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1

Topological Properties of Charge Algebras.  

National Technical Information Service (NTIS)

The basic problem studied is how far the topological properties of the metric space (A(mu), d sub mu) are reflected in the charge space (omega, A, mu), where A is a field of subsets of omega and mu is a charge on A. Considered are the properties of A and ...

K. P. S. Bhaskararao M. Bhaskararao

1973-01-01

2

Topological charges in monopole theories  

NASA Astrophysics Data System (ADS)

Let us consider a monopole theory with a compact, simply connected gauge group and the Higgs field in the adjoint representation. Using root theory we show that. (i) The homotopy class of the Higgs field is a p-tuple of integers where p is the dimension of the centre of the residual symmetry group. These “Higgs charges” can be expressed as surface integrals of differential forms. (ii) To any invariant polynomial on the Lie algebra is associated a topological invariant which turns out to be a combination of the Higgs charges. (iii) Electric charge is quantized. The monopole's magnetic charge is a combination — with the Higgs charges as coefficients — of p basic magnetic charges which satisfy generalized Dirac conditions. The example of G=SU( N) is worked out in detail.

Horváthy, P. A.; Rawnsley, J. H.

1984-12-01

3

Gribov copies and topological charge  

SciTech Connect

The existence of Gribov copies is a central feature of the field configuration space of confining gauge theories. In particular a transition between two Gribov copies with relative winding number implies a space-time configuration with topological charge. We explicitly demonstrate the proliferation of Gribov copies with relative winding number, where our focus is on localized (finite norm) configurations in Coulomb gauge. We then discuss the likelihood that some pairs of such copies are connected by Minkowski space solutions. We also comment on the relative importance of instantons and the connection to confinement.

Holdom, B. [Department of Physics, University of Toronto, Toronto, Ontario, M5S1A7 (Canada)

2010-11-15

4

Topological charges and the genus of surfaces  

Microsoft Academic Search

We show that the topological charge of the n-soliton solution of the sine-Gordon equation n[?] = (12?)[? dx?x?] is related to the genus g > 1 of a constant negative curvature compact orientable surface described by this configuration. The relation is n = 2(g ? 1), where n = 2? is even. The moduli space of complex dimension Bg =

Luis J. Boya; Antonio J. Segui-Santonja

1997-01-01

5

Charge density and topological analysis of ?-glutamine  

NASA Astrophysics Data System (ADS)

The experimental charge density and related topological properties of the amino acid L-glutamine were derived from a single crystal X-ray diffraction experiment at 130 K using conventional MoK? radiation and area detection technique. A multipolar refinement of the 6704 symmetry independent structure factors led to a 'rigid pseudoatom' model with crystallographic agreement factors R( F)=1.6%, Rw( F)=1.4%, GoF=1.04. The experimental topology in terms of Bader's 'atoms in molecules' (AIM) theory is compared to high-level ab initio calculations and to the average of the experimental topology in the 11 naturally occurring unsubstituted amino acids studied so far.

Wagner, A.; Luger, P.

2001-09-01

6

The various definitions of the derivative in linear topological spaces  

Microsoft Academic Search

The object of this article is to give a survey of the existing definitions of the operation of differentiation in linear topological spaces (l.t.s.) and to show the connections between them. There are at present more than a score of definitions of the derivative of a map of one l.t.s. into another. These definitions are stated in what are superficially

V. I. Averbukh; O. G. Smolyanov

1968-01-01

7

Measuring topological charge using Stokes parameters  

NASA Astrophysics Data System (ADS)

An alternative method to experimentally measure the topological charge of a vortex beam is presented. The method is based on the number of polarization singularities arising in the superposition of two off-axis Laguerre­-Gauss beams having orthogonal polarizations. The experimental setup consists of a modified Mach-Zehnder interferometer which provides control over the polarization structure by allowing us to introduce lateral displace­ ments as well as relative phase variations between the two arms of the interferometer. A comparison between theoretical and experimental results is done with very good agreement. This method offers an alternative for measuring orbital angular momentum content in a beam without the need of interfering with a reference plane wave. The dynamics of polarization singularities are also studied experimentally.

Perez-Garcia, Benjamin; Lopez-Mago, Dorilian; Yepiz Escalante, Adad; Hernandez-Aranda, Raul I.; Gutiérrez-Vega, Julio C.

2013-09-01

8

Topological Charge and the Laminar Structure of the QCD Vacuum  

SciTech Connect

Monte Carlo studies of pure glue SU(3) gauge theory using the overlap-based topological charge operator have revealed a laminar structure in the QCD vacuum consisting of extended, thin, coherent, locally 3-dimensional sheets of topological charge embedded in 4D space, with opposite sign sheets interleaved. In this talk I discuss the interpretation of these Monte Carlo results in terms of our current theoretical understanding of theta-dependence and topological structure in asymptotically free gauge theories.

Thacker, H. B. [University of Virginia, Charlottesville, VA 22904 (United States)

2007-02-27

9

Coherent topological charge structure in CPN-1 models and QCD  

NASA Astrophysics Data System (ADS)

In an effort to clarify the significance of the recent observation of long-range topological charge coherence in QCD gauge configurations, we study the local topological charge distributions in two-dimensional CPN-1 sigma models, using the overlap Dirac operator to construct the lattice topological charge. We find long-range sign coherence of topological charge along extended one-dimensional structures in two-dimensional spacetime. We discuss the connection between the long-range topological structure found in CPN-1 and the observed sign coherence along three-dimensional sheets in four-dimensional QCD gauge configurations. In both cases, coherent regions of topological charge form along membranelike surfaces of codimension one. We show that the Monte Carlo results, for both two-dimensional and four-dimensional gauge theory, support a view of topological charge fluctuations suggested by Lüscher and Witten. In this framework, the observed membranes are associated with boundaries between “k-vacua,” characterized by an effective local value of ? which jumps by ±2? across the boundary.

Ahmad, Saeed; Lenaghan, Jonathan T.; Thacker, H. B.

2005-12-01

10

Effect of topology on the critical charge in graphene  

SciTech Connect

We show that the critical charge for the Dirac excitations in gapless graphene depends on the spatial topology of the sample. In particular, for graphene cones, the effective value of the critical charge can tend toward zero for a suitable angle of the conical sample. We discuss the nature of the scattering phase shifts, quasibound state energies, and local density of states for a gapless graphene cone and determine the dependence of these physical quantities on the sample topology.

Chakraborty, Baishali; Gupta, Kumar S. [Theory Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700064 (India); Sen, Siddhartha [CRANN School of Physics, Trinity College, Dublin 2 (Ireland)

2011-03-15

11

Topological BPS charges in 10- and 11-dimensional supergravity  

SciTech Connect

We consider the supersymmetry algebras of the maximal supergravities in 10 and 11 dimensions. We construct expressions from which the topological charge structure of the algebras can be determined in supersymmetric curved backgrounds. These are interpreted as the topological charges of the 1/2-BPS states that are found in the theories. We consider charges for all the M-, NS- and D-branes as well as the Kaluza-Klein monopoles. We also show that the dimensional reduction relations between the 11-dimensional and IIA charges, and T-duality relations of the IIA and IIB charges, match those found for the branes themselves. Finally we consider the massive versions of the IIA and 11-dimensional theories and find that the expressions for the charges, with a slight modification, are still valid in those instances.

Callister, Andrew K.; Smith, Douglas J. [Department of Mathematical Sciences, Durham University, Science Laboratories, South Road, Durham. DH1 3LE (United Kingdom)

2008-09-15

12

Effects of topological charge in asymptotically free gauge theories  

NASA Astrophysics Data System (ADS)

In this thesis I report the results of a study of the effects of topological charge in the CPN-1 models and QCD. In QCD topological charge is responsible for the mass of the eta' particle, and is closely connected to chiral symmetry breaking, while in CP N-1 the details of the distribution of topological charge affect the behavior of the vacuum free energy and the nature of confinement. In the two-dimensional CPN-1 model a fractionally charged Wilson loop creates a 6-vacuum in the region of spacetime lying within the loop. I describe how we implemented fractionally charged Wilson loops on the lattice and present measurements of the free energy density epsilon(theta). Our lattice results show that the CP1 free energy is in good quantitative agreement with the dilute instanton gas approximation. The CP5 and CP9 models display a cusp at theta = pi which supports the large N argument for discrete, degenerate vacua. The second part of the thesis describes preliminary results of an investigation of topological charge in the three-dimensional CP 1 model. We discuss the monopole structure of topological charge and present preliminary Monte Carlo results for gauge configurations with monopole suppression. Our results suggest that gauge configurations with no monopoles may be organized into a discrete set of distinct topological sectors based upon the net number of closed magnetic flux loops that wrap around the entire lattice (periodic flux loops) in each of the three spacetime directions. We argue that a proper description of the vacuum state should include contributions from all of the topological sectors, and that regions of the phase diagram that include periodic flux loops should exhibit confinement of the zi particles. In the final chapter of the thesis I describe a calculation we performed to test a proposed equivalence between N = 1 Supersymmetric Yang-Mills theory and ordinary 1-flavor QCD. This calculation clarifies the important role of QCD topological charge in the dynamics of this equivalence. We also study the role of q q annihilation in the 1- and 2-flavor Nambu-Jonc Lasinio model, where annihilation terms arise from the chiral field determinant representing the axial U(1) anomaly.

Keith-Hynes, Patrick Thomas

13

Sub-3-cycle vortex pulses of tunable topological charge.  

PubMed

Novel types of reflective spiral micro-electro-mechanical systems were used to generate few-cycle vortex pulses of variable topological charge from a Ti:sapphire laser oscillator. The phase profile of these components was controlled by varying the temperature. The temporal properties of the pulses were characterized with spatially resolved nonlinear autocorrelation. The beam structure resembles a slightly distorted Laguerre-Gaussian distribution. The different topological charges were indicated by detecting Poynting-vector maps with a programmable Shack-Hartmann sensor of enhanced angular sensitivity. PMID:24104835

Bock, Martin; Brunne, Jens; Treffer, Alexander; König, Stefan; Wallrabe, Ulrike; Grunwald, Ruediger

2013-09-15

14

Phase transitions in charged topological-AdS black holes  

NASA Astrophysics Data System (ADS)

We study the perturbative behaviour of charged topological-AdS black holes. We calculate both analytically and numerically the quasi-normal modes of the electromagnetic and gravitational perturbations. Keeping the charge-to-mass ratio constant, we show that there is a second-order phase transition at a critical temperature at which the mass of the black hole vanishes. We pay special attention to the purely dissipative modes appearing in the spectrum as they behave singularly at the critical point.

Koutsoumbas, George; Papantonopoulos, Eleftherios; Siopsis, George

2008-05-01

15

Yang-Mills-Higgs monopole solutions of arbitrary topological charge  

Microsoft Academic Search

We propose a construction of static magnetic Yang-Mills-Higgs monopole solutions of arbitrary topological charge. They are axially symmetric and contain no free parameters except for their position. The regularity of the solutions has yet be proved; doing so would complete the constructive proof of existence.

M. K. Prasad

1981-01-01

16

Charge d-wave topological insulator  

NASA Astrophysics Data System (ADS)

Formation of a condensate of singlet electron-hole pairs in a two-dimensional metal lattice with the nesting of the Fermi contour is investigated. A numerical solution is obtained for the self-consistency equation for the insulating order parameter depending on the ratio of the coupling constants in the s- and d-wave channels of electron-hole pairing. Solutions with the pure orbital symmetry of s- and d-type are found, as well as solutions with the mixed s + d-symmetry. It is shown that in a wide range of values of the s- and d-wave coupling constants, the two-dimensional insulating order with the orbital symmetry can compete with pure ordered s- and d xy -states and mixed s + d-states. Time reversal symmetry breaking under an established real order with -wave symmetry may generate the imaginary component of the order parameter with symmetry d xy and cause a rise in topologically nontrivial d + id-wave ordering similar to the quantum Hall state in the absence of external magnetic field.

Kopaev, Yu. V.; Kapaev, V. V.; Belyavskii, V. I.

2013-10-01

17

Topological defects in mixtures of superconducting condensates with different charges  

NASA Astrophysics Data System (ADS)

We investigate the topological defects in phenomenological models describing mixtures of charged condensates with commensurate electric charges. Such situations are expected to appear for example in liquid metallic deuterium. This is modeled by a multicomponent Ginzburg-Landau theory where the condensates are coupled to the same gauge field by different coupling constants whose ratio is a rational number. We also briefly discuss the case where electric charges are incommensurate. Flux quantization and finiteness of the energy per unit length dictate that the different condensates have different winding and thus different number of (fractional) vortices. Competing attractive and repulsive interactions lead to molecule-like bound states between fractional vortices. Such bound states have finite energy and carry integer flux quanta. These can be characterized by the CP1 topological invariant that motivates their denomination as skyrmions.

Garaud, Julien; Babaev, Egor

2014-06-01

18

Topological charge and chiral anomalies in fermi superfluids  

NASA Astrophysics Data System (ADS)

We review some of the topological properties of Fermi superfluids, in particular the persistent currents in superfluid 3He. We show that the topological charge formalism developed by Garg et al. is related to the chiral anomaly viewpoint of Volovik and co-workers through the Callan-Harvey effect. We stress that the question of the existence of a "twist" term in the current induced by a texture is a history-dependent phenomenon which depends on how the textures are envisaged as being created.

Stone, Michael; Gaitan, Frank

1987-08-01

19

Magnetic Topology, Flux Emergence\\/Reconnection and Velocities from a Magnetic Charge Topology Model for Solar Active Regions  

Microsoft Academic Search

Magnetic Charge Topology (MCT) models represent the field in the solar corona as being due to collection of point magnetic charges located at or below the photosphere. These models have the advantage of providing a simple quantitative description of the field topology. We apply MCT to time series of magnetograms from the U. Hawai`i\\/Mees Solar Observatory Imaging Vector Magnetograph (IVM).

G. Barnes; D. W. Longcope; K. D. Leka

2004-01-01

20

Few-cycle vortex wavepackets with tunable topological charge  

NASA Astrophysics Data System (ADS)

The control of the orbital angular momentum (OAM) of ultrashort laser pulses with highly compact, low-dispersion and flexible devices opens new prospects for momentum-sensitive applications in plasmonics, materials processing, biochemistry, microscopy or optical data transfer. We report on the generation of few-cycle vortex pulses of variable topological charge from a Ti:sapphire laser oscillator with novel types of thermally tunable reflective, spiral-phase micro-electro-mechanical systems (MEMS). The spatial and temporal properties of the pulses were characterized by a reconfigurable, nondiffracting Shack-Hartmann wavefront autocorrelator. The intensity propagation can be described by a Laguerre-Gaussian beam with slight distortions caused by the line of maximum phase step. The different topological charges were indicated by quantitatively comparing the lengths of measured transversal Poynting-vector components to corresponding numerical simulations.

Grunwald, R.; Bock, M.; Brunne, J.; Wallrabe, U.

2014-02-01

21

Simultaneous Magnetic and Charge Doping of Topological Insulators with Carbon  

NASA Astrophysics Data System (ADS)

A two-step doping process, magnetic followed by charge or vice versa, is required to produce massive topological surface states (TSS) in topological insulators for many physics and device applications. Here, we demonstrate simultaneous magnetic and hole doping achieved with a single dopant, carbon, in Bi2Se3 by first-principles calculations. Carbon substitution for Se (CSe) results in an opening of a sizable surface Dirac gap (up to 82 meV), while the Fermi level remains inside the bulk gap and close to the Dirac point at moderate doping concentrations. The strong localization of 2p states of CSe favors spontaneous spin polarization via a p-p interaction and formation of ordered magnetic moments mediated by surface states. Meanwhile, holes are introduced into the system by CSe. This dual function of carbon doping suggests a simple way to realize insulating massive TSS.

Shen, Lei; Zeng, Minggang; Lu, Yunhao; Yang, Ming; Feng, Yuan Ping

2013-12-01

22

Simultaneous magnetic and charge doping of topological insulators with carbon.  

PubMed

A two-step doping process, magnetic followed by charge or vice versa, is required to produce massive topological surface states (TSS) in topological insulators for many physics and device applications. Here, we demonstrate simultaneous magnetic and hole doping achieved with a single dopant, carbon, in Bi2Se3 by first-principles calculations. Carbon substitution for Se (C(Se)) results in an opening of a sizable surface Dirac gap (up to 82 meV), while the Fermi level remains inside the bulk gap and close to the Dirac point at moderate doping concentrations. The strong localization of 2p states of C(Se) favors spontaneous spin polarization via a p-p interaction and formation of ordered magnetic moments mediated by surface states. Meanwhile, holes are introduced into the system by C(Se). This dual function of carbon doping suggests a simple way to realize insulating massive TSS. PMID:24476296

Shen, Lei; Zeng, Minggang; Lu, Yunhao; Yang, Ming; Feng, Yuan Ping

2013-12-01

23

C library for topological study of the electronic charge density.  

PubMed

The topological study of the electronic charge density is useful to obtain information about the kinds of bonds (ionic or covalent) and the atom charges on a molecule or crystal. For this study, it is necessary to calculate, at every space point, the electronic density and its electronic density derivatives values up to second order. In this work, a grid-based method for these calculations is described. The library, implemented for three dimensions, is based on a multidimensional Lagrange interpolation in a regular grid; by differentiating the resulting polynomial, the gradient vector, the Hessian matrix and the Laplacian formulas were obtained for every space point. More complex functions such as the Newton-Raphson method (to find the critical points, where the gradient is null) and the Cash-Karp Runge-Kutta method (used to make the gradient paths) were programmed. As in some crystals, the unit cell has angles different from 90°, the described library includes linear transformations to correct the gradient and Hessian when the grid is distorted (inclined). Functions were also developed to handle grid containing files (grd from DMol® program, CUBE from Gaussian® program and CHGCAR from VASP® program). Each one of these files contains the data for a molecular or crystal electronic property (such as charge density, spin density, electrostatic potential, and others) in a three-dimensional (3D) grid. The library can be adapted to make the topological study in any regular 3D grid by modifying the code of these functions. PMID:22865338

Vega, David; Aray, Yosslen; Rodríguez, Jesús

2012-12-01

24

Topological charge and the spectrum of exactly massless fermions on the lattice  

NASA Astrophysics Data System (ADS)

The square root of the positive definite Hermitian operator D†wDw in Neuberger's proposal of exactly massless quarks on the lattice is implemented by the recursion formula Yk+1=12(Yk+D†wDwY-1k) with Y0=1, where Y2k converges to D†wDw quadratically. The spectrum of the lattice Dirac operator for single massless fermion in two dimensional background U(1) gauge fields is investigated. For smooth background gauge fields with nonzero topological charge, the exact zero modes with definite chirality are reproduced to a very high precision on a finite lattice and the index theorem is satisfied exactly. The fermionic determinants are also computed and they are in good agreement with the continuum exact solution.

Chiu, Ting-Wai

1998-10-01

25

Topological charge pumping effect by the magnetization dynamics on the surface of three-dimensional topological insulators  

NASA Astrophysics Data System (ADS)

We discuss a current dynamics on the surface of a three-dimensional topological insulator induced by magnetization precession of an attached ferromagnet. It is found that the magnetization dynamics generates a direct charge current when the precession axis is within the surface plane. This rectification effect is due to a quantum anomaly and is topologically protected. The robustness of the rectification effect against first-varying exchange field and impurities is confirmed by explicit calculation.

Ueda, Hiroaki T.; Takeuchi, Akihito; Tatara, Gen; Yokoyama, Takehito

2012-03-01

26

Nonlinear Charged Black Holes in AdS Quasi-Topological Gravity  

NASA Astrophysics Data System (ADS)

In this paper, we present the static charged solutions of quartic quasi-topological gravity in the presence of a nonlinear electromagnetic field. Two branches of these solutions present black holes with one or two horizons or a naked singularity depending on the charge and mass of the black hole. The entropy of the charged black holes of fourth-order quasi-topological gravity through the use of Wald formula is computed and the mass, temperature and the charge of these black holes are found as well. We show that black holes with spherical, flat and hyperbolical horizon in quasi-topological gravity are stable for any allowed quasi-topological parameters. We also investigate the stability of nonlinear charged black holes.

Ghanaatian, Mohammad; Bazrafshan, Afsaneh

2013-11-01

27

Three-dimensional SCFT on conic space as hologram of charged topological black hole  

NASA Astrophysics Data System (ADS)

We construct three-dimensional = 2 supersymmetric field theories on conic spaces. Built upon the fact that the partition function depends solely on the Reeb vector of the Killing vector, we propose that holographic dual of these theories are four-dimensional, supersymmetric charged topological black holes. With the supersymmetry localization technique, we study conserved supercharges, free energy, and supersymmetric Rényi entropy. At planar large N limit, we demonstrate perfect agreement between the superconformal field theories and the supersymmetric charged topological black holes.

Huang, Xing; Rey, Soo-Jong; Zhou, Yang

2014-03-01

28

Topological charge pumping effect by the magnetization dynamics on the Surface of Three-Dimensional Topological Insulators  

NASA Astrophysics Data System (ADS)

We discuss a current dynamics on the surface of a 3-dimensional topological insulator induced by magnetization precession of a ferromagnet attached. It is found that the magnetization dynamics generates a direct charge current when the precession axis is within the surface plane. This rectification effect is due to a quantum anomaly (parity anomaly) and is topologically protected. The robustness of the rectification effect against first-varying exchange field is confirmed by the explicit calculation, where we adopt the dimensional regularization to remove the divergence which is inevitable in the study on the electromagnetic response of the Dirac system.

Ueda, Hiroaki; Takeuchi, Akihito; Tatara, Gen; Yokoyama, Takehito

2012-02-01

29

Charge and spin fractionalization in strongly correlated topological insulators.  

PubMed

We construct an effective topological Landau-Ginzburg theory that describes general SU(2) incompressible quantum liquids of strongly correlated particles in two spatial dimensions. This theory characterizes the fractionalization of quasiparticle quantum numbers and statistics in relation to the topological ground-state symmetries, and generalizes the Chern-Simons, BF ('background field') and hierarchical effective gauge theories to an arbitrary representation of the SU(2) symmetry group. We mainly focus on fractional topological insulators with time-reversal symmetry, which are treated as SU(2) generalizations of the quantum Hall effect. PMID:23209083

Nikoli?, Predrag

2013-01-16

30

Topology of the spin-polarized charge density in bcc and fcc iron.  

PubMed

We report the first investigation of the topology of spin-polarized charge density, specifically in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical. In these cases, the two spin densities are correlated: the spin-minority electrons have directional bond paths and deep minima, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of distinct spin topologies allows us to show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter involves a topological catastrophe. PMID:18232817

Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P

2008-01-11

31

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

The primary goal of this research is to develop a solid-state high definition television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels per frame. This imager offers an order of magnitude improvement in speed over CCD designs and will allow for monolithic imagers operating from the IR to the UV. The technical approach of the project focuses on the development of the three basic components of the imager and their integration. The imager chip can be divided into three distinct components: (1) image capture via an array of avalanche photodiodes (APD's), (2) charge collection, storage and overflow control via a charge transfer transistor device (CTD), and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the development of manufacturable designs for each of these component devices. In addition to the development of each of the three distinct components, work towards their integration is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail in Sections 2-4.

Hunt, W. D.; Brennan, Kevin F.

1994-01-01

32

Importance of Charge Fluctuations for the Topological Phase in SmB6  

NASA Astrophysics Data System (ADS)

Typical Kondo insulators (KIs) can have a nontrivial Z2 topology because the energy gap opens at the Fermi energy (EF) by a hybridization between odd- and even-parity bands. SmB6 deviates from such KI behavior, and it has been unclear how the insulating phase occurs. Here, we demonstrate that charge fluctuations are the origin of the topological insulating phase in SmB6. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the d-f hybridized band at the X ¯ point, which is predicted to have odd parity and is required for a topological phase, gradually shifts from below to above EF. We conclude that SmB6 is a charge-fluctuating topological insulator.

Min, Chul-Hee; Lutz, P.; Fiedler, S.; Kang, B. Y.; Cho, B. K.; Kim, H.-D.; Bentmann, H.; Reinert, F.

2014-06-01

33

Importance of Charge Fluctuations for the Topological Phase in SmB_{6}.  

PubMed

Typical Kondo insulators (KIs) can have a nontrivial Z_{2} topology because the energy gap opens at the Fermi energy (E_{F}) by a hybridization between odd- and even-parity bands. SmB_{6} deviates from such KI behavior, and it has been unclear how the insulating phase occurs. Here, we demonstrate that charge fluctuations are the origin of the topological insulating phase in SmB_{6}. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the d-f hybridized band at the X[over ¯] point, which is predicted to have odd parity and is required for a topological phase, gradually shifts from below to above E_{F}. We conclude that SmB_{6} is a charge-fluctuating topological insulator. PMID:24949780

Min, Chul-Hee; Lutz, P; Fiedler, S; Kang, B Y; Cho, B K; Kim, H-D; Bentmann, H; Reinert, F

2014-06-01

34

Topological Insulator Magnetic Tunnel Junctions: Quantum Hall Effect and Fractional Charge via Folding  

NASA Astrophysics Data System (ADS)

We provide a characterization of tunneling between coupled topological insulators in 2D and 3D under the influence of a ferromagnetic layer. We explore conditions for such systems to exhibit integer quantum Hall physics and localized fractional charge, also taking into account interaction effects for the 2D case. We show that the effects of tunneling are topologically equivalent to a certain deformation or folding of the sample geometry. Our key advance is the realization that the quantum Hall or fractional charge physics can appear in the presence of only a single magnet unlike previous proposals which involve magnetic domain walls on the surface or edges of topological insulators, respectively. We give illustrative topological folding arguments to prove our results and show that for the 2D case our results are robust even in the presence of interactions.

Meng, Qinglei; Vishveshwara, Smitha; Hughes, Taylor L.

2012-10-01

35

Measuring topological charge in monte carlo simulation of SU( N) lattice gauge theories  

NASA Astrophysics Data System (ADS)

We describe a numerical method for measuring topological charge in SU( N) lattice gauge theories, and we outline the implementation of this method on a CDC CYBER 205. We estimate the CPU requirements of a usefully accurate calculation of the low and high temperature properties of the SU(3) topological susceptibility, Xt , which controls the mass splitting between the ? particle and the pseudoscalar octet of Goldstone bosons.

Moriarty, K. J. M.; Teper, M.

1986-09-01

36

Probing the vortex beams with fractional and integral topological charges using weak random scattering screen  

NASA Astrophysics Data System (ADS)

By use of the numerical calculation based on the Kirchhoff Green's integral theorem, we study the intensity distributions of speckle fields behind the weak random scattering screens illuminated by the Laguerre-Gaussian beams. It is found that the profile of bright spot similar to the peacock-feather-like in intensity distributions of speckle field, those bright spots show uniform distribution around the central dark spots, and the number of bright spots is related to the topological charges of the vortex beams. We are able to probe the topological charges of Laguerre-Gaussian beams directly by observing the bright spots in the intensity distributions patterns.

Liu, Man

2013-11-01

37

Lifetime of charged and neutral B hadrons using event topology  

NASA Astrophysics Data System (ADS)

The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z0 decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, ?charged/?neutral, was 1.09{-0.10/+0.11} (stat.)±0.08 (syst.). By making assumptions about the B{s/0} and ?{b/0} states, the B+ and B0 meson lifetimes were determined to be ?B+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and ?B+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was: ?B+/?B0 = 1.06{-0.11/+0.13} ±0.10. The mean B lifetime was also deduced to be < ? > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps.

Adam, W.; Adye, T.; Agasi, E.; Ajinenko, I.; Aleksan, R.; Alekseev, G. D.; Allport, P. P.; Almehed, S.; Alvsvaag, S. J.; Amaldi, U.; Amato, S.; Andreazza, A.; Andrieux, M. L.; Antilogus, P.; Anykeyev, V.; Apel, W. D.; Arnoud, Y.; Åsman, B.; Augustin, J. E.; Augustinus, A.; Baillon, P.; Bambade, P.; Barao, F.; Barate, R.; Bardin, D. Y.; Barker, G. J.; Baroncelli, A.; Barring, O.; Barrio, J. A.; Bartl, W.; Bates, M. J.; Battaglia, M.; Baubillier, M.; Baudot, J.; Becks, K.-H.; Begalli, M.; Beilliere, P.; Belokopytov, Yu.; Benvenuti, A. C.; Berggren, M.; Bertrand, D.; Bianchi, F.; Bigi, M.; Bilenky, M. S.; Billoir, P.; Bloch, D.; Blume, M.; Blyth, S.; Bocci, V.; Bolognese, T.; Bonesini, M.; Bonivento, W.; Booth, P. S. L.; Borisov, G.; Bosio, C.; Bosworth, S.; Botner, O.; Bouquet, B.; Bourdarios, C.; Bowcock, T. J. V.; Bozzo, M.; Branchini, P.; Brand, K. D.; Brenner, R. A.; Bricman, C.; Brillault, L.; Brown, R. C. A.; Bruckman, P.; Brunet, J.-M.; Bugge, L.; Buran, T.; Buys, A.; Caccia, M.; Calvi, M.; Camacho Rozas, A. J.; Camporesi, T.; Canale, V.; Canepa, M.; Cankocak, K.; Cao, F.; Carena, F.; Carrilho, P.; Carroll, L.; Caso, C.; Castillo Gimenez, M. V.; Cattai, A.; Cavallo, F. R.; Cerrito, L.; Chabaud, V.; Charpentier, Ph.; Chaussard, L.; Chauveau, J.; Checchia, P.; Chelkov, G. A.; Chierici, R.; Chliapnikov, P.; Chochula, P.; Chorowicz, V.; Cindro, V.; Collins, P.; Contreras, J. L.; Contri, R.; Cortina, E.; Cosme, G.; Cossutti, F.; Crawley, H. B.; Crennell, D.; Crosetti, G.; Cuevas Maestro, J.; Czellar, S.; Dahl-Jensen, E.; Dahm, J.; Dalmagne, B.; Dam, M.; Damgaard, G.; Daum, A.; Dauncey, P. D.; Davenport, M.; da Silva, W.; Defoix, C.; Della Ricca, G.; Delpierre, P.; Demaria, N.; de Angelis, A.; de Boeck, H.; de Boer, W.; de Brabandere, S.; de Clercq, C.; de La Vaissiere, C.; de Lotto, B.; de Min, A.; de Paula, L.; de Saint-Jean, C.; Dijkstra, H.; di Ciaccio, L.; Djama, F.; Dolbeau, J.; Donszelmann, M.; Doroba, K.; Dracos, M.; Drees, J.; Drees, K. A.; Dris, M.; Dufour, Y.; Dupont, F.; Edsall, D.; Ehret, R.; Eigen, G.; Ekelof, T.; Ekspong, G.; Elsing, M.; Engel, J.-P.; Ershaidat, N.; Erzen, B.; Espirito Santo, M.; Falk, E.; Fassouliotis, D.; Feindt, M.; Ferrer, A.; Filippas, T. A.; Firestone, A.; Fischer, P. A.; Foeth, H.; Fokitis, E.; Fontanelli, F.; Formenti, F.; Franek, B.; Frenkiel, P.; Fries, D. C.; Frodesen, A. G.; Frhwirth, R.; Fulda-Quenzer, F.; Furstenau, H.; Fuster, J.; Galloni, A.; Gamba, D.; Gandelman, M.; Garcia, C.; Garcia, J.; Gaspar, C.; Gasparini, U.; Gavillet, Ph.; Gazis, E. N.; Gele, D.; Gerber, J.-P.; Gibbs, M.; Gillespie, D.; Gokieli, R.; Golob, B.; Gopal, G.; Gorn, L.; Gorski, M.; Gouz, Yu.; Gracco, V.; Graziani, E.; Grosdidier, G.; Gunnarsson, P.; Gunther, M.; Guy, J.; Haedinger, U.; Hahn, E.; Hahn, M.; Hahn, S.; Hajduk, Z.; Hallgren, A.; Hamacher, K.; Hao, W.; Harris, F. J.; Hedberg, V.; Henriques, R.; Hernandez, J. J.; Herquet, P.; Herr, H.; Hessing, T. L.; Higon, E.; Hilke, H. J.; Hill, T. S.; Holmgren, S.-O.; Holt, P. J.; Holthuizen, D.; Houlden, M.; Hrubec, J.; Huet, K.; Hultqvist, K.; Ioannou, P.; Jackson, J. N.; Jacobsson, R.; Jalocha, P.; Janik, R.; Jarlskog, G.; Jarry, P.; Jean-Marie, B.; Johansson, E. K.; Jonsson, L.; Jonsson, P.; Joram, C.; Juillot, P.; Kaiser, M.; Kalmus, G.; Kapusta, F.; Karlsson, M.; Karvelas, E.; Katsanevas, S.; Katsoufis, E. C.; Keranen, R.; Khomenko, B. A.; Khovanski, N. N.; King, B.; Kjaer, N. J.; Klein, H.; Klovning, A.; Kluit, P.; Koehne, J. H.; Koene, B.; Kokkinias, P.; Koratzinos, M.; Korcyl, K.; Kostioukhine, V.; Kourkoumelis, C.; Kouznetsov, O.; Kramer, P. H.; Krammer, M.; Kreuter, C.; Krolikowski, J.; Kronkvist, I.; Krumstein, Z.; Krupinski, W.; Kubinec, P.; Kucewicz, K.; Kurvinen, K.; Lacasta, C.; Laktineh, I.; Lamblot, S.; Lamsa, J. W.; Lanceri, L.; Lane, D. W.; Langefeld, P.; Lapin, V.; Last, I.; Laugier, J.-P.; Lauhakangas, R.; Leder, G.; Ledroit, F.; Lefebure, V.; Legan, C. K.; Leitner, R.; Lemoigne, Y.; Lemonne, J.; Lenzen, G.; Lepeltier, V.; Lesiak, T.; Liko, D.; Lindner, R.; Lipniacka, A.; Lippi, I.; Loerstad, B.; Lokajicek, M.; Loken, J. G.; Lopez, J. M.; Lopez-Fernandez, A.; Lopez Aguera, M. A.; Loukas, D.; Lutz, P.; Lyons, L.; MacNaughton, J.; Maehlum, G.; Maio, A.; Malychev, V.; Mandl, F.; Marco, J.; Marechal, B.; Margoni, M.; Marin, J.-C.; Mariotti, C.; Markou, A.; Maron, T.; Martinez-Rivero, C.; Martinez-Vidal, F.; Marti I Garcia, S.; Matorras, F.; Matteuzzi, C.; Matthiae, G.; Mazzucato, M.; Cubbin, M. Mc.; Kay, R. Mc; Nulty, R. Mc; Medbo, J.; Meroni, C.; Meyer, W. T.; Michelotto, M.; Migliore, E.; Mirabito, L.; Mitaroff, W. A.; Mjoernmark, U.; Moa, T.; Moeller, R.; Moenig, K.; Monge, M. R.; Morettini, P.; Mueller, H.; Mundim, L. M.; Murray, W. J.; Muryn, G.; Myatt, G.; Naraghi, F.; Navarria, F. L.; Navas, S.; Negri, P.

1995-09-01

38

Effect of topological defects and Coulomb charge on the low energy quantum dynamics of gapped graphene  

NASA Astrophysics Data System (ADS)

We study the combined effect of a conical topological defect and a Coulomb charge impurity on the dynamics of Dirac fermions in gapped graphene. Beyond a certain strength of the Coulomb charge, quantum instability sets in, which demarcates the boundary between sub- and supercritical values of the charge. In the subcritical regime, for certain values of the system parameters, the allowed boundary conditions in a gapped graphene cone can be classified in terms of a single real parameter. We show that the observables such as local density of states, scattering phase shifts and the bound state spectra are sensitive to the value of this real parameter, which is interesting from an empirical point of view. For a supercritical Coulomb charge, we analyze the system with a regularized potential as well as with a zigzag boundary condition and find the effect of the sample topology on the observable features of the system.

Chakraborty, Baishali; Gupta, Kumar S.; Sen, Siddhartha

2013-02-01

39

Topology of drift trajectories of charged particles in a tokamak  

NASA Astrophysics Data System (ADS)

The topology of drift orbits in a tokamak is analyzed in the entire cross section of the device both near the magnetic axis and at the periphery of the plasma column. The use of invariants of the drift equations (the generalized momentum, magnetic moment, and total energy) as variables for the entire cross section of the plasma column and self-similar variables near the magnetic axis makes it possible to comprehensively classify closed drift orbits in a tokamak. When describing orbits of different types and domains of their existence, discriminant and locus curves obtained by the methods of differential geometry are used to determine the ranges in which the invariants vary. The influence of the nonuniformity of the longitudinal current on the drift trajectories of fast particles is studied. The works in which, together with known types of orbits, trajectories along which particles leave the plasma column and can fall on the chamber wall are analyzed.

Gott, Yu. V.; Yurchenko, E. I.

2014-04-01

40

Low dimensional long range topological charge structure in the QCD vacuum  

SciTech Connect

While sign-coherent 4-dimensional structures cannot dominate topological charge fluctuations in the QCD vacuum at all scales due to reflection positivity, it is possible that enhanced coherence exists over extended space-time regions of lower dimension. Using the overlap Dirac operator to calculate topological charge density, we present evidence for such structure in pure-glue SU(3) lattice gauge theory. It is found that a typical equilibrium configuration is dominated by two oppositely-charged sign-coherent connected structures (``sheets'') covering about 80% of space-time. Each sheet is built from elementary 3-d cubes connected through 2-d faces, and approximates a low-dimensional curved manifold (or possibly a fractal structure) embedded in the 4-d space. At the heart of the sheet is a ``skeleton'' formed by about 18% of the most intense space-time points organized into a global long-range structure, involving connected parts spreading over maximal possible distances. We find that the skeleton is locally 1-dimensional and propose that its geometrical properties might be relevant for understanding the possible role of topological charge fluctuations in the physics of chiral symmetry breaking.

I. Horvath; S.J. Dong; T. Draper; F.X. Lee; K.F. Liu; N. Mathur; H.B. Thacker; J.B. Zhang

2003-12-01

41

Topology and shape optimization of induced-charge electro-osmotic micropumps  

NASA Astrophysics Data System (ADS)

For a dielectric solid surrounded by an electrolyte and positioned inside an externally biased parallel-plate capacitor, we study numerically how the resulting induced-charge electro-osmotic (ICEO) flow depends on the topology and shape of the dielectric solid. In particular, we extend existing conventional electrokinetic models with an artificial design field to describe the transition from the liquid electrolyte to the solid dielectric. Using this design field, we have succeeded in applying the method of topology optimization to find system geometries with non-trivial topologies that maximize the net induced electro-osmotic flow rate through the electrolytic capacitor in the direction parallel to the capacitor plates. Once found, the performance of the topology-optimized geometries has been validated by transferring them to conventional electrokinetic models not relying on the artificial design field. Our results show the importance of the topology and shape of the dielectric solid in ICEO systems and point to new designs of ICEO micropumps with significantly improved performance.

Gregersen, M. M.; Okkels, F.; Bazant, M. Z.; Bruus, H.

2009-07-01

42

An Acoustic Charge Transport Imager for High Definition Television  

NASA Technical Reports Server (NTRS)

This project, over its term, included funding to a variety of companies and organizations. In addition to Georgia Tech these included Florida Atlantic University with Dr. William E. Glenn as the P.I., Kodak with Mr. Mike Richardson as the P.I. and M.I.T./Polaroid with Dr. Richard Solomon as the P.I. The focus of the work conducted by these organizations was the development of camera hardware for High Definition Television (HDTV). The focus of the research at Georgia Tech was the development of new semiconductor technology to achieve a next generation solid state imager chip that would operate at a high frame rate (I 70 frames per second), operate at low light levels (via the use of avalanche photodiodes as the detector element) and contain 2 million pixels. The actual cost required to create this new semiconductor technology was probably at least 5 or 6 times the investment made under this program and hence we fell short of achieving this rather grand goal. We did, however, produce a number of spin-off technologies as a result of our efforts. These include, among others, improved avalanche photodiode structures, significant advancement of the state of understanding of ZnO/GaAs structures and significant contributions to the analysis of general GaAs semiconductor devices and the design of Surface Acoustic Wave resonator filters for wireless communication. More of these will be described in the report. The work conducted at the partner sites resulted in the development of 4 prototype HDTV cameras. The HDTV camera developed by Kodak uses the Kodak KAI-2091M high- definition monochrome image sensor. This progressively-scanned charge-coupled device (CCD) can operate at video frame rates and has 9 gm square pixels. The photosensitive area has a 16:9 aspect ratio and is consistent with the "Common Image Format" (CIF). It features an active image area of 1928 horizontal by 1084 vertical pixels and has a 55% fill factor. The camera is designed to operate in continuous mode with an output data rate of 5MHz, which gives a maximum frame rate of 4 frames per second. The MIT/Polaroid group developed two cameras under this program. The cameras have effectively four times the current video spatial resolution and at 60 frames per second are double the normal video frame rate.

Hunt, William D.; Brennan, Kevin; May, Gary; Glenn, William E.; Richardson, Mike; Solomon, Richard

1999-01-01

43

Surface states of charge carriers in epitaxial films of the topological insulator Bi2Te3  

NASA Astrophysics Data System (ADS)

The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S( k F), the wave vector k F, and the surface concentration of charge carriers n s on the frequency of magnetoresistance oscillations in p-type Bi2Te3 heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi2Te3 films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.

Luk'yanova, L. N.; Boikov, Yu. A.; Danilov, V. A.; Usov, O. A.; Volkov, M. P.; Kutasov, V. A.

2014-05-01

44

On the critical phenomena and thermodynamics of charged topological dilaton AdS black holes  

NASA Astrophysics Data System (ADS)

In this paper, we study the phase structure and equilibrium state space geometry of charged topological dilaton black holes in ( n+1)-dimensional anti-de Sitter spacetime. By considering the pairs of parameters ( P˜ V) and ( Q˜ U) as variables, we analyze the phase structure and critical phenomena of black holes and discuss the relation between the two kinds of critical phenomena. We find that the phase structures and critical phenomena drastically depend on the cosmological constant l (or the static electric charge Q of the black holes), dimensionality n and dilaton field ?.

Zhao, Ren; Zhao, Hui-Hua; Ma, Meng-Sen; Zhang, Li-Chun

2013-12-01

45

Comparison of converter topologies for charging capacitors used in pulsed load applications  

NASA Technical Reports Server (NTRS)

The authors present a qualitative comparison of different power converter topologies which may be utilized for charging capacitors in pulsed power applications requiring voltages greater than 1 kV. The operation of the converters in capacitor charging applications is described, and relevant advantages are presented. All of the converters except one may be classified in the high-frequency switching category. One of the benefits from high-frequency operation is a reduction in size and weight. The other converter discussed is a member of the command resonant changing category. The authors first describe a boost circuit which functions as a command resonant charging circuit and utilizes a single pulse of current to charge the capacitor. The discussion of high-frequency converters begins with the flyback and Ward converters. Then, the series, parallel, and series/parallel resonant converters are examined.

Nelms, R. M.; Schatz, J. E.; Pollard, Barry

1991-01-01

46

Comparative investigation of surface charge transport in graphene and topological insulator  

NASA Astrophysics Data System (ADS)

The surface state of topological insulator (TI) and graphene show similar two dimensional ambipolar electronic transport. The Dirac electrons on these surfaces share common transport properties. In this study we provide a comparative investigation based on Boltzmann transport theory to identify similarities and differences between the transport mechanisms in graphene and TI. The band structure of graphene has symmetry between the electron and hole bands, however the band structure of the surface states of TI has asymmetry between the electron and hole bands. This asymmetry in band structure results asymmetric ambipolar behavior in the charge transport. We provide a device model which includes the Dirac equation and band asymmetry to obtain the transfer and output characteristics. We anticipate that, having an enormous progress in graphene based electronics, this comparative investigation could provide a road map for electronic devices based on topological insulators.

Pince, Ercag; Kocabas, Coskun

2013-03-01

47

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

In this report we present the progress during the second six month period of the project. This includes both experimental and theoretical work on the acoustic charge transport (ACT) portion of the chip, the theoretical program modelling of both the avalanche photodiode (APD) and the charge transfer and overflow transistor and the materials growth and fabrication part of the program.

Hunt, William D.; Brennan, Kevin F.; Summers, Chris J.

1992-01-01

48

Influence of topological charges on random wandering of optical vortex propagating through turbulent atmosphere  

NASA Astrophysics Data System (ADS)

We investigate the random wandering behavior of optical vortex over propagation distance of 5 km in weak turbulence. The multiple random phase screen simulation method and vortex extracting method are utilized to calculate the optical vortex positions (x,y) on the receiver plane. Numerical results reveal that x and y are Gaussian random variables. However, the errors of Gaussian fitting become larger and the Gaussian fitting curves become broader as topological charge of optical vortex increases through the same atmospheric turbulence. Our results are crucial for free-space optical vortex communication.

Cui, Qianru; Li, Ming; Yu, Zhongyuan

2014-10-01

49

Topological charges in SL(2,R) covariant massive 11-dimensional and type IIB supergravity  

NASA Astrophysics Data System (ADS)

In this paper we construct closed expressions that correspond to the topological charges of the various 1/2-BPS states of the maximal 10- and 11-dimensional supergravity theories. These expressions are related to the structure of the supersymmetry algebras in curved spacetimes. We mainly focus on IIB supergravity and 11-dimensional supergravity in a double M9-brane background, with an emphasis on the SL(2,R) multiplet structure of the charges and how these map between theories. This includes the charges corresponding to the multiplets of 7- and 9-branes in IIB. We find that examining the possible multiplet structures of the charges provides another tool for exploring the spectrum of BPS states that appear in these theories. As a prerequisite to constructing the charges we determine the field equations and multiplet structure of the 11-dimensional gauge potentials, extending previous results on the subject. The massive gauge transformations of the fields are also discussed. We also demonstrate how these massive gauge transformations are compatible with the construction of an SL(2,R) covariant kinetic term in the 11-dimensional Kaluza-Klein monopole worldvolume action.

Callister, Andrew K.; Smith, Douglas J.

2009-12-01

50

Minimum conductivity and charge inhomogeneity in Bi2Se3 in the topological regime  

NASA Astrophysics Data System (ADS)

Using electrolytic and dielectric dual gating method, we report charge transport measurements of mechanically exfoliated Bi2Se3 in the topological insulator (TI) regime. We show that the surfaces of thin, low-doped Bi2Se3 crystals are strongly electrostatically coupled, and a gate electrode can be used to completely remove bulk charge carriers and bring both surfaces through the Dirac point nearly simultaneously with well-defined ambipolar electronic conduction of gapless surface states. In particular, we focus on linear carrier density dependent conductivity away from the Dirac point and a charge-inhomogeneous minimum conductivity region similar to that observed in graphene. An extension of the theory of charge disorder in graphene to Bi2Se3 explains well the mobility at high carrier density and the doping level at zero gate voltage. We show that the observed minimum conductivity is governed by induced carrier density that is self-consistently determined by the screened, charged impurity potential, as experimentally observed in recent STM study on surfaces of TIs.

