Qiu, Xiangzhe; Zhang, Yanjun; Feng, Hongbo; Jiang, Donglang
2016-01-01
Recent studies have demonstrated alterations in the topological organization of structural brain networks in diabetes mellitus (DM). However, the DM-related changes in the topological properties in functional brain networks are unexplored so far. We therefore used fluoro-D-glucose positron emission tomography (FDG-PET) data to construct functional brain networks of 73 DM patients and 91 sex- and age-matched normal controls (NCs), followed by a graph theoretical analysis. We found that both DM patients and NCs had a small-world topology in functional brain network. In comparison to the NC group, the DM group was found to have significantly lower small-world index, lower normalized clustering coefficients and higher normalized characteristic path length. Moreover, for diabetic patients, the nodal centrality was significantly reduced in the right rectus, the right cuneus, the left middle occipital gyrus, and the left postcentral gyrus, and it was significantly increased in the orbitofrontal region of the left middle frontal gyrus, the left olfactory region, and the right paracentral lobule. Our results demonstrated that the diabetic brain was associated with disrupted topological organization in the functional PET network, thus providing functional evidence for the abnormalities of brain networks in DM. PMID:27303259
Qiu, Xiangzhe; Zhang, Yanjun; Feng, Hongbo; Jiang, Donglang
2016-01-01
Recent studies have demonstrated alterations in the topological organization of structural brain networks in diabetes mellitus (DM). However, the DM-related changes in the topological properties in functional brain networks are unexplored so far. We therefore used fluoro-D-glucose positron emission tomography (FDG-PET) data to construct functional brain networks of 73 DM patients and 91 sex- and age-matched normal controls (NCs), followed by a graph theoretical analysis. We found that both DM patients and NCs had a small-world topology in functional brain network. In comparison to the NC group, the DM group was found to have significantly lower small-world index, lower normalized clustering coefficients and higher normalized characteristic path length. Moreover, for diabetic patients, the nodal centrality was significantly reduced in the right rectus, the right cuneus, the left middle occipital gyrus, and the left postcentral gyrus, and it was significantly increased in the orbitofrontal region of the left middle frontal gyrus, the left olfactory region, and the right paracentral lobule. Our results demonstrated that the diabetic brain was associated with disrupted topological organization in the functional PET network, thus providing functional evidence for the abnormalities of brain networks in DM. PMID:27303259
Zhao, Yanxin; Chen, Xizhuo; Zhong, Suyu; Cui, Zaixu; Gong, Gaolang; Dong, Qi; Nan, Yun
2016-01-01
Congenital amusia is a neurogenetic disorder that mainly affects the processing of musical pitch. Brain imaging evidence indicates that it is associated with abnormal structural and functional connections in the fronto-temporal region. However, a holistic understanding of the anatomical topology underlying amusia is still lacking. Here, we used probabilistic diffusion tensor imaging tractography and graph theory to examine whole brain white matter structural connectivity in 31 Mandarin-speaking amusics and 24 age- and IQ-matched controls. Amusics showed significantly reduced global connectivity, as indicated by the abnormally decreased clustering coefficient (Cp) and increased normalized shortest path length (λ) compared to the controls. Moreover, amusics exhibited enhanced nodal strength in the right inferior parietal lobule relative to controls. The co-existence of the lexical tone deficits was associated with even more deteriorated global network efficiency in amusics, as suggested by the significant correlation between the increments in normalized shortest path length (λ) and the insensitivity in lexical tone perception. Our study is the first to reveal reduced global connectivity efficiency in amusics as well as an increase in the global connectivity cost due to the co-existed lexical tone deficits. Taken together these results provide a holistic perspective on the anatomical substrates underlying congenital amusia. PMID:27211239
Zhao, Yanxin; Chen, Xizhuo; Zhong, Suyu; Cui, Zaixu; Gong, Gaolang; Dong, Qi; Nan, Yun
2016-01-01
Congenital amusia is a neurogenetic disorder that mainly affects the processing of musical pitch. Brain imaging evidence indicates that it is associated with abnormal structural and functional connections in the fronto-temporal region. However, a holistic understanding of the anatomical topology underlying amusia is still lacking. Here, we used probabilistic diffusion tensor imaging tractography and graph theory to examine whole brain white matter structural connectivity in 31 Mandarin-speaking amusics and 24 age- and IQ-matched controls. Amusics showed significantly reduced global connectivity, as indicated by the abnormally decreased clustering coefficient (Cp) and increased normalized shortest path length (λ) compared to the controls. Moreover, amusics exhibited enhanced nodal strength in the right inferior parietal lobule relative to controls. The co-existence of the lexical tone deficits was associated with even more deteriorated global network efficiency in amusics, as suggested by the significant correlation between the increments in normalized shortest path length (λ) and the insensitivity in lexical tone perception. Our study is the first to reveal reduced global connectivity efficiency in amusics as well as an increase in the global connectivity cost due to the co-existed lexical tone deficits. Taken together these results provide a holistic perspective on the anatomical substrates underlying congenital amusia. PMID:27211239
Dynamical networks with topological self-organization
NASA Technical Reports Server (NTRS)
Zak, M.
2001-01-01
Coupled evolution of state and topology of dynamical networks is introduced. Due to the well organized tensor structure, the governing equations are presented in a canonical form, and required attractors as well as their basins can be easily implanted and controlled.
Modeling the topological organization of cellular processes.
Giavitto, Jean-Louis; Michel, Olivier
2003-07-01
The cell as a dynamical system presents the characteristics of having a dynamical structure. That is, the exact phase space of the system cannot be fixed before the evolution and integrative cell models must state the evolution of the structure jointly with the evolution of the cell state. This kind of dynamical systems is very challenging to model and simulate. New programming concepts must be developed to ease their modeling and simulation. In this context, the goal of the MGS project is to develop an experimental programming language dedicated to the simulation of this kind of systems. MGS proposes a unified view on several computational mechanisms (CHAM, Lindenmayer systems, Paun systems, cellular automata) enabling the specification of spatially localized computations on heterogeneous entities. The evolution of a dynamical structure is handled through the concept of transformation which relies on the topological organization of the system components. An example based on the modeling of spatially distributed biochemical networks is used to illustrate how these notions can be used to model the spatial and temporal organization of intracellular processes. PMID:12915272
Topological phase transition in quasi-one dimensional organic conductors
Ye, Xiao-Shan; Liu, Yong-Jun; Zeng, Xiang-Hua; Wu, Guoqing
2015-01-01
We explore topological phase transition, which involves the energy spectra of field-induced spin-density-wave (FISDW) states in quasi-one dimensional (Q1D) organic conductors, using an extended Su-Schrieffer-Heeger (SSH) model. We show that, in presence of half magnetic-flux FISDW state, the system exhibits topologically nontrivial phases, which can be characterized by a nonzero Chern number. The nontrivial evolution of the bulk bands with chemical potential in a topological phase transition is discussed. We show that the system can have a similar phase diagram which is discussed in the Haldane’s model. We suggest that the topological feature should be tested experimentally in this organic system. These studies enrich the theoretical research on topologically nontrivial phases in the Q1D lattice system as compared to the Haldane topological phase appearing in the two-dimensional lattices. PMID:26612317
Topological phase transition in quasi-one dimensional organic conductors.
Ye, Xiao-Shan; Liu, Yong-Jun; Zeng, Xiang-Hua; Wu, Guoqing
2015-01-01
We explore topological phase transition, which involves the energy spectra of field-induced spin-density-wave (FISDW) states in quasi-one dimensional (Q1D) organic conductors, using an extended Su-Schrieffer-Heeger (SSH) model. We show that, in presence of half magnetic-flux FISDW state, the system exhibits topologically nontrivial phases, which can be characterized by a nonzero Chern number. The nontrivial evolution of the bulk bands with chemical potential in a topological phase transition is discussed. We show that the system can have a similar phase diagram which is discussed in the Haldane's model. We suggest that the topological feature should be tested experimentally in this organic system. These studies enrich the theoretical research on topologically nontrivial phases in the Q1D lattice system as compared to the Haldane topological phase appearing in the two-dimensional lattices. PMID:26612317
Topological phase transition in quasi-one dimensional organic conductors
NASA Astrophysics Data System (ADS)
Ye, Xiao-Shan; Liu, Yong-Jun; Zeng, Xiang-Hua; Wu, Guoqing
2015-11-01
We explore topological phase transition, which involves the energy spectra of field-induced spin-density-wave (FISDW) states in quasi-one dimensional (Q1D) organic conductors, using an extended Su-Schrieffer-Heeger (SSH) model. We show that, in presence of half magnetic-flux FISDW state, the system exhibits topologically nontrivial phases, which can be characterized by a nonzero Chern number. The nontrivial evolution of the bulk bands with chemical potential in a topological phase transition is discussed. We show that the system can have a similar phase diagram which is discussed in the Haldane’s model. We suggest that the topological feature should be tested experimentally in this organic system. These studies enrich the theoretical research on topologically nontrivial phases in the Q1D lattice system as compared to the Haldane topological phase appearing in the two-dimensional lattices.
Grid topologies for the self-organizing map.
López-Rubio, Ezequiel; Díaz Ramos, Antonio
2014-08-01
The original Self-Organizing Feature Map (SOFM) has been extended in many ways to suit different goals and application domains. However, the topologies of the map lattice that we can found in literature are nearly always square or, more rarely, hexagonal. In this paper we study alternative grid topologies, which are derived from the geometrical theory of tessellations. Experimental results are presented for unsupervised clustering, color image segmentation and classification tasks, which show that the differences among the topologies are statistically significant in most cases, and that the optimal topology depends on the problem at hand. A theoretical interpretation of these results is also developed. PMID:24861385
Topological organization of (low-dimensional) chaos
Tufillaro, N.B.
1992-12-01
Recent progress toward classifying low-dimensional chaos measured from time series data is described. This classification theory assigns a template to the time series once the time series is embedded in three dimensions. The template describes the primary folding and stretching mechanisms of phase space responsible for the chaotic motion. Topological invariants of the unstable periodic orbits in the closure of the strange set are calculated from the (reconstructed) template. These topological invariants must be consistent with &ny model put forth to describe the time series data, and are useful in invalidating (or gaining confidence in) any model intended to describe the dynamical system generating the time series.
Topological organization of (low-dimensional) chaos
Tufillaro, N.B.
1992-01-01
Recent progress toward classifying low-dimensional chaos measured from time series data is described. This classification theory assigns a template to the time series once the time series is embedded in three dimensions. The template describes the primary folding and stretching mechanisms of phase space responsible for the chaotic motion. Topological invariants of the unstable periodic orbits in the closure of the strange set are calculated from the (reconstructed) template. These topological invariants must be consistent with ny model put forth to describe the time series data, and are useful in invalidating (or gaining confidence in) any model intended to describe the dynamical system generating the time series.
Topological Defects at the Graphene/h-BN interface Abnormally Enhance Its Thermal Conductance.
Liu, Xiangjun; Zhang, Gang; Zhang, Yong-Wei
2016-08-10
Low thermal conductance across interface is often the limiting factor in managing heat in many advanced device applications. The most commonly used approach to enhance the thermal conductance is to reduce/eliminate the interfacial structural defects. Using a graphene/h-BN (Gr/h-BN) interface, we show surprisingly that topological defects are able to enhance the thermal conductance across the interface. It is found that the phonon transmission across the Gr/h-BN interface with 5|7 defects is higher than that of the pristine interface, which is in strong contrast to the common notion that interface defects promote phonon scattering. By analyzing the strain distribution and phonon vibrational spectra, we find that this abnormal enhancement in interfacial thermal conductance originates from the localization of the stress fields arising from misfit dislocations and their out-of-plane deformations at the interface. In the presence of the defects, the overall mismatch strain is reduced. In addition, the out-of-plane deformations screen the long-ranged dislocation strain fields, resulting in the stress fields to be localized only at the cores of the defects. This abnormal mechanism provides a new dimension to enhance the interfacial thermal conductance in two-dimensional heterostructures. PMID:27387848
Organic Monolayer Protected Topological Surface State.
Yang, Hung-Hsiang; Chu, Yu-Hsun; Lu, Chun-I; Butler, Christopher John; Sankar, Raman; Chou, Fang-Cheng; Lin, Minn-Tsong
2015-10-14
Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)/Bi2Se3 and Fe/PTCDA/Bi2Se3 heterointerfaces are investigated using scanning tunneling microscopy and spectroscopy. The close-packed self-assembled PTCDA monolayer possesses big molecular band gap and weak molecule-substrate interactions, which leaves the Bi2Se3 topological surface state intact under PTCDA. Formation of Fe-PTCDA hybrids removes interactions between the Fe dopant and the Bi2Se3 surface, such as doping effects and Coulomb scattering. Our findings reveal the functionality of PTCDA to prevent dopant disturbances in the TSS and provide an effective alternative for interface designs of realistic TI devices. PMID:26393876
Sethi, Moksh; Pedersen, Mangor; Jackson, Graeme D
2016-03-01
Polymicrogyria is a significant malformation of cortical development with a high incidence of epilepsy and cognitive deficits. Graph theoretic analysis is a useful approach to studying network organization in brain disorders. In this study, we used task-free functional magnetic resonance imaging (fMRI) data from four patients with polymicrogyria and refractory epilepsy. Gray matter masks from structural MRI data were parcellated into 1,024 network nodes. Functional "connectomes" were obtained based on fMRI time series between the parcellated network nodes; network analysis was conducted using clustering coefficient, path length, node degree, and participation coefficient. These graph metrics were compared between nodes within polymicrogyric cortex and normal brain tissue in contralateral homologous cortical regions. Polymicrogyric nodes showed significantly increased clustering coefficient and characteristic path length. This is the first study using functional connectivity analysis in polymicrogyria--our results indicate a shift toward a regular network topology in polymicrogyric nodes. Regularized network topology has been demonstrated previously in patients with focal epilepsy and during focal seizures. Thus, we postulate that these network alterations predispose to seizures and may be relevant to cognitive deficits in patients with polymicrogyria. PMID:26763051
Topology and structural self-organization in folded proteins
NASA Astrophysics Data System (ADS)
Lundgren, M.; Krokhotin, Andrey; Niemi, Antti J.
2013-10-01
Topological methods are indispensable in theoretical studies of particle physics, condensed matter physics, and gravity. These powerful techniques have also been applied to biological physics. For example, knowledge of DNA topology is pivotal to the understanding as to how living cells function. Here, the biophysical repertoire of topological methods is extended, with the aim to understand and characterize the global structure of a folded protein. For this, the elementary concept of winding number of a vector field on a plane is utilized to introduce a topological quantity called the folding index of a crystallographic protein. It is observed that in the case of high resolution protein crystals, the folding index, when evaluated over the entire length of the crystallized protein backbone, has a very clear and strong propensity towards integer values. The observation proposes that the way how a protein folds into its biologically active conformation is a structural self-organization process with a topological facet that relates to the concept of solitons. It is proposed that the folding index has a potential to become a useful tool for the global, topological characterization of the folding pathways.
Absence of cytoglobin promotes multiple organ abnormalities in aged mice
Thuy, Le Thi Thanh; Van Thuy, Tuong Thi; Matsumoto, Yoshinari; Hai, Hoang; Ikura, Yoshihiro; Yoshizato, Katsutoshi; Kawada, Norifumi
2016-01-01
Cytoglobin (Cygb) was identified in hepatic stellate cells (HSCs) and pericytes of all organs; however, the effects of Cygb on cellular functions remain unclear. Here, we report spontaneous and age-dependent malformations in multiple organs of Cygb−/− mice. Twenty-six percent of young Cygb−/− mice (<1 year old) showed heart hypertrophy, cystic disease in the kidney or ovary, loss of balance, liver fibrosis and lymphoma. Furthermore, 71.3% (82/115) of aged Cygb−/− mice (1–2 years old) exhibited abnormalities, such as heart hypertrophy and cancer development in multiple organs; by contrast, 5.8% (4/68) of aged wild-type (WT) mice had abnormalities (p < 0.0001). Interestingly, serum and urine analysis demonstrated that the concentration of nitric oxide metabolites increased significantly in Cygb−/− mice, resulting in an imbalance in the oxidative stress and antioxidant defence system that was reversed by NG-monomethyl-L-arginine treatment. A senescent phenotype and evidence of DNA damage were found in primary HSCs and the liver of aged Cygb−/− mice. Moreover, compared with HSC+/+, HSC−/− showed high expression of Il-6 and chemokine mRNA when cocultured with mouse Hepa 1–6 cells. Thus, the absence of Cygb in pericytes provokes organ abnormalities, possibly via derangement of the nitric oxide and antioxidant defence system and through accelerated cellular senescence. PMID:27146058
Chen, Jian-Huai; Yao, Zhi-Jian; Qin, Jiao-Long; Yan, Rui; Hua, Ling-Ling; Lu, Qing
2016-01-01
Background: Most previous neuroimaging studies have focused on the structural and functional abnormalities of local brain regions in major depressive disorder (MDD). Moreover, the exactly topological organization of networks underlying MDD remains unclear. This study examined the aberrant global and regional topological patterns of the brain white matter networks in MDD patients. Methods: The diffusion tensor imaging data were obtained from 27 patients with MDD and 40 healthy controls. The brain fractional anisotropy-weighted structural networks were constructed, and the global network and regional nodal metrics of the networks were explored by the complex network theory. Results: Compared with the healthy controls, the brain structural network of MDD patients showed an intact small-world topology, but significantly abnormal global network topological organization and regional nodal characteristic of the network in MDD were found. Our findings also indicated that the brain structural networks in MDD patients become a less strongly integrated network with a reduced central role of some key brain regions. Conclusions: All these resulted in a less optimal topological organization of networks underlying MDD patients, including an impaired capability of local information processing, reduced centrality of some brain regions and limited capacity to integrate information across different regions. Thus, these global network and regional node-level aberrations might contribute to understanding the pathogenesis of MDD from the view of the brain network. PMID:26960371
Galvanomagnetic phenomena in organic conductors under topological phase transition
NASA Astrophysics Data System (ADS)
Galbova, O.; Peschansky, V. G.; Stepanenko, D. I.
2015-07-01
The magnetoresistance of layered organic conductors with a multisheet Fermi surface (FS) is studied theoretically under conditions of the Lifshitz topological transition, where the FS topology may change in response to external effects acting on the conductor, such as pressure or doping with impurity atoms. Using as an example the Fermi surface consisting of a cylinder and two planes, which are slightly corrugated along the projection of the momentum pz=p n along the normal to the layers n, we analyze the magnetic-field dependence of the resistance and the Hall field in a strong external magnetic field H, where the cyclotron frequency ωc of the conduction electrons is much higher than their collision frequency 1/τ. In the immediate vicinity of the topological transition, where the distance between the different sheets of the FS becomes small, an electron can move from one sheet of the FS to another with the probability w due to the magnetic breakdown. In this case, a quadratic increase of the electric resistance across the layers with magnetic field, which occurs in the absence of the magnetic breakdown, is replaced by a linear dependence on H for w ≥γ=1 /ωcτ , and then reaches saturation for (1 -w )≤γ . The Hall field depends substantially on the probability of a magnetic breakdown, but in the case of ωcτ≫1 , its asymptote is independent of τ for all values of w. At w = 1, the quasi-planar sheets of the Fermi surface touch the corrugated cylinders, and under further perturbation acting on the conductor, there occurs a break of a flat sheet along the line of contact. As a result, separate sections of the flat FS sheet together with the cut halves of the corrugated cylinder form a new corrugated cylinder with the sign of charge carriers reversed. This is not the only scenario of the Lifshitz topological transition. Studies of the Hall effect will allow us to obtain further important information on the nature of changes in the topological structure of
Topological organization of connectivity strength in the rat connectome.
van den Heuvel, Martijn P; Scholtens, Lianne H; de Reus, Marcel A
2016-04-01
The mammalian brain is a complex network of anatomically interconnected regions. Animal studies allow for an invasive measurement of the connections of these networks at the macroscale level by means of neuronal tracing of axonal projections, providing a unique opportunity for the formation of detailed 'connectome maps'. Here we analyzed the macroscale connectome of the rat brain, including detailed information on the macroscale interregional pathways between 67 cortical and subcortical regions as provided by the high-quality, open-access BAMS-II database on rat brain anatomical projections, focusing in particular on the non-uniform distribution of projection strength across pathways. First, network analysis confirmed a small-world, modular and rich club organization of the rat connectome; findings in clear support of previous studies on connectome organization in other mammalian species. More importantly, analyzing network properties of different connection weight classes, we extend previous observations by showing that pathways with different topological roles have significantly different levels of connectivity strength. Among other findings, intramodular connections are shown to display a higher connectivity strength than intermodular connections and hub-to-hub rich club connections are shown to include significantly stronger pathways than connections spanning between peripheral nodes. Furthermore, we show evidence indicating that edges of different weight classes display different topological structures, potentially suggesting varying roles and origins of pathways in the mammalian brain network. PMID:25697666
Topology-based clustering using polar self-organizing map.
Xu, Lu; Chow, Tommy W S; Ma, Eden W M
2015-04-01
Cluster analysis of unlabeled data sets has been recognized as a key research topic in varieties of fields. In many practical cases, no a priori knowledge is specified, for example, the number of clusters is unknown. In this paper, grid clustering based on the polar self-organizing map (PolSOM) is developed to automatically identify the optimal number of partitions. The data topology consisting of both the distance and density is exploited in the grid clustering. The proposed clustering method also provides a visual representation as PolSOM allows the characteristics of clusters to be presented as a 2-D polar map in terms of the data feature and value. Experimental studies on synthetic and real data sets demonstrate that the proposed algorithm provides higher clustering accuracy and lower computational cost compared with six conventional methods. PMID:25312942
Self-organized topology of recurrence-based complex networks
Yang, Hui Liu, Gang
2013-12-15
With the rapid technological advancement, network is almost everywhere in our daily life. Network theory leads to a new way to investigate the dynamics of complex systems. As a result, many methods are proposed to construct a network from nonlinear time series, including the partition of state space, visibility graph, nearest neighbors, and recurrence approaches. However, most previous works focus on deriving the adjacency matrix to represent the complex network and extract new network-theoretic measures. Although the adjacency matrix provides connectivity information of nodes and edges, the network geometry can take variable forms. The research objective of this article is to develop a self-organizing approach to derive the steady geometric structure of a network from the adjacency matrix. We simulate the recurrence network as a physical system by treating the edges as springs and the nodes as electrically charged particles. Then, force-directed algorithms are developed to automatically organize the network geometry by minimizing the system energy. Further, a set of experiments were designed to investigate important factors (i.e., dynamical systems, network construction methods, force-model parameter, nonhomogeneous distribution) affecting this self-organizing process. Interestingly, experimental results show that the self-organized geometry recovers the attractor of a dynamical system that produced the adjacency matrix. This research addresses a question, i.e., “what is the self-organizing geometry of a recurrence network?” and provides a new way to reproduce the attractor or time series from the recurrence plot. As a result, novel network-theoretic measures (e.g., average path length and proximity ratio) can be achieved based on actual node-to-node distances in the self-organized network topology. The paper brings the physical models into the recurrence analysis and discloses the spatial geometry of recurrence networks.
Self-organized topology of recurrence-based complex networks
NASA Astrophysics Data System (ADS)
Yang, Hui; Liu, Gang
2013-12-01
With the rapid technological advancement, network is almost everywhere in our daily life. Network theory leads to a new way to investigate the dynamics of complex systems. As a result, many methods are proposed to construct a network from nonlinear time series, including the partition of state space, visibility graph, nearest neighbors, and recurrence approaches. However, most previous works focus on deriving the adjacency matrix to represent the complex network and extract new network-theoretic measures. Although the adjacency matrix provides connectivity information of nodes and edges, the network geometry can take variable forms. The research objective of this article is to develop a self-organizing approach to derive the steady geometric structure of a network from the adjacency matrix. We simulate the recurrence network as a physical system by treating the edges as springs and the nodes as electrically charged particles. Then, force-directed algorithms are developed to automatically organize the network geometry by minimizing the system energy. Further, a set of experiments were designed to investigate important factors (i.e., dynamical systems, network construction methods, force-model parameter, nonhomogeneous distribution) affecting this self-organizing process. Interestingly, experimental results show that the self-organized geometry recovers the attractor of a dynamical system that produced the adjacency matrix. This research addresses a question, i.e., "what is the self-organizing geometry of a recurrence network?" and provides a new way to reproduce the attractor or time series from the recurrence plot. As a result, novel network-theoretic measures (e.g., average path length and proximity ratio) can be achieved based on actual node-to-node distances in the self-organized network topology. The paper brings the physical models into the recurrence analysis and discloses the spatial geometry of recurrence networks.
Self-organized pseudo-graphene on grain boundaries in topological band insulators
NASA Astrophysics Data System (ADS)
Slager, Robert-Jan; Juričić, Vladimir; Lahtinen, Ville; Zaanen, Jan
2016-06-01
Semimetals are characterized by nodal band structures that give rise to exotic electronic properties. The stability of Dirac semimetals, such as graphene in two spatial dimensions, requires the presence of lattice symmetries, while akin to the surface states of topological band insulators, Weyl semimetals in three spatial dimensions are protected by band topology. Here we show that in the bulk of topological band insulators, self-organized topologically protected semimetals can emerge along a grain boundary, a ubiquitous extended lattice defect in any crystalline material. In addition to experimentally accessible electronic transport measurements, these states exhibit a valley anomaly in two dimensions influencing edge spin transport, whereas in three dimensions they appear as graphenelike states that may exhibit an odd-integer quantum Hall effect. The general mechanism underlying these semimetals—the hybridization of spinon modes bound to the grain boundary—suggests that topological semimetals can emerge in any topological material where lattice dislocations bind localized topological modes.
Defining the Proton Topology of the Zr6-Based Metal-Organic Framework NU-1000.
Planas, Nora; Mondloch, Joseph E; Tussupbayev, Samat; Borycz, Joshua; Gagliardi, Laura; Hupp, Joseph T; Farha, Omar K; Cramer, Christopher J
2014-11-01
Metal-organic frameworks (MOFs) constructed from Zr6-based nodes have recently received considerable attention given their exceptional thermal, chemical, and mechanical stability. Because of this, the structural diversity of Zr6-based MOFs has expanded considerably and in turn given rise to difficulty in their precise characterization. In particular it has been difficult to assign where protons (needed for charge balance) reside on some Zr6-based nodes. Elucidating the precise proton topologies in Zr6-based MOFs will have wide ranging implications in defining their chemical reactivity, acid/base characteristics, conductivity, and chemical catalysis. Here we have used a combined quantum mechanical and experimental approach to elucidate the precise proton topology of the Zr6-based framework NU-1000. Our data indicate that a mixed node topology, [Zr6(μ3-O)4(μ3-OH)4(OH)4 (OH2)4](8+), is preferred and simultaneously rule out five alternative node topologies. PMID:26278741
Topological insulators based on 2D shape-persistent organic ligand complexes.
Zhou, Qionghua; Wang, Jinlan; Chwee, Tsz Sian; Wu, Gang; Wang, Xiaobai; Ye, Qun; Xu, Jianwei; Yang, Shuo-Wang
2015-01-14
Topological insulators (TIs) represent an exciting new class of materials with potential applications in spintronics and quantum computing. In this work, we present a theoretical study on a new family of two dimensional (2D) nanomaterials based on the coordination of shape persistent organic ligands (SPOLs) to heavy transition metal ions such as Pd(2+) and Pt(2+). These 2D structures may be readily fabricated and are expected to be stable under normal atmospheric conditions. From first principles calculations and tight-binding model simulations carried out to characterize the bulk band structures, edge states, spin Chern numbers, and the Z2 topological invariants, we were able to identify candidates with non-trivial topological properties that may serve as topological insulators in real world applications. PMID:25429668
Topological insulators based on 2D shape-persistent organic ligand complexes
NASA Astrophysics Data System (ADS)
Zhou, Qionghua; Wang, Jinlan; Chwee, Tsz Sian; Wu, Gang; Wang, Xiaobai; Ye, Qun; Xu, Jianwei; Yang, Shuo-Wang
2014-12-01
Topological insulators (TIs) represent an exciting new class of materials with potential applications in spintronics and quantum computing. In this work, we present a theoretical study on a new family of two dimensional (2D) nanomaterials based on the coordination of shape persistent organic ligands (SPOLs) to heavy transition metal ions such as Pd2+ and Pt2+. These 2D structures may be readily fabricated and are expected to be stable under normal atmospheric conditions. From first principles calculations and tight-binding model simulations carried out to characterize the bulk band structures, edge states, spin Chern numbers, and the Z2 topological invariants, we were able to identify candidates with non-trivial topological properties that may serve as topological insulators in real world applications.Topological insulators (TIs) represent an exciting new class of materials with potential applications in spintronics and quantum computing. In this work, we present a theoretical study on a new family of two dimensional (2D) nanomaterials based on the coordination of shape persistent organic ligands (SPOLs) to heavy transition metal ions such as Pd2+ and Pt2+. These 2D structures may be readily fabricated and are expected to be stable under normal atmospheric conditions. From first principles calculations and tight-binding model simulations carried out to characterize the bulk band structures, edge states, spin Chern numbers, and the Z2 topological invariants, we were able to identify candidates with non-trivial topological properties that may serve as topological insulators in real world applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05247a
Modeling self-organization of communication and topology in Social Networks
NASA Astrophysics Data System (ADS)
Sneppen, Kim
2007-03-01
We introduce a model of self-organization of communication and topology in social networks with a feedback between different communication habits and the topology. To study this feedback, we let agents communicate to build a perception of a network and use this information to create strategic links. We observe a narrow distribution of links when the communication is low and a system with a broad distribution of links when the communication is high. We also analyze the outcome of chatting, cheating, and lying, as strategies to get better access to information in the network. Chatting, although only adopted by a few agents, gives a global gain in the system. Contrary, in a system with too many liars a global loss is inevitable. References: M. Rosvall and K. Sneppen. ``Modeling self-organization of communication and topology in social networks.'' Phys. Rev. E 74:16108 (2006)
Self-organized charge puddles in a three-dimensional topological material
NASA Astrophysics Data System (ADS)
Borgwardt, N.; Lux, J.; Vergara, I.; Wang, Zhiwei; Taskin, A. A.; Segawa, Kouji; van Loosdrecht, P. H. M.; Ando, Yoichi; Rosch, A.; Grüninger, M.
2016-06-01
In three-dimensional (3D) topological materials, tuning of the bulk chemical potential is of crucial importance for observing their topological properties; for example, Weyl semimetals require chemical-potential tuning to the bulk Weyl nodes, while 3D topological insulators require tuning into the bulk band gap. Such tuning is often realized by compensation, i.e., by balancing the density of acceptors and donors. Here we show that in such a compensated 3D topological material, the possibility of local chemical-potential tuning is limited by the formation of self-organized charge puddles. The puddles arise from large fluctuations of the Coulomb potential of donors and acceptors. Their emergence is akin to the case of graphene, where charge puddles are already established as a key paradigm. However, there is an important difference: Puddles in graphene are simply dictated by the static distribution of defects in the substrate, whereas we find that puddles in 3D systems self-organize in a nontrivial way and show a strong temperature dependence. Such a self-organization is revealed by measurements of the optical conductivity of the bulk-insulating 3D topological insulator BiSbTeSe2, which pinpoints the presence of puddles at low temperatures as well as their surprising "evaporation" on a temperature scale of 30-40 K. The experimental observation is described semiquantitatively by Monte Carlo simulations. These show that the temperature scale is set by the Coulomb interaction between neighboring dopants and that puddles are destroyed by thermally activated carriers in a highly nonlinear screening process. This result indicates that understanding charge puddles is crucial for the control of the chemical potential in compensated 3D topological materials.
Number theoretic example of scale-free topology inducing self-organized criticality.
Luque, Bartolo; Miramontes, Octavio; Lacasa, Lucas
2008-10-10
In this Letter we present a general mechanism by which simple dynamics running on networks become self-organized critical for scale-free topologies. We illustrate this mechanism with a simple arithmetic model of division between integers, the division model. This is the simplest self-organized critical model advanced so far, and in this sense it may help to elucidate the mechanism of self-organization to criticality. Its simplicity allows analytical tractability, characterizing several scaling relations. Furthermore, its mathematical nature brings about interesting connections between statistical physics and number theoretical concepts. We show how this model can be understood as a self-organized stochastic process embedded on a network, where the onset of criticality is induced by the topology. PMID:18999649
Chromatin topology is coupled to Polycomb group protein subnuclear organization.
Wani, Ajazul H; Boettiger, Alistair N; Schorderet, Patrick; Ergun, Ayla; Münger, Christine; Sadreyev, Ruslan I; Zhuang, Xiaowei; Kingston, Robert E; Francis, Nicole J
2016-01-01
The genomes of metazoa are organized at multiple scales. Many proteins that regulate genome architecture, including Polycomb group (PcG) proteins, form subnuclear structures. Deciphering mechanistic links between protein organization and chromatin architecture requires precise description and mechanistic perturbations of both. Using super-resolution microscopy, here we show that PcG proteins are organized into hundreds of nanoscale protein clusters. We manipulated PcG clusters by disrupting the polymerization activity of the sterile alpha motif (SAM) of the PcG protein Polyhomeotic (Ph) or by increasing Ph levels. Ph with mutant SAM disrupts clustering of endogenous PcG complexes and chromatin interactions while elevating Ph level increases cluster number and chromatin interactions. These effects can be captured by molecular simulations based on a previously described chromatin polymer model. Both perturbations also alter gene expression. Organization of PcG proteins into small, abundant clusters on chromatin through Ph SAM polymerization activity may shape genome architecture through chromatin interactions. PMID:26759081
Chromatin topology is coupled to Polycomb group protein subnuclear organization
Wani, Ajazul H.; Boettiger, Alistair N.; Schorderet, Patrick; Ergun, Ayla; Münger, Christine; Sadreyev, Ruslan I.; Zhuang, Xiaowei; Kingston, Robert E.; Francis, Nicole J.
2016-01-01
The genomes of metazoa are organized at multiple scales. Many proteins that regulate genome architecture, including Polycomb group (PcG) proteins, form subnuclear structures. Deciphering mechanistic links between protein organization and chromatin architecture requires precise description and mechanistic perturbations of both. Using super-resolution microscopy, here we show that PcG proteins are organized into hundreds of nanoscale protein clusters. We manipulated PcG clusters by disrupting the polymerization activity of the sterile alpha motif (SAM) of the PcG protein Polyhomeotic (Ph) or by increasing Ph levels. Ph with mutant SAM disrupts clustering of endogenous PcG complexes and chromatin interactions while elevating Ph level increases cluster number and chromatin interactions. These effects can be captured by molecular simulations based on a previously described chromatin polymer model. Both perturbations also alter gene expression. Organization of PcG proteins into small, abundant clusters on chromatin through Ph SAM polymerization activity may shape genome architecture through chromatin interactions. PMID:26759081
Dalapati, Sasanka; Addicoat, Matthew; Jin, Shangbin; Sakurai, Tsuneaki; Gao, Jia; Xu, Hong; Irle, Stephan; Seki, Shu; Jiang, Donglin
2015-01-01
Covalent organic frameworks (COFs) are an emerging class of highly ordered porous polymers with many potential applications. They are currently designed and synthesized through hexagonal and tetragonal topologies, limiting the access to and exploration of new structures and properties. Here, we report that a triangular topology can be developed for the rational design and synthesis of a new class of COFs. The triangular topology features small pore sizes down to 12 Å, which is among the smallest pores for COFs reported to date, and high π-column densities of up to 0.25 nm−2, which exceeds those of supramolecular columnar π-arrays and other COF materials. These crystalline COFs facilitate π-cloud delocalization and are highly conductive, with a hole mobility that is among the highest reported for COFs and polygraphitic ensembles. PMID:26178865
NASA Astrophysics Data System (ADS)
Dalapati, Sasanka; Addicoat, Matthew; Jin, Shangbin; Sakurai, Tsuneaki; Gao, Jia; Xu, Hong; Irle, Stephan; Seki, Shu; Jiang, Donglin
2015-07-01
Covalent organic frameworks (COFs) are an emerging class of highly ordered porous polymers with many potential applications. They are currently designed and synthesized through hexagonal and tetragonal topologies, limiting the access to and exploration of new structures and properties. Here, we report that a triangular topology can be developed for the rational design and synthesis of a new class of COFs. The triangular topology features small pore sizes down to 12 Å, which is among the smallest pores for COFs reported to date, and high π-column densities of up to 0.25 nm-2, which exceeds those of supramolecular columnar π-arrays and other COF materials. These crystalline COFs facilitate π-cloud delocalization and are highly conductive, with a hole mobility that is among the highest reported for COFs and polygraphitic ensembles.
Dalapati, Sasanka; Addicoat, Matthew; Jin, Shangbin; Sakurai, Tsuneaki; Gao, Jia; Xu, Hong; Irle, Stephan; Seki, Shu; Jiang, Donglin
2015-01-01
Covalent organic frameworks (COFs) are an emerging class of highly ordered porous polymers with many potential applications. They are currently designed and synthesized through hexagonal and tetragonal topologies, limiting the access to and exploration of new structures and properties. Here, we report that a triangular topology can be developed for the rational design and synthesis of a new class of COFs. The triangular topology features small pore sizes down to 12 Å, which is among the smallest pores for COFs reported to date, and high π-column densities of up to 0.25 nm(-2), which exceeds those of supramolecular columnar π-arrays and other COF materials. These crystalline COFs facilitate π-cloud delocalization and are highly conductive, with a hole mobility that is among the highest reported for COFs and polygraphitic ensembles. PMID:26178865
Chersi, Fabian; Ferro, Marcello; Pezzulo, Giovanni; Pirrelli, Vito
2014-07-01
A growing body of evidence in cognitive psychology and neuroscience suggests a deep interconnection between sensory-motor and language systems in the brain. Based on recent neurophysiological findings on the anatomo-functional organization of the fronto-parietal network, we present a computational model showing that language processing may have reused or co-developed organizing principles, functionality, and learning mechanisms typical of premotor circuit. The proposed model combines principles of Hebbian topological self-organization and prediction learning. Trained on sequences of either motor or linguistic units, the network develops independent neuronal chains, formed by dedicated nodes encoding only context-specific stimuli. Moreover, neurons responding to the same stimulus or class of stimuli tend to cluster together to form topologically connected areas similar to those observed in the brain cortex. Simulations support a unitary explanatory framework reconciling neurophysiological motor data with established behavioral evidence on lexical acquisition, access, and recall. PMID:24935737
Milan, Alberto; Avenatti, Eleonora; Puglisi, Elisabetta; Abram, Sara; Magnino, Corrado; Naso, Diego; Tosello, Francesco; Fabbri, Ambra; Vairo, Alessandro; Mulatero, Paolo; Rabbia, Franco; Veglio, Franco
2012-01-01
Hypertension-related cardiac organ damage, other than left ventricular (LV) hypertrophy (LVH), has been described: in particular, concentric remodeling, LV diastolic dysfunction (DD), and left atrial (LA) enlargement are significantly associated with cardiovascular morbility and mortality in different populations. This study evaluated the prevalence of these latter morphofunctional abnormalities, in never-treated essential hypertensive patients and the role of such a serial assessment of hypertensive cardiac damage in improving cardiovascular risk stratification in these patients. A total of 100 never-treated essential hypertensive subjects underwent a complete clinical and echocardiographic evaluation. Left ventricular morphology, systolic and diastolic function, and LA dimension (linear and volume) were evaluated by echocardiography. Left ventricular hypertrophy was present in 14% of the patients, whereas concentric remodeling was present in 25% of the subjects. Among patients free from LV morphology abnormalities, the most frequent abnormality was LA enlargement (global prevalence 57%); the percentage of patients with at least one parameter consistent with DD was 22% in the entire population, but DD was present as the only cardiac abnormality in 1% of our patient. Left atrial volume indexed for body surface area was the most sensitive parameter in identifying hypertension-related cardiac modification. The global prevalence of cardiac alteration reached 73% in never-treated hypertensive patients. Left ventricular remodeling and LA enlargement evaluation may grant a better assessment of cardiac organ damage and cardiovascular risk stratification of hypertensive patients without evidence of LVH after routine examination. PMID:22738434
Vértes, Petra E; Bullmore, Edward T
2015-01-01
Background We first give a brief introduction to graph theoretical analysis and its application to the study of brain network topology or connectomics. Within this framework, we review the existing empirical data on developmental changes in brain network organization across a range of experimental modalities (including structural and functional MRI, diffusion tensor imaging, magnetoencephalography and electroencephalography in humans). Synthesis We discuss preliminary evidence and current hypotheses for how the emergence of network properties correlates with concomitant cognitive and behavioural changes associated with development. We highlight some of the technical and conceptual challenges to be addressed by future developments in this rapidly moving field. Given the parallels previously discovered between neural systems across species and over a range of spatial scales, we also review some recent advances in developmental network studies at the cellular scale. We highlight the opportunities presented by such studies and how they may complement neuroimaging in advancing our understanding of brain development. Finally, we note that many brain and mind disorders are thought to be neurodevelopmental in origin and that charting the trajectory of brain network changes associated with healthy development also sets the stage for understanding abnormal network development. Conclusions We therefore briefly review the clinical relevance of network metrics as potential diagnostic markers and some recent efforts in computational modelling of brain networks which might contribute to a more mechanistic understanding of neurodevelopmental disorders in future. PMID:25441756
Metallacarborane-Based Metal-Organic Framework with a Complex Topology
Kennedy, RD; Clingerman, DJ; Morris, W; Wilmer, CE; Sarjeant, AA; Stern, CL; O'Keeffe, M; Snurr, RQ; Hupp, JT; Farha, OK; Mirkin, CA
2014-03-01
The long, linear cobalt(III) bis(dicarbollide)-based bis(isophthalic acid) anion was synthesized as a tetraphenylphosphonium salt in five steps from 8-iodo-closo-1,2-C2B10H11. The solvothermal reaction between the anionic bis(isophthalic acid) linker and copper(II) nitrate in acidified DMF yielded single crystals. Despite the tendency for copper(II) and analogous linear tetraacids to form members of an isoreticular family of metal-organic frameworks (MOFs) with the fof topology, single-crystal X-ray diffraction analysis revealed the growth of three different frameworks. These MOFs, NU-150, NU-151, and NU-152, have three distinct topologies: fof, sty, and hbk, respectively. NU-152 has a novel quadrinodal topology in which cuboctahedral coordination polyhedra are each connected to 10 neighboring polyhedra via the cobalt bis(dicarbollide) portions of the linkers. The formation of these frameworks illustrates the limitations of structure prediction in MOP chemistry and the possibility of using flexible linkers to generate unexpected topologies. Furthermore, this work represents the first example of the incorporation of an anionic bis(dicarbollide) unit into a MOF.
Use of the self-organizing feature map to diagnose abnormal engineering change
NASA Astrophysics Data System (ADS)
Lu, Ruei-Shan; Wu, Zhi-Ting; Peng, Kuo-Wei; Yu, Tai-Yi
2015-07-01
This study established identification manners with self-organizing feature map (SOM) to achieve the goal of monitoring Engineering Change (EC) based on historical data of a company that specializes in computers and peripherals. The product life cycle of this company is 3-6 months. The historical data were divided into three parts, each covering four months. The first part, comprising 2,343 records from January to April (the training period), comprise the Control Group. The second and third parts comprise Experimental Groups (EG) 1 and 2, respectively. For EG 1 and 2, the successful rate of recognizing information on abnormal ECs was approximately 96% and 95%, respectively. This paper shows the importance and screening procedures of abnormal engineering change for a particular company specializing in computers and peripherals.
Deng, Yanjia; Shi, Lin; Lei, Yi; Wang, Defeng
2016-09-01
Altered regional activation of high-level visual (HLV) cortices in patients with Alzheimer's disease (AD) or mild cognitive impairment (MCI) has been well documented in previous fMRI studies, which led us to investigate the underlying alteration of the HLV networks in the terms of intrinsic interaction and topological organization. First, the activation likelihood estimation, a coordinate-based meta-analysis approach, was used to define the cortical regions/nodes included in HLV networks of "what" and "where" visions. Secondly, the acquired HLV regions were used as seeds to calculate their interregional resting-state functional connectivities (RSFCs) based on the temporal correlation of rs-functional MRI (rs-fMRI) time series. Here, the rs-fMRI data of AD (n=30), late MCI (n=35), early MCI (n=52) and matched healthy controls (n=44) were obtained from the Alzheimer's Disease Neuroimaging Initiative dataset. Finally, based on the calculated pair-wise RSFCs, the "what" and "where" HLV networks were respectively constructed, and their topological properties were calculated and analyzed among groups using the graph theory method. The results demonstrated increased clustering coefficient combined with a prolonged characteristic path length of the "where" visual network in AD patients. No significant alternation of the "what" visual network was found among the groups. These results suggest that the abnormality of the HLV networks could be a late-stage outcome in AD and that the "where" visual network may be more susceptible to the AD-related neuropathological changes than the "what" visual network. In addition, the dysfunction of the "where" network is found to be characterized by a decreased integration combined with an increased local segregation. PMID:27461791
Intrinsic Two-Dimensional Organic Topological Insulators in Metal-Dicyanoanthracene Lattices.
