, Bruce

102

Geometrical Solutions of Quadratic Equations.  

ERIC Educational Resources Information Center

Demonstrates that the equation of a circle (x-h)2 + (y-k)2 = r2 with center (h; k) and radius r reduces to a quadratic equation x2-2xh + (h2 + k2 -r2) = O at the intersection with the x-axis. Illustrates how to determine the center of a circle as well as a point on a circle. (Author/ASK)

Grewal, A. S.; Godloza, L.

1999-01-01

103

Quadratic fluctuation-dissipation theorem for multilayer plasmas  

SciTech Connect

The author establishes the dynamical and static quadratic fluctuation-dissipation theorems (QFDTs) for multilayer classical one-component plasmas in the absence of external magnetic fields. Areal densities and spacings between layers need not be equal. The static QFDT is used to derive the lowest-order (in coupling parameter) Mayer cluster expansion for the layer-space matrix elements of the equilibrium three-point correlation function. {copyright} {ital 1999} {ital The American Physical Society}

Golden, K.I. [Department of Mathematics and Statistics, University of Vermont, Burlington, Vermont 05401-1455 (United States)] [Department of Mathematics and Statistics, University of Vermont, Burlington, Vermont 05401-1455 (United States)

1999-01-01

104

Direct observation of tetrahedrally coordinated Fe(III) in ferrihydrite.  

PubMed

Ferrihydrite is a common iron hydroxide nanomineral commonly found in soils, sediments, and surface waters. Reactivity with this important environmental surface often controls the fate and mobility of both essential nutrients and inorganic contaminants. Despite the critical role of ferrihydrite in environmental geochemistry, its structure is still debated. In this work, we apply bulk sensitive Fe L edge X-ray absorption spectroscopy to study the crystal field environment of the Fe in ferrihydrite and other Fe oxides of known structure. This direct probe of the local electronic structure provides verification of the presence of tetrahedrally coordinated Fe(III) in the structure of ferrihydrite and puts to rest the controversy on this issue. PMID:22369094

Peak, Derek; Regier, Tom

2012-03-20

105

Optimization of Time-Dependent Particle Tracing Using Tetrahedral Decomposition  

NASA Technical Reports Server (NTRS)

An efficient algorithm is presented for computing particle paths, streak lines and time lines in time-dependent flows with moving curvilinear grids. The integration, velocity interpolation and step-size control are all performed in physical space which avoids the need to transform the velocity field into computational space. This leads to higher accuracy because there are no Jacobian matrix approximations or expensive matrix inversions. Integration accuracy is maintained using an adaptive step-size control scheme which is regulated by the path line curvature. The problem of cell-searching, point location and interpolation in physical space is simplified by decomposing hexahedral cells into tetrahedral cells. This enables the point location to be done analytically and substantially faster than with a Newton-Raphson iterative method. Results presented show this algorithm is up to six times faster than particle tracers which operate on hexahedral cells yet produces almost identical particle trajectories.

Kenwright, David; Lane, David

1995-01-01

106

Nuclear Tetrahedral Symmetry: Possibly Present Throughout the Periodic Table  

E-print Network

More than half a century after the fundamental, spherical shell structure in nuclei has been established, theoretical predictions indicate that the shell-gaps comparable or even stronger than those at spherical shapes may exist. Group-theoretical analysis supported by realistic mean-field calculations indicate that the corresponding nuclei are characterized by the $T_d^D$ ('double-tetrahedral') group of symmetry, exact or approximate. The corresponding strong shell-gap structure is markedly enhanced by the existence of the 4-dimensional irreducible representations of the group in question and consequently it can be seen as a geometrical effect that does not depend on a particular realization of the mean-field. Possibilities of discovering the corresponding symmetry in experiment are discussed.

J. Dudek; A. Gozdz; N. Schunck; M. Miskiewicz

2002-05-21

107

Photoconductive detection of tetrahedrally coordinated hydrogen in ZnO.  

PubMed

In this Letter we apply an innovative experimental approach, which allows us to improve the sensitivity of detecting local vibrational modes (LVMs) even in highly absorbing spectral regions. This photoconductive technique allowed us to confirm a recent suggestion of a new multicenter bond for hydrogen in ZnO [A. Janotti and C. G. Van de Walle, Nature Mater. 6, 44 (2007)]. The two LVMs of the hydrogen substituting oxygen in ZnO are identified at 742 and 792 cm(-1). The modes belong to a nondegenerated A(1) and a twofold degenerated E representations of the C(3v) point group. The tetrahedral coordination of the hydrogen atom is the result of a newly detected multicenter bond for defects in solids. PMID:22680732

Koch, S G; Lavrov, E V; Weber, J

2012-04-20

108

Application of Heisenberg's S matrix program to the angular scattering of the H + D2(v(i) = 0, j(i) = 0) ? HD(v(f) = 3, j(f) = 0) + D reaction: piecewise S matrix elements using linear, quadratic, step-function, and top-hat parametrizations.  

PubMed

A previous paper by Shan and Connor (Phys. Chem. Chem. Phys. 2011, 13, 8392) reported the surprising result that four simple parametrized S matrices can reproduce the forward-angle glory scattering of the H + D(2)(v(i)=0,j(i)=0) ? HD(v(f)=3,j(f)=0) + D reaction, whose differential cross section (DCS) had been computed in a state-of-the-art scattering calculation for a state-of-the-art potential energy surface. Here, v and j are vibrational and rotational quantum numbers, respectively, and the translational energy is 1.81 eV. This paper asks the question: Can we replace the analytic functions (of class C(?)) used by Shan-Connor with simpler mathematical functions and still reproduce the forward-angle glory scattering? We first construct S matrix elements (of class C(0)) using a quadratic phase and a piecewise-continuous pre-exponential factor consisting of three pieces. Two of the pieces are constants, with one taking the value N (a real normalization constant) at small values of the total angular momentum number, J; the other piece has the value 0 at large J. These two pieces are joined at intermediate values of J by either a straight line, giving rise to the linear parametrization (denoted param L), or a quadratic curve, which defines the quadratic parametrization (param Q). We find that both param L and param Q can reproduce the glory scattering for center-of-mass reactive scattering angles, ?(R) ? 30°. Second, we use a piecewise-discontinuous pre-exponential factor and a quadratic phase, giving rise to a step-function parametrization (param SF) and a top-hat parametrization (param TH). We find that both param SF and param TH can reproduce the forward-angle scattering, even though these class C(-1) parametrizations are usually considered too simplistic to be useful for calculations of DCSs. We find that an ultrasimplistic param THz, which is param TH with a phase of zero, can also reproduce the glory scattering at forward angles. The S matrix elements for param THz are real and consist of five nonzero equal values, given by S(J) = 0.02266, for the window, J = 21(1)25. Param THz is sufficiently simple that we can derive closed forms for the partial wave scattering amplitude, f(?(R)), and the near-side (N) and far-side (F) subamplitudes. We show that window representations of f(?(R)) provide important insights into the range of J values that contribute to the reaction dynamics. Other theoretical techniques used are NF theory for the analysis of DCSs and full and NF local angular momentum theory, in both cases including up to three resummations of f(?(R)) before making the NF decomposition. Finally, we investigate the accuracy of various semiclassical glory theories for the DCS of param L. By varying one phase parameter for param L, we show that the uniform semiclassical approximation is accurate from ?(R) = 0° to close to ?(R) = 180°. Our approach is an example of a "weak" form of Heisenberg's S matrix program, which does not use a potential energy surface(s); rather it focuses on the properties of the S matrix. Our method is easy to apply to DCSs from experimental measurements or from computer simulations. PMID:22876759

Shan, Xiao; Connor, J N L

2012-11-26

109

Why Is the Tetrahedral Bond Angle 109 Degrees? The Tetrahedron-in-a-Cube  

ERIC Educational Resources Information Center

The common question of why the tetrahedral angle is 109.471 degrees can be answered using a tetrahedron-in-a-cube, along with some Year 10 level mathematics. The tetrahedron-in-a-cube can also be used to demonstrate the non-polarity of tetrahedral molecules, the relationship between different types of lattice structures, and to demonstrate that…

Lim, Kieran F.

2012-01-01

110

Quadratic algebra contractions and 2nd order superintegrable systems  

E-print Network

Quadratic algebras are generalizations of Lie algebras; they include the symmetry algebras of 2nd order superintegrable systems in 2 dimensions as special cases. The superintegrable systems are exactly solvable physical systems in classical and quantum mechanics. For constant curvature spaces we show that the free quadratic algebras generated by the 1st and 2nd order elements in the enveloping algebras of their Euclidean and orthogonal symmetry algebras correspond one-to-one with the possible superintegrable systems with potential defined on these spaces. We describe a contraction theory for quadratic algebras and show that for constant curvature superintegrable systems, ordinary Lie algebra contractions induce contractions of the quadratic algebras of the superintegrable systems that correspond to geometrical pointwise limits of the physical systems. One consequence is that by contracting function space realizations of representations of the generic superintegrable quantum system on the 2-sphere (which give the structure equations for Racah/Wilson polynomials) to the other superintegrable systems one obtains the full Askey scheme of orthogonal hypergeometric polynomials.

Ernest G. Kalnins; Willard Miller Jr

2014-01-04

111

Comparison of linear strain triangular and tetrahedral elements with isoparametric elements in two- and three-dimensional finite element analyses  

E-print Network

yy E zz s xz E yz Bu Bx Bv By Bw Bz Bu Bv ? +- By Bx Bu Bw ? +- Bz Bx Bv Bw ? +- Bx By ul VI wl u n v n w n (2. 3) in which [B] = [B & B . . . B ] (2. 4) BN. 0 i 0 Bx BN. i 0 ? 0 By B i 0 0 i Bz BN. BN. I i 0... By Bx BN. BN. i 1. 0 Bz Bx (2. S) BN BN. i Bz By and N. is the interpolation function. Substituting [B] into Eq. (2. 2), i the stiffness matrix is readily obtained. For two-dimensional continua (such as plane stress, plane strain...

Ho, Philip Wai-Sun

2012-06-07

112

Optimal Quadratic Spline Collocation Methods for the Shallow Water Equations on the Sphere  

E-print Network

: numerical weather prediction; finite element; semi­Lagrangian semi­implicit; Rossby stability; staggered present a finite element­based method, which dis­ cretizes the shallow water equations (SWEs) in time, for solving the shallow water equations (SWEs) in spherical co­ ordinates. A quadratic spline collocation

Christara, Christina C.

113

A Streaming Language Implementation of the Discontinuous Galerkin Finite Element Method  

E-print Network

StreamFEM A Streaming Language Implementation of the Discontinuous Galerkin Finite Element Method(MHD)Linear(Euler)Linear(MHD) Quadratic(Euler) Quadratic(MHD)Cubic(Euler)Cubic(MHD) Element Type (Equation Type) Sustained GFLOPS LRF BW(MHD)Linear(Euler)Linear(MHD)Quadratic(Euler)Quadratic(MHD) Cubic(Euler) Cubic(MHD) Element Type (Equation Type) Sustained GFLOPS Ops / mem access A DG Finite

Dally, William J.

114

Geometrical and Graphical Solutions of Quadratic Equations.  

ERIC Educational Resources Information Center

Presented are several geometrical and graphical methods of solving quadratic equations. Discussed are Greek origins, Carlyle's method, von Staudt's method, fixed graph methods and imaginary solutions. (CW)

Hornsby, E. John, Jr.

1990-01-01

115

Quadratic Equations and Conics A quadratic equation in two variables is an equation that's equivalent to  

E-print Network

Quadratic Equations and Conics A quadratic equation in two variables is an equation that's equivalent to an equation of the form p(x, y) = 0 where p(x, y) is a quadratic polynomial. Examples. · 4x2 - 3xy - 2y2 + x - y + 6 = 0 is a quadratic equation, as are x2 - y2 = 0 and x2 + y2 = 0 and x2 - 1 = 0

Wortman, Kevin

116

Multi-Criterion Preliminary Design of a Tetrahedral Truss Platform  

NASA Technical Reports Server (NTRS)

An efficient method is presented for multi-criterion preliminary design and demonstrated for a tetrahedral truss platform. The present method requires minimal analysis effort and permits rapid estimation of optimized truss behavior for preliminary design. A 14-m-diameter, 3-ring truss platform represents a candidate reflector support structure for space-based science spacecraft. The truss members are divided into 9 groups by truss ring and position. Design variables are the cross-sectional area of all members in a group, and are either 1, 3 or 5 times the minimum member area. Non-structural mass represents the node and joint hardware used to assemble the truss structure. Taguchi methods are used to efficiently identify key points in the set of Pareto-optimal truss designs. Key points identified using Taguchi methods are the maximum frequency, minimum mass, and maximum frequency-to-mass ratio truss designs. Low-order polynomial curve fits through these points are used to approximate the behavior of the full set of Pareto-optimal designs. The resulting Pareto-optimal design curve is used to predict frequency and mass for optimized trusses. Performance improvements are plotted in frequency-mass (criterion) space and compared to results for uniform trusses. Application of constraints to frequency and mass and sensitivity to constraint variation are demonstrated.

Wu, K. Chauncey

1995-01-01

117

Electronic properties of disordered corner-sharing tetrahedral lattices  

NASA Astrophysics Data System (ADS)

We have examined the behavior of noninteracting electrons moving on a corner-sharing tetrahedral lattice into which we introduce a uniform (box) distribution, of width W , of random on-site energies. We have used both the relative localization length and the spectral rigidity to analyze the nature of the eigenstates and have determined both the mobility-edge trajectories as a function of W and the critical disorder Wc , beyond which all states are localized. We find (i) that the mobility-edge trajectories (energies Ec versus disorder W ) are qualitatively different from those found for a simple cubic lattice and (ii) that the spectral rigidity is scale invariant at Wc and thus provides a reliable method of estimating this quantity—we find Wc/t=14.5 . We then discuss our results in the context of the metal-to-insulator transition undergone by LiAlyTi2-yO4 in a quantum-site percolation model that also includes the above-mentioned Anderson disorder. We show that the effects of an inhomogeneous distribution of on-site energies produced by the Al impurity potentials are small compared to those produced by quantum-site percolation, at least in the determination of the doping concentration at which the metal-to-insulator transition is predicted to occur.

Fazileh, F.; Chen, X.; Gooding, R. J.; Tabunshchyk, K.

2006-01-01

118

Quadratic superconducting cosmic strings revisited  

NASA Astrophysics Data System (ADS)

It has been shown that a 5-dimensional general-relativity action extended by appropriate quadratic terms admits a singular superconducting cosmic string solution. We search for cosmic strings endowed with similar and extended physical properties by directly integrating the non-linear matrix field equations thus avoiding the perturbative approach by which we constructed the above-mentioned exact solution. The most general superconducting cosmic string, subject to some constraints, will be derived and shown to be mathematically unique up to linear coordinate transformations mixing its Killing vectors. The most general solution, however, is not globally equivalent to the old one due to the existence of Killing vectors with closed orbits. Contribution under the title of Exact 5-Dimensional Cosmic String Solutions to the International Conference on Dynamics and Thermodynamics of Black Holes and Naked Singularities II, Milan, Italy, May 2007.

Azreg-Aïnou, M.

2008-03-01

119

Single-photon quadratic optomechanics.  

PubMed

We present exact analytical solutions to study the coherent interaction between a single photon and the mechanical motion of a membrane in quadratic optomechanics. We consider single-photon emission and scattering when the photon is initially inside the cavity and in the fields outside the cavity, respectively. Using our solutions, we calculate the single-photon emission and scattering spectra, and find relations between the spectral features and the system's inherent parameters, such as: the optomechanical coupling strength, the mechanical frequency, and the cavity-field decay rate. In particular, we clarify the conditions for the phonon sidebands to be visible. We also study the photon-phonon entanglement for the long-time emission and scattering states. The linear entropy is employed to characterize this entanglement by treating it as a bipartite one between a single mode of phonons and a single photon. PMID:25200128

Liao, Jie-Qiao; Nori, Franco

2014-01-01

120

Quadratic Equations: From Factored to Standard Form  

NSDL National Science Digital Library

This activity leads students to understand the utility in the factored form of a quadratic equation. Students then express quadratic equations in standard form in the corresponding factored form. The activity is concluded with four critical-thinking questions. website: http://www.mathedpage.org/ copyright information: http://www.mathedpage.org/rights.html

2011-01-01

121

Interval regression analysis by quadratic programming approach  

Microsoft Academic Search

When we use linear programming in possibilistic regression analysis, some coefficients tend to become crisp because of the characteristic of linear programming. On the other hand, a quadratic programming approach gives more diverse spread coefficients than a linear programming one. Therefore, to overcome the crisp characteristic of linear programming, we propose interval regression analysis based on a quadratic programming approach.

Hideo Tanaka; Haekwan Lee

1998-01-01

122

On integral quadratic constraints for linear uncertainty  

Microsoft Academic Search

This paper studies some of the consequences of modelling linear uncertainty with integral quadratic constraints. For such models we give necessary and sufficient conditions for robust stability and introduce the notion of a quantitative stability indicator. To illustrate, we give new examples of uncertainties that admit integral quadratic constraint descriptions

Edgardo G. Eszter; C. V. Hollot

1995-01-01

123

Robust adaptive beamforming under quadratic constraint  

Microsoft Academic Search

In this paper, a adaptive weighted computation algorithm based on quadratic constraint for a robust array antenna is presented to improve the shortcoming of linearly constrained adaptive beamformer's sensitivity to the mismatch between the prescribed and actual direction of arrival (MPDOA). The quadratic constraint is added to the weighted least squared error between the desired and the actual beam patterns

Weihai Zhong; Qun Wan; Zhijiang Shang

2010-01-01

124

An Unexpected Influence on a Quadratic  

ERIC Educational Resources Information Center

Using technology to explore the coefficients of a quadratic equation can lead to an unexpected result. This article describes an investigation that involves sliders and dynamically linked representations. It guides students to notice the effect that the parameter "a" has on the graphical representation of a quadratic function in the form…

Davis, Jon D.

2013-01-01

125

Binary Quadratic Forms: A Historical View  

ERIC Educational Resources Information Center

We present an expository account of the development of the theory of binary quadratic forms. Beginning with the formulation and proof of the Two-Square Theorem, we show how the study of forms of the type x[squared] + ny[squared] led to the discovery of the Quadratic Reciprocity Law, and how this theorem, along with the concept of reduction relates…

Khosravani, Azar N.; Beintema, Mark B.

2006-01-01

126

Existence Theorems for Some Quadratic Integral Equations  

Microsoft Academic Search

Using the theory of measures of noncompactness, we prove a few existence theorems for some quadratic integral equations. The class of quadratic integral equations considered below contains as a special case numerous integral equations encountered in the theories of radiative transfer and neutron transport, and in the kinetic theory of gases. In particular, the well-known Chandrasekhar integral equation also belongs

Józef Bana?; Millenia Lecko; Wagdy Gomaa El-Sayed

1998-01-01

127

Regular black holes in quadratic gravity  

NASA Astrophysics Data System (ADS)

The first-order correction of the perturbative solution of the coupled equations of the quadratic gravity and nonlinear electrodynamics is constructed, with the zeroth-order solution coinciding with the ones given by Ayón-Beato and Garcí a and by Bronnikov. It is shown that a simple generalization of the Bronnikov's electromagnetic Lagrangian leads to the solution expressible in terms of the polylogarithm functions. The solution is parametrized by two integration constants and depends on two free parameters. By the boundary conditions the integration constants are related to the charge and total mass of the system as seen by a distant observer, whereas the free parameters are adjusted to make the resultant line element regular at the center. It is argued that various curvature invariants are also regular there that strongly suggests the regularity of the spacetime. Despite the complexity of the problem the obtained solution can be studied analytically. The location of the event horizon of the black hole, its asymptotics and temperature are calculated. Special emphasis is put on the extremal configuration.

Berej, Waldemar; Matyjasek, Jerzy; Tryniecki, Dariusz; Woronowicz, Mariusz

2006-05-01

128

Periodic Continued Fractions A quadratic irrational is an irrational number which is a root of a quadratic equation with integer  

E-print Network

is a root of a quadratic equation with integer coefficients. · Quadratic irrationals can be expressed. Definition. A quadratic irrational is an irrational number which is a root of a quadratic equation ax2 + bx)2 = q, r2 x2 - 2rpx + (p2 - q) = 0. This is a quadratic equation with integer coefficients, and r2

Ikenaga, Bruce

129

Semiclassical origin of anomalous shell effect for tetrahedral deformation in radial power-law potential model  

E-print Network

Shell structures in single-particle energy spectra are investigated against regular tetrahedral type deformation using radial power-law potential model. Employing a natural way of shape parametrization which interpolates sphere and regular tetrahedron, we find prominent shell effects at rather large tetrahedral deformations, which bring about shell energies much larger than the cases of spherical and quadrupole type shapes. We discuss the semiclassical origin of these anomalous shell structures using periodic orbit theory.

Ken-ichiro Arita; Yasunori Mukumoto

2014-05-09

130

Nonsmooth Methods for Control Design with Integral Quadratic Constraints  

E-print Network

Nonsmooth Methods for Control Design with Integral Quadratic Constraints Pierre Apkarian to compute local solutions to synthesis problems subject to integral quadratic constraints (IQCs). We use, parametric uncertainty, integral quadratic constraint (IQC), structured controllers, NP-hard problems

Prot, Olivier

131

Robust Synchronisation of Heterogeneous Networks via Integral Quadratic Constraints  

E-print Network

Robust Synchronisation of Heterogeneous Networks via Integral Quadratic Constraints Sei Zhen Khong-- Synchronisation, heterogeneous networks, ro- bustness, integral quadratic constraints I. INTRODUCTION quadratic constraints is used to capture the structural uncertainties of the perturbations, and to give

Como, Giacomo

132

Seven Wonders of the Ancient and Modern Quadratic World.  

ERIC Educational Resources Information Center

Presents four methods for solving a quadratic equation using graphing calculator technology: (1) graphing with the CALC feature; (2) quadratic formula program; (3) table; and (4) solver. Includes a worksheet for a lab activity on factoring quadratic equations. (KHR)

Taylor, Sharon E.; Mittag, Kathleen Cage

2001-01-01

133

Tetrahedrality and structural order for hydrophobic interactions in a coarse-grained water model  

NASA Astrophysics Data System (ADS)

The hydrophobic interaction manifests two separate regimes in terms of size: Small nonpolar bodies exhibit a weak oscillatory force (versus distance) while large nonpolar surfaces exhibit a strong monotonic one. This crossover in hydrophobic behavior is typically explained in terms of water's tetrahedral structure: Its tetrahedrality is enhanced near small solutes and diminished near large planar ones. Here, we demonstrate that water's tetrahedral correlations signal this switch even in a highly simplified, isotropic, "core-softened" water model. For this task, we introduce measures of tetrahedrality based on the angular distribution of water's nearest neighbors. On a quantitative basis, the coarse-grained model of course is only approximate: (1) While greater than simple Lennard-Jones liquids, its bulk tetrahedrality remains lower than that of fully atomic models; and (2) the decay length of the large-scale hydrophobic interaction is less than has been found in experiments. Even so, the qualitative behavior of the model is surprisingly rich and exhibits numerous waterlike hydrophobic behaviors, despite its simplicity. We offer several arguments for the manner in which it should be able to (at least partially) reproduce tetrahedral correlations underlying these effects.

Chaimovich, Aviel; Shell, M. Scott

2014-02-01

134

An interface capturing method with a continuous function: The THINC method on unstructured triangular and tetrahedral meshes  

NASA Astrophysics Data System (ADS)

A novel interface-capturing method is proposed to compute moving interfaces on unstructured grids with triangular (2D) and tetrahedral (3D) elements. Different from the conventional VOF (volume of fluid) method which involves geometric reconstructions of the interface, the present method is based on the algebraic reconstruction approach originally developed in the THINC (tangent of hyperbola interface capturing) scheme by Xiao et al. (2005) [17]. A continuous multidimensional hyperbolic tangent function is employed for retrieving the jump-like distribution of the indicator function, which avoids the explicit geometric representation of the interface and thus substantially reduces the algorithmic complexity in unstructured grids. Numerical diffusion and smearing are effectively eliminated, and the compact thickness of the jump transition layer in the volume fraction is retained throughout the computation even for largely deformed interface. The solution quality of the present scheme is comparable to the VOF method with PLIC (piecewise linear interface calculation) algorithm.

Ii, Satoshi; Xie, Bin; Xiao, Feng

2014-02-01

135

A quadratically convergent VBSCF method  

NASA Astrophysics Data System (ADS)

A quadratically convergent valence bond self-consistent field method is described where the simultaneous optimisation of orbitals and the coefficients of the configurations (VB structures) is based on a Newton-Raphson scheme. The applicability of the method is demonstrated in actual calculations. The convergence and efficiency are compared with the Super-CI method. A necessary condition to achieve convergence in the Newton-Raphson method is that the Hessian is positive definite. When this is not the case, a combination of the Super-CI and Newton-Raphson methods is shown to be an optimal choice instead of shifting the eigenvalues of the Hessian to make it positive definite. In the combined method, the first few iterations are performed with the Super-CI method and then the Newton-Raphson scheme is switched on based on an internal indicator. This approach is found computationally a more economical choice than using either the Newton-Raphson or Super-CI method alone to perform a full optimisation of the nonorthogonal orbitals.

Rashid, Zahid; van Lenthe, Joop H.

2013-02-01

136

A quadratically convergent VBSCF method.  

PubMed

A quadratically convergent valence bond self-consistent field method is described where the simultaneous optimisation of orbitals and the coefficients of the configurations (VB structures) is based on a Newton-Raphson scheme. The applicability of the method is demonstrated in actual calculations. The convergence and efficiency are compared with the Super-CI method. A necessary condition to achieve convergence in the Newton-Raphson method is that the Hessian is positive definite. When this is not the case, a combination of the Super-CI and Newton-Raphson methods is shown to be an optimal choice instead of shifting the eigenvalues of the Hessian to make it positive definite. In the combined method, the first few iterations are performed with the Super-CI method and then the Newton-Raphson scheme is switched on based on an internal indicator. This approach is found computationally a more economical choice than using either the Newton-Raphson or Super-CI method alone to perform a full optimisation of the nonorthogonal orbitals. PMID:23406096

Rashid, Zahid; van Lenthe, Joop H

2013-02-01

137

HYSTERESIS ANALYSIS BASED ON INTEGRAL QUADRATIC CONSTRAINTS  

Microsoft Academic Search

It is shown how the framework of Integral Quadratic Constraints can be applied to analyze systems with hysteresis, in spite of the fact that hysteresis operators are unbounded and that not all system variable can be expected to approach zero.

A. Rantzer; A. Megretski

138

OVERPARTITIONS AND REAL QUADRATIC FIELDS JEREMY LOVEJOY  

E-print Network

OVERPARTITIONS AND REAL QUADRATIC FIELDS JEREMY LOVEJOY Abstract. It is shown that counting certain in Europe". 1 #12;2 JEREMY LOVEJOY families of overpartition theorems which are analogues of some classical

Fondements et Applications, Université Paris 7

139

Quadratic Equations...Origins, Development and Use.  

ERIC Educational Resources Information Center

There may be a social and an intellectual aspect to the process of development of mathematical knowledge. This paper describes quadratic equations as intellectual mathematics and as colloquial mathematics. Provides some historical data. (YP)

McQualter, J. W.

1988-01-01

140

Schur Stability Regions for Complex Quadratic Polynomials  

ERIC Educational Resources Information Center

Given a quadratic polynomial with complex coefficients, necessary and sufficient conditions are found in terms of the coefficients such that all its roots have absolute values less than 1. (Contains 3 figures.)

Cheng, Sui Sun; Huang, Shao Yuan

2010-01-01

141

Robust analysis, sectors, and quadratic functionals  

Microsoft Academic Search

Working from a topological separation framework it is shown that integral quadratic constraints useful for robust analysis must have the form ?-??z*S*diag{I,-I}Szd?, for some invertible (possibly frequency dependent) matrix S. It is further shown that many of the integral quadratic constraints used in robustness analysis may be put into a positivity form with a fixed or known generalized sector transform

Keat-Choon Goh; M. G. Safonov

1995-01-01

142

Integral Quadratic Separators for performance analysis  

Microsoft Academic Search

Well-posedness of feedback connected systems is considered in topological separation framework. The case when a known linear descriptor transformation is connected to an uncertain operator is considered. Well-posedness is demonstrated to hold provided an Integral Quadratic Separator satisfying both some Linear Matrix Inequalities and an Integral Quadratic Constraint. The main result is applied to three input-output performance criteria. Keywords: Robustness,

Dimitri Peaucelle; Lucie Baudouin; Fred ´ eric Gouaisbaut

143

PIECEWISE QUADRATIC APPROXIMATIONS IN CONVEX ...  

E-print Network

the “mutual linearization error” computed in xj for the i-th element of the bundle is ..... line of proof works if the number of inner iterations is finite, by just waiting long ..... co-ordinate the increase of the stabilization parameters and the decrease of ?

2010-12-11

144

The Factorability of Quadratics: Motivation for More Techniques  

ERIC Educational Resources Information Center

Typically, secondary and college algebra students attempt to utilize either completing the square or the quadratic formula as techniques to solve a quadratic equation only after frustration with factoring has arisen. While both completing the square and the quadratic formula are techniques which can determine solutions for all quadratic equations,…

Bosse, Michael J.; Nandakumar, N. R.

2005-01-01

145

Note on an Additive Characterization of Quadratic Residues Modulo p  

E-print Network

if the quadratic equation x2 = a mod p has a solution. If it has no solution then a is called a quadratic nonNote on an Additive Characterization of Quadratic Residues Modulo p Chris Monico, Michele Elia, . . . , p - 1} of positive residues modulo an odd prime p is the partition into quadratic residues

Monico, Chris

146

LINEAR-QUADRATIC CONTROL OF BACKWARD STOCHASTIC DIFFERENTIAL EQUATIONS  

E-print Network

LINEAR-QUADRATIC CONTROL OF BACKWARD STOCHASTIC DIFFERENTIAL EQUATIONS ANDREW E. B. LIM AND XUN YU differential equations (BSDEs) with a quadratic cost criteria, or backward linear-quadratic (BLQ) control differential equations (BSDEs), linear-quadratic (LQ) optimal control, Riccati equations, completion of squares

Lim, Andrew

147

Decentralized state feedback guaranteed cost control of uncertain systems with uncertainty described by integral quadratic constraints  

Microsoft Academic Search

This paper presents a procedure for constructing decentralized state feedback guaranteed cost controllers for a class of uncertain systems in which the uncertainty is described by integral quadratic constraints. The proposed procedure involves solving an algebraic Riccati equation of the Hinfin control type which is dependent on a number of scaling parameters. By treating the off-diagonal elements of the full

Ian R. Petersen

2006-01-01

148

Divisibility of class numbers of imaginary quadratic function fields by a fixed odd number  

Microsoft Academic Search

In this paper we find a new lower bound on the number of imaginary quadratic extensions of the function field $\\\\mathbb{F}_{q}(x)$ whose class groups have elements of a fixed odd order. More precisely, for $q$, a power of an odd prime, and $g$ a fixed odd positive integer $\\\\ge 3$, we show that for every $\\\\epsilon >0$, there are $\\\\gg

Pradipto Banerjee; Srinivas Kotyada

2011-01-01

149

Self-equilibrium and stability of regular truncated tetrahedral tensegrity structures  

NASA Astrophysics Data System (ADS)

This paper presents analytical conditions of self-equilibrium and super-stability for the regular truncated tetrahedral tensegrity structures, nodes of which have one-to-one correspondence to the tetrahedral group. These conditions are presented in terms of force densities, by investigating the block-diagonalized force density matrix. The block-diagonalized force density matrix, with independent sub-matrices lying on its leading diagonal, is derived by making use of the tetrahedral symmetry via group representation theory. The condition for self-equilibrium is found by enforcing the force density matrix to have the necessary number of nullities, which is four for three-dimensional structures. The condition for super-stability is further presented by guaranteeing positive semi-definiteness of the force density matrix.

Zhang, J. Y.; Ohsaki, M.

2012-10-01

150

Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)  

NASA Astrophysics Data System (ADS)

Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

Bertram, F.; Deiter, C.; Schemme, T.; Jentsch, S.; Wollschläger, J.

2013-05-01

151

Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)  

SciTech Connect

Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

Bertram, F.; Deiter, C. [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany)] [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany); Schemme, T.; Jentsch, S.; Wollschlaeger, J. [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)] [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)

2013-05-14

152

Tetrahedral-mesh-based computational human phantom for fast Monte Carlo dose calculations.  

PubMed

Although polygonal-surface computational human phantoms can address several critical limitations of conventional voxel phantoms, their Monte Carlo simulation speeds are much slower than those of voxel phantoms. In this study, we sought to overcome this problem by developing a new type of computational human phantom, a tetrahedral mesh phantom, by converting a polygonal surface phantom to a tetrahedral mesh geometry. The constructed phantom was implemented in the Geant4 Monte Carlo code to calculate organ doses as well as to measure computation speed, the values were then compared with those for the original polygonal surface phantom. It was found that using the tetrahedral mesh phantom significantly improved the computation speed by factors of between 150 and 832 considering all of the particles and simulated energies other than the low-energy neutrons (0.01 and 1 MeV), for which the improvement was less significant (17.2 and 8.8 times, respectively). PMID:24862061

Yeom, Yeon Soo; Jeong, Jong Hwi; Han, Min Cheol; Kim, Chan Hyeong

2014-06-21

153

Robust linear quadratic designs with respect to parameter uncertainty  

NASA Technical Reports Server (NTRS)

The authors derive a linear quadratic regulator (LQR) which is robust to parametric uncertainty by using the overbounding method of I. R. Petersen and C. V. Hollot (1986). The resulting controller is determined from the solution of a single modified Riccati equation. It is shown that, when applied to a structural system, the controller gains add robustness by minimizing the potential energy of uncertain stiffness elements, and minimizing the rate of dissipation of energy through uncertain damping elements. A worst-case disturbance in the direction of the uncertainty is also considered. It is proved that performance robustness has been increased with the robust LQR when compared to a mismatched LQR design where the controller is designed on the nominal system, but applied to the actual uncertain system.

Douglas, Joel; Athans, Michael

1992-01-01

154

Interatomic potential for the structure and energetics of tetrahedrally coordinated silica polymorphs  

SciTech Connect

We introduce a many-body fixed-charge potential optimized for tetrahedral silica. The potential is used to investigate the crystal structures and energetics of six tetrahedrally coordinated silica polymorphs ({alpha}- and {beta}-quartz, {alpha}- and {beta}-cristobalite, {beta}-tridymite, and coesite). The structural parameters of the different phases are found to be well-reproduced. Most importantly, the ground state of the silica polymorphs is reproduced correctly. The results are compared with previous electronic structure calculations and with the results of other empirical potentials.

Yu Jianguo; Phillpot, Simon R.; Sinnott, Susan B. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611-6400 (United States)

2007-06-15

155

7 Quadratic forms in n variables In order to understand quadratic forms in n variables over Z, one is let to study quadratic forms  

E-print Network

7 Quadratic forms in n variables In order to understand quadratic forms in n variables over Z, one is let to study quadratic forms over various rings and fields such as Q, Qp, R and Zp. This is consistent equation in Z, it is useful study the equation over other rings. Definition 7.0.8. Let R be a ring

Martin, Kimball

156

Sharp Quadratic Majorization in One Dimension  

PubMed Central

Majorization methods solve minimization problems by replacing a complicated problem by a sequence of simpler problems. Solving the sequence of simple optimization problems guarantees convergence to a solution of the complicated original problem. Convergence is guaranteed by requiring that the approximating functions majorize the original function at the current solution. The leading examples of majorization are the EM algorithm and the SMACOF algorithm used in Multidimensional Scaling. The simplest possible majorizing subproblems are quadratic, because minimizing a quadratic is easy to do. In this paper quadratic majorizations for real-valued functions of a real variable are analyzed, and the concept of sharp majorization is introduced and studied. Applications to logit, probit, and robust loss functions are discussed. PMID:21738282

de Leeuw, Jan; Lange, Kenneth

2009-01-01

157

Quadratic Integrate-and-Fire Model  

NSDL National Science Digital Library

The Quadratic Integrate-and-Fire model is a slight modification of the integrate-and-fire model. This slight modification has some drastic changes on the dynamics, although the equation is still solvable analytically in order to determine the period of a continuously-spiking neuron. Because of its simplicity, the Quadratic Integrate-and-Fire model and its variations are favorites for mathematical treatments of neural networks. The Quadratic Integrate-and-Fire model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Thomson, Colin F.