Kim, Dohun; Cho, Sungjae; Butch, Nicholas; Syers, Paul; Kirshenbaum, Kevin; Paglione, Johnpierre; Fuhrer, Michael

2012-02-01

51

Spin-charge separation of plasmonic excitations in thin topological insulators  

NASA Astrophysics Data System (ADS)

We discuss plasmonic excitations in a thin slab of topological insulators. In the limit of no hybridization of the surface states and same electronic density of the two layers, the electrostatic coupling between the top and bottom layers leads to optical and acoustic plasmons which are purely charge and spin collective oscillations. We then argue that a recent experiment on the plasmonic excitations of Bi2Se3 [Di Pietro , Nat. Nanotechnol.1748-338710.1038/nnano.2013.134 8, 556 (2013)] must be explained by including the charge response of the two-dimensional electron gas of the depletion layer underneath the two surfaces. We also present an analytic formula to fit their data.

Stauber, T.; Gómez-Santos, G.; Brey, L.

2013-11-01

52

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

The primary goal of this research is to develop a solid-state television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels/frame. This imager will offer an order of magnitude improvements in speed over CCD designs and will allow for monolithic imagers operating from the IR to UV. The technical approach of the project focuses on the development of the three basic components of the imager and their subsequent integration. The camera chip can be divided into three distinct functions: (1) image capture via an array of avalanche photodiodes (APD's); (2) charge collection, storage, and overflow control via a charge transfer transistor device (CTD); and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the optimization of each of these component devices. In addition to the development of each of the three distinct components, work towards their integration and manufacturability is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail.

Hunt, W. D.; Brennan, K. F.; Summers, C. J.

1994-01-01

53

Phase Fluctuations and the Absence of Topological Defects in Photo-excited Charge Ordered Nickelate  

SciTech Connect

The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La{sub 1.75}Sr{sub 0.25}NiO{sub 4} to reveal unforeseen photoinduced phase fluctuations of the charge order parameter. Such fluctuations preserve long-range order without creating topological defects, distinct from thermal phase fluctuations near the critical temperature in equilibrium. Importantly, relaxation of the phase fluctuations is found to be an order of magnitude slower than that of the order parameter's amplitude fluctuations, and thus limits charge order recovery. This new aspect of phase fluctuations provides a more holistic view of the phase's importance in ordering phenomena of quantum matter.

Lee, W.S.; Chuang, Y.D.; Moore, R.G.; Zhu, Y.; Patthey, L.; Trigo, M.; Lu, D.H.; Kirchmann, P.S.; Krupin, O.; Yi, M.; Langner, M.; Huse, N.; Robinson, J.S.; Chen, Y.; Zhou, S.Y.; Coslovich, G.; Huber, B.; Reis, D.A.; Kaindl, R.A.; Schoenlein, R.W.; Doering, D.

2012-05-15

54

Phase fluctuations and the absence of topological defects in photo-excited charge ordered nickelate  

SciTech Connect

The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La1.75Sr0.25NiO4 to reveal unforeseen photoinduced phase fluctuations of the charge order parameter. Such fluctuations preserve long-range order without creating topological defects, distinct from thermal phase fluctuations near the critical temperature in equilibrium. Importantly, relaxation of the phase fluctuations is found to be an order of magnitude slower than that of the order parameter's amplitude fluctuations, and thus limits charge order recovery. This new aspect of phase fluctuations provides a more holistic view of the phase's importance in ordering phenomena of quantum matter.

Lee, W.S.; Chuang, Y.D.; Moore, R.G.; Zhu, Y.; Patthey, L.; Trigo, M.; Lu, D.H.; Kirchmann, P.S.; Krupin, O.; Yi, M.; Langner, M.; Huse, N.; Robinson, J.S.; Chen, Y.; Zhou, S.Y.; Coslovich, G.; Huber, B.; Reis, D.A.; Kaindl, R.A.; Schoenlein, R.W.; Doering, D.; Denes, P.; Schlotter, W.F.; Turner, J.J.; Johnson, S.L.; F& #246; rst, M.; Sasagawa, T.; Kung, Y.F.; Sorini, A.P.; Kemper, A.F.; Moritz, B.; Devereaux, T.P.; Lee, D.-H.; Shen, Z.X.; Hussain, Z.

2012-01-01

55

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

This report covers: (1) invention of a new, ultra-low noise, low operating voltage APD which is expected to offer far better performance than the existing volume doped APD device; (2) performance of a comprehensive series of experiments on the acoustic and piezoelectric properties of ZnO films sputtered on GaAs which can possibly lead to a decrease in the required rf drive power for ACT devices by 15dB; (3) development of an advanced, hydrodynamic, macroscopic simulator used for evaluating the performance of ACT and CTD devices and aiding in the development of the next generation of devices; (4) experimental development of CTD devices which utilize a p-doped top barrier demonstrating charge storage capacity and low leakage currents; (5) refinements in materials growth techniques and in situ controls to lower surface defect densities to record levels as well as increase material uniformity and quality.

Hunt, William D.; Brennan, Kevin F.; Summers, Christopher J.

1993-01-01

56

Selective probing of photoinduced charge and spin dynamics in the bulk and surface of a topological insulator.  

PubMed

Topological insulators possess completely different spin-orbit coupled bulk and surface electronic spectra that are each predicted to exhibit exotic responses to light. Here we report time-resolved fundamental and second harmonic optical pump-probe measurements on the topological insulator Bi(2)Se(3) to independently measure its photoinduced charge and spin dynamics with bulk and surface selectivity. Our results show that a transient net spin density can be optically induced in both the bulk and surface, which may drive spin transport in topological insulators. By utilizing a novel rotational anisotropy analysis we are able to separately resolve the spin depolarization, intraband cooling, and interband recombination processes following photoexcitation, which reveal that spin and charge degrees of freedom relax on very different time scales owing to strong spin-orbit coupling. PMID:21902428

Hsieh, D; Mahmood, F; McIver, J W; Gardner, D R; Lee, Y S; Gedik, N

2011-08-12

57

Propagation of a topologically half-charge vortex light beam in a self-focusing photorefractive medium.  

PubMed

While a fundamental Gaussian light beam can form stably a spatial soliton in certain self-focusing medium, a single-wave topologically integer-n-charge vortex light beam cannot. It breaks up into 2n filaments due to symmetry breaking and azimuthal instability, in which every azimuthal section of a ? phase range from a soliton and repels itself from its azimuthal neighboring soliton. Then what happens to the half-charge vortex light beam, which contains only one section of a ? phase range? We investigate experimentally and theoretically the propagation and stability of a topologically half-charge vortex light beam in a self-focusing photorefractive medium. We observed that the light beam propagates unstably in a self-focusing medium and breaks up into three filaments. This result is confirmed by numerical simulation and perturbation analysis. PMID:24663609

Chen, Chih-Rong; Yeh, Chih-Hung; Shih, Ming-Feng

2014-02-10

58

Flux-charge duality and topological quantum phase fluctuations in quasi-one-dimensional superconductors  

NASA Astrophysics Data System (ADS)

It has long been thought that macroscopic phase coherence breaks down in effectively lower-dimensional superconducting systems even at zero temperature due to enhanced topological quantum phase fluctuations. In quasi-one-dimensional wires, these fluctuations are described in terms of ‘quantum phase-slip’ (QPS): tunneling of the superconducting order parameter for the wire between states differing by ±2? in their relative phase between the wire's ends. Over the last several decades, many deviations from conventional bulk superconducting behavior have been observed in ultra-narrow superconducting nanowires, some of which have been identified with QPS. While at least some of the observations are consistent with existing theories for QPS, other observations in many cases point to contradictory conclusions or cannot be explained by these theories. Hence, our understanding of the nature of QPS, and its relationship to the various observations, has remained imcomplete. In this paper we present a new model for QPS which takes as its starting point an idea originally postulated by Mooij and Nazarov (2006 Nature Phys. 2 169): that flux-charge duality, a classical symmetry of Maxwell's equations, can be used to relate QPS to the well-known Josephson tunneling of Cooper pairs. Our model provides an alternative, and qualitatively different, conceptual basis for QPS and the phenomena which arise from it in experiments, and it appears to permit for the first time a unified understanding of observations across several different types of experiments and materials systems.

Kerman, Andrew J.

2013-10-01

59

Topology of charge density and elastic properties of Ti3SiC2 polymorphs  

SciTech Connect

Using an all-electron, full potential first-principles method, we have investigated the topology of charge density and elastic properties of the two polymorphs, alpha and beta, of Ti3SiC2. The bonding effect was analyzed based on Bader's quantum theory of ''atoms in molecules'' (AIM). It was found that the Ti-Si bonding effect is significantly weaker in beta than in alpha, giving less stabilizing effect for beta. The Si-C bonds, which are absent in alpha, are formed in beta and provide additional stabilizing effect for beta. In contrast to conventional thinking, there is no direction interaction between Ti atoms in both alpha and beta. The calculated elastic properties are in good agreement with the experimental results, giving the bulk modulus of about 180 GPa and the Poisson's ratio of 0.2. The beta phase is generally softer than the alpha phase. As revealed by the direction dependent Young's modulus, there is only slight elastic anisotropy in Ti3SiC2. For alpha, Young's modulus is minimum in the c direction and maximum in the directions 42o from c. For beta, the maximum lies in the c direction, in part due to the formation of Si-C bonds in this direction.

Yu, Rong; Zhang, Xiao Feng; He, Lian Long; Ye, Heng Qiang

2004-06-24

60

Carrier control via charge transfer at the topological-insulator/organic-molecule interface  

NASA Astrophysics Data System (ADS)

A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications.

Tanigaki, Katsumi; Tanabe, Yoichi; Kuynh, Khuong; Urata, Takahiro; Nouchi, Ryo; Heguri, Satoshi; Shimotani, Hidekazu

2013-03-01

61

Topological charged black holes in high dimensional spacetimes and their formation from gravitational collapse of a type II fluid  

NASA Astrophysics Data System (ADS)

Topological charged black holes coupled with a cosmological constant in R2×XD-2 spacetimes are studied, where XD-2 is an Einstein space of the form (D-2)RAB=k(D-3)hAB. The global structure for the four-dimensional spacetimes with k=0 is investigated systematically. The most general solutions that represent a type II fluid in such a high dimensional spacetime are found and show that topological charged black holes can be formed from the gravitational collapse of such a fluid. When the spacetime is (asymptotically) self-similar, the collapse always forms black holes for k=0, -1, in contrast with the case k=1, where it can form either black holes or naked singularities.

Wu, Yumei; da Silva, M. F.; Santos, N. O.; Wang, Anzhong

2003-10-01

62

Effect of static charge fluctuations on the conduction along the edge of two-dimensional topological insulator  

NASA Astrophysics Data System (ADS)

Static charge disorder may create electron puddles in the bulk of a material which nominally is in the insulating state. A single puddle -- quantum dot -- coupled to the helical edge of a two-dimensional topological insulator enhances the electron backscattering within the edge. The backscattering rate increases with the electron dwelling time in the dot. While remaining inelastic, the backscattering off a dot may be far more effective than the proposed earlier inelastic processes involving a local scatterer with no internal structure. We find the temperature dependence of the dot-induced correction to the universal conductance of the edge. In addition to the single-dot effect, we calculate the classical temperature-independent conductance correction caused by a weakly conducting bulk. We use our theory to assess the effect of static charge fluctuations in a heterostructure on the edge electron transport in a two-dimensional topological insulator.

Vayrynen, Jukka; Goldstein, Moshe; Glazman, Leonid

2013-03-01

63

Charge transport and shot noise on the surface of a topological insulator with a magnetic modulation  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the transport features and the Fano factor of Dirac electrons on the surface of a three-dimensional topological insulator with a magnetic modulation. We consider a hard wall bounding condition on the edge of the topological insulator, which implies that a surface state of the topological insulator is insulating. We find that a valley of conductivity at the Dirac point is associated with a Fano factor peak, and more interestingly, this topological metal changes from insulating to metallic by controlling the effective exchange field.

Yuan, Jian-Hui; Cheng, Ze; Zhang, Jian-Jun; Zeng, Qi-Jun; Zhang, Jun-Pei

2012-04-01

64

Local description of the through phenyl transfer of a negative charge within resonance theory: topological effects in xylylene radical anions  

NASA Astrophysics Data System (ADS)

The topological effects specifying a di-substituted phenyl ring bearing a negative charge are investigated by considering the radical anions of para- and meta-xylylene isomers as model systems. The super exchange (SE) and double exchange (DE) component mechanisms describing the through phenyl transfer of a negative charge are considered and examined within `resonance' or `mesomeric' theory. The radical anion electronic events characterizing the DE and SE resonance structures are investigated by means of poly-electron population analysis. Correlated ab initio MO wavefunctions are used as the starting material in our calculations, and the various second quantized density operators are built on the basis of natural AOs. Conditional electronic events specifying SE or DE mechanisms are defined, and the corresponding probabilities are compared for meta and para topologies. The main trends are rationalized by comparing the effects provoked in phenyl ring when the negative charge is transferred from one substituent or the other. In para topology the effects are additive for the most important resonance structures, while in meta (characterized from `quantum interferences') the same effects are antagonist in all structures and for both SE and DE mechanisms.

Karafiloglou, Padeleimon; Launay, Jean-Pierre

1999-11-01

65

Fractional Topological Charge and Torons in Supersymmetric O(3) ?-MODEL and in Gauge Theories  

NASA Astrophysics Data System (ADS)

The new class of self-dual solutions with a fractional topological number in the 2d O(3) ?-model and 4d SUSY gluodynamics (SYM) are considered. The corresponding contribution to fermion condensate < bar ? ? > has finite nonzero value.

Zhitnitsky, A. R.

66

Surface state charge dynamics of a high-mobility three-dimensional topological insulator.  

PubMed

We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe, using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface-state dispersion within <1 meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics. PMID:22026887

Hancock, Jason N; van Mechelen, J L M; Kuzmenko, Alexey B; van der Marel, Dirk; Brüne, Christoph; Novik, Elena G; Astakhov, Georgy V; Buhmann, Hartmut; Molenkamp, Laurens W

2011-09-23

67

Surface State Charge Dynamics of a High-Mobility Three-Dimensional Topological Insulator  

NASA Astrophysics Data System (ADS)

We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe, using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface-state dispersion within <1meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics.

Hancock, Jason N.; van Mechelen, J. L. M.; Kuzmenko, Alexey B.; van der Marel, Dirk; Brüne, Christophe; Novik, Elena G.; Astakhov, Georgy V.; Buhmann, Hartmut; Molenkamp, Laurens W.

2011-09-01

68

Charged Particle Environment Definition for NGST: L2 Plasma Environment Statistics  

NASA Technical Reports Server (NTRS)

The plasma environment encountered by the Next Generation Space Telescope satellite in a halo orbit about L2 can include the Earth's magnetotail and magnetosheath in addition to the solar wind depending on the orbital radius chosen for the mission. Analysis of plasma environment impacts on the satellite requires knowledge of the average and extreme plasma characteristics to assess the magnitude of spacecraft charging and materials degradation expected for the mission lifetime. This report describes the analysis of plasma data from instruments onboard the IMP 8 and Geotail spacecraft used to produce the plasma database for the LRAD engineering-level phenomenology code developed to provide the NGST L2 environment definition.

Minow, Joseph I.; Blackwell, William C.; Neergaard, Linda F.; Evans, Steven W.; Hardage, Donna M.; Owens, Jerry K.

2000-01-01

69

Topologically nontrivial configurations associated with Hopf charges investigated in the two-component Ginzburg-Landau model  

NASA Astrophysics Data System (ADS)

We study the stability of Hopfions embedded in the Ginzburg-Landau (GL) model of two oppositely charged components. It has been shown by Babaev [Phys. Rev. B 65, 100512 (2002)] that this model contains the Faddeev-Skyrme (FS) model, which is known to have topologically stable configurations with a given Hopf charge, the so-called Hopfions. Hopfions are typically formed from a unit-vector field that points to a fixed direction at spatial infinity and locally forms a knot with a soft core. The GL model, however, contains extra fields beyond the unit-vector field of the FS model and this can, in principle, change the fate of topologically nontrivial configurations. We investigate the stability of Hopfions in the two-component GL model both analytically (scaling) and numerically (first order dissipative dynamics). A number of initial states with different Hopf charges are studied; we also consider various different scalar potentials, including a singular one. In all the cases studied, we find that the Hopfions tend to shrink into a thin loop that is too close to a singular configuration for our numerical methods to investigate.

Jäykkä, Juha; Hietarinta, Jarmo; Salo, Petri

2008-03-01

70

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

71

Symmetry-protected topological phases with charge and spin symmetries: Response theory and dynamical gauge theory in two and three dimensions  

NASA Astrophysics Data System (ADS)

A large class of symmetry-protected topological phases (SPT) in boson/spin systems have been recently predicted by the group cohomology theory. In this work, we consider bosonic SPT states at least with charge symmetry [U(1) or ZN] or spin-Sz rotation symmetry [U(1) or ZN] in two (2D) and three dimensions (3D) and the surface of 3D. If both are U(1), we apply external electromagnetic field/“spin gauge field” to study the charge/spin response. For the SPT examples we consider {i.e., Uc(1)?Z2T, Us(1)×Z2T, Uc(1)×[Us(1)?Z2]; subscripts c and s are short for charge and spin; Z2T and Z2 are time-reversal symmetry and ? rotation about Sy, respectively}, many variants of Witten effect in the 3D SPT bulk and various versions of anomalous surface quantum Hall effect are defined and systematically investigated. If charge or spin symmetry reduces to ZN by considering charge-N or spin-N condensate, instead of the linear response approach, we gauge the charge/spin symmetry, leading to a dynamical gauge theory with some remaining global symmetry. The 3D dynamical gauge theory describes a symmetry-enriched topological phase (SET), i.e., a topologically ordered state with global symmetry which admits nontrivial ground-state degeneracy depending on spatial manifold topology. For the SPT examples we consider, the corresponding SET states are described by dynamical topological gauge theory with topological BF term and axionic ? term in 3D bulk. In addition, the surface of SET is described by the chiral boson theory with quantum anomaly.

Ye, Peng; Wang, Juven

2013-12-01

72

Topology of electronic charge density and energetics of planar faults in fcc metals.  

PubMed

Using ab initio calculations we have studied the energetics and the evolution of the electronic charge density with shear in three fcc metals exhibiting different deformation properties, aluminum, silver, and iridium. The charge redistribution described by the change in character of specific charge density critical points (cps), is ascertained from the values of the charge density, rho(0), and its three principal curvatures, rho( parallel parallel), rho(hh), and rho(vv), respectively. The change in character of cps correlates with the energetics. For all three metals, rho(hh) vanishes near the unstable stacking configuration. The symmetry or asymmetry of the charge redistribution, measured by rho(hh)/rho(vv), may be an important factor determining stacking fault energies. PMID:11909471

Kioussis, Nicholas; Herbranson, M; Collins, E; Eberhart, M E

2002-03-25

73

[ital S][sup 1][times][ital S][sup 2] wormholes and topological charge  

SciTech Connect

I investigate solutions to the Euclidean Einstein-matter field equations with the topology [ital S][sup 1][times][ital S][sup 2][times][ital R] in a theory with a massless periodic scalar field and electromagnetism. These solutions carry the winding number of the periodic scalar as well as magnetic flux. They induce violations of a quasitopological conservation law which conserves the product of the magnetic flux and winding number on the background spacetime. I extend these solutions to a model with stable loops of superconducting cosmic string and interpret them as contributing to the decay of such loops.

Ridgway, S.A. (Physics Department, Columbia University, New York, New York 10027 (United States))

1994-07-15

74

Probing Membrane Topology of the Antimicrobial Peptide Distinctin by Solid-State NMR Spectroscopy in Zwitterionic and Charged Lipid Bilayers  

PubMed Central

Distinctin is a 47-residue antimicrobial peptide, which interacts with negatively charged membranes and is active against Gram-positive and Gram-negative bacteria. Its primary sequence comprises two linear chains of 22 (chain 1) and 25 (chain 2) residues, linked by a disulfide bridge between Cys19 of chain 1 and Cys23 of chain 2. Unlike other antimicrobial peptides, distinctin in the absence of the lipid membrane has a well-defined three-dimensional structure, which protects it from protease degradation. Here, we used static solid-state NMR spectroscopy to study the topology of distinctin in lipid bilayers. We found that In mechanically aligned lipid bilayers (charged or zwitterionic) this heterodimeric peptide adopts an ordered conformation absorbed on the surface of the membrane, with the long helix (chain 2), approximately parallel to the lipid bilayer (?5° from the membrane plane) and the short helix (chain 1) forming a ?24° angle. Since at lipid-to-protein molar ratio of 50:1 the peptide does not disrupt the macroscopic alignment of either charged or zwitterionic lipid bilayers, it is possible that higher concentrations might be needed for the hypothesized pore formation, or alternatively, distinctin elicits its cell disruption action by other mechanisms.

Verardi, Raffaello; Traaseth, Nathaniel J.; Shi, Lei; Porcelli, Fernando; Monfregola, Luca; De Luca, Stefania; Amodeo, Pietro; Veglia, Gianluigi; Scaloni, Andrea

2010-01-01

75

Spin torques and charge transport on the surface of topological insulator  

NASA Astrophysics Data System (ADS)

We study various aspects of interplay between two-dimensional helical electrons, realized on the surface of a three-dimensional topological insulator, and the magnetization of a ferromagnet coupled to them. The magnetization is assumed to be perpendicular to the surface, with small transverse fluctuations u. In the first part of this paper, we calculate spin torques that the helical electrons exert on the magnetization. Up to first orders with respect to u, space/time derivative and electric current, we have determined all torques, which include Gilbert damping, spin renormalization, current-induced spin-orbit torques, and gradient corrections to them. Thanks to the identity between the velocity and spin in this model, these torques have exact interpretation in terms of transport phenomena, namely, diagonal conductivity, (anomalous) Hall conductivity, and corrections to them due to ordinary Hall effect on top of the anomalous one. These torque (and transport) coefficients are studied in detail with particular attention to the effects of vertex corrections and type of impurities (normal and magnetic). It is shown rigorously that the conventional current-induced torques, namely, spin-transfer torque and the so-called ? term, are absent. An electromotive force generated by spin dynamics, which is the inverse to the current-induced spin-orbit torque, is also studied. In the second part, we study the feedback effects arising as combinations of current-induced spin-orbit torques and spin-dynamics-induced electromotive force. It is demonstrated that the Gilbert damping process in this system is completely understood as a feedback effect. Another feedback effect, which may be called "magnon-drag electrical conductivity," is shown to violate the exact correspondence between spin-torque and transport phenomena demonstrated in the first part.

Sakai, Akio; Kohno, Hiroshi

2014-04-01

76

Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM)  

PubMed Central

Charge densities have been determined by the Maximum Entropy Method (MEM) from the high-resolution, low-temperature (T ? 20?K) X-ray diffraction data of six different crystals of amino acids and peptides. A comparison of dynamic deformation densities of the MEM with static and dynamic deformation densities of multipole models shows that the MEM may lead to a better description of the electron density in hydrogen bonds in cases where the multipole model has been restricted to isotropic displacement parameters and low-order multipoles (l max = 1) for the H atoms. Topological properties at bond critical points (BCPs) are found to depend systematically on the bond length, but with different functions for covalent C—C, C—N and C—O bonds, and for hydrogen bonds together with covalent C—H and N—H bonds. Similar dependencies are known for AIM properties derived from static multipole densities. The ratio of potential and kinetic energy densities |V(BCP)|/G(BCP) is successfully used for a classification of hydrogen bonds according to their distance d(H?O) between the H atom and the acceptor atom. The classification based on MEM densities coincides with the usual classification of hydrogen bonds as strong, intermediate and weak [Jeffrey (1997) ?. An Introduction to Hydrogen Bonding. Oxford University Press]. MEM and procrystal densities lead to similar values of the densities at the BCPs of hydrogen bonds, but differences are shown to prevail, such that it is found that only the true charge density, represented by MEM densities, the multipole model or some other method can lead to the correct characterization of chemical bonding. Our results do not confirm suggestions in the literature that the promolecule density might be sufficient for a characterization of hydrogen bonds.

Netzel, Jeanette; van Smaalen, Sander

2009-01-01

77

Charging Dirac states at antiphase domain boundaries in the three-dimensional topological insulator Bi2Se3.  

PubMed

Using scanning tunneling microscopy and transmission electron microscopy, we demonstrate the existence of antiphase boundaries between neighboring grains shifted by a fraction of a quintuple layer in epitaxial (0001) films of the three-dimensional topological insulator Bi(2)Se(3). Scanning tunneling spectroscopy and first-principles calculations reveal that these antiphase boundaries provide electrostatic fields on the order of 10(8) V/m that locally charge the Dirac states, modulating the carrier density, and shift the Dirac point by up to 120 meV. This intrinsic electric field effect, demonstrated here near interfaces between Bi(2)Se(3) grains, provides direct experimental evidence at the atomic scale that the Dirac states are indeed robust against extended structural defects and tunable by electric field. These results also shed light on the recent observation of coexistence of Dirac states and two-dimensional electron gas on Bi(2)Se(3) (0001) after adsorption of metal atoms and gas molecules. PMID:23683233

Liu, Y; Li, Y Y; Gilks, D; Lazarov, V K; Weinert, M; Li, L

2013-05-01

78

Geometry and Topology  

NSDL National Science Digital Library

Geometry and Topology is "a fully refereed international journal dealing with all aspects of geometry and topology and their applications." The publisher, Geometry & Topology Publications (GTP), is a non-profit organization based in the Mathematics Department of the University of Warwick at Coventry, UK. Visitors can browse the journal, available free of charge electronically, or search by keyword or author. The moderate collection within the Geometry and Topology Monographs series includes research monographs and refereed conference proceedings.

79

Signatures of charge inhomogeneities in the infrared spectra of topological insulators Bi2Se3, Bi2Te3 and Sb2Te3.  

PubMed

We present the results of an infrared spectroscopy study of topological insulators Bi(2)Se(3), Bi(2)Te(3) and Sb(2)Te(3). Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi(2)Se(3), whereas in Bi(2)Te(3) and Sb(2)Te(3) it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature. PMID:23328626

Dordevic, S V; Wolf, M S; Stojilovic, N; Lei, Hechang; Petrovic, C

2013-02-20

80

Effects of bulk charged impurities on the bulk and surface transport in three-dimensional topological insulators  

SciTech Connect

In the three-dimensional topological insulator (TI), the physics of doped semiconductors exists literally side-by-side with the physics of ultrarelativistic Dirac fermions. This unusual pairing creates a novel playground for studying the interplay between disorder and electronic transport. In this mini-review, we focus on the disorder caused by the three-dimensionally distributed charged impurities that are ubiquitous in TIs, and we outline the effects it has on both the bulk and surface transport in TIs. We present self-consistent theories for Coulomb screening both in the bulk and at the surface, discuss the magnitude of the disorder potential in each case, and present results for the conductivity. In the bulk, where the band gap leads to thermally activated transport, we show how disorder leads to a smaller-than-expected activation energy that gives way to variable-range hopping at low temperatures. We confirm this enhanced conductivity with numerical simulations that also allow us to explore different degrees of impurity compensation. For the surface, where the TI has gapless Dirac modes, we present a theory of disorder and screening of deep impurities, and we calculate the corresponding zero-temperature conductivity. We also comment on the growth of the disorder potential in passing from the surface of the TI into the bulk. Finally, we discuss how the presence of a gap at the Dirac point, introduced by some source of time-reversal symmetry breaking, affects the disorder potential at the surface and the mid-gap density of states.

Skinner, B.; Chen, T.; Shklovskii, B. I., E-mail: shklovsk@physics.spa.umn.edu [University of Minnesota, Fine Theoretical Physics Institute (United States)

2013-09-15

81

Topological Solitons in Physics.  

ERIC Educational Resources Information Center

A broad definition of solitons and a discussion of their role in physics is given. Vortices and magnetic monopoles which are examples of topological solitons in two and three spatial dimensions are described in some detail. (BB)

Parsa, Zohreh

1979-01-01

82

Continuous lattices in formal topology  

Microsoft Academic Search

A representation of continuous and prime-continuous lattices via formal topology is found. This representation stems from\\u000a special examples of formal topologies in constructive analysis that give rise to the definition of the classes of locally\\u000a Stone and locally Scott formal topologies. As an application, a representation theorem for locally compact spaces is obtained.

Sara Negri

83

Topological relations between fuzzy regions in a fuzzy topological space  

NASA Astrophysics Data System (ADS)

Topological relations are one of the most important aspects in GIS modeling. The topological relations between crisp spatial objects have been well identified. However, the topological relations between fuzzy spatial objects need more investigation. This paper deals with building a special fuzzy topological space for fuzzy sets. Based on it, a formal definition of simple fuzzy region is given. A 4 × 4-intersection and furthermore a 5 × 5-intersection approach are proposed for the formalism of topological relations. Finally 152 topological relations between two simple fuzzy regions are identified based on the 4 × 4-intersection approach in R2.

Tang, Xinming; Kainz, Wolfgang; Wang, Hongyan

84

Topology in Ordered Phases  

NASA Astrophysics Data System (ADS)

I. Topology as universal concept. Optical vorticulture / M. V. Berry. On universality of mathematical structure in nature: topology / T. Matsuyama. Topology in physics / R. Jackiw. Isoholonomic problem and holonomic quantum computation / S. Tanimura -- II. Topological crystals. Topological crystals of NbSe[symbol] / S. Tanda ... [et al.]. Superconducting states on a Möbius strip / M. Hayashi ... [et al.]. Structure analyses of topological crystals using synchrotron radiation / Y. Nogami ... [et al.]. Transport measurement for topological charge density waves / T. Matsuura ... [et al.]. Theoretical study on Little-Parks oscillation in nanoscale superconducting ring / T. Suzuki, M. Hayashi and H. Ebisawa. Frustrated CDW states in topological crystals / K. Kuboki ... [et al.]. Law of growth in topological crystal / M. Tsubota ... [et al.]. Synthesis and electric properties of NbS[symbol]: possibility of room temperature charge density wave devices / H. Nobukane ... [et al.]. How does a single crystal become a Möbius strip? / T. Matsuura ... [et al.]. Development of X-ray analysis method for topological crystals / K. Yamamoto ... [et al.] -- III. Topological materials. Femtosecond-timescale structure dynamics in complex materials: the case of (NbSe[symbol])[symbol]I / D. Dvorsek and D. Mihailovic. Ultrafast dynamics of charge-density-wave in topological crystals / K. Shimatake ... [et al.]. Topology in morphologies of a folded single-chain polymer / Y. Takenaka, D. Baigl and K. Yoshikawa. One to two-dimensional conversion in topological crystals / T. Toshima, K. Inagaki and S. Tanda. Topological change of Fermi surface in Bismuth under high pressure / M. Kasami ... [et al.]. Topological change of 4, 4'-bis[9-dicarbazolyl]-2, 2'-biphenyl (CBP) by international rearrangement / K. S. Son ... [et al.]. Spin dynamics in Heisenberg triangular system VI5 cluster studied by [symbol]H-NMR / Y. Furukawa ... [et al.]. STM/STS on NbSe[symbol] nanotubes / K. Ichimura ...[et al.]. Nanofibers of hydrogen storage alloy / I. Saita ... [et al.]. Synthesis of stable icosahedral quasicrystals in Zn-Sc based alloys and their magnetic properties / S. Kashimoto and T. Ishimasa. One-armed spiral wave excited by eam pressure in accretion disks in Be/X-Ray binaries / K. Hayasaki and A. T. Okazaki -- IV. Topological defects and excitations. Topological excitations in the ground state of charge density wave systems / P. Monceau. Soliton transport in nanoscale charge-density-wave systems / K. Inagaki, T. Toshima and S. Tanda. Topological defects in triplet superconductors UPt3, Sr[symbol]RuO[symbol], etc. / K. Maki ... [et al.]. Microscopic structure of vortices in type II superconductors / K. Machida ... [et al.]. Microscopic neutron investigation of the Abrikosov state of high-temperature superconductors / J. Mesot. Energy dissipation at nano-scale topological defects of high-Tc superconductors: microwave study / A. Maeda. Pressure induced topological phase transition in the heavy Fermion compound CeAl[symbol] / H. Miyagawa ... [et al.]. Explanation for the unusual orientation of LSCO square vortex lattice in terms of nodal superconductivity / M. Oda. Local electronic states in Bi[symbol]Sr[symbol]CaCu[symbol]O[symbol] / A. Hashimoto ... [et al.] -- V. Topology in quantum phenomena. Topological vortex formation in a Bose-Einstein condensate of alkali-metal atoms / M. Nakahara. Quantum phase transition of [symbol]He confined in nano-porous media / K. Shirahama, K. Yamamoto and Y. Shibayama. A new mean-field theory for Bose-Einstein condensates / T. Kita. Spin current in topological cristals / Y. Asano. Antiferromagnetic defects in non-magnetic hidden order of the heavy-electron system URu[symbol]Si[symbol] / H. Amitsuka, K. Tenya and M. Yokoyama. Magnetic-field dependences of thermodynamic quantities in the vortex state of Type-II superconductors / K. Watanabe, T. Kita and M. Arai. Three-magnon-mediated nuclear spin relaxation in quantum ferrimagnets of topological origin / H. Hori and S, Yamamoto. Topological aspects of wave function statistics at t

Tanda, Satoshi; Matsuyama, Toyoki; Oda, Migaku; Asano, Yasuhiro; Yakubo, Kousuke

2006-08-01

85

Exploring the bond topological properties and the charge depletion-impact sensitivity relationship of high energetic TNT molecule via theoretical charge density analysis  

Microsoft Academic Search

To understand the energetic properties of 2,3,4-Trinitrotolune (TNT) molecule, a quantum chemical calculation and the electronic charge density analysis have been performed. The density functional theory (B3P86\\/6-311G??) calculation was carried out using Gaussian03 software. The energy-minimized wave function obtained from DFT was used for the charge density analysis. The inductive and steric effects of methyl and nitro substituents are not

Arputharaj David Stephen; Rajesh B. Pawar; Poomani Kumaradhas

2010-01-01

86

Topological X-Rays Revisited  

ERIC Educational Resources Information Center

We continue our study of topological X-rays begun in Lynch ["Topological X-rays and MRI's," iJMEST 33(3) (2002), pp. 389-392]. We modify our definition of a topological magnetic resonance imaging and give an affirmative answer to the question posed there: Can we identify a closed set in a box by defining X-rays to probe the interior and without…

Lynch, Mark

2012-01-01

87

Photospheric Magnetic Field Properties of Flaring vs. Flare-Quiet Active Regions II: A Magnetic Charge Topology Model and Statistical Results  

NASA Astrophysics Data System (ADS)

The complexity of the coronal magnetic field extrapolated from a Magnetic Charge Topology (MCT) model, is examined for pre-event signatures unique to solar energetic phenomena. Although extensive use has been made of quantities measured at the photosphere, it is important to consider the magnetic field in the corona, where (for example) the hard X-ray signatures of energy release in solar flares are observed. By quantifying the inferred coronal magnetic topology we are no longer limited to considering solely the magnetic state of the photosphere. MCT is applied to temporally sampled photospheric magnetic data from the U. Hawai`i Imaging Vector Magnetograph, for 24 flare-event and flare-quiet epochs from seven active regions. We outline the methodology employed for automating the application of MCT to large data sets of complex active regions: partitioning the observed Bz at the photosphere, assigning a charge to each partition, and using this charge distribution to extrapolate the field in the corona. From the resulting field we compute the connectivity matrix ? ij, the location of null points and the intersection of separatrix surfaces, i.e. separator field lines. Parameters are constructed to describe, for example, the magnetic connectivities, the magnetic flux in those connections, and the number of separators. Examining particular events results in no obvious trends in the magnitude and temporal evolution of the parameters just prior to flare events. Thus, we employ the same quantitative statistical approach outlined in Leka and Barnes [this session], i.e. applying discriminant analysis and Hotelling's T2-test, and ranking all four-variable discriminant functions as a proxy for a single all-variable discriminant function. We present those parameters which consistently appear in the best combinations, indicating that they may play an important role in defining a pre-event coronal state. This work was performed under Air Force Office of Scientific Research contracts F49620-00-C-0004, F49620-03-C-0019 and F49620-02-C-0191.

Barnes, G.; Leka, K. D.; Longcope, D. W.

2003-05-01

88

Topological superconductivity, topological confinement, and the vortex quantum Hall effect  

SciTech Connect

Topological matter is characterized by the presence of a topological BF term in its long-distance effective action. Topological defects due to the compactness of the U(1) gauge fields induce quantum phase transitions between topological insulators, topological superconductors, and topological confinement. In conventional superconductivity, because of spontaneous symmetry breaking, the photon acquires a mass due to the Anderson-Higgs mechanism. In this paper we derive the corresponding effective actions for the electromagnetic field in topological superconductors and topological confinement phases. In topological superconductors magnetic flux is confined and the photon acquires a topological mass through the BF mechanism: no symmetry breaking is involved, the ground state has topological order, and the transition is induced by quantum fluctuations. In topological confinement, instead, electric charge is linearly confined and the photon becomes a massive antisymmetric tensor via the Stueckelberg mechanism. Oblique confinement phases arise when the string condensate carries both magnetic and electric flux (dyonic strings). Such phases are characterized by a vortex quantum Hall effect potentially relevant for the dissipationless transport of information stored on vortices.

Diamantini, M. Cristina; Trugenberger, Carlo A. [INFN and Dipartimento di Fisica, University of Perugia, via A. Pascoli, I-06100 Perugia (Italy); SwissScientific, chemin Diodati 10, CH-1223 Cologny (Switzerland)

2011-09-01

89

Effect of charge, topology and orientation of the electric field on the interaction of peptides with the ?-hemolysin pore.  

PubMed

Nanopore analysis is an emerging technique of structural biology which employs nanopores, such as the ?-hemolysin pore, as a biosensor. A voltage applied across a membrane containing a nanopore generates a current, which is partially blocked when a molecule interacts with the pore. The magnitude (I) and the duration (T) of the current blockade provide an event signature for that molecule. Two peptides, CY12(+)T1 and CY12(-)T1 with net charges + 2 and - 2, respectively, were analysed using different applied voltages and all four possible orientations of the electrodes and pore. The four orientations were vestibule downstream (VD), vestibule upstream (VU), stem downstream (SD) and stem upstream (SU) where vestibule and stem refer to the side of the pore on which the peptide was placed and downstream and upstream refer to the application of a positive or negative electrophoretic force, respectively. For CY12(+)T1, the effect of voltage on the event duration was consistent with translocation in the VD and SD configurations, but only intercalation events were observed in the VU and SU configurations. For CY12(-)T1, translocations were only observed in the VD and VU configurations. The results are interpreted in terms of two energy barriers on either side of the lumen of the pore. The difference in height of the barriers determines the preferred direction of exit. Electroosmotic flow and current rectification due to the pore as well as the dipole moment and charge of the peptide also play significant roles. Thus, factors other than simple electrophoresis are important for determining the interaction of small peptides with the pore. PMID:21766390

Christensen, Christopher; Baran, Christian; Krasniqi, Besnik; Stefureac, Radu I; Nokhrin, Sergiy; Lee, Jeremy S

2011-11-01

90

Kinetic interaction analysis of human interleukin 5 receptor alpha mutants reveals a unique binding topology and charge distribution for cytokine recognition.  

PubMed

Human interleukin 5 receptor alpha (IL5Ralpha) comprises three fibronectin type III domains (D1, D2, and D3) in the extracellular region. Previous results have indicated that residues in the D1D2 domains are crucial for high affinity interaction with human interleukin 5 (IL5). Yet, it is the D2D3 domains that have sequence homology with the classic cytokine recognition motif that is generally assumed to be the minimum cytokine-recognizing unit. In the present study, we used kinetic interaction analysis of alanine-scanning mutational variants of IL5Ralpha to define the residues involved in IL5 recognition. Soluble forms of IL5Ralpha variants were expressed in S2 cells, selectively captured via their C-terminal V5 tag by anti-V5 tag antibody immobilized onto the sensor chip and examined for IL5 interaction by using a sandwich surface plasmon resonance biosensor method. Marked effects on the interaction kinetics were observed not only in D1 (Asp(55), Asp(56), and Glu(58)) and D2 (Lys(186) and Arg(188)) domains, but also in the D3 (Arg(297)) domain. Modeling of the tertiary structure of IL5Ralpha indicated that these binding residues fell into two clusters. The first cluster consists of D1 domain residues that form a negatively charged patch, whereas the second cluster consists of residues that form a positively charged patch at the interface of D2 and D3 domains. These results suggest that the IL5 x IL5Ralpha system adopts a unique binding topology, in which the cytokine is recognized by a D2D3 tandem domain combined with a D1 domain, to form an extended cytokine recognition interface. PMID:14662768

Ishino, Tetsuya; Pasut, Gianfranco; Scibek, Jeffery; Chaiken, Irwin

2004-03-01

91

Genetic neural network modeling of the selective inhibition of the intermediate-conductance Ca2+ -activated K+ channel by some triarylmethanes using topological charge indexes descriptors.  

PubMed

Selective inhibition of the intermediate-conductance Ca(2+)-activated K(+ )channel (IK (Ca)) by some clotrimazole analogs has been successfully modeled using topological charge indexes (TCI) and genetic neural networks (GNNs). A neural network monitoring scheme evidenced a highly non-linear dependence between the IK (Ca) blocking activity and TCI descriptors. Suitable subsets of descriptors were selected by means of genetic algorithm. Bayesian regularization was implemented in the network training function with the aim of assuring good generalization qualities to the predictors. GNNs were able to yield a reliable predictor that explained about 97% data variance with good predictive ability. On the contrary, the best multivariate linear equation with descriptors selected by linear genetic search, only explained about 60%. In spite of when using the descriptors from the linear equations to train neural networks yielded higher fitted models, such networks were very unstable and had relative low predictive ability. However, the best GNN BRANN 2 had a Q ( 2 ) of LOO of cross-validation equal to 0.901 and at the same time exhibited outstanding stability when calculating 80 randomly constructed training/test sets partitions. Our model suggested that structural fragments of size three and seven have relevant influence on the inhibitory potency of the studied IK (Ca) channel blockers. Furthermore, inhibitors were well distributed regarding its activity levels in a Kohonen self-organizing map (KSOM) built using the inputs of the best neural network predictor. PMID:16374673

Caballero, Julio; Garriga, Miguel; Fernández, Michael

2005-11-01

92

Topological Stereochemistry.  

National Technical Information Service (NTIS)

Results of research on two novel problems in organic stereochemistry are described: 1) Topological stereochemistry; and 2) Design and synthesis of novel organic optoelectronic materials. In the topological stereochemistry project, new methods for understa...

D. M. Walba

1988-01-01

93

Core Deformations of Topological Defects  

NASA Astrophysics Data System (ADS)

We consider phases of spontaneously broken gauge theories in which different types of topological excitations, like flux tubes, monopoles etc., coexist. We analyze the topological relations which exist between the charges, and give a description of the admissible core deformations in terms of certain cohomology groups that occur in obstruction theory. Simple examples are worked out in detail.

Bais, F. Alexander; John, Per

94

Topological censorship.  

NASA Astrophysics Data System (ADS)

Classically, all topologies are allowed as solutions to the Einstein equations. However, one does not observe any topological structures on medium range distance scales, that is scales that are smaller than the size of the observed universe but larger than the microscopic scales for which quantum gravity becomes important. Recently, Friedman, Schleich and Witt (1993) have proven that there is topological censorship on these medium range distance scales: the Einstein equations, locally positive energy, and local predictability of physics imply that any medium distance scale topological structures cannot be seen. More precisely we show that the topology of physically reasonable isolated systems is shrouded from distant observers, or in other words there is a topological censorship principle.

Schleich, K.; Witt, D. M.

95

Topological Quivers  

Microsoft Academic Search

Topological quivers are generalizations of directed graphs in which the sets of vertices and edges are locally compact Hausdorff spaces. Associated to such a topological quiver Q is a C*-correspondence, and from this correspondence one may construct a Cuntz-Pimsner algebra C*(Q). In this paper we develop the general theory of topological quiver C*-algebras and show how certain C*-algebras found in

Paul S. Muhly; Mark Tomforde

2003-01-01

96

Network Topologies  

NSDL National Science Digital Library

Network topology is the physical arrangement of the switching devices of a network connecting a group of computers or buildings. This brief interactive activity, by the Electromechanical Digital Library and Wisconsin Technical College System faculty, explains how and why these connections are made. It showcases common topologies including mesh, bus, star, and ring topologies. Users can click through these various categories at their own speed, replaying animations and rereading explanations as many times as the individual needs. This is a great resource for students and teachers alike to familiarize themselves with network topologies. [ES

Bartelt, Terry L.

2009-04-30

97

Topological activity in Bragg elliptical twisted fibers.  

PubMed

We have theoretically shown that Bragg twisted elliptical fibers manifest, in certain spectral regions, the property of topological activity--the ability to change in the reflected field the topological charge of incoming optical vortices and fundamental modes by two units. This property could be used for narrowband generation of optical vortices from Gaussian beams and for changing the topological charge of incoming optical vortices. PMID:22505114

Alexeyev, Constantine N; Fadeyeva, Tatyana A; Lapin, Boris P; Yavorsky, Maxim A

2012-04-01

98

Topological median filters.  

PubMed

This paper describes the definition and testing of a new type of median filter for images. The topological median filter implements some existing ideas and some new ideas on fuzzy connectedness to improve, over a conventional median filter, the extraction of edges in noise. The concept of alpha-connectivity is defined and used to create an algorithm for computing the degree of connectedness of a pixel to all the other pixels in an arbitrary neighborhood. The resulting connectivity map of the neighborhood effectively disconnects peaks in the neighborhood that are separated from the center pixel by a valley in the brightness topology. The median of the connectivity map is an estimate of the median of the peak or plateau to which the center pixel belongs. Unlike the conventional median filter, the topological median is relatively unaffected by disconnected features in the neighborhood of the center pixel. Four topological median filters are defined. Qualitative and statistical analyses of the four filters are presented. It is demonstrated that edge detection can be more accurate on topologically median filtered images than on conventionally median filtered images. PMID:18244615

Senel, Hakan Güray; Peters, Richard Alan; Dawant, Benoit

2002-01-01

99

Topology Explains Why Automobile Sunshades Fold Oddly  

ERIC Educational Resources Information Center

Automobile sunshades always fold into an "odd" number of loops. The explanation why involves elementary topology (braid theory and linking number, both explained in detail here with definitions and examples), and an elementary fact from algebra about symmetric group.

