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1

Quadratic and Cubic Transition Elements.  

National Technical Information Service (NTIS)

Based on the investigation of Barsoum, Henshell and Shaw, quarterpoint quadratic elements have been successfully used as crack tip elements in fracture mechanics. This concept of singular element was extended to cubic isoparametric elements. Recently it w...

M. A. Hussain J. D. Vasilakis S. L. Pu

1980-01-01

2

Finite Element LES and VMS Methods on Tetrahedral Meshes  

Microsoft Academic Search

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 discon- tinuous pressure

Volker John; Adela Kindl; Carina Suciu

2009-01-01

3

Quadratic finite elements and incompressible viscous flows.  

SciTech Connect

Pressure stabilization methods are applied to higher-order velocity finite elements for application to viscous incompressible flows. Both a standard pressure stabilizing Petrov-Galerkin (PSPG) method and a new polynomial pressure projection stabilization (PPPS) method have been implemented and tested for various quadratic elements in two dimensions. A preconditioner based on relaxing the incompressibility constraint is also tested for the iterative solution of saddle point problems arising from mixed Galerkin finite element approximations to the Navier-Stokes equations. The preconditioner is demonstrated for BB stable elements with discontinuous pressure approximations in two and three dimensions.

Dohrmann, Clark R.; Gartling, David K.

2005-01-01

4

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

SciTech Connect

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

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

1999-01-01

5

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

6

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

7

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

8

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

9

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

SciTech Connect

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

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

1998-03-01

10

Large-deformation triangular and tetrahedral element formulations for unstructured meshes  

Microsoft Academic Search

The increasing use of automatic mesh generators and remeshers has spurred the need for accurate and efficient triangular and tetrahedral elements in unstructured meshes. In large-deformation analysis of solids, accuracy and efficiency require the treatment of volumetric locking and element distortions, respectively. In this paper, a mixed formulations is proposed to treat these issues, and applied to triangular and tetrahedral

Stephen R. Beissel; Gordon R. Johnson

2000-01-01

11

Quadratic immersed finite element spaces and their approximation capabilities  

Microsoft Academic Search

This paper discusses a class of quadratic immersed finite element (IFE) spaces developed for solving second order elliptic\\u000a interface problems. Unlike the linear IFE basis functions, the quadratic IFE local nodal basis functions cannot be uniquely\\u000a defined by nodal values and interface jump conditions. Three types of one dimensional quadratic IFE basis functions are presented\\u000a together with their extensions for

Brian Camp; Tao Lin; Yanping Lin; Weiwei Sun

2006-01-01

12

Calculation of non-linear vibration of rotating beams by using tetrahedral and solid finite elements  

NASA Astrophysics Data System (ADS)

A development is presented of the non-linear dynamic equations that govern the motion of the tetrahedral and solid finite elements that undergo large displacements. The development presented is exemplified by using the four-node, 12-degree-of-freedom tetrahedral element and the eight-node, 24-degree-of-freedom solid element. It is shown that the element shape functions used in this investigation can be used to describe large translations and finite rigid body rotations. Accordingly, the non-linear formulation presented in this paper can be used in the analysis of small as well as large deformation. The element configuration is identified by using four co-ordinate systems. These co-ordinate systems are the global, body, element and intermediate element co-ordinate systems. The large displacement of the tetrahedral and solid elements is described by using a set of absolute co-ordinates that define the location and orientation of the deformable body co-ordinate systems. The non-linear differential equations of motion of the tetrahedral and solid finite elements are developed by using the principle of virtual work in dynamics. The use of the non-linear dynamic formulation presented in this investigation is demonstrated by using a flexible single robotic arm manipulator that undergoes large displacements. The results obtained by using the four-node tetrahedral elements and the eight-node solid elements are compared with the results obtained by using the three-dimensional beam element. This comparison shows that the discrepancy between the results obtained by using the solid and tetrahedral elements in beam problems is more significant in the dynamic analysis as compared to the discrepancy of 10% reported in the literature for the static analysis.

Jiang, J. J.; Hsiao, C. L.; Shabana, A. A.

1991-07-01

13

Method of Volume Coordinates — from Tetrahedral to Hexahedral Elements  

Microsoft Academic Search

In the development history of finite element method, an element model with high performance possesses important significance.\\u000a The three-dimension (3D) hexahedral isoparametric elements are widely used in scientific and engineering computations. However,\\u000a their accuracy may drop obviously in an irregular mesh division. In order to improve the robustness of these elements, many\\u000a researchers have made great efforts, and these jobs

Hongguang Li; Song Cen; Yuqiu Long; Zhangzhi Cen

14

Quadratic  

NSDL National Science Digital Library

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

15

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

16

Analytic calculation of arbitrary matrix elements for the boson exponential quadratic operator  

NASA Astrophysics Data System (ADS)

Making use of the transformation relation between the ordinary form and the antinormal product form of boson exponential quadratic operators (BEQO's), we present an effective method which can be conveniently used to calculate arbitrary matrix elements of BEQO's. By this method, some important matrix elements have been calculated analytically. As a preliminary application, we obtain the exact solution of the density matrix and partition function for the general boson quadratic Hamiltonian without any information for the energy level. As a natural extension, we also obtain the partition function for a general fermion quadratic system.

Pan, Jian-Wei; Dong, Qin-Xi; Zhang, Yong-De; Hou, Guang; Wang, Xiang-Bin

1997-09-01

17

Numerical solution of the Poisson-Boltzmann equation using tetrahedral finite-element meshes  

Microsoft Academic Search

The automatic three-dimensional mesh generation system for molecular geometries developed in our laboratory is used to solve the Poisson)Boltzmann equation numerically using a finite element method. For a number of different systems, the results are found to be in good agreement with those obtained in finite difference calculations using the DelPhi program as well as with those from boundary element

Christian M. Cortis; Richard A. Friesner

1997-01-01

18

Predictive Modeling of Defibrillation utilizing Hexahedral and Tetrahedral Finite Element Models: Recent Advances  

PubMed Central

ICD implants may be complicated by body size and anatomy. One approach to this problem has been the adoption of creative, extracardiac implant strategies using standard ICD components. Because data on safety or efficacy of such ad hoc implant strategies is lacking, we have developed image-based finite element models (FEMs) to compare electric fields and expected defibrillation thresholds (DFTs) using standard and novel electrode locations. In this paper, we review recently published studies by our group using such models, and progress in meshing strategies to improve efficiency and visualization. Our preliminary observations predict that they may be large changes in DFTs with clinically relevant variations of electrode placement. Extracardiac ICDs of various lead configurations are predicted to be effective in both children and adults. This approach may aid both ICD development and patient-specific optimization of electrode placement, but the simplified nature of current models dictates further development and validation prior to clinical or industrial utilization.

Triedman, John K.; Jolley, Matthew; Stinstra, Jeroen; Brooks, Dana H.; MacLeod, Rob

2008-01-01

19

X-ray-absorption near-edge structure of 3d transition elements in tetrahedral coordination: The effect of bond-length variation  

SciTech Connect

The x-ray-absorption near-edge structure (XANES) of transition elements in tetrahedral coordination in crystals and glasses has been studied. We have identified the XANES features in the continuum that can be assigned to multiple scattering within the first coordination shell. The energy positions E/sub r/ of the XANES peaks in the continuum follow the rule (E/sub r/-E/sub b/)d/sup 2/ = const, where E/sub b/ is the energy of the prepeak, defined as the first core excitation to the bound antibonding state of T/sub 2/ symmetry, and d is the interatomic distance. This plot allows us to determine the tetrahedral coordination of a vanadium impurity in a SiO/sub 2/ glass and to get an estimation of the vanadium-oxygen distance (1.77 +- 0.05 A).

Bianconi, A.; Fritsch, E.; Calas, G.; Petiau, J.

1985-09-15

20

Haptic Rendering of Data on Unstructured Tetrahedral Grids  

Microsoft Academic Search

An algorithm is developed to interpolate data in unstructured tetrahedral meshes for improved real-time haptic rendering. Given a Cartesian location in the data set, the containing tetrahedral element in the unstructured mesh must be located. Then the data at the nodes of this tetrahedral element are interpolated to yield the proper data value(s) to render. Comparisons are made with a

Roman Y. Novoselov; Dale A. Lawrence; Lucy Y. Pao

2002-01-01

21

Quadratic formula  

NSDL National Science Digital Library

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

Liao, David

22

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

23

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

24

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

25

Parallel adaptive tetrahedral mesh generation by the advancing front technique  

Microsoft Academic Search

A parallel adaptive tetrahedral mesh generation program using the advancing front method is described. The problem domain is initially defined by a course background mesh of tetrahedral elements which forms the input for finite element analysis and from which adaptive parameters are calculated. Parallel adaptive mesh generation is then carried out by dividing the background mesh into subdomains and refining

J. K. Wilson; B. H. V. Topping

1998-01-01

26

Quadratic elongation: A quantitative measure of distortion in coordination polyhedra  

USGS Publications Warehouse

Quadratic elongation and the variance of bond angles are linearly correlated for distorted octahedral and tetrahedral coordination complexes, both of which show variations in bond length and bond angle. The quadratic elonga tion is dimensionless, giving a quantitative measure of polyhedral distortion which is independent of the effective size of the polyhedron.

Robinson, K.; Gibbs, G. V.; Ribbe, P. H.

1971-01-01

27

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

28

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

29

Self-Replicating Quadratics  

ERIC Educational Resources Information Center

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

Withers, Christopher S.; Nadarajah, Saralees

2012-01-01

30

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

31

Band limits and the vibrational spectra of tetrahedral glasses  

Microsoft Academic Search

The primary features of the Raman and infrared spectra of AX2 tetrahedral glasses are associated with the edges of the vibrational bands calculated by Sen and Thorpe. The dominant Raman peak is assigned to a singular matrix element rather than a peak in the density of vibrational states. Simple expressions are developed which yield useful values of the vibrational force

Frank L. Galeener

1979-01-01

32

Quadratic eigenvalue problems.  

SciTech Connect

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

Walsh, Timothy Francis; Day, David Minot

2007-04-01

33

Nuclear tetrahedral configurations at spin zero  

SciTech Connect

The possibility of the existence of stable tetrahedral deformations at spin zero is investigated using the Skyrme-HFBCS approach and the generator coordinate method (GCM). The study is limited to nuclei in which the tetrahedral mode has been predicted to be favored on the basis of non-self-consistent models. Our results indicate that a clear identification of tetrahedral deformations is unlikely because they are strongly mixed with the axial octupole mode. However, the excitation energies related to the tetrahedral mode are systematically lower than those of the axial octupole mode in all the nuclei included in this study.

Zberecki, Krzysztof; Magierski, Piotr [Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, PL-00-662 Warsaw (Poland); Heenen, Paul-Henri [Service de Physique Nucleaire Theorique, U.L.B-C.P. 229, B-1050 Brussels (Belgium)

2009-01-15

34

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

35

A Special Quadratic Program.  

National Technical Information Service (NTIS)

This paper presents a characterization of the solutions of a special quadratic program. This characterization is then used in the development of an efficient algorithm for this class of problems. (Author)

R. Helgason J. Kennington H. Lall

1978-01-01

36

Interactive isosurface ray tracing of time-varying tetrahedral volumes.  

PubMed

We describe a system for interactively rendering isosurfaces of tetrahedral finite-element scalar fields using coherent ray tracing techniques 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 intersecting ray packets with tetrahedral primitives. Ray tracing is flexible, allowing for dynamic changes in isovalue and time step, visualization of multiple isosurfaces, shadows, and depth-peeling transparency effects. The resulting system offers the intuitive simplicity of isosurfacing, guaranteed-correct visual results, and ultimately a scalable, dynamic and consistently interactive solution for visualizing unstructured volumes. PMID:17968131

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

37

Quadratic spline subroutine package  

USGS Publications Warehouse

A continuous piecewise quadratic function with continuous first derivative is devised for approximating a single-valued, but unknown, function represented by a set of discrete points. The quadratic is proposed as a treatment intermediate between using the angular (but reliable, easily constructed and manipulated) piecewise linear function and using the smoother (but occasionally erratic) cubic spline. Neither iteration nor the solution of a system of simultaneous equations is necessary to determining the coefficients. Several properties of the quadratic function are given. A set of five short FORTRAN subroutines is provided for generating the coefficients (QSC), finding function value and derivatives (QSY), integrating (QSI), finding extrema (QSE), and computing arc length and the curvature-squared integral (QSK). (USGS)

Rasmussen, L. A.

1982-01-01

38

Quadratic exponential vectors  

SciTech Connect

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

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

2009-12-15

39

The quadratic programming problem with fuzzy relation inequality constraints  

Microsoft Academic Search

The quadratic programming has been widely applied to solve real world problems. The quadratic functions are often applied in the inventory management, portfolio selection, engineering design, molecular study, and economics, etc. Fuzzy relation inequalities (FRI) are important elements of fuzzy mathematics, and they have recently been widely applied in the fuzzy comprehensive evaluation and cybernetics. In view of the importance

Ali Abbasi Molai

40

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

41

A new locking-free formulation for planar, shear deformable, linear and quadratic beam finite elements based on the absolute nodal coordinate formulation  

Microsoft Academic Search

Many widely used beam finite element formulations are based either on Reissner’s classical nonlinear rod theory or the absolute\\u000a nodal coordinate formulation (ANCF). Advantages of the second method have been pointed out by several authors; among the benefits\\u000a are the constant mass matrix of ANCF elements, the isoparametric approach and the existence of a consistent displacement field\\u000a along the whole

Karin Nachbagauer; Astrid S. Pechstein; Hans Irschik; Johannes Gerstmayr

42

Quadratic knapsack problems  

Microsoft Academic Search

The quadratic knapsack (QK) model naturally arises in a variety of problems in operations research, statistics and combinatorics.\\u000a Some “upper planes” for the QK problem are derived, and their different uses in a branch-and-bound scheme for solving such\\u000a a problem are discussed. Some theoretical results concerning the class of all upper planes, as well as extensive computational\\u000a experience, are reported.

G. Gallo; P. L. Hammer; B. Simeone

43

Quadratic component analysis.  

PubMed

I present a method for analyzing multichannel recordings in response to repeated stimulus presentation. Quadratic Component Analysis (QCA) extracts responses that are stimulus-induced (triggered by the stimulus but not precisely locked in time), as opposed to stimulus-evoked (time-locked to the stimulus). Induced responses are often found in neural response data from magnetoencephalography (MEG), electroencephalography (EEG), or multichannel electrophysiological and optical recordings. The instantaneous power of a linear combination of channels can be expressed as a weighted sum of instantaneous cross-products between channel waveforms. Based on this fact, a technique known as Denoising Source Separation (DSS) is used to find the most reproducible "quadratic component" (linear combination of cross-products). The linear component with a square most similar to this quadratic component is taken to approximate the most reproducible evoked activity. Projecting out the component and repeating the analysis allows multiple induced components to be extracted by deflation. The method is illustrated with synthetic data, as well as real MEG data. At unfavorable signal-to-noise ratios, it can reveal stimulus-induced activity that is invisible to other approaches such as time-frequency analysis. PMID:22079456

de Cheveigné, Alain

2011-11-04

44

Extreme Mobility: Next Generation Tetrahedral Rovers  

Microsoft Academic Search

This paper describes the development and testing of a patented rover concept called Tetrahedral Explorer Technologies (TET), designed to provide extreme mobility and plug-and-play utility through reconfigurable addressable architecture. Here, we present the results of preliminary lab and field tests of Prototype III. Reconfigurable architecture is essential in exploration because reaching features of the great potential interest will require crossing

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

2007-01-01

45

Distorted tetrahedral shapes of nematic vesicles  

NASA Astrophysics Data System (ADS)

In membranes with internal orientational or crystalline order, there is a geometric coupling between 2D internal order and 3D shape. Nonuniformity in internal order tends to induce curvature, and curvature provides an effective potential acting on internal order. For a closed vesicle with nematic liquid-crystalline order, there must be a total topological charge of +2, which normally occurs as four defects of +1/2 each. Previous research has suggested that these four defects form a regular tetrahedron, leading to a tetrahedral shape of the vesicle, which may be useful in colloidal crystals for photonic applications. Here, we develop an explicit model to calculate energies of defect structures in nematic vesicles. When the liquid-crystal interaction energy is a purely 2D intrinsic interaction, we find that the perfect tetrahedral shape is stable only up to a maximum interaction strength (Frank constant), where it changes to an elongated rectangular configuration. When the interaction energy is a 3D extrinsic and intrinsic interaction, the perfect tetrahedral shape is never stable; the vesicle is a distorted tetrahedron for small Frank constant and a highly elongated rectangle for larger Frank constant. These results show the difficulty in designing tetrahedral structures.

Son Nguyen, Thanh; Selinger, Jonathan

2013-03-01

46

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

47

On Efficient Semidefinite Relaxations for Quadratically Constrained Quadratic Programming  

Microsoft Academic Search

Abstract Two important topics in the study of Quadratically Constrained Quadratic Programming (QCQP) are how to exactly solve a QCQP with few constraints in polynomial time and how to find an inexpensive and strong relaxation bound for a QCQP with many constraints. In this thesis, we first review some important results on QCQP, like the S-Procedure, and the strength of

Yichuan Ding

2007-01-01

48

Quadratic Lagrangians and horizons  

SciTech Connect

It has been known for some time that the standard isotropic cosmological model with an {ital R}{sup 2} Lagrangian has horizon-breaking solutions in the {ital t}{r arrow}0 singularity limit. We search for horizonless power-law solutions in the vacuum Bianchi type-I and orthogonal type-V cosmological models. We find that type V with an {ital R}{sup 2} Lagrangian does contain such solutions. At first glance this would suggest that quadratic theories might provide an alternative resolution to the horizon problem. However, for both the horizonless isotropic and type-V solutions we show that the eigenvalues of the linear vector field near the stationary points in phase space have opposite signs, demonstrating that such solutions are not Lyapunov stable. The addition of free quantum fields may stabilize the solutions.

Rothman, T.; Anninos, P. (Department of Physics and Center for Relativity, The University of Texas at Austin, Austin, Texas (USA))

1991-11-15

49

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

50

Stacking Fault Energies of Tetrahedrally Coordinated Crystals  

Microsoft Academic Search

The energies of the intrinsic stacking fault in 20 tetrahedrally coordinated crystals, determined by electron microscopy from the widths of extended dislocations, range from a few mJ\\/m2 to 300 mJ\\/m2. The reduced stacking fault energy (RSFE: stacking fault energy per bond perpendicular to the fault plane) has been found to have correlations with the effective charge, the charge redistribution index

S. Takeuchi; K. Suzuki

1999-01-01

51

Tetrahedrally bonded ternary amorphous semiconductor alloys  

Microsoft Academic Search

The properties of tetrahedrally bonded ternary amorphous semiconductors a-CSiSn:H and a-CSiGe:H are reviewed with particular emphasis on the temperature dependence of dark conductivity and the coordination in random networks. It is shown here that the dark conductivity as a function of the temperature strongly depends on the carbon content and, more precisely, on the proportion of sp3 and sp2 sites

F. Demichelis; G. Kaniadakis; A. Tagliaferro; E. Tresso

1989-01-01

52

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

53

Methods for prismatic/tetrahedral grid generation and adaptation  

NASA Astrophysics Data System (ADS)

The present work involves generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is a method for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A High Speed Civil Transport (HSCT) type of aircraft geometry is considered. The generated hybrid grid required only 170 K tetrahedra instead of an estimated two million had a tetrahedral mesh been used in the prisms region as well. A solution adaptive scheme for viscous computations on hybrid grids is also presented. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples 3-D, isotropic division of tetrahedra and 2-D, directional division of prisms.

Kallinderis, Y.

1995-10-01

54

Robust convex quadratically constrained programs  

Microsoft Academic Search

In this paper we study robust convex quadratically constrained programs, a subset of the class of robust convex programs introduced by Ben-Tal and Nemirovski (4). Unlike (4), our focus in this paper is to identify uncertainty structures that allow the corresponding robust quadratically constrained programs to be reformulated as second-order cone programs. We propose three classes of uncertainty sets that

Donald Goldfarb; Garud Iyengar

2003-01-01

55

Boundary Recovery For Delaunay Tetrahedral Meshes Using Local Topological Transformations  

PubMed Central

Numerous high-quality, volume mesh-generation systems exist. However, no strategy can address all geometry situations without some element qualities being compromised. Many 3D mesh generation algorithms are based on Delaunay tetrahedralization which frequently fails to preserve the input boundary surface topology. For biomedical applications, this surface preservation can be critical as they usually contain multiple material regions of interest coherently connected. In this paper we present an algorithm as a post-processing method that optimizes local regions of compromised element quality and recovers the original boundary surface facets (triangles) regardless of the original mesh generation strategy. The algorithm carves out a small sub-volume in the vicinity of the missing boundary facet or compromised element, creating a cavity. If the task is to recover a surface boundary facet, a natural exit hole in the cavity will be present. This hole is patched with the missing boundary surface face first followed by other patches to seal the cavity. If the task was to improve a compromised region, then the cavity is already sealed. Every triangular facet of the cavity shell is classified as an active face and can be connected to another shell node creating a tetrahedron. In the process the base of the tetrahedron is removed from the active face list and potentially 3 new active faces are created. This methodology is the underpinnings of our last resort method. Each active face can be viewed as the trunk of a tree. An exhaustive breath and depth search will identify all possible tetrahedral combinations to uniquely fill the cavity. We have streamlined this recursive process reducing the time complexity by orders of magnitude. The original surfaces boundaries (internal and external) are fully restored and the quality of compromised regions improved.

Ghadyani, Hamid; Sullivan, John; Wu, Ziji

2009-01-01

56

Pseudo-fivefold diffraction symmetries in tetrahedral packing.  

PubMed

We review the way in which atomic tetrahedra composed of metallic elements pack naturally into fused icosahedra. Orthorhombic, hexagonal, and cubic intermetallic crystals based on this packing are all shown to be united in having pseudo-fivefold rotational diffraction symmetry. A unified geometric model involving the 600-cell is presented: the model accounts for the observed pseudo-fivefold symmetries among the different Bravais lattice types. The model accounts for vertex-, edge-, polygon-, and cell-centered fused-icosahedral clusters. Vertex-centered and edge-centered types correspond to the well-known pseudo-fivefold symmetries in Ih and D5h quasicrystalline approximants. The concept of a tetrahedrally-packed reciprocal space cluster is introduced, the vectors between sites in this cluster corresponding to the principal diffraction peaks of fused-icosahedrally-packed crystals. This reciprocal-space cluster is a direct result of the pseudosymmetry and, just as the real-space clusters, can be rationalized by the 600-cell. The reciprocal space cluster provides insights for the Jones model of metal stability. For tetrahedrally-packed crystals, Jones zone faces prove to be pseudosymmetric with one another. Lower and upper electron per atom bounds calculated for this pseudosymmetry-based Jones model are shown to accord with the observed electron counts for a variety of Group 10-12 tetrahedrally-packed structures, among which are the four known Cu/Cd intermetallic compounds: CdCu2, Cd3Cu4, Cu5Cd8, and Cu3Cd10. The rationale behind the Jones lower and upper bounds is reviewed. The crystal structure of Zn11Au15Cd23, an example of a 1:1 MacKay cubic quasicrystalline approximant based solely on Groups 10-12 elements is presented. This compound crystallizes in Im3 (space group no. 204) with a = 13.842(2)?Å. The structure was solved with R1 = 3.53?%, I > 2?; = 5.33?%, all data with 1282/0/38 data/restraints/parameters. PMID:23780731

Lee, Stephen; Henderson, Ryan; Kaminsky, Corey; Nelson, Zachary; Nguyen, Jeffers; Settje, Nick F; Schmidt, Joshua Teal; Feng, Ji

2013-06-18

57

A Sequential Quadratically Constrained Quadratic Programming Method of Feasible Directions  

SciTech Connect

In this paper, a sequential quadratically constrained quadratic programming method of feasible directions is proposed for the optimization problems with nonlinear inequality constraints. At each iteration of the proposed algorithm, a feasible direction of descent is obtained by solving only one subproblem which consist of a convex quadratic objective function and simple quadratic inequality constraints without the second derivatives of the functions of the discussed problems, and such a subproblem can be formulated as a second-order cone programming which can be solved by interior point methods. To overcome the Maratos effect, an efficient higher-order correction direction is obtained by only one explicit computation formula. The algorithm is proved to be globally convergent and superlinearly convergent under some mild conditions without the strict complementarity. Finally, some preliminary numerical results are reported.

Jian Jinbao [Guangxi University, College of Mathematics and Informatics Science (China)], E-mail: jianjb@gxu.edu.cn; Hu Qingjie [Hunan Business College, Department of Information (China); Tang Chunming; Zheng Haiyan [Guangxi University, College of Mathematics and Informatics Science (China)

2007-12-15

58

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

59

Measure of disorder in tetrahedrally bonded semiconductors  

SciTech Connect

A measure of crystalline order in tetrahedrally bonded semiconductors is proposed based on optical response. This measure is obtained from the <111> critical point structure in the dielectric spectra. This descriptor is sensitive to the nature and extent of disorder in specimens and distinguishes differences in medium and short-order present in amorphous materials. Application to Ar{sup +}-irradiated Si specimens yields the threshold amorphization dose and this technique is sensitive to structural changes which occur as a function of irradiation fluence both above and beyond the amorphization threshhold. Systematic variations are also obtained in hydrogenated amorphous-Si. The general validity of the method is indicated.

Sundari, S. Tripura; Raghavan, G. [Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India)

2005-06-13

60

Design of inorganic compounds with tetrahedral anions  

NASA Astrophysics Data System (ADS)

The review deals with aspects of the modelling of the compositions and properties of inorganic compounds with tetrahedral anions on the basis of crystal-chemical information. One of the possible algorithms employing crystal-chemical data for the modelling of the compositions, structures, and properties of new compounds is proposed on the basis of the structures of six structural types (glaserite, ?-K2SO4, bredigite, palmierite, NASICON, and whitlockite). The likely usefulness of such data for the solution of various problems in materials science is demonstrated. The bibliography includes 208 references.

Lazoryak, B. I.

1996-04-01

61

Quadratic brackets from symplectic forms  

NASA Astrophysics Data System (ADS)

We give a physicist oriented survey of Poisson-Lie symmetries of classical systems. We consider finite-dimensional geometric actions and the chiral WZNW model as examples for the general construction. An essential point is the appearance of quadratic Poisson brackets for group-like variables. It is believed that upon quantization they lead to quadratic exchange algebras. On leave from the Institute for Nuclear Research, Bulgarian Academy of Sciences, Tsarigradsko Chaussee 72, BG-1784 Sofia, Bulgaria.

Alekseev, Anton Yu.; Todorov, Ivan T.

1994-06-01

62

Cavitands with introverted functionality stabilize tetrahedral intermediates.  

PubMed

The synthesis and characterization of two deepened cavitand hosts with introverted functionality--functional groups directed into the cavity--is described. Two functions can be introverted, alcohol and aldehyde, and they show the formation of hemiacetals and hemiketals on binding small guests with complementary functional groups. The structures of the bound hemiacetals are determined by 1D and 2D NMR studies. The arrangements of the guests in the cavitands enhance the equilibrium constants of carbonyl additions, K/K(ctrl), between 13- and 10(5)-fold, compared to their counterparts in solution. The stabilization of the addition products is due to the prior complexation of the guests and the organized solvation provided to the tetrahedral intermediates by a network of secondary amides at the cavitand rim. PMID:18004852

Hooley, Richard J; Restorp, Per; Iwasawa, Tetsuo; Rebek, Julius

2007-11-16

63

Concretising Factorisation of Quadratic Expressions  

ERIC Educational Resources Information Center

|The way quadratic factorisation was usually taught to students in Bukit View Secondary was through the familiar "cross-method." However, some teachers felt that a significant number of students could not use the method effectively even after careful demonstration through repeated examples. In addition, many secondary mathematics teachers find it…

Hoong, Leong Yew; Fwe, Yap Sook; Yvonne, Teo Mei Lin; Subramaniam, Thilagam d/o; Zaini, Irni Karen Bte Mohd; Chiew, Quek Eng; Karen, Tan Kang Ling

2010-01-01

64

ON CONDITIONALLY DEFINITE QUADRATIC FORMS  

Microsoft Academic Search

Second order optimality conditions may require the verification of a conditional definiteness condition of the formwhere Q(·) is a quadratic form on R and A is an m x n matrix. The prototype case, apart from that of positive definiteness, is that in which A is the n x n identity matrix—in this case the conditionally definite forms are called

D H Martin; D H Jacobson

1982-01-01

65

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

66

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

67

Accurate Calculation of Fault-Rupture Models Using the High-Order Discontinuous Galerkin Method on Tetrahedral Meshes  

Microsoft Academic Search

We present a new method for near-source ground-motion calculations due to earthquake rupture on potentially geometrically complex faults. Following the recently introduced Discontinuous Galerkin approach with local time stepping on tetrahedral meshes, we use piecewise polynomial approximations of the unknown variables inside each element and achieve the same approximation order in time and space due to the new ADER time

Martin Kaser; P. M. Mai; Michael Dumbser

2007-01-01

68

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

69

Linear and Quadratic Time-Frequency Representations.  

National Technical Information Service (NTIS)

This report is reviewing both linear and quadratic time-frequency representations. The linear representations discussed are Short-Time Fourier Transform and S-transform. The quadratic representation discussed is Wigner distribution. We outline the motivat...

T. Thayaparan

2000-01-01

70

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

71

Experiments Utilizing Spherical Hohlraums with Tetrahedral Illumination on OMEGA  

NASA Astrophysics Data System (ADS)

Tetrahedral hohlraums (spherical hohlraums with four laser entrance holes) have potential advantages over cylindrical hohlraums for symmetric implosion of ICF capsules, including the elimination of the time-dependent and time-integrated P2 mode. Experiments utilizing tetrahedral hohlraums were performed on the OMEGA laser facility which allows pure tetrahedral illumination of a spherical hohlraum. This geometry also allows the use of all 60 OMEGA beams to drive a hohlraum. The flux asymmetry on a capsule was measured by imaging the x-ray emission from imploded capsules. Initial results demonstrate a tetrahedral flux asymmetry, with core images viewed along the axis of a laser entrance hole demonstrating triangularity indicative of an m=3 mode, consistent with an implosion with a Y_3^2 component viewed along the axis.

Murphy, T. J.; Wallace, J.; Klare, K. A.; Oertel, J. A.; Barnes, Cris W.; Delamater, N. D.; Gobby, P.; Hauer, A. A.; Lindman, E.; Magelssen, G.; Landen, O. L.; Pollaine, S.; Amendt, P.; Decker, C.; Suter, L.; Hammel, B.; Turner, R.; Wallace, R.; Craxton, R. S.; Marshall, F. J.; Bradley, D.; Harding, D.; Kearney, K.; Keck, R.; Knauer, J.; Kremens, R.; Seka, W.; Cable, M.; Schnittman, J.

1997-11-01

72

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

73

Tetrahedrally coordinated cupric ion in A-zeolites  

Microsoft Academic Search

Electron spin resonance and electron spin echo studies on Cu2+ in four A-zeolites exchanged with K+, Cs+ and NH4+ indicate the formation of a new tetrahedral species, Cu(Oz)3(H2O)2+ where Oz is a zeolite oxygen and the water molecule is probably in the beta cage. The preferential formation of this tetrahedral species in these zeolites instead of the usually observed Cu(H2O)62+

M. Narayana; L. Kevan

1983-01-01

74

Lagrangian shock hydrodynamics on tetrahedral meshes: A stable and accurate variational multiscale approach  

NASA Astrophysics Data System (ADS)

In the past, a number of attempts have failed to robustly compute highly transient shock hydrodynamics flows on tetrahedral meshes. To a certain degree, this is not a surprise, as prior attempts emphasized enhancing the structure of shock-capturing operators rather than focusing on issues of stability with respect to small, linear perturbations. In this work, a new method is devised to stabilize computations on piecewise-linear tetrahedral finite elements. Spurious linear modes are prevented by means of the variational multiscale approach. The resulting algorithm can be proven stable in the linearized limit of acoustic wave propagation. Starting from this solid base, the approach is generalized to fully nonlinear shock computations, by augmenting the discrete formulation with discontinuity-capturing artificial viscosities. Extensive tests in the case of Lagrangian shock dynamics of ideas gases on triangular and tetrahedral grids confirm the stability and accuracy properties of the method. Incidentally, the same tests also reveal the lack of stability of current compatible/mimetic/staggered discretizations: This is due to the presence of specific unstable modes which are theoretically analyzed and verified in computations.

Scovazzi, G.

2012-10-01

75

Quadratic fluctuation-dissipation theorem for multilayer plasmas  

SciTech Connect

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

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

1999-01-01

76

A comparison of tetrahedral mesh improvement techniques  

SciTech Connect

Automatic mesh generation and adaptive refinement methods for complex three-dimensional domains have proven to be very successful tools for the efficient solution of complex applications problems. These methods can, however, produce poorly shaped elements that cause the numerical solution to be less accurate and more difficult to compute. Fortunately, the shape of the elements can be improved through several mechanisms, including face-swapping techniques that change local connectivity and optimization-based mesh smoothing methods that adjust grid point location. The authors consider several criteria for each of these two methods and compare the quality of several meshes obtained by using different combinations of swapping and smoothing. Computational experiments show that swapping is critical to the improvement of general mesh quality and that optimization-based smoothing is highly effective in eliminating very small and very large angles. The highest quality meshes are obtained by using a combination of swapping and smoothing techniques.

