Quantum picturalism for topological cluster-state computing
International Nuclear Information System (INIS)
Horsman, Clare
2011-01-01
Topological quantum computing (QC) is a way of allowing precise quantum computations to run on noisy and imperfect hardware. One implementation uses surface codes created by forming defects in a highly-entangled cluster state. Such a method of computing is a leading candidate for large-scale QC. However, there has been a lack of sufficiently powerful high-level languages to describe computing in this form without resorting to single-qubit operations, which quickly become prohibitively complex as the system size increases. In this paper, we apply the category-theoretic work of Abramsky and Coecke to the topological cluster-state model of QC to give a high-level graphical language that enables direct translation between quantum processes and physical patterns of measurement in a computer-a 'compiler language'. We give the equivalence between the graphical and topological information flows, and show the applicable rewrite algebra for this computing model. We show that this gives us a native graphical language for the design and analysis of topological quantum algorithms, and finish by discussing the possibilities for automating this process on a large scale.
Topological one-way quantum computation on verified logical cluster states
International Nuclear Information System (INIS)
Fujii, Keisuke; Yamamoto, Katsuji
2010-01-01
We present a scheme to improve the noise threshold for fault-tolerant topological one-way computation with constant overhead. Certain cluster states of finite size, say star clusters, are constructed with logical qubits through an efficient verification process to achieve high fidelity. Then, the star clusters are connected near-deterministically with verification to form a three-dimensional cluster state to implement topological one-way computation. The necessary postselection for verification is localized within the star clusters, ensuring the scalability of computation. By using the Steane seven-qubit code for the logical qubits, this scheme works with a high error rate of 2% and reasonable resources comparable to or less than those for the other fault-tolerant schemes. A higher noise threshold would be achieved by adopting a larger code.
Machine learning topological states
Deng, Dong-Ling; Li, Xiaopeng; Das Sarma, S.
2017-11-01
Artificial neural networks and machine learning have now reached a new era after several decades of improvement where applications are to explode in many fields of science, industry, and technology. Here, we use artificial neural networks to study an intriguing phenomenon in quantum physics—the topological phases of matter. We find that certain topological states, either symmetry-protected or with intrinsic topological order, can be represented with classical artificial neural networks. This is demonstrated by using three concrete spin systems, the one-dimensional (1D) symmetry-protected topological cluster state and the 2D and 3D toric code states with intrinsic topological orders. For all three cases, we show rigorously that the topological ground states can be represented by short-range neural networks in an exact and efficient fashion—the required number of hidden neurons is as small as the number of physical spins and the number of parameters scales only linearly with the system size. For the 2D toric-code model, we find that the proposed short-range neural networks can describe the excited states with Abelian anyons and their nontrivial mutual statistics as well. In addition, by using reinforcement learning we show that neural networks are capable of finding the topological ground states of nonintegrable Hamiltonians with strong interactions and studying their topological phase transitions. Our results demonstrate explicitly the exceptional power of neural networks in describing topological quantum states, and at the same time provide valuable guidance to machine learning of topological phases in generic lattice models.
Topological modeling and classification of mammographic microcalcification clusters.
Chen, Zhili; Strange, Harry; Oliver, Arnau; Denton, Erika R E; Boggis, Caroline; Zwiggelaar, Reyer
2015-04-01
The presence of microcalcification clusters is a primary sign of breast cancer; however, it is difficult and time consuming for radiologists to classify microcalcifications as malignant or benign. In this paper, a novel method for the classification of microcalcification clusters in mammograms is proposed. The topology/connectivity of individual microcalcifications is analyzed within a cluster using multiscale morphology. This is distinct from existing approaches that tend to concentrate on the morphology of individual microcalcifications and/or global (statistical) cluster features. A set of microcalcification graphs are generated to represent the topological structure of microcalcification clusters at different scales. Subsequently, graph theoretical features are extracted, which constitute the topological feature space for modeling and classifying microcalcification clusters. k-nearest-neighbors-based classifiers are employed for classifying microcalcification clusters. The validity of the proposed method is evaluated using two well-known digitized datasets (MIAS and DDSM) and a full-field digital dataset. High classification accuracies (up to 96%) and good ROC results (area under the ROC curve up to 0.96) are achieved. A full comparison with related publications is provided, which includes a direct comparison. The results indicate that the proposed approach is able to outperform the current state-of-the-art methods. Significance: This study shows that topology modeling is an important tool for microcalcification analysis not only because of the improved classification accuracy but also because the topological measures can be linked to clinical understanding.
Topological orders in rigid states
International Nuclear Information System (INIS)
Wen, X.G.
1990-01-01
The authors study a new kind of ordering topological order in rigid states (the states with no local gapless excitations). This paper concentrates on characterization of the different topological orders. As an example the authors discuss in detail chiral spin states of 2+1 dimensional spin systems. Chiral spin states are described by the topological Chern-Simons theories in the continuum limit. The authors show that the topological orders can be characterized by a non-Abelian gauge structure over the moduli space which parametrizes a family of the model Hamiltonians supporting topologically ordered ground states. In 2 + 1 dimensions, the non-Abelian gauge structure determines possible fractional statistics of the quasi-particle excitations over the topologically ordered ground states. The dynamics of the low lying global excitations is shown to be independent of random spatial dependent perturbations. The ground state degeneracy and the non-Abelian gauge structures discussed in this paper are very robust, even against those perturbations that break translation symmetry. The authors also discuss the symmetry properties of the degenerate ground states of chiral spin states. The authors find that some degenerate ground states of chiral spin states on torus carry non-trivial quantum numbers of the 90 degrees rotation
Complex brain networks: From topological communities to clustered ...
Indian Academy of Sciences (India)
Complex brain networks: From topological communities to clustered dynamics ... http://www.ias.ac.in/article/fulltext/pram/070/06/1087-1097 ... We find that this network of networks displays clustered synchronisation behaviour and the dynamical clusters closely coincide with the topological community structures observed in ...
Topological defect clustering and plastic deformation mechanisms in functionalized graphene
Nunes, Ricardo; Araujo, Joice; Chacham, Helio
2011-03-01
We present ab initio results suggesting that strain plays a central role in the clustering of topological defects in strained and functionalized graphene models. We apply strain onto the topological-defect graphene networks from our previous work, and obtain topological-defect clustering patterns which are in excellent agreement with recent observations in samples of reduced graphene oxide. In our models, the graphene layer, containing an initial concentration of isolated topological defects, is covered by hydrogen or hydroxyl groups. Our results also suggest a rich variety of plastic deformation mechanism in functionalized graphene systems. We acknowledge support from the Brazilian agencies: CNPq, Fapemig, and INCT-Materiais de Carbono.
Parallel Genetic Algorithms with Dynamic Topology using Cluster Computing
Directory of Open Access Journals (Sweden)
ADAR, N.
2016-08-01
Full Text Available A parallel genetic algorithm (PGA conducts a distributed meta-heuristic search by employing genetic algorithms on more than one subpopulation simultaneously. PGAs migrate a number of individuals between subpopulations over generations. The layout that facilitates the interactions of the subpopulations is called the topology. Static migration topologies have been widely incorporated into PGAs. In this article, a PGA with a dynamic migration topology (D-PGA is proposed. D-PGA generates a new migration topology in every epoch based on the average fitness values of the subpopulations. The D-PGA has been tested against ring and fully connected migration topologies in a Beowulf Cluster. The D-PGA has outperformed the ring migration topology with comparable communication cost and has provided competitive or better results than a fully connected migration topology with significantly lower communication cost. PGA convergence behaviors have been analyzed in terms of the diversities within and between subpopulations. Conventional diversity can be considered as the diversity within a subpopulation. A new concept of permeability has been introduced to measure the diversity between subpopulations. It is shown that the success of the proposed D-PGA can be attributed to maintaining a high level of permeability while preserving diversity within subpopulations.
New topologies in pentanuclear nickel/oximato clusters: structural and magnetic characterization.
Esteban, Jordi; Font-Bardia, Mercè; Costa, José Sánchez; Teat, Simon J; Escuer, Albert
2014-03-17
In the present work, five new Ni5 clusters employing the versatile 2-pyridylcyanoxime ligand have been synthesized and chemically, structurally, and magnetically characterized. The crystallographic examination of these Ni5 clusters together with those already published in the literature, giving a total number of 14 complexes, exhibiting up to 8 different topologies for which the relationship between topology, reaction conditions and magnetic response has been analyzed. DC magnetic measurements were carried in the 300-2 K range for the new complexes and the analysis of the experimental data revealed an antiferromagnetic response for the oximato mediated interactions with a variety of ground states (S = 0, 1, 3) as function of the cluster topology.
Classical topology and quantum states
Indian Academy of Sciences (India)
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 - and ∞ - structures) can be reconstructed using Gel'fand–Naimark theory and ...
Composition and topology of activity cliff clusters formed by bioactive compounds.
Stumpfe, Dagmar; Dimova, Dilyana; Bajorath, Jürgen
2014-02-24
The assessment of activity cliffs has thus far mostly focused on compound pairs, although the majority of activity cliffs are not formed in isolation but in a coordinated manner involving multiple active compounds and cliffs. However, the composition of coordinated activity cliff configurations and their topologies are unknown. Therefore, we have identified all activity cliff configurations formed by currently available bioactive compounds and analyzed them in network representations where activity cliff configurations occur as clusters. The composition, topology, frequency of occurrence, and target distribution of activity cliff clusters have been determined. A limited number of large cliff clusters with unique topologies were identified that were centers of activity cliff formation. These clusters originated from a small number of target sets. However, most clusters were of small to moderate size. Three basic topologies were sufficient to describe recurrent activity cliff cluster motifs/topologies. For example, frequently occurring clusters with star topology determined the scale-free character of the global activity cliff network and represented a characteristic activity cliff configuration. Large clusters with complex topology were often found to contain different combinations of basic topologies. Our study provides a first view of activity cliff configurations formed by currently available bioactive compounds and of the recurrent topologies of activity cliff clusters. Activity cliff clusters of defined topology can be selected, and from compounds forming the clusters, SAR information can be obtained. The SAR information of activity cliff clusters sharing a/one specific activity and topology can be compared.
PEPS as ground states: Degeneracy and topology
Schuch, Norbert; Cirac, Ignacio; Pérez-García, David
2010-10-01
We introduce a framework for characterizing Matrix Product States (MPS) and Projected Entangled Pair States (PEPS) in terms of symmetries. This allows us to understand how PEPS appear as ground states of local Hamiltonians with finitely degenerate ground states and to characterize the ground state subspace. Subsequently, we apply our framework to show how the topological properties of these ground states can be explained solely from the symmetry: We prove that ground states are locally indistinguishable and can be transformed into each other by acting on a restricted region, we explain the origin of the topological entropy, and we discuss how to renormalize these states based on their symmetries. Finally, we show how the anyonic character of excitations can be understood as a consequence of the underlying symmetries.
Topological states on the gold surface.
Yan, Binghai; Stadtmüller, Benjamin; Haag, Norman; Jakobs, Sebastian; Seidel, Johannes; Jungkenn, Dominik; Mathias, Stefan; Cinchetti, Mirko; Aeschlimann, Martin; Felser, Claudia
2015-12-14
Gold surfaces host special electronic states that have been understood as a prototype of Shockley surface states. These surface states are commonly employed to benchmark the capability of angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling spectroscopy. Here we show that these Shockley surface states can be reinterpreted as topologically derived surface states (TDSSs) of a topological insulator (TI), a recently discovered quantum state. Based on band structure calculations, the Z2-type invariants of gold can be well-defined to characterize a TI. Further, our ARPES measurement validates TDSSs by detecting the dispersion of unoccupied surface states. The same TDSSs are also recognized on surfaces of other well-known noble metals (for example, silver, copper, platinum and palladium), which shines a new light on these long-known surface states.
Protection of surface states in topological nanoparticles
Siroki, Gleb; Haynes, Peter D.; Lee, Derek K. K.; Giannini, Vincenzo
2017-07-01
Topological insulators host protected electronic states at their surface. These states show little sensitivity to disorder. For miniaturization one wants to exploit their robustness at the smallest sizes possible. This is also beneficial for optical applications and catalysis, which favor large surface-to-volume ratios. However, it is not known whether discrete states in particles share the protection of their continuous counterparts in large crystals. Here we study the protection of the states hosted by topological insulator nanoparticles. Using both analytical and tight-binding simulations, we show that the states benefit from the same level of protection as those on a planar surface. The results hold for many shapes and sustain surface roughness which may be useful in photonics, spectroscopy, and chemistry. They complement past studies of large crystals—at the other end of possible length scales. The protection of the nanoparticles suggests that samples of all intermediate sizes also possess protected states.
Analyzing Dynamic Probabilistic Risk Assessment Data through Topology-Based Clustering
Energy Technology Data Exchange (ETDEWEB)
Diego Mandelli; Dan Maljovec; BeiWang; Valerio Pascucci; Peer-Timo Bremer
2013-09-01
We investigate the use of a topology-based clustering technique on the data generated by dynamic event tree methodologies. The clustering technique we utilizes focuses on a domain-partitioning algorithm based on topological structures known as the Morse-Smale complex, which partitions the data points into clusters based on their uniform gradient flow behavior. We perform both end state analysis and transient analysis to classify the set of nuclear scenarios. We demonstrate our methodology on a dataset generated for a sodium-cooled fast reactor during an aircraft crash scenario. The simulation tracks the temperature of the reactor as well as the time for a recovery team to fix the passive cooling system. Combined with clustering results obtained previously through mean shift methodology, we present the user with complementary views of the data that help illuminate key features that may be otherwise hidden using a single methodology. By clustering the data, the number of relevant test cases to be selected for further analysis can be drastically reduced by selecting a representative from each cluster. Identifying the similarities of simulations within a cluster can also aid in the drawing of important conclusions with respect to safety analysis.
International Nuclear Information System (INIS)
Motoba, Toshio
1982-01-01
The lightest (p, n, Λ) closed-shell hypernucleus sub(ΛΛ) sup(6)He can be considered as a most likely candidate for the unit of hypernuclear cluster structure. First the internal structure of lambpha, α sub(Λ) = sub(ΛΛ) sup(6)He, is investigated by solving the α + Λ + Λ three-body problem microscopically. The compact h. o. wave function (0 s) 6 is found to be a good description for α sub(Λ). Secondly, by using the fully microscopic GCM, we have demonstrated that di - α sub(Λ) cluster states constitute a characteristic rotational band of J = 0 + -- 6 + . The E2 transition rate from particle - stable 2 + to 0 + states is predicted to be 2 - order faster than the weak decay rate of this system. (author)
Fermionic topological quantum states as tensor networks
Wille, C.; Buerschaper, O.; Eisert, J.
2017-06-01
Tensor network states, and in particular projected entangled pair states, play an important role in the description of strongly correlated quantum lattice systems. They do not only serve as variational states in numerical simulation methods, but also provide a framework for classifying phases of quantum matter and capture notions of topological order in a stringent and rigorous language. The rapid development in this field for spin models and bosonic systems has not yet been mirrored by an analogous development for fermionic models. In this work, we introduce a tensor network formalism capable of capturing notions of topological order for quantum systems with fermionic components. At the heart of the formalism are axioms of fermionic matrix-product operator injectivity, stable under concatenation. Building upon that, we formulate a Grassmann number tensor network ansatz for the ground state of fermionic twisted quantum double models. A specific focus is put on the paradigmatic example of the fermionic toric code. This work shows that the program of describing topologically ordered systems using tensor networks carries over to fermionic models.
Topological surface states scattering in antimony
Narayan, Awadhesh
2012-11-05
In this work we study the topologically protected states of the Sb(111) surface by using ab initio transport theory. In the presence of a strong surface perturbation we obtain standing-wave states resulting from the superposition of spin-polarized surface states. By Fourier analysis, we identify the underlying two dimensional scattering processes and the spin texture. We find evidence of resonant transmission across surface barriers at quantum well state energies and evaluate their lifetimes. Our results are in excellent agreement with experimental findings. We also show that despite the presence of a step edge along a different high-symmetry direction, the surface states exhibit unperturbed transmission around the Fermi energy for states with near to normal incidence. © 2012 American Physical Society.
Clustering of resting state networks.
Directory of Open Access Journals (Sweden)
Megan H Lee
Full Text Available The goal of the study was to demonstrate a hierarchical structure of resting state activity in the healthy brain using a data-driven clustering algorithm.The fuzzy-c-means clustering algorithm was applied to resting state fMRI data in cortical and subcortical gray matter from two groups acquired separately, one of 17 healthy individuals and the second of 21 healthy individuals. Different numbers of clusters and different starting conditions were used. A cluster dispersion measure determined the optimal numbers of clusters. An inner product metric provided a measure of similarity between different clusters. The two cluster result found the task-negative and task-positive systems. The cluster dispersion measure was minimized with seven and eleven clusters. Each of the clusters in the seven and eleven cluster result was associated with either the task-negative or task-positive system. Applying the algorithm to find seven clusters recovered previously described resting state networks, including the default mode network, frontoparietal control network, ventral and dorsal attention networks, somatomotor, visual, and language networks. The language and ventral attention networks had significant subcortical involvement. This parcellation was consistently found in a large majority of algorithm runs under different conditions and was robust to different methods of initialization.The clustering of resting state activity using different optimal numbers of clusters identified resting state networks comparable to previously obtained results. This work reinforces the observation that resting state networks are hierarchically organized.
Clustering of resting state networks.
Lee, Megan H; Hacker, Carl D; Snyder, Abraham Z; Corbetta, Maurizio; Zhang, Dongyang; Leuthardt, Eric C; Shimony, Joshua S
2012-01-01
The goal of the study was to demonstrate a hierarchical structure of resting state activity in the healthy brain using a data-driven clustering algorithm. The fuzzy-c-means clustering algorithm was applied to resting state fMRI data in cortical and subcortical gray matter from two groups acquired separately, one of 17 healthy individuals and the second of 21 healthy individuals. Different numbers of clusters and different starting conditions were used. A cluster dispersion measure determined the optimal numbers of clusters. An inner product metric provided a measure of similarity between different clusters. The two cluster result found the task-negative and task-positive systems. The cluster dispersion measure was minimized with seven and eleven clusters. Each of the clusters in the seven and eleven cluster result was associated with either the task-negative or task-positive system. Applying the algorithm to find seven clusters recovered previously described resting state networks, including the default mode network, frontoparietal control network, ventral and dorsal attention networks, somatomotor, visual, and language networks. The language and ventral attention networks had significant subcortical involvement. This parcellation was consistently found in a large majority of algorithm runs under different conditions and was robust to different methods of initialization. The clustering of resting state activity using different optimal numbers of clusters identified resting state networks comparable to previously obtained results. This work reinforces the observation that resting state networks are hierarchically organized.
Self-Organized Topological State with Majorana Fermions
Vazifeh, M. M.; Franz, M.
2013-11-01
Most physical systems known to date tend to resist entering the topological phase and must be fine-tuned to reach that phase. Here, we introduce a system in which a key dynamical parameter adjusts itself in response to the changing external conditions so that the ground state naturally favors the topological phase. The system consists of a quantum wire formed of individual magnetic atoms placed on the surface of an ordinary s-wave superconductor. It realizes the Kitaev paradigm of topological superconductivity when the wave vector characterizing the emergent spin helix dynamically self-tunes to support the topological phase. We call this phenomenon a self-organized topological state.
Topological Surface States in Dense Solid Hydrogen.
Naumov, Ivan I; Hemley, Russell J
2016-11-11
Metallization of dense hydrogen and associated possible high-temperature superconductivity represents one of the key problems of physics. Recent theoretical studies indicate that before becoming a good metal, compressed solid hydrogen passes through a semimetallic stage. We show that such semimetallic phases predicted to be the most stable at multimegabar (∼300 GPa) pressures are not conventional semimetals: they exhibit topological metallic surface states inside the bulk "direct" gap in the two-dimensional surface Brillouin zone; that is, metallic surfaces may appear even when the bulk of the material remains insulating. Examples include hydrogen in the Cmca-12 and Cmca-4 structures; Pbcn hydrogen also has metallic surface states but they are of a nontopological nature. The results provide predictions for future measurements, including probes of possible surface superconductivity in dense hydrogen.
Symmetric Topological Phases and Tensor Network States
Jiang, Shenghan
Classification and simulation of quantum phases are one of main themes in condensed matter physics. Quantum phases can be distinguished by their symmetrical and topological properties. The interplay between symmetry and topology in condensed matter physics often leads to exotic quantum phases and rich phase diagrams. Famous examples include quantum Hall phases, spin liquids and topological insulators. In this thesis, I present our works toward a more systematically understanding of symmetric topological quantum phases in bosonic systems. In the absence of global symmetries, gapped quantum phases are characterized by topological orders. Topological orders in 2+1D are well studied, while a systematically understanding of topological orders in 3+1D is still lacking. By studying a family of exact solvable models, we find at least some topological orders in 3+1D can be distinguished by braiding phases of loop excitations. In the presence of both global symmetries and topological orders, the interplay between them leads to new phases termed as symmetry enriched topological (SET) phases. We develop a framework to classify a large class of SET phases using tensor networks. For each tensor class, we can write down generic variational wavefunctions. We apply our method to study gapped spin liquids on the kagome lattice, which can be viewed as SET phases of on-site symmetries as well as lattice symmetries. In the absence of topological order, symmetry could protect different topological phases, which are often referred to as symmetry protected topological (SPT) phases. We present systematic constructions of tensor network wavefunctions for bosonic symmetry protected topological (SPT) phases respecting both onsite and spatial symmetries.
Topological edge states for disordered bosonic systems
Peano, Vittorio; Schulz-Baldes, Hermann
2018-03-01
Quadratic bosonic Hamiltonians over a one-particle Hilbert space can be described by a Bogoliubov-de Gennes (BdG) Hamiltonian on a particle-hole Hilbert space. In general, the BdG Hamiltonian is not self-adjoint, but only J-self-adjoint on the particle-hole space viewed as a Krein space. Nevertheless, its energy bands can have non-trivial topological invariants like Chern numbers or winding numbers. By a thorough analysis for tight-binding models, it is proved that these invariants lead to bosonic edge modes which are robust to a large class of possibly disordered perturbations. Furthermore, general scenarios are presented for these edge states to be dynamically unstable even though the bulk modes are stable.
Topology in quantum states. PEPS formalism and beyond
Energy Technology Data Exchange (ETDEWEB)
Aguado, M [Max-Planck-Institut fuer Quantenoptik. Hans-Kopfermann-Str. 1. D-85748 Garching (Germany); Cirac, J I [Max-Planck-Institut fuer Quantenoptik. Hans-Kopfermann-Str. 1. D-85748 Garching (Germany); Vidal, G [School of Physical Sciences. University of Queensland, Brisbane, QLD, 4072 (Australia)
2007-11-15
Topology has been proposed as a tool to protect quantum information encoding and processes. Work concerning the meaning of topology in quantum states as well as its characterisation in the projected entangled pair state (PEPS) formalism and related schemes is reviewed.
Topological entanglement entropy, ground state degeneracy and holography
Energy Technology Data Exchange (ETDEWEB)
Parnachev, Andrei [School of Mathematics, Trinity College,Dublin 2 (Ireland); Institute Lorentz for Theoretical Physics, Leiden University,P.O. Box 9506, Leiden 2300RA (Netherlands); Poovuttikul, Napat [Institute Lorentz for Theoretical Physics, Leiden University,P.O. Box 9506, Leiden 2300RA (Netherlands)
2015-10-14
Topological entanglement entropy, a measure of the long-ranged entanglement, is related to the degeneracy of the ground state on a higher genus surface. The exact relation depends on the details of the topological theory. We consider a class of holographic models where such relation might be similar to the one exhibited by Chern-Simons theory in a certain large N limit. Both the non-vanishing topological entanglement entropy and the ground state degeneracy in these holographic models are consequences of the topological Gauss-Bonnet term in the dual gravitational description. A soft wall holographic model of confinement is used to generate finite correlation length but keep the disk topology of the entangling surface in the bulk, necessary for nonvanishing topological entanglement entropy.
Topological Nematic States and Non-Abelian Lattice Dislocations
Directory of Open Access Journals (Sweden)
Maissam Barkeshli
2012-08-01
Full Text Available An exciting new prospect in condensed matter physics is the possibility of realizing fractional quantum Hall states in simple lattice models without a large external magnetic field. A fundamental question is whether qualitatively new states can be realized on the lattice as compared with ordinary fractional quantum Hall states. Here we propose new symmetry-enriched topological states, topological nematic states, which are a dramatic consequence of the interplay between the lattice translational symmetry and topological properties of these fractional Chern insulators. The topological nematic states are realized in a partially filled flat band with a Chern number N, which can be mapped to an N-layer quantum Hall system on a regular lattice. However, in the topological nematic states the lattice dislocations can act as wormholes connecting the different layers and effectively change the topology of the space. Consequently, lattice dislocations become defects with a nontrivial quantum dimension, even when the fractional quantum Hall state being realized is, by itself, Abelian. Our proposal leads to the possibility of realizing the physics of topologically ordered states on high-genus surfaces in the lab even though the sample has only the disk geometry.
Symmetric-gapped surface states of fractional topological insulators
Cho, Gil Young; Teo, Jeffrey C. Y.; Fradkin, Eduardo
2017-10-01
We construct the symmetric-gapped surface states of a fractional topological insulator with an electromagnetic θ angle θem=π/3 and a discrete Z3 gauge field. They are the proper generalizations of the T-Pfaffian state and Pfaffian/antisemion state and feature an extended periodicity compared with their "integer" topological band insulator counterparts. We demonstrate that the surface states have the correct anomalies associated with time-reversal symmetry and charge conservation.
Chen, Qing; Zhang, Jinxiu; Hu, Ze
2017-02-23
This article investigates the dynamic topology control problemof satellite cluster networks (SCNs) in Earth observation (EO) missions by applying a novel metric of stability for inter-satellite links (ISLs). The properties of the periodicity and predictability of satellites' relative position are involved in the link cost metric which is to give a selection criterion for choosing the most reliable data routing paths. Also, a cooperative work model with reliability is proposed for the situation of emergency EO missions. Based on the link cost metric and the proposed reliability model, a reliability assurance topology control algorithm and its corresponding dynamic topology control (RAT) strategy are established to maximize the stability of data transmission in the SCNs. The SCNs scenario is tested through some numeric simulations of the topology stability of average topology lifetime and average packet loss rate. Simulation results show that the proposed reliable strategy applied in SCNs significantly improves the data transmission performance and prolongs the average topology lifetime.
Topological surface states on Bi$_{1-x}$Sb$_x$
DEFF Research Database (Denmark)
Zhu, Xie-Gang; Hofmann, Philip
2014-01-01
Topological insulators support metallic surface states whose existence is protected by the bulk band structure. It has been predicted early that the topology of the surface state Fermi contour should depend on several factors, such as the surface orientation and termination and this raises...... the question to what degree a given surface state is protected by the bulk electronic structure upon structural changes. Using tight-binding calculations, we explore this question for the prototypical topological insulator Bi$_{1-x}$Sb$_x$, studying different terminations of the (111) and (110) surfaces. We...
State space Newton's method for topology optimization
DEFF Research Database (Denmark)
Evgrafov, Anton
2014-01-01
We introduce a new algorithm for solving certain classes of topology optimization problems, which enjoys fast local convergence normally achieved by the full space methods while working in a smaller reduced space. The computational complexity of Newton’s direction finding subproblem in the algori......We introduce a new algorithm for solving certain classes of topology optimization problems, which enjoys fast local convergence normally achieved by the full space methods while working in a smaller reduced space. The computational complexity of Newton’s direction finding subproblem...
Complex brain networks: From topological communities to clustered ...
Indian Academy of Sciences (India)
Abstract. Recent research has revealed a rich and complicated network topology in the cortical connectivity of mammalian brains. A challenging task is to understand the implications of such network structures on the functional organisation of the brain activ- ities. We investigate synchronisation dynamics on the ...
Parafermionic wires at the interface of chiral topological states
Santos, Luiz; Hughes, Taylor
We discuss a scenario where local interactions form one-dimensional gapped interfaces between a pair of distinct chiral two-dimensional topological states such that each gapped region terminates at a domain wall separating the chiral gapless edge states of these phases. We show that this type of T-junction supports point-like fractionalized excitations obeying parafermion statistics, thus implying that the one-dimensional gapped interface forms an effective topological parafermionic wire possessing a non-trivial ground state degeneracy. The physical properties of the anyon condensate that gives rise to the gapped interface are investigated. Remarkably, this condensate causes the gapped interface to behave as a type of anyon ``Andreev reflector'' in the bulk, whereby anyons from one phase, upon hitting the interface, can be transformed into a combination of reflected anyons and outgoing anyons from the other phase. Thus, we conclude that while different topological orders can be connected via gapped interfaces, the interfaces are themselves topological.
Topological edge states of distorted photonic Kagome lattices
Ni, Xiang; Alu, Andrea; Khanikaev, Alexander B.
2017-08-01
We demonstrate that the distorted Kagome lattice formed by two-dimensional(2d) array of dielectric rods embedded in air exhibits a new class of topological states characterized by a topological invariant number in Pauli vector space. The Kagome lattice can be considered as a 2d analogue of the Su-Schrieffer-Heeger (SSH) model, which displays a phase transition by detuning the relative amplitudes of the inter-cell and intra-cell hopping terms. The phase transition is accompanied by the opening of a complete band gap in the Brillouin zone, which may host topological edge states on either the truncated end of the lattice or at the domain walls between topological nontrivial and trivial domains. To further reveal the connection between the bulk invariance and edge states, polarizations of shrunken and expanded effects are calculated. Our first-principles simulations based on finite element method (FEM) are used to design the lattice and confirm the analytic prediction.
A Cluster-Based Dual-Adaptive Topology Control Approach in Wireless Sensor Networks
Gui, Jinsong; Zhou, Kai; Xiong, Naixue
2016-01-01
Multi-Input Multi-Output (MIMO) can improve wireless network performance. Sensors are usually single-antenna devices due to the high hardware complexity and cost, so several sensors are used to form virtual MIMO array, which is a desirable approach to efficiently take advantage of MIMO gains. Also, in large Wireless Sensor Networks (WSNs), clustering can improve the network scalability, which is an effective topology control approach. The existing virtual MIMO-based clustering schemes do not either fully explore the benefits of MIMO or adaptively determine the clustering ranges. Also, clustering mechanism needs to be further improved to enhance the cluster structure life. In this paper, we propose an improved clustering scheme for virtual MIMO-based topology construction (ICV-MIMO), which can determine adaptively not only the inter-cluster transmission modes but also the clustering ranges. Through the rational division of cluster head function and the optimization of cluster head selection criteria and information exchange process, the ICV-MIMO scheme effectively reduces the network energy consumption and improves the lifetime of the cluster structure when compared with the existing typical virtual MIMO-based scheme. Moreover, the message overhead and time complexity are still in the same order of magnitude. PMID:27681731
Cyclic and Coherent States in Flocks with Topological Distance
Directory of Open Access Journals (Sweden)
Biplab eBhattacherjee
2014-01-01
Full Text Available A simple model of the two dimensional collective motion of a group of mobile agents have been studied. Like birds, these agents travel in open free space where each of them interacts with the first $n$ neighbors determined by the topological distance with a free boundary condition. Using the same prescription for interactions used in the Vicsek model with scalar noise it has been observed that the flock, in absence of the noise, arrives at a number of interesting stationary states. One of the two most prominent states is the `single sink state' where the entire flock travels along the same direction maintaining perfect cohesion and coherence. The other state is the `cyclic state' where every individual agent executes a uniform circular motion, and the correlation among the agents guarantees that the entire flock executes a pulsating dynamics i.e., expands and contracts periodically between a minimum and a maximum size of the flock. We have studied another limiting situation when refreshing rate of the interaction zone is the fastest. In this case the entire flock gets fragmented into smaller clusters of different sizes. On introduction of scalar noise a crossover is observed when the agents cross over from a ballistic motion to a diffusive motion. Expectedly the crossover time is dependent on the strength of the noise $eta$ and diverges as $eta to 0$. An even more simpler version of this model has been studied by suppressing the translational degrees of freedom of the agents but retaining their angular motion. Here agents are the spins, placed at the sites of a square lattice with periodic boundary condition. Every spin interacts with its $n$ = 2, 3 or 4 nearest neighbors. In the stationary state the entire spin pattern moves as a whole when interactions are anisotropic with $n$ = 2 and 3; but it is completely frozen when the interaction is isotropic with $n=4$. These spin configu
Hocking, John G
1988-01-01
""As textbook and reference work, this is a valuable addition to the topological literature."" - Mathematical ReviewsDesigned as a text for a one-year first course in topology, this authoritative volume offers an excellent general treatment of the main ideas of topology. It includes a large number and variety of topics from classical topology as well as newer areas of research activity.There are four set-theoretic chapters, followed by four primarily algebraic chapters. Chapter I covers the fundamentals of topological and metrical spaces, mappings, compactness, product spaces, the Tychonoff t
Quantum Entanglement and the Topological Order of Fractional Hall States
Rezayi, Edward
2015-03-01
Fractional quantum Hall states or, more generally, topological phases of matter defy Landau classification based on order parameter and broken symmetry. Instead they have been characterized by their topological order. Quantum information concepts, such as quantum entanglement, appear to provide the most efficient method of detecting topological order solely from the knowledge of the ground state wave function. This talk will focus on real-space bi-partitioning of quantum Hall states and will present both exact diagonalization and quantum Monte Carlo studies of topological entanglement entropy in various geometries. Results on the torus for non-contractible cuts are quite rich and, through the use of minimum entropy states, yield the modular S-matrix and hence uniquely determine the topological order, as shown in recent literature. Concrete examples of minimum entropy states from known quantum Hall wave functions and their corresponding quantum numbers, used in exact diagonalizations, will be given. In collaboration with Clare Abreu and Raul Herrera. Supported by DOE Grant DE-SC0002140.
Zhang, Qianfan
2012-03-27
Topological insulator is a new state of matter attracting tremendous interest due to its gapless linear dispersion and spin momentum locking topological states located near the surface. Heterostructures, which have traditionally been powerful in controlling the electronic properties of semiconductor devices, are interesting for topological insulators. Here, we studied the spatial distribution of the topological state in Sb 2Se 3-Bi 2Se 3 heterostructures by first-principle simulation and discovered that an exotic topological state exists. Surprisingly, the state migrates from the nontrivial Bi 2Se 3 into the trivial Sb 2Se 3 region and spreads across the entire Sb 2Se 3 slab, extending beyond the concept of "surface" state while preserving all of the topological surface state characteristics. This unusual topological state arises from the coupling between different materials and the modification of electronic structure near Fermi energy. Our study demonstrates that heterostructures can open up opportunities for controlling the real-space distribution of the topological state and inducing quantum phase transitions between topologically trivial and nontrivial states. © 2012 American Chemical Society.
Duo gating on a 3D topological insulator - independent tuning of both topological surface states
Li, Chuan; de Ronde, Bob; Snelder, Marieke; Stehno, Martin; Huang, Yingkai; Golden, Mark; Brinkman, Alexander; ICE Team; IOP Collaboration
ABSTRACT: Topological insulators are associated with a trove of exciting physics, such as the ability to host robust anyons, Majorana Bound States, which can be used for quantum computation. For future Majorana devices it is desirable to have the Fermi energy tuned as close as possible to the Dirac point of the topological surface state. Based on previous work on gating BSTS, we report the experimental progress towards gate-tuning of the top and bottom topological surface states of BiSbTeSe2 crystal flakes. When the Fermi level is moved across the Dirac point conduction is shown to change from electron dominated transport to hole dominated transport independently for either surface. In the high magnetic field, one can tune the system precisely between the different landau levels of both surfaces, thus a full gating map of the possible landau levels combination is established. In addition, we provide a simple capacitance model to explain the general hysteresis behaviors in topological insulator systems.
Kuratowski, Kazimierz
1968-01-01
Topology, Volume II deals with topology and covers topics ranging from compact spaces and connected spaces to locally connected spaces, retracts, and neighborhood retracts. Group theory and some cutting problems are also discussed, along with the topology of the plane. Comprised of seven chapters, this volume begins with a discussion on the compactness of a topological space, paying particular attention to Borel, Lebesgue, Riesz, Cantor, and Bolzano-Weierstrass conditions. Semi-continuity and topics in dimension theory are also considered. The reader is then introduced to the connecte
Topological Edge States in Periodically Driven Trapped-Ion Chains
Nevado, Pedro; Fernández-Lorenzo, Samuel; Porras, Diego
2017-11-01
Topological insulating phases are primarily associated with condensed-matter systems, which typically feature short-range interactions. Nevertheless, many realizations of quantum matter can exhibit long-range interactions, and it is still largely unknown the effect that these latter may exert upon the topological phases. In this Letter, we investigate the Su-Schrieffer-Heeger topological insulator in the presence of long-range interactions. We show that this model can be readily realized in quantum simulators with trapped ions by means of a periodic driving. Our results indicate that the localization of the associated edge states is enhanced by the long-range interactions, and that the localized components survive within the ground state of the model. These effects could be easily confirmed in current state-of-the-art experimental implementations.
Harmston, Nathan; Ing-Simmons, Elizabeth; Tan, Ge; Perry, Malcolm; Merkenschlager, Matthias; Lenhard, Boris
2017-09-05
Developmental genes in metazoan genomes are surrounded by dense clusters of conserved noncoding elements (CNEs). CNEs exhibit unexplained extreme levels of sequence conservation, with many acting as developmental long-range enhancers. Clusters of CNEs define the span of regulatory inputs for many important developmental regulators and have been described previously as genomic regulatory blocks (GRBs). Their function and distribution around important regulatory genes raises the question of how they relate to 3D conformation of these loci. Here, we show that clusters of CNEs strongly coincide with topological organisation, predicting the boundaries of hundreds of topologically associating domains (TADs) in human and Drosophila. The set of TADs that are associated with high levels of noncoding conservation exhibit distinct properties compared to TADs devoid of extreme noncoding conservation. The close correspondence between extreme noncoding conservation and TADs suggests that these TADs are ancient, revealing a regulatory architecture conserved over hundreds of millions of years.Metazoan genomes contain many clusters of conserved noncoding elements. Here, the authors provide evidence that these clusters coincide with distinct topologically associating domains in humans and Drosophila, revealing a conserved regulatory genomic architecture.
Aramberri, H.; Muñoz, M. C.
2017-05-01
We investigate the effects of strain on the topological order of the Bi2Se3 family of topological insulators by ab initio first-principles methods. Strain can induce a topological phase transition and we present the phase diagram for the 3D topological insulators, Bi2Te3 , Sb2Te3 , Bi2Se3 , and Sb2Se3 , under combined uniaxial and biaxial strain. Their phase diagram is universal and shows metallic and insulating phases, both topologically trivial and nontrivial. In particular, uniaxial tension can drive the four compounds into a topologically trivial insulating phase. We propose a Sb2Te3/Bi2Te3 heterojunction in which a strain-induced topological interface state arises in the common gap of this normal insulator-topological insulator heterojunction. Unexpectedly, the interface state is confined in the topologically trivial subsystem and is physically protected from ambient impurities. It can be switched on or off by means of uniaxial strain and therefore Sb2Te3 /Bi2Te3 heterojunctions provide a topological system which hosts tunable robust helical interface states with promising spintronic applications.
DEFF Research Database (Denmark)
Kirstein, Jonas Kjeld; Albrechtsen, Hans-Jørgen; Rygaard, Martin
2015-01-01
identification of potential contamination and affected consumers in contamination cases. Although still in development, the method shows potential for assisting utilities during planning of monitoring programs and as decision support tool during emergency contingency situations.......Topological clustering was explored as a tool for water supply utilities in preparation of monitoring and contamination contingency plans. A complex water distribution network model of Copenhagen, Denmark, was simplified by topological clustering into recognizable water movement patterns to: (1......) identify steady clusters for a part of the network where an actual contamination has occurred; (2) analyze this event by the use of mesh diagrams; and (3) analyze the use of mesh diagrams as a decision support tool for planning water quality monitoring. Initially, the network model was divided...
Optical conductivity of topological surface states with emergent supersymmetry
Maciejko, Joseph; Witczak-Krempa, William
Topological states of electrons present new avenues to explore the rich phenomenology of corre- lated quantum matter. Topological insulators (TIs) in particular offer an experimental setting to study novel quantum critical points (QCPs) of massless Dirac fermions, which exist on the sample's surface. Here, we obtain exact results for the zero- and finite-temperature optical conductivity at the semimetal-superconductor QCP for these topological surface states. This strongly interacting QCP is described by a scale invariant theory with emergent supersymmetry, which is a unique symmetry mixing bosons and fermions. We show that supersymmetry implies exact relations between the op- tical conductivity and two otherwise unrelated properties: the shear viscosity and the entanglement entropy. We discuss experimental considerations for the observation of these signatures in TIs. This work was supported by NSERC, CRC, CIFAR, and the University of Alberta.
Directory of Open Access Journals (Sweden)
Qing Chen
2017-02-01
Full Text Available This article investigates the dynamic topology control problemof satellite cluster networks (SCNs in Earth observation (EO missions by applying a novel metric of stability for inter-satellite links (ISLs. The properties of the periodicity and predictability of satellites’ relative position are involved in the link cost metric which is to give a selection criterion for choosing the most reliable data routing paths. Also, a cooperative work model with reliability is proposed for the situation of emergency EO missions. Based on the link cost metric and the proposed reliability model, a reliability assurance topology control algorithm and its corresponding dynamic topology control (RAT strategy are established to maximize the stability of data transmission in the SCNs. The SCNs scenario is tested through some numeric simulations of the topology stability of average topology lifetime and average packet loss rate. Simulation results show that the proposed reliable strategy applied in SCNs significantly improves the data transmission performance and prolongs the average topology lifetime.
Chiral projected entangled-pair state with topological order
Yang, Shuo; Wahl, Thorsten; Tu, Hong-Hao; Schuch, Norbert; Cirac, J. Ignacio
We show that projected entangled-pair states (PEPS) can describe chiral topologically ordered phases. For that, we construct a simple PEPS for spin-1/2 particles in a two-dimensional lattice. We reveal a symmetry in the local projector of the PEPS that gives rise to the global topological character. We also extract characteristic quantities of the edge conformal field theory using the bulk-boundary correspondence. EU projects SIQS and QALGO, the Alexander von Humboldt foundation, the Government of Canada through Industry Canada, and the Province of Ontario through the Ministry of Economic Development & Innovation.
Asbóth, János K.; Oroszlány, László; Pályi, András
2015-01-01
This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological band insulators in one and two dimensions. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. We use noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dime...
Topologically protected states in one-dimensional systems
Fefferman, C L; Weinstein, M I
2017-01-01
The authors study a class of periodic Schrödinger operators, which in distinguished cases can be proved to have linear band-crossings or "Dirac points". They then show that the introduction of an "edge", via adiabatic modulation of these periodic potentials by a domain wall, results in the bifurcation of spatially localized "edge states". These bound states are associated with the topologically protected zero-energy mode of an asymptotic one-dimensional Dirac operator. The authors' model captures many aspects of the phenomenon of topologically protected edge states for two-dimensional bulk structures such as the honeycomb structure of graphene. The states the authors construct can be realized as highly robust TM-electromagnetic modes for a class of photonic waveguides with a phase-defect.
International Nuclear Information System (INIS)
Choi, Yun-Young; Kim, Juhan; Kim, Sungsoo S.; Park, Changbom; Gott, J. Richard; Weinberg, David H.; Vogeley, Michael S.
2010-01-01
We measure the topology of the main galaxy distribution using the Seventh Data Release of the Sloan Digital Sky Survey, examining the dependence of galaxy clustering topology on galaxy properties. The observational results are used to test galaxy formation models. A volume-limited sample defined by M r -1 Mpc smoothing scale, with 4.8% uncertainty including all systematics and cosmic variance. The clustering topology over the smoothing length interval from 6 to 10 h -1 Mpc reveals a mild scale dependence for the shift (Δν) and void abundance (A V ) parameters of the genus curve. We find substantial bias in the topology of galaxy clustering with respect to the predicted topology of the matter distribution, which varies with luminosity, morphology, color, and the smoothing scale of the density field. The distribution of relatively brighter galaxies shows a greater prevalence of isolated clusters and more percolated voids. Even though early (late)-type galaxies show topology similar to that of red (blue) galaxies, the morphology dependence of topology is not identical to the color dependence. In particular, the void abundance parameter A V depends on morphology more strongly than on color. We test five galaxy assignment schemes applied to cosmological N-body simulations of a ΛCDM universe to generate mock galaxies: the halo-galaxy one-to-one correspondence model, the halo occupation distribution model, and three implementations of semi-analytic models (SAMs). None of the models reproduces all aspects of the observed clustering topology; the deviations vary from one model to another but include statistically significant discrepancies in the abundance of isolated voids or isolated clusters and the amplitude and overall shift of the genus curve. SAM predictions of the topology color dependence are usually correct in sign but incorrect in magnitude. Our topology tests indicate that, in these models, voids should be emptier and more connected and the threshold for
A cluster-based architecture to structure the topology of parallel wireless sensor networks.
Lloret, Jaime; Garcia, Miguel; Bri, Diana; Diaz, Juan R
2009-01-01
A wireless sensor network is a self-configuring network of mobile nodes connected by wireless links where the nodes have limited capacity and energy. In many cases, the application environment requires the design of an exclusive network topology for a particular case. Cluster-based network developments and proposals in existence have been designed to build a network for just one type of node, where all nodes can communicate with any other nodes in their coverage area. Let us suppose a set of clusters of sensor nodes where each cluster is formed by different types of nodes (e.g., they could be classified by the sensed parameter using different transmitting interfaces, by the node profile or by the type of device: laptops, PDAs, sensor etc.) and exclusive networks, as virtual networks, are needed with the same type of sensed data, or the same type of devices, or even the same type of profiles. In this paper, we propose an algorithm that is able to structure the topology of different wireless sensor networks to coexist in the same environment. It allows control and management of the topology of each network. The architecture operation and the protocol messages will be described. Measurements from a real test-bench will show that the designed protocol has low bandwidth consumption and also demonstrates the viability and the scalability of the proposed architecture. Our ccluster-based algorithm is compared with other algorithms reported in the literature in terms of architecture and protocol measurements.
Directory of Open Access Journals (Sweden)
Yunkyu Sohn
2011-05-01
Full Text Available The modular organization of networks of individual neurons interwoven through synapses has not been fully explored due to the incredible complexity of the connectivity architecture. Here we use the modularity-based community detection method for directed, weighted networks to examine hierarchically organized modules in the complete wiring diagram (connectome of Caenorhabditis elegans (C. elegans and to investigate their topological properties. Incorporating bilateral symmetry of the network as an important cue for proper cluster assignment, we identified anatomical clusters in the C. elegans connectome, including a body-spanning cluster, which correspond to experimentally identified functional circuits. Moreover, the hierarchical organization of the five clusters explains the systemic cooperation (e.g., mechanosensation, chemosensation, and navigation that occurs among the structurally segregated biological circuits to produce higher-order complex behaviors.
Anomalous Acoustic Plasmon Mode from Topologically Protected States
Jia, Xun; Zhang, Shuyuan; Sankar, Raman; Chou, Fang-Cheng; Wang, Weihua; Kempa, K.; Plummer, E. W.; Zhang, Jiandi; Zhu, Xuetao; Guo, Jiandong
2017-09-01
Plasmons, the collective excitations of electrons in the bulk or at the surface, play an important role in the properties of materials, and have generated the field of "plasmonics." We report the observation of a highly unusual acoustic plasmon mode on the surface of a three-dimensional topological insulator (TI) Bi2Se3 , using momentum resolved inelastic electron scattering. In sharp contrast to ordinary plasmon modes, this mode exhibits almost linear dispersion into the second Brillouin zone and remains prominent with remarkably weak damping not seen in any other systems. This behavior must be associated with the inherent robustness of the electrons in the TI surface state, so that not only the surface Dirac states but also their collective excitations are topologically protected. On the other hand, this mode has much smaller energy dispersion than expected from a continuous media excitation picture, which can be attributed to the strong coupling with surface phonons.
Disorder effects in topological states: Brief review of the recent developments
International Nuclear Information System (INIS)
Wu Binglan; Zhou Jiaojiao; Jiang Hua; Song Juntao
2016-01-01
Disorder inevitably exists in realistic samples, manifesting itself in various exotic properties for the topological states. In this paper, we summarize and briefly review the work completed over the last few years, including our own, regarding recent developments in several topics about disorder effects in topological states. For weak disorder, the robustness of topological states is demonstrated, especially for both quantum spin Hall states with Z 2 = 1 and size induced nontrivial topological insulators with Z 2 = 0. For moderate disorder, by increasing the randomness of both the impurity distribution and the impurity induced potential, the topological insulator states can be created from normal metallic or insulating states. These phenomena and their mechanisms are summarized. For strong disorder, the disorder causes a metal–insulator transition. Due to their topological nature, the phase diagrams are much richer in topological state systems. Finally, the trends in these areas of disorder research are discussed. (topical review)
Ireland, R. M.; Wu, Liang; Salehi, M.; Oh, S.; Armitage, N. P.; Katz, H. E.
2018-04-01
We demonstrate the ability to reduce the carrier concentration of thin films of the topological insulator (TI) Bi2 Se3 by utilizing a nonvolatile electrostatic gating via corona charging of electret polymers. Sufficient electric field can be imparted to a polymer-TI bilayer to result in significant electron density depletion, even without the continuous connection of a gate electrode or the chemical modification of the TI. We show that the Fermi level of Bi2 Se3 is shifted toward the Dirac point with this method. Using terahertz spectroscopy, we find that the surface chemical potential is lowered into the bulk band gap (approximately 50 meV above the Dirac point and 170 meV below the conduction-band minimum), and it is stabilized in the intrinsic regime while enhancing electron mobility. The mobility of surface state electrons is enhanced to a value as high as approximately 1600 cm2/V s at 5 K.
Electrically tunable robust edge states in graphene-based topological photonic crystal slabs
Song, Zidong; Liu, HongJun; Huang, Nan; Wang, ZhaoLu
2018-03-01
Topological photonic crystals are optical structures supporting topologically protected unidirectional edge states that exhibit robustness against defects. Here, we propose a graphene-based all-dielectric photonic crystal slab structure that supports two-dimensionally confined topological edge states. These topological edge states can be confined in the out-of-plane direction by two parallel graphene sheets. In the structure, the excitation frequency range of topological edge states can be dynamically and continuously tuned by varying bias voltage across the two parallel graphene sheets. Utilizing this kind of architecture, we construct Z-shaped channels to realize topological edge transmission with diffrerent frequencies. The proposal provides a new degree of freedom to dynamically control topological edge states and potential applications for robust integrated photonic devices and optical communication systems.
Matsushita, Stephane Yu; Huynh, Khuong Kim; Yoshino, Harukazu; Tu, Ngoc Han; Tanabe, Yoichi; Tanigaki, Katsumi
2017-10-01
We report thermoelectric (TE) properties of topological surface Dirac states (TSDS) in three-dimensional topological insulators (3D-TIs) purely isolated from the bulk by employing single-crystal B i2 -xS bxT e3 -yS ey films epitaxially grown in the ultrathin limit. Two intrinsic nontrivial topological surface states, a metallic TSDS (m-TSDS) and a gap-opened semiconducting topological state (g-TSDS), are successfully observed by electrical transport, and important TE parameters [electrical conductivity (σ), thermal conductivity (κ), and thermopower (S )] are accurately determined. Pure m-TSDS gives S =-44 μ V K-1 , which is an order of magnitude higher than those of the conventional metals and the value is enhanced to -212 μ V K-1 for g-TSDS. It is clearly shown that the semiclassical Boltzmann transport equation (SBTE) in the framework of constant relaxation time (τ) most frequently used for conventional analysis cannot be valid in 3D-TIs and strong energy dependent relaxation time τ(E ) beyond the Born approximation is essential for making intrinsic interpretations. Although σ is protected on the m-TSDS, κ is greatly influenced by the disorder on the topological surface, giving a dissimilar effect between topologically protected electronic conduction and phonon transport.
The state and creative clusters
DEFF Research Database (Denmark)
Vang, Jan; Jakobsen, Hannes
2013-01-01
Studies on the spatial organisation of so-called creative industries have exploded the last decade. This has resulted in an impressive amount of research on the clustering of creative industries, their reliance on buzz and why they are based on projects, and so forth. This literature has, however...... creative industries, especially film industries outside Hollywood. Based on an original empirical study of the Danish film cluster we show how it has emerged almost from scratch and positioned itself as a noteworthy player on the global scene industry during the last 20 years. Special attention is paid...
Building crystalline topological phases from lower-dimensional states
Huang, Sheng-Jie; Song, Hao; Huang, Yi-Ping; Hermele, Michael
2017-11-01
We study the classification of symmetry-protected topological (SPT) phases with crystalline symmetry (cSPT phases). Focusing on bosonic cSPT phases in two and three dimensions, we introduce a simple family of cSPT states, where the system is comprised of decoupled lower-dimensional building blocks that are themselves SPT states. We introduce a procedure to classify these block states, which surprisingly reproduces a classification of cSPT phases recently obtained by Thorngren and Else (arXiv:1612.00846) using very different methods, for all wallpaper and space groups. The explicit constructions underlying our results clarify the physical properties of the phases classified by Thorngren and Else, and expose additional structure in the classification. Moreover, the states we classify can be completely characterized by point-group SPT (pgSPT) invariants and related weak pgSPT invariants that we introduce. In many cases, the weak invariants can be visualized in terms of translation-symmetric stacking of lower-dimensional pgSPT states. We apply our classification to propose a Lieb-Shultz-Mattis-type constraint for two-dimensional spin systems with only crystalline symmetry, and establish this constraint by a dimensional reduction argument. Finally, the surprising matching with the Thorngren-Else classification leads us to conjecture that all SPT phases protected only by crystalline symmetry can be built from lower-dimensional blocks of invertible topological states. We argue that this conjecture holds if we make a certain physically reasonable but unproven assumption.