Feist, Curtis; Naimi, Ramin

2009-01-01

100

Topology driven 3D mesh hierarchical segmentation  

Microsoft Academic Search

In this paper, we propose to address the semantic- oriented 3D mesh hierarchical segmentation problem, us- ing enhanced topological skeletons (18). This high level information drives both the feature boundary computation as well as the feature hierarchy definition. Proposed hierar - chical scheme is based on the key idea that the topology of a feature is a more important decomposition

Julien Tierny; Jean-philippe Vandeborre; Mohamed Daoudi

2007-01-01

101

Topology Atlas  

NSDL National Science Digital Library

Hosted by York University, with support from University of Florida, University of Tennessee at Martin, Nipissing University, York University, and the University of Milan, the Topology Atlas Website calls itself a publisher of information related to topology. The site amounts to a vast repository of documents for mathematicians and others interested in topology. A preprints section offers documents dating from December 1995 to the present. An Invited Contributions section holds short surveys of specialized topics including titles like "On Variations of Continuity," and "Atlas of oriented knots and links." Also available at this site are abstracts (for books, published articles, and research announcements), journals, TopCom (a magazine for the topology community), and more.

102

Preliminary Experimental Work on Nanocomposite Polymers: Small Partial Discharges at Inception Voltage, The Existence of Possible Charging Mechanisms Below Inception Voltage and the Problem of Definitions  

NASA Astrophysics Data System (ADS)

In this paper, some results are presented from experiments concerning partial discharge (PD) behaviour of epoxy resin samples having 3 wt% nano- and 3 wt% micro-fillers, as well as epoxy samples having 3 wt%and1 wt% nanoparticles. The nano- and micro-fillers were TiO2 (titania). The main idea is to see whether a sample with PD at its inception voltage, still presents some tendency to charging effects below inception. An effort is being made to relate the present work with previous publications on the same main idea, as well as to previous research performed recently at Xian Jiaotong University, State Key Laboratory of Electrical Insulation and Power Equipment. It is indicated that with the samples investigated, although on some occasions random charging phenomena were observed below the inception voltage, it was not noted the same behaviour as with pure epoxy samples. Finally, a discussion ensues as to the definitions of the phenomena taking place below inception voltage.

Zhang, Yuan; Danikas, Michael G.; Zhao, Xu; Cheng, Yonghong

2012-03-01

103

Linking the historical and chemical definitions of diabatic states for charge and excitation energy transfer reactions in condensed phase  

NASA Astrophysics Data System (ADS)

Marcus theory of electron transfer (ET) and Förster theory of excitation energy transfer (EET) rely on the Condon approximation and the theoretical availability of initial and final states of ET and EET reactions, often called diabatic states. Recently [Subotnik et al., J. Chem. Phys. 130, 234102 (2009)], diabatic states for practical calculations of ET and EET reactions were defined in terms of their interactions with the surrounding environment. However, from a purely theoretical standpoint, the definition of diabatic states must arise from the minimization of the dynamic couplings between the trial diabatic states. In this work, we show that if the Condon approximation is valid, then a minimization of the derived dynamic couplings leads to corresponding diabatic states for ET reactions taking place in solution by diagonalization of the dipole moment matrix, which is equivalent to a Boys localization algorithm; while for EET reactions in solution, diabatic states are found through the Edmiston-Ruedenberg localization algorithm. In the derivation, we find interesting expressions for the environmental contribution to the dynamic coupling of the adiabatic states in condensed-phase processes. In one of the cases considered, we find that such a contribution is trivially evaluable as a scalar product of the transition dipole moment with a quantity directly derivable from the geometry arrangement of the nuclei in the molecular environment. Possibly, this has applications in the evaluation of dynamic couplings for large scale simulations.

Pavanello, Michele; Neugebauer, Johannes

2011-10-01

104

QCD with 2 light quark flavours: Thermodynamics on a 16[sup 3] [times] 8 lattice and glueballs and topological charge on a 16[sup 3] [times] 32 lattice  

SciTech Connect

The HTMCGC collaboration has been simulating lattice QCD with two light staggered quarks with masses m[sub q] = 0.0125 and also m[sub q] = 0.00625 on a 16[sup 3] [times] 8 lattice. We have been studying the behavior of the transition from hadronic matter to a quark-gluon plasma and the properties of that plasma. We have been measuring entropy densities, Debye and hadronic screening lengths, the spacial string tension and topological susceptibility in addition to the standard order parameters. The HEMCGC collaboration has simulated lattice QCD with two light staggered quarks,m[sub q] = 0.025 and m[sub q] = 0.010 on a 16[sup 3] [times] 32 lattice. We have measured the glueball spectrum and topological susceptibilities for these runs.

Sinclair, D.K.

1992-11-20

105

QCD with 2 light quark flavours: Thermodynamics on a 16{sup 3} {times} 8 lattice and glueballs and topological charge on a 16{sup 3} {times} 32 lattice  

SciTech Connect

The HTMCGC collaboration has been simulating lattice QCD with two light staggered quarks with masses m{sub q} = 0.0125 and also m{sub q} = 0.00625 on a 16{sup 3} {times} 8 lattice. We have been studying the behavior of the transition from hadronic matter to a quark-gluon plasma and the properties of that plasma. We have been measuring entropy densities, Debye and hadronic screening lengths, the spacial string tension and topological susceptibility in addition to the standard order parameters. The HEMCGC collaboration has simulated lattice QCD with two light staggered quarks,m{sub q} = 0.025 and m{sub q} = 0.010 on a 16{sup 3} {times} 32 lattice. We have measured the glueball spectrum and topological susceptibilities for these runs.

Sinclair, D.K.; HEMCGC collaboration; HTMCGC collaboration

1992-11-20

106

Measurement-only topological quantum computation.  

PubMed

We remove the need to physically transport computational anyons around each other from the implementation of computational gates in topological quantum computing. By using an anyonic analog of quantum state teleportation, we show how the braiding transformations used to generate computational gates may be produced through a series of topological charge measurements. PMID:18764095

Bonderson, Parsa; Freedman, Michael; Nayak, Chetan

2008-07-01

107

Simple quantum dynamics in presence of topological disorder  

Microsoft Academic Search

The theory of particles moving in topologically random disordered environment is just in its infancy. Following our previous work on classical random walk in the presence of topological disorder due to randomly distributed line defects, we analyze the problem of a quantum, spinless, charged particle moving on a topologically disordered lattice. Specifically we discuss the motion on a d=2 square

Andrzej Lusakowski; Lukasz A. Turski

1994-01-01

108

Topological Puzzles  

NSDL National Science Digital Library

In this activity, learners construct three math puzzles out of simple materials like wood, string, and Styrofoam. The first two puzzles, called "Remove the Loop" and "Two Washers," are examples of topology, an area of math about how geometric figures are different and similar. The third puzzle, "Towers of Hanoi," uses a mathematical tool called an algorithm and is also a good example of an exponential function.

Workshop, Watsonville E.

2011-01-01

109

Measurement-only topological quantum computation via anyonic interferometry  

SciTech Connect

We describe measurement-only topological quantum computation using both projective and interferometrical measurement of topological charge. We demonstrate how anyonic teleportation can be achieved using 'forced measurement' protocols for both types of measurement. Using this, it is shown how topological charge measurements can be used to generate the braiding transformations used in topological quantum computation, and hence that the physical transportation of computational anyons is unnecessary. We give a detailed discussion of the anyonics for implementation of topological quantum computation (particularly, using the measurement-only approach) in fractional quantum Hall systems.

Bonderson, Parsa [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States)], E-mail: parsab@microsoft.com; Freedman, Michael [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States)], E-mail: michaelf@microsoft.com; Nayak, Chetan [Microsoft Research, Station Q, Elings Hall, University of California, Santa Barbara, CA 93106 (United States); Department of Physics, University of California, Santa Barbara, CA 93106 (United States)], E-mail: nayak@kitp.ucsb.edu

2009-04-15

110

Topological Fluctuations and Susceptibility in SU(3) Lattice Gauge Theory.  

National Technical Information Service (NTIS)

The authors measure the topological charge density of the (Monte Carlo generated) SU(3) vacuum. Their algorithm involves first smoothening the generated configurations in a way that conserves the total charge in the continuum limit. Their work in a range ...

J. Hoek M. Teper J. Waterhouse

1986-01-01

111

Topological regular semigroups and topological inductive groupoids  

Microsoft Academic Search

The theory of topological semigroups has emerged as a separate discipline during the fifties (cf. Hofmann and Mostert [5]\\u000a and Carruth, Koch and Hildebrant [3]), but the idea of topologically consistent regularity in such semigroups does not seem\\u000a to have gained much attention. In this paper topological regular semigroups are introduced where the regularity is topologically\\u000a consistent. The topological version

A. R. Rajan

1993-01-01

112

Topological Aspects of Information Retrieval.  

ERIC Educational Resources Information Center

Discusses topological aspects of theoretical information retrieval, including retrieval topology; similarity topology; pseudo-metric topology; document spaces as topological spaces; Boolean information retrieval as a subsystem of any topological system; and proofs of theorems. (LRW)

Egghe, Leo; Rousseau, Ronald

1998-01-01

113

Is a color superconductor topological?  

SciTech Connect

A fully gapped state of matter, whether insulator or superconductor, can be asked if it is topologically trivial or nontrivial. Here we investigate topological properties of superconducting Dirac fermions in 3D having a color superconductor as an application. In the chiral limit, when the pairing gap is parity even, the right-handed and left-handed sectors of the free space Hamiltonian have nontrivial topological charges with opposite signs. Accordingly, a vortex line in the superconductor supports localized gapless right-handed and left-handed fermions with the dispersion relations E={+-}vp{sub z} (v is a parameter dependent velocity) and thus propagating in opposite directions along the vortex line. However, the presence of the fermion mass immediately opens up a mass gap for such localized fermions and the dispersion relations become E={+-}v{radical}(m{sup 2}+p{sub z}{sup 2}). When the pairing gap is parity odd, the situation is qualitatively different. The right-handed and left-handed sectors of the free space Hamiltonian in the chiral limit have nontrivial topological charges with the same sign and therefore the presence of the small fermion mass does not open up a mass gap for the fermions localized around the vortex line. When the fermion mass is increased further, there is a topological phase transition at m={radical}({mu}{sup 2}+{Delta}{sup 2}) and the localized gapless fermions disappear. We also elucidate the existence of gapless surface fermions localized at a boundary when two phases with different topological charges are connected. A part of our results is relevant to the color superconductivity of quarks.

Nishida, Yusuke [Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2010-04-01

114

Abstract Interpretation from a Topological Perspective  

Microsoft Academic Search

We develop abstract interpretation from topological principles by relaxing the definitions of open set and continuity; key\\u000a results still hold. We study families of closed and open sets and show they generate post- and pre-condition analyses, respectively.\\u000a Giacobazzi’s forwards- and backwards-complete functions are characterized by the topologically closed and continuous maps,\\u000a respectively. Finally, we show that Smyth’s upper and lower

David A. Schmidt

2009-01-01

115

Effective field theories for topological insulators by functional bosonization  

NASA Astrophysics Data System (ADS)

Effective field theories that describe the dynamics of electric current for topological insulators in general dimension D = d+1 are discussed using the functional bosonization. For non-interacting topological insulators with a conserved U(1) charge and characterized by an integer topological invariant, we derive the BF-type topological field theories supplemented with the Chern-Simons (when D is odd) or the Axion term (when D is even). For topological insulators characterized by a Z2 topological invariant, their topological field theories are obtained by dimensional reduction. Building on this effective field theory description for non- interacting topological phases, we also discuss, following the spirit of the parton construction of the fractional quantum Hall effect, the putative ``fractional'' topological insulators and their possible effective field theories.

Chan, Pak On; Hughes, Taylor L.; Ryu, Shinsei; Fradkin, Eduardo

2013-03-01

116

Interplay of Sequence, Topology and Termini Charge in Determining the Stability of the Aggregates of GNNQQNY Mutants: A Molecular Dynamics Study  

PubMed Central

This study explores the stabilities of single sheet parallel systems of three sequence variants of 1GNNQQNY7, N2D, N2S and N6D, with variations in aggregate size (5–8) and termini charge (charged or neutral). The aggregates were simulated at 300 and 330 K. These mutations decrease amyloid formation in the yeast prion protein Sup35. The present study finds that these mutations cause instability even in the peptide context. The protonation status of termini is found to be a key determinant of stabilities; other determinants are sequence, position of mutation and aggregate size. All systems with charged termini are unstable, whereas both stable and unstable systems are found when the termini are neutral. When termini are charged, the largest stable aggregate for the N2S and N6D systems has 3 to 4 peptides whereas N2D mutation supports oligomers of larger size (5-and 6-mers) as well. Mutation at 2nd position (N2S and N2D) results in fewer H-bonds at the mutated as well as neighboring (Gly1/Gln4) positions. However, no such effect is found if mutation is at 6th position (N6D). The effect of Asn?Asp mutation depends on the position and termini charge: it is more destabilizing at the 2nd position than at the 6th in case of neutral termini, however, the opposite is true in case of charged termini. Appearance of twist in stable systems and in smaller aggregates formed in unstable systems suggests that twist is integral to amyloid arrangement. Disorder, dissociation or rearrangement of peptides, disintegration or collapse of aggregates and formation of amorphous aggregates observed in these simulations are likely to occur during the early stages of aggregation also. The smaller aggregates formed due to such events have a variety of arrangements of peptides. This suggests polymorphic nature of oligomers and presence of a heterogeneous mixture of oligomers during early stages of aggregation.

Srivastava, Alka; Balaji, Petety V.

2014-01-01

117

Topological BF field theory description of topological insulators  

SciTech Connect

Research Highlights: > We show that a BF theory is the effective theory of 2D and 3D topological insulators. > The non-gauge-invariance of the bulk theory yields surface terms for a bosonized Dirac fermion. > The 'axion' term in electromagnetism is correctly obtained from gapped surfaces. > Generalizations to possible fractional phases are discussed in closing. - Abstract: Topological phases of matter are described universally by topological field theories in the same way that symmetry-breaking phases of matter are described by Landau-Ginzburg field theories. We propose that topological insulators in two and three dimensions are described by a version of abelian BF theory. For the two-dimensional topological insulator or quantum spin Hall state, this description is essentially equivalent to a pair of Chern-Simons theories, consistent with the realization of this phase as paired integer quantum Hall effect states. The BF description can be motivated from the local excitations produced when a {pi} flux is threaded through this state. For the three-dimensional topological insulator, the BF description is less obvious but quite versatile: it contains a gapless surface Dirac fermion when time-reversal-symmetry is preserved and yields 'axion electrodynamics', i.e., an electromagnetic E . B term, when time-reversal symmetry is broken and the surfaces are gapped. Just as changing the coefficients and charges of 2D Chern-Simons theory allows one to obtain fractional quantum Hall states starting from integer states, BF theory could also describe (at a macroscopic level) fractional 3D topological insulators with fractional statistics of point-like and line-like objects.

Cho, Gil Young [Department of Physics, University of California, Berkeley, CA 94720 (United States); Moore, Joel E., E-mail: jemoore@berkeley.edu [Department of Physics, University of California, Berkeley, CA 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

2011-06-15

118

Topology and the eta prime Mass in SU(3) Lattice Gauge Theory.  

National Technical Information Service (NTIS)

The topological charge density of the (Monte Carlo generated) SU(3) vacuum was measured. The algorithm was designed to be robust against lattice artifacts. The resulting topological susceptibility was found to vary with (g sub 2) like the string tension (...

J. Hoek M. Teper J. Waterhouse

1986-01-01

119

Topological susceptibility with the improved Asqtad action  

SciTech Connect

As a test of the chiral properties of the improved Asqtad (staggered fermion) action, we have been measuring the topological susceptibility as a function of quark masses for 2 + 1 dynamical flavors. We report preliminary results, which show reasonable agreement with leading order chiral perturbation theory for lattice spacing less than 0.1 fm. The total topological charge, however, shows strong persistence over Monte Carlo time.

C. Bernard et al.

2004-01-06

120

Hall conductivity as bulk signature of topological transitions in superconductors  

NASA Astrophysics Data System (ADS)

Topological superconductors (TSCs) may undergo transitions between phases with different topological numbers which are related to the presence of gapless (Majorana) edge states. In a TSC the charge Hall conductivity, \\sigma_{xy} , is not quantized and evolves continuously between different topological phases. Here we show that in two-dimensional {Z} -TSC the derivatives of \\sigma_{xy} display sharp features signaling the topological transitions. We consider in detail the case of a triplet superconductor with p-wave symmetry in the presence of Rashba spin-orbit coupling and externally applied Zeeman spin splitting. We generalize to the cases where the normal system is already topologically non-trivial.

Sacramento, P. D.; Araújo, M. A. N.; Castro, E. V.

2014-02-01

121

Orbifolds and Topological Defects  

NASA Astrophysics Data System (ADS)

We study orbifolds of two-dimensional topological field theories using defects. If the TFT arises as the twist of a superconformal field theory, we recover results on the Neveu-Schwarz and Ramond sectors of the orbifold theory, as well as bulk-boundary correlators from a novel, universal perspective. This entails a structure somewhat weaker than ordinary TFT, which however still describes a sector of the underlying conformal theory. The case of B-twisted Landau-Ginzburg models is discussed in detail, where we compute charge vectors and superpotential terms for B-type branes. Our construction also works in the absence of supersymmetry and for generalised "orbifolds" that need not arise from symmetry groups. In general, this involves a natural appearance of Hochschild (co)homology in a 2-categorical setting, in which among other things we provide simple presentations of Serre functors and a further generalisation of the Cardy condition.

Brunner, Ilka; Carqueville, Nils; Plencner, Daniel

2014-04-01

122

Topological insulators and superconductors from string theory  

SciTech Connect

Topological insulators and superconductors in different spatial dimensions and with different discrete symmetries have been fully classified recently, revealing a periodic structure for the pattern of possible types of topological insulators and superconductors, both in terms of spatial dimensions and in terms of symmetry classes. It was proposed that K theory is behind the periodicity. On the other hand, D-branes, a solitonic object in string theory, are also known to be classified by K theory. In this paper, by inspecting low-energy effective field theories realized by two parallel D-branes, we establish a one-to-one correspondence between the K-theory classification of topological insulators/superconductors and D-brane charges. In addition, the string theory realization of topological insulators and superconductors comes naturally with gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a gauge field theory of topological nature, such as ones with the Chern-Simons term or the {theta} term in various dimensions. This sheds light on topological insulators and superconductors beyond noninteracting systems, and the underlying topological field theory description thereof. In particular, our string theory realization includes the honeycomb lattice Kitaev model in two spatial dimensions, and its higher-dimensional extensions. Increasing the number of D-branes naturally leads to a realization of topological insulators and superconductors in terms of holography (AdS/CFT).

Ryu, Shinsei; Takayanagi, Tadashi [Department of Physics, University of California, Berkeley, California 94720 (United States); Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Kashiwa, Chiba 277-8582 (Japan)

2010-10-15

123

Nontrivial topological states on a Möbius band  

NASA Astrophysics Data System (ADS)

In the field of topological insulators, the topological properties of quantum states in samples with simple geometries, such as a cylinder or a ribbon, have been classified and understood during the past decade. Here we extend these studies to a Möbius band and argue that its lack of orientability prevents a smooth global definition of parity-odd quantities such as pseudovectors. In particular, the Chern number, the topological invariant for the quantum Hall effect, lies in this class. The definition of spin on the Möbius band translates into the idea of the orientable double cover, an analogy used to explain the possibility of having the quantum spin Hall effect on the Möbius band. We also provide symmetry arguments to show the possible lattice structures and Hamiltonian terms for which topological states may exist in a Möbius band, and we locate our systems in the classification of topological states. Then, we propose a method to calculate Möbius dispersions from those of the cylinder, and we show the results for a honeycomb and a kagome Möbius band with different types of edge termination. Although the quantum spin Hall effect may occur in these systems when intrinsic spin-orbit coupling is present, the quantum Hall effect is more intricate and requires the presence of a domain wall in the sample. We propose an experimental setup which could allow for the realization of the elusive quantum Hall effect in a Möbius band.

Beugeling, W.; Quelle, A.; Morais Smith, C.

2014-06-01

124

Topological insulators and superconductors  

NASA Astrophysics Data System (ADS)

Topological insulators are new states of quantum matter which cannot be adiabatically connected to conventional insulators and semiconductors. They are characterized by a full insulating gap in the bulk and gapless edge or surface states which are protected by time-reversal symmetry. These topological materials have been theoretically predicted and experimentally observed in a variety of systems, including HgTe quantum wells, BiSb alloys, and Bi2Te3 and Bi2Se3 crystals. Theoretical models, materials properties, and experimental results on two-dimensional and three-dimensional topological insulators are reviewed, and both the topological band theory and the topological field theory are discussed. Topological superconductors have a full pairing gap in the bulk and gapless surface states consisting of Majorana fermions. The theory of topological superconductors is reviewed, in close analogy to the theory of topological insulators.

Qi, Xiao-Liang; Zhang, Shou-Cheng

2011-10-01

125

Topological Circuit Layout.  

National Technical Information Service (NTIS)

In this report the topological and geometrical aspects of the circuit layout problem are compared. A circuit layout procedure, based on topological factors, is presented. Whereas most circuit layout procedures are concerned mainly with geometrical aspects...

W. M. vanCleemput

1976-01-01

126

Topological Superconductivity and Superfluidity.  

National Technical Information Service (NTIS)

We construct time reversal invariant topological superconductors and superfluids in two and three dimensions which are analogous to the recently discovered quantum spin Hall and three-d Z2 topological insulators respectively. These states have a full pair...

S. Raghu S. Zhang T. L. Hughes X. Qi

2010-01-01

127

Topologies on directed graphs  

NASA Technical Reports Server (NTRS)

Given a directed graph, a natural topology is defined and relationships between standard topological properties and graph theoretical concepts are studied. In particular, the properties of connectivity and separatedness are investigated. A metric is introduced which is shown to be related to separatedness. The topological notions of continuity and homeomorphism. A class of maps is studied which preserve both graph and topological properties. Applications involving strong maps and contractions are also presented.

Lieberman, R. N.

1972-01-01

128

Simulated annealing for topological solitons  

NASA Astrophysics Data System (ADS)

The search for solutions of field theories allowing for topological solitons requires that we find the field configuration with the lowest energy in a given sector of topological charge. The standard approach is based on the numerical solution of the static Euler-Lagrange differential equation following from the field energy. As an alternative, we propose to use a simulated annealing algorithm to minimize the energy functional directly. We have applied simulated annealing to several nonlinear classical field theories: the sine-Gordon model in one dimension, the baby Skyrme model in two dimensions and the nuclear Skyrme model in three dimensions. We describe in detail the implementation of the simulated annealing algorithm, present our results and get independent confirmation of the studies which have used standard minimization techniques.

Hale, Mark; Schwindt, Oliver; Weidig, Tom

2000-09-01

129

Bringing Definitions into High Definition  

ERIC Educational Resources Information Center

Why do definitions play such a central role in mathematics? It may seem obvious that precision about the terms one uses is necessary in order to use those terms reasonably (while reasoning). Definitions are chosen so as to be definite about the terms one uses, but also to make both the statement of, and the reasoning to justify, theorems as…

Mason, John

2010-01-01

130

Fractional topological insulators in three dimensions.  

PubMed

Topological insulators can be generally defined by a topological field theory with an axion angle ? of 0 or ?. In this work, we introduce the concept of fractional topological insulator defined by a fractional axion angle and show that it can be consistent with time reversal T invariance if ground state degeneracies are present. The fractional axion angle can be measured experimentally by the quantized fractional bulk magnetoelectric polarization P?, and a "halved" fractional quantum Hall effect on the surface with Hall conductance of the form ?H=p/q e²/2h with p, q odd. In the simplest of these states the electron behaves as a bound state of three fractionally charged "quarks" coupled to a deconfined non-Abelian SU(3) "color" gauge field, where the fractional charge of the quarks changes the quantization condition of P? and allows fractional values consistent with T invariance. PMID:21231552

Maciejko, Joseph; Qi, Xiao-Liang; Karch, Andreas; Zhang, Shou-Cheng

2010-12-10

131

Definitely Life but not Definitively  

NASA Astrophysics Data System (ADS)

Although there have been attempts at a definition of life from many disciplines, none is accepted by all as definitive. Some people believe that it is impossible to define ‘life’ adequately at the moment. We agree with this point of view on linguistic grounds, examining the different types of definition, the contexts in which they are used and their relative usefulness as aids to arriving at a scientific definition of life. We look at some of the more recent definitions and analyse them in the light of our criteria for a good definition. We argue that since there are so many linguistic and philosophical difficulties with such a definition of life, what is needed is a series of working descriptions, which are suited to the audience and context in which they are used and useful for the intended purpose. We provide some ideas and examples of the forms these may take.

Oliver, Joan D.; Perry, Randall S.

2006-12-01

132

Topological insulators from a chemist's perspective.  

PubMed

Heavy stuff: Topological insulators are formed of heavy atoms and host special surface or edge states. The electronic structure is characterized by a Dirac cone within a bulk band gap (see picture) that is generated by strong spin-orbit coupling. A chemist's perspective in terms of bonds, bands, symmetry, and nuclear charge is provided. PMID:22684869

Müchler, Lukas; Zhang, Haijun; Chadov, Stanislav; Yan, Binghai; Casper, Frederick; Kübler, Jürgen; Zhang, Shou-Cheng; Felser, Claudia

2012-07-16

133

Membranes for topological M-theory  

Microsoft Academic Search

We formulate a theory of topological membranes on manifolds with G2 holonomy. The BRST charges of the theories are the superspace Killing vectors (the generators of global supersymmetry) on the background with reduced holonomy G2?Spin(7). In the absence of spinning formulations of supermembranes, the starting point is an N = 2 target space supersymmetric membrane in seven euclidean dimensions. The

Ling Bao; Viktor Bengtsson; Martin Cederwall; Bengt E. W. Nilsson

2006-01-01

134

Effective field theories for topological insulators by functional bosonization  

NASA Astrophysics Data System (ADS)

Effective field theories that describe the dynamics of a conserved U(1) current in terms of “hydrodynamic” degrees of freedom of topological phases in condensed matter are discussed in general dimension D=d+1 using the functional bosonization technique. For noninteracting topological insulators (superconductors) with a conserved U(1) charge and characterized by an integer topological invariant [more specifically, they are topological insulators in the complex symmetry classes (class A and AIII), and in the “primary series” of topological insulators, in the eight real symmetry classes], we derive the BF-type topological field theories supplemented with the Chern-Simons (when D is odd) or the ? (when D is even) terms. For topological insulators characterized by a Z2 topological invariant (the first and second descendants of the primary series), their topological field theories are obtained by dimensional reduction. Building on this effective field theory description for noninteracting topological phases, we also discuss, following the spirit of the parton construction of the fractional quantum Hall effect by Block and Wen, the putative “fractional” topological insulators and their possible effective field theories, and use them to determine the physical properties of these nontrivial quantum phases.

Chan, AtMa; Hughes, Taylor L.; Ryu, Shinsei; Fradkin, Eduardo

2013-02-01

135

Network topology analysis.  

SciTech Connect

Emerging high-bandwidth, low-latency network technology has made network-based architectures both feasible and potentially desirable for use in satellite payload architectures. The selection of network topology is a critical component when developing these multi-node or multi-point architectures. This study examines network topologies and their effect on overall network performance. Numerous topologies were reviewed against a number of performance, reliability, and cost metrics. This document identifies a handful of good network topologies for satellite applications and the metrics used to justify them as such. Since often multiple topologies will meet the requirements of the satellite payload architecture under development, the choice of network topology is not easy, and in the end the choice of topology is influenced by both the design characteristics and requirements of the overall system and the experience of the developer.

Kalb, Jeffrey L.; Lee, David S.

2008-01-01

136

Photonic Floquet topological insulators.  

PubMed

Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on their surfaces. In two dimensions, electrons on the surface of a topological insulator are not scattered despite defects and disorder, providing robustness akin to that of superconductors. Topological insulators are predicted to have wide-ranging applications in fault-tolerant quantum computing and spintronics. Substantial effort has been directed towards realizing topological insulators for electromagnetic waves. One-dimensional systems with topological edge states have been demonstrated, but these states are zero-dimensional and therefore exhibit no transport properties. Topological protection of microwaves has been observed using a mechanism similar to the quantum Hall effect, by placing a gyromagnetic photonic crystal in an external magnetic field. But because magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatter-free edge states requires a fundamentally different mechanism-one that is free of magnetic fields. A number of proposals for photonic topological transport have been put forward recently. One suggested temporal modulation of a photonic crystal, thus breaking time-reversal symmetry and inducing one-way edge states. This is in the spirit of the proposed Floquet topological insulators, in which temporal variations in solid-state systems induce topological edge states. Here we propose and experimentally demonstrate a photonic topological insulator free of external fields and with scatter-free edge transport-a photonic lattice exhibiting topologically protected transport of visible light on the lattice edges. Our system is composed of an array of evanescently coupled helical waveguides arranged in a graphene-like honeycomb lattice. Paraxial diffraction of light is described by a Schrödinger equation where the propagation coordinate (z) acts as 'time'. Thus the helicity of the waveguides breaks z-reversal symmetry as proposed for Floquet topological insulators. This structure results in one-way edge states that are topologically protected from scattering. PMID:23579677

Rechtsman, Mikael C; Zeuner, Julia M; Plotnik, Yonatan; Lumer, Yaakov; Podolsky, Daniel; Dreisow, Felix; Nolte, Stefan; Segev, Mordechai; Szameit, Alexander

2013-04-11

137

The strong, weak and anomalous sides of weak topological insulators  

NASA Astrophysics Data System (ADS)

Disorder and topology can be thought of as two counter-driving forces. While the former pushes electron wave functions to localize in space, the latter requires them to remain coherent over the entire system. We study the interplay between these two on the surface of a ``weakly'' topological phase- the Weak Topological Insulator. Using arguments based on flux-insertions and locality, we show that such surfaces cannot undergo a localization transition even when the surface is strongly disordered. We also present a numerical study which further quantifies this result. We then reformulate the same notions, in field theory language, using a novel Z2-charge-anomaly. This anomaly generalizes the Z-charge-anomaly associated with edges of the Integer Quantum Hall Effect. Besides unifying various aspects of Topological Insulators, the anomaly allows us to calculate new topological properties of TIs in the presence of electric fields.

Ringel, Zohar

2013-03-01

138

Topological wave functions and the 4D-5D lift  

NASA Astrophysics Data System (ADS)

We revisit the holomorphic anomaly equations satisfied by the topological string amplitude from the perspective of the 4D-5D lift, in the context of ``magic'' Script N = 2 supergravity theories. In particular, we interpret the Gopakumar-Vafa relation between 5D black hole degeneracies and the topological string amplitude as the result of a canonical transformation from 4D to 5D charges. Moreover we use the known Bekenstein-Hawking entropy of 5D black holes to constrain the asymptotic behavior of the topological wave function at finite topological coupling but large Kähler classes. In the process, some subtleties in the relation between 5D black hole degeneracies and the topological string amplitude are uncovered, but not resolved. Finally we extend these considerations to the putative one-parameter generalization of the topological string amplitude, and identify the canonical transformation as a Weyl reflection inside the 3D duality group.

Gao, Peng; Pioline, Boris

2008-07-01

139

- criticality of topological black holes in Lovelock-Born-Infeld gravity  

NASA Astrophysics Data System (ADS)

To understand the effect of third order Lovelock gravity, - criticality of topological AdS black holes in Lovelock-Born-Infeld gravity is investigated. The thermodynamics is further explored with some more extensions and in some more detail than the previous literature. A detailed analysis of the limit case is performed for the seven-dimensional black holes. It is shown that, for the spherical topology, - criticality exists for both the uncharged and the charged cases. Our results demonstrate again that the charge is not the indispensable condition of - criticality. It may be attributed to the effect of higher derivative terms of the curvature because similar phenomenon was also found for Gauss-Bonnet black holes. For , there would be no - criticality. Interesting findings occur in the case , in which positive solutions of critical points are found for both the uncharged and the charged cases. However, the - diagram is quite strange. To check whether these findings are physical, we give the analysis on the non-negative definiteness condition of the entropy. It is shown that, for any nontrivial value of , the entropy is always positive for any specific volume . Since no - criticality exists for in Einstein gravity and Gauss-Bonnet gravity, we can relate our findings with the peculiar property of third order Lovelock gravity. The entropy in third order Lovelock gravity consists of extra terms which are absent in the Gauss-Bonnet black holes, which makes the critical points satisfy the constraint of non-negative definiteness condition of the entropy. We also check the Gibbs free energy graph and "swallow tail" behavior can be observed. Moreover, the effect of nonlinear electrodynamics is also included in our research.

Mo, Jie-Xiong; Liu, Wen-Biao

2014-04-01

140

An Acoustic Charge Transport Imager for High Definition Television Applications: Low-Voltage SAW Amplifiers on Multilayer GaAs/ZnO Substrates  

NASA Technical Reports Server (NTRS)

This thesis addresses the acoustoelectric issues concerning the amplification of surface acoustic waves (SAWs) and the reflection of SAWs from slanted reflector gratings on GaAs, with application to a novel acoustic charge transport (ACT) device architecture. First a simple model of the SAWAMP was developed, which was subsequently used to define the epitaxially grown material structure necessary to provide simultaneously high resistance and high electron mobility. In addition, a segmented SAWAMP structure was explored with line widths on the order of an acoustic wavelength. This resulted in the demonstration of SAWAMPS with an order of magnitude less voltage and power requirements than previously reported devices. A two-dimensional model was developed to explain the performance of devices with charge confinement layers less then 0.5 mm, which was experimentally verified. This model was extended to predict a greatly increased gain from the addition of a ZnO overlay. These overlays were experimentally attempted, but no working devices were reported due to process incompatibilities. In addition to the SAWAMP research, the reflection of SAWs from slanted gratings on GaAs was also studied and experimentally determined reflection coefficients for both 45 deg grooves and Al stripes on GaAs have been reported for the first time. The SAWAMp and reflector gratings were combined to investigate the integrated ring oscillator for application to the proposed ACT device and design parameters for this device have been provided.

Hunt, W. D.; Brennan, K. F.; Summers, C. J.; Cameron, Thomas P.

1996-01-01

141

Membrane-protein topology  

Microsoft Academic Search

In the world of membrane proteins, topology defines an important halfway house between the amino-acid sequence and the fully folded three-dimensional structure. Although the concept of membrane-protein topology dates back at least 30 years, recent advances in the field of translocon-mediated membrane-protein assembly, proteome-wide studies of membrane-protein topology and an exponentially growing number of high-resolution membrane-protein structures have given us

Gunnar von Heijne

2006-01-01

142

Considerations for Multiprocessor Topologies  

NASA Technical Reports Server (NTRS)

Choosing a multiprocessor interconnection topology may depend on high-level considerations, such as the intended application domain and the expected number of processors. It certainly depends on low-level implementation details, such as packaging and communications protocols. The authors first use rough measures of cost and performance to characterize several topologies. They then examine how implementation details can affect the realizable performance of a topology.

Byrd, Gregory T.; Delagi, Bruce A.

1987-01-01

143

Statistical topological insulators  

NASA Astrophysics Data System (ADS)

We define a class of insulators with gapless surface states protected from localization due to the statistical properties of a disordered ensemble, namely, due to the ensemble's invariance under a certain symmetry. We show that these insulators are topological, and are protected by a Z2 invariant. Finally, we prove that every topological insulator gives rise to an infinite number of classes of statistical topological insulators in higher dimensions. Our conclusions are confirmed by numerical simulations.

Fulga, I. C.; van Heck, B.; Edge, J. M.; Akhmerov, A. R.

2014-04-01

144

Cubic Topological Kondo Insulators  

NASA Astrophysics Data System (ADS)

Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of ?8 spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.

Alexandrov, Victor; Dzero, Maxim; Coleman, Piers

2013-11-01

145

Constraint propagation through electromagnetic interaction topologies  

NASA Astrophysics Data System (ADS)

The effects of electromagnetic interactions in electrical systems are of concern because of the increasing susceptibility of system components. Heuristic methods are used by engineers to solve electromagnetic interaction problems. An approximate symbolic knowledge representation of a single emitter/path/susceptor problem has been described. In this paper the approximate single emitter/path/susceptor attributes are distributed throughout the electromagnetic topology of a complex system. A constraint based approach for the modelling of the electromagnetic interactions in the system is then described. The approach taken here subdivides the modelling task into: (1) the definition of the related physical topology; (2) constraining topological nodes with specific electromagnetic attributes; and (3) the propagation of the electromagnetic constraints to determine the probability of failure. The scheme has been implemented in Quintus Prolog on a Sun Sparcstation. The electromagnet topology is represented in Prolog using an object-oriented knowledge representation methodology. A small database containing some attributes of electromagnetic components found on the Canadian NSA helicopter was developed. A coarse topological decomposition of the helicopter was made and the attributes for the various components were entered. This tool was very useful in providing understanding of all the complex interaction paths existing in complex systems.

Lovetri, Joe; Graham, Darin P. W.

1990-08-01

146

Topologically Adaptable Snakes  

Microsoft Academic Search

This paper presents a topologically adaptable snakes model for image segmentation and object representation. The model is embedded in the framework of domain subdi- vision using simplicial decomposition. This framework ex- tends the geometric and topological adaptability of snakes while retaining all of the features of traditional snakes, s uch as user interaction, and overcoming many of the limitations of

Tim Mcinerney; Demetri Terzopoulos

1995-01-01

147

Topological defects in CFT  

SciTech Connect

Areview of the notion, properties and the use of topological defects in 2d conformal field theories is presented. An emphasis is made on the recent interpretation of such operators in non-rational theories, as describing Wilson-'t Hooft loop operators of N = 2 supersymmetric 4d topological theories.

Petkova, V. B., E-mail: petkova@inrne.bas.bg [Bulgarian Academy of Sciences, Institute of Nuclear Research and Nuclear Energy (Bulgaria)

2013-10-15

148

Topological quantum distillation.  

PubMed

We construct a class of topological quantum codes to perform quantum entanglement distillation. These codes implement the whole Clifford group of unitary operations in a fully topological manner and without selective addressing of qubits. This allows us to extend their application also to quantum teleportation, dense coding, and computation with magic states. PMID:17155532

Bombin, H; Martin-Delgado, M A

2006-11-01

149

Topological properties of hypercubes  

Microsoft Academic Search

The n-dimensional hypercube is a highly concurrent loosely coupled multiprocessor based on the binary n-cube topology. Machines based on the hypercube topology have been advocated as ideal parallel architectures for their powerful interconnection features. In this paper, the authors examine the hypercube from the graph theory point of view and consider those features that make its connectivity so appealing. Among

Y. Saad; M. H. Schultz

1988-01-01

150

Superpositional Quantum Network Topologies  

Microsoft Academic Search

We introduce superposition-based quantum networks composed of (i) the classical perceptron model of multilayered, feedforward neural networks and (ii) the algebraic model of evolving reticular quantum structures as described in quantum gravity. The main feature of this model is moving from particular neural topologies to a quantum metastructure which embodies many differing topological patterns. Using quantum parallelism, training is possible

Christopher Altman; Jaroslaw Pykacz; Romàn R. Zapatrin

2004-01-01

151

Topological Insulator Materials  

NASA Astrophysics Data System (ADS)

Topological insulators represent a new quantum state of matter which is characterized by peculiar edge or surface states that show up due to a topological character of the bulk wave functions. This review presents a pedagogical account on topological insulator materials with an emphasis on basic theory and materials properties. After presenting a historical perspective and basic theories of topological insulators, it discusses all the topological insulator materials discovered as of May 2013, with some illustrative descriptions of the developments in materials discoveries in which the author was involved. A summary is given for possible ways to confirm the topological nature in a candidate material. Various synthesis techniques as well as the defect chemistry that are important for realizing bulk-insulating samples are discussed. Characteristic properties of topological insulators are discussed with an emphasis on transport properties. In particular, the Dirac fermion physics and the resulting peculiar quantum oscillation patterns are discussed in detail. It is emphasized that proper analyses of quantum oscillations make it possible to unambiguously identify surface Dirac fermions through transport measurements. The prospects of topological insulator materials for elucidating novel quantum phenomena that await discovery conclude the review.

Ando, Yoichi

2013-10-01

152

Introduction to topological analysis  

NASA Astrophysics Data System (ADS)

The topological analysis of chaotic attractors is briefly reviewed. The main concept on which this book is based is thus introduced with a simple case (the attractor solution to the Sprott D system) explicitly treated. Then some perspectives to extend the topological analysis are discussed.

Letellier, Christophe; Gilmore, Robert

2013-01-01

153

A new class of non-topological solitons  

NASA Technical Reports Server (NTRS)

A class of non-topological solitons was constructed in renormalizable scalar field theories with nonlinear self-interactions. For large charge Q, the soliton mass increases linearly with Q, i.e., the soliton mass density is approximately independent of charge. Such objects could be naturally produced in a phase transition in the early universe or in the decay of superconducting cosmic strings.

Frieman, Joshua A.; Lynn, Bryan W.

1989-01-01

154

Tunable Dirac Fermion Dynamics in Topological Insulators  

PubMed Central

Three-dimensional topological insulators are characterized by insulating bulk state and metallic surface state involving relativistic Dirac fermions which are responsible for exotic quantum phenomena and potential applications in spintronics and quantum computations. It is essential to understand how the Dirac fermions interact with other electrons, phonons and disorders. Here we report super-high resolution angle-resolved photoemission studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3 topological insulators. We have directly revealed signatures of the electron-phonon coupling and found that the electron-disorder interaction dominates the scattering process. The Dirac fermion dynamics in Bi2(Te3?xSex) topological insulators can be tuned by varying the composition, x, or by controlling the charge carriers. Our findings provide crucial information in understanding and engineering the electron dynamics of the Dirac fermions for fundamental studies and potential applications.

Chen, Chaoyu; Xie, Zhuojin; Feng, Ya; Yi, Hemian; Liang, Aiji; He, Shaolong; Mou, Daixiang; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Yu, Li; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.

2013-01-01

155

Topological phase transition without gap closing.  

PubMed

Topological phase transition is accompanied with a change of topological numbers. According to the bulk-edge correspondence, the gap closing and the breakdown of the adiabaticity are necessary at the phase transition point to make the topological number ill-defined. However, the gap closing is not always needed. In this paper, we show that two topological distinct phases can be continuously connected without gap closing, provided the symmetry of the system changes during the process. Here we propose the generic principles how this is possible by demonstrating various examples such as 1D polyacetylene with the charge-density-wave order, 2D silicene with the antiferromagnetic order, 2D silicene or quantum well made of HgTe with superconducting proximity effects and 3D superconductor Cu doped Bi2Se3. It is argued that such an unusual phenomenon can occur when we detour around the gap closing point provided the connection of the topological numbers is lost along the detour path. PMID:24071900

Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto

2013-01-01

156

Topological Phase Transition without Gap Closing  

PubMed Central

Topological phase transition is accompanied with a change of topological numbers. According to the bulk-edge correspondence, the gap closing and the breakdown of the adiabaticity are necessary at the phase transition point to make the topological number ill-defined. However, the gap closing is not always needed. In this paper, we show that two topological distinct phases can be continuously connected without gap closing, provided the symmetry of the system changes during the process. Here we propose the generic principles how this is possible by demonstrating various examples such as 1D polyacetylene with the charge-density-wave order, 2D silicene with the antiferromagnetic order, 2D silicene or quantum well made of HgTe with superconducting proximity effects and 3D superconductor Cu doped Bi2Se3. It is argued that such an unusual phenomenon can occur when we detour around the gap closing point provided the connection of the topological numbers is lost along the detour path.

Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto

2013-01-01

157

Topological susceptibility with the asqtad action  

SciTech Connect

Chiral perturbation theory predicts that in quantum chromodynamics (QCD), light dynamical quarks suppress the gauge-field topological susceptibility of the vacuum. The degree of suppression depends on quark multiplicity and masses. It provides a strong consistency test for fermion formulations in lattice QCD. Such tests are especially important for staggered fermion formulations that lack a full chiral symmetry and use the 'fourth-root' procedure to achieve the desired number of sea quarks. Over the past few years we have measured the topological susceptibility on a large database of 18 gauge field ensembles, generated in the presence of 2+1 flavors of dynamical asqtad quarks with up and down quark masses ranging from 0.05 to 1 in units of the strange quark mass and lattice spacings ranging from 0.045 fm to 0.12 fm. Our study also includes three quenched ensembles with lattice spacings ranging from 0.06 to 0.12 fm. We construct the topological susceptibility from the integrated point-to-point correlator of the discretized topological charge density F{tilde F}. To reduce its variance, we model the asymptotic tail of the correlator. The continuum extrapolation of our results for the topological susceptibility agrees nicely at small quark mass with the predictions of lowest-order SU(3) chiral perturbation theory, thus lending support to the validity of the fourth-root procedure.

Van de Water, R.; Bernard, C.; Laiho, J.; Billeter, B.; DeTar, C.; Levkova, L.; Oktay, M.B.; Gottlieb, S.; Heller, U.M.; Hetrick, J.E.; Osborn, J.; Sugar, R.L.; (MILC Collaboration)

2010-06-15

158

Topological susceptibility with the asqtad action  

SciTech Connect

Chiral perturbation theory predicts that in quantum chromodynamics (QCD), light dynamical quarks suppress the gauge-field topological susceptibility of the vacuum. The degree of suppression depends on quark multiplicity and masses. It provides a strong consistency test for fermion formulations in lattice QCD. Such tests are especially important for staggered fermion formulations that lack a full chiral symmetry and use the 'fourth-root' procedure to achieve the desired number of sea quarks. Over the past few years we have measured the topological susceptibility on a large database of 18 gauge-field ensembles, generated in the presence of 2+1 flavors of dynamical asqtad quarks with up and down quark masses ranging from 0.05 to 1 in units of the strange quark mass and lattice spacings ranging from 0.045 fm to 0.12 fm. Our study also includes three quenched ensembles with lattice spacings ranging from 0.06 to 0.12 fm. We construct the topological susceptibility from the integrated point-to-point correlator of the discretized topological charge density FF-tilde. To reduce its variance, we model the asymptotic tail of the correlator. The continuum extrapolation of our results for the topological susceptibility agrees nicely at small quark mass with the predictions of lowest-order SU(3) chiral perturbation theory, thus lending support to the validity of the fourth-root procedure.

