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1

Icosahedral and decagonal quasicrystals of intermetallic compounds are multiple twins of cubic or orthorhombic crystals composed of very large atomic complexes with icosahedral point-group symmetry in cubic close packing or body-centered packing: Structure of decagonal Al6Pd  

PubMed Central

A doubly icosahedral complex involves roughly spherical clusters of atoms with icosahedral point-group symmetry, which are themselves, in parallel orientation, icosahedrally packed. These complexes may form cubic crystallites; three structures of this sort have been identified. Analysis of electron diffraction photographs of the decagonal quasicrystal Al6Pd has led to its description as involving pentagonal twinning of an orthorhombic crystal with a = 51.6 Å, b = 37.6 Å, and c = 33.24 Å, with about 4202 atoms in the unit, comprising two 1980-atom doubly icosahedral complexes, each involving icosahedral packing of 45 44-atom icosahedral complexes (at 0 0 0 and 1/2 1/2 1/2) and 242 interstitial atoms. The complexes and clusters are oriented with one of their fivefold axes in the c-axis direction. Images PMID:16594092

Pauling, Linus

1989-01-01

2

Sigma-phase packing of icosahedral clusters in 780-atom tetragonal crystals of Cr5Ni3Si2 and V15Ni10Si that by twinning achieve 8-fold rotational point-group symmetry  

PubMed Central

A 780-atom primitive tetragonal unit with edges 27.3, 27.3, and 12.6 Å is assigned to rapidly solidified Cu5Ni3Si2 and V15Ni10Si by analysis of electron diffraction photographs with the assumption that the crystals contain icosahedral clusters. There are thirty 26-atom clusters at the sigma-phase positions. Apparent 8-fold symmetry results from 45° twinning on the basal plane. PMID:16593915

Pauling, Linus

1988-01-01

3

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

4

Visualization of Time-Reversal Symmetry in Magnetic Point Groups  

NASA Astrophysics Data System (ADS)

The direct visualization of crystallographic and magnetic point group symmetry by means of computer graphics simplifies the teaching of point group symmetry at the undergraduate and graduate levels. Still images and animated movies for all 32 crystallographic point groups, and for the 122 magnetic point groups, are presented. For each point group, the action of the symmetry operators on scalar and pseudo-scalar objects, as well as on polar and axial vectors, is represented as a three-dimensional rendered image. All images and movies are made available as supplementary educational material via a dedicated web site.

de Graef, Marc

2010-05-01

5

An Online Tutorial for Learning Symmetry and Point Groups  

NSDL National Science Digital Library

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

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 the microscopic single domain crystal symmetry. Such engineered domain structures in certain ferroelectric the domain wall, since it usually appears as a planar structure along particular crystallographic orienta

Cao, Wenwu

7

Breaking of icosahedral symmetry: C60 to C70.  

PubMed

We describe the existence and structure of large fullerenes in terms of symmetry breaking of the C60 molecule. Specifically, we describe the existence of C70 in terms of breaking of the icosahedral symmetry of C60 by the insertion into its middle of an additional H2 decagon. The surface of C70 is formed by 12 regular pentagons and 25 regular hexagons. All 105 edges of C70 are of the same length. It should be noted that the structure of the molecules is described in exact coordinates relative to the non-orthogonal icosahedral bases. This symmetry breaking process can be readily applied, and could account for and describe other larger cage cluster fullerene molecules, as well as more complex higher structures such as nanotubes. PMID:24599292

Bodner, Mark; Patera, Jiri; Szajewska, Marzena

2014-01-01

8

Breaking of Icosahedral Symmetry: C60 to C70  

PubMed Central

We describe the existence and structure of large fullerenes in terms of symmetry breaking of the molecule. Specifically, we describe the existence of in terms of breaking of the icosahedral symmetry of by the insertion into its middle of an additional decagon. The surface of is formed by 12 regular pentagons and 25 regular hexagons. All 105 edges of are of the same length. It should be noted that the structure of the molecules is described in exact coordinates relative to the non-orthogonal icosahedral bases. This symmetry breaking process can be readily applied, and could account for and describe other larger cage cluster fullerene molecules, as well as more complex higher structures such as nanotubes. PMID:24599292

Bodner, Mark; Patera, Jiri; Szajewska, Marzena

2014-01-01

9

Binary icosahedral flavor symmetry for four generations of quarks and leptons  

NASA Astrophysics Data System (ADS)

To include the quark sector, the A5? I (icosahedron) four generation lepton model is extended to a binary icosahedral symmetry I' flavor model. We find that the masses of fermions, including the heavy sectors, can be accommodated. At leading order the Cabibbo-Kobayashi-Maskawa (CKM) matrix is the identity and the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix, resulting from the same set of vacua, corresponds to tribimaximal mixings.

Chen, Chian-Shu; Kephart, Thomas W.; Yuan, Tzu-Chiang

2013-10-01

10

Theory of Nuclear Stability Using Point GROUP Symmetries: Outline and Illustrations  

NASA Astrophysics Data System (ADS)

We present what we call a new theory of nuclear stability enabled by the combination of the realistic nuclear mean-field and the group theory approaches. It allows us to simplify searches for the strong quantum shell effects at nuclear shapes that result from spectral properties deduced from group theory and geometrical symmetries rather than through `brute force numerical search'. Illustrations are presented and discussed.

Dudek, J.; Mazurek, K.; Curien, D.; Dobrowolski, A.; Gó?d?, A.; Hartley, D.; Maj, A.; Riedinger, L.; Schunck, N.

2009-03-01

11

Advance in Thomson problem and slightly broken symmetry of icosahedral viral capsids  

E-print Network

Progress in Thomson problem reveals general principles of forming variety of spherical structures (from viral capsids to colloidosomes) possessing local hexagonal order. We advance the problem by simple numerical optimization of trial spherical structures, which are deduced from icosahedral spherical lattices suggested by Caspar and Klug in their pioneer model of viral capsids. Geometric and symmetry principles found reduce strongly the number of trial structures. In the region of N from 600 to 1000, where N is the number of particles in the structure, we discover 41 new spherical crystals with the lowest ever seen energies. Curvature induced topological defects in these crystals are not the well-known elongated scars but flatten pentagons with the centers located in the vertices of spherical icosahedrons covered by perfect hexagonal order. Our method to construct 2D spherical crystals with a global slightly distorted icosahedral arrangement may be useful to study structures of misassembled viral capsids or l...

Roshal, D S; Rochal, S B

2014-01-01

12

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

PubMed

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

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

2013-11-01

13

Complex method of the plane elasticity in 2D quasicrystal with point group 10 mm tenfold rotational symmetry and holey problems  

Microsoft Academic Search

The complex method of the plane elasticity in 2D quasicrystal with point group 10 mm tenfold rotational symmetry is established.\\u000a First displacement potential function in the quasicrystal is represented by four analytic functions. Then by utilizing the\\u000a properties of analytic function and through a great deal of derivation, the complex representations of stresses and displacements\\u000a components of phonon fields and

Guanting Liu; Tianyou Fan

2003-01-01

14

Apparent icosahedral symmetry is due to directed multiple twinning of cubic crystals  

Microsoft Academic Search

A proposed structure and successful analysis of a diffraction pattern are offered to settle the question of the nature of the 'icosahedral' MAl6 alloys (where M = Cr, Mn, Fe). How a molten alloy of Mn (or Cr or Fe) and Al might react to sudden cooling is predicted. It is discovered that such an alloy on sudden cooling could

Linus Pauling

1985-01-01

15

Dislocations in icosahedral quasicrystals.  

PubMed

Dislocations in quasicrystals, as a direct result of the lack of translational symmetry in these materials, possess various salient features. The Burgers vector of a dislocation in an icosahedral quasicrystal is a 6-dimensional vector, which reflects the fact that the dislocation, besides the phonon-type strain field analogous to dislocations in ordinary crystals, is associated inseparably with a further type of defect, the phasons. Phasons are critically involved in the formation and motion of dislocations in quasicrystals and govern the macroscopic plastic behaviour of these materials. In this article the properties of dislocations in icosahedral quasicrystals are comprehensively reviewed, starting from a continuum-mechanical description, via core-structure simulation, to their full experimental characterization. The experimental results presented address the icosahedral phases in the well explored systems Al-Pd-Mn and Zn-Mg-Dy. PMID:22760204

Feuerbacher, Michael

2012-10-21

16

NEW CARBON NANOPARTICLE - ICOSAHEDRAL DIAMOND  

Microsoft Academic Search

Regular structures need not be crystalline1. The most striking example of such structures is icosahedral packing2. It has a definite structure, which is not that of a crystal, nor that of a molecule; it is not one of the space-groups (or even point groups) listed in the International Tables; it is not a twin (although it could be described in

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

17

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

18

Weyl phases in point-group symmetric superconductors  

NASA Astrophysics Data System (ADS)

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

Shivamoggi, Vasudha; Gilbert, Matthew J.

2013-10-01

19

Topological Phases of Point Group Symmetric Weyl Superconductors  

NASA Astrophysics Data System (ADS)

We study superconductivity in a Weyl semimetal with broken time-reversal symmetry and stabilized by a point-group symmetry. The resulting superconducting phase is characterized by topologically protected bulk nodes and surface states with Fermi arcs. We derive a phase diagram of possible superconducting phases which are distinguished by the number of bulk nodes and discuss novel properties of the corresponding surface states. We show how the topological behavior may be understood in terms of the properties of the parent Weyl semimetal at high-symmetry momenta.

Shivamoggi, Vasudha; Fang, Chen; Hughes, Taylor; Gilbert, Matthew

2013-03-01

20

3-dimensional indexation of the icosahedral diffraction pattern using the techniques of electron microscopy  

NASA Astrophysics Data System (ADS)

The following facts about icosahedra need wider attention. 1) The golden section ? is as fundamental to the icosahedral structure (length /edge) as ? is to the sphere (circumference /diameter). 2) The diffraction series are in restricted Fibonacci order because the ratio of adjacent terms fn/fn-1 does not vary, but is the constant ?. The series is therefore geometric. 3) Because of the tetragonal subgroup in the icosahedral point group symmetry, many axes in the icosahedral structure have identical orientation to axes in the face centered cubic matrix of Al6Mn [1] (e.g. [100] and [111]). On these bases, a three dimensional stereographic projection will be presented. 4) A quasi-Bragg law is derived that correctly represents the diffraction series in powers of ? [2]. Furthermore, by employing the normal conventions of electron microscopy, all diffraction patterns are completely indexed in three dimensions. These are the topic of this presentation. Significant consequences will be presented elsewhere: 1) The diffraction pattern intensities near all main axes are correctly simulated, and all atoms are located on a specimen image. 2) The quasi-Bragg law has a special metric. Atomic locations are consistently calculated for the first time. 3) Whereas the Bragg law transforms a crystal lattice in real space into a reciprocal lattice in diffraction space, the quasi-Bragg law transforms a geometric diffraction pattern into a hierarchic structure. 4) Hyperspatial indexation [3] is superceded. [1] Shechtman, D.; Blech, I.; Gratias, D.; Cahn, J.W., Metallic phase with long-range orientational order and no translational symmetry, Phys. Rev. Lett., 1984, 53, 1951-3. [2] Bourdillon, A. J., Nearly free electron band structures in a logarithmically periodic solid, Sol. State Comm. 2009, 149, 1221-1225. [3] Duneau, M., and Katz, A., Phys Rev Lett 54, 2688-2691

Bourdillon, Antony

2012-11-01

21

Icosahedral quasicrystals for visible wavelengths by optical interference holography.  

PubMed

Quasicrystals, realized in metal alloys, are a class of lattices exhibiting symmetries that fall outside the usual classification for periodic crystals. They do not have translational symmetry and yet the lattice points are well ordered. Furthermore, they exhibit higher rotational symmetry than periodic crystals. Because of the higher symmetry (more spherical), they are more optimal than periodic crystals in achieving complete photonic bandgaps in a new class of materials called photonic crystals in which the propagation of light in certain frequency ranges is forbidden. The potential of quasicrystals has been demonstrated in two dimensions for the infrared range and, recently, in three-dimensional icosahedral quasicrystals fabricated using a stereo lithography method for the microwave range and direct laser writing for the IR range. Here, we report the fabrication and optical characterization of icosahedral quasicrystals using a holographic lithography method for the visible range. The icosahedral pattern, generated using a novel 7-beam optical interference holography, is recorded on photoresists and holographic plates. Electron micrographs of the photoresist samples show clearly the symmetry of the icosahedral quasicrystals in the submicron range, while the holographic plate samples exhibit bandgaps in the angular-dependent transmission spectra in the visible range. Calculations of the bandgaps due to reflection planes inside the icosahedral quasicrystal show good agreement with the experimental results. PMID:19532673

Xu, Jun; Ma, Rui; Wang, Xia; Tam, Wing Yim

2007-04-01

22

About the atomic structures of icosahedral quasicrystals  

NASA Astrophysics Data System (ADS)

This paper is a survey of the crystallographic methods that have been developed these last twenty five years to decipher the atomic structures of the icosahedral stable quasicrystals since their discovery in 1982 by D. Shechtman. After a brief recall of the notion of quasiperiodicity and the natural description of Z-modules in 3-dim as projection of regular lattices in N>3-dim spaces, we give the basic geometrical ingredients useful to describe icosahedral quasicrystals as irrational 3-dim cuts of ordinary crystals in 6-dim space. Atoms are described by atomic surfaces (ASs) that are bounded volumes in the internal (or perpendicular) 3-dim space and the intersections of which with the physical space are the actual atomic positions. The main part of the paper is devoted to finding the major properties of quasicrystalline icosahedral structures. As experimentally demonstrated, they can be described with a surprisingly few high symmetry ASs located at high symmetry special points in 6-dim space. The atomic structures are best described by aggregations and intersections of high symmetry compact interpenetrating atomic clusters. We show here that the experimentally relevant clusters are derived from one generic cluster made of two concentric triacontahedra scaled by ? and an external icosidodecahedron. Depending on which ones of the orbits of this cluster are eventually occupied by atoms, the actual atomic clusters are of type Bergman, Mackay, Tsai and others….

Quiquandon, Marianne; Gratias, Denis

2014-01-01

23

Evidence from electron micrographs that icosahedral quasicrystals are icosahedral twins of cubic crystals.  

PubMed Central

An analysis of electron micrographs of Al5Mn quasicrystals obtained by rapidly cooling a molten alloy with composition Al17Mn and removing the Al matrix by electrosolution, revealing aggregates of 20 microcrystals at the corners of a pentagonal dodecahedron, supports the proposal that these microcrystals are cubic crystals twinned about an icosahedral seed, with each cubic microcrystal sharing a threefold axis and three symmetry planes with the seed. Images PMID:11607108

Pauling, L

1990-01-01

24

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

25

Icosahedral order in liquids  

SciTech Connect

The possibility of icosahedral order in liquids and its role in glass transition is discussed in a broad context of statistical mechanics of liquid. It is pointed out that the structures of glasses and liquids are described both in terms of the topology of atomic bond networks as well as the local distortion of the atomic bonds. While topology plays a dominant role in covalent glasses, local distortion is likely to be more important for metallic glasses.

Egami, Takeshi [ORNL

2007-01-01

26

Invariant Features from Interest Point Groups  

E-print Network

Invariant Features from Interest Point Groups Matthew Brown and David Lowe {mbrown points to be robustly matched between images, they must be as far as possible invariant to the imaging geometrically invariant descriptors of image regions. Feature descriptors are formed by resampling the image rel

Salvaggio, Carl

27

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

28

Symmetry  

NSDL National Science Digital Library

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

Perkins, Dexter

29

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

Microsoft Academic Search

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

Linus Pauling

1987-01-01

30

Surface oxidation of the icosahedral Ag-In-Yb quasicrystal  

Microsoft Academic Search

The oxidation of the high-symmetry surfaces of a single grain icosahedral (i) Ag-In-Yb quasicrystal has been studied using x-ray photoemission spectroscopy. The oxidation was carried out in vacuum, air, and water. It is found that air exposure results in the same degree of oxidation as exposure to oxygen in vacuum. The oxidation in water is more effective. Among the three

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

2010-01-01

31

Nanosize icosahedral quasicrystal in Mg90Ca10 glass: an ab initio molecular dynamics study.  

PubMed

Rapid solidification of Mg(90)Ca(10) from its liquid state is studied by means of an ab initio molecular dynamics technique, and its local structure is investigated by various analyzing methods. The liquid and amorphous states are found to have slightly different short range order even though the perfect and defective icosahedral bonding environments are major bonding elements of both liquid and amorphous states. Perfect icosahedrons with a small frequency exist in the liquid state, more develop during the cooling process and they become the leading building units in the glass state, indicating an icosahedral short range order in Mg(90)Ca(10) glass. Also the linked icosahedrons lead to an icosahedral medium range order. Furthermore, an ordered arrangement of some icosahedrons in the hexagonal symmetry is observed in the glass model, representing a nanoscale icosahedral quasicrystalline phase in Mg(90)Ca(10) glass. PMID:22830707

Durandurdu, Murat

2012-07-21

32

Atomic clusters and atomic surfaces in icosahedral quasicrystals.  

PubMed

This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space. The first rule is maximizing the density using simple polyhedral ASs that leads to two possible sets of ASs according to the value of the six-dimensional lattice parameter A between 0.63 and 0.79 nm. The second rule is maximizing the number of complete orbits of high symmetry to construct as large as possible atomic clusters similar to those observed in complex intermetallic structures and approximant phases. The practical use of these two rules together is demonstrated on two typical examples of icosahedral phases, i-AlMnSi and i-CdRE (RE = Gd, Ho, Tm). PMID:24815972

Quiquandon, Marianne; Portier, Richard; Gratias, Denis

2014-05-01

33

Icosahedral T1u+T1g Jahn-Teller problem  

NASA Astrophysics Data System (ADS)

The T1u+T1g multimode Jahn-Teller problem in icosahedral symmetry is investigated. It is found that the pseudo-Jahn-Teller interaction between T1u and T1g can give rise to an increase of symmetry through the development of additional troughs in the space of ungerade modes. This result is related to a continuous group invariance of the Hamiltonian. The possible relevance to the Jahn-Teller instability of negatively charged fullerides is discussed.

Ceulemans, A.; Chibotaru, L. F.

1996-02-01

34

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

35

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

36

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

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

2011-01-01

37

Beta cell device using icosahedral boride compounds  

DOEpatents

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

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

2002-01-01

38

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

39

Cryoelectron-Microscopy Image Reconstruction of Symmetry Mismatches in Bacteriophage ?29  

Microsoft Academic Search

A method has been developed for three-dimensional image reconstruction of symmetry-mismatched components in tailed phages. Although the method described here addresses the specific case where differing symmetry axes are coincident, the method is more generally applicable, for instance, to the reconstruction of images of viral particles that deviate from icosahedral symmetry. Particles are initially oriented according to their dominant symmetry,

Marc C. Morais; Yizhi Tao; Norman H. Olson; Shelley Grimes; Paul J. Jardine; Dwight L. Anderson; Timothy S. Baker; Michael G. Rossmann

2001-01-01

40

3D Printed Molecules and Extended Solid Models for Teaching Symmetry and Point Groups  

ERIC Educational Resources Information Center

Tangible models help students and researchers visualize chemical structures in three dimensions (3D). 3D printing offers a unique and straightforward approach to fabricate plastic 3D models of molecules and extended solids. In this article, we prepared a series of digital 3D design files of molecular structures that will be useful for teaching…

Scalfani, Vincent F.; Vaid, Thomas P.

2014-01-01

41

Planar defects in the icosahedral phase in quasicrystal-forming AlCuFe alloys  

NASA Astrophysics Data System (ADS)

Electron microscopy has revealed that, upon the formation of a stable icosahedral ( i) AlCuFe phase, there arise a large number of planar defects. The revealed defects are nanometer-sized coherent intergrowths of the P1-pentagonal approximant. It has been found that the formation of these defects is the result of a nonequilibrium intermediate transformation. The intergrowths are located in the planes with the fivefold symmetry axis and give rise to an elastic-strain state of the i-phase. Analysis of the diffraction contrast has revealed the presence of phason and phonon atomic displacements due to the mismatch between the quasiperiodic ( i-phase) and periodic ( P1-phase) lattices. The formed structure exhibits a higher electrical resistance as compared to the i-phase and has been considered as a model state of the imperfect icosahedral phase with preferred phonon displacements.

Shalaeva, E. V.; Prekul, A. F.; Nazarova, S. Z.; Khiller, V. V.

2012-04-01

42

Structure of the twofold surface of the icosahedral Ag-In-Yb quasicrystal.  

PubMed

The structure of the twofold surface of the icosahedral (i-)Ag-In-Yb quasicrystal has been investigated using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The LEED confirms that the surface exhibits quasicrystalline long range order with the twofold rotational symmetry expected from the bulk. STM images reveal a step-terrace structure with terrace size comparable to that of the other high symmetry surfaces of the same quasicrystal. The distribution of step heights and high resolution STM images of terraces suggest that the surface terminates at bulk planes that intersect the center of rhombic triacontahedral clusters, the building blocks of the system, as in the case of the threefold and fivefold surfaces of the system. These planes are rich in Yb and In. No facets are observed on the surface, suggesting that the twofold surface is as stable as the other high symmetry surfaces. PMID:24263167

Cui, C; Nugent, P J; Shimoda, M; Ledieu, J; Fournée, V; Tsai, A P; McGrath, R; Sharma, H R

2014-01-01

43

Topological Quantum Hashing with the Icosahedral Group  

NASA Astrophysics Data System (ADS)

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?2(1/?)), we can approximate all SU(2) matrices to an average error ? with a cost of O(log?(1/?)) in time. The algorithm is applicable to generic quantum compiling.

Burrello, Michele; Xu, Haitan; Mussardo, Giuseppe; Wan, Xin

2010-04-01

44

Confessions of an icosahedral virus crystallographer  

PubMed Central

This is a personal history of my structural studies of icosahedral viruses that evolved from crystallographic studies, to hybrid methods with electron cryo-microscopy and image reconstruction (cryoEM) and then developed further by incorporating a variety of physical methods to augment the high resolution crystallographic studies. It is not meant to be comprehensive, even for my own work, but hopefully provides some perspective on the growth of our understanding of these remarkable biologic assemblies. The goal is to provide a historical perspective for those new to the field and to emphasize the limitations of any one method, even those that provide atomic resolution information about viruses. PMID:23291268

Johnson, John E.

2013-01-01

45

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

46

Method of making an icosahedral boride structure  

DOEpatents

A method for fabricating thin films of an icosahedral boride on a silicon carbide (SiC) substrate is provided. Preferably the icosahedral boride layer is comprised of either boron phosphide (B.sub.12 P.sub.2) or boron arsenide (B.sub.12 As.sub.2). The provided method achieves improved film crystallinity and lowered impurity concentrations. In one aspect, an epitaxially grown layer of B.sub.12 P.sub.2 with a base layer or substrate of SiC is provided. In another aspect, an epitaxially grown layer of B.sub.12 As.sub.2 with a base layer or substrate of SiC is provided. In yet another aspect, thin films of B.sub.12 P.sub.2 or B.sub.12 As.sub.2 are formed on SiC using CVD or other vapor deposition means. If CVD techniques are employed, preferably the deposition temperature is above 1050.degree. C., more preferably in the range of 1100.degree. C. to 1400.degree. C., and still more preferably approximately 1150.degree. C.

Hersee, Stephen D. (3712 Silver Ave. SE., Albuquerque, NM 87108); Wang, Ronghua (939 Buena Vista Dr., SE., Apt. F203, Albuquerque, NM 87106); Zubia, David (4409 Buckingham Dr., El Paso, TX 79902); Aselage, Terrance L. (62 Avenida Del Sol, Cedar Crest, NM 87008); Emin, David (1502 Harvard Ct. NE., Albuquerque, NM 87106)

2005-01-11

47

Microscopic Symmetry Imposed by Rotational Symmetry Boundary Conditions in Molecular Dynamics Simulation  

PubMed Central

A large number of viral capsids, as well as other macromolecular assemblies, have icosahedral structure or structures with other rotational symmetries. This symmetry can be exploited during molecular dynamics (MD) to model in effect the full viral capsid using only a subset of primary atoms plus copies of image atoms generated from rotational symmetry boundary conditions (RSBC). A pure rotational symmetry operation results in both primary and image atoms at short range, and within nonbonded interaction distance of each other, so that nonbonded interactions can not be specified by the minimum image convention and explicit treatment of image atoms is required. As such an unavoidable consequence of RSBC is that the enumeration of nonbonded interactions in regions surrounding certain rotational axes must include both a primary atom and its copied image atom, thereby imposing microscopic symmetry for some forces. We examined the possibility of artifacts arising from this imposed microscopic symmetry of RSBC using two simulation systems: a water shell and human rhinovirus 14 (HRV14) capsid with explicit water. The primary unit was a pentamer of the icosahedron, which has the advantage of direct comparison of icosahedrally equivalent spatial regions, for example regions near a 2-fold symmetry axis with imposed symmetry and a 2-fold axis without imposed symmetry. Analysis of structural and dynamic properties of water molecules and protein atoms found similar behavior near symmetry axes with imposed symmetry and where the minimum image convention fails compared with that in other regions in the simulation system, even though an excluded volume effect was detected for water molecules near the axes with imposed symmetry. These results validate the use of RSBC for icosahedral viral capsids or other rotationally symmetric systems. PMID:22096451

Roy, Amitava; Post, Carol Beth

2011-01-01

48

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

49

2 antiferromagnetic Heisenberg model on fullerene-type symmetry clusters N. P. Konstantinidis  

E-print Network

s= 1 2 antiferromagnetic Heisenberg model on fullerene-type symmetry clusters N. P. Konstantinidis for spins sitting on the vertices of clusters with the connectivity of fullerene molecules and a number the icosahedral Ih fullerene clusters but only plateaux with the most pronounced for n=28. The spatial symmetry

50

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

51

Spectrum of states in icosahedral structures of the electronic configuration g n ( N = 1–7). 1. Invariant expansion for integrals and energies  

Microsoft Academic Search

The energy spectrum of the states that appear in structures of icosahedral (I,Ih symmetry with open electronic shells gN (dim g = 4; N = 1–7) is reported. The energies are obtained in terms of integral invariants (reduced matrix elements of electron-electron\\u000a interaction) Hk (g, g). The latter are analogs of the Slater-Condon parameters Fk(l,l) for atoms with the lN

B. N. Plakhutin

1997-01-01

52

Structure and reactivity of Bi allotropes on the fivefold icosahedral Al-Pd-Mn quasicrystal surface.  

PubMed

The growth of Bi on a pseudomorphic Bi monolayer on the fivefold surface of the icosahedral Al-Pd-Mn quasicrystal has been investigated using low energy electron diffraction and scanning tunnelling microscopy. Initially randomly oriented pseudocubic islands are formed with a preference for an even number of layers. Subsequently a morphological transformation takes place to hexagonal Bi islands, which align along high symmetry directions of the substrate. The Bi flux is found to have a strong effect on which island structure is preferred. When C(60) is adsorbed on the three different allotropes of Bi present in this system, hexagonal C(60) islands are formed in each case. On the pseudocubic and hexagonal islands, the C(60) islands are aligned with the substrate. We discuss the energetic, kinetic and geometrical factors which influence the morphological transformation referred to above. PMID:21403246

Smerdon, J A; Cross, N; Dhanak, V R; Sharma, H R; Young, K M; Lograsso, T A; Ross, A R; McGrath, R

2010-09-01

53

Icosahedral Platinum Alloy Nanocrystals with Enhanced Electrocatalytic Activities  

E-print Network

Supporting Information ABSTRACT: This communication describes the syn- thesis of Pt-M (M = Au, Ni, Pd) icosahedral nanocrystals based on the gas reducing agent in liquid solution method. Both CO gas and organic environment in an inert reducing gas may limit the oxidative etching of these twinned particles.9

Chen, Sow-Hsin

54

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

55

Product Jahn-Teller systems: The \\{T1?H\\}?(g+2h) icosahedral exciton  

NASA Astrophysics Data System (ADS)

The \\{T1?H\\}?(g+2h) product Jahn-Teller (JT) system offers a model Hamiltonian for the excited configuration of C60. It describes the combined JT activity of two open shells transforming as the threefold and fivefold degenerate icosahedral representations T1 and H. The two separate JT problems interfere via the interaction with common vibrational modes. In this paper we examine the structure of the resulting potential energy surface. The treatment first considers the simplified \\{T1?H\\}?(2h) problem. The coupling conditions for this problem can be represented in a two-dimensional phase diagram with a rich structure. The diagram is separated in four domains by four trough lines. These correspond to different embeddings of SO(3) in SO(5) and describe the possible spherical couplings between a three vector and a five tensor. Outside the trough lines symmetry is broken to D5d, D3d, D2h, and even C2h. Several tables offer a description of the structural aspects of these low-symmetry solutions. In the second part the full multimode Hamiltonian is treated by the method of the isostationary function. It is shown that the interconfigurational coupling term of this Hamiltonian reduces to the same tensorial form as for the simplified single mode \\{T1?H\\}?(2h) case.

Qiu, Q. C.; Chibotaru, L. F.; Ceulemans, A.