Directory of Open Access Journals (Sweden)
Xiao-Hong Li
2014-01-01
Full Text Available Cooperative communication (CC is used in topology control as it can reduce the transmission power and expand the transmission range. However, all previous research on topology control under the CC model focused on maintaining network connectivity and minimizing the total energy consumption, which would lead to low network capacity, transmission interruption, or even network paralysis. Meanwhile, without considering the balance of energy consumption in the network, it would reduce the network lifetime and greatly affect the network performance. This paper tries to solve the above problems existing in the research on topology control under the CC model by proposing a power assignment (DCCPA algorithm based on dynamic cooperative clustering in cooperative ad hoc networks. The new algorithm clusters the network to maximize network capacity and makes the clusters communicate with each other by CC. To reduce the number of redundant links between clusters, we design a static clustering method by using Kruskal algorithm. To maximize the network lifetime, we also propose a cluster head rotating method which can reach a good tradeoff between residual energy and distance for the cluster head reselection. Experimental results show that DCCPA can improve 80% network capacity with Cooperative Bridges algorithm; meanwhile, it can improve 20% network lifetime.
Neural-Network Quantum States, String-Bond States, and Chiral Topological States
Directory of Open Access Journals (Sweden)
Ivan Glasser
2018-01-01
Full Text Available Neural-network quantum states have recently been introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between neural-network quantum states in the form of restricted Boltzmann machines and some classes of tensor-network states in arbitrary dimensions. In particular, we demonstrate that short-range restricted Boltzmann machines are entangled plaquette states, while fully connected restricted Boltzmann machines are string-bond states with a nonlocal geometry and low bond dimension. These results shed light on the underlying architecture of restricted Boltzmann machines and their efficiency at representing many-body quantum states. String-bond states also provide a generic way of enhancing the power of neural-network quantum states and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of tensor networks and the efficiency of neural-network quantum states into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional tensor networks, we show that, because of their nonlocal geometry, neural-network quantum states and their string-bond-state extension can describe a lattice fractional quantum Hall state exactly. In addition, we provide numerical evidence that neural-network quantum states can approximate a chiral spin liquid with better accuracy than entangled plaquette states and local string-bond states. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of string-bond states as a tool in more traditional machine-learning applications.
Neural-Network Quantum States, String-Bond States, and Chiral Topological States
Glasser, Ivan; Pancotti, Nicola; August, Moritz; Rodriguez, Ivan D.; Cirac, J. Ignacio
2018-01-01
Neural-network quantum states have recently been introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between neural-network quantum states in the form of restricted Boltzmann machines and some classes of tensor-network states in arbitrary dimensions. In particular, we demonstrate that short-range restricted Boltzmann machines are entangled plaquette states, while fully connected restricted Boltzmann machines are string-bond states with a nonlocal geometry and low bond dimension. These results shed light on the underlying architecture of restricted Boltzmann machines and their efficiency at representing many-body quantum states. String-bond states also provide a generic way of enhancing the power of neural-network quantum states and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of tensor networks and the efficiency of neural-network quantum states into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional tensor networks, we show that, because of their nonlocal geometry, neural-network quantum states and their string-bond-state extension can describe a lattice fractional quantum Hall state exactly. In addition, we provide numerical evidence that neural-network quantum states can approximate a chiral spin liquid with better accuracy than entangled plaquette states and local string-bond states. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of string-bond states as a tool in more traditional machine-learning applications.
Kirstein, J.K.; Albrechtsen, H.-J.; Rygaard, M.
2014-01-01
Topological clustering was investigated to simplify a complex water distribution network of Copenhagen, Denmark, into recogniz- able water movement patterns. This made it possible to assess the general transport of the water and to suggest strategic sampling locations. Through a topological analysis, the network model was divided into strongly and weakly connected clusters within selected time periods. Steady connected clusters were found by conducting a cluster analysis over all chosen selec...
Observation of topological edge states of acoustic metamaterials at subwavelength scale
Dai, Hongqing; Jiao, Junrui; Xia, Baizhan; Liu, Tingting; Zheng, Shengjie; Yu, Dejie
2018-05-01
Topological states are of key importance for acoustic wave systems owing to their unique transport properties. In this study, we develop a hexagonal array of hexagonal columns with Helmholtz resonators to obtain subwavelength Dirac cones. Rotation operations are performed to open the Dirac cones and obtain acoustic valley vortex states. In addition, we calculate the angular-dependent frequencies for the band edges at the K-point. Through a topological phase transition, the topological phase of pattern A can change into that of pattern B. The calculations for the bulk dispersion curves show that the acoustic metamaterials exhibit BA-type and AB-type topological edge states. Experimental results demonstrate that a sound wave can transmit well along the topological path. This study could reveal a simple approach to create acoustic topological edge states at the subwavelength scale.
Surface states on a topologically nontrivial semimetal: The case of Sb(110)
DEFF Research Database (Denmark)
Bianchi, Marco; Guan, Dandan; Strózecka, Anna
2012-01-01
spin-orbit splitting. The bulk band structure of Sb has the characteristics of a strong topological insulator with a Z2 invariant ν0 = 1. This puts constraints on the existence of metallic surface states and the expected topology of the surface Fermi contour. However, bulk Sb is a semimetal......, not an insulator, and these constraints are therefore partly relaxed. This relation of bulk topology and expected surface-state dispersion for semimetals is discussed....
Layer Construction of 3D Topological States and String Braiding Statistics
Directory of Open Access Journals (Sweden)
Chao-Ming Jian
2014-12-01
Full Text Available While the topological order in two dimensions has been studied extensively since the discovery of the integer and fractional quantum Hall systems, topological states in three spatial dimensions are much less understood. In this paper, we propose a general formalism for constructing a large class of three-dimensional topological states by stacking layers of 2D topological states and introducing coupling between them. Using this construction, different types of topological states can be obtained, including those with only surface topological order and no bulk topological quasiparticles, and those with topological order both in the bulk and at the surface. For both classes of states, we study its generic properties and present several explicit examples. As an interesting consequence of this construction, we obtain example systems with nontrivial braiding statistics between string excitations. In addition to studying the string-string braiding in the example system, we propose a topological field-theory description for the layer-constructed systems, which captures not only the string-particle braiding statistics but also the string-string braiding statistics when the coupling is twisted. Last, we provide a proof of a general identity for Abelian string statistics and discuss an example system with non-Abelian strings.
Energy Technology Data Exchange (ETDEWEB)
Yazdani, Ali; Ong, N. Phuan; Cava, Robert J.
2016-05-03
An interconnect is disclosed with enhanced immunity of electrical conductivity to defects. The interconnect includes a material with charge carriers having topological surface states. Also disclosed is a method for fabricating such interconnects. Also disclosed is an integrated circuit including such interconnects. Also disclosed is a gated electronic device including a material with charge carriers having topological surface states.
Energy Technology Data Exchange (ETDEWEB)
Yazdani, Ali; Ong, N. Phuan; Cava, Robert J.
2017-04-04
An interconnect is disclosed with enhanced immunity of electrical conductivity to defects. The interconnect includes a material with charge carriers having topological surface states. Also disclosed is a method for fabricating such interconnects. Also disclosed is an integrated circuit including such interconnects. Also disclosed is a gated electronic device including a material with charge carriers having topological surface states.
Topologically protected bound states in one-dimensional Floquet acoustic waveguide systems
Peng, Yu-Gui; Geng, Zhi-Guo; Zhu, Xue-Feng
2018-03-01
Topological manipulation of sound has recently been a hot spot in acoustics due to the fascinating property of defect immune transport. To the best of our knowledge, the studies on one-dimensional (1D) topological acoustic systems hitherto mainly focus on the case of the Su-Schrieffer-Heeger model. Here, we show that topologically protected bound states may also exist in 1D periodically modulated acoustic waveguide systems, viz., 1D Floquet topological insulators. The results show that tuning the coupling strength in a waveguide lattice could trigger topological phase transition, which gives rise to topologically protected interface states as we put together two waveguide lattices featured with different topological phases or winding numbers. However, for the combined lattice, input at the waveguides other than the interfacial ones will excite bulk states. We have further verified the robustness of interface bound states against the variation of coupling strengths between the two distinct waveguide lattices. This work extends the scope of topological acoustics and may promote potential applications for acoustic devices with topological functionalities.
Creation and manipulation of topological states in chiral nematic microspheres
Orlova, Tetiana; Aßhoff, Sarah Jane; Yamaguchi, Tadatsugu; Katsonis, Nathalie; Brasselet, Etienne
2015-07-01
Topology is a universal concept that is encountered in daily life and is known to determine many static and dynamical properties of matter. Taming and controlling the topology of materials therefore constitutes a contemporary interdisciplinary challenge. Building on the controllable spatial properties of soft matter appears as a relevant strategy to address the challenge, in particular, because it may lead to paradigmatic model systems that allow checking theories experimentally. Here we report experimentally on a wealth of complex free-standing metastable topological architectures at the micron scale, in frustrated chiral nematic droplets. These results support recent works predicting the formation of free-standing knotted and linked disclination structures in confined chiral nematic fluids. We also demonstrate that various kinds of external fields (thermal, electrical and optical) can be used to achieve topological remote control. All this may foster the development of new devices based on topologically structured soft media.
Exploring photonic topological insulator states in a circuit-QED lattice
Li, Jing-Ling; Shan, Chuan-Jia; Zhao, Feng
2018-04-01
We propose a simple protocol to explore the topological properties of photonic integer quantum Hall states in a one-dimensional circiut-QED lattice. By periodically modulating the on-site photonic energies in such a lattice, we demonstrate that this one-dimensional lattice model can be mapped into a two-dimensional integer quantum Hall insulator model. Based on the lattice-based cavity input-output theory, we show that both the photonic topological protected edge states and topological invariants can be clearly measured from the final steady state of the resonator lattice after taking into account cavity dissipation. Interestingly, we also find that the measurement signals associated with the above topological features are quite unambitious even in five coupled dissipative resonators. Our work opens up a new prospect of exploring topological states with a small-size dissipative quantum artificial lattice, which is quite attractive to the current quantum optics community.
Topological origin of edge states in two-dimensional inversion-symmetric insulators and semimetals
Miert, Guido van; Ortix, Carmine; de Morais Smith, C.
2017-01-01
Symmetries play an essential role in identifying and characterizing topological states of matter. Here, we classify topologically two-dimensional (2D) insulators and semimetals with vanishing spin-orbit coupling using time-reversal ($\\mathcal{T}$) and inversion ($\\mathcal{I}$) symmetry. This allows
Topological superradiant state in Fermi gases with cavity induced spin-orbit coupling
Yu, Dongyang; Pan, Jian-Song; Liu, Xiong-Jun; Zhang, Wei; Yi, Wei
2018-02-01
Coherently driven atomic gases inside optical cavities hold great promise for generating rich dynamics and exotic states of matter. It was shown recently that an exotic topological superradiant state exists in a two-component degenerate Fermi gas coupled to a cavity, where local order parameters coexist with global topological invariants. In this work, we characterize in detail various properties of this exotic state, focusing on the feedback interactions between the atoms and the cavity field. In particular, we demonstrate that cavity-induced interband coupling plays a crucial role in inducing the topological phase transition between the conventional and topological superradiant states. We analyze the interesting signatures in the cavity field left by the closing and reopening of the atomic bulk gap across the topological phase boundary and discuss the robustness of the topological superradiant state by investigating the steady-state phase diagram under various conditions. Furthermore, we consider the interaction effect and discuss the interplay between the pairing order in atomic ensembles and the superradiance of the cavity mode. Our work provides many valuable insights into the unique cavity-atom hybrid system under study and is helpful for future experimental exploration of the topological superradiant state.
Peeking Network States with Clustered Patterns
Energy Technology Data Exchange (ETDEWEB)
Kim, Jinoh [Texas A & M Univ., Commerce, TX (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Sim, Alex [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2015-10-20
Network traffic monitoring has long been a core element for effec- tive network management and security. However, it is still a chal- lenging task with a high degree of complexity for comprehensive analysis when considering multiple variables and ever-increasing traffic volumes to monitor. For example, one of the widely con- sidered approaches is to scrutinize probabilistic distributions, but it poses a scalability concern and multivariate analysis is not gen- erally supported due to the exponential increase of the complexity. In this work, we propose a novel method for network traffic moni- toring based on clustering, one of the powerful deep-learning tech- niques. We show that the new approach enables us to recognize clustered results as patterns representing the network states, which can then be utilized to evaluate “similarity” of network states over time. In addition, we define a new quantitative measure for the similarity between two compared network states observed in dif- ferent time windows, as a supportive means for intuitive analysis. Finally, we demonstrate the clustering-based network monitoring with public traffic traces, and show that the proposed approach us- ing the clustering method has a great opportunity for feasible, cost- effective network monitoring.
Pressure controlled transition into a self-induced topological superconducting surface state
Zhu, Zhiyong
2014-02-07
Ab-initio calculations show a pressure induced trivial-nontrivial-trivial topological phase transition in the normal state of 1T-TiSe2. The pressure range in which the nontrivial phase emerges overlaps with that of the superconducting ground state. Thus, topological superconductivity can be induced in protected surface states by the proximity effect of superconducting bulk states. This kind of self-induced topological surface superconductivity is promising for a realization of Majorana fermions due to the absence of lattice and chemical potential mismatches. For appropriate electron doping, the formation of the topological superconducting surface state in 1T-TiSe 2 becomes accessible to experiments as it can be controlled by pressure.
Topologically protected bound states in photonic parity-time-symmetric crystals.
Weimann, S; Kremer, M; Plotnik, Y; Lumer, Y; Nolte, S; Makris, K G; Segev, M; Rechtsman, M C; Szameit, A
2017-04-01
Parity-time (PT)-symmetric crystals are a class of non-Hermitian systems that allow, for example, the existence of modes with real propagation constants, for self-orthogonality of propagating modes, and for uni-directional invisibility at defects. Photonic PT-symmetric systems that also support topological states could be useful for shaping and routing light waves. However, it is currently debated whether topological interface states can exist at all in PT-symmetric systems. Here, we show theoretically and demonstrate experimentally the existence of such states: states that are localized at the interface between two topologically distinct PT-symmetric photonic lattices. We find analytical closed form solutions of topological PT-symmetric interface states, and observe them through fluorescence microscopy in a passive PT-symmetric dimerized photonic lattice. Our results are relevant towards approaches to localize light on the interface between non-Hermitian crystals.
Effect of Temperature on Topological States of Circular DNA
Fan, Yang-Tao; Li, Xiu-Yan; Liu, Yan-Hui; Chen, Hu
2017-07-01
The different topological states of circular double-stranded DNA can be defined by their linking number. The equilibrium distribution of linking number can be obtained by circularizing a linear DNA into a circle by ligase. Based on the recent experimental results that the DNA bending rigidity and twist rigidity strongly depend on temperature, the reduced bending rigidity can be approximated by g=(3.19× {10}-19-T\\cdot 4.14× {10}-22) {erg}\\cdot {cm} over the temperature interval (5 ∼ 53) °C, and the temperature dependence of twist rigidity can be fitted by C(T)=(4588.89{exp} (-T/117.04)-251.33) nm. The temperature dependence of the linking number distribution of circular DNAs can be predicted by using Monte Carlo simulation. The variance of linking number distribution on temperature is in accordance with the previous experimental results. Compared with the temperature dependence of bending rigidity, the temperature dependence of twist rigidity causes a noticeable fluctuation in linking number distribution and mainly contribute towards the variance change of linking number distribution of circular DNA. The variance of the writhe number and twist number in the equation = + depends on the length of circular DNA. When the length of circular DNA is less than 230 nm, the variance of twist number is dominant over the variance of writhe number ( ), whereas for the condition that the length of the circular DNA is larger than 370 nm. Supported by the National Natural Science Foundation of China under Grant Nos. 11047022, 11204045, and 11464004, Guizhou Provincial Tracking Key Program of Social Development (SY20123089, SZ20113069), the General Financial Grant from the China Postdoctoral Science Foundation (2014M562341), the Research Foundation for Young University Teachers from Guizhou University (201311), and College Innovation Talent Team of Guizhou Province (2014)32
Quantum states with topological properties via dipolar interactions
Energy Technology Data Exchange (ETDEWEB)
Peter, David
2015-06-25
This thesis proposes conceptually new ways to realize materials with topological properties by using dipole-dipole interactions. First, we study a system of ultracold dipolar fermions, where the relaxation mechanism of dipolar spins can be used to reach the quantum Hall regime. Second, in a system of polar molecules in an optical lattice, dipole-dipole interactions induce spin-orbit coupling terms for the rotational excitations. In combination with time-reversal symmetry breaking this leads to topological bands with Chern numbers greater than one.
The quantum states of high-T c materials - States of topological resonances
International Nuclear Information System (INIS)
Winkler, W.; Winkler, K.
2007-01-01
The nature of the electronic states of the CuO 2 planes in high-T c materials is elaborated, being proven as a crucial revision of previous assumptions. One important aspect is the general existence of electronic pair states in two manifestations, which determine superconducting or non-superconducting properties. The decisive basis of the theory developed in this paper is derived from the various broken symmetries of the electronic states and the formation of one-dimensional electronic subspaces. The non-superconducting state is already characterized by a two-dimensional ordering of one-dimensional electronic states in space (stiffness in space), whereas the superconducting state is represented by a two-dimensional highly correlated electronic state in space and time (stiffness in space and time). Under the inclusion of lattice dynamics, the electronic ground state is reached by a topological superposition of symmetry-broken sub-states, quantized and determined in time (Topological Resonance (TR)). This forms the basis for inherent times (eigentime) of the electronic quantum states, an important but unusual characteristic of these quantum states. Under hole doping, the general nature of the electronic state of the CuO 2 plane can be characterized as a coherent quantum fluid consisting of two partial fluids (b-holes, f-holes). The characteristics of this quantum fluid state are predominantly determined by the strongly correlated b-hole fluid, whereas the f-hole fluid possesses higher internal degrees of freedom. The existence of a b-hole fluid is an indispensable precondition for the existence of a superconducting state in high-T c materials
Controlled quantum dialogue using cluster states
Kao, Shih-Hung; Hwang, Tzonelih
2017-05-01
This paper presents a new controlled quantum dialogue (CQD) protocol based on the cluster entangled states. The security analyses indicate that the proposed scheme is secure under not only various well-known attacks but also the collusive attack, where the participants may collude to communicate without the controller's permission. Compared to a previous CQD scheme, which is also robust against the conspiracy attack, the proposed protocol is more efficient in both the qubit efficiency and the hardware requirement.
DEFF Research Database (Denmark)
Kirstein, Jonas Kjeld; Albrechtsen, Hans-Jørgen; Rygaard, Martin
2014-01-01
Topological clustering was investigated to simplify a complex water distribution network of Copenhagen, Denmark, into recogniz- able water movement patterns. This made it possible to assess the general transport of the water and to suggest strategic sampling locations. Through a topological analy...
Edge states and integer quantum Hall effect in topological insulator thin films.
Zhang, Song-Bo; Lu, Hai-Zhou; Shen, Shun-Qing
2015-08-25
The integer quantum Hall effect is a topological state of quantum matter in two dimensions, and has recently been observed in three-dimensional topological insulator thin films. Here we study the Landau levels and edge states of surface Dirac fermions in topological insulators under strong magnetic field. We examine the formation of the quantum plateaux of the Hall conductance and find two different patterns, in one pattern the filling number covers all integers while only odd integers in the other. We focus on the quantum plateau closest to zero energy and demonstrate the breakdown of the quantum spin Hall effect resulting from structure inversion asymmetry. The phase diagrams of the quantum Hall states are presented as functions of magnetic field, gate voltage and chemical potential. This work establishes an intuitive picture of the edge states to understand the integer quantum Hall effect for Dirac electrons in topological insulator thin films.
A priori data-driven multi-clustered reservoir generation algorithm for echo state network.
Directory of Open Access Journals (Sweden)
Xiumin Li
Full Text Available Echo state networks (ESNs with multi-clustered reservoir topology perform better in reservoir computing and robustness than those with random reservoir topology. However, these ESNs have a complex reservoir topology, which leads to difficulties in reservoir generation. This study focuses on the reservoir generation problem when ESN is used in environments with sufficient priori data available. Accordingly, a priori data-driven multi-cluster reservoir generation algorithm is proposed. The priori data in the proposed algorithm are used to evaluate reservoirs by calculating the precision and standard deviation of ESNs. The reservoirs are produced using the clustering method; only the reservoir with a better evaluation performance takes the place of a previous one. The final reservoir is obtained when its evaluation score reaches the preset requirement. The prediction experiment results obtained using the Mackey-Glass chaotic time series show that the proposed reservoir generation algorithm provides ESNs with extra prediction precision and increases the structure complexity of the network. Further experiments also reveal the appropriate values of the number of clusters and time window size to obtain optimal performance. The information entropy of the reservoir reaches the maximum when ESN gains the greatest precision.
Topological Fulde-Ferrell and Larkin-Ovchinnikov states in spin-orbit-coupled lattice system
Guo, Yao-Wu; Chen, Yan
2018-04-01
The spin-orbit coupled lattice system under Zeeman fields provides an ideal platform to realize exotic pairing states. Notable examples range from the topological superfluid/superconducting (tSC) state, which is gapped in the bulk but metallic at the edge, to the Fulde-Ferrell (FF) state (having a phase-modulated order parameter with a uniform amplitude) and the Larkin-Ovchinnikov (LO) state (having a spatially varying order parameter amplitude). Here, we show that the topological FF state with Chern number ( C = -1) (tFF1) and topological LO state with C= 2 (tLO2) can be stabilized in Rashba spin-orbit coupled lattice systems in the presence of both in-plane and out-of-plane Zeeman fields. Besides the inhomogeneous tSC states, in the presence of a weak in-plane Zeeman field, two topological BCS phases may emerge with C = -1 (tBCS1) far from half filling and C = 2 (tBCS2) near half filling. We show intriguing effects such as different spatial profiles of order parameters for FF and LO states, the topological evolution among inhomogeneous tSC states, and different non-trivial Chern numbers for the tFF1 and tLO1,2 states, which are peculiar to the lattice system. Global phase diagrams for various topological phases are presented for both half-filling and doped cases. The edge states as well as local density of states spectra are calculated for tSC states in a 2D strip.
Probing spin helical surface states in topological HgTe nanowires
Ziegler, J.; Kozlovsky, R.; Gorini, C.; Liu, M.-H.; Weishäupl, S.; Maier, H.; Fischer, R.; Kozlov, D. A.; Kvon, Z. D.; Mikhailov, N.; Dvoretsky, S. A.; Richter, K.; Weiss, D.
2018-01-01
Nanowires with helical surface states represent key prerequisites for observing and exploiting phase-coherent topological conductance phenomena, such as spin-momentum locked quantum transport or topological superconductivity. We demonstrate in a joint experimental and theoretical study that gated nanowires fabricated from high-mobility strained HgTe, known as a bulk topological insulator, indeed preserve the topological nature of the surface states, that moreover extend phase-coherently across the entire wire geometry. The phase-coherence lengths are enhanced up to 5 μ m when tuning the wires into the bulk gap, so as to single out topological transport. The nanowires exhibit distinct conductance oscillations, both as a function of the flux due to an axial magnetic field and of a gate voltage. The observed h /e -periodic Aharonov-Bohm-type modulations indicate surface-mediated quasiballistic transport. Furthermore, an in-depth analysis of the scaling of the observed gate-dependent conductance oscillations reveals the topological nature of these surface states. To this end we combined numerical tight-binding calculations of the quantum magnetoconductance with simulations of the electrostatics, accounting for the gate-induced inhomogeneous charge carrier densities around the wires. We find that helical transport prevails even for strongly inhomogeneous gating and is governed by flux-sensitive high-angular momentum surface states that extend around the entire wire circumference.
Energy Technology Data Exchange (ETDEWEB)
Swinteck, N., E-mail: swinteck@email.arizona.edu; Matsuo, S.; Runge, K.; Lucas, P.; Deymier, P. A. [Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721 (United States); Vasseur, J. O. [Institut d' Electronique, de Micro-électronique et de Nanotechnologie, UMR CNRS 8520, Cité Scientifique, 59652 Villeneuve d' Ascq Cedex (France)
2015-08-14
Recent progress in electronic and electromagnetic topological insulators has led to the demonstration of one way propagation of electron and photon edge states and the possibility of immunity to backscattering by edge defects. Unfortunately, such topologically protected propagation of waves in the bulk of a material has not been observed. We show, in the case of sound/elastic waves, that bulk waves with unidirectional backscattering-immune topological states can be observed in a time-dependent elastic superlattice. The superlattice is realized via spatial and temporal modulation of the stiffness of an elastic material. Bulk elastic waves in this superlattice are supported by a manifold in momentum space with the topology of a single twist Möbius strip. Our results demonstrate the possibility of attaining one way transport and immunity to scattering of bulk elastic waves.
Topological Edge States at a Tilt Boundary in Gated Multilayer Graphene
Directory of Open Access Journals (Sweden)
Abolhassan Vaezi
2013-06-01
Full Text Available Despite much interest in engineering new topological surface (edge states using structural defects, such topological surface states have not been observed yet. We show that recently imaged tilt boundaries in gated multilayer graphene should support topologically protected gapless edge states. We approach the problem from two perspectives: the microscopic perspective of a tight-binding model and an ab initio calculation on a bilayer, and the symmetry-protected topological (SPT state perspective for a general multilayer. Hence, we establish the tilt-boundary edge states as the first concrete example of the edge states of symmetry-protected Z-type SPT, protected by no-valley mixing, electron-number conservation, and time-reversal T symmetries. Further, we discuss possible phase transitions between distinct SPTs upon symmetry changes. Combined with a recently imaged tilt-boundary network, our findings may explain the long-standing puzzle of subgap conductance in gated bilayer graphene. This proposal can be tested through future transport experiments on tilt boundaries. In particular, the tilt boundaries offer an opportunity for the in situ imaging of topological edge transport.
Oluwadare, Oluwatosin; Cheng, Jianlin
2017-11-14
With the development of chromosomal conformation capturing techniques, particularly, the Hi-C technique, the study of the spatial conformation of a genome is becoming an important topic in bioinformatics and computational biology. The Hi-C technique can generate genome-wide chromosomal interaction (contact) data, which can be used to investigate the higher-level organization of chromosomes, such as Topologically Associated Domains (TAD), i.e., locally packed chromosome regions bounded together by intra chromosomal contacts. The identification of the TADs for a genome is useful for studying gene regulation, genomic interaction, and genome function. Here, we formulate the TAD identification problem as an unsupervised machine learning (clustering) problem, and develop a new TAD identification method called ClusterTAD. We introduce a novel method to represent chromosomal contacts as features to be used by the clustering algorithm. Our results show that ClusterTAD can accurately predict the TADs on a simulated Hi-C data. Our method is also largely complementary and consistent with existing methods on the real Hi-C datasets of two mouse cells. The validation with the chromatin immunoprecipitation (ChIP) sequencing (ChIP-Seq) data shows that the domain boundaries identified by ClusterTAD have a high enrichment of CTCF binding sites, promoter-related marks, and enhancer-related histone modifications. As ClusterTAD is based on a proven clustering approach, it opens a new avenue to apply a large array of clustering methods developed in the machine learning field to the TAD identification problem. The source code, the results, and the TADs generated for the simulated and real Hi-C datasets are available here: https://github.com/BDM-Lab/ClusterTAD .
Ground-state structures of Hafnium clusters
Energy Technology Data Exchange (ETDEWEB)
Ng, Wei Chun; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technoloty, Multimedia University, Melaca Campus, 75450 Melaka (Malaysia)
2015-04-24
Hafnium (Hf) is a very large tetra-valence d-block element which is able to form relatively long covalent bond. Researchers are interested to search for substitution to silicon in the semi-conductor industry. We attempt to obtain the ground-state structures of small Hf clusters at both empirical and density-functional theory (DFT) levels. For calculations at the empirical level, charge-optimized many-body functional potential (COMB) is used. The lowest-energy structures are obtained via a novel global-minimum search algorithm known as parallel tempering Monte-Carlo Basin-Hopping and Genetic Algorithm (PTMBHGA). The virtue of using COMB potential for Hf cluster calculation lies in the fact that by including the charge optimization at the valence shells, we can encourage the formation of proper bond hybridization, and thus getting the correct bond order. The obtained structures are further optimized using DFT to ensure a close proximity to the ground-state.
Blind Quantum Signature with Controlled Four-Particle Cluster States
Li, Wei; Shi, Jinjing; Shi, Ronghua; Guo, Ying
2017-08-01
A novel blind quantum signature scheme based on cluster states is introduced. Cluster states are a type of multi-qubit entangled states and it is more immune to decoherence than other entangled states. The controlled four-particle cluster states are created by acting controlled-Z gate on particles of four-particle cluster states. The presented scheme utilizes the above entangled states and simplifies the measurement basis to generate and verify the signature. Security analysis demonstrates that the scheme is unconditional secure. It can be employed to E-commerce systems in quantum scenario.
Multiple Coexisting Dirac Surface States in Three-Dimensional Topological Insulator PbBi₆Te₁₀.
Papagno, Marco; Eremeev, Sergey V; Fujii, Jun; Aliev, Ziya S; Babanly, Mahammad B; Mahatha, Sanjoy Kr; Vobornik, Ivana; Mamedov, Nazim T; Pacilé, Daniela; Chulkov, Evgueni V
2016-03-22
By means of angle-resolved photoemission spectroscopy (ARPES) measurements, we unveil the electronic band structure of three-dimensional PbBi6Te10 topological insulator. ARPES investigations evidence multiple coexisting Dirac surface states at the zone-center of the reciprocal space, displaying distinct electronic band dispersion, different constant energy contours, and Dirac point energies. We also provide evidence of Rashba-like split states close to the Fermi level, and deeper M- and V-shaped bands coexisting with the topological surface states. The experimental findings are in agreement with scanning tunneling microscopy measurements revealing different surface terminations according to the crystal structure of PbBi6Te10. Our experimental results are supported by density functional theory calculations predicting multiple topological surface states according to different surface cleavage planes.
Two-dimensional lattice model for the surface states of topological insulators
Zhou, Yan-Feng; Jiang, Hua; Xie, X. C.; Sun, Qing-Feng
2017-06-01
The surface states in three-dimensional (3D) topological insulators can be described by a two-dimensional (2D) continuous Dirac Hamiltonian. However, there exists the fermion doubling problem when putting the continuous 2D Dirac equation into a lattice model. In this paper, we introduce a Wilson term with a zero bare mass into the 2D lattice model to overcome the difficulty. By comparing with a 3D Hamiltonian, we show that the modified 2D lattice model can faithfully describe the low-energy electrical and transport properties of surface states of 3D topological insulators. So this 2D lattice model provides a simple and cheap way to numerically simulate the surface states of 3D topological-insulator nanostructures. Based on the 2D lattice model, we also establish the wormhole effect in a topological-insulator nanowire by a magnetic field along the wire and show the surface states being robust against disorder. The proposed 2D lattice model can be extensively applied to study the various properties and effects, such as the transport properties, Hall effect, universal conductance fluctuations, localization effect, etc. So, it paves a way to study the surface states of the 3D topological insulators.
Evidence of topological insulator state in the semimetal LaBi
Lou, R.; Fu, B.-B.; Xu, Q. N.; Guo, P.-J.; Kong, L.-Y.; Zeng, L.-K.; Ma, J.-Z.; Richard, P.; Fang, C.; Huang, Y.-B.; Sun, S.-S.; Wang, Q.; Wang, L.; Shi, Y.-G.; Lei, H. C.; Liu, K.; Weng, H. M.; Qian, T.; Ding, H.; Wang, S.-C.
2017-03-01
By employing angle-resolved photoemission spectroscopy combined with first-principles calculations, we performed a systematic investigation on the electronic structure of LaBi, which exhibits extremely large magnetoresistance (XMR), and is theoretically predicted to possess band anticrossing with nontrivial topological properties. Here, the observations of the Fermi-surface topology and band dispersions are similar to previous studies on LaSb [L.-K. Zeng, R. Lou, D.-S. Wu, Q. N. Xu, P.-J. Guo, L.-Y. Kong, Y.-G. Zhong, J.-Z. Ma, B.-B. Fu, P. Richard, P. Wang, G. T. Liu, L. Lu, Y.-B. Huang, C. Fang, S.-S. Sun, Q. Wang, L. Wang, Y.-G. Shi, H. M. Weng, H.-C. Lei, K. Liu, S.-C. Wang, T. Qian, J.-L. Luo, and H. Ding, Phys. Rev. Lett. 117, 127204 (2016), 10.1103/PhysRevLett.117.127204], a topologically trivial XMR semimetal, except the existence of a band inversion along the Γ -X direction, with one massless and one gapped Dirac-like surface state at the X and Γ points, respectively. The odd number of massless Dirac cones suggests that LaBi is analogous to the time-reversal Z2 nontrivial topological insulator. These findings open up a new series for exploring novel topological states and investigating their evolution from the perspective of topological phase transition within the family of rare-earth monopnictides.
Topological helical edge states in water waves over a topographical bottom
Wu, Shi qiao
2017-11-27
We present the discovery of topologically protected helical edge states in water wave systems, which are realized in water wave propagating over a topographical bottom whose height is modulated periodically in a two-dimensional triangular pattern. We develop an effective Hamiltonian to characterize the dispersion relation and use spin Chern numbers to classify the topology. Through full wave simulations we unambiguously demonstrate the robustness of the helical edge states which are immune to defects and disorders so that the backscattering loss is significantly reduced. A spin splitter is designed for water wave systems, where helical edge states with different spin orientations are spatially separated with each other, and potential applications are discussed.
Extraversion and Neuroticism relate to topological properties of resting-state brain networks
Directory of Open Access Journals (Sweden)
Qing eGao
2013-06-01
Full Text Available With the advent and development of modern neuroimaging techniques, there is an increasing interest in linking extraversion and neuroticism to anatomical and functional brain markers. Here we aimed to test the theoretically derived biological personality model as proposed by Eysenck using graph theoretical analyses. Specifically, the association between the topological organization of whole-brain functional networks and extraversion/neuroticism was explored. To construct functional brain networks, functional connectivity among 90 brain regions was measured by temporal correlation using resting-state functional magnetic resonance imaging (fMRI data of 71 healthy subjects. Graph theoretical analysis revealed a positive association of extraversion scores and normalized clustering coefficient values. These results suggested a more clustered configuration in brain networks of individuals high in extraversion, which could imply a higher arousal threshold and higher levels of arousal tolerance in the cortex of extraverts. On a local network level, we observed that a specific nodal measure, i.e. betweenness centrality (BC, was positively associated with neuroticism scores in the right precentral gyrus, right caudate nucleus, right olfactory cortex and bilateral amygdala. For individuals high in neuroticism, these results suggested a more frequent participation of these specific regions in information transition within the brain network and, in turn, may partly explain greater regional activation levels and lower arousal thresholds in these regions. In contrast, extraversion scores were positively correlated with BC in the right insula, while negatively correlated with BC in the bilateral middle temporal gyrus, indicating that the relationship between extraversion and regional arousal is not as simple as proposed by Eysenck.
Coupling effect of topological states and Chern insulators in two-dimensional triangular lattices
Zhang, Jiayong; Zhao, Bao; Xue, Yang; Zhou, Tong; Yang, Zhongqin
2018-03-01
We investigate topological states of two-dimensional (2D) triangular lattices with multiorbitals. Tight-binding model calculations of a 2D triangular lattice based on px and py orbitals exhibit very interesting doubly degenerate energy points at different positions (Γ and K /K' ) in momentum space, with quadratic non-Dirac and linear Dirac band dispersions, respectively. Counterintuitively, the system shows a global topologically trivial rather than nontrivial state with consideration of spin-orbit coupling due to the "destructive interference effect" between the topological states at the Γ and K /K' points. The topologically nontrivial state can emerge by introducing another set of triangular lattices to the system (bitriangular lattices) due to the breakdown of the interference effect. With first-principles calculations, we predict an intrinsic Chern insulating behavior (quantum anomalous Hall effect) in a family of the 2D triangular lattice metal-organic framework of Co(C21N3H15) (TPyB-Co) from this scheme. Our results provide a different path and theoretical guidance for the search for and design of new 2D topological quantum materials.
Topological phononic states of underwater sound based on coupled ring resonators
Energy Technology Data Exchange (ETDEWEB)
He, Cheng; Li, Zheng; Ni, Xu; Sun, Xiao-Chen; Yu, Si-Yuan [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Lu, Ming-Hui, E-mail: luminghui@nju.edu.cn; Liu, Xiao-Ping; Chen, Yan-Feng [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China)
2016-01-18
We report a design of topological phononic states for underwater sound using arrays of acoustic coupled ring resonators. In each individual ring resonator, two degenerate acoustic modes, corresponding to clockwise and counter-clockwise propagation, are treated as opposite pseudospins. The gapless edge states arise in the bandgap resulting in protected pseudospin-dependent sound transportation, which is a phononic analogue of the quantum spin Hall effect. We also investigate the robustness of the topological sound state, suggesting that the observed pseudospin-dependent sound transportation remains unless the introduced defects facilitate coupling between the clockwise and counter-clockwise modes (in other words, the original mode degeneracy is broken). The topological engineering of sound transportation will certainly promise unique design for next generation of acoustic devices in sound guiding and switching, especially for underwater acoustic devices.
Topologically Entangled Rashba-Split Shockley States on the Surface of Grey Arsenic.
Zhang, Peng; Ma, J-Z; Ishida, Y; Zhao, L-X; Xu, Q-N; Lv, B-Q; Yaji, K; Chen, G-F; Weng, H-M; Dai, X; Fang, Z; Chen, X-Q; Fu, L; Qian, T; Ding, H; Shin, S
2017-01-27
We discover a pair of spin-polarized surface bands on the (111) face of grey arsenic by using angle-resolved photoemission spectroscopy (ARPES). In the occupied side, the pair resembles typical nearly-free-electron Shockley states observed on noble-metal surfaces. However, pump-probe ARPES reveals that the spin-polarized pair traverses the bulk band gap and that the crossing of the pair at Γ[over ¯] is topologically unavoidable. First-principles calculations well reproduce the bands and their nontrivial topology; the calculations also support that the surface states are of Shockley type because they arise from a band inversion caused by crystal field. The results provide compelling evidence that topological Shockley states are realized on As(111).
Topological interface states and effects for next generation of innovative devices
International Nuclear Information System (INIS)
Kantser, Valeriu; Carlig, Sergiu
2013-01-01
Topological insulators (TI) have opened a gateway to search new quantum electronic phase of the condensed matter as well as to pave new platform of modern technology. This stems mainly on their unique surface states that are protected by time-reversal symmetry, show the Dirac cones connecting the inverted conduction and valence bands and exhibit unique spin-momentum locking property. Increasing the surface state contribution in proportion to the bulk of material is critical to investigate the surface states and for future innovative device applications. The way to achieve this is to configure topological insulators into nanostructures, which at the same time in combination with others materials significantly enlarge the variety of new states and phenomena. This article reviews the recent progress made in topological insulator nano heterostructures electronic states investigation. The state of art of different new scenario of engineering topologically interface states in the TI heterostructures are revealed, in particular by using polarization fields and antiferromagnetic ordering. Some of new proposals for innovative electronic devices are discussed. (authors)
Topologically protected edge states for out-of-plane and in-plane bulk elastic waves
Huo, Shao-Yong; Chen, Jiu-Jiu; Huang, Hong-Bo
2018-04-01
Topological phononic insulators (TPnIs) show promise for application in the manipulation of acoustic waves for the design of low-loss transmission and perfectly integrated communication devices. Since solid phononic crystals exist as a transverse polarization mode and a mixed longitudinal-transverse polarization mode, the realization of topological edge states for both out-of-plane and in-plane bulk elastic waves is desirable to enhance the controllability of the edge waves in solid systems. In this paper, a two-dimensional (2D) solid/solid hexagonal-latticed phononic system that simultaneously supports the topologically protected edge states for out-of-plane and in-plane bulk elastic waves is investigated. Firstly, two pairs of two-fold Dirac cones, respectively corresponding to the out-of-plane and in-plane waves, are obtained at the same frequency by tuning the crystal parameters. Then, a strategy of zone folding is invoked to form double Dirac cones. By shrinking and expanding the steel scatterer, the lattice symmetry is broken, and band inversions induced, giving rise to an intriguing topological phase transition. Finally, the topologically protected edge states for both out-of-plane and in-plane bulk elastic waves, which can be simultaneously located at the frequency range from 1.223 to 1.251 MHz, are numerically observed. Robust pseudospin-dependent elastic edge wave propagation along arbitrary paths is further demonstrated. Our results will significantly broaden its practical application in the engineering field.
Simon, David S.; Fitzpatrick, Casey A.; Osawa, Shuto; Sergienko, Alexander V.
2017-07-01
It is shown that quantum walks on one-dimensional arrays of special linear-optical units allow the simulation of discrete-time Hamiltonian systems with distinct topological phases. In particular, a slightly modified version of the Su-Schrieffer-Heeger (SSH) system can be simulated, which exhibits states of nonzero winding number and has topologically protected boundary states. In the large-system limit this approach uses quadratically fewer resources to carry out quantum simulations than previous linear-optical approaches and can be readily generalized to higher-dimensional systems. The basic optical units that implement this simulation consist of combinations of optical multiports that allow photons to reverse direction.
A short course on topological insulators band structure and edge states in one and two dimensions
Asbóth, János K; Pályi, András
2016-01-01
This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological insulators. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. The present approach uses noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dimensional case (the Su-Schrieffer-Heeger model for polyacetylene) to two-dimensional time-reversal invariant topological insulators (the Bernevig-Hughes-Zhang model for HgTe). In each case the discussion of simple toy models is followed by the formulation of the general arguments regarding topological insulators. The only prerequisite for the reader is a working knowledge in quantum mechanics, the relevant solid state physics background is provided as part of this self-contained text, which is complemented by end-of-chapter problems.
Alezi, Dalal
2015-04-07
Gaining control over the assembly of highly porous rare-earth (RE) based metal-organic frameworks (MOFs) remains challenging. Here we report the latest discoveries on our continuous quest for highly-connected nets. The topological exploration based on the non-compatibility of 12-connected RE polynuclear carboxylate-based cluster, points of extension matching the 12 vertices of the cuboctahedron (cuo), with 3-connected organic ligands led to the discovery of two fascinating and highly-connected minimal edge-transitive nets, pek and aea. The reduced symmetry of the employed triangular tricarboxylate ligand, as compared to the prototype highly symmetrical 1,3,5-benzene(tris)benzoic acid guided the concurrent occurrence of nonanuclear [RE9(μ3-OH)12(μ3-O)2(O2C–)12] and hexanuclear [RE6(OH)8(O2C–)8] carboxylate-based clusters as 12-connected and 8-connected molecular building blocks in the structure of a 3-periodic pek-MOF based on a novel (3,8,12)-c trinodal net. The use of a tricarboxylate ligand with modified angles between carboxylate moieties led to the formation of a second MOF containing solely nonanuclear clusters and exhibiting once more a novel and a highly-connected (3,12,12)-c trinodal net with aea topology. Notably, it is the first time that RE-MOFs with double six-membered ring (d6R) secondary building units are isolated, representing therefore a critical step forward toward the design of novel and highly coordinated materials using the supermolecular building layer approach while considering the d6Rs as building pillars. Lastly, the potential of these new MOFs for gas separation/storage was investigated by performing gas adsorption studies of various probe gas molecules over a wide range of pressures. Noticeably, pek-MOF-1 showed excellent volumetric CO2 and CH4 uptakes at high pressures.
Fingerprints of bosonic symmetry protected topological state in a quantum point contact
Zhang, Rui-Xing; Liu, Chao-Xing
2016-01-01
In this work, we study the transport through a quantum point contact for bosonic helical liquid that exists at the edge of a bilayer graphene under a strong magnetic field. We identify "smoking gun" transport signatures to distinguish bosonic symmetry protected topological (BSPT) state from fermionic two-channel quantum spin Hall (QSH) state in this system. In particular, a novel charge insulator/spin conductor phase is found for BSPT state, while either charge insulator/spin insulator or cha...
Andreev bound states and current-phase relations in three-dimensional topological insulators
Snelder, M.; Veldhorst, M.; Golubov, Alexandre Avraamovitch; Brinkman, Alexander
2013-01-01
To guide the search for the Majorana fermion, we theoretically study superconductor/topological-insulator/superconductor (S/TI/S) junctions in an experimentally relevant regime. We find that the striking features present in these systems, including the doubled periodicity of the Andreev bound states
Controllable magnetic doping of the surface state of a topological insulator
DEFF Research Database (Denmark)
Schlenk, T.; Bianchi, M.; Koleini, Mohammad
2013-01-01
principles calculations within density functional theory, these Fe substitutional impurities retain a large magnetic moment thus presenting an alternative scheme for magnetically doping the topological surface state. For both types of Fe doping, we see no indication of a gap at the Dirac point....
Pseudo-time-reversal symmetry and topological edge states in two-dimensional acoustic crystals
Mei, Jun
2016-09-02
We propose a simple two-dimensional acoustic crystal to realize topologically protected edge states for acoustic waves. The acoustic crystal is composed of a triangular array of core-shell cylinders embedded in a water host. By utilizing the point group symmetry of two doubly degenerate eigenstates at the Î
Dirac and Majorana edge states in graphene and topological superconductors
Akhmerov, Anton Roustiamovich
2011-01-01
This dissertation is about transport and electronic properties of two types of electronic states occuring at the edges, which are protected by symmetry between positive and negative energies. One type of these states is shown to occur universally in graphene. It is also described how another type of
Directory of Open Access Journals (Sweden)
Lixin Gao
2013-01-01
Full Text Available The leader-following consensus problem of higher order multiagent systems is considered. The dynamics of each agent are given in general form of linear system, and the communication topology among the agents is assumed to be directed and switching. To track the leader, two kinds of distributed observer-based consensus protocols are proposed for each following agent, whose distributed observers are used to estimate the leader’s state and tracking error based on the relative outputs of the neighboring agents, respectively. Some sufficient consensus conditions are established by using parameter-dependent Lyapunov function method under a class of directed interaction topologies. As special cases, the consensus conditions for balanced and undirected interconnection topology cases can be obtained directly. The protocol design technique is based on algebraic graph theory, Riccati equation, and Sylvester equation. Finally, a simulation example is given to illustrate our obtained result.
Number-conserving interacting fermion models with exact topological superconducting ground states
Wang, Zhiyuan; Xu, Youjiang; Pu, Han; Hazzard, Kaden R. A.
2017-09-01
We present a method to construct number-conserving Hamiltonians whose ground states exactly reproduce an arbitrarily chosen BCS-type mean-field state. Such parent Hamiltonians can be constructed not only for the usual s -wave BCS state, but also for more exotic states of this form, including the ground states of Kitaev wires and two-dimensional topological superconductors. This method leads to infinite families of locally interacting fermion models with exact topological superconducting ground states. After explaining the general technique, we apply this method to construct two specific classes of models. The first one is a one-dimensional double wire lattice model with Majorana-like degenerate ground states. The second one is a two-dimensional px+i py superconducting model, where we also obtain analytic expressions for topologically degenerate ground states in the presence of vortices. Our models may provide a deeper conceptual understanding of how Majorana zero modes could emerge in condensed matter systems, as well as inspire novel routes to realize them in experiment.
Fingerprints of a Bosonic Symmetry-Protected Topological State in a Quantum Point Contact
Zhang, Rui-Xing; Liu, Chao-Xing
2017-05-01
In this work, we study the transport through a quantum point contact for bosonic helical liquid that exists at the edge of a bilayer graphene under a strong magnetic field. We identify "smoking gun" transport signatures to distinguish a bosonic symmetry-protected topological (BSPT) state from a fermionic two-channel quantum spin Hall (QSH) state in this system. In particular, a novel charge-insulator-spin-conductor phase is found for the BSPT state, while either the charge-insulator-spin-insulator or the charge-conductor-spin-conductor phase is expected for the two-channel QSH state. Consequently, a simple transport measurement will reveal the fingerprint of bosonic topological physics in bilayer graphene systems.
Pairing States of Spin-3/2 Fermions: Symmetry-Enforced Topological Gap Functions
Venderbos, Jörn W. F.; Savary, Lucile; Ruhman, Jonathan; Lee, Patrick A.; Fu, Liang
2018-01-01
We study the topological properties of superconductors with paired j =3/2 quasiparticles. Higher spin Fermi surfaces can arise, for instance, in strongly spin-orbit coupled band-inverted semimetals. Examples include the Bi-based half-Heusler materials, which have recently been established as low-temperature and low-carrier density superconductors. Motivated by this experimental observation, we obtain a comprehensive symmetry-based classification of topological pairing states in systems with higher angular momentum Cooper pairing. Our study consists of two main parts. First, we develop the phenomenological theory of multicomponent (i.e., higher angular momentum) pairing by classifying the stationary points of the free energy within a Ginzburg-Landau framework. Based on the symmetry classification of stationary pairing states, we then derive the symmetry-imposed constraints on their gap structures. We find that, depending on the symmetry quantum numbers of the Cooper pairs, different types of topological pairing states can occur: fully gapped topological superconductors in class DIII, Dirac superconductors, and superconductors hosting Majorana fermions. Notably, we find a series of nematic fully gapped topological superconductors, as well as double- and triple-Dirac superconductors, with quadratic and cubic dispersion, respectively. Our approach, applied here to the case of j =3/2 Cooper pairing, is rooted in the symmetry properties of pairing states, and can therefore also be applied to other systems with higher angular momentum and high-spin pairing. We conclude by relating our results to experimentally accessible signatures in thermodynamic and dynamic probes.
The ATLAS collaboration
2017-01-01
The electron and photon reconstruction in ATLAS has moved towards the use of a dynamical, topo- logical cell-based approach for cluster building, owing to advancements in the calibration procedure which allow for such a method to be applied. The move to this new technique allows for improved measurements of electron and photon energies, particularly in situations where an electron radiates a bremsstrahlung photon, or a photon converts to an electron-poistron pair. This note details the changes to the ATLAS electron and photon reconstruction software, and assesses its performance under current LHC luminosity conditions using simulated data. Changes to the converted photon reconstruction are also detailed, which improve the reconstruction efficiency of double-track converted photons, as well as reducing the reconstruction of spurious one-track converted photons. The performance of the new reconstruction algorithm is also presented in a number of important topologies relevant to precision Standard Model physics,...
Topological helical edge states in water waves over a topographical bottom
Wu, Shiqiao; Wu, Ying; Mei, Jun
2018-02-01
We present the discovery of topologically protected helical edge states in water wave systems, which are realized in water wave propagating over a topographical bottom whose height is modulated periodically in a two-dimensional triangular pattern. We develop an effective Hamiltonian to characterize the dispersion relation and use spin Chern numbers to classify the topology. Through full-wave simulations we unambiguously demonstrate the robustness of the helical edge states which are immune to defects and disorders so that the backscattering loss is significantly reduced. A spin splitter is designed for water wave systems, where helical edge states with different spin orientations are spatially separated with each other, and potential applications are discussed.
Hurst, Hilary M.; Efimkin, Dmitry K.; Galitski, Victor
We consider the proximity effect between Dirac states at the surface of a topological insulator and a ferromagnet with easy plane anisotropy, which is described by the XY-model and undergoes a Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Classical magnetic fluctuations interacting with the surface states of a topological insulator can be described by an effective gauge field. This model can be mapped onto the problem of Dirac fermions in a random magnetic field, however this analogy is only partial in the presence of electron-hole asymmetry or warping of the Dirac dispersion which results in screening of magnetic fluctuations. We show that this proximity coupling leads to anomalous transport behavior of the surface states near the BKT transition temperature.
Topological edge state with zero Hall conductivity in quasi-one dimensional system
Directory of Open Access Journals (Sweden)
Xiao-Shan Ye
2016-09-01
Full Text Available We explore the structure of the energy spectra of quasi-one dimensional (Q1D system subjected to spin-density-wave SDW states. The structure of the energy spectra opens energy gaps with Zeeman field. Theses gaps result in plateaus for the Quantum Hall conductivity which is associated with edge states. Different from the SSH Hofstadter model, here we show that there are a doublet of edge states contribution to zero Hall conductivity. These edge states are allowed for magnetic control of spin currents. The topological effects predicted here could be tested directly in organic conductors system.
Instability of the topological surface state in Bi2Se3 upon deposition of gold
Polyakov, A.; Tusche, C.; Ellguth, M.; Crozier, E. D.; Mohseni, K.; Otrokov, M. M.; Zubizarreta, X.; Vergniory, M. G.; Geilhufe, M.; Chulkov, E. V.; Ernst, A.; Meyerheim, H. L.; Parkin, S. S. P.
2017-05-01
Momentum-resolved photoemission spectroscopy indicates the instability of the Dirac surface state upon deposition of gold on the (0001) surface of the topological insulator Bi2Se3 . Based on the structure model derived from extended x-ray absorption fine structure experiments showing that gold atoms substitute bismuth atoms, first-principles calculations provide evidence that a gap appears due to hybridization of the surface state with gold d states near the Fermi level. Our findings provide insights into the mechanisms affecting the stability of the surface state.
Directory of Open Access Journals (Sweden)
Yu Wang
2002-01-01
Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.