Zhang, L Z; Wang, Z F; Huang, B; Cui, B; Wang, Zhiming; Du, S X; Gao, H-J; Liu, Feng
2016-03-01
We predict theoretical existence of intrinsic two-dimensional organic topological insulator (OTI) states in Cu-dicyanoanthracene (DCA) lattice, a system that has also been grown experimentally on Cu substrate, based on first-principle density functional theory calculations. The pz-orbital Kagome bands having a Dirac point lying exactly at the Fermi level are found in the freestanding Cu-DCA lattice. The tight-binding model analysis, the calculated Chern numbers, and the semi-infinite Dirac edge states within the spin-orbit coupling gaps all confirm its intrinsic topological properties. The intrinsic TI states are found to originate from a proper number of electrons filling of the hybridized bands from Cu atomic and DCA molecular orbitals based on which similar lattices containing noble metal atoms (Au and Cu) and those molecules with two CN groups (DCA and cyanogens) are all predicted to be intrinsic OTIs. PMID:26866565
Self-organizing Ising model of artificial financial markets with small-world network topology
NASA Astrophysics Data System (ADS)
Zhao, Haijie; Zhou, Jie; Zhang, Anghui; Su, Guifeng; Zhang, Yi
2013-01-01
We study a self-organizing Ising-like model of artificial financial markets with underlying small-world (SW) network topology. The asset price dynamics results from the collective decisions of interacting agents which are located on a small-world complex network (the nodes symbolize the agents of a financial market). The model incorporates the effects of imitation, the impact of external news and private information. We also investigate the influence of different network topologies, from regular lattice to random graph, on the asset price dynamics by adjusting the probability of the rewiring procedure. We find that a specific combination of model parameters reproduce main stylized facts of real-world financial markets.
Self-organization processes and topological defects in nanolayers in a nematic liquid crystal
Chuvyrov, A. N.; Girfanova, F. M. Mal'tsev, I. S.
2008-05-15
Atomic force microscopy is used to study the self-organization processes that occur during the formation of topological defects in nanomolecular layers in a nematic liquid crystal with the homeotropic orientation of its molecules with respect to the substrate. In this case, a smectic monolayer with a thickness of one molecule length (about 2.2 nm) forms on the substrate, and a nanomolecular layer of a nematic liquid crystal forms above this monolayer. In such virtually two-dimensional layers, numerous different nanoclusters, namely, hut structures, pyramids, raft structures with symmetry C{sub nm} (where n = 2, 4, 5, 6, 7, ?, {infinity}), cones, and nanopools, form [1]. They have a regular shape close to the geometry of solid crystals. Modulated linear structures and topological point defects appear spontaneously in the nanopools and raft structures.
Controlling the Spin Texture of Topological Insulators by Rational Design of Organic Molecules.
Jakobs, Sebastian; Narayan, Awadhesh; Stadtmüller, Benjamin; Droghetti, Andrea; Rungger, Ivan; Hor, Yew S; Klyatskaya, Svetlana; Jungkenn, Dominik; Stöckl, Johannes; Laux, Martin; Monti, Oliver L A; Aeschlimann, Martin; Cava, Robert J; Ruben, Mario; Mathias, Stefan; Sanvito, Stefano; Cinchetti, Mirko
2015-09-01
We present a rational design approach to customize the spin texture of surface states of a topological insulator. This approach relies on the extreme multifunctionality of organic molecules that are used to functionalize the surface of the prototypical topological insulator (TI) Bi2Se3. For the rational design we use theoretical calculations to guide the choice and chemical synthesis of appropriate molecules that customize the spin texture of Bi2Se3. The theoretical predictions are then verified in angular-resolved photoemission experiments. We show that, by tuning the strength of molecule-TI interaction, the surface of the TI can be passivated, the Dirac point can energetically be shifted at will, and Rashba-split quantum-well interface states can be created. These tailored interface properties-passivation, spin-texture tuning, and creation of hybrid interface states-lay a solid foundation for interface-assisted molecular spintronics in spin-textured materials. PMID:26262825
Kostcheev, Serguei; Turover, Daniel; Salas-Montiel, Rafael; Nomenyo, Komla; Gokarna, Anisha; Lerondel, Gilles
2014-01-01
Summary Our aim was to elaborate a novel method for fully controllable large-scale nanopatterning. We investigated the influence of the surface topology, i.e., a pre-pattern of hydrogen silsesquioxane (HSQ) posts, on the self-organization of polystyrene beads (PS) dispersed over a large surface. Depending on the post size and spacing, long-range ordering of self-organized polystyrene beads is observed wherein guide posts were used leading to single crystal structure. Topology assisted self-organization has proved to be one of the solutions to obtain large-scale ordering. Besides post size and spacing, the colloidal concentration and the nature of solvent were found to have a significant effect on the self-organization of the PS beads. Scanning electron microscope and associated Fourier transform analysis were used to characterize the morphology of the ordered surfaces. Finally, the production of silicon molds is demonstrated by using the beads as a template for dry etching. PMID:25161854
Thangavelautham, Jekanthan; D'Eleuterio, Gabriele M T
2012-04-01
A key challenge in evolving control systems for robots using neural networks is training tractability. Evolving monolithic fixed topology neural networks is shown to be intractable with limited supervision in high dimensional search spaces. Common strategies to overcome this limitation are to provide more supervision by encouraging particular solution strategies, manually decomposing the task and segmenting the search space and network. These strategies require a supervisor with domain knowledge and may not be feasible for difficult tasks where novel concepts are required. The alternate strategy is to use self-organized task decomposition to solve difficult tasks with limited supervision. The artificial neural tissue (ANT) approach presented here uses self-organized task decomposition to solve tasks. ANT inspired by neurobiology combines standard neural networks with a novel wireless signaling scheme modeling chemical diffusion of neurotransmitters. These chemicals are used to dynamically activate and inhibit wired network of neurons using a coarse-coding framework. Using only a global fitness function that does not encourage a predefined solution, modular networks of neurons are shown to self-organize and perform task decomposition. This approach solves the sign-following task found to be intractable with conventional fixed and variable topology networks. In this paper, key attributes of the ANT architecture that perform self-organized task decomposition are shown. The architecture is robust and scalable to number of neurons, synaptic connections, and initialization parameters. PMID:24805039
Topological insulator Bi2Te3 films synthesized by metal organic chemical vapor deposition
NASA Astrophysics Data System (ADS)
Cao, Helin; Venkatasubramanian, Rama; Liu, Chang; Pierce, Jonathan; Yang, Haoran; Zahid Hasan, M.; Wu, Yue; Chen, Yong P.
2012-10-01
Topological insulator (TI) materials such as Bi2Te3 and Bi2Se3 have attracted strong recent interests. Large scale, high quality TI thin films are important for developing TI-based device applications. In this work, structural and electronic properties of Bi2Te3 thin films deposited by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrates were characterized via x-ray diffraction (XRD), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and electronic transport measurements. The characteristic topological surface states with a single Dirac cone have been clearly revealed in the electronic band structure measured by ARPES, confirming the TI nature of the MOCVD Bi2Te3 films. Resistivity and Hall effect measurements have demonstrated relatively high bulk carrier mobility of ˜350 cm2/Vs at 300 K and ˜7400 cm2/Vs at 15 K. We have also measured the Seebeck coefficient of the films. Our demonstration of high quality topological insulator films grown by a simple and scalable method is of interests for both fundamental research and practical applications of thermoelectric and TI materials.
Exploiting data topology in visualization and clustering of self-organizing maps.
Taşdemir, Kadim; Merényi, Erzsébet
2009-04-01
The self-organizing map (SOM) is a powerful method for visualization, cluster extraction, and data mining. It has been used successfully for data of high dimensionality and complexity where traditional methods may often be insufficient. In order to analyze data structure and capture cluster boundaries from the SOM, one common approach is to represent the SOM's knowledge by visualization methods. Different aspects of the information learned by the SOM are presented by existing methods, but data topology, which is present in the SOM's knowledge, is greatly underutilized. We show in this paper that data topology can be integrated into the visualization of the SOM and thereby provide a more elaborate view of the cluster structure than existing schemes. We achieve this by introducing a weighted Delaunay triangulation (a connectivity matrix) and draping it over the SOM. This new visualization, CONNvis, also shows both forward and backward topology violations along with the severity of forward ones, which indicate the quality of the SOM learning and the data complexity. CONNvis greatly assists in detailed identification of cluster boundaries. We demonstrate the capabilities on synthetic data sets and on a real 8-D remote sensing spectral image. PMID:19228556
Topological organization of the human brain functional connectome across the lifespan.
Cao, Miao; Wang, Jin-Hui; Dai, Zheng-Jia; Cao, Xiao-Yan; Jiang, Li-Li; Fan, Feng-Mei; Song, Xiao-Wei; Xia, Ming-Rui; Shu, Ni; Dong, Qi; Milham, Michael P; Castellanos, F Xavier; Zuo, Xi-Nian; He, Yong
2014-01-01
Human brain function undergoes complex transformations across the lifespan. We employed resting-state functional MRI and graph-theory approaches to systematically chart the lifespan trajectory of the topological organization of human whole-brain functional networks in 126 healthy individuals ranging in age from 7 to 85 years. Brain networks were constructed by computing Pearson's correlations in blood-oxygenation-level-dependent temporal fluctuations among 1024 parcellation units followed by graph-based network analyses. We observed that the human brain functional connectome exhibited highly preserved non-random modular and rich club organization over the entire age range studied. Further quantitative analyses revealed linear decreases in modularity and inverted-U shaped trajectories of local efficiency and rich club architecture. Regionally heterogeneous age effects were mainly located in several hubs (e.g., default network, dorsal attention regions). Finally, we observed inverse trajectories of long- and short-distance functional connections, indicating that the reorganization of connectivity concentrates and distributes the brain's functional networks. Our results demonstrate topological changes in the whole-brain functional connectome across nearly the entire human lifespan, providing insights into the neural substrates underlying individual variations in behavior and cognition. These results have important implications for disease connectomics because they provide a baseline for evaluating network impairments in age-related neuropsychiatric disorders. PMID:24333927
Contribution of Topological Domains and Loop Formation to 3D Chromatin Organization
Ea, Vuthy; Baudement, Marie-Odile; Lesne, Annick; Forné, Thierry
2015-01-01
Recent investigations on 3D chromatin folding revealed that the eukaryote genomes are both highly compartmentalized and extremely dynamic. This review presents the most recent advances in topological domains’ organization of the eukaryote genomes and discusses the relationship to chromatin loop formation. CTCF protein appears as a central factor of these two organization levels having either a strong insulating role at TAD borders, or a weaker architectural role in chromatin loop formation. TAD borders directly impact on chromatin dynamics by restricting contacts within specific genomic portions thus confining chromatin loop formation within TADs. We discuss how sub-TAD chromatin dynamics, constrained into a recently described statistical helix conformation, can produce functional interactions by contact stabilization. PMID:26226004
Kitajima, Y; Inoue, S; Yaoita, H
1989-01-01
Distinctive abnormality in the organization of keratin intermediate filaments (KIFs) was found for the first time in cultured epidermal keratinocytes from two patients with hereditary epidermolysis bullosa simplex (EBS), which showed cleavages above the basement membrane zone due to the fragility of basal cells. KIFs in EBS keratinocytes revealed an irregular radial arrangement composed of sparse but thick KIF bundles. Furthermore, these KIF bundles in many cells changed into numerous ball-like keratin aggregates and disappeared beyond these keratin aggregates in the peripheral cytoplasm. Electron microscopy of cultured EBS keratinocytes showed that many ball-like structures consisting of fine filaments or granules or homogeneous substances were scattered in the peripheral regions of the cell attaching to the dish, and intermediate filaments appeared to be emanating from or surrounding the structures. These ball-like keratin aggregates have never been observed in normal human keratinocytes. PMID:2471468
Eya1-deficient mice lack ears and kidneys and show abnormal apoptosis of organ primordia.
Xu, P X; Adams, J; Peters, H; Brown, M C; Heaney, S; Maas, R
1999-09-01
Haploinsufficiency for human EYA1, a homologue of the Drosophila melanogaster gene eyes absent (eya), results in the dominantly inherited disorders branchio-oto-renal (BOR) syndrome and branchio-oto (BO) syndrome, which are characterized by craniofacial abnormalities and hearing loss with (BOR) or without (BO) kidney defects. To understand the developmental pathogenesis of organs affected in these syndromes, we inactivated the gene Eya1 in mice. Eya1 heterozygotes show renal abnormalities and a conductive hearing loss similar to BOR syndrome, whereas Eya1 homozygotes lack ears and kidneys due to defective inductive tissue interactions and apoptotic regression of the organ primordia. Inner ear development in Eya1 homozygotes arrests at the otic vesicle stage and all components of the inner ear and specific cranial sensory ganglia fail to form. In the kidney, Eya1 homozygosity results in an absence of ureteric bud outgrowth and a subsequent failure of metanephric induction. Gdnf expression, which is required to direct ureteric bud outgrowth via activation of the c-ret Rtk (refs 5, 6, 7, 8), is not detected in Eya1-/- metanephric mesenchyme. In Eya1-/- ear and kidney development, Six but not Pax expression is Eya1 dependent, similar to a genetic pathway elucidated in the Drosophila eye imaginal disc. Our results indicate that Eya1 controls critical early inductive signalling events involved in ear and kidney formation and integrate Eya1 into the genetic regulatory cascade controlling kidney formation upstream of Gdnf. In addition, our results suggest that an evolutionarily conserved Pax-Eya-Six regulatory hierarchy is used in mammalian ear and kidney development. PMID:10471511
Congenital hydrocephalus and abnormal subcommissural organ development in Sox3 transgenic mice.
Lee, Kristie; Tan, Jacqueline; Morris, Michael B; Rizzoti, Karine; Hughes, James; Cheah, Pike See; Felquer, Fernando; Liu, Xuan; Piltz, Sandra; Lovell-Badge, Robin; Thomas, Paul Q
2012-01-01
Congenital hydrocephalus (CH) is a life-threatening medical condition in which excessive accumulation of CSF leads to ventricular expansion and increased intracranial pressure. Stenosis (blockage) of the Sylvian aqueduct (Aq; the narrow passageway that connects the third and fourth ventricles) is a common form of CH in humans, although the genetic basis of this condition is unknown. Mouse models of CH indicate that Aq stenosis is associated with abnormal development of the subcommmissural organ (SCO) a small secretory organ located at the dorsal midline of the caudal diencephalon. Glycoproteins secreted by the SCO generate Reissner's fibre (RF), a thread-like structure that descends into the Aq and is thought to maintain its patency. However, despite the importance of SCO function in CSF homeostasis, the genetic program that controls SCO development is poorly understood. Here, we show that the X-linked transcription factor SOX3 is expressed in the murine SCO throughout its development and in the mature organ. Importantly, overexpression of Sox3 in the dorsal diencephalic midline of transgenic mice induces CH via a dose-dependent mechanism. Histological, gene expression and cellular proliferation studies indicate that Sox3 overexpression disrupts the development of the SCO primordium through inhibition of diencephalic roof plate identity without inducing programmed cell death. This study provides further evidence that SCO function is essential for the prevention of hydrocephalus and indicates that overexpression of Sox3 in the dorsal midline alters progenitor cell differentiation in a dose-dependent manner. PMID:22291885
Congenital Hydrocephalus and Abnormal Subcommissural Organ Development in Sox3 Transgenic Mice
Lee, Kristie; Tan, Jacqueline; Morris, Michael B.; Rizzoti, Karine; Hughes, James; Cheah, Pike See; Felquer, Fernando; Liu, Xuan; Piltz, Sandra; Lovell-Badge, Robin; Thomas, Paul Q.
2012-01-01
Congenital hydrocephalus (CH) is a life-threatening medical condition in which excessive accumulation of CSF leads to ventricular expansion and increased intracranial pressure. Stenosis (blockage) of the Sylvian aqueduct (Aq; the narrow passageway that connects the third and fourth ventricles) is a common form of CH in humans, although the genetic basis of this condition is unknown. Mouse models of CH indicate that Aq stenosis is associated with abnormal development of the subcommmissural organ (SCO) a small secretory organ located at the dorsal midline of the caudal diencephalon. Glycoproteins secreted by the SCO generate Reissner's fibre (RF), a thread-like structure that descends into the Aq and is thought to maintain its patency. However, despite the importance of SCO function in CSF homeostasis, the genetic program that controls SCO development is poorly understood. Here, we show that the X-linked transcription factor SOX3 is expressed in the murine SCO throughout its development and in the mature organ. Importantly, overexpression of Sox3 in the dorsal diencephalic midline of transgenic mice induces CH via a dose-dependent mechanism. Histological, gene expression and cellular proliferation studies indicate that Sox3 overexpression disrupts the development of the SCO primordium through inhibition of diencephalic roof plate identity without inducing programmed cell death. This study provides further evidence that SCO function is essential for the prevention of hydrocephalus and indicates that overexpression of Sox3 in the dorsal midline alters progenitor cell differentiation in a dose-dependent manner. PMID:22291885
Xu, Pengfei; Huang, Ruiwang; Wang, Jinhui; Van Dam, Nicholas T; Xie, Teng; Dong, Zhangye; Chen, Chunping; Gu, Ruolei; Zang, Yu-Feng; He, Yong; Fan, Jin; Luo, Yue-jia
2014-04-15
Opening and closing the eyes are fundamental behaviors for directing attention to the external versus internal world. However, it remains unclear whether the states of eyes-open (EO) relative to eyes-closed (EC) are associated with different topological organizations of functional neural networks for exteroceptive and interoceptive processing (processing the external world and internal state, respectively). Here, we used resting-state functional magnetic resonance imaging and neural network analysis to investigate the topological properties of functional networks of the human brain when the eyes were open versus closed. The brain networks exhibited higher cliquishness and local efficiency, but lower global efficiency during the EO state compared to the EC state. These properties suggest an increase in specialized information processing along with a decrease in integrated information processing in EO (vs. EC). More importantly, the "exteroceptive" network, including the attentional system (e.g., superior parietal gyrus and inferior parietal lobule), ocular motor system (e.g., precentral gyrus and superior frontal gyrus), and arousal system (e.g., insula and thalamus), showed higher regional nodal properties (nodal degree, efficiency and betweenness centrality) in EO relative to EC. In contrast, the "interoceptive" network, composed of visual system (e.g., lingual gyrus, fusiform gyrus and cuneus), auditory system (e.g., Heschl's gyurs), somatosensory system (e.g., postcentral gyrus), and part of the default mode network (e.g., angular gyrus and anterior cingulate gyrus), showed significantly higher regional properties in EC vs. EO. In addition, the connections across sensory modalities were altered by volitional eye opening. The synchronicity between the visual system and the motor, somatosensory and auditory systems, characteristic of EC, was attenuated in EO. Further, the connections between the visual system and the attention, arousal and subcortical systems were
Tuning the Topology and Functionality of Metal–Organic Frameworks by Ligand Design
Zhao, Dan; Timmons, Daren J; Yuan, Daqiang; Zhou, Hong-Cai
2011-02-15
Metal–organic frameworks (MOFs)—highly crystalline hybrid materials that combine metal ions with rigid organic ligands—have emerged as an important class of porous materials. The organic ligands add flexibility and diversity to the chemical structures and functions of these materials. In this Account, we summarize our laboratory’s experience in tuning the topology and functionality of MOFs by ligand design. These investigations have led to new materials with interesting properties. By using a ligand that can adopt different symmetry conformations through free internal bond rotation, we have obtained two MOFs that are supramolecular stereoisomers of each other at different reaction temperatures. In another case, where the dimerized ligands function as a D₃-Piedfort unit spacer, we achieve chiral (10,3)-a networks. In the design of MOF-based materials for hydrogen and methane storage, we focused on increasing the gas affinity of frameworks by using ligands with different geometries to control the pore size and effectively introduce unsaturated metal centers (UMCs) into the framework. Framework interpenetration in PCN-6 (PCN stands for porous coordination network) can lead to higher hydrogen uptake. Because of the proper alignment of the UMCs, PCN-12 holds the record for uptake of hydrogen at 77 K/760 Torr. In the case of methane storage, PCN-14 with anthracene-derived ligand achieves breakthrough storage capacity, at a level 28% higher than the U.S. Department of Energy target. Selective gas adsorption requires a pore size comparable to that of the target gas molecules; therefore, we use bulky ligands and network interpenetration to reduce the pore size. In addition, with the help of an amphiphilic ligand, we were able to use temperature to continuously change pore size in a 2D layer MOF. Adding charge to an organic ligand can also stabilize frameworks. By ionizing the amine group within mesoMOF-1, the resulting electronic repulsion keeps the network from
Dong, Liang; Kim, Youngkuk; Er, Dequan; Rappe, Andrew M; Shenoy, Vivek B
2016-03-01
The quantum anomalous Hall (QAH) insulator is a novel topological state of matter characterized by a nonzero quantized Hall conductivity without an external magnetic field. Using first-principles calculations, we predict the QAH state in monolayers of covalent-organic frameworks based on the newly synthesized X_{3}(C_{18}H_{12}N_{6})_{2} structure where X represents 5d transition metal elements Ta, Re, and Ir. The π conjugation between X d_{xz} and d_{yz} orbitals, mediated by N p_{z} and C p_{z} orbitals, gives rise to a massive Dirac spectrum in momentum space with a band gap of up to 24 meV due to strong spin-orbit coupling. We show that the QAH state can appear by chemically engineering the exchange field and the Fermi level in the monolayer structure, resulting in nonzero Chern numbers. Our results suggest a reliable pathway toward the realization of a QAH phase at temperatures between 100 K and room temperature in covalent-organic frameworks. PMID:26991189
NASA Astrophysics Data System (ADS)
Dong, Liang; Kim, Youngkuk; Er, Dequan; Rappe, Andrew M.; Shenoy, Vivek B.
2016-03-01
The quantum anomalous Hall (QAH) insulator is a novel topological state of matter characterized by a nonzero quantized Hall conductivity without an external magnetic field. Using first-principles calculations, we predict the QAH state in monolayers of covalent-organic frameworks based on the newly synthesized X3(C18H12N6) 2 structure where X represents 5 d transition metal elements Ta, Re, and Ir. The π conjugation between X dx z and dy z orbitals, mediated by N pz and C pz orbitals, gives rise to a massive Dirac spectrum in momentum space with a band gap of up to 24 meV due to strong spin-orbit coupling. We show that the QAH state can appear by chemically engineering the exchange field and the Fermi level in the monolayer structure, resulting in nonzero Chern numbers. Our results suggest a reliable pathway toward the realization of a QAH phase at temperatures between 100 K and room temperature in covalent-organic frameworks.
NASA Astrophysics Data System (ADS)
Wu, Liang; Ireland, R. M.; Salehi, M.; Cheng, B.; Koirala, N.; Oh, S.; Katz, H. E.; Armitage, N. P.
2016-05-01
In this work, we use charge extraction via organic overlayer deposition to lower the chemical potential of topological insulator (TI) Bi2Se3 thin films into the intrinsic (bulk-insulating) regime. We demonstrate the tuning and stabilization of intrinsic topological insulators at high mobility with low-cost organic films. With the protection of the organic charge extraction layers tetrafluorotetracyanoquinodimethane or tris(acetylacetonato)cobalt(III) (Co(acac)3), the sample is stable in the atmosphere with chemical potential ˜135 meV above the Dirac point (85 meV below the conduction band minimum, well within the topological insulator regime) after four months, which is an extraordinary level of environmental stability. The Co complex demonstrates the use of an organometallic for modulating TI charge density. The mobility of surface state electrons is enhanced as high as ˜2000 cm2/V s. Even at room temperature, a true topologically insulating state is realized and stabilized for months' exposure to the atmosphere.
NASA Astrophysics Data System (ADS)
Katsenis, Athanassios D.; Puškarić, Andreas; Štrukil, Vjekoslav; Mottillo, Cristina; Julien, Patrick A.; Užarević, Krunoslav; Pham, Minh-Hao; Do, Trong-On; Kimber, Simon A. J.; Lazić, Predrag; Magdysyuk, Oxana; Dinnebier, Robert E.; Halasz, Ivan; Friščić, Tomislav
2015-03-01
Chemical and physical transformations by milling are attracting enormous interest for their ability to access new materials and clean reactivity, and are central to a number of core industries, from mineral processing to pharmaceutical manufacturing. While continuous mechanical stress during milling is thought to create an environment supporting nonconventional reactivity and exotic intermediates, such speculations have remained without proof. Here we use in situ, real-time powder X-ray diffraction monitoring to discover and capture a metastable, novel-topology intermediate of a mechanochemical transformation. Monitoring the mechanochemical synthesis of an archetypal metal-organic framework ZIF-8 by in situ powder X-ray diffraction reveals unexpected amorphization, and on further milling recrystallization into a non-porous material via a metastable intermediate based on a previously unreported topology, herein named katsenite (kat). The discovery of this phase and topology provides direct evidence that milling transformations can involve short-lived, structurally unusual phases not yet accessed by conventional chemistry.
Liu, Tian -Fu; Feng, Dawei; Chen, Ying -Pin; Zou, Lanfang; Bosch, Mathieu; Yuan, Shuai; Wei, Zhangwen; Fordham, Stephen; Wang, Kecheng; Zhou, Hong -Cai
2015-01-14
Through a topology-guided strategy, a series of Zr₆-containing isoreticular porphyrinic metal–organic frameworks (MOFs), PCN-228, PCN-229, and PCN-230, with ftw-a topology were synthesized using the extended porphyrinic linkers. The bulky porphyrin ring ligand effectively prevents the network interpenetration which often appears in MOFs with increased linker length. The pore apertures of the structures range from 2.5 to 3.8 nm, and PCN-229 demonstrates the highest porosity and BET surface area among the previously reported Zr-MOFs. Additionally, by changing the relative direction of the terminal phenyl rings, this series replaces a Zr₈ cluster with a smaller Zr₆ cluster in a topologically identical framework. The high connectivity of the Zr₆ cluster yields frameworks with enhanced stability despite high porosity and ultralarge linker. As a representative example, PCN-230, constructed with the most extended porphyrinic linker, shows excellent stability in aqueous solutions with pH values ranging from 0 to 12 and demonstrates one of the highest pH tolerances among all porphyrinic MOFs. This work not only presents a successful example of rational design of MOFs with desired topology, but also provides a strategy for construction of stable mesoporous MOFs.
Kelch, Inken D.; Bogle, Gib; Sands, Gregory B.; Phillips, Anthony R. J.; LeGrice, Ian J.; Rod Dunbar, P.
2015-01-01
Understanding of the microvasculature has previously been limited by the lack of methods capable of capturing and modelling complete vascular networks. We used novel imaging and computational techniques to establish the topology of the entire blood vessel network of a murine lymph node, combining 63706 confocal images at 2 μm pixel resolution to cover a volume of 3.88 mm3. Detailed measurements including the distribution of vessel diameters, branch counts, and identification of voids were subsequently re-visualised in 3D revealing regional specialisation within the network. By focussing on critical immune microenvironments we quantified differences in their vascular topology. We further developed a morphology-based approach to identify High Endothelial Venules, key sites for lymphocyte extravasation. These data represent a comprehensive and continuous blood vessel network of an entire organ and provide benchmark measurements that will inform modelling of blood vessel networks as well as enable comparison of vascular topology in different organs. PMID:26567707
Abe, Jun; Bomze, David; Cremasco, Viviana; Scandella, Elke; Stein, Jens V.; Turley, Shannon J.; Ludewig, Burkhard
2016-01-01
Fibroblastic reticular cells (FRCs) form the cellular scaffold of lymph nodes (LNs) and establish distinct microenvironmental niches to provide key molecules that drive innate and adaptive immune responses and control immune regulatory processes. Here, we have used a graph theory-based systems biology approach to determine topological properties and robustness of the LN FRC network in mice. We found that the FRC network exhibits an imprinted small-world topology that is fully regenerated within 4 wk after complete FRC ablation. Moreover, in silico perturbation analysis and in vivo validation revealed that LNs can tolerate a loss of approximately 50% of their FRCs without substantial impairment of immune cell recruitment, intranodal T cell migration, and dendritic cell-mediated activation of antiviral CD8+ T cells. Overall, our study reveals the high topological robustness of the FRC network and the critical role of the network integrity for the activation of adaptive immune responses. PMID:27415420
Novkovic, Mario; Onder, Lucas; Cupovic, Jovana; Abe, Jun; Bomze, David; Cremasco, Viviana; Scandella, Elke; Stein, Jens V; Bocharov, Gennady; Turley, Shannon J; Ludewig, Burkhard
2016-07-01
Fibroblastic reticular cells (FRCs) form the cellular scaffold of lymph nodes (LNs) and establish distinct microenvironmental niches to provide key molecules that drive innate and adaptive immune responses and control immune regulatory processes. Here, we have used a graph theory-based systems biology approach to determine topological properties and robustness of the LN FRC network in mice. We found that the FRC network exhibits an imprinted small-world topology that is fully regenerated within 4 wk after complete FRC ablation. Moreover, in silico perturbation analysis and in vivo validation revealed that LNs can tolerate a loss of approximately 50% of their FRCs without substantial impairment of immune cell recruitment, intranodal T cell migration, and dendritic cell-mediated activation of antiviral CD8+ T cells. Overall, our study reveals the high topological robustness of the FRC network and the critical role of the network integrity for the activation of adaptive immune responses. PMID:27415420
NASA Astrophysics Data System (ADS)
Nenashev, A. V.; Wiemer, M.; Dvurechenskii, A. V.; Gebhard, F.; Koch, M.; Baranovskii, S. D.
2016-07-01
The apparent order δ of non-geminate recombination higher than δ = 2 has been evidenced in numerous experiments on organic bulk heterojunction (BHJ) structures intensively studied for photovoltaic applications. This feature is claimed puzzling, since the rate of the bimolecular recombination in organic BHJ systems is proportional to the product of the concentrations of recombining electrons and holes and therefore the reaction order δ = 2 is expected. In organic BHJ structures, electrons and holes are confined to two different material phases: electrons to the acceptor material (usually a fullerene derivative) while holes to the donor phase (usually a polymer). The non-geminate recombination of charge carriers can therefore happen only at the interfaces between the two phases. Considering a simple geometrical model of the BHJ system, we show that the apparent order of recombination can deviate from δ = 2 due solely to the topological structure of the system.
Bogdanov, Mikhail; Heacock, Philip N; Dowhan, William
2010-01-01
A protocol is described using lipid mutants and thiol-specific chemical reagents to study lipid-dependent and host-specific membrane protein topogenesis by the substituted-cysteine accessibility method as applied to transmembrane domains (SCAM). SCAM is adapted to follow changes in membrane protein topology as a function of changes in membrane lipid composition. The strategy described can be adapted to any membrane system. PMID:20419405
Le, Phung Khanh; Pak, William L.; Tse, Stephanie; Ocorr, Karen; Huang, Taosheng
2009-01-01
Optic Atrophy 1 (OPA1) is a ubiquitously expressed dynamin-like GTPase in the inner mitochondrial membrane. It plays important roles in mitochondrial fusion, apoptosis, reactive oxygen species (ROS) and ATP production. Mutations of OPA1 result in autosomal dominant optic atrophy (DOA). The molecular mechanisms by which link OPA1 mutations and DOA are not fully understood. Recently, we created a Drosophila model to study the pathogenesis of optic atrophy. Heterozygous mutation of Drosophila OPA1 (dOpa1) by P-element insertion results in no obvious morphological abnormalities, whereas homozygous mutation is embryonic lethal. In eye-specific somatic clones, homozygous mutation of dOpa1 causes rough (mispatterning) and glossy (decreased lens deposition) eye phenotypes in adult Drosophila. In humans, heterozygous mutations in OPA1 have been associated with mitochondrial dysfunction, which is predicted to affect multiple organs. In this study, we demonstrated that heterozygous dOpa1 mutation perturbs the visual function and an ERG profile of the Drosophila compound eye. We independently showed that antioxidants delayed the onset of mutant phenotypes in ERG and improved larval vision function in phototaxis assay. Furthermore, heterozygous dOpa1 mutation also caused decreased heart rate, increased heart arrhythmia, and poor tolerance to stress induced by electrical pacing. However, antioxidants had no effects on the dysfunctional heart of heterozygous dOpa1 mutants. Under stress, heterozygous dOpa1 mutations caused reduced escape response, suggesting abnormal function of the skeletal muscles. Our results suggest that heterozygous mutation of dOpa1 shows organ-specific pathogenesis and is associated with multiple organ abnormalities in an age-dependent and organ-specific manner. PMID:19718456
Neu, N.; Hala, K.; Dietrich, H.; Wick, G.
1985-12-01
In this study the authors investigated the genetic background of primary abnormalities found in the thyroid gland of Obese strain (OS) chickens with spontaneous autoimmune thyroiditis (SAT), i.e., susceptibility to passively transferred antibodies to thyroglobulin (TgAb) and incomplete suppression of iodine uptake by thyroxine (T4). Several crosses between the B15/B15 subline of OS chickens and the inbred CB line (B12/B12) were done and the progeny was analyzed for thyroiditis after injection of OS serum containing high titers of TgAb. It was found that passive transfer of TgAb increased the lymphoid infiltration in the thyroids of OS chickens, but had no effect on CB birds. A genetic analysis of backcrosses revealed that this trait is, in the case of simple Mendelian inheritance, encoded by at least three recessive genes. The thyroidal T I uptake of these crosses under T4 was also determined and they found that this trait is most probably encoded by only one recessive gene.
Lowery, Jason; Jain, Nikhil; Kuczmarski, Edward R.; Mahammad, Saleemulla; Goldman, Anne; Gelfand, Vladimir I.; Opal, Puneet; Goldman, Robert D.
2016-01-01
Giant axonal neuropathy (GAN) is a rare disease caused by mutations in the GAN gene, which encodes gigaxonin, an E3 ligase adapter that targets intermediate filament (IF) proteins for degradation in numerous cell types, including neurons and fibroblasts. The cellular hallmark of GAN pathology is the formation of large aggregates and bundles of IFs. In this study, we show that both the distribution and motility of mitochondria are altered in GAN fibroblasts and this is attributable to their association with vimentin IF aggregates and bundles. Transient expression of wild-type gigaxonin in GAN fibroblasts reduces the number of IF aggregates and bundles, restoring mitochondrial motility. Conversely, silencing the expression of gigaxonin in control fibroblasts leads to changes in IF organization similar to that of GAN patient fibroblasts and a coincident loss of mitochondrial motility. The inhibition of mitochondrial motility in GAN fibroblasts is not due to a global inhibition of organelle translocation, as lysosome motility is normal. Our findings demonstrate that it is the pathological changes in IF organization that cause the loss of mitochondrial motility. PMID:26700320
Ovchinnikov, Igor V.
2011-05-15
Here, a scenario is proposed, according to which a generic self-organized critical (SOC) system can be looked upon as a Witten-type topological field theory (W-TFT) with spontaneously broken Becchi-Rouet-Stora-Tyutin (BRST) symmetry. One of the conditions for the SOC is the slow driving noise, which unambiguously suggests Stratonovich interpretation of the corresponding stochastic differential equation (SDE). This, in turn, necessitates the use of Parisi-Sourlas-Wu stochastic quantization procedure, which straightforwardly leads to a model with BRST-exact action, i.e., to a W-TFT. In the parameter space of the SDE, there must exist full-dimensional regions where the BRST symmetry is spontaneously broken by instantons, which in the context of SOC are essentially avalanches. In these regions, the avalanche-type SOC dynamics is liberated from overwise a rightful dynamics-less W-TFT, and a Goldstone mode of Fadeev-Popov ghosts exists. Goldstinos represent moduli of instantons (avalanches) and being gapless are responsible for the critical avalanche distribution in the low-energy, long-wavelength limit. The above arguments are robust against moderate variations of the SDE's parameters and the criticality is 'self-tuned'. The proposition of this paper suggests that the machinery of W-TFTs may find its applications in many different areas of modern science studying various physical realizations of SOC. It also suggests that there may in principle exist a connection between some SOC's and the concept of topological quantum computing.
Zhang, Yue-Biao; Furukawa, Hiroyasu; Ko, Nakeun; Nie, Weixuan; Park, Hye Jeong; Okajima, Satoshi; Cordova, Kyle E.; Deng, Hexiang; Kim, Jaheon; Yaghi, Omar M.
2015-02-25
Metal–organic framework-177 (MOF-177) is one of the most porous materials whose structure is composed of octahedral Zn_{4}O(-COO)_{6} and triangular 1,3,5-benzenetribenzoate (BTB) units to make a three-dimensional extended network based on the qom topology. This topology violates a long-standing thesis where highly symmetric building units are expected to yield highly symmetric networks. In the case of octahedron and triangle combinations, MOFs based on pyrite (pyr) and rutile (rtl) nets were expected instead of qom. In this study, we have made 24 MOF-177 structures with different functional groups on the triangular BTB linker, having one or more functionalities. We find that the position of the functional groups on the BTB unit allows the selection for a specific net (qom, pyr, and rtl), and that mixing of functionalities (-H, -NH_{2}, and -C_{4}H_{4}) is an important strategy for the incorporation of a specific functionality (-NO_{2}) into MOF-177 where otherwise incorporation of such functionality would be difficult. Such mixing of functionalities to make multivariate MOF-177 structures leads to enhancement of hydrogen uptake by 25%.
Jung, Wi Hoon; Chang, Ki Jung; Kim, Nam Hee
2016-04-30
Given that partial posttraumatic stress disorder (pPTSD) may be a specific risk factor for the development of posttraumatic stress disorder (PTSD), it is important to understand the neurobiology of pPTSD. However, there are few extant studies in this domain. Using resting-state functional magnetic resonance imaging (rs-fMRI) and a graph theoretical approach, we compared the topological organization of the whole-brain functional network in trauma-exposed firefighters with pPTSD (pPTSD group, n=9) with those without pPTSD (PC group, n=8) and non-traumatized healthy controls (HC group, n=11). We also examined changes in the network topology of five individuals with pPTSD before and after eye movement desensitization and reprocessing (EMDR) therapy. Individuals with pPTSD exhibited altered global properties, including a reduction in values of a normalized clustering coefficient, normalized local efficiency, and small-worldness. We also observed altered local properties, particularly in the association cortex, including the temporal and parietal cortices, across groups. These disruptive global and local network properties presented in pPTSD before treatment were ameliorated after treatment. Our preliminary results suggest that subthreshold manifestation of PTSD may be due to a disruption in the optimal balance in the functional brain networks and that this disruption can be ameliorated by psychotherapy. PMID:27107156
Zhang, Yue-Biao; Furukawa, Hiroyasu; Ko, Nakeun; Nie, Weixuan; Park, Hye Jeong; Okajima, Satoshi; Cordova, Kyle E; Deng, Hexiang; Kim, Jaheon; Yaghi, Omar M
2015-02-25
Metal-organic framework-177 (MOF-177) is one of the most porous materials whose structure is composed of octahedral Zn4O(-COO)6 and triangular 1,3,5-benzenetribenzoate (BTB) units to make a three-dimensional extended network based on the qom topology. This topology violates a long-standing thesis where highly symmetric building units are expected to yield highly symmetric networks. In the case of octahedron and triangle combinations, MOFs based on pyrite (pyr) and rutile (rtl) nets were expected instead of qom. In this study, we have made 24 MOF-177 structures with different functional groups on the triangular BTB linker, having one or more functionalities. We find that the position of the functional groups on the BTB unit allows the selection for a specific net (qom, pyr, and rtl), and that mixing of functionalities (-H, -NH2, and -C4H4) is an important strategy for the incorporation of a specific functionality (-NO2) into MOF-177 where otherwise incorporation of such functionality would be difficult. Such mixing of functionalities to make multivariate MOF-177 structures leads to enhancement of hydrogen uptake by 25%. PMID:25646798
Liu, Chao; Gao, Chao-Ying; Yang, Weiting; Chen, Fang-Yuan; Pan, Qing-Jiang; Li, Jiyang; Sun, Zhong-Ming
2016-06-01
Two 3D uranyl organic frameworks (UOFs) with entangled structures, (HPhen)2[(UO2)2L2]·4.5H2O (1) and [(UO2)3(H2O)4L2]·6H2O (2), were synthesized using a rigid tripodal linker (4,4',4″-(phenylsilanetriyl)tribenzoic acid, H3L). Compound 1 represents a 2-fold interpenetrating UOF with the unique (10,3)-b topology. Compound 2 is composed of three interlocked sets of identical singlet networks and thus exhibits a rare 3D polythreading network with (3,4)-connected topology. These two compounds have been characterized by IR, UV-vis, and photoluminescent spectroscopy. A density functional theory (DFT) study on the model compounds of 1 and 2 shows good agreement of structural parameters and U═O stretching vibrational frequencies with experimental data. The experimentally measured absorption bands were well reproduced by the time-dependent DFT calculations. PMID:27171364
Symmetry-Guided Synthesis of Highly Porous Metal-Organic Frameworks with Fluorite Topology
Zhang, MW; Chen, YP; Bosch, M; Gentle, T; Wang, KC; Feng, DW; Wang, ZYU; Zhou, HC
2013-11-11
Two stable, non-interpenetrated MOFs, PCN-521 and PCN-523, were synthesized by a symmetry-guided strategy. Augmentation of the 4-connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8-connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN-521 has the largest BET surface area (3411 m(2) g(-1)), pore size (20.5 x 20.5 x 37.4 angstrom) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non-interpenetrated MOFs with high porosity.
Self-organized topological superconductivity in a Yu-Shiba-Rusinov chain
NASA Astrophysics Data System (ADS)
Schecter, Michael; Flensberg, Karsten; Christensen, Morten H.; Andersen, Brian M.; Paaske, Jens
2016-04-01
We study a chain of magnetic moments exchange coupled to a conventional three-dimensional superconductor. In the normal state the chain orders into a collinear configuration, while in the superconducting phase we find that ferromagnetism is unstable to the formation of a magnetic spiral state. Beyond weak exchange coupling the spiral wave vector greatly exceeds the inverse superconducting coherence length as a result of the strong spin-spin interaction mediated through the subgap band of Yu-Shiba-Rusinov states. Moreover, the simple spin-spin exchange description breaks down as the subgap band crosses the Fermi energy, wherein the spiral phase becomes stabilized by the spontaneous opening of a p -wave superconducting gap within the band. This leads to the possibility of electron-driven topological superconductivity with Majorana boundary modes using magnetic atoms on superconducting surfaces.