2002-01-01

56

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

57

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

58

Creep behaviour of icosahedral Al–Cu–Fe  

Microsoft Academic Search

Transient creep experiments have been performed on poly-quasicrystalline specimens of the icosahedral Al–Cu–Fe phase. Three temperatures (870, 960 and 1000K) have been selected in the ductile regime for creep stresses that range between 30 and 320MPa. In these experiments, the specimens are first loaded in constant strain-rate conditions, then the testing machine is switched to load control and the specimens

E Giacometti; N Baluc; J Bonneville

2000-01-01

59

A coordination chemistry dichotomy for icosahedral carborane-based ligands.  

PubMed

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

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

2011-08-01

60

Optical rotation in RbTiOAsO4 (point group mm2) W. Kaminsky*, I  

E-print Network

Optical rotation in RbTiOAsO4 (point group mm2) W. Kaminsky*, I , P. A. ThomasII and A. M. Glazer, UK Received March 5, 2001; accepted September 13, 2001 Abstract. Measurement of optical rotation in RbTiOAsO4 (RTA) with the tilter method resulted in an optical rotation of r12 ¼ þ17ð3� /mm

Kaminsky, Werner

61

Prediction of the structure of symmetrical protein assemblies  

E-print Network

, icosahedral, or helical symmetry that play roles in processes ranging from allosteric control and molecular and molecular motors gener- ating rotational motion. Another common point-group symmetry is the dihedral group

Baker, David

62

Exploring Metric Symmetry  

SciTech Connect

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

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

2006-07-31

63

Non-centro-symmetric electron diffraction pattern of icosahedral quasicrystal induced by combination of linear phason strain and curvature of Ewald sphere.  

PubMed

Non-centro-symmetric characteristics are observed in the experimental electron diffraction patterns (EDPs) from the icosahedral quasicrystalline precipitates in ZrAlNiCuNb alloys. Different from the well-known breaking of the Friedel's law, where a strong dynamical effect will reveal in EDPs the concealed non-centro-symmetry originated from the crystal structures themselves, the current results can be interpreted in terms of changes in deviation parameters due to a delicate combination of the linear phason strain characteristic of quasicrystals and the curvature of Ewald sphere. After taking this effect into consideration, the corresponding simulated EDPs fit quite well to the experimental data. PMID:24041584

Xiong, Dongxia; Lu, Lu; Wang, Jianbo; Zhao, Dongshan; Sun, Yufeng

2013-01-01

64

SCA: symmetry-based center assignment of 2D projections of symmetric 3D objects.  

PubMed

A method for finding the center of cryo-EM images which correspond to the projections of a symmetric 3D structure, based on mathematical properties of symmetry adapted functions and the Fourier-Bessel transform, is presented. It is a model independent one-step procedure with no parameters to be chosen by the user. The proposed method is tested in one synthetic tetrahedral case with different noise levels and in two real cases with D7 and icosahedral symmetries. PMID:17029843

Estrozi, Leandro Farias; Trapani, Stefano; Navaza, Jorge

2007-02-01

65

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

66

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

Microsoft Academic Search

For a nonhydrostatic global model that is run efficiently at super-high resolution, we propose the use of an icosahedral grid, which is one of the quasi-homogeneous grid systems. In this paper, we concentrate mainly on the description of the numerical scheme of a new dynamical framework using the icosahedral grid. The numerical method guarantees conservations of mass and total energy.

Hirofumi Tomita; Masaki Satoh

2004-01-01

67

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.

68

Stable Zn-Mg-rare-earth face-centred icosahedral alloys with pentagonal dodecahedral solidification morphology  

Microsoft Academic Search

A thermodynamically stable face-centred icosahedral phase with a pentagonal dodecahedral solidification morphology has been found in Zn?Mg?RE (RE ? Y, Tb, Dy, Ho or Er) alloys. We report here the structure, stability and morphology in this new group of icosahedral alloys on the basis of results for the Zn?Mg?Y system.

A. Niikura; A. P. Tsai; A. Inoue; T. Masumoto

1994-01-01

69

Melting of bcc Transition Metals and Icosahedral Clustering  

SciTech Connect

In contrast to polyvalent metals, transition metals have low melting slopes(dT/dP) that are due to partially filled d-bands that allow for a lowering of liquid phase energy through s-d electron transfer and the formation of local structures. In the case of bcc transition metals we show the apparent discrepancy of DAC melting measurements with shock melting of Mo can be understood by reexamining the shock data for V and Ta and introducing the presence of an icosahedral short range order (ISRO) melt phase.

Ross, M; Boehler, R; Japel, S

2006-05-26

70

The atomic structure of the threefold surface of the icosahedral Ag-In-Yb quasicrystal  

NASA Astrophysics Data System (ADS)

We report a study of the atomic structure of the threefold icosahedral (i-)Ag-In-Yb quasicrystal surface using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The LEED confirms that the surface exhibits quasicrystalline long-range order with the threefold symmetry expected from the bulk. The STM reveals large atomically flat terraces separated by steps of different heights. A comparison of atomically resolved STM images for the terraces and the step-height distribution with the bulk structure of isostructural i-Cd-Yb shows that the terraces are formed at bulk planes intersecting the centers of the rhombic triacontahedral clusters that make up the bulk structure of the system. However, the stability of particular terraces may be influenced by the density of atoms in the interstices (glue atoms that bind the clusters) in the terraces and also by the chemical environment in the underlying atomic plane. The surface exhibits screw dislocations, which is explained in terms of a continuous atomic density along the threefold axis.

Cui, C.; Nugent, P. J.; Shimoda, M.; Ledieu, J.; Fournée, V.; Tsai, A. P.; McGrath, R.; Sharma, H. R.

2012-11-01

71

The atomic structure of the threefold surface of the icosahedral Ag-In-Yb quasicrystal.  

PubMed

We report a study of the atomic structure of the threefold icosahedral (i-)Ag-In-Yb quasicrystal surface using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The LEED confirms that the surface exhibits quasicrystalline long-range order with the threefold symmetry expected from the bulk. The STM reveals large atomically flat terraces separated by steps of different heights. A comparison of atomically resolved STM images for the terraces and the step-height distribution with the bulk structure of isostructural i-Cd-Yb shows that the terraces are formed at bulk planes intersecting the centers of the rhombic triacontahedral clusters that make up the bulk structure of the system. However, the stability of particular terraces may be influenced by the density of atoms in the interstices (glue atoms that bind the clusters) in the terraces and also by the chemical environment in the underlying atomic plane. The surface exhibits screw dislocations, which is explained in terms of a continuous atomic density along the threefold axis. PMID:23044476

Cui, C; Nugent, P J; Shimoda, M; Ledieu, J; Fournée, V; Tsai, A P; McGrath, R; Sharma, H R

2012-11-01

72

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

73

Synthesis of Vertex-Differentiated Icosahedral closo-Boranes: Polyfunctional Scaffolds for Targeted Drug Delivery  

PubMed Central

We report methods for the synthesis of vertex-differentiated icosahedral closo-boranes. A single B-OH vertex of the icosahedral borane [closo-B12(OH)12]2? was derivatized to prepare [closo-B12(OR)(OH)11]2? using optimized alkylation conditions and purification procedures. Several representative vertex-differentiated icosahedral closo-boranes were prepared utilizing carbonate ester and azide-alkyne click chemistries on the surface of the closo-B122? core. PMID:23164043

Goswami, Lalit N.; Houston, Zachary H.; Sarma, Saurav J.; Li, Hairong; Jalisatgi, Satish S.; Hawthorne, M. Frederick

2012-01-01

74

Melting of icosahedral nickel clusters under hydrostatic pressure.  

PubMed

The thermal stabilities and melting behavior of icosahedral nickel clusters under hydrostatic pressure have been studied by constant-pressure molecular dynamics simulation. The potential energy and Lindemann index are calculated. The overall melting temperature exhibits a strong dependence on pressure. The Lindemann index of solid structure before melting varies slowly and is almost independent of pressure. However, after the clusters melt completely, the Lindemann index at the overall melting point strongly depends on pressure. The overall melting temperature is found to be increasing nonlinearly with increasing pressure, while the volume change during melting decreases linearly with increasing pressure. Under a high pressure and temperature environment, similar angular distributions were found between liquid and solid structures, indicating the existence of a converging local structure. © 2014 Wiley Periodicals, Inc. PMID:25241855

Fu, Bing; Chen, Li; Wang, Feifei; Xie, Yiqun; Ye, Xiang

2014-12-01

75

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

76

Concentric Symmetry  

E-print Network

The quantification of symmetries in complex networks is typically done globally in terms of automorphisms. In this work we focus on local symmetries around nodes, which we call connectivity patterns. We develop two topological transformations that allow a concise characterization of the different types of symmetry appearing on networks and apply these concepts to six network models, namely the Erd\\H{o}s-R\\'enyi, Barab\\'asi-Albert, random geometric graph, Waxman, Voronoi and rewired Voronoi models. Real-world networks, namely the scientific areas of Wikipedia, the world-wide airport network and the street networks of Oldenburg and San Joaquin, are also analyzed in terms of the proposed symmetry measurements. Several interesting results, including the high symmetry exhibited by the Erd\\H{o}s-R\\'enyi model, are observed and discussed.

Silva, Filipi N; Peron, Thomas K DM; Rodrigues, Francisco A; Ye, Cheng; Wilson, Richard C; Hancock, Edwin; Costa, Luciano da F

2014-01-01

77

Evolution of icosahedral clusters during the rapid solidification of liquid TiAl alloy  

NASA Astrophysics Data System (ADS)

The evolution characteristics of icosahedral clusters during the rapid solidification of TiAl alloy under different cooling rates are investigated based on molecular dynamics simulations. The short-range order structural properties of liquid and amorphous TiAl alloy are analyzed by several structural characterization methods. It is found that the cooling rate plays a key role during the evolution of icosahedral clusters and has significant effect on the glass transition temperature. Simultaneously, the medium-range order structural evolutions are described in detail by quantitative method and visualization technology during the rapid solidification. The results reveal that the medium-range order icosahedral clusters have good structural stability and configural continuity during the rapid cooling process. Furthermore, the icosahedral structures have significant improvements with decreasing cooling rate. The structures block the crystal nucleation and improve the glass forming ability of supercooled liquid.

Xie, Zhuo-Cheng; Gao, Ting-Hong; Guo, Xiao-Tian; Qin, Xin-Mao; Xie, Quan

2014-05-01

78

Design and manufacture of an icosahedral virus model for educational use  

E-print Network

A model of an icosahedral virus was designed and manufactured. Much consideration was given to the design of different aspects of the part. though there were many uncertainties about some parameters that disallowed precise ...

Stach, Laurie A. (Laurie Anna)

2005-01-01

79

Nanoprecipitates of icosahedral phase in quasicrystal-strengthened Mg-Zn-Y alloys  

Microsoft Academic Search

Extensive microstructural studies have been performed with respect to the formation of the icosahedral quasicrystalline phase and its relationship to other phases in Mg95Zn4.2Y0.8 alloy. The icosahedral phase forms as an intergranular eutectic phase as well as precipitates in the matrix. The precipitates are nanosized (typically 50 nm) with a definite orientation relationship with the matrix, sharply faceted on twofold

Alok Singh; A. P. Tsai; M. Nakamura; M. Watanabe; A. Kato

2003-01-01

80

A face-sharing bi-icosahedral model for Al23(-).  

PubMed

A face-sharing bi-icosahedral motif is proposed as a candidate structure of the magic cluster, Al23(-), on the basis of DFT calculations. The structure can be viewed as a quasi-molecule made of two Al13 (D3d) superatoms with an open electronic configuration via constructive overlap of 1F and 2P superatomic orbitals. A face-sharing tri-icosahedral motif is also predicted for Al33(-). PMID:25199061

Koyasu, K; Tsukuda, T

2014-10-21

81

Experimental Observation and Confirmation of Icosahedral W@Au12 and Mo@Au12 Molecules  

SciTech Connect

The recently predicted W@Au12 cluster has been observed and probed experimentally using anion photoelectron spectroscopy. It is shown that this unique molecule and its Mo congener indeed possess an icosahedral structure and a large HOMO-LUMO gap. Relativistic density functional theory is used to calculate their geometries, energetics, and energy spectra. The simulated density-of-states spectra are in good agreement with the photoelectron spectra, confirming the icosahedral structure of these complexes.

Li, Xi; Boggavarapu, Kiran; Li, Jun; Zhai, Hua Jin; Wang, Lai-Sheng

2002-12-16

82

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

83

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

84

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

85

Mechanical properties of icosahedral boron carbide explained from first principles  

NASA Astrophysics Data System (ADS)

An exhaustive DFT study of the structural defects of icosahedral B4C and of their behavior under high pressure has been performed. Among the possible atomic structures, the lowest value of the formation energy has been found for the polar model B4C^P, which consists of one distorted icosahedron and of one CBC chain. This result, together with the inspection of the vibrational and NMR spectra, has proved that B4C^P is the proper structural model for B4C.[1,2] Consequently, B4C^P has been used as a matrix to isolate the defects. The native defects have been identified and shown to be energetically stable at high pressure. Most vacancy locations in B4C^P are found to be energetically unstable and only a boron vacancy in the CBC chain is stable. A cluster of this vacancy is shown to induce a dynamical instability of the icosahedra when the pressure is increased. The dynamical failure of shocked B4C [3] is attributed to the increase in the concentration of these unstable vacancies under plastic deformation. 1. R. Lazzari, N.Vast, J.M. Besson, S. Baroni and A. Dal Corso, Phys. Rev. Lett. 83 (1999) 3230. 2. F. Mauri, N. Vast and C.J. Pickard, Phys. Rev. Lett. 87 (2001) 085506. 3. T. Vogler, W. Reinhart and L. Chhabildas, J. Appl. Phys. 95 (2004) 4173.

Raucoules, Roman; Vast, Nathalie; Betranhandy, Emmanuel; Sjakste, Jelena

2011-03-01

86

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

PubMed Central

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

87

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

88

Design of Three-shell Icosahedral Matryoshka Clusters A@B12@A20 (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

89

Structural stability of boron clusters with octahedral and tetrahedral symmetries.  

PubMed

The structural stability of cagelike boron clusters with octahedral and tetrahedral symmetries has been investigated by means of first-principles calculations. Twenty-eight cluster models, ranging from B(10) to B(66), were systematically constructed using regular and semiregular polyhedra as prototypes. The binding energies per atom were, on the whole, slightly lower than those of icosahedral clusters B(80) and B(100), which are supposed to be the most stable in the icosahedral group. The larger clusters did not always have higher binding energies. Isothermal molecular dynamics simulations were performed to determine the deformation temperatures at which clusters began to break or change their structures. We found eight clusters that had nonzero deformation temperatures, indicating that they are in metastable states. The octahedral cluster B(18) had the highest deformation temperature among these, similar to that of icosahedral B(80) and B(100). The analysis of the electronic structure of B(18) showed that it attained this high stability owing to Jahn-Teller distortion. PMID:21675744

Hayami, Wataru; Otani, Shigeki

2011-07-28

90

Symmetry breaking and hole localization in multiple core electron ionization.  

PubMed

Motivated by recent opportunitites to study hollow molecules with multiple core holes offered by X-ray free electron lasers, we revisit the core-hole localization and symmetry breaking problem, now studying ionization of more than one core electron. It is shown, using a N2 molecule with one, two, three, and four core holes, for example, that in a multiconfigurational determination of the core ionization potentials employing a molecular point group with broken inversion symmetry, one particular configuration is sufficient to account for the symmetry breaking relaxation energy in an independent particle approximation in the case of one or three holes, whereas the choice of point group symmetry is unessential for two and four holes. The relaxation energy follows a quadratic dependence on the number of holes in both representations. PMID:23859627

Carravetta, V; Ågren, H

2013-08-01

91

Icosahedral quasicrystals of intermetallic compounds are icosahedral twins of cubic crystals of three kinds, consisting of large (about 5000 atoms) icosahedral complexes in either a cubic body-centered or a cubic face-centered arrangement or smaller (about 1350 atoms) icosahedral complexes in the ?-tungsten arrangement  

PubMed Central

The twofold-axis electron-diffraction photographs of icosahedral quasicrystals are of three kinds, reflecting three different structures of the cubic crystals that by icosahedral twinning form the quasicrystals. The first kind, represented by Al13Cu4Fe3, contains two very large icosahedral complexes, each of about 4680 atoms, in the body-centered arrangement, with six smaller icosahedral complexes (104 atoms each) in the principal interstices. The second kind, represented by Al5Mn, contains four of the very large complexes in the face-centered arrangement (cubic close packing), with four of the smaller clusters in the interstices. The third kind, represented by Al6CuLi3, contains eight icosahedral complexes, each of about 1350 atoms, in the ?-W arrangement. The supporting evidence for these cubic structures is discussed as well as other evidence showing that the simple quasicrystal theory, which states that quasicrystals do not involve any translational identity operations, has to be modified. Images PMID:16594078

Pauling, Linus

1989-01-01

92

The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases  

NASA Technical Reports Server (NTRS)

Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si(3), for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron X-ray and high flux neutron facilities.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.; Holland-Moritz, D.; Curreri, Peter A. (Technical Monitor)

2002-01-01

93

The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation of Ordered Phases  

NASA Technical Reports Server (NTRS)

Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si, for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

Curreri, Peter A. (Technical Monitor); Kelton, K. F.; Gangopadhyay, A.; Lee, G. W.; Hyers, R. W.; Rathz, R. J.; Rogers, J.; Schenk, T.; Simonet, V.; Holland-Moritz, D.

2003-01-01

94

The Connection Between Local Icosahedral Order in Metallic Liquids and the Nucleation Behavior of Ordered Phases  

NASA Technical Reports Server (NTRS)

Over fifty years ago, David Turnbull showed that the temperature of many metallic liquids could be decreased far below their equilibrium melting temperature before crystallization occurred. To explain those surprising results, Charles Frank hypothesized that the local structures of undercooled metallic liquids are different from those of crystal phases, containing a significant degree of icosahedral order that is incompatible with extended periodicity. Such structural differences must create a barrier to the formation crystal phases, explaining the observed undercooling behavior. If true, the nucleation from the liquid of phases with extended icosahedral order should be easier. Icosahedral order is often favored in small clusters, as observed recently in liquid-like clusters of pure Pb on the (111) surface of Si[3], for example. However, it has never been shown that an increasing preference for icosahedral phase formation can be directly linked with the development of icosahedral order in the undercooled liquid. Owing to the combination of very recent advances in levitation techniques and the availability of synchrotron x-ray and high flux neutron facilities, this is shown here.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.; Robinson, M. B.; Schenk, T.; Simonet, V.

2003-01-01

95

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

96

Structure of the Top a-t component of alfalfa mosaic virus. A non-icosahedral virion.  

PubMed

Neutron-scattering in combination with quasi-elastic light-scattering and electron microscopy was used to derive a model for the capsid structure of the Top a-t component of alfalfa mosaic virus (AMV-Ta-t). In the electron microscope, AMV-Ta-t appears as an irregular ellipsoidal particle with apparent dimensions 275 (+/- 31) A X 225 (+/- 22) A. Assuming that the particles are monodisperse, model calculations show that the neutron-scattering data are best explained by an oblate ellipsoidal shape for the virion with external dimensions 284 A X 284 A X 216 A. Based on this result, and in combination with the known composition of the virion, it is suggested that the capsid structure could be based on a deltahedron with 52 pointgroup symmetry and comprising 120 subunits. Such a model would imply a greater deviation from equivalent subunit interactions than normally necessary in icosahedral capsids. The neutron and photon correlation data, however, do not allow us to rule out the possibility that Top a-t is a slightly polydisperse preparation of irregular prolate shapes with mean dimensions 312 A X 232 A X 232 A. Both possibilities support the concept of alfalfa mosaic virus coat protein being capable of a wide range of intersubunit interactions, this flexibility resulting in considerable polymorphism in capsid structures. PMID:6655690

Cusack, S; Oostergetel, G T; Krijgsman, P C; Mellema, J E

1983-12-01

97

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

98

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

E-print Network

bursaria Chlorella virus-1 is an icosahedrally shaped, 1,900-Ã?-diameter virus that infects unicellular cryoelectron microscopy reconstruction Paramecium bursaria Chlorella virus-1 cell entry specialized vertex protein Paramecium bursaria Chlorella virus-1 (PBCV-1) belongs to the genus Chlorovirus

Baker, Timothy S.

99

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

100

Dressing symmetries  

NASA Astrophysics Data System (ADS)

We study the group of dressing transformations in soliton theories. We show that it is generated by the monodromy matrix. This provides a new proof of their Lie-Poisson property. We treat in detail the examples of the Toda field theories and the Heisenberg model. We show that the group of dressing transformations is the classical precursor of the various manifestations of quantum groups in these models, e.g. algebraic Bethe ansatz, non-local currents, or quantum group symmetries. Finally, we define field multiplets supporting a linear representation of the dressing group and we show that their exchange algebras are encoded in the classical double.

Babelon, Olivier; Bernard, Denis

1992-10-01

101

Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants  

NASA Astrophysics Data System (ADS)

In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra- and inter-icosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.

Takagiwa, Yoshiki; Kimura, Kaoru

2014-08-01

102

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

103

Relation between icosahedral short-range ordering and plastic deformation in Zr–Nb–Cu–Ni–Al bulk metallic glasses  

Microsoft Academic Search

The relation between icosahedral short-range ordering (ISRO) and plastic deformation was investigated in Zr70?xNbxCu13.5Ni8.5Al8 (at.%, x=0, 2, 4, 6, 7, 8, 10) bulk metallic glasses (BMG). The formation of icosahedral quasicrystal (I-phase) during the annealing process implies that ISRO widely exists in these materials. The degree of ISRO is thermodynamically evaluated to show that ISRO increases with increasing Nb content.

Z. W. Zhu; L. Gu; G. Q. Xie; W. Zhang; A. Inoue; H. F. Zhang; Z. Q. Hu

2011-01-01

104

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 0Point-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

105

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

106

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

107

Layer Resolved Structural Relaxation at the Surface of Magnetic FePt Icosahedral Nanoparticles  

NASA Astrophysics Data System (ADS)

The periodic shell structure and surface reconstruction of metallic FePt nanoparticles with icosahedral structure has been quantitatively studied by high-resolution transmission electron microscopy with focal series reconstruction with sub-angstrom resolution. The icosahedral FePt nanoparticles fabricated by the gas phase condensation technique in vacuum have been found to be surprisingly oxidation resistant and stable under electron beam irradiation. We find the lattice spacing of (111) planes in the surface region to be size dependent and to expand by as much as 9% with respect to the bulk value of Fe52Pt48. Controlled removal of the (111) surface layers in situ results in a similar outward relaxation of the new surface layer. This unusually large layerwise outward relaxation is discussed in terms of preferential Pt segregation to the surface forming a Pt enriched shell around a Fe-rich Fe/Pt core.

Wang, R. M.; Dmitrieva, O.; Farle, M.; Dumpich, G.; Ye, H. Q.; Poppa, H.; Kilaas, R.; Kisielowski, C.

2008-01-01

108

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, Mickael 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

109

Correlations between electric, magnetic, and galvanomagnetic quantities in stable icosahedral phases based on aluminum  

SciTech Connect

On the basis of the results of the experimental investigation of the correlations between the electric, magnetic, and galvanomagnetic properties, the nature of the electronic phenomena leading to the difference of icosahedral quasicrystals from typical metals and insulators (low conductivity and negative temperature coefficient of resistance, diamagnetism of the ground state and its decrease with increasing temperature, and existence of residual and thermally induced charge carriers) is discussed.

Prekul, A. F., E-mail: prekul@imp.uran.ru; Shchegolikhina, N. I. [Russian Academy of Sciences, Institute of Metal Physics, Ural Division (Russian Federation)

2007-11-15

110

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

111

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

2006-06-30

112

Symmetries in nuclei  

SciTech Connect

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

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

2011-03-21

113

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

PubMed

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. In our implementation, we introduced a recursive method for deriving higher order ISAFs from three lower order seed functions. We demonstrate improvements of our new method in both the noise suppression and the effective resolution in 3D reconstruction over the commonly used Fourier-Bessel synthesis method introduced by Crowther et al. three decades ago. Our 3D reconstruction method can be extended to macromolecular complexes with other symmetry types and is thus likely to impact future high-resolution cryoEM single-particle reconstruction efforts in general. PMID:17977017

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

2008-01-01

114

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

115

High Pressure X-ray Diffraction Study on Icosahedral Boron Arsenide (B12As2)  

SciTech Connect

The high pressure properties of icosahedral boron arsenide (B12As2) were studied by in situ X-ray diffraction measurements at pressures up to 25.5 GPa at room temperature. B12As2 retains its rhombohedral structure; no phase transition was observed in the pressure range. The bulk modulus was determined to be 216 GPa with the pressure derivative 2.2. Anisotropy was observed in the compressibility of B12As2-c-axis was 16.2% more compressible than a-axis. The boron icosahedron plays a dominant role in the compressibility of boron-rich compounds.

J Wu; H Zhu; D Hou; C Ji; C Whiteley; J Edgar; Y Ma

2011-12-31

116

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

NSDL National Science Digital Library

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

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

2006-05-17

117

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

SciTech Connect

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

Kycia, S.

1996-04-23

118

Symmetries in Physics  

NASA Astrophysics Data System (ADS)

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

Brading, Katherine; Castellani, Elena

2010-01-01

119

Structural, electronic and energetic properties of giant icosahedral fullerenes up to C6000: insights from an ab initio hybrid DFT study.  

PubMed

The properties of the (n,n) icosahedral family of carbon fullerenes up to n = 10 (6000 atoms) have been investigated through ab initio quantum-mechanical simulation by using a Gaussian type basis set of double zeta quality with polarization functions (84,000 atomic orbitals for the largest case), the hybrid B3LYP functional and the CRYSTAL14 code featuring generalization of symmetry treatment. The geometry of giant fullerenes shows hybrid features, between a polyhedron and a sphere; as n increases, it approaches the former. Hexagon rings at face centres take a planar, graphene-like configuration; the 12 pentagon rings at vertices impose, however, a severe structural constraint to which hexagon rings at the edges must adapt smoothly, adopting a bent (rather than sharp) transversal profile and an inward longitudinal curvature. The HOMO and LUMO electronic levels, as well as the band gap, are well described using power laws. The gap is predicted to become zero for n ? 34 (69,360 atoms). The atomic excess energy with respect to the ideal graphene sheet goes to zero following the log(Nat)/Nat law, which is well described through the continuum elastic theory applied to graphene; the limits for the adopted model are briefly outlined. Compared to larger fullerenes of the series, C60 shows unique features with respect to all the considered properties; C240 presents minor structural and energetic peculiarities, too. PMID:24879509

Noël, Yves; De La Pierre, Marco; Zicovich-Wilson, Claudio M; Orlando, Roberto; Dovesi, Roberto

2014-07-14

120

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

121

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

122

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

123

Competition between fcc and icosahedral short-range orders in pure and samarium-doped liquid aluminum from first principles  

NASA Astrophysics Data System (ADS)

Development of structural order in liquid aluminum upon rapid cooling is studied by ab initio molecular-dynamics simulations and the recently developed atomistic cluster alignment method. We show that there is a strong competition between icosahedral and fcc short-range orders (SROs) in the system. Although the liquid eventually crystallizes into fcc structure when T ? 800 K, the icosahedral short-range order (ISRO) is found to be much stronger than the fcc SRO in the liquid. Doping of Sm in Al liquid can hinder the fcc crystallization and enhance the ISRO.

Fang, X. W.; Wang, C. Z.; Yao, Y. X.; Ding, Z. J.; Ho, K. M.

2011-06-01

124

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

125

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

126

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

127

Inorg. Chem. 1995,34, 2095-2100 2095 Facile Electrophilic Iodination of Icosahedral Carboranes. Synthesis of Carborane  

E-print Network

Inorg. Chem. 1995,34, 2095-2100 2095 Facile Electrophilic Iodination of Icosahedral Carboranes icosahedralcloso-1,2-C2BIOHI2 and closo-1,7-C2BIOHI2 using 2 molar equiv of iodine monochloride in the presence electrophilic catalysts in organic reactions. In our ongoing "~arborod"~and "carbo- ra~ycle"~research, rigid rod

Zheng, Zhiping

128

Geometrical symmetries in atomic nuclei: From theory predictions to experimental verifications  

NASA Astrophysics Data System (ADS)

In the lectures delivered at the 2012 Predeal School an overview has been presented of the contemporary theory of the nuclear geometrical (shape) symmetries. The formalism combines two most powerful theory tools applicable in the context: The group- and group-representation theory together with the modern realistic mean-field theory. We suggest that all point-groups of symmetry of the mean-field Hamiltonian, sufficiently rich in symmetry elements (as discussed in the text) may lead to the magic numbers that characterise such a group in analogy with the spherical magic gaps characterising nuclear sphericity. We discuss in simple terms the mathematical and physical arguments for the presence of such symmetries in nuclei. In our opinion: It is not so much the question of Whether? - but rather: Where in the Nuclear Chart several of the point group-symmetries will be seen? We focus our presentation on the tetrahedral symmetry with the magic numbers calculated to be 32, 40, 56, 64, 70, 90 and 136, and discuss qualitatively the problem of the formulation of the experimental criteria which would allow for the final discovery of the tetrahedral symmetry in subatomic physics.

Dudek, J.; Gó?d?, A.; Molique, H.; Curien, D.