Rzucidlo, Justyna K; Roseman, Paige L; Laurienti, Paul J; Dagenbach, Dale
2013-01-01
Graph-theory based analyses of resting state functional Magnetic Resonance Imaging (fMRI) data have been used to map the network organization of the brain. While numerous analyses of resting state brain organization exist, many questions remain unexplored. The present study examines the stability of findings based on this approach over repeated resting state and working memory state sessions within the same individuals. This allows assessment of stability of network topology within the same state for both rest and working memory, and between rest and working memory as well. fMRI scans were performed on five participants while at rest and while performing the 2-back working memory task five times each, with task state alternating while they were in the scanner. Voxel-based whole brain network analyses were performed on the resulting data along with analyses of functional connectivity in regions associated with resting state and working memory. Network topology was fairly stable across repeated sessions of the same task, but varied significantly between rest and working memory. In the whole brain analysis, local efficiency, Eloc, differed significantly between rest and working memory. Analyses of network statistics for the precuneus and dorsolateral prefrontal cortex revealed significant differences in degree as a function of task state for both regions and in local efficiency for the precuneus. Conversely, no significant differences were observed across repeated sessions of the same state. These findings suggest that network topology is fairly stable within individuals across time for the same state, but also fluid between states. Whole brain voxel-based network analyses may prove to be a valuable tool for exploring how functional connectivity changes in response to task demands.
Energy Technology Data Exchange (ETDEWEB)
Borges Junior, Itamar; Silva, Alexander M., E-mail: itamar@ime.eb.br [Instituto Militar de Engenharia (IME), Rio de Janeiro-RJ (Brazil). Programa de Pos-Graduacao em Engenharia de Defesa
2012-10-15
A general two-step theoretical approach to study electronic redistributions in catalytic processes is presented. In the first step, density functional theory (DFT) is used to fully optimize two geometries: the cluster representing the catalyst and the cluster plus adsorbed molecule system. In the second step, the converged electron density is divided into multipoles centered on atomic sites according to a distributed multipole analysis which provides detailed topological information on the charge redistribution of catalyst and molecule before and after adsorption. This approach is applied to thiophene adsorption on the 10{sup -}10 metal edge of Ni(Co)MoS catalysts and compared to the same reaction on bare MoS{sub 2}. Calculated adsorption energies, geometries and multipole analysis indicate weak thiophene chemisorption on both cases. A Coulombic bond model showed that surface metal-sulfur bond strengths in Ni(Co)MoS promoted catalysts are considerably smaller than in bare MoS{sub 2}, thus confirming the origin of the enhancement of hydrodesulfurization (HDS) activity in these catalysts. (author)
Topology and criticality in the resonating Affleck-Kennedy-Lieb-Tasaki loop spin liquid states
Li, Wei; Yang, Shuo; Cheng, Meng; Liu, Zheng-Xin; Tu, Hong-Hao
2014-05-01
We exploit a natural projected entangled-pair state (PEPS) representation for the resonating Affleck-Kennedy-Lieb-Tasaki loop (RAL) state. By taking advantage of PEPS-based analytical and numerical methods, we characterize the RAL states on various two-dimensional lattices. On square and honeycomb lattices, these states are critical since the dimer-dimer correlations decay as a power law. On the kagome lattice, the RAL state has exponentially decaying correlation functions, supporting the scenario of a gapped spin liquid. We provide further evidence that the RAL state on the kagome lattice is a Z2 spin liquid, by identifying the four topological sectors and computing the topological entropy. Furthermore, we construct a one-parameter family of PEPS states interpolating between the RAL state and a short-range resonating valence bond state and find a critical point, consistent with the fact that the two states belong to two different phases. We also perform a variational study of the spin-1 kagome Heisenberg model using this one-parameter PEPS.
Selective buckling via states of self-stress in topological metamaterials.
Paulose, Jayson; Meeussen, Anne S; Vitelli, Vincenzo
2015-06-23
States of self-stress--tensions and compressions of structural elements that result in zero net forces--play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices.
Majorana bound states from exceptional points in non-topological superconductors
San-Jose, Pablo; Cayao, Jorge; Prada, Elsa; Aguado, Ramón
2016-02-01
Recent experimental efforts towards the detection of Majorana bound states have focused on creating the conditions for topological superconductivity. Here we demonstrate an alternative route, which achieves fully localised zero-energy Majorana bound states when a topologically trivial superconductor is strongly coupled to a helical normal region. Such a junction can be experimentally realised by e.g. proximitizing a finite section of a nanowire with spin-orbit coupling, and combining electrostatic depletion and a Zeeman field to drive the non-proximitized (normal) portion into a helical phase. Majorana zero modes emerge in such an open system without fine-tuning as a result of charge-conjugation symmetry, and can be ultimately linked to the existence of ‘exceptional points’ (EPs) in parameter space, where two quasibound Andreev levels bifurcate into two quasibound Majorana zero modes. After the EP, one of the latter becomes non-decaying as the junction approaches perfect Andreev reflection, thus resulting in a Majorana dark state (MDS) localised at the NS junction. We show that MDSs exhibit the full range of properties associated to conventional closed-system Majorana bound states (zero-energy, self-conjugation, 4π-Josephson effect and non-Abelian braiding statistics), while not requiring topological superconductivity.
Universal quantum computing using (Zd) 3 symmetry-protected topologically ordered states
Chen, Yanzhu; Prakash, Abhishodh; Wei, Tzu-Chieh
2018-02-01
Measurement-based quantum computation describes a scheme where entanglement of resource states is utilized to simulate arbitrary quantum gates via local measurements. Recent works suggest that symmetry-protected topologically nontrivial, short-ranged entangled states are promising candidates for such a resource. Miller and Miyake [npj Quantum Inf. 2, 16036 (2016), 10.1038/npjqi.2016.36] recently constructed a particular Z2×Z2×Z2 symmetry-protected topological state on the Union Jack lattice and established its quantum-computational universality. However, they suggested that the same construction on the triangular lattice might not lead to a universal resource. Instead of qubits, we generalize the construction to qudits and show that the resulting (d -1 ) qudit nontrivial Zd×Zd×Zd symmetry-protected topological states are universal on the triangular lattice, for d being a prime number greater than 2. The same construction also holds for other 3-colorable lattices, including the Union Jack lattice.
Bilayer Graphene as a Platform for Bosonic Symmetry-Protected Topological States.
Bi, Zhen; Zhang, Ruixing; You, Yi-Zhuang; Young, Andrea; Balents, Leon; Liu, Chao-Xing; Xu, Cenke
2017-03-24
Bosonic symmetry protected topological (BSPT) states, the bosonic analogue of topological insulators, have attracted enormous theoretical interest in the last few years. Although BSPT states have been classified by various approaches, there is so far no successful experimental realization of any BSPT state in two or higher dimensions. In this paper, we propose that a two-dimensional BSPT state with U(1)×U(1) symmetry can be realized in bilayer graphene in a magnetic field. Here the two U(1) symmetries represent total spin S^{z} and total charge conservation, respectively. The Coulomb interaction plays a central role in this proposal-it gaps out all the fermions at the boundary, so that only bosonic charge and spin degrees of freedom are gapless and protected at the edge. Based on the above conclusion, we propose that the bulk quantum phase transition between the BSPT and trivial phase, which can be driven by applying both magnetic and electric fields, can become a "bosonic phase transition" with interactions. That is, only bosonic modes close their gap at the transition, which is fundamentally different from all the well-known topological insulator to trivial insulator transitions that occur for free fermion systems. We discuss various experimental consequences of this proposal.
Selective buckling via states of self-stress in topological metamaterials
Paulose, Jayson; Meeussen, Anne S.; Vitelli, Vincenzo
2015-01-01
States of self-stress—tensions and compressions of structural elements that result in zero net forces—play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices. PMID:26056303
Quantification of the clustering properties of nuclear states
International Nuclear Information System (INIS)
Beck, R.; Dickmann, F.
1985-05-01
The amount of particular type of clustering in a nuclear state is defined in this paper as the norm square of the projection of the wave function onto the particular cluster model subspace. It is pointed out that, although the clusters can not be localized in space by measurement, the amount of clustering characterizes the cluster formation in close analogy with a quantum mechanical probability. The cluster model component of the wave function is proved to have a variational property. This facilitates the computation of the amount of clustering. The model dependence of the amounts of various clusterings and their relationship to the corresponding spectroscopic factors are studied via numerical examples for two models of sup(6)Li. It is concluded that, in a relative sense, the spectroscopic factor, which is more directly related to experiment, is also characteristic of the clustering contents of different states of the same nucleus, but it can not be used for comparisons between different nuclei or clusterings. (author)
Topological states at the (001) surface of SrTiO3
Vivek, Manali; Goerbig, Mark O.; Gabay, Marc
2017-04-01
Defect-free SrTiO3 (STO) is a band insulator but angle resolved photoemission spectroscopy (ARPES) experiments have demonstrated the existence of a nanometer thin two-dimensional electron liquid (2DEG) at the (001) oriented surface of this compound. The bulk is a trivial insulator, but our theoretical study reveals that the parity of electronic wave functions in this 2DEG is inverted in the vicinity of special points in reciprocal space where the low-energy dispersion consists of four gapped Dirac cones with a tilted and anisotropic shape. This gives rise to linearly dispersing topological edge states at the one-dimensional boundary. We propose to probe these modes by measuring the Josephson radiation from gapless bound Andreev states in STO based junctions, as it is predicted that they display distinctive signatures of topology.
Search for C+ C clustering in Mg ground state
Indian Academy of Sciences (India)
2017-01-04
Jan 4, 2017 ... Abstract. In the backdrop of many models, the heavy cluster structure of the ground state of 24Mg has been probed experimentally for the first time using the heavy cluster knockout reaction 24Mg(12C,212C)12C in the quasifree scattering kinematic domain. In the (12C,212C) reaction, the direct ...
Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2.
Guan, Syu-You; Chen, Peng-Jen; Chu, Ming-Wen; Sankar, Raman; Chou, Fangcheng; Jeng, Horng-Tay; Chang, Chia-Seng; Chuang, Tien-Ming
2016-11-01
The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level ( E F ) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe 2 . Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross E F , on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe 2 as a promising candidate for TSC.
Surface Andreev Bound States and Odd-Frequency Pairing in Topological Superconductor Junctions
Tanaka, Yukio; Tamura, Shun
2018-04-01
In this review, we summarize the achievement of the physics of surface Andreev bound states (SABS) up to now. The route of this activity has started from the physics of SABS of unconventional superconductors where the pair potential has a sign change on the Fermi surface. It has been established that SABS can be regarded as a topological edge state with topological invariant defined in the bulk Hamiltonian. On the other hand, SABS accompanies odd-frequency pairing like spin-triplet s-wave or spin-singlet p-wave. In a spin-triplet superconductor junction, induced odd-frequency pairing can penetrate into a diffusive normal metal (DN) attached to the superconductor. It causes so called anomalous proximity effect where the local density of states of quasiparticle in DN has a zero energy peak. When bulk pairing symmetry is spin-triplet px-wave, the anomalous proximity effect becomes prominent and the zero bias voltage conductance is always quantized independent of the resistance in DN and interface. Finally, we show that the present anomalous proximity effect is realized in an artificial topological superconducting system, where a nanowire with spin-orbit coupling and Zeeman field is put on the conventional spin-singlet s-wave superconductor.
Exotic Non-Abelian Topological Defects in Lattice Fractional Quantum Hall States
Liu, Zhao; Möller, Gunnar; Bergholtz, Emil J.
2017-09-01
We investigate extrinsic wormholelike twist defects that effectively increase the genus of space in lattice versions of multicomponent fractional quantum Hall systems. Although the original band structure is distorted by these defects, leading to localized midgap states, we find that a new lowest flat band representing a higher genus system can be engineered by tuning local single-particle potentials. Remarkably, once local many-body interactions in this new band are switched on, we identify various Abelian and non-Abelian fractional quantum Hall states, whose ground-state degeneracy increases with the number of defects, i.e, with the genus of space. This sensitivity of topological degeneracy to defects provides a "proof of concept" demonstration that genons, predicted by topological field theory as exotic non-Abelian defects tied to a varying topology of space, do exist in realistic microscopic models. Specifically, our results indicate that genons could be created in the laboratory by combining the physics of artificial gauge fields in cold atom systems with already existing holographic beam shaping methods for creating twist defects.
Topologically protected refraction of robust kink states in valley photonic crystals
Gao, Fei; Xue, Haoran; Yang, Zhaoju; Lai, Kueifu; Yu, Yang; Lin, Xiao; Chong, Yidong; Shvets, Gennady; Zhang, Baile
2018-02-01
Recently discovered valley photonic crystals (VPCs) mimic many of the unusual properties of two-dimensional (2D) gapped valleytronic materials. Of the utmost interest to optical communications is their ability to support topologically protected chiral edge (kink) states at the internal domain wall between two VPCs with opposite valley-Chern indices. Here we experimentally demonstrate valley-polarized kink states with polarization multiplexing in VPCs, designed from a spin-compatible four-band model. When the valley pseudospin is conserved, we show that the kink states exhibit nearly perfect out-coupling efficiency into directional beams, through the intersection between the internal domain wall and the external edge separating the VPCs from ambient space. The out-coupling behaviour remains topologically protected even when we break the spin-like polarization degree of freedom (DOF), by introducing an effective spin-orbit coupling in one of the VPC domains. This also constitutes the first realization of spin-valley locking for topological valley transport.
Energy Technology Data Exchange (ETDEWEB)
Chen, Y
2011-08-18
Angle resolved photoemission spectroscopy (ARPES) study on TlBiTe2 and TlBiSe2 from a Thallium-based III-V-VI2 ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe{sub 2}, the large bulk gap ({approx} 200meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe{sub 2}, the observed negative bulk gap indicates it as a semi-metal, rather than a narrow gap semi-conductor as conventionally believed; this semi-metality naturally explains its mysteriously small thermoelectric figure of merit comparing to other compounds in the family. Finally, the unique band structures of TlBiTe{sub 2} also suggests it as a candidate for topological superconductors.
Dirac cones in the gapless interface states between two topological insulators
Takahashi, Ryuji; Murakami, Shuichi
2012-02-01
When two topological insulators are attached together, the states on the interface become gapped due to the hybridization between the surface states. We have shown that if the two topological insulators have the opposite signs for the Dirac velocities, there exist gapless interface states [1]. In the last March meeting we showed a general proof for the existence of the gapless states using the mirror Chern number, which fixes the chirality of the surface states. In this presentation, we report the dispersions of these gapless interface states. They are in general a collection of Dirac cones. For example, if the system has threefold rotational symmetry, the interface states have six Dirac cones. By using the Fu-Kane-Mele model, which is the tight-binding model on the diamond lattice with the spin-orbit interaction, we calculate the dispersion of this gapless interface states, and discuss the relationship with the mirror Chern number.[4pt] [1] R. Takahashi, S. Murakami, Phys. Rev. Lett. 107,166805 (2011).
Multi-scale clustering by building a robust and self correcting ultrametric topology on data points.
Directory of Open Access Journals (Sweden)
Hsieh Fushing
Full Text Available The advent of high-throughput technologies and the concurrent advances in information sciences have led to an explosion in size and complexity of the data sets collected in biological sciences. The biggest challenge today is to assimilate this wealth of information into a conceptual framework that will help us decipher biological functions. A large and complex collection of data, usually called a data cloud, naturally embeds multi-scale characteristics and features, generically termed geometry. Understanding this geometry is the foundation for extracting knowledge from data. We have developed a new methodology, called data cloud geometry-tree (DCG-tree, to resolve this challenge. This new procedure has two main features that are keys to its success. Firstly, it derives from the empirical similarity measurements a hierarchy of clustering configurations that captures the geometric structure of the data. This hierarchy is then transformed into an ultrametric space, which is then represented via an ultrametric tree or a Parisi matrix. Secondly, it has a built-in mechanism for self-correcting clustering membership across different tree levels. We have compared the trees generated with this new algorithm to equivalent trees derived with the standard Hierarchical Clustering method on simulated as well as real data clouds from fMRI brain connectivity studies, cancer genomics, giraffe social networks, and Lewis Carroll's Doublets network. In each of these cases, we have shown that the DCG trees are more robust and less sensitive to measurement errors, and that they provide a better quantification of the multi-scale geometric structures of the data. As such, DCG-tree is an effective tool for analyzing complex biological data sets.
Reduce, reuse, recycle for robust cluster-state generation
International Nuclear Information System (INIS)
Horsman, Clare; Brown, Katherine L.; Kendon, Vivien M.; Munro, William J.
2011-01-01
Efficient generation of cluster states is crucial for engineering large-scale measurement-based quantum computers. Hybrid matter-optical systems offer a robust, scalable path to this goal. Such systems have an ancilla which acts as a bus connecting the qubits. We show that by generating the cluster in smaller sections of interlocking bricks, reusing one ancilla per brick, the cluster can be produced with maximal efficiency, requiring fewer than half the operations compared with no bus reuse. By reducing the time required to prepare sections of the cluster, bus reuse more than doubles the size of the computational workspace that can be used before decoherence effects dominate. A row of buses in parallel provides fully scalable cluster-state generation requiring only 20 controlled-phase gates per bus use.
Hybrid cluster state proposal for a quantum game
International Nuclear Information System (INIS)
Paternostro, M; Tame, M S; Kim, M S
2005-01-01
We propose an experimental implementation of a quantum game algorithm in a hybrid scheme combining the quantum circuit approach and the cluster state model. An economical cluster configuration is suggested to embody a quantum version of the Prisoners' Dilemma. Our proposal is shown to be within the experimental state of the art and can be realized with existing technology.The effects of relevant experimental imperfections are also carefully examined
Hybrid cluster state proposal for a quantum game
Energy Technology Data Exchange (ETDEWEB)
Paternostro, M; Tame, M S; Kim, M S [School of Mathematics and Physics, The Queen' s University, Belfast BT7 1NN (United Kingdom)
2005-10-15
We propose an experimental implementation of a quantum game algorithm in a hybrid scheme combining the quantum circuit approach and the cluster state model. An economical cluster configuration is suggested to embody a quantum version of the Prisoners' Dilemma. Our proposal is shown to be within the experimental state of the art and can be realized with existing technology.The effects of relevant experimental imperfections are also carefully examined.
Topologically distinct classes of valence-bond solid states with their parent Hamiltonians
International Nuclear Information System (INIS)
Tu Honghao; Zhang Guangming; Xiang Tao; Liu Zhengxin; Ng Taikai
2009-01-01
We present a general method to construct one-dimensional translationally invariant valence-bond solid states with a built-in Lie group G and derive their matrix product representations. The general strategies to find their parent Hamiltonians are provided so that the valence-bond solid states are their unique ground states. For quantum integer-spin-S chains, we discuss two topologically distinct classes of valence-bond solid states: one consists of two virtual SU(2) spin-J variables in each site and another is formed by using two SO(2S+1) spinors. Among them, a spin-1 fermionic valence-bond solid state, its parent Hamiltonian, and its properties are discussed in detail. Moreover, two types of valence-bond solid states with SO(5) symmetries are further generalized and their respective properties are analyzed as well.
Surface states of topological insulators: the Dirac fermion in curved two-dimensional spaces.
Lee, Dung-Hai
2009-11-06
The surface of a topological insulator is a closed two-dimensional manifold. The surface states are described by the Dirac Hamiltonian in curved two-dimensional spaces. For a slablike sample with a magnetic field perpendicular to its top and bottom surfaces, there are chiral states delocalized on the four side faces. These "chiral sheets" carry both charge and spin currents. In strong magnetic fields, the quantized charge Hall effect [sigma(xy) = (2n + 1)e2/h] will coexist with spin Hall effect.
Topological surface states of strained Mercury-Telluride probed by ARPES
Crauste, Olivier; Ohtsubo, Yoshiyuki; Ballet, Philippe; Delplace, Pierre André Louis; Carpentier, David; Bouvier, Clément; Meunier, Tristan; Taleb-Ibrahimi, Amina; Lévy, Laurent
2013-01-01
with supplementary material; The topological surface states of strained HgTe have been measured using high-resolution ARPES measurements. The dispersion of surface states form a Dirac cone, which origin is close to the top of the \\ghh band: the top half of the Dirac cone is inside the stress-gap while the bottom half lies within the heavy hole bands and keeps a linear dispersion all the way to the X-point. The circular dichroism of the photo-emitted electron intensity has also been measured f...
Fingerprints of bosonic symmetry protected topological state in a quantum point contact
Zhang, Rui-Xing; Liu, Chao-Xing
In this work, we study the transport through a quantum point contact for two-channel interacting helical liquids that exist at the edge of a bilayer graphene under a strong magnetic field. We identify ``smoking gun'' transport signatures to distinguish bosonic symmetry protected topological (BSPT) state from fermionic two-channel quantum spin Hall (QSH) state in this system. In particular, a novel charge insulator/spin conductor phase is found for a weak repulsive interaction in the BSPT state, while either charge insulator/spin insulator or charge conductor/spin conductor phase is expected for the two-channel QSH state. In the strong interaction limit, shot noise measurement for the BSPT state is expect to reveal charge-2e instanton tunneling, in comparison with the charge-e tunneling in the two-channel QSH phase.
Thermoelectric Transport by Surface States in Bi2Se3-Based Topological Insulator Thin Films
International Nuclear Information System (INIS)
Li Long-Long; Xu Wen
2015-01-01
We develop a tractable theoretical model to investigate the thermoelectric (TE) transport properties of surface states in topological insulator thin films (TITFs) of Bi 2 Se 3 at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi 2 Se 3 -based TITFs as high-performance TE materials and devices. (paper)
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.
Kunst, Flore K.; Trescher, Maximilian; Bergholtz, Emil J.
2017-08-01
The hallmark of topological phases is their robust boundary signature whose intriguing properties—such as the one-way transport on the chiral edge of a Chern insulator and the sudden disappearance of surface states forming open Fermi arcs on the surfaces of Weyl semimetals—are impossible to realize on the surface alone. Yet, despite the glaring simplicity of noninteracting topological bulk Hamiltonians and their concomitant energy spectrum, the detailed study of the corresponding surface states has essentially been restricted to numerical simulation. In this work, however, we show that exact analytical solutions of both topological and trivial surface states can be obtained for generic tight-binding models on a large class of geometrically frustrated lattices in any dimension without the need for fine-tuning of hopping amplitudes. Our solutions derive from local constraints tantamount to destructive interference between neighboring layer lattices perpendicular to the surface and provide microscopic insights into the structure of the surface states that enable analytical calculation of many desired properties including correlation functions, surface dispersion, Berry curvature, and the system size dependent gap closing, which necessarily occurs when the spatial localization switches surface. This further provides a deepened understanding of the bulk-boundary correspondence. We illustrate our general findings on a large number of examples in two and three spatial dimensions. Notably, we derive exact chiral Chern insulator edge states on the spin-orbit-coupled kagome lattice, and Fermi arcs relevant for recently synthesized slabs of pyrochlore-based Eu2Ir2O7 and Nd2Ir2O7 , which realize an all-in-all-out spin configuration, as well as for spin-ice-like two-in-two-out and one-in-three-out configurations, which are both relevant for Pr2Ir2O7 . Remarkably, each of the pyrochlore examples exhibit clearly resolved Fermi arcs although only the one
Benalcazar, Wladimir A.; Bernevig, B. Andrei; Hughes, Taylor L.
2017-12-01
We extend the theory of dipole moments in crystalline insulators to higher multipole moments. As first formulated in Benalcazar et al. [Science 357, 61 (2017), 10.1126/science.aah6442], we show that bulk quadrupole and octupole moments can be realized in crystalline insulators. In this paper, we expand in great detail the theory presented previously [Benalcazar et al., Science 357, 61 (2017), 10.1126/science.aah6442] and extend it to cover associated topological pumping phenomena, and a class of three-dimensional (3D) insulator with chiral hinge states. We start by deriving the boundary properties of continuous classical dielectrics hosting only bulk dipole, quadrupole, or octupole moments. In quantum mechanical crystalline insulators, these higher multipole bulk moments manifest themselves by the presence of boundary-localized moments of lower dimension, in exact correspondence with the electromagnetic theory of classical continuous dielectrics. In the presence of certain symmetries, these moments are quantized, and their boundary signatures are fractionalized. These multipole moments then correspond to new symmetry-protected topological phases. The topological structure of these phases is described by "nested" Wilson loops, which we define. These Wilson loops reflect the bulk-boundary correspondence in a way that makes evident a hierarchical classification of the multipole moments. Just as a varying dipole generates charge pumping, a varying quadrupole generates dipole pumping, and a varying octupole generates quadrupole pumping. For nontrivial adiabatic cycles, the transport of these moments is quantized. An analysis of these interconnected phenomena leads to the conclusion that a new kind of Chern-type insulator exists, which has chiral, hinge-localized modes in 3D. We provide the minimal models for the quantized multipole moments, the nontrivial pumping processes, and the hinge Chern insulator, and describe the topological invariants that protect them.
Quantization State of Baryonic Mass in Clusters of Galaxies
Directory of Open Access Journals (Sweden)
Potter F.
2007-01-01
Full Text Available The rotational velocity curves for clusters of galaxies cannot be explained by Newtonian gravitation using the baryonic mass nor does MOND succeed in reducing this discrepancy to acceptable differences. The dark matter hypothesis appears to offer a solution; however, non-baryonic dark matter has never been detected. As an alternative approach, quantum celestial mechanics (QCM predicts that galactic clusters are in quantization states determined solely by the total baryonic mass of the cluster and its total angular momentum. We find excellent agreement with QCM for ten galactic clusters, demonstrating that dark matter is not needed to explain the rotation velocities and providing further support to the hypothesis that all gravitationally bound systems have QCM quantization states.
Cluster expansion for ground states of local Hamiltonians
Directory of Open Access Journals (Sweden)
Alvise Bastianello
2016-08-01
Full Text Available A central problem in many-body quantum physics is the determination of the ground state of a thermodynamically large physical system. We construct a cluster expansion for ground states of local Hamiltonians, which naturally incorporates physical requirements inherited by locality as conditions on its cluster amplitudes. Applying a diagrammatic technique we derive the relation of these amplitudes to thermodynamic quantities and local observables. Moreover we derive a set of functional equations that determine the cluster amplitudes for a general Hamiltonian, verify the consistency with perturbation theory and discuss non-perturbative approaches. Lastly we verify the persistence of locality features of the cluster expansion under unitary evolution with a local Hamiltonian and provide applications to out-of-equilibrium problems: a simplified proof of equilibration to the GGE and a cumulant expansion for the statistics of work, for an interacting-to-free quantum quench.
Solid state and aqueous behavior of uranyl peroxide cage clusters
Pellegrini, Kristi Lynn
Uranyl peroxide cage clusters include a large family of more than 50 published clusters of a variety of sizes, which can incorporate various ligands including pyrophosphate and oxalate. Previous studies have reported that uranyl clusters can be used as a method to separate uranium from a solid matrix, with potential applications in reprocessing of irradiated nuclear fuel. Because of the potential applications of these novel structures in an advanced nuclear fuel cycle and their likely presence in areas of contamination, it is important to understand their behavior in both solid state and aqueous systems, including complex environments where other ions are present. In this thesis, I examine the aqueous behavior of U24Pp 12, as well as aqueous cluster systems with added mono-, di-, and trivalent cations. The resulting solutions were analyzed using dynamic light scattering and ultra-small angle X-ray scattering to evaluate the species in solution. Precipitates of these systems were analyzed using powder X-ray diffraction, X-ray fluorescence spectrometry, and Raman spectroscopy. The results of these analyses demonstrate the importance of cation size, charge, and concentration of added cations on the aqueous behavior of uranium macroions. Specifically, aggregates of various sizes and shapes form rapidly upon addition of cations, and in some cases these aggregates appear to precipitate into an X-ray amorphous material that still contains U24Pp12 clusters. In addition, I probe aggregation of U24Pp12 and U60, another uranyl peroxide cage cluster, in mixed solvent water-alcohol systems. The aggregation of uranyl clusters in water-alcohol systems is a result of hydrogen bonding with polar organic molecules and the reduction of the dielectric constant of the system. Studies of aggregation of uranyl clusters also allow for comparison between the newer uranyl polyoxometalate family and century-old transition metal polyoxometalates. To complement the solution studies of uranyl
Alpha particle cluster states in (fp)-shell nuclei
International Nuclear Information System (INIS)
Merchant, A.C.
1987-07-01
Alpha particle cluster structure is known experimentally to persist throughout the mass range 16 ≤ A ≤ 20, and has been very successfully described in this region in terms of the Buck-Dover-Vary local potential cluster model. It is argued that an analogous cluster structure should be present in nuclei at the beginning of the (fp) - shell, and the available experimental data are examined to determine likely alpha particle cluster state candidates in the mass range 40 ≤ A ≤ 44. Calculations of the cluster state spectra and mean square cluster-core separation distances (which may be readily used to evaluate E2 electromagnetic transition rates) for sup(40)Ca, sup(42)Ca, sup(42)Sc, sup(43)Sc, sup(43)Ti and sup(44)Ti using the above mentioned model are presented, and compared with experimental measurements where possible. The agreement between theory and experiment is generally good (although inferior to that obtained in the (sd)-shell) and points to the desirability of an extension and improvement of the measurements of the properties of the excited states in these nuclei. (author)
Topological Insulator State in Thin Bismuth Films Subjected to Plane Tensile Strain
Demidov, E. V.; Grabov, V. M.; Komarov, V. A.; Kablukova, N. S.; Krushel'nitskii, A. N.
2018-03-01
The results of experimental examination of galvanomagnetic properties of thin bismuth films subjected to plane tensile strain resulting from the difference in thermal expansion coefficients of the substrate material and bismuth are presented. The resistivity, the magnetoresistance, and the Hall coefficient were studied at temperatures ranging from 5 to 300 K in magnetic fields as strong as 0.65 T. Carrier densities were calculated. A considerable increase in carrier density in films thinner than 30 nm was observed. This suggests that surface states are more prominent in thin bismuth films on mica substrates, while the films themselves may exhibit the properties of a topological insulator.
Radiative width of molecular-cluster states
International Nuclear Information System (INIS)
Alhassid, Y.; Gai, M.; Bertsch, G.F.
1982-01-01
Molecular states are characterized by enhanced electromagnetic deexcitations of many different multipolarities. The expected enhancement of E1, E2, and E3 transitions is examined by deriving molecular sum rules for radiative deexcitation widths and via a dimensionality approach. The enhancement of the E1 transitions is the most striking
Dirac-Screening Stabilized Surface-State Transport in a Topological Insulator
Directory of Open Access Journals (Sweden)
Christoph Brüne
2014-12-01
Full Text Available We report magnetotransport studies on a gated strained HgTe device. This material is a three-dimensional topological insulator and exclusively shows surface-state transport. Remarkably, the Landau-level dispersion and the accuracy of the Hall quantization remain unchanged over a wide density range (3×10^{11} cm^{−2}
Stability of the Bi2Se3(111) topological state: Electron-phonon and electron-defect scattering
DEFF Research Database (Denmark)
Hatch, Richard Cannon; Bianchi, Marco; Guan, Dandan
2011-01-01
by introducing a small concentration of surface defects via ion bombardment. It is found that, in contrast to the bulk states, the topological state can no longer be observed in the photoemission spectra, and this cannot merely be attributed to surface defect-induced momentum broadening....... is possible. The electron-phonon coupling constant is found to be λ = 0.25(5), more than an order of magnitude higher than the corresponding value for intraband scattering in the noble-metal surface states. The stability of the topological state with respect to surface irregularities was also tested...
Topology of sustainable management in dynamical Earth system models with desirable states
Heitzig, J.; Kittel, T.
2015-03-01
To keep the Earth system in a desirable region of its state space, such as the recently suggested "tolerable environment and development window", "planetary boundaries", or "safe (and just) operating space", one not only needs to understand the quantitative internal dynamics of the system and the available options for influencing it (management), but also the structure of the system's state space with regard to certain qualitative differences. Important questions are: which state space regions can be reached from which others with or without leaving the desirable region? Which regions are in a variety of senses "safe" to stay in when management options might break away, and which qualitative decision problems may occur as a consequence of this topological structure? In this article, as a complement to the existing literature on optimal control which is more focussed on quantitative optimization and is much applied in both the engineering and the integrated assessment literature, we develop a mathematical theory of the qualitative topology of the state space of a dynamical system with management options and desirable states. We suggest a certain terminology for the various resulting regions of the state space and perform a detailed formal classification of the possible states with respect to the possibility of avoiding or leaving the undesired region. Our results indicate that before performing some form of quantitative optimization, the sustainable management of the Earth system may require decisions of a more discrete type that come in the form of several dilemmata, e.g., choosing between eventual safety and uninterrupted desirability, or between uninterrupted safety and increasing flexibility. We illustrate the concepts and dilemmata with conceptual models from classical mechanics, climate science, ecology, economics, and coevolutionary Earth system modelling and discuss their potential relevance for the climate and sustainability debate.
Selective scattering between Floquet-Bloch and Volkov states in a topological insulator
Mahmood, Fahad; Chan, Ching-Kit; Alpichshev, Zhanybek; Gardner, Dillon; Lee, Young; Lee, Patrick A.; Gedik, Nuh
2016-04-01
The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter. The strong time-periodic potential of intense laser light can be used to generate hybrid photon-electron states. Interaction of light with Bloch states leads to Floquet-Bloch states, which are essential in realizing new photo-induced quantum phases. Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time- and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.
Inhofer, A.; Tchoumakov, S.; Assaf, B. A.; Fève, G.; Berroir, J. M.; Jouffrey, V.; Carpentier, D.; Goerbig, M. O.; Plaçais, B.; Bendias, K.; Mahler, D. M.; Bocquillon, E.; Schlereth, R.; Brüne, C.; Buhmann, H.; Molenkamp, L. W.
2017-11-01
It is well established that topological insulators sustain Dirac fermion surface states as a consequence of band inversion in the bulk. These states have a helical spin polarization and a linear dispersion with large Fermi velocity. We report on a set of experimental observations supporting the existence of additional massive surface states. These states are also confined by the band inversion at a topological-trivial semiconductor heterojunction. While first introduced by Volkov and Pankratov (VP) before the understanding of the topological nature of such a junction, they were not experimentally identified. Here we identify their signatures on transport properties at high electric field. By monitoring the ac admittance of HgTe topological-insulator field-effect capacitors, we access the compressibility and conductivity of surface states in a broad range of energies and electric fields. The Dirac states are characterized by a compressibility minimum, a linear energy dependence, and a high mobility persisting up to energies much larger than the transport band gap of the bulk. At higher energies, we observe multiple anomalous behaviors in conductance, charge metastability, and Hall resistance that point towards the contribution of massive surface states in transport scattering and charge transfer to the bulk. The spectrum of these anomalies agrees with predictions of a phenomenological model of VP states in a smooth topological heterojunction. The model accounts for the finite interface depth, the effect of electric fields including Dirac screening, and predicts the energy of the first VP state. The massive surface states are a hallmark of topological heterojunctions, whose understanding is crucial for transport studies and applications.
Emerging Trends in Topological Insulators and Topological ...
Indian Academy of Sciences (India)
Moreover, proximity induced superconductivity in these systemscan lead to a state that supports zero energy Majoranafermions, and the phase is known as topological superconductors.In this article, the basic idea of topological insulatorsand topological superconductors are presented alongwith their experimental ...
Dipole cluster states in light, medium heavy and heavy nuclei
International Nuclear Information System (INIS)
Gai, Moshe
1984-01-01
Tests of the Vibron cluster model in sup(18)O, sup(218)Ra and sup(156)Yb are reported, as well as a test in progress in sup(52)Ti. Low lying negative parity states which appear to be members of rotational bands of alternating parity states with enhanced B(E1) intraband deexcitation rates are found. The cluster band, within the model framework, is also characterized by large alpha decay widths and enhanced radiative deexcitation widths of several multipolarities B(E1), B(E2), B(E3). A discussion of the model and the underlying, newly suggested dipole degree of freedom is presented. (author)
Three-body cluster state in 11B
International Nuclear Information System (INIS)
Kawabata, T.; Akimune, H.; Fujita, H.; Fujita, Y.; Fujiwara, M.; Hara, K.; Hatanaka, K.; Itoh, M.; Kanada-En'yo, Y.; Kishi, S.; Nakanishi, K.; Sakaguchi, H.; Shimbara, Y.; Tamii, A.; Terashima, S.; Uchida, M.; Wakasa, T.; Yasuda, Y.; Yoshida, H.P.; Yosoi, M.
2007-01-01
The cluster structures of the excited states in 11 B are studied by analyzing the isoscalar monopole and quadrupole strengths in the 11 B(d,d ' ) reaction at E d =200 MeV. The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the 3/2 3 - state at E x =8.56 MeV is well described by the AMD calculation and is an evidence for a developed three-body 2α+t cluster structure
Generation of cluster states with Josephson charge qubits
International Nuclear Information System (INIS)
Zheng, Xiao-Hu; Dong, Ping; Xue, Zheng-Yuan; Cao, Zhuo-Liang
2007-01-01
A scheme for the generation of the cluster states based on the Josephson charge qubits is proposed. The two-qubit generation case is introduced first, and then generalized to multi-qubit case. The successful probability and fidelity of current multi-qubit cluster state are both 1.0. The scheme is simple and can be easily manipulated, because any two charge qubits can be selectively and effectively coupled by a common inductance. More manipulations can be realized before decoherence sets in. All the devices in the scheme are well within the current technology
Detecting brain dynamics during resting state: a tensor based evolutionary clustering approach
Al-sharoa, Esraa; Al-khassaweneh, Mahmood; Aviyente, Selin
2017-08-01
Human brain is a complex network with connections across different regions. Understanding the functional connectivity (FC) of the brain is important both during resting state and task; as disruptions in connectivity patterns are indicators of different psychopathological and neurological diseases. In this work, we study the resting state functional connectivity networks (FCNs) of the brain from fMRI BOLD signals. Recent studies have shown that FCNs are dynamic even during resting state and understanding the temporal dynamics of FCNs is important for differentiating between different conditions. Therefore, it is important to develop algorithms to track the dynamic formation and dissociation of FCNs of the brain during resting state. In this paper, we propose a two step tensor based community detection algorithm to identify and track the brain network community structure across time. First, we introduce an information-theoretic function to reduce the dynamic FCN and identify the time points that are similar topologically to combine them into a tensor. These time points will be used to identify the different FC states. Second, a tensor based spectral clustering approach is developed to identify the community structure of the constructed tensors. The proposed algorithm applies Tucker decomposition to the constructed tensors and extract the orthogonal factor matrices along the connectivity mode to determine the common subspace within each FC state. The detected community structure is summarized and described as FC states. The results illustrate the dynamic structure of resting state networks (RSNs), including the default mode network, somatomotor network, subcortical network and visual network.
DIVERSE PROTOSTELLAR EVOLUTIONARY STATES IN THE YOUNG CLUSTER AFGL961
International Nuclear Information System (INIS)
Williams, Jonathan P.; Mann, Rita K.; Beaumont, Christopher N.; Swift, Jonathan J.; Adams, Joseph D.; Hora, Joe; Kassis, Marc; Lada, Elizabeth A.; Roman-Zuniga, Carlos G.
2009-01-01
We present arcsecond resolution mid-infrared and millimeter observations of the center of the young stellar cluster AFGL961 in the Rosette molecular cloud. Within 0.2 pc of each other, we find an early B star embedded in a dense core, a neighboring star of similar luminosity with no millimeter counterpart, a protostar that has cleared out a cavity in the circumcluster envelope, and two massive, dense cores with no infrared counterparts. An outflow emanates from one of these cores, indicating a deeply embedded protostar, but the other is starless, bound, and appears to be collapsing. The diversity of states implies either that protostellar evolution is faster in clusters than in isolation or that clusters form via quasi-static rather than dynamic collapse. The existence of a pre-stellar core at the cluster center shows that some star formation continues after and in close proximity to massive, ionizing stars.
Unidirectional edge states in topological honeycomb-lattice membrane photonic crystals.
Anderson, P Duke; Subramania, Ganapathi
2017-09-18
Photonic analogs of electronic systems with topologically non-trivial behavior such as unidirectional scatter-free propagation has tremendous potential for transforming photonic systems. Like in electronics topological behavior can be observed in photonics for systems either preserving time-reversal (TR) symmetry or explicitly breaking it. TR symmetry breaking requires magneto-optic photonics crystals (PC) or generation of synthetic gauge fields. For on-chip photonics that operate at optical frequencies both are quite challenging because of poor magneto-optic response of materials or substantial nanofabrication challenges in generating synthetic gauge fields. A recent work by Ma, et al. [Phys. Rev. Lett.114, 223901 (2015)] based on preserving pseudo TR symmetry offers a promising design scheme for observing unidirectional edge states in a modified honeycomb photonic crystal (PC) lattice of circular rods that offers encouraging alternatives. Here we propose through bandstructure calculations the inverse system of modified honeycomb PC of circular holes in a dielectric membrane which is more attractive from fabrication standpoint for on-chip applications. We observe trivial and non-trivial bandgaps as well as unidirectional edge states of opposite helicity propagating in opposite directions at the interface of a trivial and non-trivial PC structures. Around 1550nm operating wavelength ~55nm of bandwidth is possible for practicable values of design parameters (lattice constant, hole radii, membrane thickness, scaling factor etc.) and robust to reasonable variations in those parameters.
Interplay between surface and bulk states in the Topological Kondo Insulator SmB6
Biswas, Sangram; Hatnean, Monica Ciomaga; Balakrishnan, Geetha; Bid, Aveek
Kondo insulator SmB6 is predicted to have topologically protected conducting surface states(TSS). We have studied electrical transport through surface states(SS) at ultra-low temperatures in single crystals of SmB6 using local-nonlocal transport scheme and found a large nonlocal signal at temperatures lower than bulk Kondo gap scale. Using resistance fluctuation spectroscopy, we probed the local and nonlocal transport channels and showed that at low temperatures, transport in this system takes place only through SS. The measured noise in this temperature range arises due to Universal Conductance Fluctuations whose statistics was found to be consistent with theoretical predictions for that of 2D systems in the Symplectic symmetry class. We studied the temperature dependence of noise and found that, unlike the topological insulators of the dichalcogenide family, the noise in surface and bulk conduction channels in SmB6 are uncorrelated - at sufficiently low temperatures, the bulk has no discernible contribution to electrical transport in SmB6 making it an ideal platform for probing the physics of TSS. Nanomission, Department of Science & Technology (DST) and Indian Institute of Scienc and EPSRC, UK, Grant EP/L014963/1.
Baum, Yuval; Refael, Gil
2018-03-01
When a d -dimensional quantum system is subjected to a periodic drive, it may be treated as a (d +1 )-dimensional system, where the extra dimension is a synthetic one. This approach, however, affords only a limited level of control of the effective potential along the synthetic direction. In this work, we introduce a new mean for controlling the Floquet synthetic dimension. We show that arbitrary potentials, as well as edges in the synthetic dimension, could be introduced using a memory component in the system's dynamics. We demonstrate this principle by exploring topological edge states propagating normal to synthetic dimensions. Such systems may act as an optical isolator which allows the transmission of light in a directional way. Also, we suggest an experimental realization of the memory effect in spins coupled to nanofabricated Weyl semimetal surface states.
Simple scheme for encoding and decoding a qubit in unknown state for various topological codes
Łodyga, Justyna; Mazurek, Paweł; Grudka, Andrzej; Horodecki, Michał
2015-03-01
We present a scheme for encoding and decoding an unknown state for CSS codes, based on syndrome measurements. We illustrate our method by means of Kitaev toric code, defected-lattice code, topological subsystem code and 3D Haah code. The protocol is local whenever in a given code the crossings between the logical operators consist of next neighbour pairs, which holds for the above codes. For subsystem code we also present scheme in a noisy case, where we allow for bit and phase-flip errors on qubits as well as state preparation and syndrome measurement errors. Similar scheme can be built for two other codes. We show that the fidelity of the protected qubit in the noisy scenario in a large code size limit is of , where p is a probability of error on a single qubit per time step. Regarding Haah code we provide noiseless scheme, leaving the noisy case as an open problem.
Systematic study of transport via surface and bulk states in Bi2Te3 topological insulator
de Castro, S.; Peres, M. L.; Chitta, V. A.; Gratens, X.; Soares, D. A. W.; Fornari, C. I.; Rappl, P. H. O.; Abramof, E.; Oliveira, N. F., Jr.
2016-07-01
We performed magnetoresistance measurements on Bi2Te3 thin film in the temperature range of T = 1.2-4.0 K and for magnetic fields up to 2 T. The curves exhibited anomalous behavior for temperatures below 4.0 K. Different temperature intervals revealed electrical transport through different conductive channels with clear signatures of weak antilocalization. The magnetoresistance curves were explained using the Hikami-Larkin-Nagaoka model and the 2D Dirac modified model. The comparison between the parameters obtained from the two models revealed the transport via topological surface states and bulk states. In addition, a superconductive like transition is observed for the lowest temperatures and we suggest that this effect can be originated from the misfit dislocations caused by strain, giving rise to a superconductive channel between the interface of the film and the substrate.
Excited electronic state decomposition mechanisms of clusters of ...
Indian Academy of Sciences (India)
Excited electronic state decomposition mechanisms of clusters of dimethylnitramine and aluminum. ANUPAM BERA and ATANU BHATTACHARYA. ∗. Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India e-mail: atanub@ipc.iisc.ernet.in. MS received 5 September 2014; ...
An entanglement concentration protocol for cluster states using ...
Indian Academy of Sciences (India)
Abstract. The purpose of this paper is a proposal on entanglement concentration protocol for cluster states. The protocol uses CNOT gate operation and is assisted with a single qubit. Moreover, the local and non-local operations are performed by a single party. We also make a comparative numerical study of the residual ...
Search for C+ C clustering in Mg ground state
Indian Academy of Sciences (India)
2017-01-04
12C+12C) structure models for the ground state of 24Mg. Keywords. Direct nuclear reactions; heavy cluster knockout; structure of 24Mg(g.s); C–C optical potential. PACS Nos 24.50.+g; 24.10.Eq; 24.10.Ht; 25.40.−h; 25.40.Cl; 25.60.−t.
Excited electronic state decomposition mechanisms of clusters of ...
Indian Academy of Sciences (India)
In this report, electronically non-adiabatic decomposition pathways of clusters of dimethylnitramine and aluminum (DMNA-Al and DMNA-Al2) are discussed in comparison to isolated dimethylnitramine (DMNA). Electronically excited state processes of DMNA-Al and DMNA-Al2 are explored using the complete active space ...
Two-phonon states in alkali-metal clusters
International Nuclear Information System (INIS)
Abada, A.; Vautherin, D.
1992-12-01
Two phonon-states of alkali-metal clusters (treated as jellium spheres) are calculated by using a method based on a perturbative construction of periodic orbits of the time-dependent mean-field equations. Collective vibrations with various multipolarities in charged Na 21 + are considered. (author) 26 refs.; 2 figs.; 3 tabs
Normalized cut group clustering of resting-state FMRI data.
Directory of Open Access Journals (Sweden)
Martijn van den Heuvel
Full Text Available BACKGROUND: Functional brain imaging studies have indicated that distinct anatomical brain regions can show coherent spontaneous neuronal activity during rest. Regions that show such correlated behavior are said to form resting-state networks (RSNs. RSNs have been investigated using seed-dependent functional connectivity maps and by using a number of model-free methods. However, examining RSNs across a group of subjects is still a complex task and often involves human input in selecting meaningful networks. METHODOLOGY/PRINCIPAL FINDINGS: We report on a voxel based model-free normalized cut graph clustering approach with whole brain coverage for group analysis of resting-state data, in which the number of RSNs is computed as an optimal clustering fit of the data. Inter-voxel correlations of time-series are grouped at the individual level and the consistency of the resulting networks across subjects is clustered at the group level, defining the group RSNs. We scanned a group of 26 subjects at rest with a fast BOLD sensitive fMRI scanning protocol on a 3 Tesla MR scanner. CONCLUSIONS/SIGNIFICANCE: An optimal group clustering fit revealed 7 RSNs. The 7 RSNs included motor/visual, auditory and attention networks and the frequently reported default mode network. The found RSNs showed large overlap with recently reported resting-state results and support the idea of the formation of spatially distinct RSNs during rest in the human brain.
Asymmetric electroresistance of cluster glass state in manganites
Lourembam, James
2014-03-31
We report the electrostatic modulation of transport in strained Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films grown on SrTiO3 by gating with ionic liquid in electric double layer transistors (EDLT). In such manganite films with strong phase separation, a cluster glass magnetic state emerges at low temperatures with a spin freezing temperature of about 99 K, which is accompanied by the reentrant insulating state with high resistance below 30 K. In the EDLT, we observe bipolar and asymmetric modulation of the channel resistance, as well as an enhanced electroresistance up to 200% at positive gate bias. Our results provide insights on the carrier-density-dependent correlated electron physics of cluster glass systems.
Arnold, Vladimir; Zorich, Anton
1999-01-01
This volume offers an account of the present state of the art in pseudoperiodic topology-a young branch of mathematics, born at the boundary between the ergodic theory of dynamical systems, topology, and number theory. Related topics include the theory of algorithms, convex integer polyhedra, Morse inequalities, real algebraic geometry, statistical physics, and algebraic number theory. The book contains many new results. Most of the articles contain brief surveys on the topics, making the volume accessible to a broad audience. From the Preface by V.I. Arnold: "The authors … have done much to s
Two-dimensional solid-state NMR reveals two topologies of sarcolipin in oriented lipid bilayers.
Buffy, Jarrod J; Traaseth, Nathaniel J; Mascioni, Alessandro; Gor'kov, Peter L; Chekmenev, Eduard Y; Brey, William W; Veglia, Gianluigi
2006-09-12
Sarcolipin (SLN), a 31 amino acid integral membrane protein, regulates SERCA1a and SERCA2a, two isoforms of the sarco(endo)plasmic Ca-ATPase, by lowering their apparent Ca(2+) affinity and thereby enabling muscle relaxation. SLN is expressed in both fast-twitch and slow-twitch muscle fibers with significant expression levels also found in the cardiac muscle. SLN shares approximately 30% identity with the transmembrane domain of phospholamban (PLN), and recent solution NMR studies carried out in detergent micelles indicate that the two polypeptides bind to SERCA in a similar manner. Previous 1D solid-state NMR experiments on selectively (15)N-labeled sites showed that SLN crosses the lipid bilayer with an orientation nearly parallel to the bilayer normal. With a view toward the characterization of SLN structure and its interactions with both lipids and SERCA, herein we report our initial structural and topological assignments of SLN in mechanically oriented DOPC/DOPE lipid bilayers as mapped by 2D (15)N PISEMA experiments. The PISEMA spectra obtained on uniformly (15)N-labeled protein as well as (15)N-Leu, (15)N-Ile and (15)N-Val map the secondary structure of SLN and, simultaneously, reveal that SLN exists in two distinct topologies. Both the major and the minor populations assume an orientation with the helix axis tilted by approximately 23 degrees with respect to the lipid bilayer normal, but vary in the rotation angle about the helix axis by approximately 5 degrees . The existence of the multiple populations in model membranes may be a significant requirement for SLN interaction with SERCA.
Buchner, Abel-John; Lozano-Durán, Adrián; Kitsios, Vassili; Atkinson, Callum; Soria, Julio
2016-04-01
Previous works have shown that momentum transfer in the wall-normal direction within turbulent wall-bounded flows occurs primarily within coherent structures defined by regions of intense Reynolds stress [1]. Such structures may be classified into wall-attached and wall-detached structures with the latter being typically weak, small-scale, and isotropically oriented, while the former are larger and carry most of the Reynolds stresses. The mean velocity fluctuation within each structure may also be used to separate structures by their dynamic properties. This study aims to extract information regarding the scales, kinematics and dynamics of these structures within the topological framework of the invariants of the velocity gradient tensor (VGT). The local topological characteristics of these intense Reynolds stress structures are compared to the topological characteristics of vortex clusters defined by the discriminant of the velocity gradient tensor. The alignment of vorticity with the principal strain directions within these structures is also determined, and the implications of these findings are discussed.
International Nuclear Information System (INIS)
Kawabata, T; Akimune, H; Fujita, H; Fujita, Y; Fujiwara, M; Hara, K; Hatanaka, K; Itoh, M; Kanada-En'yo, Y; Kishi, S; Nakanishi, K; Sakaguchi, H; Shimbara, Y; Tamii, A; Terashima, S; Uchida, M; Wakasa, T; Yasuda, Y; Yoshida, H P; Yosoi, M
2006-01-01
The cluster structures of the excited states in 11 B are studied by analyzing the isoscalar monopole and quadrupole strengths in the 11 B(d, d') reaction at E d = 200 MeV. The excitation strengths are compared with the theoretical predictions by the antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the 3/2 - 3 state at E x = 8.56 MeV is well described by the AMD wave function with a dilute 2α + tcluster structure
Single-molecule study on polymer diffusion in a melt state: Effect of chain topology
Habuchi, Satoshi
2013-08-06
We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction. © 2013 American Chemical Society.
Quantum phase transitions between a class of symmetry protected topological states
Energy Technology Data Exchange (ETDEWEB)
Tsui, Lokman; Jiang, Hong-Chen; Lu, Yuan-Ming; Lee, Dung-Hai
2015-07-01
The subject of this paper is the phase transition between symmetry protected topological states (SPTs). We consider spatial dimension d and symmetry group G so that the cohomology group, Hd+1(G,U(1)), contains at least one Z2n or Z factor. We show that the phase transition between the trivial SPT and the root states that generate the Z2n or Z groups can be induced on the boundary of a (d+1)-dimensional View the MathML source-symmetric SPT by a View the MathML source symmetry breaking field. Moreover we show these boundary phase transitions can be “transplanted” to d dimensions and realized in lattice models as a function of a tuning parameter. The price one pays is for the critical value of the tuning parameter there is an extra non-local (duality-like) symmetry. In the case where the phase transition is continuous, our theory predicts the presence of unusual (sometimes fractionalized) excitations corresponding to delocalized boundary excitations of the non-trivial SPT on one side of the transition. This theory also predicts other phase transition scenarios including first order transition and transition via an intermediate symmetry breaking phase.