Zhang, Xin; Zhang, Xu; Johnson, Jacob A; Chen, Yu-Sheng; Zhang, Jian
2016-07-13
Two non-interpenetrated zirconium metal-organic frameworks (Zr-MOFs), NPF-200 and NPF-201, were synthesized via the assembly of elongated tetrahedral linkers with Zr6 and Zr8 clusters. They represent the first examples of MOFs to have the β-UH3-like, 4,12,12T1 topology. Upon activation, NPF-200 exhibits the largest BET surface area (5463 m(2) g(-1)) and void volume (81.6%) among all MOFs formed from tetrahedral ligands. Composed of negative-charged boron-centered tetrahedral linkers, NPF-201 is an anionic Zr-MOF which selectively uptakes photoactive [Ru(bpy)3](2+) for heterogeneous photo-oxidation of thioanisole. PMID:27341503
Wu, Kai; Taki, Yasuyuki; Sato, Kazunori; Hashizume, Hiroshi; Sassa, Yuko; Takeuchi, Hikaru; Thyreau, Benjamin; He, Yong; Evans, Alan C.; Li, Xiaobo; Kawashima, Ryuta; Fukuda, Hiroshi
2013-01-01
Recent studies have demonstrated developmental changes of functional brain networks derived from functional connectivity using graph theoretical analysis, which has been rapidly translated to studies of brain network organization. However, little is known about sex- and IQ-related differences in the topological organization of functional brain networks during development. In this study, resting-state fMRI (rs-fMRI) was used to map the functional brain networks in 51 healthy children. We then investigated the effects of age, sex, and IQ on economic small-world properties and regional nodal properties of the functional brain networks. At a global level of whole networks, we found significant age-related increases in the small-worldness and local efficiency, significant higher values of the global efficiency in boys compared with girls, and no significant IQ-related difference. Age-related increases in the regional nodal properties were found predominately in the frontal brain regions, whereas the parietal, temporal, and occipital brain regions showed age-related decreases. Significant sex-related differences in the regional nodal properties were found in various brain regions, primarily related to the default mode, language, and vision systems. Positive correlations between IQ and the regional nodal properties were found in several brain regions related to the attention system, whereas negative correlations were found in various brain regions primarily involved in the default mode, emotion, and language systems. Together, our findings of the network topology of the functional brain networks in healthy children and its relationship with age, sex, and IQ bring new insights into the understanding of brain maturation and cognitive development during childhood and adolescence. PMID:23390528
Máthé, Csaba; Beyer, Dániel; Erdodi, Ferenc; Serfozo, Zoltán; Székvölgyi, Lóránt; Vasas, Gábor; M-Hamvas, Márta; Jámbrik, Katalin; Gonda, Sándor; Kiss, Andrea; Szigeti, Zsuzsa M; Surányi, Gyula
2009-05-01
Microcystin-LR (MC-LR) is a heptapeptide cyanotoxin, known to be a potent inhibitor of type 1 and 2A protein phosphatases in eukaryotes. Our aim was to investigate the effect of MC-LR on the organization of microtubules and mitotic chromatin in relation to its possible effects on cell and whole organ morphology in roots of common reed (Phragmites australis). P. australis is a widespread freshwater and brackish water aquatic macrophyte, frequently exposed to phytotoxins in eutrophic waters. Reed plantlets regenerated from embryogenic calli were treated with 0.001-40 microg ml(-1) (0.001-40.2 microM) MC-LR for 2-20 days. At 0.5 microg ml(-1) MC-LR and at higher cyanotoxin concentrations, the inhibition of protein phosphatase activity by MC-LR induced alterations in reed root growth and morphology, including abnormal lateral root development and the radial swelling of cells in the elongation zone of primary and lateral roots. Both short-term (2-5 days) and long-term (10-20 days) of cyanotoxin treatment induced microtubule disruption in meristems and in the elongation and differentiation zones. Microtubule disruption was accompanied by root cell shape alteration. At concentrations of 0.5-5 microg ml(-1), MC-LR increased mitotic index at long-term exposure and induced the increase of the percentage of meristematic cells in prophase as well as telophase and cytokinesis of late mitosis. High cyanotoxin concentrations (10-40 microg ml(-1)) inhibited mitosis at as short as 2 days of exposure. The alteration of microtubule organization was observed in mitotic cells at all exposure periods studied, at cyanotoxin concentrations of 0.5-40 microg ml(-1). MC-LR induced spindle anomalies at the metaphase-anaphase transition, the formation of asymmetric anaphase spindles and abnormal sister chromatid separation. This paper reports for the first time that MC-LR induces cytoskeletal changes that lead to alterations of root architecture and development in common reed and generally, in
Shu, Ni; Duan, Yunyun; Xia, Mingrui; Schoonheim, Menno M; Huang, Jing; Ren, Zhuoqiong; Sun, Zheng; Ye, Jing; Dong, Huiqing; Shi, Fu-Dong; Barkhof, Frederik; Li, Kuncheng; Liu, Yaou
2016-01-01
The brain connectome of multiple sclerosis (MS) has been investigated by several previous studies; however, it is still unknown how the network changes in clinically isolated syndrome (CIS), the earliest stage of MS, and how network alterations on a functional level relate to the structural level in MS disease. Here, we investigated the topological alterations of both the structural and functional connectomes in 41 CIS and 32 MS patients, compared to 35 healthy controls, by combining diffusion tensor imaging and resting-state functional MRI with graph analysis approaches. We found that the structural connectome showed a deviation from the optimal pattern as early as the CIS stage, while the functional connectome only showed local changes in MS patients, not in CIS. When comparing two patient groups, the changes appear more severe in MS. Importantly, the disruptions of structural and functional connectomes in patients occurred in the same direction and locally correlated in sensorimotor component. Finally, the extent of structural network changes was correlated with several clinical variables in MS patients. Together, the results suggested early disruption of the structural brain connectome in CIS patients and provided a new perspective for investigating the relationship of the structural and functional alterations in MS. PMID:27403924
Shu, Ni; Duan, Yunyun; Xia, Mingrui; Schoonheim, Menno M.; Huang, Jing; Ren, Zhuoqiong; Sun, Zheng; Ye, Jing; Dong, Huiqing; Shi, Fu-Dong; Barkhof, Frederik; Li, Kuncheng; Liu, Yaou
2016-01-01
The brain connectome of multiple sclerosis (MS) has been investigated by several previous studies; however, it is still unknown how the network changes in clinically isolated syndrome (CIS), the earliest stage of MS, and how network alterations on a functional level relate to the structural level in MS disease. Here, we investigated the topological alterations of both the structural and functional connectomes in 41 CIS and 32 MS patients, compared to 35 healthy controls, by combining diffusion tensor imaging and resting-state functional MRI with graph analysis approaches. We found that the structural connectome showed a deviation from the optimal pattern as early as the CIS stage, while the functional connectome only showed local changes in MS patients, not in CIS. When comparing two patient groups, the changes appear more severe in MS. Importantly, the disruptions of structural and functional connectomes in patients occurred in the same direction and locally correlated in sensorimotor component. Finally, the extent of structural network changes was correlated with several clinical variables in MS patients. Together, the results suggested early disruption of the structural brain connectome in CIS patients and provided a new perspective for investigating the relationship of the structural and functional alterations in MS. PMID:27403924
Cañadillas-Delgado, Laura; Fabelo, Oscar; Pasán, Jorge; Déniz, Mariadel; Martínez-Benito, Carla; Díaz-Gallifa, Pau; Martín, Tomás; Ruiz-Pérez, Catalina
2014-02-01
Three new metal-organic framework structures containing Eu(III) and the little explored methanetriacetate (C7H7O6(3-), mta(3-)) ligand have been synthesized. Gel synthesis yields a two-dimensional framework with the formula [Eu(mta)(H2O)3]n·2nH2O, (I), while two polymorphs of the three-dimensional framework material [Eu(mta)(H2O)]n·nH2O, (II) and (III), are obtained through hydrothermal synthesis at either 423 or 443 K. Compounds (I) and (II) are isomorphous with previously reported Gd(III) compounds, but compound (III) constitutes a new phase. Compound (I) can be described in terms of dinuclear [Eu2(H2O)4](6+) units bonded through mta(3-) ligands to form a two-dimensional framework with topology corresponding to a (6,3)-connected binodal (4(3))(4(6)6(6)8(3))-kgd net, where the dinuclear [Eu2(H2O)4](6+) units are considered as a single node. Compounds (II) and (III) have distinct three-dimensional topologies, namely a (4(12)6(3))(4(9)6(6))-nia net for (II) and a (4(10)6(5))(4(11)6(4))-K2O2; 36641 net for (III). The crystal density of (III) is greater than that of (II), consistent with the increase of temperature, and thereby autogeneous pressure, in the hydrothermal synthesis. PMID:24441124
Martínez-Montes, Eduardo
2013-01-01
This paper aims to study the abnormal patterns of brain glucose metabolism co-variations in Alzheimer disease (AD) and Mild Cognitive Impairment (MCI) patients compared to Normal healthy controls (NC) using the Alzheimer Disease Neuroimaging Initiative (ADNI) database. The local cerebral metabolic rate for glucose (CMRgl) in a set of 90 structures belonging to the AAL atlas was obtained from Fluro-Deoxyglucose Positron Emission Tomography data in resting state. It is assumed that brain regions whose CMRgl values are significantly correlated are functionally associated; therefore, when metabolism is altered in a single region, the alteration will affect the metabolism of other brain areas with which it interrelates. The glucose metabolism network (represented by the matrix of the CMRgl co-variations among all pairs of structures) was studied using the graph theory framework. The highest concurrent fluctuations in CMRgl were basically identified between homologous cortical regions in all groups. Significant differences in CMRgl co-variations in AD and MCI groups as compared to NC were found. The AD and MCI patients showed aberrant patterns in comparison to NC subjects, as detected by global and local network properties (global and local efficiency, clustering index, and others). MCI network’s attributes showed an intermediate position between NC and AD, corroborating it as a transitional stage from normal aging to Alzheimer disease. Our study is an attempt at exploring the complex association between glucose metabolism, CMRgl covariations and the attributes of the brain network organization in AD and MCI. PMID:23894356
Gurzhiy, Vladislav V.
2015-09-15
Single crystals of seven novel uranyl oxysalts of selenium with protonated methylamine molecules, [C{sub 2}H{sub 8}N]{sub 2}[(UO{sub 2})(SeO{sub 4}){sub 2}(H{sub 2}O)] (I), [C{sub 2}H{sub 8}N]{sub 2}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O)] (II), [C{sub 4}H{sub 15}N{sub 3}][H{sub 3}O]{sub 0.5}[(UO{sub 2}){sub 2}(SeO{sub 4}){sub 2.93}(SeO{sub 3}){sub 0.07}(H{sub 2}O)](NO{sub 3}){sub 0.5} (III), [C{sub 2}H{sub 8}N]{sub 3}[H{sub 5}O{sub 2}][(UO{sub 2}){sub 2}(SeO{sub 4}){sub 3}(H{sub 2}O){sub 2}]{sub 2}(H{sub 2}O){sub 5} (IV), [C{sub 2}H{sub 8}N]{sub 2}[H{sub 3}O][(UO{sub 2}){sub 3}(SeO{sub 4}){sub 4}(HSeO{sub 3})(H{sub 2}O)](H{sub 2}SeO{sub 3}){sub 0.2} (V), [C{sub 4}H{sub 12}N]{sub 3}[H{sub 3}O][(UO{sub 2}){sub 3}(SeO{sub 4}){sub 5}(H{sub 2}O)] (VI), and [C{sub 2}H{sub 8}N]{sub 3}(C{sub 2}H{sub 7}N)[(UO{sub 2}){sub 3}(SeO{sub 4}){sub 4}(HSeO{sub 3})(H{sub 2}O)] (VII) have been prepared by isothermal evaporation from aqueous solutions. Their crystal structures have been solved by direct methods and their uranyl selenate and selenite–selenate units investigated using black-and-white graphs from the viewpoints of topology of interpolyhedral linkages and isomeric variations. The crystal structure of IV is based upon complex layers with unique topology, which has not been observed previously in uranyl selenates. Investigations of the statistics and local distribution of the U–O{sub br}–Se bond angles demonstrates that shorter angles associate with undulations, whereas larger angles correspond to planar areas of the uranyl selenite layers. - Graphical abstract: Crystal structures of the seven novel Se-contaning uranyl oxysalts that contain protonated organic molecules as interlayer species have been investigated from the viewpoints of topology of interpolyhedral linkages, isomeric variations and flexibility of structural units. - Highlights: • Single crystals of seven novel uranyl oxysalts were prepared by evaporation method. • The graph theory was used
Miner, Daniel; Triesch, Jochen
2016-01-01
Understanding the structure and dynamics of cortical connectivity is vital to understanding cortical function. Experimental data strongly suggest that local recurrent connectivity in the cortex is significantly non-random, exhibiting, for example, above-chance bidirectionality and an overrepresentation of certain triangular motifs. Additional evidence suggests a significant distance dependency to connectivity over a local scale of a few hundred microns, and particular patterns of synaptic turnover dynamics, including a heavy-tailed distribution of synaptic efficacies, a power law distribution of synaptic lifetimes, and a tendency for stronger synapses to be more stable over time. Understanding how many of these non-random features simultaneously arise would provide valuable insights into the development and function of the cortex. While previous work has modeled some of the individual features of local cortical wiring, there is no model that begins to comprehensively account for all of them. We present a spiking network model of a rodent Layer 5 cortical slice which, via the interactions of a few simple biologically motivated intrinsic, synaptic, and structural plasticity mechanisms, qualitatively reproduces these non-random effects when combined with simple topological constraints. Our model suggests that mechanisms of self-organization arising from a small number of plasticity rules provide a parsimonious explanation for numerous experimentally observed non-random features of recurrent cortical wiring. Interestingly, similar mechanisms have been shown to endow recurrent networks with powerful learning abilities, suggesting that these mechanism are central to understanding both structure and function of cortical synaptic wiring. PMID:26866369
Miner, Daniel; Triesch, Jochen
2016-02-01
Understanding the structure and dynamics of cortical connectivity is vital to understanding cortical function. Experimental data strongly suggest that local recurrent connectivity in the cortex is significantly non-random, exhibiting, for example, above-chance bidirectionality and an overrepresentation of certain triangular motifs. Additional evidence suggests a significant distance dependency to connectivity over a local scale of a few hundred microns, and particular patterns of synaptic turnover dynamics, including a heavy-tailed distribution of synaptic efficacies, a power law distribution of synaptic lifetimes, and a tendency for stronger synapses to be more stable over time. Understanding how many of these non-random features simultaneously arise would provide valuable insights into the development and function of the cortex. While previous work has modeled some of the individual features of local cortical wiring, there is no model that begins to comprehensively account for all of them. We present a spiking network model of a rodent Layer 5 cortical slice which, via the interactions of a few simple biologically motivated intrinsic, synaptic, and structural plasticity mechanisms, qualitatively reproduces these non-random effects when combined with simple topological constraints. Our model suggests that mechanisms of self-organization arising from a small number of plasticity rules provide a parsimonious explanation for numerous experimentally observed non-random features of recurrent cortical wiring. Interestingly, similar mechanisms have been shown to endow recurrent networks with powerful learning abilities, suggesting that these mechanism are central to understanding both structure and function of cortical synaptic wiring. PMID:26866369
Ferket, P R; Oviedo-Rondón, E O; Mente, P L; Bohórquez, D V; Santos, A A; Grimes, J L; Richards, J D; Dibner, J J; Felts, V
2009-01-01
Leg problems and resulting mortality can exceed 1% per week in turkey toms starting at approximately 15 wk of age. Dietary supplementation of organic trace minerals (MIN) and 25-hydroxycholecalciferol (HyD) may improve performance, decrease incidence of leg abnormalities, and increase bone strength. Nicholas 85X700 toms were assigned to 4 treatments consisting of a factorial arrangement of 2 concentrations of MIN (0 and 0.1% of Mintrex P(Se), which adds 40, 40, 20, and 0.3 mg/kg of Zn, Mn, Cu, and Se, respectively) and 2 concentrations of HyD (0 and 92 microg/kg of HyD). Diets were formulated to be equal in nutrient content and fed ad libitum as 8 feed phases. Feed intake and BW were measured at 6, 12, 15, 17, and 20 wk of age. Valgus, varus, and shaky leg defects were determined at 12, 15, 17, and 20 wk of age. Tibia and femur biomechanical properties were evaluated by torsion and bending tests at 17 wk of age. There were no treatment effects on BW. Only MIN significantly improved feed conversion ratio through to 20 wk of age. Cumulative mortality at 3 wk of age was greater among the MIN birds, but it was lower by 20 wk (P = 0.085). The MIN decreased the incidence of varus defects at 17 wk of age; shaky leg at 12, 15, and 17 wk of age; and valgus defects at 15, 17, and 20 wk of age. There were no MIN x HyD interaction effects on individual gait problems. Maximum load and the bending stress required for tibias to break in a 4-point assay were increased with MIN supplementation, especially when HyD was also added. Maximum shear stress at failure of femoral bones in a torsion assay was increased by supplementation with both MIN and HyD together. Dietary supplementation of MIN and HyD may improve biomechanical properties of bones. Dietary MIN supplementation may improve feed conversion of turkeys, likely by decreasing leg problems. PMID:19096066
1993-12-31
Chapter 19, describes meiotic abnormalities. These include nondisjunction of autosomes and sex chromosomes, genetic and environmental causes of nondisjunction, misdivision of the centromere, chromosomally abnormal human sperm, male infertility, parental age, and origin of diploid gametes. 57 refs., 2 figs., 1 tab.
Chen, Qing; Xue, Wei; Lin, Jian-Bin; Wei, Yong-Sheng; Yin, Zheng; Zeng, Ming-Hua; Kurmoo, Mohamedally; Chen, Xiao-Ming
2016-08-16
A series of highly connected metal-organic frameworks (MOFs), [Co8 (O)(OH)4 (H2 O)4 (ina)8 ](NO3 )2 ⋅2 C2 H5 OH⋅4 H2 O (1), [Co8 (O)(OH)4 (H2 O)4 (pba)8 ](NO3 )2 ⋅8 C2 H5 OH⋅28 H2 O (2), and [Co8 (O)(OH)4 (H2 O)4 (pbba)8 ](NO3 )2 ⋅guest (3), in which ina=isonicotinate, pba=4-pyridylbenzoate, and pbba=4-(pyridine-4-yl)phenylbenzoate, is reported. These MOFs contain a new secondary building unit (SBU), with a square Co4 (μ4 -O) central unit having the rare μ4 -O(2-) motif, which is decorated by the other four peripheral cobalt atoms through μ3 -OH in a windmill-like shape. This SBU holds 16 divergent connecting organic ligands, pyridyl-carboxylates, to form three different frameworks. The high porosity of desolvated 2 is shown by the efficient gas absorption of N2 , CO2 , CH4 , and H2 . In addition, 1 and 2 exhibit unusual canted antiferromagnetic behavior with spin-glass-like relaxation, with blocking temperatures that are fairly high, 20 K (1) and 10 K (2), for cobalt materials. The relationship between the metal clusters and linkers has been studied, in which the size and rotational degrees of freedom of the ligands are found to control the topology, gas sorption, and magnetic properties. PMID:27383009
NASA Astrophysics Data System (ADS)
Schleich, K.; Witt, D. M.
Classically, all topologies are allowed as solutions to the Einstein equations. However, one does not observe any topological structures on medium range distance scales, that is scales that are smaller than the size of the observed universe but larger than the microscopic scales for which quantum gravity becomes important. Recently, Friedman, Schleich and Witt (1993) have proven that there is topological censorship on these medium range distance scales: the Einstein equations, locally positive energy, and local predictability of physics imply that any medium distance scale topological structures cannot be seen. More precisely we show that the topology of physically reasonable isolated systems is shrouded from distant observers, or in other words there is a topological censorship principle.
... serious health problems (e.g. Down syndrome ). Single-Gene Abnormalities Sometimes the chromosomes are normal in number, ... blood flow to the fetus impair fetal growth. Alcohol consumption and certain drugs during pregnancy significantly increase ...
... of the skull and face. Craniofacial abnormalities are birth defects of the face or head. Some, like cleft ... palate, are among the most common of all birth defects. Others are very rare. Most of them affect ...
... include: Arthritis of the leg or foot joints Conversion disorder (a psychological disorder) Foot problems (such as a ... injuries. For an abnormal gait that occurs with conversion disorder, counseling and support from family members are strongly ...
... decade, newer techniques have been developed that allow scientists and doctors to screen for chromosomal abnormalities without using a microscope. These newer methods compare the patient's DNA to a normal DNA ...
Nail abnormalities are problems with the color, shape, texture, or thickness of the fingernails or toenails. ... Fungus or yeast cause changes in the color, texture, and shape of the nails. Bacterial infection may ...
Wang, Zhenqiang; Tanabe, Kristine K; Cohen, Seth M
2009-01-01
2-Amino-1,4-benzenedicarboxylic acid (NH(2)-BDC) has been found to be a compatible building block for the construction of two new metal-organic frameworks (MOFs) that have structures isoreticular to reported MOFs that use 1,4-benzenedicarboxylic acid (BDC) as a building block. DMOF-1-NH(2) (DABCO MOF-1-NH(2)) is a derivative of a previously studied MOF that contains two-dimensional square grids based on NH(2)-BDC and zinc(II) paddle-wheel units; the grid layers are connected by DABCO (1,4-diazabicyclo[2.2.2]octane) molecules that coordinate in the axial positions of the paddlewheel secondary-building units (SBUs). UMCM-1-NH(2) is an NH(2)-BDC derivative of UMCM-1 (University of Michigan Crystalline Material-1), a highly porous MOF reported by Matzger et al., and consists of both NH(2)-BDC and BTB (BTB = 4,4',4''-benzene-1,3,5-triyl-tribenzoate) linkers with Zn(4)O SBUs. The structure of UMCM-1-NH(2) was confirmed by single-crystal X-ray diffraction. By using NH(2)-BDC to generate these MOFs, the pendant amino groups can serve as a chemical handle that can be manipulated via postsynthetic modification with alkyl anhydrides. Reactions of each MOF and different anhydrides have been performed to compare the extent of conversion, thermal and structural stability, and Brunauer-Emmett-Teller surface areas afforded by the resulting materials. Under comparable reaction conditions, (1)H NMR of digested samples show that UMCM-1-NH(2) has conversions comparable to that of IRMOF-3, while DMOF-1-NH(2) only shows high conversions with smaller anhydrides. Under specific reaction conditions, higher conversions were obtained with complete retention of crystallinity, as verified by single-crystal X-ray diffraction experiments. The results presented here demonstrate three important findings: (a) NH(2)-BDC can be used as a surrogate for BDC in a number of MOFs thereby providing a handle for postsynthetic modification, (b) postsynthetic modification is a general strategy to
Liu, TF; Feng, DW; Chen, YP; Zou, LF; Bosch, M; Yuan, S; Wei, ZW; Fordham, S; Wang, KC; Zhou, HC
2015-01-14
Through a topology-guided strategy, a series of Zr-6-containing isoreticular porphyrinic metalorganic frameworks (MOFs), PCN-228, PCN-229, and PCN-230, with ftw-a topology were synthesized using the extended porphyrinic linkers. The bulky porphyrin ring ligand effectively prevents the network interpenetration which often appears in MOFs with increased linker length. The pore apertures of the structures range from 2.5 to 3.8 nm, and PCN-229 demonstrates the highest porosity and BET surface area among the previously reported Zr-MOFs. Additionally, by changing the relative direction of the terminal phenyl rings, this series replaces a Zr-8 cluster with a smaller Zr-6 cluster in a topologically identical framework. The high connectivity of the Zr-6 cluster yields frameworks with enhanced stability despite high porosity and ultralarge linker. As a representative example, PCN-230, constructed with the most extended porphyrinic linker, shows excellent stability in aqueous solutions with pH values ranging from 0 to 12 and demonstrates one of the highest pH tolerances among all porphyrinic MOFs. This work not only presents a successful example of rational design of MOFs with desired topology, but also provides a strategy for construction of stable mesoporous MOFs.
NASA Astrophysics Data System (ADS)
Zhang, Yan; Liu, Qi-Feng; Xing, Guang'en; Zhang, Zhong-Qiang
2015-04-01
Presented here are two new luminescent Zn(II) coordination polymers, [Zn3(pdc)3(Hmtz)]n (1) and [Zn3(ntd)(mtz)4(DMA)2]n (2) (H2pdc = terephthalic acid, H2ntd = 2,6-naphthalenedicarboxylic acid, Hmtz = 5-methyl-1H-tetrazole). Single crystal X-ray diffraction analysis reveals that compound 1 features a 8-connected hex topological framework with the schläfli symbol of {36.418.53.6}, while compound 2 features a (3,4)-connected tfi topological framework with the schläfli symbol of {62.84}{62.8}2. The thermal stabilities and luminescent properties of 1-2 were also investigated.
Xia, Shugao; Foxe, John J.; Sroubek, Ariane E.; Branch, Craig; Li, Xiaobo
2013-01-01
Background: Attention-deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed childhood psychiatric disorder. Disrupted sustained attention is one of the most significant behavioral impairments in this disorder. We mapped systems-level topological properties of the neural network responsible for sustained attention during a visual sustained task, on the premise that strong associations between anomalies in network features and clinical measures of ADHD would emerge. Methods: Graph theoretic techniques (GTT) and bivariate network-based statistics (NBS) were applied to fMRI data from 22 children with ADHD combined-type and 22 age-matched neurotypicals, to evaluate the topological and nodal-pairing features in the functional brain networks. Correlation testing for relationships between network properties and clinical measures were then performed. Results: The visual attention network showed significantly reduced local-efficiency and nodal-efficiency in frontal and occipital regions in ADHD. Measures of degree and between-centrality pointed to hyper-functioning in anterior cingulate cortex and hypo-functioning in orbito-frontal, middle-occipital, superior-temporal, supra-central, and supra-marginal gyri in ADHD. NBS demonstrated significantly reduced pair-wise connectivity in an inner-network, encompassing right parietal and temporal lobes and left occipital lobe, in the ADHD group. Conclusions: These data suggest that atypical topological features of the visual attention network contribute to classic ADHD symptomatology, and may underlie the inattentiveness and hyperactivity/impulsivity that are characteristics of this syndrome. PMID:24688465
NASA Astrophysics Data System (ADS)
Yang, Zhaoju; Gao, Fei; Shi, Xihang; Lin, Xiao; Gao, Zhen; Chong, Yidong; Zhang, Baile
2015-03-01
The manipulation of acoustic wave propagation in fluids has numerous applications, including some in everyday life. Acoustic technologies frequently develop in tandem with optics, using shared concepts such as waveguiding and metamedia. It is thus noteworthy that an entirely novel class of electromagnetic waves, known as "topological edge states," has recently been demonstrated. These are inspired by the electronic edge states occurring in topological insulators, and possess a striking and technologically promising property: the ability to travel in a single direction along a surface without backscattering, regardless of the existence of defects or disorder. Here, we develop an analogous theory of topological fluid acoustics, and propose a scheme for realizing topological edge states in an acoustic structure containing circulating fluids. The phenomenon of disorder-free one-way sound propagation, which does not occur in ordinary acoustic devices, may have novel applications for acoustic isolators, modulators, and transducers.
Yang, Zhaoju; Gao, Fei; Shi, Xihang; Lin, Xiao; Gao, Zhen; Chong, Yidong; Zhang, Baile
2015-03-20
The manipulation of acoustic wave propagation in fluids has numerous applications, including some in everyday life. Acoustic technologies frequently develop in tandem with optics, using shared concepts such as waveguiding and metamedia. It is thus noteworthy that an entirely novel class of electromagnetic waves, known as "topological edge states," has recently been demonstrated. These are inspired by the electronic edge states occurring in topological insulators, and possess a striking and technologically promising property: the ability to travel in a single direction along a surface without backscattering, regardless of the existence of defects or disorder. Here, we develop an analogous theory of topological fluid acoustics, and propose a scheme for realizing topological edge states in an acoustic structure containing circulating fluids. The phenomenon of disorder-free one-way sound propagation, which does not occur in ordinary acoustic devices, may have novel applications for acoustic isolators, modulators, and transducers. PMID:25839273
Senyuk, Bohdan; Liu, Qingkun; He, Sailing; Kamien, Randall D; Kusner, Robert B; Lubensky, Tom C; Smalyukh, Ivan I
2013-01-10
Smoke, fog, jelly, paints, milk and shaving cream are common everyday examples of colloids, a type of soft matter consisting of tiny particles dispersed in chemically distinct host media. Being abundant in nature, colloids also find increasingly important applications in science and technology, ranging from direct probing of kinetics in crystals and glasses to fabrication of third-generation quantum-dot solar cells. Because naturally occurring colloids have a shape that is typically determined by minimization of interfacial tension (for example, during phase separation) or faceted crystal growth, their surfaces tend to have minimum-area spherical or topologically equivalent shapes such as prisms and irregular grains (all continuously deformable--homeomorphic--to spheres). Although toroidal DNA condensates and vesicles with different numbers of handles can exist and soft matter defects can be shaped as rings and knots, the role of particle topology in colloidal systems remains unexplored. Here we fabricate and study colloidal particles with different numbers of handles and genus g ranging from 1 to 5. When introduced into a nematic liquid crystal--a fluid made of rod-like molecules that spontaneously align along the so-called 'director'--these particles induce three-dimensional director fields and topological defects dictated by colloidal topology. Whereas electric fields, photothermal melting and laser tweezing cause transformations between configurations of particle-induced structures, three-dimensional nonlinear optical imaging reveals that topological charge is conserved and that the total charge of particle-induced defects always obeys predictions of the Gauss-Bonnet and Poincaré-Hopf index theorems. This allows us to establish and experimentally test the procedure for assignment and summation of topological charges in three-dimensional director fields. Our findings lay the groundwork for new applications of colloids and liquid crystals that range from
NASA Astrophysics Data System (ADS)
Luminet, Jean-Pierre
2015-08-01
Cosmic Topology is the name given to the study of the overall shape of the universe, which involves both global topological features and more local geometrical properties such as curvature. Whether space is finite or infinite, simply-connected or multi-connected like a torus, smaller or greater than the portion of the universe that we can directly observe, are questions that refer to topology rather than curvature. A striking feature of some relativistic, multi-connected "small" universe models is to create multiples images of faraway cosmic sources. While the most recent cosmological data fit the simplest model of a zero-curvature, infinite space model, they are also consistent with compact topologies of the three homogeneous and isotropic geometries of constant curvature, such as, for instance, the spherical Poincaré Dodecahedral Space, the flat hypertorus or the hyperbolic Picard horn. After a "dark age" period, the field of Cosmic Topology has recently become one of the major concerns in cosmology, not only for theorists but also for observational astronomers, leaving open a number of unsolved issues.
Kim, Seok-Hyung; Scott, Sarah A.; Bennett, Michael J.; Carson, Robert P.; Fessel, Joshua; Brown, H. Alex; Ess, Kevin C.
2013-01-01
Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) is a severe mitochondrial disorder featuring multi-organ dysfunction. Mutations in either the ETFA, ETFB, and ETFDH genes can cause MADD but very little is known about disease specific mechanisms due to a paucity of animal models. We report a novel zebrafish mutant dark xavier (dxavu463) that has an inactivating mutation in the etfa gene. dxavu463 recapitulates numerous pathological and biochemical features seen in patients with MADD including brain, liver, and kidney disease. Similar to children with MADD, homozygote mutant dxavu463 zebrafish have a spectrum of phenotypes ranging from moderate to severe. Interestingly, excessive maternal feeding significantly exacerbated the phenotype. Homozygous mutant dxavu463 zebrafish have swollen and hyperplastic neural progenitor cells, hepatocytes and kidney tubule cells as well as elevations in triacylglycerol, cerebroside sulfate and cholesterol levels. Their mitochondria were also greatly enlarged, lacked normal cristae, and were dysfunctional. We also found increased signaling of the mechanistic target of rapamycin complex 1 (mTORC1) with enlarged cell size and proliferation. Treatment with rapamycin partially reversed these abnormalities. Our results indicate that etfa gene function is remarkably conserved in zebrafish as compared to humans with highly similar pathological, biochemical abnormalities to those reported in children with MADD. Altered mTORC1 signaling and maternal nutritional status may play critical roles in MADD disease progression and suggest novel treatment approaches that may ameliorate disease severity. PMID:23785301
NASA Astrophysics Data System (ADS)
Lian, Xiao-Min; Zhao, Wen; Zhao, Xiao-Li
2013-04-01
The combination of divalent zinc ions, 4-(4-carboxybenzamido)benzoic acid and exo-bidendate bipyridine ligands gave rise to a series of new MOFs: [ZnL(bipy)]·DMF·H2O (1), [ZnL(bpe)]·1.5H2O (2), [ZnL(bpa)]·4H2O (3) and [ZnL(bpp)]·1.75H2O (4) (MOF=metal-organic framework, bipy=4,4'-bipyridine, bpe=trans-1,2-bis(4-pyridyl)ethylene, bpa=1,2-bis(4-pyridinyl)ethane, bpp=1,3-bis(4-pyridinyl)propane, H2L=4,4'-(carbonylimino)dibenzoic acid). Fine tune over the topology of the MOFs was achieved via systematically varying the geometric length of the second ligating bipyridine ligands. Single-crystal X-ray analysis reveals that complex 1 has a triply interpenetrated three-dimensional (3D) framework with elongated primitive cubic topology, whereas isostructural complexes 2 and 3 each possesses a 6-fold interpenetrated diamondiod 3D framework. Further expansion of the length of the bipyridine ligand to bpp leads to the formation of 4, which features an interesting entangled architecture of 2D→3D parallel polycatenation. In addition, the thermogravimetric analyses and solid-state photoluminescent properties of the selected complexes are investigated.
Lian, Xiao-Min; Zhao, Wen; Zhao, Xiao-Li
2013-04-15
The combination of divalent zinc ions, 4-(4-carboxybenzamido)benzoic acid and exo-bidendate bipyridine ligands gave rise to a series of new MOFs: [ZnL(bipy)]·DMF·H{sub 2}O (1), [ZnL(bpe)]·1.5H{sub 2}O (2), [ZnL(bpa)]·4H{sub 2}O (3) and [ZnL(bpp)]·1.75H{sub 2}O (4) (MOF=metal-organic framework, bipy=4,4′-bipyridine, bpe=trans-1,2-bis(4-pyridyl)ethylene, bpa=1,2-bis(4-pyridinyl)ethane, bpp=1,3-bis(4-pyridinyl)propane, H{sub 2}L=4,4′-(carbonylimino)dibenzoic acid). Fine tune over the topology of the MOFs was achieved via systematically varying the geometric length of the second ligating bipyridine ligands. Single-crystal X-ray analysis reveals that complex 1 has a triply interpenetrated three-dimensional (3D) framework with elongated primitive cubic topology, whereas isostructural complexes 2 and 3 each possesses a 6-fold interpenetrated diamondiod 3D framework. Further expansion of the length of the bipyridine ligand to bpp leads to the formation of 4, which features an interesting entangled architecture of 2D→3D parallel polycatenation. In addition, the thermogravimetric analyses and solid-state photoluminescent properties of the selected complexes are investigated. - Graphical abstract: The incorporation of exo-bidendate bipyridine spacers into the Zn–H{sub 2}L system has yielded a series of new MOFs exhibiting topological evolution from 3-fold interpenetration to 6-fold interpenetration and 2D→3D parallel polycatenation. Highlights: ► The effect of the pyridyl-based spacers on the formation of MOFs was explored. ► Fine tune over the topology of the MOFs was achieved. ► An interesting structure of 2D→3D parallel polycatenation is reported.
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. PMID:23603781
Jiang Xiujuan; Du Miao; Sun Yan; Guo, Jian-Hua; Li, Jin-Shan
2009-11-15
Reactions of different metal salts with 3-pyridin-4-yl-benzoic acid (3,4-Hpybz) under ambient condition afford a series of 3-D metal-organic frameworks with two new types of (3,6)-connected net topologies. In the isomorphic complexes [M{sub 2}(mu-H{sub 2}O)(3,4-pybz){sub 4}]{sub n} (M{sup II}=Mn{sup II} for 1, Zn{sup II} for 2, or Cd{sup II} for 3), the octahedral metal nodes are extended by the 3-connected pybz tectons to constitute 3-D arrays with the Schlaefli symbol of (3.4.5)(3{sup 2}.4{sup 4}.5{sup 5}.6{sup 2}.7{sup 2}), whereas [Pb(3,4-pybz){sub 2}]{sub n} (4) shows a completely different 3-D (4{sup 2}.6){sub 2}(4{sup 4}.6{sup 2}.8{sup 9}) framework, which represents a subnet of the (4,8)-connected fluorite lattice. - Graphical abstract: This work presents a series of 3-D metal-organic frameworks with 3-pyridin-4-yl-benzoate, which display new (3,6)-connected net topologies of (3.4.5)(3{sup 2}.4{sup 4}.5{sup 5}.6{sup 2}.7{sup 2}) for Mn{sup II}/Zn{sup II}/Cd{sup II} and (4{sup 2}.6){sub 2}(4{sup 4}.6{sup 2}.8{sup 9}) for Pb{sup II} species.
Domingo, Luis R; Pérez, Patricia
2014-07-21
ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P(k)(o) Parr functions of the iminium cation, and the nucleophilic P(k)(-) Parr functions of Cp makes the characterisation of the most favourable two-center interaction along the formation of the C-C single bond possible. PMID:24901220
Li, Yuxiang; Weng, Zhehui; Wang, Yanlong; Chen, Lanhua; Sheng, Daopeng; Diwu, Juan; Chai, Zhifang; Albrecht-Schmitt, Thomas E; Wang, Shuao
2016-01-21
Three thorium(iv)-based metal-organic hybrid compounds with 2D layered and 3D framework structures exhibiting graphene-like (6,3) sheet topologies were prepared with linkers with threefold symmetry. These compounds contain rare and relatively anisotropic coordination environments for low-valent actinides that are similar to those often observed for high-valent actinide ions. PMID:26672441
Topological Aspects of Information Retrieval.
ERIC Educational Resources Information Center
Egghe, Leo; Rousseau, Ronald
1998-01-01
Discusses topological aspects of theoretical information retrieval, including retrieval topology; similarity topology; pseudo-metric topology; document spaces as topological spaces; Boolean information retrieval as a subsystem of any topological system; and proofs of theorems. (LRW)
Ginovart, N; Marcel, D; Bezin, L; Garcia, C; Gagne, C; Pujol, J F; Weissmann, D
1996-05-20
Tyrosine hydroxylase phenotype expression was investigated in the catecholaminergic population of the locus coeruleus neurons of two pure inbred mouse strains, Balb/C and C57Black/6. Therefore, we have characterized the precise organization of tyrosine hydroxylase-expressing perikarya population, in control animals and following RU24722 treatment, which is known to induce tyrosine hydroxylase expression. Serial coronal sections were selected along the caudo-rostral extent of the structure and were processed for tyrosine hydroxylase immunocytochemistry. Three days after the treatment, an increase in the number of cells which expressed tyrosine hydroxylase was observed all along the locus coeruleus in the Balb/C strain only. This increase equalized the catecholaminergic neuron populations of the two strains. In the caudal subdivision of the structure, these newly detected perikarya were intermingled with the perikarya which expressed tyrosine hydroxylase in control conditions. In the rostral half, the additional immunoreactive perikarya enlarged the mean coerulean space, defined as the area delimited by the tyrosine hydroxylase-containing perikarya. These results demonstrate a plasticity of the tyrosine hydroxylase phenotype expression, topologically organized and specific to the Balb/C strain. PMID:8793080
Pereira, Joana B; Mijalkov, Mite; Kakaei, Ehsan; Mecocci, Patricia; Vellas, Bruno; Tsolaki, Magda; Kłoszewska, Iwona; Soininen, Hilka; Spenger, Christian; Lovestone, Simmon; Simmons, Andrew; Wahlund, Lars-Olof; Volpe, Giovanni; Westman, Eric
2016-08-01
Recent findings suggest that Alzheimer's disease (AD) is a disconnection syndrome characterized by abnormalities in large-scale networks. However, the alterations that occur in network topology during the prodromal stages of AD, particularly in patients with stable mild cognitive impairment (MCI) and those that show a slow or faster progression to dementia, are still poorly understood. In this study, we used graph theory to assess the organization of structural MRI networks in stable MCI (sMCI) subjects, late MCI converters (lMCIc), early MCI converters (eMCIc), and AD patients from 2 large multicenter cohorts: ADNI and AddNeuroMed. Our findings showed an abnormal global network organization in all patient groups, as reflected by an increased path length, reduced transitivity, and increased modularity compared with controls. In addition, lMCIc, eMCIc, and AD patients showed a decreased path length and mean clustering compared with the sMCI group. At the local level, there were nodal clustering decreases mostly in AD patients, while the nodal closeness centrality detected abnormalities across all patient groups, showing overlapping changes in the hippocampi and amygdala and nonoverlapping changes in parietal, entorhinal, and orbitofrontal regions. These findings suggest that the prodromal and clinical stages of AD are associated with an abnormal network topology. PMID:27178195
Pereira, Joana B.; Mijalkov, Mite; Kakaei, Ehsan; Mecocci, Patricia; Vellas, Bruno; Tsolaki, Magda; Kłoszewska, Iwona; Soininen, Hilka; Spenger, Christian; Lovestone, Simmon; Simmons, Andrew; Wahlund, Lars-Olof; Volpe, Giovanni; Westman, Eric
2016-01-01
Recent findings suggest that Alzheimer's disease (AD) is a disconnection syndrome characterized by abnormalities in large-scale networks. However, the alterations that occur in network topology during the prodromal stages of AD, particularly in patients with stable mild cognitive impairment (MCI) and those that show a slow or faster progression to dementia, are still poorly understood. In this study, we used graph theory to assess the organization of structural MRI networks in stable MCI (sMCI) subjects, late MCI converters (lMCIc), early MCI converters (eMCIc), and AD patients from 2 large multicenter cohorts: ADNI and AddNeuroMed. Our findings showed an abnormal global network organization in all patient groups, as reflected by an increased path length, reduced transitivity, and increased modularity compared with controls. In addition, lMCIc, eMCIc, and AD patients showed a decreased path length and mean clustering compared with the sMCI group. At the local level, there were nodal clustering decreases mostly in AD patients, while the nodal closeness centrality detected abnormalities across all patient groups, showing overlapping changes in the hippocampi and amygdala and nonoverlapping changes in parietal, entorhinal, and orbitofrontal regions. These findings suggest that the prodromal and clinical stages of AD are associated with an abnormal network topology. PMID:27178195
Sidlauskaite, Justina; Caeyenberghs, Karen; Sonuga-Barke, Edmund; Roeyers, Herbert; Wiersema, Jan R
2015-01-01
Prior studies demonstrate altered organization of functional brain networks in attention-deficit/hyperactivity disorder (ADHD). However, the structural underpinnings of these functional disturbances are poorly understood. In the current study, we applied a graph-theoretic approach to whole-brain diffusion magnetic resonance imaging data to investigate the organization of structural brain networks in adults with ADHD and unaffected controls using deterministic fiber tractography. Groups did not differ in terms of global network metrics - small-worldness, global efficiency and clustering coefficient. However, there were widespread ADHD-related effects at the nodal level in relation to local efficiency and clustering. The affected nodes included superior occipital, supramarginal, superior temporal, inferior parietal, angular and inferior frontal gyri, as well as putamen, thalamus and posterior cerebellum. Lower local efficiency of left superior temporal and supramarginal gyri was associated with higher ADHD symptom scores. Also greater local clustering of right putamen and lower local clustering of left supramarginal gyrus correlated with ADHD symptom severity. Overall, the findings indicate preserved global but altered local network organization in adult ADHD implicating regions underpinning putative ADHD-related neuropsychological deficits. PMID:26640763
Quantification of topological features in cell meshes to explore E-cadherin dysfunction.
Mestre, Tânia; Figueiredo, Joana; Ribeiro, Ana Sofia; Paredes, Joana; Seruca, Raquel; Sanches, João Miguel
2016-01-01
In cancer, defective E-cadherin leads to cell detachment, migration and metastization. Further, alterations mediated by E-cadherin dysfunction affect cell topology and tissue organization. Herein, we propose a novel quantitative approach, based on microscopy images, to analyse abnormal cellular distribution patterns. We generated undirected graphs composed by sets of triangles which accurately reproduce cell positioning and structural organization within each image. Network analysis was developed by exploring triangle geometric features, namely area, edges length and formed angles, as well as their variance, when compared with the respective equilateral triangles. We generated synthetic networks, mimicking the diversity of cell-cell interaction patterns, and evaluated the applicability of the selected metrics to study topological features. Cells expressing wild-type E-cadherin and cancer-related mutants were used to validate our strategy. Specifically, A634V, R749W and P799R cancer-causing mutants present more disorganized spatial distribution when compared with wild-type cells. Moreover, P799R exhibited higher length and angle distortions and abnormal cytoskeletal organization, suggesting the formation of very dynamic and plastic cellular interactions. Hence, topological analysis of cell network diagrams is an effective tool to quantify changes in cell-cell interactions and, importantly, it can be applied to a myriad of processes, namely tissue morphogenesis and cancer. PMID:27151223
Quantification of topological features in cell meshes to explore E-cadherin dysfunction
Mestre, Tânia; Figueiredo, Joana; Ribeiro, Ana Sofia; Paredes, Joana; Seruca, Raquel; Sanches, João Miguel
2016-01-01
In cancer, defective E-cadherin leads to cell detachment, migration and metastization. Further, alterations mediated by E-cadherin dysfunction affect cell topology and tissue organization. Herein, we propose a novel quantitative approach, based on microscopy images, to analyse abnormal cellular distribution patterns. We generated undirected graphs composed by sets of triangles which accurately reproduce cell positioning and structural organization within each image. Network analysis was developed by exploring triangle geometric features, namely area, edges length and formed angles, as well as their variance, when compared with the respective equilateral triangles. We generated synthetic networks, mimicking the diversity of cell-cell interaction patterns, and evaluated the applicability of the selected metrics to study topological features. Cells expressing wild-type E-cadherin and cancer-related mutants were used to validate our strategy. Specifically, A634V, R749W and P799R cancer-causing mutants present more disorganized spatial distribution when compared with wild-type cells. Moreover, P799R exhibited higher length and angle distortions and abnormal cytoskeletal organization, suggesting the formation of very dynamic and plastic cellular interactions. Hence, topological analysis of cell network diagrams is an effective tool to quantify changes in cell-cell interactions and, importantly, it can be applied to a myriad of processes, namely tissue morphogenesis and cancer. PMID:27151223
Gao, Wen-Yang; Chen, Yao; Niu, Youhong; Williams, Kia; Cash, Lindsay; Perez, Pastor J.; Wojtas, Lukasz; Cai, Jianfeng; Chen, Yu-Sheng; Ma, Shengqian
2015-02-20
Crystal engineering of the nbo metal–organic framework (MOF) platform MOF-505 with a custom-designed azamacrocycle ligand (1,4,7,10-tetrazazcyclododecane-N,N',N'',N'''-tetra-p-methylbenzoic acid) leads to a high density of well-oriented Lewis active sites within the cuboctahedral cage in MMCF-2, [Cu₂(Cu-tactmb)(H₂O)₃(NO₃)₂]. This MOF demonstrates high catalytic activity for the chemical fixation of CO₂ into cyclic carbonates at room temperature under 1 atm pressure.
NASA Astrophysics Data System (ADS)
Hewitt, Andrew; Boltersdorf, Jonathon; Maggard, Paul; Dougherty, Daniel
Topological insulators (TIs) have a spin-textured surface state protected by time-reversal symmetry within a bulk insulating gap. Typical approaches to breaking time-reversal symmetry have been to introduce dilute magnetic impurities into a solid-solution synthesis. Organic molecules offer another route for magnetic-doping of TIs. It has been shown that a coupling may exist, along with a new hybrid-interface state, between the magnetic molecule Manganese Phthalocyanine (MnPc) and the TI Bi2Te3. We report the modification of the electronic band structure by the adsorption of MnPc molecules as measured by ultraviolet photoelectron spectroscopy. We show a new state emerging below the Fermi level at less than a monolayer coverage of MnPc molecules. We also observe an n-doping effect as charge is transferred from the molecule to the TI substrate in agreement with recent work. We suggest that this interface system may have important implications for understanding the role of local time reversal symmetry breaking in TI's and in controlling spin injection into these novel materials.
