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1

Nonconforming tetrahedral finite elements for fourth order elliptic equations  

NASA Astrophysics Data System (ADS)

This paper is devoted to the construction of nonconforming finite elements for the discretization of fourth order elliptic partial differential operators in three spatial dimensions. The newly constructed elements include two nonconforming tetrahedral finite elements and one quasi-conforming tetrahedral element. These elements are proved to be convergent for a model biharmonic equation in three dimensions. In particular, the quasi-conforming tetrahedron element is a modified Zienkiewicz element, while the nonmodified Zienkiewicz element (a tetrahedral element of Hermite type) is proved to be divergent on a special grid.

Ming, Wang; Xu, Jinchao

2007-03-01

2

Quadratic trianqular element for diffuse optical tomography  

NASA Astrophysics Data System (ADS)

Finite element method is a general approach for diffuse optical tomography, and the accuracy of which is closely related to the type of elements used. In this paper, we investigate the differences between linear element and quadratic triangular element in the forward problem of diffuse optical tomography. The results show that quadratic element is a better compromise between high accuracy and low time consumption compared to the linear element. This means high order element is a better choice for the diffuse optical tomography.

Zhang, Xuanxuan; Deng, Yong; Xu, Jun; Luo, Zhaoyang; Gong, Hui; Luo, Qingming

2012-12-01

3

Finite element LES and VMS methods on tetrahedral meshes  

NASA Astrophysics Data System (ADS)

Finite element methods for problems given in complex domains are often based on tetrahedral meshes. This paper demonstrates that the so-called rational Large Eddy Simulation model and a projection-based Variational Multiscale method can be extended in a straightforward way to tetrahedral meshes. Numerical studies are performed with an inf-sup stable second order pair of finite elements with discontinuous pressure approximation.

John, Volker; Kindl, Adela; Suciu, Carina

2010-04-01

4

Tetrahedral mesh improvement via optimization of the element condition number  

SciTech Connect

The authors present a new shape measure for tetrahedral elements that is optimal in that it gives the distance of a tetrahedron from the set of inverted elements. This measure is constructed from the condition number of the linear transformation between a unit equilateral tetrahedron and any tetrahedron with positive volume. Using this shape measure, they formulate two optimization objective functions that are differentiated by their goal: the first seeks to improve the average quality of the tetrahedral mesh; the second aims to improve the worst-quality element in the mesh. They review the optimization techniques used with each objective function and presents experimental results that demonstrate the effectiveness of the mesh improvement methods. They show that a combined optimization approach that uses both objective functions obtains the best-quality meshes for several complex geometries.

FREITAG,LORI A.; KNUPP,PATRICK

2000-05-22

5

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

6

Suitable low-order, eight-node tetrahedral finite element for solids.  

National Technical Information Service (NTIS)

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 d...

S. W. Key M. S. Heinstein C. M. Stone F. J. Mello M. L. Blanford

1998-01-01

7

Quadratic finite element methods for unilateral contact problems  

Microsoft Academic Search

The present paper is concerned with the frictionless unilateral contact problem between two elastic bodies in a bidimensional context. We consider a mixed formulation in which the unknowns are the displacement field and the contact pressure. We introduce a finite element method using quadratic elements and continuous piecewise quadratic multipliers on the contact zone. The discrete unilateral non-interpenetration condition is

Patrick Hild; Patrick Laborde

2002-01-01

8

Two mixed finite element formulations with area bubble functions for tetrahedral elements  

Microsoft Academic Search

We address the solution of geometrically linear elastic problems for three-dimensional solid mechanics using tetrahedral finite elements. Starting from a five field weak formulation involving fields for compatible displacements, incompatible displacements, pressure, enhanced strains and stresses, both, the mixed method of incompatible modes and the mixed method of enhanced strains are considered as special cases. As a key idea, area

Rolf Mahnken; Ismail Caylak; Gottfried Laschet

2008-01-01

9

A 3D Frictional Segment-to-Segment Contact Method for Large Deformations and Quadratic Elements  

SciTech Connect

Node-on-segment contact is the most common form of contact used today but has many deficiencies ranging from potential locking to non-smooth behavior with large sliding. Furthermore, node-on-segment approaches are not at all applicable to higher order discretizations (e.g. quadratic elements). In a previous work, [3, 4] we developed a segment-to-segment contact approach for eight node hexahedral elements based on the mortar method that was applicable to large deformation mechanics. The approach proved extremely robust since it eliminated the over-constraint that caused 'locking' and provided smooth force variations in large sliding. Here, we extend this previous approach to treat frictional contact problems. In addition, the method is extended to 3D quadratic tetrahedrals and hexahedrals. The proposed approach is then applied to several challenging frictional contact problems that demonstrate its effectiveness.

Puso, M; Laursen, T; Solberg, J

2004-04-01

10

Stress intensity factor analyses of three-dimensional interface cracks using tetrahedral finite elements  

NASA Astrophysics Data System (ADS)

A numerical method is proposed for evaluating the stress intensity factors of a three-dimensional bimaterial interfacial crack using tetrahedral finite elements. This technique is based on the M1-integral method and employs the moving least-squares approximation. Stress or strain in the M1-integral equation is automatically approximated from the nodal displacements obtained by the finite element analysis using the moving least-squares method. Therefore, the presented method needs no elemental information from the finite element analysis. In this study, stress intensity factor analyses of some typical three-dimensional interface crack problems using the tetrahedral finite elements are demonstrated.

Nagai, Masaki; Ikeda, Toru; Miyazaki, Noriyuki

2013-05-01

11

Phase-Accuracy Comparisons and Improved Far-Field Estimates for 3-D Edge Elements on Tetrahedral Meshes  

NASA Astrophysics Data System (ADS)

Edge-element methods have proved very effective for 3-D electromagnetic computations and are widely used on unstructured meshes. However, the accuracy of standard edge elements can be criticised because of their low order. This paper analyses discrete dispersion relations together with numerical propagation accuracy to determine the effect of tetrahedral shape on the phase accuracy of standard 3-D edge-element approximations in comparison to other methods. Scattering computations for the sphere obtained with edge elements are compared with results obtained with vertex elements, and a new formulation of the far-field integral approximations for use with edge elements is shown to give improved cross sections over conventional formulations.

Monk, Peter; Parrott, Kevin

2001-07-01

12

A QUADRATIC LAYER ELEMENT FOR ANALYZING STRESS WAVES IN FGMS AND ITS APPLICATION IN MATERIAL CHARACTERIZATION  

Microsoft Academic Search

A novel method is presented for investigating elastic waves in functionally graded material (FGM) plates excited by plane pressure waves. The FGM plate is first divided into quadratic layer elements (QLEs). A general solution for the equation of motion governing the QLE has been derived. The general solution is then used together with the boundary and continuity conditions to obtain

X. HAN; G. R. LIU; K. Y. LAM; T. OHYOSHI

2000-01-01

13

Tetrahedral windmill  

SciTech Connect

A wind-adjustable air turbine consisting of: 1. A tetrahedral support structure, 2. At least one blade extending into opposite tetrahedral edges, and 3. An axis of rotation extending from the structure's center and movable into any of the edges' centers, whereby the blade's rotation and/or drag is changed.

Groeger, T.O.

1983-02-22

14

Fully adaptive finite element based tomography using tetrahedral dual-meshing for fluorescence enhanced optical imaging in tissue.  

PubMed

We have developed fluorescence enhanced optical tomography based upon fully adaptive finite element method (FEM) using tetrahedral dual-meshing wherein one of the two meshes discretizes the forward variables and the other discretizes the unknown parameters to be estimated. We used the 8-subtetrahedron subdivision scheme to create the nested dualmesh in which each are independently refined. However, two tetrahedrons from the two different meshes pose an intersection problem that needs to be resolved in order to find the common regions that the forward variables (the fluorescent diffuse photon fluence fields) and the parameter estimates (the fluorescent absorption coefficients) can be mutually assigned. Using an efficient intersection algorithm in the nested tetrahedral environments previously developed by the authors, we demonstrate fully adaptive tomography using a posteriori error estimates. Performing the iterative reconstructions using the simulated boundary measurement data, we demonstrate that small fluorescent targets embedded in the breast simulating phantom in point illumination/detection geometry can be resolved at reasonable computational cost. PMID:19547011

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

2007-05-28

15

Finite-element analysis of earing using non-quadratic yield surfaces  

SciTech Connect

During deep draw cupping, the phenomenon known as earing may occur as the cup wall is formed, resulting in a periodic variation of cup wall height around the perimeter of the finished cup. This is generally due to planar anisotropy of flow in rolled sheet product. It is generally observed that the anisotropy parameter R will vary in the plane of the sheet when ears are observed in cupping, with a parameter {Delta}R describing the variation of R in the plane of the sheet. For many common textures in face-centered and body-centered materials, the ears form relative to the sheet rolling direction at 0{degrees} and 90{degrees} around the perimeter if {Delta}R>0, and at -45{degrees} and +45{degrees} if {Delta}R<0. There is extensive experimental evidence that ear height shows a linear correlation with {Delta}R/R, but attempts to duplicate this using the finite-element method are highly dependent on both the methodology and yield surface used. It was shown previously that using a coarse mesh and the quadratic Hill yield surface tends to greatly under predict earing. In this study, we have used two different finite-element codes developed at LLNL to examine the predicted earing using both quadratic Hill and alternative non-quadratic yield surfaces. These results are compared to experimental data and conclusions drawn about the most desirable closed-form yield surfaces to duplicate the observed earing phenomena.

Logan, R.W.

1995-06-18

16

Computation of a finite element-conformal tetrahedral mesh approximation for simulated soft tissue deformation using a deformable surface model.  

PubMed

In this article, we present a new method for the generation of surface meshes of biological soft tissue. The method is based on the deformable surface model technique and is extended to histological data sets. It relies on an iterative adjustment towards polygonal segments describing the histological structures of the soft tissue. The generated surface meshes allow for the construction of volumetric meshes through a standard constrained Delaunay approach and, thus, for the application in finite element methods. The geometric properties of volumetric meshes have an immediate influence on the numerical conditioning and, therewith, on the stability of the finite element method and the convergence of iterative solvers. In this article, the influence of the surface meshes on the quality of the volumetric meshes is analysed in terms of the spectral condition number of the stiffness matrices, which are assembled within Newton's method. The non-linear material behavior of biological soft tissue is modeled by the Mooney-Rivlin material law. The subject is motivated by the requirements of virtual surgery. PMID:20411435

Weichert, Frank; Schröder, Andreas; Landes, Constantin; Shamaa, Ali; Awad, Said Kamel; Walczak, Lars; Müller, Heinrich; Wagner, Mathias

2010-06-01

17

A posteriori error estimates for mixed finite element approximation of nonlinear quadratic optimal control problems  

Microsoft Academic Search

In this paper, we obtain an a posteriori error analysis for mixed finite element approximation of convex optimal control problems governed by a nonlinear second-order elliptic equation. Our results are based on the approximation for both the coupled state variables and the control variable. We propose to improve the error estimates, which can be used to construct an adaptive finite

Yanping Chen; Zuliang Lu; Min Fu

2012-01-01

18

Strongly cumulative second harmonic generation in a plate with quadratic nonlinearity: Finite element simulation  

NASA Astrophysics Data System (ADS)

A comprehensive analysis for guided wave preferred fundamental excitation that satisfies cumulative conditions of second harmonic generation in a weakly nonlinear plate has been carried out and then confirmed by finite element modeling for selected cases. The properties of nonlinear forcing terms and secondary mode shapes are manipulated to determine the cumulative second harmonics. Analysis shows that the synchronism points with higher power flux intensity are the preferred fundamental excitations that are suitable for nonlinear guided wave NDE. Finite element modeling of SH mode and Lamb mode fundamental excitation has been conducted on the excitation points selected by the co-analysis method. A linear increase of qualitative nonlinear parameter over the propagation distance has been observed for both Lamb wave and SH wave fundamental excitations.

Liu, Yang; Lissenden, Cliff J.; Rose, J. L.

2013-01-01

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.

University, Tufts

2004-01-01

20

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.

Liao, David

21

Quadratic Damping  

ERIC Educational Resources Information Center

Quadratic friction involves a discontinuous damping term in equations of motion in order that the frictional force always opposes the direction of the motion. Perhaps for this reason this topic is usually omitted from beginning texts in differential equations and physics. However, quadratic damping is more realistic than viscous damping in many…

Fay, Temple H.

2012-01-01

22

Tetrahedral and Hexahedral Mesh Adaptation for CFD Problems  

NASA Technical Reports Server (NTRS)

This paper presents two unstructured mesh adaptation schemes for problems in computational fluid dynamics. The procedures allow localized grid refinement and coarsening to efficiently capture aerodynamic flow features of interest. The first procedure is for purely tetrahedral grids; unfortunately, repeated anisotropic adaptation may significantly deteriorate the quality of the mesh. Hexahedral elements, on the other hand, can be subdivided anisotropically without mesh quality problems. Furthermore, hexahedral meshes yield more accurate solutions than their tetrahedral counterparts for the same number of edges. Both the tetrahedral and hexahedral mesh adaptation procedures use edge-based data structures that facilitate efficient subdivision by allowing individual edges to be marked for refinement or coarsening. However, for hexahedral adaptation, pyramids, prisms, and tetrahedra are used as buffer elements between refined and unrefined regions to eliminate hanging vertices. Computational results indicate that the hexahedral adaptation procedure is a viable alternative to adaptive tetrahedral schemes.

Biswas, Rupak; Strawn, Roger C.; Chancellor, Marisa K. (Technical Monitor)

1997-01-01

23

Parallel tetrahedral mesh refinement with MOAB.  

SciTech Connect

In this report, we present the novel functionality of parallel tetrahedral mesh refinement which we have implemented in MOAB. This report details work done to implement parallel, edge-based, tetrahedral refinement into MOAB. The theoretical basis for this work is contained in [PT04, PT05, TP06] while information on design, performance, and operation specific to MOAB are contained herein. As MOAB is intended mainly for use in pre-processing and simulation (as opposed to the post-processing bent of previous papers), the primary use case is different: rather than refining elements with non-linear basis functions, the goal is to increase the number of degrees of freedom in some region in order to more accurately represent the solution to some system of equations that cannot be solved analytically. Also, MOAB has a unique mesh representation which impacts the algorithm. This introduction contains a brief review of streaming edge-based tetrahedral refinement. The remainder of the report is broken into three sections: design and implementation, performance, and conclusions. Appendix A contains instructions for end users (simulation authors) on how to employ the refiner.

Thompson, David C.; Pebay, Philippe Pierre

2008-12-01

24

Streaming simplification of tetrahedral meshes.  

PubMed

Unstructured tetrahedral meshes are commonly used in scientific computing to represent scalar, vector, and tensor fields in three dimensions. Visualization of these meshes can be difficult to perform interactively due to their size and complexity. By reducing the size of the data, we can accomplish real-time visualization necessary for scientific analysis. We propose a two-step approach for streaming simplification of large tetrahedral meshes. Our algorithm arranges the data on disk in a streaming, I/O-efficient format that allows coherent access to the tetrahedral cells. A quadric-based simplification is sequentially performed on small portions of the mesh in-core. Our output is a coherent streaming mesh which facilitates future processing. Our technique is fast, produces high quality approximations, and operates out-of-core to process meshes too large for main memory. PMID:17093343

Vo, Huy T; Callahan, Steven P; Lindstrom, Peter; Pascucci, Valerio; Silva, Cláudio T

2007-01-01

25

Lattice cleaving: a multimaterial tetrahedral meshing algorithm with guarantees.  

PubMed

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, to reduce element counts in regions of homogeneity. Additionally, we provide proofs showing that both element quality and geometric fidelity are bounded using this approach. PMID:24356365

Bronson, Jonathan; Levine, Joshua A; Whitaker, Ross

2014-02-01

26

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.

Wang, Jun; Yu, Zeyun

2012-01-01

27

REGTET: A Program for Computing Regular Tetrahedralizations.  

National Technical Information Service (NTIS)

REGTET, a Fortran 77 program for computing a regular tetrahedralization for a finite set of weighted points in 3-dimensional space, is discussed. REGTET is based on an algorithm by Edelsbrunner and Shah for constructing regular tetrahedralizations with in...

J. Bernal

2001-01-01

28

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

29

Deuterium occupation of tetrahedral sites in palladium  

NASA Astrophysics Data System (ADS)

The long-standing controversy over the occupation by hydrogen of tetrahedral interstices in palladium has been addressed experimentally and theoretically. Using the highest resolution neutron powder diffractometer available, diffraction profiles were recorded from single-phase samples obtained by loading Pd with deuterium in situ at 310°C , at D2 pressures up to 90 bar. Rietveld profile analysis showed that a model including tetrahedral occupancy was necessary to properly fit the experimental diffraction profiles. The maximum absolute tetrahedral occupancy was found at a deuterium-to-metal atomic ratio of 0.6, where about one-third of all D atoms were in tetrahedral sites. At the lowest and highest D concentration, the tetrahedral fraction approached zero. The energy of formation was calculated, based on density-functional theory, for numerous configurations of octahedral and tetrahedral interstitials in a supercell, which modeled stoichiometries Pd8Hn such that n=1,2,…8 . For Pd8H3 , the minimum formation energy was found with 1-2 tetrahedral atoms. For all other stoichiometries, the minimum formation energy was 0-1 tetrahedral atoms. Thus, the calculations are in excellent qualitative agreement with experiment and support the reality of tetrahedral occupancy.

McLennan, K. G.; Gray, E. Maca.; Dobson, J. F.

2008-07-01

30

Resolvability and the Tetrahedral Configuration of Carbon.  

ERIC Educational Resources Information Center

Discusses evidence for the tetrahedral configuration of the carbon atom, indicating that three symmetrical configurations are theoretically possible for coordination number four. Includes table indicating that resolvability of compounds of type CR'R"R"'R"" is a necessary but not sufficient condition for proving tetrahedral configuration. (JN)

Kauffman, George B.

1983-01-01

31

Refitted tetrahedral covalent radii for solids  

NASA Astrophysics Data System (ADS)

The previous systems of molecular single-, double-, and triple-bond self-consistent, additive covalent radii R(AB) = r(A) + r(B) are now completed with a fit for crystals, where both atoms are tetrahedrally coordinated. A self-consistent primary fit is carried out using elements such as Si and binary compounds such as GaAs or ZnS. Further checks involve also ternary compounds such as chalcopyrites, CuInS2, and the quaternary compounds Cu2ZnSnS4 and Cu2ZnSnSe4, the latter two with both kesterite and stannite structures. The input bond lengths R are taken from experimental or theoretical data. For the 30 elements in the primary fit, the mean-square deviation of the predicted R(AB) values is only 0.67 pm for the 48 systems used. The results are compared to earlier radii by Pauling and Huggins [Z. Kristallogr. A 87, 205 (1934)] or by Van Vechten and Phillips [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.2.2160 2, 2160 (1970)], and to the recent molecular covalent radii.

Pyykkö, Pekka

2012-01-01

32

Tetrahedral Mesh Generation for Environmental Problems over Complex Terrains  

Microsoft Academic Search

In the finite element simulation of environmental processes that occur in a three-dimensional domain defined over an irregular\\u000a terrain, a mesh generator capable of adapting itself to the topographic characteristics is essential. The present study develops\\u000a a code for generating a tetrahedral mesh from an ”optimal” node distribution in the domain. The main ideas for the construction\\u000a of the initial

Rafael Montenegro; Gustavo Montero; José María Escobar; Eduardo Rodríguez; José María González-yuste

2002-01-01

33

Interactive Isosurface Ray Tracing of Time-Varying Tetrahedral Volumes  

Microsoft Academic Search

We describe a system for interactively rendering isosurfaces of tetrahedral finite-element scalar fields using coherent ray tracing tech- niques on the CPU. By employing state-of-the art methods in polygonal ray tracing, namely aggressive packet\\/frustum traversal of a bounding volume hierarchy, we can accomodate large and time-varying unstructured data. In conjunction with this efficiency structure, we introduce a novel technique for

Ingo Wald; Heiko Friedrich; Aaron Knoll; Charles D. Hansen

2007-01-01

34

Quadratic Functions: Workshop 4  

NSDL National Science Digital Library

Lesson 1 of two lessons requires students to explore quadratic functions by examining the family of functions described by y = a (x - h)squared+ k. In Lesson 2 students explore quadratic functions by using a motion detector known as a Calculator Based Ranger (CBR) to examine the heights of the different bounces of a ball. Students will represent each bounce with a quadratic function of the form y = a (x - h)squared + k. Background information, resources, references and videos of the lessons are included. Students work in teams of four.

Annenberg Media, Insights into Algebra, Teaching for Learning

2009-12-23

35

Tetrahedral Hohlraum Visualization and Pointings  

NASA Astrophysics Data System (ADS)

In designing experiments for Omega, the tetrahedral hohlraum (a sphere with four holes) can make full use of all 60 beams. There are some complications: the beams must clear the laser entrance hole (LEH), must miss a central capsule, absolutely must not go out the other LEHs, and should distribute in the interior of the hohlraum to maximize the uniformity of irradiation on the capsule while keeping reasonable laser spot sizes. We created a 15-offset coordinate system with which an IDL program computes clearances, writes a file for QuickDraw 3D (QD3D) visualization, and writes input for the viewfactor code RAYNA IV. Visualizing and adjusting the parameters by eye gave more reliable results than computer optimization. QD3D images permitted quick live rotations to determine offsets. The clearances obtained insured safe operation and good physics. The viewfactor code computes the initial irradiation of the hohlraum and capsule or of a uniform hohlraum source with the loss through the four LEHs and shows a high degree of uniformity with both, better for lasers because this deposits more energy near the LEHs to compensate for the holes.

Klare, K. A.; Wallace, J. M.; Drake, D.

1997-11-01

36

Neutrino Mixing and the Double Tetrahedral Group  

NASA Astrophysics Data System (ADS)

In the spirit of a previous study of the tetrahedral group T ?A4, we discuss a minimalist scheme to derive the neutrino mixing matrix using the double tetrahedral group T?, the double cover of T. The new features are three distinct two-dimensional representations and complex Clebsch-Gordan coefficients, which can result in a geometric source of CP violation in the neutrino mass matrix. In an appendix, we derive explicitly the relevant group theory for the tetrahedral group T and its double cover T?.

Bentov, Yoni; Zee, A.

2013-11-01

37

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

38

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

39

PARAMETRIC QUADRATIC PROGRAMMING METHOD FOR ELASTIC CONTACT FRACTURE ANALYSIS  

Microsoft Academic Search

A solution procedure for elastic contact fracture mechanics has been proposed in this paper. The procedure is based on the quadratic programming and finite element method (FEM). In this paper, parametric quadratic programming method for two-dimensional contact mechanics analysis is applied to the crack problems involving the crack surfaces in frictional contact. Based on a linear complementary contact condition, the

R. K. L. SU; Y. ZHU; A. Y. T. LEUNG

2002-01-01

40

Parametric quadratic programming method for elastic contact fracture analysis  

Microsoft Academic Search

A solution procedure for elastic contact fracture mechanics has been proposed in this paper. The procedure is based on the quadratic programming and finite element method (FEM). In this paper, parametric quadratic programming method for two-dimensional contact mechanics analysis is applied to the crack problems involving the crack surfaces in frictional contact. Based on a linear complementary contact condition, the

R. K. L. Su; Y. Zhu; A. Y. T. Leung

2002-01-01

41

The Quadratic Assignment Problem  

Microsoft Academic Search

This paper aims at describing the state of the art on quadratic assignment problems (QAPs). It discusses the most important developments in all aspects of the QAP such as linearizations, QAP polyhedra, algorithms to solve the problem to optimality, heuristics, polynomially solvable special cases, and asymptotic behavior. Moreover, it also considers problems related to the QAP, e.g. the biquadratic assignment

Rainer E. Burkard; Eranda Cela; Panos M. Pardalos; Leonidas S. Pitsoulis

1998-01-01

42

A Quadratic Spring Equation  

ERIC Educational Resources Information Center

Through numerical investigations, we study examples of the forced quadratic spring equation [image omitted]. By performing trial-and-error numerical experiments, we demonstrate the existence of stability boundaries in the phase plane indicating initial conditions yielding bounded solutions, investigate the resonance boundary in the [omega]…

Fay, Temple H.

2010-01-01

43

Spin dynamics of a tetrahedral cluster magnet  

NASA Astrophysics Data System (ADS)

We study the magnetism of a lattice of coupled tetrahedral spin-1/2 clusters which might be of relevance to the tellurate compounds Cu2Te2O5X2, with X=Cl, Br. Using the flow equation method we perform a series expansion in terms of the inter-tetrahedral exchange couplings starting from the quadrumer limit. Results will be given for the magnetic instabilities of the quadrumer phase and the dispersion of elementary triplet excitations. In limiting cases of our model of one- or two-dimensional character we show our results to be consistent with findings on previously investigated decoupled tetrahedral chains and the Heisenberg model on the 1/5-depleted square lattice.

Brenig, Wolfram

2003-02-01

44

Extension of Karmarkar's algorithm onto convex quadratically constrained quadratic problems  

Microsoft Academic Search

Convex quadratically constrained quadratic problems are considered. It is shown that such problems can be transformed to aconic form. The feasible set of the conic form is the intersection of a direct product of standard quadratic cones intersected with\\u000a a hyperplane (the analogue of a simplex), and a linear subspace. For a problem of such form, the analogue of Karmarkar's

Arkadii Nemirovskii; Katya Scheinberg

1996-01-01

45

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

46

Evidence for Tetrahedral Symmetry in O16  

NASA Astrophysics Data System (ADS)

We derive the rotation-vibration spectrum of a 4? configuration with tetrahedral symmetry Td and show evidence for the occurrence of this symmetry in the low-lying spectrum of O16. All vibrational states with A, E, and F symmetry appear to have been observed as well as the rotational bands with LP=0+, 3-, 4+, 6+ on the A states and part of the rotational bands built on the E, F states. We derive analytic expressions for the form factors and B(EL) values of the ground-state rotational band and show that the measured values support the tetrahedral symmetry of this band.

Bijker, R.; Iachello, F.

2014-04-01

47

A finite element computational 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 are interpolated using complete quadratic shape functions, and the pressure is interpolated using linear shape functions which are defined on a triangular element for the two-dimensional case and on a tetrahedral element for the three-dimensional case. The triangular element and the tetrahedral element are contained inside the complete bi- and tri-quadratic elements for velocity variables for two and three dimensional cases, respectively, so that the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow of Reynolds numbers 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 favorably with the finite difference computational results and/or experimental data available. It was found that the present method can capture the delicate pressure driven recirculation zones, that the method did not yield any spurious pressure modes, and that the method requires fewer grid points than the finite difference methods to obtain comparable computational results.

Kim, Sang-Wook

1987-01-01

48

Analysis of the T(X)(e+2t2) Jahn-Teller problem for a tetrahedral cluster  

Microsoft Academic Search

The T(X)(e+2t2) Jahn-Teller (JT) system is studied analytically in strong coupling on a tetrahedral cluster model by transformation methods. Using an energy minimization procedure, the system is shown to be localized in potential-energy minima of tetragonal, trigonal or orthorhombic symmetry depending upon the relative strengths of the e and the two t2 coupling constants and on the quadratic coupling constants.

P. J. Kirk; C. A. Bates; J. L. Dunn

1994-01-01

49

Tetrahedral Mesh Generation for Medical Imaging  

Microsoft Academic Search

We describe the open source implementation of an adap- tive tetrahedral mesh generator particularly targeted for non-rigid FEM registration of MR images. While many medical imaging applications re- quire robust mesh generation, there are few codes available. Moreover, most of the practical implementations are commercial. The algorithm we have implemented has been previously evaluated for simulations of highly deformable objects,

Andriy Fedorov; Nikos Chrisochoides; Ron Kikinis

50

Magnetism of a tetrahedral spin-chain  

NASA Astrophysics Data System (ADS)

Magnetic properties of a completely frustrated tetrahedral chain are summarized. Using exact diagonalization, and bond-operator theory results for the ground-state phase diagram, the one-triplet excitations and the Raman spectrum are given. The link to novel tellurate materials is clarified.

Brenig, Wolfram; Becker, Klaus W.; Lemmens, Peter

2002-03-01

51

Tetrahedral colliding beam nuclear fusion  

US Patent & Trademark Office Database

The subject invention is a nuclear fusion reactor. It operates by colliding particle beams from at least four different directions. The beams collide in a matrix that guides the particles to the reaction's center by their mutual electrostatic repulsion. In the preferred embodiment the reactor comprises primarily four high energy particle accelerators (11a, 11b, 11c, and 11d). At the reactor's center, the accelerators' four beams intersect at angles of approximately 109.471220634491 degrees. The exact measure of the preferred angle is given by the measure of the obtuse interior angle of an isosceles triangle that has two sides measuring the square root of three units and a base measuring twice the square root of two units. Accelerated to fusion producing velocities, the four particle beams intersect in a high-vacuum reaction chamber (12). The resulting collision matrix funnels the accelerated particles into the center of the reaction zone causing some of the fuel particles to fuse rather than to scatter. This reactor's collision matrix should result in a higher collision rate than that of previous non-neutralized beam-beam reactors. When the reactor is inducing fusion with lightweight elements such as deuterium, energy is released, although not necessarily more energy than it consumes. This reactor is inherently safe in that it cannot melt down or explode. Since the fuel for fusion is cheap and in virtually unlimited supply this reactor or some future improvement of its design could possibly yield virtually unlimited power.

1998-10-20

52

Electron phonon interaction in tetrahedral semiconductors  

NASA Astrophysics Data System (ADS)

Considerable progress has been made in recent years in the field of ab initio calculations of electronic band structures of semiconductors and insulators. The one-electron states (and the concomitant two-particle excitations) have been obtained without adjustable parameters, with a high degree of reliability. Also, more recently, the electron-hole excitation frequencies responsible for optical spectra have been calculated. These calculations, however, are performed with the constituent atoms fixed in their crystallographic positions and thus neglect the effects of the lattice vibrations (i.e. electron-phonon interaction) which can be rather large, even larger than the error bars assumed for ab initio calculations. Effects of electron-phonon interactions on the band structure can be experimentally investigated in detail by measuring the temperature dependence of energy gaps or critical points (van Hove singularities) of the optical excitation spectra. These studies have been complemented in recent years by observing the dependence of such spectra on isotopic mass whenever different stable isotopes of a given atom are available at affordable prices. In crystals composed of different atoms, the effect of the vibration of each separate atom can thus be investigated by isotopic substitution. Because of the zero-point vibrations, such effects are present even at zero temperature ( T=0). In this paper, we discuss state-of-the-art calculations of the dielectric function spectra and compare them with experimental results, with emphasis on the differences introduced by the electron-phonon interaction. The temperature dependence of various optical parameters will be described by means of one or two (in a few cases three) Einstein oscillators, except at the lowest temperatures where the T4 law (contrary to the Varshni T2 result) will be shown to apply. Increasing an isotopic mass increases the energy gaps, except in the case of monovalent Cu (e.g. CuCl) and possibly Ag (e.g. AgGaS 2). It will be shown that the gaps of tetrahedral materials containing an element of the first row of the periodic table (C,N,O) are strongly affected by the electron-phonon interaction. It will be conjectured that this effect is related to the superconductivity recently observed in heavily boron-doped carbon.

Cardona, Manuel

2005-01-01

53

LBB stability of a mixed Galerkin finite element pair for fluid flow simulations  

NASA Astrophysics Data System (ADS)

We introduce a new mixed finite element for solving the 2- and 3-dimensional wave equations and equations of incompressible flow. The element, which we refer to as P1-P2, uses discontinuous piecewise linear functions for velocity and continuous piecewise quadratic functions for pressure. The aim of introducing the mixed formulation is to produce a new flexible element choice for triangular and tetrahedral meshes which satisfies the LBB stability condition and hence has no spurious zero-energy modes. The advantage of this particular element choice is that the mass matrix for velocity is block diagonal so it can be trivially inverted; it also allows the order of the pressure to be increased to quadratic whilst maintaining LBB stability which has benefits in geophysical applications with Coriolis forces. We give a normal mode analysis of the semi-discrete wave equation in one dimension which shows that the element pair is stable, and demonstrate that the element is stable with numerical integrations of the wave equation in two dimensions, an analysis of the resultant discrete Laplace operator in two and three dimensions on various meshes which shows that the element pair does not have any spurious modes. We provide convergence tests for the element pair which confirm that the element is stable since the convergence rate of the numerical solution is quadratic.

Cotter, Colin J.; Ham, David A.; Pain, Christopher C.; Reich, Sebastian

2009-02-01

54

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

55

Crystallization of tetrahedral patchy particles in silico  

NASA Astrophysics Data System (ADS)

We investigate the competition between glass formation and crystallization of open tetrahedral structures for particles with tetrahedral patchy interactions. We analyze the outcome of such competition as a function of the potential parameters. Specifically, we focus on the separate roles played by the interaction range and the angular width of the patches, and show that open crystal structures (cubic and hexagonal diamond and their stacking hybrids) spontaneously form when the angular width is smaller than about 30°. Evaluating the temperature and density dependence of the chemical potential of the fluid and of the crystal phases, we find that adjusting the patch width affects the fluid and crystal in different ways. As a result of the different scaling, the driving force for spontaneous self-assembly rapidly grows as the fluid is undercooled for small-width patches, while it only grows slowly for large-width patches, in which case crystallization is pre-empted by dynamic arrest into a network glass.

Romano, Flavio; Sanz, Eduardo; Sciortino, Francesco

2011-05-01

56

Algebraic cluster model with tetrahedral symmetry  

SciTech Connect

We propose an algebraic treatment of a four-body system in terms of a U(10) spectrum generating algebra. The formalism for the case of four identical objects is developed in detail. This includes a discussion of the permutation symmetry, a study of special solutions which are shown to correspond to the harmonic oscillator, the deformed oscillator and the spherical top with tetrahedral symmetry.

Bijker, Roelof [ICN-UNAM, AP 70-543, 04510 Mexico, DF (Mexico)

2010-12-23

57

Haemocompatibility of tetrahedral amorphous carbon films  

Microsoft Academic Search

Tetrahedral amorphous carbon (ta-C) films have been prepared by filtered arc deposition (FAD). The structure of the ta-C films was characterised by Raman Spectroscopy. The haemocompatibility of the formed films was studied by measurement of haemolysis ratio and observation of platelet adhesion. Compared with low-temperature isotropic pyrolytic carbon (LTI-carbon), which is being used as the material for artificial heart valves

L. J Yu; X Wang; X. H Liu

2000-01-01

58

Understanding tetrahedral liquids through patchy colloids  

NASA Astrophysics Data System (ADS)

We investigate the structural properties of a simple model for tetrahedral patchy colloids in which the patch width and the patch range can be tuned independently. For wide bond angles, a fully bonded network can be generated by standard Monte Carlo or molecular dynamics simulations of the model, providing a good method for generating defect-free random tetrahedral networks. This offers the possibility of focusing on the role of the patch angular width on the structure of the fully bonded network. The analysis of the fully bonded configurations as a function of the bonding angle shows how the bonding angle controls the system compressibility, the strength of the pre-peak in the structure factor, and ring size distribution. Comparison with models of liquid water and silica allows us to find the best mapping between these continuous potentials and the colloidal one. Building on previous studies focused on the connection between angular range and crystallization, the mapping makes it possible to shed new light on the glass-forming ability of network-forming tetrahedral liquids.

Saika-Voivod, Ivan; Smallenburg, Frank; Sciortino, Francesco

2013-12-01

59

Understanding tetrahedral liquids through patchy colloids.  

