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1

Point Group Symmetry  

NSDL National Science Digital Library

This is a reference web site for group theory and the properties of symmetry point groups. It covers the mathematics and science applications of symmetry relations, including the impact on interactions with specific reference to dipole-transition selection rules. Unit cells, stereograms, and 3D animated molecules are presented as examples of each point group. This web site also provides other symmetry related links and a link to references for symmetry in physics and chemistry.

Goss, Jonathan

2008-12-23

2

Teaching Point-Group Symmetry with Three-Dimensional Models  

ERIC Educational Resources Information Center

|Three tools for teaching symmetry in the context of an upper-level undergraduate or introductory graduate course on the chemical applications of group theory are presented. The first is a collection of objects that have the symmetries of all the low-symmetry and high-symmetry point groups and the point groups with rotational symmetries from…

Flint, Edward B.

2011-01-01

3

Size-dependent fivefold and icosahedral symmetry in silver clusters  

SciTech Connect

Trapped ion electron diffraction measurements on silver cluster cations, Ag{sub n}{sup +} for sizes n=36-46,55 at {approx}120 K describe an evolution in structural symmetry with increasing cluster size. Diffraction patterns characterize fivefold symmetry at smaller sizes which evolves to icosahedral symmetry at n=55. Low energy isomer structures were identified by statistical search methods and optimized by density-functional calculations. Comparison of diffraction data with these theoretical structures confirms the presence of local order having fivefold symmetry for sizes n=36-39,43 and global order having icosahedral symmetry at the closed shell size n=55.

Xing Xiaopeng; Danell, Ryan M.; Burns, Michael M.; Parks, Joel H. [Rowland Institute at Harvard, 100 Edwin H. Land Boulevard, Cambridge, Massachusetts 02142 (United States); Garzon, Ignacio L.; Michaelian, Karo [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, A.P. 20-364, 01000 Mexico, DF (Mexico); Blom, Martine N. [Institut fuer Nanotechnologie, Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe (Germany)

2005-08-15

4

Symmetry, stability, and diffraction properties of icosahedral crystals  

SciTech Connect

In a remarkable experiment on an Mn-Al alloy, Shechtman et al. observed a diffraction spectrum with icosahedral symmetry. This is inconsistent with discrete translational invariance since the symmetry includes a five-fold axis. In this paper, it is shown that the crystallography and diffraction pattern can be described by a six-dimensional space group. The crystal structure in 3d is obtained as a cut along a 3d hyperplane in a regular 6d crystal. Displacements of the 6d crystal along 6 orthogonal directions define 6 continuous symmetries for the icosahedral crystal, three of which are phase symmetries describing internal rearrangements of the atoms.

Bak, P.

1985-01-01

5

Symmetry, stability, and elastic properties of icosahedral incommensurate crystals  

Microsoft Academic Search

The symmetry and stability of icosahedral incommensurate structures and generalized two-dimensional Penrose pentagonal structures are studied. The crystallographic properties of Penrose lattices are described by five-dimensional (5D) super space groups, and the icosahedral structures are described by 6D space groups, with or without improper translations. The density in real space is given as the density along a three-dimensional plane in

Per Bak

1985-01-01

6

An Online Tutorial for Learning Symmetry and Point Groups  

NSDL National Science Digital Library

This free web-based tutorial provides the student with explanations and examples of symmetry elements and makes extensive use of interactive Java applets and flash animation to guide students in seeing the symmetry elements in real molecules. The Java applets provide images generated from crystallographic databases that can be rotated freely in real time. This interactive feature allows students to explore the symmetry of selected molecules and also to test their own understanding. Mouse-over and other flash animations also provide students with a guided means to interpret symmetry elements and how they are depicted. Each symmetry element is discussed in turn with examples and short self-tests that provide immediate feedback to the student.

7

Symmetry based fast marching method for icosahedral virus segmentation  

NASA Astrophysics Data System (ADS)

Segmentation of icosahedral virus density map from cryo-electron microscope (CryoEM) is a challenging task because virus structure is complex and density map is at low resolution. Fast marching method is widely used in segmentation, in which seed selection is essential for correct segmentation results. However, the selection of an appropriate seed is difficult. In this paper, we present the method of selecting the seed in fast marching algorithm by making use of the shape symmetry to improve the fast marching method for icosahedral virus segmentation. Based on the feature of icosahedron, we compute and get its symmetry axes inside the density map. With these symmetry axes, we specify the initial seeds with the local maxima value along symmetry axes. Further, the new data structures are presented, which can effectively reduce the memory cost when implement the fast marching algorithm. Experimental results show that the approach can obtain segmentation results of the density maps fast and accurately.

Shan, Guihua; Liu, Jun; Ye, Liang; Chi, Xuebin

2010-02-01

8

The Effect of Instructional Modality and Prior Knowledge on Learning Point Group Symmetry  

ERIC Educational Resources Information Center

Many topics in chemistry are difficult for learners to understand, including symmetry. Reasons for this difficulty include its multi-level content, instructional methodologies utilized, and learner variables. This study examined the effect of initial instructional modality and prior knowledge on learning of point group symmetry. Forty-four…

Nottis, Katharyn E. K.; Kastner, Margaret E.

2005-01-01

9

Point Groups  

NSDL National Science Digital Library

This exercise involves identifying symmetry in crystals and using that information to assign crystals to crystal systems and point groups. Students examine cardboard models and wooden blocks and fill their symmetry elements into a table. Then they figure out what what crystal system and point group each sample belongs to and fill in another table.

Perkins, Dexter

10

Icosahedral (A5) family symmetry and the golden ratio prediction for solar neutrino mixing  

Microsoft Academic Search

We investigate the possibility of using icosahedral symmetry as a family symmetry group in the lepton sector. The rotational icosahedral group, which is isomorphic to A5, the alternating group of five elements, provides a natural context in which to explore (among other possibilities) the intriguing hypothesis that the solar neutrino mixing angle is governed by the golden ratio, varphi=(1+5)\\/2. We

Lisa L. Everett; Alexander J. Stuart

2009-01-01

11

Mechanical Deformation of Spherical Viruses with Icosahedral Symmetry  

PubMed Central

Virus capsids and crystalline surfactant vesicles are two examples of self-assembled shells in the nano- to micrometer size range. Virus capsids are particularly interesting since they have to sustain large internal pressures while encapsulating and protecting the viral DNA. We therefore study the mechanical properties of crystalline shells of icosahedral symmetry on a substrate under a uniaxial applied force by computer simulations. We predict the elastic response for small deformations, and the buckling transitions at large deformations. Both are found to depend strongly on the number of elementary building blocks N (the capsomers in the case of viral shells), the Föppl-von Kármán number ? (which characterizes the relative importance of shear and bending elasticity), and the confining geometry. In particular, we show that whereas large shells are well described by continuum elasticity-theory, small shells of the size of typical viral capsids behave differently already for small deformations. Our results are essential to extract quantitative information about the elastic properties of viruses and vesicles from deformation experiments.

Vliegenthart, Gerard Adriaan; Gompper, Gerhard

2006-01-01

12

Mechanical deformation of spherical viruses with icosahedral symmetry.  

PubMed

Virus capsids and crystalline surfactant vesicles are two examples of self-assembled shells in the nano- to micrometer size range. Virus capsids are particularly interesting since they have to sustain large internal pressures while encapsulating and protecting the viral DNA. We therefore study the mechanical properties of crystalline shells of icosahedral symmetry on a substrate under a uniaxial applied force by computer simulations. We predict the elastic response for small deformations, and the buckling transitions at large deformations. Both are found to depend strongly on the number of elementary building blocks N (the capsomers in the case of viral shells), the Föppl-von Kármán number gamma (which characterizes the relative importance of shear and bending elasticity), and the confining geometry. In particular, we show that whereas large shells are well described by continuum elasticity-theory, small shells of the size of typical viral capsids behave differently already for small deformations. Our results are essential to extract quantitative information about the elastic properties of viruses and vesicles from deformation experiments. PMID:16679375

Vliegenthart, Gerard Adriaan; Gompper, Gerhard

2006-05-05

13

Icosahedral (A5) family symmetry and the golden ratio prediction for solar neutrino mixing  

NASA Astrophysics Data System (ADS)

We investigate the possibility of using icosahedral symmetry as a family symmetry group in the lepton sector. The rotational icosahedral group, which is isomorphic to A5, the alternating group of five elements, provides a natural context in which to explore (among other possibilities) the intriguing hypothesis that the solar neutrino mixing angle is governed by the golden ratio, ?=(1+5)/2. We present a basic toolbox for model building using icosahedral symmetry, including explicit representation matrices and tensor product rules. As a simple application, we construct a minimal model at tree level in which the solar angle is related to the golden ratio, the atmospheric angle is maximal, and the reactor angle vanishes to leading order. The approach provides a rich setting in which to investigate the flavor puzzle of the standard model.

Everett, Lisa L.; Stuart, Alexander J.

2009-04-01

14

Symmetry based fast marching method for icosahedral virus segmentation  

Microsoft Academic Search

Segmentation of icosahedral virus density map from cryo-electron microscope (CryoEM) is a challenging task because virus structure is complex and density map is at low resolution. Fast marching method is widely used in segmentation, in which seed selection is essential for correct segmentation results. However, the selection of an appropriate seed is difficult. In this paper, we present the method

Guihua Shan; Jun Liu; Liang Ye; Xuebin Chi

2010-01-01

15

Assessing and improving the accuracy of T-matrix calculation of homogeneous particles with point-group symmetries  

NASA Astrophysics Data System (ADS)

We present an approach for improving the accuracy of T-matrix calculation of particles with point-group symmetries that eliminates from consideration some elements of the T matrix with low accuracy. A high accuracy approach (HAA) is suggested based on symmetry related comparative analysis of the accuracy rating of evaluation of surface integrals by the extended boundary condition method (EBCM).The symmetry relation for elements of the T matrix is a consequence of the general symmetry relation for particles with point-group symmetries. A simple comparative accuracy criterion composed of matrix norms rc(Q)=?RgQ???Q-1? is suggested, where Q and RgQ are matrices computed with evaluation of surface integrals by the EBCM. An example of practical HAA application is given and results of numerical modeling of light scattering on finite polyhedral prisms are analyzed.

Volkov, Sergei N.; Samokhvalov, Ignatii V.; Kim, Dukhyeon

2013-07-01

16

Colloidal Crystallization in Confinement: Icosahedral Symmetry & Plastic-Crystal Transitions  

NASA Astrophysics Data System (ADS)

The crystallization of spherical nanoparticles in liquid droplets results under certain conditions in crystals with an icosahedral shape. Experiments with larger spherical colloids and computers simulations of hard particles demonstrate that such crystal shapes do not rely on energetic arguments, but already result from confinement and entropy alone. Experiments on rod shaped fluorescent colloidal particles that are monodisperse enough to form nematic and smectic liquid crystal phases under conditions where the double layer thickness is small compared to the diameter of the rods show that if the double layer thickness is significantly larger than the rod length plastic crystals with a body centered crystal structure are formed. In such crystals there is three dimensional positional order, but no orientational order of the rods. These plastic crystals under strong planar confinement show intriguing phase behavior where plastic crystal and full crystal phases alternate as a function of the separation between the confining plates.

van Blaaderen, Alfons

2013-03-01

17

Full Spin and Spatial Symmetry Adapted Technique for Correlated Electronic Hamiltonians: Application to an Icosahedral Cluster  

Microsoft Academic Search

One of the long standing problems in quantum chemistry had been the inability to exploit full spatial and spin symmetry of an electronic Hamiltonian belonging to a non-Abelian point group. Here we present a general technique which can utilize all the symmetries of an electronic (magnetic) Hamiltonian to obtain its full eigenvalue spectrum. This is a hybrid method based on

Shaon Sahoo; S. Ramasesha

2010-01-01

18

Point Groups, Symmetries And Non-dimensional Parameters Of Environmental Flows  

NASA Astrophysics Data System (ADS)

Patterns of environmental flows and their laboratory analogues contain continuously changing and discrete elements. A fine structure that is a set of high gradient interfaces helps to identify basic elements in patterns of vortex, convective cells and waves. Dif- ferent illustrating slides are presented. The goal of the paper is to derive conditions of adequate modelling and some observed parameters from a set of governing equa- tions directly. We apply continuous (Lie) groups theory to study general properties of solutions. To perform numerous auxiliary calculations symbolic calculations sys- tem Maple was adopted. We have investigated symmetry properties of a general set of multi-component stratified fluid equations and different well-known models: sta- tionary equations, Boussinesq approximation, 1D and 2D flows, elimination of diffu- sion, temperature transfer and viscosity effects, the boundary layer model and different well-known models of turbulence. In general case we have performed detail investiga- tion of the effects of algebraic equation of state on the symmetry properties of the set of governing equations. We found that the general set off governing equations is char- acterised by basic set of symmetries, which contains ten-parametric Galilean group of symmetry and infinite-dimensional sub-algebra of pressure shifts. Additional ex- pansion groups can be found if the state equation is taken in a right form. Diffusion impact on invariant properties more essentially than viscosity. 1D transient and sta- tionary problems are characterised by irreducible set of symmetries. One of specific generators corresponding to the expansion group of the heat conduction equation de- scribes set of diffusion induced internal boundary currents producing sets of boundary layers on a moving body. Analysis of symmetries in the expanded space of jets includ- ing all known non-dimensional parameters reveal the number of non-dimensional pa- rameters completely describing stratified flows. Model of isotropic turbulence does not satisfy the Galilean principle of relativity. Some more sophisticated energy-dissipation models have no the rotational symmetries. Constructed exact solutions, recommenda- tions for the choice of the sets of basic solutions and conditions of applicability of superposition principle for non-linear phenomena are presented. Data of laboratory experiments are used to illustrate main theoretical conclusions.

Baydulov, Vasiliy G.; Chashechkin, Yuli D.

19

Nuclear Point-Group Symmetries and New Ideas about Nuclear Stability:. AN Overview  

NASA Astrophysics Data System (ADS)

The nuclear mean-field theory and the group representation theory can be used to optimise the search for strong nuclear shell effects. The two theories allow to correlate the symmetry aspects with the presence of large gaps in the single-particle spectra, facilitate in this way the conditions of search for strong nucleonic- and nuclear-binding and thus for an increased nuclear stability. In this article we give a short overview of the related on-going research, focussing on the results of the TetraNuc Collaboration.

Dudek, J.; Curien, D.; Gó?d?, A.; Mazurek, K.

20

Human Rhinovirus Subviral A Particle Binds to Lipid Membranes over a Twofold Axis of Icosahedral Symmetry.  

PubMed

Minor group human rhinoviruses bind low-density lipoprotein (LDL) receptors for endocytosis. Once they are inside endosomes, the acidic pH triggers their dissociation from the receptors and conversion into hydrophobic subviral A particles; these attach to the membrane and transfer their single-strand, positive-sense RNA genome into the cytosol. Here, we allowed human rhinovirus 2 (HRV2) A particles, produced in vitro by incubation at pH 5.4, to attach to liposomes; cryo-electron microscopy 3-dimensional single-particle image reconstruction revealed that they bind to the membrane around a 2-fold icosahedral symmetry axis. PMID:23946453

Kumar, Mohit; Blaas, Dieter

2013-08-14

21

Point-group symmetrized boson representation. Algebraic solution for symmetry-adapted bases of {ital O}{sub {ital h}}  

SciTech Connect

A point group symmetrized boson representation (SBR) is introduced that is particularly convenient for describing molecular vibrations. In this paper the SBR is elucidated using the example of the molecule {ital SF}{sub 6} with {ital O}{sub {ital h}} symmetry. The advantages of the SBR are that its basis vectors have a clear physical picture, their number is very small (equal to one-eighth of the dimension of the reducible representation for {ital O}{sub {ital h}}), and the irreducible bases for any concrete cases can be obtained trivially from those for the general case without any projection. All the irreducible bases for the group chains {ital O}{sub {ital h}}{improper_superset}{ital D}{sub 4}{improper_superset}{ital C}{sub 4} or {ital O}{sub {ital h}}{improper_superset}{ital D}{sub 4}{improper_superset}{ital D}{sub 2} are tabulated once and for all. As an application, the Hamiltonian in the algebraic model of Iachello and Oss for stretching vibrations of the molecule {ital SF}{sub 6} is diagonalized in the symmetry adapted bases. {copyright} {ital 1996 American Institute of Physics.}

Chen, J. [Department of Physics, Nanjing University, Nanjing, 210008, Peoples Republic of (China)]|[Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States); Klein, A. [Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States); Ping, J. [Department of Physics, Nanjing Normal University, Nanjing, 210097, Peoples Republic of (China)

1996-05-01

22

C70, C80, C90 and carbon nanotubes by breaking of the icosahedral symmetry of C60.  

PubMed

The icosahedral symmetry group H3 of order 120 and its dihedral subgroup H2 of order 10 are used for exact geometric construction of polytopes that are known to exist in nature. The branching rule for the H3 orbit of the fullerene C60 to the subgroup H2 yields a union of eight orbits of H2: four of them are regular pentagons and four are regular decagons. By inserting into the branching rule one, two, three or n additional decagonal orbits of H2, one builds the polytopes C70, C80, C90 and nanotubes in general. A minute difference should be taken into account depending on whether an even or odd number of H2 decagons are inserted. Vertices of all the structures are given in exact coordinates relative to a non-orthogonal basis naturally appropriate for the icosahedral group, as well as relative to an orthonormal basis. Twisted fullerenes are defined. Their surface consists of 12 regular pentagons and 20 hexagons that have three and three edges of equal length. There is an uncountable number of different twisted fullerenes, all with precise icosahedral symmetry. Two examples of the twisted C60 are described. PMID:24132219

Bodner, Mark; Patera, Ji?í; Szajewska, Marzena

2013-09-12

23

Normal mode calculations of icosahedral viruses with full dihedral flexibility by use of molecular symmetry.  

PubMed

The study of the dynamics and thermodynamics of small icosahedral virus capsids is an active field of research. Normal mode analysis is one of the computational tools that can provide important insights into the conformational changes of the virus associated with cell entry or caused by changing of the physicochemical environment. Normal mode analysis of virus capsids has been limited due to the size of these systems, which often exceed 50,000 residues. Here we present the first normal mode calculation with full dihedral flexibility of several virus capsids, including poliovirus, rhinovirus, and cowpea chlorotic mottle virus. The calculations were made possible by applying group theoretical methods, which greatly simplified the calculations without any approximation beyond the all-atom force field representations in general use for smaller protein systems. Since a full Cartesian basis set was too large to be handled by the available computer memory, we used a basis set that includes all internal dihedral angles of the system with the exception of the peptide bonds, which were assumed rigid. The fluctuations of the normal modes are shown to correlate well with crystallographic temperature factors. The motions of the first several normal modes of each symmetry type are described. A hinge bending motion in poliovirus was found that may be involved in the mechanism by which bound small molecules inhibit conformational changes of the capsid. Fully flexible normal mode calculations of virus capsids are expected to increase our understanding of virus dynamics and thermodynamics, and can be useful in the refinement of cryo-electron microscopy structures of viruses. PMID:15922356

van Vlijmen, Herman W T; Karplus, Martin

2005-04-07

24

Crystallography of Icosahedral Crystals.  

National Technical Information Service (NTIS)

The crystallography of icosahedral crystals is constructed. The actual three-dimensional crystal is represented by a three-dimensional cut in a regular six-dimensional periodic crystal with symmetry described by a six-dimensional space group, and the posi...

P. Bak

1986-01-01

25

Crystallography of icosahedral crystals  

Microsoft Academic Search

The crystallography of icosahedral crystals is constructed. The actual three-dimensional crystal is represented by a three-dimensional cut in a regular six-dimensional periodic crystal with symmetry described by a six-dimensional space group, and the positions of atoms correspond to an arrangement of hypersurface segments. The resulting crystal cannot in general be viewed as a space-filling arrangemment of a small number of

P. Bak

1986-01-01

26

Crystallography of icosahedral crystals  

SciTech Connect

The crystallography of icosahedral crystals is constructed. The actual three-dimensional crystal is represented by a three-dimensional cut in a regular six-dimensional periodic crystal with symmetry described by a six-dimensional space group, and the positions of atoms correspond to an arrangement of hypersurface segments. The resulting crystal cannot in general be viewed as a space-filling arrangemment of a small number of different ''Penrose tiles.'' The intensities of Bragg spots are given directly as the intensities of Bragg spots of the six-dimensional crystal. 16 refs., 2 figs.

Bak, P.

1986-01-01

27

Metallic phase with long-range orientational order and no translational symmetry  

Microsoft Academic Search

A metallic solid (Al-14-at. pct.-Mn) with long-range orientational order, but with icosahedral point group symmetry, which is inconsistent with lattice translations, has been observed. Its diffraction spots are as sharp as those of crystals but cannot be indexed to any Bravais lattice. The solid is metastable and forms from the melt by a first-order transition.

D. Shechtman; I. Blech; D. Gratias; J. W. Cahn

1984-01-01

28

Algebraic expressions for irreducible bases of icosahedral group  

SciTech Connect

The recently discovered point-group symmetrized boson representation (SBR) is constructed for the icosahedral group I{sub h}. With the aid of the SBR, succinct algebraic expressions for the irreducible bases and irreducible matrices have been found. Irreducible bases for non-regular representations can be found easily from those of the regular representation without projections. Explicit expressions of the irreducible bases are given for the molecule B{sub 12}H{sub 12} for several important cases. It is shown that, far from being {open_quotes}chaotic{close_quotes} in structure, the 120 irreducible matrices of I{sub h} have a high degree of symmetry in that the 14400 entries can be reproduced from a few dozen entries according to three rules. {copyright} {ital 1997 American Institute of Physics.}

Chen, J. [Department of Physics, Nanjing University, Nanjing, 210008, Peoples Republic of (China)]|[Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States); Ping, J. [Department of Physics, Nanjing Normal University, Nanjing, 210097, Peoples Republic of (China)]|[Department of Physics, Yale University, New Haven, Connecticut 06511-6666 (United States)

1997-01-01

29

Lattice vibrations of the icosahedral solid ?-boron  

NASA Astrophysics Data System (ADS)

Crystalline ?-boron consists of B12 icosahedra in a rhombohedral lattice of R3¯m space-group symmetry. We here carry out a classical force-field analysis of the lattice vibrations. The q=0 Brillouin-zone vibrations are treated as those of a D3d-point-group-symmetry B12 cluster perturbed by intericosahedral crystalline forces; valence-force constants are fitted to account for Raman and ir spectral data. Two-centered intericosahedral bonds are found to be twice as strong as intraicosahedral bonds, while three-centered crystalline bonds are almost as strong as those within a B12 unit. The highest-frequency Raman line arises from the breathing mode, strongly perturbed by the two-centered interactions. The lowest-observed-frequency Raman line is attributed to B12 libration. As crystal-force-field strengths are turned up, noncrossing of frequencies is encountered; we, therefore, correlate ?-crystal modes with Ih regular-icosahedral and D3d B12-cluster modes through eigenvector expansions. Useful classical predictions are made of ir intensities for wave vector q=0 modes by considering adjacent bond stretching; a prediction of Raman intensities in terms of bond polarizabilities appears to be of very limited value. The phonon analysis is extended from the Brillouin-zone center to the edges by introducing phase-angle differences along two distinct (one C3 and one C2) rotational-symmetry axes. The acoustical-branch wave speeds are predicted to be 1.1×106 and 0.38×106 cm/sec for the c-direction longitudinal and transverse components, respectively. Finally, we consider possible origins of the 525-cm-1 Raman line with anomalous polarization and width; most likely this is a Raman electronic line associated with vacancies and B11 units.

Beckel, Charles L.; Yousaf, Mohammad; Fuka, Mary Z.; Raja, Shagufta Y.; Lu, Ning

1991-08-01

30

Weyl phases in point-group symmetric superconductors  

NASA Astrophysics Data System (ADS)

We study superconductivity in a Weyl semimetal with broken time-reversal symmetry and stabilized by a point-group symmetry. The resulting superconducting phase is characterized by topologically protected bulk nodes and surface states with Fermi arcs. The topological invariant governing the system is calculated using changes in eigenvalues of the point-group operator along high-symmetry momentum lines. We show that this invariant is determined by the Fermi surface topology of the Weyl semimetal. We discuss the effect of surface orientation and C4-breaking strain as possible experimental consequences.

Shivamoggi, Vasudha; Gilbert, Matthew J.

2013-10-01

31

Six-dimensional structure model for the icosahedral quasicrystal Al6CuLi3  

NASA Astrophysics Data System (ADS)

The structure of icosahedral quasicrystals can be described either by a quasiperiodic density function in three-dimensional (physical) space, or by a periodic density function in six-dimensional (6D) space. The real structure is obtained as a particular 3D section of the 6D density function. The 6D description involves 6D bodies, which on intersection by 3D space give rise to atoms in physical space. In this paper we derive all possible perpendicular-space shapes belonging to the 6D atoms, which arise for 6D structures describing any decoration of the 3D Penrose tiling. These results are applied to icosahedral Al6CuLi3, for which a 6D structure model is proposed. Refinement of this model on single-crystal x-ray-diffraction data shows the structure to be close to that of a decorated Penrose tiling. Unlike Al73Mn21Si6, it is found that a perpendicular-space shape is necessary which has a lower internal symmetry than given by the icosahedral point group.

van Smaalen, Sander; de Boer, Jan L.; Shen, Yong

1991-01-01

32

Form, symmetry and packing of biomacromolecules. V. Shells with boundaries at anti-nodes of resonant vibrations in icosahedral RNA viruses.  

PubMed

The RNA viruses cowpea chlorotic mottle, satellite tobacco mosaic, pariacoto and MS2, already considered in part IV of this series of papers [Janner, A. (2011a), Acta Cryst. A67, 517-520], are investigated further, with the aim to arrive at a possible physical basis for their structural properties. The shell structure of the filled capsid is analyzed in terms of successive spherical boundaries of the sets of icosahedral equivalent chains. By inversion in the sphere enclosing the capsid, the internal boundaries are transformed into external ones, which are more easily visualized. This graphical procedure reveals the presence of regularly spaced shells with boundaries fitting with anti-nodal surfaces of the virus considered as an elastic resonator. The centers of gravity of the various chains occur in the nodal regions of eigenvibrations with wavelength ? = R(0)/K(0), where R(0) is the radius of the virus and K(0) takes one of the values 12, 6, 4, 3, depending on the mode. The resonator model is consistent with practically all spherical shell boundaries, whereas deviations are observed for the icosahedral axial modes, which apparently play a secondary role with respect to the spherical ones. Both the spherical and the axial anti-nodal surfaces fit very well with the packed structure of the viruses in the crystal which, accordingly, is expected to have eigenfrequencies related to those of the virus. These results open the way to a better understanding of the possibility of breaking the capsid using resonant forced oscillations excited, for example, by an applied elastic shock or by irradiation with femtosecond laser pulses, as already realised by K.-T. Tsen and co-workers. An alternative `plywood' model connected to the extreme elastic properties of the capsid is also considered. PMID:22011468

Janner, A

2011-10-13

33

Highly symmetric Mn sites in icosahedral Ti-Mn  

SciTech Connect

We find that the {sup 55}Mn NMR linewidth and Knight shift of icosahedral Ti{sub 63}Mn{sub 37} ({ital i}-TiMn) are identical to those of the crystalline phases obtained upon annealing. Comparison of the linewidth in {ital i}-TiMn and a bcc Ti-Mn solid solution shows that the Mn sites in both phases have a nearly cubic or higher symmetry. These measurements and our analysis provide strong evidence for a large density of structurally ordered, highly symmetric sites in an icosahedral alloy and demonstrate that a high degree of structural disorder is not an intrinsic property of the icosahedral phase.

Jeong, E.; Holzer, J.C.; Carlsson, A.E.; Conradi, M.S.; Fedders, P.A.; Kelton, K.F. (Department of Physics, Washington University, St Louis, Missouri 63130 (US))

1990-01-15

34

Bulk topological invariants in noninteracting point group symmetric insulators  

NASA Astrophysics Data System (ADS)

We survey various quantized bulk physical observables in two- and three-dimensional topological band insulators invariant under translational symmetry and crystallographic point group symmetries (PGS). In two-dimensional insulators, we show that (i) the Chern number of a Cn-invariant insulator can be determined, up to a multiple of n, by evaluating the eigenvalues of symmetry operators at high-symmetry points in the Brillouin zone; (ii) the Chern number of a Cn-invariant insulator is also determined, up to a multiple of n, by the Cn eigenvalue of the Slater determinant of a noninteracting many-body system; and (iii) the Chern number vanishes in insulators with dihedral point groups Dn, and the quantized electric polarization is a topological invariant for these insulators. In three-dimensional insulators, we show that (i) only insulators with point groups Cn, Cnh, and Sn PGS can have nonzero 3D quantum Hall coefficient and (ii) only insulators with improper rotation symmetries can have quantized magnetoelectric polarization P3 in the term P3E·B, the axion term in the electrodynamics of the insulator (medium).

Fang, Chen; Gilbert, Matthew J.; Bernevig, B. Andrei

2012-09-01

35

The space groups of icosahedral quasicrystals and cubic, orthorhombic, monoclinic, and triclinic crystals  

NASA Astrophysics Data System (ADS)

In 1962 Bienenstock and Ewald described a simple and systematic method for computing all the crystallographic space groups in Fourier space. Their approach is reformulated and further simplified, starting from the definition of the point group of a structure as the set of operations that take it into something indistinguishable and not merely identical to within a translation. The reformulation does not require periodicity, making it possible to define and compute on an equal footing the space groups for crystals, quasicrystals, and incommensurately modulated structures, without having to digress into the crystallography of unphysically many dimensions, and using only simple geometry and the most elementary properties of symmetry groups. The general scheme is illustrated by a unified computation of all the icosahedral, cubic, orthorhombic, monoclinic, and triclinic space groups. The remaining (axial) crystallographic and quasicrystallographic space groups have been discussed in a companion paper.

Mermin, N. David

1992-01-01

36

Symmetry Tutorial  

NSDL National Science Digital Library

An interactive collection of over 60 unique molecules with interactive display of all symmetry elements and animation of all operations. In addition, an interactive point group symmetry tutorial using the Jmol Java and Chime is available.

Johnson, Dean

37

Towards a classification of icosahedral viruses in terms of indexed polyhedra  

NASA Astrophysics Data System (ADS)

The surface structures of viral capsids are described in terms of polyhedra with icosahedral symmetry and rational indices. It is shown that the Caspar-Klug and the Twarock approaches can be embedded into this framework. The crystallographic scaling transformations are worked out explicitly and are used to derive the icosahedral forms for some viruses, including the Caspar-Klug and Twarock cases.

Janner, A.

2006-09-01

38

Symmetry  

NSDL National Science Digital Library

This website contains interactive activities and explanations of reflective and rotational symmetry. Interactive explorations include identifying letters with reflective symmetry, identifying common symbols and objects with rotational symmetry, creating and guessing tile patterns with rotational and reflective symmetry, and creating a snowflake. Other pages include examples created through using these tools and information for teachers.

Edkins, Jo

2007-01-01

39

Icosahedral Structure of Aluminum-Lithium Aluminum-Copper and Aluminum-Copper Alloys  

NASA Astrophysics Data System (ADS)

Icosahedral alloys are materials whose diffraction patterns display the symmetry of the icosahedron, which is incompatible with the translational symmetry of a crystal. This dissertation describes several diffraction experiments on icosahedral alloys. The incommensurability of icosahedrally symmetric structures leads to extra degrees of freedom in their description; we attempt to understand the unusual disorder of icosahedral phases linked to these extra degrees of freedom. In Chapter I we review the unique properties of icosahedral phases, and then present the results of diffraction experiments in the remaining five chapters. The first (Chapter II) is a crystallographic refinement of a crystalline phase, R Al_{5 cdot 6}Li_{2 cdot 9} Cu, related to icosahedral Al-Li-Cu. We find that this phase is a body centered cubic (BCC) packing of nearly -icosahedral clusters of atoms. Next we present in Chapter III the measurement of over 200 diffraction peaks from a single grain sample of icosahedral Al-Li-Cu. Both integrated intensity of diffraction peaks and their half width at half maximum (HWHM) are modeled as functions of both G _parallel (normal reciprocal space wavevector) and G_bot (the three extra degrees of freedom arising from the icosahedral structure). Chapter IV presents measurements of diffuse scattering in i-(AlLiCu). In Chapter V x-ray diffraction peaks of the icosahedral phase of Al-Cu-Ru are found to have no dependence of HWHM on G_bot , as had been the case of all other alloys previously studied. Finally Chapter VI describes diffraction measurements of icosahedral Al-Cu-Fe, from samples annealed at various temperatures. Annealing at 600^circ C introduces phason disorder into the alloy, while annealing at 700^circC removes it. This result is consistent with random tiling models of the icosahedral phase.

Guryan, Christopher Alan

1990-08-01

40

Truncated Icosahedral Gravitational Wave Antenna.  

NASA Astrophysics Data System (ADS)

A spherical gravitational wave detector can be equally sensitive to a wave from any direction, and also able to measure its direction and polarization. We derive a set of equations to describe the mechanics of a spherical antenna coupled to an arbitrary number of attached mechanical resonators. A special arrangement of 6 resonators is proposed, which we term a Truncated Icosahedral Gravitational Wave Antenna, or TIGA. An analytic solution to the equations of motion is found for this case. We find that direct deconvolution of the gravitational tensor components can be accomplished with a specified set of linear combinations of the resonator outputs, which we call the mode channels. We develop one simple noise model for this system and calculate the resulting strain noise spectrum. We conclude that the angle-averaged energy sensitivity will be 56 times better than for the typical equivalent bar-type antenna with the same noise temperature. We have constructed a prototype TIGA. This shape was machined from an Al 6063 cylindrical bar, is 84 cm in diameter, has its first quadrupole resonances near 3200 Hz, and is suspended from its center of mass. The frequencies of the lowest seven multiplets were found to closely match those calculated for a sphere. We observed the motion of the prototype's surface using 6 accelerometers attached to its surface in the symmetric truncated icosahedral arrangement. We have tested a first order direction finding algorithm, which uses fixed linear combinations of six accelerometer responses to first infer the relative amplitudes of the quadrupole modes and from these the location of the impulse. The six accelerometers were then replaced by six mechanical resonators. A strain gauge was used to monitor the radial motion of each resonator. The frequency response of the of coupled system was measured and compared to the eigenvalue solutions of the equations of motion. It was concluded that deviations from perfect symmetry have a second order effect on our ability to observe the prototype's quadrupole modes and thus determine the location and direction of the initial excitation.

Merkowitz, Stephen Michael

1995-01-01

41

Symmetry  

NSDL National Science Digital Library

This is an introduction to basic symmetry elements. Students make drawings that show good examples of rotation axes and mirror planes and inversion centers with and without a 2-fold axis. They describe real objects a mirror plane, an inversion center, and 2, 3, 4, and 6-fold axes in 3D. They think about symmetry in atomic structures and indicate which symmetry elements are present in ball and stick models of minerals. Then they count the different kinds of symmetry elements present in wooden blocks and real minerals.

Perkins, Dexter

42

Cubic Icosahedra? A Problem in Assigning Symmetry  

ERIC Educational Resources Information Center

|There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…

Lloyd, D. R.

2010-01-01

43

Polynomial tensors for double point groups  

Microsoft Academic Search

Generating functions for (Gammar,Gammam) tensors for each pair of irreducible representations Gammar and Gammam are calculated for each double point group. A (Gammar,Gammam) tensor transforms according to Gammar and its components are polynomials in another tensor transforming by Gammam. The actual tensors are given for the groups (d)Cn, (d)Dn, (d)T and for some representations Gammam of (d)0. Certain of the

P. E. Desmier; R. T. Sharp

1979-01-01

44

Disorder in Al-li-cu and Al-mn-si icosahedral alloys.  

PubMed

Faceted dendrites of icosahedral AL(6)Li(3)Cu have been studied by high-resolution x-ray scattering. The samples display long-range icosahedral symmetry both in their diffraction patterns and in their macroscopic morphology. Despite the appearance of well-defined facets, the samples have a high degree of atomic disorder. The Bragg peaks have symmetry-dependent shapes and widths that scale linearly with G perpendicular (phason momentum). The peak widths are surprisingly similar to those found in icosahedral Al-Mn-Si alloys in both their absolute magnitude and their dependence on G perpendicular. The origin of these features in models for the icosahedral phase is discussed. PMID:17816544

Heiney, P A; Bancel, P A; Horn, P M; Jordan, J L; Laplaca, S; Angilello, J; Gayle, F W

1987-10-30

45

New icosahedral nanoclusters in crystal structures of intermetallic compounds: Topological types of 50-atom deltahedra D50 in samson phases ?-Mg2Al3 and ?-Mg23Al30  

NASA Astrophysics Data System (ADS)

A database of intermetallic compounds has been compiled using the TOPOS program package. This database includes 514 topological types, containing 12- and 13-atom icosahedral i clusters. An isolated group of 1649 i clusters is described by 14 point groups and their maximum symmetry D 3 d (bar 3 m) and T h ( m bar 3) is established, respectively, in 47 and 25 types of crystal structures. A structural analysis of the outer quasispherical shells showed that local 63-atom i configurations 1@12@50, which contain 50 atoms in the second layer, are implemented in 8 out of 19 cases. Examples of new topologically different types of 50-atom D50 deltahedra in the Samson phases ?-Mg23Al30 and ?-Mg2Al3 are presented. Four topologically different sites with coordination numbers of 5, 6, 6, or 7 are established in the ? shell and seven sites with coordination numbers of 5, 5, 6, 6, 6, 6, or 7 are found in the ? shell. The inner i clusters for the ?-Mg2Al3 structure (with the symmetry bar 3 m) and the ?-Mg23Al30 structure (with the symmetry bar 3) have a similar chemical composition, i.e., Mg7Al6 and Mg6Al7, and their 50-atom shells are chemically identical to 18Mg + 32Al. The configurations found supplement the series of known two-layer icosahedral Bergman and Mackay clusters in the form of deltahedra with 32- and 42-atom shells.

Blatov, V. A.; Ilyushin, G. D.

2012-12-01

46

Structures of giant icosahedral eukaryotic dsDNA viruses  

PubMed Central

In the last twenty years, numerous giant, dsDNA, icosahedral viruses have been discovered and assigned to the nucleocytoplasmic large dsDNA virus (NCLDV) clade. The major capsid proteins of these viruses consist of two consecutive jelly-roll domains, assembled into trimers, with pseudo 6-fold symmetry. The capsomers are assembled into arrays that have either p6 (as in Paramecium bursaria Chlorella virus-1) or p3 symmetry (as in Mimivirus). Most of the NCLDV viruses have a membrane that separates the nucleocapsid from the external capsid.

Xiao, Chuan; Rossmann, Michael G.

2011-01-01

47

Group theory of icosahedral virus capsid vibrations: a top-down approach.  

PubMed

We explore the use of a top-down approach to analyse the dynamics of icosahedral virus capsids and complement the information obtained from bottom-up studies of viral vibrations available in the literature. A normal mode analysis based on protein association energies is used to study the frequency spectrum, in which we reveal a universal plateau of low-frequency modes shared by a large class of Caspar-Klug capsids. These modes break icosahedral symmetry and are potentially relevant to the genome release mechanism. We comment on the role of viral tiling theory in such dynamical considerations. PMID:19014954

Peeters, Kasper; Taormina, Anne

2008-10-29

48

Formation of an icosahedral structure during the freezing of gold nanoclusters: surface-induced mechanism.  

PubMed

The freezing behavior of gold nanoclusters was studied by employing molecular dynamics simulations based on the semiempirical embedded-atom method. Investigations of the gold nanoclusters revealed that, just after freezing, ordered nanosurfaces with a fivefold symmetry were formed with interior atoms remaining in the disordered state. Further lowering of temperatures induced nanocrystallization of the interior atoms that proceeded from the surface towards the core region, finally leading to an icosahedral structure. These dynamic processes explain why the icosahedral cluster structure is dominantly formed in spite of its energetic metastability. PMID:12513216

Nam, H-S; Hwang, Nong M; Yu, B D; Yoon, J-K

2002-12-18

49

So-called icosahedral and decagonal quasicrystals are twins of an 820-atom cubic crystal  

NASA Astrophysics Data System (ADS)

It is proposed that a molten alloy may contain a 104-atom cluster with icosahedral symmetry and largely icosahedral packing. The cluster may be described as involving twenty interpenetrating Friauf (1927) polyhedra. On rapid freezing these clusters form cubic crystals related to the beta-W structure. The structure is compatible with X-ray and neutron powder diffraction patterns, the single-crystal precession X-ray patterns of CuLi3Al6, the electron diffraction photographs, and the high-resolution electron micrographs.

Pauling, Linus

1987-01-01

50

Distinct band gaps and isotropy combined in icosahedral band gap materials  

NASA Astrophysics Data System (ADS)

Icosahedral band gap materials (BGMs) optimally combine the distinct band gaps of periodic BGMs with the high rotational symmetry of quasiperiodic structures. This is shown experimentally for longitudinal and transverse polarized elastic waves in a phononic crystal based on the three-dimensional Penrose tiling (3D-PT) and applies equally to photonic crystals. The ability of icosahedral BGMs to form Bragg-type band gaps follows from the similarity between the 3D-PT and the face-centered cubic structure (its periodic average structure). The 3D quasiperiodic BGM lacks bands of strong transmission like random or disordered BGMs but shows clear band gaps like periodic BGMs do.

Sutter-Widmer, D.; Neves, P.; Itten, P.; Sainidou, R.; Steurer, W.

2008-02-01

51

Order in metallic glasses and icosahedral crystals  

Microsoft Academic Search

The relationship between short-range icosahedral order in metallic glasses and long-range order in icosahedral crystals is explored. Metallic-glass structure factors are assumed to describe liquids in metastable equilibrium just above the glass transition. A density-functional mean-field theory is then used to search for nearby crystalline states with a lower free energy. We find that undercooled liquids are metastable with respect

Subir Sachdev; David R. Nelson

1985-01-01

52

Exploring the Symmetry and Mechanism of Virus Capsid Maturation Via an Ensemble of Pathways  

PubMed Central

Many icosahedral viruses undergo large-scale conformational transitions between icosahedrally symmetric conformations during their life cycles. However, whether icosahedral symmetry is maintained along the transition pathways for this process is unknown. By employing a simplified and directed structure-based potential we compute an ensemble of transition pathways for the maturation transition of bacteriophage HK97. We observe localized symmetry-breaking events, but find that the large-scale displacements are dominated by icosahedrally symmetric deformation modes. We find that all pathways obey a common mechanism characterized by formation of pentameric contacts early in the transition.

May, Eric R.; Feng, Jun; Brooks, Charles L.

2012-01-01

53

A homology modeling method of an icosahedral viral capsid: inclusion of surrounding protein structures 1 1 Color Plates for this article are on pages 137–142  

Microsoft Academic Search

A methodological development is presented for homology modeling of an icosahedrally symmetric assembly of proteins. In the method, a main-chain structure of an asymmetric unit of a protein assembly is constructed and structure refinement is performed, taking the surrounding symmetry-related proteins into consideration with rotational symmetry boundary conditions. To test the procedure, three models of a poliovirus capsid were constructed

Teruyo Yoneda; Shigetaka Yoneda; Naoko Takayama; Masako Kitazawa; Hideaki Umeyama

1999-01-01

54

Surface structures of Al-Pd-Mn and Al-Cu-Fe icosahedral quasicrystals  

SciTech Connect

In this dissertation, the author reports on the surface structure of i-Al-Pd-Mn twofold, threefold, fivefold and i-Al-Cu-Fe fivefold surfaces. The LEED studies indicate the existence of two distinct stages in the regrowth of all four surfaces after Ar{sup +} sputtering. In the first stage, upon annealing at relatively low temperature: 500K--800K (depending on different surfaces), a cubic phase appears. The cubic LEED patterns transform irreversibly to unreconstructed quasicrystalline patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically-identical, but symmetrically-inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. These results may be general among Al-rich, icosahedral materials. STM study of Al-Pd-Mn fivefold surface shows that terrace-step-kink structures start to form on the surface after annealing above 700K. Large, atomic ally-flat terraces were formed after annealing at 900K. Fine structures with fivefold icosahedral symmetry were found on those terraces. Data analysis and comparison of the STM images and structure model of icosahedral Al-Pd-Mn suggest that the fine structures in the STM images may be the pseudo Mackay (PMI) clusters which are the structure units of the structure model. Based upon his results, he can conclude that quasicrystalline structures are the stable structures of quasicrystal surfaces. In other words, quasicrystalline structures extend from the bulk to the surface. As a result of the effort reported in this dissertation, he believes that he has increased his understanding of the surface structure of icosahedral quasicrystals to a new level.

Shen, Z.

1999-02-12

55

Beta cell device using icosahedral boride compounds  

DOEpatents

A beta cell for converting beta-particle energies into electrical energy having a semiconductor junction that incorporates an icosahedral boride compound selected from B.sub.12 As.sub.2, B.sub.12 P.sub.2, elemental boron having an .alpha.-rhombohedral structure, elemental boron having a .beta.-rhombohedral structure, and boron carbides of the chemical formula B.sub.12-x C.sub.3-x, where 0.15icosahedral boride compound self-heals, resisting degradation from radiation damage.

Aselage, Terrence L. (62 Avenida Del Sol, Cedar Crest, NM 87008); Emin, David (1502 Harvard Ct., NE., Albuquerque, NM 87106-3712)

2002-01-01

56

Experimental Evidence of Icosahedral and Decahedral Packing in One-Dimensional Nanostructures  

PubMed Central

The packing of spheres is a subject that has drawn the attention of mathematicians and philosophers for centuries, and that currently attracts the interest of the scientific community in several fields. At the nanoscale, the packing of atoms affect the chemical and structural properties of the material, and hence, its potential applications. This report describes the experimental formation of five-fold nanostructures by the packing of interpenetrated icosahedral and decahedral units. These nanowires, formed by the reaction of a mixture of metal salts (Au and Ag) in the presence of oleylamine, are obtained when the chemical composition is specifically Ag/Au=3/1. The experimental images of the icosahedral nanowires have a high likelihood with simulated electron micrographs of structures formed by two or three Boerdijk-Coxeter-Bernal helices roped on a single structure, whereas for the decahedral wires, simulations using a model of adjacent decahedra match the experimental structures. To our knowledge, this is the first report of the synthesis of nanowires formed by the packing of structures with five-fold symmetry. These icosahedral nanowire structures remind those of quasicrystals that can only be formed if at least two atomic species are present and in which icosahedral and decahedral packing has been found for bulk crystals.