2012-11-06

158

Guises and Disguises of Quadratic Divergences  

E-print Network

In this contribution, we present a new perspective on the control of quadratic divergences in quantum field theory, in general, and in the Higgs naturalness problem, in particular. Our discussion is essentially based on an approach where UV divergences are parameterized, after being reduced to basic divergent integrals (BDI) in one internal momentum, as functions of a cutoff and a renormalization group scale $\\lambda$. We illustrate our proposal with well-known examples, such as the gluon vacuum self energy of QCD and the Higgs decay in two photons within this approach. We also discuss frameworks in effective low-energy QCD models, where quadratic divergences are indeed fundamental.

A. L. Cherchiglia; A. R. Vieira; Brigitte Hiller; A. P. Baêta Scarpelli; Marcos Sampaio

2014-10-04

159

Guises and disguises of quadratic divergences  

NASA Astrophysics Data System (ADS)

In this contribution, we present a new perspective on the control of quadratic divergences in quantum field theory, in general, and in the Higgs naturalness problem, in particular. Our discussion is essentially based on an approach where UV divergences are parameterized, after being reduced to basic divergent integrals (BDI) in one internal momentum, as functions of a cutoff and a renormalization group scale ?. We illustrate our proposal with well-known examples, such as the gluon vacuum self energy of QCD and the Higgs decay in two photons within this approach. We also discuss frameworks in effective low-energy QCD models, where quadratic divergences are indeed fundamental.

Cherchiglia, A. L.; Vieira, A. R.; Hiller, Brigitte; Baêta Scarpelli, A. P.; Sampaio, Marcos

2014-12-01

160

Optical power flow with sequential quadratic programming  

NASA Astrophysics Data System (ADS)

Newton's method as an approach to solve the optimal power flow problem in electric power plants is presented. A general formulation of the optimal flow problem is given. Newton's method is applied to solve the nonlinear Kuhn-Tucker conditions by iteration. Every Newton step is calculated by solving a quadratic programming problem. Variations of the sequential quadratic programming method are presented. Byproducts of the optimization, namely the Lagrange multipliers and their interpretation as marginal costs and shadow prices, are outlined. The most important computer programs are enclosed.

Vanamerongen, R. A. M.

1985-01-01

161

Quadratic Algebra Approach to an Exactly Solvable Position-Dependent Mass Schrödinger Equation in Two Dimensions  

E-print Network

An exactly solvable position-dependent mass Schr\\"odinger equation in two dimensions, depicting a particle moving in a semi-infinite layer, is re-examined in the light of recent theories describing superintegrable two-dimensional systems with integrals of motion that are quadratic functions of the momenta. To get the energy spectrum a quadratic algebra approach is used together with a realization in terms of deformed parafermionic oscillator operators. In this process, the importance of supplementing algebraic considerations with a proper treatment of boundary conditions for selecting physical wavefunctions is stressed. Some new results for matrix elements are derived. This example emphasizes the interest of a quadratic algebra approach to position-dependent mass Schr\\"odinger equations.

Christiane Quesne

2007-05-17

162

Quadratic RK shooting solution for a environmental parameter prediction boundary value problem  

NASA Astrophysics Data System (ADS)

Using tools of Information Geometry, the minimum distance between two elements of a statistical manifold is defined by the corresponding geodesic, e.g. the minimum length curve that connects them. Such a curve, where the probability distribution functions in the case of our meteorological data are two parameter Weibull distributions, satisfies a 2nd order Boundary Value (BV) system. We study the numerical treatment of the resulting special quadratic form system using Shooting method. We compare the solutions of the problem when we employ a classical Singly Diagonally Implicit Runge Kutta (SDIRK) 4(3) pair of methods and a quadratic SDIRK 5(3) pair . Both pairs have the same computational costs whereas the second one attains higher order as it is specially constructed for quadratic problems.

Famelis, Ioannis Th.; Tsitouras, Ch.

2014-10-01

163

Tetrahedral Fe2+ in Nb-Doped Yttrium Iron Garnet Detected by the Angular Variation of Induced Anisotropy  

Microsoft Academic Search

The presence of Fe2+ ions in tetrahedral sites of iron garnets has been detected for the first time. The particular material in which this occurred was flux-grown Nb-doped yttrium iron garnet. Proof of occupancy of tetrahedral sites by Fe2+ ions was obtained by Tucciarone's recently developed method of the angular variation of induced anisotropy.

B. Antonini; S. Geller; A. Paoletti; P. Paroli; A. Tucciarone

1978-01-01

164

Evidence for subpicosecond thermal spikes in the formation of tetrahedral amorphous carbon N. A. Marks  

E-print Network

material having useful semiconducting properties and a high thermal conductivity. The latter property to the liquid quench method. In this paper the lifetime of the thermal spike in ta-C is estimated using threeEvidence for subpicosecond thermal spikes in the formation of tetrahedral amorphous carbon N. A

Adler, Joan

165

Insights into Substrate Specificity and Metal Activation of Mammalian Tetrahedral Aspartyl Aminopeptidase*S  

E-print Network

Insights into Substrate Specificity and Metal Activation of Mammalian Tetrahedral Aspartyl of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965 and the § Center for Proteomics and Bioinformatics, Center for Synchrotron Biosciences, School of Medicine, Case Western Reserve University

Palczewski, Krzysztof

166

Multi-Dimensional, Inviscid Flux Reconstruction for Simulation of Hypersonic Heating on Tetrahedral Grids  

NASA Technical Reports Server (NTRS)

The quality of simulated hypersonic stagnation region heating on tetrahedral meshes is investigated by using a three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. Two test problems are investigated: hypersonic flow over a three-dimensional cylinder with special attention to the uniformity of the solution in the spanwise direction and hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problem provides a sensitive test for algorithmic effects on heating. This investigation is believed to be unique in its focus on three-dimensional, rotated upwind schemes for the simulation of hypersonic heating on tetrahedral grids. This study attempts to fill the void left by the inability of conventional (quasi-one-dimensional) approaches to accurately simulate heating in a tetrahedral grid system. Results show significant improvement in spanwise uniformity of heating with some penalty of ringing at the captured shock. Issues with accuracy near the peak shear location are identified and require further study.

Gnoffo, Peter A.

2009-01-01

167

DOI: 10.1002/adem.200800090 Topological Analysis of Foams and Tetrahedral Structures**  

E-print Network

DOI: 10.1002/adem.200800090 Topological Analysis of Foams and Tetrahedral Structures** By Gad Frenkel,* Raphael Blumenfeld, Peter R. King and Martin J. Blunt The analysis of morphology of porous of pore-scale networks. The Minkowski functionals are part of the data that describes statistically

Blumenfeld, Rafi

168

Tetrahedral calcite crystals facilitate self-assembly at the air-water interface S. M. Hashmi  

E-print Network

Tetrahedral calcite crystals facilitate self-assembly at the air-water interface S. M. Hashmi; published 26 October 2005 Calcite crystals often nucleate and grow in solutions of calcium carbonate out of aqueous solution is known to form fractal aggregates of micron-sized rhombohedral calcite

169

Aging of Tetrahedral Structure in a Lennard-Jones Glass1 Gianguido C. CIANCI2  

E-print Network

Aging of Tetrahedral Structure in a Lennard-Jones Glass1 Gianguido C. CIANCI2 and Eric R. WEEKS3,4 Summary We study the aging of a glassy Lennard-Jones binary mixture with molecular dy- namics simulations. We follow the evolution of the packing as a function of the system's age tw, the time passed since

Weeks, Eric R.

170

TetSplat: Real-time Rendering and Volume Clipping of Large Unstructured Tetrahedral Meshes  

E-print Network

and explo- ration of large unstructured tetrahedral meshes. These massive 3D meshes are used in mission to partition it into non-convex boundaries and internal fragments that are subsequently encoded into compressed by QSplat, employs a simple but highly efficient splatting technique that guarantees interactive frame

171

Tetrahedral symmetry in Zr nuclei: calculations of low-energy excitations with Gogny interaction  

NASA Astrophysics Data System (ADS)

We report on the results of the calculations of the low energy excitation patterns for three Zirconium isotopes, viz 80Zr40, 96Zr56 and 110Zr70, reported by other authors to be doubly-magic tetrahedral nuclei (with tetrahedral magic numbers Z = 40 and N = 40, 56 and 70). We employ the realistic Gogny effective interactions using three variants of their parametrization and the particle-number, parity and the angular-momentum projection techniques. We confirm quantitatively that the resulting spectra directly follow the pattern expected from the group theory considerations for the tetrahedral symmetric quantum objects. We also find out that, for all the nuclei studied, the correlation energy obtained after the angular momentum projection is very large for the tetrahedral deformation as well as other octupole deformations. The lowering of the energies of the resulting configurations is considerable, i.e. by about 10 MeV or even more, once again confirming the significance of the angular-momentum projections techniques in the mean-field nuclear structure calculations.

Tagami, Shingo; Shimizu, Yoshifumi R.; Dudek, Jerzy

2015-01-01

172

3D Harmonic Mapping and Tetrahedral Meshing of Brain Imaging Data  

E-print Network

3D Harmonic Mapping and Tetrahedral Meshing of Brain Imaging Data Yalin Wang1 , Xianfeng Gu2 , Paul algorithm finds a harmonic map from a 3-manifold to a 3D solid sphere and the second is a novel sphere of magnetic resonance images (MRI). A heat flow method is used to solve the volumetric harmonic mapping

Thompson, Paul

173

Compressive-stress-induced formation of thin-film tetrahedral amorphous carbon  

Microsoft Academic Search

Thin tetrahedrally coordinated amorphous carbon (ta-C) films have been grown using a filtered vacuum arc. ta-C is a new allotrope of carbon whose existence was previously thought to be unlikely. A model is proposed which accounts for the formation and structure of these films on the basis of the compressive stress generated by the shallow implantation of carbon ions. An

D. R. McKenzie; D. Muller; B. A. Pailthorpe

1991-01-01

174

Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry  

ERIC Educational Resources Information Center

This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, "Journal of Chemical…

Lewthwaite, Brian; Wiebe, Rick

2011-01-01

175

Formation of pyramid elements for hexahedra to tetrahedra transitions  

SciTech Connect

New algorithms are proposed for the modification of a mixed hexahedra-tetrahedra element mesh to maintain compatibility by the insertion of pyramid elements. Several methods for generation of the pyramids are presented involving local tetrahedral transformations and/or node insertion near the hex/tet interface. Local smoothing and topological operations improve the quality of the transition region. Results show superior performance of the resulting elements in a commercial finite element code over non-conforming interface conditions.

OWEN,STEVEN J.; SAIGAL,SUNIL

2000-02-24

176

A Streaming Language Implementation of the Discontinuous Galerkin Finite Element Method  

E-print Network

StreamFEM A Streaming Language Implementation of the Discontinuous Galerkin Finite Element Method(MHD)Linear(Euler)Linear(MHD)Quadratic(Euler)Quadratic(MHD) Cubic(Euler) Cubic(MHD) Element Type (Equation Type) Sustained GFLOPS Ops / mem access A DG Finite Element Method for Conservation Laws ·Scalar Advection (1 PDE) ·Euler Equations (4 PDEs

Dally, William J.

177

Competing nonlinearities in quadratic nonlinear waveguide arrays  

E-print Network

Competing nonlinearities in quadratic nonlinear waveguide arrays Frank Setzpfandt,1, * Dragomir N demonstrate experimentally the existence of competing focusing and defocusing nonlinearities in a double- tively. If an optical system, however, exhibits so- called competing nonlinearities a laser beam can ex

178

Quadratic engel curves and consumer demand  

Microsoft Academic Search

This paper presents a model of consumer demand that is consistent with the observed expenditure patterns of individual consumers in a long time series of expenditure surveys and is also able to provide a detailed welfare analysis of shifts in relative prices. A nonparametric analysis of consumer expenditure patterns suggests that Engel curves require quadratic terms in the logarithm of

James Banks; Richard Blundell; Arthur Lewbel

1997-01-01

179

Decision making with fuzzy quadratic programming  

Microsoft Academic Search

Decision making in civil engineering systems necessarily involves imprecise data. Fuzzy linear programming (FLP) has been used to deal with imprecision in parameter definitions. In this paper, it is argued that present methods of FLP can be improved upon by using a new method of fuzzy quadratic programming (FQP) which enables the modelling of independent fuzzy parameters. Several numerical examples

W. Cui; D. I. Blockley

1990-01-01

180

Integral quadratic constraint approach vs. multiplier approach  

Microsoft Academic Search

Integral quadratic constraints (IQC) arise in many optimal and\\/or robust control problems. The IQC approach can be viewed as a generalization of the classical multiplier approach in the absolute stability theory. In this paper, we study the relationship between the two approaches for robust stability analysis. The key result shows that for many applications, the existence of an IQC is

Minyue Fu; Soura Dasgupta; Yeng Chai Sohz

2002-01-01

181

Mapping integral quadratic constraints into parameter space  

Microsoft Academic Search

This paper presents the mapping equations for integral quadratic constraints (IQCs). In particular it is shown that IQCs with bounded rational multipliers can be mapped into parameter space. Using IQCs not only provides a uniform framework to map specifications into parameter space, but provides a unified approach to parameter space based robustness analysis and synthesis with respect to nonlinearities, time

Michael Muhler; Jiirgen Ackermann

2004-01-01

182

Solitons as harmonic oscillators with quadratic constraints  

Microsoft Academic Search

Integrable systems represented by partial differential equations, in particular those having soliton solutions, are different aspects of one and the same system: harmonic oscillators with quadratic constraints. This result is illustrated here by means of one example, the non-linear Schrödinger equation, whose soliton is described by four oscillators with two constraints.

Fernando Lund

1981-01-01

183

Integral quadratic constraint approach vs. multiplier approach  

Microsoft Academic Search

Integral quadratic constraints (IQC) arise in many optimal and\\/or robust control problems. The IQC approach can be viewed as a generalization of the classical multiplier approach in the absolute stability theory. In this paper, we study the relationship between the two approaches for robust stability analysis. Using a slightly modified multiplier approach, we show that the existence of an IQC

Minyue Fu; Soura Dasgupta; Yeng Chai Soh

2005-01-01

184

System analysis via integral quadratic constraints  

Microsoft Academic Search

This paper introduces a unified approach to robustness analysis with respect to nonlinearities, time variations, and uncertain parameters. From an original idea by Yakubovich (1967), the approach has been developed under a combination of influences from the Western and Russian traditions of control theory. It is shown how a complex system can be described, using integral quadratic constraints (IQC) for

Alexandre Megretski; Anders Rantzer

1997-01-01

185

Distributed Control with Integral Quadratic Constraints  

Microsoft Academic Search

In this paper, stability conditions for distributed system under general integral quadratic constraints (IQC) for interconnections are derived. These results take the form of coupled linear matrix inequalities (LMIs), and the multipliers are shaped by the underlying IQCs to model these interconnections. It is further shown that these results can be exploited for distributed controllers synthesis similar to the gain-scheduling

Hui Fang; Panos J. Antsaklis

186

System analysis via integral quadratic constraints  

Microsoft Academic Search

It is demonstrated how a number of widely used tools for stability analysis can be conveniently unified and generalized using integral quadratic constraints (IQCs). The approach has emerged under a combination of influences from the western and Russian traditions of control theory. An IQC based stability theorem is presented, which covers classical small gain conditions with anti-causal multipliers, but gains

A. Rantzer; A. Megretski

1994-01-01

187

Representations of integers by ternary quadratic forms  

Microsoft Academic Search

We investigate the representation of integers by quadratic forms whose theta series lie in Kohnen's plus space M+ 3\\/2(4p), where p is a prime. Conditional upon certain GRH hypotheses, we show eectively that every suciently large discriminant with bounded divisibility by p is represented by the form, up to local conditions. We give an algorithm for explicitly calculating the bounds.

BEN KANE

2010-01-01

188

Block Ciphers and Systems of Quadratic Equations  

Microsoft Academic Search

In this paper we compare systems of multivariate poly- nomials, which completely define the block ciphers Khazad, Misty1, Kasumi, Camellia, Rijndael and Serpent in the view of a potential danger of an algebraic re-linearization attack. Keywords: Block ciphers, multivariate quadratic equations, lineariza- tion, Khazad, Misty, Camellia, Rijndael, Serpent.

Alex Biryukov; Christophe De Cannière

2003-01-01

189

Solving Underdefined Systems of Multivariate Quadratic Equations  

Microsoft Academic Search

The security of several recent digital signature schemes is based on the difficulty of solving large systems of quadratic multivariate polynomial equations over a finite field F. This problem, sometimes called MQ, is known to be NP-hard. When the number m of equations is equal to the number n of variables, and if n< 15, Grobner base algorithms have been

Nicolas Courtois; Louis Goubin; Willi Meier; Jean-daniel Tacier

2002-01-01

190

On quadratic integral equation of fractional orders  

Microsoft Academic Search

We present an existence theorem for a nonlinear quadratic integral equations of fractional orders, arising in the queuing theory and biology, in the Banach space of real functions defined and continuous on a bounded and closed interval. The concept of measure of noncompactness and a fixed point theorem due to Darbo are the main tool in carrying out our proof.

Mohamed Abdalla Darwish

2005-01-01

191

Quadratic equations and monodromy evolving deformations  

E-print Network

We give a basic theory on monodromy evolving deformations. proposed by Chakravarty and Ablowitz in 1996. We show that Halphen's second quadratic system can be described by monodromy evolving deformations. Our result is a generalization of the work on the DH-V system by Chakravarty and Ablowitz.

Yousuke Ohyama

2007-09-28

192

A Practical Approach to Quadratic Equations.  

ERIC Educational Resources Information Center

The usual methods for solving quadratic equations are noted to require either the use of numerical formula or curve plotting on graph paper. The method described here enables pupils to solve equations using only a 45 degree setsquare, graph paper, and a pencil for those which have both real roots and real coefficients. (Author/MP)

Light, Peter

1983-01-01

193

Theory of the Quadratic Zeeman Effect  

Microsoft Academic Search

The experiments of Jenkins and Segrè, reported in the accompanying paper, are considered theoretically. The quadratic Zeeman effect observed in absorption to large orbits in strong magnetic fields is due to the diamagnetic term in the Hamiltonian, which is proportional to the square of the vector potential and hence to the square of the magnetic field. For the alkalis, the

L. I. Schiff; H. Snyder

1939-01-01

194

Integration of the Quadratic Function and Generalization  

ERIC Educational Resources Information Center

We will first recall useful formulas in integration that simplify the calculation of certain definite integrals with the quadratic function. A main formula relies only on the coefficients of the function. We will then explore a geometric proof of one of these formulas. Finally, we will extend the formulas to more general cases. (Contains 3…

Mitsuma, Kunio

2011-01-01

195

An arbitrarily high order transport method of the characteristic type for unstructured tetrahedral grids  

NASA Astrophysics Data System (ADS)

An extension of the Arbitrarily High-Order Transport Method of the Characteristic type to three-dimensional unstructured tetrahedral grids is proposed in this work which resolves the difficulties encountered in the earlier formulation of the method. A thorough literature review is presented of the development of characteristic methods as a specific class of spatial discretization to the discrete-ordinates approximation of the stationary transport equation. A classical derivation of the Arbitrarily High-Order Transport Method of the Characteristic Type for Unstructured Grids (AHOT-C-UG) is performed, which is based on a consistent generalization of lower-order short characteristic methods in structured grids. Novel techniques, such as coordinate transformations and series expansions of spatial moments, are introduced in order to avoid previous difficulties regarding computational precision and the treatment of internal voids. In addition, the arbitrary-order characteristic relation is re-derived in a form which satisfies exactly the arbitrary-order balance equation. The consequences of the equivalence are twofold: it provides an exact relation that is numerically stable as the computational cells become optically thin, and it underscores the fact that the characteristic relation conserves the local balance of all computed spatial moments of the particle population, which is an important property of good spatial discretizations to the transport equation. Furthermore, the AHOT-C-UG approach is subsequently reintroduced as a Discontinuous Petrov-Galerkin projection, which allows us to bridge the gap between characteristic methods that are consistent with AHOT-C-UG and general finite element methods by providing a common setting from the point of view of variational analysis. Remaining mathematical and computational challenges regarding the AHOT-C-UG approach are noted and practical solutions to these issues are suggested. A rudimentary performance model of the method is introduced in order to address practical concerns regarding computational resources and runtime performance. Numerical results are shown which verify the validity of the performance model. In addition, the expected behavior of the method's convergence rate, based on the behavior of the error with respect to mesh refinement for a specified set of spatial expansion orders, is verified by performing a set of numerical experiments. Finally, a set of computational benchmarks are solved in order to show that the formalism can be used to analyze realistic radiation transport problems.

Ferrer, Rodolfo M.

196

Cr(1/3)Zr?P?O?? with unusual tetrahedral coordination of Cr(III): peculiarities of the formation, thermal stability and application as a pigment.  

PubMed

All the known chromium(III) NASICON-related phosphates are considered to be solid solutions. In these compounds chromium atoms share their position in the basic framework of the crystal lattice with other structure forming elements such as zirconium. In our study, we have hypothesised a completely new way of structural organisation of the chromium(III) zirconium(IV) NASICON framework, consisting in the distribution of chromium over the charge-compensating atom sites with tetrahedral oxygen coordination. The possibility of formation of the corresponding phosphate, Cr(1/3)Zr2P3O12, was studied using a classical ceramic route and a sol-gel method. Structural affiliation of the obtained pure phase product was studied using XRD analysis. The results confirmed that the Cr(1/3)Zr2P3O12 phosphate belongs to monoclinic SW-subtype of the NASICON family. In this structure, chromium atoms occupy charge-compensating sites with a strongly distorted tetrahedral oxygen environment. To the best of our knowledge, it is the first example of tetrahedral coordination of chromium(III) in phosphates. Along with the unusual crystallographic characteristics of chromium, special attention in this paper is devoted to the thermal stability of this phosphate and to its performance as an inorganic pigment. The sample was characterised by heating microscopy and DTA study, particle size distribution analysis, and IR- and VIS-spectroscopy. The stability of the obtained powder in a glaze environment, its colouring performance and lightfastness are discussed as well. PMID:25189199

Gorodylova, Nataliia; Kosinová, Veronika; Šulcová, Petra; B?lina, Petr; Vl?ek, Milan

2014-11-01

197

Geometric Approaches to Quadratic Equations from Other Times and Places.  

ERIC Educational Resources Information Center

Focuses on geometric solutions of quadratic problems. Presents a collection of geometric techniques from ancient Babylonia, classical Greece, medieval Arabia, and early modern Europe to enhance the quadratic equation portion of an algebra course. (KHR)

Allaire, Patricia R.; Bradley, Robert E.

2001-01-01

198

Bound States of the Dirac Equation for a Class of Effective Quadratic Plus Inversely Quadratic Potentials  

E-print Network

The Dirac equation is exactly solved for a pseudoscalar linear plus Coulomb-like potential in a two-dimensional world. This sort of potential gives rise to an effective quadratic plus inversely quadratic potential in a Sturm-Liouville problem, regardless the sign of the parameter of the linear potential, in sharp contrast with the Schroedinger case. The generalized Dirac oscillator already analyzed in a previous work is obtained as a particular case.

Antonio S. de Castro

2003-11-10

199

THE EFFECTIVENESS OF QUADRATS FOR MEASURING VASCULAR PLANT DIVERSITY  

EPA Science Inventory

Quadrats are widely used for measuring characteristics of vascular plant communities. It is well recognized that quadrat size affects measurements of frequency and cover. The ability of quadrats of varying sizes to adequately measure diversity has not been established. An exha...

200

Number Theory 2010 Exercise list 3: quadratic forms  

E-print Network

Number Theory 2010 Yuri Bilu Exercise list 3: quadratic forms Unless the contrary is stated f; · "form" means "quadratic form". 1. In this exercise we prove the Theorem of Witt: if f1 and f2 and U2 are called in this case isometric. (a) Let u be an anisotropic vector of a quadratic space U

Bilu, Yuri F.

201

On rational quadratic differential forms H.L. Trentelman  

E-print Network

multipliers or integral quadratic constraints (for the previous works on related topics, see e.g. MegretskiOn rational quadratic differential forms K. Takaba H.L. Trentelman J.C. Willems Department Lyapunov functions, energy storage, performance measures, e.t.c. Such a quadratic functional is called

202

UNCERTAIN SYSTEMS, BEHAVIOURS AND QUADRATIC DIFFERENTIAL FORMS 1  

E-print Network

definition is closely related to the integral quadratic constraint uncertainty description commonly found as a behavioural generalization of the frequency domain integral quadratic constraint (IQC) 1 This workUNCERTAIN SYSTEMS, BEHAVIOURS AND QUADRATIC DIFFERENTIAL FORMS 1 Ian R. Petersen Jan C. Willems

203

Constrained Quadratic Minimizations for Signal Processing and Communications  

E-print Network

. The problem is to minimize a quadratic form, under a set of linear or quadratic constraints. We derive) with respect to W, subject to a set of linear or quadratic constraints. WH RW is the covariance matrix of V. Then, the constraint is WH = LH VH , (2) This work is supported by the DARPA Integrated Sensing

Scharf, Louis

204

Linear and quadratic time-frequency signal representations  

Microsoft Academic Search

A tutorial review of both linear and quadratic representations is given. The linear representations discussed are the short-time Fourier transform and the wavelet transform. The discussion of quadratic representations concentrates on the Wigner distribution, the ambiguity function, smoothed versions of the Wigner distribution, and various classes of quadratic time-frequency representations. Examples of the application of these representations to typical problems

F. Hlawatsch; G. F. Boudreaux-Bartels

1992-01-01

205

A Quadratic Gradient Equation for pricing Mortgage-Backed Securities  

E-print Network

A Quadratic Gradient Equation for pricing Mortgage-Backed Securities Marco Papi Institute for Applied Computing - CNR Rome (Italy) A Quadratic Gradient Equation for pricing Mortgage-Backed Securities call option on a corresponding fixed-rate bond. A Quadratic Gradient Equation for pricing Mortgage

Monneau, Régis

206

HOW DO YOU SOLVE A QUADRATIC EQUATION? GEORGE E._ FORSYTHE  

E-print Network

cs40 HOW DO YOU SOLVE A QUADRATIC EQUATION? BY GEORGE E._ FORSYTHE TECHNICAL REPORT NO. CS40 JUNE;1 \\- c. `L L t HOW DO YOU SOLVE A QUADRATIC EQUATION? bY George E. Forsythe Abstract The nature-point computation are illustrated by the formula for solving a quadratic equation. An accurate way of solving

Jiang, Shidong

207

REGULARIZED TOTAL LEAST SQUARES BASED ON QUADRATIC EIGENVALUE PROBLEM SOLVERS  

Microsoft Academic Search

This paper presents a new computational approach for solving the Regularized Total Least Squares problem. The problem is formulated by adding a quadratic constraint to the Total Least Square minimization problem. Starting from the fact that a quadrat- ically constrained Least Squares problem can be solved via a quadratic eigenvalue problem, an iterative procedure for solving the regularized Total Least

DIANA M. SIMA; SABINE VAN HUFFEL; GENE H. GOLUB

2003-01-01

208

Higgsed Stueckelberg vector and Higgs quadratic divergence  

NASA Astrophysics Data System (ADS)

Here we show that, a hidden vector field whose gauge invariance is ensured by a Stueckelberg scalar and whose mass is spontaneously generated by the Standard Model Higgs field contributes to quadratic divergences in the Higgs boson mass squared, and even leads to its cancellation at one-loop when Higgs coupling to gauge field is fine-tuned. In contrast to mechanisms based on hidden scalars where a complete cancellation cannot be achieved, stabilization here is complete in that the hidden vector and the accompanying Stueckelberg scalar are both free from quadratic divergences at one-loop. This stability, deriving from hidden exact gauge invariance, can have important implications for modeling dark phenomena like dark matter, dark energy, dark photon and neutrino masses. The hidden fields can be produced at the LHC.

Demir, Durmu? Ali; Karahan, Canan Nurhan; Korutlu, Beste

2015-01-01

209

Planar flows and quadratic relations over semirings  

E-print Network

It is well known, due to Lindstr\\"om, that the minors of a matrix can be expressed in terms of weights of flows in a planar directed graph. Another fact is that there are plenty of quadratic relations involving minors, of which Pl\\"ucker ones are most popular. Generalizing and unifying these facts and their tropical counterparts, we consider a wide class of functions which are generated by flows in a planar graph and take values in an arbitrary commutative semiring. We show that the "universal" quadratic relations performed by such functions can be described in terms of certain matchings, and as a consequence, give combinatorial necessary and sufficient conditions for these relations. Also we give applications and discuss related topics.

Danilov, Vladimir I; Koshevoy, Gleb A

2011-01-01

210

Stellar objects in the quadratic regime  

NASA Astrophysics Data System (ADS)

We model a charged anisotropic relativistic star with a quadratic equation of state. Physical features of an exact solution of the Einstein-Maxwell system are studied by incorporating the effect of the nonlinear term from the equation of state. It is possible to regain the masses, radii and central densities for a linear equation of state in our analysis. We generate masses for stellar compact objects and perform a detailed study of PSR J1614-2230 in particular. We also show the influence of the nonlinear equation of state on physical features of the matter distribution. We demonstrate that it is possible to incorporate the effects of charge, anisotropy and a quadratic term in the equation of state in modelling a compact relativistic body.

Mafa Takisa, P.; Maharaj, S. D.; Ray, Subharthi

2014-12-01

211

Stellar objects in the quadratic regime  

E-print Network

We model a charged anisotropic relativistic star with a quadratic equation of state. Physical features of an exact solution of the Einstein-Maxwell system are studied by incorporating the effect of the nonlinear term from the equation of state. It is possible to regain the masses, radii and central densities for a linear equation of state in our analysis. We generate masses for stellar compact objects and perform a detailed study of PSR J1614-2230 in particular. We also show the influence of the nonlinear equation of state on physical features of the matter distribution. We demonstrate that it is possible to incorporate the effects of charge, anisotropy and a quadratic term in the equation of state in modelling a compact relativistic body.

P. Mafa Takisa; S. D. Maharaj; Subharthi Ray

2014-12-28

212

Regular models with quadratic equation of state  

E-print Network

We provide new exact solutions to the Einstein-Maxwell system of equations which are physically reasonable. The spacetime is static and spherically symmetric with a charged matter distribution. We utilise an equation of state which is quadratic relating the radial pressure to the energy density. Earlier models, with linear and quadratic equations of state, are shown to be contained in our general class of solutions. The new solutions to the Einstein-Maxwell are found in terms of elementary functions. A physical analysis of the matter and electromagnetic variables indicates that the model is well behaved and regular. In particular there is no singularity in the proper charge density at the stellar centre unlike earlier anisotropic models in the presence of the electromagnetic field.

S. D. Maharaj; P. Mafa Takisa

2013-01-08

213

Portfolio optimization and mixed integer quadratic programming  

SciTech Connect

We begin with the well-known Markowitz model of risk and return fora portfolio of stocks. This model is used to choose a minimum risk portfolio from a universe of stocks that achieves a specified level of expected return subject to a budget constraint and possibly other (linear) constraints. This model is a convex quadratic programming model over continuous variables. As such, many of the variables may have small and unrealistic values in an optimal solution. In addition, a minimum risk portfolio may contain far too many stocks for an investor to hold. Eliminating these unwanted characteristics of minimum risk solutions can be accomplished using binary decision variables. We discuss an implementation of branch-and-bound for convex quadratic programming using the Optimization Subroutine Library. We then discuss how the structure of these particular types of additional constraints can be used to obtain a more efficient implementation. We present some computational experience with instances from the finance industry.

Jensen, D.

1994-12-31

214

Atomic Scale Picture of the Ion Conduction Mechanism in Tetrahedral Network of Lanthanum Barium Gallate  

SciTech Connect

Combined experimental study of impedance spectroscopy, neutron powder diffraction and quasielastic neutron scattering was performed to shed light into the atomic scale ion migration processes in proton and oxide ion conductor; La0.8Ba1.2GaO3.9 . This material consist of tetrahedral GaO4 units, which are rather flexible and rocking motion of these units promotes the ionic migration process. The oxide ion (vacancy) conduction takes place on channels along c axis, involving a single elementary step, which occurs between adjacent tetrahedron (inter-tetrahedron jump). The proton conduction mechanism consists of intra-tetrahedron and inter-tetrahedron elementary processes. The intra-tetrahedron proton transport is the rate-limiting process, with activation energy of 0.44 eV. The rocking motion of the GaO4 tetrahedron aids the inter-tetrahedral proton transport, which has the activation energy of 0.068 eV.

Jalarvo, Niina H [ORNL] [ORNL; Gourdon, Olivier [ORNL] [ORNL; Bi, Zhonghe [ORNL] [ORNL; Gout, Delphine J [ORNL] [ORNL; Ohl, Michael E [ORNL] [ORNL; Paranthaman, Mariappan Parans [ORNL] [ORNL

2013-01-01

215

Low symmetry tetrahedral nematic liquid crystal phases: Ambidextrous chirality and ambidextrous helicity.  

PubMed

We discuss the symmetry properties as well as the dynamic behavior of various non-polar nematic liquid crystal phases with tetrahedral order. We concentrate on systems that show biaxial nematic order coexisting with octupolar (tetrahedral) order. Non-polar examples are phases with D2 and S4 symmetries, which can be characterized as biaxial nematics lacking inversion symmetry. It is this combination that allows for new features in the statics and dynamics of these phases. The D2-symmetric phase is chiral, even for achiral molecules, and shows ambidextrous chirality in all three preferred directions. The achiral S4-symmetric phase allows for ambidextrous helicity, similar to the higher-symmetric D2d-symmetric phase. Such phases are candidates for nematic phases made from banana-shaped molecules. PMID:24566665

Pleiner, Harald; Brand, Helmut R

2014-02-01

216

Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry  

NASA Astrophysics Data System (ADS)

This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, Journal of Chemical Education 83(1), 49-55, 2006) to the teaching of chemistry. The project in its entirety is based upon several theoretical models in fostering chemistry teacher development (in particular Bronfenbrenner's bio-ecological model). These models are described, as is the progress made by teachers based upon the use of a Chemistry Teacher Inventory and associated teacher responses. Overall, statistical analysis of perceptions of their own teaching and comments made by teachers suggests they are showing limited development towards a tetrahedral orientation, albeit in a manner consistent with the curriculum. Ongoing research-based activities in this project are also described.

Lewthwaite, Brian; Wiebe, Rick

2011-11-01

217

Extended Decentralized Linear-Quadratic-Gaussian Control  

NASA Technical Reports Server (NTRS)

A straightforward extension of a solution to the decentralized linear-Quadratic-Gaussian problem is proposed that allows its use for commonly encountered classes of problems that are currently solved with the extended Kalman filter. This extension allows the system to be partitioned in such a way as to exclude the nonlinearities from the essential algebraic relationships that allow the estimation and control to be optimally decentralized.

Carpenter, J. Russell

2000-01-01

218

Numerical analysis of a quadratic matrix equation  

Microsoft Academic Search

The quadratic matrix equation AX2+BX +C = 0 in n \\\\Theta n matrices arises inapplications and is of intrinsic interest as one of the simplest nonlinear matrix equations.We give a complete characterization of solutions in terms of the generalizedSchur decomposition and describe and compare various numerical solution techniques.In particular, we give a thorough treatment of functional iteration methodsbased on Bernoulli's

NICHOLAS J. HIGHAM; HYUN-MIN KIM

1999-01-01

219

Characterization of a Quadratic Function in Rn  

ERIC Educational Resources Information Center

It is proved that a scalar-valued function "f"(x) defined in "n"-dimensional space must be quadratic, if the intersection of tangent planes at x[subscript 1] and x[subscript 2] always contains the midpoint of the line joining x[subscript 1] and x[subscript 2]. This is the converse of a result of Stenlund proved in this JOURNAL in 2001.