PubMed

We investigate the structural properties of a simple model for tetrahedral patchy colloids in which the patch width and the patch range can be tuned independently. For wide bond angles, a fully bonded network can be generated by standard Monte Carlo or molecular dynamics simulations of the model, providing a good method for generating defect-free random tetrahedral networks. This offers the possibility of focusing on the role of the patch angular width on the structure of the fully bonded network. The analysis of the fully bonded configurations as a function of the bonding angle shows how the bonding angle controls the system compressibility, the strength of the pre-peak in the structure factor, and ring size distribution. Comparison with models of liquid water and silica allows us to find the best mapping between these continuous potentials and the colloidal one. Building on previous studies focused on the connection between angular range and crystallization, the mapping makes it possible to shed new light on the glass-forming ability of network-forming tetrahedral liquids. PMID:24359387

Saika-Voivod, Ivan; Smallenburg, Frank; Sciortino, Francesco

2013-12-21

60

A Hermite WENO reconstruction-based discontinuous Galerkin method for the Euler equations on tetrahedral grids  

NASA Astrophysics Data System (ADS)

A Hermite WENO reconstruction-based discontinuous Galerkin method RDG(P1P2), designed not only to enhance the accuracy of discontinuous Galerkin method but also to ensure linear stability of the RDG method, is presented for solving the compressible Euler equations on tetrahedral grids. In this RDG(P1P2) method, a quadratic polynomial solution (P2) is first reconstructed using a least-squares method from the underlying linear polynomial (P1) discontinuous Galerkin solution. By taking advantage of handily available and yet invaluable information, namely the derivatives in the DG formulation, the stencils used in the reconstruction involve only von Neumann neighborhood (adjacent face-neighboring cells) and thus are compact and consistent with the underlying DG method. The final quadratic polynomial solution is then obtained using a WENO reconstruction, which is necessary to ensure linear stability of the RDG method. The developed RDG method is used to compute a variety of flow problems on tetrahedral meshes to demonstrate its accuracy, efficiency, robustness, and versatility. The numerical experiments demonstrate that the developed RDG(P1P2) method is able to maintain the linear stability, achieve the designed third-order of accuracy: one order accuracy higher than the underlying DG method without significant increase in computing costs and storage requirements.

Luo, Hong; Xia, Yidong; Li, Shujie; Nourgaliev, Robert; Cai, Chunpei

2012-06-01

61

The general quadratic Radon transform  

NASA Astrophysics Data System (ADS)

The general quadratic Radon transform in two dimensions is investigated. Whereas the classical Radon transform of a smooth function represents the integration over all lines, the general quadratic Radon transform integrates over all conic sections. First, the parabolic isofocal Radon transform, i.e. the restriction of the general quadratic Radon transform to all parabolae with focus in the origin, is defined and illustrated. We show its intense relation to the classical Radon transform, deduce a support theorem, formulate an extension of the support theorem and derive an inversion formula. The natural extension to a more general class of isofocal quadratic Radon transforms is outlined. We show how the general quadratic Radon transform can be derived from the integrals over all parabolae by solving the related Cauchy problem. Finally, we introduce an entirely geometrical definition of a generalized Radon transform, the oriented generalized Radon transform.

Denecker, Koen; Van Overloop, Jeroen; Sommen, Frank

1998-06-01

62

Dark Matter from Binary Tetrahedral Flavor Symmetry  

NASA Astrophysics Data System (ADS)

Binary Tetrahedral Flavor Symmetry, originally developed as a quark family symmetry and later adapted to leptons, has proved both resilient and versatile over the past decade. In 2008 a minimal T' model was developed to accommodate quark and lepton masses and mixings using a family symmetry of (T'xZ2). We examine an expansion of this earlier model using an additional Z2 group that facilitates predictions of WIMP dark matter, the Cabibbo angle, and deviations from Tribimaximal Mixing, while giving hints at the nature of leptogenesis.

Eby, David; Frampton, Paul

2012-03-01

63

Magnetism of a tetrahedral cluster spin chain  

NASA Astrophysics Data System (ADS)

We discuss the magnetic properties of a dimerized and completely frustrated tetrahedral spin-1/2 chain. Using a combination of exact diagonalization and bond-operator theory the quantum phase diagram is shown to incorporate a singlet product, a dimer, and a Haldane phase. In addition we consider one- and two-triplet excitations in the dimer phase and evaluate the magnetic Raman cross section which is found to be strongly renormalized by the presence of a two-triplet bound state. The link to a novel tellurate materials is clarified.

Brenig, Wolfram; Becker, Klaus W.

2001-12-01

64

Quadratic as Parametric Linear Programming.  

National Technical Information Service (NTIS)

The paper describes an approximate solution procedure for quadratic programming problems using parametric linear programming. Limited computational experience suggests that the approximation can be expected to be good. (Author)

R. J. Townsley W. Candler

1972-01-01

65

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

66

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

67

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

68

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

69

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

70

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

71

Preliminary design of a large tetrahedral truss/hexagonal heatshield panel aerobrake  

NASA Technical Reports Server (NTRS)

An aerobrake structural concept is introduced which consists of two primary components: (1) a lightweight erectable tetrahedral support truss; and (2) sandwich hexagonal heatshield panels which, when attached to the truss, form a continuous impermeable aerobraking surface. Generic finite element models and a general analysis procedure to design tetrahedral truss/hexagonal heatshield panel aerobrakes is developed, and values of the aerobrake design parameters which minimize mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed. The results show that a 120-foot-diameter aerobrake is viable using the concept presented (i.e., the aerobrake mass is less than or equal to 15 percent of the payload spacecraft mass). Minimizing the aerobrake mass (by increasing the number of rings in the support truss) however, leads to aerobrakes with the highest part count.

Dorsey, John T.; Mikulas, Martin M., Jr.

1989-01-01

72

A reconstructed discontinuous Galerkin method based on a Hierarchical WENO reconstruction for compressible flows on tetrahedral grids  

NASA Astrophysics Data System (ADS)

A reconstructed discontinuous Galerkin (RDG) method based on a hierarchical WENO reconstruction, termed HWENO (P1P2) in this paper, designed not only to enhance the accuracy of discontinuous Galerkin methods but also to ensure the nonlinear stability of the RDG method, is presented for solving the compressible Euler equations on tetrahedral grids. In this HWENO (P1P2) method, a quadratic polynomial solution (P2) is first reconstructed using a Hermite WENO reconstruction from the underlying linear polynomial (P1) discontinuous Galerkin solution to ensure the linear stability of the RDG method and to improve the efficiency of the underlying DG method. By taking advantage of handily available and yet invaluable information, namely the derivatives in the DG formulation, the stencils used in the reconstruction involve only von Neumann neighborhood (adjacent face-neighboring cells) and thus are compact. The first derivatives of the quadratic polynomial solution are then reconstructed using a WENO reconstruction in order to eliminate spurious oscillations in the vicinity of strong discontinuities, thus ensuring the nonlinear stability of the RDG method. The developed HWENO (P1P2) method is used to compute a variety of flow problems on tetrahedral meshes to demonstrate its accuracy, robustness, and non-oscillatory property. The numerical experiments indicate that the HWENO (P1P2) method is able to capture shock waves within one cell without any spurious oscillations, and achieve the designed third-order of accuracy: one order accuracy higher than the underlying DG method.

Luo, Hong; Xia, Yidong; Spiegel, Seth; Nourgaliev, Robert; Jiang, Zonglin

2013-03-01

73

Experimental and computational analysis of random tetrahedral packings with applications  

NASA Astrophysics Data System (ADS)

Random packings are prevalent in chemical engineering applications and they can serve as prototype models of particulate materials. In this research, comprehensive studies on tetrahedral packings were carried out experimentally. Experiment was conducted on regular tetrahedral dice. MRI imaging was used to image the tetrahedral packs, an algorithm was developed which allowed us to retrieve each of the particle center positions as well as the 3D orientation from the digital data. To our best knowledge this is the first time that such an in-depth analysis was performed on non spherical objects. This numerical approach makes it possible to study detailed packing structure, packing density, the onset of ordering, and wall effects. Important applications for tetrahedral packings include multiphase flow in catalytic beds, heat transfer, bulk storage and transportation, and manufacturing of fibrous composites.

Jaoshvili, Alexander

74

Quadratic Forms and Manifold Normal Distributions.  

National Technical Information Service (NTIS)

The distribution of quadratic forms in matrix normal variables is considered. An application of the distribution of quadratic forms is given by deriving distributions on manifolds of multivariate normal distributions. Special cases are, for instance, the ...

D. J. Dewaal

1982-01-01

75

Natural Exponential Families with Quadratic Variance Functions  

Microsoft Academic Search

The normal, Poisson, gamma, binomial, and negative binomial distributions are univariate natural exponential families with quadratic variance functions (the variance is at most a quadratic function of the mean). Only one other such family exists. Much theory is unified for these six natural exponential families by appeal to their quadratic variance property, including infinite divisibility, cumulants, orthogonal polynomials, large deviations,

Carl N. Morris

1982-01-01

76

Bayesian Quadratic Network Game Filters  

NASA Astrophysics Data System (ADS)

A repeated network game where agents have quadratic utilities that depend on information externalities -- an unknown underlying state -- as well as payoff externalities -- the actions of all other agents in the network -- is considered. Agents play Bayesian Nash Equilibrium strategies with respect to their beliefs on the state of the world and the actions of all other nodes in the network. These beliefs are refined over subsequent stages based on the observed actions of neighboring peers. This paper introduces the Quadratic Network Game (QNG) filter that agents can run locally to update their beliefs, select corresponding optimal actions, and eventually learn a sufficient statistic of the network's state. The QNG filter is demonstrated on a Cournot market competition game and a coordination game to implement navigation of an autonomous team.

Eksin, Ceyhun; Molavi, Pooya; Ribeiro, Alejandro; Jadbabaie, Ali

2014-05-01

77

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

78

Antenna Modeling Using 3D Hybrid Finite Element - Finite Difference Time Domain Method  

Microsoft Academic Search

D Hybrid Finite Element - Finite Difference Time Domain (FE\\/FDTD) Method is developed and applied to the numerical modeling of antennas. The antenna geometry is modeled using tetrahedral finite element mesh. Pyramidal elements are introduced in the transition from unstructured tetrahedral elements to structured hexahedral elements. The finite element formulation incorporates the excitation of antennas using coaxial line or stripline

Neelakantam Venkatarayalu; Yeow-Beng Gan; Robert Lee; Le-Wei Li

79

THE GENERATION OF TETRAHEDRAL MESH MODELS FOR NEUROANATOMICAL MRI  

PubMed Central

In this article, we describe a detailed method for automatically generating tetrahedral meshes from 3D images having multiple region labels. An adaptively sized tetrahedral mesh modeling approach is described that is capable of producing meshes conforming precisely to the voxelized regions in the image. Efficient tetrahedral construction is performed minimizing an energy function containing three terms: a smoothing term to remove the voxelization, a fidelity term to maintain continuity with the image data, and a novel elasticity term to prevent the tetrahedra from becoming flattened or inverted as the mesh deforms while allowing the voxelization to be removed entirely. The meshing algorithm is applied to structural MR image data that has been automatically segmented into 56 neuroanatomical sub-divisions as well as on two other examples. The resulting tetrahedral representation has several desirable properties such as tetrahedra with dihedral angles away from 0 and 180 degrees, smoothness, and a high resolution. Tetrahedral modeling via the approach described here has applications in modeling brain structure in normal as well as diseased brain in human and non-human data and facilitates examination of 3D object deformations resulting from neurological illness (e.g. Alzheimer’s Disease), development, and/or aging.

Lederman, Carl; Joshi, Anand; Dinov, Ivo; Vese, Luminita; Toga, Arthur; Van Horn, John Darrell

2010-01-01

80

Skyrme-Hartree and Hartree-Fock Calculations for Nuclei with Tetrahedral Deformation  

Microsoft Academic Search

Hartree-Fock-Bogolyubov solutions corresponding to the tetrahedral deformation are found in six tetrahedrally doubly-magic nuclei. Values of the beta32 deformation, depths of the tetrahedral minima, and their energies relative to the co-existing quadrupole minima are determined for several versions of the Skyrme force. Reduction of the tetrahedral deformation energies by pairing correlations is quantitatively analysed. In light nuclei, shallow tetrahedral minima

P. Olbratowski; J. Dobaczewski; P. Powalowski; M. Sadziak; K. Zberecki

2006-01-01

81

Nucleation barriers in tetrahedral liquids spanning glassy and crystallizing regimes  

NASA Astrophysics Data System (ADS)

Crystallization and vitrification of tetrahedral liquids are important both from a fundamental and a technological point of view. Here, we study via extensive umbrella sampling Monte Carlo computer simulations the nucleation barriers for a simple model for tetrahedral patchy particles in the regime where open tetrahedral crystal structures (namely, cubic and hexagonal diamond and their stacking hybrids) are thermodynamically stable. We show that by changing the angular bond width, it is possible to move from a glass-forming model to a readily crystallizing model. From the shape of the barrier we infer the role of surface tension in the formation of the crystalline clusters. Studying the trends of the nucleation barriers with the temperature and the patch width, we are able to identify an optimal value of the patch size that leads to easy nucleation. Finally, we find that the nucleation barrier is the same, within our numerical precision, for both diamond crystals and for their stacking forms.

Saika-Voivod, Ivan; Romano, Flavio; Sciortino, Francesco

2011-09-01

82

Assembly of tetrahedral gold nanoclusters from binary colloidal mixtures  

NASA Astrophysics Data System (ADS)

We experimentally investigate the structures that form when colloidal gold nanospheres cluster around smaller spheres. We use nanoparticles coated with complementary DNA sequences to assemble the clusters, and we observe them under electron microscopy. Previous experiments using polystyrene microspheres indicate that a 90% yield of tetrahedral clusters is possible near a critical diameter ratio; random sphere parking serves as a useful model for understanding this phenomenon. Here we examine how this approach can be scaled down by an order of magnitude in size, using gold building blocks. We study how this method can be used to assemble tetrahedral plasmonic resonators in order to create a bulk, isotropic, optical metamaterial.

Schade, Nicholas B.; ``Peter''sun, Dazhi; Holmes-Cerfon, Miranda C.; Chen, Elizabeth R.; Gehrels, Emily W.; Fan, Jonathan A.; Gang, Oleg; Manoharan, Vinothan N.

2013-03-01

83

ADAPTIVE PHYSICS BASED TETRAHEDRAL MESH GENERATION USING LEVEL SETS  

Microsoft Academic Search

We present a tetrahedral mesh generation algorithm designed for the Lagrangian simulation of deformable bodies. The algorithm's input is a level set (i.e., a signed distance function on a Cartesian grid or octree). First a bounding box of the object is covered with a uniform lattice of subdivision-invariant tetrahedra. The level set is then used to guide a red green

Robert Bridson; Joseph Teran; Neil Molino; Ronald Fedkiw

2004-01-01

84

Selective refinement queries for volume visualization of unstructured tetrahedral meshes.  

PubMed

In this paper, we address the problem of the efficient visualization of large irregular volume data sets by exploiting a multiresolution model based on tetrahedral meshes. Multiresolution models, also called Level-Of-Detail (LOD) models, allow encoding the whole data set at a virtually continuous range of different resolutions. We have identified a set of queries for extracting meshes at variable resolution from a multiresolution model, based on field values, domain location, or opacity of the transfer function. Such queries allow trading off between resolution and speed in visualization. We define a new compact data structure for encoding a multiresolution tetrahedral mesh built through edge collapses to support selective refinement efficiently and show that such a structure has a storage cost from 3 to 5.5 times lower than standard data structures used for tetrahedral meshes. The data structures and variable resolution queries have been implemented together with state-of-the art visualization techniques in a system for the interactive visualization of three-dimensional scalar fields defined on tetrahedral meshes. Experimental results show that selective refinement queries can support interactive visualization of large data sets. PMID:15382696

Cignoni, Paolo; De Floriani, Leila; Magillo, Paola; Puppo, Enrico; Scopigno, Roberto

2004-01-01

85

Tetrahedral Models of Learning: Application to College Reading.  

ERIC Educational Resources Information Center

J. D. Bransford's tetrahedral model of learning considers four variables: (1) learning activities, (2) characteristics of the learner, (3) criterial tasks, and (4) the nature of the materials. Bransford's model provides a research-based theoretical framework that can be used to teach, model, and have students apply a variety of study strategies to…

Nist, Sherrie L.

86

Maintaining tetrahedral mesh quality in response to time-dependent topological and geometrical deformation  

SciTech Connect

When modeling deformation of geometrically complex regions, unstructured tetrahedral meshes provide the flexibility necessary to track interfaces as they change geometrically and topologically. In the class of time-dependent simulations considered in this paper, multimaterial interfaces are represented by sets of triangular facets, and motion of the interfaces is controlled by physical considerations. The motion of interior points in the conforming tetrahedral mesh (i.e., points not on interfaces) is arbitrary and may be chosen to produce good element shapes. In the context of specified boundary motion driven by physical considerations, they have found that a rather large glossary of mesh changes is required to allow the simulation to survive all the transitions of interface geometry and topology that occur during time evolution. This paper will describe mesh changes required to maintain good element quality as the geometry evolves, as well as mesh changes required to capture changes i n topology that occur when material regions collapse or pinch off. This paper will present a detailed description of mesh changes necessary for capturing the aforementioned geometrical and topological changes, as implemented in the code GRAIN3D, and will provide examples from a metallic grain growth simulation in which the normal velocity of the grain boundary is proportional to mean curvature.

Kuprat, A.; George, D.

1998-12-01

87

Tableau-based protein substructure search using quadratic programming  

PubMed Central

Background Searching for proteins that contain similar substructures is an important task in structural biology. The exact solution of most formulations of this problem, including a recently published method based on tableaux, is too slow for practical use in scanning a large database. Results We developed an improved method for detecting substructural similarities in proteins using tableaux. Tableaux are compared efficiently by solving the quadratic program (QP) corresponding to the quadratic integer program (QIP) formulation of the extraction of maximally-similar tableaux. We compare the accuracy of the method in classifying protein folds with some existing techniques. Conclusion We find that including constraints based on the separation of secondary structure elements increases the accuracy of protein structure search using maximally-similar subtableau extraction, to a level where it has comparable or superior accuracy to existing techniques. We demonstrate that our implementation is able to search a structural database in a matter of hours on a standard PC.

Stivala, Alex; Wirth, Anthony; Stuckey, Peter J

2009-01-01

88

Tetrahedral homonuclear organoelement clusters and subhalides of aluminium, gallium and indium  

NASA Astrophysics Data System (ADS)

This review is focused on the synthesis and the reactivity of tetrahedral organoelement clusters of the heavier elements of third main-group aluminium, gallium, and indium, which have been known for about a decade. They possess the elements in an unusually low oxidation state of +1 and have direct element-element interactions between their four constituents. Each cluster atom is further attached to one terminal and in most cases a bulky organic substituent, which prevents disproportionation by steric shielding. The synthesis of these compounds succeeds by different methods such as the reduction of suitable organoelement(III) halides with alkali metals and magnesium or the treatment of element(I) halides with lithium organyls. They are deeply coloured, and their bonding situation may best be described by delocalized molecular orbitals. They show a singular chemical reactivity, which results in the formation of many secondary products possessing unprecedented structures and properties. The synthesis of organoelement subhalides still containing the elements in low oxidation states is discussed in more detail in the second part of this review. These compounds are easily accessible by the careful oxidation of the clusters with halogen donors such as hexachloroethane or with AlX3/X2 mixtures. They produce dimers via halogen bridges, but in certain cases monomers were observed even for the solid state. They are very effective starting compounds for secondary reactions and the generation of new products containing the elements in unusual oxidation states by salt-elimination reactions, for instance.

Uhl, Werner

89

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

90

Structural stiffness, strength and dynamic characteristics of large tetrahedral space truss structures  

NASA Technical Reports Server (NTRS)

Physical characteristics of large skeletal frameworks for space applications are investigated by analyzing one concept: the tetrahedral truss, which is idealized as a sandwich plate with isotropic faces. Appropriate analytical relations are presented in terms of the truss column element properties which for calculations were taken as slender graphite/epoxy tubes. Column loads, resulting from gravity gradient control and orbital transfer, are found to be small for the class structure investigated. Fundamental frequencies of large truss structures are shown to be an order of magnitude lower than large earth based structures. Permissible loads are shown to result in small lateral deflections of the truss due to low-strain at Euler buckling of the slender graphite/epoxy truss column elements. Lateral thermal deflections are found to be a fraction of the truss depth using graphite/epoxy columns.

Mikulas, M. M., Jr.; Bush, H. G.; Card, M. F.

1977-01-01

91

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

92

Ferromagnetism and electron pairing in tetrahedral Hubbard clusters  

NASA Astrophysics Data System (ADS)

The canonical and grand canonical calculations in exactly solvable three dimensional tetrahedrons elucidate the origin of Mott-Hubbard-like transition, electron pairing and ferromagnetism in frustrated Hubbard clusters. The thermal properties of planar and tetrahedral clusters in magnetic field with one hole off half-filling provide a rigorous proof for the existence of Mott-Hubbard type insulators with spontaneous magnetization in the ground state and finite temperatures. Rigorous conditions for electron pairing instability and phase separation in frustrated tetrahedral cluster for all U>0 is also provided. We show that Nagaoka-type spin flip instability with ``unsaturated ferromagnetism'' is equivalent to electron charge and spin pairing instabilities with minimal, zero spin. The theory gives strong evidence for existence of charge- spin separation in three dimensional clusters and calculated phase diagram for condensation crossover temperatures at various instabilities encompass a number of phases recently discovered in clusters, small nanoparticles, transition metal oxides and high Tc cuprates.

Kocharian, Armen; Fernando, Gayanath; Wang, Tun; Palandage, Kalum

2007-03-01

93

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

94

Mesh quality control for multiply-refined tetrahedral grids  

NASA Technical Reports Server (NTRS)

A new algorithm for controlling the quality of multiply-refined tetrahedral meshes is presented in this paper. The basic dynamic mesh adaption procedure allows localized grid refinement and coarsening to efficiently capture aerodynamic flow features in computational fluid dynamics problems; however, repeated application of the procedure may significantly deteriorate the quality of the mesh. Results presented show the effectiveness of this mesh quality algorithm and its potential in the area of helicopter aerodynamics and acoustics.

Biswas, Rupak; Strawn, Roger

1994-01-01

95

Ordered Self-Assembling of Tetrahedral Oxide Nanocrystals  

Microsoft Academic Search

Self-assembling of size, shape, and phase controlled nanocrystals into superlattices with translational and even orientational ordering is a new approach for engineering nanocrystal materials and devices. High purity tetrahedral nanocrystals of CoO, with edge lengths of 4.4 6 0.2 nm, were synthesized and separated from Co nanocrystals, using a novel magnetic field phase-selection technique. Self- assembling of the faceted CoO

J. S. Yin; Z. L. Wang

1997-01-01

96

Time-domain simulation of power electronics circuits using state variable quadratic extrapolations  

Microsoft Academic Search

A new stepwise time-domain analysis technique for power electronics circuits is presented. At each simulation step the rate of change of each state variable is determined by the corresponding reactive element parasitic resistance and state value obtained after performing a modified nodal analysis (MNA). A quadratic state trajectory description for each reactive element is formulated. To ensure the correct topological

B. K. H. Wong; H. Chung

1999-01-01

97

Tetrahedral gray code for visualization of genome information.  

PubMed

We propose a tetrahedral Gray code that facilitates visualization of genome information on the surfaces of a tetrahedron, where the relative abundance of each [Formula: see text]-mer in the genomic sequence is represented by a color of the corresponding cell of a triangular lattice. For biological significance, the code is designed such that the [Formula: see text]-mers corresponding to any adjacent pair of cells differ from each other by only one nucleotide. We present a simple procedure to draw such a pattern on the development surfaces of a tetrahedron. The thus constructed tetrahedral Gray code can demonstrate evolutionary conservation and variation of the genome information of many organisms at a glance. We also apply the tetrahedral Gray code to the honey bee (Apis mellifera) genome to analyze its methylation structure. The results indicate that the honey bee genome exhibits CpG overrepresentation in spite of its methylation ability and that two conserved motifs, CTCGAG and CGCGCG, in the unmethylated regions are responsible for the overrepresentation of CpG. PMID:24475080

Ichinose, Natsuhiro; Yada, Tetsushi; Gotoh, Osamu

2014-01-01

98

Phase diagram of the asymmetric tetrahedral Ising Heisenberg chain  

NASA Astrophysics Data System (ADS)

The asymmetric tetrahedron is composed of all edges of a tetrahedron represented by Ising interactions except for one, which has a Heisenberg-type interaction. This asymmetric tetrahedron is arranged by connecting a vertex whose edges are only Ising-type interactions to another vertex with the same structure for another tetrahedron. The process is replicated and this kind of lattice we call the asymmetric Ising-Heisenberg chain. We have studied the ground-state phase diagram for this kind of model. In particular, we consider two situations in the Heisenberg-type interaction: (i) the asymmetric tetrahedral spin-(1/2, 1/2) Ising-XYZ chain and (ii) the asymmetric tetrahedral spin-(1/2, 1) Ising-XXZ chain, where we have found a rich phase diagram and a number of multicritical points. Additionally we have also studied their thermodynamical properties and the correlation function, using the decorated transformation. We have mapped the asymmetric tetrahedral Ising-Heisenberg chain in an effective Ising chain, and we have also concluded that it is possible to evaluate the partition function including a longitudinal external magnetic field.

Valverde, J. S.; Rojas, Onofre; de Souza, S. M.

2008-08-01

99

Tetrahedral Gray Code for Visualization of Genome Information  

PubMed Central

We propose a tetrahedral Gray code that facilitates visualization of genome information on the surfaces of a tetrahedron, where the relative abundance of each -mer in the genomic sequence is represented by a color of the corresponding cell of a triangular lattice. For biological significance, the code is designed such that the -mers corresponding to any adjacent pair of cells differ from each other by only one nucleotide. We present a simple procedure to draw such a pattern on the development surfaces of a tetrahedron. The thus constructed tetrahedral Gray code can demonstrate evolutionary conservation and variation of the genome information of many organisms at a glance. We also apply the tetrahedral Gray code to the honey bee (Apis mellifera) genome to analyze its methylation structure. The results indicate that the honey bee genome exhibits CpG overrepresentation in spite of its methylation ability and that two conserved motifs, CTCGAG and CGCGCG, in the unmethylated regions are responsible for the overrepresentation of CpG.

Ichinose, Natsuhiro; Yada, Tetsushi; Gotoh, Osamu

2014-01-01

100

Interactive point-based rendering of higher-order tetrahedral data.  

PubMed

Computational simulations frequently generate solutions defined over very large tetrahedral volume meshes containing many millions of elements. Furthermore, such solutions may often be expressed using non-linear basis functions. Certain solution techniques, such as discontinuous Galerkin methods, may even produce non-conforming meshes. Such data is difficult to visualize interactively, as it is far too large to fit in memory and many common data reduction techniques, such as mesh simplification, cannot be applied to non-conforming meshes. We introduce a point-based visualization system for interactive rendering of large, potentially non-conforming, tetrahedral meshes. We propose methods for adaptively sampling points from non-linear solution data and for decimating points at run time to fit GPU memory limits. Because these are streaming processes, memory consumption is independent of the input size. We also present an order-independent point rendering method that can efficiently render volumes on the order of 20 million tetrahedra at interactive rates. PMID:17080856

Zhou, Yuan; Garland, Michael

2006-01-01

101

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

102

Quadratic Functionals with General Boundary Conditions  

SciTech Connect

The purpose of this paper is to give the Reid 'Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in terms of Riccati equation solutions.

Dosla, Z.; Dosly, O. [Department of Mathematics, Masaryk University, Janackovo nam. 2a, 66295 Brno (Czech Republic)

1997-11-15

103

Quadratic mutual information for dimensionality reduction and classification  

NASA Astrophysics Data System (ADS)

A research area based on the application of information theory to machine learning has attracted considerable interest in the last few years. This research area has been coined information-theoretic learning within the community. In this paper we apply elements of information-theoretic learning to the problem of automatic target recognition (ATR). A number of researchers have previously shown the benefits of designing classifiers based on maximizing the mutual information between the class data and the class labels. Following prior research in information-theoretic learning, in the current results we show that quadratic mutual information, derived using a special case of the more general Renyi's entropy, can be used for classifier design. In this implementation, a simple subspace projection classifier is formulated to find the optimal projection weights such that the quadratic mutual information between the class data and the class labels is maximized. This subspace projection accomplishes a dimensionality reduction of the raw data set wherein information about the class membership is retained while irrelevant information is discarded. A subspace projection based on this criterion preserves as much class discriminability as possible within the subspace. For this paper, laser radar images are used to demonstrate the results. Classification performance against this data set is compared for a gradient descent MLP classifier and a quadratic mutual information MLP classifier.

Gray, David M.; Principe, José C.

2010-04-01

104

Self-assembly of a tetrahedral 58-nuclear barium vanadium oxide cluster.  

PubMed

We report the synthesis and characterization of a molecular barium vanadium oxide cluster featuring high nuclearity and high symmetry. The tetrameric, 2.3 nm cluster H(5)[Ba(10)(NMP)(14)(H(2)O)(8)[V(12)O(33)](4)Br] is based on a bromide-centred, octahedral barium scaffold which is capped by four previously unknown [V(12)O(33)](6-) clusters in a tetrahedral fashion. The compound represents the largest polyoxovanadate-based heterometallic cluster known to date. The cluster is formed in organic solution and it is suggested that the bulky N-methyl-2-pyrrolidone (NMP) solvent ligands allow the isolation of this giant molecule and prevent further condensation to a solid-state metal oxide. The cluster is fully characterized using single-crystal XRD, elemental analysis, ESI mass spectrometry and other spectroscopic techniques. PMID:23168572

Kastner, Katharina; Puscher, Bianka; Streb, Carsten

2013-01-01

105

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

106

uv Studies of Tetrahedral Bonding in Diamondlike Amorphous Carbon  

SciTech Connect

We report ultraviolet (uv) Raman scattering studies of hydrogen-free, diamondlike amorphous carbon thin films with a wide range of tetrahedral bonding. The uv Raman spectra are shown to provide direct evidence for the presence of sp{sup 3}-bonded C atoms in these materials. The experimental results are found to be in excellent agreement with theoretical predictions and contribute to an improved understanding of the mechanism by which the diamondlike fraction develops within the amorphous carbon network. {copyright} {ital 1997} {ital The American Physical Society}

Merkulov, V.I.; Lannin, J.S. [Department of Physics, Penn State University, University Park, Pennsylvania 16802 (United States)] [Department of Physics, Penn State University, University Park, Pennsylvania 16802 (United States); Munro, C.H.; Asher, S.A. [Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Veerasamy, V.S.; Milne, W.I. [Engineering Department, University of Cambridge, Cambridge CB2 1PZ (United Kingdom)] [Engineering Department, University of Cambridge, Cambridge CB2 1PZ (United Kingdom)

1997-06-01

107

Practical implementation of tetrahedral mesh reconstruction in emission tomography  

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

108

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

2007-11-01

109

Platelet adhesion on phosphorus-incorporated tetrahedral amorphous carbon films  

NASA Astrophysics Data System (ADS)

The haemocompatibility of phosphorus-incorporated tetrahedral amorphous carbon (ta-C:P) films, synthesized by filtered cathodic vacuum arc technique with PH 3 as the dopant source, was assessed by in vitro platelet adhesion tests. Results based on scanning electron microscopy and contact angle measurements reveal that phosphorus incorporation improves the wettability and blood compatibility of ta-C film. Our studies may provide a novel approach for the design and synthesis of doped ta-C films to repel platelet adhesion and reduce thrombosis risk.

Liu, Aiping; Zhu, Jiaqi; Liu, Meng; Dai, Zhifei; Han, Xiao; Han, Jiecai

2008-11-01

110

An aluminophosphate molecular sieve with 36 crystallographically distinct tetrahedral sites.  

PubMed

The structure of the new medium-pore aluminophosphate molecular sieve PST-6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X-ray powder diffraction, and computer modeling. PST-6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure-directing agent, which is thought to contain bridging hydroxy groups. PST-6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved. PMID:24862164

Lee, Jun Kyu; Turrina, Alessandro; Zhu, Liangkui; Seo, Seungwan; Zhang, Daliang; Cox, Paul A; Wright, Paul A; Qiu, Shilun; Hong, Suk Bong

2014-07-14

111

Nonlinear dynamics of quadratically cubic systems  

NASA Astrophysics Data System (ADS)

We propose a modified form of the well-known nonlinear dynamic equations with quadratic relations used to model a cubic nonlinearity. We show that such quadratically cubic equations sometimes allow exact solutions and sometimes make the original problem easier to analyze qualitatively. Occasionally, exact solutions provide a useful tool for studying new phenomena. Examples considered include nonlinear ordinary differential equations and Hopf, Burgers, Korteweg-de Vries, and nonlinear Schrödinger partial differential equations. Some problems are solved exactly in the space-time and spectral representations. Unsolved problems potentially solvable by the proposed approach are listed.

Rudenko, O. V.

2013-07-01

112

Indirect quantum tomography of quadratic Hamiltonians  

NASA Astrophysics Data System (ADS)

A number of many-body problems can be formulated using Hamiltonians that are quadratic in the creation and annihilation operators. Here, we show how such quadratic Hamiltonians can be efficiently estimated indirectly, employing very few resources. We found that almost all the properties of the Hamiltonian are determined by its surface and that these properties can be measured even if the system can only be initialized to a mixed state. Therefore, our method can be applied to various physical models, with important examples including coupled nano-mechanical oscillators, hopping fermions in optical lattices and transverse Ising chains.

Burgarth, Daniel; Maruyama, Koji; Nori, Franco

2011-01-01

113

A general-oriented simulation technique for power electronic systems using quadratic branch voltage extrapolation  

Microsoft Academic Search

A new general oriented time-domain simulation technique for power electronic systems is developed. The algorithm is based on stepwise quadratic extrapolations on the branch voltages across each reactive element, together with progressive validation of the switches' operation. The power of this new technique lies in its simplicity in solving purely resistive networks for each topological configuration, generality in requiring no

Billy K. H. Wong; Henry Shu-hung Chung

1997-01-01

114

Synthesis and characterization of tetrahedral and square planar Bis(iminopyrrolyl) complexes of cobalt(II).  

PubMed

A series of 2-iminopyrrole ligand precursors with increasing bulkiness [HNC4H3C(R)=N-2,6-R'2C6H3] (R = R' = H, 1a; R = Me, R'= H, 1b; R = H, R' = Me, 1c; R = R' = Me, 1d; R = H, R' = iPr, 1e; R = Me, R' = iPr, 1f) were synthesized and deprotonated with NaH to give the corresponding iminopyrrolyl sodium salts 2a-f. A set of homoleptic bis-ligand Co(II) complexes of the type [Co(kappa2N,N'-NC4H3C(R)=N-2,6-R'2C6H3)2] (R = R'= H, 3a; R = Me, R'= H, 3b; R = H, R' = Me, 3c; R = R' = Me, 3d; R = H, R' = iPr, 3e; R = Me, R' = iPr, 3f) was prepared by reaction of CoCl2 with the corresponding iminopyrrolyl sodium salts 2a-f. The new complexes were characterized by elemental analysis, magnetic susceptibility measurements, in powder and in solution, UV/vis/NIR, and, in some cases, X-ray crystallography. According to X-ray diffraction and magnetic measurements, the Co complexes 3a-e proved to be tetrahedral, which is the preferred geometry for Co(II) compounds. However, a square planar geometry is observed in the case of 3f, as determined by several characterization techniques. In this case, DFT calculations suggest the square planar geometry is slightly more stable than the tetrahedral one probably due to a combination of steric and electronic reasons. PMID:17658870

Carabineiro, Sónia A; Silva, Leonel C; Gomes, Pedro T; Pereira, Laura C J; Veiros, Luís F; Pascu, Sofia I; Duarte, M Teresa; Namorado, Sónia; Henriques, Rui T

2007-08-20

115

Grid-characteristic method on unstructured tetrahedral meshes  

NASA Astrophysics Data System (ADS)

The goal of this paper is to develop a grid-characteristic method intended for high-performance computer systems and implemented on unstructured tetrahedral hierarchical meshes with the use of a multiple time step and high-order interpolation, including interpolation with a limiter, piecewise parabolic interpolation, and monotone interpolation. The method is designed for simulating complex three-dimensional dynamical processes in heterogeneous media. It involves accurately stated contact conditions and produces physically correct solutions of problems in seismology and seismic exploration. Hierarchical meshes make it possible to take into account numerous inhomogeneous inclusions (cracks, cavities, etc.) and to solve problems in a real-life formulation. The grid-characteristic method enables the use of a multiple time step. As a result, the computation time is considerably reduced and the efficiency of the method is raised. The method is parallelized on a computer cluster with an optimal use of system resources.

