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1

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 2-fold…

Flint, Edward B.

2011-01-01

2

Parity-time symmetry broken by point-group symmetry  

SciTech Connect

We discuss a parity-time (PT) symmetric Hamiltonian with complex eigenvalues. It is based on the dimensionless Schrödinger equation for a particle in a square box with the PT-symmetric potential V(x, y) = iaxy. Perturbation theory clearly shows that some of the eigenvalues are complex for sufficiently small values of |a|. Point-group symmetry proves useful to guess if some of the eigenvalues may already be complex for all values of the coupling constant. We confirm those conclusions by means of an accurate numerical calculation based on the diagonalization method. On the other hand, the Schrödinger equation with the potential V(x, y) = iaxy{sup 2} exhibits real eigenvalues for sufficiently small values of |a|. Point group symmetry suggests that PT-symmetry may be broken in the former case and unbroken in the latter one.

Fernández, Francisco M., E-mail: fernande@quimica.unlp.edu.ar; Garcia, Javier [INIFTA (UNLP, CCT La Plata-CONICET), División Química Teórica, Blvd. 113 S/N, Sucursal 4, Casilla de Correo 16, 1900 La Plata (Argentina)] [INIFTA (UNLP, CCT La Plata-CONICET), División Química Teórica, Blvd. 113 S/N, Sucursal 4, Casilla de Correo 16, 1900 La Plata (Argentina)

2014-04-15

3

Do All Spherical Viruses Have Icosahedral Symmetry?  

E-print Network

Recent high resolution structures for viral capsids with 12, 32 and 72 subunits ($T1$, $T3$ and $T7$ viruses) have confirmed theoretical predictions of an icosadeltahedral structure with 12 subunits having five nearest neighbors (pentamers) and $(10T+2)-12$ subunits having six nearest neighbor subunits (hexamers). Here we note that theoretical considerations of energy strain for $T4$, $T9$ $T16$ and $T25$ viruses by aligned pentamers and energy strain along with the sheer number of possible arrangement of pentamers as the number of subunits grows, and simulations for such numbers of subunits make an icosadeltahedral configuration either miraculously unlikely or indicate that there must be a principle of capsid assembly of unprecedented fidelity in Nature. We predict, for example, that high resolution data will show $T4$ capsids to have $D_{5h}$ not icosahedral symmetry.

Eric Lewin Altschuler; Antonio Pérez--Garrido

2009-02-24

4

Crystallography of decahedral and icosahedral particles. II - High symmetry orientations  

NASA Technical Reports Server (NTRS)

Based on the exact crystal structure of decahedral and icosahedral particles, high energy electron diffraction patterns and image profiles have been derived for various high symmetry orientations of the particles with respect to the incident beam. These results form a basis for the identification of small metal particle structures with advanced methods of transmission electron microscopy.

Yang, C. Y.; Yacaman, M. J.; Heinemann, K.

1979-01-01

5

Multi-Weyl Topological Semimetals Stabilized by Point Group Symmetry Chen Fang,1  

E-print Network

Multi-Weyl Topological Semimetals Stabilized by Point Group Symmetry Chen Fang,1 Matthew J. Gilbert theories at band crossing points in 3D semimetals with n-fold rotation symmetry and broken time-reversal symmetry. Using this classification, we show the existence of new 3D topological semimetals characterized

Gilbert, Matthew

6

Allowed mesoscopic point group symmetries in domain average engineering of perovskite ferroelectric crystals  

E-print Network

Allowed mesoscopic point group symmetries in domain average engineering of perovskite ferroelectric average engineering in proper ferroelectric systems arising from the cubic Pm3¯m symmetry perovskite­4 Both solid solution systems have a perovskite structure. Poling along one of the pseudocubic axes

Cao, Wenwu

7

Origin of icosahedral symmetry in viruses  

PubMed Central

With few exceptions, the shells (capsids) of sphere-like viruses have the symmetry of an icosahedron and are composed of coat proteins (subunits) assembled in special motifs, the T-number structures. Although the synthesis of artificial protein cages is a rapidly developing area of materials science, the design criteria for self-assembled shells that can reproduce the remarkable properties of viral capsids are only beginning to be understood. We present here a minimal model for equilibrium capsid structure, introducing an explicit interaction between protein multimers (capsomers). Using Monte Carlo simulation we show that the model reproduces the main structures of viruses in vivo (T-number icosahedra) and important nonicosahedral structures (with octahedral and cubic symmetry) observed in vitro. Our model can also predict capsid strength and shed light on genome release mechanisms. PMID:15486087

Zandi, Roya; Reguera, David; Bruinsma, Robijn F.; Gelbart, William M.; Rudnick, Joseph

2004-01-01

8

Effective nonlinearity coefficients for three-wave interactions in biaxial crystal of mm2 point group symmetry  

Microsoft Academic Search

The effective nonlinearity coefficients for three-wave interactions in the orthorhombic biaxial crystal of mm2 point group symmetry for six different assignments between the crystallophysical (optical) and crystallographic (piezoelectric) coordinate systems have been obtained. In the former coordinate system the dielectric permeability tensor is the diagonal one, in the latter the square nonlinearity tensor is defined. The point group mm2 includes

V. G. Dmitriev; D. N. Nikogosyan

1993-01-01

9

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. PMID:16679375

Vliegenthart, Gerard Adriaan; Gompper, Gerhard

2006-01-01

10

New implementation of molecular double point-group symmetry in four-component relativistic Gaussian-type spinors  

NASA Astrophysics Data System (ADS)

A new, practical implementation of double-group symmetry to relativistic Gaussian spinors is presented for four-component relativistic molecular calculations. We show that the systematic adaptability to irreducible representations under arbitrary point-group symmetry, as well as Kramers (time-reversal) symmetry, is inherent in the present basis spinors, which possess the analytic structure of Dirac atomic spinors. The implementation of double-group symmetry entails significant computational efficiencies in the relativistic second-order Møller-Plesset perturbation calculation on Au2 and the density functional theory (DFT) calculation with the B3LYP functional on octahedral UF6, in which the highest symmetries used are, respectively, C6h* and D4h*. The four-component B3LYP equilibrium geometry of UF6 is reported.

Yanai, Takeshi; Harrison, Robert J.; Nakajima, Takahito; Ishikawa, Yasuyuki; Hirao, Kimihiko

11

Virus-Templated Plasmonic Nanoclusters with Icosahedral Symmetry via Directed Self-Assembly  

PubMed Central

The assembly of plasmonic nanoparticles with precise spatial and orientational order may lead to structures with new electromagnetic properties at optical frequencies. The directed self-assembly method presented controls the interparticle-spacing and symmetry of the resulting nanometer-sized elements in solution. The self-assembly of three-dimensional (3D), icosahedral plasmonic nanosclusters (NCs) with resonances at visible wavelengths is demonstrated experimentally. The ideal NCs consist of twelve gold (Au) nanospheres (NSs) attached to thiol groups at predefined locations on the surface of a genetically engineered cowpea mosaic virus with icosahedral symmetry. In situ dynamic light scattering (DLS) measurements confirm the NSs assembly on the virus. Transmission electron micrographs (TEM) demonstrate the ability of the self-assembly method to control the nanoscopic symmetry of the bound NSs, which reflects the icosahedral symmetry of the virus. Both, TEM and DLS show that the NCs comprise of a distribution of capsids mostly covered (i.e., 6–12 NS/capsid) with NSs. 3D finite-element simulations of aqueous suspensions of NCs reproduce the experimental bulk absorbance measurements and major features of the spectra. Simulations results show that the fully assembled NCs give rise to a 10-fold surface-averaged enhancement of the local electromagnetic field. PMID:24733721

Fontana, Jake; Dressick, Walter J; Phelps, Jamie; Johnson, John E; Rendell, Ronald W; Sampson, Travian; Ratna, Banahalli R; Soto, Carissa M

2014-01-01

12

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

13

Point Groups and Space Groups in Geometric Algebra  

Microsoft Academic Search

Abstract. Geometric algebra provides the essential foundation for a new approach to symmetry,groups. Each of the 32 lattice point groups and 230 space groups in three dimensions is generated from a set of three symmetry vectors. This greatly facilitates representation, analysis and application of the groups to molecular modeling and crystal- lography.

David Hestenes

14

Topological Invariants in Point Group Symmetric Photonic Topological Insulators  

E-print Network

We proposed a group-theory method to calculate topological invariant in bi-isotropic photonic crystals invariant under crystallographic point group symmetries. Spin Chern number has been evaluated by the eigenvalues of rotation operators at high symmetry k-points after the pseudo-spin polarized fields are retrieved. Topological characters of photonic edge states and photonic band gaps can be well predicted by total spin Chern number. Nontrivial phase transition is found in large magnetoelectric coupling due to the jump of total spin Chern number. Light transport is also issued at the {\\epsilon}/{\\mu} mismatching boundary between air and the bi-isotropic photonic crystal. This finding presents the relationship between group symmetry and photonic topological systems, which enables the design of photonic nontrivial states in a rational manner.

Chen, Xiao-Dong; Chen, Wen-Jie; Wang, Jia-Rong; Dong, Jian-Wen

2014-01-01

15

Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement  

NASA Astrophysics Data System (ADS)

Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential. Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure. Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.

de Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, Marjolein

2015-01-01

16

Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement.  

PubMed

Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential. Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure. Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures. PMID:25173580

de Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D; Groenendijk, Dirk J; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, Marjolein

2015-01-01

17

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

18

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. PMID:21909343

Xiao, Chuan; Rossmann, Michael G.

2011-01-01

19

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

20

Alternative approaches to onion-like icosahedral fullerenes.  

PubMed

The fullerenes of the C60 series (C60, C240, C540, C960, C1500, C2160 etc.) form onion-like shells with icosahedral Ih symmetry. Up to C2160, their geometry has been optimized by Dunlap & Zope from computations according to the analytic density-functional theory and shown by Wardman to obey structural constraints derived from an affine-extended Ih group. In this paper, these approaches are compared with models based on crystallographic scaling transformations. To start with, it is shown that the 56 symmetry-inequivalent computed carbon positions, approximated by the corresponding ones in the models, are mutually related by crystallographic scalings. This result is consistent with Wardman's remark that the affine-extension approach simultaneously models different shells of a carbon onion. From the regularities observed in the fullerene models derived from scaling, an icosahedral infinite C60 onion molecule is defined, with shells consisting of all successive fullerenes of the C60 series. The structural relations between the C60 onion and graphite lead to a one-parameter model with the same Euclidean symmetry P63mc as graphite and having a c/a = ?(2) ratio, where ? = 1.618… is the golden number. This ratio approximates (up to a 4% discrepancy) the value observed in graphite. A number of tables and figures illustrate successive steps of the present investigation. PMID:24572318

Janner, A

2014-03-01

21

Point Groups Based on Methane and Adamantane (Td) Skeletons.  

ERIC Educational Resources Information Center

Describes a procedure for constructing point groups based on the symmetric parent molecules of methane and adamantane. Intended for use in teaching concepts such as subgroups and cosets to beginners in group theory. (TW)

Fujita, Shinsaku

1986-01-01

22

Icosahedral to double-icosahedral shape transition of copper clusters  

NASA Astrophysics Data System (ADS)

The lowest-energy isomers of CuN clusters for N = 20-30 are identified using an unbiased search algorithm and density functional theory calculations. The low-energy structures over this size range are dominated by those based on a 13-atom icosahedral (Ih) core and a 19-atom double icosahedron (DIh) core. A transition in the ground-state isomers from Ih-based to DIh-based structures is predicted overt N = 21-23. We discuss this transition in the broader context of the growth pattern for CuN over N = 2-30 that features regions of gradual evolution in which atoms successively add to the cluster surface, separated by sudden changes to a different structural organization and more compact shape. These transitions result from a competition between interatomic bonding energy and surface energy. The implications of this growth pattern for the further evolution of copper from microstructure to bulk are discussed.

Jiang, Minglong; Zeng, Qun; Zhang, Tingting; Yang, Mingli; Jackson, Koblar Alan

2012-03-01

23

Enhanced Icosahedral Order in Supercooled Liquid Iron  

NASA Astrophysics Data System (ADS)

As part of a study of metallic glass-forming ability, we perform first-principles molecular dynamics simulations of supercooled liquid Iron. Analyzing the results according to the icosahedral order parameter W6, we find that Iron exhibits enhanced icosahedral order compared with supercooled Copper and compared with dense random packing. Voronoi analysis confirms the enhanced order is in the form of 13-atom icosahedral clusters as well as characteristic Frank-Kasper type disclinated icosahedra. Upon further cooling the sample crystallizes to a BCC lattice, with the icosahedra clustering to form a novel point defect.

Ganesh, P.; Widom, Mike

2007-03-01

24

Two-Dimensional Crystals of Icosahedral Viruses at Liquid interfaces  

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) assembly of turnip yellow mosaic virus (TYMV) on cationic lipid monolayers is investigated at the air-water interface. TYMV, an icosahedral virus with a diameter of 28 nm, exhibits well-defined roughness, charge distribution, and hydrophilic/hydrophobic patches on its surface. The electrostatic attraction to the lipid-coated aqueous interface provides means to impose a specific virus orientation and hence reduce the number of possible inter-particle interactions. The 2D geometry is particularly advantageous in dissecting the role of anisotropy in aqueous-media assembly, which involves various types of similarly weak interactions. We show that the assembly approach used not only facilitates crystallization but also provides insights on how complex anisotropic interactions can be exploited to generate long-range order. Specifically, we report an in situ x-ray scattering observation of novel 2D crystal forms of TYMV that reflect the virus' icosahedral symmetry. The symmetry, shape, and surface heterogeneities of TYMV suggest a mechanism by which these crystals are stabilized by a combination of hydrophobic, electrostatic, and steric interactions.

Fukuto, Masafumi; Yang, Lin; Checco, Antonio; Kuzmenko, Ivan; Nguyen, Quyen; Mank, Nick; Wang, Qian

2012-02-01

25

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

26

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. PMID:21790155

Velázquez-Salazar, J. Jesús; Esparza, Rodrigo; Mejía-Rosales, Sergio Javier; Estrada-Salas, Rubén; Ponce, Arturo; Deepak, Francis Leonard; Castro-Guerrero, Carlos; José-Yacamán, Miguel

2011-01-01

27

Coulomb energies of icosahedral h orbitals  

NASA Astrophysics Data System (ADS)

Matrix elements of all two-electron and three-electron operators that are scalar with respect to the icosahedral group I have been tabulated for the icosahedral configurations hN. These operators represent the Coulomb interaction between electrons occupying h orbitals, and also the effects (to the lowest orders of perturbation theory) of configuration interaction on the levels of hN. States and operators are labelled by the irreducible representations (irreps) of the continuous groups SO(3) and SO(5) in addition to the irreps of I. An alternative scheme is introduced in which the irreps W of SO(5) are retained, but the orbital angular-momentum quantum numbers L associated with SO(3) are replaced by the irreps of the permutation groups S5 and S6, the latter corresponding to the interchanges (possibly nonfeasible) of the six fivefold axes of an icosahedron among themselves. The kaleidoscope operator K, which rotates the weight space of SO(5) by ?/2, is an element of S5 and S6, and can be used to characterize the operators. The energy matrices in the second scheme are particularly simple, the scalar or pseudoscalar nature of the operators with respect to S5 leading to block forms either on the diagonal or off the diagonal, respectively. Operators of the former kind are invariant under the K operation and, in the hypothetical absence of the pseudoscalars, would lead to every level of icosahedral type T1 being degenerate with a level of type T2.

Judd, B. R.; Lo, Edwin

1999-10-01

28

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

29

Enhanced magnetocaloric effect in frustrated magnetic molecules with icosahedral symmetry  

Microsoft Academic Search

We investigate the magnetocaloric properties of certain antiferromagnetic spin systems that have already been or very likely can be synthesized as magnetic molecules. It turns out that the special geometric frustration which is present in antiferromagnets that consist of corner-sharing triangles leads to an enhanced magnetocaloric effect with high cooling rates in the vicinity of the saturation field. These findings

Jürgen Schnack; Reimar Schmidt; Johannes Richter

2007-01-01

30

X-ray diffuse scattering from icosahedral Al-Pd-Mn quasicrystals  

NASA Astrophysics Data System (ADS)

The diffuse scattering of the thermodynamically stable icosahedral phase i-AlPdMn has been studied by means of x-ray-diffraction technique. The overall diffuse intensity shows two main characteristics: (1) the global diffuse scattering intensity map is well taken into account by a Huang effect in the formalism developed by Jari? and Nelson [Phys. Rev. B 37, 4458 (1988)] for icosahedral symmetry which reproduces at once both the ``background'' diffuse intensity and the profile shape around the Bragg peaks; (2) the intensity level of the diffuse scattering is crucially dependent on the chemical composition of the sample; it varies drastically from almost free diffuse scattering samples close to an ``ideal'' composition, up to an overall increase by a factor of 20 of the diffuse scattering for samples with an off-stoichiometry less than 0.5% in manganese and palladium content. The relative shapes of the diffuse scattering contours around the Bragg peaks are qualitatively fairly well reproduced using the sole phason-phason term of hydrodynamical modes in the formalism of Jari? and Nelson [Phys. Rev. B 37, 4458 (1988)], suggesting that phasons in these F-type icosahedral quasicrystals induce minor relaxations in the atomic positions surrounding the flip locations.

Capitan, M. J.; Calvayrac, Y.; Quivy, A.; Joulaud, J. L.; Lefebvre, S.; Gratias, D.

1999-09-01

31

Surface structural phase transitions on icosahedral Al–Pd–Mn  

Microsoft Academic Search

The sputtering of alloy surfaces with Ar+ ions may change their chemical composition by preferentially removing particular atomic species. For the icosahedral quasicrystal Al–Pd–Mn this produces reversible surface phase transitions either to a cubic structure or to a decagonal quasicrystal, depending on the temperature. In both the cases, the original icosahedral structure is restored upon annealing. We discuss the orientation

B. Bolliger; M. Erbudak; A. Hensch; D. D. Vvedensky

2000-01-01

32

Topological Quantum Hashing with the Icosahedral Group  

SciTech Connect

We study an efficient algorithm to hash any single-qubit gate into a braid of Fibonacci anyons represented by a product of icosahedral group elements. By representing the group elements by braid segments of different lengths, we introduce a series of pseudogroups. Joining these braid segments in a renormalization group fashion, we obtain a Gaussian unitary ensemble of random-matrix representations of braids. With braids of length O(log{sup 2}(1/{epsilon})), we can approximate all SU(2) matrices to an average error {epsilon} with a cost of O(log(1/{epsilon})) in time. The algorithm is applicable to generic quantum compiling.

Burrello, Michele [International School for Advanced Studies (SISSA), Via Beirut 2-4, I-34014 Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Trieste (Italy); Xu Haitan [Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027 (China); Mussardo, Giuseppe [International School for Advanced Studies (SISSA), Via Beirut 2-4, I-34014 Trieste (Italy); International Centre for Theoretical Physics (ICTP), I-34014 Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Trieste (Italy); Wan Xin [Asia Pacific Center for Theoretical Physics (APCTP), Pohang, Gyeongbuk 790-784 (Korea, Republic of); Department of Physics, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027 (China)

2010-04-23

33

Density waves theory of the capsid structure of small icosahedral viruses  

E-print Network

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 viral capsid shell. Corresponding density distribution function which generates the positions has 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. The quasiequivalence of protein environments in viral capsid and peculiarities of the assembly thermodynamics are also discussed.

V. L. Lorman; S. B. Rochal

2006-11-24

34

Observation of anomalous plasmon linewidth in the icosahedral Al-Mn quasicrystals  

NASA Astrophysics Data System (ADS)

The linewidth of bulk plasmons in a rapid-quench Al6Mn quasi-crystal is found to increase by about 40 percent as compared with that observed in a thermally annealed crystalline Al6Mn sample. A narrower plasmon linewidth is also observed in a sputtered amorphous Al6Mn thin-film sample. It is believed that the unusual plasmon line broadening in Al6Mn quasi-crystals is a result of increased interband transitions due to the icosahedral symmetry of the quasi-crystal, and not a consequence of lattice disorder.

Chen, C. H.; Joy, D. C.; Chen, H. S.; Hauser, J. J.

1986-08-01

35

Symmetry-adapted spherical harmonics method for high-resolution 3D single-particle reconstructions  

Microsoft Academic Search

Three-dimensional (3D) reconstruction is the last and an essential step toward high-resolution structural determination in single-particle cryo-electron microscopy (cryoEM). We have implemented a new algorithm for reconstructing 3D structures of macromolecular complexes with icosahedral symmetry from cryoEM images. Icosahedral symmetry-adapted functions (ISAFs) are used to interpolate structural factors in the reciprocal space to generate a 3D reconstruction in spherical coordinates.

Hongrong Liu; Lingpeng Cheng; Songjun Zeng; Canying Cai; Z. Hong Zhou; Qibin Yang

2008-01-01

36

Fibonacci sequence in the structure of the icosahedral quasicrystal  

Microsoft Academic Search

The surface of the icosahedral Al70Pd20Mn10 quasicrystal possesses a bulk-terminated structure. Sputtering the pentagonal surface followed by a brief annealing favors the formation of terraces with step heights arranged according the Fibonacci sequence.

B. Bolliger; M. Erbudak; A. Hensch

2001-01-01

37

Vibrational Dynamics of Icosahedrally Symmetric Biomolecular Assemblies Compared with Predictions Based on Continuum Elasticity  

PubMed Central

Coarse-grained elastic network models elucidate the fluctuation dynamics of proteins around their native conformations. Low-frequency collective motions derived by simplified normal mode analysis are usually involved in biological function, and these motions often possess noteworthy symmetries related to the overall shape of the molecule. Here, insights into these motions and their frequencies are sought by considering continuum models with appropriate symmetry and boundary conditions to approximately represent the true atomistic molecular structure. We solve the elastic wave equations analytically for the case of spherical symmetry, yielding a symmetry-based classification of molecular motions together with explicit predictions for their vibrational frequencies. We address the case of icosahedral symmetry as a perturbation to the spherical case. Applications to lumazine synthase, satellite tobacco mosaic virus, and brome mosaic virus show that the spherical elastic model efficiently provides insights on collective motions that are otherwise obtained by detailed elastic network models. A major utility of the continuum models is the possibility of estimating macroscopic material properties such as the Young's modulus or Poisson's ratio for different types of viruses. PMID:19486668

Yang, Zheng; Bahar, Ivet; Widom, Michael

2009-01-01

38

The local atomic quasicrystal structure of the icosahedral Mg25Y11Zn64 alloy  

NASA Astrophysics Data System (ADS)

A local and medium range atomic structure model for the face centred icosahedral (fci) Mg25Y11Zn64 alloy has been established in a sphere of r = 27 Å. The model was refined by least squares techniques using the atomic pair distribution (PDF) function obtained from synchrotron powder diffraction. Three hierarchies of the atomic arrangement can be found: (i) five types of local coordination polyhedra for the single atoms, four of which are of Frank-Kasper type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104 atoms, which is condensed sharing its outer shell with its neighbouring clusters, and (iii) a cluster connecting scheme corresponding to a three-dimensional tiling leaving space for a few glue atoms. Inside adjacent clusters, Y8 cubes are tilted with respect to each other and thus allow for overall icosahedral symmetry. It is shown that the title compound is essentially isomorphic to its holmium analogue. Therefore, fci-Mg-Y-Zn can be seen as the representative structure type for the other rare earth analogues fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.

Brühne, S.; Uhrig, E.; Gross, C.; Assmus, W.; Masadeh, A. S.; Billinge, S. J. L.

2005-03-01

39

Effects of Superfine Structure Level-Cluster Crossing on Amplitude and Phase Revival Dynamics: Comparing Tetrahedral and Octahedral Spherical Rotors with Icosahedral Rotors  

NASA Astrophysics Data System (ADS)

Quantum revivals or "super-beats" are predicted to occur when angularly localized symmetric tops states are free to evolve. Similar types of dynamics are expected to involve spherical top superfine and superhyperfine level clusters that are labeled by induced representations of octahedral or tetrahedral symmetries for XY_4, XY_6, and related molecules. A considerably more complicated set of effects are expected for the icosahedral molecule C_ {60} and its related isotopomers. An important difference for icosahedral symmetry is that its superfine splitting ratios are most-irrational (Golden-ratio) fractions that preclude perfect Poincare recurrence of quantum phase while the octahedral splitting ratios are rational. William Harter and Justin Mitchell, International Journal of Molecular Science, 14, 714 (2013).

Harter, William G.; Li, Alvason Zhenhua

2013-06-01

40

Electronic structure of icosahedral AlMnPd quasicrystals from valence and core level photoemission  

NASA Astrophysics Data System (ADS)

A study of the electronic structure of quasicrystals is important for an understanding of the unusual physical properties of these materials. We have investigated the core and valence level photoemission of icosahedral AlPdMn quasicrystals using synchrotron radiation. Spectra were recorded from the fivefold surface of cleaved crystals (in order to provide unperturbed stoichiometry) as well as sputter/annealed surfaces which exhibit good quasicrystalline order. The intensities of the core level lines exhibit a pronounced dependence on polar and azimuthal emission angle which is attributed to photoelectron diffraction effects. Resonance and cross section effects were used to identify the contribution of the different constituent atoms to the valence level region. The valence level emission also shows a clear intensity dependence as a function of emission angle, reflecting the symmetry of the valence states in these compounds. These results are interpreted in terms of the electronic structure of quasicrystals with reference to recent theoretical work.

Barman, S. R.; Paggel, J. J.; Gehrmann, S.; Horn, K.; Rotenberg, E.; Ebert, Ph.; Urban, K.

1998-03-01

41

Symmetry arguments in?chemistry  

PubMed Central

The use (and misuse) of symmetry arguments in constructing molecular models and in the interpretation of experimental observations bearing on molecular structure (spectroscopy, diffraction, etc.) is discussed. Examples include the development of point groups and space groups for describing the external and internal symmetry of crystals, the derivation of molecular symmetry by counting isomers (the benzene structure), molecular chirality, the connection between macroscopic and molecular chirality, pseudorotation, the symmetry group of nonrigid molecules, and the use of orbital symmetry arguments in discussing aspects of chemical reactivity. PMID:8962036

Dunitz, Jack?D.

1996-01-01

42

Icosahedral phase formation in rapidly quenched aluminum-ruthenium alloys  

E-print Network

Icosahedral phase formation in rapidly quenched aluminum- ruthenium alloys Steven M. Anlagea phases as a function of composition. We have chosen the aluminum-ruthenium alloy system because of aluminum and ruthenium were formed by inductively heating the elemental metals in an alumina crucible

Anlage, Steven

43

Generation of filamentous instead of icosahedral particles by repression of African swine fever virus structural protein pB438L.  

PubMed

The mechanisms involved in the construction of the icosahedral capsid of the African swine fever virus (ASFV) particle are not well understood at present. Capsid formation requires protein p72, the major capsid component, but other viral proteins are likely to play also a role in this process. We have examined the function of the ASFV structural protein pB438L, encoded by gene B438L, in virus morphogenesis. We show that protein pB438L associates with membranes during the infection, behaving as an integral membrane protein. Using a recombinant ASFV that inducibly expresses protein pB438L, we have determined that this structural protein is essential for the formation of infectious virus particles. In the absence of the protein, the virus assembly sites contain, instead of icosahedral particles, large aberrant tubular structures of viral origin as well as bilobulate forms that present morphological similarities with the tubules. The filamentous particles, which possess an aberrant core shell domain and an inner envelope, are covered by a capsid-like layer that, although containing the major capsid protein p72, does not acquire icosahedral morphology. This capsid, however, is to some extent functional, as the filamentous particles can move from the virus assembly sites to the plasma membrane and exit the cell by budding. The finding that, in the absence of protein pB438L, the viral particles formed have a tubular structure in which the icosahedral symmetry is lost supports a role for this protein in the construction or stabilization of the icosahedral vertices of the virus particle. PMID:17005638

Epifano, Carolina; Krijnse-Locker, Jacomine; Salas, María L; Salas, José; Rodríguez, Javier M

2006-12-01

44

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

PubMed Central

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 one minute. 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.

2013-01-01

45

Structure of the icosahedral Ti-Zr-Ni quasicrystal  

NASA Astrophysics Data System (ADS)

The atomic structure of the icosahedral Ti-Zr-Ni quasicrystal is determined by invoking similarities to periodic crystalline phases, diffraction data, and the results from ab initio calculations. The structure is modeled by decorations of the canonical-cell tiling geometry. The initial decoration model is based on the structure of the Frank-Kasper phase W-TiZrNi, the 1/1-approximant structure of the quasicrystal. The decoration model is optimized using a method of structural analysis combining a least-squares refinement of diffraction data with results from ab initio calculations. The resulting structural model of icosahedral Ti-Zr-Ni is interpreted as a simple decoration rule and structural details are discussed.

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

2003-04-01

46

Implications of Nonfeasible Transformations among Icosahedral h Orbitals  

NASA Astrophysics Data System (ADS)

The symmetric group S6 that permutes the six fivefold axes of an icosahedron is introduced to go beyond the simple rotations that constitute the icosahedral group I. Owing to the correspondence h<-->d, the calculation of the Coulomb energies for the icosahedral configurations hN based on the sequence O\\(5\\)?S6?S5?I can be brought to bear on Racah's classic theory for the atomic d shell based on SO\\(5\\)?SO L\\(3\\)?I. Among the elements of S6 is the kaleidoscope operator K that rotates the weight space of SO(5) by ?2. Its use explains some puzzling degeneracies in d3 involving the spectroscopic terms 2P, 2F, 2G, and 2H.

Lo, Edwin; Judd, B. R.

1999-04-01

47

Decagonal Epilayers on the Icosahedral Quasicrystal Al70Pd20Mn10  

Microsoft Academic Search

The pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10 becomes decagonal upon sputtering with Ar+ ions at elevated temperatures. This decagonal surface has a vastly different chemical composition ( Al22Pd56Mn22) than bulk decagonal quasicrystals ( Al70Pd10Mn20) and is coherent with the icosahedral substrate across the entire macroscopic sample. The transformation of this surface back to the original icosahedral structure and composition

B. Bolliger; M. Erbudak; D. D. Vvedensky; A. R. Kortan

1999-01-01

48

Crystalline surface structures induced by ion sputtering of Al-rich icosahedral quasicrystals  

SciTech Connect

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below {approximately}700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) 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. The model explains not only the symmetries of the cubic surface terminations, but also the number and orientation of domains. {copyright} {ital 1998} {ital The American Physical Society}

Shen, Z. [Ames Laboratory of the DOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States); Kramer, M.J. [Ames Laboratory of the DOE and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States); Jenks, C.J. [Ames Laboratory of the DOE, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE, Iowa State University, Ames, Iowa 50011 (United States); Goldman, A.I. [Ames Laboratory of the DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States); Lograsso, T. [Ames Laboratory of the DOE and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States); Delaney, D. [Ames Laboratory of the DOE, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE, Iowa State University, Ames, Iowa 50011 (United States); Heinzig, M. [Ames Laboratory of the DOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States); Raberg, W. [Institut fuer Physikalische Chemie, Universitaet Bonn, Wegelerstrasse 12, 53115 Bonn (Germany)] [Institut fuer Physikalische Chemie, Universitaet Bonn, Wegelerstrasse 12, 53115 Bonn (Germany); Thiel, P.A. [Ames Laboratory of the DOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory of the DOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)

1998-10-01

49

Crystalline surface structures induced by ion sputtering of Al-rich icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below ~700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) 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. The model explains not only the symmetries of the cubic surface terminations, but also the number and orientation of domains.

Shen, Z.; Kramer, M. J.; Jenks, C. J.; Goldman, A. I.; Lograsso, T.; Delaney, D.; Heinzig, M.; Raberg, W.; Thiel, P. A.

1998-10-01

50

Decagonal Epilayers on the Icosahedral Quasicrystal Al70Pd20Mn10  

NASA Astrophysics Data System (ADS)

The pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10 becomes decagonal upon sputtering with Ar+ ions at elevated temperatures. This decagonal surface has a vastly different chemical composition ( Al22Pd56Mn22) than bulk decagonal quasicrystals ( Al70Pd10Mn20) and is coherent with the icosahedral substrate across the entire macroscopic sample. The transformation of this surface back to the original icosahedral structure and composition during annealing is followed in real space and in real time with secondary-electron imaging. The structural changes during this transformation are discussed in light of current models of decagonal and icosahedral quasicrystals.

Bolliger, B.; Erbudak, M.; Vvedensky, D. D.; Kortan, A. R.

1999-01-01

51

Irreducible bases and correlations of spin states for double point groups  

E-print Network

In terms of the irreducible bases of the group space of the octahedral double group {\\bf O'}, an analytic formula is obtained to combine the spin states $|j,\\mu \\rangle$ into the symmetrical adapted bases, belonging to a given row of a given irreducible representation of {\\bf O'}. This method is effective for all double point groups. However, for the subgroups of {\\bf O'}, there is another way to obtain those combinations. As an example, the correlations of spin states for the tetrahedral double group {\\bf T'} are calculated explicitly.

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

1998-11-28

52

Non-Hermitian Hamiltonians with unitary and antiunitary symmetries  

SciTech Connect

We analyse several non-Hermitian Hamiltonians with antiunitary symmetry from the point of view of their point-group symmetry. It enables us to predict the degeneracy of the energy levels and to reduce the dimension of the matrices necessary for the diagonalization of the Hamiltonian in a given basis set. We can also classify the solutions according to the irreducible representations of the point group and thus analyse their properties separately. One of the main results of this paper is that some PT-symmetric Hamiltonians with point-group symmetry C{sub 2v} exhibit complex eigenvalues for all values of a potential parameter. In such cases the PT phase transition takes place at the trivial Hermitian limit which suggests that the phenomenon is not robust. Point-group symmetry enables us to explain such anomalous behaviour and to choose a suitable antiunitary operator for the PT symmetry. -- Highlights: •PT-symmetric Hamiltonians exhibit real eigenvalues when PT symmetry is unbroken. •PT-symmetric multidimensional oscillators appear to show PT phase transitions. •This transition was conjectured to be a high-energy phenomenon. •We show that point group symmetry is useful for predicting broken PT symmetry in multidimensional oscillators. •PT-symmetric oscillators with C{sub 2v} symmetry exhibit phase transitions at the trivial Hermitian limit.

Fernández, Francisco M., E-mail: fernande@quimica.unlp.edu.ar; Garcia, Javier

2014-03-15

53

Shallow Water Model on a Modified Icosahedral Geodesic Grid by Using Spring Dynamics  

Microsoft Academic Search

We develop a shallow water model on an icosahedral geodesic grid with several grid modifications. Discretizations of differential operators in the equations are based on the finite volume method, so that the global integrations of transported quantities are numerically conserved. Ordinarily, the standard grid is obtained by recursive grid division starting from the lowest order icosahedral grid. From the viewpoint

Hirofumi Tomita; Motohiko Tsugawa; Masaki Satoh; Koji Goto

2001-01-01

54

Icosahedral Shallow Water Model (ICOSWM): results of shallow water test cases and sensitivity to model parameters  

Microsoft Academic Search

The Icosahedral Shallow Water Model (ICOSWM) has been a first step in the development of the ICON (acronym for ICOsahedral Nonhydrostatic) models. ICON is a joint project of the Max Planck Institute for Meteorology in Hamburg (MPI-M) and Deutscher Wetterdienst (DWD) for the development of new unified general circulation models for climate modeling and numerical weather forecasting on global or

P. Rípodas; A. Gassmann; J. Förstner; D. Majewski; M. Giorgetta; P. Korn; L. Kornblueh; H. Wan; G. Zängl; L. Bonaventura; T. Heinze

2009-01-01

55

Static and dynamic characterization of regular truncated icosahedral and dodecahedral tensegrity modules  

Microsoft Academic Search

Static and dynamic properties of a pair of dual spherical tensegrity modules invented by Buckminster Fuller are investigated. They are regular truncated icosahedral and dodecahedral tensegrity modules. The computation of the Maxwell number and the use of Calladine's relation reveal that regular truncated icosahedral and dodecahedral tensegrity modules possess 55 infinitesimal mechanism modes. A reduced equilibrium matrix is presented for

Hidenori Murakami; Yoshitaka Nishimura

2001-01-01

56

Free energy and surface tension of arbitrarily large Mackay icosahedral clusters  

E-print Network

Free energy and surface tension of arbitrarily large Mackay icosahedral clusters Richard B. Mc for predicting the free energy of arbitrarily large Mackay icosahedral clusters. van der Waals clusters free energies for larger clusters 561 atoms . Combining these predictions with correlations

Goddard III, William A.

57

Soft materials design via self assembly of functionalized icosahedral particles  

NASA Astrophysics Data System (ADS)

In this work we simulate self assembly of icosahedral building blocks using a coarse grained model of the icosahedral capsid of virus 1m1c. With significant advancements in site-directed functionalization of these macromolecules [1], we propose possible application of such self-assembled materials for drug delivery. While there have been some reports on organization of viral particles in solution through functionalization, exploiting this behaviour for obtaining well-ordered stoichiometric structures has not yet been explored. Our work is in well agreement with the earlier simulation studies of icosahedral gold nanocrystals, giving chain like patterns [5] and also broadly in agreement with the wet lab works of Finn, M.G. et al., who have shown small predominantly chain-like aggregates with mannose-decorated Cowpea Mosaic Virus (CPMV) [22] and small two dimensional aggregates with oligonucleotide functionalization on the CPMV capsid [1]. To quantify the results of our Coarse Grained Molecular Dynamics Simulations I developed analysis routines in MATLAB using which we found the most preferable nearest neighbour distances (from the radial distribution function (RDF) calculations) for different lengths of the functional groups and under different implicit solvent conditions, and the most frequent coordination number for a virus particle (histogram plots further using the information from RDF). Visual inspection suggests that our results most likely span the low temperature limits explored in the works of Finn, M.G. et al., and show a good degree of agreement with the experimental results in [1] at an annealing temperature of 4°C. Our work also reveals the possibility of novel stoichiometric N-mer type aggregates which could be synthesized using these capsids with appropriate functionalization and solvent conditions.

Muthukumar, Vidyalakshmi Chockalingam

58

Spinor representation of icosahedral g orbitals  

NASA Astrophysics Data System (ADS)

The four components of an icosahedral g orbital are represented by the irreducible spinor representation 0953-4075/32/5/003/img1 of 0953-4075/32/5/003/img2 (or, equivalently, SO(4)), where the two SO(3) groups are associated with the irreducible representations (IRs) 0953-4075/32/5/003/img3 and 0953-4075/32/5/003/img4 of the icosahedral group I. This enables the properties of the icosahedral configurations 0953-4075/32/5/003/img5 to be calculated by the familiar techniques of angular-momentum theory. The Coulomb interaction is broken into three parts 0953-4075/32/5/003/img6, two of which (0953-4075/32/5/003/img7 and 0953-4075/32/5/003/img8) are SO(4) scalars, the third 0953-4075/32/5/003/img9 belonging to a combination of the various components 0953-4075/32/5/003/img10 and 0953-4075/32/5/003/img11 of the IR (22) that form the scalar IR A of I. The similar matrix elements of 0953-4075/32/5/003/img12 for different N are explained by introducing the concepts of quasispin and complementarity that are analogous to those used in atomic shell theory. Our angular-momentum basis is related to the icosahedral basis of Pooler with the aid of automorphisms of I that interchange 0953-4075/32/5/003/img3 and 0953-4075/32/5/003/img4. This is formalized through the introduction of the kaleidoscope operator 0953-4075/32/5/003/img15, and the degeneracy of the 0953-4075/32/5/003/img3 and 0953-4075/32/5/003/img4 terms for all 0953-4075/32/5/003/img5 is expressed as a result of the invariance of the Coulomb interaction to the operations of the cyclic automorphism group 0953-4075/32/5/003/img19.

Judd, B. R.; Lo, Edwin

1999-03-01

59

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

60

The Asymmetric Structure of an Icosahedral Virus Bound to Its Receptor Suggests a Mechanism for Genome Release  

PubMed Central

Summary Simple, spherical RNA viruses have well-understood, symmetric protein capsids, but little structural information is available for their asymmetric components, such as minor proteins and their genomes, which are vital for infection. Here, we report an asymmetric structure of bacteriophage MS2, attached to its receptor, the F-pilus. Cryo-electron tomography and subtomographic averaging of such complexes result in a structure containing clear density for the packaged genome, implying that the conformation of the genome is the same in each virus particle. The data also suggest that the single-copy viral maturation protein breaks the symmetry of the capsid, occupying a position that would be filled by a coat protein dimer in an icosahedral shell. This capsomere can thus fulfill its known biological roles in receptor and genome binding and suggests an exit route for the genome during infection. PMID:23810697

Dent, Kyle C.; Thompson, Rebecca; Barker, Amy M.; Hiscox, Julian A.; Barr, John N.; Stockley, Peter G.; Ranson, Neil A.