Karmakar, Anirban; Oliver, Clive L; Roy, Somnath; Öhrström, Lars
2015-06-14
A novel chiral metal-organic framework, [Cu4(HL)2(H2O)4(MeO)4]n (), has been successfully synthesized from a tripodal flexible ligand (2S,2'S,2''S)-2,2',2''-(benzenetricarbonyltris(azanediyl))tripropanoic acid (H3L). Compound was characterized by IR and X-ray powder diffraction analysis. The structure was determined by X-ray single crystal diffraction analysis revealing that possesses a 3D network, featuring a tetranuclear cubane-type secondary building block [Cu4(MeO)4](4+), formed via the connection of four metal ions to four methoxide ions. These secondary building blocks are linked by four different HL(2-) ligands to construct a porous three dimensional framework of the dia topology with one-dimensional channels. Compound also acts as a heterogeneous catalyst for the diastereoselective nitroaldol (Henry) reaction, providing high yields (up to 91%) and good diastereoselectivities under ambient conditions. This catalyst can be recycled without significant loss of activity. PMID:25645371
Aberrant Topological Patterns of Structural Cortical Networks in Psychogenic Erectile Dysfunction
Zhao, Lu; Guan, Min; Zhu, Xiaobo; Karama, Sherif; Khundrakpam, Budhachandra; Wang, Meiyun; Dong, Minghao; Qin, Wei; Tian, Jie; Evans, Alan C.; Shi, Dapeng
2015-01-01
Male sexual arousal (SA) has been known as a multidimensional experience involving closely interrelated and coordinated neurobehavioral components that rely on widespread brain regions. Recent functional neuroimaging studies have shown relation between abnormal/altered dynamics in these circuits and male sexual dysfunction. However, alterations in the topological1 organization of structural brain networks in male sexual dysfunction are still unclear. Here, we used graph theory2 to investigate the topological properties of large-scale structural brain networks, which were constructed using inter-regional correlations of cortical thickness between 78 cortical regions in 40 patients with psychogenic erectile dysfunction (pED) and 39 normal controls. Compared with normal controls, pED patients exhibited a less optimal global topological organization with reduced global and increased local efficiencies. Our results suggest disrupted neural integration among distant brain regions in pED patients, consistent with previous reports of impaired white matter structure and abnormal functional integrity in pED. Additionally, disrupted global network topology in pED was observed to be primarily relevant to altered subnetwork and nodal properties within the networks mediating the cognitive, motivational and inhibitory processes of male SA, possibly indicating disrupted integration of these networks in the whole brain networks and might account for pED patients' abnormal cognitive, motivational and inhibitory processes for male SA. In total, our findings provide evidence for disrupted integrity in large-scale brain networks underlying the neurobehavioral processes of male SA in pED and provide new insights into the understanding of the pathophysiological mechanisms of pED. PMID:26733849
NASA Astrophysics Data System (ADS)
Sun, Yayong; Zhao, Siwei; Ma, Haoran; Han, Yi; Liu, Kang; Wang, Lei
2016-06-01
Two novel three-dimensional (3D) pillar-layered metal-organic frameworks (MOFs), namely [Zn2(μ2-OH)(boaba)(1,4-bmimb)]n (1) and {[Zn5K2(μ2-H2O)2(boaba)4(1,2-bmimb)2(H2O)2]·H2O}n (2), were prepared by hydrothermal reactions (H3boaba=3,5-bis-oxyacetate-benzoic acid; 1,4-bmimb=1,4-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene; 1,2-bmimb =1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene). Notably, 1 exhibits a (3,5)-connected binodal (63)(69·8)-gra net with binuclear [Zn2(μ2-OH)(COO)]2+ clusters, while 2 shows a novel (4,4,5,9)-connected 4-nodal net constructed from the unique Zn(II)-K(I) heterometal rod-like substructures. The results indicate that the disposition of the 2-methylimidazolyl groups of bis(imidazole) ligands have a significant effect on structural diversity. Moreover, the photoluminescence properties of 1 and 2 have been investigated.
Induced topological pressure for topological dynamical systems
Xing, Zhitao; Chen, Ercai
2015-02-15
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.
Spectrum-Based and Collaborative Network Topology Analysis and Visualization
ERIC Educational Resources Information Center
Hu, Xianlin
2013-01-01
Networks are of significant importance in many application domains, such as World Wide Web and social networks, which often embed rich topological information. Since network topology captures the organization of network nodes and links, studying network topology is very important to network analysis. In this dissertation, we study networks by…
... cause. Can a longstanding head turn lead to any permanent problems? Yes, a significant abnormal head posture could cause permanent ... occipitocervical synostosis and unilateral hearing loss. Are there any ... postures? Yes. Abnormal head postures can usually be improved depending ...
... straw-yellow. Abnormally colored urine may be cloudy, dark, or blood-colored. Causes Abnormal urine color may ... red blood cells, or mucus in the urine. Dark brown but clear urine is a sign of ...
NASA Technical Reports Server (NTRS)
Lieberman, R. N.
1972-01-01
Given a directed graph, a natural topology is defined and relationships between standard topological properties and graph theoretical concepts are studied. In particular, the properties of connectivity and separatedness are investigated. A metric is introduced which is shown to be related to separatedness. The topological notions of continuity and homeomorphism. A class of maps is studied which preserve both graph and topological properties. Applications involving strong maps and contractions are also presented.
NASA Astrophysics Data System (ADS)
Yang, Ling; Li, Yu; You, Ao; Jiang, Juan; Zou, Xun-Zhong; Chen, Jin-Wei; Gu, Jin-Zhong; Kirillov, Alexander M.
2016-09-01
4-(5-Carboxypyridin-2-yl)isophthalic acid (H3L) was applied as a flexible, multifunctional N,O-building block for the hydrothermal self-assembly synthesis of two novel coordination compounds, namely 2D [Zn(μ3-HL)(H2O)]n·nH2O (1) and 3D [Pb2(μ5-HL)(μ6-HL)]n (2) coordination polymers (CPs). These compounds were obtained in aqueous medium from a mixture containing zinc(II) or lead(II) nitrate, H3L, and sodium hydroxide. The products were isolated as stable crystalline solids and were characterized by IR spectroscopy, elemental, thermogravimetric (TGA), powder (PXRD) and single-crystal X-ray diffraction analyses. Compound 1 possesses a 2D metal-organic layer with the fes topology, which is further extended into a 3D supramolecular framework via hydrogen bonds. In contrast, compound 2 features a very complex network structure, which was topologically classified as a binodal 5,6-connected net with the unique topology defined by the point symbol of (47.63)(49.66). Compounds 1 and 2 disclose an intense blue or green luminescent emission at room temperature.
Colloquium: Topological band theory
NASA Astrophysics Data System (ADS)
Bansil, A.; Lin, Hsin; Das, Tanmoy
2016-04-01
The first-principles band theory paradigm has been a key player not only in the process of discovering new classes of topologically interesting materials, but also for identifying salient characteristics of topological states, enabling direct and sharpened confrontation between theory and experiment. This review begins by discussing underpinnings of the topological band theory, which involve a layer of analysis and interpretation for assessing topological properties of band structures beyond the standard band theory construct. Methods for evaluating topological invariants are delineated, including crystals without inversion symmetry and interacting systems. The extent to which theoretically predicted properties and protections of topological states have been verified experimentally is discussed, including work on topological crystalline insulators, disorder and interaction driven topological insulators (TIs), topological superconductors, Weyl semimetal phases, and topological phase transitions. Successful strategies for new materials discovery process are outlined. A comprehensive survey of currently predicted 2D and 3D topological materials is provided. This includes binary, ternary, and quaternary compounds, transition metal and f -electron materials, Weyl and 3D Dirac semimetals, complex oxides, organometallics, skutterudites, and antiperovskites. Also included is the emerging area of 2D atomically thin films beyond graphene of various elements and their alloys, functional thin films, multilayer systems, and ultrathin films of 3D TIs, all of which hold exciting promise of wide-ranging applications. This Colloquium concludes by giving a perspective on research directions where further work will broadly benefit the topological materials field.
Abnormal Uterine Bleeding (Beyond the Basics)
... Approach to abnormal uterine bleeding in nonpregnant reproductive-age women Differential diagnosis of genital tract bleeding in women Postmenopausal uterine bleeding The following organizations also provide reliable health information. ● National Library of Medicine ( www.nlm.nih.gov/ ...
McLean, H S; Chen, H; Ryutov, D D
2003-01-23
Tangled magnetic field lines are common in laboratory and space plasmas, but determining the geometrical structure of magnetic fields in the presence of plasma is a difficult and still unresolved problem. To address this open question we developed and tested a new technique for measuring the magnetic field-line topology in magnetically confined plasmas. Our field-line tracing diagnostic (FLIRT) uses a high-power, short-pulse laser to launch a burst of energetic ({approx}100 keV) electrons from a target passing through the plasma. These electrons then generally follow magnetic-field lines until they strike a solid surface, where a burst of x-rays is produced. The field-line connection length can be determined from the time delay between the laser pulse and the burst of x-rays. The topology of the field lines can be inferred by measuring the connection length as a function of initial target location inside the plasma. Measuring the spatial distribution of x-ray production provides further information on the field topology, including the effects of magnetic field fluctuations and stochasticity. The goals of this experiment were to test the appropriate x-ray detectors; measure the background x-ray emission in a spheromak plasma; measure the energetic electron production by a short-pulse, high-power laser; make preliminary measurements of the edge field line topology in the Sustained Spheromak Physics Experiment (SSPX), and perform analytic studies of electron production. These results are reported in detail in three publications listed. A brief summary is given.
EDITORIAL: Topological data analysis Topological data analysis
NASA Astrophysics Data System (ADS)
Epstein, Charles; Carlsson, Gunnar; Edelsbrunner, Herbert
2011-12-01
methods for discretizing and compressing the information present in a geometric object so as to provide a useful, small representation of the object. The articles in this special issue are concerned with the applications of topology to the analysis of data sets. The adaptation of topological techniques from pure mathematics to the study of data from real systems is a project which has been undertaken during the past two decades, and the present volume contains various contributions to that project. At the current state of development, homology and persistence are two of the most popular topological techniques used in this context. Homology goes back to the beginnings of topology in Poincaré's influential papers. It is the idea that the connectivity of a space is determined by its cycles of different dimensions, and that these cycles organize themselves into abelian groups, called homology groups. Better known than these groups are their ranks, the Betti numbers of the space, which are non-negative integers that count the number of independent cycles in each dimension. To give an example, the zeroth Betti number counts the components, and the first counts the loops. A crucial feature of homology groups is that, given a reasonably explicit description of a space, their computation is an exercise in linear algebra. Even better known than the Betti numbers is the Euler characteristic, which we know from Poincaré's work, is equal to the alternating sum of the Betti numbers, which can be computed without computing the homology groups themselves. To give evidence that these numbers have relevant practical applications, we mention that integrating the Euler characteristic over a domain with sensor information can be used to count objects in the domain. This alone would not explain the popularity of homology groups, which we see rooted in the fact that they hit a sweet-spot that offers relatively strong discriminative power, and a clear intuitive meaning, all at a surprisingly
EDITORIAL: Topological data analysis Topological data analysis
NASA Astrophysics Data System (ADS)
2011-12-01
methods for discretizing and compressing the information present in a geometric object so as to provide a useful, small representation of the object. The articles in this special issue are concerned with the applications of topology to the analysis of data sets. The adaptation of topological techniques from pure mathematics to the study of data from real systems is a project which has been undertaken during the past two decades, and the present volume contains various contributions to that project. At the current state of development, homology and persistence are two of the most popular topological techniques used in this context. Homology goes back to the beginnings of topology in Poincaré's influential papers. It is the idea that the connectivity of a space is determined by its cycles of different dimensions, and that these cycles organize themselves into abelian groups, called homology groups. Better known than these groups are their ranks, the Betti numbers of the space, which are non-negative integers that count the number of independent cycles in each dimension. To give an example, the zeroth Betti number counts the components, and the first counts the loops. A crucial feature of homology groups is that, given a reasonably explicit description of a space, their computation is an exercise in linear algebra. Even better known than the Betti numbers is the Euler characteristic, which we know from Poincaré's work, is equal to the alternating sum of the Betti numbers, which can be computed without computing the homology groups themselves. To give evidence that these numbers have relevant practical applications, we mention that integrating the Euler characteristic over a domain with sensor information can be used to count objects in the domain. This alone would not explain the popularity of homology groups, which we see rooted in the fact that they hit a sweet-spot that offers relatively strong discriminative power, and a clear intuitive meaning, all at a surprisingly
Triple Point Topological Metals
NASA Astrophysics Data System (ADS)
Zhu, Ziming; Winkler, Georg W.; Wu, QuanSheng; Li, Ju; Soluyanov, Alexey A.
2016-07-01
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.
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.
Hutchinson incisors; Abnormal tooth shape; Peg teeth; Mulberry teeth; Conical teeth ... The appearance of normal teeth varies, especially the molars. ... conditions. Specific diseases can affect tooth shape, tooth ...
Hutchinson incisors; Abnormal tooth shape; Peg teeth; Mulberry teeth; Conical teeth ... from many different conditions. Specific diseases can affect tooth shape, tooth color, time of appearance, or absence ...
Weng Huasen; Lin Jiandi; Long Xifa; Li Zhihua; Lin Ping; Du Shaowu
2009-06-15
A new tetradentate imidazolate ligand 1,1',1'',1'''-(2,2',4,4',6,6'-hexamethylbiphenyl-3,3',5,5'-tetrayl) tetrakis(methylene)(1H-imidazole) (L) and four Ag(I)/Cu(I) coordination polymers, namely [(MCN){sub 3}L]{sub n} (1: M=Ag; 2: M=Cu), and [(MSCN){sub 2}L]{sub n} (3: M=Ag; 4: M=Cu) are described. All four new coordination polymers were fully characterized by infrared spectroscopy, elemental analysis and single-crystal X-ray diffraction. Compound 1 features a 3D supramolecular framework constructed by 1D chains through inter-chain Ag-N(CN) and inter-layer Ag-N(L) weak interactions with an uninodal 6{sup 6} topology. Complex 2 presents a 3D framework characterized by a tetranodal (3,4)-connected (3.4.5.10{sup 2}.11)(3.4.5.6.7.9)(3.6.7)(6.10{sup 2}) topology. Complexes 3 and 4 are isostructural, and both have a 3D network of trinodal 4-connected (4.8{sup 5}){sub 2}(4{sup 2}.8{sup 2}.10{sup 2})(4{sup 2}.8{sup 4}){sub 2} topology. The luminescent properties for these compounds in the solid state as well as the possible ferroelectric behavior of 1 are discussed. - Graphical abstract: Four coordination polymers built upon Ag(I)/Cu(I) pseudohalides and a imidazolate ligand have been solvothermally synthesized. The luminescent properties for these compounds and the possible ferroelectric behavior of 1 are discussed.
Membrane topology of hedgehog acyltransferase.
Matevossian, Armine; Resh, Marilyn D
2015-01-23
Hedgehog acyltransferase (Hhat) is a multipass transmembrane enzyme that mediates the covalent attachment of the 16-carbon fatty acid palmitate to the N-terminal cysteine of Sonic Hedgehog (Shh). Palmitoylation of Shh by Hhat is critical for short and long range signaling. Knowledge of the topological organization of Hhat transmembrane helices would enhance our understanding of Hhat-mediated Shh palmitoylation. Bioinformatics analysis of transmembrane domains within human Hhat using 10 different algorithms resulted in highly consistent predictions in the C-terminal, but not in the N-terminal, region of Hhat. To empirically determine the topology of Hhat, we designed and exploited Hhat constructs containing either terminal or 12 different internal epitope tags. We used selective permeabilization coupled with immunofluorescence as well as a protease protection assay to demonstrate that Hhat contains 10 transmembrane domains and 2 re-entrant loops. The invariant His and highly conserved Asp residues within the membrane-bound O-acyltransferase (MBOAT) homology domain are segregated on opposite sides of the endoplasmic reticulum membrane. The localization of His-379 on the lumenal membrane surface is consistent with a role for this invariant residue in catalysis. Analysis of the activity and stability of the Hhat constructs revealed that the C-terminal MBOAT domain is especially sensitive to manipulation. Moreover, there was remarkable similarity in the overall topological organization of Hhat and ghrelin O-acyltransferase, another MBOAT family member. Knowledge of the topological organization of Hhat could serve as an important tool for further design of selective Hhat inhibitors. PMID:25488661
Structurally abnormal human autosomes
1993-12-31
Chapter 25, discusses structurally abnormal human autosomes. This discussion includes: structurally abnormal chromosomes, chromosomal polymorphisms, pericentric inversions, paracentric inversions, deletions or partial monosomies, cri du chat (cat cry) syndrome, ring chromosomes, insertions, duplication or pure partial trisomy and mosaicism. 71 refs., 8 figs.
Topological Mirror Superconductivity
NASA Astrophysics Data System (ADS)
Zhang, Fan; Kane, C. L.; Mele, E. J.
2013-08-01
We demonstrate the existence of topological superconductors (SCs) protected by mirror and time-reversal symmetries. D-dimensional (D=1, 2, 3) crystalline SCs are characterized by 2D-1 independent integer topological invariants, which take the form of mirror Berry phases. These invariants determine the distribution of Majorana modes on a mirror symmetric boundary. The parity of total mirror Berry phase is the Z2 index of a class DIII SC, implying that a DIII topological SC with a mirror line must also be a topological mirror SC but not vice versa and that a DIII SC with a mirror plane is always time-reversal trivial but can be mirror topological. We introduce representative models and suggest experimental signatures in feasible systems. Advances in quantum computing, the case for nodal SCs, the case for class D, and topological SCs protected by rotational symmetries are pointed out.
Considerations for Multiprocessor Topologies
NASA Technical Reports Server (NTRS)
Byrd, Gregory T.; Delagi, Bruce A.
1987-01-01
Choosing a multiprocessor interconnection topology may depend on high-level considerations, such as the intended application domain and the expected number of processors. It certainly depends on low-level implementation details, such as packaging and communications protocols. The authors first use rough measures of cost and performance to characterize several topologies. They then examine how implementation details can affect the realizable performance of a topology.
NASA Astrophysics Data System (ADS)
Nash, Lisa; Kleckner, Dustin; Vitelli, Vincenzo; Turner, Ari M.; Irvine, William T. M.
2015-03-01
Topologically protected states can arise in electronic systems with broken time-reversal symmetry. We present a classical mechanical model for a solid in which broken time-reversal symmetry gives rise to topologically protected edge-modes, analogous to the edge modes in the quantum Hall effect. We will discuss numerical and experimental observations of these chiral edge-modes, their topological characterization, robustness and broader phenomenology.
Topological Phenotypes in Complex Leaf Venation Networks
NASA Astrophysics Data System (ADS)
Ronellenfitsch, Henrik; Lasser, Jana; Daly, Douglas; Katifori, Eleni
2015-03-01
The leaves of vascular plants contain highly complex venation networks consisting of recursively nested, hierarchically organized loops. We analyze the topology of the venation of leaves from ca. 200 species belonging to ca. 10 families, defining topological metrics that quantify the hierarchical nestedness of the network cycles. We find that most of the venation variability can be described by a two dimensional phenotypic space, where one dimension consists of a linear combination of geometrical metrics and the other dimension of topological, previously uncharacterized metrics. We show how this new topological dimension in the phenotypic space significantly improves identification of leaves from fragments, by calculating a ``leaf fingerprint'' from the topology and geometry of the higher order veins. Further, we present a simple model suggesting that the topological phenotypic traits can be explained by noise effects and variations in the timing of higher order vein developmental events. This work opens the path to (a) new quantitative identification techniques for leaves which go beyond simple geometric traits such as vein density and (b) topological quantification of other planar or almost planar networks such as arterial vaculature in the neocortex and lung tissue.
Scaffold topologies. 2. Analysis of chemical databases.
Wester, Michael J; Pollock, Sara N; Coutsias, Evangelos A; Allu, Tharun Kumar; Muresan, Sorel; Oprea, Tudor I
2008-07-01
We have systematically enumerated graph representations of scaffold topologies for up to eight-ring molecules and four-valence atoms, thus providing coverage of the lower portion of the chemical space of small molecules (Pollock et al. J. Chem. Inf. Model., this issue). Here, we examine scaffold topology distributions for several databases: ChemNavigator and PubChem for commercially available chemicals, the Dictionary of Natural Products, a set of 2742 launched drugs, WOMBAT, a database of medicinal chemistry compounds, and two subsets of PubChem, "actives" and DSSTox comprising toxic substances. We also examined a virtual database of exhaustively enumerated small organic molecules, GDB (Fink et al. Angew. Chem., Int. Ed. 2005, 44, 1504-1508), and we contrast the scaffold topology distribution from these collections to the complete coverage of up to eight-ring molecules. For reasons related, perhaps, to synthetic accessibility and complexity, scaffolds exhibiting six rings or more are poorly represented. Among all collections examined, PubChem has the greatest scaffold topological diversity, whereas GDB is the most limited. More than 50% of all entries (13 000 000+ actual and 13 000 000+ virtual compounds) exhibit only eight distinct topologies, one of which is the nonscaffold topology that represents all treelike structures. However, most of the topologies are represented by a single or very small number of examples. Within topologies, we found that three-way scaffold connections (3-nodes) are much more frequent compared to four-way (4-node) connections. Fused rings have a slightly higher frequency in biologically oriented databases. Scaffold topologies can be the first step toward an efficient coarse-grained classification scheme of the molecules found in chemical databases. PMID:18605681
NASA Astrophysics Data System (ADS)
Tanda, Satoshi; Matsuyama, Toyoki; Oda, Migaku; Asano, Yasuhiro; Yakubo, Kousuke
2006-08-01
I. Topology as universal concept. Optical vorticulture / M. V. Berry. On universality of mathematical structure in nature: topology / T. Matsuyama. Topology in physics / R. Jackiw. Isoholonomic problem and holonomic quantum computation / S. Tanimura -- II. Topological crystals. Topological crystals of NbSe[symbol] / S. Tanda ... [et al.]. Superconducting states on a Möbius strip / M. Hayashi ... [et al.]. Structure analyses of topological crystals using synchrotron radiation / Y. Nogami ... [et al.]. Transport measurement for topological charge density waves / T. Matsuura ... [et al.]. Theoretical study on Little-Parks oscillation in nanoscale superconducting ring / T. Suzuki, M. Hayashi and H. Ebisawa. Frustrated CDW states in topological crystals / K. Kuboki ... [et al.]. Law of growth in topological crystal / M. Tsubota ... [et al.]. Synthesis and electric properties of NbS[symbol]: possibility of room temperature charge density wave devices / H. Nobukane ... [et al.]. How does a single crystal become a Möbius strip? / T. Matsuura ... [et al.]. Development of X-ray analysis method for topological crystals / K. Yamamoto ... [et al.] -- III. Topological materials. Femtosecond-timescale structure dynamics in complex materials: the case of (NbSe[symbol])[symbol]I / D. Dvorsek and D. Mihailovic. Ultrafast dynamics of charge-density-wave in topological crystals / K. Shimatake ... [et al.]. Topology in morphologies of a folded single-chain polymer / Y. Takenaka, D. Baigl and K. Yoshikawa. One to two-dimensional conversion in topological crystals / T. Toshima, K. Inagaki and S. Tanda. Topological change of Fermi surface in Bismuth under high pressure / M. Kasami ... [et al.]. Topological change of 4, 4'-bis[9-dicarbazolyl]-2, 2'-biphenyl (CBP) by international rearrangement / K. S. Son ... [et al.]. Spin dynamics in Heisenberg triangular system VI5 cluster studied by [symbol]H-NMR / Y. Furukawa ... [et al.]. STM/STS on NbSe[symbol] nanotubes / K. Ichimura ...[et al
Qin, Yuan-cheng; Feng, Xue-feng; Luo, Feng; Sun, Gong-ming; Song, Yu-mei; Tian, Xiao-zhao; Huang, Hai-xiao; Zhu, Yan; Yuan, Zi-jun; Luo, Ming-biao; Liu, Shu-juan; Xu, Wen-yuan
2013-01-01
Reported here is a new microporous metal-organic framework, namely [Zn(2)(L)(btc)(Hbtc)] [NH(2)(CH(3))(2)]·(DMF)(2)(H(2)O)(4) (1), which is synthesized solvo(hydro)thermally by the self-assembly of Zn(NO(3))(2), N(4),N(4)-di(pyridin-3-yl)-[1,1'-biphenyl]-4,4'-dicarboxamide (L) and 1,3,5-benzenetricarboxylate acid (H(3)btc). Its topology can be described as a four-connecting 4(2)6(4) matrix containing both tetrahedral metal and ligand nodes. Interestingly, such a matrix has the same topology symbol as that observed in the well known sodalite (SOD) net, but the td10 of 434 is different from the td10 of 791 for the SOD net, indicative of an exceptional four-connecting 4(2)6(4) net. Another outstanding point is the highly selective adsorption of CO(2) over N(2), possibly contributed by a combined effect from the charged skeleton, the existence of functional groups of -CONH- and -COOH in 1. PMID:23108437
Expediting topology data gathering for the TOPDB database
Dobson, László; Langó, Tamás; Reményi, István; Tusnády, Gábor E.
2015-01-01
The Topology Data Bank of Transmembrane Proteins (TOPDB, http://topdb.enzim.ttk.mta.hu) contains experimentally determined topology data of transmembrane proteins. Recently, we have updated TOPDB from several sources and utilized a newly developed topology prediction algorithm to determine the most reliable topology using the results of experiments as constraints. In addition to collecting the experimentally determined topology data published in the last couple of years, we gathered topographies defined by the TMDET algorithm using 3D structures from the PDBTM. Results of global topology analysis of various organisms as well as topology data generated by high throughput techniques, like the sequential positions of N- or O-glycosylations were incorporated into the TOPDB database. Moreover, a new algorithm was developed to integrate scattered topology data from various publicly available databases and a new method was introduced to measure the reliability of predicted topologies. We show that reliability values highly correlate with the per protein topology accuracy of the utilized prediction method. Altogether, more than 52 000 new topology data and more than 2600 new transmembrane proteins have been collected since the last public release of the TOPDB database. PMID:25392424
Expediting topology data gathering for the TOPDB database.
Dobson, László; Langó, Tamás; Reményi, István; Tusnády, Gábor E
2015-01-01
The Topology Data Bank of Transmembrane Proteins (TOPDB, http://topdb.enzim.ttk.mta.hu) contains experimentally determined topology data of transmembrane proteins. Recently, we have updated TOPDB from several sources and utilized a newly developed topology prediction algorithm to determine the most reliable topology using the results of experiments as constraints. In addition to collecting the experimentally determined topology data published in the last couple of years, we gathered topographies defined by the TMDET algorithm using 3D structures from the PDBTM. Results of global topology analysis of various organisms as well as topology data generated by high throughput techniques, like the sequential positions of N- or O-glycosylations were incorporated into the TOPDB database. Moreover, a new algorithm was developed to integrate scattered topology data from various publicly available databases and a new method was introduced to measure the reliability of predicted topologies. We show that reliability values highly correlate with the per protein topology accuracy of the utilized prediction method. Altogether, more than 52,000 new topology data and more than 2600 new transmembrane proteins have been collected since the last public release of the TOPDB database. PMID:25392424
A global topology map of the Saccharomyces cerevisiae membrane proteome
NASA Astrophysics Data System (ADS)
Kim, Hyun; Melén, Karin; Österberg, Marie; von Heijne, Gunnar
2006-07-01
The yeast Saccharomyces cerevisiae is, arguably, the best understood eukaryotic model organism, yet comparatively little is known about its membrane proteome. Here, we report the cloning and expression of 617 S. cerevisiae membrane proteins as fusions to a C-terminal topology reporter and present experimentally constrained topology models for 546 proteins. By homology, the experimental topology information can be extended to 15,000 membrane proteins from 38 fully sequenced eukaryotic genomes. membrane proteins | membrane proteomics | yeast
"Jeopardy" in Abnormal Psychology.
ERIC Educational Resources Information Center
Keutzer, Carolin S.
1993-01-01
Describes the use of the board game, Jeopardy, in a college level abnormal psychology course. Finds increased student interaction and improved application of information. Reports generally favorable student evaluation of the technique. (CFR)
... Abnormal uterine bleeding is any bleeding from the uterus (through your vagina) other than your normal monthly ... or fibroids (small and large growths) in the uterus can also cause bleeding. Rarely, a thyroid problem, ...
... as cancer of the uterus, cervix, or vagina • Polycystic ovary syndrome How is abnormal bleeding diagnosed? Your health care ... before the fetus can survive outside the uterus. Polycystic Ovary Syndrome: A condition characterized by two of the following ...
NASA Astrophysics Data System (ADS)
Dzero, Maxim; Xia, Jing; Galitski, Victor; Coleman, Piers
2016-03-01
This article reviews recent theoretical and experimental work on a new class of topological material -- topological Kondo insulators, which develop through the interplay of strong correlations and spin-orbit interactions. The history of Kondo insulators is reviewed along with the theoretical models used to describe these heavy fermion compounds. The Fu-Kane method of topological classification of insulators is used to show that hybridization between the conduction electrons and localized f electrons in these systems gives rise to interaction-induced topological insulating behavior. Finally, some recent experimental results are discussed, which appear to confirm the theoretical prediction of the topological insulating behavior in samarium hexaboride, where the long-standing puzzle of the residual low-temperature conductivity has been shown to originate from robust surface states.
Charged topological entanglement entropy
NASA Astrophysics Data System (ADS)
Matsuura, Shunji; Wen, Xueda; Hung, Ling-Yan; Ryu, Shinsei
2016-05-01
A charged entanglement entropy is a new measure which probes quantum entanglement between different charge sectors. We study symmetry-protected topological (SPT) phases in (2+1)-dimensional space-time by using this charged entanglement entropy. SPT phases are short-range entangled states without topological order and hence cannot be detected by the topological entanglement entropy. We demonstrate that the universal part of the charged entanglement entropy is nonzero for nontrivial SPT phases and therefore it is a useful measure to detect short-range entangled topological phases. We also discuss that the classification of SPT phases based on the charged topological entanglement entropy is related to that of the braiding statistics of quasiparticles.
Hao, F.; Li, S.; Dong, W.; Hu, Z.; Huang, B.
1998-01-01
Three superimposed pressure systems are present in the Yinggehai Basin, South China Sea. A number of commercial, thermogenic gas accumulations have been found in an area in which shale diapirs occur. Because the reservoir intervals are shallow and very young, they must have filled with gas rapidly. The thick (up to 17 km) Tertiary and Quaternary sedimentary succession is dominated by shales, and is not disrupted by major faulting in the study area, a factor which seems to have had an important effect on both hydrocarbon generation and fluid migration. Organic-matter maturation in the deepest, most overpressured compartment has been significantly retarded as a result of the combined effects of excess pressure, the presence of large volumes of water, and the retention of generated hydrocarbons. This retardation is indicated by both kerogen-related parameters (vitrinite reflectance and Rock-Eval T(max)); and also by parameters based on the analysis of soluble organic matter (such as the C15+ hydrocarbon content, and the concentration of isoprenoid hydrocarbons relative to adjacent normal alkanes). In contrast to this, organic-matter maturation in shallow, normally-pressured strata in the diapiric area has been enhanced by hydrothermal fluid flow, which is clearly not topography-driven in origin. As a result, the hydrocarbon generation 'window' in the basin is considerably wider than could be expected from traditional geochemical modelling. These two unusual and contrasting anomalies in organic-matter maturation, together with other lines of evidence, suggest that there was a closed fluid system in the overpressured compartment until shale diapirs developed. The diapirs developed as a result of the intense overpressuring, and their growth was triggered by regional extensional stresses. They served as conduits through which fluids (both water and hydrocarbons) retained in the closed system could rapidly migrate. Fluid migration led to the modification of the thermal
Chromosomal Abnormalities and Schizophrenia
BASSETT, ANNE S.; CHOW, EVA W.C.; WEKSBERG, ROSANNA
2011-01-01
Schizophrenia is a common and serious psychiatric illness with strong evidence for genetic causation, but no specific loci yet identified. Chromosomal abnormalities associated with schizophrenia may help to understand the genetic complexity of the illness. This paper reviews the evidence for associations between chromosomal abnormalities and schizophrenia and related disorders. The results indicate that 22q11.2 microdeletions detected by fluorescence in-situ hybridization (FISH) are significantly associated with schizophrenia. Sex chromosome abnormalities seem to be increased in schizophrenia but insufficient data are available to indicate whether schizophrenia or related disorders are increased in patients with sex chromosome aneuploidies. Other reports of chromosomal abnormalities associated with schizophrenia have the potential to be important adjuncts to linkage studies in gene localization. Advances in molecular cytogenetic techniques (i.e., FISH) have produced significant increases in rates of identified abnormalities in schizophrenia, particularly in patients with very early age at onset, learning difficulties or mental retardation, or dysmorphic features. The results emphasize the importance of considering behavioral phenotypes, including adult onset psychiatric illnesses, in genetic syndromes and the need for clinicians to actively consider identifying chromosomal abnormalities and genetic syndromes in selected psychiatric patients. PMID:10813803
Linked topological colloids in a nematic host.
Martinez, Angel; Hermosillo, Leonardo; Tasinkevych, Mykola; Smalyukh, Ivan I
2015-04-14
Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. Thus far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Here we develop a topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogs of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex composite materials with interlinking-based structural organization. PMID:25825765
Linked topological colloids in a nematic host
Martinez, Angel; Hermosillo, Leonardo; Tasinkevych, Mykola; Smalyukh, Ivan I.
2015-01-01
Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. Thus far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Here we develop a topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogs of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex composite materials with interlinking-based structural organization. PMID:25825765
Colossal magnetoresistance in topological Kondo insulator
NASA Astrophysics Data System (ADS)
Slieptsov, Igor O.; Karnaukhov, Igor N.
2016-04-01
Abnormal electronic properties of complex systems require new ideas concerning explanation of their behavior and possibility of realization. In this acticle we show that a colossal magnetoresistance is realized in the state of the topological Kondo insulator, that is similar to the Kondo insulator state in the Kondo lattice. The mechanism of the phenomenon is the following: in the spin gapless phase an external magnetic field induces the gap in the spectrum of spin excitations, the gap in the spectrum of fermions is opened due to a hybridization between spin and fermion subsystems at half-filling, as the result the magnetic field leads to metal–insulator (or bad metal–insulator) phase transition. A model of the topological Kondo lattice defined on a honeycomb lattice is studied for the case when spinless fermion bands are half-filled. It is shown that the hybridization between local moments and itinerant fermions should be understood as the hybridization between corresponding Majorana fermions of the spin and charge sectors. The system is a topological insulator, single fermion and spin excitations at low energies are massive. We will show that a spin gap induces a gap in the charge channel, it leads to an appearance of a topological insulator state with chiral gapless edge modes and the Chern number one or two depending on the exchange integrals’ values. The relevance of this to the traditional Kondo insulator state is discussed.
NASA Astrophysics Data System (ADS)
Knitter, Sebastian; Fatt Liew, Seng; Xiong, Wen; Guy, Mikhael I.; Solomon, Glenn S.; Cao, Hui
2016-01-01
We introduce a topological defect to a regular photonic crystal defect cavity with anisotropic unit cell. Spatially localized resonances are formed and have high quality factor. Unlike the regular photonic crystal defect states, the localized resonances in the topological defect structures support powerflow vortices. Experimentally we realize lasing in the topological defect cavities with optical pumping. This work shows that the spatially inhomogeneous variation of the unit cell orientation adds another degree of freedom to the control of lasing modes, enabling the manipulation of the field pattern and energy flow landscape.
Topological Solitons in Physics.
ERIC Educational Resources Information Center
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)
Aperiodic Weak Topological Superconductors.
Fulga, I C; Pikulin, D I; Loring, T A
2016-06-24
Weak topological phases are usually described in terms of protection by the lattice translation symmetry. Their characterization explicitly relies on periodicity since weak invariants are expressed in terms of the momentum-space torus. We prove the compatibility of weak topological superconductors with aperiodic systems, such as quasicrystals. We go beyond usual descriptions of weak topological phases and introduce a novel, real-space formulation of the weak invariant, based on the Clifford pseudospectrum. A nontrivial value of this index implies a nontrivial bulk phase, which is robust against disorder and hosts localized zero-energy modes at the edge. Our recipe for determining the weak invariant is directly applicable to any finite-sized system, including disordered lattice models. This direct method enables a quantitative analysis of the level of disorder the topological protection can withstand. PMID:27391744
Aperiodic Weak Topological Superconductors
NASA Astrophysics Data System (ADS)
Fulga, I. C.; Pikulin, D. I.; Loring, T. A.
2016-06-01
Weak topological phases are usually described in terms of protection by the lattice translation symmetry. Their characterization explicitly relies on periodicity since weak invariants are expressed in terms of the momentum-space torus. We prove the compatibility of weak topological superconductors with aperiodic systems, such as quasicrystals. We go beyond usual descriptions of weak topological phases and introduce a novel, real-space formulation of the weak invariant, based on the Clifford pseudospectrum. A nontrivial value of this index implies a nontrivial bulk phase, which is robust against disorder and hosts localized zero-energy modes at the edge. Our recipe for determining the weak invariant is directly applicable to any finite-sized system, including disordered lattice models. This direct method enables a quantitative analysis of the level of disorder the topological protection can withstand.
Polariton Z Topological Insulator
NASA Astrophysics Data System (ADS)
Nalitov, A. V.; Solnyshkov, D. D.; Malpuech, G.
2015-03-01
We demonstrate that honeycomb arrays of microcavity pillars behave as an optical-frequency two-dimensional photonic topological insulator. We show that the interplay between the photonic spin-orbit coupling natively present in this system and the Zeeman splitting of exciton polaritons in external magnetic fields leads to the opening of a nontrivial gap characterized by a C =±2 set of band Chern numbers and to the formation of topologically protected one-way edge states.
Recipe for Topological Polaritons
NASA Astrophysics Data System (ADS)
Karzig, Torsten; Bardyn, Charles-Edouard; Lindner, Netanel; Refael, Gil
2015-03-01
The interaction between light and matter can give rise to novel topological states. This principle was recently exemplified in Floquet topological insulators, where classical light was used to induce a topological electronic band structure. Here, in contrast, we show that mixing single photons with excitons can result in new topological polaritonic states -- or ``topolaritons''. Taken separately, the underlying photons and excitons are topologically trivial. Combined appropriately, however, they give rise to non-trivial polaritonic bands with chiral edge modes allowing for unidirectional polariton propagation. The main ingredient in our construction is an exciton-photon coupling with a phase that winds in momentum space. We demonstrate how this winding emerges from spin-orbit coupling in the electronic system and an applied Zeeman field. We discuss the requirements for obtaining a sizable topological gap in the polariton spectrum. Funded by the Institute for Quantum Information and Matter, the Bi-National Science Foundation and I-Core: the Israeli Excellence Center ``Circle of Light'', and Darpa under funding for FENA, and the Swiss National Science Foundation.
Tunable Topological Phononic Crystals
NASA Astrophysics Data System (ADS)
Chen, Ze-Guo; Wu, Ying
2016-05-01
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.
PhyBin: binning trees by topology.
Newton, Ryan R; Newton, Irene L G
2013-01-01
A major goal of many evolutionary analyses is to determine the true evolutionary history of an organism. Molecular methods that rely on the phylogenetic signal generated by a few to a handful of loci can be used to approximate the evolution of the entire organism but fall short of providing a global, genome-wide, perspective on evolutionary processes. Indeed, individual genes in a genome may have different evolutionary histories. Therefore, it is informative to analyze the number and kind of phylogenetic topologies found within an orthologous set of genes across a genome. Here we present PhyBin: a flexible program for clustering gene trees based on topological structure. PhyBin can generate bins of topologies corresponding to exactly identical trees or can utilize Robinson-Fould's distance matrices to generate clusters of similar trees, using a user-defined threshold. Additionally, PhyBin allows the user to adjust for potential noise in the dataset (as may be produced when comparing very closely related organisms) by pre-processing trees to collapse very short branches or those nodes not meeting a defined bootstrap threshold. As a test case, we generated individual trees based on an orthologous gene set from 10 Wolbachia species across four different supergroups (A-D) and utilized PhyBin to categorize the complete set of topologies produced from this dataset. Using this approach, we were able to show that although a single topology generally dominated the analysis, confirming the separation of the supergroups, many genes supported alternative evolutionary histories. Because PhyBin's output provides the user with lists of gene trees in each topological cluster, it can be used to explore potential reasons for discrepancies between phylogenies including homoplasies, long-branch attraction, or horizontal gene transfer events. PMID:24167782
PhyBin: binning trees by topology
Newton, Ryan R.
2013-01-01
A major goal of many evolutionary analyses is to determine the true evolutionary history of an organism. Molecular methods that rely on the phylogenetic signal generated by a few to a handful of loci can be used to approximate the evolution of the entire organism but fall short of providing a global, genome-wide, perspective on evolutionary processes. Indeed, individual genes in a genome may have different evolutionary histories. Therefore, it is informative to analyze the number and kind of phylogenetic topologies found within an orthologous set of genes across a genome. Here we present PhyBin: a flexible program for clustering gene trees based on topological structure. PhyBin can generate bins of topologies corresponding to exactly identical trees or can utilize Robinson-Fould’s distance matrices to generate clusters of similar trees, using a user-defined threshold. Additionally, PhyBin allows the user to adjust for potential noise in the dataset (as may be produced when comparing very closely related organisms) by pre-processing trees to collapse very short branches or those nodes not meeting a defined bootstrap threshold. As a test case, we generated individual trees based on an orthologous gene set from 10 Wolbachia species across four different supergroups (A–D) and utilized PhyBin to categorize the complete set of topologies produced from this dataset. Using this approach, we were able to show that although a single topology generally dominated the analysis, confirming the separation of the supergroups, many genes supported alternative evolutionary histories. Because PhyBin’s output provides the user with lists of gene trees in each topological cluster, it can be used to explore potential reasons for discrepancies between phylogenies including homoplasies, long-branch attraction, or horizontal gene transfer events. PMID:24167782
Omura, Yoshiaki; O'Young, Brian; Jones, Marilyn; Nihrane, Abdalla; Duvvi, Harsha; Paluch, Kamila; Shimotsuura, Yasuhiro; Ohki, Motomu
2012-01-01
Diagnoses of bone marrow associated malignancies such as Acute & Chronic Lymphocytic Leukemia, Acute & Chronic Myelogenous (Myeloid) Leukemia, Hodgkin's Lymphoma & Non-Hodgkin's Lymphoma, and Multiple Myeloma are often missed without a blood test. However, in 2008, Omura Y reported several newly discovered organ representation areas that exist between the lower end of the eyebrows and upper end of the upper eyelid. This space was divided into 5 organ representation areas. The first space (more than 1/4 of entire space) near the side of the face (temple) is the bone marrow representation area (BMRA). Therefore, we examined the bone marrow representation areas non-invasively using the Bi-Digital O-Ring Test (BDORT). When the small rectangular shaped part of the BMRA is strong negative (-) with more than -2, often there is a malignancy associated with bone marrow. In this area, we found 1) Integrin alpha5beta1 & Oncogen C-fos Ab2 increased very significantly between 125-300 ng BDORT units; 2) very high Chrysotile Asbestos (0.11-0.14 mg); 3) markedly reduced Acetylcholine of less than 1 ng; 4) significantly reduced telomere of less than 1 yg (= 10(-24) g); and 5) Increased 8-OH-dG (often more than 5 ng). Once the abnormal small rectangular area is localized by BDORT, by detecting the specific microscope slide which produces EMF (electromagnetic field) resonance, one can diagnose these malignancies non-invasively in about 10 minutes. When a subject has any one of the above 7 types of bone marrow associated malignancies, the 5 aforementioned abnormal parameters can be detected. When Acetylcholine is markedly reduced to 0.25 ng or less, 8-OH-dG is 10 ng or higher, and Sirtuin 1 (one of the 7 mammalian longevity genes products) in both the Hippocampus and the body is 0.025 pg or less, most of the patients have a very poor prognosis. However, we found that increasing normal cell telomere & longevity gene product Sirtuin 1 can often improve both pathology & prognosis. All
LHCb Topological Trigger Reoptimization
NASA Astrophysics Data System (ADS)
Likhomanenko, Tatiana; Ilten, Philip; Khairullin, Egor; Rogozhnikov, Alex; Ustyuzhanin, Andrey; Williams, Michael
2015-12-01
The main b-physics trigger algorithm used by the LHCb experiment is the so- called topological trigger. The topological trigger selects vertices which are a) detached from the primary proton-proton collision and b) compatible with coming from the decay of a b-hadron. In the LHC Run 1, this trigger, which utilized a custom boosted decision tree algorithm, selected a nearly 100% pure sample of b-hadrons with a typical efficiency of 60-70%; its output was used in about 60% of LHCb papers. This talk presents studies carried out to optimize the topological trigger for LHC Run 2. In particular, we have carried out a detailed comparison of various machine learning classifier algorithms, e.g., AdaBoost, MatrixNet and neural networks. The topological trigger algorithm is designed to select all ’interesting” decays of b-hadrons, but cannot be trained on every such decay. Studies have therefore been performed to determine how to optimize the performance of the classification algorithm on decays not used in the training. Methods studied include cascading, ensembling and blending techniques. Furthermore, novel boosting techniques have been implemented that will help reduce systematic uncertainties in Run 2 measurements. We demonstrate that the reoptimized topological trigger is expected to significantly improve on the Run 1 performance for a wide range of b-hadron decays.
Platform for engineering topological superconductors: Superlattices on Rashba superconductors
NASA Astrophysics Data System (ADS)
Lu, Yao; He, Wen-Yu; Xu, Dong-Hui; Lin, Nian; Law, K. T.
2016-07-01
The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose an experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without or with little fine tuning of the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.
Morphological abnormalities in elasmobranchs.
Moore, A B M
2015-08-01
A total of 10 abnormal free-swimming (i.e., post-birth) elasmobranchs are reported from The (Persian-Arabian) Gulf, encompassing five species and including deformed heads, snouts, caudal fins and claspers. The complete absence of pelvic fins in a milk shark Rhizoprionodon acutus may be the first record in any elasmobranch. Possible causes, including the extreme environmental conditions and the high level of anthropogenic pollution particular to The Gulf, are briefly discussed. PMID:25903257
Chromosome abnormalities in glioma
Li, Y.S.; Ramsay, D.A.; Fan, Y.S.
1994-09-01
Cytogenetic studies were performed in 25 patients with gliomas. An interesting finding was a seemingly identical abnormality, an extra band on the tip of the short arm of chromosome 1, add(1)(p36), in two cases. The abnormality was present in all cells from a patient with a glioblastoma and in 27% of the tumor cells from a patient with a recurrent irradiated anaplastic astrocytoma; in the latter case, 7 unrelated abnormal clones were identified except 4 of those clones shared a common change, -Y. Three similar cases have been described previously. In a patient with pleomorphic astrocytoma, the band 1q42 in both homologues of chromosome 1 was involved in two different rearrangements. A review of the literature revealed that deletion of the long arm of chromosome 1 including 1q42 often occurs in glioma. This may indicate a possible tumor suppressor gene in this region. Cytogenetic follow-up studies were carried out in two patients and emergence of unrelated clones were noted in both. A total of 124 clonal breakpoints were identified in the 25 patients. The breakpoints which occurred three times or more were: 1p36, 1p22, 1q21, 1q25, 3q21, 7q32, 8q22, 9q22, 16q22, and 22q13.