Muratov, M. V.; Petrov, I. B.; Sannikov, I. V.; Favorskaya, A. V.

2014-05-01

116

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

117

Multiplicative Updates for Nonnegative Quadratic Programming  

Microsoft Academic Search

Many problems in neural computation and statistical learning involve optimizations with nonnegativity constraints. In this paper, we study convex problems in quadratic program- ming where the optimization is confined to an axis-aligned region in the nonnegative orthant. For these problems, we derive multiplicative updates that improve the value of the objective function at each iteration and converge monotonically to the

Fei Sha; Yuanqing Lin; Lawrence K. Saul; Daniel D. Lee

2007-01-01

118

Transfer function with quadratic detection - Coherent illumination  

NASA Astrophysics Data System (ADS)

The visibility of the interference terms over the image irradiance of a complex amplitude object immersed in a uniform background is described by an interference transfer function (ITF). It is shown that the ITF is the linear transfer function for coherent optical systems with quadratic detection when the test object either has low contrast or is periodic.

Ojeda-Castaneda, J.; Jara, E.

1980-04-01

119

Curious Consequences of a Miscopied Quadratic  

ERIC Educational Resources Information Center

The starting point of this article is a search for pairs of quadratic polynomials x[superscript 2] + bx plus or minus c with the property that they both factor over the integers. The search leads quickly to some number theory in the form of primitive Pythagorean triples, and this paper develops the connection between these two topics.

Poet, Jeffrey L.; Vestal, Donald L., Jr.

2005-01-01

120

Mating Non-Renormalizable Quadratic Polynomials  

NASA Astrophysics Data System (ADS)

In this paper we prove the existence and uniqueness of matings of the basilica with any quadratic polynomial which lies outside of the 1/2-limb of {mathcal {M}} , is non- renormalizable, and does not have any non-repelling periodic orbits.

Aspenberg, Magnus; Yampolsky, Michael

2009-04-01

121

Linear quadratic optimal learning control (LQL)  

Microsoft Academic Search

A learning control solution to the problem of finding a finite-time optimal control history that minimizes a quadratic cost is presented. Learning achieves optimization without requiring detailed knowledge of the system, which may be affected by unknown but repetitive disturbances. The optimal solution is synthesized one basis function at a time, reaching optimality in a finite number of trials. These

James A. Frueh; Minh Q. Phan

1998-01-01

122

Mammogram enhancement using alpha weighted quadratic filter  

Microsoft Academic Search

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

Yicong Zhou; Karen Panetta; Sos Agaian

2009-01-01

123

Quadratic Gabor filters for object detection  

Microsoft Academic Search

We present a new class of quadratic filters that are capable of creating spherical, elliptical, hyperbolic and linear decision surfaces which result in better detection and classification capabilities than the linear decision surfaces obtained from correlation filters. Each filter comprises of a number of separately designed linear basis filters. These filters are linearly combined into several macro filters; the output

David M. Weber; David P. Casasent

2001-01-01

124

Probabilistic robust design with linear quadratic regulators  

Microsoft Academic Search

In this paper, we study robust design of uncertain systems in a probabilistic setting by means of linear quadratic regulators. We consider systems affected by random bounded nonlinear uncertainty so that classical optimization methods based on linear matrix inequalities cannot be used without conservatism. The approach followed here is a blend of randomization techniques for the uncertainty together with convex

B. T. Polyak; R. Tempo

2000-01-01

125

Probabilistic robust design with linear quadratic regulators  

Microsoft Academic Search

In this paper, we study robust design of uncertain systems in a probabilistic setting by means of linear quadratic regulators (LQR). We consider systems affected by random bounded nonlinear uncertainty so that classical optimization methods based on linear matrix inequalities cannot be used without conservatism. The approach followed here is a blend of randomization techniques for the uncertainty together with

B. T. Polyak; R. Tempo

2001-01-01

126

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

127

Image enhancement based on quadratic programming  

Microsoft Academic Search

In this paper, a simple but efficient image enhancement algorithm is proposed. We model the image enhancement problem as a quadratic programming problem, and the cost function of the optimization problem is formulated based on local gradients of an image. By adjusting the definitions of gain function and weighting function in the cost function, we can derive various kinds of

Tzu-cheng Jen; Sheng-jyh Wang

2008-01-01

128

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

129

Approximation of the Quadratic Set Covering problem  

Microsoft Academic Search

We study in this article the polynomial approximation properties of the Quadratic Set Covering problem. This problem, which arises in many applications, is a natural generalization of the usual Set Covering problem. We show that this problem is very hard to approximate in the general case, and even in classical subcases (when the size of each set or when the

Bruno Escoffier; Peter L. Hammer

2007-01-01

130

Convex half-quadratic criteria and interacting auxiliary variables for image restoration.  

PubMed

This paper deals with convex half-quadratic criteria and associated minimization algorithms for the purpose of image restoration. It brings a number of original elements within a unified mathematical presentation based on convex duality. Firstly, the Geman and Yang's and Geman and Reynolds's constructions are revisited, with a view to establishing the convexity properties of the resulting half-quadratic augmented criteria, when the original nonquadratic criterion is already convex. Secondly, a family of convex Gibbsian energies that incorporate interacting auxiliary variables is revealed as a potentially fruitful extension of the Geman and Reynolds's construction. PMID:18249673

Idier, J

2001-01-01

131

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

132

Linear State Feedback, Quadratic Weights, and Closed Loop Eigenstructures.  

National Technical Information Service (NTIS)

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 multiva...

P. M. Thompson

1979-01-01

133

High order Godunov mixed methods on tetrahedral meshes for density driven flow simulations in porous media  

NASA Astrophysics Data System (ADS)

Two-dimensional Godunov mixed methods have been shown to be effective for the numerical solution of density-dependent flow and transport problems in groundwater even when concentration gradients are high and the process is dominated by density effects. This class of discretization approaches solves the flow equation by means of the mixed finite element method, thus guaranteeing mass conserving velocity fields, and discretizes the transport equation by mixed finite element and finite volumes techniques combined together via appropriate time splitting. In this paper, we extend this approach to three dimensions employing tetrahedral meshes and introduce a spatially variable time stepping procedure that improves computational efficiency while preserving accuracy by adapting the time step size according to the local Courant-Friedrichs-Lewy (CFL) constraint. Careful attention is devoted to the choice of a truly three-dimensional limiter for the advection equation in the time-splitting technique, so that to preserve second order accuracy in space (in the sense that linear functions are exactly interpolated). The three-dimensional Elder problem and the saltpool problem, recently introduced as a new benchmark for testing three-dimensional density models, provide assessments with respect to accuracy and reliability of this numerical approach.

Mazzia, Annamaria; Putti, Mario

2005-09-01

134

Quadratic divergences and quantum gravitational contributions to gauge coupling constants  

Microsoft Academic Search

The calculation of quadratic divergences in Einstein-Maxwell theory with a possible cosmological constant is considered. We describe a method of calculation, using the background-field method, that is sensitive to quadratic divergences, is respectful of gauge invariance, and is independent of gauge conditions. A standard renormalization group analysis is applied to the result where it is shown that the quadratic divergences

David J. Toms

2011-01-01

135

Quadratic Spline Models for Producer's Supply and Demand Functions  

Microsoft Academic Search

In this paper, the authors propose and estimate a system of producer output supply and input demand functions that generalizes the standard normalized quadratic form. The generalization adds either linear or quadratic splines in a time (or technical change) variable, yet retains the main attractive property of the normalized quadratic, which is that it can provide a local second order

W. E. Diewert; T. J. Wales

1992-01-01

136

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

137

Quadratic harmonic morphisms and O-systems  

Microsoft Academic Search

We introduce O-systems (Definition \\\\ref{DO}) of orthogonal transformations of ${\\\\Bbb R}^{m}$, and establish $1-1$ correspondences both between equivalence classes of Clifford systems and that of O-systems, and between O-systems and orthogonal multiplications of the form $\\\\mu :{\\\\Bbb R}^{n} \\\\times {\\\\Bbb R}^{m} \\\\longrightarrow {\\\\Bbb R}^{m} $, which allow us to solve the existence problems both for O-systems and for umbilical quadratic

Ye-lin Ou

1995-01-01

138

Quadratic stability and singular SISO switching systems  

Microsoft Academic Search

In this note we consider the problem of determining necessary and su-cient condi- tions for the existence of a common quadratic Lyapunov function for a pair of stable linear time-invariant systems whose system matrices are of the form A, A ¡ ghT, and where one of the matrices is singular. A necessary and su-cient condition for the existence of such

R. Shorten; M. Corless; S. Klinge; R. Middleton

2008-01-01

139

Quadratic Stability and Singular SISO Switching Systems  

Microsoft Academic Search

In this note, we consider the problem of determining necessary and sufficient conditions for the existence of a common quadratic Lyapunov function for a pair of stable linear time-invariant systems whose system matrices are of the form A, A-ghT, and where one of the matrices is singular. A necessary and sufficient condition for the existence of such a function is

Robert Shorten; Martin Corless; Kai Wulff; Steffi Klinge; Richard Middleton

2009-01-01

140

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

141

Monotone and convex quadratic spline interpolation  

NASA Technical Reports Server (NTRS)

A method for producing interpolants that preserve the monotonicity and convexity of discrete data is described. It utilizes the quadratic spline proposed by Schumaker (1983) which was subsequently characterized by De Vore and Yan (1986). The selection of first order derivatives at the given data points is essential to this spline. An observation made by De Vore and Yan is generalized, and an improved method to select these derivatives is proposed. The resulting spline is completely local, efficient, and simple to implement.

Lam, Maria H.

1990-01-01

142

Stochastic Linear Quadratic Optimal Control Problems  

SciTech Connect

This paper is concerned with the stochastic linear quadratic optimal control problem (LQ problem, for short) for which the coefficients are allowed to be random and the cost functional is allowed to have a negative weight on the square of the control variable. Some intrinsic relations among the LQ problem, the stochastic maximum principle, and the (linear) forward-backward stochastic differential equations are established. Some results involving Riccati equation are discussed as well.

Chen, S. [Department of Mathematics, Zhejiang University, Hangzhou 310027 (China); Yong, J. [Laboratory of Mathematics for Nonlinear Sciences, Department of Mathematics, and Institute of Mathematical Finance, Fudan University, Shanghai 200433 (China)

2001-07-01

143

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

144

Constrained quadratic correlation filters for target detection.  

PubMed

A method for designing and implementing quadratic correlation filters (QCFs) for shift-invariant target detection in imagery is presented. The QCFs are quadratic classifiers that operate directly on the image data without feature extraction or segmentation. In this sense the QCFs retain the main advantages of conventional linear correlation filters while offering significant improvements in other respects. Not only is more processing required for detection of peaks in the outputs of multiple linear filters but choosing the most suitable among them is an error-prone task. All channels in a QCF work together to optimize the same performance metric and to produce a combined output that leads to considerable simplification of the postprocessing scheme. The QCFs that are developed involve hard constraints on the output of the filter. Inasmuch as this design methodology is indicative of the synthetic discriminant function (SDF) approach for linear filters, the filters that we develop here are referred to as quadratic SDFs (QSDFs). Two methods for designing QSDFs are presented, an efficient architecture for achieving them is discussed, and results from the Moving and Stationary Target Acquisition and Recognition synthetic aperture radar data set are presented. PMID:14735950

Muise, Robert; Mahalanobis, Abhijit; Mohapatra, Ram; Li, Xin; Han, Deguang; Mikhael, Wasfy

2004-01-10

145

Constrained quadratic correlation filters for target detection  

NASA Astrophysics Data System (ADS)

A method for designing and implementing quadratic correlation filters (QCFs) for shift-invariant target detection in imagery is presented. The QCFs are quadratic classifiers that operate directly on the image data without feature extraction or segmentation. In this sense the QCFs retain the main advantages of conventional linear correlation filters while offering significant improvements in other respects. Not only is more processing required for detection of peaks in the outputs of multiple linear filters but choosing the most suitable among them is an error-prone task. All channels in a QCF work together to optimize the same performance metric and to produce a combined output that leads to considerable simplification of the postprocessing scheme. The QCFs that are developed involve hard constraints on the output of the filter. Inasmuch as this design methodology is indicative of the synthetic discriminant function (SDF) approach for linear filters, the filters that we develop here are referred to as quadratic SDFs (QSDFs). Two methods for designing QSDFs are presented, an efficient architecture for achieving them is discussed, and results from the Moving and Stationary Target Acquisition and Recognition synthetic aperture radar data set are presented.

Muise, Robert; Mahalanobis, Abhijit; Mohapatra, Ram; Li, Xin; Han, Deguang; Mikhael, Wasfy

2004-01-01

146

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

147

Theoretical Studies of Routes to Synthesis of Tetrahedral N4  

NASA Technical Reports Server (NTRS)

A paper [Chem. Phys. Lett. 345, 295 (2001)] describes theoretical studies of excited electronic states of nitrogen molecules, with a view toward utilizing those states in synthesizing tetrahedral N4, or Td N4 a metastable substance under consideration as a high-energy-density rocket fuel. Several ab initio theoretical approaches were followed in these studies, including complete active space self-consistent field (CASSCF), state-averaged CASSCF (SA-CASSCF), singles configuration interaction (CIS), CIS with second-order and third-order correlation corrections [CIS(D) and CIS(3)], and linear response singles and doubles coupled-cluster (LRCCSD). Standard double zeta polarized and triple zeta double polarized one-particle basis sets were used. The CASSCF calculations overestimated the excitation energies, while SACASSCF calculations partly corrected these overestimates. The accuracy of the CIS calculations varied, depending on the particular state, while the CIS(D), CIS(3), and LRCCSD results were in generally good agreement. The energies of the lowest six excited singlet states of Td N4 as calculated by the LRCCSD were compared with the energies of possible excited states of N2 + N2 fragments, leading to the conclusion that the most likely route for synthesis of Td N4 would involve a combination of two bound quintet states of N2.

Lee, Timothy J.; Dateo, Christopher E.

2007-01-01

148

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

149

Natural frequency of uniform and optimized tetrahedral truss platforms  

NASA Technical Reports Server (NTRS)

Qualitative and quantitative estimates for the fundamental frequency of uniform and optimized tetrahedral truss platforms are determined. A semiempirical equation is developed for the frequency of free-free uniform trusses as a function of member material properties, truss dimensions, and parasitic (nonstructural) mass fraction Mp/Mt. Optimized trusses with frequencies approximately two times those of uniform trusses are determined by varying the cross-sectional areas of member groups. Trusses with 3 to 8 rings, no parasitic mass, and member areas up to 25 times the minimum area are optimized. Frequencies computed for ranges of both Mp/Mt and the ratio of maximum area to minimum area are normalized to the frequency of a uniform truss with no parasitic mass. The normalized frequency increases with the number of rings, and both frequency and the ratio of maximum area to minimum area decrease with increasing Mp/Mt. Frequency improvements that are achievable with a limited number of member areas are estimated for a 3-ring truss by using Taguchi methods. Joint stiffness knockdown effects are also considered. Comparison of optimized and baseline uniform truss frequencies indicates that tailoring can significantly increase structural frequency; maximum gains occur for trusses with low values of Mp/Mt. This study examines frequency trends for ranges of structural parameters and may be used as a preliminary design guide.

Wu, K. Chauncey; Lake, Mark S.

1994-01-01

150

Interpenetrating metal-organic frameworks formed by self-assembly of tetrahedral and octahedral building blocks  

SciTech Connect

To investigate the relationship between topological types and molecular building blocks (MBBs), we have designed and synthesized a series of three-dimensional (3D) interpenetrating metal-organic frameworks based on different polygons or polyhedra under hydrothermal conditions, namely [Cd(bpib){sub 0.5}(L{sup 1})] (1), [Cd(bpib){sub 0.5}(L{sup 2})].H{sub 2}O (2), [Cd(bpib){sub 0.5}(L{sup 3})] (3) and [Cd(bib){sub 0.5}(L{sup 1})] (4), where bpib=1,4-bis(2-(pyridin-2-yl)-1H-imidazol-1-yl)butane, bib=1,4-bis(1H-imidazol-1-yl)butane, H{sub 2}L{sup 1}=4-(4-carboxybenzyloxy)benzoic acid, H{sub 2}L{sup 2}=4,4'-(ethane-1,2-diylbis(oxy))dibenzoic acid and H{sub 2}L{sup 3}=4,4'-(1,4-phenylenebis(methylene))bis(oxy)dibenzoic acid, respectively. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. Compounds 1-3 display alpha-Po topological nets with different degrees of interpenetration based on the similar octahedral [Cd{sub 2}(-COO){sub 4}] building blocks. Compound 4 is a six-fold interpenetrating diamondoid net based on tetrahedral MBBs. By careful inspection of these structures, we find that various carboxylic ligands and N-donor ligands with different coordination modes and conformations, and metal centers with different geometries are important for the formation of the different MBBs. It is believed that different topological types lie on different MBBs with various polygons or polyhedra. Such as four- and six-connected topologies are formed by tetrahedral and octahedral building blocks. In addition, with the increase of carboxylic ligands' length, the degrees of interpenetration have been changed in the alpha-Po topological nets. And the luminescent properties of these compounds have been investigated in detail. - Graphical abstract: A series of three-dimensional interpenetrating metal-organic frameworks based on different polygons or polyhedra has been synthesized. The crystal structures and topological analysis of these compounds, along with a systematic investigation of the relationship between topological types and molecular building blocks, will be discussed.

Lu Yongming; Lan Yaqian; Xu Yanhong [Institute of Functional Material Chemistry, Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024 (China); Su Zhongmin, E-mail: zmsu@nenu.edu.c [Institute of Functional Material Chemistry, Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024 (China); Li Shunli, E-mail: lishunli@yahoo.c [Institute of Functional Material Chemistry, Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024 (China); Zang Hongying; Xu Guangjuan [Institute of Functional Material Chemistry, Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024 (China)

2009-11-15

151

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

152

Linear quadratic stationkeeping on travelling ellipses  

NASA Technical Reports Server (NTRS)

An automatic controller for Space Shuttle stationkeeping or formationkeeping is presented. The controller, which is a candidate for future on-orbit autopilot enhancement, uses a fuel 'optimized' limit cycle trajectory in a feedforward loop for precise control at nonequilibrium set points. Disturbance rejection is accomplished by a discrete time, linear quadratic regulator, which is employed for tracking of the feedforward model. Feedback gain selection is done to provide good limit cycling performance and low fuel consumption. Velocity correlations are carried out by use of a pseudo 6 degree-of-freedom jet selection scheme. Results indicate that 20 ft precision can be achieved using current sensors.

Adams, Neil J.; Redding, David C.; Cox, Kenneth J.

1987-01-01

153

Double exchange in tetrameric tetrahedral clusters with two-electron transfer: magnetic properties  

Microsoft Academic Search

A theoretical model is worked out to study the magnetic properties of mixed-valence tetrameric tetrahedral clusters dn-dn-dn+1-dn+1 (n = 0–4) with two-electron transfer. To calculate the energy levels of systems a computational procedure based on the second quantization technique and group theory approach is used. The exchange-tunnel states of dn-dn-dn+1-dn+1 (n = 0–4) tetrahedral tetrameric clusters with two-electron transfer are

V. P. Coropceanu; F. G. Paladi; S. I. Boldyrev; V. J. Gamurar

1997-01-01

154

Binding of tetrahedral halocomplexes of polyvalent metal ions in an ionic model  

Microsoft Academic Search

Summary  Long-lived tetrahedral coordination of polyvalent metal ions by halogen ions is known to be stable in a number of liquid halide\\u000a mixtures. We evaluate the binding of isolated tetrahedral halocomplexes for the alkaline earth metals and for Al, with the\\u000a main aim of assessing their stability and their bond length. An appropriate interionic force model is available for the halides

Wang Li; M. P. Tosi

1988-01-01

155

On the classification of quadratic harmonic morphisms between Euclidean spaces  

Microsoft Academic Search

We give a classification of quadratic harmonic morphisms between Euclidean spaces (Theorem 2.4) after proving a Rank Lemma. We also find a correspondence between umbilical (Definition 2.7) quadratic harmonic morphisms and Clifford systems. In the case $ {\\\\Bbb R}^{4}\\\\longrightarrow {\\\\Bbb R}^{3} $, we determine all quadratic harmonic morphisms and show that, up to a constant factor, they are all bi-equivalent

Ye-lin Ou; J. C. Wood

1995-01-01

156

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

157

Steller Structure Treatment of Quadratic Gravity  

NASA Astrophysics Data System (ADS)

A scheme for considering stellar structure by taking advantage of the quadratic theory of gravitation in four-dimensions is proposed, citing the fact that the possible deviation of gravity in astrophysical systems from the Newtonian inverse square law can be explained through the use of this theory. A modified Lane-Emden equation is derived by making use of the linearized static field equation of quadratic gravity and the polytropic equation of state for a fluid. The influence on stellar structure of the additional force included in quadratic gravity is investigated. It is shown that the additional force can be treated as a perturbation of a bound system by solutions of the modified Lane-Emden equation and an order-of-magnitude analysis. %ZY. Fujii, Nature (London) 234 (1971), 5; Phys. Rev. D9 (1974), 874. D. R. Long, Phys. Rev. D 9 (1974), 850. J. O'Hanlon, Phys. Rev. Lett. 29 (1972), 137. D. R. Mikkelson and M. J. Newman, Phys. Rev. D 16 (1977), 919. R. V. Wagoner, Phys. Rev. D 1 (1970), 3209. J. Z. Xu and Y. H. Chen, Gen. Relat. Gravit. J. 23 (1991), 169. K. S. Stelle, Gen. Relat. Gravit. J. 8 (1978), 631. C. Xu and G. F. R. Ellis, Class. Quant. Grav. 8 (1991), 1747. A. Eddington, The Mathematical Theory of Relativity, 2nd ed. (Cambridge University Press, Cambridge, 1924). W. Pauli, Theory of Relativity (Pergamon Press, New York, 1921). H. A. Buchdahl, Proc. Edinburgh Math. Soc. 8 (1948), 89. J. D. Barrow and A. C. Ottewill, J. of Phys. A 16 (1983), 2757. M. B. Mijic, M. S. Morris and W. M. Suen, Phys. Rev. D 34 (1986), 2934. A. L. Berkin, Phys. Rev. D 42 (1990), 1017. N. D. Birrell and P. C. W. Davies, Quantum Field in Curved Space (Cambridge University Press, 1982). E. T. Tomboulis, Quantum Theory of Gravity, ed. S. M. Christensen (Bristol: Adam Hilger 1984). H. J. Treder, Ann. der Phys. 32 (1975), 383. S. Weinberg, Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity (Wiley, New York 1972). E. N. Glass and G. Szamosi, Phys. Rev. D 35 (1987), 1205.

Chen, Y.; Shao, C.; Chen, X.

2001-07-01

158

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

159

Photon blockade in quadratically coupled optomechanical systems  

NASA Astrophysics Data System (ADS)

We study the steady-state photon statistics of a quadratically coupled optomechanical cavity, which is weakly driven by a monochromatic laser field. We examine the photon blockade by evaluating the second-order correlation function of the cavity photons. By restricting the system within the zero-, one-, and two-photon subspace, we obtain an approximate analytical expression for the correlation function. We also numerically investigate the correlation function by solving the quantum master equation including both optical and mechanical dissipations. The results show that, in the deep-resolved-sideband and single-photon strong-coupling regimes, the single-photon resonant driving will induce a photon blockade, which is limited by the thermal noise of the mechanical environment.

Liao, Jie-Qiao; Nori, Franco

2013-08-01

160

Extended linear quadratic Gaussian control: Further extensions  

NASA Astrophysics Data System (ADS)

The extended linear quadratic Gaussian (ELQG) control method (Georgakakos and Marks, 1987) is a stochastic control algorithm for the optimal operation of multiobjective reservoirs. Mathematically, this method optimizes a general functional of a stochastic system in state-space form with upper and lower release constraints and probabilistic storage bounds. ELQG is a sequential algorithm which accounts for stochastic effects by preserving the first two statistical moments of the system's inputs and storages. In this paper, the method is first extended to handle nongaussian features which frequently characterize reservoir inputs. Second, ELQG's efficiency with respect to reliability storage constraints is discussed, and a new barrier function method is researched. These modifications are tested in case studies with the Savannah river system.

Georgakakos, Aristidis P.

1989-02-01

161

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

162

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

163

A boundary element-finite element procedure for porous and fractured media flow  

Microsoft Academic Search

A coupled boundary element-finite element procedure is presented for linear and nonlinear fluid flow simulation in porous and fractured aquifers. Quadratic variation of both element geometry and fundamental singularity is used in the constitutively linear direct boundary element formulation. Compatible 3-to 9-noded Lagrangian finite elements are used to represent the plane flow domain for mixed linear and nonlinear flows, alike.

Derek Elsworth

1987-01-01

164

Theory of exciton transport with quadratic exciton-phonon coupling  

Microsoft Academic Search

The coupling of excitons with phonons is an important process determining the mechanism of exciton transport in molecular crystals. Although linear exciton–phonon coupling has been extensively treated before, there has been little work on quadratic coupling. In this paper the theory of exciton transport is extended to take weak quadratic coupling into account, and the diffusion constant computed for a

R. W. Munn; R. Silbey

1978-01-01

165

On copositive programming and standard quadratic optimization problems  

Microsoft Academic Search

A standard quadratic problem consists of finding global maximizers of a quadratic form over the standard simplex. In this paper, the usual semidefinite programming relaxation is strengthened by replacing the cone of positive semidefinite matrices by the cone of completely positive matrices (the positive semidefinite matrices which allow a factorization FFT whereF is some non-negative matrix). The dual of this

Immanuel M. Bomze; Mirjam Dür; Etienne de Klerk; Cornelis Roos; Arie J. Quist; Tamás Terlaky

2000-01-01

166

Design and application of quadratic correlation filters for target detection  

Microsoft Academic Search

We introduce a method for designing and implementing quadratic correlation filters (QCFs) for shift-invariant target detection in imagery. The QCFs are a quadratic classifier that operates directly on the image data without feature extraction or segmentation. In this sense, the QCFs retain the main advantages of conventional linear correlation filters while offering significant improvements in other respects. Not only is

ABHIJIT MAHALANOBIS; ROBERT R. MUISE; S. R. Stanfill; A. Van Nevel

2004-01-01

167

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

168

Natural Exponential Families with Quadratic Variance Functions: Statistical Theory  

Microsoft Academic Search

The normal, Poisson, gamma, binomial, negative binomial, and NEFGHS distributions are the six univariate natural exponential families (NEF) with quadratic variance functions (QVF). This sequel to Morris (1982) treats certain statistical topics that can be handled within this unified NEF-QVF formulation, including unbiased estimation, Bhattacharyya and Cramer-Rao lower bounds, conditional distributions and moments, quadratic regression, conjugate prior distributions, moments of

Carl N. Morris

1983-01-01

169

Quadratic divergences and quantum gravitational contributions to gauge coupling constants  

NASA Astrophysics Data System (ADS)

The calculation of quadratic divergences in Einstein-Maxwell theory with a possible cosmological constant is considered. We describe a method of calculation, using the background-field method, that is sensitive to quadratic divergences, is respectful of gauge invariance, and is independent of gauge conditions. A standard renormalization group analysis is applied to the result where it is shown that the quadratic divergences do lead to asymptotic freedom as found in the original paper of Robinson and Wilczek. The role and nature of these quadratic divergences is critically evaluated in light of recent criticism. Within the context of the background-field method, it is shown that it is possible to define the charge in a physically motivated way in which the quadratic divergences do not play a role. This latter view is studied in more depth in a toy model described in an appendix.

Toms, David J.

2011-10-01

170

Quadratic divergences and quantum gravitational contributions to gauge coupling constants  

SciTech Connect

The calculation of quadratic divergences in Einstein-Maxwell theory with a possible cosmological constant is considered. We describe a method of calculation, using the background-field method, that is sensitive to quadratic divergences, is respectful of gauge invariance, and is independent of gauge conditions. A standard renormalization group analysis is applied to the result where it is shown that the quadratic divergences do lead to asymptotic freedom as found in the original paper of Robinson and Wilczek. The role and nature of these quadratic divergences is critically evaluated in light of recent criticism. Within the context of the background-field method, it is shown that it is possible to define the charge in a physically motivated way in which the quadratic divergences do not play a role. This latter view is studied in more depth in a toy model described in an appendix.

Toms, David J. [School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom)

2011-10-15

171

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

172

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

NASA Astrophysics Data System (ADS)

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).

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

2014-06-01

173

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

174

Optimal power flow using sequential quadratic programming  

NASA Astrophysics Data System (ADS)

Optimal power flow (OPF) is an operational as well as a planning tool used by electric utilities to help them operate their network in the most economic and secure mode of operation. Various algorithms to solve the OPF problem evolved over the past three decades; linear programming (LP) techniques were among the major mathematical programming methods utilized. The linear models of the objective function and the linearization of the constraints are the main features of these techniques. The main advantages of the LP approach are simplicity and speed. Nonlinear programming techniques have been applied to OPF solution. The major drawback is the expensive solution of large sparse systems of equations. This research is concerned with the development of a new OPF solution algorithm using sequential quadratic programming (SQP). In this formulation, a small dense system the size of which is equal to the number of control variables is solved in an inner loop. The Jacobian and Hessian terms are calculated in an outer loop. The total number of outer loop iterations is comparable to those in an ordinary load flow in contrast to 20--30 iterations in other nonlinear methods. In addition, the total number of floating point operations is less than that encountered in direct methods by two orders of magnitude. We also model dispatch over a twenty four-hour time horizon in a transmission constrained power network that includes price-responsive loads where large energy customers can operate their loads in time intervals with lowest spot prices.

Nejdawi, Imad M.

1999-11-01

175

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

176

Three-dimensional finite-element method with edge elements for electromagnetic waveguide discontinuities  

Microsoft Academic Search

When three-dimensional electromagnetic problems are solved by the finite-element method based on a functional with three components of electric or magnetic field, spurious solutions appear if the traditional tetrahedral elements are used. It is shown in the present work that the finite-element method using edge elements succeeds in suppressing spurious solutions and that it succeeds in analyzing three-dimensional electromagnetic waveguide

Kiyoshi Ise; Kazuhiro Inoue; Masanori Koshiba

1991-01-01

177

Quadratic Analysis of Linear Transport Equations.  

National Technical Information Service (NTIS)

Performing transport computations on Lagrangian mesh is often difficult, because finite elements or finite differences methods are not directly implementable. One way to get ride of this is to formulate the problem in terms of even parity flux problem: Th...

D. Verwaerde

1987-01-01

178

The period function of reversible quadratic centers  

NASA Astrophysics Data System (ADS)

In this paper we investigate the bifurcation diagram of the period function associated to a family of reversible quadratic centers, namely the dehomogenized Loud's systems. The local bifurcation diagram of the period function at the center is fully understood using the results of Chicone and Jacobs [C. Chicone, M. Jacobs, Bifurcation of critical periods for plane vector fields, Trans. Amer. Math. Soc. 312 (1989) 433-486]. Most of the present paper deals with the local bifurcation diagram at the polycycle that bounds the period annulus of the center. The techniques that we use here are different from the ones in [C. Chicone, M. Jacobs, Bifurcation of critical periods for plane vector fields, Trans. Amer. Math. Soc. 312 (1989) 433-486] because, while the period function extends analytically at the center, it has no smooth extension to the polycycle. At best one can hope that it has some asymptotic expansion. Another major difficulty is that the asymptotic development has to be uniform with respect to the parameters, in order to prove that a parameter is not a bifurcation value. We study also the bifurcations in the interior of the period annulus and we show that there exist three germs of curves in the parameter space that correspond to this type of bifurcation. Moreover we determine some regions in the parameter space for which the corresponding period function has at least one or two critical periods. Finally we propose a complete conjectural bifurcation diagram of the period function of the dehomogenized Loud's systems. Our results can also be viewed as a contribution to the proof of Chicone's conjecture [C. Chicone, review in MathSciNet, ref. 94h:58072].

Mardeši?, P.; Marín, D.; Villadelprat, J.

179

Nanotribological and nanomechanical properties of 5–80 nm tetrahedral amorphous carbon films on silicon  

Microsoft Academic Search

Nanoscratch testing has been used to investigate the tribological behaviour of 5, 20, 60 and 80 nm tetrahedral amorphous carbon (ta-C) thin films deposited on silicon by the filtered cathodic vacuum arc method. The nanoscratch behaviour of the films was found to depend on the film thickness, with 60 and 80 nm films undergoing border cracking and then at higher

Ben D. Beake; S. P. Lau

2005-01-01

180

Tetrahedral tetrazolate frameworks for high CO2 and H2 uptake.  

PubMed

Three tetrahedral tetrazolate frameworks with two different 4-connected topologies including lonsdaleite (lon, for 1) and diamond (dia, for 2 and 3) have been synthesized, and the lon-type framework with high CO2 and H2 uptake capacity can irreversibly transform to the dia-type framework via solvent-exchange. PMID:24352555

Wang, Fei; Hou, Duan-Chuan; Yang, Hui; Kang, Yao; Zhang, Jian

2014-02-28

181

Polyhedrin sequence determines the tetrahedral shape of occlusion bodies in Thysanoplusia orichalcea single-nucleocapsid nucleopolyhedrovirus.  

PubMed

A nucleopolyhedrovirus (NPV) isolated from the looper Thysanoplusia orichalcea L. (Lepidoptera: Noctuidae) (ThorNPV) is occluded in a tetrahedral protein matrix. The ORF of the ThorNPV polyhedrin gene contains 738 nt which code for 246 amino acids of the putative polyhedrin protein with an estimated molecular mass of 28,778 Da. The promoter of this gene is similar in length to the promoter of Spodoptera frugiperda NPV (SfMNPV), with a 5 nt deletion before the start codon compared to those of other NPVs. When the polyhedrin gene of Autographa californica NPV (AcMNPV), whose occlusion bodies (OBs) are polyhedral, was replaced by the polyhedrin gene of ThorNPV, which produces tetrahedral OBs, tetrahedral polyhedra with properly occluded virions were produced. This work establishes the importance of the polyhedrin protein sequence in determining OB shape. Leucine at position 43 of ThorNPV polyhedrin was identified as responsible for the tetrahedral shape of ThorNPV OBs by PCR-based site-directed mutagenesis. Susceptibility to alkaline buffer of OBs formed by recombinant AcMNPV (RECAcV) carrying the polyhedrin gene of ThorNPV was slightly greater than that of native ThorNPV OBs. The LD50 of RECAcV for third-instar beet armyworm (Spodoptera exigua) was significantly lower than that of AcMNPV (253 and 31 OBs per larva, respectively). PMID:9780063

Cheng, X W; Carner, G R; Fescemyer, H W

1998-10-01

182

Adaptive mesh seismic tomography based on tetrahedral and Voronoi diagrams: Application to Parkfield, California  

Microsoft Academic Search

We have developed an adaptive mesh seismic tomography method based on tetrahedral and Voronoi diagrams to automatically match the inversion mesh to the data distribution. Two different irregular mesh interpolation methods, linear and natural neighbor, are evaluated. A synthetic test shows that the adaptive mesh seismic tomography method recovers the true synthetic model well in both the linear and natural

Haijiang Zhang; Clifford Thurber

2005-01-01

183

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

National Technical Information Service (NTIS)

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-...