2013-01-01

61

Nonhydrostatic icosahedral atmospheric model (NICAM) for global cloud resolving simulations  

NASA Astrophysics Data System (ADS)

A new type of ultra-high resolution atmospheric global circulation model is developed. The new model is designed to perform "cloud resolving simulations" by directly calculating deep convection and meso-scale circulations, which play key roles not only in the tropical circulations but in the global circulations of the atmosphere. Since cores of deep convection have a few km in horizontal size, they have not directly been resolved by existing atmospheric general circulation models (AGCMs). In order to drastically enhance horizontal resolution, a new framework of a global atmospheric model is required; we adopted nonhydrostatic governing equations and icosahedral grids to the new model, and call it Nonhydrostatic ICosahedral Atmospheric Model (NICAM). In this article, we review governing equations and numerical techniques employed, and present the results from the unique 3.5-km mesh global experiments—with O(10 9) computational nodes—using realistic topography and land/ocean surface thermal forcing. The results show realistic behaviors of multi-scale convective systems in the tropics, which have not been captured by AGCMs. We also argue future perspective of the roles of the new model in the next generation atmospheric sciences.

Satoh, M.; Matsuno, T.; Tomita, H.; Miura, H.; Nasuno, T.; Iga, S.

2008-03-01

62

Magnetic line groups. III. Corepresentations of the magnetic line groups isogonal to the point groups Dn, Cnv, Dnd, and Dnh  

NASA Astrophysics Data System (ADS)

The irreducible corepresentations of the 42 families of the magnetic line groups isogonal to the point groups Dn, Cnv, Dnd, and Dnh are presented. Some general properties of these representations are discussed.

Damnjanovi?, Milan; Miloevi?, Ivanka

1991-06-01

63

Viruses and Fullerenes - Symmetry as a Common Thread?  

E-print Network

We apply here the principle of affine symmetry to the nested fullerene cages (carbon onions) that arise in the context of carbon chemistry. Previous work on affine extensions of the icosahedral group has revealed a new organisational principle in virus structure and assembly. We adapt this group theoretic framework here to the physical requirements dictated by carbon chemistry, and show that we can derive mathematical models for carbon onions within this affine symmetry approach. This suggests the applicability of affine symmetry in a wider context in Nature, as well as offering a novel perspective on the geometric principles underpinning carbon chemistry.

Dechant, Pierre-Philippe; Keef, Tom; Twarock, Reidun

2014-01-01

64

Viruses and Fullerenes - Symmetry as a Common Thread?  

E-print Network

We apply here the principle of affine symmetry to the nested fullerene cages (carbon onions) that arise in the context of carbon chemistry. Previous work on affine extensions of the icosahedral group has revealed a new organisational principle in virus structure and assembly. We adapt this group theoretic framework here to the physical requirements dictated by carbon chemistry, and show that we can derive mathematical models for carbon onions within this affine symmetry approach. This suggests the applicability of affine symmetry in a wider context in Nature, as well as offering a novel perspective on the geometric principles underpinning carbon chemistry.

Pierre-Philippe Dechant; Jess Wardman; Tom Keef; Reidun Twarock

2014-02-18

65

Finite size specimens with cracks of icosahedral Al—Pd—Mn quasicrystals  

NASA Astrophysics Data System (ADS)

Icosahedral quasicrystals are the most important and thermodynamically stable in all about 200 kinds of quasicrystals currently observed. Beyond the scope of classical elasticity, apart from a phonon displacement field, there is a phason displacement field in the elasticity of the quasicrystal, which induces an important effect on the mechanical properties of the material and makes an analytical solution difficult to obtain. In this paper, a finite element algorithm for the static elasticity of icosahedral quasicrystals is developed by transforming the elastic boundary value problem of the icosahedral quasicrystals into an equivalent variational problem. Analytical and numerical solutions for an icosahedral Al—Pd—Mn quasicrystal cuboid subjected to a uniaxial tension with different phonon—phason coupling parameters are given to verify the validity of the numerical approach. A comparison between the analytical and numerical solutions of the specimen demonstrates the accuracy and efficiency of the present algorithm. Finally, in order to reveal the fracture behavior of the icosahedral Al—Pd—Mn quasicrystal, a cracked specimen with a finite size of matter is investigated, both with and without phonon—phason coupling. Meanwhile, the geometry factors are calculated, including the stress intensity factor and the crack opening displacement for the finite-size specimen. Computational results reveal the importance of phonon—phason coupling effect on the icosahedral Al—Pd—Mn quasicrystal. Furthermore, the finite element procedure can be used to solve more complicated boundary value problems.

Yang, Lian-Zhi; Ricoeur, Andreas; He, Fan-Min; Gao, Yang

2014-05-01

66

Projective symmetry of partons in the Kitaev honeycomb model  

NASA Astrophysics Data System (ADS)

Low-energy states of quantum spin liquids are thought to involve partons living in a gauge-field background. We study the spectrum of Majorana fermions of the Kitaev honeycomb model on spherical clusters. The gauge field endows the partons with half-integer orbital angular momenta. As a consequence, the multiplicities do not reflect the point-group symmetries of the cluster, but rather its projective symmetries, operations combining physical and gauge transformations. The projective symmetry group of the ground state is the double cover of the point group.

Mellado, Paula; Petrova, Olga; Tchernyshyov, Oleg

2015-01-01

67

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

68

Bilbao Crystallographic Server. II. Representations of crystallographic point groups and space groups.  

PubMed

The Bilbao Crystallographic Server is a web site with crystallographic programs and databases freely available on-line (http://www.cryst.ehu.es). The server gives access to general information related to crystallographic symmetry groups (generators, general and special positions, maximal subgroups, Brillouin zones etc.). Apart from the simple tools for retrieving the stored data, there are programs for the analysis of group-subgroup relations between space groups (subgroups and supergroups, Wyckoff-position splitting schemes etc.). There are also software packages studying specific problems of solid-state physics, structural chemistry and crystallography. This article reports on the programs treating representations of point and space groups. There are tools for the construction of irreducible representations, for the study of the correlations between representations of group-subgroup pairs of space groups and for the decompositions of Kronecker products of representations. PMID:16489249

Aroyo, Mois I; Kirov, Asen; Capillas, Cesar; Perez-Mato, J M; Wondratschek, Hans

2006-03-01

69

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

70

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

71

Semiconducting icosahedral boron arsenide crystal growth for neutron detection  

NASA Astrophysics Data System (ADS)

Semiconducting icosahedral boron arsenide, B12As2, is an excellent candidate for neutron detectors, thermoelectric converters, and radioisotope batteries, for which high quality single crystals are required. Thus, the present study was undertaken to grow B12As2 crystals by precipitation from metal solutions (nickel) saturated with elemental boron (or B12As2 powder) and arsenic in a sealed quartz ampoule. B12As2 crystals of 10-15 mm were produced when a homogeneous mixture of the three elements was held at 1150 °C for 48-72 h and slowly cooled (3.5 °C/h). The crystals varied in color and transparency from black and opaque to clear and transparent. X-ray topography (XRT), and elemental analysis by energy dispersive X-ray spectroscopy (EDS) confirmed that the crystals had the expected rhombohedral structure and chemical stoichiometry. The concentrations of residual impurities (nickel, carbon, etc.) were low, as measured by Raman spectroscopy and secondary ion mass spectrometry (SIMS). Additionally, low etch-pit densities (4.4×107 cm-2) were observed after etching in molten KOH at 500 °C. Thus, the flux growth method is viable for growing large, high-quality B12As2 crystals.

Whiteley, C. E.; Zhang, Y.; Gong, Y.; Bakalova, S.; Mayo, A.; Edgar, J. H.; Kuball, M.

2011-03-01

72

Is space-time symmetry a suitable generalization of parity-time symmetry?  

NASA Astrophysics Data System (ADS)

We discuss space-time symmetric Hamiltonian operators of the form H =H0 + igH?, where H0 is Hermitian and g real. H0 is invariant under the unitary operations of a point group G while H? is invariant under transformation by elements of a subgroup G? of G. If G exhibits irreducible representations of dimension greater than unity, then it is possible that H has complex eigenvalues for sufficiently small nonzero values of g. In the particular case that H is parity-time symmetric then it appears to exhibit real eigenvalues for all 0 < g Point-group symmetry and perturbation theory enable one to predict whether H may exhibit real or complex eigenvalues for g > 0. We illustrate the main theoretical results and conclusions of this paper by means of two- and three-dimensional Hamiltonians exhibiting a variety of different point-group symmetries.

Amore, Paolo; Fernández, Francisco M.; Garcia, Javier

2014-11-01

73

Interactive PDF files with embedded 3D designs as support material to study the 32 crystallographic point groups  

NASA Astrophysics Data System (ADS)

Crystallography and X-ray diffraction techniques are essential topics in geosciences and other solid-state sciences. Their fundamentals, which include point symmetry groups, are taught in the corresponding university courses. In-depth meaningful learning of symmetry concepts is difficult and requires capacity for abstraction and spatial vision. Traditionally, wooden crystallographic models are used as support material. In this paper, we describe a new interactive tool, freely available, inspired in such models. Thirty-two PDF files containing embedded 3D models have been created. Each file illustrates a point symmetry group and can be used to teach/learn essential symmetry concepts and the International Hermann-Mauguin notation of point symmetry groups. Most interactive computer-aided tools devoted to symmetry deal with molecular symmetry and disregard crystal symmetry so we have developed a tool that fills the existing gap.

Arribas, Victor; Casas, Lluís; Estop, Eugènia; Labrador, Manuel

2014-01-01

74

Design of three-shell icosahedral matryoshka clusters A@B??@A2?? (A = Sn, Pb; B = Mg, Zn, Cd, Mn).  

PubMed

We propose a series of icosahedral matryoshka clusters of A@B12@A20 (A = Sn, Pb; B = Mg, Zn, Cd), which possess large HOMO-LUMO gaps (1.29 to 1.54?eV) and low formation energies (0.06 to 0.21?eV/atom). A global minimum search using a genetic algorithm and density functional theory calculations confirms that such onion-like three-shell structures are the ground states for these A21B12 binary clusters. All of these icosahedral matryoshka clusters, including two previously found ones, i.e., [As@Ni12@As20](3-) and [Sn@Cu12@Sn20](12-), follow the 108-electron rule, which originates from the high Ih symmetry and consequently the splitting of superatom orbitals of high angular momentum. More interestingly, two magnetic matryoshka clusters, i.e., Sn@Mn12@Sn20 and Pb@Mn12@Pb20, are designed, which combine a large magnetic moment of 28 µB, a moderate HOMO-LUMO gap, and weak inter-cluster interaction energy, making them ideal building blocks in novel magnetic materials and devices. PMID:25376938

Huang, Xiaoming; Zhao, Jijun; Su, Yan; Chen, Zhongfang; King, R Bruce

2014-01-01

75

Design of Three-shell Icosahedral Matryoshka Clusters A@B12@A20 (A = Sn, Pb; B = Mg, Zn, Cd, Mn)  

NASA Astrophysics Data System (ADS)

We propose a series of icosahedral matryoshka clusters of A@B12@A20 (A = Sn, Pb; B = Mg, Zn, Cd), which possess large HOMO-LUMO gaps (1.29 to 1.54 eV) and low formation energies (0.06 to 0.21 eV/atom). A global minimum search using a genetic algorithm and density functional theory calculations confirms that such onion-like three-shell structures are the ground states for these A21B12 binary clusters. All of these icosahedral matryoshka clusters, including two previously found ones, i.e., [As@Ni12@As20]3- and [Sn@Cu12@Sn20]12-, follow the 108-electron rule, which originates from the high Ih symmetry and consequently the splitting of superatom orbitals of high angular momentum. More interestingly, two magnetic matryoshka clusters, i.e., Sn@Mn12@Sn20 and Pb@Mn12@Pb20, are designed, which combine a large magnetic moment of 28 µB, a moderate HOMO-LUMO gap, and weak inter-cluster interaction energy, making them ideal building blocks in novel magnetic materials and devices.

Huang, Xiaoming; Zhao, Jijun; Su, Yan; Chen, Zhongfang; King, R. Bruce

2014-11-01

76

A family of binary magnetic icosahedral quasicrystals based on rare earths and cadmium.  

PubMed

Examples of stable binary icosahedral quasicrystals are relatively rare, and at present there are no known examples featuring localized magnetic moments. These would represent an ideal model system for attaining a deeper understanding of the nature of magnetic interactions in aperiodic lattices. Here we report the discovery of a family of at least seven rare earth icosahedral binary quasicrystals, i-R-Cd (R? = ?Gd to Tm, Y), six of which bear localized magnetic moments. Our work highlights the importance of carefully motivated searches through phase space and supports the proposal that, like icosahedral Sc12Zn88 (ref. ), binary quasicrystalline phases may well exist nearby known crystalline approximants, perhaps as peritectically forming compounds with very limited liquidus surfaces, offering very limited ranges of composition/temperature for primary solidification. PMID:23749264

Goldman, Alan I; Kong, Tai; Kreyssig, Andreas; Jesche, Anton; Ramazanoglu, Mehmet; Dennis, Kevin W; Bud'ko, Sergey L; Canfield, Paul C

2013-08-01

77

Fourth class of convex equilateral polyhedron with polyhedral symmetry related to fullerenes and viruses  

PubMed Central

The three known classes of convex polyhedron with equal edge lengths and polyhedral symmetry––tetrahedral, octahedral, and icosahedral––are the 5 Platonic polyhedra, the 13 Archimedean polyhedra––including the truncated icosahedron or soccer ball––and the 2 rhombic polyhedra reported by Johannes Kepler in 1611. (Some carbon fullerenes, inorganic cages, icosahedral viruses, geodesic structures, and protein complexes resemble these fundamental shapes.) Here we add a fourth class, “Goldberg polyhedra,” which are also convex and equilateral. We begin by decorating each of the triangular facets of a tetrahedron, an octahedron, or an icosahedron with the T vertices and connecting edges of a “Goldberg triangle.” We obtain the unique set of internal angles in each planar face of each polyhedron by solving a system of n equations and n variables, where the equations set the dihedral angle discrepancy about different types of edge to zero, and the variables are a subset of the internal angles in 6gons. Like the faces in Kepler’s rhombic polyhedra, the 6gon faces in Goldberg polyhedra are equilateral and planar but not equiangular. We show that there is just a single tetrahedral Goldberg polyhedron, a single octahedral one, and a systematic, countable infinity of icosahedral ones, one for each Goldberg triangle. Unlike carbon fullerenes and faceted viruses, the icosahedral Goldberg polyhedra are nearly spherical. The reasoning and techniques presented here will enable discovery of still more classes of convex equilateral polyhedra with polyhedral symmetry. PMID:24516137

Schein, Stan; Gayed, James Maurice

2014-01-01

78

Fourth class of convex equilateral polyhedron with polyhedral symmetry related to fullerenes and viruses.  

PubMed

The three known classes of convex polyhedron with equal edge lengths and polyhedral symmetry--tetrahedral, octahedral, and icosahedral--are the 5 Platonic polyhedra, the 13 Archimedean polyhedra--including the truncated icosahedron or soccer ball--and the 2 rhombic polyhedra reported by Johannes Kepler in 1611. (Some carbon fullerenes, inorganic cages, icosahedral viruses, geodesic structures, and protein complexes resemble these fundamental shapes.) Here we add a fourth class, "Goldberg polyhedra," which are also convex and equilateral. We begin by decorating each of the triangular facets of a tetrahedron, an octahedron, or an icosahedron with the T vertices and connecting edges of a "Goldberg triangle." We obtain the unique set of internal angles in each planar face of each polyhedron by solving a system of n equations and n variables, where the equations set the dihedral angle discrepancy about different types of edge to zero, and the variables are a subset of the internal angles in 6gons. Like the faces in Kepler's rhombic polyhedra, the 6gon faces in Goldberg polyhedra are equilateral and planar but not equiangular. We show that there is just a single tetrahedral Goldberg polyhedron, a single octahedral one, and a systematic, countable infinity of icosahedral ones, one for each Goldberg triangle. Unlike carbon fullerenes and faceted viruses, the icosahedral Goldberg polyhedra are nearly spherical. The reasoning and techniques presented here will enable discovery of still more classes of convex equilateral polyhedra with polyhedral symmetry. PMID:24516137

Schein, Stan; Gayed, James Maurice

2014-02-25

79

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

80

First Low-Temperature Radiotracer Studies of Diffusion in Icosahedral Quasicrystals  

NASA Astrophysics Data System (ADS)

The diffusivities of implanted, radioactive 103Pd and 195Au in icosahedral Al70.4Pd20.8Mn8.8 quasicrystals were measured between 810 and 270 °C by a radiotracer technique, where serial sectioning was done by high-precision grinding or ion-beam sputtering. Both diffusion coefficients obey different Arrhenius laws above and below 450 °C. Whereas diffusion above this temperature is explained in terms of a vacancy mechanism that reflects the heterogeneity of the icosahedral structure, diffusion below 450 °C is proposed to occur via a phason-assisted direct mechanism.

Blüher, Renate; Scharwaechter, Peter; Frank, Werner; Kronmüller, Helmut

1998-02-01

81

Surface preparation and characterization of the icosahedral Al-Pd-Mn-Ga quasicrystal  

SciTech Connect

Auger electron spectroscopy and low-energy electron diffraction (LEED) provide basic information about the structure and composition of the fivefold surface of the quaternary quasicrystal, icosahedral Al67Pd4Mn21Ga8. Surface preparation techniques established previously for two of the icosahedral ternary alloys, Al-Pd-Mn and Al-Cu-Fe, appear to be similarly effective for Al-Pd-Mn-Ga. After annealing in the range 600-950 K, the surface concentration of Ga is constant and low. After annealing in the range 900-950 K, a good LEED pattern is obtained. LEED indicates that Ga changes the surface structure significantly.

Heinzig, Mark; Jenks, Cynthia J.; Van Hove, Michel; Fisher, Ian; Canfield, Paul; Thiel, Patricia A.

2002-01-08

82

Self-diffusion of manganese in Al-Pd-Mn icosahedral quasicrystals  

Microsoft Academic Search

Self-diffusion of Mn in Al72Pd20Mn8 icosahedral quasicrystals has been investigated over the temperature range from 723 to 1022 K. Concentration depth profiles of the radioisotope Mn in the Al–Pd–Mn quasicrystals and crystals have been measured by an ion-beam sputter-sectioning technique. The temperature dependence of the self-diffusivity of Mn in Al72Pd20Mn8 icosahedral quasicrystals is expressed asThe self-diffusivity of Mn in Al72Pd20Mn8

H. Nakajima; J. Asai; K. Nonaka; I. Shinbo; A. P. Tsai; T. Masumoto

1993-01-01

83

CdTe and PbTe nanostructures on the oxidized pentagonal surface of an icosahedral AlPdMn quasicrystal  

NASA Astrophysics Data System (ADS)

By means of congruent evaporation, we have deposited CdTe and PbTe onto the oxidized fivefold-symmetry surface of an icosahedral AlPdMn quasicrystal. This procedure results in the formation of nanocrystals in both cases. While the azimuthal orientations of the crystallites are random, the polar orientations are well defined. The crystalline CdTe and PbTe domains expose their (1 1 1) and (0 0 1) faces, respectively, which are aligned parallel to the pentagonal surface of the quasicrystal. The nanometric size of the domains is not a result of the lattice mismatch between the growing film and the substrate as usually observed in molecular-beam epitaxy, but of the limited size of the oxide domains of the substrate surface.

Longchamp, J.-N.; Burkardt, S.; Erbudak, M.; Weisskopf, Y.

2007-12-01

84

The nonabelian tensor square of Bieberbach group of dimension five with dihedral point group of order eight  

NASA Astrophysics Data System (ADS)

The nonabelian tensor product was originated in homotopy theory as well as in algebraic K-theory. The nonabelian tensor square is a special case of the nonabelian tensor product where the product is defined if the two groups act on each other in a compatible way and their action are taken to be conjugation. In this paper, the computation of nonabelian tensor square of a Bieberbach group, which is a torsion free crystallographic group, of dimension five with dihedral point group of order eight is determined. Groups, Algorithms and Programming (GAP) software has been used to assist and verify the results.

Fauzi, Wan Nor Farhana Wan Mohd; Idrus, Nor'ashiqin Mohd; Masri, Rohaidah; Sarmin, Nor Haniza

2014-07-01

85

Formation of quasi-icosahedral structures with multi-conjoint fivefold deformation twins in fivefold twinned metallic nanowires  

NASA Astrophysics Data System (ADS)

We show by molecular dynamics simulations that symmetrical quasi-icosahedral structures can be formed in fivefold twinned metallic nanowires (Cu, Au, and Ag) under dynamic tensile loading. The quasi-icosahedral structure, different from the icosahedral nanoclusters found in the past, consists of a twisted original fivefold twinned axis and ten secondary fivefold deformation twins, with five preexisting prismatic and fifteen tetrahedral subunits joined adjacently. Formation of these structures is observed in the necking region during the plastic deformation with successive twinning processes and is found to be independent on the cross-sectional shape as well as the tensile strain rate of the nanowires.

Jiang, Shan; Shen, Yonggang; Zheng, Yonggang; Chen, Zhen

2013-07-01

86

‘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. PMID:20382998

Schiltz, Marc; Bricogne, Gérard

2010-01-01

87

Symmetry-specific densities of vibrational levels for polyatomic molecules  

NASA Astrophysics Data System (ADS)

An extension of the algorithm of Stein and Rabinovitch for exact counting of the densities and sums of vibrational states of polyatomic molecules is described. The new algorithm permits the same sort of efficient computation of exact counts by symmetry species. Several examples for molecules belonging to various point groups are given, and a high-energy limiting distribution among various symmetry species is conjectured.

Sinha, Amitabha; Kinsey, James L.

1984-03-01

88

Symmetry and equivalence restrictions in electronic structure calculations  

NASA Technical Reports Server (NTRS)

A simple method for obtaining MCSCF orbitals and CI natural orbitals adapted to degenerate point groups, with full symmetry and equivalnece restrictions, is described. Among several advantages accruing from this method are the ability to perform atomic SCF calculations on states for which the SCF energy expression cannot be written in terms of Coulomb and exchange integrals over real orbitals, and the generation of symmetry-adapted atomic natural orbitals for use in a recently proposed method for basis set contraction.

Bauschlicher, Charles W., Jr.; Taylor, Peter R.

1988-01-01

89

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

90

Role of molecular symmetry in inverse magnetochiral birefringence  

Microsoft Academic Search

The constant magnetization is calculated which is induced in optically active isotropic media by arbitrarily polarized light. The mechanisms responsible for the effect are described in terms of magnetic-dipole and electric-quadrupole polarizability tensors. The point group symmetries of molecules admitting these mechanisms are determined.

S. Wozniak; G. Wagnière; R. Zawodny

1991-01-01

91

Energetics and local spin magnetic moment of single 3,4d impurities encapsulated in an icosahedral Au12 cage  

Microsoft Academic Search

The energetics and local spin magnetic moment of a single 3,4d impurity (Sc-Ni, Y-Pd) encapsulated in an icosahedral Au12 cage have been studied theoretically by using a real-space first-principles cluster method with generalized gradient approximation for exchange-correlation functional. The relativistic effect is considered by scalar relativistic pseudopotentials. All doped clusters show unexpected large relative binding energies compared with icosahedral Au13

Shan-Ying Wang; Jing-Zhi Yu; Hiroshi Mizuseki; Qiang Sun; Chong-Yu Wang; Yoshiyuki Kawazoe

2004-01-01

92

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

93

An icosahedral algal virus has a complex unique vertex decorated by a spike  

PubMed Central

Paramecium bursaria Chlorella virus-1 is an icosahedrally shaped, 1,900-?-diameter virus that infects unicellular eukaryotic green algae. A 5-fold symmetric, 3D reconstruction using cryoelectron microscopy images has now shown that the quasiicosahedral virus has a unique vertex, with a pocket on the inside and a spike structure on the outside of the capsid. The pocket might contain enzymes for use in the initial stages of infection. The unique vertex consists of virally coded proteins, some of which have been identified. Comparison of shape, size, and location of the spike with similar features in bacteriophages T4 and P22 suggests that the spike might be a cell-puncturing device. Similar asymmetric features may have been missed in previous analyses of many other viruses that had been assumed to be perfectly icosahedral. PMID:19541619

Cherrier, Mickaël V.; Kostyuchenko, Victor A.; Xiao, Chuan; Bowman, Valorie D.; Battisti, Anthony J.; Yan, Xiaodong; Chipman, Paul R.; Baker, Timothy S.; Van Etten, James L.; Rossmann, Michael G.

2009-01-01

94

Analytical models of icosahedral shells for 3D optical imaging of viruses  

E-print Network

A modulated icosahedral shell with an inclusion is a concise description of many viruses, including recently-discovered large double-stranded DNA ones. Many X-ray scattering patterns of such viruses show major polygonal fringes, which can be reproduced in image reconstruction with a homogeneous icosahedral shell. A key question regarding a low-resolution reconstruction is how to introduce further changes to the 3D profile in an efficient way with only a few parameters. Here, we derive and compile different analytical models of such an object with consideration of practical optical setups and typical structures of such viruses. The benefits of such models include 1) inherent filtering and suppressing different numerical errors of a discrete grid, 2) providing a concise and meaningful set of descriptors for feature extraction in high-throughput classification/sorting and higher-resolution cumulative reconstructions, 3) disentangling (physical) resolution from (numerical) discretization step and having a vector ...

Jafarpour, Aliakbar

2014-01-01

95

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

96

B12Hn and B12Fn: planar vs icosahedral structures  

PubMed Central

Using density functional theory and quantum Monte Carlo calculations, we show that B12Hn and B12Fn (n = 0 to 4) quasi-planar structures are energetically more favorable than the corresponding icosahedral clusters. Moreover, we show that the fully planar B12F6 cluster is more stable than the three-dimensional counterpart. These results open up the possibility of designing larger boron-based nanostructures starting from quasi-planar or fully planar building blocks. PMID:22546348

2012-01-01

97

Electrostriction in quasicrystals and in the icosahedral liquid crystalline Blue Phases  

Microsoft Academic Search

In the electrostriction process crystals are deformed by an electric field in quadratic order. The components of the corresponding electrostriction tensor, which relates the square of the electric field components to the components of the strain tensor, have been measured recently for the cubic liquid crystalline Blue Phases. In quasiperiodic systems, like the icosahedral metallic alloys AlMn or AlCuFe, or

H.-R. Trebin; W. Fink; H. Stark

1991-01-01

98

Voids and pits on sputter-annealed fivefold terraces of icosahedral Al-Pd-Mn quasicrystals  

Microsoft Academic Search

Our scanning tunneling microscope studies on clean surfaces of fivefold icosahedral Al70.2Pd20.7Mn9.1 reveal that, after annealing at 900?K, two types of flat depressions are visible on terraces: voids (small, shallow, flat-bottomed depressions bordered by 2.5?Å steps) and pits (deeper, and often larger, depressions). They are different not only in their dimensions but in their behavior: voids preferentially nucleate on some

B. Unal; T. A. Lograsso; A. R. Ross; C. J. Jenks; P. A. Thiel

2006-01-01

99

Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals  

Microsoft Academic Search

The optical reflectivity of Al-based and Ti-based quasicrystalline and approximant samples were investigated versus the quality of their structural morphology using optical reflectometry, x-ray diffraction, and transmission electron microscopy. The different structural morphologies were obtained using three different preparation processes: sintering, pulsed laser deposition, and reactive cathodic magnetron sputtering. The work demonstrates that the canonical behavior of icosahedral state in

Valérie Brien; Anne Dauscher; Francis Machizaud

2006-01-01

100

The surface structure of icosahedral Al 68 Pd 23 Mn 9 measured by STM and LEED  

Microsoft Academic Search

For the first time the surface structure of an icosahedral quasicrystal has been successfully investigated in Ultra-High Vacuum (UHV) by Scanning Tunneling Microscopy (STM) and Low-Energy Electron Diffraction (LEED). After cleaning an i-Al68Pd23Mn9 sample in UHV by cycles of ion-sputtering and annealing at temperatures close to the melting point atomically flat terraces are observed by STM. Successive step heights show

Th. M. Schaub; D. E. Bürgler; H.-J. Güntherodt; J. B. Suck; M. Audier

1995-01-01

101

The surface structure of icosahedral Al68Pd23Mn9 measured by STM and LEED  

Microsoft Academic Search

For the first time the surface structure of an icosahedral quasicrystal has been successfully investigated in Ultra-High Vacuum (UHV) by Scanning Tunneling Microscopy (STM) and Low-Energy Electron Diffraction (LEED). After cleaning an i-Al68Pd23Mn9 sample in UHV by cycles of ion-sputtering and annealing at temperatures close to the melting point atomically flat terraces are observed by STM. Successive step heights show

Th. M. Schaub; D. E. Bürgler; H.-J. Güntherodt; J. B. Suck; M. Audier

1995-01-01

102

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

Microsoft Academic Search

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

Tanhong Cai

2001-01-01

103

The surface structure of icosahedral Al68Pd23Mn9 measured by STM and LEED  

Microsoft Academic Search

For the first time the surface structure of an icosahedral quasicrystal has been successfully investigated in Ultra-High Vacuum (UHV) by Scanning Tunneling Microscopy (STM) and Low-Energy Electron Diffraction (LEED). After cleaning an i-Al 68Pd 23Mn 9 sample in UHV by cycles of ion-sputtering and annealing at temperatures close to the melting point atomically flat terraces are observed by STM. Successive

Th. M Schaub; D. E. Bürgler; H.-J. Güntherodt; J. B. Suck; M. Audier

1995-01-01

104

Voids and pits on sputter-annealed fivefold terraces of icosahedral Al–Pd–Mn quasicrystals  

Microsoft Academic Search

Our scanning tunneling microscope studies on clean surfaces of fivefold icosahedral Al70.2Pd20.7Mn9.1 reveal that, after annealing at 900?K, two types of flat depressions are visible on terraces: voids (small, shallow, flat-bottomed depressions bordered by 2.5?Å steps) and pits (deeper, and often larger, depressions). They are different not only in their dimensions but in their behavior: voids preferentially nucleate on some

B. Unal; T. A. Lograsso; A. R. Ross; C. J. Jenks; P. A. Thiel

2006-01-01

105

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

Microsoft Academic Search

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

H. R. Sharma; G. Simutis; V. R. Dhanak; P. J. Nugent; C. Cui; M. Shimoda; R. McGrath; A. P. Tsai; Y. Ishii

2010-01-01

106

First Low-Temperature Radiotracer Studies of Diffusion in Icosahedral Quasicrystals  

Microsoft Academic Search

The diffusivities of implanted, radioactive 103Pd and 195Au in icosahedral Al70.4Pd20.8Mn8.8 quasicrystals were measured between 810 and 270 °C by a radiotracer technique, where serial sectioning was done by high-precision grinding or ion-beam sputtering. Both diffusion coefficients obey different Arrhenius laws above and below 450 °C. Whereas diffusion above this temperature is explained in terms of a vacancy mechanism that

Renate Blüher; Peter Scharwaechter; Werner Frank; Helmut Kronmüller

1998-01-01

107

Electronic structure of icosahedral AlMnPd quasicrystals from valence and core level photoemission  

Microsoft Academic Search

A study of the electronic structure of quasicrystals is important for an understanding of the unusual physical properties of these materials. We have investigated the core and valence level photoemission of icosahedral AlPdMn quasicrystals using synchrotron radiation. Spectra were recorded from the fivefold surface of cleaved crystals (in order to provide unperturbed stoichiometry) as well as sputter\\/annealed surfaces which exhibit

S. R. Barman; J. J. Paggel; S. Gehrmann; K. Horn; E. Rotenberg; Ph. Ebert; K. Urban

1998-01-01

108

SEM and AFM studies of a 5-fold surface of icosahedral AlPdMn  

Microsoft Academic Search

A 5-fold surface of the icosahedral AlPdMn (i-AlPdMn) quasicrystal (QC) was studied by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM) under ambient conditions. We show that a very complicated inhomogeneous surface morphology may develop on the 5-fold surface prepared by ion sputtering and annealing cycles in UHV. Sputtering and sublimation both contribute to material removal on

Fuxiao Yu; Maarten Bischoff; Amy R. Ross; Thomas A. Lograsso; Herman van Kempen; Ted Janssen

2004-01-01

109

Computational self-assembly of a one-component icosahedral quasicrystal.  

PubMed

Icosahedral quasicrystals (IQCs) are a form of matter that is ordered but not periodic in any direction. All reported IQCs are intermetallic compounds and either of face-centred-icosahedral or primitive-icosahedral type, and the positions of their atoms have been resolved from diffraction data. However, unlike axially symmetric quasicrystals, IQCs have not been observed in non-atomic (that is, micellar or nanoparticle) systems, where real-space information would be directly available. Here, we show that an IQC can be assembled by means of molecular dynamics simulations from a one-component system of particles interacting via a tunable, isotropic pair potential extending only to the third-neighbour shell. The IQC is body-centred, self-assembles from a fluid phase, and in parameter space neighbours clathrates and other tetrahedrally bonded crystals. Our findings elucidate the structure and dynamics of the IQC, and suggest routes to search for it and design it in soft matter and nanoscale systems. PMID:25485986

Engel, Michael; Damasceno, Pablo F; Phillips, Carolyn L; Glotzer, Sharon C

2015-01-01

110

Computational self-assembly of a one-component icosahedral quasicrystal  

NASA Astrophysics Data System (ADS)

Icosahedral quasicrystals (IQCs) are a form of matter that is ordered but not periodic in any direction. All reported IQCs are intermetallic compounds and either of face-centred-icosahedral or primitive-icosahedral type, and the positions of their atoms have been resolved from diffraction data. However, unlike axially symmetric quasicrystals, IQCs have not been observed in non-atomic (that is, micellar or nanoparticle) systems, where real-space information would be directly available. Here, we show that an IQC can be assembled by means of molecular dynamics simulations from a one-component system of particles interacting via a tunable, isotropic pair potential extending only to the third-neighbour shell. The IQC is body-centred, self-assembles from a fluid phase, and in parameter space neighbours clathrates and other tetrahedrally bonded crystals. Our findings elucidate the structure and dynamics of the IQC, and suggest routes to search for it and design it in soft matter and nanoscale systems.

Engel, Michael; Damasceno, Pablo F.; Phillips, Carolyn L.; Glotzer, Sharon C.

2015-01-01

111

Precipitation of an icosahedrally symmetric ordered phase in Zr-Ti-Cu-Ni-Al metallic glasses  

NASA Astrophysics Data System (ADS)

Results from a study of the precipitation of an icosahedrally symmetric ordered phase in Zr62- xTixCu20Ni8Al10 amorphous alloys are presented. The data indicate the development of icosahedral short-range order (similar to that in the ordered phase) in the undercooled melt during quenching, and in the amorphous phase with annealing in the supercooled liquid region. Precipitation is controlled by long-range diffusion in alloys made with less than 3 at. % Ti. The resulting lower nucleation rates and longer induction times lead to a fine microstructure that contains icosahedral phase (i phase) grains ranging from 50 to 100 nm in diameter. In the glasses made with 5-7.5 at. % Ti, the composition of the precipitating phase is more similar to that of the glass, lowering the kinetic nucleation barrier and leading to an extremely fine nanostructured devitrified material, with i phase grain sizes from 2 to 5 nm. The x-ray diffraction pattern from this phase is similar to that of the i phase. However, because the grain size is nearly the same as the edge length of the unit cell of a high-order crystal approximate phase, no distinction can be made between the i phase and crystal approximate phases in such nanostructured materials.

Xing, L. Q.; Shen, Y. T.; Kelton, K. F.

2002-10-01

112

Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals  

SciTech Connect

The optical reflectivity of Al-based and Ti-based quasicrystalline and approximant samples were investigated versus the quality of their structural morphology using optical reflectometry, x-ray diffraction, and transmission electron microscopy. The different structural morphologies were obtained using three different preparation processes: sintering, pulsed laser deposition, and reactive cathodic magnetron sputtering. The work demonstrates that the canonical behavior of icosahedral state in specular reflectivity is extremely sensitive to different and very fine aspects of the microstructure: sizes of grains smaller than 50 nm, slight local diffuse disorder, and shifts away from the icosahedral crystallographic structure (approximants). The work explains why the optical properties of the same kind of quasicrystals found in literature sometimes reveal a different behavior from one author to another. The study then confirms the work of some authors and definitely shows that the canonical behavior of icosahedral state in specular reflectivity over the 30 000-50 000 cm{sup -1} domain is characterized by a decreasing function made of steps. It also shows that this behavior can be interpreted thanks to the cluster hierarchy of the model of Janot [Phys. Rev. B 53, 181 (1996)].

Brien, Valerie; Dauscher, Anne; Machizaud, Francis [Laboratoire de Science et Genie des Materiaux et de Metallurgie, UMR CNRS-INPL 7584, Parc de Saurupt, ENSMN, F-54042 Nancy Cedex (France); Laboratoire de Physique des Materiaux, UMR CNRS-INPL-UHP 7556, Parc de Saurupt, ENSMN, F-54042 Nancy Cedex (France); Laboratoire de Science et Genie des Materiaux et de Metallurgie, UMR CNRS-INPL 7584, Parc de Saurupt, ENSMN, F-54042 Nancy Cedex (France)

2006-08-15

113

Optical reflectivity as a simple diagnostic method for testing structural quality of icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

The optical reflectivity of Al-based and Ti-based quasicrystalline and approximant samples were investigated versus the quality of their structural morphology using optical reflectometry, x-ray diffraction, and transmission electron microscopy. The different structural morphologies were obtained using three different preparation processes: sintering, pulsed laser deposition, and reactive cathodic magnetron sputtering. The work demonstrates that the canonical behavior of icosahedral state in specular reflectivity is extremely sensitive to different and very fine aspects of the microstructure: sizes of grains smaller than 50nm, slight local diffuse disorder, and shifts away from the icosahedral crystallographic structure (approximants). The work explains why the optical properties of the same kind of quasicrystals found in literature sometimes reveal a different behavior from one author to another. The study then confirms the work of some authors and definitely shows that the canonical behavior of icosahedral state in specular reflectivity over the 30000-50000cm-1 domain is characterized by a decreasing function made of steps. It also shows that this behavior can be interpreted thanks to the cluster hierarchy of the model of Janot [Phys. Rev. B 53, 181 (1996)].

Brien, Valérie; Dauscher, Anne; Machizaud, Francis

2006-08-01

114

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

115

Symmetry Classes  

E-print Network

Physical systems exhibiting stochastic or chaotic behavior are often amenable to treatment by random matrix models. In deciding on a good choice of model, random matrix physics is constrained and guided by symmetry considerations. The notion of 'symmetry class' (not to be confused with 'universality class') expresses the relevance of symmetries as an organizational principle. Dyson, in his 1962 paper referred to as the Threefold Way, gave the prime classification of random matrix ensembles based on a quantum mechanical setting with symmetries. In this article we review Dyson's Threefold Way from a modern perspective. We then describe a minimal extension of Dyson's setting to incorporate the physics of chiral Dirac fermions and disordered superconductors. In this minimally extended setting, where Hilbert space is replaced by Fock space equipped with the anti-unitary operation of particle-hole conjugation, symmetry classes are in one-to-one correspondence with the large families of Riemannian symmetric spaces.

Martin R. Zirnbauer

2010-01-05

116

More Stuff on Groups Groups Acting on Itself Icosahedral Group Operations on Subsets Sylow Theorems Homework Math 451: Abstract Algebra I  

E-print Network

Homework Math 451: Abstract Algebra I Wolmer V. Vasconcelos Set 3 Fall 2009 #12;More Stuff on Groups Groups Acting on Itself Icosahedral Group Operations on Subsets Sylow Theorems Homework Outline 1 More Stuff on Groups 2 Groups Acting on Itself 3 Icosahedral Group 4 Operations on Subsets 5 Sylow Theorems 6 Homework

Vasconcelos, Wolmer

117

Symmetry Energy  

E-print Network

Examination of symmetry energy is carried out on the basis of an elementary binding-energy formula. Constraints are obtained on the energy value at the normal nuclear density and on the density dependence of the energy at subnormal densities.