Bazavov, A.; Toussaint, D. [Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States); Bernard, C.; Laiho, J. [Department of Physics, Washington University, St. Louis, Missouri 63130 (United States); Billeter, B.; DeTar, C.; Levkova, L.; Oktay, M. B. [Physics Department, University of Utah, Salt Lake City, Utah 84112 (United States); Gottlieb, Steven [Department of Physics, Indiana University, Bloomington, Indiana 47405, USA, NCSA, University of Illinois, Urbana, Illinois 61801 (United States); Heller, U. M. [American Physical Society, One Research Road, Ridge, New York 11961 (United States); Hetrick, J. E. [Physics Department, University of the Pacific, Stockton, California 95211 (United States); Osborn, J. [Argonne National Laboratory, Argonne, Illinois 60439 (United States); Sugar, R. L. [Department of Physics, University of California, Santa Barbara, California 93106 (United States); Van de Water, R. S. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2010-06-01

159

Topological magnon insulator in insulating ferromagnet  

NASA Astrophysics Data System (ADS)

In the ferromagnetic insulator with the Dzyaloshinskii-Moriya interaction, we theoretically predict and numerically verify a topological magnon insulator, where the charge-free magnon is topologically protected for transporting along the edge/surface while it is insulating in the bulk. The chiral edge states form a connected loop as a 4?- or 8?-period Möbius strip in the spin-wave vector space, showing the nontrivial topology of magnonic bands. Using the nonequilibrium Green's function method, we explicitly demonstrate that the one-way chiral edge transport is indeed topologically protected from defects or disorders. Moreover, we show that the topological edge state mainly localizes around edges and leaks into the bulk with oscillatory decay. Although the chiral edge magnons and energy current prefer to travel along one edge from the hot region to the cold one, the anomalous transports are identified in the opposite edge, which reversely flow from the cold region to the hot one. Our findings could be validated within wide energy ranges in various magnonic crystals, such as Lu2V2O7.

Zhang, Lifa; Ren, Jie; Wang, Jian-Sheng; Li, Baowen

2013-04-01

160

Effect of improving the lattice gauge action on QCD topology  

SciTech Connect

We use lattice topology as a laboratory to-compare the Wilson action (WA) with the Symanzik-Weisz (SW) action constructed from a combination of (1 x 1) and (1 x 2) Wilson loops, and the estimate of the renormalization trajectory (RT)[1] from a renormalization group transformation (RGT) which also includes higher representations of the (1 x 1) loop. Topological charges are computed using the geometric (Luscher`s) and plaquette methods on the uncooled lattice, and also by using cooling to remove ultraviolet artifacts. We show that as the action improves by approaching the RT, the topological charges for individual configurations, computed using these three methods become more highly correlated, suggesting that artificial lattice renormalizations to the topological susceptibility can be suppressed by improving the action.

Grandy, J. [Lawrence Livermore National Lab., CA (United States); Kilcup, G. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics

1996-08-19

161

Topologically nontrivial narrow bands in ultrathin SnTe films with defect superstructures  

NASA Astrophysics Data System (ADS)

It is shown that a two-dimensional topological insulator can be realized and the band topology (equivalently, the edge states) may be further controlled by charge doping in an ultrathin SnTe film with a defect superstructure. Based on first-principles density functional theory (DFT), we predict that a Sn-Te bilayer, if exfoliated from three-dimensional bulk SnTe in the (1?1?1) direction, has a trivial band topology in its pristine form, but is made topologically nontrivial by introducing an appropriate array of defects. The emergence of the topological state is ascribed to the formation of topologically nontrivial narrow bands near the Fermi level by spin–orbit splitting of defect-induced bands. In addition, we demonstrate that a transition between a topological insulator and a normal insulator is possible under the electron or hole doping which can be useful for controlling the topological edge states.

Kim, Minsung; Ihm, Jisoon

2014-06-01

162

Topological solitons in 8-spinor mie electrodynamics  

SciTech Connect

We investigate the effective 8-spinor field model suggested earlier as the generalization of nonlinear Mie electrodynamics. We first study in pure spinorial model the existence of topological solitons endowed with the nontrivial Hopf invariant Q{sub H}, which can be interpreted as the lepton number. Electromagnetic field being included as the perturbation, we estimate the energy and the spin of the localized charged configuration.

Rybakov, Yu. P., E-mail: soliton4@mail.ru [Peoples' Friendship University of Russia, Department of Theoretical Physics (Russian Federation)

2013-10-15

163

Topological wave functions and the 4D-5D lift  

Microsoft Academic Search

We revisit the holomorphic anomaly equations satisfied by the topological string amplitude from the perspective of the 4D-5D lift, in the context of ``magic'' Script N = 2 supergravity theories. In particular, we interpret the Gopakumar-Vafa relation between 5D black hole degeneracies and the topological string amplitude as the result of a canonical transformation from 4D to 5D charges. Moreover

Peng Gao; Boris Pioline

2008-01-01

164

Topology of Discrete Strategies.  

National Technical Information Service (NTIS)

This paper explores a topological perspective of planning in the presence of uncertainty focusing on tasks specified by goal states in discrete spaces. The paper introduces strategy complexes. A strategy complex is the collection of all plans for attainin...

M. Erdmann

2009-01-01

165

Spin-3 topologically massive gravity  

NASA Astrophysics Data System (ADS)

In this Letter, we study the spin-3 topologically massive gravity (TMG), paying special attention to its properties at the chiral point. We propose an action describing the higher spin fields coupled to TMG. We discuss the traceless spin-3 fluctuations around the AdS vacuum and find that there is an extra local massive mode, besides the left-moving and right-moving boundary massless modes. At the chiral point, such extra mode becomes massless and degenerates with the left-moving mode. We show that at the chiral point the only degrees of freedom in the theory are the boundary right-moving graviton and spin-3 field. We conjecture that spin-3 chiral gravity with generalized Brown-Henneaux boundary condition is holographically dual to 2D chiral CFT with classical W algebra and central charge c=3l/G.

Chen, Bin; Long, Jiang; Wu, Jun-bao

2011-11-01

166

Higher-dimensional Algebra and Topological Quantum Field Theory  

Microsoft Academic Search

The study of topological quantum field theories increasingly relies upon concepts from higher-dimensional algebra such as n-categories and n-vector spaces. We review progress towards a definition of n-category suited for this purpose, and outline a program in which n-dimensional TQFTs are to be described as n-category representations. First we describe a \\

John C. Baez; James Dolan

1995-01-01

167

25 CFR 38.3 - Definitions.  

Code of Federal Regulations, 2011 CFR

...BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR EDUCATION EDUCATION PERSONNEL § 38.3 Definitions. As used in...Agency School Board. Agency Superintendent for Education (ASE) means the Bureau official in charge...

2011-04-01

168

25 CFR 214.1 - Definition.  

Code of Federal Regulations, 2011 CFR

...MINERALS LEASING OF OSAGE RESERVATION LANDS, OKLAHOMA, FOR MINING, EXCEPT OIL AND GAS § 214.1 Definition. The...the Commissioner of Indian Affairs to take charge of leasing or mining operations under the regulations in this...

2011-04-01

169

40 CFR 60.161 - Definitions.  

Code of Federal Regulations, 2010 CFR

...Performance for Primary Copper Smelters § 60.161 Definitions...part. (a) Primary copper smelter means any installation...of separate layers of molten slag, molten copper, and/or...fossil fuel. (k) Total smelter charge means the...

2010-07-01

170

40 CFR 60.161 - Definitions.  

Code of Federal Regulations, 2010 CFR

...Performance for Primary Copper Smelters Sec. 60.161 Definitions...part. (a) Primary copper smelter means any installation...of separate layers of molten slag, molten copper, and...a fossil fuel. (k) Total smelter charge means the weight...

2009-07-01

171

Interaction effects and quantum phase transitions in topological insulators  

SciTech Connect

We study strong correlation effects in topological insulators via the Lanczos algorithm, which we utilize to calculate the exact many-particle ground-state wave function and its topological properties. We analyze the simple, noninteracting Haldane model on a honeycomb lattice with known topological properties and demonstrate that these properties are already evident in small clusters. Next, we consider interacting fermions by introducing repulsive nearest-neighbor interactions. A first-order quantum phase transition was discovered at finite interaction strength between the topological band insulator and a topologically trivial Mott insulating phase by use of the fidelity metric and the charge-density-wave structure factor. We construct the phase diagram at T=0 as a function of the interaction strength and the complex phase for the next-nearest-neighbor hoppings. Finally, we consider the Haldane model with interacting hard-core bosons, where no evidence for a topological phase is observed. An important general conclusion of our work is that despite the intrinsic nonlocality of topological phases their key topological properties manifest themselves already in small systems and therefore can be studied numerically via exact diagonalization and observed experimentally, e.g., with trapped ions and cold atoms in optical lattices.

Varney, Christopher N. [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Joint Quantum Institute and Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Sun Kai; Galitski, Victor [Joint Quantum Institute and Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Rigol, Marcos [Department of Physics, Georgetown University, Washington, DC 20057 (United States)

2010-09-15

172

Theory of Topological Insulators  

NASA Astrophysics Data System (ADS)

Topological insulators are materials with a bulk excitation gap generated by the spin orbit interaction, and which are different from conventional insulators. This distinction is characterized by Z2 topological invariants, which characterize the ground state. In two dimensions a single Z2 invariant describes the quantum spin Hall insulator phase. In three dimensions there are four Z2 invariants, distinguishing ``weak'' (WTI) and ``strong'' (STI) topological insulators. The STI phase is characterized by the presence of unique gapless surface states whose Fermi surface encloses an odd number of 2D Dirac points. We will argue theoretically that the semiconducting alloy Bi1-xSbx is a strong topological insulator -- a prediction that has recently been confirmed experimentally. We will next show that the proximity effect between this unique surface phase and an ordinary superconductor leads to a two dimensional state that resembles a spinless px+ipy superconductor, but does not break time reversal symmetry. This state supports zero energy Majorana bound states at vortices, and may provide a new venue to realize proposals for topological quantum computing.

Fu, Liang

2009-03-01

173

Analysis of systematic errors in the calculation of renormalization constants of the topological susceptibility on the lattice  

SciTech Connect

A Ginsparg-Wilson based calibration of the topological charge is used to calculate the renormalization constants which appear in the field-theoretical determination of the topological susceptibility on the lattice. A systematic comparison is made with calculations based on cooling. The two methods agree within present statistical errors (3%-4%). We also discuss the independence of the multiplicative renormalization constant Z from the background topological charge used to determine it.

Alles, B. [INFN, Sezione di Pisa, Pisa (Italy); D'Elia, M. [Dipartimento di Fisica, Universita di Genova and INFN, Genoa (Italy); Di Giacomo, A.; Pica, C. [Dipartimento di Fisica, Universita di Pisa and INFN, Pisa (Italy)

2006-11-01

174

Preliminary measurement of time-dependent B{sub d}{sup 0}-B{sub d}{sup 0} mixing using topology and charge selected semi-leptonic B decays  

SciTech Connect

The time dependence of B{sub d}{sup 0}-B{sub d}{sup 0} mixing has been measured using a sample of 150,000 hadronic Z{sup 0} decays collected by the SLD experiment at the SLC between 1993 and 1995. The analysis identifies the semileptonic decays of B mesons with high (p, p{sub t}) leptons and reconstructs the B meson decay length and charge by vertexing the lepton with a partially reconstructed D meson. Vertex charge is used to enrich the selection of neutral over charged B mesons. This method results in a sample of 581 neutral decays with high charge purity. The B candidate is tagged at production with a combined tag that exploits the large polarized b forward-backward asymmetry in conjunction with the opposite hemisphere b jet charge. The final state is tagged by the sign of the high (p, p{sub t}) lepton. From their preliminary analysis the authors find a mass difference between the two B{sub d}{sup 0} mass eigenstates of, {Delta}m{sub d} = 0.452 {+-} 0.074(stat) {+-} 0.049(syst) ps{sup {minus}1}.

NONE

1996-07-01

175

Topology change and quantum physics.  

National Technical Information Service (NTIS)

The role of topology in elementary quantum physics is discussed in detail. It is argued that attributes of classical spatial topology emerge from properties of state vectors with suitably smooth time evolution. Equivalently, they emerge from consideration...

A. P. Balachandran G. Bimonte G. Marmo A. Simoni

1995-01-01

176

Optimality in Fuzzy Topological Polysystems. .  

National Technical Information Service (NTIS)

After presenting the necessary background information for fuzzy sets and fuzzy topological spaces, the author formalizes fuzzy topological polysystems. The paper contains a discussion of reachable set of events and boundary of a fuzzy set. An optimal solu...

R. H. Warren

1976-01-01

177

A Complete Topology Management Mechanism for the Advanced Switching Interconnect Technology  

Microsoft Academic Search

The advanced switching technology is a new high-performance standard serial inter-connect. Its specification establishes a management infrastructure in charge of maintaining the fabric operation after the occurrence of a topological change. When the change is detected, the management mechanism discovers the new topology, obtains a set of fabric paths, and finally distributes them to the endpoints. The main contribution of

Antonio Robles-gómez; Aurelio Bermúdez; Rafael Casado; Francisco J. Quiles

2007-01-01

178

Opportunities in chemistry and materials science for topological insulators and their nanostructures  

Microsoft Academic Search

Electrical charges on the boundaries of topological insulators favour forward motion over back-scattering at impurities, producing low-dissipation, metallic states that exist up to room temperature in ambient conditions. These states have the promise to impact a broad range of applications from electronics to the production of energy, which is one reason why topological insulators have become the rising star in

Desheng Kong; Yi Cui

2011-01-01

179

Topological solitons in the noncommutative plane and quantum Hall Skyrmions  

NASA Astrophysics Data System (ADS)

We analyze topological solitons in the noncommutative plane by taking a concrete instance of the quantum Hall system with the SU(N) symmetry, where a soliton is identified with a Skyrmion. It is shown that a topological soliton induces an excitation of the electron number density from the ground-state value around it. When a judicious choice of the topological charge density J0(x) is made, it acquires a physical reality as the electron density excitation ??cl(x) around a topological soliton, ??cl(x)=-J0(x). Hence a noncommutative soliton carries necessarily the electric charge proportional to its topological charge. A field-theoretical state is constructed for a soliton state irrespectively of the Hamiltonian. In general, it involves an infinitely many parameters. They are fixed by minimizing its energy once the Hamiltonian is chosen. We study explicitly the cases where the system is governed by the hard-core interaction and by the noncommutative CPN-1 model, where all these parameters are determined analytically and the soliton excitation energy is obtained.

Ezawa, Z. F.; Tsitsishvili, G.

2005-10-01

180

Topological insulators avoid the parity anomaly  

NASA Astrophysics Data System (ADS)

The surface of a 3+1d-topological insulator hosts an odd number of gapless Dirac fermions when charge conjugation and time-reversal symmetries are preserved. Viewed as a purely 2+1d system, this surface theory would necessarily explicitly break parity and time-reversal when coupled to a fluctuating gauge field. Here, we explain why such a state can exist on the boundary of a 3+1d system without breaking these symmetries, even if the number of boundary components is odd. This is accomplished from two complementary perspectives: topological quantization conditions and regularization. We first discuss the conditions under which (continuous) large gauge transformations may exist when the theory lives on a boundary of a higher-dimensional space-time. Next, we show how the higher-dimensional bulk theory is essential in providing a parity-invariant regularization of the theory living on the lower-dimensional boundary or defect.

Mulligan, Michael; Burnell, F. J.

2013-08-01

181

Rendering of quantum topological atoms and bonds.  

PubMed

In this article, we describe and apply an algorithm that visualizes atoms and bonds in molecules and van der Waals complexes, based on the topology of the electron density. The theory of quantum chemical topology defines both atoms and bonds via a single consistent procedure, and enables the association of an atomic shape with an atomic property (charge, dipole moment, volume, ...). Special attention is paid to the bridging of gaps arising in interatomic surfaces, in the presence of ring critical points or high ellipticity. This algorithm, in conjunction with the graphical user interface of the computer program MORPHY enables robust and efficient rendering of complicated interatomic surfaces, as found in larger systems. PMID:15970447

Rafat, M; Devereux, M; Popelier, P L A

2005-10-01

182

Measuring shape with topology  

NASA Astrophysics Data System (ADS)

We propose a measure of shape which is appropriate for the study of a complicated geometric structure, defined using the topology of neighborhoods of the structure. One aspect of this measure gives a new notion of fractal dimension. We demonstrate the utility and computability of this measure by applying it to branched polymers, Brownian trees, and self-avoiding random walks.

MacPherson, Robert; Schweinhart, Benjamin

2012-07-01

183

Order, topology and preference  

NASA Technical Reports Server (NTRS)

Some standard order-related and topological notions, facts, and methods are brought to bear on central topics in the theory of preference and the theory of optimization. Consequences of connectivity are considered, especially from the viewpoint of normally preordered spaces. Examples are given showing how the theory of preference, or utility theory, can be applied to social analysis.

Sertel, M. R.

1971-01-01

184

Topological Hall insulator  

NASA Astrophysics Data System (ADS)

We examine physical transformations that preserve the well known properties of the Hall effect in the GaAs/AlGaAs 2D system and show that the Hall effect is immune to certain deformations such as the insertion of holes, inversion transformations, and superposition. From the results, we conclude that the ordinary Hall effect includes topological protection for the above mentioned operations.

Kriisa, Annika; Mani, R. G.; Wegscheider, W.

2013-12-01

185

TOPPER: Topology Prediction of Transmembrane Protein Based on Evidential Reasoning  

PubMed Central

The topology prediction of transmembrane protein is a hot research field in bioinformatics and molecular biology. It is a typical pattern recognition problem. Various prediction algorithms are developed to predict the transmembrane protein topology since the experimental techniques have been restricted by many stringent conditions. Usually, these individual prediction algorithms depend on various principles such as the hydrophobicity or charges of residues. In this paper, an evidential topology prediction method for transmembrane protein is proposed based on evidential reasoning, which is called TOPPER (topology prediction of transmembrane protein based on evidential reasoning). In the proposed method, the prediction results of multiple individual prediction algorithms can be transformed into BPAs (basic probability assignments) according to the confusion matrix. Then, the final prediction result can be obtained by the combination of each individual prediction base on Dempster's rule of combination. The experimental results show that the proposed method is superior to the individual prediction algorithms, which illustrates the effectiveness of the proposed method.

Deng, Xinyang; Liu, Qi; Hu, Yong; Deng, Yong

2013-01-01

186

Topological Insulators in Three Dimensions  

Microsoft Academic Search

We study three dimensional generalizations of the quantum spin Hall (QSH) effect. Unlike two dimensions, where the QSH effect is distinguished by a single Z2 topological invariant, in three dimensions there are 4 invariants distinguishing 16 ``topological insulator'' phases. There are two general classes: weak (WTI) and strong (STI) topological insulators. The WTI states are equivalent to layered 2D QSH

Liang Fu; Charles Kane; Eugene Mele

2007-01-01

187

Topology of Document Retrieval Systems.  

ERIC Educational Resources Information Center

Explains the use of a topological structure to examine the closeness between documents in retrieval systems and analyzes the topological structure of a vector-space model, a fuzzy-set model, an extended Boolean model, a probabilistic model, and a TIRS (Topological Information Retrieval System) model. Proofs for the results are appended. (17…

Everett, Daniel M.; Cater, Steven C.

1992-01-01

188

Topological censorship and chronology protection  

NASA Astrophysics Data System (ADS)

Over the past two decades, substantial efforts have been made to understand the way in which physics enforces the ordinary topology and causal structure that we observe on observed scales - from subnuclear to cosmological. We review the status of topological censorship and the topology of event horizons; chronology protection in classical and semiclassical gravity; and related progress in establishing quantum energy inequalities.

Friedman, J.; Higuchi, A.

2006-01-01

189

Topological censorship and chronology protection.  

NASA Astrophysics Data System (ADS)

Despite the presence of closed timelike curves and of structures with noneuclidean topology in the space of solutions to the vacuum Einstein equations, neither appears common in the macroscopic universe. Several recent results on topological censorship and chronology protection seek to explain why the macroscopic topology and causal structure of spacetime are ordinary.

Friedman, J. L.

190

On continuity: aristotle versus topology?  

Microsoft Academic Search

This paper begins by pointing out that the Aristotelian conception of continuity (synecheia) and the contemporary topological account share the same intuitive, proto-topological basis: the conception of a ‘natural whole’ or unity without joints or seams. An argument of Aristotle to the effect that what is continuous cannot be constituted of ‘indivisibles’ (e.g., points) is examined from a topological perspective.

Michael J. White

1988-01-01

191

Quantum foam and topological strings  

Microsoft Academic Search

We find an interpretation of the recent connection found between topological strings on Calabi-Yau threefolds and crystal melting: Summing over statistical mechanical configuration of melting crystal is equivalent to a quantum gravitational path integral involving fluctuations of Kähler geometry and topology. We show how the limit shape of the melting crystal emerges as the average geometry and topology of the

Amer Iqbal; Cumrun Vafa; Nikita Nekrasov; Andrei Okounkov

2008-01-01

192

Classification of topological defects in Abelian topological states  

NASA Astrophysics Data System (ADS)

We propose the most general classification of pointlike and linelike extrinsic topological defects in (2+1)-dimensional Abelian topological states. We first map generic extrinsic defects to boundary defects, and then provide a classification of the latter. Based on this classification, the most generic point defects can be understood as domain walls between topologically distinct boundary regions. We show that topologically distinct boundaries can themselves be classified by certain maximal subgroups of mutually bosonic quasiparticles, called Lagrangian subgroups. We study the topological properties of the point defects, including their quantum dimension, localized zero modes, and projective braiding statistics.

Barkeshli, Maissam; Jian, Chao-Ming; Qi, Xiao-Liang

2013-12-01

193

Topology Preserving SOM with Transductive Confidence Machine  

NASA Astrophysics Data System (ADS)

We propose a novel topology preserving self-organized map (SOM) classifier with transductive confidence machine (TPSOM-TCM). Typically, SOM acts as a dimension reduction tool for mapping training samples from a high-dimensional input space onto a neuron grid. However, current SOM-based classifiers can not provide degrees of classification reliability for new unlabeled samples so that they are difficult to be used in risk-sensitive applications where incorrect predictions may result in serious consequences. Our method extends a typical SOM classifier to allow it to supply such reliability degrees. To achieve this objective, we define a nonconformity measurement with which a randomness test can predict how nonconforming a new unlabeled sample is with respect to the training samples. In addition, we notice that the definition of nonconformity measurement is more dependent on the quality of topology preservation than that of quantization error reduction. We thus incorporate the grey relation coefficient (GRC) into the calculation of neighborhood radii to improve the topology preservation without increasing the quantization error. Our method is able to improve the time efficiency of a previous method kNN-TCM, when the number of samples is large. Extensive experiments on both the UCI and KDDCUP 99 data sets show the effectiveness of our method.

Tong, Bin; Qin, Zhiguang; Suzuki, Einoshin

194

Changing topology by topological defects in three-dimensional topologically ordered phases  

NASA Astrophysics Data System (ADS)

A hallmark feature of topologically ordered states of matter is the dependence of ground-state degeneracy (GSD) on the topology of the manifold determined by the global shape of the system. Although the topology of a physical system is practically hard to manipulate, recently, it was shown that in certain topologically ordered phases, topological defects can introduce extra topological GSD. Here the topological defects can be viewed as effectively changing the topology of the physical system. Previous studies have been focusing on two spatial dimensions with pointlike topological defects. In three dimensions, linelike topological defects can appear. They are closed loops in the bulk that can be linked and knotted, effectively leading to complex three-dimensional manifolds in certain topologically ordered states. This paper studies the properties of such line defects in a particular context: the lattice dislocations. We give an analytical construction, together with support from exact numerical calculations, for the dependence of the GSD on dislocations of certain doubled versions of the exactly solvable Kitaev's toric code models in both two and three dimensions. We find that the GSD of the 3D model depends only on the total number of dislocation loops, no matter how they are linked or knotted. The results are extended to Zn generalizations of the model. Additionally, we consider the phases in which the crystalline orders are destroyed through proliferation of double dislocations. The resulting phases are shown to host topological orders described by non-Abelian gauge theories.

Mesaros, Andrej; Kim, Yong Baek; Ran, Ying

2013-07-01

195

Topological similarities in electrical and hydrological drainage networks  

Microsoft Academic Search

Under an electric field, spherical conducting particles in a dielectric liquid assemble into a dendritic tree in order to dissipate charge. Several topological measures characterize such networks, including degree distributions, Strahler numbers, and total external pathlengths. Here, scaling laws relating these measures to the number of nodes in the system are presented and shown to match diffusion limited aggregation (DLA)

Vishal H. Soni; Pia M. Ketisch; Juan D. Rodríguez; Alexander Shpunt; Alfred W. Hübler

2011-01-01

196

Symmetry enforced non-Abelian topological order at the surface of a topological insulator  

NASA Astrophysics Data System (ADS)

The surfaces of three-dimensional topological insulators (3D TIs) are generally described as Dirac metals, with a single Dirac cone. It was previously believed that a gapped surface implied breaking of either time-reversal T or U(1) charge conservation symmetry. Here, we discuss a possibility in the presence of interactions, a surface phase that preserves all symmetries but is nevertheless gapped and insulating. Then, the surface must develop topological order of a kind that can not be realized in a two-dimensional (2D) system with the same symmetries. We discuss candidate surface states, non-Abelian quantum Hall states which, when realized in 2D, have ?xy=1/2 and hence break T symmetry. However, by constructing an exactly soluble 3D lattice model, we show they can be realized as T-symmetric surface states. The corresponding 3D phases are confined, and have ? =? magnetoelectric response. Two candidate states have the same 12-particle topological order, the (Read-Moore) Pfaffian state with the neutral sector reversed, which we term T-Pfaffian topological order, but differ in their T transformation. Although we are unable to connect either of these states directly to the superconducting TI surface, we argue that one of them describes the 3D TI surface, while the other differs from it by a bosonic topological phase. We also discuss the 24-particle Pfaffian-antisemion topological order (which can be connected to the superconducting TI surface) and demonstrate that it can be realized as a T-symmetric surface state.

Chen, Xie; Fidkowski, Lukasz; Vishwanath, Ashvin

2014-04-01

197

Network topology mapper  

DOEpatents

A method enables the topology of an acyclic fully propagated network to be discovered. A list of switches that comprise the network is formed and the MAC address cache for each one of the switches is determined. For each pair of switches, from the MAC address caches the remaining switches that see the pair of switches are located. For each pair of switches the remaining switches are determined that see one of the pair of switches on a first port and the second one of the pair of switches on a second port. A list of insiders is formed for every pair of switches. It is determined whether the insider for each pair of switches is a graph edge and adjacent ones of the graph edges are determined. A symmetric adjacency matrix is formed from the graph edges to represent the topology of the data link network.

Quist, Daniel A. (Los Alamos, NM); Gavrilov, Eugene M. (Los Alamos, NM); Fisk, Michael E. (Jemez, NM)

2008-01-15

198

Anomaly detection using topology  

NASA Astrophysics Data System (ADS)

In this paper we present a new topology-based algorithm for anomaly detection in dimensionally large datasets. The motivating application is hyperspectral imaging where the dataset can be a collection of ~ 106 points in Rk, representing the reflected (or radiometric) spectra of electromagnetic radiation. The algorithm begins by building a graph whose edges connect close pairs of points. The background points are the points in the largest components of this graph and all other points are designated as anomalies. The anomalies are ranked according to their distance to the background. The algorithm is termed Topological Anomaly Detection (TAD). The algorithm is tested on hyperspectral imagery collected with the HYDICE sensor which contains targets of known reflectance and spatial location. Anomaly maps are created and compared to results from the common anomaly detection algorithm RX. We show that the TAD algorithm performs better than RX by achieving greater separation of the anomalies from the background for this dataset.

Basener, Bill; Ientilucci, Emmett J.; Messinger, David W.

2007-04-01

199

Aharonov-Casher Effect Without Line Charge  

Microsoft Academic Search

It is shown that the case considered by Casella, which has no path-enclosed charge and was claimed to have different topology from the original Aharonov-Casher case of line charge, is actually equivalent to the Aharonov-Casher case.

Taeyeon Lee

1996-01-01

200

PM wind generator topologies  

Microsoft Academic Search

The objective of this paper is to provide a comparison among permanent magnet (PM) wind generators of different topologies. Seven configurations are chosen for the comparison, consisting of both radial-flux and axial-flux machines. The comparison is done at seven power levels ranging from 1 to 200 kW. The basis for the comparison is discussed and implemented in detail in the

Yicheng Chen; Pragasen Pillay; Azeem Khan

2005-01-01

201

Topological quantum computation  

Microsoft Academic Search

The theory of quantum computation can be constructed from the abstract study\\u000aof anyonic systems. In mathematical terms, these are unitary topological\\u000amodular functors. They underlie the Jones polynomial and arise in\\u000aWitten-Chern-Simons theory. The braiding and fusion of anyonic excitations in\\u000aquantum Hall electron liquids and 2D-magnets are modeled by modular functors,\\u000aopening a new possibility for the realization

Michael H. Freedman; Alexei Kitaev; Michael J. Larsen; Zhenghan Wang; L. D. Landau; Michael H. Freedman

2002-01-01

202

Modulated Floquet topological insulators.  

PubMed

The application of spatially uniform light on conventional insulators can induce Floquet spectra with characteristics akin to those of topological insulators. We demonstrate that spatial modulation of light allows for remarkable control of the properties in these systems. We provide configurations to generate one-dimensional bulk modes, photoinduced currents, as well as fractionalized excitations. We show a close analogy to p-wave superconductors and use this analogy to explain our results. PMID:23383821

Katan, Yaniv Tenenbaum; Podolsky, Daniel

2013-01-01

203

Topological confinement and superconductivity  

SciTech Connect

We derive a Kondo Lattice model with a correlated conduction band from a two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence of a robust pairing mechanism in a model that only contains repulsive interactions. The mechanism is due to topological confinement and results from the interplay between antiferromagnetism and delocalization. By using Density-Matrix-Renormalization-Group (DMRG) we demonstrate that this mechanism leads to dominant superconducting correlations in aID-system.

Al-hassanieh, Dhaled A [Los Alamos National Laboratory; Batista, Cristian D [Los Alamos National Laboratory

2008-01-01

204

Topological FDR for neuroimaging  

PubMed Central

In this technical note, we describe and validate a topological false discovery rate (FDR) procedure for statistical parametric mapping. This procedure is designed to deal with signal that is continuous and has, in principle, unbounded spatial support. We therefore infer on topological features of the signal, such as the existence of local maxima or peaks above some threshold. Using results from random field theory, we assign a p-value to each maximum in an SPM and identify an adaptive threshold that controls false discovery rate, using the Benjamini and Hochberg (BH) procedure (1995). This provides a natural complement to conventional family wise error (FWE) control on local maxima. We use simulations to contrast these procedures; both in terms of their relative number of discoveries and their spatial accuracy (via the distribution of the Euclidian distance between true and discovered activations). We also assessed two other procedures: cluster-wise and voxel-wise FDR procedures. Our results suggest that (a) FDR control of maxima or peaks is more sensitive than FWE control of peaks with minimal cost in terms of false-positives, (b) voxel-wise FDR is substantially less accurate than topological FWE or FDR control. Finally, we present an illustrative application using an fMRI study of visual attention.

Chumbley, J.; Worsley, K.; Flandin, G.; Friston, K.

2010-01-01

205

Extended topological defects as sources and outlets of dislocations in spherical hexagonal crystals  

NASA Astrophysics Data System (ADS)

Extended topological defects (ETDs) arising in spherical hexagonal crystals due to their curvature are considered. These prevalent defects carry a unit total topological charge and are surrounded by scalene pentagonal boundaries. Topological peculiarities of reactions between ETDs and dislocations are considered. Similarly to boundaries of the usual planar crystalline order the ETDs emit and absorb the dislocations without preservation of their dislocational charge. Dislocations located inside the ETD area lose it and the enforced ETD decay can proceed in different ways without conservation of the total Burgers vector of the dislocations emitted.

Roshal, D. S.; Petrov, K. Yu.; Myasnikova, A. E.; Rochal, S. B.

2014-04-01

206

Evidence of Distributed Robust Surface Current Flow in 3D Topological Insulators  

NASA Astrophysics Data System (ADS)

The topologically protected conducting state is expected to exist on the entire surface of three-dimensional topological insulators (TIs). Using concurrent measurements of the local and nonlocal conduction, we provide experimental evidence for the topological robustness of the surface-conducting states of bulk-insulating Bi1.5Sb0.5Te1.7Se1.3 crystalline flakes. The detailed investigation of local and nonlocal charge conductance on the top surfaces, combining with the comprehensive numerical simulation, reveals that the charge current is widely distributed over the entire surface of a TI. Our findings show evidence of the presence of the topologically protected conducting state at the side wall with irregularly stacked edges between the top and bottom surfaces. This study provides a reliable means of accurately characterizing the topological surface states with inherent nonlocal surface-dominant conducting channels in a TI.

Lee, Janghee; Lee, Jae-Hyeong; Park, Joonbum; Kim, Jun Sung; Lee, Hu-Jong

2014-01-01

207

Transportation Network Topologies  

NASA Technical Reports Server (NTRS)

A discomforting reality has materialized on the transportation scene: our existing air and ground infrastructures will not scale to meet our nation's 21st century demands and expectations for mobility, commerce, safety, and security. The consequence of inaction is diminished quality of life and economic opportunity in the 21st century. Clearly, new thinking is required for transportation that can scale to meet to the realities of a networked, knowledge-based economy in which the value of time is a new coin of the realm. This paper proposes a framework, or topology, for thinking about the problem of scalability of the system of networks that comprise the aviation system. This framework highlights the role of integrated communication-navigation-surveillance systems in enabling scalability of future air transportation networks. Scalability, in this vein, is a goal of the recently formed Joint Planning and Development Office for the Next Generation Air Transportation System. New foundations for 21st thinking about air transportation are underpinned by several technological developments in the traditional aircraft disciplines as well as in communication, navigation, surveillance and information systems. Complexity science and modern network theory give rise to one of the technological developments of importance. Scale-free (i.e., scalable) networks represent a promising concept space for modeling airspace system architectures, and for assessing network performance in terms of scalability, efficiency, robustness, resilience, and other metrics. The paper offers an air transportation system topology as framework for transportation system innovation. Successful outcomes of innovation in air transportation could lay the foundations for new paradigms for aircraft and their operating capabilities, air transportation system architectures, and airspace architectures and procedural concepts. The topology proposed considers air transportation as a system of networks, within which strategies for scalability of the topology may be enabled by technologies and policies. In particular, the effects of scalable ICNS concepts are evaluated within this proposed topology. Alternative business models are appearing on the scene as the old centralized hub-and-spoke model reaches the limits of its scalability. These models include growth of point-to-point scheduled air transportation service (e.g., the RJ phenomenon and the Southwest Effect). Another is a new business model for on-demand, widely distributed, air mobility in jet taxi services. The new businesses forming around this vision are targeting personal air mobility to virtually any of the thousands of origins and destinations throughout suburban, rural, and remote communities and regions. Such advancement in air mobility has many implications for requirements for airports, airspace, and consumers. These new paradigms could support scalable alternatives for the expansion of future air mobility to more consumers in more places.

Holmes, Bruce J.; Scott, John

2004-01-01

208

Transportation Network Topologies  

NASA Technical Reports Server (NTRS)

A discomforting reality has materialized on the transportation scene: our existing air and ground infrastructures will not scale to meet our nation's 21st century demands and expectations for mobility, commerce, safety, and security. The consequence of inaction is diminished quality of life and economic opportunity in the 21st century. Clearly, new thinking is required for transportation that can scale to meet to the realities of a networked, knowledge-based economy in which the value of time is a new coin of the realm. This paper proposes a framework, or topology, for thinking about the problem of scalability of the system of networks that comprise the aviation system. This framework highlights the role of integrated communication-navigation-surveillance systems in enabling scalability of future air transportation networks. Scalability, in this vein, is a goal of the recently formed Joint Planning and Development Office for the Next Generation Air Transportation System. New foundations for 21PstP thinking about air transportation are underpinned by several technological developments in the traditional aircraft disciplines as well as in communication, navigation, surveillance and information systems. Complexity science and modern network theory give rise to one of the technological developments of importance. Scale-free (i.e., scalable) networks represent a promising concept space for modeling airspace system architectures, and for assessing network performance in terms of scalability, efficiency, robustness, resilience, and other metrics. The paper offers an air transportation system topology as framework for transportation system innovation. Successful outcomes of innovation in air transportation could lay the foundations for new paradigms for aircraft and their operating capabilities, air transportation system architectures, and airspace architectures and procedural concepts. The topology proposed considers air transportation as a system of networks, within which strategies for scalability of the topology may be enabled by technologies and policies. In particular, the effects of scalable ICNS concepts are evaluated within this proposed topology. Alternative business models are appearing on the scene as the old centralized hub-and-spoke model reaches the limits of its scalability. These models include growth of point-to-point scheduled air transportation service (e.g., the RJ phenomenon and the 'Southwest Effect'). Another is a new business model for on-demand, widely distributed, air mobility in jet taxi services. The new businesses forming around this vision are targeting personal air mobility to virtually any of the thousands of origins and destinations throughout suburban, rural, and remote communities and regions. Such advancement in air mobility has many implications for requirements for airports, airspace, and consumers. These new paradigms could support scalable alternatives for the expansion of future air mobility to more consumers in more places.

Holmes, Bruce J.; Scott, John M.

2004-01-01

209

Topological aspects of fermions on hyperdiamond  

SciTech Connect

Motivated by recent results on the index of the Dirac operator D={gamma}{sup {mu}}D{sub {mu}} of QCD on lattice and also by results on topological features of electrons and holes of two-dimensional graphene, we compute in this paper the index of D for fermions living on a family of even-dimensional lattices denoted as L{sub 2N} and describing the 2N-dimensional generalization of the graphene honeycomb. The calculation of this topological index is done by using the direct method based on solving explicitly the gauged Dirac equation and also by using specific properties of the lattices L{sub 2N}, which are shown to be intimately linked with the weight lattices of SU(2N+ 1). The index associated with the two leading N= 1 and N= 2 elements of this family describe precisely the chiral anomalies of graphene and QCD{sub 4}. Comments on the method using the spectral flow approach as well as the computation of the topological charges on 2-cycles of 2N-dimensional compact supercell in L{sub 2N} and applications to QCD{sub 4} are also given.

Saidi, E. H. [Hassan II Academy of Science and Technology, Avenue Mohammed VI, KM 4, Souissi, Rabat (Morocco); Lab Of High Energy Physics, Modeling and Simulations, Faculty of Science, University Mohammed V-Agdal, Rabat (Morocco); Fassi-Fehri, O.; Bousmina, M. [Hassan II Academy of Science and Technology, Avenue Mohammed VI, KM 4, Souissi, Rabat (Morocco)

2012-07-15

210

Communication: An approximation to Bader's topological atom  

NASA Astrophysics Data System (ADS)

A new, more flexible definition of fuzzy Voronoi cells is proposed as a computationally efficient alternative to Bader's Quantum Theory of Atoms in Molecules (QTAIM) partitioning of the physical space for large-scale routine calculations. The new fuzzy scheme provides atomic charges, delocalization indices, and molecular energy components very close to those obtained using QTAIM. The method is flexible enough to either ignore the presence of spurious non-nuclear attractors or to readily incorporate them by introducing additional fuzzy Voronoi cells.

Salvador, Pedro; Ramos-Cordoba, Eloy

2013-08-01

211

Holographic RG flows from Quasi-Topological Gravity  

NASA Astrophysics Data System (ADS)

We investigate the holographic Renormalization Group (RG) flows and the critical phenomena that take place in the QFT's dual to the d-dimensional cubic Quasi-Topological Gravity coupled to scalar matter. The knowledge of the corresponding flat Domain Walls (DW's) solutions allows us to derive the explicit form of the QFT's ?-functions, as well as of the trace anomalies a(l) and c(l), in terms of the matter superpotential. As a consequence we are able to determine the complete set of CFT data characterizing the universality classes of the UV and IR critical points and to follow the particular RG evolution of this data. We further analyse the dependence of the critical properties of such dual QFT's on the values of the Lovelock couplings and on the shape of the superpotential. For odd values of d, the explicit form of the "a and c-central charges" as functions of the running coupling constant, enable us to establish the conditions under which the a&c-Theorems for their decreasing are valid. The restrictions imposed on the massless holographic RG flows by the requirements of the positivity of the energy fluxes are derived. The particular case of quartic Higgs-like superpotential is studied in detail. It provides an example of unitary dual QFT's having few c?a-critical points representing second or infinite order phase transitions. Depending on the range of the values of the coupling constant they exhibit massive and massless phases, described by a chain of distinct DW's solutions sharing common boundaries. Remember that the definition of the new maximal "h-scale" in the case of negative h<0 is given by fh=L2/(.

Camara da Silva, U.; Sotkov, G. M.

2013-09-01

212

Topology Optimized Synthesis of Planar Kinematic Rigid Body Mechanisms  

Microsoft Academic Search

Regarding the essential engineering design tasks in the systematic development process of rigid body mechanisms, three major\\u000a stages can be distinguished (Erdman, 1995; Olson, 1985; Sandor, Erdman, 1984). The first step deals with the problem definition with respect to the functional and topological requirements. The desired\\u000a functionality and kinematic behavior as well as the complexity of the mechanism, the degree

Peter Eberhard; Timo Gaugele; Kai Sedlaczek

213

Topological catastrophe and isostructural phase transition in calcium.  

PubMed

We predict a quantum phase transition in fcc Ca under hydrostatic pressure. Using density functional theory, we find, at pressures below 80 kbar, the topology of the electron charge density is characterized by nearest neighbor atoms connected through bifurcated bond paths and deep minima in the octahedral holes. At pressures above 80 kbar, the atoms bond through non-nuclear maxima that form in the octahedral holes. This topological change in the charge density softens the C' elastic modulus of fcc Ca, while C44 remains unchanged. We propose an order parameter based on applying Morse theory to the charge density, and we show that near the critical point it follows the expected mean-field scaling law with reduced pressure. PMID:21231679

Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P

2010-12-31

214

Continuous-variable topological codes  

NASA Astrophysics Data System (ADS)

Topological code is a stabilizer quantum error correcting code whose generators are local but logical operators are topologically nontrivial and nonlocal. It offers interesting features such as the homological deformations of string operators and anyonic excitations on it. Topological codes are also closely related to the “topological order,” which has been an important concept in condensed-matter physics. In this paper, we consider continuous-variable versions of topological codes, including the toric code by Kitaev [A. Y. Kitaev, Ann. Phys.APNYA60003-491610.1016/S0003-4916(02)00018-0 303, 2 (2003)] with a single type of stabilizer on the checkerboard lattice, and the color code by Bombin and Martin-Delgado [H. Bombin and M. A. Martin-Delgado, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.97.180501 97, 180501 (2006)]. We show that it is possible to consider continuous-variable analog of these topological codes.

Morimae, Tomoyuki

2013-10-01

215

Noncommuting momenta of topological solitons.  

PubMed

We show that momentum operators of a topological soliton may not commute among themselves when the soliton is associated with the second cohomology H^{2} of the target space. The commutation relation is proportional to the winding number, taking a constant value within each topological sector. The noncommutativity makes it impossible to specify the momentum of a topological soliton, and induces a Magnus force. PMID:24877932

Watanabe, Haruki; Murayama, Hitoshi

2014-05-16

216

Topological Features Of Inviscid Flows  

Microsoft Academic Search

\\u000a The Euler equations for an incompressible inviscid fluid in dimension three possess a wealth of topological phenomena woven\\u000a into the dynamical and geometric properties of the fluid. Focusing first on steady Euler fields, we outline known results,\\u000a giving special attention to the Beltrami fields and the contemporary topological techniques required to elucidate their dynamical\\u000a features. We also propose a topological

Robert Ghrist; Rafal Komendarczyk

217

Topological defects in nematic droplets of hard spherocylinders  

NASA Astrophysics Data System (ADS)

Using computer simulations we investigate the microscopic structure of the singular director field within a nematic droplet. As a theoretical model for nematic liquid crystals we take hard spherocylinders. To induce an overall topological charge, the particles are either confined to a two-dimensional circular cavity with homeotropic boundary or to the surface of a three-dimensional sphere. Both systems exhibit half-integer topological point defects. The isotropic defect core has a radius of the order of one particle length and is surrounded by free-standing density oscillations. The effective interaction between two defects is investigated. All results should be experimentally observable in thin sheets of colloidal liquid crystals.

Dzubiella, Joachim; Schmidt, Matthias; Löwen, Hartmut

2000-10-01

218

Spectroscopic topological Stokes polarimeter  

NASA Astrophysics Data System (ADS)

In this paper, we have developed a spectroscopic topological Stokes polarimeter using an axisymmetrical quarter wave plate (AQWP). The AQWP is fabricated by the alignment of segments of quarter wave films. The azimuthal angles of the polarization element are changed in according with its own segment. This element works as same the technique as the rotating quarter wave plate. In the experiment, we evaluated birefringence distribution of the AQWP. By changing a position of polarized singularity point in the beam spot, we can measure states of polarization. We demonstrate that the change of polarization states is corresponded with the change of the polarized singularity points.

Wakayama, Toshitaka; Otani, Yukitoshi; Yoshizawa, Toru

2010-11-01

219

Topology of Light's Darkness  

NASA Astrophysics Data System (ADS)

We numerically study the topology of optical vortex lines (nodal lines) in volumes of optical speckle, modeled as superpositions of random plane waves. It is known that the vortex lines may be infinitely long, or form closed loops. Loops are occasionally threaded by infinite lines, or linked with other loops. We find the probability of a loop not being threaded decays exponentially with the length of the loop. This behavior has a similarity to scaling laws studied in superfluid turbulence, and polymers modeled as random walks.

O'Holleran, Kevin; Dennis, Mark R.; Padgett, Miles J.