N. T. Frink S. Z. Pirzadeh

1998-01-01

184

Electron Damage in In2Te3 - A Defect Tetrahedral Semiconductor.  

National Technical Information Service (NTIS)

Indium sesquitelluride (In2Te3) is typical of a large class of defect semiconductors which are tetrahedrally bonded but which possess room temperature vacancy concentrations of the order of 5.5x10 to the 21st power/cc. It has been proposed that these semi...

H. Swenson D. R. Locker J. M. Meese J. C. Manthuruthil

1974-01-01

185

Discrete-Time Markovian Jump Linear Quadratic Optimal Control.  

National Technical Information Service (NTIS)

This paper is concerned with the optimal control of discrete-time linear systems that possess randomly jumping parameters described by finite state Markov processes. For problems having quadratic costs and perfect observations, the optimal control laws an...

H. J. Chizeck A. S. Willsky D. Castanon

1985-01-01

186

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

187

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

188

Quadratic Optimal Control of Abstract Linear Systems: The Stable Case.  

National Technical Information Service (NTIS)

The authors consider the infinite horizon quadratic cost minimization problem for a stable abstract linear control system, and show that it can be reduced to a spectral factorization problem in the (usually finite-dimensional) control space. More precisel...

O. J. Staffans

1995-01-01

189

Linear State Feedback, Quadratic Weights, and Closed Loop Eigenstructures.  

National Technical Information Service (NTIS)

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 derive...

P. M. Thompson

1980-01-01

190

Use of non-quadratic yield surfaces in design of optimal deep-draw blank geometry  

SciTech Connect

Planar anisotropy in the deep-drawing of sheet can lead to the formation of ears in cylindrical cups and to undesirable metal flow in the blankholder in the general case. For design analysis purposes in non-linear finite-element codes, this anisotropy is characterized by the use of an appropriate yield surface which is then implemented into codes such as DYNA3D . The quadratic Hill yield surface offers a relatively straightforward implementation and can be formulated to be invariant to the coordinate system. Non-quadratic yield surfaces can provide more realistic strength or strain increment ratios, but they may not provide invariance and thus demand certain approximations. Forms due to Hosford and Badat et al. have been shown to more accurately address the earning phenomenon. in this work, use is made of these non-quadratic yield surfaces in order to determine the optimal blank shape for cups and other shapes using ferrous and other metal blank materials with planar anisotropy. The analyses are compared to previous experimental studies on non-uniform blank motion due to anisotropy and asymmetric geometry.

Logan, R.W.

1995-12-01

191

Mobility of Discrete Solitons in Quadratically Nonlinear Media  

Microsoft Academic Search

We study the mobility of solitons in lattices with quadratic (chi(2), alias second-harmonic-generating) nonlinearity. Using the notion of the Peierls-Nabarro potential and systematic numerical simulations, we demonstrate that, in contrast with their cubic (chi(3)) counterparts, the discrete quadratic solitons are mobile not only in the one-dimensional (1D) setting, but also in two dimensions (2D), in any direction. We identify parametric

H. Susanto; P. G. Kevrekidis; R. Carretero-González; B. A. Malomed; D. J. Frantzeskakis

2007-01-01

192

Jump linear quadratic Gaussian control in continuous time  

Microsoft Academic Search

The optimal quadratic control of continuous-time linear systems that possess randomly jumping parameters which can be described by finite-state Markov processes is addressed. The systems are also subject to Gaussian input and measurement noise. The optimal solution for the jump linear-quadratic-Gaussian (JLQC) problem is given. This solution is based on a separation theorem. The optimal state estimator is sample-path dependent.

Yuandong Ji; Howard J. Chizeck

1992-01-01

193

Selecting Knots Locally for Curve Interpolation with Quadratic Precision  

NASA Astrophysics Data System (ADS)

There are several prevailing methods for selecting knots for curve interpolation. A desirable criterion for knot selection is whether the knots can assist an interpolation scheme to achieve the reproduction of polynomial curves of certain degree if the data points to be interpolated are taken from such a curve. For example, if the data points are sampled from an underlying quadratic polynomial curve, one would wish to have the knots selected such that the resulting interpolation curve reproduces the underlying quadratic curve; and in this case the knot selection scheme is said to have quadratic precision. In this paper we propose a local method for determining knots with quadratic precision. This method improves on upon our previous method that entails the solution of a global equation to produce a knot sequence with quadratic precision. We show that this new knot selection scheme results in better interpolation error than other existing methods, including the chord-length method, the centripetal method and Foley's method, which do not possess quadratic precision.

Caiming, Zhang; Wenping, Wang; Jiaye, Wang; Xuemei, Li

194

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.

1988-01-01

195

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

196

High accuracy 3D electromagnetic finite element analysis  

SciTech Connect

A high accuracy 3D electromagnetic finite element field solver employing quadratic hexahedral elements and quadratic mixed-order one-form basis functions will be described. The solver is based on an object-oriented C++ class library. Test cases demonstrate that frequency errors less than 10 ppm can be achieved using modest workstations, and that the solutions have no contamination from spurious modes. The role of differential geometry and geometrical physics in finite element analysis will also be discussed.

Nelson, E.M.

1996-11-01

197

A transient, quadratic nodal method for triangular-Z geometry  

SciTech Connect

Many systematically-derived nodal methods have been developed for Cartesian geometry due to the extensive interest in Light Water Reactors. These methods typically model the transverse-integrated flux as either an analytic or low order polynomial function of position within the node. Recently, quadratic nodal methods have been developed for R-Z and hexagonal geometry. A static and transient quadratic nodal method is developed for triangular-Z geometry. This development is particularly challenging because the quadratic expansion in each node must be performed between the node faces and the triangular points. As a consequence, in the 2-D plane, the flux and current at the points of the triangles must be treated. Quadratic nodal equations are solved using a non-linear iteration scheme, which utilizes the corrected, mesh-centered finite difference equations, and forces these equations to match the quadratic equations by computing discontinuity factors during the solution. Transient nodal equations are solved using the improved quasi-static method, which has been shown to be a very efficient solution method for transient problems. Several static problems are used to compare the quadratic nodal method to the Coarse Mesh Finite Difference (CMFD) method. The quadratic method is shown to give more accurate node-averaged fluxes. However, it appears that the method has difficulty predicting node leakages near reactor boundaries and severe material interfaces. The consequence is that the eigenvalue may be poorly predicted for certain reactor configurations. The transient methods are tested using a simple analytic test problem, a heterogeneous heavy water reactor benchmark problem, and three thermal hydraulic test problems. Results indicate that the transient methods have been implemented correctly.

DeLorey, T.F.

1993-06-01

198

Analysis of inhomogeneously filled cavities by vector finite element method  

Microsoft Academic Search

Accurate analysis of inhomogeneously filled cavities by vector finite element method (VFEM) is presented in this paper. A generalized theory is presented and a tetrahedral subdivision element is exerted for the analysis of inhomogeneously loaded cavities. As a validation, the resonant frequencies of the rectangular and cylindrical cavities filled with dielectric of different types are computed and a comparison with

Runeng Zhong; Qinhong Zheng; Jinhui Peng; Bin Yao; Wansong Xu; Tai Xiang; Lin Li

2011-01-01

199

Near-field testing of the 5-meter model of the tetrahedral truss antenna  

NASA Technical Reports Server (NTRS)

This report documents the technical results from near-field testing of the General Dynamics 5-meter model of the tetrahedral truss antenna at the Martin Marietta Denver Aerospace facility. A 5-meter square side of the tetrahedral served as the perimeter of the antenna, and a mesh surface and extensive surface contouring cord network was used to create a parabolic aperture shape to within an rms accuracy of 30 mils or better. Pattern measurements were made with offset feed systems radiating at frequencies of 7.73, 11.60, 2.27, and 4.26 (all in GHz). This report discusses the method of collecting the data, system measurement accuracy, the test data compiled, and diagostics and isolation of causes of pattern results. The technique of using near-field phase for measuring surface mechanical tolerances is included. Detailed far field antenna patterns and their implications are provided for all tests conducted.

Kefauver, Neill; Cencich, Tom; Osborn, Jim; Osmanski, J. T.

1986-01-01

200

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

201

Boson peak in the Raman spectra of amorphous gallium arsenide: Generalization to amorphous tetrahedral semiconductors  

NASA Astrophysics Data System (ADS)

We report on the observation of the boson peak in amorphous (a) GaAs formed by high-energy ion bombardment of the crystalline lattice. The experimental data are analyzed according to the theory of inelastic light scattering from fractons. The correlation length ? and the spectral dimension d~ of the fractal are determined. In comparison to a-Si:H the crossover frequency from the phonon to the fracton scattering regime, ?co1, is lower and scales according to mass law, confirming the vibrational character of the boson peak. The origin of the fractals in tetrahedral amorphous semiconductors is discussed in terms of strained nanometer blobs of host atoms whose overcoordination is relaxed through bond percolation. The intensity increase of the boson peak relative to the amorphous component during the process of amorphization of GaAs, and the increase in the carbon content in a-Si:H, shows a composite structure that consists of a strained fractal region in the relaxed network. Some experimentally observed anomalies such as low values of the sound velocity in tetrahedral amorphous semiconductors, and transformation of the vibrational spectrum by quenching in As2S3 are qualitatively explained by the fractal model. On the basis of maximum positions of the boson peak and the first sharp diffraction peak observed in the structure factor of inelastic x-ray or neutron scattering of amorphous semiconductors, the correlation lengths of medium-range order (MRO) are determined and compared for different tetrahedral and vitreous amorphous semiconductors. The observed three to four times shorter value of MRO in tetrahedral relative to vitreous amorphous semiconductors is used to explain a number of differences between their properties.

Ivanda, M.; Hartmann, I.; Kiefer, W.

1995-01-01

202

Nanoindentation-induced deformation behaviour of tetrahedral amorphous carbon coating deposited by filtered cathodic vacuum arc  

Microsoft Academic Search

The nanoindentation-induced deformation behaviour of a ta-C (tetrahedral amorphous carbon) coating deposited on to a silicon substrate by a filtered vacuum cathodic vapour arc technique was investigated. The 0.17-?m-thick ta-C coating was subjected to nanoindentation with a spherical indenter and the residual indents were examined by cross-sectional transmission electron microscopy. The hard (~30GPa) ta-C coatings exhibited very little localized plastic

A. J. Haq; P. R. Munroe; M. Hoffman; P. J. Martin; A. Bendavid

2010-01-01

203

Comparing hardness and wear data for tetrahedral amorphous carbon and hydrogenated amorphous carbon thin films  

Microsoft Academic Search

We compared nanoindentation and nanoscratch testing of 10 and 50nm thick tetrahedral amorphous carbon (ta-C) and hydrogenated amorphous carbon (a-C:H). Raman spectroscopy shows the expected spectral features for the two carbon forms, however, luminescence from the ceramic substrate can alter the spectra. We find that hard ta-C films can blunt the diamond tip and hence use a tip area function

P. Lemoine; J. P. Quinn; P. Maguire; J. A. McLaughlin

2004-01-01

204

Stress relief of tetrahedral amorphous carbon films by post-deposition thermal annealing  

Microsoft Academic Search

The stress relief of tetrahedral amorphous carbon (ta-C) films by post-deposition thermal annealing was investigated. The films were subjected to rapid thermal annealing (RTA) for 2min and conventional furnace annealing (CFA) for 30min. In both cases, the films were annealed in vacuum with argon (4×10?2Torr) at successive higher temperatures ranging from 500 to 800°C. It was found that annealing by

B. K. Tay; X. Shi; E. Liu; S. P. Lau; L. K. Cheah; Z. Sun; J. Shi

1999-01-01

205

A tetrahedrally coordinated cobalt(II) aminophosphonate containing one-dimensional channels  

NASA Astrophysics Data System (ADS)

A tetrahedrally coordinated cobalt(II) phosphonate, Co(O 3PCH 2CH 2NH 2), has been synthesized using hydrothermal techniques. X-ray diffraction indicates that this material is a three-dimensional open framework with rings aligned along a single axis forming infinite one-dimensional channels. The framework decomposes just above 400 °C. Magnetic susceptibility data are consistent with weak antiferromagnetic ordering at low temperatures.

Gemmill, William R.; Smith, Mark D.; Reisner, Barbara A.

2005-09-01

206

Simulation of Stagnation Region Heating in Hypersonic Flow on Tetrahedral Grids  

NASA Technical Reports Server (NTRS)

Hypersonic flow simulations using the node based, unstructured grid code FUN3D are presented. Applications include simple (cylinder) and complex (towed ballute) configurations. Emphasis throughout is on computation of stagnation region heating in hypersonic flow on tetrahedral grids. Hypersonic flow over a cylinder provides a simple test problem for exposing any flaws in a simulation algorithm with regard to its ability to compute accurate heating on such grids. Such flaws predominantly derive from the quality of the captured shock. The importance of pure tetrahedral formulations are discussed. Algorithm adjustments for the baseline Roe / Symmetric, Total-Variation-Diminishing (STVD) formulation to deal with simulation accuracy are presented. Formulations of surface normal gradients to compute heating and diffusion to the surface as needed for a radiative equilibrium wall boundary condition and finite catalytic wall boundary in the node-based unstructured environment are developed. A satisfactory resolution of the heating problem on tetrahedral grids is not realized here; however, a definition of a test problem, and discussion of observed algorithm behaviors to date are presented in order to promote further research on this important problem.

Gnoffo, Peter A.

2007-01-01

207

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

208

Tetrahedral finite-volume solutions to the Navier-Stokes equations on complex configurations  

NASA Astrophysics Data System (ADS)

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 USA 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.

1999-09-01

209

Quadratic Integrate-and-Fire Neuron Network Model  

NSDL National Science Digital Library

The Quadratic Integrate-and-Fire Neuron Network Model uses a network of Quadratic Integrate-and-Fire neurons to demonstrate how connectivity influences network synchrony. The user selects the number of neurons and the degree of connectivity, and can see how the neurons synchronize over time. In addition, the user can watch the potential of a single neuron. Although the dynamics of a single neuron do not change, the network architecture has a dramatic effect on how quickly the neurons will synchronize. The Quadratic Integrate-and-Fire Neuron Network 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.

2012-12-22

210

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

211

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

212

Tetrahedral Kites  

NSDL National Science Digital Library

Students construct "a tetrahedron and describe the linear, area and volume using non-traditional 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." (from NCTM Illuminations)

Mathematics, Illuminations N.

2009-05-12

213

Mobility of Discrete Solitons in Quadratically Nonlinear Media  

NASA Astrophysics Data System (ADS)

We study the mobility of solitons in lattices with quadratic (?(2), alias second-harmonic-generating) nonlinearity. Using the notion of the Peierls-Nabarro potential and systematic numerical simulations, we demonstrate that, in contrast with their cubic (?(3)) counterparts, the discrete quadratic solitons are mobile not only in the one-dimensional (1D) setting, but also in two dimensions (2D), in any direction. We identify parametric regions where an initial kick applied to a soliton leads to three possible outcomes: staying put, persistent motion, or destruction. On the 2D lattice, the solitons survive the largest kick and attain the largest speed along the diagonal direction.

Susanto, H.; Kevrekidis, P. G.; Carretero-González, R.; Malomed, B. A.; Frantzeskakis, D. J.

2007-11-01

214

Selectable linear or quadratic coupling in an optomechanical system  

NASA Astrophysics Data System (ADS)

There has been much interest recently in the analysis of optomechanical systems incorporating dielectric nano- or microspheres inside a cavity field. We analyze here the situation when one of the mirrors of the cavity itself is also allowed to move. We reveal that the interplay between the two oscillators yields a cross-coupling that results in, e.g., appreciable cooling and squeezing of the motion of the sphere, despite its nominal quadratic coupling. We also discuss a simple modification that would allow this cross-coupling to be removed at will, thereby yielding a purely quadratic coupling for the sphere.

Xuereb, André; Paternostro, Mauro

2013-02-01

215

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

216

Remarks on quadratic bundles related to Hermitian symmetric spaces  

NASA Astrophysics Data System (ADS)

We consider quadratic bundles related to Hermitian symmetric spaces of the type SU(m+n)/S(U(m)×U(n)). We discuss the spectral properties of scattering operator, develop the direct scattering problem associated with it and stress on the effect of reduction on these. By applying a modification of Zakharov-Shabat's dressing procedure we demonstrate how one can obtain reflectionless potentials. That way one is able to generate soliton solutions to the nonlinear evolution equations belonging to the integrable hierarchy associated with quadratic bundles under study.

Valchev, Tihomir

2014-03-01

217

Finite element approximations of nonlinear eigenvalue problems in quantum physics  

Microsoft Academic Search

In this paper, we study finite element approximations of a class of nonlinear eigenvalue problems arising from quantum physics. We derive both a priori and a posteriori finite element error estimates and obtain optimal convergence rates for both linear and quadratic finite element approximations. In particular, we analyze the convergence and complexity of an adaptive finite element method. In our

Huajie Chen; Lianhua He; Aihui Zhou

2011-01-01

218

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

219

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

220

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

NASA Astrophysics Data System (ADS)

Shell structures in single-particle energy spectra are investigated against regular tetrahedral type deformation using a radial power-law potential model. Employing a natural way of shape parametrization which interpolates sphere and regular tetrahedron, we find prominent shell effects for 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.

Arita, Ken-ichiro; Mukumoto, Yasunori

2014-05-01

221

A Dynamical Systems Analysis of Semidefinite Programming with Application to Quadratic Optimization with Pure Quadratic Equality Constraints  

SciTech Connect

This paper considers the problem of minimizing a quadratic cost subject to purely quadratic equality constraints. This problem is tackled by first relating it to a standard semidefinite programming problem. The approach taken leads to a dynamical systems analysis of semidefinite programming and the formulation of a gradient descent flow which can be used to solve semidefinite programming problems. Though the reformulation of the initial problem as a semidefinite pro- gramming problem does not in general lead directly to a solution of the original problem, the initial problem is solved by using a modified flow incorporating a penalty function.

Orsi, R. J. [Department of Electrical and Electronic Engineering, University of Melbourne, Parkville, VIC 3052 (Australia); Mahony, R. E. [Heudiasyc - UTC UMR 6599, Centre de Recherche de Royallieu, BP 20529, 60205 Compiegne Cedex (France); Moore, J. B. [Department of Systems Engineering, RSISE, Australian National University, Canberra, ACT 0200 (Australia)

1999-09-15

222

Relativistic nuclear matter with a quadratic scalar coupling  

Microsoft Academic Search

A coupling between the nucleon and the scalar meson, quadratic in the scalar field, has been added to the standard Walecka Lagrangian. The coupling constants have been determined to reproduce the binding energy and Fermi momentum of the empirical saturation point and the compression modulus of nuclear matter. Since this latter quantity has not yet been precisely determined, the model

J. C. Caillon; J. Labarsouque

1999-01-01

223

Quadratic phase coupling analysis for infrasound vehicle detection  

Microsoft Academic Search

The low attenuation characteristic of infrasound enables it to propagate long distances making it possible for the detection of infrasound sources. In this paper, a comparison in terms of the detection range between an acoustic microphone and an infrasound sensor in the context of vehicle detection is made. We propose to employ the bispectrum based quadratic phase coupling (QPC) analysis

Renshi Li; Vinod V. Reddy; Andy W. H. Khong

2010-01-01

224

An efficient method for quadratic Riccati differential equation  

NASA Astrophysics Data System (ADS)

In this paper, a new form of homotopy perturbation method (NHPM) has been adopted for solving the quadratic Riccati differential equation. In this technique, the solution is considered as a Taylor series expansion converges rapidly to the exact solution of the nonlinear equation. Having found the exact solution of the Riccati equation, the capability and the simplicity of the proposed technique is clarified.

Aminikhah, Hossein; Hemmatnezhad, Milad

2010-04-01

225

Clustered Self Organising Migrating Algorithm for the Quadratic Assignment Problem  

NASA Astrophysics Data System (ADS)

An approach of population dynamics and clustering for permutative problems is presented in this paper. Diversity indicators are created from solution ordering and its mapping is shown as an advantage for population control in metaheuristics. Self Organising Migrating Algorithm (SOMA) is modified using this approach and vetted with the Quadratic Assignment Problem (QAP). Extensive experimentation is conducted on benchmark problems in this area.

Davendra, Donald; Zelinka, Ivan; Senkerik, Roman

2009-08-01

226

Efficient Color Histogram Indexing for Quadratic Form Distance Functions  

Microsoft Academic Search

In image retrieval based on color, the weighted distance between color histograms of two images, represented as a quadratic form, may be defined as a match measure. However, this distance measure is computationally expensive and it operates on high dimensional features (O(N)). We propose the use of low-dimensional, simple to compute distance measures between the color distributions, and show that

James L. Hafner; Harpreet S. Sawhney; William Equitz; Myron Flickner; Wayne Niblack

1995-01-01

227

ECONOMIC ACCEPTANCE SAMPLING BY VARIABLES WITH QUADRATIC QUALITY COSTS  

Microsoft Academic Search

An economic model is developed, to assist in the selection of minimum cost acceptance sampling plans by variables. The quadratic Taguchi loss function is adopted to model the cost of accepting items, with quality characteristics deviating from the target value. The case of a normally distributed quality characteristic with known variance is examined, and a simple and efficient optimization algorithm

GEORGE TAGARAS

1994-01-01

228

A connection between half-quadratic criteria and EM algorithms  

Microsoft Academic Search

Iteratively Reweighted Least Squares (IRLS) and Residual Steepest descent (RSD) algorithms of robust statistics arise as special cases of half-quadratic schemes . Here, we adopt a statistical framework and we show that both algorithms are instances of the EM algorithm. The augmented dataset respectively involves a scale and a location mixture of Gaussians. The sufficient conditions for the construction cover

Frédéric Champagnat; Jérôme Idier

2004-01-01

229

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

230

Velocity-locked solitary waves in quadratic media.  

PubMed

We demonstrate experimentally the existence of three-wave resonant interaction solitary triplets in quadratic media. Stable velocity-locked bright-dark-bright spatial solitary triplets, determined by the balance between the energy exchange rates and the velocity mismatch between the interacting waves, are excited in a KTP crystal. PMID:20366477

Baronio, Fabio; Conforti, Matteo; De Angelis, Costantino; Degasperis, Antonio; Andreana, Marco; Couderc, Vincent; Barthélémy, Alain

2010-03-19

231

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

232

Parallel Ant Colonies for the quadratic assignment problem  

Microsoft Academic Search

Ant Colonies optimization take inspiration from the behavior of real ant colonies to solve optimization problems. This paper presents a parallel model for ant colonies to solve the quadratic assignment problem (QAP). The cooperation between simulated ants is provided by a pheromone matrix that plays the role of a global memory. The exploration of the search space is guided by

El-ghazali Talbi; Olivier H. Roux; Cyril Fonlupt; Denis Robillard

2001-01-01

233

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

234

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

235

Least Squares Quadratic (LSQ) Approximation to Lognormal Sum Distributions  

Microsoft Academic Search

In this paper, least squares (LS) approximation approach is used to solve the approximation problem of a sum of lognormal random variables. It is shown that least squares quadratic (LSQ) approximation exhibits an excellent match with the simulation results in a wide range of the distributions of the summands. Using the coefficients obtained from the LSQ method, closed-form expressions for

Lian Zhao; Jiu Ding

2006-01-01

236

Quadrat Sampling: A Computer-Generated Laboratory Exercise  

NSDL National Science Digital Library

Obtaining spatial distributions by quadrat sampling can be difficult because field work tends to yield inconclusive data. This article describes a computer program that generates different spatial patterns for two species. It produces meaningful comparisons between two or more different habitats and uses cluster points which determine the interactions within and between species.

Boyer, John F.

2010-02-16

237

How Big the Set of Infinitely Renormalizable Quadratics Is.  

National Technical Information Service (NTIS)

The Mandelbrot set M is the bifurcation diagram of the complex quadratic family P(sub c): z -> z(squared) + c viewed dynamically. Despite the one line definition (see below), this set has quite a complicated structure, so that there is a little change to ...

M. Lyubich

1996-01-01

238

Linear-Quadratic Problems and the Riccati Equation.  

National Technical Information Service (NTIS)

An overview of the results relating the Riccati equation with the Linear Quadratic (LQ) control problem is given. It is demonstrated that the LQ problem can be solved by using the Riccati equation or its generalization, the dissipation inequality. The sin...

A. H. W. Geerts M. L. J. Hautus

1989-01-01

239

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

240

Robust Estimation and Tests based on Quadratic Inference Function 1  

Microsoft Academic Search

Robust estimators and tests based on the quadratic inference function (QIF) are considered. The QIF enables one to combine a set of extended score functions effi- ciently. For example,one can create an adaptive estimator between the mean and median that is fully efficient at the normal model but is highly robust,with a 25% asymptotic breakdown point. In addition to providing

Chanseok Park; Bruce G. Lindsay

1999-01-01

241

Binary Mosaics and Point Quadrat Sampling in Ecology.  

National Technical Information Service (NTIS)

Point quadrat sampling is a method for estimating the proportional cover p of a plant species over a planar region, whereby the presence or absence of the species is recorded at each of N sample points. Then, if n is the number of points at which the spec...

C. J. F. ter Braak

1980-01-01

242

Shape functions and integration formulas for three-dimensional finite element analysis  

Microsoft Academic Search

Shape functions and numerical integration formulas for 3D finite element analysis as found in most finite element reference books are incomplete. For example, shape functions and integration formulas for a pyramid with a quadrilateral base are missing. It is also difficult to find symmetric higher-order integration formulas for triangular and tetrahedral elements. In general, these shape functions and integration formulas

G. Bedrosian

1992-01-01

243

A special class of simple 24-vertex polyhedra and tetrahedrally coordinated structures of gas hydrates.  

PubMed

It is established that the eight-dimensional lattice E(8) and the Mathieu group M(12) determine a unique sequence of algebraic geometry constructions which define a special class of simple 24-vertex, 14-face polyhedra with four-, five- and six-edge faces. As an example, the graphs of the ten stereohedra that generate most known tetrahedrally coordinated water cages of gas hydrates have been derived a priori. A structural model is proposed for the phase transition between gas hydrate I and ice. PMID:20720325

Samoylovich, M I; Talis, A L

2010-09-01

244

Preliminary design of a large tetrahedral truss/hexagonal panel aerobrake structural system  

NASA Technical Reports Server (NTRS)

This paper introduces an aerobrake structural concept consisting of two primary components: (1) a lightweight erectable tetrahedral support truss, and (2) a heatshield composed of individual sandwich hexagonal panels which, when attached to the truss, function as a continuous aerobraking surface. A general preliminary analysis procedure to design the aerobrake components is developed, and values of the aerobrake design parameters which minimize the mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed.

Dorsey, John T.; Mikulas, Martin M., Jr.

1990-01-01

245

Nuclear tetrahedral states and high-spin states studied using the quantum number projection method  

NASA Astrophysics Data System (ADS)

We have recently developed an efficient method for performing the full quantum number projection from the most general mean-field (Hartree–Fock–Bogoliubov-type) wavefunctions including the angular momentum and parity, as well as the proton and neutron particle numbers. With this method, we have investigated several nuclear structure mechanisms. In this paper, we discuss the quantum rotational spectra obtained for the tetrahedral nuclear states, formulating certain experimentally verifiable criteria for the high-spin states, focusing on the wobbling bands and chiral bands, and for the drip-line nuclei, as illustrative examples.

Tagami, S.; Shimada, M.; Fujioka, Y.; Shimizu, Y. R.; Dudek, J.

2014-05-01

246

Controlled synthesis of concave tetrahedral palladium nanocrystals by reducing Pd(acac){sub 2} with carbon monoxide  

SciTech Connect

Graphical abstract: By using CO as a reducing agent, uniform and well-defined concave tetrahedral Pd nanocrystals were successfully synthesized. CO flow rate was the most essential for the formation of the concave tetrahedral nanostructures. The morphologies and sizes of the final products can be well controlled by adjusting the flow rate of CO. Highlights: ? By using CO as a reducing agent, concave tetrahedral Pd nanocrystals were obtained. ? CO flow rate is critical to the formation of concave tetrahedral Pd nanocrystals. ? The selective adsorption of CO on (1 1 0) facets is essential to concave Pd tetrahedra. -- Abstract: CO reducing strategy to control the morphologies of palladium nanocrystals was investigated. By using CO as a reducing agent, uniform and well-defined concave tetrahedral Pd nanocrystals with a mean size of about 55 ± 2 nm were readily synthesized with Pd(acac){sub 2} as a precursor and PVP as a stabilizer. The structures of the as-prepared Pd nanocrystals were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), ultraviolet–visible (UV–vis) absorption spectroscopy and electrochemical measurements. The results demonstrated that CO was the most essential for the formation of the concave tetrahedral Pd nanostructures. The morphologies and sizes of the final products can be well controlled by adjusting the flow rate of CO. The most appropriate CO flow rate, temperature and time for the formation of the ideal concave tetrahedral Pd nanocrystals was 0.033 mL s{sup ?1}, 100 °C and 3 h, respectively.

Zhu, Hai; Chi, Quan; Zhao, Yanxi; Li, Chunya; Tang, Heqing; Li, Jinlin [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074 (China)] [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074 (China); Huang, Tao, E-mail: huangt6628@yahoo.com.cn [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074 (China)] [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074 (China); Liu, Hanfan [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074 (China) [Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission and Ministry of Education, Hubei Province, College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074 (China); Institute of Chemistry, Chinese Academy of Science, Beijing 100080 (China)

2012-11-15

247

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

248

On classical state space realisability of quadratic input–output differential equations  

Microsoft Academic Search

This article studies the realisability property of continuous-time quadratic input–output (i\\/o) equations in the classical state space form. Constraints on the parameters of the quadratic i\\/o model are suggested that lead to realisable models. The complete list of second- and third-order realisable i\\/o quadratic models is given and two subclasses of the n-th order realisable i\\/o quadratic systems are suggested.

Ü. Kotta; P. Kotta; M. Tõnso; A. S. I. Zinober

2009-01-01

249

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

2013-07-01

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

Applicability of quadratic and threshold models to motion discrimination in the rabbit retina  

Microsoft Academic Search

Computational and behavioral studies suggest that visual motion discrimination is based on quadratic nonlinearities. This raises the question of whether the behavior of motion sensitive neurons early in the visual system is actually quadratic. Theoretical studies show that mechanisms proposed for retinal directional selectivity do not behave quadratically at high stimulus contrast. However, for low contrast stimuli, models for these

Norberto M. Grzywacz; F. R. Amthor; L. A. Mistler

1990-01-01

252

Single-molecule orientation measurements with a quadrated pupil  

NASA Astrophysics Data System (ADS)

We present a means of measuring the dipole orientation of a fluorescent, rotationally fixed single molecule (SM), using a specially designed phase mask, termed a "quadrated pupil," conjugate to the back focal plane of a conventional widefield microscope. In comparison to image-fitting techniques that infer orientation by matching simulations to defocused or excessively magnified images, the quadrated pupil approach is more robust to minor modeling discrepancies, defocus, and optical aberrations. Precision on the order of 1°-5° is achieved in proofof- concept experiments for both azimuthal (?) and polar (?) angles. Since the phase mask is implemented on a liquid-crystal spatial light modulator (SLM) that may be deactivated without any mechanical perturbation of the sample or imaging system, the technique may be readily integrated into conventional imaging studies.

Backer, Adam S.; Backlund, Mikael P.; Lew, Matthew D.; Diezmann, Alexander R.; Sahl, Steffen J.; Moerner, W. E.

2014-03-01

253

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

254

Optical continuous-variable quadratic phase gate via Faraday interaction.  

PubMed

The continuous-variable (CV) quadratic phase gate is one of the most fundamental CV quantum gates for universal CV quantum computation, while its experimental realization still remains a challenge. Here we propose a novel and experimentally feasible scheme to realize optical CV quadratic phase gate via Faraday interaction in an atomic ensemble. The gate is performed by simply sending an optical beam three times through an atomic medium prepared in coherent spin state. The fidelity of the gate can ideally run up to one. We show that the scheme also works well as a device to generate optical polarization squeezing. Considering the noise effects due to atomic decoherence and light losses, we find that the observed fidelities of gate operation and the attainable degree of polarization squeezing are still quite high. PMID:24787808

Wang, Ming-Feng; Jiang, Nian-Quan; Zheng, Yi-Zhuang

2014-04-21

255

Evidence for quadratic tidal tensor bias from the halo bispectrum  

NASA Astrophysics Data System (ADS)

The relation between the clustering properties of luminous matter in the form of galaxies and the underlying dark matter distribution is of fundamental importance for the interpretation of ongoing and upcoming galaxy surveys. The so-called local bias model, where galaxy density is a function of local matter density, is frequently discussed as a means to infer the matter power spectrum or correlation function from the measured galaxy correlation. However, gravitational evolution generates a term quadratic in the tidal tensor and thus nonlocal in the Eulerian density field, even if this term is absent in the initial conditions (Lagrangian space). Because the term is quadratic, it contributes as a loop correction to the power spectrum, so the standard linear bias picture still applies on very large scales; however, it contributes at leading order to the bispectrum for which it is significant on all scales. Such a term could also be present in Lagrangian space if halo formation were influenced by the tidal field. We measure the corresponding coupling strengths from the matter-matter-halo bispectrum in numerical simulations and find a nonvanishing coefficient for the tidal tensor term. We find no scale dependence of the inferred bias parameters up to k˜0.1hMpc-1 and that the tidal effect is increasing with halo mass. While the local Lagrangian bias picture is a better description of our results than the local Eulerian bias picture, our results suggest that there might be a tidal tensor bias already in the initial conditions. We also find that the coefficients of the quadratic density term deviate quite strongly from the theoretical predictions based on the spherical collapse model and a universal mass function. Both quadratic density and tidal tensor bias terms must be included in the modeling of galaxy clustering of current and future surveys if one wants to achieve the high precision cosmology promise of these data sets.

Baldauf, Tobias; Seljak, Uroš; Desjacques, Vincent; McDonald, Patrick

2012-10-01

256

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

257

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

258

Discrete-time markovian-jump linear quadratic optimal control  

Microsoft Academic Search

This paper is concerned with the optimal control of discrete-time linear systems that possess randomly jumping parameters described by finite-state Markov processes. For problems having quadratic costs and perfect observations, the optimal control laws and expected costs-to-go can be precomputed from a set of coupled Riccati-like matrix difference equations. Necessary and sufficient conditions are derived for the existence of optimal

H. J. CHIZECK; A. S. WILLSKY; D. CASTANON

1986-01-01

259

Stability of Julia sets for a quadratic random dynamical system  

Microsoft Academic Search

For a sequence (cn) of complex numbers, the quadratic polynomials fcn:= z2 + Cn and the sequence (Fn) of iterates Fn: = fcn ? ? ? fc1 are considered. The Fatou set F(Cn) is defined as the set of all\\u000a $$z \\\\in \\\\hat {\\\\mathbb{C}}: = {\\\\mathbb{C}} \\\\cup \\\\left\\\\{ \\\\infty \\\\right\\\\}$$\\u000a such that (Fn) is normal in some neighbourhood of z,

Gong Zhimin; Qiu Weiyuan; Wang Jian

2002-01-01

260

Observers for Systems with Nonlinearities Satisfying an Incremental Quadratic Inequality  

NASA Technical Reports Server (NTRS)

We consider the problem of state estimation for nonlinear time-varying systems whose nonlinearities satisfy an incremental quadratic inequality. These observer results unifies earlier results in the literature; and extend it to some additional classes of nonlinearities. Observers are presented which guarantee that the state estimation error exponentially converges to zero. Observer design involves solving linear matrix inequalities for the observer gain matrices. Results are illustrated by application to a simple model of an underwater.