Velazquez-Salazar, J. Jesus; Esparza, Rodrigo; Mejia-Rosales, Sergio Javier; Estrada-Salas, Ruben; Ponce, Arturo; Deepak, Francis Leonard; Castro-Guerrero, Carlos; Jose-Yacaman, Miguel

2011-01-01

57

Landau theory of crystallization and the capsid structures of small icosahedral viruses  

NASA Astrophysics Data System (ADS)

A new approach to the capsid structures of small viruses with spherical topology and icosahedral symmetry is proposed. It generalizes Landau theory of crystallization to describe icosahedral viral shells self-assembled from identical asymmetric proteins. An explicit method which predicts the positions of centers of mass for the proteins constituting the shell is discussed in detail. The method is based on irreducible density distribution function which generates the protein positions. The universal form of the density distribution function which contains no fitting parameter permits to classify the capsids structures of small viruses. The theory describes in a uniform way both the structures satisfying the well-known Caspar and Klug geometrical model for capsid construction and those violating it. A group theory analysis of the Caspar and Klug model and of the “quasiequivalence” principle for protein environments in viral capsids is given. The molecular basis of difference in protein environments and peculiarities in the assembly thermodynamics are also discussed.

Lorman, V. L.; Rochal, S. B.

2008-06-01

58

Quantum transport through single and multilayer icosahedral fullerenes  

NASA Astrophysics Data System (ADS)

We use a tight-binding Hamiltonian and Green functions methods to calculate the quantum transmission through single-wall fullerenes and bilayered and trilayered onions of icosahedral symmetry attached to metallic leads. The electronic structure of the onion-like fullerenes takes into account the curvature and finite size of the fullerenes layers as well as the strength of the intershell interactions depending on to the number of interacting atom pairs belonging to adjacent shells. Misalignment of the symmetry axes of the concentric iscosahedral shells produces breaking of the level degeneracies of the individual shells, giving rise some narrow quasi-continuum bands instead of the localized discrete peaks of the individual fullerenes. As a result, the transmission function for non symmetrical onions is rapidly varying functions of the Fermi energy. Furthermore, we found that most of the features of the transmission through the onions are due to the electronic structure of the outer shell with additional Fano-like antiresonances arising from coupling with or between the inner shells.

Lovey, Daniel A.; Romero, Rodolfo H.

2013-10-01

59

Theoretical study on icosahedral water clusters  

NASA Astrophysics Data System (ADS)

Here we present a structural study of different gas hydrates using the B3LYP hybrid DFT exchange-correlation functional. A new concept for viewing the icosahedral cluster as an expansion of dodecahedral subclusters is introduced. The investigated structures consist of 280 water molecules. Structural and orientational features of various guest molecules occupying the central cavity of the clusters are established. It was found that water as the guest molecule has the highest stabilization energy in studied clusters. The conformational changes in dimer and trimer water molecules upon incorporation into hydrate cavity are discussed. The influence of second- and third-order solvent shells is illustrated on example of icosahedral water cluster derivatives.

Loboda, Oleksandr; Goncharuk, Vladyslav

2010-01-01

60

Density-Wave Theory of the Capsid Structure of Small Icosahedral Viruses  

NASA Astrophysics Data System (ADS)

We apply Landau theory of crystallization to explain and to classify the capsid structures of small viruses with spherical topology and icosahedral symmetry. We develop an explicit method which predicts the positions of centers of mass for the proteins constituting the viral capsid shell. Corresponding density distribution function which generates the positions has a universal form without any fitting parameter. The theory describes in a uniform way both the structures satisfying the well-known Caspar and Klug geometrical model for capsid construction and those violating it.

Lorman, V. L.; Rochal, S. B.

2007-05-01

61

Icosahedral Short-Range Order in Deeply Undercooled Metallic Melts  

NASA Astrophysics Data System (ADS)

Experimental evidence of icosahedral short-range order in stable and deeply undercooled melts of pure metallic elements is obtained using the combination of electromagnetic levitation with neutron scattering. This icosahedral short-range order is shown to occur in the bulk metallic melt independently of the system investigated. It strongly increases with the degree of undercooling.

Schenk, T.; Holland-Moritz, D.; Simonet, V.; Bellissent, R.; Herlach, D. M.

2002-07-01

62

Atomic structure of icosahedral Al6Mg4Cu  

NASA Astrophysics Data System (ADS)

An atomic structural model (quasiperiodic configuration of icosahedral clusters , or QCIC, model) for icosahedral Al6Mg4Cu was developed under the following assumptions: (1) The structural framework of the icosahedral phase is a three-dimensional (3D) Penrose tiling (PT). (2) The atomic arrangement is divided into two structural elements; those are the (Al,Cu)25Mg20 icosahedral cluster which is located at the twelvefold vertex in 3D PT, and the glue atoms between the icosahedral clusters. For a test of the validity of the QCIC model, the x-ray structure factor S(q) and the pair distribution function ?(r) of the model were compared with those determined experimentally. The ?(r) of the QCIC model is found to be in better agreement with the experimental ?(r) than that of the Henley-Elser model. The S(q) of the QCIC model is also found to agree satisfactorily with the experimental S(q).

Sakurai, Yoshiharu; Tanaka, Yoshikazu; Watanabe, Yasuhiro; Nanao, Susumu

1990-04-01

63

Structural stability of an icosahedral Cd-Yb quasicrystal and its crystalline approximant under high pressure  

NASA Astrophysics Data System (ADS)

Synchrotron x-ray powder diffraction studies on an icosahedral Cd-Yb quasicrystal (iCd-Yb), its crystalline approximant of Cd6Yb (cCd-Yb) and the related Cd25Eu4 (cCd-Eu) material were performed under pressures of up to about 40 GPa at room temperature. The icosahedral lattice of the atomic cluster in iCd-Yb and the bcc lattices in cCd-Yb and cCd-Eu were found to be stable under pressure. Although the Tsai-type atomic cluster can possibly be distorted in various ways, low-symmetry distortion modes do not seem to develop even at high pressure. It is considered that the cluster structure of centrosymmetric dense atomic packing prevented low-symmetry distortions and consequently provided the cluster lattice stability. The bulk moduli were also determined to be B0(iCd-Yb) = 49.2(3) GPa, B0(cCd-Yb) = 46.1(7) GPa and B0(cCd-Eu) = 49.6(3) GPa, which were much lower than the typical reported values for other quasicrystalline alloys.

Watanuki, T.; Sato, T. J.; Tsai, A. P.

2010-03-01

64

Determination of the composition of the icosahedral phase in rapidly solidified Al-Mn quasicrystals at high spatial resolution  

SciTech Connect

Phenomenological models based on Landau theory with the point symmetry of the icosahedron and quasiperiodic or incommensurate translational order have been presented. These models accurately reproduce the observed diffraction patterns, but the position of the most intense peaks scale with tau/sup -1/ unlike the experiments where they scale with tau/sup -3/. An alternative approach is to interpret the experimental data as a projection in three dimensions of a six-dimensional regular crystal. Katz and Duneau and independently, Elser have computed the diffraction pattern of a three-dimensional Penrose pattern using an elegant projection scheme from a higher dimensional periodic lattice. The find delta-function peaks that are dense in reciprocal space, where the most intense peaks not only account for the peak positions in the Al-Mn diffraction patterns but also scale as tau/sup -3/. However, an understanding of the peak intensities is as yet non-existent, for this would entail a detailed knowledge of the distribution of the aluminum and manganese atoms in the quasilattice. In order to solve this problem, it is necessary to first determine the composition of the icosahedral phase as accurately as possible. This is complicated because the icosahedral phase is formed over a range of starting compositions (10-25 atom-percent manganese) and the microstructure is such that these grains with icosahedral symmetry typically reach an average diameter of only 1-2 microns and they are embedded in an aluminum-rich matrix phase. Preliminary studies suggest an average optimal manganese content of 22 at%. In this report, the authors present the first results of determination of the composition of the icosahedral phase by energy dispersive x-ray spectroscopy measurements using convergent electron probes.

Krishnan, K.M.; Gronsky, R.; Tanner, L.E.

1986-02-01

65

Identify Symmetry  

NSDL National Science Digital Library

This unit will teach you how to identify symmetry in everyday objects and mathematical shapes in lines and rotational symmetry. What is line symmetry? Click on the link to find out: Line Symmetry Here is a line activity to see if you understand it: Line Symmetry Class Zone See if you understand the concepts by doing the following quiz: Line Symmetry Work Now for rotational symmetry: Rotational Symmetry See if you understand rotational symmetry by taking this quiz: Rotational Symmetry Work ...

Neubert, Mrs.

2011-03-03

66

Analysis of phases in the structure determination of an icosahedral virus  

SciTech Connect

The constraints imposed on structure-factor phases by noncrystallographic symmetry (NCS) allow phase improvement, phase extension to higher resolution and hence ab initio phase determination. The more numerous the NCS redundancy and the greater the volume used for solvent flattening, the greater the power for phase determination. In a case analyzed here the icosahedral NCS phasing appeared to have broken down, although later successful phase extension was possible when the envelope around the NCS region was tightened. The phases from the failed phase-determination attempt fell into four classes, all of which satisfied the NCS constraints. These four classes corresponded to the correct solution, opposite enantiomorph, Babinet inversion and opposite enantiomorph with Babinet inversion. These incorrect solutions can be seeded from structure factors belonging to reciprocal-space volumes that lie close to icosahedral NCS axes where the structure amplitudes tend to be large and the phases tend to be 0 or {pi}. Furthermore, the false solutions can spread more easily if there are large errors in defining the envelope designating the region in which NCS averaging is performed.

Plevka, Pavel; Kaufmann, Bärbel; Rossmann, Michael G. (Purdue)

2012-03-15

67

Analysis of phases in the structure determination of an icosahedral virus  

PubMed Central

The constraints imposed on structure-factor phases by non­crystallographic symmetry (NCS) allow phase improvement, phase extension to higher resolution and hence ab initio phase determination. The more numerous the NCS redundancy and the greater the volume used for solvent flattening, the greater the power for phase determination. In a case analyzed here the icosahedral NCS phasing appeared to have broken down, although later successful phase extension was possible when the envelope around the NCS region was tightened. The phases from the failed phase-determination attempt fell into four classes, all of which satisfied the NCS constraints. These four classes corresponded to the correct solution, opposite enantiomorph, Babinet inversion and opposite enantiomorph with Babinet inversion. These incorrect solutions can be seeded from structure factors belonging to reciprocal-space volumes that lie close to icosahedral NCS axes where the structure amplitudes tend to be large and the phases tend to be 0 or ?. Furthermore, the false solutions can spread more easily if there are large errors in defining the envelope designating the region in which NCS averaging is performed.

Plevka, Pavel; Kaufmann, Barbel; Rossmann, Michael G.

2011-01-01

68

Physical characterization of icosahedral virus ultra structure, stability, and integrity using electrospray differential mobility analysis.  

PubMed

We present a rapid and quantitative method to physically characterize the structure and stability of viruses. Electrospray differential mobility analysis (ES-DMA) is used to determine the size of capsomers (i.e., hexons) and complete capsids. We demonstrate how to convert the measured mobility size into the icosahedral dimensions of a virus, which for PR772 become 68.4 nm for vertex-to-vertex, 54.4 nm for facet-to-facet, and 58.2 nm for edge-to-edge lengths, in reasonable agreement with dimensions from transmission electron microscopy for other members of the family Tectiviridae (e.g., PRD1). These results indicate ES-DMA's mobility diameter most closely approximates the edge-to-edge length. Using PR772's edge length (36.0 nm) and the size of the major capsid hexon (?8.4 nm) from ES-DMA with icosahedral geometry, PR772's T = 25 symmetry is confirmed and the number of proteins in the capsid shell is determined. We also demonstrate the use of ES-DMA to monitor the temporal disintegration of PR772, the thermal degradation of PP7, and the appearance of degradation products, essential to viral stability assays. These results lay groundwork essential for the use of ES-DMA for a variety of applications including monitoring of vaccine and gene therapy vector products, confirmation of viral inactivation, and theoretical studies of self-assembling macromolecular structures. PMID:21302934

Pease, Leonard F; Tsai, De-Hao; Brorson, Kurt A; Guha, Suvajyoti; Zachariah, Michael R; Tarlov, Michael J

2011-02-08

69

Microindentation of Al-Cu-Fe icosahedral quasicrystal  

SciTech Connect

Many different microindentation experiments have been performed at ambient temperature on icosahedral quasicrystals (QCs). They have shown that icosahedral QCs, such as Al-Cu-Fe, Al-Pd-Mn, Al-Li-Cu, Al-Ru-Cu and Mg-Zn-Y are rather hard and exhibit a low fracture toughness. In other respects, compression experiments have shown that these materials exhibit a brittle-to-ductile transition temperature (BDTT) at about 0.7 T{sub m} where T{sub m} is the melting temperature. Few results have been reported concerning microindentation experiments performed at high temperatures, either in the brittle or in the ductile regime. The hardness behavior of icosahedral QCs as a function of temperature has been presented in two cases, however: Al-Li-Cu and Al-Pd-Mn. This paper is aimed at providing information about microindentation measurements performed on an icosahedral Al-Cu-Fe alloy over an extended temperature range. The results are analyzed within the frame used for previous results obtained in the same alloy by means of compression experiments.

Giacometti, E.; Baluc, N.; Bonneville, J.; Rabier, J.

1999-10-08

70

Stable Icosahedral Quasicrystals in the Cd-Mg-RE (\\textbf{RE} = \\textbf{Rare Earth Element}) Systems  

NASA Astrophysics Data System (ADS)

A stable icosahedral phase has been found in a series of Cd65Mg20RE15 (RE=Y, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) alloys. These icosahedral alloys have quasilattice parameters from 0.5571 to 0.5799 nm. Electron diffraction study confirmed that the icosahedral quasicrystals have a primitive icosahedral structure.

Guo, Junqing; Abe, Eiji; Tsai, An-Pang

2000-08-01

71

Three-dimensional reconstruction of icosahedral particles from single micrographs in real time at the microscope.  

PubMed

Single particle analysis is a valuable tool in cryo-electron microscopy for determining the structure of biological complexes. However, the conformational state and the preparation of the sample are factors that play a critical role in the ultimate attainable resolution. In some cases extensive analysis at the microscope of a sample under different conditions is required to derive the optimal acquisition conditions. Currently this analysis is limited to raw micrographs, thus conveying only limited information on the structure of the complex. We are developing a computing system that generates a three-dimensional reconstruction from a single micrograph acquired under cryogenic and low dose conditions, and containing particles with icosahedral symmetry. The system provides the microscopist with immediate structural information from a sample while it is in the microscope and during the preliminary acquisition stage. The system is designed to run without user intervention on a multi-processor computing resource and integrates all the processing steps required for the analysis. Tests performed on experimental data sets show that the probability of obtaining a reliable reconstruction from one micrograph is primarily determined by the quality of the sample, with success rates close to 100% when sample conditions are optimal, and decreasing to about 60% when conditions are sub-optimal. The time required to generate a reconstruction depends significantly on the diameter of the particles, and in most instances takes about 1min. The proposed approach can provide valuable three-dimensional information, albeit at low resolution, on conformational states, epitope binding, and stoichiometry of icosahedral multi-protein complexes. PMID:23891839

Cardone, Giovanni; Yan, Xiaodong; Sinkovits, Robert S; Tang, Jinghua; Baker, Timothy S

2013-07-25

72

Symmetry, stability, and dynamics of multidomain and multicomponent protein systems  

PubMed Central

Symmetry is commonly observed in many biological systems. Here we discuss representative examples of the role of symmetry in structural molecular biology. Point group symmetries are observed in many protein oligomers whose three-dimensional atomic structures have been elucidated by x-ray crystallography. Approximate symmetry also occurs in multidomain proteins. Symmetry often confers stability on the molecular system and results in economical usage of basic components to build the macromolecular structure. Symmetry is also associated with cooperativity. Mild perturbation from perfect symmetry may be essential in some systems for dynamic functions.

Blundell, Tom L.; Srinivasan, N.

1996-01-01

73

Are Gauge Symmetries Symmetries.  

National Technical Information Service (NTIS)

In topologically non-trivial gauge theories there is in general an obstruction for implementing gauge transformations on the fields, and even those which can be implemented may fail to be symmetries. For instantons no non-trivial gauge transformation can ...

P. A. Horvathy J. H. Rawnsley

1984-01-01

74

Chiral symmetry and charge symmetry.  

National Technical Information Service (NTIS)

The interconnection of charge symmetry and chiral symmetry breaking are discussed. Some consequences of a partial restoration of chiral symmetry in nuclei is brought out by means of the Nambu-Jona-Lasinio model. 22 refs., 10 figs.

E. M. Henley

1989-01-01

75

Encapsulation of a polymer by an icosahedral virus  

NASA Astrophysics Data System (ADS)

The coat proteins of many viruses spontaneously form icosahedral capsids around nucleic acids or other polymers. Elucidating the role of the packaged polymer in capsid formation could promote biomedical efforts to block viral replication and enable use of capsids in nanomaterials applications. To this end, we perform Brownian dynamics on a coarse-grained model that describes the dynamics of icosahedral capsid assembly around a flexible polymer. We identify several mechanisms by which the polymer plays an active role in its encapsulation, including cooperative polymer-protein motions. These mechanisms are related to experimentally controllable parameters such as polymer length, protein concentration and solution conditions. Furthermore, the simulations demonstrate that assembly mechanisms are correlated with encapsulation efficiency, and we present a phase diagram that predicts assembly outcomes as a function of experimental parameters. We anticipate that our simulation results will provide a framework for designing in vitro assembly experiments on single-stranded RNA virus capsids.

Elrad, Oren M.; Hagan, Michael F.

2010-12-01

76

Encapsulation of a polymer by an icosahedral virus  

PubMed Central

The coat proteins of many viruses spontaneously form icosahedral capsids around nucleic acids or other polymers. Elucidating the role of the packaged polymer in capsid formation could promote biomedical efforts to block viral replication and enable use of capsids in nanomaterials applications. To this end, we perform Brownian dynamics on a coarse-grained model that describes the dynamics of icosahedral capsid assembly around a flexible polymer. We identify several mechanisms by which the polymer plays an active role in its encapsulation, including cooperative polymer-protein motions. These mechanisms are related to experimentally controllable parameters such as polymer length, protein concentration, and solution conditions. Furthermore, the simulations demonstrate that assembly mechanisms are correlated to encapsulation efficiency, and we present a phase diagram that predicts assembly outcomes as a function of experimental parameters. We anticipate that our simulation results will provide a framework for designing in vitro assembly experiments on single-stranded RNA virus capsids.

Elrad, Oren M.; Hagan, Michael F.

2011-01-01

77

Icosahedral Short-Range Order in Amorphous Alloys  

Microsoft Academic Search

We have characterized the icosahedral short-range order in amorphous solids using local environment probes. Such topological local order is pronounced even in an amorphous alloy that does not form quasicrystalline phases upon crystallization, as demonstrated by the extended x-ray absorption fine structure and x-ray absorption near-edge structure of a Ni-Ag amorphous alloy analyzed through reverse Monte Carlo simulations.

W. K. Luo; H. W. Sheng; F. M. Alamgir; J. M. Bai; J. H. He; E. Ma

2004-01-01

78

A coordination chemistry dichotomy for icosahedral carborane-based ligands  

Microsoft Academic Search

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune the sterics and electronics of coordinating moieties, we describe here how icosahedral carboranes—boron-rich clusters—can influence metal–ligand interactions. Using a series of phosphine–thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum–sulfur interaction

Alexander M. Spokoyny; Charles W. Machan; Daniel J. Clingerman; Mari S. Rosen; Michael J. Wiester; Robert D. Kennedy; Charlotte L. Stern; Amy A. Sarjeant; Chad A. Mirkin

2011-01-01

79

A coordination chemistry dichotomy for icosahedral carborane-based ligands  

Microsoft Academic Search

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune the sterics and electronics of coordinating moieties, we describe here how icosahedral carboranes---boron-rich clusters---can influence metal-ligand interactions. Using a series of phosphine-thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum-sulfur interaction

Alexander M. Spokoyny; Charles W. Machan; Daniel J. Clingerman; Mari S. Rosen; Michael J. Wiester; Robert D. Kennedy; Charlotte L. Stern; Amy A. Sarjeant; Chad A. Mirkin

2011-01-01

80

An Optimization of the Icosahedral Grid Modified by Spring Dynamics  

NASA Astrophysics Data System (ADS)

We have investigated an optimum form of the modified icosahedral grid that is generated by applying the spring dynamics to the standard icosahedral grid system. The spring dynamics can generate a more homogeneous grid system than the standard icosahedral grid system by tuning the natural spring lenght: as the natural spring length becomes longer, the ratio of maximum grid interval to minimum one becomes closer to unit. When the natural spring length is larger than a critical value, however, the spring dynamic system does not have a stable equilibrium. By setting the natural spring length to be the marginally critical value, we can obtain the most homogeneous grid system, which is most efficient in terms of the CFL condition. We have analyzed eigenmodes involved in the initial error of the geostrophic balance problem [test case 2 of D. L. Williamson et al. (1992, J. Comput. Phys.102, 211)]. Since the balance state in the discrete system differs slightly from the exact solution of the analytic system, the initial error field includes both the gravity wave mode and the Rossby wave mode. As the results of the analysis are based on Hough harmonics decompositions, we detected Rossby and gravity wave modes with zonal wavenumber 5, which are asymmetric against the equator. These errors are associated with icosahedral grid structure. The symmetric gravity wave mode with zonal wavenumber 0 also appears in the error field. To clarify the evolution of Rossby waves, we introduce divergence damping to reduce the gravity wave mode. From the simulated results of the geostrophic problem with various grid systems, we found that the spuriously generated Rossby wave mode is eliminated most effectively when the most homogeneously distributed grid system is used. It is therefore, concluded that the most homogeneous grid system is the best choice from the viewpoint of numerical accuracy as well as computational efficiency.

Tomita, Hirofumi; Satoh, Masaki; Goto, Koji

2002-11-01

81

A coordination chemistry dichotomy for icosahedral carborane-based ligands  

NASA Astrophysics Data System (ADS)

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune the sterics and electronics of coordinating moieties, we describe here how icosahedral carboranes—boron-rich clusters—can influence metal-ligand interactions. Using a series of phosphine-thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum-sulfur interaction of platinum(II)-thioether complexes. Experimental observations, supported by computational work, show that icosahedral carboranes can act either as strong electron-withdrawing ligands or electron-donating moieties (similar to aryl- or alkyl-based groups, respectively), depending on which atom of the carborane cage is attached to the thioether moiety. These and similar results with carborane-selenol derivatives suggest that, in contrast to carbon-based ligands, icosahedral carboranes exhibit a significant dichotomy in their coordination chemistry, and can be used as a versatile class of electronically tunable building blocks for various ligand platforms.

Spokoyny, Alexander M.; Machan, Charles W.; Clingerman, Daniel J.; Rosen, Mari S.; Wiester, Michael J.; Kennedy, Robert D.; Stern, Charlotte L.; Sarjeant, Amy A.; Mirkin, Chad A.

2011-08-01

82

A coordination chemistry dichotomy for icosahedral carborane-based ligands.  

PubMed

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune the sterics and electronics of coordinating moieties, we describe here how icosahedral carboranes-boron-rich clusters-can influence metal-ligand interactions. Using a series of phosphine-thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum-sulfur interaction of platinum(II)-thioether complexes. Experimental observations, supported by computational work, show that icosahedral carboranes can act either as strong electron-withdrawing ligands or electron-donating moieties (similar to aryl- or alkyl-based groups, respectively), depending on which atom of the carborane cage is attached to the thioether moiety. These and similar results with carborane-selenol derivatives suggest that, in contrast to carbon-based ligands, icosahedral carboranes exhibit a significant dichotomy in their coordination chemistry, and can be used as a versatile class of electronically tunable building blocks for various ligand platforms. PMID:21778977

Spokoyny, Alexander M; Machan, Charles W; Clingerman, Daniel J; Rosen, Mari S; Wiester, Michael J; Kennedy, Robert D; Stern, Charlotte L; Sarjeant, Amy A; Mirkin, Chad A

2011-07-22

83

Coherent coexistence of nanodiamonds and carbon onions in icosahedral core-shell particles  

PubMed Central

The general approach for describing and designing complex hierarchical icosahedral structures is discussed. Structural models of icosahedral carbon nanoparticles in which the local arrangement of atoms is virtually identical to that in diamond are derived. It is shown that icosahedral diamond-like particles can be transformed into onion-like shell structures (and vice versa) by the consecutive smoothing (puckering) of atomic networks without disturbance of their topological integrity. The possibility of coherent coexistence of icosahedral diamond-like core with onion shells is shown.

Shevchenko, Vladimir Ya.; Madison, Alexey E.; Mackay, Alan L.

2007-01-01

84

Exploring Metric Symmetry  

SciTech Connect

Relatively minor perturbations to a crystal structure can in some cases result in apparently large changes in symmetry. Changes in space group or even lattice can be induced by heavy metal or halide soaking (Dauter et al, 2001), flash freezing (Skrzypczak-Jankun et al, 1996), and Se-Met substitution (Poulsen et al, 2001). Relations between various space groups and lattices can provide insight in the underlying structural causes for the symmetry or lattice transformations. Furthermore, these relations can be useful in understanding twinning and how to efficiently solve two different but related crystal structures. Although (pseudo) symmetric properties of a certain combination of unit cell parameters and a space group are immediately obvious (such as a pseudo four-fold axis if a is approximately equal to b in an orthorhombic space group), other relations (e.g. Lehtio, et al, 2005) that are less obvious might be crucial to the understanding and detection of certain idiosyncrasies of experimental data. We have developed a set of tools that allows straightforward exploration of possible metric symmetry relations given unit cell parameters and a space group. The new iotbx.explore{_}metric{_}symmetry command produces an overview of the various relations between several possible point groups for a given lattice. Methods for finding relations between a pair of unit cells are also available. The tools described in this newsletter are part of the CCTBX libraries, which are included in the latest (versions July 2006 and up) PHENIX and CCI Apps distributions.

Zwart, P.H.; Grosse-Kunstleve, R.W.; Adams, P.D.

2006-07-31

85

SYMMETRIES AND \\  

Microsoft Academic Search

The Lagrangian of the classical n-body problem has well known symmetries: isome- tries of the ambient euclidean space (translations, rotations, reflexions) and changes of scale coming from the homogeneity of the potential. To these symmetries are associated \\

A. CHENCINER

2003-01-01

86

The catalytic adsorption and dissociation of carbon dioxide on a double icosahedral Ru19 nanocluster - A theoretical study  

NASA Astrophysics Data System (ADS)

Using density-functional theory, we investigated the adsorption and dissociation of CO2 on Ru19 clusters of nm size. According to our results, the CO2 molecule adsorbed on the rhombus-center region of a double icosahedral Ru19 nanocluster has the largest adsorption energy, -1.48 eV, and the greatest elongation of C-O bond. Dissociating the first C-O bond of a CO2 molecule we got a reaction barrier of 0.78 eV, smaller than that of adsorbed on otherwise octahedral and low-symmetry Ru19 cluster structures. To understand the electronic properties, we calculated the electron localization functions and local densities of states, and the result was explicable.

Li, Han-Jung; Yeh, Chen-Hao; Ho, Jia-Jen

2013-10-01

87

Magnetic Color Symmetry of Lattice Rotations in a Diamagnetic Material  

Microsoft Academic Search

Oxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. Here we show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry. We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin

S. Denev; A. Kumar; M. D. Biegalski; H. W. Jang; C. M. Folkman; A. Vasudevarao; Y. Han; I. M. Reaney; S. Trolier-McKinstry; C.-B. Eom; D. G. Schlom; V. Gopalan

2008-01-01

88

A Global Ocean Model Based on Icosahedral-Hexagonal Grids With a Hybrid Vertical Coordinate  

Microsoft Academic Search

This talk will present results from a new ocean general circulation model (OGCM). The ocean model uses an icosahedral-hexagonal grid to tile the surface of the sphere and hybrid (floating) coordinates to discretize the vertical depth of the ocean. The use of icosahedral-hexagonal grids leads to a highly uniform and isotropic discretization of the sphere and eliminates problematic grid singularities

T. D. Ringler; J. Baumgardner; D. A. Randall

2003-01-01

89

Unusual properties of icosahedral boron-rich solids  

SciTech Connect

Icosahedral boron-rich solids are materials containing boron-rich units in which atoms reside at an icosahedron's 12 vertices. These materials are known for their exceptional bonding and the unusual structures that result. This article describes how the unusual bonding generates other distinctive and useful effects. In particular, radiation-induced atomic vacancies and interstitials spontaneously recombine to produce the 'self-healing' that underlies these materials' extraordinary radiation tolerance. Furthermore, boron carbides, a group of icosahedral boron-rich solids, possess unusual electronic, magnetic and thermal properties. For example, the charge carriers, holes, localize as singlet pairs on icosahedra. The unusual origin of this localization is indicated by the absence of a concomitant photo-ionization. The thermally assisted hopping of singlet pairs between icosahedra produces Seebeck coefficients that are unexpectedly large and only weakly dependent on carrier concentration. These properties are exploited in devices: (1) long-lived high-power high-capacity beta-voltaic cells (2) very high temperature thermoelectrics and (3) solid-state neutron detectors. - Graphical abstract: Very high-resolution transmission electron microscopy shows no damage to B{sub 12}P{sub 2} after an intense bombardment (10{sup 18} electrons/cm{sup 2} s) by 400 keV electrons to a net dose of about 10{sup 23} electrons/cm{sup 2}.

Emin, David [Department of Physics and Astronomy, 800 Yale Boulevard NE (MSC 07 4220), University of New Mexico, Albuquerque, NM 87131 (United States)]. E-mail: emin@unm.edu

2006-09-15

90

High-symmetry transition-metal sites in Ti56Ni(28-x)Fe(x)Si16 quasicrystals  

NASA Astrophysics Data System (ADS)

Rapidly solidified Ti-Ni-Fe-Si alloys are found to form a metastable phase with X-ray diffraction patterns which can be indexed to a structure with icosahedral symmetry. Fe-57 Moessbauer effect spectra show a negligible quadrupole splitting for the icosahedral phase. This observation, along with a comparison of the measured X-ray diffraction line intensities with calculated values, suggests a structure based on a decoration of a three-dimensional Penrose tiling, with transition-metal atoms in sites with local icosahedral symmetry. Magnetic susceptibility measurements show that a local moment of about 0.2 mu(B) forms on the Fe atom. These results are discussed in terms of possible local Fe environments.

Dunlap, R. A.; McHenry, M. E.; O'Handley, R. C.; Bahadur, D.; Srinivas, V.

1988-11-01

91

VIRUS-LIKE PARTICLES WITH T=19 ICOSAHEDRAL SYMMETRY IN A HUMAN GASTROENTERITIS STOOL  

EPA Science Inventory

Virus-like particles not previously described were observed in a human gastroenteritis stool using negative-stain TEM. The stool was among a number of acute-phase illness stools which had been collected in Egypt during 1980. The particles measured 65-70 nm in diameter, and it was...

92

The Formation and Structure of Aluminum-Copper - (lithium, Magnesium) Icosahedral Alloys.  

NASA Astrophysics Data System (ADS)

Quasicrystals have orientational order but lack periodic translational order. Sharp electron diffraction spots imply that they differ from amorphous materials. On the other hand, the aperiodic array of diffraction spots is inconsistent with conventional crystallography, which allows only two-, three-, four-, or sixfold symmetry axes. The discovery of the first icosahedral quasicrystal in a rapidly solidified Al-Mn alloy has created a flurry of activities in studying their structure and thermodynamics. AlCuLi icosahedral phase (i-phase) is the first stable quasicrystalline phase; and centimeter size quasicrystals can be obtained. Thus, AlCuLi i-phase is a model system for understanding the structure and thermodynamics of quasicrystalline materials. The research I have done consists of three parts: (1) Structural studies using high resolution x-ray diffraction. We found that Al(Cu) were decorated at the edge centers and vertices of two types of Penrose tiles, which are the basic units of Penrose tiling. Our results are the first successful determination of the atomic position in quasicrystalline materials, and prove that the Penrose tiling is a better description of quasicrystalline materials than other structural models. (2) Structural studies using pulsed neutron scattering. The dominant contribution to the AlCuLi x-ray spectrum comes from Al and Cu atoms since Li is a weak scatterer. However, the scattering length of the Li atom in neutron diffraction is comparable to that of Al(Cu). Furthermore, Li and Mg have opposite signs in scattering length. Thus, isomorphic substitution of Li by Mg results in contrast variation in neutron diffraction spectra, which demonstrates how Li atoms affect the diffraction. Using the pair distribution function analysis, we convincingly reveal the role of Li atoms in the structure. (3) Stability and formation. We investigate the formation of i-phase by varying preparation condition and stoichiometry. By using differential scanning calorimetry and x-ray diffraction, we established the thermodynamic relationship between the i-phase and the related crystalline phase.

Shen, Yong

93

Applying Symmetries of Common Objects to Help Students Understand Stereoselectivity for Apparently Symmetric Substrates  

ERIC Educational Resources Information Center

|We have found it an effective way of teaching symmetry in the context of stereoselectivity, to use common everyday objects with the same point groups as the substrates involved. This has helped students to distinguish between those symmetry elements which allow for stereospecificity and those which preclude it. Two symmetry elements, the simple…

Jittam, Piyachat; Ruenwongsa, Pintip; Panijpan, Bhinyo

2008-01-01

94

Symmetry Breaking  

Microsoft Academic Search

Symmetries in constraint satisfaction or combinatorial optimization problems can cause considerable dificulties for exact\\u000a solvers. One way to overcome the problem is to employ sophisticated models with no or at least less symmetries. However, this\\u000a often requires a lot of experience from the user who is carrying out the modeling. Moreover, some problems even contain inherent\\u000a symmetries that cannot be

Torsten Fahle; Stefan Schamberger; Meinolf Sellmann

2001-01-01

95

Symmetries IV  

NSDL National Science Digital Library

This geometry lesson, one in a series of lessons on symmetries from Illuminations, looks at glide reflection. Glide reflection is a symmetry transformation that is made up of two other symmetry transformations (a translation and a reflection). Graphic representations of the material are included to help students visualize the concepts. The lesson is intended for grades 9-12 and should require 1 class period to complete.

2010-12-21

96

Mirror Symmetry  

Microsoft Academic Search

We prove mirror symmetry for supersymmetric sigma models on Kahler manifolds in 1+1 dimensions. The proof involves establishing the equivalence of the gauged linear sigma model, embedded in a theory with an enlarged gauge symmetry, with a Landau-Ginzburg theory of Toda type. Standard R -> 1\\/R duality and dynamical generation of superpotential by vortices are crucial in the derivation. This

Kentaro Hori; Cumrun Vafa

2000-01-01

97

Icosahedral capsid formation by capsomers and short polyions  

NASA Astrophysics Data System (ADS)

Kinetical and structural aspects of the capsomer-polyion co-assembly into icosahedral viruses have been simulated by molecular dynamics using a coarse-grained model comprising cationic capsomers and short anionic polyions. Conditions were found at which the presence of polyions of a minimum length was necessary for capsomer formation. The largest yield of correctly formed capsids was obtained at which the driving force for capsid formation was relatively weak. Relatively stronger driving forces, i.e., stronger capsomer-capsomer short-range attraction and/or stronger electrostatic interaction, lead to larger fraction of kinetically trapped structures and aberrant capsids. The intermediate formation was investigated and different evolving scenarios were found by just varying the polyion length.

Zhang, Ran; Linse, Per

2013-04-01

98

'Broken symmetries' in macromolecular crystallography: phasing from unmerged data  

PubMed Central

The space-group symmetry of a crystal structure imposes a point-group symmetry on its diffraction pattern, giving rise to so-called symmetry-equivalent reflections. Instances in macromolecular crystallography are discussed in which the sym­metry in reciprocal space is broken, i.e. where symmetry-related reflections are no longer equivalent. Such a situation occurs when the sample suffers from site-specific radiation damage during the X-ray measurements. Another example of broken symmetry arises from the polarization anisotropy of anomalous scattering. In these cases, the genuine intensity differences between symmetry-related reflections can be exploited to yield phase information in the structure-solution process. In this approach, the usual separation of the data merging and phasing steps is abandoned. The data are kept unmerged down to the Harker construction, where the symmetry-breaking effects are explicitly modelled and refined and become a source of supplementary phase information.

Schiltz, Marc; Bricogne, Gerard

2010-01-01

99

Roles of icosahedral and crystal-like order in the hard spheres glass transition  

NASA Astrophysics Data System (ADS)

A link between structural ordering and slow dynamics has recently attracted much attention from the context of the origin of glassy slow dynamics. Candidates for such structural order are icosahedral, exotic amorphous and crystal-like. Each type of order is linked to a different scenario of glass transition. Here we experimentally access local structural order in polydisperse hard spheres by particle-level confocal microscopy. We identify the key structures as icosahedral and FCC-like order, both statistically associated with slow particles. However, when approaching the glass transition, the icosahedral order does not grow in size, whereas crystal-like order grows. It is the latter that governs the dynamics and is linked to dynamic heterogeneity. This questions the direct role of the local icosahedral ordering in glassy slow dynamics and suggests that the growing length scale of structural order is essential for the slowing down of dynamics and the non-local cooperativity in particle motion.

Leocmach, Mathieu; Tanaka, Hajime

2012-07-01

100

Scanning tunneling microscopy studies of surface structures of icosahedral aluminum-copper-iron quasicrystals  

NASA Astrophysics Data System (ADS)

We investigate the atomic structure of fivefold surface of icosahedral (i-) Al-Cu-Fe quasicrystal using scanning tunneling microscopy (STM) under ultra high vacuum (UHV). Annealing the sputtered surface at appropriate temperature produces a step-terrace structure on the surface. Our STM analysis indicates that the terraces are separated with primarily two stepheights in the ratio of t=5+1 /2 , a characteristic ratio in quasiperiodic structures. The measurements agree with the results from dynamical low energy electron diffraction (LEED) calculations. The spatial distribution of stepheights along the fivefold axis does not follow the quasiperiodic Fibonacci sequence. The existence of such stacking defects in the bulk structure is confirmed with the screw dislocations often observed in the STM scans. The first atomic resolution STM images on this type of material are obtained. The flat terraces are dominated with "ten-petal flower-like" motif, locally arranged with fivefold symmetry. Similar structural features can be identified in the atomically-dense planes generated from one of the available bulk structure models. Based on these results, we conclude that the fivefold i-AlCuFe surface corresponds to a two-dimensional cut of the bulk material. After examining the clean surface, we investigate the nucleation and growth of aluminium metallic thin films on the quasicrystalline i-Al-Cu-Fe fivefold surface. Upon deposition at room temperature, aluminium adatoms nucleate as pentagonal "starfish" with uniform size and in the same orientation. The same structure features are observed for different fluxes at low coverages. Based on the experimental results and the available bulk structure model, we identify the specific nucleation sites on the substrate and develop a model for the formation of the pentagonal starfish.

Cai, Tanhong

2001-07-01

101

Structure and lattice dynamics of rational approximants to icosahedral Al-Cu-Li  

NASA Astrophysics Data System (ADS)

We present a detailed theoretical investigation of the structure and the dynamical properties of icosahedral Al-Cu-Li alloys. Structural models of the quasicrystalline structure have been constructed on the basis of three-dimensional Penrose- and canonical-cell tilings. We show that the periodic approximants (up to ?~5/3) are stable under molecular-dynamics (MD) annealing with realistic pair forces and that the partial-pair-correlation functions, powder- and single-crystal and neutron- and x-ray diffraction data are in good agreement with experiment, with a slight preference for the canonical-cell models. The vibrational spectrum (spectral functions, densities of state) and inelastic neutron-scattering intensities have been calculated using a real-space recursion technique and the same interatomic forces as used in the MD annealing. Well-defined propagating longitudinal and transverse acoustic modes are found in the vicinity of quasiperiodically distributed special points in k space, the ? points of the reciprocal quasilattice. At higher energy, a hierarchy of stationary modes is predicted around other high-symmetry points corresponding to quasi-Brillouin-zone boundaries. For the propagating low-energy modes, the predictions are in very good agreement with inelastic neutron-scattering experiments on single crystals of i-Al-Cu-Li. However, certain discrepancies subsist between the predicted vibrational density of states (DOS) and the experiments with powdered samples. Quite generally, the calculated DOS shows more structure (with again only minor differences between the Penrose- and canonical-cell models) than the experimental result. This is probably to be attributed to the influence of phason disorder in the real quasicrystals.

Windisch, M.; Hafner, J.; Kraj?í, M.; Mihalkovi?, M.

1994-04-01

102

Chirality-selective Carbon Nucleation and Nanotube Formation on Icosahedral Fe13 Surface  

NASA Astrophysics Data System (ADS)

Using ab initio molecular dynamics, we show that adsorptions on the faces and bridges of triangles of a pentagonal pyramid of icosahedral Fe13 in the presence of symmetric distribution of carbon atoms or carbon atoms and dimers or a carbon ring of ten atoms lead to nanotube formation of (5, 0) chirality. Tip growth after initial nanotube formation is promoted by interaction with carbon chains and hexagonal rings. We propose icosahedral catalysts as candidates for chirality-controlled growth.

Tefera, Anteneh; Mochena, Mogus

2013-03-01

103

Synthesis and process characterization of mechanically alloyed icosahedral phase Mg-Zn-Al  

Microsoft Academic Search

The formation process of the icosahedral i-Mg32 (Zn, Al)49 phase during mechanical alloying has been studied. In the case of synthesis of i-phase from the metal powder mixture, the intermediate amorphous phase appeared during the first stages of mechanical alloying. In contrast the transformation of the cubic Frank-Kasper phase into the icosahedral one, was accompanied by progressive broadening and disappearance

E. Ivanov; B. Bokhonov; I. Konstanchuk

1991-01-01

104

Structure of Al-Li-Cu icosahedral crystals and Penrose tiling  

Microsoft Academic Search

Synchrotron X-ray powder-diffraction measurements of the Al-Li-Cu icosahedral phase are reported. The results are found to be in agreement with the computed diffraction intensities of the three-dimensional Penrose tiling when Al and Cu atoms are randomly positioned at the vertices and edge centers of the unit cells. Comparison is also made with a similarly decorated icosahedral structure constructed by dense

Y. Shen; S. J. Poon; G. J. Shiflet; W. Dmowski; T. Egami

1987-01-01

105

Structure of Al-Li-Cu icosahedral crystals and Penrose tiling  

SciTech Connect

We report synchrotron x-ray powder-diffraction measurements of the Al-Li-Cu icosahedral phase. Our results are found to be in agreement with the computed diffraction intensities of the three-dimensional Penrose tiling when Al and Cu atoms are randomly positioned at the vertices and edge centers of the unit cells. Comparison is also made with a similarly decorated icosahedral structure constructed by dense packing of icosahedra. The agreement is less satisfactory.

Shen, Y.; Poon, S.J.; Dmowski, W.; Egami, T.; Shiflet, G.J.

1987-04-06

106

Structure of Al-Li-Cu icosahedral crystals and Penrose tiling  

NASA Astrophysics Data System (ADS)

Synchrotron X-ray powder-diffraction measurements of the Al-Li-Cu icosahedral phase are reported. The results are found to be in agreement with the computed diffraction intensities of the three-dimensional Penrose tiling when Al and Cu atoms are randomly positioned at the vertices and edge centers of the unit cells. Comparison is also made with a similarly decorated icosahedral structure constructed by dense packing of icosahedra; the agreement is less satisfactory.

Shen, Y.; Poon, S. J.; Shiflet, G. J.; Dmowski, W.; Egami, T.

1987-04-01

107

Continuum elastic sphere vibrations as a model for low lying optical modes in icosahedral quasicrystals  

Microsoft Academic Search

The nearly dispersionless, so-called 'optical' vibrational modes observed by inelastic neutron scattering from icosahedral Al-Pd-Mn and Zn-Mg-Y quasicrystals are found to correspond well to modes of a continuum elastic sphere that has the same diameter as the corresponding icosahedral basic units of the quasicrystal. When the sphere is considered as free, most of the experimentally found modes can be accounted

E. Duval; L. Saviot; A. Mermet; D. B. Murray

2005-01-01

108

Formation of large-scale icosahedral clusters in a simple liquid approaching the glass transition  

Microsoft Academic Search

A number of singularities observed in super-cooled liquids approaching the glass transition point are commonly interpreted as indicating spatial heterogeneity. This conjecture assumes that the whole volume is decomposed into structurally distinct domains. In simple super-cooled liquids, the assumed domain structure is usually associated with icosahedral clustering; however, no evidence for growing length scale of icosahedral ordering in a super-cooled

F. H. M Zetterling; M. Dzugutov; S. I Simdyankin

2001-01-01

109

Symmetries I  

NSDL National Science Digital Library

This unit from Illuminations provides students with the opportunity to learn about the mathematical properties of rotations. These lessons investigate rotational symmetry by fixing the center of an object and then turning it. The relationship between rotations and symmetry is also examined. The unit consists of 4 lessons, each of which should require 1 class period to complete. The material is appropriate for grades 9-12.

2010-12-07

110

Phonon-phason coupling constant in icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

The elastic theory(M. Widom, Phil. Mag. Lett. 64), 297 (1991). of icosahedral quasicrystals addresses the possible instabilities of the quasicrystalline state to modulated phase and approximant phase. There are five elastic constants in this theory; two being the usual phonon elastic constants, two contributing to phason modes which would be frozen for a quenched quasicrystal, and one, called K, setting the phonon-phason coupling Hamiltonian. The response of a quasicrystal to shear stress leads to a measure of the coupling constant K. Using realistically oscillating(Mihalkovic et al. Phys. Rev. B 53), 9002 (1996). interatomic potentials(We thank J. Hafner for the AlCuLi pseudo-binary potentials.) as well as short range model potentials, we measure K for two classes of decoration models: canonical cell based Al-Mn models^2, and Henley-Elser structural models for AlCuLi. The sign of K is not universal. A dimensionless measure of the magnitude of K, K^2/S T_m, where S is the shear modulus, and Tm the melting temperature, is found to be of order unity or larger, indicating the importance of phonon-phason coupling mechanism in the theory. clickable link

Zhu, Wei-Jing; Henley, Christopher L.

1997-03-01

111

Icosahedral quasicrystalline (Ti1.6V0.4Ni)100?xScx alloys: Synthesis, structure and their application in Ni-MH batteries  

NASA Astrophysics Data System (ADS)

Thanks to the revolutionary discovery of 5-fold symmetry contributed by Shechtman, quasicrystal is now recognized as another solid-state existing form. As the second largest class of quasicrystals, titanium-based icosahedral quasicrystals are very promising for hydrogen storage applications owing to their inherent abundant interstitial sites and favorable hydrogen-metal chemistry. In this context, (Ti1.6V0.4Ni)100?xScx (x=0.5–6) quaternary icosahedral quasicrystals have been successfully synthesized via arc-melting and subsequent melt-spinning techniques, and then their electrochemical performance toward hydrogen is explored. When the molar ratio of Sc addition is under 1%, a maximum discharge capacity of about 270 mA h g?1 can be delivered. With further increasing Sc amount to 6%, good cycling stability as well as significantly retarded self-discharge rate (capacity retention 94% after 24 h relaxation) is observed. But meanwhile, the discharge capacities fall into 250-240 mA h g?1, and the electrocatalytic activity improvement is highly demanded.