2013-02-01

129

Symmetries of Toric Duality  

Microsoft Academic Search

This paper serves to elucidate the nature of toric duality dubbed in hep-th\\/0003085 in the construction for world volume theories of D-branes probing arbitrary toric singularities. This duality will be seen to be due to certain permutation symmetries of multiplicities in the gauged linear sigma model fields. To this symmetry we shall refer as `multiplicity symmetry'. We present beautiful combinatorial

Bo Feng; Sebastián Franco; Amihay Hanany; Yang-Hui He

2002-01-01

130

Is symmetry informative?  

PubMed

Is symmetry informative? The answer is both yes and no. We examine what information and symmetry are and how they are related. Our approach is primarily mathematical, not because mathematics provides the final word, but because it provides an insightful and relatively precise starting point. Information theory treats transformations that messages undergo from source to destination. Symmetries are information that leave some property of interest unchanged. In this respect the studies of information and symmetry can both be regarded as a Quest for the identity transformation. PMID:9224554

Gray, J E; Vogt, A

1997-01-01

131

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

132

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; Coute, Yohann; Rivkina, Elizaveta; Abergel, Chantal; Claverie, Jean-Michel

2014-01-01

133

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

134

Single particle analysis integrated with microscopy: a high-throughput approach for reconstructing icosahedral particles.  

PubMed

In cryo-electron microscopy and single particle analysis, data acquisition and image processing are generally carried out in sequential steps and computation of a three-dimensional reconstruction only begins once all the micrographs have been acquired. We are developing an integrated system for processing images of icosahedral particles during microscopy to provide reconstructed density maps in real-time at the highest possible resolution. The system is designed as a combination of pipelines to run in parallel on a computer cluster and analyzes micrographs as they are acquired, handling automatically all the processing steps from defocus estimation and particle picking to origin/orientation determination. An ab initio model is determined independently from the first micrographs collected, and new models are generated as more particles become available. As a proof of concept, we simulated data acquisition sessions using three sets of micrographs of good to excellent quality that were previously recorded from different icosahedral viruses. Results show that the processing of single micrographs can keep pace with an acquisition rate of about two images per minute. The reconstructed density map improves steadily during the image acquisition phase and its quality at the end of data collection is only moderately inferior to that obtained by expert users who processed semi-automatically all the micrographs after the acquisition. The current prototype demonstrates the advantages of integrating three-dimensional image processing with microscopy, which include an ability to monitor acquisition in terms of the final structure and to predict how much data and microscope resources are needed to achieve a desired resolution. PMID:24613762

Yan, Xiaodong; Cardone, Giovanni; Zhang, Xing; Zhou, Z Hong; Baker, Timothy S

2014-04-01

135

Party Hat Symmetry  

NSDL National Science Digital Library

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

Houston, Children'S M.

2011-01-01

136

Emergence of symmetries  

E-print Network

The mechanism of symmetry formation is discussed in the framework of multidimensional gravity. It is shown that this process is strictly connected to the entropy decrease of compact space. The existence of low energy symmetries is not postulated from the beginning. They could be absent during the inflationary stage under certain conditions discussed in the paper.

A. A. Kirillov; A. A. Korotkevich; S. G. Rubin

2012-05-05

137

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

2009-03-17

138

Evidence for nuclear shell symmetries  

NASA Astrophysics Data System (ADS)

Empirical evidence is presented for SO(8) and Sp(6) fermion dynamical symmetries in nuclei. As predicted by the fermion dynamical symmetry model, actinide nuclei possess Sp(6) symmetry; nuclei with 36 symmetry, and for rare-earth nuclei and neutrons possess SO(8) and Sp(6) symmetries, respectively.

Xiao-Ling, Han; Guidry, Mike W.; da, Hsuan, Feng; Ke-Xia, Wang; Cheng-Li, Wu

1987-07-01

139

Twisted symmetries and integrable systems  

E-print Network

Symmetry properties are at the basis of integrability. In recent years, it appeared that so called "twisted symmetries" are as effective as standard symmetries in many respects (integrating ODEs, finding special solutions to PDEs). Here we discuss how twisted symmetries can be used to detect integrability of Lagrangian systems which are not integrable via standard symmetries.

G. Cicogna; G. Gaeta

2010-02-07

140

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

141

The superstable 25 kDa monolayer protected silver nanoparticle: measurements and interpretation as an icosahedral Ag152(SCH2CH2Ph)60 cluster.  

PubMed

A cluster obtained in high yield from the reduction of a silver-thiolate precursor, Ag-SCH(2)CH(2)Ph, exhibited a single sharp peak near 25 kDa in the matrix-assisted laser desorption mass spectrum (MALDI MS) and a well-defined metal core of ~2 nm measured with transmission electron microscopy (TEM). The cluster yields a single fraction in high-performance liquid chromatography (HPLC). Increased laser fluence fragments the cluster until a new peak near 19 kDa predominates, suggesting that the parent cluster-Ag(152)(SCH(2)CH(2)Ph)(60)-evolves into a stable inorganic core-Ag(152)S(60). Exploiting combined insights from investigations of clusters and surface science, a core-shell structure model was developed, with a 92-atom silver core having icosahedral-dodecahedral symmetry and an encapsulating protective shell containing 60 Ag atoms and 60 thiolates arranged in a network of six-membered rings resembling the geometry found in self-assembled monolayers on Ag(111). The structure is in agreement with small-angle X-ray scattering (SAXS) data. The protective layer encapsulating this silver cluster may be the smallest known three-dimensional self-assembled monolayer. First-principles electronic structure calculations show, for the geometry-optimized structure, the development of a ~0.4 eV energy gap between the highest-occupied and lowest-unoccupied states, originating from a superatom 90-electron shell-closure and conferring stability to the cluster. The optical absorption spectrum of the cluster resembles that of plasmonic silver nanoparticles with a broad single feature peaking at 460 nm, but the luminescence spectrum shows two maxima with one attributed to the ligated shell and the other to the core. PMID:23094944

Chakraborty, Indranath; Govindarajan, Anuradha; Erusappan, Jayanthi; Ghosh, Atanu; Pradeep, T; Yoon, Bokwon; Whetten, Robert L; Landman, Uzi

2012-11-14

142

Three-dimensional chaotic flows with discrete symmetries.  

PubMed

There are a number of well-known three-dimensional flows with quadratic nonlinearities, which demonstrate a chaotic behavior. The most popular among them are Lorenz and Rössler systems. Using an exhaustive computer search, J. Sprott found 19 examples of chaotic flows with either five terms and two quadratic nonlinearities or six terms and one nonlinearity [Phys. Rev. E 50, R647 (1994)]. In contrast to this approach, we use symmetry-related considerations to construct types of chaotic flows with an arbitrary dimension. The discussion is based on our previous work devoted to nonlinear dynamics of the physical systems with discrete symmetries [see Physica D 117, 43 (1998), etc.]. Here, we present all possible chaotic flows with quadratic nonlinearities which are invariant under the action of 32 point groups of crystallographic symmetry. These systems demonstrate a typical chaotic behavior as well as general dynamical properties of nonlinear systems with discrete symmetries. In particular, we found a dynamical system with the point symmetry group D2 which seems to be more simple and more elegant than those by Lorenz and Rössler. PMID:15089387

Chechin, G M; Ryabov, D S

2004-03-01

143

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

PubMed Central

Studies on viral capsid architectures and coat protein folds have revealed the evolutionary lineages of viruses branching to all three domains of life. A widespread group of icosahedral tailless viruses, the PRD1-adenovirus lineage, was the first to be established. A double ?-barrel fold for a single major capsid protein is characteristic of these viruses. Similar viruses carrying genes coding for two major capsid proteins with a more complex structure, such as Thermus phage P23-77 and haloarchaeal virus SH1, have been isolated. Here, we studied the host range, life cycle, biochemical composition, and genomic sequence of a new isolate, Haloarcula hispanica icosahedral virus 2 (HHIV-2), which resembles SH1 despite being isolated from a different location. Comparative analysis of these viruses revealed that their overall architectures are very similar except that the genes for the receptor recognition vertex complexes are unrelated even though these viruses infect the same hosts. PMID:22357274

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

2012-01-01

144

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

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

Defect-induced Symmetry Distortions in Doped Cubic Boron Nitride  

NASA Astrophysics Data System (ADS)

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

Patton, David C.; Harrison, Joseph G.

1996-03-01

148

Point symmetry in x-ray shadow imaging systems  

SciTech Connect

General geometrical features have been examined to identify point-group symmetries in x-ray imaging systems. In a stereospecific system, the group is the b/w antisymmetry group 2/m'. In a computerized tomography system, the symmetry is described by the limiting Curie group /infinity//m/center dot/m, while for a tomosynthesis system (transaxial tomography), it is /infinity//m. The operations in these groups have been examined in the production of shadow images involving distributed attenuation coefficients, particularly for stereospecific images recorded with an MIR-3 x-ray microscope. Curie's principle is used to show that reconstructed paired images for two intersecting objects can be considered as the equivalent of stereoscopic pairs for computer-aided tomography, which is not so for transaxial tomography.

Aristov, V.V.; Shabel'nikov, L.G.

1988-04-01

149

Symmetry and Degeneracy  

NSDL National Science Digital Library

This online text is an exhaustive description of the role of symmetry in the degeneracy of a single-particle bound state system in quantum mechanics. Both non-relativistic and relativistic examples are studied.

Mcintosh, Harold

2006-07-22

150

Symmetries in Physics  

NASA Astrophysics Data System (ADS)

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

Castaños, Octavio

2010-09-01

151

Second order symmetry operators  

E-print Network

Using systematic calculations in spinor language, we obtain simple descriptions of the second order symmetry operators for the conformal wave equation, the Dirac-Weyl equation and the Maxwell equation on a curved four dimensional Lorentzian manifold. The conditions for existence of symmetry operators for the different equations are seen to be related. Computer algebra tools have been developed and used to systematically reduce the equations to a form which allows geometrical interpretation.

Lars Andersson; Thomas Bäckdahl; Pieter Blue

2014-02-25

152

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

153

Finite group symmetry breaking  

E-print Network

Finite group symmetry is commonplace in Physics, in particular through crystallographic groups occurring in condensed matter physics -- but also through the inversions (C,P,T and their combinations) occurring in high energy physics and field theory. The breaking of finite groups symmetry has thus been thoroughly studied, and general approaches exist to investigate it. In Landau theory, the state of a system is described by a finite dimensional variable (the {\\it order parameter}), and physical states correspond to minima of a potential, invariant under a group. In this article we describe the basics of symmetry breaking analysis for systems described by a symmetric polynomial; in particular we discuss generic symmetry breakings, i.e. those determined by the symmetry properties themselves and independent on the details of the polynomial describing a concrete system. We also discuss how the plethora of invariant polynomials can be to some extent reduced by means of changes of coordinates, i.e. how one can reduce to consider certain types of polynomials with no loss of generality. Finally, we will give some indications on extension of this theory, i.e. on how one deals with symmetry breakings for more general groups and/or more general physical systems.

G. Gaeta

2005-10-02

154

Symmetry-protected Majorana fermions in topological crystalline superconductors: theory and application to Sr2RuO4.  

PubMed

Crystal point group symmetry is shown to protect Majorana fermions (MFs) in spinfull superconductors (SCs). We elucidate the condition necessary to obtain MFs protected by the point group symmetry. We argue that superconductivity in Sr2RuO4 hosts a topological phase transition to a topological crystalline SC, which accompanies a d-vector rotation under a magnetic field along the c axis. Taking all three bands and spin-orbit interactions into account, symmetry-protected MFs in the topological crystalline SC are identified. Detection of such MFs provides evidence of the d-vector rotation in Sr2RuO4 expected from Knight shift measurements but not yet verified. PMID:24010466

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

2013-08-23

155

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

156

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 deg. 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 {mu}V/K and 136 {mu}V/K for samples grown at 1350 deg. C with AsH{sub 3}/B{sub 2}H{sub 6} flow ratio equals to 1:1 and 3:5, respectively.

Gong, Y.; Kuball, M. [H.H. Wills Physics Laboratory, Centre for Device Thermography and Reliability (CDTR), University of Bristol, Bristol BS8 1TL (United Kingdom); Zhang, Y.; Dudley, M. [Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York 11794-2275 (United States); Zhang, Y.; Edgar, J. H. [Department of Chemical Engineering, Kansas State University, Manhattan, Kansas 66506 (United States); Heard, P. J. [Interface Analysis Centre, University of Bristol, Bristol BS2 8BS (United Kingdom)

2010-10-15

157

Comparative studies of T = 3 and T = 4 icosahedral RNA insect viruses  

PubMed Central

Summary Crystallographic and molecular biological studies of T = 3 nodaviruses (180 identical subunits in the particle) and T = 4 tetraviruses (240 identical subunits in the particle) have revealed similarity in both the architecture of the particles and the strategy for maturation. The comparative studies provide a novel opportunity to examine an apparent evolution of particle size, from smaller (T = 3) to larger (T = 4), with both particles based on similar subunits. The BBV and FHV nodavirus structures are refined at 2.8 Å and 3 Å respectively, while the N?V structure is at 6 Å resolution. Nevertheless, the detailed comparisons of the noda and tetravirus X-ray electron density maps show that the same type of switching in subunit twofold contacts is used in the T = 3 and T = 4 capsids, although differences must exist between quasi and icosahedral threefold contacts in the T = 4 particle that have not yet been detected. The analyses of primary and tertiary structures of noda and tetraviruses show that N?V subunits undergo a post assembly cleavage like that observed in nodaviruses and that the cleaved 76 C-terminal residues remain associated with the particle. PMID:8032278

Johnson, J. E.; Munshi, S.; Liljas, L.; Agrawal, D.; Olson, N. H.; Reddy, V.; Fisher, A.; McKinney, B.; Schmidt, T.; Baker, T. S.

2014-01-01

158

The Gardner method for symmetries  

NASA Astrophysics Data System (ADS)

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

Rasin, Alexander G.; Schiff, Jeremy

2013-04-01

159

Icosahedral quasicrystals as twins of cubic crystals containing large icosahedral clusters of atoms: The 1012-atom primitive cubic structure of Al6CuLi3, the C-phase Al37Cu3Li21Mg3, and GaMg2Zn3  

PubMed Central

Single-grain precession x-ray diffraction photographs of Al6CuLi3 have been successfully indexed on the basis of icosahedral twinning of cubic crystals with a 1012-atom primitive cubic unit with edge 25.70 Å, giving support to the proposal that the so-called icosahedral quasicrystals are twins of crystals containing eight large icosahedral clusters in the ?-W arrangement. In this compound two of the clusters consist of 104 atoms and six consist of 136 atoms, with 24 atoms shared. The same structure is assigned to the C-phase, Al37Cu3Li21Mg3, and to GaMg2Zn3. A theory of icosahedral quasicrystals and amorphous metals is described. PMID:16593929

Pauling, Linus

1988-01-01

160

Symmetry of quasicrystals  

NASA Astrophysics Data System (ADS)

The definition of an aperiodic crystal (quasicrystal) as a solid that is characterized by the forbidden symmetry suggests the existence of an unsolved problem, because, in a mutually exclusive manner, it appeals to the fundamental theorem of classical crystallography. Using the Penrose tiling as an example, we have investigated the symmetry properties of aperiodic tilings for the purpose to establish the allowed symmetry groups of quasicrystals. The filling of the Euclidean space according to an aperiodic law is considered as the action of an infinite number of group elements on a fundamental domain in the non-Euclidean space. It is concluded that all locally equivalent tilings have a common "parent" structure and, consequently, the same symmetry group. An idealized object, namely, an infinitely refined tiling, is introduced. It is shown that the symmetry operations of this object are operations of the similarity (rotational homothety). A positive answer is given to the question about a possible composition of operations of the similarity with different singular points. It is demonstrated that the transformations of orientation-preserving aperiodic crystals are isomorphic to a discrete subgroup of the Möbius group PSL(2, ?); i.e., they can be realized as discrete subgroups of the full group of motions in the Lobachevsky space. The problem of classification of the allowed types of aperiodic tilings is reduced to the procedure of enumeration of the aforementioned discrete subgroups.

Madison, A. E.

2013-04-01

161

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

PubMed Central

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

Pauling, Linus

1988-01-01

162

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

163

Symmetry constraint for foreground extraction.  

PubMed

Symmetry as an intrinsic shape property is often observed in natural objects. In this paper, we discuss how explicitly taking into account the symmetry constraint can enhance the quality of foreground object extraction. In our method, a symmetry foreground map is used to represent the symmetry structure of the image, which includes the symmetry matching magnitude and the foreground location prior. Then, the symmetry constraint model is built by introducing this symmetry structure into the graph-based segmentation function. Finally, the segmentation result is obtained via graph cuts. Our method encourages objects with symmetric parts to be consistently extracted. Moreover, our symmetry constraint model is applicable to weak symmetric objects under the part-based framework. Quantitative and qualitative experimental results on benchmark datasets demonstrate the advantages of our approach in extracting the foreground. Our method also shows improved results in segmenting objects with weak, complex symmetry properties. PMID:23797312

Fu, Huazhu; Cao, Xiaochun; Tu, Zhuowen; Lin, Dongdai

2014-05-01

164

Symmetry and Snell's law  

Microsoft Academic Search

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

David R. Bergman

2005-01-01

165

Cosmology and spacetime symmetries  

E-print Network

Cosmological models often contain scalar fields, which can acquire global nonzero expectation values that change with the comoving time. Among the possible consequences of these scalar-field backgrounds, an accelerated cosmological expansion, varying couplings, and spacetime-symmetry violations have recently received considerable attention. This talk studies the interplay of these three key signatures of cosmologically varying scalars within a supergravity framework.

Ralf Lehnert

2005-08-31

166

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

167

DIPLOMA THESIS SYMMETRIES AND  

E-print Network

found by Lie group analysis a conservation law can be found. #12;The mass of mathematical truthDIPLOMA THESIS SYMMETRIES AND CONSERVATION LAWS OBTAINED BY LIE GROUP ANALYSIS FOR CERTAIN PHYSICAL made in terms of differential equations. Conservation laws can be found for any system of linear or non

168

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.

Houston, Children'S M.

2014-09-19

169

Active fluctuation symmetries  

NASA Astrophysics Data System (ADS)

In contrast with the understanding of fluctuation symmetries for entropy production, similar ideas applied to the time-symmetric fluctuation sector have been less explored. Here we give detailed derivations of time-symmetric fluctuation symmetries in boundary-driven particle systems such as the open Kawasaki lattice gas and the zero-range model. As a measure of time-symmetric dynamical activity over time T we count the difference (N? - Nr)/T between the number of particle jumps in or out at the left edge and those at the right edge of the system. We show that this quantity satisfies a fluctuation symmetry from which we derive a new Green-Kubo-type relation. It will follow then that the system is more active at the edge connected to the particle reservoir with the largest chemical potential. We also apply these exact relations derived for stochastic particle models to a deterministic case, the spinning Lorentz gas, where the symmetry relation for the activity is checked numerically.

Maes, Christian; Salazar, Alberto

2014-01-01

170

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

SciTech Connect

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

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

2012-04-26

171

Dislocation mechanism of high-temperature plastic deformation of Al–Cu–Fe and Al–Pd–Mn icosahedral quasicrystals  

Microsoft Academic Search

Microstructures in hot-impacted Al62.5Cu25Fe12.5 and Al70.4Pd21.2Mn8.4 icosahedral quasicrystals (IQCs) were studied by transmission electron microscopy (TEM). Densely distributed dislocations and stacking fault (SF) type contrast were observed for the first time in Al–Cu–Fe IQC. This result confirms that dislocation motion is an important deformation mechanism for Al–Cu–Fe IQC. Moving dislocations in quasicrystalline materials leave phason-type SFs behind. In situ TEM

Renhui Wang; Wenge Yang; Jianian Gui; Knut Urban

2000-01-01

172

Abelian family symmetries and Leptogenesis  

E-print Network

We study the impact of a set of horizontal symmetries on the requirements for producing the baryon asymmetry of the universe via leptogenesis. We find that Abelian horizontal symmetries lead to a simple description of the parameters describing leptogenesis in terms of the small expansion parameter that arises from spontaneous symmetry breaking. If the family symmetry is made discrete, then an enhancement in the amount of leptogenesis can result.

M. S. Berger

1999-06-24

173

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

174

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

175

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

176

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

2008-11-10

177

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

178

Strong Electroweak Symmetry Breaking  

E-print Network

Models of spontaneous breaking of electroweak symmetry by a strong interaction do not have fine tuning/hierarchy problem. They are conceptually elegant and use the only mechanism of spontaneous breaking of a gauge symmetry that is known to occur in nature. The simplest model, minimal technicolor with extended technicolor interactions, is appealing because one can calculate by scaling up from QCD. But it is ruled out on many counts: inappropriately low quark and lepton masses (or excessive FCNC), bad electroweak data fits, light scalar and vector states, etc. However, nature may not choose the minimal model and then we are stuck: except possibly through lattice simulations, we are unable to compute and test the models. In the LHC era it therefore makes sense to abandon specific models (of strong EW breaking) and concentrate on generic features that may indicate discovery. The Technicolor Straw Man is not a model but a parametrized search strategy inspired by a remarkable generic feature of walking technicolor,...

Grinstein, Benjamin

2011-01-01

179

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

180

Adding the Third Dimension to Virus Life Cycles: Three-Dimensional Reconstruction of Icosahedral Viruses from Cryo-Electron Micrographs  

PubMed Central

Viruses are cellular parasites. The linkage between viral and host functions makes the study of a viral life cycle an important key to cellular functions. A deeper understanding of many aspects of viral life cycles has emerged from coordinated molecular and structural studies carried out with a wide range of viral pathogens. Structural studies of viruses by means of cryo-electron microscopy and three-dimensional image reconstruction methods have grown explosively in the last decade. Here we review the use of cryo-electron microscopy for the determination of the structures of a number of icosahedral viruses. These studies span more than 20 virus families. Representative examples illustrate the use of moderate- to low-resolution (7- to 35-?) structural analyses to illuminate functional aspects of viral life cycles including host recognition, viral attachment, entry, genome release, viral transcription, translation, proassembly, maturation, release, and transmission, as well as mechanisms of host defense. The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical. PMID:10585969

Baker, T. S.; Olson, N. H.; Fuller, S. D.

1999-01-01

181

Nuclear Symmetries and Anomalies  

Microsoft Academic Search

First in a single-j-shell calculation (j = f7\\/2) we discuss various symmetries, e.g., two to one in 44Ti vs. 43Ti. We note that the wave function amplitudes for T(higher) states are coefficients of fractional parentage, and that orthogonality of T(higher) and T(lower) states leads to useful results. Then we consider what happens if T = 0 two-body matrix elements are

Larry Zamick; Alberto Escuderos

2007-01-01

182

Symmetry issue in Galileons  

E-print Network

The symmetry issue for Galileons has been studied. In particular we address scaling (conformal) and Noether symmetrized Galileons. We have been proven a series of theorems about the form of Noether conserved charge (current) for irregular (not quadratic) dynamical systems. Special attentions have been made on Galileons. We have been proven that for Galileons always is possible to find a way to "symmetrized" Galileo's field .

Davood Momeni; Ratbay Myrzakulov

2014-10-04

183

Symmetry and Condensed Matter Physics  

NASA Astrophysics Data System (ADS)

Preface; 1. Symmetry and physics; 2. Symmetry and group theory; 3. Group representations: concepts; 4. Group representations: formalism and methodology; 5. Dixon's method for computing group characters; 6. Group action and symmetry projection operators; 7. Construction of the irreducible representations; 8. Product groups and product representations; 9. Induced representations; 10. Crystallographic symmetry and space-groups; 11. Space groups: Irreps; 12. Time-reversal symmetry: color groups and the Onsager relations; 13. Tensors and tensor fields; 14. Electronic properties of solids; 15. Dynamical properties of molecules, solids and surfaces; 16. Experimental measurements and selection rules; 17. Landau's theory of phase transitions; 18. Incommensurate systems and quasi-crystals; References; Bibliography; Index.

El-Batanouny, M.; Wooten, F.

2008-03-01

184

Symmetries in Physics: Philosophical Reflections  

E-print Network

This is the introductive paper to the volume "Symmetries in Physics: Philosophical Reflections", Cambridge University Press, 2003. We begin with a brief description of the historical roots and emergence of the concept of symmetry that is at work in modern physics. Then, in section 2, we mention the different varieties of symmetry that fall under this general umbrella, outlining the ways in which they were introduced into physics. We also distinguish between two different uses of symmetry: symmetry principles versus symmetry arguments. In section 3 we make some remarks of a general nature concerning the status and significance of symmetries in physics. Finally, in section 4, we outline the structure of the book and the contents of each part.

Katherine Brading; Elena Castellani

2003-01-19

185

Quantized response and topology of magnetic insulators with inversion symmetry  

NASA Astrophysics Data System (ADS)

We study three-dimensional insulators with inversion symmetry in which other point group symmetries, such as time reversal, are generically absent. We find that certain information about such materials’ behavior is determined by just the eigenvalues under inversion symmetry of occupied states at time reversal invariant momenta (TRIM parities). In particular, if the total number of -1 eigenvalues at all TRIMs is odd then the material cannot be an insulator. A likely possibility is that it is then a “Weyl” semimetal. Additionally if the material is an insulator and has vanishing Hall conductivity, then a magnetoelectric response, parameterized by ?, can be defined, and is quantized to ?=0,?. The value is ? if the total number of TRIM parities equal to -1 is twice an odd number. This generalizes the rule of Fu and Kane that applies to materials in which time reversal is unbroken. This result may be useful in the search for magnetic insulators with large ?. These two results are obtained as part of a classification of the band topology of inversion-symmetric insulators. Such band structures can be classified by two sets of numbers: the TRIM parities and three Chern numbers. The TRIM parities have the physical implications just described, and additionally they constrain the values of the Chern numbers modulo 2. An alternate geometrical derivation of our results is obtained by using the entanglement spectrum of the ground-state wave function.

Turner, Ari M.; Zhang, Yi; Mong, Roger S. K.; Vishwanath, Ashvin

2012-04-01

186

Metal Core Bonding Motifs of Monodisperse Icosahedral Au13 and Larger Au Monolayer-Protected Clusters As Revealed by X-ray Absorption Spectroscopy and  

E-print Network

advanced methods of electron microscopy and X-ray absorption spectroscopy. The number of gold atoms structure (EXAFS) spectra suggest that the Au metal cores of each of these complexes adopt an icosahedral extended to larger thiolate-protected gold clusters showing a broader distribution in nanoparticle core

Frenkel, Anatoly

187

Growth of Ag icosahedral nanocrystals on a SrTiO3,,001... support Fabien Silly and Martin R. Castella  

E-print Network

the structure and morphology of self-assembled silver nanocrystals supported on a SrTiO3 001 - 2 1 substrateGrowth of Ag icosahedral nanocrystals on a SrTiO3,,001... support Fabien Silly and Martin R nanocrystals grown on single- crystal SrTiO3 001 . The STM images show that Ag nano- crystals adopt five

Castell, Martin

188

Symmetry lowering of LiNbO3\\/LiTaO3 superlattice thin films studied by SHG  

Microsoft Academic Search

LiNbO3(LN)\\/LiTaO3(LT) superlattice thin films (SL) with several LT\\/(LN?+?LT) ratios and LN mono-layered films with several thicknesses are fabricated by the pulsed laser deposition (PLD) method. Structural analyses by XRD reveals that these films have a structure similar to those of LN and LT bulk crystals. The reduction of the point group symmetry from rhombohedral 3?m to monoclinic m is observed

T. Kobata; G. Tsukahara; Y. Uesu

2011-01-01

189

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

190

Symmetry, shape, and order  

E-print Network

Packing problems have been of great interest in many diverse contexts for many centuries. The optimal packing of identical objects has been often invoked to understand the nature of low temperature phases of matter. In celebrated work, Kepler conjectured that the densest packing of spheres is realized by stacking variants of the face-centered cubic lattice and has a packing fraction of $\\pi/(3\\sqrt{2}) \\sim 0.7405$. Much more recently, an unusually high density packing of approximately 0.770732 was achieved for congruent ellipsoids. Such studies are relevant for understanding the structure of crystals, glasses, the storage and jamming of granular materials, ceramics, and the assembly of viral capsid structures. Here we carry out analytical studies of the stacking of close-packed planar layers of systems made up of truncated cones possessing uniaxial symmetry. We present examples of high density packing whose order is characterized by a {\\em broken symmetry} arising from the shape of the constituent objects. We find a biaxial arrangement of solid cones with a packing fraction of $\\pi/4$. For truncated cones, there are two distinct regimes, characterized by different packing arrangements, depending on the ratio $c$ of the base radii of the truncated cones with a transition at $c^*=\\sqrt{2}-1$.

Antonio Trovato; Trinh X. Hoang; Jayanth R. Banavar; Amos Maritan

2007-12-17

191

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

192

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

193

Strong Electroweak Symmetry Breaking  

E-print Network

Models of spontaneous breaking of electroweak symmetry by a strong interaction do not have fine tuning/hierarchy problem. They are conceptually elegant and use the only mechanism of spontaneous breaking of a gauge symmetry that is known to occur in nature. The simplest model, minimal technicolor with extended technicolor interactions, is appealing because one can calculate by scaling up from QCD. But it is ruled out on many counts: inappropriately low quark and lepton masses (or excessive FCNC), bad electroweak data fits, light scalar and vector states, etc. However, nature may not choose the minimal model and then we are stuck: except possibly through lattice simulations, we are unable to compute and test the models. In the LHC era it therefore makes sense to abandon specific models (of strong EW breaking) and concentrate on generic features that may indicate discovery. The Technicolor Straw Man is not a model but a parametrized search strategy inspired by a remarkable generic feature of walking technicolor, that technivector mesons are light, narrow and decay readily into electroweak vector mesons and photons. While walking technicolor is popular among practitioners, alternatives exist and the Straw Man may not lead to their discovery.