Xu, Conway

2010-01-01

220

Numerical solution of quadratic matrix equations for free vibration analysis of structures  

NASA Technical Reports Server (NTRS)

This paper is concerned with the efficient and accurate solution of the eigenvalue problem represented by quadratic matrix equations. Such matrix forms are obtained in connection with the free vibration analysis of structures, discretized by finite 'dynamic' elements, resulting in frequency-dependent stiffness and inertia matrices. The paper presents a new numerical solution procedure of the quadratic matrix equations, based on a combined Sturm sequence and inverse iteration technique enabling economical and accurate determination of a few required eigenvalues and associated vectors. An alternative procedure based on a simultaneous iteration procedure is also described when only the first few modes are the usual requirement. The employment of finite dynamic elements in conjunction with the presently developed eigenvalue routines results in a most significant economy in the dynamic analysis of structures.

Gupta, K. K.

1975-01-01

221

Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry  

Microsoft Academic Search

This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development\\u000a project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds\\u000a to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, Journal of Chemical Education 83(1), 49–55,\\u000a 2006) to the teaching of chemistry.

Brian Lewthwaite; Rick Wiebe

222

A Reactor Pressure Vessel Dosimetry Calculation Using ATTILA, An Unstructured Tetrahedral Mesh Discrete-Ordinates Code  

SciTech Connect

Recently, a new state-of-the-art discrete-ordinates code, ATTILA, was developed. ATTILA provides the capabilities to solve geometrically complex 3-D transport problems by using an unstructured tetrahedral mesh. In this paper we describe the application of ATTILA to a 3-D reactor pressure vessel dosimetry problem. We provide numerical results from ATTILA and the Monte Carlo code, MCNP. The results demonstrate the effectiveness and efficiency of ATTILA for such calculations.

Wareing, T.A.; Parsons, D.K. [Los Alamos National Lab., NM (United States); Pautz, S. [Texas A and M Univ., College Station, TX (United States). Dept. of Nuclear Engineering

1997-12-31

223

Bioprinting vessel-like constructs using hyaluronan hydrogels crosslinked with tetrahedral polyethylene glycol tetracrylates  

Microsoft Academic Search

Bioprinting enables deposition of cells and biomaterials into spatial orientations and complexities that mirror physiologically relevant geometries. To facilitate the development of bioartificial vessel-like grafts, two four-armed polyethylene glycol (PEG) derivatives with different PEG chain lengths, TetraPEG8 and TetraPEG13, were synthesized from tetrahedral pentaerythritol derivatives. The TetraPEGs are unique multi-armed PEGs with a compact and symmetrical core. The TetraPEGs were

Aleksander Skardal; Jianxing Zhang; Glenn D. Prestwich

2010-01-01

224

A first collision source method for ATTILA, an unstructured tetrahedral mesh discrete ordinates code  

SciTech Connect

A semi-analytic first collision source method is developed for the transport code, ATTILA, a three-dimensional, unstructured tetrahedral mesh, discrete-ordinates code. This first collision source method is intended to mitigate ray effects due to point sources. The method is third-order accurate, which is the same order of accuracy as the linear-discontinuous spatial differencing scheme used in ATTILA. Numerical results are provided to demonstrate the accuracy and efficiency of the first collision source method.

Wareing, T.A.; Morel, J.E.; Parsons, D.K.

1998-12-01

225

Quadratic Programming for Allocating Control Effort  

NASA Technical Reports Server (NTRS)

A computer program calculates an optimal allocation of control effort in a system that includes redundant control actuators. The program implements an iterative (but otherwise single-stage) algorithm of the quadratic-programming type. In general, in the quadratic-programming problem, one seeks the values of a set of variables that minimize a quadratic cost function, subject to a set of linear equality and inequality constraints. In this program, the cost function combines control effort (typically quantified in terms of energy or fuel consumed) and control residuals (differences between commanded and sensed values of variables to be controlled). In comparison with prior control-allocation software, this program offers approximately equal accuracy but much greater computational efficiency. In addition, this program offers flexibility, robustness to actuation failures, and a capability for selective enforcement of control requirements. The computational efficiency of this program makes it suitable for such complex, real-time applications as controlling redundant aircraft actuators or redundant spacecraft thrusters. The program is written in the C language for execution in a UNIX operating system.

Singh, Gurkirpal

2005-01-01

226

Quadratic optimization in ill-posed problems  

NASA Astrophysics Data System (ADS)

Ill-posed quadratic optimization frequently occurs in control and inverse problems and is not covered by the Lax-Milgram-Riesz theory. Typically, small changes in the input data can produce very large oscillations on the output. We investigate the conditions under which the minimum value of the cost function is finite and we explore the 'hidden connection' between the optimization problem and the least-squares method. Eventually, we address some examples coming from optimal control and data completion, showing how relevant our contribution is in the knowledge of what happens for various ill-posed problems. The results we state bring a substantial improvement to the analysis of the regularization methods applied to the ill-posed quadratic optimization problems. Indeed, for the cost quadratic functions bounded from below the Lavrentiev method is just the Tikhonov regularization for the 'hidden least-squares' problem. As a straightforward result, Lavrentiev's regularization exhibits better regularization and convergence results than expected at first glance.

Ben Belgacem, F.; Kaber, S.-M.

2008-10-01

227

A FAST ITERATIVE METHOD FOR SOLVING THE EIKONAL EQUATION ON TETRAHEDRAL DOMAINS  

PubMed Central

Generating numerical solutions to the eikonal equation and its many variations has a broad range of applications in both the natural and computational sciences. Efficient solvers on cutting-edge, parallel architectures require new algorithms that may not be theoretically optimal, but that are designed to allow asynchronous solution updates and have limited memory access patterns. This paper presents a parallel algorithm for solving the eikonal equation on fully unstructured tetrahedral meshes. The method is appropriate for the type of fine-grained parallelism found on modern massively-SIMD architectures such as graphics processors and takes into account the particular constraints and capabilities of these computing platforms. This work builds on previous work for solving these equations on triangle meshes; in this paper we adapt and extend previous two-dimensional strategies to accommodate three-dimensional, unstructured, tetrahedralized domains. These new developments include a local update strategy with data compaction for tetrahedral meshes that provides solutions on both serial and parallel architectures, with a generalization to inhomogeneous, anisotropic speed functions. We also propose two new update schemes, specialized to mitigate the natural data increase observed when moving to three dimensions, and the data structures necessary for efficiently mapping data to parallel SIMD processors in a way that maintains computational density. Finally, we present descriptions of the implementations for a single CPU, as well as multicore CPUs with shared memory and SIMD architectures, with comparative results against state-of-the-art eikonal solvers. PMID:25221418

Fu, Zhisong; Kirby, Robert M.; Whitaker, Ross T.

2014-01-01

228

Ultrahigh-Resolution ?-Ray Spectroscopy of Gd156: A Test of Tetrahedral Symmetry  

NASA Astrophysics Data System (ADS)

Tetrahedral symmetry in strongly interacting systems would establish a new class of quantum effects at subatomic scale. Excited states in Gd156 that could carry the information about the tetrahedral symmetry were populated in the Gd155(n,?)Gd156 reaction and studied using the GAMS4/5 Bragg spectrometers at the Institut Laue-Langevin. We have identified the 51-?31- transition of 131.983(12) keV in Gd156 and determined its intensity to be 1.9(3)x10-6 per neutron capture. The lifetime ?=220-30+180fs of the 51- state in Gd156 has been measured using the GRID technique. The resulting B(E2)=293-134+61Weisskopf unit rate of the 131.983 keV transition provides the intrinsic quadrupole moment of the 51- state in Gd156 to be Q0=7.1-1.6+0.7b. This large value, comparable to the quadrupole moment of the ground state in Gd156, gives strong evidence against tetrahedral symmetry in the lowest odd-spin, negative-parity band of Gd156.

Jentschel, M.; Urban, W.; Krempel, J.; Tonev, D.; Dudek, J.; Curien, D.; Lauss, B.; de Angelis, G.; Petkov, P.

2010-06-01

229

Tetrahedral Finite-Volume Solutions to the Navier-Stokes Equations on Complex Configurations  

NASA Technical Reports Server (NTRS)

A review of the algorithmic features and capabilities of the unstructured-grid flow solver USM3Dns is presented. This code, along with the tetrahedral grid generator, VGRIDns, is being extensively used throughout the U.S. for solving the Euler and Navier-Stokes equations on complex aerodynamic problems. Spatial discretization is accomplished by a tetrahedral cell-centered finite-volume formulation using Roe's upwind flux difference splitting. The fluxes are limited by either a Superbee or MinMod limiter. Solution reconstruction within the tetrahedral cells is accomplished with a simple, but novel, multidimensional analytical formula. Time is advanced by an implicit backward-Euler time-stepping scheme. Flow turbulence effects are modeled by the Spalart-Allmaras one-equation model, which is coupled with a wall function to reduce the number of cells in the near-wall region of the boundary layer. The issues of accuracy and robustness of USM3Dns Navier-Stokes capabilities are addressed for a flat-plate boundary layer, and a full F-16 aircraft with external stores at transonic speed.

Frink, N. T.; Pirzadeh, S. Z.

1998-01-01

230

Recent Development in the CESE Method for the Solution of the Navier-Stokes Equations Using Unstructured Triangular or Tetrahedral Meshes With High Aspect Ratio  

NASA Technical Reports Server (NTRS)

In the multidimensional CESE development, triangles and tetrahedra turn out to be the most natural building blocks for 2D and 3D spatial meshes. As such the CESE method is compatible with the simplest unstructured meshes and thus can be easily applied to solve problems with complex geometries. However, because the method uses space-time staggered stencils, solution decoupling may become a real nuisance in applications involving unstructured meshes. In this paper we will describe a simple and general remedy which, according to numerical experiments, has removed any possibility of solution decoupling. Moreover, in a real-world viscous flow simulation near a solid wall, one often encounters a case where a boundary with high curvature or sharp corner is surrounded by triangular/tetrahedral meshes of extremely high aspect ratio (up to 106). For such an extreme case, the spatial projection of a space-time compounded conservation element constructed using the original CESE design may become highly concave and thus its centroid (referred to as a spatial solution point) may lie far outside of the spatial projection. It could even be embedded beyond a solid wall boundary and causes serious numerical difficulties. In this paper we will also present a new procedure for constructing conservation elements and solution elements which effectively overcomes the difficulties associated with the original design. Another difficulty issue which was addressed more recently is the wellknown fact that accuracy of gradient computations involving triangular/tetrahedral grids deteriorates rapidly as the aspect ratio of grid cells increases. The root cause of this difficulty was clearly identified and several remedies to overcome it were found through a rigorous mathematical analysis. However, because of the length of the current paper and the complexity of mathematics involved, this new work will be presented in another paper.

Chang, Sin-Chung; Chang, Chau-Lyan; Yen, Joseph C.

2013-01-01

231

On the influence of tetrahedral covalent-hybridization on electronic band structure of topological insulators from first principles  

NASA Astrophysics Data System (ADS)

Based on first-principles calculations, we investigate the influence of tetrahedral covalent-hybridization between main-group and transition-metal atoms on the topological band structures of binary HgTe and ternary half-Heusler compounds, respectively. Results show that, for the binary HgTe, when its zinc-blend structure is artificially changed to rock-salt one, the tetrahedral covalent-hybridization will be removed and correspondingly the topologically insulating band character lost. While for the ternary half-Heusler system, the strength of covalent-hybridization can be tuned by varying both chemical compositions and atomic arrangements, and the competition between tetrahedral and octahedral covalent-hybridization has been discussed in details. As a result, we found that a proper strength of tetrahedral covalent-hybridization is probably in favor to realizing the topologically insulating state with band inversion occurring at the ? point of the Brillouin zone.

Zhang, X. M.; Xu, G. Z.; Liu, E. K.; Liu, Z. Y.; Wang, W. H.; Wu, G. H.

2015-01-01

232

Mixed finite element formulation in large deformation frictional contact problem  

E-print Network

Mixed finite element formulation in large deformation frictional contact problem Laurent Baillet using the 2D finite element code PLAST21 . The first contact algorithm is the classical node and compared for linear and quadratic elements. KEY WORDS: contact, mixed finite element, friction, dynamic

Paris-Sud XI, Université de

233

The tetrahedral framework in glasses and melts — inferences from molecular orbital calculations and implications for structure, thermodynamics, and physical properties  

Microsoft Academic Search

Results of ab initio molecular orbital (MO) calculations provide a basis for the interpretation of structural and thermodynamic properties of crystals, glasses, and melts containing tetrahedrally coordinated Si, Al, and B. Calculated and experimental tetrahedral atom-oxygen (TO) bond lengths are in good agreement and the observed average SiO and AlO bond lengths remain relatively constant in crystalline, glassy, and molten

A. Navrotsky; K. L. Geisinger; P. McMillan; G. V. Gibbs

1985-01-01

234

Linear state feedback, quadratic weights, and closed loop eigenstructures. M.S. Thesis. Final Report  

NASA Technical Reports Server (NTRS)

Equations are derived for the angles of general multivariable root loci and linear quadratic optimal root loci, including angles of departure and approach. The generalized eigenvalue problem is used to compute angles of approach. Equations are also derived to find the sensitivity of closed loop eigenvalue and the directional derivatives of closed loop eigenvectors. An equivalence class of quadratic weights that produce the same asymptotic eigenstructure is defined, a canonical element is defined, and an algorithm to find it is given. The behavior of the optimal root locus in the nonasymptotic region is shown to be different for quadratic weights with the same asymptotic properties. An algorithm is presented that can be used to select a feedback gain matrix for the linear state feedback problem which produces a specified asymptotic eigenstructure. Another algorithm is given to compute the asymptotic eigenstructure properties inherent in a given set of quadratic weights. Finally, it is shown that optimal root loci for nongeneric problems can be approximated by generic ones in the nonasymptotic region.

Thompson, P. M.

1980-01-01

235

New approach based on tetrahedral-mesh geometry for accurate 4D Monte Carlo patient-dose calculation  

NASA Astrophysics Data System (ADS)

In the present study, to achieve accurate 4D Monte Carlo dose calculation in radiation therapy, we devised a new approach that combines (1) modeling of the patient body using tetrahedral-mesh geometry based on the patient’s 4D CT data, (2) continuous movement/deformation of the tetrahedral patient model by interpolation of deformation vector fields acquired through deformable image registration, and (3) direct transportation of radiation particles during the movement and deformation of the tetrahedral patient model. The results of our feasibility study show that it is certainly possible to construct 4D patient models (= phantoms) with sufficient accuracy using the tetrahedral-mesh geometry and to directly transport radiation particles during continuous movement and deformation of the tetrahedral patient model. This new approach not only produces more accurate dose distribution in the patient but also replaces the current practice of using multiple 3D voxel phantoms and combining multiple dose distributions after Monte Carlo simulations. For routine clinical application of our new approach, the use of fast automatic segmentation algorithms is a must. In order to achieve, simultaneously, both dose accuracy and computation speed, the number of tetrahedrons for the lungs should be optimized. Although the current computation speed of our new 4D Monte Carlo simulation approach is slow (i.e. ~40 times slower than that of the conventional dose accumulation approach), this problem is resolvable by developing, in Geant4, a dedicated navigation class optimized for particle transportation in tetrahedral-mesh geometry.

Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Kim, Seonghoon; Sohn, Jason W.

2015-02-01

236

New approach based on tetrahedral-mesh geometry for accurate 4D Monte Carlo patient-dose calculation.  

PubMed

In the present study, to achieve accurate 4D Monte Carlo dose calculation in radiation therapy, we devised a new approach that combines (1) modeling of the patient body using tetrahedral-mesh geometry based on the patient's 4D CT data, (2) continuous movement/deformation of the tetrahedral patient model by interpolation of deformation vector fields acquired through deformable image registration, and (3) direct transportation of radiation particles during the movement and deformation of the tetrahedral patient model. The results of our feasibility study show that it is certainly possible to construct 4D patient models (= phantoms) with sufficient accuracy using the tetrahedral-mesh geometry and to directly transport radiation particles during continuous movement and deformation of the tetrahedral patient model. This new approach not only produces more accurate dose distribution in the patient but also replaces the current practice of using multiple 3D voxel phantoms and combining multiple dose distributions after Monte Carlo simulations. For routine clinical application of our new approach, the use of fast automatic segmentation algorithms is a must. In order to achieve, simultaneously, both dose accuracy and computation speed, the number of tetrahedrons for the lungs should be optimized. Although the current computation speed of our new 4D Monte Carlo simulation approach is slow (i.e. ~40 times slower than that of the conventional dose accumulation approach), this problem is resolvable by developing, in Geant4, a dedicated navigation class optimized for particle transportation in tetrahedral-mesh geometry. PMID:25615567

Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Kim, Seonghoon; Sohn, Jason W

2015-02-21

237

Tetrahedral Kites  

NSDL National Science Digital Library

In this math lesson, each learner constructs a tetrahedron and describes the linear dimensions, area and volume using nonâtraditional units of measure. Four tetrahedra are combined to form a similar tetrahedron, whose linear dimensions are twice the original tetrahedron. The area and volume relationships between the first and second tetrahedra are explored, and generalizations for the relationships are developed. This lesson guide includes questions for learners, assessment options, extensions, and reflection questions.

Warloe, Kris A.

2008-01-01

238

Tetrahedral lander  

NASA Technical Reports Server (NTRS)

An apparatus and method is disclosed for decelerating and absorbing impact of a re-entry vehicle suitable for payloads that are relatively light as well as payloads weighing several tons or more. The apparatus includes four inflatable legs displaced equidistantly from each other around a capsule or housing which contains a payload. The legs are inflated at a designated altitude after entering earth's atmosphere to slow the descent of the re-entry vehicle. Connected between each of the four legs are drag inducing surfaces that deploy as the legs inflate. The drag inducing surfaces are triangularly shaped with one such surface being connected between each pair of legs for a total of six drag inducing surfaces. The legs have drag inducing outer surfaces which act to slow the descent of the re-entry vehicle.

Roberts, Michael L. (inventor)

1993-01-01

239

Chemical Excision of Tetrahedral FeSe2 Chains from the Superconductor FeSe: Synthesis, Crystal Structure, and Magnetism of Fe3Se4(en)2  

PubMed Central

Fragments of the superconducting FeSe layer, FeSe2 tetrahedral chains, were stabilized in the crystal structure of a new mixed-valent compound Fe3Se4(en)2 (en = ethylenediamine) synthesized from elemental Fe and Se. The FeSe2 chains are separated from each other by means of Fe(en)2 linkers. Mössbauer spectroscopy and magnetometry reveal strong magnetic interactions within the FeSe2 chains which result in antiferromagnetic ordering below 170 K. According to DFT calculations, anisotropic transport and magnetic properties are expected for Fe3Se4(en)2. This compound offers a unique way to manipulate the properties of the Fe-Se infinite fragments by varying the topology and charge of the Fe-amino linkers. PMID:24299423

Pak, Chongin; Kamali, Saeed; Pham, Joyce; Lee, Kathleen; Greenfield, Joshua T.; Kovnir, Kirill

2014-01-01

240

Extensions of representations of integral quadratic forms  

Microsoft Academic Search

Let N and M be quadratic ?-lattices, and K be a sublattice of N. A representation ?:K?M is said to be extensible to N if there exists a representation ?:N?M such that ?\\u000a |\\u000a \\u000a K\\u000a =?. We prove in this paper a local–global principle for extensibility of representation, which is a generalization of the main\\u000a theorems on representations by positive definite ?-lattices by Hsia, Kitaoka and

Wai Kiu Chan; Byeong Moon Kim; Myung-Hwan Kim; Byeong-Kweon Oh

2008-01-01

241

Oscillations of a quadratically damped pendulum  

NASA Astrophysics Data System (ADS)

A physical pendulum consisting of a circular disk at the end of a thin metal rod is connected to a low-friction rotary motion sensor, so that its angular position and velocity can be accurately measured. The disk can be oriented either perpendicular or parallel to the plane of swing to give significant or negligible air drag, respectively. The motion is analytically modeled in phase space. A quadratic dependence of the damping torque on the angular velocity fits the results. This laboratory experiment is suitable for undergraduate physics majors taking a first or second course in classical mechanics.

Mungan, Carl E.; Lipscombe, Trevor C.

2013-09-01

242

Nonconvex Problems of Global Optimization: Linear-Quadratic Control Problems with Quadratic Constraints  

Microsoft Academic Search

In this paper, we study a class of optimization problems,which are of certain interest for control theory. These problemsare of global constrained optimization and may be nonconvex ingeneral. A simple approach to their solution is presented. Aspecial attention is paid to the case when the objective andconstraints functions are quadratic functionals on a Hilbertspace. As an example of an application

A. Matveev; V. Yakubovich

1997-01-01

243

Restrictions of Quadratic Forms to Lagrangian Planes, Quadratic Matrix Equations, and Gyroscopic Stabilization  

Microsoft Academic Search

We discuss the symplectic geometry of linear Hamiltonian systems with nondegenerate Hamiltonians. These systems can be reduced to linear second-order differential equations characteristic of linear oscillation theory. This reduction is related to the problem on the signatures of restrictions of quadratic forms to Lagrangian planes. We study vortex symplectic planes invariant with respect to linear Hamiltonian systems. These planes are

V. V. Kozlov

2005-01-01

244

Runge-Kutta methods for quadratic ordinary differential equations  

Microsoft Academic Search

Many systems of ordinary differential equations are quadratic: the derivative can be expressed as a quadratic function of\\u000a the dependent variable. We demonstrate that this feature can be exploited in the numerical solution by Runge-Kutta methods,\\u000a since the quadratic structure serves to decrease the number of order conditions. We discuss issues related to construction\\u000a design and implementation and present a

Arieh Iserles; Geetha Ramaswami; Mark Sofroniou

1998-01-01

245

LARGE TIME SOLUTION FOR QUADRATIC SCHRODINGER EQUATIONS IN HANTAEK BAE  

E-print Network

LARGE TIME SOLUTION FOR QUADRATIC SCHR¨ODINGER EQUATIONS IN 2D AND 3D HANTAEK BAE Abstract. The aim of this paper is to establish the large time well-posedness of the quadratic Schr¨odinger equation in 2D and 3D for the solvability of (1.1), see [5]. In this paper, we consider the Schr¨odinger equation with quadratic

Yorke, James

246

A ROBUST ARBITRARILY HIGH ORDER TRANSPORT METHOD OF THE CHARACTERISTIC TYPE FOR UNSTRUCTURED TETRAHEDRAL GRIDS  

SciTech Connect

We present a robust arbitrarily high order transport method of the characteristic type for unstructured tetrahedral grids. Previously encountered difficulties have been addressed through the reformulation of the method based on coordinate transformations, evaluation of the moments balance relation as a linear system of equations involving the expansion coefficients of the projected basis, and the asymptotic expansion of the integral kernels in the thin cell limit. The proper choice of basis functions for the high-order spatial expansion of the solution is discussed and its effect on problems involving scattering discussed. Numerical tests are presented to illustrate the beneficial effect of these improvements, and the improved robustness they yield.

R. M. Ferrer; Y. Y. Azmy

2009-05-01

247

Fast intersections on nested tetrahedrons (FINT): An algorithm for adaptive finite element based distributed parameter estimation  

Microsoft Academic Search

A variety of biomedical imaging techniques such as optical and fluorescence tomography, electrical impedance tomography, and ultrasound imaging can be cast as inverse problems, wherein image reconstruction involves the estimation of spatially distributed parameter(s) of the PDE system describing the physics of the imaging process. Finite element discretization of imaged domain with tetrahedral elements is a popular way of solving

Jae Hoon Lee; Amit Joshi; Eva M. Sevick-Muraca

2008-01-01

248

Calculation of transient 3D eddy current using edge-elements  

Microsoft Academic Search

The calculation of transient 3-D eddy current using edge elements in the modified A-method is presented. Quadratic 36-edge elements on the 20-node isoparametric elements are proposed. Specifically, the test problems of a square plate and a hollow sphere are solved with linear 12-edge and quadratic 36-edge elements, and the results are compared with the analytical solutions. The results using the

Akihisa Kameari

1990-01-01

249

Three-dimensional dynamic rupture simulation with a high-order discontinuous Galerkin method on unstructured tetrahedral meshes  

NASA Astrophysics Data System (ADS)

Accurate and efficient numerical methods to simulate dynamic earthquake rupture and wave propagation in complex media and complex fault geometries are needed to address fundamental questions in earthquake dynamics, to integrate seismic and geodetic data into emerging approaches for dynamic source inversion, and to generate realistic physics-based earthquake scenarios for hazard assessment. Modeling of spontaneous earthquake rupture and seismic wave propagation by a high-order discontinuous Galerkin (DG) method combined with an arbitrarily high-order derivatives (ADER) time integration method was introduced in two dimensions by de la Puente et al. (2009). The ADER-DG method enables high accuracy in space and time and discretization by unstructured meshes. Here we extend this method to three-dimensional dynamic rupture problems. The high geometrical flexibility provided by the usage of tetrahedral elements and the lack of spurious mesh reflections in the ADER-DG method allows the refinement of the mesh close to the fault to model the rupture dynamics adequately while concentrating computational resources only where needed. Moreover, ADER-DG does not generate spurious high-frequency perturbations on the fault and hence does not require artificial Kelvin-Voigt damping. We verify our three-dimensional implementation by comparing results of the SCEC TPV3 test problem with two well-established numerical methods, finite differences, and spectral boundary integral. Furthermore, a convergence study is presented to demonstrate the systematic consistency of the method. To illustrate the capabilities of the high-order accurate ADER-DG scheme on unstructured meshes, we simulate an earthquake scenario, inspired by the 1992 Landers earthquake, that includes curved faults, fault branches, and surface topography.

Pelties, Christian; de la Puente, Josep; Ampuero, Jean-Paul; Brietzke, Gilbert B.; Käser, Martin

2012-02-01

250

A Reconstructed Discontinuous Galerkin Method for the Compressible Flows on Unstructured Tetrahedral Grids  

SciTech Connect

A reconstruction-based discontinuous Galerkin (RDG) method is presented for the solution of the compressible Navier-Stokes equations on unstructured tetrahedral grids. The RDG method, originally developed for the compressible Euler equations, is extended to discretize viscous and heat fluxes in the Navier-Stokes equations using a so-called inter-cell reconstruction, where a smooth solution is locally reconstructed using a least-squares method from the underlying discontinuous DG solution. Similar to the recovery-based DG (rDG) methods, this reconstructed DG method eliminates the introduction of ad hoc penalty or coupling terms commonly found in traditional DG methods. Unlike rDG methods, this RDG method does not need to judiciously choose a proper form of a recovered polynomial, thus is simple, flexible, and robust, and can be used on unstructured grids. The preliminary results indicate that this RDG method is stable on unstructured tetrahedral grids, and provides a viable and attractive alternative for the discretization of the viscous and heat fluxes in the Navier-Stokes equations.

Hong Luo; Yidong Xia; Robert Nourgaliev; Chunpei Cai

2011-06-01

251

Verification of the three-dimensional tetrahedral grid S{sub N} code THOR  

SciTech Connect

In this work current capabilities implemented in the novel, arbitrary-order, tetrahedral-grid short characteristics S{sub N} radiation transport code THOR are verified based on four benchmark problems: (1) A one-group Method of Manufactured Solution (MMS) problem on a cuboidal domain, (2) an infinite medium eigenvalue problem with up-scattering, (3) a homogeneous torus and (4) a bare cube eigenvalue problem with anisotropic scattering up to order three. The first benchmark problem exercises the various spatial discretization options available in THOR: The short characteristics method in conjunction with polynomial expansions of the source and face fluxes either using the complete or Lagrange family of arbitrary orders. Using the numerical solution's order of convergence test in the framework of a mesh refinement study, correct implementation of a selection of spatial expansion orders is demonstrated for two meshes with tetrahedral aspect ratios close to unity and 50. The second benchmark problem exercises the implementation of angular fluxes on reflective boundary faces that are implicit within a mesh sweep, and up-scattering. The third benchmark problem comprises cyclic dependencies within the mesh sweep thus exercising the algorithm devised for 'breaking' the cyclic dependencies. Finally, the fourth benchmark problem, a simple bare cube, is used to test correct implementation of the anisotropic scattering capability. For all test problems THOR obtains solutions that converge to the reference/exact solution with the expected rate thereby contributing to our confidence in the correctness of its tested features in the present implementation. (authors)

Schunert, S. [Department of Nuclear Engineering, North Carolina State University (United States); Ferrer, R. [Studsvik Scandpower, Idaho Falls, ID (United States); Azmy, Y. [Department of Nuclear Engineering, North Carolina State University (United States)

2013-07-01

252

Mammogram enhancement using alpha weighted quadratic filter.  

PubMed

Mammograms are widely used to detect breast cancer in women. The quality of the image may suffer from poor resolution or low contrast due to the limitations of the X-ray hardware systems. Image enhancement is a powerful tool to improve the visual quality of mammograms. This paper introduces a new powerful nonlinear filter called the alpha weighted quadratic filter for mammogram enhancement. The user has the flexibility to design the filter by selecting all of the parameters manually or using an existing quantitative measure to select the optimal enhancement parameters. Computer simulations show that excellent enhancement results can be obtained with no apriori knowledge of the mammogram contents. The filter can also be used for automatic segmentation. PMID:19965002

Zhou, Yicong; Panetta, Karen; Agaian, Sos

2009-01-01

253

Linear stability analysis of dynamical quadratic gravity  

NASA Astrophysics Data System (ADS)

We study the linear stability of dynamical, quadratic gravity, focusing on two particular subclasses (the even-parity sector, exemplified by Einstein-Dilaton-Gauss-Bonnet gravity, and the odd-parity sector, exemplified by dynamical Chern-Simons modified gravity) in the high-frequency, geometric optics approximation. This analysis is carried out by studying gravitational and scalar modes propagating on spherically symmetric and axially symmetric, vacuum solutions of the theory and finding the associated dispersion relations. These relations are solved in two separate cases (the scalar regime and the gravitational wave regime, defined by requiring the ratio of the amplitude of the perturbations to be much greater or smaller than unity) and found in both cases to not lead to exponential growth of the propagating modes, suggesting linearly stability. The modes are found to propagate at subluminal and superluminal speeds, depending on the propagating modes' direction relative to the background geometry, just as in dynamical Chern-Simons gravity.

Ayzenberg, Dimitry; Yagi, Kent; Yunes, Nicolás

2014-02-01

254

Quadratic quantum cosmology with Schutz' perfect fluid  

NASA Astrophysics Data System (ADS)

We study the classical and quantum models of a Friedmann-Robertson-Walker (FRW) cosmology, coupled to a perfect fluid, in the context of the f(R) gravity. Using Schutz' representation for the perfect fluid, we show that, under a particular gauge choice, it may lead to the identification of a time parameter for the corresponding dynamical system. Moreover, this formalism gives rise to a Schrödinger-Wheeler-DeWitt (SWD) equation for the quantum-mechanical description of the model under consideration, the eigenfunctions of which can be used to construct the wavefunction of the universe. In the case of f(R) = R2 (pure quadratic model), for some particular choices of the perfect fluid source, exact solutions to the SWD equation can be obtained and the corresponding results are compared to the usual f(R) = R model.

Vakili, Babak

2010-01-01

255

Some Paradoxical Results for the Quadratically Weighted Kappa  

ERIC Educational Resources Information Center

The quadratically weighted kappa is the most commonly used weighted kappa statistic for summarizing interrater agreement on an ordinal scale. The paper presents several properties of the quadratically weighted kappa that are paradoxical. For agreement tables with an odd number of categories "n" it is shown that if one of the raters uses the same…

Warrens, Matthijs J.

2012-01-01

256

CLOSURES OF QUADRATIC MODULES JAKA CIMPRIC, MURRAY MARSHALL, TIM NETZER  

E-print Network

CLOSURES OF QUADRATIC MODULES JAKA CIMPRIC, MURRAY MARSHALL, TIM NETZER Abstract. We consider the problem of determining the closure M of a quadratic module M in a commutative R-algebra with respect]. The closure of a semiordering is also considered, and it is shown that the space YM consisting of all

Marshall, Murray

257

Estimating species richness from quadrat sampling data: a general approach  

E-print Network

as the asymptote of a cumulative species-area curve). This approach is thus not appropriate to dealEstimating species richness from quadrat sampling data: a general approach J´er^ome Dupuis IMT of species (denoted by S) of a biological community located in a region composed of n quadrats. To address

Paris-Sud XI, Université de

258

Statistical Mechanics of Linear Systems & Quadratic Path Integrals  

E-print Network

Homework 5 Optional Statistical Mechanics of Linear Systems & Quadratic Path Integrals 1. Examine(r) = k 2 x2 . It also represents the imaginary time path integral of an electron in a quadratic potential constraints, the system is free to fluctuate at temperature T. So you can define the partition function with x

Deutsch, Josh

259

1 Statistical Mechanics of Linear Systems and Quadratic Path Integrals  

E-print Network

Homework 6 Due 6/4/08 1 Statistical Mechanics of Linear Systems and Quadratic Path Integrals 1 potential v(r) = k 2 x2 . It also represents the imaginary time path integral of an electron in a quadratic these two constraints, the system is free to fluctuate at temperature T. So you can define the partition

Deutsch, Josh

260

Weaving a Parabola Web with the Quadratic Transformer  

NSDL National Science Digital Library

Investigate how the graph of a quadratic function and its symbolic expression relate to each other. Start with a set of four graphs, which we?ll call a Parabola Web. Experiment with manipulating them with transformations such as shifting and reflection. Learn about quadratic equations in vertex and root form, and explore how changing these equations affect the graphs.

2012-07-19

261

Sketching the General Quadratic Equation Using Dynamic Geometry Software  

ERIC Educational Resources Information Center

This paper explores a geometrical way to sketch graphs of the general quadratic in two variables with Geometer's Sketchpad. To do this, a geometric procedure as described by De Temple is used, bearing in mind that this general quadratic equation (1) represents all the possible conics (conics sections), and the fact that five points (no three of…

Stols, G. H.

2005-01-01

262

Improved perturbation bounds for general quadratic matrix equations  

Microsoft Academic Search

Perturbation analysis of general algebraic quadratic matrix equations is presented, which include as particular cases the standard and descriptor algebraic matrix Riccati equations, arising in the optimal control and filtering of continuous, time-invariant, linear systems. The perturbation bounds derived are superior to the bounds, already available in the literature. They are applicable to the error analysis of general quadratic matrix

M. M. Konstantinov; P. Hr. Petkov; D. W. Gu

1999-01-01

263

Effects of Classroom Instruction on Students' Understanding of Quadratic Equations  

ERIC Educational Resources Information Center

Two hundred and thirty-one students in six Grade 9 classes in two government secondary schools located near Chiang Mai, Thailand, attempted to solve the same 18 quadratic equations before and after participating in 11 lessons on quadratic equations. Data from the students' written responses to the equations, together with data in the form of…

Vaiyavutjamai, Pongchawee; Clements, M. A.

2006-01-01

264

Tangent Lines without Derivatives for Quadratic and Cubic Equations  

ERIC Educational Resources Information Center

In the quadratic equation, y = ax[superscript 2] + bx + c, the equation y = bx + c is identified as the equation of the line tangent to the parabola at its y-intercept. This is extended to give a convenient method of graphing tangent lines at any point on the graph of a quadratic or a cubic equation. (Contains 5 figures.)

Carroll, William J.

2009-01-01

265

Problems in Presenting Quadratics as a Unifying Topic.  

ERIC Educational Resources Information Center

A sequence for teaching quadratic equations is presented. Considered are: multiplying arithmetic binomials, multiplying algebraic polynomials, reversing the process, missing terms, perfect squares, other special forms and diagrams, quadratic equations, completing the square, systematizing the process, the general form, graphing equations, and…

MacDonald, Theodore H.

1986-01-01

266

THE EFFECTIVENESS OF QUADRATS FOR MEASURING VASCULAR DIVERSITY: JOURNAL ARTICLE  

EPA Science Inventory

NRMRL-ADA- 98217 Jorgensen*, E.E., and Tunnell, S.J. The Effectiveness of Quadrats for Measuring Vascular Diversity. The Texas Journal of Science 53 (4):365-368 (2001). EPA/600/J-02/027. Quadrats are widely used for measuring characterist...