Hu, Wen; Yi, Jianhong; Zheng, Biju; Wang, Limin

2013-06-01

112

Magnetism and chemical ordering in icosahedral Al-Pd-Mn quasicrystal  

NASA Astrophysics Data System (ADS)

Even after nearly two decades of research efforts, the origin of the outstanding magnetic properties of icosahedral quasicrystals containing Mn remains unclear. Experiments have demonstrated that only a rather small fraction of the Mn atoms carry rather large magnetic moments, but it remains unclear whether these sites are intrinsic to the quasicrystalline structure or represent defects. We present ab initio density-functional calculations of the magnetic properties of a large 2/1 approximant to icosahedral (i) Al-Pd-Mn, performed in the semilocal generalized gradient approximation. Structures for rational approximants to the quasicrystalline structure of bulk i -Al-Pd-Mn have been constructed using the cut-and-projection technique in six-dimensional (6D) hyperspace according to the Katz-Gratias-Boudard model. We studied magnetism in models of the 2/1 approximant with idealized coordinates obtained by projection from 6D hyperspace in models with coordinates relaxed using Hellmann-Feynman forces and in models simulating the structure of the quasicrystal at high temperature. In some idealized structural models a majority of the Mn atoms carry a large magnetic moment. Although this contradicts experiments demonstrating that only a very small fraction of the Mn atoms are magnetic, this provides the opportunity to investigate in detail the mechanisms leading to the formation of magnetic moments on the Mn atoms. We identify two major mechanisms: a loosely packed environment of the Mn atoms and a direct Mn-Pd interactions leading to a shift of the Mn d band toward the Fermi level. The dominant contribution is the Mn-Pd interaction. A large magnetic moment on a Mn atom is formed at special sites where the Mn atom has two or three Pd nearest neighbors. These special sites are located at those regions of the quasiperiodic lattice where the pseudo-Mackay and Bergman clusters building the structure are linked along the threefold axes. At these sites, the building principles of the Mackay and Bergman clusters are in conflict: from the side of the Mackay cluster, occupation with an Al atom is required, whereas the symmetry of the Bergman cluster suggests occupation by a Pd atom. We have found that a small modification of the chemical decoration of these sites (corresponding to a slight modification of the internal shell structure of the occupation domains in the 6D hyperspace) can lead to a complete disappearance of magnetism in i -Al-Pd-Mn. Total energy calculations show that models with a chemical ordering disfavoring formation of magnetic moments on Mn atoms have the lowest energies. This re-establishes agreement with experiment. The ground state of i -Al-Pd-Mn is nonmagnetic; but at these specific sites, Al atoms can be replaced by Pd at low energetic cost and without strong violation of the building principles of the quasicrystalline structure, resulting in the formation of large local magnetic moments.

Kraj?í, M.; Hafner, J.

2008-12-01

113

Inherited Symmetry  

ERIC Educational Resources Information Center

|In a first calculus course, it is not unusual for students to encounter the theorems which state: If f is an even (odd) differentiable function, then its derivative is odd (even). In our paper, we prove some theorems which show how the symmetry of a continuous function f with respect to (i) the vertical line: x = a or (ii) with respect to the…

Attanucci, Frank J.; Losse, John

2008-01-01

114

Lattice vibrations of icosahedral boron-rich solids  

NASA Astrophysics Data System (ADS)

The rhombohedral lattices for ?-boron, boron arsenide, and boron phosphide are each of D3d symmetry and have bases that include B12 icosahedra. Boron carbide with B4C stoichiometry has near-D3d symmetry and is almost certainly composed of B11C icosahedra and C-B-C chains. Comparable classical force field models are applied to each of these crystals to correlate q=0 phonon structure with experimental Raman and IR spectra. We here describe our methods and contrast interaction strengths for different materials. Vibrations are correlated in the different crystals through normal mode eigenvector expansions. Acoustic wave velocities from Brillouin zone dispersion curves in two distinct symmetry-axis directions are presented and contrasted for ?-boron and B12As2. The origin of lines with anomalous polarization and width in ?-boron, B12As2, and B12P2 is considered.

Beckel, Charles L.; Yousaf, Mohammad

1991-07-01

115

Symmetry and Reduced Symmetry in Model Checking  

Microsoft Academic Search

Symmetry reduction methods exploit symmetry in a system in order to efficiently verify its temporal properties. Two problems may prevent the use of symmetry reduction in practice: (1) the property to be checked may distinguish symmetric states and hence not be preserved by the symmetry, and (2) the system may exhibit little or no symmetry. In this article, we present

A. Prasad Sistla; Patrice Godefroid

2001-01-01

116

Spherical symmetry  

NASA Astrophysics Data System (ADS)

In all areas of physics and mathematics it is common to search for insight into a theory by finding exact solutions of its fundamental equations and by studying these solutions in detail. This goal is particularly difficult in non-linear theories and the usual approach consists of assuming particular symmetries and searching for solutions with these symmetries. Stripped of inessential features and simplified in this way, the search for exact solutions becomes easier. In a sense, this approach betrays a reductionist point of view but, pragmatically, it is often crucial to gain an understanding of the theory that cannot be obtained otherwise and that no physicist or mathematician would want to renounce to. In this chapter we discuss exact solutions of ETGs with spherical symmetry. In addition to gaining insight into the theory, spherically symmetric solutions are particularly important in astrophysics as models for stars and compact objects, including black holes, which are important theoretical laboratories for theories of quantum gravity. The next section discusses spherical symmetry in GR and in metric f(R) gravity and presents static spherically symmetric solutions and a Noether symmetry approach. Then, the more difficult is- sue of non-static and non-asymptotically flat solutions is discussed. The second part of the chapter is devoted to the study of spherically symmetric solutions in general scalar-tensor theories and of the Jebsen-Birkhoff theorem. The chapter ends with a discussion of black holes in ETGs and of a map from spherical to axially symmetric solutions. An example is given. A spherically symmetric solution in Palatini f(R) gravity has already been given in Sect. 3.4.2.

Capozziello, Salvatore; Faraoni, Valerio

117

Thermal rearrangement mechanisms in icosahedral carboranes and metallocarboranes.  

PubMed

Ab initio MD and potential energy surface sampling has been used to study the rearrangement processes in carboranes and their derivatives. A new mechanism is found, in addition to those previously proposed. The fact that theoretical activation energies are lower than those observed experimentally, and the differing activity of technetium and rhenium complexes, are rationalised by orbital symmetry constraints. PMID:23254297

Sugden, Isaac J; Plant, David F; Bell, Robert G

2012-12-19

118

Magnetic Color Symmetry of Lattice Rotations in a Non-magnetic Material  

Microsoft Academic Search

Oxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. Here we show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry. We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin

Sava Denev; A. Kumar; M. D. Biegalski; H. W. Jang; C. M. Folkman; A. Vasudevarao; Y. Han; I. M. Reaney; S. Trolier-McKinstry; C.-B. Eom; D. G. Schlom; V. Gopalan

2009-01-01

119

Dynamic Paper Constructions for Easier Visualization of Molecular Symmetry  

ERIC Educational Resources Information Center

|A system for construction of simple poster-board models is described. The models dynamically demonstrate the symmetry operations of proper rotation, improper rotation, reflection, and inversion for the chemically important point groups D[subscript 3h], D[subscript 4h], D[subscript 5h], D[subscript 6h], T[subscript d], and O[subscript h]. The…

Sein, Lawrence T., Jr.

2010-01-01

120

Theory of color symmetry for periodic and quasiperiodic crystals  

Microsoft Academic Search

The author presents a theory of color symmetry applicable to the description and classification of periodic as well as quasiperiodic colored crystals. This theory is an extension to multicomponent fields of the Fourier-space approach of Rokhsar, Wright, and Mermin. It is based on the notion of indistinguishability and a generalization of the traditional concepts of color point group and color

Ron Lifshitz

1997-01-01

121

Growth and characterization of single grain icosahedral AlCuFe quasicrystals  

NASA Astrophysics Data System (ADS)

In this talk we will review the growth of Al-rich quasicrystals from metallic solutions. In particular we will discuss the growth of single grains of icosahedral AlCuFe from the ternary melt. Whereas the growths of single grain decagonal phase AlNiCo and icosahedral phase AlPdMn from metallic solutions are rather simple, the growth of sizable single grains of icosahedral phase AlCuFe presents a more difficult problem, but single grains as large as several cubic mm can be produced. Structural data from electron microscopy as well as thermodynamic and transport data will be presented and discussed. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences.

Kelso, N.; Canfield, P. C.; Bud'Ko, S. L.

2002-03-01

122

Synthesis and characterization of monodispersed icosahedral Au using spherical aberration correction  

NASA Astrophysics Data System (ADS)

Monodisperse icosahedral Au nanoparticles were synthesized using one step protocol. The morphology and structural characteristics of the icosahedral Au nanoparticles with uniform size were studied in detail using ultra-high resolution scanning electron microscope (SEM) FEG Hitachi S-5500 (0.4 nm at 30 kV) with BF/DF Duo-STEM detector, high resolution transmission electron microscope (HRTEM) Jeol JEM-2010F with an accelerating voltage of 200 kV (resolution 0.19 nm point-to-point) and a scanning transmission electron microscope Jeol JEM-ARM200F (STEM) attachment with a spherical aberration corrector. The average size of the icosahedral Au nanoparticles was 10 nm. STEM Cs-corrected images showed the atomic structure of the nanoparticles, oriented mainly on the five and two fold exes. The nanoparticles were also characterized using UV/vis absorption spectrum.

Velazquez-Salazar, J. Jesus; Esparza, Rodrigo; Yacaman, Miguel Jose

2010-10-01

123

Icosahedral quasiperiodic packing of fibres parallel to fivefold and threefold axes.  

PubMed

Building rules are examined for an icosahedral quasiperiodic packing of fibres with axes parallel to the ten threefold axes, first employing an experimental construction and afterwards a mathematical demonstration using the cut-and-project method applied in hyperspace. As a result of this latter approach, very simple two-dimensional (2D) building rules are proposed. Similar simple 2D rules have also been proposed for the case of an icosahedral quasiperiodic packing with fibre axes parallel to the six fivefold axes [Duneau & Audier (1999). Acta Cryst. A55, 746-754]. Finally, the construction of another icosahedral quasiperiodic packing resulting from a combination of two groups of fibres respectively parallel to six fivefold and ten threefold axes is reported. A brief discussion is given on different particular mechanical behaviours which might a priori be expected from the various enantiomorphic properties of these packings. PMID:10874416

Audier, M; Duneau, M

2000-01-01

124

Does an icosahedral short-range order prevail in glass-forming Zr-Cu melts?  

NASA Astrophysics Data System (ADS)

We report on investigations of the static structure factors of glass-forming Zr-Cu alloy melts by combination of the containerless processing technique of electrostatic levitation with diffraction of neutron and synchrotron radiation. The partial Bhatia-Thornton structure factors SNN and SNC were determined from the two total structure factors. While it is widely assumed in literature that the good glass-forming ability of Zr-Cu is related to an icosahedral short-range order prevailing in the melt, our partial structure factors demonstrate that the liquid Zr-Cu is not characterized by a dominant icosahedral short-range order.

Holland-Moritz, Dirk; Yang, Fan; Kordel, Tobias; Klein, Stefan; Kargl, Florian; Gegner, Jan; Hansen, Thomas; Bednarcik, Jozef; Kaban, Ivan; Shuleshova, Olga; Mattern, Norbert; Meyer, Andreas

2012-12-01

125

Determination of the crystal structure of icosahedral Al-Cu-Li  

NASA Astrophysics Data System (ADS)

The x-ray diffraction of a single crystal of the icosahedral phase of Al-Cu-Li has been measured on a diffractometer. Only 37 symmetrically inequivalent reflections were found with nonzero intensity. The structures considered, decorations of the Penrose packing with edge length 0.5039 nm, were refined to match the intensity data. An excellent agreement (RF=7.0%) is obtained for Cu or Al occupying vertex and edge-center positions of both rhombohedra and Li or Al occupying two body-diagonal sites of the prolate rhombohedron. The icosahedral and cubic structure are compared.

Elswijk, Herman B.; de Hosson, Jeff Th. M.; van Smaalen, Sander; de Boer, Jan L.

1988-07-01

126

Medium-range icosahedral order in quasicrystal-forming Zr2Pd binary metallic glass  

NASA Astrophysics Data System (ADS)

Medium-range order in Zr2Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr2Pd metallic glass.

Huang, Li; Fang, X. W.; Wang, C. Z.; Kramer, M. J.; Ding, Z. J.; Ho, K. M.

2011-06-01

127

Correlation of Atomic Cluster Symmetry and Glass-Forming Ability of Metallic Glass  

SciTech Connect

Local structures play a crucial role in glass formation and properties. In addition to topological short-range order, the geometric property of site symmetry is another important but less known characteristic of local structures. It is shown that the observed sharp increase of glass forming ability of Ce{sub 70-x}Al{sub 10}Cu{sub 20}Co{sub x} upon Co addition is correlated with a dramatic increase of Al site symmetry, as reflected by decreasing quadrupole frequency measured by {sup 27}Al NMR. The result is consistent with the structure model of Al-centered icosahedral clusters as the predominant structural building blocks.

Xi Xuekui; Li Lilong; Wu Yue [Department of Physics and Astronomy and Curriculum in Applied and Materials Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3255 (United States); Zhang Bo; Wang Weihua [Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

2007-08-31

128

Capping-agent-free synthesis of substrate-supported porous icosahedral gold nanoparticles  

NASA Astrophysics Data System (ADS)

We report a new capping-agent-free strategy for the synthesis of substrate-supported porous icosahedral Au nanoparticles (NPs) with rough naked surfaces, based on the crystallization from substrate-supported thin solution layers followed by solid-phase thermolysis. The plasmonic properties of icosahedral Au NPs have been studied using single particle dark-field scattering microscopy and spectroscopy. The two distinct localized surface plasmon resonance (LSPR) bands observed in the single particle dark-field spectra can be ascribed to the quadrupole resonance at ca. 425 nm and the size-dependent dipole resonance in the red region (645-708 nm). The unique rough naked surface, the facile synthesis, together with the ability to control the nanoparticle size and to vary the LSPR frequency in the red region, would make the substrate-supported porous icosahedral Au NPs promising on multiple levels in the applications of catalysis, ultrasensitive biosensors, and in surface-enhanced Raman scattering (SERS).We report a new capping-agent-free strategy for the synthesis of substrate-supported porous icosahedral Au nanoparticles (NPs) with rough naked surfaces, based on the crystallization from substrate-supported thin solution layers followed by solid-phase thermolysis. The plasmonic properties of icosahedral Au NPs have been studied using single particle dark-field scattering microscopy and spectroscopy. The two distinct localized surface plasmon resonance (LSPR) bands observed in the single particle dark-field spectra can be ascribed to the quadrupole resonance at ca. 425 nm and the size-dependent dipole resonance in the red region (645-708 nm). The unique rough naked surface, the facile synthesis, together with the ability to control the nanoparticle size and to vary the LSPR frequency in the red region, would make the substrate-supported porous icosahedral Au NPs promising on multiple levels in the applications of catalysis, ultrasensitive biosensors, and in surface-enhanced Raman scattering (SERS). Electronic supplementary information (ESI) available: SEM images of icosahedral Au(iii) NPs before being subjected to solid-phase thermolysis. See DOI: 10.1039/c3nr34000g

Wu, Ji Hong; Guan, Zhenping; Yang, Su Ke; Yuan, Peiyan; Xu, Qing-Hua; Xu, Guo Qin

2013-03-01

129

Report of a Subcommittee on the Nomenclature of n-Dimensional Crystallography. I. Symbols for point-group transformations, families, systems and geometric crystal classes.  

PubMed

The notation of crystallography in arbitrary dimensions is considered. Recommended symbols for point-group transformations, geometric crystal classes, families and systems are presented. PMID:10927287

Janssen; Birman; Koptsik; Senechal; Weigel; Yamamoto; Abrahams; Hahn

1999-07-01

130

Chiral Symmetry and Chiral-Symmetry Breaking.  

National Technical Information Service (NTIS)

These lectures concern the dynamics of fermions in strong interaction with gauge fields. Systems of fermions coupled by gauge forces have a very rich structure of global symmetries, which are called chiral symmetries. These lectures will focus on the real...

M. E. Peskin

1982-01-01

131

Overview of Molecular Symmetry Operations and Symmetry  

NSDL National Science Digital Library

This site provides an overview of symmetry operations from a chemistry perspective. The site includes animated and interactive activities designed for students learning about symmetry operations. Tutorial exercises are provided.

132

Systematic Mapping of Icosahedral Short-Range Order in a Melt-Spun Zr36Cu64 Metallic Glass  

NASA Astrophysics Data System (ADS)

By analyzing the angular correlations in scanning electron nanodiffraction patterns from a melt-spun Zr36Cu64 glass, the dominant local order was identified as icosahedral clusters. Mapping the extent of this icosahedral short-range order demonstrates that the medium-range order in this material is consistent with a face-sharing or interpenetrating configuration. These conclusions support results from atomistic modeling and a structural basis for the glass formability of this system.

Liu, A. C. Y.; Neish, M. J.; Stokol, G.; Buckley, G. A.; Smillie, L. A.; de Jonge, M. D.; Ott, R. T.; Kramer, M. J.; Bourgeois, L.

2013-05-01

133

Hexane-driven icosahedral to cuboctahedral structure transformation of gold nanoclusters.  

PubMed

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au(13) clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure-property correlation and its strong dependence on the chemical environment for metal nanoclusters. PMID:23051636

Li, Yuanyuan; Cheng, Hao; Yao, Tao; Sun, Zhihu; Yan, Wensheng; Jiang, Yong; Xie, Yi; Sun, Yongfu; Huang, Yuanyuan; Liu, Shoujie; Zhang, Jing; Xie, Yaning; Hu, Tiandou; Yang, Lina; Wu, Ziyu; Wei, Shiqiang

2012-10-19

134

Locations of carbohydrate sites on alphavirus glycoproteins show that E1 forms an icosahedral scaffold.  

PubMed

There are 80 spikes on the surface of Sindbis virus arranged as an icosahedral surface lattice. Each spike consists of three copies of each of the glycoproteins E1 and E2. There are two glycosylation sites on E1 and two on E2. These four sites have been located by removal of the glycosylation recognition motifs using site-specific mutagenesis, followed by cryoelectron microscopy. The positions of these sites have demonstrated that E2 forms the protruding spikes and that E1 must be long and narrow, lying flat on the viral surface, forming an icosahedral scaffold analogous to the arrangement of the E glycoprotein in flaviviruses. This arrangement of E1 leads to both dimeric and trimeric intermolecular contacts, consistent with the observed structural changes that occur on fusion with host cell membranes, suggesting a similar fusion mechanism for alpha- and flaviviruses. PMID:11301008

Pletnev, S V; Zhang, W; Mukhopadhyay, S; Fisher, B R; Hernandez, R; Brown, D T; Baker, T S; Rossmann, M G; Kuhn, R J

2001-04-01

135

Scanning Tunneling Microscopy Studies of Surface Structures of Icosahedral Al-Cu-Fe Quasicrystals  

SciTech Connect

Three papers are included in this dissertation. The first paper: ''Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED studies'', is in press with ''Surface Science''. The second paper: ''An STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface'' is submitted to ''Physical Review B, Rapid Communication''. The third paper: ''Pseudomorphic starfish: arrangement of extrinsic metal atoms on a quasicrystalline substrate'' is submitted to ''Nature''. Following the third paper are general conclusions and appendices that document the published paper ''Structural aspects of the three-fold surface of icosahedral Al-Pd-Mn'' (appearing in volume 461, issue 1-3 of ''Surface Science'' on page L521-L527, 2000), the design as well as the specifications of the aluminum evaporator used in the aluminum deposition study in this dissertation, an extended discussion of the aluminum deposition on the quasicrystalline surface, and the STM database.

Tanhong Cai

2002-12-31

136

A multilingual parallelization of the icosahedral-hexagonal grid system for integration on the sphere  

SciTech Connect

This project set out to use these multilingual programming techniques to parallelize an existing Fortran program. This program is an implementation of the shallow water equations using the icosahedral hexagonal grid system to integrate over a sphere. Our objective was to test the usefulness of multilingual techniques, to evaluate the new language PCN (Program Composition Notation), and to investigate the parallel execution characteristics of the icosahedral-hexagonal algorithm. Two features of PCN make it a useful language for parallelization. The first of these is single assignment variables. Communication and synchronization between processes is represented by reading and writing to these variables. This feature simplifies the specification of complex protocols, reducing them to variable creation and assignment. Second, PCN decouples process mapping from concurrent execution. Mapping is specified annotations to procedure calls, which indicate the processor on which execution of the procedure is to take place. Variables passed into the procedure then become message streams to that processor. 8 refs., 2 figs.

Hammond, S.J. (Maine Univ., Orono, ME (USA). Dept. of Computer Science)

1991-01-01

137

Finite - Temperature Chirality-selective Carbon Nucleation and Nanotube Formation on Icosahedral Fe13 Surface  

NASA Astrophysics Data System (ADS)

We performed finite - temperature ab initio molecular dynamics calculations to see if our earlier ground state ab initio molecular dynamics results hold. Adsorptions on the faces and bridges of triangles of a pentagonal pyramid of icosahedral Fe13 in the presence of symmetric distribution of carbon atoms or carbon atoms and dimers still lead to nanotube formation of (5, 0) chirality. On the other hand, in contrast to the ground state result, carbon rings of ten carbon atoms do not form nanotubes. Tip growth after initial nanotube formation is promoted by interaction with carbon chains and hexagonal rings at finite temperature as well. We propose icosahedral catalysts as candidates for chirality-controlled growth at finite temperature.

Tefera, Anteneh; Mochena, Mogus

2013-03-01

138

Group theory of icosahedral virus capsids: a dynamical top-down approach  

Microsoft Academic Search

We explore the use of a top-down approach to analyse the dynamics of icosahedral virus capsids and complement the information obtained from bottom-up studies of viral vibrations available in the literature. A normal mode analysis based on protein association energies is used to study the frequency spectrum, in which we reveal a universal plateau of low-frequency modes shared by a

Kasper Peeters; Anne Taormina

2008-01-01

139

Near-atomic resolution reconstructions of icosahedral viruses from electron cryo-microscopy  

PubMed Central

Nine different near-atomic resolution structures of icosahedral viruses, determined by electron cryo-microscopy and published between early 2008 and late 2010, fulfill predictions made 15 years ago that single-particle cryo-EM techniques could visualize molecular detail at 3 – 4 Å resolution. This review summarizes technical developments, both in instrumentation and in computation, that have led to the new structures, which advance our understanding of virus assembly and cell entry.

Grigorieff, Nikolaus; Harrison, Stephen C.

2011-01-01

140

Icosahedral Al–Pd–Mn, a melting pot for diffusion mechanisms  

Microsoft Academic Search

The diffusion of 71Ge, 195Au, 103Pd, and 59Fe in icosahedral (i-)Al–Pd–Mn was studied by means of a radiotracer technique. In addition, for 195Au and 103Pd, the effect of proton irradiation during diffusion annealing was investigated. Based on the large body of diffusion data available for i-Al–Pd–Mn, a comprehensive discussion of the diffusion mechanisms operating in this quasicrystal is presented.

W Frank; R Blüher; I Schmich

2002-01-01

141

Low-temperature thermal properties of icosahedral Al-Re-Pd  

Microsoft Academic Search

We report measurements of the thermal conductivity lambda(T) and the specific heat Cp(T) of icosahedral Al70Re8.6Pd21.4 at low temperatures. Below 1 K, the behaviour of the quasilattice thermal conductivity lambdaph(T) is compatible with the scattering of vibrational excitations involving tunnelling states and grain boundaries. The specific heat Cp(T) contains a small linear contribution gamma T. Our lambdaph(T) results indicate that

M. A. Chernikov; A. Bianchi; E. Felder; U. Gubler; H. R. Ott

1996-01-01

142

Determination of the crystal structure of icosahedral Al-Cu-Li  

Microsoft Academic Search

The x-ray diffraction of a single crystal of the icosahedral phase of Al-Cu-Li has been measured on a diffractometer. Only 37 symmetrically inequivalent reflections were found with nonzero intensity. The structures considered, decorations of the Penrose packing with edge length 0.5039 nm, were refined to match the intensity data. An excellent agreement (RF=7.0%) is obtained for Cu or Al occupying

Herman B. Elswijk; Jeff Th. M. de Hosson; Sander van Smaalen; Jan L. de Boer

1988-01-01

143

The Capsid Proteins of a Large, Icosahedral dsDNA Virus  

PubMed Central

Summary Chilo iridescent virus (CIV) is a large (~1850 Å diameter) insect virus with an icosahedral, T=147 capsid, a dsDNA genome, and an internal lipid membrane. The structure of CIV was determined to 13 Å resolution by means of cryo-electron microscopy (cryoEM) and three-dimensional image reconstruction. A homology model of P50, the CIV major capsid protein (MCP), was built based on its amino acid sequence and the structure of the homologous Paramecium bursaria chlorella virus 1 (PBCV-1) Vp54 MCP. This model was fitted into the cryoEM density for each of the 25 trimeric CIV capsomers per icosahedral asymmetric unit. A difference map, in which the fitted CIV MCP capsomers were subtracted from the CIV cryoEM reconstruction, showed that there are at least three different types of minor capsid proteins associated with the capsomers outside the lipid membrane. “Finger” proteins are situated at many, but not all, of the spaces between three adjacent capsomers within each trisymmetron, and “zip” proteins are situated between sets of three adjacent capsomers at the boundary between neighboring trisymmetrons and pentasymmetrons. Based on the results of segmentation and density correlations, there are at least eight finger proteins, and three dimeric and two monomeric zip proteins in one asymmetric unit of the CIV capsid. These minor proteins appear to stabilize the virus by acting as intercapsomer cross-links. One transmembrane “anchor” protein per icosahedral asymmetric unit, which extends from beneath one of the capsomers in the pentasymmetron to the internal leaflet of the lipid membrane, may provide additional stabilization for the capsid. These results are consistent with the observations for other large, icosahedral dsDNA viruses that also utilize minor capsid proteins for stabilization and determining their assembly.

Yan, Xiaodong; Yu, Zeyun; Zhang, Ping; Battisti, Anthony J.; Chipman, Paul R.; Bajaj, Chandrajit; Bergoin, Max; Rossmann, Michael G.; Baker, Timothy S.

2010-01-01

144

A new dynamical framework of nonhydrostatic global model using the icosahedral grid  

NASA Astrophysics Data System (ADS)

For a nonhydrostatic global model that is run efficiently at super-high resolution, we propose the use of an icosahedral grid, which is one of the quasi-homogeneous grid systems. In this paper, we concentrate mainly on the description of the numerical scheme of a new dynamical framework using the icosahedral grid. The numerical method guarantees conservations of mass and total energy. To reduce the computational cost, the time-splitting scheme is employed and the set of equations is solved explicitly in the horizontal directions and implicitly in the vertical direction. This scheme only requires solving a one-dimensional Helmholtz equation for the vertical momentum. With the combination of this conservative nonhydrostatic scheme and the icosahedral grid, it is expected that the new model will efficiently run for super-high resolution simulations. For the first assessment of the performance of the new dynamical core, we performed fundamental wave propagation tests; acoustic waves, gravity waves, mountain waves, equatorial waves, and planetary waves. In order to check the performance as a climate model, we also performed the Held-Suarez Test Case as a statistical test. As a result, our model result has good correspondence with that of other established models.

Tomita, Hirofumi; Satoh, Masaki

2004-06-01

145

The Icosahedral Ti-Zr-Ni Quasicrystal - A Ground State Quasicrystal?  

NASA Astrophysics Data System (ADS)

The icosahedral Ti-Zr-Ni quasicrystal is known to be thermodynamically stable [1]. Most stable quasicrystals form at high temperatures from the liquid phase. In contrast to those quasicrystals, however, the Ti-Zr-Ni quasicrystal forms at lower temperatures, near 570^circC, by a solid state transformation of crystal phases that are stable at higher temperatures. A decorated canonical cell tiling for the structure of this quasicrystal was determined by a refinement to x-ray and neutron diffraction data and results from ab initio calculations. The energetic stability of the icosahedral Ti-Zr-Ni quasicrystal was investigated by total energy calculations using the density-functional code VASP [2]. The ternary ground state phase diagram for Ti-Zr-Ni was determined. The energy of the structural model of the quasicrystal is found to be lower than the energy of any known competing phase. This result, coupled with the continued stability with long anneals at lower temperatures, strongly suggest that the icosahedral Ti-Zr-Ni quasicrystal is a ground state quasicrystal. [1] K. F. Kelton, W. J. Kim, and R. M. Stroud. Appl. Phys. Let. 70, 3230 (1997). [2] G. Kresse and J. Hafner, Phys. Rev. B47, RC 558 (1993); G. Kresse and J. Furthmüller, Phys. Rev. B54, 11169 (1996).

Hennig, R. G.; Carlsson, A. E.; Kelton, K. F.; Henley, C. L.

2001-03-01

146

General Symmetry Breaking Constraints  

Microsoft Academic Search

We describe some new propagators for breaking symmetries in constraint satisfaction problems. We also introduce symmetry break- ing constraints to deal with symmetries acting simultaneously on vari- ables and values, conditional symmetries, as well as symmeties acting on set and other types of variables.

Toby Walsh

2006-01-01

147

Beauty in nature: Symmetry  

NASA Astrophysics Data System (ADS)

After an historical introduction of the concept of symmetry, the many ways in which symmetry is used in physics are briefly reviewed. A generalization of the concept of symmetry to supersymmetry is also briefly reviewed. Examples of dynamic symmetries and supersymmetries are shown.

Iachello, Francesco

2012-10-01

148

Paying Attention to Symmetry  

Microsoft Academic Search

Humans are very sensitive to symmetry in visual patterns. Symmetry is detected and recognized very rapidly. While viewing symmetrical patterns eye fixations are concentrated along the axis of symmetry or the symmetrical center of the patterns. This suggests that symmetry is a highly salient feature. Existing computational models of saliency, however, have mainly focused on contrast as a measure of

Gert Kootstra; Arco Nederveen; Bart de Boer

2008-01-01

149

Some Symmetries in Nuclei.  

National Technical Information Service (NTIS)

Internal and space-time symmetries are discussed in this group of lectures. The first of the lectures deals with an internal symmetry, or rather two related symmetries called charge independence and charge symmetry. The next two discuss space-time symmetr...

E. M. Henley

1981-01-01

150

Relativistic Pseudospin Symmetry  

SciTech Connect

We show that the pseudospin symmetry that Akito Arima discovered many years ago (with collaborators) is a symmetry of the the Dirac Hamiltonian for which the sum of the scalar and vector potentials are a constant. In this paper we discuss some of the implications of this relativistic symmetry and the experimental data that support these predictions. In his original paper Akito also discussed pseudo-U(3) symmetry. We show that pseudo-U(3) symmetry is a symmetry of the Dirac Hamiltonian for which the sum of harmonic oscillator vector and scalar potentials are equal to a constant, and we give the generators of pseudo-U(3) symmetry. Going beyond the mean field we summarize new results on non relativistic shell model Hamiltonians that have pseudospin symmetry and pseudo-orbital angular momentum symmetry as a dynamical symmetries.

Ginocchio, Joseph N. [MS 283, Los Alamos National Laboratory, Los Alamos, NM, 87545 (United States)

2011-05-06

151

Relativistic Pseudospin Symmetry  

NASA Astrophysics Data System (ADS)

We show that the pseudospin symmetry that Akito Arima discovered many years ago (with collaborators) is a symmetry of the the Dirac Hamiltonian for which the sum of the scalar and vector potentials are a constant. In this paper we discuss some of the implications of this relativistic symmetry and the experimental data that support these predictions. In his original paper Akito also discussed pseudo-U(3) symmetry. We show that pseudo-U(3) symmetry is a symmetry of the Dirac Hamiltonian for which the sum of harmonic oscillator vector and scalar potentials are equal to a constant, and we give the generators of pseudo-U(3) symmetry. Going beyond the mean field we summarize new results on non relativistic shell model Hamiltonians that have pseudospin symmetry and pseudo-orbital angular momentum symmetry as a dynamical symmetries.

Ginocchio, Joseph N.

2011-05-01

152

Symmetries in nuclei  

SciTech Connect

The use of dynamical symmetries or spectrum generating algebras for the solution of the nuclear many-body problem is reviewed. General notions of symmetry and dynamical symmetry in quantum mechanics are introduced and illustrated with simple examples such as the SO(4) symmetry of the hydrogen atom and the isospin symmetry in nuclei. Two nuclear models, the shell model and the interacting boson model, are reviewed with particular emphasis on their use of group-theoretical techniques.

Van Isacker, P. [Grand Accelerateur National d'Ions Lourds, CEA/DSM-CNRS/IN2P3 BP 55027, F-14076 Caen Cedex 5 (France)

2011-03-21

153

Magnetic color symmetry of lattice rotations in a diamagnetic material.  

PubMed

Oxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. Here we show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry. We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin film that exhibits ferroelectric (4mm) and antiferrodistortive (4{'}mm{'}) phases evolving through independent phase transitions. The approach has broader applicability for probing materials with lattice rotations that can be mapped to color groups. PMID:18643702

Denev, S; Kumar, A; Biegalski, M D; Jang, H W; Folkman, C M; Vasudevarao, A; Han, Y; Reaney, I M; Trolier-McKinstry, S; Eom, C-B; Schlom, D G; Gopalan, V

2008-06-23

154

Spontaneous symmetry breaking and chiral symmetry  

NASA Astrophysics Data System (ADS)

In this introductory lecture, some basic features of the spontaneous symmetry breaking are discussed. More specifically, ?-model, non-linear realization, and some examples of spontaneous symmetry breaking in the non-relativistic system are discussed in details. The approach here is more pedagogical than rigorous and the purpose is to get some simple explanation of some useful topics in this rather wide area. .

Li, Ling-Fong

2000-08-01

155

Symmetry and Symmetry Breaking in Software Patterns  

Microsoft Academic Search

Software patterns draw on the work of the architect Christopher Alexander, which in turn builds on foundations that may be more suitable to software than the architectural metaphors themselves. Patterns have a longstanding identity in the scientific community as results of a phenomenon called symmetry breaking. Symmetry breaking can be defined formally in terms of group theory. We establish formal

James O. Coplien; Liping Zhao

2000-01-01

156

Symmetries in Physics  

NASA Astrophysics Data System (ADS)

Preface; Copyright acknowledgements; List of contributors; 1. Introduction; Part I. Continuous Symmetries: 2. Classic texts: extracts from Weyl and Wigner; 3. Review paper: On the significance of continuous symmetry to the foundations of physics C. Martin; 4. The philosophical roots of the gauge principle: Weyl and transcendental phenomenological idealism T. Ryckman; 5. Symmetries and Noether's theorems K. A. Brading and H. R. Brown; 6. General covariance, gauge theories, and the Kretschmann objection J. Norton; 7. The interpretation of gauge symmetry M. Redhead; 8. Tracking down gauge: an ode to the constrained Hamiltonian formalism J. Earman; 9. Time-dependent symmetries: the link between gauge symmetries and indeterminism D. Wallace; 10. A fourth way to the Aharanov-Bohm effect A. Nounou; Part II. Discrete Symmetries: 11. Classic texts: extracts from Lebniz, Kant and Black; 12. Review paper: Understanding permutation symmetry S. French and D. Rickles; 13. Quarticles and the identity of discernibles N. Hugget; 14. Review paper: Handedness, parity violation, and the reality of space O. Pooley; 15. Mirror symmetry: what is it for a relational space to be orientable? N. Huggett; 16. Physics and Leibniz's principles S. Saunders; Part III. Symmetry Breaking: 17: Classic texts: extracts from Curie and Weyl; 18. Extract from G. Jona-Lasinio: Cross-fertilization in theoretical physics: the case of condensed matter and particle physics G. Jona-Lasinio; 19. Review paper: On the meaning of symmetry breaking E. Castellani; 20. Rough guide to spontaneous symmetry breaking J. Earman; 21. Spontaneous symmetry breaking: theoretical arguments and philosophical problems M. Morrison; Part IV. General Interpretative Issues: 22. Classic texts: extracts from Wigner; 23. Symmetry as a guide to superfluous theoretical structure J. Ismael and B. van Fraassen; 24. Notes on symmetries G. Belot; 25. Symmetry, objectivity, and design P. Kosso; 26. Symmetry and equivalence E. Castellani.

Brading, Katherine; Castellani, Elena

2010-01-01

157

Symmetries in Physics  

NASA Astrophysics Data System (ADS)

Preface; Copyright acknowledgements; List of contributors; 1. Introduction; Part I. Continuous Symmetries: 2. Classic texts: extracts from Weyl and Wigner; 3. Review paper: On the significance of continuous symmetry to the foundations of physics C. Martin; 4. The philosophical roots of the gauge principle: Weyl and transcendental phenomenological idealism T. Ryckman; 5. Symmetries and Noether's theorems K. A. Brading and H. R. Brown; 6. General covariance, gauge theories, and the Kretschmann objection J. Norton; 7. The interpretation of gauge symmetry M. Redhead; 8. Tracking down gauge: an ode to the constrained Hamiltonian formalism J. Earman; 9. Time-dependent symmetries: the link between gauge symmetries and indeterminism D. Wallace; 10. A fourth way to the Aharanov-Bohm effect A. Nounou; Part II. Discrete Symmetries: 11. Classic texts: extracts from Lebniz, Kant and Black; 12. Review paper: Understanding permutation symmetry S. French and D. Rickles; 13. Quarticles and the identity of discernibles N. Hugget; 14. Review paper: Handedness, parity violation, and the reality of space O. Pooley; 15. Mirror symmetry: what is it for a relational space to be orientable? N. Huggett; 16. Physics and Leibniz's principles S. Saunders; Part III. Symmetry Breaking: 17: Classic texts: extracts from Curie and Weyl; 18. Extract from G. Jona-Lasinio: Cross-fertilization in theoretical physics: the case of condensed matter and particle physics G. Jona-Lasinio; 19. Review paper: On the meaning of symmetry breaking E. Castellani; 20. Rough guide to spontaneous symmetry breaking J. Earman; 21. Spontaneous symmetry breaking: theoretical arguments and philosophical problems M. Morrison; Part IV. General Interpretative Issues: 22. Classic texts: extracts from Wigner; 23. Symmetry as a guide to superfluous theoretical structure J. Ismael and B. van Fraassen; 24. Notes on symmetries G. Belot; 25. Symmetry, objectivity, and design P. Kosso; 26. Symmetry and equivalence E. Castellani.

Brading, Katherine; Castellani, Elena

2003-12-01

158

Approximate flavor symmetries  

SciTech Connect

We discuss the idea of approximate flavor symmetries. Relations between approximate flavor symmetries and natural flavor conservation and democracy models is explored. Implications for neutrino physics are also discussed.

Rasin, A.

1994-04-01

159

Symmetry in Your World  

NSDL National Science Digital Library

This unit focuses on symmetrical shapes and objects in the real world. Students learn how to identify lines of symmetry as well as complete the missing halves of symmetrical figures. Students apply their knowledge of symmetry to real world objects.

Service, National S.

2009-04-24

160

Symmetries in Nuclei.  

National Technical Information Service (NTIS)

I reviewed the topic fundamental symmetries in nuclei. Among the various discrete fundamental symmetries three in particular, isospin (I), parity (P) and time-reversal (T), can be usefully probed by experiments in conventional nuclei. I confine myself to ...

E. G. Adelberger

1985-01-01

161

Aspects of symmetry violation  

SciTech Connect

Violations of symmetries have been used to determine (or test) the theoretical dynamics or to study structure. Recent experiments on parity non-conservation and time reversal symmetry, and that depend on spin properties, are used to illustrate both applications.

Henley, E.M.

1992-01-01

162

Aspects of symmetry violation  

SciTech Connect

Violations of symmetries have been used to determine (or test) the theoretical dynamics or to study structure. Recent experiments on parity non-conservation and time reversal symmetry, and that depend on spin properties, are used to illustrate both applications.

Henley, E.M.

1992-12-31

163

Experimenting with Symmetry  

NSDL National Science Digital Library

In this activity, learners use pattern blocks and mirrors to explore symmetry. Learners work in pairs and build mirror images of each other's designs. In doing so, learners will examine principles of symmetry and reflection.

Exploratorium

2010-01-01

164

Studies in Symmetry  

NSDL National Science Digital Library

This engaging lesson simultaneously involves animals, flowers, mathematical patterns, and art. Students will learn to discern between radial symmetry, bilateral symmetry, and asymmetry by observing and classifying objects, shapes, and photos and by determ

Eichinger, John

2009-05-30

165

Polynomial Graphs and Symmetry  

ERIC Educational Resources Information Center

|Most quadratic functions are not even, but every parabola has symmetry with respect to some vertical line. Similarly, every cubic has rotational symmetry with respect to some point, though most cubics are not odd. We show that every polynomial has at most one point of symmetry and give conditions under which the polynomial has rotational or…

Goehle, Geoff; Kobayashi, Mitsuo

2013-01-01

166

Dynamical x-ray diffraction from an icosahedral Al-Pd-Mn quasicrystal  

SciTech Connect

Primary extinction effects in diffraction from single grains of Al-Pd- Mn, and presumably many other FCI alloys, may be significant and should be corrected for prior to use of diffraction data in structural determinations. Probes based on dynamical diffraction effects, such as x-ray standing wave fluorescence, multiple beam interference, and x-ray transmission topographs, may now be used to study the bulk and surface structure of some quasicrystals. The observation of dynamical diffraction from icosahedral Al-Pd-Mn is a striking confirmation of the fact that quasicrystals can present a degree of structural perfection comparable to that found in the best periodic intermetallic crystals.

Kycia, S.

1996-04-23

167

Solution growth of a binary icosahedral quasicrystal of Sc[subscript 12]Zn[subscript 88  

SciTech Connect

We report the discovery of a binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra, and rhombic triacontahedra, under only marginally different growth conditions. These two morphologies manifest different degrees of quasicrystalline order. The discovery of i-Sc{sub 12}Zn{sub 88} suggests that a re-examination of binary phase diagrams at compositions close to crystalline approximant structures may reveal other binary quasicrystalline phases.

Canfield, P.C.; Caudle, M.L.; Ho, C.-S.; Kreyssig, A.; Nandi, S.; Kim, M.G.; Lin, X.; Kracher, A.; Dennis, K.W.; McCallum, R.W.; Goldman, A.I. (Iowa State)

2010-07-23

168

Low-temperature thermal properties of icosahedral Al?Re?Pd  

Microsoft Academic Search

We report measurements of the thermal conductivity ?(T) and the specific heat,C\\u000a \\u000a p\\u000a \\u000a (T) of icosahedral Al70Re8.6Pd21.4 at low temperatures. Below 1 K, the behaviour of the quasilattice thermal conductivity ?ph(T) is compatible with the scattering of vibrational excitations involving tunneling states and grain boundaries. The specific\\u000a heatC\\u000a \\u000a p\\u000a \\u000a (T) contains a small contribution ??T. Our ?ph(T) results indicate that

M. A. Chernikov; A. Bianchi; E. Felder; U. Gubler; H. R. Ott

1996-01-01

169

A realistic model structure of Frank-Kasper-type icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

The paper deals with construction of a model structure of Frank-Kasper-type icosahedral quasi-crystals based on the three-dimensional Penrose lattice decorated according a method based on the structural units composing the (Al,Zn)49Mg32 Frank-Kasper crystalline phase, and relaxed by interatomic potentials. Procedures for producing the model structure are summarized: (1) constructing the three-dimensional Penrose lattice by a generalized dual method; (2) decorating the prolate and oblate rhombohedral units; (3) searching for the rhombic dodecahedral configurations (composed of two prolate and oblate rhombohedral units which allow overlapping) and modifying the decoration; and (4) relaxing the structure by interatomic potentials.

Tei, Tetsushoku; Kimura, Kaoru; Takeuchi, Shin

1990-03-01

170

Icosahedral packing of polymer-tethered nanospheres and stabilization of the Gyroid Phase  

NSDL National Science Digital Library

We present results of molecular simulations that predict the phases formed by the selfassembly of model nanospheres functionalized with a single polymer âtetherâ. Microphase separation of the immiscible tethers and nanospheres induces the formation of the double gyroid, perforated lamella and crystalline bilayer phases. Confinement effects promote the formation of icosahedral arrangements of nanoparticles that help to stabilize the gyroid and perforated lamella phases. We also present a new metric for determining the local arrangement of particles in liquid and solid configurations. Preprint, link to published version can be found below.

Iacovella, Christopher R.; Keys, Aaron S.; Horsch, Mark A.; Glotzer, Sharon C.

2006-05-17

171

Chiral symmetry and chiral-symmetry breaking  

SciTech Connect

These lectures concern the dynamics of fermions in strong interaction with gauge fields. Systems of fermions coupled by gauge forces have a very rich structure of global symmetries, which are called chiral symmetries. These lectures will focus on the realization of chiral symmetries and the causes and consequences of thier spontaneous breaking. A brief introduction to the basic formalism and concepts of chiral symmetry breaking is given, then some explicit calculations of chiral symmetry breaking in gauge theories are given, treating first parity-invariant and then chiral models. These calculations are meant to be illustrative rather than accurate; they make use of unjustified mathematical approximations which serve to make the physics more clear. Some formal constraints on chiral symmetry breaking are discussed which illuminate and extend the results of our more explicit analysis. Finally, a brief review of the phenomenological theory of chiral symmetry breaking is presented, and some applications of this theory to problems in weak-interaction physics are discussed. (WHK)

Peskin, M.E.

1982-12-01

172

Connectivity of icosahedral network and a dramatically growing static length scale in Cu-Zr binary metallic glasses  

NASA Astrophysics Data System (ADS)

We report on and characterize, via molecular dynamics studies, the evolution of the structure of Cu50Zr50 and Cu64Zr36 metallic glasses (MGs) as temperature is varied. Interestingly, a percolating icosahedral network appears in the Cu64Zr36 system as it is supercooled. This leads us to introduce a static length scale, which grows dramatically as this three-dimensional system approaches the glass transition. Amidst interpenetrating connections, noninterpenetrating connections between icosahedra are shown to become prevalent upon supercooling and to greatly enhance the connectivity of the MG's icosahedral network. Additionally, we characterize the chemical compositions of the icosahedral networks and their components. These findings demonstrate the importance of noninterpenetrating connections for facilitating extensive structural networks in Cu-Zr MGs, which in turn drive dynamical slowing in these materials.