RKKY interaction in P-N junction based on surface states of 3D topological insulator
Zhang, Shuhui; Yang, Wen; Chang, Kai
The RKKY interaction mediated by conduction electrons supplies a mechanism to realize the long-range coupling of localized spins which is desired for the spin devices. Here, we examine the controllability of RKKY interaction in P-N junction (PNJ) based on surface states of 3D topological insulator (3DTI). In this study, through quantum way but not usual classical analogy to light propagation, the intuitive picture for electron waves across the interface of PNJ is obtained, e.g., Klein tunneling, negative refraction and focusing. Moreover, we perform the numerical calculations for all kinds of RKKY interaction including the Heisenberg, Ising, and Dzyaloshinskii-Moriya terms. We find the focusing of surface states leads to the local augmentation of RKKY interaction. Most importantly, a dimension transition occurs, i.e., the decay rate of RKKY interaction from the deserved 1/R 2 to 1/ R . In addition, the quadratic gate-dependence of RKKY interaction is also beneficial to the application of 3DTI PNJ in the fields of spintronics and quantum computation. This work was supported by the MOST (Grant No. 2015CB921503, and No. 2014CB848700) and NSFC (Grant No. 11434010, No. 11274036, No. 11322542, and No. 11504018).
Group-theoretical and topological analysis of localized rotation-vibration states
International Nuclear Information System (INIS)
Sadovskii, D.A.; Zhilinskii, B.I.
1993-01-01
A general scheme of qualitative analysis is applied to molecular rovibrational problems. The classical-quantum correspondence provides a description of different classes of localized quantum rotation-vibration states associated with localized classical motion. A description of qualitative features, such as localized motion, and of qualitative changes, such as localization phenomena, is based on the concept of the simplest Hamiltonian. It uses only the topological properties of the compact reduced phase space and the action of the symmetry group on this space. The qualitative changes of the simplest Hamiltonian are analyzed as bifurcations caused by rotational or vibrational excitation. The relation between the stationary points of the classical Hamiltonian function on the reduced phase space and the principal periodic trajectories in the coordinate space is analyzed for vibrational Hamiltonians. In particular, the relation between the nonlinear normal modes, proposed by Montaldi, Roberts, and Stewart [Philos. Trans. R. Soc. London, Ser. A 325, 237 (1988)], and normal- and local-mode models widely used in molecular physics is discussed. Along with a general consideration of localized rotational and vibrational states a more detailed analysis of the vibrational dynamics of an X 3 molecule with the D 3h symmetry, such as the H 3 + molecular ion, is given
Gartside, Jack C.; Arroo, Daan M.; Burn, David M.; Bemmer, Victoria L.; Moskalenko, Andy; Cohen, Lesley F.; Branford, Will R.
2018-01-01
Arrays of non-interacting nanomagnets are widespread in data storage and processing. As current technologies approach fundamental limits on size and thermal stability, enhancing functionality through embracing the strong interactions present at high array densities becomes attractive. In this respect, artificial spin ices are geometrically frustrated magnetic metamaterials that offer vast untapped potential due to their unique microstate landscapes, with intriguing prospects in applications from reconfigurable logic to magnonic devices or hardware neural networks. However, progress in such systems is impeded by the inability to access more than a fraction of the total microstate space. Here, we demonstrate that topological defect-driven magnetic writing—a scanning probe technique—provides access to all of the possible microstates in artificial spin ices and related arrays of nanomagnets. We create previously elusive configurations such as the spin-crystal ground state of artificial kagome dipolar spin ices and high-energy, low-entropy `monopole-chain' states that exhibit negative effective temperatures.
Cluster-state quantum computation: the role of entanglement
Energy Technology Data Exchange (ETDEWEB)
Annovi, Filippo [Department of Philosophy, University of Bologna (Italy)
2013-07-01
Cluster-state quantum computation is computationally equivalent to the traditional circuit model, but the pictures of computational processes outlined by the two are radically different. Here are investigated some of the consequences of this situation for the explanation of the quantum speed-up, whit particular regard to the role played by entanglement. At first sight, the evolution of a cluster-state computer seems to be disentangling (at each step one qubit is measured and discarded), but in a fully-unitary dynamical account it appears to be entangling (at each step a correlation is established between one qubit and its respective recorder). It is thus suggested that the different uses made of the features of quantum systems by the two frameworks, do not rule out the thesis that the speed-up is achieved by means of an entangling transformation. However, in this last case entanglement is created step by step, and thus the main difference between the two frameworks seems to remain the absence of ''quantum parallelism''. The only entangling-generating unitary transformations acting at the same time on all the qubits are the controlled-phase operation involved in the preparation of the cluster. Thus, the explanation of the quantum speed-up should be looked for just in these type of transformations.
Photonic Floquet topological insulators
Rechtsman, Mikael C.; Zeuner, Julia M.; Plotnik, Yonatan; Lumer, Yaakov; Podolsky, Daniel; Dreisow, Felix; Nolte, Stefan; Segev, Mordechai; Szameit, Alexander
2013-09-01
Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on the surface. In two dimensions, surface electrons in topological insulators do not scatter despite defects and disorder, providing robustness akin to superconductors. Topological insulators are predicted to have wideranging applications in fault-tolerant quantum computing and spintronics. Recently, large theoretical efforts were directed towards achieving topological insulation 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. However, since magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatterfree edge states requires a fundamentally different mechanism - one that is free of magnetic fields. Recently, a number of proposals for photonic topological transport have been put forward. Specifically, one suggested temporally modulating 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, where temporal variations in solidstate systems induce topological edge states. Here, we propose and experimentally demonstrate the first external field-free photonic topological insulator 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 acts as `time'. Thus the waveguides
Galilo, Bogdan; Lee, Derek K. K.; Barnett, Ryan
2017-11-01
In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states. We also find that the number of edge states crossing the gap is increased in the presence of a harmonic trap, and the edge modes experience an energy shift while traversing the first Brillouin zone which is related to the topological properties of the system. We find an analytical expression for the edge-state energies and our comparison with numerical computation shows excellent agreement.
Galilo, Bogdan; Lee, Derek K K; Barnett, Ryan
2017-11-17
In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states. We also find that the number of edge states crossing the gap is increased in the presence of a harmonic trap, and the edge modes experience an energy shift while traversing the first Brillouin zone which is related to the topological properties of the system. We find an analytical expression for the edge-state energies and our comparison with numerical computation shows excellent agreement.
Lane, T. L. M.; Andelković, M.; Wallbank, J. R.; Covaci, L.; Peeters, F. M.; Fal'ko, V. I.
2018-01-01
We show that delaminations in bilayer graphene (BLG) with electrostatically induced interlayer symmetry can provide one with ballistic channels for electrons with energies inside the electrostatically induced BLG gap. These channels are formed by a combination of valley-polarized evanescent states propagating along the delamination edges (which persist in the presence of a strong magnetic field) and standing waves bouncing between them inside the delaminated region (in a strong magnetic field, these transform into Landau levels in the monolayers). For inverted stackings in BLGs on the left and right of the delamination (AB-2ML-BA or BA-2ML-AB, where 2ML indicates two decoupled monolayers of graphene), the lowest-energy ballistic channels are gapless, have linear dispersion, and appear to be weakly topologically protected. When BLG stackings on both sides of the delamination are the same (AB-2ML-AB or BA-2ML-BA), the lowest-energy ballistic channels are gapped, with a gap ɛg scaling as ɛg∝W-1 with delamination width and ɛg∝δ-1 with the on-layer energy difference in the delaminated part of the structure. Depending on the width, delaminations may also support several "higher-energy" waveguide modes. Our results are based on both the analytical study of the wave matching of Dirac states and tight-binding model calculations, and we analyze in detail the dependence of the delamination spectrum on the electrostatic conditions in the structure, such as the vertical displacement field.
Tahir, Muhammad
2013-05-01
We show that the surface states of magnetic topological insulators realize an activated behavior and Shubnikov de Haas oscillations. Applying an external magnetic field perpendicular to the surface of the topological insulator in the presence of Zeeman interaction, we investigate the opening of a gap at the Dirac point, making the surface Dirac fermions massive, and the effects on the transport properties. Analytical expressions are derived for the collisional conductivity for elastic impurity scattering in the first Born approximation. We also calculate the Hall conductivity using the Kubo formalism. Evidence for a transition from gapless to gapped surface states at n = 0 and activated transport is found from the temperature and magnetic-field dependence of the collisional and Hall conductivities. © Copyright EPLA, 2013.
Geographical Clusters and Predictors of Rabies in Three Southeastern States.
Reilly, Sara; Sanderson, Wayne T; Christian, W Jay; Browning, Steven R
2017-06-01
The rabies virus causes progressive encephalomyelitis that is fatal in nearly 100% of untreated cases. In the United States, wildlife act as the primary reservoir for rabies; prevention, surveillance, and control costs remain high. The purpose of this study is to understand the current distribution of wildlife rabies in three southeastern states, with particular focus on raccoons as the primary eastern reservoir, as well as identify demographic and geographic factors which may affect the risk of human exposure. This ecologic study obtained county-level rabies surveillance data from state health departments and the United States Department of Agriculture Wildlife services for North Carolina, Virginia, and West Virginia from 2010 to 2013. A spatial statistical analysis was performed to identify county clusters with high or low rates of raccoon rabies in the three states. Potential demographic and geographic factors associated with these varying rates of rabies were assessed using a multivariable negative binomial regression model. In North Carolina, raccoons constituted 50% of positive tests, in Virginia, 49%, and in West Virginia, 50%. Compared to persons residing in West Virginia counties, persons in North Carolina counties had 1.67 times the risk of exposure (p rabies exposure. Further research is needed to better understand the effect of the oral rabies vaccine program in controlling the risk of human exposure to raccoon rabies.
Energy Technology Data Exchange (ETDEWEB)
Sobota, Jonathan
2012-03-14
Using femtosecond time- and angle-resolved photoemission spectroscopy, we investigated the nonequilibrium dynamics of the topological insulator Bi{sub 2}Se{sub 3}. We studied p-type Bi{sub 2}Se{sub 3}, in which the metallic Dirac surface state and bulk conduction bands are unoccupied. Optical excitation leads to a meta-stable population at the bulk conduction band edge, which feeds a nonequilibrium population of the surface state persisting for >10 ps. This unusually long-lived population of a metallic Dirac surface state with spin texture may present a channel in which to drive transient spin-polarized currents.
Jiao, Bingqing; Zhang, Delong; Liang, Aiying; Liang, Bishan; Wang, Zengjian; Li, Junchao; Cai, Yuxuan; Gao, Mengxia; Gao, Zhenni; Chang, Song; Huang, Ruiwang; Liu, Ming
2017-10-01
Previous studies have indicated a tight linkage between resting-state functional connectivity of the human brain and creative ability. This study aimed to further investigate the association between the topological organization of resting-state brain networks and creativity. Therefore, we acquired resting-state fMRI data from 22 high-creativity participants and 22 low-creativity participants (as determined by their Torrance Tests of Creative Thinking scores). We then constructed functional brain networks for each participant and assessed group differences in network topological properties before exploring the relationships between respective network topological properties and creative ability. We identified an optimized organization of intrinsic brain networks in both groups. However, compared with low-creativity participants, high-creativity participants exhibited increased global efficiency and substantially decreased path length, suggesting increased efficiency of information transmission across brain networks in creative individuals. Using a multiple linear regression model, we further demonstrated that regional functional integration properties (i.e., the betweenness centrality and global efficiency) of brain networks, particularly the default mode network (DMN) and sensorimotor network (SMN), significantly predicted the individual differences in creative ability. Furthermore, the associations between network regional properties and creative performance were creativity-level dependent, where the difference in the resource control component may be important in explaining individual difference in creative performance. These findings provide novel insights into the neural substrate of creativity and may facilitate objective identification of creative ability. Copyright © 2017 Elsevier B.V. All rights reserved.
Topological surface states of Bi{sub 2}Te{sub 2}Se are robust against surface chemical modification
Energy Technology Data Exchange (ETDEWEB)
Thomas, Conor R.; Sahasrabudhe, Girija; Kushwaha, Satya Kumar; Cava, Robert J.; Schwartz, Jeffrey [Department of Chemistry, Princeton University, Princeton, NJ (United States); Xiong, Jun [Department of Physics, Princeton University, Princeton, NJ (United States)
2014-12-01
The robustness of the Dirac-like electronic states on the surfaces of topological insulators (TIs) during materials process-ing is a prerequisite for their eventual device application. Here, the (001) cleavage surfaces of crystals of the topological insulator Bi{sub 2}Te{sub 2}Se (BTS) were subjected to several surface chemical modification procedures that are common for electronic materials. Through measurement of Shubnikov-de Hass (SdH) oscillations, which are the most sensitive measure of their quality, the surface states of the treated surfaces were compared to those of pristine BTS that had been exposed to ambient conditions. In each case - surface oxidation, deposition of thin layers of Ti or Zr oxides, or chemical modification of the surface oxides - the robustness of the topological surface electronic states was demonstrated by noting only very small changes in the frequency and amplitude of the SdH oscillations. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Li, Hai; Zhao, Yuan Yuan
2017-11-22
In the framework of the Bogoliubov-de Gennes equation, we investigate the thermal transport properties in topological-insulator-based superconducting hybrid structures with mixed spin-singlet and spin-triplet pairing states, and emphasize the different manifestations of the spin-singlet and spin-triplet pairing states in the thermal transport signatures. It is revealed that the temperature-dependent differential thermal conductance strongly depends on the components of the pairing state, and the negative differential thermal conductance only occurs in the spin-singlet pairing state dominated regime. It is also found that the thermal conductance is profoundly sensitive to the components of the pairing state. In the spin-singlet pairing state controlled regime, the thermal conductance obviously oscillates with the phase difference and junction length. With increasing the proportion of the spin-triplet pairing state, the oscillating characteristic of the thermal conductance fades out distinctly. These results suggest an alternative route for distinguishing the components of pairing states in topological-insulator-based superconducting hybrid structures.
α cluster structures in unbound states in 19Ne
Otani, Reiji; Iwasaki, Masataka; Ito, Makoto
2016-06-01
Cluster structures in 19Ne are studied by the microscopic and macroscopic cluster models. In the microscopic calculation, the coupled-channels problem of (3He+16O) + (α+15O) is solved, and the adiabatic energy surfaces, which are the series of the energy eigenvalues as a function of the He-O distance, are investigated. In the adiabatic energy curves, the several local minima are generated in the spatial region of the small core distance, where the neutron hole inside of the He or O nucleus is strongly coupled to the residual nuclei. The energy spectra, which are constructed from the strong coupling states, nicely reproduce the the low-lying energy levels in the 19Ne nucleus. In the macroscopic approach, the α + 15O potential is evaluated from the elastic scattering of the α + 15N system, and the resonant levels of the α + 15O system are calculated under the absorbing boundary condition. The potential model predicts the existence of the resonances above the α threshold, which has a weak-coupling scheme of the α particle and one hole inside of the 16O nucleus. The extended microscopic calculations of (3He+16O) + (α+15O) + (5He+14O) are performed in order to see the coupling effect of the 5p-2h configuration, which corresponds to the shell model limit of the 5He + 14O cluster configuration. The extended calculation suggests that the 5He + 14O configuration plays an important role on the formation of the 3/2+ resonance at 0.5 MeV with respect to the α threshold.
α cluster structures in unbound states in 19Ne
Directory of Open Access Journals (Sweden)
Otani Reiji
2016-01-01
Full Text Available Cluster structures in 19Ne are studied by the microscopic and macroscopic cluster models. In the microscopic calculation, the coupled-channels problem of (3He+16O + (α+15O is solved, and the adiabatic energy surfaces, which are the series of the energy eigenvalues as a function of the He–O distance, are investigated. In the adiabatic energy curves, the several local minima are generated in the spatial region of the small core distance, where the neutron hole inside of the He or O nucleus is strongly coupled to the residual nuclei. The energy spectra, which are constructed from the strong coupling states, nicely reproduce the the low-lying energy levels in the 19Ne nucleus. In the macroscopic approach, the α + 15O potential is evaluated from the elastic scattering of the α + 15N system, and the resonant levels of the α + 15O system are calculated under the absorbing boundary condition. The potential model predicts the existence of the resonances above the α threshold, which has a weak-coupling scheme of the α particle and one hole inside of the 16O nucleus. The extended microscopic calculations of (3He+16O + (α+15O + (5He+14O are performed in order to see the coupling effect of the 5p-2h configuration, which corresponds to the shell model limit of the 5He + 14O cluster configuration. The extended calculation suggests that the 5He + 14O configuration plays an important role on the formation of the 3/2+ resonance at 0.5 MeV with respect to the α threshold.
Topological Gyroscopic Metamaterials
Nash, Lisa Michelle
Topological materials are generally insulating in their bulk, with protected conducting states on their boundaries that are robust against disorder and perturbation of material property. The existence of these conducting edge states is characterized by an integer topological invariant. Though the phenomenon was first discovered in electronic systems, recent years have shown that topological states exist in classical systems as well. In this thesis we are primarily concerned with the topological properties of gyroscopic materials, which are created by coupling networks of fast-spinning objects. Through a series of simulations, numerical calculations, and experiments, we show that these materials can support topological edge states. We find that edge states in these gyroscopic metamaterials bear the hallmarks of topology related to broken time reversal symmetry: they transmit excitations unidirectionally and are extremely robust against experimental disorder. We also explore requirements for topology by studying several lattice configurations and find that topology emerges naturally in gyroscopic systems.A simple prescription can be used to create many gyroscopic lattices. Though many of our gyroscopic networks are periodic, we explore amorphous point-sets and find that topology also emerges in these networks.
State selective dynamics of molecules, clusters, and nanostructures
Energy Technology Data Exchange (ETDEWEB)
Keto, John W. [Univ. of Texas, Austin, TX (United States)
2005-06-01
Early objectives of this grant were: (1) Measure two-photon excitation of even parity excitons in liquid an solid xenon, (2) Study state-to-state energy transver between two-photon laser excited states or rare-gas atoms to other rare has atoms, (3) study reactive half-collisions between xenon and chlorine leading to the XeCl* B state, (4) measure the spectra of ro-vibrational states of cluster ions and radicals formed in high-pressure discharges and to study their dynamics, (5) measure the surface and bulk electronic states of nanoparticles produced by a unique method of synthesis--laser ablation of microspheres (LAM). Using near-field and microluminescence techniques, we obtained spectra of single nanocrystals to compare with spectra obtained in a supersonic jet apparatus using resonance excitation followed by photoionization (REMPI) with time-of-flight mass analysis. These materials combine the functional advantages obtained from the size-tunable properties of nanocomposite materials with the fabrication and direct-write advantages of NPs manufactured by LAM. We demostrated that CdSe nanoparticles produced by LAM were efficiient fluorescers, even when deposited dry on sapphire substrates. Si nanoparticles were fluorescent when captured in ethylene glycol. We also obtiained efficient fluorescence from Er doped phosphate glass nanopartiicles which have application to gain wafeguides in integrated optics or to nanoslush lasers. We used a femptosecond laser to study the nonlinear spectra of NC composites. We are currently measuring fluorescence and second and third-order susceptibilities of composites of Ag, Si, and GaN nanoparticles encapsulated within thin films of sapphire or SiO _{2}.
State selective dynamics of molecules, clusters, and nanostructures
International Nuclear Information System (INIS)
John W. Keto
2005-01-01
Early objectives of this grant were: (1) Measure two-photon excitation of even parity excitons in liquid an solid xenon, (2) Study state-to-state energy transfer between two-photon laser excited states or rare-gas atoms to other rare has atoms, (3) study reactive half-collisions between xenon and chlorine leading to the XeCl* B state, (4) measure the spectra of ro-vibrational states of cluster ions and radicals formed in high-pressure discharges and to study their dynamics, (5) measure the surface and bulk electronic states of nanoparticles produced by a unique method of synthesis--laser ablation of microspheres (LAM). Using near-field and microluminescence techniques, we obtained spectra of single nanocrystals to compare with spectra obtained in a supersonic jet apparatus using resonance excitation followed by photoionization (REMPI) with time-of-flight mass analysis. These materials combine the functional advantages obtained from the size-tunable properties of nanocomposite materials with the fabrication and direct-write advantages of NPs manufactured by LAM. We demonstrated that CdSe nanoparticles produced by LAM were efficient fluorescers, even when deposited dry on sapphire substrates. Si nanoparticles were fluorescent when captured in ethylene glycol. We also obtained efficient fluorescence from Er doped phosphate glass nanoparticles which have application to gain waveguides in integrated optics or to nanoslush lasers. We used a femptosecond laser to study the nonlinear spectra of NC composites. We are currently measuring fluorescence and second and third-order susceptibilities of composites of Ag, Si, and GaN nanoparticles encapsulated within thin films of sapphire or SiO2
Singh, Bahadur; Zhou, Xiaoting; Lin, Hsin; Bansil, Arun
2018-02-01
Topological nodal-line semimetals are exotic conductors that host symmetry-protected conducting nodal lines in their bulk electronic spectrum and nontrivial drumhead states on the surface. Based on first-principles calculations and an effective model analysis, we identify the presence of topological nodal-line semimetal states in the low crystalline symmetric T T'X family of compounds (T ,T' = transition metal, X = Si or Ge) in the absence of spin-orbit coupling (SOC). Taking ZrPtGe as an exemplar system, we show that owing to small lattice symmetry this material harbors a single nodal line on the ky=0 plane with large energy dispersion and unique drumhead surface state with a saddlelike energy dispersion. When the SOC is included, the nodal line gaps out and the system transitions to a strong topological insulator state with Z2=(1 ;000 ) . The topological surface state evolves from the drumhead surface state via the sharing of its saddlelike energy dispersion within the bulk energy gap. These features differ remarkably from those of the currently known topological surface states in topological insulators such as Bi2Se3 with Dirac-cone-like energy dispersions.
Topological states in a two-dimensional metal alloy in Si surface: BiAg/Si(111)-4 ×4 surface
Zhang, Xiaoming; Cui, Bin; Zhao, Mingwen; Liu, Feng
2018-02-01
A bridging topological state with a conventional semiconductor platform offers an attractive route towards future spintronics and quantum device applications. Here, based on first-principles and tight-binding calculations, we demonstrate the existence of topological states hosted by a two-dimensional (2D) metal alloy in a Si surface, the BiAg/Si(111)-4 ×4 surface, which has already been synthesized experimentally. It exhibits a topological insulating state with an energy gap of 71 meV (˜819 K ) above the Fermi level and a topological metallic state with quasiquantized conductance below the Fermi level. The underlying mechanism leading to the formation of such nontrivial states is revealed by analysis of the "charge-transfer" and "orbital-filtering" effect of the Si substrate. A minimal effective tight-binding model is employed to reveal the formation mechanism of the topological states. Our finding opens opportunities to detect topological states and measure its quantized conductance in a large family of 2D surface metal alloys, which have been or are to be grown on semiconductor substrates.
Quantum teleportation and information splitting via four-qubit cluster state and a Bell state
Ramírez, Marlon David González; Falaye, Babatunde James; Sun, Guo-Hua; Cruz-Irisson, M.; Dong, Shi-Hai
2017-10-01
Quantum teleportation provides a "bodiless" way of transmitting the quantum state from one object to another, at a distant location, using a classical communication channel and a previously shared entangled state. In this paper, we present a tripartite scheme for probabilistic teleportation of an arbitrary single qubit state, without losing the information of the state being teleported, via a fourqubit cluster state of the form | ϕ>1234 = α|0000>+ β|1010>+ γ|0101>- η|1111>, as the quantum channel, where the nonzero real numbers α, β, γ, and η satisfy the relation j αj2 + | β|2 + | γ|2 + | η|2 = 1. With the introduction of an auxiliary qubit with state |0>, using a suitable unitary transformation and a positive-operator valued measure (POVM), the receiver can recreate the state of the original qubit. An important advantage of the teleportation scheme demonstrated here is that, if the teleportation fails, it can be repeated without teleporting copies of the unknown quantum state, if the concerned parties share another pair of entangled qubit. We also present a protocol for quantum information splitting of an arbitrary two-particle system via the aforementioned cluster state and a Bell-state as the quantum channel. Problems related to security attacks were examined for both the cases and it was found that this protocol is secure. This protocol is highly efficient and easy to implement.
He, Yan; Wright, Kevin; Kouachi, Said; Chien, Chih-Chun
2018-02-01
One-dimensional superlattices with periodic spatial modulations of onsite potentials or tunneling coefficients can exhibit a variety of properties associated with topology or symmetry. Recent developments of ring-shaped optical lattices allow a systematic study of those properties in superlattices with or without boundaries. While superlattices with additional modulating parameters are shown to have quantized topological invariants in the augmented parameter space, we also found localized or zero-energy states associated with symmetries of the Hamiltonians. Probing those states in ultracold atoms is possible by utilizing recently proposed methods analyzing particle depletion or the local density of states. Moreover, we summarize feasible realizations of configurable optical superlattices using currently available techniques.
Unconventional pairing in three-dimensional topological insulators with a warped surface state
Vasenko, A. S.; Golubov, A. A.; Silkin, V. M.; Chulkov, E. V.
2017-01-01
We study the effect of the Fermi surface anisotropy (hexagonal warping) on the superconducting pair potential, induced in a three-dimensional topological insulator (TI) by proximity with an s-wave superconductor (S) in presence of a magnetic moment of a nearby ferromagnetic insulator (FI). In the
Fang, Lei; Yao, Zhijun; An, Jianping; Chen, Xuejiao; Xie, Yuanwei; Zhao, Hui; Mao, Junfeng; Liang, Wangsheng; Ma, Xiangxing
2016-01-01
This study aimed to investigate the metabolic brain network and its relationship with depression symptoms using 18F-fluorodeoxyglucose positron emission tomography data in 78 pre-chemotherapy cancer patients with depression and 80 matched healthy subjects. Functional and structural imbalance or disruption of brain networks frequently occur following chemotherapy in cancer patients. However, few studies have focused on the topological organization of the metabolic brain network in cancer with depression, especially those without chemotherapy. The nodal and global parameters of the metabolic brain network were computed for cancer patients and healthy subjects. Significant decreases in metabolism were found in the frontal and temporal gyri in cancer patients compared with healthy subjects. Negative correlations between depression and metabolism were found predominantly in the inferior frontal and cuneus regions, whereas positive correlations were observed in several regions, primarily including the insula, hippocampus, amygdala, and middle temporal gyri. Furthermore, a higher clustering efficiency, longer path length, and fewer hubs were found in cancer patients compared with healthy subjects. The topological organization of the whole-brain metabolic networks may be disrupted in cancer. Finally, the present findings may provide a new avenue for exploring the neurobiological mechanism, which plays a key role in lessening the depression effects in pre-chemotherapy cancer patients.
Directory of Open Access Journals (Sweden)
Minkyung Kim
2017-06-01
Full Text Available How the brain reconstitutes consciousness and cognition after a major perturbation like general anesthesia is an important question with significant neuroscientific and clinical implications. Recent empirical studies in animals and humans suggest that the recovery of consciousness after anesthesia is not random but ordered. Emergence patterns have been classified as progressive and abrupt transitions from anesthesia to consciousness, with associated differences in duration and electroencephalogram (EEG properties. We hypothesized that the progressive and abrupt emergence patterns from the unconscious state are associated with, respectively, continuous and discontinuous synchronization transitions in functional brain networks. The discontinuous transition is explainable with the concept of explosive synchronization, which has been studied almost exclusively in network science. We used the Kuramato model, a simple oscillatory network model, to simulate progressive and abrupt transitions in anatomical human brain networks acquired from diffusion tensor imaging (DTI of 82 brain regions. To facilitate explosive synchronization, distinct frequencies for hub nodes with a large frequency disassortativity (i.e., higher frequency nodes linking with lower frequency nodes, or vice versa were applied to the brain network. In this simulation study, we demonstrated that both progressive and abrupt transitions follow distinct synchronization processes at the individual node, cluster, and global network levels. The characteristic synchronization patterns of brain regions that are “progressive and earlier” or “abrupt but delayed” account for previously reported behavioral responses of gradual and abrupt emergence from the unconscious state. The characteristic network synchronization processes observed at different scales provide new insights into how regional brain functions are reconstituted during progressive and abrupt emergence from the unconscious
Directory of Open Access Journals (Sweden)
Adam J. Schwarz
2012-01-01
Full Text Available Network analysis of functional imaging data reveals emergent features of the brain as a function of its topological properties. However, the brain is not a homogeneous network, and the dependence of functional connectivity parameters on neuroanatomical substrate and parcellation scale is a key issue. Moreover, the extent to which these topological properties depend on underlying neurochemical changes remains unclear. In the present study, we investigated both global statistical properties and the local, voxel-scale distribution of connectivity parameters of the rat brain. Different neurotransmitter systems were stimulated by pharmacological challenge (d-amphetamine, fluoxetine, and nicotine to discriminate between stimulus-specific functional connectivity and more general features of the rat brain architecture. Although global connectivity parameters were similar, mapping of local connectivity parameters at high spatial resolution revealed strong neuroanatomical dependence of functional connectivity in the rat brain, with clear differentiation between the neocortex and older brain regions. Localized foci of high functional connectivity independent of drug challenge were found in the sensorimotor cortices, consistent with the high neuronal connectivity in these regions. Conversely, the topological properties and node roles in subcortical regions varied with neurochemical state and were dependent on the specific dynamics of the different functional processes elicited.
Hierarchical Controlled Remote State Preparation by Using a Four-Qubit Cluster State
Ma, Peng-Cheng; Chen, Gui-Bin; Li, Xiao-Wei; Zhan, You-Bang
2018-02-01
We propose a scheme for hierarchical controlled remote preparation of an arbitrary single-qubit state via a four-qubit cluster state as the quantum channel. In this scheme, a sender wishes to help three agents to remotely prepare a quantum state, respectively. The three agents are divided into two grades, that is, an agent is in the upper grade and other two agents are in the lower grade. In this process of remote state preparation, the agent of the upper grade only needs the assistance of any one of the other two agents for recovering the sender's original state, while an agent of the lower grade needs the collaboration of all the other two agents. In other words, the agents of two grades have different authorities to reconstruct sender's original state.
Trifunovic, Luka; Brouwer, Piet
2017-11-01
Using a dimensional reduction scheme based on scattering theory, we show that the classification tables for topological insulators and superconductors with reflection symmetry can be organized in two period-2 and four period-8 cycles, similar to the Bott periodicity found for topological insulators and superconductors without spatial symmetries. With the help of the dimensional reduction scheme, the classification in arbitrary dimensions d ≥1 can be obtained from the classification in one dimension, for which we present a derivation based on relative homotopy groups and exact sequences to classify one-dimensional insulators and superconductors with reflection symmetry. The resulting classification is fully consistent with a comprehensive classification obtained recently by Shiozaki and Sato [Phys. Rev. B 90, 165114 (2014), 10.1103/PhysRevB.90.165114]. The use of a scattering-matrix-inspired method allows us to address the second descendant Z2 phase, for which the topological nontrivial phase was previously reported to be vulnerable to perturbations that break translation symmetry.
Energy Technology Data Exchange (ETDEWEB)
Choi, Hyunwoo, E-mail: chw0089@gmail.com [Department of Electrical and Computer Engineering, University of Seoul, Seoul 02504 (Korea, Republic of); Kim, Tae Geun, E-mail: tgkim1@korea.ac.kr [School of Electrical Engineering, Korea University, Seoul 02841 (Korea, Republic of); Shin, Changhwan, E-mail: cshin@uos.ac.kr [Department of Electrical and Computer Engineering, University of Seoul, Seoul 02504 (Korea, Republic of)
2017-06-15
Highlights: • The quantum capacitance in topological insulator (TI) at room temperature is directly revealed. • The physical origin of quantum capacitance, the two dimensional surface state of TI, is experimentally validated. • Theoretically calculated results of ideal quantum capacitance can well predict the experimental data. - Abstract: A topological insulator (TI) is a new kind of material that exhibits unique electronic properties owing to its topological surface state (TSS). Previous studies focused on the transport properties of the TSS, since it can be used as the active channel layer in metal-oxide-semiconductor field-effect transistors (MOSFETs). However, a TI with a negative quantum capacitance (QC) effect can be used in the gate stack of MOSFETs, thereby facilitating the creation of ultra-low power electronics. Therefore, it is important to study the physics behind the QC in TIs in the absence of any external magnetic field, at room temperature. We fabricated a simple capacitor structure using a TI (TI-capacitor: Au-TI-SiO{sub 2}-Si), which shows clear evidence of QC at room temperature. In the capacitance-voltage (C-V) measurement, the total capacitance of the TI-capacitor increases in the accumulation regime, since QC is the dominant capacitive component in the series capacitor model (i.e., C{sub T}{sup −1} = C{sub Q}{sup −1} + C{sub SiO2}{sup −1}). Based on the QC model of the two-dimensional electron systems, we quantitatively calculated the QC, and observed that the simulated C-V curve theoretically supports the conclusion that the QC of the TI-capacitor is originated from electron–electron interaction in the two-dimensional surface state of the TI.
Energy Technology Data Exchange (ETDEWEB)
Mason, Peter [Laboratoire de Physique Statistique, Ecole Normale Superieure, UPMC Paris 06, Universite Paris Diderot, CNRS, 24 rue Lhomond, F-75005 Paris (France); Institut Jean Le Rond D' Alembert, UMR 7190 CNRS-UPMC, 4 place Jussieu, F-75005 Paris (France); Aftalion, Amandine [CNRS and Universite Versailles-Saint-Quentin-en-Yvelines, Laboratoire de Mathematiques de Versailles, CNRS UMR 8100, 45 avenue des Etats-Unis, F-78035 Versailles Cedex (France)
2011-09-15
We classify the ground states and topological defects of a rotating two-component condensate when varying several parameters: the intracomponent coupling strengths, the intercomponent coupling strength, and the particle numbers. No restriction is placed on the masses or trapping frequencies of the individual components. We present numerical phase diagrams which show the boundaries between the regions of coexistence, spatial separation, and symmetry breaking. Defects such as triangular coreless vortex lattices, square coreless vortex lattices, and giant skyrmions are classified. Various aspects of the phase diagrams are analytically justified thanks to a nonlinear {sigma} model that describes the condensate in terms of the total density and a pseudo-spin representation.
Reconfigurable topological photonic crystal
Shalaev, Mikhail I.; Desnavi, Sameerah; Walasik, Wiktor; Litchinitser, Natalia M.
2018-02-01
Topological insulators are materials that conduct on the surface and insulate in their interior due to non-trivial topology of the band structure. The edge states on the interface between topological (non-trivial) and conventional (trivial) insulators are topologically protected from scattering due to structural defects and disorders. Recently, it was shown that photonic crystals (PCs) can serve as a platform for realizing a scatter-free propagation of light waves. In conventional PCs, imperfections, structural disorders, and surface roughness lead to significant losses. The breakthrough in overcoming these problems is likely to come from the synergy of the topological PCs and silicon-based photonics technology that enables high integration density, lossless propagation, and immunity to fabrication imperfections. For many applications, reconfigurability and capability to control the propagation of these non-trivial photonic edge states is essential. One way to facilitate such dynamic control is to use liquid crystals (LCs), which allow to modify the refractive index with external electric field. Here, we demonstrate dynamic control of topological edge states by modifying the refractive index of a LC background medium. Background index is changed depending on the orientation of a LC, while preserving the topology of the system. This results in a change of the spectral position of the photonic bandgap and the topological edge states. The proposed concept might be implemented using conventional semiconductor technology, and can be used for robust energy transport in integrated photonic devices, all-optical circuity, and optical communication systems.
Electron localization, polarons and clustered states in manganites
International Nuclear Information System (INIS)
Mannella, N.
2004-01-01
Full text: A recent multi-spectroscopic study of prototypical colossal magnetoresistance (CMR) compounds La 1-x Sr x MnO 3 (LSMO, x = 0.3, 0.4) using photoemission (PE), x-ray absorption (XAS), x-ray emission (XES) and extended x-ray absorption e structure (EXAFS) has exposed a dramatic change in the electronic structure on crossing the ferromagnetic-to-paramagnetic transition temperature (T C ). In particular, this investigation revealed an increase of the Mn magnetic moment by ca. 1 Bohr magneton and charge transfer to the Mn atom on crossing T C concomitant with the presence of Jahn-Teller distortions, thus providing direct evidence of lattice polaron formation. These results thus challenge the belief of some authors that the LSMO compounds are canonical double-exchange (DE) systems in which polaron formation is unimportant, and thus help to unify the theoretical description of the CMR oxides. The relationship of these data to other recent work suggesting electron localization, polarons and phase separation, along with additional measurements of magnetic susceptibility indicating the formation of ferromagnetic clusters in the metallic paramagnetic state above T C will be discussed
Resource-efficient generation of linear cluster states by linear optics with postselection
International Nuclear Information System (INIS)
Uskov, D B; Alsing, P M; Fanto, M L; Szep, A; Smith, A M; Kaplan, L; Kim, R
2015-01-01
We report on theoretical research in photonic cluster-state computing. Finding optimal schemes of generating non-classical photonic states is of critical importance for this field as physically implementable photon–photon entangling operations are currently limited to measurement-assisted stochastic transformations. A critical parameter for assessing the efficiency of such transformations is the success probability of a desired measurement outcome. At present there are several experimental groups that are capable of generating multi-photon cluster states carrying more than eight qubits. Separate photonic qubits or small clusters can be fused into a single cluster state by a probabilistic optical CZ gate conditioned on simultaneous detection of all photons with 1/9 success probability for each gate. This design mechanically follows the original theoretical scheme of cluster state generation proposed more than a decade ago by Raussendorf, Browne and Briegel. The optimality of the destructive CZ gate in application to linear optical cluster state generation has not been analyzed previously. Our results reveal that this method is far from the optimal one. Employing numerical optimization we have identified that the maximal success probability of fusing n unentangled dual-rail optical qubits into a linear cluster state is equal to (1/2) n−1 ; an m-tuple of photonic Bell pair states, commonly generated via spontaneous parametric down-conversion, can be fused into a single cluster with the maximal success probability of (1/4) m−1 . (paper)
Choi, Hyunwoo; Kim, Tae Geun; Shin, Changhwan
2017-06-01
A topological insulator (TI) is a new kind of material that exhibits unique electronic properties owing to its topological surface state (TSS). Previous studies focused on the transport properties of the TSS, since it can be used as the active channel layer in metal-oxide-semiconductor field-effect transistors (MOSFETs). However, a TI with a negative quantum capacitance (QC) effect can be used in the gate stack of MOSFETs, thereby facilitating the creation of ultra-low power electronics. Therefore, it is important to study the physics behind the QC in TIs in the absence of any external magnetic field, at room temperature. We fabricated a simple capacitor structure using a TI (TI-capacitor: Au-TI-SiO2-Si), which shows clear evidence of QC at room temperature. In the capacitance-voltage (C-V) measurement, the total capacitance of the TI-capacitor increases in the accumulation regime, since QC is the dominant capacitive component in the series capacitor model (i.e., CT-1 = CQ-1 + CSiO2-1). Based on the QC model of the two-dimensional electron systems, we quantitatively calculated the QC, and observed that the simulated C-V curve theoretically supports the conclusion that the QC of the TI-capacitor is originated from electron-electron interaction in the two-dimensional surface state of the TI.
Alpha cluster states and molecular orbitals in sd-shell nuclei
Energy Technology Data Exchange (ETDEWEB)
Kimura, M. [Creative Research Institution Sousei Research Department, Hokkaido University, Sapporo 001-0021 (Japan); Furutachi, N. [Meme Media Laboratory, Hokkaido University, Sapporo 060-8628 (Japan); Kanada-En' yo, Y. [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)
2010-03-01
The alpha-clustering and molecular-orbitals of {sup 22}Ne and F isotopes are investigated based on antisymmetrized molecular dynamics (AMD). The observed candidates for the alpha cluster state of {sup 22}Ne are understood as the molecular-orbital states and alpha+{sup 18}O di-nuclei states. The presence of the molecular-orbital states in the O and F isotopes and the drastic reduction of their excitation energy near the neutron-drip line are predicted.
p-topological Cauchy completions
Directory of Open Access Journals (Sweden)
J. Wig
1999-01-01
Full Text Available The duality between “regular” and “topological” as convergence space properties extends in a natural way to the more general properties “p-regular” and “p-topological.” Since earlier papers have investigated regular, p-regular, and topological Cauchy completions, we hereby initiate a study of p-topological Cauchy completions. A p-topological Cauchy space has a p-topological completion if and only if it is “cushioned,” meaning that each equivalence class of nonconvergent Cauchy filters contains a smallest filter. For a Cauchy space allowing a p-topological completion, it is shown that a certain class of Reed completions preserve the p-topological property, including the Wyler and Kowalsky completions, which are, respectively, the finest and the coarsest p-topological completions. However, not all p-topological completions are Reed completions. Several extension theorems for p-topological completions are obtained. The most interesting of these states that any Cauchy-continuous map between Cauchy spaces allowing p-topological and p′-topological completions, respectively, can always be extended to a θ-continuous map between any p-topological completion of the first space and any p′-topological completion of the second.
Misawa, Tetsuro; Yokoyama, Takehito; Murakami, Shuichi
2012-02-01
Recent photoelectron spectroscopy experiments have revealed the presence of the Dirac cone on the surface of the topological insulator and its spin-splitting due to the spin-orbit interaction. In general, on spin-orbit coupled systems, electric fields induce spin polarizations as linear and nonlinear responses. Here we investigate the inverse Faraday effect on the surface of the topological insulator. The inverse Faraday effect is a non-linear optical effect where a circularly polarized light induces a dc spin polarization. We employ the Keldysh Green's function method to calculate the induced spin polarization and discuss its frequency dependence. In particular, in the low frequency limit, our analytical result gives the spin polarization proportional to the frequency and the square of the lifetime. As for the finite frequency regime, we employ numerical methods to discuss the resonance due to interband transitions. We also discuss the photogalvanic effect, where an illumination of a circular polarized light generates the dc charge current. Lastly, we evaluate those quantities with realistic parameters.[4pt] [1] T. Misawa, T. Yokoyama, S. Murakami, Phys. Rev. B84, 165407 (2011).
Indian Academy of Sciences (India)
2017-09-27
Sep 27, 2017 ... while CuCoNO, Co3NO, Cu3CoNO, Cu2Co3NO, Cu3Co3NO and Cu6CoNO clusters display stronger chemical stability. Magnetic and electronic properties are also discussed. The magnetic moment is affected by charge transfer and the spd hybridization. Keywords. CumConNO (m + n = 2–7) clusters; ...
Rozen, Todd D; Fishman, Royce S
2012-06-15
To present results from the United States Cluster Headache Survey regarding gender differences in cluster headache demographics, clinical characteristics, diagnostic delay, triggers, treatment response and personal burden. Very few studies have looked at the gender differences in cluster headache presentation. The United States Cluster Headache Survey is the largest study of cluster headache sufferers ever completed in the United States and it is also the largest study of female cluster headache patients ever presented. The total survey consisted of 187 multiple choice questions which dealt with various issues related to cluster headache including: demographics, clinical characteristics, concomitant medical conditions, family history, triggers, smoking history, diagnosis, treatment response and personal burden. A group of questions were specifically targeted to female cluster headache patients. The survey was placed on a website from October to December 2008. For all survey responders the diagnosis of cluster headache needed to be made by a neurologist but there was no validation of the headache diagnosis by the authors. 1134 individuals completed the survey (816 male, 318 female). Key Points that define the differences between female and male cluster headache include: a. Age of onset: women develop cluster headache at an earlier age than men and are more likely to develop a second peak of cluster headache onset after 50 years of age. b. Family history: woman cluster headache sufferers are more likely to have a family history of both cluster headache and migraine and have an increased familial risk of Parkinson's disease. c. Comorbid conditions: female cluster headaches sufferers are significantly more likely to experience depression and have asthma than males. d. Aura issues: aura with cluster headache is equally common in both sexes, but aura duration is shorter in women. Women are much more likely to experience sensory, language and brainstem auras. e. Pain
Energy Technology Data Exchange (ETDEWEB)
Hoefer, Katharina; Becker, Christoph; Rata, Diana; Thalmeier, Peter; Tjeng, Liu Hao [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Swanson, Jesse [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); University of British Columbia, Vancouver (Canada)
2015-07-01
Topological insulators represent a new state of matter that open up new opportunities to create unique quantum particles. Many exciting experiments have been proposed by theory, yet, the main obstacle for their execution is material quality and cleanliness of the experimental conditions. The presence of tiny amounts of defects in the bulk or contaminants at the surface already mask these phenomena. We present the preparation, structural and spectroscopic characterisation of MBE-grown Bi{sub 2}Te{sub 3} thin films that are insulating in the bulk. Moreover, temperature dependent four-point-probe resistivity measurements of the Dirac states on surfaces that are intrinsically clean were conducted. The total amount of surface charge carries is in the order of 10{sup 12} cm{sup -2} and mobilities up to 4600 cm{sup 2}/Vs are observed. Importantly, these results are achieved by carrying out the preparation and characterisation all in-situ under ultra-high-vacuum conditions.
Cluster-state quantum computing enhanced by high-fidelity generalized measurements.
Biggerstaff, D N; Kaltenbaek, R; Hamel, D R; Weihs, G; Rudolph, T; Resch, K J
2009-12-11
We introduce and implement a technique to extend the quantum computational power of cluster states by replacing some projective measurements with generalized quantum measurements (POVMs). As an experimental demonstration we fully realize an arbitrary three-qubit cluster computation by implementing a tunable linear-optical POVM, as well as fast active feedforward, on a two-qubit photonic cluster state. Over 206 different computations, the average output fidelity is 0.9832+/-0.0002; furthermore the error contribution from our POVM device and feedforward is only of O(10(-3)), less than some recent thresholds for fault-tolerant cluster computing.
Low oxidation state aluminum-containing cluster anions: Cp∗AlnH-, n = 1-3
Zhang, Xinxing; Ganteför, Gerd; Eichhorn, Bryan; Mayo, Dennis; Sawyer, William H.; Gill, Ann F.; Kandalam, Anil K.; Schnöckel, Hansgeorg; Bowen, Kit
2016-08-01
Three new, low oxidation state, aluminum-containing cluster anions, Cp*AlnH-, n = 1-3, were prepared via reactions between aluminum hydride cluster anions, AlnHm-, and Cp*H ligands. These were characterized by mass spectrometry, anion photoelectron spectroscopy, and density functional theory based calculations. Agreement between the experimentally and theoretically determined vertical detachment energies and adiabatic detachment energies validated the computed geometrical structures. Reactions between aluminum hydride cluster anions and ligands provide a new avenue for discovering low oxidation state, ligated aluminum clusters.
Plasmonics in Topological Insulators
Directory of Open Access Journals (Sweden)
Yi-Ping Lai
2014-04-01
Full Text Available With strong spin-orbit coupling, topological insulators have an insulating bulk state, characterized by a band gap, and a conducting surface state, characterized by a Dirac cone. Plasmons in topological insulators show high frequency-tunability in the mid-infrared and terahertz spectral regions with transverse spin oscillations, also called “spin-plasmons”. This paper presents a discussion and review of the developments in this field from the fundamental theory of plasmons in bulk, thin-film, and surface-magnetized topological insulators to the techniques of plasmon excitation and future applications.
Simulation and Validation of the ATLAS Level-1 Topological Trigger
Bakker, Pepijn Johannes; The ATLAS collaboration
2017-01-01
The ATLAS experiment has recently commissioned a new component of its first-level trigger: the L1 topological trigger. This system, using state-of-the-art FPGA processors, makes it possible to reject events by applying topological requirements, such as kinematic criteria involving clusters, jets, muons, and total transverse energy. The data recorded using the L1Topological trigger demonstrates that this innovative trigger strategy allows for an improved rejection rate without efficiency loss. This improvement has been shown for several relevant physics processes leading to low-$p_T$ leptons, including $H\\to{}\\tau{}\\tau{}$ and $J/\\Psi\\to{}\\mu{}\\mu{}$. In addition, an accurate simulation of the L1Topological trigger is used to validate and optimize the performance of this trigger. To reach such an accuracy, this simulation must take into account the fact that the firmware algorithms are executed on a FPGA architecture, while the simulation is executed on a floating point architecture.
Mental State Talk Structure in Children’s Narratives: A Cluster Analysis
Directory of Open Access Journals (Sweden)
Giuliana Pinto
2017-01-01
Full Text Available This study analysed children’s Theory of Mind (ToM as assessed by mental state talk in oral narratives. We hypothesized that the children’s mental state talk in narratives has an underlying structure, with specific terms organized in clusters. Ninety-eight children attending the last year of kindergarten were asked to tell a story twice, at the beginning and at the end of the school year. Mental state talk was analysed by identifying terms and expressions referring to perceptual, physiological, emotional, willingness, cognitive, moral, and sociorelational states. The cluster analysis showed that children’s mental state talk is organized in two main clusters: perceptual states and affective states. Results from the study confirm the feasibility of narratives as an outlet to inquire mental state talk and offer a more fine-grained analysis of mental state talk structure.
Cluster emission in superdeformed Sr isotopes in the ground state ...
Indian Academy of Sciences (India)
is found that inclusion of excitation energy increases the decay rate (decreases T1/2 value) considerably and these nuclei become unstable against decay. These findings support earlier observation of Gupta et al based on PCM. Keywords. Cluster decay; exotic decay. PACS Nos 23.70.+j; 23.60.+e; 27.50.+e. 1. Introduction.
Tang, Jingwu; Peng, Zhaohui
2010-01-01
We propose teleporting a specific family of tripartite entangled pure states, which include both the Greenberger-Horne-Zeilinger (GHZ) state and the W-class state, with the five-qubit cluster state. In this scheme, two different measurement strategies are introduced and the successful probability of both is one theoretically. In cavity quantum electrodynamics (QED), we propose generating the five-qubit cluster state and discuss the local measurement of the Bell state and the five-qubit cluster state. It is shown that our scheme may be realizable based on present cavity QED technology. In future, our scheme may be useful for establishing general tripartite entanglement in remote nodes of the communication network.
Indian Academy of Sciences (India)
has been investigated electrochemically in positive and negative microenvironments, both in solution and in film. Charge nature around the active centre ... in plants, bacteria and also in mammals. This cluster is also an important constituent of a ..... selection of non-cysteine amino acid in the active centre of Rieske proteins.
Quantum Hall effect on top and bottom surface states of topological insulator (Bi1-xSbx)2Te3 films.
Yoshimi, R; Tsukazaki, A; Kozuka, Y; Falson, J; Takahashi, K S; Checkelsky, J G; Nagaosa, N; Kawasaki, M; Tokura, Y
2015-04-14
The three-dimensional topological insulator is a novel state of matter characterized by two-dimensional metallic Dirac states on its surface. To verify the topological nature of the surface states, Bi-based chalcogenides such as Bi2Se3, Bi2Te3, Sb2Te3 and their combined/mixed compounds have been intensively studied. Here, we report the realization of the quantum Hall effect on the surface Dirac states in (Bi1-xSbx)2Te3 films. With electrostatic gate-tuning of the Fermi level in the bulk band gap under magnetic fields, the quantum Hall states with filling factor ±1 are resolved. Furthermore, the appearance of a quantum Hall plateau at filling factor zero reflects a pseudo-spin Hall insulator state when the Fermi level is tuned in between the energy levels of the non-degenerate top and bottom surface Dirac points. The observation of the quantum Hall effect in three-dimensional topological insulator films may pave a way toward topological insulator-based electronics.
Topological insulators and topological superconductors
Bernevig, Andrei B
2013-01-01
This graduate-level textbook is the first pedagogical synthesis of the field of topological insulators and superconductors, one of the most exciting areas of research in condensed matter physics. Presenting the latest developments, while providing all the calculations necessary for a self-contained and complete description of the discipline, it is ideal for graduate students and researchers preparing to work in this area, and it will be an essential reference both within and outside the classroom. The book begins with simple concepts such as Berry phases, Dirac fermions, Hall conductance and its link to topology, and the Hofstadter problem of lattice electrons in a magnetic field. It moves on to explain topological phases of matter such as Chern insulators, two- and three-dimensional topological insulators, and Majorana p-wave wires. Additionally, the book covers zero modes on vortices in topological superconductors, time-reversal topological superconductors, and topological responses/field theory and topolo...
Habib, K M Masum; Sajjad, Redwan N; Ghosh, Avik W
2015-05-01
We show that the interplay between chiral tunneling and spin-momentum locking of helical surface states leads to spin amplification and filtering in a 3D topological insulator (TI). Our calculations show that the chiral tunneling across a TI pn junction allows normally incident electrons to transmit, while the rest are reflected with their spins flipped due to spin-momentum locking. The net result is that the spin current is enhanced while the dissipative charge current is simultaneously suppressed, leading to an extremely large, gate-tunable spin-to-charge current ratio (∼20) at the reflected end. At the transmitted end, the ratio stays close to 1 and the electrons are completely spin polarized.
Search for 12 C+ 12 C clustering in 24 Mg ground state
Indian Academy of Sciences (India)
In the backdrop of many models, the heavy cluster structure of the ground state of 24 Mg has been probed experimentally for the first time using the heavy cluster knockout reaction 24 Mg( 12 C, 212 C) 12 C in thequasifree scattering kinematic domain. In the ( 12 C, 212 C) reaction, the direct 12 C-knockout cross-section was ...
Ground state structures and properties of Si3Hn (n= 1–6) clusters
Indian Academy of Sciences (India)
The ground state structures and properties of Si3H (1 ≤ ≤ 6) clusters have been calculated using Car–Parrinello molecular dynamics with simulated annealing and steepest descent optimization methods. We have studied cohesive energy per particle and first excited electronic level gap of the clusters as a function of ...
Topological Methods for Visualization
Energy Technology Data Exchange (ETDEWEB)
Berres, Anne Sabine [Los Alamos National Lab. (LANL), Los Alamos, NM (United Stat
2016-04-07
This slide presentation describes basic topological concepts, including topological spaces, homeomorphisms, homotopy, betti numbers. Scalar field topology explores finding topological features and scalar field visualization, and vector field topology explores finding topological features and vector field visualization.