2009-04-01

220

Topological Structure of the Magnetic Solar Corona  

NASA Astrophysics Data System (ADS)

The solar corona is a highly complex and active plasma environment, containing many exotic phenomena such as solar flares, coronal mass ejections, prominences, coronal loops, and bright points. The fundamental element giving coherence to all this apparent diversity is the strong coronal magnetic field, the dominant force shaping the plasma there. In this thesis, I model the 3D magnetic fields of various coronal features using the techniques of magnetic charge topology (MCT) in a potential field. Often the real coronal field has departures from its potential state, but these are so small that the potential field method is accurate enough to pick out the essential information about the structure and evolution of the magnetic field. First I perform a topological analysis of the magnetic breakout model for an eruptive solar flare. Breakout is represented by a topological bifurcation that allows initially enclosed flux from the newly emerging region in my MCT model of a delta sunspot to reconnect out to large distances. I produce bifurcation diagrams showing how this behaviour can be caused by changing the strength or position of the emerging flux source, or the force-free parameter ?. I also apply MCT techniques to observational data of a coronal bright point, and compare the results to 3D numerical MHD simulations of the effects of rotating the sources that underlie the bright point. The separatrix surfaces that surround each rotating source are found to correspond to locations of high parallel electric field in the simulations, which is a signature of magnetic reconnection. The large-scale topological structure of the magnetic field is robust to changes in the method of deriving point magnetic sources from the magnetogram. Next, I use a Green's function expression for the magnetic field to relax the standard topological assumption of a flat photosphere and extend the concept of MCT into a spherical geometry, enabling it to be applied to the entire global coronal magnetic field. I perform a comprehensive study of quadrupolar topologies in this new geometry, producing several detailed bifurcation diagrams. These results are compared to the equivalent study for a flat photosphere. A new topological state is found on the sphere which has no flat photosphere analogue; it is named the dual intersecting state because of its twin separators joining a pair of magnetic null points. The new spherical techniques are then applied to develop a simple six-source topological model of global magnetic field reversal during the solar cycle. The evolution of the large-scale global magnetic field is modelled through one complete eleven-year cycle, beginning at solar minimum. Several distinct topological stages are exhibited: active region flux connecting across the equator to produce transequatorial loops; the dominance of first the leading and then the following polarities of the active regions; the magnetic isolation of the poles; the reversal of the polar field; the new polar field connecting back to the active regions; the polar flux regaining its dominance; and the disappearance of the transequatorial loops.

Maclean, R. C.

2007-12-01

221

Topology (Program Description)  

NSF Publications Database

Standard eligibility criteria as defined in the Grant Proposal Guide apply to this program. This program adheres to the budget definition and preparation instructions described in the Grant Proposal Guide and has no additional requirements or limitations. Award Conditions: Standard NSF award conditions apply.

222

Topology of viral evolution  

PubMed Central

The tree structure is currently the accepted paradigm to represent evolutionary relationships between organisms, species or other taxa. However, horizontal, or reticulate, genomic exchanges are pervasive in nature and confound characterization of phylogenetic trees. Drawing from algebraic topology, we present a unique evolutionary framework that comprehensively captures both clonal and reticulate evolution. We show that whereas clonal evolution can be summarized as a tree, reticulate evolution exhibits nontrivial topology of dimension greater than zero. Our method effectively characterizes clonal evolution, reassortment, and recombination in RNA viruses. Beyond detecting reticulate evolution, we succinctly recapitulate the history of complex genetic exchanges involving more than two parental strains, such as the triple reassortment of H7N9 avian influenza and the formation of circulating HIV-1 recombinants. In addition, we identify recurrent, large-scale patterns of reticulate evolution, including frequent PB2-PB1-PA-NP cosegregation during avian influenza reassortment. Finally, we bound the rate of reticulate events (i.e., 20 reassortments per year in avian influenza). Our method provides an evolutionary perspective that not only captures reticulate events precluding phylogeny, but also indicates the evolutionary scales where phylogenetic inference could be accurate.

Chan, Joseph Minhow; Carlsson, Gunnar; Rabadan, Raul

2013-01-01

223

Topological Anderson insulator phenomena  

NASA Astrophysics Data System (ADS)

We study the nature of the disorder-induced quantized conductance, i.e., the phenomena of topological Anderson insulator (TAI). The disorder effect in several different systems where the anomalous Hall effect exists is numerically studied using the tight-binding Hamiltonian. It is found that the TAI phenomena can also exist in the modified Dirac model where the quadratic corrections k2?z are included and the electron-hole symmetry is kept. These phenomena also occur in the graphene system with the next-nearest-neighbor coupling and the staggered sublattice potential. For the graphene sheet with Rashba spin-orbit interaction as well as an exchange field, a precursor of TAI is observed. A comparison between the localization length of the two-dimensional ribbon and two-dimensional cylinder structures clearly reveals the topological nature of these phenomena. Furthermore, analysis on the local current density in anomalous quantum Hall systems where the TAI phenomena may or may not arise reveals the nature of TAI phenomena. In the presence of small disorders, the conductance is not quantized and the bulk and edge states coexist in the system. As disorder strength increases, the bulk state is quickly destroyed, while the robust edge state may survive. When the edge state is robust enough to sustain the strong disorder that completely kills the bulk state, TAI phenomena arise.

Xing, Yanxia; Zhang, Lei; Wang, Jian

2011-07-01

224

A natural topological insulator.  

PubMed

The earth's crust and outer space are rich sources of technologically relevant materials which have found application in a wide range of fields. Well-established examples are diamond, one of the hardest known materials, or graphite as a suitable precursor of graphene. The ongoing drive to discover novel materials useful for (opto)electronic applications has recently drawn strong attention to topological insulators. Here, we report that Kawazulite, a mineral with the approximate composition Bi2(Te,Se)2(Se,S), represents a naturally occurring topological insulator whose electronic properties compete well with those of its synthetic counterparts. Kawazulite flakes with a thickness of a few tens of nanometers were prepared by mechanical exfoliation. They exhibit a low intrinsic bulk doping level and correspondingly a sizable mobility of surface state carriers of more than 1000 cm(2)/(V s) at low temperature. Based on these findings, further minerals which due to their minimized defect densities display even better electronic characteristics may be identified in the future. PMID:23438015

Gehring, P; Benia, H M; Weng, Y; Dinnebier, R; Ast, C R; Burghard, M; Kern, K

2013-03-13

225

Formal Definitions in Mathematics  

ERIC Educational Resources Information Center

The definition is an important language form in the register of mathematics. Students need to understand the structure of a definition so that they can make sense of the definitions they encounter and so that they can construct their own definitions as part of organising their thoughts about the concepts they have explored. This article suggests…

Shield, Mal

2004-01-01

226

FLIC-overlap fermions and topology  

NASA Astrophysics Data System (ADS)

APE smearing the links in the irrelevant operators of clover fermions (Fat-Link Irrelevant Clover (FLIC) fermions) provides significant improvement in the condition number of the Hermitian-Dirac operator and gives rise to a factor of two savings in computing the overlap operator. This report investigates the effects of using a highly-improved definition of the lattice field-strength tensor F ?? in the fermion action, made possible through the use of APE-smeared fat links in the construction of the irrelevant operators. Spurious double-zero crossings in the spectral flow of the Hermitian-Wilson Dirac operator associated with lattice artifacts at the scale of the lattice spacing are removed with FLIC fermions composed with anO (? 4)-improved lattice field strength tensor. Hence, FLIC-Overlap fermions provide an additional benefit to the overlap formalism: a correct realization of topology in the fermion sector on the lattice.

Kamleh, W.; Kusterer, D. J.; Leinweber, D. B.; Williams, A. G.

2003-05-01

227

Detecting Communities Based on Network Topology  

PubMed Central

Network methods have had profound influence in many domains and disciplines in the past decade. Community structure is a very important property of complex networks, but the accurate definition of a community remains an open problem. Here we defined community based on three properties, and then propose a simple and novel framework to detect communities based on network topology. We analyzed 16 different types of networks, and compared our partitions with Infomap, LPA, Fastgreedy and Walktrap, which are popular algorithms for community detection. Most of the partitions generated using our approach compare favorably to those generated by these other algorithms. Furthermore, we define overlapping nodes that combine community structure with shortest paths. We also analyzed the E. Coli. transcriptional regulatory network in detail, and identified modules with strong functional coherence.

Liu, Wei; Pellegrini, Matteo; Wang, Xiaofan

2014-01-01

228

Efficient lookup on unstructured topologies  

Microsoft Academic Search

We present LMS, a protocol for efficient lookup on unstructured networks. Our protocol uses a virtual namespace without imposing specific topologies. It is more efficient than existing lookup protocols for unstructured networks, and thus is an attractive alternative for applications in which the topology cannot be structured as a Distributed Hash Table (DHT).We present analytic bounds for the worst-case performance

Ruggero Morselli; Bobby Bhattacharjee; Aravind Srinivasan; Michael A. Marsh

2005-01-01

229

Topological Insulators in Three Dimensions  

Microsoft Academic Search

We study three-dimensional generalizations of the quantum spin Hall (QSH) effect. Unlike two dimensions, where a single Z2 topological invariant governs the effect, in three dimensions there are 4 invariants distinguishing 16 phases with two general classes: weak (WTI) and strong (STI) topological insulators. The WTI are like layered 2D QSH states, but are destroyed by disorder. The STI are

Liang Fu; C. L. Kane; E. J. Mele

2007-01-01

230

Does topology control reduce interference?  

Microsoft Academic Search

Topology control in ad-hoc networks tries to lower node energy consumption by reducing transmission power and by confining interference, collisions and consequently retransmissions. Commonly low interference is claimed to be a consequence to sparseness of the resulting topology. In this paper we disprove this implication. In contrast to most of the related work claiming to solve the interference issue by

Martin Burkhart; Pascal von Rickenbach; Roger Wattenhofer; Aaron Zollinger

2004-01-01

231

Topology of Chaotic Mixing Patterns  

Microsoft Academic Search

A stirring device consisting of a periodic motion of rods induces a mapping of the fluid domain to itself, which can be regarded as a continuous mapping of a punctured surface. Having the rods undergo a topologically-complex motion guarantees a minimal amount of stretching of material lines, which is important for chaotic mixing. We use topological considerations to describe the

Jean-Luc Thiffeault; Matthew D. Finn; Emmanuelle Gouillart; Toby Hall

2008-01-01

232

Topological Mirrors and Quantum Rings  

Microsoft Academic Search

Aspects of duality and mirror symmetry in string theory are discussed. We emphasize, through examples, the importance of loop spaces for a deeper understanding of the geometrical origin of dualities in string theory. Moreover we show that mirror symmetry can be reformulated in very simple terms as the statement of equivalence of two classes of topological theories: Topological sigma models

Cumrun Vafa

1991-01-01

233

Tunnel reinforcement via topology optimization  

Microsoft Academic Search

Anchoring is a fundamental method for supporting tunnels. It reinforces the original rock mass and reduces the deformation along the tunnel surface. The topological complexity of its layouts renders a design methodology difficult. A numerical approach to reinforce the host ground becomes desirable. The present paper proposes a topology optimization method based on a two-phase cell model and finite-element discretization

Luzhong Yin; Wei Yang; Tianfu Guo

2000-01-01

234

Propagating topological singularities: the photon  

Microsoft Academic Search

At its foundations, Maxwell's theory of Electrodynamics, like thermodynamics, is a topological theory independent from geometric constraints of metric, scales, or gauge symmetries. One of the most interesting features of Electromagnetism is its relationship to the transport of momentum and energy by means of photons. This article utilizes a topological perspective to discuss the classical features and quantum concepts associated

R. M. Kiehn

2005-01-01

235

Tunable geometric phase of Dirac fermions in a topological junction  

NASA Astrophysics Data System (ADS)

We predict a tunable and nonadiabatic Berry phase effect of Dirac fermions, which is an electronic analog of the Pancharatnam phase of polarized light. The Berry phase occurs as a scattering phase shift in a single scattering event of transmission or reflection of Dirac fermions at a junction with a spatially nonuniform mass gap, unveiling the topological aspects of scattering of chiral Dirac fermions. This geometric phase plays different roles in solids as compared with the Pancharatnam phase in optics. It provides a unique approach of detecting the Chern number of the insulator side in a metal-insulator junction of Dirac fermions, implying a different type of bulk-edge correspondence at the boundary between a metal and an insulator. This phase also modifies the quantization rule of Dirac fermions, suggesting geometric-phase devices with nontrivial charge and spin transport such as a topological waveguide and a topological transistor.

Choi, Sang-Jun; Park, Sunghun; Sim, H.-S.

2013-04-01

236

Topological defects in flat geometry: the role of density inhomogeneity.  

PubMed

Topological defects are found in particles confined to planar disks interacting via the 1/r Coulomb potential. The total interior topological charge is found to monotonically converge to a negative value as the energy decreases during the relaxation process regardless of initial configurations; it is more negative in a larger cluster. The comparison with a uniform hyperbolic tessellation reveals an underlying hyperbolic structure in a low-energy configuration where the particle density increases from the center of the disk to its boundary. An elliptic structure is identified in an opposite particle distribution where the particle density decreases from the center to the edge of the disk. The novel mechanism of density inhomogeneity driven topological defects as well as the underlying geometric structure may shed light in understanding a wide variety of relevant systems. PMID:24074106

Yao, Zhenwei; Olvera de la Cruz, Monica

2013-09-13

237

Concept Model on Topological Learning  

NASA Astrophysics Data System (ADS)

We discuss a new model for concept based on topological learning, where the learning process on the neural network is represented by mathematical topology. The topological learning of neural networks is summarized by a quotient of input space and the hierarchical step induces a tree where each node corresponds to a quotient. In general, the concept acquisition is a difficult problem, but the emotion for a subject is represented by providing the questions to a person. Therefore, a kind of concept is captured by such data and the answer sheet can be mapped into a topology consisting of trees. In this paper, we will discuss a way of mapping the emotional concept to a topological learning model.

Ae, Tadashi; Kioi, Kazumasa

2010-11-01

238

New Precharge and Submodule Capacitor Voltage Balancing Topologies of Modular Multilevel Converter for VSC-HVDC Application  

Microsoft Academic Search

This paper presents two novel topologies on precharge and submodule capacitor voltage balancing schemes of Modular Multilevel Converter (MMC) for VSC-HVDC application respectively. Firstly, A traditional precharge process of MMC was modeled in PSCAD\\/EMTDC, its drawbacks were summarized and a novel topology was proposed based on submodules charged synchronously; Secondly, we analyzed the principles of a traditional submodule capacitor voltage

Jianzhong Xu; Chengyong Zhao; Baoshun Zhang; Li Lu

2011-01-01

239

Dense topological spaces and dense continuity  

NASA Astrophysics Data System (ADS)

There are several attempts to generalize (or "widen") the concept of topological space. This paper uses equivalence relations to generalize the concept of topological space via the concept of equivalence relations. By the generalization, we can introduce from particular topology on a nonempty set X many new topologies, we call anyone of these new topologies a dense topology. In addition, we formulate some simple properties of dense topologies and study suitable generalizations of the concepts of limit points, closeness and continuity, as well as Jackson, Nörlund and Hahn dense topologies.

Aldwoah, Khaled A.

2013-09-01

240

Transportation Network Topologies  

NASA Technical Reports Server (NTRS)

The existing U.S. hub-and-spoke air transportation system is reaching saturation. Major aspects of the current system, such as capacity, safety, mobility, customer satisfaction, security, communications, and ecological effects, require improvements. The changing dynamics - increased presence of general aviation, unmanned autonomous vehicles, military aircraft in civil airspace as part of homeland defense - contributes to growing complexity of airspace. The system has proven remarkably resistant to change. NASA Langley Research Center and the National Institute of Aerospace conducted a workshop on Transportation Network Topologies on 9-10 December 2003 in Williamsburg, Virginia. The workshop aimed to examine the feasibility of traditional methods for complex system analysis and design as well as potential novel alternatives in application to transportation systems, identify state-of-the-art models and methods, conduct gap analysis, and thus to lay a foundation for establishing a focused research program in complex systems applied to air transportation.

Alexandrov, Natalia (Editor)

2004-01-01

241

Topological R4 inflation  

NASA Astrophysics Data System (ADS)

We consider the possibility that higher-curvature corrections could drive inflation after the compactification to four dimensions. Assuming that the low-energy limit of the fundamental theory is eleven-dimensional supergravity to the lowest order, including curvature corrections and taking the descent from eleven dimensions to four via an intermediate five-dimensional theory, as favored by recent considerations of unification at some scale around ~1016 GeV, we may obtain a simple model of inflation in four dimensions. The effective degrees of freedom are two scalar fields and the metric. The scalars arise as the large five-dimensional modulus and the self-interacting conformal mode of the metric. The effective potential has a local maximum in addition to the more usual minimum. However, the potential is quite flat at the top, and admits topological inflation. We show that the model can resolve cosmological problems and provide a mechanism for structure formation with very little fine tuning.

Ellis, John; Kaloper, Nemanja; Olive, Keith A.; Yokoyama, Jun'ichi

1999-05-01

242

Analytic estimates and topological properties of the weak stability boundary  

NASA Astrophysics Data System (ADS)

The weak stability boundary (WSB) is the transition region of the phase space where the change from gravitational escape to ballistic capture occurs. Studies on this complicated region of chaotic motion aim to investigate its unique, fuel saving properties to enlarge the frontiers of low energy transfers. This "fuzzy stability" region is characterized by highly sensitive motion, and any analysis of it has been carried out almost exclusively using numerical methods. On the contrary this paper presents, for the planar circular restricted 3-body problem, (1) an analytic definition of the WSB which is coherent with the known algorithmic definitions; (2) a precise description of the topology of the WSB; (3) analytic estimates on the "stable region" (nearby the smaller primary) whose boundary is, by definition, the WSB.

Ceccaroni, Marta; Biggs, James; Biasco, Luca

2012-10-01

243

Surface states of the Topological Insulator Bi1-x Sbx  

NASA Astrophysics Data System (ADS)

The alloy Bi1-xSbx is a narrow gap semiconductor for .07topological insulator (STI). The STI is distinguished from ordinary insulators by a Z2 topological invariant characterizing the bulk and by the presence of topological protected surface states, whose Fermi arc encloses an odd number of Dirac point. Here we study the surface states of the 111 face of Bi1-xSbx using a semi infinite tight binding model. This calculation demonstrates explicitly the topological character of the surface states. In addition, we examine other robust, model independent features of the surface states which arise due to (1) charge neutrality at the surface, (2) the presence in the bulk bandstructure of a 3 dimensional Dirac point with a small mass and (3) the presence of mirror symmetry, which leads to an additional topological characterization of the band structure in terms of a mirror Chern integer. Implications for photoemission experiments will be discussed.

Teo, Jeffrey; Fu, Liang; Kane, Charles

2008-03-01

244

Flat bands in topological media  

NASA Astrophysics Data System (ADS)

Topological media are systems whose properties are protected by topology and thus are robust to deformations of the system. In topological insulators and superconductors the bulk-surface and bulk-vortex correspondence gives rise to the gapless Weyl, Dirac or Majorana fermions on the surface of the system and inside vortex cores. Here we show that in gapless topological media, the bulk-surface and bulk-vortex correspondence is more effective: it produces topologically protected gapless fermions without dispersion—the fiat band. Fermion zero modes forming the flat band are localized on the surface of topological media with protected nodal lines [A. P. Schnyder and S. Ryu, Phys. Rev. B 84, 060504(R) (2011); T. T. Heikkil G. E. Volovik, JETP Lett. 93, 59 (2011)] and in the vortex core in systems with topologically protected Fermi points (Weyl points) [G. E. Volovik, JETP Lett. 93, 66 (2011)]. Flat band has an extremely singular density of states, and we show that this property may give rise in particular to surface superconductivity which could exist even at room temperature.

Heikkilä, T. T.; Kopnin, N. B.; Volovik, G. E.

2011-10-01

245

Z2 anomaly and boundaries of topological insulators  

NASA Astrophysics Data System (ADS)

We study the edge and surface theories of topological insulators from the perspective of anomalies and identify a Z2 anomaly associated with charge conservation. The anomaly is manifested through a two-point correlation function involving creation and annihilation operators on two decoupled boundaries. Although charge conservation on each boundary requires this quantity to vanish, we find that it diverges. A corollary result is that under an insertion of a flux quantum, the ground state evolves to an exactly orthogonal state independent of the rate at which the flux is inserted. The anomaly persists in the presence of disorder and imposes sharp restrictions on possible low-energy theories. Being formulated in a many-body, field-theoretical language, the anomaly allows one to test the robustness of topological insulators to interactions in a concise way.

Ringel, Zohar; Stern, Ady

2013-09-01

246

Topological Insulators in Three Dimensions  

NASA Astrophysics Data System (ADS)

We study three-dimensional generalizations of the quantum spin Hall (QSH) effect. Unlike two dimensions, where a single Z2 topological invariant governs the effect, in three dimensions there are 4 invariants distinguishing 16 phases with two general classes: weak (WTI) and strong (STI) topological insulators. The WTI are like layered 2D QSH states, but are destroyed by disorder. The STI are robust and lead to novel “topological metal” surface states. We introduce a tight binding model which realizes the WTI and STI phases, and we discuss its relevance to real materials, including bismuth.

Fu, Liang; Kane, C. L.; Mele, E. J.

2007-03-01

247

Topological insulators in three dimensions.  

PubMed

We study three-dimensional generalizations of the quantum spin Hall (QSH) effect. Unlike two dimensions, where a single Z2 topological invariant governs the effect, in three dimensions there are 4 invariants distinguishing 16 phases with two general classes: weak (WTI) and strong (STI) topological insulators. The WTI are like layered 2D QSH states, but are destroyed by disorder. The STI are robust and lead to novel "topological metal" surface states. We introduce a tight binding model which realizes the WTI and STI phases, and we discuss its relevance to real materials, including bismuth. PMID:17358555

Fu, Liang; Kane, C L; Mele, E J

2007-03-01

248

Semilinear (topological) spaces and applications  

NASA Technical Reports Server (NTRS)

Semivector spaces are defined and some of their algebraic aspects are developed including some structure theory. These spaces are then topologized to obtain semilinear topological spaces for which a hierarchy of local convexity axioms is identified. A number of fixed point and minmax theorems for spaces with various local convexity properties are established. The spaces of concern arise naturally as various hyperspaces of linear and semilinear (topological) spaces. It is indicated briefly how all this can be applied in socio-economic analysis and optimization.

Prakash, P.; Sertel, M. R.

1971-01-01

249

Topology of chaotic mixing patterns  

NASA Astrophysics Data System (ADS)

A stirring device consisting of a periodic motion of rods induces a mapping of the fluid domain to itself, which can be regarded as a homeomorphism of a punctured surface. Having the rods undergo a topologically complex motion guarantees at least a minimal amount of stretching of material lines, which is important for chaotic mixing. We use topological considerations to describe the nature of the injection of unmixed material into a central mixing region, which takes place at injection cusps. A topological index formula allow us to predict the possible types of unstable foliations that can arise for a fixed number of rods.

Thiffeault, Jean-Luc; Finn, Matthew D.; Gouillart, Emmanuelle; Hall, Toby

2008-09-01

250

Focus on topological quantum computation  

NASA Astrophysics Data System (ADS)

Topological quantum computation started as a niche area of research aimed at employing particles with exotic statistics, called anyons, for performing quantum computation. Soon it evolved to include a wide variety of disciplines. Advances in the understanding of anyon properties inspired new quantum algorithms and helped in the characterization of topological phases of matter and their experimental realization. The conceptual appeal of topological systems as well as their promise for building fault-tolerant quantum technologies fuelled the fascination in this field. This ‘focus on’ collection brings together several of the latest developments in the field and facilitates the synergy between different approaches.

Pachos, Jiannis K.; Simon, Steven H.

2014-06-01

251

Fractional topological insulators of Cooper pairs induced by the proximity effect.  

PubMed

Certain insulating materials with strong spin-orbit interaction can conduct currents along their edges or surfaces owing to the nontrivial topological properties of their electronic band structure. This phenomenon is somewhat similar to the integer quantum Hall effect of electrons in strong magnetic fields. Topological insulators analogous to the fractional quantum Hall effect are also possible, but have not yet been observed in any material. Here we show that a quantum well made from a topological band insulator such as Bi2Se3 or Bi2Te3, placed in contact with a superconductor, can be used to realize a two-dimensional topological state with macroscopic many-body quantum entanglement whose excitations carry fractional amounts of an electron's charge and spin. This fractional topological insulator is a "pseudogap" state of induced spinful p-wave Cooper pairs, a new strongly correlated quantum phase with possible applications to spintronic devices and quantum computing. PMID:23679757

Nikoli?, Predrag; Duric, Tanja; Tešanovi?, Zlatko

2013-04-26

252

Radiation-induced coordination topological defects in chalcogenide glasses  

NASA Astrophysics Data System (ADS)

The radiation-induced (gamma-quanta of Co-60 source) coordination topological defect formation in chalcogenide glasses of quasi-binary AS(2)S(3)-GeS2 system is studied using experimental techniques of IR Fourier spectroscopy and positron annihilation lifetime measurements. The new model of open-volume microvoids connected with negatively charged under-coordinated defects is developed at the basis of the obtained results.

Shpotyuk, O. I.; Filipecki, J.; Kozdras, A.; Balitska, V.

2003-01-01

253

Black hole mass and angular momentum in topologically massive gravity  

NASA Astrophysics Data System (ADS)

We extend the Abbott Deser Tekin approach to the computation of the Killing charge for a solution of topologically massive gravity (TMG) linearized around an arbitrary background. This is then applied to evaluate the mass and angular momentum of black hole solutions of TMG with non-constant curvature asymptotics. The resulting values, together with the appropriate black hole entropy, fit nicely into the first law of black hole thermodynamics.

Bouchareb, Adel; Clément, Gérard

2007-11-01

254

42 CFR 405.509 - Determining the inflation-indexed charge.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Determining the inflation-indexed charge. 405.509... § 405.509 Determining the inflation-indexed charge. (a) Definition. For purposes of this section, inflation-indexed charge means...

2013-10-01

255

Topological properties of spaces ordered by preferences  

Microsoft Academic Search

In this paper, we analyze the main topological properties of a relevant class of topologies associated with spaces ordered by preferences (asymmetric, negatively transi- tive binary relations). This class consists of certain continuous topologies which include the order topology. The concept of saturated identification is introduced in order to provide a natural proof of the fact that all these spaces

J. C. R. Alcantud

1999-01-01

256

Topological Perspective on the Hybrid Proof Rules  

Microsoft Academic Search

We consider the non-orthodox proof rules of hybrid logic from the viewpoint of topological semantics. Topological semantics is more general than Kripke semantics. We show that the hybrid proof rule BG is topologically not sound. Indeed, among all topological spaces the BG rule characterizes those that can be represented as a Kripke frame (i.e., the Alexandro spaces). We also demonstrate

Balder Ten Cate; Tadeusz Litak

2007-01-01

257

Evolving Neural Networks through Augmenting Topologies  

Microsoft Academic Search

An important question in neuroevolution is how to gain an advantage from evolving neural network topologies along with weights. We present a method, NeuroEvolution of Augmenting Topologies (NEAT), which outperforms the best fixed-topology method on a challenging benchmark reinforcement learning task. We claim that the increased efficiency is due to (1) employing a principled method of crossover of different topologies,

Kenneth O. Stanley; Risto Miikkulainen

2002-01-01

258

Classification of engineered topological superconductors  

NASA Astrophysics Data System (ADS)

I perform a complete classification of two-dimensional, quasi-one-dimensional (1D) and 1D topological superconductors which originate from the suitable combination of inhomogeneous Rashba spin-orbit coupling, magnetism and superconductivity. My analysis reveals alternative types of topological superconducting platforms for which Majorana fermions are accessible. Specifically, I observe that for quasi-1D systems with Rashba spin-orbit coupling and time-reversal violating superconductivity, such as for instance due to a finite Josephson current flow, Majorana fermions can emerge even in the absence of magnetism. Furthermore, for the classification I also consider situations where additional ‘hidden’ symmetries emerge, with a significant impact on the topological properties of the system. The latter generally originate from a combination of space group and complex conjugation operations that separately do not leave the Hamiltonian invariant. Finally, I suggest alternative directions in topological quantum computing for systems with additional unitary symmetries.

Kotetes, Panagiotis

2013-10-01

259

Phonon-induced topological insulation  

NASA Astrophysics Data System (ADS)

We develop an approximate theory of phonon-induced topological insulation in Dirac materials. In the weak-coupling regime, long-wavelength phonons may favor topological phases in Dirac insulators with direct and narrow band gaps. This phenomenon originates from electron-phonon matrix elements, which change qualitatively under a band inversion. A similar mechanism applies to weak Coulomb interactions and spin-independent disorder; however, the influence of these on band topology is largely independent of temperature. As applications of the theory, we evaluate the temperature dependence of the critical thickness and the critical stoichiometric ratio for the topological transition in CdTe/HgTe quantum wells and in BiTl(S1-?Se?)2, respectively.

Saha, Kush; Garate, Ion

2014-05-01

260

Time-Varying Contour Topology  

PubMed Central

The contour tree has been used to compute the topology of isosurfaces, generate a minimal seed set for accelerated isosurface extraction, and provide a user interface to segment individual contour components in a scalar field. In this paper, we extend the benefits of the contour tree to time-varying data visualization. We define temporal correspondence of contour components and describe an algorithm to compute the correspondence information in time-dependent contour trees. A graph representing the topology changes of time-varying isosurfaces is constructed in real-time for any selected isovalue using the precomputed correspondence information. Quantitative properties, such as surface area and volume of contour components, are computed and labeled on the graph. This topology change graph helps users to detect significant topological and geometric changes in time-varying isosurfaces. The graph is also used as an interactive user interface to segment, track. and visualize the evolution of any selected contour components over time.

Sohn, Bong-Soo; Bajaj, Chandrajit

2009-01-01

261

Clinical definitions of melioidosis.  

PubMed

Clinical definitions of melioidosis and inhalation-acquired melioidosis (Burkholderia pseudomallei infection) are described together with the evidence used to develop these definitions. Such definitions support accurate public health reporting, preparedness planning for deliberate B. pseudomallei release, design of experimental models, and categorization of naturally acquired melioidosis. PMID:23468355

Cheng, Allen C; Currie, Bart J; Dance, David A B; Funnell, Simon G P; Limmathurotsakul, Direk; Simpson, Andrew J H; Peacock, Sharon J

2013-03-01

262

Topological discrete kinks  

NASA Astrophysics Data System (ADS)

A spatially discrete version of the general kink-bearing nonlinear Klein-Gordon model in (1 + 1) dimensions is constructed which preserves the topological lower bound on kink energy. It is proved that, provided the lattice spacing h is sufficiently small, there exist static kink solutions attaining this lower bound centred anywhere relative to the spatial lattice. Hence there is no Peierls-Nabarro (PN) barrier impeding the propagation of kinks in this discrete system. An upper bound on h is derived and given a physical interpretation in terms of the radiation of the system. The construction, which works most naturally when the nonlinear Klein-Gordon model has a squared polynomial interaction potential, is applied to a recently proposed continuum model of polymer twistons. Numerical simulations are presented which demonstrate that kink pinning is eliminated, and radiative kink deceleration is greatly reduced in comparison with the conventional discrete system. So even on a very coarse lattice, kinks behave much as they do in the continuum. It is argued, therefore, that the construction provides a natural means of numerically simulating kink dynamics in nonlinear Klein-Gordon models of this type. The construction is compared with the inverse method of Flach, Zolotaryuk and Kladko. Using the latter method, alternative spatial discretizations of the twiston and sine-Gordon models are obtained which are also free of the PN barrier.

Speight, J. M.

1999-09-01

263

Magnetic topology of blinkers  

NASA Astrophysics Data System (ADS)

Context: Co-spatial and co-temporal spectroscopic, imaging and magnetogram data enable us to better understand various solar transient phenomena. Here, we study brightening events in the transition region of the quiet Sun, also called “blinkers”. Aims: We aim to investigate the physical mechanism responsible for blinkers. Methods: An automated blinker identification procedure (BLIP) is used to identify blinker events in SoHO/CDS data. The 3D magnetic topology of the magnetic field in the blinker region is reconstructed based on SoHO/MDI magnetogram data. Results: During 3 h of SoHO/CDS observations on 2006 January 18, 66 blinkers were identified in the O v 629 Å emission line. Out of them, a group comprising of 16 events were modelled here. They were found to be associated with the emergence of magnetic flux which gave rise to the appearance of, and multiple magnetic reconnection events across, an upper atmosphere (coronal) magnetic null point, along with a loop structure as observed with TRACE. Conclusions: This blinker group results from the release of energy that was accumulated during flux emergence, although whether all blinkers follow the same formation scenario requires further investigation using additional multi-instrument/multi-mission studies. 2 movies are only available in electronic form at http://star.arm.ac.uk/preprints/ and http://www.aanda.org

Subramanian, S.; Madjarska, M. S.; Maclean, R. C.; Doyle, J. G.; Bewsher, D.

2008-09-01

264

Higher Hochschild Homology, Topological Chiral Homology and Factorization Algebras  

NASA Astrophysics Data System (ADS)

We study the higher Hochschild functor, factorization algebras and their relationship with topological chiral homology. To this end, we emphasize that the higher Hochschild complex is a functor sSet ? × CDGA ? where sSet and CDGA ? are the (?,1)-categories of simplicial sets and commutative differential graded algebras, and give an axiomatic characterization of this functor. From the axioms, we deduce several properties and computational tools for this functor. We study the relationship between the higher Hochschild functor and factorization algebras by showing that, in good cases, the Hochschild functor determines a constant commutative factorization algebra. Conversely, every constant commutative factorization algebra is naturally equivalent to a Hochschild chain factorization algebra. Similarly, we study the relationship between the above concepts and topological chiral homology. In particular, we show that on their common domains of definition, the higher Hochschild functor is naturally equivalent to topological chiral homology. Finally, we prove that topological chiral homology determines a locally constant factorization algebra and, further, that this functor induces an equivalence between locally constant factorization algebras on a manifold and (local system of) E n -algebras.

Ginot, Grégory; Tradler, Thomas; Zeinalian, Mahmoud

2014-03-01

265

Topology optimization of flow networks  

Microsoft Academic Search

The field of topology optimization is well developed for load carrying trusses, but so far not for other similar network problems. The present paper is a first study in the direction of topology optimization of flow networks. A linear network flow model based on Hagen–Poiseuille’s equation is used. Cross-section areas of pipes are design variables and the objective of the

Anders Klarbring; Joakim Petersson; Bo Torstenfelt; Matts Karlsson

2003-01-01

266

Refining the shifted topological vertex  

SciTech Connect

We study aspects of the refining and shifting properties of the 3d MacMahon function C{sub 3}(q) used in topological string theory and BKP hierarchy. We derive the explicit expressions of the shifted topological vertex S{sub {lambda}}{sub {mu}}{sub {nu}}(q) and its refined version T{sub {lambda}}{sub {mu}}{sub {nu}}(q,t). These vertices complete results in literature.

Drissi, L. B.; Jehjouh, H.; Saidi, E. H. [Faculte des Sciences, Laboratory/UFR-Physique des Hautes Energies, Rabat, 1014 (Morocco); Groupement National de Physique des Hautes Energies (GNPHE), Siege focal:FS, Rabat, 1014 (Morocco)

2009-01-15

267

Z2 Topological Anderson Insulator  

NASA Astrophysics Data System (ADS)

Effects of disorder on a two-dimensional Z2 topological insulator are studied numerically. We propose and study the phase diagram of a variant of Bernevig-Hughes-Zhang model, which takes account of the sz non-conserving spin-orbit coupling. Using scaling analyses, we determine the phase boundary and the critical exponent characterizing the transition between metallic and the topologically insulating phases.

Yamakage, Ai; Nomura, Kentaro; Imura, Ken-Ichiro; Kuramoto, Yoshio

2012-12-01

268

Topological mirror symmetry with fluxes  

Microsoft Academic Search

Motivated by SU(3) structure compactifications, we show explicitly how to construct half-flat topological mirrors to Calabi-Yau manifolds with NS fluxes. Units of flux are exchanged with torsion factors in the cohomology of the mirror; this is the topological complement of previous differential-geometric mirror rules. The construction modifies explicit SYZ fibrations for compact Calabi-Yaus. The results are of independent interest for

Alessandro Tomasiello

2005-01-01

269

Candidates for novel RNA topologies.  

PubMed

Because the functional repertiore of RNA molecules, like proteins, is closely linked to the diversity of their shapes, uncovering RNA's structural repertoire is vital for identifying novel RNAs, especially in genomic sequences. To help expand the limited number of known RNA families, we use graphical representation and clustering analysis of RNA secondary structures to predict novel RNA topologies and their abundance as a function of size. Representing the essential topological properties of RNA secondary structures as graphs enables enumeration, generation, and prediction of novel RNA motifs. We apply a probabilistic graph-growing method to construct the RNA structure space encompassing the topologies of existing and hypothetical RNAs and cluster all RNA topologies into two groups using topological descriptors and a standard clustering algorithm. Significantly, we find that nearly all existing RNAs fall into one group, which we refer to as "RNA-like"; we consider the other group "non-RNA-like". Our method predicts many candidates for novel RNA secondary topologies, some of which are remarkably similar to existing structures; interestingly, the centroid of the RNA-like group is the tmRNA fold, a pseudoknot having both tRNA-like and mRNA-like functions. Additionally, our approach allows estimation of the relative abundance of pseudoknot and other (e.g. tree) motifs using the "edge-cut" property of RNA graphs. This analysis suggests that pseudoknots dominate the RNA structure universe, representing more than 90% when the sequence length exceeds 120 nt; the predicted trend for <100 nt agrees with data for existing RNAs. Together with our predictions for novel "RNA-like" topologies, our analysis can help direct the design of functional RNAs and identification of novel RNA folds in genomes through an efficient topology-directed search, which grows much more slowly in complexity with RNA size compared to the traditional sequence-based search. PMID:15321711

Kim, Namhee; Shiffeldrim, Nahum; Gan, Hin Hark; Schlick, Tamar

2004-08-27

270

Interface-Induced Topological Insulator Transition in GaAs/Ge/GaAs Quantum Wells  

NASA Astrophysics Data System (ADS)

We demonstrate theoretically that interface engineering can drive germanium, one of the most commonly used semiconductors, into a topological insulating phase. Utilizing giant electric fields generated by charge accumulation at GaAs/Ge/GaAs opposite semiconductor interfaces and band folding, the new design can reduce the sizable gap in Ge and induce large spin-orbit interaction, which leads to a topological insulator transition. Our work provides a new method to realize topological insulators in commonly used semiconductors and suggests a promising approach to integrate it in well-developed semiconductor electronic devices.

Zhang, Dong; Lou, Wenkai; Miao, Maosheng; Zhang, Shou-cheng; Chang, Kai

2013-10-01

271

Role of sequence bias in the topology of the multidrug transporter EmrE.  

PubMed

EmrE is the prototype of small multidrug resistance transporters and has emerged as a model of membrane protein evolution. Analysis of the distances separating symmetry-related site-specific spin labels, correlation of topological sequence bias to C-terminal orientation, to membrane insertion efficiency, and to resistance to ethidium bromide collectively demonstrate that EmrE monomers adopt a parallel topology in the functional dimer. We propose a coupled insertion and assembly model for EmrE in which the favorable energetics of the parallel dimer interface override topological constraints arising from weak asymmetry in positive charge distribution. PMID:18616286

McHaourab, Hassane S; Mishra, Sanjay; Koteiche, Hanane A; Amadi, Sepan H

2008-08-01

272

Galois conjugates of topological phases  

NASA Astrophysics Data System (ADS)

Galois conjugation relates unitary conformal field theories and topological quantum field theories (TQFTs) to their nonunitary counterparts. Here we investigate Galois conjugates of quantum double models, such as the Levin-Wen model. While these Galois-conjugated Hamiltonians are typically non-Hermitian, we find that their ground-state wave functions still obey a generalized version of the usual code property (local operators do not act on the ground-state manifold) and hence enjoy a generalized topological protection. The key question addressed in this paper is whether such nonunitary topological phases can also appear as the ground states of Hermitian Hamiltonians. Specific attempts at constructing Hermitian Hamiltonians with these ground states lead to a loss of the code property and topological protection of the degenerate ground states. Beyond this, we rigorously prove that no local change of basis can transform the ground states of the Galois-conjugated doubled Fibonacci theory into the ground states of a topological model whose Hermitian Hamiltonian satisfies Lieb-Robinson bounds. These include all gapped local or quasilocal Hamiltonians. A similar statement holds for many other nonunitary TQFTs. One consequence is that these nonunitary TQFTs do not describe physical realizations of topological phases. In particular, this implies that the “Gaffnian” wave function can not be the ground state of a gapped fractional quantum Hall state.

Freedman, M. H.; Gukelberger, J.; Hastings, M. B.; Trebst, S.; Troyer, M.; Wang, Z.

2012-01-01

273

Communication: An approximation to Bader's topological atom.  

PubMed

A new, more flexible definition of fuzzy Voronoi cells is proposed as a computationally efficient alternative to Bader's Quantum Theory of Atoms in Molecules (QTAIM) partitioning of the physical space for large-scale routine calculations. The new fuzzy scheme provides atomic charges, delocalization indices, and molecular energy components very close to those obtained using QTAIM. The method is flexible enough to either ignore the presence of spurious non-nuclear attractors or to readily incorporate them by introducing additional fuzzy Voronoi cells. PMID:23968064

Salvador, Pedro; Ramos-Cordoba, Eloy

2013-08-21

274

The finite thermodynamic topology of photons  

NASA Astrophysics Data System (ADS)

All physical measurements are based on finite intervals of space and time. It follows that the appropriate topologies of measurement must be finite. However, there are only two types of finite power set topologies: T0 topologies and Not-T0 topologies. All singlet subsets of T0 (Kolmogorov) topologies are topologically distinguishable. Therefor it is natural that such topologies should be called Particle-like topologies. On the otherhand, some, if not all, singlet subsets of Not-T0 topologies are indistinguishable. Hence such topologies will be called Statistical, Wave-like, or Photon topologies. This article starts with a short review of the topological properties of Kolomogorov T0 particle topologies using processes that generate homotopic evolution of those exterior differential 1-forms chosed to describe thermodynamic states. Not-T0 topologies can use homotopic evolution of N-form densities to generate systems of partial differential equations that describe both reversible and irreversible dynamics. Numerous examples will be presented to demonstrate continuous topological evolution of complex exterior differential form densities in terms of Cartan's homotopic magic formula.

Kiehn, R. M.

2013-10-01

275

Topological Characterization of Fractional Quantum Hall Ground States from Microscopic Hamiltonians  

NASA Astrophysics Data System (ADS)

We show how to numerically calculate several quantities that characterize topological order starting from a microscopic fractional quantum Hall Hamiltonian. To find the set of degenerate ground states, we employ the infinite density matrix renormalization group method based on the matrix-product state representation of fractional quantum Hall states on an infinite cylinder. To study localized quasiparticles of a chosen topological charge, we use pairs of degenerate ground states as boundary conditions for the infinite density matrix renormalization group. We then show that the wave function obtained on the infinite cylinder geometry can be adapted to a torus of arbitrary modular parameter, which allows us to explicitly calculate the non-Abelian Berry connection associated with the modular T transformation. As a result, the quantum dimensions, topological spins, quasiparticle charges, chiral central charge, and Hall viscosity of the phase can be obtained using data contained entirely in the entanglement spectrum of an infinite cylinder.

Zaletel, Michael P.; Mong, Roger S. K.; Pollmann, Frank

2013-06-01

276

Spin-transfer torque generated by a topological insulator.  

PubMed

Magnetic devices are a leading contender for the implementation of memory and logic technologies that are non-volatile, that can scale to high density and high speed, and that do not wear out. However, widespread application of magnetic memory and logic devices will require the development of efficient mechanisms for reorienting their magnetization using the least possible current and power. There has been considerable recent progress in this effort; in particular, it has been discovered that spin-orbit interactions in heavy-metal/ferromagnet bilayers can produce strong current-driven torques on the magnetic layer, via the spin Hall effect in the heavy metal or the Rashba-Edelstein effect in the ferromagnet. In the search for materials to provide even more efficient spin-orbit-induced torques, some proposals have suggested topological insulators, which possess a surface state in which the effects of spin-orbit coupling are maximal in the sense that an electron's spin orientation is fixed relative to its propagation direction. Here we report experiments showing that charge current flowing in-plane in a thin film of the topological insulator bismuth selenide (Bi2Se3) at room temperature can indeed exert a strong spin-transfer torque on an adjacent ferromagnetic permalloy (Ni81Fe19) thin film, with a direction consistent with that expected from the topological surface state. We find that the strength of the torque per unit charge current density in Bi2Se3 is greater than for any source of spin-transfer torque measured so far, even for non-ideal topological insulator films in which the surface states coexist with bulk conduction. Our data suggest that topological insulators could enable very efficient electrical manipulation of magnetic materials at room temperature, for memory and logic applications. PMID:25056062

Mellnik, A R; Lee, J S; Richardella, A; Grab, J L; Mintun, P J; Fischer, M H; Vaezi, A; Manchon, A; Kim, E-A; Samarth, N; Ralph, D C

2014-07-23

277

Search for Topological Superconductivity in Superconducting Doped Topological Insulators  

NASA Astrophysics Data System (ADS)

Recent discovery of topological insulators (TIs) which can be characterized by topologically protected gapless surface states stimulated the search for an even more exotic state of matter, a topological superconductor (TSC), which is also predicted to have a topologically protected gapless surface state consisting of massless Majorana fermions as its distinctive characteristic. Low-carrier-density semiconductors with a strong spin-orbit coupling and a Fermi surface that is centered around time-reversal-invariant momenta, such as superconducting doped TIs, are predicted to be prime candidates for TSCs [1]. Following this prediction, we studied the nature of superconductivity in doped TIs, CuxBi2Se3 and Sn1-xInxTe, by employing a conductance spectroscopy [2, 3]. I will present our latest results together with recent spectroscopy data from other groups, and summarize the current understanding of topological superconductivity in superconducting doped TIs. Work in collaboration with M. Kriener, Z. Ren, A. A. Taskin, K. Segawa, Y. Ando (Osaka Univ.), K. Yada, M. Sato, Y. Tanaka (Nagoya), and L. Fu (MIT). [4pt] [1] L. Fu and E. Berg, Phys. Rev. Lett. 105, 097001 (2010). [2] S. Sasaki, M. Kriener, K. Segawa, K. Yada, Y. Tanaka, M. Sato, and Y. Ando Phys. Rev. Lett. 107, 217001 (2011). [3] S. Sasaki, Z. Ren, A. A. Taskin, K. Segawa, L. Fu, and Y. Ando, arXiv:1208.0059 (2012).