Acikmese, Ahmet Behcet; Corless, Martin

2004-01-01

261

DISTINGUISHED REPRESENTATIONS AND QUADRATIC BASE CHANGE FOR GL(3)  

Microsoft Academic Search

Let E=F be a quadratic extension of number elds. Suppose that every real place of F splits in E and let H be the unitary group in 3 variables. Suppose that is an automorphic cuspidal representation of GL(3;EA). We prove that there is a form in the space of such that the integral of over H(F )nH(FA) is non zero.

HERVE JACQUET; YANGBO YE

262

Periodic solutions of quadratic Weyl fractional integral equations  

NASA Astrophysics Data System (ADS)

In this paper, we study periodic solutions of quadratic Weyl fractional integral equations. We derive the convergence, periodicity, continuity and boundedness of Weyl kernel. With the help of these basic properties, we prove the existence of 2?-periodic solutions of the desired equation by using a technique of measure of noncompactness via Schauder fixed point theorem. Moreover, we obtain uniform local attractivity of the 2?-periodic solutions. Finally, an example is given to illustrate the obtained results.

Chen, Qian; Wang, JinRong; Chen, Fulai; Zhang, Yuruo

2014-06-01

263

Finite element approximation of free vibration of folded plates  

Microsoft Academic Search

In this paper a finite element approximation of the free vibration of folded plates is studied. Naghdi model, including bending, shear and membrane terms for the plate, is considered. Quadrilateral low order MITC (Mixed Interpolation Tensorial Component) elements are used for the bending and shear effect, coupled with standard quadratic elements enriched with a drilling degree of freedom for the

Erwin Hernández; Luis Hervella-Nieto

2009-01-01

264

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

265

The suggested presence of tetrahedral symmetry in the ground-state configuration of the _{40}^{96}\\text{Zr}_{56}^{{}} nucleus  

NASA Astrophysics Data System (ADS)

We discuss predictions made by large scale calculations using the realistic realization of phenomenological nuclear mean-field theory. The calculations indicate that certain zirconium nuclei are tetrahedrally symmetric in their ground states. After a short overview of past research into nuclear tetrahedral symmetry we analyse the predictive capacities of the method and focus on the 96Zr nucleus, which is expected to be tetrahedral in its ground state.

Dudek, J.; Curien, D.; Rouvel, D.; Mazurek, K.; Shimizu, Y. R.; Tagami, S.

2014-05-01

266

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

267

Advances in 3D electromagnetic finite element modeling  

SciTech Connect

Numerous advances in electromagnetic finite element analysis (FEA) have been made in recent years. The maturity of frequency domain and eigenmode calculations, and the growth of time domain applications is briefly reviewed. A high accuracy 3D electromagnetic finite element field solver employing quadratic hexahedral elements and quadratic mixed-order one-form basis functions will also be described. The solver is based on an object-oriented C++ class library. Test cases demonstrate that frequency errors less than 10 ppm can be achieved using modest workstations, and that the solutions have no contamination from spurious modes. The role of differential geometry and geometrical physics in finite element analysis is also discussed.

Nelson, E.M.

1997-08-01

268

A unified multigrid solver for the Navier-Stokes equations on mixed element meshes  

NASA Technical Reports Server (NTRS)

A unified multigrid solution technique is presented for solving the Euler and Reynolds-averaged Navier-Stokes equations on unstructured meshes using mixed elements consisting of triangles and quadrilaterals in two dimensions, and of hexahedra, pyramids, prisms, and tetrahedra in three dimensions. While the use of mixed elements is by no means a novel idea, the contribution of the paper lies in the formulation of a complete solution technique which can handle structured grids, block structured grids, and unstructured grids of tetrahedra or mixed elements without any modification. This is achieved by discretizing the full Navier-Stokes equations on tetrahedral elements, and the thin layer version of these equations on other types of elements, while using a single edge-based data-structure to construct the discretization over all element types. An agglomeration multigrid algorithm, which naturally handles meshes of any types of elements, is employed to accelerate convergence. An automatic algorithm which reduces the complexity of a given triangular or tetrahedral mesh by merging candidate triangular or tetrahedral elements into quadrilateral or prismatic elements is also described. The gains in computational efficiency afforded by the use of non-simplicial meshes over fully tetrahedral meshes are demonstrated through several examples.

Mavriplis, D. J.; Venkatakrishnan, V.

1995-01-01

269

Synthesis, evaluation and defect compensation of tetrahedral glasses as possible solar cell materials. Final report, February 1, 1979-April 30, 1980  

SciTech Connect

The work reported was directed towards evaluation of new amorphous compounds for application in solar cells. The ternary A/sup II/B/sup IV/C/sub 2//sup V/ chalcopyrite systems were selected because of their inexpensive constituent elements and tetrahedral geometry. Polycrystalline samples of the ternary arsenides with Cd and Zn as the group II element and Ge, Si, Sn as the group IV element were synthesized. Thin films were deposited by vacuum evaporation of the bulk ternary arsenides. The stoichiometries of the films were irreproducible and were usually deficient in the lower vapor pressure group IV element. Films made by evaporating polycrystalline ZnAs/sub 2/, which also has a tetrahedral bonding structure, had stoichiometries generally in the range from Zn/sub 3/As/sub 2/ to ZnAs/sub 2/. The former compound is formed by the decomposition of ZnAs/sub 2/ to Zn/sub 3/As/sub 2/ and As/sub 4/. The intermediate stoichiometries are thought to be mixtures of the decomposition products. Preliminary results from annealing of the films indicate that heat treatment produces the stoichiometries expected for one of the two forms of zinc arsenide. The as-deposited films are amorphous when the substrate temperature is kept below 100/sup 0/C. The a-ZnAs/sub x/ films were characterized. EDAX and Auger analysis showed that films were homogeneous in the plane of the substrate, but that some variation occurred in the depth profile of the films. This change in composition is consistent with the sample decomposition which occurs during the evaporation. The as-prepared films were p-type with room temperature resistivities on the order of 10/sup 2/-10/sup 4/..cap omega..-cm. Optical absorption measurements gave optical band gap values of 1.2 eV for a-Zn/sub 3/As/sub 2/ and 1.5 eV for a-ZnAs/sub 2/. The ZnAs/sub x/ films were photoconductive.

Rauh, R.D.; Rose, T.L.; Scoville, A.N.

1980-04-01

270

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

271

Self-assembly of tetrahedral CdSe nanocrystals: effective "patchiness" via anisotropic steric interaction.  

PubMed

Controlling the spontaneous organization of nanoscale objects remains a fundamental challenge of materials design. Here we present the first characterization of self-assembled superlattices (SLs) comprised of tetrahedral nanocrystal (NCs). We observe self-assembly of CdSe nanotetrahedra into an open structure (estimated space-filling fraction ? ? 0.59) which has not been anticipated by many recent theoretical studies and simulations of tetrahedron packings. This finding highlights a gap in the understanding of the hierarchy of energy scales acting on colloidal NCs during self-assembly. We propose a strong dependence of ligand-ligand interaction potential on NC surface curvature. This effect favors spatial proximity of vertices in the dense colloidal crystal and may be considered an emergent "patchiness" acting through chemically identical ligand molecules. PMID:24655011

Boles, Michael A; Talapin, Dmitri V

2014-04-23

272

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

PubMed Central

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

2014-01-01

273

First-principles calculation of vibrational Raman spectra of tetrahedral amorphous carbon  

NASA Astrophysics Data System (ADS)

The nonresonant vibrational Raman spectra of tetrahedral amorphous carbon are calculated from first principles. The structural model was generated using Car-Parinello molecular dynamics, the vibrational modes are determined using the linear response approach and Raman tensors are calculated using the finite electric field method. Our theoretical visible and reduced Raman spectra show an overall good agreement with experimental spectra, and better than previous calculated results. The analysis in terms of atomic vibrations shows that the Raman spectrum mainly comes from sp 2 contribution, G peak is due to the stretching vibration of any pair of sp 2 atoms and only a small sp 3 contribution can be noticed. The differences between peak intensities of reduced theoretical and experimental results mainly come from defects and the high sp 3 content in our simulated structure.

Niu, Li; Zhu, Jiaqi; Gao, Wei; Liu, Aiping; Han, Xiao; Du, Shanyi

2008-10-01

274

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

275

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

276

Near-field supersonic flow predictions by an adaptive unstructured tetrahedral grid solver  

NASA Technical Reports Server (NTRS)

Applicability of a three-dimensional solution adaptive unstructured tetrahedral Euler flow solver about generic models for near-field sonic boom pressure signature predictions is evaluated. Comparisons of computational and experimental data demonstrates the capability of the method for predicting inviscid solutions useful for high speed calculations about simple 3-D geometries. The approach has promising features and results indicate potential for application to more complex configurations. The mesh generation is based on the advancing front technique, and steady state solutions of the Euler equations are achieved by explicit time integration. Spatial discretization uses the Taylor-Galerkin approach; an alternate time integration, based on the Runge-Kutta method, is also included. The solution-adaptive grid procedure is based on either remeshing or mesh refinement techniques. An alternative geometry-adaptive grid procedure has also been incorporated.

Djomehri, M. J.; Erickson, Larry L.

1993-01-01

277

Theoretical study of the O? interaction with a tetrahedral Al? cluster.  

PubMed

Employing both multireference configuration interaction (MRCI) and density functional theory (DFT) methods, we have studied the interaction of O? with a tetrahedral Al? cluster in the total spin triplet state. For a parallel to the base approach of O? facing an apex of the pyramid, the O? adsorption is hindered by a barrier. Both the MRCI and the DFT calculations show that after a small barrier, there are two local energy minima: a shallow one just above the apex atom and another deeper one below the apex atom. The latter corresponds to dissociative O? adsorption. We discuss the implications of these findings for the understanding of O? adsorption on defect sites of Al surfaces. PMID:20942497

Bacalis, N C; Metropoulos, A; Gross, A

2010-11-01

278

Evaluation of a 3D point cloud tetrahedral tomographic reconstruction method.  

PubMed

Tomographic reconstruction on an irregular grid may be superior to reconstruction on a regular grid. This is achieved through an appropriate choice of the image space model, the selection of an optimal set of points and the use of any available prior information during the reconstruction process. Accordingly, a number of reconstruction-related parameters must be optimized for best performance. In this work, a 3D point cloud tetrahedral mesh reconstruction method is evaluated for quantitative tasks. A linear image model is employed to obtain the reconstruction system matrix and five point generation strategies are studied. The evaluation is performed using the recovery coefficient, as well as voxel- and template-based estimates of bias and variance measures, computed over specific regions in the reconstructed image. A similar analysis is performed for regular grid reconstructions that use voxel basis functions. The maximum likelihood expectation maximization reconstruction algorithm is used. For the tetrahedral reconstructions, of the five point generation methods that are evaluated, three use image priors. For evaluation purposes, an object consisting of overlapping spheres with varying activity is simulated. The exact parallel projection data of this object are obtained analytically using a parallel projector, and multiple Poisson noise realizations of these exact data are generated and reconstructed using the different point generation strategies. The unconstrained nature of point placement in some of the irregular mesh-based reconstruction strategies has superior activity recovery for small, low-contrast image regions. The results show that, with an appropriately generated set of mesh points, the irregular grid reconstruction methods can out-perform reconstructions on a regular grid for mathematical phantoms, in terms of the performance measures evaluated. PMID:20736496

Pereira, N F; Sitek, A

2010-09-21

279

Evaluation of a 3D point cloud tetrahedral tomographic reconstruction method  

NASA Astrophysics Data System (ADS)

Tomographic reconstruction on an irregular grid may be superior to reconstruction on a regular grid. This is achieved through an appropriate choice of the image space model, the selection of an optimal set of points and the use of any available prior information during the reconstruction process. Accordingly, a number of reconstruction-related parameters must be optimized for best performance. In this work, a 3D point cloud tetrahedral mesh reconstruction method is evaluated for quantitative tasks. A linear image model is employed to obtain the reconstruction system matrix and five point generation strategies are studied. The evaluation is performed using the recovery coefficient, as well as voxel- and template-based estimates of bias and variance measures, computed over specific regions in the reconstructed image. A similar analysis is performed for regular grid reconstructions that use voxel basis functions. The maximum likelihood expectation maximization reconstruction algorithm is used. For the tetrahedral reconstructions, of the five point generation methods that are evaluated, three use image priors. For evaluation purposes, an object consisting of overlapping spheres with varying activity is simulated. The exact parallel projection data of this object are obtained analytically using a parallel projector, and multiple Poisson noise realizations of these exact data are generated and reconstructed using the different point generation strategies. The unconstrained nature of point placement in some of the irregular mesh-based reconstruction strategies has superior activity recovery for small, low-contrast image regions. The results show that, with an appropriately generated set of mesh points, the irregular grid reconstruction methods can out-perform reconstructions on a regular grid for mathematical phantoms, in terms of the performance measures evaluated.

Pereira, N. F.; Sitek, A.

2010-09-01

280

Microstructure and tribological performance of self-lubricating diamond/tetrahedral amorphous carbon composite film  

NASA Astrophysics Data System (ADS)

In order to smooth the rough surface and further improve the wear-resistance of coarse chemical vapor deposition diamond films, diamond/tetrahedral amorphous carbon composite films were synthesized by a two-step preparation technique including hot-filament chemical vapor deposition for polycrystalline diamond (PCD) and subsequent filtered cathodic vacuum arc growth for tetrahedral amorphous carbon (ta-C). The microstructure and tribological performance of the composite films were investigated by means of various characterization techniques. The results indicated that the composite films consisted of a thick well-grained diamond base layer with a thickness up to 150 ?m and a thin covering ta-C layer with a thickness of about 0.3 ?m, and sp 3-C fraction up to 73.93%. Deposition of a smooth ta-C film on coarse polycrystalline diamond films was proved to be an effective tool to lower the surface roughness of the polycrystalline diamond film. The wear-resistance of the diamond film was also enhanced by the self-lubricating effect of the covering ta-C film due to graphitic phase transformation. Under dry pin-on-disk wear test against Si 3N 4 ball, the friction coefficients of the composite films were much lower than that of the single PCD film. An extremely low friction coefficient (˜0.05) was achieved for the PCD/ta-C composite film. Moreover, the addition of Ti interlayer between the ta-C and the PCD layers can further reduce the surface roughness of the composite film. The main wear mechanism of the composite films was abrasive wear.

Chen, Xinchun; Peng, Zhijian; Yu, Xiang; Fu, Zhiqiang; Yue, Wen; Wang, Chengbiao

2011-02-01

281

Steady tetrahedral and cubic patterns of spherical shell convection with temperature-dependent viscosity  

NASA Astrophysics Data System (ADS)

Steady thermal convection of an infinite Prandtl number, Boussinesq fluid with temperature-dependent viscosity is systematically examined in a three-dimensional, basally heated spherical shell with isothermal and stress-free boundaries. Convective flows exhibiting cubic (l=2, m={0,4}) and tetrahedral (l=3, m=2) symmetry are generated with a finite-volume numerical model for various combinations of Rayleigh number Ra (defined with viscosity based on the average of the boundary temperatures) and viscosity contrast r? (ratio of maximum to minimum viscosities). The range of Ra for which these symmetric flows in spherical geometry can be maintained in steady state is sharply reduced by even mild viscosity variations (r?<=30), in contrast with analogous calculations in Cartesian geometry in which relatively simple, three-dimensional convective planforms remain steady for r?~104. The mild viscosity contrasts employed place some solutions marginally in the sluggish-lid transition regime in Ra-r? parameter space. Global heat transfer, given by the Nusselt number Nu, is found to obey a single power law relation with Ra when Ra is scaled by its critical value. A power law of the form Nu~(Ra/Racrit)1/4 (Racrit is the minimum critical value of Ra for the onset of convection) is obtained, in agreement with previous results for isoviscous spherical shell convection with cubic and tetrahedral symmetry. The calculations of this paper demonstrate that temperature dependent viscosity exerts a strong control on the nature of three-dimensional convection in spherical geometry, an effect that is likely to be even more important at Rayleigh numbers and viscosity contrasts more representative of the mantles of terrestrial planets. The robustness of the Nu-Ra relation, when scaled by Racrit, is important for studies of planetary thermal history that rely on parameterizations of convective heat transport and account for temperature dependence of mantle viscosity.

Ratcliff, James Todd; Schubert, Gerald; Zebib, Abdelfattah

1996-11-01

282

The possibility of measuring linear and quadratic magnetooptical effects in magnetic field under conditions of magnetomechanical resonance  

NASA Astrophysics Data System (ADS)

We have considered the possibility of measuring the linear and quadratic (in magnetic field) magnetooptical effects in magnetooptical crystals that are simultaneously exposed to a constant (polarizing) magnetic field and to an alternating magnetic field under conditions of magnetomechanical resonance. The use of a Mueller polarimeter in combination with spectral analysis of the intensity of the light wave at the output of the polarimeter makes it possible to selectively determine elements of the Mueller matrix and minimize the amount of measurements. We have shown that there is a possibility of solving the inverse problem on finding two components of the alternating magnetic field in which a magnetooptical crystal is placed.

Linchevskyi, I. V.

2013-11-01

283

Mobility of Discrete Solitons in Quadratically Nonlinear Media  

Microsoft Academic Search

We study the mobility of solitons in second-harmonic-generating lattices.\\u000aContrary to what is known for their cubic counterparts, discrete quadratic\\u000asolitons are mobile not only in the one-dimensional (1D) setting, but also in\\u000atwo dimensions (2D). We identify parametric regions where an initial kick\\u000aapplied to a soliton leads to three possible outcomes, namely, staying put,\\u000apersistent motion, or destruction.

H. Susanto; P. G. Kevrekidis; R. Carretero-Gonzalez; Boris A. Malomed; D. J. Frantzeskakis

2007-01-01

284

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

285

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

286

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

287

Discrete-time Markovian-jump linear quadratic optimal control  

NASA Technical Reports Server (NTRS)

This paper is concerned with the optimal control of discrete-time linear systems that possess randomly jumping parameters described by finite-state Markov processes. For problems having quadratic costs and perfect observations, the optimal control laws and expected costs-to-go can be precomputed from a set of coupled Riccati-like matrix difference equations. Necessary and sufficient conditions are derived for the existence of optimal constant control laws which stabilize the controlled system as the time horizon becomes infinite, with finite optimal expected cost.

Chizeck, H. J.; Willsky, A. S.; Castanon, D.

1986-01-01

288

Pulse propagation in an elastic medium with quadratic nonlinearity (L).  

PubMed

This letter examines the propagation of an acoustic pulse in an elastic medium with weak quadratic nonlinearity. Both a displacement pulse and a stress pulse of arbitrary shapes are used to generate the wave motion in the solid. By obtaining the explicit solutions for arbitrary pulse shapes, it is shown that for a sinusoidal tone-burst, in addition to a second order harmonic field, a radiation induced static strain field is also generated. These results help clarify some confusion in the recent literature regarding the shape of the propagating static displacement pulse. PMID:22423681

Qu, Jianmin; Nagy, Peter B; Jacobs, Laurence J

2012-03-01

289

Analysis of electroperforated materials using the quadrat counts method  

NASA Astrophysics Data System (ADS)

The electroperforation distribution in thin porous materials is investigated using the quadrat counts method (QCM), a classical statistical technique aimed to evaluate the deviation from complete spatial randomness (CSR). Perforations are created by means of electrical discharges generated by needle-like tungsten electrodes. The objective of perforating a thin porous material is to enhance its air permeability, a critical issue in many industrial applications involving paper, plastics, textiles, etc. Using image analysis techniques and specialized statistical software it is shown that the perforation locations follow, beyond a certain length scale, a homogeneous 2D Poisson distribution.

Miranda, E.; Garzón, C.; Martínez-Cisneros, C.; Alonso, J.; García-García, J.

2011-06-01

290

Fluctuation estimates for sub-quadratic gradient field actions  

NASA Astrophysics Data System (ADS)

In this article we estimate fluctuations of the scalar field ? for a special class of sub-quadratic actions which grow like |??|2?, 0 < ? < 1. In particular if ? = 1/2 we show that in three dimensions is bounded for ? small. For each edge (jk) we introduce an auxiliary field tjk?R to express the action as a superposition of Gaussian free fields. The effective action which arises from integrating over the Gaussian field is shown to be convex in t. The Brascamp-Lieb inequality is then applied to obtain the desired estimates on a nonuniformly elliptic Green's function.

Brydges, David; Spencer, Thomas

2012-09-01

291

A-REI A Linear and Quadratic System  

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: Consider the linear and quadratic functions appearing in the figure below. What are the coordinates of the point Q? Show step-by-step algebra work. Wha...

292

Electronic Transitions as a Probe of Tetrahedral versus Octahedral Coordination in Nickel(II) Complexes: An Undergraduate Inorganic Chemistry Experiment.  

ERIC Educational Resources Information Center

Discusses procedures, theoretical considerations, and results of an experiment involving the preparation of a tetrahedral nickel(II) complex and its transformation into an octahedral species. Suggests that fundamental aspects of coordination chemistry can be demonstrated by simple experiments performed in introductory level courses. (Author/JN)

Filgueiras, Carlos A. L.; Carazza, Fernando

1980-01-01

293

Wavefront Construction (WF) Ray Tracing in Tetrahedral Models -Application to 3-D Traveltime and Ray Path Computations.  

National Technical Information Service (NTIS)

For the purpose of building a fast and accurate tool for the computation of traveltimes and ray paths for 3-D depth imaging, we combine the techniques of tetrahedral model representation and 3-D wavefront construction (WF) ray tracing. The scheme is robus...

Z. Meng, N. Bleistein

1997-01-01

294

Nanosecond UV laser graphitization and delamination of thin tetrahedral amorphous carbon films with different sp 3\\/sp 2 content  

Microsoft Academic Search

We have produced hydrogen-free tetrahedral amorphous carbon films with different densities and Young's modulus by coating silicon with a filtered vacuum arc under different angles. The films were modified with a pulsed laser (wavelength 355nm) into sp2 rich amorphous carbon and nano crystalline carbon films. The graphitization threshold of the films depends on the film thickness as well as on

T. Roch; A. Lasagni; E. Beyer

2011-01-01

295

Sterically controlled self-assembly of tetrahedral M(6)L(4) cages via cationic N-donor ligands.  

PubMed

Tripodal cationic N-donor ligands exhibit sterically controlled self-assembly of tetrahedral M6L4 coordination cages that promote selective anion encapsulation (PF6(-) > OTf(-)) in the solid state. The described method is a potential template for stepwise assembly of hetero-ligand coordination cages and polymers. PMID:24718313

Peuronen, Anssi; Forsblom, Samu; Lahtinen, Manu

2014-05-28

296

Bond-energy force-constant relationship for bent XY2, pyramidal XY3 and tetrahedral XY4 molecules  

Microsoft Academic Search

A relation between the force constants and bond energies of polyatomic molecules of bent XY2, pyramidal XY3, and tetrahedral XY4 types has been deduced by employing an approximately separable potential function for the molecules and using specific functional forms for the bonded and nonbonded interactions. To test the validity of the relation deduced, bond energies were calculated from the available

G. Thyagarajan; C. R. Sarma; M. K. Subhedar

1969-01-01

297

An Instability Index Theory for Quadratic Pencils and Applications  

NASA Astrophysics Data System (ADS)

Primarily motivated by the stability analysis of nonlinear waves in second-order in time Hamiltonian systems, in this paper we develop an instability index theory for quadratic operator pencils acting on a Hilbert space. In an extension of the known theory for linear pencils, explicit connections are made between the number of eigenvalues of a given quadratic operator pencil with positive real parts to spectral information about the individual operators comprising the coefficients of the spectral parameter in the pencil. As an application, we apply the general theory developed here to yield spectral and nonlinear stability/instability results for abstract second-order in time wave equations. More specifically, we consider the problem of the existence and stability of spatially periodic waves for the "good" Boussinesq equation. In the analysis our instability index theory provides an explicit, and somewhat surprising, connection between the stability of a given periodic traveling wave solution of the "good" Boussinesq equation and the stability of the same periodic profile, but with different wavespeed, in the nonlinear dynamics of a related generalized Korteweg-de Vries equation.

Bronski, Jared; Johnson, Mathew A.; Kapitula, Todd

2014-04-01

298

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

299

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

300

Half-quadratic based Iterative Minimization for Robust Sparse Representation.  

PubMed

Robust sparse representation has shown significant potential in solving challenging problems in computer vision such as biometrics and visual surveillance. Although several robust sparse models have been proposed and promising results have been obtained, they are either for error correction or for error detection, and learning a general framework that systematically unifies these two aspects and explore their relation is still an open problem. In this paper, we develop a half-quadratic (HQ) framework to solve the robust sparse representation problem. By defining different kinds of half-quadratic functions, the proposed HQ framework is applicable to performing both error correction and error detection. More specifically, by using the additive form of HQ, we propose an L1-regularized error correction method by iteratively recovering corrupted data from errors incurred by noises and outliers; by using the multiplicative form of HQ, we propose an L1-regularized error detection method by learning from uncorrupted data iteratively. We also show that the L1-regularization solved by soft-thresholding function has a dual relationship to Huber M-estimator, which theoretically guarantees the performance of robust sparse representation in terms of M-estimation. Experiments on robust face recognition under severe occlusion and corruption validate our framework and findings. PMID:23712994

He, Ran; Zheng, Wei-Shi; Tan, Tieniu; Sun, Zhenan

2013-05-21

301

Frictionless contact-detachment analysis: iterative linear complementarity and quadratic programming approaches  

NASA Astrophysics Data System (ADS)

The object of the paper concerns a consistent formulation of the classical Signorini's theory regarding the frictionless contact problem between two elastic bodies in the hypothesis of small displacements and strains. The employment of the symmetric Galerkin boundary element method, based on boundary discrete quantities, makes it possible to distinguish two different boundary types, one in contact as the zone of potential detachment, called the real boundary, the other detached as the zone of potential contact, called the virtual boundary. The contact-detachment problem is decomposed into two sub-problems: one is purely elastic, the other regards the contact condition. Following this methodology, the contact problem, dealt with using the symmetric boundary element method, is characterized by symmetry and in sign definiteness of the matrix coefficients, thus admitting a unique solution. The solution of the frictionless contact-detachment problem can be obtained: (i) through an iterative analysis by a strategy based on a linear complementarity problem by using boundary nodal quantities as check quantities in the zones of potential contact or detachment; (ii) through a quadratic programming problem, based on a boundary min-max principle for elastic solids, expressed in terms of nodal relative displacements of the virtual boundary and nodal forces of the real one.

Salerno, M.; Terravecchia, S.; Zito, L.

2013-04-01

302

Rays of Small Integer Solutions of Homogeneous Ternary Quadratic Equations  

NASA Astrophysics Data System (ADS)

We have dealt with the general ternary quadratic equation: ax2 + by^ {2} + cz2 + dxy + exz + fyz = 0 with integer coefficients. After giving a matrix-reduction formula for a quadratic equation in any number of variables, of which the reduction of the above ternary equation is an easy consequence, we have devoted our attention to the reduced equation: ax^ {2} + by2 + cz^{2 } = 0. We have devised an algorithm for reducing Dirichlet's possibly larger solutions to this prescribed range of Holzer's. Then we have generalized Holzer's theorem to the case of the ternary equation: ax^{2 } + by2 + cz2 + dxy + exz + fyz = 0, giving in this context a new range called the CM-range, of which the Holzer's range is a particular case when d = e = f = 0. We have described an algorithm for getting a solution of the general ternary within this CM-range. After that we have devised an algorithm for getting all the solutions of the Legendre's equation ax 2 + by2 + cz^ {2} = 0 within the Holzer's range--and have shown that if we regard this Legendre's equation as a double cone, these solutions within the Holzer's range lie along some definite rays, here called the CM-rays, which are completely determined by the prime factors of the coefficients a, b and c. After giving an algorithm for detecting these CM-rays of the reduced equation: ax^2 + by^2 + cz^2 = 0, we have shown how one can produce some similar rays of solutions of the above general ternary quadratic equation: ax2 + by2 + cz2 + dxy + exz + fyz = 0. Note that apart from the method of exhausting all the possibilities, so far there has been no precisely stated algorithm to find the minimum solutions of the above ternary equations. Towards the end, observing in the context of our main result an inequality involving two functions, namely C and PCM from doubz_sp{*} {3} to doubz_+, and simultaneously presenting some tables of these positive CM-rays or PCM-rays lying in the positive octant, we have concluded this work with a number of hints for some possible future investigations. (Abstract shortened with permission of author.).

Mishra, Sudhakara

1991-02-01

303

The reversible macrocyclization of Tyrocidine A aldehyde: a hemiaminal reminiscent of the tetrahedral intermediate of macrolactamization.  

PubMed

In spite of the important role of peptide macrocyclizations for the generation of conformationally constrained biological ligands, our knowledge of factors that determine the inclination of a substrate to cyclize is low. Therefore, methods that give access to the thermodynamic characterization of these processes are desirable. In this work, we present the isosteric substitution of the amide ligation site of a cyclopeptide by an imine. Applied to the decapeptide antibiotic Tyrocidine A (TycA), the reversible cyclization of the linear aldehyde TycA-CHO resulted in the unexpectedly stable hemiaminal Psi[CH(OH)NH]-TycA, which is equivalent to the tetrahedral intermediate of macrolactamization, and which is observed for the first time in a peptidic structure. On the basis of NMR spectroscopy and molecular modeling, we discuss the observed high stereoselectivity of hemiaminal formation, as well as its reluctance to be dehydrated to the imine. As required for thermodynamic analysis, it is possible to establish a pH- and temperature-dependent cyclization equilibrium, which allows determination of the entropy loss of the peptide chain, and quantification of the extent of preorientation of the cyclization precursor. PMID:20090972

Enck, Sebastian; Kopp, Florian; Marahiel, Mohamed A; Geyer, Armin

2010-02-01

304

Isosurface Computation Made Simple: Hardware acceleration,Adaptive Refinement and tetrahedral Stripping  

SciTech Connect

This paper presents a simple approach for rendering isosurfaces of a scalar field. Using the vertex programming capability of commodity graphics cards, we transfer the cost of computing an isosurface from the Central Processing Unit (CPU), running the main application, to the Graphics Processing Unit (GPU), rendering the images. We consider a tetrahedral decomposition of the domain and draw one quadrangle (quad) primitive per tetrahedron. A vertex program transforms the quad into the piece of isosurface within the tetrahedron (see Figure 2). In this way, the main application is only devoted to streaming the vertices of the tetrahedra from main memory to the graphics card. For adaptively refined rectilinear grids, the optimization of this streaming process leads to the definition of a new 3D space-filling curve, which generalizes the 2D Sierpinski curve used for efficient rendering of triangulated terrains. We maintain the simplicity of the scheme when constructing view-dependent adaptive refinements of the domain mesh. In particular, we guarantee the absence of T-junctions by satisfying local bounds in our nested error basis. The expensive stage of fixing cracks in the mesh is completely avoided. We discuss practical tradeoffs in the distribution of the workload between the application and the graphics hardware. With current GPU's it is convenient to perform certain computations on the main CPU. Beyond the performance considerations that will change with the new generations of GPU's this approach has the major advantage of avoiding completely the storage in memory of the isosurface vertices and triangles.

Pascucci, V

2004-02-18

305

Surface sites and unrelaxed surface energies of tetrahedral silica polymorphs and silicate  

NASA Astrophysics Data System (ADS)

Surface properties of respirable silica, which represents a major occupational safety concern, were investigated computationally, and a model for quantitative characterization of crystalline silica surface sites was developed. It was found that the surface energy of crystalline solids, such as silica and silicates, can be calculated as a product of the surface site density and site energy. The energies of sites formed by faceting tetrahedral silica polymorphs and aluminosilicate were determined by parametric fitting ab initio surface energies to site densities. Boltzmann's statistics was used to describe the distribution of faces as an exponential function of unrelaxed surface energy in the comminuted crystalline solids. Using these findings, crystallographic face distributions on fractured quartz, coesite, tridymite, and cristobalite were derived and average silanol hydroxyl densities in fractured particulate of these materials were estimated as 0.070, 0.059, 0.058, and 0.055 Å -2, respectively. The proposed method of quantitative characterization of the surface bridges the gap between microscopic simulations and measurable observables, such as cytotoxicity of respirable silica.

Murashov, Vladimir V.; Demchuk, Eugene

2005-12-01

306

TiO2 Surface Defects with the Tetrahedral Cationic Coordination  

NASA Astrophysics Data System (ADS)

Titanium dioxide is one of the most extensively investigated transition metal oxide. It has well-known applications in catalytically converting toxic organic and inorganic materials to benign products, as well as turning solar energy into a chemical. In these processes, it is believed that surface defects with lower coordination and/or stoichiometry play crucial roles. Our study of a (22 x2) R45 reconstructed TiO2(001) using scanning tunneling microscopy and density functional theory reveals that the basic building blocks of the reconstruction can be modeled as fully stoichiometric nanocluster defects. As in the bulk-terminated (001) surface, the atoms in the nanocluster are under-coordinated, for example, 4-coordinated Ti, 1-coordinated, and 2-coordinated O atoms. However, the absence of neighboring atoms drives the nanocluster to relax into a structure, which possesses tetrahedrally coordinated Ti atoms. This result will be compared and discussed with the reported nanocluster defects on TiO2(110).

Park, Ken; Meunier, Vincent; Hsin Yu, Nan; Plummer, Ward

2013-03-01

307

Collision-induced absorption in mixtures of symmetrical linear and tetrahedral molecules - Methane-nitrogen  

NASA Technical Reports Server (NTRS)

The far infrared absorption of a CH4-N2 mixture was measured at 297, 195, and 162 K from 30 to 650/cm. The spectral invariants gamma1 and alpha1, proportional, respectively, to the zeroth and first spectral moments, due to bimolecular collisions between CH4 and N2 were obtained from these data and compared with theoretical values. The theory for collision-induced dipoles between a tetrahedral and a diatomic or symmetrical linear molecule includes contributions not previously considered. Whereas the theoretical values of gamma1 are only somewhat greater than experiment at all temperatures, the theoretical values of alpha1 are significantly lower than the experimental values. From the theoretical spectral moments for the various induced dipole components, the parameters of the BC shape were computed, and theoretical spectra were constructed. Good agreement was obtained at the lower frequencies, but with increasing frequencies the theoretical spectra were increasingly less intense than the experimental spectra. Although the accuracy of the theoretical results may suffer from the lack of a reliable potential function, it does not appear that this high frequency discrepancy can be removed by any conceivable modification in the potential.

Birnbaum, G.; Borysow, A.; Buechele, A.

1993-01-01

308

Studying the growth of cubic boron nitride on amorphous tetrahedral carbon interlayers.  

PubMed

The growth of cubic boron nitride (cBN) films on bare silicon and amorphous tetrahedral carbon (ta-C) layers prepared on silicon substrates was studied. The cBN films were prepared by radio frequency magnetron sputter deposition at approximately 870 degrees C. The original ta-C interlayers were graphitized and restructured under high temperature and possibly under ion bombardment during BN deposition. The majority of graphitic basal planes were nearly perpendicular to the surface of silicon substrates. The BN films grown on these restructured carbon layers were deposited with higher content of cubic phase and did not show delamination signs. Turbostratic BN (tBN) basal planes extended carbon basal planes and their edges served as cBN nucleation sites. The cBN films grown on textured ta-C interlayers were insensitive to the ambient environment. The residual sp(3)-bonded carbon phase confined in the interlayers probably acts as a diffusion barrier preventing the oxidation of dangling bonds near BN interface and thus precludes weakening the interface as a result of volume expansion. The carbon interlayers also improve the crystallinity of the oriented tBN because they are continuation of carbon graphitic basal planes so that the volume fraction of nitrogen-void (N-void) defects in the sp(2)-bonded BN intermediate layers is reduced. The strong sp(3)-bonded carbon matrix could thereto withstand large compressive stress and facilitates deposition of thicker cBN films. PMID:16853068

Leung, Kar Man; Chan, Chit Yiu; Chong, Yat Ming; Yao, Yuen; Ma, Kwok Leung; Bello, Igor; Zhang, Wen Jun; Lee, Shuit Tong

2005-09-01

309

Zintl-phase compounds with SnSb4 tetrahedral anions: electronic structure and thermoelectric properties  

SciTech Connect

We report the investigation of Zintl-phase Na(K){sub 8}SnSb{sub 4} and related compounds that contain SnSb{sub 4} tetrahedral anions using first principles electronic structure, Boltzmann transport, and density functional phonon calculations. We find that these compounds are narrow-gap semiconductors and there is a combination of heavy and light bands at valence band edge, which may lead to a combination of high thermopower and reasonable conductivity. High values of the thermopower are found for p-type doping within the Boltzmann transport theory. Furthermore, these materials are expected to have low thermal conductivity due to their structures that consist of a network of weakly coupled SnSb{sub 4} clusters, which leads to low phonon frequencies. In particular, we find low-frequency optical phonons that should effectively scatter the heat-carrying acoustic phonons. These results are discussed in terms of the structure, which consists of anionic clusters. Based on the results, it is suggested that such compounds may represent a useful paradigm for finding new thermoelectric materials.