Directory of Open Access Journals (Sweden)
R. Wu
2016-05-01
Full Text Available Two-dimensional topological insulators with a large bulk band gap are promising for experimental studies of quantum spin Hall effect and for spintronic device applications. Despite considerable theoretical efforts in predicting large-gap two-dimensional topological insulator candidates, none of them have been experimentally demonstrated to have a full gap, which is crucial for quantum spin Hall effect. Here, by combining scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy, we reveal that ZrTe_{5} crystal hosts a large full gap of ∼100 meV on the surface and a nearly constant density of states within the entire gap at the monolayer step edge. These features are well reproduced by our first-principles calculations, which point to the topologically nontrivial nature of the edge states.
State of the art of parallel scientific visualization applications on PC clusters
International Nuclear Information System (INIS)
Juliachs, M.
2004-01-01
In this state of the art on parallel scientific visualization applications on PC clusters, we deal with both surface and volume rendering approaches. We first analyze available PC cluster configurations and existing parallel rendering software components for parallel graphics rendering. CEA/DIF has been studying cluster visualization since 2001. This report is part of a study to set up a new visualization research platform. This platform consisting of an eight-node PC cluster under Linux and a tiled display was installed in collaboration with Versailles-Saint-Quentin University in August 2003. (author)
Graph topologies on closed multifunctions
Directory of Open Access Journals (Sweden)
Giuseppe Di Maio
2003-10-01
Full Text Available In this paper we study function space topologies on closed multifunctions, i.e. closed relations on X x Y using various hypertopologies. The hypertopologies are in essence, graph topologies i.e topologies on functions considered as graphs which are subsets of X x Y . We also study several topologies, including one that is derived from the Attouch-Wets filter on the range. We state embedding theorems which enable us to generalize and prove some recent results in the literature with the use of known results in the hyperspace of the range space and in the function space topologies of ordinary functions.
Sacramento, P. D.; Vieira, V. R.
2018-04-01
Mappings between models may be obtained by unitary transformations with preservation of the spectra but in general a change in the states. Non-canonical transformations in general also change the statistics of the operators involved. In these cases one may expect a change of topological properties as a consequence of the mapping. Here we consider some dualities resulting from mappings, by systematically using a Majorana fermion representation of spin and fermionic problems. We focus on the change of topological invariants that results from unitary transformations taking as examples the mapping between a spin system and a topological superconductor, and between different fermionic systems.
Goodman, Sue E
2009-01-01
Beginning Topology is designed to give undergraduate students a broad notion of the scope of topology in areas of point-set, geometric, combinatorial, differential, and algebraic topology, including an introduction to knot theory. A primary goal is to expose students to some recent research and to get them actively involved in learning. Exercises and open-ended projects are placed throughout the text, making it adaptable to seminar-style classes. The book starts with a chapter introducing the basic concepts of point-set topology, with examples chosen to captivate students' imaginations while i
Identifying Subgroups of Tinnitus Using Novel Resting State fMRI Biomarkers and Cluster Analysis
2017-10-13
applied to the resting-state data to identify tinnitus subgroups within the patient population and pair them with specific behavioral ...and behavioral data Specific Aim 2: Determine tinnitus subgroups using automated cluster analysis of resting state data and associate the subgroups...data analysis and clustering method previously developed to apply to current tinnitus data set o Percentage of completion at end of Year 2 (24 months
Fault-tolerant measurement-based quantum computing with continuous-variable cluster states.
Menicucci, Nicolas C
2014-03-28
A long-standing open question about Gaussian continuous-variable cluster states is whether they enable fault-tolerant measurement-based quantum computation. The answer is yes. Initial squeezing in the cluster above a threshold value of 20.5 dB ensures that errors from finite squeezing acting on encoded qubits are below the fault-tolerance threshold of known qubit-based error-correcting codes. By concatenating with one of these codes and using ancilla-based error correction, fault-tolerant measurement-based quantum computation of theoretically indefinite length is possible with finitely squeezed cluster states.
Signatures of topological superconductivity
Energy Technology Data Exchange (ETDEWEB)
Peng, Yang
2017-07-19
The prediction and experimental discovery of topological insulators brought the importance of topology in condensed matter physics into the limelight. Topology hence acts as a new dimension along which more and more new states of matter start to emerge. One of these topological states of matter, namely topological superconductors, comes into the focus because of their gapless excitations. These gapless excitations, especially in one dimensional topological superconductors, are Majorana zero modes localized at the ends of the superconductor and exhibit exotic nonabelian statistics, which can be potentially applied to fault-tolerant quantum computation. Given their highly interesting physical properties and potential applications to quantum computation, both theorists and experimentalists spend great efforts to realize topological supercondoctors and to detect Majoranas. In two projects within this thesis, we investigate the properties of Majorana zero modes in realistic materials which are absent in simple theoretical models. We find that the superconducting proximity effect, an essential ingredient in all existing platforms for topological superconductors, plays a significant role in determining the localization property of the Majoranas. Strong proximity coupling between the normal system and the superconducting substrate can lead to strongly localized Majoranas, which can explain the observation in a recent experiment. Motivated by experiments in Molenkamp's group, we also look at realistic quantum spin Hall Josephson junctions, in which charge puddles acting as magnetic impurities are coupled to the helical edge states. We find that with this setup, the junction generically realizes an exotic 8π periodic Josephson effect, which is absent in a pristine Josephson junction. In another two projects, we propose more pronounced signatures of Majoranas that are accessible with current experimental techniques. The first one is a transport measurement, which uses
Study of radicals, clusters and transition state species by anion photoelectron spectroscopy
International Nuclear Information System (INIS)
Arnold, D.W.
1994-08-01
Free radicals, elemental and van der Waals clusters and transition state species for bimolecular chemical reactions are investigated using anion photoelectron spectroscopy. Several low-lying electronic states of ozone have been identified via photoelectron spectroscopy of O 3 - . A characterization of these states is important to models for atmospheric ozone reaction kinetics. The fluoroformyloxyl radical, FCO 2 , has been investigated, providing vibrational frequencies and energies for two electronic states. The technique has also been employed to make the first direct observation and characterization of the NNO 2 molecule. Several electronic states are observed for this species which is believed to play a role as a reactive intermediate in the N + NO 2 reaction. The experimental results for all three of these radicals are supplemented by ab initio investigations of their molecular properties. The clusters investigations include studies of elemental carbon clusters (C 2 - - C 11 - ), and van der Waals clusters (X - (CO 2 ) n , X = I, Br, Cl; n ≤ 13 and I - (N 2 O) n=1--11 ). Primarily linear clusters are observed for the smaller carbon clusters, while the spectra of the larger clusters contain contribution from cyclic anion photodetachment. Very interesting ion-solvent interactions are observed in the X - (CO 2 )n clusters. The transition state regions for several bimolecular chemical reactions have also been investigated by photodetachment of a negative ion precursor possessing a geometry similar to that of the transition state species. These spectra show features which are assigned to motions of the unstable neutral complex existing between reactants and products
Study of radicals, clusters and transition state species by anion photoelectron spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Arnold, Don Wesley [Univ. of California, Berkeley, CA (United States)
1994-08-01
Free radicals, elemental and van der Waals clusters and transition state species for bimolecular chemical reactions are investigated using anion photoelectron spectroscopy. Several low-lying electronic states of ozone have been identified via photoelectron spectroscopy of O_{3}^{-}. A characterization of these states is important to models for atmospheric ozone reaction kinetics. The fluoroformyloxyl radical, FCO_{2}, has been investigated, providing vibrational frequencies and energies for two electronic states. The technique has also been employed to make the first direct observation and characterization of the NNO_{2} molecule. Several electronic states are observed for this species which is believed to play a role as a reactive intermediate in the N + NO_{2} reaction. The experimental results for all three of these radicals are supplemented by ab initio investigations of their molecular properties. The clusters investigations include studies of elemental carbon clusters (C_{2}^{-} - C_{11}^{-}), and van der Waals clusters (X^{-}(CO_{2})_{n}, X = I, Br, Cl; n {le} 13 and I^{-} (N_{2}O)_{n=1--11}). Primarily linear clusters are observed for the smaller carbon clusters, while the spectra of the larger clusters contain contribution from cyclic anion photodetachment. Very interesting ion-solvent interactions are observed in the X^{-}(CO_{2})n clusters. The transition state regions for several bimolecular chemical reactions have also been investigated by photodetachment of a negative ion precursor possessing a geometry similar to that of the transition state species. These spectra show features which are assigned to motions of the unstable neutral complex existing between reactants and products.
Barttfeld, Pablo; Wicker, Bruno; Cukier, Sebastian; Navarta, Silvana; Lew, Sergio; Leiguarda, Ramon; Sigman, Mariano
2012-01-01
Anatomical and functional brain studies have converged to the hypothesis that autism spectrum disorders (ASD) are associated with atypical connectivity. Using a modified resting-state paradigm to drive subjects' attention, we provide evidence of a very marked interaction between ASD brain functional connectivity and cognitive state. We show that…
Steady state subchannel analysis of AHWR fuel cluster
International Nuclear Information System (INIS)
Dasgupta, A.; Chandraker, D.K.; Vijayan, P.K.; Saha, D.
2006-09-01
Subchannel analysis is a technique used to predict the thermal hydraulic behavior of reactor fuel assemblies. The rod cluster is subdivided into a number of parallel interacting flow subchannels. The conservation equations are solved for each of these subchannels, taking into account subchannel interactions. Subchannel analysis of AHWR D-5 fuel cluster has been carried out to determine the variations in thermal hydraulic conditions of coolant and fuel temperatures along the length of the fuel bundle. The hottest regions within the AHWR fuel bundle have been identified. The effect of creep on the fuel performance has also been studied. MCHFR has been calculated using Jansen-Levy correlation. The calculations have been backed by sensitivity analysis for parameters whose values are not known accurately. The sensitivity analysis showed the calculations to have a very low sensitivity to these parameters. Apart from the analysis, the report also includes a brief introduction of a few subchannel codes. A brief description of the equations and solution methodology used in COBRA-IIIC and COBRA-IV-I is also given. (author)
Indian Academy of Sciences (India)
Topology is usually taught in India in the second year of a master's degree programme. Much of the time is spent on developing such basic notions as connectedness, compactness, product topology, and the course ends with. Tychonov's theorem or Urysohn's lemma. At best, the student learns a bit about the fundamental ...
An equation of state for purely kinetic k-essence inspired by cosmic topological defects
Energy Technology Data Exchange (ETDEWEB)
Cordero, Ruben; Gonzalez, Eduardo L.; Queijeiro, Alfonso [Instituto Politecnico Nacional, Departamento de Fisica, Escuela Superior de Fisica y Matematicas, Ciudad de Mexico (Mexico)
2017-06-15
We investigate the physical properties of a purely kinetic k-essence model with an equation of state motivated in superconducting membranes. We compute the equation of state parameter w and discuss its physical evolution via a nonlinear equation of state. Using the adiabatic speed of sound and energy density, we restrict the range of parameters of the model in order to have an acceptable physical behavior. We study the evolution of the scale factor and address the question of the possible existence of finite-time future singularities. Furthermore, we analyze the evolution of the luminosity distance d{sub L} with redshift z by comparing (normalizing) it with the ΛCDM model. Since the equation of state parameter is z-dependent the evolution of the luminosity distance is also analyzed using the Alcock-Paczynski test. (orig.)
Arango, Yulieth C.; Huang, Liubing; Chen, Chaoyu; Avila, Jose; Asensio, Maria C.; Grützmacher, Detlev; Lüth, Hans; Lu, Jia Grace; Schäpers, Thomas
2016-01-01
We report on low-temperature transport and electronic band structure of p-type Sb2Te3 nanowires, grown by chemical vapor deposition. Magnetoresistance measurements unravel quantum interference phenomena, which depend on the cross-sectional dimensions of the nanowires. The observation of periodic Aharonov-Bohm-type oscillations is attributed to transport in topologically protected surface states in the Sb2Te3 nanowires. The study of universal conductance fluctuations demonstrates coherent transport along the Aharonov-Bohm paths encircling the rectangular cross-section of the nanowires. We use nanoscale angle-resolved photoemission spectroscopy on single nanowires (nano-ARPES) to provide direct experimental evidence on the nontrivial topological character of those surface states. The compiled study of the bandstructure and the magnetotransport response unambiguosly points out the presence of topologically protected surface states in the nanowires and their substantial contribution to the quantum transport effects, as well as the hole doping and Fermi velocity among other key issues. The results are consistent with the theoretical description of quantum transport in intrinsically doped quasi-one-dimensional topological insulator nanowires. PMID:27581169
Experimental observation of chimera and cluster states in a minimal globally coupled network
Energy Technology Data Exchange (ETDEWEB)
Hart, Joseph D. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Bansal, Kanika [Department of Mathematics, University at Buffalo, SUNY Buffalo, New York 14260 (United States); US Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States); Murphy, Thomas E. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Department of Electrical and Computer Engineering, University of Maryland, College Park, Maryland 20742 (United States); Roy, Rajarshi [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)
2016-09-15
A “chimera state” is a dynamical pattern that occurs in a network of coupled identical oscillators when the symmetry of the oscillator population is broken into synchronous and asynchronous parts. We report the experimental observation of chimera and cluster states in a network of four globally coupled chaotic opto-electronic oscillators. This is the minimal network that can support chimera states, and our study provides new insight into the fundamental mechanisms underlying their formation. We use a unified approach to determine the stability of all the observed partially synchronous patterns, highlighting the close relationship between chimera and cluster states as belonging to the broader phenomenon of partial synchronization. Our approach is general in terms of network size and connectivity. We also find that chimera states often appear in regions of multistability between global, cluster, and desynchronized states.
Wei, Luqing; Zhang, Jiuquan; Long, Zhiliang; Wu, Guo-Rong; Hu, Xiaofei; Zhang, Yanling; Wang, Jian
2014-01-01
Parkinson's disease (PD) is mainly characterized by dopamine depletion of the cortico-basal ganglia (CBG) motor circuit. Given that dopamine dysfunction could affect functional brain network efficiency, the present study utilized resting-state fMRI (rs-fMRI) and graph theoretical approach to investigate the topological efficiency changes of the CBG motor network in patients with PD during a relatively hypodopaminergic state (12 hours after a last dose of dopamimetic treatment). We found that PD compared with controls had remarkable decreased efficiency in the CBG motor network, with the most pronounced changes observed in rostral supplementary motor area (pre-SMA), caudal SMA (SMA-proper), primary motor cortex (M1), primary somatosensory cortex (S1), thalamus (THA), globus pallidus (GP), and putamen (PUT). Furthermore, reduced efficiency in pre-SMA, M1, THA and GP was significantly correlated with Unified Parkinson's Disease Rating Scale (UPDRS) motor scores in PD patients. Together, our results demonstrate that individuals with PD appear to be less effective at information transfer within the CBG motor pathway, which provides a novel perspective on neurobiological explanation for the motor symptoms in patients. These findings are in line with the pathophysiology of PD, suggesting that network efficiency metrics may be used to identify and track the pathology of PD.
Abu-Baker, Shadi; Lu, Jun-Xia; Chu, Shidong; Shetty, Kiran K; Gor'kov, Peter L; Lorigan, Gary A
2007-11-01
For the first time, 15N solid-state NMR experiments were conducted on wild-type phospholamban (WT-PLB) embedded inside mechanically oriented phospholipid bilayers to investigate the topology of its cytoplasmic and transmembrane domains. 15N solid-state NMR spectra of site-specific 15N-labeled WT-PLB indicate that the transmembrane domain has a tilt angle of 13 degrees+/-6 degrees with respect to the POPC (1-palmitoyl-2-oleoyl-sn-glycero-phosphocholine) bilayer normal and that the cytoplasmic domain of WT-PLB lies on the surface of the phospholipid bilayers. Comparable results were obtained from site-specific 15N-labeled WT-PLB embedded inside DOPC/DOPE (1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) mechanically oriented phospholipids' bilayers. The new NMR data support a pinwheel geometry of WT-PLB, but disagree with a bellflower structure in micelles, and indicate that the orientation of the cytoplasmic domain of the WT-PLB is similar to that reported for the monomeric AFA-PLB mutant.
Directory of Open Access Journals (Sweden)
E. Kalesaki
2014-01-01
Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.
Topology with applications topological spaces via near and far
Naimpally, Somashekhar A
2013-01-01
The principal aim of this book is to introduce topology and its many applications viewed within a framework that includes a consideration of compactness, completeness, continuity, filters, function spaces, grills, clusters and bunches, hyperspace topologies, initial and final structures, metric spaces, metrization, nets, proximal continuity, proximity spaces, separation axioms, and uniform spaces. This book provides a complete framework for the study of topology with a variety of applications in science and engineering that include camouflage filters, classification, digital image processing, forgery detection, Hausdorff raster spaces, image analysis, microscopy, paleontology, pattern recognition, population dynamics, stem cell biology, topological psychology, and visual merchandising. It is the first complete presentation on topology with applications considered in the context of proximity spaces, and the nearness and remoteness of sets of objects. A novel feature throughout this book is the use of near and...
Physical-depth architectural requirements for generating universal photonic cluster states
Morley-Short, Sam; Bartolucci, Sara; Gimeno-Segovia, Mercedes; Shadbolt, Pete; Cable, Hugo; Rudolph, Terry
2018-01-01
Most leading proposals for linear-optical quantum computing (LOQC) use cluster states, which act as a universal resource for measurement-based (one-way) quantum computation. In ballistic approaches to LOQC, cluster states are generated passively from small entangled resource states using so-called fusion operations. Results from percolation theory have previously been used to argue that universal cluster states can be generated in the ballistic approach using schemes which exceed the critical threshold for percolation, but these results consider cluster states with unbounded size. Here we consider how successful percolation can be maintained using a physical architecture with fixed physical depth, assuming that the cluster state is continuously generated and measured, and therefore that only a finite portion of it is visible at any one point in time. We show that universal LOQC can be implemented using a constant-size device with modest physical depth, and that percolation can be exploited using simple pathfinding strategies without the need for high-complexity algorithms.
Cognition Is Related to Resting-State Small-World Network Topology: An Magnetoencephalographic Study
Douw, L.; Schoonheim, M.M.; Landi, D.; van der Meer, M.L.; Geurts, J.J.G.; Reijneveld, J.C.; Klein, M.; Stam, C.J.
2011-01-01
Brain networks and cognition have recently begun to attract attention: studies suggest that more efficiently wired resting-state brain networks are indeed correlated with better cognitive performance. "Small-world" brain networks combine local segregation with global integration, hereby subserving
Buchstaber, Victor M
2015-01-01
This book is about toric topology, a new area of mathematics that emerged at the end of the 1990s on the border of equivariant topology, algebraic and symplectic geometry, combinatorics, and commutative algebra. It has quickly grown into a very active area with many links to other areas of mathematics, and continues to attract experts from different fields. The key players in toric topology are moment-angle manifolds, a class of manifolds with torus actions defined in combinatorial terms. Construction of moment-angle manifolds relates to combinatorial geometry and algebraic geometry of toric v
Franz, Marcel
2013-01-01
Topological Insulators, volume six in the Contemporary Concepts of Condensed Matter Series, describes the recent revolution in condensed matter physics that occurred in our understanding of crystalline solids. The book chronicles the work done worldwide that led to these discoveries and provides the reader with a comprehensive overview of the field. Starting in 2004, theorists began to explore the effect of topology on the physics of band insulators, a field previously considered well understood. However, the inclusion of topology brings key new elements into this old field. Whereas it was
Energy Technology Data Exchange (ETDEWEB)
Kobayashi, Yasuaki [Meme Media Laboratory, Hokkaido University, Sapporo 060-0813 (Japan); Kori, Hiroshi [Division of Advanced Sciences, Ochadai Academic Production, Ochanomizu University, Tokyo 112-8610 (Japan)], E-mail: kobayashi@nsc.es.hokudai.ac.jp, E-mail: kori.hiroshi@ocha.ac.jp
2009-03-15
A theoretical framework is developed for the precise control of spatial patterns in oscillatory media using nonlinear global feedback, where a proper form of the feedback function corresponding to a specific pattern is predicted through the analysis of a phase diffusion equation with global coupling. In particular, feedback functions that generate the following spatial patterns are analytically given: (i) 2-cluster states with an arbitrary population ratio, (ii) equally populated multi-cluster states and (iii) a desynchronized state. Our method is demonstrated numerically by using the Brusselator model in the oscillatory regime. Experimental realization is also discussed.
Exotic Non-Abelian Topological Defects in Lattice Fractional Quantum Hall States
Liu, Zhao; Möller, Gunnar; Bergholtz, Emil J.
2017-01-01
We investigate extrinsic wormhole-like twist defects that effectively increase the genus of space in lattice versions of multi-component fractional quantum Hall systems. Although the original band structure is distorted by these defects, leading to localized midgap states, we find that a new lowest flat band representing a higher genus system can be engineered by tuning local single-particle potentials. Remarkably, once local many-body interactions in this new band are switched on, we identif...
Event-by-Event Cluster Analysis of Final States from Heavy Ion Collisions
International Nuclear Information System (INIS)
Fialkowski, K.; Wit, R.
1999-01-01
We present an event-by-event analysis of the cluster structure of final multihadron states resulting from heavy ion collisions. A comparison of experimental data with the states obtained from Monte Carlo generators is shown. The analysis of the first available experimental events suggests that the method is suitable for selecting some different types of events. (author)
Strategies for the preparation of large cluster states using non-deterministic gates
International Nuclear Information System (INIS)
Rohde, Peter P; Barrett, Sean D
2007-01-01
The cluster state model for quantum computation has paved the way for schemes that allow scalable quantum computing, even when using non-deterministic quantum gates. Here the initial step is to prepare a large entangled state using non-deterministic gates. A key question in this context is the relative efficiencies of different 'strategies', i.e. in what order should the non-deterministic gates be applied, in order to maximize the size of the resulting cluster states? In this paper we consider this issue in the context of 'large' cluster states. Specifically, we assume an unlimited resource of qubits and ask what the steady state rate at which 'large' clusters are prepared from this resource is, given an entangling gate with particular characteristics. We measure this rate in terms of the number of entangling gate operations that are applied. Our approach works for a variety of different entangling gate types, with arbitrary failure probability. Our results indicate that strategies whereby one preferentially bonds together clusters of identical length are considerably more efficient than those in which one does not. Additionally, compared to earlier analytic results, our numerical study offers substantially improved resource scaling
de Tudela, Ricardo Pérez; Barragán, Patricia; Prosmiti, Rita; Villarreal, Pablo; Delgado-Barrio, Gerardo
2011-03-31
Classical and path integral Monte Carlo (CMC, PIMC) "on the fly" calculations are carried out to investigate anharmonic quantum effects on the thermal equilibrium structure of the H5(+) cluster. The idea to follow in our computations is based on using a combination of the above-mentioned nuclear classical and quantum statistical methods, and first-principles density functional (DFT) electronic structure calculations. The interaction energies are computed within the DFT framework using the B3(H) hybrid functional, specially designed for hydrogen-only systems. The global minimum of the potential is predicted to be a nonplanar configuration of C(2v) symmetry, while the next three low-lying stationary points on the surface correspond to extremely low-energy barriers for the internal proton transfer and to the rotation of the H2 molecules, around the C2 axis of H5(+), connecting the symmetric C(2v) minima in the planar and nonplanar orientations. On the basis of full-dimensional converged PIMC calculations, results on the quantum vibrational zero-point energy (ZPE) and state of H5(+) are reported at a low temperature of 10 K, and the influence of the above-mentioned topological features of the surface on its probability distributions is clearly demonstrated.
An entanglement concentration protocol for cluster states using ...
Indian Academy of Sciences (India)
Entanglement is the most precious quantum resource in the theory of quantum information and communication [1,2]. ... quantum system with the environment, and also after some use has been made of an entan- gled state, the ..... [2] D McMahon, Quantum computing explained (John Wiley and Sons, 2007). [3] A Einstein, B ...
An entanglement concentration protocol for cluster states using ...
Indian Academy of Sciences (India)
Permanent link: http://www.ias.ac.in/article/fulltext/pram/086/05/0973-0983 ... The purpose of this paper is a proposal on entanglement concentration protocol forcluster states. The protocol ... We also make a comparative numerical study of the residual entanglement left out after the execution of each step of the protocol.
An entanglement concentration protocol for cluster states using ...
Indian Academy of Sciences (India)
The purpose of this paper is a proposal on entanglement concentration protocol forcluster states. The protocol uses CNOT gate operation and is assisted with a single qubit. Moreover, the local and non-local operations are performed by a single party. We also make a comparative numerical study of the residual ...
Directory of Open Access Journals (Sweden)
Serkan Karatas
2016-12-01
Full Text Available In this paper, we redefine the neutrosophic set operations and, by using them, we introduce neutrosophic topology and investigate some related properties such as neutrosophic closure, neutrosophic closure, neutrosophic interior, neutrosophic exterior, neutrosophic boundary and neutrosophic subspace.
Tunable Topological Phononic Crystals
Chen, Zeguo
2016-05-27
Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.
Topological phases: Wormholes in quantum matter
Schoutens, K.
2009-01-01
Proliferation of so-called anyonic defects in a topological phase of quantum matter leads to a critical state that can be visualized as a 'quantum foam', with topology-changing fluctuations on all length scales.
ATLAS Level-1 Topological Trigger
Zheng, Daniel; The ATLAS collaboration
2018-01-01
The ATLAS experiment has introduced and recently commissioned a completely new hardware sub-system of its first-level trigger: the topological processor (L1Topo). L1Topo consist of two AdvancedTCA blades mounting state-of-the-art FPGA processors, providing high input bandwidth (up to 4 Gb/s) and low latency data processing (200 ns). L1Topo is able to select collision events by applying kinematic and topological requirements on candidate objects (energy clusters, jets, and muons) measured by calorimeters and muon sub-detectors. Results from data recorded using the L1Topo trigger will be presented. These results demonstrate a significantly improved background event rejection, thus allowing for a rate reduction without efficiency loss. This improvement has been shown for several physics processes leading to low-pT leptons, including H->tau tau and J/Psi->mu mu. In addition to describing the L1Topo trigger system, we will discuss the use of an accurate L1Topo simulation as a powerful tool to validate and optimize...
Khamari, Bramhachari; Kashikar, Ravi; Nanda, B. R. K.
2018-01-01
Density functional calculations and model tight-binding Hamiltonian studies are carried out to examine the bulk and surface electronic structure of the largely unexplored perovskite family of A BiO3 , where A is a group I-II element. From the study, we reveal the existence of two TI states, one in valence band (V-TI) and the other in conduction band (C-TI), as the universal feature of A BiO3 . The V-TI and C-TI are, respectively, born out of bonding and antibonding states caused by Bi-{s ,p } -O-{p } coordinated covalent interactions. Further, we outline a classification scheme in this family where one class follows spin orbit coupling and the other follows the second neighbor Bi-Bi hybridization to induce s-p band inversion for the realization of C-TI states. Below a certain critical thickness of the film, which varies with A , TI states of top and bottom surfaces couple to destroy the Dirac type linear dispersion and consequently to open narrow surface energy gaps.
Entangled states decoherence in coupled molecular spin clusters
Troiani, Filippo; Szallas, Attila; Bellini, Valerio; Affronte, Marco
2010-03-01
Localized electron spins in solid-state systems are widely investigated as potential building blocks of quantum devices and computers. While most efforts in the field have been focused on semiconductor low-dimensional structures, molecular antiferromagnets were recently recognized as alternative implementations of effective few-level spin systems. Heterometallic, Cr-based spin rings behave as effective spin-1/2 systems at low temperature and show long decoherence times [1]; besides, they can be chemically linked and magnetically coupled in a controllable fascion [2]. Here, we theoretically investigate the decoherence of the Bell states in such ring dimers, resulting from hyperfine interactions with nuclear spins. Based on a microscopic description of the molecules [3], we simulate the effect of inhomogeneous broadening, spectral diffusion and electron-nuclear entanglement on the electron-spin coherence, estimating the role of the different nuclei (and of possible chemical substitutions), as well as the effect of simple spin-echo sequences. References: [1] F. Troiani, et al., Phys. Rev. Lett. 94, 207208 (2005). [2] G. A. Timco, S: Carretta, F. Troiani et al., Nature Nanotech. 4, 173 (2009). [3] F. Troiani, V. Bellini, and M. Affronte, Phys. Rev. B 77, 054428 (2008).
A Novel Quantum Blind Signature Scheme with Four-Particle Cluster States
Fan, Ling
2016-03-01
In an arbitrated quantum signature scheme, the signer signs the message and the receiver verifies the signature's validity with the assistance of the arbitrator. We present an arbitrated quantum blind signature scheme by measuring four-particle cluster states and coding. By using the special relationship of four-particle cluster states, we cannot only support the security of quantum signature, but also guarantee the anonymity of the message owner. It has a wide application to E-payment system, E-government, E-business, and etc.
α-cluster states in {sup 46,54}Cr from double-folding potentials
Energy Technology Data Exchange (ETDEWEB)
Mohr, Peter [Diakonie-Klinikum, Schwaebisch Hall (Germany); Institute for Nuclear Research (Atomki), Debrecen (Hungary)
2017-10-15
α-cluster states in {sup 46}Cr and {sup 54}Cr are investigated in the double-folding model. This study complements a recent similar work by Souza and Miyake, Eur. Phys. J. A 53, 146 (2017), which was based on a specially shaped potential. Excitation energies, reduced widths, intercluster separations, and intra-band transition strengths are calculated and compared to experimental values for the ground state bands in {sup 46}Cr and {sup 54}Cr. The α-cluster potential is also applied to elastic scattering at low and intermediate energies. Here, as a byproduct, a larger radial extent of the neutron density in {sup 50}Ti is found. (orig.)
The NIDS Cluster: Scalable, Stateful Network Intrusion Detection on Commodity Hardware
Energy Technology Data Exchange (ETDEWEB)
Tierney, Brian L; Vallentin, Matthias; Sommer, Robin; Lee, Jason; Leres, Craig; Paxson, Vern; Tierney, Brian
2007-09-19
In this work we present a NIDS cluster as a scalable solution for realizing high-performance, stateful network intrusion detection on commodity hardware. The design addresses three challenges: (i) distributing traffic evenly across an extensible set of analysis nodes in a fashion that minimizes the communication required for coordination, (ii) adapting the NIDS's operation to support coordinating its low-level analysis rather than just aggregating alerts; and (iii) validating that the cluster produces sound results. Prototypes of our NIDS cluster now operate at the Lawrence Berkeley National Laboratory and the University of California at Berkeley. In both environments the clusters greatly enhance the power of the network security monitoring.
Energy Technology Data Exchange (ETDEWEB)
Liang, Wenchuan [Univ. of California, Berkeley, CA (United States)
1994-11-01
X-ray absorption spectroscopy (XAS) was performed on Photosystem II (PSII)-enriched membranes prepared from spinach to explore: (1) the correlation between structure and magnetic spin state of the Mn cluster in the oxygen evolving complex (OEC) in the S_{2} state; and (2) the oxidation state changes of the Mn cluster in the flash-induced S-states. The structure of the Mn cluster in the S_{2} state with the g~4 electron paramagnetic resonance (EPR) signal (S_{2}-g4 state) was compared with that in the S_{2} state with multiline signal (S_{2}-MLS state) and the S_{1} state. The S_{2}-g4 state has a higher XAS inflection point energy than that of the S_{1} state, indicating the oxidation of Mn in the advance from the S_{1} to the S_{2}-g4 state. Differences in the edge shape and in the extended X-ray absorption fine structure (EXAFS) show that the structure of the Mn cluster in the S_{2}-g4 state is different from that in the S_{2}-MLS or the S_{1} state. In the S_{2}-g4 state, the second shell of backscatterers from the Mn absorber contains two Mn-Mn distances of 2.73 Å and 2.85 Å. Very little distance disorder exists in the second shell of the S_{1} or S_{2}-MLS states. The third shell of the S_{2}-g4 state at about 3.3 Å also contains increased heterogeneity relative to that of the S_{2}-MLS or the S_{1} state. Various S-states were prepared at room-temperature by saturating, single-turnover flashes. The flash-dependent oscillation in the amplitude of the MLS was used to characterize the S-state composition and to construct "pure" S-state Mn K-edge spectra. The edge position shifts to higher energy by 1.8 eV upon the S_{1} → S_{2} transition.
Huang, Huaqing; Jin, Kyung-Hwan; Zhang, Shunhong; Liu, Feng
2018-02-22
Two-dimensional (2D) electrides are layered ionic crystals in which anionic electrons are confined in the interlayer space. Here, we report a discovery of nontrivial [Formula: see text] topology in the electronic structures of 2D electride Y 2 C. Based on first-principles calculations, we found a topological [Formula: see text] invariant of (1; 111) for the bulk band and topologically protected surface states in the surfaces of Y 2 C, signifying its nontrivial electronic topology. We suggest a spin-resolved angle-resolved photoemission spectroscopy (ARPES) measurement to detect the unique helical spin texture of the spin-polarized topological surface state, which will provide characteristic evidence for the nontrivial electronic topology of Y 2 C. Furthermore, the coexistence of 2D surface electride states and topological surface state enables us to explain the outstanding discrepancy between the recent ARPES experiments and theoretical calculations. Our findings establish a preliminary link between the electride in chemistry and the band topology in condensed-matter physics, which are expected to inspire further interdisciplinary research between these fields.
Directory of Open Access Journals (Sweden)
L. Baulieu
2016-11-01
Full Text Available We extend to a possibly infinite chain the conformally invariant mechanical system that was introduced earlier as a toy model for understanding the topological Yang–Mills theory. It gives a topological quantum model that has interesting and computable zero modes and topological invariants. It confirms the recent conjecture by several authors that supersymmetric quantum mechanics may provide useful tools for understanding robotic mechanical systems (Vitelli et al. and condensed matter properties (Kane et al., where trajectories are allowed or not by the conservation of topological indices. The absences of ground state and mass gaps are special features of such systems.
Long-lived charge-separated states in ligand-stabilized silver clusters
Pelton, Matthew
2012-07-25
Recently developed synthesis methods allow for the production of atomically monodisperse clusters of silver atoms stabilized in solution by aromatic thiol ligands, which exhibit intense absorption peaks throughout the visible and near-IR spectral regions. Here we investigated the time-dependent optical properties of these clusters. We observed two kinetic processes following ultrafast laser excitation of any of the absorption peaks: a rapid decay, with a time constant of 1 ps or less, and a slow decay, with a time constant that can be longer than 300 ns. Both time constants decrease as the polarity of the solvent increases, indicating that the two processes correspond to the formation and recombination, respectively, of a charge-separated state. The long lifetime of this state and the broad optical absorption spectrum mean that the ligand-stabilized silver clusters are promising materials for solar energy harvesting. © 2012 American Chemical Society.
Milewski, Emil G
2013-01-01
REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Topology includes an overview of elementary set theory, relations and functions, ordinals and cardinals, topological spaces, continuous functions, metric spaces and normed spaces, co
Warner, S
1993-01-01
This text brings the reader to the frontiers of current research in topological rings. The exercises illustrate many results and theorems while a comprehensive bibliography is also included. The book is aimed at those readers acquainted with some very basic point-set topology and algebra, as normally presented in semester courses at the beginning graduate level or even at the advanced undergraduate level. Familiarity with Hausdorff, metric, compact and locally compact spaces and basic properties of continuous functions, also with groups, rings, fields, vector spaces and modules, and with Zorn''s Lemma, is also expected.
Jiang, J.; Schröter, N. B. M.; Wu, S.-C.; Kumar, N.; Shekhar, C.; Peng, H.; Xu, X.; Chen, C.; Yang, H. F.; Hwang, C.-C.; Mo, S.-K.; Felser, C.; Yan, B. H.; Liu, Z. K.; Yang, L. X.; Chen, Y. L.
2018-02-01
The recent discovery of the extreme magnetoresistance (XMR) in the nonmagnetic rare-earth monopnictides La X (X = P, As, Sb, Bi,), a recently proposed new topological semimetal family, has inspired intensive research effort in the exploration of the correlation between the XMR and their electronic structures. In this work, using angle-resolved photoemission spectroscopy to investigate the three-dimensional band structure of LaBi, we unraveled its topologically nontrivial nature with the observation of multiple topological surface Dirac fermions, as supported by our ab initio calculations. Furthermore, we observed substantial imbalance between the volume of electron and hole pockets, which rules out the electron-hole compensation as the primary cause of the XMR in LaBi.
Czech Academy of Sciences Publication Activity Database
Brabec, Jiří; Bhaskaran-Neir, K.; Govind, N.; Pittner, Jiří
2012-01-01
Roč. 137, č. 17 (2012), s. 171101 ISSN 0021-9606 R&D Projects: GA ČR GAP208/11/2222 Institutional support: RVO:61388955 Keywords : coupled cluster calculations * electron correlations * excited states Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.164, year: 2012
Czech Academy of Sciences Publication Activity Database
Banik, Subrata; Ravichandran, Lalitha; Brabec, J.; Hubač, I.; Kowalski, K.; Pittner, Jiří
2015-01-01
Roč. 142, č. 11 (2015), s. 114106 ISSN 0021-9606 R&D Projects: GA MŠk LH13117; GA ČR GAP208/11/2222 Institutional support: RVO:61388955 Keywords : QUADRUPLY EXCITED CLUSTER S * QUASI-DEGENERATE STATES * DOUBLE-EXCITATION MODEL Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.894, year: 2015
Search for 12 C+ 12 C clustering in 24 Mg ground state
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 88; Issue 2. Search for 12C+12C clustering in 24Mg ground state. B N JOSHI ARUN K JAIN D C BISWAS B V JOHN Y K GUPTA L S DANU R P VIND G K PRAJAPATI S MUKHOPADHYAY A SAXENA. Regular Volume 88 Issue 2 February 2017 Article ID 29 ...
Identifying Subgroups of Tinnitus Using Novel Resting State fMRI Biomarkers and Cluster Analysis
2016-10-01
project activities, for the purpose of enhancing public understanding and increasing interest in learning and careers in science, technology, and the... Unsupervised hierarchical clustering of resting state functional connectivity data to identify patients with mild tinnitus. Poster session presented...including drafting of IRB behavioral and scanning protocols, advising on recruiting and initial data collection. She also supervised analysis of data and
Vibrational dynamics of aniline (N2)1 clusters in their first excited singlet state
Hineman, M. F.; Kim, S. K.; Bernstein, E. R.; Kelley, D. F.
1992-04-01
The first excited singlet state S1 vibrational dynamics of aniline(N2)1 clusters are studied and compared to previous results on aniline(CH4)1 and aniline(Ar)1. Intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) rates fall between the two extremes of the CH4 (fast IVR, slow VP) and Ar (slow IVR, fast VP) cluster results as is predicted by a serial IVR/VP model using Fermi's golden rule to describe IVR processes and a restricted Rice-Ramsperger-Kassel-Marcus (RRKM) theory to describe unimolecular VP rates. The density of states is the most important factor determining the rates. Two product states, 00 and 10b1, of bare aniline and one intermediate state ˜(00) in the overall IVR/VP process are observed and time resolved measurements are obtained for the 000 and ˜(000) transitions. The results are modeled with the serial mechanism described above.
Open-Source Sequence Clustering Methods Improve the State Of the Art.
Kopylova, Evguenia; Navas-Molina, Jose A; Mercier, Céline; Xu, Zhenjiang Zech; Mahé, Frédéric; He, Yan; Zhou, Hong-Wei; Rognes, Torbjørn; Caporaso, J Gregory; Knight, Rob
2016-01-01
Sequence clustering is a common early step in amplicon-based microbial community analysis, when raw sequencing reads are clustered into operational taxonomic units (OTUs) to reduce the run time of subsequent analysis steps. Here, we evaluated the performance of recently released state-of-the-art open-source clustering software products, namely, OTUCLUST, Swarm, SUMACLUST, and SortMeRNA, against current principal options (UCLUST and USEARCH) in QIIME, hierarchical clustering methods in mothur, and USEARCH's most recent clustering algorithm, UPARSE. All the latest open-source tools showed promising results, reporting up to 60% fewer spurious OTUs than UCLUST, indicating that the underlying clustering algorithm can vastly reduce the number of these derived OTUs. Furthermore, we observed that stringent quality filtering, such as is done in UPARSE, can cause a significant underestimation of species abundance and diversity, leading to incorrect biological results. Swarm, SUMACLUST, and SortMeRNA have been included in the QIIME 1.9.0 release. IMPORTANCE Massive collections of next-generation sequencing data call for fast, accurate, and easily accessible bioinformatics algorithms to perform sequence clustering. A comprehensive benchmark is presented, including open-source tools and the popular USEARCH suite. Simulated, mock, and environmental communities were used to analyze sensitivity, selectivity, species diversity (alpha and beta), and taxonomic composition. The results demonstrate that recent clustering algorithms can significantly improve accuracy and preserve estimated diversity without the application of aggressive filtering. Moreover, these tools are all open source, apply multiple levels of multithreading, and scale to the demands of modern next-generation sequencing data, which is essential for the analysis of massive multidisciplinary studies such as the Earth Microbiome Project (EMP) (J. A. Gilbert, J. K. Jansson, and R. Knight, BMC Biol 12:69, 2014, http
Sau, Jay D.; Tewari, Sumanta; Lutchyn, Roman M.; Stanescu, Tudor D.; Das Sarma, S.
2010-12-01
We show that an ordinary semiconducting thin film with spin-orbit coupling can, under appropriate circumstances, be in a quantum topologically ordered state supporting exotic Majorana excitations which follow non-Abelian statistics. The key to the quantum topological order is the coexistence of spin-orbit coupling with proximity-induced s -wave superconductivity and an externally induced Zeeman coupling of the spins. For the Zeeman coupling below a critical value, the system is a nontopological (proximity-induced) s -wave superconductor. However, for a range of Zeeman coupling above the critical value, the lowest energy excited state inside a vortex is a zero-energy Majorana fermion state. The system, thus, has entered into a non-Abelian s -wave superconducting state via a topological quantum phase transition (TQPT) tuned by the Zeeman coupling. In the topological phase, since the time-reversal symmetry is explicitly broken by the Zeeman term in the Hamiltonian, the edge of the film constitutes a chiral Majorana wire. Just like the s -wave superconductivity, the Zeeman coupling can also be proximity induced in the film by an adjacent magnetic insulator. We show this by an explicit model tight-binding calculation for both types of proximity effects in the heterostructure geometry. Here we show that the same TQPT can be accessed by varying the interface transparency between the film and the superconductor. For the transparency below (above) a critical value, the system is a topological (regular) s -wave superconductor. In the one-dimensional version of the same structure and for the Zeeman coupling above the critical value, there are localized Majorana zero-energy modes at the two ends of a semiconducting quantum nanowire. In this case, the Zeeman coupling can be induced more easily by an external magnetic field parallel to the wire, obviating the need for a magnetic insulator. We show that, despite the fact that the superconducting pair potential in the nanowire is
Proposal for demonstration of long-range cluster state entanglement in the presence of photon loss
Directory of Open Access Journals (Sweden)
Thomas Nutz
2017-06-01
Full Text Available Photonic cluster states are a crucial resource for optical quantum computing. Recently a quantum dot single photon source has been demonstrated to produce strings of single photons in a small linear cluster state. Sources of this kind could produce much larger cluster states, but high photon loss rates make it impossible to characterize the entanglement generated by quantum state tomography. We present a benchmarking method for such sources that can be used to demonstrate useful long-range entanglement with currently available collection/detection efficiencies below 1%. The measurement of the polarization state of single photons in different bases can provide an estimate for the three-qubit correlation function ⟨ZXZ⟩. This value constrains correlations spanning more than three qubits, which in turn provide a lower bound for the localizable entanglement between any two qubits in the large state produced by the source. Finite localizable entanglement can be established by demonstrating ⟨ZXZ⟩>23. This result enables photonic experiments demonstrating computationally useful entanglement with currently available technology.
Energy Technology Data Exchange (ETDEWEB)
Li, Xiao-Ling [College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal University, Luoyang 471934 (China); Liu, Guang-Zhen, E-mail: gzliuly@126.com [College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal University, Luoyang 471934 (China); Xin, Ling-Yun [College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal University, Luoyang 471934 (China); Wang, Li-Ya [College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal University, Luoyang 471934 (China); College of Chemistry and Pharmacy Engineering, Nanyang Normal University, Nanyang, Henan 473061 (China)
2017-02-15
Two topologically new Mn(II) coordination polymers, namely ([Mn{sub 2}(H{sub 4}ipca)(4,4′-bpy){sub 1.5}(CH{sub 3}CH{sub 2}OH){sub 0.5}(H{sub 2}O){sub 1.5}]·0.5CH{sub 3}CH{sub 2}OH·2.5H{sub 2}O){sub n} (1) and (Mn{sub 4}(H{sub 4}ipca){sub 2}(bze)(H{sub 2}O){sub 4}){sub n} (2) were prepared by the solvothermal reactions of Mn(II) acetate with 5-(2’,3’-dicarboxylphenoxy)isophthalic acid (H{sub 4}ipca) in the presence of different N-donor coligands (4,4′-bpy=4,4′-bipyridyl and bze=1, 4-bis(1-imidazoly)benzene). The single crystal X-ray diffractions reveal that two complexes display 3D metal-organic frameworks with binuclear and tetranuclear Mn(II) units, respectively. Complex 1 features a (3,4,6)-connected porous framework based on dinuclear Mn(II) unit with the (4.5{sup 2}){sub 2}(4{sup 2}.6{sup 8}.8{sup 3}.9{sup 2})(5{sup 2}.8.9{sup 2}.10) new topology, and complex 2 possesses a (3,8)-connected network based on tetranuclear Mn(II) unit with the (4{sup 2}.6){sub 2}(4{sup 4}.6{sup 14}.7{sup 7}.8{sup 2}.9) new topology. Magnetic analyses indicate that both two compounds show weak antiferromagnetic interactions within binuclear and tetranuclear Mn(II) units. - Graphical abstract: Two topologically new Mn(II) metal-organic frameworks with dinuclear and tetranuclear Mn(II) units respectively were assembled by using 5-(2′,3′-Dicarboxylphenoxy)isophthalic acid and N-donor ancillary coligands. Magnetic analysis revealed the existence of dominant antiferromagnetic interactions within the polynuclear Mn(II) units. - Highlights: • Mixed ligand strategy produces two topologically new MOFs with dinuclear and tetranuclear Mn(II) respectively. • Magnetic fitting gives weak antiferromagnetic interactions within the polynuclear Mn(II) units.
Galois conjugates of topological phases
Freedman, M. H.; Gukelberger, J.; Hastings, M. B.; Trebst, S.; Troyer, M.; Wang, Z.
2012-01-01
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.
Excitations in Topological Superfluids and Superconductors
Wu, Hao
In this thesis I present the theoretical work on Fermionic surface states, and %the bulk Bosonic collective excitations in topological superfluids and superconductors. Broken symmetries %Bulk-edge correspondence in topological condensed matter systems have implications for the spectrum of Fermionic excitations confined on surfaces or topological defects. (Abstract shortened by ProQuest.).
Oliver, Bob; Pawałowski, Krzystof
1991-01-01
As part of the scientific activity in connection with the 70th birthday of the Adam Mickiewicz University in Poznan, an international conference on algebraic topology was held. In the resulting proceedings volume, the emphasis is on substantial survey papers, some presented at the conference, some written subsequently.
DEFF Research Database (Denmark)
Bendsøe, Martin P.; Sigmund, Ole
2007-01-01
Taking as a starting point a design case for a compliant mechanism (a force inverter), the fundamental elements of topology optimization are described. The basis for the developments is a FEM format for this design problem and emphasis is given to the parameterization of design as a raster image...
Indian Academy of Sciences (India)
TOPOLOGY. Allen Hatcher. October 2004 Volume 9 Number 10. GENERAL ARTICLES. 10 Taylor the Sailor. V Radhakrishnan. 19 Twisted Winged Endoparasitoids. An Enigma for Entomologists. Alpana Mazumdar. 25 Xanthan - A Versatile Gum. Anil Lachke. 34 From Natural Numbers to Numbers and. Curves in Nature - II.
Frank-Kamenetskii, Maxim D.
2013-01-01
A new variety on non-coding RNA has been discovered by several groups: circular RNA (circRNA). This discovery raises intriguing questions about the possibility of the existence of knotted RNA molecules and the existence of a new class of enzymes changing RNA topology, RNA topoisomerases.
Indian Academy of Sciences (India)
tion - 6. How Architectural Features Affect. Building During Earthquakes? C VRMurty. 48 Turbulence and Dispersion. K 5 Gandhi. BOOK REVIEWS. 86 Algebraic Topology. Siddhartha Gadgil. Front Cover. - .. ..-.......... -. Back Cover. Two-dimensional vertical section through a turbulent plume. (Courtesy: G S Shat, CAOS, IISc.).
Storage of polarization-encoded cluster states in an atomic system
Yuan, Chun-Hua; Chen, Li-Qing; Zhang, Weiping
2009-05-01
We present a scheme for entanglement of macroscopic atomic ensembles which are four spatially separate regions of an atomic cloud using cluster-correlated beams. We show that the cluster-type polarization-encoded entanglement could be mapped onto the long-lived collective ground state of the atomic ensembles, and the stored entanglement could be retrieved based on the technique of electromagnetically induced transparency. We also discuss the efficiency of, the lifetime of, and some quantitative restrictions to the proposed quantum memory.
Frantzeskakis, E.; de Jong, N.; Zwartsenberg, B.; Bay, T.V.; Huang, Y.K.; Ramankutty, S.V.; Tytarenko, A.; Wu, D.; Pan, Y.; Hollanders, S.; Radovic, M.; Plumb, N.C.; Xu, N.; Shi, M.; Lupulescu, C.; Arion, T.; Ovsyannikov, R.; Varykhalov, A.; Eberhardt, W.; de Visser, A.; van Heumen, E.; Golden, M.S.
2015-01-01
Topological insulators are a novel materials platform with high applications potential in fields ranging from spintronics to quantum computation. In the ongoing scientific effort to demonstrate controlled manipulation of their electronic structure by external means, i. e., the provision of knobs
Wavelet-based clustering of resting state MRI data in the rat
Medda, Alessio; Hoffmann, Lukas; Magnuson, Matthew; Thompson, Garth; Pan, Wen-Ju; Keilholz, Shella
2015-01-01
While functional connectivity has typically been calculated over the entire length of the scan (5-10 min), interest has been growing in dynamic analysis methods that can detect changes in connectivity on the order of cognitive processes (seconds). Previous work with sliding window correlation has shown that changes in functional connectivity can be observed on these time scales in the awake human and in anesthetized animals. This exciting advance creates a need for improved approaches to characterize dynamic functional networks in the brain. Previous studies were performed using sliding window analysis on regions of interest defined based on anatomy or obtained from traditional steady-state analysis methods. The parcellation of the brain may therefore be suboptimal, and the characteristics of the time-varying connectivity between regions are dependent upon the length of the sliding window chosen. This manuscript describes an algorithm based on wavelet decomposition that allows data-driven clustering of voxels into functional regions based on temporal and spectral properties. Previous work has shown that different networks have characteristic frequency fingerprints, and the use of wavelets ensures that both the frequency and the timing of the BOLD fluctuations are considered during the clustering process. The method was applied to resting state data acquired from anesthetized rats, and the resulting clusters agreed well with known anatomical areas. Clusters were highly reproducible across subjects. Wavelet cross-correlation values between clusters from a single scan were significantly higher than the values from randomly-matched clusters that shared no temporal information, indicating that wavelet-based analysis is sensitive to the relationship between areas. PMID:26481903
Towards rational design of catalysts supported on a topological insulator substrate
Xiao, Jianping; Kou, Liangzhi; Yam, Chi-Yung; Frauenheim, Thomas; Yan, Binghai
2015-01-01
Exotic and robust metallic surface states of topological insulators (TIs) have been expected to provide a promising platform for novel surface chemistry and catalysis. However, it is still an unprecedented field how TIs affect the activity of catalysts. In this work, we study the effects of topological surface states (TSSs) on the activity of transition metal clusters (Au, Ag, Cu, Pt, and Pd), which are supported on a TI Bi2Se3 substrate. It was found the adsorption energy of oxygen on the su...
Fomenko, Anatoly
2016-01-01
This classic text of the renowned Moscow mathematical school equips the aspiring mathematician with a solid grounding in the core of topology, from a homotopical perspective. Its comprehensiveness and depth of treatment are unmatched among topology textbooks: in addition to covering the basics—the fundamental notions and constructions of homotopy theory, covering spaces and the fundamental group, CW complexes, homology and cohomology, homological algebra—the book treats essential advanced topics, such as obstruction theory, characteristic classes, Steenrod squares, K-theory and cobordism theory, and, with distinctive thoroughness and lucidity, spectral sequences. The organization of the material around the major achievements of the golden era of topology—the Adams conjecture, Bott periodicity, the Hirzebruch–Riemann–Roch theorem, the Atiyah–Singer index theorem, to name a few—paints a clear picture of the canon of the subject. Grassmannians, loop spaces, and classical groups play a central role ...
Synchronous and asynchronous Mott transitions in topological insulator ribbons
Medhi, Amal; Shenoy, Vijay B.; Krishnamurthy, H. R.
2012-06-01
We address how the nature of linearly dispersing edge states of two-dimensional (2D) topological insulators evolves with increasing electron-electron correlation engendered by a Hubbard-like on-site repulsion U in finite ribbons of two models of topological band insulators. Using an inhomogeneous cluster slave-rotor mean-field method developed here, we show that electronic correlations drive the topologically nontrivial phase into a Mott insulating phase via two different routes. In a synchronous transition, the entire ribbon attains a Mott insulating state at one critical U that depends weakly on the width of the ribbon. In the second, asynchronous route, Mott localization first occurs on the edge layers at a smaller critical value of electronic interaction, which then propagates into the bulk as U is further increased until all layers of the ribbon become Mott localized. We show that the kind of Mott transition that takes place is determined by certain properties of the linearly dispersing edge states which characterize the topological resilience to Mott localization.
Low oxidation state aluminum-containing cluster anions: Cp(∗)AlnH(-), n = 1-3.