Benjamin Grinstein

2011-02-19

194

Squash operator and symmetry  

SciTech Connect

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

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

2010-01-15

195

Pairing symmetry in cuprate superconductors  

Microsoft Academic Search

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

C. C. Tsuei; J. R. Kirtley

2000-01-01

196

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

NASA Astrophysics Data System (ADS)

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 C60 on the two allotropes of Pb. Scanning tunneling microcopy reveals that a high corrugation of the quasicrystalline Pb limits the diffusion of the C60 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 C60 molecules atop the Pb islands approaches zero, regardless of the overall C60 coverage.

Sharma, H. R.; Smerdon, J. A.; Nugent, P. J.; Ribeiro, A.; McLeod, I.; Dhanak, V. R.; Shimoda, M.; Tsai, A. P.; McGrath, R.

2014-05-01

197

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

PubMed

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 C60 on the two allotropes of Pb. Scanning tunneling microcopy reveals that a high corrugation of the quasicrystalline Pb limits the diffusion of the C60 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 C60 molecules atop the Pb islands approaches zero, regardless of the overall C60 coverage. PMID:24811658

Sharma, H R; Smerdon, J A; Nugent, P J; Ribeiro, A; McLeod, I; Dhanak, V R; Shimoda, M; Tsai, A P; McGrath, R

2014-05-01

198

Chiral Symmetry in Nuclei  

E-print Network

The impact of chiral symmetry on nuclear physics is discussed in the context of recent advances in the few-nucleon systems and of dimensional power counting. The tractability of few-nucleon calculations, illustrated by very recent solutions for $A = 2-6$, is shown to follow from power counting based on chiral Lagrangians. The latter predicts the suppression of $N$-body forces, as originally shown by Weinberg. Isospin violation in the nuclear force is similarly analyzed using the results of van Kolck, and this is shown to be consistent with results from the Nijmegen phase-shift analysis. Conventional $\\rho - \\omega$ and $\\pi - \\eta$ mixing models with on-shell mixing strength are not inconsistent with naive power counting. Meson-exchange currents calculated in chiral perturbation theory are in good agreement with experiment.

Jim Friar

1995-03-29

199

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

200

Symmetry and Condensed Matter Physics  

Microsoft Academic Search

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

M. El-Batanouny; F. Wooten

2008-01-01

201

Superflavor symmetry for heavy particles  

NASA Astrophysics Data System (ADS)

We extend the heavy quark spin and flavor symmetry discussed by Voloshin and Shifman and by Isgur and Wise to systems in which the heavy colored particles have different spins. We discuss in detail the superflavor symmetry between a heavy quark and a heavy color triplet scalar.

Georgi, Howard; Wise, Mark B.

1990-06-01

202

Lambda and mu-symmetries  

E-print Network

Lambda-symmetries of ODEs were introduced by Muriel and Romero, and discussed by C. Muriel in her talk at SPT2001. Here we provide a geometrical characterization of lambda-prolongations, and a generalization of these -- and of lambda-symmetries -- to PDEs and systems thereof.

G. Gaeta

2005-02-09

203

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

204

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

205

Geometrical spin symmetry and spin  

SciTech Connect

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

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

2011-07-15

206

The Limits of Custodial Symmetry  

NASA Astrophysics Data System (ADS)

We introduce a toy model implementing the proposal of using a custodial symmetry to protect the ZbL bar bL coupling from large corrections. This "doublet-extended standard model" adds a weak doublet of fermions (including a heavy partner of the top quark) to the particle content of the standard model in order to implement an O(4) × U(1)X SU(2)L × SU(2)R × PLR × U(1)X symmetry in the top-quark mass generating sector. This symmetry is softly broken to the gauged SU(2)L × U(1)Y electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value of M allows us to explore the range of possibilities between the O(4)-symmetric (M ? 0) and standard-model-like (M ? ?) limits.

Sekhar Chivukula, R.; Foadi, Roshan; Simmons, Elizabeth H.; di Chiara, Stefano

2011-01-01

207

The Limits of Custodial Symmetry  

NASA Astrophysics Data System (ADS)

We introduce a toy model implementing the proposal of using a custodial symmetry to protect the ZbL bar {b}L coupling from large corrections. This "doublet-extended standard model" adds a weak doublet of fermions (including a heavy partner of the top quark) to the particle content of the standard model in order to implement an O(4) × U(1)X SU(2)L × SU(2)R × PLR × U(1)X symmetry in the top-quark mass generating sector. This symmetry is softly broken to the gauged SU(2)L × U(1)Y electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value of M allows us to explore the range of possibilities between the O(4)-symmetric (M ? 0) and standard-model-like (M ? ?) limits.

Chivukula, R. Sekhar; Foadi, Roshan; Simmons, Elizabeth H.; di Chiara, Stefano

208

Symmetries of the Einstein Equations  

E-print Network

Generalized symmetries of the Einstein equations are infinitesimal transformations of the spacetime metric that formally map solutions of the Einstein equations to other solutions. The infinitesimal generators of these symmetries are assumed to be local, \\ie at a given spacetime point they are functions of the metric and an arbitrary but finite number of derivatives of the metric at the point. We classify all generalized symmetries of the vacuum Einstein equations in four spacetime dimensions and find that the only generalized symmetry transformations consist of: (i) constant scalings of the metric (ii) the infinitesimal action of generalized spacetime diffeomorphisms. Our results rule out a large class of possible ``observables'' for the gravitational field, and suggest that the vacuum Einstein equations are not integrable.

C. G. Torre; I. M. Anderson

1993-02-23

209

Dynamical symmetries in nuclear structure  

SciTech Connect

In recent years the concept of dynamical symmetries in nuclei has witnessed a renaissance of interest and activity. Much of this work has been developed in the context of the Interacting Boson Approximation (or IBA) model. The appearance and properties of dynamical symmetries in nuclei will be reviewed, with emphasis on their characteristic signatures and on the role of the proton-neutron interaction in their formation, systematics and evolution. 36 refs., 20 figs.

Casten, R.F.

1986-01-01

210

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

211

Superflavor symmetry for heavy particles  

Microsoft Academic Search

We extend the heavy quark spin and flavor symmetry discussed by Voloshin and Shifman and by Isgur and Wise to systems in which the heavy colored particles have different spins. We discuss in detail the superflavor symmetry between a heavy quark and a heavy color triplet scalar. Research supported in part by the Department of Energy under contract No. DE-ACO381-ER40050.

Howard Georgi; Mark B. Wise

1990-01-01

212

Flavored Peccei-Quinn symmetry  

E-print Network

In an attempt to uncover any underlying physics in the standard model (SM), we suggest a $\\mu$--$\\tau$ power law in the lepton sector, such that relatively large 13 mixing angle with bi-large ones can be derived. On the basis of this, we propose a neat and economical model for both the fermion mass hierarchy problem of the SM and a solution to the strong CP problem, in a way that no domain wall problem occurs, based on $A_{4}\\times U(1)_{X}$ symmetry in a supersymmetric framework. Here we refer to the global $U(1)_X$ symmetry that can explain the above problems as "flavored Peccei-Quinn symmetry". In the model, a direct coupling of the SM gauge singlet flavon fields responsible for spontaneous symmetry breaking to ordinary quarks and leptons, both of which are charged under $U(1)_X$, comes to pass through Yukawa interactions, and all vacuum expectation values breaking the symmetries are connected each other. So, the scale of Peccei-Quinn symmetry breaking is shown to be roughly located around $10^{12}$ GeV se...

Ahn, Y H

2014-01-01

213

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

214

New building blocks in the 2/1 crystalline approximant of a Bergman-type icosahedral quasicrystal  

PubMed Central

The refined x-ray crystal structure of the phase Mg27Al10.7(2)Zn47.3(2) (Pa3) establishes it as the new 2/1 Bergman-type approximant of the icosahedral quasicrystal. The primitive cubic lattice consists of condensed triacontahedral and novel prolate rhombohedral (PR) clusters. Each triacontahedron encapsulates the traditional, multiply endohedral Bergman-type clusters, and each PR encapsulates an Al2 dimer. This phase exhibits the same long-range order as recently established for the Tsai-type Sc–Mg–Zn 2/1 approximant crystal, with substantial geometric and atomic distribution differences between the two only in the short range orders. This common feature suggests that Bergman- and Tsai-type quasicrystals may be more similar than earlier conceived. Factors germane to the formation of, and the differences between, Bergman- vs. Tsai-type 1/1 and 2/1 approximate structures are considered, including notably different distributions of the more electropositive elements. PMID:16950873

Lin, Qisheng; Corbett, John D.

2006-01-01

215

The Pentameric Vertex Proteins Are Necessary for the Icosahedral Carboxysome Shell to Function as a CO2 Leakage Barrier  

PubMed Central

Background Carboxysomes are polyhedral protein microcompartments found in many autotrophic bacteria; they encapsulate the CO2 fixing enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) within a thin protein shell and provide an environment that enhances the catalytic capabilities of the enzyme. Two types of shell protein constituents are common to carboxysomes and related microcompartments of heterotrophic bacteria, and the genes for these proteins are found in a large variety of bacteria. Methodology/Principal Findings We have created a Halothiobacillus neapolitanus knockout mutant that does not produce the two paralogous CsoS4 proteins thought to occupy the vertices of the icosahedral carboxysomes and related microcompartments. Biochemical and ultrastructural analyses indicated that the mutant predominantly forms carboxysomes of normal appearance, in addition to some elongated microcompartments. Despite their normal shape, purified mutant carboxysomes are functionally impaired, although the activities of the encapsulated enzymes are not negatively affected. Conclusions/Significance In the absence of the CsoS4 proteins the carboxysome shell loses its limited permeability to CO2 and is no longer able to provide the catalytic advantage RubisCO derives from microcompartmentalization. This study presents direct evidence that the diffusion barrier property of the carboxysome shell contributes significantly to the biological function of the carboxysome. PMID:19844578

Cai, Fei; Menon, Balaraj B.; Cannon, Gordon C.; Curry, Kenneth J.; Shively, Jessup M.; Heinhorst, Sabine

2009-01-01

216

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

217

Generalised CP and $?(96)$ Family Symmetry  

E-print Network

We perform a comprehensive study of the $\\Delta (96)$ family symmetry combined with the generalised CP symmetry $H_{\\rm{CP}}$. We investigate the lepton mixing parameters which can be obtained from the original symmetry $\\Delta (96)\\rtimes H_{\\rm{CP}}$ breaking to different remnant symmetries in the neutrino and charged lepton sectors, namely $G_{\

Gui-Jun Ding; Stephen F. King

2014-03-24

218

Physical symmetry and lattice symmetry in the lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

The lattice Boltzmann method (LBM) is regarded as a specific finite difference discretization for the kinetic equation of the discrete velocity distribution function. We argue that for finite sets of discrete velocity models, such as LBM, the physical symmetry is necessary for obtaining the correct macroscopic Navier-Stokes equations. In contrast, the lattice symmetry and the Lagrangian nature of the scheme, which is often used in the lattice gas automaton method and the existing lattice Boltzmann methods and directly associated with the property of particle dynamics, is not necessary for recovering the correct macroscopic dynamics. By relaxing the lattice symmetry constraint and introducing other numerical discretization, one can also obtain correct hydrodynamics. In addition, numerical simulations for applications, such as nonuniform meshes and thermohydrodynamics can be easily carried out and numerical stability can be ensured by the Courant-Friedricks-Lewey condition and using the semi-implicit collision scheme.

Cao, Nianzheng; Chen, Shiyi; Jin, Shi; Martínez, Daniel

1997-01-01

219

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

220

Symmetry-protected entanglement renormalization  

NASA Astrophysics Data System (ADS)

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

Singh, Sukhwinder; Vidal, Guifre

2013-09-01

221

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

222

Symmetries, Lie Algebras and Representations  

NASA Astrophysics Data System (ADS)

Preface; 1. Symmetries and conservation laws; 2. Basic examples; 3. The Lie algebra su(3) and hadron symmetries; 4. Formalization: algebras and Lie algebras; 5. Representations; 6. The Cartan-Weyl basis; 7. Simple and affine Lie algebras; 8. Real Lie algebras and real forms; 9. Lie groups; 10. Symmetries of the root system. The Weyl group; 11. Automorphisms of Lie algebras; 12. Loop algebras and central extensions; 13. Highest weight representations; 14. Verma modules, Casimirs, and the character formula; 15. Tensor products of representations; 16. Clebsch-Gordan coefficients and tensor operators; 17. Invariant tensors; 18. Subalgebras and branching rules; 19. Young tableaux and the symmetric group; 20. Spinors, Clifford algebras, and supersymmetry; 21. Representations on function spaces; 22. Hopf algebras and representation rings; Epilogue; References; Index.

Fuchs, Jürgen; Schweigert, Christoph

2003-10-01

223

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

224

Chiral symmetry in nuclear matter  

SciTech Connect

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

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

1988-11-15

225

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

226

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

227

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

228

Development of an icosahedral quasicrystal and two approximants in the Ca-Au-Sn system: syntheses and structural analyses.  

PubMed

The realm of Tsai-type (YCd(6)-type) quasicrystals (QCs) and their approximants (ACs) continues to expand to the east in the periodic table. The heavy tetrel Sn is now one of the major components in the new Ca(15.0(5))Au(60.0(4))Sn(25.0(2)) (atom %) icosahedral QC and in the corresponding 1/1 and 2/1 ACs. (The 2/1 AC with Yb is also established.) Single-crystal X-ray diffraction on a 1/1 AC gives the refined formula of Ca(3)Au(14.36(3))Sn(4.38(5)) in space group Im3, a = 15.131(1) Å, whereas a representative 2/1 AC gives Ca(13)Au(47.2(1))Sn(28.1(1)), Pa3 and a = 24.444(1) Å. Both ACs contain five-shell multiply endohedral triacontahedral clusters as the common building blocks, as in the parent structure of YCd(6). The 2/1 AC also contains four Ca(2)-dimer-centered prolate rhombohedra (PRs) in the unit cell. The long-range order between triacontahedra and PRs in the 2/1 AC is the same as those in Bergman-type 2/1 ACs. A TB-LMTO-ASA calculation on an ideal 1/1 AC model reveals a shallow pseudogap in the total densities-of-states data around the Fermi energy, as expected. The depth of the pseudogap is considerably enhanced through interactions between the Ca 3d states and s and p states of Au and Sn. PMID:20939550

Lin, Qisheng; Corbett, John D

2010-11-15

229

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

230

Superdeformations and fermion dynamical symmetries  

NASA Astrophysics Data System (ADS)

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

Cheng-Li, Wu

1991-01-01

231

The Symmetry of Natural Laws.  

ERIC Educational Resources Information Center

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

Brown, Laurie M.

232

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

233

Electrical and magnetic property of Al62Cu25.5Fe12.5 icosahedral quasicrystal: Spin-orbit scattering  

NASA Astrophysics Data System (ADS)

We report here electrical and magnetic properties of Al62Cu25.5Fe12.5 icosahedral quasicrystal. We have measured the electrical resistivity from 2K to 300K and observed negative temperature coefficient of resistivity above 15K. Below 15K we see a decrease in resistivity showing maxima around 15K. Upon application of a high magnetic field of 5 Tesla the maxima disappears and below 15 K the resistivity rises sharply. Magnetoresistance was measured at various temperatures as a function of applied field and we observe positive magnetoresistance for all temperatures. We have attributed these effects arising due to spin-orbit scattering.

Ray, M. K.; Bagani, K.; Ghosh, B.; Sardar, M.; Banerjee, S.; Srivastava, V. C.; Mukhopadhyay, N. K.

2013-02-01

234

Na{sub 12}K{sub 38}Tl{sub 48}Au{sub 2}: A metallic Zintl phase with naked icosahedral fragments Tl{sub 7}{sup 7{minus}} and Tl{sub 9}{sup 9{minus}} plus Au{sup {minus}}  

SciTech Connect

The title compound is synthesized by direct reaction of the elements at 500 C followed by slow cooling. Na{sub 12}K{sub 38}Tl{sub 48}Au{sub 2} crystallizes hexagonal and is constituted (in terms of oxidation states) as (Na{sup +}){sub 12}(K{sup +}){sub 38}(Tl{sub 7}{sup 7{minus}}){sub 3}(Tl{sub 9}{sup 9{minus}}){sub 3}(Au{sup {minus}}){sub 2}. Both clusters have C{sub 2{nu}} symmetry and can be viewed as fragments of a centered icosahedral Tl{sub 13}. The Tl{sub 7}{sup 7{minus}} cluster is an oblate pentagonal bipyramid with an apex-apex bond distance of 3.39 {angstrom}, and Tl{sub 9}{sup 9{minus}} can be best derived from the centered icosahedron by removal of four adjoining vertexes (or as two fused pentagonal bipyramids). The isolated Au{sup {minus}} is bound in a trigonal antiprism of potassium. The compound is structurally electron-precise (Zintl phase), but it shows characteristics of a very poor metal ({rho}{sub 298} {approximately} 760 {mu}{Omega}(cm)) with a Pauli-like susceptibility of {approximately}1.4 {times} 10{sup {minus}3} emu/mol over 50--300 K after correction for Larmor precession of cluster orbitals. EHMO results for the bonding in Tl{sub 7}{sup 7{minus}} and factors that stabilize this compound are presented and discussed.

Huang, D.P.; Dong, Z.D.; Corbett, J.D. [Ames Lab., IA (United States)] [Ames Lab., IA (United States); [Iowa State Univ., IA (United States). Dept. of Chemistry

1998-11-02

235

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

236

Flavored Peccei-Quinn symmetry  

E-print Network

In an attempt to uncover any underlying physics in the standard model (SM), we suggest a $\\mu$--$\\tau$ power law in the lepton sector, such that relatively large 13 mixing angle with bi-large ones can be derived. On the basis of this, we propose a neat and economical model for both the fermion mass hierarchy problem of the SM and a solution to the strong CP problem, in a way that no domain wall problem occurs, based on $A_{4}\\times U(1)_{X}$ symmetry in a supersymmetric framework. Here we refer to the global $U(1)_X$ symmetry that can explain the above problems as "flavored Peccei-Quinn symmetry". In the model, a direct coupling of the SM gauge singlet flavon fields responsible for spontaneous symmetry breaking to ordinary quarks and leptons, both of which are charged under $U(1)_X$, comes to pass through Yukawa interactions, and all vacuum expectation values breaking the symmetries are connected each other. So, the scale of Peccei-Quinn symmetry breaking is shown to be roughly located around $10^{12}$ GeV section through its connection to the fermion masses. The model predictions are shown to lie on the testable regions in the very near future through on-going experiments for neutrino oscillation, neutrinoless double beta decay and axion. We examine the model predictions, arisen from the $\\mu$--$\\tau$ power law, on leptonic $CP$ violation, neutrinoless double beta decay and atmospheric mixing angle, and show that the fermion mass and mixing hierarchies are in good agreement with the present data. Interestingly, we show the model predictions on the axion mass $m_a\\simeq2.53\\times10^{-5}$ eV and the axion coupling to photon $g_{a\\gamma\\gamma}\\simeq1.33\\times10^{-15}~{\\rm GeV}^{-1}$. And subsequently the square of the ratio between them is shown to be 1 or 2 orders of magnitude lower than that of the conventional axion model.

Y. H. Ahn

2014-10-07

237

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.

238

General Formalism for the BRST Symmetry  

NASA Astrophysics Data System (ADS)

Abstract In this paper we will discuss Faddeev—Popov method for gauge theories with a general form of gauge symmetry in an abstract way. We will then develope a general formalism for dealing with the BRST symmetry. This formalism will make it possible to analyse the BRST symmetry for any theory.

Suhail, Ahmad

2013-04-01

239

Symmetry analysis of differential equations with Mathematica  

Microsoft Academic Search

We will discuss three different methods for finding symmetry solutions based on the Fréchet derivative common to each procedure. The methods discussed are Lie's standard procedure of symmetry analysis, the nonclassical method, and the derivation of potential symmetries. A ferromagnet in a strong external field represented by a nonlinear telegraph equation serves as an example describing the application of all

G. Baumann

1997-01-01

240

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

241

Somalwar0804 1 Of Symmetries Good and Bad,Of Symmetries Good and Bad,  

E-print Network

Somalwar0804 1 Of Symmetries Good and Bad,Of Symmetries Good and Bad, Seen and Unseen Principles And from breaking these symmetries #12;Somalwar0804 7 Discrete Symmetries First P (Parity these individually. Can't tell left from right using strong/EM interactions Weak interactions violate P (and C) badly

Glashausser, Charles

242

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

243

Synthesis and relaxivity studies of a DOTA-based nanomolecular chelator assembly supported by an icosahedral closo-B??²? core for MRI: a click chemistry approach.  

PubMed

An icosahedral closo-B??²? scaffold based nano-sized assembly capable of carrying a high payload of Gd³?-chelates in a sterically crowded configuration is developed by employing the azide-alkyne click reaction. The twelve copies of DO3A-t-Bu-ester ligands were covalently attached to an icosahedral closo-B??²? core via suitable linkers through click reaction. This nanomolecular structure supporting a high payload of Gd³?-chelate is a new member of the closomer MRI contrast agents that we are currently developing in our laboratory. The per Gd ion relaxivity (r?) of the newly synthesized MRI contrast agent was obtained in PBS, 2% tween/PBS and bovine calf serum using a 7 Tesla micro MRI instrument and was found to be slightly higher (r? = 4.7 in PBS at 25 °C) compared to the clinically used MRI contrast agents Omniscan (r? = 4.2 in PBS at 25 °C) and ProHance (r? = 3.1 in PBS at 25 °C). PMID:23899836

Goswami, Lalit N; Ma, Lixin; Kueffer, Peter J; Jalisatgi, Satish S; Hawthorne, M Frederick

2013-01-01

244

Symmetry restoration and quantumness reestablishment  

PubMed Central

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. PMID:25231796

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

2014-01-01

245

Symmetry restoration and quantumness reestablishment  

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

246

Spinor structure and internal symmetries  

E-print Network

Space-time and internal symmetries are considered within one theoretical framework based on the generalized spin and abstract Hilbert space. Complex momentum is understood as a generating kernel of the underlying spinor structure. It is shown that tensor products of biquaternion algebras are associated with the each irreducible representation of the Lorentz group. Space-time discrete symmetries $P$, $T$ and their combination $PT$ are generated by the fundamental automorphisms of this algebraic background (Clifford algebras). Charge conjugation $C$ is presented by a pseudoautomorphism of the complex Clifford algebra. This description of the operation $C$ allows one to distinguish charged and neutral particles including particle-antiparticle interchange and truly neutral particles. Quotient representations of the Lorentz group and their possible relations with $P$- and $CP$-violations are considered. Spin and charge multiplets, based on the interlocking representations of the Lorentz group, are introduced. A ce...

Varlamov, V V

2014-01-01

247

Critical Point Symmetries in Nuclei  

E-print Network

Critical Point Symmetries (CPS) appear in regions of the nuclear chart where a rapid change from one symmetry to another is observed. The first CPSs, introduced by F. Iachello, were E(5), which corresponds to the transition from vibrational [U(5)] to gamma-unstable [O(6)] behaviour, and X(5), which represents the change from vibrational [U(5)] to prolate axially deformed [SU(3)] shapes. These CPSs have been obtained as special solutions of the Bohr collective Hamiltonian. More recent special solutions of the same Hamiltonian, to be described here, include Z(5) and Z(4), which correspond to maximally triaxial shapes (the latter with ``frozen'' gamma=30 degrees), as well as X(3), which corresponds to prolate shapes with ``frozen'' gamma=0. CPSs have the advantage of providing predictions which are parameter free (up to overall scale factors) and compare well to experiment. However, their mathematical structure [with the exception of E(5)] needs to be clarified.

Dennis Bonatsos; D. Lenis; D. Petrellis; P. A. Terziev; I. Yigitoglu

2005-10-31

248

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

249

Nonlinear Realizations of Chiral Symmetry  

Microsoft Academic Search

We explore possible realizations of chiral symmetry, based on isotopic multiplets of fields whose transformation rules involve only isotopic-spin matrices and the pion field. The transformation rules are unique, up to possible redefinitions of the pion field. Chiral-invariant Lagrangians can be constructed by forming isotopic-spin-conserving functions of a covariant pion derivative, plus other fields and their covariant derivatives. The resulting

Steven Weinberg

1968-01-01

250

Entanglement and symmetry in permutation symmetric states  

E-print Network

We investigate the relationship between multipartite entanglement and symmetry, focusing on permutation symmetric states. We use the Majorana representation, where these states correspond to points on a sphere. Symmetry of the representation under rotation is equivalent to symmetry of the states under products of local unitaries. The geometric measure of entanglement is thus phrased entirely as a geometric optimisation, and a condition for the equivalence of entanglement measures written in terms of point symmetries. Finally we see that different symmetries of the states correspond to different types of entanglement with respect to SLOCC interconvertibility.

Damian J. H. Markham

2010-01-03

251

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

252

Symmetry breaking in neural nets.  

PubMed

In this paper two well-known homogeneous models of neural nets undergoing symmetry-breaking transitions are studied in order to see if, after the transition, there is the appearance of Goldstone modes. These have been found only in an approximate way; there are indications, however, that they can play a prominent role when the tissue is subjected to external inputs, constraining it to be slaved to the characteristics of those. This circumstance should be essential in explaining how a structured net can store complex inputs and give subsequently ordered outputs. PMID:3196771

Pessa, E

1988-01-01

253

Reflectionless Potentials and PT Symmetry  

E-print Network

Large families of Hamiltonians that are non-Hermitian in the conventional sense have been found to have all eigenvalues real, a fact attributed to an unbroken PT symmetry. The corresponding quantum theories possess an unconventional scalar product. The eigenvalues are determined by differential equations with boundary conditions imposed in wedges in the complex plane. For a special class of such systems, it is possible to impose the PT-symmetric boundary conditions on the real axis, which lies on the edges of the wedges. The PT-symmetric spectrum can then be obtained by imposing the more transparent requirement that the potential be reflectionless.

Zafar Ahmed; Carl M. Bender; M. V. Berry

2005-08-16

254

Bimetric theory with exchange symmetry  

SciTech Connect

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

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

2008-08-15

255

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

PubMed

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 C_{nv} 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 C_{nv} 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. PMID:25259991

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

2014-09-12

256

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

257

Symmetry Energy of Dilute Warm Nuclear Matter  

SciTech Connect

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

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

2010-05-21

258

Dynamical symmetries of the Kepler problem  

NASA Astrophysics Data System (ADS)

This paper comes from a first-year undergraduate research project on hidden symmetries of the dynamics for classical Hamiltonian systems. For pedagogical reasons the main subject chosen was Kepler’s problem of motion under a central potential, since it is a completely solved system. It is well known that for this problem the group of dynamical symmetries is strictly larger than the isometry group O(3), the extra symmetries corresponding to hidden symmetries of the dynamics. By taking the point of view of examining the group action of the dynamical symmetries on the allowed trajectories, it is possible to teach the basic elements of many important physics subjects in the same project, including the Hamiltonian formalism, hidden symmetries, integrable systems, group theory and the use of manifolds.

Cariglia, Marco; Silva Araújo, Eduardo

2013-09-01

259

Thermal symmetry of the Markovian master equation  

NASA Astrophysics Data System (ADS)

The quantum Markovian master equation of the reduced dynamics of a harmonic oscillator coupled to a thermal reservoir is shown to possess thermal symmetry. This symmetry is revealed by a Bogoliubov transformation that can be represented by a hyperbolic rotation acting on the Liouville space of the reduced dynamics. The Liouville space is obtained as an extension of the Hilbert space through the introduction of tilde variables used in the thermofield dynamics formalism. The angle of rotation depends on the temperature of the reservoir, as well as the value of Planck’s constant. This symmetry relates the thermal states of the system at any two temperatures. This includes absolute zero, at which purely quantum effects are revealed. The Caldeira-Leggett equation and the classical Fokker-Planck equation also possess thermal symmetry. We compare the thermal symmetry obtained from the Bogoliubov transformation in related fields and discuss the effects of the symmetry on the shape of a Gaussian wave packet.

Tay, B. A.; Petrosky, T.

2007-10-01

260

Thermal symmetry of the Markovian master equation  

SciTech Connect

The quantum Markovian master equation of the reduced dynamics of a harmonic oscillator coupled to a thermal reservoir is shown to possess thermal symmetry. This symmetry is revealed by a Bogoliubov transformation that can be represented by a hyperbolic rotation acting on the Liouville space of the reduced dynamics. The Liouville space is obtained as an extension of the Hilbert space through the introduction of tilde variables used in the thermofield dynamics formalism. The angle of rotation depends on the temperature of the reservoir, as well as the value of Planck's constant. This symmetry relates the thermal states of the system at any two temperatures. This includes absolute zero, at which purely quantum effects are revealed. The Caldeira-Leggett equation and the classical Fokker-Planck equation also possess thermal symmetry. We compare the thermal symmetry obtained from the Bogoliubov transformation in related fields and discuss the effects of the symmetry on the shape of a Gaussian wave packet.