267

RQL: global placement via relaxed quadratic spreading and linearization  

Microsoft Academic Search

This paper describes a simple and effective quadratic placement algorithm called RQL. We show that a good quadratic placement, followed by local wirelength-driven spreading can produce excellent results on large-scale industrial ASIC designs. As opposed to the current top performing academic placers [4, 7, 11], RQL does not embed a linearization technique within the solver. Instead, it only requires a

Natarajan Viswanathan; Gi-Joon Nam; Charles J. Alpert; Paul Villarrubia; Haoxing Ren; Chris Chu

2007-01-01

268

RQL: Global Placement via Relaxed Quadratic Spreading and Linearization  

E-print Network

RQL: Global Placement via Relaxed Quadratic Spreading and Linearization Natarajan Viswanathan 1}@iastate.edu ABSTRACT This paper describes a simple and effective quadratic place- ment algorithm called RQL. We show,7,11], RQL does not embed a linearization tech- nique within the solver. Instead, it only requires a simpler

Chu, Chris C.-N.

269

Elastic Model Transitions Using Quadratic Inequality Constrained Least Squares  

NASA Technical Reports Server (NTRS)

A technique is presented for initializing multiple discrete finite element model (FEM) mode sets for certain types of flight dynamics formulations that rely on superposition of orthogonal modes for modeling the elastic response. Such approaches are commonly used for modeling launch vehicle dynamics, and challenges arise due to the rapidly time-varying nature of the rigid-body and elastic characteristics. By way of an energy argument, a quadratic inequality constrained least squares (LSQI) algorithm is employed to e ect a smooth transition from one set of FEM eigenvectors to another with no requirement that the models be of similar dimension or that the eigenvectors be correlated in any particular way. The physically unrealistic and controversial method of eigenvector interpolation is completely avoided, and the discrete solution approximates that of the continuously varying system. The real-time computational burden is shown to be negligible due to convenient features of the solution method. Simulation results are presented, and applications to staging and other discontinuous mass changes are discussed

Orr, Jeb S.

2012-01-01

270

Quadratic algebras for three-dimensional superintegrable systems  

SciTech Connect

The three-dimensional superintegrable systems with quadratic integrals of motion have five functionally independent integrals, one among them is the Hamiltonian. Kalnins, Kress, and Miller have proved that in the case of nondegenerate potentials with quadratic integrals of motion there is a sixth quadratic integral, which is linearly independent of the other integrals. The existence of this sixth integral implies that the integrals of motion form a ternary parafermionic-like quadratic Poisson algebra with five generators. In this contribution we investigate the structure of this algebra. We show that in all the nondegenerate cases there is at least one subalgebra of three integrals having a Poisson quadratic algebra structure, which is similar to the two-dimensional case.

Daskaloyannis, C., E-mail: daskalo@math.auth.gr; Tanoudis, Y. [Aristotle University of Thessaloniki, Mathematics Department (Greece)

2010-02-15

271

Optimal and suboptimal quadratic forms for noncentered Gaussian processes  

NASA Astrophysics Data System (ADS)

Individual random trajectories of stochastic processes are often analyzed by using quadratic forms such as time averaged (TA) mean square displacement (MSD) or velocity auto-correlation function (VACF). The appropriate quadratic form is expected to have a narrow probability distribution in order to reduce statistical uncertainty of a single measurement. We consider the problem of finding the optimal quadratic form that minimizes a chosen cumulant moment (e.g., the variance) of the probability distribution, under the constraint of fixed mean value. For discrete noncentered Gaussian processes, we construct the optimal quadratic form by using the spectral representation of cumulant moments. Moreover, we obtain a simple explicit formula for the smallest achievable cumulant moment that may serve as a quality benchmark for other quadratic forms. We illustrate the optimality issues by comparing the optimal variance with the variances of the TA MSD and TA VACF of fractional Brownian motion superimposed with a constant drift and independent Gaussian noise.

Grebenkov, Denis S.

2013-09-01

272

Adaptive mesh generation for edge-element finite element method  

SciTech Connect

An adaptive mesh generation method for two- and three-dimensional finite element methods using edge elements is proposed. Since the tangential component continuity is preserved when using edge elements, the strategy of creating new nodes is based on evaluation of the normal component of the magnetic vector potential across element interfaces. The evaluation is performed at the middle point of edge of a triangular element for two-dimensional problems or at the gravity center of triangular surface of a tetrahedral element for three-dimensional problems. At the boundary of two elements, the error estimator is the ratio of the normal component discontinuity to the maximum value of the potential in the same material. One or more nodes are set at the middle points of the edges according to the value of the estimator as well as the subdivision of elements where new nodes have been created. A final mesh will be obtained after several iterations. Some computation results of two- and three-dimensional problems using the proposed method are shown. {copyright} 2001 American Institute of Physics.

Tsuboi, Hajime; Gyimothy, Szabolcs

2001-06-01

273

A decentralized linear quadratic control design method for flexible structures  

NASA Technical Reports Server (NTRS)

A decentralized suboptimal linear quadratic control design procedure which combines substructural synthesis, model reduction, decentralized control design, subcontroller synthesis, and controller reduction is proposed for the design of reduced-order controllers for flexible structures. The procedure starts with a definition of the continuum structure to be controlled. An evaluation model of finite dimension is obtained by the finite element method. Then, the finite element model is decomposed into several substructures by using a natural decomposition called substructuring decomposition. Each substructure, at this point, still has too large a dimension and must be reduced to a size that is Riccati-solvable. Model reduction of each substructure can be performed by using any existing model reduction method, e.g., modal truncation, balanced reduction, Krylov model reduction, or mixed-mode method. Then, based on the reduced substructure model, a subcontroller is designed by an LQ optimal control method for each substructure independently. After all subcontrollers are designed, a controller synthesis method called substructural controller synthesis is employed to synthesize all subcontrollers into a global controller. The assembling scheme used is the same as that employed for the structure matrices. Finally, a controller reduction scheme, called the equivalent impulse response energy controller (EIREC) reduction algorithm, is used to reduce the global controller to a reasonable size for implementation. The EIREC reduced controller preserves the impulse response energy of the full-order controller and has the property of matching low-frequency moments and low-frequency power moments. An advantage of the substructural controller synthesis method is that it relieves the computational burden associated with dimensionality. Besides that, the SCS design scheme is also a highly adaptable controller synthesis method for structures with varying configuration, or varying mass and stiffness properties.

Su, Tzu-Jeng; Craig, Roy R., Jr.

1990-01-01

274

EVA assembly of large space structure element  

NASA Technical Reports Server (NTRS)

The results of a test program to assess the potential of manned extravehicular activity (EVA) assembly of erectable space trusses are described. Seventeen tests were conducted in which six "space-weight" columns were assembled into a regular tetrahedral cell by a team of two "space"-suited test subjects. This cell represents the fundamental "element" of a tetrahedral truss structure. The tests were conducted under simulated zero-gravity conditions. Both manual and simulated remote manipulator system modes were evaluated. Articulation limits of the pressure suit and zero gravity could be accommodated by work stations with foot restraints. The results of this study have confirmed that astronaut EVA assembly of large, erectable space structures is well within man's capabilities.

Bement, L. J.; Bush, H. G.; Heard, W. L., Jr.; Stokes, J. W., Jr.

1981-01-01

275

Quasicrystal-related phases in tetrahedral semiconductors: Structure, disorder, and ab initio calculations  

NASA Astrophysics Data System (ADS)

We show that special structural changes (phason atomic jumps) can transform the BC8 and R8 phases, known to occur in Si and Ge, into a phase with tetrahedral coordination. These structural changes are analogous to the BC8-R8 transformation. The phase has the body-centered-tetragonal symmetry (the space group C64h-I41/a) with 16 atoms per unit cell or 8 atoms per primitive cell and will be referred to as BT8. All the atoms occupy equivalent general positions x,y,z and there are three different tetrahedral bonds. It is shown that all three phases, BT8, BC8, and R8 may be considered as a result of phason-ordering transitions from a disordered phase with Ia3¯d symmetry. An infinite number of other structures with tetrahedral bonding (ordered and disordered) can be constructed this way. The phason jumps are typical of these phases because they are related to hypothetical icosahedral quasicrystals. In particular, the BC8 and the recently suggested BC32 structure may be considered as 1/0 and 1/1 cubic approximants of the same quasicrystal. We present a detailed ab initio study of BT8 and BC32 phases in silicon within density-functional theory in the local-density approximation. Our results show that the energetics and diffraction patterns of the BT8 phase are very similar to those of the BC8 and R8 phases. We conclude that the available diffraction data do not exclude the existence of the BT8 phase. In contrast, the energy of the BC32 structure is significantly larger (for positive pressure), and the existence of this phase is therefore questionable. The pressure dependence of the bond lengths, angles, and the lattice parameters of the BT8 phase is investigated. Our estimation of the energy barrier for phason defect formation in the BC8 phase is about 0.12 eV per jumping atom and the energy of the defect is very small (less then 0.02 eV per jumping atom), therefore this type of defect could be present in real samples. Finally, we show that the computed elastic constants of the BC8 phase are almost isotropic as expected for the approximants of icosahedral quasicrystals.

Dmitrienko, V. E.; Kléman, M.; Mauri, F.

1999-10-01

276

New insight into the structure of nanocrystalline ferrihydrite: EXAFS evidence for tetrahedrally coordinated iron(III)  

NASA Astrophysics Data System (ADS)

Ferrihydrite (Fh) is a short-range ordered nanocrystalline iron(III) (oxyhydr)oxide that has been recognized to play an important role in contaminant sequestration and in iron cycling in geological and biological systems. Despite intensive research for the two last decades, the structure of Fh is still a subject of debate. In the present study, we report extended X-ray absorption fine structure (EXAFS) spectroscopy data collected on a large set of ferrihydrites and model compounds samples including especially nano-crystalline maghemite (Mh), goethite (Gt), and akaganeite (Aka). This set of EXAFS data recorded at cryogenic temperature over a wide energy range allows us to precisely determine the Fe-O mean distance () in the first coordination shell of iron for this large set of iron (oxyhydr)oxides. Our EXAFS analysis includes both classical shell-by-shell fits of Fourier-filtered and unfiltered data as well as analysis of Fe-O distance distribution in the first coordination shell of iron using the Landweber iteration method. determined by these complementary EXAFS analyses are similar: is shorter in Mh (1.96 ± 0.01 Å) that contains 37.5% of tetrahedral iron, than in Gt (2.01 ± 0.01 Å), Aka (2.00 ± 0.01 Å) and hematite (Hm) (2.01 ± 0.01 Å) that do not contain tetrahedral iron. for the five Fh samples investigated (1.97 ± 0.01 Å) was found to be slightly longer than in Mh and significantly shorter than those in Gt, Aka and Hm. This short distance in Fh indicates the presence of significant amount of tetrahedrally coordinated iron(III) in all Fh samples studied, which ranges between 20 ± 5% and 30 ± 5% of total iron. In addition, our analysis of Fe-Fe distances observed by EXAFS is consistent with a Keggin-like motif at a local scale (˜5 Å) in the Fh structure.

Maillot, Fabien; Morin, Guillaume; Wang, Yuheng; Bonnin, Dominique; Ildefonse, Philippe; Chaneac, Corinne; Calas, Georges

2011-05-01

277

The electronic transport mechanism in amorphous tetrahedrally-coordinated carbon films  

SciTech Connect

The electronic transport mechanism in tetrahedrally coordinated amorphous carbon was investigated using measurements of stress relaxation, thermal evolution of electrical conductivity, and temperature dependent conductivity measurements. Stress relaxation measurements were used to determine the change in 3-fold coordinated carbon concentration, and the electrical conductivity was correlated to this change. It was found that the conductivity was exponentially proportional to the change in 3-fold concentration, indicating a tunneling or hopping transport mechanism. It was also found that the activation energy for transport decreased with increasing anneal temperature. The decrease in activation energy was responsible for the observed increase in electrical conductivity. A model is described wherein the transport in this material is described by thermally activated conduction along 3-fold linkages or chains with variable range and variable orientation hopping. Thermal annealing leads to chain ripening and a reduction in the activation energy for transport.

Sullivan, J.P.; Friedmann, T.A.; Dunn, R.G.; Stechel, E.B.; Schultz, P.A.

1998-02-01

278

Electric dipole moments in {sup 230,232}U and implications for tetrahedral shapes  

SciTech Connect

The nuclei {sup 230}U and {sup 232}U were populated in the compound nucleus reactions {sup 232}Th({alpha},6n) and {sup 232}Th({alpha},4n), respectively. Gamma rays from these nuclei were observed in coincidence with a recoil detector. A comprehensive set of in-band E2 transitions were observed in the lowest lying negative-parity band of {sup 232}U while one E2 transition was also observed for {sup 230}U. These allowed B(E1;I{sup -{yields}}I{sup +}-1)/B(E2;I{sup -{yields}}I{sup -}-2) ratios to be extracted and compared with systematics. The values are similar to those of their Th and Ra isotones. The possibility of a tetrahedral shape for the negative-parity U bands appears difficult to reconcile with the measured Q{sub 2} values for the isotone {sup 226}Ra.

Ntshangase, S. S. [Department of Physics, University of Cape Town, Rondebosch 7700 (South Africa); iThemba LABS, P.O. Box 722, Somerset West 7129 (South Africa); Bark, R. A.; Datta, P.; Lawrie, E. A.; Lawrie, J. J.; Lieder, R. M.; Mullins, S. M. [iThemba LABS, P.O. Box 722, Somerset West 7129 (South Africa); Aschman, D. G.; Mohammed, H.; Stankiewicz, M. A. [Department of Physics, University of Cape Town, Rondebosch 7700 (South Africa); Bvumbi, S.; Masiteng, P. L.; Shirinda, O. [iThemba LABS, P.O. Box 722, Somerset West 7129 (South Africa); Department of Physics, University of the Western Cape, Bellville ZA-7535 (South Africa); Davidson, P. M.; Nieminen, P.; Wilson, A. N. [Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200 (Australia); Dinoko, T. S.; Sharpey-Shafer, J. F. [Department of Physics, University of the Western Cape, Bellville ZA-7535 (South Africa); Elbasher, M. E. A. [iThemba LABS, P.O. Box 722, Somerset West 7129 (South Africa); Department of Physics, University of Stellenbosch, 7601 Matieland (South Africa); Juhasz, K. [Department of Information Technology, University of Debrecen, Egyetem ter 1, H-4032 Debrecen (Hungary)

2010-10-15

279

Comparative morphology of configurations with reduced part count derived from the octahedral-tetrahedral truss  

NASA Technical Reports Server (NTRS)

Morphology (the study of structure and form) of the octahedral-tetrahedral (octet) truss is described. Both the geometry and symmetry of the octet truss are considered. Morphological techniques based on symmetry operations are presented which enable the derivation of reduced-part-count truss configurations from the octet truss by removing struts and nodes. These techniques are unique because their Morphological origination and they allow for the systematic generation and analysis of a large variety of structures. Methods for easily determining the part count and redundancy of infinite truss configurations are presented. Nine examples of truss configurations obtained by applying the derivation techniques are considered. These configurations are structurally stable while at the same time exhibiting significant reductions in part count. Some practical and analytical considerations, such as structural performance, regarding the example reduced-part-count truss geometries are briefly discussed.

Lalvani, Haresh; Collins, Timothy J.

1991-01-01

280

Released Plasmonic Electric Field of Ultrathin Tetrahedral-Amorphous-Carbon Films Coated Ag Nanoparticles for SERS  

NASA Astrophysics Data System (ADS)

We have demonstrated the plasmonic characteristics of an ultrathin tetrahedral amorphous carbon (ta-C) film coated with Ag nanoparticles. The simulation result shows that, under resonant and non-resonant excitations, the strongest plasmonic electric field of 1 nm ta-C coated Ag nanoparticle is not trapped within the ta-C layer but is released to its outside surface, while leaving the weaker electric field inside ta-C layer. Moreover, this outside plasmonic field shows higher intensity than that of uncoated Ag nanoparticle, which is closely dependent on the excitation wavelength and size of Ag particles. These observations are supported by the SERS measurements. We expect that the ability for ultrathin ta-C coated Ag nanoparticles as the SERS substrates to detect low concentrations of target biomolecules opens the door to the applications where it can be used as a detection tool for integrated, on-chip devices.

Liu, Fanxin; Tang, Chaojun; Zhan, Peng; Chen, Zhuo; Ma, Hongtao; Wang, Zhenlin

2014-03-01

281

Photonuclear sum rules and the tetrahedral configuration of {sup 4}He  

SciTech Connect

Three well-known photonuclear sum rules (SR), i.e., the Thomas-Reiche-Kuhn, the bremsstrahlungs and the polarizability SR are calculated for {sup 4}He with the realistic nucleon-nucleon potential Argonne V18 and the three-nucleon force Urbana IX. The relation between these sum rules and the corresponding energy weighted integrals of the cross section is discussed. Two additional equivalences for the bremsstrahlungs SR are given, which connect it to the proton-neutron and neutron-neutron distances. Using them, together with our result for the bremsstrahlungs SR, we find a deviation from the tetrahedral symmetry of the spatial configuration of {sup 4}He. The possibility to access this deviation experimentally is discussed.

Gazit, Doron; Barnea, Nir [Racah Institute of Physics, Hebrew University, 91904 Jerusalem (Israel); Bacca, Sonia [Gesellschaft fuer Schwerionenforschung, Planckstr. 1, D-64291 Darmstadt (Germany); Leidemann, Winfried; Orlandini, Giuseppina [Department of Physics, George Washington University, Washington DC 20052 (United States); Istituto Nazionale di Fisica Nucleare, Gruppo Collegato di Trento (Italy)

2006-12-15

282

Temperature dependence of the mechanical properties of tetrahedrally coordinated amorphous carbon thin films  

NASA Astrophysics Data System (ADS)

The complete elastic properties of tetrahedrally coordinated amorphous carbon (ta-C) thin films have been measured in the temperature range of 300-873K. Flexural and torsional mechanical oscillators were fabricated from ta-C, and using the resonant frequency of the oscillators as a function of temperature, we calculated the temperature-dependent Young's and shear moduli (658±24 and 271±6.6GPa, at 300K, respectively). From these values, we calculated the bulk modulus, Poisson's ratio, and the elastic stiffness and compliance constants as a function of temperature. In addition, the temperature dependence of the coefficient of thermal expansion of ta-C was determined using a wafer curvature technique.

Czaplewski, David A.; Sullivan, J. P.; Friedmann, T. A.; Wendt, J. R.

2005-10-01

283

Programmable engineering of a biosensing interface with tetrahedral DNA nanostructures for ultrasensitive DNA detection.  

PubMed

Self-assembled DNA nanostructures with precise sizes allow a programmable "soft lithography" approach to engineer the interface of electrochemical DNA sensors. By using millimeter-sized gold electrodes modified with several types of tetrahedral DNA nanostructures (TDNs) of different sizes, both the kinetics and thermodynamics of DNA hybridization were profoundly affected. Because each DNA probe is anchored on an individual TDN, its lateral spacing and interactions are finely tuned by the TDN size. By simply varying the size of the TDNs, the hybridization time was decreased and the hybridization efficiency was increased. More significantly, the detection limit for DNA detection was tuned over four orders of magnitude with differentially nanostructured electrodes, and achieved attomolar sensitivity with polymeric enzyme amplification. PMID:25556850

Lin, Meihua; Wang, Jingjing; Zhou, Guobao; Wang, Jianbang; Wu, Na; Lu, Jianxin; Gao, Jimin; Chen, Xiaoqing; Shi, Jiye; Zuo, Xiaolei; Fan, Chunhai

2015-02-01

284

Electrochemical switching with 3D DNA tetrahedral nanostructures self-assembled at gold electrodes.  

PubMed

Nanomechanical switching of functional three-dimensional (3D) DNA nanostructures is crucial for nanobiotechnological applications such as nanorobotics or self-regulating sensor and actuator devices. Here, DNA tetrahedral nanostructures self-assembled onto gold electrodes were shown to undergo the electronically addressable nanoswitching due to their mechanical reconfiguration upon external chemical stimuli. That enables construction of robust surface-tethered electronic nanodevices based on 3D DNA tetrahedra. One edge of the tetrahedron contained a partially self-complementary region with a stem-loop hairpin structure, reconfigurable upon hybridization to a complementary DNA (stimulus DNA) sequence. A non-intercalative ferrocene (Fc) redox label was attached to the reconfigurable tetrahedron edge in such a way that reconfiguration of this edge changed the distance between the electrode and Fc. PMID:24802004

Abi, Alireza; Lin, Meihua; Pei, Hao; Fan, Chunhai; Ferapontova, Elena E; Zuo, Xiaolei

2014-06-11

285

EPR parameters and defect structure of the tetrahedral Ti3+ defect center in beryl crystal  

NASA Astrophysics Data System (ADS)

The EPR parameters (g factors gi and hyperfine structure constants Ai, where iDx, y, z) of Ti3+ ion at the tetrahedral Si4+ site of beryl crystals are calculated within the rhombic symmetry approximation from the high-order perturbation formulas based on the two-spin-orbit (SO)-parameter model. In these formulas both the contribution due to the SO coupling parameter of the central 3d1 ion and that of ligand ions are considered. From the calculations, the defect structure of the Ti3+ defect center in beryl crystal is estimated and the EPR parameters gx, gy, gz and Ay are reasonably explained. The values of the parameters Ax and Az (which were not reported) are suggested and remain to be checked by the further experimental studies.

Yang, Mei; Xiao-Xuan, Wu; Wen-Chen, Zheng

286

Spectroscopic characterization of carbon chains in nanostructured tetrahedral carbon films synthesized by femtosecond pulsed laser deposition.  

PubMed

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120 fs and 30 ns pulsed laser ablation of graphite. The presence of sp(1) chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200 cm(-1) in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp(1)-, sp(2)-, and sp(3)-bonded carbon are approximately 6%, approximately 43%, and approximately 51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp(2) clusters and sp(1) chains. PMID:17461657

Hu, A; Lu, Q-B; Duley, W W; Rybachuk, M

2007-04-21

287

Spectroscopic characterization of carbon chains in nanostructured tetrahedral carbon films synthesized by femtosecond pulsed laser deposition  

NASA Astrophysics Data System (ADS)

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120fs and 30ns pulsed laser ablation of graphite. The presence of sp1 chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200cm-1 in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp1-, sp2-, and sp3-bonded carbon are ?6%, ?43%, and ?51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp2 clusters and sp1 chains.

Hu, A.; Lu, Q.-B.; Duley, W. W.; Rybachuk, M.

2007-04-01

288

Growth and band gap of the filled tetrahedral semiconductor Li 3AlP 2  

NASA Astrophysics Data System (ADS)

AlP-like Li 3AlP 2 crystallizes in an orthorhombic structure in contrast to cubic nitride semiconductors such as Li 3AlN 2 and Li 3GaN 2. Li 3AlP 2 can be viewed as the zincblende-like (Li 0.5Al 0.5P) - lattice filled with He-like Li + ions at the empty tetrahedral sites. Li 3AlP 2 is grown by direct reaction of Li, Al, and P in an evacuated quartz ampoule. A typical reaction temperature is 1073 K and the temperature is maintained for 100 h. As-grown crystals, which are yellow in color, are confirmed to be a single phase of Li 3AlP 2 (space group: Ibca) with a=11.43 Å, b=11.93 Å, and c=12.03 Å by a powder X-ray diffraction method. Twelve Raman peaks are observed, which are consistent with 12 Raman active modes (3A g+3B 1g+3B 2g+3B 3g) evaluated by a factor group analysis for Li 3AlP 2. The band gap of as-grown Li 3AlP 2 evaluated using photoacoustic spectroscopy is ˜2.75 eV. The gap value is slightly larger than that of AlP ( Eg=2.43 eV), suggesting that the band gap of Li 3AlP 2 is essentially attributed to the six ionic Li-P bonds in the {1}/{8}-sublattice as well as the Li-N bonds in the filled tetrahedral semiconductors Li 3AlN 2 and Li 3GaN 2.

Kuriyama, K.; Anzawa, J.; Kushida, K.

2008-04-01

289

Shock Wave Admissibility for Quadratic Conservation Laws  

NASA Astrophysics Data System (ADS)

In this work we present a new approach to the study of the stability of admissible shock wave solutions for systems of conservation laws that change type. The systems we treat have quadratic flux functions. We employ the fundamental wave manifold W as a global framework to characterize shock waves that comply with the viscosity admissibility criterion. Points of W parametrize dynamical systems associated with shock wave solutions. The region of W comprising admissible shock waves is bounded by the loci of structurally unstable dynamical systems. Explicit formulae are presented for the loci associated with saddle-node, Hopf, and Bogdanov-Takens bifurcation, and with straight-line heteroclinic connections. Using Melnikov's integral analysis, we calculate the tangent to the homoclinic part of the admissibility boundary at Bogdanov-Takens points of W. Furthermore, using numerical methods, we explore the heteroclinic loci corresponding to curved connecting orbits and the complete homoclinic locus. We find the region of admissible waves for a generic, two-dimensional slice of the fundamental wave manifold, and compare it with the set of shock points that comply with the Lax admissibility criterion, thereby elucidating how this criterion differs from viscous profile admissibility.

Canic, S.; Plohr, B. J.

290

A Quadratic Closure for Compressible Turbulence  

SciTech Connect

We have investigated a one-point closure model for compressible turbulence based on third- and higher order cumulant discard for systems undergoing rapid deformation, such as might occur downstream of a shock or other discontinuity. In so doing, we find the lowest order contributions of turbulence to the mean flow, which lead to criteria for Adaptive Mesh Refinement. Rapid distortion theory (RDT) as originally applied by Herring closes the turbulence hierarchy of moment equations by discarding third order and higher cumulants. This is similar to the fourth-order cumulant discard hypothesis of Millionshchikov, except that the Millionshchikov hypothesis was taken to apply to incompressible homogeneous isotropic turbulence generally, whereas RDT is applied only to fluids undergoing a distortion that is 'rapid' in the sense that the interaction of the mean flow with the turbulence overwhelms the interaction of the turbulence with itself. It is also similar to Gaussian closure, in which both second and fourth-order cumulants are retained. Motivated by RDT, we develop a quadratic one-point closure for rapidly distorting compressible turbulence, without regard to homogeneity or isotropy, and make contact with two equation turbulence models, especially the K-{var_epsilon} and K-L models, and with linear instability growth. In the end, we arrive at criteria for Adaptive Mesh Refinement in Finite Volume simulations.

Futterman, J A

2008-09-16

291

Models for the 3D singular isotropic oscillator quadratic algebra  

SciTech Connect

We give the first explicit construction of the quadratic algebra for a 3D quantum superintegrable system with nondegenerate (4-parameter) potential together with realizations of irreducible representations of the quadratic algebra in terms of differential-differential or differential-difference and difference-difference operators in two variables. The example is the singular isotropic oscillator. We point out that the quantum models arise naturally from models of the Poisson algebras for the corresponding classical superintegrable system. These techniques extend to quadratic algebras for superintegrable systems in n dimensions and are closely related to Hecke algebras and multivariable orthogonal polynomials.

Kalnins, E. G., E-mail: math0236@waikato.ac.n [University of Waikato, Department of Mathematics (New Zealand); Miller, W.; Post, S. [University of Minnesota, School of Mathematics (United States)

2010-02-15

292

Numerical approximation for the infinite-dimensional discrete-time optimal linear-quadratic regulator problem  

NASA Technical Reports Server (NTRS)

An abstract approximation framework is developed for the finite and infinite time horizon discrete-time linear-quadratic regulator problem for systems whose state dynamics are described by a linear semigroup of operators on an infinite dimensional Hilbert space. The schemes included the framework yield finite dimensional approximations to the linear state feedback gains which determine the optimal control law. Convergence arguments are given. Examples involving hereditary and parabolic systems and the vibration of a flexible beam are considered. Spline-based finite element schemes for these classes of problems, together with numerical results, are presented and discussed.

Gibson, J. S.; Rosen, I. G.

1986-01-01

293

Determination of Antiferromagnetic Exchange Coupling in the Tetrahedral Thiolate-Bridged Diferrous Complex [Fe2(SEt)6]2-  

E-print Network

Determination of Antiferromagnetic Exchange Coupling in the Tetrahedral Thiolate-Bridged Diferrous in the all-ferrous state of the nitrogenase P-cluster provides an imperative for determination of exchange K) indicates that no excited orbital states are appreciably populated at temperatures less than 300

Osterloh, Frank

294

Elasticity, strength, and toughness of single crystal silicon carbide, ultrananocrystalline diamond, and hydrogen-free tetrahedral amorphous  

E-print Network

Elasticity, strength, and toughness of single crystal silicon carbide, ultrananocrystalline diamond report the mechanical properties of three emerging materials in thin film form: single crystal silicon carbide 3C-SiC , ultrananocrystalline diamond, and hydrogen-free tetrahedral amorphous carbon

Espinosa, Horacio D.

295

Vibrations of Tetrahedral Pentatomic Molecules. Part I. Potential Energy. Part II. Kinetic Energy and Normal Frequencies of Vibration  

Microsoft Academic Search

Part I. It is shown that the most general potential energy function consistent with tetrahedral symmetry involves five force constants, also that with a suitable choice of variables this expression may be written in a quite simple form convenient for the discussion of different types of vibration. Special cases of potential energy such as the \\

Jenny E. Rosenthal

1934-01-01

296

A theory of mechanical relaxation of substitutional-interstitial (tetrahedral) atom complexes in the b.c.c. lattice  

Microsoft Academic Search

The relaxation of an atom pair consisting of a substitutional atom and a tetrahedral interstitial atom in the b.c.c. lattice is studied theoretically. The pair exhibits three relaxation modes: one T2g and two Eg modes. The relative relaxation magnitude of the two Eg modes depends strongly on the anisotropy of the ? tensor. Experimental results of internal friction studies of

Masahiro Koiwa; Shunya Ishioka; G. Cannelli; R. Cantelli

1983-01-01

297

Regular zeros of quadratic maps and their application  

SciTech Connect

Sufficient conditions for the existence of regular zeros of quadratic maps are obtained. Their applications are indicated to certain problems of analysis related to the inverse function theorem in a neighbourhood of an abnormal point. Bibliography: 13 titles.

Arutyunov, Aram V; Karamzin, Dmitry Yu

2011-06-30

298

Integrable Hamiltonian systems and interactions through quadratic constraints  

Microsoft Academic Search

On-invariant classical relativistic field theories in one time and one space dimension with interactions that are entirely due to quadratic constraints are shown to be closely related to integrable Hamiltonian systems.

K. Pohlmeyer

1976-01-01

299

Geometric Procedures for Graphing the General Quadratic Equation.  

ERIC Educational Resources Information Center

How tedious algebraic manipulations for simplifying general quadratic equations can be supplemented with simple geometric procedures is discussed. These procedures help students determine the type of conic and its axes and allow a graph to be sketched quickly. (MNS)

DeTemple, Duane W.

1984-01-01

300

Consensus over Ring Networks as a Quadratic Optimal Control Problem  

E-print Network

Consensus over Ring Networks as a Quadratic Optimal Control Problem J. A. Rogge J. A. K. Suykens-mail: {jonathan.rogge,dirk.aeyels}@ugent.be) K. U. Leuven, ESAT-SCD, Kasteelpark Arenberg 10, B-3001 Leuven

301

Towards Practical Non-interactive Public Key Cryptosystems Using Non-maximal Imaginary Quadratic Orders (Extended Abstract)  

Microsoft Academic Search

We present a new non-interactive public key distribution system based on the class group of a non-maximal imaginary quadratic\\u000a order Cl(?p). The main advantage of our system over earlier proposals based on (?\\/n?). [19],[21] is that embedding id information into group elements in a cyclic subgroup of the class group is easy (straight-forward embedding\\u000a into prime ideals suffices) and secure,

Detlef Hühnlein; Damian Weber

302

AdS waves as exact solutions to quadratic gravity  

SciTech Connect

We give an exact solution of the quadratic gravity in D dimensions. The solution is a plane-fronted wave metric with a cosmological constant. This metric solves not only the full quadratic gravity field equations but also the linearized ones which include the linearized equations of the recently found critical gravity. A subset of the solutions change the asymptotic structure of the anti-de Sitter space due to their logarithmic behavior.

Guellue, Ibrahim; Sisman, Tahsin Cagri; Tekin, Bayram [Department of Physics, Middle East Technical University, 06531 Ankara (Turkey); Guerses, Metin [Department of Mathematics, Faculty of Sciences Bilkent University, 06800 Ankara (Turkey)

2011-04-15

303

RQL: Global Placement via Relaxed Quadratic Spreading and Linearization  

Microsoft Academic Search

This paper describes a simple and effective quadratic place- ment algorithm called RQL. We show that a good quadratic placement, followed by local wirelength-driven spreading can produce excellent results on large-scale industrial ASIC de- signs. As opposed to the current top performing academic placers (4,7,11), RQL does not embed a linearization tech- nique within the solver. Instead, it only requires

Natarajan Viswanathan; Gi-joon Nam; Charles J. Alpert; Paul Villarrubia; Haoxing Ren; Chris C. N. Chu

2007-01-01

304

Fast algorithms for convex quadratic programming and multicommodity flows  

Microsoft Academic Search

In the first part of the paper, we extend Karmarkar's interior point method to give an algorithm for Convex Quadratic Programming which requires O(Na'~7(logL)(logN)L) arithmetic operations. At each iteration, Karmarkar's method locally minimizes the linear (convex) numerator of a transformed objective function in the transformed domain. However, in the case of Convex Quadratic Programming the numerator of the transformed objective

Sanjiv Kapoor; Pravin M. Vaidya

1986-01-01

305

Adaptive mesh refinement for time-domain electromagnetics using vector finite elements :a feasibility study.  

SciTech Connect

This report investigates the feasibility of applying Adaptive Mesh Refinement (AMR) techniques to a vector finite element formulation for the wave equation in three dimensions. Possible error estimators are considered first. Next, approaches for refining tetrahedral elements are reviewed. AMR capabilities within the Nevada framework are then evaluated. We summarize our conclusions on the feasibility of AMR for time-domain vector finite elements and identify a path forward.

Turner, C. David; Kotulski, Joseph Daniel; Pasik, Michael Francis

2005-12-01

306

Solutions of the Schrödinger equation with inversely quadratic Hellmann plus inversely quadratic potential using Nikiforov-Uvarov method  

NASA Astrophysics Data System (ADS)

By using the Nikiforov-Uvarov (NU) method, the Schrödinger equation has been solved for the interaction of inversely quadratic Hellmann (IQHP) and inversely quadratic potential (IQP) for any angular momentum quantum number, l. The energy eigenvalues and their corresponding eigenfunctions have been obtained in terms of Laguerre polynomials. Special cases of the sum of these potentials have been considered and their energy eigenvalues also obtained.

Ita, B. I.; Ehi-Eromosele, C. O.; Edobor-Osoh, A.; Ikeuba, A. I.

2014-11-01

307

Discontinuous Finite Element S{sub N} Methods on 3-D Unstructured Grids  

SciTech Connect

Discontinuous finite element methods for the S{sub N} equations on 3-D unstructured tetrahedral and hexahedral meshes are presented. Solution Techniques including Source Iteration and diffusion-synthetic acceleration are described. Numerical results are presented which demonstrate the accuracy and efficiency of these methods.

Wareing, T.A.; McGhee, J.M.; Morel, J.E.; Pautz, S.D.

1999-09-27

308

Quadratic 0-1 programming: Geometric methods and duality analysis  

NASA Astrophysics Data System (ADS)

The unconstraint quadratic binary problem (UBQP), as a classical combinatorial problem, finds wide applications in broad field and human activities including engineering, science, finance, etc. The NP-hardness of the combinatorial problems makes a great challenge to solve the ( UBQP). The main purpose of this research is to develop high performance solution method for solving (UBQP) via the geometric properties of the objective ellipse contour and the optimal solution. This research makes several contributions to advance the state-of-the-art of geometric approach of (UBQP). These contributions include both theoretical and numerical aspects as stated below. In part I of this dissertation, certain rich geometric properties hidden behind quadratic 0-1 programming are investigated. Especially, we derive new lower bounding methods and variable fixation techniques for quadratic 0-1 optimization problems by investigating geometric features of the ellipse contour of a (perturbed) convex quadratic function. These findings further lead to some new optimality conditions for quadratic 0-1 programming. Integrating these novel solution schemes into a proposed solution algorithm of a branch-and-bound type, we obtain promising preliminary computational results. In part II of this dissertation, we present new results of the duality gap between the binary quadratic optimization problem and its Lagrangian dual. We first derive a necessary and sufficient condition for the zero duality gap and discuss its relationship with the polynomial solvability of the problem. We then characterize the zeroness of duality gap by the distance, delta, between the binary set and certain affine space C. Finally, we discuss a computational procedure of the distance delta. These results provide new insights into the duality gap and polynomial solvability of binary quadratic optimization problems.