P. Danielewicz

2006-07-15

118

A 3-D Finite-Volume Non-hydrostatic Icosahedral Model (NIM)  

NASA Astrophysics Data System (ADS)

The Nonhydrostatic Icosahedral Model (NIM) formulates the latest numerical innovation of the three-dimensional finite-volume control volume on the quasi-uniform icosahedral grid suitable for ultra-high resolution simulations. NIM's modeling goal is to improve numerical accuracy for weather and climate simulations as well as to utilize the state-of-art computing architecture such as massive parallel CPUs and GPUs to deliver routine high-resolution forecasts in timely manner. NIM dynamic corel innovations include: * A local coordinate system remapped spherical surface to plane for numerical accuracy (Lee and MacDonald, 2009), * Grid points in a table-driven horizontal loop that allow any horizontal point sequence (A.E. MacDonald, et al., 2010), * Flux-Corrected Transport formulated on finite-volume operators to maintain conservative positive definite transport (J.-L, Lee, ET. Al., 2010), *Icosahedral grid optimization (Wang and Lee, 2011), * All differentials evaluated as three-dimensional finite-volume integrals around the control volume. The three-dimensional finite-volume solver in NIM is designed to improve pressure gradient calculation and orographic precipitation over complex terrain. NIM dynamical core has been successfully verified with various non-hydrostatic benchmark test cases such as internal gravity wave, and mountain waves in Dynamical Cores Model Inter-comparisons Projects (DCMIP). Physical parameterizations suitable for NWP are incorporated into NIM dynamical core and successfully tested with multimonth aqua-planet simulations. Recently, NIM has started real data simulations using GFS initial conditions. Results from the idealized tests as well as real-data simulations will be shown in the conference.

Lee, Jin

2014-05-01

119

Electrostriction in quasicrystals and in the icosahedral liquid crystalline Blue Phases  

NASA Astrophysics Data System (ADS)

In the electrostriction process crystals are deformed by an electric field in quadratic order. The components of the corresponding electrostriction tensor, which relates the square of the electric field components to the components of the strain tensor, have been measured recently for the cubic liquid crystalline Blue Phases. In quasiperiodic systems, like the icosahedral metallic alloys AlMn or AlCuFe, or in the icosahedral model for the Blue Phase III the electric field can also induce phason strain. Here we determine the corresponding generalized electrostriction tensor for icosahedral and decagonal phases and relate it to the generalized elastic and elasto-optic tensors. For certain values of the field, quasiperiodic systems can become periodic either along the field direction or perpendicular to it. Sous l'effet de l'électrostriction, les cristaux sont déformés par un champ électrique en second ordre. Les coefficients du tenseur d'électrostriction rattachant le champ électrique aux composantes du tenseur des déformations ont été mesurés pour les mésophases cubiques Phase Bleue I et II. Dans un système quasi périodique, par exemple dans les quasi-cristaux icosaédriques AlMn ou AlCuFe, ou dans le modèle icosaédrique de la Phase Bleue III le champ électrique peut aussi causer une déformation des phasons. Ici nous déterminons le tenseur d'électrostriction généralisé pour des phases icosaédriques et décagonales et nous le mettons en rapport avec les tenseurs généralisés élastiques et élasto-optiques. Il y a des valeurs du champ électrique où les systèmes quasi périodiques peuvent devenir périodiques ou bien en direction du champ électrique ou bien perpendiculaire à lui.

Trebin, H.-R.; Fink, W.; Stark, H.

1991-10-01

120

Elastic Analysis of a Griffith Crack in Icosahedral Quasicrystal Al-Pd-Mn Quasicrystal  

NASA Astrophysics Data System (ADS)

The elastic analysis of a Griffith crack in an icosahedral quasicrystal is performed using the general solution and systematic Fourier transform-dual integral equations method, the analytic expressions for the displacement and stress fields are obtained. The asymptotic behavior of the stress field around the crack tip indicates that the stress near the crack tip exhibits the square root singularity. The singularity in the phason stress field arising from those of the phonon and phonon-phason coupling is also discussed. The most important physical quantities of fracture theory, crack stress intensity factor and energy release rate, are determined.

Zhu, Ai-Yu; Fan, Tian-You

121

Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = |{{{\\boldsymbol{J}} }large}|/|{{{\\boldsymbol{J}} }small}|, reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

Takeuchi, Tsunehiro

2014-12-01

122

Studies of inactivation mechanism of non-enveloped icosahedral virus by a visible ultrashort pulsed laser  

PubMed Central

Background Low-power ultrashort pulsed (USP) lasers operating at wavelengths of 425 nm and near infrared region have been shown to effectively inactivate viruses such as human immunodeficiency virus (HIV), M13 bacteriophage, and murine cytomegalovirus (MCMV). It was shown previously that non-enveloped, helical viruses such as M13 bacteriophage, were inactivated by a USP laser through an impulsive stimulated Raman scattering (ISRS) process. Recently, enveloped virus like MCMV has been shown to be inactivated by a USP laser via protein aggregation induced by an ISRS process. However, the inactivation mechanism for a clinically important class of viruses – non-enveloped, icosahedral viruses remains unknown. Results and discussions We have ruled out the following four possible inactivation mechanisms for non-enveloped, icosahedral viruses, namely, (1) inactivation due to ultraviolet C (UVC) photons produced by non-linear optical process of the intense, fundamental laser beam at 425 nm; (2) inactivation caused by thermal heating generated by the direct laser absorption/heating of the virion; (3) inactivation resulting from a one-photon absorption process via chromophores such as porphyrin molecules, or indicator dyes, potentially producing reactive oxygen or other species; (4) inactivation by the USP lasers in which the extremely intense laser pulse produces shock wave-like vibrations upon impact with the viral particle. We present data which support that the inactivation mechanism for non-enveloped, icosahedral viruses is the impulsive stimulated Raman scattering process. Real-time PCR experiments show that, within the amplicon size of 273 bp tested, there is no damage on the genome of MNV-1 caused by the USP laser irradiation. Conclusion We conclude that our model non-enveloped virus, MNV-1, is inactivated by the ISRS process. These studies provide fundamental knowledge on photon-virus interactions on femtosecond time scales. From the analysis of the transmission electron microscope (TEM) images of viral particles before and after USP laser irradiation, the locations of weak structural links on the capsid of MNV-1 were revealed. This important information will greatly aid our understanding of the structure of non-enveloped, icosahedral viruses. We envision that this non-invasive, efficient viral eradication method will find applications in the disinfection of pharmaceuticals, biologicals and blood products in the near future. PMID:24495489

2014-01-01

123

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

124

Icosahedral Order, Frustration, and the Glass Transition: Evidence from Time-Dependent Nucleation and Supercooled Liquid Structure Studies  

SciTech Connect

One explanation for the glass transition is a geometrical frustration owing to the development of non-space-filling short-range order (icosahedral, tetrahedral). However, experimental demonstrations of this are lacking. Here, the first quantitative measurements of the time-dependent nucleation rate in a Zr59Ti3Cu20Ni8Al10 bulk metallic glass are combined with the first measurements of the evolution of the supercooled liquid structure to near the glass transition temperature to provide strong support for an icosahedral-order-based frustration model for the glass transition in Zr-based glasses.

Shen, Y.T.; Kim, T.H.; Gangopadhyay, A.K.; Kelton, K.F.; (WSU)

2009-06-05

125

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. PMID:19164552

Luque, Daniel; Rivas, Germán; Alfonso, Carlos; Carrascosa, José L.; Rodríguez, José F.; Castón, José R.

2009-01-01

126

The Marine Algal Virus PpV01 Has an Icosahedral Capsid with T=219 Quasisymmetry  

PubMed Central

Phaeocystis pouchetii virus (PpV01) infects and lyses the haptophyte Phaeocystis pouchetii (Hariot) Lagerheim and was first isolated from Norwegian coastal waters. We have used electron cryomicroscopy and three-dimensional image reconstruction methods to examine the native morphology of PpV01 at a resolution of 3 nm. The icosahedral capsid of PpV01 has a maximum diameter of 220 nm and is composed of 2,192 capsomers arranged with T=219 quasisymmetry. One specific capsomer in each asymmetric unit contains a fiber-like protrusion. Density attributed to the presence of a lipid membrane appears just below (inside) the capsid. PpV01 is the largest icosahedral virus whose capsid structure has been determined in three dimensions from images of vitrified samples. Striking similarities in the structures of PpV01 and a number of other large double-stranded DNA viruses are consistent with a growing body of evidence that they share a common evolutionary origin. PMID:15994818

Yan, Xiaodong; Chipman, Paul R.; Castberg, Tonje; Bratbak, Gunnar; Baker, Timothy S.

2005-01-01

127

The Structure of the NTPase That Powers DNA Packaging into Sulfolobus Turreted Icosahedral Virus 2  

PubMed Central

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

2013-01-01

128

Cluster packing geometry for Al-based F-type icosahedral alloys  

E-print Network

This paper presents a new highly stable periodic approximant to the Al-based F-type icosahedral quasicrystals, i-Al-Pd-TM (TM=transition metals). The structure of this intermetallic Al-Pd-Cr-Fe compound is determined ab initio using single-crystal X-ray diffraction, where the space group is identified to be Pa-3 and the lattice constant 40.5 angstrom. The structure is well described as a dense packing of clusters of two kinds, which are known in the literature as the pseudo-Mackay type and the Bergman type clusters. The clusters are centered at the vertices of a canonical cell tiling, in which the parity of each vertex determines the kind of the associated cluster. Adjacent clusters can be markedly interpenetrated, while the structure requires no glue atoms to fill in the gaps between the clusters. It is shown that the crystal can be designated as a 2x2x2 superstructure of the ordinary cubic 3/2 rational approximant. The superlattice ordering is shown to be of a different kind from the P-type superlattice ordering previously reported in i-Al-Pd-Mn. The present results will greatly improve the understanding of atomic structures of F-type icosahedral quasicrystals and their approximants.

Nobuhisa Fujita; Hikari Takano; Akiji Yamamoto; An-Pang Tsai

2013-01-29

129

DIFFRACTION PHYSICS AND OPTICS such that icosahedral nano-clusters occur in fcc crystal. At the same  

E-print Network

DIFFRACTION PHYSICS AND OPTICS C434 such that icosahedral nano-clusters occur in fcc crystal fields in the crystal. Using the diffraction data, we could establish that such fields are able to cause appears in the case of electron diffraction with strained nano-clusters. [1] Chmelevskaya V.S., et. al

Cambridge, University of

130

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

131

Performance Analysis of high-order remap-type advection scheme on icosahedral-hexagonal grid  

NASA Astrophysics Data System (ADS)

A comparative performance analysis on computational cost of second order advection schemes FF-CSLAM (Flux form conservative semi-Lagrangian multi-tracer transport scheme) and it's two simplifications on Icosahedral grid has been presented. Tracer transport is one of the main building blocks in atmospheric models and hence their performance greatly determines the overall performance of the model. FF-CSLAM falls in the category of arbitrary Lagrangian Eulerian (ALE) scheme. It exploits the finite volume formulation and therefore it is inherently conservative. Flux-area through edges are approximated with great circle arcs in an upwind fashion. Bi-quadratic sub-grid scale reconstructions using weighted least-squares method is employed to approximate trace field. Area integrals on the overlapped region of flux-area and static Eulerian meshes are evaluated via line-integrals. A brief description of implementation of FF-CSLAM on icosahedral -hexagonal meshes along with and its numerical accuracy in terms of standard test cases will be presented. A comparative analysis of the computational overhead is necessary to assess the suitability of FF-CSLAM for massively parallel and multi-threading computer architectures in comparison to other advection schemes implemented on icosahedral grids. The main focus of this work is to present the implementation of the shared memory parallelization and to describe the memory access pattern of the numerical scheme. FF-CSLAM is a remap-type advection scheme, thus extra calculation are done in comparison to the other advection schemes. The additional computations are associated with the search required to find the overlap area between the area swept through the edge and the underlining grid. But the experiments shows that the associated computational overhead is minimal for multi-tracer transport. It will be shown that for the Courant Number less than one, FF-CSLAM, the computations are not expensive. Since the grid cells are arranged in rectangular array just like cubed-sphere or lat-lon grids, the schemes computational performance is similar to that of the similar schemes on geodesic grids.

Mittal, Rashmi; Dubey, Sarvesh; Saxena, Vaibhav; Meurdesoif, Yann

2014-05-01

132

Broken Symmetry  

ScienceCinema

- Physics, as we know it, attempts to interpret the diverse natural phenomena as particular manifestations of general laws. This vision of a world ruled by general testable laws is relatively recent in the history of mankind. Basically it was initiated by the Galilean inertial principle. The subsequent rapid development of large-scale physics is certainly tributary to the fact that gravitational and electromagnetic forces are long-range and hence can be perceived directly without the mediation of highly sophisticated technical devices. - The discovery of subatomic structures and of the concomitant weak and strong short-range forces raised the question of how to cope with short-range forces in relativistic quantum field theory. The Fermi theory of weak interactions, formulated in terms of point-like current-current interaction, was well-defined in lowest order perturbation theory and accounted for existing experimental data.However, it was inconsistent in higher orders because of uncontrollable divergent quantum fluctuations. In technical terms, in contradistinction to quantum electrodynamics, the Fermi theorywas not ?renormalizable?. This difficulty could not be solved by smoothing the point-like interaction by a massive, and therefore short-range, charged ?vector? particle exchange: theories with massive charged vector bosons were not renormalizable either. In the early nineteen sixties, there seemed to be insuperable obstacles to formulating a consistent theory with short-range forces mediated by massive vectors. - The breakthrough came from the notion of spontaneous symmetry breaking which arose in the study of phase transitions and was introduced in field theory by Nambu in 1960. - Ferromagnets illustrate the notion in phase transitions. Although no direction is dynamically preferred, the magnetization selects a global orientation. This is a spontaneous broken symmetry(SBS)of rotational invariance. Such continuous SBS imply the existence of ?massless? modes (here spin-waves), which are the ancestors of the NG bosons discussed below. Fluctuations of the order parameter (the magnetization) are described by a ?massive? SBS mode. - In field theory, Nambu showed that broken chiral symmetry from a spontaneous generation of hadron masses induces massless pseudoscalar modes (identified with a massless limit of pion fields). This illustrates a general phenomenon made explicit by Goldstone: massless Nambu-Goldstone (NG) bosons are a necessary concomitant of spontaneously broken continuous symmetries. Massive SBS scalars bosons describe, as in phase transitions, the fluctuations of the SBS order parameters. - In 1964, with Robert Brout, we discovered a mechanism based on SBS by which short range interactions are generated from long range ones. A similar proposal was then made independently by Higgs in a different approach. Qualitatively, our mechanism works as follows. The long range fundamental electromagnetic and gravitational interactions are governed by extended symmetries,called gauge symmetries, which were supposed to guarantee that the elementary field constituents which transmit the forces, photons or gravitons, be massless. We considered a generalization of the electromagnetic ?vector? field, known as Yang-Mills fields, and coupled them to fields which acquire from SBS constant values in the vacuum. These fields pervade space, as did magnetization, but they have no spatial orientation: they are ?scalar?? fields. The vector Yang-Mills fields which interact with the scalar fields become massive and hence the forces they mediate become short ranged. We also showed that the mechanism can survive in absence of elementary scalar fields. - Because of the extended symmetries, the nature of SBS is profoundly altered: the NG fields are absorbed into the massive vector Yang-Mills fields and restore the gauge symmetry. This has a dramatic consequence. To confront precision experiments, the mechanism should be consistent at the quantum mechanical level, or in technical terms, should yield a ?renormalizable? theory. From our analysi

None

2011-10-06

133

Thermal Conductivity and Seebeck Coefficients of Icosahedral Boron Arsenide Films on Silicon Carbide  

SciTech Connect

The thermal conductivity of icosahedral boron arsenide (B{sub 12}As{sub 2}) films grown on (0001) 6H-SiC substrates by chemical vapor deposition was studied by the 3{omega} 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 {micro}V/K and 136 {micro}V/K for samples grown at 1350 C with AsH{sub 3}/B{sub 2}H{sub 6} flow ratio equals to 1:1 and 3:5, respectively.

Y Gong; Y Zhang; M Dudley; Y Zhang; J Edgar; P Heard; M Kuball

2011-12-31

134

Formation of an Icosahedral Quasicrystal in the Mg-Al-Pt System  

NASA Astrophysics Data System (ADS)

A Frank-Kasper-type (FK-type) icosahedral phase (i-phase) has been found to form in the Mg-Al-Pt system of Mg45Al42Pt13 composition. The i-phase is formed by heating an amorphous phase produced by a melt-spinning technique up to 673 K@. We have also investigated the formation of the FK-type i-phase in the ternary Mg-Al-X (X=Co, Ni, Rh and Au) systems and find no trace of the FK-type i-phase. The formation criteria for the FK-type i-phase have been discussed in terms of the electron number in the outer shell, the atomic size and the electronegativity of the third element in Mg-Al-X.

Koshikawa, Naokiyo; Yoda, Shinichi; Edagawa, Keiichi; Takeuchi, Shin

2001-06-01

135

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

136

Terrace-dependent nucleation of small Ag clusters on a five-fold icosahedral quasicrystal surface  

SciTech Connect

Nucleation of Ag islands on the five-fold surface of icosahedral Al-Pd-Mn is influenced strongly by trap sites. Submonolayers of Ag prepared by deposition at 365 K and with a flux of 1 x 10{sup -3} monolayers/s exhibit a variation in Ag island densities across different terraces. Comparisons with previous work and with rate equation analysis indicate that trap sites are not saturated under these experimental conditions and that the difference in island densities is not necessarily due to variation in trap densities. While it could have a number of different origins, our results point to a terrace-dependent value of the effective diffusion barrier for Ag adatoms.

Unal, B.; Evans, J.W.; Lograsso, T.A.; Ross, A.R.; Jenks, C.J.; Thiel, P.A.

2007-07-21

137

Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology.  

PubMed

The largest known DNA viruses infect Acanthamoeba and belong to two markedly different families. The Megaviridae exhibit pseudo-icosahedral virions up to 0.7 ?m in diameter and adenine-thymine (AT)-rich genomes of up to 1.25 Mb encoding a thousand proteins. Like their Mimivirus prototype discovered 10 y ago, they entirely replicate within cytoplasmic virion factories. In contrast, the recently discovered Pandoraviruses exhibit larger amphora-shaped virions 1 ?m in length and guanine-cytosine-rich genomes up to 2.8 Mb long encoding up to 2,500 proteins. Their replication involves the host nucleus. Whereas the Megaviridae share some general features with the previously described icosahedral large DNA viruses, the Pandoraviruses appear unrelated to them. Here we report the discovery of a third type of giant virus combining an even larger pandoravirus-like particle 1.5 ?m in length with a surprisingly smaller 600 kb AT-rich genome, a gene content more similar to Iridoviruses and Marseillevirus, and a fully cytoplasmic replication reminiscent of the Megaviridae. This suggests that pandoravirus-like particles may be associated with a variety of virus families more diverse than previously envisioned. This giant virus, named Pithovirus sibericum, was isolated from a >30,000-y-old radiocarbon-dated sample when we initiated a survey of the virome of Siberian permafrost. The revival of such an ancestral amoeba-infecting virus used as a safe indicator of the possible presence of pathogenic DNA viruses, suggests that the thawing of permafrost either from global warming or industrial exploitation of circumpolar regions might not be exempt from future threats to human or animal health. PMID:24591590

Legendre, Matthieu; Bartoli, Julia; Shmakova, Lyubov; Jeudy, Sandra; Labadie, Karine; Adrait, Annie; Lescot, Magali; Poirot, Olivier; Bertaux, Lionel; Bruley, Christophe; Couté, Yohann; Rivkina, Elizaveta; Abergel, Chantal; Claverie, Jean-Michel

2014-03-18

138

Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology  

PubMed Central

The largest known DNA viruses infect Acanthamoeba and belong to two markedly different families. The Megaviridae exhibit pseudo-icosahedral virions up to 0.7 ?m in diameter and adenine–thymine (AT)-rich genomes of up to 1.25 Mb encoding a thousand proteins. Like their Mimivirus prototype discovered 10 y ago, they entirely replicate within cytoplasmic virion factories. In contrast, the recently discovered Pandoraviruses exhibit larger amphora-shaped virions 1 ?m in length and guanine–cytosine-rich genomes up to 2.8 Mb long encoding up to 2,500 proteins. Their replication involves the host nucleus. Whereas the Megaviridae share some general features with the previously described icosahedral large DNA viruses, the Pandoraviruses appear unrelated to them. Here we report the discovery of a third type of giant virus combining an even larger pandoravirus-like particle 1.5 ?m in length with a surprisingly smaller 600 kb AT-rich genome, a gene content more similar to Iridoviruses and Marseillevirus, and a fully cytoplasmic replication reminiscent of the Megaviridae. This suggests that pandoravirus-like particles may be associated with a variety of virus families more diverse than previously envisioned. This giant virus, named Pithovirus sibericum, was isolated from a >30,000-y-old radiocarbon-dated sample when we initiated a survey of the virome of Siberian permafrost. The revival of such an ancestral amoeba-infecting virus used as a safe indicator of the possible presence of pathogenic DNA viruses, suggests that the thawing of permafrost either from global warming or industrial exploitation of circumpolar regions might not be exempt from future threats to human or animal health. PMID:24591590

Legendre, Matthieu; Bartoli, Julia; Shmakova, Lyubov; Jeudy, Sandra; Labadie, Karine; Adrait, Annie; Lescot, Magali; Poirot, Olivier; Bertaux, Lionel; Bruley, Christophe; Couté, Yohann; Rivkina, Elizaveta; Abergel, Chantal; Claverie, Jean-Michel

2014-01-01

139

Prediction of the behavior for fullerene C20 inside the icosahedral outer shell of C240  

NASA Astrophysics Data System (ADS)

In this work, we study the behavioral regularity of fullerene C20 inside the icosahedral outer shell of fullerene C240. The feature of such two-shell fullerenes is that the internal fullerene will move at low temperatures in a certain way: between the potential wells. The aim of this work is to reveal the regularities for motion of small fullerenes in nanospace of large external icosahedral fullerene, including the identification of the spatial configuration for a multi-well potential of interaction between two objects and prediction of possible movement for the internal object between potential wells. For the fullerene C20 it was found twenty potential wells in the direction of the fifth order axes for icosahedron of fullerene C240 cage, thirty towards in the direction of the middle of the ribs and twenty potential wells towards centers of the faces of the icosahedron. The prediction of possible moving for the internal object between potential wells and the regularities of this movement were made based on the relief analysis of the interaction energy surface of fullerenes. The numerical simulation of C20 motion in the field of C240 was carried out to test the prediction of movement. As results of the experiment, it was found that the fullerene C20 is easy to jump between the potential wells even at low temperatures up to 300K. Molecular dynamics simulations confirmed our conclusions about regularities of C20 movement between potential wells. Thus, one can conclude that the analysis of the topology of the energy surface of van der Waals interaction between the components of nanoparticles gives a true predictive picture of the regularities of the internal molecule behavior. Probably, the phenomenon of fullerene C20 movement in a cell of another fullerene can be used in modern technologies, such as determining a local temperature by increase of jumping velocity.

Glukhova, O. E.; Kolesnikova, A. S.; Slepchenkov, M. M.; Shunaev, V. V.

2014-05-01

140

Symmetry detection through local skewed symmetries  

E-print Network

Symmetry detection through local skewed symmetries Tat-Jen Cham and Roberto Cipolla We explore how global symmetry can be detected prior to segmentation and under noise and occlusion. The definition of local symmetries is extended to affine geometries by consider- ing the tangents and curvatures of local

Cham, Tat Jen

141

Additional evidence from x-ray powder diffraction patterns that icosahedral quasi-crystals of intermetallic compounds are twinned cubic crystals  

SciTech Connect

Analysis of the measured values of Q for the weak peaks (small maxima, usually considered to be background fluctuations, noise) on the x-ray powder diffraction curves for 17 rapidly quenched alloys leads directly to the conclusion that they are formed by an 820-atom or 1012-atom primitive cubic structure that by icosahedral twinning produces the so-called icosahedral quasi-crystals.

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

1988-07-01

142

Additional evidence from x-ray powder diffraction patterns that icosahedral quasi-crystals of intermetallic compounds are twinned cubic crystals.  

PubMed

Analysis of the measured values of Q for the weak peaks (small maxima, usually considered to be background fluctuations, "noise") on the x-ray powder diffraction curves for 17 rapidly quenched alloys leads directly to the conclusion that they are formed by an 820-atom or 1012-atom primitive cubic structure that by icosahedral twinning produces the so-called icosahedral quasi-crystals. PMID:16593948

Pauling, L

1988-07-01

143

First-principles study of the electronic structures of icosahedral TiN (N=13,19,43,55) clusters.  

PubMed

We have studied the electronic structures of icosahedral Ti(N) clusters (N=13, 19, 43, and 55) by using a real-space first-principles cluster method with generalized gradient approximation for exchange-correlation potential. The hexagonal close-packed and fcc close-packed clusters have been studied additionally for comparisons. It is found that the icosahedral structures are the most stable ones except for Ti(43), where fcc close-packed structure is favorable in energy. We present and discuss the variation of bond length, the features of the highest occupied molecular orbitals and the lowest unoccupied molecular orbital, the evolution of density of states, and the magnetic moment in detail. The results are in good agreement with the predictions from the collision-induced dissociation and size-selected anion photoelectron spectroscopy experiments. PMID:15267771

Wang, Shan-Ying; Yu, Jing-Zhi; Mizuseki, Hiroshi; Yan, Jia-An; Kawazoe, Yoshiyuki; Wang, Chong-Yu

2004-05-01

144

Rovibronic species, overall allowed species, and nuclear spin statistical weights for symmetric top molecules. II. Point groups Cnv and Cnh (n <= 6)  

NASA Astrophysics Data System (ADS)

The method described in I [A. Weber, J. Chem. Phys. 73, 1952 (1980); 74, 4754 (1981)] has been used to derive the rovibronic species, overall allowed species, and the nuclear spin statistical weights for symmetric top molecules belonging to the point groups Cnv or Cnh with n?6. Rules are presented by means of which the rovibronic species of Cnv and Cnh molecules are obtained from the results given in I. The overall species and the nuclear spin statistical weights are given in a new set of tables.

Weber, Alfons

1982-04-01

145

Icosahedral AlCuFe quasicrystal at high pressure and temperature and its implications for the stability of icosahedrite.  

PubMed

The first natural-occurring quasicrystal, icosahedrite, was recently discovered in the Khatyrka meteorite, a new CV3 carbonaceous chondrite. Its finding raised fundamental questions regarding the effects of pressure and temperature on the kinetic and thermodynamic stability of the quasicrystal structure relative to possible isochemical crystalline or amorphous phases. Although several studies showed the stability at ambient temperature of synthetic icosahedral AlCuFe up to ~35?GPa, the simultaneous effect of temperature and pressure relevant for the formation of icosahedrite has been never investigated so far. Here we present in situ synchrotron X-ray diffraction experiments on synthetic icosahedral AlCuFe using multianvil device to explore possible temperature-induced phase transformations at pressures of 5?GPa and temperature up to 1773?K. Results show the structural stability of i-AlCuFe phase with a negligible effect of pressure on the volumetric thermal expansion properties. In addition, the structural analysis of the recovered sample excludes the transformation of AlCuFe quasicrystalline phase to possible approximant phases, which is in contrast with previous predictions at ambient pressure. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite. PMID:25070248

Stagno, Vincenzo; Bindi, Luca; Shibazaki, Yuki; Tange, Yoshinori; Higo, Yuji; Mao, H-K; Steinhardt, Paul J; Fei, Yingwei

2014-01-01

146

Snapshot of virus evolution in hypersaline environments from the characterization of a membrane-containing Salisaeta icosahedral phage 1  

PubMed Central

The multitude of archaea and bacteria inhabiting extreme environments has only become evident during the last decades. As viruses apply a significant evolutionary force to their hosts, there is an inherent value in learning about viruses infecting these extremophiles. In this study, we have focused on one such unique virus–host pair isolated from a hypersaline environment: an icosahedral, membrane-containing double-stranded DNA virus—Salisaeta icosahedral phage 1 (SSIP-1) and its halophilic host bacterium Salisaeta sp. SP9-1 closely related to Salisaeta longa. The architectural principles, virion composition, and the proposed functions associated with some of the ORFs of the virus are surprisingly similar to those found in viruses belonging to the PRD1–adenovirus lineage. The virion structure, determined by electron cryomicroscopy, reveals that the bulk of the outer protein capsid is composed of upright standing pseudohexameric capsomers organized on a T = 49 icosahedral lattice. Our results give a comprehensive description of a halophilic virus–host system and shed light on the relatedness of viruses based on their virion architecture. PMID:22509017

Aalto, Antti P.; Bitto, David; Ravantti, Janne J.; Bamford, Dennis H.; Huiskonen, Juha T.; Oksanen, Hanna M.

2012-01-01

147

Symmetry analysis and numerical simulation of mode characteristics for equilateral-polygonal optical microresonators  

NASA Astrophysics Data System (ADS)

Mode characteristics for two-dimensional equilateral-polygonal microresonators are investigated based on symmetry analysis and finite-difference time-domain numerical simulation. The symmetries of the resonators can be described by the point group CNv , accordingly, the confined modes in these resonators can be classified into irreducible representations of the point group CNv . Compared with circular resonators, the modes in equilateral-polygonal resonators have different characteristics due to the break of symmetries, such as the split of double-degenerate modes, high field intensity in the center region, and anomalous traveling-wave modes, which should be considered in the designs of the polygonal resonator microlasers or optical add-drop filters.

Yang, Yue-De; Huang, Yong-Zhen

2007-08-01

148

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

149

Zwitterionic weak-link approach complexes based on anionic icosahedral monocarbaboranes.  

PubMed

The anionic hemilabile phosphinothioether ligand, [1-(Ph2PCH2CH2S)-closo-1-CB11H11 ](-), which is functionalized with an anionic icosahedral monocarbaborane anion, was synthesized in three steps from [HNMe3][closo-CB11H12]. The ligand was used to synthesize a family of zwitterionic Weak-Link Approach (WLA) complexes that contain platinum(II), palladium(II), and rhodium(I). These complexes were characterized using multinuclear NMR spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction analyses. Although the C-bound [closo-CB11H11](-) anion behaves as an electron-withdrawing moiety, hemilabile phosphinothioether ligands that are based on this unit are strongly chelating, as determined via the measurement of the chloride association constant. The chelating strength is comparable to that of hemilabile ligands that are functionalized with the very electron-rich B-bound closo-1,7-C2B10H11 moiety, thus demonstrating the use of charge to influence ligand coordination strength. The anionic Rh(I) WLA complex that is synthesized using this ligand can act as the noncoordinating anion of a regular cationic Rh(I) WLA complex. Thus, an unprecedented type of salt, in which the anion and cation are mutually isostructural and isoelectronic WLA complexes, has been synthesized and characterized crystallographically. PMID:24266387

Kennedy, Robert D; Stern, Charlotte L; Mirkin, Chad A

2013-12-16

150

Proteomic Analysis of Sulfolobus solfataricus During Sulfolobus Turreted Icosahedral Virus Infection  

PubMed Central

Where there is life, there are viruses. The impact of viruses on evolution, global nutrient cycling, and disease has driven research on their cellular and molecular biology. Knowledge exists for a wide range of viruses, however, a major exception are viruses with archaeal hosts. Archaeal virus-host systems are of great interest because they have similarities to both eukaryotic and bacterial systems and often live in extreme environments. Here we report the first proteomics-based experiments on archaeal host response to viral infection. Sulfolobus Turreted Icosahedral Virus (STIV) infection of Sulfolobus solfataricus P2 was studied using 1D and 2D differential gel electrophoresis (DIGE) to measure abundance and redox changes. Cysteine reactivity was measured using novel fluorescent zwitterionic chemical probes that, together with abundance changes, suggest that virus and host are both vying for control of redox status in the cells. Proteins from nearly 50% of the predicted viral open reading frames were found along with a new STIV protein with a homolog in STIV2. This study provides insight to features of viral replication novel to the archaea, makes strong connections to well described mechanisms used by eukaryotic viruses such as ESCRT-III mediated transport, and emphasizes the complementary nature of different omics approaches. PMID:22217245

Maaty, Walid S.; Selvig, Kyla; Ryder, Stephanie; Tarlykov, Pavel; Hilmer, Jonathan K.; Heinemann, Joshua; Steffens, Joseph; Snyder, Jamie C.; Ortmann, Alice C.; Movahed, Navid; Spicka, Kevin; Chetia, Lakshindra; Grieco, Paul A.; Dratz, Edward A.; Douglas, Trevor; Young, Mark J.; Bothner, Brian

2012-01-01

151

A mutant hepatitis B virus core protein mimics inhibitors of icosahedral capsid self-assembly  

PubMed Central

Understanding self-assembly of icosahedral virus capsids is critical to developing assembly-directed antiviral approaches and will also contribute to the development of self-assembling nanostructures. One approach to controlling assembly would be through the use of assembly inhibitors. Here we use Cp149, the assembly domain of the hepatitis B virus capsid protein, together with an assembly-defective mutant, Cp149-Y132A, to examine the limits of the efficacy assembly inhibitors. By itself, Cp149-Y132A will not form capsids. However, Cp-Y132A will co-assemble with wildtype protein based on light scattering and size exclusion chromatography. The resulting capsids appear indistinguishable from normal capsids. However, co-assembled capsids are more fragile, with disassembly observed by chromatography under mildly destabilizing conditions. The relative persistence of capsids assembled under conditions where association energy is weak compared to the fragility of those where association is strong suggests a mechanism of “thermodynamic editing” that allows replacement of defective proteins in a weakly associated complex. There is fine line between weak assembly, where assembly-defective protein is edited from a growing capsid, and relatively strong assembly, where assembly defective subunits may dramatically compromise virus stability. Thus, attempts to control virus self-assembly (with small molecules or defective proteins) must take into account the competing process of thermodynamic editing. PMID:19196007

Bourne, Christina R.; Katen, Sarah P.; Fultz, Matthew J.; Packianathan, Charles; Zlotnick, Adam

2009-01-01

152

Atomistic modeling of the low-frequency mechanical modes and Raman spectra of icosahedral virus capsids  

NASA Astrophysics Data System (ADS)

We describe a technique for calculating the low-frequency mechanical modes and frequencies of a large symmetric biological molecule where the eigenvectors of the Hessian matrix are determined with full atomic detail. The method, which follows order N methods used in electronic structure theory, determines the subset of lowest-frequency modes while using group theory to reduce the complexity of the problem. We apply the method to three icosahedral viruses of various T numbers and sizes; the human viruses polio and hepatitis B, and the cowpea chlorotic mottle virus, a plant virus. From the normal-mode eigenvectors, we use a bond polarizability model to predict a low-frequency Raman scattering profile for the viruses. The full atomic detail in the displacement patterns combined with an empirical potential-energy model allows a comparison of the fully atomic normal modes with elastic network models and normal-mode analysis with only dihedral degrees of freedom. We find that coarse-graining normal-mode analysis (particularly the elastic network model) can predict the displacement patterns for the first few (˜10) low-frequency modes that are global and cooperative.

Dykeman, Eric C.; Sankey, Otto F.

2010-02-01

153

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

NASA Astrophysics Data System (ADS)

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 Yb4f -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 Yb5d band with the Ag5p and In5p 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.; Cui, C.; Shimoda, M.; McGrath, R.; Tsai, A. P.; Ishii, Y.

2010-03-01

154

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

155

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  

Microsoft Academic Search

A unified structure theory of icosahedral quasicrystals, combining the twinned-cubic-crystal theory and the Penrose-tilling-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.

Linus Pauling

1988-01-01

156

Site symmetry of surface adsorbed molecules  

NASA Astrophysics Data System (ADS)

A procedure for determining the allowed local site symmetry groups S for surface adsorbed molecules is presented. An analogy can be drawn between the perturbing field experienced by a matrix isolated molecule in a three-dimensional crystal and that experienced by a molecule adsorbed on a surface. In the former case the field has the symmetry of the host lattice site whereas in the latter case the field has the symmetry of the adsite. If the surface is viewed as a homogeneous two-dimensional plane, then the symmetry of the adsite is described by the group G = C?v. If the surface cannot be viewed as an unstructured homogeneous plane so that the perturbing field experienced by the adsorbed molecule must be considered on a microscopic level, then the adsite symmetry will be described by the group appropriate for the substrate atoms. This can only be one of the groups G = Cn or G = Cnv. The symmetry operations of the local site symmetry group S consist of an operation in the molecular point group M applied to the molecule combined with an operation in G applied to the substrate. A mapping of the operations in M and G to operations in their isomorphous Longuet-Higgins groups allows the operations to be identified as permutation P or permutation-inversion P operations. The operations in S are restricted to be combinations of P operations in M with P operations in G and P operations in M with P operations in G. An adsorbed molecule having M = D3h symmetry is used as an example to demonstrate the procedure for determining S. The local site symmetry group of the adsorbed molecule is, in general, different for the homogeneous surface approximation as opposed to the microscopic surface approximation. An attempt is made to apply predicted spectroscopic selection rules to adsorbed pyridine and ethylene. Several factors which complicate the interpretation of Raman spectra of molecules adsorbed on metal surfaces are discussed, one of these being depolarization effects due to rough surfaces.

Nichols, Henry; Hexter, Robert M.

1981-09-01

157

Lattice Regularization and Symmetries  

E-print Network

Finding the relation between the symmetry transformations in the continuum and on the lattice might be a nontrivial task as illustrated by the history of chiral symmetry. Lattice actions induced by a renormalization group procedure inherit all symmetries of the continuum theory. We give a general procedure which gives the corresponding symmetry transformations on the lattice.

Peter Hasenfratz; Ferenc Niedermayer; Reto von Allmen

2006-07-01

158

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

159

Defects in Mg-Zn-Y-Nd Alloys with Icosahedral Phase  

NASA Astrophysics Data System (ADS)

Recently it was reported that icosahedral phase (I-phase) with quasicrystalline structure is formed in some lightweight Mg alloys. It was found that Mg alloys containing I-phase exhibit improved mechanical properties which make them attractive for industrial applications. This work presents microstructure investigations and defect studies of squeeze cast Mg-Y-Nd-Zr (WE43) alloy with addition of 14 wt.% and 26 wt.% Zn. For comparison WE43 alloy without any Zn was investigated as well. Presence of the quasicrystalline I-phase was detected by electron diffraction and X-ray diffraction in both WE43 alloys modified by Zn addition. On the other hand, WE43 without Zn does not contain any I-phase. Mechanical properties of as-cast alloys were examined by Vickers microhardness (HV) testing. It was found that presence of I-phase leads to a significant hardening. Defects in as-cast alloys were investigated by positron lifetime (LT) spectroscopy combined with coincidence Doppler broadening (CDB). Reference sample WE43 alloy without Zn exhibits a single-component LT spectrum with lifetime of ? 224 ps which is close to the Mg bulk lifetime. On the other hand, vacancy-like defects characterized by positron lifetime of ? 300 ps were found in WE43 alloys modified by Zn addition. CDB investigations revealed that chemical environment of these defects is enriched with Zn and Y. Hence, our results indicate the existence of vacancy-like defects connected with the I-phase. We suggest that these defects are located at the interfaces between the I-phase and the Mg-matrix.

Vl?ek, M.; ?ížek, J.; Smola, B.; Stulíková, I.; Procházka, I.; Kužel, R.; Jäger, A.; Lej?ek, P.

160

THOR-ICO: a General Circulation Model for Exoplanets on an Icosahedral Grid  

NASA Astrophysics Data System (ADS)

The study of extrasolar planets has become important since the discovery of a large number of these astronomical objects. The diversity of planetary characteristics observed raises questions about the variety of climates. The influence of the astronomical and planetary bulk parameters in driving the atmospheric circulations continues to be poorly understood. In the solar system the results from planetary spacecraft missions have demonstrated how different the planetary climate and atmospheric circulations can be. The study of exoplanets is going to require a study of a far greater range of physical and orbital parameters than the ones that characterise our neighbour planets (in the solar system). For this reason the study of exoplanets will involve an even greater diversity of circulation and climate regimes. We are developing a dedicated General Circulation Model (GCM) for extrasolar planets called "Exoclimes Simulation Platform". This model will solve the complex physical and dynamical equations that include fundamental principles of atmospheric fluid dynamics and various idealisations of, for example, radiative transfer [1] and dry or moist convection. The interpretation and analysis of the results from this complex model will help us to have a better understanding on the diversity of climates and atmospheric circulations. Here we present the first results of our recent scheme which represents the fluid dynamical phenomena in the atmosphere. This new code solves the atmospheric fluid equations in a rotating sphere (fully compressible - elastic - nonhydrostatic system) using an icosahedral grid. The grid is also modified to improve the uniformity of the grid point distribution applying a method called spring dynamics [2]. The results shown include 3D experiments of gravity and acustic waves, Held-Suarez test case [3] and an idealized hot-Jupiter case.

Mendonca, J.; Heng, K.; Grimm, S.

2014-04-01

161

Precipitation of icosahedral quasicrystalline phase in Hf65Al7.5Ni10Cu12.5Pd5 metallic glass  

NASA Astrophysics Data System (ADS)

An icosahedral quasicrystalline phase was found in a Hf65Al7.5Ni10Cu12.5Pd5 metallic glass annealed in the supercooled liquid region. Upon annealing at high temperature, the quasicrystalline phase was found to decompose to regular crystalline phases, indicating that it is a metastable phase. The present alloy was compared with the previously reported Zr- and Ti-based alloys with the formation of icosahedral quasicrystalline phases. Hf, Zr, and Ti belong to the same 4A column in the element periodical table. Based on the above comparison, conditions in terms of atomic radius and alloy composition which favor the formation of icosahedral quasicrystalline phase in 4A element based alloys, were suggested.