Sasaki, Satoshi

2013-03-01

278

Topological defects and textures in complex magnets  

NASA Astrophysics Data System (ADS)

Magnetic materials support an astounding array of ordered phases, but some of the most interesting phenomena occur when conventional magnetic order is suppressed in the presence of competing interactions. Such frustrated magnets come in many forms, both classical and quantum. In this thesis I study three cases of frustrated magnetism---artificial spin ice, skyrmion crystals in chiral magnets, and the Kitaev honeycomb model, an exactly solvable quantum spin liquid. Spin ice is a phase of geometrically frustrated ferromagnets that is best known for giving rise to emergent magnetic monopoles. Spin ice on the kagome lattice finds its mesoscopic counterpart in artificial spin ice---a honeycomb network of single domain magnetic nanowires. In the first part of this work I present a model of magnetization reversal in artificial spin ice that is mediated by the magnetic charges moving through the system. The dynamics is dissipative and is influenced strongly by quenched disorder and Coulomb interactions between the charges. A skyrmion is a topologically stable magnetic texture where magnetization points in every possible direction on the sphere. Although it is tempting to think of such objects as regular point particles when solving for their low-energy dynamics, we found that due to their non-trivial topology, one has to take into account the geometric Berry phase---the time derivative term in the Lagrangian that is linear in velocity. Combining that with the elastic potential energy of a crystal, we arrive at the low-frequency spin wave spectrum for skyrmion crystals, which has two branches: a "magnetophonon" branch with a quadratic dispersion and a cyclotron branch with a finite frequency in the long-wavelength limit. Anyons are exotic quasiparticles with fractional exchange statistics that are conjectured to exist in two dimensional systems exhibiting topological order. Non-Abelian anyons are of particular interest due to their potential applications in quantum computing. The gapped phase of Kitaev's honeycomb model gives rise to Abelian anyons that are magnetic fluxes going through lattice plaquettes. In this work I demonstrate that introducing dislocations into the model enriches its properties by binding a zero energy Majorana mode to each defect. Majoranas from a dislocation pair can be combined into a non-local fermion mode that is created or annihilated whenever a flux winds around a dislocation. The nature of the flux itself also changes in this process, reflecting the non-Abelian exchange statistics associated with the dislocations.

Petrova, Olga

279

Bulk charges in eleven dimensions  

NASA Astrophysics Data System (ADS)

Eleven dimensional supergravity has electric type currents arising from the Chern-Simon and anomaly terms in the action. However the bulk charge integrates to zero for asymptotically flat solutions with topological trivial spatial sections. We show that by relaxing the boundary conditions to generalisations of the ALE and ALF boundary conditions in four dimensions one can obtain static solutions with a bulk charge. Solutions involving anomaly terms preserve between 1/16 and 1/4 of the supersymmetries but Chern-Simons fluxes generally break all of the remaining supersymmetry. One can introduce membranes with the same sign of charge into these backgrounds. This raises the possibility that these generalized membranes might decay quantum mechanically to leave just a bulk distribution of charge. Alternatively and more probably, a bulk distribution of charge can decay into a collection of singly charged membranes. Dimensional reductions of these solutions lead to novel representations of extreme black holes in four dimensions with up to four charges. We discuss how the eleven-dimensional Kaluza-Klein monopole wrapped around a space with non-zero first Pontryagin class picks up an electric charge proportional to the Pontryagin number.

Hawking, S. W.; Taylor-Robinson, M. M.

1998-07-01

280

Topological polymer chemistry: systematic classification of nonlinear polymer topologies.  

PubMed

Nonlinear polymer topologies composed of cyclic and branched polymer segments are systematically classified by reference to constitutional isomerism in a series of alkanes (CnH2n+2), monocycloalkanes (CnH2n), and polycycloalkanes (CnH2n-2, CnH2n-4, etc). Thus, the total number of chain ends (termini) and of branch points (junctions) are maintained as invariant parameters, as well as the number of branches at each junction and the connectivity of junction. On the other hand, the distance between two adjacent junctions and that between the junction and terminus are taken as variant parameters. On the basis of the classification of polymer topologies, a novel synthetic strategy by an "electrostatic self-assembly and covalent fixation" technique has been proposed to construct a variety of topologically unique polymer architectures. PMID:11716710

Tezuka, Y; Oike, H

2001-11-28

281

Topological Insulators at Room Temperature  

SciTech Connect

Topological insulators are new states of quantum matter with surface states protected by the time-reversal symmetry. In this work, we perform first-principle electronic structure calculations for Sb{sub 2}Te{sub 3}, Sb{sub 2}Se{sub 3}, Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} crystals. Our calculations predict that Sb{sub 2}Te{sub 3}, Bi{sub 2}T e{sub 3} and Bi{sub 2}Se{sub 3} are topological insulators, while Sb{sub 2}Se{sub 3} is not. In particular, Bi{sub 2}Se{sub 3} has a topologically non-trivial energy gap of 0.3eV , suitable for room temperature applications. We present a simple and unified continuum model which captures the salient topological features of this class of materials. These topological insulators have robust surface states consisting of a single Dirac cone at the {Lambda} point.

Zhang, Haijun; /Beijing, Inst. Phys.; Liu, Chao-Xing; /Tsinghua U., Beijing; Qi, Xiao-Liang; /Stanford U., Phys. Dept.; Dai, Xi; Fang, Zhong; /Beijing, Inst. Phys.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-03-25

282

Strong correlations and topological order in one-dimensional systems  

NASA Astrophysics Data System (ADS)

This thesis presents theoretical studies of strongly correlated systems as well as topologically ordered systems in 1D. Non-Fermi liquid behavior characteristic of interacting 1D electron systems is investigated with an emphasis on experimentally relevant setups and observables. The existence of end Majorana fermions in a 1D p-wave superconductor subject to periodic, incommensurate and disordered potentials is studied. The Tomonaga-Luttinger liquid (TLL), a model of interacting electrons in one spatial dimension, is considered in the context of two systems of experimental interest. First, a study of the electronic properties of single-walled armchair carbon nanotubes in the presence of transverse electric and magnetic fields is presented. As a result of their effect on the band structure and electron wave functions, fields alter the nature of the (effective) Coulomb interaction in tubes. In particular, it is found that fields couple to nanotube bands (or valleys), a quantum degree of freedom inherited from the underlying graphene lattice. As revealed by a detailed TLL calculation, it is predicted that fields induce electrons to disperse into their spin, band, and charge components. Fields also provide a means of tuning the shell-filling behavior associated with short tubes. The phenomenon of charge fractionalization is investigated in a one-dimensional ring. TLL theory predicts that momentum-resolved electrons injected into the ring will fractionalize into clockwise- and counterclockwise-moving quasiparticles. As a complement to transport measurements in quantum wires connected to leads, non-invasive measures involving the magnetic field profiles around the ring are proposed. Topological aspects of 1D p-wave superconductors are explored. The intimate connection between non-trivial topology (fermions) and spontaneous symmetry breaking (spins) in one-dimension is investigated. Building on this connection, a spin ladder system endowed with vortex degrees of freedom is proposed in order to study the effects that inhomogeneous potentials have on the topological phase diagram. Periodic vortex patterns yield a rich parameter space for tuning into a topologically non-trivial phase. This analysis hinges on the development of a topological invariant based on the wave function of Majorana fermions which inhabit the ends of the system and are robust to disorder. The method is generalized to aperiodic and disordered potentials. The topological phase diagram of such systems is studied; numerical and analytic results are found to be in close agreement.

De Gottardi, Wade Wells

283

Take Charge!  

NSDL National Science Digital Library

Students come to understand static electricity by learning about the nature of electric charge, and different methods for charging objects. In a hands-on activity, students induce an electrical charge on various objects, and experiment with electrical repulsion and attraction.

Integrated Teaching And Learning Program

284

Topological strings and 5d T N partition functions  

NASA Astrophysics Data System (ADS)

We evaluate the Nekrasov partition function of 5d gauge theories engineered by webs of 5-branes, using the refined topological vertex on the dual Calabi-Yau three-folds. The theories include certain non-Lagrangian theories such as the T N theory. The refined topological vertex computation generically contains contributions from decoupled M2-branes which are not charged under the 5d gauge symmetry engineered. We argue that, after eliminating them, the refined topological string partition function agrees with the 5d Nekrasov partition function. We explicitly check this for the T 3 theory as well as Sp(1) gauge theories with N f = 2 , 3 , 4 flavors. In particular, our method leads to a new expression of the Sp(1) Nekrasov partition functions without any contour integrals. We also develop prescriptions to calculate the partition functions of theories obtained by Higgsing the T N theory. We compute the partition function of the E 7 theory via this prescription, and find the E 7 global symmetry enhancement. We finally discuss a potential application of the refined topological vertex to non-toric web diagrams.

Hayashi, Hirotaka; Kim, Hee-Cheol; Nishinaka, Takahiro

2014-06-01

285

Landau theory of topological defects in multiferroic hexagonal manganites  

NASA Astrophysics Data System (ADS)

Topological defects in ordered states with spontaneously broken symmetry often have unusual physical properties, such as fractional electric charge or a quantized magnetic field flux, originating from their non-trivial topology. Coupled topological defects in systems with several coexisting orders give rise to unconventional functionalities, such as the electric-field control of magnetization in multiferroics resulting from the coupling between the ferroelectric and ferromagnetic domain walls. Hexagonal manganites provide an extra degree of freedom: in these materials, both ferroelectricity and magnetism are coupled to an additional, non-ferroelectric structural order parameter. Here we present a theoretical study of topological defects in hexagonal manganites based on Landau theory with parameters determined from first-principles calculations. We explain the observed flip of electric polarization at the boundaries of structural domains, the origin of the observed discrete vortices, and the clamping between ferroelectric and antiferromagnetic domain walls. We show that structural vortices induce magnetic ones and that, consistent with a recent experimental report, ferroelectric domain walls can carry a magnetic moment.

Artyukhin, Sergey; Delaney, Kris T.; Spaldin, Nicola A.; Mostovoy, Maxim

2014-01-01

286

Characterization of heterocyclic rings through quantum chemical topology.  

PubMed

Five-membered rings are found in a myriad of molecules important in a wide range of areas such as catalysis, nutrition, and drug and agrochemical design. Systematic insight into their largely unexplored chemical space benefits from first principle calculations presented here. This study comprehensively investigates a grand total of 764 different rings, all geometry optimized at the B3LYP/6-311+G(2d,p) level, from the perspective of Quantum Chemical Topology (QCT). For the first time, a 3D space of local topological properties was introduced, in order to characterize rings compactly. This space is called RCP space, after the so-called ring critical point. This space is analogous to BCP space, named after the bond critical point, which compactly and successfully characterizes a chemical bond. The relative positions of the rings in RCP space are determined by the nature of the ring scaffold, such as the heteroatoms within the ring or the number of ?-bonds. The summed atomic QCT charges of the five ring atoms revealed five features (number and type of heteroatom, number of ?-bonds, substituent and substitution site) that dictate a ring's net charge. Each feature independently contributes toward a ring's net charge. Each substituent has its own distinct and systematic effect on the ring's net charge, irrespective of the ring scaffold. Therefore, this work proves the possibility of designing a ring with specific properties by fine-tuning it through manipulation of these five features. PMID:23795608

Griffiths, Mark Z; Popelier, Paul L A

2013-07-22

287

Topology of Chaotic Mixing Patterns  

NASA Astrophysics Data System (ADS)

A stirring device consisting of a periodic motion of rods induces a mapping of the fluid domain to itself, which can be regarded as a continuous mapping of a punctured surface. Having the rods undergo a topologically-complex motion guarantees a minimal amount of stretching of material lines, which is important for chaotic mixing. We use topological considerations to describe the nature of the injection of unmixed material into a central mixing region, which takes place at injection cusps. A topological index formula allow us to predict the possible types of unstable foliations that can arise for a fixed number of rods. See http://arxiv.org/abs/0804.2520 (Chaos, in press).

Thiffeault, Jean-Luc; Finn, Matthew; Gouillart, Emmanuelle; Hall, Toby

2008-11-01

288

Borohydrides: from sheet to framework topologies.  

PubMed

The five novel compounds ALiM(BH4)4 (A = K or Rb; M = Mg or Mn) and K3Li2Mg2(BH4)9 crystallizing in the space groups Aba2 and P2/c, respectively, represent the first two-dimensional topologies amongst homoleptic borohydrides. The crystal structures have been solved, refined and characterized by synchrotron X-ray powder diffraction, neutron powder diffraction and solid-state DFT calculations. Minimal energies of ordered models corroborate crystal symmetries retrieved from diffraction data. The layered Li-Mg substructure forms negatively charged uninodal 4-connected networks. It is shown that this connectivity cannot generate the long sought-after, bimetallic Li-Mg borohydrides without countercations when assuming preferred coordination polyhedra as found in Mg(BH4)2 and LiBH4. The general properties of the trimetallic compound series are analogous with the anhydrous aluminosilicates. Additionally, a relationship with zeolites is suggested, which are built from three-dimensional Al-Si-O networks with a negative charge on them. The ternary metal borohydride systems are of interest due to their potential as novel hydridic frameworks and will allow exploration of the structural chemistry of light-metal systems otherwise subject to eutectic melting. PMID:24699844

Schouwink, P; Ley, M B; Jensen, T R; Smr?ok, L'; ?erný, R

2014-06-01

289

Tunable multifunctional topological insulators in ternary Heusler and related compounds  

NASA Astrophysics Data System (ADS)

Recently the quantum spin Hall effect was theoretically predicted and experimentally realized in quantum wells based on the binary semiconductor HgTe. The quantum spin Hall state and topological insulators are new states of quantum matter interesting for both fundamental condensed-matter physics and material science. Many Heusler compounds with C1b structure are ternary semiconductors that are structurally and electronically related to the binary semiconductors. The diversity of Heusler materials opens wide possibilities for tuning the bandgap and setting the desired band inversion by choosing compounds with appropriate hybridization strength (by the lattice parameter) and magnitude of spin--orbit coupling (by the atomic charge). Based on first-principle calculations we demonstrate that around 50 Heusler compounds show band inversion similar to that of HgTe. The topological state in these zero-gap semiconductors can be created by applying strain or by designing an appropriate quantumwell structure, similar to the case of HgTe. Many of these ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the rare-earth element Ln, which can realize additional properties ranging from superconductivity (for example LaPtBi) to magnetism (for example GdPtBi) and heavy fermion behaviour (for example YbPtBi). These properties can open new research directions in realizing the quantized anomalous Hall effect and topological superconductors. Heusler compounds are similar to a stuffed diamond, correspondingly, it should be possible to find the "high Z" equivalent of graphene in a graphite-like structure with 18 valence electrons and with inverted bands. Indeed the ternary compounds, such as LiAuSe and KHgSb with a honeycomb structure of their Au-Se and Hg-Sb layers feature band inversion very similar to HgTe which is a strong precondition for existence of the topological surface states. These materials have a gap at the Fermi energy and are therefore candidates for 3D-topological insulators. Additionally they are centro-symmetric, therefore, it is possible to determine the parity of their wave functions, and hence, their topological character. Surprisingly, the compound KHgSb with the strong SOC is topologically trivial, whereas LiAuSe is found to be a topological non-trivial insulator.

Felser, Claudia

2011-03-01

290

Braid topologies for quantum computation.  

PubMed

In topological quantum computation, quantum information is stored in states which are intrinsically protected from decoherence, and quantum gates are carried out by dragging particlelike excitations (quasiparticles) around one another in two space dimensions. The resulting quasiparticle trajectories define world lines in three-dimensional space-time, and the corresponding quantum gates depend only on the topology of the braids formed by these world lines. We show how to find braids that yield a universal set of quantum gates for qubits encoded using a specific kind of quasiparticle which is particularly promising for experimental realization. PMID:16241636

Bonesteel, N E; Hormozi, L; Zikos, G; Simon, S H

2005-09-30

291

Lectures on the Topological Vertex  

Microsoft Academic Search

In this lectures, I will summarize the approach to Gromov–Witten invariants on toric Calabi–Yau threefolds based on large\\u000a N dualities. Since the large N duality\\/topological vertex approach computes Gromov–Witten invariants in terms of Chern–Simons knot and link invariants,\\u000a Sect. 2 is devoted to a review of these. Section 3 reviews topological strings and Gromov–Witten invariants, and gives some\\u000a information about

M. Mariño

292

Topology of Minimal Walking Technicolor  

NASA Astrophysics Data System (ADS)

We perform a lattice study of the topological susceptibility and instanton size distribution of the SU(2) gauge theory with two adjoint Dirac fermions (also known as Minimal Walking Technicolor), which is known to be in the conformal window. In the theory deformed with a small mass term, by drawing a comparison with the pure gauge theory, we find that topological observables are decoupled from the fermion dynamics. This provides further evidence for the infrared conformality of the theory. A study of the instanton size distribution shows that this quantity can be used to detect the onset of finite size effects.

Bennett, Ed; Lucini, Biagio

2013-05-01

293

Novel topological index F based on incidence matrix.  

PubMed

Based on incidence matrix W, the novel topological index F is defined by the matrices L, W, X as F = LWX. The properties, the chemical environments, and the interaction of the vertexes in a molecule are taken into account in this definition. Several good QSPR models in the hetero-atom-containing organic compounds and inorganic compounds are obtained. Moreover, based on the definition of F and the values C(i) of the vertexes or the values (m)F(ij) of the chemical bonds, we have obtained serial indices, (m)F(v), (m)F(b), and F(w). They are successfully applied to QSPR models and good correlation results have been obtained as well. PMID:12964200

Yang, Feng; Wang, Zhen-Dong; Huang, Yun-Ping; Zhu, Hai-Liang

2003-11-15

294

EDITORIAL: Progress in topological insulators Progress in topological insulators  

NASA Astrophysics Data System (ADS)

One of the most remarkable discoveries of the last few years in condensed matter physics is that the established distinction of crystalline solids in metals and insulators—which relies on the material band-structure—is incomplete. During the last several decades, the band structure of an uncountable variety of compounds of increasing complexity have been computed, and yet it has been overlooked that in the presence of sufficiently strong spin-orbit interaction, a new class of materials can be realized, that intrinsically behaves as insulators in their bulk and as metals at their surface. The discovery of this new class of materials was made only recently by Kane and Mele, during their theoretical studies of graphene in the presence of a sufficiently strong intrinsic spin-orbit interaction. Although the strength of the spin-orbit interaction in graphene is not sufficient to make the topological insulating state visible experimentally under currently reachable conditions, the validity and the originality of the concept were fully appreciated. Predictions for the occurrence of a two-dimensional topological insulating state in HgTe/CdTe heterostructures were made by Bernevig, Hughes and Zhang, and were followed by the experimental verification at Würzburg, in the Molenkamp group. Within a couple of years, this work brought the concept of topological insulator from an abstract theoretical discovery to an experimental reality, which stimulated further work. The concept of topological insulators was extended to the case of three-dimensional systems, for which an ideal experimental probe is angle-resolved photo-emission spectroscopy. Using this technique, specific theoretical predictions that had been made regarding the topological insulating character of different materials (e.g., for Bi-based compounds such as BiSb, Bi2Se3 or Bi2Te3), were verified experimentally through the direct observation of the Dirac surface fermions. This research was sufficient to put on solid theoretical and experimental grounds the notion of topological insulators, but, clearly, the excitement associated with this new concept goes well beyond the initial predictions and verifications. Theoretically, it is interesting to extend the concept of topological insulating states to interacting systems, to investigate the interplay of this new state of matter with other phenomena, such as superconductivity or magnetism, and to analyze all possible different experimental manifestations of the topologically insulating state. Furthermore, it is interesting to classify topological insulators and topological superconductors in both the absence and the presence of Coulomb interactions. Experimentally, the angle-resolved experimental measurements are only a first step, and what one would really like to do is, for instance, to realize nano-electronic devices with this new class of materials, much in the same way as is being done for graphene. It is in these new directions that current work is focusing, trying to solve experimental difficulties which are often present due to the limited material control of these systems that we currently have. The articles that are published in this issue provide an excellent demonstration of the spectrum of activities that is being pursued, as well as an introduction to some of the most established achievements in the field. As such, they will serve as a useful guideline for the interested reader to different important aspects in the field, from its start to the present.

Morpurgo, Alberto; Trauzettel, Björn

2012-12-01

295

Center vortex model for the infrared sector of SU(3) Yang-Mills theory: Topological susceptibility  

SciTech Connect

The topological susceptibility of the SU(3) random vortex world-surface ensemble, an effective model of infrared Yang-Mills dynamics, is investigated. The model is implemented by composing vortex world surfaces of elementary squares on a hypercubic lattice, supplemented by an appropriate specification of vortex color structure on the world surfaces. Topological charge is generated in this picture by writhe and self-intersection of the vortex world surfaces. Systematic uncertainties in the evaluation of the topological charge, engendered by the hypercubic construction, are discussed. Results for the topological susceptibility are reported as a function of temperature and compared to corresponding measurements in SU(3) lattice Yang-Mills theory. In the confined phase, the topological susceptibility of the random vortex world-surface ensemble appears quantitatively consistent with Yang-Mills theory. As the temperature is raised into the deconfined regime, the topological susceptibility falls off rapidly, but significantly less so than in SU(3) lattice Yang-Mills theory. Possible causes of this deviation, ranging from artefacts of the hypercubic description to more physical sources, such as the adopted vortex dynamics, are discussed.

Engelhardt, M. [Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003 (United States)

2011-01-15

296

Organic topological insulators in organometallic lattices  

NASA Astrophysics Data System (ADS)

Topological insulators are a recently discovered class of materials having insulating bulk electronic states but conducting boundary states distinguished by nontrivial topology. So far, several generations of topological insulators have been theoretically predicted and experimentally confirmed, all based on inorganic materials. Here, based on first-principles calculations, we predict a family of two-dimensional organic topological insulators made of organometallic lattices. Designed by assembling molecular building blocks of triphenyl-metal compounds with strong spin-orbit coupling into a hexagonal lattice, this new classes of organic topological insulators are shown to exhibit nontrivial topological edge states that are robust against significant lattice strain. We envision that organic topological insulators will greatly broaden the scientific and technological impact of topological insulators.

Wang, Z. F.; Liu, Zheng; Liu, Feng

2013-02-01

297

Topological States and Adiabatic Pumping in Quasicrystals  

NASA Astrophysics Data System (ADS)

The unrelated discoveries of quasicrystals and topological insulators have in turn challenged prevailing paradigms in condensed-matter physics. We find a surprising connection between quasicrystals and topological phases of matter: (i) quasicrystals exhibit nontrivial topological properties and (ii) these properties are attributed to dimensions higher than that of the quasicrystal. Specifically, we show, both theoretically and experimentally, that one-dimensional quasicrystals are assigned two-dimensional Chern numbers and, respectively, exhibit topologically protected boundary states equivalent to the edge states of a two-dimensional quantum Hall system. We harness the topological nature of these states to adiabatically pump light across the quasicrystal. We generalize our results to higher-dimensional systems and other topological indices. Hence, quasicrystals offer a new platform for the study of topological phases while their topology may better explain their surface properties.

Kraus, Yaacov E.; Lahini, Yoav; Ringel, Zohar; Verbin, Mor; Zilberberg, Oded

2012-09-01

298

Topological States and adiabatic pumping in quasicrystals.  

PubMed

The unrelated discoveries of quasicrystals and topological insulators have in turn challenged prevailing paradigms in condensed-matter physics. We find a surprising connection between quasicrystals and topological phases of matter: (i) quasicrystals exhibit nontrivial topological properties and (ii) these properties are attributed to dimensions higher than that of the quasicrystal. Specifically, we show, both theoretically and experimentally, that one-dimensional quasicrystals are assigned two-dimensional Chern numbers and, respectively, exhibit topologically protected boundary states equivalent to the edge states of a two-dimensional quantum Hall system. We harness the topological nature of these states to adiabatically pump light across the quasicrystal. We generalize our results to higher-dimensional systems and other topological indices. Hence, quasicrystals offer a new platform for the study of topological phases while their topology may better explain their surface properties. PMID:23005308

Kraus, Yaacov E; Lahini, Yoav; Ringel, Zohar; Verbin, Mor; Zilberberg, Oded

2012-09-01

299

Inland Wetland Definitions  

Microsoft Academic Search

This work is the result of a year-long study of the definitions of inland wetlands in which definitions from geology, hydrogeology, hydrology, pedology, biology, systems ecology, sociology, economics, political sciences, public health and law were considered. Of these, geology, hydrogeology, hydrology, biology, systems ecology and economics are discussed in detail in this report and used in writing a final theoretical

Michael W Lefor; William C Kennard

1977-01-01

300

Common Set of Definitions.  

National Technical Information Service (NTIS)

A common set of definitions for Title XX services is found in this booklet. The service descriptors were prepared from a study conducted by Boston College Graduate School of Social Work under a grant from HEW. The definitions, program elements, and activi...

1979-01-01

301

Definitions of Entomological Terms  

NSDL National Science Digital Library

A list of of morphological definitions and word roots useful to Entomology students and teachers. The list contains concise and easily understandable definitions for a number of morphological and physiological terms and specifies where on the insect these terms apply. A good reference for students in introductory entomology or insect morphology classes. Requires Adobe Acrobat Reader or equivalent software to read .pdf documents.

0002-11-30

302

An Acoustic Charge Transport Imager for High Definition Television Applications: Reliability Modeling and Parametric Yield Prediction of GaAs Multiple Quantum Well Avalanche Photodiodes. Degree awarded Oct. 1997  

NASA Technical Reports Server (NTRS)

Reliability modeling and parametric yield prediction of GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiodes (APDs), which are of interest as an ultra-low noise image capture mechanism for high definition systems, have been investigated. First, the effect of various doping methods on the reliability of GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiode (APD) structures fabricated by molecular beam epitaxy is investigated. Reliability is examined by accelerated life tests by monitoring dark current and breakdown voltage. Median device lifetime and the activation energy of the degradation mechanism are computed for undoped, doped-barrier, and doped-well APD structures. Lifetimes for each device structure are examined via a statistically designed experiment. Analysis of variance shows that dark-current is affected primarily by device diameter, temperature and stressing time, and breakdown voltage depends on the diameter, stressing time and APD type. It is concluded that the undoped APD has the highest reliability, followed by the doped well and doped barrier devices, respectively. To determine the source of the degradation mechanism for each device structure, failure analysis using the electron-beam induced current method is performed. This analysis reveals some degree of device degradation caused by ionic impurities in the passivation layer, and energy-dispersive spectrometry subsequently verified the presence of ionic sodium as the primary contaminant. However, since all device structures are similarly passivated, sodium contamination alone does not account for the observed variation between the differently doped APDs. This effect is explained by the dopant migration during stressing, which is verified by free carrier concentration measurements using the capacitance-voltage technique.

Hunt, W. D.; Brennan, K. F.; Summers, C. J.; Yun, Ilgu

1994-01-01

303

Correlated topological insulators with mixed valence.  

PubMed

We propose the local density approximation+Gutzwiller method incorporating a Green's function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB(6), we find its nontrivial Z(2) topology, indicating that SmB(6) is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators. PMID:23496729

Lu, Feng; Zhao, JianZhou; Weng, Hongming; Fang, Zhong; Dai, Xi

2013-03-01

304

Correlated Topological Insulators with Mixed Valence  

NASA Astrophysics Data System (ADS)

We propose the local density approximation+Gutzwiller method incorporating a Green’s function scheme to study the topological physics of correlated materials from the first principles. Applying this method to typical mixed valence materials SmB6, we find its nontrivial Z2 topology, indicating that SmB6 is a strongly correlated topological insulator. The unique feature of this compound is that its surface states contain three Dirac cones in contrast to most known topological insulators.

Lu, Feng; Zhao, JianZhou; Weng, Hongming; Fang, Zhong; Dai, Xi

2013-03-01

305

Positive topological entropy and $\\\\ell_1$  

Microsoft Academic Search

We characterize positive topological entropy for quasi-state space homeomorphisms induced from $C^*$-algebra automorphisms in terms of dynamically generated subspaces isomorphic to $\\\\ell_1$. This geometric condition is also used to give a description of the topological Pinsker algebra. In particular we obtain a geometric characterization of positive entropy for topological dynamical systems, as well as an analogue for completely positive topological

David Kerr; Hanfeng Li

2003-01-01

306

Superconductivity in the topological semimetal YPtBi  

NASA Astrophysics Data System (ADS)

The noncentrosymmetric half Heusler compound YPtBi exhibits superconductivity below a critical temperature Tc=0.77 K with a zero-temperature upper critical field Hc2(0)=1.5 T. Magnetoresistance and Hall measurements support theoretical predictions that this material is a topologically nontrivial semimetal having a surprisingly low positive charge-carrier density of 2×1018 cm-3. Unconventional linear magnetoresistance and beating in Shubnikov-de Haas oscillations point to spin-orbit split Fermi surfaces. The sensitivity of magnetoresistance to surface roughness suggests a possible contribution from surface states. The combination of noncentrosymmetry and strong spin-orbit coupling in YPtBi presents a promising platform for the investigation of topological superconductivity.

Butch, N. P.; Syers, P.; Kirshenbaum, K.; Hope, A. P.; Paglione, J.

2011-12-01

307

Generalized Ablowitz–Ladik hierarchy in topological string theory  

NASA Astrophysics Data System (ADS)

This paper addresses the issue of integrable structures in topological string theory on generalized conifolds. Open string amplitudes of this theory can be expressed as the matrix elements of an operator on the Fock space of 2D charged free fermion fields. The generating function of these amplitudes with respect to the product of two independent Schur functions becomes a tau function of the 2D Toda hierarchy. The associated Lax operators turn out to have a particular factorized form. This factorized form of the Lax operators characterizes a generalization of the Ablowitz–Ladik hierarchy embedded in the 2D Toda hierarchy. The generalized Ablowitz–Ladik hierarchy is thus identified as a fundamental integrable structure of topological string theory on the generalized conifolds.

Takasaki, Kanehisa

2014-04-01

308

Topological interactions in broken gauge theories  

NASA Astrophysics Data System (ADS)

This thesis deals with planar gauge theories in which some gauge group G is spontaneously broken to a finite subgroup H. The spectrum consists of magnetic vortices, global H charges and dyonic combinations exhibiting topological Aharonov-Bohm interactions. Among other things, we review the Hopf algebra D(H) related to this residual discrete H gauge theory, which provides an unified description of the spin, braid and fusion properties of the aforementioned particles. The implications of adding a Chern-Simons (CS) term to these models are also addressed. We recall that the CS actions for a compact gauge group G are classified by the cohomology group H^4(BG,Z). For finite groups H this classification boils down to the cohomology group H^3(H,U(1)). Thus the different CS actions for a finite group H are given by the inequivalent 3-cocycles of H. It is argued that adding a CS action for the broken gauge group G leads to additional topological interactions for the vortices governed by a 3-cocycle for the residual finite gauge group H determined by a natural homomorphism from H^4(BG,Z) to H^3(H,U(1)). Accordingly, the related Hopf algebra D(H) is deformed into a quasi-Hopf algebra. These general considerations are illustrated by CS theories in which the direct product of some U(1) gauge groups is broken to a finite subgroup H. It turns out that not all conceivable 3-cocycles for finite abelian gauge groups H can be obtained in this way. Those that are not reached are the most interesting. A Z_2 x Z_2 x Z_2 CS theory given by such a 3-cocycle, for instance, is dual to an ordinary gauge theory with nonabelian gauge group the dihedral group of order eight. Finally, the CS theories with nonabelian finite gauge group a dihedral or double dihedral group are also discussed in full detail.

de Wild Propitius, Mark

1995-11-01

309

Topologies for uninterruptible power supplies  

Microsoft Academic Search

The authors review the development of uninterruptible power supply (hereafter referred to as UPS) over the years from one with a SCR front end charger with isolation at line frequency to one with a sinusoidal current input charger with isolation at high frequency (HF). The authors discuss the developments in the single phase low-power (less than 1 kVA) UPS topologies.

R. Krishnan; S. Srinivasan

1993-01-01

310

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

Gardiner, T. A.; Frank, A.

2000-01-01

311

Topological Insulators in Three Dimensions  

NASA Astrophysics Data System (ADS)

We study three dimensional generalizations of the quantum spin Hall (QSH) effect. Unlike two dimensions, where the QSH effect is distinguished by a single Z2 topological invariant, in three dimensions there are 4 invariants distinguishing 16 ``topological insulator'' phases. There are two general classes: weak (WTI) and strong (STI) topological insulators. The WTI states are equivalent to layered 2D QSH states, but are fragile because disorder continuously connects them to band insulators. The STI states are robust and have surface states that realize the 2+1 dimensional parity anomaly without fermion doubling, giving rise to a novel ``topological metal'' surface phase. We show that the Z2 invariants can be easily determined for systems with inversion symmetry. This allows us to predict specific materials are STI's, including semiconducting alloy Bi1-x Sbx as well as ?-Sn and HgTe under uniaxial strain.1. Liang Fu, C.L. Kane, E.J. Mele, cond-mat/0607699. 2. Liang Fu, C.L. Kane, cond- mat/0611341.

Fu, Liang; Kane, Charles; Mele, Eugene

2007-03-01

312

The topology of elementary submodels  

Microsoft Academic Search

Given a topological space ? X,T?, we take an elementary submodel M of a sufficiently large initial fragment of the universe containing ? X,T? and naturally define a space XM. We consider under what circumstances XM is a (nice image of a) subspace of X, and what properties of X are retained by XM.

Lúcia R. Junqueira; Franklin D. Tall

1998-01-01

313

Independent Study Project, Topic: Topology.  

ERIC Educational Resources Information Center

Using this guide and the four popular books noted in it, a student, working independently, will learn about some of the classical ideas and problems of topology: the Meobius strip and Klein bottle, the four color problem, genus of a surface, networks, Euler's formula, and the Jordan Curve Theorem. The unit culminates in a project of the students'…

Notre Dame High School, Easton, PA.

314

Classical topology and quantum states  

NASA Astrophysics Data System (ADS)

Any two infinite-dimensional (separable) Hilbert spaces are unitarily isomorphic. The sets of all their self-adjoint operators are also therefore unitarily equivalent. Thus if all self-adjoint operators can be observed, and if there is no further major axiom in quantum physics than those formulated for example in Dirac's `quantum mechanics', then a quantum physicist would not be able to tell a torus from a hole in the ground. We argue that there are indeed such axioms involving observables with smooth time evolution: they contain commutative subalgebras from which the spatial slice of spacetime with its topology (and with further refinements of the axiom, its CK- and CY- structures) can be reconstructed using Gel'fand--Naimark theory and its extensions. Classical topology is an attribute of only certain quantum observables for these axioms, the spatial slice emergent from quantum physics getting progressively less differentiable with increasingly higher excitations of energy and eventually altogether ceasing to exist. After formulating these axioms, we apply them to show the possibility of topology change and to discuss quantized fuzzy topologies. Fundamental issues concerning the role of time in quantum physics are also addressed.

Balachandran, A. P.

2001-02-01

315

Phantom stars and topology change  

SciTech Connect

In this work, we consider time-dependent dark-energy star models, with an evolving parameter {omega} crossing the phantom divide {omega}=-1. Once in the phantom regime, the null energy condition is violated, which physically implies that the negative radial pressure exceeds the energy density. Therefore, an enormous negative pressure in the center may, in principle, imply a topology change, consequently opening up a tunnel and converting the dark-energy star into a wormhole. The criteria for this topology change are discussed and, in particular, we consider a Casimir energy approach involving quasilocal energy difference calculations that may reflect or measure the occurrence of a topology change. We denote these exotic geometries consisting of dark-energy stars (in the phantom regime) and phantom wormholes as phantom stars. The final product of this topological change, namely, phantom wormholes, have far-reaching physical and cosmological implications, as in addition to being used for interstellar shortcuts, an absurdly advanced civilization may manipulate these geometries to induce closed timelike curves, consequently violating causality.

DeBenedictis, Andrew; Garattini, Remo; Lobo, Francisco S. N. [Pacific Institute for the Mathematical Sciences, Simon Fraser University Site and Department of Physics, Simon Fraser University Burnaby, British Columbia, V5A IS6 (Canada); Universita degli Studi di Bergamo, Facolta di Ingegneria, Viale Marconi 5, 24044 Dalmine (Bergamo) ITALY and INFN - Sezione di Milano, Via Celoria 16, Milan (Italy); Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 2EG, UK and Centro de Astronomia e Astrofisica da Universidade de Lisboa, Campo Grande, Ed. C8 1749-016 Lisboa (Portugal)

2008-11-15

316

Crystallographic topology and its applications  

SciTech Connect

Geometric topology and structural crystallography concepts are combined to define a new area we call Structural Crystallographic Topology, which may be of interest to both crystallographers and mathematicians. In this paper, we represent crystallographic symmetry groups by orbifolds and crystal structures by Morse - functions. The Morse function uses mildly overlapping Gaussian thermal-motion probability density functions centered on atomic sites to form a critical net with peak, pass, pale, and pit critical points joined into a graph by density gradient-flow separatrices. Critical net crystal structure drawings can be made with the ORTEP-III graphics pro- An orbifold consists of an underlying topological space with an embedded singular set that represents the Wyckoff sites of the crystallographic group. An orbifold for a point group, plane group, or space group is derived by gluing together equivalent edges or faces of a crystallographic asymmetric unit. The critical-net-on-orbifold model incorporates the classical invariant lattice complexes of crystallography and allows concise quotient-space topological illustrations to be drawn without the repetition that is characteristic of normal crystal structure drawings.

Johnson, C.K.; Burnett, M.N. [Oak Ridge National Lab., TN (United States); Dunbar, W.D. [Simon`s Rock Coll., Great Barrington, MA (United States). Div. of Natural Sciences and Mathematics

1996-10-01

317

Geometry, Topology and String Theory.  

National Technical Information Service (NTIS)

A variety of scenarios are considered which shed light upon the uses and limitations of classical geometric and topological notions in string theory. The primary focus is on situations in which D-brane or string problems of a given classical space-time se...

U. Varadarajan

2003-01-01

318

Topology of evolving pore networks  

NASA Astrophysics Data System (ADS)

Morphological and topological quantification of complex pore networks is of great relevance for environmental engineering, earth science and industry. Recent developments of 3D imaging techniques such as X-ray microtomography or X-ray microscopy provide an opportunity to perform a comprehensive analysis of the pore network topology. Such an analysis is crucial to understand how transport or mechanical properties evolve during the growth and/or the aging of a pore network, especially near a percolation threshold. In the first part of this work, we present some properties related to the graph of retraction of a 3D pore network, a powerful way to characterize the topological evolution. In the second part, we analyze the topology of an evolving 3D pore network in the vicinity of a percolation transition. Two distinct scenarii of evolution are presented. The last part is dedicated to an experimental example of evolving pore network: the setting of an ordinary cement paste probed in its early age by synchrotron X-ray microcomputerized tomography.

Levitz, P.; Tariel, V.; Stampanoni, M.; Gallucci, E.

2012-11-01

319

A topological perspective on diagnosis  

Microsoft Academic Search

We propose a topological perspective on the diagnosis problem for discrete-event systems. In an infinitary framework, we argue that the construction of a centralized diagnoser is conditioned by two fundamental properties: saturation and openness. We show that these properties are decidable for omega-regular languages. Usually, openness is guaranteed implicitly in practical settings. In contrast to this, we prove that the

Andreas Bauer; S. Pinchinat

2008-01-01

320

Quantum Gravity and World Topology  

Microsoft Academic Search

The path integral of quantum gravity probes space-times with nontrivial topology and induces chiral symmetry breaking via an anomaly proportional to ?munurhosigmaRalphabetamunuRbetaalpharhosigma in the divergence of the axial fermion number current. The corresponding classical instanton solution of Einstein's equations with cosmological term is found. The Euler-Poincaré characteristic and ordinary instanton number are also discussed.

Tohru Eguchi; Peter G. O. Freund

1976-01-01

321

Topology lattice as quantum logic  

SciTech Connect

We discuss the relations between the lattice of topologies for the simplest case of a three-point set and quantum logic. A hypothetical {open_quotes}topologymeter{close_quotes} is considered as a measuring apparatus, and it is shown that it necessarily possesses some quantum features, such as complementarity. 9 refs., 3 figs.

Grib, A.A.; Zapatrin, R.R. [N.A. Voznesensky, St. Petersburg (Russian Federation)

1992-07-01

322

Identifying non-Abelian topological ordered state and transition by momentum polarization  

NASA Astrophysics Data System (ADS)

Using a method called momentum polarization, we study the quasiparticle topological spin and the edge-state chiral central charge of non-Abelian topological ordered states described by Gutzwiller-projected wave functions. Our results verify that the fractional Chern insulator state obtained by Gutzwiller projection of two partons in bands of Chern number 2 is described by SU(2)2 Chern-Simons theory coupled to fermions, rather than the pure SU(2)2 Chern-Simons theory. In addition, by introducing an adiabatic deformation between one Chern-number-2 band and two Chern-number-1 bands, we show that the topological order in the Gutzwiller-projected state does not always agree with the expectation of topological field theory. Even if the parton mean-field state is adiabatically deformed, the Gutzwiller projection can introduce a topological phase transition between Abelian and non-Abelian topologically ordered states. Our approach applies to more general topologically ordered states described by Gutzwiller-projected wave functions.

Zhang, Yi; Qi, Xiao-Liang

2014-05-01

323

Controlling the carriers of topological insulators by bulk and surface doping  

NASA Astrophysics Data System (ADS)

We report a systematic study of bulk and surface chemical doping effects on single Dirac cone topological insulator Bi2Se3 and Bi2Te3. By bulk doping, we were able to achieve full range control of charge carrier types and concentration, with the exact Fermi energy measured by angle-resolved photoemission spectroscopy (ARPES). Due to the unusual robustness of the topological surface state, we further realized the bi-polar control of the surface carriers by gaseous or alkaline surface doping without affecting the topological nature of these materials. The doping progress monitored by in situ ARPES study clearly demonstrated the switching between different carrier types through the Dirac point. The ability to control the carrier types and the concentration of topological insulators will greatly facilitate future applications.

Zhou, Bo; Liu, Z. K.; Analytis, J. G.; Igarashi, K.; Mo, S. K.; Lu, D. H.; Moore, R. G.; Fisher, I. R.; Sasagawa, T.; Shen, Z. X.; Hussain, Z.; Chen, Y. L.

2012-12-01

324

Topological constraints on basic PWM converters  

NASA Astrophysics Data System (ADS)

A modeling and synthesis technique is introduced for single-ended ladder-structured dc-dc converter topologies. Topological constraints are derived that enhance the understanding of structural properties of converter circuits and clarify the roles of inductors and capacitors in various converters using magnetic or capacitive energy storage/transfer mechanisms. The exact duality relationships among the basic converter topologies are established.

Liu, Kwang-Hwa; Lee, Fred C.

325

Continuity and Separation in Symmetric Topologies  

ERIC Educational Resources Information Center

In this note, it is shown that in a symmetric topological space, the pairs of sets separated by the topology determine the topology itself. It is then shown that when the codomain is symmetric, functions which separate only those pairs of sets that are already separated are continuous, generalizing a result found by M. Lynch.

Harris, J.; Lynch, M.

2007-01-01

326

Topology management in ad hoc networks  

Microsoft Academic Search

The efficiency of a communication network depends not only on its control protocols, but also on its topology. We propose a distributed topology management algorithm that constructs and maintains a backbone topology based on a minimal dominating set (MDS) of the network. According to this algorithm, each node determines the membership in the MDS for itself and its one-hop neighbors

Lichun Bao; J. J. Garcia-Luna-Aceves

2003-01-01

327

Robust Energy-Efficient Adder Topologies  

Microsoft Academic Search

In this paper we explore the relationship between adder topology and energy efficiency. We compare the energy-delay tradeoff curves of selected 32-bit adder topologies, to determine how architectural features and design techniques affect energy efficiency. Optimizing different adders for the supply and threshold voltages, and transistor sizing, we show that topologies with the least number of logic stages having an

Dinesh Patil; Omid Azizi; Mark Horowitz; Ron Ho; Rajesh Ananthraman

2007-01-01

328

Topological chaos in spatially periodic mixers  

Microsoft Academic Search

Topologically chaotic fluid advection is examined in two-dimensional flows with either or both directions spatially periodic. Topological chaos is created by driving flow with moving stirrers whose trajectories are chosen to form various braids. For spatially periodic flows, in addition to the usual stirrer-exchange braiding motions, there are additional topologically nontrivial motions corresponding to stirrers traversing the periodic directions. This

Matthew D. Finn; Jean-Luc Thiffeault; Emmanuelle Gouillart

2006-01-01

329

Topological chaos in spatially periodic mixers  

Microsoft Academic Search

In many industrial fluid stirring processes it is desirable to produce a high stretching rate of material lines. In two-dimensional flows this stretching rate is given by the topological entropy of the flow. Topological Chaos offers a way of constructing flows that have a rigorous topological entropy lower bound that is robust against changes in fluid properties and the exact

Matthew D. Finn; Emmanuelle Gouillart

2005-01-01

330

Topology dependent electronic and dielectric properties of free standing alloyed ultrathin nanowires of noble metals  

NASA Astrophysics Data System (ADS)

Structural, electronic and dielectric properties of free standing ultrathin alloyed nanowires of noble metals (AgAu, AgCu, AgPt, AuCu, AuPt and CuPt) in various topologies (linear, ladder and double zigzag) have been studied by using ab initio density functional theory. Among the different topologies of alloyed ultrathin nanowires of noble metals, double zigzag (DZZ) topology has been found to be most stable and the linear topology the least stable. Also the binding energy of alloyed nanowires of AgAu and AuCu for all the studied topologies is found to be larger than the average binding energy of the corresponding pristine nanowires, indicating a strong alloying effect for these topologies. Among electronic properties, the alloyed nanowires of different topologies containing Pt (AgPt, AuPt and AuCu) are found to be ferromagnetic in nature, a result of d charge depletion in Ag, Au and Cu sites and d charge gain at Pt sites. On the other hand, all the topologies (except ladder topology) of alloyed nanowires viz. AgAu, AgCu and AuCu are found to be semiconducting in nature. The optical properties of the studied alloyed nanowires have been found to be different from their corresponding pristine nanowires due to change in the band structure on alloying. The linear topology of AgAu, AgCu and AuCu and DZZ topologies (DZZ1, DZZ2 and DZZ3) of Ag, Au, Cu, AgAu, AgCu and AuCu are semiconducting in nature with band gap lying in the infrared region, causing absorption of photons from a visible spectrum leading to blackish appearance. Whereas, remaining topologies are found to be metallic in nature, with plasmon frequency lying in the energy range of 0.35 eV to 1.62 eV, which is in the infrared region and hence these nanowires shall appear to be transparent to the visible region.

Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.

2014-08-01

331

Topology of molecular interaction networks.  