Zhang, Lijun [ORNL; Du, Mao-Hua [ORNL; Singh, David J [ORNL

2010-01-01

310

Zintl-phase compounds with SnSb4 tetrahedral anions: Electronic structure and thermoelectric properties  

SciTech Connect

We report the investigation of Zintl-phase Na(K){sub 8}SnSb{sub 4} and related compounds that contain SnSb{sub 4} tetrahedral anions using first principles electronic structure, Boltzmann transport, and density functional phonon calculations. We find that these compounds are narrow-gap semiconductors and there is a combination of heavy and light bands at valence band edge, which may lead to a combination of high thermopower and reasonable conductivity. High values of the thermopower are found for p-type doping within the Boltzmann transport theory. Furthermore, these materials are expected to have low thermal conductivity due to their structures that consist of a network of weakly coupled SnSb{sub 4} clusters, which leads to low phonon frequencies. In particular, we find low-frequency optical phonons that should effectively scatter the heat-carrying acoustic phonons. These results are discussed in terms of the structure, which consists of anionic clusters. Based on the results, it is suggested that such compounds may represent a useful paradigm for finding new thermoelectric materials.

Zhang, Lijun; Du, Mao-Hua; Singh, David J.

2010-01-01

311

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

SciTech Connect

Aminopeptidases are key enzymes involved in the regulation of signaling peptide activity. Here, we present a detailed biochemical and structural analysis of an evolutionary highly conserved aspartyl aminopeptidase called DNPEP. We show that this peptidase can cleave multiple physiologically relevant substrates, including angiotensins, and thus may play a key role in regulating neuron function. Using a combination of x-ray crystallography, x-ray absorption spectroscopy, and single particle electron microscopy analysis, we provide the first detailed structural analysis of DNPEP. We show that this enzyme possesses a binuclear zinc-active site in which one of the zinc ions is readily exchangeable with other divalent cations such as manganese, which strongly stimulates the enzymatic activity of the protein. The plasticity of this metal-binding site suggests a mechanism for regulation of DNPEP activity. We also demonstrate that DNPEP assembles into a functionally relevant tetrahedral complex that restricts access of peptide substrates to the active site. These structural data allow rationalization of the enzyme's preference for short peptide substrates with N-terminal acidic residues. This study provides a structural basis for understanding the physiology and bioinorganic chemistry of DNPEP and other M18 family aminopeptidases.

Chen, Yuanyuan; Farquhar, Erik R.; Chance, Mark R.; Palczewski, Krzysztof; Kiser, Philip D. (Case Western)

2012-07-11

312

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.

Raimunda, Daniel; Subramanian, Poorna; Stemmler, Timothy; Arguello, Jose M.

2012-01-01

313

Inhibition of human folylpolyglutamate synthetase by diastereomeric phosphinic acid mimics of the tetrahedral intermediate  

PubMed Central

Phosphorus-containing pseudopeptides, racemic at the C-terminal ?-carbon, are potent mechanism-based inhibitors of folylpolyglutamate synthetase (FPGS). They are mimics of the tetrahedral intermediate postulated to form during FPGS-catalyzed biosynthesis of poly(?-L-glutamates). In the present paper, the FPGS inhibitory activity of each diastereomer coupled to three heterocycles is reported. The high Rf pseudopeptide containing the 5,10-dideazatetrahydropteroyl (DDAH4Pte) heterocycle is most potent (Kis = 1.7 nM). While the heterocyclic portion affects absolute FPGS inhibitory potency, the high Rf species is more potent in each pair containing the same heterocycle. This species presumably has the same stereochemistry as the natural folate polyglutamate, i.e., (L-Glu-?-L-Glu). Unexpectedly, the low Rf (presumed L-Glu-?-D-Glu) species are only slightly less potent (<30-fold) less potent than their diastereomers. Further study of this phenomenon comparing L-Glu-?-L-Glu and L-Glu-?-D-Glu dipeptide-containing FPGS substrates shows that <1% contamination of commercial D-Glu precursors by L-Glu may give misleading information if L-Glu-?-L-Glu substrates have low Km values.

McGuire, John J.; Bartley, David M.; Tomsho, John W.; Haile, William H.; Coward, James K.

2009-01-01

314

Dynamics in a tetrahedral network glassformer: Vibrations, network rearrangements, and diffusion  

NASA Astrophysics Data System (ADS)

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.

Kawasaki, Takeshi; Kim, Kang; Onuki, Akira

2014-05-01

315

Temperature dependence of the barrier at the tetrahedral amorphous carbon-silicon interface  

NASA Astrophysics Data System (ADS)

Tetrahedral amorphous carbon film (ta-C, rich in sp3 bonds), 50 nm thick, was deposited by magnetron sputtering on n-type Si substrate at room temperature. Ohmic contact to the ta-C film was formed by depositing stoichiometric titanium nitride (TiN) by magnetron sputtering or aluminum (Al) by electron-gun evaporation at room temperature. The capacitance-voltage characteristics at different temperatures show negligible hysteresis, indicating low concentration of mobile charges. Electrical conduction in the TiN (Al)/ta-C/n-Si structure, with the TiN or Al biased positively with respect to Si, was investigated in the temperature range 80-300 K. Under high-field conditions, the electrical conduction is consistent with thermally assisted Fowler-Nordheim tunnelling of electrons from the Si substrate into the ta-C film for temperatures for 80-260 K and trap-assisted band-to-band indirect tunnelling for higher temperatures. Under low-field conditions, Poole-Frenkel emission dominates over tunnelling for temperatures even well below room temperature. The temperature dependence of the tunnelling current was explained in terms of the change in the effective barrier height at the ta-C/n-Si interface.

Hastas, N. A.; Dimitriadis, C. A.; Logothetidis, S.; Angelis, C. T.; Konofaos, N.; Evangelou, E. K.

2001-06-01

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

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

319

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

320

Dislocation parity effects in crystals with quadratic nonlinear response.  

PubMed

The effect of edge topological dislocations on the phase matching spectrum of quadratic nonlinear photonic crystals was studied theoretically and experimentally. We have found that the parity of the dislocation's topological charge governs the transfer of energy between an input wave and its second harmonic. A dislocation with an odd topological charge nulls the efficiency of the otherwise optimal phase matched wavelength, whereas high conversion is now achieved at new wavelengths that exhibited low efficiency without the dislocation. However, when the topological charge is an even number, the dislocation has a negligible effect on the efficiency curve. This effect is observed in periodically poled crystals having a single peak in the phase matching spectrum, as well as in phase-reversed and quasiperiodic nonlinear photonic crystals that are characterized by multiple efficiency peaks, where a dimple is imprinted on each spectral peak. PMID:24580591

Sharabi, Shani; Voloch-Bloch, Noa; Juwiler, Irit; Arie, Ady

2014-02-01

321

A Fixed-Point Iteration Method with Quadratic Convergence  

SciTech Connect

The fixed-point iteration algorithm is turned into a quadratically convergent scheme for a system of nonlinear equations. Most of the usual methods for obtaining the roots of a system of nonlinear equations rely on expanding the equation system about the roots in a Taylor series, and neglecting the higher order terms. Rearrangement of the resulting truncated system then results in the usual Newton-Raphson and Halley type approximations. In this paper the introduction of unit root functions avoids the direct expansion of the nonlinear system about the root, and relies, instead, on approximations which enable the unit root functions to considerably widen the radius of convergence of the iteration method. Methods for obtaining higher order rates of convergence and larger radii of convergence are discussed.

Walker, Kevin P. [Engineering Science Software, Inc.; Sham, Sam [ORNL

2012-01-01

322

Criteria for correction of quadratic field-dependent aberrations.  

PubMed

Aberrations of imaging systems can be described by using a polynomial expansion of the dependence on field position, or the off-axis distance of a point object. On-axis, or zero-order, aberrations can be calculated directly. It is well-known that aberrations with linear field dependence can be calculated and controlled by using the Abbe sine condition, which evaluates only on-axis behavior. We present a new set of relationships that fully describe the aberrations that depend on the second power of the field. A simple set of equations is derived by using Hamilton's characteristic functions and simplified by evaluating astigmatism in the pupil. The equations, which we call the pupil astigmatism criteria, use on-axis behavior to evaluate and control all aberrations with quadratic dependence on the field and arbitrary dependence on the pupil. These relations are explained and are validated by using several specific optical designs. PMID:12413132

Zhao, Chunyu; Burge, James H

2002-11-01

323

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

324

Wind turbine power tracking using an improved multimodel quadratic approach.  

PubMed

In this paper, an improved multimodel optimal quadratic control structure for variable speed, pitch regulated wind turbines (operating at high wind speeds) is proposed in order to integrate high levels of wind power to actively provide a primary reserve for frequency control. On the basis of the nonlinear model of the studied plant, and taking into account the wind speed fluctuations, and the electrical power variation, a multimodel linear description is derived for the wind turbine, and is used for the synthesis of an optimal control law involving a state feedback, an integral action and an output reference model. This new control structure allows a rapid transition of the wind turbine generated power between different desired set values. This electrical power tracking is ensured with a high-performance behavior for all other state variables: turbine and generator rotational speeds and mechanical shaft torque; and smooth and adequate evolution of the control variables. PMID:20434153

Khezami, Nadhira; Benhadj Braiek, Naceur; Guillaud, Xavier

2010-07-01

325

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

326

Spectroscopy of one-dimensionally inhomogeneous media with quadratic nonlinearity  

SciTech Connect

We present a brief review of the results of fifty years of development efforts in spectroscopy of one-dimensionally inhomogeneous media with quadratic nonlinearity. The recent original results obtained by the authors show the fundamental possibility of determining, from experimental data, the coordinate dependences of complex quadratic susceptibility tensor components of a onedimensionally inhomogeneous (along the z axis) medium with an arbitrary frequency dispersion, if the linear dielectric properties of the medium also vary along the z axis and are described by a diagonal tensor of the linear dielectric constant. It is assumed that the medium in question has the form of a plane-parallel plate, whose surfaces are perpendicular to the direction of the inhomogeneity. Using the example of several components of the tensors X{sup (2)}(z, {omega}{sub 1} {+-} {omega}{sub 2}; {omega}{sub 1}, {+-} {omega}{sub 2}), we describe two methods for finding their spatial profiles, which differ in the interaction geometry of plane monochromatic fundamental waves with frequencies {omega}{sub 1} and {omega}{sub 2}. The both methods are based on assessing the intensity of the waves propagating from the plate at the sum or difference frequency and require measurements over a range of angles of incidence of the fundamental waves. Such measurements include two series of additional estimates of the intensities of the waves generated under special conditions by using the test and additional reference plates, which eliminates the need for complicated phase measurements of the complex amplitudes of the waves at the sum (difference) frequency.

Golubkov, A A; Makarov, Vladimir A

2011-11-30

327

3D Finite Element Meshing from Imaging Data ?  

PubMed Central

This paper describes an algorithm to extract adaptive and quality 3D meshes directly from volumetric imaging data. The extracted tetrahedral and hexahedral meshes are extensively used in the Finite Element Method (FEM). A top-down octree subdivision coupled with the dual contouring method is used to rapidly extract adaptive 3D finite element meshes with correct topology from volumetric imaging data. The edge contraction and smoothing methods are used to improve the mesh quality. The main contribution is extending the dual contouring method to crack-free interval volume 3D meshing with feature sensitive adaptation. Compared to other tetrahedral extraction methods from imaging data, our method generates adaptive and quality 3D meshes without introducing any hanging nodes. The algorithm has been successfully applied to constructing the geometric model of a biomolecule in finite element calculations.

Zhang, Yongjie; Bajaj, Chandrajit; Sohn, Bong-Soo

2009-01-01

328

Tetrahedral magnetic order and the metal-insulator transition in the pyrochlore lattice of Cd2Os2O7.  

PubMed

Cd2Os2O7 shows a peculiar metal-insulator transition at 227 K with magnetic ordering in a frustrated pyrochlore lattice, but its magnetic structure in the ordered state and the transition origin are yet uncovered. We observed a commensurate magnetic peak by resonant x-ray scattering in a high-quality single crystal. X-ray diffraction and Raman scattering experiments confirmed that the transition is not accompanied with any spatial symmetry breaking. We propose a noncollinear all-in-all-out spin arrangement on the tetrahedral network made of Os atoms. Based on this we suggest that the transition is not caused by the Slater mechanism as believed earlier but by an alternative mechanism related to the formation of the specific tetrahedral magnetic order on the pyrochlore lattice in the presence of strong spin-orbit interactions. PMID:23004317

Yamaura, J; Ohgushi, K; Ohsumi, H; Hasegawa, T; Yamauchi, I; Sugimoto, K; Takeshita, S; Tokuda, A; Takata, M; Udagawa, M; Takigawa, M; Harima, H; Arima, T; Hiroi, Z

2012-06-15

329

Study of intercalated Ti atom in tetrahedral or octahedral sites of titanium disulfide (001) surfaces: Theoretical scanning tunneling microscopy images  

Microsoft Academic Search

We have performed ab initio linear combination of atomic orbitals-density functional theory calculations on biperiodic supercells to model the electronic and geometrical involvements of Ti intercalated atom in either octahedral or tetrahedral sites of the (001) TiS2 surfaces. For each type of defect, both the relaxed atomic structure and the electronic properties of the defect states were carefully analyzed. For

E. Amzallag; I. Baraille; H. Martinez; M. Rérat; D. Gonbeau

2008-01-01

330

The origins of tetrahedral coordination in molten and glassy ZnCl2 and other group-2B metal dihalides  

NASA Astrophysics Data System (ADS)

We report the results of first-principles calculations carried out within a relativistic density-functional method, on the molecular trimers of the MX2 compounds (with M = Zn or Cd and X = Cl, Br, or I), showing how a distorted tetrahedral coordination of a group-2B metal atom by halogens first arises. The trimers of HgX2 are also discussed, both in unstable and in stable configurations.

Özen, A. S.; Akdeniz, Z.; Ruberto, R.; Pastore, G.; Tosi, M. P.

2014-01-01

331

An application of evolutionary computations to economic load dispatch with piecewise quadratic cost functions  

Microsoft Academic Search

Presents evolutionary computations to solve the problems of economic load dispatch (ELD) with single quadratic cost functions and piecewise quadratic cost functions. Genetic algorithms (GAs), evolutionary programming (EP) and evolution strategies (ESs) are applied to the ELD problems. To improve these methods in nonlinear optimization problems, two hybrid optimization methods exploiting the advantages of each evolutionary computation are developed. Optimization

J. H. Park; S. O. Yang; K. J. Mun; H. S. Lee; J. W. Jung

1998-01-01

332

A Quadratic Curve Equating Method to Equate the First Three Moments in Equipercentile Equating  

Microsoft Academic Search

A quadratic curve test equating method for equating different test forms under a random-groups data collec tion design is proposed. This new method extends the linear equating method by adding a quadratic term to the linear function and equating the first three central moments (mean, standard deviation, and skewness) of the test forms. Procedures for implementing the method and related

Tianyou Wang; Michael J. Kolen

1996-01-01

333

Band narrowing and susceptibility enhancement by a quadratic electron-phonon interaction  

Microsoft Academic Search

It is shown that a quadratic electron-phonon interaction leads, under certain conditions, to temperature-dependent band narrowing and an inverse lifetime quadratic in the phonon occupation numbers. These explain the prominent metallic properties of organic metals of the TTF-TCNQ family, in particular the enhancement of the magnetic susceptibility.

O. Entin-Wohlman; H. Gutfreund; M. Weger

1985-01-01

334

Minimum-Energy Redundancy Resolution of Robot Manipulators Unified by Quadratic Programming and its Online Solution  

Microsoft Academic Search

This paper presents the latest result regarding the unification of minimum-energy redundancy resolution of robot manipulators via a quadratic program. The presented quadratic programming (QP) formulation is general in the sense that it incorporates equality, inequality and bound constraints, simultaneously. This QP formulation covers the online avoidance of joint physical limits and environmental obstacles, as well as the optimization of

Yunong Zhang; Shugen Mai

2007-01-01

335

Class groups of quadratic fields of 3-rank at least 2: Effective bounds  

Microsoft Academic Search

In this paper, we give parametric families of both real and complex quadratic number fields whose class group has 3-rank at least 2. As a consequence, we obtain that for all large positive real numbers x, the number of both real and complex quadratic fields whose class group has 3-rank at least 2 and absolute value of the discriminant ?x

Florian Luca; Allison M. Pacelli

2008-01-01

336

Geometrical Solutions of Some Quadratic Equations with Non-Real Roots  

ERIC Educational Resources Information Center

This note gives geometrical/graphical methods of finding solutions of the quadratic equation ax[squared] + bx + c = 0, a [not equal to] 0, with non-real roots. Three different cases which give rise to non-real roots of the quadratic equation have been discussed. In case I a geometrical construction and its proof for finding the solutions of the…

Pathak, H. K.; Grewal, A. S.

2002-01-01

337

Quadratic Correlation Filter Design Methodology for Target Detection and Surveillance Applications  

Microsoft Academic Search

A novel method is presented for optimization of quadratic correlation filters (QCFs) for shift-invariant target detection in imagery. The QCFs are quadratic classifiers that operate directly on the image data without feature extraction or segmentation. In this sense, the QCFs retain the main advantages of conventional linear correlation filters while offering significant improvements in other respects. For example, multiple correlators

Abhijit Mahalanobis; Robert R. Muise; S. Robert Stanfill

2004-01-01

338

ON THE QUADRATE OF SINRAPTOR DONGI (THEROPODA: ALLOSAUROIDEA) FROM THE LATE JURASSIC OF CHINA  

Microsoft Academic Search

1 Abstract: When Sinraptor dongi was described in 1993, the quadrate was illustrated but not described. The omission of the description of this bone was unfortunate in that there is a lot of information about the quadrate that would be useful in the phylogenetic analysis of this important animal.

Philip J. CURRIE

339

A recipe for semidefinite relaxation for (0,1)-quadratic programming  

Microsoft Academic Search

We review various relaxations of (0,1)-quadratic programming problems. These include semidefinite programs, parametric trust region problems and concave quadratic maximization. All relaxations that we consider lead to efficiently solvable problems. The main contributions of the paper are the following. Using Lagrangian duality, we prove equivalence of the relaxations in a unified and simple way. Some of these equivalences have been

S. Poljak; F. Rendl; H. Wolkowicz

1995-01-01

340

Matlab code for Nash feedback equilibrium of a linear quadratic dynamic game  

Microsoft Academic Search

This program computes the Nash feedback equilibrium of a linear quadratic dynamic game. Each of two players solves a linear quadratic optimization problem, taking as given and known the sequence of linear feedback rules used by his opponent. The particular game analyzed is a price-quantity setting game suggested by Ken Judd.

Thomas Sargent

341

Computing Exact Rational Offsets of Quadratic Triangular B´ ezier Surface Patches  

Microsoft Academic Search

The offset surfaces to non-developable quadratic triangular Bezier patches are rational surfaces. In this paper we give a direct proof of this result and formulate an algorithm for computing the parameteriza- tion of the offsets. Based on the observation that quadratic triangular patches are capable of producing C1 smooth surfaces, we use this algo- rithm to generate rational approximations to

Bohum ´ ir Bastl; Bert Juttler; Jir ´ i Kosinka; Miroslav Lavicka

342

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

343

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

344

Octahedral-tetrahedral equilibrium and solvent exchange of cobalt(II) ions in primary alkylamines.  

PubMed

The enthalpy differences (Delta H degrees ) of the equilibrium between the octahedral and tetrahedral solvated cobalt(II) complexes were obtained in some primary alkylamines such as propylamine (pa, 36.1 +/- 2.3 kJ mol(-1)), n-hexylamine (ha, 34.9 +/- 1.0 kJ mol(-1)), 2-methoxyethylamine (meea, 44.8 +/- 3.1 kJ mol(-1)), and benzylamine (ba, 50.1 +/- 3.6 kJ mol(-1)) by the spectrophotometric method. The differences in the energy levels between the two geometries of the cobalt(II) complexes in the spherically symmetric field (Delta E(spher)) were estimated from the values of Delta H degrees by offsetting the ligand field stabilization energies. It was indicated that the value of Delta E(spher) is the decisive factor in determining the value of Delta H degrees and is largely dependent on the electronic repulsion between the d-electrons and the donor atoms and the interelectronic repulsion in the d orbitals. The comparison between activation enthalpies (Delta H(++)) for the solvent exchange reactions of octahedral cobalt(II) ions in pa and meea revealed that the unexpectedly large rate constant and small Delta H(++) in pa are attributed to the strong electronic repulsion in the ground state and removal of the electronic repulsion in the dissociative transition state, which can give the small Delta E(spher) between the ground and transition states. Differences in the solvent exchange rates and the DeltaH(++) values of the octahedral metal(II) ions in some other solvents are discussed in connection with the electronic repulsive factors. PMID:12184774

Aizawa, Sen-ichi; Funahashi, Shigenobu

2002-08-26

345

Simple shearing flow of dry soap foams with tetrahedrally close-packed structure  

SciTech Connect

The microrheology of dry soap foams subjected to quasistatic, simple shearing flow 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 using the Surface Evolver to calculate foam structures that minimize total surface area at each value of strain. 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 structure associated with each stable solution branch results from an avalanche 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. (c) 2000 Society of Rheology.

Reinelt, Douglas A. [Department of Mathematics, Southern Methodist University, Dallas, Texas 75275-0156 (United States)] [Department of Mathematics, Southern Methodist University, Dallas, Texas 75275-0156 (United States); Kraynik, Andrew M. [Engineering Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico 87185-0834 (United States)] [Engineering Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico 87185-0834 (United States)

2000-05-01

346

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

PubMed

The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values of 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-centered-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-centered-cubic crystal becomes more stable than the body-centered-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-centered-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centered-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-centered-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. PMID:20572725

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

2010-06-21

347

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

NASA Astrophysics Data System (ADS)

The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values of 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-centered-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-centered-cubic crystal becomes more stable than the body-centered-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-centered-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centered-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-centered-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.

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

2010-06-01

348

AESOP- INTERACTIVE DESIGN OF LINEAR QUADRATIC REGULATORS AND KALMAN FILTERS  

NASA Technical Reports Server (NTRS)

AESOP was developed to solve a number of problems associated with the design of controls and state estimators for linear time-invariant systems. The systems considered are modeled in state-variable form by a set of linear differential and algebraic equations with constant coefficients. Two key problems solved by AESOP are the linear quadratic regulator (LQR) design problem and the steady-state Kalman filter design problem. AESOP is designed to be used in an interactive manner. The user can solve design problems and analyze the solutions in a single interactive session. Both numerical and graphical information are available to the user during the session. The AESOP program is structured around a list of predefined functions. Each function performs a single computation associated with control, estimation, or system response determination. AESOP contains over sixty functions and permits the easy inclusion of user defined functions. The user accesses these functions either by inputting a list of desired functions in the order they are to be performed, or by specifying a single function to be performed. The latter case is used when the choice of function and function order depends on the results of previous functions. The available AESOP functions are divided into several general areas including: 1) program control, 2) matrix input and revision, 3) matrix formation, 4) open-loop system analysis, 5) frequency response, 6) transient response, 7) transient function zeros, 8) LQR and Kalman filter design, 9) eigenvalues and eigenvectors, 10) covariances, and 11) user-defined functions. The most important functions are those that design linear quadratic regulators and Kalman filters. The user interacts with AESOP when using these functions by inputting design weighting parameters and by viewing displays of designed system response. Support functions obtain system transient and frequency responses, transfer functions, and covariance matrices. AESOP can also provide the user with open-loop system information including stability, controllability, and observability. The AESOP program is written in FORTRAN IV for interactive execution and has been implemented on an IBM 3033 computer using TSS 370. As currently configured, AESOP has a central memory requirement of approximately 2 Megs of 8 bit bytes. Memory requirements can be reduced by redimensioning arrays in the AESOP program. Graphical output requires adaptation of the AESOP plot routines to whatever device is available. The AESOP program was developed in 1984.

Lehtinen, B.

1994-01-01

349

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

350

A coupled edge-\\/face-based smoothed finite element method for structural–acoustic problems  

Microsoft Academic Search

The edge-based smoothed finite element method (ES-FEM) and the face-based smoothed finite element method (FS-FEM) developed recently have shown great efficiency in solving solid mechanics problems with triangular and tetrahedral meshes. In this paper, a coupled ES-\\/FS-FEM model is extended to solve the structural–acoustic problems consisting of a plate structure interacting with the fluid medium. Three-node triangular elements and four-node

Z. C. He; G. R. Liu; Z. H. Zhong; X. Y. Cui; G. Y. Zhang; A. G. Cheng

2010-01-01

351

Self-consistent linearization of non-linear BEM formulations with quadratic convergence  

NASA Astrophysics Data System (ADS)

In this work, a general technique to obtain the self-consistent linearization of non-linear formulations of the boundary element method (BEM) is presented. In the incremental-iterative procedure required to solve the non-linear problem the convergence is quadratic, being the solution obtained from the consistent tangent operator. This technique is applied to non-linear BEM formulations for plates where two independent problems are discussed: the plate bending and the stretching problem. For both problems an equilibrium equation is written in terms of strains and internal forces and then the consistent tangent operator is derived by applying the Newton-Raphson’s scheme. The Von Mises criterion is adopted to govern the elasto-plastic material behaviour checked at points along the plate thickness, although the presented formulations can be used with any non-linear model. Numerical examples are presented showing the accuracy of the results as well as the high convergence rate of the iterative procedure.

Fernandes, G. R.; de Souza Neto, E. A.

2013-11-01

352

Generation and dynamics of quadratic birefringent spatial gap solitons  

SciTech Connect

A method is proposed to generate and study the dynamics of spatial light solitons in a birefringent medium with quadratic nonlinearity. Although no analytical expression for propagating solitons has been obtained, our numerical simulations show the existence of stable localized spatial solitons in the frequency forbidden band gap of the medium. The dynamics of these objects is quite rich and manifests for instance elastic reflections, or inelastic collisions where two solitons merge and propagate as a single solitary wave. We derive the dynamics of the slowly varying envelopes of the three fields (second harmonic pump and two-component signal) and study this new system theoretically. We show that it does present a threshold for nonlinear supratransmission that can be calculated from a series expansion approach with a very high accuracy. Specific physical implications of our theoretical predictions are illustrated on LiGaTe{sub 2} (LGT) crystals. Once irradiated by a cw laser beam of 10 {mu}m wavelength, at an incidence beyond the extinction angle, such crystals will transmit light, in the form of spatial solitons generated in the nonlinear regime above the nonlinear supratransmission threshold.

Anghel-Vasilescu, P. [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Str. 38, D-01187 Dresden (Germany); Dorignac, J.; Geniet, F.; Leon, J. [Laboratoire Charles Coulomb, Departement de Physique Theorique, UMR 5221 CNRS-UM2, Universite Montpellier 2, F-34095 Montpellier Cedex 5 (France); Taki, A. [Laboratoire de Physique des Lasers, Atomes et Molecules, CNRS-INP-UMR8523, Universite des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq (France)

2011-04-15

353

Linear versus quadratic portfolio optimization model with transaction cost  

NASA Astrophysics Data System (ADS)

Optimization model is introduced to become one of the decision making tools in investment. Hence, it is always a big challenge for investors to select the best model that could fulfill their goal in investment with respect to risk and return. In this paper we aims to discuss and compare the portfolio allocation and performance generated by quadratic and linear portfolio optimization models namely of Markowitz and Maximin model respectively. The application of these models has been proven to be significant and popular among others. However transaction cost has been debated as one of the important aspects that should be considered for portfolio reallocation as portfolio return could be significantly reduced when transaction cost is taken into consideration. Therefore, recognizing the importance to consider transaction cost value when calculating portfolio' return, we formulate this paper by using data from Shariah compliant securities listed in Bursa Malaysia. It is expected that, results from this paper will effectively justify the advantage of one model to another and shed some lights in quest to find the best decision making tools in investment for individual investors.

Razak, Norhidayah Bt Ab; Kamil, Karmila Hanim; Elias, Siti Masitah

2014-06-01

354

Dynamics and linear quadratic optimal control of flexible multibody systems  

NASA Astrophysics Data System (ADS)

An efficient algorithm for the modeling, dynamic analysis, and optimal control of flexible multibody systems (FMBS) is presented. The cantilevered Bernoulli-Euler beam model and the assumed mode method are used to represent flexibility of elastic bodies in 3D vibration problems. Centrifugal stiffening effects are introduced to correctly represent the dynamic response. The governing equations of motion are based on Kane's equations, adopting a recursive formulation and strategic positioning of the generalized coordinates. The linear quadratic optimization scheme is employed to formulate the vibration control problem. The solutions to the Riccati equation and the use of Kalman gain as optimal control feedbacks to the control of flexibility are also introduced. Based on the optimal control theory and the property of the built-in redundancy for flexible multibody systems, the performance index measure in the optimization control of such systems can be classified into two manifolds: (1) using the extra degrees of freedom resulting from redundancy as control inputs and choosing an integral-type performance index which results in a global optimization scheme and (2) using the joint forces and torques as control inputs and allowing the system output state to keep close track to a reference state while the performance index is kept minimum. Several numerical examples are presented to demonstrate the effectiveness of the methodologies developed.

Tung, Chin-Wei

1994-12-01

355

Phase transitions in the quadratic contact process on complex networks.  

PubMed

The quadratic contact process (QCP) is a natural extension of the well-studied linear contact process where infected (1) individuals infect susceptible (0) neighbors at rate ? and infected individuals recover (1?0) at rate 1. In the QCP, a combination of two 1's is required to effect a 0?1 change. We extend the study of the QCP, which so far has been limited to lattices, to complex networks. We define two versions of the QCP: vertex-centered (VQCP) and edge-centered (EQCP) with birth events 1-0-1?1-1-1 and 1-1-0?1-1-1, respectively, where "-" represents an edge. We investigate the effects of network topology by considering the QCP on random regular, Erd?s-Rényi, and power-law random graphs. We perform mean-field calculations as well as simulations to find the steady-state fraction of occupied vertices as a function of the birth rate. We find that on the random regular and Erd?s-Rényi graphs, there is a discontinuous phase transition with a region of bistability, whereas on the heavy-tailed power-law graph, the transition is continuous. The critical birth rate is found to be positive in the former but zero in the latter. PMID:23848741

Varghese, Chris; Durrett, Rick

2013-06-01

356

Gap solitons in a nonlinear quadratic negative-index cavity.  

PubMed

We predict the existence of gap solitons in a nonlinear, quadratic Fabry-Pérot negative index cavity. A peculiarity of a single negative index layer is that if magnetic and electric plasma frequencies are different it forms a photonic band structure similar to that of a multilayer stack composed of ordinary, positive index materials. This similarity also results in comparable field localization and enhancement properties that under appropriate conditions may be used to either dynamically shift the band edge, or for efficient energy conversion. We thus report that an intense, fundamental pump pulse is able to shift the band edge of a negative index cavity, and make it possible for a weak second harmonic pulse initially tuned inside the gap to be transmitted, giving rise to a gap soliton. The process is due to cascading, a well-known phenomenon that occurs far from phase matching conditions that limits energy conversion rates, it resembles a nonlinear third-order process, and causes pulse compression due to self-phase modulation. The symmetry of the equations of motion under the action of either an electric or a magnetic nonlinearity suggests that both nonlinear polarization and magnetization, or a combination of both, can lead to solitonlike pulses. More specifically, the antisymmetric localization properties of the electric and magnetic fields cause a nonlinear polarization to generate a dark soliton, while a nonlinear magnetization spawns a bright soliton. PMID:17677375

Scalora, Michael; de Ceglia, Domenico; D'Aguanno, Giuseppe; Mattiucci, Nadia; Akozbek, Neset; Centini, Marco; Bloemer, Mark J

2007-06-01

357

Quadratic Optimization in the Problems of Active Control of Sound  

NASA Technical Reports Server (NTRS)

We analyze the problem of suppressing the unwanted component of a time-harmonic acoustic field (noise) on a predetermined region of interest. The suppression is rendered by active means, i.e., by introducing the additional acoustic sources called controls that generate the appropriate anti-sound. Previously, we have obtained general solutions for active controls in both continuous and discrete formulations of the problem. We have also obtained optimal solutions that minimize the overall absolute acoustic source strength of active control sources. These optimal solutions happen to be particular layers of monopoles on the perimeter of the protected region. Mathematically, minimization of acoustic source strength is equivalent to minimization in the sense of L(sub 1). By contrast. in the current paper we formulate and study optimization problems that involve quadratic functions of merit. Specifically, we minimize the L(sub 2) norm of the control sources, and we consider both the unconstrained and constrained minimization. The unconstrained L(sub 2) minimization is certainly the easiest problem to address numerically. On the other hand, the constrained approach allows one to analyze sophisticated geometries. In a special case, we call compare our finite-difference optimal solutions to the continuous optimal solutions obtained previously using a semi-analytic technique. We also show that the optima obtained in the sense of L(sub 2) differ drastically from those obtained in the sense of L(sub 1).

Loncaric, J.; Tsynkov, S. V.; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

358

Photoswitching of the second-order nonlinearity of a tetrahedral octupolar multi DTE-based copper(I) complex.  

PubMed

The modulation of the quadratic NLO response of an octupolar metal-based chromophore featuring four photochromic dithienylethene units is reported. Quantum mechanical simulations are consistent with a full switching of the DTE units and reproduce the strong enhancement of the NLO response. PMID:22986301

Nitadori, Hiroyuki; Ordronneau, Lucie; Boixel, Julien; Jacquemin, Denis; Boucekkine, Abdou; Singh, Anu; Akita, Munetaka; Ledoux, Isabelle; Guerchais, Véronique; Le Bozec, Hubert

2012-10-28

359

Chirped Microwave Pulse Generation Using a Photonic Microwave Delay-Line Filter With a Quadratic Phase Response  

Microsoft Academic Search

We propose an optical approach to generating chirped microwave pulses using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response. If a chirp-free broadband microwave pulse is inputted into the filter, a chirped microwave pulse is generated thanks to the quadratic phase response of the filter. To design a PMDLF with a quadratic phase response, complex tap coefficients

Yitang Dai; Jianping Yao

2009-01-01

360

Stable vortex solitons supported by competing quadratic and cubic nonlinearities  

NASA Astrophysics Data System (ADS)

We address the stability problem for vortex solitons in two-dimensional media combining quadratic and self-defocusing cubic [ ?(2) : ?(3) - ] nonlinearities. We consider the propagation of spatial beams with intrinsic vorticity S in such bulk optical media. It was earlier found that the S=1 and S=2 solitons can be stable, provided that their power (i.e., transverse size) is large enough, and it was conjectured that all the higher-order vortices with S?3 are always unstable. On the other hand, it was recently shown that vortex solitons with S>2 and very large transverse size may be stable in media combining cubic self-focusing and quintic self-defocusing nonlinearities. Here, we demonstrate that the same is true in the ?(2) : ?(3) - model, the vortices with S=3 and S=4 being stable in regions occupying, respectively, ?3% and 1.5% of their existence domain. The vortex solitons with S>4 are also stable in tiny regions. The results are obtained through computation of stability eigenvalues, and are then checked in direct simulations, with a conclusion that the stable vortices are truly robust ones, easily self-trapping from initial beams with embedded vorticity. The dependence of the stability region on the ?(2) phase-mismatch parameter is specially investigated. We thus conclude that the stability of higher-order two-dimensional vortex solitons in narrow regions is a generic feature of optical media featuring the competition between self-focusing and self-defocusing nonlinearities. A qualitative analytical explanation to this feature is proposed.