[Congenital foot abnormalities].
Delpont, M; Lafosse, T; Bachy, M; Mary, P; Alves, A; Vialle, R
2015-03-01
The foot may be the site of birth defects. These abnormalities are sometimes suspected prenatally. Final diagnosis depends on clinical examination at birth. These deformations can be simple malpositions: metatarsus adductus, talipes calcaneovalgus and pes supinatus. The prognosis is excellent spontaneously or with a simple orthopedic treatment. Surgery remains outstanding. The use of a pediatric orthopedist will be considered if malposition does not relax after several weeks. Malformations (clubfoot, vertical talus and skew foot) require specialized care early. Clubfoot is characterized by an equine and varus hindfoot, an adducted and supine forefoot, not reducible. Vertical talus combines equine hindfoot and dorsiflexion of the forefoot, which is performed in the midfoot instead of the ankle. Skew foot is suspected when a metatarsus adductus is resistant to conservative treatment. Early treatment is primarily orthopedic at birth. Surgical treatment begins to be considered after walking age. Keep in mind that an abnormality of the foot may be associated with other conditions: malposition with congenital hip, malformations with syndromes, neurological and genetic abnormalities. PMID:25524290
Topological analysis of chaotic time series
NASA Astrophysics Data System (ADS)
Gilmore, Robert
1997-10-01
Topological methods have recently been developed for the classification, analysis, and synthesis of chaotic time series. These methods can be applied to time series with a Lyapunov dimension less than three. The procedure determines the stretching and squeezing mechanisms which operate to create a strange attractor and organize all the unstable periodic orbits in the attractor in a unique way. Strange attractors are identified by a set of integers. These are topological invariants for a two dimensional branched manifold, which is the infinite dissipation limit of the strange attractor. It is remarkable that this topological information can be extracted from chaotic time series. The data required for this analysis need not be extensive or exceptionally clean. The topological invariants: (1) are subject to validation/invalidation tests; (2) describe how to model the data; and (3) do not change as control parameters change. Topological analysis is the first step in a doubly discrete classification scheme for strange attractors. The second discrete classification involves specification of a 'basis set' set of periodic orbits whose presence forces the existence of all other periodic orbits in the strange attractor. The basis set of orbits does change as control parameters change. Quantitative models developed to describe time series data are tested by the methods of entrainment. This analysis procedure has been applied to analyze a number of data sets. Several analyses are described.
Adiabatic topological quantum computing
NASA Astrophysics Data System (ADS)
Cesare, Chris; Landahl, Andrew J.; Bacon, Dave; Flammia, Steven T.; Neels, Alice
2015-07-01
Topological quantum computing promises error-resistant quantum computation without active error correction. However, there is a worry that during the process of executing quantum gates by braiding anyons around each other, extra anyonic excitations will be created that will disorder the encoded quantum information. Here, we explore this question in detail by studying adiabatic code deformations on Hamiltonians based on topological codes, notably Kitaev's surface codes and the more recently discovered color codes. We develop protocols that enable universal quantum computing by adiabatic evolution in a way that keeps the energy gap of the system constant with respect to the computation size and introduces only simple local Hamiltonian interactions. This allows one to perform holonomic quantum computing with these topological quantum computing systems. The tools we develop allow one to go beyond numerical simulations and understand these processes analytically.
Topology optimized microbioreactors.
Schäpper, Daniel; Lencastre Fernandes, Rita; Lantz, Anna Eliasson; Okkels, Fridolin; Bruus, Henrik; Gernaey, Krist V
2011-04-01
This article presents the fusion of two hitherto unrelated fields--microbioreactors and topology optimization. The basis for this study is a rectangular microbioreactor with homogeneously distributed immobilized brewers yeast cells (Saccharomyces cerevisiae) that produce a recombinant protein. Topology optimization is then used to change the spatial distribution of cells in the reactor in order to optimize for maximal product flow out of the reactor. This distribution accounts for potentially negative effects of, for example, by-product inhibition. We show that the theoretical improvement in productivity is at least fivefold compared with the homogeneous reactor. The improvements obtained by applying topology optimization are largest where either nutrition is scarce or inhibition effects are pronounced. PMID:21404253
Abnormal pressures as hydrodynamic phenomena
Neuzil, C.E.
1995-01-01
So-called abnormal pressures, subsurface fluid pressures significantly higher or lower than hydrostatic, have excited speculation about their origin since subsurface exploration first encountered them. Two distinct conceptual models for abnormal pressures have gained currency among earth scientists. The static model sees abnormal pressures generally as relict features preserved by a virtual absence of fluid flow over geologic time. The hydrodynamic model instead envisions abnormal pressures as phenomena in which flow usually plays an important role. This paper develops the theoretical framework for abnormal pressures as hydrodynamic phenomena, shows that it explains the manifold occurrences of abnormal pressures, and examines the implications of this approach. -from Author
Raghu, S.
2010-03-02
We consider extended Hubbard models with repulsive interactions on a honeycomb lattice, and the transitions from the semimetal to Mott insulating phases at half-filling. Because of the frustrated nature of the second-neighbor interactions, topological Mott phases displaying the quantum Hall and the quantum spin Hall effects are found for spinless and spin fermion models, respectively. The mean-field phase diagram is presented and the fluctuations are treated within the random phase approximation. Renormalization group analysis shows that these states can be favored over the topologically trivial Mott insulating states.
Zhang, Jingrong; Tang, Wei; Huang, Yulan; Niu, Xiangli; Zhao, Yu; Han, Yi; Liu, Yongsheng
2015-01-01
The indeterminate gametophyte1 (ig1) mutation was first characterized to modulate female gametophyte development in maize (Zea mays). However, the function of its rice orthologue, OsIG1, remains unknown. For this, we first analysed OsIG1 localization from differential tissues in rice. Real-time quantitative PCR (qRT-PCR) and histochemical staining results demonstrated that the expression signal of OsIG1 was strongly detected in young inflorescence, moderately in mature flower and weakly in leaf. Furthermore, RNA in situ hybridization analyses exhibited that OsIG1 was strongly expressed in inflorescence meristems, floral meristems, empty-glume- and floret- primordia, especially in the primordia of stamens and immature ovules, and the micropylar side of the mature ovary. In OsIG1-RNAi lines, wrinkled blade formation was accompanied by increased leaf inclination angle. Cross-section further showed that the number of bulliform cells located between the vasculatures was significantly increased, indicating that OsIG1 is involved in division and differentiation of bulliform cell and lateral growth during leaf development. OsIG1-RNAi suppression lines showed pleiotropic phenotypes, including degenerated palea, glume-like features and open hull. In addition, a single OsIG1-RNAi floret is characterized by frequently developing double ovules with abnormal embryo sac development. Additionally, down-regulation of OsIG1 differentially affected the expression of genes associated with the floral organ development including EG1, OsMADS6 and OsMADS1. Taken together, these results demonstrate that OsIG1 plays an essential role in the regulation of empty-glume identity, floral organ number control and female gametophyte development in rice. PMID:25324400
Feeling Abnormal: Simulation of Deviancy in Abnormal and Exceptionality Courses.
ERIC Educational Resources Information Center
Fernald, Charles D.
1980-01-01
Describes activity in which student in abnormal psychology and psychology of exceptional children classes personally experience being judged abnormal. The experience allows the students to remember relevant research, become sensitized to the feelings of individuals classified as deviant, and use caution in classifying individuals as abnormal.…
Hemorheological abnormalities in human arterial hypertension
NASA Astrophysics Data System (ADS)
Lo Presti, Rosalia; Hopps, Eugenia; Caimi, Gregorio
2014-05-01
Blood rheology is impaired in hypertensive patients. The alteration involves blood and plasma viscosity, and the erythrocyte behaviour is often abnormal. The hemorheological pattern appears to be related to some pathophysiological mechanisms of hypertension and to organ damage, in particular left ventricular hypertrophy and myocardial ischemia. Abnormalities have been observed in erythrocyte membrane fluidity, explored by fluorescence spectroscopy and electron spin resonance. This may be relevant for red cell flow in microvessels and oxygen delivery to tissues. Although blood viscosity is not a direct target of antihypertensive therapy, the rheological properties of blood play a role in the pathophysiology of arterial hypertension and its vascular complications.
Topological structure dynamics revealing collective evolution in active nematics
Shi, Xia-qing; Ma, Yu-qiang
2013-01-01
Topological defects frequently emerge in active matter like bacterial colonies, cytoskeleton extracts on substrates, self-propelled granular or colloidal layers and so on, but their dynamical properties and the relations to large-scale organization and fluctuations in these active systems are seldom touched. Here we reveal, through a simple model for active nematics using self-driven hard elliptic rods, that the excitation, annihilation and transportation of topological defects differ markedly from those in non-active media. These dynamical processes exhibit strong irreversibility in active nematics in the absence of detailed balance. Moreover, topological defects are the key factors in organizing large-scale dynamic structures and collective flows, resulting in multi-spatial temporal effects. These findings allow us to control the self-organization of active matter through topological structures. PMID:24346733
Topological dynamics in supramolecular rotors.
Palma, Carlos-Andres; Björk, Jonas; Rao, Francesco; Kühne, Dirk; Klappenberger, Florian; Barth, Johannes V
2014-08-13
Artificial molecular switches, rotors, and machines are set to establish design rules and applications beyond their biological counterparts. Herein we exemplify the role of noncovalent interactions and transient rearrangements in the complex behavior of supramolecular rotors caged in a 2D metal-organic coordination network. Combined scanning tunneling microscopy experiments and molecular dynamics modeling of a supramolecular rotor with respective rotation rates matching with 0.2 kcal mol(-1) (9 meV) precision, identify key steps in collective rotation events and reconfigurations. We notably reveal that stereoisomerization of the chiral trimeric units entails topological isomerization whereas rotation occurs in a topology conserving, two-step asynchronous process. In supramolecular constructs, distinct displacements of subunits occur inducing a markedly lower rotation barrier as compared to synchronous mechanisms of rigid rotors. Moreover, the chemical environment can be instructed to control the system dynamics. Our observations allow for a definition of mechanical cooperativity based on a significant reduction of free energy barriers in supramolecules compared to rigid molecules. PMID:25078022
Topological states in photonic systems
NASA Astrophysics Data System (ADS)
Lu, Ling; Joannopoulos, John D.; Soljačić, Marin
2016-07-01
Optics played a key role in the discovery of geometric phase. It now joins the journey of exploring topological physics, bringing bosonic topological states that equip us with the ability to make perfect photonic devices using imperfect interfaces.
Abnormal human sex chromosome constitutions
1993-12-31
Chapter 22, discusses abnormal human sex chromosome constitution. Aneuploidy of X chromosomes with a female phenotype, sex chromosome aneuploidy with a male phenotype, and various abnormalities in X chromosome behavior are described. 31 refs., 2 figs.
Exercises to Improve Gait Abnormalities
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Dynamic and topological complexity
NASA Astrophysics Data System (ADS)
Turalska, Malgorzata; Geneston, Elvis; Grigolini, Paolo
2010-03-01
Cooperative phenomena in complex networks are expected to display unusual characteristics, associated with the peculiar topology of these systems. In this context we study networks of interacting stochastic two-state units as a model of cooperative decision making. Each unit in isolation generates a Poisson process with rate g. We show that when the cooperation is introduced, the decision-making process becomes intermittent. The decision-time distribution density characterized by inverse power-law behavior is defined as a dynamic complexity. Further, the onset of intermittency, expressed in terms of the coupling parameter K, is used as a measure of dynamic efficiency of investigated topologies. We find that the dynamic complexity emerges from regular and small-world topologies. In contrast, both random and scale-free networks correspond to fast transition into exponential decision-time distribution. This property is accompanied by high dynamic efficiency of the decision-making process. Our results indicate that complex dynamical processes occurring on networks could be related to relatively simple topologies.
Rendering the Topological Spines
Nieves-Rivera, D.
2015-05-05
Many tools to analyze and represent high dimensional data already exits yet most of them are not flexible, informative and intuitive enough to help the scientists make the corresponding analysis and predictions, understand the structure and complexity of scientific data, get a complete picture of it and explore a greater number of hypotheses. With this in mind, N-Dimensional Data Analysis and Visualization (ND²AV) is being developed to serve as an interactive visual analysis platform with the purpose of coupling together a number of these existing tools that range from statistics, machine learning, and data mining, with new techniques, in particular with new visualization approaches. My task is to create the rendering and implementation of a new concept called topological spines in order to extend ND²AV's scope. Other existing visualization tools create a representation preserving either the topological properties or the structural (geometric) ones because it is challenging to preserve them both simultaneously. Overcoming such challenge by creating a balance in between them, the topological spines are introduced as a new approach that aims to preserve them both. Its render using OpenGL and C++ and is currently being tested to further on be implemented on ND²AV. In this paper I will present what are the Topological Spines and how they are rendered.
Synthesising Topological Links
Baas, Nils A.; Seeman, Nadrian C.; Stacey, Andrew
2014-01-01
We discuss the chemical synthesis of topological links, in particular higher order links which have the Brunnian property (namely that removal of any one component unlinks the entire system). Furthermore, we suggest how to obtain both two dimensional and three dimensional objects (surfaces and solids, respectively) which also have this Brunnian property. PMID:25678732
Topological Crystalline Insulators
NASA Astrophysics Data System (ADS)
Hsieh, Timothy
2015-03-01
Topological crystalline insulators (TCI) are new phases of matter in which nontrivial band topology and crystal symmetry unite to protect metallic states on the boundary. Remarkably, TCIs have been predicted and observed in the conveniently simple rocksalt SnTe class of IV-VI semiconductors. Despite the simple crystal structure, the interplay between topology and crystal symmetry in these materials have led to a rich variety of new phenomena, including the coexistence of massless and massive Dirac fermions arising from ferroelectric distortion and strain-induced flat band superconductivity. These new physical mechanisms are not only of intrinsic interest but may also find application in new transistor devices. After discussing the topological nature and potential uses of IV-VI family TCIs, I will present recent predictions of TCIs in several anti-perovskite materials. The origin of TCI in this new class of materials is strikingly different and involves the band inversion of two J = 3/2 quartets of Dirac fermions, which together form a ``Dirac octet.'' As interactions play a significant role in many anti-perovskites, this prediction serves as first step toward realizing TCIs in strongly correlated systems. This work is supported by NSF Graduate Research Fellowship No. 0645960 and DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010526.
Spontaneous origin of topological complexity in the cerebral cortex
Chapline, G.
1995-04-07
Attention is drawn to the possibility of regarding the cerebral cortex as a physical system whose only excitations are topological. An attractive feature of such a hypothesis is that it is possible to understand how local dynamics could spontaneously give rise to a large scale organization of neurons and synapses that one might associate with sophisticated cognitive capabilities. It is suggested that the spontaneous appearance of topological disorder in the topological phases of 2-D and 4-D quantum gravity illustrates how the topological complexity of the human brain can develop. In particular the cooperative behavior of different neural circuits in the cerebral cortex may be closely related to the topology of certain 4-manifolds.
Noncommuting Momenta of Topological Solitons
NASA Astrophysics Data System (ADS)
Watanabe, Haruki; Murayama, Hitoshi
2014-05-01
We show that momentum operators of a topological soliton may not commute among themselves when the soliton is associated with the second cohomology H2 of the target space. The commutation relation is proportional to the winding number, taking a constant value within each topological sector. The noncommutativity makes it impossible to specify the momentum of a topological soliton, and induces a Magnus force.
Topology of Document Retrieval Systems.
ERIC Educational Resources Information Center
Everett, Daniel M.; Cater, Steven C.
1992-01-01
Explains the use of a topological structure to examine the closeness between documents in retrieval systems and analyzes the topological structure of a vector-space model, a fuzzy-set model, an extended Boolean model, a probabilistic model, and a TIRS (Topological Information Retrieval System) model. Proofs for the results are appended. (17…
Topological defects at finite temperature
Bazeia, D.; Eboli, O.J.P.; Guerra, J.M. Jr.; Marques, G.C.
1987-11-15
We obtain the phase diagram of gauge theories by studying the influence of topologically nontrivial boundary conditions. For this reason, we develop a scheme for computing the free energy of topological defects at finite temperature. As an application, the free energy of topological defects for the minimal SU(5) model are evaluated in the semiclassical approximation.
Retinal abnormalities in β-thalassemia major.
Bhoiwala, Devang L; Dunaief, Joshua L
2016-01-01
Patients with beta (β)-thalassemia (β-TM: β-thalassemia major, β-TI: β-thalassemia intermedia) have a variety of complications that may affect all organs, including the eye. Ocular abnormalities include retinal pigment epithelial degeneration, angioid streaks, venous tortuosity, night blindness, visual field defects, decreased visual acuity, color vision abnormalities, and acute visual loss. Patients with β-thalassemia major are transfusion dependent and require iron chelation therapy to survive. Retinal degeneration may result from either retinal iron accumulation from transfusion-induced iron overload or retinal toxicity induced by iron chelation therapy. Some who were never treated with iron chelation therapy exhibited retinopathy, and others receiving iron chelation therapy had chelator-induced retinopathy. We will focus on retinal abnormalities present in individuals with β-thalassemia major viewed in light of new findings on the mechanisms and manifestations of retinal iron toxicity. PMID:26325202
Schizophrenia and abnormal brain network hubs
Rubinov, Mikail; Bullmore, Ed.
2013-01-01
Schizophrenia is a heterogeneous psychiatric disorder of unknown cause or characteristic pathology. Clinical neuroscientists increasingly postulate that schizophrenia is a disorder of brain network organization. In this article we discuss the conceptual framework of this dysconnection hypothesis, describe the predominant methodological paradigm for testing this hypothesis, and review recent evidence for disruption of central/hub brain regions, as a promising example of this hypothesis. We summarize studies of brain hubs in large-scale structural and functional brain networks and find strong evidence for network abnormalities of prefrontal hubs, and moderate evidence for network abnormalities of limbic, temporal, and parietal hubs. Future studies are needed to differentiate network dysfunction from previously observed gray- and white-matter abnormalities of these hubs, and to link endogenous network dysfunction phenotypes with perceptual, behavioral, and cognitive clinical phenotypes of schizophrenia. PMID:24174905
Spirometric abnormalities among welders
Rastogi, S.K.; Gupta, B.N.; Husain, T.; Mathur, N.; Srivastava, S. )
1991-10-01
A group of manual welders age group 13-60 years having a mean exposure period of 12.4 {plus minus} 1.12 years were subjected to spirometry to evaluate the prevalence of spirometric abnormalities. The welders showed a significantly higher prevalence of respiratory impairment than that observed among the unexposed controls as a result of exposure to welding gases which comprised fine particles of lead, zinc, chromium, and manganese. This occurred despite the lower concentration of the pollutants at the work place. In the expose group, the smoking welders showed a prevalence of respiratory impairment significantly higher than that observed in the nonsmoking welders. The results of the pulmonary function tests showed a predominantly restrictive type of pulmonary impairment followed by a mixed ventilatory defect among the welders. The effect of age on pulmonary impairment was not discernible. Welders exposed for over 10 years showed a prevalence of respiratory abnormalities significantly higher than those exposed for less than 10 years. Smoking also had a contributory role.
Yin, Yingying; Wang, Zan; Zhang, Zhijun; Yuan, Yonggui
2016-08-26
To investigate the alteration of resting-state functional connectivity (FC) and topological organization of the default mode network (DMN), and their contribution to the cognitive impairment in remitted late-onset depression (rLOD) patients. Thirty-three rLOD patients and thirty-one healthy controls underwent clinical and cognitive evaluations as well as resting-state functional magnetic resonance imaging (R-fMRI) scans. The FC networks were constructed by thresholding Pearson correlation metrics of the DMN regions, and their topological properties were analyzed using graph theory-based approaches. Nonparametric permutation tests were further used for group comparisons of topological metrics. Finally, multiple linear regression analyses were performed to examine the relationships between the network measures and cognitive performances. Patients displayed universally decreased FC of DMN and abnormal global topology of the DMN (i.e., increased characteristic path length Lp and reduced global efficiency Eglob) compared with healthy controls. According to the distance-dependent FC results, the long-distance connections were mainly involved in the connectivity between anterior and posterior hubs, and the short-distance connections were primarily located in the frontal lobe. There were significant correlations between the global topology and the episodic memory performance in rLOD patients. In conclusion, the present study indicated that the disrupted topological organization of the DMN might be considered as a potential biomarker of the episodic memory deficits in rLOD patients. PMID:27365133
Topological Photonic Quasicrystals: Fractal Topological Spectrum and Protected Transport
NASA Astrophysics Data System (ADS)
Bandres, Miguel A.; Rechtsman, Mikael C.; Segev, Mordechai
2016-01-01
We show that it is possible to have a topological phase in two-dimensional quasicrystals without any magnetic field applied, but instead introducing an artificial gauge field via dynamic modulation. This topological quasicrystal exhibits scatter-free unidirectional edge states that are extended along the system's perimeter, contrary to the states of an ordinary quasicrystal system, which are characterized by power-law decay. We find that the spectrum of this Floquet topological quasicrystal exhibits a rich fractal (self-similar) structure of topological "minigaps," manifesting an entirely new phenomenon: fractal topological systems. These topological minigaps form only when the system size is sufficiently large because their gapless edge states penetrate deep into the bulk. Hence, the topological structure emerges as a function of the system size, contrary to periodic systems where the topological phase can be completely characterized by the unit cell. We demonstrate the existence of this topological phase both by using a topological index (Bott index) and by studying the unidirectional transport of the gapless edge states and its robustness in the presence of defects. Our specific model is a Penrose lattice of helical optical waveguides—a photonic Floquet quasicrystal; however, we expect this new topological quasicrystal phase to be universal.
Topological properties of hierarchical networks
NASA Astrophysics Data System (ADS)
Agliari, Elena; Barra, Adriano; Galluzzi, Andrea; Guerra, Francesco; Tantari, Daniele; Tavani, Flavia
2015-06-01
Hierarchical networks are attracting a renewal interest for modeling the organization of a number of biological systems and for tackling the complexity of statistical mechanical models beyond mean-field limitations. Here we consider the Dyson hierarchical construction for ferromagnets, neural networks, and spin glasses, recently analyzed from a statistical-mechanics perspective, and we focus on the topological properties of the underlying structures. In particular, we find that such structures are weighted graphs that exhibit a high degree of clustering and of modularity, with a small spectral gap; the robustness of such features with respect to the presence of thermal noise is also studied. These outcomes are then discussed and related to the statistical-mechanics scenario in full consistency. Last, we look at these weighted graphs as Markov chains and we show that in the limit of infinite size, the emergence of ergodicity breakdown for the stochastic process mirrors the emergence of metastabilities in the corresponding statistical mechanical analysis.
The space group classification of topological band insulators
NASA Astrophysics Data System (ADS)
Juricic, Vladimir; Slager, Robert-Jan; Mesaros, Andrej; Zaanen, Jan
2013-03-01
The existing classification of topological band insulators(TBIs) departs from time-reversal symmetry, but the role of the crystal symmetries in the physics of these topological states remained elusive. I will discuss the classification of TBIs protected not only by time-reversal, but also by space group symmetries. I find three broad classes of topological states: (a) Γ-states robust against general time-reversal invariant perturbations; (b) Translationally-active states protected from elastic scattering, but susceptible to topological crystalline disorder; (c) Valley topological insulators sensitive to the effects of non-topological and crystalline disorder. These three classes give rise to 18 different two-dimensional, and, at least 70 three-dimensional TBIs. I will show how some of these topological states can be realized in two dimensions when tight-binding M-B model, originally introduced for HgTe quantum wells, is generalized to include longer-range hoppings. Finally, experimental implications of our classification scheme with an emphasis on topological states in Sn-based materials will be discussed. V. J. acknowledges the support of the Netherlands Organization for Scientific Research (NWO).
Floquet topological insulators for sound
Fleury, Romain; Khanikaev, Alexander B; Alù, Andrea
2016-01-01
The unique conduction properties of condensed matter systems with topological order have recently inspired a quest for the similar effects in classical wave phenomena. Acoustic topological insulators, in particular, hold the promise to revolutionize our ability to control sound, allowing for large isolation in the bulk and broadband one-way transport along their edges, with topological immunity against structural defects and disorder. So far, these fascinating properties have been obtained relying on moving media, which may introduce noise and absorption losses, hindering the practical potential of topological acoustics. Here we overcome these limitations by modulating in time the acoustic properties of a lattice of resonators, introducing the concept of acoustic Floquet topological insulators. We show that acoustic waves provide a fertile ground to apply the anomalous physics of Floquet topological insulators, and demonstrate their relevance for a wide range of acoustic applications, including broadband acoustic isolation and topologically protected, nonreciprocal acoustic emitters. PMID:27312175
Floquet topological insulators for sound
NASA Astrophysics Data System (ADS)
Fleury, Romain; Khanikaev, Alexander B.; Alù, Andrea
2016-06-01
The unique conduction properties of condensed matter systems with topological order have recently inspired a quest for the similar effects in classical wave phenomena. Acoustic topological insulators, in particular, hold the promise to revolutionize our ability to control sound, allowing for large isolation in the bulk and broadband one-way transport along their edges, with topological immunity against structural defects and disorder. So far, these fascinating properties have been obtained relying on moving media, which may introduce noise and absorption losses, hindering the practical potential of topological acoustics. Here we overcome these limitations by modulating in time the acoustic properties of a lattice of resonators, introducing the concept of acoustic Floquet topological insulators. We show that acoustic waves provide a fertile ground to apply the anomalous physics of Floquet topological insulators, and demonstrate their relevance for a wide range of acoustic applications, including broadband acoustic isolation and topologically protected, nonreciprocal acoustic emitters.
Floquet topological insulators for sound.
Fleury, Romain; Khanikaev, Alexander B; Alù, Andrea
2016-01-01
The unique conduction properties of condensed matter systems with topological order have recently inspired a quest for the similar effects in classical wave phenomena. Acoustic topological insulators, in particular, hold the promise to revolutionize our ability to control sound, allowing for large isolation in the bulk and broadband one-way transport along their edges, with topological immunity against structural defects and disorder. So far, these fascinating properties have been obtained relying on moving media, which may introduce noise and absorption losses, hindering the practical potential of topological acoustics. Here we overcome these limitations by modulating in time the acoustic properties of a lattice of resonators, introducing the concept of acoustic Floquet topological insulators. We show that acoustic waves provide a fertile ground to apply the anomalous physics of Floquet topological insulators, and demonstrate their relevance for a wide range of acoustic applications, including broadband acoustic isolation and topologically protected, nonreciprocal acoustic emitters. PMID:27312175
Moncayo, Jorge; Bogousslavsky, Julien
2012-01-01
Generation and control of eye movements requires the participation of the cortex, basal ganglia, cerebellum and brainstem. The signals of this complex neural network finally converge on the ocular motoneurons of the brainstem. Infarct or hemorrhage at any level of the oculomotor system (though more frequent in the brain-stem) may give rise to a broad spectrum of eye movement abnormalities (EMAs). Consequently, neurologists and particularly stroke neurologists are routinely confronted with EMAs, some of which may be overlooked in the acute stroke setting and others that, when recognized, may have a high localizing value. The most complex EMAs are due to midbrain stroke. Horizontal gaze disorders, some of them manifesting unusual patterns, may occur in pontine stroke. Distinct varieties of nystagmus occur in cerebellar and medullary stroke. This review summarizes the most representative EMAs from the supratentorial level to the brainstem. PMID:22377853
On the topology of chromatin fibres
Barbi, Maria; Mozziconacci, Julien; Victor, Jean-Marc; Wong, Hua; Lavelle, Christophe
2012-01-01
The ability of cells to pack, use and duplicate DNA remains one of the most fascinating questions in biology. To understand DNA organization and dynamics, it is important to consider the physical and topological constraints acting on it. In the eukaryotic cell nucleus, DNA is organized by proteins acting as spools on which DNA can be wrapped. These proteins can subsequently interact and form a structure called the chromatin fibre. Using a simple geometric model, we propose a general method for computing topological properties (twist, writhe and linking number) of the DNA embedded in those fibres. The relevance of the method is reviewed through the analysis of magnetic tweezers single molecule experiments that revealed unexpected properties of the chromatin fibre. Possible biological implications of these results are discussed. PMID:24098838
Topological analysis of chaotic dynamical systems
NASA Astrophysics Data System (ADS)
Gilmore, Robert
1998-10-01
Topological methods have recently been developed for the analysis of dissipative dynamical systems that operate in the chaotic regime. They were originally developed for three-dimensional dissipative dynamical systems, but they are applicable to all ``low-dimensional'' dynamical systems. These are systems for which the flow rapidly relaxes to a three-dimensional subspace of phase space. Equivalently, the associated attractor has Lyapunov dimension dL<3. Topological methods supplement methods previously developed to determine the values of metric and dynamical invariants. However, topological methods possess three additional features: they describe how to model the dynamics; they allow validation of the models so developed; and the topological invariants are robust under changes in control-parameter values. The topological-analysis procedure depends on identifying the stretching and squeezing mechanisms that act to create a strange attractor and organize all the unstable periodic orbits in this attractor in a unique way. The stretching and squeezing mechanisms are represented by a caricature, a branched manifold, which is also called a template or a knot holder. This turns out to be a version of the dynamical system in the limit of infinite dissipation. This topological structure is identified by a set of integer invariants. One of the truly remarkable results of the topological-analysis procedure is that these integer invariants can be extracted from a chaotic time series. Furthermore, self-consistency checks can be used to confirm the integer values. These integers can be used to determine whether or not two dynamical systems are equivalent; in particular, they can determine whether a model developed from time-series data is an accurate representation of a physical system. Conversely, these integers can be used to provide a model for the dynamical mechanisms that generate chaotic data. In fact, the author has constructed a doubly discrete classification of strange
Study of the Topological-insulator-based Topological Superconductors
NASA Astrophysics Data System (ADS)
Qian, Dong
Three-dimensional topological insulators possess nontrivial spin-momentum locked surface states under the protection of time-reversal symmetry. The interplay between topological order and superconductivity can lead to topological superconducting state. In this talk, I will discuss our recent progress in topological-insulator-based topological superconductors. Using molecular beam epitaxy (MBE) method, we succeeded in fabricating very high quality TI/s-wave superconductor heterostructure by growing topological insulator thin films on the conventional superconductor niobium diselenide (NbSe2) substrate. Using low temperature scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoemission spectroscopy (ARPES), we systematically studied its electronic structure and superconducting behavior. Through superconducting proximity effect, coexistence of Cooper pairs and topological surface states on the surface of topological insulator film was realized. By exploring the superconducting vortex core state as the function of film thickness, existing of nontrivial superconducting state on the TI's surface was proposed. Our topological insulator/superconductor heterostructure may host single zero-energy Majorana mode in the vortex core. In addition, I will also discuss STM and ARPES studies on the recently discovered superconducting Sr-doped Bi2Se3 bulk crystals. Our results suggest that Sr-doped Bi2Se3 could be an excellent candidate for exploring topological superconducting states. Supported by the Ministry of Science and Technology of China and NSFC.
Quist, Daniel A.; Gavrilov, Eugene M.; Fisk, Michael E.
2008-01-15
A method enables the topology of an acyclic fully propagated network to be discovered. A list of switches that comprise the network is formed and the MAC address cache for each one of the switches is determined. For each pair of switches, from the MAC address caches the remaining switches that see the pair of switches are located. For each pair of switches the remaining switches are determined that see one of the pair of switches on a first port and the second one of the pair of switches on a second port. A list of insiders is formed for every pair of switches. It is determined whether the insider for each pair of switches is a graph edge and adjacent ones of the graph edges are determined. A symmetric adjacency matrix is formed from the graph edges to represent the topology of the data link network.
Topological entanglement entropy.
Kitaev, Alexei; Preskill, John
2006-03-24
We formulate a universal characterization of the many-particle quantum entanglement in the ground state of a topologically ordered two-dimensional medium with a mass gap. We consider a disk in the plane, with a smooth boundary of length L, large compared to the correlation length. In the ground state, by tracing out all degrees of freedom in the exterior of the disk, we obtain a marginal density operator rho for the degrees of freedom in the interior. The von Neumann entropy of rho, a measure of the entanglement of the interior and exterior variables, has the form S(rho) = alphaL - gamma + ..., where the ellipsis represents terms that vanish in the limit L --> infinity. We show that - gamma is a universal constant characterizing a global feature of the entanglement in the ground state. Using topological quantum field theory methods, we derive a formula for gamma in terms of properties of the superselection sectors of the medium. PMID:16605802
Topological confinement and superconductivity
Al-hassanieh, Dhaled A; Batista, Cristian D
2008-01-01
We derive a Kondo Lattice model with a correlated conduction band from a two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence of a robust pairing mechanism in a model that only contains repulsive interactions. The mechanism is due to topological confinement and results from the interplay between antiferromagnetism and delocalization. By using Density-Matrix-Renormalization-Group (DMRG) we demonstrate that this mechanism leads to dominant superconducting correlations in aID-system.
Estrada, Rolando; Tomasi, Carlo; Schmidler, Scott C; Farsiu, Sina
2015-08-01
Tree-like structures are fundamental in nature, and it is often useful to reconstruct the topology of a tree - what connects to what - from a two-dimensional image of it. However, the projected branches often cross in the image: the tree projects to a planar graph, and the inverse problem of reconstructing the topology of the tree from that of the graph is ill-posed. We regularize this problem with a generative, parametric tree-growth model. Under this model, reconstruction is possible in linear time if one knows the direction of each edge in the graph - which edge endpoint is closer to the root of the tree - but becomes NP-hard if the directions are not known. For the latter case, we present a heuristic search algorithm to estimate the most likely topology of a rooted, three-dimensional tree from a single two-dimensional image. Experimental results on retinal vessel, plant root, and synthetic tree data sets show that our methodology is both accurate and efficient. PMID:26353004
Transformable topological mechanical metamaterials
NASA Astrophysics Data System (ADS)
Rocklin, D. Zeb; Zhou, Shangnan; Sun, Kai; Mao, Xiaoming
We present a class of mechanical metamaterials characterized by a uniform soft deformation--a large, zero-energy homogeneous elastic deformation mode of the structure--that may be used to induce topological transitions and dramatically change mechanical and acoustic properties of the structure. We show that the existence of such a mode determines certain exotic mechanical and acoustic properties of the structure and its activation can reversibly alter and tune these properties. This serves as the basis for a design principle for mechanical metamaterials with tunable properties. When the structure's uniform mode is primarily dilational (shearing) its surface (bulk) possesses phonon modes with vanishing speed of sound. Maxwell lattices comprise a subclass of such material which, owing to their critical coordination number (four, in 2D), necessarily possess such a uniform zero mode, often termed a Guest mode, and which may be topologically polarized, such that zero modes are moved from one edge to another. We show that activating the deformation can alter the shear/dilational character of the mode and topologically polarize the structure, thereby altering the bulk and surface properties at no significant energy cost. arXiv:1510.06389 [cond-mat.soft] NWO, Delta Institute of Physics, ICAM fellowship (DZR) and NSF Grant PHY-1402971 at University of Michigan (KS).
Estrada, Rolando; Tomasi, Carlo; Schmidler, Scott C.; Farsiu, Sina
2015-01-01
Tree-like structures are fundamental in nature, and it is often useful to reconstruct the topology of a tree—what connects to what—from a two-dimensional image of it. However, the projected branches often cross in the image: the tree projects to a planar graph, and the inverse problem of reconstructing the topology of the tree from that of the graph is ill-posed. We regularize this problem with a generative, parametric tree-growth model. Under this model, reconstruction is possible in linear time if one knows the direction of each edge in the graph—which edge endpoint is closer to the root of the tree—but becomes NP-hard if the directions are not known. For the latter case, we present a heuristic search algorithm to estimate the most likely topology of a rooted, three-dimensional tree from a single two-dimensional image. Experimental results on retinal vessel, plant root, and synthetic tree datasets show that our methodology is both accurate and efficient. PMID:26353004
A non-topological mechanism for negative linear compressibility.
Binns, Jack; Kamenev, Konstantin V; Marriott, Katie E R; McIntyre, Garry J; Moggach, Stephen A; Murrie, Mark; Parsons, Simon
2016-06-14
Negative linear compressibility (NLC), the increase in a unit cell length with pressure, is a rare phenomenon in which hydrostatic compression of a structure promotes expansion along one dimension. It is usually a consequence of crystal structure topology. We show that the source of NLC in the Co(ii) citrate metal-organic framework UTSA-16 lies not in framework topology, but in the relative torsional flexibility of Co(ii)-centred tetrahedra compared to more rigid octahedra. PMID:27203683
Liang, Feng Lan; Ma, De Yun; Qin, Liang
2016-05-01
Metal-organic frameworks (MOFs) are a new class of porous materials that have received widespread attention due to their potential applications in gas storage and/or separation, catalysis, luminescence, and so on. The title compound, poly[[(μ2-3,3'-dimethyl-4,4'-bipyridine-κ(2)N:N')bis(μ4-4,4'-oxydibenzoato-κ(4)O:O':O'':O''')dizinc] tetrahydrate], {[Zn2(C14H8O5)2(C12H12N2)]·4H2O}n, has been prepared by the solvothermal assembly of Zn(NO3)2·6H2O, 4,4'-oxydi(benzoic acid) and 3,3'-dimethyl-4,4'-bipyridine. The two Zn(II) atoms adopt the same five-coordinated distorted square-pyramidal geometry (i.e. ZnO4N), bonding to four O atoms from four different 4,4'-oxydibenzoate (oba) ligands and one N atom from a 3,3'-dimethyl-4,4'-bipyridine (dmbpy) ligand. The supramolecular secondary building unit (SBU) is a paddle-wheel [Zn2(COO)4] unit and these units are linked by oba ligands within the layer to form a two-dimensional net parallel to the b axis, with the dmbpy ligands pointing alternately up and down, which is further extended by dmbpy ligands to form a three-dimensional framework with rob topology. The single net leaves voids that are filled by mutual interpenetration of an independent equivalent framework in a twofold interpenetrating architecture. The title compound shows thermal stability up to 673 K and is stable in aqueous solutions in the pH range 5-9. Excitation and luminescence data observed at room temperature show that it emits a bright-blue fluorescence. PMID:27146564
Transportation Network Topologies
NASA Technical Reports Server (NTRS)
Holmes, Bruce J.; Scott, John M.
2004-01-01
A discomforting reality has materialized on the transportation scene: our existing air and ground infrastructures will not scale to meet our nation's 21st century demands and expectations for mobility, commerce, safety, and security. The consequence of inaction is diminished quality of life and economic opportunity in the 21st century. Clearly, new thinking is required for transportation that can scale to meet to the realities of a networked, knowledge-based economy in which the value of time is a new coin of the realm. This paper proposes a framework, or topology, for thinking about the problem of scalability of the system of networks that comprise the aviation system. This framework highlights the role of integrated communication-navigation-surveillance systems in enabling scalability of future air transportation networks. Scalability, in this vein, is a goal of the recently formed Joint Planning and Development Office for the Next Generation Air Transportation System. New foundations for 21PstP thinking about air transportation are underpinned by several technological developments in the traditional aircraft disciplines as well as in communication, navigation, surveillance and information systems. Complexity science and modern network theory give rise to one of the technological developments of importance. Scale-free (i.e., scalable) networks represent a promising concept space for modeling airspace system architectures, and for assessing network performance in terms of scalability, efficiency, robustness, resilience, and other metrics. The paper offers an air transportation system topology as framework for transportation system innovation. Successful outcomes of innovation in air transportation could lay the foundations for new paradigms for aircraft and their operating capabilities, air transportation system architectures, and airspace architectures and procedural concepts. The topology proposed considers air transportation as a system of networks, within
Transportation Network Topologies
NASA Technical Reports Server (NTRS)
Holmes, Bruce J.; Scott, John
2004-01-01
A discomforting reality has materialized on the transportation scene: our existing air and ground infrastructures will not scale to meet our nation's 21st century demands and expectations for mobility, commerce, safety, and security. The consequence of inaction is diminished quality of life and economic opportunity in the 21st century. Clearly, new thinking is required for transportation that can scale to meet to the realities of a networked, knowledge-based economy in which the value of time is a new coin of the realm. This paper proposes a framework, or topology, for thinking about the problem of scalability of the system of networks that comprise the aviation system. This framework highlights the role of integrated communication-navigation-surveillance systems in enabling scalability of future air transportation networks. Scalability, in this vein, is a goal of the recently formed Joint Planning and Development Office for the Next Generation Air Transportation System. New foundations for 21st thinking about air transportation are underpinned by several technological developments in the traditional aircraft disciplines as well as in communication, navigation, surveillance and information systems. Complexity science and modern network theory give rise to one of the technological developments of importance. Scale-free (i.e., scalable) networks represent a promising concept space for modeling airspace system architectures, and for assessing network performance in terms of scalability, efficiency, robustness, resilience, and other metrics. The paper offers an air transportation system topology as framework for transportation system innovation. Successful outcomes of innovation in air transportation could lay the foundations for new paradigms for aircraft and their operating capabilities, air transportation system architectures, and airspace architectures and procedural concepts. The topology proposed considers air transportation as a system of networks, within which
Topological semimetals and nodal superconductors
NASA Astrophysics Data System (ADS)
Chang, Po-Yao
Besides topological band insulators, which have a full bulk gap, there are also gapless phases of matter that belong to the broad class of topological materials, such as topological semimetals and nodal superconductors. We systematically study these gapless topological phases described by the Bloch and Bogoliubov-de Gennes Hamiltonians. We discuss a generalized bulk-boundary correspondence, which relates the topological properties in the bulk of gapless topological phases and the protected zero-energy states at the boundary. We study examples of gapless topological phases, focusing in particular on nodal superconductors, such as nodal noncentrosymmetric superconductors (NCSs). We compute the surface density of states of nodal NCSs and interpret experimental measurements of surface states. In addition, we investigate Majorana vortex-bound states in both nodal and fully gapped NCSs using numerical and analytical methods. We show that different topological properties of the bulk Bogoliubov-quasiparticle wave functions reflect themselves in different types of zero-energy vortex-bound states. In particular, in the case of NCSs with tetragonal point-group symmetry, we find that the stability of these Majorana zero modes is guaranteed by a combination of reflection, time-reversal, and particle-hole symmetries. Finally, by using K-theory arguments and a dimensional reduction procedure from higher-dimensional topological insulators and superconductors, we derive a classification of topologically stable Fermi surfaces in semimetals and nodal lines in superconductors.
Ictal Cardiac Ryhthym Abnormalities
Ali, Rushna
2016-01-01
Cardiac rhythm abnormalities in the context of epilepsy are a well-known phenomenon. However, they are under-recognized and often missed. The pathophysiology of these events is unclear. Bradycardia and asystole are preceded by seizure onset suggesting ictal propagation into the cortex impacting cardiac autonomic function, and the insula and amygdala being possible culprits. Sudden unexpected death in epilepsy (SUDEP) refers to the unanticipated death of a patient with epilepsy not related to status epilepticus, trauma, drowning, or suicide. Frequent refractory generalized tonic-clonic seizures, anti-epileptic polytherapy, and prolonged duration of epilepsy are some of the commonly identified risk factors for SUDEP. However, the most consistent risk factor out of these is an increased frequency of generalized tonic–clonic seizures (GTC). Prevention of SUDEP is extremely important in patients with chronic, generalized epilepsy. Since increased frequency of GTCS is the most consistently reported risk factor for SUDEP, effective seizure control is the most important preventive strategy. PMID:27347227
Whitaker, Lucy; Critchley, Hilary O D
2016-07-01
Abnormal uterine bleeding (AUB) is a common and debilitating condition with high direct and indirect costs. AUB frequently co-exists with fibroids, but the relationship between the two remains incompletely understood and in many women the identification of fibroids may be incidental to a menstrual bleeding complaint. A structured approach for establishing the cause using the Fédération International de Gynécologie et d'Obstétrique (FIGO) PALM-COEIN (Polyp, Adenomyosis, Leiomyoma, Malignancy (and hyperplasia), Coagulopathy, Ovulatory disorders, Endometrial, Iatrogenic and Not otherwise classified) classification system will facilitate accurate diagnosis and inform treatment options. Office hysteroscopy and increasing sophisticated imaging will assist provision of robust evidence for the underlying cause. Increased availability of medical options has expanded the choice for women and many will no longer need to recourse to potentially complicated surgery. Treatment must remain individualised and encompass the impact of pressure symptoms, desire for retention of fertility and contraceptive needs, as well as address the management of AUB in order to achieve improved quality of life. PMID:26803558
Scaling in topological properties of brain networks
Singh, Soibam Shyamchand; Khundrakpam, Budhachandra; Reid, Andrew T.; Lewis, John D.; Evans, Alan C.; Ishrat, Romana; Sharma, B. Indrajit; Singh, R. K. Brojen
2016-01-01
The organization in brain networks shows highly modular features with weak inter-modular interaction. The topology of the networks involves emergence of modules and sub-modules at different levels of constitution governed by fractal laws that are signatures of self-organization in complex networks. The modular organization, in terms of modular mass, inter-modular, and intra-modular interaction, also obeys fractal nature. The parameters which characterize topological properties of brain networks follow one parameter scaling theory in all levels of network structure, which reveals the self-similar rules governing the network structure. Further, the calculated fractal dimensions of brain networks of different species are found to decrease when one goes from lower to higher level species which implicates the more ordered and self-organized topography at higher level species. The sparsely distributed hubs in brain networks may be most influencing nodes but their absence may not cause network breakdown, and centrality parameters characterizing them also follow one parameter scaling law indicating self-similar roles of these hubs at different levels of organization in brain networks. The local-community-paradigm decomposition plot and calculated local-community-paradigm-correlation co-efficient of brain networks also shows the evidence for self-organization in these networks. PMID:27112129
Scaling in topological properties of brain networks.