Zhang, Xinxing; Ganteför, Gerd; Eichhorn, Bryan; Mayo, Dennis; Sawyer, William H; Gill, Ann F; Kandalam, Anil K; Schnöckel, Hansgeorg; Bowen, Kit
2016-08-21
Three new, low oxidation state, aluminum-containing cluster anions, Cp*AlnH(-), n = 1-3, were prepared via reactions between aluminum hydride cluster anions, AlnHm (-), and Cp*H ligands. These were characterized by mass spectrometry, anion photoelectron spectroscopy, and density functional theory based calculations. Agreement between the experimentally and theoretically determined vertical detachment energies and adiabatic detachment energies validated the computed geometrical structures. Reactions between aluminum hydride cluster anions and ligands provide a new avenue for discovering low oxidation state, ligated aluminum clusters.
Multi-party Measurement-Device-Independent Quantum Key Distribution Based on Cluster States
Liu, Chuanqi; Zhu, Changhua; Ma, Shuquan; Pei, Changxing
2018-03-01
We propose a novel multi-party measurement-device-independent quantum key distribution (MDI-QKD) protocol based on cluster states. A four-photon analyzer which can distinguish all the 16 cluster states serves as the measurement device for four-party MDI-QKD. Any two out of four participants can build secure keys after the analyzers obtains successful outputs and the two participants perform post-processing. We derive a security analysis for the protocol, and analyze the key rates under different values of polarization misalignment. The results show that four-party MDI-QKD is feasible over 280 km in the optical fiber channel when the key rate is about 10- 6 with the polarization misalignment parameter 0.015. Moreover, our work takes an important step toward a quantum communication network.
Globular cluster neutron stars and the determination of the dense matter equation of state
Guillot, Sebastien
2016-09-01
Combining measurements of the mass and radius of multiple neutron stars (NSs) represents the most promising way to determine the equation of state of dense NS matter. NSs in quiescent low-mass x-ray binaries (qLMXB) located in globular clusters have placed useful constraints on the equation of state. The statistical approaches combining measurements from multiple NSs can be further improved by the addition of more NS observations. We propose here to obtain a high signal to noise spectrum of the qLMXB in M30, the only low-absorption globular cluster qLMXBs that does not have deep X-ray observations, and which requires Chandra unmatched angular resolution. The 300 ks proposed observation will permit measurement of the NS radius with 12-15% uncertainties.
Multi-party Measurement-Device-Independent Quantum Key Distribution Based on Cluster States
Liu, Chuanqi; Zhu, Changhua; Ma, Shuquan; Pei, Changxing
2017-12-01
We propose a novel multi-party measurement-device-independent quantum key distribution (MDI-QKD) protocol based on cluster states. A four-photon analyzer which can distinguish all the 16 cluster states serves as the measurement device for four-party MDI-QKD. Any two out of four participants can build secure keys after the analyzers obtains successful outputs and the two participants perform post-processing. We derive a security analysis for the protocol, and analyze the key rates under different values of polarization misalignment. The results show that four-party MDI-QKD is feasible over 280 km in the optical fiber channel when the key rate is about 10- 6 with the polarization misalignment parameter 0.015. Moreover, our work takes an important step toward a quantum communication network.
Directory of Open Access Journals (Sweden)
Ioana COMSULEA
2014-12-01
Full Text Available Business intelligence and knowledge management seems to gain the attention of the society regarding the benefits that brings to it when this two domains are considered as a whole. The advantage of using business intelligence in order to take decisions and bring innovation to the business, are convincing more and more entrepreneurs to implement this solution. The challenge in managing and using the knowledge that the business intelligence offers to the business, comes with the integration of the information with state administrative structures datas that have to be available to business clusters in order to improve their decisional process. In our paper, we demonstrate the benefits of using business intelligence in Romanian state administrative structures underlying the way that this adoption would support the activity of innovative and creative clusters.
Hyperdeformed states in 36Ar and 48Cr in the cranked cluster model
Rae, W. D. M.; Merchant, A. C.
1992-04-01
The pure harmonic oscillator model predicts a family of axially symmetric hyperdeformed states with 3:1 major to minor axis ratios. Two members of this family have previously been identified in 12C and 24Mg within the Bloch-Brink alpha-cluster model. Here we present cranked cluster model calculations for similar hyperdeformed states in 36Ar and 48Cr. We suggest that the configuration in 48Cr is associated with resonances observed in 24Mg+24Mg scattering, while that in 36Ar may be involved in the excitation of the 12C+12C barrier resonances reported recently in the 12C(24Mg, 12C, 12C)12C reaction and also in the excitation of those resonances previously observed in the 20Ne+16O reaction. Permanent address: Instituto de Estudos Avançados, Centro Técnico Aeroespacial, 12225 Sa~o José dos Campos, Sa~o Paulo, Brazil.
Geographical Clusters of Rape in the United States: 2000-2012
Amin, Raid; Nabors, Nicole S.; Nelson, Arlene M.; Saqlain, Murshid; Kulldorff, Martin
2016-01-01
Background While rape is a very serious crime and public health problem, no spatial mapping has been attempted for rape on the national scale. This paper addresses the three research questions: (1) Are reported rape cases randomly distributed across the USA, after being adjusted for population density and age, or are there geographical clusters of reported rape cases? (2) Are the geographical clusters of reported rapes still present after adjusting for differences in poverty levels? (3) Are there geographical clusters where the proportion of reported rape cases that lead to an arrest is exceptionally low or exceptionally high? Methods We studied the geographical variation of reported rape events (2003-2012) and rape arrests (2000-2012) in the 48 contiguous states of the USA. The disease Surveillance software SaTScan™ with its spatial scan statistic is used to evaluate the spatial variation in rapes. The spatial scan statistic has been widely used as a geographical surveillance tool for diseases, and we used it to identify geographical areas with clusters of reported rape and clusters of arrest rates for rape. Results The spatial scan statistic was used to identify geographical areas with exceptionally high rates of reported rape. The analyses were adjusted for age, and in secondary analyses, for both age and poverty level. We also identified geographical areas with either a low or a high proportion of reported rapes leading to an arrest. Conclusions We have identified geographical areas with exceptionally high (low) rates of reported rape. The geographical problem areas identified are prime candidates for more intensive preventive counseling and criminal prosecution efforts by public health, social service, and law enforcement agencies Geographical clusters of high rates of reported rape are prime areas in need of expanded implementation of preventive measures, such as changing attitudes in our society toward rape crimes, in addition to having the criminal
State-of-the-art multi-wavelength observations of nearby brightest group/cluster galaxies
Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie
2018-01-01
Nearby galaxy groups and clusters are crucial to our understanding of the impact of nuclear outbursts on the intracluster medium as their proximity allows us to study in detail the processes of feedback from active galactic nuclei in these systems. In this talk, I will present state-of-the-art multi-wavelength observations signatures of this mechanism.I will first show results on multi-configuration 230-470 MHz observations of the Perseus cluster from the Karl G. Jansky Very Large Array, probing the non-thermal emission from the old particle population of the AGN outflows. These observations reveal a multitude of new structures associated with the “mini-halo” and illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies.Second, I will present new observations with the optical imaging Fourier transform spectrometer SITELLE (CFHT) of NGC 1275, the Perseus cluster's brightest galaxy. With its wide field of view, it is the only integral field unit spectroscopy instrument able to cover the large emission-line filamentary nebula in NGC 1275. I will present the first detailed velocity map of this nebula in its entirety and tackle the question of its origin (residual cooling flow or dragged gas).Finally, I will present deep Chandra observations of the nearby early-type massive elliptical galaxy NGC 4472, the most optically luminous galaxy in the local Universe, lying on the outskirts of the Virgo cluster. Enhanced X-ray rims around the radio lobes are detected and interpreted as gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to constitute a significant fraction of the total outburst energy.I will thus show how these high-fidelity observations of nearby brightest group/cluster galaxies are improving our understanding of the AGN feedback mechanism taking place in galaxy groups and clusters.
Construction of the basis states with l=2 for a three-cluster system
International Nuclear Information System (INIS)
Filippov, G.F.; Dotsenko, I.S.; Lisetskiy, A.P.
1995-01-01
The harmonic-oscillator basis with L=2 for the description of three-cluster systems is constructed in the Fock-Bargmann representation. An algorithm of constructing the basis states by using the symmetry properties of the overlap integrals and the Wigner D-functions is developed. Some properties of the basis are analysed. The idea that the results of the present work hold also for the Two Rotor Model is stressed. 12 refs., 2 tab
Many Worlds, the Cluster-state Quantum Computer, and the Problem of the Preferred Basis
Cuffaro, Michael
2011-01-01
I argue that the many worlds explanation of quantum computation is not licensed by, and in fact is conceptually inferior to, the many worlds interpretation of quantum mechanics from which it is derived. I argue that the many worlds explanation of quantum computation is incompatible with the recently developed cluster state model of quantum computation. Based on these considerations I conclude that we should reject the many worlds explanation of quantum computation.
Impact of network topology on self-organized criticality
Hoffmann, Heiko
2018-02-01
The general mechanisms behind self-organized criticality (SOC) are still unknown. Several microscopic and mean-field theory approaches have been suggested, but they do not explain the dependence of the exponents on the underlying network topology of the SOC system. Here, we first report the phenomena that in the Bak-Tang-Wiesenfeld (BTW) model, sites inside an avalanche area largely return to their original state after the passing of an avalanche, forming, effectively, critically arranged clusters of sites. Then, we hypothesize that SOC relies on the formation process of these clusters, and present a model of such formation. For low-dimensional networks, we show theoretically and in simulation that the exponent of the cluster-size distribution is proportional to the ratio of the fractal dimension of the cluster boundary and the dimensionality of the network. For the BTW model, in our simulations, the exponent of the avalanche-area distribution matched approximately our prediction based on this ratio for two-dimensional networks, but deviated for higher dimensions. We hypothesize a transition from cluster formation to the mean-field theory process with increasing dimensionality. This work sheds light onto the mechanisms behind SOC, particularly, the impact of the network topology.
Energy Technology Data Exchange (ETDEWEB)
Alpichshev, Zhanybek; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept.; Analytis, J.G.; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept.; Chu, J.-H.; Fisher, I.R.; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.; Chen, Y.L.; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept.; Shen, Z.X.; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.; Fang, A.; /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.; Kapitulnik, A.; /SIMES, Stanford /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.
2010-06-02
Scanning tunneling spectroscopy studies on high-quality Bi{sub 2}Te{sub 3} crystals exhibit perfect correspondence to ARPES data, hence enabling identification of different regimes measured in the local density of states (LDOS). Oscillations of LDOS near a step are analyzed. Within the main part of the surface band oscillations are strongly damped, supporting the hypothesis of topological protec- tion. At higher energies, as the surface band becomes concave, oscillations appear which disperse with a particular wave-vector that may result from an unconventional hexagonal warping term.
Alexandropoulos, Dimitris I; Cunha-Silva, Luís; Lorusso, Giulia; Evangelisti, Marco; Tang, Jinkui; Stamatatos, Theocharis C
2016-01-28
A family of interwoven molecular inorganic knots, shaped like the 'Star of David', was prepared by the employment of naphthalene-2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion.
Litinski, Daniel; Kesselring, Markus S.; Eisert, Jens; von Oppen, Felix
2017-07-01
We present a scalable architecture for fault-tolerant topological quantum computation using networks of voltage-controlled Majorana Cooper pair boxes and topological color codes for error correction. Color codes have a set of transversal gates which coincides with the set of topologically protected gates in Majorana-based systems, namely, the Clifford gates. In this way, we establish color codes as providing a natural setting in which advantages offered by topological hardware can be combined with those arising from topological error-correcting software for full-fledged fault-tolerant quantum computing. We provide a complete description of our architecture, including the underlying physical ingredients. We start by showing that in topological superconductor networks, hexagonal cells can be employed to serve as physical qubits for universal quantum computation, and we present protocols for realizing topologically protected Clifford gates. These hexagonal-cell qubits allow for a direct implementation of open-boundary color codes with ancilla-free syndrome read-out and logical T gates via magic-state distillation. For concreteness, we describe how the necessary operations can be implemented using networks of Majorana Cooper pair boxes, and we give a feasibility estimate for error correction in this architecture. Our approach is motivated by nanowire-based networks of topological superconductors, but it could also be realized in alternative settings such as quantum-Hall-superconductor hybrids.
Performance assessment of topologically diverse power systems subjected to hurricane events
International Nuclear Information System (INIS)
Winkler, James; Duenas-Osorio, Leonardo; Stein, Robert; Subramanian, Devika
2010-01-01
Large tropical cyclones cause severe damage to major cities along the United States Gulf Coast annually. A diverse collection of engineering and statistical models are currently used to estimate the geographical distribution of power outage probabilities stemming from these hurricanes to aid in storm preparedness and recovery efforts. Graph theoretic studies of power networks have separately attempted to link abstract network topology to transmission and distribution system reliability. However, few works have employed both techniques to unravel the intimate connection between network damage arising from storms, topology, and system reliability. This investigation presents a new methodology combining hurricane damage predictions and topological assessment to characterize the impact of hurricanes upon power system reliability. Component fragility models are applied to predict failure probability for individual transmission and distribution power network elements simultaneously. The damage model is calibrated using power network component failure data for Harris County, TX, USA caused by Hurricane Ike in September of 2008, resulting in a mean outage prediction error of 15.59% and low standard deviation. Simulated hurricane events are then applied to measure the hurricane reliability of three topologically distinct transmission networks. The rate of system performance decline is shown to depend on their topological structure. Reliability is found to correlate directly with topological features, such as network meshedness, centrality, and clustering, and the compact irregular ring mesh topology is identified as particularly favorable, which can influence regional lifeline policy for retrofit and hardening activities to withstand hurricane events.
Performance assessment of topologically diverse power systems subjected to hurricane events
Energy Technology Data Exchange (ETDEWEB)
Winkler, James, E-mail: jwinkler@rice.ed [Rice University, Department of Civil and Environmental Engineering, 6100 Main Street, Houston, TX 77005 (United States); Duenas-Osorio, Leonardo, E-mail: leonardo.duenas-osorio@rice.ed [Rice University, Department of Civil and Environmental Engineering, 6100 Main Street, Houston, TX 77005 (United States); Stein, Robert, E-mail: stein@rice.ed [Rice University, Department of Political Science, 6100 Main Street, Houston, TX 77005 (United States); Subramanian, Devika, E-mail: devika@rice.ed [Rice University, Department of Computer Science, 6100 Main Street, Houston, TX 77005 (United States); Rice University, Department of Electrical Engineering, 6100 Main Street, Houston, TX 77005 (United States)
2010-04-15
Large tropical cyclones cause severe damage to major cities along the United States Gulf Coast annually. A diverse collection of engineering and statistical models are currently used to estimate the geographical distribution of power outage probabilities stemming from these hurricanes to aid in storm preparedness and recovery efforts. Graph theoretic studies of power networks have separately attempted to link abstract network topology to transmission and distribution system reliability. However, few works have employed both techniques to unravel the intimate connection between network damage arising from storms, topology, and system reliability. This investigation presents a new methodology combining hurricane damage predictions and topological assessment to characterize the impact of hurricanes upon power system reliability. Component fragility models are applied to predict failure probability for individual transmission and distribution power network elements simultaneously. The damage model is calibrated using power network component failure data for Harris County, TX, USA caused by Hurricane Ike in September of 2008, resulting in a mean outage prediction error of 15.59% and low standard deviation. Simulated hurricane events are then applied to measure the hurricane reliability of three topologically distinct transmission networks. The rate of system performance decline is shown to depend on their topological structure. Reliability is found to correlate directly with topological features, such as network meshedness, centrality, and clustering, and the compact irregular ring mesh topology is identified as particularly favorable, which can influence regional lifeline policy for retrofit and hardening activities to withstand hurricane events.
Heitzig, Jobst; Kittel, Tim; Donges, Jonathan; Molkenthin, Nora
2016-04-01
To keep the Earth System in a desirable region of its state space, such as defined by the recently suggested "tolerable environment and development window", "guardrails", "planetary boundaries", or "safe (and just) operating space for humanity", one not only needs to understand the quantitative internal dynamics of the system and the available options for influencing it (management), but also the structure of the system's state space with regard to certain qualitative differences. Important questions are: Which state space regions can be reached from which others with or without leaving the desirable region? Which regions are in a variety of senses "safe" to stay in when management options might break away, and which qualitative decision problems may occur as a consequence of this topological structure? In this work, we develop a mathematical theory of the qualitative topology of the state space of a dynamical system with management options and desirable states, as a complement to the existing literature on optimal control which is more focussed on quantitative optimization and is much applied in both the engineering and the integrated assessment literature. We suggest a certain terminology for the various resulting regions of the state space and perform a detailed formal classification of the possible states with respect to the possibility of avoiding or leaving the undesired region. Our results indicate that before performing some form of quantitative optimization such as of indicators of human well-being for achieving certain sustainable development goals, a sustainable and resilient management of the Earth System may require decisions of a more discrete type that come in the form of several dilemmas, e.g., choosing between eventual safety and uninterrupted desirability, or between uninterrupted safety and larger flexibility. We illustrate the concepts and dilemmas drawing on conceptual models from climate science, ecology, coevolutionary Earth System modeling
Perturbative triples corrections in state-specific multireference coupled cluster theory.
Evangelista, Francesco A; Prochnow, Eric; Gauss, Jürgen; Schaefer, Henry F
2010-02-21
We formulated and implemented a perturbative triples correction for the state-specific multireference coupled cluster approach with singles and doubles suggested by Mukherjee and co-workers, Mk-MRCCSD [Mol. Phys. 94, 157 (1998)]. Our derivation of the energy correction [Mk-MRCCSD(T)] is based on a constrained search for stationary points of the Mk-MRCC energy functional together with a perturbative expansion with respect to the appearing triples cluster operator. The Lambda-Mk-MRCCSD(T) approach derived in this way consists in (1) a correction to the off-diagonal matrix elements of the effective Hamiltonian which is unique to coupled cluster methods based on the Jeziorski-Monkhorst ansatz, and (2) an asymmetric energy correction to the diagonal elements of the effective Hamiltonian. The Mk-MRCCSD(T) correction is obtained from the Lambda-Mk-MRCCSD(T) method by approximating the singles and doubles Lagrange multipliers with the corresponding cluster amplitudes. We investigate the performance of the Mk-MRCCSD(T) method by applying it to the potential energy curve of the BeH(2) model and F(2) and the geometry and harmonic vibrational frequencies of ozone. Computation of the energy difference between the mono- and bicyclic forms of the 2,6-pyridyne diradical illustrates the potential of Mk-MRCCSD(T) as a tool for the study of realistic chemical problems requiring multireference zeroth-order wave functions.
Gonzalez, Robert; Suppes, Trisha; Zeitzer, Jamie; McClung, Colleen; Tamminga, Carol; Tohen, Mauricio; Forero, Angelica; Dwivedi, Alok; Alvarado, Andres
2018-02-19
Multiple types of chronobiological disturbances have been reported in bipolar disorder, including characteristics associated with general activity levels, sleep, and rhythmicity. Previous studies have focused on examining the individual relationships between affective state and chronobiological characteristics. The aim of this study was to conduct a variable cluster analysis in order to ascertain how mood states are associated with chronobiological traits in bipolar I disorder (BDI). We hypothesized that manic symptomatology would be associated with disturbances of rhythm. Variable cluster analysis identified five chronobiological clusters in 105 BDI subjects. Cluster 1, comprising subjective sleep quality was associated with both mania and depression. Cluster 2, which comprised variables describing the degree of rhythmicity, was associated with mania. Significant associations between mood state and cluster analysis-identified chronobiological variables were noted. Disturbances of mood were associated with subjectively assessed sleep disturbances as opposed to objectively determined, actigraphy-based sleep variables. No associations with general activity variables were noted. Relationships between gender and medication classes in use and cluster analysis-identified chronobiological characteristics were noted. Exploratory analyses noted that medication class had a larger impact on these relationships than the number of psychiatric medications in use. In a BDI sample, variable cluster analysis was able to group related chronobiological variables. The results support our primary hypothesis that mood state, particularly mania, is associated with chronobiological disturbances. Further research is required in order to define these relationships and to determine the directionality of the associations between mood state and chronobiological characteristics.
Guillemin, Victor
2010-01-01
Differential Topology provides an elementary and intuitive introduction to the study of smooth manifolds. In the years since its first publication, Guillemin and Pollack's book has become a standard text on the subject. It is a jewel of mathematical exposition, judiciously picking exactly the right mixture of detail and generality to display the richness within. The text is mostly self-contained, requiring only undergraduate analysis and linear algebra. By relying on a unifying idea-transversality-the authors are able to avoid the use of big machinery or ad hoc techniques to establish the main
A topological quantum optics interface.
Barik, Sabyasachi; Karasahin, Aziz; Flower, Christopher; Cai, Tao; Miyake, Hirokazu; DeGottardi, Wade; Hafezi, Mohammad; Waks, Edo
2018-02-09
The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder. Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored. We demonstrate a strong interface between single quantum emitters and topological photonic states. Our approach creates robust counterpropagating edge states at the boundary of two distinct topological photonic crystals. We demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends. This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
Effect of mesoscopic fluctuations on equation of state in cluster-forming systems
Directory of Open Access Journals (Sweden)
A. Ciach
2012-06-01
Full Text Available Equation of state for systems with particles self-assembling into aggregates is derived within a mesoscopic theory combining density functional and field-theoretic approaches. We focus on the effect of mesoscopic fluctuations in the disordered phase. The pressure - volume fraction isotherms are calculated explicitly for two forms of the short-range attraction long-range repulsion potential. Mesoscopic fluctuations lead to an increased pressure in each case, except for very small volume fractions. When large clusters are formed, the mechanical instability of the system is present at much higher temperature than found in mean-field approximation. In this case phase separation competes with the formation of periodic phases (colloidal crystals. In the case of small clusters, no mechanical instability associated with separation into dilute and dense phases appears.
Directory of Open Access Journals (Sweden)
Cui Jia
2017-05-01
Full Text Available With the purpose of reinforcing correlation analysis of risk assessment threat factors, a dynamic assessment method of safety risks based on particle filtering is proposed, which takes threat analysis as the core. Based on the risk assessment standards, the method selects threat indicates, applies a particle filtering algorithm to calculate influencing weight of threat indications, and confirms information system risk levels by combining with state estimation theory. In order to improve the calculating efficiency of the particle filtering algorithm, the k-means cluster algorithm is introduced to the particle filtering algorithm. By clustering all particles, the author regards centroid as the representative to operate, so as to reduce calculated amount. The empirical experience indicates that the method can embody the relation of mutual dependence and influence in risk elements reasonably. Under the circumstance of limited information, it provides the scientific basis on fabricating a risk management control strategy.
Cui, Jia; Hong, Bei; Jiang, Xuepeng; Chen, Qinghua
2017-05-01
With the purpose of reinforcing correlation analysis of risk assessment threat factors, a dynamic assessment method of safety risks based on particle filtering is proposed, which takes threat analysis as the core. Based on the risk assessment standards, the method selects threat indicates, applies a particle filtering algorithm to calculate influencing weight of threat indications, and confirms information system risk levels by combining with state estimation theory. In order to improve the calculating efficiency of the particle filtering algorithm, the k-means cluster algorithm is introduced to the particle filtering algorithm. By clustering all particles, the author regards centroid as the representative to operate, so as to reduce calculated amount. The empirical experience indicates that the method can embody the relation of mutual dependence and influence in risk elements reasonably. Under the circumstance of limited information, it provides the scientific basis on fabricating a risk management control strategy.
International Nuclear Information System (INIS)
Evans, P.A.; Topping, K.D.; Woolfson, D.N.; Dobson, C.M.
1991-01-01
Chemical shifts of resonances of specific protons in the 1H NMR spectrum of thermally denatured hen lysozyme have been determined by exchange correlation with assigned native state resonances in 2D NOESY spectra obtained under conditions where the two states are interconverting. There are subtle but widespread deviations of the measured shifts from the values which would be anticipated for a random coil; in the case of side chain protons these are virtually all net upfield shifts and it is shown that this may be the averaged effect of interactions with aromatic rings in a partially collapsed denatured state. In a very few cases, notably that of two sequential tryptophan residues, it is possible to interpret these effects in terms of specific, local interresidue interactions. Generally, however, there is no correlation with either native state shift perturbations or with sequence proximity to aromatic groups. Diminution of most of the residual shift perturbations on reduction of the disulfide cross-links confirms that they are not simply effects of residues adjacent in the sequence. Similar effects of chemical denaturants, with the disulfides intact, demonstrate that the shift perturbations reflect an enhanced tendency to side chain clustering in the thermally denatured state. The temperature dependences of the shift perturbations suggest that this clustering is noncooperative and is driven by small, favorable enthalpy changes. While the extent of conformational averaging is clearly much greater than that observed for a homologous protein, alpha-lactalbumin, in its partially folded molten globule state, the results clearly show that thermally denatured lysozyme differs substantially from a random coil, principally in that it is partially hydrophobically collapsed
International Nuclear Information System (INIS)
Nakatsuji, H.
1979-01-01
The solutions of the SAC (symmetry-adapated-cluster) and SAC CI theories for the study of electron correlations in ground and excited states, respectively have been summarized. Variational and non-variational solutions are considered for both theories and their features are discussed. (Auth.)
Qin, Lei; Zhou, Guo-Jun; Yu, You-Zhu; Nojiri, Hiroyuki; Schröder, Christian; Winpenny, Richard E P; Zheng, Yan-Zhen
2017-11-15
The creation of a perfect hollow nanoscopic sphere of metal centers is clearly an unrealizable synthetic challenge. It is, however, an inspirational challenge from the viewpoint of chemical architecture and also as finite molecular species may provide unique microscopic insight into the origin and onset of phenomena such as topological spin-frustration effects found in infinite 2D and 3D systems. Herein, we report a series of high-symmetry gadolinium(III) (S = 7/2) polyhedra, Gd 20 , Gd 32 , Gd 50 , and Gd 60 , to test an approach based on assembling polymetallic fragments that contain different polygons. Structural analysis reveals that the Gd 20 cage resembles a dodecahedron; the vertices of the Gd 32 polyhedron exactly reveal symmetry O h ; Gd 50 displays an unprecedented polyhedron in which an icosidodecahedron Gd 30 core is encapsulated by an outer Gd 20 dodecahedral shell with approximate I h symmetry; and the Gd 60 shows a truncated octahedron geometry. Experimental and theoretical magnetic studies show that this series produces the expected antiferromagnetic interaction that can be modeled based on classical spins at the Gd sites. From the magnetization analyses, we can roughly correlate the derivative bands to the Gd-O-Gd angles. Such a magneto-structural correlation may be used as "fingerprints" to identify these cages.
Zhou, Yun-Jing; Tao, Yuan-Hong
2018-02-01
In this letter,we propose a broadcast-based multiparty remote state preparation scheme which realizes the process among three participants. It allows two distant receivers to obtain the arbitrary single-qubit states separately and simultaneously, and the success probability is {d2}/{1+d2}, thus generalize the results in Yu et al. (Quantum. Inf. Process 16(2), 41, 2017).
Alpha cluster states in light nuclei populated through the (6Li,d) reaction
International Nuclear Information System (INIS)
Borello-Lewin, Thereza; Rodrigues, M.R.D.; Horodynski-Matsushigue, L.B.; Duarte, J.L.M.; Rodrigues, C.L.; Souza, M.A.; Cunsolo, A.; Cappuzzello, F.; Ukita, Gilberto Mitsuo
2011-01-01
Full text: The alpha cluster correlation is an important concept in the nuclear physics of light nuclei. The main purpose of the research program in progress is the investigation of the alpha clustering phenomenon in (xα) and(xα+ν) nuclei through the ( 6 Li,d) alpha transfer reaction. In fact, there is scarce experimental information on the subject, in particular associated with resonant states predicted near (xα) and (xα+ν) thresholds. Measurements of the 12 , 13 C( 6 Li,d) 16 , 17 O reactions, at an incident energy of 25.5 MeV, have been performed employing the Sao Paulo Pelletron-Enge Split-Pole facility and the nuclear emulsion detection technique. The work is under way and an experimental energy resolution of 30 keV was obtained. Near the (4α) breakup threshold in 16 O, three narrow alpha resonances, not previously measured, were detected, revealing important α + 12 C(G.S.) components. One of these resonances corresponds to the known 0 + state at 15.1 MeV[5] of excitation that has probably, according to Funaki et al., the gas like configuration of the 4α condensate state, with a very dilute density and a large component of α + 12 C(Hoyle) configuration. As was already mentioned, our experimental information points to the necessity of including the α + 12 C(G.S.) component in the wave function. (author)
Margalef-Roig, J
1992-01-01
...there are reasons enough to warrant a coherent treatment of the main body of differential topology in the realm of Banach manifolds, which is at the same time correct and complete. This book fills the gap: whenever possible the manifolds treated are Banach manifolds with corners. Corners add to the complications and the authors have carefully fathomed the validity of all main results at corners. Even in finite dimensions some results at corners are more complete and better thought out here than elsewhere in the literature. The proofs are correct and with all details. I see this book as a reliable monograph of a well-defined subject; the possibility to fall back to it adds to the feeling of security when climbing in the more dangerous realms of infinite dimensional differential geometry. Peter W. Michor
Findings in resting-state fMRI by differences from K-means clustering.
Chyzhyk, Darya; Graña, Manuel
2014-01-01
Resting state fMRI has growing number of studies with diverse aims, always centered on some kind of functional connectivity biomarker obtained from correlation regarding seed regions, or by analytical decomposition of the signal towards the localization of the spatial distribution of functional connectivity patterns. In general, studies are computationally costly and very sensitive to noise and preprocessing of data. In this paper we consider clustering by K-means as a exploratory procedure which can provide some results with little computational effort, due to efficient implementations that are readily available. We demonstrate the approach on a dataset of schizophrenia patients, finding differences between patients with and without auditory hallucinations.
Excited-state relaxation of Ag8 clusters embedded in helium droplets
International Nuclear Information System (INIS)
Radcliffe, Paul; Przystawik, Andreas; Diederich, Thomas; Doeppner, Tilo; Tiggesbaeumker, Josef; Meiwes-Broer, Karl-Heinz
2004-01-01
Neutral silver clusters Ag N are grown in ultracold helium nanodroplets. By exploiting a strong absorption resonance recently found for Ag 8 , first photoelectron spectra of this neutral species are recorded. Variation of the laser photon energy reveals that direct vertical two-photon ionization is hindered by rapid relaxation into the lower edge of a long-living excited state manifold. The analysis of the dynamics gives a precise value of (6.89±0.09) eV for the vertical ionization potential of Ag 8 . The influence of the helium matrix on photoemission is discussed
International Nuclear Information System (INIS)
Basu, C.; Adhikari, S.; Mitra, A.K.; Bhattacharya, S.; Bhattacharya, C.; Ghosh, T.K.; Banerjee, K.; Rana, T.K.; Pandey, R.; Prajapati, G.; Dey, A.; Meena, J.K.; Ray, S.
2011-01-01
In this work the study of α + 208 Pb elastic scattering have been undertaken to study the alpha spectroscopic properties of the cluster states of 212 Po and also obtain a α + 208 Pb potential to describe both elastic scattering and to predict the alpha cluster states and their properties in 212 Po. This two body cluster core picture is appropriate as both the components are closed shell nuclei. The measurements are performed at higher energy and analyzed in terms of the microscopic folding model for elastic scattering
Induced topological pressure for topological dynamical systems
International Nuclear Information System (INIS)
Xing, Zhitao; Chen, Ercai
2015-01-01
In this paper, inspired by the article [J. Jaerisch et al., Stochastics Dyn. 14, 1350016, pp. 1-30 (2014)], we introduce the induced topological pressure for a topological dynamical system. In particular, we prove a variational principle for the induced topological pressure
Two-dimensional topological photonics
Khanikaev, Alexander B.; Shvets, Gennady
2017-12-01
Originating from the studies of two-dimensional condensed-matter states, the concept of topological order has recently been expanded to other fields of physics and engineering, particularly optics and photonics. Topological photonic structures have already overturned some of the traditional views on wave propagation and manipulation. The application of topological concepts to guided wave propagation has enabled novel photonic devices, such as reflection-free sharply bent waveguides, robust delay lines, spin-polarized switches and non-reciprocal devices. Discrete degrees of freedom, widely used in condensed-matter physics, such as spin and valley, are now entering the realm of photonics. In this Review, we summarize the latest advances in this highly dynamic field, with special emphasis on the experimental work on two-dimensional photonic topological structures.
Positive XPS binding energy shift of supported Cu{sub N}-clusters governed by initial state effects
Energy Technology Data Exchange (ETDEWEB)
Peters, S.; Peredkov, S. [Technische Universität Berlin, IOAP, Strasse des 17. Juni 135, 10623 Berlin (Germany); Al-Hada, M. [Department of Physics, College of Education and Linguistics, University of Amran (Yemen); Neeb, M., E-mail: matthias.neeb@helmholtz-berlin.de [Helmholtz-Zentrum Berlin, Wilhelm-Conrad-Röntgen-Campus Adlershof, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489 Berlin (Germany); Eberhardt, W. [Technische Universität Berlin, IOAP, Strasse des 17. Juni 135, 10623 Berlin (Germany); DESY, Center for Free Electron Laser Science (CFEL), Notkestr. 85, 22607 Hamburg (Germany)
2014-01-01
Highlights: • Size dependent initial and final state effects of mass-selected deposited clusters. • Initial state effect dominates positive XPS shift in supported Cu-clusters. • Size dependent Coulomb correlation shift in the Auger final state of Cu cluster. • Size-dependent Auger parameter analysis. • Positive XPS shift differs from negative surface core level shift in crystalline copper. - Abstract: An initial state effect is established as origin for the positive 2p core electron binding energy shift found for Cu{sub N}-clusters supported by a thin silica layer of a p-doped Si(1 0 0) wafer. Using the concept of the Auger parameter and taking into account the usually neglected Coulomb correlation shift in the Auger final state (M{sub 4,5}M{sub 4,5}) it is shown that the initial state shift is comparable to the measured XPS shift while the final state relaxation shift contributes only marginally to the binding energy shift. The cluster results differ from the negative surface core-level shift of crystalline copper which has been explained in terms of a final state relaxation effect.
Topological Photonics for Continuous Media
Silveirinha, Mario
Photonic crystals have revolutionized light-based technologies during the last three decades. Notably, it was recently discovered that the light propagation in photonic crystals may depend on some topological characteristics determined by the manner how the light states are mutually entangled. The usual topological classification of photonic crystals explores the fact that these structures are periodic. The periodicity is essential to ensure that the underlying wave vector space is a closed surface with no boundary. In this talk, we prove that it is possible calculate Chern invariants for a wide class of continuous bianisotropic electromagnetic media with no intrinsic periodicity. The nontrivial topology of the relevant continuous materials is linked with the emergence of edge states. Moreover, we will demonstrate that continuous photonic media with the time-reversal symmetry can be topologically characterized by a Z2 integer. This novel classification extends for the first time the theory of electronic topological insulators to a wide range of photonic platforms, and is expected to have an impact in the design of novel photonic systems that enable a topologically protected transport of optical energy. This work is supported in part by Fundacao para a Ciencia e a Tecnologia Grant Number PTDC/EEI-TEL/4543/2014.
Topology change and quantum physics
International Nuclear Information System (INIS)
Balachandran, A.P.; Marmo, G.; Simoni, A.
1995-03-01
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 considerations on the domain of the quantum Hamiltonian, this domain being often specified by boundary conditions in elementary quantum physics. Several examples are presented where classical topology is changed by smoothly altering the boundary conditions. When the parameters labelling the latter are treated as quantum variables, quantum states need not give a well-defined classical topology, instead they can give a quantum superposition of such topologies. An existing argument of Sorkin based on the spin-statistics connection and indicating the necessity of topology change in quantum gravity is recalled. It is suggested therefrom and our results here that Einstein gravity and its minor variants are effective theories of a deeper description with additional novel degrees of freedom. Other reasons for suspecting such a microstructure are also summarized. (author). 22 refs, 3 figs
Lieb polariton topological insulators
Li, Chunyan; Ye, Fangwei; Chen, Xianfeng; Kartashov, Yaroslav V.; Ferrando, Albert; Torner, Lluis; Skryabin, Dmitry V.
2018-02-01
We predict that the interplay between the spin-orbit coupling, stemming from the transverse electric-transverse magnetic energy splitting, and the Zeeman effect in semiconductor microcavities supporting exciton-polariton quasiparticles, results in the appearance of unidirectional linear topological edge states when the top microcavity mirror is patterned to form a truncated dislocated Lieb lattice of cylindrical pillars. Periodic nonlinear edge states are found to emerge from the linear ones. They are strongly localized across the interface and they are remarkably robust in comparison to their counterparts in honeycomb lattices. Such robustness makes possible the existence of nested unidirectional dark solitons that move steadily along the lattice edge.
Single atom anisotropic magnetoresistance on a topological insulator surface
Narayan, Awadhesh
2015-03-12
© 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. We demonstrate single atom anisotropic magnetoresistance on the surface of a topological insulator, arising from the interplay between the helical spin-momentum-locked surface electronic structure and the hybridization of the magnetic adatom states. Our first-principles quantum transport calculations based on density functional theory for Mn on Bi2Se3 elucidate the underlying mechanism. We complement our findings with a two dimensional model valid for both single adatoms and magnetic clusters, which leads to a proposed device setup for experimental realization. Our results provide an explanation for the conflicting scattering experiments on magnetic adatoms on topological insulator surfaces, and reveal the real space spin texture around the magnetic impurity.
Topology Optimisation of Wireless Sensor Networks
Directory of Open Access Journals (Sweden)
Thike Aye Min
2016-01-01
Full Text Available Wireless sensor networks are widely used in a variety of fields including industrial environments. In case of a clustered network the location of cluster head affects the reliability of the network operation. Finding of the optimum location of the cluster head, therefore, is critical for the design of a network. This paper discusses the optimisation approach, based on the brute force algorithm, in the context of topology optimisation of a cluster structure centralised wireless sensor network. Two examples are given to verify the approach that demonstrate the implementation of the brute force algorithm to find an optimum location of the cluster head.
Earthquake Clustering on Normal Faults: Insight from Rate-and-State Friction Models
Biemiller, J.; Lavier, L. L.; Wallace, L.
2016-12-01
Temporal variations in slip rate on normal faults have been recognized in Hawaii and the Basin and Range. The recurrence intervals of these slip transients range from 2 years on the flanks of Kilauea, Hawaii to 10 kyr timescale earthquake clustering on the Wasatch Fault in the eastern Basin and Range. In addition to these longer recurrence transients in the Basin and Range, recent GPS results there also suggest elevated deformation rate events with recurrence intervals of 2-4 years. These observations suggest that some active normal fault systems are dominated by slip behaviors that fall between the end-members of steady aseismic creep and periodic, purely elastic, seismic-cycle deformation. Recent studies propose that 200 year to 50 kyr timescale supercycles may control the magnitude, timing, and frequency of seismic-cycle earthquakes in subduction zones, where aseismic slip transients are known to play an important role in total deformation. Seismic cycle deformation of normal faults may be similarly influenced by its timing within long-period supercycles. We present numerical models (based on rate-and-state friction) of normal faults such as the Wasatch Fault showing that realistic rate-and-state parameter distributions along an extensional fault zone can give rise to earthquake clusters separated by 500 yr - 5 kyr periods of aseismic slip transients on some portions of the fault. The recurrence intervals of events within each earthquake cluster range from 200 to 400 years. Our results support the importance of stress and strain history as controls on a normal fault's present and future slip behavior and on the characteristics of its current seismic cycle. These models suggest that long- to medium-term fault slip history may influence the temporal distribution, recurrence interval, and earthquake magnitudes for a given normal fault segment.
Electronic Structure and Oxidation State Changes in the Mn (4) Ca Cluster of Photosystem II
Energy Technology Data Exchange (ETDEWEB)
Yano, J.; Pushkar, Y.; Messinger, J.; Bergmann, U.; Glatzel, P.; Yachandra, V.K.; /SLAC
2012-08-17
Oxygen-evolving complex (Mn{sub 4}Ca cluster) of Photosystem II cycles through five intermediate states (S{sub i}-states, i = 0-4) before a molecule of dioxygen is released. During the S-state transitions, electrons are extracted from the OEC, either from Mn or alternatively from a Mn ligand. The oxidation state of Mn is widely accepted as Mn{sub 4}(III{sub 2},IV{sub 2}) and Mn{sub 4}(III,IV{sub 3}) for S{sub 1} and S{sub 2} states, while it is still controversial for the S{sub 0} and S{sub 3} states. We used resonant inelastic X-ray scattering (RIXS) to study the electronic structure of Mn{sub 4}Ca complex in the OEC. The RIXS data yield two-dimensional plots that provide a significant advantage by obtaining both K-edge pre-edge and L-edge-like spectra (metal spin state) simultaneously. We have collected data from PSII samples in the each of the S-states and compared them with data from various inorganic Mn complexes. The spectral changes in the Mn 1s2p{sub 3/2} RIXS spectra between the S-states were compared to those of the oxides of Mn and coordination complexes. The results indicate strong covalency for the electronic configuration in the OEC, and we conclude that the electron is transferred from a strongly delocalized orbital, compared to those in Mn oxides or coordination complexes. The magnitude for the S{sub 0} to S{sub 1}, and S{sub 1} to S{sub 2} transitions is twice as large as that during the S{sub 2} to S{sub 3} transition, indicating that the electron for this transition is extracted from a highly delocalized orbital with little change in charge density at the Mn atoms.
The shape of velocity dispersion profiles and the dynamical state of galaxy clusters
Costa, A. P.; Ribeiro, A. L. B.; de Carvalho, R. R.
2018-01-01
Motivated by the existence of the relationship between the dynamical state of clusters and the shape of the velocity dispersion profiles (VDPs), we study the VDPs for Gaussian (G) and non-Gaussian (NG) systems for a subsample of clusters from the Yang catalogue. The groups cover a redshift interval of 0.03 ≤ z ≤ 0.1 with halo mass ≥1014 M⊙. We use a robust statistical method, Hellinger Distance, to classify the dynamical state of the systems according to their velocity distribution. The stacked VDP of each class, G and NG, is then determined using either Bright or Faint galaxies. The stacked VDP for G groups displays a central peak followed by a monotonically decreasing trend which indicates a predominance of radial orbits, with the Bright stacked VDP showing lower velocity dispersions in all radii. The distinct features we find in NG systems are manifested not only by the characteristic shape of VDP, with a depression in the central region, but also by a possible higher infall rate associated with galaxies in the Faint stacked VDP.
Kwong, Justin D.; Messinger, David W.; Middleton, William D.
2009-08-01
This project is an application of hyperspectral classification and unmixing in support of an ongoing archaeological study. The study region is the Oaxaca Valley located in the state of Oaxaca, Mexico on the southern coast. This was the birthplace of the Zapotec civilization which grew into a complex state level society. Hyperion imagery is being collected over a 30,000 km2 area. Classification maps of regions of interest are generated using K-means clustering and a novel algorithm called Gradient Flow. Gradient Flow departs from conventional stochastic or deterministic approaches, using graph theory to cluster spectral data. Spectral unmixing is conducted using the RIT developed algorithm Max-D to automatically find end members. Stepwise unmixing is performed to better model the data using the end members found be Max-D. Data are efficiently shared between imaging scientists and archaeologists using Google Earth to stream images over the internet rather than downloading them. The overall goal of the project is to provide archaeologists with useful information maps without having to interpret the raw data.
Introduction to topological quantum matter & quantum computation
Stanescu, Tudor D
2017-01-01
What is -topological- about topological quantum states? How many types of topological quantum phases are there? What is a zero-energy Majorana mode, how can it be realized in a solid state system, and how can it be used as a platform for topological quantum computation? What is quantum computation and what makes it different from classical computation? Addressing these and other related questions, Introduction to Topological Quantum Matter & Quantum Computation provides an introduction to and a synthesis of a fascinating and rapidly expanding research field emerging at the crossroads of condensed matter physics, mathematics, and computer science. Providing the big picture, this book is ideal for graduate students and researchers entering this field as it allows for the fruitful transfer of paradigms and ideas amongst different areas, and includes many specific examples to help the reader understand abstract and sometimes challenging concepts. It explores the topological quantum world beyond the well-know...
International Nuclear Information System (INIS)
Heinisch, H.L.
1997-01-01
The intracascade evolution of the defect distributions of cascades in copper is investigated using stochastic annealing simulations applied to cascades generated with molecular dynamics (MD). The temperature and energy dependencies of annihilation, clustering and free defect production are determined for individual cascades. The annealing simulation results illustrate the strong influence on intracascade evolution of the defect configuration existing in the primary damage state. Another factor significantly affecting the evolution of the defect distribution is the rapid one-dimensional diffusion of small, glissile interstitial loops produced directly in cascades. This phenomenon introduces a cascade energy dependence of defect evolution that is apparent only beyond the primary damage state, amplifying the need for further study of the annealing phase of cascade evolution and for performing many more MD cascade simulations at higher energies
Directory of Open Access Journals (Sweden)
Gopikrishna Deshpande
2010-12-01
Full Text Available Brain state classification has been accomplished using features such as voxel intensities, derived from functional magnetic resonance imaging (fMRI data, as inputs to efficient classifiers such as support vector machines (SVM and is based on the spatial localization model of brain function. With the advent of the connectionist model of brain function, features from brain networks may provide increased discriminatory power for brain state classification.In this study, we introduce a novel framework where in both functional connectivity (FC based on instantaneous temporal correlation and effective connectivity (EC based on causal influence in brain networks are used as features in an SVM classifier. In order to derive those features, we adopt a novel approach recently introduced by us called correlation-purged Granger causality (CPGC in order to obtain both FC and EC from fMRI data simultaneously without the instantaneous correlation contaminating Granger causality. In addition, statistical learning is accelerated and performance accuracy is enhanced by combining recursive cluster elimination (RCE algorithm with the SVM classifier. We demonstrate the efficacy of the CPGC-based RCE-SVM approach using a specific instance of brain state classification exemplified by disease state prediction. Accordingly, we show that this approach is capable of predicting with 90.3% accuracy whether any given human subject was prenatally exposed to cocaine or not, even when no significant behavioral differences were found between exposed and healthy subjects.The framework adopted in this work is quite general in nature with prenatal cocaine exposure being only an illustrative example of the power of this approach. In any brain state classification approach using neuroimaging data, including the directional connectivity information may prove to be a performance enhancer. When brain state classification is used for disease state prediction, our approach may aid the
Topology without cooling: instantons and monopoles near to deconfinement
International Nuclear Information System (INIS)
Feurstein, M.; Markum, H.; Thurner, S.
1998-01-01
In an attempt to describe the change of topological structure of pure SU(2) gauge theory near deconfinement a renormalization group inspired method is tested. Instead of cooling, blocking and subsequent inverse blocking is applied to Monte Carlo configurations to capture topological features at a well-defined scale. We check that this procedure largely conserves long range physics like string tension. UV fluctuations and lattice artefacts are removed which otherwise spoil topological charge density and Abelian monopole currents. We report the behaviour of topological susceptibility and monopole current densities across the deconfinement transition and relate the two faces of topology to each other. First results of a cluster analysis are described. (orig.)
Axion topological field theory of topological superconductors
Qi, Xiao-Liang; Witten, Edward; Zhang, Shou-Cheng
2013-04-01
Topological superconductors are gapped superconductors with gapless and topologically robust quasiparticles propagating on the boundary. In this paper, we present a topological field theory description of three-dimensional time-reversal invariant topological superconductors. In our theory the topological superconductor is characterized by a topological coupling between the electromagnetic field and the superconducting phase fluctuation, which has the same form as the coupling of “axions” with an Abelian gauge field. As a physical consequence of our theory, we predict the level crossing induced by the crossing of special “chiral” vortex lines, which can be realized by considering s-wave superconductors in proximity with the topological superconductor. Our theory can also be generalized to the coupling with a gravitational field.
DEFF Research Database (Denmark)
Marcussen, Lars
2003-01-01
Rummets topologi, Historiens topologi: betragtninger om menneskets orientering til rum - fra hulen over beherskelse af flere akser til det flydende rum.......Rummets topologi, Historiens topologi: betragtninger om menneskets orientering til rum - fra hulen over beherskelse af flere akser til det flydende rum....
Optical image encryption topology.
Yong-Liang, Xiao; Xin, Zhou; Qiong-Hua, Wang; Sheng, Yuan; Yao-Yao, Chen
2009-10-15
Optical image encryption topology is proposed based on the principle of random-phase encoding. Various encryption topological units, involving peer-to-peer, ring, star, and tree topologies, can be realized by an optical 6f system. These topological units can be interconnected to constitute an optical image encryption network. The encryption and decryption can be performed in both digital and optical methods.
Wu, Liang; Tse, Wang-Kong; Brahlek, M; Morris, C M; Aguilar, R Valdés; Koirala, N; Oh, S; Armitage, N P
2015-11-20
We have utilized time-domain magnetoterahertz spectroscopy to investigate the low-frequency optical response of the topological insulator Cu_{0.02}Bi_{2}Se_{3} and Bi_{2}Se_{3} films. With both field and frequency dependence, such experiments give sufficient information to measure the mobility and carrier density of multiple conduction channels simultaneously. We observe sharp cyclotron resonances (CRs) in both materials. The small amount of Cu incorporated into the Cu_{0.02}Bi_{2}Se_{3} induces a true bulk insulator with only a single type of conduction with a total sheet carrier density of ~4.9×10^{12}/cm^{2} and mobility as high as 4000 cm^{2}/V·s. This is consistent with conduction from two virtually identical topological surface states (TSSs) on the top and bottom of the film with a chemical potential ~145 meV above the Dirac point and in the bulk gap. The CR broadens at high fields, an effect that we attribute to an electron-phonon interaction. This assignment is supported by an extended Drude model analysis of the zero-field Drude conductance. In contrast, in normal Bi_{2}Se_{3} films, two conduction channels were observed, and we developed a self-consistent analysis method to distinguish the dominant TSSs and coexisting trivial bulk or two-dimensional electron gas states. Our high-resolution Faraday rotation spectroscopy on Cu_{0.02}Bi_{2}Se_{3} paves the way for the observation of quantized Faraday rotation under experimentally achievable conditions to push the chemical potential in the lowest Landau level.
Alpha cluster states in light nuclei populated through the (6Li,d) reaction
Energy Technology Data Exchange (ETDEWEB)
Borello-Lewin, Thereza; Rodrigues, M.R.D.; Horodynski-Matsushigue, L.B.; Duarte, J.L.M.; Rodrigues, C.L.; Souza, M.A. [Universidade de Sao Paulo (IF/USP), SP (Brazil). Inst. de Fisica; Cunsolo, A.; Cappuzzello, F. [Universita di Catania (Italy). Istituto Nazionale di Fisica Nucleare. Lab. Nazionali del Sud; Ukita, Gilberto Mitsuo [Universidade de Santo Amaro (UNISA), Sao Paulo, SP (Brazil). Fac. de Psicologia
2011-07-01
Full text: The alpha cluster correlation is an important concept in the nuclear physics of light nuclei. The main purpose of the research program in progress is the investigation of the alpha clustering phenomenon in (x{alpha}) and(x{alpha}+{nu}) nuclei through the ({sup 6}Li,d) alpha transfer reaction. In fact, there is scarce experimental information on the subject, in particular associated with resonant states predicted near (x{alpha}) and (x{alpha}+{nu}) thresholds. Measurements of the {sup 12},{sup 13}C({sup 6}Li,d) {sup 16},{sup 17}O reactions, at an incident energy of 25.5 MeV, have been performed employing the Sao Paulo Pelletron-Enge Split-Pole facility and the nuclear emulsion detection technique. The work is under way and an experimental energy resolution of 30 keV was obtained. Near the (4{alpha}) breakup threshold in {sup 16}O, three narrow alpha resonances, not previously measured, were detected, revealing important {alpha} + {sup 12}C(G.S.) components. One of these resonances corresponds to the known 0{sup +} state at 15.1 MeV[5] of excitation that has probably, according to Funaki et al., the gas like configuration of the 4{alpha} condensate state, with a very dilute density and a large component of {alpha} + {sup 12}C(Hoyle) configuration. As was already mentioned, our experimental information points to the necessity of including the {alpha} + {sup 12}C(G.S.) component in the wave function. (author)
Poilblanc, Didier; Schuch, Norbert
2013-04-01
Gapped Z2 spin liquids have been proposed as candidates for the ground state of the S=1/2 quantum antiferromagnet on the kagome lattice. We extend the use of projected entangled pair states to construct (on the cylinder) resonating valence bond (RVB) states including both nearest-neighbor and next-nearest-neighbor singlet bonds. Our ansatz—dubbed “simplex spin liquid”—allows for an asymmetry between the two types of triangles (of order 2%-3% in the energy density after optimization) leading to the breaking of inversion symmetry. We show that the topological Z2 structure is still preserved and, by considering the presence or the absence of spinon and vison lines along an infinite cylinder, we explicitly construct four orthogonal RVB minimally entangled states. The spinon and vison coherence lengths are extracted from a finite size scaling with regard to the cylinder perimeter of the energy splittings of the four sectors and are found to be of the order of the lattice spacing. The entanglement spectrum of a partitioned (infinite) cylinder is found to be gapless, suggesting the occurrence, on a cylinder with real open boundaries, of gapless edge modes formally similar to Luttinger liquid (nonchiral) spin and charge modes. When inversion symmetry is spontaneously broken, the RVB spin liquid exhibits an extra Ising degeneracy, which might have been observed in recent exact diagonalization studies.