Freitag, L.A.; Ollivier-Gooch, C. [Argonne National Lab., IL (United States). Mathematics and Computer Science Div.

1996-12-01

77

Tetrahedral and polyhedral mesh evaluation for cerebral hemodynamic simulation--a comparison.  

PubMed

Computational fluid dynamic (CFD) based on patient-specific medical imaging data has found widespread use for visualizing and quantifying hemodynamics in cerebrovascular disease such as cerebral aneurysms or stenotic vessels. This paper focuses on optimizing mesh parameters for CFD simulation of cerebral aneurysms. Valid blood flow simulations strongly depend on the mesh quality. Meshes with a coarse spatial resolution may lead to an inaccurate flow pattern. Meshes with a large number of elements will result in unnecessarily high computation time which is undesirable should CFD be used for planning in the interventional setting. Most CFD simulations reported for these vascular pathologies have used tetrahedral meshes. We illustrate the use of polyhedral volume elements in comparison to tetrahedral meshing on two different geometries, a sidewall aneurysm of the internal carotid artery and a basilar bifurcation aneurysm. The spatial mesh resolution ranges between 5,119 and 228,118 volume elements. The evaluation of the different meshes was based on the wall shear stress previously identified as a one possible parameter for assessing aneurysm growth. Polyhedral meshes showed better accuracy, lower memory demand, shorter computational speed and faster convergence behavior (on average 369 iterations less). PMID:19964600

Spiegel, Martin; Redel, Thomas; Zhang, Y; Struffert, Tobias; Hornegger, Joachim; Grossman, Robert G; Doerfler, Arnd; Karmonik, Christof

2009-01-01

78

Unidirectional formation of tetrahedral voids in irradiated silicon carbide  

NASA Astrophysics Data System (ADS)

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

Kondo, S.; Katoh, Y.; Snead, L. L.

2008-10-01

79

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

80

Growth of the Ideal Generated by a Quadratic Boolean Function  

Microsoft Academic Search

\\u000a We give exact formulas for the growth of the ideal A? for ? a quadratic element of the algebra of Boolean functions over the Galois field GF(2). That is, we calculate dimAk l<\\/font\\u000a>\\\\dim A_k \\\\lambda where A\\u000a \\u000a k\\u000a is the subspace of elements of degree less than or equal to k. These results clarify some of the assertions made

Jintai Ding; Timothy J. Hodges; Victoria Kruglov

2010-01-01

81

Binary Quadratic Forms: A Historical View  

ERIC Educational Resources Information Center

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

Khosravani, Azar N.; Beintema, Mark B.

2006-01-01

82

Binary Quadratic Forms: A Historical View  

ERIC Educational Resources Information Center

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

Khosravani, Azar N.; Beintema, Mark B.

2006-01-01

83

How to solve a Quadratic Equation  

Microsoft Academic Search

One of the author's favorite experiences in high school mathematics was learning how to solve quadratic equations. As is usual with life, things are not as simple as they were in high school. There are several problems with the quadratic formula. In this article, the author talks about these problems and various solutions to them.

James F. Blinn

2005-01-01

84

Another Look at the Quadratic Formula.  

ERIC Educational Resources Information Center

An exploration of a problem called solving quadratic congruences modulo p is detailed and is built around an alternate method of deriving the quadratic formula. Three practical pedagogical values that have been experienced by students and instructor when the material was presented to classes are noted. (MP)

Obermeyer, Dean D.

1982-01-01

85

Analysis of quark mixing using binary tetrahedral flavor symmetry  

NASA Astrophysics Data System (ADS)

Using the binary tetrahedral group T', the three angles and phase of the quark CKM mixing matrix are pursued by symmetry-breaking which involves T'-doublet VEVs and the Chen-Mahanthappa CP-violation mechanism. The NMRT'M, next-to-minimal renormalizable-T' model is described, and its one parameter comparison to experimental data is explored.

Eby, David A.; Frampton, Paul H.; Matsuzaki, Shinya

2009-09-01

86

Hardware-Based Ray Casting for Tetrahedral Meshes  

Microsoft Academic Search

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

Manfred Weiler; Martin Kraus; Markus Merz; Thomas Ertl

2003-01-01

87

Liquid simulation on lattice-based tetrahedral meshes  

Microsoft Academic Search

We describe a method for animating incompressible liquids with detailed free surfaces. For each time step, semi- Lagrangian contouring computes a new fluid boundary (represented as a fine surface triangulation) from the previous time step's fluid boundary and velocity field. Then a mesh generation algorithm called isosurface stuffing discretizes the region enclosed by the new fluid boundary, creating a tetrahedral

Nuttapong Chentanez; Bryan E. Feldman; François Labelle; James F. O'brien; Jonathan Richard Shewchuk

2007-01-01

88

Regular black holes in quadratic gravity  

NASA Astrophysics Data System (ADS)

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

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

2006-05-01

89

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

90

Quadratic prediction problems in multivariate linear models  

Microsoft Academic Search

Linear and quadratic prediction problems in finite populations have become of great interest to many authors recently. In the present paper, we mainly aim to extend the problem of quadratic prediction from a general linear model, of form y=X?+e,e?N(0,?2V), to a multivariate linear model, denoted by Y=XB+E,V ec(E)?N(0,??V) with Y=(yij)n×q=(y1,…,yq). Firstly, the optimal invariant quadratic unbiased (OIQU) predictor and the

Xu-Qing Liu; Dong-Dong Wang; Jian-Ying Rong

2009-01-01

91

Synthesis, Evaluation and Defect Compensation of Tetrahedral Glasses as Possible Solar Cell Materials. Final Report, February 1, 1979-April 30, 1980.  

National Technical Information Service (NTIS)

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...

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

1980-01-01

92

Tetrahedral order in homologous disaccharide-water mixtures  

NASA Astrophysics Data System (ADS)

The present work aims at evidencing the ``kosmotrope'' nature of trehalose through the analysis of inelastic neutron scattering measurements on trehalose and sucrose water solutions at different temperatures. Neutron spectra were collected by using the spectrometer MARI at the ISIS pulsed neutron source of the Rutherford Appleton Laboratory (Chilton, UK). To study the structural modifications induced on the tetrahedral hydrogen-bond network of water by homologous disaccharides, as a first step, the vibrational properties of pure water at different temperatures have been investigated. In particular, the temperature behavior of the intramolecular OH stretching mode has been analyzed. Successively, the vibrational properties for pure water have been compared with those of the sugar water solutions focusing the attention on the tetrahedral network-forming tendency. Finally, the obtained findings have been compared with previous Raman scattering evidences, and the results interpreted in the frame of recent molecular dynamics simulation works.

Branca, C.; Maccarrone, S.; Magazù, S.; Maisano, G.; Bennington, S. M.; Taylor, J.

2005-05-01

93

Tetrahedral order in homologous disaccharide-water mixtures.  

PubMed

The present work aims at evidencing the "kosmotrope" nature of trehalose through the analysis of inelastic neutron scattering measurements on trehalose and sucrose water solutions at different temperatures. Neutron spectra were collected by using the spectrometer MARI at the ISIS pulsed neutron source of the Rutherford Appleton Laboratory (Chilton, UK). To study the structural modifications induced on the tetrahedral hydrogen-bond network of water by homologous disaccharides, as a first step, the vibrational properties of pure water at different temperatures have been investigated. In particular, the temperature behavior of the intramolecular OH stretching mode has been analyzed. Successively, the vibrational properties for pure water have been compared with those of the sugar water solutions focusing the attention on the tetrahedral network-forming tendency. Finally, the obtained findings have been compared with previous Raman scattering evidences, and the results interpreted in the frame of recent molecular dynamics simulation works. PMID:15910051

Branca, C; Maccarrone, S; Magazù, S; Maisano, G; Bennington, S M; Taylor, J

2005-05-01

94

The statistical mechanics of ion-dipole-tetrahedral quadrupole mixtures  

NASA Astrophysics Data System (ADS)

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

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

95

Phase diagram of a coupled tetrahedral Heisenberg model  

Microsoft Academic Search

The phase diagram of a coupled tetrahedral Heisenberg model is obtained. The quantum chain has a local gauge symmetry and its eigenspectrum is obtained by the composition of the eigenspectra of spin-1\\/2 XXZ chains with arbitrary distribution of spin-3\\/2 impurities. The phase diagram is quite rich with an infinite number of phases with ferromagnetic, antiferromagnetic, or ferrimagnetic order. In some

Onofre Rojas; F. C. Alcaraz

2003-01-01

96

Structural and chemical changes in binary versus ternary tetrahedral semiconductors  

Microsoft Academic Search

The properties of a prototype ternary semiconductor with the chalcopyrite structure-MgSiP2-are studied for the first time as a function of lattice constant, tetragonal distortion, and anion displacement with the use of the ab initio density-functional method. This system is then used as a general model for understanding the chemical and structure differences between a binary tetrahedral semiconductor (e.g., zinc blende)

José Luís Martins; Alex Zunger

1985-01-01

97

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

98

Strict sensitivity analysis in fuzzy quadratic programming  

Microsoft Academic Search

Quadratic programming can be seen both as a general approach to linear programming and a special class of non-linear programming. Moreover, quadratic programming problems are of utmost importance in an increasing variety of practical fields, such as, regression, efficient production and portfolio selection. As ambiguity and vagueness are natural and ever-present in real-life situations requiring solutions, it makes perfect sense

B. Kheirfam; J. L. Verdegay

99

Perturbations of quadratic centers of genus one  

Microsoft Academic Search

We propose a program for finding the cyclicity of period annuli of quadratic\\u000asystems with centers of genus one. As a first step, we classify all such\\u000asystems and determine the essential one-parameter quadratic perturbations which\\u000aproduce the maximal number of limit cycles. We compute the associated\\u000aPoincare-Pontryagin-Melnikov functions whose zeros control the number of limit\\u000acycles. To illustrate our

Sébastien Gautier; Lubomir Gavrilov; Iliya D. Iliev

2009-01-01

100

Water and other tetrahedral liquids: order, anomalies and solvation.  

PubMed

In order to understand the common features of tetrahedral liquids with water-like anomalies, the relationship between local order and anomalies has been studied using molecular dynamics simulations for three categories of such liquids: (a) atomistic rigid-body models for water (TIP4P, TIP4P/2005, mTIP3P, SPC/E), (b) ionic melts, BeF(2) (TRIM model) and SiO(2) (BKS potential) and (c) Stillinger-Weber liquids parametrized to model water (mW) and silicon. Rigid-body, atomistic models for water and the Stillinger-Weber liquids show a strong correlation between tetrahedral and pair correlation order and the temperature for the onset of the density anomaly is close to the melting temperature. In contrast, the ionic melts show weaker and more variable degrees of correlation between tetrahedral and pair correlation metrics, and the onset temperature for the density anomaly is more than twice the melting temperature. In the case of water, the relationship between water-like anomalies and solvation is studied by examining the hydration of spherical solutes (Na(+), Cl(-), Ar) in water models with different temperature regimes of anomalies (SPC/E, TIP4P and mTIP3P). For both ionic and nonpolar solutes, the local structure and energy of water molecules is essentially the same as in bulk water beyond the second-neighbour shell. The local order and binding energy of water molecules are not perturbed by the presence of a hydrophobic solute. In the case of ionic solutes, the perturbation is largely localized within the first hydration shell. The binding energies for the ions are strongly dependent on the water models and clearly indicate that the geometry of the partial charge distributions, and the associated multipole moments, play an important role. However the anomalous behaviour of the water network has been found to be unimportant for polar solvation. PMID:22739063

Jabes, B Shadrack; Nayar, Divya; Dhabal, Debdas; Molinero, Valeria; Chakravarty, Charusita

2012-06-27

101

Computational studies of polyvinyl alcohol encapsulated tetrahedral cadmium sulphide cluster  

NASA Astrophysics Data System (ADS)

In the present work theoretical encapsulation of tetrahedral cluster of cadmium sulphide within polyvinyl alcohol (PVA) chains has been studied. Density of states, binding energy and optical properties are calculated using density functional theory (DFT) as implemented in SIESTA code with local density approximation (LDA) functionals. We observe that PVA chains strongly interact with [Cd4(SH)10]2- cluster through-OH groups and results in broadening of the band gap. Absorption spectrum of hybrid structure is also computed which is comparable to experimental results.

Bala, Vaneeta; Tripathi, S. K.; Kumar, Ranjan

2013-06-01

102

Tetrahedral aminopeptidase: a novel large protease complex from archaea  

PubMed Central

A dodecameric protease complex with a tetrahedral shape (TET) was isolated from Haloarcula marismortui, a salt-loving archaeon. The 42 kDa monomers in the complex are homologous to metal-binding, bacterial aminopeptidases. TET has a broad aminopeptidase activity and can process peptides of up to 30–35 amino acids in length. TET has a central cavity that is accessible through four narrow channels (<17 ? wide) and through four wider channels (21 ? wide). This architecture is different from that of all the proteolytic complexes described to date that are made up by rings or barrels with a single central channel and only two openings.

Franzetti, B.; Schoehn, G.; Hernandez, J.-F.; Jaquinod, M.; Ruigrok, R.W.H.; Zaccai, G.

2002-01-01

103

Crystal Engineering of Tetrahedral `Nano Molecules' Constructed by POSS Cages  

NASA Astrophysics Data System (ADS)

Functional hybrid materials provide us a powerful approach to acquire novel hierarchical structures and exceptional properties. Designed nanoparticle building blocks with specific interactions can self-assemble into targeted ordered structures with intriguing shapes, sizes and functionalities. Classical high symmetric `nano atoms', Polyhedral Oligomeric Silsesquioxane (POSS) can be utilized to construct `nano molecules' with different symmetry, which can further act as novel nanoparticle building blocks. Very interesting rigid tetrahedral `nano molecules' covalent linking four POSS cages were synthesized. Their close packing structures in crystal were determined by transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD).

Huang, Mingjun; Mei, Shan; Cheng, Stephen

2013-03-01

104

Sharp Quadratic Majorization in One Dimension  

PubMed Central

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

de Leeuw, Jan; Lange, Kenneth

2009-01-01

105

The Quadratic-Chi Histogram Distance Family  

Microsoft Academic Search

\\u000a We present a new histogram distance family, the Quadratic-Chi (QC). QC members are Quadratic-Form distances with a cross-bin\\u000a ?\\u000a 2-like normalization. The cross-bin ?\\u000a 2-like normalization reduces the effect of large bins having undo influence. Normalization was shown to be helpful in many\\u000a cases, where the ?\\u000a 2 histogram distance outperformed the L\\u000a 2 norm. However, ?\\u000a 2 is sensitive

Ofir Pele; Michael Werman

2010-01-01

106

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

107

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

108

An r-Dimensional Quadratic Placement Algorithm  

Microsoft Academic Search

In this paper the solution to the problem of placing n connected points (or nodes) in r-dimensional Euclidean space is given. The criterion for optimality is minimizing a weighted sum of squared distances between the points subject to quadratic constraints of the form X'X - 1, for each of the r unknown coordinate vectors. It is proved that the problem

Kenneth M. Hall

1970-01-01

109

Adaptive linear quadratic control using policy iteration  

Microsoft Academic Search

In this paper we present the stability and convergence results for dynamic programming-based reinforcement learning applied to linear quadratic regulation (LQR). The specific algorithm we analyze is based on Q-learning and it is proven to converge to an optimal controller provided that the underlying system is controllable and a particular signal vector is persistently excited. This is the first convergence

Steven J. Bradtke; B. Erik Ydstie; A. G. Barto

1994-01-01

110

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

111

Applications of Multivariate Quadratic Public Key Systems  

Microsoft Academic Search

In this article, we investigate the class of multivariate quadratic (MQ) public key systems. These systems are becoming a serious alternative to RSA or ECC based systems. After introducing the main ideas and sketching some relevant systems, we deal with the advantages and disadvantages of these kinds of schemes. Based on our observations, we determine application domains in which MQ-schemes

Christopher Wolf; Bart Preneel

2005-01-01

112

Factorization Using the Quadratic Sieve Algorithm  

Microsoft Academic Search

Since the cryptosecurity of the RSA two key cryptoalgorithm is no greater than the difficulty of factoring the modulus (product of two secret primes), a code that implements the Quadratic Sieve factorization algorithm on the CRAY I computer has been developed at the Sandia National Laboratories to determine as sharply as possible the current state-of-the-art in factoring. Because all viable

James A. Davis; Diane B. Holdridge

1983-01-01

113

Factorization Using the Quadratic Sieve Algorithm.  

National Technical Information Service (NTIS)

Since the cryptosecurity of the RSA two key cryptoalgorithm is no greater than the difficulty of factoring the modulus (product of two secret primes), a code that implements the Quadratic Sieve factorization algorithm on the CRAY I computer has been devel...

J. A. Davis D. B. Holdridge

1983-01-01

114

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

115

The period function of quadratic centers  

Microsoft Academic Search

In this paper we investigate the bifurcation diagram of the period function associated to a family of 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 (4). Most of the present paper deals with the local bifurcation diagram at the polycycle

P. Marde; J. Villadelprat

116

Quadratic forms involving Green's and Robin functions  

SciTech Connect

General inequalities for quadratic forms with coefficients depending on the values of Green's and Robin functions are obtained. These inequalities cover also the reduced moduli of strips and half-strips. Some applications of the results obtained to extremal partitioning problems and related questions of geometric function theory are discussed. Bibliography: 29 titles.

Dubinin, Vladimir N [Institute of Applied Mathematics, Far-Eastern Branch of the Russian Academy of Sciences, Vladivostok (Russian Federation)

2009-10-31

117

Experiments with successive quadratic programming algorithms  

Microsoft Academic Search

There are many variants of successive quadratic programming (SQP) algorithms. Important issues include: the choice of either line search or trust region strategies; the QP formulation to be used; and how the QP is to be solved. Here, we consider the QP's proposed by Fletcher and Powell and discuss a specialized reduced-gradient procedure for solving them. A computer implementation is

Y. Fan; S. Sarkar; L. Lasdon

1988-01-01

118

Tetrahedral vs. polyhedral mesh size evaluation on flow velocity and wall shear stress for cerebral hemodynamic simulation.  

PubMed

Haemodynamic factors, in particular wall shear stresses (WSSs) may have significant impact on growth and rupture of cerebral aneurysms. Without a means to measure WSS reliably in vivo, computational fluid dynamic (CFD) simulations are frequently employed to visualise and quantify blood flow from patient-specific computational models. With increasing interest in integrating these CFD simulations into pretreatment planning, a better understanding of the validity of the calculations in respect to computation parameters such as volume element type, mesh size and mesh composition is needed. In this study, CFD results for the two most common aneurysm types (saccular and terminal) are compared for polyhedral- vs. tetrahedral-based meshes and discussed regarding future clinical applications. For this purpose, a set of models were constructed for each aneurysm with spatially varying surface and volume mesh configurations (mesh size range: 5119-258, 481 volume elements). WSS distribution on the model wall and point-based velocity measurements were compared for each configuration model. Our results indicate a benefit of polyhedral meshes in respect to convergence speed and more homogeneous WSS patterns. Computational variations of WSS values and blood velocities are between 0.84 and 6.3% from the most simple mesh (tetrahedral elements only) and the most advanced mesh design investigated (polyhedral mesh with boundary layer). PMID:21161794

Spiegel, Martin; Redel, Thomas; Zhang, Y Jonathan; Struffert, Tobias; Hornegger, Joachim; Grossman, Robert G; Doerfler, Arnd; Karmonik, Christof

2010-12-01

119

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

NASA Astrophysics Data System (ADS)

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)0.5(L1)] (1), [Cd(bpib)0.5(L2)]·H2O (2), [Cd(bpib)0.5(L3)] (3) and [Cd(bib)0.5(L1)] (4), where bpib=1,4-bis(2-(pyridin-2-yl)-1H-imidazol-1-yl)butane, bib=1,4-bis(1H-imidazol-1-yl)butane, H2L1=4-(4-carboxybenzyloxy)benzoic acid, H2L2=4,4?-(ethane-1,2-diylbis(oxy))dibenzoic acid and H2L3=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 ?-Po topological nets with different degrees of interpenetration based on the similar octahedral [Cd2(-COO)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 ?-Po topological nets. And the luminescent properties of these compounds have been investigated in detail.

Lu, Yong-Ming; Lan, Ya-Qian; Xu, Yan-Hong; Su, Zhong-Min; Li, Shun-Li; Zang, Hong-Ying; Xu, Guang-Juan

2009-11-01

120

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

2012-03-09

121

Computational materials design of filled tetrahedral compound magnetic semiconductors  

NASA Astrophysics Data System (ADS)

Based on first-principles calculations within the density functional theory, materials design of filled tetrahedral compound magnetic semiconductors is proposed. By using the Korringa-Kohn-Rostoker coherent potential approximation, electronic structures of Mn-doped LiZnAs, LiZnP and LiZnN are calculated. First, by estimating free energy, phase diagrams of these systems are predicted. It is shown that these systems are phase separating systems and favor spinodal decomposition. However, by introducing Li vacancies, spinodal decomposition is strongly suppressed and Mn can be doped up to high concentration. Moreover, the introduced Li vacancies induce ferromagnetic interaction between Mn and thus we can expect high Curie temperature (TC) in these systems. To see the chemical trend, electronic structure and TC of Li(Zn, Cr)As are also calculated.

Sato, K.; Fujimoto, S.; Fujii, H.; Fukushima, T.; Katayama-Yoshida, H.

2012-08-01

122

Near-field Raman spectroscopy using a tetrahedral SNOM tip  

NASA Astrophysics Data System (ADS)

An example of near-field Raman spectroscopy based on the tip-enhancement at an apertureless tetrahedral scanning near-field optical tip (t-tip) is presented. Tip-enhanced Raman spectroscopy (TERS) is based on the excitation of localized surface plasmons (LSP) in the cavity of tip and surface. The LSP provide a highly confined and large field enhancement at the tip apex which allows molecular spectroscopy at the nanoscale. The t-tip consists, in contrast to other TERS configurations which use opaque tips, of a gold coated glass tip which is irradiated from the inside. We demonstrate TERS spectra of the dye malachite green isothiocyanate and show an increased bleaching of the dye in presence of the tip. Data analysis show that the actual experimental conditions support moderate enhancement of the Raman signal.

Klein, Stefan; Reichert, Joachim; Fuchs, Harald; Fischer, Ulrich

2006-05-01

123

Electron emission induced modifications in amorphous tetrahedral diamondlike carbon  

SciTech Connect

The cold-cathode electron emission properties of amorphous tetrahedral diamondlike carbon are promising for flat-panel display and vacuum microelectronics technologies. The onset of electron emission is, typically, preceded by {open_quotes}conditioning{close_quotes} where the material is stressed by an applied electric field. To simulate conditioning and assess its effect, we combined the spatially localized field and current of a scanning tunneling microscope tip with high-spatial-resolution characterization. Scanning force microscopy shows that conditioning alters surface morphology and electronic structure. Spatially resolved electron-energy-loss spectroscopy indicates that the predominant bonding configuration changes from predominantly fourfold to threefold coordination. {copyright} {ital 1998 American Institute of Physics.}

Mercer, T.W. [Department of Physics and Atmospheric Science, Drexel University, Philadelphia, Pennsylvania19104 (United States); DiNardo, N.J. [Department of Physics and Atmospheric Science, Drexel University, Philadelphia, Pennsylvania 19104 (United States)]|[Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Rothman, J.B. [Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Siegal, M.P.; Friedmann, T.A. [Sandia National Laboratory, Albuquerque, New Mexico87185 (United States); Martinez-Miranda, L.J. [Department of Materials and Nuclear Engineering, University of Maryland, College Park, Maryland20742 (United States)

1998-05-01

124

The Symmetric Formulation of the Simplex Method for Quadratic Programming.  

National Technical Information Service (NTIS)

For the solution of convex quadratic programming problem, a number of efficient methods have been developed. The most well-known methods are the Simplex method for quadratic programming, discovered by Dantzig and, together with the closely related dual me...

C. van de Panne A. Whinston

1966-01-01

125

On the Linear and Quadratic Discriminators for Pattern Recognition.  

National Technical Information Service (NTIS)

In this report, two problems in pattern recognition are considered: (1) when the likelihood ratio criterion results in a quadratic discriminant function, it may be possible to factor the quadratic form into two linear discriminant functions. It is shown t...

P. S. R. S. Rao

1967-01-01

126

A SEQUENTIAL QUADRATIC PROGRAMMING ALGORITHM UTILIZING QR MATRIX FACTORIZATION  

Microsoft Academic Search

Some recent studies indicate that the sequential quadratic programming (SQP) approach has a sound theoretical basis and promising empirical results for solving general constrained optimization problems. This paper presents a variant of the SQP method which utilizes QR matrix factorization to solve the quadratic programming subproblem which result from taking a quadratic approximation of the original problem. Theoretically, the QR

CHIANG KAO; SHIH PEN CHEN

1994-01-01

127

Two-phase Method to Solve Fuzzy Quadratic Programming Problems  

Microsoft Academic Search

Quadratic programming problems are of up most importance in a variety of relevant practical fields, as e.g., portfolio selection. This work presents and develops an original and novel fuzzy sets based method that solves a class of quadratic programming problems with vagueness in the set of constraints. The method uses two phases to solve fuzzy quadratic programming problems, which eventually

Ricardo C. Silva; José L. Verdegay; Akebo Yamakami

2007-01-01

128

Factorization using the quadratic sieve algorithm  

SciTech Connect

Since the cryptosecurity of the RSA two key cryptoalgorithm is no greater than the difficulty of factoring the modulus (product of two secret primes), a code that implements the Quadratic Sieve factorization algorithm on the CRAY I computer has been developed at the Sandia National Laboratories to determine as sharply as possible the current state-of-the-art in factoring. Because all viable attacks on RSA thus far proposed are equivalent to factorization of the modulus, sharper bounds on the computational difficulty of factoring permit improved estimates for the size of RSA parameters needed for given levels of cryptosecurity. Analysis of the Quadratic Sieve indicates that it may be faster than any previously published general purpose algorithm for factoring large integers. The high speed of the CRAY I coupled with the capability of the CRAY to pipeline certain vectorized operations make this algorithm (and code) the front runner in current factoring techniques.

Davis, J.A.; Holdridge, D.B.

1983-12-01

129

Factorization using the quadratic sieve algorithm  

SciTech Connect

Since the cryptosecurity of the RSA two key cryptoalgorithm is no greater than the difficulty of factoring the modulus (product of two secret primes), a code that implements the Quadratic Sieve factorization algorithm on the CRAY I computer has been developed at the Sandia National Laboratories to determine as sharply as possible the current state-of-the-art in factoring. Because all viable attacks on RSA thus far proposed are equivalent to factorization of the modulus, sharper bounds on the computational difficulty of factoring permit improved estimates for the size of RSA parameters needed for given levels of cryptosecurity. Analysis of the Quadratic Sieve indicates that it may be faster than any previously published general purpose algorithm for factoring large integers. The high speed of the CRAY I coupled with the capability of the CRAY to pipeline certain vectorized operations make this algorithm (and code) the front runner in current factoring techniques.

Davis, J.A.; Holdridge, D.B.

1983-01-01

130

Interface solitons in quadratic nonlinear photonic lattices  

SciTech Connect

We study the properties of two-color nonlinear localized modes which may exist at the interfaces separating two different periodic photonic lattices in quadratic media, focusing on the impact of phase mismatch of the photonic lattices on the properties, stability, and threshold power requirements for the generation of interface localized modes. We employ both an effective discrete model and continuum model with periodic potential and find good qualitative agreement between both models. Dynamic excitation of interface modes shows that a two-color interface twisted mode splits into two beams with different escaping angles and carrying different energies when entering a uniform medium from the quadratic photonic lattice. The output position and energy contents of each two-color interface solitons can be controlled by judicious tuning of the lattice parameters.

Xu Zhiyong; Kivshar, Yuri S. [Nonlinear Physics Center, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia); Molina, Mario I. [Departmento de Fisica, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, 7800024 Nunoa, Santiago (Chile)

2009-07-15

131

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

ERIC Educational Resources Information Center

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

Lim, Kieran F.

2012-01-01

132

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

Microsoft Academic Search

We introduce a many-body fixed-charge potential optimized for tetrahedral silica. The potential is used to investigate the crystal structures and energetics of six tetrahedrally coordinated silica polymorphs ( alpha - and beta -quartz, alpha - and beta -cristobalite, beta -tridymite, and coesite). The structural parameters of the different phases are found to be well-reproduced. Most importantly, the ground state of

Jianguo Yu; Simon R. Phillpot; Susan B. Sinnott

2007-01-01

133

Collision between deformable objects using fast-marching on tetrahedral models  

Microsoft Academic Search

This paper presents an approach to handling collision between deformable objects using tetrahedral decomposition. The tetrahedral volumetric model is often used to simulate deformable objects that handle cuts and splits. Interaction between such objects in a complex environment is still an open problem in interactive simulation. This paper is mainly focused on obtaining a fast computation of a reliable penalty

D. Marchal; F. Aubert; C. Chaillou

2004-01-01

134

Collision Between Deformable Objects Using Fast-Marching on Tetrahedral Models  

Microsoft Academic Search

This paper presents an approach to handling collision between deformable objects using tetrahedral decomposi- tion. The tetrahedral volumetric model is often used to simulate deformable objects that handle cuts and splits. Interaction between such objects in a complex environment is still an open problem in interactive simulation. This paper is mainly focused on obtaining a fast computation of a reliable

D. Marchal; F. Aubert; C. Chailloux

135

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

ERIC Educational Resources Information Center

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

Lim, Kieran F.

2012-01-01

136

A parameterized hessian quadratic programming problem  

Microsoft Academic Search

We present a general active set algorithm for the solution of a convex quadratic programming problem having a parametrized\\u000a Hessian matrix. The parametric Hessian matrix is a positive semidefinite Hessian matrix plus a real parameter multiplying\\u000a a symmetric matrix of rank one or two. The algorithm solves the problem for all parameter values in the open interval upon\\u000a which the

M. J. Best; R. J. Caron

1986-01-01

137

Testing for Cointegration in Linear Quadratic Models  

Microsoft Academic Search

This article evaluates the finite-sample performance of various tests for cointegration by Monte Carlo methods. The evaluation takes place within the linear quadratic model. The results indicate sharp differences in the ability of the tests to detect cointegrating relations, especially when the cost-of-adjustment term and the number of regressors are large. Although no single test dominates for all the parameter

Allan W. Gregory

1994-01-01

138

Tracking Algorithm Base on Quadratic BOC  

Microsoft Academic Search

Binary Offset Carrier (BOC) modulated signal has multi-correlation peaks, whose S curve of Phase Detector (PD) having several cross-zero points, this can lead to do error judge on receiver tracking. So, a new tracking algorithm is proposed in this paper, it using the quadratic BOC to removing the effect of several cross-zero points on S curve. The comparing analysis and

Li Yang; ChengSheng Pan; YanChun Wang; HaiYan Liu

2010-01-01

139

Electron clusters in a quadratic potential  

NASA Astrophysics Data System (ADS)

Clusters of electrons in a quadratic external potential are studied. By expanding in inverse powers of the space dimensionality the ground state energy of the N-electron cluster is found in the whole range of variation of the problem's parameter. The rearrangement of electron orbitals in the crossover region is investigated. On leave from the Institute of Cybernetics, Mathematics and Physics (ICIMAF), Calle O No. 8, Havana, Cuba.

Belov, A. A.; Lozovik, Yu. E.; Gonzalez, A.

1989-12-01

140

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

141

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

NASA Astrophysics Data System (ADS)

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 features allow us to significantly reduce the computational cost of the simulations. Moreover, we have designed an efficient CPML absorbing boundary condition, both in terms of absorption and computational cost, by combining approximation orders in the numerical domain. A quadratic interpolation is typically used in the medium to obtain the required accuracy, while lower approximation orders are used in the CPMLs to reduce the total computational cost and to obtain a well-balanced workload over the processors. While the efficiency of DG-FEMs have been largely demonstrated for high approximation orders, we favour the use of low approximation orders as they are more appropriate to the applications we are interested in. In particular, we address the issues of seismic modelling and seismic imaging in cases of complex geological structures that require a fine discretization of the medium. We illustrate the efficiency of our approach within the framework of the EUROSEISTEST verification and validation project, which is designed to compare high-frequency (up to 4 Hz) numerical predictions of ground motion in the Volvi basin (Greece). Through the tetrahedral meshing, we have achieved fine discretization of the basin, which appears to be a sine qua non condition for accurate computation of surface waves diffracted at the basin edges. We compare our results with predictions computed with the spectral element method (SEM), and demonstrate that our method yields the same level of accuracy with computation times of the same order of magnitude.