Singh, Soibam Shyamchand; Khundrakpam, Budhachandra; Reid, Andrew T; Lewis, John D; Evans, Alan C; Ishrat, Romana; Sharma, B Indrajit; Singh, R K Brojen
2016-01-01
The organization in brain networks shows highly modular features with weak inter-modular interaction. The topology of the networks involves emergence of modules and sub-modules at different levels of constitution governed by fractal laws that are signatures of self-organization in complex networks. The modular organization, in terms of modular mass, inter-modular, and intra-modular interaction, also obeys fractal nature. The parameters which characterize topological properties of brain networks follow one parameter scaling theory in all levels of network structure, which reveals the self-similar rules governing the network structure. Further, the calculated fractal dimensions of brain networks of different species are found to decrease when one goes from lower to higher level species which implicates the more ordered and self-organized topography at higher level species. The sparsely distributed hubs in brain networks may be most influencing nodes but their absence may not cause network breakdown, and centrality parameters characterizing them also follow one parameter scaling law indicating self-similar roles of these hubs at different levels of organization in brain networks. The local-community-paradigm decomposition plot and calculated local-community-paradigm-correlation co-efficient of brain networks also shows the evidence for self-organization in these networks. PMID:27112129
ERIC Educational Resources Information Center
Lynch, Mark
2012-01-01
We continue our study of topological X-rays begun in Lynch ["Topological X-rays and MRI's," iJMEST 33(3) (2002), pp. 389-392]. We modify our definition of a topological magnetic resonance imaging and give an affirmative answer to the question posed there: Can we identify a closed set in a box by defining X-rays to probe the interior and without…
The topology of gyroscopic metamaterials
NASA Astrophysics Data System (ADS)
Nash, Lisa M.; Kleckner, Dustin; Read, Alismari; Vitelli, Vincenzo; Turner, Ari M.; Irvine, William T. M.
Mechanical metamaterials can have topologically protected states, much like their electronic and optical counterparts. We recently demonstrated this in experiment by building a meta-material composed of coupled gyroscopes on a honeycomb lattice. This system breaks time-reversal symmetry and exhibits topologically protected one-way edge modes. In this talk we will explore the relationship between the topology of the band structure and the geometry of the lattice.
Biochemical abnormalities in Pearson syndrome.
Crippa, Beatrice Letizia; Leon, Eyby; Calhoun, Amy; Lowichik, Amy; Pasquali, Marzia; Longo, Nicola
2015-03-01
Pearson marrow-pancreas syndrome is a multisystem mitochondrial disorder characterized by bone marrow failure and pancreatic insufficiency. Children who survive the severe bone marrow dysfunction in childhood develop Kearns-Sayre syndrome later in life. Here we report on four new cases with this condition and define their biochemical abnormalities. Three out of four patients presented with failure to thrive, with most of them having normal development and head size. All patients had evidence of bone marrow involvement that spontaneously improved in three out of four patients. Unique findings in our patients were acute pancreatitis (one out of four), renal Fanconi syndrome (present in all patients, but symptomatic only in one), and an unusual organic aciduria with 3-hydroxyisobutyric aciduria in one patient. Biochemical analysis indicated low levels of plasma citrulline and arginine, despite low-normal ammonia levels. Regression analysis indicated a significant correlation between each intermediate of the urea cycle and the next, except between ornithine and citrulline. This suggested that the reaction catalyzed by ornithine transcarbamylase (that converts ornithine to citrulline) might not be very efficient in patients with Pearson syndrome. In view of low-normal ammonia levels, we hypothesize that ammonia and carbamylphosphate could be diverted from the urea cycle to the synthesis of nucleotides in patients with Pearson syndrome and possibly other mitochondrial disorders. PMID:25691415
First-Trimester Detection of Surface Abnormalities
Rousian, Melek; Koning, Anton H. J.; Bonsel, Gouke J.; Eggink, Alex J.; Cornette, Jérôme M. J.; Schoonderwaldt, Ernst M.; Husen-Ebbinge, Margreet; Teunissen, Katinka K.; van der Spek, Peter J.; Steegers, Eric A. P.; Exalto, Niek
2014-01-01
The aim was to determine the diagnostic performance of 3-dimensional virtual reality ultrasound (3D_VR_US) and conventional 2- and 3-dimensional ultrasound (2D/3D_US) for first-trimester detection of structural abnormalities. Forty-eight first trimester cases (gold standard available, 22 normal, 26 abnormal) were evaluated offline using both techniques by 5 experienced, blinded sonographers. In each case, we analyzed whether each organ category was correctly indicated as normal or abnormal and whether the specific diagnosis was correctly made. Sensitivity in terms of normal or abnormal was comparable for both techniques (P = .24). The general sensitivity for specific diagnoses was 62.6% using 3D_VR_US and 52.2% using 2D/3D_US (P = .075). The 3D_VR_US more often correctly diagnosed skeleton/limb malformations (36.7% vs 10%; P = .013). Mean evaluation time in 3D_VR_US was 4:24 minutes and in 2D/3D_US 2:53 minutes (P < .001). General diagnostic performance of 3D_VR_US and 2D/3D_US apparently is comparable. Malformations of skeleton and limbs are more often detected using 3D_VR_US. Evaluation time is longer in 3D_VR_US. PMID:24440996
OPTIMAL NETWORK TOPOLOGY DESIGN
NASA Technical Reports Server (NTRS)
Yuen, J. H.
1994-01-01
This program was developed as part of a research study on the topology design and performance analysis for the Space Station Information System (SSIS) network. It uses an efficient algorithm to generate candidate network designs (consisting of subsets of the set of all network components) in increasing order of their total costs, and checks each design to see if it forms an acceptable network. This technique gives the true cost-optimal network, and is particularly useful when the network has many constraints and not too many components. It is intended that this new design technique consider all important performance measures explicitly and take into account the constraints due to various technical feasibilities. In the current program, technical constraints are taken care of by the user properly forming the starting set of candidate components (e.g. nonfeasible links are not included). As subsets are generated, they are tested to see if they form an acceptable network by checking that all requirements are satisfied. Thus the first acceptable subset encountered gives the cost-optimal topology satisfying all given constraints. The user must sort the set of "feasible" link elements in increasing order of their costs. The program prompts the user for the following information for each link: 1) cost, 2) connectivity (number of stations connected by the link), and 3) the stations connected by that link. Unless instructed to stop, the program generates all possible acceptable networks in increasing order of their total costs. The program is written only to generate topologies that are simply connected. Tests on reliability, delay, and other performance measures are discussed in the documentation, but have not been incorporated into the program. This program is written in PASCAL for interactive execution and has been implemented on an IBM PC series computer operating under PC DOS. The disk contains source code only. This program was developed in 1985.
Monolayer Topological Insulators: Silicene, Germanene, and Stanene
NASA Astrophysics Data System (ADS)
Ezawa, Motohiko
2015-12-01
We report the recent progress on the theoretical aspects of monolayer topological insulators including silicene, germanene and stanene, which are monolayer honeycomb structures of silicon, germanium and tin, respectively. They show quantum spin Hall effects in nature due to the spin-orbit interaction. The band gap can be tuned by applying perpendicular electric field, which induces a topological phase transition. We also analyze the topological properties of generic honeycomb systems together with the classification of topological insulators. Phase diagrams of topological insulators and superconductors in honeycomb systems are explicitly determined. We also investigate topological electronics including a topological field-effect transistor, the topological Kirchhoff's law and the topological spin-valleytronics.
Topological forms of information
Baudot, Pierre; Bennequin, Daniel
2015-01-13
We propose that entropy is a universal co-homological class in a theory associated to a family of observable quantities and a family of probability distributions. Three cases are presented: 1) classical probabilities and random variables; 2) quantum probabilities and observable operators; 3) dynamic probabilities and observation trees. This gives rise to a new kind of topology for information processes. We discuss briefly its application to complex data, in particular to the structures of information flows in biological systems. This short note summarizes results obtained during the last years by the authors. The proofs are not included, but the definitions and theorems are stated with precision.
Holey topological thermoelectrics
NASA Astrophysics Data System (ADS)
Tretiakov, O. A.; Abanov, Ar.; Sinova, Jairo
2011-09-01
We study the thermoelectric properties of three-dimensional topological insulators with many holes (or pores) in the bulk. We show that at high density of these holes, the thermoelectric figure of merit, ZT, can be large due to the contribution of the conducting surfaces and the suppressed phonon thermal conductivity. The maximum efficiency can be tuned by an induced gap in the surface states dispersion through tunneling or external magnetic fields. The large values of ZT, much higher than unity for reasonable parameters, make this system a strong candidate for applications in heat management of nanodevices, especially at low temperatures.
ERIC Educational Resources Information Center
Aviation/Space, 1980
1980-01-01
This is a list of aerospace organizations and other groups that provides educators with assistance and information in specific areas. Both government and nongovernment organizations are included. (Author/SA)
Visualizing vector field topology in fluid flows
NASA Technical Reports Server (NTRS)
Helman, James L.; Hesselink, Lambertus
1991-01-01
Methods of automating the analysis and display of vector field topology in general and flow topology in particular are discussed. Two-dimensional vector field topology is reviewed as the basis for the examination of topology in three-dimensional separated flows. The use of tangent surfaces and clipping in visualizing vector field topology in fluid flows is addressed.
Electrocardiograph abnormalities revealed during laparoscopy
Nijjer, Sukhjinder; Dubrey, Simon William
2010-01-01
This brief case presents a well patient in whom an electrocardiograph abnormality consistent with an accessory pathway was found during a routine procedure. We present the electrocardiographs, explain the underlying condition, and consider why the abnormality was revealed in this manner. PMID:22419949
Abnormal pressure in hydrocarbon environments
Law, B.E.; Spencer, C.W.
1998-01-01
Abnormal pressures, pressures above or below hydrostatic pressures, occur on all continents in a wide range of geological conditions. According to a survey of published literature on abnormal pressures, compaction disequilibrium and hydrocarbon generation are the two most commonly cited causes of abnormally high pressure in petroleum provinces. In young (Tertiary) deltaic sequences, compaction disequilibrium is the dominant cause of abnormal pressure. In older (pre-Tertiary) lithified rocks, hydrocarbon generation, aquathermal expansion, and tectonics are most often cited as the causes of abnormal pressure. The association of abnormal pressures with hydrocarbon accumulations is statistically significant. Within abnormally pressured reservoirs, empirical evidence indicates that the bulk of economically recoverable oil and gas occurs in reservoirs with pressure gradients less than 0.75 psi/ft (17.4 kPa/m) and there is very little production potential from reservoirs that exceed 0.85 psi/ft (19.6 kPa/m). Abnormally pressured rocks are also commonly associated with unconventional gas accumulations where the pressuring phase is gas of either a thermal or microbial origin. In underpressured, thermally mature rocks, the affected reservoirs have most often experienced a significant cooling history and probably evolved from an originally overpressured system.
Haem degradation in abnormal haemoglobins.
Brown, S B; Docherty, J C
1978-01-01
The coupled oxidation of certain abnormal haemoglobins leads to different bile-pigment isomer distributions from that of normal haemoglobin. The isomer pattern may be correlated with the structure of the abnormal haemoglobin in the neighbourhood of the haem pocket. This is support for haem degradation by an intramolecular reaction. PMID:708385
Topologically protected excitons in porphyrin thin films
NASA Astrophysics Data System (ADS)
Yuen-Zhou, Joel; Saikin, Semion K.; Yao, Norman Y.; Aspuru-Guzik, Alán
2014-11-01
The control of exciton transport in organic materials is of fundamental importance for the development of efficient light-harvesting systems. This transport is easily deteriorated by traps in the disordered energy landscape. Here, we propose and analyse a system that supports topological Frenkel exciton edge states. Backscattering of these chiral Frenkel excitons is prohibited by symmetry, ensuring that the transport properties of such a system are robust against disorder. To implement our idea, we propose a two-dimensional periodic array of tilted porphyrins interacting with a homogeneous magnetic field. This field serves to break time-reversal symmetry and results in lattice fluxes that mimic the Aharonov-Bohm phase acquired by electrons. Our proposal is the first blueprint for realizing topological phases of matter in molecular aggregates and suggests a paradigm for engineering novel excitonic materials.
Topologically protected excitons in porphyrin thin films.
Yuen-Zhou, Joel; Saikin, Semion K; Yao, Norman Y; Aspuru-Guzik, Alán
2014-11-01
The control of exciton transport in organic materials is of fundamental importance for the development of efficient light-harvesting systems. This transport is easily deteriorated by traps in the disordered energy landscape. Here, we propose and analyse a system that supports topological Frenkel exciton edge states. Backscattering of these chiral Frenkel excitons is prohibited by symmetry, ensuring that the transport properties of such a system are robust against disorder. To implement our idea, we propose a two-dimensional periodic array of tilted porphyrins interacting with a homogeneous magnetic field. This field serves to break time-reversal symmetry and results in lattice fluxes that mimic the Aharonov-Bohm phase acquired by electrons. Our proposal is the first blueprint for realizing topological phases of matter in molecular aggregates and suggests a paradigm for engineering novel excitonic materials. PMID:25242533
Topology of three-dimensional separated flows
NASA Technical Reports Server (NTRS)
Tobak, M.; Peake, D. J.
1981-01-01
Based on the hypothesis that patterns of skin-friction lines and external streamlines reflect the properties of continuous vector fields, topology rules define a small number of singular points (nodes, saddle points, and foci) that characterize the patterns on the surface and on particular projections of the flow (e.g., the crossflow plane). The restricted number of singular points and the rules that they obey are considered as an organizing principle whose finite number of elements can be combined in various ways to connect together the properties common to all steady three dimensional viscous flows. Introduction of a distinction between local and global properties of the flow resolves an ambiguity in the proper definition of a three dimensional separated flow. Adoption of the notions of topological structure, structural stability, and bifurcation provides a framework to describe how three dimensional separated flows originate and succeed each other as the relevant parameters of the problem are varied.
NASA Astrophysics Data System (ADS)
Bonneau, Philippe
Following a preceding paper showing how the introduction of a t.v.s. topology on quantum groups led to a remarkable unification and rigidification of the different definitions, we adapt here, in the same way, the definition of quantum double. This topological double is dualizable and reflexive (even for infinite dimensional algebras). In a simple case we show, considering the double as the "zero class" of an extension theory, the uniqueness of the double structure as a quasi-Hopf algebra. A la suite d'un précédent article montrant comment l'introduction d'une topologie d'e.v.t. sur les groupes quantiques permet une unification et une rigidification remarquables des différentes définitions, on adapte ici de la même manière la définition du double quantique. Ce double topologique est alors dualisable et reflexif (même pour des algèbres de dimension infinie). Dans un cas simple on montre, en considérant le double comme la "classe zéro" d'une théorie d'extensions, l'unicité de cette structure comme algèbre quasi-Hopf.
Topological invariants in interacting topological insulators: Success and Breakdown
NASA Astrophysics Data System (ADS)
He, Yuan-Yao; Wu, Han-Qing; Meng, Zi Yang; Lu, Zhong-Yi
The content of this talk is twofold. In the first part, we provide a paradigm of efficient numerical evaluation scheme for topological invariants via zero-frequency single-particle Green's function in quantum Monte Carlo (QMC) simulations. Especially, we introduce a periodization process to overcome the ubiquitous finite-size effect and make use of symmetry properties of the underlying systems to reduce the computational effort. This scheme is tested to be successful on models of interacting topological insulators, where there is single-particle gap closing at the transition. In the second part, we apply the above scheme to wider classes of interacting topological insulators, in which the breakdown of constructing topological invariant via single-particle Green's functions is presented. These systems host novel interaction-driven topological phase transitions without symmetry breaking, and hence fermionic degree of freedom is not involved at the critical point, instead, collective bosonic mode become critical.
Akasaka, Hironari; So, Shui-Ping; Ruan, Ke-He
2015-06-16
In vascular inflammation, prostaglandin E2 (PGE₂) is largely biosynthesized by microsomal PGE₂ synthase-1 (mPGES-1), competing with other downstream eicosanoid-synthesizing enzymes, such as PGIS, a synthase of a vascular protector prostacyclin (PGI₂), to isomerize the cyclooxygenase (COX)-2-derived prostaglandin H2 (PGH₂). In this study, we found that a majority of the product from the cells co-expressing human COX-2, mPGES-1, and PGIS was PGE₂. We hypothesize that the molecular and cellular mechanisms are related to the post-translational endoplasmic reticulum (ER) arrangement of those enzymes. A set of fusion enzymes, COX-2-linker [10 amino acids (aa)]-PGIS and COX-2-linker (22 amino acids)-PGIS, were created as "The Bioruler", in which the 10 and 22 amino acids are defined linkers with known helical structures and distances (14.4 and 30.8 Å, respectively). Our experiments have shown that the efficiency of PGI₂ biosynthesis was reduced when the separation distance increased from 10 to 22 amino acids. When COX-2-10aa-PGIS (with a 14.4 Å separation) was co-expressed with mPGES-1 on the ER membrane, a major product was PGE₂, but not PGI₂. However, expression of COX-2-10aa-PGIS and mPGES-1 on a separated ER with a distance of ≫30.8 Å reduced the level of PGE₂ production. These data indicated that the mPGES-1 is "complex-likely" colocalized with COX-2 within a distance of 14.4 Å. In addition, the cells co-expressing COX-1-10aa-PGIS and mPGES-1 produced PGI₂ mainly, but not PGE₂. This indicates that mPGES-1 is expressed much farther from COX-1. These findings have led to proposed models showing the different post-translational ER organization between COX-2 and COX-1 with respect to the topological arrangement of the mPGES-1 during vascular inflammation. PMID:25988363
Chromosomal abnormalities in human sperm
Martin, R.H.
1985-01-01
The ability to analyze human sperm chromosome complements after penetration of zona pellucida-free hamster eggs provides the first opportunity to study the frequency and type of chromosomal abnormalities in human gametes. Two large-scale studies have provided information on normal men. We have studied 1,426 sperm complements from 45 normal men and found an abnormality rate of 8.9%. Brandriff et al. (5) found 8.1% abnormal complements in 909 sperm from 4 men. The distribution of numerical and structural abnormalities was markedly dissimilar in the 2 studies. The frequency of aneuploidy was 5% in our sample and only 1.6% in Brandriff's, perhaps reflecting individual variability among donors. The frequency of 24,YY sperm was low: 0/1,426 and 1/909. This suggests that the estimates of nondisjunction based on fluorescent Y body data (1% to 5%) are not accurate. We have also studied men at increased risk of sperm chromosomal abnormalities. The frequency of chromosomally unbalanced sperm in 6 men heterozygous for structural abnormalities varied dramatically: 77% for t11;22, 32% for t6;14, 19% for t5;18, 13% for t14;21, and 0% for inv 3 and 7. We have also studied 13 cancer patients before and after radiotherapy and demonstrated a significant dose-dependent increase of sperm chromosome abnormalities (numerical and structural) 36 months after radiation treatment.
Haematological abnormalities in mitochondrial disorders
Finsterer, Josef; Frank, Marlies
2015-01-01
INTRODUCTION This study aimed to assess the kind of haematological abnormalities that are present in patients with mitochondrial disorders (MIDs) and the frequency of their occurrence. METHODS The blood cell counts of a cohort of patients with syndromic and non-syndromic MIDs were retrospectively reviewed. MIDs were classified as ‘definite’, ‘probable’ or ‘possible’ according to clinical presentation, instrumental findings, immunohistological findings on muscle biopsy, biochemical abnormalities of the respiratory chain and/or the results of genetic studies. Patients who had medical conditions other than MID that account for the haematological abnormalities were excluded. RESULTS A total of 46 patients (‘definite’ = 5; ‘probable’ = 9; ‘possible’ = 32) had haematological abnormalities attributable to MIDs. The most frequent haematological abnormality in patients with MIDs was anaemia. 27 patients had anaemia as their sole haematological problem. Anaemia was associated with thrombopenia (n = 4), thrombocytosis (n = 2), leucopenia (n = 2), and eosinophilia (n = 1). Anaemia was hypochromic and normocytic in 27 patients, hypochromic and microcytic in six patients, hyperchromic and macrocytic in two patients, and normochromic and microcytic in one patient. Among the 46 patients with a mitochondrial haematological abnormality, 78.3% had anaemia, 13.0% had thrombopenia, 8.7% had leucopenia and 8.7% had eosinophilia, alone or in combination with other haematological abnormalities. CONCLUSION MID should be considered if a patient’s abnormal blood cell counts (particularly those associated with anaemia, thrombopenia, leucopenia or eosinophilia) cannot be explained by established causes. Abnormal blood cell counts may be the sole manifestation of MID or a collateral feature of a multisystem problem. PMID:26243978
Concept Model on Topological Learning
NASA Astrophysics Data System (ADS)
Ae, Tadashi; Kioi, Kazumasa
2010-11-01
We discuss a new model for concept based on topological learning, where the learning process on the neural network is represented by mathematical topology. The topological learning of neural networks is summarized by a quotient of input space and the hierarchical step induces a tree where each node corresponds to a quotient. In general, the concept acquisition is a difficult problem, but the emotion for a subject is represented by providing the questions to a person. Therefore, a kind of concept is captured by such data and the answer sheet can be mapped into a topology consisting of trees. In this paper, we will discuss a way of mapping the emotional concept to a topological learning model.
Signatures of topological Josephson junctions
NASA Astrophysics Data System (ADS)
Peng, Yang; Pientka, Falko; Berg, Erez; Oreg, Yuval; von Oppen, Felix
2016-08-01
Quasiparticle poisoning and diabatic transitions may significantly narrow the window for the experimental observation of the 4 π -periodic dc Josephson effect predicted for topological Josephson junctions. Here, we show that switching-current measurements provide accessible and robust signatures for topological superconductivity which persist in the presence of quasiparticle poisoning processes. Such measurements provide access to the phase-dependent subgap spectrum and Josephson currents of the topological junction when incorporating it into an asymmetric SQUID together with a conventional Josephson junction with large critical current. We also argue that pump-probe experiments with multiple current pulses can be used to measure the quasiparticle poisoning rates of the topological junction. The proposed signatures are particularly robust, even in the presence of Zeeman fields and spin-orbit coupling, when focusing on short Josephson junctions. Finally, we also consider microwave excitations of short topological Josephson junctions which may complement switching-current measurements.
Transportation Network Topologies
NASA Technical Reports Server (NTRS)
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.
Detectability of nontrivial topologies
Kunz, M.; Aghanim, N.; Riazuelo, A.; Forni, O.
2008-01-15
We study how the uncertainty in the cosmological parameters impacts on the detection of topological signals, focussing on three cubic torus universes and using three tests: the information content, the S/N statistic, and the Bayesian evidence. We find, within the concordance cosmological model, that 3D torus universes with a size of {approx}29 Gpc{sup 3} or larger cannot be detected. For the toroidal models that can be detected, the detection significance is primarily influenced by {omega}{sub {lambda}}, which enters both in the noise amplitude due to the Integrated Sachs-Wolfe effect and in the size of the causal horizon which limits the accessible fundamental domain. On large angular scales l<40, only {omega}{sub {lambda}} significantly alters the detection for all three estimators considered here.
Gear tooth topological modification
NASA Technical Reports Server (NTRS)
Kish, Jules G. (Inventor); Isabelle, Charles (Inventor)
1994-01-01
The topology of parallel axis gears, such as spur and helical gears is modified to produce quieter and more smoothly operating gear sets with more uniform load distribution. A finite element analysis of the gear in its operating mode is made to produce a plot of radial and tangential deflections of the pinion and gear tooth surfaces which will occur when the gears are loaded during operation. The resultant plot is then inverted to produce a plot, or set of coordinates, which will define the path of travel of the gear tooth grinding wheel, which path is a mirror image of the plot of the finite element analysis. The resulting gears, when subjected to operating loads, will thus be deflected tangentially and radially to their optimum operating, or theoretical true involute, positions so as to produce quieter, smoother, and more evenly loaded gear trains.
Probing Topological Superconductors
NASA Astrophysics Data System (ADS)
Schmeltzer, David
2015-03-01
The presence of attractive interaction on the surface of a 3D topological insulator which is characterized by spinors carrying a Berry phase of π gives rise to superconductivity that support space time half vortices (Majorana zero modes). We construct the effective dual action for the superconductor with the vortices, and show that the 2 n Majorana fermions are localized and can be replaced with n spinless fermions. The effect of the Majorana zero modes can be observed trough the the Andreev cross reflection when metallic leads are attached to the superconductor. The presence of the Majorana fermions can be detected with transverse sound waves. We have computed the effect of elastic strain fields and obtain an anomalous response indicating the presence of the Majorana fermions.
Coagulation abnormalities in sepsis.
Tsao, Cheng-Ming; Ho, Shung-Tai; Wu, Chin-Chen
2015-03-01
Although the pathophysiology of sepsis has been elucidated with the passage of time, sepsis may be regarded as an uncontrolled inflammatory and procoagulant response to infection. The hemostatic changes in sepsis range from subclinical activation of blood coagulation to acute disseminated intravascular coagulation (DIC). DIC is characterized by widespread microvascular thrombosis, which contributes to multiple organ dysfunction/failure, and subsequent consumption of platelets and coagulation factors, eventually causing bleeding manifestations. The diagnosis of DIC can be made using routinely available laboratory tests, scoring algorithms, and thromboelastography. In this cascade of events, the inhibition of coagulation activation and platelet function is conjectured as a useful tool for attenuating inflammatory response and improving outcomes in sepsis. A number of clinical trials of anticoagulants were performed, but none of them have been recognized as a standard therapy because recombinant activated protein C was withdrawn from the market owing to its insufficient efficacy in a randomized controlled trial. However, these subgroup analyses of activated protein C, antithrombin, and thrombomodulin trials show that overt coagulation activation is strongly associated with the best therapeutic effect of the inhibitor. In addition, antiplatelet drugs, including acetylsalicylic acid, P2Y12 inhibitors, and glycoprotein IIb/IIIa antagonists, may reduce organ failure and mortality in the experimental model of sepsis without a concomitant increased bleeding risk, which should be supported by solid clinical data. For a state-of-the-art treatment of sepsis, the efficacy of anticoagulant and antiplatelet agents needs to be proved in further large-scale prospective, interventional, randomized validation trials. PMID:25544351
ERIC Educational Resources Information Center
Chian, Edward S. K.; DeWalle, Foppe B.
1978-01-01
Presents water analysis literature for 1978. This review is concerned with organics, and it covers: (1) detergents and surfactants; (2) aliphatic and aromatic hydrocarbons; (3) pesticides and chlorinated hydrocarbons; and (4) naturally occurring organics. A list of 208 references is also presented. (HM)
ERIC Educational Resources Information Center
Callison, Daniel
2000-01-01
Focuses on "organizers," tools or techniques that provide identification and classification along with possible relationships or connections among ideas, concepts, and issues. Discusses David Ausubel's research and ideas concerning advance organizers; the implications of Ausubel's theory to curriculum and teaching; "webbing," a specific…
Neuroimaging of schizophrenia: structural abnormalities and pathophysiological implications
Buckley, Peter F
2005-01-01
Schizophrenia, once considered a psychological malady devoid of any organic brain substrate, has been the focus of intense neuroimaging research. Findings reveal mild but generalized tissue loss as well as more selective focal loss. It is unclear whether these abnormalities reflect neurodevelopmental or neurodegenerative processes, or some combination of each; current evidence favors a preponderance of neurodevelopmental abnormalities. The pattern of brain abnormalities is also influenced by environmental and genetic risk factors, as well as by the course (and possibly even treatment) of this illness. These findings are described in this article. PMID:18568069
The Dynamics of Network Topology
NASA Astrophysics Data System (ADS)
Voicu, Ramiro; Legrand, Iosif; Newman, Harvey; Barczyk, Artur; Grigoras, Costin; Dobre, Ciprian
2011-12-01
Network monitoring is vital to ensure proper network operation over time, and is tightly integrated with all the data intensive processing tasks used by the LHC experiments. In order to build a coherent set of network management services it is very important to collect in near real-time information about the network topology, the main data flows, traffic volume and the quality of connectivity. A set of dedicated modules were developed in the MonALISA framework to periodically perform network measurements tests between all sites. We developed global services to present in near real-time the entire network topology used by a community. For any LHC experiment such a network topology includes several hundred of routers and tens of Autonomous Systems. Any changes in the global topology are recorded and this information is can be easily correlated with traffic patterns. The evolution in time of global network topology is shown a dedicated GUI. Changes in the global topology at this level occur quite frequently and even small modifications in the connectivity map may significantly affect the network performance. The global topology graphs are correlated with active end to end network performance measurements, done with the Fast Data Transfer application, between all sites. Access to both real-time and historical data, as provided by MonALISA, is also important for developing services able to predict the usage pattern, to aid in efficiently allocating resources globally.
Topological number of edge states
NASA Astrophysics Data System (ADS)
Hashimoto, Koji; Kimura, Taro
2016-05-01
We show that the edge states of the four-dimensional class A system can have topological charges, which are characterized by Abelian/non-Abelian monopoles. The edge topological charges are a new feature of relations among theories with different dimensions. From this novel viewpoint, we provide a non-Abelian analog of the TKNN number as an edge topological charge, which is defined by an SU(2) 't Hooft-Polyakov BPS monopole through an equivalence to Nahm construction. Furthermore, putting a constant magnetic field yields an edge monopole in a noncommutative momentum space, where D-brane methods in string theory facilitate study of edge fermions.
Semilinear (topological) spaces and applications
NASA Technical Reports Server (NTRS)
Prakash, P.; Sertel, M. R.
1971-01-01
Semivector spaces are defined and some of their algebraic aspects are developed including some structure theory. These spaces are then topologized to obtain semilinear topological spaces for which a hierarchy of local convexity axioms is identified. A number of fixed point and minmax theorems for spaces with various local convexity properties are established. The spaces of concern arise naturally as various hyperspaces of linear and semilinear (topological) spaces. It is indicated briefly how all this can be applied in socio-economic analysis and optimization.
Topological properties of the interaction between focusing regions kind cusped.
Martínez-Niconoff, G; Santos-García, S I De Los; Torres-Rodríguez, M A; Xique, R Suárez; Vargas-Morales, M; Vara, P Martinez; Carbajal-Domínguez, A
2016-06-27
We study here the cusped-cusped interaction between two kinds of Pearcey optical fields by analyzing its topological structure. We do it in two steps; the first one is an irradiance interaction that allows us to identify organization regions. The second one is an amplitude interaction, where it is shown that the interference fringes are organized around the irradiance distribution. The topological behavior of the optical field is analyzed identifying regions with different phase functions, one of them, corresponds with a catastrophe function which has associated a focusing region, the other region can be approximated by a quadratic function. The main consequence heritage from the phase structure is interference fringes emerge from focusing regions having similar features like a topological charges. We show computational and experimental results which are in very well agreement with the theoretical model. PMID:27410617
Neems, Daniel S.; Garza-Gongora, Arturo G.; Smith, Erica D.; Kosak, Steven T.
2016-01-01
The linear distribution of genes across chromosomes and the spatial localization of genes within the nucleus are related to their transcriptional regulation. The mechanistic consequences of linear gene order, and how it may relate to the functional output of genome organization, remain to be fully resolved, however. Here we tested the relationship between linear and 3D organization of gene regulation during myogenesis. Our analysis has identified a subset of topologically associated domains (TADs) that are significantly enriched for muscle-specific genes. These lineage-enriched TADs demonstrate an expression-dependent pattern of nuclear organization that influences the positioning of adjacent nonenriched TADs. Therefore, lineage-enriched TADs inform cell-specific genome organization during myogenesis. The reduction of allelic spatial distance of one of these domains, which contains Myogenin, correlates with reduced transcriptional variability, identifying a potential role for lineage-specific nuclear topology. Using a fusion-based strategy to decouple mitosis and myotube formation, we demonstrate that the cell-specific topology of syncytial nuclei is dependent on cell division. We propose that the effects of linear and spatial organization of gene loci on gene regulation are linked through TAD architecture, and that mitosis is critical for establishing nuclear topologies during cellular differentiation. PMID:26957603
Phonon-induced topological insulation
NASA Astrophysics Data System (ADS)
Saha, Kush; Garate, Ion
2014-05-01
We develop an approximate theory of phonon-induced topological insulation in Dirac materials. In the weak-coupling regime, long-wavelength phonons may favor topological phases in Dirac insulators with direct and narrow band gaps. This phenomenon originates from electron-phonon matrix elements, which change qualitatively under a band inversion. A similar mechanism applies to weak Coulomb interactions and spin-independent disorder; however, the influence of these on band topology is largely independent of temperature. As applications of the theory, we evaluate the temperature dependence of the critical thickness and the critical stoichiometric ratio for the topological transition in CdTe/HgTe quantum wells and in BiTl(S1-δSeδ)2, respectively.
Comprehensible Presentation of Topological Information
Weber, Gunther H.; Beketayev, Kenes; Bremer, Peer-Timo; Hamann, Bernd; Haranczyk, Maciej; Hlawitschka, Mario; Pascucci, Valerio
2012-03-05
Topological information has proven very valuable in the analysis of scientific data. An important challenge that remains is presenting this highly abstract information in a way that it is comprehensible even if one does not have an in-depth background in topology. Furthermore, it is often desirable to combine the structural insight gained by topological analysis with complementary information, such as geometric information. We present an overview over methods that use metaphors to make topological information more accessible to non-expert users, and we demonstrate their applicability to a range of scientific data sets. With the increasingly complex output of exascale simulations, the importance of having effective means of providing a comprehensible, abstract overview over data will grow. The techniques that we present will serve as an important foundation for this purpose.
Schwerdtfeger, Peter; Wirz, Lukas N; Avery, James
2015-01-01
Fullerenes are carbon molecules that form polyhedral cages. Their bond structures are exactly the planar cubic graphs that have only pentagon and hexagon faces. Strikingly, a number of chemical properties of a fullerene can be derived from its graph structure. A rich mathematics of cubic planar graphs and fullerene graphs has grown since they were studied by Goldberg, Coxeter, and others in the early 20th century, and many mathematical properties of fullerenes have found simple and beautiful solutions. Yet many interesting chemical and mathematical problems in the field remain open. In this paper, we present a general overview of recent topological and graph theoretical developments in fullerene research over the past two decades, describing both solved and open problems. WIREs Comput Mol Sci 2015, 5:96–145. doi: 10.1002/wcms.1207 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website. PMID:25678935
Experimental Realizations of Magnetic Topological Insulator and Topological Crystalline Insulator
NASA Astrophysics Data System (ADS)
Xu, Suyang
2013-03-01
Over the past few years the experimental research on three-dimensional topological insulators have emerged as one of the most rapidly developing fields in condensed matter physics. In this talk, we report on two new developments in the field: The first part is on the dynamic interplay between ferromagnetism and the Z2 topological insulator state (leading to a magnetic topological insulator). We present our spin-resolved photoemission and magnetic dichroic experiments on MBE grown films where a hedgehog-like spin texture is revealed on the magnetically ordered surface of Mn-Bi2Se3 revealing a Berry's phase gradient in energy-momentum space of the crystal. A chemically/electrically tunable Berry's phase switch is further demonstrated via the tuning of the spin groundstate in Mn-Bi2Se3 revealed in our data (Nature Physics 8, 616 (2012)). The second part of this talk describes our experimental observation of a new topological phase of matter, namely a topological crystalline insulator where space group symmetries replace the role of time-reversal symmetry in an otherwise Z2 topological insulator predicted in theory. We experimentally investigate the possibility of a mirror symmetry protected topological phase transition in the Pb1-xSnxTe alloy system, which has long been known to contain an even number of band inversions based on band theory. Our experimental results show that at a composition below the theoretically predicted band inversion, the system is fully gapped, whereas in the band-inverted regime, the surface exhibits even number of spin-polarized Dirac cone states revealing mirror-protected topological order (Nature Communications 3, 1192 (2012)) distinct from that observed in Z2 topological insulators. We discuss future experimental possibilities opened up by these new developments in topological insulators research. This work is in collaboration with M. Neupane, C. Liu, N. Alidoust, I. Belopolski, D. Qian, D.M. Zhang, A. Richardella, A. Marcinkova, Q
Refining the shifted topological vertex
Drissi, L. B.; Jehjouh, H.; Saidi, E. H.
2009-01-15
We study aspects of the refining and shifting properties of the 3d MacMahon function C{sub 3}(q) used in topological string theory and BKP hierarchy. We derive the explicit expressions of the shifted topological vertex S{sub {lambda}}{sub {mu}}{sub {nu}}(q) and its refined version T{sub {lambda}}{sub {mu}}{sub {nu}}(q,t). These vertices complete results in literature.
Topological excitations in semiconductor heterostructures
Koushik, R.; Mukerjee, Subroto; Ghosh, Arindam; Baenninger, Matthias; Narayan, Vijay; Pepper, Michael; Farrer, Ian; Ritchie, David A.
2013-12-04
Topological defects play an important role in the melting phenomena in two-dimensions. In this work, we report experimental observation of topological defect induced melting in two-dimensional electron systems (2DES) in the presence of strong Coulomb interaction and disorder. The phenomenon is characterised by measurement of conductivity which goes to zero in a Berezinskii-Kosterlitz-Thouless like transition. Further evidence is provided via low-frequency conductivity noise measurements.
Topological solitons in optical oscillators
NASA Astrophysics Data System (ADS)
Yaparov, V. V.; Taranenko, V. B.
2016-07-01
We present an overview of theoretical and experimental works on self-sustaining localized structures—spatial solitons—which can be formed in optical bistable oscillators with laser and/or parametric gain. The main attention is paid to the existence and dynamical properties of spatial solitons containing phase and polarization topological defects including vortices, points of circular polarizations and lines of linear polarization, domain walls and composed domain walls with Néel point topological defects.
Topics in topological band systems
NASA Astrophysics Data System (ADS)
Huang, Zhoushen
The discovery of integer quantum Hall effect and its subsequent theoretical formulation heralded a new paradigm of thinking in condensed matter physics, which has by now blossomed into the rapidly growing field of topological phases. In this work we investigate several mutually related topics in the framework of topological band theory. In Chapter 2, we study solutions to boundary states on a lattice and see how they are related to the bulk topology. To elicit a real space manifestation of the non-trivial topology, the presence of a physical edge is not strictly necessary. We study two other possibilities, namely the entanglement spectrum associated with an imaginary spatial boundary, and the localization centers of Wannier functions, in Chapters 3,4, and 5. Topological classification through discrete indices is so far possible only for systems described by pure quantum states---in the existing scheme, quantization is lost for systems in mixed states. In Chapter 6, we present a program through which discrete topological indices can be defined for topological band systems at finite temperature, based on Uhlmann's parallel transport of density matrices. The potential of topologocal insulators in realistic applications lies in the existence of Dirac nodes on its surface spectrum. Dirac physics, however, is not exclusive to TI surfaces. In a recently discovered class of materials known as Weyl semimetals, energy nodes which emit linear dispersions also occur in the bulk material. In Chapter 7, we study the possibility of resonance states induced by localized impurities near the nodal energy in Weyl semimetals, which will help us in understanding the stability of density-of-state suppression at the energy nodes. Finally, in Chapter 8, we apply the topological characterization developed for noninteracting particles to a class of interacting spin models in 3D, which are generalizations of Kitaev's honeycomb model, and identify several exotic quantum phases such as spin
Fractional (Chern and topological) insulators
NASA Astrophysics Data System (ADS)
Neupert, Titus; Chamon, Claudio; Iadecola, Thomas; Santos, Luiz H.; Mudry, Christopher
2015-12-01
We review various features of interacting Abelian topological phases of matter in two spatial dimensions, placing particular emphasis on fractional Chern insulators (FCIs) and fractional topological insulators (FTIs). We highlight aspects of these systems that challenge the intuition developed from quantum Hall physics—for instance, FCIs are stable in the limit where the interaction energy scale is much larger than the band gap, and FTIs can possess fractionalized excitations in the bulk despite the absence of gapless edge modes.
Topological edge states in pnictides
NASA Astrophysics Data System (ADS)
Youmans, Cody; Ghaemi, Pouyan; Kargarian, Mehdi
In some members of the ferro-pnictides, non-trivial topology in the bulk band-structure is related to potentially observable gapless edge states. We study these states numerically and analytically for a range of parameters, with and without superconductivity and antiferromagnetic SDW ordering, and their relation to the symmetries and topologically non-trivial aspects of our model Hamiltonian. Support was provided by the Doctoral Student Research Grant program at the Graduate Center, CUNY.
Kinks in topological soft matter
NASA Astrophysics Data System (ADS)
Chen, Bryan; Upadhyaya, Nitin; Vitelli, Vincenzo
2014-03-01
Weakly connected mechanical systems near the isostatic threshold are fragile in the sense that they exhibit large deformations in response to tiny perturbations. Kane and Lubensky have recently defined a new topological invariant of isostatic mechanical lattices which leads within linear elasticity to zero energy modes at the boundary akin to the edge modes studied in topological quantum matter. What happens when such prototype topological soft materials are subject to an external mechanical perturbation? In our work, we demonstrate that the linear soft modes can often integrate to non-linear deformations described by topological solitons. These solitons that are moving kinks between distinct topological phases are the basic excitations of fragile mechanical systems. We illustrate the general soliton construction in the context of a 1D chain of rotors connected by springs that can be considered the archetype of a topological mechanical structure. In the continuum limit, this chain is described by a Lorentz invariant ϕ4 theory and the corresponding solitons exhibit a Lorentz contraction of the width, as their speed is raised.
Topological Photonics for Continuous Media
NASA Astrophysics Data System (ADS)
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.
Topological Insulators from Group Cohomology
NASA Astrophysics Data System (ADS)
Alexandradinata, A.; Wang, Zhijun; Bernevig, B. Andrei
2016-04-01
We classify insulators by generalized symmetries that combine space-time transformations with quasimomentum translations. Our group-cohomological classification generalizes the nonsymmorphic space groups, which extend point groups by real-space translations; i.e., nonsymmorphic symmetries unavoidably translate the spatial origin by a fraction of the lattice period. Here, we further extend nonsymmorphic groups by reciprocal translations, thus placing real and quasimomentum space on equal footing. We propose that group cohomology provides a symmetry-based classification of quasimomentum manifolds, which in turn determines the band topology. In this sense, cohomology underlies band topology. Our claim is exemplified by the first theory of time-reversal-invariant insulators with nonsymmorphic spatial symmetries. These insulators may be described as "piecewise topological," in the sense that subtopologies describe the different high-symmetry submanifolds of the Brillouin zone, and the various subtopologies must be pieced together to form a globally consistent topology. The subtopologies that we discover include a glide-symmetric analog of the quantum spin Hall effect, an hourglass-flow topology (exemplified by our recently proposed KHgSb material class), and quantized non-Abelian polarizations. Our cohomological classification results in an atypical bulk-boundary correspondence for our topological insulators.
Gravity asymptotics with topological parameters
NASA Astrophysics Data System (ADS)
Sengupta, Sandipan
2013-07-01
In four-dimensional gravity theory, the Barbero-Immirzi parameter has a topological origin, and can be identified as the coefficient multiplying the Nieh-Yan topological density in the gravity Lagrangian, as proposed by Date et al. [Phys. Rev. D 79, 044008 (2009)]. Based on this fact, a first order action formulation for spacetimes with boundaries is introduced. The bulk Lagrangian, containing the Nieh-Yan density, needs to be supplemented with suitable boundary terms so that it leads to a well-defined variational principle. Within this general framework, we analyze spacetimes with and without a cosmological constant. For locally anti-de Sitter (or de Sitter) asymptotia, the action principle has nontrivial implications. It admits an extremum for all such solutions provided the SO(3,1) Pontryagin and Euler topological densities are added to it with fixed coefficients. The resulting Lagrangian, while containing all three topological densities, has only one independent topological coupling constant, namely, the Barbero-Immirzi parameter. In the final analysis, it emerges as a coefficient of the SO(3,2) [or SO(4,1)] Pontryagin density, and is present in the action only for manifolds for which the corresponding topological index is nonzero.
Molecular abnormalities in Ewing's sarcoma.
Burchill, Susan Ann
2008-10-01
Ewing's sarcoma is one of the few solid tumors for which the underlying molecular genetic abnormality has been described: rearrangement of the EWS gene on chromosome 22q12 with an ETS gene family member. These translocations define the Ewing's sarcoma family of tumors (ESFT) and provide a valuable tool for their accurate and unequivocal diagnosis. They also represent ideal targets for the development of tumor-specific therapeutics. Although secondary abnormalities occur in over 80% of primary ESFT the clinical utility of these is currently unclear. However, abnormalities in genes that regulate the G(1)/S checkpoint are frequently described and may be important in predicting outcome and response. Increased understanding of the molecular events that arise in ESFT and their role in the development and maintenance of the malignant phenotype will inform the improved stratification of patients for therapy and identify targets and pathways for the design of more effective cancer therapeutics. PMID:18925858
Complex patterns of abnormal heartbeats
NASA Technical Reports Server (NTRS)
Schulte-Frohlinde, Verena; Ashkenazy, Yosef; Goldberger, Ary L.; Ivanov, Plamen Ch; Costa, Madalena; Morley-Davies, Adrian; Stanley, H. Eugene; Glass, Leon
2002-01-01
Individuals having frequent abnormal heartbeats interspersed with normal heartbeats may be at an increased risk of sudden cardiac death. However, mechanistic understanding of such cardiac arrhythmias is limited. We present a visual and qualitative method to display statistical properties of abnormal heartbeats. We introduce dynamical "heartprints" which reveal characteristic patterns in long clinical records encompassing approximately 10(5) heartbeats and may provide information about underlying mechanisms. We test if these dynamics can be reproduced by model simulations in which abnormal heartbeats are generated (i) randomly, (ii) at a fixed time interval following a preceding normal heartbeat, or (iii) by an independent oscillator that may or may not interact with the normal heartbeat. We compare the results of these three models and test their limitations to comprehensively simulate the statistical features of selected clinical records. This work introduces methods that can be used to test mathematical models of arrhythmogenesis and to develop a new understanding of underlying electrophysiologic mechanisms of cardiac arrhythmia.