Liu, Chunli

309

Stress, microstructure and mechanical properties of graded multilayer tetrahedral amorphous carbon films  

NASA Astrophysics Data System (ADS)

Tetrahedral amorphous carbon (ta-C) films deposited using a filtered cathodic vacuum arc (FCVA) system, have high intrinsic stress which limits their application as protective coatings. To reduce the film stress and to improve the adhesion, a multilayer structure is deposited at a gradient substrate negative bias from 1500 V to 80 V. This paper investigates the stress, microstructure and nano-mechanical properties of graded multilayer ta-C film on Si substrates. Compared with that of single-layer films deposited at optimised bias, the graded multilayer film has low stress without a decline in hardness and Young’s modulus. Microstructural evaluation of the multilayer film using visible Raman spectra shows that the average content of the sp3 bonds of the multilayer film remain at a high level. Nanoscratch testing illustrates favorable scratch resistance and good adhesion of the multilayer film. Scanning electron microscope (SEM) observation confirms the collapse of the film surface along the scratching trace. Finally, deposition on single crystal germanium substrates of a durable coating ˜ 1100 nm thick, and composed of three graded multilayer films is demonstrated.

Han, Xiao; Zhu, Jiaqi; Han, Jiecai; Tan, Manlin; Gao, Wei

2008-06-01

310

Residual stress and Raman spectra of laser deposited highly-tetrahedral-coordinated-amorphous-carbon films  

SciTech Connect

We are studying carbon thin films by using a pulsed excimer laser to ablate pyrolytic graphite targets to form highly tetrahedral coordinated amorphous carbon ({alpha}t-C) films. These films have been grown on room temperature p-type Si (100) substrates without the intentional incorporation of hydrogen. In order to understand and optimize the growth of {alpha}t-C films, parametric studies of the growth parameters have been performed. We have also introduced various background gases (H{sub 2}, N{sub 2} and Ar) and varied the background gas pressure during deposition. The residual compressive stress levels in the films have been measured and correlated to changes in the Raman spectra of the {alpha}t-C band near 1565 cm{sup {minus}1}. The residual compressive stress falls with gas pressure, indicating a decreasing atomic sp{sup 3}-bonded carbon fraction. We find that reactive gases such as hydrogen and nitrogen significantly alter the Raman spectra at higher pressures. These effects are due to a combination of chemical incorporation of nitrogen and hydrogen into the film as well as collisional cooling of the ablation plume. In contrast, films grown in non-reactive Ar background gases show much less dramatic changes in the Raman spectra at similar pressures.

Friedmann, T.A.; Siegal, M.P.; Tallant, D.R.; Simpson, R.L.; Dominguez, F.

1994-05-01

311

The deposition of a thick tetrahedral amorphous carbon film by argon ion bombardment  

NASA Astrophysics Data System (ADS)

The argon (Ar) ion bombardment is used in the deposition of a thick multilayer tetrahedral amorphous carbon (ta-C) films. The bonding structure and surface morphology of the ta-C films are modified when the films are bombarded by Ar ion with different energy. Visible Raman spectroscopy and X-ray photoelectron spectroscopy is used to study the modification respectively. The results show that surface layer is etched, the bonding structure of the films is totally modified, and some sp3 bonds convert to sp2 bonds in the surface layer of the films. The sp2 cluster of the bulk increases with the increment of Ar ion energy. Hence, a soft top layer on the films is formed and the stress of the bulk is released. The RMS of roughness and etching pits on the surface of films were increased with the increment of the bombarding energy of Ar ion, which can increase the adhesion between layers. These are very important to deposit thick ta-C film. The surface morphology is tested by AFM. The RMS roughness of thick ta-C film is about 0.54 nm. Using visible Raman spectroscopy, the sp3 fraction of as-deposited ta-C film with 1 ?m thickness is estimated to be about 70%.

Liang, Han; Delian, Liu; Xian, Chen; Li, Yang; Yuqing, Zhao

2012-03-01

312

Output-Adaptive Tetrahedral Cut-Cell Validation for Sonic Boom Prediction  

NASA Technical Reports Server (NTRS)

A cut-cell approach to Computational Fluid Dynamics (CFD) that utilizes the median dual of a tetrahedral background grid is described. The discrete adjoint is also calculated, which permits adaptation based on improving the calculation of a specified output (off-body pressure signature) in supersonic inviscid flow. These predicted signatures are compared to wind tunnel measurements on and off the configuration centerline 10 body lengths below the model to validate the method for sonic boom prediction. Accurate mid-field sonic boom pressure signatures are calculated with the Euler equations without the use of hybrid grid or signature propagation methods. Highly-refined, shock-aligned anisotropic grids were produced by this method from coarse isotropic grids created without prior knowledge of shock locations. A heuristic reconstruction limiter provided stable flow and adjoint solution schemes while producing similar signatures to Barth-Jespersen and Venkatakrishnan limiters. The use of cut-cells with an output-based adaptive scheme completely automated this accurate prediction capability after a triangular mesh is generated for the cut surface. This automation drastically reduces the manual intervention required by existing methods.

Park, Michael A.; Darmofal, David L.

2008-01-01

313

Thermoelectric power of nitrogen-incorporated tetrahedral amorphous-carbon films  

NASA Astrophysics Data System (ADS)

Tetrahedral amorphous-carbon (ta-C) films were deposited using a filtered cathodic vacuum arc in which nitrogen was incorporated up to an atomic fraction (fN) of 30%. Electrical conductivity and specially thermoelectric power (S) have been performed over a wide range of temperature. The room-temperature conductivity of these samples initially increases with fN up to several orders of magnitude compared to that of ta-C, followed by no dramatic change at higher nitrogen concentration. The sign of the S is negative in the samples with fN below ˜17%, then changes to a positive value with a higher fN. From thermal annealing of the nitrogenated samples a change of the sign of S and its dependence on fN has been analyzed. The small values of both room-temperature S and small variation of conductivity at high fN in all the samples suggest that electrical properties of these films are controlled by compensation of defects.

Bhattacharyya, Somnath; Richter, F.; Starke, U.; Griessmann, H.; Heinrich, A.

2001-12-01

314

Tetrahedral oxyanions-assisted supramolecular assemblies of pyridine-based tectons into hydrogen-bonding networks  

NASA Astrophysics Data System (ADS)

The systematic research has been done into structural variations of supramolecular architectures by the self assembly of two pyridine-based potential anion receptors, 1-(4-pyridyl)piperazine (L1) and 4-pyrrolidinopyridine (L2), and different inorganic acids (HCl, HBr, HI, HNO3, HClO4, HIO4, H2SO4 and H3PO4). The formation of four fascinating salts, i.e. (H2L12+)·(H2PO4-)2 (1), (H2L12+)·(ClO4-)2 (2), (HL2+)·(ClO4-) (3) and (HL2+)·(IO4-) (4), indicates that N-heterocyclic L1 and L2 are prone to cocrystallize with tetrahedral oxyanions and anionic topologies play a crucial role in the crystallization process. Structural analyses reveal that various intermolecular ring motifs have been generated by robust hydrogen-bonding interactions in compounds 1-4. In particular, interesting substructures were observed in H2PO4- from salts 1 due to its polytopic potential hydrogen-bonding donor and acceptor oxygen atoms, including ring motifs, 1D ribbons and 2D supramolecular framework. Much to our surprise, crystal 4 proves to be a member of few supramolecular salts crystallizing with IO4- anion according to the Cambridge Structure Database (CSD).

Ding, Xue-Hua; Wang, Shi; Li, Yong-Hua; Huang, Wei

2015-01-01

315

Quantitative measure of tetrahedral-sp3 geometries in amorphous phase-change alloys  

NASA Astrophysics Data System (ADS)

Phase change or Ovonic memory technology has gained much interest in the past decade as a viable solution for the rapid increase in the demand for memory storage. This unique technology, first proposed by S. Ovshinsky in 1968, is based on storing information on the crystalline and amorphous phases of a material. The most common phase-change materials (PCMs) use chalcogenide alloys such as the Ge2Sb2Te5 (GST225). However, while the structure of its crystalline phase is relatively well characterized as consisting of a rhombohedrally distorted rock-salt lattice, the corresponding amorphous phase remains still poorly understood. Here, we show that Sn119 Mössbauer spectroscopy and angular constraint counting of simulated structures can provide a quantitative measure of the sp3 tetrahedral fraction of Ge or Si cation in amorphous phase-change binary tellurides GexTe1-x and SixTe1-x. This represents the first quantitative estimate of such local structures, and reveals the fraction to be nearly 50%, while also revealing implications for the phase-change mechanism itself.

Micoulaut, M.; Gunasekera, K.; Ravindren, S.; Boolchand, P.

2014-09-01

316

Dynamics in a tetrahedral network glassformer: vibrations, network rearrangements, and diffusion.  

PubMed

We perform molecular dynamics simulation on a tetrahedral network glassformer using a model for viscous SiO2 by Coslovich and Pastore [J. Phys.: Condens. Matter 21, 285107 (2009)]. In this system, Si and O particles form a random network at low temperature T. We attach an ellipsoid to each particle to represent its time-averaged vibration tensor. We then examine the anisotropic vibrations of Si and O, where the ellipsoid orientations are correlated with the network. The ellipsoids exhibit marked vibrational heterogeneity. The configuration changes occur as breakage and reorganization of the network, where only one or two particles undergo large jumps at each rearrangement leading to diffusion. To the time-correlation functions, however, the particles surrounding these largely displaced ones yield significantly T-dependent contributions, resulting in a weak violation of the Stokes-Einstein relation. This crossover is mild in silica due to the small Si-O bond numbers per particle, while it is strong in fragile glassformers with large coordination numbers. On long timescales, jump events tend to occur in the same regions forming marked dynamic heterogeneity. We also calculate the diffusion constants and the viscosity. The diffusion obeys activation dynamics and may be studied by short-time analysis of irreversible jumps. PMID:24832283

Kawasaki, Takeshi; Kim, Kang; Onuki, Akira

2014-05-14

317

Non-Axial Octupole Deformations and Tetrahedral Symmetry in Heavy Nuclei  

SciTech Connect

The total energies of about 120 nuclei in the Thorium region have been calculated within the macroscopic-microscopic method in the 5-dimensional space of deformation parameters {alpha}20, {alpha}22, {alpha}30, {alpha}32 and {alpha}40. The macroscopic energy term contains the nuclear surface-curvature dependence as proposed within the LSD approach. The microscopic energies are calculated with the Woods-Saxon single particle potential employing the universal set of parameters.We study a possible presence of the octupole axial and non-axial degrees of freedom all-over in the ({beta}, {gamma})-plane focussing on the ground-states, secondary minima and in the saddle points. In fact, a competition between axial and tri-axial octupole deformation parameters is obtained at the saddle points and in the secondary minima for many isotones with N > 136. The presence of the tetrahedral symmetry minima is predicted in numerous nuclei in the discussed region, although most of the time at relatively high excitation energies.

Mazurek, Katarzyna [Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow (Poland); Dudek, Jerzy [Institut de Recherches Subatomiques, F-67037 Strasbourg Cedex 2 (France); Universite Louis Pasteur, F-67037 Strasbourg Cedex 2 (France)

2005-11-21

318

A tetrahedral coordination of Zinc during transmembrane transport by P-type Zn2+-ATPases  

PubMed Central

Zn2+ is an essential transition metal required in trace amounts by all living organisms. However, metal excess is cytotoxic and leads to cell damage. Cells rely on transmembrane transporters, with the assistance of other proteins, to establish and maintain Zn2+ homeostasis. Metal coordination during transport is key to specific transport and unidirectional translocation without the backward release of free metal. The coordination details of Zn2+ at the transmembrane metal binding site responsible for transport have now been established. Escherichia coli ZntA is a well-characterized Zn2+-ATPase responsible for intracellular Zn2+ efflux. A truncated form of the protein lacking regulatory metal sites and retaining the transport site was constructed. Metrical parameters of the metal-ligand coordination geometry for the zinc bound isolated form were characterized using x-ray absorption spectroscopy (XAS). Our data support a nearest neighbor ligand environment of (O/N)2S2 that is compatible with the proposed invariant metal coordinating residues present in the transmembrane region. This ligand identification and the calculated bond lengths support a tetrahedral coordination geometry for Zn2+ bound to the TM-MBS of P-type ATPase transporters. PMID:22387457

Raimunda, Daniel; Subramanian, Poorna; Stemmler, Timothy; Argüello, José M.

2012-01-01

319

Erasing no-man's land by thermodynamically stabilizing the liquid-liquid transition in tetrahedral particles.  

PubMed

One of the most controversial hypotheses for explaining the origin of the thermodynamic anomalies characterizing liquid water postulates the presence of a metastable second-order liquid-liquid critical point [1] located in the "no-man's land" [2]. In this scenario, two liquids with distinct local structure emerge near the critical temperature. Unfortunately, since spontaneous crystallization is rapid in this region, experimental support for this hypothesis relies on significant extrapolations, either from the metastable liquid or from amorphous solid water [3, 4]. Although the liquid-liquid transition is expected to feature in many tetrahedrally coordinated liquids, including silicon [5], carbon [6] and silica, even numerical studies of atomic and molecular models have been unable to conclusively prove the existence of this transition. Here we provide such evidence for a model in which it is possible to continuously tune the softness of the interparticle interaction and the flexibility of the bonds, the key ingredients controlling the existence of the critical point. We show that conditions exist where the full coexistence is thermodynamically stable with respect to crystallization. Our work offers a basis for designing colloidal analogues of water exhibiting liquid-liquid transitions in equilibrium, opening the way for experimental confirmation of the original hypothesis. PMID:25264453

Smallenburg, Frank; Filion, Laura; Sciortino, Francesco

2014-09-01

320

Efficient calculation of the quasi-static electrical potential on a tetrahedral mesh and its implementation in STEPS  

PubMed Central

We describe a novel method for calculating the quasi-static electrical potential on tetrahedral meshes, which we call E-Field. The E-Field method is implemented in STEPS, which performs stochastic spatial reaction-diffusion computations in tetrahedral-based cellular geometry reconstructions. This provides a level of integration between electrical excitability and spatial molecular dynamics in realistic cellular morphology not previously achievable. Deterministic solutions are also possible. By performing the Rallpack tests we demonstrate the accuracy of the E-Field method. Efficient node ordering is an important practical consideration, and we find that a breadth-first search provides the best solutions, although principal axis ordering suffices for some geometries. We discuss potential applications and possible future directions, and predict that the E-Field implementation in STEPS will play an important role in the future of multiscale neural simulations. PMID:24194715

Hepburn, Iain; Cannon, Robert; De Schutter, Erik

2013-01-01

321

(C4H12N2)[CoCl4]: tetrahedrally coordinated Co(2+) without the orbital degeneracy.  

PubMed

We report on the synthesis, crystal structure and magnetic properties of a previously unreported Co(2+) S = {3\\over 2} compound, (C4H12N2)[CoCl4], based upon a tetrahedral crystalline environment. The S = {3\\over 2} magnetic ground state of Co(2+), measured with magnetization, implies an absence of spin-orbit coupling and orbital degeneracy. This contrasts with compounds based upon an octahedral and even known tetrahedral Co(2+) [Cotton et al. (1961). J. Am. Chem. Soc. 83, 4690] systems where a sizable spin-orbit coupling is measured. The compound is characterized with single-crystal X-ray diffraction, magnetic susceptibility, IR and UV-vis spectroscopy. Magnetic susceptibility measurements find no magnetic ordering above 2?K. The results are also compared with the previously known monoclinic hydrated analogue. PMID:25643712

Decaroli, C; Arevalo-Lopez, A M; Woodall, C H; Rodriguez, E E; Attfield, J P; Parker, S F; Stock, C

2015-02-01

322

Intense photo- and tribo-luminescence of three tetrahedral manganese(ii) dihalides with chelating bidentate phosphine oxide ligand.  

PubMed

Three air-stable tetrahedral manganese(ii) dihalide complexes [MnX2(DPEPO)] (DPEPO = bis[2-(diphenylphosphino)phenyl]ether oxide; X = Cl, Br and I) were prepared. All of the obtained compounds were structurally characterized by single-crystal X-ray diffraction analyses, which reveal that they crystallize in centrosymmetric space groups and feature an isolated mononuclear structure with Mn(2+) in a tetrahedral environment. Interestingly, these complexes show excellent photoluminescent performance in neat solid form, with the highest total quantum yield (?total) of up to 70% recorded for the dibromide complex. Intense green flashes of light could be observed by the naked eye when rubbing the manganese(ii) complexes. PMID:25597698

Chen, Jun; Zhang, Qing; Zheng, Fa-Kun; Liu, Zhi-Fa; Wang, Shuai-Hua; Wu, A-Qing; Guo, Guo-Cong

2015-02-01

323

Unraveling the voltage fade mechanism in layer Li-Mn-rich electrode: formation of the tetrahedral cations for spinel conversion  

SciTech Connect

Discovery of high-voltage layered lithium-and manganese-rich (LMR) composite oxide electrode has dramatically enhanced the energy density of current Li-ion energy storage systems. However, practical usage of these materials is currently not viable because of their inability to maintain a consistent voltage profile (voltage fading) during subsequent charge-discharge cycles. This report rationalizes the cause of this voltage fade by providing the evidence of layer to spinel-like (LSL) structural evolution pathways in the host Li1.2Mn0.55Ni0.15Co0.1O2 LMR composite oxide. By employing neutron powder diffraction, and temperature dependent magnetic susceptibility, we show that LSL structural rearrangement in LMR oxide occurs through a tetrahedral cation intermediate via: i) diffusion of lithium atoms from octahedral to tetrahedral sites of the lithium layer [(LiLioct LiLitet] which is followed by the dispersal of the lithium ions from the adjacent octahedral site of the metal layer to the tetrahedral sites of lithium layer [LiTM oct LiLitet]; and ii) migration of Mn from the octahedral sites of the transition metal layer to the permanent octahedral site of lithium layer via tetrahedral site of lithium layer [MnTMoct MnLitet MnLioct)]. The findings opens the door to the potential routes to mitigate this atomic restructuring in the high-voltage LMR composite oxide cathodes by manipulating the composition/structure for practical use in high-energy-density lithium-ion batteries.

Mohanty, Debasish [ORNL; Li, Jianlin [ORNL; Abraham, Daniel P [Argonne National Laboratory (ANL); Huq, Ashfia [ORNL; Payzant, E Andrew [ORNL; Wood III, David L [ORNL; Daniel, Claus [ORNL

2014-01-01

324

Synthesis, further characterisation and catalytic activity of iron-substituted zeolite LTL, prepared using tetrahedral oxo-anion species  

Microsoft Academic Search

Iron substituted zeolite LTL has been prepared, using tetrahedral potassium ferrate(VI), and characterised using X-ray diffraction, Fourier transform infra-red analysis, thermal analysis, chemical analysis and electron microscopy [K. Latham, C.D. Williams, C.V.A. Duke, Zeolites 17 (1996) 513; C.V.A. Duke, K. Latham, C.D. Williams, Zeolites 15 (1995) 213]. Further characterisation using X-ray photoelectron spectroscopy and magnetic susceptibility, confirmed the presence of

Kay Latham; Catherine I Round; Craig D Williams

2000-01-01

325

Control over connectivity and magnetism of tetrahedral FeSe2 chains through coordination Fe-amine complexes.  

PubMed

The synthesis and structural characterization is reported for [Fe(dien)2][FeSe2]2 and [Fe(tren)][FeSe2]2, two new mixed-valence compounds that contain infinite ?(1)(FeSe2) tetrahedral chains separated by Fe-amine complexes. The inter- and intra-chain magnetic interactions can be controlled by changing the denticity of the amine while preserving the general structural motif. PMID:25482568

Greenfield, Joshua T; Pak, Chongin; Kamali, Saeed; Lee, Kathleen; Kovnir, Kirill

2014-12-01

326

Activity of Cu{sup 2+} ions on the tetrahedral and octahedral sites of spinel oxide catalysts for CO oxidation  

SciTech Connect

In studies of CO oxidation on substituted copper chromite spinel oxide catalyst decreases as the Cu{sup 2+} content of the catalyst decreases, either by substitution with a divalent ion, i.e., Cu{sub 1-x} Mg{sub x} [Cr{sub 2}]O{sub 4}, or by reduction of Cu{sup 2+} to Cu{sup 1+}. Crystallographic studies have shown that Cu[Cr{sub 2}]O{sub 4} changes from normal to partially inverse when Cr{sup 3+} is replaced by Al{sup 3+}. Thus, in aluminum-substituted copper chromite catalysts, copper is present on both tetrahedral and octahedral sites of the spinel lattice, i.e., Cu{sub 1-x}Al{sub x} [Cu{sub x}Cr{sub 2-(x+y)}Al{sub y}]O{sub 4}. ESCA studies have shown that upon Al substitution some of the tetrahedral Cu{sup 2+} ions are reduced to Cu{sup 1+} and this causes a reduction in the catalytic activity of the catalysts. The present work was taken up to compare the activity of Cu{sup 2+} on tetrahedral sites with that on octahedral sites of the spinel oxide catalysts. For this, CO oxidation studies were carried out on the inverse spinel CuFe{sub 2}O{sub 4} and on the normal spinel CuRh{sub 2}O{sub 4} catalysts. 7 refs., 1 fig.

Ghose, J. [Indian Institute of Technology, Kharagpur (India)] [Indian Institute of Technology, Kharagpur (India); Murthy, K.S.R.C. [Indian Telephone Industries, Ltd., Bangalore (India)] [Indian Telephone Industries, Ltd., Bangalore (India)

1996-09-01

327

Synthesis and Catalytic Activity of Pt Monolayer on Pd Tetrahedral Nanocrystals with CO-adsorption-induced Removal of Surfactants  

SciTech Connect

We synthesized the Pt monolayer shell-Pd tetrahedral core electrocatalysts that are notable for their high activity and stable performance. A small number of low-coordination sites and defects, and high content of the (1 1 1)-oriented facets on Pd tetrahedron makes them a suitable support for a Pt monolayer to obtain an active O{sub 2} reduction reaction (ORR) electrocatalyst. The surfactants, used to control size and shape of Pd tetrahedral nanoparticles, are difficult to remove and cause adverse effects on the ORR. We describe a simple and noninvasive method to synthesize high-purity tetrahedral Pd nanocrystals (TH Pd) by combining a hydrothermal route and CO adsorption-induced removal of surfactants. Poly(vinylpyrrolidone) (PVP), used as a protecting and reducing agent in hydrothermal reactions, is strongly bonded to the surface of the resulting nanocrystals. We demonstrate that PVP was displaced efficiently by adsorbed CO. A clean surface was achieved upon CO stripping at a high potential (1.0 V vs RHE). It played a decisive role in improving the activity of the Pt monolayer/TH Pd electrocatalyst for the ORR. Furthermore, the results demonstrate a versatile method for removal of surfactants from various nanoparticles that severely limited their applications.

Gong K.; Vukmirovic M.B.; Ma C.; Zhu Y.; Adzic R.R.

2011-11-01

328

Homotopy approach to optimal, linear quadratic, fixed architecture compensation  

NASA Technical Reports Server (NTRS)

Optimal linear quadratic Gaussian compensators with constrained architecture are a sensible way to generate good multivariable feedback systems meeting strict implementation requirements. The optimality conditions obtained from the constrained linear quadratic Gaussian are a set of highly coupled matrix equations that cannot be solved algebraically except when the compensator is centralized and full order. An alternative to the use of general parameter optimization methods for solving the problem is to use homotopy. The benefit of the method is that it uses the solution to a simplified problem as a starting point and the final solution is then obtained by solving a simple differential equation. This paper investigates the convergence properties and the limitation of such an approach and sheds some light on the nature and the number of solutions of the constrained linear quadratic Gaussian problem. It also demonstrates the usefulness of homotopy on an example of an optimal decentralized compensator.

Mercadal, Mathieu

1991-01-01

329

A class of quadratic deformations of Lie superalgebras  

E-print Network

We study certain Z_2-graded, finite-dimensional polynomial algebras of degree 2 which are a special class of deformations of Lie superalgebras, which we call quadratic Lie superalgebras. Starting from the formal definition, we discuss the generalised Jacobi relations in the context of the Koszul property, and give a proof of the PBW basis theorem. We give several concrete examples of quadratic Lie superalgebras for low dimensional cases, and discuss aspects of their structure constants for the `type I' class. We derive the equivalent of the Kac module construction for typical and atypical modules, and a related direct construction of irreducible modules due to Gould. We investigate in detail one specific case, the quadratic generalisation gl_2(n/1) of the Lie superalgebra sl(n/1). We formulate the general atypicality conditions at level 1, and present an analysis of zero-and one-step atypical modules for a certain family of Kac modules.

Peter Jarvis; Gerd Rudolph; Luke Yates

2010-10-19

330

Quadratic algebra approach to relativistic quantum Smorodinsky-Winternitz systems  

SciTech Connect

There exists a relation between the Klein-Gordon and the Dirac equations with scalar and vector potentials of equal magnitude and the Schroedinger equation. We obtain the relativistic energy spectrum for the four relativistic quantum Smorodinsky-Winternitz systems from their quasi-Hamiltonian and the quadratic algebras studied by Daskaloyannis in the nonrelativistic context. We also apply the quadratic algebra approach directly to the initial Dirac equation for these four systems and show that the quadratic algebras obtained are the same than those obtained from the quasi-Hamiltonians. We point out how results obtained in context of quantum superintegrable systems and their polynomial algebras can be applied to the quantum relativistic case.

Marquette, Ian [Department of Mathematics, University of York, Heslington, York YO10 5DD (United Kingdom)

2011-04-15

331

The use of tetrahedral mesh geometries in Monte Carlo simulation of applicator based brachytherapy dose distributions.  

PubMed

Accounting for brachytherapy applicator attenuation is part of the recommendations from the recent report of AAPM Task Group 186. To do so, model based dose calculation algorithms require accurate modelling of the applicator geometry. This can be non-trivial in the case of irregularly shaped applicators such as the Fletcher Williamson gynaecological applicator or balloon applicators with possibly irregular shapes employed in accelerated partial breast irradiation (APBI) performed using electronic brachytherapy sources (EBS). While many of these applicators can be modelled using constructive solid geometry (CSG), the latter may be difficult and time-consuming. Alternatively, these complex geometries can be modelled using tessellated geometries such as tetrahedral meshes (mesh geometries (MG)). Recent versions of Monte Carlo (MC) codes Geant4 and MCNP6 allow for the use of MG. The goal of this work was to model a series of applicators relevant to brachytherapy using MG. Applicators designed for (192)Ir sources and 50?kV EBS were studied; a shielded vaginal applicator, a shielded Fletcher Williamson applicator and an APBI balloon applicator. All applicators were modelled in Geant4 and MCNP6 using MG and CSG for dose calculations. CSG derived dose distributions were considered as reference and used to validate MG models by comparing dose distribution ratios. In general agreement within 1% for the dose calculations was observed for all applicators between MG and CSG and between codes when considering volumes inside the 25% isodose surface. When compared to CSG, MG required longer computation times by a factor of at least 2 for MC simulations using the same code. MCNP6 calculation times were more than ten times shorter than Geant4 in some cases. In conclusion we presented methods allowing for high fidelity modelling with results equivalent to CSG. To the best of our knowledge MG offers the most accurate representation of an irregular APBI balloon applicator. PMID:25210788

Fonseca, Gabriel Paiva; Landry, Guillaume; White, Shane; D'Amours, Michel; Yoriyaz, Hélio; Beaulieu, Luc; Reniers, Brigitte; Verhaegen, Frank

2014-10-01

332

The stability of a crystal with diamond structure for patchy particles with tetrahedral symmetry  

E-print Network

The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values for the range of the potential, with the aim of investigating the conditions under which a diamond crystal can be formed. We find that the diamond phase is never stable for our longer-ranged potential. At low temperatures and pressures, the fluid freezes into a body-centred-cubic solid that can be viewed as two interpenetrating diamond lattices with a weak interaction between the two sublattices. Upon compression, an orientationally ordered face-centred-cubic crystal becomes more stable than the body-centred-cubic crystal, and at higher temperatures a plastic face-centered-cubic phase is stabilized by the increased entropy due to orientational disorder. A similar phase diagram is found for the shorter-ranged potential, but at low temperatures and pressures, we also find a region over which the diamond phase is thermodynamically favored over the body-centred-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centred-cubic solid explains why it is stable even though the enthalpy of the latter phase is lower. Some preliminary studies on the growth of the diamond structure starting from a crystal seed were performed. Even though the diamond phase is never thermodynamically stable for the longer-ranged model, direct coexistence simulations of the interface between the fluid and the body-centred-cubic crystal and between the fluid and the diamond crystal show that, at sufficiently low pressures, it is quite probable that in both cases the solid grows into a diamond crystal, albeit involving some defects. These results highlight the importance of kinetic effects in the formation of diamond crystals in systems of patchy particles.

Eva G. Noya; Carlos Vega; Jonathan P. K. Doye; Ard A. Louis

2010-05-27

333

Simple shearing flow of dry soap foams with TCP structure[Tetrahedrally Close-Packed  

SciTech Connect

The microrheology of dry soap foams subjected to large, quasistatic, simple shearing deformations is analyzed. Two different monodisperse foams with tetrahedrally close-packed (TCP) structure are examined: Weaire-Phelan (A15) and Friauf-Laves (C15). The elastic-plastic response is evaluated by calculating foam structures that minimize total surface area at each value of strain. The minimal surfaces are computed with the Surface Evolver program developed by Brakke. The foam geometry and macroscopic stress are piecewise continuous functions of strain. The stress scales as T/V{sup 1/3} where T is surface tension and V is cell volume. Each discontinuity corresponds to large changes in foam geometry and topology that restore equilibrium to unstable configurations that violate Plateau's laws. The instabilities occur when the length of an edge on a polyhedral foam cell vanishes. The length can tend to zero smoothly or abruptly with strain. The abrupt case occurs when a small increase in strain changes the energy profile in the neighborhood of a foam structure from a local minimum to a saddle point, which can lead to symmetry-breaking bifurcations. In general, the new foam topology associated with each stable solution branch results from a cascade of local topology changes called T1 transitions. Each T1 cascade produces different cell neighbors, reduces surface energy, and provides an irreversible, film-level mechanism for plastic yield behavior. Stress-strain curves and average stresses are evaluated by examining foam orientations that admit strain-periodic behavior. For some orientations, the deformation cycle includes Kelvin cells instead of the original TCP structure; but the foam does not remain perfectly ordered. Bifurcations during subsequent T1 cascades lead to disorder and can even cause strain localization.

REINELT,DOUGLAS A.; KRAYNIK,ANDREW M.

2000-02-16

334

The use of tetrahedral mesh geometries in Monte Carlo simulation of applicator based brachytherapy dose distributions  

NASA Astrophysics Data System (ADS)

Accounting for brachytherapy applicator attenuation is part of the recommendations from the recent report of AAPM Task Group 186. To do so, model based dose calculation algorithms require accurate modelling of the applicator geometry. This can be non-trivial in the case of irregularly shaped applicators such as the Fletcher Williamson gynaecological applicator or balloon applicators with possibly irregular shapes employed in accelerated partial breast irradiation (APBI) performed using electronic brachytherapy sources (EBS). While many of these applicators can be modelled using constructive solid geometry (CSG), the latter may be difficult and time-consuming. Alternatively, these complex geometries can be modelled using tessellated geometries such as tetrahedral meshes (mesh geometries (MG)). Recent versions of Monte Carlo (MC) codes Geant4 and MCNP6 allow for the use of MG. The goal of this work was to model a series of applicators relevant to brachytherapy using MG. Applicators designed for 192Ir sources and 50?kV EBS were studied; a shielded vaginal applicator, a shielded Fletcher Williamson applicator and an APBI balloon applicator. All applicators were modelled in Geant4 and MCNP6 using MG and CSG for dose calculations. CSG derived dose distributions were considered as reference and used to validate MG models by comparing dose distribution ratios. In general agreement within 1% for the dose calculations was observed for all applicators between MG and CSG and between codes when considering volumes inside the 25% isodose surface. When compared to CSG, MG required longer computation times by a factor of at least 2 for MC simulations using the same code. MCNP6 calculation times were more than ten times shorter than Geant4 in some cases. In conclusion we presented methods allowing for high fidelity modelling with results equivalent to CSG. To the best of our knowledge MG offers the most accurate representation of an irregular APBI balloon applicator.

Paiva Fonseca, Gabriel; Landry, Guillaume; White, Shane; D'Amours, Michel; Yoriyaz, Hélio; Beaulieu, Luc; Reniers, Brigitte; Verhaegen, Frank

2014-10-01

335

Rational quadratic Bézier curve fitting by simulated annealing technique  

NASA Astrophysics Data System (ADS)

A metaheuristic algorithm, which is an approximation method called simulated annealing is implemented in order to have the best rational quadratic Bézier curve from a given data points. This technique is used to minimize sum squared errors in order to improve the middle control point position and the value of weight. As a result, best fitted rational quadratic Bézier curve and its mathematical function that represents all the given data points is obtained. Numerical and graphical examples are also presented to demonstrate the effectiveness and robustness of the proposed method.

Mohamed, Najihah; Abd Majid, Ahmad; Mt Piah, Abd Rahni

2013-04-01

336

Stability of the Quadratic Equation of Pexider Type  

Microsoft Academic Search

We will investigate the stability problem of the quadratic equation (1) and extend the results of Borelli and Forti, Czerwik,\\u000a and Rassias. By applying this result and an improved theorem of the author, we will also prove the stability of the quadratic\\u000a functional equation of Pexider type,f\\u000a 1 (x +y) + f2(x -y) =f\\u000a 3(x) +f\\u000a 4(y), for a large

Soon-Mo Jung

2000-01-01

337

Analysis of integral controls in linear quadratic regulator design  

NASA Technical Reports Server (NTRS)

The application of linear optimal control to the design of systems with integral control action on specified outputs is considered. Using integral terms in a quadratic performance index, an asymptotic analysis is used to determine the effect of variable quadratic weights on the eigenvalues and eigenvectors of the closed loop system. It is shown that for small integral terms the placement of integrator poles and gain calculation can be effectively decoupled from placement of the primary system eigenvalues. This technique is applied to the design of integral controls for a STOL aircraft outer loop guidance system.

Slater, G. L.

1979-01-01

338

Frequency comb generation in quadratic nonlinear media  

E-print Network

Optical frequency combs are nowadays routinely used tools in a wide range of scientific and technological applications. Different techniques have been developed for generating optical frequency combs, like mode-locking in lasers and third-order interactions in microresonators, or to extend their spectral capabilities, using frequency conversion processes in nonlinear materials. Here, we experimentally demonstrate and theoretically explain the onset of optical frequency combs in a simple cavity-enhanced second-harmonic-generation system, exploiting second-order nonlinear interactions. We develop an elemental model which provides a deep physical insight into the observed dynamics. Moreover, despite the different underlying physical mechanism, the proposed model is remarkably similar to the description of third-order effects in microresonators, revealing a potential variety of new effects to be explored. Finally, exploiting a nonlinearity intrinsically stronger than the third-order one, our work lays the groundw...

Ricciardi, Iolanda; Parisi, Maria; Maddaloni, Pasquale; Santamaria, Luigi; De Natale, Paolo; De Rosa, Maurizio

2014-01-01

339

Three isoparametric solid elements for NASTRAN. [for static, dynamic, buckling, and heat transfer analyses  

NASA Technical Reports Server (NTRS)

Linear, quadratic, and cubic isoparametric hexahedral solid elements have been added to the element library of NASTRAN. These elements are available for static, dynamic, buckling, and heat-transfer analyses. Because the isoparametric element matrices are generated by direct numerical integration over the volume of the element, variations in material properties, temperatures, and stresses within the elements are represented in the computations. In order to compare the accuracy of the new elements, three similar models of a slender cantilever were developed, one for each element. All elements performed well. As expected, however, the linear element model yielded excellent results only when shear behavior predominated. In contrast, the results obtained from the quadratic and cubic element models were excellent in both shear and bending.