Strongly Correlated Topological Insulators
2016-02-03
Strongly Correlated Topological Insulators In the past year, the grant was used for work in the field of topological phases, with emphasis on finding...surface of topological insulators. In the past 3 years, we have started a new direction, that of fractional topological insulators. These are materials...in which a topologically nontrivial quasi-flat band is fractionally filled and then subject to strong interactions. The views, opinions and/or
Gamelin, Theodore W
1999-01-01
A fresh approach to introductory topology, this volume explains nontrivial applications of metric space topology to analysis, clearly establishing their relationship. Also, topics from elementary algebraic topology focus on concrete results with minimal algebraic formalism. The first two chapters consider metric space and point-set topology; the second two, algebraic topological material. 1983 edition. Solutions to Selected Exercises. List of Notations. Index. 51 illustrations.
The edge engineering of topological Bi(111) bilayer
Li, Xiao; Liu, Hai-Wen; Jiang, Hua; Wang, Fa; Feng, Ji
2014-01-01
A topological insulator is a novel quantum state, characterized by symmetry-protected non-trivial edge/surface states. Our first-principle simulations show the significant effects of the chemical decoration on edge states of topological Bi(111) bilayer nanoribbon, which remove the trivial edge state and recover the Dirac linear dispersion of topological edge state. By comparing the edge states with and without chemical decoration, the Bi(111) bilayer nanoribbon offers a simple system for asse...
Menegassi Lima, Elizangela,; Pona, Jorge,; Sacomano, Jose,; Reis, João,; Lobo, Debora,
2015-01-01
Part 1: Collaborative Networks; International audience; The objective of this research is to evaluate the relationships of the network formed by the important milk cluster in the city of Umuarama, State of Parana (PR)/BRAZIL, using the Social Network Analysis (SNA) focusing on the collective gains and competitive advantages of this cluster. The methodology used was qualitative and quantitative. Questionnaires were applied to the network for the characterization of the existing relationships b...
Energy Technology Data Exchange (ETDEWEB)
Ku, Wai Lim; Girvan, Michelle; Ott, Edward [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)
2015-12-15
In this paper, we study dynamical systems in which a large number N of identical Landau-Stuart oscillators are globally coupled via a mean-field. Previously, it has been observed that this type of system can exhibit a variety of different dynamical behaviors. These behaviors include time periodic cluster states in which each oscillator is in one of a small number of groups for which all oscillators in each group have the same state which is different from group to group, as well as a behavior in which all oscillators have different states and the macroscopic dynamics of the mean field is chaotic. We argue that this second type of behavior is “extensive” in the sense that the chaotic attractor in the full phase space of the system has a fractal dimension that scales linearly with N and that the number of positive Lyapunov exponents of the attractor also scales linearly with N. An important focus of this paper is the transition between cluster states and extensive chaos as the system is subjected to slow adiabatic parameter change. We observe discontinuous transitions between the cluster states (which correspond to low dimensional dynamics) and the extensively chaotic states. Furthermore, examining the cluster state, as the system approaches the discontinuous transition to extensive chaos, we find that the oscillator population distribution between the clusters continually evolves so that the cluster state is always marginally stable. This behavior is used to reveal the mechanism of the discontinuous transition. We also apply the Kaplan-Yorke formula to study the fractal structure of the extensively chaotic attractors.
Study of the Ground-State Geometry of Silicon Clusters Using Artificial Neural Networks
Directory of Open Access Journals (Sweden)
M.R. Lemes
2002-09-01
Full Text Available Theoretical determination of the ground-state geometry of Si clusters is a difficult task. As the number of local minima grows exponentially with the number of atoms, to find the global minimum is a real challenge. One may start the search procedure from a random distribution of atoms but it is probably wiser to make use of any available information to restrict the search space. Here, we introduce a new approach, the Assisted Genetic Optimization (AGO that couples an Artificial Neural Network (ANN to a Genetic Algorithm (GA. Using available information on small Silicon clusters, we trained an ANN to predict good starting points (initial population for the GA. AGO is applied to Si10 and Si20 and compared to pure GA. Our results indicate: i AGO is, at least, 5 times faster than pure GA in our test case; ii ANN training can be made very fast and successfully plays the role of an experienced investigator; iii AGO can easily be adapted to other optimization problems.
Topological phases of topological-insulator thin films
Asmar, Mahmoud M.; Sheehy, Daniel E.; Vekhter, Ilya
2018-02-01
We study the properties of a thin film of topological insulator material. We treat the coupling between helical states at opposite surfaces of the film in the properly-adapted tunneling approximation, and show that the tunneling matrix element oscillates as a function of both the film thickness and the momentum in the plane of the film for Bi2Se3 and Bi2Te3 . As a result, while the magnitude of the matrix element at the center of the surface Brillouin zone gives the gap in the energy spectrum, the sign of the matrix element uniquely determines the topological properties of the film, as demonstrated by explicitly computing the pseudospin textures and the Chern number. We find a sequence of transitions between topological and nontopological phases, separated by semimetallic states, as the film thickness varies. In the topological phase, the edge states of the film always exist but only carry a spin current if the edge potentials break particle-hole symmetry. The edge states decay very slowly away from the boundary in Bi2Se3 , making Bi2Te3 , where this scale is shorter, a more promising candidate for the observation of these states. Our results hold for free-standing films as well as heterostructures with large-gap insulators.
Energy-Aware Topology Evolution Model with Link and Node Deletion in Wireless Sensor Networks
Directory of Open Access Journals (Sweden)
Xiaojuan Luo
2012-01-01
Full Text Available Based on the complex network theory, a new topological evolving model is proposed. In the evolution of the topology of sensor networks, the energy-aware mechanism is taken into account, and the phenomenon of change of the link and node in the network is discussed. Theoretical analysis and numerical simulation are conducted to explore the topology characteristics and network performance with different node energy distribution. We find that node energy distribution has the weak effect on the degree distribution P(k that evolves into the scale-free state, nodes with more energy carry more connections, and degree correlation is nontrivial disassortative. Moreover, the results show that, when nodes energy is more heterogeneous, the network is better clustered and enjoys higher performance in terms of the network efficiency and the average path length for transmitting data.
Topological Phases of Sound and Light
Directory of Open Access Journals (Sweden)
V. Peano
2015-07-01
Full Text Available Topological states of matter are particularly robust, since they exploit global features of a material’s band structure. Topological states have already been observed for electrons, atoms, and photons. It is an outstanding challenge to create a Chern insulator of sound waves in the solid state. In this work, we propose an implementation based on cavity optomechanics in a photonic crystal. The topological properties of the sound waves can be wholly tuned in situ by adjusting the amplitude and frequency of a driving laser that controls the optomechanical interaction between light and sound. The resulting chiral, topologically protected phonon transport can be probed completely optically. Moreover, we identify a regime of strong mixing between photon and phonon excitations, which gives rise to a large set of different topological phases and offers an example of a Chern insulator produced from the interaction between two physically distinct particle species, photons and phonons.
Magnonic topological insulators in antiferromagnets
Nakata, Kouki; Kim, Se Kwon; Klinovaja, Jelena; Loss, Daniel
2017-12-01
Extending the notion of symmetry protected topological phases to insulating antiferromagnets (AFs) described in terms of opposite magnetic dipole moments associated with the magnetic N e ´el order, we establish a bosonic counterpart of topological insulators in semiconductors. Making use of the Aharonov-Casher effect, induced by electric field gradients, we propose a magnonic analog of the quantum spin Hall effect (magnonic QSHE) for edge states that carry helical magnons. We show that such up and down magnons form the same Landau levels and perform cyclotron motion with the same frequency but propagate in opposite direction. The insulating AF becomes characterized by a topological Z2 number consisting of the Chern integer associated with each helical magnon edge state. Focusing on the topological Hall phase for magnons, we study bulk magnon effects such as magnonic spin, thermal, Nernst, and Ettinghausen effects, as well as the thermomagnetic properties of helical magnon transport both in topologically trivial and nontrivial bulk AFs and establish the magnonic Wiedemann-Franz law. We show that our predictions are within experimental reach with current device and measurement techniques.
Quail, M Thomas
2017-01-01
Silicosis is the oldest know occupational pulmonary disease. It is a progressive disease and any level of exposure to respirable crystalline silica particles or dust has the potential to develop into silicosis. Silicosis is caused by silica particles or dust entering the lungs and damaging healthy lung tissue. The damage restricts the ability to breathe. Exposure to silica increases a worker’s risk of developing cancer or tuberculosis. This special report will provide background history of silicosis in the U.S., including the number of workers affected and their common industries. Over the years, these industries have impeded government oversight, resulting in silicosis exposure clusters. The risk of acquiring silicosis is diminished when industry implements safety measures with oversight by governmental agencies. Reputable authorities believe that the current innovative drilling techniques such as fracking will generate future cases of silicosis in the U.S. if safety measures to protect workers are ignored.
Birman—Wenzl—Murakami Algebra and Topological Basis
Zhou, Cheng-Cheng; Xue, Kang; Wang, Gang-Cheng; Sun, Chun-Fang; Du, Gui-Jiao
2012-02-01
In this paper, we use entangled states to construct 9 × 9-matrix representations of Temperley—Lieb algebra (TLA), then a family of 9 × 9-matrix representations of Birman—Wenzl—Murakami algebra (BWMA) have been presented. Based on which, three topological basis states have been found. And we apply topological basis states to recast nine-dimensional BWMA into its three-dimensional counterpart. Finally, we find the topological basis states are spin singlet states in special case.
Recent Progress in the Study of Topological Semimetals
Bernevig, Andrei; Weng, Hongming; Fang, Zhong; Dai, Xi
2018-04-01
The topological semimetal is a new, theoretically predicted and experimentally discovered, topological state of matter. In one of its several realizations, the topological semimetal hosts Weyl fermions, elusive particles predicted more than 85 years ago, sought after in high-energy experiments, but only recently found in a condensed-matter setting. In the present review, we catalogue the most recent progress in this fast-developing research field. We give special attention to topological invariants and the material realization of three different types of topological semimetal. We also discuss various photo emission, transport and optical experimental observables that characterize the appearance of topological semimetal phases.
Topological Insulator Nanowires and Nanoribbons
Kong, Desheng
2010-01-13
Recent theoretical calculations and photoemission spectroscopy measurements on the bulk Bi2Se3 material show that it is a three-dimensional topological insulator possessing conductive surface states with nondegenerate spins, attractive for dissipationless electronics and spintronics applications. Nanoscale topological insulator materials have a large surface-to-volume ratio that can manifest the conductive surface states and are promising candidates for devices. Here we report the synthesis and characterization of high quality single crystalline Bi2Se5 nanomaterials with a variety of morphologies. The synthesis of Bi 2Se5 nanowires and nanoribbons employs Au-catalyzed vapor-liquid-solid (VLS) mechanism. Nanowires, which exhibit rough surfaces, are formed by stacking nanoplatelets along the axial direction of the wires. Nanoribbons are grown along [1120] direction with a rectangular cross-section and have diverse morphologies, including quasi-one-dimensional, sheetlike, zigzag and sawtooth shapes. Scanning tunneling microscopy (STM) studies on nanoribbons show atomically smooth surfaces with ∼ 1 nm step edges, indicating single Se-Bi-Se-Bi-Se quintuple layers. STM measurements reveal a honeycomb atomic lattice, suggesting that the STM tip couples not only to the top Se atomic layer, but also to the Bi atomic layer underneath, which opens up the possibility to investigate the contribution of different atomic orbitais to the topological surface states. Transport measurements of a single nanoribbon device (four terminal resistance and Hall resistance) show great promise for nanoribbons as candidates to study topological surface states. © 2010 American Chemical Society.
Topology of polymer chains under nanoscale confinement.
Satarifard, Vahid; Heidari, Maziar; Mashaghi, Samaneh; Tans, Sander J; Ejtehadi, Mohammad Reza; Mashaghi, Alireza
2017-08-24
Spatial confinement limits the conformational space accessible to biomolecules but the implications for bimolecular topology are not yet known. Folded linear biopolymers can be seen as molecular circuits formed by intramolecular contacts. The pairwise arrangement of intra-chain contacts can be categorized as parallel, series or cross, and has been identified as a topological property. Using molecular dynamics simulations, we determine the contact order distributions and topological circuits of short semi-flexible linear and ring polymer chains with a persistence length of l p under a spherical confinement of radius R c . At low values of l p /R c , the entropy of the linear chain leads to the formation of independent contacts along the chain and accordingly, increases the fraction of series topology with respect to other topologies. However, at high l p /R c , the fraction of cross and parallel topologies are enhanced in the chain topological circuits with cross becoming predominant. At an intermediate confining regime, we identify a critical value of l p /R c , at which all topological states have equal probability. Confinement thus equalizes the probability of more complex cross and parallel topologies to the level of the more simple, non-cooperative series topology. Moreover, our topology analysis reveals distinct behaviours for ring- and linear polymers under weak confinement; however, we find no difference between ring- and linear polymers under strong confinement. Under weak confinement, ring polymers adopt parallel and series topologies with equal likelihood, while linear polymers show a higher tendency for series arrangement. The radial distribution analysis of the topology reveals a non-uniform effect of confinement on the topology of polymer chains, thereby imposing more pronounced effects on the core region than on the confinement surface. Additionally, our results reveal that over a wide range of confining radii, loops arranged in parallel and cross
Topological insulators fundamentals and perspectives
Ortmann, Frank; Valenzuela, Sergio O
2015-01-01
There are only few discoveries and new technologies in physical sciences that have the potential to dramatically alter and revolutionize our electronic world. Topological insulators are one of them. The present book for the first time provides a full overview and in-depth knowledge about this hot topic in materials science and condensed matter physics. Techniques such as angle-resolved photoemission spectrometry (ARPES), advanced solid-state Nuclear Magnetic Resonance (NMR) or scanning-tunnel microscopy (STM) together with key principles of topological insulators such as spin-locked electronic
Emerging Trends in Topological Insulators and Topological ...
Indian Academy of Sciences (India)
Emerging Trends in Topological Insulators and. Topological Superconductors. Arijit Saha and Arun M Jayannavar. Arijit Saha is a Reader-F at the Institute of Physics,. Bhubaneswar. His research interest lies broadly in the areas of mesoscopic physics and strongly correlated electrons. Arun M Jayannavar is a.
A topological derivative method for topology optimization
DEFF Research Database (Denmark)
Norato, J.; Bendsøe, Martin P.; Haber, RB
2007-01-01
We propose a fictitious domain method for topology optimization in which a level set of the topological derivative field for the cost function identifies the boundary of the optimal design. We describe a fixed-point iteration scheme that implements this optimality criterion subject to a volumetric...
Valley Topological Phases in Bilayer Sonic Crystals
Lu, Jiuyang; Qiu, Chunyin; Deng, Weiyin; Huang, Xueqin; Li, Feng; Zhang, Fan; Chen, Shuqi; Liu, Zhengyou
2018-03-01
Recently, the topological physics in artificial crystals for classical waves has become an emerging research area. In this Letter, we propose a unique bilayer design of sonic crystals that are constructed by two layers of coupled hexagonal array of triangular scatterers. Assisted by the additional layer degree of freedom, a rich topological phase diagram is achieved by simply rotating scatterers in both layers. Under a unified theoretical framework, two kinds of valley-projected topological acoustic insulators are distinguished analytically, i.e., the layer-mixed and layer-polarized topological valley Hall phases, respectively. The theory is evidently confirmed by our numerical and experimental observations of the nontrivial edge states that propagate along the interfaces separating different topological phases. Various applications such as sound communications in integrated devices can be anticipated by the intriguing acoustic edge states enriched by the layer information.
Boundary Hamiltonian Theory for Gapped Topological Orders
Hu, Yuting; Wan, Yidun; Wu, Yong-Shi
2017-06-01
We report our systematic construction of the lattice Hamiltonian model of topological orders on open surfaces, with explicit boundary terms. We do this mainly for the Levin-Wen string-net model. The full Hamiltonian in our approach yields a topologically protected, gapped energy spectrum, with the corresponding wave functions robust under topology-preserving transformations of the lattice of the system. We explicitly present the wavefunctions of the ground states and boundary elementary excitations. The creation and hopping operators of boundary quasi-particles are constructed. It is found that given a bulk topological order, the gapped boundary conditions are classified by Frobenius algebras in its input data. Emergent topological properties of the ground states and boundary excitations are characterized by (bi-) modules over Frobenius algebras.
Book Review: Computational Topology
DEFF Research Database (Denmark)
Raussen, Martin
2011-01-01
Computational Topology by Herbert Edelsbrunner and John L. Harer. American Matheamtical Society, 2010 - ISBN 978-0-8218-4925-5......Computational Topology by Herbert Edelsbrunner and John L. Harer. American Matheamtical Society, 2010 - ISBN 978-0-8218-4925-5...
Symmetry-protected topological insulator and its symmetry-enriched topologically ordered boundary
Wang, Juven; Wen, Xiao-Gang; Witten, Edward
We propose a mechanism for achieving symmetry-enriched topologically ordered boundaries for symmetry-protected topological states, including those of topological insulators. Several different boundary phases and their phase transitions are considered, including confined phases, deconfined phases, symmetry-breaking, gapped and gapless phases. National Science Foundation PHY-1606531, Corning Glass Works Foundation Fellowship, NSF Grant DMR- 1506475 and NSFC 11274192, the BMO Financial Group and the John Templeton Foundation No. 39901.
Elementary concepts of topology
Alexandroff, Paul
1961-01-01
Concise work presents topological concepts in clear, elementary fashion without sacrificing their profundity or exactness. Author proceeds from basics of set-theoretic topology, through topological theorems and questions based on concept of the algebraic complex, to the concept of Betti groups.
Free Boolean Topological Groups
Directory of Open Access Journals (Sweden)
Ol’ga Sipacheva
2015-11-01
Full Text Available Known and new results on free Boolean topological groups are collected. An account of the properties that these groups share with free or free Abelian topological groups and properties specific to free Boolean groups is given. Special emphasis is placed on the application of set-theoretic methods to the study of Boolean topological groups.
Low oxidation state aluminum-containing cluster anions: LAlH-and LAln-(n = 2-4, L = N[Si(Me)3]2).
Zhang, Xinxing; Wang, Linjie; Montone, Georgia R; Gill, Ann F; Ganteför, Gerd; Eichhorn, Bryan; Kandalam, Anil K; Bowen, Kit H
2017-06-14
Several low oxidation state aluminum-containing cluster anions, LAlH - and LAl n - (n = 2-4, L = N[Si(Me) 3 ] 2 ), were produced via reactions between aluminum hydride cluster anions, Al x H y - , and hexamethyldisilazane (HMDS). These clusters were characterized by mass spectrometry, anion photoelectron spectroscopy, and density functional theory (DFT) based calculations. Agreement between the experimental and theoretical vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) validated the computed geometrical structures. Reactions between aluminum hydride cluster anions and ligands promise to be a new synthetic scheme for low oxidation state, ligated aluminum clusters.
Onoda, Keiichi; Yamaguchi, Shuhei
2015-10-01
Apathy is defined as a mental state characterized by a lack of goal-directed behavior. However, the underlying mechanisms of apathy remain to be fully understood. Apathy shares certain symptoms with depression and both these affective disorders are known to be associated with dysfunctions of the frontal cortex-basal ganglia circuits. It is expected that clarifying differences in neural mechanisms between the two conditions would lead to an improved understanding of apathy. The present study was designed to investigate whether apathy and depression depend on different network properties of the frontal cortex-basal ganglia circuits, by using resting state fMRI. Resting-state fMRI measurement and neuropsychological testing were conducted on middle-aged and older adults (N=392). Based on graph theory, we estimated nodal efficiency (functional integration), local efficiency (functional segregation), and betweenness centrality. We conducted multiple regression analyses for the network parameters using age, sex, apathy, and depression as predictors. Interestingly, results indicated that the anterior cingulate cortex showed lower nodal efficiency, local efficiency, and betweenness centrality in apathy, whereas in depression, it showed higher nodal efficiency and betweenness centrality. The anterior cingulate cortex constitutes the so-called "salience network", which detects salient experiences. Our results indicate that apathy is characterized by decreased salience-related processing in the anterior cingulate cortex, whereas depression is characterized by increased salience-related processing. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Glinka, Yuri D., E-mail: ydglinka@mail.wvu.edu [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506-6315 (United States); Institute of Physics, National Academy of Sciences of Ukraine, Kiev 03028 (Ukraine); Babakiray, Sercan; Lederman, David [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)
2015-10-07
Raman measurements of a Fano-type surface phonon mode associated with Dirac surface states (SS) in Bi{sub 2}Se{sub 3} topological insulator thin films allowed an unambiguous determination of the electron-phonon coupling strength in Dirac SS as a function of film thickness ranging from 2 to 40 nm. A non-monotonic enhancement of the electron-phonon coupling strength with maximum for the 8–10 nm thick films was observed. The non-monotonicity is suggested to originate from plasmon-phonon coupling which enhances electron-phonon coupling when free carrier density in Dirac SS increases with decreasing film thickness and becomes suppressed for thinnest films when anharmonic coupling between in-plane and out-of-plane phonon modes occurs. The observed about four-fold enhancement of electron-phonon coupling in Dirac SS of the 8–10 nm thick Bi{sub 2}Se{sub 3} films with respect to the bulk samples may provide new insights into the origin of superconductivity in this-type materials and their applications.
Zhang, Qiang; Cao, Huibo; Liu, Jinyu; Tennant, Alan; Ditusa, John; Mao, Zhiqiang
Very recently, Liu et al (arxiv.org/pdf/1507.07978, (2015)) discovered the first magnetic topological semimetal Sr1-yMn1-zSb2(0HFIR, we found a long-range FM order with Mn moments along b-axis below TC = 565 K, followed by another magnetic transition to a canted C-type antiferromagnetic (AFM) order at TFM - AFM = 304 K. In the canted C-type AFM state, the Mn moments are aligned with the a-axis along with a canting toward the b-axis, leading to a net FM moment lying along the b - axis. The Mn moments along the a - and b-axes at 5 K are found to be 3.789(3) and 0.741(4) µB, respectively. The discovered FM order in Sr1-yMn1-zSb2, either the FM ordering at 304< T<565 K or the FM component of the canted AFM order for T<304 K, is sufficient to break time-reversal symmetry likely creating a Weyl semimetal. This work is supported by the U.S. Department of Energy under EPSCoR Grant No. DE-SC0012432 with additional support from the Louisiana Board of Regents.
Topological antiferromagnetic spintronics
Šmejkal, Libor; Mokrousov, Yuriy; Yan, Binghai; MacDonald, Allan H.
2018-03-01
The recent demonstrations of electrical manipulation and detection of antiferromagnetic spins have opened up a new chapter in the story of spintronics. Here, we review the emerging research field that is exploring the links between antiferromagnetic spintronics and topological structures in real and momentum space. Active topics include proposals to realize Majorana fermions in antiferromagnetic topological superconductors, to control topological protection and Dirac points by manipulating antiferromagnetic order parameters, and to exploit the anomalous and topological Hall effects of zero-net-moment antiferromagnets. We explain the basic concepts behind these proposals, and discuss potential applications of topological antiferromagnetic spintronics.
Exploring complex networks via topological embedding on surfaces.
Aste, Tomaso; Gramatica, Ruggero; Di Matteo, T
2012-09-01
We demonstrate that graphs embedded on surfaces are a powerful and practical tool to generate, to characterize, and to simulate networks with a broad range of properties. Any network can be embedded on a surface with sufficiently high genus and therefore the study of topologically embedded graphs is non-restrictive. We show that the local properties of the network are affected by the surface genus which determines the average degree, which influences the degree distribution, and which controls the clustering coefficient. The global properties of the graph are also strongly affected by the surface genus which is constraining the degree of interwovenness, changing the scaling properties of the network from large-world kind (small genus) to small- and ultrasmall-world kind (large genus). Two elementary moves allow the exploration of all networks embeddable on a given surface and naturally introduce a tool to develop a statistical mechanics description for these networks. Within such a framework, we study the properties of topologically embedded graphs which dynamically tend to lower their energy towards a ground state with a given reference degree distribution. We show that the cooling dynamics between high and low "temperatures" is strongly affected by the surface genus with the manifestation of a glass-like transition occurring when the distance from the reference distribution is low. We prove, with examples, that topologically embedded graphs can be built in a way to contain arbitrary complex networks as subgraphs. This method opens a new avenue to build geometrically embedded networks on hyperbolic manifolds.
Ground state structures and properties of Si3Hn (n = 1–6) clusters
Indian Academy of Sciences (India)
Unknown
D BALAMURUGAN and R PRASAD*. Department of Physics, Indian Institute of Technology, Kanpur ... bond (Balamurugan and Prasad 2001). We find that Si3H6 cluster is most stable and Si3H3 cluster is .... Gallego S, Avila J, Martin M, Blasé X, Taleb A, Dumas P and. Asensio M C 2000 Phys. Rev. B61 12628. Gupte G R ...
Energy Technology Data Exchange (ETDEWEB)
Kalb, Jeffrey L.; Lee, David S.
2008-01-01
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.
Real Topological Cyclic Homology
DEFF Research Database (Denmark)
Høgenhaven, Amalie
The main topics of this thesis are real topological Hochschild homology and real topological cyclic homology. If a ring or a ring spectrum is equipped with an anti-involution, then it induces additional structure on the topological Hochschild homology spectrum. The group O(2) acts on the spectrum......, where O(2) is the semi-direct product of T, the multiplicative group of complex number of modulus 1, by the group G=Gal(C/R). We refer to this O(2)-spectrum as the real topological Hochschild homology. This generalization leads to a G-equivariant version of topological cyclic homology, which we call...... real topological cyclic homology. The first part of the thesis computes the G-equivariant homotopy type of the real topological cyclic homology of spherical group rings at a prime p with anti-involution induced by taking inverses in the group. The second part of the thesis investigates the derived G...
Triple Point Topological Metals
Directory of Open Access Journals (Sweden)
Ziming Zhu
2016-07-01
Full Text Available Topologically protected fermionic quasiparticles appear in metals, where band degeneracies occur at the Fermi level, dictated by the band structure topology. While in some metals these quasiparticles are direct analogues of elementary fermionic particles of the relativistic quantum field theory, other metals can have symmetries that give rise to quasiparticles, fundamentally different from those known in high-energy physics. Here, we report on a new type of topological quasiparticles—triple point fermions—realized in metals with symmorphic crystal structure, which host crossings of three bands in the vicinity of the Fermi level protected by point group symmetries. We find two topologically different types of triple point fermions, both distinct from any other topological quasiparticles reported to date. We provide examples of existing materials that host triple point fermions of both types and discuss a variety of physical phenomena associated with these quasiparticles, such as the occurrence of topological surface Fermi arcs, transport anomalies, and topological Lifshitz transitions.
International Nuclear Information System (INIS)
Popescu, C.; Biro, L.; Iftode, I.; Turcu, I.
1975-10-01
The RAP-3A computer code is designed for calculating the main steady state thermo-hydraulic parameters of multirod fuel clusters with liquid metal cooling. The programme provides a double accuracy computation of temperatures and axial enthalpy distributions of pressure losses and axial heat flux distributions in fuel clusters before boiling conditions occur. Physical and mathematical models as well as a sample problem are presented. The code is written in FORTRAN-4 language and is running on a IBM-370/135 computer
Topological insulators Dirac equation in condensed matter
Shen, Shun-Qing
2017-01-01
This new edition presents a unified description of these insulators from one to three dimensions based on the modified Dirac equation. It derives a series of solutions of the bound states near the boundary, and describes the current status of these solutions. Readers are introduced to topological invariants and their applications to a variety of systems from one-dimensional polyacetylene, to two-dimensional quantum spin Hall effect and p-wave superconductors, three-dimensional topological insulators and superconductors or superfluids, and topological Weyl semimetals, helping them to better understand this fascinating field. To reflect research advances in topological insulators, several parts of the book have been updated for the second edition, including: Spin-Triplet Superconductors, Superconductivity in Doped Topological Insulators, Detection of Majorana Fermions and so on. In particular, the book features a new chapter on Weyl semimetals, a topic that has attracted considerable attention and has already b...
Gapped boundary phases of topological insulators via weak coupling
Seiberg, Nathan; Witten, Edward
2016-12-01
The standard boundary state of a topological insulator in 3 + 1 dimensions has gapless charged fermions. We present model systems that reproduce this standard gapless boundary state in one phase, but also have gapped phases with topological order. Our models are weakly coupled and all the dynamics is explicit. We rederive some known boundary states of topological insulators and construct new ones. Consistency with the standard spin/charge relation of condensed matter physics places a nontrivial constraint on models.
International Nuclear Information System (INIS)
Ehara, Masahiro; Piecuch, Piotr; Lutz, Jesse J.; Gour, Jeffrey R.
2012-01-01
Graphical abstract: Electronically excited states of CuCl 4 2- and CuBr 4 2- are determined using the scalar relativistic symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster calculations. The results are compared with experimental spectra. Highlights: ► Electronic spectra of CuCl 4 2- and CuBr 4 2- are examined by SAC-CI and EOMCC methods. ► Relativistic SAC-CI and EOMCC results are compared with experimental spectra. ► An assignment of bands in the CuCl 4 2- and CuBr 4 2- absorption spectra is obtained. ► Relativistic effects affect excitation energies and ground-state geometries. ► The effect of relativity on the oscillator strengths is generally small. - Abstract: The valence excitation spectra of the copper tetrachloride and copper tetrabromide open-shell dianions, CuCl 4 2- and CuBr 4 2- , respectively, are investigated by a variety of symmetry-adapted-cluster configuration-interaction (SAC-CI) and equation-of-motion coupled-cluster (EOMCC) methods. The valence excited states of the CuCl 4 2- and CuBr 4 2- species that correspond to transitions from doubly occupied molecular orbitals (MOs) to a singly occupied MO (SOMO), for which experimental spectra are available, are examined with the ionized (IP) variants of the SAC-CI and EOMCC methods. The higher-energy excited states of CuCl 4 2- and CuBr 4 2- that correspond to transitions from SOMO to unoccupied MOs, which have not been characterized experimentally, are determined using the electron-attached (EA) SAC-CI and EOMCC approaches. An emphasis is placed on the scalar relativistic SAC-CI and EOMCC calculations based on the spin-free part of the second-order Douglass–Kroll–Hess Hamiltonian (DKH2) and on a comparison of the results of the IP and EA SAC-CI and EOMCC calculations with up to 2-hole-1-particle (2h-1p) and 2-particle-1-hole (2p-1h) excitations, referred to as the IP-SAC-CI SD-R and IP-EOMCCSD(2h-1p) methods in the IP case and EA-SAC-CI SD-R and EA
Transportation Network Topologies
Alexandrov, Natalia (Editor)
2004-01-01
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.
Topological Phases in the Real World
Hsu, Yi-Ting
The experimental discovery and subsequent theoretical understanding of the integer quantum Hall effect, the first known topological phase, has started a revolutionary breakthrough in understanding states of matter since its discovery four decades ago. Topological phases are predicted to have many generic signatures resulting from their underlying topological nature, such as quantized Hall transport, robust boundary states, and possible fractional excitations. The intriguing nature of these signatures and their potential applications in quantum computation has intensely fueled the efforts of the physics community to materialize topological phases. Among various topological phases initially predicted on theoretical grounds, chiral topological superconductors and time-reversal symmetric topological insulators (TI) in three dimension (3D) are two promising candidates for experimental realization and application. The family of materials, Bi2X3 (X = Se, Te), has been predicted and shown experimentally to be time-reversal symmetric 3D TIs through the observation of robust Dirac surface states with Rashba-type spin-winding. Due to their robust surface states with spin-windings, these 3D TIs are expected to be promising materials for producing large spin-transfer torques which are advantageous for spintronics application. As for topological superconductors, despite the exotic excitations that have been extensively proposed as qubits for topological quantum computing, materials hosting topological superconductivity are rare to date and the leading candidate in two dimensions (2D), Sr 2RuO4, has a low transition temperature (Tc ). The goal of my phd study is to push forward the current status of realization of topological phases by materializing higher Tc topological superconductors and investigating the stability of Dirac surface states in 3D TIs. In the first part of this thesis, I will discuss our double-pronged objective for topological superconductors: to propose how to
International Nuclear Information System (INIS)
Closser, Kristina D.; Head-Gordon, Martin; Gessner, Oliver
2014-01-01
The dynamics resulting from electronic excitations of helium clusters were explored using ab initio molecular dynamics. The simulations were performed with configuration interaction singles and adiabatic classical dynamics coupled to a state-following algorithm. 100 different configurations of He 7 were excited into the 2s and 2p manifold for a total of 2800 trajectories. While the most common outcome (90%) was complete fragmentation to 6 ground state atoms and 1 excited state atom, 3% of trajectories yielded bound, He 2 * , and <0.5% yielded an excited helium trimer. The nature of the dynamics, kinetic energy release, and connections to experiments are discussed
Liévanos, Raoul S
2015-11-01
This article contributes to environmental inequality outcomes research on the spatial and demographic factors associated with cumulative air-toxic health risks at multiple geographic scales across the United States. It employs a rigorous spatial cluster analysis of census tract-level 2005 estimated lifetime cancer risk (LCR) of ambient air-toxic emissions from stationary (e.g., facility) and mobile (e.g., vehicular) sources to locate spatial clusters of air-toxic LCR risk in the continental United States. It then tests intersectional environmental inequality hypotheses on the predictors of tract presence in air-toxic LCR clusters with tract-level principal component factor measures of economic deprivation by race and immigrant status. Logistic regression analyses show that net of controls, isolated Latino immigrant-economic deprivation is the strongest positive demographic predictor of tract presence in air-toxic LCR clusters, followed by black-economic deprivation and isolated Asian/Pacific Islander immigrant-economic deprivation. Findings suggest scholarly and practical implications for future research, advocacy, and policy. Copyright © 2015 Elsevier Inc. All rights reserved.
Directory of Open Access Journals (Sweden)
Xiaowei Li
2017-01-01
Full Text Available A large number of studies demonstrated that major depressive disorder (MDD is characterized by the alterations in brain functional connections which is also identifiable during the brain’s “resting-state.” But, in the present study, the approach of constructing functional connectivity is often biased by the choice of the threshold. Besides, more attention was paid to the number and length of links in brain networks, and the clustering partitioning of nodes was unclear. Therefore, minimum spanning tree (MST analysis and the hierarchical clustering were first used for the depression disease in this study. Resting-state electroencephalogram (EEG sources were assessed from 15 healthy and 23 major depressive subjects. Then the coherence, MST, and the hierarchical clustering were obtained. In the theta band, coherence analysis showed that the EEG coherence of the MDD patients was significantly higher than that of the healthy controls especially in the left temporal region. The MST results indicated the higher leaf fraction in the depressed group. Compared with the normal group, the major depressive patients lost clustering in frontal regions. Our findings suggested that there was a stronger brain interaction in the MDD group and a left-right functional imbalance in the frontal regions for MDD controls.
DEFF Research Database (Denmark)
Broojeni, Kianoosh; Amini, M. Hadi; Nejadpak, Arash
2016-01-01
There has been an increasing demand for connectivity of the clusters of microgrids to increase their flexibility and security. This paper presents a framework for implementation, simulation, and evaluation of a novel power routing algorithm for clusters of microgrids. The presumed cluster....... The key contribution of this paper is that each microgrid in the cluster is unaware of the current state and other flows of the cluster. In this approach, the optimal power flow problem is solved for the system while managing congestion and mitigating power losses. The proposed methodology works for both...... radial and non-radial networks regardless of the network topology, scale, and number of microgrids involved in the cluster. Therefore, it is also well suited for large-scale optimal power routing problems that will emerge in the future clusters of microgrids. The effectiveness of the proposed algorithm...
WenJun Zhang; QuHuan Li
2014-01-01
In present study we used self-organizing map (SOM) neural network to conduct the non-supervisory clustering of invertebrate orders in rice field. Four topological functions, i.e., cossintopf, sincostopf, acossintopf, and expsintopf, established on the template in toolbox of Matlab, were used in SOM neural network learning. Results showed that clusters were different when using different topological functions because different topological functions will generate different spatial structure of ...
Complete theory of symmetry-based indicators of band topology.
Po, Hoi Chun; Vishwanath, Ashvin; Watanabe, Haruki
2017-06-30
The interplay between symmetry and topology leads to a rich variety of electronic topological phases, protecting states such as the topological insulators and Dirac semimetals. Previous results, like the Fu-Kane parity criterion for inversion-symmetric topological insulators, demonstrate that symmetry labels can sometimes unambiguously indicate underlying band topology. Here we develop a systematic approach to expose all such symmetry-based indicators of band topology in all the 230 space groups. This is achieved by first developing an efficient way to represent band structures in terms of elementary basis states, and then isolating the topological ones by removing the subset of atomic insulators, defined by the existence of localized symmetric Wannier functions. Aside from encompassing all earlier results on such indicators, including in particular the notion of filling-enforced quantum band insulators, our theory identifies symmetry settings with previously hidden forms of band topology, and can be applied to the search for topological materials.Understanding the role of topology in determining electronic structure can lead to the discovery, or appreciation, of materials with exotic properties such as protected surface states. Here, the authors present a framework for identifying topologically distinct band-structures for all 3D space groups.
Clay, Adam
2016-01-01
This book deals with the connections between topology and ordered groups. It begins with a self-contained introduction to orderable groups and from there explores the interactions between orderability and objects in low-dimensional topology, such as knot theory, braid groups, and 3-manifolds, as well as groups of homeomorphisms and other topological structures. The book also addresses recent applications of orderability in the studies of codimension-one foliations and Heegaard-Floer homology. The use of topological methods in proving algebraic results is another feature of the book. The book was written to serve both as a textbook for graduate students, containing many exercises, and as a reference for researchers in topology, algebra, and dynamical systems. A basic background in group theory and topology is the only prerequisite for the reader.
Two-dimensional topological photonic systems
Sun, Xiao-Chen; He, Cheng; Liu, Xiao-Ping; Lu, Ming-Hui; Zhu, Shi-Ning; Chen, Yan-Feng
2017-09-01
The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.
Differential topology an introduction
Gauld, David B
2006-01-01
Offering classroom-proven results, Differential Topology presents an introduction to point set topology via a naive version of nearness space. Its treatment encompasses a general study of surgery, laying a solid foundation for further study and greatly simplifying the classification of surfaces.This self-contained treatment features 88 helpful illustrations. Its subjects include topological spaces and properties, some advanced calculus, differentiable manifolds, orientability, submanifolds and an embedding theorem, and tangent spaces. Additional topics comprise vector fields and integral curv
Directory of Open Access Journals (Sweden)
S. Nazmul
2014-03-01
Full Text Available Notions of Lowen type fuzzy soft topological space are introduced and some of their properties are established in the present paper. Besides this, a combined structure of a fuzzy soft topological space and a fuzzy soft group, which is termed here as fuzzy soft topological group is introduced. Homomorphic images and preimages are also examined. Finally, some definitions and results on fuzzy soft set are studied.
Topological Foundations of Electromagnetism
Barrett, Terrence W
2008-01-01
Topological Foundations of Electromagnetism seeks a fundamental understanding of the dynamics of electromagnetism; and marshals the evidence that in certain precisely defined topological conditions, electromagnetic theory (Maxwell's theory) must be extended or generalized in order to provide an explanation and understanding of, until now, unusual electromagnetic phenomena. Key to this generalization is an understanding of the circumstances under which the so-called A potential fields have physical effects. Basic to the approach taken is that the topological composition of electromagnetic field
Rocca, Corinne H; Goodman, Suzan; Grossman, Daniel; Cadwallader, Kara; Thompson, Kirsten M J; Talmont, Elizabeth; Speidel, J Joseph; Harper, Cynthia C
2018-01-01
Understanding how contraceptive choices and access differ for women having medication abortions compared to aspiration procedures can help to identify priorities for improved patient-centered postabortion contraceptive care. The objective of this study was to investigate the differences in contraceptive counseling, method choices, and use between medication and aspiration abortion patients. This subanalysis examines data from 643 abortion patients from 17 reproductive health centers in a cluster, randomized trial across the United States. We recruited participants aged 18-25 years who did not desire pregnancy and followed them for 1 year. We measured the effect of a full-staff contraceptive training and abortion type on contraceptive counseling, choice, and use with multivariable regression models, using generalized estimating equations for clustering. We used survival analysis with shared frailty to model actual intrauterine device and subdermal implant initiation over 1 year. Overall, 26% of participants (n = 166) had a medication abortion and 74% (n = 477) had an aspiration abortion at the enrollment visit. Women obtaining medication abortions were as likely as those having aspiration abortions to receive counseling on intrauterine devices or the implant (55%) and on a short-acting hormonal method (79%). The proportions of women choosing to use these methods (29% intrauterine device or implant, 58% short-acting hormonal) were also similar by abortion type. The proportions of women who actually used short-acting hormonal methods (71% medication vs 57% aspiration) and condoms or no method (20% vs 22%) within 3 months were not significantly different by abortion type. However, intrauterine device initiation over a year was significantly lower after the medication than the aspiration abortion (11 per 100 person-years vs 20 per 100 person-years, adjusted hazard ratio, 0.50; 95% confidence interval, 0.28-0.89). Implant initiation rates were low and similar by
Morita, K
1989-01-01
Being an advanced account of certain aspects of general topology, the primary purpose of this volume is to provide the reader with an overview of recent developments.The papers cover basic fields such as metrization and extension of maps, as well as newly-developed fields like categorical topology and topological dynamics. Each chapter may be read independently of the others, with a few exceptions. It is assumed that the reader has some knowledge of set theory, algebra, analysis and basic general topology.
Observation of a phononic quadrupole topological insulator
Serra-Garcia, Marc; Peri, Valerio; Süsstrunk, Roman; Bilal, Osama R.; Larsen, Tom; Villanueva, Luis Guillermo; Huber, Sebastian D.
2018-03-01
The modern theory of charge polarization in solids is based on a generalization of Berry’s phase. The possibility of the quantization of this phase arising from parallel transport in momentum space is essential to our understanding of systems with topological band structures. Although based on the concept of charge polarization, this same theory can also be used to characterize the Bloch bands of neutral bosonic systems such as photonic or phononic crystals. The theory of this quantized polarization has recently been extended from the dipole moment to higher multipole moments. In particular, a two-dimensional quantized quadrupole insulator is predicted to have gapped yet topological one-dimensional edge modes, which stabilize zero-dimensional in-gap corner states. However, such a state of matter has not previously been observed experimentally. Here we report measurements of a phononic quadrupole topological insulator. We experimentally characterize the bulk, edge and corner physics of a mechanical metamaterial (a material with tailored mechanical properties) and find the predicted gapped edge and in-gap corner states. We corroborate our findings by comparing the mechanical properties of a topologically non-trivial system to samples in other phases that are predicted by the quadrupole theory. These topological corner states are an important stepping stone to the experimental realization of topologically protected wave guides in higher dimensions, and thereby open up a new path for the design of metamaterials.
Kazuyosi, IKEDA; Department of Applied Physics, Osaka University
1982-01-01
The radius of convergence of the cluster series (expressing the equation of state) is discussed in connection with the distribution of zeros of the grand partition function on the complex z (= activity) plane, by giving various examples of circular distribution. Anomalous phase transitions and phase transitions of third order are considered by showing some examples of circular distribution of zeros. For the ideal Fermi-Dirac gas, the distribution function of zeros, lying on the part of the ne...
Tensor Network Wavefunctions for Topological Phases
Ware, Brayden Alexander
The combination of quantum effects and interactions in quantum many-body systems can result in exotic phases with fundamentally entangled ground state wavefunctions--topological phases. Topological phases come in two types, both of which will be studied in this thesis. In topologically ordered phases, the pattern of entanglement in the ground state wavefunction encodes the statistics of exotic emergent excitations, a universal indicator of a phase that is robust to all types of perturbations. In symmetry protected topological phases, the entanglement instead encodes a universal response of the system to symmetry defects, an indicator that is robust only to perturbations respecting the protecting symmetry. Finding and creating these phases in physical systems is a motivating challenge that tests all aspects--analytical, numerical, and experimental--of our understanding of the quantum many-body problem. Nearly three decades ago, the creation of simple ansatz wavefunctions--such as the Laughlin fractional quantum hall state, the AKLT state, and the resonating valence bond state--spurred analytical understanding of both the role of entanglement in topological physics and physical mechanisms by which it can arise. However, quantitative understanding of the relevant phase diagrams is still challenging. For this purpose, tensor networks provide a toolbox for systematically improving wavefunction ansatz while still capturing the relevant entanglement properties. In this thesis, we use the tools of entanglement and tensor networks to analyze ansatz states for several proposed new phases. In the first part, we study a featureless phase of bosons on the honeycomb lattice and argue that this phase can be topologically protected under any one of several distinct subsets of the crystalline lattice symmetries. We discuss methods of detecting such phases with entanglement and without. In the second part, we consider the problem of constructing fixed-point wavefunctions for
General Topology of the Universe
Pandya, Aalok
2002-01-01
General topology of the universe is descibed. It is concluded that topology of the present universe is greater or stronger than the topology of the universe in the past and topology of the future universe will be stronger or greater than the present topology of the universe. Consequently, the universe remains unbounded.
Classical topology and quantum states
Indian Academy of Sciences (India)
Abstract. 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 ...
Topological photonic orbital-angular-momentum switch
Luo, Xi-Wang; Zhang, Chuanwei; Guo, Guang-Can; Zhou, Zheng-Wei
2018-04-01
The large number of available orbital-angular-momentum (OAM) states of photons provides a unique resource for many important applications in quantum information and optical communications. However, conventional OAM switching devices usually rely on precise parameter control and are limited by slow switching rate and low efficiency. Here we propose a robust, fast, and efficient photonic OAM switch device based on a topological process, where photons are adiabatically pumped to a target OAM state on demand. Such topological OAM pumping can be realized through manipulating photons in a few degenerate main cavities and involves only a limited number of optical elements. A large change of OAM at ˜10q can be realized with only q degenerate main cavities and at most 5 q pumping cycles. The topological photonic OAM switch may become a powerful device for broad applications in many different fields and motivate a topological design of conventional optical devices.
Multiple topological phases in phononic crystals
Chen, Zeguo
2017-11-20
We report a new topological phononic crystal in a ring-waveguide acoustic system. In the previous reports on topological phononic crystals, there are two types of topological phases: quantum Hall phase and quantum spin Hall phase. A key point in achieving quantum Hall insulator is to break the time-reversal (TR) symmetry, and for quantum spin Hall insulator, the construction of pseudo-spin is necessary. We build such pseudo-spin states under particular crystalline symmetry (C-6v) and then break the degeneracy of the pseudo-spin states by introducing airflow to the ring. We study the topology evolution by changing both the geometric parameters of the unit cell and the strength of the applied airflow. We find that the system exhibits three phases: quantum spin Hall phase, conventional insulator phase and a new quantum anomalous Hall phase.
Societal burden of cluster headache in the United States: a descriptive economic analysis.
Ford, Janet H; Nero, Damion; Kim, Gilwan; Chu, Bong Chul; Fowler, Robert; Ahl, Jonna; Martinez, James M
2018-01-01
To estimate direct and indirect costs in patients with a diagnosis of cluster headache in the US. Adult patients (18-64 years of age) enrolled in the Marketscan Commercial and Medicare Databases with ≥2 non-diagnostic outpatient (≥30 days apart between the two outpatient claims) or ≥1 inpatient diagnoses of cluster headache (ICD-9-CM code 339.00, 339.01, or 339.02) between January 1, 2009 and June 30, 2014, were included in the analyses. Patients had ≥6 months of continuous enrollment with medical and pharmacy coverage before and after the index date (first cluster headache diagnosis). Three outcomes were evaluated: (1) healthcare resource utilization, (2) direct healthcare costs, and (3) indirect costs associated with work days lost due to absenteeism and short-term disability. Direct costs included costs of all-cause and cluster headache-related outpatient, inpatient hospitalization, surgery, and pharmacy claims. Indirect costs were based on an average daily wage, which was estimated from the 2014 US Bureau of Labor Statistics and inflated to 2015 dollars. There were 9,328 patients with cluster headache claims included in the analysis. Cluster headache-related total direct costs (mean [standard deviation]) were $3,132 [$13,396] per patient per year (PPPY), accounting for 17.8% of the all-cause total direct cost. Cluster headache-related inpatient hospitalizations ($1,604) and pharmacy ($809) together ($2,413) contributed over 75% of the cluster headache-related direct healthcare cost. There were three sub-groups of patients with claims associated with indirect costs that included absenteeism, short-term disability, and absenteeism + short-term disability. Indirect costs PPPY were $4,928 [$4,860] for absenteeism, $803 [$2,621] for short-term disability, and $3,374 [$3,198] for absenteeism + disability. Patients with cluster headache have high healthcare costs that are associated with inpatient admissions and pharmacy fulfillments, and high
Performance of Topological Insulator Interconnects
Philip, Timothy M.; Hirsbrunner, Mark R.; Park, Moon Jip; Gilbert, Matthew J.
2016-01-01
The poor performance of copper interconnects at the nanometer scale calls for new material solutions for continued scaling of integrated circuits. We propose the use of three dimensional time-reversal-invariant topological insulators (TIs), which host backscattering-protected surface states, for this purpose. Using semiclassical methods, we demonstrate that nanoscale TI interconnects have a resistance 1-3 orders of magnitude lower than copper interconnects and graphene nanoribbons at the nano...
Topological Insulator Nanowires and Nanoribbons
Energy Technology Data Exchange (ETDEWEB)
Kong, D.S.
2010-06-02
Recent theoretical calculations and photoemission spectroscopy measurements on the bulk Bi{sub 2}Se{sub 3} material show that it is a three-dimensional topological insulator possessing conductive surface states with nondegenerate spins, attractive for dissipationless electronics and spintronics applications. Nanoscale topological insulator materials have a large surface-to-volume ratio that can manifest the conductive surface states and are promising candidates for devices. Here we report the synthesis and characterization of high quality single crystalline Bi{sub 2}Se{sub 3} nanomaterials with a variety of morphologies. The synthesis of Bi{sub 2}Se{sub 3} nanowires and nanoribbons employs Au-catalyzed vapor-liquid-solid (VLS) mechanism. Nanowires, which exhibit rough surfaces, are formed by stacking nanoplatelets along the axial direction of the wires. Nanoribbons are grown along [11-20] direction with a rectangular crosssection and have diverse morphologies, including quasi-one-dimensional, sheetlike, zigzag and sawtooth shapes. Scanning tunneling microscopy (STM) studies on nanoribbons show atomically smooth surfaces with {approx}1 nm step edges, indicating single Se-Bi-Se-Bi-Se quintuple layers. STM measurements reveal a honeycomb atomic lattice, suggesting that the STM tip couples not only to the top Se atomic layer, but also to the Bi atomic layer underneath, which opens up the possibility to investigate the contribution of different atomic orbitals to the topological surface states. Transport measurements of a single nanoribbon device (four terminal resistance and Hall resistance) show great promise for nanoribbons as candidates to study topological surface states.
Experimental demonstration of topological effects in bianisotropic metamaterials
Slobozhanyuk, Alexey P.; Khanikaev, Alexander B.; Filonov, Dmitry S.; Smirnova, Daria A.; Miroshnichenko, Andrey E.; Kivshar, Yuri S.
2016-01-01
Existence of robust edge states at interfaces of topologically dissimilar systems is one of the most fascinating manifestations of a novel nontrivial state of matter, a topological insulator. Such nontrivial states were originally predicted and discovered in condensed matter physics, but they find their counterparts in other fields of physics, including the physics of classical waves and electromagnetism. Here, we present the first experimental realization of a topological insulator for electromagnetic waves based on engineered bianisotropic metamaterials. By employing the near-field scanning technique, we demonstrate experimentally the topologically robust propagation of electromagnetic waves around sharp corners without backscattering effects. PMID:26936219
Geometry and groups for cosmic topology
International Nuclear Information System (INIS)
Kramer, Peter
2011-01-01
The Cosmic Microwave Background is measured by satellite observation with great precision. It offers insight into its origin in early states of the universe. Unexpected low multipole amplitudes of the incoming CMB radiation may be due to a multiply connected topology of cosmic 3-space. We present and analyze the geometry and homotopy for the family of Platonic spherical 3-manifolds, provide their harmonic analysis, and formulate topological selection rules.
Topological nodal line semimetals predicted from first-principles calculations
Yu, Rui; Fang, Zhong; Dai, Xi; Weng, Hongming
2017-06-01
Topological semimetals are newly discovered states of quantum matter, which have extended the concept of topological states from insulators to metals and attracted great research interest in recent years. In general, there are three kinds of topological semimetals, namely Dirac semimetals, Weyl semimetals, and nodal line semimetals. Nodal line semimetals can be considered as precursor states for other topological states. For example, starting from such nodal line states, the nodal line structure might evolve into Weyl points, convert into Dirac points, or become a topological insulator by introducing the spin-orbit coupling (SOC) or mass term. In this review paper, we introduce theoretical materials that show the nodal line semimetal state, including the all-carbon Mackay-Terrones crystal (MTC), anti-perovskite Cu3PdN, pressed black phosphorus, and the CaP3 family of materials, and we present the design principles for obtaining such novel states of matter.
Modeling Internet Topology Dynamics
Haddadi, H.; Uhlig, S.; Moore, A.; Mortier, R.; Rio, M.
Despite the large number of papers on network topology modeling and inference, there still exists ambiguity about the real nature of the Internet AS and router level topology. While recent findings have illustrated the inaccuracies in maps inferred from BGP peering and traceroute measurements,
Topology optimization approaches
DEFF Research Database (Denmark)
Sigmund, Ole; Maute, Kurt
2013-01-01
Topology optimization has undergone a tremendous development since its introduction in the seminal paper by Bendsøe and Kikuchi in 1988. By now, the concept is developing in many different directions, including “density”, “level set”, “topological derivative”, “phase field”, “evolutionary...
Manufacturing tolerant topology optimization
DEFF Research Database (Denmark)
Sigmund, Ole
2009-01-01
(dilated) structures compared to the intended topology. Examples are MEMS devices manufactured using etching processes, nano-devices manufactured using e-beam lithography or laser micro-machining and macro structures manufactured using milling processes. In the suggested robust topology optimization...