Soklaski, Ryan; Nussinov, Zohar; Markow, Zachary; Kelton, K. F.; Yang, Li

2013-05-01

173

Correlation between structural relaxation and connectivity of icosahedral clusters in CuZr metallic glass-forming liquids  

NASA Astrophysics Data System (ADS)

The correlation between structural relaxation and the medium-range structures formed by icosahedral cluster packing in CuZr supercooled metallic glass-forming liquids was studied via molecular dynamics simulations. We find that compared to the amount of icosahedral clusters, the medium-range structures formed by icosahedral cluster packing play more important and controlling roles in the structural relaxation process of the supercooled liquids. The relaxation times of local structures depend exponentially on the connectivity of local structures. Despite the argument whether there is a specific connection between the static structure and dynamic property of glass formers in particle level, it does exist on larger length scale. Our results demonstrate that dynamical heterogeneity is indeed correlated with the medium-range static atomic structures in the supercooled glass-forming liquids.

Wu, Z. W.; Li, M. Z.; Wang, W. H.; Liu, K. X.

2013-08-01

174

Positron-annihilation studies on Al-Cu-Fe: Their significance for the structural models of icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

We have investigated the vacancy defects in samples of quasicrystalline Al-Cu-Fe using positron-lifetime measurements as a function of various heat treatments and alloy compositions. In general, a two-component positron-annihilation-lifetime spectrum seems characteristic of quasicrystalline Al-Cu-Fe and other icosahedral quasicrystals. This can be interpreted in terms of vacancy defects, whose concentrations are about three orders of magnitude more than what one usually observes in crystalline metals at room temperature. We discuss the significance of the results of our studies for the structure of icosahedral quasicrystals, for which several models have been postulated in the literature. The concentration of the vacancy defects observed by us seems incompatible with the icosahedral-twin model or, at first sight, with the space-filling Penrose tiling based models or random-tiling models.

Chidambaram, R.; Sanyal, M. K.; Raghunathan, V. S.; Nambissan, P. M. G.; Sen, P.

1993-08-01

175

Medium-range icosahedral order in quasicrystal-forming Zr{sub 2}Pd binary metallic glass  

SciTech Connect

Medium-range order in Zr{sub 2}Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr{sub 2}Pd metallic glass.

Huang Li [Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011 (United States); Fang, X. W. [Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011 (United States); Department of Physics and Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, C. Z.; Ho, K. M. [Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011 (United States); Department of Physics, Iowa State University, Ames, Iowa 50011 (United States); Kramer, M. J. [Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011 (United States); Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States); Ding, Z. J. [Department of Physics and Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2011-06-06

176

The Architecture and Chemical Stability of the Archaeal Sulfolobus Turreted Icosahedral Virus ?  

PubMed Central

Viruses utilize a diverse array of mechanisms to deliver their genomes into hosts. While great strides have been made in understanding the genome delivery of eukaryotic and prokaryotic viruses, little is known about archaeal virus genome delivery and the associated particle changes. The Sulfolobus turreted icosahedral virus (STIV) is a double-stranded DNA (dsDNA) archaeal virus that contains a host-derived membrane sandwiched between the genome and the proteinaceous capsid shell. Using cryo-electron microscopy (cryo-EM) and different biochemical treatments, we identified three viral morphologies that may correspond to biochemical disassembly states of STIV. One of these morphologies was subtly different from the previously published 27-Å-resolution electron density that was interpreted with the crystal structure of the major capsid protein (MCP). However, these particles could be analyzed at 12.5-Å resolution by cryo-EM. Comparing these two structures, we identified the location of multiple proteins forming the large turret-like appendages at the icosahedral vertices, observed heterogeneous glycosylation of the capsid shell, and identified mobile MCP C-terminal arms responsible for tethering and releasing the underlying viral membrane to and from the capsid shell. Collectively, our studies allow us to propose a fusogenic mechanism of genome delivery by STIV, in which the dismantled capsid shell allows for the fusion of the viral and host membranes and the internalization of the viral genome.

Khayat, Reza; Fu, Chi-yu; Ortmann, Alice C.; Young, Mark J.; Johnson, John E.

2010-01-01

177

Infectious bursal disease virus is an icosahedral polyploid dsRNA virus  

PubMed Central

Viruses are a paradigm of the economy of genome resources, reflected in their multiplication strategy and for their own structure. Although there is enormous structural diversity, the viral genome is always enclosed within a proteinaceous coat, and most virus species are haploid; the only exception to this rule are the highly pleomorphic enveloped viruses. We performed an in-depth characterization of infectious bursal disease virus (IBDV), a non-enveloped icosahedral dsRNA virus with a bisegmented genome. Up to 6 natural populations can be purified, which share a similar protein composition but show higher sedimentation coefficients as particle density increases. Stoichiometry analysis of their genome indicated that these biophysical differences correlate with the copy number of dsRNA segments inside the viral capsid. This is a demonstration of a functional polyploid icosahedral dsRNA virus. We show that IBDV particles with greater genome copy number have higher infectivity rates. Our results show an unprecedented replicative strategy for dsRNA viruses and suggest that birnaviruses are living viral entities encompassing numerous functional and structural characteristics of positive and negative ssRNA viruses.

Luque, Daniel; Rivas, German; Alfonso, Carlos; Carrascosa, Jose L.; Rodriguez, Jose F.; Caston, Jose R.

2009-01-01

178

The structure of the NTPase that powers DNA packaging into Sulfolobus turreted icosahedral virus 2.  

PubMed

Biochemical reactions powered by ATP hydrolysis are fundamental for the movement of molecules and cellular structures. One such reaction is the encapsidation of the double-stranded DNA (dsDNA) genome of an icosahedrally symmetric virus into a preformed procapsid with the help of a genome-translocating NTPase. Such NTPases have been characterized in detail from both RNA and tailed DNA viruses. We present four crystal structures and the biochemical activity of a thermophilic NTPase, B204, from the nontailed, membrane-containing, hyperthermoacidophilic archaeal dsDNA virus Sulfolobus turreted icosahedral virus 2. These are the first structures of a genome-packaging NTPase from a nontailed, dsDNA virus with an archaeal host. The four structures highlight the catalytic cycle of B204, pinpointing the molecular movement between substrate-bound (open) and empty (closed) active sites. The protein is shown to bind both single-stranded and double-stranded nucleic acids and to have an optimum activity at 80°C and pH 4.5. The overall fold of B204 places it in the FtsK-HerA superfamily of P-loop ATPases, whose cellular and viral members have been suggested to share a DNA-translocating mechanism. PMID:23698307

Happonen, Lotta J; Oksanen, Esko; Liljeroos, Lassi; Goldman, Adrian; Kajander, Tommi; Butcher, Sarah J

2013-05-22

179

Classifying fractionalization: Symmetry classification of gapped Z2 spin liquids in two dimensions  

NASA Astrophysics Data System (ADS)

We classify distinct types of quantum number fractionalization occurring in two-dimensional topologically ordered phases, focusing in particular on phases with Z2 topological order, that is, on gapped Z2 spin liquids. We find that the fractionalization class of each anyon is an equivalence class of projective representations of the symmetry group, corresponding to elements of the cohomology group H2(G,Z2). This result leads us to a symmetry classification of gapped Z2 spin liquids, such that two phases in different symmetry classes cannot be connected without breaking symmetry or crossing a phase transition. Symmetry classes are defined by specifying a fractionalization class for each type of anyon. The fusion rules of anyons play a crucial role in determining the symmetry classes. For translation and internal symmetries, braiding statistics plays no role, but can affect the classification when point group symmetries are present. For square lattice space group, time-reversal, and SO(3) spin rotation symmetries, we find 2098176?221 distinct symmetry classes. Our symmetry classification is not complete, as we exclude, by assumption, permutation of the different types of anyons by symmetry operations. We give an explicit construction of symmetry classes for square lattice space group symmetry in the toric code model. Via simple examples, we illustrate how information about fractionalization classes can, in principle, be obtained from the spectrum and quantum numbers of excited states. Moreover, the symmetry class can be partially determined from the quantum numbers of the four degenerate ground states on the torus. We also extend our results to arbitrary Abelian topological orders (limited, though, to translations and internal symmetries), and compare our classification with the related projective symmetry group classification of parton mean-field theories. Our results provide a framework for understanding and probing the sharp distinctions among symmetric Z2 spin liquids and are a first step toward a full classification of symmetric topologically ordered phases.

Essin, Andrew M.; Hermele, Michael

2013-03-01

180

Space Group Symmetry  

NSDL National Science Digital Library

In this problem set, students are given space group symmetry diagrams for primitive (P) orthorhombic space groups. For each diagram they must write down the symmetry axis (either 2 or 21) that is parallel to each major axis, and give the symmetry plane (a, b, c, n, or m) that is normal (perpendicular)to each. They must also give the simplified Hermann-Mauguin symbol for the space group.

181

From molecular clusters to bulk matter. II. Crossover from icosahedral to crystalline structures in CO2 clusters  

Microsoft Academic Search

The change in structure with size in (CO2)N clusters has been investigated in the crossover regime from icosahedral to cubic morphology (N=19 to 55) by molecular dynamics simulation. All the minima in the potential energy surface (PES) visited by the solid clusters at finite temperature have been characterized using a local structure analysis method. A simple picture of the change

Jean-Bernard Maillet; Anne Boutin; Alain H. Fuchs

1999-01-01

182

Bridged Heterocyclium Dicationic closo-Icosahedral Perfluoroborane, Borane, and Carborane Salts via Aqueous, Open-Air Benchtop Synthesis (Postprint).  

National Technical Information Service (NTIS)

Thirteen bridged triazolium and imidazolium dicationic salts, which uniquely pair closo-icosahedral perfluoroborane B12F12(2)-, borane B12H1(2)2-, or carborane CB11H1(2)- anionic species with unsaturated bridged heterocyclium dications, were synthesized u...

A. K. Wheaton J. A. Boatz J. L. Belletire S. Schneider S. A. Shackelford

2010-01-01

183

The structure of tobacco ringspot virus: a link in the evolution of icosahedral capsids in the picornavirus superfamily  

Microsoft Academic Search

Background: Tobacco ringspot virus (TRSV) is a member of the nepovirus genus of icosahedral RNA plant viruses that cause disease in fruit crops. Nepoviruses, comoviruses and picornaviruses are classified in the picornavirus superfamily. Crystal structures of comoviruses and picornaviruses and the molecular mass of the TRSV subunit (sufficient to accommodate three ?-barrel domains) suggested that nepoviruses may represent a link

Veda Chandrasekar; John E Johnson

1998-01-01

184

The Symmetries of QCD  

ScienceCinema

The symmetries of a quantum field theory can be realized in a variety of ways. Symmetries can be realized explicitly, approximately, through spontaneous symmetry breaking or, via an anomaly, quantum effects can dynamically eliminate a symmetry of the theory that was present at the classical level.  Quantum Chromodynamics (QCD), the modern theory of the strong interactions, exemplify each of these possibilities. The interplay of these effects determine the spectrum of particles that we observe and, ultimately, account for 99% of the mass of ordinary matter. 

185

Icosahedral B{sub 12}, macropolyhedral boranes, {beta}-rhombohedral boron and boron-rich solids  

SciTech Connect

The preference for icosahedral B{sub 12} amongst polyhedral boranes and elemental boron is explained based on an optimization of overlap model. The ingenious ways in which elemental boron and boron-rich solids achieve icosahedron-related structures are explained by a fragment approach. The Jemmis mno rules are used to get the electron requirements. The extra occupancies and vacancies in {beta}-rhombohedral structures are shown to be inevitable results of electron requirements. The detailed understanding of the structure suggests ways of doping {beta}-rhombohedral boron with metals for desired properties. Theoretical studies of model {beta}-rhombohedral solids with metal dopings provide support for the analysis. - Graphical abstract: A short legend: Principal building blocks B{sub 12}, B{sub 57}, and B{sub 84} of elemental boron and boron-rich solids.

Jemmis, Eluvathingal D. [School of Chemistry, University of Hyderabad, Hyderabad 500046 (India) and Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India)]. E-mail: jemmis@ipc.iisc.ernet.in; Prasad, Dasari L.V.K. [School of Chemistry, University of Hyderabad, Hyderabad 500046 (India); Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India)

2006-09-15

186

Electronic structure and optical properties of Si-containing icosahedral boron crystals  

SciTech Connect

The electronic structure and the optical properties of two models of (Bi{sub 10}Si{sub 2})Si{sub 2} icosahedral crystal are studied by first-principles local-density calculations. Both models have a central Si-Si chain as in the rhombohedral B{sub 12}P{sub 2} crystal and two Si atoms replacing two B atoms in the B{sub 12} icosahedron. Model I has a Si-Si link between the substituted icohasedra, while model II does not have such a link. Both are found to be semiconductors with gaps of 1.29 and 1.72 eV, respectively. Model I is found to have a slightly lower total energy. The calculated electronic and optical properties are compared with other B-rich compounds with a similar rhombohedral structure. {copyright} {ital 1998} {ital The American Physical Society}

Ching, W.Y. [Max-Plank Institut fuer Metallforschung, Seestrasse 92, D-70174Stuttgart (Germany)]|[Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri64110 (United States); Li, D. [Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri64110 (United States)

1998-02-01

187

Thermal conductivity and Seebeck coefficients of icosahedral boron arsenide films on silicon carbide  

NASA Astrophysics Data System (ADS)

The thermal conductivity of icosahedral boron arsenide (B12As2) films grown on (0001) 6H-SiC substrates by chemical vapor deposition was studied by the 3? technique. The room temperature thermal conductivity decreased from 27.0 to 15.3 W/m K as the growth temperature was decreased from 1450 to 1275 °C. This is mainly attributed to the differences in the impurity concentration and microstructure, determined from secondary ion mass spectrometry and high resolution transmission electron microscopy, respectively. Callaway's theory was applied to calculate the temperature-dependent thermal conductivity, and the results are in good agreement with the experimental data. Seebeck coefficients were determined as 107 ?V/K and 136 ?V/K for samples grown at 1350 °C with AsH3/B2H6 flow ratio equals to 1:1 and 3:5, respectively.

Gong, Y.; Zhang, Y.; Dudley, M.; Zhang, Y.; Edgar, J. H.; Heard, P. J.; Kuball, M.

2010-10-01

188

Axial Symmetry Simulation  

NSDL National Science Digital Library

In this simulation, you will learn about axial symmetry and the difference between the axes. Just drag and drop the shapes onto the grid and choose between the different axes of symmetry to see the effect it has on the various shapes.

2007-01-01

189

Symmetries in Lagrangian Dynamics  

ERIC Educational Resources Information Center

|In the framework of Noether's theorem, a distinction between Lagrangian and dynamical symmetries is made, in order to clarify some aspects neglected by textbooks. An intuitive setting of the concept of invariance of differential equations is presented. The analysis is completed by deriving the symmetry properties in the motion of a charged…

Ferrario, Carlo; Passerini, Arianna

2007-01-01

190

Better Verification Through Symmetry  

Microsoft Academic Search

We address the state explosion problem in automatic verification of finite-state systemsby exploiting symmetries in the system description.We make symmetries easy to detect by introducing a new data type scalarset, a finiteand unordered set, to our description language. The set of operations on scalarsets arerestricted so that states are guaranteed to have the same future behavior, up to permutationof the

C. Norris Ip

1993-01-01

191

Party Hat Symmetry  

NSDL National Science Digital Library

In this hands-on activity, learners make New Year's Eve party hats out of wrapping paper. Learners use symmetry and measurement to cut out shapes they need to assemble the hats. In a related video, Mr. O and his assistants explain how to make the party hats using rotational symmetry. Learners can watch this video before creating their hats.

Houston, Children'S M.

2011-01-01

192

Quantum mechanics and symmetries  

Microsoft Academic Search

Symmetries have always played an important role in physics. With quantum mechanics, however, the interplay between physics and symmetries has reached a new dimension. The very structure of quantum mechanics invites the application of group theoretical methods to an extent that physicists would have been led to invent various concepts of group theory, such as Lie groups, by quantum mechanics

J. Wess

2000-01-01

193

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

194

Unbreaking chiral symmetry  

SciTech Connect

In quantum chromodynamics (QCD) the eigenmodes of the Dirac operator with small absolute eigenvalues have a close relationship to the dynamical breaking of the chiral symmetry. In a simulation with two dynamical quarks, we study the behavior of meson propagators when removing increasingly more of those modes in the valence sector, thus partially removing effects of chiral symmetry breaking. We find that some of the symmetry aspects are restored (e.g., the masses of {rho} and a{sub 1} approach each other) while confining properties persist.

Lang, C. B.; Schroeck, Mario [Institut fuer Physik, FB Theoretische Physik, Universitaet Graz, A-8010 Graz (Austria)

2011-10-15

195

Dynamical systems and ?-symmetries  

NASA Astrophysics Data System (ADS)

A deformation of the standard prolongation operation, defined on sets of vector fields in involution rather than on single ones, was recently introduced and christened ‘?-prolongation’ correspondingly, one has ‘?-symmetries’ of differential equations. These can be used to reduce the equations under study, but the general reduction procedure under ?-symmetries fails for equations of order 1. In this paper, we discuss how ?-symmetries can be used to reduce dynamical systems, i.e. sets of first-order ODEs in the form \\dot{x}^a = f^a (x).

Cicogna, G.; Gaeta, G.; Walcher, S.

2013-06-01

196

Sequential flavor symmetry breaking  

SciTech Connect

The gauge sector of the standard model exhibits a flavor symmetry that allows for independent unitary transformations of the fermion multiplets. In the standard model the flavor symmetry is broken by the Yukawa couplings to the Higgs boson, and the resulting fermion masses and mixing angles show a pronounced hierarchy. In this work we connect the observed hierarchy to a sequence of intermediate effective theories, where the flavor symmetries are broken in a stepwise fashion by vacuum expectation values of suitably constructed spurion fields. We identify the possible scenarios in the quark sector and discuss some implications of this approach.

Feldmann, Thorsten [Physik Department T31, Technische Universitaet Muenchen, D-85747 Garching (Germany); Jung, Martin [Theoretische Physik 1, Fachbereich Physik, Universitaet Siegen, D-57068 Siegen (Germany); Instituto de Fisica Corpuscular, CSIC-Universitat de Valencia, Apartado de Correos 22085, E-46071 Valencia (Spain); Mannel, Thomas [Theoretische Physik 1, Fachbereich Physik, Universitaet Siegen, D-57068 Siegen (Germany)

2009-08-01

197

Structural relaxation of the melt-spun icosahedral phase and a new type of approximant in Al-Cu-Ru alloys  

Microsoft Academic Search

The formation range and thermal stability of the icosahedral phase produced by melt spinning were investigated in ternary Al?Cu?Ru alloys by X-ray diffraction and transmission electron microscopy. The stable face-centred icosahedral (FCI) phase is formed in a wide region where the condition for the valence electron-to-atom ratio e\\/a?1·75 is satisfied. Shifts of diffraction peaks to larger angles were observed during

K. Araki; A. Waseda; K. Kimura; H. Ino

1993-01-01

198

Another Broken Symmetry  

ERIC Educational Resources Information Center

|Resistance destroys symmetry. In this note, a graphical exploration serves as a guide to a rigorous elementary proof of a specific asymmetry in the trajectory of a point projectile in a medium offering linear resistance.|

Groetsch, C. W.

2005-01-01

199

Animal Gaits and Symmetry  

NASA Astrophysics Data System (ADS)

Many gaits of four-legged animals are described by symmetry. For example, when a horse paces it moves both left legs in unison and then both right legs and so on. The motion is described by two symmetries: Interchange front and back legs, and swap left and right legs with a half-period phase shift. Biologists postulate the existence of a central pattern generator (CPG) in the neuronal system that sends periodic signals to the legs. CPGs can be thought of as electrical circuits that produce periodic signals and can be modeled by systems with symmetry. In this lecture we discuss animal gaits; use gait symmetries to construct a simplest CPG architecture that naturally produces quadrupedal gait rhythms; and make several testable predictions about gaits.

Golubitsky, Martin

2012-04-01

200

Symmetries in Physics  

NASA Astrophysics Data System (ADS)

The purpose of this course is to study the evolution of the symmetry concept and establish its influence in the knowledge of the fundamental laws of nature. Physicist have been using the symmetry concept in two ways: to solve problems and to search for new understanding of the world around us. In quantum physics symmetry plays a key role in gaining an understanding of the physical laws governing the behavior of matter and field systems. It provides, generally, a shortcut based on geometry for discovering the secrets of the Universe. Because it is believed that the laws of physics are invariant under discrete and continuous transformation operations of the space and time, there are continuous symmetries, for example, energy and momentum together with discrete ones corresponding to charge, parity and time reversal operations.

Castaños, Octavio

2010-09-01

201

Polymer quantization and symmetries  

NASA Astrophysics Data System (ADS)

Polymer quantization was rediscoveredPlease see acknowledgements. during the construction of loop quantum cosmology. For the simplest quantum theory of one degree of freedom, the implications for dynamics were studied for the harmonic oscillator as well as some other potentials. For more degrees of freedom, the possibility of continuous, kinematic symmetries arises. While these are realized on the Hilbert space of polymer quantum mechanics, their infinitesimal versions are not supported. For an invariant Hamiltonian, these symmetry realizations imply infinite degeneracy suggesting that the symmetry should be spontaneously or explicitly broken. The estimation of symmetry violations in some cases have been analysed before. Here, we explore the alternative of shifting the arena to the distributional states. We discuss both the polymer quantum mechanics case and the polymer-quantized scalar field.

Date, Ghanashyam; Kajuri, Nirmalya

2013-04-01

202

Symmetry, beauty and evolution  

Microsoft Academic Search

HUMANS and certain other species find symmetrical patterns more attractive than asymmetrical ones. These preferences may appear in response to biological signals1-3, or in situations where there is no obvious signalling context, such as exploratory behaviour4,5 and human aesthetic response to pattern6-8. It has been proposed9,10 that preferences for symmetry have evolved in animals because the degree of symmetry in

Magnus Enquist; Anthony Arak

1994-01-01

203

Symmetry and cleavage fracture  

SciTech Connect

The role of the symmetry of the interaction of shock waves with free and supported surfaces in the formation of cleavage fractures is studied. A qualitative analysis is made of the schemes of two limiting cases of the development of relief processes in a plate compressed by a shock wave. The results of the analysis are compared with our experiments and those of other researchers. The data obtained indicate that the process of cleavage fractures can be controlled by changing the loading symmetry.

Lebedev, M.A.; Litvinov, B.V.

1995-11-01

204

Closely Related Archaeal Haloarcula hispanica Icosahedral Viruses HHIV-2 and SH1 Have Nonhomologous Genes Encoding Host Recognition Functions  

PubMed Central

Studies on viral capsid architectures and coat protein folds have revealed the evolutionary lineages of viruses branching to all three domains of life. A widespread group of icosahedral tailless viruses, the PRD1-adenovirus lineage, was the first to be established. A double ?-barrel fold for a single major capsid protein is characteristic of these viruses. Similar viruses carrying genes coding for two major capsid proteins with a more complex structure, such as Thermus phage P23-77 and haloarchaeal virus SH1, have been isolated. Here, we studied the host range, life cycle, biochemical composition, and genomic sequence of a new isolate, Haloarcula hispanica icosahedral virus 2 (HHIV-2), which resembles SH1 despite being isolated from a different location. Comparative analysis of these viruses revealed that their overall architectures are very similar except that the genes for the receptor recognition vertex complexes are unrelated even though these viruses infect the same hosts.

Jaakkola, Salla T.; Penttinen, Reetta K.; Vilen, Silja T.; Jalasvuori, Matti; Ronnholm, Gunilla; Bamford, Jaana K. H.; Bamford, Dennis H.

2012-01-01

205

Ab initio Ti-Zr-Ni phase diagram predicts stability of icosahedral TiZrNi quasicrystals  

NASA Astrophysics Data System (ADS)

The ab initio phase diagram determines the energetic stability of the icosahedral TiZrNi quasicrystal. The complete ab initio zero-temperature ternary phase diagram is constructed from the calculated energies of the elemental, binary and ternary Ti-Zr-Ni phases. For this, the icosahedral i -TiZrNi quasicrystal is approximated by periodic structures of up to 123 atoms/unit cell, based on a decorated-tiling model [R. G. Hennig, K. F. Kelton, A. E. Carlsson, and C. L. Henley, Phys. Rev. B 67, 134202 (2003)]. The approximant structures containing the 45-atom Bergman cluster are nearly degenerate in energy, and are all energetically stable against the competing phases. It is concluded that i -TiZrNi is a ground-state quasicrystal, as it is experimentally the low-temperature phase for its composition.

Hennig, R. G.; Carlsson, A. E.; Kelton, K. F.; Henley, C. L.

2005-04-01

206

Degree of structural perfection of icosahedral quasicrystalline grains investigated by synchrotron X-ray diffractometry and imaging techniques  

Microsoft Academic Search

A study of the structural perfection of icosahedral quasicrystalline grains of various alloys (Al-Pd-Mn, Zn-Mg-RE (RE L rare earth) and Al-Cu-Fe), grown by different slow solidification techniques (Czochralski, Bridgman, flux and annealing) was performed using high-resolution diffraction, including recording rocking curves combined with X-ray topography and phase contrast radiography, at a third-generation synchrotron radiation source (European Synchrotron Radiation Facility, Grenoble,

J. Gastaldi; S. Agliozzo; A. Létoublon; J. Wang; L. Mancini; H. Klein; J. Härtwig; J. Baruchel; I. R. Fisher; T. Sato; A. P. Tsai; A. M. de Boissieu

2003-01-01

207

Defect-induced Symmetry Distortions in Doped Cubic Boron Nitride  

NASA Astrophysics Data System (ADS)

We have studied the substitution of silicon and beryllium for boron in cubic boron nitride with several first-principles methods. The Be and Si defects are proto-typical p- and n-type dopants respectively.(O. Mishima, S. Yamoka, and O. Fukunaga, Science 238), 181 (1987). The substitutionals have orbitally degenerate ground states leading to symmetry-lowering distortions of the Td point-group symmetry about the boron sites. Calculated IR absorption modes associated with the defects are compared with recent experimental determination of bulk modes.(M. I. Eremets, M. Gauthier, A. Polian, J. C. Chervin, J. M. Besson, G. A. Dubitskii, and Y. Y. Semenova, Phys. Rev. B 52), 8854 (1995). Changes in Fermi contact interaction terms as an effect of the distortions are discussed as a possible way of characterizing the distortions experimentally.

Patton, David C.; Harrison, Joseph G.

1996-03-01

208

The Gardner method for symmetries  

NASA Astrophysics Data System (ADS)

The Gardner method, traditionally used to generate conservation laws of integrable equations, is generalized to generate symmetries. The method is demonstrated for the KdV, Camassa-Holm and sine-Gordon equations. The method involves identifying a generating symmetry which depends upon a parameter; expansion of this symmetry in a (formal) power series in the parameter then gives the usual infinite hierarchy of symmetries. We show that the obtained symmetries commute, discuss the relation of the Gardner method with Lenard recursion (both for symmetries and conservation laws), and also the connection between the symmetries of continuous integrable equations and their discrete analogues.

Rasin, Alexander G.; Schiff, Jeremy

2013-04-01

209

Investigation of 5D point symmetry groups with an invariant 3D plane and immobile point on it  

NASA Astrophysics Data System (ADS)

To reveal the structure of 5D point symmetry groups with an invariant 3D plane and immobile point on it, we review in detail the catalog of 1208 3D point groups of ten rosette P-symmetries at P ? G 20, which interpret (accurate to the structure) the aforementioned symmetry groups of the 5D Euclidean space of the category G 530, where the numbers in the index 530 indicate successively the dimension of space and the dimensions of invariant subspaces in this space.

Palistrant, A. F.

2013-05-01

210

Scanning tunneling microscopy of cleaved AlPdMn icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

Quasicrystal surfaces produced by in-situ cleavage in ultra-high vacuum have been investigated by scanning tunneling microscopy. Twofold and fivefold surfaces of icosahedral AlPdMn single-quasicrystals have been studied. The surfaces were found to be rough. Their structure is determined by cluster aggregates of various sizes formed on the basis of an elementary cluster whose contrast behavior and diameter of about 1 nm point to the Mackay-type cluster [1]. The surface of these elementary clusters exhibits a smooth density of electronic states. These observations agree with the predictions of recent models on the quasicrystal structure and electronic properties in which the Mackay-type clusters play a dominant role [2]. In particular, these clusters are believed to act as deep potential wells leading to electron states primarily bound to these. Crack propagation during cleavage occurs along zones of lower strength between the clusters indicating that these act as rigid entities. This corroborates the assumption made in modern treatments of quasicrystal plasticity that the Mackay-type clusters control the mechanical properties [3,4]. [1] Ph. Ebert, M. Feuerbacher, N. Tamura, M. Wollgarten, and K. Urban, Phys. Rev. Lett. 77, 3827 (1996). [2] C. Janot, Phys. Rev. B 53, 181 (1996). [3] M. Feuerbacher, B. Baufeld, R. Rosenfeld, M. Bartsch, G. Hanke, M. Beyss, M. Wollgarten, and K. Urban, Philos. Mag. Lett. 71, 91 (1995). [4] F. Krul, R. Mikulla, P. Gumbsch, and H.-R. Trebin (to be published).

Urban, K.

1997-03-01

211

The icosahedral RNA virus as a grotto: organizing the genome into stalagmites and stalactites.  

PubMed

There are two important problems in the assembly of small, icosahedral RNA viruses. First, how does the capsid protein select the viral RNA for packaging, when there are so many other candidate RNA molecules available? Second, what is the mechanism of assembly? With regard to the first question, there are a number of cases where a particular RNA sequence or structure--often one or more stem-loops--either promotes assembly or is required for assembly, but there are others where specific packaging signals are apparently not required. With regard to the assembly pathway, in those cases where stem-loops are involved, the first step is generally believed to be binding of the capsid proteins to these "fingers" of the RNA secondary structure. In the mature virus, the core of the RNA would then occupy the center of the viral particle, and the stem-loops would reach outward, towards the capsid, like stalagmites reaching up from the floor of a grotto towards the ceiling. Those viruses whose assembly does not depend on protein binding to stem-loops could have a different structure, with the core of the RNA lying just under the capsid, and the fingers reaching down into the interior of the virus, like stalactites. We review the literature on these alternative structures, focusing on RNA selectivity and the assembly mechanism, and we propose experiments aimed at determining, in a given virus, which of the two structures actually occurs. PMID:23860866

Harvey, Stephen C; Zeng, Yingying; Heitsch, Christine E

2013-04-27

212

Aqua Planet Experiments with a new AGCM using Icosahedral-hexagonal grids  

NASA Astrophysics Data System (ADS)

A numerical scheme is presented which has been used for developing a new dynamical core on icosahedral-hexagonal grid. This global model is based on the governing equations of a well established atmospheric general circulation model (LMDZ). The discrete form of equations as implemented in the design of this new model is described. The two dynamical cores - LMDZ model and the new model - are then tested using standard test cases. Indeed, the dynamical core of a general circulation model can be isolated from the physics and can be tested independently. Following this philosophy, dry dynamics is first tested with Jablonowski-Williamson idealized baroclinic wave test case (to assess the capacity of model to capture steep gradients. Then the Held-Suarez test is performed to obtain a balanced state of the atmosphere after a long term model integration. The moisture tendency (transport) equation is tested separately for the cosine bell and idealized cyclogenesis test cases. Finally some aqua-planet experiments are performed with the new model. The results for this test case are presented along with a discussion on possible limitations that have been noted for the new model

Mittal, R.; Upadhyaya, H. C.; Sharma, O. P.

2009-04-01

213

Dynamics of relaxation and fragmentation in size-selected icosahedral Arn[NO-(v = 1)] clusters  

NASA Astrophysics Data System (ADS)

We study the vibrational relaxation and solvation dynamics in size-selected icosahedral Arn(NO-) at 300 K, where NO-(X3?-) is in v = 1 and n = 1-12, using a classical dynamics method and an interaction model consisting of detailed host-guest and host-host interactions. Two relaxation time scales are found: (i) the short-time (<200 ps), in which rate is nearly independent of cluster size, and (ii) the ns scale, in which a slow energy transfer process occurs between NO- vibration and argon modes at a rate (~108 s-1) decreasing slightly from n = 12 to 6 and rapidly from n = 5 to 1 (~106 s-1). In Ar12(NO-), less than one-quarter of the host atoms sampled evaporate, nearly 60% of evaporation occurring within 200 ps caused by rapid energy transfer from NO- at short time. The fraction of evaporation decreases nearly exponentially with increasing evaporation time, but ~16% of evaporation still occurs on a time scale longer than 1 ns. Evaporation from one hemisphere of Ar12(NO-) dominates the rest. Final cluster sizes commonly produced from the fragmentation of Ar12(NO-) are n = 6-11 (evaporation of 6-1 atoms) and n = 12 (no evaporation).

Shin, H. K.

2011-03-01

214

Valence band structure of the icosahedral Ag-In-Yb quasicrystal  

SciTech Connect

The valence band structure of the icosahedral (i) Ag-In-Yb quasicrystal, which is isostructural to the binary i-Cd-Yb system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold i-Ag-In-Yb surfaces reveal that the valence band near to the Fermi level is dominated by Yb 4f-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the Yb 5d band with the Ag 5p and In 5p bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work function of i-Ag-In-Yb measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.

Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; McGrath, R. [Surface Science Research Centre and Department of Physics, University of Liverpool, Liverpool L69 3BX (United Kingdom); Cui, C. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Shimoda, M. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Tsai, A. P. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Ishii, Y. [Department of Physics, Chuo University, Kasuga, Tokyo 112-8551 (Japan)

2010-03-01

215

Symmetry-Protected Majorana Fermions in Topological Crystalline Superconductors: Theory and Application to Sr2RuO4  

NASA Astrophysics Data System (ADS)

Crystal point group symmetry is shown to protect Majorana fermions (MFs) in spinfull superconductors (SCs). We elucidate the condition necessary to obtain MFs protected by the point group symmetry. We argue that superconductivity in Sr2RuO4 hosts a topological phase transition to a topological crystalline SC, which accompanies a d-vector rotation under a magnetic field along the c axis. Taking all three bands and spin-orbit interactions into account, symmetry-protected MFs in the topological crystalline SC are identified. Detection of such MFs provides evidence of the d-vector rotation in Sr2RuO4 expected from Knight shift measurements but not yet verified.

Ueno, Yuji; Yamakage, Ai; Tanaka, Yukio; Sato, Masatoshi

2013-08-01

216

The Symmetry of Longevity  

PubMed Central

We tested the hypothesis that relatively symmetrical flies live longer. Vein measurements on the left and right wings from the same individual were used to characterize bilateral symmetry in relationship to age-specific survival in defined cohorts. A longitudinal cohort study supported the hypothesis of a correlation between bilateral symmetry and longevity. For another type of experiment, wings were removed from females and males at approximately the beginning of adult life. Thus, there would be no effect of wings per se on adult survival. These wings were measured to characterize bilateral asymmetry, and the day of death of each dewinged individual was determined. Wing symmetry of females and males proved to be a statistically significant predictor of life span, especially for males.

Harshman, Lawrence G.; Muller, Hans-Georg; Liu, Xueli; Wang, Yue; Carey, James R.

2008-01-01

217

Electroweak symmetry breaking  

SciTech Connect

The Higgs mechanism is reviewed in its most general form, requiring the existence of a new symmetry-breaking force and associated particles, which need not however be Higgs bosons. The first lecture reviews the essential elements of the Higgs mechanism, which suffice to establish low energy theorems for the scattering of longitudinally polarized W and Z gauge bosons. An upper bound on the scale of the symmetry-breaking physics then follows from the low energy theorems and partial wave unitarity. The second lecture reviews particular models, with and without Higgs bosons, paying special attention to how the general features discussed in lecture 1 are realized in each model. The third lecture focuses on the experimental signals of strong WW scattering that can be observed at the SSC above 1 TeV in the WW subenergy, which will allow direct measurement of the strength of the symmetry-breaking force. 52 refs., 10 figs.

Chanowitz, M.S.

1990-09-01

218

Nuclear symmetry energy  

NASA Astrophysics Data System (ADS)

To study the nuclear symmetry energy, we extend the Dirac-Brueckner approach with a Bonn one-boson-exchange nucleon-nucleon interaction to the general case of asymmetric nuclear matter. We extract the symmetry energy coefficient at the saturation to be about 31 MeV, which is in good agreement with the empirical value of 30+/-4 MeV. The symmetry energy is found to increase almost linearly with the density, which differs considerably from the results of nonrelativistic approaches. This finding also supports the linear parametrization of Prakash, Ainsworth, and Lattimer. We find, furthermore, that the higher-order dependence of the nuclear equation of state on the asymmetry parameter is unimportant.

Lee, C.-H.; Kuo, T. T. S.; Li, G. Q.; Brown, G. E.

1998-06-01

219

Supersymmetric electroweak symmetry breaking  

SciTech Connect

In the minimal supersymmetric standard model (the MSSM), the electroweak symmetry is restored as supersymmetry-breaking terms are turned off. We describe a generic extension of the MSSM where the electroweak symmetry is broken in the supersymmetric limit. We call this limit the ''sEWSB'' phase, short for supersymmetric electroweak symmetry breaking. We define this phase in an effective field theory that only contains the MSSM degrees of freedom. The sEWSB vacua naturally have an inverted scalar spectrum, where the heaviest CP-even Higgs state has standard model-like couplings to the massive vector bosons; experimental constraints in the scalar Higgs sector are more easily satisfied than in the MSSM.

Batra, Puneet; Ponton, Eduardo [Department of Physics, Columbia University, 538 West 120th Street, New York, New York 10027 (United States)

2009-02-01

220

Magnetic Color Symmetry of Lattice Rotations in a Non-magnetic Material  

NASA Astrophysics Data System (ADS)

Oxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. Here we show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry. We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin film that exhibits ferroelectric (4mm) and antiferrodistortive (4'mm') phases evolving through independent phase transitions. The approach has broader applicability for probing materials with lattice rotations that can be mapped to color groups.

Denev, Sava; Kumar, A.; Biegalski, M. D.; Jang, H. W.; Folkman, C. M.; Vasudevarao, A.; Han, Y.; Reaney, I. M.; Trolier-McKinstry, S.; Eom, C.-B.; Schlom, D. G.; Gopalan, V.

2009-03-01

221

Gravity and global symmetries  

SciTech Connect

There exists a widely held notion that gravitational effects can strongly violate global symmetries. If this is correct, it may lead to many important consequences. We argue, in particular, that nonperturbative gravitational effects in the axion theory lead to a strong violation of {ital CP} invariance unless they are suppressed by an extremely small factor {ital g}{approx_lt}10{sup {minus}82}. One could hope that this problem disappears if one represents the global symmetry of a pseudoscalar axion field as a gauge symmetry of the Ogievetsky-Polubarinov-Kalb-Ramond antisymmetric tensor field. We show, however, that this gauge symmetry does not protect the axion mass from quantum corrections. The amplitude of gravitational effects violating global symmetries could be strongly suppressed by {ital e}{sup {minus}{ital S}}, where {ital S} is the action of a wormhole which may absorb the global charge. Unfortunately, in a wide variety of theories based on the Einstein theory of gravity the action appears to be fairly small, {ital S}{similar_to}10. However, we find that the existence of wormholes and the value of their action are extremely sensitive to the structure of space on the nearly Planckian scale. We consider several examples (Kaluza-Klein theory, conformal anomaly, {ital R}{sup 2} terms) which show that modifications of the Einstein theory on the length scale {ital l}{approx_lt}10{ital M}{sub {ital P}}{sup {minus}1} may strongly suppress violation of global symmetries. We find also that in string theory there exists an additional suppression of topology change by the factor {ital e}{sup {minus}8{pi}2}/{ital g}{sup 2}. This effect is strong enough to save the axion theory for the natural values of the stringy gauge coupling constant.

Kallosh, R.; Linde, A.; Linde, D.; Susskind, L. [Department of Physics, Stanford University, Stanford, California 94305-4060 (United States)]|[California Institute of Technology, Pasadena, California 91125 (United States)

1995-07-15

222

BSSN in spherical symmetry  

NASA Astrophysics Data System (ADS)

The BSSN (Baumgarte Shapiro Shibata Nakamura) formulation of the Einstein evolution equations is written in spherical symmetry. These equations can be used to address a number of technical and conceptual issues in numerical relativity in the context of a single Schwarzschild black hole. One of the benefits of spherical symmetry is that the numerical grid points can be tracked on a Kruskal Szekeres diagram. Boundary conditions suitable for puncture evolution of a Schwarzschild black hole are presented. Several results are shown for puncture evolution using a fourth-order finite difference implementation of the equations.

Brown, J. David

2008-10-01

223

Skewed Rotation Symmetry Group Detection  

Microsoft Academic Search

Abstract—We present a novel and effective algorithm for affinely skewed,rotation symmetry,group detection from real-world images. We define a complete,skewed,rotation symmetry,detection problem,as discovering,five independent,properties of a skewed,rotation symmetry,group: (1) the center of rotation; (2) the affine deformation; (3) the type of the symmetry,group; (4) the cardinality of the symmetry,group; and (5) the supporting,region of the symmetry,group in the image. We propose,a

Seungkyu Lee; Yanxi Liu

2010-01-01

224

Symmetries of hadrons after unbreaking the chiral symmetry  

NASA Astrophysics Data System (ADS)

We study hadron correlators upon artificial restoration of the spontaneously broken chiral symmetry. In a dynamical lattice simulation we remove the lowest lying eigenmodes of the Dirac operator from the valence quark propagators and study the evolution of the hadron masses obtained. All mesons and baryons in our study, except for a pion, survive the unbreaking of the chiral symmetry and their exponential decay signals become essentially better. From the analysis of the observed spectroscopic patterns we conclude that confinement still persists while the chiral symmetry is restored. All hadrons fall into different chiral multiplets. The broken U(1)A symmetry does not get restored upon unbreaking the chiral symmetry. We also observe signals of some higher symmetry that includes chiral symmetry as a subgroup. Finally, from comparison of the ?-N splitting before and after the unbreaking of the chiral symmetry, we conclude that both the color-magnetic and the flavor-spin quark-quark interactions are of equal importance.

Glozman, L. Ya.; Lang, C. B.; Schröck, M.

2012-07-01

225

Symmetry and Model Checking  

Microsoft Academic Search

We show how to exploit symmetry in model checking for concurrent systems containing many identical or isomorphic components. We focus in particular on those composed of many isomorphic processes. In many cases we are able to obtain significant, even exponential, savings in the complexity of model checking.

E. Allen Emerson; A. Prasad Sistla

1993-01-01

226

Symmetry in Constraint Programming  

Microsoft Academic Search

Symmetry in constraints has always been important but in recent years has become a ma- jor research area in its own right. A key problem in constraint programming has long been recognised: search can revisit equivalent states over and over again. In principle this prob- lem has been solved, with a number of different techniques. As we write, research remains

Ian P. Gent; Karen E. Petrie; Jean-Francois Puget

227

Tessellations: Geometry and Symmetry  

NSDL National Science Digital Library

This lesson is designed to develop students' understanding of polygons and symmetry by exploring tessellations and their geometric properties. This lesson provides links to discussions and activities related to tessellations as well as suggested ways to integrate them into the lesson. Finally, the lesson provides links to follow-up lessons designed for use in succession with the current one.

2010-01-01

228

ASPECTS of W? SYMMETRY  

Microsoft Academic Search

We review the structure of W? algebras, their super and topological extensions, and their contractions down to (super) w?. Emphasis is put on the field theoretic realisations of these algebras. We also review the structure of w? and W? gravities and comment on various applications of W? symmetry.

Ergin Sezgin

229

Symmetry and Snell's law  

Microsoft Academic Search

A connection between the acoustic rays in a moving fluid medium (with a sound speed and subsonic flow each depending arbitrarily on position and time) and the null geodesics of a pseudo-Riemannian manifold allows one to derive several well-known results used in underwater and atmospheric acoustic ray theory from one single underlying symmetry principle, isometry. These results being well known

David R. Bergman

2005-01-01

230

Introduction to chiral symmetry  

SciTech Connect

These lectures are an attempt to a pedagogical introduction into the elementary concepts of chiral symmetry in nuclear physics. Effective chiral models such as the linear and nonlinear sigma model will be discussed as well as the essential ideas of chiral perturbation theory. Some applications to the physics of ultrarelativistic heavy ion collisions will be presented.

Koch, V.

1996-01-08

231

Dynamical (super) symmetry breaking  

SciTech Connect

Dynamical Symmetry Breaking (DSB) is a concept theoristsrely on very often in the discussions of strong dynamics, model building,and hierarchy problems. In this talk, I will discuss why this is such apermeating concept among theorists and how they are used in understandingphysics. I also briefly review recent progress in using dynamicalsymmetry breaking to construct models of supersymmetry breaking andfermion masses.

Murayama, Hitoshi

2000-10-03

232

Symmetry the Trademark Way.  

ERIC Educational Resources Information Center

|Trademark designs provide a familiar yet innovative way for students to look at a number of mathematical concepts. How line and rotational symmetry can be presented using trademarks is the focus of this article. The emphasis is on the design of bulletin boards. (MNS)|

Renshaw, Barbara S.

1986-01-01

233

Unified structure theory of icosahedral quasicrystals: Evidence from neutron powder diffraction patterns that AlCrFeMnSi, AlCuLiMg, and TiNiFeSi icosahedral quasicrystals are twins of cubic crystals containing about 820 or 1012 atoms in a primitive unit cube.  

PubMed

A unified structure theory of icosahedral quasicrystals, combining the twinned-cubic-crystal theory and the Penrose-tiling-six-dimensional-projection theory, is described. Values of the primitive-cubic lattice constant for several quasicrystals are evaluated from x-ray and neutron diffraction data. The fact that the low-angle diffraction maxima can be indexed with cubic unit cells provides additional support for the twinned-cubic-crystal theory of icosahedral quasicrystals. PMID:16593990

Pauling, L

1988-11-01

234

Unified structure theory of icosahedral quasicrystals: Evidence from neutron powder diffraction patterns that AlCrFeMnSi, AlCuLiMg, and TiNiFeSi icosahedral quasicrystals are twins of cubic crystals containing about 820 or 1,012 atoms in a primitive unit cube  

SciTech Connect

A unified structure theory of icosahedral quasicrystals, combining the twinned-cubic-crystal theory and the Penrose-tiling-six-dimensional-projection theory, is described. Values of the primitive-cubic lattice constant for several quasicrystals are evaluated from x-ray and neutron diffraction data. The fact that the low-angle diffraction maxima can be indexed with cubic unit cells provides additional support for the twinned-cubic-crystal theory of icosahedral quasicrystals.