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

2010-11-01

142

Reconstruction of the cleavage faces of tetrahedrally coordinated compound semiconductors  

NASA Astrophysics Data System (ADS)

Tetrahedrally coordinated compound semiconductors occur in two crystallographic allotropes: zincblende and wurtzite. Zincblende materials exhibit a single cleavage face: The (110) surface consisting of equal numbers of anions and cations which form zig-zag chains directed along <110> directions in the surface. Wurtzite materials exhibit two cleavage faces, both consisting of equal numbers of anion and cation species. The (10overline 1 0) cleavage surfaces consist of isolated anion-cation dimers back bonded to the layer beneath whereas the (10overline 2 0) surfaces consist of anion-cation chains, analogous to those on zincblende (110) but with four rather than two inequivalent atoms per surface unit cell. All three surfaces exhibit reconstructions which do not alter the symmetry of the surface unit cell but which lead to large (? 1 Å) deviations of the positions of the atomic species in the uppermost layer(s) from those in the truncated bulk solid. These reconstructed surface geometries have been determined quantitatively for the (110) surfaces of zincblende structure AlP, AlAs, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe and CdTe; the (10overline 1 0) surfaces of wurtzite structure ZnO and CdSe; and the (11overline 2 0) surfaces of CdSe. Theoretical predictions of these reconstructed geometries have been given which are in either quantitative or semiquantitative correspondence with the experimentally determined structures. Analysis of the trends exhibited by the members of each class of cleavage surface and comparison thereof with theoretical predictions permit the extraction from these results of generalizations characteristic of novel types of surface chemical bonding. The most important of these is the notion that for each class of surface the atomic geometries are approximately "universal" when their coordinates are properly scaled with the bulk lattice constant. A quantitative description of this result is presented which reveals that extensions of the concepts of inorganic molecular coordination chemistry are required to predict the cleavage-surface atomic geometries and electronic structures of binary tetrahedrally coordinated compound semiconductors.

Duke, C. B.

143

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

144

Efficient quadratic regularization for expression arrays.  

PubMed

Gene expression arrays typically have 50 to 100 samples and 1000 to 20,000 variables (genes). There have been many attempts to adapt statistical models for regression and classification to these data, and in many cases these attempts have challenged the computational resources. In this article we expose a class of techniques based on quadratic regularization of linear models, including regularized (ridge) regression, logistic and multinomial regression, linear and mixture discriminant analysis, the Cox model and neural networks. For all of these models, we show that dramatic computational savings are possible over naive implementations, using standard transformations in numerical linear algebra. PMID:15208198

Hastie, Trevor; Tibshirani, Robert

2004-07-01

145

Modeling Lattice Structures of DNA-Coated Nanoparticles with Tetrahedral Linkers  

NASA Astrophysics Data System (ADS)

Much attention has recently focused on using DNA as a linking agent to engineer nanoparticle (NP) lattices with specific geometries. There has been success generating a broad range of crystal symmetries, but the formation of a tetrahedral or diamond lattice has been particularly challenging. We use molecular simulations to examine a combination of NP uniformly coated with DNA that connect via linking units that incorporate tetrahedral structure. We test the stability of spherical NP-DNA complexes with tetrahedral linkers in a 1:1 ratio, which allow for a variety of lattices, including a diamond structure. Previously postulated interpenetrating diamond lattices are also possible.

Neitzel, Joshua; Gang, Oleg; Starr, Francis

2013-03-01

146

Low acidity alumina-bound zeolites containing tetrahedral boron, gallium, indium and/or thallium  

SciTech Connect

This patent describes a method of preparing a composition comprising a zeolite and a matrix comprising alumina wherein the composition exhibits an alpha value of the zeolite, wherein the zeolite has a SiO/sub 2//Al/sub 2/O/sub 3/ molar ratio of at least about 10, ahs an alpha value of less than about 100 and contains a framework tetrahedral element selected from the group consisting of B, Ga, In and Tl, wherein the method comprises: (a) providing the zeolite containing an alkylammonium salt; (b) ion exchanging the zeolite to replace alkali metal cations with ammonium cations; (c) binding the zeolite with an aluminum containing material; and (d) calcining the zeolite containing aluminum material to decompose organic material and convert the zeolite to the acid or hydrogen form, and thereby producing the composition having the alpha value which is the alpha value of the zeolite in the acid or hydrogen form, absent the matrix. The method of claim 1, wherein the zeolite containing aluminum material is dried to eliminate excess water, prior to calcining.

Degman, T.F. Jr.; Lutner, J.D.; Chen, N.Y.

1988-11-29

147

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

148

Magnetoelectronic properties of Gd-implanted tetrahedral amorphous carbon  

NASA Astrophysics Data System (ADS)

The structural, electronic, magnetic, and magnetoelectronic properties of tetrahedral amorphous carbon (ta-C) thin films doped with gadolinium via ion implantation (ta-C1-x:Gdx, x = 0.02 ˜ 0.20) have been studied, both as prepared and after annealing, with Xe-implanted samples as control samples. Gd implantation causes significant increases in electrical conductivity, showing that Gd adds carriers as in other rare earth-semiconductor systems. Gd also provides a large local moment from its half-filled f shell. Carrier-mediated Gd-Gd interactions are strong but very frustrated, causing a spin-glass state < 10 K for higher x. An enormous negative magnetoresistance (about -103 at 3 K in a 70-kOe field for x = 0.088) is observed at low T (<30 K), an indication of carrier-moment interactions that cause magnetic disorder-induced localization and consequent magnetic field-induced delocalization as Gd moments align with the magnetic field. Gd implantation causes substantial changes in Raman intensity, associated with conversion of C-C bonds into Raman inactive bonds, which induce further graphitization after annealing. The changing nature of the C-C bonding with increasing x or with annealing causes the electrical transport properties to depend on Gd concentration x with a nonmonotonic dependence. Systematic but nonmonotonic trends are seen on comparing the magnetic and magnetotransport properties of Gd-doped a-C, a-Si, and a-Ge matrices, suggesting that electron concentration and band gap play separate important roles.

Zeng, Li; Zutz, H.; Hellman, F.; Helgren, E.; Ager, J. W., III; Ronning, C.

2011-10-01

149

Analysis of stiffened plates under lateral loading using sequential quadratic programming (SQP)  

Microsoft Academic Search

The paper presents a methodology for the analysis of multi-stiffened plates under lateral loading. The structure is idealized as assembled plate and beam elements, rigidly connected at their junctions. The strain energy of the idealized structure is then derived in terms of generalized in- and out-of-plane displacement functions. Treating the coefficients of these functions as design variables, sequential quadratic programming

O. K. Bedair

1997-01-01

150

A calculator?based computational approach. Part 2. Quadratic functions and equations  

Microsoft Academic Search

This paper is a natural extension of the computational approach from linear?type problems, discussed in the first article [1], to quadratic functions, equations and related word problems. The additional complexity leads to a discussion about the structure of diagrams (series and parallel), the restrictions on the input variable (domain and range), the multi?valued functions (inversion of\\/: x?x)and elements of optimization

Josef Brody

1988-01-01

151

Anisotropy of quadratic magneto-optic effects in reflection  

NASA Astrophysics Data System (ADS)

Quadratic or second-order magneto-optic effects in reflection significantly effect in-plane magnetization measurements. While the magneto-optic effects linear in magnetization are independent of orientation of cubic crystal axes, the amplitude and sign of the quadratic effects change significantly under crystal rotation. Theoretical formulas for the magneto-optic effects have been derived using a permittivity tensor including terms quadratic in magnetization. A method for separation of the diagonal and off-diagonal quadratic magneto-optic tensor components (G11-G12) and 2G44 is proposed. The theory was completed by an experimental observation of the quadratic effect anisotropy in an epitaxial Fe layer prepared on a MgO substrate. The influence of the magnetization components on the magneto-optic vector magnetometry is discussed for an interface, a single layer, and exchange coupled bilayer system for a general magnetization direction including the quadratic magneto-optic effect anisotropy.

Postava, K.; Hrabovský, D.; Pištora, J.; Fert, A. R.; Viš?ovský, Š.; Yamaguchi, T.

2002-05-01

152

Plane and Guided Wave Effects and Devices Via Quadratic Cascading  

Microsoft Academic Search

\\u000a Quadratic cascading, i. e. the sequence of two second-order nonlinear processes, has assumed an important role in recent years\\u000a as one of the possibilities for a low power, lossless, ultrafast approach to all-optical processing of signals. [1–5] The foundation of quadratic cascading is as old as quadratic nonlinear optics itself, but its implications were brought\\u000a up later on in several

Gaetano Assanto; Katia Gallo; Claudio Conti

153

Optical Absorption of Tetrahedral Co3+ and Co2+ in Garnets  

Microsoft Academic Search

Optical spectra of single crystals of high-purity garnets YIG (Y3Fe5O12), YAG (Y3Al5O12), and YGG (Y3Ga5O12) containing cobalt ions have been investigated. With the pure materials the spectra for all three crystals are essentially the same, and the spectrum has been attributed to the rarely observed tetrahedral Co3+. Small amounts of tetrahedral Co2+ also in evidence in YAG and to a

D. L. Wood; J. P. Remeika

1967-01-01

154

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

Microsoft Academic Search

We introduce a many-body fixed-charge potential optimized for tetrahedral silica. The potential is used to investigate the crystal structures and energetics of six tetrahedrally coordinated silica polymorphs (α- and β-quartz, α- and β-cristobalite, β-tridymite, and coesite). The structural parameters of the different phases are found to be well-reproduced. Most importantly, the ground state of the silica polymorphs is reproduced correctly.

Yu Jianguo; Simon R. Phillpot; Susan B. Sinnott

2007-01-01

155

Surface modification of thin tetrahedral amorphous carbon films by means of UV direct laser interference patterning  

Microsoft Academic Search

In this work, direct laser interference patterning of hydrogen-free tetrahedral amorphous carbon (ta-C) thin films using an ultraviolet (UV) nanosecond pulsed laser is investigated. Using this method, line-like arrays with submicrometer resolution were fabricated. In particular, a 180nm grating period was successfully produced. In addition, it was found that depending on the laser energy density, the tetrahedral carbon film either

Teja Roch; Eckhard Beyer; Andrés Lasagni

2010-01-01

156

Formation, atomic structural optimization and electronic structures of tetrahedral carbon onion  

Microsoft Academic Search

The carbon onion with a tetrahedral structure was produced by electron-beam irradiation on amorphous carbon synthesized from polyvinyl alcohol. Atomic structure analysis and structural optimization of the onion were carried out by high-resolution electron microscopy, image simulation, molecular mechanics and molecular orbital calculations. A structure model of C84@C276 was proposed at the center of the tetrahedral carbon onion.

Takeo Oku; Ichihito Narita; Atsushi Nishiwaki

2004-01-01

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

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

159

Linear-quadratic games of resource depletion  

SciTech Connect

In this paper we describe some methods for quantitatively analyzing dynamic, multiple agent models in which at least one agent takes into account his influence on the aggregate environment such as the degree of competitiveness in the petroleum industry. We confine our attention to models in which the agents solve stochastic, quadratic optimization problems subject to linear constraints. Discussion is presented in the context of a resource depletion example. The players are resource suppliers; the task is to compare their behavior when they play alternative dynamic games. Our approach to solving these models of dynamic games is first to deduce the stochastic Euler equations for each of the agents and then to simultaneously solve these stochastic Euler equations subject to the respective transversality conditions. The solution strategy involves factoring the characteristic polynomial of the system of stochastic difference equations. 22 refs.

Epple, D.; Hansen, L.P.; Roberds, W.

1983-01-01

160

Quasimultipartite entanglement measure based on quadratic functions  

SciTech Connect

We develop an entanglement measure by extending Jaeger's Minkowskian norm entanglement measure. This measure can be applied to a much wider class of multipartite mixed states, although still 'quasi' in the sense that it is still incapable of dividing precisely the sets of all separable and entangled states. As a quadratic scalar function of the system density matrix, the quasimeasure can be easily expressed in terms of the so-called coherence vector of the system density matrix, by which we show the basic properties of the quasimeasure including (1) zero entanglement for all separable states, (2) invariance under local unitary operations, and (3) nonincreasing under local positive operator-valued measure measurements. These results open up perspectives in further studies of dynamical problems in open systems, especially the dynamic evolution of entanglement, and the entanglement preservation against the environment-induced decoherence effects.

Zhang Jing; Li Chunwen; Wu Jianwu; Wu Rebing; Tarn Tzyhjong [Department of Automation, Tsinghua University, Beijing 100084 (China); Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Department of Electrical and Systems Engineering, Washington University, St. Louis, Missouri 63130 (United States)

2006-02-15

161

Quadratic dynamical decoupling with nonuniform error suppression  

SciTech Connect

We analyze numerically the performance of the near-optimal quadratic dynamical decoupling (QDD) single-qubit decoherence errors suppression method [J. West et al., Phys. Rev. Lett. 104, 130501 (2010)]. The QDD sequence is formed by nesting two optimal Uhrig dynamical decoupling sequences for two orthogonal axes, comprising N{sub 1} and N{sub 2} pulses, respectively. Varying these numbers, we study the decoherence suppression properties of QDD directly by isolating the errors associated with each system basis operator present in the system-bath interaction Hamiltonian. Each individual error scales with the lowest order of the Dyson series, therefore immediately yielding the order of decoherence suppression. We show that the error suppression properties of QDD are dependent upon the parities of N{sub 1} and N{sub 2}, and near-optimal performance is achieved for general single-qubit interactions when N{sub 1}=N{sub 2}.

Quiroz, Gregory; Lidar, Daniel A. [Department of Physics and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States); Departments of Electrical Engineering, Chemistry, and Physics, and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089 (United States)

2011-10-15

162

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

163

Quadratic Assignment Problem Algorithms and the Location of Indivisible Facilities  

Microsoft Academic Search

This paper discusses the problem of assigning locations to indivisible facilities and its relation to the quadratic assignment problem. It also develops two suboptimal algorithms, one dealing with the general quadratic assignment problem and the other with an interesting special case. Qualitative and quantitative comparisons with existing suboptimal algorithms are presented.

Frederick S. Hillier; Michael M. Connors

1966-01-01

164

Sketching the General Quadratic Equation Using Dynamic Geometry Software  

ERIC Educational Resources Information Center

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

Stols, G. H.

2005-01-01

165

Analytical placement: A linear or a quadratic objective function?  

Microsoft Academic Search

This paper addresses the problem of cell placement which is considered crucial for layout quality. Based on the combined analytical and partitioning strategy successfully applied in the GORDIAN placement tool, we discuss the consequences of using linear or quadratic ob- jective functions. By joining the linear objective with an efficient quadratic programming approach, and by applying a refined iterative partitioning

Georg Sigl; Konrad Doll; Frank M. Johannes

1991-01-01

166

Real irreducible sesquilinear-quadratic tensor concomitants of complex bivectors  

Microsoft Academic Search

Irreducible tensor concomitants of an arbitrary complex antisymmetric second rank tensor, or bivector, in a Minkowski space-time are presented. These tensors are quadratic in the complex bivector and invariant under an overall multiplicative phase change of the bivector; in other words, they are sesquilinear-quadratic tensor concomitants of the complex bivector. The tensors are real and irreducible under the full real

T. D. Carozzi; J. E. S. Bergman

2006-01-01

167

Quadratic phase coupling of the maturing hippocampal EEG  

Microsoft Academic Search

Bispectral analysis is used in this paper to examine the status of quadratic phase couplings in developing neuronal interactions of two hippocampal subfields, CA1 and the dentate gyrus. It was found that the frequency bands where active quadratic phase coupling occurs gradually shift from a low theta range (5-7 Hz) for animals of 15 days of age to a high

Taikaug Ning; J. V. Tranquillo; J. D. Bronzino

1996-01-01

168

Finding Quadratic Schedules for Affine Recurrence Equations Via Nonsmooth Optimization  

Microsoft Academic Search

Frequently, affine recurrence equations can be scheduled more efficiently by quadratic scheduling functions than by linear scheduling functions. In this paper, the problem of finding optimal quadratic schedules for affine recurrence equations is formulated as a convex nonsmooth programming problem. In particular, sufficient constraints for causality are used generalizing Lamport's condition. In this way, the presented problem formulation becomes independent

Wolfgang Achtziger; Karl-heinz Zimmermann

2000-01-01

169

Linear quadratic optimal control for an experimental OHS aircraft  

Microsoft Academic Search

This paper describes the computer simulation and experimentation of a remotely controlled model aircraft under linear quadratic control. The aircraft is first modelled mathematically using Newton's laws and coordinate transformations which form a set of nonlinear differential equations. The mathematical model is linearized and used as the basis for the linear quadratic problem. The control system is simulated and then

J. S. Mukherjee; J. K. Pieper

2000-01-01

170

Some Paradoxical Results for the Quadratically Weighted Kappa  

ERIC Educational Resources Information Center

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

Warrens, Matthijs J.

2012-01-01

171

Optimal and suboptimal quadratic forms for noncentered Gaussian processes  

NASA Astrophysics Data System (ADS)

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

Grebenkov, Denis S.

2013-09-01

172

Quadratic algebras for three-dimensional superintegrable systems  

SciTech Connect

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

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

2010-02-15

173

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

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

A Quadratic Closure for Compressible Turbulence  

SciTech Connect

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

Futterman, J A

2008-09-16

176

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

177

Optical band gap of the filled tetrahedral semiconductor LiZnN  

NASA Astrophysics Data System (ADS)

The optical band gap of the filled tetrahedral semiconductor LiZnN [viewed as a hypothetical zinc-blende (ZnN)- lattice partially filled with He-like Li+ interstitials] was studied. The band-gap nature of LiZnN predicted theoretically by an ``interstitial insertion rule'' is confirmed to be direct with a forbidden gap of 1.91 eV at room temperature. The band gap is closer to a value calculated using a nonrelativistic augmented-spherical-wave method rather than that predicted from the empirical trend of band gaps between the filled tetrahedral (LiZnAs and LiZnP) and zinc-blende (GaAs and GaP) structures. The difference on the bonding character between the filled tetrahedral and zinc-blende compounds is discussed.

Kuriyama, K.; Kato, Tomoharu; Tanaka, T.

1994-02-01

178

Vibrations of the nonlinear oscillator with quadratic nonlinearity  

NASA Astrophysics Data System (ADS)

In this paper the vibration of a mass-spring oscillator with strong quadratic nonlinearity and one degree of freedom is analyzed. The both, strong and hard, springs are considered. The restoring force in the spring which is the function of the quadratic deformation has to satisfy the condition of antisymmetry. The mathematical model is an ordinary second order differential equation where the quadratic nonlinear term changes the sign. The quantitative and the qualitative analysis of the equation is done. The exact analytical solution is obtained. It depends on the Jacobi elliptic function.

Cveticanin, L.

2004-10-01

179

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

180

Quadratic-Exponential Moment Error Bounds for Digital Communication Systems.  

National Technical Information Service (NTIS)

By utilizing the theory of moment spaces, upper and lower bounds to error probability of digital communication systems, based on the use of quadratic-exponential moments of the intersymbol interference random variables, are obtained. Some bounds can be ev...

K. Yao

1976-01-01

181

Duality and Sensitivity in Quadratic Optimization over a Sphere.  

National Technical Information Service (NTIS)

Duality is introduced for the problem of optimizing a quadratic form over an ellipsoid. Based on the duality results, some existing solution procedures are interpreted as in fact solving the dual. The duality relations also provide a natural framework for...

O. E. Flippo B. Jansen

1992-01-01

182

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

183

A transient, quadratic nodal method for triangular-Z geometry  

Microsoft Academic Search

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

DeLorey

1993-01-01

184

Digital filter bank design quadratic-constrained formulation  

Microsoft Academic Search

Formulate the filter bank design problem as an quadratic-constrained least-squares minimization problem. The solution of the minimization problem converges very quickly since the cost function as well as the constraints are quadratic functions with respect to the unknown parameters. The formulations of the perfect-reconstruction cosine-modulated filter bank, of the near-perfect-reconstruction pseudo-QMF bank, and of the two-channel biorthogonal linear-phase filter bank

Truong Q. Nguyen

1995-01-01

185

On the Convergence of Successive Linear-Quadratic Programming Algorithms  

Microsoft Academic Search

Abstract The global convergence properties of a class of penalty methods for nonlinear pro- gramming,are analyzed. These methods include successive linear programming,ap- proaches, and more specically , the successive linear-quadratic programming approach presented by Byrd, Gould, Nocedal and Waltz (Math. Programming 100(1):27{48, 2004). Every iteration requires the solution of two trust-region subproblems involving piecewise linear and quadratic models, respectively. It

Richard H. Byrd; Nicholas I. M. Gould; Jorge Nocedal; Richard A. Waltz

2005-01-01

186

Reactive-power dispatch by successive quadratic programming  

Microsoft Academic Search

The reactive-power dispatch is formulated as the minimization of real-power losses in the system, utilizing a full set of control variables: generator voltages, switchable shunt susceptances, and transformer taps. The solution of the loss problem is obtained by successively solving quadratic programming problems. First- and second-order loss sensitivity coefficients are derived for the quadratic problem formulation. The derivations are based

V. H. Quintana; M. Santos-Nieto

1989-01-01

187

Highly degenerate quadratic forms over finite fields of characteristic 2  

Microsoft Academic Search

Let K\\/F be an extension of finite fields of characteristic two. We consider quadratic forms written as the trace of xR(x), where R(x) is a linearized polynomial. We show all quadratic forms can be so written, in an essentially unique way. We classify those R, with coefficients 0 or 1, where the form has a codimension 2 radical. This is

Robert W. Fitzgerald

2005-01-01

188

Finite difference and finite element methods  

Microsoft Academic Search

The relationships between and relative advantages of finite difference and finite element methods are discussed. The less familiar finite element methods are described first for equilibrium problems: it is shown how quadratic elements on right triangles lead to natural generalisations of the powerful, fourth order accurate nine-point difference scheme for the Laplacian. For evolutionary problems, the recent development of more

K. W. Morton

1976-01-01

189

Finite Element Surface Fitting for Bridge Management  

Microsoft Academic Search

We propose a new finite element surface fitting method which can handle very large databases. This method uses finite element discretization to find an approximation of a smooth function which minimizes a sum of data residuals and second derivatives under some constraints on data. The finite element discretization derives a large scale constrained quadratic program, which can be reformulated as

Xiaojun Chen; Takuma Kimura

2006-01-01

190

Sulfate-templated self-assembly of new M4L6 tetrahedral metal organic cages.  

PubMed

Six equivalents of N,N'-bis(4-aminobenzyl)urea, 12 equivalents of 2-formylpyridine and four equivalents of FeSO(4) or NiSO(4) undergo subcomponent self-assembly in aqueous solution to form tetrahedral cages around a single, encapsulated sulfate anion. PMID:22983087

Yi, Song; Brega, Valentina; Captain, Burjor; Kaifer, Angel E

2012-10-25

191

The electrostatic energy of micas as a function of Si, Al tetrahedral ordering  

Microsoft Academic Search

The Si, Al distribution in tetrahedral sheets of micas has been analysed by the use of Monte Carlo simulation and by the calculation of electrostatic energies. A new method for the calculation of electrostatic energies for short-range-ordered distributions has been developed. The results of the analysis demonstrate that the Si, Al distribution is mainly controlled by the electrostatic requirements of

C. P. Herrero; J. Sanz; J. M. Serratosa

1986-01-01

192

Algebraic approach to vibrational spectra of tetrahedral molecules: a case study of silicon tetrafluoride  

NASA Astrophysics Data System (ADS)

Both the stretch and bend vibrational spectrum and the intensity of infrared transitions in a tetrahedral molecule are studied in a U(2) algebraic model, where the spurious states in the model Hamiltonian and the wavefunctions are exactly removed. As an example, we apply the model to silicon tetrafluoride SiF$_4$.

Hou, X.

1998-02-01

193

Algebraic approach to vibrational spectra of tetrahedral molecules: a case study of silicon tetrafluoride  

Microsoft Academic Search

Both the stretch and bend vibrational spectrum and the intensity of infrared transitions in a tetrahedral molecule are studied in a U(2) algebraic model, where the spurious states in the model Hamiltonian and the wavefunctions are exactly removed. As an example, we apply the model to silicon tetrafluoride SiF4.

Xi-Wen Hou; Shi-Hai Dong; Mi Xie; Zhong-Qi Ma

1998-01-01

194

Study of the influence of the tetrahedral reflectors properties on autocollimating systems characteristics  

Microsoft Academic Search

Improving of the autocollimating systems characteristics is a line of optical engineering development. It is associated with study of initial errors and ways of their reduction. Study is devoted to the influence of tetrahedral reflectors properties (errors of dihedral angles) on the characteristics (accuracy et al) of autocollimating and autoreflection opticalelectronic systems for positioning control. The MATLAB mathematical model of

Andrey G. Anisimov; Elena A. Tsyganok; Igor A. Konyakhin

2010-01-01

195

Computational study of tetrahedral Al-Si and octahedral Al-Mg ordering in phengite  

NASA Astrophysics Data System (ADS)

As part of a wider study of the nature and origins of cation order-disorder in micas, a variety of computational techniques have been used to investigate the nature of tetrahedral and octahedral ordering in phengite, K2[6](Al3Mg)[4](Si7Al)O20(OH)4. Values of the atomic exchange interaction parameters Jn used to model the energies of order-disorder were calculated. Both tetrahedral Al-Si and octahedral Al-Mg ordering were studied and hence three types of interaction parameter were necessary: for T-T, O-O and T-O interactions (where T denotes tetrahedral sites and O denotes octahedral sites). Values for the T-T and O-O interactions were taken from results on other systems, whilst we calculated new values for the T-O interactions. We have demonstrated that modelling the octahedral and tetrahedral sheets alone and independently produces different results from modelling a whole T-O-T layer, hence justifying the inclusion of the T-O interactions. Simulations of a whole T-O-T layer of phengite indicated the presence of short-range order, but no long-range order was observed.

Palin, E. J.; Dove, M. T.; Redfern, S. A. T.; Saniz-Díaz, C. I.; Lee, W. T.

196

On the question of symmetry classification of ordered tetrahedrally coordinated structures  

Microsoft Academic Search

Substructures of tetrahedrally coordinated polytopes (4D polyhedra) are determined as ``polytopes'' {136} and {408}, which are divided into nonintersecting 17-vertex aggregations of four centered tetrahedra. It is shown that 17-vertex polyhedra of the diamond structure and polytopes , {240}, , and {5, 3, 3} differ only by the angle of synchronous rotation of external vertex triads, and the cell of

A. L. Talis; O. A. Belyaev; A. A. Reu; R. A. Talis

2008-01-01

197

Extended orientational correlation study for molecular liquids containing distorted tetrahedral molecules: Application to methylene halides  

NASA Astrophysics Data System (ADS)

The method of Rey [Rey, J. Chem. Phys. 126, 164506 (2007)] for describing how molecules orient toward each other in systems with perfect tetrahedral molecules is extended to the case of distorted tetrahedral molecules of c2v symmetry by means of introducing 28 subgroups. Additionally, the original analysis developed for perfect tetrahedral molecules, based on six groups, is adapted for molecules with imperfect tetrahedral shape. Deriving orientational correlation functions have been complemented with detailed analyses of dipole-dipole correlations. This way, (up to now) the most complete structure determination can be carried out for such molecular systems. In the present work, these calculations have been applied for particle configurations resulting from reverse Monte Carlo computer modeling. These particle arrangements are fully consistent with structure factors from neutron and x-ray diffraction measurements. Here we present a complex structural study for methylene halide (chloride, bromide, and iodide) molecular liquids, as possibly the best representative examples. It has been found that the most frequent orientations of molecules are of the 2:2 type over the entire distance range in these liquids. Focusing on the short range orientation, neighboring molecules turn toward each other with there ``H,Y''-``H,Y'' (Y: Cl, Br, I) edges, apart from CH2Cl2 where the H,H-H,Cl arrangement is the most frequent. In general, the structure of methylene chloride appears to be different from the structure of the other two liquids.

Pothoczki, Szilvia; Temleitner, László; Pusztai, László

2010-04-01

198

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

199

Accumulation of Tetrahedral Intermediates in Cholinesterase Catalysis: A Secondary Isotope Effect Study  

PubMed Central

In a previous communication, kinetic ?-deuterium secondary isotope effects were reported that support a mechanism for substrate-activated turnover of acetylthiocholine by human butyrylcholinesterase (BuChE) wherein the accumulating reactant state is a tetrahedral intermediate (Tormos, J. R., et al. (2005) JACS 127, 14538–14539). In this paper additional isotope effect experiments are described with acetyl-labeled acetylthiocholines (CL3COSCH2CH2N+Me3; L = H or D) that also support accumulation of the tetrahedral intermediate in Drosophila melanogaster acetylcholinesterase (DmAChE) catalysis. In contrast to the aforementioned BuChE-catalyzed reaction, for this reaction the dependence of initial rates on substrate concentration is marked by pronounced substrate inhibition at high substrate concentrations. Moreover, kinetic ? -deuterium secondary isotope effects for turnover of acetylthiocholine depended on substrate concentration, and gave the following: D3kcat/Km = 0.95 ± 0.03, D3kcat = 1.12 ± 0.02 and D3 ? kcat = 0.97 ± 0.04. The inverse isotope effect on kcat/Km is consistent with conversion of the sp2 hybridized substrate carbonyl in the E + A reactant state into a quasi-tetrahedral transition state in the acylation stage of catalysis, whereas the markedly normal isotope effect on kcat is consistent with hybridization change from sp3 toward sp2 as the reactant state for deacylation is converted into the subsequent transition state. Transition states for Drosophila melanogaster AChE-catalyzed hydrolysis of acetylthiocholine were further characterized by measuring solvent isotope effects and determining proton inventories. These experiments indicated that the transition state for rate-determining decomposition of the tetrahedral intermediate is stabilized by multiple protonic interactions. Finally, a simple model is proposed for the contribution that tetrahedral intermediate stabilization provides to the catalytic power of acetylcholinesterase.

Tormos, Jose R.; Wiley, Kenneth L.; Wang, Yi; Fournier, Didier; Masson, Patrick; Nachon, Florian; Quinn, Daniel M.

2010-01-01

200

Parallel Higher-order Finite Element Method for Accurate Field Computations in Wakefield and PIC Simulations  

SciTech Connect

Over the past years, SLAC's Advanced Computations Department (ACD), under SciDAC sponsorship, has developed a suite of 3D (2D) parallel higher-order finite element (FE) codes, T3P (T2P) and Pic3P (Pic2P), aimed at accurate, large-scale simulation of wakefields and particle-field interactions in radio-frequency (RF) cavities of complex shape. The codes are built on the FE infrastructure that supports SLAC's frequency domain codes, Omega3P and S3P, to utilize conformal tetrahedral (triangular)meshes, higher-order basis functions and quadratic geometry approximation. For time integration, they adopt an unconditionally stable implicit scheme. Pic3P (Pic2P) extends T3P (T2P) to treat charged-particle dynamics self-consistently using the PIC (particle-in-cell) approach, the first such implementation on a conformal, unstructured grid using Whitney basis functions. Examples from applications to the International Linear Collider (ILC), Positron Electron Project-II (PEP-II), Linac Coherent Light Source (LCLS) and other accelerators will be presented to compare the accuracy and computational efficiency of these codes versus their counterparts using structured grids.

Candel, A.; Kabel, A.; Lee, L.; Li, Z.; Limborg, C.; Ng, C.; Prudencio, E.; Schussman, G.; Uplenchwar, R.; Ko, K.; /SLAC

2009-06-19

201

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

NASA Astrophysics Data System (ADS)

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

Ferrer, Rodolfo M.

202

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

203

A 2-D five-noded finite element to model power singularity  

Microsoft Academic Search

A 2-D five-noded finite element which contains a ? singularity is developed. The new element is compatible with cubic standard isoparametric elements. The main advantage of using cubic isoparametric elements over quadratic elements is to reduce the number of elements required to model a structure for results of comparable accuracy. The element is tested on two different examples. In the

M. M. Abdel Wahab; G. Roeck

1986-01-01

204

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

205

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

206

Application of quadratic neural networks to seismic signal classification  

NASA Astrophysics Data System (ADS)

This paper solves the seismic signal classification problem using the quadratic neural networks with closed-boundary discriminating surfaces. In this study, we have demonstrated the quadratic neural network (QNN) potential capabilities in application to the seismic signal classification problems and show that the efficiency achieved here, is much better to what obtained with conventional multilayer neural networks. Firstly, we have performed some pre-processing on the long period recordings to cancel out the instrumental and attenuation side effects. Secondly, we have extracted the ARMA filter coefficients of the windowed P-wave phase through some matrix manipulations using the conventional Prony ARMA modeling scheme. The derived coefficients are then applied to QNN for training and classification. The results have shown that a quadratic neuron is likely to have a performance similar to that of a multilayer perceptron when the target is to discriminate distribution of points in clusters within the input space.

Allameh Zadeh, M.; Nassery, P.

1999-06-01

207

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

208

A 3D Finite-Volume Scheme for the Euler Equations on Adaptive Tetrahedral Grids  

NASA Astrophysics Data System (ADS)

The paper describes the development and application of a new Euler solver for adaptive tetrahedral grids. Spatial discretization uses a finite-volume, node-based scheme that is of central-differencing type. A second-order Taylor series expansion is employed to march the solution in time according to the Lax-Wendroff approach. Special upwind-like smoothing operators for unstructured grids are developed for shock-capturing, as well as for suppression of solution oscillations. The scheme is formulated so that all operations are edge-based, which reduces the computational effort significantly. An adaptive grid algorithm is employed in order to resolve local flow features. This is achieved by dividing the tetrahedral cells locally, guided by a flow feature detection algorithm. Application cases include transonic flow around the ONERA M6 wing and transonic flow past a transport aircraft configuration. Comparisons with experimental data evaluate accuracy of the developed adaptive solver.