Li, Chunfei; Saida, Junji; Matsushita, Mitsuhide; Inoue, Akihisa

2000-07-01

162

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

163

Symmetry Breaking NICTA and UNSW  

E-print Network

Symmetry Breaking Toby Walsh NICTA and UNSW #12;Outline · What · What is symmetry? · Why · Why is symmetry a problem? · How · How do we deal with symmetry? #12;Apology · Symmetry in constraint programming workshop, Nantes 2006 · 1st International Symmetry Conference, Edinburgh 2007 #12;Symmetry · Within objects

Walsh, Toby

164

Thermal Rectification in Bulk Material Through Unusual Behavior of Electron Thermal Conductivity of Al-Cu-Fe Icosahedral Quasicrystal  

NASA Astrophysics Data System (ADS)

In this study, a new thermal rectifier working at high temperatures above 300 K was developed using Al61.5Cu26.5Fe12 icosahedral quasicrystal and Ag2Te. The thermal conductivity of Al61.5Cu26.5Fe12 increased drastically with temperature and, at 1000 K, reached a value nine times larger than that at 300 K. The thermal conductivity of Ag2Te showed a sudden decrease at around 400 K, and the thermal conductivity at 423 K became 60% smaller than that at 300 K. By making a composite consisting of Al61.5Cu26.5Fe12 icosahedral quasicrystal and Ag2Te, we succeeded in obtaining a large thermal rectification ratio (TRR) of |J large|/|J small| = 1.63 using two heat reservoirs maintained at T H = 543 K and T L = 300 K. The obtained TRR value is the largest among those ever reported for bulk thermal rectifiers.

Nakayama, Ryu-suke; Takeuchi, Tsunehiro

2014-05-01

165

Thermal Rectification in Bulk Material Through Unusual Behavior of Electron Thermal Conductivity of Al-Cu-Fe Icosahedral Quasicrystal  

NASA Astrophysics Data System (ADS)

In this study, a new thermal rectifier working at high temperatures above 300 K was developed using Al61.5Cu26.5Fe12 icosahedral quasicrystal and Ag2Te. The thermal conductivity of Al61.5Cu26.5Fe12 increased drastically with temperature and, at 1000 K, reached a value nine times larger than that at 300 K. The thermal conductivity of Ag2Te showed a sudden decrease at around 400 K, and the thermal conductivity at 423 K became 60% smaller than that at 300 K. By making a composite consisting of Al61.5Cu26.5Fe12 icosahedral quasicrystal and Ag2Te, we succeeded in obtaining a large thermal rectification ratio (TRR) of | J large|/| J small| = 1.63 using two heat reservoirs maintained at T H = 543 K and T L = 300 K. The obtained TRR value is the largest among those ever reported for bulk thermal rectifiers.

Nakayama, Ryu-suke; Takeuchi, Tsunehiro

2015-01-01

166

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

167

Structure of icosahedral quasicrystals and density-matrix functional theory for correlation effects  

NASA Astrophysics Data System (ADS)

In the first part of this work, the atomic and electronic structure as well as the energetics of the icosahedral TiZrNi quasicrystal and the 1/1 approximant W-TiZrNi were determined. An atomic decoration model for the quasicrystal was developed invoking similarities to the structure of the 1/1 approximant. The structure of the quasicrystal was refined using a combined approach of diffraction refinement and ab initio calculations. The ternary ground state phase diagram was calculated using density-functional calculations. It was found that the TiZrNi quasicrystal is lower in energy than the competing phases indicating that it is a ground state quasicrystal. The electronic density of states of the quasicrystals shows a pseudogap. The hydrogen site energy distribution of the approximant was calculated and it was shown that a determination of the distribution by chemical potential measurements is impossible due to its complexity and the strong temperature and concentration dependent hydrogen-hydrogen interactions. In the second part of this work a density-matrix functional for isolated impurities was developed. The density-matrix functional for the electron interaction energy, was based on two theorems proved in this work. It was shown that the second-moment approximation yields the exact ground state for a dimer molecule with arbitrary on-site and inter-site Coulomb interactions. The second-moment approximation is implemented as a variational method. By comparison to results from exact diagonalization and the Hartree-Fock method it was shown that the functional was accurate in the case of isolated impurities. The combined effect of disorder and electron interactions for the model of an Anderson impurity in a random alloy were investigated and unexpected crossover behavior in the effects of disorder and electron interactions on the spin fluctuations was found. As a first application of the second-moment approximation, the electronic structure of dangling-bond defects in amorphous silicon was studied. In the second-moment approximation the splitting of the defect state in the energy gap is smaller than expected from Hartree-Fock calculations and approaches a finite limit of 0.55 eV for large values of the Coulomb repulsion. In agreement with experimental results and spin-polarized density functional calculations, it was found that the spin of the defect state is strongly localized on the dangling bond orbital while the charge is mostly delocalized.

Hennig, Richard Georg

168

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

169

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

170

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

171

Symmetries in physics  

E-print Network

The concept of symmetries in physics is briefly reviewed. In the first part of these lecture notes, some of the basic mathematical tools needed for the understanding of symmetries in nature are presented, namely group theory, Lie groups and Lie algebras, and Noether's theorem. In the second part, some applications of symmetries in physics are discussed, ranging from isospin and flavor symmetry to more recent developments involving the interacting boson model and its extension to supersymmetries in nuclear physics.

Roelof Bijker

2005-09-02

172

Neutrinos and Symmetries  

E-print Network

Three facets of symmetries in neutrino physics are briefly reviewed: i) The SO(5) symmetry of the neutrino mass and and its connection to the see-saw mechanism; ii) Flavor SU(N) symmetries of dense, self-interacting neutrino gases in astrophysical settings; iii) The neutrino mixing angle theta13 and possible CP-violation in the neutrino sector.

A. B. Balantekin

2009-10-09

173

Symmetry Breaking Toby Walsh #  

E-print Network

Symmetry Breaking Toby Walsh # National ICT Australia and School of CSE, University of New South Wales, Sydney, Australia, tw@cse.unsw.edu.au Symmetry occurs in many problems in aritifical intelligence be able to swap them around without changing the performance of the computer. Symmetries come in many di

Walsh, Toby

174

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

175

Electrochemically shape-controlled synthesis in deep eutectic solvents: triambic icosahedral platinum nanocrystals with high-index facets and their enhanced catalytic activity.  

PubMed

Pt triambic icosahedral nanocrystals (TIH NCs) enclosed by {771} high-index facets were successfully synthesized electrochemically, for the first time, in ChCl-urea based deep eutectic solvents, and exhibited higher electrocatalytic activity and stability towards ethanol electrooxidation than a commercial Pt black catalyst. PMID:24084858

Wei, Lu; Zhou, Zhi-You; Chen, Sheng-Pei; Xu, Chang-Deng; Su, Dangsheng; Schuster, Manfred Erwin; Sun, Shi-Gang

2013-12-11

176

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

177

Symmetry broken and restored coupled-cluster theory: I. Rotational symmetry and angular momentum  

NASA Astrophysics Data System (ADS)

We extend coupled-cluster (CC) theory performed on top of a Slater determinant breaking rotational symmetry to allow for the exact restoration of the angular momentum at any truncation order. The main objective relates to the description of near-degenerate finite quantum systems with an open-shell character. As such, the newly developed many-body formalism offers a wealth of potential applications and further extensions dedicated to the ab initio description of, e.g., doubly open-shell atomic nuclei and molecule dissociation. The formalism, which encompasses both single-reference CC theory and projected Hartree–Fock theory as particular cases, permits the computation of usual sets of connected diagrams while consistently incorporating static correlations through the highly non-perturbative restoration of rotational symmetry. Interestingly, the yrast spectroscopy of the system, i.e. the lowest energy associated with each angular momentum, is accessed within a single calculation. A key difficulty presently overcome relates to the necessity to handle generalized energy and norm kernels for which naturally terminating CC expansions could be eventually obtained. The present work focuses on SU(2) but can be extended to any (locally) compact Lie group and to discrete groups, such as most point groups. In particular, the formalism will be soon generalized to U(1) symmetry associated with particle number conservation. This is relevant to Bogoliubov CC theory that was recently applied to singly open-shell nuclei.

Duguet, T.

2015-02-01

178

Symmetry broken and restored coupled-cluster theory I. Rotational symmetry and angular momentum  

E-print Network

We extend coupled-cluster theory performed on top of a Slater determinant breaking rotational symmetry to allow for the exact restoration of the angular momentum at any truncation order. The main objective relates to the description of near-degenerate finite quantum systems with an open-shell character. As such, the newly developed many-body formalism offers a wealth of potential applications and further extensions dedicated to the ab initio description of, e.g., doubly open-shell atomic nuclei and molecule dissociation. The formalism, which encompasses both single-reference coupled cluster theory and projected Hartree-Fock theory as particular cases, permits the computation of usual sets of connected diagrams while consistently incorporating static correlations through the highly non-perturbative restoration of rotational symmetry. Interestingly, the yrast spectroscopy of the system, i.e. the lowest energy associated with each angular momentum, is accessed within a single calculation. A key difficulty presently overcome relates to the necessity to handle generalized energy {\\it and} norm kernels for which naturally terminating coupled-cluster expansions could be eventually obtained. The present work focuses on $SU(2)$ but can be extended to any (locally) compact Lie group and to discrete groups, such as most point groups. In particular, the formalism will be soon generalized to $U(1)$ symmetry associated with particle number conservation. This is relevant to Bogoliubov coupled cluster theory that was recently formulated and applied to singly open-shell nuclei.

T. Duguet

2014-11-03

179

Crystalline and quasicrystalline allotropes of Pb formed on the fivefold surface of icosahedral Ag-In-Yb  

SciTech Connect

Crystalline and quasicrystalline allotropes of Pb are formed by evaporation on the fivefold surface of the icosahedral (i) Ag-In-Yb quasicrystal under ultra-high vacuum. Lead grows in three dimensional quasicrystalline order and subsequently forms fivefold-twinned islands with the fcc(111) surface orientation atop of the quasicrystalline Pb. The islands exhibit specific heights (magic heights), possibly due to the confinement of electrons in the islands. We also study the adsorption behavior of C{sub 60} on the two allotropes of Pb. Scanning tunneling microcopy reveals that a high corrugation of the quasicrystalline Pb limits the diffusion of the C{sub 60} molecules and thus produces a disordered film, similar to adsorption behavior of the same molecules on the clean substrate surface. However, the sticking coefficient of C{sub 60} molecules atop the Pb islands approaches zero, regardless of the overall C{sub 60} coverage.

Sharma, H. R., E-mail: H.R.Sharma@liv.ac.uk; Smerdon, J. A.; Nugent, P. J.; Ribeiro, A.; McGrath, R. [Surface Science Research Centre and Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom)] [Surface Science Research Centre and Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom); McLeod, I.; Dhanak, V. R. [Department of Physics and the Stephenson Institute for Renewable Energy, The University of Liverpool, Liverpool L69 3BX (United Kingdom)] [Department of Physics and the Stephenson Institute for Renewable Energy, The University of Liverpool, Liverpool L69 3BX (United Kingdom); Shimoda, M. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)] [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Tsai, A. P. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan) [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan)

2014-05-07

180

Explicit Electroweak symmetry breaking?  

E-print Network

We hypothesise that all electroweak symmetry breaking terms such as fermion masses and the W and Z gauge boson masses arise radiatively from just one explicit symmetry breaking term in the Lagrangian. Our hypothesis is motivated by the lack of experimental support and the lack of predictivity of the standard symmetry breaking scenario. We construct a simple model which illustrates our ideas. We also discuss the possible importance of scale invariance.

R. Foot; Tran Anh Tuan

1994-02-07

181

Detection of symmetry and anti-symmetry.  

PubMed

To assess the role of second-order channels in symmetry perception we measured the effects of check size, spatial frequency content, eccentricity and grey scale range on the detection of symmetrical and anti-symmetrical patterns. Thresholds for symmetrical stimuli were only moderately affected by these manipulations. Anti-symmetrical stimuli composed of large black and white checks elicited low thresholds. However, anti-symmetry became essentially undetectable at small check sizes. Removing low frequencies from large-check-size, anti-symmetrical stimuli had little effect on thresholds whereas removing high frequencies had a pronounced effect. Moving the stimuli from fixation to 8 degrees eccentricity caused a dramatic increase in thresholds for anti-symmetrical stimuli but not symmetrical stimuli. When the grey scale range was increased anti-symmetry was undetectable at any check size whereas symmetry was easily seen at all. We argue that these results and others in the literature suggest that anti-symmetry is only detected under conditions favourable to selective attention. PMID:15845246

Mancini, Sandra; Sally, Sharon L; Gurnsey, Rick

2005-07-01

182

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. 

Sekhar Chivukula

2010-01-08

183

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; David L. Dill

1996-01-01

184

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

185

QFT, Antimatter, and Symmetry  

E-print Network

A systematic analysis is made of the relations between the symmetries of a classical field and the symmetries of the one-particle quantum system that results from quantizing that field in regimes where interactions are weak. The results are applied to gain a greater insight into the phenomenon of antimatter.

David Wallace

2009-07-03

186

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

187

Tuning NIF drive symmetry with symmetry capsules  

Microsoft Academic Search

Symmetry capsules or ‘symcaps’ are inertial-fusion capsules that resemble ignition capsules but lack cryogenic fuel. The shape of an imploded symcap, as revealed by images of its x-ray emission near stagnation, contains information about the degree of radiation drive asymmetry that drove its implosion. We have carried out many numerical studies of how symcaps perform, tested their response to variations

N M Hoffman; D C Wilson; M J Edwards; D H Kalantar; G A Kyrala; S R Goldman; S V Weber; N Izumi; D A Callahan; N Meezan; N D Delamater; I L Tregillis; M J Schmitt; P A Bradley; A Seifter; O S Jones; J L Milovitch; C A Thomas

2008-01-01

188

The quasicrystal–crystal interface between icosahedral Al–Pd–Mn and deposited Co: Evidence for the affinity of the quasicrystal structure to the CsCl structure  

Microsoft Academic Search

We have evaporated Co on the pentagonal surface of an icosahedral Al–Pd–Mn quasicrystal kept at room temperature. For submonolayer Co deposits, five AlCo domains are formed exposing their (110) faces parallel to the surface and rotated by 72° with respect to each other. The orientational relationship between these domains and the substrate is determined by the optimum matching of the

Y. Weisskopf; S. Burkardt; M. Erbudak; J.-N. Longchamp

2007-01-01

189

Scanning tunneling microscopy studies of fivefold surfaces of icosahedral aluminum-palladium-manganese quasicrystals and of thin silver films on those surfaces  

Microsoft Academic Search

Quasicrystals are non-periodic but well-ordered solids. Their unusual atomic structures foster peculiar surface properties such as low friction and enhanced oxidation resistance. This is well established at least for aluminum-rich icosahedral (i) quasicrystals. It is also very well known that sputter-annealed surfaces of i-Al-Pd-Mn possess step-terrace morphology even though a network of Bergman and Mackay clusters defines its bulk structure.

Baris Unal

2008-01-01

190

Low Temperature Heat Capacity of the Quasicrystalline Icosahedral ALUMINUM(80)MANGANESE(20) and Decagonal ALUMINUM(78)MANGANESE(22) Alloys.  

NASA Astrophysics Data System (ADS)

We have developed an extension of the square-wave excitation (SWEX) method for heat capacity measurement. This method ("ripple" method) operates in the limit where the period of the heat excitation is smaller than the thermal relaxation time of the calorimeter-sample system. In this limit it was found that the thermal ripple induced by the heat is inversely proportional to the heat capacity. This technique allows also real time measurement as in the conventional ac-method, but using the SWEX instrumentation. The ripple method was demonstrated by measuring the heat capacity of strained Al near {rm T_{c }} (=1.194 K). A broadening in {rm T_{c}} (~eq 29. mK) due to the existence of strain was observed. The ripple method was also used to study the low temperature heat capacity of the quasicrystalline icosahedral {rm Al_{80}Mn} _{20} and decagonal { rm Al_{78}Mn}_{22 } alloys. The measurements were carried out for 0.5 <= T <= 5. K and for applied magnetic field up to 12.7 kOe. Both samples indicated no enhancement in linear specific heat associated with density of conduction electron states at the Fermi energy. Both samples also had a cubic-term well in excess of the lattice contribution of comparable crystalline phases. The excess in the {rm T} ^3-term was interpreted as originating from a small number of low energy modes similar to what is seen in metallic glasses. In addition, a bump-shaped peak in the specific heat was seen in the vicinity of 2K. The low temperature side of this peak indicated a minimum energy level spacing of about 3.6K in both materials. Part of this specific heat is of magnetic origin in the icosahedral phase material, but all of the peak in the decagonal phase was non-magnetic. This peak could be fit to the Einstein model for the specific heat with an energy level spacing of 3.7K (3.6K) and with a total of N = 3.9 times 10 ^{-3} {rm N _{o}} (3.2 times 10^{-3} {rm N_{o}}) modes ({ rm N_{o}} is Avogadro's number) for the I-{rm Al_{80 }Mn}_{20} (T- {rm Al_{78}Mn}_ {22}) sample. The magnetic properties indicated a spin-glass like behavior in both samples.

Machado, Fernando Luis De Araujo

191

Spin-Orbit-Free Topological Insulators without Time-Reversal Symmetry  

NASA Astrophysics Data System (ADS)

We explore the 32 crystallographic point groups and identify topological phases of matter with robust surface modes. For n=3,4, and 6 of the Cnv groups, we find the first-known 3D topological insulators without spin-orbit coupling, and with surface modes that are protected only by point groups; i.e., the relevant symmetries are purely crystalline and do not include time reversal. To describe these Cnv systems, we introduce the notions of (a) a halved mirror chirality, an integer invariant which characterizes half-mirror-planes in the 3D Brillouin zone, and (b) a bent Chern number, the traditional Thouless-Kohmoto-Nightingale-den Nijs invariant generalized to bent 2D manifolds. We find that a Weyl semimetallic phase intermediates two gapped phases with distinct halved chiralities. In addition to electronic systems without spin-orbit coupling, our findings also apply to intrinsically spinless systems such as photonic crystals and ultracold atoms.

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

2014-09-01

192

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

193

String Theory Symmetries  

E-print Network

A brief review of the status of duality symmetries in string theory is presented. The evidence is accumulating rapidly that an enormous group of duality symmetries, including perturbative T dualities and non-perturbative S-dualities, underlies string theory. It is my hope that an understanding of these symmetries will suggest the right way to formulate non-perturbative string theory. Whether or not this hope is realized, it has already been demonstrated that this line of inquiry leads to powerful new tools for understanding gauge theories and new evidence for the uniqueness of string theory, as well as deep mathematical results.

John H. Schwarz

1995-03-20

194

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

195

Dynamical symmetries for fermions  

SciTech Connect

An introduction is given to the Fermion Dynamical Symmetry Model (FDSM). The analytical symmetry limits of the model are then applied to the calculation of physical quantities such as ground-state masses and B(E{sub 2}) values in heavy nuclei. These comparisons with data provide strong support for a new principle of collective motion, the Dynamical Pauli Effect, and suggest that dynamical symmetries which properly account for the pauli principle are much more persistent in nuclear structure than the corresponding boson symmetries. Finally, we present an assessment of criticisms which have been voiced concerning the FDSM, and a discussion of new phenomena and exotic spectroscopy'' which may be suggested by the model. 14 refs., 8 figs., 4 tabs.

Guidry, M.

1989-01-01

196

Symmetry Restoration By Acceleration  

E-print Network

The restoration of spontaneous symmetry breaking for a scalar field theory for an accelerated observer is discussed by the one-loop effective potential calculation and by considering the effective potential for composite operators. Above a critical acceleration, corresponding to the critical restoration temperature,T_c, for a Minkowski observer by Unruh relation, i.e. a_c/2\\pi=T_c, the symmetry is restored. This result confirms other recent calculations in effective field theories that symmetry restoration can occur for an observer with an acceleration larger than some critical value. From the physical point of view, a constant acceleration is locally equivalent to a gravitational field and the critical acceleration to restore the spontaneous symmetry breaking corresponds to a huge gravitational effect which, therefore, prevents boson condensation.

P. Castorina; M. Finocchiaro

2012-07-16

197

Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap  

NASA Astrophysics Data System (ADS)

We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above EF provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.

Maniraj, M.; Rai, Abhishek; Barman, S. R.; Kraj?í, M.; Schlagel, D. L.; Lograsso, T. A.; Horn, K.

2014-09-01

198

African swine fever virus protein p17 is essential for the progression of viral membrane precursors toward icosahedral intermediates.  

PubMed

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. PMID:20504920

Suárez, Cristina; Gutiérrez-Berzal, Javier; Andrés, Germán; Salas, María L; Rodríguez, Javier M

2010-08-01

199

Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap  

SciTech Connect

We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i?Al?Pd?Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i?Al?Pd?Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above EF provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.

Maniraj, M [UGC-DAE Confortium for Scientific Research; Rai, Abhishek [UGC-DAE Confortium for Scientific Research; Barman, S R [UGC-DAE Confortium for Scientific Research; Krajci, M [Slovak Academy of Sciences; Schlagel, Deborah L [Ames Laboratory; Lograsso, Thomas A [Ames Laboratory; Horn, K [Fritz-Haber-Institut der Max-Planck-Gesellschaft

2014-09-01

200

Heavy-quark symmetry  

Microsoft Academic Search

We review the current status of heavy-quark symmetry and its applications to weak decays of hadrons containing a single heavy quark. After an introduction to the underlying physical ideas, we discuss in detail the formalism of the heavy-quark effective theory, including a comprehensive treatment of symmetry breaking corrections. We then illustrate some nonperturbative approaches, which aim at a dynamical, QCD-based

Matthias Neubert

1994-01-01

201

Internal Symmetry Marijn Heule1  

E-print Network

Internal Symmetry Marijn Heule1 and Toby Walsh2 1 Delft University of Technology, The Netherlands studying the internal symmetries within an individual solution of a constraint satisfaction problem [1]. Such inter- nal symmetries can be compared with solution symmetries which map between different solutions

Flener, Pierre

202

Symmetry in Numbers David Marshall  

E-print Network

Symmetry in Numbers David Marshall Monmouth University April 13, 2005 808 -2 3 + 3 -169 54 + 1007 18 + 3 -169 54 - 1007 18 ­ Typeset by FoilTEX ­ #12;Symmetry One of the guiding principles group of symmetries. -Paul Yale, in Geometry and Symmetry 2. Due or just proportion; harmony of parts

Marshall, David

203

Emergence of colour symmetry in free-vibration acoustic resonance of a nonlinear hyperelastic material  

PubMed Central

We investigated free-vibration acoustic resonance (FVAR) of two-dimensional St Venant–Kirchhoff-type hyperelastic materials and revealed the existence and structure of colour symmetry embedded therein. The hyperelastic material is isotropic and frame indifferent and includes geometrical nonlinearity in its constitutive equation. The FVAR state is formulated using the principle of stationary action with a subsidiary condition. Numerical analysis based on the Ritz method revealed the existence of four types of nonlinear FVAR modes associated with the irreducible representations of a linearized system. Projection operation revealed that the FVAR modes can be classified on the basis of a single colour (black or white) and three types of bicolour (black and white) magnetic point groups: , , and . These results demonstrate that colour symmetry naturally arises in the finite amplitude nonlinear FVAR modes, and its vibrational symmetries are explained in terms of magnetic point groups rather than the irreducible representations that have been used for linearized systems. We also predicted a grey colour nonlinear FVAR mode which cannot be derived from a linearized system. PMID:24204182

Tarumi, Ryuichi

2013-01-01

204

Symmetry of composite crystals  

NASA Astrophysics Data System (ADS)

Composite crystals are crystals that consist of two or more subsystems, in first approximation each one having its own three-dimensional periodicity. The symmetry of these subsystems is then characterized by an ordinary space group. Due to their mutual interaction the true structure consists of a collection of incommensurately modulated subsystems. In this paper we derive some general properties for intergrowth structures, using the superspace-group theory as developed by Janner and Janssen [Acta Crystallogr. A36, 408 (1980)]. In particular, the pseudoinverse is defined of the matrices relating the subsystem periodicities to the translation vectors in superspace. This pseudoinverse is then used to reformulate the relations between the structure and symmetry in three-dimensional space and in (3+d)-dimensional superspace. As an extension of the theory, subsystem superspace groups are defined, that characterize the symmetry of the individual, incommen- surately modulated subsystems. The relation between a unified description of the symmetry and an independent description of the subsystems is analyzed in detail, both on the level of the basic structure (translational symmetric subsystems) and on the level of the modulated structure (incommensurately modulated subsystems). The concepts are illustrated by the analysis of the diffraction symmetry of the intergrowth compound Hg3-?AsF6.

van Smaalen, Sander

1991-05-01

205

Symmetry in Multiferroics  

NASA Astrophysics Data System (ADS)

Symmetries govern Nature ubiquitously from the beauty of human faces to the local gauge invariance of quantum field theory. Magnetic order in frustrated magnets can occur without space inversion symmetry. When it relaxes to the magnetically-ordered configuration through exchange-striction, lattice can also loose inversion symmetry, leading to the presence of ferroelectric polarization. In these magnetically-driven ferroelectrics, dielectric properties turn out to be highly susceptible to applied magnetic fields. Both symmetric and antisymmetric exchange coupling can be involved in the exchange-striction. One form of symmetry often broken in Nature is the symmetry between left- and right-handedness. For example, the manner in which light propagates naturally selects one handedness, and is customarily described by a right-handed rule, depicting the relationship among the oscillating electric field, magnetic field and propagation vector of light. Chiral molecules also have a definite handedness, and given the preponderance of chiral molecules, it is not surprising that most complex proteins as well as their constituent amino acids are chiral. What is remarkable however, is that most of naturally occurring amino acids share the same chirality; only left-handedness. Such handedness, or chirality, appears to be a characteristic signature of life. In the multiferroic spinel CoCr2O4, conical magnetic order accompanies ferroelectric polarization as well as ferromagnetic moment. The relevant handedness and chirality in the multiferroic state will be also discussed.

Cheong, Sang-Wook

2008-03-01

206

Crystal Symmetry Algorithms in a High-Throughput Framework for Materials  

NASA Astrophysics Data System (ADS)

The high-throughput framework AFLOW that has been developed and used successfully over the last decade is improved to include fully-integrated software for crystallographic symmetry characterization. The standards used in the symmetry algorithms conform with the conventions and prescriptions given in the International Tables of Crystallography (ITC). A standard cell choice with standard origin is selected, and the space group, point group, Bravais lattice, crystal system, lattice system, and representative symmetry operations are determined. Following the conventions of the ITC, the Wyckoff sites are also determined and their labels and site symmetry are provided. The symmetry code makes no assumptions on the input cell orientation, origin, or reduction and has been integrated in the AFLOW high-throughput framework for materials discovery by adding to the existing code base and making use of existing classes and functions. The software is written in object-oriented C++ for flexibility and reuse. A performance analysis and examination of the algorithms scaling with cell size and symmetry is also reported.

Taylor, Richard

207

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. PMID:16282553

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

2008-01-01

208

Essays on symmetry  

NASA Astrophysics Data System (ADS)

Structures of many different sorts arise in physics, e.g., the concrete structures of material bodies, the structure exemplified by the spatiotemporal configuration of a set of bodies, the structures of more abstract objects like states, state-spaces, laws, and so on. To each structure of any of these types there corresponds a set of transformations which map it onto itself. These are its symmetries. Increasingly ubiquitous in theoretical discussions in physics, the notion of symmetry is also at the root of some time-worn philosophical debates. This dissertation consists of a set of essays on topics drawn from places where the two fields overlap. The first essay is an informal introduction to the mathematical study of symmetry. The second essay defends a famous principle of Pierre Curie which states that the symmetries of a cause are always symmetries of its effect. The third essay takes up the case of reflection in space in the context of a controversy stemming from one of Kant's early arguments for the substantivality of space. The fourth essay is a discussion of the general conditions under which an asymmetry in a phenomenon suggests an asymmetry in the laws which govern it. The case of reflection in time-specifically, the theoretical strategy used in statistical mechanics to subsume the time-asymmetric phenomena of Thermodynamics under the time-symmetric classical dynamical laws-is used to illustrate the general points. The philosophical heart of the thesis lies in its fifth essay. Here a somewhat novel way of conceiving scientific theorizing is articulated, one suggested by the abstract mathematical perspective of symmetry.

Ismael, Jenann Tareq

1997-04-01

209

Understanding the interface of six-shell cuboctahedral and icosahedral palladium clusters on reduced graphene oxide: experimental and theoretical study.  

PubMed

Studies on noble-metal-decorated carbon nanostructures are reported almost on a daily basis, but detailed studies on the nanoscale interactions for well-defined systems are very rare. Here we report a study of reduced graphene oxide (rGOx) homogeneously decorated with palladium (Pd) nanoclusters with well-defined shape and size (2.3 ± 0.3 nm). The rGOx was modified with benzyl mercaptan (BnSH) to improve the interaction with Pd clusters, and N,N-dimethylformamide was used as solvent and capping agent during the decoration process. The resulting Pd nanoparticles anchored to the rGOx-surface exhibit high crystallinity and are fully consistent with six-shell cuboctahedral and icosahedral clusters containing ~600 Pd atoms, where 45% of these are located at the surface. According to X-ray photoelectron spectroscopy analysis, the Pd clusters exhibit an oxidized surface forming a PdO(x) shell. Given the well-defined experimental system, as verified by electron microscopy data and theoretical simulations, we performed ab initio simulations using 10 functionalized graphenes (with vacancies or pyridine, amine, hydroxyl, carboxyl, or epoxy groups) to understand the adsorption process of BnSH, their further role in the Pd cluster formation, and the electronic properties of the graphene-nanoparticle hybrid system. Both the experimental and theoretical results suggest that Pd clusters interact with functionalized graphene by a sulfur bridge while the remaining Pd surface is oxidized. Our study is of significant importance for all work related to anchoring of nanoparticles on nanocarbon-based supports, which are used in a variety of applications. PMID:24758410

Gracia-Espino, Eduardo; Hu, Guangzhi; Shchukarev, Andrey; Wågberg, Thomas

2014-05-01

210

The Force of Symmetry  

NASA Astrophysics Data System (ADS)

The Force of Symmetry gives an elementary introduction to the spectacular interplay among the three great themes of contemporary physics: quantum behavior, relativity, and symmetry. In clear, nontechnical language, it explores many fascinating aspects of modern physics, discussing the nature and interaction of force and matter. All these themes are drawn together toward the end of the book to describe the most successful physics theory in history, the "standard model" of subatomic particles. The book is suitable for undergraduate students in physics and mathematics.

Icke, Vincent

1995-02-01

211

Atkin-Lehner symmetry  

NASA Astrophysics Data System (ADS)

The vanishing of the one-loop string cosmological constant in nontrivial non supersymmetric backgrounds can be understood by viewing the path integral as an inner product of orthogonal wave functions. For special backgrounds the string theory has an extra symmetry, expressed as a transformation on moduli space. When left- and right-moving wave functions transform in different representations of this symmetry the cosmological constant must vanish. Specific examples of the mechanism are given at one loop for theories in two and four dimensions. Various suggestions are made for the higher loop extension of this idea.

Moore, Gregory

212

Characterization of the Archaeal Thermophile Sulfolobus Turreted Icosahedral Virus Validates an Evolutionary Link among Double-Stranded DNA Viruses from All Domains of Life  

PubMed Central

Icosahedral nontailed double-stranded DNA (dsDNA) viruses are present in all three domains of life, leading to speculation about a common viral ancestor that predates the divergence of Eukarya, Bacteria, and Archaea. This suggestion is supported by the shared general architecture of this group of viruses and the common fold of their major capsid protein. However, limited information on the diversity and replication of archaeal viruses, in general, has hampered further analysis. Sulfolobus turreted icosahedral virus (STIV), isolated from a hot spring in Yellowstone National Park, was the first icosahedral virus with an archaeal host to be described. Here we present a detailed characterization of the components forming this unusual virus. Using a proteomics-based approach, we identified nine viral and two host proteins from purified STIV particles. Interestingly, one of the viral proteins originates from a reading frame lacking a consensus start site. The major capsid protein (B345) was found to be glycosylated, implying a strong similarity to proteins from other dsDNA viruses. Sequence analysis and structural predication of virion-associated viral proteins suggest that they may have roles in DNA packaging, penton formation, and protein-protein interaction. The presence of an internal lipid layer containing acidic tetraether lipids has also been confirmed. The previously presented structural models in conjunction with the protein, lipid, and carbohydrate information reported here reveal that STIV is strikingly similar to viruses associated with the Bacteria and Eukarya domains of life, further strengthening the hypothesis for a common ancestor of this group of dsDNA viruses from all domains of life. PMID:16840341

Maaty, Walid S. A.; Ortmann, Alice C.; Dlaki?, Mensur; Schulstad, Katie; Hilmer, Jonathan K.; Liepold, Lars; Weidenheft, Blake; Khayat, Reza; Douglas, Trevor; Young, Mark J.; Bothner, Brian

2006-01-01

213

Plasmon mediated shape and size selective synthesis of icosahedral silver nanoparticles via oxidative etching and their 1-D transformation to pentagonal pins  

NASA Astrophysics Data System (ADS)

A size- and shape-selective synthesis of pentagonally twinned silver icosahedral nanoparticles (AgIhNPs), one of the five platonic solid morphologies, has been developed by integrating three key factors: nuclei templating by copper, photochemical development using violet LED light and chemical oxidative etching. The presence of copper is essential for AgIhNP shape selection via the promotion of icosahedral nuclei in precursor NPs. Violet light (401-410 nm) is crucial to promote plasmonic selection of near-spherical AgIhNPs. Oxidative etching with hydrogen peroxide and photochemical reduction with citrate establishes a red-ox equilibrium for the photochemical selection of AgIhNPs. The addition of chloride ions improves size- and shape-selectivity. Finally, the demonstration of 1-D growth of AgIhNPs to pentagonal pins initiated at AgIhNP pentagonal-twinned defects highlights a universal role of twinned defects for the formation of anisotropic nanoparticles.A size- and shape-selective synthesis of pentagonally twinned silver icosahedral nanoparticles (AgIhNPs), one of the five platonic solid morphologies, has been developed by integrating three key factors: nuclei templating by copper, photochemical development using violet LED light and chemical oxidative etching. The presence of copper is essential for AgIhNP shape selection via the promotion of icosahedral nuclei in precursor NPs. Violet light (401-410 nm) is crucial to promote plasmonic selection of near-spherical AgIhNPs. Oxidative etching with hydrogen peroxide and photochemical reduction with citrate establishes a red-ox equilibrium for the photochemical selection of AgIhNPs. The addition of chloride ions improves size- and shape-selectivity. Finally, the demonstration of 1-D growth of AgIhNPs to pentagonal pins initiated at AgIhNP pentagonal-twinned defects highlights a universal role of twinned defects for the formation of anisotropic nanoparticles. Electronic supplementary information (ESI) available: Additional information on the synthesis series. See DOI: 10.1039/c4nr01477d

Keunen, R.; Cathcart, N.; Kitaev, V.

2014-06-01

214

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

215

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

216

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

217

Symmetry Fold-Overs  

NSDL National Science Digital Library

In this math activity, learners experiment with the concept of symmetry. Learners use mirrors to identify which pictures, letters, and shapes are symmetrical and then complete the missing halves for images. This activity guide contains a material list, sample questions to ask, literary connections, extensions, and alignment to local and national standards.

Children's Museum of Houston

2014-09-19

218

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

219

symmetry in myxobacteria  

E-print Network

in flies, worms, and vertebrates use cell-surface signals such as Notch, Hedgehog and Wnt. Although programs capable of breaking symmetry are also found in bacteria. The view that bacteria are asocial cells program uses two cell­cell signals: first, the diffusible, quorum sensing A-signal that initiates fruiting

Oster, George

220

Associate symmetries: A novel procedure for finding contact symmetries  

NASA Astrophysics Data System (ADS)

A new method for finding contact symmetries is proposed for both ordinary and partial differential equations. Symmetries more general than Lie point are often difficult to find owing to an increased dependency of the infinitesimal functions on differential quantities. As a consequence, the invariant surface condition is often unable to be “split” into a reasonably sized set of determining equations, if at all. The problem of solving such a system of determining equations is here reduced to the problem of finding its own point symmetries and thus subsequent similarity solutions to these equations. These solutions will (in general) correspond to some subset of symmetries of the original differential equations. For this reason, we have termed such symmetries associate symmetries. We use this novel method of associate symmetries to determine new contact symmetries for a non-linear PDE and a second order ODE which could not previously be found using computer algebra packages; such symmetries for the latter are particularly difficult to find. We also consider a differential equation with known contact symmetries in order to illustrate that the associate symmetry procedure may, in some cases, be able to retrieve all such symmetries.

Jefferson, G. F.; Carminati, J.

2014-03-01

221

Gauging without Initial Symmetry  

E-print Network

The gauge principle is at the heart of a good part of fundamental physics: Starting with a group G of so-called rigid symmetries of a functional defined over space-time Sigma, the original functional is extended appropriately by additional Lie(G)-valued 1-form gauge fields so as to lift the symmetry to Maps(Sigma,G). Physically relevant quantities are then to be obtained as the quotient of the solutions to the Euler-Lagrange equations by these gauge symmetries. In this article we show that one can construct a gauge theory for a standard sigma model in arbitrary space-time dimensions where the target metric is not invariant with respect to any rigid symmetry group, but satisfies a much weaker condition: It is sufficient to find a collection of vector fields v_a on the target M satisfying the extended Killing equation v_{a(i;j)}=0 for some connection acting on the index a. For regular foliations this is equivalent to requiring the conormal bundle to the leaves with its induced metric to be invariant under leaf-preserving diffeomorphisms of M, which in turn generalizes Riemannian submersions to which the notion reduces for smooth leaf spaces M/~. The resulting gauge theory has the usual quotient effect with respect to the original ungauged theory: in this way, much more general orbits can be factored out than usually considered. In some cases these are orbits that do not correspond to an initial symmetry, but still can be generated by a finite dimensional Lie group G. Then the presented gauging procedure leads to an ordinary gauge theory with Lie algebra valued 1-form gauge fields, but showing an unconventional transformation law. In general, however, one finds that the notion of an ordinary structural Lie group is too restrictive and should be replaced by the much more general notion of a structural Lie groupoid.

Alexei Kotov; Thomas Strobl

2014-03-31

222

Symmetry in Logos and Hubcaps.  

ERIC Educational Resources Information Center

Described is a way to illustrate cyclic and dihedral groups through symmetry using corporate logos and hubcaps. Examples of the different kinds of symmetry groups are explained in terms of Leonardo's Theorem. (KR)

Gallian, Joseph A.

1990-01-01

223

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

224

SYMMETRY AND HETEROGENEITY IN HIGH  

E-print Network

SYMMETRY AND HETEROGENEITY IN HIGH TEMPERATURE SUPERCONDUCTORS #12;#12;Kluwer Academic Publishers Dordrecht/Boston/London Published in cooperation with NATO Scientific Affairs Division SYMMETRY AND EXCHANGE-LIKE PAIRING SCENARIOS 1 I.1 Symmetry and Higher Superconductivity in the Lower Elements N. W

225

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

226

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

227

Breaking Generator Symmetry George Katsirelos  

E-print Network

Breaking Generator Symmetry George Katsirelos NICTA Sydney, Australia george problematic. One solution is to focus on just sym- metries that generate the symmetry group. Whilst there are special cases where breaking just the symmetries in a generating set is complete, there are also cases

Walsh, Toby

228

Symmetry Energy in Nuclear Surface  

E-print Network

Interplay between the dependence of symmetry energy on density and the variation of nucleonic densities across nuclear surface is discussed. That interplay gives rise to the mass dependence of the symmetry coefficient in an energy formula. Charge symmetry of the nuclear interactions allows to introduce isoscalar and isovector densities that are approximately independent of the magnitude of neutron-proton asymmetry.

Pawel Danielewicz; Jenny Lee

2008-12-25

229

Helical symmetry in linear systems  

SciTech Connect

We investigate properties of solutions of the scalar wave equation and Maxwell's equations on Minkowski space with helical symmetry. Existence of local and global solutions with this symmetry is demonstrated with and without sources. The asymptotic properties of the solutions are analyzed. We show that the Newman-Penrose retarded and advanced scalars exhibit specific symmetries and generalized peeling properties.