Pauling, L. (Linus Pauling Institute of Science and Medicine, Palo Alto, CA (USA))

1988-11-01

235

Link between liquid structure and the nucleation barrier for icosahedral quasicrystal, polytetrahedral, and simple crystalline phases in Ti-Zr-Ni alloys: Verification of Frank's hypothesis  

NASA Astrophysics Data System (ADS)

Comprehensive undercooling experiments on a large number of simple crystalline, polytetrahedral, and icosahedral quasicrystalline phase forming compositions in Ti-Zr-Ni alloys have been carried out using electrostatic levitation (ESL) techniques for containerless processing. Consistent with Frank’s hypothesis, a direct correlation was found between the reduced undercooling [ ?Tr=(Tl-Tr)/Tl , where Tr and Tl are the nucleation and liquidus temperatures, respectively] and the icosahedral short-range order in the solid. The reduced undercooling is less for liquids that form the icosahedral quasicrystal ( i phase) than for those that form the hcp C14 Laves polytetrahedral phase. For many compositions near 21at.% Ni, the primary nucleation of a metastable i phase instead of a stable C14 Laves phase demonstrates that the interfacial free energy between the liquid and the i phase is smaller than between the liquid and the C14 Laves phase, indicating icosahedral local order in the undercooled liquid. This is in agreement with a classical-nucleation-theory-based estimate of the interfacial free energy and the work of formation of the critical cluster from the undercooling data. Taken together with high-energy x-ray diffraction studies of the undercooled liquid, these results demonstrate that the local structure of liquids in Ti-Zr-Ni alloys is icosahedral, as postulated by Frank over a half century ago.

Lee, G. W.; Gangopadhyay, A. K.; Croat, T. K.; Rathz, T. J.; Hyers, R. W.; Rogers, J. R.; Kelton, K. F.

2005-11-01

236

Photoluminescence investigation of the indirect band gap and shallow impurities in icosahedral B12As2  

NASA Astrophysics Data System (ADS)

The indirect band gap of icosahedral B12As2 (IBA) has been determined by variable temperature photoluminescence measurements (8 K-294 K) on solution-grown bulk samples. In addition, evidence of three shallow acceptor levels and one shallow donor level is reported. The low-temperature spectra were characterized by broad and intense deep defect emission, donor-acceptor pair (DAP) bands, and exciton recombination. The appearance of DAP emission verifies the incorporation of a donor in IBA, which has not been reported previously. The temperature dependence of the free exciton (FE) intensity reflected a FE binding energy of 45 meV. The variation of the FE peak position with temperature was fitted with both Varshni and Pässler models to determine an expression for the temperature dependence of the indirect band gap. The resulting low and room temperature band gaps are Eg(0) = 3.470 eV and Eg(294 K) = 3.373 eV, respectively. The latter is not consistent with previous reports of the room temperature band gap, 3.20 eV and 3.47 eV, derived from band structure calculations and optical absorption, respectively. The origin of these discrepancies is discussed. The DAP spectra reveal three relatively shallow acceptors with binding energies of ~175, 255, and 291 meV, and a shallow donor with binding energy ~25 meV. Although the identity of the individual acceptors is not known, they appear to be associated with the light-hole band. The small donor binding energy is suggestive of an interstitial donor impurity, which is suspected to be Ni.

Klein, P. B.; Nwagwu, Ugochukwu; Edgar, J. H.; Freitas, J. A.

2012-07-01

237

Symmetry Building and Symmetry Breaking in Synchronized Movement  

Microsoft Academic Search

Mirror symmetry between individuals is a behavioral phenomenon that is commonly observed in conversation: individuals tend to mimic each other's postures and gestures as a part of a shared dia- log. The present work studies the process of symmetry building and symmetry breaking in the movements of pairs of individuals while imitating each others' movements in dance. Spatial and temporal

Steven M. Boker; Jennifer L. Rotondo

238

REVIEW ARTICLE: Symmetries and reversing symmetries of toral automorphisms  

Microsoft Academic Search

Toral automorphisms, represented by unimodular integer matrices, are investigated with respect to their symmetries and reversing symmetries. We characterize the symmetry groups of {GL}(n,Z) matrices with a simple spectrum through their connection with unit groups in orders of algebraic number fields. For the question of reversibility, we derive necessary conditions in terms of the characteristic polynomial and the polynomial invariants.

Michael Baake; John A. G. Roberts

2001-01-01

239

Gravity from Lorentz Symmetry Violation  

SciTech Connect

In general relativity, the masslessness of gravitons can be traced to symmetry under diffeomorphisms. In this talk, we consider another possibility, whereby the masslessness arises from spontaneous violation of Lorentz symmetry.

Potting, Robertus [CENTRA, FCT, University of the Algarve, 8005-139 Faro (Portugal); Physics Department, FCT, University of the Algarve, 8005-139 Faro (Portugal)

2006-06-19

240

Formation ranges of icosahedral, amorphous and crystalline phases in rapidly solidified Ti-Zr-Hf-Ni alloys  

SciTech Connect

From the quaternary Ti-Zr-Hf-Ni phase diagram, the cross-section at 20 at.% Ni was selected for investigation. The icosahedral quasicrystalline, crystalline and amorphous phases were observed to form in nine kinds of rapidly solidified (Ti{sub x}Zr{sub y}Hf{sub z}){sub 80}Ni{sub 20} (x + y + z = 1) alloys at different compositions. The quasilattice constants of 0.519 and 0.531 nm were obtained for the icosahedral phase formed in the melt-spun Ti{sub 40}Zr{sub 20}Hf{sub 20}Ni{sub 20} and Ti{sub 20}Zr{sub 40}Hf{sub 20}Ni{sub 20} alloys, respectively. The icosahedral phase formed in the melt-spun Ti{sub 40}Zr{sub 20}Hf{sub 20}Ni{sub 20} alloy especially is thermodynamically stable. The supercooled liquid region of the Ti{sub 20}Zr{sub 20}Hf{sub 40}Ni{sub 20} glassy alloy reached 64 K. From these results a comparison of quasicrystal-forming and glass-forming abilities was carried out. The quasicrystal-forming ability was reduced and glass-forming ability was improved with an increase in Hf and Zr contents in the (Ti{sub x}Zr{sub y}Hf{sub z}){sub 80}Ni{sub 20} alloys. On the other hand, an increase in Ti content caused an improvement in quasicrystal-forming ability.

Chen, N. [Department of Materials Science, Graduate School, Tohoku University, Sendai 980-8577 (Japan) and Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577 (Japan)]. E-mail: asyzxy@imr.edu; Louzguine, D.V. [Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577 (Japan); Ranganathan, S. [Department of Metallurgy, Indian Institute of Science, Bangalore 560 012 (India); Inoue, A. [Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577 (Japan)

2005-02-01

241

Structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys and defects of the icosahedral phase  

Microsoft Academic Search

Transmission electron microscopy was used to investigate structural and phase transformations and defects of the icosahedral\\u000a (?) phase that is formed upon isothermal annealings (T\\u000a ann = 550–700°C) of quenched quasicrystal-forming alloys Al61Cu26Fe13 and Al63Cu25Fe12 (? solid solution + ? phase). It has been established that in the Al63Cu25Fe12 alloy there occurs a reversible ?-R-approximant transformation, whereas in the Al61Cu26Fe13

E. V. Shalaeva; A. F. Prekul

2010-01-01

242

Icosahedral short-range order in amorphous Cu80Si20 by ab initio molecular dynamics simulation study  

SciTech Connect

Short-range order in liquid and amorphous structures of Cu80Si20 is studied by ab initio molecular dynamics simulations. We performed the simulations at 1140 and 300 K respectively to investigate the local structure change from liquid to amorphous. The result of structure factor in comparison with experimental data indicates that our simulation of amorphous Cu80Si20 is reliable. By using the bond-angle distribution function, Honeycutt–Andersen index, Voronoi tessellation method, and the atomistic cluster alignment method, the icosahedral short-range order in the system is revealed. Strong Cu–Si interaction was also observed.

Wu, S.; Kramer, Matthew J.; Fang, Xiaowei; Wang, Shy-Guey; Wang, Cai-Zhuang; Ho, Kai-Ming; Ding, Z.J.; Chen, L.Y.

2012-04-26

243

Plasticity of single-grain icosahedral Al-Pd-Mn quasi-crystals deformed at room temperature  

SciTech Connect

Transmission electron microscopy observations have been performed on icosahedral Al-Pd-Mn quasi-crystal samples deformed at 20 deg. C under a high confining pressure. They reveal a large density of wavy walls from which several climbing dislocations are emitted. Near-screw dislocations have been found at the wall terminations with a Burgers vector contained in the wall plane. Careful plane determinations and dislocation analyses are not consistent with a glide and cross-slip mechanism. The results can be better interpreted as a deformation by cracks in mode III followed by a re-healing process.

Mompiou, F.; Caillard, D

2004-07-12

244

Icositetrahedral and icosahedral atomic configurations observed in the Nb-Ag metallic glasses synthesized by ion beam mixing  

SciTech Connect

Metallic glasses are obtained in an immiscible Nb-Ag system by ion beam mixing and an atomic configuration in the amorphous structure is discovered, i.e., an icositetrahedral ordering, which, together with an icosahedral ordering also observed in the Nb-Ag metallic glasses and in some previously reported systems, helps in formulating a structural spectrum of the amorphous solids. The experimental characterization and atomistic modeling with an ab initio derived Nb-Ag potential demonstrate the significance of structural heredity, i.e., the crystalline structures of the constituent metals play a decisive role in determining the atomic structure of the metallic glasses in the system.

Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Lai, W. S.; Liu, B. X. [Advanced Materials Laboratory, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)

2006-08-28

245

Dynamical Symmetries in Classical Mechanics  

ERIC Educational Resources Information Center

|We show how symmetries of a classical dynamical system can be described in terms of operators that act on the state space for the system. We illustrate our results by considering a number of possible symmetries that a classical dynamical system might have, and for each symmetry we give examples of dynamical systems that do and do not possess that…

Boozer, A. D.

2012-01-01

246

Reflections on Symmetry and Proof  

ERIC Educational Resources Information Center

|The concept of symmetry is fundamental to mathematics. Arguments and proofs based on symmetry are often aesthetically pleasing because they are subtle and succinct and non-standard. This article uses notions of symmetry to approach the solutions to a broad range of mathematical problems. It responds to Krutetskii's criteria for mathematical…

Merrotsy, Peter

2008-01-01

247

Symmetry as a Continuous Feature  

Microsoft Academic Search

Symmetry is treated as a continuous featureand a Continuous Measure of Distance from Symmetry inshapes is defined. The Symmetry Distance (SD) of a shape isdefined to be the minimum mean squared distance requiredto move points of the original shape in order to obtain asymmetrical shape. This general definition of a symmetrymeasure enables a comparison of the "amount" of symmetryof different

Hagit Zabrodsky; Shmuel Peleg; David Avnir

1995-01-01

248

Symmetry for successful interactive systems  

Microsoft Academic Search

HCI has some rich and suggestive ideas, like affordance and direct manipulation. Abstract (not just geometrical) symmetry is a powerful explanation of why these concepts work, and it can be generalised to guide new design for more effective user interfaces. Symmetry makes user interfaces easier to learn, easier to use, and easier to program --- and hence more reliable. Symmetry

Harold Thimbleby

2002-01-01

249

In search of symmetry lost  

Microsoft Academic Search

Powerful symmetry principles have guided physicists in their quest for nature's fundamental laws. The successful gauge theory of electroweak interactions postulates a more extensive symmetry for its equations than are manifest in the world. The discrepancy is ascribed to a pervasive symmetry-breaking field, which fills all space uniformly, rendering the Universe a sort of exotic superconductor. So far, the evidence

Frank Wilczek

2005-01-01

250

Dark discrete gauge symmetries  

SciTech Connect

We investigate scenarios in which dark matter is stabilized by an Abelian Z{sub N} discrete gauge symmetry. Models are surveyed according to symmetries and matter content. Multicomponent dark matter arises when N is not prime and Z{sub N} contains one or more subgroups. The dark sector interacts with the visible sector through the renormalizable kinetic mixing and Higgs portal operators, and we highlight the basic phenomenology in these scenarios. In particular, multiple species of dark matter can lead to an unconventional nuclear recoil spectrum in direct detection experiments, while the presence of new light states in the dark sector can dramatically affect the decays of the Higgs at the Tevatron and LHC, thus providing a window into the gauge origin of the stability of dark matter.

Batell, Brian [Perimeter Institute for Theoretical Physics, Waterloo, ON, N2J 2W9 (Canada)

2011-02-01

251

Symmetry and Tessellations  

NSDL National Science Digital Library

This website provides 30 suggested activities in Symmetry and Tessellations using resources available across the World Wide Web. The author, Jill Britton, has complied this collection of links to coordinate with the chapters and activities from her publication, Investigating Patterns: Symmetry and Tessellations (Grades 5-8). The activities begin with What is Mathematics? and move on to cover topics such as Pythagoras? observations of music, patterns on Ukrainian Easter eggs, and tessellating art. She provides a short comment on each of the websites and the links are arranged by activity topic. Links at the bottom of the website will take visitors to other collections of links relating to more pattern-related activities.

2007-12-12

252

Symmetries in general relativity  

Microsoft Academic Search

The purpose is to study those non-flat space-times in General Relativity that admit high dimensional Lie groups of symmetries, in particular motions, homotheties, conformals and affines, and to improve a theorem on the relationship between the first three of these, first proved by Bilyalov and also by Defrise-Carter. The basic mathematical theory and notations are set, covering manifolds, tensors, Lie

John D. Steele

1989-01-01

253

Chiral symmetry and pentaquarks  

SciTech Connect

Spontaneous chiral symmetry breaking, mesons and baryons are illustrated in the language of the Dirac theory. Various forces acting between quarks inside baryons are discussed. I explain why the naive quark models typically overestimate pentaquark masses by some 500 MeV and why in the fully relativistic approach to baryons pentaquarks turn out to be light. I discuss briefly why it can be easier to produce pentaquarks at low than at high energies.

Dmitri Diakonov

2004-07-01

254

Local atomic three-dimensional real-space structural analysis of icosahedral Mg--Zn--RE (RE = Y or Ho) alloys: strategy, method and models  

Microsoft Academic Search

The local structure of any condensed matter is accessible via an atomic pair distribution function (PDF) analysis. Here, the local atomic structure of the well-ordered face-centred icosahedral (fci)-Mg25Y11Zn64, fci-Ho9Mg26Zn65 and simple icosahedral Ho11Mg15Zn74 quasicrystals have been investigated by PDFs obtained from in-house X-ray and synchrotron powder data. Least-squares refinements using periodic 1\\/1 and 2\\/1 approximants as models for the local

S. Brühne; E. Uhrig; G. Kreiner; W. Assmus

2006-01-01

255

Symmetry in quantum walks  

NASA Astrophysics Data System (ADS)

A discrete-time quantum walk on a graph is the repeated application of a unitary evolution operator to a Hilbert space corresponding to the graph. Hitting times for discrete quantum walks on graphs give an average time before the walk reaches an ending condition. We derive an expression for hitting time using superoperators, and numerically evaluate it for the walk on the hypercube for various coins and decoherence models. The hitting time for a classical random walk on a connected graph will always be finite. We show that, by contrast, quantum walks can have infinite hitting times for some initial states. We seek criteria to determine if a given walk on a graph will have infinite hitting times, and find a sufficient condition, which for discrete time quantum walks is that the degeneracy of the evolution operator be greater than the degree of the graph. The phenomenon of infinite hitting times is in general a consequence of the symmetry of the graph and its automorphism group. Symmetries of a graph, given by its automorphism group, can be inherited by the evolution operator. Using the irreducible representations of the automorphism group, we derive conditions such that quantum walks defined on this graph must have infinite hitting times for some initial states. Symmetry can cause the walk to also be confined to a subspace of the original Hilbert space for cartain initial states. We show that a quantum walk confined to the subspace corresponding to this symmetry group can be seen as a different quantum walk on a smaller quotient graph. We give an explicit construction of the quotient graph for any subgroup H of the automorphism group. The automorphisms of the quotient graph which are inherited from the original graph are the original automorphism group modulo the subgroup H used to construct it. We conjecture that the existence of a small quotient graph with finite hitting times is necessary for a walk to exhibit a quantum speed-up. Finally, we use symmetry and the theory of decoherence-free subspaces to determine when the subspace of the quotient graph is a decoherence-free subspace of the dynamics.

Krovi, Hari

256

Improved Statistics for Determining the Patterson Symmetry fromUnmerged Diffraction Intensities  

SciTech Connect

We examine procedures for detecting the point-group symmetryof macromolecular datasets and propose enhancements. To validate apoint-group, it is sufficient to compare pairs of Bragg reflections thatare related by each of the group's component symmetry operators.Correlation is commonly expressed in the form of a single statisticalquantity (such as Rmerge) that incorporates information from all of theobserved reflections. However, the usual practice of weighting all pairsof symmetry-related intensities equally can obscure the fact that thevarious symmetry operators of the point-group contribute differingfractions of the total set. In some cases where particular symmetryelements are significantly under-represented, statistics calculatedglobally over all observations do not permit conclusions about thepoint-group and Patterson symmetry. The problem can be avoided byrepartitioning the data in a way that explicitly takes note of individualoperators. The new analysis methods, incorporated into the programLABELIT (cci.lbl.gov/labelit), can be performed early enough during dataacquisition, and are quick enough, that it is feasible to pause tooptimize the data collection strategy.

Sauter, Nicholas K.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2006-01-09

257

Simulations of the Structure and Properties of Large Icosahedral Boron Clusters Based on a Novel Semi-Empirical Hamiltonian  

NASA Astrophysics Data System (ADS)

A successful development of a parameterized semi-empirical Hamiltonian (SCED-LCAO) for boron based on a LCAO framework using a sp^3 basis set will be discussed. The semi-empirical Hamiltonian contains environment-dependency and electron screening effects of a many-body Hamiltonian and allows for charge self-consistency. We have optimized the parameters of the SCED-LCAO Hamiltonian for boron by fitting the properties (e.g., the binding energy, bond length, etc.) of boron sheets, small clusters and boron alpha to first-principles calculations based on DFT calculations. Although extended phases of boron alpha and beta have been studied, large clusters of boron with icosahedral structures such as those cut from boron alpha are difficult if not impossible to simulate with ab initio methods. We will demonstrate the effectiveness of the SCED-LCAO Hamiltonian in studying icosahedral boron clusters containing up to 800 atoms and will report on some novel boron clusters and computational speed. [1] C. Leahy, et al, Phys. Rev. B 74,155408 (2006). [2] P. Tandy, et al, Bulletin of the APS, 2009 APS March Meeting Vol. 54, Num.1, Sess. D26, [3] Ming Yu, et al, J. Chem. Phys. 130,184708 (2009). [4] Ming Yu, S.Y. Wu, and C.S. Jayanthi, Physica E 42, 1 (2009).

Tandy, Paul; Yu, Ming; Jayanthi, C. S.; Wu, Shi-Yu

2013-03-01

258

Time reversal symmetry breaking chiral spin liquids: Projective symmetry group approach of bosonic mean-field theories  

NASA Astrophysics Data System (ADS)

Projective symmetry groups are the mathematical tools which make it possible to list and classify mean-field spin liquids (SLs) based on a parton construction. The seminal work of Wen [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.65.165113 65, 165113 (2002)] and its subsequent extension to bosons by Wang and Vishwanath [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.174423 74, 174423 (2006)] concerned the so-called symmetric SLs; i.e., states that break neither lattice symmetries nor time reversal invariance. Here we generalize this tool to chiral (time reversal symmetry breaking) SLs described in a Schwinger boson mean-field approach and illustrate it on the triangular lattice, which can harbor nine different weakly symmetric SLs (two symmetric SLs and seven chiral SLs) with nearest neighbor bond operators only. Results for other lattices (square and kagome) are given in the Appendixes. Application of this new approach has recently led to the discovery of two chiral ground states on the kagome lattice [Messio , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.207204 108, 207204 (2012); Fåk , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.109.037208 109, 037208 (2012)]. The signature of a time reversal symmetry breaking SL is the presence in the ground state of nontrivial fluxes of loop operators that break some lattice point group symmetries. The physical significance of these gauge invariant quantities is discussed both in the classical limit and in the quantum SL and their expressions in terms of spin observables are given.

Messio, Laura; Lhuillier, Claire; Misguich, Grégoire

2013-03-01

259

Oxidizing Borcherds symmetries  

NASA Astrophysics Data System (ADS)

The tensor hierarchy of maximal supergravity in D dimensions is known to be closely related to a Borcherds (super)algebra that is constructed from the global symmetry group E 11- D . We here explain how the Borcherds algebras in different dimensions are embedded into each other and can be constructed from a unifying Borcherds algebra. The construction also has a natural physical explanation in terms of oxidation. We then go on to show that the Hodge duality that is present in the tensor hierarchy has an algebraic counterpart. For D > 8 the Borcherds algebras we find differ from the ones existing in the literature although they generate the same tensor hierarchy.

Kleinschmidt, Axel; Palmkvist, Jakob

2013-03-01

260

Symmetry and perturbation theory  

NASA Astrophysics Data System (ADS)

A co-chain map for the G invariant De Rham complex -- New examples of trihamiltonian structures linking different Lenard chains -- Wave propagation in an elastic medium: GDS equations -- Parametric excitation in nonlinear dynamics -- Collisionless action-minimizing trajectories for the equivariant 3-body problem in R2 -- The Lagrangian and Hamiltonian formulations for a special class of non-conservative systems -- Shadowing chains of collision orbits for the elliptic 3-body problem -- Similarity reductions of an optical model -- Fold, transcritical and pitchfork singularities for time-reversible systems -- Homographic three-body motions with positive and negative masses -- Remarks on conformal Killing tensors and separation of variables -- A regularity theory for optimal partition problems -- Lambda and mu-symmetries -- Potential symmetries and linearization of some evolution equations -- Periodic solutions for zero mass nonlinear wave equations -- Fundamental covariants in the invariant theory of Killing tensors -- Global geometry of 3-body trajectories with vanishing angular momentum -- The relation between the topological structure of the set of controllable affine systems and topological structures of the set of controllable homogenuous systems in low dimension -- On preservation of action variables for satellite librations in elliptic orbits with account of solar light pressure -- An explicit solution of the (quantum) elliptic Calogero-Sutherland model -- An application of the Melnikov integral to a restricted three body problem -- Reductions of integrable equations and automorphic Lie algebras -- Geometric reduction of Poisson operators -- Closed manifolds admitting metrics with the same geodesics -- A transcritical-flip bifurcation in a model for a robot-arm -- Alignment and the classification of Lorentz-signature tensors -- Renormalization group symmetry and gas dynamics -- Refined computation of hypernormal forms -- New order reductions for Euler-Lagrange equations -- Regularity of pseudogroup orbits -- Relaxation times to equilibrium in Fermi-Pasta-Ulam system -- Energy cascade in Fermi-Pasta-Ulam models -- On Birkhoff method for integrable lagrangian systems -- Symmetry of singularities and orbit spaces of compact linear groups -- Symmetric solutions in molecular potentials -- Variational approach to soliton generation and stability analysis of multidimensional nonlinear Schrodinger equation -- Differential invariants for infinite-dimensional algebras.

Gaeta, Giuseppe

261

Quasiclassical symmetry properties II  

NASA Astrophysics Data System (ADS)

Proofs are given that the quasiclassical approach proposed previously is able to work in conjunction with the 1/N method. Accordingly, the expansion parameter k = 2l + N - a of the shifted 1/N method should be chosen, order by order, such that the sum of corrections to the zeroth-order result vanishes. This interconnection criterion leads to order-dependent algebraic equations for the parameter k. In turn, the underlying phase-space quantum becomes just half the parameter k implied in this way. Alternative fixing conditions, based on the selection of a dominant potential term, can also be proposed. Quasiclassical symmetry transformations leaving corresponding equivalence classes of Hamiltonian forms invariant are established. Then energy levels and couplings characterizing such Hamiltonians become subject to mutual conversions. Scaling properties of the phase-space quantum are discussed. In addition, this quantum exhibits a covariance behaviour with respect to the quasiclassical symmetry transformations mentioned above. Critical coupling for several short-range potentials are given to first order. Generalizations to resonances and nonlinear quantum-mechanical potentials are also made. Except for dyons, we restrict ourselves to spherically symmetric nonrelativistic Hamiltonians.

Papp, E.

1988-04-01

262

Squash operator and symmetry  

SciTech Connect

This article begins with a simple proof of the existence of squash operators compatible with the Bennett-Brassard 1984 (BB84) protocol that suits single-mode as well as multimode threshold detectors. The proof shows that, when a given detector is symmetric under cyclic group C{sub 4}, and a certain observable associated with it has rank two as a matrix, then there always exists a corresponding squash operator. Next, we go on to investigate whether the above restriction of 'rank two' can be eliminated; i.e., is cyclic symmetry alone sufficient to guarantee the existence of a squash operator? The motivation behind this question is that, if this were true, it would imply that one could realize a device-independent and unconditionally secure quantum key distribution protocol. However, the answer turns out to be negative, and moreover, one can instead prove a no-go theorem that any symmetry is, by itself, insufficient to guarantee the existence of a squash operator.

Tsurumaru, Toyohiro [Mitsubishi Electric Corporation, Information Technology R and D Center, 5-1-1 Ofuna, Kamakura-shi, Kanagawa, 247-8501 Japan (Japan)

2010-01-15

263

Symmetry, shape, and order  

PubMed Central

Packing problems have been of great interest in many diverse contexts for many centuries. The optimal packing of identical objects has been often invoked to understand the nature of low-temperature phases of matter. In celebrated work, Kepler conjectured that the densest packing of spheres is realized by stacking variants of the face-centered-cubic lattice and has a packing fraction of ?/(32)?0.7405. Much more recently, an unusually high-density packing of ?0.770732 was achieved for congruent ellipsoids. Such studies are relevant for understanding the structure of crystals, glasses, the storage and jamming of granular materials, ceramics, and the assembly of viral capsid structures. Here, we carry out analytical studies of the stacking of close-packed planar layers of systems made up of truncated cones possessing uniaxial symmetry. We present examples of high-density packing whose order is characterized by a broken symmetry arising from the shape of the constituent objects. We find a biaxial arrangement of solid cones with a packing fraction of ?/4. For truncated cones, there are two distinct regimes, characterized by different packing arrangements, depending on the ratio c of the base radii of the truncated cones with a transition at c*=2?1.

Trovato, Antonio; Hoang, Trinh Xuan; Banavar, Jayanth R.; Maritan, Amos

2007-01-01

264

Hopf Algebra Symmetry and String  

NASA Astrophysics Data System (ADS)

We investigate the Hopf algebra structure in string worldsheet theory and give a unified formulation of the quantization of string and the space-time symmetry. We reformulate the path integral quantization of string as a Drinfeld twist at the worldsheet level. The coboundary relation shows that the Drinfeld twist defines a module algebra which is equivalent to operators with normal ordering. Upon applying the twist, the space-time diffeomorphism is deformed into a twisted Hopf algebra, while the Poincaré symmetry is unchanged. This suggests a characterization of the symmetry: unbroken symmetries are twist invariant Hopf subalgebras, while broken symmetries are realized as twisted ones. We provide arguments that relate this twisted Hopf algebra to symmetries in path integral quantization.

Asakawa, T.; Mori, M.; Watamura, S.

2008-10-01

265

Bridged Heterocyclium Di-Cationic closo-Icosahedral Perfluoroborane, Borane, and Carborane Salts via Aqueous, Open-Air Benchtop Synthesis (Preprint).  

National Technical Information Service (NTIS)

Thirteen unreported bridged triazolium and imidazolium di-cationic salts, that uniquely pair closo-icosahedral perfluoroborane (B12F12)(exp 2-), borane (B12H12)(exp 2-), or carborane (CB11H12)(exp -) anionic species with unsaturated bridged heterocyclium ...

A. K. Wheaton J. A. Boatz J. L. Belletire S. Schneider S. A. Shackelford

2010-01-01

266

Pairing symmetry in cuprate superconductors  

Microsoft Academic Search

Pairing symmetry in the cuprate superconductors is an important and controversial topic. The recent development of phase-sensitive tests, combined with the refinement of several other symmetry-sensitive techniques, has for the most part settled this controversy in favor of predominantly d-wave symmetry for a number of optimally hole- and electron-doped cuprates. This paper begins by reviewing the concepts of the order

C. C. Tsuei; J. R. Kirtley

2000-01-01

267

Parity symmetry in QED3  

SciTech Connect

Schwinger-Dyson equations are used to study spontaneous chiral and parity symmetry breaking of three-dimensional quantum electrodynamics with two-component fermions. This theory admits a topological photon mass that explicitly breaks parity symmetry and generates a fermion mass. We show for the first time that it is possible to spontaneously break both parity and chiral symmetry. We also find that chiral symmetry is restored at a critical number of fermion flavors in our truncation scheme. Finally, the Coleman-Hill theorem is used to demonstrate that the results are reasonably accurate.

Lo, Pok Man; Swanson, Eric S. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)

2011-03-15

268

Givental Graphs and Inversion Symmetry  

NASA Astrophysics Data System (ADS)

Inversion symmetry is a very non-trivial discrete symmetry of Frobenius manifolds. It was obtained by Dubrovin from one of the elementary Schlesinger transformations of a special ODE associated to a Frobenius manifold. In this paper, we review the Givental group action on Frobenius manifolds in terms of Feynman graphs and obtain an interpretation of the inversion symmetry in terms of the action of the Givental group. We also consider the implication of this interpretation of the inversion symmetry for the Schlesinger transformations and for the Hamiltonians of the associated principle hierarchy.

Dunin-Barkowski, Petr; Shadrin, Sergey; Spitz, Loek

2013-05-01

269

Dynamical Diffraction and X-Ray Standing Waves from Atomic Planes Normal to a Twofold Symmetry Axis of the Quasicrystal AlPdMn  

SciTech Connect

We have observed dynamical diffraction in the 0240{ovr 2}4 and 0460{ovr 4}6 reflections of the icosahedral quasicrystal AlPdMn in the back-reflection geometry ({theta}{sub B}=90{degree} ). The x-ray fluorescence from the Al and Pd atoms exhibits strong standing wave behavior, similar to that observed in crystalline materials. The data indicate a long-range order of each species of atoms, with the coherent positions attributable to distributions of the Al and Pd, which we compare to a centrosymmetric model. We observe deviations from the model which imply small departures from inversion symmetry along the twofold symmetry axis and from the expected coherent fractions for Al. {copyright} {ital 1999} {ital The American Physical Society}

Jach, T. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Zhang, Y.; Colella, R. [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); de Boissieu, M.; Boudard, M. [LTPCM-ENSEEG, BP 75, 38402 St. Martin d`Heres Cedex (France); Goldman, A.I.; Lograsso, T.A.; Delaney, D.W. [Department of Physics and Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States); Kycia, S. [CHESS, Cornell University, Ithaca, New York 14853 (United States)

1999-04-01

270

Capsomer dynamics and stabilization in particles with T=12 quasi-symmetry; the cryoEM reconstructions of the marine bacteriophage SIO-2 and its procapsid  

PubMed Central

We report the sub nanometer cryo-electron microscopy (cryoEM) reconstruction of a novel marine siphovirus, the Vibrio phage SIO-2. This phage is lytic for related Vibrio species with significant ecological importance including the broadly antagonistic bacterium Vibrio sp. SWAT3. The three dimensional structure of the 800Å SIO-2, icosahedrally averaged, head of the tailed particle revealed a novel T=12 quasi-symmetry not previously described in a bacteriophage. Two, morphologically distinct, types of auxiliary proteins were also identified; one species bound to the surface of hexamers and the other bound to pentamers. The secondary structure, evident in the electron density, shows that the major capsid protein has the HK97-like fold. The three-dimensional structure of the procapsid form, also presented here, has no “decoration” proteins and reveals a novel capsomer organization due to the constraints of the T=12 symmetry.

Lander, Gabriel C.; Baudoux, Anne-Claire; Azam, Farooq; Potter, Clinton S.; Carragher, Bridget; Johnson, John E.

2012-01-01

271

Symmetry and surface symmetry energies in finite nuclei  

SciTech Connect

A study of the properties of the symmetry energy of nuclei is presented based on density-functional theory. Calculations for finite nuclei are given so that the study includes isospin-dependent surface symmetry considerations as well as isospin-independent surface effects. Calculations are done at both zero and nonzero temperature. It is shown that the surface symmetry energy term is the most sensitive to the temperature while the bulk energy term is the least sensitive. It is also shown that the temperature-dependence terms are insensitive to the force used and even more insensitive to the existence of neutron skin. Results for a symmetry energy with both volume and surface terms are compared with a symmetry energy with only volume terms along the line of {beta} stability. Differences of several MeV are shown over a good fraction of the total mass range in A. Also given are calculations for the bulk, surface and Coulomb terms.

Lee, S. J. [Department of Physics, Kyung Hee University, Yongin, KyungGiDo (Korea, Republic of); Mekjian, A. Z. [Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854 (United States)

2010-12-15

272

Symmetries in nuclei  

NASA Astrophysics Data System (ADS)

Using the second quantization method, we introduce the supergroup U(281+4) for the nucleon LS-coupled shell S = {(nl)N}. Then by use of the method to obtain Lie subalgebras and the method of coupled tensor operators, we get its subgroups and its subgroup structures.In this way we describe the complete symmetries of the shell in a unified way, and derive some branching rules. Returning to the atomic case we have the group SOO), which is a direct product of SUS(2) and SOQ(3), so that we can introduce the quasi-spin formalism more naturally. To the jj-couping case we derive sane branching rules for the reduction SO(4j+2)? SUQ(2) × USp(2j+1).

Feng, Cheng-Tian

273

Symmetry boundary conditions  

SciTech Connect

A simple approach to energy conserving boundary conditions using exact symmetries is described which is especially useful for numerical simulations using the finite difference method. Each field in the simulation is normally either symmetric (even) or antisymmetric (odd) with respect to the simulation boundary. Another possible boundary condition is an antisymmetric perturbation about a nonzero value. One of the most powerful aspects of this approach is that it can be easily implemented in curvilinear coordinates by making the scale factors of the coordinate transformation symmetric about the boundaries. The method is demonstrated for magnetohydrodynamics (MHD), reduced MHD, and a hybrid code with particle ions and fluid electrons. These boundary conditions yield exact energy conservation in the limit of infinite time and space resolution. Also discussed is the interpretation that the particle charge reverses sign at a conducting boundary with boundary normal perpendicular to the background magnetic field.

Denton, R.E. [Dartmouth College, Department of Physics and Astronomy, 6127 Wilder Lab, Hanover, NH 03755 (United States)], E-mail: rdjcp@rdenton.fastem.com; Hu, Y. [Dartmouth College, Department of Physics and Astronomy, 6127 Wilder Lab, Hanover, NH 03755 (United States)

2009-07-20

274

Symmetry in Sign Language Poetry  

ERIC Educational Resources Information Center

This paper considers the range of ways that sign languages use geometric symmetry temporally and spatially to create poetic effect. Poets use this symmetry in sign language art to highlight duality and thematic contrast, and to create symbolic representations of beauty, order and harmony. (Contains 8 tables, 14 figures and 6 notes.)

Sutton-Spence, Rachel; Kaneko, Michiko

2007-01-01

275

Symmetry: It's All Around You  

NSDL National Science Digital Library

This website provides text, images, animations, and interactive Java applets to teach bilateral and rotational symmetry. Learners are given drawing and painting challenges as well as recreational activities such as making a virtual kaleidoscope. Clicking on the first button 'Best Symmetry Animation' takes students through the entire sequence.

2011-01-01

276

Symmetry in the Car Park  

ERIC Educational Resources Information Center

|In this article, the author presents a lesson on rotational symmetry which she developed for her students. The aim of the lesson was "to identify objects with rotational symmetry in the staff car park" and the success criteria were "pictures or sketches of at least six objects with different orders of rotation". After finding examples of…

Hancock, Karen

2007-01-01

277

Algebraic aspects of chiral symmetry  

SciTech Connect

Algebraic realization of chiral symmetry and its implications are studied. Hadrons are classified by linear representations with mixing when chiral symmetry is spontaneously broken. The axial vector coupling constant is then determined by representation mixing. Phenomenological test for measuring g{sub A} of a nucleon resonance is discussed.

Hosaka, Atsushi [Research Center for Nuclear Physics, Osaka University, Mihogaoka 10-1, Ibaraki 567-0047 (Japan)

2010-12-28

278

Symmetry in Sign Language Poetry  

ERIC Educational Resources Information Center

|This paper considers the range of ways that sign languages use geometric symmetry temporally and spatially to create poetic effect. Poets use this symmetry in sign language art to highlight duality and thematic contrast, and to create symbolic representations of beauty, order and harmony. (Contains 8 tables, 14 figures and 6 notes.)|

Sutton-Spence, Rachel; Kaneko, Michiko

2007-01-01

279

Symmetry and Condensed Matter Physics  

Microsoft Academic Search

Unlike existing texts, this book blends for the first time three topics in physics - symmetry, condensed matter physics and computational methods - into one pedagogical textbook. It includes new concepts in mathematical crystallography, experimental methods capitalizing on symmetry aspects, non-conventional applications such as Fourier crystallography, color groups, quasicrystals and incommensurate systems, as well as concepts and techniques behind the

M. El-Batanouny; F. Wooten

2008-01-01

280

Violation of Particle Antiparticle Symmetry  

Microsoft Academic Search

Symmetry is a fundamental concept which can be found in the whole range of human activities e. g. from arts to science. The beauty of a statues is often related to its symmetric form. In physics, all the laws are related to some sort of symmetry. Equally important is a small breakdown ofsymmetry. Even for the case of a statue,

Z Nakada

2001-01-01

281

Symmetry and Human Facial Attractiveness  

Microsoft Academic Search

Symmetry may act as a marker of phenotypic and genetic quality and is preferred during mate selection in a variety of species. Measures of human body symmetry correlate with attractiveness, but studies manipulating human face images report a preference for asymmetry. These results may reflect unnatural feature shapes and changes in skin textures introduced by image processing. When the shape

David I Perrett; D. Michael Burt; Ian S Penton-Voak; Kieran J Lee; Duncan A Rowland; Rachel Edwards

1999-01-01

282

Internal symmetries of cellular automata.  

PubMed

(Internal) transformations on the space Sigma of automaton configurations are defined as bi-infinite sequences of permutations of the cell symbols. A pair of transformations (gamma,theta) is said to be an internal symmetry of a cellular automaton f:Sigma-->Sigma if f=theta(-1)fgamma. It is shown that the full group of internal symmetries of an automaton f can be encoded as a group homomorphism F such that theta=F(gamma). The domain and image of the homomorphism F have, in general, infinite order and F is presented by a local automaton-like rule. Algorithms to compute the symmetry homomorphism F and to classify automata by their symmetries are presented. Examples on the types of dynamical implications of internal symmetries are discussed in detail. (c) 1997 American Institute of Physics. PMID:12779672

Urias, Jesus; Enciso, Agustin

1997-09-01

283

Supersymmetric Unification and R Symmetries  

NASA Astrophysics Data System (ADS)

We review the role of R symmetries in models of supersymmetric unification in four and more dimensions, and in string theory. We show that, if one demands anomaly freedom and fermion masses, only R symmetries can forbid the supersymmetric Higgs mass term ?. We then review the proof that R symmetries are not available in conventional grand unified theories (GUTs) and argue that this prevents natural solutions to the doublet-triplet splitting problem in four dimensions. On the other hand, higher-dimensional GUTs do not suffer from this problem. We briefly comment on an explicit string-derived model in which the ? and dimension-5 proton decay problems are solved simultaneously by an order four discrete R symmetry. We also comment on the higher-dimensional origin of this symmetry.

Chen, Mu-Chun; Fallbacher, Maximilian; Ratz, Michael

2012-12-01

284

Symmetries in geology and geophysics.  

PubMed

Symmetries have played an important role in a variety of problems in geology and geophysics. A large fraction of studies in mineralogy are devoted to the symmetry properties of crystals. In this paper, however, the emphasis will be on scale-invariant (fractal) symmetries. The earth's topography is an example of both statistically self-similar and self-affine fractals. Landforms are also associated with drainage networks, which are statistical fractal trees. A universal feature of drainage networks and other growth networks is side branching. Deterministic space-filling networks with side-branching symmetries are illustrated. It is shown that naturally occurring drainage networks have symmetries similar to diffusion-limited aggregation clusters. PMID:11607719

Turcotte, D L; Newman, W I

1996-12-10

285

Hadronic Symmetries of Skyrmions  

NASA Astrophysics Data System (ADS)

After reviewing the minimal SU(2) Skyrme model, we generalize it to a composite model. The predictions are found to be in good agreement with experiment, and an interpretation of solitons as quarks is suggested. To include vector mesons, we propose a lagrangian such that all the mesons (pseudoscalars and vectors) are treated equally. This model agrees with the usual meson physics and gives a new mass relation among the mesons. After reducing the model to an SU(4) Skyrme model, we introduce a soliton ansatz and find the mass spectra of the solitons. The model is compared with the approach of introducing vector mesons as gauge bosons. These two models are shown to coincide at low energies. We propose a fermionic quantization prescription and obtain a hadronic superalgebra from the Skyrme operators. A possible supersymmetry realization and its implications in the Skyrme model are also discussed. The effective hamiltonian of the semi-relativistic quark model is derived. We discuss the mass spectrum and hadronic symmetries of the quark model and the Skyrme model.

Cheung, Hay Yeung

286

Lorentz symmetry violation without violation of relativistic symmetry  

NASA Astrophysics Data System (ADS)

Within the framework of the Finslerian approach to the problem of violation of Lorentz symmetry, consideration is given to a flat axially symmetric Finslerian space of events, which is the generalization of Minkowski space. Such an event space arises from the spontaneous breaking of initial gauge symmetry and from the formation of anisotropic fermion antifermion condensate. It is shown that the appearance of an anisotropic condensate breaks Lorentz symmetry; relativistic symmetry, realized by means of the 3-parameter group of generalized Lorentz boosts, remains valid here nevertheless. We have obtained the bispinor representation of the group of generalized Lorentz boosts, which makes it possible to construct the Lagrangian for an interaction of fundamental fields with anisotropic condensate.

Bogoslovsky, G. Yu.

2006-01-01

287

Geometrical spin symmetry and spin  

SciTech Connect

Unification of General Theory of Relativity and Quantum Mechanics leads to General Quantum Mechanics which includes into itself spindynamics as a theory of spin phenomena. The key concepts of spindynamics are geometrical spin symmetry and the spin field (space of defining representation of spin symmetry). The essence of spin is the bipolar structure of geometrical spin symmetry induced by the gravitational potential. The bipolar structure provides a natural derivation of the equations of spindynamics. Spindynamics involves all phenomena connected with spin and provides new understanding of the strong interaction.

Pestov, I. B., E-mail: pestov@theor.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)

2011-07-15

288

Symmetries in the Schwarzschild Problem  

NASA Astrophysics Data System (ADS)

The two-body problem associated to a force field described by a potential of the form U = A/r + B/r3 (r is a distance between particles, A and B are real parameters) is resumed from the only standpoint of symmetries. Such symmetries, expressed in Hamiltonian coordinates, or in standard polar coordinates, are recovered for McGehee-type coordinates of both collision-blow-up and infinity-blow-up kind. They form isomorphic commutative groups endowed with an idempotent structure. Expressed in Levi-Civita's coordinates, the problem exhibits a larger group of symmetries, also commutative and presenting an idempotent structure.

Mioc, V.

289

Nuclear structure, reactions and symmetries  

SciTech Connect

This book, presented in two volumes, discusses the papers on nuclear structure and symmetries. The topics of discussion were octupole and dipole modes, interacting boson version of reflection-asymmetric deformation, alpha decay of actinide nuclei, experimental studies of symmetries, high spin physics, theory of unified nuclei, odd-even nuclei, boson densities by electron scattering, symmetries in reactions, nuclear structure in heavy-ion collisions, nuclear orientation of isotopes, experimental techniques and studies and present status of investigations in theory. Also discussed are recent theoretical developments of nuclear physics in form of various models like Coriolis Coupling model and Shell Correction method.

Meyer, R.A.; Paar, V.

1986-01-01

290

Reemission Ball and Symmetry-Capsule diagnostics for symmetry measurements  

NASA Astrophysics Data System (ADS)

The most recent Livermore NIF design is a gas filled hohlraum without shine shields [1]. Two symmetry diagnostics, reemission ball and symmetry-capsule, are examined using the new ignition design. Both reemission ball and symmetry-capsules have been used in the past to measure capsule symmetry on NOVA experiments. [2-5] Livermore and Los Alamos scientists are now pursuing both concepts to study symmetry on NIF. [6] Here we compare the predicted symmetry for the two techniques. Issues related to the three-dimensional nature of the reemit diagnostic will be discussed. Issues such as the viewing holes in the hohlraum wall will be addressed by applying a three-dimensional view-factor code. [1] Steve Haan et al., private communication [2] Magelssen et al., Phy. Rev. E 57, 4663 (1998). [3] Delamater et al., Phy. Rev. E 53, 5240 (1996). [4] Hauer et al., Phys. Plasmas 2 (6), 2488 (1995). [5] Harris et al., Bull. Am. Phys. Soc. 38, 1885 (1993). [6] Don Meeker private, communication and Nels Hoffman, private communication

Magelssen, G. R.; Bradley, P. A.; Delamater, N. D.

2006-10-01

291

Large-Scale Molecular Dynamics Simulations of Shock Waves in Laves Crystals and Icosahedral Quasicrystals  

NASA Astrophysics Data System (ADS)

Quasicrystals and ordinary crystals both possess long-range translational order. But quasicrystals are aperiodic since their symmetry is non-crystallographic. The aim of this project is to study the behavior of shock waves in periodic and aperiodic structures and to compare the results. The expectation is that new types of defects are generated in the aperiodic materials. The materials studied are two models of (AlCu)Li quasicrystals and the C15 Laves phase, a low-order approximant of the quasicrystals. An elastic wave is found in the simulations up to a piston velocity of about up < 0.25 cl. Between 0.5 < up/cl < 0.5 the slope of elastic wave velocity slows down, and a new plastic wave is observed. Extended defect are generated, but no simple two-dimensional walls. The defect bands have finite width and a disordered structure. If the crystal is quenched a polycrystalline phase is obtained. For the quasicrystal the transformation is more complex since ring processes occur in the elastic regime already. Starting at about up < 0.5 cl a single plastic shock wave is observed. In this range all structures are destroyed completely.

Roth, Johannes

2002-07-01

292

Trace formula for broken symmetry  

SciTech Connect

We derive a trace formula for systems that exhibit an approximate continuous symmetry. It interpolates between the sum over continuous families of periodic orbits that holds in the case of exact continuous symmetry, and the discrete sum over isolated orbits that holds when the symmetry is completely broken. It is based on a simple perturbation expansion of the classical dynamics, centered around the case of exact symmetry, and gives an approximation to the usual Gutzwiller formula when the perturbation is large. We illustrate the computation with some 2-dimensional examples: the deformation of the circular billiard into an ellipse, and anisotropic and anharmonic perturbations of a harmonic oscillator. Copyright {copyright} 1996 Academic Press, Inc.

Creagh, S.C. [Institut fuer Theoretische Physik, Unversitaet Regensburg, D-93040 Regensburg (Germany)

1996-05-01

293

Dynamic Symmetry in Radio Design  

Microsoft Academic Search

This paper reviews some of the principles of dynamic symmetry, the science of vital relations of areas, which was the basis of ancient Greek art, as rediscovered by Jay Hambidge about fifteen years ago, and described in his works \\

A. Van Dyck

1932-01-01

294

Electroweak Symmetry Breaking: With Dynamics  

SciTech Connect

In this note I provide a brief description of models of dynamical electroweak symmetry breaking, including walking technicolor, top-color assisted technicolor, the top-quark seesaw model, and little higgs theories.