Tay, B. A.; Petrosky, T. [Department of Physics, Faculty of Science, University Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Center for Complex Quantum Systems, University of Texas at Austin, 1 University Station C1600, Austin, Texas 78712 (United States)

2007-10-15

261

Dynamical symmetries of the Kepler problem  

E-print Network

This work originates from a first year undergraduate research project on hidden symmetries of the dynamics for classical Hamiltonian systems, under the program 'Jovens talentos para a Ciencia' of Brazilian funding agency Capes. For pedagogical reasons the main subject chosen was Kepler's problem of motion under a central potential, since it is a completely solved system. It is well known that for this problem the group of dynamical symmetries is strictly larger than the isometry group O(3), the extra symmetries corresponding to hidden symmetries of the dynamics. By taking the point of view of examining the group action of the dynamical symmetries on the allowed trajectories, it is possible to teach in the same project basic elements of as many important subjects in physics as: Hamiltonian formalism, hidden symmetries, integrable systems, group theory, and the use of manifolds.

Cariglia, Marco

2013-01-01

262

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

263

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

2006-12-24

264

Parameter counting in models with global symmetries  

E-print Network

We present rules for determining the number of physical parameters in models with exact flavor symmetries. In such models the total number of parameters (physical and unphysical) needed to described a matrix is less than in a model without the symmetries. Several toy examples are studied in order to demonstrate the rules. The use of global symmetries in studying the minimally supersymmetric standard model (MSSM) is examined.

Joshua Berger; Yuval Grossman

2008-11-06

265

$f(T)$ 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

2011-12-13

266

Lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.  

PubMed

A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and computational study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare these to the lattice dynamics of the cubic 1/1-approximant Zn6Sc. The two phases, quasicrystal and approximant, are built up from the same atomic clusters, which are packed either quasiperiodically or on a body centered cubic lattice, respectively. Using inelastic neutron scattering and atomic scale simulations, we show that the vibrational spectra of these three systems are very similar, however, they contain a clear signature of the increasing structural complexity from approximant to quasicrystal. PMID:24445750

Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M

2014-02-01

267

Evidence for tetrahedral symmetry in 16O  

E-print Network

We derive the rotation-vibration spectrum of a 4-alpha configuration with tetrahedral symmetry, T_d, and show evidence for the occurrence of this symmetry in the low-lying spectrum of 16O. All vibrational states with A, E and F symmetry appear to have been observed, as well as the rotational bands with L(P)=0(+), 3(-), 4(+), 6(+) on the A states, and part of the rotational bands built on the E, F states. We derive analytic expressions for the form factors and B(EL) values of the ground state rotational band and show that the measured values support the tetrahedral symmetry of this band.

R. Bijker; F. Iachello

2014-03-26

268

Evidence for tetrahedral symmetry in 16O  

E-print Network

We derive the rotation-vibration spectrum of a 4-alpha configuration with tetrahedral symmetry, T_d, and show evidence for the occurrence of this symmetry in the low-lying spectrum of 16O. All vibrational states with A, E and F symmetry appear to have been observed, as well as the rotational bands with L(P)=0(+), 3(-), 4(+), 6(+) on the A states, and part of the rotational bands built on the E, F states. We derive analytic expressions for the form factors and B(EL) values of the ground state rotational band and show that the measured values support the tetrahedral symmetry of this band.

Bijker, R

2014-01-01

269

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

270

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

271

Metal Core Bonding Motifs of Monodisperse Icosahedral Au13 and Larger Au Monolayer-Protected Clusters as Revealed by X-ray Absorption Spectroscopy and Transmission Electron Microscopy  

SciTech Connect

The atomic metal core structures of the subnanometer clusters Au{sub 13}[PPh{sub 3}]{sub 4}[S(CH{sub 2}){sub 11}CH{sub 3}]{sub 2}Cl{sub 2} and Au{sub 13}[PPh{sub 3}]{sub 4}[S(CH{sub 2}){sub 11}CH{sub 3}]{sub 4} were characterized using advanced methods of electron microscopy and X-ray absorption spectroscopy. The number of gold atoms in the cores of these two clusters was determined quantitatively using high-angle annular dark field scanning transmission electron microscopy. Multiple-scattering-path analyses of extended X-ray absorption fine structure (EXAFS) spectra suggest that the Au metal cores of each of these complexes adopt an icosahedral structure with a relaxation of the icosahedral strain. Data from microscopy and spectroscopy studies extended to larger thiolate-protected gold clusters showing a broader distribution in nanoparticle core sizes (183 {+-} 116 Au atoms) reveal a bulklike fcc structure. These results further support a model for the monolayer-protected clusters (MPCs) in which the thiolate ligands bond preferentially at 3-fold atomic sites on the nanoparticle surface, establishing an average composition for the MPC of Au{sub 180}[S(CH{sub 2}){sub 11}CH{sub 3}]{sub 40}. Results from EXAFS measurements of a gold(I) dodecanethiolate polymer are presented that offer an alternative explanation for observations in previous reports that were interpreted as indicating Au MPC structures consisting of a Au core, Au2S shell, and thiolate monolayer.

Menard,L.; Xu, H.; Gao, S.; Twesten, R.; Harper, A.; Song, Y.; Wang, G.; Douglas, A.; Yang, J.; et al.

2006-01-01

272

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

273

Polarization and Symmetry of Electronic Transitions in Long Fluorescence Lifetime Triangulenium Dyes  

PubMed Central

To fully exploit the capabilities of fluorescence probes in modern experiments, where advanced instrumentation is used to probe complex environments, other photophysical properties than emission color and emission intensity are monitored. Each dye property can be addressed individually as well as collectively to provide in-depth information unavailable from the standard intensity measurements. Dyes with long emission lifetimes and strongly polarized transitions enable the monitoring of lifetime changes as well as emission polarization (or anisotropy). Thus experiments can be designed to follow slow dynamics. In this article the UV and visible electronic transitions of a series of red emitting dyes based on the triangulenium motif are investigated. We resolve overlapping features in the spectra and assign transition moment of the molecular axes. The result is the complete Jablonski diagram for the UV and visible spectral region. The symmetries of the studied dyes are shown to have a large influence on the optical response and they are clearly separated into two groups of symmetry by their photophysical properties. The C2v symmetric dyes: azadioxatriangulenium (ADOTA+) and diazaoxatriangulenium (DAOTA+) have high emission anisotropies, fluorescence lifetimes around 20 ns, and fluorescence quantum yields of ~50%. The trioxatriangulenium (TOTA+) and triazatriangulenium (TATA+) dyes—nominally of D3h symmetry—have fluorescence lifetimes around 10 ns lifetimes and fluorescence quantum yields of 10-15%. However, the D3h-symmetry is shown to be lowered to a point group, where the axes transform uniquely such that the degeneracy of the E’-states is lifted. PMID:23391292

Thyrhaug, Erling; S?rensen, Thomas Just; Gryczynski, Ignacy; Gryczynski, Zygmunt; Laursen, Bo W.

2013-01-01

274

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

275

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

276

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

277

Symmetry violations and rare decays  

SciTech Connect

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

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

1989-01-01

278

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

279

Quantum Group and Quantum Symmetry  

E-print Network

This is a self-contained review on the theory of quantum group and its applications to modern physics. A brief introduction is given to the Yang-Baxter equation in integrable quantum field theory and lattice statistical physics. The quantum group is primarily introduced as a systematic method for solving the Yang-Baxter equation. Quantum group theory is presented within the framework of quantum double through quantizing Lie bi-algebra. Both the highest weight and the cyclic representations are investigated for the quantum group and emphasis is laid on the new features of representations for $q$ being a root of unity. Quantum symmetries are explored in selected topics of modern physics.

Zhe Chang

1995-08-30

280

Intersection rules, dynamics and symmetries  

E-print Network

We consider theories containing gravity, at most one dilaton and form field strengths. We show that the existence of particular BPS solutions of intersecting extremal closed branes select the theories, which upon dimensional reduction to three dimensions possess a simple simply laced Lie group symmetry G. Furthermore these theories can be fully reconstructed from the dynamics of such branes and of their openings. Amongst such theories are the effective actions of the bosonic sector of M-theory and of the bosonic string. The BPS intersecting brane solutions form representations of a subgroup of the group of Weyl reflections and outer automorphisms of the triple Kac-Moody extension G+++ of the G algebra, which cannot be embedded in the overextended Kac-Moody subalgebra G++ characterising the cosmological Kasner solutions.

Francois Englert; Laurent Houart; Peter West

2003-07-02

281

Symmetries in collective neutrino oscillations  

E-print Network

We discuss the relationship between a symmetry in the neutrino flavour evolution equations and neutrino flavour oscillations in the collective precession mode. This collective precession mode can give rise to spectral swaps (splits) when conditions can be approximated as homogeneous and isotropic. Multi-angle numerical simulations of supernova neutrino flavour transformation show that when this approximation breaks down, non-collective neutrino oscillation modes decohere kinematically, but the collective precession mode still is expected to stand out. We provide a criterion for significant flavour transformation to occur if neutrinos participate in a collective precession mode. This criterion can be used to understand the suppression of collective neutrino oscillations in anisotropic environments in the presence of a high matter density. This criterion is also useful in understanding the breakdown of the collective precession mode when neutrino densities are small.

Huaiyu Duan; George M. Fuller; Yong-Zhong Qian

2008-08-14

282

Electroweak Symmetry Breaking by QCD  

E-print Network

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 $\\lesssim m_S\\lesssim 3$ TeV, with the upper bound obtained from renormalization group evolution. This implies that the colored boson can be produced at LHC. If the colored boson is electrically charged, the branching fraction of the Higgs decaying into two photons can slightly increase, and moreover, it can be produced at future linear colliders.

Kubo, Jisuke; Lindner, Manfred

2014-01-01

283

Electroweak Symmetry Breaking via QCD  

E-print Network

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 $\\lesssim m_S\\lesssim $ 3 TeV, with the upper bound obtained from perturbative renormalization group evolution. This implies that the colored boson can be produced at LHC. If the colored boson is electrically charged, the branching fraction of the Higgs decaying into two photons can slightly increase, and moreover, it can be produced at future linear colliders. Our idea of non-perturbative EW scale generation can serve as a new starting point for more realistic model building in solving the hierarchy problem.

Jisuke Kubo; Kher Sham Lim; Manfred Lindner

2014-03-17

284

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

Microsoft Academic Search

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

Maher Moakher; Andrew N. Norris

2006-01-01

285

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.

286

Flavor symmetries and fermion masses  

SciTech Connect

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

Rasin, A.

1994-04-01

287

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

288

Inferring Probabilities From Symmetries Michael Strevens  

E-print Network

Inferring Probabilities From Symmetries Michael Strevens Noûs, 32:231­246, 1998 A This paper justifies the inference of physical probabilities from symmetries. I supply some examples of important 1). Paint one face red, and it may be used as a die. What is the probability that such a die, when

Strevens, Michael

289

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

290

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

291

Secret Symmetries in AdS/CFT  

E-print Network

We discuss special quantum group (secret) symmetries of the integrable system associated to the AdS/CFT correspondence. These symmetries have by now been observed in a variety of forms, including the spectral problem, the boundary scattering problem, n-point amplitudes, the pure-spinor formulation and quantum affine deformations.

Marius de Leeuw; Takuya Matsumoto; Sanefumi Moriyama; Vidas Regelskis; Alessandro Torrielli

2012-04-11

292

Secret Symmetries in AdS/CFT  

E-print Network

We discuss special quantum group (secret) symmetries of the integrable system associated to the AdS/CFT correspondence. These symmetries have by now been observed in a variety of forms, including the spectral problem, the boundary scattering problem, n-point amplitudes, the pure-spinor formulation and quantum affine deformations.

de Leeuw, Marius; Moriyama, Sanefumi; Regelskis, Vidas; Torrielli, Alessandro

2012-01-01

293

Remnant of chiral symmetry on the lattice  

Microsoft Academic Search

A new criterion for chiral symmetry in lattice theories of fermions is derived within a block-spin formalism. This ''remnant''-symmetry criterion properly incorporates the Adler-Bell-Jackiw anomaly and avoids the fermion-doubling problem of other lattice fermion methods. Some obstacles to implementing this approach in the presence of fully dynamical gauge fields are discussed.

Paul Ginsparg; Kenneth Wilson

1982-01-01

294

Atomic and optical tests of Lorentz symmetry  

E-print Network

This article reports on the Fourth Meeting on Lorentz and CPT Symmetry, CPT '07, held in August 2007 in Bloomington, Indiana, USA. The focus is on recent tests of Lorentz symmetry using atomic and optical physics. Results presented at the meeting include improved bounds on Lorentz violation in the photon sector, and the first bounds on several coefficients in the gravity sector.

Neil Russell

2008-07-12

295

Symmetry in Concurrent Games Simon Castellan  

E-print Network

Clairambault Glynn Winskel Computer Laboratory, University of Cambridge, UK Abstract--Behavioural symmetry operational: moves in a game correspond to computation steps. As such it is increasingly exploited to provideSymmetry in Concurrent Games Simon Castellan Ecole Normale Sup´erieure de Lyon, France Pierre

Winskel, Glynn

296

PREFACE: Symmetries and Integrability of Difference Equations  

Microsoft Academic Search

The notion of integrability was first introduced in the 19th century in the context of classical mechanics with the definition of Liouville integrability for Hamiltonian flows. Since then, several notions of integrability have been introduced for partial and ordinary differential equations. Closely related to integrability theory is the symmetry analysis of nonlinear evolution equations. Symmetry analysis takes advantage of the

Adam Doliwa; Risto Korhonen; Stéphane Lafortune

2007-01-01

297

Nuclear symmetry energy: An experimental overview  

E-print Network

The nuclear symmetry energy is a fundamental quantity important for studying the structure of systems as diverse as the atomic nucleus and the neutron star. Considerable efforts are being made to experimentally extract the symmetry energy and its dependence on nuclear density and temperature. In this article, we review experimental studies carried out up-to-date and their current status.

D. V. Shetty; S. J. Yennello

2010-02-01

298

Covariant quantum mechanics and quantum symmetries  

E-print Network

Covariant quantum mechanics and quantum symmetries Josef JanyŸska 1 , Marco Modugno 2 , Dirk Saller: quantum mechanics, classical mechanics, general relativity, infinitesimal symmetries. 2000 MSC: 81P99, 81Q Introduction 2 2 Covariant quantum mechanics 5 2.1 Classical background

JanyÂ?ka, Josef

299

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

300

Ghost Symmetries Peter J. Olver y  

E-print Network

Ghost Symmetries Peter J. Olver y School of Mathematics University of Minnesota Minneapolis, MN Amsterdam The Netherlands jansa@cs.vu.nl, wang@cs.vu.nl Abstract. We introduce the notion of a ghost symmetry for nonlocal differential equations. Ghosts are essential for maintaining the validity

301

Mathematical models of spontaneous symmetry breaking  

E-print Network

The Higgs mechanism of mass generation is the main ingredient in the contemporary Standard Model and its various generalizations. However, there is no comprehensive theory of spontaneous symmetry breaking. We summarize the relevant mathematical results characterizing spontaneous symmetry breaking phenomena in algebraic quantum theory, axiomatic quantum field theory, group theory, and classical gauge theory.

G. Sardanashvily

2008-02-17

302

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

303

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

304

Chiral symmetries associated with angular momentum  

NASA Astrophysics Data System (ADS)

In quantum mechanics courses, symmetries of a physical system are usually introduced as operators which commute with the Hamiltonian. In this paper we will consider chiral symmetries which anticommute with the Hamiltonian. Typically, introductory courses at the (under)graduate level do not discuss these simple, useful and beautiful symmetries at all. The first time a student encounters them is when the Dirac equation is discussed in a course on relativistic quantum mechanics, or when particle-hole symmetry is studied in the context of superconductivity. In this paper, we will show how chiral symmetries can be simply elucidated using the theory of angular momentum, which is taught in virtually all introductory quantum mechanics courses.

Bhattacharya, M.; Kleinert, M.

2014-03-01

305

Chiral symmetries associated with angular momentum  

E-print Network

In beginning quantum mechanics courses, symmetries of a physical system are usually introduced as operators which commute with the Hamiltonian. In this article we will consider chiral symmetries which anticommute with the Hamiltonian. Typically, introductory courses at the (under)graduate level do not discuss these simple, useful and beautiful symmetries at all. The first time a student typically encounters them is when the Dirac equation is discussed in a course on relativistic quantum mechanics, or when particle-hole symmetry is studied in the context of superconductivity. In this article, we will show how chiral symmetries can be simply elucidated using the theory of angular momentum, which is taught in virtually all introductory quantum mechanics courses.

M. Bhattacharya; M. Kleinert

2013-11-29

306

Symmetry-protected adiabatic quantum transistors  

E-print Network

Adiabatic quantum transistors allow quantum logic gates to be performed by applying a large field to a quantum many-body system prepared in its ground state, without the need for local control. The basic operation of such a device can be viewed as driving a spin chain from a symmetry protected phase to a trivial phase, and this perspective offers an avenue to generalise the adiabatic quantum transistor and to design several improvements. The performance of quantum logic gates is shown to depend only on universal symmetry properties of a symmetry-protected phase rather than fine tuned parent Hamiltonians, and it is possible to implement a universal set of logic gates in this way by combining several different types of symmetry protected matter. Such symmetry-protected adiabatic quantum transistors are argued to be robust to a range of relevant noise processes.

Dominic J. Williamson; Stephen D. Bartlett

2014-08-14

307

Lie symmetries and 2D Material Physics  

E-print Network

Inspired from Lie symmetry classification, we establish a correspondence between rank two Lie symmetries and 2D material physics. The material unit cell is accordingly interpreted as the geometry of a root system. The hexagonal cells, appearing in graphene like models, are analyzed in some details and are found to be associated with A_2 and G_2 Lie symmetries. This approach can be applied to Lie supersymmetries associated with fermionic degrees of freedom. It has been suggested that these extended symmetries can offer a new way to deal with doping material geometries. Motivated by Lie symmetry applications in high energy physics, we speculate on a possible connection with (p,q) brane networks used in the string theory compactification on singular Calabi-Yau manifolds.

Adil Belhaj; Moulay Brahim Sedra

2014-04-18

308

Complex Networks and Symmetry I: A Review  

E-print Network

In this review we establish various connections between complex networks and symmetry. While special types of symmetries (e.g., automorphisms) are studied in detail within discrete mathematics for particular classes of deterministic graphs, the analysis of more general symmetries in real complex networks is far less developed. We argue that real networks, as any entity characterized by imperfections or errors, necessarily require a stochastic notion of invariance. We therefore propose a definition of stochastic symmetry based on graph ensembles and use it to review the main results of network theory from an unusual perspective. The results discussed here and in a companion paper show that stochastic symmetry highlights the most informative topological properties of real networks, even in noisy situations unaccessible to exact techniques.

Diego Garlaschelli; Franco Ruzzenenti; Riccardo Basosi

2010-06-20

309

Symmetry breaking patterns in 3HDM  

E-print Network

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-Higgs sectors.

Ivanov, I P

2014-01-01

310

Heavy Diquark Symmetry Constraints for Strong Decays  

NASA Astrophysics Data System (ADS)

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 3P0 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 3P0 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 ?, ?c and ?b baryons.

Eakins, B.; Roberts, W.

2012-10-01

311

Noether theorem for mu-symmetries  

E-print Network

We give a version of Noether theorem adapted to the framework of mu-symmetries; this extends to such case recent work by Muriel, Romero and Olver in the framework of lambda-symmetries, and connects mu-symmetries of a Lagrangian to a suitably modified conservation law. In some cases this "mu-conservation law'' actually reduces to a standard one; we also note a relation between mu-symmetries and conditional invariants. We also consider the case where the variational principle is itself formulated as requiring vanishing variation under mu-prolonged variation fields, leading to modified Euler-Lagrange equations. In this setting mu-symmetries of the Lagrangian correspond to standard conservation laws as in the standard Noether theorem. We finally propose some applications and examples.

G. Cicogna; G. Gaeta

2007-08-23

312

Hidden symmetry-breaking picture of symmetry-protected topological order  

NASA Astrophysics Data System (ADS)

We generalize the hidden symmetry-breaking picture of symmetry-protected topological (SPT) order developed by Kennedy and Tasaki in the context of the Haldane phase. Our generalization applies to a wide class of SPT phases in one-dimensional spin chains, protected by an on-site representation of a finite Abelian group. This generalization takes the form of a nonlocal unitary map that relates local symmetry-respecting Hamiltonians in an SPT phase to local Hamiltonians in a symmetry-broken phase. Using this unitary, we establish a relation between the two-point correlation functions that characterize fully symmetry-broken phases with the string-order correlation functions that characterize the SPT phases, therefore establishing the perspective in these systems that SPT phases are characterized by hidden symmetry breaking. Our generalization is also applied to systems with continuous symmetries, including SO(2k+1) and SU(k).

Else, Dominic V.; Bartlett, Stephen D.; Doherty, Andrew C.

2013-08-01

313

Symmetry and twinning in boltwoodite  

SciTech Connect

The authors give the results of an x-ray diffraction and chemical analysis of boltwoodite from Namibia. Chemical analysis revealed that as well as potassium there was a considerable amount of sodium; thus one may speak of sodium boltwoodite with the molecular ratio K/sub 2/O:Na/sub 2/O = 2 : 1. The potassium and sodium are partly replaced by H/sub 3/O. The idealized formula is (K,Na)/sub 2-x/(H/sub 2/O)/sub x/ x (UO/sub 2/SiO/sub 4/) x H/sub 2/O; the symmetry is monoclinic, the space group being C/sup 2//sub 2h/ = P2/sub 1//m, with a = 6.65 A, b = 7.07 A, c = 7.11 A, ..beta.. = 105/sup 0/30', Z = 2. The acicular crystals are elongated along (010) with a very pronounced cleavage in 001. The cleavage plane is (101). The mineral bears a very marked resemblance to kasolite.

Strunz, H.; Tennyson, C.

1981-11-01

314

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

315

Symmetries of doubly heavy baryons  

NASA Astrophysics Data System (ADS)

For very heavy quarks, the two heavy quarks in a doubly heavy baryon are expected to form a pointlike, heavy diquark in an antitriplet color configuration. In this limit the dynamics of the light degrees of freedom 'factorize' from the dynamics of the heavy diquark system, and a superflavor symmetry emerges which relates the properties of doubly heavy baryons to heavy mesons. The charm quark may not be heavy enough for the cc diquark in a ?cc to be regarded as pointlike. However, there are indications from the results of a nonrelativistic constituent quark model that many of the consequences of factorization emerge even though the model does not assume a quark-diquark structure and the mean separation of the two heavy quarks in the model is not small. We discuss the consequences of factorization for the spectroscopy of doubly heavy baryons and compare these consequences to results from a quark model. We also discuss the possibility of treating the strange quark as a heavy quark and applying these ideas to the ?.

Eakins, Benjamin; Roberts, Winston

2013-10-01

316

Symmetries of Doubly Heavy Baryons  

E-print Network

For very heavy quarks, the two heavy quarks in a doubly heavy baryon are expected to form a pointlike, heavy diquark in an antitriplet color configuration. In this limit the dynamics of the light degrees of freedom `factorize' from the dynamics of the heavy diquark system, and a superflavor symmetry emerges which relates the properties of doubly heavy baryons to heavy mesons. The charm quark may not be heavy enough for the $cc$ diquark in a $\\Xi_{cc}$ to be regarded as pointlike. However, there are indications from the results of a nonrelativistic constituent quark model that many of the consequences of factorization emerge even though the model does not assume a quark-diquark structure and the mean separation of the two heavy quarks in the model is not small. We discuss the consequences of factorization for the spectroscopy of doubly heavy baryons and compare these consequences to results from a quark model. We also discuss the possibility of treating the strange quark as a heavy quark and applying these ideas to the $\\Xi$.

Benjamin Eakins; Winston Roberts

2012-08-22

317

Symmetries of Doubly Heavy Baryons  

E-print Network

For very heavy quarks, the two heavy quarks in a doubly heavy baryon are expected to form a pointlike, heavy diquark in an antitriplet color configuration. In this limit the dynamics of the light degrees of freedom `factorize' from the dynamics of the heavy diquark system, and a superflavor symmetry emerges which relates the properties of doubly heavy baryons to heavy mesons. The charm quark may not be heavy enough for the $cc$ diquark in a $\\Xi_{cc}$ to be regarded as pointlike. However, there are indications from the results of a nonrelativistic constituent quark model that many of the consequences of factorization emerge even though the model does not assume a quark-diquark structure and the mean separation of the two heavy quarks in the model is not small. We discuss the consequences of factorization for the spectroscopy of doubly heavy baryons and compare these consequences to results from a quark model. We also discuss the possibility of treating the strange quark as a heavy quark and applying these ide...

Eakins, Benjamin

2012-01-01

318

Symmetries in fluctuations far from equilibrium.  

PubMed

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

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

2011-05-10

319

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

320

Explorations of SU(3) family gauge symmetry  

NASA Astrophysics Data System (ADS)

The origin of fermion masses and mixings is the least understood aspect of the standard model of particle physics. In this thesis, we try to understand part of it by exploring a framework for the computation of quark and charged lepton mass ratios and CKM mixing angles based on an SU(3) family gauge symmetry. Firstly, we list the field content and the Lagrangian of our model, which has enough global symmetries to protect the first two generations of fermions from developing masses before turning on the family gauge interaction. With the family gauge coupling weak enough and turned on, those mass ratios and mixing angles can be perturbatively calculated, and the results can fit experimental data very well. The neutrino mass matrix is accommodated through a small global symmetry breaking operator. Secondly, by analyzing the symmetry breaking pattern and pseudo Nambu-Goldstone bosons in our model, one U(1) symmetry is found to be unbroken by any of the phenomenologically necessary interactions of the effective field theory, except for QCD anomalies. Thus it can he used as a Peccei-Quinn symmetry to solve the strong CP problem. Then we study the phenomenological consequences of our model such as flavor-changing neutral current processes, which constrain the family gauge symmetry breaking scale to be above 1000 TeV. Finally, in order to address the CP violation in the standard model, we study generally the spontaneous breaking of discrete symmetries in spontaneously broken gauge theories. Depending on the parameters in the effective theory, the discrete symmetry can be broken and the intrinsic violation is naturally of order unity.

Bai, Yang

321

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

322

Quantum Spherical Spins with Local Symmetry  

E-print Network

We construct a quantum system of spherical spins with a continuous local symmetry. The model is exactly soluble in the thermodynamic limit and exhibits a number of interesting properties. We show that the local symmetry is spontaneously broken at finite as well as zero temperatures, implying the existence of classical and quantum phase transitions with a nontrivial critical behavior. The dynamical generation of gauge fields and the equivalence with the $CP^{(\\mathcal{N}-1)}$ model in the limit $\\mathcal{N}\\rightarrow\\infty$ are investigated. The dynamical generation of gauge fields is a consequence of the restoration of the local symmetry.

Gomes, Pedro R S

2014-01-01

323

Spacetime Symmetries of the Quantum Hall Effect  

E-print Network

We study the symmetries of non-relativistic systems with an emphasis on applications to the fractional quantum Hall effect. A source for the energy current of a Galilean system is introduced and the non-relativistic diffeomorphism invariance studied in previous work is enhanced to a full spacetime symmetry, allowing us to derive a number of Ward identities. These symmetries are smooth in the massless limit of the lowest Landau level. We develop a formalism for Newton-Cartan geometry with torsion to write these Ward identities in a covariant form. Previous results on the connection between Hall viscosity and Hall conductivity are reproduced.

Michael Geracie; Dam Thanh Son; Chaolun Wu; Shao-Feng Wu

2014-07-04

324

Spacetime Symmetries of the Quantum Hall Effect  

E-print Network

We study the symmetries of non-relativistic systems with an emphasis on applications to the fractional quantum Hall effect. A source for the energy current of a Galilean system is introduced and the non-relativistic diffeomorphism invariance studied in previous work is enhanced to a full spacetime symmetry, allowing us to derive a number of Ward identities. These symmetries are smooth in the massless limit of the lowest Landau level. We develop a formalism for Newton-Cartan geometry with torsion to write these Ward identities in a covariant form. Previous results on the connection between Hall viscosity and Hall conductivity are reproduced.

Geracie, Michael; Wu, Chaolun; Wu, Shao-Feng

2014-01-01

325

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

326

Global Symmetries and N=2 SUSY  

E-print Network

We prove that N=2 theories that arise by taking n free hypermultiplets and gauging a subgroup of Sp(n), the non-R global symmetry of the free theory, have a remaining global symmetry which is a direct sum of unitary, symplectic, and special orthogonal factors. This implies that theories that have SU(N) but not U(N) global symmetries, such as Gaiotto's T_N theories, are not likely to arise as IR fixed points of RG flows from weakly coupled N=2 gauge theories.

Jock McOrist; Ilarion V. Melnikov; Brian Wecht

2013-12-12

327

Analysis of pulsed-neutron powder diffraction patterns of the icosahedral quasicrystals Pd3Siu and AlCuLiMg (three alloys) as twinned cubic crystals with large units.  