Vijayan, P.; Kallinderis, Y.

1994-08-01

209

A 3D finite-volume scheme for the Euler equations on adaptive tetrahedral grids  

SciTech Connect

The paper describes the development and application of a new Euler solver for adaptive tetrahedral grids. Spatial discretization uses a finite-volume, node-based scheme that is of central-differencing type. A second-order Taylor series expansion is employed to march the solution in time according to the Lax-Wendroff approach. Special upwind-like smoothing operators for unstructured grids are developed for shock-capturing, as well as for suppression of solution oscillations. The scheme is formulated so that all operations are edge-based, which reduces the computational effort significantly. An adaptive grid algorithm is employed in order to resolve local flow features. This is achieved by dividing the tetrahedral cells locally, guided by a flow feature detection algorithm. Application cases include transonic flow around the ONERA M6 wing and transonic flow past a transport aircraft configuration. Comparisons with experimental data evaluate accuracy of the developed adaptive solver. 31 refs., 33 figs.

Vijayan, P.; Kallinderis, Y. (Univ. of Texas, Austin, TX (United States))

1994-08-01

210

On the question of symmetry classification of ordered tetrahedrally coordinated structures  

NASA Astrophysics Data System (ADS)

Substructures of tetrahedrally coordinated polytopes (4D polyhedra) are determined as “polytopes” {136} and {408}, which are divided into nonintersecting 17-vertex aggregations of four centered tetrahedra. It is shown that 17-vertex polyhedra of the diamond structure and polytopes <136>, {240}, <408>, and {5, 3, 3} differ only by the angle of synchronous rotation of external vertex triads, and the cell of each structure is determined by the two nearest nonintersecting 17-vertex polyhedra. The following sequence is proposed as a basis for symmetry classification of ordered tetrahedrally coordinated structures: diamond structure <136> {240} ? <408> ? {5, 3, 3}. The possibilities of the developed approach are demonstrated by the example of constructing a rod with the screw axis 82 from cells of the polytope <136>; this rod can be transformed into a diamond substructure: a helicoid of diamond parallelohedra with the screw axis 41.

Talis, A. L.; Belyaev, O. A.; Reu, A. A.; Talis, R. A.

2008-05-01

211

On the triplet ground state of tetrahedral X4 clusters (X = Li, Na, K, Cu).  

PubMed

The lowest electronic state of distorted tetrahedral X(4) clusters (with X = Li, Na, K, Cu) is studied at coupled-cluster level using high-quality atomic basis sets. The ground state is found to have a triplet spin symmetry for this kind of geometry and for all the considered atomic species. The equilibrium geometries correspond to Jahn-Teller-distorted oblate tetrahedra having D(2d) symmetry, and tetrahedric structures are local minima on the potential-energy surfaces for the triplet states. Their energies lie between 0.2 eV (for the K(4) cluster) and 0.9 eV (for Cu(4)) above the absolute minimum of the corresponding systems, which is a spin singlet having a rhombus geometry. PMID:22401434

Verdicchio, Marco; Evangelisti, Stefano; Leininger, Thierry; Monari, Antonio

2012-03-01

212

Low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon films  

Microsoft Academic Search

The low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon (ta-C) films was investigated. Ta-C films prepared by a filtered arc deposition technique were annealed at 400 °C for 60-120 min in a nitrogen atmosphere. The density and sp3 content in as-grown film were 3.3 g cm-3 and ~90%, respectively. After annealing, no obvious changes in film density

Z. Y. Chen; J. P. Zhao; X. Wang; Y. H. Yu; T. S. Shi

2000-01-01

213

A high-silica zeolite with a 14-tetrahedral-atom pore opening  

Microsoft Academic Search

ZEOLITES (microporous aluminosilicates) and related molecular sieves have found wide application as catalysts, sorbents and ion-exchange materials. New zeolites with large pores are much in demand1-4, and have been sought for several decades4-7. All known zeolites, both natural and synthetic, contain pores comprised of 12 or fewer tetrahedrally coordinated silicon or aluminium atoms (T-atoms), but several microporous aluminophosphates with wider

C. C. Freyhardt; M. Tsapatsis; R. F. Lobo; K. J. Balkus; M. E. Davis

1996-01-01

214

Hole-type mixed-valence tetrahedral cluster: Exchange-tunnel states and magnetic properties  

Microsoft Academic Search

The paper deals with the exchange-tunnel states of a tetrahedral tetrameric hole-type cluster d1-d2-d2-d2 used as a model of metal core of vrious protiens. A new method for group-theoretic classification ofthe quantum states of mixed-valence clusters is suggested. The nature ofthe ground spin state of the above systems has been investigated. The effect of partial spin alignment depending on the

V. P. Coropceanu; Sh. N. Gifeisman; B. S. Tsukerblat

1993-01-01

215

Evaluation on corrosion behavior and haemocompatibility of phosphorus incorporated tetrahedral amorphous carbon films  

Microsoft Academic Search

Phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films are deposited on biomedical titanium alloy (Ti6Al4V) by filtered cathodic vacuum arc technique. The structural properties of ta-C:P films are evaluated by X-ray photoelectron spectroscopy and Raman spectroscopy. Potentiodynamic polarization tests are employed to assess the corrosion performances of ta-C:P coated and uncoated Ti alloys in 0.89 wt.% NaCl solution. In vitro platelet adhesion

Aiping Liu; Jiecai Han; Jiaqi Zhu; Songhe Meng; Xiaodong He

2008-01-01

216

A 3D Finite-Volume Scheme for the Euler Equations on Adaptive Tetrahedral Grids  

Microsoft Academic Search

The paper describes the development and application of a new Euler solver for adaptive tetrahedral grids. Spatial discretization uses a finite-volume, node-based scheme that is of central-differencing type. A second-order Taylor series expansion is employed to march the solution in time according to the Lax-Wendroff approach. Special upwind-like smoothing operators for unstructured grids are developed for shock-capturing, as well as

P. Vijayan; Y. Kallinderis

1994-01-01

217

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

NASA Astrophysics Data System (ADS)

A tetrahedrally coordinated cobalt(II) phosphonate, Co(O3PCH2CH2NH2), 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

218

Amorphous-amorphous transformation at high pressure in gallo-germanosilicate tetrahedral network glasses  

NASA Astrophysics Data System (ADS)

We report the existence of structurally distinct amorphous states upon compression in sodium gallo-germanosilicate glasses. In situ x-ray absorption spectroscopy provides clear evidence for a transition at high pressure to a more compact arrangement of atoms based on Ga and Ge octahedral sites. This study extends previous works on simple and open tetrahedral networks ( SiO2 and GeO2 ) by showing the compression behavior of stuffed (by Na cations) and mixed network glasses.

Cormier, L.; Ferlat, G.; Itié, J.-P.; Galoisy, L.; Calas, G.; Aquilanti, G.

2007-10-01

219

Amorphous-amorphous transformation at high pressure in gallo-germanosilicate tetrahedral network glasses  

SciTech Connect

We report the existence of structurally distinct amorphous states upon compression in sodium gallo-germanosilicate glasses. In situ x-ray absorption spectroscopy provides clear evidence for a transition at high pressure to a more compact arrangement of atoms based on Ga and Ge octahedral sites. This study extends previous works on simple and open tetrahedral networks (SiO{sub 2} and GeO{sub 2}) by showing the compression behavior of stuffed (by Na cations) and mixed network glasses.

Cormier, L.; Ferlat, G.; Galoisy, L.; Calas, G. [Institut de Mineralogie et Physique des Milieux Condenses, Universite Paris 6, Universite Paris 7, CNRS UMR 7590, IPGP, 140 rue de Lourmel, 75015 Paris (France); Itie, J.-P. [Synchrotron SOLEIL, L'Orme des Merisiers, Boite Postale 48, 91192 Gif s/Yvette Cedex (France); Aquilanti, G. [European Synchrotron Radiation Facility, 6 rue Jules Horowitz, Boite Postale 220, 38043 Grenoble Cedex (France)

2007-10-01

220

Anisotropic potentials from the rainbow scattering of sodium atoms and tetrahedral molecules  

Microsoft Academic Search

Differential cross sections have been measured for Na scattered by the tetrahedral molecules SiCl4, C(CH3)4, Si(CH3)4 and Sn(CH3)4 in the thermal energy range. Due to the high velocity resolution (Deltag\\/g≈4 per cent) the rainbow structure with primary and at least one secondary rainbow has been resolved. The broadening and quenching of this structure has been used for the determination of

U. Buck; V. Khare; M. Kick

1978-01-01

221

A 3-D time-dependent unstructured tetrahedral-mesh SP{sub N} method  

SciTech Connect

We have developed a 3-D time-dependent multigroup SP{sub n} method for unstructured tetrahedral meshes. The SP{sub n} equations are expressed in a canonical form which allows them to be solved using standard diffusion solution techniques in conjunction with source iteration, diffusion-synthetic acceleration, and fission-source acceleration. A computational comparison of our SP{sub n} method with an even-parity S{sub n} method is given.

Morel, J.E.; McGhee, J.M. [Los Alamos National Lab., NM (United States); Larsen, E.W. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Nuclear Engineering

1994-10-01

222

Optical band gap of the filled tetrahedral semiconductor LiZnN  

Microsoft Academic Search

The optical band gap of the filled tetrahedral semiconductor LiZnN [viewed as a hypothetical zinc-blende (ZnN)- lattice partially filled with He-like Li+ interstitials] was studied. The band-gap nature of LiZnN predicted theoretically by an ``interstitial insertion rule'' is confirmed to be direct with a forbidden gap of 1.91 eV at room temperature. The band gap is closer to a value

K. Kuriyama; Tomoharu Kato; T. Tanaka

1994-01-01

223

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

SciTech Connect

A tetrahedrally coordinated cobalt(II) phosphonate, Co(O{sub 3}PCH{sub 2}CH{sub 2}NH{sub 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 deg. C. Magnetic susceptibility data are consistent with weak antiferromagnetic ordering at low temperatures.

Gemmill, William R. [Department of Chemistry, James Madison University, Harrisonburg, VA 22807 (United States); Smith, Mark D. [Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Reisner, Barbara A. [Department of Chemistry, James Madison University, Harrisonburg, VA 22807 (United States)]. E-mail: reisneba@jmu.edu

2005-09-15

224

On the question of symmetry classification of ordered tetrahedrally coordinated structures  

Microsoft Academic Search

Substructures of tetrahedrally coordinated polytopes (4D polyhedra) are determined as “polytopes” {136} and {408}, which are\\u000a divided into nonintersecting 17-vertex aggregations of four centered tetrahedra. It is shown that 17-vertex polyhedra of the\\u000a diamond structure and polytopes ?136?, {240}, ?408?, and {5, 3, 3} differ only by the angle of synchronous rotation of external\\u000a vertex triads, and the cell of

A. L. Talis; O. A. Belyaev; A. A. Reu; R. A. Talis

2008-01-01

225

Toward the Solution Synthesis of the Tetrahedral Au{sub 20} Cluster  

SciTech Connect

We report solution synthesis of the recently discovered tetrahedral Au{sub 20} cluster coordinated with eight PPh{sub 3} (Ph = Phenyl) ligands. The composition and molecular weight of the Au{sub 20} (PPh{sub 3}){sub 8} complex were confirmed by the isotopic pattern of its doubly charged cation using high resolution mass spectrometry. Collision-induced dissociation experiment showed that four PPh{sub 3} can be easily dissociated from Au{sub 20} (PPh{sub 3}){sub 8}{sup 2+}, resulting in a highly stable Au{sub 20} (PPh{sub 3}){sub 4}{sup 2+} molecule. This observation is consistent with the tetrahedral structure, in which the four apex sites are expected to be strongly bound to the PPh{sub 3} ligands, and is confirmed by theoretical calculations, which predicted a highly stable Au{sub 20} (PH{sub 3}){sub 4} complex with Au-PH{sub 3} bond energies of {approx}1 eV. The current experimental and theoretical observations suggest that large quantity of ligand-stabilized tetrahedral Au{sub 20} can be obtained, opening the door for exploring its anticipated novel chemical, optical, and catalytical properties.

Zhang, Haifeng; Stender, Matthias; Zhang, Rui; Wang, Chong M.; Li, Jun; Wang, Lai S.

2004-08-19

226

Study of the influence of the tetrahedral reflectors properties on autocollimating systems characteristics  

NASA Astrophysics Data System (ADS)

Improving of the autocollimating systems characteristics is a line of optical engineering development. It is associated with study of initial errors and ways of their reduction. Study is devoted to the influence of tetrahedral reflectors properties (errors of dihedral angles) on the characteristics (accuracy et al) of autocollimating and autoreflection opticalelectronic systems for positioning control. The MATLAB mathematical model of tetrahedral reflector was developed for these purposes; results of simulation were compared with Zemax simulation. It is important to notice that the process of image formation is quite complex, it explains by superposition of six reflected and deflected beams. Because of the dihedral angle errors six compound images separate or overlap; that causes the redistribution of energy and image becomes complicated for processing. The aim is to study the influence of reflector properties on position of the image energy center, because it defines the measurement error. The influence of the tetrahedral reflector properties on system's characteristics is shown by example of shift control system based on autoreflection scheme.

Anisimov, Andrey G.; Tsyganok, Elena A.; Konyakhin, Igor A.

2010-08-01

227

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

228

Three Dimensional Finite Element Studies. Part One: Service Routines.  

National Technical Information Service (NTIS)

In the report, service routines are developed for linear, quadratic and cubic finite elements for two and three dimensional regions. Also, an equation solver of very large capacity is developed for systems of linear equations where the matrix of coefficie...

G. Cantin

1972-01-01

229

Near-optimal placement using a quadratic objective function  

Microsoft Academic Search

Placement algorithms for IC layout which are optimal are known to be NP-complete 5. As a result, heuristics such as pairwise-interchange techniques must be employed to generate satisfactory placements. Unfortunately, with these algorithms, there is generally no way of knowing just how far away the result is from optimum. With the quadratic metric used in this study, however, a useful

John P. Blanks

1985-01-01

230

Quadratic stabilization of sampled-data systems with quantization  

Microsoft Academic Search

A design method of memoryless quantizers in sampled-data systems is proposed. The design objective is quadratic stability in the continuous-time domain, and thus the decay rate between sampling times is guaranteed. Our general treatment enables us to look for quantizers efficient in terms of data rate.

Hideaki Ishii; Bruce A. Francis

2003-01-01

231

The decimal scale for releves of permanent quadrats  

Microsoft Academic Search

For vegetation analyses of permanent quadrats the author formerly used a modified scale of Braun-Blanquet with smaller intervals than in the original. For calculations of difference- and change quotients etc., on the basis of coverage, the symbols of this scale have to be converted to values proportional to the real coverage percentages. A conversion in simple terms is not possible;

G. Londo

1976-01-01

232

Finding the Best Quadratic Approximation of a Function  

ERIC Educational Resources Information Center

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

Yang, Yajun; Gordon, Sheldon P.

2011-01-01

233

Distribution of Quadratic Forms in the Multivariate Singular Normal Distribution.  

National Technical Information Service (NTIS)

The purpose of this paper is to investigate the distribution and independence properties of quadratic forms of the type X'AX where X, a pxl random vector, has the multivariate normal distribution with the corresponding mean vector mu and the pxp variance ...

P. C. Davis C. H. Kapadia J. T. Webster

1969-01-01

234

Linear quadratic stochastic control of atomic hydrogen masers  

Microsoft Academic Search

Data are given showing the results of using the linear quadratic Gaussian (LQG) technique to steer remote hydrogen masers to Coordinated Universal Time (UTC) as given by the United States Naval Observatory (USNO) via two-way satellite time transfer and the Global Positioning System (GPS). Data also are shown from the results of steering a hydrogen maser to the real-time USNO

Paul Koppang; Robert Leland

1999-01-01

235

Stanley decomposition of the joint covariants of three quadratics  

NASA Astrophysics Data System (ADS)

The Stanley decomposition of the joint covariants of three quadratics is computed using a new transvectant algorithm and computer algebra. This is sufficient to compute the general form of the normal form with respect to a nilpotent with three 3-dimensional irreducible blocks.

Sanders, Jan A.

2007-12-01

236

On constrained infinite-time linear quadratic optimal control  

Microsoft Academic Search

This work presents a solution to the infinite-time linear quadratic optimal control (ITLQOC) problem with state and control constraints. It is shown that a single, finite dimensional, convex program of known size can yield this solution. Properties of the resulting value function, with respect to initial conditions, are also established and are shoen to be useful in determining the aforementioned

D. Chmielewski; V. Manousiouthakis

1996-01-01

237

Detection of quadratic phase coupling in shallow underwater channel  

Microsoft Academic Search

This paper addresses the problem of detection of quadratic phase coupling (QPC) at the receiver when the source signal has traversed through an underwater channel. The channel has been numerically modeled using normal mode theory In a bounded underwater channel, the phase associated with each frequency varies with range as well as due to the characteristics of the channel. We

Tanmay Roy; Arun Kumar; Rajendar Bahl

2002-01-01

238

Unravelling Student Challenges with Quadratics: A Cognitive Approach  

ERIC Educational Resources Information Center

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

Kotsopoulos, Donna

2007-01-01

239

Defining Classes of Quadratic Systems in the Plane.  

National Technical Information Service (NTIS)

The definition of classes of quadratic systems in the plane is studied. Taking into account their index and multiplicity, possible combinations of singular points, both in the finite part of the plane and at infinity, lead to the definition of 173 classes...

J. W. Reyn

1991-01-01

240

Analysis of Quadratic Diophantine Equations with Fibonacci Number Solutions  

ERIC Educational Resources Information Center

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

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

2004-01-01

241

Zero-sum linear quadratic stochastic integral games and BSVIEs  

Microsoft Academic Search

This paper formulates and studies a linear quadratic (LQ for short) game problem governed by linear stochastic Volterra integral equation. Sufficient and necessary condition of the existence of saddle points for this problem are derived. As a consequence we solve the problems left by Chen and Yong in [3]. Firstly, in our framework, the term GX^2(T) is allowed to be

Tianxiao Wang; Yufeng Shi

2010-01-01

242

Optimal Control and Geodesics on Quadratic Matrix Lie Groups  

Microsoft Academic Search

The purpose of this paper is to extend the symmetric representation of the rigid body equations from the group SO(n) to other groups. These groups are matrix subgroups of the general linear group that are defined by a quadratic ma- trix identity. Their corresponding Lie algebras include several classical semisim- ple matrix Lie algebras. The approach is to start with

Anthony M. Bloch; Peter E. Crouch; Jerrold E. Marsden; Amit K. Sanyal

2008-01-01

243

An extension of Karmarkar's projective algorithm for convex quadratic programming  

Microsoft Academic Search

We present an extension of Karmarkar's linear programming algorithm for solving a more general group of optimization problems: convex quadratic programs. This extension is based on the iterated application of the objective augmentation and the projective transformation, followed by optimization over an inscribing ellipsoid centered at the current solution. It creates a sequence of interior feasible points that converge to

Yinyu Ye; Edison Tse

1989-01-01

244

A Quadratic Programming Model for Political Districting Problem  

Microsoft Academic Search

Political Districting Problem is one of the critical issues in political elections, it can be expressed as: how to partition a state into reasonable districts for parliament election and presiden- tial election. In this paper, the political districting problem for parliament election is modelled as a doubly weighted graph partition problem and it is formulated into quadratic programming model. Using

Zhenping Li; Rui-Sheng Wang; Yong Wang

245

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

246

Solving quadratic lambda-matrix problems without factorization  

Microsoft Academic Search

An algorithm is presented for computing the eigenvalues of smallest magnitude and their associated eigenvectors of the quadratic lambda-matrix M lambda² + C lambda + K. M, C, and K are assumed to be symmetric matrices with K positive definite and M negative definite. The algorithm is based on a generalization of the Rayleigh quotient and the Lanczos method for

D. S. Scott; R. C. Ward

1981-01-01

247

Dual support method for solving convex quadratic programs  

Microsoft Academic Search

In this article, we present a new dual method for solving convex (but not strictly convex) quadratic programs (QPs). Our method is the generalization of the dual support method, developed by Gabasov and co-workers in 1981, for solving convex QPs. It proceeds in two phases: the first is to construct the initial support, called coordinator support, for the problem and

Belkacem Brahmi; Mohand Ouamer Bibi

2010-01-01

248

A dual method for solving general convex quadratic programs  

Microsoft Academic Search

In this paper, we present a new method for solving quadratic programming problems, not strictly convex. Constraints of the problem are linear equalities and inequalities, with bounded variables. The suggested method combines the active-set strategies and support methods. The algorithm of the method and numerical experiments are presented, while comparing our approach with the active set method on randomly generated

Belkacem BRAHMI; Mohand Ouamer BIBI

2009-01-01

249

The Quadratic Spinor Lagrangian, Axial Torsion Current and Generalizations  

Microsoft Academic Search

We show that the Einstein-Hilbert, the Einstein-Palatini, and the Holst actions can be derived from the Quadratic Spinor Lagrangian (QSL), when the three classes of Dirac spinor fields, under Lounesto spinor field classification, are considered. To each one of these classes, there corresponds an unique kind of action for a covariant gravity theory. In other words, it is shown to

R. Da Rocha; J. G. Pereira

2007-01-01

250

Dynamics of quadratic polynomials, III: Parapuzzle and SBR measures  

Microsoft Academic Search

This is a continuation of notes on dynamics of quadratic polynomials. In this part we transfer the our prior geometric result to the parameter plane. To any parameter value c in the Mandelbrot set (which lies outside of the main cardioid and little Mandelbrot sets attached to it) we associate a ``principal nest of parapuzzle pieces'' and show that the

Mikhail Lyubich

1996-01-01

251

Moving localized structures in quadratic media with a saturable absorber  

Microsoft Academic Search

Spatial moving pulses are found in an optical resonator with a quadratic medium coupled to an intra-cavity saturable absorber. In the context of frequency degenerate optical parametric oscillators, the saturable absorber is shown to be able to generate large amplitude asymmetric pulses in the transverse section of the signal beam. They arise in a regime where the lasing solution undergoes

A. Barsella; C. Lepers; M. Taki; M. Tlidi

2004-01-01

252

A greedy genetic algorithm for the quadratic assignment problem  

Microsoft Academic Search

The Quadratic Assignment Problem (QAP) is one of the classical combinatorial optimization problems and is known for its diverse applications. In this paper, we suggest a genetic algorithm for the QAP and report its computational behavior. The genetic algorithm incorporates many greedy principles in its design and, hence, we refer to it as a greedy genetic algorithm. The ideas we

Ravindra K. Ahuja; James B. Orlin; Ashish Tiwari

2000-01-01

253

A Greedy Genetic Algorithm for the Quadratic Assignment Problem  

Microsoft Academic Search

The Quadratic Assignment Problem (QAP) is one of the classical combinatorial optimizationproblems and is known for its diverse applications. In this paper, we suggest a genetic algorithm for theQAP and report its computational behavior. The genetic algorithm incorporates many greedyprinciples in its design and, hence, is called the greedy genetic algorithm. The ideas we incorporate inthe greedy genetic algorithm include

Ravindra K. Ahuja; James B. Orlin

1997-01-01

254

Pseudorandom Number Assignment in Quadratic Response Surface Designs  

Microsoft Academic Search

This paper examines three general strategies for the assignment of pseudorandom number streams to simulation experiments in quadratic response surface designs. Comparisons of these variance-reduction schemes are presented for four design criteria that collectively address the two goals of response surface methodology: prediction and optimization.

James R. Hussey; Raymond H. Myers; Ernest C. Houck

1987-01-01

255

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

256

Fast Fourier Transform Solvers and Preconditioners for Quadratic Spline Collocation  

Microsoft Academic Search

Quadratic Spline Collocation (QSC) methods of optimal order of convergence have been recently developed for the solution of elliptic Partial Differentia l Equations (PDEs). In this paper, linear solvers based on Fast Fourier Transforms (FFT) are developed for the solution of the QSC equations. The complexity of the FFT solvers is , where is the gridsize in one dimension. These

Christina C. Christara; Kit Sun Ng

2000-01-01

257

Perturbative metric of charged black holes in quadratic gravity  

Microsoft Academic Search

We consider perturbative solutions to the classical field equations coming from a quadratic gravitational Lagrangian in four dimensions. We study the charged, spherically symmetric black hole, and explicitly give corrections up to third order (in the coupling constant beta multiplying the RmunuRmunu term) to the Reissner-Nordström metric. We discuss the thermodynamics of such black holes; in particular, we compute explicitly

M. Campanelli; C. O. Lousto; J. Audretsch

1995-01-01

258

Comparative benthic plant ecology by SCUBA-monitored quadrats  

Microsoft Academic Search

The feasibility of permanent benthic quadrats checked by SCUBA divers was tested. Stations were set up on the bottom of six representative aquatic habitats, both marine and inland, including oligotrophic and eutrophic ponds, river, coastal lagoon, estuary, and open marine coast. Data include physical-chemical factors, species composition, number and height of shoots, and general observations. From volume\\/length constants, the standing

R. D. Wood; Paul E. Hargraves

1969-01-01

259

On Quadratic Bottom Drag, Geostrophic Turbulence, and Oceanic Mesoscale Eddies  

Microsoft Academic Search

Many investigators have idealized the oceanic mesoscale eddy field with numerical simulations of geo- strophic turbulence forced by a horizontally homogeneous, baroclinically unstable mean flow. To date such studies have employed linear bottom Ekman friction (hereinafter, linear drag). This paper presents simu- lations of two-layer baroclinically unstable geostrophic turbulence damped by quadratic bottom drag, which is generally thought to be

Brian K. Arbic; Robert B. Scott

2008-01-01

260

Quadratic: manipulating algebraic expressions on an interactive tabletop  

Microsoft Academic Search

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

Jochen Rick

2010-01-01

261

Decentralized robust control via quadratically invariant model projection  

Microsoft Academic Search

We propose a computational approach to systematically find decentralized H? suboptimal controllers for general unstructured models. Exploiting the quadratically invariant model projection and the classical robust control synthesis techniques, we show that the original nonconvex problem can be conservatively solved by a series of convex optimization problems.

Jong-Han Kim; Sanjay Lall; Walter Merrill; Alireza Behbahani

2011-01-01

262

Reactive power optimization using successive quadratic programming method  

Microsoft Academic Search

This paper presents a reactive power optimization model that is based on successive quadratic programming (SQP) methods. Mathematical formulation and unified algorithm suppose different objective functions (OF) of reactive power optimization, depending on type and purposes of current reactive power control or planning problem. A bicriterion reactive power optimization model, that represents compromise between economical and security objective functions, is

N. Grudinin

1998-01-01

263

Interior-point methods for reduced Hessian successive quadratic programming  

Microsoft Academic Search

Typical chemical process optimization problems have a large number of equations, but relatively few degrees of freedom. A reduced Hessian successive quadratic programming (rSQP) algorithm has been shown to be successful in solving these types of models efficiently. While the rSQP algorithm reduces the dimension of the QP subproblem solved at each iteration, the number of inequality constraints could still

David J. Ternet; Lorenz T. Biegler

1999-01-01

264

Tetrahedral lander  

NASA Astrophysics Data System (ADS)

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.

1993-11-01

265

A Unified Study on the Cyclicity of Period Annulus of the Reversible Quadratic Hamiltonian Systems  

Microsoft Academic Search

The cyclicity of the period annulus of reversible quadratic Hamiltonian systems under quadratic perturbations was studied by several authors for different cases by using different methods. In this paper, we study this problem in a unified way.

Chengzhi Li; Jaume Llibre

2004-01-01

266

FIBER OPTIC POINT QUADRAT SYSTEM FOR IMPROVED ACCURACY IN VEGETATION SAMPLING  

EPA Science Inventory

An automated, fiber optic point quadrat system for vegetation sampling is described. Because the effective point diameter of the system never exceeds 25um it minimizes the substantial errors which can arise with conventional point quadrats. Automatic contact detection eliminates ...

267

Tetrahedral site ordering in synthetic gallium albite: A 29Si MAS NMR study  

NASA Astrophysics Data System (ADS)

The ordering of Si in the tetrahedral sites of gallium albite (NaGaSi3O8) has been studied by MAS NMR and Rietveld structure refinement of X-ray powder diffraction data. Low structural state (ordered) material was annealed at about 800°C under a load pressure of 1 kbar, and by Rietveld refinement has tetrahedral-site occupancies for Si of T1O = 0.24(3), T1m = 0.89(2), T2O = 0.98(2), and T2m = 0.89(2), respectively. Corresponding Si occupancies for high structural state (disordered) material are 0.71(2), 0.78(1), 0.76(2), and 0.74(2), respectively. The 29Si MAS NMR spectra of low gallium albite is equivalent to the three-peak spectrum of natural (Amelia) albite, with resonances at -89.6, -96.4, and -104.2 ppm but with relative peak areas of 0.79:1.0:0.77. The tetrahedral-site occupancies derived from the MAS NMR spectrum are in good agreement with those obtained by Rietveld refinement and, in particular, indicate that the -96.4 ppm peak must correspond to Si in T2O. This is the first independent assignment of the 29Si peak at -96 ppm in the spectrum of ordered albite to the T2O site. A peak at -96 ppm is also resolved in the spectrum of high gallium albite. The systematic differences in peak position between the 29Si MAS NMR spectra of low gallium albite and those of Amelia albite cannot be explained simply by the direct replacement of Al by Ga, without a change in angle at the bridging oxygen atoms.

Sherriff, Barbara L.; Fleet, Michael E.; Burns, Peter C.

1991-09-01

268

A QUADRATIC PROGRAMMING APPROACH TO THE DESIGN OF ACTIVE–PASSIVE VIBRATION ISOLATION SYSTEMS  

Microsoft Academic Search

A quadratic programming algorithm is presented for studying the design tradeoffs of active–passive vibration isolation systems. The novelty of the technique is that the optimal control problem is posed as a quadratic optimization with linear constraints. The quadratic cost function represents the mean square response of the payload acceleration and isolator stroke, and the linear constraints represent asymptotic tracking requirements

D. J. Leo; D. J. Inman

1999-01-01

269

a Quadratic Programming Approach to the Design of Active-Passive Vibration Isolation Systems  

Microsoft Academic Search

A quadratic programming algorithm is presented for studying the design tradeoffs of active-passive vibration isolation systems. The novelty of the technique is that the optimal control problem is posed as a quadratic optimization with linear constraints. The quadratic cost function represents the mean square response of the payload acceleration and isolator stroke, and the linear constraints represent asymptotic tracking requirements

D. J. Leo; D. J. Inman

1999-01-01

270

A Parametric Approach to Solve Quadratic Programming Problems with Fuzzy Environment in the Set of Constraints  

Microsoft Academic Search

Quadratic programming can be seen both as a gen- eral approach to linear programming and a special class of nonlin- ear programming. Moreover, Quadratic Programming problems are of utmost importance in a variety of relevant practical fields, such as, portfolio selection. This work presents and develops a novel fuzzy-sets-based method that solves a class of quadratic program- ming problems with

Carlos Cruz; Ricardo C. Silva; José L. Verdegay; Akebo Yamakami

2009-01-01

271

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

272

Existence, attractiveness and stability of solutions for quadratic Urysohn fractional integral equations  

NASA Astrophysics Data System (ADS)

Two nonlinear quadratic Urysohn fractional integral equations are studied. Existence and locally attractive results of solutions for a nonlinear quadratic Urysohn fractional integral equation on an unbounded interval are proved. Some interesting stability results of solutions for another quadratic Urysohn fractional integral equation in three certain sets are presented.

Wang, Jinrong; Dong, Xiwang; Zhou, Yong

2012-02-01

273

The Hua Loo-Keng problem on prime numbers representable by given quadratic forms  

NASA Astrophysics Data System (ADS)

In this paper, we solve the Hua Loo-Keng problem with prime numbers representable by given primitive positive-definite binary quadratic forms whose discriminants coincide with those of the imaginary quadratic fields in which the quadratic forms decompose into linear factors.

Gritsenko, Sergey A.

2007-06-01

274

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

SciTech Connect

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

R. M. Ferrer; Y. Y. Azmy

2009-05-01

275

Crystal Spectra of Metal Coordination Compounds. I. Tetrahedral Cobalt(II)  

Microsoft Academic Search

A reflecting microscope has been used to measure the absorption spectra, in polarized light, of a number of cobalt(II) compounds in which the ligands are arranged tetrahedrally. These compounds are Cs3CoCl5, cobalt di-p-toluidine dichloride, cobalt dipyridine dibromide, and cobalt dipyridine diiodide. The two transitions, 4A2?4T1(F) in the near infrared and 4A2?4T1(P) in the visible, have been compared in the different

J. Ferguson

1960-01-01

276

Inversion of configuration of tetrahedral BIS(4-(iminomethyl)pyrazole-5-thiolato(selenolato) nickels  

SciTech Connect

This paper records the process of the interconversion of enantiomeric tetrahedral structures by the dynamic-NMR method for inner-complex compounds with a chelate entity of NiN/sub 2/X/sub 2/ (X = S, Se), namely systematic series of bis(4-(iminomethyl)pyrazole-5-thiolato(selenolato) )nickels. The values of the activation barriers to interconversion are determined by the steric structure of the substituents on the coordinated nitrogen tom and increase with rise in the steric hindrance in the planar form of the complexes, which indicates that the reaction goes by the diagonal-twist mechanism.