Mihalache, D.; Mazilu, D.; Malomed, B. A.; Lederer, F.

2004-06-01

361

Moments for general quadratic densities in n dimensions  

SciTech Connect

We present the calculation of the generating functions and the rth-order correlations for densities of the form {rho}(x) {proportional_to} where g(s) is a non-negative function of the quadratic ''action'' s(x)={summation}{sub i,j}H{sub ij}x{sub i}x{sub j}, where x = (x{sub 1},x{sub 2}...,x{sub n}) is a real n-dimensional vector and H is a real, symmetric n x n matrix whose eigenvalues are strictly positive. In particular, we find the connection between the (r+2)th-order and rth-order correlations, which constitutes a generalization of the Gaussian moment theorem, which corresponds to the particular choice g(s)=e{sup -s/2}. We present several examples for specific choices for g(s), including the explicit expression for the generating function for each case and the subspace projection of {rho}(x) in a few cases. We also provide the straightforward generalizations to: (1) the case where g=g(s(x)+a {center_dot} x), where a=(a{sub 1},a{sub 2},...,a{sub n}) is an arbitrary real n-dimensional vector, and (2) the complex case, in which the action is of the form s(z) = {summation}{sub i,j}H{sub ij}z{sup *}{sub i} z{sub j} where z=(z{sub 1},z{sub 2}...z{sub n}) is an n-dimensional complex vector and H is a Hermitian n x n matrix whose eigenvalues are strictly positive.

Furman, Miguel A.

2002-03-20

362

Selective encapsulation and sequential release of guests within a self-sorting mixture of three tetrahedral cages.  

PubMed

A mixture of two triamines, one diamine, 2-formylpyridine and a Zn(II) salt was found to self-sort, cleanly producing a mixture of three different tetrahedral cages. Each cage bound one of three guests selectively. These guests could be released in a specific sequence following the addition of 4-methoxyaniline, which reacted with the cages, opening each in turn and releasing its guest. The system here described thus behaved in an organized way in three distinct contexts: cage formation, guest encapsulation, and guest release. Such behavior could be used in the context of a more complex system, where released guests serve as signals to other chemical actors. PMID:24692286

Jiménez, Azucena; Bilbeisi, Rana A; Ronson, Tanya K; Zarra, Salvatore; Woodhead, Craig; Nitschke, Jonathan R

2014-04-25

363

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

364

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

365

Surface structure of tetrahedral-coordinated amorphous diamond-like carbon films grown by pulsed laser deposition  

SciTech Connect

The structure and composition of tetrahedral-coordinated amorphous diamond-like carbon films (a-tC) grown by pulsed laser deposition (PLD) of graphite has been studied with atomic force microscopy (AFM). The nanometer-scale surface structure has been studied as a function of growth parameters (e.g., laser energy density and film thickness) using contact-mode and tapping-mode AFM. Although the surfaces were found to be generally smooth, they exhibited reproducible structural features on several size scales which correlate with the variation of laser energy and th excited ion etching.

Mercer, T.W. [Drexel Univ., Philadelphia, PA (United States). Dept. of Physics and Atmospheric Science; DiNardo, N.J. [Drexel Univ., Philadelphia, PA (United States). Dept. of Physics and Atmospheric Science]|[Pennsylvania Univ., Philadelphia, PA (United States); Martinez-Miranda, L.J.; Fang, F. [Pennsylvania Univ., Philadelphia, PA (United States); Friedmann, T.A.; Sullivan, J.P.; Siegal, M.P. [Sandia National Labs., Albuquerque, NM (United States)

1994-12-31

366

Infrared spectroscopy of tetrahedral quantum spin systems Cu {2}Te {2} O {5} X {2} (X = Br and Cl)  

NASA Astrophysics Data System (ADS)

Cu2Te2O5X2, with X = Br and Cl, are spin-tetrahedral systems displaying magnetic ordering at low temperatures. We have performed optical reflectivity measurements over a broad spectral range as a function of temperature and magnetic field. We have identified the resonance frequencies of the infrared optically active phonon modes and estimated the value of the electronic gap in both tellurate compounds. No variation of the spectra has been observed while crossing the magnetic ordering transition temperature or by applying a magnetic field. The implications of these findings are discussed in relation to the nature of the phase transition.

Perucchi, A.; Degiorgi, L.; Berger, H.; Millet, P.

2004-03-01

367

Friedmann Models and Cosmological Solutions in the Bimetric Theory with a Quadratic Lagrangian  

Microsoft Academic Search

Cosmological models are investigated within the framework of the bimetric theory of gravitation with a Lagrangian that is quadratic with respect to “intensities” gik|l. It is shown that the theory predicts not only singular but also nonsingular solutions.

A. H. Yeranyan

2001-01-01

368

Note: Probing quadratic magneto-optical Kerr effects with a dual-beam system.  

PubMed

In this Note, we present a dual-beam magneto-optical Kerr effect (MOKE) magnetometer for the study of quadratic MOKE in magnetic thin films. The two beams simultaneously probe the sample, located in the middle of a quadrupole magnet, at two angles of incidence (0 degrees and 45 degrees). This combination of two systems allows one to automatically and routinely perform measurements that are sensitive to the combined longitudinal and quadratic MOKE signals (45 degrees), or the quadratic effect alone (0 degrees). Orientation-dependent and automated quantitative analyses of the quadratic effect's amplitude are also implemented. We present representative measurements on Heusler compound thin films to illustrate the newly combined capabilities of this instrument. PMID:20192522

Trudel, Simon; Wolf, Georg; Schultheiss, Helmut; Hamrle, Jaroslav; Hillebrands, Burkard; Kubota, Takahide; Ando, Yasuo

2010-02-01

369

Using Simple Quadratic Equations to Estimate Equilibrium Concentrations of an Acid  

ERIC Educational Resources Information Center

Application of quadratic equations to standard problem in chemistry like finding equilibrium concentrations of ions in an acid solution is explained. This clearly shows that pure mathematical analysis has meaningful applications in other areas as well.

Brilleslyper, Michael A.

2004-01-01

370

The existence of periodic orbits and invariant tori for some 3-dimensional quadratic systems.  

PubMed

We use the normal form theory, averaging method, and integral manifold theorem to study the existence of limit cycles in Lotka-Volterra systems and the existence of invariant tori in quadratic systems in ?(3). PMID:24982980

Jiang, Yanan; Han, Maoan; Xiao, Dongmei

2014-01-01

371

The Existence of Periodic Orbits and Invariant Tori for Some 3-Dimensional Quadratic Systems  

PubMed Central

We use the normal form theory, averaging method, and integral manifold theorem to study the existence of limit cycles in Lotka-Volterra systems and the existence of invariant tori in quadratic systems in ?3.

Jiang, Yanan; Han, Maoan; Xiao, Dongmei

2014-01-01

372

Observers for a class of systems with nonlinearities satisfying an incremental quadratic inequality  

NASA Technical Reports Server (NTRS)

We consider the problem of state estimation from nonlinear time-varying system whose nonlinearities satisfy an incremental quadratic inequality. Observers are presented which guarantee that the state estimation error exponentially converges to zero.

Acikmese, Ahmet Behcet; Martin, Corless

2004-01-01

373

Quadratic Forms on Complex Random Matrices and Multi-Antenna Channel Capacity.  

National Technical Information Service (NTIS)

Quadratic forms on complex random matrices and their joint eigenvalue densities are derived for applications in information theory. These densities are represented by complex hypergeometric functions of matrix arguments which can be expressed in terms of ...

T. Ratnarajah R. Vaillancourt

2004-01-01

374

Matlab code for limit of a Nash linear quadratic two-player dynamic game  

Microsoft Academic Search

This program computes the limit of a Nash linear quadratic two-player dynamic game. The program constructs the Nash feedback equilibrium by iterating on the pair of Ricatti equations corresponding to the two player's problem.

Thomas Sargent

375

Vanishing Higgs one-loop quadratic divergence in the scotogenic model and beyond  

NASA Astrophysics Data System (ADS)

It is shown that the inherent one-loop quadratic divergence of the Higgs mass renormalization of the standard model may be avoided in the well-studied scotogenic model of radiative neutrino mass as well as other analogous extensions.

Ma, Ernest

2014-05-01

376

Transfer Pricing in a Decentralized Firm: A Decomposition Algorithm for Quadratic Programming.  

National Technical Information Service (NTIS)

A discussion of the importance of transfer pricing and a review of the relevant literature are followed by a decomposition algorithm for quadratic programming, using the problem of transfer pricing with externalities as a vehicle for its development. A nu...

J. E. Hass

1967-01-01

377

Multistate vibronic interactions in the fluorobenzene radical cation: The importance of quadratic coupling terms  

Microsoft Academic Search

The multi-mode multi-state vibronic interactions in the set of X?2B1–D?2A1 electronic states of the monofluoro benzene radical cation are investigated theoretically, based on a quadratic vibronic coupling approach. The underlying ionization potentials and coupling constants are obtained from ab initio coupled-cluster calculations. Previous investigations (relying on the linear coupling approach) are extended by including all (diagonal) quadratic coupling constants for

Etienne Gindensperger; Ioan Bâldea; Jan Franz; Horst Köppel

2007-01-01

378

Metastability of dark snoidal-type waves in quadratic nonlinear media.  

PubMed

We report the existence and basic properties of dark snoidal-type waves self-sustained in quadratic nonlinear media. Using a stability analysis technique, we reveal that they are almost completely stable, or metastable, in suitable ranges of input energy flows and material parameters. This opens the way to the experimental observation of dark-type multicolor periodic wave patterns supported by quadratic nonlinearities. PMID:14683067

Kartashov, Yaroslav V; Egorov, Alexey A; Zelenina, Anna S; Vysloukh, Victor A; Torner, Lluis

2003-10-01

379

Zhang Neural Network Versus Gradient Neural Network for Online Time-Varying Quadratic Function Minimization  

Microsoft Academic Search

With the proved efficacy on solving linear time-varying matrix or vector equations, Zhang neural network (ZNN) could be generalized\\u000a and developed for the online minimization of time-varying quadratic functions. The minimum of a time-varying quadratic function\\u000a can be reached exactly and rapidly by using Zhang neural network, as compared with conventional gradient-based neural networks\\u000a (GNN). Computer-simulation results substantiate further that

Yunong Zhang; Zhan Li; Chenfu Yi; Ke Chen

2008-01-01

380

Learning Algorithm of LS-SVM Based on Quadratic Renyi-Entropy and Empirical Analysis  

Microsoft Academic Search

This paper applies quadratic Renyi entropy to enterprise financial distress prediction and puts forward a learning algorithm of least squares support vector machines (LS-SVM) based on quadratic Renyi entropy. By respectively analysis and comparison of the algorithm with the traditional LS-SVM, the standard SVM, MLR and BP-ANN, we can see that this algorithm is significantly superior to other algorithms and

Guanhua Zhao; Zhao Juan

2009-01-01

381

Sequential design of discrete linear quadratic regulators via optimal root-locus techniques  

NASA Technical Reports Server (NTRS)

A sequential method employing classical root-locus techniques has been developed in order to determine the quadratic weighting matrices and discrete linear quadratic regulators of multivariable control systems. At each recursive step, an intermediate unity rank state-weighting matrix that contains some invariant eigenvectors of that open-loop matrix is assigned, and an intermediate characteristic equation of the closed-loop system containing the invariant eigenvalues is created.

Shieh, Leang S.; Yates, Robert E.; Ganesan, Sekar

1989-01-01

382

Optimal quadratic control of jump linear systems with Gaussian noise in discrete-time  

Microsoft Academic Search

An optimal discrete-time jump linear quadratic Gaussian (JLQG) control problem is investigated. The system to be controlled is linear, except for randomly jumping parameters which obey a discrete-time finite-state Markov process. A quadratic expected cost is minimized, for systems subject to additive Gaussian input and measurement noise. It is assumed that the system structure (i.e. jumping parameters) is known at

Howard J. Chizeck; Yuandong Ji

1988-01-01

383

Optical solitons due to quadratic nonlinearities: from basic physics to futuristic applications  

Microsoft Academic Search

We present an overview of nonlinear phenomena related to optical quadratic solitons—intrinsically multi-component localized states of light, which can exist in media without inversion symmetry at the molecular level. Starting with presentation of a few derivation schemes of basic equations describing three-wave parametric wave mixing in diffractive and\\/or dispersive quadratic media, we discuss their continuous wave solutions and modulational instability

Alexander V. Buryak; Paolo Di Trapani; Dmitry V. Skryabin; Stefano Trillo

2002-01-01

384

Quadratic spatial soliton generation by seeded down conversion of a strong pump beam  

Microsoft Academic Search

Quadratic spatial solitons have been generated during second-harmonic generation under easy-to-achieve conditions and should be pervasive in other second-order nonlinear interactions. One of the more interesting cases is the downconversion process, which is the essence of parametric generators and oscillators. In this investigation, we report on the generation of two-dimensional quadratic spatial solitons (QSS) in a KTP crystal near the

M. T. G. Canva; R. A. Fuerst; D. Baboiu; G. I. Stegeman; G. Assanto

1998-01-01

385

Second harmonic ?erenkov radiation in bulk birefringent quadratic medium without any ?(2) modulation  

NASA Astrophysics Data System (ADS)

We carry out experimental studies of second harmonic ?erenkov radiation in the bulk birefringent quadratic medium without any quadratic ? modulation. We give a detailed investigation on the phase matching condition of frequency conversion process and the spatial distribution of ?erenkov patterns. We analyze the intensity dependence of the emitted ?erenkov waves on the polarization and wavelengths of the incident fundamental wave. We show that the experimental results closely follow the theoretical predictions.

Wang, Wenjie; Sheng, Yan; Niu, Xiaoying; Huang, Ming; Zheng, Shoujun; Kong, Yongfa

2014-06-01

386

Globally Solving Box-Constrained Nonconvex Quadratic Programs with Semidefinite-Based Finite Branch  

Microsoft Academic Search

Abstract We consider a recent branch-and-bound algorithm of the authors for nonconvex quadratic programming. The algorithm is characterized by its use of semidefinite relaxations within a finite branching scheme. In this paper, we specialize the algorithm to the box-constrained case and study its implementation, which is shown to be a state-of-the-art method for globally solving box-constrained nonconvex quadratic programs.

Samuel Burer; Dieter Vandenbussche

387

Hydrogeniridate(VI) Anion and the Geometries of Tetrahedral Oxo-anions.  

PubMed

The compound KHIrO4, potassium hydrogentetraoxidoiridate(VI)(1-), crystallizes in a Scheelite-type structure containing discrete, slightly flattened, [Ir(O3OH)](-) tetrahedra-the first observation of a group 9 element in the 6+ oxidation state as an oxoanion. PMID:24819546

Weller, Mark T; Galati, Rosa

2014-06-01

388

An evaluation of three approaches to tetrahedral mesh generation for deformable registration of brain MR images  

Microsoft Academic Search

In this paper we evaluate three conceptually different approaches to mesh generation for deformable Finite Element Method (FEM) registration of Magnetic Resonance (MR) images of brain volume. Precise approximation of brain volume segmentations and good shape of the mesh tetrahedra are the main requirements imposed by the application. Our contributions are (1) application-motivated com- parison and analysis of practical mesh

Andriy Fedorov; Nikos Chrisochoides; Ron Kikinis; Simon K. Warfield

2006-01-01

389

Study of intercalated Ti atom in tetrahedral or octahedral sites of titanium disulfide (001) surfaces: theoretical scanning tunneling microscopy images.  

PubMed

We have performed ab initio linear combination of atomic orbitals-density functional theory calculations on biperiodic supercells to model the electronic and geometrical involvements of Ti intercalated atom in either octahedral or tetrahedral sites of the (001) TiS2 surfaces. For each type of defect, both the relaxed atomic structure and the electronic properties of the defect states were carefully analyzed. For the titanium atom in the van der Waals gap, the partial filling of the conduction band is in agreement with the metallic behavior reported by experimental studies and the last filled states in the bottom of the conduction band--mainly developed on titanium 3d orbitals--permit us to explain the dark defects observed on the scanning tunneling microscopy image of the (001) TiS2 surfaces. On the other hand, the intercalated titanium atom in the tetrahedral site which is just below the top sulfur atom plane governs the electronic density detected by the tip. It permits us to explain the triangular defect with a clear maximum of intensity in its center and dark sides. PMID:18190213

Amzallag, E; Baraille, I; Martinez, H; Rérat, M; Gonbeau, D

2008-01-01

390

Study of intercalated Ti atom in tetrahedral or octahedral sites of titanium disulfide (001) surfaces: Theoretical scanning tunneling microscopy images  

NASA Astrophysics Data System (ADS)

We have performed ab initio linear combination of atomic orbitals-density functional theory calculations on biperiodic supercells to model the electronic and geometrical involvements of Ti intercalated atom in either octahedral or tetrahedral sites of the (001) TiS2 surfaces. For each type of defect, both the relaxed atomic structure and the electronic properties of the defect states were carefully analyzed. For the titanium atom in the van der Waals gap, the partial filling of the conduction band is in agreement with the metallic behavior reported by experimental studies and the last filled states in the bottom of the conduction band-mainly developed on titanium 3d orbitals-permit us to explain the dark defects observed on the scanning tunneling microscopy image of the (001) TiS2 surfaces. On the other hand, the intercalated titanium atom in the tetrahedral site which is just below the top sulfur atom plane governs the electronic density detected by the tip. It permits us to explain the triangular defect with a clear maximum of intensity in its center and dark sides.

Amzallag, E.; Baraille, I.; Martinez, H.; Rérat, M.; Gonbeau, D.

2008-01-01

391

Effect of mesh element type of Finite Element Model (FEM) on unimorph cantilever vibration  

NASA Astrophysics Data System (ADS)

This paper discusses mesh refinement methods used to perform Finite Element Analysis (FEA) for vibration based MEMS Energy Harvester. The three types of meshing elements, 1) Linear Hexahedral, 2) Parabolic Hexahedral and 3) Parabolic Tetrahedral, were used in this study. The meshing methods are used to ensure accurate simulation result particularly in stress, and strain analysis obtained, since they are determined by the displacement of each node in the physical structure. The study of the accuracy of an mesh analysis is also known as mesh convergence study which element aspect ratios must be refined consistently. In this paper the dimensions of each elements were also varied in order to investigate the significant of this methods in achieving better ratios of simulation to theoretical results.

Aris, H.; Fitrio, D.; Singh, J.

2013-12-01

392

An hp-adaptive discontinuous Galerkin finite-element method for 3-D elastic wave modelling  

Microsoft Academic Search

We present a discontinuous Galerkin finite-element method (DG-FEM) formulation with Convolutional Perfectly Matched Layer (CPML) absorbing boundary condition for 3-D elastic seismic wave modelling. This method makes use of unstructured tetrahedral meshes locally refined according to the medium properties (h-adaptivity), and of approximation orders that can change from one element to another according to an adequate criterion (p-adaptivity). These two

V. Etienne; E. Chaljub; J. Virieux; N. Glinsky

2010-01-01

393

Finite-element-based computational methods for cardiovascular fluid-structure interaction  

Microsoft Academic Search

In this paper a combined arbitrary Lagrange-Euler fictitious domain (ALE-FD) method for fluid-structure interaction problems in cardiovascular biomechanics is derived in terms of a weighted residual finite-element formulation. For both fluid flow of blood and solid mechanics of vascular tissue, the performance of tetrahedral and hexahedral Crouzeix-Raviart elements are evaluated. Comparable convergence results are found, although for the test cases

F. N. van de Vosse; J. de Hart; D. Bessems; T. W. M. Gunther; A. Segal; B. J. B. M. Wolters; J. M. A. Stijnen; F. P. T. Baaijens

2003-01-01

394

A new boundary element method formulation for the forward problem solution of electro-magnetic source imaging  

Microsoft Academic Search

Numerical solution of the potential and magnetic fields for a given electrical source distribution in the human brain is the essential part of electro-magnetic source imaging. In this study, the performance of Boundary Element Method (BEM) with different surface element types is explored. A new BEM formulation is derived that makes use of isoparametric linear and quadratic elements. It is

I. Oguz Tanzer; N. G. Gencer

1997-01-01

395

Unleashing the Quadratic Nonlinear Optical Responses of Graphene by Confining White-Graphene (h-BN) Sections in Its Framework.  

PubMed

In an attempt to diversify the options in designing graphene-based systems bearing large second order nonlinear optical (NLO) responses of octupolar and/or dipolar character, the subject of the quadratic NLO properties of hybrid boron nitride (BN) graphene flakes is opened up. State of the art ab initio and density functional theory methods applied on a toolbox of book-text octupolar and arbitrary dipolar planar hybrid h-BN-graphene nanosized systems reveal that by confining finite h-BN sections in the internal network of graphene, the capacity of the ?-electron network of graphene species in delivering giant second order NLO responses could be fully exploited. Configuration interaction (CIS) and time-dependent density functional (TD) computations, within the sum-overstate (SOS) perturbational approach, expose that the prevailing (hyper)polarization mechanism, lying under the sizable computed octupolar hyperpolarizabilities, is fueled by alternating positive and negative atomic charges located in the internal part of the hybrid flakes, and more precisely at the BN/graphene intersections. This type of charge transfer mechanism distinguishes, in fact, the elemental graphene dipoles/octupoles we report here from other conventional NLO dipoles or octupoles. More interestingly, it is shown that by controlling the shape, size, and covering area of the h-BN domain (or domains), one can effectively regulate "à volonté" both the magnitudes and types of the second order NLO responses switching from dipolar to octupolar and vice versa. Especially in the context of the latter class of NLO properties, this communication brings into surface novel, graphene-based, octupolar planar or quasiplanar motifs. The take home message of this communication is summarized as follows: When the right BN segment is incorporated in the right section of the right graphene flake, systems of giant quadratic NLO octupolar and/or dipolar responses may emerge. PMID:24779531

Karamanis, Panaghiotis; Otero, Nicolás; Pouchan, Claude

2014-05-21

396

Augmented weak forms and element-by-element preconditioners: Efficient iterative strategies for structural finite elements. A preliminary study  

NASA Technical Reports Server (NTRS)

A weak formulation in structural analysis that provides well conditioned matrices suitable for iterative solutions is presented. A mixed formulation ensures the proper representation of the problem and the constitutive relations are added in a penalized form. The problem is solved by a double conjugate gradient algorithm combined with an element by element approximate factorization procedure. The double conjugate gradient strategy resembles Uzawa's variable-length type algorithms the main difference is the presence of quadratic terms in the mixed variables. In the case of shear deformable beams these terms ensure that the proper finite thickness solution is obtained.

Muller, A.; Hughes, T. J. R.

1984-01-01

397

Classification of the quantum two-dimensional superintegrable systems with quadratic integrals and the Staeckel transforms  

SciTech Connect

The two-dimensional quantum superintegrable systems with quadratic integrals of motion on a manifold are classified by using the quadratic associative algebra of the integrals of motion. There are six general fundamental classes of quantum superintegrable systems corresponding to the classical ones. Analytic formulas for the involved integrals are calculated in all the cases. All the known quantum superintegrable systems with quadratic integrals are classified as special cases of these six general classes. The coefficients of the quadratic associative algebra of integrals are calculated and they are compared to the coefficients of the corresponding coefficients of the Poisson quadratic algebra of the classical systems. The quantum coefficients are similar to the classical ones multiplied by a quantum coefficient -{h_bar}{sup 2} plus a quantum deformation of order {h_bar}{sup 4} and {h_bar}{sup 6}. The systems inside the classes are transformed using Staeckel transforms in the quantum case as in the classical case. The general form of the Staeckel transform between superintegrable systems is discussed.

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

2008-05-15

398

A Wavelet Bicoherence-Based Quadratic Nonlinearity Feature for Translational Axis Condition Monitoring  

PubMed Central

The translational axis is one of the most important subsystems in modern machine tools, as its degradation may result in the loss of the product qualification and lower the control precision. Condition-based maintenance (CBM) has been considered as one of the advanced maintenance schemes to achieve effective, reliable and cost-effective operation of machine systems, however, current vibration-based maintenance schemes cannot be employed directly in the translational axis system, due to its complex structure and the inefficiency of commonly used condition monitoring features. In this paper, a wavelet bicoherence-based quadratic nonlinearity feature is proposed for translational axis condition monitoring by using the torque signature of the drive servomotor. Firstly, the quadratic nonlinearity of the servomotor torque signature is discussed, and then, a biphase randomization wavelet bicoherence is introduced for its quadratic nonlinear detection. On this basis, a quadratic nonlinearity feature is proposed for condition monitoring of the translational axis. The properties of the proposed quadratic nonlinearity feature are investigated by simulations. Subsequently, this feature is applied to the real-world servomotor torque data collected from the X-axis on a high precision vertical machining centre. All the results show that the performance of the proposed feature is much better than that of original condition monitoring features.

Li, Yong; Wang, Xiufeng; Lin, Jing; Shi, Shengyu

2014-01-01

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

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

401

Cut-off and phase constants of partially filled axially magnetized, gyromagnetic waveguides using finite elements  

Microsoft Academic Search

A three component vector finite element formulation to model the propagation characteristics of partially filled, axially magnetized, gyromagnetic waveguides is described. Covariant-projection elements have been used to avoid spurious modes and periodic boundary conditions have been implemented to improve numerical efficiency. The classic quadratic functional derived from the vector, curlcurl, magnetic field equation is suited to evaluating the cut-off planes

Bernice M. Dillon; Andrew A. P. Gibson; Jon P. Webb

1993-01-01

402

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

NASA Astrophysics Data System (ADS)

In this work, the authors 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. The materials are being employed in micro- and nanoelectromechanical systems. Several reports addressed some of the mechanical properties of these materials but they are based in different experimental approaches. Here, they use a single testing method, the membrane deflection experiment, to compare these materials' Young's moduli, characteristic strengths, fracture toughnesses, and theoretical strengths. Furthermore, they analyze the applicability of Weibull theory [Proc. Royal Swedish Inst. Eng. Res. 153, 1 (1939); ASME J. Appl. Mech. 18, 293 (1951)] in the prediction of these materials' failure and document the volume- or surface-initiated failure modes by fractographic analysis. The findings are of particular relevance to the selection of micro- and nanoelectromechanical systems materials for various applications of interest.

Espinosa, H. D.; Peng, B.; Moldovan, N.; Friedmann, T. A.; Xiao, X.; Mancini, D. C.; Auciello, O.; Carlisle, J.; Zorman, C. A.; Merhegany, M.

2006-08-01

403

Calculated total cross sections of electron-impact ionization and excitations in tetrahedral (XY4) and SF6 molecules  

NASA Astrophysics Data System (ADS)

Various total cross sections for collisions of electrons in the energy range 10 2000 eV are calculated for the tetrahedral CH4, SiH4, GeH4, CF4, SiF4, and CCl4 targets and SF6. Molecular total inelastic cross sections determined in the complex potential formalism are partitioned to account for the ionization and cumulative electronic-excitation channels. The present total cross sections and total ionization cross sections are found to be consistent with the previous data. The cumulative total excitation cross sections reported here indicate the relative importance of ionization together with electronic excitation channels including neutral dissociation of these molecules by electron impact.

Joshipura, K. N.; Vinodkumar, Minaxi; Limbachiya, C. G.; Antony, B. K.

2004-02-01

404

Tetrahedral silicon-centered imidazolyl derivatives: Promising candidates for OLEDs and fluorescence response of Ag (I) ion  

Microsoft Academic Search

A series of novel tetrahedral silicon-centered imidazolyl derivatives, Bis(4-(imidazol-1-yl)phenyl)dimethylsilane (1), Tri(4-(imidazol-1-yl)phenyl)methyl silane (2), Bis(4-(imidazol-1-yl)phenyl)diphenylsilane (3), Tri(4-(imidazol-1-yl)phenyl)phenylsilane (4), [Bis(4-(imidazol-1-yl)phenyl)](4-bromophenyl)phenylsilane (5) and [Tri(4-(imidazol-1-yl)phenyl)](4-bromophenyl)silane (6) have been synthesized and characterized by FTIR, 1H NMR, 13C NMR and mass spectroscopy. They all display high thermal stability, are fluorescent with emission in the region of violet to blue, and possess large HOMO-LUMO energy gaps ranging

Dengxu Wang; Yuzhong Niu; Yike Wang; Jianjun Han; Shengyu Feng

2010-01-01

405

Constructions of two polycatenanes and one polypseudo-rotaxane by discrete tetrahedral cages and stool-like building units  

PubMed Central

Mechanically Interlocked molecules, such as catenanes and rotaxanes, are of great interest due to their fascinating structures and potential applications, while such molecules have been mainly restricted to comprising components of interlocked rings or polygons. The constructions of infinite polycatenanes and polyrotaxanes by discrete cages remain great challenge, and only two infinite polycatenanes fabricated by discrete cages have been reported so far, while the structures of polyrotaxanes and polypseudo-rotaxanes fabricated by discrete build units have not been documented to date. Herein we report the first example of a two-dimensional (2D) polypseudo-rotaxane fabricated by stool-like build units, the second example of a one-dimensional (1D) polycatenane, and the second example of a three-dimensional (3D) polycatenane, which were assemblied by discrete tetrahedral cages. The pores of dehydrated 3D polycatenane are dynamic, and display size-dependent adsorption/desorption behaviors of alcohols.

Jiang, Long; Ju, Ping; Meng, Xian-Rui; Kuang, Xiao-Jun; Lu, Tong-Bu

2012-01-01

406

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

407

Velocity-pressure integrated versus penalty finite element methods for high Reynolds number flows  

Microsoft Academic Search

Velocity-pressure integrated and consistent penalty finite element computations of high Reynolds number, laminar flows are presented. In both of the methods, the pressure has been interpolated using linear shape functions for a triangular element. The triangular element is contained inside the bi-quadratic isoparametric element. It has been reported previously that the pressure interpolation method, when used in the velocity-pressure integrated

Sang-Wook Kim

1988-01-01

408

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

409

Lie algebraic approach and quantum treatment of an anisotropic charged particle via the quadratic invariant  

NASA Astrophysics Data System (ADS)

We consider the problem of a charged harmonic oscillator under the influence of a constant magnetic field. The system is assumed to be anisotropic and the magnetic field is applied along z-axis. A canonical transformation is invoked to remove the interaction term and the system is reduced to a model contains two uncoupled harmonic oscillators. Two classes of real and complex quadratic invariants (constants of motion) are obtained. We employ the Lie algebraic technique to find the most general solution for the wave-function for both real and complex invariants. The quadratic invariant is also used to derive two classes of creation and annihilation operators from which the wave-functions in the coherent states and number states are obtained. Some discussion related to the advantage of using the quadratic invariants to solve the Cauchy problem instead of the direct use of the Hamiltonian itself is also given.

Abdalla, M. Sebawe; Leach, P. G. L.

2011-08-01

410

Fast parallel DNA-based algorithms for molecular computation: quadratic congruence and factoring integers.  

PubMed

Assume that n is a positive integer. If there is an integer such that M (2) ? C (mod n), i.e., the congruence has a solution, then C is said to be a quadratic congruence (mod n). If the congruence does not have a solution, then C is said to be a quadratic noncongruence (mod n). The task of solving the problem is central to many important applications, the most obvious being cryptography. In this article, we describe a DNA-based algorithm for solving quadratic congruence and factoring integers. In additional to this novel contribution, we also show the utility of our encoding scheme, and of the algorithm's submodules. We demonstrate how a variety of arithmetic, shifted and comparative operations, namely bitwise and full addition, subtraction, left shifter and comparison perhaps are performed using strands of DNA. PMID:21914574

Chang, Weng-Long

2012-03-01

411

Resurrecting quadratic inflation in no-scale supergravity in light of BICEP2  

NASA Astrophysics Data System (ADS)

The magnitude of primordial tensor perturbations reported by the BICEP2 experiment is consistent with simple models of chaotic inflation driven by a single scalar field with a power-law potential propto phin : n simeq 2, in contrast to the WMAP and Planck results, which favored models resembling the Starobinsky R+R2 model if running of the scalar spectral index could be neglected. While models of inflation with a quadratic potential may be constructed in simple N = 1 supergravity, these constructions are more challenging in no-scale supergravity. We discuss here how quadratic inflation can be accommodated within supergravity, focusing primarily on the no-scale case. We also argue that the quadratic inflaton may be identified with the supersymmetric partner of a singlet (right-handed) neutrino, whose subsequent decay could have generated the baryon asymmetry via leptogenesis.

Ellis, John; García, Marcos A. G.; Nanopoulos, Dimitri V.; Olive, Keith A.

2014-05-01

412

An Accelerated Proximal Gradient Algorithm for Singly Linearly Constrained Quadratic Programs with Box Constraints  

PubMed Central

Recently, the existed proximal gradient algorithms had been used to solve non-smooth convex optimization problems. As a special nonsmooth convex problem, the singly linearly constrained quadratic programs with box constraints appear in a wide range of applications. Hence, we propose an accelerated proximal gradient algorithm for singly linearly constrained quadratic programs with box constraints. At each iteration, the subproblem whose Hessian matrix is diagonal and positive definite is an easy model which can be solved efficiently via searching a root of a piecewise linear function. It is proved that the new algorithm can terminate at an ?-optimal solution within O(1/?) iterations. Moreover, no line search is needed in this algorithm, and the global convergence can be proved under mild conditions. Numerical results are reported for solving quadratic programs arising from the training of support vector machines, which show that the new algorithm is efficient.

Han, Congying; Zhao, Tong; Guo, Tiande

2013-01-01

413

Temporal dynamics of spatially localized waves in quadratic nonlinear waveguide arrays  

NASA Astrophysics Data System (ADS)

We study experimentally and theoretically the temporal dynamics of laser pulses propagating under conditions of spatial self-focusing in quadratic nonlinear waveguide arrays made from periodically poled lithium niobate. We observed temporal pulse breakup and temporal pulse narrowing and studied the dynamics of these effects in different waveguides. We investigated the influence of the frequency dependence of the mode indices as a limiting factor for soliton formation. Our experimental results are in good agreement with the theoretical model developed from coupled-mode theory, providing a detailed understanding of pulse dynamics and beam distribution in waveguide arrays with quadratic nonlinearity.

Setzpfandt, Frank; Solntsev, Alexander S.; Neshev, Dragomir N.; Pertsch, Thomas; Sohler, Wolfgang; Schiek, Roland

2014-03-01

414

Nonadiabatic Effects in Ultracold Molecules via Anomalous Linear and Quadratic Zeeman Shifts  

NASA Astrophysics Data System (ADS)

Anomalously large linear and quadratic Zeeman shifts are measured for weakly bound ultracold $^{88}$Sr$_2$ molecules near the intercombination-line asymptote. Nonadiabatic Coriolis coupling and the nature of long-range molecular potentials explain how this effect arises and scales roughly cubically with the size of the molecule. The linear shifts yield nonadiabatic mixing angles of the molecular states. The quadratic shifts are sensitive to nearby opposite $f$-parity states and exhibit fourth-order corrections, providing a stringent test of a state-of-the-art \\textit{ab initio} model.

McGuyer, B. H.; Osborn, C. B.; McDonald, M.; Reinaudi, G.; Skomorowski, W.; Moszynski, R.; Zelevinsky, T.