PubMed

Molecular interactions are often represented as network models which have become the common language of many areas of biology. Graphs serve as convenient mathematical representations of network models and have themselves become objects of study. Their topology has been intensively researched over the last decade after evidence was found that they share underlying design principles with many other types of networks.Initial studies suggested that molecular interaction network topology is related to biological function and evolution. However, further whole-network analyses did not lead to a unified view on what this relation may look like, with conclusions highly dependent on the type of molecular interactions considered and the metrics used to study them. It is unclear whether global network topology drives function, as suggested by some researchers, or whether it is simply a byproduct of evolution or even an artefact of representing complex molecular interaction networks as graphs.Nevertheless, network biology has progressed significantly over the last years. We review the literature, focusing on two major developments. First, realizing that molecular interaction networks can be naturally decomposed into subsystems (such as modules and pathways), topology is increasingly studied locally rather than globally. Second, there is a move from a descriptive approach to a predictive one: rather than correlating biological network topology to generic properties such as robustness, it is used to predict specific functions or phenotypes.Taken together, this change in focus from globally descriptive to locally predictive points to new avenues of research. In particular, multi-scale approaches are developments promising to drive the study of molecular interaction networks further. PMID:24041013

Winterbach, Wynand; Van Mieghem, Piet; Reinders, Marcel; Wang, Huijuan; de Ridder, Dick

2013-01-01

332

Quark masses, the Dashen phase, and gauge field topology  

SciTech Connect

The CP violating Dashen phase in QCD is predicted by chiral perturbation theory to occur when the up–down quark mass difference becomes sufficiently large at fixed down-quark mass. Before reaching this phase, all physical hadronic masses and scattering amplitudes are expected to behave smoothly with the up-quark mass, even as this mass passes through zero. In Euclidean space, the topological susceptibility of the gauge fields is positive at positive quark masses but diverges to negative infinity as the Dashen phase is approached. A zero in this susceptibility provides a tentative signal for the point where the mass of the up quark vanishes. I discuss potential ambiguities with this determination. -- Highlights: •The CP violating Dashen phase in QCD occurs when the up quark mass becomes sufficiently negative. •Before reaching this phase, all physical hadronic masses and scattering amplitudes behave smoothly with the up-quark mass. •The topological susceptibility of the gauge fields diverges to negative infinity as the Dashen phase is approached. •A zero in the topological susceptibility provides a tentative signal for the point where the mass of the up quark vanishes. •The universality of this definition remains unproven. Potential ambiguities are discussed.

Creutz, Michael, E-mail: creutz@bnl.gov

2013-12-15

333

Topological insulators and the QCD vacuum: The theta parameter as a Berry phase  

NASA Astrophysics Data System (ADS)

There is considerable evidence, based on large Nc chiral dynamics, holographic QCD, and Monte Carlo studies, that the QCD vacuum is permeated by discrete quasivacua separated by domain walls across which the local value of the topological ? parameter jumps by ±2?. This scenario is realized in a 2D U(1) gauge theory, the CPN -1 sigma model, where a pointlike charge is a domain wall, and ? describes the background electric flux and the polarization of charged pairs in the vacuum. The transition between discrete ? vacua occurs via the transport of integer units of charge between the two spatial boundaries of the domain. We show that this screening process, and the role of ? as an order parameter describing electric polarization, are naturally formulated in terms of Bloch wave eigenstates of the Dirac Hamiltonian in the background gauge field. This formulation is similar to the Berry phase description of electric polarization and quantized charge transport in topological insulators. The Bloch waves are quasiperiodic superpositions of localized Dirac zero modes and the charge transport takes place coherently via topological charge-induced spectral flow. The adiabatic spectral parameter becomes the Bloch wave momentum, which defines a Berry connection around the Brillouin zone of the zero mode band. It describes the local polarization of vacuum pairs, analogous to its role in topological insulator theory. In 4D Yang-Mills theory, the ? domain walls are 2+1-dimensional Chern-Simons membranes, and the ? parameter describes the local polarization of brane-antibrane pairs. The topological description of polarization in 2D U(1) gauge theory generalizes to membrane polarization in 4D QCD by exploiting a relationship between the Berry connection and the gauge cohomology structure encoded in the descent equations of 4D Yang-Mills theory.

Thacker, H. B.

2014-06-01

334

Coordinate rings of topological Klingenberg planes I: The affine perspective  

Microsoft Academic Search

Although the coordinate ternary field of a topological affine plane is topological, the converse does not hold. However, an affine plane is topological precisely when its coordinate biternary fields are topological. We extend this result to topological biternary rings and their topological affine Klingenberg planes. Then we examine the locally compact situation. Finally, following the ideas of Knarr and Weigand,

C. A. Baker

1995-01-01

335

7/3 fractional quantum Hall effect: topology, trion excitations and edge states  

NASA Astrophysics Data System (ADS)

Exact diagonalization studies on finite systems show that the quasihole and quasiparticle excitations in the 7/3 fractional quantum Hall (FQH) state are qualitatively distinct from those of the 1/3 state, suggesting the possibility of different topological origins for the two states. We perform composite-fermion diagonalization on larger systems and also evaluate the entanglement spectrum, which shows that in spite of these strong finite size deviations, the 7/3 and 1/3 FQH states have the same topological structure in the thermodynamic limit. Nonetheless, there are substantial non-topological differences between the two, arising from the stronger residual interaction between composite fermions at 7/3. In particular, we show that the lowest energy charged excitations of the 7/3 state are complex trions of composite fermions, which have a much larger size than the charged excitations at 1/3. We discuss many observable consequences of our results.

Balram, Ajit C.; Wu, Ying-Hai; Sreejith, G. J.; Wójs, Arkadiusz; Jain, J. K.

2013-03-01

336

Operational Transconductance Amplifier Based Two-Stage Differential Charge Amplifiers  

Microsoft Academic Search

\\u000a A novel approach to the design of high-performance operational-amplifier-based differential charge amplifiers is proposed.\\u000a It is based on a two-stage topology: The first stage performs a differential measurement to single ended signal conversion,\\u000a providing a common mode rejection that only depends on the matching between two resistors; the second stage filters the signal.\\u000a These novel topologies that are based on

Dinesh. B. Bhoyar; Bharati Y. Masram

2010-01-01

337

Topological aspects of polarization structured beams  

NASA Astrophysics Data System (ADS)

Polarization structured optical beams have half-integer topological structures: star, lemon, monstar in ?-symmetric polarization ellipse orientation tensor field and integer-index topological structures: saddle, spiral, node in 2?-symmetric Poynting vector field. Topological approach to study the polarization structured optical beams is carried out and presented here in some detail. These polarization structured light beams are demonstrated to be the best platform to explore the topological interdependencies. The dependence of one type of topological structure on the other is used to control the Poynting vector density distribution and locally enhance the angular momentum density as compared to its constituent beam fields.

Kumar, Vijay; Viswanathan, Nirmal K.

2014-02-01

338

Topological mass generation in four dimensions.  

PubMed

We show that in a large class of physically interesting systems the mass-generation phenomenon can be understood in terms of topological structures, without requiring a detailed knowledge of the underlying dynamics. This is first demonstrated by showing that Schwinger's mechanism for mass generation relies on topological structures of a two-dimensional gauge theory. In the same manner, corresponding four-dimensional topological entities give rise to topological mass generation in four dimensions. This formulation offers a unified topological description of some seemingly unrelated phenomena, such as two-dimensional superconductivity, and the generation of eta' and axion masses by QCD, and possibly by gravity. PMID:16606166

Dvali, Gia; Jackiw, R; Pi, So-Young

2006-03-01

339

Molecular assembly of amino acid interlinked, topologically symmetric, ?-complementary donor-acceptor-donor triads  

PubMed Central

Summary Amino acid interlinked pyrene and naphthalenediimide (NDI) based novel donor–acceptor–donor (D-A-D) triads are designed to exploit their topological symmetry and complementary ?-character for facile charge-transfer complexation. Consequently, free-floating high-aspect-ratio supercoiled nanofibres and hierarchical helical bundles of triads are realized by modulating the chemical functionality of interlinking amino acids.

Avinash, M B; Sandeepa, K V

2013-01-01

340

Charge-induced unfolding of multiply charged polyethylene glycol ions.  

PubMed

The electrical mobility of mass-selected single poly(ethylene glycol) (PEG) chains of mass m (<14 kDalton) and charge state z (+1 to +5) reveals a near-spherical shape above a critical mass m(z) approximately z(2). The abrupt unfolding observed at m < m(z) shows that the polymer molecules behave as liquid drops upon reaching the Rayleigh limit, with an apparent surface energy of 0.026 N/m at ion diameters from 1.7 to 3.2 nm. Other nonspherical shape families with structures independent of charge, and with charge-dependent stability domains, are observed. Highly charged ions adopt approximately linear highly stretched configurations where the mobility depends only on m/z, independently of z. An operational definition of the surface energy of a single long chain molecule that is computable and agrees with the measured surface energy is provided. PMID:15382955

Ude, S; Fernández de la Mora, J; Thomson, B A

2004-09-29

341

Classical topological order in kagome ice.  

PubMed

We examine the onset of classical topological order in a nearest neighbour kagome ice model. Using Monte Carlo simulations, we characterize the topological sectors of the ground state using a nonlocal cut measure which circumscribes the toroidal geometry of the simulation cell. We demonstrate that simulations which employ global loop updates that are allowed to wind around the periodic boundaries cause the topological sector to fluctuate, while restricted local loop updates freeze the simulation into one topological sector. The freezing into one topological sector can also be observed in the susceptibility of the real magnetic spin vectors projected onto the kagome plane. The ability of the susceptibility to distinguish between fluctuating and non-fluctuating topological sectors should motivate its use as a local probe of topological order in a variety of related systems. PMID:21471623

Macdonald, Andrew J; Holdsworth, Peter C W; Melko, Roger G

2011-04-27

342

Formation of a topological non-Fermi liquid in MnSi.  

PubMed

Fermi liquid theory provides a remarkably powerful framework for the description of the conduction electrons in metals and their ordering phenomena, such as superconductivity, ferromagnetism, and spin- and charge-density-wave order. A different class of ordering phenomena of great interest concerns spin configurations that are topologically protected, that is, their topology can be destroyed only by forcing the average magnetization locally to zero. Examples of such configurations are hedgehogs (points at which all spins are either pointing inwards or outwards) and vortices. A central question concerns the nature of the metallic state in the presence of such topologically distinct spin textures. Here we report a high-pressure study of the metallic state at the border of the skyrmion lattice in MnSi, which represents a new form of magnetic order composed of topologically non-trivial vortices. When long-range magnetic order is suppressed under pressure, the key characteristic of the skyrmion lattice--that is, the topological Hall signal due to the emergent magnetic flux associated with the topological winding--is unaffected in sign or magnitude and becomes an important characteristic of the metallic state. The regime of the topological Hall signal in temperature, pressure and magnetic field coincides thereby with the exceptionally extended regime of a pronounced non-Fermi-liquid resistivity. The observation of this topological Hall signal in the regime of the NFL resistivity suggests empirically that spin correlations with non-trivial topological character may drive a breakdown of Fermi liquid theory in pure metals. PMID:23636328

Ritz, R; Halder, M; Wagner, M; Franz, C; Bauer, A; Pfleiderer, C

2013-05-01

343

Human Services Inventory: Definitions.  

National Technical Information Service (NTIS)

Definitions are presented of 24 categories of human services and of specific programs within the categories. The service categories defined are as follows: alcoholism, children and youth, community care, community groups/associations, consumer services, c...

M. Marks

1976-01-01

344

Definition of the Mesoscale  

NSDL National Science Digital Library

This module provides a working definition of mesoscale meteorology. The module briefly touches on many topics crucial to forecasting mesoscale weather phenomena, such as non-hydrostatic processes, the importance of terrain, NWP model resolution, and impact on sensible weather.

Spangler, Tim

1999-05-01

345

Definition of Death.  

National Technical Information Service (NTIS)

The Legislative Service Commission on April 27, 1976, directed the investigation of the various legal definitions of death and conducted a comprehensive survey of the legal, medical, and ethical aspects of the artificial sustaining of life. This report ha...

1977-01-01

346

Definition of UTC.  

National Technical Information Service (NTIS)

The current definition of Coordinated Universal Time (UTC) is related to the unpredictable, variable rotation rate of the Earth. This is accomplished by irregular insertions of leap seconds, which create unpredictable discontinuities in the UTC. With the ...

D. D. McCarthy

2000-01-01

347

Building Consistent Dictionary Definitions  

Microsoft Academic Search

This paper is focused on the syntactic and semantic structures of dictionary definitions (in Czech). The former are explored\\u000a by means of the partial syntactic parser Dis and their main types are presented together with their frequencies obtained from\\u000a the sample of thousands dictionary definitions. It is shown that it is important to know valency frames for nouns that serve

Karel Pala; Eva Mráková

2003-01-01

348

Chromatography Nomenclature and Definitions  

NSDL National Science Digital Library

This website gives the International Union of Pure and Applied Chemistry approved definitions in the field of chromatography. It is critical for students to appreciate the importance of using standardized nomenclature and definitions. Sections of the site include general terminology, terms related to the chromatographic system, terms related to the chromatographic process and the theory of chromatography, terms related to detection, ion exchange, liquid-liquid distribution (solvent extraction) and other related subjects.

2011-05-12

349

Topological approach to neural complexity.  

PubMed

Considerable effort in modern statistical physics is devoted to the study of networked systems. One of the most important example of them is the brain, which creates and continuously develops complex networks of correlated dynamics. An important quantity which captures fundamental aspects of brain network organization is the neural complexity C(X) introduced by Tononi et al. [Proc. Natl. Acad. Sci. USA 91, 5033 (1994)]. This work addresses the dependence of this measure on the topological features of a network in the case of a Gaussian stationary process. Both analytical and numerical results show that the degree of complexity has a clear and simple meaning from a topological point of view. Moreover, the analytical result offers a straightforward and faster algorithm to compute the complexity of a graph than the standard one. PMID:15697665

De Lucia, M; Bottaccio, M; Montuori, M; Pietronero, L

2005-01-01

350

Plasmonics in Dirac systems: from graphene to topological insulators.  

PubMed

Recent developments in the emerging field of plasmonics in graphene and other Dirac systems are reviewed and a comprehensive introduction to the standard models and techniques is given. In particular, we discuss intrinsic plasmon excitation of single and bilayer graphene via hydrodynamic equations and the random phase approximation, but also comment on double and multilayer structures. Additionally, we address Dirac systems in the retardation limit and also with large spin–orbit coupling including topological insulators. Finally, we summarize basic properties of the charge, current and photon linear response functions in an appendix. PMID:24598974

Stauber, Tobias

2014-03-26

351

Topological interactions in spacetimes with thick line defects  

NASA Astrophysics Data System (ADS)

In this work we study the topologically induced electric self-energy and self-force on a long, straight, wire in two distinct, but similar, spacetimes: (i) the Gott-Hiscock thick cosmic string spacetime, and (ii) the spacetime of a continuous distribution of infinitely thin cosmic strings over a disk of finite radius. In each case we obtain the electric self-energy and self-force both in the internal and external regions of the defect distribution. The self-force is always repulsive, independently of the sign of the charge, and is maximum on the string’s surface, in both cases.

Moraes, Fernando; Carvalho, A. M.; Costa, Ismael V.; Oliveira, F. A.; Furtado, Claudio

2003-08-01

352

Topological defects in extended inflation  

NASA Technical Reports Server (NTRS)

The production of topological defects, especially cosmic strings, in extended inflation models was considered. In extended inflation, the Universe passes through a first-order phase transition via bubble percolation, which naturally allows defects to form at the end of inflation. The correlation length, which determines the number density of the defects, is related to the mean size of bubbles when they collide. This mechanism allows a natural combination of inflation and large scale structure via cosmic strings.

Copeland, Edmund J.; Kolb, Edward W.; Liddle, Andrew R.

1990-01-01

353

Topological strings on noncommutative manifolds  

Microsoft Academic Search

We identify a deformation of the N=2 supersymmetric sigma model on a Calabi-Yau manifold X which has the same effect on B-branes as a noncommutative deformation of X. We show that for hyperkahler X such deformations allow one to interpolate continuously between the A-model and the B-model. For generic values of the noncommutativity and the B-field, properties of the topologically

Anton Kapustin

2003-01-01

354

Topological correlations in soap froths  

NASA Astrophysics Data System (ADS)

Correlation in two-dimensional soap froth is analyzed with the introduction of two point correlators and topological distance. Cells with an equal number of sides repel (with linear correlation) while cells with a different number of sides attract (with nonbilinear correlation) for nearest neighbors, which cannot be explained by the maximum entropy argument. Also, the analysis indicates that froth is correlated up to the third shell neighbors at least.

Szeto, K. Y.; Aste, T.; Tam, W. Y.

1998-08-01

355

On topological F-theory  

Microsoft Academic Search

We consider the construction of a topological version of F-theory on a particular Spin(7) 8-manifold which is a Calabi-Yau 3-fold times a 2-torus. We write an action for this theory in eight dimensions and reduce it to lower dimensions using Hitchin's gradient flow method. A symmetry of the eight-dimensional theory which follows from modular transformations of the torus induces duality

Lilia Anguelova; Paul de Medeiros; Annamaria Sinkovics

2005-01-01

356

Kinks, Cobordisms and Topology Change  

NASA Astrophysics Data System (ADS)

A formula is presented which computes the number of metrical kinks on a given hypersurface by integrating a suitable Jacobian-like quantity. The formula is applied in 2+1 dimensions to both spherical and toroidal hypersurfaces. The results are in agreement with a formula due to Low which describes how topology change that is mediated between hypersurfaces by a Lorentz cobordism gives rise to a relationship between kink numbers and Euler numbers.

Harriott, Tina A.; Williams, J. G.

2006-11-01

357

On the Topology of Plans  

Microsoft Academic Search

This paper explores a topological perspective of planning. A series of examples and theorems establishes a fundamental coupling\\u000a between tasks on graphs and simplicial complexes. Planning under uncertainty is one application. The paper introduces strategy and loopback complexes. The paper’s main theorem shows that tasks specified by goal states in nondeterministic graphs have guaranteed\\u000a solutions if and only if their

Michael Erdmann

2008-01-01

358

Inconsistency of topologically massive hypergravity  

NASA Technical Reports Server (NTRS)

The coupled topologically massive spin-5/2 gravity system in D = 3 dimensions whose kinematics represents dynamical propagating gauge invariant massive spin-5/2 and spin-2 excitations, is shown to be inconsistent, or equivalently, not locally hypersymmetric. In contrast to D = 4, the local constraints on the system arising from failure of the fermionic Bianchi identities do not involve the 'highest spin' components of the field, but rather the auxiliary spinor required to construct a consistent massive model.

Aragone, C.; Deser, S.

1985-01-01

359

Finite-temperature topological order in two-dimensional topological color codes  

SciTech Connect

In this work the topological order at finite temperature in two-dimensional color code is studied. The topological entropy is used to measure the behavior of the topological order. Topological order in color code arises from the colored string-net structures. By imposing the hard constrained limit the exact solution of the entanglement entropy becomes possible. For finite size systems, by raising the temperature, one type of string-net structure is thermalized and the associative topological entropy vanishes. In the thermodynamic limit the underlying topological order is fragile even at very low temperatures. Taking first the thermodynamic limit and then the zero-temperature limit and vice versa does not commute, and their difference is related only to the topology of regions. The contribution of the colors and symmetry of the model in the topological entropy is also discussed. It is shown how the gauge symmetry of the color code underlies the topological entropy.

Kargarian, Mehdi [Department of Physics, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of)

2009-07-15

360

Search for New Topological Insulators  

NASA Astrophysics Data System (ADS)

Topological insulators (TIs) host a novel quantum phase of electrons which is characterized by topologically protected surface states originating from the effects of spin-orbit and time-reversal symmetries. While several families of TIs have already been found, the intense world-wide search for new classes of TIs continues unabated. This interest is driven by the need for materials with greater structural flexibility and tunability to enable viable applications in spintronics and quantum computing. We have used first-principles band theory computations in combination with angle-resolved photoemission experiments to successfully predict many new classes of topologically interesting materials, including Bi2Se3 series, the ternary half-Heusler compounds, thallium-based chalcogenides, and the Li2AgSb and GenBi2mTe3m+n families. [1-5] Work supported by the Office of Basic Energy Sciences, US DOE.[4pt] [1] H. Lin, R. S. Markiewicz, L. A. Wray, L. Fu, M. Z. Hasan, and A. Bansil, Physical Review Letters 105, 036404 (2010). [0pt] [2] H. Lin, L. A. Wray, Y. Xia. S. Y. Xu, S. Jia, R. J. Cava, A. Bansil, and M. Z. Hasan, Nature Materials 9, 546 (2010). [0pt] [3] W. Al-Sawai et al., Physical Review B 82, 125208 (2010). [0pt] [4] L. A. Wray et al., Nature Physics (2010, in press).[0pt] [5] S.-Y. Xu et al., arXiv:1007.5111 (2010).

Lin, Hsin; Wray, L. A.; Xu, S.-Y.; Hasan, M. Z.; Das, T.; Wang, Y. J.; Markiewicz, R. S.; Bansil, Arun

2011-03-01

361

Topological gravity and transgression holography  

NASA Astrophysics Data System (ADS)

We show that Poincaré-invariant topological gravity in even dimensions can be formulated as a transgression field theory in one higher dimension whose gauge connections are associated to linear and nonlinear realizations of the Poincaré group ISO(d-1,1). The resulting theory is a gauged Wess-Zumino-Witten (WZW) model whereby the transition functions relating gauge fields live in the coset ISO(d-1,1)/SO(d-1,1). The coordinate parametrizing the coset space is identified with the scalar field in the adjoint representation of the gauge group of the even-dimensional topological gravity theory. The supersymmetric extension leads to topological supergravity in two dimensions starting from a transgression field theory which is invariant under the supersymmetric extension of the Poincaré group in three dimensions. We also apply this construction to a three-dimensional Chern-Simons theory of gravity which is invariant under the Maxwell algebra and obtain the corresponding WZW model.

Salgado, Patricio; Szabo, Richard J.; Valdivia, Omar

2014-04-01

362

Flanking Residues Help Determine Whether a Hydrophobic Segment Adopts a Monotopic or Bitopic Topology in the Endoplasmic Reticulum Membrane*  

PubMed Central

Proteins interacting with membranes via a single hydrophobic segment can be classified as either monotopic or bitopic. Here, we probe the topology of a membrane-attached enzyme, the ? isoform of human diacylglycerol kinase (DGK?), when inserted into rough microsomes and compare it with the monotopic membrane protein mouse caveolin-1. In contrast to previous findings, the N-terminal hydrophobic stretch in DGK? attains a bitopic rather than a monotopic topology in our experimental system. In addition, we find that charged flanking residues as well as proline residues embedded in the hydrophobic segment are important determinants of monotopic versus bitopic topology.

N?rholm, Morten H. H.; Shulga, Yulia V.; Aoki, Satoko; Epand, Richard M.; von Heijne, Gunnar

2011-01-01

363

Flanking residues help determine whether a hydrophobic segment adopts a monotopic or bitopic topology in the endoplasmic reticulum membrane.  

PubMed

Proteins interacting with membranes via a single hydrophobic segment can be classified as either monotopic or bitopic. Here, we probe the topology of a membrane-attached enzyme, the ? isoform of human diacylglycerol kinase (DGK?), when inserted into rough microsomes and compare it with the monotopic membrane protein mouse caveolin-1. In contrast to previous findings, the N-terminal hydrophobic stretch in DGK? attains a bitopic rather than a monotopic topology in our experimental system. In addition, we find that charged flanking residues as well as proline residues embedded in the hydrophobic segment are important determinants of monotopic versus bitopic topology. PMID:21606504

Nørholm, Morten H H; Shulga, Yulia V; Aoki, Satoko; Epand, Richard M; von Heijne, Gunnar

2011-07-15

364

Behavioural Semantics: A Comparison between Topologic and Algebraic Scaling in the Measurement of Human Dignity. No. 33.  

ERIC Educational Resources Information Center

Topological and algebraic scales were compared in the representation of the concept of human worth in behavioral-semantic terms. In a first experiment, seven doctoral students of Business Administration in Sweden explored the notion of worth using definitions from at least 10 dictionaries as the intentional-semantic content. Each subject served as…

Bierschenk, Bernhard

365

Polymer Amide as an Early Topology  

PubMed Central

Hydrophobic polymer amide (HPA) could have been one of the first normal density materials to accrete in space. We present ab initio calculations of the energetics of amino acid polymerization via gas phase collisions. The initial hydrogen-bonded di-peptide is sufficiently stable to proceed in many cases via a transition state into a di-peptide with an associated bound water molecule of condensation. The energetics of polymerization are only favorable when the water remains bound. Further polymerization leads to a hydrophobic surface that is phase-separated from, but hydrogen bonded to, a small bulk water complex. The kinetics of the collision and subsequent polymerization are discussed for the low-density conditions of a molecular cloud. This polymer in the gas phase has the properties to make a topology, viz. hydrophobicity allowing phase separation from bulk water, capability to withstand large temperature ranges, versatility of form and charge separation. Its flexible tetrahedral carbon atoms that alternate with more rigid amide groups allow it to deform and reform in hazardous conditions and its density of hydrogen bonds provides adhesion that would support accretion to it of silicon and metal elements to form a stellar dust material.

McGeoch, Julie E. M.; McGeoch, Malcolm W.

2014-01-01

366

Theory of defects in Abelian topological states  

NASA Astrophysics Data System (ADS)

The structure of extrinsic defects in topologically ordered states of matter is host to a rich set of universal physics. Extrinsic defects in 2+1-dimensional topological states include linelike defects, such as boundaries between topologically distinct states, and pointlike defects, such as junctions between different line defects. Gapped boundaries in particular can themselves be topologically distinct, and the junctions between them can localize topologically protected zero modes, giving rise to topological ground-state degeneracies and projective non-Abelian statistics. In this paper, we develop a general theory of point defects and gapped line defects in 2+1-dimensional Abelian topological states. We derive a classification of topologically distinct gapped boundaries in terms of certain maximal subgroups of quasiparticles with mutually bosonic statistics, called Lagrangian subgroups. The junctions between different gapped boundaries provide a general classification of point defects in topological states, including as a special case the twist defects considered in previous works. We derive a general formula for the quantum dimension of these point defects and a general understanding of their localized “parafermion” zero modes and we define a notion of projective non-Abelian statistics for them. The critical phenomena between topologically distinct gapped boundaries can be understood in terms of a general class of quantum spin chains or, equivalently, “generalized parafermion” chains. This provides a way of realizing exotic 1+1D generalized parafermion conformal field theories in condensed-matter systems.

Barkeshli, Maissam; Jian, Chao-Ming; Qi, Xiao-Liang

2013-12-01

367

A V2G vector control model of electric car charging and discharging machine  

Microsoft Academic Search

circuit topology structure of electric vehicle charging and discharging inverter based on space vector is presented. The control strategy uses rotation vector of the directional three-phase active tide reversible PWM converter, and the circuit topology is two-way control DC\\/DC converter with double buck reversible structure. In order to improve the efficiency of the charging and discharging machine, the main circuit

Xiaolei Wang; Pan Yan; Liang Yang; Wendao Yao; Guangwen Shi

2011-01-01

368

CHARGE syndrome  

Microsoft Academic Search

CHARGE syndrome was initially defined as a non-random association of anomalies (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, Ear anomalies\\/deafness). In 1998, an expert group defined the major (the classical 4C's: Choanal atresia, Coloboma, Characteristic ears and Cranial nerve anomalies) and minor criteria of CHARGE syndrome. Individuals with all four major characteristics or three major and

Kim D Blake; Chitra Prasad

2006-01-01

369

Topological polymer dispersed liquid crystals with bulk nematic defect lines pinned to handlebody surfaces.  

PubMed

Polymer dispersed liquid crystals are a useful model system for studying the relationship between surface topology and defect structures. They are comprised of a polymer matrix with suspended spherical nematic drops and are topologically constrained to host defects of an elementary hedgehog charge per droplet, such as bulk or surface point defects or closed disclination loops. We control the genus of the closed surfaces confining such micrometer-sized nematic drops with tangential boundary conditions for molecular alignment imposed by the polymer matrix, allowing us to avoid defects or, on the contrary, to generate them in a controlled way. We show, both experimentally and through numerical modeling, that topological constraints in nematic microdrops can be satisfied by hosting topologically stable half-integer bulk defect lines anchored to opposite sides of handlebody surfaces. This enriches the interplay of topologies of closed surfaces and fields with nonpolar symmetry, yielding new unexpected configurations that cannot be realized in vector fields, having potential implications for topologically similar defects in cosmology and other fields. PMID:24877965

Campbell, Michael G; Tasinkevych, Mykola; Smalyukh, Ivan I

2014-05-16

370

Topological Polymer Dispersed Liquid Crystals with Bulk Nematic Defect Lines Pinned to Handlebody Surfaces  

NASA Astrophysics Data System (ADS)

Polymer dispersed liquid crystals are a useful model system for studying the relationship between surface topology and defect structures. They are comprised of a polymer matrix with suspended spherical nematic drops and are topologically constrained to host defects of an elementary hedgehog charge per droplet, such as bulk or surface point defects or closed disclination loops. We control the genus of the closed surfaces confining such micrometer-sized nematic drops with tangential boundary conditions for molecular alignment imposed by the polymer matrix, allowing us to avoid defects or, on the contrary, to generate them in a controlled way. We show, both experimentally and through numerical modeling, that topological constraints in nematic microdrops can be satisfied by hosting topologically stable half-integer bulk defect lines anchored to opposite sides of handlebody surfaces. This enriches the interplay of topologies of closed surfaces and fields with nonpolar symmetry, yielding new unexpected configurations that cannot be realized in vector fields, having potential implications for topologically similar defects in cosmology and other fields.

Campbell, Michael G.; Tasinkevych, Mykola; Smalyukh, Ivan I.

2014-05-01

371

Robustness of topological order in semiconductor-superconductor nanowires in the Coulomb blockade regime  

NASA Astrophysics Data System (ADS)

Semiconductor-superconductor hybrid systems are promising candidates for the realization of Majorana fermions and topological order, i.e. topologically protected degeneracies, in solid state devices. We show that the topological order is mirrored in the excitation spectra and can be observed in nonlinear Coulomb blockade transport through a ring-shaped nanowire. Especially, the excitation spectrum is almost independent of magnetic flux in the topologically trivial phase but acquires a characteristic h/e magnetic flux periodicity in the non-trivial phase. The transition between the trivial and non-trivial phase is reflected in the closing and reopening of an excitation gap. We show that the signatures of topological order are robust against details of the geometry, electrostatic disorder and the existence of additional subbands and only rely on the topology of the nanowire and the existence of a superconducting gap. Finally, we show that the coherence length in the non-trivial phase is much longer than in the trivial phase. This opens the possibility to coat the nanowire with superconducting nanograins and thereby significantly reduce the current due to cotunnelling of Cooper pairs and to enhance the Coulomb charging energy without destroying the superconducting gap.

Zocher, Björn; Horsdal, Mats; Rosenow, Bernd

2013-08-01

372

Ecotourism: The Evolving Contemporary Definition  

Microsoft Academic Search

A rise in the popularity of ecotourism has coincided with voluminous definitional discourse. Amongst stakeholders, confusion has resulted from the disparate nature of these definitions. In the absence of a common definition or set of key tenets the challenge has been to ensure operational ecotourism that adheres to the theoretical underpinnings of the concept. Without some semblance of definitional consensus,

Holly M. Donohoe; Roger D. Needham

2006-01-01

373

Topology, cosmic strings and quantum dynamics - a case study with graphene  

NASA Astrophysics Data System (ADS)

We explore the possibility to study the quantum dynamics of Dirac fermions in presence of a cosmic string by introducing a conical topological defect in gapped graphene in the presence of a Coulomb charge. When the Coulomb charge exceeds a certain critical strength, quantum instability sets in. Below the critical regime and for certain values of the system parameters, the allowed boundary conditions in gapped graphene cone can be classified in terms of a single real quantity. Observables such as local density of states, scattering phase shifts and the bound state spectra are dependent on the value of this real parameter, which has to be determined empirically. For a supercritical Coulomb charge, we analyze the system with a regularized potential as well as with a zigzag boundary condition and find the effect of the sample topology on the observable features of the system.

Chakraborty, Baishali; Gupta, Kumar S.; Sen, Siddhartha

2013-06-01

374

Topological phase transitions in frustrated magnets  

NASA Astrophysics Data System (ADS)

The role of topological excitations in frustrated Heisenberg antiferromagnets between two and three spatial dimensions is considered. In particular, the antiferromagnetic Heisenberg model on a stacked triangular geometry with a finite number of layers is studied using Monte Carlo methods. A phase transition that is purely topological in nature occurs at a finite temperature for all film thicknesses. The results indicate that topological excitations are important for a complete understanding of the critical properties of the model between two and three dimensions.

Southern, B. W.; Peles, A.

2006-06-01

375

Algebra and topology for applications to physics  

NASA Technical Reports Server (NTRS)

The principal concepts of algebra and topology are examined with emphasis on applications to physics. In particular, attention is given to sets and mapping; topological spaces and continuous mapping; manifolds; and topological groups and Lie groups. The discussion also covers the tangential spaces of the differential manifolds, including Lie algebras, vector fields, and differential forms, properties of differential forms, mapping of tangential spaces, and integration of differential forms.

Rozhkov, S. S.

1987-01-01

376

Ultragraph C * -algebras via topological quivers  

Microsoft Academic Search

Given an ultragraph in the sense of Tomforde, we construct a topological\\u000aquiver in the sense of Muhly and Tomforde in such a way that the universal\\u000aC*-algebras associated to the two objects coincide. We apply results of Muhly\\u000aand Tomforde for topological quiver algebras and of Katsura for topological\\u000agraph C*-algebras to study the K-theory and gauge-invariant ideal structure

Takeshi Katsura; Paul S. Muhly; Aidan Sims; Mark Tomforde

2008-01-01

377

Opportunities in chemistry and materials science for topological insulators and their nanostructures  

NASA Astrophysics Data System (ADS)

Electrical charges on the boundaries of topological insulators favour forward motion over back-scattering at impurities, producing low-dissipation, metallic states that exist up to room temperature in ambient conditions. These states have the promise to impact a broad range of applications from electronics to the production of energy, which is one reason why topological insulators have become the rising star in condensed-matter physics. There are many challenges in the processing of these exotic materials to use the metallic states in functional devices, and they present great opportunities for the chemistry and materials science research communities.

Kong, Desheng; Cui, Yi

2011-11-01

378

Conductance modulation in topological insulator Bi2Se3 thin films with ionic liquid gating  

NASA Astrophysics Data System (ADS)

A Bi2Se3 topological insulator field effect transistor is investigated by using ionic liquid as an electric double layer gating material, leading to a conductance modulation of 365% at room temperature. We discuss the role of charged impurities on the transport properties. The conductance modulation with gate bias is due to a change in the carrier concentration, whereas the temperature dependent conductance change is originated from a change in mobility. Large conductance modulation at room temperature along with the transparent optical properties makes topological insulators as an interesting (opto)electronic material.

Son, Jaesung; Banerjee, Karan; Brahlek, Matthew; Koirala, Nikesh; Lee, Seoung-Ki; Ahn, Jong-Hyun; Oh, Seongshik; Yang, Hyunsoo

2013-11-01

379

Josephson-Majorana cycle in topological single-electron hybrid transistors  

NASA Astrophysics Data System (ADS)

Charge transport through a small topological superconducting island in contact with a normal and a superconducting electrode occurs through a cycle that involves coherent oscillations of Cooper pairs and tunneling in/out the normal electrode through a Majorana bound state, the Josephson-Majorana cycle. We illustrate this mechanism by studying the current-voltage characteristics of a superconductor-topological superconductor-normal metal single-electron transistor. At low bias and temperature the Josephson-Majorana cycle is the dominant mechanism for transport. We discuss a three-terminal configuration where the nonlocal character of the Majorana bound states is emergent.

Didier, Nicolas; Gibertini, Marco; Moghaddam, Ali G.; König, Jürgen; Fazio, Rosario

2013-07-01

380

Teleportation-induced entanglement of two nanomechanical oscillators coupled to a topological superconductor  

NASA Astrophysics Data System (ADS)

A one-dimensional topological superconductor features a single fermionic zero mode that is delocalized over two Majorana bound states located at the ends of the system. We study a pair of spatially separated nanomechanical oscillators tunnel coupled to these Majorana modes. Most interestingly, we demonstrate that the combination of electron-phonon coupling and a finite charging energy on the mesoscopic topological superconductor can lead to an effective superexchange between the oscillators via the nonlocal fermionic zero mode. We further show that this electron teleportation mechanism leads to entanglement of the two oscillators over distances that can significantly exceed the coherence length of the superconductor.

Walter, Stefan; Budich, Jan Carl

2014-04-01

381

Critical charge calculations for a bipolar SRAM array  

Microsoft Academic Search

The critical charge, Q{sub crit}, of a memory array storage cell is defined as the largest charge that can be injected without changing the cell`s logic state. The Q{sub crit} of a Schottky-coupled complementary bipolar SRAM array is evaluated in detail. An operational definition of critical charge is made, and the critical charge for the cell is determined by circuit

Leo B. Freeman

1996-01-01

382

Definition of phenotype.  

PubMed

Definition of the phenotype is crucial in designing any genetic study, especially an association study, intended to detect the disease predisposing genes. In this chapter, we review the different types of phenotypes such as discrete or continuous and discuss the issues impacting on the phenotype definition related to study design, specifically, the impact of diagnostic error (misclassification) in case-control studies and measurement error in continuous traits. We show that the power of a study depends heavily on the phenotype measured and that misclassification or measurement error can dramatically reduce the power. We also suggest some possible responses to these challenges. PMID:18358317

Wojczynski, Mary K; Tiwari, Hemant K

2008-01-01

383

SEDS experiment design definition  

NASA Technical Reports Server (NTRS)

The Small Expendable-tether Deployment System (SEDS) was developed to design, build, integrate, fly, and safely deploy and release an expendable tether. A suitable concept for an on-orbit test of SEDS was developed. The following tasks were performed: (1) Define experiment objectives and requirements; (2) Define experiment concepts to reach those objectives; (3) Support NASA in experiment concept selection and definition; (4) Perform analyses and tests of SEDS hardware; (5) Refine the selected SEDS experiment concept; and (6) Support interactive SEDS system definition process. Results and conclusions are given.

Carroll, Joseph A.; Alexander, Charles M.; Oldson, John C.

1990-01-01

384

Magnetic topological insulators at finite temperature  

NASA Astrophysics Data System (ADS)

In this paper, we study the two-dimensional magnetic topological insulators from the correlated Chern insulator and the correlated Z2 topological insulator at finite temperature. For the 2D correlated Chern insulator, we find that the thermal-fluctuation-induced magnetic topological insulator (MTI) appears in the intermediate interaction region of the correlated Chern insulator. On the contrary, for the correlated Z2 topological insulator, thermal-fluctuation-induced MTI does not exist. Finally, we offer an explanation on the difference between the two cases.

Zhu, Y.-X.; He, J.; Zang, C.-L.; Liang, Y.; Kou, S.-P.

2014-04-01

385

On the topology of flux transfer events  

NASA Technical Reports Server (NTRS)

A topological analysis is made of a simple model magnetic field of a perturbation at the magnetopause that shares magnetic properties with flux transfer events. The aim is to clarify a number of topological aspects that arise in the case of fully three-dimensional magnetic fields. It is shown that a localized perturbation at the magnetopause can in principle open a closed magnetosphere by establishing magnetic connections across the magnetopause by the formation of a ropelike magnetic field structure. For this purpose a global topological model of a closed magnetosphere is considered as the unperturbed state. The topological substructure of the model flux rope is discussed in detail.

Hesse, Michael; Birn, Joachim; Schindler, Karl

1990-01-01

386

Proximity effects in topological insulator heterostructures  

NASA Astrophysics Data System (ADS)

Topological insulators (TIs) are bulk insulators that possess robust helical conducting states along their interfaces with conventional insulators. A tremendous research effort has recently been devoted to Tl-based heterostructures, in which conventional proximity effects give rise to a series of exotic physical phenomena. This paper reviews our recent studies on the potential existence of topological proximity effects at the interface between a topological insulator and a normal insulator or other topologically trivial systems. Using first-principles approaches, we have realized the tunability of the vertical location of the topological helical state via intriguing dual-proximity effects. To further elucidate the control parameters of this effect, we have used the graphene-based heterostructures as prototypical systems to reveal a more complete phase diagram. On the application side of the topological helical states, we have presented a catalysis example, where the topological helical state plays an essential role in facilitating surface reactions by serving as an effective electron bath. These discoveries lay the foundation for accurate manipulation of the real space properties of the topological helical state in TI-based heterostructures and pave the way for realization of the salient functionality of topological insulators in future device applications.

Li, Xiao-Guang; Zhang, Gu-Feng; Wu, Guang-Fen; Chen, Hua; Dimitrie, Culcer; Zhang, Zhen-Yu

2013-09-01

387

Topology of music recommendation networks  

NASA Astrophysics Data System (ADS)

We study the topology of several music recommendation networks, which arise from relationships between artist, co-occurrence of songs in play lists or experts' recommendation. The analysis uncovers the emergence of complex network phenomena in these kinds of recommendation networks, built considering artists as nodes and their resemblance as links. We observe structural properties that provide some hints on navigation and possible optimizations on the design of music recommendation systems. Finally, the analysis derived from existing music knowledge sources provides a deeper understanding of the human music similarity perception.

Cano, Pedro; Celma, Oscar; Koppenberger, Markus; Buldú, Javier M.

2006-03-01

388

Magnetic models on various topologies  

NASA Astrophysics Data System (ADS)

A brief review is given on the study of the thermodynamic properties of spin models defined on different topologies like small-world, scale-free networks, random graphs and regular and random lattices. Ising, Potts and Blume-Capel models are considered. They are defined on complex lattices comprising Appolonian, Barabási-Albert, Voronoi-Delauny and small-world networks. The main emphasis is given on the corresponding phase transitions, transition temperatures, critical exponents and universality, compared to those obtained by the same models on regular Bravais lattices.

Lima, F. W. S.; Plascak, J. A.

2014-03-01

389

Entanglement Spectrum In Topological Phasess  

NASA Astrophysics Data System (ADS)

I will review the information that entanglement spectra give for a wide range of systems in condensed matter physics, such as fractional quantum hall effect, quantum spin chains, topological insulators, and disordered systems. I will also show how the entanglement spectrum is a unique tool to examine previously unknown many-body wavefunctions such as the ground-states of Fractional Chern Insulators (the results are based on a series of works performed in collaboration with N. Regnault, M. Hermanns, B. Estienne, Yangle Wu, Aris Alexandadinata, R. Thomale, A Sterdyniak, Z. Papic, T.L. Hughes, E. Prodan, D.P. Arovas, P. Bonderson)

Bernevig, B. Andrei

2012-02-01

390

Topological order and reflection positivity  

NASA Astrophysics Data System (ADS)

The focus of this paper is twofold. First, we observe that Hamiltonians displaying both topological order and reflection positivity have an interesting property: expectations in different ground-state vectors of a given local operator WA have the same sign. Secondly, we illustrate this result with a specific Majorana Hamiltonian, related to the toric code which is widely studied in quantum information theory. We show that expectations of reflection-symmetric loops in ground states of this Hamiltonian are vortex-free or vortex-full.

Jaffe, Arthur; Pedrocchi, Fabio L.

2014-02-01

391

Topological Map: An Efficient Tool to Compute Incrementally Topological Features on 3D Images  

Microsoft Academic Search

In this paper, we show how to use the three dimensional topological map in order to compute efficiently topological features on objects contained in a 3D image. These features are useful for example\\u000a in image processing to control operations or in computer vision to characterize objects. Topological map is a combinatorial\\u000a model which represents both topological and geometrical information of

Guillaume Damiand; Samuel Peltier; Laurent Fuchs; Pascal Lienhardt

2006-01-01

392

Physics of Three-Dimensional Bosonic Topological Insulators: Surface-Deconfined Criticality and Quantized Magnetoelectric Effect  

NASA Astrophysics Data System (ADS)

We discuss physical properties of “integer” topological phases of bosons in D=3+1 dimensions, protected by internal symmetries like time reversal and/or charge conservation. These phases invoke interactions in a fundamental way but do not possess topological order; they are bosonic analogs of free-fermion topological insulators and superconductors. While a formal cohomology-based classification of such states was recently discovered, their physical properties remain mysterious. Here, we develop a field-theoretic description of several of these states and show that they possess unusual surface states, which, if gapped, must either break the underlying symmetry or develop topological order. In the latter case, symmetries are implemented in a way that is forbidden in a strictly two-dimensional theory. While these phases are the usual fate of the surface states, exotic gapless states can also be realized. For example, tuning parameters can naturally lead to a deconfined quantum critical point or, in other situations, to a fully symmetric vortex metal phase. We discuss cases where the topological phases are characterized by a quantized magnetoelectric response ?, which, somewhat surprisingly, is an odd multiple of 2?. Two different surface theories are shown to capture these phenomena: The first is a nonlinear sigma model with a topological term. The second invokes vortices on the surface that transform under a projective representation of the symmetry group. We identify a bulk-field theory consistent with these properties, which is a multicomponent background-field theory supplemented, crucially, with a topological term. We also provide bulk sigma-model field theories of these phases and discuss a possible topological phase characterized by the thermal analog of the magnetoelectric effect.

Vishwanath, Ashvin; Senthil, T.

2013-01-01

393

Topology synthesis and size optimization of morphing wing structures  

NASA Astrophysics Data System (ADS)

This research demonstrates a novel topology and size optimization methodology for synthesis of distributed actuation systems with specific applications to morphing air vehicle structures. The main emphasis is placed on the topology and size optimization problem formulations and the development of computational modeling concepts. The analysis model is developed to meet several important criteria: It must allow a rigid-body displacement, as well as a variation in planform area, with minimum strain on structural members while retaining acceptable numerical stability for finite element analysis. Topology optimization is performed on a semi-ground structure with design variables that control the system configuration. In effect, the optimization process assigns morphing members as "soft" elements, non-morphing load-bearing members as "stiff' elements, and non-existent members as "voids." The optimization process also determines the optimum actuator placement, where each actuator is represented computationally by equal and opposite nodal forces with soft axial stiffness. In addition, the configuration of attachments that connect the morphing structure to a non-morphing structure is determined simultaneously. Several different optimization problem formulations are investigated to understand their potential benefits in solution quality, as well as meaningfulness of the formulations. Extensions and enhancements to the initial concept and problem formulations are made to accommodate multiple-configuration definitions. In addition, the principal issues on the external-load dependency and the reversibility of a design, as well as the appropriate selection of a reference configuration, are addressed in the research. The methodology to control actuator distributions and concentrations is also discussed. Finally, the strategy to transfer the topology solution to the sizing optimization is developed and cross-sectional areas of existent structural members are optimized under applied aerodynamic loads. That is, the optimization process is implemented in sequential order: The actuation system layout is first determined through multi-disciplinary topology optimization process, and then the thickness or cross-sectional area of each existent member is optimized under given constraints and boundary conditions. Sample problems are solved to demonstrate the potential capabilities of the presented methodology. The research demonstrates an innovative structural design procedure from a computational perspective and opens new insights into the potential design requirements and characteristics of morphing structures.