Nivorozhkin, A.L.; Konstantinovskii, L.E.; Korobov, M.S.; Minkin, V.I.

1985-10-10

277

Observation of sp3 bonding in tetrahedral amorphous carbon using visible Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm-1 was observed. It consisted of two features centered on ~1270 and ~1170 cm-1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond.

Chen, Z. Y.; Zhao, J. P.; Yano, T.; Ooie, T.; Yoneda, M.; Sakakibara, J.

2000-09-01

278

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

279

The quadratic spinor Lagrangian, axial torsion current, and generalizations  

Microsoft Academic Search

We show that the Einstein-Hilbert, the Einstein-Palatini, and the Holst\\u000aactions can be derived from the Quadratic Spinor Lagrangian (QSL), when the\\u000athree classes of Dirac spinor fields, under Lounesto spinor field\\u000aclassification, are considered. To each one of these classes, there corresponds\\u000aa unique kind of action for a covariant gravity theory. In other words, it is\\u000ashown to

Roldao da Rocha; J. G. Pereira

2007-01-01

280

A quadratic motion-based object-oriented video codec  

Microsoft Academic Search

A novel motion-based object-oriented codec for video transmission at very low bit-rates is proposed. The object motion is modeled by quadratic transform with coefficients estimated via a nonlinear quasi-Newton method. The segmentation problem is put forward as a constrained optimization problem which interacts with the motion estimation process in the course of region growing. A context-based shape coding method which

Y. Yemez; B. Sankur; E. Anar?m

2000-01-01

281

Extremum seeking loops with quadratic functions: Estimation and control  

Microsoft Academic Search

Extremum-seeking (also peak-seeking ) controllers are designed to operate at an a priori unknown set-point that extremizes the value of a performance function. Traditional approaches to the problem assume a time-scale separation between the gradient computation and function minimization and the system dynamics. The work here, in contrast, assumes that the performance function can be approximated by a quadratic function

R. N. Banavar

2003-01-01

282

Bi-impulse response design of isotropic quadratic filters  

Microsoft Academic Search

The bi-impulse response of a 1-D or 2-D quadratic Volterra filter is introduced as a mathematical tool able to completely describe the nonlinear operator. The conditions that must be satisfied in order to obtain isotropic input\\/output relations are studied. The result is a formal framework that allows simple but effective operators (particularly for image enhancement and preprocessing) to be designed

G. Ramponi

1990-01-01

283

Symmetry-breaking instability of quadratic soliton bound states  

SciTech Connect

We study both numerically and experimentally two-dimensional soliton bound states in quadratic media and demonstrate their symmetry-breaking instability. The experiment is performed in a potassium titanyl phosphate crystal in a type-II configuration. The bound state is generated by the copropagation of the antisymmetric fundamental beam locked in phase with the symmetrical second harmonic one. Experimental results are in good agreement with numerical simulations of the nonlinear wave equations.

Delque, Michaeel [Service OPERA-photonique, CP194/5, Universite Libre de Bruxelles U.L.B. Avenue F.D. Roosevelt, B-1050 Bruxelles (Belgium); Departement d'Optique P.M. Duffieux, Institut FEMTO-ST, Universite de Franche-Comte, CNRS UMR 6174, F-25030 Besancon (France); Fanjoux, Gil; Maillotte, Herve; Kockaert, Pascal; Sylvestre, Thibaut; Haelterman, Marc [Departement d'Optique P.M. Duffieux, Institut FEMTO-ST, Universite de Franche-Comte, CNRS UMR 6174, F-25030 Besancon (France)

2011-01-15

284

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

285

Approximation algorithms for homogeneous polynomial optimization with quadratic constraints  

Microsoft Academic Search

In this paper, we consider approximation algorithms for optimizing a generic multi-variate homogeneous polynomial function, subject to homogeneous quadratic constraints. Such optimiza- tion models have wide applications, e.g., in signal processing, magnetic resonance imaging (MRI), data training, approximation theory, and portfolio selection. Since polynomial functions are non- convex in general, the problems under consideration are all NP-hard. In this paper

Simai He; Zhening Li; Shuzhong Zhang

2010-01-01

286

Induced motion of domain walls in multiferroics with quadratic interaction  

NASA Astrophysics Data System (ADS)

We theoretically study the dynamics of 180-degree domain wall of the ab-type in magnetic materials with quadratic magnetoelectric interaction in external alternating magnetic and electric fields. The features of the oscillatory and translational motions of the domain walls and stripe structures depending on the parameters of external fields and characteristics of the multiferroics are discussed. The possibility of the domain walls drift in a purely electric field is established.

Gerasimchuk, Victor S.; Shitov, Anatoliy A.

2013-10-01

287

Discrete quadratic solitons with competing second-harmonic components  

SciTech Connect

We describe families of discrete solitons in quadratic waveguide arrays supported by competing cascaded nonlinear interactions between one fundamental and two second-harmonic modes. We characterize the existence, stability, and excitation dynamics of these solitons and show that their features may resemble those of solitons in saturable media. Our results also demonstrate that a power threshold may appear for soliton formation, leading to a suppression of beam self-focusing which explains recent experimental observations.

Setzpfandt, Frank; Pertsch, Thomas [Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, D-07743 Jena (Germany); Sukhorukov, Andrey A. [Nonlinear Physics Center, Research School of Physics and Engineering, Australian National University, Canberra, 0200 ACT (Australia)

2011-11-15

288

Noncommutative classical and quantum mechanics for quadratic Lagrangians (Hamiltonians)  

Microsoft Academic Search

Classical and quantum mechanics based on an extended Heisenberg algebra with additional canonical commutation relations for\\u000a position and momentum coordinates are considered. In this approach additional noncommutativity is removed from the algebra\\u000a by a linear transformation of coordinates and transferred to the Hamiltonian (Lagrangian). This linear transformation does\\u000a not change the quadratic form of the Hamiltonian (Lagrangian), and Feynman’s path

Branko Dragovich; Zoran Raki?

2009-01-01

289

Solving Large Quadratic Assignment Problems on Computational Grids  

Microsoft Academic Search

The quadratic assignment problem (QAP) is among the hardest combinatorial optimization prob- lems. Some instances of size 30 have remained unsolved for decades. The solution of these problems requires both improvements in mathematical programming algorithms and the utilization of powerful com- putational platforms. In this article we describe a novel ap proach to solve QAPs using a state-of-the-art branch-and-bound algorithm

Kurt Anstreicher; Nathan Brixius; Jean-Pierre Goux; Jeff Linderoth

2000-01-01

290

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

291

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.

2013-05-01

292

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

293

Direct atomic imaging and dynamical fluctuations of the tetrahedral Au20 cluster  

NASA Astrophysics Data System (ADS)

We report real-space, atomic-resolution images of Au20 clusters obtained with the aberration-corrected Scanning Transmission Electron Microscopy. The proposed tetrahedral (FCC segment) pyramid structure is confirmed. The clusters cycle between isomers under the electron beam in the time-lapse images acquired. Disordered variants on the high symmetry forms are commonly observed. We believe that the direct experimental identification of these kinds of atomic structure, and the fluctuations between them, is fundamental to our understanding of nanoparticle structures, as well as applications such as heterogeneous catalysis.We report real-space, atomic-resolution images of Au20 clusters obtained with the aberration-corrected Scanning Transmission Electron Microscopy. The proposed tetrahedral (FCC segment) pyramid structure is confirmed. The clusters cycle between isomers under the electron beam in the time-lapse images acquired. Disordered variants on the high symmetry forms are commonly observed. We believe that the direct experimental identification of these kinds of atomic structure, and the fluctuations between them, is fundamental to our understanding of nanoparticle structures, as well as applications such as heterogeneous catalysis. Electronic supplementary information (ESI) available: The full-size images corresponding to Fig. 1(a) and (d). See DOI: 10.1039/c2nr31071f

Wang, Z. W.; Palmer, R. E.

2012-07-01

294

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

295

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

296

A comparative study of GLS finite elements with velocity and pressure equally interpolated for solving incompressible viscous flows  

Microsoft Academic Search

SUMMARY A comparative study of the bi-linear and bi-quadratic quadrilateral elements and the quadratic triangular element for solving incompressible viscous flows is presented. These elements make use of the stabilized finite element formulation of the Galerkin\\/least-squares method to simulate the flows, with the pressure and velocity fields interpolated with equal orders. The tangent matrices are explicitly derived and the Newton-

Yongtao Wei; Philippe H. Geubelle

2009-01-01

297

The inherent displacive flexibility of the hexacelsian tetrahedral framework and its relationship to polymorphism in Ba-hexacelsian  

NASA Astrophysics Data System (ADS)

The results of a rigid unit mode (RUM) analysis of the inherent displacive structural flexibility of the tetrahedral framework of the ideal hexacelsian structure type are presented. One of the three types of RUM found to exist is characterized by modulation wave vectors perpendicular to <110> and atomic displacement patterns involving tetrahedral rotation around the parent c axis while a second type of RUM is found to be soft at any modulation wave vector and to involve tetrahedral rotation about in-plane rotation axes. It is shown how a combination of these two types of RUM motion associated with the same q=1/2<1101>* modulation wave vector enables the outstanding crystal chemical problems and apparently mutually contradictory results as regards polymorphism in Ba-hexacelsian to be resolved.

Withers, R. L.; Tabira, Y.; Valgoma, J. A.; Aroyo, M.; Dove, M. T.

298

Properties of the advection scheme employed in Finite-Element North Atlantic (FENA) model  

Microsoft Academic Search

Finite Element North Atlantic (FENA) model developed at AWI is based on the primitive equations and serves to model ocean circulation on a temporal scale from years to decades (a complete description of the model to appear in Ocean Modelling, 2003). It uses tetrahedral spatial discretization, backward Euler time stepping and approximates the model fields by linear functions on elements.

S. Danilov; G. Kivman; S. Harig; J. Schroeter

2003-01-01

299

Aeroelastic wing response analysis using finite elements in a large deformation direct Eulerian-Lagrangian formulation  

Microsoft Academic Search

In this dissertation, a finite element wing structural model with nonlinear large deformation capabilities is developed for the three-dimensional transonic flutter problem and aeroelastic calculations are presented for a series of flexible wings. The flow field is represented by the unsteady Euler equations, written in the Direct Eulerian-Lagrangian approach based on the Galerkin finite element method that employs a tetrahedral

Guclu Seber

2004-01-01

300

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

301

Creepers: Real quadratic orders with large class number  

NASA Astrophysics Data System (ADS)

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

Patterson, Roger

2007-03-01

302

Fluctuation-dissipation inequality for quadratic open systems  

NASA Astrophysics Data System (ADS)

For open systems derived from quadratic total Hamiltonians, we derive a dynamic fluctuation-dissipation (FD) inequality valid for any total initial state and without regard to the sign of the dissipation. With the added constraint that this state be factorized with the reservoir in thermal equilibrium, an uncertainty relation arises naturally from the FD inequality that can be stronger than the usual uncertainty principle in the form ??2/4. We discuss some of the properties of the uncertainty relation relevant to decoherence.

Tameshtit, Allan

2013-11-01

303

On Exponential Hedging and Related Quadratic Backward Stochastic Differential Equations  

SciTech Connect

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

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

2006-09-15

304

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

305

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

306

Multipole-mode interface solitons in quadratic nonlinear photonic lattices  

NASA Astrophysics Data System (ADS)

We address the properties of nonlinear multipole modes supported by an interface between two distinct optical lattices imprinted in two-dimensional nonlinear quadratic media. Such multipole-mode solitons feature out of phase between neighboring lobes, which may be located in two different sides of the lattices. We analyze the impact of guiding parameters of lattices on the existence and stability of multipole-mode interface solitons in different phase mismatching conditions. Remarkably, our results show that multipole-mode interface solitons have the highly asymmetric shape and they are stable in the broad range of system parameters.

Xu, Zhiyong

2009-11-01

307

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

308

Ergodic Type Bellman Equations of First Order with Quadratic Hamiltonian  

SciTech Connect

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

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

2009-02-15

309

Adaptive, quadratic preprocessing of document images for binarization.  

PubMed

This paper presents an adaptive algorithm for preprocessing document images prior to binarization in character recognition problems. Our method is similar in its approach to the blind adaptive equalization of binary communication channels. The adaptive filter utilizes a quadratic system model to provide edge enhancement for input images that have been corrupted by noise and other types of distortions during the scanning process. Experimental results demonstrating significant improvement in the quality of the binarized images over both direct binarization and a previously available preprocessing technique are also included. PMID:18276315

Mo, S; Mathews, J

1998-01-01

310

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

NASA Astrophysics Data System (ADS)

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

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

2007-04-01

311

X-ray topography of a natural twinned diamond of unusual pseudo-tetrahedral morphology  

NASA Astrophysics Data System (ADS)

The internal morphology of a natural twinned diamond was investigated using X-ray section topography. The diamond consisted of two crystals joined along a {1 1 1} plane whose remote ends were triangular {1 1 1} faces with sizes approximately 4 mm on the edge. A coating of fibrous growth obscured the morphology of the good quality diamond inside. Although the coat displayed re-entrant surfaces near the twin plane along three edges of the crystal, X-ray topography showed the inner crystal to protrude outwards along these same edges. The good quality inner core displayed the classical “spinel law” twinned octahedral morphology whereas the fibrous rim showed a typical sphalerite-like twinned tetrahedral morphology. A possible growth mechanism which could account for this is discussed.

Fritsch, Emmanuel; Moore, Moreton; Rondeau, Benjamin; Waggett, Richard G.

2005-06-01

312

The electronic transport mechanism in amorphous tetrahedrally-coordinated carbon films  

SciTech Connect

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

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

1998-02-01

313

Interplay between spin frustration and thermal entanglement in the exactly solved Ising-Heisenberg tetrahedral chain  

NASA Astrophysics Data System (ADS)

The spin-1/2 Ising-Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry (the total spin of the Heisenberg bonds is locally conserved) and the transfer-matrix approach. Exact results derived for spin-spin correlation functions are employed to obtain the frustration temperature. In addition, we have exactly calculated a concurrence quantifying thermal entanglement. It is shown that the frustration and threshold temperature coincide at sufficiently low temperatures, while they exhibit a very different behavior in the high-temperature region when tending towards completely different asymptotic limits. The threshold temperature additionally shows a notable reentrant behavior when it extends over a narrow temperature region above the classical ground state without any quantum correlations.

Rojas, Onofre; Stre?ka, Jozef; Lyra, Marcelo L.

2013-05-01

314

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

315

Tetrahedral Amorphous Carbon (ta-C) Ultra Thin Films for Slider Overcoat Application  

NASA Astrophysics Data System (ADS)

Tetrahedral Amorphous Carbon (ta-C) thin film by using Filtered Cathodic Vacuum Arc (FCVA) technique has proven to be wear-resistive and corrosion resistant for a wide range of electrical, optical, and mechanical applications. Many investigations have shown that the ta-C film prepared by the FCVA technique can provide a superior ultra thin overcoat for the sliders and media compared to ECR-CVD and IBD coating technology. The ta-C film excels in terms of the film density, hardness, surface roughness and corrosion resistance. Nanofilm Technology International (NTI) has successfully developed and commercialized the FCVA coating system (FS series) for the slider overcoat application, which provides a good quality film with a high hardness (~50 GPa), low stress (2~3 GPa), low macro-particle density (~1/cm2 for particles > 0.3 ?m), good uniformity (< 4%$ in 8 inch coating area) and high production repeatability (< 5%).

Shi, X.; Hu, Y. H.; Hu, L.

316

Expressions of Effective Hamiltonian Parameters of XY4Molecules in the Tetrahedral Formalism  

NASA Astrophysics Data System (ADS)

We have derived expressions of second-order effective Hamiltonian parameters of XY4molecules in the tetrahedral formalism (1992, J. P. Championet al.,``Spectroscopy of the Earth's Atmosphere and Interstellar Medium: Spherical Top Spectra,'' Academic Press, San Diego). They are written as a function of the force constants of the potential expanded in terms of the dimensionless normal coordinates. These expressions can be used in the isolated band scheme as well as in the polyad one. The ambiguity of the effective Hamiltonian parameters is treated. Relations between the parameters forq2andq4terms and Hecht's anharmonicity constants (1960, K. T. Hecht,J. Mol. Spectrosc.5, 355-389) in the isolated band scheme are established.

Mourbat, A.; Loëte, M.

1998-05-01

317

Stability analysis of a Galerkin/Runge-Kutta Navier-Stokes discretisation on unstructured tetrahedral grids  

SciTech Connect

This paper presents a timestep stability analysis for a class of discretisations applied to the linearised form of the Navier-Stokes equations on a 3D domain with periodic boundary conditions. Using a suitable definition of the {open_quotes}perturbation energy{close_quotes} it is shown that the energy is monotonically decreasing for both the original p.d.e. and the semi-discrete system of o.d.e.`s arising from a Galerkin discretisation on a tetrahedral grid. Using recent theoretical results concerning algebraic and generalised stability, sufficient stability limits are obtained for both global and local timesteps for fully discrete algorithms using Runge-Kutta time integration. 18 refs., 2 figs., 1 tab.

Giles, M.B. [Oxford Univ. Computing Lab. (United Kingdom)

1997-04-01

318

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

319

Correlation of Tetrahedral and Trihedral Bonding Properties in Amorphous Camphoric Carbon Thin Films  

NASA Astrophysics Data System (ADS)

The tetrahedral carbon (ta-C) and boron doped amorphous carbon (a-C:B) thin films have been grown by pulsed laser deposition. The respective effects of diamond percentages by weight in the target (Dwt%) and boron percentages by weight in the camphoric carbon target (Bwt%), on the tetrahedral (sp3) and trihedral (sp2) bonding properties are discussed. The optical gap Eg and electrical resistivity ? increase with Dwt%, up to 1.6 eV and 5.63 × 107 ? cm respectively, for the film deposited using target with 50 Dwt%. We found that the Dwt% has modified the sp3 bonds content and the morphology of the carbon films. On the other hand, the Eg of a-C:B films is almost unchanged at about 0.95 eV up to 10 Bwt% and decreases thereafter to 0.6 eV at 16 Bwt%. The ? increases initially to 2.29 × 106 ? cm at 2 Bwt%, and decreases thereafter up to 4.58 × 105 and 1.82 × 104 ? cm at 10 and 16 Bwt%, respectively. The variation of structural properties, Eg and ?, can be related to the successful doping of B in the a-C films at low content of Bwt% (up to 10 Bwt%), as the structural properties and Eg remain almost unchanged and the ? decreased. Since both Eg and ? decreased sharply with higher Bwt%, this phenomenon can be related to graphitization. In this paper, the dependence of sp3 and sp2 impurity content on the growth and growth conditions of the films are also studied.

Rusop, M.; Soga, T.; Jimbo, T.

320

Cooperative mechanisms of fast-ion conduction in gallium-based oxides with tetrahedral moieties  

NASA Astrophysics Data System (ADS)

The need for greater energy efficiency has garnered increasing support for the use of fuel-cell technology, a prime example being the solid-oxide fuel cell. A crucial requirement for such devices is a good ionic (O2- or H+) conductor as the electrolyte. Traditionally, fluorite- and perovskite-type oxides have been targeted, although there is growing interest in alternative structure types for intermediate-temperature (400-700?C) solid-oxide fuel cells. In particular, structures containing tetrahedral moieties, such as La1-xCaxMO4-x/2(M=Ta,Nb,P) (refs 7,8), La1-xBa1+xGaO4-x/2 (refs 9,10) and La9.33+xSi6O26+3x/2 (ref. 11), have been attracting considerable attention recently. However, an atomic-scale understanding of the conduction mechanisms in these systems is still lacking; such mechanistic detail is important for developing strategies for optimizing the conductivity, as well as identifying next-generation materials. In this context, we report a combined experimental and computational modelling study of the La1-xBa1+xGaO4-x/2 system, which exhibits both proton and oxide-ion conduction. Here we show that oxide-ion conduction proceeds via a cooperative `cog-wheel'-type process involving the breaking and re-forming of Ga2O7 units, whereas the rate-limiting step for proton conduction is intra-tetrahedron proton transfer. Both mechanisms are unusual for ceramic oxide materials, and similar cooperative processes may be important in related systems containing tetrahedral moieties.

Kendrick, Emma; Kendrick, John; Knight, Kevin S.; Islam, M. Saiful; Slater, Peter R.

2007-11-01

321

Cooperative mechanisms of fast-ion conduction in gallium-based oxides with tetrahedral moieties.  

PubMed

The need for greater energy efficiency has garnered increasing support for the use of fuel-cell technology, a prime example being the solid-oxide fuel cell. A crucial requirement for such devices is a good ionic (O(2-) or H+) conductor as the electrolyte. Traditionally, fluorite- and perovskite-type oxides have been targeted, although there is growing interest in alternative structure types for intermediate-temperature (400-700 ( composite function)C) solid-oxide fuel cells. In particular, structures containing tetrahedral moieties, such as La(1-x)Ca(x)MO(4-x/2)(M=Ta,Nb,P) (refs 7,8), La(1-x)Ba(1+x)GaO(4-x/2) (refs 9,10) and La(9.33+x)Si(6)O(26+3x/2) (ref. 11), have been attracting considerable attention recently. However, an atomic-scale understanding of the conduction mechanisms in these systems is still lacking; such mechanistic detail is important for developing strategies for optimizing the conductivity, as well as identifying next-generation materials. In this context, we report a combined experimental and computational modelling study of the La(1-x)Ba(1+x)GaO(4-x/2) system, which exhibits both proton and oxide-ion conduction. Here we show that oxide-ion conduction proceeds via a cooperative 'cog-wheel'-type process involving the breaking and re-forming of Ga(2)O(7) units, whereas the rate-limiting step for proton conduction is intra-tetrahedron proton transfer. Both mechanisms are unusual for ceramic oxide materials, and similar cooperative processes may be important in related systems containing tetrahedral moieties. PMID:17952081

Kendrick, Emma; Kendrick, John; Knight, Kevin S; Islam, M Saiful; Slater, Peter R

2007-10-21

322

Total decoupling of general quadratic pencils, Part I: Theory  

NASA Astrophysics Data System (ADS)

The notion of quadratic pencils, ?M+?C+K, where M, C, and K are n×n real matrices with or without some additional properties such as symmetry or positive definiteness, plays critical roles in many important applications. It has been long desirable, yet with very limited success, to reduce a complicated high-degree-of-freedom system to some simpler low-degree-of-freedom subsystems. Recently, Garvey, Friswell and Prells proposed a promising approach by which, under some mild assumptions, a general quadratic pencils can be converted by real-valued isospectral transformations into a totally decoupled system. This approach, if numerically feasible, would reduce the original n-degree-of-freedom second-order system to n totally independent single-degree-of-freedom second-order subsystems. Such a claim would be a striking breakthrough in the common knowledge that generally no three matrices M, C, and K can be diagonalized simultaneously. This paper intends to serve three purposes: to clarify some of the ambiguities in the original proposition, to simplify some of the computational details and, most importantly, to complete the theory of existence by matrix polynomial factorization tactics.

Chu, Moody T.; Del Buono, Nicoletta

2008-01-01

323

Linear quadratic stochastic control of atomic hydrogen masers.  

PubMed

Data are given showing the results of using the linear quadratic Gaussian (LQG) technique to steer remote hydrogen masers to Coordinated Universal Time (UTC) as given by the United States Naval Observatory (USNO) via two-way satellite time transfer and the Global Positioning System (GPS). Data also are shown from the results of steering a hydrogen maser to the real-time USNO mean. A general overview of the theory behind the LQG technique also is given. The LQG control is a technique that uses Kalman filtering to estimate time and frequency errors used as input into a control calculation. A discrete frequency steer is calculated by minimizing a quadratic cost function that is dependent on both the time and frequency errors and the control effort. Different penalties, chosen by the designer, are assessed by the controller as the time and frequency errors and control effort vary from zero. With this feature, controllers can be designed to force the time and frequency differences between two standards to zero, either more or less aggressively depending on the application. PMID:18238452

Koppang, P; Leland, R

1999-01-01

324

Learning quadratic receptive fields from neural responses to natural stimuli.  

PubMed

Models of neural responses to stimuli with complex spatiotemporal correlation structure often assume that neurons are selective for only a small number of linear projections of a potentially high-dimensional input. In this review, we explore recent modeling approaches where the neural response depends on the quadratic form of the input rather than on its linear projection, that is, the neuron is sensitive to the local covariance structure of the signal preceding the spike. To infer this quadratic dependence in the presence of arbitrary (e.g., naturalistic) stimulus distribution, we review several inference methods, focusing in particular on two information theory-based approaches (maximization of stimulus energy and of noise entropy) and two likelihood-based approaches (Bayesian spike-triggered covariance and extensions of generalized linear models). We analyze the formal relationship between the likelihood-based and information-based approaches to demonstrate how they lead to consistent inference. We demonstrate the practical feasibility of these procedures by using model neurons responding to a flickering variance stimulus. PMID:23607557

Rajan, Kanaka; Marre, Olivier; Tka?ik, Gašper

2013-04-22

325

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

326

Single-molecule orientation measurements with a quadrated pupil.  

PubMed

This Letter presents a means of measuring the dipole orientation of a fluorescent, orientationally fixed single molecule, which uses a specially designed phase mask, termed a "quadrated pupil," conjugate to the back focal plane of a conventional wide-field microscope. The method leverages the spatial anisotropy of the far-field emission pattern of a dipole emitter and makes this anisotropy amenable to quantitative analysis at the image plane. In comparison to older 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 and optical aberrations. Precision of 1°-5° is achieved in proof-of-concept experiments for both azimuthal (?) and polar (?) angles without defocusing. Since the phase mask is implemented on a liquid-crystal spatial light modulator that may be deactivated without any mechanical perturbation of the sample or imaging system, the technique may be readily integrated into clear aperture imaging studies. PMID:23632538

Backer, Adam S; Backlund, Mikael P; Lew, Matthew D; Moerner, W E

2013-05-01

327

Implementation of Multivariate Quadratic Quasigroup for Wireless Sensor Network  

NASA Astrophysics Data System (ADS)

Wireless sensor networks (WSN) consists of sensor nodes with limited energy, processing, communication and memory. Security in WSN is becoming critical with the emergence of applications that require mechanisms for authenticity, integrity and confidentiality. Due to resource constraints in WSN, matching public key cryptosystems (PKC) for these networks is an open research problem. Recently a new PKC based on quasigroups multivariate quadratic. Experiments performed show that MQQ performed in less time than existing major PKC, so that some articles claim that has MQQ speed of a typical symmetric block cipher. Considering features promising to take a new path in the difficult task of providing wireless sensor networks in public key cryptosystems. This paper implements in nesC a new class of public key algorithm called Multivariate Quadratic Quasigroup. This implementation focuses on modules for encryption and decryption of 160-bit MQQ, the modules have been implemented on platforms TelosB and MICAz. We measured execution time and space occupied in the ROM and RAM of the sensors.

Maia, Ricardo José Menezes; Barreto, Paulo Sérgio Licciardi Messeder; de Oliveira, Bruno Trevizan

328

Electric current quadratic in an applied electric field  

NASA Astrophysics Data System (ADS)

The theory of the photogalvanic effect in a low frequency electric field is developed. We complete the semiclassical theory of the effect in bulk samples lacking inversion symmetry, taking into account contributions from the asymmetry of scattering, the shift current, and the effect of Berry's phase. We consider the effect in such samples both in the presence and absence of a constant magnetic field. It is found that by experimentally measuring this effect, that Berry's curvature and the average shift of the center of mass of an electron during a scattering event can be extracted. We also investigate the magnetic field dependence of the part of the electrical current which is quadratic in voltage in mesoscopic conductors. We find that the part of the current which is quadratic in bias voltage, and linear in an applied magnetic field can be related to the effective electron-electron interaction strength. We also find that in the case when the magnetic field is oriented parallel to the plane of a two dimensional sample, that the spin-orbit scattering rate can be measured.

Deyo, Eric

329

On the Use of Finite Elements in gOcad  

Microsoft Academic Search

This work describes the implementation of a plug-in that adds finite element pre- and post-processing capabilities to gOcad. The gFEM plug-in implements an algorithm for generating unstructured tetrahedral finite element meshes in arbitrarily shaped three-dimensional regions. This meshing algorithm incorporates aspects of well-known meshing procedures, but includes some original steps. It uses an advancing front technique that generates good shape

Luiz Fernando Martha; João Luiz Campos; Joaquim Cavalcante Neto

330

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

331

Development of a Fully Automated CFD System for Three-Dimensional Flow Simulations Based on Hybrid Prismatic-Tetrahedral Grids.  

National Technical Information Service (NTIS)

In this paper an assessment of CFD methods based on the underlying grid type is made. It is safe to say that emerging CFD methods based on hybrid body-fitted grids of tetrahedral and prismatic cells using unstructured data storage schemes have the potenti...

J. W. van der Burg J. E. J. Maseland B. Oskam

1996-01-01

332

The role of fcc tetrahedral subunits in the phase behavior of medium sized Lennard-Jones clusters.  

PubMed

The free energy of a 600-atom Lennard-Jones cluster is calculated as a function of surface and bulk crystallinity in order to study the structural transformations that occur in the core of medium sized clusters. Within the order parameter range studied, we find the existence of two free energy minima at temperatures near freezing. One minimum, at low values of both bulk and surface order, belongs to the liquid phase. The second minimum exhibits a highly ordered core with a disordered surface and is related to structures containing a single fcc-tetrahedral subunit, with an edge length of seven atoms (l=7), located in the particle core. At lower temperatures, a third minimum appears at intermediate values of the bulk order parameter which is shown to be related to the formation of multiple l=6 tetrahedra in the core of the cluster. We also use molecular dynamics simulations to follow a series of nucleation events and find that the clusters freeze to structures containing l=5, 6, 7, and 8 sized tetrahedra as well as those containing no tetrahedral units. The structural correlations between bulk and surface order with the size of the tetrahedral units in the cluster core are examined. Finally, the relationships between the formation of fcc tetrahedral subunits in the core, the phase behavior of medium sized clusters and the nucleation of noncrystalline global structures such as icosahedra and decahedra are discussed. PMID:20726648

Saika-Voivod, Ivan; Poon, Louis; Bowles, Richard K

2010-08-21

333

Molecular dynamics simulation of polymorphic and polyamorphic transitions in tetrahedral network glasses: BeF 2 and GeO 2  

Microsoft Academic Search

It is well know that tetrahedral network glasses have anomalous properties such as a density maximum and bulk modulus minimum. The magnitudes of such anomalous properties are different among tetrahedral network glasses. The origin of this anomaly has not been explained yet. We had already analyzed the local structural changes in SiO2 in terms of transformation of ‘structon’. The fragments

A. Takada; P. Richet; C. R. A. Catlow; G. D. Price

2007-01-01

334

Integrability of Quadratic Non-autonomous Quantum Linear Systems  

NASA Astrophysics Data System (ADS)

The Quantum Harmonic Oscillator is one of the most important models in Quantum Mechanics. Analogous to the classical mass vibrating back and forth on a spring, the quantum oscillator system has attracted substantial attention over the years because of its importance in many advanced and difficult quantum problems. This dissertation deals with solving generalized models of the time-dependent Schrodinger equation which are called generalized quantum harmonic oscillators, and these are characterized by an arbitrary quadratic Hamiltonian of linear momentum and position operators. The primary challenge in this work is that most quantum models with timedependence are not solvable explicitly, yet this challenge became the driving motivation for this work. In this dissertation, the methods used to solve the time-dependent Schrodinger equation are the fundamental singularity (or Green's function) and the Fourier (eigenfunction expansion) methods. Certain Riccati- and Ermakov-type systems arise, and these systems are highlighted and investigated. The overall aims of this dissertation are to show that quadratic Hamiltonian systems are completely integrable systems, and to provide explicit approaches to solving the time-dependent Schr¨odinger equation governed by an arbitrary quadratic Hamiltonian operator. The methods and results established in the dissertation are not yet well recognized in the literature, yet hold for high promise for further future research. Finally, the most recent results in the dissertation correspond to the harmonic oscillator group and its symmetries. A simple derivation of the maximum kinematical invariance groups of the free particle and quantum harmonic oscillator is constructed from the view point of the Riccati- and Ermakov-type systems, which shows an alternative to the traditional Lie Algebra approach. To conclude, a missing class of solutions of the time-dependent Schrodinger equation for the simple harmonic oscillator in one dimension is constructed. Probability distributions of the particle linear position and momentum, are emphasized with Mathematica animations. The eigenfunctions qualitatively differ from the traditional standing waves of the one-dimensional Schrodinger equation. The physical relevance of these dynamic states is still questionable, and in order to investigate their physical meaning, animations could also be created for the squeezed coherent states. This will be addressed in future work.