PubMed Central

The low-Q peaks on three pulsed-neutron powder patterns (total, U differential, and Pd differential) of the icosahedral quasicrystal Pd3SiU have been indexed on the basis of an assumed cubic structure of the crystals that by icosahedral twinning form the quasicrystal. The primitive unit cube is found to have edge length 56.20 A and to contain approximately 12,100 atoms. Similar analyses of pulsed-neutron patterns of Al55Cu10Li35, Al55Cu10Li30Mg5, and Al510Cu125Li235Mg130 give values of the cube edge length 58.3, 58.5, and 58.4 A, respectively, with approximately 11,650 atoms in the unit cube. It is suggested that the unit contains eight complexes in the beta-W positions, plus some small interstitial groups of atoms, with each complex consisting of a centered icosahedron of 13 clusters, each of 116 atoms with the icosahedral structure found in the body-centered cubic crystal Mg32(Al,Zn)49. PMID:11607201

Pauling, L

1991-01-01

328

On the electronic structure and stability of icosahedral r-X2Z10H12 and Z12H(12)(2-) clusters; r = {ortho, meta, para}, X = {C, Si}, Z = {B, Al}.  

PubMed

We report on the electronic structure of the 12-vertex icosahedral clusters r-X(2)Z(10)H(12) and Z(12)H(12)(2-), where X = {C, Si} and Z = {B, Al}. The least stable cluster--with the lowest HOMO-LUMO gap (E(g))--corresponds to the ortho-X(2)Z(10)H(12) isomers for all values of X = {C, Si} and Z = {B, Al}. The well-known energetic order E(para) < E(meta) < E(ortho) for r-carboranes is also valid for all compounds except r-C(2)Al(10)H(12). Substitution of two atoms of carbon or silicon into the icosahedral cage B(12)H(12)(2-) enhances considerably the stability of the system as analyzed from E(g) gaps, as opposite to Al(12)H(12)(2-), where similar gaps are found upon double carbon or silicon substitution regardless of the positions in the cage. In order to highlight similarities and differences in the title clusters, topological analysis of the electron density was performed, together with analysis of the deviation from polyhedron icosahedral form with (i) volumes, skewness and kurtosis calculations; and (ii) continuous shape measures. PMID:20442949

Oliva, Josep M; Schleyer, Paul von Ragué; Aullón, Gabriel; Burgos, José I; Fernández-Barbero, Antonio; Alkorta, Ibon

2010-05-21

329

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

330

Spatial Symmetries of the Local Densities  

SciTech Connect

Spatial symmetries of the densities appearing in the nuclear Density Functional Theory are discussed. General forms of the local densities are derived by using methods of construction of isotropic tensor fields. The spherical and axial cases are considered.

Rohozinski, S. [Warsaw University; Dobaczewski, J. [Warsaw University; Nazarewicz, Witold [ORNL

2010-01-01

331

Symmetry reduction of quasi-free states  

NASA Astrophysics Data System (ADS)

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

Torre, C. G.

2009-06-01

332

Symmetry reduction of quasi-free states  

SciTech Connect

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

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

2009-06-15

333

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

334

On a symmetry relating gravity with antigravity  

E-print Network

I investigate the impact of a "would be" fundamental symmetry of the laws of nature under the interchange of gravity and antigravity, on the understanding of negative energies in general relativity. For this purpose a toy model that is based on Einstein-Hilbert gravity with two minimally coupled self-interacting scalar fields is explored, where the second (exotic) scalar field with negative energy density may be regarded, alternatively, as an antigravitating field with positive energy. Spontaneous breakdown of reflection symmetry is then considered in order to discuss the implications the proposed "would be" fundamental symmetry might have for the vanishing of the cosmological constant. A possible connection of the gravity-antigravity symmetry with the so called quintom field is also explored.

Israel Quiros

2014-09-18

335

On a symmetry relating gravity with antigravity  

E-print Network

I investigate the impact of a "would be" fundamental symmetry of the laws of nature under the interchange of gravity and antigravity, on the understanding of negative energies in general relativity. For this purpose a toy model that is based on Einstein-Hilbert gravity with two minimally coupled self-interacting scalar fields is explored, where the second (exotic) scalar field with negative energy density may be regarded, alternatively, as an antigravitating field with positive energy. Spontaneous breakdown of reflection symmetry is then considered in order to discuss the implications the proposed "would be" fundamental symmetry might have for the vanishing of the cosmological constant. A possible connection of the gravity-antigravity symmetry with the so called quintom field is also explored.

Quiros, Israel

2014-01-01

336

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.

Bevan, Adrian J

2014-01-01

337

HIGHENERGY NUCLEAR PHYSICS WITH LORENTZ SYMMETRY VIOLATION  

E-print Network

HIGH­ENERGY NUCLEAR PHYSICS WITH LORENTZ SYMMETRY VIOLATION Luis GONZALEZ­MESTRES 1 Laboratoire de­energy nuclear physics. 1 Introduction In previous papers (Gonzalez­Mestres, 1997a and 1997b) we suggested that

338

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

339

Folding and Symmetry: 1.5  

NSDL National Science Digital Library

These 4 activities, part of the Mathematics Developmental Continuum of the State of Victoria, Australia, are intended to introduce young learners to line and rotational symmetry. Supporting documents, materials, and progress indicators are included.

2009-09-24

340

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

341

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

342

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.

Eakins, B

2012-01-01

343

Symmetries and Systematics of Doubly Heavy Hadrons  

NASA Astrophysics Data System (ADS)

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.

Eakins, B.; Roberts, W.

344

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

345

Breaking so(4) symmetry without degeneracy lift  

E-print Network

On the example of the quantum motion on S3, perturbed by the trigonometric Scarf potential (Scarf I) with one quantized and one continuous parameter, we argue that the breakdown by external scales of a Lie-algebraic symmetry of a quantum system must not necessarily amount to a lift of the degeneracies in the spectrum. To be specific, we show that though the spectrum under discussion carries hydrogen-like degeneracies, the corresponding wave functions do not transform according to so(4) carrier spaces but are finite linear combinations of so(4) representation functions describing carrier spaces of different dimensionality. Alternatively, these decompositions are also expansions in powers of the symmetry breaking scale, and allow to quantitatively describe the order to which the symmetry is violated. We conclude on the general possibility to break perturbatively an intact Lie algebraic symmetry, so(4) in our case, by external scales, such as the continuous parameter of Scarf I, and without leaving trace in the ...

Pallares-Rivera, A; Kirchbach, M

2013-01-01

346

Neutrino mass textures and partial ? -? symmetry  

NASA Astrophysics Data System (ADS)

We discuss the viability of the ? -? interchange symmetry imposed on the neutrino mass matrix in the flavor space. Whereas the exact symmetry is shown to lead to textures of a completely degenerate spectrum, which is incompatible with the neutrino oscillation data, introducing small perturbations into the preceding textures, inserted in a minimal way, leads, however, to four deformed textures representing an approximate ?-? symmetry. We motivate the form of these "minimal" textures, which disentangle the effects of the perturbations, and present some concrete realizations assuming exact ? -? at the Lagrangian level but at the expense of adding new symmetries and matter fields. We find that all of these deformed textures are capable of accommodating the experimental data, and in all types of neutrino mass hierarchies, particularly the nonvanishing value for the smallest mixing angle.

Lashin, E. I.; Chamoun, N.; Hamzaoui, C.; Nasri, S.

2014-05-01

347

Tests of Spacetime Symmetry with Particle Traps  

E-print Network

Lorentz and CPT symmetry have been tested at high precision in numerous experiments. A general theoretical framework incorporating possible Lorentz and CPT violation in an extension of the standard model of particle physics has been developed. In this framework, analyses of several precision experiments have been performed to find unsuppressed symmetry-violating signals. This paper discusses features of the theory, presents results for trapped-particle systems, and reports bounds from recent experiments.

Neil Russell

2000-11-13

348

Algebraic cluster model with tetrahedral symmetry  

SciTech Connect

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

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

2010-12-23

349

Infinite Chiral Symmetry in Four Dimensions  

E-print Network

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 ${\\mathcal N}=2$ superconformal symmetry.

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

2013-12-18

350

Real fermionic symmetry in type II supergravity  

NASA Astrophysics Data System (ADS)

It is known that the transformations of fermionic T-duality, derived from the worldsheet theory, generically transform real supergravity backgrounds to complex supergravity backgrounds. We consider the low-energy target space theory and show that the type II supergravity equations admit a symmetry that transforms the Ramond-Ramond fields and the dilaton. The transformations given by this symmetry involve Killing spinors and include the transformations of Berkovits and Maldacena. However, we show that they also allow real transformations.

Godazgar, Hadi; Perry, Malcolm J.

2011-01-01

351

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

352

Sign-symmetry of temperature structure functions.  

PubMed

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

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

2004-06-01

353

Nuclear symmetry energy: An experimental overview  

Microsoft Academic Search

The nuclear symmetry energy is a fundamental quantity important for studying the structure of systems as diverse as the atomic\\u000a nucleus and the neutron star. Considerable efforts are being made to experimentally extract the symmetry energy and its dependence\\u000a on nuclear density and temperature. In this article, the experimental studies carried out up-to-date and their current status\\u000a are reviewed.

D. V. Shetty; S. J. Yennello

2010-01-01

354

Noether's second theorem for BRST symmetries  

SciTech Connect

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

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

2005-05-01

355

Neutrino Masses and Mixings from Continuous Symmetries  

E-print Network

Flavour symmetries are fundamental tools in the search for an explanation to the flavour puzzle: fermion mass hierarchies, the neutrino mass ordering, the differences between the mixing matrices in the quark and lepton sector, can all find an explanation in models where the fermion generations undergo specific geometric relations. An overview on the implementation of continuous symmetries in the flavour sector is presented here, focussing on the lepton sector.

Merlo, Luca

2014-01-01

356

Social influence, evolutionary theory, and symmetry  

E-print Network

of the UNIVERSITY UNDERGRADUATE RESEARCH FELLOWS April 2000 Group: Psychology 2 SOCIAL INFLUENCE, EVOLUTIONARY THEORY, AND SYMMETRY A Senior Honors Thesis By AMY ELIZABETH PINXHAM Submitted to the Office of Honors Programs k Academic Scholarships Texas... 2000 Group: Psychology 2 ABSTRACT Social Influence, Evolutionary Theory, and Symmetry. (April 2000) Amy Elizabeth Pinkham Department of Psychology Texas A&M University Fellows Advisor: Dr. William G. Graziano Department of Psychology...

Pinkham, Amy Elizabeth

2013-02-22

357

Asymptotic symmetries in an optical lattice  

E-print Network

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

G. Gaeta

2005-10-02

358

Local Conformal Symmetry: the Missing Symmetry Component for Space and Time  

E-print Network

Local conformal symmetry is usually considered to be an approximate symmetry of nature, which is explicitly and badly broken. Arguments are brought forward here why it has to be turned into an exact symmetry that is spontaneously broken. As in the B.E.H. mechanism in Yang-Mills theories, we then will have a mechanism for disclosing the small-distance structure of the gravitational force. The symmetry could be as fundamental as Lorentz invariance, and guide us towards a complete understanding of physics at the ultra short distance scale.

Hooft, Gerard T

2014-01-01

359

A mimetic, semi-implicit, forward-in-time, finite volume shallow water model: comparison of hexagonal-icosahedral and cubed sphere grids  

NASA Astrophysics Data System (ADS)

A new algorithm is presented for the solution of the shallow water equations on quasi-uniform spherical grids. It combines a mimetic finite volume spatial discretization with a Crank-Nicolson time discretization of fast waves and an accurate and conservative forward-in-time advection scheme for mass and potential vorticity (PV). The algorithm is implemented and tested on two families of grids: hexagonal-icosahedral Voronoi grids, and modified equiangular cubed-sphere grids. Results of a variety of tests are presented, including convergence of the discrete scalar Laplacian and Coriolis operators, advection, solid body rotation, flow over an isolated mountain, and a barotropically unstable jet. The results confirm a number of desirable properties for which the scheme was designed: exact mass conservation, very good available energy and potential enstrophy conservation, consistent mass, PV and tracer transport, and good preservation of balance including vanishing ∇ × ∇, steady geostrophic modes, and accurate PV advection. The scheme is stable for large wave Courant numbers and advective Courant numbers up to about 1. In the most idealized tests the overall accuracy of the scheme appears to be limited by the accuracy of the Coriolis and other mimetic spatial operators, particularly on the cubed sphere grid. On the hexagonal grid there is no evidence for damaging effects of computational Rossby modes, despite attempts to force them explicitly.

Thuburn, J.; Cotter, C. J.; Dubos, T.

2013-12-01

360

Spectroscopic observation of (N{sub 2}){sub 2} dimers in free icosahedral N{sub 2} and Ar-N{sub 2} clusters  

SciTech Connect

Supersonic-jet luminescence spectroscopy was applied to study vibronic transitions in icosahedral N{sub 2} and Ar-N{sub 2} clusters having from 100 to 400 particles per cluster. In the case of mixed Ar-N{sub 2} clusters, the w {sup 1}{Delta}{sub u}{yields} X {sup 1}{Sigma}{sub g}{sup +} transitions were observed to occur in single N{sub 2} molecules in an Ar environment, in very much the same way as in Ar-N{sub 2} bulk samples. In N{sub 2} clusters, however, a band series was detected which, to our knowledge, was never observed earlier. In the spectra of Ar-N{sub 2} clusters, this series coexisted with the ''bulk''w {sup 1}{Delta}{sub u}{yields} X{sup 1}{Sigma}{sub g}{sup +} transitions. Our analysis demonstrated that the series should be assigned to emission of van der Waals (N{sub 2}){sub 2} dimers from inside clusters. Earlier, such dimers were only observed in molecular beams and gaseous nitrogen; this paper reports their observation in the solid phase of nitrogen. Our results can be of interest from the viewpoint of producing polymeric nitrogen since (N{sub 2}){sub 2} dimers can be considered to be a starting species for its synthesis.

Doronin, Yu. S.; Libin, M. Yu.; Samovarov, V. N.; Vakula, V. L. [B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Lenin Avenue, Kharkiv, 61103 (Ukraine)

2011-08-15

361

Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc  

NASA Astrophysics Data System (ADS)

A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn6Sc [1]. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a ‘single molecule’ and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to Tc = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.

Euchner, H.; Yamada, T.; Rols, S.; Ishimasa, T.; Kaneko, Y.; Ollivier, J.; Schober, H.; Mihalkovic, M.; de Boissieu, M.

2013-03-01

362

Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.  

PubMed

A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn(6)Sc. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T(c) = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system. PMID:23411496

Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Kaneko, Y; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M

2013-03-20

363

Averaging Tens to Hundreds of Icosahedral Particle Images to Resolve Protein Secondary Structure Elements using a Multi-Path Simulated Annealing Optimization Algorithm  

PubMed Central

Accurately determining a cryoEM particle’s alignment parameters is crucial to high resolution single particle 3-D reconstruction. We developed Multi-Path Simulated Annealing, a Monte Carlo type of optimization algorithm, for globally aligning the center and orientation of a particle simultaneously. A consistency criterion was developed to ensure the alignment parameters are correct and to remove some bad particles from a large pool of images of icosahedral particles. Without using any a priori model, this procedure is able to reconstruct a structure from a random initial model. Combining the procedure above with a new empirical double threshold particle selection method, we are able to pick tens of best quality particles to reconstruct a subnanometer resolution map from scratch. Using the best 62 particles of rice dwarf virus, the reconstruction reached 9.6Å resolution at which 4 helices of the P3A subunit of RDV are resolved. Furthermore, with the 284 best particles, the reconstruction is improved to 7.9Å resolution, and 21 of 22 helices and 6 of 7 beta sheets are resolved. PMID:17698370

Liu, Xiangan; Jiang, Wen; Jakana, Joanita; Chiu, Wah

2007-01-01

364

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

365

Devil's staircases in loop networks with symmetry locking  

NASA Astrophysics Data System (ADS)

In this work we analyze symmetry locking phenomena in loop networks with periodically switched connections. Exploiting the spatio-temporal symmetry properties of the system, we compute the rotation numbers of locked periodic regimes for which symmetry locking occurs. As a bifurcation parameter is varied, we compute the complete Devil's staircase reporting the symmetry of the locked periodic regimes.

Russo, Lucia; Mancusi, Erasmo

2013-10-01

366

Non-abelian symmetries in tensor networks: a quantum symmetry space approach  

E-print Network

A general framework for non-abelian symmetries is presented for matrix-product and tensor-network states in the presence of orthonormal local as well as effective basis sets. The two crucial ingredients, the Clebsch-Gordan algebra for multiplet spaces as well as the Wigner-Eckart theorem for operators, are accounted for in a natural, well-organized, and computationally straightforward way. The unifying tensor-representation for quantum symmetry spaces, dubbed QSpace, is particularly suitable to deal with standard renormalization group algorithms such as the numerical renormalization group (NRG), the density matrix renormalization group (DMRG), or also more general tensor networks such as the multi-scale entanglement renormalization ansatz (MERA). In this paper, the focus is on the application of the non-abelian framework within the NRG. A detailed analysis is given for a fully screened spin-3/2 three-channel Anderson impurity model in the presence of conservation of total spin, particle-hole symmetry, and SU(3) channel symmetry. The same system is analyzed using several alternative symmetry scenarios. This includes the more traditional symmetry setting SU(2)^4, the larger symmetry SU(2)*U(1)*SU(3), and their much larger enveloping symplectic symmetry SU(2)*Sp(6). These are compared in detail, including their respective dramatic gain in numerical efficiency. In the appendix, finally, an extensive introduction to non-abelian symmetries is given for practical applications, together with simple self-contained numerical procedures to obtain Clebsch-Gordan coefficients and irreducible operators sets. The resulting QSpace tensors can deal with any set of abelian symmetries together with arbitrary non-abelian symmetries with compact, i.e. finite-dimensional, semi-simple Lie algebras.

Andreas Weichselbaum

2012-02-25

367

Energy bands: Chern numbers and symmetry  

SciTech Connect

Energy bands formed by rotation-vibrational states of molecules in the presence of symmetry and their qualitative modifications under variation of some control parameters are studied within the semi-quantum model. Rotational variables are treated as classical whereas a finite set of vibrational states is considered as quantum. In the two-state approximation the system is described in terms of a fiber bundle with the base space being a two-dimensional sphere, the classical phase space for rotational variables. Generically this rank 2 complex vector bundle can be decomposed into two complex line bundles characterized by a topological invariant, the first Chern class. A general method of explicit calculation of Chern classes and of their possible modifications under variation of control parameters in the presence of symmetry is suggested. The construction of iso-Chern diagrams which split the space of control parameters into connected domains with fixed Chern numbers is suggested. A detailed analysis of the rovibrational model Hamiltonian for a D{sub 3} invariant molecule possessing two vibrational states transforming according to the two-dimensional irreducible representation is done to illustrate non-trivial restrictions imposed by symmetry on possible values of Chern classes. - Highlights: > Complex line bundles associated with eigenvalues of 2x2 Hermitian matrix Hamiltonians. > Hamiltonians are defined on the 2-sphere and invariant under symmetry groups. > Symmetry permits only some special integers as Chern numbers. > For SO(2) symmetry, the possible values are 0, {+-}K, where K is an index of the representation. > For D{sub 3} symmetry, the possible values are {+-}2, {+-}4 within our model Hamiltonians.

Iwai, T., E-mail: iwai@amp.i.kyoto-u.ac.jp [Kyoto University, 606-8501 Kyoto (Japan); Zhilinskii, B., E-mail: zhilin@univ-littoral.fr [Kyoto University, 606-8501 Kyoto (Japan); Universite du Littoral Cote d'Opale, 59140 Dunkerque (France)

2011-12-15

368

Facial symmetry detection ability changes across the menstrual cycle.  

PubMed

The effects of menstrual cycle phase and hormones on women's visual ability to detect symmetry and visual preference for symmetry were examined. Participants completed tests of symmetry detection and preference for male facial symmetry at two of three menstrual cycle phases (menses, periovulatory, and luteal). Women were better at detecting facial symmetry during the menses than luteal phase of their cycle. A trend indicated the opposite pattern for dot symmetry detection. Similarly, change in salivary progesterone levels across the cycle was negatively related to change in facial symmetry detection scores. However, there was no clear evidence of a greater preference for facial symmetry at any cycle phase, despite an overall preference for facial symmetry across phases. These findings suggest a menses phase advantage and a low progesterone advantage in women's ability to detect facial symmetry. The results are discussed in the context of hormonal, evolutionary mate selection, and functional neurocognitive theories. PMID:17316956

Oinonen, Kirsten A; Mazmanian, Dwight

2007-05-01

369

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

370

Gauge Noninvariance as Tests of Emergent Gauge Symmetry  

NASA Astrophysics Data System (ADS)

We motivate the concept of emergent gauge symmetry and discuss ways that this concept can be tested. The key idea is that if a symmetry is emergent, one should look for small violations of this symmetry because the underlying fundamental theory does not contain the symmetry. We describe our recent work implementing this idea in the gravity sector. We also describe the reasons why violations of gauge symmetry may well be linked to violations of Lorentz invariance.

Donoghue, John F.; Anber, Mohamed M.; Aydemir, Ufuk

2011-12-01

371

Group Parametrized Tunneling and Local Symmetry Conditions  

NASA Astrophysics Data System (ADS)

Recently, Hougen showed an ad hoc symmetry-based parameterization scheme for analyzing tunneling dynamics and high resolution spectra of fluxional molecular structure similar to S-parameter analysis of superfine structure in SF_6 or NH_3 maser inversion dynamics by Feynman et.al. The problem is that ad hoc parametrization, like path integration in general, can lead to logjams of parameters or ``paths'' with no way to pick out the relevant ones. We show a way to identify and use relevant parameters for a tunneling Hamiltonian H having global G-symmetry-defined bases by first expressing H as a linear combination bar ? ^i {bar g}_i of operators in dual symmetry group bar G. The coefficients bar ? ^i are parameters that define a complete set of allowed paths for any H with G-symmetry and are related thru spectral decomposition of G to eigensolutions of H. Quantum G vs.bar G duality generalizes lab -vs. -body and state -vs. -particle. The number of relevant bar ? ^i-parameters is reduced if a system tends to stick in states of a local symmetry subgroup LsubsetG so the H spectrum forms level clusters labeled by induced representations d(?)(L)\\uparrowG. A cluster-(?) has one E(epsilon)-level labeled by G species (epsilon) for each L species (?) in Depsilon(G)downarrowL by Frobenius reciprocity. Then we apply local symmetry conditions to each irrep Depsilon(bar ? ^i {bar g}_i) that has already been reduced with respect to local symmetry L. This amounts to setting each off-diagonal component Dj,kepsilon(H) to zero. Local symmetry conditions may tell which bar ? ^i-parameters are redundant or zero and directly determine d(?)\\uparrowG tunneling matrix eigenvalues that give E(epsilon)-levels as well as eigenvectors. Otherwise one may need to choose a particular localizing subgroup chain LsubsetL_1subsetL_2...G and further reduce the number of path parameters to facilitate spectral fitting. J.T. Hougen, 2009 MSS RJ01, {J Mol Spect 123, 197 (1987) W.G. Harter and J. C. Mitchell, 2009 MSS RJ05 (See also following talk.) R.P. Feynman, R. B. Leighton, M. Sands, Lectures on Physics Vol.3 (Addison Wesley 1964) p.9-1 W.G. Harter, Principles of Symmetry, Dynamics, and Spectroscopy, (Wiley Interscience, 1993) p.265

Harter, William; Mitchell, Justin

2010-06-01

372

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

373

Symmetry Energy II: Isobaric Analog States  

E-print Network

Using excitation energies to isobaric analog states (IAS) and charge invariance, we extract nuclear symmetry coefficients, from a mass formula, on a nucleus-by-nucleus basis. Consistently with charge invariance, the coefficients vary weakly across an isobaric chain. However, they change strongly with nuclear mass and range from a_a~10 MeV at mass A~10 to a_a~22 MeV at A~240. Following the considerations of a Hohenberg-Kohn functional for nuclear systems, we determine how to find in practice the symmetry coefficient using neutron and proton densities, even when those densities are simultaneously affected by significant symmetry-energy and Coulomb effects. These results facilitate extracting the symmetry coefficients from Skyrme-Hartree-Fock (SHF) calculations, that we carry out using a variety of Skyrme parametrizations in the literature. For the parametrizations, we catalog novel short-wavelength instabilities. In comparing the SHF and IAS results for the symmetry coefficients, we arrive at narrow (+-2.4 MeV)...

Danielewicz, Pawel

2014-01-01

374

Symmetry in social exchange and health  

NASA Astrophysics Data System (ADS)

Symmetry is a relevant concept in sociological theories of exchange. It is rooted in the evolutionary old norm of social reciprocity and is particularly important in social contracts. Symmetry breaking through violation of the norm of reciprocity generates strain in micro-social systems and, above all, in victims of non-symmetric exchange. In this contribution, adverse healthconsequences of symmetry breaking in contractual social exchange are analysed, with a main focus on the employment contract. Scientific evidence is derived from prospective epidemiological studies testing the model of effort-reward imbalance at work. Overall, a twofold elevated risk of incident disease is observed in employed men and women who are exposed to non-symmetric exchange. Health risks include coronary heart disease, depression and alcohol dependence, among others. Preliminary results suggest similar effects on health produced by symmetry breaking in other types of social relationships (e.g. partnership, parental roles). These findings underline the importance of symmetry in contractual social exchange for health and well-being.

Siegrist, Johannes

2005-10-01

375

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

376

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

377

Gaussian states and geometrically uniform symmetry  

NASA Astrophysics Data System (ADS)

Quantum Gaussian states can be considered as the majority of the practical quantum states used in quantum communications and more generally in quantum information. Here we consider their properties in relation to the geometrically uniform symmetry, a property of quantum states that greatly simplifies the derivation of the optimal decision by means of the square root measurements. In a general framework of the N-mode Gaussian states we show the general properties of this symmetry and the application of the optimal quantum measurements. An application example is presented to quantum communication systems employing pulse position modulation. We prove that the geometrically uniform symmetry can be applied to the general class of multimode Gaussian states.

Cariolaro, Gianfranco; Corvaja, Roberto; Pierobon, Gianfranco

2014-10-01

378

Automorphic Lie algebras with dihedral symmetry  

NASA Astrophysics Data System (ADS)

The concept of automorphic Lie algebras arises in the context of reduction groups introduced in the early 1980s in the field of integrable systems. automorphic Lie algebras are obtained by imposing a discrete group symmetry on a current algebra of Krichever-Novikov type. Past work shows remarkable uniformity between algebras associated to different reduction groups. For example, if the base Lie algebra is \\mathfrak{s}{{\\mathfrak{l}}_{2}}({C}) and the poles of the automorphic Lie algebra are restricted to an exceptional orbit of the symmetry group, changing the reduction group does not affect the Lie algebra structure. In this research we fix the reduction group to be the dihedral group and vary the orbit of poles as well as the group action on the base Lie algebra. We find a uniform description of automorphic Lie algebras with dihedral symmetry, valid for poles at exceptional and generic orbits.

Knibbeler, V.; Lombardo, S.; Sanders, J. A.

2014-09-01

379

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

380

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

381

Spontaneous symmetry breaking in amnestically induced persistence.  

PubMed

We investigate a recently proposed non-Markovian random walk model characterized by loss of memories of the recent past and amnestically induced persistence. We report numerical and analytical results showing the complete phase diagram, consisting of four phases, for this system: (i) classical nonpersistence, (ii) classical persistence, (iii) log-periodic nonpersistence, and (iv) log-periodic persistence driven by negative feedback. The first two phases possess continuous scale invariance symmetry, however, log-periodicity breaks this symmetry. Instead, log-periodic motion satisfies discrete scale invariance symmetry, with complex rather than real fractal dimensions. We find for log-periodic persistence evidence not only of statistical but also of geometric self-similarity. PMID:18517569

da Silva, Marco Antonio Alves; Viswanathan, G M; Ferreira, A S; Cressoni, J C

2008-04-01

382

Symmetry methods for harmonically trapped, interacting particles  

NASA Astrophysics Data System (ADS)

We present a new method for exploiting the symmetries of interacting few-body systems trapped in harmonic potentials to achieve efficient numerical calculations of energy eigenstates. Precision experiments with ultracold atoms trapped in deep optical wells, as well as connections to recombination loss rates in trapped BECs, have driven experimental interest in this topic. Our method has two key elements. First, transformations from the particle observables into the center-of-mass/Jacobi observables can be implemented using the U(Nd) symmetries of N harmonic oscillators in d dimensions. Second, particle exchange symmetries are realized geometrically as orthogonal transformations in Jacobi relative hypercoordinates. Despite this apparent mathematical complexity, the results are easy to implement and interpret, and the method provides simple classifications of particle clustering in configurations and eigenstates. As a side benefit, the entanglement spectroscopy of few-body systems with tunable interactions can be explored.

Harshman, Nathan

2013-03-01

383

Gaussian states and geometrically uniform symmetry  

E-print Network

Quantum Gaussian states can be considered as the majority of the practical quantum states used in quantum communications and more generally in quantum information. Here we consider their properties in relation with the geometrically uniform symmetry, a property of quantum states that greatly simplifies the derivation of the optimal decision by means of the square root measurements. In a general framework of the $N$-mode Gaussian states we show the general properties of this symmetry and the application of the optimal quantum measurements. An application example is presented, to quantum communication systems employing pulse position modulation. We prove that the geometrically uniform symmetry can be applied to the general class of multimode Gaussian states.