Looping around Reprogramming: The Topological Memory of Induced Pluripotency.
Gonzales, Kevin Andrew Uy; Ng, Huck-Hui
2016-05-01
Genome architecture is associated with cellular identity, but how this organization changes during reprogramming is not well understood. Now in Cell Stem Cell, Krijger et al. (2016) and Beagan et al. (2016) report 3D chromatin interaction maps before and after reprogramming, providing evidence for topological memory in induced pluripotent stem cells. PMID:27152435
Topological BF field theory description of topological insulators
Cho, Gil Young; Moore, Joel E.
2011-06-15
Research Highlights: > We show that a BF theory is the effective theory of 2D and 3D topological insulators. > The non-gauge-invariance of the bulk theory yields surface terms for a bosonized Dirac fermion. > The 'axion' term in electromagnetism is correctly obtained from gapped surfaces. > Generalizations to possible fractional phases are discussed in closing. - Abstract: Topological phases of matter are described universally by topological field theories in the same way that symmetry-breaking phases of matter are described by Landau-Ginzburg field theories. We propose that topological insulators in two and three dimensions are described by a version of abelian BF theory. For the two-dimensional topological insulator or quantum spin Hall state, this description is essentially equivalent to a pair of Chern-Simons theories, consistent with the realization of this phase as paired integer quantum Hall effect states. The BF description can be motivated from the local excitations produced when a {pi} flux is threaded through this state. For the three-dimensional topological insulator, the BF description is less obvious but quite versatile: it contains a gapless surface Dirac fermion when time-reversal-symmetry is preserved and yields 'axion electrodynamics', i.e., an electromagnetic E . B term, when time-reversal symmetry is broken and the surfaces are gapped. Just as changing the coefficients and charges of 2D Chern-Simons theory allows one to obtain fractional quantum Hall states starting from integer states, BF theory could also describe (at a macroscopic level) fractional 3D topological insulators with fractional statistics of point-like and line-like objects.
[Emotion Disorders and Abnormal Perspiration].
Umeda, Satoshi
2016-08-01
This article reviewed the relationship between emotional disorders and abnormal perspiration. First, I focused on local brain areas related to emotional processing, and summarized the functions of the emotional network involving those local areas. Functional disorders followed by the damage in the amygdala, orbitofrontal cortex, and insular cortex were reviewed, including related abnormal perspiration. I then addressed the mechanisms of how autonomic disorders influence emotional processing. Finally, possible future directions for integrated understanding of the connection between neural activities and bodily reactions were discussed. PMID:27503817
Ultrasonographic assessment of abnormal pregnancy.
England, G C
1998-07-01
Ultrasonographic imaging is widely used in small animal practice for the diagnosis of pregnancy and the determination of fetal number. Ultrasonography can also be used to monitor abnormal pregnancies, for example, conceptuses that are poorly developed for their gestational age (and therefore are likely to fail), and pregnancies in which there is embryonic resorption or fetal abortion. An ultrasound examination may reveal fetal abnormalities and therefore alter the management of the pregnant bitch or queen prior to parturition. There are, however, a number of ultrasonographic features of normal pregnancies that may mimic disease, and these must be recognized. PMID:9698618
Chromosomal abnormalities associated with cyclopia and synophthalmia.
Howard, R O
1977-01-01
At the present time, essentially all known facts concerning cyclopia are consistent with some chromosomal disease, including clinical features of the pregnancy (fetal wastage, prematurity, intrauterine growth retardation, maternal age factor, complications of pregnancy), the generalized developmental abnormalities, specific ocular dysgenesis, by the high incidence of chromosomal abnormality already demonstrated, and the possibility of error in those cases of cyclopia with normal chromosomes. Even if chromosomal aberrations represent only one group of several different etiologic factors leading to cyclopia, at the present time chromosomal errors would seem to be the most common cause of cyclopia now recognized. Further studies will establish or disprove a chromosomal error in those instances which are now considered to be the result of an environmental factor alone or those with apparent familial patterns of inheritance. This apparent diverse origin of cyclopia can be clarified if future cyclopic specimens are carefully investigated. The evaluation should include a careful gross and microscopic examination of all organs, including the eye, and chromosome banding studies of all organs, including the eye, and chromosome banding studies of at least two cyclopic tissues. Then the presence or absence of multiple causative factors can be better evaluated. Images FIGURE 2 A FIGURE 2 B FIGURE 1 A FIGURE 1 B FIGURE 1 C FIGURE 1 D FIGURE 1 E FIGURE 1 F FIGURE 3 A FIGURE 3 B FIGURE 4 A FIGURE 4 B FIGURE 4 C FIGURE 4 D FIGURE 5 FIGURE 6 FIGURE 7 A FIGURE 7 B PMID:418547
NASA Astrophysics Data System (ADS)
Ilyushin, G. D.; Pisarevskii, Yu. V.
2015-11-01
The supramolecular chemistry of vanadyl sulfates, consisting of polyhedral clusters V(O, OH, H2O)6 with octahedral O coordination (M polyhedra) and SO4 tetrahedra (T polyhedra) and forming molecular (island) and framework 3D MT structures, is considered. Algorithms of combinatorial and topological analysis are developed that make it possible to reconstruct (based on known structural data) the symmetry and topological code of the matrix convergent self-assembly of crystal structure. Cluster modeling of the selfassembly of molecular (island) MT structures of the V2O2(H2O)6(SO4)2 · 4H2O (anorthominasragrite (ANM)) and V2O2(H2O)6(SO4)2 (bobjonesite (BBN)) compositions and topologically different framework 3D MT structures with covalent bonds, V2O2(SO4)2 (pauflerite (PAF) and synthetic phase (SYN)), is performed. A 3D reconstruction of the self-assembly mechanism in the form nanocluster precursor S 0 3 → primary chain → S 1 3 microlayer S 2 3 → microframework S 3 3 has revealed an invariant type of cyclic cluster precursor M2T2 (with a symmetry g = overline 1 ) for all compounds; differences in the self-assembly mechanisms are found for ANM and BBN in the stage of formation of primary chain S 1 3 and for PAF and SYN in the stage of formation of microlayer S 2 3. Basic 2D and 3D nets are presented in the form of graphs, the sites of which correspond to the positions of centroids of cluster precursors M2T2. The same topological type of basic 2D nets (4.4.4.4) is ascertained for all compounds. A basic 3D net corresponding to a simple cubic structure of Po (coordination number (CN) = 6) is established for ANM, SYN, and PAF; the basic 3D net for BBN corresponds to the cubic F structure of Cu (CN = 12).
Extracellular Matrix Abnormalities in Schizophrenia
Berretta, Sabina
2011-01-01
Emerging evidence points to the involvement of the brain extracellular matrix (ECM) in the pathophysiology of schizophrenia (SZ). Abnormalities affecting several ECM components, including Reelin and chondroitin sulfate proteoglycans (CSPGs), have been described in subjects with this disease. Solid evidence supports the involvement of Reelin, an ECM glycoprotein involved in corticogenesis, synaptic functions and glutamate NMDA receptor regulation, expressed prevalently in distinct populations of GABAergic neurons, which secrete it into the ECM. Marked changes of Reelin expression in SZ have typically been reported in association with GABA-related abnormalities in subjects with SZ and bipolar disorder. Recent findings from our group point to substantial abnormalities affecting CSPGs, a main ECM component, in the amygdala and entorhinal cortex of subjects with schizophrenia, but not bipolar disorder. Striking increases of glial cells expressing CSPGs were accompanied by reductions of perineuronal nets, CSPG- and Reelin-enriched ECM aggregates enveloping distinct neuronal populations. CSPGs developmental and adult functions, including neuronal migration, axon guidance, synaptic and neurotransmission regulation are highly relevant to the pathophysiology of SZ. Together with reports of anomalies affecting several other ECM components, these findings point to the ECM as a key component of the pathology of SZ. We propose that ECM abnormalities may contribute to several aspects of the pathophysiology of this disease, including disrupted connectivity and neuronal migration, synaptic anomalies and altered GABAergic, glutamatergic and dopaminergic neurotransmission. PMID:21856318
Plexciton Dirac points and topological modes
Yuen-Zhou, Joel; Saikin, Semion K.; Zhu, Tony; Onbasli, Mehmet C.; Ross, Caroline A.; Bulovic, Vladimir; Baldo, Marc A.
2016-01-01
Plexcitons are polaritonic modes that result from the strong coupling between excitons and plasmons. Here, we consider plexcitons emerging from the interaction of excitons in an organic molecular layer with surface plasmons in a metallic film. We predict the emergence of Dirac cones in the two-dimensional band-structure of plexcitons due to the inherent alignment of the excitonic transitions in the organic layer. An external magnetic field opens a gap between the Dirac cones if the plexciton system is interfaced with a magneto-optical layer. The resulting energy gap becomes populated with topologically protected one-way modes, which travel at the interface of this plexcitonic system. Our theoretical proposal suggests that plexcitons are a convenient and simple platform for the exploration of exotic phases of matter and for the control of energy flow at the nanoscale. PMID:27278258
Plexciton Dirac points and topological modes.
Yuen-Zhou, Joel; Saikin, Semion K; Zhu, Tony; Onbasli, Mehmet C; Ross, Caroline A; Bulovic, Vladimir; Baldo, Marc A
2016-01-01
Plexcitons are polaritonic modes that result from the strong coupling between excitons and plasmons. Here, we consider plexcitons emerging from the interaction of excitons in an organic molecular layer with surface plasmons in a metallic film. We predict the emergence of Dirac cones in the two-dimensional band-structure of plexcitons due to the inherent alignment of the excitonic transitions in the organic layer. An external magnetic field opens a gap between the Dirac cones if the plexciton system is interfaced with a magneto-optical layer. The resulting energy gap becomes populated with topologically protected one-way modes, which travel at the interface of this plexcitonic system. Our theoretical proposal suggests that plexcitons are a convenient and simple platform for the exploration of exotic phases of matter and for the control of energy flow at the nanoscale. PMID:27278258
Plexciton Dirac points and topological modes
NASA Astrophysics Data System (ADS)
Yuen-Zhou, Joel; Saikin, Semion K.; Zhu, Tony; Onbasli, Mehmet C.; Ross, Caroline A.; Bulovic, Vladimir; Baldo, Marc A.
2016-06-01
Plexcitons are polaritonic modes that result from the strong coupling between excitons and plasmons. Here, we consider plexcitons emerging from the interaction of excitons in an organic molecular layer with surface plasmons in a metallic film. We predict the emergence of Dirac cones in the two-dimensional band-structure of plexcitons due to the inherent alignment of the excitonic transitions in the organic layer. An external magnetic field opens a gap between the Dirac cones if the plexciton system is interfaced with a magneto-optical layer. The resulting energy gap becomes populated with topologically protected one-way modes, which travel at the interface of this plexcitonic system. Our theoretical proposal suggests that plexcitons are a convenient and simple platform for the exploration of exotic phases of matter and for the control of energy flow at the nanoscale.
Plexciton Dirac points and topological modes
Yuen-Zhou, Joel; Saikin, Semion K.; Zhu, Tony; Onbasli, Mehmet C.; Ross, Caroline A.; Bulovic, Vladimir; Baldo, Marc A.
2016-06-09
Plexcitons are polaritonic modes that result from the strong coupling between excitons and plasmons. Here, we consider plexcitons emerging from the interaction of excitons in an organic molecular layer with surface plasmons in a metallic film. We predict the emergence of Dirac cones in the two-dimensional band-structure of plexcitons due to the inherent alignment of the excitonic transitions in the organic layer. An external magnetic field opens a gap between the Dirac cones if the plexciton system is interfaced with a magneto-optical layer. The resulting energy gap becomes populated with topologically protected one-way modes, which travel at the interface ofmore » this plexcitonic system. Furthermore, our theoretical proposal suggests that plexcitons are a convenient and simple platform for the exploration of exotic phases of matter and for the control of energy flow at the nanoscale.« less
Numerical Studies of Topological phases
NASA Astrophysics Data System (ADS)
Geraedts, Scott
The topological phases of matter have been a major part of condensed matter physics research since the discovery of the quantum Hall effect in the 1980s. Recently, much of this research has focused on the study of systems of free fermions, such as the integer quantum Hall effect, quantum spin Hall effect, and topological insulator. Though these free fermion systems can play host to a variety of interesting phenomena, the physics of interacting topological phases is even richer. Unfortunately, there is a shortage of theoretical tools that can be used to approach interacting problems. In this thesis I will discuss progress in using two different numerical techniques to study topological phases. Recently much research in topological phases has focused on phases made up of bosons. Unlike fermions, free bosons form a condensate and so interactions are vital if the bosons are to realize a topological phase. Since these phases are difficult to study, much of our understanding comes from exactly solvable models, such as Kitaev's toric code, as well as Levin-Wen and Walker-Wang models. We may want to study systems for which such exactly solvable models are not available. In this thesis I present a series of models which are not solvable exactly, but which can be studied in sign-free Monte Carlo simulations. The models work by binding charges to point topological defects. They can be used to realize bosonic interacting versions of the quantum Hall effect in 2D and topological insulator in 3D. Effective field theories of ''integer'' (non-fractionalized) versions of these phases were available in the literature, but our models also allow for the construction of fractional phases. We can measure a number of properties of the bulk and surface of these phases. Few interacting topological phases have been realized experimentally, but there is one very important exception: the fractional quantum Hall effect (FQHE). Though the fractional quantum Hall effect we discovered over 30
Topological Insulators at Room Temperature
Zhang, Haijun; Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-03-25
Topological insulators are new states of quantum matter with surface states protected by the time-reversal symmetry. In this work, we perform first-principle electronic structure calculations for Sb{sub 2}Te{sub 3}, Sb{sub 2}Se{sub 3}, Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} crystals. Our calculations predict that Sb{sub 2}Te{sub 3}, Bi{sub 2}T e{sub 3} and Bi{sub 2}Se{sub 3} are topological insulators, while Sb{sub 2}Se{sub 3} is not. In particular, Bi{sub 2}Se{sub 3} has a topologically non-trivial energy gap of 0.3eV , suitable for room temperature applications. We present a simple and unified continuum model which captures the salient topological features of this class of materials. These topological insulators have robust surface states consisting of a single Dirac cone at the {Lambda} point.
Effective Topological Charge Cancelation Mechanism
NASA Astrophysics Data System (ADS)
Mesarec, Luka; Góźdź, Wojciech; Iglič, Aleš; Kralj, Samo
2016-06-01
Topological defects (TDs) appear almost unavoidably in continuous symmetry breaking phase transitions. The topological origin makes their key features independent of systems’ microscopic details; therefore TDs display many universalities. Because of their strong impact on numerous material properties and their significant role in several technological applications it is of strong interest to find simple and robust mechanisms controlling the positioning and local number of TDs. We present a numerical study of TDs within effectively two dimensional closed soft films exhibiting in-plane orientational ordering. Popular examples of such class of systems are liquid crystalline shells and various biological membranes. We introduce the Effective Topological Charge Cancellation mechanism controlling localised positional assembling tendency of TDs and the formation of pairs {defect, antidefect} on curved surfaces and/or presence of relevant “impurities” (e.g. nanoparticles). For this purpose, we define an effective topological charge Δmeff consisting of real, virtual and smeared curvature topological charges within a surface patch Δς identified by the typical spatially averaged local Gaussian curvature K. We demonstrate a strong tendency enforcing Δmeff → 0 on surfaces composed of Δς exhibiting significantly different values of spatially averaged K. For Δmeff ≠ 0 we estimate a critical depinning threshold to form pairs {defect, antidefect} using the electrostatic analogy.
Effective Topological Charge Cancelation Mechanism
Mesarec, Luka; Góźdź, Wojciech; Iglič, Aleš; Kralj, Samo
2016-01-01
Topological defects (TDs) appear almost unavoidably in continuous symmetry breaking phase transitions. The topological origin makes their key features independent of systems’ microscopic details; therefore TDs display many universalities. Because of their strong impact on numerous material properties and their significant role in several technological applications it is of strong interest to find simple and robust mechanisms controlling the positioning and local number of TDs. We present a numerical study of TDs within effectively two dimensional closed soft films exhibiting in-plane orientational ordering. Popular examples of such class of systems are liquid crystalline shells and various biological membranes. We introduce the Effective Topological Charge Cancellation mechanism controlling localised positional assembling tendency of TDs and the formation of pairs {defect, antidefect} on curved surfaces and/or presence of relevant “impurities” (e.g. nanoparticles). For this purpose, we define an effective topological charge Δmeff consisting of real, virtual and smeared curvature topological charges within a surface patch Δς identified by the typical spatially averaged local Gaussian curvature K. We demonstrate a strong tendency enforcing Δmeff → 0 on surfaces composed of Δς exhibiting significantly different values of spatially averaged K. For Δmeff ≠ 0 we estimate a critical depinning threshold to form pairs {defect, antidefect} using the electrostatic analogy. PMID:27250777
Effective Topological Charge Cancelation Mechanism.
Mesarec, Luka; Góźdź, Wojciech; Iglič, Aleš; Kralj, Samo
2016-01-01
Topological defects (TDs) appear almost unavoidably in continuous symmetry breaking phase transitions. The topological origin makes their key features independent of systems' microscopic details; therefore TDs display many universalities. Because of their strong impact on numerous material properties and their significant role in several technological applications it is of strong interest to find simple and robust mechanisms controlling the positioning and local number of TDs. We present a numerical study of TDs within effectively two dimensional closed soft films exhibiting in-plane orientational ordering. Popular examples of such class of systems are liquid crystalline shells and various biological membranes. We introduce the Effective Topological Charge Cancellation mechanism controlling localised positional assembling tendency of TDs and the formation of pairs {defect, antidefect} on curved surfaces and/or presence of relevant "impurities" (e.g. nanoparticles). For this purpose, we define an effective topological charge Δmeff consisting of real, virtual and smeared curvature topological charges within a surface patch Δς identified by the typical spatially averaged local Gaussian curvature K. We demonstrate a strong tendency enforcing Δmeff → 0 on surfaces composed of Δς exhibiting significantly different values of spatially averaged K. For Δmeff ≠ 0 we estimate a critical depinning threshold to form pairs {defect, antidefect} using the electrostatic analogy. PMID:27250777
Topology and hemodynamics of the cortical cerebrovascular system
Hirsch, Sven; Reichold, Johannes; Schneider, Matthias; Székely, Gábor; Weber, Bruno
2012-01-01
The cerebrovascular system continuously delivers oxygen and energy substrates to the brain, which is one of the organs with the highest basal energy requirement in mammals. Discontinuities in the delivery lead to fatal consequences for the brain tissue. A detailed understanding of the structure of the cerebrovascular system is important for a multitude of (patho-)physiological cerebral processes and many noninvasive functional imaging methods rely on a signal that originates from the vasculature. Furthermore, neurodegenerative diseases often involve the cerebrovascular system and could contribute to neuronal loss. In this review, we focus on the cortical vascular system. In the first part, we present the current knowledge of the vascular anatomy. This is followed by a theory of topology and its application to vascular biology. We then discuss possible interactions between cerebral blood flow and vascular topology, before summarizing the existing body of the literature on quantitative cerebrovascular topology. PMID:22472613
A New Platform for Engineering Topological Superconductors: Superlattices on Rashba Superconductors
NASA Astrophysics Data System (ADS)
Lu, Yao; Law, Kam Tuen
The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose a new experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without fine-tuning the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.
Topologically Dissociable Patterns of Development of the Human Cerebral Cortex
Vandekar, Simon N.; Shinohara, Russell T.; Raznahan, Armin; Roalf, David R.; Ross, Michelle; DeLeo, Nicholas; Ruparel, Kosha; Verma, Ragini; Wolf, Daniel H.; Gur, Ruben C.; Gur, Raquel E.
2015-01-01
Over 90 years ago, anatomists noted the cortex is thinner in sulci than gyri, suggesting that development may occur on a fine scale driven by local topology. However, studies of brain development in youth have focused on describing how cortical thickness varies over large-scale functional and anatomic regions. How the relationship between thickness and local sulcal topology arises in development is still not well understood. Here, we investigated the spatial relationships between cortical thickness, folding, and underlying white matter organization to elucidate the influence of local topology on human brain development. Our approach included using both T1-weighted imaging and diffusion tensor imaging (DTI) in a cross-sectional sample of 932 youths ages 8–21 studied as part of the Philadelphia Neurodevelopmental Cohort. Principal components analysis revealed separable development-related processes of regionally specific nonlinear cortical thickening (from ages 8–14) and widespread linear cortical thinning that have dissociable relationships with cortical topology. Whereas cortical thinning was most prominent in the depths of the sulci, early cortical thickening was present on the gyri. Furthermore, decline in mean diffusivity calculated from DTI in underlying white matter was correlated with cortical thinning, suggesting that cortical thinning is spatially associated with white matter development. Spatial permutation tests were used to assess the significance of these relationships. Together, these data demonstrate that cortical remodeling during youth occurs on a local topological scale and is associated with changes in white matter beneath the cortical surface. PMID:25589754
Fractionalized topological defects in optical lattices
NASA Astrophysics Data System (ADS)
Zhang, Xing-Hai; Fan, Wen-Jun; Shi, Jin-Wei; Kou, Su-Peng
2015-10-01
Topological objects are interesting topics in various fields of physics ranging from condensed matter physics to the grand unified and superstring theories. Among those, ultracold atoms provide a playground to study the complex topological objects. In this paper we present a proposal to realize an optical lattice with stable fractionalized topological objects. In particular, we generate the fractionalized topological fluxes and fractionalized skyrmions on two-dimensional optical lattices and fractionalized monopoles on three-dimensional optical lattices. These results offer a new approach to study the quantum many-body systems on optical lattices of ultracold quantum gases with controllable topological defects, including dislocations, topological fluxes and monopoles.
Topological Insulators from Electronic Superstructures
NASA Astrophysics Data System (ADS)
Sugita, Yusuke; Motome, Yukitoshi
2016-07-01
The possibility of realizing topological insulators by the spontaneous formation of electronic superstructures is theoretically investigated in a minimal two-orbital model including both the spin-orbit coupling and electron correlations on a triangular lattice. Using the mean-field approximation, we show that the model exhibits several different types of charge-ordered insulators, where the charge disproportionation forms a honeycomb or kagome superstructure. We find that the charge-ordered insulators in the presence of strong spin-orbit coupling can be topological insulators showing quantized spin Hall conductivity. Their band gap is dependent on electron correlations as well as the spin-orbit coupling, and even vanishes while showing the massless Dirac dispersion at the transition to a trivial charge-ordered insulator. Our results suggest a new route to realize and control topological states of quantum matter by the interplay between the spin-orbit coupling and electron correlations.
Quantum Capacitance in Topological Insulators
Xiu, Faxian; Meyer, Nicholas; Kou, Xufeng; He, Liang; Lang, Murong; Wang, Yong; Yu, Xinxin; Fedorov, Alexei V.; Zou, Jin; Wang, Kang L.
2012-01-01
Topological insulators show unique properties resulting from massless, Dirac-like surface states that are protected by time-reversal symmetry. Theory predicts that the surface states exhibit a quantum spin Hall effect with counter-propagating electrons carrying opposite spins in the absence of an external magnetic field. However, to date, the revelation of these states through conventional transport measurements remains a significant challenge owing to the predominance of bulk carriers. Here, we report on an experimental observation of Shubnikov-de Haas oscillations in quantum capacitance measurements, which originate from topological helical states. Unlike the traditional transport approach, the quantum capacitance measurements are remarkably alleviated from bulk interference at high excitation frequencies, thus enabling a distinction between the surface and bulk. We also demonstrate easy access to the surface states at relatively high temperatures up to 60 K. Our approach may eventually facilitate an exciting exploration of exotic topological properties at room temperature. PMID:22993694
Fidelity approach in topological superconductors
NASA Astrophysics Data System (ADS)
Yao, Dao-Xin; Tian, Wen-Chuan; Huang, Guang-Yao; Wang, Zhi
We study topological superconductivity in the spin-orbit coupling nanowire system by using the fidelity approach. The wire is modeled as a one layer lattice chain with Zeeman energy and spin-orbital 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. Our study shows that fidelity and fidelity susceptibility are very useful to investigate the topological quantum phase transition in superconductors. This work is supported by NSFC-11574404, 11275279, and NBRPC-2012CB821400.
Abnormal Bleeding During Menopause Hormone Therapy: Insights for Clinical Management
de Medeiros, Sebastião Freitas; Yamamoto, Márcia Marly Winck; Barbosa, Jacklyne Silva
2013-01-01
Objective Our objective was to review the involved mechanisms and propose actions for controlling/treating abnormal uterine bleeding during climacteric hormone therapy. Methods A systemic search of the databases SciELO, MEDLINE, and Pubmed was performed for identifying relevant publications on normal endometrial bleeding, abnormal uterine bleeding, and hormone therapy bleeding. Results Before starting hormone therapy, it is essential to exclude any abnormal organic condition, identify women at higher risk for bleeding, and adapt the regimen to suit eachwoman’s characteristics. Abnormal bleeding with progesterone/progestogen only, combined sequential, or combined continuous regimens may be corrected by changing the progestogen, adjusting the progestogen or estrogen/progestogen doses, or even switching the initial regimen to other formulation. Conclusion To diminish the occurrence of abnormal bleeding during hormone therapy (HT), it is important to tailor the regimen to the needs of individual women and identify those with higher risk of bleeding. The use of new agents as adjuvant therapies for decreasing abnormal bleeding in women on HT awaits future studies. PMID:24665210
Quantum cosmology with nontrivial topologies
Vargas, T.
2008-10-10
Quantum creation of a universe with a nontrivial spatial topology is considered. Using the Euclidean functional integral prescription, we calculate the wave function of such a universe with cosmological constant and without matter. The minisuperspace path integral is calculated in the semiclassical approximation, and it is shown that in order to include the nontrivial topologies in the path integral approach to quantum cosmology, it is necessary to generalize the sum over compact and smooth 4-manifolds to sum over finite-volume compact 4-orbifolds.
Optimal Network-Topology Design
NASA Technical Reports Server (NTRS)
Li, Victor O. K.; Yuen, Joseph H.; Hou, Ting-Chao; Lam, Yuen Fung
1987-01-01
Candidate network designs tested for acceptability and cost. Optimal Network Topology Design computer program developed as part of study on topology design and analysis of performance of Space Station Information System (SSIS) network. Uses efficient algorithm to generate candidate network designs consisting of subsets of set of all network components, in increasing order of total costs and checks each design to see whether it forms acceptable network. Technique gives true cost-optimal network and particularly useful when network has many constraints and not too many components. Program written in PASCAL.
GLIAL ABNORMALITIES IN MOOD DISORDERS
Öngür, Dost; Bechtholt, Anita J.; Carlezon, William A.; Cohen, Bruce M.
2015-01-01
Multiple lines of evidence indicate that mood disorders are associated with abnormalities in the brain's cellular composition, especially in glial cells. Considered inert support cells in the past, glial cells are now known to be important for brain function. Treatments for mood disorders enhance glial cell proliferation, and experimental stimulation of cell growth has antidepressant effects in animal models of mood disorders. These findings suggest that the proliferation and survival of glial cells may be important in the pathogenesis of mood disorders and may be possible targets for the development of new treatments. In this chapter, we will review the evidence for glial abnormalities in mood disorders. We will discuss glial cell biology and evidence from postmortem studies of mood disorders. This is not carry out a comprehensive review; rather we selectively discuss existing evidence in building an argument for the role of glial cells in mood disorders. PMID:25377605
EDITORIAL: Progress in topological insulators Progress in topological insulators
NASA Astrophysics Data System (ADS)
Morpurgo, Alberto; Trauzettel, Björn
2012-12-01
One of the most remarkable discoveries of the last few years in condensed matter physics is that the established distinction of crystalline solids in metals and insulators—which relies on the material band-structure—is incomplete. During the last several decades, the band structure of an uncountable variety of compounds of increasing complexity have been computed, and yet it has been overlooked that in the presence of sufficiently strong spin-orbit interaction, a new class of materials can be realized, that intrinsically behaves as insulators in their bulk and as metals at their surface. The discovery of this new class of materials was made only recently by Kane and Mele, during their theoretical studies of graphene in the presence of a sufficiently strong intrinsic spin-orbit interaction. Although the strength of the spin-orbit interaction in graphene is not sufficient to make the topological insulating state visible experimentally under currently reachable conditions, the validity and the originality of the concept were fully appreciated. Predictions for the occurrence of a two-dimensional topological insulating state in HgTe/CdTe heterostructures were made by Bernevig, Hughes and Zhang, and were followed by the experimental verification at Würzburg, in the Molenkamp group. Within a couple of years, this work brought the concept of topological insulator from an abstract theoretical discovery to an experimental reality, which stimulated further work. The concept of topological insulators was extended to the case of three-dimensional systems, for which an ideal experimental probe is angle-resolved photo-emission spectroscopy. Using this technique, specific theoretical predictions that had been made regarding the topological insulating character of different materials (e.g., for Bi-based compounds such as BiSb, Bi2Se3 or Bi2Te3), were verified experimentally through the direct observation of the Dirac surface fermions. This research was sufficient to put on
Topological field theory of dynamical systems
Ovchinnikov, Igor V.
2012-09-15
Here, it is shown that the path-integral representation of any stochastic or deterministic continuous-time dynamical model is a cohomological or Witten-type topological field theory, i.e., a model with global topological supersymmetry (Q-symmetry). As many other supersymmetries, Q-symmetry must be perturbatively stable due to what is generically known as non-renormalization theorems. As a result, all (equilibrium) dynamical models are divided into three major categories: Markovian models with unbroken Q-symmetry, chaotic models with Q-symmetry spontaneously broken on the mean-field level by, e.g., fractal invariant sets (e.g., strange attractors), and intermittent or self-organized critical (SOC) models with Q-symmetry dynamically broken by the condensation of instanton-antiinstanton configurations (earthquakes, avalanches, etc.) SOC is a full-dimensional phase separating chaos and Markovian dynamics. In the deterministic limit, however, antiinstantons disappear and SOC collapses into the 'edge of chaos.' Goldstone theorem stands behind spatio-temporal self-similarity of Q-broken phases known under such names as algebraic statistics of avalanches, 1/f noise, sensitivity to initial conditions, etc. Other fundamental differences of Q-broken phases is that they can be effectively viewed as quantum dynamics and that they must also have time-reversal symmetry spontaneously broken. Q-symmetry breaking in non-equilibrium situations (quenches, Barkhausen effect, etc.) is also briefly discussed.
Topological entropy of catalytic sets: Hypercycles revisited
NASA Astrophysics Data System (ADS)
Sardanyés, Josep; Duarte, Jorge; Januário, Cristina; Martins, Nuno
2012-02-01
The dynamics of catalytic networks have been widely studied over the last decades because of their implications in several fields like prebiotic evolution, virology, neural networks, immunology or ecology. One of the most studied mathematical bodies for catalytic networks was initially formulated in the context of prebiotic evolution, by means of the hypercycle theory. The hypercycle is a set of self-replicating species able to catalyze other replicator species within a cyclic architecture. Hypercyclic organization might arise from a quasispecies as a way to increase the informational containt surpassing the so-called error threshold. The catalytic coupling between replicators makes all the species to behave like a single and coherent evolutionary multimolecular unit. The inherent nonlinearities of catalytic interactions are responsible for the emergence of several types of dynamics, among them, chaos. In this article we begin with a brief review of the hypercycle theory focusing on its evolutionary implications as well as on different dynamics associated to different types of small catalytic networks. Then we study the properties of chaotic hypercycles with error-prone replication with symbolic dynamics theory, characterizing, by means of the theory of topological Markov chains, the topological entropy and the periods of the orbits of unimodal-like iterated maps obtained from the strange attractor. We will focus our study on some key parameters responsible for the structure of the catalytic network: mutation rates, autocatalytic and cross-catalytic interactions.
A road to reality with topological superconductors
NASA Astrophysics Data System (ADS)
Beenakker, Carlo; Kouwenhoven, Leo
2016-07-01
Topological matter can host low-energy quasiparticles, which, in a superconductor, are Majorana fermions described by a real wavefunction. The absence of complex phases provides protection for quantum computations based on topological superconductivity.
Topological excitations in magnetic materials
NASA Astrophysics Data System (ADS)
Bazeia, D.; Doria, M. M.; Rodrigues, E. I. B.
2016-05-01
In this work we propose a new route to describe topological excitations in magnetic systems through a single real scalar field. We show here that spherically symmetric structures in two spatial dimensions, which map helical excitations in magnetic materials, admit this formulation and can be used to model skyrmion-like structures in magnetic materials.
Phantom stars and topology change
DeBenedictis, Andrew; Garattini, Remo; Lobo, Francisco S. N.
2008-11-15
In this work, we consider time-dependent dark-energy star models, with an evolving parameter {omega} crossing the phantom divide {omega}=-1. Once in the phantom regime, the null energy condition is violated, which physically implies that the negative radial pressure exceeds the energy density. Therefore, an enormous negative pressure in the center may, in principle, imply a topology change, consequently opening up a tunnel and converting the dark-energy star into a wormhole. The criteria for this topology change are discussed and, in particular, we consider a Casimir energy approach involving quasilocal energy difference calculations that may reflect or measure the occurrence of a topology change. We denote these exotic geometries consisting of dark-energy stars (in the phantom regime) and phantom wormholes as phantom stars. The final product of this topological change, namely, phantom wormholes, have far-reaching physical and cosmological implications, as in addition to being used for interstellar shortcuts, an absurdly advanced civilization may manipulate these geometries to induce closed timelike curves, consequently violating causality.
Topological Signatures for Population Admixture
Technology Transfer Automated Retrieval System (TEKTRAN)
Topological Signatures for Population AdmixtureDeniz Yorukoglu1, Filippo Utro1, David Kuhn2, Saugata Basu3 and Laxmi Parida1* Abstract Background: As populations with multi-linear transmission (i.e., mixing of genetic material from two parents, say) evolve over generations, the genetic transmission...
Crystallographic topology and its applications
Johnson, C.K.; Burnett, M.N.; Dunbar, W.D.
1996-10-01
Geometric topology and structural crystallography concepts are combined to define a new area we call Structural Crystallographic Topology, which may be of interest to both crystallographers and mathematicians. In this paper, we represent crystallographic symmetry groups by orbifolds and crystal structures by Morse - functions. The Morse function uses mildly overlapping Gaussian thermal-motion probability density functions centered on atomic sites to form a critical net with peak, pass, pale, and pit critical points joined into a graph by density gradient-flow separatrices. Critical net crystal structure drawings can be made with the ORTEP-III graphics pro- An orbifold consists of an underlying topological space with an embedded singular set that represents the Wyckoff sites of the crystallographic group. An orbifold for a point group, plane group, or space group is derived by gluing together equivalent edges or faces of a crystallographic asymmetric unit. The critical-net-on-orbifold model incorporates the classical invariant lattice complexes of crystallography and allows concise quotient-space topological illustrations to be drawn without the repetition that is characteristic of normal crystal structure drawings.
Topological design of torsional metamaterials
NASA Astrophysics Data System (ADS)
Vitelli, Vincenzo; Paulose, Jayson; Meeussen, Anne; Topological Mechanics Lab Team
Frameworks - stiff elements with freely hinged joints - model the mechanics of a wide range of natural and artificial structures, including mechanical metamaterials with auxetic and topological properties. The unusual properties of the structure depend crucially on the balance between degrees of freedom associated with the nodes, and the constraints imposed upon them by the connecting elements. Whereas networks of featureless nodes connected by central-force springs have been well-studied, many real-world systems such as frictional granular packings, gear assemblies, and flexible beam meshes incorporate torsional degrees of freedom on the nodes, coupled together with transverse shear forces exerted by the connecting elements. We study the consequences of such torsional constraints on the mechanics of periodic isostatic networks as a foundation for mechanical metamaterials. We demonstrate the existence of soft modes of topological origin, that are protected against disorder or small perturbations of the structure analogously to their counterparts in electronic topological insulators. We have built a lattice of gears connected by rigid beams that provides a real-world demonstration of a torsional metamaterial with topological edge modes and mechanical Weyl modes.
Independent Study Project, Topic: Topology.
ERIC Educational Resources Information Center
Notre Dame High School, Easton, PA.
Using this guide and the four popular books noted in it, a student, working independently, will learn about some of the classical ideas and problems of topology: the Meobius strip and Klein bottle, the four color problem, genus of a surface, networks, Euler's formula, and the Jordan Curve Theorem. The unit culminates in a project of the students'…
Magnetic Field Topology in Jets
NASA Technical Reports Server (NTRS)
Gardiner, T. A.; Frank, A.
2000-01-01
We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.
Network topology and functional connectivity disturbances precede the onset of Huntington's disease.
Harrington, Deborah L; Rubinov, Mikail; Durgerian, Sally; Mourany, Lyla; Reece, Christine; Koenig, Katherine; Bullmore, Ed; Long, Jeffrey D; Paulsen, Jane S; Rao, Stephen M
2015-08-01
Cognitive, motor and psychiatric changes in prodromal Huntington's disease have nurtured the emergent need for early interventions. Preventive clinical trials for Huntington's disease, however, are limited by a shortage of suitable measures that could serve as surrogate outcomes. Measures of intrinsic functional connectivity from resting-state functional magnetic resonance imaging are of keen interest. Yet recent studies suggest circumscribed abnormalities in resting-state functional magnetic resonance imaging connectivity in prodromal Huntington's disease, despite the spectrum of behavioural changes preceding a manifest diagnosis. The present study used two complementary analytical approaches to examine whole-brain resting-state functional magnetic resonance imaging connectivity in prodromal Huntington's disease. Network topology was studied using graph theory and simple functional connectivity amongst brain regions was explored using the network-based statistic. Participants consisted of gene-negative controls (n = 16) and prodromal Huntington's disease individuals (n = 48) with various stages of disease progression to examine the influence of disease burden on intrinsic connectivity. Graph theory analyses showed that global network interconnectivity approximated a random network topology as proximity to diagnosis neared and this was associated with decreased connectivity amongst highly-connected rich-club network hubs, which integrate processing from diverse brain regions. However, functional segregation within the global network (average clustering) was preserved. Functional segregation was also largely maintained at the local level, except for the notable decrease in the diversity of anterior insula intermodular-interconnections (participation coefficient), irrespective of disease burden. In contrast, network-based statistic analyses revealed patterns of weakened frontostriatal connections and strengthened frontal-posterior connections that evolved as disease
Liu, Lanfang; Li, Hehui; Zhang, Manli; Wang, Zhengke; Wei, Na; Liu, Li; Meng, Xiangzhi; Ding, Guosheng
2016-07-01
Prior work has extensively studied neural deficits in children with reading impairment (RI) in their native language but has rarely examined those of RI children in their second language (L2). A recent study revealed that the function of the local brain regions was disrupted in children with RI in L2, but it is not clear whether the disruption also occurs at a large-scale brain network level. Using fMRI and graph theoretical analysis, we explored the topology of the whole-brain functional network during a phonological rhyming task and network reconfigurations across task and short resting phases in Chinese children with English reading impairment versus age-matched typically developing (TD) children. We found that, when completing the phonological task, the RI group exhibited higher local network efficiency and network modularity compared with the TD group. When switching between the phonological task and the short resting phase, the RI group showed difficulty with network reconfiguration, as reflected in fewer changes in the local efficiency and modularity properties and less rearrangement of the modular communities. These findings were reproducible after controlling for the effects of in-scanner accuracy, participant gender, and L1 reading performance. The results from the whole-brain network analyses were largely replicated in the task-activated network. These findings provide preliminary evidence supporting that RI in L2 is associated with not only abnormal functional network organization but also poor flexibility of the neural system in responding to changing cognitive demands. PMID:27321248
Continuity and Separation in Symmetric Topologies
ERIC Educational Resources Information Center
Harris, J.; Lynch, M.
2007-01-01
In this note, it is shown that in a symmetric topological space, the pairs of sets separated by the topology determine the topology itself. It is then shown that when the codomain is symmetric, functions which separate only those pairs of sets that are already separated are continuous, generalizing a result found by M. Lynch.
Electroweak-Skyrmion as topological dark matter
NASA Astrophysics Data System (ADS)
Kitano, Ryuichiro; Kurachi, Masafumi
2016-07-01
We show the existence of a nontrivial topological configuration of the Higgs field in the Standard Model with the Skyrme term. It is shown that the current upper bound of the mass of the topological object is about 34 TeV. We discuss the impact of the existence of the topological object on cosmology.
Topology of molecular interaction networks.
Winterbach, Wynand; Van Mieghem, Piet; Reinders, Marcel; Wang, Huijuan; de Ridder, Dick
2013-01-01
Molecular interactions are often represented as network models which have become the common language of many areas of biology. Graphs serve as convenient mathematical representations of network models and have themselves become objects of study. Their topology has been intensively researched over the last decade after evidence was found that they share underlying design principles with many other types of networks.Initial studies suggested that molecular interaction network topology is related to biological function and evolution. However, further whole-network analyses did not lead to a unified view on what this relation may look like, with conclusions highly dependent on the type of molecular interactions considered and the metrics used to study them. It is unclear whether global network topology drives function, as suggested by some researchers, or whether it is simply a byproduct of evolution or even an artefact of representing complex molecular interaction networks as graphs.Nevertheless, network biology has progressed significantly over the last years. We review the literature, focusing on two major developments. First, realizing that molecular interaction networks can be naturally decomposed into subsystems (such as modules and pathways), topology is increasingly studied locally rather than globally. Second, there is a move from a descriptive approach to a predictive one: rather than correlating biological network topology to generic properties such as robustness, it is used to predict specific functions or phenotypes.Taken together, this change in focus from globally descriptive to locally predictive points to new avenues of research. In particular, multi-scale approaches are developments promising to drive the study of molecular interaction networks further. PMID:24041013
Topology of molecular interaction networks
2013-01-01
Molecular interactions are often represented as network models which have become the common language of many areas of biology. Graphs serve as convenient mathematical representations of network models and have themselves become objects of study. Their topology has been intensively researched over the last decade after evidence was found that they share underlying design principles with many other types of networks. Initial studies suggested that molecular interaction network topology is related to biological function and evolution. However, further whole-network analyses did not lead to a unified view on what this relation may look like, with conclusions highly dependent on the type of molecular interactions considered and the metrics used to study them. It is unclear whether global network topology drives function, as suggested by some researchers, or whether it is simply a byproduct of evolution or even an artefact of representing complex molecular interaction networks as graphs. Nevertheless, network biology has progressed significantly over the last years. We review the literature, focusing on two major developments. First, realizing that molecular interaction networks can be naturally decomposed into subsystems (such as modules and pathways), topology is increasingly studied locally rather than globally. Second, there is a move from a descriptive approach to a predictive one: rather than correlating biological network topology to generic properties such as robustness, it is used to predict specific functions or phenotypes. Taken together, this change in focus from globally descriptive to locally predictive points to new avenues of research. In particular, multi-scale approaches are developments promising to drive the study of molecular interaction networks further. PMID:24041013
Making chromosome abnormalities treatable conditions.
Cody, Jannine DeMars; Hale, Daniel Esten
2015-09-01
Individuals affected by the classic chromosome deletion syndromes which were first identified at the beginning of the genetic age, are now positioned to benefit from genomic advances. This issue highlights five of these conditions (4p-, 5p-, 11q-, 18p-, and 18q-). It focuses on the increased in understanding of the molecular underpinnings and envisions how these can be transformed into effective treatments. While it is scientifically exciting to see the phenotypic manifestations of hemizygosity being increasingly understood at the molecular and cellular level, it is even more amazing to consider that we are now on the road to making chromosome abnormalities treatable conditions. PMID:26351122
Foot abnormalities of wild birds
Herman, C.M.; Locke, L.N.; Clark, G.M.
1962-01-01
The various foot abnormalities that occur in birds, including pox, scaly-leg, bumble-foot, ergotism and freezing are reviewed. In addition, our findings at the Patuxent Wildlife Research Center include pox from dove, mockingbird, cowbird, grackle and several species of sparrows. Scaly-leg has been particularly prevalent on icterids. Bumble foot has been observed in a whistling swan and in a group of captive woodcock. Ergotism is reported from a series of captive Canada geese from North Dakota. Several drug treatments recommended by others are presented.
International migration network: Topology and modeling
NASA Astrophysics Data System (ADS)
Fagiolo, Giorgio; Mastrorillo, Marina
2013-07-01
This paper studies international migration from a complex-network perspective. We define the international migration network (IMN) as the weighted-directed graph where nodes are world countries and links account for the stock of migrants originated in a given country and living in another country at a given point in time. We characterize the binary and weighted architecture of the network and its evolution over time in the period 1960-2000. We find that the IMN is organized around a modular structure with a small-world binary pattern displaying disassortativity and high clustering, with power-law distributed weighted-network statistics. We also show that a parsimonious gravity model of migration can account for most of observed IMN topological structure. Overall, our results suggest that socioeconomic, geographical, and political factors are more important than local-network properties in shaping the structure of the IMN.
Systemic risk on different interbank network topologies
NASA Astrophysics Data System (ADS)
Lenzu, Simone; Tedeschi, Gabriele
2012-09-01
In this paper we develop an interbank market with heterogeneous financial institutions that enter into lending agreements on different network structures. Credit relationships (links) evolve endogenously via a fitness mechanism based on agents' performance. By changing the agent's trust on its neighbor's performance, interbank linkages self-organize themselves into very different network architectures, ranging from random to scale-free topologies. We study which network architecture can make the financial system more resilient to random attacks and how systemic risk spreads over the network. To perturb the system, we generate a random attack via a liquidity shock. The hit bank is not automatically eliminated, but its failure is endogenously driven by its incapacity to raise liquidity in the interbank network. Our analysis shows that a random financial network can be more resilient than a scale free one in case of agents' heterogeneity.