Bicak, Jiri [Institute of Theoretical Physics, Faculty of Mathematics Physics, Charles University, Prague (Czech Republic); Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, D-14476 Golm (Germany); Schmidt, Bernd G. [Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, D-14476 Golm (Germany)

2007-11-15

230

Shape evolution of decahedral and icosahedral Ag flags and their intermediates from Ag nanorod seeds in DMF solution in the presence of polyvinylpyrrolidone  

NASA Astrophysics Data System (ADS)

We previously reported that trapezoid, plate-like and mono- or bi-tetrahedral Ag-flag structures are evolved from side facets of Ag-nanorod (NR) seeds when AgNO3 was reduced in N,N-dimethylformamide (DMF) in the presence of polyvinylpyrrolidone (PVP). In this study, we examined what shapes are grown by further growth of bitetrahedral flags based on TEM and SEM observations. For this purpose, we initially studied effects of the reaction temperature, concentrations of PVP, and molecular weights of PVP for the shape evolution of flag types of Ag nanostructures from Ag-NR seeds. Results show that shape and size of flags can be controlled by changing these parameters and reaction times. Under an appropriate experimental condition, we found that decahedral and icosahedral flags and their intermediates having {1 1 1} facets were finally grown by stepwise growth of tetrahedral units, although yield of perfect decahedral and icosahedral flags were low because of occurrence of homogenous nucleation at high AgNO3 concentration.

Tsuji, Masaharu; Nakamura, Nozomi; Tang, Xinling; Uto, Keiko; Matsunaga, Mika

2014-11-01

231

PSEUDOSPIN SYMMETRY IN NUCLEI, SPIN SYMMETRY IN HADRONS  

SciTech Connect

Ginocchio argued that chiral symmetry breaking in QCD is responsible for the relativistic pseudospin symmetry in the Dirac equation, explaining the observed approximate pseudospin symmetry in sizable nuclei. On a much smaller scale, it is known that spin-orbit splittings in hadrons are small. Specifically, new experimental data from CLEO indicate small splittings in D-mesons. For heavy-light mesons we identify a cousin of pseudospin symmetry that suppresses these splittings in the Dirac equation, known as spin symmetry. We suggest an experimental test of the implications of spin symmetry for wave functions in electron-positron annihilation. We investigate how QCD can give rise to two different dynamical symmetries on nuclear and hadronic scales.

P. PAGE; T. GOLDMAN; J. GINOCCHIO

2000-08-01

232

Binary-Symmetry Detection  

NASA Technical Reports Server (NTRS)

Transmission errors for zeros and ones tabulated separately. Binary-symmetry detector employs psuedo-random data pattern used as test message coming through channel. Message then modulo-2 added to locally generated and synchronized version of test data pattern in same manner found in manufactured test sets of today. Binary symmetrical channel shows nearly 50-percent ones to 50-percent zeroes correspondence. Degree of asymmetry represents imbalances due to either modulation, transmission, or demodulation processes of system when perturbed by noise.

Lopez, Hiram

1987-01-01

233

Symmetry in music  

NASA Astrophysics Data System (ADS)

Music and Physics are very close because of the symmetry that appears in music. A periodic wave is what music really is, and there is a field of Physics devoted to waves researching. The different musical scales are the base of all kind of music. This article tries to show how this musical scales are made, how the consonance is the base of many of them and how symmetric they are.

Herrero, O. F.

2010-06-01

234

Invariants of broken discrete symmetries.  

PubMed

The parity and Bloch theorems are generalized to the case of broken global symmetry. Local inversion or translation symmetries in one dimension are shown to yield invariant currents that characterize wave propagation. These currents map the wave function from an arbitrary spatial domain to any symmetry-related domain. Our approach addresses any combination of local symmetries, thus applying, in particular, to acoustic, optical, and matter waves. Nonvanishing values of the invariant currents provide a systematic pathway to the breaking of discrete global symmetries. PMID:25126903

Kalozoumis, P A; Morfonios, C; Diakonos, F K; Schmelcher, P

2014-08-01

235

Invariants of Broken Discrete Symmetries  

NASA Astrophysics Data System (ADS)

The parity and Bloch theorems are generalized to the case of broken global symmetry. Local inversion or translation symmetries in one dimension are shown to yield invariant currents that characterize wave propagation. These currents map the wave function from an arbitrary spatial domain to any symmetry-related domain. Our approach addresses any combination of local symmetries, thus applying, in particular, to acoustic, optical, and matter waves. Nonvanishing values of the invariant currents provide a systematic pathway to the breaking of discrete global symmetries.

Kalozoumis, P. A.; Morfonios, C.; Diakonos, F. K.; Schmelcher, P.

2014-08-01

236

Symmetries in laminated composite plates  

NASA Technical Reports Server (NTRS)

The different types of symmetry exhibited by laminated anisotropic fibrous composite plates are identified and contrasted with the symmetries of isotropic and homogeneous orthotropic plates. The effects of variations in the fiber orientation and the stacking sequence of the layers on the symmetries exhibited by composite plates are discussed. Both the linear and geometrically nonlinear responses of the plates are considered. A simple procedure is presented for exploiting the symmetries in the finite element analysis. Examples are given of square, skew and polygonal plates where use of symmetry concepts can significantly reduce the scope and cost of analysis.

Noor, A. K.

1976-01-01

237

A molecular symmetry analysis of the electronic states and transition dipole moments for molecules with two torsional degrees of freedom.  

PubMed

We present a molecular symmetry analysis of electronic states and transition dipole moments for molecules which undergo large amplitude intramolecular torsions. The method is based on the correlation between the point group of the molecule at highly symmetric configurations and the molecular symmetry group. As an example, we determine the global irreducible representations of the electronic states and transition dipole moments for the quinodimethane derivative 2-[4-(cyclopenta-2,4-dien-1-ylidene)cyclohexa-2,5-dien-1-ylidene]-2H-1,3-dioxole for which two torsional degrees of freedom can be activated upon photo-excitation and construct the resulting symmetry adapted transition dipole functions. PMID:25681914

Obaid, R; Leibscher, M

2015-02-14

238

Geometrodynamics and Lorentz symmetry  

NASA Astrophysics Data System (ADS)

We study the dynamics of gauge theory and general relativity using fields of local observers, thus maintaining local Lorentz symmetry despite a space/time splitting of fields. We start with Yang-Mills theory, where observer fields are defined as normalized future-timelike vector fields. We then define observers without a fixed geometry, and find these play two related roles in general relativity: splitting fields into spatial and temporal parts, and 'breaking' gauge symmetry, effectively reducing the spacetime SO(n, 1) connection to an observer-dependent spatial SO(n) connection. In both gauge theory and gravity, the observer field reduces the action to canonical form, without using gauge fixing. In the 4d gravity case, the result is a manifestly Lorentz covariant counterpart of the Ashtekar-Barbero formulation. We also explain how this leads geometrically to a picture of general relativity in terms of 'observer space' rather than spacetime - a setting where both spacetime symmetry and the dynamical description are simultaneously available.

Wise, D. K.

2014-09-01

239

Symmetry and symmetry-breaking bifurcations in fluid dynamics  

NASA Astrophysics Data System (ADS)

The fundamental principles of equivariant or covariant bifurcation theory are reviewed, and the results of recent applications from the field of fluid dynamics are summarized and illustrated with graphs and photographs. Topics discussed include steady-state bifurcations with circular or reflection symmetry, Hopf bifurcation without symmetry, symmetry and linear theory, symmetry breaking and stability, single-mode theory, mode interactions, and imperfect symmetries. Applications considered involve the time evolution of a convection pattern in a circular container at fixed Rayleigh number, spiral vortices and ribbons in Taylor-Couette flow, convection in binary fluid systems, the oscillatory instability of convection rolls, parametrically excited surface waves, mode interaction in Taylor-Couette experiments, and Takens-Bogdanov bifurcation with O(2) symmetry.

Crawford, John David; Knobloch, Edgar

240

Quantum Mechanics in symmetry language  

E-print Network

We consider symmetry as a foundational concept in quantum mechanics and rewrite quantum mechanics and measurement axioms in this description. We argue that issues related to measurements and physical reality of states can be better understood in this view. In particular, the abstract concept of symmetry provides a basis-independent definition for observables. Moreover, we show that the apparent projection/collapse of the state as the final step of measurement or decoherence is the result of breaking of symmetries. This phenomenon is comparable with a phase transition by spontaneous symmetry breaking, and makes the process of decoherence and classicality a natural fate of complex systems consisting of many interacting subsystems. Additionally, we demonstrate that the property of state space as a vector space representing symmetries is more fundamental than being an abstract Hilbert space, and its $L2$ integrability can be obtained from the imposed condition of being a representation of a symmetry group and general properties of probability distributions.

Houri Ziaeepour

2014-09-17

241

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. PMID:23580619

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

2013-01-01

242

Symmetry planes of Paleozoic crinoids  

E-print Network

- crinida, whereas the other, Tram pidocrinus, is placed with equal certainty in the order Sageno- crinida. Consequently, these flexible crinoids, dis- tinguished by a homocrinid type of symmetry, are not judged to be closely related, even though both have a..., illustrated by Galateacrinus (after Moore, 1962). 2. Homocrinid (E-EC) symmetry plane (after Ubaghs, 1953). 3. Heterocrinid (D-AB) symmetry plane (after Ubaghs, 1953). 4 -5. Infrabasal, basal, and radial circlets of Permian flex- ible crinoids, Tram pidocrinus...

Lane, N. G.; Webster, G. D.

1967-11-30

243

Galactic oscillator symmetry  

NASA Technical Reports Server (NTRS)

Riemann ellipsoids model rotating galaxies when the galactic velocity field is a linear function of the Cartesian coordinates of the galactic masses. In nuclear physics, the kinetic energy in the linear velocity field approximation is known as the collective kinetic energy. But, the linear approximation neglects intrinsic degrees of freedom associated with nonlinear velocity fields. To remove this limitation, the theory of symplectic dynamical symmetry is developed for classical systems. A classical phase space for a self-gravitating symplectic system is a co-adjoint orbit of the noncompact group SP(3,R). The degenerate co-adjoint orbit is the 12 dimensional homogeneous space Sp(3,R)/U(3), where the maximal compact subgroup U(3) is the symmetry group of the harmonic oscillator. The Hamiltonian equations of motion on each orbit form a Lax system X = (X,F), where X and F are elements of the symplectic Lie algebra. The elements of the matrix X are the generators of the symplectic Lie algebra, viz., the one-body collective quadratic functions of the positions and momenta of the galactic masses. The matrix F is composed from the self-gravitating potential energy, the angular velocity, and the hydostatic pressure. Solutions to the hamiltonian dynamical system on Sp(3,R)/U(3) are given by symplectic isospectral deformations. The Casimirs of Sp(3,R), equal to the traces of powers of X, are conserved quantities.

Rosensteel, George

1995-01-01

244

Applications of chiral symmetry  

SciTech Connect

The author discusses several topics in the applications of chiral symmetry at nonzero temperature. First, where does the rho go? The answer: up. The restoration of chiral symmetry at a temperature T{sub {chi}} implies that the {rho} and a{sub 1} vector mesons are degenerate in mass. In a gauged linear sigma model the {rho} mass increases with temperature, m{sub {rho}}(T{sub {chi}}) > m{sub {rho}}(0). The author conjectures that at T{sub {chi}} the thermal {rho} - a{sub 1}, peak is relatively high, at about {approximately}1 GeV, with a width approximately that at zero temperature (up to standard kinematic factors). The {omega} meson also increases in mass, nearly degenerate with the {rho}, but its width grows dramatically with temperature, increasing to at least {approximately}100 MeV by T{sub {chi}}. The author also stresses how utterly remarkable the principle of vector meson dominance is, when viewed from the modern perspective of the renormalization group. Secondly, he discusses the possible appearance of disoriented chiral condensates from {open_quotes}quenched{close_quotes} heavy ion collisions. It appears difficult to obtain large domains of disoriented chiral condensates in the standard two flavor model. This leads to the last topic, which is the phase diagram for QCD with three flavors, and its proximity to the chiral critical point. QCD may be very near this chiral critical point, and one might thereby generated large domains of disoriented chiral condensates.

Pisarski, R.D.

1995-03-01

245

Givental graphs and inversion symmetry  

E-print Network

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.

P. Dunin-Barkowski; S. Shadrin; L. Spitz

2012-12-17

246

Energy band structure and optical response function of icosahedral B12As2 : A spectroscopic ellipsometry and first-principles calculational study  

NASA Astrophysics Data System (ADS)

An experimental and theoretical study on the dielectric-response function of icosahedral B12As2 in the spectral region between 1.24 and 9.8 eV is presented. Comprehensive experimental information on the energy band structure from the analysis of features in the optical dispersion was complemented by spin-orbit first-principles calculations. The lowest indirect band gap width is 3.2 eV; the two lowest direct interband transitions are at 3.46 and 3.9 eV. High-energy critical points are assigned to specific electron transitions in the Brillouin zone and their dimensionality was determined. The static dielectric constant of B12As2 is uniaxially anisotropic with values of 7.84 and 9.02 for polarization perpendicular and parallel to the trigonal axis. Hole and electron effective masses are derived from the band dispersions.

Bakalova, S.; Gong, Y.; Cobet, C.; Esser, N.; Zhang, Y.; Edgar, J. H.; Zhang, Y.; Dudley, M.; Kuball, M.

2010-02-01

247

Robert B. Howlett Chapter 1: Symmetry  

E-print Network

Aspects of Symmetry Robert B. Howlett #12;Contents Chapter 1: Symmetry §1a An example of abstract symmetry 2 §1b Structure preserving transformations 3 §1c The symmetries of some structured sets 7 §1d Some and inadmissibility proofs 105 Index of notation 110 Index 111 iv #12;1Symmetry Of the following geometrical objects

Howlett, Robert Brian

248

Gender Symmetry, Sexism, & Intimate Partner Violence 1 Running Head: Gender Symmetry, Sexism, & Intimate Partner Violence  

E-print Network

Gender Symmetry, Sexism, & Intimate Partner Violence 1 Running Head: Gender Symmetry, Sexism, & Intimate Partner Violence Gender Symmetry, Sexism, & Intimate Partner Violence Christopher T. Allen University of New York #12;Gender Symmetry, Sexism, & Intimate Partner Violence 2 Abstract The current study

Almor, Amit

249

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

250

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

251

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

252

Natural selection of visual symmetries  

Microsoft Academic Search

Implicitly, Wynn's target article starts from the transformational definition of symmetry. Unlike his suggestion, this traditional definition and the recent holographic definition are relevant to the discussion on the cognitive evolution of visual symmetries. These definitions reveal underlying properties and, thereby, they support the natural selection hypothesis. The holographic definition even agrees with an indirect test of this hypothesis

Peter A. van der Helm

2002-01-01

253

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

254

Generalized Atkin-Lehner symmetry  

NASA Astrophysics Data System (ADS)

Atkin-Lehner symmetry was proposed several years ago as a mechanism for obtaining a vanishing one-loop cosmological constant in nonsupersymmetric superstring models, but for models formulated in four-dimensional spacetime this symmetry cannot be realized. We therefore investigate various means of retaining the general Atkin-Lehner idea without having strict Atkin-Lehner symmetry. We first explicitly construct non-Atkin-Lehner-symmetric partition functions which not only lead to vanishing cosmological constants but which also avoid a recent proof that Atkin-Lehner-symmetric partition functions cannot arise from physically viable string models in greater than two dimensions. We then develop a systematic generalization of Atkin-Lehner symmetry, basing our considerations on the use of non-Hermitian operators as well as on a general class of possible congruence subgroups of the full modular group. We find that whereas in many instances our resulting symmetries reduce to either strict Atkin-Lehner symmetry or symmetries closely related to it, in other cases we obtain symmetries of a fundamentally new character. Our results therefore suggest possible new avenues for retaining the general Atkin-Lehner ``selection rule'' approach for obtaining a vanishing one-loop cosmological constant.

Dienes, Keith R.

1990-09-01

255

Ultraviolet completion without symmetry restoration  

NASA Astrophysics Data System (ADS)

We show that it is not possible to UV complete certain low-energy effective theories with spontaneously broken spacetime symmetries by embedding them into linear sigma models, that is, by adding "radial" modes and restoring the broken symmetries. When such a UV completion is not possible, one can still raise the cutoff up to arbitrarily higher energies by adding fields that transform nonlinearly under the broken symmetries, that is, new Goldstone bosons. However, this (partial) UV completion does not necessarily restore any of the broken symmetries. We illustrate this point by considering a concrete example in which a combination of spacetime and internal symmetries is broken down to a diagonal subgroup. Along the way, we clarify a recently proposed interpretation of inverse Higgs constraints as gauge-fixing conditions.

Endlich, Solomon; Nicolis, Alberto; Penco, Riccardo

2014-03-01

256

Symmetry inheritance of scalar fields  

E-print Network

Matter fields don't necessarily have to share the symmetries with the spacetime they live in. When this happens, we speak of the symmetry inheritance of fields. In this paper we classify the obstructions of symmetry inheritance by the scalar fields, both real and complex, and look more closely at the special cases of stationary and axially symmetric spacetimes. Since the symmetry noninheritance is present in the scalar fields of boson stars and may enable the existence of the black hole scalar hair, our results narrow the possible classes of such solutions. Finally, we define and analyse the symmetry noninheritance contributions to Komar mass and angular momentum of the black hole scalar hair.

Smoli?, Ivica

2015-01-01

257

Mixed Symmetry Nuclear Shell Model  

E-print Network

A mixed-symmetry nuclear shell-model scheme for carrying out calculations in regimes where there is a competition between two or more modes is proposed. A one-dimensional toy model is used to demonstrate the concept. The theory is then applied to $^{24}Mg$ and $^{44}Ti$. For lower pf-shell nuclei such as $^{44-48}Ti$ and $^{48}Cr$ there is strong SU(3) symmetry breaking due to the spin-orbit interaction. However, the quadrupole collectivity as measured by B(E2) transition strengths in the yrast band remain high even though SU(3) appears to be broken. Some results for the so-called X(5) symmetry that falls along the U(5) $\\leftrightarrow$ SU(3) leg of the Interacting Boson Model are also considered. The results show that the mixed-symmetry concept is effective, even when strong symmetry breaking occurs.

J. P. Draayer; V. G. Gueorguiev; Feng Pan; Yanan Luo

2003-11-26

258

Symmetry in Nonlinear Mathematical Physics 1997, V.1, 130137. Nonclassical Potential Symmetries  

E-print Network

Symmetry in Nonlinear Mathematical Physics 1997, V.1, 130­137. Nonclassical Potential Symmetries Puerto Real, Cadiz, Spain E-mail: mlgand@merlin.uca.es Abstract In this paper, new classes of symmetries symmetries called nonclassical potential symmetries, are neither potential symmetries nor nonclassical

Popovych, Roman

259

Chiral Symmetry and Scalars  

E-print Network

The suggestion by Jaffe that if $\\sigma$ is a light $q^{2}\\bar{q}^{2}$ state $0^{++}$ then even the fundamental chiral transformation properties of the $\\sigma$ becomes {\\bf unclear}, has stimulated much interest. Adler pointed out that in fact the seminal work on chiral symmetry via PCAC consistency, is really quite consistent with the $\\sigma$ being predominantly $q^{2}\\bar{q}^{2}$. This interpretation was actually backed by subsequent work on effective Lagrangian methods for linear and non linear realizations. More recent work of Achasov suggests that intermediate four-quark states determine amplitudes involving other scalars $a_{0}(980)$ and $f_{0}(980)$ below 1 GeV, and the report by Ning Wu that study on $\\sigma$ meson in $J/\\psi \\to \\omega\\pi^{+}\\pi^{-}$ continue to support a non $q\\bar{q}$ $\\sigma$ with mass as low as 390 MeV. It is also noted that more recent re-analysis of $\\pi K$ scattering by S. Ishida {\\em et al.} together with the work of the E791 Collaboration, support the existence of the scalar $\\kappa$ particle with comparatively light mass as well.

S. F. Tuan

2001-09-20

260

Spectral theorem and partial symmetries  

SciTech Connect

A novel method of the decompositon of a quantum system's Hamiltonian is presented. In this approach the criterion of the decomposition is determined by the symmetries possessed by the sub-Hamiltonians. This procedure is rather generic and independent of the actual global symmetry, or the lack of it, of the full Hamilton operator. A detailed investigation of the time evolution of the various sub-Hamiltonians, therefore the change in time of the symmetry of the physical object, is presented for the case of a vibrator-plus-rotor model. Analytical results are illustrated by direct numerical calculations.

Gozdz, A. [University of Maria Curie-Sklodowska, Department of Mathematical Physics, Institute of Physics (Poland); Gozdz, M. [University of Maria Curie-Sklodowska, Department of Complex Systems and Neurodynamics, Institute of Informatics (Poland)

2012-10-15

261

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

262

Higgs family symmetry and supersymmetry  

E-print Network

In this thesis we investigate building models of family symmetry that give the Higgs fields family structure. We construct several models, starting with 2 generation models then moving onto 3 generation models. These models ...

Patt, Brian Lawrence

2006-01-01

263

Classification of Arnold-Beltrami Flows and their Hidden Symmetries  

E-print Network

In the context of mathematical hydrodynamics, we consider the group theory structure which underlies the ABC-flow introduced by Beltrami, Arnold and Childress. Beltrami equation is the eigenstate equation for the first order Laplace-Beltrami operator *d, which we solve by using harmonic analysis. Taking torus T^3 constructed as R^3/L, where L is a crystallographic lattice, we present a general algorithm to construct solutions of Beltrami equation which utilizes as main ingredient the orbits under the action of the point group P_L of three-vectors in the momentum lattice L*. We introduce the new notion of a Universal Classifying Group GU_L which contains all crystallographic space groups as proper subgroups. We show that the *d-eigenfunctions are naturally arranged into irreducible representations of GU_L and by means of a systematic use of the branching rules with respect to various possible subgroups H of GU_L we search and find Beltrami fields with non trivial hidden symmetries. In the case of the cubic lat...

Fre, Pietro

2015-01-01

264

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

265

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

266

Symmetry breaking from Lorentz transformation  

E-print Network

Symmetry breaking is discussed in this paper which comes from the Lorentz transformation of special relativity and changes our view that two relatively moving bodies always have the relative speed equal in magnitude and opposite in direction. An appeal was made for the test of Lorentz transformation in a multimedia environment which has the fundamental significance that it may reveal the origin of symmetry breaking in many physical phenomena.

Bin-Guang Ma

2005-08-10

267

Symmetry and quaternionic integrable systems  

NASA Astrophysics Data System (ADS)

Given a hyperkahler manifold M, the hyperkahler structure defines a triple of symplectic structures on M; with these, a triple of Hamiltonians defines a so-called hyperHamiltonian dynamical system on M. These systems are integrable when can be mapped to a system of quaternionic oscillators. We discuss the symmetry of integrable hyperHamiltonian systems, i.e. quaternionic oscillators, and conversely how these symmetries characterize, at least in the Euclidean case, integrable hyperHamiltonian systems.

Gaeta, G.; Rodríguez, M. A.

2015-01-01

268

Discrete symmetries and neutrino masses  

E-print Network

We constructed a model of neutrino masses using Froggatt-Nielsen mechanism with $U(1) \\times Z_3 \\times Z_2$ flavor symmetry. The model predicts that $(2/3)m_2/m_3 \\sim \\sqrt{2}\\sin\\theta_{13}$ at lepton number violating scale $M_1$. It is shown that the small values for $m_2/m_3$ and $\\sin\\theta_{13}$ are consequences of breaking discrete symmetries.

Kim Siyeon

2005-05-27

269

Broken Symmetries and Magnetic Dynamos  

NASA Technical Reports Server (NTRS)

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.

2007-01-01

270

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

271

Highly Specific Salt Bridges Govern Bacteriophage P22 Icosahedral Capsid Assembly: Identification of the Site in Coat Protein Responsible for Interaction with Scaffolding Protein  

PubMed Central

ABSTRACT Icosahedral virus assembly requires a series of concerted and highly specific protein-protein interactions to produce a proper capsid. In bacteriophage P22, only coat protein (gp5) and scaffolding protein (gp8) are needed to assemble a procapsid-like particle, both in vivo and in vitro. In scaffolding protein's coat binding domain, residue R293 is required for procapsid assembly, while residue K296 is important but not essential. Here, we investigate the interaction of scaffolding protein with acidic residues in the N-arm of coat protein, since this interaction has been shown to be electrostatic. Through site-directed mutagenesis of genes 5 and 8, we show that changing coat protein N-arm residue 14 from aspartic acid to alanine causes a lethal phenotype. Coat protein residue D14 is shown by cross-linking to interact with scaffolding protein residue R293 and, thus, is intimately involved in proper procapsid assembly. To a lesser extent, coat protein N-arm residue E18 is also implicated in the interaction with scaffolding protein and is involved in capsid size determination, since a cysteine mutation at this site generated petite capsids. The final acidic residue in the N-arm that was tested, E15, is shown to only weakly interact with scaffolding protein's coat binding domain. This work supports growing evidence that surface charge density may be the driving force of virus capsid protein interactions. IMPORTANCE Bacteriophage P22 infects Salmonella enterica serovar Typhimurium and is a model for icosahedral viral capsid assembly. In this system, coat protein interacts with an internal scaffolding protein, triggering the assembly of an intermediate called a procapsid. Previously, we determined that there is a single amino acid in scaffolding protein required for P22 procapsid assembly, although others modulate affinity. Here, we identify partners in coat protein. We show experimentally that relatively weak interactions between coat and scaffolding proteins are capable of driving correctly shaped and sized procapsids and that the lack of these proper protein-protein interfaces leads to aberrant structures. The present work represents an important contribution supporting the hypothesis that virus capsid assembly is governed by seemingly simple interactions. The highly specific nature of the subunit interfaces suggests that these could be good targets for antivirals. PMID:24600011

Cortines, Juliana R.; Motwani, Tina; Vyas, Aashay A.

2014-01-01

272

Scanning tunneling microscopy studies of fivefold surfaces of icosahedral aluminum-palladium-manganese quasicrystals and of thin silver films on those surfaces  

NASA Astrophysics Data System (ADS)

Quasicrystals are non-periodic but well-ordered solids. Their unusual atomic structures foster peculiar surface properties such as low friction and enhanced oxidation resistance. This is well established at least for aluminum-rich icosahedral (i) quasicrystals. It is also very well known that sputter-annealed surfaces of i-Al-Pd-Mn possess step-terrace morphology even though a network of Bergman and Mackay clusters defines its bulk structure. Using scanning tunneling microscope (STM) we have investigated clean fivefold surfaces of i-Al-Pd-Mn quasicrystals. In addition, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystals in terms of the densities, compositions and interplanar spacings for the fivefold planes. We focus on four models that contain no partial or mixed occupancies, but we have made some comparisons to a fifth model containing such sites. Each of the four models contains paired planes (layers) that can be separated into two main families on the basis of three features: the relative densities of the two planes, the gap separating the layer from the nearest atomic plane, and the Pd content in the topmost plane. We have compared these families with the available experimental data obtained for the fivefold surfaces. The experimental data and other arguments lead to the conclusion that the family with no Pd in the top plane is favored. We have studied the nucleation and growth of Ag islands on the fivefold surface of the i-Al-Pd-Mn quasicrystal using STM. From 127 K to 300 K, the density of Ag islands remains constant but it drops as temperature increases beyond 300 K. To understand this behavior, we have developed a mean field rate equation model that takes into account the enhanced nucleation at traps relative to nucleation at regular terrace sites. The best fit to the model suggests that the critical sizes for the nucleation at both sites are large, especially at the traps, where six Ag atoms form stable clusters, and that binding between Ag atoms at the traps is stronger than at the regular terrace sites. In addition, we have identified these trap sites as the cut clusters in the aforementioned structure analysis.

Unal, Baris

273

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

274

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

275

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

276

Symmetry in Matrix Models Pierre Flener  

E-print Network

Symmetry in Matrix Models Pierre Flener , Alan Frisch ¡ , Brahim Hnich ¢ , Zeynep Kiziltan models, sym- metry is an important feature. We study and generalise symmetry-breaking techniques with symmetry in such models in a uniform way. We thereby reduce the burden on the user of eliminating symmetry

Walsh, Toby

277

Stillness in Motion The Essence of Symmetry  

E-print Network

Stillness in Motion The Essence of Symmetry Carl Lee University of Kentucky Chellgren Presentation -- October 2014 Carl Lee Symmetry October 2014 1 / 39 #12;Key Idea #1 An object is symmetrical if it "remains or transformation. Carl Lee Symmetry October 2014 2 / 39 #12;Product Design (Hubcap) Carl Lee Symmetry October 2014

Lee, Carl

278

Partial Symmetry Breaking Iain McDonald  

E-print Network

Partial Symmetry Breaking Iain McDonald University of St Andrews, Fife, Scotland, iain@dcs.st-and.ac.uk Abstract. In this paper I de#12;ne partial symmetry breaking, a concept that has been used in many previous of partial symmetry breaking in constraint programming. I show experimentally that performing symmetry

Rossi, Francesca

279

The symmetry of wallpaper David Morawski  

E-print Network

The symmetry of wallpaper David Morawski University of Minnesota Math Club, University of Minnesota 25 March, 2011 #12;"Symmetry is everywhere" In art: The Alhambra, Spain David Morawski (UMN) The symmetry of wallpaper 25 March, 2011 2 / 35 #12;"Symmetry is everywhere" In architecture: Apartment

Weinberger, Hans

280

Symmetry in Chinese Arts Yip Lixia, Sabrina  

E-print Network

scales and the structure of the music itself. #12;5 Symmetry in Chinese Literature Symmetry has Cuttings · Symmetry in Chinese buildings · Chinese Music · Conclusion · Bibliography #12;3 Introduction influence in the arts is pervasive. In music, we hear the symmetry of exposition and recapitulation

Aslaksen, Helmer

281

Symmetry in polarimetric remote sensing  

NASA Technical Reports Server (NTRS)

Relationships among polarimetric backscattering coefficients are derived from the viewpoint of symmetry groups. For both reciprocal and non-reciprocal media, symmetry encountered in remote sensing due to reflection, rotation, azimuthal, and centrical symmetry groups is considered. The derived properties are general and valid to all scattering mechanisms, including volume and surface scatterings and their interactions, in a given symmetrical configuration. The scattering coefficients calculated from theoretical models for layer random media and rough surfaces are shown to obey the symmetry relations. Use of symmetry properties in remote sensing of structural and environmental responses of scattering media is also discussed. Orientations of spheroidal scatterers described by spherical, uniform, planophile, plagiothile, erectophile, and extremophile distributions are considered to derive their polarimetric backscattering characteristics. These distributions can be identified from the observed scattering coefficients by comparison with theoretical symmetry calculations. A new parameter is then defined to study scattering structures in geophysical media. Observations from polarimetric data acquired by the Jet Propulsion Laboratory airborne synthetic aperture radar over forests, sea ice, and sea surface are presented. Experimental evidences of the symmetry relationships are shown and their use in polarimetric remote sensing is illustrated. For forests, the coniferous forest in Mt. Shasta area (California) and mixed forest near Presque Isle (Maine) exhibit characteristics of the centrical symmetry at C-band. For sea ice in the Beaufort Sea, multi-year sea ice has a cross-polarized ratio e close to e(sub 0), calculated from symmetry, due to the randomness in the scattering structure. First-year sea ice has e much smaller than e(sub 0) due to the preferential alignment of the columnar structure of the ice. From polarimetric data of a sea surface in the Bering Sea, it is observed that e and e(sub 0) are increasing with incident angle and e is greater than e(sub 0) at L-band because of the directional feature of sea surface waves. Symmetry properties of geophysical media can also be used to calibrate polarimetric radars.

Nghiem, S. V.; Yueh, S. H.; Kwok, R.

1993-01-01

282

Cooperativity and symmetry at biological scales A. Carbone z  

E-print Network

: the example of bacteriophage HK97. The crystal structure of the mature empty capsid of the double­stranded DNA bacteriophage HK97 was recently determined at 3.6 š A resolution [3]. It is an icosahedral capsid of 660 š to bacteriophage HK97: it undergoes several capsid large­scale conformational changes which transform precur

Carbone, Alessandra

283

Symmetry protected topological orders and the group cohomology of their symmetry group  

E-print Network

Symmetry protected topological orders and the group cohomology of their symmetry group Xie Chen,1 Canada Symmetry protected topological (SPT) phases are gapped short-range-entangled quantum phases with a symmetry G, which can all be smoothly connected to the same trivial product state if we break the symmetry

Wen, Xiao-Gang

284

Center Symmetry with Fundamentally Charged Scalars Chiral Symmetry with Quarks and Mesons  

E-print Network

Motivation Center Symmetry with Fundamentally Charged Scalars Chiral Symmetry with Quarks with Fundamentally Charged Scalars Chiral Symmetry with Quarks and Mesons Table of Contents 1 Motivation 2 Center Symmetry with Fundamentally Charged Scalars 3 Chiral Symmetry with Quarks and Mesons The Nf -Flavor Quark

Seyfarth, Andre

285

cRGD Peptide-Conjugated Icosahedral closo-B12 2? Core Carrying Multiple Gd3+-DOTA Chelates for ?v?3 Integrin-Targeted Tumor Imaging (MRI)  

PubMed Central

A vertex-differentiated icosahedral closo-B122? core was utilized to construct a ?v?3 integrin receptor-targeted (via cRGD peptide) high payload MRI contrast agent (CA-12) carrying 11 copies of Gd3+-DOTA chelates attached to the closo-B122? surface via suitable linkers. The resulting polyfunctional MRI contrast agent possessed a higher relaxivity value per-Gd compared to Omniscan, a small molecular contrast agent commonly used in clinical settings. The ?v?3 integrin receptor specificity of CA-12 was confirmed via in vitro cellular binding experiments and in vivo MRI of mice bearing human PC-3 prostate cancer xenografts. Integrin ?v?3-positive MDA-MB-231 cells exhibited 300% higher uptake of CA-12 than ?v?3-negative T47D cells. Serial T1-weighted MRI showed superior contrast enhancement of tumors by CA-12 compared to both a non-targeted 12-fold Gd3+-DOTA closomer control (CA-7) and Omniscan. Contrast enhancement by CA-12 persisted for 4 h post-injection, and subsequent enhancement of kidney tissue indicated a renal elimination route similar to Omniscan. No toxic effects of CA-12 were apparent in any mice for up to 24 h post-injection. Post-mortem ICP-OES analysis at 24 hours detected no residual Gd in any of the tissue samples analyzed. PMID:23391150

Goswami, Lalit N.; Ma, Lixin; Cai, Quanyu; Sarma, Saurav J.; Jalisatgi, Satish S.; Hawthorne, M. Frederick

2013-01-01

286

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. PMID:19474243

Ambrose, Rebecca L.; Lander, Gabriel C.; Maaty, Walid S.; Bothner, Brian; Johnson, John E.; Johnson, Karyn N.

2009-01-01

287

Symmetry protected topological orders and the group cohomology of their symmetry group  

E-print Network

Symmetry protected topological (SPT) phases are gapped short-range-entangled quantum phases with a symmetry G. They can all be smoothly connected to the same trivial product state if we break the symmetry. The Haldane phase ...

Chen, Xie

288

The master symmetry and time dependent symmetries of the differential–difference KP equation  

NASA Astrophysics Data System (ADS)

We first obtain the master symmetry of the differential–difference KP equation. Then we show how this master symmetry, through sl(2,{C})-representation of the equation, can construct generators of time dependent symmetries.

Khanizadeh, Farbod

2014-10-01

289

Chiral Symmetry Breaking in Graphene  

E-print Network

The question of whether the Coulomb interaction is strong enough to break the sublattice symmetry of un-doped graphene is discussed. We formulate a strong coupling expansion where the ground state of the Coulomb Hamiltonian is found exactly and the kinetic hopping Hamiltonian is treated as a perturbation. We argue that many of the properties of the resulting system would be shared by graphene with a Hubbard model interaction. In particular, the best candidate sublattice symmetry breaking ground state is an antiferromagnetic Mott insulator. We discuss the results of some numerical simulations which indicate that the Coulomb interaction is indeed subcritical. We also point out the curious fact that, if the electron did not have spin degeneracy, the tendency to break chiral symmetry would be much greater and even relatively weak Coulomb interactions would likely gap the spectrum.

Gordon W. Semenoff

2011-08-15

290

Iterates of maps with symmetry  

NASA Technical Reports Server (NTRS)

Fixed-point bifurcation, period doubling, and Hopf bifurcation (HB) for iterates of equivariant mappings are investigated analytically, with a focus on HB in the presence of symmetry. An algebraic formulation for the hypotheses of the theorem of Ruelle (1973) is derived, and the case of standing waves in a system of ordinary differential equations with O(2) symmetry is considered in detail. In this case, it is shown that HB can lead directly to motion on an invariant 3-torus, with an unexpected third frequency due to drift of standing waves along the torus.

Chossat, Pascal; Golubitsky, Martin

1988-01-01

291

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

292

Chiral symmetry in quarkyonic matter  

SciTech Connect

The 1/N{sub c} expansion classifies nuclear matter, deconfined quark matter, and Quarkyonic matter in low temperature region. We investigate the realization of chiral symmetry in Quarkyonic matter by taking into account condensations of chiral particle-hole pairs. It is argued that chiral symmetry and parity are locally violated by the formation of chiral spirals, <{psi}-bar exp (2i{mu}{sub q} z{gamma}{sup 0} {gamma}{sup z}){psi}> . An extension to multiple chiral spirals is also briefly discussed.

Kojo, T., E-mail: torujj@quark.phy.bnl.gov [Brookhaven National Laboratory, RIKEN BNL Research Center (United States)

2012-05-15

293

Symmetries of coupled harmonic oscillators  

NASA Technical Reports Server (NTRS)

It is shown that the system of two coupled harmonic oscillators possesses many interesting symmetries. It is noted that the symmetry of a single oscillator is that of the three-parameter group Sp(2). Thus two uncoupled oscillator exhibits a direct product of two Sp(2) groups, with six parameters. The coupling can be achieved through a rotation in the two-dimensional space of two oscillator coordinates. The closure of the commutation relations for the generators leads to the ten-parameter group Sp(4) which is locally isomorphic to the deSitter group O(3,2).

Han, D.; Kim, Y. S.

1993-01-01

294

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

295

Symmetry analysis of cellular automata  

NASA Astrophysics Data System (ADS)

By means of B-calculus [V. García-Morales, Phys. Lett. A 376 (2012) 2645] a universal map for deterministic cellular automata (CAs) has been derived. The latter is shown here to be invariant upon certain transformations (global complementation, reflection and shift). When constructing CA rules in terms of rules of lower range a new symmetry, “invariance under construction” is uncovered. Modular arithmetic is also reformulated within B-calculus and a new symmetry of certain totalistic CA rules, which calculate the Pascal simplices modulo an integer number p, is then also uncovered.

García-Morales, V.

2013-01-01

296

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

297

Rotation-reversal symmetries in crystals and handed structures  

E-print Network

: List of roto point groups indicated in Figure 2b that are invariance groups of a net (non-zero) spin (S of roto point groups indicated in Figure 2b that are invariance groups of non-zero (net) spin (S), non-zero (net) electric polarization (P), non-zero (net) static rotation (), and combinations thereof. Net Spin

Gopalan, Venkatraman

298

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

299

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

300

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

301

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

302

Honours Project Symmetry Classifications of  

E-print Network

's periodic tilings in Table 1 (see appendix). Firstly, it aims to provide the readers an overview in Table 1 (appendix). Therefore, finally, given an Escher's periodic tiling the reader would be ableHonours Project Symmetry Classifications of Periodic Tilings ­ Escher's drawings Name: Kavitha d

Aslaksen, Helmer

303

Fundamental Symmetries and Conservation Laws  

E-print Network

I discuss recent progress in low-energy tests of symmetries and conservation laws, including parity nonconservation in atoms and nuclei, electric dipole moment tests of time-reversal invariance, beta-decay correlation studies, and decays violating separate (family) and total lepton number.

W. C. Haxton

2009-02-09

304

Fearful Symmetries: Factoring, Graph Isomorphism,  

E-print Network

for the electron has two solutions. Four years later, the positron was found in the laboratory. #12;Conservation we have any right to expect) #12;Computer Science Fig. 2: The Adversary Problems: are artificial is Symmetry p = mv F = ma perhaps you are more familiar with and ; try with H = (1/2)mv2 + V (x) Conservation

Moore, Cris

305

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

306

Baryon and chiral symmetry breaking  

SciTech Connect

We briefly review the generalized Skyrmion model for the baryon recently suggested by us. It takes into account the tower of vector and axial mesons as well as the chiral symmetry breaking. The generalized Skyrmion model provides the qualitative explanation of the Ioffe’s formula for the baryon mass.

Gorsky, A. [Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia and Moscow Institute of Physics and Technology (MIPT), Dolgoprudny (Russian Federation); Krikun, A. [NORDITA, KTH Royal Institute of Technology and Stockholm University Stockholm, Sweden and Institute for Theoretical and Experimental Physics (ITEP), Moscow (Russian Federation)

2014-07-23

307

Basic logic: reflection, symmetry, visibility.  