Johnson, S. E.; Field, E. I.

1973-01-01

340

An analysis of spectral envelope-reduction via quadratic assignment problems  

NASA Technical Reports Server (NTRS)

A new spectral algorithm for reordering a sparse symmetric matrix to reduce its envelope size was described. The ordering is computed by associating a Laplacian matrix with the given matrix and then sorting the components of a specified eigenvector of the Laplacian. In this paper, we provide an analysis of the spectral envelope reduction algorithm. We described related 1- and 2-sum problems; the former is related to the envelope size, while the latter is related to an upper bound on the work involved in an envelope Cholesky factorization scheme. We formulate the latter two problems as quadratic assignment problems, and then study the 2-sum problem in more detail. We obtain lower bounds on the 2-sum by considering a projected quadratic assignment problem, and then show that finding a permutation matrix closest to an orthogonal matrix attaining one of the lower bounds justifies the spectral envelope reduction algorithm. The lower bound on the 2-sum is seen to be tight for reasonably 'uniform' finite element meshes. We also obtain asymptotically tight lower bounds for the envelope size for certain classes of meshes.

George, Alan; Pothen, Alex

1994-01-01

341

Approximation theory for LQG (Linear-Quadratic-Gaussian) optimal control of flexible structures  

NASA Technical Reports Server (NTRS)

An approximation theory is presented for the LQG (Linear-Quadratic-Gaussian) optimal control problem for flexible structures whose distributed models have bounded input and output operators. The main purpose of the theory is to guide the design of finite dimensional compensators that approximate closely the optimal compensator. The optimal LQG problem separates into an optimal linear-quadratic regulator problem and an optimal state estimation problem. The solution of the former problem lies in the solution to an infinite dimensional Riccati operator equation. The approximation scheme approximates the infinite dimensional LQG problem with a sequence of finite dimensional LQG problems defined for a sequence of finite dimensional, usually finite element or modal, approximations of the distributed model of the structure. Two Riccati matrix equations determine the solution to each approximating problem. The finite dimensional equations for numerical approximation are developed, including formulas for converting matrix control and estimator gains to their functional representation to allow comparison of gains based on different orders of approximation. Convergence of the approximating control and estimator gains and of the corresponding finite dimensional compensators is studied. Also, convergence and stability of the closed-loop systems produced with the finite dimensional compensators are discussed. The convergence theory is based on the convergence of the solutions of the finite dimensional Riccati equations to the solutions of the infinite dimensional Riccati equations. A numerical example with a flexible beam, a rotating rigid body, and a lumped mass is given.

Gibson, J. S.; Adamian, A.

1988-01-01

342

FIVE SQUARES IN ARITHMETIC PROGRESSION OVER QUADRATIC FIELDS  

E-print Network

FIVE SQUARES IN ARITHMETIC PROGRESSION OVER QUADRATIC FIELDS ENRIQUE GONZ´ALEZ-JIM´ENEZ AND XAVIER) there is a non-constant arithmetic progression of five squares. This is carried out by translating the problem that the only non-constant arithmetic progression of five squares over Q( 409), up to equivalence, is 72 , 132

González, Enrique

343

The Ant System Applied to the Quadratic Assignment Problem  

Microsoft Academic Search

In recent years, there has been growing interest in algorithms inspired by the observation of natural phenomena to define computational procedures that can solve complex problems. We describe a distributed heuristic algorithm that was inspired by the observation of the behavior of ant colonies, and we propose its use for the quadratic assignment problem. The results obtained in solving several

Vittorio Maniezzo; Alberto Colorni

1999-01-01

344

Unravelling Student Challenges with Quadratics: A Cognitive Approach  

ERIC Educational Resources Information Center

The author's secondary school mathematics students have often reported to her that quadratic relations are one of the most conceptually challenging aspects of the high school curriculum. From her own classroom experiences there seemed to be several aspects to the students' challenges. Many students, even in their early secondary education, have…

Kotsopoulos, Donna

2007-01-01

345

Cosmological Vorticity in a Gravity with Quadratic Order Curvature Couplings  

E-print Network

We analyse the evolution of the rotational type cosmological perturbation in a gravity with general quadratic order gravitational coupling terms. The result is expressed independently of the generalized nature of the gravity theory, and is simply interpreted as a conservation of the angular momentum.

J. Hwang; H. Noh

1997-10-07

346

DIMACS Technical Report 9940 Camel Sequences and Quadratic Residues  

E-print Network

DIMACS Technical Report 99­40 Camel Sequences and Quadratic Residues by V. Gurvich 1 DIMACS generate them, will be called the camel distributions and camel sequences, respectively up­camel and down­camel. For example, the first sequence above is down­camel, and the second one is up­camel. Camel sequences have

347

Analysis of Quadratic Diophantine Equations with Fibonacci Number Solutions  

ERIC Educational Resources Information Center

An analysis is made of the role of Fibonacci numbers in some quadratic Diophantine equations. A general solution is obtained for finding factors in sums of Fibonacci numbers. Interpretation of the results is facilitated by the use of a modular ring which also permits extension of the analysis.

Leyendekkers, J. V.; Shannon, A. G.

2004-01-01

348

Number theoretic transforms over the golden section quadratic field  

Microsoft Academic Search

A new number theoretic transform (NTT) over the real quadratic field Q(?5) is suggested and analyzed. Conventional NTTs are used for fast convolution of integer sequences. A new approach for computing number theoretic transforms (NTTs) is proposed, allowing real signals to be processed as well. The method is based on a Diophantine approximation of the input real signal before the

Vassil S. Dimitrov; T. V. Cosklev; B. Bonevsky

1995-01-01

349

Discriminative learning quadratic discriminant function for handwriting recognition  

Microsoft Academic Search

In character string recognition integrating segmentation and classification, high classification accuracy and resistance to noncharacters are desired to the underlying classifier. In a previous evaluation study, the modified quadratic discriminant function (MQDF) proposed by Kimura et al. was shown to be superior in noncharacter resistance but inferior in classification accuracy to neural networks. This paper proposes a discriminative learning algorithm

Cheng-Lin Liu; Hiroshi Sako; Hiromichi Fujisawa

2004-01-01

350

Characterization of local quadratic growth for strong minima in the ...  

E-print Network

Oct 14, 2011 ... Our aim is to characterize local quadratic growth for the cost function J in .... there exists a constant Cs depending only on s, such that yu ? + yu 2,s ..... u ? K is a Pontryagin extremal in integral form with respect to U if. ?. ?.

2011-10-14

351

Some Remarks for a Decomposition of Linear-Quadratic Optimal ...  

E-print Network

Aug 9, 2013 ... and it is given algorithm for solving Linear-Quadratic optimal Control .... Note2: Since xn+1 is unknown constant (parameter) in the interval [0, 2] (see, .... boundary of the integral of minimizing functional is known as in example ...

352

Sobolev seminorm of quadratic functions with applications to ...  

E-print Network

36,14]. The following quadratic interpolation plays an important role in Conn and Toint ... remaining freedom is to minimize some functional subject to the interpolation constraints, that is to .... Because of symmetry, the integral of xTGg is zero.

2012-01-18

353

Mixed-integer Quadratic Programming is in NP  

E-print Network

Jul 17, 2014 ... showing that if the decision version of mixed-integer quadratic ... where the minimal binary encoding length of any feasible integral ..... for every S ? {1,...,n}; note that the complexity of the additional constraints is O(n) and.

2014-07-17

354

System Analysis via Integral Quadratic Constraints - Part I  

Microsoft Academic Search

This paper introduces a unified approach to robustness analysis with respect to nonlinearities, time-variations and uncertain parameters. From an original idea by Yakubovich, the approach has been developed under a combination of influences from the western and russian traditions of control theory. It is shown how a complex system can be described by using certain integral quadratic constraints (IQC's), derived

Alexander Megretski; Anders Rantzer

1995-01-01

355

A Rigorous Global Filtering Algorithm for Quadratic Constraints  

Microsoft Academic Search

Abstract: This paper introduces a new filtering algorithm for handling systems of quadratic equations and inequations. Such constraints are widely used to model distance relations in numerous application areas ranging from robotics to chemistry. Classical filtering algorithms are based upon local consistencies and thus, are often unable to achieve a significant pruning of the domains of the variables occurring in

Yahia Lebbah; Claude Michel; Michel Rueher

2005-01-01

356

A double integral quadratic cost and tolerance of feedback nonlinearities  

Microsoft Academic Search

A double integral quadratic cost with an associated integral constraint on state trajectories is shown to result in a stable feedback control law for linear time-varying differential systems. The gain matrix for this control is obtained by integrating a Riccati-type matrix differential equation over a finite time interval and is shown to allow for a large class of nonlinearities in

W. Kwon; A. Pearson

1979-01-01

357

Holomorphic quantum mechanics with a quadratic Hamiltonian constraint  

Microsoft Academic Search

A finite-dimensional system with a quadratic Hamiltonian constraint is Dirac quantized in holomorphic, antiholomorphic, and mixed representations. A unique inner product is found by imposing Hermitian conjugacy relations on an operator algebra. The different representations yield drastically different Hilbert spaces. In particular, all the spaces obtained in the antiholomorphic representation violate classical expectations for the spectra of certain operators, whereas

Jorma Louko

1993-01-01

358

System Analysis via Integral Quadratic Constraints Part IIa: Abstract theory  

Microsoft Academic Search

In this second report on system analysis via integral quadratic con- straints, the theory is refined compared to Part I (6), to cover a number of additional cases. The report is split into two halfs, denoted Part IIa and Part IIb. Unbounded operators are treated by encapsulating them in a feedback loop,thathasboundedclosedloopgain.Ageneraltheoremforwell-posedness of suchfeedback loops is given. A concept of

A. Rantzer; A. Megretski

359

Control synthesis with dynamic integral quadratic constraints-LMI approach  

Microsoft Academic Search

In this paper, we consider the control synthesis problem when the disturbance input w is within a set defined by several dynamic integral quadratic constraints (IQC). We show that the condition on the existence of a stabilizing controller can be expressed as a set of linear matrix inequalities (LMI). We also show that the stabilizing controllers, if they exist, have

Chung-Yao Kao; Muralidhar Ravuri; Alexandre Megretski

2000-01-01

360

Integral quadratic constraints for monotonic and slope restricted diagonal operators  

Microsoft Academic Search

Studies the description, by means of integral quadratic constraints (IQCs), of a class of static diagonal operators with equal diagonal entries. In particular, the diagonal entries considered are monotonic and slope-restricted nonlinearities. First, we give new IQCs for this type of operators which exploit the equality among nonlinearities. Then we show how these results can be used to derive new

F. J. D'Amato; U. T. Jonson; A. Megretski; M. A. Rotea

1999-01-01

361

Stability analysis with Popov multipliers and integral quadratic constraints  

Microsoft Academic Search

It is shown that a general form of Popov multipliers can be used in stability analysis based on integral quadratic constraints (IQC). The Popov multiplier is nonproper and a condition that the nominal plant is strictly proper will be imposed in order to ensure boundedness of the IQC corresponding to the Popov multiplier. A consequence of our main result is

Ulf Jönsson

1997-01-01

362

A Unified Approach to Teaching Quadratic and Cubic Equations.  

ERIC Educational Resources Information Center

Presents a simple method for teaching the algebraic solution of cubic equations via completion of the cube. Shows that this method is readily accepted by students already familiar with completion of the square as a method for quadratic equations. (Author/KHR)

Ward, A. J. B.

2003-01-01

363

Finding the Best Quadratic Approximation of a Function  

ERIC Educational Resources Information Center

This article examines the question of finding the best quadratic function to approximate a given function on an interval. The prototypical function considered is f(x) = e[superscript x]. Two approaches are considered, one based on Taylor polynomial approximations at various points in the interval under consideration, the other based on the fact…

Yang, Yajun; Gordon, Sheldon P.

2011-01-01

364

Quadratic function fields with exponent two ideal class group  

Microsoft Academic Search

It has been shown by Madden that there are only finitely many quadratic extensions of k(x), k a finite field, in which the ideal class group has exponent two and the infinity place of k(x) ramifies. We give a characterization of such fields that allow us to find a full list of all such field extensions for future reference. In

Victor Bautista-Ancona; Javier Diaz-Vargas

2006-01-01

365

Quadratic Function Fields with Exponent Two Ideal Class Group  

Microsoft Academic Search

It has been shown by Madden that there are only finitely many quadratic extensions of k(x), k a finite field, in which the ideal class group has exponent two and the infinity place of k(x) ramifies. We give a characterization of such fields that allow us to find a full list of all such field extensions for future reference. In

Victor Bautista-Ancona; Javier Diaz-Vargas

2005-01-01

366

An Improved Algorithm for the Generalized Quadratic Assignment ...  

E-print Network

This paper is concerned with solving GQAPs (generalized quadratic .... Even though the GQAP was formulated only recently, special cases have been studied extensively. Related problems, other than the QAP and the GAP, include the ...... Department of Mechanical and Industrial Engineering, University of Toronto, Toronto ...

artur

2008-05-15

367

Semidefinite-Based Branch-and-Bound for Nonconvex Quadratic ...  

E-print Network

Jun 27, 2005 ... This paper presents a branch-and-bound algorithm for nonconvex quadratic pro- ... †Department of Mechanical and Industrial Engineering, University of ... Recent work by Bomze and de Klerk (2002) has studied ... Such SDPs—including the related ones introduced in this paper—are too large to be solved.

2005-06-27

368

On the Number of Representation of Integers into Quadratic Forms  

E-print Network

We give formulas for the number of representations of non negative integers into quadratic forms. We also consider the case cubic and quintic forms. Finally we give a mean value asymptotic formula, for the behavior of the function that counts the number of representations of an integer as sum of two squares, known also as Gauss circle problem.

Nikos Bagis; M. L Glasser

2014-12-18

369

Time-Inconsistent Stochastic LinearQuadratic Control Hanqing Jin  

E-print Network

, France. This author is partially supported by the Marie Curie ITN Grant, "Controlled Systems", GA no at the initial time); see, e.g., [20] and all the follow-up works to date on the Markowitz problem, as wellTime-Inconsistent Stochastic Linear­Quadratic Control Ying Hu Hanqing Jin Xun Yu Zhou November 3

370

Lower Bounds and Exact Algorithms for the Quadratic Minimum ...  

E-print Network

Dec 16, 2013 ... an algorithm based on artificial bee colony. A local search ...... Once the branching edge is determined, two new nodes are created. For one of them, we ..... Information Technology and Control, 39:257–268, 2010. [28] David ... A swarm intelligence approach to the quadratic minimum spanning tree problem.

2013-12-16

371

Feasibility testing for systems of real quadratic equations  

Microsoft Academic Search

We consider the problem of deciding whether a given system of quadratic homogeneous equations over the reals has non-trivial solution. We design an approximative algorithm whose complexity is polynomial in the number of variables and exponential in the number of equations. Some applications to general systems of polynomial equations and inequalities over the reals are discussed.

Alexander I. Barvinok

1992-01-01

372

Finding Optimal Gains In Linear-Quadratic Control Problems  

NASA Technical Reports Server (NTRS)

Analytical method based on Volterra factorization leads to new approximations for optimal control gains in finite-time linear-quadratic control problem of system having infinite number of dimensions. Circumvents need to analyze and solve Riccati equations and provides more transparent connection between dynamics of system and optimal gain.

Milman, Mark H.; Scheid, Robert E., Jr.

1990-01-01

373

Monotonic solutions of a quadratic integral equation of fractional order  

Microsoft Academic Search

In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112–119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with

Józef Bana?; Beata Rzepka

2007-01-01

374

Visualising the Complex Roots of Quadratic Equations with Real Coefficients  

ERIC Educational Resources Information Center

The roots of the general quadratic equation y = ax[superscript 2] + bx + c (real a, b, c) are known to occur in the following sets: (i) real and distinct; (ii) real and coincident; and (iii) a complex conjugate pair. Case (iii), which provides the focus for this investigation, can only occur when the values of the real coefficients a, b, and c are…

Bardell, Nicholas S.

2012-01-01

375

Feasibility Testing for Systems of Real Quadratic Equations  

Microsoft Academic Search

We consider the problem of deciding whether a given system of quadratic homogeneous equations over the reals has nontrivial\\u000a solution. We design an algorithm which, for a fixed number of equations, uses a number of arithmetic operations bounded by\\u000a a polynomial in the number of variables only.

Alexander I. Barvinok

1993-01-01

376

Quadratic Expressions by Means of "Summing All the Matchsticks"  

ERIC Educational Resources Information Center

This note presents demonstrations of quadratic expressions that come about when particular problems are posed with respect to matchsticks that form regular triangles, squares, pentagons and so on. Usually when such "matchstick" problems are used as ways to foster algebraic thinking, the expressions for the number of matchstick quantities are…

Gierdien, M. Faaiz

2012-01-01

377

Linear quadratic regulators with eigenvalue placement in a horizontal strip  

NASA Technical Reports Server (NTRS)

A method for optimally shifting the imaginary parts of the open-loop poles of a multivariable control system to the desirable closed-loop locations is presented. The optimal solution with respect to a quadratic performance index is obtained by solving a linear matrix Liapunov equation.

Shieh, Leang S.; Dib, Hani M.; Ganesan, Sekar

1987-01-01

378

On a bi-quadratic functional equation and its stability  

Microsoft Academic Search

In this paper, we obtain the general solution and the generalized Hyers–Ulam stability of the bi-quadratic functional equation f(x+y,z+w)+f(x+y,z-w)+f(x-y,z+w)+f(x-y,z-w)=4[f(x,z)+f(x,w)+f(y,z)+f(y,w)].

Won-Gil Park; Jae-Hyeong Bae

2005-01-01

379

Monotonic solutions of a quadratic integral equation of Volterra type  

Microsoft Academic Search

We study a nonlinear quadratic integral equation of Volterra type in the Banach space of real functions defined and continuous on a bounded and closed interval. With the help of a suitable measure of noncompactness, we show that the mentioned integral equation has monotonic solutions.

A. Martinon

2004-01-01

380

Neural net solutions to fuzzy problems: The quadratic equation  

Microsoft Academic Search

This paper continues our research on using neural nets to solve fuzzy equations. After outlining our general method of employing neural nets to solve fuzzy problems we concentrate on solving the fuzzy quadratic equation. We show how neural nets can produce both real, and complex, fuzzy number solutions.

J. J. Buckley; E. Eslami

1997-01-01

381

A Factorization Approach to the Linear Regulator Quadratic Cost Problem  

NASA Technical Reports Server (NTRS)

A factorization approach to the linear regulator quadratic cost problem is developed. This approach makes some new connections between optimal control, factorization, Riccati equations and certain Wiener-Hopf operator equations. Applications of the theory to systems describable by evolution equations in Hilbert space and differential delay equations in Euclidean space are presented.

Milman, M. H.

1985-01-01

382

Homotopy analysis method for quadratic Riccati differential equation  

Microsoft Academic Search

In this paper, the quadratic Riccati differential equation is solved by means of an analytic technique, namely the homotopy analysis method (HAM). Comparisons are made between Adomian’s decomposition method (ADM), homotopy perturbation method (HPM) and the exact solution and the homotopy analysis method. The results reveal that the proposed method is very effective and simple.

Yue Tan; Saeid Abbasbandy

2008-01-01

383

Linear and Quadratic Change: A Problem from Japan  

ERIC Educational Resources Information Center

In the fall of 2003, the author conducted research on the student teaching process in Japan. The basis for most of the lessons observed was rich mathematics problems. Upon returning to the US, the author used one such problem while teaching an algebra 2 class. This article introduces that problem, which gives rise to both linear and quadratic

Peterson, Blake E.

2006-01-01

384

Quadratic-Argument Approach to the Davey-Stewartson Equations  

E-print Network

The Davey-Stewartson equations are used to describe the long time evolution of a three-dimensional packets of surface waves. Assuming that the argument functions are quadratic in spacial variables, we find in this paper various exact solutions modulo the most known symmetry transformations for the Davey-Stewartson equations.

Xiaoping Xu

2008-12-10

385

Interactive Isosurfaces with Quadratic C1 Splines on Truncated  

E-print Network

Universität Mannheim ABSTRACT The reconstruction of a continuous function from discrete data is a basic task: piecewise quadratic polynomials, volume data, GPU ray casting, isosurfaces 1. INTRODUCTION One of the main challenges for the visualization of isosurfaces from discrete data sets is to find a continuous function

Goesele, Michael

386

An adaptive algorithm for bound constrained quadratic minimization \\Lambda  

E-print Network

Bielschowsky Ana Friedlander Francisco A. M. Gomes Jos'e Mario Mart'inez Marcos Raydan May 2, 1997 Abstract gradient'' introduced by Friedlander and Mart'inez in 1989. This strategy guarantees global convergence convex quadratics and Friedlander, Mart'inez and Raydan [15] extended the proof to singular problems

Gomes, Francisco A. M.

387

Quadratic-Time Certificates in Linear Algebra* Erich L. Kaltofen  

E-print Network

. Forming the product costs matrix multiplication time, O(n ) with > 2.37. We accept probabilistic algorithms, as in Rusins M. Freivalds's famous 1979 quadratic time certification for the matrix product. Our Manipulation--Algorithms General Terms: theory, algorithms, verification Keywords: randomization, probabilistic

Kaltofen, Erich

388

Tuning a fuzzy controller using quadratic response surfaces  

NASA Technical Reports Server (NTRS)

Response surface methodology, an alternative method to traditional tuning of a fuzzy controller, is described. An example based on a simulated inverted pendulum 'plant' shows that with (only) 15 trial runs, the controller can be calibrated using a quadratic form to approximate the response surface.

Schott, Brian; Whalen, Thomas

1992-01-01

389

An Exact Algorithm for Quadratic Integer Minimization using Nonconvex Relaxations  

Microsoft Academic Search

We propose a branch-and-bound algorithm for minimizing a not necessarily convex quadratic function over integer variables. The algorithm is based on lower bounds computed as continuous minima of the objective function over appropriate ellipsoids. In the nonconvex case, we use ellipsoids enclosing the feasible region of the problem. In spite of the nonconvexity, these minima can be computed quickly. We

Christoph Buchheim; Marianna De Santis; Laura Palagi; Mauro Piacentini

2012-01-01

390

Analyzing Quadratic Unconstrained Binary Optimization Problems Via Multicommodity Flows  

PubMed Central

Quadratic Unconstrained Binary Optimization (QUBO) problems concern the minimization of quadratic polynomials in n {0, 1}-valued variables. These problems are NP-complete, but prior work has identified a sequence of polynomial-time computable lower bounds on the minimum value, denoted by C2, C3, C4,…. It is known that C2 can be computed by solving a maximum-flow problem, whereas the only previously known algorithms for computing Ck (k > 2) require solving a linear program. In this paper we prove that C3 can be computed by solving a maximum multicommodity flow problem in a graph constructed from the quadratic function. In addition to providing a lower bound on the minimum value of the quadratic function on {0, 1}n, this multicommodity flow problem also provides some information about the coordinates of the point where this minimum is achieved. By looking at the edges that are never saturated in any maximum multicommodity flow, we can identify relational persistencies: pairs of variables that must have the same or different values in any minimizing assignment. We furthermore show that all of these persistencies can be detected by solving single-commodity flow problems in the same network. PMID:20161596

Wang, Di; Kleinberg, Robert D.

2009-01-01

391

Analyzing Quadratic Unconstrained Binary Optimization Problems Via Multicommodity Flows.  

PubMed

Quadratic Unconstrained Binary Optimization (QUBO) problems concern the minimization of quadratic polynomials in n {0, 1}-valued variables. These problems are NP-complete, but prior work has identified a sequence of polynomial-time computable lower bounds on the minimum value, denoted by C(2), C(3), C(4),…. It is known that C(2) can be computed by solving a maximum-flow problem, whereas the only previously known algorithms for computing C(k) (k > 2) require solving a linear program. In this paper we prove that C(3) can be computed by solving a maximum multicommodity flow problem in a graph constructed from the quadratic function. In addition to providing a lower bound on the minimum value of the quadratic function on {0, 1}(n), this multicommodity flow problem also provides some information about the coordinates of the point where this minimum is achieved. By looking at the edges that are never saturated in any maximum multicommodity flow, we can identify relational persistencies: pairs of variables that must have the same or different values in any minimizing assignment. We furthermore show that all of these persistencies can be detected by solving single-commodity flow problems in the same network. PMID:20161596

Wang, Di; Kleinberg, Robert D

2009-11-28

392

Quadratic Jordan superpairs covered by grids Dedicated to Ottmar Loos  

E-print Network

Quadratic Jordan superpairs covered by grids Dedicated to Ottmar Loos on the occasion of his 60th of Jordan superpairs defined over (su- per)commutative superrings. Our framework has two novelties: we allow that it is possible to work in this generality we classify Jordan superpairs covered by a grid. There has recently

393

Confidence set interference with a prior quadratic bound. [in geophysics  

NASA Technical Reports Server (NTRS)

Neyman's (1937) theory of confidence sets is developed as a replacement for Bayesian interference (BI) and stochastic inversion (SI) when the prior information is a hard quadratic bound. It is recommended that BI and SI be replaced by confidence set interference (CSI) only in certain circumstances. The geomagnetic problem is used to illustrate the general theory of CSI.

Backus, George E.

1989-01-01

394

Quadratic: manipulating algebraic expressions on an interactive tabletop  

Microsoft Academic Search

This paper introduces Quadratic---a virtual manipulative for two people to explore algebraic expressions on an interactive tabletop. Users assemble rectangles out of fundamental components: 1, x, and x2. As the area of a rectangle is both the product of its sides and the sum of its components, users can explore how the product of two linear expressions (the rectangle's sides)

Jochen Rick

2010-01-01

395

Quadratically gated mixture of experts for incomplete data classification  

Microsoft Academic Search

We introduce quadratically gated mixture of experts (QGME), a statistical model for multi-class nonlinear classiflcation. The QGME is formulated in the setting of incom- plete data, where the data values are partially observed. We show that the missing val- ues entail joint estimation of the data mani- fold and the classifler, which allows adaptive imputation during classifler learning. The expectation

Xuejun Liao; Hui Li; Lawrence Carin

2007-01-01

396

QUADRATIC FORMS AND FOUR PARTITION FUNCTIONS MODULO 3 JEREMY LOVEJOY AND ROBERT OSBURN  

E-print Network

QUADRATIC FORMS AND FOUR PARTITION FUNCTIONS MODULO 3 JEREMY LOVEJOY AND ROBERT OSBURN Abstract. partitions, overpartitions, congruences, binary quadratic forms, sums of squares. 1 #12;2 JEREMY LOVEJOY

Osburn, Robert

397

Local Linear Convergence of ADMM on Quadratic or Linear Daniel Boley  

E-print Network

: Alternating Direction Method of Multipliers, ADMM, linear programming, quadratic programming. AMSLocal Linear Convergence of ADMM on Quadratic or Linear Programs Daniel Boley University of Minnesota Minneapolis, MN 55455 USA Abstract In this paper, we analyze the convergence of the Alternating

Boley, Daniel

398

Finite Element Flux-Corrected Transport (FEM-FCT) for the Euler and Navier-Stokes equations  

NASA Technical Reports Server (NTRS)

A high resolution finite element method for the solution of problems involving high speed compressible flows is presented. The method uses the concepts of flux-corrected transport and is presented in a form which is suitable for implementation on completely unstructured triangular or tetrahedral meshes. Transient and steady state examples are solved to illustrate the performance of the algorithm.

Loehner, Rainald; Morgan, Ken; Peraire, Jaime; Vahdati, Mehdi

1987-01-01

399

Finite element flux-corrected transport (FEM-FCT) for the Euler and Navier-Stokes equations  

NASA Technical Reports Server (NTRS)

A high resolution finite element method for the solution of problems involving high speed compressible flows is presented. The method uses the concepts of flux-corrected transport and is presented in a form which is suitable for implementation on completely unstructured triangular or tetrahedral meshes. Transient and steady-state examples are solved to illustrate the performance of the algorithm.

Lohner, Rainald; Morgan, Ken; Peraire, Jaime; Vahdati, Mehdi

1987-01-01

400

On the time-weighted quadratic sum of linear discrete systems  

NASA Technical Reports Server (NTRS)

A method is proposed for obtaining the time-weighted quadratic sum for linear discrete systems. The formula of the weighted quadratic sum is obtained from matrix z-transform formulation. In addition, it is shown that this quadratic sum can be derived in a recursive form for several useful weighted functions. The discussion presented parallels that of MacFarlane (1963) for weighted quadratic integral for linear continuous systems.

Jury, E. I.; Gutman, S.

1975-01-01

401

Efficient Implementation of Cryptosystems Based on Non-maximal Imaginary Quadratic Orders  

Microsoft Academic Search

In [14] there is proposed an ElGamal-type cryptosystem based on non-maximal imaginary quadratic orders with trapdoor decryption.\\u000a The trapdoor information is the factorization of the non-fundamental discriminant ?p = ?1\\u000a p\\u000a 2. The NICE-cryptosystem (New Ideal Coset En-cryption) [24, 12] is an efficient variant thereof, which uses an element \\u000a \\u000a\\u000a\\u000a\\u000a\\u000a\\u000a\\\\mathfrakgk Î<\\/font\\u000a> Ker(Æ<\\/font\\u000a>cl -<\\/font\\u000a> 1 ) Í<\\/font\\u000a>

Detlef Hühnlein

1999-01-01

402

Implementation of an Evolving non Quadratic Anisotropic Behaviour for the Closed Packed Materials  

SciTech Connect

In this paper, the mechanical behaviour of alpha-titanium alloys is modelised for the cold forming processes. The elasto-plastic constitutive law is decomposed in an anisotropic plastic criterion, an isotropic hardening and a kinematic hardening. Non quadratic criteria have been developed by Cazacu et al.[1], to model the plasticity of hexagonal closed packed materials. The implementation of this model in a finite element software switch between two bases, the equilibrium is calculated in a reference basis and the anisotropy axes define a local basis, updated by the deformation gradient. An identification procedure, based on tensile tests, allows defining all the parameters needed to model the elasto-plastic behaviour. Simulations of cold forming processes (bulging and deep drawing) have been done to validate this model. Numerical results are compared with experimental data, obtained from speckles analysis.

Revil-Baudard, Benoit; Massoni, Elisabeth [CEMEF Mines ParisTech, B.P. 207, F-06904 Sophia-Antipolis (France)

2010-06-15

403

Mo-containing tetrahedral amorphous carbon deposited by dualfiltered cathodic vacuum arc with selective pulsed bias voltage  

SciTech Connect

Metal-containing tetrahedral amorphous carbon films were produced by dual filtered cathodic vacuum arc (FCVA) plasma sources operated in sequential pulsed mode. A negatively pulsed bias was applied to the substrate only when carbon plasma was generated. Films thickness was measured after deposition by profilometry. Glass slides with silver pads were used as substrate for the of the measurement sheet resistance. The microstructure and composition of the films were characterized by Raman spectroscopy and Rutherford backscattering, respectively. It found that the electrical resistivity decreases with an increase of the Mo content, which can be ascribed to an increase of sp2 content and an increase of the sp2 cluster size.

Pasaja, Nitisak; Sansongsiri, Sakon; Anders, Andre; Vilaithong,Thiraphat; Intasiri, Sawate

2006-09-10

404

Mo-containing tetrahedral amorphous carbon deposited by dualfiltered cathodic vacuum arc with selective pulsed bias voltage  

SciTech Connect

Metal-containing tetrahedral amorphous carbon films wereproduced by dual filtered cathodic vacuum arc plasma sources operatedinsequentially pulsed mode. Negatively pulsed bias was applied to thesubstrate when carbon plasma was generated, whereas it was absentwhen themolybdenum plasma was presented. Film thickness was measured afterdeposition by profilometry. Glass slides with silver padswere used assubstrates for the measurement of the sheet resistance. Themicrostructure and composition of the films were characterizedbyRamanspectroscopy and Rutherford backscattering, respectively. It was foundthat the electrical resistivity decreases with an increaseof the Mocontent, which can be ascribed to an increase of the sp2 content and anincrease of the sp2 cluster size.

Pasaja, Nitisak; Sansongsiri, Sakon; Intasiri, Sawate; Vilaithong, Thiraphat; Anders, Andre

2007-01-24

405

Tuning of tetrahedrality in a silicon potential yields a series of monatomic (metal-like) glassformers of very high fragility  

E-print Network

We obtain monatomic glass formers in simulations by modifying the tetrahedral character in a silicon potential to explore a triple point zone between potentials favoring diamond (dc) and bcc crystals. dc crystallization is always preceded by a polyamorphic transformation of the liquid, and is frustrated when the Kauzmann temperature of the high temperature liquid intersects the liquid-liquid coexistence line. The glass forming liquids are extraordinarily fragile. Our results suggest that Si and Ge liquids may be vitrified at a pressure close to the diamond-beta-tin-liquid triple point.

Valeria Molinero; Srikanth Sastry; C. Austen Angell

2006-08-15

406

Optimal Control of Rigid Body Angular Velocity with Quadratic Cost1  

E-print Network

interval with a quadratic integral penalty on the control variables and a terminal constraint on the state. In Section 3 we completely characterize the family of quadratic integrals of the unforced system and weOptimal Control of Rigid Body Angular Velocity with Quadratic Cost1 P. Tsiotras2, M. Corless3 and M

Tsiotras, Panagiotis

407

QUADRATIC SURFACE LYAPUNOV FUNCTIONS IN THE ANALYSIS OF FEEDBACK SYSTEMS WITH  

E-print Network

, and Integral Quadratic Constraints (IQCs). Nominal Plant Uncertainty P(s) s f(t) k s+k 2 p Figure 2: NominalQUADRATIC SURFACE LYAPUNOV FUNCTIONS IN THE ANALYSIS OF FEEDBACK SYSTEMS WITH DOUBLE INTEGRATORS 91125 jmg@cds.caltech.edu http://www.cds.caltech.edu/#24;jmg/ Keywords: Quadratic surface Lyapunov

Gonçalves, Jorge

408

Consensus analysis via integral quadratic constraints Sei Zhen Khong, Enrico Lovisari and Anders Rantzer  

E-print Network

Consensus analysis via integral quadratic constraints Sei Zhen Khong, Enrico Lovisari and Anders problems via the use of integral quadratic constraints (IQCs) without recourse to loop transfor- mations-agent systems, feedback sys- tems, integral quadratic constraints AMS Subject Classifications--93A15, 93C05, 93C

Como, Giacomo

409

Fourteen years of mapped, permanent quadrats in a northern mixed prairie, USA  

Technology Transfer Automated Retrieval System (TEKTRAN)

This historical dataset consists of 44 permanent 1-m2 quadrats located on northern mixed prairie in eastern Montana, USA. Individual plants in these quadrats were identified and mapped annually from 1932 through 1945. Quadrats were located in six pastures assigned to cattle grazing treatments with l...

410

Algorithms to solve massively under-defined systems of multivariate quadratic equations  

E-print Network

Algorithms to solve massively under-defined systems of multivariate quadratic equations Yasufumi chosen multivariate quadratic equations over a finite field is NP-hard. However, when the number quadratic equations; one is for the case of n (about) m2 -2m3/2 +2m and the other is for the case of n m

411

Properties of quadratic equations and their application to power system analysis  

E-print Network

Properties of quadratic equations and their application to power system analysis Y.V. Makarova,1 and control can be described by algebraic sets of quadratic equations of the form fx y gx 0 1 where x Rn x as a quadratic equations set with the Jacobian matrix Jx being a linear function of unknown variables. In any

Hiskens, Ian A.

412

A Hybrid Linear Equation Solver and its Application in Quadratic Placement  

E-print Network

A Hybrid Linear Equation Solver and its Application in Quadratic Placement Haifeng Qian and Sachin-- This paper presents a new hybrid linear equation solver for quadratic placement. The new solver widely used approaches fall into several different paradigms: quadratic placement [6

Sapatnekar, Sachin

413

Solving Quadratic Equations via PhaseLift when There Are About As Many Equations As Unknowns  

E-print Network

Solving Quadratic Equations via PhaseLift when There Are About As Many Equations As Unknowns vector x0 Cn exactly from on the order of n quadratic equations of the form | ai, x0 |2 = bi, i = 1 Introduction Suppose we wish to solve quadratic equations of the form | ai, x0 |2 = bi, i = 1, . . . , m, (1

Candes, Emmanuel J.