Mendelson, Bert
1990-01-01
Highly regarded for its exceptional clarity, imaginative and instructive exercises, and fine writing style, this concise book offers an ideal introduction to the fundamentals of topology. It provides a simple, thorough survey of elementary topics, starting with set theory and advancing to metric and topological spaces, connectedness, and compactness. 1975 edition.
Czech Academy of Sciences Publication Activity Database
Demel, Ondřej; Kedžuch, S.; Noga, J.; Pittner, Jiří
2013-01-01
Roč. 111, 16-17 (2013), s. 2477-2488 ISSN 0026-8976 R&D Projects: GA ČR GPP208/10/P041; GA ČR GAP208/11/2222 Institutional support: RVO:61388955 Keywords : explicitly correlated * coupled cluster * multireference Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.642, year: 2013
A Computational Study of Rare Gas Clusters: Stepping Stones to the Solid State
Glendening, Eric D.; Halpern, Arthur M.
2012-01-01
An upper-level undergraduate or beginning graduate project is described in which students obtain the Lennard-Jones 6-12 potential parameters for Ne[subscript 2] and Ar[subscript 2] from ab initio calculations and use the results to express pairwise interactions between the atoms in clusters containing up to N = 60 atoms. The students use simulated…
Metal-halide systems: From molecular clusters to liquid-state structure
Directory of Open Access Journals (Sweden)
Mario P. Tosi
2015-03-01
Full Text Available I present a short review of the relationship between quantum-mechanical calculations on small molecular clusters of some metal-ion halides and studies of the microscopic structure in the condensed liquid phases of these compounds. The review is dedicated to the memory of Professor Vincenzo Grasso.
Amorphous Gyroscopic Topological Metamaterials
Mitchell, Noah P.; Nash, Lisa M.; Hexner, Daniel; Turner, Ari M.; Irvine, William T. M.
Mechanical topological metamaterials display striking mechanical responses, such as unidirectional surface modes that are impervious to disorder. This behavior arises from the topology of their vibrational spectra. All examples of topological metamaterials to date are finely-tuned structures such as crystalline lattices or jammed packings. Here, we present robust recipes for building amorphous topological metamaterials with arbitrary underlying structure and no long-range order. Using interacting gyroscopes as a model system, we demonstrate through experiment, simulation, and theoretical methods that the local geometry and interactions are sufficient to generate topological mobility gaps, allowing for spatially-resolved, real-space calculations of the Chern number. The robustness of our approach enables the design and self-assembly of non-crystalline materials with protected, unidirectional waveguides on the micro and macro scale.
Interactive Topology Optimization
DEFF Research Database (Denmark)
Nobel-Jørgensen, Morten
Interactivity is the continuous interaction between the user and the application to solve a task. Topology optimization is the optimization of structures in order to improve stiffness or other objectives. The goal of the thesis is to explore how topology optimization can be used in applications...... in an interactive and intuitive way. By creating such applications with an intuitive and simple user interface we allow non-engineers like designers and architects to easily experiment with boundary conditions, design domains and other optimization settings. This is in contrast to commercial topology optimization...... software where the users are assumed to be well-educated both in the finite element method and topology optimization. This dissertation describes how various topology optimization methods have been used for creating cross-platform applications with high performance. The user interface design is based...
Directory of Open Access Journals (Sweden)
Klaudius eKalcher
2015-12-01
Full Text Available Identifying venous voxels in fMRI datasets is important to increase the specificity of fMRI analyses to microvasculature in the vicinity of the neural processes triggering the BOLD response. This is, however, difficult to achieve in particular in typical studies where magnitude images of BOLD EPI are the only data available. In this study, voxelwise functional connectivity graphs were computed on minimally preprocessed low TR (333 ms multiband resting-state fMRI data, using both high positive and negative correlations to define edges between nodes (voxels. A high correlation threshold for binarization ensures that most edges in the resulting sparse graph reflect the high coherence of signals in medium to large veins. Graph clustering based on the optimization of modularity was then employed to identify clusters of coherent voxels in this graph, and all clusters of 50 or more voxels were then interpreted as corresponding to medium to large veins. Indeed, a comparison with SWI reveals that 75.6 ± 5.9% of voxels within these large clusters overlap with veins visible in the SWI image or lie outside the brain parenchyma. Some of the remainingdifferences between the two modalities can be explained by imperfect alignment or geometric distortions between the two images. Overall, the graph clustering based method for identifying venous voxels has a high specificity as well as the additional advantages of being computed in the same voxel grid as the fMRI dataset itself and not needingany additional data beyond what is usually acquired (and exported in standard fMRI experiments.
Topological color codes and two-body quantum lattice Hamiltonians
Kargarian, M.; Bombin, H.; Martin-Delgado, M. A.
2010-02-01
Topological color codes are among the stabilizer codes with remarkable properties from the quantum information perspective. In this paper, we construct a lattice, the so-called ruby lattice, with coordination number 4 governed by a two-body Hamiltonian. In a particular regime of coupling constants, in a strong coupling limit, degenerate perturbation theory implies that the low-energy spectrum of the model can be described by a many-body effective Hamiltonian, which encodes the color code as its ground state subspace. Ground state subspace corresponds to a vortex-free sector. The gauge symmetry Z2×Z2 of the color code could already be realized by identifying three distinct plaquette operators on the ruby lattice. All plaquette operators commute with each other and with the Hamiltonian being integrals of motion. Plaquettes are extended to closed strings or string-net structures. Non-contractible closed strings winding the space commute with Hamiltonian but not always with each other. This gives rise to exact topological degeneracy of the model. A connection to 2-colexes can be established via the coloring of the strings. We discuss it at the non-perturbative level. The particular structure of the two-body Hamiltonian provides a fruitful interpretation in terms of mapping onto bosons coupled to effective spins. We show that high-energy excitations of the model have fermionic statistics. They form three families of high-energy excitations each of one color. Furthermore, we show that they belong to a particular family of topological charges. The emergence of invisible charges is related to the string-net structure of the model. The emerging fermions are coupled to nontrivial gauge fields. We show that for particular 2-colexes, the fermions can see the background fluxes in the ground state. Also, we use the Jordan-Wigner transformation in order to test the integrability of the model via introducing Majorana fermions. The four-valent structure of the lattice prevents the
Müller, Viktor; Perdikis, Dionysios; von Oertzen, Timo; Sleimen-Malkoun, Rita; Jirsa, Viktor; Lindenberger, Ulman
2016-01-01
Resting-state and task-related recordings are characterized by oscillatory brain activity and widely distributed networks of synchronized oscillatory circuits. Electroencephalographic recordings (EEG) were used to assess network structure and network dynamics during resting state with eyes open and closed, and auditory oddball performance through phase synchronization between EEG channels. For this assessment, we constructed a hyper-frequency network (HFN) based on within- and cross-frequency coupling (WFC and CFC, respectively) at 10 oscillation frequencies ranging between 2 and 20 Hz. We found that CFC generally differentiates between task conditions better than WFC. CFC was the highest during resting state with eyes open. Using a graph-theoretical approach (GTA), we found that HFNs possess small-world network (SWN) topology with a slight tendency to random network characteristics. Moreover, analysis of the temporal fluctuations of HFNs revealed specific network topology dynamics (NTD), i.e., temporal changes of different graph-theoretical measures such as strength, clustering coefficient, characteristic path length (CPL), local, and global efficiency determined for HFNs at different time windows. The different topology metrics showed significant differences between conditions in the mean and standard deviation of these metrics both across time and nodes. In addition, using an artificial neural network approach, we found stimulus-related dynamics that varied across the different network topology metrics. We conclude that functional connectivity dynamics (FCD), or NTD, which was found using the HFN approach during rest and stimulus processing, reflects temporal and topological changes in the functional organization and reorganization of neuronal cell assemblies.
Müller, Viktor; Perdikis, Dionysios; von Oertzen, Timo; Sleimen-Malkoun, Rita; Jirsa, Viktor; Lindenberger, Ulman
2016-01-01
Resting-state and task-related recordings are characterized by oscillatory brain activity and widely distributed networks of synchronized oscillatory circuits. Electroencephalographic recordings (EEG) were used to assess network structure and network dynamics during resting state with eyes open and closed, and auditory oddball performance through phase synchronization between EEG channels. For this assessment, we constructed a hyper-frequency network (HFN) based on within- and cross-frequency coupling (WFC and CFC, respectively) at 10 oscillation frequencies ranging between 2 and 20 Hz. We found that CFC generally differentiates between task conditions better than WFC. CFC was the highest during resting state with eyes open. Using a graph-theoretical approach (GTA), we found that HFNs possess small-world network (SWN) topology with a slight tendency to random network characteristics. Moreover, analysis of the temporal fluctuations of HFNs revealed specific network topology dynamics (NTD), i.e., temporal changes of different graph-theoretical measures such as strength, clustering coefficient, characteristic path length (CPL), local, and global efficiency determined for HFNs at different time windows. The different topology metrics showed significant differences between conditions in the mean and standard deviation of these metrics both across time and nodes. In addition, using an artificial neural network approach, we found stimulus-related dynamics that varied across the different network topology metrics. We conclude that functional connectivity dynamics (FCD), or NTD, which was found using the HFN approach during rest and stimulus processing, reflects temporal and topological changes in the functional organization and reorganization of neuronal cell assemblies. PMID:27799906
Spin-torque generation in topological insulator based heterostructures
Fischer, Mark H.
2016-03-11
Heterostructures utilizing topological insulators exhibit a remarkable spin-torque efficiency. However, the exact origin of the strong torque, in particular whether it stems from the spin-momentum locking of the topological surface states or rather from spin-Hall physics of the topological-insulator bulk, remains unclear. Here, we explore a mechanism of spin-torque generation purely based on the topological surface states. We consider topological-insulator-based bilayers involving ferromagnetic metal (TI/FM) and magnetically doped topological insulators (TI/mdTI), respectively. By ascribing the key theoretical differences between the two setups to location and number of active surface states, we describe both setups within the same framework of spin diffusion of the nonequilibrium spin density of the topological surface states. For the TI/FM bilayer, we find large spin-torque efficiencies of roughly equal magnitude for both in-plane and out-of-plane spin torques. For the TI/mdTI bilayer, we elucidate the dominance of the spin-transfer-like torque. However, we cannot explain the orders of magnitude enhancement reported. Nevertheless, our model gives an intuitive picture of spin-torque generation in topological-insulator-based bilayers and provides theoretical constraints on spin-torque generation due to topological surface states.
Energy Technology Data Exchange (ETDEWEB)
Juliachs, M
2004-07-01
In this state of the art on parallel scientific visualization applications on PC clusters, we deal with both surface and volume rendering approaches. We first analyze available PC cluster configurations and existing parallel rendering software components for parallel graphics rendering. CEA/DIF has been studying cluster visualization since 2001. This report is part of a study to set up a new visualization research platform. This platform consisting of an eight-node PC cluster under Linux and a tiled display was installed in collaboration with Versailles-Saint-Quentin University in August 2003. (author)
Anyonic entanglement and topological entanglement entropy
Bonderson, Parsa; Knapp, Christina; Patel, Kaushal
2017-10-01
We study the properties of entanglement in two-dimensional topologically ordered phases of matter. Such phases support anyons, quasiparticles with exotic exchange statistics. The emergent nonlocal state spaces of anyonic systems admit a particular form of entanglement that does not exist in conventional quantum mechanical systems. We study this entanglement by adapting standard notions of entropy to anyonic systems. We use the algebraic theory of anyon models (modular tensor categories) to illustrate the nonlocal entanglement structure of anyonic systems. Using this formalism, we present a general method of deriving the universal topological contributions to the entanglement entropy for general system configurations of a topological phase, including surfaces of arbitrary genus, punctures, and quasiparticle content. We analyze a number of examples in detail. Our results recover and extend prior results for anyonic entanglement and the topological entanglement entropy.
Electrically Tunable Magnetism in Magnetic Topological Insulators
Energy Technology Data Exchange (ETDEWEB)
Wang, Jing; Lian, Biao; Zhang, Shou-Cheng
2015-07-14
The external controllability of the magnetic properties in topological insulators would be important both for fundamental and practical interests. Here we predict the electric-field control of ferromagnetism in a thin film of insulating magnetic topological insulators. The decrease of band inversion by the application of electric fields results in a reduction of magnetic susceptibility, and hence in the modification of magnetism. Remarkably, the electric field could even induce the magnetic quantum phase transition from ferromagnetism to paramagnetism. We further propose a transistor device in which the dissipationless charge transport of chiral edge states is controlled by an electric field. In particular, the field-controlled ferromagnetism in a magnetic topological insulator can be used for voltage based writing of magnetic random access memories in magnetic tunnel junctions. The simultaneous electrical control of magnetic order and chiral edge transport in such devices may lead to electronic and spintronic applications for topological insulators.
Bistable Topological Insulator with Exciton-Polaritons
Kartashov, Yaroslav V.; Skryabin, Dmitry V.
2017-12-01
The functionality of many nonlinear and quantum optical devices relies on the effect of optical bistability. Using microcavity exciton-polaritons in a honeycomb arrangement of microcavity pillars, we report the resonance response and bistability of topological edge states. A balance between the pump, loss, and nonlinearity ensures a broad range of dynamical stability and controls the distribution of power between counterpropagating states on the opposite edges of the honeycomb lattice stripe. Tuning energy and polarization of the pump photons, while keeping their momentum constant, we demonstrate control of the propagation direction of the dominant edge state. Our results facilitate the development of practical applications of topological photonics.
All-carbon-based porous topological semimetal for Li-ion battery anode material.
Liu, Junyi; Wang, Shuo; Sun, Qiang
2017-01-24
Topological state of matter and lithium batteries are currently two hot topics in science and technology. Here we combine these two by exploring the possibility of using all-carbon-based porous topological semimetal for lithium battery anode material. Based on density-functional theory and the cluster-expansion method, we find that the recently identified topological semimetal bco-C 16 is a promising anode material with higher specific capacity (Li-C 4 ) than that of the commonly used graphite anode (Li-C 6 ), and Li ions in bco-C 16 exhibit a remarkable one-dimensional (1D) migration feature, and the ion diffusion channels are robust against the compressive and tensile strains during charging/discharging. Moreover, the energy barrier decreases with increasing Li insertion and can reach 0.019 eV at high Li ion concentration; the average voltage is as low as 0.23 V, and the volume change during the operation is comparable to that of graphite. These intriguing theoretical findings would stimulate experimental work on topological carbon materials.
Nonreciprocal lasing in topological cavities of arbitrary geometries
Bahari, Babak; Ndao, Abdoulaye; Vallini, Felipe; El Amili, Abdelkrim; Fainman, Yeshaiahu; Kanté, Boubacar
2017-11-01
Resonant cavities are essential building blocks governing many wave-based phenomena, but their geometry and reciprocity fundamentally limit the integration of optical devices. We report, at telecommunication wavelengths, geometry-independent and integrated nonreciprocal topological cavities that couple stimulated emission from one-way photonic edge states to a selected waveguide output with an isolation ratio in excess of 10 decibels. Nonreciprocity originates from unidirectional edge states at the boundary between photonic structures with distinct topological invariants. Our experimental demonstration of lasing from topological cavities provides the opportunity to develop complex topological circuitry of arbitrary geometries for the integrated and robust generation and transport of photons in classical and quantum regimes.
Surfaces and slabs of fractional topological insulator heterostructures
Sahoo, Sharmistha; Sirota, Alexander; Cho, Gil Young; Teo, Jeffrey C. Y.
2017-10-01
Fractional topological insulators (FTIs) are electronic topological phases in (3 +1 ) dimensions enriched by time reversal (TR) and charge U (1 ) conservation symmetries. We focus on the simplest series of fermionic FTIs, whose bulk quasiparticles consist of deconfined partons that carry fractional electric charges in integral units of e*=e /(2 n +1 ) and couple to a discrete Z2 n +1 gauge theory. We propose massive symmetry preserving or breaking FTI surface states. Combining the long-ranged entangled bulk with these topological surface states, we deduce the novel topological order of quasi-(2 +1 ) -dimensional FTI slabs as well as their corresponding edge conformal field theories.
Health state evaluation of shield tunnel SHM using fuzzy cluster method
Zhou, Fa; Zhang, Wei; Sun, Ke; Shi, Bin
2015-04-01
Shield tunnel SHM is in the path of rapid development currently while massive monitoring data processing and quantitative health grading remain a real challenge, since multiple sensors belonging to different types are employed in SHM system. This paper addressed the fuzzy cluster method based on fuzzy equivalence relationship for the health evaluation of shield tunnel SHM. The method was optimized by exporting the FSV map to automatically generate the threshold value. A new holistic health score(HHS) was proposed and its effectiveness was validated by conducting a pilot test. A case study on Nanjing Yangtze River Tunnel was presented to apply this method. Three types of indicators, namely soil pressure, pore pressure and steel strain, were used to develop the evaluation set U. The clustering results were verified by analyzing the engineering geological conditions; the applicability and validity of the proposed method was also demonstrated. Besides, the advantage of multi-factor evaluation over single-factor model was discussed by using the proposed HHS. This investigation indicated the fuzzy cluster method and HHS is capable of characterizing the fuzziness of tunnel health, and it is beneficial to clarify the tunnel health evaluation uncertainties.
Elements of differential topology
Shastri, Anant R
2011-01-01
Derived from the author's course on the subject, Elements of Differential Topology explores the vast and elegant theories in topology developed by Morse, Thom, Smale, Whitney, Milnor, and others. It begins with differential and integral calculus, leads you through the intricacies of manifold theory, and concludes with discussions on algebraic topology, algebraic/differential geometry, and Lie groups.The first two chapters review differential and integral calculus of several variables and present fundamental results that are used throughout the text. The next few chapters focus on smooth manifo
Chatterjee, D
2007-01-01
About the Book: This book provides exposition of the subject both in its general and algebraic aspects. It deals with the notions of topological spaces, compactness, connectedness, completeness including metrizability and compactification, algebraic aspects of topological spaces through homotopy groups and homology groups. It begins with the basic notions of topological spaces but soon going beyond them reaches the domain of algebra through the notions of homotopy, homology and cohomology. How these approaches work in harmony is the subject matter of this book. The book finally arrives at the
2016-10-31
AFRL-AFOSR-UK-TR-2017-0002 Global Topology Optimisation Robert Jack UNIVERSITY OF BATH Final Report 10/31/2016 DISTRIBUTION A: Distribution approved...01 Aug 2015 to 31 Jul 2016 4. TITLE AND SUBTITLE Global Topology Optimisation 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-15-1-0317 5c...future work. 15. SUBJECT TERMS EOARD, Topology Optimization, Non Convex 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18
Algebraic topology and concurrency
DEFF Research Database (Denmark)
Fajstrup, Lisbeth; Raussen, Martin; Goubault, Eric
2006-01-01
We show in this article that some concepts from homotopy theory, in algebraic topology,are relevant for studying concurrent programs. We exhibit a natural semantics of semaphore programs, based on partially ordered topological spaces, which are studied up to “elastic deformation” or homotopy...... differences between ordinary and directed homotopy through examples. We also relate the topological view to a combinatorial view of concurrent programs closer to transition systems, through the notion of a cubical set. Finally we apply some of these concepts to the proof of the safeness of a two...
Flegg, H Graham
2001-01-01
This excellent introduction to topology eases first-year math students and general readers into the subject by surveying its concepts in a descriptive and intuitive way, attempting to build a bridge from the familiar concepts of geometry to the formalized study of topology. The first three chapters focus on congruence classes defined by transformations in real Euclidean space. As the number of permitted transformations increases, these classes become larger, and their common topological properties become intuitively clear. Chapters 4-12 give a largely intuitive presentation of selected topics.
Barr, Stephen
1989-01-01
""A mathematician named KleinThought the Moebius band was divine.Said he: 'If you glueThe edges of two,You'll get a weird bottle like mine.' "" - Stephen BarrIn this lively book, the classic in its field, a master of recreational topology invites readers to venture into such tantalizing topological realms as continuity and connectedness via the Klein bottle and the Moebius strip. Beginning with a definition of topology and a discussion of Euler's theorem, Mr. Barr brings wit and clarity to these topics:New Surfaces (Orientability, Dimension, The Klein Bottle, etc.)The Shortest Moebius StripThe
Elementary topology problem textbook
Viro, O Ya; Netsvetaev, N Yu; Kharlamov, V M
2008-01-01
This textbook on elementary topology contains a detailed introduction to general topology and an introduction to algebraic topology via its most classical and elementary segment centered at the notions of fundamental group and covering space. The book is tailored for the reader who is determined to work actively. The proofs of theorems are separated from their formulations and are gathered at the end of each chapter. This makes the book look like a pure problem book and encourages the reader to think through each formulation. A reader who prefers a more traditional style can either find the pr
Topologically massive supergravity
Directory of Open Access Journals (Sweden)
S. Deser
1983-01-01
Full Text Available The locally supersymmetric extension of three-dimensional topologically massive gravity is constructed. Its fermionic part is the sum of the (dynamically trivial Rarita-Schwinger action and a gauge-invariant topological term, of second derivative order, analogous to the gravitational one. It is ghost free and represents a single massive spin 3/2 excitation. The fermion-gravity coupling is minimal and the invariance is under the usual supergravity transformations. The system's energy, as well as that of the original topological gravity, is therefore positive.
Topological pregauge-pregeometry
International Nuclear Information System (INIS)
Akama, Keiichi; Oda, Ichiro.
1990-12-01
The pregauge-pregeometric action, i.e. the fundamental matter action whose quantum fluctuations give rise to the Einstein-Hilbert and the Yang-Mills actions is investigated from the viewpoint of the topological field theory. We show that the scalar pregauge-pregeometric action is a topological invariant for appropriate choices of the internal gauge group. This model realizes the picture that the gravitational and internal gauge theory at the low energy scale is induced as the quantum effects of the topological field theory at the Planck scale. (author)
Topological systems versus attachment relations | Guido ...
African Journals Online (AJOL)
... localification procedure introduced by S. Vickers for topological systems. Keywords: Adjoint functor, algebra, attachment relation, embedding functor, localification of topological systems, spatialization of topological systems, topological system, topological theory, variety of algebras. Quaestiones Mathematicae 37(2014), ...
Reflection-Symmetric Second-Order Topological Insulators and Superconductors.
Langbehn, Josias; Peng, Yang; Trifunovic, Luka; von Oppen, Felix; Brouwer, Piet W
2017-12-15
Second-order topological insulators are crystalline insulators with a gapped bulk and gapped crystalline boundaries, but with topologically protected gapless states at the intersection of two boundaries. Without further spatial symmetries, five of the ten Altland-Zirnbauer symmetry classes allow for the existence of such second-order topological insulators in two and three dimensions. We show that reflection symmetry can be employed to systematically generate examples of second-order topological insulators and superconductors, although the topologically protected states at corners (in two dimensions) or at crystal edges (in three dimensions) continue to exist if reflection symmetry is broken. A three-dimensional second-order topological insulator with broken time-reversal symmetry shows a Hall conductance quantized in units of e^{2}/h.
Hou, Chang-Yu; Chamon, Claudio
2006-01-01
We study a tunneling geometry defined by a single point-contact constriction that brings to close vicinity two points sitting at the same edge of a quantum Hall liquid, shortening the trip between the otherwise spatially separated points along the normal chiral edge path. This ``wormhole''-like geometry allows for entrapping bulk quasiparticles between the edge path and the tunnel junction, possibly realizing a topologically protected qubit if the quasiparticles have non-Abelian statistics. W...
Topological properties of complex networks in protein structures
Kim, Kyungsik; Jung, Jae-Won; Min, Seungsik
2014-03-01
We study topological properties of networks in structural classification of proteins. We model the native-state protein structure as a network made of its constituent amino-acids and their interactions. We treat four structural classes of proteins composed predominantly of α helices and β sheets and consider several proteins from each of these classes whose sizes range from amino acids of the Protein Data Bank. Particularly, we simulate and analyze the network metrics such as the mean degree, the probability distribution of degree, the clustering coefficient, the characteristic path length, the local efficiency, and the cost. This work was supported by the KMAR and DP under Grant WISE project (153-3100-3133-302-350).
Topology Optimisation for Coupled Convection Problems
DEFF Research Database (Denmark)
Alexandersen, Joe
This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport in a sur......This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport...... in a surrounding uid, governed by a convection-diffusion equation, where the convective velocity field is found from solving the isothermal incompressible steady-state Navier-Stokes equations. Topology optimisation is also applied to steady-state natural convection problems. The modelling is done using stabilised...... finite element formulation is implemented in an object-oriented parallel finite element framework programmed in the C++ programming language, developed by the Top-Opt research group of the Department of Mechanical Engineering at The Technical University of Denmark. The presented work is seen...
Topological structure of dictionary graphs
International Nuclear Information System (INIS)
Fuks, Henryk; Krzeminski, Mark
2009-01-01
We investigate the topological structure of the subgraphs of dictionary graphs constructed from WordNet and Moby thesaurus data. In the process of learning a foreign language, the learner knows only a subset of all words of the language, corresponding to a subgraph of a dictionary graph. When this subgraph grows with time, its topological properties change. We introduce the notion of the pseudocore and argue that the growth of the vocabulary roughly follows decreasing pseudocore numbers-that is, one first learns words with a high pseudocore number followed by smaller pseudocores. We also propose an alternative strategy for vocabulary growth, involving decreasing core numbers as opposed to pseudocore numbers. We find that as the core or pseudocore grows in size, the clustering coefficient first decreases, then reaches a minimum and starts increasing again. The minimum occurs when the vocabulary reaches a size between 10 3 and 10 4 . A simple model exhibiting similar behavior is proposed. The model is based on a generalized geometric random graph. Possible implications for language learning are discussed.
Topological Sound and Flocking on Curved Surfaces
Directory of Open Access Journals (Sweden)
Suraj Shankar
2017-09-01
Full Text Available Active systems on curved geometries are ubiquitous in the living world. In the presence of curvature, orientationally ordered polar flocks are forced to be inhomogeneous, often requiring the presence of topological defects even in the steady state because of the constraints imposed by the topology of the underlying surface. In the presence of spontaneous flow, the system additionally supports long-wavelength propagating sound modes that get gapped by the curvature of the underlying substrate. We analytically compute the steady-state profile of an active polar flock on a two-sphere and a catenoid, and show that curvature and active flow together result in symmetry-protected topological modes that get localized to special geodesics on the surface (the equator or the neck, respectively. These modes are the analogue of edge states in electronic quantum Hall systems and provide unidirectional channels for information transport in the flock, robust against disorder and backscattering.
Topological Sound and Flocking on Curved Surfaces
Shankar, Suraj; Bowick, Mark J.; Marchetti, M. Cristina
2017-07-01
Active systems on curved geometries are ubiquitous in the living world. In the presence of curvature, orientationally ordered polar flocks are forced to be inhomogeneous, often requiring the presence of topological defects even in the steady state because of the constraints imposed by the topology of the underlying surface. In the presence of spontaneous flow, the system additionally supports long-wavelength propagating sound modes that get gapped by the curvature of the underlying substrate. We analytically compute the steady-state profile of an active polar flock on a two-sphere and a catenoid, and show that curvature and active flow together result in symmetry-protected topological modes that get localized to special geodesics on the surface (the equator or the neck, respectively). These modes are the analogue of edge states in electronic quantum Hall systems and provide unidirectional channels for information transport in the flock, robust against disorder and backscattering.
Topological qubit design and leakage
Energy Technology Data Exchange (ETDEWEB)
Ainsworth, R; Slingerland, J K, E-mail: robert.ainsworth@nuim.ie, E-mail: joost@thphys.nuim.ie [Department of Mathematical Physics, National University of Ireland Maynooth, Co. Kildare (Ireland)
2011-06-15
We examine how best to design qubits for use in topological quantum computation. These qubits are topological Hilbert spaces associated with small groups of anyons. Operations are performed on these by exchanging the anyons. One might argue that in order to have as many simple single-qubit operations as possible, the number of anyons per group should be maximized. However, we show that there is a maximal number of particles per qubit, namely 4, and more generally a maximal number of particles for qudits of dimension d. We also look at the possibility of having topological qubits for which one can perform two-qubit gates without leakage into non-computational states. It turns out that the requirement that all two-qubit gates are leakage free is very restrictive and this property can only be realized for two-qubit systems related to Ising-like anyon models, which do not allow for universal quantum computation by braiding. Our results follow directly from the representation theory of braid groups, which implies that they are valid for all anyon models. We also make some remarks about generalizations to other exchange groups.
Topological Solitons in Physics.
Parsa, Zohreh
1979-01-01
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)
Topological susceptibility from slabs
Energy Technology Data Exchange (ETDEWEB)
Bietenholz, Wolfgang [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P. 70-543, Distrito Federal, C.P. 04510 (Mexico); Forcrand, Philippe de [Institute for Theoretical Physics, ETH Zürich,CH-8093 Zürich (Switzerland); CERN, Physics Department, TH Unit, CH-1211 Geneva 23 (Switzerland); Gerber, Urs [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P. 70-543, Distrito Federal, C.P. 04510 (Mexico); Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo,Edificio C-3, Apdo. Postal 2-82, Morelia, Michoacán, C.P. 58040 (Mexico)
2015-12-14
In quantum field theories with topological sectors, a non-perturbative quantity of interest is the topological susceptibility χ{sub t}. In principle it seems straightforward to measure χ{sub t} by means of Monte Carlo simulations. However, for local update algorithms and fine lattice spacings, this tends to be difficult, since the Monte Carlo history rarely changes the topological sector. Here we test a method to measure χ{sub t} even if data from only one sector are available. It is based on the topological charges in sub-volumes, which we denote as slabs. Assuming a Gaussian distribution of these charges, this method enables the evaluation of χ{sub t}, as we demonstrate with numerical results for non-linear σ-models.
Wilansky, Albert
2008-01-01
Three levels of examples and problems make this volume appropriate for students and professionals. Abundant exercises, ordered and numbered by degree of difficulty, illustrate important topological concepts. 1970 edition.
Topological Susceptibility from Slabs
Bietenholz, Wolfgang; Gerber, Urs
2015-01-01
In quantum field theories with topological sectors, a non-perturbative quantity of interest is the topological susceptibility chi_t. In principle it seems straightforward to measure chi_t by means of Monte Carlo simulations. However, for local update algorithms and fine lattice spacings, this tends to be difficult, since the Monte Carlo history rarely changes the topological sector. Here we test a method to measure chi_t even if data from only one sector are available. It is based on the topological charges in sub-volumes, which we denote as slabs. Assuming a Gaussian distribution of these charges, this method enables the evaluation of chi_t, as we demonstrate with numerical results for non-linear sigma-models.
Games for topological fixpoint logic
Bezhanishvili, N.; Kupke, C.
2016-01-01
Topological fixpoint logics are a family of logics that admits topological models and where the fixpoint operators are defined with respect to the topological interpretations. Here we consider a topological fixpoint logic for relational structures based on Stone spaces, where the fixpoint operators
Effects of topology versus disorder on the vibrational properties of amorphous semiconductors
International Nuclear Information System (INIS)
Sen, P.N.; Yndurain, F.
1977-01-01
We propose a method to isolate the effects of topology, present in the form of rings, etc., from those of disorder due to bond-angle variation. For a representative cluster based on the Polk model, we find that the effects of disorder dominate over those due to rings. The so-called LA-LO peaks in the local vibrational density of states appear only if more than six sixfold rings pass through the atom. These are suppressed if the angular disorder exceeds a critical value
Partitional clustering algorithms
2015-01-01
This book summarizes the state-of-the-art in partitional clustering. Clustering, the unsupervised classification of patterns into groups, is one of the most important tasks in exploratory data analysis. Primary goals of clustering include gaining insight into, classifying, and compressing data. Clustering has a long and rich history that spans a variety of scientific disciplines including anthropology, biology, medicine, psychology, statistics, mathematics, engineering, and computer science. As a result, numerous clustering algorithms have been proposed since the early 1950s. Among these algorithms, partitional (nonhierarchical) ones have found many applications, especially in engineering and computer science. This book provides coverage of consensus clustering, constrained clustering, large scale and/or high dimensional clustering, cluster validity, cluster visualization, and applications of clustering. Examines clustering as it applies to large and/or high-dimensional data sets commonly encountered in reali...
Topological properties of instantons
International Nuclear Information System (INIS)
Mello, E.R.B. de.
1978-07-01
The pure Yang-Mills theory defined in R 4 space is considered and some relevant properties of gauge field like Instanton are shown. The vacuum structure of the theory is discussed, as well as the problem of topological numbers associated with the Instantons and anti-Instantons solutions. A procedure is presented showing how we can alter this topological number by of any variation in the field parameters. (Author) [pt
The refined topological vertex
International Nuclear Information System (INIS)
Iqbal, Amer; Kozcaz, Can; Vafa, Cumrun
2009-01-01
We define a refined topological vertex which depends in addition on a parameter, which physically corresponds to extending the self-dual graviphoton field strength to a more general configuration. Using this refined topological vertex we compute, using geometric engineering, a two-parameter (equivariant) instanton expansion of gauge theories which reproduce the results of Nekrasov. The refined vertex is also expected to be related to Khovanov knot invariants.
Manufacturing tolerant topology optimization
Sigmund, Ole
2009-01-01
In this paper we present an extension of the topology optimization method to include uncertainties during the fabrication of macro, micro and nano structures. More specifically, we consider devices that are manufactured using processes which may result in (uniformly) too thin (eroded) or too thick (dilated) structures compared to the intended topology. Examples are MEMS devices manufactured using etching processes, nano-devices manufactured using e-beam lithography or laser micro-machining an...
Noncommutative topological dynamics
International Nuclear Information System (INIS)
Ramos, C. Correia; Martins, Nuno; Severino, Ricardo; Ramos, J. Sousa
2006-01-01
We study noncommutative dynamical systems associated to unimodal and bimodal maps of the interval. To these maps we associate subshifts and the correspondent AF-algebras and Cuntz-Krieger algebras. As an example we consider systems having equal topological entropy log(1 + φ), where φ is the golden number, but distinct chaotic behavior and we show how a new numerical invariant allows to distinguish that complexity. Finally, we give a statistical interpretation to the topological numerical invariants associated to bimodal maps
Teodoro, Paulo Eduardo; de Oliveira-Júnior, José Francisco; da Cunha, Elias Rodrigues; Correa, Caio Cezar Guedes; Torres, Francisco Eduardo; Bacani, Vitor Matheus; Gois, Givanildo; Ribeiro, Larissa Pereira
2016-04-01
The State of Mato Grosso do Sul (MS) located in Brazil Midwest is devoid of climatological studies, mainly in the characterization of rainfall regime and producers' meteorological systems and rain inhibitors. This state has different soil and climatic characteristics distributed among three biomes: Cerrado, Atlantic Forest and Pantanal. This study aimed to apply the cluster analysis using Ward's algorithm and identify those meteorological systems that affect the rainfall regime in the biomes. The rainfall data of 32 stations (sites) of the MS State were obtained from the Agência Nacional de Águas (ANA) database, collected from 1954 to 2013. In each of the 384 monthly rainfall temporal series was calculated the average and applied the Ward's algorithm to identify spatial and temporal variability of rainfall. Bartlett's test revealed only in January homogeneous variance at all sites. Run test showed that there was no increase or decrease in trend of monthly rainfall. Cluster analysis identified five rainfall homogeneous regions in the MS State, followed by three seasons (rainy, transitional and dry). The rainy season occurs during the months of November, December, January, February and March. The transitional season ranges between the months of April and May, September and October. The dry season occurs in June, July and August. The groups G1, G4 and G5 are influenced by South Atlantic Subtropical Anticyclone (SASA), Chaco's Low (CL), Bolivia's High (BH), Low Levels Jet (LLJ) and South Atlantic Convergence Zone (SACZ) and Maden-Julian Oscillation (MJO). Group G2 is influenced by Upper Tropospheric Cyclonic Vortex (UTCV) and Front Systems (FS). The group G3 is affected by UTCV, FS and SACZ. The meteorological systems' interaction that operates in each biome and the altitude causes the rainfall spatial and temporal diversity in MS State.
Basis for calculations in the topological expansion
International Nuclear Information System (INIS)
Levinson, M.A.
1982-12-01
Investigations aimed at putting the topological theory of particles on a more quantitative basis are described. First, the incorporation of spin into the topological structure is discussed and shown to successfully reproduce the observed lowest mass hadron spectrum. The absence of parity-doubled states represents a significant improvement over previous efforts in similar directions. This theory is applied to the lowest order calculation of elementary hadron coupling constant ratios. SU(6)/sub W/ symmetry is maintained and extended via the notions of topological supersymmetry and universality. Finally, efforts to discover a perturbative basis for the topological expansion are described. This has led to the formulation of off-shell Feynman-like rules which provide a calculational scheme for the strong interaction components of the topological expansion once the zero-entropy connected parts are known. These rules are shown to imply a topological asymptotic freedom. Even though the nonlinear zero-entropy problem cannot itself be treated perturbatively, plausible general assumptions about zero-entropy amplitudes allow immediate qualitative inferences concerning physical hadrons. In particular, scenarios for mass splittings beyond the supersymmetric level are described
Nonlocalized clustering and evolution of cluster structure in nuclei
Horiuchi, H.
2017-06-01
It is shown that the THSR (Tohsaki-Horiuchi-Schuck-Roepke) wave function describe well not only cluster-gas like structures but also ordinary cluster structures with spatial localization of clusters. Based on this fact, the container model has been proposed as a new model of cluster dynamics. For better description of cluster dynamics, extended version of container model has been introduced. The container model of cluster dynamics teaches us how is the evolution of cluster structure which starts from the ground state having shell-model structure to many kinds of cluster states up to the cluster-gas states.
Sharma, Pramod; Das, Soumitra; Vatsa, Rajesh K.
2017-07-01
Systematic manipulation of ionic-outcome in laser-cluster interaction process has been realized for studies carried out on tetramethyltin (TMT) clusters under picosecond laser conditions, determined by choice of laser wavelength and intensity. As a function of laser intensity, TMT clusters exhibit gradual enhancement in overall ionization of its cluster constituents, up to a saturation level of ionization, which was distinct for different wavelengths (266, 355, and 532 nm). Simultaneously, systematic appearance of higher multiply charged atomic ions and shift in relative abundance of multiply charged atomic ions towards higher charge state was observed, using time-of-flight mass spectrometer. At saturation level, multiply charged atomic ions up to (C2+, Sn2+) at 266 nm, (C4+, Sn4+) at 355 nm, and (C4+, Sn6+) at 532 nm were detected. In addition, at 355 nm intra-cluster ion chemistry within the ionized cluster leads to generation of molecular hydrogen ion (H2 +) and triatomic molecular hydrogen ion (H3 +). Generation of multiply charged atomic ions is ascribed to efficient coupling of laser pulse with the cluster media, facilitated by inner-ionized electrons produced within the cluster, at the leading edge of laser pulse. Role of inner-ionized electrons is authenticated by measuring kinetic energy distribution of electrons liberated upon disintegration of excessively ionized cluster, under the influence of picosecond laser pulse.
Essentials of topology with applications
Krantz, Steven G
2009-01-01
Fundamentals What Is Topology? First Definitions Mappings The Separation Axioms Compactness Homeomorphisms Connectedness Path-Connectedness Continua Totally Disconnected Spaces The Cantor Set Metric Spaces Metrizability Baire's Theorem Lebesgue's Lemma and Lebesgue NumbersAdvanced Properties of Topological Spaces Basis and Sub-Basis Product Spaces Relative Topology First Countable, Second Countable, and So ForthCompactifications Quotient Topologies Uniformities Morse Theory Proper Mappings Paracompactness An Application to Digital ImagingBasic Algebraic Topology Homotopy Theory Homology Theory
Commissioning and validation of the ATLAS Level-1 topological trigger
AUTHOR|(SzGeCERN)788741; The ATLAS collaboration; Hong, Tae Min
2017-01-01
The ATLAS experiment has recently commissioned a new hardware component of its first-level trigger: the topological processor (L1Topo). This innovative system, using state-of-the-art FPGA processors, selects events by applying kinematic and topological requirements on candidate objects (energy clusters, jets, and muons) measured by calorimeters and muon sub-detectors. Since the first-level trigger is a synchronous pipelined system, such requirements are applied within a latency of 200ns. We will present the first results from data recorded using the L1Topo trigger; these demonstrate a significantly improved background event rejection, thus allowing for a rate reduction without efficiency loss. This improvement has been shown for several physics processes leading to low-$P_{T}$ leptons, including $H\\to{}\\tau{}\\tau{}$ and $J/\\Psi\\to{}\\mu{}\\mu{}$. In addition, we will discuss the use of an accurate L1Topo simulation as a powerful tool to validate and optimize the performance of this new trigger system. To reach ...
Energy Technology Data Exchange (ETDEWEB)
Wu, Liang [Johns Hopkins Univ., Baltimore, MD (United States). The Inst. of Quantum Matter; Tse, Wang-Kong [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Morris, C. M. [Johns Hopkins Univ., Baltimore, MD (United States). The Inst. of Quantum Matter; Brahlek, M. [Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics and Astronomy; Koirala, N. [Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics and Astronomy; Oh, S. [Rutgers Univ., Piscataway, NJ (United States). Dept. of Physics and Astronomy; Armitage, N. P. [Johns Hopkins Univ., Baltimore, MD (United States). The Inst. of Quantum Matter
2015-02-05
We have utilized magneto-optical time-domain spectroscopy to investigate the low frequency optical response of topological insulator Cu_{0.02}Bi_{2}Se_{3} and Bi_{2}Se_{3} films. With both field and frequency depedence, such experiments give sufficient information to measure the mobility and carrier density of multiple conduction channels simultaneously. We observe sharp cyclotron resonances (CRs) in both samples. The small amount of Cu substitution into the Cu_{0.02}Bi_{2}Se_{3} induces a true bulk insulator with only a single conduction channel with total sheet carrier density 4.9 x 10^{12}/cm^{2} and mobility as large as 4000 cm^{2}/V s. This is consistent with pure topological surface state (TSSs) conduction with a chemical potential 150 meV above the Dirac point. Hence, a true topological insulator with an insulating bulk is realized. The CR broadens at high fields, an e ect that we attribute to an electron-phonon interaction. This assignment is supported by an extended Drude model analysis on the zero field data. In contrast to Cu_{0.02}Bi_{2}Se_{3}, two charge channels were observed in normal Bi_{2}Se_{3} films. We demonstrate a method to distinguish between the dominant TSSs and trivial bulk/2DEG states. The dominant channel exhibits a CR with a carrier density of ~2.0 x 10^{13}/cm^{2} and mobility ~3200 cm^{2}/V s, consistent with TSSs with a chemical potential ~350meV above the Dirac point.
International Nuclear Information System (INIS)
Li Jian; Song Danjie; Guo Xiaojing; Jing Bo
2012-01-01
In order to transmit secure messages, a quantum secure direct communication protocol based on a five-particle cluster state and classical XOR operation is presented. The five-particle cluster state is used to detect eavesdroppers, and the classical XOR operation serving as a one-time-pad is used to ensure the security of the protocol. In the security analysis, the entropy theory method is introduced, and three detection strategies are compared quantitatively by using the constraint between the information that the eavesdroppers can obtain and the interference introduced. If the eavesdroppers intend to obtain all the information, the detection rate of the original ping-pong protocol is 50%; the second protocol, using two particles of the Einstein-Podolsky-Rosen pair as detection particles, is also 50%; while the presented protocol is 89%. Finally, the security of the proposed protocol is discussed, and the analysis results indicate that the protocol in this paper is more secure than the other two. (authors)
Best, Andrew; Kapalo, Katelynn A.; Warta, Samantha F.; Fiore, Stephen M.
2016-05-01
Human-robot teaming largely relies on the ability of machines to respond and relate to human social signals. Prior work in Social Signal Processing has drawn a distinction between social cues (discrete, observable features) and social signals (underlying meaning). For machines to attribute meaning to behavior, they must first understand some probabilistic relationship between the cues presented and the signal conveyed. Using data derived from a study in which participants identified a set of salient social signals in a simulated scenario and indicated the cues related to the perceived signals, we detail a learning algorithm, which clusters social cue observations and defines an "N-Most Likely States" set for each cluster. Since multiple signals may be co-present in a given simulation and a set of social cues often maps to multiple social signals, the "N-Most Likely States" approach provides a dramatic improvement over typical linear classifiers. We find that the target social signal appears in a "3 most-likely signals" set with up to 85% probability. This results in increased speed and accuracy on large amounts of data, which is critical for modeling social cognition mechanisms in robots to facilitate more natural human-robot interaction. These results also demonstrate the utility of such an approach in deployed scenarios where robots need to communicate with human teammates quickly and efficiently. In this paper, we detail our algorithm, comparative results, and offer potential applications for robot social signal detection and machine-aided human social signal detection.
Mazzeo, Paolo P; Maini, Lucia; Petrolati, Alex; Fattori, Valeria; Shankland, Kenneth; Braga, Dario
2014-07-07
Organo-copper(i) halide complexes with a Cu4I4 cubane core and cyclic amines as ligands have been synthesized and their crystal structures have been defined. Their solid state photophysical properties have been measured and correlated with the crystal structure and packing. A unique and remarkably high luminescence quantum yield (76%) has been measured for one of the complexes having the cubane clusters arranged in a columnar structure and held together by N-HI hydrogen bonds. This high luminescence quantum yield is correlated with a slow radiationless deactivation rate of the excited state and suggests a rather strong enhancement of the cubane core rigidity bestowed by the hydrogen bond pattern. Some preliminary thin film deposition experiments show that these compounds could be considered to be good candidates for applications in electroluminescent devices because of their bright luminescence, low cost and relatively easy synthesis processes.
A Novel Cluster Head Selection Algorithm Based on Fuzzy Clustering and Particle Swarm Optimization.
Ni, Qingjian; Pan, Qianqian; Du, Huimin; Cao, Cen; Zhai, Yuqing
2017-01-01
An important objective of wireless sensor network is to prolong the network life cycle, and topology control is of great significance for extending the network life cycle. Based on previous work, for cluster head selection in hierarchical topology control, we propose a solution based on fuzzy clustering preprocessing and particle swarm optimization. More specifically, first, fuzzy clustering algorithm is used to initial clustering for sensor nodes according to geographical locations, where a sensor node belongs to a cluster with a determined probability, and the number of initial clusters is analyzed and discussed. Furthermore, the fitness function is designed considering both the energy consumption and distance factors of wireless sensor network. Finally, the cluster head nodes in hierarchical topology are determined based on the improved particle swarm optimization. Experimental results show that, compared with traditional methods, the proposed method achieved the purpose of reducing the mortality rate of nodes and extending the network life cycle.
Cluster decay of Ba isotopes from ground state and as an excited ...
Indian Academy of Sciences (India)
Abstract. The decay properties of various even–even isotopes of barium in the range 112 ≤ A ≤. 122 is studied by modifying the Coulomb and proximity potential model for both the ground and excited state decays, using recent mass tables. Most of the values predicted for ground state decays are within the experimental ...
Cluster decay of 112− 122 Ba isotopes from ground state and as an ...
Indian Academy of Sciences (India)
A≤122 is studied by modifying the Coulomb and proximity potential model for both the ground and excited state decays, using recent mass tables. Most of the values predicted for ground state decays are within the experimental limit for ...
Rozen, Todd D
2018-03-14
To present results from the United States Cluster Headache Survey comparing the clinical presentation of tobacco nonexposed and tobacco-exposed cluster headache patients. Cluster headache is uniquely tied to a personal history of tobacco usage/cigarette smoking and, if the individual cluster headache sufferer did not smoke, it has been shown that their parent(s) typically did and that individual had significant secondary smoke exposure as a child. The true nontobacco exposed (no personal or secondary exposure) cluster headache sufferer has never been fully studied. The United States Cluster Headache Survey consisted of 187 multiple choice questions related to cluster headache including: patient demographics, clinical headache characteristics, family history, triggers, smoking history (personal and secondary), and headache-related disability. The survey was placed on a website from October through December 2008. One thousand one hundred thirty-four individuals completed the survey. One hundred thirty-three subjects or 12% of the surveyed population had no personal smoking/tobacco use history and no secondary smoke exposure as an infant/child, thus a nontobacco exposed population. In the nonexposed population, there were 87 males and 46 females with a gender ratio of 1.9:1. Episodic cluster headache occurred in 80% of nonexposed subjects. One thousand and one survey responders or 88% were tobacco-exposed (729 males and 272 females) with a gender ratio of 2.7:1. Eighty-three percent had a personal smoking history, while only 17% just had parents who smoked with secondary smoke exposure. Eighty-five percent of smokers had double exposure with a personal smoking history and secondary exposure as a child. Nonexposed cluster headache subjects are significantly more likely to develop cluster headache at ages 40 years and younger, while the exposed sufferers are significantly more likely to develop cluster headache at 40 years of age and older. Nonexposed patients have a
Hou, Chang-Yu; Chamon, Claudio
2006-10-06
We study a tunneling geometry defined by a single point-contact constriction that brings to close vicinity two points sitting at the same edge of a quantum Hall liquid, shortening the trip between the otherwise spatially separated points along the normal chiral edge path. This wormhole-like geometry allows for entrapping bulk quasiparticles between the edge path and the tunnel junction, possibly realizing a topologically protected qubit if the quasiparticles have non-Abelian statistics. We show how either noise or simpler voltage measurements along the edge can probe the non-Abelian nature of the trapped quasiparticles.
Liu, Ming-Yu; Tuzel, Oncel; Ramalingam, Srikumar; Chellappa, Rama
2014-01-01
We propose a new objective function for clustering. This objective function consists of two components: the entropy rate of a random walk on a graph and a balancing term. The entropy rate favors formation of compact and homogeneous clusters, while the balancing function encourages clusters with similar sizes and penalizes larger clusters that aggressively group samples. We present a novel graph construction for the graph associated with the data and show that this construction induces a matroid--a combinatorial structure that generalizes the concept of linear independence in vector spaces. The clustering result is given by the graph topology that maximizes the objective function under the matroid constraint. By exploiting the submodular and monotonic properties of the objective function, we develop an efficient greedy algorithm. Furthermore, we prove an approximation bound of (1/2) for the optimality of the greedy solution. We validate the proposed algorithm on various benchmarks and show its competitive performances with respect to popular clustering algorithms. We further apply it for the task of superpixel segmentation. Experiments on the Berkeley segmentation data set reveal its superior performances over the state-of-the-art superpixel segmentation algorithms in all the standard evaluation metrics.
Hidden topological constellations and polyvalent charges in chiral nematic droplets.
Posnjak, Gregor; Čopar, Simon; Muševič, Igor
2017-02-21
Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=-2, -3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules.
Optimization-based topology identification of complex networks
International Nuclear Information System (INIS)
Tang Sheng-Xue; Chen Li; He Yi-Gang
2011-01-01
In many cases, the topological structures of a complex network are unknown or uncertain, and it is of significance to identify the exact topological structure. An optimization-based method of identifying the topological structure of a complex network is proposed in this paper. Identification of the exact network topological structure is converted into a minimal optimization problem by using the estimated network. Then, an improved quantum-behaved particle swarm optimization algorithm is used to solve the optimization problem. Compared with the previous adaptive synchronization-based method, the proposed method is simple and effective and is particularly valid to identify the topological structure of synchronization complex networks. In some cases where the states of a complex network are only partially observable, the exact topological structure of a network can also be identified by using the proposed method. Finally, numerical simulations are provided to show the effectiveness of the proposed method. (general)
Directory of Open Access Journals (Sweden)
Andrew D Haddow
Full Text Available BACKGROUND: Although La Crosse virus (LACV is one of the most common causes of pediatric arboviral infections in the United States, little has been done to assess its geographic distribution, identify areas of higher risk of disease, and to provide a national picture of its clinical presentation. Therefore, the objective of this study was to investigate the geographic distribution of LACV infections reported in the United States, to identify hot-spots of infection, and to present its clinical picture. METHODS AND FINDINGS: Descriptive and cluster analyses were performed on probable and confirmed cases of LACV infections reported to the Centers for Disease Control and Prevention from 2003-2007. A total of 282 patients had reported confirmed LACV infections during the study period. Of these cases the majority (81 percent presented during the summer, occurred in children 15 years and younger (83.3 percent, and were found in male children (64.9 percent. Clinically, the infections presented as meningioencephalitis (56.3 percent, encephalitis (20.7 percent, meningitis (17.2 percent, or uncomplicated fever (5 percent. Deaths occurred in 1.9 percent of confirmed cases, and in 8.6 percent of patients suffering from encephalitis. The majority of these deaths were in patients 15 years and younger. The county-level incidence risk among counties (n = 136 reporting both probable and confirmed cases for children 15 years and younger (n = 355 ranged from 0.2 to 228.7 per 100,000 persons. The southern United States experienced a significantly higher (p<0.05 incidence risk during the months of June, July, August, and October then the northern United States. There was significant (p<0.05 clustering of high risk in several geographic regions with three deaths attributed to complications from LAC encephalitis occurring in two of these hot-spots of infections. CONCLUSIONS: Both the incidence risk and case fatality rates were found to be higher than previously
Fidelity approach in topological superconductors with disorders
International Nuclear Information System (INIS)
Tian, Wen-Chuan; Huang, Guang-Yao; Wang, Zhi; Yao, Dao-Xin
2015-01-01
We apply the fidelity approach to study the topological superconductivity in spin–orbit coupling nanowire system. The wire is modeled as a one layer lattice chain with Zeeman energy and spin–orbit coupling, which is in proximity to a multi-layer superconductor. In particular, we study the effects of disorders and find that the fidelity susceptibility has multiple peaks. It is revealed that one peak indicates the topological quantum phase transition, while other peaks are signaling the pinning of the Majorana bound states by disorders. - Highlights: • We introduce fidelity approach to study the topological superconducting nanowire with disorders. • We study the quantum phase transition in the wire. • We investigate the disorder pinning of the Majorana bound states in the wire