E-print Network

Basic logic: reflection, symmetry, visibility. Giovanni Sambin - Giulia Battilotti - Claudia Faggian Abstract We introduce a sequent calculus B for a new logic, named basic logic. The aim of basic logic is to find a structure in the space of logics. Classical, intuitionistic, quantum and non

Sambin, Giovanni

308

Which Symmetry? Noether, Weyl, and  

E-print Network

a unified theory of electromagnetism and gravitation by generalising the geometry on which Gen- eral failed, and that Weyl re-applied the gauge idea in the context of quantum theory in 1929,1 there giving known, and applies to symmetry transformations that depend on arbitrary functions and their derivatives

Brading, Katherine

309

Symmetry Breaking During Drosophila Oogenesis  

PubMed Central

The orthogonal axes of Drosophila are established during oogenesis through a hierarchical series of symmetry-breaking steps, most of which can be traced back to asymmetries inherent in the architecture of the ovary. Oogenesis begins with the formation of a germline cyst of 16 cells connected by ring canals. Two of these 16 cells have four ring canals, whereas the others have fewer. The first symmetry-breaking step is the selection of one of these two cells to become the oocyte. Subsequently, the germline cyst becomes surrounded by somatic follicle cells to generate individual egg chambers. The second symmetry-breaking step is the posterior positioning of the oocyte within the egg chamber, a process mediated by adhesive interactions with a special group of somatic cells. Posterior oocyte positioning is accompanied by a par gene-dependent repolarization of the microtubule network, which establishes the posterior cortex of the oocyte. The next two steps of symmetry breaking occur during midoogenesis after the volume of the oocyte has increased about 10-fold. First, a signal from the oocyte specifies posterior follicle cells, polarizing a symmetric prepattern present within the follicular epithelium. Second, the posterior follicle cells send a signal back to the oocyte, which leads to a second repolarization of the oocyte microtubule network and the asymmetric migration of the oocyte nucleus. This process again requires the par genes. The repolarization of the microtubule network results in the transport of bicoid and oskar mRNAs, the anterior and posterior determinants, respectively, of the embryonic axis, to opposite poles of the oocyte. The asymmetric positioning of the oocyte nucleus defines a cortical region of the oocyte where gurken mRNA is localized, thus breaking the dorsal–ventral symmetry of the egg and embryo. PMID:20066085

Roth, Siegfried; Lynch, Jeremy A.

2009-01-01

310

Universal Formulation For Symmetries In Computed Flows  

NASA Technical Reports Server (NTRS)

Universal formulation for high-order symmetries in boundary conditions on flows devised. Eliminates need for special procedures to incorporate symmetries and corresponding boundary conditions into computer codes solving Navier-Stokes and Euler equations of flow.

Pao, S. Paul; Abdol-Hamid, Khaled S.

1995-01-01

311

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

312

Testing Lorentz symmetry with atoms and Light  

E-print Network

This article reports on the Fifth Meeting on CPT and Lorentz Symmetry, CPT'10, held at the end of June 2010 in Bloomington, Indiana, USA. The focus is on recent tests of Lorentz symmetry using atomic and optical physics.

Neil Russell

2011-09-04

313

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

314

From Additional Symmetries to Linearization of Virasoro Symmetries  

E-print Network

We construct the additional symmetries and derive the Adler-Shiota-van Moerbeke formula for the two-component BKP hierarchy. We also show that the Drinfeld-Sokolov hierarchies of type D, which are reduced from the two-component BKP hierarchy, possess symmetries written as the action of a series of linear 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.

Chao-Zhong Wu

2011-12-01

315

$PT$ Symmetry, Conformal Symmetry, and the Metrication of Electromagnetism  

E-print Network

We present some interesting connections between $PT$ symmetry and conformal symmetry. We use them to develop a metricated theory of electromagnetism in which the electromagnetic field is present in the geometric connection. However, unlike Weyl who first advanced this possibility, we do not take the connection to be real but to instead be $PT$ symmetric, with it being $iA_{\\mu}$ rather than $A_{\\mu}$ itself that then appears in the connection. With this modification the standard minimal coupling of electromagnetism to fermions is obtained. Through the use of torsion we obtain a metricated theory of electromagnetism that treats its electric and magnetic sectors symmetrically, with a conformal invariant theory of gravity being found to emerge. An extension to the non-Abelian case is provided.

Philip D. Mannheim

2015-01-28

316

High-symmetry polarization domains in low-symmetry ferroelectrics.  

PubMed

We present experimental evidence for polygonal domain faceting in the ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) films with the lower orthorhombic crystallographic symmetry. It is proposed that this effect can arise from purely electrostatic depolarizing forces. We show that, in contrast to magnetic bubble shape domains, where such type of deformation instability has a predominantly elliptical character, the emergence of more symmetrical circular harmonics is favored in ferroelectrics with high dielectric constants. PMID:25420186

Lukyanchuk, I; Sharma, P; Nakajima, T; Okamura, S; Scott, J F; Gruverman, A

2014-12-10

317

High-Symmetry Polarization Domains in Low-Symmetry Ferroelectrics  

NASA Astrophysics Data System (ADS)

We present experimental evidence for hexagonal domain faceting in the ferroelectric polymer PVDF-TrFE films having the lower orthorhombic crystallographic symmetry. This effect can arise from purely electrostatic depolarizing forces. We show that in contrast to magnetic bubble shape domains where such type of deformation instability has a predominantly elliptical character, the emergence of more symmetrical circular harmonics is favored in ferroelectrics with high dielectric constant.

Lukyanchuk, I.; Sharma, P.; Nakajima, T.; Okamura, S.; Scott, J. F.; Gruverman, A.

2014-12-01

318

Conditional Symmetry Breaking Ian P. Gent1  

E-print Network

Conditional Symmetry Breaking Ian P. Gent1 , Tom Kelsey1 , Steve A. Linton1 , Iain McDonald1 , Ian,tom,sal,iain,ianm}@dcs.st-and.ac.uk, bms@4c.ucc.ie Abstract. We introduce the study of Conditional symmetry breaking in constraint-problem satisfies some condition under which additional symetries hold. Conditional symmetry can cause redun- dancy

Miguel, Ian

319

Physica D 112 (1998) 275280 Stellarator symmetry  

E-print Network

Physica D 112 (1998) 275­280 Stellarator symmetry R.L. Dewar , S.R. Hudson 1 Department of stellarator symmetry is presented and its relation to previous definitions discussed. It is shown that the field-line flow in systems possessing stellarator symmetry is time-reversal invariant

Hudson, Stuart

320

Symmetry violation in nuclei Vladimir Gudkov1  

E-print Network

Symmetry violation in nuclei Vladimir Gudkov1 1 Department of Physics and Astronomy, University of South Carolina, Columbia, SC, 29208 The study of symmetry violation in nuclei, including parity (PV of the fundamental symmetries tests and a search for new physics is underlined in the third recommendation

321

The Symmetry Detection Mechanisms are Color Selective  

E-print Network

The Symmetry Detection Mechanisms are Color Selective Chia-Ching Wu1 & Chien-Chung Chen2 1 of the symmetry detection mechanism. In each trial, a vertical symmetric target was randomly presented in one increased. This suggests that the symmetry detection mechanisms are color selective and only extract local

Chen, Chein Chung

322

Symmetry-Breaking Constraints for Matrix Models  

E-print Network

Symmetry-Breaking Constraints for Matrix Models Zeynep Kiziltan1 and Barbara M. Smith2 1 Department their rows and/or columns. Eliminating all such symmetry can be very costly as there are in general exponentially many symme- tries. Cost-effective methods have been proposed to break much of the symmetry

Flener, Pierre

323

Approximate Noether gauge symmetries of Bardeen model  

E-print Network

We investigate the approximate Noether gauge symmetries of the geodesic Lagrangian for the Bardeen spacetime model. This is accommodated by a set of new approximate Noether gauge symmetry relations for the perturbed geodesic Lagrangian in the spacetime. A detailed analysis to the spacetime of Bardeen model up to third-order approximate Noether gauge symmetries is presented.

U. Camci

2014-10-28

324

Man Sik Park Symmetry and Separability In  

E-print Network

Man Sik Park Symmetry and Separability In Spatial-Temporal Processes Man Sik Park, Montserrat Fuentes Symmetry and Separability In Spatial-Temporal Processes 1 #12;Man Sik Park Motivation · In general-pollution data. Symmetry and Separability In Spatial-Temporal Processes 2 #12;Man Sik Park Research Objectives 1

325

Detecting Symmetry and Symmetric Constellations of Features  

Microsoft Academic Search

A novel and efficient method is presented for grouping feature points on the basis of their underlying symmetry and characterising the symmetries present in an image. We show how symmetric pairs of features can be efficiently detected, how the symmetry bonding each pair is extracted and evaluated, and how these can be grouped into symmetric constellations that specify the domi-

Gareth Loyand; Jan-olof Eklundh

2006-01-01

326

No role for colour in symmetry perception  

Microsoft Academic Search

Bilateral colour symmetry, such as that evident in a Siberian tiger's face (Fig. 1a), is relevant to many animals,, including humans,. We examined the role of colour in symmetry perception by asking observers to detect colour symmetry in regular grids of coloured squares (a colour-symmetrical image has regions of the same colour located equidistantly from a vertical axis). Our results

Dawn Morales; Harold Pashler

1999-01-01

327

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.

328

Symmetry in Nonlinear Mathematical Physics 1997, V.2, 321327. Higher Symmetries of the Wave Equation  

E-print Network

Symmetry in Nonlinear Mathematical Physics 1997, V.2, 321­327. Higher Symmetries of the Wave@apmat.freenet.kiev.ua Abstract Higher order symmetry operators for the wave equation with scalar and vector po- tentials are investigated. All scalar potentials which admit second order symmetry operators are found explicitly

Nikitin, Anatoly

329

Symmetry in Nonlinear Mathematical Physics 1997, V.1, 8997. Lie Symmetries and Preliminary Classification of  

E-print Network

Symmetry in Nonlinear Mathematical Physics 1997, V.1, 89­97. Lie Symmetries and Preliminary) of the form u (k) n (t) = Fn(t, un+a, . . . , un+b) with k 2 are studied for Lie symmetries and preliminary classification. Explicit forms of equations are given for those admitting at least one intrinsic Lie symmetry

Popovych, Roman

330

Instantaneous Symmetry and Symmetry on Average in the CouetteTaylor and Faraday  

E-print Network

Instantaneous Symmetry and Symmetry on Average in the Couette­Taylor and Faraday Experiments November 16, 1993 Abstract We describe some recent results on symmetry of attractors for dy­ namical systems with symmetry and consider the implications for the Couette­Taylor experiment and the Faraday

331

Quantum ergodicity and symmetry reduction  

E-print Network

We study the ergodic properties of eigenfunctions of Schr\\"odinger operators on a closed connected Riemannian manifold $M$ in case that the underlying Hamiltonian system possesses certain symmetries. More precisely, let $M$ carry an isometric effective action of a compact connected Lie group $G$. We prove an equivariant quantum ergodicity theorem assuming that the symmetry-reduced Hamiltonian flow on the principal stratum of the singular symplectic reduction of $M$ is ergodic. We deduce the theorem by proving an equivariant version of the semiclassical Weyl law, relying on recent results on singular equivariant asymptotics. It implies an equivariant version of the Shnirelman-Zelditch-Colin-de-Verdi\\`{e}re theorem, as well as a representation theoretic equidistribution theorem. In case that $G$ is trivial, one recovers the classical results.

Benjamin Küster; Pablo Ramacher

2014-10-04

332

Gravitating fluids with Lie symmetries  

E-print Network

We analyse the underlying nonlinear partial differential equation which arises in the study of gravitating flat fluid plates of embedding class one. Our interest in this equation lies in discussing new solutions that can be found by means of Lie point symmetries. The method utilised reduces the partial differential equation to an ordinary differential equation according to the Lie symmetry admitted. We show that a class of solutions found previously can be characterised by a particular Lie generator. Several new families of solutions are found explicitly. In particular we find the relevant ordinary differential equation for all one-dimensional optimal subgroups; in several cases the ordinary differential equation can be solved in general. We are in a position to characterise particular solutions with a linear barotropic equation of state.

Msomi, A M; Maharaj, S D

2010-01-01

333

Symmetries of Optical Phase Conjugation  

E-print Network

Various algebraic structures of degenerate four-wave mixing equations of optical phase conjugation are analyzed. Two approaches (the spinorial and the Lax-pair based), complementary to each other, are utilized for a systematic derivation of conserved quantities. Symmetry groups of both the equations and the conserved quantities are determined, and the corresponding generators are written down explicitly. Relation between these two symmetry groups is found. Conserved quantities enable the introduction of new methods for integration of the equations in the cases when the coupling $\\Gamma$ is either purely real or purely imaginary. These methods allow for both geometries of the process, namely the transmission and the reflection, to be treated on an equal basis. One approach to introduction of Hamiltonian and Lagrangian structures for the 4WM systems is explored, and the obstacles in successful implementation of that programe are identified. In case of real coupling these obstacles are removable, and full Hamilt...

Stojkov, P L; Jaric, M V; Stojkov, Predrag L.; Belic, Milivoj R.; Jaric, Marko V.

2000-01-01

334

Symmetry restoration and quantumness reestablishment  

E-print Network

A realistic quantum many-body system, characterized by a generic microscopic Hamiltonian, is accessible only through approximation methods. The mean field theories, as the simplest practices of approximation methods, commonly serve as a powerful tool, but unfortunately often violate the symmetry of the Hamiltonian. The conventional BCS theory, as an excellent mean field approach, violates the particle number conservation and completely erases quantumness characterized by concurrence and quantum discord between different modes. We restore the symmetry by using the projected BCS theory and the exact numerical solution and find that the lost quantumness is synchronously reestablished. We show that while entanglement remains unchanged with the particle numbers, quantum discord behaves as an extensive quantity with respect to the system size. Surprisingly, discord is hardly dependent on the interaction strengths. The new feature of discord offers promising applications in modern quantum technologies.

Guo-Mo Zeng; Lian-Ao Wu; Hai-Jun Xing

2014-07-02

335

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

336

Interfacial fermi loops from interfacial symmetries.  

PubMed

We propose a concept of interfacial symmetries such as interfacial particle-hole symmetry and interfacial time-reversal symmetry, which appear in interfaces between two regions related to each other by particle-hole or time-reversal transformations. These symmetries result in novel dispersion of interface states. In particular, for the interfacial particle-hole symmetry, the gap closes along a loop ("Fermi loop") at the interface. We numerically demonstrate this for the Fu-Kane-Mele tight-binding model. We show that the Fermi loop originates from a sign change of a Pfaffian of a product between the Hamiltonian and a constant matrix. PMID:25554901

Takahashi, Ryuji; Murakami, Shuichi

2014-12-19

337

Interfacial Fermi Loops from Interfacial Symmetries  

NASA Astrophysics Data System (ADS)

We propose a concept of interfacial symmetries such as interfacial particle-hole symmetry and interfacial time-reversal symmetry, which appear in interfaces between two regions related to each other by particle-hole or time-reversal transformations. These symmetries result in novel dispersion of interface states. In particular, for the interfacial particle-hole symmetry, the gap closes along a loop ("Fermi loop") at the interface. We numerically demonstrate this for the Fu-Kane-Mele tight-binding model. We show that the Fermi loop originates from a sign change of a Pfaffian of a product between the Hamiltonian and a constant matrix.

Takahashi, Ryuji; Murakami, Shuichi

2014-12-01

338

Symmetry Detection In Human Vision  

NASA Astrophysics Data System (ADS)

A basic assumption underlying this paper is that the construction of a high-speed, high-accuracy, and general-purpose artificial recognition system might profit from theories and data about the principles of the human visual system. More specifically, it is argued that perceptual organization in general and symmetry detection in particular are interesting processes required between the initial stage of edge detection and the final stage of object recognition. Therefore, theories and data about detection of regularities such as symmetry in human vision are summarized. Furthermore, a general scheme is proposed that might enable the detection of image regularities in a way that is in good agreement with these experimental data and theoretical models. In addition, some of our own experiments about human detection of bilateral and skewed symmetry in dot-patterns are presented to show the plausibility of the scheme. Although the results are promising, a lot of work remains to be done, both with respect to the empirical foundation of the model and with respect to its mathematical and computational specification.

Wagemans, Johan; van Gool, Luc J.; Wambacq, Patrick; D'Ydewalle, G.; Oosterlinck, Andre J.

1989-09-01

339

Geometric endoscopy and mirror symmetry  

NASA Astrophysics Data System (ADS)

The geometric Langlands correspondence has been interpreted as the mirror symmetry of the Hitchin fibrations for two dual reductive groups. This mirror symmetry, in turn, reduces to T-duality on the generic Hitchin fibers, which are smooth tori. In this paper, we study what happens when the Hitchin fibers on the B-model side develop orbifold singularities. These singularities correspond to local systems with finite groups of automorphisms. In the classical Langlands program, local systems of this type are called endoscopic. They play an important role in the theory of automorphic representations, in particular, in the stabilization of the trace formula. Our goal is to use the mirror symmetry of the Hitchin fibrations to expose the special role played by these local systems in the geometric theory. The study of the categories of A-branes on the dual Hitchin fibers allows us to uncover some interesting phenomena associated with the endoscopy in the geometric Langlands correspondence. We then follow our predictions back to the classical theory of automorphic functions. This enables us to test and confirm them. The geometry we use is similar to that which is exploited in recent work by Ngô, a fact which could be significant for understanding the trace formula.

Frenkel, Edward; Witten, Edward

340

Relativity symmetries and Lie algebra contractions  

NASA Astrophysics Data System (ADS)

We revisit the notion of possible relativity or kinematic symmetries mutually connected through Lie algebra contractions under a new perspective on what constitutes a relativity symmetry. Contractions of an SO(m , n) symmetry as an isometry on an m + n dimensional geometric arena which generalizes the notion of spacetime are discussed systematically. One of the key results is five different contractions of a Galilean-type symmetry G(m , n) preserving a symmetry of the same type at dimension m + n - 1, e.g. a G(m , n - 1) , together with the coset space representations that correspond to the usual physical picture. Most of the results are explicitly illustrated through the example of symmetries obtained from the contraction of SO(2 , 4) , which is the particular case for our interest on the physics side as the proposed relativity symmetry for 'quantum spacetime'. The contractions from G(1 , 3) may be relevant to real physics.

Cho, Dai-Ning; Kong, Otto C. W.

2014-12-01

341

Enhanced Facial Symmetry Assessment in Orthodontists  

PubMed Central

Assessing facial symmetry is an evolutionarily important process, which suggests that individual differences in this ability should exist. As existing data are inconclusive, the current study explored whether a group trained in facial symmetry assessment, orthodontists, possessed enhanced abilities. Symmetry assessment was measured using face and non-face stimuli among orthodontic residents and two control groups: university participants with no symmetry training and airport security luggage screeners, a group previously shown to possess expert visual search skills unrelated to facial symmetry. Orthodontic residents were more accurate at assessing symmetry in both upright and inverted faces compared to both control groups, but not for non-face stimuli. These differences are not likely due to motivational biases or a speed-accuracy tradeoff—orthodontic residents were slower than the university participants but not the security screeners. Understanding such individual differences in facial symmetry assessment may inform the perception of facial attractiveness. PMID:24319342

Jackson, Tate H.; Clark, Kait; Mitroff, Stephen R.

2013-01-01

342

Unified framework of topological phases with symmetry  

NASA Astrophysics Data System (ADS)

In topological phases in 2 +1 dimensions, anyons fall into representations of quantum group symmetries. As proposed in our work [Hung and Wan, Int. J. Mod. Phys. B 28, 1450172 (2014), 10.1142/S0217979214501720], the physics of a symmetry enriched phase can be extracted by the mathematics of (hidden) quantum group symmetry breaking of a "parent phase." This offers a unified framework and classification of the symmetry enriched (topological) phases, including symmetry protected trivial phases as well. In this paper, we extend our investigation to the case where the "parent" phases are non-Abelian topological phases. We show explicitly how one can obtain the topological data and symmetry transformations of the symmetry enriched phases from that of the "parent" non-Abelian phase. Two examples are computed: (1) the Ising×Ising¯ phase breaks into the Z2 toric code with Z2 global symmetry; (2) the SU (2) 8 phase breaks into the chiral Fibonacci × Fibonacci phase with a Z2 symmetry, a first non-Abelian example of symmetry enriched topological phase beyond the gauge-theory construction.

Gu, Yuxiang; Hung, Ling-Yan; Wan, Yidun

2014-12-01

343

Relativistic RPA in axial symmetry  

E-print Network

Covariant density functional theory, in the framework of self-consistent Relativistic Mean Field (RMF) and Relativistic Random Phase approximation (RPA), is for the first time applied to axially deformed nuclei. The fully self-consistent RMF+RRPA equations are posed for the case of axial symmetry and non-linear energy functionals, and solved with the help of a new parallel code. Formal properties of RPA theory are studied and special care is taken in order to validate the proper decoupling of spurious modes and their influence on the physical response. Sample applications to the magnetic and electric dipole transitions in $^{20}$Ne are presented and analyzed.

D. Pena Arteaga; P. Ring

2009-09-12

344

Detecting Broken PT-Symmetry  

E-print Network

A fundamental problem in the theory of PT-invariant quantum systems is to determine whether a given system `respects' this symmetry or not. If not, the system usually develops non-real eigenvalues. It is shown in this contribution how to algorithmically detect the existence of complex eigenvalues for a given PT-symmetric matrix. The procedure uses classical results from stability theory which qualitatively locate the zeros of real polynomials in the complex plane. The interest and value of the present approach lies in the fact that it avoids diagonalization of the Hamiltonian at hand.

Stefan Weigert

2006-02-16

345

Symmetry properties in polarimetric remote sensing  

NASA Technical Reports Server (NTRS)

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 a set of equations which restrict the number of independent parameters in the polarimetric covariance matrix. The properties derived under these transformations are general and apply to all scattering mechanisms in a given symmetrical configuration. The scattering coefficients calculated from theoretical models for layer random media and rough surfaces are shown to obey the derived symmetry relations. Use of symmetry properties in remote sensing of structural and environmental responses of scattering media is discussed. As a practical application, the results from this paper provide new methods for the external calibration of polarimetric radars without the deployment of man-made calibration targets.

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

1992-01-01

346

Symmetry energy of dilute warm nuclear matter  

E-print Network

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 (QS) 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.

J. B. Natowitz; G. Ropke; S. Typel; D. Blaschke; A. Bonasera; K. Hagel; T. Klahn; S. Kowalski; L. Qin; S. Shlomo; R. Wada; H. H. Wolter

2010-02-25

347

Symmetry and Dirac points in graphene spectrum  

E-print Network

Existence and stability of Dirac points in the dispersion relation of operators periodic with respect to the hexagonal lattice is investigated for different sets of additional symmetries. The following symmetries are considered: rotation by $2\\pi/3$ and inversion, rotation by $2\\pi/3$ and horizontal reflection, inversion or reflection with weakly broken rotation symmetry, and the case where no Dirac points arise: rotation by $2\\pi/3$ and vertical reflection. All proofs are based on symmetry considerations and are elementary in nature. In particular, existence of degeneracies in the spectrum is proved by a transplantation argument (which is deduced from the (co)representation of the relevant symmetry group). The conical shape of the dispersion relation is obtained from its invariance under rotation by $2\\pi/3$. Persistence of conical points when the rotation symmetry is weakly broken is proved using a geometric phase in one case and parity of the eigenfunctions in the other.

Gregory Berkolaiko; Andrew Comech

2014-12-28

348

Dynamics-dependent symmetries in Newtonian mechanics  

E-print Network

We exhibit two symmetries of one-dimensional Newtonian mechanics whereby a solution is built from the history of another solution via a generally nonlinear and complex potential-dependent transformation of the time. One symmetry intertwines the square roots of the kinetic and potential energies and connects solutions of the same dynamical problem (the potential is an invariant function). The other symmetry connects solutions of different dynamical problems (the potential is a scalar function). The existence of corresponding conserved quantities is examined using Noethers theorem and it is shown that the invariant-potential symmetry is correlated with energy conservation. In the Hamilton-Jacobi picture the invariant-potential transformation provides an example of a field-dependent symmetry in point mechanics. It is shown that this transformation is not a symmetry of the Schroedinger equation.

Peter Holland

2014-09-19

349

Using Wilson's renormalization group to repair symmetries  

NASA Astrophysics Data System (ADS)

Wilson's renormalization group can be used to approximate the behavior of an extremely large number of coupled degrees of freedom. A transformation runs a cutoff that limits the number of coupled states, and its action can be approximated by following the evolution of a finite number of relevant and marginal operators in most theories of physical interest. Symmetries usually constrain these operators; however, if the cutoff itself violates a symmetry, symmetry-breaking operators appear, and in general some sort of fine tuning is required to fix their strengths so that the symmetry is restored in physical quantities. I discuss a simple constraint on the renormalization group flow (coupling coherence) that can be used to isolate and repair such hidden symmetries and give several examples. These ideas have been employed to restore Lorentz and gauge symmetries in light-front QED and QCD calculations, which are also briefly discussed.

Perry, Robert J.

2001-07-01

350

Dynamics-dependent symmetries in Newtonian mechanics  

E-print Network

We exhibit two symmetries of one-dimensional Newtonian mechanics whereby a solution is built from the history of another solution via a generally nonlinear and complex potential-dependent transformation of the time. One symmetry intertwines the square roots of the kinetic and potential energies and connects solutions of the same dynamical problem (the potential is an invariant function). The other symmetry connects solutions of different dynamical problems (the potential is a scalar function). The existence of corresponding conserved quantities is examined using Noethers theorem and it is shown that the invariant-potential symmetry is correlated with energy conservation. In the Hamilton-Jacobi picture the invariant-potential transformation provides an example of a field-dependent symmetry in point mechanics. It is shown that this transformation is not a symmetry of the Schroedinger equation.

Holland, Peter

2014-01-01

351

Beyond bilateral symmetry: geometric morphometric methods for any type of symmetry  

PubMed Central

Background Studies of symmetric structures have made important contributions to evolutionary biology, for example, by using fluctuating asymmetry as a measure of developmental instability or for investigating the mechanisms of morphological integration. Most analyses of symmetry and asymmetry have focused on organisms or parts with bilateral symmetry. This is not the only type of symmetry in biological shapes, however, because a multitude of other types of symmetry exists in plants and animals. For instance, some organisms have two axes of reflection symmetry (biradial symmetry; e.g. many algae, corals and flowers) or rotational symmetry (e.g. sea urchins and many flowers). So far, there is no general method for the shape analysis of these types of symmetry. Results We generalize the morphometric methods currently used for the shape analysis of bilaterally symmetric objects so that they can be used for analyzing any type of symmetry. Our framework uses a mathematical definition of symmetry based on the theory of symmetry groups. This approach can be used to divide shape variation into a component of symmetric variation among individuals and one or more components of asymmetry. We illustrate this approach with data from a colonial coral that has ambiguous symmetry and thus can be analyzed in multiple ways. Our results demonstrate that asymmetric variation predominates in this dataset and that its amount depends on the type of symmetry considered in the analysis. Conclusions The framework for analyzing symmetry and asymmetry is suitable for studying structures with any type of symmetry in two or three dimensions. Studies of complex symmetries are promising for many contexts in evolutionary biology, such as fluctuating asymmetry, because these structures can potentially provide more information than structures with bilateral symmetry. PMID:21958045

2011-01-01

352

$f(T)$ cosmology via Noether symmetry  

E-print Network

We consider Noether symmetry approach to find out exact cosmological solutions in $f(T)$-gravity. Instead of taking into account phenomenological models, we apply the Noether symmetry to the $f(T)$ gravity. As a result, the presence of such symmetries selects viable models and allow to solve the equations of motion. We show that the generated $f(T)$ leads to a power law expansion for the cosmological scale factor.

K. Atazadeh; F. Darabi

2012-05-10

353

Relativistic Harmonic Oscillator with Spin Symmetry  

E-print Network

The eigenfunctions and eigenenergies for a Dirac Hamiltonian with equal scalar and vector harmonic oscillator potentials are derived. Equal scalar and vector potentials may be applicable to the spectrum of an antinucleion imbedded in a nucleus. Triaxial, axially deformed, and spherical oscillator potentials are considered. The spectrum has a spin symmetry for all cases and, for the spherical harmonic oscillator potential, a higher symmetry analogous to the SU(3) symmetry of the non-relativistic harmonic oscillator is discussed.

Joseph N. Ginocchio

2005-03-25

354

Modified pure spinors and mirror symmetry  

Microsoft Academic Search

It has been argued recently that mirror symmetry exchanges two pure spinors characterizing a generic manifold with SU(3) structure. We show that quantities involved in stability conditions for topological D-branes, and containing gauge fields in their expressions, are exchanged by mirror symmetry. This exchange can be considered as an open-string version of the mirror symmetry between pure spinors. It emerges

Pascal Grange; Ruben Minasian

2006-01-01

355

Galileo Symmetries in Polymer Particle Representation  

E-print Network

To illustrate the conceptual problems for the low-energy symmetries in the continuum of spacetime emerging from the discrete quantum geometry, Galileo symmetries are investigated in the polymer particle representation of a non-relativistic particle as a simple toy model. The complete Galileo transformations (translation, rotation and Galileo boost) are naturally defined in the polymer particle Hilbert space and Galileo symmetries are recovered with highly suppressed deviations in the low-energy regime from the underlying polymer particle description.

Dah-Wei Chiou

2007-04-10

356

Multifragmentation and Symmetry Energy Studied with AMD  

E-print Network

The antisymmetrized molecular dynamics (AMD) simulations suggest that the isospin composition of fragments produced dynamically in multifragmentation reactions is basically governed by the symmetry energy of low-density uniform nuclear matter rather than the symmetry energy for the ground-state finite nuclei. After the statistical secondary decay of the excited fragments, the symmetry energy effect still remains in the fragment isospin composition, though the effect in the isoscaling parameter seems a very delicate problem.

Akira Ono

2006-05-02

357

Contact Symmetries and Hamiltonian Thermodynamics  

E-print Network

In this work we analyze several aspects of the application of contact geometry to thermodynamics. We first investigate the role of gauge transformations and Legendre symmetries in thermodynamics, with respect to both the contact and the metric structures. Then we present a novel mathematical characterization of first order phase transitions as equilibrium processes on the thermodynamic phase space for which the Legendre symmetry is broken. Moreover, using contact Hamiltonian dynamics, we propose a formalism for thermodynamics that resembles the classical Hamiltonian formulation of conservative mechanics. We find out the general functional form for the relevant contact Hamiltonian in thermodynamics and show that it is a measure of the entropy production along thermodynamic processes. Therefore, we use such property to give a precise definition of thermodynamically admissible processes according to the Second Law of thermodynamics. Finally, we also show that we can give an equivalent formulation in terms of the Fisher-Rao metric, in analogy with the Theory of Relativity, where the metric structure defines admissible paths.

A. Bravetti; C. S. Lopez-Monsalvo; F. Nettel

2014-09-25

358

Symmetry Principles of the Unified Field Theory  

E-print Network

The principles of energy, symmetry, entropy, and causality conservation are discussed in a "Tetrahedron Model" of a conceptually complete "T.O.E.:" "The charges of matter are the symmetry debts of light" (Noether's Theorem). Symmetry debts for each force as well as gravitation's conservation roles are considered. Special attention is given to the weak force. Charge invariance (including "Lorentz Invariance") and "Noether's Theorem" are seen as keys to understanding the local action of the forces. A synthesis between the "Tetrahedron Model" and global vs local gauge symmetry concepts as found in the "Standard Model" of physics is presented.

John A. Gowan

2009-07-03

359

Elliptic-symmetry vector optical fields.  

PubMed

We present in principle and demonstrate experimentally a new kind of vector fields: elliptic-symmetry vector optical fields. This is a significant development in vector fields, as this breaks the cylindrical symmetry and enriches the family of vector fields. Due to the presence of an additional degrees of freedom, which is the interval between the foci in the elliptic coordinate system, the elliptic-symmetry vector fields are more flexible than the cylindrical vector fields for controlling the spatial structure of polarization and for engineering the focusing fields. The elliptic-symmetry vector fields can find many specific applications from optical trapping to optical machining and so on. PMID:25321015

Pan, Yue; Li, Yongnan; Li, Si-Min; Ren, Zhi-Cheng; Kong, Ling-Jun; Tu, Chenghou; Wang, Hui-Tian

2014-08-11

360

Symmetry energy in nuclear density functional theory  

E-print Network

The nuclear symmetry energy represents a response to the neutron-proton asymmetry. In this survey we discuss various aspects of symmetry energy in the framework of nuclear density functional theory, considering both non-relativistic and relativistic self-consistent mean-field realizations side-by-side. Key observables pertaining to bulk nucleonic matter and finite nuclei are reviewed. Constraints on the symmetry energy and correlations between observables and symmetry-energy parameters, using statistical covariance analysis, are investigated. Perspectives for future work are outlined in the context of ongoing experimental efforts.

W. Nazarewicz; P. -G. Reinhard; W. Satula; D. Vretenar

2013-07-22

361

Asymptotic symmetries of Yang-Mills theory  

NASA Astrophysics Data System (ADS)

Asymptotic symmetries at future null infinity ( +) of Minkowski space for electrodynamics with massless charged fields, as well as nonabelian gauge theories with gauge group G, are considered at the semiclassical level. The possibility of charge/color flux through + suggests the symmetry group is infinite-dimensional. It is conjectured that the symmetries include a G Kac-Moody symmetry whose generators are "large" gauge transformations which approach locally holomorphic functions on the conformal two-sphere at + and are invariant under null translations. The Kac-Moody currents are constructed from the gauge field at the future boundary of +. The current Ward identities include Weinberg's soft photon theorem and its colored extension.

Strominger, Andrew

2014-07-01

362

Functional ferroic heterostructures with tunable integral symmetry  

NASA Astrophysics Data System (ADS)

The relation between symmetry and functionality was pinpointed by Pierre Curie who stated that it is the symmetry breaking that creates physical properties. This fundamental principle is nowadays used for engineering heterostructures whose integral symmetry leads to exotic phenomena such as one-way transparency. For switching devices, however, such symmetry-related functionalities cannot be used because the symmetry in conventional heterostructures is immutable once the material has been synthesized. Here we demonstrate a concept for post-growth symmetry control in PbZr0.2Ti0.8O3 and BiFeO3-based heterostructures. A conducting oxide is sandwiched between two ferroelectric layers, and inversion symmetry is reversibly switched on or off by layer-selective electric-field poling. The generalization of our approach to other materials and symmetries is discussed. We thus establish ferroic trilayer structures as device components with reversibly tunable symmetry and demonstrate their use as light emitters that can be activated and deactivated by applying moderate electric voltages.

Becher, C.; Trassin, M.; Lilienblum, M.; Nelson, C. T.; Suresha, S. J.; Yi, D.; Yu, P.; Ramesh, R.; Fiebig, M.; Meier, D.

2014-07-01

363

Chiral symmetry on the edge of two-dimensional symmetry protected topological phases  

E-print Network

Symmetry protected topological (SPT) states are short-range entangled states with symmetry. The boundary of a SPT phases has either gapless excitations or degenerate ground states, around a gapped bulk. Recently, we proposed ...

Chen, Xie

364

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

365

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

366

Covering Clusters in Icosahedral Quasicrystals  

NASA Astrophysics Data System (ADS)

In this chapter we examine the local environments in i-AlCuFe and i-AlPdMn models about Wyckoff positions of the 6D lattice. We consider extended Bergman clusters of 6 shells that appear naturally in the Katz-Gratias model. We discuss the cell decomposition of the atomic surfaces and the variable occupation number of some of the shells. We show that a fixed extended Bergman cluster of 6 shells and 106 atoms covers about 98% of atomic positions. We also prove that a variable extended Bergman cluster of 6 shells, which contains the previous fixed cluster, covers all atomic positions of the theoretical model.

Duneau, Michel; Gratias, Denis

367

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.

368

Effect of temperature on symmetry breaking excited state charge separation: restoration of symmetry at elevated temperature.  

PubMed

With an increase in temperature, an unprecedented restoration of symmetry in the symmetry breaking excited state charge transfer is observed in a geminal pair of near-orthogonally connected perylenimide dimers. Such restoration of symmetry could be attributed to the interchromophoric planarization and/or loss of solvation asymmetry at elevated temperature resulting in enhanced fluorescence quantum yield. PMID:23051919

Khandelwal, Hitesh; Mallia, Ajith R; Cheriya, Rijo T; Hariharan, Mahesh

2012-11-28

369

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

370

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

371

Symmetry properties of positive solutions of parabolic equations: a survey  

E-print Network

Symmetry properties of positive solutions of parabolic equations: a survey P. Pol´acik School certain reflectional symmetries, the presented results show how positive solutions reflect the symmetries. Depending on the class of solutions con- sidered, the symmetries for all times or asymptotic symmetries

Polacik, Peter

372

Graphic Design: Using Symmetry to Create Corporate Logos  

NSDL National Science Digital Library

This activity teaches students to describe three types of symmetry, to categorize symmetric figures based on type of symmetry, and to create figures using different type of symmetry. The activities use familiar logos and signs to show how symmetry is used in the world of design, and to help differentiate between the different kinds of symmetry used in these examples.

Math, Pbs T.; Pbs

1995-01-01

373

Electroweak symmetry breaking via QCD.  

PubMed

We propose a new mechanism to generate the electroweak scale within the framework of QCD, which is extended to include conformally invariant scalar degrees of freedom belonging to a larger irreducible representation of SU(3)c. The electroweak symmetry breaking is triggered dynamically via the Higgs portal by the condensation of the colored scalar field around 1 TeV. The mass of the colored boson is restricted to be 350??GeV?mS?3??TeV, with the upper bound obtained from perturbative renormalization group evolution. This implies that the colored boson can be produced at the LHC. If the colored boson is electrically charged, the branching fraction of the Higgs boson decaying into two photons can slightly increase, and moreover, it can be produced at future linear colliders. Our idea of nonperturbative electroweak scale generation can serve as a new starting point for more realistic model building in solving the hierarchy problem. PMID:25215976

Kubo, Jisuke; Lim, Kher Sham; Lindner, Manfred

2014-08-29

374

Electroweak Symmetry Breaking via QCD  

NASA Astrophysics Data System (ADS)

We propose a new mechanism to generate the electroweak scale within the framework of QCD, which is extended to include conformally invariant scalar degrees of freedom belonging to a larger irreducible representation of SU(3)c. The electroweak symmetry breaking is triggered dynamically via the Higgs portal by the condensation of the colored scalar field around 1 TeV. The mass of the colored boson is restricted to be 350 GeV ?mS?3 TeV, with the upper bound obtained from perturbative renormalization group evolution. This implies that the colored boson can be produced at the LHC. If the colored boson is electrically charged, the branching fraction of the Higgs boson decaying into two photons can slightly increase, and moreover, it can be produced at future linear colliders. Our idea of nonperturbative electroweak scale generation can serve as a new starting point for more realistic model building in solving the hierarchy problem.

Kubo, Jisuke; Lim, Kher Sham; Lindner, Manfred

2014-08-01

375

PREFACE: Symmetries in Science XVI  

NASA Astrophysics Data System (ADS)

This volume of the proceedings ''Symmetries in Science XVI'' is dedicated to the memory of Miguel Lorente and Allan Solomon who both participated several times in these Symposia. We lost not only two great scientists and colleagues, but also two wonderful persons of high esteem whom we will always remember. Dieter Schuch, Michael Ramek There is a German saying ''all good things come in threes'' and ''Symmetries in Science XVI'', convened July 20–26, 2013 at the Mehrerau Monastery, was our third in the sequel of these symposia since taking it over from founder Bruno Gruber who instigated it in 1988 (then in Lochau). Not only the time seemed to have been perfect (one week of beautiful sunshine), but also the medley of participants could hardly have been better. This time, 34 scientists from 16 countries (more than half outside the European Union) came together to report and discuss their latest results in various fields of science, all related to symmetries. The now customary grouping of renowned experts and talented newcomers was very rewarding and stimulating for all. The informal, yet intense, discussions at ''Gasthof Lamm'' occurred (progressively later) each evening till well after midnight and finally till almost daybreak! However, prior to the opening ceremony and during the conference, respectively, we were informed that Miguel Lorente and Allan Solomon had recently passed away. Both attended the SIS Symposia several times and had many friends among present and former participants. Professor Peter Kramer, himself a long–standing participant and whose 80th birthday commemoration prevented him from attending SIS XVI, kindly agreed to write the obituary for Miguel Lorente. Professors Richard Kerner and Carol Penson (both also former attendees) penned, at very short notice, the tribute to Allan Solomon. The obituaries are included in these Proceedings and further tributes have been posted to our conference website. In 28 lectures and an evening poster–session, topics ranging from theoretical chemistry and molecular physics via fundamental problems in quantum theory to thermodynamics, nonlinear dynamics, soliton theory and finally cosmology, were examined and lively discussed. Nearly all the talks can also be viewed on the conference website. The majority of participants contributed to these Proceedings but some were unable to do so as their results were either previously submitted or published elsewhere. We refer to: · Quesne C 2013, J. Math. Phys. 54, 102102. · Spera M 2013, (Nankai Series in Pure, Applied Mathematics and Theoretical Physics): 11 Symmetries and Groups in Contemporary Physics: pp. 593–598 Proceedings of the XXIX International Colloquium on Group–Theoretical Methods in Physics Tianjin, China, 20 – 26 August 2012 (World Scientific, Singapore) · Snobl L and Winternitz P 2014, Classification and Identification of Lie Algebras, CRM Monograph Series 33 (Montreal) ISBN–10: 0–8218–4355–9, ISBN–13: 978–0–8218–4355–0 (http://www.ams.org/bookstore?fn=20&arg1=crmmseries&ikey=CRMM-33). Our personal thanks to Daniel and family! Endless support from the Schenk Family who, among other things, sponsored (yet again) the entire conference dinner (including wines and banquet hall) meant that some costs could be alleviated. We could therefore assist various colleagues from economically–weak countries, despite the lack of external funding. A financial deficit meant we would have had to forego the Conference Proceedings, published in previous years by IOP. After long deliberations, and with donations from Gerhard Berssenbrügge, Dr. Dr. Stephan Hauk and Dr. Volker Weisswange, this could be facilitated. We are very grateful to these private donors for their generous and wholehearted support. The staff of Collegium Mehrerau is also to be thanked for their hospitality. Finally, our sincere thanks to Yvette not only for her preparatory work and support during the conference, but also for her persistent interest and help in producing the Proceedings within a reasonable time. Dieter Schuc

2014-10-01

376

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

377

Wormhole dynamics in spherical symmetry  

E-print Network

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.