Gianfranco Cariolaro; Roberto Corvaja; Gianfranco Pierobon

2014-10-20

384

Investigating Lorentz and CPT Symmetry with Antihydrogen  

E-print Network

This talk discusses theoretical aspects of tests of CPT and Lorentz Symmetry that will in principle be possible with trapped antihydrogen. The framework is the standard-model extension, which admits minuscule violations of CPT and Lorentz symmetry in a general manner without giving up other features of the standard model of particle physics. Spectroscopic transitions in hydrogen and antihydrogen that exhibit leading-order effects are identified. Such comparisons of spectral frequencies in antimatter with the corresponding frequencies in regular matter will bound parameter combinations that are not accessible with regular-matter atoms alone.

Neil Russell

2002-09-23

385

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.

Donos, Aristomenis

2014-01-01

386

A new symmetry in collective motion  

SciTech Connect

The purity of intrinsic states of nuclei with respect to a proton-neutron boson symmetry (F-spin) is shown to be largely determined by the difference between proton and neutron deformations and not by whether the Hamiltonian is an F-spin scalar. F-spin mixing in the ground state band of {sup 165}Ho is estimated using recent pion single-charge-exchange data. A B(M1) sum rule is derived using F-spin symmetry. 27 refs., 1 fig.

Ginocchio, J.N.

1991-01-01

387

Symmetries of Bianchi I space-times  

NASA Astrophysics Data System (ADS)

All diagonal proper Bianchi I space-times are determined which admit certain important symmetries. It is shown that for Homothetic motions, Conformal motions and Kinematic Self-Similarities the resulting space-times are defined explicitly in terms of a set of parameters, whereas Affine Collineations, Ricci Collineations, and Curvature Collineations, if they are admitted, they determine the metric modulo certain algebraic conditions. In all cases the symmetry vectors are explicitly computed. The physical and the geometrical consequences of the results are discussed and a new anisotropic fluid, physically valid solution which admits a proper conformal Killing vector, is given.

Tsamparlis, Michael; Apostolopoulos, Pantelis S.

2000-11-01

388

The "Ghost" Symmetry of the BKP hierarchy  

E-print Network

In this paper, we systematically develop the "ghost" symmetry of the BKP hierarchy through its actions on the Lax operator $L$, the eigenfunctions and the $\\tau$ function. In this process, the spectral representation of the eigenfunctions and a new potential are introduced by using squared eigenfunction potential(SEP) of the BKP hierarchy. Moreover, the bilinear identity of the constrained BKP hierarchy and Adler-Shiota-van-Moerbeke formula of the BKP hierarchy are re-derived compactly by means of the spectral representation and "ghost" symmetry.

Jipeng Cheng; Jingsong He; Sen Hu

2010-03-31

389

Holographic metals and insulators with helical symmetry  

NASA Astrophysics Data System (ADS)

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.

Donos, Aristomenis; Goutéraux, Blaise; Kiritsis, Elias

2014-09-01

390

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

391

Chimera Death: Symmetry Breaking in Dynamical Networks  

NASA Astrophysics Data System (ADS)

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.

Zakharova, Anna; Kapeller, Marie; Schöll, Eckehard

2014-04-01

392

Symmetries, Supersymmetries, and Pairing in Nuclei  

SciTech Connect

These summer school lectures cover the use of algebraic techniques in various subfields of nuclear physics. After a brief description of groups and algebras, concepts of dynamical symmetry, dynamical supersymmetry, and supersymmetric quantum mechanics are introduced. Appropriate tools such as quasiparticles, quasispin, and Bogoliubov transformations are discussed with an emphasis on group theoretical foundations of these tools. To illustrate these concepts three physics applications are worked out in some detail: i) Pairing in nuclear physics; ii) Subbarrier fusion and associated group transformations; and iii) Symmetries of neutrino mass and of a related neutrino many-body problem.

Balantekin, A. B. [Physics Department, University of Wisconsin, Madison, WI 53706 (United States)

2011-03-21

393

Local unitary symmetries of hypergraph states  

E-print Network

Hypergraph states are multiqubit states whose combinatorial description and entanglement properties generalize the well-studied class of graph states. Graph states are important in applications such as measurement-based quantum computation and quantum error correction. The study of hypergraph states, with their richer multipartite entanglement and other nonlocal properties, has a promising outlook for new insight into multipartite entanglement. We present results analyzing local unitary symmetries of hypergraph states, including both continuous and discrete families of symmetries. In particular, we show how entanglement types can be detected and distinguished by certain configurations in the hypergraphs from which hypergraph states are constructed.

David W. Lyons; Daniel J. Upchurch; Scott N. Walck; Chase D. Yetter

2014-10-15

394

Symmetry energy II: Isobaric analog states  

NASA Astrophysics Data System (ADS)

Using excitation energies to isobaric analog states (IAS) and charge invariance, we extract nuclear symmetry coefficients, representing a mass formula, on a nucleus-by-nucleus basis. Consistently with charge invariance, the coefficients vary weakly across an isobaric chain. However, they change strongly with nuclear mass and range from aa˜10 MeV at mass A˜10 to aa˜22 MeV at A˜240. Variation with mass can be understood in terms of dependence of nuclear symmetry energy on density and the rise in importance of low densities within nuclear surface in smaller systems. At A?30, the dependence of coefficients on mass can be well described in terms of a macroscopic volume-surface competition formula with aaV?33.2 MeV and aaS?10.7 MeV. Our further investigation shows, though, that the fitted surface symmetry coefficient likely significantly underestimates that for the limit of half-infinite matter. Following the considerations of a Hohenberg-Kohn functional for nuclear systems, we determine how to find in practice the symmetry coefficient using neutron and proton densities, even when those densities are simultaneously affected by significant symmetry-energy and Coulomb effects. These results facilitate extracting the symmetry coefficients from Skyrme-Hartree-Fock (SHF) calculations, that we carry out using a variety of Skyrme parametrizations in the literature. For the parametrizations, we catalog novel short-wavelength instabilities. In our further analysis, we retain only those parametrizations which yield systems that are adequately stable both in the long- and short-wavelength limits. In comparing the SHF and IAS results for the symmetry coefficients, we arrive at narrow (±2.4 MeV) constraints on the symmetry-energy values S(?) at 0.04???0.13 fm. Towards normal density the constraints significantly widen, but the normal value of energy aaV and the slope parameter L are found to be strongly correlated. To narrow the constraints, we reach for the measurements of asymmetry skins and arrive at aaV=30.2-33.7 MeV and L=35-70 MeV, with those values being again strongly positively correlated along the diagonal of their combined region. Inclusion of the skin constraints allows to narrow the constraints on S(?), at 0.04???0.13 fm, down to ±1.1 MeV. Several microscopic calculations, including variational, Bruckner-Hartree-Fock and Dirac-Bruckner-Hartree-Fock, are consistent with our constraint region on S(?).

Danielewicz, Pawel; Lee, Jenny

2014-02-01

395

Symmetry in systems with gyroscopic forces  

E-print Network

We consider a generalization of the notion of a natural mechanical system to the case of additional forces of gyroscopic type. Such forces appear, for example, as a result of global reduction of a natural system with symmetry. We study symmetries in the systems with gyroscopic forces to find out when these systems admit a global analogue of a cyclic integral. The results are applied to the problem of the motion of a rigid body about a fixed point in potential and gyroscopic forces to find the most general form of such forces admitting the global area type integral.

M. P. Kharlamov

2014-02-04

396

Discrete flavor symmetry and minimal seesaw mechanism  

E-print Network

This work proposes a neutrino mass model that is derived using the minimal seesaw mechanism which contains only two right-handed neutrinos, under the non-abelian discrete flavor symmetry $\\mathbb{S}_4\\otimes\\mathbb{Z}_2$. Two standard model doublets, $L_\\mu$ and $L_\\tau$, are assigned simultaneously to a $\\mathbf{2}$ representation of $\\mathbb{S}_4$. When the scalar fields introduced in this model, addition to the Standard Model Higgs, and the leptons are coupled within the symmetry, the seesaw mechanism results in the tri-bi-maximal neutrino mixing. This study examined the possible deviations from TBM mixing related to the experimental data.

K. H. Nam; N. W. Park; Kim Siyeon

2011-01-21

397

Topological zero modes and Dirac points protected by spatial symmetry and chiral symmetry  

NASA Astrophysics Data System (ADS)

We explore a new class of topologically stable zero-energy modes which are protected by coexisting chiral and spatial symmetries. If a chiral-symmetric Hamiltonian has an additional spatial symmetry such as reflection, inversion, and rotation, the Hamiltonian can be separated into independent chiral-symmetric subsystems by the eigenvalue of the space symmetry operator. Each subsystem supports chiral zero-energy modes when a topological index assigned to the block is nonzero. By applying the argument to Bloch electron systems, we detect band touching at symmetric points in the Brillouin zone. In particular, we show that Weyl nodes appearing in honeycomb lattice (e.g., graphene) and in half-flux square lattice are protected by threefold and twofold rotation symmetry, respectively. We also present several examples of Dirac semimetal with isolated band-touching points in three-dimensional k space, which are protected by combined symmetry of rotation and reflection. The zero-mode protection by spatial symmetry is distinct from that by the conventional winding number. We demonstrate that symmetry-protected band touching points emerge even though the winding number is zero. Finally, we identify relevant topological charges assigned to the gapless points.

Koshino, Mikito; Morimoto, Takahiro; Sato, Masatoshi

2014-09-01

398

Symmetry, winding number, and topological charge of vortex solitons in discrete-symmetry media  

SciTech Connect

We determine the functional behavior near the discrete rotational symmetry axis of discrete vortices of the nonlinear Schroedinger equation. We show that these solutions present a central phase singularity whose charge is restricted by symmetry arguments. Consequently, we demonstrate that the existence of high-charged discrete vortices is related to the presence of other off-axis phase singularities, whose positions and charges are also restricted by symmetry arguments. To illustrate our theoretical results, we offer two numerical examples of high-charged discrete vortices in photonic crystal fibers showing hexagonal discrete rotational invariance.

Garcia-March, Miguel-Angel; Zacares, Mario [Institut Universitari de Matematica Pura i Aplicada (IUMPA), Universitat Politecnica de Valencia, Cami de Vera, s/n, E-46022 Valencia (Spain); Ferrando, Albert [Departament d'Optica, Universitat de Valencia, Dr. Moliner, 50, E-46100 Burjassot (Valencia) (Spain); Sahu, Sarira [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Circuito Exterior, C.U., A. Postal 70-543, 04510 Mexico DF (Mexico); Ceballos-Herrera, Daniel E. [Institut Universitari de Matematica Pura i Aplicada (IUMPA), Universitat Politecnica de Valencia, Cami de Vera, s/n, E-46022 Valencia (Spain); Centro de Investigaciones en Optica A.C., Leon, Gto. 37170 (Mexico)

2009-05-15

399

From Old Symmetries to New Symmetries: Quarks, Leptons and B-L  

E-print Network

The Baryon-Lepton difference ($B-L$) is increasingly emerging as a possible new symmetry of the weak interactions of quarks and leptons as a way to understand the small neutrino masses. There is the possibility that current and future searches at colliders and in low energy rare processes may provide evidence for this symmetry. This paper provides a brief overview of the early developments that led to B-L as a possible symmetry beyond the standard model, and also discusses some recent developments.

Rabindra N. Mohapatra

2014-09-26

400

The Symmetry Group of the Permutahedron  

ERIC Educational Resources Information Center

Although it can be visualized fairly easily and its symmetry group is easy to calculate, the permutahedron is a somewhat neglected combinatorial object. We propose it as a useful case study in abstract algebra. It supplies concrete examples of group actions, the difference between right and left actions, and how geometry and algebra can work…

Crisman, Karl-Dieter

2011-01-01

401

Studying fundamental symmetries with atoms and molecules  

E-print Network

are magnetic moment and weak coupling constant of the unpaired nucleon (gp 4.5; gn 1). For heavy nuclei and time-reversal symmetry T in atomic physics. · Weak charge, anapole moment, and Schiff moment of the nucleus and electric dipole moment of the electron. · High accuracy ab initio calculations for atoms

Pines, Alexander

402

SFT Symmetry, Mathematics (Experimental): 5212.48.  

ERIC Educational Resources Information Center

This is the third in a series of four guidebooks on minimum course content designed to develop geometric concepts intuitively, using the "slides, flips, and turns" approach developed by the University of Illinois, Committee on School Mathematics. Topics include the development of the concept of symmetry, triangles and quadrilateral…

Dade County Public Schools, Miami, FL.

403

Folded Fashions: Symmetry in Clothing Design.  

ERIC Educational Resources Information Center

Fashion design is a field perceived as both a female and male domain that utilizes mathematics. Presents creative activities to teach the concept of symmetry as applied in fashion designs in the style of the famous French designer Madeleine Vionnet. (MDH)

Evered, Lisa J.

1992-01-01

404

Einstein-Yang-Mills theory: Asymptotic symmetries  

NASA Astrophysics Data System (ADS)

Asymptotic symmetries of the Einstein-Yang-Mills system with or without cosmological constant are explicitly worked out in a unified manner. In agreement with a recent conjecture, one finds a Virasoro-Kac-Moody type algebra not only in three dimensions but also in the four-dimensional asymptotically flat case.

Barnich, Glenn; Lambert, Pierre-Henry

2013-11-01

405

Magnetic translation symmetry on the lattice  

E-print Network

Magnetic translation symmetry on a finite periodic square lattice is investigated for an arbitrary uniform magnetic field in arbitrary dimensions. It can be used to classify eigenvectors of the Hamiltonian. The system can be converted to another system of half or lower dimensions. A higher dimensional generalization of Harper equation is obtained for tight-binding systems.

Ken-ichi Sekiguchi; Tomohiro Okamoto; Takanori Fujiwara

2008-12-08

406

Scaling Symmetry and Integrable Spherical Hydrostatics  

E-print Network

Any symmetry reduces a second-order differential equation to a first integral: variational symmetries of the action (exemplified by central field dynamics) lead to conservation laws, but symmetries of only the equations of motion (exemplified by scale-invariant hydrostatics) yield first-order {\\em non-conservation laws} between invariants. We obtain these non-conservation laws by extending Noether's Theorem to non-variational symmetries and present an innovative variational formulation of spherical adiabatic hydrostatics. For the scale-invariant case, this novel synthesis of group theory, hydrostatics, and astrophysics allows us to recover all the known properties of polytropes and define a {\\em core radius}, inside which polytropes of index $n$ share a common core mass density structure, and outside of which their envelopes differ. The Emden solutions (regular solutions of the Lane-Emden equation) are obtained, along with useful approximations. An appendix discusses the $n=3$ polytrope in order to emphasize how the same mechanical structure allows different thermal structures in relativistic degenerate white dwarfs and zero age main sequence stars.

Sidney Bludman; Dallas C. Kennedy

2011-12-19

407

Visual symmetry in objects and gaps.  

PubMed

It is known that perceptual organization modulates the salience of visual symmetry. Reflectional symmetry is more quickly detected when it is a property of a single object than when it is formed by a gap between two objects. Translational symmetry shows the reverse effect, being more quickly detected when it is a gap between objects. We investigated the neural correlates of this interaction. Electroencephalographic data was recorded from 40 participants who were presented with reflected and translated contours in one- or two-object displays. Half of the participants discriminated regularity, half distinguished number of objects. An event-related potential known as the Sustained Posterior Negativity (SPN) distinguished between reflection and translation. A similar ERP distinguished between one and two object presentations, but these waves summed with the SPN, rather than altering it. All stimuli produced desynchronization of 8-13 Hz alpha oscillations over the bilateral parietal cortex. In the Discriminate Regularity group, this effect was right lateralized. The SPN and alpha desynchronization index different stages of visual symmetry discrimination. However, neither component displayed the Regularity × Objecthood interaction that is observed in speeded discrimination tasks, suggesting that integration of visual regularity with objectness is not inevitable. Instead, both attributes may be processed in parallel and independently. PMID:24610955

Makin, Alexis D J; Rampone, Giulia; Wright, Alexander; Martinovic, Jasna; Bertamini, Marco

2014-01-01

408

Reducing Symmetry in Matrix Models # Zeynep Kzltan  

E-print Network

Reducing Symmetry in Matrix Models # Zeynep K�z�ltan Department of Information Science, Uppsala played in a given week w and period p [12]. S Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Period 1 S scheduling problem, the weeks are indistin­ guishable, and so are the periods. A solution is thus symmetric

Rossi, Francesca

409

Geometry and symmetries in lattice spinor gravity  

SciTech Connect

Lattice spinor gravity is a proposal for regularized quantum gravity based on fermionic degrees of freedom. In our lattice model the local Lorentz symmetry is generalized to complex transformation parameters. The difference between space and time is not put in a priori, and the euclidean and the Minkowski quantum field theory are unified in one functional integral. The metric and its signature arise as a result of the dynamics, corresponding to a given ground state or cosmological solution. Geometrical objects as the vierbein, spin connection or the metric are expectation values of collective fields built from an even number of fermions. The quantum effective action for the metric is invariant under general coordinate transformations in the continuum limit. The action of our model is found to be also invariant under gauge transformations. We observe a 'geometrical entanglement' of gauge- and Lorentz-transformations due to geometrical objects transforming non-trivially under both types of symmetry transformations. - Highlights: Black-Right-Pointing-Pointer We formulate the geometrical aspects of a proposal for a lattice regularized model of quantum gravity. Black-Right-Pointing-Pointer The vierbein shows an entanglement between Lorentz symmetry and gauge symmetry. Black-Right-Pointing-Pointer Euclidean and Minkowski signatures of the collective metric and the vierbein are described within the same functional integral.

Wetterich, C., E-mail: c.wetterich@thphys.uni-heidelberg.de

2012-09-15

410

Gender Symmetry, Sexism, and Intimate Partner Violence  

ERIC Educational Resources Information Center

This study of a predominantly Hispanic sample of 92 male and 140 female college students examines both gender symmetry in intimate partner violence (IPV) and inconsistent relationships found in previous studies between sexist attitudes and IPV. Results indicate that although comparable numbers of men and women perpetrate and are victimized in…

Allen, Christopher T.; Swan, Suzanne C.; Raghavan, Chitra

2009-01-01

411

Neutronics computational applications of symmetry algebras  

SciTech Connect

Lie groups of point transformations and their corresponding symmetry algebras are determined for a general system of second order differential equations, special cases of which include the multigroup diffusion equations and the ''FLIP form'' of the P/sub L/ equations. It is shown how Lie symmetry algebras can be used to motivate, formulate and simplify double sweep algorithms for solving two-point boundary value problems that involve systems of second order differential equations. A matrix Riccati equation that appears in double sweep algorithms is solved exactly by regarding a set of first integrals of the second order system as a set of first order differential invariants of the group of point transformations that is admitted by the system. A second computational application of symmetry algebras is the determination of invariant difference schemes which are defined as difference schemes that admit the same groups of point transformations as those admitted by the differential equations that they simulate. Prolongations of symmetry algebra vector fields that are required to construct invariant difference equations are defined and found. Examples of invariant difference schemes are constructed from the basic difference equation invariance conditions and shown to be exact. 15 refs.

Axford, R.A.

1989-01-01

412

The Differential Form Method for Finding Symmetries  

E-print Network

This article reviews the use of differential forms and Lie derivatives to find symmetries of differential equations, as originally presented by Harrison and Estabrook, J. Math. Phys., 12 (1971), 653. An outline of the method is given, followed by examples and references to recent papers using the method.

B. Kent Harrison

2005-10-18

413

Spontaneously broken supergauge symmetries and goldstone spinors  

Microsoft Academic Search

We present a model with a spontaneously broken supergauge symmetry which results in the appearance of a massless Goldstone spinor. The model combines supergauge invariance with ordinary gauge invariance. After the breaking the gauge boson acquires a mass as a result of the Higgs mechanism. Laboratoire propre du CNRS, associéà l'Ecole Normale Supérieure et à l'Université Paris Sud. Postal address

P. Fayet; J. Iliopoulos

1974-01-01

414

Tests for symmetry with right censoring  

Microsoft Academic Search

Permutation tests for symmetry are suggested using data that are subject to right censoring. Such tests are directly relevant to the assumptions that underlie the generalized Wilcoxon test since the symmetric logistic distribution for log-errors has been used to motivate Wilcoxon scores in the censored accelerated failure time model. Its principal competitor is the log-rank (LGR) test motivated by an

Ehab F. Abd-Elfattah; Ronald W. Butler

2011-01-01

415

Low Lying Scalar Resonances and Chiral Symmetry  

E-print Network

Current theoretical studies on the $\\sigma$ and $\\kappa$ resonances are reviewed. It is emphasized that all evidences accumulated so far are consistent with the picture that the $\\sigma$ meson is the chiral partner of the Nambu--Goldstone bosons in a linear realization of chiral symmetry.

Hanqing Zheng

2008-02-08

416

Electroweak symmetry breaking from monopole condensation.  

PubMed

We argue that the electroweak symmetry of the standard model (SM) could be broken via condensation of magnetic monopole bilinears. We present an extension of the SM where this could indeed happen, and where the heavy top mass is also a consequence of the magnetic interactions. PMID:21405319

Csáki, Csaba; Shirman, Yuri; Terning, John

2011-01-28

417

Symmetry and bifurcations of momentum mappings  

Microsoft Academic Search

The zero set of a momentum mapping is shown to have a singularity at each point with symmetry. The zero set is diffeomorphic to the product of a manifold and the zero set of a homogeneous quadratic function. The proof uses the Kuranishi theory of deformations. Among the applications, it is shown that the set of all solutions of the

Judith M. Arms; Jerrold E. Marsden; Vincent Moncrief

1981-01-01

418

Cosmology and the fate of dilatation symmetry  

Microsoft Academic Search

We discuss the cosmological constant problem in the light of dilatation symmetry and its possible anomaly. For dilatation symmetric quantum theories realistic asymptotic cosmology is obtained provided the effective potential has a nontrivial minimum. For theories with dilatation anomaly one needs as a nontrivial ``cosmon condition'' that the energy-momentum tensor in the vacuum is purely anomalous. Such a condition is

C. Wetterich

1988-01-01

419

A gravity term from spontaneous symmetry breaking  

E-print Network

In this model, the gravity term in the Lagrangean comes from spontaneous symmetry breaking of an additional scalar quadruplet field $\\Upsilon$. The resulting gravitational field is approximate to one of the models of coframe gravity with parameters $\\rho_1 + 4 \\rho_2 = 0$, $\\rho_3 = 0$. This article includes an exact solution of coframe gravity with model parameters $\\rho_1 \

Mihai Moise

2014-01-02

420

Symmetries in confined classical Coulomb systems  

SciTech Connect

The properties of charged particles confined in a harmonic oscillator potential have become of increased interest lately in view of the development of techniques in ion traps and storage rings. The symmetries in such systems intrigued the imagination of Ted Hecht in connection with the storage ring at Heidelberg, and so perhaps it is an appropriate subject for this symposium.

Schiffer, J.P.

1991-01-01

421

Weyl-Gauge Symmetry of Graphene  

E-print Network

The conformal invariance of the low energy limit theory governing the electronic properties of graphene is explored. In particular, it is noted that the massless Dirac theory in point enjoys local Weyl symmetry, a very large symmetry. Exploiting this symmetry in the two spatial dimensions and in the associated three dimensional spacetime, we find the geometric constraints that correspond to specific shapes of the graphene sheet for which the electronic density of states is the same as that for planar graphene, provided the measurements are made in accordance to the inner reference frame of the electronic system. These results rely on the (surprising) general relativistic-like behavior of the graphene system arising from the combination of its well known special relativistic-like behavior with the less explored Weyl symmetry. Mathematical structures, such as the Virasoro algebra and the Liouville equation, naturally arise in this three-dimensional context and can be related to specific profiles of the graphene sheet. Speculations on possible applications of three-dimensional gravity are also proposed.

Alfredo Iorio

2010-07-28

422

Exploiting group symmetry in semidefinite programming relaxations ...  

E-print Network

ment problem, and show how to exploit group symmetry in the problem data. Thus we .... An arbitrary nonnegative matrix Y ? 0 has the same sparsity pattern if and only ..... Consider the matrix A with 2n rows indexed by all elements of {0, 1

2009-02-24

423

Electroweak Symmetry Breaking due to Confinement  

E-print Network

Within the framework of gauge mediated supersymmetry breaking, we consider an electroweak symmetry breaking pattern in which there is no conventional $\\mu$ term. The pattern is made appealing through realizing it as low energy effective description of a supersymmetric Yang-Mills theory which is of confinement. Phenomenological implications are discussed.

Chun Liu

1999-03-18

424

The "ghost" symmetry in the CKP hierarchy  

E-print Network

In this paper, we systematically study the "ghost" symmetry in the CKP hierarchy through its actions on the Lax operator, dressing operator, eigenfunctions and the tau function. In this process, the spectral representation of the eigenfunction is developed and the squared eigenfunction potential is investigated.

Jipeng Cheng; Jingsong He

2014-02-27

425

The "ghost" symmetry in the CKP hierarchy  

NASA Astrophysics Data System (ADS)

In this paper, we systematically study the "ghost" symmetry in the CKP hierarchy through its actions on the Lax operator, dressing operator, eigenfunctions and the tau function. In this process, the spectral representation of the eigenfunction is developed and the squared eigenfunction potential is investigated.

Cheng, Jipeng; He, Jingsong

2014-06-01

426

Neutrino mass and mixing with discrete symmetry.  

PubMed

This is a review paper about neutrino mass and mixing and flavour model building strategies based on discrete family symmetry. After a pedagogical introduction and overview of the whole of neutrino physics, we focus on the PMNS mixing matrix and the latest global fits following the Daya Bay and RENO experiments which measure the reactor angle. We then describe the simple bimaximal, tri-bimaximal and golden ratio patterns of lepton mixing and the deviations required for a non-zero reactor angle, with solar or atmospheric mixing sum rules resulting from charged lepton corrections or residual trimaximal mixing. The different types of see-saw mechanism are then reviewed as well as the sequential dominance mechanism. We then give a mini-review of finite group theory, which may be used as a discrete family symmetry broken by flavons either completely, or with different subgroups preserved in the neutrino and charged lepton sectors. These two approaches are then reviewed in detail in separate chapters including mechanisms for flavon vacuum alignment and different model building strategies that have been proposed to generate the reactor angle. We then briefly review grand unified theories (GUTs) and how they may be combined with discrete family symmetry to describe all quark and lepton masses and mixing. Finally, we discuss three model examples which combine an SU(5) GUT with the discrete family symmetries A?, S? and ?(96). PMID:23645075

King, Stephen F; Luhn, Christoph

2013-05-01

427

Lecture notes on "Geometric Dynamics and Symmetry"  

E-print Network

Lecture notes on "Geometric Dynamics and Symmetry" Bob Rink December 2, 2009 Contents 1 Mechanical systems 4 1.1 Two classical examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 One degree of freedom mechanical systems . . . . . . . . . . . . . . . . . . 6 1.3 More degrees of freedom

Rink, Bob

428

Lecture notes on "Geometric Dynamics and Symmetry"  

E-print Network

Lecture notes on "Geometric Dynamics and Symmetry" Bob Rink May 9, 2012 Contents 1 Mechanical systems 4 1.1 Two classical examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 One degree of freedom mechanical systems . . . . . . . . . . . . . . . . . . 6 1.3 More degrees of freedom

Rink, Bob

429

Equivalence among fermion symmetry-multiplets and choice of the symmetry group for strong interactions  

Microsoft Academic Search

Summary  The definition of an « equivalence principle » among all symmetry multiplets is discussed from the point of view of its relevance\\u000a on the possible choice of the « correct » symmetry group under which the strong interactions are invariant. In Sect. 1 the\\u000a problem, already discussed byMoravcsik (6) andGerstein (7), is formulated; in Sect. 2, the limitations introduced by

A. Simoni; B. Vitale

1964-01-01

430

Fermion Systems in Discrete Space-Time - Outer Symmetries and Spontaneous Symmetry Breaking  

E-print Network

A systematic procedure is developed for constructing fermion systems in discrete space-time which have a given outer symmetry. The construction is illustrated by simple examples. For the symmetric group, we derive constraints for the number of particles. In the physically interesting case of many particles and even more space-time points, this result shows that the permutation symmetry of discrete space-time is always spontaneously broken by the fermionic projector.

Felix Finster

2006-01-19

431

On Symmetry, Perspectivity, and Level-Set-Based Segmentation  

E-print Network

We introduce a novel variational method for the extraction of objects with either bilateral or rotational symmetry in the presence of perspective distortion. Information on the symmetry axis of the object and the distorting ...

Riklin-Raviv, Tammy

432

Gapped symmetry preserving surface state for the electron topological insulator  

E-print Network

It is well known that the three-dimensional (3D) electronic topological insulator (TI) with charge-conservation and time-reversal symmetry cannot have a trivial insulating surface that preserves symmetry. It is often ...

Wang, Chong

433

Optical Activities as Computing Resources for Space-time Symmetries  

E-print Network

It is known that optical activities can perform rotations. It is shown that the rotation, if modulated by attenuations, can perform symmetry operations of Wigner's little group which dictates the internal space-time symmetries of elementary particles.

Y. S. Kim

2009-02-23

434

Synchronous Symmetry Breaking in Neurons with Different Neurite Counts  

E-print Network

As neurons develop, several immature processes (i.e., neurites) grow out of the cell body. Over time, each neuron breaks symmetry when only one of its neurites grows much longer than the rest, becoming an axon. This symmetry ...

Wissner-Gross, Zachary D.