Lopez, Raquel

335

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

336

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

337

Quadratic Forms for the Fermionic Unitary Gas Model  

NASA Astrophysics Data System (ADS)

We consider a quantum system in dimension three composed by a group of N identical fermions, with mass 1/2, interacting via zero-range interaction with a group of M identical fermions of a different type, with mass m/2. Exploiting a renormalization procedure, we construct the corresponding quadratic form and define the so-called Skornyakov-Ter-Martirosyan extension H?, which is the natural candidate as a possible Hamiltonian of the system. It is shown that if the form is unbounded from below then H? is not a self-adjoint and bounded from below operator, and this in particular suggests that the so-called Thomas effect could occur. In the special case N = 2, M = 1 we prove that this is in fact the case when a suitable condition on the parameter m is satisfied.

Finco, Domenico; Teta, Alessandro

2012-04-01

338

Kaluza-Klein reduction of a quadratic curvature model  

NASA Astrophysics Data System (ADS)

Palatini variational principle is implemented on a five dimensional quadratic curvature gravity model, rendering two sets of equations, which can be interpreted as the field equations and the stress-energy tensor. Unification of gravity with electromagnetism and the scalar dilaton field is achieved through the Kaluza-Klein dimensional reduction mechanism. The reduced curvature invariant, field equations and the stress-energy tensor are obtained in the actual four dimensional spacetime. The structure of the interactions among the constituent fields is exhibited in detail. It is shown that the Lorentz force density naturally emerges from the reduced field equations and the equations of the standard Kaluza-Klein theory are demonstrated to be intrinsically contained in this model.

Ba?kal, Sibel; Kuyrukcu, Halil

2013-02-01

339

Constrained multiple indicator kriging using sequential quadratic programming  

NASA Astrophysics Data System (ADS)

Multiple indicator kriging (MIK) is a nonparametric method used to estimate conditional cumulative distribution functions (CCDF). Indicator estimates produced by MIK may not satisfy the order relations of a valid CCDF which is ordered and bounded between 0 and 1. In this paper a new method has been presented that guarantees the order relations of the cumulative distribution functions estimated by multiple indicator kriging. The method is based on minimizing the sum of kriging variances for each cutoff under unbiasedness and order relations constraints and solving constrained indicator kriging system by sequential quadratic programming. A computer code is written in the Matlab environment to implement the developed algorithm and the method is applied to the thickness data.

Soltani-Mohammadi, Saeed; Erhan Tercan, A.

2012-11-01

340

Repopulation Kinetics and the Linear-Quadratic Model  

NASA Astrophysics Data System (ADS)

The standard Linear-Quadratic (LQ) survival model for radiotherapy is used to investigate different schedules of radiation treatment planning for advanced head and neck cancer. We explore how these treament protocols may be affected by different tumour repopulation kinetics between treatments. The laws for tumour cell repopulation include the logistic and Gompertz models and this extends the work of Wheldon et al. [1], which was concerned with the case of exponential repopulation between treatments. Treatment schedules investigated include standarized and accelerated fractionation. Calculations based on the present work show, that even with growth laws scaled to ensure that the repopulation kinetics for advanced head and neck cancer are comparable, considerable variation in the survival fraction to orders of magnitude emerged. Calculations show that application of the Gompertz model results in a significantly poorer prognosis for tumour eradication. Gaps in treatment also highlight the differences in the LQ model with the effect of repopulation kinetics included.

O'Rourke, S. F. C.; McAneney, H.; Starrett, C.; O'Sullivan, J. M.

2009-08-01

341

Consultant-Guided Search Algorithms for the Quadratic Assignment Problem  

NASA Astrophysics Data System (ADS)

Consultant-Guided Search (CGS) is a recent swarm intelligence metaheuristic for combinatorial optimization problems, inspired by the way real people make decisions based on advice received from consultants. Until now, CGS has been successfully applied to the Traveling Salesman Problem. Because a good metaheuristic should be able to tackle efficiently a large variety of problems, it is important to see how CGS behaves when applied to other classes of problems. In this paper, we propose an algorithm for the Quadratic Assignment Problem (QAP), which hybridizes CGS with a local search procedure. Our experimental results show that CGS is able to compete in terms of solution quality with one of the best Ant Colony Optimization algorithms, the MAX-MIN Ant System.

Iordache, Serban

342

Impact of a global quadratic potential on galactic rotation curves.  

PubMed

We present a conformal gravity fit to the 20 largest of a sample of 110 spiral galaxies. We identify the presence of a universal quadratic potential V(?)(r)=-?c²r²/2 with ?=9.54×10??? cm?² induced by cosmic inhomogeneities. When V(?)(r) is taken in conjunction with both a universal linear potential V(??)(r)=??c²r/2 with ??=3.06×10?³? cm?¹ generated by the homogeneous cosmic background and the contribution generated by the local luminous matter in galaxies, the theory then accounts for the rotation curve systematics observed in the entire 110 galaxies, without the need for any dark matter whatsoever. Our study suggests that using dark matter may be nothing more than an attempt to describe global effects in purely local galactic terms. With V(?)(r) being negative, galaxies can only support bound orbits up to distances of order ??/?=100kpc, with global physics imposing a limit on the size of galaxies. PMID:21517292

Mannheim, Philip D; O'Brien, James G

2011-03-23

343

On quadratic stochastic processes and related differential equations  

NASA Astrophysics Data System (ADS)

It is known that the theory of Markov process is a rapidly developing field with numerous applications to many branches of mathematics and physics, biology and so on. But there are some physical models which cannot be described by such processes. One of such models is related to population genetics. These processes are called quadratic stochastic processes (q.s.p.). In this theory it is important to construct nontrivial examples of such processes. In the present paper we are going to provide a construction of q.s.p. by means of two given processes. We should stress that such a construction allows us to produce lots of nontrivial examples of q.s.o. We also associate to given q.s.p. two kind of processes. Note that one of such processes is Markov. It is proved that such kind of processes uniquely define q.s.p. Moreover, we also derive some differential equations for q.s.p.

Mukhamedov, Farrukh; Akma Supar, Nurul; Hee, Pah Chin

2013-04-01

344

Half-optical-cycle damped solitons in quadratic nonlinear media  

NASA Astrophysics Data System (ADS)

In this paper, Using a classical model of the radiation-matter interaction, we show that the propagation of (1+1) dimensional few-optical-cycle pulses in quadratic nonlinear media, taking moderate absorption into account, can be described by the Korteweg-de Vries-Burgers’ (KdVB) equation without using the slowly varying envelope approximation. To fulfill this purpose we use the reductive perturbation method and consider the long-wave approximation, assuming that the characteristic frequency of the pulse is much lower than the resonance frequency of the atoms. We also study both analytical and numerical solution of the KdVB equation describing damped few-optical-cycle soliton propagation.

Kimiaee Asadi, Faezeh; Shokri, Babak; Leblond, Hervé

2013-05-01

345

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

346

Linear quadratic Gaussian differential games with different information patterns  

NASA Astrophysics Data System (ADS)

A discrete-time linear-quadratic-Gaussian (LQG) differential game is considered where the players have access to unshared control- and measurement-histories. The particular problem that is solved is where one adversary has access to only noisy partial information of the state while the other makes a perfect measurement of the state vector. The system dynamics are assumed linear with additive process noise. The solutions show a significant departure from previously published results. First, process noise is included in the dynamical system and a quadratic weighting in the state is included in the cost criterion. Secondly, no prior assumption is made about the structure of the strategies. Specifically, the equilibrium strategies of both players are shown to be finite-dimensional, not infinite-dimensional as was originally thought. Thirdly, it is assumed that the perfect-measurement adversary's control matrix is in the range space of the other adversary's measurement matrix. Then, by a limit of the linear-exponential-Gaussian game solution to the LQG game solution, it is seen that the partial information player avoids reproducing an estimated version of his adversary's strategy. A key feature of this problem solution is the filter structure of the player with partial measurements. In particular, the error of the filter is a Gaussian random variable whose statistics are independent of the opponent's control history. This filter also allows the partial measurement player to estimate the entire state without having to guess/estimate his opponent's strategy. It is noted that for this class of stochastic games, for all possible pure control strategy pairs, there always exist correlations using which each player can improve his performance. Since the error variance of the filter derived here is independent of the opponent's strategy and his control action, the improvements in cost for each player appears minimal. This property is used to extend the notion of a saddle point for deterministic games to that of a saddle interval in pure strategies for games with uncertainty.

Swarup, Ashitosh

347

Confidence set inference with a prior quadratic bound  

NASA Astrophysics Data System (ADS)

In the uniqueness part of a geophysical inverse problem, the observer wants to predict all likely values of P unknown numerical properties z = (z sub 1,...,z sub p) of the earth from measurement of D other numerical properties y(0)=(y sub 1(0),...,y sub D(0)) knowledge of the statistical distribution of the random errors in y(0). The data space Y containing y(0) is D-dimensional, so when the model space X is infinite-dimensional the linear uniqueness problem usually is insoluble without prior information about the correct earth model x. If that information is a quadratic bound on x (e.g., energy or dissipation rate), Bayesian inference (BI) and stochastic inversion (SI) inject spurious structure into x, implied by neither the data nor the quadratic bound. Confidence set inference (CSI) provides an alternative inversion technique free of this objection. CSI is illustrated in the problem of estimating the geomagnetic field B at the core-mantle boundary (CMB) from components of B measured on or above the earth's surface. Neither the heat flow nor the energy bound is strong enough to permit estimation of B(r) at single points on the CMB, but the heat flow bound permits estimation of uniform averages of B(r) over discs on the CMB, and both bounds permit weighted disc-averages with continous weighting kernels. Both bounds also permit estimation of low-degree Gauss coefficients at the CMB. The heat flow bound resolves them up to degree 8 if the crustal field at satellite altitudes must be treated as a systematic error, but can resolve to degree 11 under the most favorable statistical treatment of the crust. These two limits produce circles of confusion on the CMB with diameters of 25 deg and 19 deg respectively.

Backus, George E.

1988-09-01

348

Sensitivity Analysis of Parameters in Linear-Quadratic Radiobiologic Modeling  

SciTech Connect

Purpose: Radiobiologic modeling is increasingly used to estimate the effects of altered treatment plans, especially for dose escalation. The present article shows how much the linear-quadratic (LQ) (calculated biologically equivalent dose [BED] varies when individual parameters of the LQ formula are varied by {+-}20% and by 1%. Methods: Equivalent total doses (EQD2 = normalized total doses (NTD) in 2-Gy fractions for tumor control, acute mucosal reactions, and late complications were calculated using the linear- quadratic formula with overall time: BED = nd (1 + d/ [{alpha}/{beta}]) - log{sub e}2 (T - Tk) / {alpha}Tp, where BED is BED = total dose x relative effectiveness (RE = nd (1 + d/ [{alpha}/{beta}]). Each of the five biologic parameters in turn was altered by {+-}10%, and the altered EQD2s tabulated; the difference was finally divided by 20. EQD2 or NTD is obtained by dividing BED by the RE for 2-Gy fractions, using the appropriate {alpha}/{beta} ratio. Results: Variations in tumor and acute mucosal EQD ranged from 0.1% to 0.45% per 1% change in each parameter for conventional schedules, the largest variation being caused by overall time. Variations in 'late' EQD were 0.4% to 0.6% per 1% change in the only biologic parameter, the {alpha}/{beta} ratio. For stereotactic body radiotherapy schedules, variations were larger, up to 0.6 to 0.9 for tumor and 1.6% to 1.9% for late, per 1% change in parameter. Conclusions: Robustness occurs similar to that of equivalent uniform dose (EUD), for the same reasons. Total dose, dose per fraction, and dose-rate cause their major effects, as well known.

Fowler, Jack F. [Departments of Human Oncology and Medical Physics, School of Medicine, University of Wisconsin, Madison, WI (United States)], E-mail: jackfowlersbox@gmail.com

2009-04-01

349

The effect of element topology on variational multiscale methods for LES  

NASA Astrophysics Data System (ADS)

The variational multiscale method developed by Hughes, Mazzei, and Jansen has been extended to make use of a hierarchical basis. This hierarchical basis provides a natural scale separation. Modeling is confined to the effect of a small-scale Reynolds stress, in contrast with classical LES in which the entire subgrid-scale stress is modeled. Both hexahedral and tetrahedral discretizations will be considered. We will also consider the relative sizes of the two spaces and the effect this choice has on simulation quality. For example, when considering a hierarchic basis that is complete to order cubic, should the resolved space include linear and quadratic modes or should the resolved space be restricted to linears, leaving the the quadratic and cubic modes to fill out the fine scale space where modeling is performed? Smagorinsky models will be shown to be quite effective with this type of modeling though other possibilities will also be discussed.

Jansen, Kenneth

2000-11-01

350

Mixed tetrahedral anionic framework in the K3Ga2(PO4)3 crystal structure  

NASA Astrophysics Data System (ADS)

The crystal structure of a new synthetic potassium gallophosphate K3Ga2(PO4)3 grown from a solution in the melt of a mixture of GaPO4 and K2MoO4 is determined using X-ray diffraction (Bruker Smart diffractometer, 2?max= 56.6°, R = 0.044 for 2931 reflections, T = 100 K). The main crystal data are as follows: a = 8.661(2) Å, b = 17.002(4) Å, c = 8.386(2) Å, space group Pna21, Z= 4, and ?calcd = 2.91 g/cm3. The synthesized crystals represent the third phase in the structure type previously established for the K3Al2[(As,P)O4]3 compound. It is shown that the structure consists of a three-dimensional anionic microporous tetrahedral framework of the mixed type, which is formed by PO4 and GaO4 tetrahedra shared by vertices. Large-sized cations K+ occupy channels of the zeolite-like framework. The crystal chemical features of the formation of structure types of compounds with mixed frameworks described by the general formula A {3/+} M {2/3+}( TO4)3 (where A = K, Rb, (NH4), Tl; M = Al, Ga, Fe, Sc, Yb; T = P, As) are analyzed.

Yakubovich, O. V.; Steele, I.; Kireev, V. V.

2008-11-01

351

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

352

Importance of tetrahedral intermediate formation in the catalytic mechanism of the serine proteases chymotrypsin and subtilisin.  

PubMed

Two new inhibitors in which the terminal ?-carboxyl groups of Z-Ala-Ala-Phe-COOH and Z-Ala-Pro-Phe-COOH have been replaced with a proton to give Z-Ala-Ala-Phe-H and Z-Ala-Pro-Phe-H, respectively, have been synthesized. Using these inhibitors, we estimate that for ?-chymotrypsin and subtilisin Carlsberg the terminal carboxylate group decreases the level of inhibitor binding 3-4-fold while a glyoxal group increases the level of binding by 500-2000-fold. We show that at pH 7.2 the effective molarities of the catalytic hydroxyl group of the active site serine are 41000-229000 and 101000-159000 for ?-chymotrypsin and subtilisin Carlsberg, respectively. It is estimated that oxyanion stabilization and the increased effective molarity of the catalytic serine hydroxyl group can account for the catalytic efficiency of the reaction. We argue that substrate binding induces the formation of a strong hydrogen bond or low-barrier hydrogen bond between histidine-57 and aspartate-102 that increases the pK(a) of the active site histidine, allowing it to be an effective general base catalyst for the formation of the tetrahedral intermediate and increasing the effective molarity of the catalytic hydroxyl group of serine-195. A catalytic mechanism for acyl intermediate formation in the serine proteases is proposed. PMID:22757750

Petrillo, Teodolinda; O'Donohoe, Catrina A; Howe, Nicole; Malthouse, J Paul G

2012-07-25

353

Orientational ordering of tetrahedral clusters in CaCd6 alloy  

NASA Astrophysics Data System (ADS)

In icosahedral CaCd quasicrystals and related alloy structures, each icosahedral cluster contains an innermost tetrahedral shell that is loosely coupled with its shell. We extract an effective potential for the pair interaction V(,') of the orientations ? of neighboring clusters, as mediated by the intervening atoms. Using the EAM potentials of Brommer et al., ootnotetextBrommer, G"ahler, and Mihalkovic, Phil. Mag. 87, 2671 (2007)we relax all atoms, with each tetrahedron constrained to a chosen (continuously variable) overall orientation but allowing distortions. Using singular value decomposition, the relaxed energies are represented as V(,')=?jAjfj(?) f'j(?') where only a few terms are important and the fj's have simple sinusoidal forms (which can be understood physically). We thus obtain a fit with only a few parameters, in place of the 46-parameter fit of Brommer et al^1 based on 12 discrete orientations. By Monte Carlo simulations with the obtained interaction, we determine the pattern of the orientationally ordered state seen experimentally below ˜90K, and check the ordering transition previously simulated only in small system sizes^1.

Choi, Woosong; Mihalkovic, Marek; Henley, Chris

2012-02-01

354

A Rac1-GDP Trimer Complex Binds Zinc with Tetrahedral and Octahedral Coordination, Displacing Magnesium  

SciTech Connect

The Rho family of small GTPases represent well characterized signaling molecules that regulate many cellular functions such as actin cytoskeletal arrangement and the cell cycle by acting as molecular switches. A Rac1-GDP-Zn complex has been crystallized in space group P3{sub 2}21 and its crystal structure has been solved at 1.9 {angstrom} resolution. These trigonal crystals reveal the unexpected ability of Rac1 to coordinate Zn atoms in a tetrahedral fashion by use of its biologically relevant switch I and switch II regions. Upon coordination of zinc, the switch I region is stabilized in the GDP-bound conformation and contributes to a Rac1 trimer in the asymmetric unit. Zinc coordination causes switch II to adopt a novel conformation with a symmetry-related molecule. Additionally, zinc was found to displace magnesium from its octahedral coordination at switch I, although GDP binding remained stable. This structure represents the first reported Rac1-GDP-Zn complex, which further underscores the conformational flexibility and versatility of the small GTPase switch regions.

Prehna,G.; Stebbins, E.

2007-01-01

355

Argon Implantation in Tetrahedral Amorphous Carbon Deposited by Filtered Cathodic Vacuum Arc  

NASA Astrophysics Data System (ADS)

The implantation of argon in tetrahedral amorphous carbon (ta-C), deposited by the filtered cathodic vacuum arc technique and concurrently bombarded with argon ions (Ar+), is investigated in this study. The ta-C films were prepared with a 5-ms DC-pulsed arc, a current of 190 A, and a frequency of 3 Hz, and they were deposited on a ground substrate holder. The argon atoms were implanted into the film by simultaneously bombarding the films with a beam of Ar+ in the 0-180 eV energy range. The concentration of argon, determined by Rutherford backscattering spectroscopy, was investigated as a function of the Ar+ energy. Raman scattering spectroscopy was used to investigate the structure of the films. The stress of the films depends on the Ar+ energy and reduces significantly as a function of the annealing temperature. A study of argon effusion, ranging from room temperature up to 1000 °C, shows that the argon atoms evolve from the films at different temperatures depending on the Ar+ energy. Scanning electron microscopy revealed the formation of bubbles after argon effusion. It was observed that the structural transformations that promote the relaxation of the carbon matrix and the argon effusion are different from each other.

Marques, F. C.; Viana, G. A.; Motta, E. F.; Silva, D. S.; Wisnivesky, D.; Côrtes, A. D. S.; Aguiar, M. R.

2013-05-01

356

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

SciTech Connect

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

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

1994-05-01

357

AEM investigation of tetrahedrally coordinated Ti{sup 4+} in nickel-titanate spinel  

SciTech Connect

Stoichiometry and site distribution of metastable nickel-titanate spinel was studied with AEM. Results of EDXS and EELS agree that the metastable spinel is nonstoichiometric and titanium-deficient relative to its hypothetical endmember composition, ``Ni{sub 2}TiO{sub 4}``. The titanium deficiency has been determined by EELS to be {Delta} = 0.025 {plus_minus} 0.005. Channeling-enhanced microanalysis and ELNES studies indicate that the Ti{sup 4+} and Ni{sup 2+} cations are in tetrahedral and octahedral coordination, respectively, so that the metastable spinel has the normal cation distribution: Ti{sub l-{Delta}}[Ni{sub 2(1+{Delta})}]O{sub 4}. This is consistent with neutron powder-diffraction studies and SiO{sub 2}-solubility measurements of similar equilibrated and quenched spinel-containing specimens. Metastable nickel-titanate spinel therefore contrasts with stable stoichiometric spinels which tend to the inverse cation distribution, Me[MeTi]O{sub 4}.

Anderson, I.M. [Oak Ridge National Lab., TN (United States)]|[Minnesota Univ., Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science; Bentley, J. [Oak Ridge National Lab., TN (United States); Carter, C.B. [Minnesota Univ., Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Science

1994-12-31

358

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

359

Steering of Frequency Standards by the Use of Linear Quadratic Gaussian Control Theory.  

National Technical Information Service (NTIS)

Linear quadratic Gaussian control is a technique that uses Kalman filtering to estimate a state vector used for input into a control calculation. A control correction is calculated by minimizing a quadratic cost function that is dependent on both the stat...

P. Koppang R. Leland

1995-01-01

360

Provably fast integer factoring with quasi-uniform small quadratic residues  

Microsoft Academic Search

Finding small quadratic residues modulo n, when n is a large composite number of unknown factorisation is almost certainly a computationally hard problem. This problem arises in a natural way when factoring n by the use of congruences of squares. We construct here a polynomial-time algorithm based on the use of lattices, which finds in a near uniform way quadratic

Brigitte Vallée

1989-01-01

361

Hidden Lessons: How a Focus on Slope-Like Properties of Quadratic Functions Encouraged Unexpected Generalizations  

ERIC Educational Resources Information Center

|This article presents secondary students' generalizations about the connections between algebraic and graphical representations of quadratic functions, focusing specifically on the roles of the parameters a, b, and c in the general form of a quadratic function, y = ax[superscript 2] + bx + c. Students' generalizations about these connections led…

Ellis, Amy B.; Grinstead, Paul

2008-01-01

362

Global Models for the Orientation Field of Fingerprints: An Approach Based on Quadratic Differentials  

Microsoft Academic Search

Quadratic differentials naturally define analytic orientation fields on planar surfaces. We propose to model orientation fields of fingerprints by specifying quadratic differentials. Models for all fingerprint classes such as arches, loops and whorls are laid out. These models are parametrised by few, geometrically interpretable parameters which are invariant under Euclidean motions. We demonstrate their ability in adapting to given, observed

Stephan Huckemann; Thomas Hotz; Axel Munk

2008-01-01

363

Modified Quadratic Discriminant Functions and the Application to Chinese Character Recognition  

Microsoft Academic Search

Issues in the quadratic discriminant functions (QDF) are discussed and two types of modified quadratic disriminant functions (MQDF1, MQDF2) which are less sensitive to the estimation error of the covariance matrices are proposed. The MQDF1 is a function which employs a kind of a (pseudo) Bayesian estimate of the covariance matrix instead of the maximum likelihood estimate ordinarily used in

Fumitaka Kimura; Kenji Takashina; Shinji Tsuruoka; Yasuji Miyake

1987-01-01

364

Inelastic scattering in a local polaron model with quadratic coupling to bosons  

Microsoft Academic Search

We calculate the inelastic scattering probabilities in the wide band limit of a local polaron model with quadratic coupling to bosons. The central object is a two-particle Green's function which is calculated exactly using a purely algebraic approach. Compared with the usual linear interaction term a quadratic interaction term gives higher probabilities for inelastic scattering involving a large number of

Thomas Olsen

2009-01-01

365

An analytic solution of projectile motion with the quadratic resistance law using the homotopy analysis method  

Microsoft Academic Search

We consider the problem of two-dimensional projectile motion in which the resistance acting on an object moving in air is proportional to the square of the velocity of the object (quadratic resistance law). It is well known that the quadratic resistance law is valid in the range of the Reynolds number: 1 × 103 ~ 2 × 105 (for instance,

Kazuki Yabushita; Mariko Yamashita; Kazuhiro Tsuboi

2007-01-01

366

Fast Parallel DNA-Based Algorithms for Molecular Computation: Quadratic Congruence and Factoring Integers  

Microsoft Academic Search

Assume that $n$ is a positive integer. If there is an integer $0< M < n$ such that $M ^{2}\\\\equiv C~({\\\\rm mod} ~n)$, i.e., the congruence has a solution, then $C$ is said to be a quadratic congruence $({\\\\rm mod}~ n)$. If the congruence does not have a solution, then $C$ is said to be a quadratic noncongruence $({\\\\rm mod}~

2012-01-01

367

The cyclicity of period annuli of some classes of reversible quadratic systems  

Microsoft Academic Search

The cyclicity of period annuli of some classes of reversible and non-Hamiltonian quadratic systems under quadratic perturbations are studied. The argument principle method and the centroid curve method are combined to prove that the related Abelian integral has at most two zeros.

G. Chen; C. LI; C. Liu; J. Llibre

2006-01-01

368

The cyclicity of period annulus of a quadratic reversible Lotka-Volterra system  

NASA Astrophysics Data System (ADS)

We prove that by perturbing the periodic annulus of the quadratic polynomial reversible Lotka-Volterra differential system \\dot x=y+\\case{3}{2}(x^2-y^2) , \\dot y=-x(1-y) , inside the class of all quadratic polynomial differential systems we can obtain at most two limit cycles.

Li, Chengzhi; Llibre, Jaume

2009-12-01

369

The cyclicity of period annulus of a quadratic reversible Lotka-Volterra system  

Microsoft Academic Search

We prove that by perturbing the periodic annulus of the quadratic polynomial reversible Lotka-Volterra differential system \\\\dot x=y+\\\\case{3}{2}(x^2-y^2) , \\\\dot y=-x(1-y) , inside the class of all quadratic polynomial differential systems we can obtain at most two limit cycles.

Chengzhi Li; Jaume Llibre

2009-01-01

370

The evaluation of completely general quadratic force fields using theory and experimental data  

Microsoft Academic Search

A semiempirical method was developed to calculate completely general quadratic potential functions using a combination of molecular orbital calculations and limited vibrational data. In the molecular orbital constraint using interaction coordinates (MOSCIC) method symmetry interaction displacement coordinates are constrained in nonlinear least squares determination of quadratic compliance constants. The only experimental data required in the MOCIC method are the frequencies

T. H. Arnold

1979-01-01

371

An efficient interior point method for sequential quadratic programming based optimal power flow  

Microsoft Academic Search

This paper presents a new sequential quadratic programming algorithm for solving the optimal power flow problem. The algorithm is structured with an outer linearization loop and an inner optimization loop. The inner loop solves a relaxed reduced quadratic programming problem. Because constraint relaxation keeps the inner loop problem of small dimension, the algorithm is quite efficient. Its outer loop iteration

Imad M. Nejdawi; Kevin A. Clements; Paul W. Davis

2000-01-01

372

Generalized Quadratic Stabilization for Perturbated Discrete-time Singular Systems with Delayed State  

Microsoft Academic Search

This paper discusses a generalized quadratic stabilization problem for a class of discrete-time singular system with time-delay and nonlinear perturbation (DSSDP) which satisfies Lipschitz condition. By means of Sprocedure approach, necessary and sufficient condition is presented via matrix inequality such that the control system is generalized quadratically stabilizable. An explicit expression of static state feedback controllers is obtained via some

Guoping Lu; Daniel W. C. Ho

2003-01-01

373

Robust stabilization of uncertain linear systems: quadratic stabilizability and H? control theory  

Microsoft Academic Search

The problem of robustly stabilizing a linear uncertain system is considered with emphasis on the interplay between the time-domain results on the quadratic stabilization of uncertain systems and the frequency-domain results on H? optimization. A complete solution to a certain quadratic stabilization problem in which uncertainty enters both the state and the input matrices of the system is given. Relations

PRAMOD P. KHARGONEKAR; IAN R. PETERSEN; KEMIN ZHOU

1990-01-01

374

The photoexcitation and photoluminescence of the crystalline tetrahedral complexes of manganese(II) chloride with hydrochloride of phenazone and aminophenazone  

NASA Astrophysics Data System (ADS)

The excitation and emission spectra of the complexes (PH)2MnCl4 and (APH)2. MnCl4 have been studied. All the bands characteristic of excitation transitions of d 5 configuration — the manganese(II) ion being of tetrahedral symmetry — were identified. The spectrum was interpreted in terms of the Orgel's weak field matrix for quartet levels d 5; and the Racah's parameters B and C, the secular determinants, the ground terms and the field strength of thsse complexes were calculated. The 10 Dq value for either of the two compounds was found to be 400 cm-1. The theories of a harmonic oscillator make possible the determination of characteristic parameters from the emission spectrum. The character and the arrangement of bands of excitation and emission spectra — green luminescence — of the crystals are indicative of tetrahedral structure of the complexes. The phenomenon of luminescence has been explained by the4 T 1( G) ? ?6 A 1( S) transition.

Nikoli?, K.; Buri?, I.; Aleksi?, A.

1984-06-01

375

Computing first-arrival seismic traveltimes on unstructured 3-D tetrahedral grids using the Fast Marching Method  

NASA Astrophysics Data System (ADS)

The Fast Marching Method is an efficient numerical algorithm for propagating interfaces such as first-arrival seismic wave fronts travelling through a velocity distribution. Fast Marching solutions have been developed for use on rectilinear grids in 2-D and 3-D. We are interested in unstructured grids as they provide some computational advantages when dealing with complicated shapes that are difficult to represent with rectilinear grids. Fast Marching solutions have also been developed for unstructured 2-D triangular grids but this has yet to be extended to unstructured 3-D tetrahedral grids. In this paper, we extend the Fast Marching Method to unstructured 3-D tetrahedral grids using a derivation that follows the 2-D case. The resulting equations are discussed in intuitive terms and an error analysis is performed. Our method is applied to a simple synthetic example and to a more complicated model based on the Voisey's Bay massive sulphide deposit in Labrador, Canada.

Lelièvre, Peter G.; Farquharson, Colin G.; Hurich, Charles A.

2011-02-01

376

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

377

Improving organic light-emitting devices by modifying indium tin oxide anode with an ultrathin tetrahedral amorphous carbon film  

Microsoft Academic Search

The characteristics of organic light-emitting devices based on tris-(8-hydroxyqunoline) aluminum with an ultrathin tetrahedral amorphous carbon (ta-C) film on indium tin oxide have been investigated. The device with a 1.0-nm ta-C layer has the highest current and power efficiency. The current efficiency of a device with a ta-C layer thickness of 1.0 nm is 3.7 cd?A at 20 mA?cm2, however,

B. J. Chen; X. W. Sun; Y. Divayana; B. K. Tay

2005-01-01

378

Improving organic light-emitting devices by modifying indium tin oxide anode with an ultrathin tetrahedral amorphous carbon film  

Microsoft Academic Search

The characteristics of organic light-emitting devices based on tris-(8-hydroxyqunoline) aluminum with an ultrathin tetrahedral amorphous carbon (ta-C) film on indium tin oxide have been investigated. The device with a 1.0-nm ta-C layer has the highest current and power efficiency. The current efficiency of a device with a ta-C layer thickness of 1.0 nm is 3.7 cd\\/A at 20 mA\\/cm2, however,

B. J. Chen; X. W. Sun; Y. Divayana; B. K. Tay

2005-01-01

379

Bond-bending modes and stability of tetrahedral semiconductors under high pressure: a puzzle of AlN  

Microsoft Academic Search

Lattice vibrations of the wurtzite-type AlN have been studied by Raman spectroscopy under high pressure up to the structural phase transition at 20 GPa. We have shown that the widely debated bond-bending E_2^1 mode of w-AlN has an abnormal positive pressure shift up to the threshold of the phase transition, whereas in many tetrahedral semiconductors the bond-bending modes soften on

Ekaterina V. Iakovenko; Michel Gauthier; Alain Polian

2003-01-01

380

Evaluating the fracture properties and fatigue wear of tetrahedral amorphous carbon films on silicon by nano-impact testing  

Microsoft Academic Search

A repetitive contact technique, nano-impact testing, has been used to investigate the fracture properties of tetrahedral amorphous carbon (ta-C) thin films deposited on silicon by the filtered cathodic vacuum arc method. The impact test has shown clear differences in the resistance to impact wear of ta-C films with their thickness, for film thicknesses between 5 and 80 nm. The resistance

Ben D. Beake; S. P. Lau; James F. Smith

2004-01-01

381

The photoexcitation and photoluminescence of the crystalline tetrahedral complexes of manganese(II) chloride with hydrochloride of phenazone and aminophenazone  

Microsoft Academic Search

Summary The excitation and emission spectra of the complexes (PH)2MnCl4 and (APH)2. MnCl4 have been studied. All the bands characteristic of excitation transitions ofd5 configuration — the manganese(II) ion being of tetrahedral symmetry — were identified. The spectrum was interpreted in terms of the Orgel's weak field matrix for quartet levelsd5; and the Racah's parametersB andC, the secular determinants, the

K. Nikolic; I. Buri?; A. Aleksic

1984-01-01

382

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

Microsoft Academic Search

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

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

2006-01-01

383

Parallel adaptive mesh-refining scheme on a three-dimensional unstructured tetrahedral mesh and its applications  

Microsoft Academic Search

The development of a parallel three-dimensional (3-D) adaptive mesh refinement (PAMR) scheme for an unstructured tetrahedral mesh using dynamic domain decomposition on a memory-distributed machine is presented in detail. A memory-saving cell-based data structure is designed such that the resulting mesh information can be readily utilized in both node- or cell-based numerical methods. The general procedures include isotropic refinement from

Y.-Y. Lian; K.-H. Hsu; Y.-L. Shao; Y.-M. Lee; Y.-W. Jeng; J.-S. Wu

2006-01-01

384

Correlation of surface, mechanical and microproperties of tetrahedral amorphous carbon films deposited under different magnetic confinement conditions  

Microsoft Academic Search

The effect of using a magnetic field to confine and focus the carbon plasma in a filtered cathodic vacuum arc (FCVA) deposition system was investigated in the preparation of tetrahedrally bonded amorphous carbon (ta-C) thin films. The design of the magnetic field was such that the plasma can be confined into a high-density focussed spot of ?2cm diameter or de-focussed

Daniel H. C Chua; K. B. K. Teo; T. H Tsai; W. I. Milne; D. Sheeja; B. K Tay; D. Schneider

2004-01-01

385

Solid-state shifts of core-electron binding energies in tetrahedral semiconductors from tight-binding theory  

Microsoft Academic Search

Solid-state shifts of core-electron binding energies are claculated for tetrahedral semiconductors with the valence-band maximum as reference level. A Born-Haber cycle is used to relate binding-energy shifts to changes of bond energies due to the excitation of core electrons. These energies are obtained from tight-binding theory with universal parameters. Metallization was included as a correction to the bond-orbital approximation. Shifts

R. Enderlein; W. A. Harrison

1984-01-01

386

Electronic structures of filled tetrahedral semiconductors LiMgN and LiZnN: conduction band distortion  

Microsoft Academic Search

The band structures of the filled tetrahedral semiconductors LiMgN and LiZnN, viewed as the zinc-blende (MgN)- and (ZnN)- lattices partially filled with He-like Li+ ion interstitials, were studied using the full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The conduction band distortions of LiMgN and LiZnN, compared to their \\

L. H. Yu; K. L. Yao; Z. L. Liu

2004-01-01

387

Ultrafast and octave-spanning optical nonlinearities from strongly phase-mismatched quadratic interactions.  