Inoyama, Daisaku

394

Chaos, Topology, and Social Organization.  

ERIC Educational Resources Information Center

Applies chaos theory to complex social organization, beginning with a mathematical definition of chaos. Shows how a nonlinear equation might be used to describe organization. The conclusion section identifies three approaches to analyzing chaos in social organization: metaphorical analysis, mathematical modeling, and data collection. (36…

Marion, Russ

1992-01-01

395

Assessment and control of electrostatic charges. [hazards to space missions  

NASA Technical Reports Server (NTRS)

The experience is described of NASA and DOD with electrostatic problems, generation mechanisms, and type of electrostatic hazards. Guidelines for judging possible effects of electrostatic charges on space missions are presented along with mathematical formulas and definitions.

Barrett, M.

1974-01-01

396

Charge Falling Through a Charged Ring Model  

NSDL National Science Digital Library

The Charge Falling Through a Charged Ring shows dynamics of a charged ball as it is released and falls through a ring of charge. The ball and the ring can be charged with a positive blue) or a (red) negative charge.

Krizaj, Dejan

2010-11-09

397

Charge-consistent redefinition of Fock integrals  

NASA Astrophysics Data System (ADS)

The Fock integrals in the Hartree-Fock (HF) theory have been redefined such that every orbital pair density of an electron appearing in the conventional definition is replaced by a net neutral density that is the sum of the orbital pair density and an appropriate portion of the nuclear charge density. These charge-consistent Fock integrals in the canonical HF orbitals are shown to differ from the conventional ones only in the diagonal elements and by merely a constant, thus not altering the HF energy, orbitals, correlation energies, etc. They are shown numerically to converge much more rapidly with respect to the number of unit cells included in the lattice sums for one-dimensional solids because they contain no charge-multipole interactions in their definition unlike the conventional Fock integrals. The multipole expansion of the long-range lattice sums in the charge-consistent Fock integrals is also formulated and implemented for one-dimensional solids.

Ohnishi, Yu-ya; Hirata, So

2012-06-01

398

Fast tools for calculation of atomic charges well suited for drug design.  

PubMed

Two novel approaches to construct empirical schemes for partial atomic charge calculation were proposed. The charge schemes possess important benefits. First, they produce both topologically symmetrical and environment dependent charges. Second, they can be parameterised to reasonably reproduce ab initio molecular electrostatic potential (MEP), which guarantees their successful use in molecular modelling. To validate the approaches, the parameters of the proposed charge schemes were fitted to best reproduce MEP simultaneously on grids around a set of 227 diverse organic compounds. The residual errors in MEP reproduction due to calculated atomic charges were compared to those due to charges from known charge schemes. PMID:18311641

Shulga, D A; Oliferenko, A A; Pisarev, S A; Palyulin, V A; Zefirov, N S

2008-01-01

399

positive definite Toeplitz matrix  

Microsoft Academic Search

Recent progress in signal processing and estimation has gener- ated considerable interest in the problem of computing the smallest eigenvalue of symmetric positive definite Toeplitz matrices. Several algorithms have been proposed in the literature. Many of them com- pute the smallest eigenvalue in an iterative fashion, relying on the Levinson-Durbin solution of sequences of Yule-Walker systems. Exploiting the properties of

Nicola Mastronardi; Marc Van Barel; Raf Vandebril

400

POETRY FOR CREATIVE DEFINITIONS.  

ERIC Educational Resources Information Center

ONE OF THE USES FOR POETRY IN THE CLASSROOM IS THAT OF STUDYING THE WAY A POET EMPLOYS FIGURATIVE LANGUAGE AND THE CONCRETE, SENSUAL IMAGE TO BRING INTO SHARP FOCUS, OR SUGGEST BY CONNOTATION, THE DEFINITION OF A SINGLE WORD. THIS, IN TURN, CAN LEAD TO STUDENT EXERCISES IN DEFINING WORDS IN CONCRETE SENSUAL LANGUAGE. BY TAKING A POEM WHICH SEEMS…

WIENER, HARVEY S.

401

VSCE technology definition study  

NASA Technical Reports Server (NTRS)

Refined design definition of the variable stream control engine (VSCE) concept for advanced supersonic transports is presented. Operating and performance features of the VSCE are discussed, including the engine components, thrust specific fuel consumption, weight, noise, and emission system. A preliminary engine design is presented.

Howlett, R. A.; Hunt, R. B.

1979-01-01

402

The definition of abstinence.  

PubMed

A teen's definition of sexual activity most often does not include oral or anal sex. Abstinence only programs vary widely as to how they define sexual behavior and may be contributing to misinformation about STD transmission. Unknown is the extent to which declining teen pregnancy rates are due to non-coital activities replacing vaginal intercourse. PMID:15749587

Nicoletti, Angela

2005-02-01

403

A Definition of Planet  

Microsoft Academic Search

It had proposed some definitions about what a planet is. It seems clear that the planet's mass superior limit should be lower than the threshold for deuterium thermonuclear fusion. However the inferior limit is more elusive. It had proposed either Pluto's mass or the minimum mass to produce a spherical form. The Working Group on Extrasolar Planets (WGESP) of the

H. J. Durand-Manterola

2005-01-01

404

Semiclassical geometry of charged black holes  

SciTech Connect

At the classical level, two-dimensional dilaton gravity coupled to an abelian gauge field has charged black hole solutions, which have much in common with four-dimensional Reissner-Nordstroem black holes, including multiple asymptotic regions, timelike curvature singularities, and Cauchy horizons. The black hole spacetime is, however, significantly modified by quantum effects, which can be systematically studied in this two-dimensional context. In particular, the back-reaction on the geometry due to pair-creation of charged fermions destabilizes the inner horizon and replaces it with a spacelike curvature singularity. The semiclassical geometry has the same global topology as an electrically neutral black hole.

Frolov, Andrei V.; Kristjansson, Kristjan R.; Thorlacius, Larus [KIPAC/SITP, Stanford University, Stanford, California 94305-4060 (United States); University of Iceland, Science Institute, Dunhaga 3, 107 Reykjavik (Iceland)

2005-07-15

405

Gravity's Rainbow induces topology change  

NASA Astrophysics Data System (ADS)

In this work, we explore the possibility that quantum fluctuations induce a topology change, in the context of Gravity's Rainbow. A semiclassical approach is adopted, where the graviton one-loop contribution to a classical energy in a background spacetime is computed through a variational approach with Gaussian trial wave functionals. The energy density of the graviton one-loop contribution, or equivalently the background spacetime, is then let to evolve, and consequently the classical energy is determined. More specifically, the background metric is fixed to be Minkowskian in the equation governing the quantum fluctuations, which behaves essentially as a backreaction equation, and the quantum fluctuations are let to evolve; the classical energy, which depends on the evolved metric functions, is then evaluated. Analyzing this procedure, a natural ultraviolet cutoff is obtained, which forbids the presence of an interior spacetime region, and this may result in a multiply connected spacetime. Thus, in the context of Gravity's Rainbow, this process may be interpreted as a change in topology, and in principle it results in the presence of a planckian wormhole.

Garattini, Remo; Lobo, Francisco S. N.

2014-05-01

406

Topological fluid mechanics of stirring  

NASA Astrophysics Data System (ADS)

A new approach to regular and chaotic fluid advection is presented that utilizes the Thurston Nielsen classification theorem. The prototypical two-dimensional problem of stirring by a finite number of stirrers confined to a disk of fluid is considered. The theory shows that for particular ‘stirring protocols’ a significant increase in complexity of the stirred motion known as topological chaos occurs when three or more stirrers are present and are moved about in certain ways. In this sense prior studies of chaotic advection with at most two stirrers, that were, furthermore, usually fixed in place and simply rotated about their axes, have been ‘too simple’. We set out the basic theory without proofs and demonstrate the applicability of several topological concepts to fluid stirring. A key role is played by the representation of a given stirring protocol as a braid in a (2+1)-dimensional space time made up of the flow plane and a time axis perpendicular to it. A simple experiment in which a viscous liquid is stirred by three stirrers has been conducted and is used to illustrate the theory.

Boyland, Philip L.; Aref, Hassan; Stremler, Mark A.

2000-01-01

407

Model Hamiltonian for topological insulators  

NASA Astrophysics Data System (ADS)

In this paper we give the full microscopic derivation of the model Hamiltonian for the three-dimensional topological insulators in the Bi2Se3 family of materials ( Bi2Se3 , Bi2Te3 and Sb2Te3 ). We first give a physical picture to understand the electronic structure by analyzing atomic orbitals and applying symmetry principles. Subsequently, we give the full microscopic derivation of the model Hamiltonian introduced by Zhang [Nat. Phys. 5, 438 (2009)]10.1038/nphys1270 based both on symmetry principles and the k?p perturbation theory. Two different types of k3 terms, which break the in-plane full rotation symmetry down to threefold rotation symmetry, are taken into account. An effective Hamiltonian is derived for the topological surface states. Both bulk and surface models are investigated in the presence of an external magnetic field, and the associated Landau level structure is presented. For a more quantitative fitting to the first principle calculations, we also present a model Hamiltonian including eight energy bands.

Liu, Chao-Xing; Qi, Xiao-Liang; Zhang, Haijun; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng

2010-07-01

408

Study on the Optimal Charging with Neural Networks Prediction and Variable Structure Fuzzy Control  

Microsoft Academic Search

Based on a number of charging and discharging experiments and in-depth study on the electrochemical mechanism of lead-acid\\u000a battery, a charging thought is put forward with the variable structure fuzzy control and neural networks predictor, and a\\u000a new-type Buck\\/Boost topology that uses a two-unit IPM is performed charging and depolarized discharging. The experiment results\\u000a indicated that charging efficiency was raised

Jing-zhao Li; Chong-wei Zhang

409

Charged holostars  

Microsoft Academic Search

A charged holostar is an exact solution of the Einstein field equations. Its interior matter distribution rho = 1 \\/ (8 pi r^2) is singularity free with an overall string equation of state. It has a boundary membrane of tangential pressure (but no mass-energy) situated roughly a Planck coordinate distance outside of the outer horizon of the RN-solution with the

Michael Petri

2003-01-01

410

Quantum Axiomatics: Topological and Classical Properties of State Property Systems  

NASA Astrophysics Data System (ADS)

The definition of `classical state' from (Aerts in K. Engesser, D. Gabbay and D. Lehmann (Eds.), Handbook of Quantum Logic and Quantum Structures. Elsevier, Amsterdam, 2009), used e.g. in Aerts et al. ( http://arxiv.org/abs/quant-ph/0503083 , 2010) to prove a decomposition theorem internally in the language of State Property Systems, presupposes as an additional datum an orthocomplementation on the property lattice of a physical system. In this paper we argue on the basis of the ( ?, d)-model on the Poincaré sphere that a notion of topologicity for states can be seen as an alternative (operationally foundable) classicality notion in the absence of an orthocomplementation, and compare it to the known and operationally founded concept of classicality.

Aerts, Diederik; D'Hooghe, Bart; Sioen, Mark

2011-12-01

411

Topological Proximity Effects in Graphene Nanoribbon Heterostructures  

NASA Astrophysics Data System (ADS)

Topological insulators (TI) are bulk insulators that possess robust chiral conducting states along their interfaces with normal insulators. A tremendous research effort has recently been devoted to TI-based heterostructures, in which conventional proximity effects give rise to many exotic physical phenomena. Here we establish the potential existence of ``topological proximity effect'' at the interface of a topological graphene nanoribbon (GNR) and a normal GNR. Specifically, we show that the location of the topological edge states exhibits versatile tunability as a function of the interface orientation, as well as the strengths of the interface coupling and spin-orbit coupling in the normal GNR. For zigzag and bearded GNRs, the topological edge state can be tuned to be either at the interface or outer edge of the normal ribbon. For armchair GNR, the potential location of the topological edge state can be further enriched to be at the edge of or within the normal ribbon, at the interface, or diving into the topological GNR. We also discuss potential experimental realization of the predicted topological proximity effects, which may pave the way for integrating the salient functionality of TI and graphene in future device applications.

Zhang, Gufeng; Li, Xiaoguang; Wu, Guangfen; Wang, Jie; Culcer, Dimitrie; Kaxiras, Efthimios; Zhang, Zhenyu

2013-03-01

412

Topology and Phase Transitions I. Preliminary Results  

Microsoft Academic Search

In this first paper, we demonstrate a theorem that establishes a first step toward proving a necessary topological condition for the occurrence of first or second order phase transitions: we prove that the topology of certain submanifolds of configuration space must necessarily change at the phase transition point. The theorem applies to smooth, finite-range and confining potentials V bounded below,

Roberto Franzosi; Marco Pettini; Lionel Spinelli

2005-01-01

413

T-snakes: Topology adaptive snakes  

Microsoft Academic Search

We present a new class of deformable contours (snakes) and apply them to the segmentation of medical images. Our snakes are defined in terms of an affine cell image decomposition (ACID). The 'snakes in ACID' framework significantly extends conventional snakes, enabling topological flexibility among other features. The resulting topology adaptive snakes, or 'T-snakes', can be used to segment some of

Tim McInerney; Demetri Terzopoulos

1999-01-01

414

Topology optimization of energy-absorbing structures  

Microsoft Academic Search

This paper presents a method for and examples of topology optimization of energy absorption structures. The topology optimization problem is solved by using the elements as design variables. The sensitivity number of an element is derived from using an adjoint method to address two principal design parameters, namely absorbed energy per unit volume, e1, and absorbed energy ratio, e2. Filter

X Huang; Y M Xie; G Lu

2007-01-01

415

Transmembrane Topology of a CLC Chloride Channel  

Microsoft Academic Search

CLC chloride channels form a large and conserved gene family unrelated to other channel proteins. Knowledge of the transmembrane topology of these channels is important for understanding the effects of mutations found in human myotonia and inherited hypercalciuric kidney stone diseases and for the interpretation of structure--function studies. We now systematically study the topology of human CIC-1, a prototype CLC

Thomas Schmidt-Rose; Thomas J. Jentsch

1997-01-01

416

A Topological Model of Bilingual Intercalation Behavior.  

ERIC Educational Resources Information Center

This paper reviews issues and analyses in bilingual switching, or intercalation, and offers a topological model to represent the activity of code switching, sometimes under the same environmental conditions and with the same interlocutors. The topological notion of catastrophe is proposed as a means to model the various factors that influence code…

Attinasi, John; And Others

417

An integrated environment for intelligent topological design  

Microsoft Academic Search

This paper describes an integrated environment for the topological design of packet-switched computer networks. Based on artificial intelligence techniques, this system called SIDRO integrates four main modules: an initial topology generator, an example generator, an inductive learning module and a user interface module. Such a system is suitable for designing large scale data switching computer networks, in the sense that

Samuel PIERRE

1993-01-01

418

The workshop on internet topology (wit) report  

Microsoft Academic Search

Internet topology analysis has recently experienced a surge of in- terest in computer science, physics, and the mathematical sciences. However, researchers from these different disciplines tend to ap- proach the same problem from different angles. As a result, the field of Internet topology analysis and modeling must untang le sets of inconsistent findings, conflicting claims, and contradic ting state- ments.

Dmitri V. Krioukov; Kimberly C. Claffy; Marina Fomenkov; Fan Chung; Alessandro Vespignani; Walter Willinger

2007-01-01

419

Mirror Manifolds And Topological Field Theory  

Microsoft Academic Search

These notes are devoted to explaining aspects of the mirror manifold problem that can be naturally understood from the point of view of topological field theory. Basically this involves studying the topological field theories made by twisting $N=2$ sigma models. This is mainly a review of old results, except for the discussion in \\\\S7 of certain facts that may be

Edward Witten

1991-01-01

420

Holomorphic anomalies in topological field theories  

Microsoft Academic Search

We study the stringy genus-one partition function of N = 2 SCFTs. It is shown how to compute this using an anomaly in decoupling of BRST trivial states from the partition function. A particular limit of this partition function yields the partition function of topological theory coupled to topological gravity. As an application we compute the number of holomorphic elliptic

M. Bershadsky; S. Cecotti; H. Ooguri; C. Vafa; S. Katz

1993-01-01

421

Topological patterns identification for sneak circuit analysis  

Microsoft Academic Search

In sneak circuit analysis, it demands to identify the basic topological patterns which are the causes of sneak circuits. In this paper we formulate the problem of identifying the basic topological patterns into that of enumerating subgraphs homeomorphic to five specific signed trees in signed graphs, and give methods to simplify signed graphs and an algorithm to find all paths

Bolin Chen

2009-01-01

422

Topology design for free space optical networks  

Microsoft Academic Search

In this paper, we consider the problem of designing a topology for deploying a free space optical (FSO) link based network. The problem is to create a topology with strong connectivity and short diameter with uniform degree bounds on each node. Two centralized approaches are presented. The first approach constructs a backbone network by Delaunay triangulation. The basic structure is

Prabhanjan C Gurumohan; Joseph Hui

2003-01-01

423

Quasi-Uniform Topologies on Local Observables.  

National Technical Information Service (NTIS)

Quasi-uniform topologies on algebras of local observables are introduced. For the BCS-model it is shown that with the help of these topologies one gets a completion of the algebra of local observables on which the dynamics is given by a one-parameter grou...

G. Lassner

1978-01-01

424

Critical fluctuations in topologically massive superconductors.  

National Technical Information Service (NTIS)

We consider a topologically massive Ginzburg-Landau model of superconductivity. In the context of a mean field calculation, we show that there is an increase in the critical temperature driven by the topological term. It is shown that this effect persists...

A. P. C. Malbouisson F. S. Nogueira N. F. Svaiter

1996-01-01

425

The HMMTOP transmembrane topology prediction server  

Microsoft Academic Search

Summary: The HMMTOP transmembrane topology pre- diction server predicts both the localization of helical trans- membrane segments and the topology of transmembrane proteins. Recently, several improvements have been intro- duced to the original method. Now, the user is allowed to submit additional information about segment localization to enhance the prediction power. This option improves the prediction accuracy as well as

Gábor E. Tusnády; István Simon

2001-01-01

426

Hall viscosity, topological states and effective theories  

NASA Astrophysics Data System (ADS)

Hall viscosity is a dissipationless transport coefficient whose value is quantized in units of the density in some topological phases and may be used as a measure of topological order. I give an overview of the Hall viscosity, its relation to Hall conductivity in Galilean invariant theories and its realization in effective theories.

Hoyos, Carlos

2014-03-01

427

Topological Higgs mechanism with ordinary Higgs mechanism.  

National Technical Information Service (NTIS)

Topological Higgs mechanism in higher dimensions is analyzed when ordinary Higgs potential exists. It is shown that if one-form B-field becomes massive by the ordinary Higgs mechanism, another D-2 form C-field also becomes massive through topological term...

Oda Ichiro Yahikozawa Shigeaki

1989-01-01

428

Effects of the parametric interaction on the toplogical charge of acoustical vortices.  

NASA Astrophysics Data System (ADS)

Acoustical vortices are one of the three kinds of phase singularity corresponding to screw dislocations of the wavefront. They are characterized by an helical phase winding up around their axis of propagation along which the phase is singular (undefined). This kind of waves possesses several interesting properties like robustness to wavefront distortion in heterogeneous media or non diffracting propagation due to their relation to Bessel beams. Here we are interested by their potential to transmit information and perform basic arithmetics. We experimentally show that parametric interaction has a double effect on such a beam. First of all, the classical effect of creation of frequencies corresponding to all linear combinations of the primary frequencies is recovered. This classical manifestation of the quadratic nonlinearity in fluids is not new but leads to interesting properties for the spatial information of acoustical vortices as it is possible to do some arithmetics with acoustical vortices. Indeed, it is observed that for a frequency generated by a linear combination of the primary frequencies, the topological charge (number of twists made by the wavefront for one wavelength) is obtained by the same linear combination applied to the topological charges of the primary frequencies. For instance, vortices with negative topological charge appear for a secondary beam at the frequency corresponding to the difference of two primary beams with a positive topological charge when the highest frequency corresponds to the lowest topological charge. This phenomenon is studied for frequencies without and with a common divisor. In the latter case, generated frequencies can be degenerated, i.e two different linear combinations give the same frequency. However there is no reason to have the same common divisor for the topological charge so that two waves at the same frequency but with two different charges are propagating colinearly. In this case, the topological charge can be determined using energetic arguments. Finally, the potential applications are briefly discussed.

Marchiano, Régis; Thomas, Jean-Louis

2008-06-01

429

Spin-charge soldering from tensor Higgs mechanism  

NASA Astrophysics Data System (ADS)

Spin-charge separation, a crucial ingredient in 2D models of strongly correlated systems, is mostly considered in condensed matter applications. In this paper we present a relativistic field-theoretic model in which charged particles of spin 1/2 emerge by soldering spinless charges and magnetic vortices in a confinement quantum phase transition modeled as a tensor Higgs mechanism. The model involves two gauge fields, a vector one and a two-form gauge field interacting by the topological BF-term. When this tensor gauge symmetry is spontaneously broken charges are soldered to the ends of magnetic vortices and thus confined by a linear potential. If the vector potential has a topological ?-term with value ? =?, the constituents of this "meson" acquire spin 1/2 in this transition.

Diamantini, M. Cristina; Trugenberger, Carlo A.

2014-05-01

430

Ambipolar field effect in the ternary topological insulator (Bi(x)Sb(1-x))2Te3 by composition tuning.  

PubMed

Topological insulators exhibit a bulk energy gap and spin-polarized surface states that lead to unique electronic properties, with potential applications in spintronics and quantum information processing. However, transport measurements have typically been dominated by residual bulk charge carriers originating from crystal defects or environmental doping, and these mask the contribution of surface carriers to charge transport in these materials. Controlling bulk carriers in current topological insulator materials, such as the binary sesquichalcogenides Bi2Te3, Sb2Te3 and Bi2Se3, has been explored extensively by means of material doping and electrical gating, but limited progress has been made to achieve nanostructures with low bulk conductivity for electronic device applications. Here we demonstrate that the ternary sesquichalcogenide (Bi(x)Sb(1-x))2Te3 is a tunable topological insulator system. By tuning the ratio of bismuth to antimony, we are able to reduce the bulk carrier density by over two orders of magnitude, while maintaining the topological insulator properties. As a result, we observe a clear ambipolar gating effect in (Bi(x)Sb(1-x))2Te3 nanoplate field-effect transistor devices, similar to that observed in graphene field-effect transistor devices. The manipulation of carrier type and density in topological insulator nanostructures demonstrated here paves the way for the implementation of topological insulators in nanoelectronics and spintronics. PMID:21963714

Kong, Desheng; Chen, Yulin; Cha, Judy J; Zhang, Qianfan; Analytis, James G; Lai, Keji; Liu, Zhongkai; Hong, Seung Sae; Koski, Kristie J; Mo, Sung-Kwan; Hussain, Zahid; Fisher, Ian R; Shen, Zhi-Xun; Cui, Yi

2011-11-01

431

Massive Dirac Fermion on the Surface of a Magnetically Doped Topological Insulator  

SciTech Connect

Topological insulators are characterized by a massless Dirac surface state and a bulk energy gap. An insulating massive Dirac fermion state is predicted to occur if the breaking of the time reversal symmetry opens an energy gap at the Dirac point, provided that the Fermi-energy resides inside both the surface and bulk gaps. By introducing magnetic dopants into the three dimensional topological insulator Bi{sub 2}Se{sub 3} to break the time reversal symmetry, we observed the formation of a massive Dirac fermion on the surface; simultaneous magnetic and charge doping furthermore positioned the Fermi-energy inside the Dirac gap. The insulating massive Dirac Fermion state thus obtained may provide a tool for studying a range of topological phenomena relevant to both condensed matter and particle physics.

Chen, Y.L.; Chu, J.-H.; Analytis, J.G.; Liu, Z.K.; Igarashi, K.; Kuo, H.-H.; Qi, X.L.; Mo, S.K.; Moore, R.G.; Lu, D.H.; Hashimoto, M.; Sasagawa, T.; Zhang, S.C.; Fisher, I.R.; Hussain, Z.; Shen, Z.-X.; /SLAC; ,

2011-05-20

432

The formation of topological defects in phase transitions  

NASA Technical Reports Server (NTRS)

It was argued, and fought through numerical work that the results of non-dynamical Monte Carlo computer simulations cannot be applied to describe the formation of topological defects when the correlation length at the Ginzburg temperature is significantly smaller than the horizon size. To test the current hypothesis that infinite strings at formation are essentially described by Brownian walks of size the correlation length at the Ginzburg temperature, fields at the Ginzburg temperature were equilibrated. Infinite structure do not exist in equilibrium for reasonable definitions of the Ginzburg temperature, and horizons must be included in a proper treatment. A phase transition, from small-scale to large-scale string or domain wall structure, is found to occur very close to the Ginzburg temperature, in agreement with recent work. The formation process of domain walls and global strings were investigated through the breaking of initially ordered states. To mimic conditions in the early Universe, cooling times are chosen so that horizons exist in the sample volume when topological structure formation occurs. The classical fields are evolved in real-time by the numerical solution of Langevin equations of motion on a three dimensional spatial lattice. The results indicate that it is possible for most of the string energy to be in small loops, rather than in long strings, at formation.

Hodges, Hardy M.

1989-01-01

433

Inferring topological features of proteins from amino acid residue networks  

NASA Astrophysics Data System (ADS)

Topological properties of native folds are obtained from statistical analysis of 160 low homology proteins covering the four structural classes. This is done analyzing one, two and three-vertex joint distribution of quantities related to the corresponding network of amino acid residues. Emphasis on the amino acid residue hydrophobicity leads to the definition of their center of mass as vertices in this contact network model with interactions represented by edges. The network analysis helps us to interpret experimental results such as hydrophobic scales and fraction of buried accessible surface area in terms of the network connectivity. Moreover, those networks show assortative mixing by degree. To explore the vertex-type dependent correlations, we build a network of hydrophobic and polar vertices. This procedure presents the wiring diagram of the topological structure of globular proteins leading to the following attachment probabilities between hydrophobic-hydrophobic 0.424(5), hydrophobic-polar 0.419(2) and polar-polar 0.157(3) residues.

Alves, Nelson Augusto; Martinez, Alexandre Souto

2007-02-01

434

Disentangling topological degeneracy in the entanglement spectrum of one-dimensional symmetry-protected topological phases  

NASA Astrophysics Data System (ADS)

One-dimensional valence bond solid (VBS) states represent the simplest symmetry-protected topological phases. We show that their ground state entanglement spectrum contains both topological and nontopological structures. For the SO(3) symmetric VBS states with odd-integer spins, the twofold topological degeneracy is associated with an underlying Z2×Z2 symmetry that protects the corresponding topological phase. In general, for the SO(2S+1) symmetric VBS states with integer spins S, the corresponding protecting symmetry is identified as the (Z2×Z2)S symmetry, yielding the 2S-fold topological degeneracy. The topological degeneracy and associated protecting symmetry can be identified by a nonlocal unitary transformation, which changes the topological order of the VBS states into conventional ferromagnetic order.

Rao, Wen-Jia; Zhang, Guang-Ming; Yang, Kun

2014-03-01

435

Measuring the topology of the universe  

PubMed Central

Observations of microwave background fluctuations can yield information not only about the geometry of the universe but potentially about the topology of the universe. If the universe is negatively curved, then the characteristic scale for the topology of the universe is the curvature radius. Thus, if we are seeing the effects of the geometry of the universe, we can hope to soon see signatures of the topology of the universe. The cleanest signature of the topology of the universe is written on the microwave sky: There should be thousands of pairs of matched circles. These circles can be used to determine the precise topology and volume of the universe. Because we see hundreds of slices through the fundamental domain of the universe, we can use the microwave observations to reconstruct the initial conditions of the entire universe on the scale of a few megaparsecs.

Cornish, Neil J.; Spergel, David N.; Starkman, Glenn D.

1998-01-01

436

QCD as a topologically ordered system  

SciTech Connect

We argue that QCD belongs to a topologically ordered phase similar to many well-known condensed matter systems with a gap such as topological insulators or superconductors. Our arguments are based on an analysis of the so-called “deformed QCD” which is a weakly coupled gauge theory, but nevertheless preserves all the crucial elements of strongly interacting QCD, including confinement, nontrivial ? dependence, degeneracy of the topological sectors, etc. Specifically, we construct the so-called topological “BF” action which reproduces the well known infrared features of the theory such as non-dispersive contribution to the topological susceptibility which cannot be associated with any propagating degrees of freedom. Furthermore, we interpret the well known resolution of the celebrated U(1){sub A} problem where the would be ?{sup ?} Goldstone boson generates its mass as a result of mixing of the Goldstone field with a topological auxiliary field characterizing the system. We then identify the non-propagating auxiliary topological field of the BF formulation in deformed QCD with the Veneziano ghost (which plays the crucial role in resolution of the U(1){sub A} problem). Finally, we elaborate on relation between “string-net” condensation in topologically ordered condensed matter systems and long range coherent configurations, the “skeletons”, studied in QCD lattice simulations. -- Highlights: •QCD may belong to a topologically ordered phase similar to condensed matter (CM) systems. •We identify the non-propagating topological field in deformed QCD with the Veneziano ghost. •Relation between “string-net” condensates in CM systems and the “skeletons” in QCD lattice simulations is studied.

Zhitnitsky, Ariel R., E-mail: arz@physics.ubc.ca

2013-09-15

437

Spin Charge Separation in the Quantum Spin Hall State  

SciTech Connect

The quantum spin Hall state is a topologically non-trivial insulator state protected by the time reversal symmetry. We show that such a state always leads to spin-charge separation in the presence of a {pi} flux. Our result is generally valid for any interacting system. We present a proposal to experimentally observe the phenomenon of spin-charge separation in the recently discovered quantum spin Hall system.

Qi, Xiao-Liang; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-03-19

438

Optimizing oxide charge balanced devices for Unclamped Inductive Switching (UIS)  

Microsoft Academic Search

Power MOSFET designs have been moving to higher performance particularly in the medium voltage area. (60V to 300V) New designs require lower Specific On-resistance while not sacrificing Unclamped Inductive Switching (UIS) capability or increasing turn-off losses. Two charge balance technologies currently address these needs, the PN junction and the Shielded Gate Charge Balance device topologies. This paper will study the

J. Yedinak; D. Probst; G. Dolny; A. Challa; J. Andrews

2010-01-01

439

HYBRID DC ACCURATE CHARGE AMPLIFIER FOR LINEAR PIEZOELECTRIC POSITIONING  

Microsoft Academic Search

Abstract: Piezoelectric transducers are known,to exhibit l ess hysterisis when,driven with current or charge rather than voltage. Despite this advanta ge, such methods have found little practical application due to the poor low frequency response of present current and charge driver designs. This paper introduces a new circuit topology free from low-frequency drift and DC load offsets. The hybrid load

Andrew J. Fleming; S. O. Reza Moheimani

440

Wavefunctions for topological quantum registers  

SciTech Connect

We present explicit wavefunctions for quasi-hole excitations over a variety of non-abelian quantum Hall states: the Read-Rezayi states with k {>=} 3 clustering properties and a paired spin-singlet quantum Hall state. Quasi-holes over these states constitute a topological quantum register, which can be addressed by braiding quasi-holes. We obtain the braid properties by direct inspection of the quasi-hole wavefunctions. We establish that the braid properties for the paired spin-singlet state are those of 'Fibonacci anyons', and thus suitable for universal quantum computation. Our derivations in this paper rely on explicit computations in the parafermionic conformal field theories that underly these particular quantum Hall states.

Ardonne, E. [Microsoft station Q, Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States) and Center for the Physics of Information, California Institute of Technology, Pasadena, CA 91125 (United States)]. E-mail: ardonne@kitp.ucsb.edu; Schoutens, K. [Institute for Theoretical Physics, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands)

2007-01-15

441

Topological approach of Jungian psychology.  

PubMed

In this work, we compare two global approaches which are usually considered as completely unconnected one with the other. The former is Thom's topology and the latter is Jung's psychology. More precisely, it seemed to us interesting to adapt some morphologies of Thom's catastrophe theory to some Jung's notions. Thus, we showed that the swallowtail, which is one of these morphologies, was able to describe geometrically the structural organisation of the psyche according to Jung, with its collective unconscious, personal unconscious and conscious. Moreover, we have correlated this morphology with Jung's evolutive processes like individualization and individuation. These comparisons incited us to think that some morphologies of Thom's catastrophe theory are the geometrical dealing of Jung's archetypes. PMID:20658172

Viret, Jacques

2010-09-01

442

Topologically massive higher spin gravity  

NASA Astrophysics Data System (ADS)

We look at the generalisation of topologically massive gravity (TMG) to higher spins, specifically spin-3. We find a special "chiral" point for the spin-three, analogous to the spin-two example, which actually coincides with the usual spin-two chiral point. But in contrast to usual TMG, there is the presence of a non-trivial trace and its logarithmic partner at the chiral point. The trace modes carry energy opposite in sign to the traceless modes. The logarithmic partner of the traceless mode carries negative energy indicating an instability at the chiral point. We make several comments on the asymptotic symmetry and its possible deformations at this chiral point and speculate on the higher spin generalisation of LCFT2 dual to the spin-3 massive gravity at the chiral point.

Bagchi, Arjun; Lal, Shailesh; Saha, Arunabha; Sahoo, Bindusar

2011-10-01

443

Stability of topological black holes  

NASA Astrophysics Data System (ADS)

We explore the classical stability of topological black holes in d-dimensional anti-de Sitter spacetime, where the horizon is an Einstein manifold of negative curvature. According to the gauge invariant formalism of Ishibashi and Kodama, gravitational perturbations are classified as being of scalar, vector, or tensor type, depending on their transformation properties with respect to the horizon manifold. For the massless black hole, we show that the perturbation equations for all modes can be reduced to a simple scalar field equation. This equation is exactly solvable in terms of hypergeometric functions, thus allowing an exact analytic determination of potential gravitational instabilities. We establish a necessary and sufficient condition for stability, in terms of the eigenvalues ? of the Lichnerowicz operator on the horizon manifold, namely ??-4(d-2). For the case of negative mass black holes, we show that a sufficient condition for stability is given by ??-2(d-3).

Birmingham, Danny; Mokhtari, Susan

2007-12-01

444

A Consistent Definition for Quantiles.  

ERIC Educational Resources Information Center

Considers definitions of quantiles. Describes median and quartiles. Compares the usefulness of 3 different definitions of quartile using a computer program to simulate 500 quantiles on a sample of a fixed size. Five references are listed. (YP)

Fleet, Tony

1989-01-01

445

Fractional topological excitations and quantum phase transition in a bilayer two-dimensional electron gas adjacent to a superconductor film  

NASA Astrophysics Data System (ADS)

We study a bilayer two-dimension-electron-gas (2DEG) adjacent to a type-II superconductor thin film with a pinned vortex lattice. We find that with increasing interlayer tunneling, the system of half-filling presents three phases: gapped phase-I (topological insulator), gapless critical phase-II (metal), and gapped phase-III (band insulator). The total Hall conductance for phase-I/III is 2/0 e2/h , and has nonquantized values in phase-II. The excitation (response to topological defect, a local vortex defect) in these three phases shows different behaviors due to the topological property of the system, including fractional charge e/2 for each layer in phase-I. While in the case of quarter-filling, the system undergoes a quantum phase transition from metallic phase to topological insulator phase.

Hao, Ningning; Zhang, Wei; Wang, Zhigang; Wang, Yupeng; Zhang, Ping

2010-03-01

446

Charged poles?  

NSDL National Science Digital Library

A significant portion of the recent work in the field of physics education research has been concerned with the identification of alternate conceptions (Driver and Easley, 1978) that students have about physical systems. Most of this work has been concentrated in the area of mechanics. There has been some work done in the area of electricity and magnetism but, by comparison, this area has received relatively little attention. The author reports on a study designed to determine if student difficulties in understanding the interactions of electric charges with magnetic fields might be caused, at least in part, by an alternate conception. In discussions among physics teachers one often hears several reasons proposed for these difficulties. One reason given is that magnetic force situations are three dimensional. A second one is that the right hand rule is an unusual procedure which is often misunderstood. These matters are almost certainly involved, but might there not also be some alternate conception causing students difficulty? The purpose of the study was to determine whether the students thought of magnetic poles as exerting forces directly on electric charges, in a manner similar to the behaviour of electrostatic charges.

Maloney, David

2006-05-24

447

TRW CHARGED DROPLET SCRUBBER CORROSION STUDIES  

EPA Science Inventory

The report gives results of corrosion studies to provide definitive data concerning the corrosive nature of coke-oven waste-heat flue gas and its effects on wet electrostatic precipitators, and specifically on TRW's Charged Droplet Scrubber (CDS). The study characterized the chem...

448

NASA assurance terms and definitions  

NASA Technical Reports Server (NTRS)

This publication provides a compendium of commonly used safety, reliability, maintainability, and quality assurance (SRM&QA) definitions to ensure standardized assurance communications among NASA Field Installations, Headquarters, and contractors. This list of standard assurance terms and definitions shall be utilized by all NASA organizations and contractors. Program/project tailoring of these definitions may be permitted for specific program applications.

1993-01-01

449

State Definitions of Emotional Disturbance  

ERIC Educational Resources Information Center

This article examines definitions state education agencies use to describe the federal education disability called "emotional disturbance." State definitions were collected so that various aspects of them could be analyzed and compared with results of similar studies completed in the 1970s and 1980s. Among results are that state definitions have…

Wery, Jessica J.; Cullinan, Douglas

2013-01-01

450

Dirac electron states formed at the heterointerface between a topological insulator and a conventional semiconductor.  

PubMed

Topological insulators are a class of semiconductor exhibiting charge-gapped insulating behaviour in the bulk, but hosting a spin-polarized massless Dirac electron state at the surface. The presence of a topologically protected helical edge channel has been verified for the vacuum-facing surface of several topological insulators by means of angle-resolved photoemission spectroscopy and scanning tunnelling microscopy. By performing tunnelling spectroscopy on heterojunction devices composed of p-type topological insulator (Bi1?xSbx)2Te3 and n-type conventional semiconductor InP, we report the observation of such states at the solid-state interface. Under an applied magnetic field, we observe a resonance in the tunnelling conductance through the heterojunction due to the formation of Landau levels of two-dimensional Dirac electrons at the interface. Moreover, resonant tunnelling spectroscopy reveals a systematic dependence of the Fermi velocity and Dirac point energy on the composition x. The successful formation of robust non-trivial edge channels at a solid-state interface is an essential step towards functional junctions based on topological insulators. PMID:24553653

Yoshimi, R; Tsukazaki, A; Kikutake, K; Checkelsky, J G; Takahashi, K S; Kawasaki, M; Tokura, Y

2014-03-01

451

Topological phases: An expedition off lattice  

SciTech Connect

Highlights: > Models of topological phases where the lattice topology is a dynamical variable. > We discuss off-lattice hazards that destroy topological protection. > The Cheeger constant yields upper bound to the energy of excited states. > Baby universes meet condensed matter physics. > We study the graph Laplacian of loop gases and string nets on fluctuating lattices. - Abstract: Motivated by the goal to give the simplest possible microscopic foundation for a broad class of topological phases, we study quantum mechanical lattice models where the topology of the lattice is one of the dynamical variables. However, a fluctuating geometry can remove the separation between the system size and the range of local interactions, which is important for topological protection and ultimately the stability of a topological phase. In particular, it can open the door to a pathology, which has been studied in the context of quantum gravity and goes by the name of 'baby universe', here we discuss three distinct approaches to suppressing these pathological fluctuations. We complement this discussion by applying Cheeger's theory relating the geometry of manifolds to their vibrational modes to study the spectra of Hamiltonians. In particular, we present a detailed study of the statistical properties of loop gas and string net models on fluctuating lattices, both analytically and numerically.

Freedman, Michael H. [Microsoft Station Q, University of California, Santa Barbara, CA 93106 (United States); Gamper, Lukas [Theoretische Physik, ETH Zurich, 8093 Zurich (Switzerland); Gils, Charlotte [Theoretische Physik, ETH Zurich, 8093 Zurich (Switzerland); Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Ave, Toronto, ON M5G 1X5 (Canada); Isakov, Sergei V., E-mail: isakov@itp.phys.ethz.ch [Theoretische Physik, ETH Zurich, 8093 Zurich (Switzerland); Trebst, Simon [Microsoft Station Q, University of California, Santa Barbara, CA 93106 (United States); Troyer, Matthias [Theoretische Physik, ETH Zurich, 8093 Zurich (Switzerland)

2011-08-15

452

Polarization switching ability dependent on multidomain topology in a uniaxial organic ferroelectric.  

PubMed

The switching of electric polarization induced by electric fields, a fundamental functionality of ferroelectrics, is closely associated with the motions of the domain walls that separate regions with distinct polarization directions. Therefore, understanding domain-walls dynamics is of essential importance for advancing ferroelectric applications. In this Letter, we show that the topology of the multidomain structure can have an intrinsic impact on the degree of switchable polarization. Using a combination of polarization hysteresis measurements and piezoresponse force microscopy on a uniaxial organic ferroelectric, ?-6,6'-dimethyl-2,2'-bipyridinium chloranilate, we found that the head-to-head (or tail-to-tail) charged domain walls are strongly pinned and thus impede the switching process; in contrast, if the charged domain walls are replaced with electrically neutral antiparallel domain walls, bulk polarization switching is achieved. Our findings suggest that manipulation of the multidomain topology can potentially control the switchable polarization. PMID:24329117

Kagawa, Fumitaka; Horiuchi, Sachio; Minami, Nao; Ishibashi, Shoji; Kobayashi, Kensuke; Kumai, Reiji; Murakami, Youichi; Tokura, Yoshinori

2014-01-01

453

Measurement of the B+and B0 Lifetimes Using Topological Reconstruction of Inclusive and Semileptonic Decays  

Microsoft Academic Search

The lifetimes of B+ and B0 mesons are measured using a sample of 150 000 hadronic Z0 decays collected by the SLD experiment at the SLAC Linear Collider between 1993 and 1995. Two analyses are presented in which the decay length and charge of the B meson are reconstructed. The first method uses a novel topological vertexing technique while the

K. Abe; T. Akagi; N. J. Allen; W. W. Ash; D. Aston; K. G. Baird; C. Baltay; H. R. Band; M. B. Barakat; G. Baranko; O. Bardon; T. L. Barklow; G. L. Bashindzhagyan; A. O. Bazarko; R. Ben-David; A. C. Benvenuti; G. M. Bilei; D. Bisello; G. Blaylock; J. R. Bogart; B. Bolen; T. Bolton; G. R. Bower; J. E. Brau; M. Breidenbach; W. M. Bugg; D. Burke; T. H. Burnett; P. N. Burrows; W. Busza; A. Calcaterra; D. O. Caldwell; D. Calloway; B. Camanzi; M. Carpinelli; R. Cassell; R. Castaldi; A. Castro; M. Cavalli-Sforza; A. Chou; E. Church; H. O. Cohn; J. A. Coller; V. Cook; R. Cotton; R. F. Cowan; D. G. Coyne; G. Crawford; A. D'Oliveira; C. J. Damerell; M. Daoudi; R. de Sangro; R. dell'Orso; P. J. Dervan; M. Dima; D. N. Dong; P. Y. Du; R. Dubois; B. I. Eisenstein; R. Elia; E. Etzion; S. Fahey; D. Falciai; C. Fan; J. P. Fernandez; M. J. Fero; R. Frey; K. Furuno; T. Gillman; G. Gladding; S. Gonzalez; E. L. Hart; J. L. Harton; A. Hasan; Y. Hasegawa; K. Hasuko; S. J. Hedges; S. S. Hertzbach; M. D. Hildreth; J. Huber; M. E. Huffer; E. W. Hughes; H. Hwang; Y. Iwasaki; D. J. Jackson; P. Jacques; J. A. Jaros; A. S. Johnson; J. R. Johnson; R. A. Johnson; T. Junk; R. Kajikawa; M. Kalelkar; H. J. Kang; I. Karliner; H. Kawahara; H. W. Kendall; Y. D. Kim; M. E. King; R. King; R. R. Kofler; N. M. Krishna; R. S. Kroeger; J. F. Labs; M. Langston; A. Lath; J. A. Lauber; D. W. Leith; V. Lia; M. X. Liu; X. Liu; M. Loreti; A. Lu; H. L. Lynch; J. Ma; G. Mancinelli; S. Manly; G. Mantovani; T. W. Markiewicz; T. Maruyama; H. Masuda; E. Mazzucato; A. K. McKemey; B. T. Meadows; R. Messner; P. M. Mockett; K. C. Moffeit; T. B. Moore; D. Muller; T. Nagamine; S. Narita; U. Nauenberg; H. Neal; M. Nussbaum; Y. Ohnishi; L. S. Osborne; R. S. Panvini; C. H. Park; T. J. Pavel; I. Peruzzi; M. Piccolo; L. Piemontese; E. Pieroni; K. T. Pitts; R. J. Plano; R. Prepost; C. Y. Prescott; G. D. Punkar; J. Quigley; B. N. Ratcliff; T. W. Reeves; J. Reidy; P. L. Reinertsen; P. E. Rensing; L. S. Rochester; P. C. Rowson; J. J. Russell; O. H. Saxton; T. Schalk; R. H. Schindler; B. A. Schumm; S. Sen; V. V. Serbo; M. H. Shaevitz; J. T. Shank; G. Shapiro; D. J. Sherden; K. D. Shmakov; C. Simopoulos; N. B. Sinev; S. R. Smith; M. B. Smy; J. A. Snyder; P. Stamer; H. Steiner; R. Steiner; M. G. Strauss; D. Su; F. Suekane; A. Sugiyama; S. Suzuki; M. Swartz; A. Szumilo; T. Takahashi; F. E. Taylor; E. Torrence; A. I. Trandafir; J. D. Turk; T. Usher; J. Va'Vra; C. Vannini; E. Vella; J. P. Venuti; R. Verdier; P. G. Verdini; D. L. Wagner; S. R. Wagner; A. P. Waite; S. J. Watts; A. W. Weidemann; E. R. Weiss; J. S. Whitaker; S. L. White; F. J. Wickens; D. A. Williams; S. H. Williams; S. Willocq; R. J. Wilson; W. J. Wisniewski; M. Woods; G. B. Word; J. Wyss; R. K. Yamamoto; J. M. Yamartino; X. Yang; J. Yashima; S. J. Yellin; C. C. Young; H. Yuta; G. Zapalac; R. W. Zdarko; J. Zhou