435

Symmetry-protected topological phases, generalized Laughlin argument, and orientifolds  

NASA Astrophysics Data System (ADS)

We generalize Laughlin's flux insertion argument, originally discussed in the context of the quantum Hall effect, to topological phases protected by non-on-site unitary symmetries, in particular by parity symmetry or parity symmetry combined with an on-site unitary symmetry. As a model, we discuss fermionic or bosonic systems in two spatial dimensions with CP symmetry, which are, by the CPT theorem, related to time-reversal symmetric topological insulators (e.g., the quantum spin Hall effect). In particular, we develop the stability/instability (or "gappability"/"ingappablity") criteria for nonchiral conformal field theories with parity symmetry that may emerge as an edge state of a symmetry-protected topological phase. A necessary ingredient, as it turns out, is to consider the edge conformal field theories on unoriented surfaces, such as the Klein bottle, which arises naturally from enforcing parity symmetry by a projection operation.

Hsieh, Chang-Tse; Sule, Olabode Mayodele; Cho, Gil Young; Ryu, Shinsei; Leigh, Robert G.

2014-10-01

436

Role of symmetry potential in nuclear symmetry energy and its density slope parameter  

NASA Astrophysics Data System (ADS)

Using a density dependent finite-range effective interaction of Yukawa form the nuclear mean field in asymmetric nuclear matter is expanded in terms of power series of asymmetry ? (={?n-?p?) as u?(k,?,?)=u0(k,?)±u(k,?)?+u(?)?2. The behavior of nuclear symmetry potential u(k,?) around the Fermi momentum kf is found to be connected to the density dependence of symmetry energy Esym(?) and nucleon effective mass m}/{0*m (k=kf,?) in symmetric nuclear matter. Two different trends of momentum dependence for nuclear symmetry potential is observed depending on the choice of strength parameters of exchange interaction, but at Fermi momentum it is found to be independent of the choice of parameters. The nuclear symmetry energy Esym(?) and its slope L(?) are expressed analytically in terms of nuclear mean field in isospin asymmetric nuclear matter using the same interaction. We find that the second order nuclear symmetry potential u(?) cannot be neglected while calculating the density slope of symmetry energy L(?) as well as the nuclear mean field in extremely neutron (proton) rich nuclear matter.

Chakraborty, S.; Sahoo, B.; Sahoo, S.

2013-08-01

437

Chiral symmetry on the edge of 2D symmetry protected topological phases  

E-print Network

Symmetry protected topological (SPT) states are short-range entangled states with symmetry, which have symmetry protected gapless edge states around a gapped bulk. Recently, we proposed a systematic construction of SPT phases in interacting bosonic systems, however it is not very clear what is the form of the low energy excitations on the gapless edge. In this paper, we answer this question for two dimensional bosonic SPT phases with Z_N and U(1) symmetry. We find that while the low energy modes of the gapless edges are non-chiral, symmetry acts on them in a chiral way, i.e. acts on the right movers and the left movers differently. This special realization of symmetry protects the gaplessness of the otherwise unstable edge states by prohibiting a direct scattering between the left and right movers. Moreover, understanding of the low energy effective theory leads to experimental predictions about the SPT phases. In particular, we find that all the 2D U(1) SPT phases have even integer quantized Hall conductance.

Xie Chen; Xiao-Gang Wen

2012-06-14

438

Nuclear symmetry energy at subnormal densities from measured nuclear masses  

SciTech Connect

The symmetry energy coefficients for nuclei with mass number A=20-250 are extracted from more than 2000 measured nuclear masses. With the semiempirical connection between the symmetry energy coefficients of finite nuclei and the nuclear symmetry energy at reference densities, we investigate the density dependence of the symmetry energy of nuclear matter at subnormal densities. The obtained results are compared with those extracted from other methods.

Liu Min [Key Laboratory of Beam Technology and Material Modification of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Department of Physics, Guangxi Normal University, Guilin 541004 (China); Beijing Radiation Center, Beijing 100875 (China); Wang Ning [Department of Physics, Guangxi Normal University, Guilin 541004 (China); Li Zhuxia [China Institute of Atomic Energy, Beijing 102413 (China); Zhang Fengshou [Key Laboratory of Beam Technology and Material Modification of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Beijing Radiation Center, Beijing 100875 (China)

2010-12-15

439

Nuclear symmetry energy at subnormal densities from measured nuclear masses  

E-print Network

The symmetry energy coefficients for nuclei with mass number A=20~250 are extracted from more than 2000 measured nuclear masses. With the semi-empirical connection between the symmetry energy coefficients of finite nuclei and the nuclear symmetry energy at reference densities, we investigate the density dependence of symmetry energy of nuclear matter at subnormal densities. The obtained results are compared with those extracted from other methods.

Min Liu; Ning Wang; Zhuxia Li; Fengshou Zhang

2010-11-17

440

Investigation of the nonsymmetry of effective nonlinear optical coefficient expressions for low-symmetry crystals  

NASA Astrophysics Data System (ADS)

For low-symmetry crystals that belong to 2 and m point groups, two kinds of nonlinear optical coefficients matrix were derived after the positive directions of the optical coordinate axes were defined with the aid of the piezoelectric coordinate axes. These two kinds of nonlinear optical coefficient matrix are the cause of the nonsymmetry of the effective nonlinear optical coefficients about the x, y, and z optical coordinate planes. For the corresponding wave vector k(?,?) in the Nth quadrant, the effective nonlinear optical coefficient expressions are deffI=aie2[dijk(?3,?2,?1)]N+2aje1ake1 (Type I) and deffII=aie2[dijk(?3,?2,?1)]N+1aje1ake2 (Type II), where N is the number of the quadrant. Only one kind of nonlinear optical coefficient matrix is the maximum effective nonlinear optical coefficient. It is necessary to find out which quadrant, in which the wave vector k(?,?) is located, corresponds to the maximum effective nonlinear optical coefficient.

Xin, Yin; Shaojun, Zhang; Zhaobing, Tian

2005-10-01

441

Symmetry Concerns as a Symptom of Body Dysmorphic Disorder  

PubMed Central

Symmetry obsessions are a common symptom of obsessive-compulsive disorder (OCD) and have several demographic and clinical correlates. Appearance-related symmetry concerns appear common in body dysmorphic disorder (BDD); however, no published studies have examined this topic. This study examined the clinical features, prevalence, and correlates of symmetry concerns involving physical appearance in two BDD samples (N=160 and N=115). More than 25% of participants in each sample reported symmetry concerns for a body part with which they were preoccupied (total of 18 body parts in sample 1 and 18 in sample 2). In sample 1, BDD participants with appearance-related symmetry concerns were older than those without appearance-related symmetry concerns. In sample 2, those with appearance-related symmetry concerns reported poorer mental health-related quality of life, were more likely to have experienced lifetime suicidal ideation, had better BDD-related insight, and were less likely to have a lifetime eating disorder. In both samples, participants with appearance-related symmetry concerns were more likely to have lifetime OCD but not OCD-related symmetry obsessions. Thus, symmetry is a common appearance concern in BDD that is associated with comorbid OCD but not with OCD symmetry concerns specifically, suggesting that symmetry concerns may have a different mechanism/pathophysiology in BDD versus OCD. PMID:24058899

Hart, Ashley S.; Phillips, Katharine A.

2013-01-01

442

On the complete symmetry group of the classical Kepler system  

Microsoft Academic Search

A rather strong concept of symmetry is introduced in classical mechanics, in the sense that some mechanical systems can be completely characterized by the symmetry laws they obey. Accordingly, a ‘‘complete symmetry group’’ realization in mechanics must be endowed with the following two features: (1) the group acts freely and transitively on the manifold of all allowed motions of the

J. Krause

1994-01-01

443

Symmetric Prismatic Tensegrity Structures: Part II. Symmetry-adapted Formulations  

E-print Network

Symmetric Prismatic Tensegrity Structures: Part II. Symmetry-adapted Formulations J.Y. Zhang a S for the symmetry-adapted equilibrium, force density and geometrical stiffness matrices for prismatic tensegrity derived. Key words: Tensegrity; Symmetry; Dihedral Group; Group Representation Theory; Block

Guest, Simon

444

Breaking and Restoring of Diffeomorphism Symmetry in Discrete Gravity  

SciTech Connect

We discuss the fate of diffeomorphism symmetry in discrete gravity. Diffeomorphism symmetry is typically broken by the discretization. This has repercussions for the observable content and the canonical formulation of the theory. It might however be possible to construct discrete actions, so-called perfect actions, with exact symmetries and we will review first steps towards this end.

Bahr, B. [DAMTP, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Dittrich, B. [MPI f. Gravitational Physics, Albert Einstein Institute, Am Muehlenberg 1, D-14476 Potsdam (Germany)

2009-12-15

445

SO(4) symmetry in the relativistic hydrogen atom  

E-print Network

We show that the relativistic hydrogen atom possesses an SO(4) symmetry by introducing a kind of pseudo-spin vector operator. The same SO(4) symmetry is still preserved in the relativistic quantum system in presence of an U(1) monopolar vector potential as well as a nonabelian vector potential. Lamb shift and SO(4) symmetry breaking are also discussed.

Jing-Ling Chen; Dong-Ling Deng; Ming-Guang Hu

2007-11-01

446

Breaking Row and Column Symmetries in Matrix Models  

Microsoft Academic Search

We identify an important class of symmetries in constraint programming, arising from matrices of decision variables where rows and columns can be swapped. Whilst lexicographically ordering the rows (columns) breaks all the row (column) symmetries, lexicographically or- dering both the rows and the columns fails to break all the compositions of the row and column symmetries. Nevertheless, our experimental re-

Pierre Flener; Alan M. Frisch; Brahim Hnich; Zeynep Kiziltan; Ian Miguel; Justin Pearson; Toby Walsh

2002-01-01

447

Improved flavor symmetry in Kogut-Susskind fermion actions  

NASA Astrophysics Data System (ADS)

We study improved Kogut-Susskind fermion actions focusing on flavor symmetry restoration. Several variants of fat actions suitable for dynamical simulations are considered, including an action with no tree level O( a2) errors. The spectrum of all the pions is computed and used as a measure of flavor symmetry violation. Finally, the Naik term is introduced to restore rotational symmetry.

Orginos, K.; Sugar, R.; Toussaint, D.

448

Broken Symmetries and the Higgs Boson  

NASA Astrophysics Data System (ADS)

The 40 years old Standard Model, the theory of particle physics, seems to describe all experimental data very well. The theory is based on symmetries, some of them are broken, mostly by the weak interaction. All of its elementary particles were identified and studied apart from the Higgs boson until 2012, when the two main experiments of the Large Hadron Collider at CERN, CMS and ATLAS observed a new particle with properties close to those predicted for the Higgs boson. The discovery of the Higgs boson proves the validity of the Brout-Englert-Higgs mechanism of spontaneous symmetry breaking and François Englert and Peter Higgs received the 2013 Nobel Prize in Physics. There are several questions yet concerning the possible theoretical significance of the mass of the new particle.

Horváth, Dezs?

2014-09-01

449

The Symmetry Detection Mechanisms are Color Selective  

PubMed Central

We investigated the role of color in the feature integration process for global form perception. For this, we used a 2AFC noise masking paradigm to measure the color selectivity of the symmetry detection mechanism. In each trial, a vertical symmetric target was randomly presented in one of the two intervals while a random dot control, in the other. The observers' task was to determine which interval contained the symmetric target. The image elements varied in chromaticity. The target density threshold was measured at various combinations of target and mask chromaticity. A noise mask with the same chromaticity as the target always produced the largest masking effect (threshold increment) on the detection on that target. The masking effect decreased as the difference in chromaticity between the target and mask increased. This suggests that the symmetry detection mechanisms are color selective and only extract local image features of a specific chromaticity. PMID:24463695

Wu, Chia-Ching; Chen, Chien-Chung

2014-01-01

450

Symmetries of Type N Pure Radiation Fields  

NASA Astrophysics Data System (ADS)

The geometrical symmetries corresponding to the continuous groups of collineations and motions generated by a null vector l are considered. These symmetries have been translated into the language of Newman-Penrose formalism for pure radiation (PR) type N fields. It is seen that for such fields, conformal, special conformal and homothetic motions degenerate to motion. The concept of free curvature, matter curvature and matter affine collineations have been discussed and the conditions under which PR type N fields admit such collineations have been obtained. Moreover, it is shown that the projective collineation degenerate to matter affine, special projective, conformal, special conformal, null geodesic and special null geodesic collineations. It is also seen that type N pure radiation fields admit Maxwell collineation along the propagation vector l.

Ahsan, Zafar; Ali, Musavvir

2014-10-01

451

Symmetries of Type D Pure Radiation Fields  

NASA Astrophysics Data System (ADS)

The geometrical symmetries corresponding to the continuous groups of collineations and motions generated by a null vector l are considered. These symmetries have been translated into the language of Newman-Penrose formalism for pure radiation (PR) type D fields. It is seen that for such fields, conformal, special conformal and homothetic motions degenerate to motion. The concept of free curvature, matter curvature and matter affine collineations have been introduced and the conditions under which PR type D fields admit such collineations have been obtained. Moreover, it is shown that the projective collineation degenerate to matter affine, special projective, conformal, special conformal, null geodesic and special null geodesic collineations. It is also seen that type D pure radiation fields admit Maxwell collineation along the propagation vector l.

Ahsan, Zafar; Ali, Musavvir

2012-07-01

452

Capsule Implosion Symmetry in NIF Hohlraums  

NASA Astrophysics Data System (ADS)

A key requirement for the achievement of ignition on the National Ignition Facility (NIF) is to adequately control the hotspot low mode shape. This is diagnosed by measuring the X-ray self-emission from the imploding capsule, either in surrogate symmetry capsule, or in layered implosions. The primary method of controlling the equatorial drive symmetry is to vary the power balance between the inner and outer cones either directly or by crossbeam energy transfer. Varying the power balance within the inner cones controls the azimuthal asymmetry. This paper will review the status of the low-mode shape of layered implosions and compare to integrated simulations using a new backscatter model and in-line crossbeam power transfer model.

Town, R. P. J.; Michel, P. A.; Divol, L.; Callahan, D. A.; Jones, O. S.; Milovich, J.; Rosen, M. D.; Moody, J. D.; Benedetti, L. R.; Bradley, D. K.; Glenn, S.; Izumi, N.; Khan, S. F.; Pak, A. E.; Smalyuk, V. A.; Tommasini, R.; Bailey, D. S.; Harte, J. A.; Zimmerman, G. B.; Kyrala, G. A.; Scott, R.

2012-10-01

453

Chiral symmetry in strongly interacting matter  

E-print Network

This is a brief summary of topics that were presented as lectures within the programme "New Frontiers in QCD 2010" at the Yukawa Institute of Theoretical Physics in Kyoto. The basic subject is phases and symmetry breaking patterns as they emerge from the approximate chiral symmetry of QCD. Part I focuses on the QCD interface with nuclear physics via chiral effective field theory. This includes nuclear thermodynamics and, in particular, constraints for compressed and hot baryonic matter provided by the density and temperature dependence of the chiral condensate. Part II explores aspects of the QCD phase diagram using a non-local improved version of the Polyakov - Nambu - Jona-Lasinio (PNJL) model. A prominent feature of such an approach is the occurence of a dynamical entanglement between chiral and deconfinement crossover transitions. Comparisons with available results from lattice QCD thermodynamics will be made.

Wolfram Weise

2010-09-30

454

Kappa symmetry, generalized calibrations and spinorial geometry  

E-print Network

We extend the spinorial geometry techniques developed for the solution of supergravity Killing spinor equations to the kappa symmetry condition for supersymmetric brane probe configurations in any supergravity background. In particular, we construct the linear systems associated with the kappa symmetry projector of M- and type II branes acting on any Killing spinor. As an example, we show that static supersymmetric M2-brane configurations which admit a Killing spinor representing the SU(5) orbit of $Spin(10,1)$ are generalized almost hermitian calibrations and the embedding map is pseudo-holomorphic. We also present a bound for the Euclidean action of M- and type II branes embedded in a supersymmetric background with non-vanishing fluxes. This leads to an extension of the definition of generalized calibrations which allows for the presence of non-trivial Born-Infeld type of fields in the brane actions.

G. Papadopoulos; P. Sloane

2006-01-23

455

Empirically charting dynamical chiral symmetry breaking.  

SciTech Connect

Conclusions are: (1) Dynamical Chiral Symmetry Breaking (DCSB) impacts dramatically upon observables - Spectrum; e.g., splittings: {sigma}-{pi} and a{sub 1}-{rho}, Elastic and Transition Form Factors; (2) But M(p{sup 2}) is an essentially quantum field theoretical effect - Exposing & elucidating its effect in hadron physics requires nonperturbative, symmetry preserving framework; i.e., Poincare covariance, chiral and e.m. current conservation, etc.; (3) DSEs provide such a framework - Studies underway will identify observable signals of M(p{sup 2}), the most important mass-generating mechanism for visible matter in the Universe; and (4) DSEs - Tool enabling insight to be drawn from experiment into long-range piece of interaction between light-quarks.

Chang, L.; Roberts, C. D. (Physics); (Inst. of Applied Physics and Computational Mathematics); (Peking Univ.)

2010-01-01

456

Viscoelasticity breaks the symmetry of impacting jets.  

PubMed

A jet of a Newtonian liquid impacting on a wall at right angle spreads as a thin liquid sheet which preserves the radial symmetry of the jet. We report that for a viscoelastic jet (solution of polyethylene glycol in water) this symmetry can break; close to the wall, the jet cross section becomes faceted and radial steady liquid films (wings) form, which connect the cross-section vertices to the sheet. The number of wings increases with increasing the viscoelastic relaxation time of the solution, but also with increasing jet velocity and decreasing distance from the jet nozzle to the wall. We propose a mechanism for this surprising destabilization of the jet shape, which develops perpendicularly to the direction expected for a buckling mechanism, and explain these dependencies. We also discuss the large-scale consequences of the jet destabilization on the sheet spreading and fragmentation, which show through the faceting of hydraulic jumps and of suspended (Savart) sheets. PMID:25415909

Lhuissier, H; Néel, B; Limat, L

2014-11-01

457

Discrete Flavor Symmetries and Mass Matrix Textures  

E-print Network

We show how introducing discrete Abelian flavor symmetries can produce texture zeros in the fermion mass matrices, while preserving the correct relationships with the low-energy data on quark and lepton masses. We outline a procedure for defining texture zeros as suppressed entries in Yukawa matrices. These texture zeros can account for the coexistence of the observed large mixing in atmospheric neutrino oscillations with a hierarchy in the neutrino masses, and offer the possibility of alignment of the quark and squark mass matrices, and thus giving a solution to the supersymmetric flavor problem. A requirement that the flavor symmetry commutes with the SU(5) grand unified group can be used to explain the lepton mass hierarchies as well as the neutrino parameters, including the large mixing observed in the atmospheric neutrino data. We present one such model that yields a large atmospheric neutrino mixing angle, as well as a solar neutrino mixing angle of order $\\lambda \\simeq 0.22$.

M. S. Berger; Kim Siyeon

2000-05-24

458

Compositional inversion symmetry breaking in ferroelectric perovskites  

PubMed

Cubic perovskite compounds of the form (A(1/3)A(')(1/3)A(")(1/3))BO3 and A(B(1/3)B(')(1/3)B(")(1/3))O3, in which the differentiated cations form an alternating series of monolayers, are studied using first-principles methods. Such compounds are representative of a possible new class of materials in which ferroelectricity is perturbed by compositional breaking of inversion symmetry. For isovalent substitution the ferroelectric double-well potential becomes asymmetric, so that minority domains may no longer survive. The symmetry breaking is enormously stronger for heterovalent substitution; here the double-well behavior is destroyed. Tuning between these behaviors may allow for the optimization of desired materials properties. PMID:10991013

Sai; Meyer; Vanderbilt

2000-06-12

459

Symmetry Algebra of IIB Superstring Scattering  

E-print Network

The graviton scattering in IIB superstring theory is examined in the context of S-duality and symmetry. There is an algebra that generates all of the terms in the four-point function to any order in derivatives. A map from the algebra to the scattering is given; it suggests the correctness of the full four-point function with the S-duality. The higher point functions are expected to follow a similar pattern.

Gordon Chalmers

2005-10-26

460

From scale invariance to Lorentz symmetry.  

PubMed

It is shown that a unitary translationally invariant field theory in 1+1 dimensions, satisfying isotropic scale invariance, standard assumptions about the spectrum of states and operators, and the requirement that signals propagate with finite velocity, possesses an infinite dimensional symmetry given by one or a product of several copies of conformal algebra. In particular, this implies the presence of one or several Lorentz groups acting on the operator algebra of the theory. PMID:24996083

Sibiryakov, Sergey

2014-06-20

461

Dynamic symmetries at the critical point  

PubMed

A new class of dynamic symmetries is introduced. It is suggested that an element of this class, associated with zeros of Bessel functions, be used to describe spectra of nuclei at or around the critical point of the U(5)-SO(6) shape phase transition, and, in general, spectra of systems undergoing a (second order) phase transition between the algebraic structures U(n-1) and SO(n). PMID:11030955

Iachello

2000-10-23

462

New symmetries in heavy flavor physics  

SciTech Connect

Isgur and Wise have found that the formal limit M{sub b}, M{sub c} {yields} {infinity} leads to very great simplification in the general structure of the electroweak matrix elements of hadrons containing those quarks. In additions, interesting new symmetries appear in this limit. Their results are discussed, as well as some natural extensions to matrix elements of products of currents. 11 refs.

Bjorken, J.D. (Istituto Nazionale di Fisica Nucleare, Pisa (Italy) Stanford Linear Accelerator Center, Menlo Park, CA (USA))

1990-06-01

463

A Symmetry Approach to CP Violation  

Microsoft Academic Search

One of the greatest challenges for particle physics in the 1990's is\\u000aunderstanding the broken symmetry of CP violation. It is now almost 30 years\\u000asince the discovery in 1964 of the $K_{L} \\\\rightarrow 2\\\\pi$ decay. What has\\u000ahappened since? Why has there been no significant new experimental input in\\u000athis long period? The original $K_{L} \\\\rightarrow 2\\\\pi$ decay experiment

Harry J. Lipkin

1993-01-01

464

A Symmetry Approach to CP Violation  

Microsoft Academic Search

One of the greatest challenges for particle physics in the 1990's is understanding the broken symmetry of CP violation. It is now almost 30 years since the discovery in 1964 of the $K_{L} \\\\rightarrow 2\\\\pi$ decay. What has happened since? Why has there been no significant new experimental input in this long period? The original $K_{L} \\\\rightarrow 2\\\\pi$ decay experiment

Harry J. Lipkin

1993-01-01

465

Symmetries in Scattering of Slow Neutrons  

Microsoft Academic Search

Reciprocity, detailed balance, and other symmetry laws for slow-neutron scattering are discussed for the case of anisotropic media. While Friedel's law, stating that Sigma(v-->v')=Sigma(-v-->- v'), may fail for polar absorbing media, reciprocity as a consequence of time-reversal invariance, and of thermal equilibrium of the medium, remains valid. The optical theorem helps to derive a reciprocity relation for the total cross

I. Ku Scer; G. C. Summerfield

1969-01-01

466

Symmetry analysis for anisotropic field theories  

SciTech Connect

The purpose of this paper is to study with the help of Noether's theorem the symmetries of anisotropic actions for arbitrary fields which generally depend on higher order spatial derivatives, and to find the corresponding current densities and the Noether charges. We study in particular scale invariance and consider the cases of higher derivative extensions of the scalar field, electrodynamics and Chern-Simons theory.

Parra, Lorena; Vergara, J. David [Instituto de Ciencias Nucleares, UNAM, Circuito Exterior s/n, Ciudad Universitaria. Delg. Coyoacan. C.P. 04510 Mexico DF (Mexico)

2012-08-24

467

Extra gauge symmetries in BHT gravity  

E-print Network

We study the canonical structure of the Bergshoeff-Hohm-Townsend massive gravity, linearized around a maximally symmetric background. At the critical point in the space of parameters, defined by $\\Lambda_0/m^2=-1$, we discover an extra gauge symmetry, which reflects the existence of the partially massless mode. The number of the Lagrangian degrees of freedom is found to be 1. We show that the canonical structure of the theory at the critical point is unstable under linearization.

M. Blagojevi?; B. Cvetkovi?

2011-03-11

468

Extra gauge symmetries in BHT gravity  

NASA Astrophysics Data System (ADS)

We study the canonical structure of the Bergshoeff-Hohm-Townsend massive gravity, linearized around a maximally symmetric background. At the critical point in the space of parameters, defined by ? 0/ m 2 = -1, we discover an extra gauge symmetry, which reflects the existence of the partially massless mode. The number of the Lagrangian degrees of freedom is found to be 1. We show that the canonical structure of the theory at the critical point is unstable under linearization.

Blagojevi?, M.; Cvetkovi?, B.

2011-03-01

469

Extra gauge symmetries in BHT gravity  

E-print Network

We study the canonical structure of the Bergshoeff-Hohm-Townsend massive gravity, linearized around a maximally symmetric background. At the critical point in the space of parameters, defined by $\\Lambda_0/m^2=-1$, we discover an extra gauge symmetry, which reflects the existence of the partially massless mode. The number of the Lagrangian degrees of freedom is found to be 1. We show that the canonical structure of the theory at the critical point is unstable under linearization.

Blagojevi?, M

2011-01-01

470

Lorentz Transformation from Symmetry of Reference Principle  

NASA Astrophysics Data System (ADS)

The Lorentz Transformation is traditionally derived requiring the Principle of Relativity and light-speed universality. While the latter can be relaxed, the Principle of Relativity is seen as core to the transformation. The present letter relaxes both statements to the weaker, Symmetry of Reference Principle. Thus the resulting Lorentz transformation and its consequences (time dilatation, length contraction) are, in turn, effects of how we manage space and time.

Petre, M.; Dima, M.; Dima, A.; Petre, C.; Precup, I.

2010-01-01

471

Approximate symmetry groups of inhomogeneous metrics  

Microsoft Academic Search

A useful step toward understanding inhomogeneous space-times would be to classify them, perhaps in a fashion analogous to that used for spatially homogeneous space-times. To that end, a technique for determining an approximate simply-transitive three-parameter symmetry group of a three-dimensional positive-definite Riemannian metric is developed. The technique employs a variational principle to find a set of three orthonormal vectors whose

Alan Spero; Ralph Baierlein

1977-01-01

472

Approximate symmetry groups of inhomogeneous metrics: Examples  

Microsoft Academic Search

By definition, an N-dimensional positive-definite inhomogeneous metric is not invariant under any N-parameter, simply-transitive continuous group of motions. Nonetheless, it is possible to construct a group (simply-transitive and of N parameters) that comes closest to leaving the given metric invariant. We call this group the approximate symmetry group of the metric. In an earlier paper, we described a technique for

Alan Spero; Ralph Baierlein

1978-01-01

473

Lagrangian generators of the Poincare gauge symmetries  

SciTech Connect

We have systematically computed the generators of the symmetries arising in Poincare gauge theory formulation of gravity, both in 2+1 and 3+1 dimensions. This was done using a completely Lagrangian approach. The results are expected to be valid in any dimensions, as seen through lifting the results of the 2+1 dimensional example into the 3+1 dimensional one.

Banerjee, Rabin; Roy, Debraj; Samanta, Saurav [S. N. Bose National Centre for Basic Sciences, Block-JD, Sector III, Salt Lake, Kolkata-700098 (India); Narasinha Dutt College, 129, Belilious Road, Howrah-711101 (India)

2010-08-15

474

Condensate mechanism of conformal symmetry breaking  

E-print Network

The low energy Gell-Mann-Oakes-Renner relation, Higgs particle mass value, and the new observational cosmological data are considered as evidence of the condensate mechanism of conformal symmetry breaking at the quantum level. The condensate mechanism occurs by means of normal ordering of field operators in QCD, Minimal Standard Model of electroweak interactions without the Higgs potential, and the Dirac conformal General Relativity with long range forces.

V. Pervushin; A. Arbuzov; B. Barbashov; A. Cherny; A. Dorokhov; A. Borowiec; R. Nazmitdinov; A. Pavlov; V. Shilin; A. Zakharov

2012-11-19

475

Ermakov-Lewis symmetry in photonic lattices.  

PubMed

We present a class of waveguide arrays that is the classical analog of a quantum harmonic oscillator, where the mass and frequency depend on the propagation distance. In these photonic lattices, refractive indices and second-neighbor couplings define the mass and frequency of the analog quantum oscillator, while first-neighbor couplings are a free parameter to adjust the model. The quantum model conserves the Ermakov-Lewis invariant, thus the photonic crystal also possesses this symmetry. PMID:24686680

Rodríguez-Lara, B M; Aleahmad, P; Moya-Cessa, H M; Christodoulides, D N

2014-04-01

476

Chiral symmetry, massive gluons and confinement  

SciTech Connect

It is quite difficult to obtain non-trivial chiral symmetry breaking solutions for the quark gap equation in the presence of dynamically generated gluon masses. An effective confining propagator has recently been proposed by Cornwall in order to solve this problem. We study phenomenological consequences of this approach, showing its compatibility with the experimental data. We argue that this confining propagator should be restricted to a small region of momenta, leading to effective four-fermion interactions at low energy.

Natale, A. A. [Instituto de Fisica Teorica - UNESP Rua Dr. Bento T. Ferraz, 271, Bl.II - 01140-070, Sao Paulo, SP (Brazil)

2013-03-25

477