PubMed

Cascaded nonlinearities have attracted much interest, but ultrafast applications have been seriously hampered by the simultaneous requirements of being near phase matching and having ultrafast femtosecond response times. Here we show that in strongly phase-mismatched nonlinear frequency conversion crystals the pump pulse can experience a large and extremely broadband self-defocusing cascaded Kerr-like nonlinearity. The large cascaded nonlinearity is ensured through interaction with the largest quadratic tensor element in the crystal, and the strong phase mismatch ensures an ultrafast nonlinear response with an octave-spanning bandwidth. We verify this experimentally by showing few-cycle soliton compression with noncritical cascaded second-harmonic generation: Energetic 47 fs infrared pulses are compressed in a just 1-mm long bulk lithium niobate crystal to 17 fs (under 4 optical cycles) with 80% efficiency, and upon further propagation an octave-spanning supercontinuum is observed. Such ultrafast cascading is expected to occur for a broad range of pump wavelengths spanning the near- and mid-IR using standard nonlinear crystals. PMID:23006089

Zhou, B B; Chong, A; Wise, F W; Bache, M

2012-07-26

388

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

389

Wave scattering by an elastic inclusion with quadratic nonlinearity  

NASA Astrophysics Data System (ADS)

This paper studies the problem of three-dimensional wave scattering by an elastic inclusion with quadratic nonlinearity in an otherwise linear elastic medium. Due to the nonlinearity of the inclusion, second order wave appears in the scattered field. Under the incidence of a plane longitudinal wave, solution to the scattered second order field is derived explicitly in terms of the Green's function. A far field approximation of the scattered field is also obtained. The results of far field show that the scattered second harmonic field consists of a longitudinal spherical wave and a shear spherical wave. Furthermore, it is found that the amplitude of the forward scattered field is proportional to the acoustic nonlinearity parameter ? averaged over the volume of the inclusion, and the amplitude of backscattered field is proportional to a spatially weighted average of ?. Finally, a method is described to nondestructively obtain the statistics of the spatial variation of ? over the inclusion such as the mean, the variance and autocorrelation length.

Tang, Guangxin; Jacobs, Laurence J.; Qu, Jianmin

2012-05-01

390

Estimating species richness from quadrat sampling data: a general approach.  

PubMed

We consider the problem of estimating the number of species (denoted by S) of a biological community located in a region divided into n quadrats. To address this question, different hierarchical parametric approaches have been recently developed. Despite a detailed modeling of the underlying biological processes, they all have some limitations. Indeed, some assume that n is theoretically infinite; as a result, n and the sampling fraction are not a part of such models. Others require some prior information on S to be efficiently implemented. Our approach is more general in that it applies without limitation on the size of n, and it can be used in the presence, as well as in the absence, of prior information on S. Moreover, it can be viewed as an extension of the approach of Dorazio and Royle (2005, Journal of the American Statistical Association 100, 389-398) in that n is a part of the model and a prior distribution is placed on S. Despite serious computational difficulties, we have perfected an efficient Markov chain Monte Carlo algorithm, which allows us to obtain the Bayesian estimate of S. We illustrate our approach by estimating the number of species of a bird community located in a forest. PMID:21504418

Dupuis, Jérôme A; Goulard, Michel

2011-04-19

391

Graph Modeling for Quadratic Assignment Problems Associated with the Hypercube  

SciTech Connect

In the paper we consider the quadratic assignment problem arising from channel coding in communications where one coefficient matrix is the adjacency matrix of a hypercube in a finite dimensional space. By using the geometric structure of the hypercube, we first show that there exist at least n different optimal solutions to the underlying QAPs. Moreover, the inherent symmetries in the associated hypercube allow us to obtain partial information regarding the optimal solutions and thus shrink the search space and improve all the existing QAP solvers for the underlying QAPs.Secondly, we use graph modeling technique to derive a new integer linear program (ILP) models for the underlying QAPs. The new ILP model has n(n-1) binary variables and O(n{sup 3} log(n)) linear constraints. This yields the smallest known number of binary variables for the ILP reformulation of QAPs. Various relaxations of the new ILP model are obtained based on the graphical characterization of the hypercube, and the lower bounds provided by the LP relaxations of the new model are analyzed and compared with what provided by several classical LP relaxations of QAPs in the literature.

Mittelmann, Hans [Department of Mathematics, Arizona State University, Tempe, AZ 85287-1804 (United States); Peng Jiming [Department of Industrial and Enterprise System Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801 (United States); Wu Xiaolin [Department of Electrical and Computer Engineering, McMaster University, Ontario (Canada)

2009-07-02

392

The Quadratic Spinor Lagrangian, Axial Torsion Current and Generalizations  

NASA Astrophysics Data System (ADS)

We show that the Einstein-Hilbert, the Einstein-Palatini, and the Holst actions can be derived from the Quadratic Spinor Lagrangian (QSL), when the three classes of Dirac spinor fields, under Lounesto spinor field classification, are considered. To each one of these classes, there corresponds an unique kind of action for a covariant gravity theory. In other words, it is shown to exist a one-to-one correspondence between the three classes of non-equivalent solutions of the Dirac equation, and Einstein-Hilbert, Einstein-Palatini, and Holst actions. Furthermore, it arises naturally, from Lounesto spinor field classification, that any other class of spinor field — Weyl, Majorana, flagpole, or flag-dipole spinor fields — yields a trivial (zero) QSL, up to a boundary term. To investigate this boundary term, we do not impose any constraint on the Dirac spinor field, and consequently we obtain new terms in the boundary component of the QSL. In the particular case of a teleparallel connection, an axial torsion one-form current density is obtained. New terms are also obtained in the corresponding Hamiltonian formalism. We then discuss how these new terms could shed new light on more general investigations.

Da Rocha, R.; Pereira, J. G.

393

Evolution of universes in quadratic theories of gravity  

SciTech Connect

We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Because of the complicated nature of the equations of motion we focus on the stability of exact solutions and find that there exists an isotropic Friedmann-Robertson-Walker (FRW) universe acting as a past attractor. This may indicate that there is an isotropization mechanism at early times for these kind of theories. We also discuss the Kasner universes, elucidate the associated center manifold structure, and show that there exists a set of nonzero measure which has the Kasner solutions as a past attractor. Regarding the late-time behavior, the stability shows a dependence of the parameters of the theory. We give the conditions under which the de Sitter solution is stable and also show that for certain values of the parameters there is a possible late-time behavior with phantomlike behavior. New types of anisotropic inflationary behavior are found which do not have counterparts in general relativity.

Barrow, John D. [DAMTP, Centre for Mathematical Sciences, Cambridge University, Wilberforce Rd., Cambridge CB3 0WA (United Kingdom); Hervik, Sigbjoern [Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia, B3H 3J5 (Canada)

2006-12-15

394

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

395

Time-averaged quadratic functionals of a Gaussian process  

NASA Astrophysics Data System (ADS)

The characterization of a stochastic process from its single random realization is a challenging problem for most single-particle tracking techniques which survey an individual trajectory of a tracer in a complex or viscoelastic medium. We consider two quadratic functionals of the trajectory: the time-averaged mean-square displacement (MSD) and the time-averaged squared root mean-square displacement (SRMS). For a large class of stochastic processes governed by the generalized Langevin equation with arbitrary frictional memory kernel and harmonic potential, the exact formulas for the mean and covariance of these functionals are derived. The formula for the mean value can be directly used for fitting experimental data, e.g., in optical tweezers microrheology. The formula for the variance (and covariance) allows one to estimate the intrinsic fluctuations of measured (or simulated) time-averaged MSD or SRMS for choosing the experimental setup appropriately. We show that the time-averaged SRMS has smaller fluctuations than the time-averaged MSD, in spite of much broader applications of the latter one. The theoretical results are successfully confirmed by Monte Carlo simulations of the Langevin dynamics. We conclude that the use of the time-averaged SRMS would result in a more accurate statistical analysis of individual trajectories and more reliable interpretation of experimental data.

Grebenkov, Denis S.

2011-06-01

396

The paucity problem for simultaneous quadratic and biquadratic equations  

NASA Astrophysics Data System (ADS)

The problem of constructing non-diagonal solutions to systems of symmetric diagonal equations has attracted intense investigation for centuries (see [5, 6] for a history of such problems) and remains a topic of current interest (see, for example, [2-4]). In contrast, the problem of bounding the number of such non-diagonal solutions has commanded attention only comparatively recently, the first non-trivial estimates having been obtained around thirty years ago through the sieve methods applied by Hooley [10, 11] and Greaves [7] in their investigations concerning sums of two kth powers. As a further contribution to the problem of establishing the paucity of non-diagonal solutions in certain systems of diagonal diophantine equations, in this paper we bound the number of non-diagonal solutions of a system of simultaneous quadratic and biquadratic equations. Let S(P) denote the number of solutions of the simultaneous diophantine equationsformula herewith 0[less-than-or-eq, slant]xi, yi[less-than-or-eq, slant]P(1[less-than-or-eq, slant]i[less-than-or-eq, slant]3), and let T(P) denote the corresponding number of solutions with (x1, x2, x3) a permutation of (y1, y2, y3). In Section 4 below we establish the upper and lower bounds for S(P)[minus sign]T(P) contained in the following theorem.

Tsui, W. Y.; Wooley, T. D.

1999-03-01

397

Two Simple Approximations to the Distributions of Quadratic Forms*  

PubMed Central

Many test statistics are asymptotically equivalent to quadratic forms of normal variables, which are further equivalent to T=?i=1d?izi2 with zi being independent and following N(0, 1). Two approximations to the distribution of T have been implemented in popular software and are widely used in evaluating various models. It is important to know how accurate these approximations are when compared to each other and to the exact distribution of T. The paper systematically studies the quality of the two approximations and examines the effect of ?i's and the degrees of freedom d by analysis and Monte Carlo. The results imply that the adjusted distribution for T can be as good as knowing its exact distribution. When the coefficient of variation of the ?i's is small, the rescaled statistic TR=dT?(?i=1d?i) is also adequate for practical model inference. But comparing TR against ?d2 will inflate type I errors when substantial differences exist among the ?i's, especially, when d is also large.

Yuan, Ke-Hai; Bentler, Peter M.

2010-01-01

398

Hydroxyl functionalized thermosensitive microgels with quadratic crosslinking density distribution.  

PubMed

N-isopropylacrylamide (NIPA) based uniform thermosensitive microgels were synthesized by dispersion polymerization by using relatively hydrophilic crosslinking agents with hydroxyl functionality. Glycerol dimethacrylate (GDMA), pentaerythritol triacrylate (PETA) and pentaerythritol propoxylate triacrylate (PEPTA) were used as crosslinking agents with different hydrophilicities. A protocol was first proposed to determine the crosslinking density distribution in the thermosensitive microgel particles by confocal laser scanning microscopy (CLSM). The microgels were fluorescently labeled by using hydroxyl group of the crosslinking agent. The CLSM observations performed with the microgels synthesized by three different crosslinking agents showed that the crosslinking density exhibited a quadratic decrease with the increasing radial distance in the spherical microgel particles. This structure led to the formation of more loose gel structure on the particle surface with respect to the center. Then the use of hydrophilic crosslinking agents in the dispersion polymerization of NIPA made possible the synthesis of thermosensitive microgels carrying long, flexible and chemically derivatizable (i.e., hydroxyl functionalized) fringes on the surface by a single-stage dispersion polymerization. The microgels with all crosslinking agents exhibited volume phase transition with the increasing temperature. The microgel obtained by the most hydrophilic crosslinking agent, GDMA exhibited higher hydrodynamic diameters in the fully swollen form at low temperatures than those obtained by PETA and PEPTA. Higher hydrodynamic size decrease from fully swollen form to the fully shrunken form was also observed with the same microgel. PMID:17532327

Elmas, Begum; Tuncel, Murvet; Senel, Serap; Patir, S; Tuncel, Ali

2007-04-27

399

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); Kraynik, Andrew M. [Engineering Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico 87185-0834 (United States)

2000-05-01

400

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

SciTech Connect

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

REINELT,DOUGLAS A.; KRAYNIK,ANDREW M.

2000-02-16

401

Electroanalytical performance of nitrogen-containing tetrahedral amorphous carbon thin-film electrodes.  

PubMed

Tetrahedral amorphous carbon (ta-C) consists of a mixture of sp(3)- and sp(2)-bonded carbon ranging from 60 to 40% (sp(3)/sp(3)+sp(2)) depending on the deposition conditions. The physical, chemical, and electrochemical properties depend on the sp(2)/sp(3) bonding ratio as well as the presence of incorporated impurities, such as hydrogen or nitrogen. The ability to grow ta-C at lower temperatures (25-100 °C) on a wider variety of substrates as compared to CVD diamond is an advantage of this material. Herein, we report on the structural and electrochemical properties of nitrogen-incorporated ta-C thin films (ta-C:N). The incorporation of nitrogen into the films decreases the electrical resistivity from 613 ± 60 (0 sccm N(2)) to 1.10 ± 0.07 ?-cm (50 sccm N(2)), presumably by increasing the sp(2)-bonded carbon content and the connectedness of these domains. Similar to boron-doped diamond, these materials are characterized by a low background voltammetric current, a wide working potential window (~ 3 V), and relatively rapid electron-transfer kinetics for aqueous redox systems, including Fe(CN)(6)(-3/-4) and Ru(NH(3))(6)(+3/+2), without conventional pretreatment. Additionally, there is weak molecular adsorption of polar molecules (methylene blue) on the ta-C surface. Overall, the properties of the ta-C and ta-C:N electrodes are such that they could be excellent new choices for electroanalytical measurements. PMID:22715911

Yang, Xingyi; Haubold, Lars; DeVivo, Gabriel; Swain, Greg M

2012-07-03

402

Parallel finite element solutions of nonlinear aeroelastic and aeroservoelastic problems in three-dimensional transonic flows  

Microsoft Academic Search

In this dissertation, computational solutions of three-dimensional aeroelastic and aeroservoelastic problems of flexible wings in the transonic flow regime are presented. The aeroelastic solutions are based on the Galerkin finite element method, implemented on a tetrahedral unstructured mesh. A new flutter suppression scheme based on dynamic twist control is also explored. The results show that this scheme is both robust

Guang-Yaw Hwang

1997-01-01

403

Finite element multigrid solution of Euler flows past installed aero-engines  

Microsoft Academic Search

A finite element based procedure for the solution of the compressible Euler equations on unstructured tetrahedral grids is described. The spatial discretisation is accomplished by means of an approximate variational formulatin, with the explicit addition of a matrix form of artificial viscosity. The solution is advanced in time by means of an explicit multi-stage time stepping procedure. The method is

J. Peraire; J. Peiró; K. Morgan

1993-01-01

404

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

SciTech Connect

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

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

1999-09-27

405

Tetra-hedral zinc in tetra-kis-(1-methyl-1H-imidazole-?N 3)zinc bis-(tetra-fluorido-borate)  

PubMed Central

In the title compound, [Zn(C4H6N2)4](BF4)2, the ZnII ion is in a slightly distorted tetra­hedral coordination geometry, with Zn—N distances in the range 1.980?(2)–1.991?(2)?Å. The tetra­hedral angles are in the range 104.93?(9)–118.81?(9)°.

Reedijk, Jan; van Albada, Gerard A.; Limburg, Bart; Mutikainen, Ilpo; Turpeinen, Urho

2012-01-01

406

Reduced order parameter estimation using quasilinearization and quadratic programming  

NASA Astrophysics Data System (ADS)

The ability of a particular model to accurately predict how a system responds to forcing is predicated on various model parameters that must be appropriately identified. There are many algorithms whose purpose is to solve this inverse problem, which is often computationally intensive. In this study, we propose a new algorithm that significantly reduces the computational burden associated with parameter identification. The algorithm is an extension of the quasilinearization approach where the governing system of differential equations is linearized with respect to the parameters. The resulting inverse problem therefore becomes a linear regression or quadratic programming problem (QP) for minimizing the sum of squared residuals; the solution becomes an update on the parameter set. This process of linearization and regression is repeated until convergence takes place. This algorithm has not received much attention, as the QPs can become quite large, often infeasible for real-world systems. To alleviate this drawback, proper orthogonal decomposition is applied to reduce the size of the linearized model, thereby reducing the computational burden of solving each QP. In fact, this study shows that the snapshots need only be calculated once at the very beginning of the algorithm, after which no further calculations of the reduced-model subspace are required. The proposed algorithm therefore only requires one linearized full-model run per parameter at the first iteration followed by a series of reduced-order QPs. The method is applied to a groundwater model with about 30,000 computation nodes where as many as 15 zones of hydraulic conductivity are estimated.

Siade, Adam J.; Putti, Mario; Yeh, William W.-G.

2012-06-01

407

Mismatch management for optical and matter-wave quadratic solitons  

SciTech Connect

We propose a way to control solitons in {chi}{sup (2)} (quadratically nonlinear) systems by means of periodic modulation imposed on the phase-mismatch parameter ('mismatch management', MM). It may be realized in the cotransmission of fundamental-frequency (FF) and second-harmonic (SH) waves in a planar optical waveguide via a long-period modulation of the usual quasi-phase-matching pattern of ferroelectric domains. In an altogether different physical setting, the MM may also be implemented by dint of the Feshbach resonance in a harmonically modulated magnetic field in a hybrid atomic-molecular Bose-Einstein condensate (BEC), with the atomic and molecular mean fields (MFs) playing the roles of the FF and SH, respectively. Accordingly, the problem is analyzed in two different ways. First, in the optical model, we identify stability regions for spatial solitons in the MM system, in terms of the MM amplitude and period, using the MF equations for spatially inhomogeneous configurations. In particular, an instability enclave is found inside the stability area. The robustness of the solitons is also tested against variation of the shape of the input pulse, and a threshold for the formation of stable solitons is found in terms of the power. Interactions between stable solitons are virtually unaffected by the MM. The second method (parametric approximation), going beyond the MF description, is developed for spatially homogeneous states in the BEC model. It demonstrates that the MF description is valid for large modulation periods, while, at smaller periods, non-MF components acquire gain, which implies destruction of the MF under the action of the high-frequency MM.

Driben, R.; Oz, Y.; Malomed, B. A.; Gubeskys, A.; Yurovsky, V. A. [Department of Interdisciplinary Studies, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel); School of Chemistry, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)

2007-02-15

408

Post-Newtonian, quasicircular binary inspirals in quadratic modified gravity  

NASA Astrophysics Data System (ADS)

We consider a general class of quantum gravity-inspired, modified gravity theories, where the Einstein-Hilbert action is extended through the addition of all terms quadratic in the curvature tensor coupled to scalar fields with standard kinetic energy. This class of theories includes Einstein-Dilaton-Gauss-Bonnet and Chern-Simons modified gravity as special cases. We analytically derive and solve the coupled field equations in the post-Newtonian approximation, assuming a comparable-mass, spinning black hole binary source in a quasicircular, weak-field/slow-motion orbit. We find that a naive subtraction of divergent piece associated with the point-particle approximation is ill-suited to represent compact objects in these theories. Instead, we model them by appropriate effective sources built so that known strong-field solutions are reproduced in the far-field limit. In doing so, we prove that black holes in Einstein-Dilaton-Gauss-Bonnet and Chern-Simons theory can have hair, while neutron stars have no scalar monopole charge, in diametrical opposition to results in scalar-tensor theories. We then employ techniques similar to the direct integration of the relaxed Einstein equations to obtain analytic expressions for the scalar field, metric perturbation, and the associated gravitational wave luminosity measured at infinity. We find that scalar field emission mainly dominates the energy flux budget, sourcing electric-type (even-parity) dipole scalar radiation and magnetic-type (odd-parity) quadrupole scalar radiation, correcting the General Relativistic prediction at relative -1PN and 2PN orders. Such modifications lead to corrections in the emitted gravitational waves that can be mapped to the parameterized post-Einsteinian framework. Such modifications could be strongly constrained with gravitational wave observations.

Yagi, Kent; Stein, Leo C.; Yunes, Nicolás; Tanaka, Takahiro

2012-03-01

409

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

410

Part I. Nanostructured semiconductor photoelectrochemical cells. Part II. Electrodes of tetrahedral amorphous carbon containing nitrogen  

NASA Astrophysics Data System (ADS)

In Part I, preparation of CdS and CdSe films on various electrode materials including nanoporous TiO2 and their photoresponses were demonstrated. Both electrochemical and chemical deposition methods successfully produced Cd-chalcogenide films and post-thermal treatment was done to develop respectable photoactivity. Chemical and photo-electrochemical etching were also performed to remove impurities and increase film stability. Transparency issues for a sandwich type of a solar cell based on semiconductor thin films on a TiO 2 porous nanostructure were examined by measuring transmittances of different wavelengths of laser light. Porous TiO2 films were made from both Degussa P25 TiO2 and Ti(IV) isopropoxide sol-gels. CdSe films on both TiO2 substrates showed comparable photospectra, but the sol-gel one is more transparent and shows better net response. In Part II, electrodes of conductive nitrogen-incorporated tetrahedral amorphous carbon films (taC:N) deposited at ambient temperatures were shown to possess an extraordinary combination of the stability associated with boron-doped diamonds, yet with much enhanced electrocatalytic properties. In this study on the electrochemistry of deposited thin films of taC:N, we showed that this material demonstrates more active charge transfer properties on a variety of systems relative to the H-terminated, highly boron-doped diamond (B-diamond). Stability was shown by chlorine evolution from HCl solution for >104 times the coulombs necessary for 4e/C-atom oxidation to CO2 of a 40 nm thick taC:N film without noticeable change of the voltammetry. Cu deposition and stripping on taC:N electrodes have revealed several distinctive features comparative to other electrodes. From stationary and rotating disk voltammograms, we observed a larger nucleation overpotential of Cu deposition on a taC:N electrode, and the extraordinary Cu stripping pattern, two peak or shoulder-peak, at the position about a higher (more positive) potential than normal bulk Cu stripping peak potential, in the region of the Cu(I)/Cu(II) process. RRDE evidence clearly showed a mixed process of oxidation of Cu(0) to Cu(I) or Cu(0) to Cu(II), and, especially, the presence of Cu(II) in the product stream.

Yoo, Kwangsun

411

Quadratic non-linear optical properties of N-(4-nitrostilbenyl) (S) prolinol  

NASA Astrophysics Data System (ADS)

N-(4-nitrostilbenyl) (S) prolinol (NSP), an asymmetric molecule, presents a high molecular quadratic hyperpolarizability in solution. Experimental results and semi-empirical calculations are used to analyze its non-linear optical properties.

Lequan, Minh; Lequan, Rose Marie; Ching, Kathleen Chane; Barzoukas, Marguerite; Fort, Alain; Bravic, Georges; Chasseau, Daniel; Barrans, Yvette; Huché, Michel

1993-10-01

412

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

413

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

414

Pressure Dependence of Energy Gaps and Refractive Indices of Tetrahedrally Bonded Semiconductors.  

National Technical Information Service (NTIS)

The pressure dependence of energy gaps for a number of elemental and compound semiconductors is investigated employing the empirical pseudopotential method. The compressibility and the empirical pseudopotential form factors appropriate for describing the ...

Y. F. Tsay S. S. Mitra B. Bendow

1974-01-01

415

Elementary symmetric functions of two solvents of a quadratic matrix equation  

Microsoft Academic Search

Quadratic matrix equations occur in a variety of applications. In this paper\\u000awe introduce new permutationally invariant functions of two solvents of the n\\u000aquadratic matrix equation X^2- L1X - L0 = 0, playing the role of the two\\u000aelementary symmetric functions of the two roots of a quadratic scalar equation.\\u000aOur results rely on the connection existing between the

M. A. Jivulescu; A. Napoli; A. Messina

2008-01-01

416

Models of quadratic quantum algebras and their relation to classical superintegrable systems  

SciTech Connect

We show how to construct realizations (models) of quadratic algebras for 2D second order superintegrable systems in terms of differential or difference operators in one variable. We demonstrate how various models of the quantum algebras arise naturally from models of the Poisson algebras for the corresponding classical superintegrable system. These techniques extend to quadratic algebras related to superintegrable systems in n dimensions and are intimately related to multivariable orthogonal polynomials.

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

2009-05-15

417

Existence and uniqueness of solutions to a quasilinear parabolic equation with quadratic gradients in financial markets  

Microsoft Academic Search

A quasilinear parabolic equation with quadratic gradient terms is analyzed. The equation models an optimal portfolio in so-called incomplete financial markets consisting of risky assets and non-tradable state variables. Its solution allows to compute an optimal portfolio strategy. The quadratic gradient terms are essentially connected to the assumption that the so-called relative risk aversion function is not logarithmic. The existence

Ansgar Jüngel

2005-01-01

418

GENERALIZED QUADRATIC STABILIZATION FOR DISCRETE-TIME SINGULAR SYSTEMS WITH TIME-DELAY AND NONLINEAR PERTURBATION  

Microsoft Academic Search

This paper discusses a generalized quadratic stabilization problem for a class of discrete-time singular systems with time-delay and nonlinear per- turbation (DSSDP), which the satisfies Lipschitz condition. By means of the S-procedure approach, necessary and sufficient conditions are presented via a matrix inequality such that the control system is generalized quadratically stabilizable. An explicit expression of the static state feedback

Guoping Lu; Daniel W. C. Ho

2005-01-01

419

Construction of a quadratic model using modified Angstrom coefficients to estimate global solar radiation  

SciTech Connect

In this paper, a new correlation for the estimation of monthly average daily global solar radiation will be presented and compared with the correlations of Rietveld, Benson et al., Oegelman et al., and a recent formulation by Gopinathan. The overall results show that the quadratic form gives better performance in terms of global applicability. The new quadratic model should be preferred for the monthly average global solar radiation estimation when the data for bright sunshine hours are available.

Akinoglu, B.G.; Ecevit, A. (Middle East Technical Univ., Ankara (Turkey))

1990-01-01

420

Robustness analysis of the Zhang neural network for online time-varying quadratic optimization  

Microsoft Academic Search

A general type of recurrent neural network (termed as Zhang neural network, ZNN) has recently been proposed by Zhang et al for the online solution of time-varying quadratic-minimization (QM) and quadratic-programming (QP) problems. Global exponential convergence of the ZNN could be achieved theoretically in an ideal error-free situation. In this paper, with the normal differentiation and dynamics-implementation errors considered, the

Yunong Zhang; Gongqin Ruan; Kene Li; Yiwen Yang

2010-01-01

421

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

422

Analytic, Computational, and Approximate Forms for Ratios of Noncentral and Central Gaussian Quadratic Forms  

PubMed Central

Many useful statistics equal the ratio of a possibly noncentral chi-square to a quadratic form in Gaussian variables with all positive weights. Expressing the density and distribution function as positively weighted sums of corresponding F functions has many advantages. The mixture forms have analytic value when embedded within a more complex problem. The mixture forms also have computational value. The expansions work well with quadratic forms having few components and small degrees of freedom. A more general algorithm from earlier literature can take longer or fail to converge in the same setting. Many approximations have been suggested for the problem. a positively weighted noncentral quadratic form can always have two moments matched to a noncentral chi-square. For a single quadratic form, the noncentral form performs neither uniformly more or less accurately than older approximations. The approach also gives a noncentral F approximation for any ratio of a positively weighted noncentral form to a positively weighted central quadratic form. The method provides better accuracy for noncentral ratios than approximations based on a single chi-square. The accuracy suffices for many practical applications, such as power analysis, even with few degrees of freedom. Naturally the approximation proves much faster and simpler to compute than any exact method. Embedding the approximation in analytic expressions provides simple forms which correctly guarantee only positive values have nonzero probabilities, and also automatically reduce to partially or fully exact results when either quadratic form has only one term.

Kim, Hae-Young; Gribbin, Matthew J.; Muller, Keith E.; Taylor, Douglas J.

2013-01-01

423

Hookean atom with four electrons: On the formation of a tetrahedral Wigner molecule in the weak trapping limit  

SciTech Connect

Numerical results are presented on states {sup 5}S{sub u} and {sup 3}P{sub g} of the Hookean atom with four electrons. Using standard ab initio quantum chemistry methods, the quintet configuration is shown to be the ground state for the weak harmonic trapping constant k. For large k values, there is a crossover to the triplet {sup 3}P{sub g} ground state. Finally, it is concluded that the Coulombic potential energy approaches the localized electron limit of a tetrahedral Wigner molecule as the harmonic force constant k tends to zero.

Amovilli, C.; March, N. H. [Dipartimento di Chimica e Chimica Industriale, Universita di Pisa, Via Risorgimento 35, I-56126 Pisa (Italy); Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp (Belgium)

2011-04-15

424

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

425

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

426

Electronic structures of filled tetrahedral semiconductors LiMgN and LiZnN: conduction band distortion  

Microsoft Academic Search

The band structures of the filled tetrahedral semiconductors LiMgN and LiZnN, viewed as the zinc-blende (MgN)? and (ZnN)? lattices partially filled with He-like Li+ ion interstitials, were studied using the full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The conduction band distortions of LiMgN and LiZnN, compared to their “parent” zinc-blende analog AlN and GaN, are discussed.

L. H. Yu; K. L. Yao; Z. L. Liu

2004-01-01

427

Elements of class groups and Shafarevich-Tate groups of elliptic curves  

Microsoft Academic Search

The problem of estimating the number of imaginary quadratic fields\\u000awhose ideal class group has an element of order ??2$ is\\u000aclassical in number theory. Analogous questions for quadratic twists\\u000aof elliptic curves have been the focus of recent interest. Whereas\\u000aworks of C. Stewart and J. Top [ST], and of F. Gouvêa and\\u000aB. Mazur [GM] address the nontriviality

Antal Balog; Ken Ono

2003-01-01

428

Mesh considerations for finite element blast modelling in biomechanics.  

PubMed

Finite element (FE) modelling is a popular tool for studying human body response to blast exposure. However, blast modelling is a complex problem owing to more numerous fluid-structure interactions (FSIs) and the high-frequency loading that accompanies blast exposures. This study investigates FE mesh design for blast modelling using a sphere in a closed-ended shock tube meshed with varying element sizes using both tetrahedral and hexahedral elements. FSI was consistent for sphere-to-fluid element ratios between 0.25 and 4, and acceleration response was similar for both element types (R(2) = 0.997). Tetrahedral elements were found to become increasingly volatile following shock loading, causing higher pressures and stresses than predicted with the hexahedral elements. Deviatoric stress response was dependent on the sphere mesh size (p < 0.001), while the pressure response was dependent on the shock tube mesh size (p < 0.001). The results of this study highlight the necessity for mesh sensitivity analysis in blast models. PMID:22185582

Panzer, Matthew B; Myers, Barry S; Bass, Cameron R

2011-12-21

429

Molecular orbital studies of enzyme activity: I: Charge relay system and tetrahedral intermediate in acylation of serine proteinases.  

PubMed Central

The charge relay ststem and its role in the acylation of serine proteinases is studied using the partial retention of diatomic differential overlap (PRDDO) technique to perform approximate ab initio molecular orbital calculations on a model of the enzyme-substrate complex. The aspartate in the charge relay system is seen to act as the ultimate proton acceptor during the charging of the serine nucleophile. A projection of the potential energy surface is obtained in a subspace corresponding to this charge transfer and to the coupled motions of active site residues and the substrate. These results together with extended basis set results for cruder models suggest that a concerted transfer of protons from Ser-195 to His-57 and from His-57 to Asp-102 occurs with an energy barrier of 20-25 kcal/mole (84-105 kJ/mole). The subsequent nucleophilic attack on the scissile peptide linkage by the charged serine is then seen to proceed energetically downhill to the tetrahedral intermediate. The formation of the tetrahedral intermediate from the Michaelis complex is calculated to be nearly thermoneutral.