414

Geodesic diameter of sets defined by few quadratic equations and inequalities  

E-print Network

Geodesic diameter of sets defined by few quadratic equations and inequalities Michel Coste of the unit ball in Rn described by a fixed number of quadratic equations and inequalities, whichO(k) for the geodesic diameter of (a bounded part of) a semialgebraic subset of Rn defined by k quadratic equations

Paris-Sud XI, Université de

415

SOLVING A QUADRATIC MATRIX EQUATION BY NEWTON'S METHOD WITH EXACT LINE SEARCHES  

E-print Network

SOLVING A QUADRATIC MATRIX EQUATION BY NEWTON'S METHOD WITH EXACT LINE SEARCHES NICHOLAS J. HIGHAM for solving the quadratic matrix equation AX2 + BX + C = 0, where A, B and C are square matrices. The line the backward error of an approximate solution. Key words. quadratic matrix equation, solvent, Newton's method

Higham, Nicholas J.

416

REMARKS ON THE CAUCHY PROBLEM FOR THE ONE-DIMENSIONAL QUADRATIC (FRACTIONAL) HEAT EQUATION  

E-print Network

REMARKS ON THE CAUCHY PROBLEM FOR THE ONE-DIMENSIONAL QUADRATIC (FRACTIONAL) HEAT EQUATION LUC quadratic (fractional) heat equation: ut = D2 x u u2 , t (0, T), x R or T, with 0 introduced by Bejenaru-Tao [1] for a one-dimensional quadratic Schr¨odinger equation. This approach is based

Boyer, Edmond

417

Department of Mathematics 7.1: Quadratic Equations: Completing the Square  

E-print Network

UNLV Department of Mathematics §7.1: Quadratic Equations: Completing the Square 1. Review) Quadratic Equation: An equation that can be written in the form ax2 + bx + c = 0 where a, b and c are real numbers and a = 0 is called a quadratic equation. (c) To Solve an Equation by Factoring i. Add or subtract

Ahmad, Sajjad

418

STATIONARY STATES OF QUADRATIC DIFFUSION EQUATIONS WITH LONG-RANGE ATTRACTION  

E-print Network

STATIONARY STATES OF QUADRATIC DIFFUSION EQUATIONS WITH LONG-RANGE ATTRACTION M. BURGER, M. DI to a nonlocal aggregation equation with quadratic diffusion arising in many contexts in population dynamics. The equation is the Wasserstein gradient flow generated by the energy E, which is the sum of a quadratic free

Soatto, Stefano

419

Article Submitted to IMA Journal of Numerical Analysis On a quadratic matrix equation associated  

E-print Network

Article Submitted to IMA Journal of Numerical Analysis On a quadratic matrix equation associated 0A2, Canada (chguo@math.uregina.ca) Abstract We study the quadratic matrix equation X2 - EX - F = 0, where E is diagonal and F is an M-matrix. Quadratic matrix equations of this type arise in noisy Wiener

Guo, Chun-Hua

420

Alignment-orientation conversion by quadratic Zeeman effect: Analysis and observation for Te2  

E-print Network

Alignment-orientation conversion by quadratic Zeeman effect: Analysis and observation for Te2 I. P momenta into orientation due to quadratic correction to Zeeman effect. Circularity rate up to 0 of the quadratic correction to the Zeeman effect in diatomic mol- ecules. In particular, we direct now our

Auzinsh, Marcis

421

Experimental Observation of Self-Accelerating Beams in Quadratic Nonlinear Media Ido Dolev,1  

E-print Network

, experiments with Airy beams in quadratic media include the generation and manipulation of Airy beams throughExperimental Observation of Self-Accelerating Beams in Quadratic Nonlinear Media Ido Dolev,1 Ido present the experimental observation of 1D and 2D self-accelerating nonlinear beams in quadratic media

Arie, Ady

422

American Elements  

NSDL National Science Digital Library

This company's web site features an interactive periodic chart that provides information on the elements, including a description, physical and thermal properties, abundance, isotopes, ionization energy, the element's discoverer, translations of element names into several languages, and bibliographic information on research-and-development publications involving the element. Additional information includes technical information and information on manufactured products for elemental metals, metallic compounds, and ceramic and crystalline products. The American Elements company manufactures engineered and advanced material products.

2006-02-27

423

Chemical Elements  

NSDL National Science Digital Library

To find quick facts on elements The Photographic Periodic Table of Elements-shows a photograhpic representation of most of the elements (remember some are invisible gases) The Element Song Click on the following links to find quick facts about the elements and peridoic table: Periodic Table of Elements: LANL - Originally this resource, the Periodic Table, was created by Robert Husted at Los Alamos National Laboratory during his time ...

Schultz, Ms.

2007-03-08

424

Synthesis and characterization of Na5M(2+x)Sn(10-x) (x approximately = 0.5, M = Zn, Hg)--a doped tetrahedral framework structure.  

PubMed

Two homologous and isostructural compounds Na(5)M(2+x)Sn(10-x) (M = Zn, Hg) were obtained by direct reaction of the elements at high temperature. The crystal structures of these novel phases were determined from single-crystal X-ray diffraction data and represent a new structure type in tin chemistry. They crystallize in the space group Pbcn (No. 60, Z = 4) with a = 12.772(1), b = 10.804(1), and c = 12.777(1) A, V = 1763.1(2) A(3) for Na(5)Zn(2.28)Sn(9.72(2)) (I) and a = 12.958(1), b = 10.984(1), and c = 12.960(1) A, V = 1844.5(2) A(3) for Na(5)Hg(2.39)Sn(9.61(1)) (II). The structures consist of an anionic 3D open framework of tetrahedrally coordinated Sn and M atoms interwoven with a cationic 2D array of interconnected {NaNa(4)} tetrahedra. The framework can be partitioned into fragments of realgar-like units {Sn(8-x)M(x)}(2x-) and twice as many {Sn-M}(2-) dimers. Formally, the compounds are charge-balanced Zintl phases for x = 0.5. As the structure refinements lead to x = 0.28 and 0.39 for I and II, respectively, both structures are electron-rich and expected to be metallic. Theoretical investigations at the density functional theory level reveal a deep minimum at the Fermi level for x = 0.5. According to rigid band analyses, the electronic structure of the phases with the experimentally observed compositions corresponds to heavily doped semiconductors, thereby meeting an important requirement of thermoelectric materials. PMID:19621968

Ponou, Siméon; Kim, Sung-Jin; Fässler, Thomas F

2009-07-29

425

Multi-level homotopy perturbation and projection techniques for the reanalysis of quadratic eigenvalue problems: The application of stability analysis  

NASA Astrophysics Data System (ADS)

Complex eigenvalue analysis is widely used to investigate the stability of a dynamical system with frictional contact. For finite element models, iterative solvers are needed to precisely calculate complex modes and eigenvalues. However, in cases such as reanalysis studies, optimization or uncertainty propagation processes, computational cost can quickly become too time consuming. For multiple samplings, two methods combining homotopy perturbation and projection techniques are proposed for the reanalysis of quadratic eigenvalue problems. To highlight the efficiency of the proposed methods, a complete numerical application including nominal and perturbed solution calculations, coalescence graph and parametric analysis, is performed. The precision of results and computational time are compared with those obtained using commercial software.

Massa, F.; Lallemand, B.; Tison, T.

2015-02-01

426

Electrical and Electrochemical Properties of Nitrogen-Containing Tetrahedral Amorphous Carbon (ta-C) Thin Films  

NASA Astrophysics Data System (ADS)

Tetrahedral amorphous carbon (ta-C) is a diamond-like carbon (DLC) material comprised of a mixture of sp2 (˜40%) and sp3-bonded (˜60%) carbon domains. The physicochemical structure and electrochemical properties depend strongly on the sp2/sp3 bonding ratio as well as the incorporation of impurities, such as hydrogen or nitrogen. The ability to grow ta-C films at lower temperatures (25-100 °C) on a wider variety of substrates is a potential advantage of these materials as compared with diamond films. In this project, the basic structural and electrochemical properties of nitrogen-incorporated ta-C thin films will be discussed. The major goal of this work was to determine if the ta-C:N films exhibit electrochemical properties more closely aligned with those of boron-doped diamond (sp 3 carbon) or glassy carbon (amorphous sp2 carbon). Much like diamond, ta-C:N thin-film electrodes are characterized by a low background voltammetric current, a wide working potential window, relatively rapid electron-transfer kinetics for aqueous redox systems, such as Fe(CN) 6-3/-4 and Ru(NH3)6+3/+2 , and weak adsorption of polar molecules from solution. For example, negligible adsorption of methylene blue was found on the ta-C:N films in contrast to glassy carbon; a surface on which this molecule strongly adsorbs. The film microstructure was studied with x-ray photoelectron microscopy (XPS), visible Raman spectroscopy and electron-energy loss spectroscopy (EELS); all of which revealed the sp2-bonded carbon content increased with increasing nitrogen. The electrical properties of ta-C:N films were studied by four-point probe resistance measurement and conductive-probe AFM (CP-AFM). The incorporation of nitrogen into ta-C films increased the electrical conductivity primarily by increasing the sp2-bonded carbon content. CP-AFM showed the distribution of the conductive sp2-carbon on the film surface was not uniform. These films have potential to be used in field emission area. The heterogeneous electrochemical properties were studied with scanning electron microscopy (SECM). If was found that more electrically conducting sites were isolated by less conducting or even insulating sites. Consistent with the heterogeneous electrical properties, heterogeneous electrochemical activity was observed for different aqueous redox analytes. Flow injection analysis with electrochemical detection (EC-FIA) of dopamine and norepinephrine were carried out using the N-ta:C films. Detection figures of merit for these biomolecules were determined. These biomolecules can be detected stably and reproducible in PBS buffer at constant potential by N-ta:C film. The N-ta:C films provide good limits of detection for these biomolecules. N-ta:C films show great promise in the electroanalytical field. Compared with the diamond, the growth condition is much milder. These N-ta:C films are commercially available and could be produced in large scale. All of these virtues make N-ta:C films excellent choices for electroanalytical measurements.

Yang, Xingyi

427

The effect of tetrahedral Al 3+ on the partitioning of water between clinopyroxene and silicate melt  

NASA Astrophysics Data System (ADS)

This experimental study examines the influence of tetrahedrally coordinated Al 3+ ( IVAl 3+) on the partitioning of H + between high-Ca clinopyroxene and silicate melt. Experiments were carried out at 1.5 GPa and 1275 to 1350 °C on a natural high-alumina basalt and a compositionally similar synthetic basalt that is nominally alumina free. The results extend the compositional range of clinopyroxene for which partitioning has been determined experimentally to both higher and lower IVAl 3+, thereby clarifying its role in maintaining charge neutrality during H + incorporation. Clinopyroxene-melt partition coefficients for H + ( DH2OCpx - Melt) determined for the high-alumina basalt are among largest ever reported ( DH2OCpx - Melt = 0.0228 to 0.0477), while those determined for the nominally alumina-free starting composition are the smallest ( DH2OCpx - Melt = 0.00445 to 0.0071). Our results confirm that H + is incorporated into clinopyroxene through two independent mechanisms: (1) the creation of metal vacancies and coupled hydroxyl defects and (2) a coupled substitution involving IVAl 3+ that creates isolated hydroxyl defects. The relative importance of each of these incorporation mechanisms was quantified by formulating DH2OCpx - Melt as the sum of a metal vacancy-related partition coefficient ( DH2OVMe) and an Al-coupled substitution-related partition coefficient ( DH2OAl) and fitting the resulting expression to all available experimental data. The contribution of DH2OVMe to DH2OCpx - Melt is relatively constant at 0.006 ± 0.002, but is sensitive to pressure, temperature, H 2O fugacity and pyroxene composition. The contribution of DH2OAl varies from ˜ 0 to 0.038 and is strongly dependent on phase composition, but insensitive to pressure and temperature. Two parameterizations of DH2OCpx - Melt that account for the potential effects of temperature, pressure and phase composition were calibrated using our data and experimentally determined partition coefficients from the literature. The first parameterization considers only compositional effects and can be used to estimate DH2OCpx - Melt in cases where pressure and/or temperature are unknown. This equation was used to demonstrate that the pre-eruptive H 2O contents of arc lavas calculated on the basis of H + in clinopyroxene phenocrysts are systematically higher than those inferred from olivine-hosted melt inclusions, so that the former provide a record that is closer to primary (undegassed) values. The second parameterization considers the effects of pressure and temperature in addition to phase composition and provides a moderately better fit to the experimental data. This equation was used to re-evaluate the influence of H 2O on the depth at which peridotite partial melting begins beneath oceanic spreading centers. Our calculations indicate that partial melting begins at depths that are shallower than suggested by previous estimates. For a potential temperature of 1350 °C, peridotite containing 50, 100, 150, and 200 ppm H 2O dissolved in nominally anhydrous minerals begins melting at depths of 75, 79, 83, and 87 km, respectively.

O'Leary, Julie A.; Gaetani, Glenn A.; Hauri, Erik H.

2010-08-01

428

Large Deviation Principle for Benedicks-Carleson Quadratic Maps  

NASA Astrophysics Data System (ADS)

Since the pioneering works of Jakobson and Benedicks & Carleson and others, it has been known that a positive measure set of quadratic maps admit invariant probability measures absolutely continuous with respect to Lebesgue. These measures allow one to statistically predict the asymptotic fate of Lebesgue almost every initial condition. Estimating fluctuations of empirical distributions before they settle to equilibrium requires a fairly good control over large parts of the phase space. We use the sub-exponential slow recurrence condition of Benedicks & Carleson to build induced Markov maps of arbitrarily small scale and associated towers, to which the absolutely continuous measures can be lifted. These various lifts together enable us to obtain a control of recurrence that is sufficient to establish a level 2 large deviation principle, for the absolutely continuous measures. This result encompasses dynamics far from equilibrium, and thus significantly extends presently known local large deviations results for quadratic maps.

Chung, Yong Moo; Takahasi, Hiroki

2012-11-01

429

Multiresolution analysis over triangles, based on quadratic Hermite interpolation  

NASA Astrophysics Data System (ADS)

Given a triangulation T of , a recipe to build a spline space over this triangulation, and a recipe to refine the triangulation T into a triangulation T', the question arises whether , i.e., whether any spline surface over the original triangulation T can also be represented as a spline surface over the refined triangulation T'. In this paper we will discuss how to construct such a nested sequence of spaces based on Powell-Sabin 6-splits for a regular triangulation. The resulting spline space consists of piecewise C1-quadratics, and refinement is obtained by subdividing every triangle into four subtriangles at the edge midpoints. We develop explicit formulas for wavelet transformations based on quadratic Hermite interpolation, and give a stability result with respect to a natural norm.

Dæhlen, M.; Lyche, T.; Mørken, K.; Schneider, R.; Seidel, H.-P.

2000-07-01

430

Linear quadratic regulators with eigenvalue placement in a specified region  

NASA Technical Reports Server (NTRS)

A linear optimal quadratic regulator is developed for optimally placing the closed-loop poles of multivariable continuous-time systems within the common region of an open sector, bounded by lines inclined at + or - pi/2k (k = 2 or 3) from the negative real axis with a sector angle of pi/2 or less, and the left-hand side of a line parallel to the imaginary axis in the complex s-plane. The design method is mainly based on the solution of a linear matrix Liapunov equation, and the resultant closed-loop system with its eigenvalues in the desired region is optimal with respect to a quadratic performance index.

Shieh, Leang S.; Dib, Hani M.; Ganesan, Sekar

1988-01-01

431

Spinor condensates with a laser-induced quadratic Zeeman effect  

SciTech Connect

We show that an effective quadratic Zeeman effect for trapped atoms can be generated by proper laser configurations and, in particular, by the dipole trap itself. The induced quadratic Zeeman effect leads to a rich ground-state phase diagram, e.g., for a degenerate {sup 52}Cr gas, can be used to induce topological defects by controllably quenching across transitions between phases of different symmetries, allows for the observability of the Einstein-de Haas effect for relatively large magnetic fields, and may be employed to create S=1/2 systems with spinor dynamics. Similar ideas could be explored in other atomic species opening an exciting new control tool in spinor systems.

Santos, L. [Institut fuer Theoretische Physik, Leibniz Universitaet Hannover, Appelstr. 2, D-30167 Hannover (Germany); Fattori, M.; Stuhler, J.; Pfau, T. [5. Physikalisches Institut, Universitaet Stuttgart, Pfaffenwaldring 57 V, D-70550 Stuttgart (Germany)

2007-05-15

432

Quadratic nonlinear Klein-Gordon equation in one dimension  

NASA Astrophysics Data System (ADS)

We study the initial value problem for the quadratic nonlinear Klein-Gordon equation vtt + v - vxx = ?v2, t ? R, x ? R, with initial conditions v(0, x) = v0(x), vt(0, x) = v1(x), x ? R, where v0 and v1 are real-valued functions, ? ? R. Using the method of normal forms of Shatah ["Normal forms and quadratic nonlinear Klein-Gordon equations," Commun. Pure Appl. Math. 38, 685-696 (1985)], we obtain a sharp asymptotic behavior of small solutions without the condition of a compact support on the initial data, which was assumed in the previous work of J.-M. Delort ["Existence globale et comportement asymptotique pour l'équation de Klein-Gordon quasi-linéaire á données petites en dimension 1," Ann. Sci. Ec. Normale Super. 34(4), 1-61 (2001)].

Hayashi, Nakao; Naumkin, Pavel I.

2012-10-01

433

On the Distribution in Arithmetic Progressions of Reducible Quadratic Polynomials  

NASA Astrophysics Data System (ADS)

By using Weil's estimate for Kloosterman sums, we obtain a result on the distribution of the sequence n(n+2), beyond the classical level, when a bilinear form with support over pairs of prime moduli is considered. We also obtain an analogous result in the case of a trilinear form, but only by using the recent results of Deshouillers-Iwaniec for sums of Kloosterman sums. Furthermore, the method is extended to general reducible quadratic polynomials.

Salerno, S.; Vitolo, A.

1995-02-01

434

Ultracold two-level atom in a quadratic potential  

E-print Network

We use a right unitary decomposition to study an ultracold two-level atom interacting with a quantum field. We show that such a right unitary approach simplifies the numerical evolution for arbitrary position-dependent atom-field couplings. In particular, we provide a closed form, analytic time evolution operator for atom-field couplings with quadratic dependence on the position of the atom.

F. Soto-Eguibar; A. Zúñiga-Segundo; B. M. Rodríguez-Lara; H. M. Moya-Cessa

2014-12-17

435

Quantum integrals of motion for variable quadratic Hamiltonians  

SciTech Connect

We construct integrals of motion for several models of the quantum damped oscillators in a framework of a general approach to the time-dependent Schroedinger equation with variable quadratic Hamiltonians. An extension of the Lewis-Riesenfeld dynamical invariant is given. The time-evolution of the expectation values of the energy-related positive operators is determined for the oscillators under consideration. A proof of uniqueness of the corresponding Cauchy initial value problem is discussed as an application.

Cordero-Soto, Ricardo, E-mail: ricardojavier81@gmail.co [Mathematical, Computational and Modeling Sciences Center, Arizona State University, Tempe, AZ 85287-1804 (United States); Suazo, Erwin, E-mail: erwin.suazo@upr.ed [Department of Mathematical Sciences, University of Puerto Rico, Mayaquez, call box 9000, PR 00681-9000 (Puerto Rico); Suslov, Sergei K., E-mail: sks@asu.ed [School of Mathematical and Statistical Sciences and Mathematical, Computational and Modeling Sciences Center, Arizona State University, Tempe, AZ 85287-1804 (United States)

2010-09-15

436

Metric operators for non-Hermitian quadratic su(2) Hamiltonians  

NASA Astrophysics Data System (ADS)

A class of non-Hermitian quadratic su(2) Hamiltonians having an anti-linear symmetry is constructed. This is achieved by analysing the possible symmetries of such systems in terms of automorphisms of the algebra. In fact, different realizations for this type of symmetry are obtained, including the natural occurrence of charge conjugation together with parity and time reversal. Once specified, the underlying anti-linear symmetry of the Hamiltonian, the former, if unbroken, leads to a purely real spectrum and the latter can be mapped to a Hermitian counterpart by, amongst other possibilities, a similarity transformation. Here, Lie-algebraic methods which were used to investigate the generalized Swanson Hamiltonian (Assis and Fring 2009 J. Phys. A: Math. Theor. 42 015203) are employed to identify the class of quadratic Hamiltonians that allow for such a mapping to the Hermitian counterpart. Whereas for the linear su(2) system, every Hamiltonian of this type can be mapped to a Hermitian counterpart by a transformation which is itself an exponential of a linear combination of su(2) generators, the situation is more complicated for quadratic Hamiltonians. Therefore, the possibility of more elaborate similarity transformations, including quadratic exponents, is also explored in detail. The existence of finite-dimensional representations for the su(2) Hamiltonian, as opposed to the su(1, 1) studied before, allows for comparison with explicit diagonalization results for finite matrices. Finally, the similarity transformations constructed are compared with the analogue of Swanson's method for exact diagonalization of the problem, establishing a simple relation between both approaches.

Assis, Paulo E. G.

2011-07-01

437

Quadratic performance index generation for optimal regular design.  

NASA Technical Reports Server (NTRS)

Application of optimal control theory to practical problems has been limited by the difficulty of prescribing a performance index which accurately reflects design requirements. The task of deriving equivalent performance indices is considered in the present paper for a plant that is a completely controllable, scalar linear system with state feedback. A quadratic index is developed which leads to an optimal design performance satisfying some of the classical performance criteria.

Bullock, T. E.; Elder, J. M.

1971-01-01

438

Path-Integral for Quadratic Hamiltonian Systems and Boundary Conditions  

Microsoft Academic Search

A path-integral representation for the kernel of the evolution operator of\\u000ageneral Hamiltonian systems is reviewed. We study the models with bosonic and\\u000afermionic degrees of freedom. A general scheme for introducing boundary\\u000aconditions in the path-integral is given. We calculate the path-integral for\\u000athe systems with quadratic first class constraints and present an explicit\\u000aformula for the heat kernel

A. T. Filippov; A. P. Isaev

1998-01-01

439

Path-Integral for Quadratic Hamiltonian Systems and Boundary Conditions  

Microsoft Academic Search

A path-integral representation for the kernel of the evolution operator of general Hamiltonian systems is reviewed. We study the models with bosonic and fermionic degrees of freedom. A general scheme for introducing boundary conditions in the path-integral is given. We calculate the path-integral for the systems with quadratic first class constraints and present an explicit formula for the heat kernel

A. T. Filippov; A. P. Isaev

1998-01-01

440

Efficient solution of linear matrix inequalities for integral quadratic constraints  

Microsoft Academic Search

Discusses how to implement an efficient interior-point algorithm for the semi-definite programs that result from integral quadratic constraints. The algorithm is a primal-dual potential reduction method, and the computational effort is dominated by a least-squares system that has to be solved in each iteration. The key to an efficient implementation is to utilize iterative methods and the specific structure of

Anders Hansson; Lieven Vandenberghe

2000-01-01

441

Structure and factorization of quadratic constraints for robustness analysis  

Microsoft Academic Search

This paper extends and generalizes the preliminary results of Goh and Safonov (1995), linking the integral quadratic constraint (IQC) approach for robust analysis to previous work on generalized sectors, dissipativity and J-spectral factorization\\/indefinite scalar products. The emphasis is on the factorization theory associated with the fact that IQCs for robust analysis must have a J-spectral factorization ? -??z*S* (?)diag(I,-I)S(?)z d?.

Keat-Choon Gohl

1996-01-01

442

Quadratic thermal terms in the deconfined phase from holography  

E-print Network

Recent lattice simulation has uncovered many interesting properties of SU(N) gauge theory at finite temperature. Especially, above the deconfinement phase transition all the thermodynamics quantities acquire significant quadratic contributions in inverse temperature. Such a term is also found to dominate the logarithmic of the renormalized Polyakov loop. Using the Hawking-Page transition in Anti-de Sitter space as an example, we show how such contributions can be naturally generated in the holographic approach.

Fen Zuo; Yi-Hong Gao

2014-03-10

443

Design of Linear Quadratic Regulators and Kalman Filters  

NASA Technical Reports Server (NTRS)

AESOP solves problems associated with design of controls and state estimators for linear time-invariant systems. Systems considered are modeled in state-variable form by set of linear differential and algebraic equations with constant coefficients. Two key problems solved by AESOP are linear quadratic regulator (LQR) design problem and steady-state Kalman filter design problem. AESOP is interactive. User solves design problems and analyzes solutions in single interactive session. Both numerical and graphical information available to user during the session.

Lehtinen, B.; Geyser, L.

1986-01-01

444

Hirota quadratic equations for the extended Toda hierarchy  

Microsoft Academic Search

The extended Toda hierarchy (ETH) was introduced by E. Getzler [Ge] and independently by Y. Zhang [Z] in order to describe an integrable hierarchy that governs the Gromov-Witten invariants of $\\\\mathbb{C}P^1$ . The Lax-type presentation of the ETH was given in [CDZ]. In this article, we give a description of the ETH in terms of tau functions and Hirota quadratic

Todor E. Milanov

2007-01-01

445

A fixed point approach to stability of a quadratic equation  

Microsoft Academic Search

.  Using the fixed point alternative theorem we establish the orthogonal stability of the quadratic functional equation of Pexider\\u000a type f (x+y)+g(x?y) = h(x)+k(y), where f, g, h, k are mappings from a symmetric orthogonality space to a Banach space, by orthogonal additive mappings under a necessary and\\u000a sufficient condition on f.

M. Mirzavaziri; M. S. Moslehian

2006-01-01

446

Central Control, Sewers and (0,1) quadratic programming  

NASA Astrophysics Data System (ADS)

We consider small sewer systems that combine foul water and storm water sewer functions in flat terrain. These systems are a combination of local gravity flow networks connected by pumps. The pumps are usually fixed speed, so they are on or off. We formulate a (0,1) quadratic programming problem, provide an overview of known solution methods and examine the relative speed of different solution methods.

Kolechkina, Alla; van Nooijen, Ronald

2013-04-01

447

Nonlinear regularization path for quadratic loss support vector machines.  

PubMed

Regularization path algorithms have been proposed to deal with model selection problem in several machine learning approaches. These algorithms allow computation of the entire path of solutions for every value of regularization parameter using the fact that their solution paths have piecewise linear form. In this paper, we extend the applicability of regularization path algorithm to a class of learning machines that have quadratic loss and quadratic penalty term. This class contains several important learning machines such as squared hinge loss support vector machine (SVM) and modified Huber loss SVM. We first show that the solution paths of this class of learning machines have piecewise nonlinear form, and piecewise segments between two breakpoints are characterized by a class of rational functions. Then we develop an algorithm that can efficiently follow the piecewise nonlinear path by solving these rational equations. To solve these rational equations, we use rational approximation technique with quadratic convergence rate, and thus, our algorithm can follow the nonlinear path much more precisely than existing approaches such as predictor-corrector type nonlinear-path approximation. We show the algorithm performance on some artificial and real data sets. PMID:21880570

Karasuyama, Masayuki; Takeuchi, Ichiro

2011-10-01

448

Quadratic constrained mixed discrete optimization with an adiabatic quantum optimizer  

E-print Network

We extend the family of problems that may be implemented on an adiabatic quantum optimizer (AQO). When a quadratic optimization problem has at least one set of discrete controls and the constraints are linear, we call this a quadratic constrained mixed discrete optimization (QCMDO) problem. QCMDO problems are NP-hard, and no efficient classical algorithm for their solution is known. Included in the class of QCMDO problems are combinatorial optimization problems constrained by a linear partial differential equation (PDE) or system of linear PDEs. An essential complication commonly encountered in solving this type of problem is that the linear constraint may introduce many intermediate continuous variables into the optimization while the computational cost grows exponentially with problem size. We resolve this difficulty by developing a constructive mapping from QCMDO to quadratic unconstrained binary optimization (QUBO) such that the size of the QUBO problem depends only on the number of discrete control variables. With a suitable embedding, taking into account the physical constraints of the realizable coupling graph, the resulting QUBO problem can be implemented on an existing AQO. The mapping itself is efficient, scaling cubically with the number of continuous variables in the general case and linearly in the PDE case if an efficient preconditioner is available.

Rishabh Chandra; N. Tobias Jacobson; Jonathan E. Moussa; Steven H. Frankel; Sabre Kais

2014-03-20

449

Understanding Elements  

NSDL National Science Digital Library

Students examine the periodic table and the properties of elements. They learn the basic definition of an element and the 18 elements that compose most of the matter in the universe. The periodic table is described as one method of organization for the elements. The concepts of physical and chemical properties are also reviewed.

Integrated Teaching And Learning Program

450

A refined higher-order C° plate bending element  

Microsoft Academic Search

A general finite element formulation for plate bending problem based on a higher-order displacement model and a threedimensional state of stress and strain is attempted. The theory incorporates linear and quadratic variations of transverse normal strain and transverse shearing strains and stresses respectively through the thickness of the plate. The 9-noded quadrilateral from the family of two dimensional Co continuous

TARUN KANT; D. R. J. OWENS; C. ZIENKIEWICZQ

1982-01-01

451

Water Adsorption at the Tetrahedral Titania Surface Layer of SrTiO3(110)-(4 × 1)  

PubMed Central

The interaction of water with oxide surfaces is of great interest for both fundamental science and applications. We present a combined theoretical (density functional theory (DFT)) and experimental (scanning tunneling microscopy (STM) and photoemission spectroscopy (PES)) study of water interaction with the two-dimensional titania overlayer that terminates the SrTiO3(110)-(4 × 1) surface and consists of TiO4 tetrahedra. STM and core-level and valence band PES show that H2O neither adsorbs nor dissociates on the stoichiometric surface at room temperature, whereas it does dissociate at oxygen vacancies. This is in agreement with DFT calculations, which show that the energy barriers for water dissociation on the stoichiometric and reduced surfaces are 1.7 and 0.9 eV, respectively. We propose that water weakly adsorbs on two-dimensional, tetrahedrally coordinated overlayers. PMID:24353755

2013-01-01

452

Creepers: Real quadratic orders with large class number  

NASA Astrophysics Data System (ADS)

Shanks's sequence of quadratic fields Q(sqrt{S_{n}}) where S_{n}=(2^n+1)^2 + 2^{n+2} instances a class of quadratic fields for which the class number is large and, therefore, the continued fraction period is relatively short. Indeed, that period length increases linearly with n, that is: in arithmetic progression. The fields have regulator O(n^2). In the late nineties, these matters intrigued Irving Kaplansky, and led him to compute period length of the square root of sequences a^2x^{2n}+bx^{n}+c for integers a, b, c, and x. In brief, Kap found unsurprisingly that, generically, triples (a,b,c) are `leapers': they yield sequences with period length increasing at exponential rate. But there are triples yielding sequences with constant period length, Kap's `sleepers'. Finally, there are triples, as exemplified by the Shanks's sequence, for which the period lengths increase in arithmetic progression. Felicitously, Kaplansky called these `creepers'. It seems that the sleepers and creepers are precisely those for which one is able to detail the explicit continued fraction expansion for all n. Inter alia, this thesis noticeably extends the known classes of creepers and finds that not all are `kreepers' (of the shape identified by Kaplansky) and therefore not of the shape of examples studied by earlier authors looking for families of quadratic number fields with explicitly computable unit and of relatively large regulator. The work of this thesis includes the discovery of old and new families of hyperelliptic curves of increasing genus g and torsion divisor of order O(g^2). It follows that the apparent trichotomy leaper/sleeper/creeper coincides with the folk belief that the just-mentioned torsion is maximum possible.

Patterson, Roger

2007-03-01

453

Hierarchically structured meso-macroporous aluminosilicates with high tetrahedral aluminium content in acid catalysed esterification of fatty acids.  

PubMed

A simple synthesis pathway has been developed for the design of hierarchically structured spongy or spherical voids assembled meso-macroporous aluminosilicates with high tetrahedral aluminium content on the basis of the aqueous polymerisation of new stabilized alkoxy-bridged single molecular precursors. The intimate mixing of an aluminosilicate ester (sec-BuO)(2)-Al-O-Si(OEt)(3) and a silica co-reactant (tetramethoxysilane, TMOS) with variable ratios and the use of alkaline solutions (pH 13.0 and 13.5) improve significantly the heterocondensation rates between the highly reactive aluminium alkoxide part of the single precursor and added silica co-reactant, leading to aluminosilicate materials with high intra-framework aluminium content and low Si/Al ratios. The spherically-shaped meso-macroporosity was spontaneously generated by the release of high amount of liquid by-products (water/alcohol molecules) produced during the rapid hydrolysis and condensation processes of this double alkoxide and the TMOS co-reactant. It has been observed that both pH value and Al-Si/TMOS molar ratio can strongly affect the macroporous structure formation. Increasing pH value, even slightly from 13 to 13.5, can significantly favour the incorporation of Al atoms in tetrahedral position of the framework. After the total ionic exchange of Na(+) compensating cations, catalytic tests of obtained materials were realised in the esterification reaction of high free fatty acid (FFA) oils, showing their higher catalytic activity compared to commercial Bentonite clay, and their potential applications as catalyst supports in acid catalysed reactions. PMID:21875708

Lemaire, Arnaud; Wang, Quan-Yi; Wei, Yingxu; Liu, Zhongmin; Su, Bao-Lian

2011-11-15

454

Toward Verification of USM3D Extensions for Mixed Element Grids  

NASA Technical Reports Server (NTRS)

The unstructured tetrahedral grid cell-centered finite volume flow solver USM3D has been recently extended to handle mixed element grids composed of hexahedral, prismatic, pyramidal, and tetrahedral cells. Presently, two turbulence models, namely, baseline Spalart-Allmaras (SA) and Menter Shear Stress Transport (SST), support mixed element grids. This paper provides an overview of the various numerical discretization options available in the newly enhanced USM3D. Using the SA model, the flow solver extensions are verified on three two-dimensional test cases available on the Turbulence Modeling Resource website at the NASA Langley Research Center. The test cases are zero pressure gradient flat plate, planar shear, and bump-inchannel. The effect of cell topologies on the flow solution is also investigated using the planar shear case. Finally, the assessment of various cell and face gradient options is performed on the zero pressure gradient flat plate case.

Pandya, Mohagna J.; Frink, Neal T.; Ding, Ejiang; Parlette, Edward B.

2013-01-01

455

Element Research  

NSDL National Science Digital Library

You have been assigned an element during class. Your mission is to research information about your element. Create a Word document with the title of your element. Save your work regularly! Next, use the resources on this page to find and record the following information in your word document. (Hint: copy and paste the questions into your word document, then answer them.) See It s Elemental for electron configuration - ...

Wall, Mr.

2008-12-09

456

Rigorous performance bounds for quadratic and nested dynamical decoupling  

SciTech Connect

We present rigorous performance bounds for the quadratic dynamical decoupling pulse sequence which protects a qubit from general decoherence, and for its nested generalization to an arbitrary number of qubits. Our bounds apply under the assumptions of instantaneous pulses and of bounded perturbing environment and qubit-environment Hamiltonians such as those realized by baths of nuclear spins in quantum dots. We prove that if the total sequence time is fixed then the trace-norm distance between the unperturbed and protected system states can be made arbitrarily small by increasing the number of applied pulses.

Xia, Yuhou; Uhrig, Goetz S.; Lidar, Daniel A. [Department of Mathematics and Department of Physics, Haverford College, Haverford, Pennsylvania 19041 (United States); Lehrstuhl fuer Theoretische Physik I, Technische Universitaet Dortmund, Otto-Hahn Strasse 4, D-44221 Dortmund (Germany); Department of Electrical Engineering, Department of Chemistry, and Department of Physics, Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States)

2011-12-15

457

Relativistic Stellar Model Admitting a Quadratic Equation of State  

NASA Astrophysics Data System (ADS)

A class of solutions describing the interior of a static spherically symmetric compact anisotropic star is reported. The analytic solution has been obtained by utilizing the Finch and Skea [Class. Quantum Grav.6 (1989) 467] ansatz for the metric potential grr which has a clear geometric interpretation for the associated background spacetime. Based on physical grounds, appropriate bounds on the model parameters have been obtained and it has been shown that the model admits an equation of state (EOS) which is quadratic in nature.

Sharma, R.; Ratanpal, B. S.