Chivukula, R. Sekhar [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

2005-03-22

295

Symmetry Equation Package for Reduce.  

National Technical Information Service (NTIS)

The REDUCE package developed for computation of symmetries of partial differential equations using total derivative operators is described. The WEB source code of the implementations of this method for REDUCE is given. Directions of use and an example of ...

T. Vanbemmelen

1992-01-01

296

A Winged-Helix Protein From Sulfolobus Turreted Icosahedral Virus Points Toward Stabilizing Disulfide Bonds in the Intracellular Proteins of a Hyperthermophilic Virus  

SciTech Connect

Sulfolobus turreted icosahedral virus (STIV) was the first non-tailed icosahedral virus to be isolated from an archaeal host. Like other archaeal viruses, its 37 open reading frames generally lack sequence similarity to genes with known function. The roles of the gene products in this and other archaeal viruses are thus largely unknown. However, a protein's three-dimensional structure may provide functional and evolutionary insight in cases of minimal sequence similarity. In this vein, the structure of STIV F93 reveals a homodimer with strong similarity to the winged-helix family of DNA-binding proteins. Importantly, an interchain disulfide bond is found at the dimer interface, prompting analysis of the cysteine distribution in the putative intracellular proteins of the viral proteome. The analysis suggests that intracellular disulfide bonds are common in cellular STIV proteins, where they enhance the thermostability of the viral proteome.

Larson, E.T.; Eilers, B.; Menon, S.; Reiter, D.; Ortmann, A.; Young, M.J.; Lawrence, C.M.

2009-06-03

297

Anomalies and Discrete Chiral Symmetries  

SciTech Connect

The quantum anomaly that breaks the U(1) axial symmetry of massless multi-flavored QCD leaves behind a discrete flavor-singlet chiral invariance. With massive quarks, this residual symmetry has a close connection with the strong CP-violating parameter theta. One result is that if the lightest quarks are degenerate, then a first order transition will occur when theta passes through pi. The resulting framework helps clarify when the rooting prescription for extrapolating in the number of flavors is valid.

Creutz, M.

2009-09-07

298

Nonholonomic mechanical systems with symmetry  

Microsoft Academic Search

This work develops the geometry and dynamics of mechanical systems with nonholonomic constraints and symmetry from the perspective of Lagrangian mechanics and with a view to control-theoretical applications. The basic methodology is that of geometric mechanics applied to the Lagrange-d'Alembert formulation, generalizing the use of connections and momentum maps associated with a given symmetry group to this case. We begin

Anthony M. Bloch; P. S. Krishnaprasad; Jerrold E. Marsden; Richard M. Murray

1996-01-01

299

Contrapositive symmetry of fuzzy implications  

Microsoft Academic Search

Contrapositive symmetry of R- and QL-implications defined from t-norms, t-conorms and strong negations is studied. For R-implications, characterizations of contrapositive symmetry are proved when the underlying t-norm satisfies a residuation condition. Contrapositive symmetrization of R-implications not having this property makes it possible to define a conjunction so that the residuation principle is preserved. Cases when this associated conjunction is a

J' Anos C. Fodor

1995-01-01

300

Broken symmetries and magnetic dynamos  

SciTech Connect

Phase space symmetries inherent in the statistical theory of ideal magnetohydrodynamic (MHD) turbulence are known to be broken dynamically to produce large-scale coherent magnetic structure. Here, results of a numerical study of decaying MHD turbulence are presented that show large-scale coherent structure also arises and persists in the presence of dissipation. Dynamically broken symmetries in MHD turbulence may thus play a fundamental role in the dynamo process.

Shebalin, John V. [Astromaterials Research and Exploration Science Office, NASA Johnson Space Center, Houston, Texas 77058 (United States)

2007-10-15

301

Exploiting Symmetry In Temporal Logic Model Checking  

Microsoft Academic Search

In practice, finite state concurrent systems often exhibit considerable symmetry. We investigate techniques for reducing the complexity of temporal logic model checking in the presence of symmetry. In particular, we show that symmetry can frequently be used to reduce the size of the state space that must be explored during model checking. In the past, symmetry has been exploited in

Edmund M. Clarke; Thomas Filkorn; Somesh Jha

1993-01-01

302

Exploiting Symmetry in Temporal Logic Model Checking  

Microsoft Academic Search

In practice, finite state concurrent systems often exhibit considerable symmetry. We investigate techniques for reducing the complexity of temporal logic model checking in the presence of symmetry. In particular, we show that symmetry can frequently be used to reduce the size of the state space that must be explored during model checking. In the past, symmetry has been exploited in

Edmund M. Clarke; Somesh Jha; Reinhard Enders; Thomas Filkorn

1996-01-01

303

Symmetry properties in polarimetric remote sensing  

Microsoft Academic Search

This paper presents the relations among polarimetric backscattering coefficients from the viewpoint of symmetry groups. Symmetry of geophysical media encountered in remote sensing due to reflection, rotation, azimuthal, and centrical symmetry groups is considered for both reciprocal and nonreciprocal cases. On the basis of the invariance under symmetry transformations in the linear polarization basis, the scattering coefficients are related by

S. V. Nghiem; S. H. Yueh; R. Kwok; F. K. Li

1992-01-01

304

Time-reversal symmetry breaking Pomeranchuk instabilities in hexagonal systems: emergence of the ? phase  

NASA Astrophysics Data System (ADS)

We show how nematic order that breaks time reversal symmetry can be stabilized by longer-range repulsive interactions in a variety of hexagonal systems. For the triangular, honeycomb and Kagome lattices at the van Hove filling, we show how spinful fermions can enter the so called ? phase, in analogy to the B phase in superfluid ^3He. This Pomeranchuk instability in the spin channel involves a splitting of the Fermi surface into two parts, with the spin direction winding in momentum space. This is possible for angular momentum l=2 nematics, since these form a doubly degenerate irreducible representation of the C6v point group symmetry of the lattices in question. We demonstrate how our results are exact in the weak coupling limit, although separate numerical studies have shown that these phases can persist at stronger coupling.

Maharaj, Akash; Thomale, Ronny; Raghu, Srinivas

2013-03-01

305

Calculated phase diagram of doped BaFe2As2 superconductor in a C4-symmetry breaking model  

NASA Astrophysics Data System (ADS)

We develop a minimal multiorbital tight-binding model with realistic hopping parameters. The model breaks the symmetry of the tetragonal point group by lowering it from C4 to D2d, which accurately describes the Fermi surface evolution of the electron-doped BaFe2-xCoxAs2 and hole-doped Ba1-yKyFe2As2 compounds. An investigation of the phase diagram with a mean-field t\\text{-}U\\text{-}V Bogoliubov-de Gennes Hamiltonian results in agreement with the experimentally observed electron- and hole-doped phase diagram with only one set of t, U and V parameters. Additionally, the self-consistently calculated superconducting order parameter exhibits s^+/- -wave pairing symmetry with a small d-wave pairing admixture in the entire doping range, which is the subtle result of the weakly broken symmetry and competing interactions in the multiorbital mean-field Hamiltonian.

Tai, Yuan-Yen; Zhu, Jian-Xin; Graf, Matthias J.; Ting, C. S.

2013-09-01

306

Visualization of uncorrelated, tandem symmetry mismatches in the internal genome packaging apparatus of bacteriophage T7  

PubMed Central

Motor-driven packaging of a dsDNA genome into a preformed protein capsid through a unique portal vertex is essential in the life cycle of a large number of dsDNA viruses. We have used single-particle electron cryomicroscopy to study the multilayer structure of the portal vertex of the bacteriophage T7 procapsid, the recipient of T7 DNA in packaging. A focused asymmetric reconstruction method was developed and applied to selectively resolve neighboring pairs of symmetry-mismatched layers of the portal vertex. However, structural features in all layers of the multilayer portal vertex could not be resolved simultaneously. Our results imply that layers with mismatched symmetries can join together in several different relative orientations, and that orientations at different interfaces assort independently to produce structural isomers, a process that we call combinatorial assembly isomerism. This isomerism explains rotational smearing in previously reported asymmetric reconstructions of the portal vertex of T7 and other bacteriophages. Combinatorial assembly isomerism may represent a new regime of structural biology in which globally varying structures assemble from a common set of components. Our reconstructions collectively validate previously proposed symmetries, compositions, and sequential order of T7 portal vertex layers, resolving in tandem the 5-fold gene product 10 (gp10) shell, 12-fold gp8 portal ring, and an internal core stack consisting of 12-fold gp14 adaptor ring, 8-fold bowl-shaped gp15, and 4-fold gp16 tip. We also found a small tilt of the core stack relative to the icosahedral fivefold axis and propose that this tilt assists DNA spooling without tangling during packaging.

Guo, Fei; Liu, Zheng; Vago, Frank; Ren, Yue; Wu, Weimin; Wright, Elena T.; Serwer, Philip; Jiang, Wen

2013-01-01

307

African Swine Fever Virus Protein p17 Is Essential for the Progression of Viral Membrane Precursors toward Icosahedral Intermediates?  

PubMed Central

The first morphological evidence of African swine fever virus (ASFV) assembly is the appearance of precursor viral membranes, thought to derive from the endoplasmic reticulum, within the assembly sites. We have shown previously that protein p54, a viral structural integral membrane protein, is essential for the generation of the viral precursor membranes. In this report, we study the role of protein p17, an abundant transmembrane protein localized at the viral internal envelope, in these processes. Using an inducible virus for this protein, we show that p17 is essential for virus viability and that its repression blocks the proteolytic processing of polyproteins pp220 and pp62. Electron microscopy analyses demonstrate that when the infection occurs under restrictive conditions, viral morphogenesis is blocked at an early stage, immediately posterior to the formation of the viral precursor membranes, indicating that protein p17 is required to allow their progression toward icosahedral particles. Thus, the absence of this protein leads to an accumulation of these precursors and to the delocalization of the major components of the capsid and core shell domains. The study of ultrathin serial sections from cells infected with BA71V or the inducible virus under permissive conditions revealed the presence of large helicoidal structures from which immature particles are produced, suggesting that these helicoidal structures represent a previously undetected viral intermediate.

Suarez, Cristina; Gutierrez-Berzal, Javier; Andres, German; Salas, Maria L.; Rodriguez, Javier M.

2010-01-01

308

Particle Assembly and Ultrastructural Features Associated with Replication of the Lytic Archaeal Virus Sulfolobus Turreted Icosahedral Virus?  

PubMed Central

Little is known about the replication cycle of archaeal viruses. We have investigated the ultrastructural changes of Sulfolobus solfataricus P2 associated with infection by Sulfolobus turreted icosahedral virus (STIV). A time course of a near synchronous STIV infection was analyzed using both scanning and transmission electron microscopy. Assembly of STIV particles, including particles lacking DNA, was observed within cells, and fully assembled STIV particles were visible by 30 h postinfection (hpi). STIV was determined to be a lytic virus, causing cell disruption beginning at 30 hpi. Prior to cell lysis, virus infection resulted in the formation of pyramid-like projections from the cell surface. These projections, which have not been documented in any other host-virus system, appeared to be caused by the protrusion of the cell membrane beyond the bordering S-layer. These structures are thought to be sites at which progeny virus particles are released from infected cells. Based on these observations of lysis, a plaque assay was developed for STIV. From these studies we propose an overall assembly model for STIV.

Brumfield, Susan K.; Ortmann, Alice C.; Ruigrok, Vincent; Suci, Peter; Douglas, Trevor; Young, Mark J.

2009-01-01

309

- Gauges and Global Gauge Symmetry Breaking  

NASA Astrophysics Data System (ADS)

The concept of (global) gauge symmetry breaking plays an important role in many areas of physics. Since the corresponding symmetry is a gauge symmetry, its breaking is actually gauge-dependent. Thus, it is possible to design gauges which restore the symmetry as good as possible. Such gauge constructions will be detailed here, illustrated with the use of lattice gauge theory. Their use will be discussed for the cases of the Higgs effect, high-baryon density color superconductors, and BRST symmetry.

Maas, Axel

2012-12-01

310

Symmetry-protected entanglement renormalization  

NASA Astrophysics Data System (ADS)

Entanglement renormalization is a real-space renormalization group (RG) transformation for quantum many-body systems. It generates the multiscale entanglement renormalization ansatz (MERA), a tensor network capable of efficiently describing a large class of many-body ground states, including those of systems at a quantum critical point or with topological order. The MERA has also been proposed to be a discrete realization of the holographic principle of string theory. Here we propose the use of symmetric tensors as a mechanism to build a symmetry-protected RG flow, and discuss two important applications of this construction. First, we argue that symmetry-protected entanglement renormalization produces the proper structure of RG fixed points, namely, a fixed-point for each symmetry-protected phase. Second, in the context of holography, we show that by using symmetric tensors, a global symmetry at the boundary becomes a local symmetry in the bulk, thus explicitly realizing in the MERA a characteristic feature of the AdS/CFT correspondence.

Singh, Sukhwinder; Vidal, Guifre

2013-09-01

311

Annular symmetry nonlinear frequency converters.  

PubMed

We present a new type of two-dimensional nonlinear structure for quasi-phase matching. This structure has continuous rotational symmetry, and in contrary to the commonly used periodic structures, is not lattice shaped and has no translation symmetry. It is shown that this annular symmetry structure possesses interesting phase matching attributes that are significantly different than those of periodic structures. In particular, it enables simultaneous phase-matched frequency doubling of the same pump into several different directions. Moreover, it has extremely wide phase-mismatch tolerance, since a change in the phase matching conditions does not change the second harmonic power, but only changes its propagation direction. Several structures were fabricated using either the indirect e-beam method in LiNbO(3) or the electric field poling method in stoichiometric LiTaO(3), and their conversion efficiencies, as well as angular and thermal dependencies, were characterized by second harmonic generation. PMID:19529321

Kasimov, Dror; Arie, Ady; Winebrand, Emil; Rosenman, Gil; Bruner, Ariel; Shaier, Pnina; Eger, David

2006-10-01

312

The Broken Symmetry of Time  

SciTech Connect

This paper seeks to clarify features of time asymmetry in terms of symmetry breaking. It is observed that, in general, a contingent situation or event requires the breaking of an underlying symmetry. The distinction between the universal anisotropy of temporal processes and the irreversibility of certain physical processes is clarified. It is also proposed that the Transactional Interpretation of quantum mechanics offers an effective way to explain general thermodynamic asymmetry in terms of the time asymmetry of radiation, where prior such efforts have fallen short.

Kastner, Ruth E. [Department of Philosophy, University of Maryland, College Park, MD 20742 (United States)

2011-11-29

313

Chiral symmetry in nuclear matter  

SciTech Connect

We use the chiral sigma--..omega.. model at zero temperature to study the role of chiral symmetry in nuclear matter. The central role played by the pion propagator in connection with the energy density of nuclear matter and the problem of chiral phase transitions is pointed out. Results obtained previously are reexamined from the standpont of chiral symmetry. Consequences of baryon current conservation and the renormalization of the neutral vector boson field in connection with many-body problems are also treated in detailed. copyright 1988 Academic Press, Inc.

Bentz, W.; Liu, L.G.; Arima, A.

1988-11-15

314

Chiral symmetry on the lattice  

SciTech Connect

The author reviews some of the difficulties associated with chiral symmetry in the context of a lattice regulator. The author discusses the structure of Wilson Fermions when the hopping parameter is in the vicinity of its critical value. Here one flavor contrasts sharply with the case of more, where a residual chiral symmetry survives anomalies. The author briefly discusses the surface mode approach, the use of mirror Fermions to cancel anomalies, and finally speculates on the problems with lattice versions of the standard model.

Creutz, M.

1994-11-01

315

Dynamical symmetries in relativistic kinetic theory  

NASA Astrophysics Data System (ADS)

This paper is part of a program investigating symmetries that are defined at a physical or observational level rather than purely geometrically. Here we generalize previous work on dynamical “matter” symmetries of relativistic gases. If the matter symmetry vector is surface-forming with the dynamical Liouville vector, then Einstein's equations reduce it to a Killing symmetry of the metric. We show that this conclusion is unaltered if the gas particles are subject to a nongravitational force (including the electromagnetic force on charged particles) or if the gravitational field obeys higher-order field equations. In the Brans-Dicke theory, the matter symmetry reduces to a homothetic symmetry of the metric. This is also the case for a generalized conformal symmetry in Einstein's theory. We consider the problem of relaxing the surface-forming assumption in an attempt to determine whether there are dynamical symmetries that do not necessarily reduce to geometrical symmetries of the metric.

Maartens, R.; Taylor, D. R.

1994-08-01

316

A model of intrinsic symmetry breaking  

NASA Astrophysics Data System (ADS)

Different from the symmetry breaking associated with a phase transition, which occurs when the controlling parameter is manipulated across a critical point, the symmetry breaking presented in this Letter does not need parameter manipulation. Instead, the system itself suddenly undergoes symmetry breaking at a certain time during its evolution, which is intrinsic symmetry breaking. Through a polymer model, it is revealed that the origin of the intrinsic symmetry breaking is nonlinearity, which produces instability at the instance when the evolution crosses an inflexion point, where this instability breaks the original symmetry.

Ge, Li; Li, Sheng; George, Thomas F.; Sun, Xin

2013-11-01

317

Charge Symmetry at the Partonic Level  

SciTech Connect

This review article discusses the experimental and theoretical status of partonic charge symmetry. It is shown how the partonic content of various structure functions gets redefined when the assumption of charge symmetry is relaxed. We review various theoretical and phenomenological models for charge symmetry violation in parton distribution functions. We summarize the current experimental upper limits on charge symmetry violation in parton distributions. A series of experiments are presented, which might reveal partonic charge symmetry violation, or alternatively might lower the current upper limits on parton charge symmetry violation.

J.T. Londergan, J.-C. Peng, A.W. Thomas

2010-07-01

318

Charge symmetry at the partonic level  

SciTech Connect

This review article discusses the experimental and theoretical status of partonic charge symmetry. It is shown how the partonic content of various structure functions gets redefined when the assumption of charge symmetry is relaxed. Various theoretical and phenomenological models for charge-symmetry violation in parton distribution functions are reviewed. After summarizing the current experimental upper limits on charge-symmetry violation in parton distributions, a series of new experiments are proposed, which might reveal partonic charge-symmetry violation or alternatively might lower the current upper limits on parton charge-symmetry violation.

Londergan, J. T.; Peng, J. C.; Thomas, A. W. [Department of Physics and Nuclear Theory Center, Indiana University, Bloomington, Indiana 47404 (United States); Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Thomas Jefferson National Laboratory, 12000 Jefferson Avenue, Newport News, Virginia 23606, USA and CSSM, School of Chemistry and Physics, University of Adelaide, Adelaide, South Australia 5005 (Australia)

2010-07-15

319

Nonlocal-symmetry Ward identities  

SciTech Connect

We derive and discuss Ward identities associated with the nonlocal symmetry found in certain two-dimensional field theories. We show the identities are satisfied by the fermion propagator in the presence of the dynamical mass generation occurring in the O(N) Gross-Neveu model as N..-->..infinity.

Curtright, T.L.; Zachos, C.K.

1981-11-15

320

Unitary Symmetry and Leptonic Decays  

Microsoft Academic Search

An analysis of leptonic decays based on unitary symmetry for strong ; interactions (eightfold way) and the V-A theory for weak interactions is ; presented. An explanation for the observed predominance of the LAMBDA yields ; + e⁻ + nu decay over the LAMBDA ⁻ yields n + e⁻ + nu ; decay is obtained. Branching ratios predicted for electron

Nicola Cabibbo

1963-01-01

321

Entanglement renormalization and gauge symmetry  

SciTech Connect

A lattice gauge theory is described by a redundantly large vector space that is subject to local constraints and can be regarded as the low-energy limit of an extended lattice model with a local symmetry. We propose a numerical coarse-graining scheme to produce low-energy, effective descriptions of lattice models with a local symmetry such that the local symmetry is exactly preserved during coarse-graining. Our approach results in a variational ansatz for the ground state(s) and low-energy excitations of such models and, by extension, of lattice gauge theories. This ansatz incorporates the local symmetry in its structure and exploits it to obtain a significant reduction of computational costs. We test the approach in the context of a Z{sub 2} lattice gauge theory formulated as the low-energy theory of a specific regime of the toric code with a magnetic field, for lattices with up to 16x16 sites (16{sup 2}x2=512 spins) on a torus. We reproduce the well-known ground-state phase diagram of the model, consisting of a deconfined and spin-polarized phases separated by a continuous quantum phase transition, and obtain accurate estimates of energy gaps, ground-state fidelities, Wilson loops, and several other quantities.

Tagliacozzo, L.; Vidal, G. [School of Mathematics and Physics, University of Queensland, QLD 4072 (Australia)

2011-03-15

322

Symmetry and separation of variables  

Microsoft Academic Search

This book is concerned with the relation between symmetries of a linear second-order partial differential equation of mathematical physics, the coordinate systems in which the equation admits solutions by the separation of variables, and the properties of the special functions that arise in this manner. Some modern group-theoretic twists in the separation of variables method that can be used to

W Miller; W. Jr

1977-01-01

323

Platonic Symmetry and Geometric Thinking  

ERIC Educational Resources Information Center

|Cubic symmetry is used to build the other four Platonic solids and some formalism from classical geometry is introduced. Initially, the approach is via geometric construction, e.g., the "golden ratio" is necessary to construct an icosahedron with pentagonal faces. Then conventional elementary vector algebra is used to extract quantitative…

Zsombor-Murray, Paul

2007-01-01

324

From symmetries to number theory  

SciTech Connect

It is shown that the finite-operator calculus provides a simple formalism useful for constructing symmetry-preserving discretizations of quantum-mechanical integrable models. A related algebraic approach can also be used to define a class of Appell polynomials and of L series.

Tempesta, P., E-mail: p.tempesta@fis.ucm.e [Universidad Complutense, Departamento de Fisica Teorica II, Facultad de Fisicas (Spain)

2009-05-15

325

Circular Symmetry of Pinwheel Diffraction  

Microsoft Academic Search

.  A method is given for explicitly determining the autocorrelation of the pinwheel tiling by use of the substitution system\\u000a generating the tiling. Using this a new proof of the circular symmetry of the diffraction of the pinwheel tiling is given.\\u000a \\u000a Communicated by Jean Bellissard

Robert V. Moody; Derek Postnikoff; Nicolae Strungaru

2006-01-01

326

Bifurcation and Symmetry in Convection  

Microsoft Academic Search

The theory of bifurcation with symmetry is applied to the onset of convection in a fluid layer heated from below. Doubly diffusive convection illustrates the general theory, which describes selection between the possible cellular patterns: rolls, hexagons, triangles, squares, and rectangles. Double periodicity in the horizontal plane is imposed, thus allowing only a finite number of convection rolls to become

James William Swift

1985-01-01

327

Superdeformations and fermion dynamical symmetries  

SciTech Connect

In this talk, I will present a link between nuclear collective motions and their underlying fermion dynamical symmetries. In particular, I will focus on the microscopic understanding of deformations. It is shown that the SU{sub 3} of the one major shell fermion dynamical symmetry model (FDSM) is responsible for the physics of low and high spins in normal deformation. For the recently observed phenomena of superdeformation, the physics of the problem dictates a generalization to a supershell structure (SFDSM), which also has an SU{sub 3} fermion dynamical symmetry. Many recently discovered feature of superdeformation are found to be inherent in such an SU{sub 3} symmetry. In both cases the dynamical Pauli effect plays a vital role. A particularly noteworthy discovery from this model is that the superdeformed ground band is not the usual unaligned band but the D-pair aligned (DPA) band, which sharply crosses the excited bands. The existence of such DPA band is a key point to understand many properties of superdeformation. Our studies also poses new experimental challenge. This is particularly interesting since there are now plans to build new and exciting {gamma}-ray detecting systems, like the GAMMASPHERE, which could provide answers to some of these challenges. 34 refs., 11 figs., 5 tabs.

Wu, Cheng-Li (Drexel Univ., Philadelphia, PA (USA). Dept. of Physics and Atmospheric Science Tennessee Univ., Knoxville, TN (USA). Dept. of Physics and Astronomy Joint Inst. for Heavy Ion Research, Oak Ridge, TN (USA))

1990-01-01

328

Concomitant Ordering and Symmetry Lowering  

ERIC Educational Resources Information Center

|Examples of concomitant ordering include magnetic ordering, Jahn-Teller cooperative ordering, electronic ordering, ionic ordering, and ordering of partially-filled sites. Concomitant ordering sets in when a crystal is cooled and always lowers the degree of symmetry of the crystal. Concomitant ordering concepts can also be productively applied to…

Boo, William O. J.; Mattern, Daniell L.

2008-01-01

329

Curvature perturbations from broken symmetries  

SciTech Connect

We present a new general mechanism to generate curvature perturbations after the end of the slow-roll phase of inflation. Our model is based on the simple assumption that the potential driving inflation is characterized by an underlying global symmetry which is slightly broken.

Kolb, Edward W.; Riotto, Antonio; Vallinotto, Alberto [Particle Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States) and Department of Astronomy and Astrophysics, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637-1433 (United States); INFN, Sezione di Padova, via Marzolo 8, I-35131 (Italy); Physics Department, University of Chicago, Chicago, Illinois 60637-1433 (United States) and Particle Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States)

2005-02-15

330

Chiral Symmetry in Nuclear Physics  

Microsoft Academic Search

The role of chiral symmetry in nuclear physics is summarized. The topics\\u000atreated are the chiral bag model for nucleon structure resulting from large\\u000a$N_c$ QCD, the pion cloud in chiral perturbation theory for low-energy\\u000aelectroweak nuclear response functions, ``swelled hadrons\\

Mannque Rho

1998-01-01

331

Approximate Nature of Physical Symmetries  

Microsoft Academic Search

Since Leibniz it has become clearer and clearer that a priori judgment is inadequate to establish the presence of exact symmetries in the physical laws, and the exact conservation laws which flow from them. The latest example has been the Yang-Lee demonstration of the failure of mirror invariance in the weak interactions. It is possible to conjecture that even the

P. Morrison

1958-01-01

332

Hamiltonian Hopf Bifurcation with Symmetry  

Microsoft Academic Search

In this paper we study the appearance of branches of relative periodic orbits in Hamiltonian Hopf bifurcation processes in\\u000a the presence of compact symmetry groups that do not generically exist in the dissipative framework. The theoretical study\\u000a is illustrated with several examples.

Pascal Chossat; Juan-Pablo Ortega; Tudor S. Ratiu

2002-01-01

333

Turning Students into Symmetry Detectives  

ERIC Educational Resources Information Center

|Exploring mathematical symmetry is one way of increasing students' understanding of art. By asking students to search designs and become pattern detectives, teachers can potentially increase their appreciation of art while reinforcing their perception of the use of math in their day-to-day lives. This article shows teachers how they can interest…

Wilders, Richard; VanOyen, Lawrence

2011-01-01

334

The Geometry of Reflectance Symmetries.  

PubMed

Different materials reflect light in different ways, and this reflectance interacts with shape, lighting, and viewpoint to determine an object's image. Common materials exhibit diverse reflectance effects, and this is a significant source of difficulty for image analysis. One strategy for dealing with this diversity is to build computational tools that exploit reflectance symmetries, such as reciprocity and isotropy, that are exhibited by broad classes of materials. By building tools that exploit these symmetries, one can create vision systems that are more likely to succeed in real-world, non-Lambertian environments. In this paper, we develop a framework for representing and exploiting reflectance symmetries. We analyze the conditions for distinct surface points to have local view and lighting conditions that are equivalent under these symmetries, and we represent these conditions in terms of the geometric structure they induce on the Gaussian sphere and its abstraction, the projective plane. We also study the behavior of these structures under perturbations of surface shape and explore applications to both calibrated and un-calibrated photometric stereo. PMID:21339528

Tan, Ping; Quan, Long; Zickler, Todd

2011-02-17

335

Kohn's theorem and Galilean symmetry  

NASA Astrophysics Data System (ADS)

The relation between the separability of a system of charged particles in a uniform magnetic field and Galilean symmetry is revisited using Duval's "Bargmann framework". If the charge-to-mass ratios of the particles are identical, e/m=? for all particles, then the Bargmann space of the magnetic system is isometric to that of an anisotropic harmonic oscillator. Assuming that the particles interact through a potential which only depends on their relative distances, the system splits into one representing the center of mass plus a decoupled internal part, and can be mapped further into an isolated system using Niederer's transformation. Conversely, the manifest Galilean boost symmetry of the isolated system can be "imported" to the oscillator and to the magnetic systems, respectively, to yield the symmetry used by Gibbons and Pope to prove the separability. For vanishing interaction potential the isolated system is free and our procedure endows all our systems with a hidden Schrödinger symmetry, augmented with independent internal rotations. All these properties follow from the cohomological structure of the Galilei group, as explained by Souriau's "décomposition barycentrique".

Zhang, P.-M.; Horvathy, P. A.

2011-08-01

336

The Symmetry of Natural Laws.  

ERIC Educational Resources Information Center

|This document is a monograph intended for advanced undergraduate students, or beginning graduate students, who have some knowledge of modern physics as well as classical physics, including the elementary quantum mechanical treatment of the hydrogen atom and angular momentum. The first chapter introduces symmetry and relates it to the mathematical…

Brown, Laurie M.

337

Symmetry-Based Photo Editing  

Microsoft Academic Search

Based on high-level geometric knowledge, especially sym- metry, imposed upon objects in images, we demonstrate in this paper how to edit images in terms of correct 3-D shape and relationships of the objects, without explicitly perform- ing full 3-D reconstruction. Symmetry is proposed as the central notation that unifies both conceptually and algorith- mically all types geometric regularities such as

Kun Huang; Wei Hong; Yi Ma

2003-01-01

338

Approximate Symmetries of a Viscoelastic Model  

NASA Astrophysics Data System (ADS)

Approximate symmetries of a mathematical model describing one-dimensional motion in a viscoelastic medium with a small viscosity coefficient are studied. An approximate invariant solution is obtained through the approximate generator of the first-order approximate symmetries.

Valenti, Antonino

2008-04-01

339

Parton Charge Symmetry and Spin Dependence  

SciTech Connect

We report on recent developments in charge symmetry of parton distributions. We summarize recent estimates of the sign and magnitude of charge symmetry violation in parton spin distributions. These have the potential to make corrections to the Bjorken Sum Rule.

Londergan, J. T. [Dept. of Physics and Center for Exploration of Energy and Matter, Indiana University, Bloomington, IN, 47405 (United States)

2011-12-14

340

Symmetry properties and reduction procedures for ODE's  

NASA Astrophysics Data System (ADS)

The notion of ?-symmetries for systems of ODE's and for dynamical systems is presented and discussed. It is shown that it ensures, together with the notion of orbital symmetry for dynamical systems, interesting forms of reduction of the equations.

Cicogna, Giampaolo

2012-09-01

341

From additional symmetries to linearization of Virasoro symmetries  

NASA Astrophysics Data System (ADS)

We construct the additional symmetries and derive the Adler-Shiota-van Moerbeke formula for the two-component BKP hierarchy. Considered as certain reductions of the two-component BKP hierarchy, the Drinfeld-Sokolov hierarchies of type D are proved to possess symmetries written as the linear action of a series of Virasoro operators on the tau function. It results in that the Drinfeld-Sokolov hierarchies of type D coincide with Dubrovin and Zhang’s hierarchies associated to the Frobenius manifolds for Coxeter groups of type D, and that every solution of such a hierarchy together with the string equation is annihilated by certain combinations of the Virasoro operators and the time derivations of the hierarchy.

Wu, Chao-Zhong

2013-04-01

342

Symmetry, broken symmetry, and handedness in bimanual coordination dynamics  

Microsoft Academic Search

The symmetrical dynamics of 1:1 rhythmic bimanual coordination may be specified by an order parameter equation involving the relative phase between rhythmic components, and an interlimb coupling which determines the relative attractiveness of in-phase and anti-phase patterns. Symmetry breaking of these dynamics can occur via the difference in the natural frequencies, ??, of the left and right rhythmic components, or

P. J. Treffner; M. T. Turvey

1996-01-01

343

Symmetry-Breaking Predicates for Search Problems  

Microsoft Academic Search

Many reasoning and optimization problemsexhibit symmetries. Previous work hasshown how special purpose algorithms canmake use of these symmetries to simplifyreasoning. We present a general schemewhereby symmetries are exploited by adding"symmetry-breaking" predicates to the theory.Our approach can be used on any propositionalsatisfiability problem, and can beused as a pre-processor to any (systematicor non-systematic) reasoning method. In thegeneral case adding...

James M. Crawford; Matthew L. Ginsberg; Eugene M. Luks; Amitabha Roy

1996-01-01

344

Symmetry numbers and chemical reaction rates  

Microsoft Academic Search

This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them\\u000a to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational\\u000a symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i)\\u000a if the reaction

Antonio Fernández-Ramos; Benjamin A. Ellingson; Rubén Meana-Pañeda; Jorge M. C. Marques; Donald G. Truhlar

2007-01-01

345

Facial symmetry and the perception of beauty  

Microsoft Academic Search

Evolutionary, as well as cultural, pressures may contribute to our perceptions of facial attractiveness. Biologists predict\\u000a that facial symmetry should be attractive, because it may signal mate quality. We tested the prediction that facial symmetry\\u000a is attractive by manipulating the symmetry of individual faces and observing the effect on attractiveness, and by examining\\u000a whether natural variations in symmetry (between faces)

Gillian Rhodes; Fiona Proffitt; Jonathon M. Grady; Alex Sumich

1998-01-01

346

Local structures and structural phase change in Ni-Zr-Nb glassy alloys composed of Ni5Zr5Nb3 icosahedral clusters  

NASA Astrophysics Data System (ADS)

We construct a local structural model for Ni-Zr-Nb glassy alloys, Ni48Zr40Nb24, which contains eight icosahedra of Ni5Zr5Nb3 as the structural units. We fully optimize the 112-atom structures by first principles calculation, and find two characteristic phases in the structures depending on the alignment of the icosahedra: an amorphous phase where the icosahedral structure well remains and a periodic phase corresponding to crystallization where the icosahedra change to fcc-like cuboctahedra. Nb atom-clustering may play a key role in anti-crystallization.

Fujima, Nobuhisa; Hoshino, Toshiharu; Fukuhara, Mikio

2013-08-01

347

An Animated Interactive Overview of Molecular Symmetry  

NSDL National Science Digital Library

An Animated Interactive Overview of Molecular Symmetry is a series of Web pages designed to help instructors teach molecular symmetry. These pages combine interactive Jmol images and instructional text that allow students to examine and explore the operations and elements that give rise to molecular symmetry.

348

Higher-level mechanisms detect facial symmetry  

PubMed Central

The role of symmetry detection in early visual processing and the sensitivity of biological visual systems to symmetry across a wide range of organisms suggest that symmetry can be detected by low-level visual mechanisms. However, computational and functional considerations suggest that higher-level mechanisms may also play a role in facial symmetry detection. We tested this hypothesis by examining whether symmetry detection is better for faces than comparable patterns, which share low-level properties with faces. Symmetry detection was better for upright faces than for inverted faces (experiment 1) and contrast-reversed faces (experiment 2), implicating high-level mechanisms in facial symmetry detection. In addition, facial symmetry detection was sensitive to spatial scale, unlike low-level symmetry detection mechanisms (experiment 3), and showed greater sensitivity to a 45° deviation from vertical than is found for other aspects of face perception (experiment 4). These results implicate specialized, higher-level mechanisms in the detection of facial symmetry. This specialization may reflect perceptual learning resulting from extensive experience detecting symmetry in faces or evolutionary selection pressures associated with the important role of facial symmetry in mate choice and ‘mind-reading’ or both.

Rhodes, Gillian; Peters, Marianne; Lee, Kieran; Morrone, M. Concetta; Burr, David

2005-01-01

349

Spontaneous symmetry breaking due to randomness  

NASA Astrophysics Data System (ADS)

The discrete chiral and the discrete (lattice) translational symmetry of a random non-interacting fermion system are considered. We define order parameters related to both symmetries and show the existence of lower bounds for these quantities which corresponds with spontaneous symmetry breaking. On leave from the GHS Essen, D-4300 Essen, FR Germany. This work was supported by the Deutsche Forschungs-gemeinschaft.

Ziegler, K.

350

Superalgebra and fermion-boson symmetry  

PubMed Central

Fermions and bosons are quite different kinds of particles, but it is possible to unify them in a supermultiplet, by introducing a new mathematical scheme called superalgebra. In this article we discuss the development of the concept of symmetry, starting from the rotational symmetry and finally arriving at this fermion-boson (FB) symmetry.

Miyazawa, Hironari

2010-01-01

351

Ether symmetry unification theory (ESU)  

SciTech Connect

The ether symmetry unification (ESU) theory postulates a mechanism that accounts for the formation of the universe as well as the formation of the original mass particles following the big bang. The essential role of the medium-vacuum of the theory of prerelativity is explained. The ultra-high energy particles described in the Ether Symmetry Unification Theory are compared with high energy magnetic monopoles described by Supersymmetry. Phase transitions of high energy events to low energy events and the associated media-vacua involved, postulated by the ESU, are then compared to the low energy events of the standard model within the critical phases of the first two seconds of quantum field theory`s time line.

Cunningham, R.B.

1995-10-01

352

Chiral symmetry and nucleon structure  

SciTech Connect

Recently it has been realized that significant tests of the validity of QCD are available in low energy experiments (E < 500 MeV) by exploiting the property of (broken) chiral symmetry. This technique has been highly developed in The Goldstone boson sector by the work of Gasser and Leutwyler. Application to the nucleon system is much more difficult and is now being carefully developed.

Holstein, B.R. (Massachusetts Univ., Amherst, MA (United States). Dept. of Physics and Astromony Washington Univ., Seattle, WA (United States). Inst. for Nuclear Theory)

1992-01-01

353

Symmetry in Integer Linear Programming  

Microsoft Academic Search

\\u000a An integer linear program (ILP) is symmetric if its variables can be permuted without changing the structure of the problem.\\u000a Areas where symmetric ILPs arise range from applied settings (scheduling on identical machines), to combinatorics (code construction),\\u000a and to statistics (statistical designs construction). Relatively small symmetric ILPs are extremely difficult to solve using\\u000a branch-and-cut codes oblivious to the symmetry in

François Margot

354

Time Dependent Hohlraum Symmetry Control  

NASA Astrophysics Data System (ADS)

NIF indirect-drive ICF simulations suggest that excessive time-dependent flux asymmetry excursions can impose irreversible distortions on imploding capsules, leading to reduced compression and loss of ignition. (J.D. Lindl, Phys. Plasmas), (1995)., (S.W. Haan et al.), Phys. Plasmas (1995). Flux asymmetries for the baseline NIF cylindrical hohlraum illuminated by rings of laser beams vary in time principally due to motion of the hot laser illuminated rings of plasma as the hohlraum wall blows inward. NIF ignition hohlraums are designed to provide adequate continuous control for these asymmetries by varying the power ratio between at least two sets of beam rings, a technique demonstrated recently at the Nova facility. A simpler, rudimentary demonstration of time-dependent control of the lowest order flux asymmetry in hohlraums has also been performed at the Omega laser facility, by staggering appropriately pointed beams in time. In this fashion, the asymmetry excursion due to wall motion could be either enhanced or reduced while maintaining time-integrated symmetry. Time-resolved hohlraum asymmetries are inferred in all cases from micron-accuracy measurements of contour distortions in imploding witness capsules and foam balls. The results that distinguish between attempts at enhancing and reducing symmetry swing are in agreement with simulations, and hence demonstrate understanding of time-dependent symmetry control. The results are also well matched by a simple, semi-empirical, time-dependent view factor model incorporating both wall motion and changing hohlraum albedo. The model has also proved useful in gaining insight into time-dependent flux asymmetry behavior in other recent Omega symmetry experiments investigating NIF-like multiple ring illumination schemes.

Landen, O. L.

1998-11-01

355

The New Charge Symmetry Breaking  

SciTech Connect

For few body systems, the treatment of charge symmetry breaking (CSB) that is based on meson-exchange models is being replaced by effective field theories whose CSB originates in the down-up quark mass difference and quark electromagnetic effects. In parallel, two new observations of CSB in {pi}0 production (the fore-aft asymmetry in n+p{yields}d+{pi}0 and the total cross section for d+d{yields}4He+{pi}0) provide applicable data.

Stephenson, E. J. [Indiana University Cyclotron Facility, 2401 Milo B. Sampson Lane, Bloomington, IN 47408 (United States)

2007-06-13

356

Inhomogeneous chiral symmetry breaking phases  

SciTech Connect

We investigate inhomogeneous chiral symmetry breaking phases in the phase diagram of the two-flavor Nambu-Jona-Lasinio model, concentrating on phases with one-dimensional modulations. It is found that the first-order transition line in the phase diagram of homogeneous phases gets completely covered by an inhomogeneous phase which is bordered by second-order transition lines. The inhomogeneous phase turns out to be remarkably stable when vector interactions are included.

Buballa, M., E-mail: michael.buballa@physik.tu-darmstadt.de; Carignano, S., E-mail: carignano@crunch.ikp.physik.tu-darmstadt.de [Technische Universitaet Darmstadt, Institut fuer Kernphysik (Germany); Nickel, D., E-mail: mdjn@u.washington.edu [University of Washington, Institute for Nuclear Theory (United States)

2012-06-15

357

Compatibility and generalised conditional symmetries  

Microsoft Academic Search

It is shown that the determining equations for generalised conditional symmetries (GCSs) of order n, of an evolution equation of arbitrary order, can be found as a consequence of compatibility with an nth-order invariant surface condition. The compatibility technique is demonstrated on a second-order nonlinear diffusion–convection equation with absorption and used to find new GCSs of a linear diffusion equation

Joanna Goard

2007-01-01

358

CP Symmetry and Phase Transitions  

NASA Astrophysics Data System (ADS)

The analytic behaviour of ?-vacuum energy at ? = 0 and ? = ? in QCD is related to the existence of phase transitions which might involve CP symmetry breaking. The appearance of cusp singularities is a signal of CP symmetry breaking by non-perturbative effects. The only cusp singularities that could arise in the vacuum energy density are due to the presence of Lee-Yang zeros but these singularities are always ? cusp singularities and never ? cusps, which in the case ? = 0 is incompatible with the Vafa-Witten diamagnetic inequality. The argument is very similar to that used in the derivation of Bank-Casher formula. In this case the topological charge condensate is proportional to the density of Lee-Yang zeros at the CP invariant points. The fact that this density is always positive provides a key missing link in the Vafa-Witten proof of parity symmetry conservation in vector-like gauge theories like QCD. However, this property does not exclude the existence of a first phase transition at ? = ? with a ? cusp singularity, or a second order phase transition at ? = 0, which might be very relevant for interpretation of the anomalous behavior of the topological susceptibility in the CP1 sigma model.

Aguado, M.; Asorey, M.

2011-04-01

359

Symmetry tuning for DIME Campaign  

NASA Astrophysics Data System (ADS)

Defect Induced Mix Experiment (DIME) investigates the effects of 4 pi as well as surface feature-driven mix on the directly driven ICF capsule implosion. To minimize the effects of the laser-drive asymmetry, beam pointings, pulse shape, and the energy distribution between the lasers need to be optimized for a particular capsule and shot energy. In support of the DIME experimental campaigns on OMEGA and NIF, symmetry tuning was performed with the rad-hydro code HYDRA. To assess the impact on the symmetry, synthetic radiographs and self-emission images were examined and compared with the experimental results from OMEGA and NIF shots. The dynamics of the capsules imploded under polar direct drive conditions were compared with symmetrically driven ones and the effects of cross-beam transfer and the laser imprinting on the symmetry were also investigated. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.

Krasheninnikova, Natalia; Schmitt, Mark; Tregillis, Ian; Bradley, P.; Cobble, J.; Kyrala, G.; Murphy, T.; Obrey, K.; Hsu, S.; Shah, R.; Batha, S.; Craxton, S.; McKenty, P.

2012-10-01

360

Symmetry theory of the flexomagnetoelectric effect in the Bloch lines  

NASA Astrophysics Data System (ADS)

It was shown that there are 48 magnetic point groups of the Bloch lines including 22 (11 time-invariant and 11 time-noninvariant) enantiomorphic and 26 non-enantiomorphic groups. The Bloch lines with the time-noninvariant enantiomorphism have identical types (parities) of the magnetization and polarization dependences. The list of soliton-like Bloch lines is derived from the symmetry classification. The tip electrode method of the creation of these Bloch lines is suggested for the potential applications in the magnetoelectric memory devices. The method of the experimental determination of the flexomagnetoelectric properties of the Bloch lines carried by the Bloch domain wall has been suggested. New type of the flexomagnetoelectric coupling, which is determined by the spatial derivatives of the electric polarization, can be found in the vicinity of the Curie temperature or compensation point of the ferrimagnets. The multi-state Bloch line magnetoelectric/multiferroic memory is proposed. It can be considered as a concept of the magnetoelectric enhancement of existing Bloch line memory invention.

Tanygin, B. M.

2012-05-01

361

Ginsparg-Wilson-Lüscher symmetry and ultralocality  

NASA Astrophysics Data System (ADS)

Important recent discoveries suggest that Ginsparg-Wilson-Lüscher (GWL) symmetry has analogous dynamical consequences for the theory on the lattice as chiral symmetry does in the continuum. While it is well known that an inherent property of lattice chiral symmetry is fermion doubling, we show here that an inherent property of GWL symmetry is that the infinitesimal symmetry transformation couples fermionic degrees of freedom at arbitrarily large lattice distances (non-ultralocality). The consequences of this result for the ultralocality of symmetric actions are discussed.

Horváth, Ivan

1999-08-01

362

Investigation of the surface terminations of icosahedral AlPdMn quasicrystal based on a modified non-spherical model  

NASA Astrophysics Data System (ADS)

The atomic positions are obtained from a modified non-spherical model of icosahedral AlPdMn quasicrystal (Fang et al 2003 J. Phys.: Condens. Matter 15 4947) by the cut method. The four-shell pseudo-Mackay clusters (PMCs) were searched for in a box of 400 Å × 400 Å × 400 Å. The results show that the number of atoms in the fourth shell, an icosidodecahedron, of the pseudo-Mackay cluster can vary from 15 to 30 because of the cluster overlap, and about 99.96% of the total atoms are included in such incomplete pseudo-Mackay clusters. The characteristics of the atom distribution in the planes perpendicular to a fivefold axis indicate that the planes, which are 1.56 Å apart from their neighbouring planes, are expected to be the terminal surfaces. If one such a plane and its closest neighbouring plane, between which the spacing is 0.48 Å, are considered as a thin layer or a corrugated surface, these layers are also the layers with the maximum density. The pair of corrugated surfaces that are 1.56 Å apart have almost identical chemical composition. These planes form terraces that follow the rule of the Fibonacci sequence with two step heights, 6.60 and 4.08 Å. On the corrugated surfaces perpendicular to a fivefold axis the pentagonal holes arise from the interspaces of adjacent incomplete PMCs. For the atomic planes normal to a twofold axis, the planes with spacing of 1.48 Å from their adjacent planes might be expected to be the terminal surfaces, which form terraces with step heights of 6.28 and 3.88 Å following the rule of the Fibonacci sequence. For the atomic planes normal to a threefold axis, the planes with spacing of 0.86 Å from their adjacent planes might be expected to be the terminal surfaces. No similar results were found for the atomic layers perpendicular to a pseudo-twofold axis.