2013-12-01

415

An application of nonlinear programming to the design of regulators of a linear-quadratic formulation  

NASA Technical Reports Server (NTRS)

A design technique is proposed for linear regulators in which a feedback controller of fixed structure is chosen to minimize an integral quadratic objective function subject to the satisfaction of integral quadratic constraint functions. Application of a nonlinear programming algorithm to this mathematically tractable formulation results in an efficient and useful computer aided design tool. Particular attention is paid to computational efficiency and various recommendations are made. Two design examples illustrate the flexibility of the approach and highlight the special insight afforded to the designer. One concerns helicopter longitudinal dynamics and the other the flight dynamics of an aerodynamically unstable aircraft.

Fleming, P.

1983-01-01

416

On the Rigorous Derivation of the 3D Cubic Nonlinear Schrödinger Equation with a Quadratic Trap  

NASA Astrophysics Data System (ADS)

We consider the dynamics of the three-dimensional N-body Schrödinger equation in the presence of a quadratic trap. We assume the pair interaction potential is N 3 ?-1 V( N ? x). We justify the mean-field approximation and offer a rigorous derivation of the three-dimensional cubic nonlinear Schrödinger equation (NLS) with a quadratic trap. We establish the space-time bound conjectured by Klainerman and Machedon (Commun Math Phys 279:169-185, 2008) for by adapting and simplifying an argument in Chen and Pavlovi? (Annales Henri Poincaré, 2013) which solves the problem for in the absence of a trap.

Chen, Xuwen

2013-11-01

417

Classification of ?(s)-Quadratic Stochastic Operators on 2D simplex  

NASA Astrophysics Data System (ADS)

A quadratic stochastic operator (in short QSO) is usually used to present the time evolution of differing species in biology. Some QSO has been studied by Lotka and Volterra. The general problem in the nonlinear operator theory is to study the behavior of operators. This problem was not fully finished even for the quadratic stochastic operators. To study this problem it was investigated several classes of such QSO. In this paper we study ?(s)-QSO class of operators. We study such kind of operators on 2D simplex. We first classify these ?(s)-QSO into 20 classes. Further, we investigate the dynamics of one class of such operators.

Mukhamedov, Farrukh; Saburov, Mansoor; Qaralleh, Izzat

2013-04-01

418

Nonadiabatic effects in ultracold molecules via anomalous linear and quadratic Zeeman shifts.  

PubMed

Anomalously large linear and quadratic Zeeman shifts are measured for weakly bound ultracold 88Sr2 molecules near the intercombination-line asymptote. Nonadiabatic Coriolis coupling and the nature of long-range molecular potentials explain how this effect arises and scales roughly cubically with the size of the molecule. The linear shifts yield nonadiabatic mixing angles of the molecular states. The quadratic shifts are sensitive to nearby opposite f-parity states and exhibit fourth-order corrections, providing a stringent test of a state-of-the-art ab initio model. PMID:24483652

McGuyer, B H; Osborn, C B; McDonald, M; Reinaudi, G; Skomorowski, W; Moszynski, R; Zelevinsky, T

2013-12-13

419

Contractions and deformations of quasiclassical Lie algebras preserving a nondegenerate quadratic Casimir operator  

SciTech Connect

By means of contractions of Lie algebras, we obtain new classes of indecomposable quasiclassical Lie algebras that satisfy the Yang-Baxter equations in its reformulation in terms of triple products. These algebras are shown to arise naturally from noncompact real simple algebras with nonsimple complexification, where we impose that a nondegenerate quadratic Casimir operator is preserved by the limiting process. We further consider the converse problem and obtain sufficient conditions on integrable cocycles of quasiclassical Lie algebras in order to preserve nondegenerate quadratic Casimir operators by the associated linear deformations.

Campoamor-Stursberg, R., E-mail: rutwig@mat.ucm.e [Universidad Complutense, Departamento de Geometria y Topologia (Spain)

2008-05-15

420

Design of linear quadratic regulators with eigenvalue placement in a specified region  

NASA Technical Reports Server (NTRS)

Two linear quadratic regulators are developed for placing the closed-loop poles of linear multivariable continuous-time systems within the common region of an open sector, bounded by lines inclined at +/- pi/2k (for a specified integer k not less than 1) from the negative real axis, and the left-hand side of a line parallel to the imaginary axis in the complex s-plane, and simultaneously minimizing a quadratic performance index. The design procedure mainly involves the solution of either Liapunov equations or Riccati equations. The general expression for finding the lower bound of a constant gain gamma is also developed.

Shieh, Leang-San; Zhen, Liu; Coleman, Norman P.

1990-01-01

421

Intramolecular N-HCl hydrogen bonds in the outer coordination sphere of a bipyridyl bisurea-based ligand stabilize a tetrahedral FeLCl2 complex.  

PubMed

A bipyridyl-based anion receptor is utilized as a ligand in a tetrahedral FeCl2 complex and demonstrates secondary coordination sphere influence through intramolecular hydrogen bonding to the chloride ligands as evidenced by X-ray crystallography. PMID:24854889

Gavette, Jesse V; Klug, Christina M; Zakharov, Lev N; Shores, Matthew P; Haley, Michael M; Johnson, Darren W

2014-06-10

422

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

423

An adaptive linear quadratic regulator with repetitive controller applied to uninterruptible power supplies  

Microsoft Academic Search

This paper proposes a discrete time adaptive linear quadratic regulator (LQR) with a repetitive controller (RP) for uninterruptible power supplies (UPS). In the controller design, the gains are determined by minimizing a cost function which reduces the tracking error and the control signal. A recursive least squares (RLS) estimator identifies the plant parameters at different load conditions. Then, the LQR

Vinicius Foletto Montagner; Emerson Giovani Carati; H. A. Grundling

2000-01-01

424

Normal mode splitting due to quadratic reactive coupling in a microdisk-waveguide optomechanical system  

NASA Astrophysics Data System (ADS)

We study the effects of quadratic reactive coupling on normal mode splitting in a microdisk-waveguide optomechanical system, whose stability can be determined by the Routh-Hurwitz criterion. We find that the quadratic reactive coupling is important for the mode splitting of a Stokes field only in the presence of a strong pump field. For a large enough pump power, the quadratic reactive coupling will lead to larger and asymmetric frequency shifts for the two Stokes modes, which are however smaller and symmetric when only the linear reactive coupling is considered. Such a unique normal mode splitting happens in an efficient four-wave-mixing process of optomechanical interaction. This is why an anti-Stokes field is seen to arise in the presence of an excited waveguide oscillation. The anti-Stokes field has a much stronger interaction with the lower-frequency Stokes mode because their frequencies and amplitudes change remarkably in a similar way when the quadratic coupling constant is gradually increased.

Fu, Chang-Bao; Gu, Kai-Hui; Yan, Xiao-Bo; Yang, Xin; Cui, Cui-Li; Wu, Jin-Hui

2012-12-01

425

Ab initio quadratic configuration interaction calculations of isotropic hyperfine coupling constants  

Microsoft Academic Search

Results are presented from quadratic configuration interaction (QCISD) calculations of the isotropic component of the magnetic hyperfine coupling in the electronic ground states of the atoms B-F and of some radicals and radical cations derived from associated diatomic hydrides. Moderately large basis sets of contracted Gaussian functions are employed. Starting from unrestricted Hartree-Fock (UHF) reference spaces the unpaired spin density

Ian Carmichael

1991-01-01

426

On the rank of quadratic twists of elliptic curvers over function fields  

Microsoft Academic Search

We prove quantitative upper bounds for the number of quadratic twists of a given elliptic curve $E\\/\\\\Fp_q(C)$ over a function field over a finite field that have rank $\\\\geq 2$, and for their average rank. The main tools are constructions and results of Katz and uniform versions of the Chebotarev density theorem for varieties over finite fields. Moreover, we conditionally

Emmanuel Kowalski

2005-01-01

427

Friedmann Models and Cosmological Solutions in the Bimetric Theory with a Quadratic Lagrangian  

Microsoft Academic Search

Cosmological models are investigated within the framework of the bimetric theory of gravitation with a Lagrangian that is quadratic with respect to intensities g ik|l . It is shown that the theory predicts not only singular but also nonsingular solutions.

A. H. Yeranyan

2001-01-01

428

A Quadratic Curve Equating Method to Equate the First Three Moments in Equipercentile Equating.  

ERIC Educational Resources Information Center

A quadratic curve test equating method for equating different test forms under a random-groups data collection design is proposed that equates the first three central moments of the test forms. When applied to real test data, the method performs as well as other equating methods. Procedures from implementing the test are described. (SLD)

Wang, Tianyou; Kolen, Michael J.

1996-01-01

429

The wave function and minimum uncertainty function of the bound quadratic Hamiltonian system  

NASA Technical Reports Server (NTRS)

The bound quadratic Hamiltonian system is analyzed explicitly on the basis of quantum mechanics. We have derived the invariant quantity with an auxiliary equation as the classical equation of motion. With the use of this invariant it can be determined whether or not the system is bound. In bound system we have evaluated the exact eigenfunction and minimum uncertainty function through unitary transformation.

Yeon, Kyu Hwang; Um, Chung IN; George, T. F.

1994-01-01

430

Calculating a relaxation spectrum from experimental data via quadratic programming with and without regularization  

Microsoft Academic Search

The regularization quadratic programming approach to infer relaxation spectra from experimental mechanical data was studied. It was found that the inferior of the sum of the squared difference between the input data and the back-calculated values did not yield a satisfactory relaxation spectrum as the regularization weighting parameter ? was increased. A modification was made to the function to be

C. Y.-C. Lee; D. R. Wiff; V. G. Rodgers

1981-01-01

431

Frequency hopping spread spectrum signalling using code quadratic FSK technique for multichannel  

Microsoft Academic Search

In this paper, we have proposed and designed a code quadratic frequency shift keying technique based frequency hopping (CQFSK\\/FH) spread spectrum signaling for multichannels of wireless personal communication. The dependence of BER and bandwidth on hope size of the technique is shown. It is seen that the bandwidth of the proposed signaling scheme with four channels is five times less

P. P. Sahu; S. Panda

2010-01-01

432

Second-harmonic generation in disordered quadratic media: Role of a ferroelectric domain structure  

Microsoft Academic Search

We study theoretically the second harmonic generation in a nonlinear quadratic crystal with random distribution of ferroelectric domains. We show that the specific features of disordered domain structure greatly affect the emission pattern of the generated harmonics. This phenomenon can be used to characterize the degree of disorder in nonlinear photonic structures.

V. Roppo; K. Kalinowski; W. Wang; C. Cojocaru; J. Trull; R. Vilaseca; M. Scalora; W. Krolikowski; Y. Kivshar

2010-01-01

433

A Class of Quadratic FIR Filters with Applications to Spectral Shaping and Narrow Band Generation  

Microsoft Academic Search

In signal processing problems involving quadratic performance functional and stationary signals, solutions often involve a first stage of filtering called whitening. The whitening filter is a characterization of the signal power spectrum. For this reason, whitening and spectral estimation problems are closely related. The whitening filter obtained by Yule-Walker equations uncorrelates N samples of the output with the past input

Issa M. S. Panahi; Kripasagar Venkat

2005-01-01

434

Linear and Quadratic Rules: What Are They and When Are They Used?  

ERIC Educational Resources Information Center

Discriminant analysis is a multivariate method of analysis with two purposes: (1) to describe differences among groups; or (2) to classify participants into groups. Either linear or quadratic rules can be used in both descriptive discriminant analysis (DDA) and predictive discriminant analysis (PDA). In both DDA and PDA the researcher wants to use…

Altman, Daniel R.

435

Quadratic mixed integer programming and support vectors for deleting outliers in robust regression  

Microsoft Academic Search

We consider the problem of deleting bad influential observations (outliers) in linear regression models. The problem is formulated as a Quadratic Mixed Integer Programming (QMIP) problem, where penalty costs for discarding outliers are used into the objective function. The optimum solution defines a robust regression estimator called penalized trimmed squares (PTS). Due to the high computational complexity of the resulting

G. Zioutas; Leonidas S. Pitsoulis; Antonios Avramidis

2009-01-01

436

An Algorithm for Construction of Test Cases for the Quadratic Assignment Problem  

Microsoft Academic Search

In this paper we present an algorithm for generating quadratic assignment problem (QAP) instances with known provably optimal solution. The flow matrix of such instances is con- structed from the matrices corresponding to special graphs whose size may reach the dimension of the problem. In this respect, the algorithm generalizes some existing algorithms based on the iterative selection of triangles

Gintaras Palubeckis

2000-01-01

437

Example of a quadratic system with two cycles appearing in a homoclinic loop bifurcation  

NASA Astrophysics Data System (ADS)

We give here a planar quadratic differential system depending on two parameters, ?, ?. There is a curve in the ?-? space corresponding to a homoclinic loop bifurcation (HLB). The bifurcation is degenerate at one point of the curve and we get a narrow tongue in which we have two limit cycles. This is the first example of such a bifurcation in planar quadratic differential systems. We propose also a model for the bifurcation diagram of a system with two limit cycles appearing at a singular point from a degenerate Hopf bifurcation, and dying in a degenerate HLB. This model shows a deep duality between degenerate Hopf bifurcations and degenerate HLBs. We give a bound for the maximal number of cycles that can appear in certain simultaneous Hopf and homoclinic loop bifurcations. We also give an example of quadratic system depending on three parameters which has at one place a degenerate Hopf bifurcation of order 3, and at another place a Hopf bifurcation of order 2 together with a HLB. We characterize the planar quadratic systems which are integrable in the neighbourhood of a homoclinic loop.

Rousseau, Christiane

438

A differential transformation based computational method for switched linear quadratic optimal control  

Microsoft Academic Search

A computational method based on differential transformation is proposed for solving switched linear quadratic (SLQ) optimal control problems with a predefined switching sequence. From the necessary conditions for optimality, the SLQ optimal control problem is first converted into a two-point boundary value problem (TPBVP) with additional transverse conditions at the switching times. Then we propose a differential transformation algorithm for

Jinhua Li; Dzung Du; Inseok Hwang

2007-01-01

439

Performance of quadratic time-frequency distributions as instantaneous frequency estimators  

Microsoft Academic Search

General performance analysis of the shift covariant class of quadratic time-frequency distributions (TFDs) as instantaneous frequency (IF) estimators, for an arbitrary frequency-modulated (FM) signal, is presented. Expressions for the estimation bias and variance are derived. This class of distributions behaves as an unbiased estimator in the case of monocomponent signals with a linear IF. However, when the IF is not

Veselin N. Ivanovic; M. Dakovic; L. Stankovic

2003-01-01

440

On a general approach to the formal cohomology of quadratic Poisson structures  

Microsoft Academic Search

We propose a general approach to the formal Poisson cohomology of r-matrix induced quadratic structures, we apply this device to compute the cohomology of structure 2 of the Dufour–Haraki classification, and provide complete results also for the cohomology of structure 7.

Mohsen Masmoudi; Norbert Poncin

2007-01-01

441

Multistart Tabu Search and Diversification Strategies for the Quadratic Assignment Problem  

Microsoft Academic Search

The quadratic assignment problem (QAP) is a well- known combinatorial optimization problem with a wide variety of applications, prominently including the facility location problem. The acknowledged difficulty of the QAP has made it the focus of many metaheuristic solution approaches. In this paper, we show the benefit of utilizing strategic diversification within the tabu search (TS) framework for the QAP,

Tabitha James; César Rego; Fred Glover

2009-01-01

442

Sequential design of a linear quadratic controller for the Deep Space Network antennas  

Microsoft Academic Search

A new linear quadratic controller design procedure is proposed for the NASA\\/JPL Deep Space Network antennas. The antenna model is divided into a tracking subsystem and a flexible subsystem. Controllers for the flexible and tracking parts are designed separately by adjusting the performance index weights. Ad hoc weights are chosen for the tracking part of the controller and the weights

W. Gawronski

1992-01-01

443

SOLVABILITY OF LINEAR-QUADRATIC DIFFERENTIAL GAMES ASSOCIATED WITH PURSUIT-EVASION PROBLEMS  

Microsoft Academic Search

A finite horizon zero-sum linear-quadratic differential game with a generalized cost functional, involving a Lebesgue integral with a measure that has both discrete and distributed parts, is considered. Sufficient conditions for the solvability of such a game are established in terms of the eigenvalues of an integral operator in Hilbert space. The game solution is based on solving an impulsive

JOSEF SHINAR; VLADIMIR TURETSKY; VALERY Y. GLIZER; EDUARD IANOVSKY

2008-01-01

444

The quadratic speedup in Grover's search algorithm from the entanglement perspective  

NASA Astrophysics Data System (ADS)

We show that Grover's algorithm can be described as an iterative change of the bipartite entanglement, which leads to a necessary and sufficient condition for quadratic speedup. This allows us to reestablish, from the entanglement perspective, that Grover's search algorithm is the only optimal pure state search algorithm.

Rungta, Pranaw

2009-07-01

445

Quadratic Convergence of the Simplified Mizuno-Todd-Ye Algorithm for Linear Programming.  

National Technical Information Service (NTIS)

It is known that the Mizuno-Todd-Ye predictor-corrector primaldual Newton interior-point method generates a duality-gap sequence which converges quadratically to zero, and this is accomplished with an iteration complexity of O (square root of n L).

C. C. Gonzaga R. A. Tapia

1994-01-01

446

Incremental Local Search in Ant Colony Optimization: Why It Fails for the Quadratic Assignment Problem  

Microsoft Academic Search

Ant colony optimization algorithms are currently among the best performing algorithms for the quadratic assignment problem. These algorithms contain two main search procedures: solution construction by articial ants and local search to improve the solutions constructed by the ants. Incremental local search is an approach that consists in re- optimizing partial solutions by a local search algorithm at regular inter-

Prasanna Balaprakash; Mauro Birattari; Thomas Stützle; Marco Dorigo

2006-01-01

447

??????????????????????????????????????????????????????????????????????????????????????? ????? COMPARING TWO ESTIMATING TECHNIQUES ON CORAL GROWTH FORMS USING RANDOM AND QUADRAT SAMPLING TECHNIQUES  

Microsoft Academic Search

This study aims at estimating coral growth forms at Khanom - Mu Koh Tale Tai Marine National Park. Two techniques were used to estimate coral growth forms: random and quadrat sampling techniques. Researcher took coral photographs with a digital camera and underwater casing. Coral images were classified into one of seven coral forms and used these percentages to calculate coral

Chairote Yaiprasert; Suntorn Surabun; Siriwan Wongkoon; Mullica Jaroensutasinee

448

Linear quadratic Gaussian controller design for plasma current, position and shape control system in ITER  

Microsoft Academic Search

This paper is focused on the linear quadratic Gaussian (LQG) controller synthesis methodology for the ITER plasma current, position and shape control system as well as power derivative management system. It has been shown that some poloidal field (PF) coils have less influence on reference plasma-wall gaps control during plasma disturbances and hence they have been used to reduce total

V Belyakov; A Kavin; V Kharitonov; B Misenov; Y Mitrishkin; A Ovsyannikov; D Ovsyannikov; E Rumyantsev; E Veremei; A Zhabko

1999-01-01

449

A parametric model for the quadratic sampling of a bandlimited signal  

Microsoft Academic Search

The paper treats the problem of ambiguity resolution using non-uniform sampling. This problem occurs for Doppler estimation in coherent pulsed Doppler radar. In the paper, the authors study the case where the duration between two samples is a linear function of time: quadratic sampling. Assuming that the continuous signal is stationary, the sampled signal will be non-stationary. The autocorrelation of

A. Ferrari; R. Lorion; G. Alengrin

1995-01-01

450

A new neural network for solving linear and quadratic programming problems  

Microsoft Academic Search

A new neural network for solving linear and quadratic programming problems is presented and is shown to be globally convergent. The new neural network improves existing neural networks for solving these problems: it avoids the parameter turning problem, it is capable of achieving the exact solutions, and it uses only simple hardware in which no analog multipliers for variables are

Youshen Xia

1996-01-01

451

Comparision of two soft computing techniques for economic dispatch with piece wise quadratic cost function  

Microsoft Academic Search

This paper presents two modern approaches for solving economic dispatch (ED) problem considering piece wise quadratic cost function. Practical Economic dispatch problems have non-smooth fuel cost function with equality and inequality constraints which make it difficult to be effectively solved. In this paper modern heuristic methods such as shuffled frog leaping algorithm (SFLA) and harmony search (HS) are proposed for

Ch. Satish Babu; T. Mabu Subhani; A. Srinivasa Reddy; K. Vaisakh

2012-01-01

452

Advanced Nonlinear Latent Variable Modeling: Distribution Analytic LMS and QML Estimators of Interaction and Quadratic Effects  

ERIC Educational Resources Information Center

Interaction and quadratic effects in latent variable models have to date only rarely been tested in practice. Traditional product indicator approaches need to create product indicators (e.g., x[superscript 2] [subscript 1], x[subscript 1]x[subscript 4]) to serve as indicators of each nonlinear latent construct. These approaches require the use of…

Kelava, Augustin; Werner, Christina S.; Schermelleh-Engel, Karin; Moosbrugger, Helfried; Zapf, Dieter; Ma, Yue; Cham, Heining; Aiken, Leona S.; West, Stephen G.

2011-01-01

453

Minimum mean square error estimates of invariant parameters in the quadrate of ISAR signal amplitude  

Microsoft Academic Search

A minimum mean square error (MMSE) method for estimation of the invariant geometric and kinematic parameters of the quadrate amplitude of the inverse synthetic aperture radar (ISAR) signal. is suggested. This method is an alternative to the correlation-spectral techniques used for ISAR signal processing. This computational technique is based on minimizing the mean square error in the approximation of the

Andon Dimitrov Lazarov

2001-01-01

454

Controllability, observability and discrete-time markovian jump linear quadratic control  

Microsoft Academic Search

This paper is concerned with the controllability and observability of discrete-time linear systems that possess randomly jumping parameters described by finite-stale Markov processes, and the relationship between these properties and the solution of the infinite time jump linear quadratic (JLQ) optimal control problem. The solution of the markovian JLQ problem with finite or infinite time horizons is known. Necessary and

YUANDONG JI; HOWARD J. CHIZECK

1988-01-01

455

Asymptotic formulas for partial sums of class numbers of indefinite binary quadratic forms  

Microsoft Academic Search

Sarnak obtained the asymptotic formula of the sum of the class numbers of indefinite binary quadratic forms from the prime geodesic theorem for the modular group. In the present paper, we show several asymptotic formulas of partial sums of the class numbers by using the prime geodesic theorems for the congruence subgroups of the modular group.

Yasufumi Hashimoto

2008-01-01

456

Analysis of a Mathematics Achievement Test via the Linear Logistic Test Model and Quadratic Assignment.  

ERIC Educational Resources Information Center

The cognitive structure of an algebra test was defined and validated using the linear test model (LLTM) and quadratic assignment (QA) techniques. The LLTM is an extension of the Rasch model with a linear constraint that describes item difficulty in terms of the cognitive operations required to solve the item. The model permits the specification of…

Medina-Diaz, Maria

457

The fuzzy quadratic assignment problem with penalty: New models and genetic algorithm  

Microsoft Academic Search

The assignment problem is to find the total costs optimal jobs assignment schedule where n jobs are allocated to n workers, and each worker receives exactly just one job, such that the total cost is optimal. The quadratic assignment problem with penalty takes three types of costs into consideration: direct cost, interactive cost an penalty. In this paper, the fuzzy

Linzhong Liu; Yinzhen Li

2006-01-01

458

On the exact solutions of nonlinear diffusion-reaction equations with quadratic and cubic nonlinearities  

NASA Astrophysics Data System (ADS)

Attempts have been made to look for the soliton content in the solutions of the recently studied nonlinear diffusion-reaction equations [R S Kaushal, J. Phys. 38, 3897 (2005)] involving quadratic or cubic nonlinearities in addition to the convective flux term which renders the system nonconservative and the corresponding Hamiltonian non-Hermitian.

Kaushal, R. S.; Kumar, Ranjit; Prasad, Awadhesh

2006-08-01

459

Pointwise linear quadratic optimal control of a tandem cold rolling mill  

Microsoft Academic Search

The tandem cold rolling of metal strip is a complex nonlinear multivariable process whose optimization presents significant challenges to the control design. Existing systems using the present technology are limited in their capability for improvement in performance and robustness and therefore the need arises for a better approach. It is considered that a pointwise linear quadratic optimal control might fulfill

John Pittner; Marwan A. Simaan

2004-01-01

460

Intelligent local search strategies for solving facility layout problems with the quadratic assignment problem formulation  

Microsoft Academic Search

In this paper, we implement a tabu search heuristic, a probabilistic tabu search heuristic, a simulated annealing heuristic, and a hybrid tabu search heuristic to solve facility layout problems with the Quadratic Assignment Problem formulation Classical problems are used as a benchmark for performance comparison. Extensive computational experiments were conducted, and the results were statistically analyzed to observe the behavior

Wen-Chyuan Chiang; Chi Chiang

1998-01-01

461

Robust generation, properties and potential applications of quadratic spatial solitons generated by optical parametric amplification  

Microsoft Academic Search

Quadratic spatial solitary waves are predicted and observed experimentally near degeneracy for Type II optical parametric amplification in bulk KTP, by seeding an intense pump optical field with a control signal at half the pump wave frequency. The self-trapping of light at the two wavelengths has been shown to be insensitive to phase, polarization and magnitude of the control input,

R. A. Fuerst; M. T. G. Canva; G. I. Stegeman; G. Leo; G. Assanto

1998-01-01

462

Iterated He’s homotopy perturbation method for quadratic Riccati differential equation  

Microsoft Academic Search

In this paper, iterated He’s homotopy perturbation method is proposed to solving quadratic Riccati differential equation. Comparisons are made between Adomian’s decomposition method (ADM) and the exact solution and the proposed method. The results reveal that the method is very effective and simple.

S. Abbasbandy

2006-01-01

463

Homotopy perturbation method for quadratic Riccati differential equation and comparison with Adomian's decomposition method  

Microsoft Academic Search

In this paper, a homotopy perturbation method is proposed to solve quadratic Riccati differential equation. Comparisons are made between Adomian’s decomposition method (ADM) and the exact solution and the proposed method. The results reveal that the proposed method is very effective and simple.

Saeid Abbasbandy

2006-01-01

464

The soft coral community on a sheltered reef quadrat at Laing Island (Papua New Guinea)  

Microsoft Academic Search

Thirty-one species of soft corals have been found on a 30×20 m quadrat on the sheltered shore of Laing Island, on the north coast of Papua New Guinea. Their contribution to the living coverage has been quantified, with special attention to zonation. The observed distribution patterns are discussed and the importance of vegetative propagation for some of the species is

B. Tursch; A. Tursch

1982-01-01

465

Graphical Representation of Complex Solutions of the Quadratic Equation in the "xy" Plane  

ERIC Educational Resources Information Center

This paper presents a visual representation of complex solutions of quadratic equations in the xy plane. Rather than moving to the complex plane, students are able to experience a geometric interpretation of the solutions in the xy plane. I am also working on these types of representations with higher order polynomials with some success.

McDonald, Todd

2006-01-01

466

Solution to Projectile Motion with Quadratic Drag and Graphing the Trajectory in Spreadsheets  

ERIC Educational Resources Information Center

This note gives the analytical solution to projectile motion with quadratic drag by decomposing the velocity vector to "x," "y" coordinate directions. The solution is given by definite integrals. First, the impact angle is estimated from above, then the projectile coordinates are computed, and the trajectory is graphed at various launch angles and…

Benacka, Jan

2010-01-01

467

A new capability of cascaded quadratic processes: controllable red and blue shift of femtosecond pulses  

Microsoft Academic Search

We theoretically and experimentally demonstrate the controllable frequency shift of femtosecond pulses in quadratic media in the presence of group velocity mismatch. Applications of this new capability to the compensation of Raman scattering and high-energy pulse compression are discussed.

F. O. Ilday; K. Beckwitt; H. Lim; F. W. Wise

2003-01-01

468

Experimental appraisal of linear and quadratic objective functions effect on force directed method for analog placement  

Microsoft Academic Search

This paper advocates the use of linear objective function in analytic analog placement. The role of linear and quadratic objctive functions in the behavior and results of an analog placement algorithm based on the force directed method is discussed. Experimental results for a MCNC benchmark circuit and another one from text books are shown to demonstrate the effect of a

I. I. Mahmoud; K. Asakura; T. Nishibu; T. Ohtsuki

1994-01-01

469

Linear and quadratic objective function effects on force directed method based analog placement  

Microsoft Academic Search

This paper advocates the use of linear objective function in analytic analog placement. The role of linear and quadratic objective functions in the behavior and results of an analog placement algorithm based on the force directed method is discussed. Experimental results for a MCNC benchmark circuit and another one from text books are shown to demonstrate the effect of a

Imbaby I. Mahmoud

1996-01-01

470

Prompt critical control of the ACRR using a linear quadratic regulator design  

Microsoft Academic Search

This paper describes the application of linear control design techniques to the problem of nuclear reactor control. The control algorithm consists of generating a nominal trajectory within the control authority of the reactor rod drives, and then following this trajectory with a gain scheduled linear quadratic regulator (LQR). A controller based on this algorithm has generated power pulses up to

Gilkey

1992-01-01

471

Prompt critical control of the ACRR using a linear quadratic regulator design  

Microsoft Academic Search

This paper describes the application of ``Modern Control'' design techniques to the problem of nuclear reactor control. The control algorithm consists of generating a nominal trajectory within the control authority of the reactor rod drives, and then following this trajectory with a gain scheduled linear quadratic regulator (LQR). A controller based on this algorithm has generated power pulses up to

Jeffrey C. Gilkey

1993-01-01

472

Prompt critical control of the ACRR using a linear quadratic regulator design  

Microsoft Academic Search

This paper describes the application of ‘‘Modern Control’’ design techniques to the problem of nuclear reactor control. The control algorithm consists of generating a nominal trajectory within the control authority of the reactor rod drives, and then following this trajectory with a gain scheduled linear quadratic regulator (LQR). A controller based on this algorithm has generated power pulses up to

Jeffrey C. Gilkey

1993-01-01

473

Error-correcting codes for QAM from integer rings of an Euclidean complex quadratic field  

Microsoft Academic Search

New error-correcting block codes for two-dimensional signal constellations such as QAM are given. They can correct one error in each component of the codewords, with only one redundant symbol. We also prove that these new block codes can be constructed for any Euclidean complex quadratic field

J. Rifa; M. Villannueva

1998-01-01

474

Horizontal Distance Travelled by a Mobile Experiencing a Quadratic Drag Force: Normalized Distance and Parametrization  

ERIC Educational Resources Information Center

We investigate the problem of the horizontal distance travelled by a mobile experiencing a quadratic drag force. We show that by introducing a normalized distance, the problem can be greatly simplified. In order to parametrize this distance, we use the Pearson VII function, and we find that the optimal launch angle as a function of the initial…

Vial, Alexandre

2007-01-01

475

Quadratic Convergence of a Squared Smoothing Newton Method for Nonsmooth Matrix Equations and Its Applications in Semidefinite Optimization Problems  

Microsoft Academic Search

We study a smoothing Newton method for solving a nonsmooth matrix equation that includes semidefinite programming and the semidefinte complementarity problem as special cases. This method, if specialized for solving semidefinite programs, needs to solve only one linear system per iteration and achieves quadratic convergence under strict complementarity. We also establish quadratic convergence of this method applied to the semidefinite

Jie Sun; Defeng Sun; Liqun Qi

476

New RE microporous heteropolyhedral silicates containing 4(1)5(1)6(1)8(2) tetrahedral sheets.  

PubMed

Four heteropolyhedral microporous silicates, A(3)RESi(6)O(15).2.25H(2)O, crystallizing in the Cmm2 space group and based on 4(1)5(1)6(1)8(2) tetrahedral sheets [A(3) = Na(2.74)K(0.26), RE = Ce, abbreviated as TR05; TR06: A(3) = Na(2.72)K(0.28), RE = La; TR07: A(3) = Na(3), RE = La; TR08: A(3) = Na(2.74)(H(3)O)(0.26), RE = La(0.68)Eu(0.32)] have been hydrothermally synthesized in Teflon-lined autoclaves at 503 K and structurally characterized using X-ray diffraction single-crystal data. Except for TR05, diffraction data have been collected on {001} twins by merohedry. The four structures are isotypic and based on strongly corrugated 4(1)5(1)6(1)8(2) silicate sheets interconnected along [010] by seven-coordinated RE polyhedra to form a microporous heteropolyhedral framework. The framework is crossed by three systems of ellipsoidal channels that host H(2)O molecules and alkaline ions. The channels run either parallel or perpendicular to the silicate sheets; the largest effective channel width is 4.7 x 2 A. In TR08 some (H(3)O)(+) replaces alkalis. Although the H atoms have not been localized, the configuration of the hydrogen bonding has been deduced from bond lengths and angles. PMID:20305349

Cadoni, Marcella; Cheah, Yan Ling; Ferraris, Giovanni

2010-04-01

477

Effects of tetrahedral Fe2+ on the structural, magnetic and electronic properties of solution-based titanomagnetite thin films  

NASA Astrophysics Data System (ADS)

Polycrystalline titanomagnetite (Ti x Fe3- x O4) thin films prepared by using a sol-gel process exhibited a phase-pure spinel structure for Ti compositions up to x = 0.6. An X-ray photoelectron spectroscopy (XPS) investigation disclosed an increase of the Fe2+ concentration with increasing x, indicating a reduction in ionic valence, Fe3+ ? Fe2+, induced by Ti4+ occupation of the cationic sublattice. Analyses on XPS and X-ray diffraction spectra of the Ti x Fe3- x O4 samples suggest that the Fe2+ ions prefer the tetrahedral sites while the Ti4+ ions prefer the octahedral sites of the sublattice. Magnetic hysteresis measurements on the Ti x Fe3- x O4 films revealed significant loss of the saturation magnetization (M s ) with increasing x: M s is reduced to 50% that of Fe3O4 for x = 0.10 and to 10% for x = 0.60. The big loss of M s caused by small Ti doping suggests a significant disruption of the inter-site Fe3+-Fe3+ super-exchange interaction in thin-film titanomagnetites.

Kim, Kwang Joo; Koh, Tae Young; Kim, Chul Sung; Lee, Young Bae

2014-01-01

478

Electronic and vibronic cluster models for the T24(G) level of d5 ions in tetrahedral symmetry  

NASA Astrophysics Data System (ADS)

Electronic and vibronic cluster models are proposed to elaborate a general model for the T24(G) orbital triplet levels of d5 ions in tetrahedral symmetry. These models involve perturbation schemes and the diagonalization of the molecular electronic structure and vibronic Hamiltonian. First, the electronic fine structure is determined from the first- and second-order molecular spin-orbit (MSO) interaction. Then, Ham’s perturbation model for vibronic interactions is used in conjunction with the molecular model to analyze the vibronic interactions corresponding to a strong coupling to ? -vibrational modes. Then, a more general model is considered to account for the energy-level schemes and the strong intensity transfer observed, for example, on the fine structure lines of the T24(G) level of Mn2+ in ZnS and ZnSe. This model involves the diagonalization of the vibronic Hamiltonian for the T24(G) level and a perturbation model to account for vibronic interactions with all other multiplets of the d5 configuration. It is shown that the energy-level schemes as well as the strong intensity transfer of the fine structure lines of the T24(G) level of Mn2+ in ZnS and ZnSe are very well accounted for from the electronic molecular model involving the first- and second-order MSO interaction and from the proposed diagonalization and perturbation models for the coupling to ? -vibrational modes.

Parrot, R.; Boulanger, D.

2006-08-01

479

Shape distribution and correlation between size and shape of tetrahedral lattice chains in athermal and theta systems  

NASA Astrophysics Data System (ADS)

Chains embedded in the tetrahedral lattice have been produced by means of Monte Carlo simulation for athermal and for theta conditions. Nonreversal random walks (random walks without backfolding bonds) have been generated as a reference. Probability distributions of an asphericity factor ?*, of a prolatness factor S*, and of shape factors sfi* have been evaluated, the quantities being based on