2013-11-01

458

Quadratic Residues and Non-residues in Arithmetic Progression  

E-print Network

Let S be an infinite set of non-empty, finite subsets of the nonnegative integers. If p is an odd prime, let c(p) denote the cardinality of the set {T {\\in} S : T {\\subseteq} {1,...,p-1} and T is a set of quadratic residues (respectively, non-residues) of p}. When S is constructed in various ways from the set of all arithmetic progressions of nonnegative integers, we determine the sharp asymptotic behavior of c(p) as p {\\to} +{\\infty}. Generalizations and variations of this are also established, and some problems connected with these results that are worthy of further study are discussed.

Wright, Steve

2011-01-01

459

Two multivariate quadratic transformations of elliptic hypergeometric integrals  

E-print Network

Eric Rains conjectured several quadratic transformations between multivariate elliptic hypergeometric functions in "Elliptic Littlewood Identities", with the integrand multiplied by interpolation functions. In this article two of these conjectures are proven in the case where the interpolation functions are constant, and we obtain a third conjecture as a corollary. Two other equations for elliptic Selberg integrals with 10 parameters, two of which multiplying to pq/t, are given, as they are needed in the proof. The proofs consist essentially of a calculation which strings together many elliptic Dixon transformations. Some remarks are made about using Fubini in cases in which product contours do not exist.

van de Bult, Fokko Joppe

2011-01-01

460

Active flutter suppression using Linear Quadratic Gaussian theory  

NASA Technical Reports Server (NTRS)

This paper describes the application of Linear Quadratic Gaussian (LQG) methodology to the design of active control systems for suppression of aerodynamic flutter. A full-size wind tunnel model of a supercritical wing with associated sensors and actuators comprises the system to be controlled. Results of a synthesis methodology that provide small values of rms response, insensitivity to flight condition, and robust stability are presented. Results of control surface and sensor position optimization are also presented. Both frequency response matching and residualization are used to obtain practical flutter controllers.

Mahesh, J. K.; Stone, C. R.; Garrard, W. L.; Dunn, H. J.

1980-01-01

461

Frontogenesis driven by horizontally quadratic distributions of density  

NASA Technical Reports Server (NTRS)

Attention is given to the quadratic density distribution in a channel, which has been established by Simpson and Linden to be the simplest case of the horizontally nonlinear distribution of fluid density required for the production of frontogenesis. The porous-media and Boussinesq flow models are examined, and their evolution equations are reduced to one-dimensional systems. While both the porous-media and the inviscid/nondiffusive Boussinesq systems exhibit classic frontogenesis behavior, the viscous Boussinesq system exhibits a more complex behavior: boundary-layer effects force frontogenesis away from the lower boundary, and at late times the steepest density gradients are close to mid-channel.

Jacqmin, David

1991-01-01

462

Ergodic Type Bellman Equations of First Order with Quadratic Hamiltonian  

SciTech Connect

We consider Bellman equations of ergodic type in first order. The Hamiltonian is quadratic on the first derivative of the solution. We study the structure of viscosity solutions and show that there exists a critical value among the solutions. It is proved that the critical value has the representation by the long time average of the kernel of the max-plus Schroedinger type semigroup. We also characterize the critical value in terms of an invariant density in max-plus sense, which can be understood as a counterpart of the characterization of the principal eigenvalue of the Schroedinger operator by an invariant measure.

Kaise, Hidehiro [Nagoya University, Graduate School of Information Science (Japan)], E-mail: kaise@is.nagoya-u.ac.jp; Sheu, S.-J. [Academia Sinica, Institute of Mathematics (China)], E-mail: sheusj@math.sinica.edu.tw

2009-02-15

463

Strange Quark Star Model with Quadratic Equation of State  

E-print Network

In this paper, we studied the behaviour of compact relativistic objects with anisotropic matter distribution considering quadratic equation of state of Feroze and Siddiqui (2011). We specify the gravitational potential Z(x) in order to integrate the fields equations and there has been calculated the energy density, the radial pressure, the anisotropy and the mass function. The new solutions to the Einstein-Maxwell system of equations are found in term of elementary functions. For n=2, we have obtained the expressions for mass function, energy density, radius and metric functions of the model of Thirukkanesh and Ragel (2012) with polytropic equation of state.

Malaver, Manuel

2014-01-01

464

The Schrodinger Equation From a Quadratic Hamiltonian System  

E-print Network

We regard the real and imaginary parts of the Schrodinger wave function as canonical conjugate variables.With this pair of conjugate variables and some other 2n pairs, we construct a quadratic Hamiltonian density. We then show that the Schrodinger Equation follows from the Hamilton's Equation of motion when the Planck frequency is much larger than the characteristic frequencies of the Hamiltonian system. The Hamiltonian and the normal mode solutions coincide, respectively, with the energy expectation value and the energy eigenstates of the corresponding quantum mechanical system.

Wai Bong Yeung

1999-11-02

465

Relativistic stellar model admitting a quadratic equation of state  

E-print Network

A class of solutions describing the interior of a static spherically symmetric compact anisotropic star is reported. The analytic solution has been obtained by utilizing the Finch and Skea ({\\it Class. Quant. Grav.} {\\bf 6} (1989) 467) ansatz for the metric potential $g_{rr}$ which has a clear geometric interpretation for the associated background space-time. Based on physical grounds appropriate bounds on the model parameters have been obtained and it has been shown that the model admits an equation of state (EOS) which is quadratic in nature.

Ranjan Sharma; B. S. Ratanpal

2013-07-02

466

On Exponential Hedging and Related Quadratic Backward Stochastic Differential Equations  

SciTech Connect

The dual optimization problem for the exponential hedging problem is addressed with a cone constraint. Without boundedness conditions on the terminal payoff and the drift of the Ito-type controlled process, the backward stochastic differential equation, which has a quadratic growth term in the drift, is derived as a necessary and sufficient condition for optimality via a variational method and dynamic programming. Further, solvable situations are given, in which the value and the optimizer are expressed in closed forms with the help of the Clark-Haussmann-Ocone formula.

Sekine, Jun [Institute of Economic Research, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501 (Japan)], E-mail: sekine@kier.kyoto-u.ac.jp

2006-09-15

467

Strange Quark Star Model with Quadratic Equation of State  

E-print Network

In this paper, we studied the behaviour of compact relativistic objects with anisotropic matter distribution considering quadratic equation of state of Feroze and Siddiqui (2011). We specify the gravitational potential Z(x) in order to integrate the fields equations and there has been calculated the energy density, the radial pressure, the anisotropy and the mass function. The new solutions to the Einstein-Maxwell system of equations are found in term of elementary functions. For n=2, we have obtained the expressions for mass function, energy density, radius and metric functions of the model of Thirukkanesh and Ragel (2012) with polytropic equation of state.

Manuel Malaver

2014-07-03

468

Nios II hardware acceleration of the epsilon quadratic sieve algorithm  

NASA Astrophysics Data System (ADS)

The quadratic sieve (QS) algorithm is one of the most powerful algorithms to factor large composite primes used to break RSA cryptographic systems. The hardware structure of the QS algorithm seems to be a good fit for FPGA acceleration. Our new ?-QS algorithm further simplifies the hardware architecture making it an even better candidate for C2H acceleration. This paper shows our design results in FPGA resource and performance when implementing very long arithmetic on the Nios microprocessor platform with C2H acceleration for different libraries (GMP, LIP, FLINT, NRMP) and QS architecture choices for factoring 32-2048 bit RSA numbers.

Meyer-Bäse, Uwe; Botella, Guillermo; Castillo, Encarnacion; García, Antonio

2010-04-01

469

High Resolution Spectra of Novae and the Quadratic Zeeman Effect  

E-print Network

High resolution spectra of novae after outburst reveal distinctive characteristics in the line profiles and intensities. The higher Balmer lines are often broader than the lower members of the series, and the relative profiles and intensities of the [O I] \\lambda\\lambda6300, 6364 doublet differ from normal values. We suggest these features may be caused by the Quadratic Zeeman Effect from magnetic fields exceeding B=10^6 gauss. Taken together the emission and absorption lines point to multiple origins for the ejecta on both the erupting white dwarf and the cool secondary star.

Robert Williams; Elena Mason

2006-02-27

470

Cyclicity of a fake saddle inside the quadratic vector fields  

NASA Astrophysics Data System (ADS)

This paper concerns the study of small-amplitude limit cycles that appear in the phase portrait near an unfolded fake saddle singularity. This degenerate singularity is also known as an impassable grain. The canonical form of the unperturbed vector field is like a degenerate flow box. Near the singularity, the phase portrait consists of parallel fibers, all but one of which have no singular points, and at the singular fiber, there is one node. We demonstrate different techniques in order to show that the cyclicity is bigger than or equal to two when the canonical form is quadratic.

De Maesschalck, P.; Rebollo-Perdomo, S.; Torregrosa, J.

2015-01-01

471

Robust stationary mechanical squeezing in a kicked quadratic optomechanical system  

NASA Astrophysics Data System (ADS)

We propose a scheme for the generation of a robust stationary squeezed state of a mechanical resonator in a quadratically coupled optomechanical system, driven by a pulsed laser. The intracavity photon number presents periodic intense peaks suddenly stiffening the effective harmonic potential felt by the mechanical resonator. These "optical spring kicks" tend to squeeze the resonator position, and due to the interplay with fluctuation-dissipation processes one can generate a stationary state with more than 10 dB of squeezing in a realistic scenario, even starting from moderately "precooled" initial thermal states.

Asjad, M.; Agarwal, G. S.; Kim, M. S.; Tombesi, P.; Giuseppe, G. Di; Vitali, D.

2014-02-01

472

TRACE ELEMENTS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Trace elements are defined as mineral elements that occur in living systems in micrograms per gram of body weight or less. Trace elements of greatest practical concern in human health are iodine, iron and zinc. Suggestive evidence is emerging that cobalt (as vitamin B12), copper, selenium, boron and...

473

Performance Enhancement of Bandgap Printed Antennas Using Finite Element Method and Size/Topology Optimization Methods  

E-print Network

Performance Enhancement of Bandgap Printed Antennas Using Finite Element Method and Size. This will be achieved by employing size optimization. Performance enhancement can further be achieved by applying with antenna simulators based on the finite element and sequential quadratic programming method or genetic

Papalambros, Panos

474

Symmetric global partition polynomials for reproducing kernel elements  

NASA Astrophysics Data System (ADS)

The reproducing kernel element method is a numerical technique that combines finite element and meshless methods to construct shape functions of arbitrary order and continuity, yet retains the Kronecker- property. Central to constructing these shape functions is the construction of global partition polynomials on an element. This paper shows that asymmetric interpolations may arise due to such things as changes in the local to global node numbering and that may adversely affect the interpolation capability of the method. This issue arises due to the use of incomplete polynomials that are subsequently non-affine invariant. This paper lays out the new framework for generating general, symmetric, truly minimal and complete affine invariant global partition polynomials for triangular and tetrahedral elements. Optimal convergence rates were observed in the solution of Kirchhoff plate problems with rectangular domains.

Juha, Mario J.; Simkins, Daniel C.

2014-11-01

475

Doubly-curved variable-thickness isoparametric heterogeneous finite element  

NASA Technical Reports Server (NTRS)

This paper describes an element streamlined for the analysis of doubly-curved, variable-thickness structural components and illustrates its effective application to vibration and static problems. The element is isoparametric, doubly-curved, thin-shell and triangular with variable thickness and accounts for anisotropic, inhomogeneous elastic material behavior. The element has six nodes (three corner and three mid-side) with five degrees-of-freedom (DOF) per node - three translations and two rotations. Quadratic isoparametric interpolation polynomials are used to express the element geometry and displacement variables in terms of corresponding nodal variables.

Minich, M. D.; Chamis, C. C.

1977-01-01

476

Antimalarial, antimicrobial, cytotoxic, DNA interaction and SOD like activities of tetrahedral copper(II) complexes  

NASA Astrophysics Data System (ADS)

The mononuclear copper(II) complexes with P, O-donor ligand and different fluoroquinolones have been synthesized and characterized by elemental analysis, electronic spectra, TGA, EPR, FT-IR and LC-MS spectroscopy. An antimicrobial efficiency of the complexes has been tested against five different microorganisms in terms of minimum inhibitory concentration (MIC) and displays very good antimicrobial activity. The binding strength and binding mode of the complexes with Herring Sperm DNA (HS DNA) have been investigated by absorption titration and viscosity measurement studies. The studies suggest the classical intercalative mode of DNA binding. Gel electrophoresis assay determines the ability of the complexes to cleave the supercoiled form of pUC19 DNA. Synthesized complexes have been tested for their SOD mimic activity using nonenzymatic NBT/NADH/PMS system and found to have good antioxidant activity. All the complexes show good cytotoxic and in vitro antimalarial activities.

Mehta, Jugal V.; Gajera, Sanjay B.; Patel, Mohan N.

2015-02-01

477

The Distribution of Pairs of Quadratic Residues and Nonresidues of a Special Form  

NASA Astrophysics Data System (ADS)

Nontrivial estimates are obtained for sums of Legendre symbols of a quadratic polynomial over primes in an arithmetic progression. These estimates are used to prove a theorem concerning the number of pairs of the form (p + a, p + b), p \\equiv l (\\operatorname{mod} k), p\\le N, for which p + a is a quadratic residue (nonresidue), p + b is a quadratic residue (nonresidue) modulo the prime q, and N > k^3q^{0.75+\\varepsilon}. Bibliography: 27 titles.

Karatsuba, A. A.

1988-04-01

478

F-BF, A-SSE Building a General Quadratic Function  

NSDL National Science Digital Library

This is a task from the Illustrative Mathematics website that is one part of a complete illustration of the standard to which it is aligned. Each task has at least one solution and some commentary that addresses important asects of the task and its potential use. Here are the first few lines of the commentary for this task: In ``Building an explicit quadratic function'' a particular quadratic function was rewritten by completing the square. The quadratic function used was ...

479

Accelerated expansion from a modified-quadratic gravity  

NASA Astrophysics Data System (ADS)

We investigate the late-time dynamics of a four-dimensional universe based on modified scalar field gravity in which the standard Einstein-Hilbert action R is replaced by f( ?) R+ f( R) where f( ?)= ? 2 and f( R)= AR 2+ BR ?? R ??,( A, B)??. We discussed two independent cases: in the first model, the scalar field potential is quartic and for this special form it was shown that the universe is dominated by dark energy with equation of state parameter w?-0.2 and is accelerated in time with a scale factor evolving like a( t)? t 5/3 and B+3 A?0.036. When, B+3 A?? which corresponds for the purely quadratic theory, the scale factor evolves like a( t)? t 1/2 whereas when B+3 A?0 which corresponds for the purely scalar tensor theory we found when a( t)? t 1.98. In the second model, we choose an exponential potential and we conjecture that the scalar curvature and the Hubble parameter vary respectively like R=? Hdot{?}/?,?inmathbb{R} and H=?dot{?}^{?},(?,?)inmathbb{R}. It was shown that for some special values of ?, the universe is free from the initial singularity, accelerated in time, dominated by dark or phantom energy whereas the model is independent of the quadratic gravity corrections. Additional consequences are discussed.

Ahmad Rami, El-Nabulsi

2011-04-01

480

Accelerated expansion from a modified-quadratic gravity  

NASA Astrophysics Data System (ADS)

We investigate the late-time dynamics of a four-dimensional universe based on modified scalar field gravity in which the standard Einstein-Hilbert action R is replaced by f( ?) R+ f( R) where f( ?)= ? 2 and f( R)= AR 2+ BR ?? R ??,( A, B)??. We discussed two independent cases: in the first model, the scalar field potential is quartic and for this special form it was shown that the universe is dominated by dark energy with equation of state parameter w?-0.2 and is accelerated in time with a scale factor evolving like a( t)? t 5/3 and B+3 A?0.036. When, B+3 A?? which corresponds for the purely quadratic theory, the scale factor evolves like a( t)? t 1/2 whereas when B+3 A?0 which corresponds for the purely scalar tensor theory we found when a( t)? t 1.98. In the second model, we choose an exponential potential and we conjecture that the scalar curvature and the Hubble parameter vary respectively like R=? Hdot{?}/?,?in{R} and H=?dot{?}^{?},(?,?)in{R}. It was shown that for some special values of ?, the universe is free from the initial singularity, accelerated in time, dominated by dark or phantom energy whereas the model is independent of the quadratic gravity corrections. Additional consequences are discussed.

El-Nabulsi, Ahmad Rami

2011-04-01

481

Linear-Quadratic-Gaussian Regulator Developed for a Magnetic Bearing  

NASA Technical Reports Server (NTRS)

Linear-Quadratic-Gaussian (LQG) control is a modern state-space technique for designing optimal dynamic regulators. It enables us to trade off regulation performance and control effort, and to take into account process and measurement noise. The Structural Mechanics and Dynamics Branch at the NASA Glenn Research Center has developed an LQG control for a fault-tolerant magnetic bearing suspension rig to optimize system performance and to reduce the sensor and processing noise. The LQG regulator consists of an optimal state-feedback gain and a Kalman state estimator. The first design step is to seek a state-feedback law that minimizes the cost function of regulation performance, which is measured by a quadratic performance criterion with user-specified weighting matrices, and to define the tradeoff between regulation performance and control effort. The next design step is to derive a state estimator using a Kalman filter because the optimal state feedback cannot be implemented without full state measurement. Since the Kalman filter is an optimal estimator when dealing with Gaussian white noise, it minimizes the asymptotic covariance of the estimation error.

Choi, Benjamin B.

2002-01-01

482

Quadratic Reciprocity and the Group Orders of Particle States  

SciTech Connect

The construction of inverse states in a finite field F{sub P{sub P{alpha}}} enables the organization of the mass scale by associating particle states with residue class designations. With the assumption of perfect flatness ({Omega}total = 1.0), this approach leads to the derivation of a cosmic seesaw congruence which unifies the concepts of space and mass. The law of quadratic reciprocity profoundly constrains the subgroup structure of the multiplicative group of units F{sub P{sub {alpha}}}* defined by the field. Four specific outcomes of this organization are (1) a reduction in the computational complexity of the mass state distribution by a factor of {approximately}10{sup 30}, (2) the extension of the genetic divisor concept to the classification of subgroup orders, (3) the derivation of a simple numerical test for any prospective mass number based on the order of the integer, and (4) the identification of direct biological analogies to taxonomy and regulatory networks characteristic of cellular metabolism, tumor suppression, immunology, and evolution. It is generally concluded that the organizing principle legislated by the alliance of quadratic reciprocity with the cosmic seesaw creates a universal optimized structure that functions in the regulation of a broad range of complex phenomena.

DAI,YANG; BORISOV,ALEXEY B.; LONGWORTH,JAMES W.; BOYER,KEITH; RHODES,CHARLES K.

2001-06-01

483

Confidence set inference with a prior quadratic bound  

NASA Technical Reports Server (NTRS)

In the uniqueness part of a geophysical inverse problem, the observer wants to predict all likely values of P unknown numerical properties z=(z sub 1,...,z sub p) of the earth from measurement of D other numerical properties y (sup 0) = (y (sub 1) (sup 0), ..., y (sub D (sup 0)), using full or partial knowledge of the statistical distribution of the random errors in y (sup 0). The data space Y containing y(sup 0) is D-dimensional, so when the model space X is infinite-dimensional the linear uniqueness problem usually is insoluble without prior information about the correct earth model x. If that information is a quadratic bound on x, Bayesian inference (BI) and stochastic inversion (SI) inject spurious structure into x, implied by neither the data nor the quadratic bound. Confidence set inference (CSI) provides an alternative inversion technique free of this objection. Confidence set inference is illustrated in the problem of estimating the geomagnetic field B at the core-mantle boundary (CMB) from components of B measured on or above the earth's surface.

Backus, George E.

1989-01-01

484

Learning quadratic receptive fields from neural responses to natural stimuli.  

PubMed

Models of neural responses to stimuli with complex spatiotemporal correlation structure often assume that neurons are selective for only a small number of linear projections of a potentially high-dimensional input. In this review, we explore recent modeling approaches where the neural response depends on the quadratic form of the input rather than on its linear projection, that is, the neuron is sensitive to the local covariance structure of the signal preceding the spike. To infer this quadratic dependence in the presence of arbitrary (e.g., naturalistic) stimulus distribution, we review several inference methods, focusing in particular on two information theory-based approaches (maximization of stimulus energy and of noise entropy) and two likelihood-based approaches (Bayesian spike-triggered covariance and extensions of generalized linear models). We analyze the formal relationship between the likelihood-based and information-based approaches to demonstrate how they lead to consistent inference. We demonstrate the practical feasibility of these procedures by using model neurons responding to a flickering variance stimulus. PMID:23607557

Rajan, Kanaka; Marre, Olivier; Tka?ik, Gašper

2013-07-01

485

Quadratic Isocurvature Cross-Correlation, Ward Identity, and Dark Matter  

E-print Network

Sources of isocurvature perturbations and large non-Gaussianities include field degrees of freedom whose vacuum expectation values are smaller than the expansion rate of inflation. The inhomogeneities in the energy density of such fields are quadratic in the fields to leading order in the inhomogeneity expansion. Although it is often assumed that such isocurvature perturbations and inflaton-driven curvature perturbations are uncorre- lated, this is not obvious from a direct computational point of view due to the form of the minimal gravitational interactions. We thus compute the irreducible gravitational contributions to the quadratic isocurvature-curvature cross-correlation. We find a small but non-decaying cross-correlation, which in principle serves as a consistency prediction of this large class of isocurvature perturbations. We apply our cross-correlation result to two dark matter isocurvature perturbation scenarios: QCD axions and WIMPZILLAs. On the technical side, we utilize a gravita- tional Ward identity in a novel manner to demonstrate the gauge invariance of the computation. Furthermore, the detailed computation is interpreted in terms of a soft-{\\zeta} theorem and a gravitational Ward identity. Finally, we also identify explicitly all the counterterms that are necessary for renormalizing the isocurvature perturbation composite operator in inflationary cosmological backgrounds.

Daniel J. H. Chung; Hojin Yoo; Peng Zhou

2013-03-25

486

A macro finite element formulation for cardiac electrophysiology simulations using hybrid unstructured grids  

PubMed Central

Electrical activity in cardiac tissue can be described by the bidomain equations whose solution for large scale simulations still remains a computational challenge. Therefore, improvements in the discrete formulation of the problem which decrease computational and/or memory demands are highly desirable. In this study, we propose a novel technique for computing shape functions of finite elements. The technique generates macro finite elements (MFEs) based on the local decomposition of elements into tetrahedral sub-elements with linear shape functions. Such an approach necessitates the direct use of hybrid meshes composed of different types of elements. MFEs are compared to classic standard finite elements with respect to accuracy and RAM memory usage under different scenarios of cardiac modeling including bidomain and monodomain simulations in 2D and 3D for simple and complex tissue geometries. In problems with analytical solutions, MFEs displayed the same numerical accuracy of standard linear triangular and tetrahedral elements. In propagation simulations, conduction velocity and activation times agreed very well with those computed with standard finite elements. However, MFEs offer a significant decrease in memory requirements. We conclude that hybrid meshes composed of MFEs are well suited for solving problems in cardiac computational electrophysiology. PMID:20699206

Rocha, Bernardo M.; Kickinger, Ferdinand; Prassl, Anton J.; Haase, Gundolf; Vigmond, Edward J.; dos Santos, Rodrigo Weber; Zaglmayr, Sabine; Plank, Gernot

2011-01-01

487

Forward problem solution of electromagnetic source imaging using a new BEM formulation with high-order elements.  

PubMed

Representations of the active cell populations on the cortical surface via electric and magnetic measurements are known as electromagnetic source images (EMSIs) of the human brain. Numerical solution of the potential and magnetic fields for a given electrical source distribution in the human brain is an essential part of electromagnetic source imaging. In this study, the performance of the boundary element method (BEM) is explored with different surface element types. A new BEM formulation is derived that makes use of isoparametric linear, quadratic or cubic elements. The surface integration is performed with Gauss quadrature. The potential fields are solved assuming a concentric three-shell model of the human head for a tangential dipole at different locations. In order to achieve 2% accuracy in potential solutions, the number of quadratic elements is of the order of hundreds. However, with linear elements, this number is of the order of ten thousand. The relative difference measures (RDMs) are obtained for the numerical models that use different element types. The numerical models that employ quadratic and cubic element types provide superior performance over linear elements in terms of accuracy in solutions. Assuming a homogeneous sphere model of the head, the RDMs are also obtained for the three components (radial and tangential) of the magnetic fields. The RDMs obtained for the tangential fields are, in general, much higher than those obtained for the radial fields. Both quadratic and cubic elements provide superior performance compared with linear elements for a wide range of dipole locations. PMID:10495121

Gençer, N G; Tanzer, I O

1999-09-01

488

Use of edge-based finite elements for solving three dimensional scattering problems  

NASA Technical Reports Server (NTRS)

Edge based finite elements are free from drawbacks associated with node based vectorial finite elements and are, therefore, ideal for solving 3-D scattering problems. The finite element discretization using edge elements is checked by solving for the resonant frequencies of a closed inhomogeneously filled metallic cavity. Great improvements in accuracy are observed when compared to the classical node based approach with no penalty in terms of computational time and with the expected absence of spurious modes. A performance comparison between the edge based tetrahedra and rectangular brick elements is carried out and tetrahedral elements are found to be more accurate than rectangular bricks for a given storage intensity. A detailed formulation for the scattering problem with various approaches for terminating the finite element mesh is also presented.

Chatterjee, A.; Jin, J. M.; Volakis, John L.

1991-01-01

489

Thermodynamics of charged Lifshitz black holes with quadratic corrections  

E-print Network

In arbitrary dimension, we consider the Einstein-Maxwell Lagrangian supplemented by the more general quadratic-curvature corrections. For this model, we derive four classes of charged Lifshitz black hole solutions for which the metric function is shown to depend on a unique integration constant. The masses of these solutions are computed using the quasilocal formalism based on the relation established between the off-shell ADT and Noether potentials. Among these four solutions, three of them are interpreted as extremal in the sense that their mass vanishes identically. For the last family of solutions, the quasilocal mass and the electric charge both are shown to depend on the integration constant. Finally, we verify that the first law of thermodynamics holds for each solution and a Smarr formula is also established for the four solutions.

Bravo-Gaete, Moises

2015-01-01

490

Discriminative learning quadratic discriminant function for handwriting recognition.  

PubMed

In character string recognition integrating segmentation and classification, high classification accuracy and resistance to noncharacters are desired to the underlying classifier. In a previous evaluation study, the modified quadratic discriminant function (MQDF) proposed by Kimura et al. was shown to be superior in noncharacter resistance but inferior in classification accuracy to neural networks. This paper proposes a discriminative learning algorithm to optimize the parameters of MQDF with aim to improve the classification accuracy while preserving the superior noncharacter resistance. We refer to the resulting classifier as discriminative learning QDF (DLQDF). The parameters of DLQDF adhere to the structure of MQDF under the Gaussian density assumption and are optimized under the minimum classification error (MCE) criterion. The promise of DLQDF is justified in handwritten digit recognition and numeral string recognition, where the performance of DLQDF is comparable to or superior to that of neural classifiers. The results are also competitive to the best ones reported in the literature. PMID:15384535

Liu, Cheng-Lin; Sako, Hiroshi; Fujisawa, Hiromichi

2004-03-01

491

Consultant-Guided Search Algorithms for the Quadratic Assignment Problem  

NASA Astrophysics Data System (ADS)

Consultant-Guided Search (CGS) is a recent swarm intelligence metaheuristic for combinatorial optimization problems, inspired by the way real people make decisions based on advice received from consultants. Until now, CGS has been successfully applied to the Traveling Salesman Problem. Because a good metaheuristic should be able to tackle efficiently a large variety of problems, it is important to see how CGS behaves when applied to other classes of problems. In this paper, we propose an algorithm for the Quadratic Assignment Problem (QAP), which hybridizes CGS with a local search procedure. Our experimental results show that CGS is able to compete in terms of solution quality with one of the best Ant Colony Optimization algorithms, the MAX-MIN Ant System.

Iordache, Serban

492

Application of quadratic optimization to supersonic inlet control  

NASA Technical Reports Server (NTRS)

The application of linear stochastic optimal control theory to the design of the control system for the air intake (inlet) of a supersonic air-breathing propulsion system is discussed. The controls must maintain a stable inlet shock position in the presence of random airflow disturbances and prevent inlet unstart. Two different linear time invariant control systems are developed. One is designed to minimize a nonquadratic index, the expected frequency of inlet unstart, and the other is designed to minimize the mean square value of inlet shock motion. The quadratic equivalence principle is used to obtain the best linear controller that minimizes the nonquadratic performance index. The two systems are compared on the basis of unstart prevention, control effort requirements, and sensitivity to parameter variations.

Lehtinen, B.; Zeller, J. R.

1971-01-01

493

Half-optical-cycle damped solitons in quadratic nonlinear media  

NASA Astrophysics Data System (ADS)

In this paper, Using a classical model of the radiation-matter interaction, we show that the propagation of (1+1) dimensional few-optical-cycle pulses in quadratic nonlinear media, taking moderate absorption into account, can be described by the Korteweg-de Vries-Burgers' (KdVB) equation without using the slowly varying envelope approximation. To fulfill this purpose we use the reductive perturbation method and consider the long-wave approximation, assuming that the characteristic frequency of the pulse is much lower than the resonance frequency of the atoms. We also study both analytical and numerical solution of the KdVB equation describing damped few-optical-cycle soliton propagation.

Kimiaee Asadi, Faezeh; Shokri, Babak; Leblond, Hervé

2013-05-01

494

Lensless imaging by entangled photons from quadratic nonlinear photonic crystals  

NASA Astrophysics Data System (ADS)

Lenses play a key role in quantum imaging but inevitably constrain the spatial resolution and working wavelength. In this work we develop and demonstrate a lensless quantum ghost imaging by engineering quadratic nonlinear photonic crystals. With a transverse parabolic domain modulation introduced into the lithium tantalate crystal, the entangled photon pairs generated from parametric down-conversion will self-focus. Therefore we can dispense with additional lenses to construct imaging in a nonlocal way. The lensless imaging is found to follow a specific imaging formula where the effective focal length is determined by the domain modulation and pump wavelength. Additionally, two nonlocal images can be retrieved when the entangled photon pair is generated under two concurrent noncollinear phase-matching geometries. Our work provides a principle and method to realize lensless ghost imaging, which may be extended to other wavelengths and stimulate new types of practical quantum technologies.

Xu, P.; Leng, H. Y.; Zhu, Z. H.; Bai, Y. F.; Jin, H.; Gong, Y. X.; Yu, X. Q.; Xie, Z. D.; Mu, S. Y.; Zhu, S. N.

2012-07-01

495

Frequency weighted system identification and linear quadratic controller design  

NASA Technical Reports Server (NTRS)

Application of filters for frequency weighting of Markov parameters (pulse response functions) is described in relation to system/observer identification. The time domain identification approach recovers a model which has a pulse response weighted according to frequency. The identified model is composed of the original system and filters. The augmented system is in a form which can be used directly for frequency weighted linear quadratic controller design. Data from either single or multiple experiments can be used to recover the Markov parameters. Measured acceleration signals from a truss structure are used for system identification and the model obtained is used for frequency weighted controller design. The procedure makes the identification and controler design complementary problems.

Horta, Lucas G.; Phan, Minh; Juang, Jer-Nan; Longman, Richard W.; Sulla, Jeffrey L.

1991-01-01

496

Exact Nonnull Wavelike Solutions to Gravity with Quadratic Lagrangians  

E-print Network

Solutions to gravity with quadratic Lagrangians are found for the simple case where the only nonconstant metric component is the lapse $N$ and the Riemann tensor takes the form $R^{t}_{.itj}=-k_{i}k_{j}, i,j=1,2,3$; thus these solutions depend on cross terms in the Riemann tensor and therefore complement the linearized theory where it is the derivatives of the Riemann tensor that matter. The relationship of this metric to the null gravitational radiation metric of Peres is given. Gravitaional energy Poynting vectors are construcetd for the solutions and one of these, based on the Lanczos tensor, supports the indication in the linearized theory that nonnull gravitational radiation can occur.

Mark D. Roberts

1999-04-04

497

Determination of ventilatory threshold through quadratic regression analysis.  

PubMed

Ventilatory threshold (VT) has been used to measure physiological occurrences in athletes through models via gas analysis with limited accuracy. The purpose of this study is to establish a mathematical model to more accurately detect the ventilatory threshold using the ventilatory equivalent of carbon dioxide (VE/VCO2) and the ventilatory equivalent of oxygen (VE/Vo2). The methodology is primarily a mathematical analysis of data. The raw data used were archived from the cardiorespiratory laboratory in the Department of Kinesiology at Midwestern State University. Procedures for archived data collection included breath-by-breath gas analysis averaged every 20 seconds (ParVoMedics, TrueMax 2400). A ramp protocol on a Velotron bicycle ergometer was used with increased work at 25 W.min beginning with 150 W, until volitional fatigue. The subjects consisted of 27 healthy, trained cyclists with age ranging from 18 to 50 years. All subjects signed a university approved informed consent before testing. Graphic scatterplots and statistical regression analyses were performed to establish the crossover and subsequent dissociation of VE/Vo2 to VE/VCO2. A polynomial trend line along the scatterplots for VE/VO2 and VE/VCO2 was used because of the high correlation coefficient, the coefficient of determination, and trend line. The equations derived from the scatterplots and trend lines were quadratic in nature because they have a polynomial degree of 2. A graphing calculator in conjunction with a spreadsheet was used to find the exact point of intersection of the 2 trend lines. After the quadratic regression analysis, the exact point of VE/Vo2 and VE/VCO2 crossover was established as the VT. This application will allow investigators to more accurately determine the VT in subsequent research. PMID:20802290

Gregg, Joey S; Wyatt, Frank B; Kilgore, J Lon

2010-09-01

498

Confidence set inference with a prior quadratic bound  

NASA Technical Reports Server (NTRS)

In the uniqueness part of a geophysical inverse problem, the observer wants to predict all likely values of P unknown numerical properties z = (z sub 1,...,z sub p) of the earth from measurement of D other numerical properties y(0)=(y sub 1(0),...,y sub D(0)) knowledge of the statistical distribution of the random errors in y(0). The data space Y containing y(0) is D-dimensional, so when the model space X is infinite-dimensional the linear uniqueness problem usually is insoluble without prior information about the correct earth model x. If that information is a quadratic bound on x (e.g., energy or dissipation rate), Bayesian inference (BI) and stochastic inversion (SI) inject spurious structure into x, implied by neither the data nor the quadratic bound. Confidence set inference (CSI) provides an alternative inversion technique free of this objection. CSI is illustrated in the problem of estimating the geomagnetic field B at the core-mantle boundary (CMB) from components of B measured on or above the earth's surface. Neither the heat flow nor the energy bound is strong enough to permit estimation of B(r) at single points on the CMB, but the heat flow bound permits estimation of uniform averages of B(r) over discs on the CMB, and both bounds permit weighted disc-averages with continous weighting kernels. Both bounds also permit estimation of low-degree Gauss coefficients at the CMB. The heat flow bound resolves them up to degree 8 if the crustal field at satellite altitudes must be treated as a systematic error, but can resolve to degree 11 under the most favorable statistical treatment of the crust. These two limits produce circles of confusion on the CMB with diameters of 25 deg and 19 deg respectively.

Backus, George E.

1988-01-01

499

Elemental health  

SciTech Connect

Trace elements used in nutritional supplements and vitamins are discussed in the article. Relevant studies are briefly cited regarding the health effects of selenium, chromium, germanium, silicon, zinc, magnesium, silver, manganese, ruthenium, lithium, and vanadium. The toxicity and food sources are listed for some of the elements. A brief summary is also provided of the nutritional supplements market.

Tonneson, L.C.

1997-01-01

500

Robust stabilization of uncertain linear systems: quadratic stabilizability and H? control theory  

Microsoft Academic Search

The problem of robustly stabilizing a linear uncertain system is considered with emphasis on the interplay between the time-domain results on the quadratic stabilization of uncertain systems and the frequency-domain results on H? optimization. A complete solution to a certain quadratic stabilization problem in which uncertainty enters both the state and the input matrices of the system is given. Relations

PRAMOD P. KHARGONEKAR; IAN R. PETERSEN; KEMIN ZHOU

1990-01-01