Yu, Fengmei; Zou, Huamin; Wang, Jianbo; Wang, Renhui

2004-10-01

363

Are there capacity limitations in symmetry perception?  

PubMed

Previous researchers have proposed that there are two types of symmetry detection: one based on crude preattentive symmetry judgments and another based on detailed scrutiny of individual parts (Barlow & Reeves, 1979; S. E. Palmer & Hemenway, 1978; Royer, 1981). Four experiments were conducted to examine capacity limits in different symmetry judgments. Observers were required to discriminate between random patterns and approximate symmetry (Experiments 1 and 3) or between perfect and approximate symmetry (Experiments 2 and 4). The patterns were divided into two sets of dots, presented either simultaneously or successively. A comparison of accuracy under these two presentation conditions suggested that symmetry detection involves an analysis that is spatially parallel but coarse, regardless of either task difficulty or task type (detecting symmetry vs. detecting asymmetry). PMID:15732695

Huang, Liqiang; Pashler, Harold; Junge, Justin A

2004-10-01

364

Non-Abelian discrete R symmetries  

NASA Astrophysics Data System (ADS)

We discuss non-Abelian discrete R symmetries which might have some conceivable relevance for model building. The focus is on settings with supersymmetry, where the superspace coordinate transforms in a one-dimensional representation of the non-Abelian discrete symmetry group. We derive anomaly constraints for such symmetries and find that novel patterns of Green-Schwarz anomaly cancellation emerge. In addition we show that perfect groups, also in the non- R case, are always anomaly-free. An important property of models with non-Abelian discrete R symmetries is that superpartners come in different representations of the group. We present an example model, based on a symmetry, to discuss generic features of models which unify discrete R symmetries, entailing solutions to the ? and proton decay problems of the MSSM, with non-Abelian discrete flavor symmetries.

Chen, Mu-Chun; Ratz, Michael; Trautner, Andreas

2013-09-01

365

Emergence of symmetry in complex networks.  

PubMed

Many real networks have been found to have a rich degree of symmetry, which is a universal structural property of complex networks, yet has been rarely studied so far. One of the fascinating problems related to symmetry is exploration of the origin of symmetry in real networks. For this purpose, we summarized the statistics of local symmetric motifs that contribute to local symmetry of networks. Analysis of these statistics shows that the symmetry of complex networks is a consequence of similar linkage pattern, which means that vertices with similar degrees tend to share common neighbors. An improved version of the Baraba?i-Albert model integrating similar linkage pattern successfully reproduces the symmetry of real networks, indicating that similar linkage pattern is the underlying ingredient that is responsible for the emergence of symmetry in complex networks. PMID:18643337

Xiao, Yanghua; Xiong, Momiao; Wang, Wei; Wang, Hui

2008-06-11

366

Reflection symmetry-integrated image segmentation.  

PubMed

This paper presents a new symmetry-integrated region-based image segmentation method. The method is developed to obtain improved image segmentation by exploiting image symmetry. It is realized by constructing a symmetry token that can be flexibly embedded into segmentation cues. Interesting points are initially extracted from an image by the SIFT operator and they are further refined for detecting the global bilateral symmetry. A symmetry affinity matrix is then computed using the symmetry axis and it is used explicitly as a constraint in a region growing algorithm in order to refine the symmetry of the segmented regions. A multi-objective genetic search finds the segmentation result with the highest performance for both segmentation and symmetry, which is close to the global optimum. The method has been investigated experimentally in challenging natural images and images containing man-made objects. It is shown that the proposed method outperforms current segmentation methods both with and without exploiting symmetry. A thorough experimental analysis indicates that symmetry plays an important role as a segmentation cue, in conjunction with other attributes like color and texture. PMID:22201051

Sun, Yu; Bhanu, Bir

2012-09-01

367

Gaugeon Formalism with BRST Symmetry  

NASA Astrophysics Data System (ADS)

We provide a BRST symmetric version of Yokoyama's Type I gaugeon formalism for quantum electrodynamics; the similar theory by Izawa can be considered as a BRST symmetrized Type II theory. With the help of the BRST symmetry, Yokoyama's physical subsidiary conditions are replaced by the Kugo-Ojima type condition. As a result, the formalism becomes applicable even in the background gravitational field. We show how the Hilbert spaces of standard formalism in various gauges are embedded in the single Hilbert space of the present formalism. We also give a path integral derivation of the Lagrangian.

Koseki, M.; Sato, M.; Endo, R.

1993-11-01

368

Dynamical symmetries in noncommutative theories  

SciTech Connect

In the present work we study dynamical space-time symmetries in noncommutative relativistic theories by using the minimal canonical extension of the Doplicher, Fredenhagen, and Roberts algebra. Our formalism is constructed in an extended space-time with independent degrees of freedom associated with the object of noncommutativity {theta}{sup {mu}}{sup {nu}}. In this framework we consider theories that are invariant under the Poincare group P or under its extension P{sup '}, when translations in the extra dimensions are permitted. The Noether's formalism adapted to such extended x+{theta} space-time is employed.

Amorim, Ricardo [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21945-970 Rio de Janeiro (Brazil)

2008-11-15

369

Bimetric theory with exchange symmetry  

SciTech Connect

We propose an extension of general relativity with two different metrics. To each metric we define a Levi-Cevita connection and a curvature tensor. We then consider two types of fields, each of which moves according to one of the metrics and its connection. To obtain the field equations for the second metric we impose an exchange symmetry on the action. As a consequence of this ansatz, additional source terms for Einstein's field equations are generated. We discuss the properties of these additional fields, and consider the examples of the Schwarzschild solution, and the Friedmann-Robertson-Walker metric.

Hossenfelder, S. [Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, Ontario, N2L 2Y5 (Canada)

2008-08-15

370

Robust object recognition using symmetry  

NASA Astrophysics Data System (ADS)

This paper describes an object recognition technique based on the concept of local symmetry. A technique is described which can detect 1D features under situations of extreme low contrast. The effectiveness of the technique is shown through application to DNA autoradiographs. The technique is then expanded so that 2D objects can be located and then recognized. In the 2D case the resulting output of the technique is a locus which can be compared to those in a database. It is further shown how the technique is robust against changes in both scale and orientation.

Walmsley, Nicholas P.; Curtis, K. M.

1994-09-01

371

Molecular symmetry in mitochondrial cardiolipins.  

PubMed

Cardiolipin is a unique mitochondrial phospholipid with an atypical fatty acid profile, but the significance of its acyl specificity has not been understood. We explored the enormous combinatorial diversity among cardiolipin species, which results from the presence of four fatty acids in each molecule, by integrated use of high-performance liquid chromatography, mass spectrometry, diacylglycerol species analysis, fatty acid analysis, and selective cleavage of fatty acids by phospholipase A2. The most abundant cardiolipin species from various organisms and tissues (human heart, human lymphoblasts, rat liver, Drosophila, sea urchin sperm, yeast, mung bean hypocotyls) contained only one or two types of fatty acids, which generated a high degree of structural uniformity and molecular symmetry. However, an exception was found in patients with Barth syndrome, in whom an acyltransferase deficiency led to loss of acyl selectivity and formation of multiple molecular species. These results suggest that restriction of the number of fatty acid species, rather than the selection of a particular kind of fatty acid, is the common theme of eukaryotic cardiolipins. This limits the structural diversity of the cardiolipin species and creates molecular symmetry with implications for the stereochemistry of cardiolipin. PMID:16226238

Schlame, Michael; Ren, Mindong; Xu, Yang; Greenberg, Miriam L; Haller, Ivan

2005-09-07

372

Duality symmetries in string theory  

SciTech Connect

The search for a unified theory of quantum gravity and gauge interactions leads naturally to string theory. This field of research has received a revival of interest after the discovery of duality symmetries in recent years. We present a self contained account of some non-perturbative aspects of string theory which have been recently understood. The spectrum and interactions of the five consistent superstring theories in ten dimensions are recollected and the fundamental principles underlying this initial stage in the construction of the theory are briefly reviewed. We next discuss some evidences that these apparently different superstrings are just different aspects of one unique theory. The key to this development is given by the non-perturbative duality symmetries which have modified and improved our understanding of string dynamics in many ways. In particular, by relating the fundamental objects of one theory to solitons of another theory, they have unraveled the presence of extended objects in the theory which stand on an equal footing with strings. We introduce these higher dimensional objects, named D-branes, and discuss applications of D-brane physics.

Nunez, Carmen A. [Instituto de Astronomia y Fisica del Espacio-CONICET C.C. 67-Suc. 28, 1428 Buenos Aires (Argentina)

1999-10-25

373

Symmetry analysis in parametrisation of complex systems  

NASA Astrophysics Data System (ADS)

The symmetry analysis method based on the theory of group representations is used for description of complex systems and their behavior in this work. The first trial of using the symmetry analysis in modeling of behavior of complex social system is presented. The evacuation of large building scenarios are discussed as transition from chaotic to ordered states, described as movements of individuals according to fields of displacements, calculated correspondingly to given scenario. The symmetry of the evacuation space is taken into account in calculation of displacements field - the displacements related to every point of this space are presented in the coordinate frame in the best way adapted to given symmetry space group, which is the set of basic vectors of irreducible representation of given symmetry group. The results got with using the symmetry consideration are compared with corresponding results calculated under assumption of shortest way to exits (Voronoi assumption).

Sikora, W.; Malinowski, J.

2010-03-01

374

Symmetry Energy of Dilute Warm Nuclear Matter  

SciTech Connect

The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions, and astrophysical phenomena. New data from heavy-ion collisions can be used to extract the free symmetry energy and the internal symmetry energy at subsaturation densities and temperatures below 10 MeV. Conventional theoretical calculations of the symmetry energy based on mean-field approaches fail to give the correct low-temperature, low-density limit that is governed by correlations, in particular, by the appearance of bound states. A recently developed quantum-statistical approach that takes the formation of clusters into account predicts symmetry energies that are in very good agreement with the experimental data. A consistent description of the symmetry energy is given that joins the correct low-density limit with quasiparticle approaches valid near the saturation density.

Natowitz, J. B.; Hagel, K.; Kowalski, S.; Qin, L.; Shlomo, S.; Wada, R. [Cyclotron Institute, Texas A and M University, College Station, Texas 77843-3366 (United States); Roepke, G. [Institut fuer Physik, Universitaet Rostock, Universitaetsplatz 3, D-18055 Rostock (Germany); Typel, S. [Excellence Cluster Universe, Technische Universitaet Muenchen, Boltzmannstrasse 2, D-85748 Garching (Germany); GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Theorie, Planckstrasse 1, D-64291 Darmstadt (Germany); Blaschke, D. [Instytut Fizyki Teoretycznej, Uniwersytet Wroclawski, plac Maksa Borna 9, 50-204 Wroclaw (Poland); Bogoliubov Laboratory for Theoretical Physics, JINR Dubna, Joliot-Curie street 6, 141980 Dubna (Russian Federation); Bonasera, A. [Cyclotron Institute, Texas A and M University, College Station, Texas 77843-3366 (United States); Laboratori Nazionali del Sud-INFN, via Santa Sofia 64, 95123 Catania (Italy); Klaehn, T. [Instytut Fizyki Teoretycznej, Uniwersytet Wroclawski, plac Maksa Borna 9, 50-204 Wroclaw (Poland); Theory Group, Physics Division, Building 203, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Wolter, H. H. [Fakultaet fuer Physik, Universitaet Muenchen, Am Coulombwall 1, D-85748 Garching (Germany)

2010-05-21

375

State symmetry effects on electron transfer reactions  

Microsoft Academic Search

To study state symmetry effects on electron transfer reactions, three donor-spacer-acceptor electron transfer molecules were synthesized and structurally characterized. The electron donor was 1,4-dimethoxyanthracene. The electron acceptors were 1,1-dicyanoethylene or 1,2-dicarbomethoxyethylene. The spacers were saturated cyclic hydrocarbons. The spacer of the [open quotes]symmetry allowed[close quotes] molecules oriented the acceptor, 1,1-dicyanoethylene, in such a way that the electronic symmetry of the

Zeng

1992-01-01

376

Are there capacity limitations in symmetry perception?  

Microsoft Academic Search

Previous researchers have proposed that there are two types of symmetry detection: one based on crude preattentive symmetry\\u000a judgments and another based on detailed scrutiny of individual parts (Barlow & Reeves, 1979; S. E. Palmer & Hemenway, 1978;\\u000a Royer, 1981). Four experiments were conducted to examine capacity limits in different symmetry judgments. Observers were required\\u000a to discriminate between random patterns

Liqiang Huang; Harold Pashler; Justin A. Junge

2004-01-01

377

Symmetry and symmetry breaking in Rydberg-atom intrashell dynamics  

NASA Astrophysics Data System (ADS)

We have investigated experimentally and theoretically the dynamics of Stark-Zeeman split states in Li(n=25) Rydberg atoms when they are exposed to a superposition of a slowly varying field and a harmonic RF field. Regular oscillatory structures are observed in the intrashell transitions. By solving the time-dependent Schrödinger equation for the problem it is shown that the dynamics is strongly influenced by the nonhydrogenic core which breaks the dynamical symmetry of the Coulomb problem. It is also shown that the dynamics effectively reduces to that of a two-level atom. The oscillations are remnants of interferences that arise partly due to a phase difference which develops between the two levels when they go through two consecutive one-photon resonances, and partly due to an effective change of the carrier-envelope phase of the coupling field.

Pilskog, I.; Fregenal, D.; Frette, Ø.; Førre, M.; Horsdal, E.; Waheed, A.

2011-04-01

378

Symmetry and symmetry breaking in Rydberg-atom intrashell dynamics  

SciTech Connect

We have investigated experimentally and theoretically the dynamics of Stark-Zeeman split states in Li(n=25) Rydberg atoms when they are exposed to a superposition of a slowly varying field and a harmonic RF field. Regular oscillatory structures are observed in the intrashell transitions. By solving the time-dependent Schroedinger equation for the problem it is shown that the dynamics is strongly influenced by the nonhydrogenic core which breaks the dynamical symmetry of the Coulomb problem. It is also shown that the dynamics effectively reduces to that of a two-level atom. The oscillations are remnants of interferences that arise partly due to a phase difference which develops between the two levels when they go through two consecutive one-photon resonances, and partly due to an effective change of the carrier-envelope phase of the coupling field.

Pilskog, I. [Department of Physics and Technology, University of Bergen, N-5007 Bergen (Norway); Laboratoire de Chimie Physique Matiere et Rayonnement, Universite Pierre et Marie Curie - CNRS (UMR 7614), F-75231 Paris Cedex 05 (France); Fregenal, D. [Centro Atomico Bariloche and Consejo Nacional de Investigaciones Cienticas y Tecnicas. R8402AGP S.C. de Bariloche (Argentina); Frette, O.; Foerre, M. [Department of Physics and Technology, University of Bergen, N-5007 Bergen (Norway); Horsdal, E. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Waheed, A. [Department of Physics and Technology, University of Bergen, N-5007 Bergen (Norway); Higher Education Commission of Pakistan, Islamabad (Pakistan)

2011-04-15

379

Discrete gauge symmetry in continuum theories  

SciTech Connect

We point out that local symmetries can masquerade as discrete global symmetries to an observer equipped with only low-energy probes. The existence of the underlying local gauge invariance can, however, result in observable Aharonov-Bohm-type effects. Black holes can therefore carry discrete gauge charges: a form of nonclassical ''hair.'' Neither black-hole evaporation, wormholes, nor anything else can violate discrete gauge symmetries. In supersymmetric unified theories such discrete symmetries can forbid proton-decay amplitudes that might otherwise be catastrophic.

Krauss, L.M.; Wilczek, F.

1989-03-13

380

Noether gauge symmetry approach in quintom cosmology  

NASA Astrophysics Data System (ADS)

In literature usual point like symmetries of the Lagrangian have been introduced to study the symmetries and the structure of the fields. This kind of Noether symmetry is a subclass of a more general family of symmetries, called Noether gauge symmetries (NGS). Motivated by this mathematical tool, in this paper, we study the generalized Noether symmetry of quintom model of dark energy, which is a two component fluid model with quintessence and phantom scalar fields. Our model is a generalization of the Noether symmetries of a single and multiple components which have been investigated in detail before. We found the general form of the quintom potential in which the whole dynamical system has a point like symmetry. We investigated different possible solutions of the system for diverse family of gauge function. Specially, we discovered two family of potentials, one corresponds to a free quintessence (phantom) and the second is in the form of quadratic interaction between two components. These two families of potential functions are proposed from the symmetry point of view, but in the quintom models they are used as phenomenological models without clear mathematical justification. From integrability point of view, we found two forms of the scale factor: one is power law and second is de-Sitter. Some cosmological implications of the solutions have been investigated.

Aslam, Adnan; Jamil, Mubasher; Momeni, Davood; Myrzakulov, Ratbay; Rashid, Muneer Ahmad; Raza, Muhammad

2013-08-01

381

Issues in standard model symmetry breaking  

SciTech Connect

This work discusses the symmetry breaking sector of the SU(2) x U(1) electroweak model. The first two chapters discuss Higgs masses in two simple Higgs models. The author proves low-enery theorems for the symmetry breaking sector: The threshold behavior of gauge-boson scattering is completely determined, whenever the symmetry breaking sector meets certain simple conditions. The author uses these theorems to derive event rates for the superconducting super collider (SSC). The author shows that the SSC may be able to determine whether the interactions of the symmetry breaking sector are strong or weak. 54 refs.

Golden, M.

1988-04-01

382

Symmetry and complexity in dynamical systems  

NASA Astrophysics Data System (ADS)

Historically, static symmetric bodies and ornaments are geometric idealizations in the Platonic tradition. Actually, symmetries are locally and globally broken by phase transitions of instability in dynamical systems generating a variety of new order and partial symmetries with increasing complexity. The states of complex dynamical systems can refer to, for example, atomic clusters, crystals, biomolecules, organisms and brains, social and economic systems. The paper discusses dynamical balance as dynamical symmetry in dynamical systems, which can be simulated by computational systems. Its emergence is an interdisciplinary challenge of nonlinear systems science. The philosophy of science analyses the common methodological framework of symmetry and complexity.

Mainzer, Klaus

2005-10-01

383

T flavor symmetry and decaying dark matter  

NASA Astrophysics Data System (ADS)

We study a new flavor symmetric model with non-Abelian discrete symmetry T. The T group is isomorphic to Z?Z, and it is the minimal group having two complex triplets in the irreducible representations. We show that the T symmetry can derive lepton masses and mixings consistently. Moreover, if we assume a gauge-singlet fermionic decaying dark matter, its decay operators are also constrained by the T symmetry so that only dimension six operators of leptonic decay are allowed. We find that the cosmic-ray anomalies reported by PAMELA and Fermi-LAT are well explained by decaying dark matter controlled by the T flavor symmetry.

Kajiyama, Yuji; Okada, Hiroshi

2011-07-01

384

Interpretation of symmetry experiments on Omega  

NASA Astrophysics Data System (ADS)

The interpretation of the symmetry experiments performed on Omega in 2005 with 3 cone LMJ-like irradiation is presented here. The goal of this campaign was the characterization of the irradiation symmetry by X-ray imaging of the D2Ar capsule. Images of backlit implosion (as done in earlier campaigns with foam balls) and core emission were obtained on the same shot, and can be compared to FCI2 simulations. This set of shots comfirms former results with foam balls of a good symmetry control with 3 cones in empty hohlraums. The influence of the hohlraum shape on symmetry is also studied by comparison of cylindrical hohlraums vs rugby ones.

Lours, Laurence; Bastian, Josiane; Monteil, Marie-Christine; Philippe, Franck; Jadaud, Jean-Paul

2006-10-01

385

Symmetry and group theory throughout physics  

NASA Astrophysics Data System (ADS)

As noticed in 1884 by Pierre Curie [1], physical properties of matter are tightly related to the kind of symmetry of the medium. Group theory is a systematic tool, though not always easy to handle, to exploit symmetry properties, for instance to find the eigenvectors and eigenvalues of an operator. Certain properties (optical activity, piezoelectricity) are forbidden in molecules or crystals of high symmetry. A few theorems (Noether, Goldstone) establish general relations between physical properties and symmetry. Applications of group theory to condensed matter physics, elementary particle physics, quantum mechanics, electromagnetism are reviewed. Group theory is not only a tool, but also a beautiful construction which casts insight into natural phenomena.

Villain, J.

2012-03-01

386

PREFACE: Symmetries in Science XV  

NASA Astrophysics Data System (ADS)

Logo Bregenz, the peaceful monastery of Mehrerau and the Opera on the Floating Stage again provided the setting for the international symposium 'Symmetries in Science'. The series which has been running for more than 30 years brings together leading theoreticians whose area of research is, in one way or another, related to symmetry. Since 1992 the meeting took place biannually in Brengez until 2003. In 2009, with the endorsement of the founder, Professor Bruno Gruber, we succeeded in re-establishing the series without external funding. The resounding success of that meeting encouraged us to continue in 2011 and, following on the enthusiasm and positive feedback of the participants, we expect to continue in 2013. Yet again, our meeting in 2011 was very international in flavour and brought together some 30 participants representing 12 nationalities, half of them from countries outside the European Union (from New Zealand to Mexico, Russia to Israel). The broad spectrum, a mixture of experienced experts and highly-motivated newcomers, the intensive exchange of ideas in a harmonious and relaxed atmosphere and the resulting joint projects are probably the secrets of why this meeting is considered to be so special to its participants. At the resumption in 2009 some leading experts and younger scientists from economically weak countries were unable to attend due to the lack of financial resources. This time, with the very worthy and unbureaucratic support of the 'Vereinigung von Freunden und Förderern der J W Goethe-Universität Frankfurt am Main' (in short: 'Friends and Supporters of the Frankfurt University'), it was possible for all candidates to participate. In particular some young, inspired scientists had the chance of presenting their work to a very competent, but also friendly, audience. We wish to thank the 'Freunde und Förderer' for supporting Symmetries in Science XV. Almost all participants contributed to the publication of this Conference Proceedings. There were also two colleagues who would have liked to participate but were unable to do so (M Horn and A Solomon); we agreed to incorporate their manuscripts into the Proceedings. We would like to thank the staff of Collegium Mehrerau for their hospitality. Once more special thanks to the Schenk Family for their continuing friendship and generous support. The informal evening meetings in these stimulating surroundings probably contributed as much to the scientific success as the lectures during the day and many personal contacts were made. Last, but not least, we would like to thank Yvette again for her unremitting support. Dieter Schuch and Michael Ramek Frankfurt am Main and Graz, July 2012 Conference photograph

Schuch, Dieter; Ramek, Michael

2012-08-01

387

A complete list of symmetry adapted expressions to the fourth power for compact bending potentials in molecules with ? symmetry from a general symbolic algebra program  

NASA Astrophysics Data System (ADS)

An algorithm is proposed to perform the reduction of direct product representations of finite groups and, in particular, to perform the complete symmetry adaption of power representations, which may be used to obtain compact analytical representations of potential energy surfaces following an idea described in Marquardt and Quack [J. Chem. Phys. 109, 10628 (1998)]. The algorithm is general in the sense that it can be applied to any finite group being characterized by its set of irreducible representations. It is automatic in the sense that, in case the reduction yields multiple degenerate irreducible subspaces of the same species, all degenerate irreducible subspaces are obtained with a coherent phase relation. The algorithm is based on the standard reduction rule of traditional representation theory. A symbolic algebra computer program based on MAPLE is presented and applied here to obtain the complete list of symmetry adapted expressions of bond angle coordinates up to the fourth power in all irreducible representations of the C3v and Td point groups.

Marquardt, Roberto; Sagui, Kenneth

388

Symmetry Elevation and Symmetry Breaking: Keys to Describe and Explain Excitonic Complexes in Semiconductor Quantum Dots  

SciTech Connect

The results of a group theoretical analysis of the excitonic fine structure are presented and compared with spectroscopic data on single quantum dots. The spectral features reveal the signatures of a symmetry higher than the crystal symmetry (C{sub 3v}). A consistent picture of the fine structure patterns for various exciton complexes is obtained with group theory and the concepts of symmetry elevation and symmetry breaking.

Karlsson, K. F. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne (Switzerland); Linkoeping University, Department of Physics, Chemistry, and Biology (IFM), Semiconductor Materials, S-58183 Linkoeping (Sweden); Dupertuis, M. A.; Oberli, D. Y.; Pelucchi, E.; Rudra, A.; Kapon, E. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne (Switzerland); Holtz, P. O. [Linkoeping University, Department of Physics, Chemistry, and Biology (IFM), Semiconductor Materials, S-58183 Linkoeping (Sweden)

2011-12-23

389

QCD string and chiral symmetry  

NASA Astrophysics Data System (ADS)

We assume that QCD can be described in a certain kinematical regime by an effective string theory. This hadronic string must couple to background chiral fields in a chirally invariant manner, taking into account the true chirally non-invariant QCD vacuum. By requiring conformal symmetry of the string and the unitarity constraint on chiral fields we reconstruct the equations of motion for the latter ones. These provide a consistent background for the propagation of the string. By further requiring locality of the effective action we recover the Lagrangian of non-linear sigma model of pion interactions. The prediction is totally unambiguous and parameter-free. The estimated chiral structural constants of Gasser and Leutwyler fit very well the phenomenological values.

Andrianov, A. A.; Espriu, D.

2003-04-01

390

Symmetry violations and rare decays  

SciTech Connect

This constitutes the report of the working group on symmetry violations and rare decays. The next generation of CP violating kaon decay experiments (the 2{pi} and {pi}{sup 0}e{sup +}e{sup {minus}} modes) were considered at the Tevatron and at the proposed Main Injector, effectively building upon the work of the earlier Fermilab Workshop on Physics at the Main Injector. The optimizations for the electromagnetic calorimeter and for background rejection are treated in some detail. Very precise CPT tests in the 2{pi} decay modes are also treated. A sensitive experiment looking for flavor violation at the Main Injector (K{sub L} {yields} {mu}e) is discussed. The significant advantages of possible stretcher and prebooster rings are mentioned. 27 refs., 5 figs., 3 tabs.

Coleman, R.; Bock, G.; Enagonio, J.; Hsiung, B.; Yamanaka, T. (Fermi National Accelerator Lab., Batavia, IL (USA)); Winstein, B.; Wah, Y.; Yamamoto, H. (Chicago Univ., IL (USA)); Cooper, M. (Los Alamos National Lab., NM (USA)); Ewin, A. (Wisconsin Univ., Madison, WI (USA)); Fry, J. (Liverpool Univ. (UK)); Greenlee, H. (Yale Univ., New Haven, CT (USA)); McFarlane, K. (Temple Univ., Philadelphia, PA (USA

1989-01-01

391

Wormhole dynamics in spherical symmetry  

SciTech Connect

A dynamical theory of traversable wormholes is detailed in spherical symmetry. Generically a wormhole consists of a tunnel of trapped surfaces between two mouths, defined as temporal outer trapping horizons with opposite senses, in mutual causal contact. In static cases, the mouths coincide as the throat of a Morris-Thorne wormhole, with surface gravity providing an invariant measure of the radial curvature or ''flaring-out''. The null energy condition must be violated at a wormhole mouth. Zeroth, first, and second laws are derived for the mouths, as for black holes. Dynamic processes involving wormholes are reviewed, including enlargement or reduction, and interconversion with black holes. A new area of wormhole thermodynamics is suggested.

Hayward, Sean A. [Center for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

2009-06-15

392

Symmetry, constrained bosons and collectivity  

NASA Astrophysics Data System (ADS)

Collective states in a given nucleus can be associated with a subset of states of the oscillator shell model (OSM). This subset is characterized by a definite irreducible representation (irrep) of the orthogonal subgroup O(n) of the U(3n) symmetry group of the OSM, where n is the number of nucleons. We show that these collective states can be described with the help of s and d bosons also constrained by the same irrep of O(n) and indicate a procedure by which these bosons can be determined as functions of the coordinates a and momenta of the many nucleon problem. An analogy with the Zeeman effect for a one particle problem in an oscillator potential, illustrates the elementary nature of the concepts involved.

Moshinsky, Marcos

1984-06-01

393

Mirror symmetry for Enriques surfaces  

NASA Astrophysics Data System (ADS)

In this thesis, we investigate three separate but related projects. In the first one, we describe the geometric backgrounds of Type II string theory which are given by Enriques surfaces and their mirrors. We also study the effect of various string dualities on such backgrounds, in particular phase change in Gauged Linear Sigma Models and mirror symmetry. In the second project, we investigate special Kahler geometry in order to find canonical coordinates on the moduli of generalised Calabi-Yau spaces and the associated (2, 2) superconformal field theories. In the third project, we develop a general technique for computing the massless spectrum of (0, 2) quantum field theory compactified on a proper stack or an orbifold. We produce general formulas for the contribution of the twisted sectors and compute specific examples of compactifications on gerbes on projective spaces and Calabi-Yau threefolds.

Lakuriqi, Enkeleida

394

Symmetries of S-systems.  

PubMed

An S-system is a set of first-order nonlinear differential equations that all have the same structure: The derivative of a variable is equal to the difference of two products of power-law functions. S-systems have been used as models for a variety of problems, primarily in biology. In addition, S-systems possess the interesting property that large classes of differential equations can be recast exactly as S-systems, a feature that has been proven useful in statistics and numerical analysis. Here, simple criteria are introduced that determine whether an S-system possesses certain types of symmetries and how the underlying transformation groups can be constructed. If a transformation group exists, families of solutions can be characterized, the number of S-system equations necessary for solution can be reduced, and some boundary value problems can be reduced to initial value problems. PMID:1591448

Voit, E O

1992-04-01

395

The Closest Elastic Tensor of Arbitrary Symmetry to an Elasticity Tensor of Lower Symmetry  

Microsoft Academic Search

The closest tensors of higher symmetry classes are derived in explicit form for a given elasticity tensor of arbitrary symmetry. The mathematical problem is to minimize the elastic length or distance between the given tensor and the closest elasticity tensor of the specified symmetry. Solutions are presented for three distance functions, with particular attention to the Riemannian and log-Euclidean distances.

Maher Moakher; Andrew N. Norris

2006-01-01

396

SymmetryApp; An Interactive Computer Program To Help Students Learn Molecular Symmetry Elements and Operations  

NSDL National Science Digital Library

SymmetryApp is a new visualization program characterized by a high level of user interactivity. Specifically, it is able to define a symmetry element anywhere in the molecule and determine the effect of the corresponding symmetry operation. This allows students to capitalize on the most important aspect of interactive learning?to make mistakes and to learn from them.

397

Atomic structure of the 75 MDa extremophile Sulfolobus turreted icosahedral virus determined by CryoEM and X-ray crystallography  

PubMed Central

Sulfolobus turreted icosahedral virus (STIV) was isolated in acidic hot springs where it infects the archeon Sulfolobus solfataricus. We determined the STIV structure using near-atomic resolution electron microscopy and X-ray crystallography allowing tracing of structural polypeptide chains and visualization of transmembrane proteins embedded in the viral membrane. We propose that the vertex complexes orchestrate virion assembly by coordinating interactions of the membrane and various protein components involved. STIV shares the same coat subunit and penton base protein folds as some eukaryotic and bacterial viruses, suggesting that they derive from a common ancestor predating the divergence of the three kingdoms of life. One architectural motif (?-jelly roll fold) forms virtually the entire capsid (distributed in three different gene products), indicating that a single ancestral protein module may have been at the origin of its evolution.

Veesler, David; Ng, Thiam-Seng; Sendamarai, Anoop K.; Eilers, Brian J.; Lawrence, C. Martin; Lok, Shee-Mei; Young, Mark J.; Johnson, John E.; Fu, Chi-yu

2013-01-01

398

Neutrino properties and fundamental symmetries  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). There are two components to this work. The first is a development of a new detection scheme for neutrinos. The observed deficit of neutrinos from the Sun may be due to either a lack of understanding of physical processes in the Sun or may be due to neutrinos oscillating from one type to another during their transit from the Sun to the Earth. The Sudbury Neutrino Observatory (SNO) is designed to use a water Cerenkov detector employing one thousand tonnes of heavy water to resolve this question. The ability to distinguish muon and tau neutrinos from electron neutrinos is crucial in order to carry out a model-independent test of neutrino oscillations. We describe a developmental exploration of a novel technique to do this using {sup 3}He proportional counters. Such a method offers considerable advantages over the initially proposed method of using Cerenkov light from capture on NaCl in the SNO. The second component of this work is an exploration of optimal detector geometry for a time-reversal invariance experiment. The question of why time moves only in the forward direction is one of the most puzzling problems in modern physics. We know from particle physics measurements of the decay of kaons that there is a charge-parity symmetry that is violated in nature, implying time-reversal invariance violation. Yet, we do not understand the origin of the violation of this symmetry. To promote such an understanding, we are developing concepts and prototype apparatus for a new, highly sensitive technique to search for time-reversal-invariance violation in the beta decay of the free neutron. The optimized detector geometry is seven times more sensitive than that in previous experiments. 15 refs.

Bowles, T.J.

1996-07-01

399

Rare Isotopes and Fundamental Symmetries  

NASA Astrophysics Data System (ADS)

Experiments searching for new interactions in nuclear beta decay / Klaus P. Jungmann -- The beta-neutrino correlation in sodium-21 and other nuclei / P. A. Vetter ... [et al.] -- Nuclear structure and fundamental symmetries/ B. Alex Brown -- Schiff moments and nuclear structure / J. Engel -- Superallowed nuclear beta decay: recent results and their impact on V[symbol] / J. C. Hardy and I. S. Towner -- New calculation of the isospin-symmetry breaking correlation to superallowed Fermi beta decay / I. S. Towner and J. C. Hardy -- Precise measurement of the [symbol]H to [symbol]He mass difference / D. E. Pinegar ... [et al.] -- Limits on scalar currents from the 0+ to 0+ decay of [symbol]Ar and isospin breaking in [symbol]Cl and [symbol]Cl / A. Garcia -- Nuclear constraints on the weak nucleon-nucleon interaction / W. C. Haxton -- Atomic PNC theory: current status and future prospects / M. S. Safronova -- Parity-violating nucleon-nucleon interactions: what can we learn from nuclear anapole moments? / B. Desplanques -- Proposed experiment for the measurement of the anapole moment in francium / A. Perez Galvan ... [et al.] -- The Radon-EDM experiment / Tim Chupp for the Radon-EDM collaboration -- The lead radius Eexperiment (PREX) and parity violating measurements of neutron densities / C. J. Horowitz -- Nuclear structure aspects of Schiff moment and search for collective enhancements / Naftali Auerbach and Vladimir Zelevinsky -- The interpretation of atomic electric dipole moments: Schiff theorem and its corrections / C. -P. Liu -- T-violation and the search for a permanent electric dipole moment of the mercury atom / M. D. Swallows ... [et al.] -- The new concept for FRIB and its potential for fundamental interactions studies / Guy Savard -- Collinear laser spectroscopy and polarized exotic nuclei at NSCL / K. Minamisono -- Environmental dependence of masses and coupling constants / M. Pospelov.

Brown, B. Alex; Engel, Jonathan; Haxton, Wick; Ramsey-Musolf, Michael; Romalis, Michael; Savard, Guy

2009-01-01

400

Flavor symmetries and fermion masses  

SciTech Connect

We introduce several ways in which approximate flavor symmetries act on fermions and which are consistent with observed fermion masses and mixings. Flavor changing interactions mediated by new scalars appear as a consequence of approximate flavor symmetries. We discuss the experimental limits on masses of the new scalars, and show that the masses can easily be of the order of weak scale. Some implications for neutrino physics are also discussed. Such flavor changing interactions would easily erase any primordial baryon asymmetry. We show that this situation can be saved by simply adding a new charged particle with its own asymmetry. The neutrality of the Universe, together with sphaleron processes, then ensures a survival of baryon asymmetry. Several topics on flavor structure of the supersymmetric grand unified theories are discussed. First, we show that the successful predictions for the Kobayashi-Maskawa mixing matrix elements, V{sub ub}/V{sub cb} = {radical}m{sub u}/m{sub c} and V{sub td}/V{sub ts} = {radical}m{sub d}/m{sub s}, are a consequence of a large class of models, rather than specific properties of a few models. Second, we discuss how the recent observation of the decay {beta} {yields} s{gamma} constrains the parameter space when the ratio of the vacuum expectation values of the two Higgs doublets, tan{Beta}, is large. Finally, we discuss the flavor structure of proton decay. We observe a surprising enhancement of the branching ratio for the muon mode in SO(10) models compared to the same mode in the SU(5) model.

Rasin, A.

1994-04-01

401

Polarization and symmetry of electronic transitions in long fluorescence lifetime triangulenium dyes.  

PubMed

To fully exploit the capabilities of fluorescence probes in modern experiments, where advanced instrumentation is used to probe complex environments, other photophysical properties than emission color and emission intensity are monitored. Each dye property can be addressed individually as well as collectively to provide in-depth information unavailable from the standard intensity measurements. Dyes with long emission lifetimes and strongly polarized transitions enable the monitoring of lifetime changes as well as emission polarization (anisotropy). Thus experiments can be designed to follow slow dynamics. The UV and visible electronic transitions of a series of red-emitting dyes based on the triangulenium motif are investigated. We resolve overlapping features in the spectra and assign the orientation of the transition moments to the molecular axes. The result is the complete Jablonski diagram for the UV and visible spectral region. The symmetries of the studied dyes are shown to have a large influence on the optical response, and they are clearly separated into two groups of symmetry by their photophysical properties. The C(2v) symmetric dyes, azadioxatriangulenium (ADOTA(+)) and diazaoxatriangulenium (DAOTA(+)), have high emission anisotropies, fluorescence lifetimes around 20 ns, and fluorescence quantum yields of ?50%. The trioxatriangulenium (TOTA(+)) and triazatriangulenium (TATA(+)) dyes-nominally of D(3h) symmetry-have fluorescence lifetimes around 10 ns lifetimes and fluorescence quantum yields of 10-15%. However, the D(3h) symmetry is shown to be lowered to a point group, where the axes transform uniquely such that the degeneracy of the E' states is lifted. PMID:23391292

Thyrhaug, Erling; Sørensen, Thomas Just; Gryczynski, Ignacy; Gryczynski, Zygmunt; Laursen, Bo W

2013-03-06

402

Symmetries in particle physics beyond the Standard Model: Supersymmetry, conformal symmetry and accidental Lorentz symmetry  

NASA Astrophysics Data System (ADS)

The Standard Model provides a successful description of presently known particle phenomena up to scale of hundreds of GeV. Still, the Standard Model is a work in progress and could be extended to describe physics at higher energies, for instance, the TeV scale which will be explored soon at the Large Hadron Collider. In this thesis, we present several projects exploring possible new physics beyond Standard Model and their collider signatures. The first part is dedicated to a particular supersymmetric scenario characterized by cascade decays with copious lepton production. The scenario has striking signatures that can be probed by the Large Hadron Collider even in the 10 TeV run with as little as 200 pb-1 of data, provided the squark masses are about 1 TeV. Its spectrum arises in several well-motivated models and its signatures are long-lived sleptons, numerous isolated leptons, abundant Higgs production, rather energetic jets, and no missing energy. The Higgs can be discovered in the h ? bb¯ mode via the 4 leptons+4 jets channel because the leptons accompanying Higgs production suppress the background. We present a low-scale gaugino mediation model that realizes the scenario and reconstruct the spectrum via several clean channels. The second part explores scenarios where the electroweak symmetry breaking sector is nearly scale invariant and consequently gives rise to a light CP even scalar particle. We study the couplings of the light scalar to the Standard Model particles that can arise from the explicit breaking of scale invariance focusing on the possible differences with the minimal Standard Model. The couplings of the light scalar to light fermions, as well as to the massless gauge bosons, can be significantly enhanced. We find possible new discovery channels due to the decays of the conformal scalar into e +e- and mu+mu - pairs as well as new production channels via, light quark annihilation. In the third part, we present a calculable 'node! of electroweak symmetry breaking in which the Higgs doublet emerges from the meta-stable supersymmetry breaking sector as a pseudo Nambu-Goldstone boson. The Higgs boson mass is further protected by the little Higgs mechanism, and naturally suppressed by a two-loop factor from the supersymmetry breaking scale of 10 TeV. The last part discusses one Lorentz violation scheme where the spacetime symmetry is a subgroup of the full Lorentz group and atomic experiment constraints on this scheme.

Fan, Jiji

403

Detection of interest points using symmetry  

Microsoft Academic Search

An operator based on the intuitive motion of symmetry, which effectively locates interest points in real time and can be incorporated also in active visual systems, is introduced. The results of its operation agree with some psychophysical evidence concerning symmetry as well as evidence concerning fixation points. The operator can be applied successfully without prior knowledge of the world. Combining

Daniel Reisfeld; H. Wolfson; Y. Yeshurun

1990-01-01

404

Smoothed Local Symmetries and Their Implementation  

Microsoft Academic Search

We introduce a novel representation of two-dimensional shape that we call smoothed local symmetries (SLS). Smoothed local symmetries represent both the bounding contour of a shape fragment and the region that it occupies. In this paper we develop the main features of the SLS repre sentation and describe an implemented algorithm that com putes it. The performance of the algorithm

Michael Brady; Haruo Asada

1984-01-01

405

Symmetry-Based Indexing of Image Databases  

Microsoft Academic Search

The use of shape as a cue for indexing into pictorial databases has been traditionally based on global invariant statistics and deformable templates, on the one hand, and local edge correlation on the other. This paper proposes an intermediate approach based on a characterization of the symmetry in edge maps. The use of symmetry matching as a joint correlation measure

Daniel Sharvit; Jacky Chan; Hüseyin Tek; Benjamin B. Kimia

1998-01-01

406

Symmetries and invariances in classical physics  

Microsoft Academic Search

Symmetry, intended as invariance with respect to a transformation (more precisely, with respect to a transformation group), has acquired more and more importance in modern physics. This Chapter explores in 8 Sections the meaning, application and interpretation of symmetry in classical physics. This is done both in general, and with attention to specific topics. The general topics include illustration of

Katherine Brading; Elena Castellani

407

Symmetry and control: spatially extended chaotic systems  

Microsoft Academic Search

In a recent paper (Phys. Rev. E 57 (1998) 1550) it was demonstrated that the symmetries of the evolution equation and the target state have a profound effect on controlling the chaotic behavior. In the present paper we extend these results to the cases of time-periodic target trajectories and inexact symmetries, and apply the developed formalism to the problem of

Roman O. Grigoriev

2000-01-01

408

PT-symmetry in honeycomb photonic lattices  

SciTech Connect

We apply gain and loss to honeycomb photonic lattices and show that the dispersion relation is identical to tachyons--particles with imaginary mass that travel faster than the speed of light. This is accompanied by -symmetry breaking in this structure. We further show that the -symmetry can be restored by deforming the lattice.

Szameit, Alexander; Rechtsman, Mikael C.; Bahat-Treidel, Omri; Segev, Mordechai [Physics Department and Solid State Institute, Technion, 32000 Haifa (Israel)

2011-08-15

409

Enhanced gauge symmetries in superstring theories  

Microsoft Academic Search

Certain four-dimensional N = 4 supersymmetric theories have special vacua in which massive charged vector supermultiplets become massless, resulting in an enhanced non-abelian gauge symmetry. We show here that any two N = 4 theories having the same Bogomolnyi spectrum at corresponding points of their moduli spaces have the same enhanced symmetry groups. In particular, the K3 × T2 compactified

C. M. Hull; P. K. Townsend

1995-01-01

410

Dynamical Symmetry of the Hydrogen Atom  

Microsoft Academic Search

We examine a hidden symmetry of the hydrogen atom in quantum mechan- ics using the quantum mechanical analog of the classical Lenz vector and its relation to the generators of the familiar SO(3) rotational group. We use as our tool some basic concepts in algebraic group theory. The result is a mathemati- cal description of a higher-dimension symmetry under the

Lulu Liu

411

Pedestrian detection using color symmetry phases  

Microsoft Academic Search

Pedestrian detection is one of the most important research contents of road safety. The crucial idea behind such pedestrian safety systems is to protect the driver and pedestrian from any accident. In this paper, a pedestrian feature extraction based on color symmetry phases is presented. By examining symmetry phases in multiple color spaces, the segmentation results are significantly improved which

J. Janta; P. Kumsawat; K. Attakitmongcol; A. Srikaew

2008-01-01

412

Study of symmetry in Constraint Satisfaction Problems  

Microsoft Academic Search

. Constraint satisfactionproblems (CSP's) involve findingvalues for variables subject to constraintson which combinations ofvalues are permitted. Symmetricalvalues of a CSP variable are ina sense redundant. Their removalwill simplify the problem space. Inthis paper we give the principleof symmetry and show that theconcept of interchangeability introducedby Freuder, is a particularcase of symmetry. Some symmetriescan be computed efficiently thanksto the structure of

Belaid Benhamou

1994-01-01

413

PT-symmetry in honeycomb photonic lattices  

NASA Astrophysics Data System (ADS)

We apply gain and loss to honeycomb photonic lattices and show that the dispersion relation is identical to tachyons—particles with imaginary mass that travel faster than the speed of light. This is accompanied by -symmetry breaking in this structure. We further show that the -symmetry can be restored by deforming the lattice.

Szameit, Alexander; Rechtsman, Mikael C.; Bahat-Treidel, Omri; Segev, Mordechai

2011-08-01

414

Topological symmetry breaking by quantum wormholes  

SciTech Connect

In multiply connected spacetimes which contain quantum wormholes it may be possible to break gauge symmetries without the usual Higgs fields. In a simple model, symmetry breaking is favored by the quantum effects of Dirac Fermions and leads to vector boson masses related to the wormhole separation.

Mignemi, S.; Moss, I. (Department of Physics, University of Newcastle upon Tyne, NE1 7RU (United Kingdom))

1993-10-15

415

Discrete symmetry analysis of lattice systems  

NASA Astrophysics Data System (ADS)

Discrete dynamical systems and mesoscopic lattice models are considered from the point of view of their symmetry groups. Some peculiarities in behavior of discrete systems induced by symmetries are pointed out. We reveal also the group origin of moving soliton-like structures similar to “spaceships” in cellular automata.

Kornyak, V. V.