Scheiner, S; Kleier, D A; Lipscomb, W N

1975-01-01

430

Parallel adaptive mesh-refining scheme on a three-dimensional unstructured tetrahedral mesh and its applications  

NASA Astrophysics Data System (ADS)

The development of a parallel three-dimensional (3-D) adaptive mesh refinement (PAMR) scheme for an unstructured tetrahedral mesh using dynamic domain decomposition on a memory-distributed machine is presented in detail. A memory-saving cell-based data structure is designed such that the resulting mesh information can be readily utilized in both node- or cell-based numerical methods. The general procedures include isotropic refinement from one parent cell into eight child cells and then followed by anisotropic refinement which effectively removes hanging nodes. A simple but effective mesh-quality control mechanism is employed to preserve the mesh quality. The resulting parallel performance of this PAMR is found to scale approximately as N for N?32. Two test cases, including a particle method (parallel DSMC solver for rarefied gas dynamics) and an equation-based method (parallel Poisson Boltzmann equation solver for electrostatic field), are used to demonstrate the generality of the PAMR module. It is argued that this PAMR scheme can be applied in any numerical method if the unstructured tetrahedral mesh is adopted.

Lian, Y.-Y.; Hsu, K.-H.; Shao, Y.-L.; Lee, Y.-M.; Jeng, Y.-W.; Wu, J.-S.

2006-12-01

431

Vestibular integrator neurons have quadratic functions due to voltage dependent conductances.  

PubMed

The nonlinear properties of the dendrites of the prepositus hypoglossi nucleus (PHN) neurons are essential for the operation of the vestibular neural integrator that converts a head velocity signal to one that controls eye position. A novel system of frequency probing, namely quadratic sinusoidal analysis (QSA), was used to decode the intrinsic nonlinear behavior of these neurons under voltage clamp conditions. Voltage clamp currents were measured at harmonic and interactive frequencies using specific nonoverlapping stimulation frequencies. Eigenanalysis of the QSA matrix reduces it to a remarkably compact processing unit, composed of just one or two dominant components (eigenvalues). The QSA matrix of rat PHN neurons provides signatures of the voltage dependent conductances for their particular dendritic and somatic distributions. An important part of the nonlinear response is due to the persistent sodium conductance (gNaP), which is likely to be essential for sustained effects needed for a neural integrator. It was found that responses in the range of 10 mV peak to peak could be well described by quadratic nonlinearities suggesting that effects of higher degree nonlinearities would add only marginal improvement. Therefore, the quadratic response is likely to sufficiently capture most of the nonlinear behavior of neuronal systems except for extremely large synaptic inputs. Thus, neurons have two distinct linear and quadratic functions, which shows that piecewise linear?+?quadratic analysis is much more complete than just piecewise linear analysis; in addition quadratic analysis can be done at a single holding potential. Furthermore, the nonlinear neuronal responses contain more frequencies over a wider frequency band than the input signal. As a consequence, they convert limited amplitude and bandwidth input signals to wider bandwidth and more complex output responses. Finally, simulations at subthreshold membrane potentials with realistic PHN neuron models suggest that the quadratic functions are fundamentally dominated by active dendritic structures and persistent sodium conductances. PMID:23519443

Magnani, Christophe; Eugène, Daniel; Idoux, Erwin; Moore, Lee E

2013-03-22

432

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

Microsoft Academic Search

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.

Rainald Loehner; Ken Morgan; Jaime Peraire; Mehdi Vahdati

1987-01-01

433

Hierarchical bases of finite-element spaces in the discretization of nonsymmetric elliptic boundary value problems  

Microsoft Academic Search

In the case of symmetric and positive definite plane elliptic boundary value problems, the condition numbers of the stiffness matrices arising from finite element discretizations grow only quadratically with the number of refinement levels, if one uses hierarchical bases of the finite element spaces instead of the usual nodal bases; see [9]. Here we show that results of the same

H. Yserentant

1985-01-01

434

An advanced boundary element method (BEM) implementation for the forward problem of electromagnetic source imaging  

Microsoft Academic Search

The forward problem of electromagnetic source imaging has two components: a numerical model to solve the related integral equations and a model of the head geometry. This study is on the boundary element method (BEM) implementation for numerical solutions and realistic head modelling. The use of second-order (quadratic) isoparametric elements and the recursive integration technique increase the accuracy in the

Zeynep Akalin-Acar; Nevzat G. Gençer

2004-01-01

435

Effects of planar element formulation and numerical integration order on checkerboard material layouts  

Microsoft Academic Search

The effects of selected planar finite element formulations, and their associated integration schemes, on the stiffness of\\u000a a checkerboard material layout are investigated. Standard 4-node bilinear elements, 8- and 9-node quadratic elements, as well\\u000a as 4-node elements with drilling degrees of freedom are considered. Integration schemes evaluated include popular Gauss quadrature\\u000a rules, as well as modified 5- and 8-point integration

Craig S. Long; Philip W. Loveday; Albert A. Groenwold

2009-01-01

436

A stable elemental decomposition for dynamic process optimization  

Microsoft Academic Search

In Cervantes and Biegler (A.I.Ch.E.J. 44 (1998) 1038), we presented a simultaneous nonlinear programming problem (NLP) formulation for the solution of DAE optimization problems. Here, by applying collocation on finite elements, the DAE system is transformed into a nonlinear system. The resulting optimization problem, in which the element placement is fixed, is solved using a reduced space successive quadratic programming

Arturo M Cervantes; Lorenz T Biegler

2000-01-01

437

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

2011-09-12

438

Propagator for the time-dependent charged oscillator via linear and quadratic invariants  

SciTech Connect

The problem of a charged particle in the presence of a variable magnetic field is considered. Using the linear and the quadratic invariants as a tool, the wave functions in Fock state as well as in coherent state are obtained. The corresponding propagators which propagate the wave functions in the space-time are derived. Using numerical computations we have managed to draw some plots for the real, imaginary, and absolute values of the propagators. This has been used to analyze the properties of the propagators associated with both of the linear and the quadratic invariants. It has been shown that there is no essential difference between the behavior of the absolute value of the propagators in both of the linear and the quadratic invariants.

Abdalla, M. Sebawe [Mathematics Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)], E-mail: m.sebaweh@physics.org; Choi, Jeong-Ryeol [Department of Physics and Advanced Materials Science, Sun Moon University, Asan 336-708 (Korea, Republic of)

2007-12-15

439

Multiconfigurational quadratic response functions for singlet and triplet perturbations - The phosphorescence lifetime of formaldehyde  

NASA Astrophysics Data System (ADS)

A formalism is presented for the calculation of quadratic response functions of multiconfigurational self-consistent field reference wave functions. The formalism is general in the sense that it applies equally well to singlet and triplet perturbations and it does not assume any permutational symmetry in the integrals of the perturbational operators. This formalism can be used to derive expressions for various properties related to singlet or triplet quadratic response functions and their residues. We focus on the spin-forbidden dipole transitions between singlet and triplet electronic states responsible for the long lifetime of phosphorescent states. The singlet-triplet transition moments are evaluated as the residues of quadratic response functions. Sample calculations are presented for the formaldehyde molecule.

Vahtras, Olav; Agren, Hans; Jorgensen, Poul; Jensen, Hans J. A.; Helgaker, Trygve; Olsen, Jeppe

1992-12-01

440

Clifford group, stabilizer states, and linear and quadratic operations over GF(2)  

SciTech Connect

We describe stabilizer states and Clifford group operations using linear operations and quadratic forms over binary vector spaces. We show how the n-qubit Clifford group is isomorphic to a group with an operation that is defined in terms of a (2n+1)x(2n+1) binary matrix product and binary quadratic forms. As an application we give two schemes to efficiently decompose Clifford group operations into one- and two-qubit operations. We also show how the coefficients of stabilizer states and Clifford group operations in a standard basis expansion can be described by binary quadratic forms. Our results are useful for quantum error correction, entanglement distillation, and possibly quantum computing.

Dehaene, Jeroen; Moor, Bart de [Katholieke Universiteit Leuven, ESAT-SCD, Kasteelpark Arenberg 10, B-3001 Leuven (Belgium)

2003-10-01

441

A tetrahedral coordination compound for second-order nonlinear optics: synthesis, crystal structure and SHG of Zn(2NH 2py) 2Cl 2  

Microsoft Academic Search

A coordination compound with a tetrahedral molecular configuration, Zn(NH2py)2Cl2(2-NH2py=2-aminopyridine), was prepared. It is transparent in the visible region and shows second harmonic generation (SHG) effect 8.0 times as strong as that of KDP. X-ray single crystal structure analysis reveals that all Zn(NH2py)2Cl2 molecules are aligned in a fully parallel direction. The advantages and disadvantages of tetrahedral zinc coordination compounds as

Jingui Qin; Nanbing Su; Chaoyang Dai; Chuluo Yang; Daoyu Liu; Michael W. Day; Baichang Wu; Chuangtian Chen

1999-01-01

442

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

443

Newton equation for canonical, Lie-algebraic, and quadratic deformation of classical space  

SciTech Connect

The Newton equation describing particle motion in a constant external field force on canonical, Lie-algebraic, and quadratic space-time is investigated. We show that for canonical deformation of space-time the dynamical effects are absent, while in the case of Lie-algebraic noncommutativity, when spatial coordinates commute to the time variable, the additional acceleration of the particle is generated. We also indicate that in the case of spatial coordinates commuting in a Lie-algebraic way, as well as for quadratic deformation, there appear additional velocity and position-dependent forces.

Daszkiewicz, Marcin [Institute of Theoretical Physics, University of Wroclaw, pl. Maxa Borna 9, 50 - 206 Wroclaw (Poland); Walczyk, Cezary J. [Department of Physics, University of Bialystok, ul. Lipowa 41, 15 - 424 Bialystok (Poland)

2008-05-15

444

Boron K-edge XANES of boron oxides: tetrahedral B-O distances and near-surface alteration  

NASA Astrophysics Data System (ADS)

Synchrotron radiation boron K-edge XANES spectra collected in fluorescence yield mode are reported for monoclinic metaboric acid [HBO2(II)], sinhalite (MgAlBO4), and a selection of boron oxides in which B is exclusively in trigonal coordination ([3]B). The anomalously high divergence of tetrahedral ([4]B-O) bond lengths in HBO2(II) and sinhalite is used to resolve fine structure at the [4]B K edge due to splitting of ?*(t2) antibonding orbitals. For HBO2(II), XANES peaks at 196.9 and 199.3eV are assigned to [4]B-O distances of 1.564 and 1.440 (×3) Å, respectively, and, for sinhalite, peaks at 196.8, 197.9, and 199.6eV are assigned to distances of 1.586, 1.483 (×2), and 1.442Å, respectively. A correlation between peak splitting at the [4]B K edge and divergence of tetrahedral bond length is established for borates and borosilicates using data for sinhalite, HBO2(II), ferroaxinite, danburite, datolite, and BPO4. B K-edge XANES spectra collected in total electron yield mode, which probes to <60Å, show that almost all [4]B in HBO2(II) and about one-third of the [4]B in sinhalite are converted to [3]B in the near-surface structure. Moreover, HBO2(II), HBO2(III), sassolite (boric acid; H3BO3), and v-B2O3, which have markedly different bulk structures, have a similar near-surface layer composed of a relaxed anhydrous network of BO3 groups.

Fleet, M. E.; Liu, X.

445

The bonding of ferrous iron to sulfur and oxygen in tetrahedral coordination: A comparative study using SCF X scattered wave molecular orbital calculations  

Microsoft Academic Search

Molecular quantum mechanical calculations have been performed on high-spin ferrous iron tetrahedrally coordinated to sulfur and oxygen, respectively. The molecular orbital energies obtained from the calculations are compared with experimental optical and X-ray emission spectra. Good agreement was found between calculated and experimental spectral transition energies for the optical absorption spectra of Fe 2+ in sphalerite, of Fe 2+ in

D. J. Vaughan; K. H. Johnson; J. A. Tossell

1974-01-01

446

Studies of the electronic structure and excitation properties of vanadium-oxygen compounds with tetrahedral and octahedral V-O coordination. Part 1: Vanadium Pentoxide  

Microsoft Academic Search

Vanadium-oxygen compounds are the subject of active current interest. The investigation of vanadium pentoxide is the first part of a larger project devoted to studies of five series of oxides, vanadates, and bronzes. Characteristic for all these materials is the enclosure of vanadium atoms within rigid oxygen cages with tetrahedral or octahedral V-O coordination. The previous XPS, EELS, and APS

I. M. Curelaru; K. S. Din; J. Barth; G. P. Williams; N. Lucas

1984-01-01

447

Quadratic Food Engel Curves with Measurement Error: Evidence from a Budget Survey  

Microsoft Academic Search

In this paper we estimate quadratic food Engel curves with measurement error using the 1994 Ethiopian Urban Household Budget Survey. In sharp contrast to the findings from developed countries, food share is found to increase with expenditure, and only starts to decline after some threshold level of expenditure. We establish the robustness of this inverted-U relationship by estimating a more

Sourafel Girma; Abbi M. Kedir

2003-01-01

448

Optimized GM (1, 1) based on Romber algorithm and quadratic interpolation method  

Microsoft Academic Search

This text analyzed the reason of generating error of GM (1, 1), from the integral calculus angle discrete GM (1, 1). A kind of method putting forward making use of Romberg integral calculus formula and quadratic interpolation method to construct the background value of the model, raised simulation and prediction precision of GM(1,1), and the actual example verify the feasibility

Bo Li; Sheng-Li Zhao; Ling Fang

2009-01-01

449

Model validation for robust control of uncertain systems with an integral quadratic constraint  

Microsoft Academic Search

This paper presents a new approach to the model validation problem for a class of uncertain systems in which the uncertainty is described by an integral quadratic constraint. The proposed model validation algorithm is based on the solution to a game-type Riccati differential equation and a set of state equations closely related to a robust Kalman filtering problem.

Andrey V. Savkin; Ian R. Petersen

1996-01-01

450

Identification of Local Minimizers in Inertia-Controlling Methods for Quadratic Programming.  

National Technical Information Service (NTIS)

The verification of a local minimizer of a general (i.e., nonconvex) quadratic program is in general an NP-hard problem. The difficulty concerns the optimality of certain points (which we call dead points) at which the first-order necessary conditions for...

A. L. Forsgren P. E. Gill W. Murray

1989-01-01

451

Optimization of the quadratic assignment problem using an ant colony algorithm  

Microsoft Academic Search

Ant algorithm is a multi-agent systems inspired by the behaviors of real ant colonies function to solve optimization problems. In this paper an ant colony optimization algorithm is developed to solve the quadratic assignment problem. The local search process of the algorithm is simulated annealing. In the exploration of the search space, the evaluation of pheromones which are laid on

Nihan Çetin Demirel; M. Duran Toksari

2006-01-01

452

Isomonodromy deformations for the ZS-AKNS system with quadratic spectral variables  

NASA Astrophysics Data System (ADS)

We solve the monodromy problem and prove the Painleve property for self-similar ZS-AKNS flows with a quadratic spectral variable in this report. In particular, we obtain meromorphic solutions for the Cauchy problem of the self-similar derivative nonlinear Schrödinger equation.

Wu, Derchyi

2003-10-01

453

Continuity of SRB measure and entropy for Benedicks–Carleson quadratic maps  

Microsoft Academic Search

We consider the quadratic family of maps given by fa(x) = 1 ? ax2 on I = [?1, 1], for the Benedicks–Carleson parameters. On this positive Lebesgue measure set of parameters close to a = 2, fa presents an exponential growth of the derivative along the orbit of the critical point and has an absolutely continuous Sinai–Ruelle–Bowen (SRB) invariant measure.

Jorge Milhazes Freitas

2005-01-01

454

Quadratic phase coupling analysis of passive sonar data using biphase techniques  

Microsoft Academic Search

In this work we report on the application of a higher order statistics based method that can be used to improve passive signature estimation over the conventional bispectrum methods. The method employs the biphase for extraction of frequency triplets with possible quadratic phase coupling. We demonstrate the method using data recorded by bottom mounted hydrophones during a sea trial in

L. Persson; R. K. Lennartsson; J. W. C. Robinson; S. McLaughlin

2000-01-01

455

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

456

Evaluating the delay robustness of interconnected passive systems with a frequency-dependent integral quadratic constraint  

Microsoft Academic Search

We consider interconnections of output strictly passive systems and study their robustness in the presence of delay. We establish a new integral quadratic constraint (IQC), which captures the magnitude roll-off at high frequencies. The benefit of the roll-off IQC is exemplified in a study of the stability of a cyclic interconnection structure. When used in conjunction with the IQC describing

Erin Summers; Murat Arcak; Andrew Packard

2011-01-01

457

On quadratic first integrals of the geodesic equations for type { 22 } spacetimes  

Microsoft Academic Search

It is shown that every type {22} vacuum solution of Einstein's equations admits a quadratic first integral of the null geodesic equations (conformal Killing tensor of valence 2), which is independent of the metric and of any Killing vectors arising from symmetries. In particular, the charged Kerr solution (with or without cosmological constant) is shown to admit a Killing tensor

Martin Walker; Roger Penrose

1970-01-01

458

Robust control of a flexible robot arm using the quadratic d-stability approach  

Microsoft Academic Search

This paper shows how the quadratic d-stability design method provides a solution to a flexible robot arm control problem. The experimental process exhibits time delay, nonminimum phase behavior and lightly damped modes. The method is based on pole placement considerations and involves the resolution of two parameter dependent Riccati equations with an extra condition. Performances achieved numerically by the designed

Jamal Daafouz; Germain Garcia; Jacques Bernussou

1998-01-01

459

Quadratic Parametric Programming for Portfolio Selection with Random Problem Generation and Computational Experience  

Microsoft Academic Search

For researchers intending to investigate mid- to large-scale portfolio se- lection, good, inexpensive and understandable quadratic parametric pro- gramming software, capable of computing the e-cient frontiers of prob- lems with up to two thousand securities without simpliflcations to the covariance matrix, is hardly known to be available anywhere. As an alter- native to Markowitz's critical line method, a full explication

Markus Hirschberger; Yue Qi; Ralph E. Steuer

460

Hybridizing harmony search algorithm with sequential quadratic programming for engineering optimization problems  

Microsoft Academic Search

This study presents a hybrid harmony search algorithm (HHSA) to solve engineering optimization problems with continuous design variables. Although the harmony search algorithm (HSA) has proven its ability of finding near global regions within a reasonable time, it is comparatively inefficient in performing local search. In this study sequential quadratic programming (SQP) is employed to speed up local search and

M. Fesanghary; M. Mahdavi; M. Minaryjolandan; Y. Alizadeh

2008-01-01

461

Soliton emission at a phase-mismatch boundary in a quadratic nonlinear film waveguide  

NASA Astrophysics Data System (ADS)

We report the experimental demonstration of spatial nonlinear beam displacement caused by an interface between periodically modulated and uniform quadratic nonlinearity. We observe intensity- and phase-mismatch-dependent spatial beam displacement at 1548 nm in lithium niobate waveguides. The device has the potential to provide a soliton-emission-based, ultrafast all-optical switch.

Baronio, Fabio; de Angelis, Costantino; Pioger, Paul-Henri; Couderc, Vincent; Barthélémy, Alain; Min, Yoohong; Quiring, Victor; Sohler, Wolfgang

2003-12-01

462

Series Nash Solution of Two-Person Nonzero-Sum Linear-Quadratic Differential Games.  

National Technical Information Service (NTIS)

It is well-known that the Nash equilibrium solution of a two-person nonzero-sum linear differential game with a quadratic cost function can be expressed in terms of the solution of coupled generalized Riccati-type matrix differential equations. For high o...

J. B. Cruz C. I. Chen

1970-01-01

463

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

464

Linear and quadratic models of the southern Murray-Darling basin.  

PubMed

Linear programming (LP), a well-established technique for modelling agricultural and other systems, has been extensively used to model irrigation systems in Australia. The models constructed have been used to assess the effects of changing water charges on farm incomes, water use, and the effects of trade in water allocations. An LP model that reflects actual farm behaviour requires a large amount of data. Moreover, demand and supply functions estimated with LP models are necessarily stepped rather than smooth. Howitt has suggested a way of escaping from these problems of LP models. His positive programming approach replaces an LP model with a simpler quadratic programming model. In this paper, Howitt's approach is used to develop a quadratic programming model from an existing LP model of irrigated agriculture in the southern Murray-Darling basin of Australia. A comparison of the quadratic and linear models indicates that the quadratic programming model is smaller and simpler to specify and that it produces similar results to the linear model, in terms of cropping, trade, and demand for irrigation water. The choice of modelling technique depends on the problem and the available resources. Positive programming can be a valuable addition to the farm modellers' arsenal. PMID:11697673

Hall, N

2001-09-01

465

On the prediction of free turbulent jets with swirl using a quadratic pressure-strain model  

Microsoft Academic Search

Data from free turbulent jets both with and without swirl are used to assess the performance of the pressure-strain model of Speziale, Sarkar and Gatski which is quadratic in the Reynolds stresses. Comparative predictions are also obtained with the two versions of the Launder, Reece and Rodi model which are linear in the same terms. All models are used as

Bassam A. Younis; Thomas B. Gatski; Charles G. Speziale

1994-01-01

466

Prediction of Free Turbulent Jets with Swirl Using a Quadratic Pressure-Strain Model.  

National Technical Information Service (NTIS)

Data from free turbulent jets both with and without swirl are used to assess the performance of the pressure-strain model of Speziale, Sarkar and Gatski which is quadratic in the Reynolds stresses. Comparative predictions are also obtained with the two ve...

B. A. Younis T. B. Gatski C. G. Speziale

1994-01-01

467

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

468

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…

Benacka, Jan

2010-01-01

469

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

470

An FPGA implementation of a sparse quadratic programming solver for constrained predictive control  

Microsoft Academic Search

Model predictive control (MPC) is an advanced industrial control technique that relies on the solution of a quadratic programming (QP) problem at every sampling instant to determine the input action required to control the current and future behaviour of a physical system. Its ability in handling large multiple input multiple output (MIMO) systems with physical constraints has led to very

Juan Luis Jerez; George Anthony Constantinides; Eric C. Kerrigan

2011-01-01

471

Optimal supervisory control of a central chilled water plant with heuristic search sequential quadratic programming  

Microsoft Academic Search

A new methodology for adapting rigorous simulation programs to optimal supervisory control of a central chilled water plant is proposed in this article, which solves plant operation mode optimization and set points optimization by combining heuristic search with sequential quadratic programming. The mathematical basis of this algorithm is developed. A new derivative calculation strategy is introduced in set points optimization.

Jian Sun

2010-01-01

472

Welfare Impacts of Rising Food Prices in Rural Ethiopia: a Quadratic Almost Ideal Demand System Approach  

Microsoft Academic Search

Ethiopia has experienced high food prices, especially since 2005. This paper examines the welfare impacts of rising food prices in rural Ethiopia using Quadratic Almost Ideal Demand System (QUAIDS) approach controlled for expenditure endogeniety and zero consumption expenditure. The elasticity coefficients from QUAIDS are used to estimate Compensated Variations (CV), which explicitly accounts for profit function and substitution effects. The

Nigussie Tefera Uregia; Mulat Demeke Desta; Shahidur Rashid

2012-01-01

473

Welfare Impacts of Rising Food Prices in Rural Ethiopia: a Quadratic Almost Ideal Demand System Approach  

Microsoft Academic Search

Ethiopia has experienced high food prices since early 2004. This paper examines the welfare impacts of rising food prices in rural Ethiopia using Quadratic Almost Ideal Demand System (QUAIDS) approach controlled for expenditure endogeniety and zero consumption expenditure. The elasticity coefficients from QUAIDS are used to estimate Compensated Variations (CV), which explicitly accounts for profit function and substitution effects. The

Nigussie Tefera Uregia; Mulat Demeke Desta; Shahidur Rashid

2012-01-01

474

New approaches to relaxed quadratic stability condition of fuzzy control systems  

Microsoft Academic Search

This paper deals with the quadratic stability conditions of fuzzy control systems that relax the existing conditions reported in the previous literatures. Two new conditions are proposed and shown to be useful in analyzing and designing fuzzy control systems. The first one employs the S-procedure to utilize information regarding the premise parts of the fuzzy systems. The next one enlarges

Euntai Kim; Heejin Lee

2000-01-01

475

A re-investigation of the quadratic electrostriction of alkali halides of rocksalt type  

Microsoft Academic Search

In order to clarify the reasons for the contradictory results regarding quadratic electrostriction in alkali halides reported by various authors, we developed an improved capacitive dilatometer. Employing the frequency-modulation technique, the resolution of the experimental set-up reaches icons\\/Journals\\/Common\\/Delta\\

J. Schreuer; S. Haussühl

1999-01-01

476

Optimal control development for chilled water plants using a quadratic representation  

Microsoft Academic Search

Optimal supervisory control strategy for the set points of controlled variables in the cooling plants has been studied by computer simulation. A quadratic linear regression equation for predicting the total cooling system power in terms of the controlled and uncontrolled variables was developed using simulated data collected under different values of controlled and uncontrolled variables. The optimal set temperatures such

B. C. Ahn; J. W. Mitchell

2001-01-01

477

Sequential Linear-Quadratic Method for Differential Games with Air Combat Applications  

Microsoft Academic Search

We present a numerical method for computing a local Nash (saddle-point) solution to a zero-sum differential game for a nonlinear system. Given a solution estimate to the game, we define a subproblem, which is obtained from the original problem by linearizing its system dynamics around the solution estimate and expanding its payoff function to quadratic terms around the same solution

H. Mukai; A. Tanikawa; ?. Tunay; ?. A. Ozcan; I. N. Katz; H. Schättler; P. Rinaldi; G. J. Wang; L. Yang; Y. Sawada

2003-01-01

478

Phase Portraits of Quadratic Systems. Higher Order Singularities and Separatrix Cycles.  

National Technical Information Service (NTIS)

In the thesis phase portraits of quadratic systems of differential equations in the plane are studied. First a classification is given of all phase portraits with a higher order singular point with two zero eigenvalues. Then a classification is given of a...

P. de Jager

1989-01-01

479

Underprediction of human skin erythema at low doses per fraction by the linear quadratic model  

Microsoft Academic Search

Background and purpose. The erythematous response of human skin to radiotherapy has proven useful for testing the predictions of the linear quadratic (LQ) model in terms of fractionation sensitivity and repair half time. No formal investigation of the response of human skin to doses less than 2 Gy per fraction has occurred. This study aims to test the validity of

Christopher S. Hamilton; James W. Denham; Maree O'Brien; Patricia Ostwald; Tomas Kron; Suzanne Wright; Wolfgang Dörr

1996-01-01

480

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

481

The incorporation of HVDC equations in optimal power flow methods using sequential quadratic programming techniques  

Microsoft Academic Search

The author presents the formulation and solution method of an optimal power flow problem using a sequential quadratic programming technique for an AC-DC power system with one or more multiterminal DC systems. The algorithm developed has been tested on a number of sample AC-DC systems. The convergence characteristics, insofar as the number of the major iteration goes, is comparable with

C. N. Lu; S. S. Chen; C. M. Ing

1988-01-01

482

Quadratic neural unit is a good compromise between linear models and neural networks for industrial applications  

Microsoft Academic Search

The paper discusses the quadratic neural unit (QNU) and highlights its attractiveness for industrial applications such as for plant modeling, control, and time series prediction. Linear systems are still often preferred in industrial control applications for their solvable and single solution nature and for the clarity to the most application engineers. Artificial neural networks are powerful cognitive nonlinear tools, but

Ivo Bukovsky; Noriyasu Homma; Ladislav Smetana; Ricardo Rodriguez; Martina Mironovova; Stanislav Vrana

2010-01-01

483

A Linear Quadratic Guidance law for solid fuel, space-based interceptors  

Microsoft Academic Search

The paper discusses the use of Linear Quadratic Guidance to design acceleration profiles for interceptors launched from a space platform against an accelerating threat. It is assumed that the interceptor has a solid propellant which burns continuously from ignition, but that the graining is segmented so that different levels of acceleration are available over different portions of the trajectory. Simulation

G. C. Schmidt; J. W. Hardtla

1986-01-01

484

Quadratic alternating direction implicit iteration for the fast solution of algebraic Riccati equations  

Microsoft Academic Search

Algebraic Riccati equations (AREs) spread over many branches of signal processing and system design problems. Solution of large scale AREs, however, can be computationally prohibitive. This paper introduces a novel second order extension to the alternating direction implicit (ADI) iteration, called quadratic ADI or QADI, for the efficient solution of an ARE. QADI is simple to code and exhibits fast

Ngai Wong; V. Balakrishnan

2005-01-01

485

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

486

Landau-Zener transition in quadratic nonlinear two-state systems  

SciTech Connect

A comprehensive theory of the Landau-Zener transition in quadratic nonlinear two-state systems is developed. A compact analytic formula involving elementary functions only is derived for the final transition probability. The formula provides a highly accurate approximation for the whole rage of the variation of the Landau-Zener parameter.

Ishkhanyan, A. M. [Institute for Physical Research of NAS of Armenia, 0203 Ashtarak-2 (Armenia)

2010-05-15

487

Brief note on Ashtekar-Magnon-Das conserved quantities in quadratic curvature theories  

SciTech Connect

In this note, we correct a mistake in the mass formula in [N. Okuyama and J. i. Koga, Phys. Rev. D 71, 084009 (2005).] which generalizes the Ashtekar-Magnon-Das method to incorporate extended gravities with quadratic curvature terms. The corrected mass formula confirms that the black hole masses for recently discovered critical gravities vanish.

Pang Yi [Kavli Institute for Theoretical Physics, Key Laboratory of Frontiers in Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2011-04-15

488

Quadratic Statistical MAX Approximation for Parametric Yield Estimation of Analog\\/RF Integrated Circuits  

Microsoft Academic Search

In this paper, we propose an efficient numerical algo- rithm for estimating the parametric yield of analog\\/RF circuits, considering large-scale process variations. Unlike many tradi- tional approaches that assume normal performance distributions, the proposed approach is particularly developed to handle mul- tiple correlated nonnormal performance distributions, thereby providing better accuracy than the traditional techniques. Starting from a set of quadratic

Xin Li; Yaping Zhan; Lawrence T. Pileggi

2008-01-01

489

A Comparison of Methods for Estimating Quadratic Effects in Nonlinear Structural Equation Models  

Microsoft Academic Search

Two Monte Carlo simulations were performed to compare methods for estimating and testing hypotheses of quadratic effects in latent variable regression models. The methods considered in the current study were (a) a 2-stage moderated regression approach using latent variable scores, (b) an unconstrained product indicator approach, (c) a latent moderated structural equation method, (d) a fully Bayesian approach, and (e)

Jeffrey R. Harring; Brandi A. Weiss; Jui-Chen Hsu

2012-01-01

490

Intelligent Linear-Quadratic Optimal Output Feedback Regulator for a Deregulated Automatic Generation Control System  

Microsoft Academic Search

One of the main observed problems in the control of automatic generation control systems is the limitation to access and measurement of state variables in the real world. In order to solve this problem, an optimal output feedback method, the linear-quadratic regulator controller, is used. In the output feedback method, only measurable state variables within each control area are required

Elyas Rakhshani

2012-01-01

491

On the Distribution of Quadratic Residues and Nonresidues Modulo a Prime Number  

Microsoft Academic Search

Let P be a prime number and a 1 ; :::; a t be distinct integers modulo P . Letx be chosen at random with uniform distribution in Z P and let y i = x+a i . Weprove that the joint distribution of the quadratic characters of the y i \\

René Peralta

1992-01-01

492

The Structural Optimization of Gearbox Based on Sequential Quadratic Programming Method  

Microsoft Academic Search

Taking the gearbox of medium-sized motor truck for example and According to structural features and design requirements of the gearbox, the mathematical model of optimization which takes the basic design parameters of gearbox as design variable and takes weight loss as the target was established. Optimization tool box of MATLAB and Sequential Quadratic Programming (SQP) method were used to optimize

Huang Wei; Fu Lingling; Liu Xiohuai; Wen Zongyin; Zhao Leisheng

2009-01-01

493

Quadratic forms on complex random matrices and multiple-antenna systems  

Microsoft Academic Search

In this correspondence, the densities of quadratic forms on complex random matrices and their joint eigenvalue densities are derived for applications to information theory. These densities are represented by complex hypergeometric functions of matrix arguments, which can be expressed in terms of complex zonal polynomials. The derived densities are used to evaluate the two most important information-theoretic measures, the so-called

Tharmalingam Ratnarajah; Remi Vaillancourt

2005-01-01

494

Stable, effective fuzzy DMC algorithms with on-line quadratic optimization  

Microsoft Academic Search

Stable fuzzy DMC (FDMC) algorithms are presented in the paper. The algorithms consist in solving only quadratic optimization problems at each time instant. Therefore, they are effective and relatively little complicated. The stabilization mechanisms introduced are simple and easy to implement. These mechanisms can be used in conjunction with any variant of FDMC (fuzzy dynamic matrix control) algorithm. Exemplary simulation

P. Marusak; P. Tatjewski