Sean A. Hayward

2009-03-31

378

Invisibility and PT-symmetry  

E-print Network

For a general complex scattering potential defined on a real line, we show that the equations governing invisibility of the potential are invariant under the combined action of parity and time-reversal (PT) transformation. We determine the PT-symmetric an well as non-PT-symmetric invisible configurations of an easily realizable exactly solvable model that consists of a two-layer planar slab consisting of optically active material. Our analysis shows that although PT-symmetry is neither necessary nor sufficient for the invisibility of a scattering potential, it plays an important role in the characterization of the invisible configurations. A byproduct of our investigation is the discovery of certain configurations of our model that are effectively reflectionless in a spectral range as wide as several hundred nanometers.

Ali Mostafazadeh

2012-12-18

379

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

380

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

381

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

382

Symmetry aspects of nonholonomic field theories  

E-print Network

The developments in this paper are concerned with nonholonomic field theories in the presence of symmetries. Having previously treated the case of vertical symmetries, we now deal with the case where the symmetry action can also have a horizontal component. As a first step in this direction, we derive a new and convenient form of the field equations of a nonholonomic field theory. Nonholonomic symmetries are then introduced as symmetry generators whose virtual work is zero along the constraint submanifold, and we show that for every such symmetry, there exists a so-called momentum equation, describing the evolution of the associated component of the momentum map. Keeping up with the underlying geometric philosophy, a small modification of the derivation of the momentum lemma allows us to treat also generalized nonholonomic symmetries, which are vector fields along a projection. Such symmetries arise for example in practical examples of nonholonomic field theories such as the Cosserat rod, for which we recover both energy conservation (a previously known result), as well as a modified conservation law associated with spatial translations.

J. Vankerschaver; D. Martin de Diego

2007-12-14

383

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

384

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

385

Teaching symmetry in the introductory physics curriculum  

SciTech Connect

Modern physics is largely defined by fundamental symmetry principles and Noether's Theorem. Yet these are not taught, or rarely mentioned, to beginning students, thus missing an opportunity to reveal that the subject of physics is as lively and contemporary as molecular biology, and as beautiful as the arts. We prescribe a symmetry module to insert into the curriculum, of a week's length.

Hill, Christopher T.; Lederman, Leon M.

2000-01-01

386

Broken chiral symmetry on a null plane  

SciTech Connect

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. -- Highlights: •A proof (the first) of Goldstone’s theorem on a null-plane is given. •The puzzle of chiral-symmetry breaking condensates on a null-plane is solved. •The emergence of spin-flavor symmetries in null-plane QCD is demonstrated.

Beane, Silas R., E-mail: silas@physics.unh.edu

2013-10-15

387

On systems having Poincaré and Galileo symmetry  

NASA Astrophysics Data System (ADS)

Using the wave equation in d ? 1 space dimensions it is illustrated how dynamical equations may be simultaneously Poincaré and Galileo covariant with respect to different sets of independent variables. This provides a method to obtain dynamics-dependent representations of the kinematical symmetries. When the field is a displacement function both symmetries have a physical interpretation. For d = 1 the Lorentz structure is utilized to reveal hitherto unnoticed features of the non-relativistic Chaplygin gas including a relativistic structure with a limiting case that exhibits the Carroll group, and field-dependent symmetries and associated Noether charges. The Lorentz transformations of the potentials naturally associated with the Chaplygin system are given. These results prompt the search for further symmetries and it is shown that the Chaplygin equations support a nonlinear superposition principle. A known spacetime mixing symmetry is shown to decompose into label-time and superposition symmetries. It is shown that a quantum mechanical system in a stationary state behaves as a Chaplygin gas. The extension to d > 1 is used to illustrate how the physical significance of the dual symmetries is contingent on the context by showing that Maxwell's equations exhibit an exact Galileo covariant formulation where Lorentz and gauge transformations are represented by field-dependent symmetries. A natural conceptual and formal framework is provided by the Lagrangian and Eulerian pictures of continuum mechanics.

Holland, Peter

2014-12-01

388

Broken Symmetries and Bare Coupling Constants  

Microsoft Academic Search

There are known cases of symmetry laws valid for one kind of interaction but broken by another. Each symmetry is then supposed to be exact for bare masses and coupling constants but only approximate for the renormalized quantities, like neutron and proton masses. We ask how the equality of unrenormalized constants can be rephrased as a statement about measurable quantities.

Murray Gell-Mann; Fredrik Zachariasen

1961-01-01

389

On systems having Poincaré and Galileo symmetry  

E-print Network

Using the wave equation in d > or = 1 space dimensions it is illustrated how dynamical equations may be simultaneously Poincar\\'e and Galileo covariant with respect to different sets of independent variables. This provides a method to obtain dynamics-dependent representations of the kinematical symmetries. When the field is a displacement function both symmetries have a physical interpretation. For d = 1 the Lorentz structure is utilized to reveal hitherto unnoticed features of the non-relativistic Chaplygin gas, including a relativistic structure with a limiting case that exhibits the Carroll group, and field-dependent symmetries and associated Noether charges. The Lorentz transformations of the potentials naturally associated with the Chaplygin system are given. These results prompt the search for further symmetries and it is shown that the Chaplygin equations support a nonlinear superposition principle. A known spacetime mixing symmetry is shown to decompose into label-time and superposition symmetries. It is shown that a quantum mechanical system in a stationary state behaves as a Chaplygin gas. The extension to d > 1 is used to illustrate how the physical significance of the dual symmetries is contingent on the context by showing that Maxwells equations exhibit an exact Galileo covariant formulation where Lorentz and gauge transformations are represented by field-dependent symmetries. A natural conceptual and formal framework is provided by the Lagrangian and Eulerian pictures of continuum mechanics.

Peter Holland

2014-09-19

390

CP Symmetry in Particle Introduction Results  

E-print Network

CP Symmetry in Particle Physics Introduction Results B-Factory Interpretation Exp. method Future/19Physics in Ljubljana, FMF, July 2011 j j y y #12;Introduction Why CP (A)Symmetry? Introduction Results B anti-baryons annihilated, while 1/109 baryons did not? p y anti-particles #12;Introduction Why CP (A

Â?umer, Slobodan

391

Knot soliton models, submodels, and their symmetries  

E-print Network

For some non-linear field theories which allow for soliton solutions, submodels with infinitely many conservation laws can be defined. Here we investigate the symmetries of the submodels, where in some cases we find a symmetry enhancement for the submodels, whereas in others we do not.

Adam, C

2006-01-01

392

Knot soliton models, submodels, and their symmetries  

E-print Network

For some non-linear field theories which allow for soliton solutions, submodels with infinitely many conservation laws can be defined. Here we investigate the symmetries of the submodels, where in some cases we find a symmetry enhancement for the submodels, whereas in others we do not.

C. Adam; J. Sanchez-Guillen

2005-11-21

393

A Quantitative Evaluation of Symmetry Detection Algorithms  

E-print Network

A Quantitative Evaluation of Symmetry Detection Algorithms Po-Chun Chen1 , James Hays2 , Seungkyu. This paper presents a sys- tematic, quantitative evaluation of rotation, reflection and translation sym-defined quantitative evaluation scheme for an effective validation and comparison of different symmetry detection

394

Order in the Universe: The Symmetry Principle.  

ERIC Educational Resources Information Center

The first two papers in this booklet provide a review of the pervasiveness of symmetry in nature and art, discussing how symmetry can be traced through every domain open to our understanding, from all aspects of nature to the special provinces of man; the checks and balances of government, the concept of equal justice, and the aesthetic ordering…

Foundation for Integrative Education, Inc., New York, NY.

395

Spontaneous Breaking of Space-Time Symmetries  

E-print Network

Kinematical and dynamical mechanisms leading to the spontaneous breaking of space-time symmetries are described. The symmetries affected are space and time translations, space rotations, scale and conformal transformations. Applications are made to solidification, string theory compactifications, the analysis of stable theories with no ground states, supersymmetry breaking and the determination of the value of the vacuum energy.

Rabinovici, Eliezer

2007-01-01

396

Spontaneous Breaking of Space-Time Symmetries  

E-print Network

Kinematical and dynamical mechanisms leading to the spontaneous breaking of space-time symmetries are described. The symmetries affected are space and time translations, space rotations, scale and conformal transformations. Applications are made to solidification, string theory compactifications, the analysis of stable theories with no ground states, supersymmetry breaking and the determination of the value of the vacuum energy.

Eliezer Rabinovici

2007-08-14

397

Symmetry of a liquid and symmetry breaking at the glass transition  

NASA Astrophysics Data System (ADS)

For the first time a liquid is considered from the point of view of Shubnikov antisymmetry (black-white or sign symmetry), a method that permits one to find a hidden symmetry of the liquid whose breaking reveals itself directly at the glass transition. This approach gives the opportunity to consider symmetries of different types of elementary motions in liquids, the symmetry-stipulated properties of liquids, the nature of the symmetry of the order parameter for the glass transition and, as a whole, the dynamical structure of the liquid on the scales of short-, medium-, and long-range order.

Dembovsky, S. A.

1998-02-01

398

Heavy Diquark Symmetry Constraints for Strong Decays  

E-print Network

The Heavy Diquark Symmetry (HDS) of Doubly Heavy Baryons (DHBs) provides new insights into the spectroscopy of these hadrons. We derive the consequences of this symmetry for the mass spectra and the decay widths of DHBs. We compare these symmetry constraints to results from a nonrelativistic quark model for the mass spectra and results from the $^3P_0$ model for strong decays. The quark model we implement was not constructed with these symmetries and contains interactions which explicitly break HDS. Nevertheless, these symmetries emerge. We argue that the $^3P_0$ model and any other model for strong transitions which employs a spectator assumption explicitly respects HDS. We also explore the possibility of treating the strange quark as a heavy quark and apply these ideas to $\\Xi$, $\\Xi_c$, and $\\Xi_b$ baryons.

B. Eakins; W. Roberts

2012-07-31

399

Symmetry breaking patterns in 3HDM  

NASA Astrophysics Data System (ADS)

An attractive feature of New Physics models with multiple Higgs fields is that they are equipped with discrete symmetry groups in the Higgs and flavour sectors. These symmetry groups are often broken at the global minimum of the Higgs potential, either completely or to a proper subgroup, with certain phenomenological consequences. Here, we systematically explore these symmetry breaking patterns in the scalar sector of the three-Higgs-doublet model (3HDM). We use the full list of discrete symmetry groups allowed in 3HDM, and for each group we find all possible ways it can break by the Higgs vacuum expectation value alignment. We also discuss the interplay between these symmetry groups and various forms of CP -violation in the scalar sector of 3HDM. Not only do our results solve the problem for 3HDM, but they also hint at several general features in multi-scalar sectors.

Ivanov, I. P.; Nishi, C. C.

2015-01-01

400

Exploiting Matrix Symmetries and Physical Symmetries in Matrix Product States and Tensor Trains  

E-print Network

We focus on symmetries related to matrices and vectors appearing in the simulation of quantum many-body systems. Spin Hamiltonians have special matrix-symmetry properties such as persymmetry. Furthermore, the systems may exhibit physical symmetries translating into symmetry properties of the eigenvectors of interest. Both types of symmetry can be exploited in sparse representation formats such as Matrix Product States (MPS) for the desired eigenvectors. This paper summarizes symmetries of Hamiltonians for typical physical systems such as the Ising model and lists resulting properties of the related eigenvectors. Based on an overview of Matrix Product States (Tensor Trains or Tensor Chains) and their canonical normal forms we show how symmetry properties of the vector translate into relations between the MPS matrices and, in turn, which symmetry properties result from relations within the MPS matrices. In this context we analyze different kinds of symmetries and derive appropriate normal forms for MPS representing these symmetries. Exploiting such symmetries by using these normal forms will lead to a reduction in the number of degrees of freedom in the MPS matrices. This paper provides a uniform platform for both well-known and new results which are presented from the (multi-)linear algebra point of view.

T. Huckle; K. Waldherr; T. Schulte-Herbrueggen

2013-01-04

401

Symmetry-protected topological phases in noninteracting fermion systems  

E-print Network

Symmetry-protected topological (SPT) phases are gapped quantum phases with a certain symmetry, which can all be smoothly connected to the same trivial product state if we break the symmetry. For noninteracting fermion ...

Wen, Xiao-Gang

402

Symmetry-Protected Quantum Spin Hall Phases in Two Dimensions  

E-print Network

Symmetry-protected topological (SPT) states are short-range entangled states with symmetry. Nontrivial SPT states have symmetry-protected gapless edge excitations. In 2 dimension (2D), there are an infinite number of ...

Liu, Zheng-Xin

403

PREFACE: Symmetries in Science XIV  

NASA Astrophysics Data System (ADS)

Symmetries Logo This volume of the proceedings "Symmetries in Science XIV" is dedicated to the memory of our colleagues and dear friends Marcos Moshinsky and Yuri? Smirnov who regularly participated in these Symposia and were a great inspiration to many. We shall miss them. Dieter Schuch and Michael Ramek The international symposium "Symmetries in Science XIV" held at Collegium Mehrerau in Bregenz, Austria from July 19-24, 2009, attended by 32 scientists from 11 countries, was an experiment, performed by theoreticians. Aim of this experiment was to find out if the desire to revive or even continue this conference series was stronger than the very restricted pecuniary boundary conditions. It obviously was! After its establishment by Bruno Gruber in 1979, the biennial series settled in the very stimulating atmosphere of the monastery Mehrerau, which provided the ideal environment for a limited number of invited participants to exchange ideas, without parallel sessions, and pursue deeper discussions (at the latest in the evening at "Gasthof Lamm"). When the conference series terminated in 2003, former participants were quite disappointed. Meeting again at several (larger) conferences in subsequent years, there were repeated expressions of "the lack of a Bregenz-type meeting in our field nowadays" and the question of a possible "revitalization", even without external funding. After some hesitation, but also driven by our own desire to reinstate the series, we consulted Bruno who not only approved wholeheartedly but also offered his full support. It all finally led to the symposium in July 2009. The atmosphere was really like in the "good old days" and the interesting and thought-provoking presentations culminated in the publication of these Proceedings. We are grateful to Carl Bender for establishing contact with IOP making it possible for us to publish these Proceedings in the Journal of Physics Conference Series. A majority of the participants contributed to these Proceedings though some were unable to do so as their results were either previously submitted or published elsewhere. In order to make these contributions also available to readers of the Proceedings, we now list the respective references as follow: Albertsson C, Hlavatý L and Šnobl L 2008 On the Poisson-Lie T-plurality of boundary conditions J. Math. Phys. 49 032301-23, arXiv:0706.0820; Bender C M, Brody D C and Hook D W 2008 Quantum effects in classical systems having complex energy J. Phys. A: Math. Theor. 41 352003 (15 pp); Kanellopoulos V, Kleber M and Kramer T 2009 Use of Lambert's theorem for the n-dimensional Coulomb problem Phys. Rev. A 80 012101; Kramer P 2010 Platonic topology and CMB fluctuations: homotopy anisotropy and multipole selection rules Class. Quantum Grav. 27 095013 (27 pp), arXiv:0909.2758v1; Quesne C 2009 Solvable rational potentials and exceptional orthogonal polynomials in supersymmetric quantum mechanics SIGMA 5 084 (24 pp). On the other hand, some colleagues planning on attending the meeting had to forfeit their participation due to unforeseeable circumstances. As they had prepared their contributions particularly for our symposium, we have also allowed their input. The articles of Kibler, Leach, Reinisch and Wolf have therefore been included though the authors were absent. Marcos Moshinsky and Yuri? Smirnov, two long-standing colleagues and friends who attended the symposium on multiple occasions passed away in the year before the conference. A memorial service was held at the chapel of the Mehrerau during the meeting. The commemorative words from Father Vinzenz were based on information from our own experience, from an article by Alejandro Frank in Letras Libres Junio 2009, p.54 (a monthly literary magazine published by Editorial Vuelta, in Spanish) and articles from "TESTIMONIOS, Marcos Moshinsky: 80 años de vida y 60 años de trabajo científico" 2001 Frank A and Wolf K B eds. Two contributions dedicated especially in their memory are also included in thes

Schuch, Dieter; Ramek, Michael

2010-04-01

404

The lattice Schwarzian KdV equation and its symmetries  

E-print Network

In this paper we present a set of results on the symmetries of the lattice Schwarzian Korteweg-de Vries (lSKdV) equation. We construct the Lie point symmetries and, using its associated spectral problem, an infinite sequence of generalized symmetries and master symmetries. We finally show that we can use master symmetries of the lSKdV equation to construct non-autonomous non-integrable generalized symmetries.

Decio Levi; Matteo Petrera; Christian Scimiterna

2007-01-15

405

Scalar Field Theories with Polynomial Shift Symmetries  

E-print Network

We continue our study of naturalness in nonrelativistic QFTs of the Lifshitz type, focusing on scalar fields that can play the role of Nambu-Goldstone (NG) modes associated with spontaneous symmetry breaking. Such systems allow for an extension of the constant shift symmetry to a shift by a polynomial of degree $P$ in spatial coordinates. These "polynomial shift symmetries" in turn protect the technical naturalness of modes with a higher-order dispersion relation, and lead to a refinement of the proposed classification of infrared Gaussian fixed points available to describe NG modes in nonrelativistic theories. Generic interactions in such theories break the polynomial shift symmetry explicitly to the constant shift. It is thus natural to ask: Given a Gaussian fixed point with polynomial shift symmetry of degree $P$, what are the lowest-dimension operators that preserve this symmetry, and deform the theory into a self-interacting scalar field theory with the shift symmetry of degree $P$? To answer this (essen...

Griffin, Tom; Horava, Petr; Yan, Ziqi

2014-01-01

406

Geometry of Majorana neutrino and new symmetries  

E-print Network

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 the Majorana-Diraco genesis in which we have a chance to understand creation of Q(em) charge and its conservation in our D=1+3 Universe after the Big Bang. In the Majorana-Diraco genesis approach there appears a possibility to check the proton and electron non-stability on the very low energy scale. In particle physics and in our space-time geometry, the Majorana nature of the neutrino can be related to new types of symmetries which are lying beyond the binary Cartan-Killing-Lie algebras/superalgebras. This can just support a conjecture about the non-completeness of the SM in terms of binary Cartan--Killing--Lie symmetries/supersymmetries. As one of the very important applications of such new ternary symmetries could be related with explanation of the nature of the three families and three colour symmetry. The Majorana neutrino can directly indicate the existence of a new extra-dimensional geometry and thanks to new ternary space-time symmetries, could lead at high energies to the unextraordinary phenomenological consequences.

G. G. Volkov

2006-07-30

407

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. PMID:19805113

Nussinov, Zohar; Ortiz, Gerardo

2009-01-01

408

PT Symmetry and the Sign Problem  

E-print Network

Generalized PT symmetry provides crucial insight into the sign problem for two classes of models. In the case of quantum statistical models at non-zero chemical potential, the free energy density is directly related to the ground state energy of a non-Hermitian, but generalized PT-symmetric Hamiltonian. There is a corresponding class of PT-symmetric classical statistical mechanics models with non-Hermitian transfer matrices. For both quantum and classical models, the class of models with generalized PT symmetry is precisely the class where the complex weight problem can be reduced to real weights, i.e., a sign problem. The spatial two-point functions of such models can exhibit three different behaviors: exponential decay, oscillatory decay, and periodic behavior. The latter two regions are associated with PT symmetry breaking, where a Hamiltonian or transfer matrix has complex conjugate pairs of eigenvalues. The transition to a spatially modulated phase is associated with PT symmetry breaking of the ground state, and is generically a first-order transition. In the region where PT symmetry is unbroken, the sign problem can always be solved in principle. Moreover, there are models with PT symmetry which can be simulated for all parameter values, including cases where PT symmetry is broken.

Peter N. Meisinger; Michael C. Ogilvie; Timothy D. Wiser

2010-09-03

409

Bilateral symmetry across Aphrodite Terra  

NASA Technical Reports Server (NTRS)

There are three main highland areas on Venus: Beta Regio, Ishtar Terra and Aphrodite Terra. The latter is least known and the least mapped, yet existing analyses of Aphrodite Terra based on available Pioneer-Venus orbiter data suggest that it may be the site of extensive rifting. Some of the highest resolution (30 km) PV data (SAR) included most of the western half of Aphrodite Terra. Recent analysis of the SAR data together with Arecibo range-doppler topographic profiling (10 X 100 km horizontal and 10 m vertical resolution) across parts of Aphrodite, further characterized the nature of possible tectonic processes in the equatorial highlands. The existence of distinct topographic and radar morphologic linear discontinuities across the nearly east-west strike of Aphrodite Terra is indicated. Another prominent set of linear features is distinctly parallel to and orthogonal to the ground tracks of the PV spacecraft and are not included because of the possibility that they are artifacts. Study of the northwest trending cross-strike discontinuities (CSD's) and the nature of topographic and morphologic features along their strike suggest the presence of bilateral topographic and morphologic symmetry about the long axis of Aphrodite Terra.

Crumpler, L. S.; Head, J. W.; Campbell, D. B.

1987-01-01

410

Graphene, Lattice QFT and Symmetries  

E-print Network

Borrowing ideas from tight binding model, we propose a board class of Lattice QFT models that are classified by the ADE Lie algebras. In the case of su(N) series, we show that the couplings between the quantum states living at the first nearest neighbor sites of the lattice $\\mathcal{L}_{su(N)}$ are governed by the complex fundamental representations \\underline{${{\\mathbf{N}}}$} and $\\bar{{\\mathbf{N}}}$ of $su(N)$; and the second nearest neighbor interactions are described by its adjoint $\\underline{\\mathbf{N}} \\otimes \\bar{\\mathbf{N}}$. The lattice models associated with the leading su(2), su(3) and su(4) cases are explicitly studied and their fermionic field realizations are given. It is also shown that the su(2) and su(3) models describe respectively the electronic properties of the acetylene chain and the graphene. It is established as well that the energy dispersion of the first nearest neighbor couplings is completely determined by the $A_{N}$ roots $ \\mathbf{\\alpha}$ through the typical dependence $N/2+\\sum_{roots}\\cos(\\mathbf{k}.\\alpha) $ with $\\mathbf{k}$ the wave vector. Other features such as DE extension and other applications are also discussed. Keywords: Tight Binding Model, Graphene, Lattice QFT, ADE Symmetries.

L. B Drissi; E. H Saidi; M. Bousmina

2011-01-05

411

How is spontaneous symmetry breaking possible?  

E-print Network

We pose and resolve a seeming paradox about spontaneous symmetry breaking in the quantum theory of infinite systems. For a symmetry to be spontaneously broken, it must not be implementable by a unitary operator. But Wigner's theorem guarantees that every symmetry is implemented by a unitary operator that preserves transition probabilities between pure states. We show how it is possible for a unitary operator of this sort to connect the folia of unitarily inequivalent representations. This result undermines interpretations of quantum theory that hold unitary equivalence to be necessary for physical equivalence.

David John Baker; Hans Halvorson

2011-03-16

412

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.

413

Symmetry of Differential Equations and Quantum Theory  

NASA Astrophysics Data System (ADS)

The symmetry study of main differential equations of mechanics and electrodynamics has shown, that differential equations, which are invariant under transformations of groups, which are symmetry groups of mathematical numbers (considered in the frame of the number theory) determine the mathematical nature of the quantities, incoming in given equations. It allowed to proof the main postulate of quantum mechanics, that to any mechanical quantity can be set up into the correspondence the Hermitian matrix by quantization. High symmetry of Maxwell equations allows to show, that to EM-field funcions, incoming in given equations, can be set up into the correspondence the Quaternion (twice-Hermitian) matrices by their quantization.

Yerchuck, Dmitri; Dovlatova, Alla; Alexandrov, Andrey

2014-03-01

414

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

415

Nonanomalous discrete R symmetry decrees three generations.  

PubMed

We show that more than two generations of quarks and leptons are required to have an anomaly free discrete R symmetry larger than R parity, provided that the supersymmetric standard model can be minimally embedded into a grand unified theory. This connects an explanation for the number of generations with seemingly unrelated problems such as supersymmetry breaking, proton decay, the ? problem, and the cosmological constant through a discrete R symmetry. We also show that three generations is uniquely required by a nonanomalous discrete R symmetry in classes of grand unified theories such as the ones based on (semi)simple gauge groups. PMID:23215270

Evans, Jason L; Ibe, Masahiro; Kehayias, John; Yanagida, Tsutomu T

2012-11-01

416

Yang-Mills Origin of Gravitational Symmetries  

NASA Astrophysics Data System (ADS)

By regarding gravity as the convolution of left and right Yang-Mills theories together with a spectator scalar field in the biadjoint representation, we derive in linearized approximation, the gravitational symmetries of general covariance, p -form gauge invariance, local Lorentz invariance, and local supersymmetry from the flat space Yang-Mills symmetries of local gauge invariance and global super-Poincaré symmetry. As a concrete example, we focus on the new minimal (12 +12 ) off shell version of simple four-dimensional supergravity obtained by tensoring the off shell Yang-Mills multiplets (4 +4 , NL=1 ) and (3 +0 , NR=0 ).

Anastasiou, A.; Borsten, L.; Duff, M. J.; Hughes, L. J.; Nagy, S.

2014-12-01

417

Symmetry violations at BaBar  

E-print Network

Following a brief introduction I report the current status of symmetry violation tests from the BaBar experiment, including recent results on the measurement of T violation, and searches for CP and T violation in mixing.

Adrian J. Bevan

2014-11-02

418

Geometric aspects of gauge and spacetime symmetries  

E-print Network

as a viable theory. A third chapter discusses a formulation of gravity as a topological BF theory with added linear constraints that reduce the symmetries of the topological theory to those of general relativity. We discretise our constructions...

Gielen, Steffen C. M.

2011-06-07

419

Spontaneous chiral symmetry breaking in metamaterials  

NASA Astrophysics Data System (ADS)

Spontaneous chiral symmetry breaking underpins a variety of areas such as subatomic physics and biochemistry, and leads to an impressive range of fundamental phenomena. Here we show that this prominent effect is now available in artificial electromagnetic systems, enabled by the advent of magnetoelastic metamaterials where a mechanical degree of freedom leads to a rich variety of strong nonlinear effects such as bistability and self-oscillations. We report spontaneous symmetry breaking in torsional chiral magnetoelastic structures where two or more meta-molecules with opposite handedness are electromagnetically coupled, modifying the system stability. Importantly, we show that chiral symmetry breaking can be found in the stationary response of the system, and the effect is successfully demonstrated in a microwave pump-probe experiment. Such symmetry breaking can lead to a giant nonlinear polarization change, energy localization and mode splitting, which provides a new possibility for creating an artificial phase transition in metamaterials, analogous to that in ferrimagnetic domains.

Liu, Mingkai; Powell, David A.; Shadrivov, Ilya V.; Lapine, Mikhail; Kivshar, Yuri S.

2014-07-01

420

Symmetry and the Cosmic Microwave Background  

NASA Technical Reports Server (NTRS)

A brief historical introduction to the development of observational astronomy and cosmology will be presented. The close relationship between the properties of light, symmetry, and our understanding the contents of our universe will be explored.

Wollock, Edward J.

2012-01-01

421

Connections Between Symmetries and Conservation Laws  

E-print Network

This paper presents recent work on connections between symmetries and conservation laws. After reviewing Noether's theorem and its limitations, we present the Direct Construction Method to show how to find directly the conservation laws for any given system of differential equations. This method yields the multipliers for conservation laws as well as an integral formula for corresponding conserved densities. The action of a symmetry (discrete or continuous) on a conservation law yields conservation laws. Conservation laws yield non-locally related systems that, in turn, can yield nonlocal symmetries and in addition be useful for the application of other mathematical methods. From its admitted symmetries or multipliers for conservation laws, one can determine whether or not a given system of differential equations can be linearized by an invertible transformation.

George Bluman

2005-11-09

422

Symmetries and Systematics of Doubly Heavy Hadrons  

E-print Network

We discuss the extension of the superflavor symmetry of doubly heavy baryons to states which contain an excited heavy diquark, and we examine some of the consequences of this symmetry for the spectra of doubly heavy baryons and heavy mesons. We explore the ramifications of a proposed symmetry that relates heavy diquarks to doubly heavy mesons. We present a method for determining how the excitation energy of a system containing two heavy quarks will scale as one changes the strength of the interactions and the reduced mass of the system. We use this to derive consequences of the heavy diquark-doubly heavy meson symmetry. We compare these consequences to the results of a quark model as well as the experimental data for doubly and singly heavy mesons. We also discuss the possibility of treating the strange quark as a heavy quark and apply the ideas developed here to strange hadrons.

B. Eakins; W. Roberts

2012-01-23

423

Persistent Symmetry Frustration in Pollen Tubes  

PubMed Central

Pollen tubes are extremely rapidly growing plant cells whose morphogenesis is determined by spatial gradients in the biochemical composition of the cell wall. We investigate the hypothesis (MP) that the distribution of the local mechanical properties of the wall, corresponding to the change of the radial symmetry along the axial direction, may lead to growth oscillations in pollen tubes. We claim that the experimentally observed oscillations originate from the symmetry change at the transition zone, where both intervening symmetries (cylindrical and spherical) meet. The characteristic oscillations between resonating symmetries at a given (constant) turgor pressure and a gradient of wall material constants may be identified with the observed growth-cycles in pollen tubes. PMID:23144847

Pietruszka, Mariusz; Lipowczan, Marcin; Geitmann, Anja

2012-01-01

424

Composite fermions and broken symmetries in graphene  

NASA Astrophysics Data System (ADS)

The electronic properties of graphene are described by a Dirac Hamiltonian with a four-fold symmetry of spin and valley. This symmetry may yield novel fractional quantum Hall (FQH) states at high magnetic field depending on the relative strength of symmetry-breaking interactions. However, observing such states in transport remains challenging in graphene, as they are easily destroyed by disorder. In this work, we observe in the first two Landau levels the two-flux composite-fermion sequences of FQH states between each integer filling factor. In particular, the odd-numerator fractions appear between filling factors 1 and 2, suggesting a broken-valley symmetry, consistent with our observation of a gap at charge neutrality and zero field. Contrary to our expectations, the evolution of gaps in a parallel magnetic field suggests that states in the first Landau level are not spin-polarized even up to very large out-of-plane fields.

Amet, F.; Bestwick, A. J.; Williams, J. R.; Balicas, L.; Watanabe, K.; Taniguchi, T.; Goldhaber-Gordon, D.

2015-01-01

425

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

426

Spontaneous chiral symmetry breaking in metamaterials.  

PubMed

Spontaneous chiral symmetry breaking underpins a variety of areas such as subatomic physics and biochemistry, and leads to an impressive range of fundamental phenomena. Here we show that this prominent effect is now available in artificial electromagnetic systems, enabled by the advent of magnetoelastic metamaterials where a mechanical degree of freedom leads to a rich variety of strong nonlinear effects such as bistability and self-oscillations. We report spontaneous symmetry breaking in torsional chiral magnetoelastic structures where two or more meta-molecules with opposite handedness are electromagnetically coupled, modifying the system stability. Importantly, we show that chiral symmetry breaking can be found in the stationary response of the system, and the effect is successfully demonstrated in a microwave pump-probe experiment. Such symmetry breaking can lead to a giant nonlinear polarization change, energy localization and mode splitting, which provides a new possibility for creating an artificial phase transition in metamaterials, analogous to that in ferrimagnetic domains. PMID:25033837

Liu, Mingkai; Powell, David A; Shadrivov, Ilya V; Lapine, Mikhail; Kivshar, Yuri S

2014-01-01

427

Biaxial nematics with C2h symmetry composed of calamitic particles. A molecular field theory  

E-print Network

A molecular field theory of biaxial nematics formed by molecules with C2h point group symmetry has been developed by Luckhurst et al. and a Monte Carlo computer simulation study of this model has been performed by Hashim et al.. In these studies the truncated model pair potential was only applied to molecules whose long axes are taken to be along their C2 rotation axes. The present study extends this work by assuming that the molecular long axis is now perpendicular to the C2 axis, resulting in there being two possible choices of minor axes. It considers the phases formed by both cases. The molecular field theory for these models is formulated and reported here. The theoretical treatment of the present cases gives rise to a new set of order parameters. So as to simplify the pseudo-potentials only the dominant second rank order parameters are considered and evaluated to give the phase behaviour of these truncated models. The predicted phase behaviour is compared with the results from the molecular field study of the previous model potential.

Rauzah Hashim; Geoffrey R. Luckhurst; Hock-Seng Nguan

2014-03-04

428

Infinite Chiral Symmetry in Four Dimensions  

NASA Astrophysics Data System (ADS)

We describe a new correspondence between four-dimensional conformal field theories with extended supersymmetry and two-dimensional chiral algebras. The meromorphic correlators of the chiral algebra compute correlators in a protected sector of the four-dimensional theory. Infinite chiral symmetry has far-reaching consequences for the spectral data, correlation functions, and central charges of any four-dimensional theory with N=2 superconformal symmetry.

Beem, Christopher; Lemos, Madalena; Liendo, Pedro; Peelaers, Wolfger; Rastelli, Leonardo; van Rees, Balt C.

2015-01-01

429

A Hidden Symmetry of the Galileon  

E-print Network

We show that there is a special choice of parameters for which the galileon theory is invariant under an enhanced shift symmetry whose non-linear part is quadratic in the coordinates. This symmetry fixes the theory to be equivalent to one with only even powers of the field, with no free coefficients, and accounts for the improved soft limit behavior observed in the quartic galileon S-matrix.

Hinterbichler, Kurt

2015-01-01

430

Broken Isospin Symmetry in the Shell Model  

Microsoft Academic Search

We examine the effects of broken isospin symmetry within the shell model on both eigenvalue and transition strength statistics. Calculations have been performed for the nuclides ^22Na, ^26Al, and ^34Cl. The isospin-non-conserving (INC) Hamiltonian is that of Ormand and Brown [Nucl. Phys. A491, 1 (1989)]. Breaking the isospin symmetry has little effect on eigenvalue statistics; this does not agree with

J. F. Shriner Jr.; G. E. Mitchell; B. A. Brown

2001-01-01

431

Squeezing lepton pairs out of broken symmetries  

NASA Astrophysics Data System (ADS)

We discuss two possible signatures of symmetry breaking that can appear in dilepton spectra, as measured in relativistic heavy ion collisions. The first involves scalar-vector meson mixing and is related to the breaking of Lorentz symmetry by a hot medium. The second is related to the breaking of Furry's theorem by a charged quark-gluon plasma. Those signals will be accessible to upcoming measurements to be performed at the GSI, RHIC, and the LHC. .

Dutt-Mazumder, A. K.; Gale, C.; Majumder, A.; Teodorescu, O.

2002-04-01

432

Conservation Laws and Non-Lie Symmetries  

E-print Network

We introduce a method to construct conservation laws for a large class of linear partial differential equations. In contrast to the classical result of Noether, the conserved currents are generated by any symmetry of the operator, including those of the non-Lie type. An explicit example is made of the Dirac equation were we use our construction to find a class of conservation laws associated with a 64 dimensional Lie algebra of discrete symmetries that includes CPT.

Anthony C. L Ashton

2008-08-28

433

Aspects of Dynamical Chiral Symmetry Breaking  

E-print Network

Dynamical chiral symmetry breaking is a nonperturbative phenomenon that may be studied using QCD's gap equation. Model-independent results can be obtained with a nonperturbative and symmetry preserving truncation. The gap equation yields the massive dressed-quark propagator, which has a spectral representation when considered as a function of the current-quark mass. This enables an explication of the connection between the infrared limit of the QCD Dirac operator's spectrum and the quark condensate appearing in the operator product expansion.

C. D. Roberts

2003-01-21

434

Nanostructure symmetry: Relevance for physics and computing  

SciTech Connect

We review the research done in recent years in our group on the effects of nanostructure symmetry, and outline its relevance both for nanostructure physics and for computations of their electronic and optical properties. The exemples of C3v and C2v quantum dots are used. A number of surprises and non-trivial aspects are outlined, and a few symmetry-based tools for computing and analysis are shortly presented.

Dupertuis, Marc-André; Oberli, D. Y. [Laboratory for Physics of Nanostructure, EPF Lausanne (Switzerland); Karlsson, K. F. [Department of Physics, Chemistry, and Biology (IFM), Linköping University (Sweden); Dalessi, S. [Computational Biology Group, Department of Medical Genetics, University of Lausanne (Switzerland); Gallinet, B. [Nanophotonics and Metrology Laboratory, EPF Lausanne (Switzerland); Svendsen, G. [Dept. of Electronics and Telecom., Norwegian University of Science and Technology, Trondheim (Norway)

2014-03-31

435

Neutrino mass, mixing and discrete symmetries  

NASA Astrophysics Data System (ADS)

Status of the discrete symmetry approach to explanation of the lepton masses and mixing is summarized in view of recent experimental results, in particular, establishing relatively large 1-3 mixing. The lepton mixing can originate from breaking of discrete flavor symmetry Gf to different residual symmetries Gl and Gv in the charged lepton and neutrino sectors. In this framework the symmetry group condition has been derived which allows to get relations between the lepton mixing elements immediately without explicit model building. The condition has been applied to different residual neutrino symmetries Gv. For generic (mass independent) Gv = Z2 the condition leads to two relations between the mixing parameters and fixes one column of the mixing matrix. In the case of Gv = Z2 × Z2 the condition fixes the mixing matrix completely. The non-generic (mass spectrum dependent) Gv lead to relations which include mixing angles, neutrino masses and Majorana phases. The symmetries Gl, Gv, Gf are identified which lead to the experimentally observed values of the mixing angles and allow to predict the CP phase.

Smirnov, Alexei Y.

2013-07-01

436

SUGRA new inflation with Heisenberg symmetry  

SciTech Connect

We propose a realisation of ''new inflation'' in supergravity (SUGRA), where the flatness of the inflaton potential is protected by a Heisenberg symmetry. Inflation can be associated with a particle physics phase transition, with the inflaton being a (D-flat) direction of Higgs fields which break some symmetry at high energies, e.g. of GUT Higgs fields or of Higgs fields for flavour symmetry breaking. This is possible since compared to a shift symmetry, which is usually used to protect a flat inflaton potential, the Heisenberg symmetry is compatible with a (gauge) non-singlet inflaton field. In contrast to conventional new inflation models in SUGRA, where the predictions depend on unknown parameters of the Kaehler potential, the model with Heisenberg symmetry makes discrete predictions for the primordial perturbation parameters which depend only on the order n at which the inflaton appears in the effective superpotential. The predictions for the spectral index n{sub s} can be close to the best-fit value of the latest Planck 2013 results.

Antusch, Stefan; Cefalà, Francesco, E-mail: f.cefala@unibas.ch, E-mail: stefan.antusch@unibas.ch [Department of Physics, University of Basel, Klingelbergstr. 82, CH-4056 Basel (Switzerland)

2013-10-01

437

Symmetry calculation for molecules and transition states.  