2009-12-01

416

Affine Invariant Medial Axis and Skew Symmetry  

Microsoft Academic Search

Affine invariant medial axes and symmetry sets of planar shapes are introduced and studied in this paper. Two different approaches are presented. The first one is based on affine invariant distances, and defines the symmetry set, a set containing the medial axis; as the closure of the locus of points on (at least) two affine normals an affine-equidistant from the

Peter J. Giblin; Guillermo Sapiro

1998-01-01

417

Symmetry and Controllability for Quantum Spin Networks  

NASA Astrophysics Data System (ADS)

Symmetry is found to be an important tool to study the controllability problems in quantum control. Based on quantum spin networks subject to control of a single node by a local potential (Z-control), we have considered the relation of symmetriy and subspace controllability. Focusing on the single excitation subspace it is shown that for single-node Z-controls external symmetries are characterized by eigenstates of the system Hamiltonian that have zero overlap with the control node, and there are no internal symmetries. For uniformly coupled XXZ chains a characterization of all possible symmetries is derived from Bethe ansatz. Moreover, for uniform Heisenberg and XX chains, basic number theory can be used to prove that the lack of symmetry is equivalent to subspace controllability. On the other hand, symmetries in the Hamiltonian can be classified into two types: the internal and the external symmetries. Based on the external symmetries, we can rigorously prove the subspace controllability in each of the invariant subspaces for both XXZ and XYZ chains, but not for XX or Ising chains. All these results are useful to design the appropriate control strategy when implementing QIP in real physical systems.

Wang, Xiaoting; Schirmer, Sophie; Burgarth, Daniel; Pemberton-Ross, Peter; Jacobs, Kurt

2013-03-01

418

Symplectic structures, their Bäcklund transformations and hereditary symmetries  

Microsoft Academic Search

It is shown that compatible symplectic structures lead in a natural way to hereditary symmetries. (We recall that a hereditary symmetry is an operator-valued function which immediately yields a hierarchy of evolution equations, each having infinitely many commuting symmetries all generated by this hereditary symmetry. Furthermore this hereditary symmetry usually describes completely the soliton structure and the conservation laws of

B. Fuchssteiner; A. S. Fokas

1981-01-01

419

Translational spacetime symmetries in gravitational theories  

NASA Astrophysics Data System (ADS)

How to include spacetime translations in fibre bundle gauge theories has been a subject of controversy, because spacetime symmetries are not internal symmetries of the bundle structure group. The standard method for including affine symmetry in differential geometry is to define a Cartan connection on an affine bundle over spacetime. This is equivalent to (1) defining an affine connection on the affine bundle, (2) defining a zero section on the associated affine vector bundle and (3) using the affine connection and the zero section to define an 'associated solder form', whose lift to a tensorial form on the frame bundle becomes the solder form. The zero section reduces the affine bundle to a linear bundle and splits the affine connection into translational and homogeneous parts; however, it violates translational equivariance/gauge symmetry. This is the natural geometric framework for Einstein Cartan theory as an affine theory of gravitation. The last section discusses some alternative approaches that claim to preserve translational gauge symmetry.

Petti, R. J.

2006-02-01

420

Preference for symmetry: Only on Mars?  

PubMed Central

Preference for symmetry is a robust bias found throughout the animal kingdom. In humans, the bias for symmetry has been documented in numerous domains, including faces and visual patterns. The function of this potent aesthetic bias still eludes us, but prominent accounts focus on its role in mate selection and perceptual fluency. Previous studies have shown that both males and females find symmetrical faces to be more attractive, but here we show that the preference for symmetry in neutral stimuli (ie everyday and meaningless visual objects) is, on the other hand, unique to male participants. Our findings indicate that symmetry preference cannot be explained exclusively by perceptual or computational efficiency, because such an account is domain-independent yet females did not show any bias for the objects tested here. Further studies are needed to elucidate the utility of the male preference for visual object symmetry.

Shepherd, Kathrine; Bar, Moshe

2013-01-01

421

Spectrum-generating symmetries for BPS solitons  

NASA Astrophysics Data System (ADS)

We show that there exist non-linearly realised duality symmetries that are independent of the standard supergravity global symmetries, and which provide active spectrum-generating symmetries for the fundamental BPS solitons. The additional ingredient, in any space-time dimension, is a single scaling transformation that allows one to map between BPS solitons with different masses. Without the inclusion of this additional transformation, which is a symmetry of the classical equations of motion, but not the action, it is not possible to find a spectrum-generating symmetry. The necessity of including this scaling transformation highlights the vulnerability of duality multiplets to quantum anomalies. We argue that fundamental BPS solitons may be immune to this threat.

Cremmer, E.; Lü, H.; Pope, C. N.; Stelle, K. S.

1998-06-01

422

Natural electroweak breaking from a mirror symmetry.  

PubMed

We present "twin Higgs models," simple realizations of the Higgs boson as a pseudo Goldstone boson that protect the weak scale from radiative corrections up to scales of order 5-10 TeV. In the ultraviolet these theories have a discrete symmetry which interchanges each standard model particle with a corresponding particle which transforms under a twin or a mirror standard model gauge group. In addition, the Higgs sector respects an approximate global symmetry. When this global symmetry is broken, the discrete symmetry tightly constrains the form of corrections to the pseudo Goldstone Higgs potential, allowing natural electroweak symmetry breaking. Precision electroweak constraints are satisfied by construction. These models demonstrate that, contrary to the conventional wisdom, stabilizing the weak scale does not require new light particles charged under the standard model gauge groups. PMID:16803369

Chacko, Z; Goh, Hock-Seng; Harnik, Roni

2006-06-14

423

Crystal Structure Refinements of Rhombohedral Symmetry Materials Containing Boron-Rich Icosahedra.  

National Technical Information Service (NTIS)

The crystal structures of several icosahedral boron-containing compounds have been refined using MoK alpha intensity data. Preparation of crystals differs from previous procedures, with boron carbide grown from molten copper and boron arsenide by arsenic ...

B. Morosin R. S. Feigelson T. L. Aselage

1987-01-01

424

New Symmetries for a Model of Fast Diffusion  

NASA Astrophysics Data System (ADS)

The new symmetries for a mathematical model of fast diffusion are determined. A new system method is given to search for new symmetries of differential equations written in a conserved form, several new symmetry generators and exact solutions are presented.

Qin, Mao-Chang; Xu, Xue-Jun; Mei, Feng-Xiang

2004-12-01

425

Protected Edge Modes without Symmetry  

NASA Astrophysics Data System (ADS)

We discuss the question of when a gapped two-dimensional electron system without any symmetry has a protected gapless edge mode. While it is well known that systems with a nonzero thermal Hall conductance, KH?0, support such modes, here we show that robust modes can also occur when KH=0—if the system has quasiparticles with fractional statistics. We show that some types of fractional statistics are compatible with a gapped edge, while others are fundamentally incompatible. More generally, we give a criterion for when an electron system with Abelian statistics and KH=0 can support a gapped edge: We show that a gapped edge is possible if and only if there exists a subset of quasiparticle types M such that (1) all the quasiparticles in M have trivial mutual statistics, and (2) every quasiparticle that is not in M has nontrivial mutual statistics with at least one quasiparticle in M. We derive this criterion using three different approaches: a microscopic analysis of the edge, a general argument based on braiding statistics, and finally a conformal field theory approach that uses constraints from modular invariance. We also discuss the analogous result for two-dimensional boson systems.

Levin, Michael

2013-04-01

426

Sufficient symmetry conditions for Topological Quantum Order  

PubMed Central

We prove sufficient conditions for Topological Quantum Order at zero and finite temperatures. The crux of the proof hinges on the existence of low-dimensional Gauge-Like Symmetries, thus providing a unifying framework based on a symmetry principle. These symmetries may be actual invariances of the system, or may emerge in the low-energy sector. Prominent examples of Topological Quantum Order display Gauge-Like Symmetries. New systems exhibiting such symmetries include Hamiltonians depicting orbital-dependent spin exchange and Jahn–Teller effects in transition metal orbital compounds, short-range frustrated Klein spin models, and p+ip superconducting arrays. We analyze the physical consequences of Gauge-Like Symmetries (including topological terms and charges) and show the insufficiency of the energy spectrum, topological entanglement entropy, maximal string correlators, and fractionalization in establishing Topological Quantum Order. General symmetry considerations illustrate that not withstanding spectral gaps, thermal fluctuations may impose restrictions on suggested quantum computing schemes. Our results allow us to go beyond standard topological field theories and engineer systems with Topological Quantum Order.

Nussinov, Zohar; Ortiz, Gerardo

2009-01-01

427

Symmetries in fluctuations far from equilibrium.  

PubMed

Fluctuations arise universally in nature as a reflection of the discrete microscopic world at the macroscopic level. Despite their apparent noisy origin, fluctuations encode fundamental aspects of the physics of the system at hand, crucial to understand irreversibility and nonequilibrium behavior. To sustain a given fluctuation, a system traverses a precise optimal path in phase space. Here we show that by demanding invariance of optimal paths under symmetry transformations, new and general fluctuation relations valid arbitrarily far from equilibrium are unveiled. This opens an unexplored route toward a deeper understanding of nonequilibrium physics by bringing symmetry principles to the realm of fluctuations. We illustrate this concept studying symmetries of the current distribution out of equilibrium. In particular we derive an isometric fluctuation relation that links in a strikingly simple manner the probabilities of any pair of isometric current fluctuations. This relation, which results from the time-reversibility of the dynamics, includes as a particular instance the Gallavotti-Cohen fluctuation theorem in this context but adds a completely new perspective on the high level of symmetry imposed by time-reversibility on the statistics of nonequilibrium fluctuations. The new symmetry implies remarkable hierarchies of equations for the current cumulants and the nonlinear response coefficients, going far beyond Onsager's reciprocity relations and Green-Kubo formulas. We confirm the validity of the new symmetry relation in extensive numerical simulations, and suggest that the idea of symmetry in fluctuations as invariance of optimal paths has far-reaching consequences in diverse fields. PMID:21493865

Hurtado, Pablo I; Pérez-Espigares, Carlos; del Pozo, Jesús J; Garrido, Pedro L

2011-04-14

428

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

429

Exchange symmetry in description of magnetoelectrics  

NASA Astrophysics Data System (ADS)

Neutron diffraction studies of many magnetoelectrics and corresponding symmetry analysis indicate that the description of their magnetic structures requires of invoking two or more order parameters, so that the temperature proximity of their "condensation" has to be postulated when constructing a consistent thermodynamic theory. In this work, MnWO4, CuO, and CuCl2 magnetoelectrics are analyzed from the standpoint of symmetry of the exchange Hamiltonian. The magnetically ordering states observed in them are shown to be induced by one irreducible representation of the symmetry group of the exchange Hamiltonian. This fact provides the proximity of corresponding instabilities in the thermodynamic path and some features of magnetoelectrics.

Sakhnenko, V. P.; Ter-Oganessian, N. V.

2012-02-01

430

Symmetry relations for the conductivity tensor  

NASA Astrophysics Data System (ADS)

A long-standing weakness in the theoretical analysis of reciprocity relations is eliminated. The Onsager reciprocity theorem demonstrates the symmetry of phenomenological coefficients for systems described by a discrete set of variables. It has previously been demonstrated that this theorem implies that the divergence of the generalized conductivity tensor is symmetric. After some additional analysis it has been argued that the symmetry of the tensor itself is implied. This argument has been criticized in the literature. In the present paper it is shown that, when boundary conditions are appropriately incorporated into the analysis, one obtains the symmetry of the conductivity tensor from the Onsager relations.

Garrod, Claude; Hurley, James

1983-03-01

431

Exploring Symmetry to Assist Alzheimer's Disease Diagnosis  

NASA Astrophysics Data System (ADS)

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first affecting memory functions and then gradually affecting all cognitive functions with behavioral impairments and eventually causing death. Functional brain imaging as Single-Photon Emission Computed Tomography (SPECT) is commonly used to guide the clinician's diagnosis. The essential left-right symmetry of human brains is shown to play a key role in coding and recognition. In the present work we explore the implications of this symmetry in AD diagnosis, showing that recognition may be enhanced when considering this latent symmetry.

Illán, I. A.; Górriz, J. M.; Ramírez, J.; Salas-Gonzalez, D.; López, M.; Padilla, P.; Chaves, R.; Segovia, F.; Puntonet, C. G.

432

Symmetries in the Anisotropic Kepler Problem  

NASA Astrophysics Data System (ADS)

The two-body problem associated to an anisotropic Newtonian-type potential function is being considered. We point out the complex symmetries that feature this problem. Such symmetries, expressed in standard polar coordinates, are recovered for McGee-type coordinates of both collision-blow-up kind and infinity-blow-up kind. They form isomorphic commutative groups endowed with an idempotent structure. Expressed in Levi-Civita's coordinates, the problem exhibits a larger group of symmetries, also commutative and endowed with an idempotent structure.

Mioc, Vasile

433

Boundary localized symmetry breaking and topological defects  

SciTech Connect

We discuss the structure of topological defects in the context of extra dimensions where the symmetry breaking terms are localized. These defects develop structure in the extra dimension which differs from the case where symmetry breaking is not localized. This new structure can lead to corrections to the mass scale of the defects which is not captured by a simple effective theory obtained by integrating out the extra dimension. We also consider the Higgsless model of symmetry breaking and show that no finite energy defects appear in some situations where they might have been expected.

Holman, R; Martin, Matthew R [Department of Physics Carnegie Mellon University Pittsburgh, Pennsylvania 15213 (United States); T-8, Mail Stop: B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2006-04-15

434

Entanglement and inversion symmetry in topological insulators  

NASA Astrophysics Data System (ADS)

Topological band insulators are usually characterized by symmetry-protected surface modes or quantized linear-response functions (like Hall conductance). Here we present a way to characterize them based on certain bulk properties of just the ground-state wave function, specifically, the properties of its entanglement spectrum. We prove that whenever protected surface states exist, a corresponding protected “mode” exists in the entanglement spectrum as well. Besides this, the entanglement spectrum sometimes succeeds better at indicating topological phases than surface states. We discuss specifically the example of insulators with inversion symmetry which is found to act as an antiunitary symmetry on the entanglement spectrum. A Kramers degeneracy can then arise even when time-reversal symmetry is absent. This degeneracy persists for interacting systems. The entanglement spectrum is therefore a promising tool to characterize topological band insulators and superconductors beyond the free-particle approximation.

Turner, Ari M.; Zhang, Yi; Vishwanath, Ashvin

2010-12-01

435

Space and time from translation symmetry  

SciTech Connect

We show that the notions of space and time in algebraic quantum field theory arise from translation symmetry if we assume asymptotic commutativity. We argue that this construction can be applied to string theory.

Schwarz, A. [Department of Mathematics, University of California-Davis, California 95616-8633 (United States)

2010-01-15

436

Immirzi parameter, torsion, and discrete symmetries  

SciTech Connect

We point out that the new interaction of spinning particles with the torsion tensor, discussed recently, is odd under charge conjugation and time reversal. This explains rather unexpected symmetry properties of the induced effective 4-fermion interaction.

Khriplovich, I.B.; Pomeransky, A.A. [Budker Institute of Nuclear Physics, 630090, Novosibirsk (Russian Federation); Novosibirsk University, 630090, Novosibirsk (Russian Federation)

2006-05-15

437

Symmetry reduction of quasi-free states  

NASA Astrophysics Data System (ADS)

Given a group-invariant quasi-free state on the algebra of canonical commutation relations (CCR), we show how group averaging techniques can be used to obtain a symmetry-reduced CCR algebra and reduced quasi-free state. When the group is compact, this method of symmetry reduction leads to standard results which can be obtained using other methods. When the group is noncompact, the group averaging prescription relies on technically favorable conditions which we delineate. As an example, we consider symmetry reduction of the usual vacuum state for a Klein-Gordon field on Minkowski spacetime by a noncompact subgroup of the Poincaré group consisting of a 1-parameter family of boosts, a 1-parameter family of spatial translations and a set of discrete translations. We show that the symmetry-reduced CCR algebra and vacuum state correspond to that used by each of Berger, Husain, and Pierri for the polarized Gowdy T3 quantum gravity model.

Torre, C. G.

2009-06-01

438

SUSY and symmetry nonrestoration at high temperature  

NASA Astrophysics Data System (ADS)

The status of internal symmetry breaking at high temperature in super-symmetric models is shortly reviewed. This possibility could solve some well known cosmological problems, such as the domain wall, monopole and false vacuum problems.

Bajc, Borut

1999-07-01

439

Algebraic structure of the BRST symmetry.  

National Technical Information Service (NTIS)

An explicit construction of the BRST symmetry is presented in the Hamiltonian approach. The construction is based on the splitting homotopy and the transference problem. (author). 16 refs. (Atomindex citation 23:068883)

L. Tatar R. Tatar

1992-01-01

440

Symmetries In M Theory: Monsters, Inc  

Microsoft Academic Search

\\u000a We will review the algebras which have been conjectured as symmetries in M-theory. The Borcherds algebras, which are the most\\u000a general Lie algebras under control, seem natural candidates.

P. Henry-Labordère; Bernard Julia; Louis Paulot

2003-01-01

441

Symmetry reduction of quasi-free states  

SciTech Connect

Given a group-invariant quasi-free state on the algebra of canonical commutation relations (CCR), we show how group averaging techniques can be used to obtain a symmetry-reduced CCR algebra and reduced quasi-free state. When the group is compact, this method of symmetry reduction leads to standard results which can be obtained using other methods. When the group is noncompact, the group averaging prescription relies on technically favorable conditions which we delineate. As an example, we consider symmetry reduction of the usual vacuum state for a Klein-Gordon field on Minkowski spacetime by a noncompact subgroup of the Poincare group consisting of a 1-parameter family of boosts, a 1-parameter family of spatial translations and a set of discrete translations. We show that the symmetry-reduced CCR algebra and vacuum state correspond to that used by each of Berger, Husain, and Pierri for the polarized Gowdy T{sup 3} quantum gravity model.

Torre, C. G. [Department of Physics, Utah State University, Logan, Utah 84322-4415 (United States)

2009-06-15

442

The symmetries of the Manton superconductivity model  

NASA Astrophysics Data System (ADS)

The symmetries and conserved quantities of Manton's modified superconductivity model with non-relativistic Maxwell-Chern-Simons dynamics (also related to the Quantized Hall Effect) are obtained in the ``Kaluza-Klein type'' framework of Duval et al.

Hassaïne, M.; Horváthy, P. A.

2000-07-01

443

Dynamical symmetries in contemporary nuclear structure applications  

NASA Astrophysics Data System (ADS)

In terms of group theory—the language of symmetries, the concept of spontaneous symmetry breaking is represented in terms of chains of group-subgroup structures that define the dynamical symmetry of the system under consideration. This framework enables exact analytic solutions of the associated eigenvalue problems. We review two types of applications of dynamical symmetries in contemporary theoretical nuclear structure physics: first for a classification of the many-body systems under consideration, with respect to an important characteristic of their behavior; and second for the creation of exactly solvable algebraic models that describe specific aspects of this behavior. This is illustrated with the boson and fermion realizations of symplectic structures. In the first case with an application of the sp(4, R) classification scheme of even-even nuclei within the major nuclear shells and next with of the sp(4) microscopic model for the description of isovector pairing correlations.

Georgieva, A. I.; Ivanov, M. I.; Drenska, S. L.; Sviratcheva, K. D.; Draayer, J. P.

2010-12-01

444

Global symmetries in four and higher dimensions  

Microsoft Academic Search

Knowing that a four-dimensional theory with gauge group G0 is unified in theory with gauge group G puts restrictions on what global symmetries are possible in the low-energy world. Here we analyze those restrictions assuming that unification in G occurs inn four dimensions and assuming that unification occurs only in a higher-dimensional theory. There are possibilities for global symmetries which

Mark W. Goodman; Edward Witten

1986-01-01

445

Symmetry and Resonance in Periodic FPU Chains  

Microsoft Academic Search

:   The symmetry and resonance properties of the Fermi Pasta Ulam chain with periodic boundary conditions are exploited to construct\\u000a a near-identity transformation bringing this Hamiltonian system into a particularly simple form. This “Birkhoff–Gustavson\\u000a normal form” retains the symmetries of the original system and we show that in most cases this allows us to view the periodic\\u000a FPU Hamiltonian as

Bob Rink

2001-01-01

446

Noether's second theorem for BRST symmetries  

SciTech Connect

We present Noether's second theorem for graded Lagrangian systems of even and odd variables on an arbitrary body manifold X in a general case of BRST symmetries depending on derivatives of dynamic variables and ghosts of any finite order. As a preliminary step, Noether's second theorem for Lagrangian systems on fiber bundles Y{yields}X possessing gauge symmetries depending on derivatives of dynamic variables and parameters of arbitrary order is proved.

Bashkirov, D.; Giachetta, G.; Mangiarotti, L.; Sardanashvily, G. [Department of Theoretical Physics, Moscow State University, 117234 Moscow (Russian Federation); Department of Mathematics and Informatics, University of Camerino, 62032 Camerino, MC (Italy); Department of Theoretical Physics, Moscow State University, 117234 Moscow (Russian Federation)

2005-05-01

447

Sign-symmetry of temperature structure functions.  

PubMed

New scalar structure functions with different sign-symmetry properties are defined. These structure functions possess different scaling exponents even when their order is the same. Their scaling properties are investigated for second and third orders, using data from high-Reynolds-number atmospheric boundary layer. It is only when structure functions with disparate sign-symmetry properties are compared can the extended self-similarity detect two different scaling ranges that may exist, as in the example of convective turbulence. PMID:15244734

Aivalis, Konstantinos G; Kurien, Susan; Schumacher, Jörg; Sreenivasan, Katepalli R

2004-06-23

448

Zigzag graphene nanoribbons without inversion symmetry  

Microsoft Academic Search

Graphene on a substrate will suffer an inversion-symmetry-breaking (ISB) lattice potential. Taking electron-electron interaction into account, we study in this paper the possibility of half-metallicity and a noncollinear (NC) magnetic phase for graphene zigzag nanoribbons without inversion symmetry. At half-filling it is found that the half-metallic (HM) state can be achieved at an intermediate value of the ISB potential due

Lihua Pan; Jin An; Yong-Jun Liu; Chang-De Gong

2011-01-01

449

Homological Perturbation Theory and Homological Mirror Symmetry  

Microsoft Academic Search

\\u000a In this article, we discuss an application of homological perturbation theory (HPT) to homological mirror symmetry (HMS) based\\u000a on Kontsevich and Soibelman’s proposal [Kontsevich, M., Soibelman, Y. (2001) Homological mirror symmetry and torus fibrations].\\u000a After a brief review of Morse theory, Morse homotopy and the corresponding Fukaya categories, we explain the idea of deriving\\u000a a Fukaya category from a DG

Hiroshige Kajiura

450

Geometry of Majorana neutrino and new symmetries  

Microsoft Academic Search

Experimental observation of Majorana fermion matter gives a new impetus to the understanding of the Lorentz symmetry and its extension, the geometrical properties of the ambient space-time structure, matter--antimatter symmetry and some new ways to understand the baryo-genesis problem in cosmology. Based on the primordial Majorana fermion matter assumption, we discuss a possibility to solve the baryo-genesis problem through the

G. G. Volkov

2006-01-01

451

Multichannel dynamical symmetry and heavy ion resonances  

SciTech Connect

The concept of the multichannel dynamical symmetry is introduced. This symmetry may show up in an atomic nucleus due to its different cluster configurations, and connects the interactions of distinct reaction channels. The correlated distribution of different cluster states at low and high energies can serve as a signature of it. An application of the [sup 28]Si nucelus is performed in terms of the [sup 24]Mg+[alpha] and [sup 12]C+[sup 16]O fragmentations.

Cseh, J. (Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA ATOMKI) H-4001 Debrecen Pf. 51 (Hungary))

1994-10-01

452

Enhanced coset symmetries and higher derivative corrections  

SciTech Connect

After dimensional reduction to three dimensions, the lowest order effective actions for pure gravity, M theory, and the bosonic string admit an enhanced symmetry group. In this paper we initiate study of how this enhancement is affected by the inclusion of higher derivative terms. In particular we show that the coefficients of the scalar fields associated to the Cartan subalgebra are given by weights of the enhanced symmetry group.

Lambert, Neil; West, Peter [Department of Mathematics, King's College, The Strand London WC2R 2LS (United Kingdom)

2006-09-15

453

Asymptotic symmetries in an optical lattice  

NASA Astrophysics Data System (ADS)

It was recently remarked by Lutz [Phys. Rev. A 67, 051402(R) (2003)] that the equation for the marginal Wigner distribution in an optical lattice admits a scale-free distribution corresponding to Tsallis statistics. Here we show that this distribution is invariant under an asymptotic symmetry of the equation and hence that this scale-free behavior can be understood in terms of symmetry analysis.

Gaeta, Giuseppe

2005-09-01

454

Asymptotic symmetries in an optical lattice  

SciTech Connect

It was recently remarked by Lutz [Phys. Rev. A 67, 051402(R) (2003)] that the equation for the marginal Wigner distribution in an optical lattice admits a scale-free distribution corresponding to Tsallis statistics. Here we show that this distribution is invariant under an asymptotic symmetry of the equation and hence that this scale-free behavior can be understood in terms of symmetry analysis.

Gaeta, Giuseppe [Dipartimento di Matematica, Universita di Milano, via Saldini 50, I-20133 Milan (Italy)

2005-09-15

455

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

456

Temporal symmetry of individual filaments in different spatial symmetry filaments pattern in a dielectric barrier discharge  

SciTech Connect

The temporal behavior of individual filament in different spatial symmetry filaments patterns in dielectric barrier discharge is investigated by using an optical method. A series of return maps of the discharge moments of individual filaments is given. It is found that the temporal symmetry of individual filament changes with the change of the spatial symmetry of filaments pattern as the applied voltage increases. The role of wall charges for this phenomenon is analyzed.

Dong, L. F.; Xiao, H.; Fan, W. L.; Yin, Z. Q.; Zhao, H. T. [College of Physics Science and Technology, Hebei University, Baoding 071002 (China)

2010-10-15

457

Application of the Correlation Method to Vibrational Spectra of C60 and Other Fullerenes: Predicting the Number of IR- and Raman-Active Bands  

NASA Astrophysics Data System (ADS)

The C60 molecule (Buckyball/soccer ball) exhibits only 4 IR and 10 Raman bands although it possesses 174 (3 x 60 - 6) normal vibrations. This striking reduction in the number of observed bands is evidently due to the molecule's extremely high symmetry (Ih point group). First, the 120 symmetry elements of its truncated icosahedral structure are identified and the local (site) symmetry of the carbon atoms (Cc) is determined. Use of molecular models greatly facilitates the process in determining the local and molecular symmetries. Then the correlation method is used to derive a table that classifies the 174 normal vibrations into the respective symmetry species of the Ih point group. In this method, symmetry properties of atomic displacements in terms of the local point group (Cc) are correlated with those in terms of the molecular point group (Ih). After the normal vibrations are classified into respective symmetry species, the numbers of IR- and Raman-active vibrations can be determined by the symmetry selection rules for IR and Raman spectra. The vibrational spectra of C60 and C70 (rugby ball) are analyzed by the above procedure, and the results obtained for C28, C32, C50, and dodecahedrane are provided.

Nakamoto, Kazuo; McKinney, Michael A.

2000-06-01

458

A continuous symmetry analysis of chemical bonding.  

PubMed

The ability to quantify the symmetry content of a given molecular system is important both for the quantitative prediction of its physical and chemical properties, as well as for the establishment of powerful theoretical concepts that can be derived solely from symmetry considerations. The symmetry content of a complex object such as a molecule relies, however, on the level of structural description that is chosen. This may range form a simple geometrical picture in which only the position of the nuclei is indicated, to a more or less detailed description of the electronic structure given by the different quantum chemical methods. Recently, a paper was published describing a new general methodology for calculating the symmetry content of diverse mathematical objects, such as vectors, operators, matrices, functions and more. In the present work we apply that approach to explore the inversion symmetry for diatomic molecules. Although it is a very simple system, general physical conclusions on the phenomenon of chemical bonding can be easily obtained from the symmetry analysis at different levels of description. PMID:21503983

Dryzun, Chaim; Alemany, Pere; Casanova, David; Avnir, David

2011-04-18

459

Surface topography and rotational symmetry breaking.  

PubMed

The surface electroclinic effect, which is a rotation of the molecular director in the substrate plane proportional to an electric field E applied normal to the substrate, requires both a chiral environment and C(2) (or lower) rotational symmetry about E. The two symmetries typically are created in tandem by manipulating the surface topography, a process that conflates their effects. Here we use a pair of rubbed polymer-coated substrates in a twist geometry to obtain our main result, viz., that the strengths of two symmetries, in this case the rub-induced breaking of C(?) rotational symmetry and chiral symmetry, can be separated and quantified. Experimentally we observe that the strength of the reduced rotational symmetry arising from the rub-induced scratches, which is proportional to the electroclinic response, scales linearly with the induced topographical rms roughness and increases with increasing rubbing strength of the polymer. Our results also suggest that the azimuthal anchoring strength coefficient is relatively insensitive to the strength of the rubbing. PMID:23005441

Basu, Rajratan; Nemitz, Ian R; Song, Qingxiang; Lemieux, Robert P; Rosenblatt, Charles

2012-07-27

460

Surface topography and rotational symmetry breaking  

NASA Astrophysics Data System (ADS)

The surface electroclinic effect, which is a rotation of the molecular director in the substrate plane proportional to an electric field E? applied normal to the substrate, requires both a chiral environment and C2 (or lower) rotational symmetry about E?. The two symmetries typically are created in tandem by manipulating the surface topography, a process that conflates their effects. Here we use a pair of rubbed polymer-coated substrates in a twist geometry to obtain our main result, viz., that the strengths of two symmetries, in this case the rub-induced breaking of C? rotational symmetry and chiral symmetry, can be separated and quantified. Experimentally we observe that the strength of the reduced rotational symmetry arising from the rub-induced scratches, which is proportional to the electroclinic response, scales linearly with the induced topographical rms roughness and increases with increasing rubbing strength of the polymer. Our results also suggest that the azimuthal anchoring strength coefficient is relatively insensitive to the strength of the rubbing.

Basu, Rajratan; Nemitz, Ian R.; Song, Qingxiang; Lemieux, Robert P.; Rosenblatt, Charles

2012-07-01

461

Surface topography and rotational symmetry breaking  

NASA Astrophysics Data System (ADS)

The surface electroclinic effect, which is a rotation of the molecular director in the substrate plane proportional to an electric field applied normal to the substrate, requires both a chiral environment and C2 (or lower) rotational symmetry about the field. The two symmetries typically are created in tandem by manipulating the surface topography, a process that conflates their effects. Here we use a pair of rubbed polymer-coated substrates in a twist geometry to obtain our main result, viz., that the strengths of two symmetries, in this case the rub-induced breaking of C? rotational symmetry and chiral symmetry, can be separated and quantified. Experimentally we observe that the strength of the reduced rotational symmetry arising from the rub-induced scratches, which is proportional to the electroclinic response, scales linearly with the induced topographical rms roughness and increases with increasing rubbing strength of the polymer. Our results also suggest that the azimuthal anchoring strength coefficient is relatively insensitive to the strength of the rubbing.

Basu, Rajratan; Nemitz, Ian; Song, Qingxiang; Lemieux, Robert; Rosenblatt, Charles

2013-03-01

462

Gait symmetry in children with autism.  

PubMed

Most studies examining gait asymmetry have focused on infants and toddlers and have tended to use subjective methods of evaluating movement. No previous studies have examined gait symmetry in older children with autism using objective motion capture systems. The purpose of this paper was to quantify gait symmetry in children with autism versus age-matched controls. Fourteen children with autism (N = 14) and twenty-two (N = 22) age, height, and weight-matched controls participated in the study. An eight camera Vicon motion capture system and four Kistler force plates were used to compute temporal-spatial parameters and symmetry indices during walking. Group differences in these measures were tested using MANOVAs. No significant differences between the autism and control group were found for any of the temporal-spatial measures or symmetry indices. Therefore, results suggest that children with autism demonstrate typical symmetry or interlimb movement during gait. Further research is needed to examine the use of different gait inputs to the symmetry indices (e.g., joint angles and moments). A greater awareness of the movement patterns associated with autism may increase our understanding of this disorder and have important implications for treatment planning. PMID:22934175

Chester, Victoria L; Calhoun, Matthew

2012-05-20

463

Broken chiral symmetry on a null plane  

NASA Astrophysics Data System (ADS)

On a null-plane (light-front), all effects of spontaneous chiral symmetry breaking are contained in the three Hamiltonians (dynamical Poincaré generators), while the vacuum state is a chiral invariant. This property is used to give a general proof of Goldstone's theorem on a null-plane. Focusing on null-plane QCD with N degenerate flavors of light quarks, the chiral-symmetry breaking Hamiltonians are obtained, and the role of vacuum condensates is clarified. In particular, the null-plane Gell-Mann-Oakes-Renner formula is derived, and a general prescription is given for mapping all chiral-symmetry breaking QCD condensates to chiral-symmetry conserving null-plane QCD condensates. The utility of the null-plane description lies in the operator algebra that mixes the null-plane Hamiltonians and the chiral symmetry charges. It is demonstrated that in a certain non-trivial limit, the null-plane operator algebra reduces to the symmetry group SU(2N) of the constituent quark model.

Beane, Silas R.

2013-10-01

464

Scanning tuneeling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces  

SciTech Connect

The present work in this dissertation mainly focuses on the clean fivefold surfaces of i-Al-Pd-Mn quasicrystals as well as the nucleation and growth of Ag films on these surfaces. In addition, Ag film growth on NiAl(110) has been explored in the frame of this dissertation. First, we have investigated the equilibration of a fivefold surface of icosahedral Al-Pd-Mn quasicrystal at 900-915 K and 925-950 K, using Omicron variable temperature scanning tunneling microscope (STM). Annealing at low temperatures resulted in many voids on some terraces while the others were almost void-free. After annealing at 925-950K, void-rich terraces became much rarer. Our STM images suggest that through growth and coalescence of the voids, a different termination becomes exposed on host terraces. All of these observations in our study indicate that even after the quasicrystalline terrace-step structure appears, it evolves with time and temperature. More specifically, based on the STM observations, we conclude that during the annealing a wide range of energetically similar layers nucleate as surface terminations, however, with increasing temperature (and time) this distribution gets narrower via elimination of the metastable void-rich terraces. Next, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystal in terms of the densities, compositions and interplanar spacings for the fivefold planes that might represent physical surface terminations. In our analyses, we mainly have focused on four deterministic models which have no partial or mixed occupancy but we have made some comparisons with an undeterministic model. We have compared the models with each other and also with the available experimental data including STM, LEED-IV, XPD and LEIS. In all deterministic models, there are two different families of layers (a pair of planes), and the nondeterministic model contains similar group of planes. These two families differ in terms of the chemical decoration of their top planes. Hence, we name them as Pd+(with Pd) and Pd-(without Pd). Based on their planer structure and the step height, it can be said that these two families can be viable surface terminations. However, besides the Pd content, these two sets differ in terms of relative densities of their top planes as well as the gap separating the layer from the nearest atomic plane. The experimental data and other arguments lead to the conclusion that the Pd- family is favored over the Pd+. This has an important implication on the interpretation of local motifs seen in the high resolution STM images. In other words, the dark stars are not formed by cut-Bergmans rather they are formed by cut-Mackays.

Unal, Baris

2008-12-01

465

GENERAL: Approximate Symmetries and Infinite Series Symmetry Reduction Solutions to Perturbed Kuramoto-Sivashinsky Equation  

NASA Astrophysics Data System (ADS)

Starting from Lie symmetry theory and combining with the approximate symmetry method, and using the package LieSYMGRP proposed by us, we restudy the perturbed Kuramoto-Sivashinsky (KS) equation. The approximate symmetry reduction and the infinite series symmetry reduction solutions of the perturbed KS equation are constructed. Specially, if selecting the tanh-type travelling wave solution as initial approximate, we not only obtain the general formula of the physical approximate similarity solutions, but also obtain several new explicit solutions of the given equation, which are first reported here.

Yao, Ruo-Xia; Jiao, Xiao-Yu; Lou, Sen-Yue

2009-05-01

466

Lie Symmetries, Perturbation to Symmetries and Adiabatic Invariants of a Generalized Birkhoff System  

NASA Astrophysics Data System (ADS)

We study the perturbation to symmetries and adiabatic invariants of a generalized Birkhoff system. Based on the invariance of differential equations under infinitesimal transformations, Lie symmetries, laws of conservations, perturbation to the symmetries and adiabatic invariants of the generalized Birkhoff system are presented. First, the concepts of Lie symmetries and higher order adiabatic invariants of the generalized Birkhoff system are proposed. Then, the conditions for the existence of the exact invariants and adiabatic invariants are proved, and their forms are given. Finally, an example is presented to illustrate the method and results.

Li, Yan-Min

2010-01-01

467

Analysis of pulsed-neutron powder diffraction patterns of the icosahedral quasicrystals Pd3Siu and AlCuLiMg (three alloys) as twinned cubic crystals with large units.  

PubMed

The low-Q peaks on three pulsed-neutron powder patterns (total, U differential, and Pd differential) of the icosahedral quasicrystal Pd3SiU have been indexed on the basis of an assumed cubic structure of the crystals that by icosahedral twinning form the quasicrystal. The primitive unit cube is found to have edge length 56.20 A and to contain approximately 12,100 atoms. Similar analyses of pulsed-neutron patterns of Al55Cu10Li35, Al55Cu10Li30Mg5, and Al510Cu125Li235Mg130 give values of the cube edge length 58.3, 58.5, and 58.4 A, respectively, with approximately 11,650 atoms in the unit cube. It is suggested that the unit contains eight complexes in the beta-W positions, plus some small interstitial groups of atoms, with each complex consisting of a centered icosahedron of 13 clusters, each of 116 atoms with the icosahedral structure found in the body-centered cubic crystal Mg32(Al,Zn)49. PMID:11607201

Pauling, L

1991-08-01

468

Analysis of pulsed-neutron powder diffraction patterns of the icosahedral quasicrystals Pd3Siu and AlCuLiMg (three alloys) as twinned cubic crystals with large units.  

PubMed Central

The low-Q peaks on three pulsed-neutron powder patterns (total, U differential, and Pd differential) of the icosahedral quasicrystal Pd3SiU have been indexed on the basis of an assumed cubic structure of the crystals that by icosahedral twinning form the quasicrystal. The primitive unit cube is found to have edge length 56.20 A and to contain approximately 12,100 atoms. Similar analyses of pulsed-neutron patterns of Al55Cu10Li35, Al55Cu10Li30Mg5, and Al510Cu125Li235Mg130 give values of the cube edge length 58.3, 58.5, and 58.4 A, respectively, with approximately 11,650 atoms in the unit cube. It is suggested that the unit contains eight complexes in the beta-W positions, plus some small interstitial groups of atoms, with each complex consisting of a centered icosahedron of 13 clusters, each of 116 atoms with the icosahedral structure found in the body-centered cubic crystal Mg32(Al,Zn)49.

Pauling, L

1991-01-01

469

Facial symmetry is positively associated with self-reported extraversion  

Microsoft Academic Search

Fink et al. (2005) reported significant associations between facial symmetry and scores on some of the “big five” personality dimensions derived from self-report data. In particular, they identified a positive association between facial symmetry and extraversion, but negative associations between facial symmetry and both agreeableness and openness. Fink et al. (2005) used a measure of facial symmetry based on analysis

Nicholas Pound; Ian S. Penton-Voak; William M. Brown

2007-01-01

470

Perception of Mirror Symmetry in Autism Spectrum Disorders  

ERIC Educational Resources Information Center

|Gestalt grouping in autism spectrum disorders (ASD) is selectively impaired for certain organization principles but for not others. Symmetry is a fundamental Gestalt principle characterizing many biological shapes. Sensitivity to symmetry was tested using the Picture Symmetry Test, which requires finding symmetry lines on pictures. Individuals…

Falter, Christine M.; Bailey, Anthony J.

2012-01-01

471

Symmetry analysis of crystalline spin textures in dipolar spinor condensates  

SciTech Connect

We study periodic crystalline spin textures in spinor condensates with dipolar interactions via a systematic symmetry analysis of the low-energy effective theory. By considering symmetry operations which combine real- and spin-space operations, we classify symmetry groups consistent with nontrivial experimental and theoretical constraints. Minimizing the energy within each symmetry class allows us to explore possible ground states.

Cherng, R. W.; Demler, E. [Physics Department, Harvard University, Cambridge, Massachusetts 02138 (United States)

2011-05-15

472

Tunneling currents in ferromagnetic systems with multiple broken symmetries  

Microsoft Academic Search

A system exhibiting multiple simultaneously broken symmetries offers the opportunity to influence physical phenomena such as tunneling currents by means of external control parameters. In this paper, we consider the broken SU(2) (internal spin) symmetry of ferromagnetic systems coexisting with (i) the broken U(1) symmetry of superconductors and (ii) the broken spatial inversion symmetry induced by a Rashba term in

J. Linder; M. S. Grønsleth; A. Sudbø

2007-01-01

473

Parallelization of symmetry detection algorithms on a network of workstations  

Microsoft Academic Search

Detection of spatial symmetry is useful in several computer vision applications. Due to the real-time nature of the applications, it is important that symmetry detection algorithms be computationally efficient. Sequential algorithms for finding various types of planar symmetries in images are CPU-intensive, prompting us to look for fast parallel implementations. In this paper, we propose parallel algorithms for symmetry detection,

R. Parthiban; C. P. Ravikumar; R. Kakarala; J. Sivaswamy

1997-01-01

474

Group-theoretical framework for potential symmetries of evolution equations  

NASA Astrophysics Data System (ADS)

We develop algebraic approach to the problem of classification of potential symmetries of nonlinear evolution equations. It is essentially based on the recently discovered fact [R. Zhdanov, J. Math. Phys. 50, 053522 (2009)], that any such symmetry is mapped into a contact symmetry. The approach enables using the classical results on classification of contact symmetries of nonlinear evolution equations by Sokolov and Magadeev to classify evolution equations admitting potential symmetries. We construct several examples of new nonlinear fourth-order evolution equations admitting potential symmetries. Since the symmetries obtained depend on nonlocal variables, they cannot be derived by the infinitesimal Lie approach.

Huang, Qing; Qu, Changzheng; Zhdanov, Renat

2011-02-01

475

Energy bands: Chern numbers and symmetry  

SciTech Connect

Energy bands formed by rotation-vibrational states of molecules in the presence of symmetry and their qualitative modifications under variation of some control parameters are studied within the semi-quantum model. Rotational variables are treated as classical whereas a finite set of vibrational states is considered as quantum. In the two-state approximation the system is described in terms of a fiber bundle with the base space being a two-dimensional sphere, the classical phase space for rotational variables. Generically this rank 2 complex vector bundle can be decomposed into two complex line bundles characterized by a topological invariant, the first Chern class. A general method of explicit calculation of Chern classes and of their possible modifications under variation of control parameters in the presence of symmetry is suggested. The construction of iso-Chern diagrams which split the space of control parameters into connected domains with fixed Chern numbers is suggested. A detailed analysis of the rovibrational model Hamiltonian for a D{sub 3} invariant molecule possessing two vibrational states transforming according to the two-dimensional irreducible representation is done to illustrate non-trivial restrictions imposed by symmetry on possible values of Chern classes. - Highlights: > Complex line bundles associated with eigenvalues of 2x2 Hermitian matrix Hamiltonians. > Hamiltonians are defined on the 2-sphere and invariant under symmetry groups. > Symmetry permits only some special integers as Chern numbers. > For SO(2) symmetry, the possible values are 0, {+-}K, where K is an index of the representation. > For D{sub 3} symmetry, the possible values are {+-}2, {+-}4 within our model Hamiltonians.

Iwai, T., E-mail: iwai@amp.i.kyoto-u.ac.jp [Kyoto University, 606-8501 Kyoto (Japan); Zhilinskii, B., E-mail: zhilin@univ-littoral.fr [Kyoto University, 606-8501 Kyoto (Japan); Universite du Littoral Cote d'Opale, 59140 Dunkerque (France)

2011-12-15

476

Drosophila A virus is an unusual RNA virus with a T=3 icosahedral core and permuted RNA-dependent RNA polymerase  

PubMed Central

The vinegar fly, Drosophila melanogaster, is a popular model for the study of invertebrate antiviral immune responses. Several picorna-like viruses are commonly found in both wild and laboratory populations of D. melanogaster. The best-studied and most pathogenic of these is the dicistrovirus Drosophila C virus. Among the uncharacterized small RNA viruses of D. melanogaster, Drosophila A virus (DAV) is the least pathogenic. Historically, DAV has been labelled as a picorna-like virus based on its particle size and the content of its RNA genome. Here, we describe the characterization of both the genome and the virion structure of DAV. Unexpectedly, the DAV genome was shown to encode a circular permutation in the palm-domain motifs of the RNA-dependent RNA polymerase. This arrangement has only been described previously for a subset of viruses from the double-stranded RNA virus family Birnaviridae and the T=4 single-stranded RNA virus family Tetraviridae. The 8?Å (0.8?nm) DAV virion structure computed from cryo-electron microscopy and image reconstruction indicates that the virus structural protein forms two discrete domains within the capsid. The inner domain is formed from a clear T=3 lattice with similarity to the ?-sandwich domain of tomato bushy stunt virus, whilst the outer domain is not ordered icosahedrally, but forms a cage-like structure that surrounds the core domain. Taken together, this indicates that DAV is highly divergent from previously described viruses.

Ambrose, Rebecca L.; Lander, Gabriel C.; Maaty, Walid S.; Bothner, Brian; Johnson, John E.; Johnson, Karyn N.

2009-01-01

477

Effect of Icosahedral Quasicrystalline Fraction and Extrusion Ratio on Microstructure, Mechanical Properties, and Anisotropy of Mg-Zn-Gd-Based Alloys  

NASA Astrophysics Data System (ADS)

We have fabricated three types of Mg-Zn-Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) to investigate how volume fraction of the I-phase and extrusion ratio can have an impact on the microstructure, mechanical properties, and anisotropy of the as-extruded alloys. We find that grains are refined and that the ultimate tensile strength and elongation are improved as either the volume fraction of I-phase or the extrusion ratio is increased, which can be attributed to the secondary phase particle stimulate recrystallization nucleation and restrained grain boundary motion. Moreover, anisotropy is mitigated in all of the alloys as either the I-phase fraction or the extrusion ratio is increased owing to the coeffect of texture weakening and grain refinement as well as to the effect of I-phase on twinning. We also find that with the increase in the amount of the I-phase, the yield strength (YS) is decreased for the alloys extruded at a low ratio owing to the texture weakening, yet it is increased for the alloys extruded at high ratio owing to the strengthening originating from the I-phase and refined grains. The mechanical properties are improved for the alloys extruded at high ratio, which is due to their fine grains and uniform microstructure.

Huang, Hua; Yuan, Guangyin; Wang, Zhongchang; Chen, Chunlin; Ding, Wenjiang

2013-06-01

478