PubMed

The symmetry of molecules and transition states of elementary reactions is an essential property with important implications for computational chemistry. The automated identification of symmetry by computers is a very useful tool for many applications, but often relies on the availability of three-dimensional coordinates of the atoms in the molecule and hence becomes less useful when these coordinates are a priori unavailable. This article presents a new algorithm that identifies symmetry of molecules and transition states based on an augmented graph representation of the corresponding structures, in which both topology and the presence of stereocenters are accounted for. The automorphism group order of the graph associated with the molecule or transition state is used as a starting point. A novel concept of label-stereoisomers, that is, stereoisomers that arise after labeling homomorph substituents in the original molecule so that they become distinguishable, is introduced and used to obtain the symmetry number. The algorithm is characterized by its generic nature and avoids the use of heuristic rules that would limit the applicability. The calculated symmetry numbers are in agreement with expected values for a large and diverse set of structures, ranging from asymmetric, small molecules such as fluorochlorobromomethane to highly symmetric structures found in drug discovery assays. The new algorithm opens up new possibilities for the fast screening of the degree of symmetry of large sets of molecules. © 2014 Wiley Periodicals, Inc. PMID:25421576

Vandewiele, Nick M; Van de Vijver, Ruben; Van Geem, Kevin M; Reyniers, Marie-Françoise; Marin, Guy B

2015-01-30

438

Symmetry Breaking in Numeric Constraint Problems Alexandre Goldsztejn1  

E-print Network

Symmetry Breaking in Numeric Constraint Problems Alexandre Goldsztejn1 , Christophe Jermann1`atica Industrial (CSIC-UPC) Llorens i Artigas 4-6, 08028-Barcelona, Spain. surname@iri.upc.edu Abstract. Symmetry symmetries in numeric CSPs. We show that, for the variable symmetries among those, the proposed in

Paris-Sud XI, Université de

439

Symmetry of Fuzzy Data Hagit Zabrodsky Shmuel Peleg David Avnirz  

E-print Network

Symmetry of Fuzzy Data Hagit Zabrodsky Shmuel Peleg David Avnirz Institute of Computer Science and Department of Organic Chemistryz The Hebrew University of Jerusalem 91904 Jerusalem, Israel Abstract Symmetry that symmetry is a continuous feature, a Continuous Symmetry Measure CSM has been devel- oped to evaluate

Peleg, Shmuel

440

Symmetry Breaking in Quantified Boolean Formulae Gilles Audemard  

E-print Network

Symmetry Breaking in Quantified Boolean Formulae Gilles Audemard and Sa¨id Jabbour and Lakhdar Sa,jabbour,sais}@cril.univ-artois.fr Abstract Many reasoning task and combinatorial problems exhibit symmetries. Exploiting such symmetries has been proved to be very important in reducing search efforts. Breaking symmetries using addi- tional

Paris-Sud XI, Université de

441

Symmetry and Asymmetry from Local Phase Peter Kovesi  

E-print Network

Symmetry and Asymmetry from Local Phase Peter Kovesi Department of Computer Science The University of Western Australia Nedlands W.A. 6907 pk@cs.uwa.edu.au Abstract. Symmetry is an important mechanism recognizable from the symmetry, or partial symmetries that they often exhibit. Two difficulties found in most

Kovesi, Peter

442

A symmetry reduction method for continuum structural topology optimization  

E-print Network

A symmetry reduction method for continuum structural topology optimization Iku Kosakaa, 1 , Colby C design formulations. A novel symmetry reduction method is proposed, implemented and studied. While enforcing symmetry and signi®cantly reducing the size of the optimization problem, the symmetry reduction

Swan Jr., Colby Corson

443

Symmetry, sexual dimorphism in facial proportions and male facial attractiveness  

E-print Network

Symmetry, sexual dimorphism in facial proportions and male facial attractiveness I. S. Penton, University of St Andrews, St Andrews, Fife KY16 9JU, UK Facial symmetry has been proposed as a marker relationships between facial symmetry and attractiveness. It was recently proposed that symmetry

Little, Tony

444

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

445

SYMMETRY PREFERENCE AS A COGNITIVE BY-PRODUCT IN STARLINGS  

E-print Network

SYMMETRY PREFERENCE AS A COGNITIVE BY-PRODUCT IN STARLINGS by JOHN P. SWADDLE1) , JUDY P.K. CHE of interest in whether animals use trait symmetry as a visual cue to mediate behavioural interactions that symmetry can reveal the developmental history and, perhaps, tness of an individual and this is why symmetry

Swaddle, John

446

The small step toward asymmetry: Aesthetic judgment of broken symmetries  

PubMed Central

Symmetry and complexity both affect the aesthetic judgment of abstract patterns. However, although beauty tends to be associated with symmetry, there are indications that small asymmetries can also be beautiful. We investigated the influence of small deviations from symmetry on people's aesthetic liking for abstract patterns. Breaking symmetry not only decreased patterns' symmetry but also increased their complexity. While an increase of complexity normally results in a higher liking, we found that even a small decrease of symmetry has a strong effect, such that patterns with slightly broken symmetries were significantly less liked than fully symmetric ones. PMID:24349695

Gartus, Andreas; Leder, Helmut

2013-01-01

447

Symmetry Energy I: Semi-Infinite Matter  

E-print Network

Energy for a nucleus is considered in macroscopic limit, in terms of nucleon numbers. Further considered for a nuclear system is the Hohenberg-Kohn energy functional, in terms of proton and neutron densities. Finally, Skyrme-Hartree-Fock calculations are carried out for a half-infinite particle-stable nuclear-matter. In each case, the attention is focused on the role of neutron-proton asymmetry and on the nuclear symmetry energy. We extend the considerations on the symmetry term from an energy formula to the respective term in the Hohenberg-Kohn functional. We show, in particular, that in the limit of an analytic functional, and subject to possible Coulomb corrections, it is possible to construct isoscalar and isovector densities out of the proton and neutron densities, that retain a universal relation to each other, approximately independent of asymmetry. In the so-called local approximation, the isovector density is inversely proportional to the symmetry energy in uniform matter at the local isoscalar density. Generalized symmetry coefficient of a nuclear system is related, in the analytic limit of a functional, to an integral of the isovector density. We test the relations, inferred from the Hohenberg-Kohn functional, in the Skyrme-Hartree-Fock calculations of half-infinite matter. Within the calculations, we obtain surface symmetry coefficients and parameters characterizing the densities, for the majority of Skyrme parameterizations proposed in the literature. The volume-to-surface symmetry-coefficient ratio and the displacement of nuclear isovector relative to isoscalar surfaces both strongly increase as the slope of symmetry energy in the vicinity of normal density increases.

Pawel Danielewicz; Jenny Lee

2008-10-29

448

Scalar Field Theories with Polynomial Shift Symmetries  

E-print Network

We continue our study of naturalness in nonrelativistic QFTs of the Lifshitz type, focusing on scalar fields that can play the role of Nambu-Goldstone (NG) modes associated with spontaneous symmetry breaking. Such systems allow for an extension of the constant shift symmetry to a shift by a polynomial of degree $P$ in spatial coordinates. These "polynomial shift symmetries" in turn protect the technical naturalness of modes with a higher-order dispersion relation, and lead to a refinement of the proposed classification of infrared Gaussian fixed points available to describe NG modes in nonrelativistic theories. Generic interactions in such theories break the polynomial shift symmetry explicitly to the constant shift. It is thus natural to ask: Given a Gaussian fixed point with polynomial shift symmetry of degree $P$, what are the lowest-dimension operators that preserve this symmetry, and deform the theory into a self-interacting scalar field theory with the shift symmetry of degree $P$? To answer this (essentially cohomological) question, we develop a new graph-theoretical technique, and use it to prove several classification theorems. First, in the special case of $P=1$ (essentially equivalent to Galileons), we reproduce the known Galileon $N$-point invariants, and find their novel interpretation in terms of graph theory, as an equal-weight sum over all labeled trees with $N$ vertices. Then we extend the classification to $P>1$ and find a whole host of new invariants, including those that represent the most relevant (or least irrelevant) deformations of the corresponding Gaussian fixed points, and we study their uniqueness.

Tom Griffin; Kevin T. Grosvenor; Petr Horava; Ziqi Yan

2014-12-02

449

Applications of Symmetry Methods to the Theory of Plasma Physics  

E-print Network

The theory of plasma physics offers a number of nontrivial examples of partial differential equations, which can be successfully treated with symmetry methods. We propose three different examples which may illustrate the reciprocal advantage of this "interaction" between plasma physics and symmetry techniques. The examples include, in particular, the complete symmetry analysis of system of two PDE's, with the determination of some conditional and partial symmetries, the construction of group-invariant solutions, and the symmetry classification of a nonlinear PDE.

Giampaolo Cicogna; Francesco Ceccherini; Francesco Pegoraro

2006-02-03

450

Universal symmetry-protected topological invariants for symmetry-protected topological states  

E-print Network

Symmetry-protected topological (SPT) states are short-range entangled states with a symmetry G. They belong to a new class of quantum states of matter which are classified by the group cohomology H[superscript d+1](G,R/Z) ...

Hung, Ling-Yan

451

Student understanding of Symmetry and Gauss's law  

NSDL National Science Digital Library

Helping students learn why Gauss's law can or cannot be easily applied to determine the strength of the electric field at various points for a particular charge distribution, and then helping them learn to determine the shape of the Gaussian surfaces if sufficient symmetry exists can develop their reasoning and problem solving skills. We investigate the difficulties that students in calculus-based introductory physics courses have with the concepts of symmetry, electric field and electric flux that are pivotal to Gauss's law of electricity. Determination of the electric field using Gauss's law requires discerning the symmetry of a particular charge distribution and being able to predict the direction of the electric field everywhere if a high symmetry exists. It requires a good grasp of how to add the electric field vectors using the principle of superposition, and the concepts of area vector and electric flux. We administered free response and multiple-choice questions and conducted interviews with individual students using a think-aloud protocol to elucidate the difficulties students have with the concepts of symmetry, electric field and electric flux. Here we discuss student responses to some questions on a multiple-choice test administered to them. The test can be used both as a teaching and assessment tool.

Singh, Chandralekha

2010-01-18

452

Bifurcations and Symmetry in Dissipative Dynamics  

NASA Astrophysics Data System (ADS)

This work consists of applications of bifurcation theory to nonlinear dynamical systems. We begin by analyzing three instabilities that may occur in dynamical systems governed by dissipative nonlinear differential equations. One instability occurs when a fixed point with a breve {rm S}il'nikov homoclinic orbit undergoes a Hopf bifurcation. In an application this instability is found to give rise to unusual chaotically reversing waves. Next we turn to instabilities which possess spatial symmetry and analyze mode interactions involving localized solutions to a reaction-diffusion system. We first consider a single O(2) symmetric disk-shaped solution which loses stability simultaneously to radial oscillations and steady deformations with azimuthal wave number n = 2. Then we consider a stripe solution with O(2) times Z_2 symmetry which, as a system parameter changes, loses stability to zigzag and varicose perturbations. The analysis is based solely on symmetry considerations and the results therefore have potential applications in many other systems. Finally, we examine the effects of small imperfections in the symmetry of a system on resulting bifurcations. We investigate the effects of distant endwalls on both the steady-state and oscillatory instabilities of a translation invariant state. In particular we numerically investigate the O(2) equivariant Hopf normal form with terms which break rotation symmetry. The resulting homoclinic chaos resembles closely the dynamics observed in binary fluid convection experiments.

Hirschberg, Philip Conway

453

A method for quantifying rotational symmetry.  

PubMed

Here, a new approach for quantifying rotational symmetry based on vector analysis was described and compared with information obtained from a geometric morphometric analysis and a technique based on distance alone. A new method was developed that generates a polygon from the length and angle data of a structure and then quantifies the minimum change necessary to convert that polygon into a regular polygon. This technique yielded an asymmetry score (s) that can range from 0 (perfect symmetry) to 1 (complete asymmetry). Using digital images of Geranium robertianum flowers, this new method was compared with a technique based on lengths alone and with established geometric morphometric methods used to quantify shape variation. Asymmetry scores (s) more clearly described variation in symmetry and were more consistent with a visual assessment of the images than either comparative technique. This procedure is the first to quantify the asymmetry of radial structures accurately, uses easily obtainable measures to calculate the asymmetry score and allows comparisons among individuals and species, even when the comparisons involve structures with different patterns of symmetry. This technique enables the rigorous analysis of polysymmetric structures and provides a foundation for a better understanding of symmetry in nature. PMID:17688593

Frey, Frank M; Robertson, Aaron; Bukoski, Michael

2007-01-01

454

Twin and Mirror Symmetries from Presymmetry  

E-print Network

We argue that presymmetry, a hidden predynamical electroweak quark-lepton symmetry that explains the fractional charges and triplication of families, must be extended beyond the Standard Model as to have a residual presymmetry that embraces partner particles and includes the strong sector, so accounting for the twin or mirror partners proposed to alleviate the naturalness problem of the weak scale. It leads to the full duplication of fermions and gauge bosons of the Standard Model independently of the ultraviolet completion of the theory, even if the Higgs particle is discarded by experiment, which adds robustness to twin and mirror symmetries. The established connection is so strongly motivated that the search for twin or mirror matter becomes the possible test of presymmetry. If the physics beyond the Standard Model repairs its left-right asymmetry, mirror symmetry should be the one realized in nature.

Ernesto A. Matute

2011-11-11

455

Spin-flip symmetry and synchronization.  

PubMed

In the context of optimization by evolutionary algorithms (EAs), epistasis, deception, and scaling are well-known examples of problem difficulty characteristics. The presence of one such characteristic in the representation of a search problem indicates a certain type of difficulty the EA is to encounter during its search for globally optimal configurations. In this paper, we claim that the occurrence of symmetry in the representation is another problem difficulty characteristic and discuss one particular form, spin-flip symmetry, characterized by fitness invariant permutations on the alphabet. Its usual effect on unspecialized EAs, premature convergence due to synchronization problems, is discussed in detail. We discuss five different ways to specialize EAs to cope with the symmetry: adapting the genetic operators, changing the fitness function, using a niching technique, using a distributed EA, and attaching a highly redundant genotype-phenotype mapping. PMID:12450454

Van Hoyweghen, Clarissa; Naudts, Bart; Goldberg, David E

2002-01-01

456

Preserving Symmetry in Preconditioned Krylov Subspace Methods  

NASA Technical Reports Server (NTRS)

We consider the problem of solving a linear system Ax = b when A is nearly symmetric and when the system is preconditioned by a symmetric positive definite matrix M. In the symmetric case, one can recover symmetry by using M-inner products in the conjugate gradient (CG) algorithm. This idea can also be used in the nonsymmetric case, and near symmetry can be preserved similarly. Like CG, the new algorithms are mathematically equivalent to split preconditioning, but do not require M to be factored. Better robustness in a specific sense can also be observed. When combined with truncated versions of iterative methods, tests show that this is more effective than the common practice of forfeiting near-symmetry altogether.

Chan, Tony F.; Chow, E.; Saad, Y.; Yeung, M. C.

1996-01-01

457

Detection of symmetry-enriched topological phases  

NASA Astrophysics Data System (ADS)

Topologically ordered systems in the presence of symmetries can exhibit new structures which are referred to as symmetry-enriched topological (SET) phases. We introduce simple methods to detect certain SET orders directly from a complete set of topologically degenerate ground-state wave functions. In particular, we first show how to directly determine the characteristic symmetry fractionalization of the quasiparticles from the reduced density matrix of the minimally entangled states. Second, we show how a simple generalization of a nonlocal order parameter can be measured to detect SET phases. The usefulness of the proposed approach is demonstrated by examining two concrete model states which exhibit SET phases: (i) a spin-1 model on the honeycomb lattice and (ii) the resonating valence bond (RVB) state on a kagome lattice. We conclude that the spin-1 model and the RVB state are in the same SET phases.

Huang, Ching-Yu; Chen, Xie; Pollmann, Frank

2014-07-01

458

A torus bifurcation theorem with symmetry  

NASA Technical Reports Server (NTRS)

Hopf bifurcation in the presence of symmetry, in situations where the normal form equations decouple into phase/amplitude equations is described. A theorem showing that in general such degeneracies are expected to lead to secondary torus bifurcations is proved. By applying this theorem to the case of degenerate Hopf bifurcation with triangular symmetry it is proved that in codimension two there exist regions of parameter space where two branches of asymptotically stable two-tori coexist but where no stable periodic solutions are present. Although a theory was not derived for degenerate Hopf bifurcations in the presence of symmetry, examples are presented that would have to be accounted for by any such general theory.

Vangils, S. A.; Golubitsky, M.

1989-01-01

459

Geometric symmetries in superfluid vortex dynamics  

SciTech Connect

Dynamics of quantized vortex lines in a superfluid feature symmetries associated with the geometric character of the complex-valued field, w(z)=x(z)+iy(z), describing the instant shape of the line. Along with a natural set of Noether's constants of motion, which - apart from their rather specific expressions in terms of w(z) - are nothing but components of the total linear and angular momenta of the fluid, the geometric symmetry brings about crucial consequences for kinetics of distortion waves on the vortex lines, the Kelvin waves. It is the geometric symmetry that renders Kelvin-wave cascade local in the wave-number space. Similar considerations apply to other systems with purely geometric degrees of freedom.

Kozik, Evgeny [Institute for Theoretical Physics, ETH Zurich, CH-8093 Zurich (Switzerland); Svistunov, Boris [Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003 (United States); Russian Research Center 'Kurchatov Institute', 123182 Moscow (Russian Federation)

2010-10-01

460

Gravitino dark matter and flavor symmetries  

NASA Astrophysics Data System (ADS)

In supersymmetric theories without R-parity, the gravitino can play the role of a decaying Dark Matter candidate without the problem of late NLSP decays affecting Big Bang Nucleosynthesis. In this work, we elaborate on recently discussed limits on R- parity violating couplings from decays to antideuterons and discuss the implications for two classes of flavor symmetries: horizontal symmetries, and Minimal Flavor Violation. In most of the parameter space the antideuteron constraints on R-parity violating couplings are stronger than low-energy baryon-number-violating processes. Even in the absence of flavor symmetries, we find strong new limits on couplings involving third-generation fields, and discuss the implications for LHC phenomenology. For TeV scale superpartners, we find that the allowed MFV parameter space is a corner with gravitino masses smaller than (10) GeV and small tan ?.

Monteux, Angelo; Carlson, Eric; Cornell, Jonathan M.

2014-08-01

461

Conformal Symmetry for General Black Holes  

E-print Network

We show that the warp factor of a generic asymptotically flat black hole in five dimensions can be adjusted such that a conformal symmetry emerges. The construction preserves all near horizon properties of the black holes, such as the thermodynamic potentials and the entropy. We interpret the geometry with modified asymptotic behavior as the "bare" black hole, with the ambient flat space removed. Our warp factor subtraction generalizes hidden conformal symmetry and applies whether or not rotation is significant. We also find a relation to standard AdS/CFT correspondence by embedding the black holes in six dimensions. The asymptotic conformal symmetry guarantees a dual CFT description of the general rotating black holes.

Mirjam Cveti?; Finn Larsen

2011-06-16

462

Spontaneous symmetry breaking in interdependent networked game.  

PubMed

Spatial evolution game has traditionally assumed that players interact with direct neighbors on a single network, which is isolated and not influenced by other systems. However, this is not fully consistent with recent research identification that interactions between networks play a crucial rule for the outcome of evolutionary games taking place on them. In this work, we introduce the simple game model into the interdependent networks composed of two networks. By means of imitation dynamics, we display that when the interdependent factor ? is smaller than a threshold value ?(C), the symmetry of cooperation can be guaranteed. Interestingly, as interdependent factor exceeds ?(C), spontaneous symmetry breaking of fraction of cooperators presents itself between different networks. With respect to the breakage of symmetry, it is induced by asynchronous expansion between heterogeneous strategy couples of both networks, which further enriches the content of spatial reciprocity. Moreover, our results can be well predicted by the strategy-couple pair approximation method. PMID:24526076

Jin, Qing; Wang, Lin; Xia, Cheng-Yi; Wang, Zhen

2014-01-01

463

Workshop on electroweak symmetry breaking: proceedings  

SciTech Connect

A theoretical workshop on electroweak symmetry breaking at the Superconducting Supercollider was held at Lawrence Berkeley Laboratory, June 4-22, 1984. The purpose of the workshop was to focus theoretical attention on the ways in which experimentation at the SSC could reveal manifestations of the phenomenon responsible for electroweak symmetry breaking. This issue represents, at present, the most compelling scientific argument for the need to explore the energy region to be made accessible by the SSC, and a major aim of the workshop was to involve a broad cross section of particle theorists in the ongoing process of sharpening the requirements for both accelerator and detector design that will ensure detection and identification of meaningful signals, whatever form the electroweak symmetry breaking phenomenon should actually take. Separate entries were prepared for the data base for the papers presented.

Hinchliffe, I. (ed.)

1984-10-01

464

Proper conformal symmetries in SD Einstein spaces  

E-print Network

Proper conformal symmetries in self-dual (SD) Einstein spaces are considered. It is shown, that such symmetries are admitted only by the Einstein spaces of the type [N]x[N]. Spaces of the type [N]x[-] are considered in details. Existence of the proper conformal Killing vector implies existence of the isometric, covariantly constant and null Killing vector. It is shown, that there are two classes of [N]x[-]-metrics admitting proper conformal symmetry. They can be distinguished by analysis of the associated anti-self-dual (ASD) null strings. Both classes are analyzed in details. The problem is reduced to single linear PDE. Some general and special solutions of this PDE are presented.

Adam Chudecki; Michal Dobrski

2014-03-07

465

Restoration of Parity Symmetry through Presymmetry  

E-print Network

Presymmetry, the hidden symmetry underlying the charge and generational patterns of quarks and leptons, is utilized for repairing the left-right asymmetry of the standard model with Dirac neutrinos. It is shown that the restoration of parity is consequent with an indispensable left-right symmetric residual presymmetry. Thus, presymmetry substantiates left-right symmetry and the experimental search for the latter is the test of the former, with the nature of neutrinos as a crucial feature that can distinguish the left-right symmetry alone and its combination with presymmetry. This phenomenological implication is in accordance with the fact that Majorana neutrinos are usually demanded in the first case, but forbidden in the second.

Ernesto A. Matute

2011-11-11

466

Twin and Mirror Symmetries from Presymmetry  

NASA Astrophysics Data System (ADS)

We argue that presymmetry, a hidden predynamical electroweak quark-lepton symmetry that explains the fractional charges and triplication of families, must be extended beyond the Standard Model as to have a residual presymmetry that embraces partner particles and includes the strong sector, so accounting for the twin or mirror partners proposed to alleviate the naturalness problem of the weak scale. It leads to the full duplication of fermions and gauge bosons of the Standard Model independently of the ultraviolet completion of the theory, even if the Higgs particle is discarded by experiment, which adds robustness to twin and mirror symmetries. The established connection is so strongly motivated that the search for twin or mirror matter becomes the possible test of presymmetry. If the physics beyond the Standard Model repairs its left-right asymmetry, mirror symmetry should be the one realized in nature.

Matute, Ernesto A.

467

Restoration of Parity Symmetry Through Presymmetry  

NASA Astrophysics Data System (ADS)

Presymmetry, the hidden symmetry underlying the charge and generational patterns of quarks and leptons, is utilized for repairing the left-right asymmetry of the standard model with Dirac neutrinos. It is shown that the restoration of parity is consequent with an indispensable left-right symmetric residual presymmetry. Thus, presymmetry substantiates left-right symmetry and the experimental search for the latter is the test of the former, with the nature of neutrinos as a crucial feature that can distinguish the left-right symmetry alone and its combination with presymmetry. This phenomenological implication is in accordance with the fact that Majorana neutrinos are usually demanded in the first case, but forbidden in the second.

Matute, Ernesto A.

468

Broken Symmetry Phases in ABC Trilayer Graphene  

NASA Astrophysics Data System (ADS)

We study the effects of electron-electron interaction in ABC-stacked trilayer graphene (TLG) within the framework of weak coupling renormalization group (RG). We find that, when the interaction is mainly in the forward scattering channel, the system orders into a gapless phase characterized by breaking of the TLG lattice mirror symmetries. A presence of small but finite back scattering changes the nature of the leading instability and results in gapped phases. The repulsive back scattering favors layered anti-ferromagnetic order, while the attractive back scattering yields the quantum spin Hall phase (gapped in bulk only). By classifying order parameters in TLG according to irreducible representations of the TLG space group, we conclude that any orders that break the rotational symmetry (e.g., the nematic state) in TLG are disfavored compared to the orders that do not break the lattice trifold rotational symmetry. The results are discussed in the context of present experiments on TLG.

Cvetkovic, Vladimir; Vafek, Oskar

2013-03-01

469

Nature's statistical symmetries, a characterization by wavelets.  

SciTech Connect

Wavelets are the mathematical equivalent of a microscope, a means of looking at more or less detail in data. By applying wavelet transforms to remote sensing data (satellite images, atmospheric profiles, etc.), we can discover symmetries in Nature's ways of changing in lime and displaying a highly variable environment at any given time. These symmetries are not exact but statistical. The most intriguing one is 'scale-invariance' which describes how spatial statistics collected over a wide range of scales (using wave1m)follow simple power laws with respect to the scale parameter. The geometrical counterparts of statistical scale-invariance are the random fractals so often observed in Nature. This wavelet-based exploration of natural symmetry will be illustrated with clouds,

Davis, A. B. (Anthony B.)

2001-01-01

470

Spontaneous Symmetry Breaking in Interdependent Networked Game  

PubMed Central

Spatial evolution game has traditionally assumed that players interact with direct neighbors on a single network, which is isolated and not influenced by other systems. However, this is not fully consistent with recent research identification that interactions between networks play a crucial rule for the outcome of evolutionary games taking place on them. In this work, we introduce the simple game model into the interdependent networks composed of two networks. By means of imitation dynamics, we display that when the interdependent factor ? is smaller than a threshold value ?C, the symmetry of cooperation can be guaranteed. Interestingly, as interdependent factor exceeds ?C, spontaneous symmetry breaking of fraction of cooperators presents itself between different networks. With respect to the breakage of symmetry, it is induced by asynchronous expansion between heterogeneous strategy couples of both networks, which further enriches the content of spatial reciprocity. Moreover, our results can be well predicted by the strategy-couple pair approximation method. PMID:24526076

Jin, Qing; Wang, Lin; Xia, Cheng-Yi; Wang, Zhen

2014-01-01

471

New Algorithms For Automated Symmetry Recognition  

NASA Astrophysics Data System (ADS)

In this paper we present new methods for computer-based symmetry identification that combine elements of group theory and pattern recognition. Detection of symmetry has diverse applications including: the reduction of image data to a manageable subset with minimal information loss, the interpretation of sensor data,1 such as the x-ray diffraction patterns which sparked the recent discovery of a new "quasicrystal" phase of solid matter,2 and music analysis and composition.3,4,5 Our algorithms are expressed as parallel operations on the data using the matrix representation and manipulation features of the APL programming language. We demonstrate the operation of programs that characterize symmetric and nearly-symmetric patterns by determining the degree of invariance with respect to candidate symmetry transformations. The results are completely general; they may be applied to pattern data of arbitrary dimension and from any source.

Paul, Jody; Kilgore, Tammy Elaine; Klinger, Allen

1988-02-01

472

Flavor symmetry, leptogenesis and grand unification theories  

NASA Astrophysics Data System (ADS)

Many neutrino experiments in the last few years have shown concrete evidence for neutrino mass and leptonic mixing; an indication of new physics beyond the standard model. In this thesis, we systematically study the flavor symmetry indicated by the low scale neutrino experiment data with the assumption that the seesaw mechanism is the reason for the light neutrino masses. In the flavor basis, the testable exchange symmetry between muon neutrino and tau neutrino (mu - tau) is introduced to explain the near maximal atmospheric mixing angle and vanishing reactor mixing angle. This symmetry can reduce the seesaw parameters naturally and make it possible to connect the baryon asymmetry of our universe to the low scale neutrino data if leptogenesis causes the baryon asymmetry. We also show this leptonic symmetry can be extended to the quark sector and present a realistic supersymmetry SU(5) grand unification model. Motivated by solar mixing angle sin2thetasolar ? 1/3, we embed the mu - tau symmetry in an S3 permutation symmetry and obtain a so-called tri-bimaximal mixing pattern. We study the stability of the texture under radiative corrections. This S3 model is so constrained that the CP-violating phases of the low scale mixing are those generating the baryon asymmetry within leptongesis. Attempting to unify three families of fermions within the grand unification theories, we treat three families of fermions as the three dimensional irreducible representation of S4 and build a realistic model based on SO(10) gauge group. This model predicts degenerate a right-handed neutrino mass spectrum. In this thesis, we also address the issue of the natural realization of the seesaw mechanism in the supersymmetric minimal SO(10) model. We realize the type II seesaw dominance by invoking a warped extra dimension, while keeping predictivity of the model.

Yu, Haibo

2007-12-01

473

Symmetry breaking caused by large ?-charge  

NASA Astrophysics Data System (ADS)

We discuss the gauge symmetry breaking via the Hosotani mechanism by using exact results on supersymmetric gauge theories based on the localization method. We use the theories on S 2 × S 1 Euclidean space, and study how the effective potential for the Wilson line phase varies by running an imaginary chemical potential. In order to break the symmetry, we find that large ?-charge is necessary. With such large ?-charge, we study the phase structure of the theory. In addition, we observed that a finite size effect on our curved space when we take ?-charge is not so large.

Tanaka, Akinori; Tomiya, Akio; Shimotani, Takuya

2014-10-01

474

Spontaneous symmetry breaking and macroscopic entanglement  

E-print Network

In the presence of interactions with the environment, decoherence selects stable classical states, the pointer states, while suppressing arbitrary macroscopic coherent superpositions. In close analogy, the metastable symmetry-breaking ground states of many-body Hamiltonians should be the ones with the least macroscopic entanglement and thus the most classical ones among all possible quantum ground states. By considering the mutual information based on the 2-Renyi entanglement entropy and using a locality result, we show that symmetry-breaking states have the least macroscopic entanglement and, consequently, that they are the ones selected in real world by environmental decoherence.

A. Hamma; S. M. Giampaolo; F. Illuminati

2015-01-28

475

Holographic Metals and Insulators with Helical Symmetry  

E-print Network

Homogeneous, zero temperature scaling solutions with Bianchi VII spatial geometry are constructed in Einstein-Maxwell-Dilaton theory. They correspond to quantum critical saddle points with helical symmetry at finite density. Assuming $AdS_{5}$ UV asymptotics, the small frequency/(temperature) dependence of the AC/(DC) electric conductivity along the director of the helix are computed. A large class of insulating and conducting anisotropic phases is found, as well as isotropic, metallic phases. Conduction can be dominated by dissipation due to weak breaking of translation symmetry or by a quantum critical current.

Aristomenis Donos; Blaise Goutéraux; Elias Kiritsis

2014-06-24

476

Lie symmetries of nonlinear boundary value problems  

E-print Network

Nonlinear boundary value problems (BVPs) by means of the classical Lie symmetry method are studied. A new definition of Lie invariance for BVPs are proposed by the generalization of existing those on much wider class of BVPs. The class of two-dimensional nonlinear boundary value problem, modeling the process of melting and evaporation of metals, is studied in details. Using the definition proposed, all possible Lie symmetries and the relevant reductions (with physical meaning) to BVPs for ordinary differential equations are constructed. An example how to construct exact solution of the problem with correctly-specified coefficients is presented and compared with the results of numerical simulations published earlier.

Cherniha, Roman

2010-01-01

477

Flat connections in open string mirror symmetry  

NASA Astrophysics Data System (ADS)

We study a flat connection defined on the open-closed deformation space of open string mirror symmetry for type II compactifications on Calabi-Yau threefolds with D-branes. We use flatness and integrability conditions to define distinguished flat coordinates and the superpotential function at an arbitrary point in the open-closed deformation space. Integrability conditions are given for concrete deformation spaces with several closed and open string deformations. We study explicit examples for expansions around different limit points, including orbifold Gromov-Witten invariants, and brane configurations with several brane moduli. In particular, the latter case covers stacks of parallel branes with non-Abelian symmetry.

Alim, Murad; Hecht, Michael; Jockers, Hans; Mayr, Peter; Mertens, Adrian; Soroush, Masoud

2012-06-01

478

Composite gauge field models with broken symmetries  

E-print Network

We present a generalization of the non-Abelian version of the $CP^{N-1}$ models (also known as Grassmannian models) that involve composite gauge fields to accommodate partial breaking of the non-Abelian gauge symmetry. For this to be possible, in most cases, the constituent fields need to belong to an anomaly free complex representation. Symmetry is broken dynamically for large $N$ primarily by a naturally generated composite scalar which simulates Higgs mechanism. In the example studied in some detail, the gauge group SO(10) gets broken down to subgroups like SU(5) or SU(5)$\\times$U(1).

Balakrishna, B S

1994-01-01

479

Membranes with a symmetry of cohomogeneity one  

NASA Astrophysics Data System (ADS)

We study the dynamics of the Nambu-Goto membranes with cohomogeneity one symmetry, i.e., the membranes whose trajectories are foliated by homogeneous surfaces. It is shown that the equation of motion reduces to a geodesic equation on a certain manifold, which is constructed from the original spacetime and Killing vector fields thereon. A general method is presented for classifying the symmetry of cohomogeneity one membranes in a given spacetime. The classification is completely carried out in Minkowski spacetime. We analyze one of the obtained classes in depth and derive an exact solution.

Kozaki, Hiroshi; Koike, Tatsuhiko; Ishihara, Hideki

2015-01-01

480

Partial restoration of chiral symmetry inside hadrons  

E-print Network

By using the overlap-Dirac operator eigenmodes, we investigate spatial distribution of the chiral condensate around static color sources for both quark-antiquark and three quark systems. In the presence of color sources, a characteristic flux-tube structure appears among them, suggesting a linear confining potential. We show that the magnitude of the condensate is reduced inside the color flux, which indicates the partial restoration of chiral symmetry inside the "hadrons." Considering a periodic box containing a static baryon source, which mimics the "nuclear matter," we estimate the chiral symmetry restoration in the presence of finite baryon number density.

Takumi Iritani; Guido Cossu; Shoji Hashimoto

2014-12-07

481

Hopf bifurcation in the presence of symmetry  

NASA Technical Reports Server (NTRS)

Group theory is applied to obtain generalized differential equations from the Hopf bifurcation theory on branching to periodic solutions. The conditions under which the symmetry group will admit imaginary eigenvalues are delimited. The action of the symmetry group on the circle group are explored and the Liapunov-Schmidt reduction is used to prove the Hopf theorem in the symmetric case. The emphasis is on simplifying calculations of the stability of bifurcating branches. The resulting general theory is demonstrated in terms of O(2) acting on a plane, O(n) in n-space, and O(3) and an irreducible model for spherical harmonics.

Golubitsky, M.; Stewart, I.

1985-01-01

482

A quantum symmetry preserving semiclassical method  

NASA Astrophysics Data System (ADS)

Symmetry constraints are built into a semiclassical propagation scheme. It is then applied to treat H+Ne2 collisions at 30 K, where quantum selection rules restrict the final rotational states of symmetric Ne2 molecules to the even manifold. The cross sections for state-to-state transitions are calculated for symmetric and nonsymmetric isotopic compositions of Ne2. All bound and long-lived quasibound (trapped behind the centrifugal barrier) states of Ne2 are considered. This semiclassical method captures symmetry effects and shows satisfactory agreement with the quantum results.

Babikov, Dmitri; Walker, Robert B.; T Pack, Russell

2002-11-01

483

Site Symmetry and Band Representations for Phonons  

NASA Astrophysics Data System (ADS)

Site symmetry centers and band representations are considered for phonon spectra in crystals. For the case of Bravais lattices (crystals with one atom in a unit cell) it is shown that the acoustic phonon-frequency band is described by a band representation that is induced from a vectorial representation of the local symmetry group for the Wyckoff position coinciding with the location of the atom. Band representations from local groups for all other Wyckoff positions are forbidden. A consequence of this is that the topological phase for the acoustic band is zero.

Walker, M. B.; Zak, J.

1995-05-01

484

Second Order Symmetries of the Conformal Laplacian  

NASA Astrophysics Data System (ADS)

Let (M,g) be an arbitrary pseudo-Riemannian manifold of dimension at least 3. We determine the form of all the conformal symmetries of the conformal (or Yamabe) Laplacian on (M,g), which are given by differential operators of second order. They are constructed from conformal Killing 2-tensors satisfying a natural and conformally invariant condition. As a consequence, we get also the classification of the second order symmetries of the conformal Laplacian. Our results generalize the ones of Eastwood and Carter, which hold on conformally flat and Einstein manifolds respectively. We illustrate our results on two families of examples in dimension three.

Michel, Jean-Philippe; Radoux, Fabian; Šilhan, Josef

2014-02-01

485

Explorations in conformal symmetry for quantum relativity  

NASA Astrophysics Data System (ADS)

The conformal group is a supergroup of the Poincare group that leaves Maxwell's equations invariant. Conformal symmetry has many applications in physics. Can conformal symmetry be applied to bring together special relativity, which treats space and time on the same level, and quantum theory, which does not? Quantum relativity, as developed by Jaekel and Reynaud [1], introduces operators X^? for space-time localization from the generators of the conformal group in an Einsteinian operational way. We explore how this approach can help describe elementary space-time processes like pair creation and pair annihilation. [1] M.T. Jaekel and S. Reynaud, Found.Phys.28, 439-456 (1998).

Earl, Lucas; van Huele, Jean-Francois

2007-10-01

486

PT-symmetry in macroscopic magnetic structures  

E-print Network

We introduce the notion of PT-symmetry in magnetic nanostructures and show that they can support a new type of non-Hermitian dynamics. Using the simplest possible set-up consisting of two coupled ferromagnetic films, one with loss and another one with a balanced amount of gain, we demonstrate the existence of a spontaneous PT-symmetry breaking point where both the eigenfrequencies and eigenvectors are degenerate. Below this point the frequency spectrum is real indicating stable dynamics while above this point it is complex signaling unstable dynamics.

J. M. Lee; T. Kottos; B. Shapiro

2014-08-14

487

Master equations for extended Lagrangian BRST symmetries  

NASA Astrophysics Data System (ADS)

Starting from the requirement that a Lagrangian field theory be invariant under both Schwinger-Dyson BRST and Schwinger-Dyson anti-BRST symmetry, we derive the BRST-anti-BRST analogue of the Batalin-Vilkovisky formalism. This is done through standard Lagrangian gauge fixing respecting the extended BRST symmetry. The solutions of the resulting Master Equation and the gauge-fixing procedure for the quantum action can be brought into forms that coincide with those obtained earlier on algebraic grounds by Batalin, Lavrov and Tyutin.

H. Damgaard, Poul; De Jonghe, Frank

1993-05-01

488

Chimera Death: Symmetry Breaking in Dynamical Networks  

E-print Network

For a network of generic oscillators with nonlocal topology and symmetry-breaking coupling we establish novel partially coherent inhomogeneous spatial patterns, which combine the features of chimera states (coexisting incongruous coherent and incoherent domains) and oscillation death (oscillation suppression), which we call chimera death. We show that due to the interplay of nonlocality and breaking of rotational symmetry by the coupling two distinct scenarios from oscillatory behavior to a stationary state regime are possible: a transition from an amplitude chimera to chimera death via in-phase synchronized oscillations, and a direct abrupt transition for larger coupling strength.

Anna Zakharova; Marie Kapeller; Eckehard Schöll

2014-02-03

489

cRGD peptide-conjugated icosahedral closo-B12(2-) core carrying multiple Gd3+-DOTA chelates for ?(v)?3 integrin-targeted tumor imaging (MRI).  

PubMed

A vertex-differentiated icosahedral closo-B(12)(2-) core was utilized to construct a ?(v)?(3) integrin receptor-targeted (via cRGD peptide) high payload MRI contrast agent (CA-12) carrying 11 copies of Gd(3+)-DOTA chelates attached to the closo-B(12)(2-) surface via suitable linkers. The resulting polyfunctional MRI contrast agent possessed a higher relaxivity value per-Gd compared to Omniscan, a small molecular contrast agent commonly used in clinical settings. The ?(v)?(3) integrin receptor specificity of CA-12 was confirmed via in vitro cellular binding experiments and in vivo MRI of mice bearing human PC-3 prostate cancer xenografts. Integrin ?(v)?(3)-positive MDA-MB-231 cells exhibited 300% higher uptake of CA-12 than ?(v)?(3)-negative T47D cells. Serial T1-weighted MRI showed superior contrast enhancement of tumors by CA-12 compared to both a nontargeted 12-fold Gd(3+)-DOTA closomer control (CA-7) and Omniscan. Contrast enhancement by CA-12 persisted for 4 h postinjection, and subsequent enhancement of kidney tissue indicated a renal elimination route similar to Omniscan. No toxic effects of CA-12 were apparent in any mice for up to 24 h postinjection. Post-mortem ICP-OES analysis at 24 h detected no residual Gd in any of the tissue samples analyzed. PMID:23391150

Goswami, Lalit N; Ma, Lixin; Cai, Quanyu; Sarma, Saurav J; Jalisatgi, Satish S; Hawthorne, M Frederick

2013-02-18