Entropy gives rise to topologically associating domains
Vasquez, Paula A.; Hult, Caitlin; Adalsteinsson, David; Lawrimore, Josh; Forest, Mark G.; Bloom, Kerry
2016-01-01
We investigate chromosome organization within the nucleus using polymer models whose formulation is closely guided by experiments in live yeast cells. We employ bead-spring chromosome models together with loop formation within the chains and the presence of nuclear bodies to quantify the extent to which these mechanisms shape the topological landscape in the interphase nucleus. By investigating the genome as a dynamical system, we show that domains of high chromosomal interactions can arise solely from the polymeric nature of the chromosome arms due to entropic interactions and nuclear confinement. In this view, the role of bio-chemical related processes is to modulate and extend the duration of the interacting domains. PMID:27257057
Entropy gives rise to topologically associating domains.
Vasquez, Paula A; Hult, Caitlin; Adalsteinsson, David; Lawrimore, Josh; Forest, Mark G; Bloom, Kerry
2016-07-01
We investigate chromosome organization within the nucleus using polymer models whose formulation is closely guided by experiments in live yeast cells. We employ bead-spring chromosome models together with loop formation within the chains and the presence of nuclear bodies to quantify the extent to which these mechanisms shape the topological landscape in the interphase nucleus. By investigating the genome as a dynamical system, we show that domains of high chromosomal interactions can arise solely from the polymeric nature of the chromosome arms due to entropic interactions and nuclear confinement. In this view, the role of bio-chemical related processes is to modulate and extend the duration of the interacting domains. PMID:27257057
In silico network topology-based prediction of gene essentiality
NASA Astrophysics Data System (ADS)
da Silva, João Paulo Müller; Acencio, Marcio Luis; Mombach, José Carlos Merino; Vieira, Renata; da Silva, José Camargo; Lemke, Ney; Sinigaglia, Marialva
2008-02-01
The identification of genes essential for survival is important for the understanding of the minimal requirements for cellular life and for drug design. As experimental studies with the purpose of building a catalog of essential genes for a given organism are time-consuming and laborious, a computational approach which could predict gene essentiality with high accuracy would be of great value. We present here a novel computational approach, called NTPGE (Network Topology-based Prediction of Gene Essentiality), that relies on the network topology features of a gene to estimate its essentiality. The first step of NTPGE is to construct the integrated molecular network for a given organism comprising protein physical, metabolic and transcriptional regulation interactions. The second step consists in training a decision-tree-based machine-learning algorithm on known essential and non-essential genes of the organism of interest, considering as learning attributes the network topology information for each of these genes. Finally, the decision-tree classifier generated is applied to the set of genes of this organism to estimate essentiality for each gene. We applied the NTPGE approach for discovering the essential genes in Escherichia coli and then assessed its performance.
Constructing a logical, regular axis topology from an irregular topology
Faraj, Daniel A.
2014-07-01
Constructing a logical regular topology from an irregular topology including, for each axial dimension and recursively, for each compute node in a subcommunicator until returning to a first node: adding to a logical line of the axial dimension a neighbor specified in a nearest neighbor list; calling the added compute node; determining, by the called node, whether any neighbor in the node's nearest neighbor list is available to add to the logical line; if a neighbor in the called compute node's nearest neighbor list is available to add to the logical line, adding, by the called compute node to the logical line, any neighbor in the called compute node's nearest neighbor list for the axial dimension not already added to the logical line; and, if no neighbor in the called compute node's nearest neighbor list is available to add to the logical line, returning to the calling compute node.
Constructing a logical, regular axis topology from an irregular topology
Faraj, Daniel A.
2014-07-22
Constructing a logical regular topology from an irregular topology including, for each axial dimension and recursively, for each compute node in a subcommunicator until returning to a first node: adding to a logical line of the axial dimension a neighbor specified in a nearest neighbor list; calling the added compute node; determining, by the called node, whether any neighbor in the node's nearest neighbor list is available to add to the logical line; if a neighbor in the called compute node's nearest neighbor list is available to add to the logical line, adding, by the called compute node to the logical line, any neighbor in the called compute node's nearest neighbor list for the axial dimension not already added to the logical line; and, if no neighbor in the called compute node's nearest neighbor list is available to add to the logical line, returning to the calling compute node.
Myocardial perfusion abnormalities in asymptomatic patients with systemic lupus erythematosus
Hosenpud, J.D.; Montanaro, A.; Hart, M.V.; Haines, J.E.; Specht, H.D.; Bennett, R.M.; Kloster, F.E.
1984-08-01
Accelerated coronary artery disease and myocardial infarction in young patients with systemic lupus erythematosus is well documented; however, the prevalence of coronary involvement is unknown. Accordingly, 26 patients with systemic lupus were selected irrespective of previous cardiac history to undergo exercise thallium-201 cardiac scintigraphy. Segmental perfusion abnormalities were present in 10 of the 26 studies (38.5 percent). Five patients had reversible defects suggesting ischemia, four patients had persistent defects consistent with scar, and one patient had both reversible and persistent defects in two areas. There was no correlation between positive thallium results and duration of disease, amount of corticosteroid treatment, major organ system involvement or age. Only a history of pericarditis appeared to be associated with positive thallium-201 results (p less than 0.05). It is concluded that segmental myocardial perfusion abnormalities are common in patients with systemic lupus erythematosus. Whether this reflects large-vessel coronary disease or small-vessel abnormalities remains to be determined.
Topological aspects of polarization structured beams
NASA Astrophysics Data System (ADS)
Kumar, Vijay; Viswanathan, Nirmal K.
2014-02-01
Polarization structured optical beams have half-integer topological structures: star, lemon, monstar in π-symmetric polarization ellipse orientation tensor field and integer-index topological structures: saddle, spiral, node in 2π-symmetric Poynting vector field. Topological approach to study the polarization structured optical beams is carried out and presented here in some detail. These polarization structured light beams are demonstrated to be the best platform to explore the topological interdependencies. The dependence of one type of topological structure on the other is used to control the Poynting vector density distribution and locally enhance the angular momentum density as compared to its constituent beam fields.
Topological charge conservation in stochastic optical fields
NASA Astrophysics Data System (ADS)
Roux, Filippus S.
2016-05-01
The fact that phase singularities in scalar stochastic optical fields are topologically conserved implies the existence of an associated conserved current, which can be expressed in terms of local correlation functions of the optical field and its transverse derivatives. Here, we derive the topological charge current for scalar stochastic optical fields and show that it obeys a conservation equation. We use the expression for the topological charge current to investigate the topological charge flow in inhomogeneous stochastic optical fields with a one-dimensional topological charge density.
The Pea Seedling as a Model of Normal and Abnormal Morphogenesis
ERIC Educational Resources Information Center
Kurkdjian, Armen; And Others
1974-01-01
Describes several simple and inexpensive experiments designed to facilitate the study of normal and abnormal morphogenesis in the biology laboratory. Seedlings of the common garden pea are used in the experiments, and abnormal morphogenesis (tumors) are induced by a virulent strain of the crown-gall organism, Agrobacterium tumefaciens. (JR)
Abnormality on Liver Function Test
2013-01-01
Children with abnormal liver function can often be seen in outpatient clinics or inpatients wards. Most of them have respiratory disease, or gastroenteritis by virus infection, accompanying fever. Occasionally, hepatitis by the viruses causing systemic infection may occur, and screening tests are required. In patients with jaundice, the tests for differential diagnosis and appropriate treatment are important. In the case of a child with hepatitis B virus infection vertically from a hepatitis B surface antigen positive mother, the importance of the recognition of immune clearance can't be overstressed, for the decision of time to begin treatment. Early diagnosis changes the fate of a child with Wilson disease. So, screening test for the disease should not be omitted. Non-alcoholic fatty liver disease, which is mainly discovered in obese children, is a new strong candidate triggering abnormal liver function. Muscular dystrophy is a representative disease mimicking liver dysfunction. Although muscular dystrophy is a progressive disorder, and early diagnosis can't change the fate of patients, it will be better to avoid parent's blame for delayed diagnosis. PMID:24511518
Medical management of abnormal pregnancy.
Ratnam, S S; Prasad, R N
1990-06-01
Medical termination of abnormal pregnancy requires specific techniques since some conditions make therapy more effective, e.g., missed abortion intrauterine death and molar pregnancy, and others less so, e.g. anencephalic pregnancy. In all cases it is best to terminate the pregnancy as soon as possible to reduce anguish and risks of complications such as consumptive coagulopathy. Oxytocin is not consistently effective, but intraamniotic rivanol has oxytocic properties, and prostaglandins (PGs) are effective by several routes. Surgical methods are more popular in Japan and the US. A diagnostic flow chart is included and described. For missed abortion and fetal death vacuum aspiration or dilatation and evacuation are appropriate for early pregnancy, or PGs are used for later pregnancy, unless there are medical contraindications. Anencephalic pregnancy, usually diagnoses in 2nd or 3rd trimester, is resistant to medical therapy and must often be terminated by cesarean section. Molar pregnancy can be managed with vacuum aspiration at any length of gestation, but must be completed by curettage. Intraamniotic PGs are not advised for mole or fetal death. PG analogs can be administered intramuscularly, or vaginally in gel form. Other types of abnormal pregnancy that can be managed with PGs are spina bifida, hydrocephalus, hydrops fetalis, Dandy-Walker syndrome and Down's syndrome. Tubal pregnancy can be evacuated with intratubally administered PGs under laparoscopic control, thereby preserving tubal integrity. PMID:2225605
Convergent evidence for abnormal striatal synaptic plasticity in dystonia
Peterson, David A.; Sejnowski, Terrence J.; Poizner, Howard
2010-01-01
Dystonia is a functionally disabling movement disorder characterized by abnormal movements and postures. Although substantial recent progress has been made in identifying genetic factors, the pathophysiology of the disease remains a mystery. A provocative suggestion gaining broader acceptance is that some aspect of neural plasticity may be abnormal. There is also evidence that, at least in some forms of dystonia, sensorimotor “use” may be a contributing factor. Most empirical evidence of abnormal plasticity in dystonia comes from measures of sensorimotor cortical organization and physiology. However, the basal ganglia also play a critical role in sensorimotor function. Furthermore, the basal ganglia are prominently implicated in traditional models of dystonia, are the primary targets of stereotactic neurosurgical interventions, and provide a neural substrate for sensorimotor learning influenced by neuromodulators. Our working hypothesis is that abnormal plasticity in the basal ganglia is a critical link between the etiology and pathophysiology of dystonia. In this review we set up the background for this hypothesis by integrating a large body of disparate indirect evidence that dystonia may involve abnormalities in synaptic plasticity in the striatum. After reviewing evidence implicating the striatum in dystonia, we focus on the influence of two neuromodulatory systems: dopamine and acetylcholine. For both of these neuromodulators, we first describe the evidence for abnormalities in dystonia and then the means by which it may influence striatal synaptic plasticity. Collectively, the evidence suggests that many different forms of dystonia may involve abnormal plasticity in the striatum. An improved understanding of these altered plastic processes would help inform our understanding of the pathophysiology of dystonia, and, given the role of the striatum in sensorimotor learning, provide a principled basis for designing therapies aimed at the dynamic processes
Majorana Fermions and Topology in Superconductors
NASA Astrophysics Data System (ADS)
Sato, Masatoshi; Fujimoto, Satoshi
2016-07-01
Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abelian statistics, which is distinct from bose and fermi statistics, and can be utilized for application to topological quantum computation. Also, Majorana fermions give rise to various exotic phenomena such as "fractionalization", non-local correlation, and "teleportation". A pedagogical review of these subjects is presented. We also discuss interaction effects on topological classification of superconductors, and the basic properties of Weyl superconductors.
Universal Cyclic Topology in Polymer Networks.
Wang, Rui; Alexander-Katz, Alfredo; Johnson, Jeremiah A; Olsen, Bradley D
2016-05-01
Polymer networks invariably possess topological defects: loops of different orders which have profound effects on network properties. Here, we demonstrate that all cyclic topologies are a universal function of a single dimensionless parameter characterizing the conditions for network formation. The theory is in excellent agreement with both experimental measurements of hydrogel loop fractions and Monte Carlo simulations without any fitting parameters. We demonstrate the superposition of the dilution effect and chain-length effect on loop formation. The one-to-one correspondence between the network topology and primary loop fraction demonstrates that the entire network topology is characterized by measurement of just primary loops, a single chain topological feature. Different cyclic defects cannot vary independently, in contrast to the intuition that the densities of all topological species are freely adjustable. Quantifying these defects facilitates studying the correlations between the topology and properties of polymer networks, providing a key step in overcoming an outstanding challenge in polymer physics. PMID:27203346
Universal Cyclic Topology in Polymer Networks
NASA Astrophysics Data System (ADS)
Wang, Rui; Alexander-Katz, Alfredo; Johnson, Jeremiah A.; Olsen, Bradley D.
2016-05-01
Polymer networks invariably possess topological defects: loops of different orders which have profound effects on network properties. Here, we demonstrate that all cyclic topologies are a universal function of a single dimensionless parameter characterizing the conditions for network formation. The theory is in excellent agreement with both experimental measurements of hydrogel loop fractions and Monte Carlo simulations without any fitting parameters. We demonstrate the superposition of the dilution effect and chain-length effect on loop formation. The one-to-one correspondence between the network topology and primary loop fraction demonstrates that the entire network topology is characterized by measurement of just primary loops, a single chain topological feature. Different cyclic defects cannot vary independently, in contrast to the intuition that the densities of all topological species are freely adjustable. Quantifying these defects facilitates studying the correlations between the topology and properties of polymer networks, providing a key step in overcoming an outstanding challenge in polymer physics.
Complete topology of the RNF complex from Vibrio cholerae.
Hreha, Teri N; Mezic, Katherine G; Herce, Henry D; Duffy, Ellen B; Bourges, Anais; Pryshchep, Sergey; Juarez, Oscar; Barquera, Blanca
2015-04-21
RNF is a redox-driven ion (Na(+) and in one case possibly H(+)) transporter present in many prokaryotes. It has been proposed that RNF performs a variety of reactions in different organisms, delivering low-potential reducing equivalents for specific cellular processes. RNF shares strong homology with the Na(+)-pumping respiratory enzyme Na(+)-NQR, although there are significant differences in subunit and redox cofactor composition. Here we report a topological analysis of the six subunits of RNF from Vibrio cholerae. Although individual subunits from other organisms have previously been studied, this is the first complete, experimentally derived, analysis of RNF from any one source. This has allowed us to identify and confirm key properties of RNF. The putative NADH binding site in RnfC is located on the cytoplasmic side of the membrane. FeS centers in RnfB and RnfC are also located on the cytoplasmic side. However, covalently attached FMNs in RnfD and RnfG are both located in the periplasm. RNF also contains a number of acidic residues that correspond to functionally important groups in Na(+)-NQR. The acidic residues involved in Na(+) uptake and many of those implicated in Na(+) translocation are topologically conserved. The topology of RNF closely matches the topology represented in the newly published structure of Na(+)-NQR, consistent with the close relation between the two enzymes. The topology of RNF is discussed in the context of the current structural model of Na(+)-NQR, and the proposed functionality of the RNF complex itself. PMID:25831459
Abnormal EEG and calcification of the pineal gland in schizophrenia.
Sandyk, R; Kay, S R
1992-01-01
Computed tomographic (CT) studies of the brain in schizophrenic patients have demonstrated a variety of structural abnormalities. We reported recently an association between pineal calcification (PC) and cortical and prefrontal cortical atrophy, and third ventricular size on CT scan in chronic schizophrenic patients. These findings indicate that in schizophrenia PC is associated with the morphological brain abnormalities associated with the disease. If PC is, indeed, related to organic cerebral pathology, then one would expect a higher prevalence of pineal gland pathology among patients with electroencephalographic (EEG) abnormalities by comparison to those with a normal EEG. To investigate this hypothesis, we studied the prevalence of PC on CT scan in a sample of 52 neuroleptic-treated schizophrenic patients (29 men, 23 women, mean age: 51.3 years SD = 9.1), of whom 10 (19.2%) had an abnormal EEG. The prevalence of PC in patients with EEG abnormalities was significantly greater by comparison to those with a normal EEG (90.0% vs. 54.8%, X2 = 4.24, p < .05). Since both groups did not differ on any of the historical and demographic data, and since PC was unrelated to neuroleptic exposure, these findings suggest that in schizophrenia PC may be related to the disease process and that it may be a marker of subcortical pathology. PMID:1342008
Fibrillin abnormalities and prognosis in Marfan syndrome and related disorders
Aoyama, T.; Furthmayr, H.; Francke, U.; Gasner, C.
1995-08-28
Marfan syndrome (MFS), a multisystem autosomal-dominant disorder, is characterized by mutations of the fibrillin-1 (FBN1) gene and by abnormal patterns of synthesis, secretion, and matrix deposition of the fibrillin protein. To determine the sensitivity and specificity of fibrillin protein abnormalities in the diagnosis of MFS, we studied dermal fibroblasts from 57 patients with classical MFS, 15 with equivocal MFS, 8 with single-organ manifestations, and 16 with other connective tissue disorders including homocystinuria and Ehlers-Danlos syndrome. Abnormal fibrillin metabolism was identified in 70 samples that were classified into four different groups based on quantitation of fibrillin synthesis and matrix deposition. Significant correlations were found for phenotypic features including arachnodactyly, striae distensae, cardiovascular manifestations, and fibrillin groups II and IV, which included 70% of the MFS patients. In addition, these two groups were associated with shortened {open_quotes}event-free{close_quotes} survival and more severe cardiovascular complications than groups I and III. The latter included most of the equivocal MFS/single manifestation patients with fibrillin abnormalities. Our results indicate that fibrillin defects at the protein level per se are not specific for MFS, but that the drastically reduced fibrillin deposition, caused by a dominant-negative effect of abnormal fibrillin molecules in individuals defined as groups II and IV, is of prognostic and possibly diagnostic significance. 25 refs., 3 figs., 6 tabs.
Topological mechanics of gyroscopic metamaterials
Nash, Lisa M.; Kleckner, Dustin; Read, Alismari; Vitelli, Vincenzo; Turner, Ari M.; Irvine, William T. M.
2015-01-01
Topological mechanical metamaterials are artificial structures whose unusual properties are protected very much like their electronic and optical counterparts. Here, we present an experimental and theoretical study of an active metamaterial—composed of coupled gyroscopes on a lattice—that breaks time-reversal symmetry. The vibrational spectrum displays a sonic gap populated by topologically protected edge modes that propagate in only one direction and are unaffected by disorder. We present a mathematical model that explains how the edge mode chirality can be switched via controlled distortions of the underlying lattice. This effect allows the direction of the edge current to be determined on demand. We demonstrate this functionality in experiment and envision applications of these edge modes to the design of one-way acoustic waveguides. PMID:26561580
Topological Insulator and Thermoelectric Effects
NASA Astrophysics Data System (ADS)
Xu, Yong
The recent discovery of topological insulator (TI) offers new opportunities for the development of thermoelectricity, because many TIs (like Bi2Te3) are excellent thermoelectric materials. In this talk, I will first introduce our theoretical predictions of anomalous Seebeck effect and strong size effect in TI [PRL 112, 226801 (2014)]. Then I will report our recent proof experiments, which find in TI thin films that (i) the hole-type Seebeck effect and the electron-type Hall effect coexist in the same TI sample for all the measured temperatures (up to 300 K), and (ii) the thermoelectric properties depend sensitively on the film thickness. The unconventional phenomena are revealed to be closely related to the topological nature of the material. These findings may inspire new ideas for designing TI-based high-efficiency thermoelectric devices.
Topological defects on the lattice
NASA Astrophysics Data System (ADS)
Aasen, David; Mong, Roger; Fendley, Paul
We construct defects in two-dimensional classical lattice models and one-dimensional quantum chains that are topologically invariant in the continuum limit. We show explicitly that these defect lines and their trivalent junctions commute with the transfer matrix/Hamiltonian. The resulting splitting and joining properties of the defect lines are exactly those of anyons in a topological phase. One useful consequence is an explicit definition of twisted boundary conditions that yield the precise shift in momentum quantization, and so provide a natural way of relating microscopic and macroscopic properties. Another is a generalization of Kramers-Wannier duality to a wide class of height models. Even more strikingly, we derive the modular transformation matrices explicitly and exactly from purely lattice considerations. We develop this construction for a variety of examples including the two-dimensional Ising model. Institute for Quantum Information and Matter, an NSF physics frontier center with support from the Moore Foundation. NSERC-PGSD.
Probing Topological Matter with Sound
NASA Astrophysics Data System (ADS)
Schmeltzer, David
We introduce a microscopic formulation to identify the stress in a quantum fluid to compute the stress viscosity with sound waves. The viscosity stress tensor is used to determine, e.g. the ultrasound attenuation in superconductors. When an Abrikosov lattice is formed on the surface of a Topological Insulator in a external magnetic field, Majorana modes form dispersive bands. We show that the ultrasound attenuation is modified by the Majorana modes offering a novel method to identify Topological Superconductors. Moreover we compute the stress tunneling which uses Majorana modes and represent the sound analogue of the Andreev crossed reflection. We check the violation of the sound momentum conservation of systems which only exists on the boundary of a higher dimensional system,e.g. a 1 D chiral fermion which can exist at the boundary of a 2 D Quantum Hall system. Doe-Los Alamos National Laboratory.
Topology optimization of piezoelectric nanostructures
NASA Astrophysics Data System (ADS)
Nanthakumar, S. S.; Lahmer, Tom; Zhuang, Xiaoying; Park, Harold S.; Rabczuk, Timon
2016-09-01
We present an extended finite element formulation for piezoelectric nanobeams and nanoplates that is coupled with topology optimization to study the energy harvesting potential of piezoelectric nanostructures. The finite element model for the nanoplates is based on the Kirchoff plate model, with a linear through the thickness distribution of electric potential. Based on the topology optimization, the largest enhancements in energy harvesting are found for closed circuit boundary conditions, though significant gains are also found for open circuit boundary conditions. Most interestingly, our results demonstrate the competition between surface elasticity, which reduces the energy conversion efficiency, and surface piezoelectricity, which enhances the energy conversion efficiency, in governing the energy harvesting potential of piezoelectric nanostructures.
Inconsistency of topologically massive hypergravity
NASA Technical Reports Server (NTRS)
Aragone, C.; Deser, S.
1985-01-01
The coupled topologically massive spin-5/2 gravity system in D = 3 dimensions whose kinematics represents dynamical propagating gauge invariant massive spin-5/2 and spin-2 excitations, is shown to be inconsistent, or equivalently, not locally hypersymmetric. In contrast to D = 4, the local constraints on the system arising from failure of the fermionic Bianchi identities do not involve the 'highest spin' components of the field, but rather the auxiliary spinor required to construct a consistent massive model.
Topological defects in extended inflation
NASA Technical Reports Server (NTRS)
Copeland, Edmund J.; Kolb, Edward W.; Liddle, Andrew R.
1990-01-01
The production of topological defects, especially cosmic strings, in extended inflation models was considered. In extended inflation, the Universe passes through a first-order phase transition via bubble percolation, which naturally allows defects to form at the end of inflation. The correlation length, which determines the number density of the defects, is related to the mean size of bubbles when they collide. This mechanism allows a natural combination of inflation and large scale structure via cosmic strings.
Topology of modified helical gears
NASA Technical Reports Server (NTRS)
Litvin, F. L.; Zhang, J.; Handschuh, R. F.; Coy, J. J.
1989-01-01
The topology of several types of modified surfaces of helical gears is proposed. The modified surfaces allow absorption of a linear or almost linear function of transmission errors. These errors are caused by gear misalignment and an improvement of the contact of gear tooth surfaces. Principles and corresponding programs for computer aided simulation of meshing and contact of gears have been developed. The results of this investigation are illustrated with numerical examples.
Topological Insulator Nanowires and Nanoribbons
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.
Hopf algebras and topological recursion
NASA Astrophysics Data System (ADS)
Esteves, João N.
2015-11-01
We consider a model for topological recursion based on the Hopf algebra of planar binary trees defined by Loday and Ronco (1998 Adv. Math. 139 293-309 We show that extending this Hopf algebra by identifying pairs of nearest neighbor leaves, and thus producing graphs with loops, we obtain the full recursion formula discovered by Eynard and Orantin (2007 Commun. Number Theory Phys. 1 347-452).
Topological effects in quantum mechanics
Peshkin, M.; Lipkin, H.J. |
1995-08-01
We completed our analysis of experiments, some completed, some planned, and some only conceptual at present, that purport to demonstrate new kinds of non-local and topological effects in the interaction of a neutron with an external electromagnetic field. In the Aharonov-Casher effect (AC), the neutron interacts with an electric field and in the Scalar Aharonov-Bohm effect (SAB) the neutron interacts with a magnetic field. In both cases, the geometry can be arranged so that there is no force on the neutron but an interference experiment nevertheless finds a phase shift proportional to the applied field and to the neutron`s magnetic moment. Previously, we showed that the accepted interpretation of these phenomena as topological effects due to a non-local interaction between the neutron and the electromagnetic field is incorrect. Both AC and SAB follow from local torques on the neutron whose expectation values vanish at every instant but which have non-vanishing effect on the measurable spin-correlation variables S(t) = (1/2) [{sigma}{sub x}{sigma}{sub x}(t) + {sigma}{sub y}(0){sigma}{sub y}(t) + h.c.] and V(t) = [{sigma}{sub x}(0){sigma}{sub y}(t) - {sigma}{sub y}(0){sigma}{sub x}(t) + h.c.]. We have now completed this work by observing that a criterion often used for identifying a topological effect, energy independence of the phase shift between two arms of an interferometer, is only a necessary condition, and by describing a phase shifter which obeys the energy-independence condition but whose interaction with the neutron is neither topological nor even non-local.
Decay of metastable topological defects
Preskill, J. ); Vilenkin, A. Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138 )
1993-03-15
We systematically analyze the decay of metastable topological defects that arise from the spontaneous breakdown of gauge or global symmetries. Quantum-mechanical tunneling rates are estimated for a variety of decay processes. The decay rate for a global string, vortex, domain wall, or kink is typically suppressed compared to the decay rate for its gauged counterpart. We also discuss the decay of global texture, and of semilocal and electroweak strings.
Topological sigma models & dissipative hydrodynamics
NASA Astrophysics Data System (ADS)
Haehl, Felix M.; Loganayagam, R.; Rangamani, Mukund
2016-04-01
We outline a universal Schwinger-Keldysh effective theory which describes macroscopic thermal fluctuations of a relativistic field theory. The basic ingredients of our construction are three: a doubling of degrees of freedom, an emergent abelian symmetry associated with entropy, and a topological (BRST) supersymmetry imposing fluctuationdissipation theorem. We illustrate these ideas for a non-linear viscous fluid, and demonstrate that the resulting effective action obeys a generalized fluctuation-dissipation theorem, which guarantees a local form of the second law.
Two-dimensional hexagonal smectic structure formed by topological defects
NASA Astrophysics Data System (ADS)
Dolganov, P. V.; Shuravin, N. S.; Fukuda, Atsuo
2016-03-01
A two-dimensional hexagonal smectic structure formed by point topological defects and intersecting defect walls was discovered. This unique structure was predicted theoretically about 30 years ago but not observed. For a long time the hexagonal structure was a challenge for experimentalists. A different type of self-organization in smectic films was found and used to form the hexagonal structure. Methods applied for building the hexagonal phase can be used for the formation of complicated liquid-crystal structures.
What, if anything, are topological maps for?
Wilson, Stuart P; Bednar, James A
2015-06-01
What, if anything, is the functional significance of spatial patterning in cortical feature maps? We ask this question of four major theories of cortical map formation: self-organizing maps, wiring optimization, place coding, and reaction-diffusion. We argue that (i) self-organizing maps yield spatial patterning only as a by-product of efficient mechanisms for developing environmentally appropriate distributions of feature preferences, (ii) wiring optimization assumes rather than explains a map-like organization, (iii) place-coding mechanisms can at best explain only a subset of maps in functional terms, and (iv) reaction-diffusion models suggest two factors in the evolution of maps, the first based on efficient development of feature distributions, and the second based on generating feature-specific long-range recurrent cortical circuitry. None of these explanations for the existence of topological maps requires spatial patterning in maps to be useful. Thus despite these useful frameworks for understanding how maps form and how they are wired, the possibility that patterns are merely epiphenomena in the evolution of mammalian neocortex cannot be rejected. The article is intended as a nontechnical introduction to the assumptions and predictions of these four important classes of models, along with other possible functional explanations for maps. PMID:25683193
Interfacing Topological Insulators with Ferromagnetism
NASA Astrophysics Data System (ADS)
Richardella, Anthony
In topological insulators, the surface states arise from strong spin-orbit coupling while the degeneracy of the Dirac point is protected by time reversal symmetry. Introducing magnetism in proximity to the surface states breaks this symmetry, destroying the non-trivial Berry phase at the Dirac point and leads to a hedgehog spin texture near the newly opened magnetic gap. This symmetry broken phase leads to a host of unusual physics, such as the quantum anomalous Hall (QAH) effect. In this talk, we discuss the growth by molecular beam epitaxy and characterization of such magnetically interfaced and magnetically doped topological insulators. Such materials often suffer from structural defects and interfacial layers, as well as from degradation during device fabrication. In particular, it is shown that Cr doped (Bi1-x,Sbx)2Te3 can exhibit perfect Hall quantization at low temperatures despite these defects. However, the magnetic ordering of this material was found to be quite unusual, displaying a super-paramagnetic like character, perhaps reflecting this disorder. Such observations highlight the surprising behavior of such broken symmetry phases in topological materials. This work was performed in collaboration with A. Kandala, M. Liu, W. Wang, N.P. Ong, C.-X. Liu, and N. Samarth, in addition to the authors of the references cited. This work was supported by funding from ARO/MURI, DARPA and ONR.
Topology, structures, and energy landscapes of human chromosomes
Zhang, Bin; Wolynes, Peter G.
2015-01-01
Chromosome conformation capture experiments provide a rich set of data concerning the spatial organization of the genome. We use these data along with a maximum entropy approach to derive a least-biased effective energy landscape for the chromosome. Simulations of the ensemble of chromosome conformations based on the resulting information theoretic landscape not only accurately reproduce experimental contact probabilities, but also provide a picture of chromosome dynamics and topology. The topology of the simulated chromosomes is probed by computing the distribution of their knot invariants. The simulated chromosome structures are largely free of knots. Topologically associating domains are shown to be crucial for establishing these knotless structures. The simulated chromosome conformations exhibit a tendency to form fibril-like structures like those observed via light microscopy. The topologically associating domains of the interphase chromosome exhibit multistability with varying liquid crystalline ordering that may allow discrete unfolding events and the landscape is locally funneled toward “ideal” chromosome structures that represent hierarchical fibrils of fibrils. PMID:25918364
Glucose abnormalities in hepatitis C virus infection.
Huang, Jee-Fu; Yu, Ming-Lung; Dai, Chia-Yen; Chuang, Wan-Long
2013-02-01
Hepatitis C virus (HCV) infection is one of the most important causes of cirrhosis and hepatocellular carcinoma and has a tremendous impact on public health worldwide. HCV is both hepatotropic and lymphotropic. Replication of HCV in diseased extrahepatic organs and tissues may either trigger latent autoimmunity or induce autoimmune disorders. In addition to established liver injury, type 2 diabetes mellitus (T2DM) is an important feature of extrahepatic metabolic disorders which is attributed to HCV infection. It also has some impact on the disease activity, disease course, clinical outcomes, and treatment efficacy of antiviral therapy. Previous experimental and clinical findings have highly suggested that HCV per se is diabetogenic. The cause-effect interaction between a common endocrine disorder and an infectious disease is an important issue to elucidate. Although the precise mechanisms whereby HCV infection leads to insulin resistance (IR) and glucose abnormalities are not entirely clear, it differs from the usual pathogenesis of T2DM in those with non-HCV liver diseases. This review initially highlights epidemiological and pathophysiological studies addressing the mutual link between chronic HCV infection (CHC) and T2DM. The characteristics of glucose abnormalities in this special population are depicted from the current evidence. The mutual roles of IR and CHC with respect to the prediction of treatment efficacy, how treatment response affects IR, and the role of pancreatic beta cell function in the entire suite are discussed. With the rapid progression of antiviral therapy for CHC in the past decade, we have also listed some points of future perspective in this issue. PMID:23347806
Abnormalities of the Erythrocyte Membrane
Gallagher, Patrick G.
2014-01-01
Synopsis Primary abnormalities of the erythrocyte membrane, including the hereditary spherocytosis and hereditary elliptocytosis syndromes, are an important group of inherited hemolytic anemias. Classified by distinctive morphology on peripheral blood smear, these disorders are characterized by clinical, laboratory, and genetic heterogeneity. Among this group, hereditary spherocytosis patients are more likely to experience symptomatic anemia. Treatment of hereditary spherocytosis with splenectomy is curative in most patients. Once considered routine, growing recognition of the longterm risks of splenectomy, including cardiovascular disease, thrombotic disorders, and pulmonary hypertension, as well as the emergence of penicillin-resistant pneumococci, a concern for infection in overwhelming postsplenectomy infection, have led to re-evaluation of the role of splenectomy. Current management guidelines acknowledge these important considerations when entertaining splenectomy and recommend detailed discussion between health care providers, patient, and family. The hereditary elliptocytosis syndromes are the most common primary disorders of erythrocyte membrane proteins. However, most elliptocytosis patients are asymptomatic and do not require therapy. PMID:24237975
Adults with Chromosome 18 Abnormalities.
Soileau, Bridgette; Hasi, Minire; Sebold, Courtney; Hill, Annice; O'Donnell, Louise; Hale, Daniel E; Cody, Jannine D
2015-08-01
The identification of an underlying chromosome abnormality frequently marks the endpoint of a diagnostic odyssey. However, families are frequently left with more questions than answers as they consider their child's future. In the case of rare chromosome conditions, a lack of longitudinal data often makes it difficult to provide anticipatory guidance to these families. The objective of this study is to describe the lifespan, educational attainment, living situation, and behavioral phenotype of adults with chromosome 18 abnormalities. The Chromosome 18 Clinical Research Center has enrolled 483 individuals with one of the following conditions: 18q-, 18p-, Tetrasomy 18p, and Ring 18. As a part of the ongoing longitudinal study, we collect data on living arrangements, educational level attained, and employment status as well as data on executive functioning and behavioral skills on an annual basis. Within our cohort, 28 of the 483 participants have died, the majority of whom have deletions encompassing the TCF4 gene or who have unbalanced rearrangement involving other chromosomes. Data regarding the cause of and age at death are presented. We also report on the living situation, educational attainment, and behavioral phenotype of the 151 participants over the age of 18. In general, educational level is higher for people with all these conditions than implied by the early literature, including some that received post-high school education. In addition, some individuals are able to live independently, though at this point they represent a minority of patients. Data on executive function and behavioral phenotype are also presented. Taken together, these data provide insight into the long-term outcome for individuals with a chromosome 18 condition. This information is critical in counseling families on the range of potential outcomes for their child. PMID:25403900
Even-dimensional topological semimetals under disorders
NASA Astrophysics Data System (ADS)
Huang, X. J.; Zhao, Y. X.; Wang, Z. D.
A topological theory of even-dimensional, chiral symmetry-preserving topological semimetal, which is known as the counterpart of Weyl semimetal, is developed in this work. We show that, in presence of disorder, an anisotropic topological θ-term emerges in the action of effective non-linear sigma model, meanwhile, an anisotropic Chern character term in terms of U (1) gauge response theory, which gives the electromagnetic response, whose stability against disorders is ensured by the former topological ?-term, has also been derived. Moreover, it is found that this topological semimetal can be included in the family of topological quantum matter preserving chiral symmetry. The relations of this topological semimetal to odd-dimensional topological insulator and even-dimensional Dirac fermion are revealed in both effective non-linear sigma model and gauge theory. And importantly, above results can be applied to graphene if we set dimension d = 2 and thus reveal the topological character of this kind of 2-dimensional topological semimetal with two Dirac cones with opposite chiralities.
Breathing abnormalities in sleep in achondroplasia.
Waters, K A; Everett, F; Sillence, D; Fagan, E; Sullivan, C E
1993-01-01
Overnight sleep studies were performed in 20 subjects with achondroplasia to document further the respiratory abnormalities present in this group. Somatosensory evoked potentials (SEPs) were recorded in 19 of the subjects to screen for the presence of brainstem abnormalities, which are one of the potential aetiological mechanisms. Fifteen children aged 1 to 14 years, and five young adults, aged 20 to 31 years were included. All had upper airway obstruction and 15 (75%) had a pathological apnoea index (greater than five per hour). Other sleep associated respiratory abnormalities, including partial obstruction, central apnoea, and abnormal electromyographic activity of accessory muscles of respiration, also showed a high prevalence. SEPs were abnormal in eight (42%), but there was no correlation between abnormal SEPs and apnoea during sleep, either qualitatively or quantitatively. A high prevalence of both sleep related respiratory abnormalities and abnormal SEPs in young subjects with achondroplasia was demonstrated. However, the sleep related respiratory abnormalities do not always result in significant blood gas disturbances or correlate with abnormal SEPs in this group. PMID:8215519
Topological approximation of the nonlinear Anderson model
NASA Astrophysics Data System (ADS)
Milovanov, Alexander V.; Iomin, Alexander
2014-06-01
We study the phenomena of Anderson localization in the presence of nonlinear interaction on a lattice. A class of nonlinear Schrödinger models with arbitrary power nonlinearity is analyzed. We conceive the various regimes of behavior, depending on the topology of resonance overlap in phase space, ranging from a fully developed chaos involving Lévy flights to pseudochaotic dynamics at the onset of delocalization. It is demonstrated that the quadratic nonlinearity plays a dynamically very distinguished role in that it is the only type of power nonlinearity permitting an abrupt localization-delocalization transition with unlimited spreading already at the delocalization border. We describe this localization-delocalization transition as a percolation transition on the infinite Cayley tree (Bethe lattice). It is found in the vicinity of the criticality that the spreading of the wave field is subdiffusive in the limit t →+∞. The second moment of the associated probability distribution grows with time as a power law ∝ tα, with the exponent α =1/3 exactly. Also we find for superquadratic nonlinearity that the analog pseudochaotic regime at the edge of chaos is self-controlling in that it has feedback on the topology of the structure on which the transport processes concentrate. Then the system automatically (without tuning of parameters) develops its percolation point. We classify this type of behavior in terms of self-organized criticality dynamics in Hilbert space. For subquadratic nonlinearities, the behavior is shown to be sensitive to the details of definition of the nonlinear term. A transport model is proposed based on modified nonlinearity, using the idea of "stripes" propagating the wave process to large distances. Theoretical investigations, presented here, are the basis for consistency analysis of the different localization-delocalization patterns in systems with many coupled degrees of freedom in association with the asymptotic properties of the
Khedkar, Supriya; Seshasayee, Aswin Sai Narain
2016-01-01
Genomes evolve not only in base sequence but also in terms of their architecture, defined by gene organization and chromosome topology. Whereas genome sequence data inform us about the changes in base sequences for a large variety of organisms, the study of chromosome topology is restricted to a few model organisms studied using microscopy and chromosome conformation capture techniques. Here, we exploit whole genome sequence data to study the link between gene organization and chromosome topology in bacteria. Using comparative genomics across ∼250 pairs of closely related bacteria we show that: (a) many organisms show a high degree of interreplichore translocations throughout the chromosome and not limited to the inversion-prone terminus (ter) or the origin of replication (oriC); (b) translocation maps may reflect chromosome topologies; and (c) symmetric interreplichore translocations do not disrupt the distance of a gene from oriC or affect gene expression states or strand biases in gene densities. In summary, we suggest that translocation maps might be a first line in defining a gross chromosome topology given a pair of closely related genome sequences. PMID:27172194
Photonic simulation of topological excitations in metamaterials
Tan, Wei; Sun, Yong; Chen, Hong; Shen, Shun-Qing
2014-01-01
Condensed matter systems with topological order and metamaterials with left-handed chirality have attracted recently extensive interests in the fields of physics and optics. So far the topological order and chirality of electromagnetic wave are two independent concepts, and there is no work to address their connection. Here we propose to establish the relation between the topological order in condensed matter systems and the chirality in metamaterials, by mapping explicitly Maxwell's equations to the Dirac equation in one dimension. We report an experimental implement of the band inversion in the Dirac equation, which accompanies change of chirality of electromagnetic wave in metamaterials, and the first microwave measurement of topological excitations and topological phases in one dimension. Our finding provides a proof-of-principle example that electromagnetic wave in the metamaterials can be used to simulate the topological order in condensed matter systems and quantum phenomena in relativistic quantum mechanics in a controlled laboratory environment. PMID:24452532
Topological Thouless pumping of ultracold fermions
NASA Astrophysics Data System (ADS)
Nakajima, Shuta; Tomita, Takafumi; Taie, Shintaro; Ichinose, Tomohiro; Ozawa, Hideki; Wang, Lei; Troyer, Matthias; Takahashi, Yoshiro
2016-04-01
An electron gas in a one-dimensional periodic potential can be transported even in the absence of a voltage bias if the potential is slowly and periodically modulated in time. Remarkably, the transferred charge per cycle is sensitive only to the topology of the path in parameter space. Although this so-called Thouless charge pump was first proposed more than thirty years ago, it has not yet been realized. Here we report the demonstration of topological Thouless pumping using ultracold fermionic atoms in a dynamically controlled optical superlattice. We observe a shift of the atomic cloud as a result of pumping, and extract the topological invariance of the pumping process from this shift. We demonstrate the topological nature of the Thouless pump by varying the topology of the pumping path and verify that the topological pump indeed works in the quantum regime by varying the speed and temperature.
Disordered Weyl Semimetals and Their Topological Family
NASA Astrophysics Data System (ADS)
Zhao, Y. X.; Wang, Z. D.
2015-05-01
We develop a topological theory for disordered Weyl semimetals in the framework of the gauge invariance of the replica formalism and boundary-bulk correspondence of Chern insulators. An anisotropic topological θ term is analytically derived for the effective nonlinear σ model. It is this nontrivial topological term that ensures that the bulk transverse transport of Weyl semimetals is robust against disorders. Moreover, we establish a general diagram that reveals the intrinsic relations among topological terms in the nonlinear σ models and gauge response theories, respectively, for (2 n +2 ) -dimensional topological insulators, (2 n +1 ) -dimensional chiral fermions, (2 n +1 )-dimensional chiral semimetals, and (2 n )-dimensional topological insulators with n being a positive integer.
Topological characterization of periodically driven quantum systems
NASA Astrophysics Data System (ADS)
Kitagawa, Takuya; Berg, Erez; Rudner, Mark; Demler, Eugene
2010-12-01
Topological properties of physical systems can lead to robust behaviors that are insensitive to microscopic details. Such topologically robust phenomena are not limited to static systems but can also appear in driven quantum systems. In this paper, we show that the Floquet operators of periodically driven systems can be divided into topologically distinct (homotopy) classes and give a simple physical interpretation of this classification in terms of the spectra of Floquet operators. Using this picture, we provide an intuitive understanding of the well-known phenomenon of quantized adiabatic pumping. Systems whose Floquet operators belong to the trivial class simulate the dynamics generated by time-independent Hamiltonians, which can be topologically classified according to the schemes developed for static systems. We demonstrate these principles through an example of a periodically driven two-dimensional hexagonal lattice tight-binding model which exhibits several topological phases. Remarkably, one of these phases supports chiral edge modes even though the bulk is topologically trivial.
Photonic simulation of topological excitations in metamaterials.
Tan, Wei; Sun, Yong; Chen, Hong; Shen, Shun-Qing
2014-01-01
Condensed matter systems with topological order and metamaterials with left-handed chirality have attracted recently extensive interests in the fields of physics and optics. So far the topological order and chirality of electromagnetic wave are two independent concepts, and there is no work to address their connection. Here we propose to establish the relation between the topological order in condensed matter systems and the chirality in metamaterials, by mapping explicitly Maxwell's equations to the Dirac equation in one dimension. We report an experimental implement of the band inversion in the Dirac equation, which accompanies change of chirality of electromagnetic wave in metamaterials, and the first microwave measurement of topological excitations and topological phases in one dimension. Our finding provides a proof-of-principle example that electromagnetic wave in the metamaterials can be used to simulate the topological order in condensed matter systems and quantum phenomena in relativistic quantum mechanics in a controlled laboratory environment. PMID:24452532
Coverings of topological semi-abelian algebras
NASA Astrophysics Data System (ADS)
Mucuk, Osman; Demir, Serap
2016-08-01
In this work, we study on a category of topological semi-abelian algebras which are topological models of given an algebraic theory T whose category of models is semi-abelian; and investigate some results on the coverings of topological models of such theories yielding semi-abelian categories. We also consider the internal groupoid structure in the semi-abelian category of T-algebras, and give a criteria for the lifting of internal groupoid structure to the covering groupoids.
Topological Raman band in the carbon nanohorn.
Sasaki, Ken-ichi; Sekine, Yoshiaki; Tateno, Kouta; Gotoh, Hideki
2013-09-13
Raman spectroscopy has been used in chemistry and physics to investigate the fundamental process involving light and phonons. The carbon nanohorn introduces a new subject to Raman spectroscopy, namely topology. We show theoretically that a photoexcited carrier with a nonzero winding number activates a topological D Raman band through the Aharonov-Bohm effect. The topology-induced D Raman band can be distinguished from the ordinary D Raman band for a graphene edge by its peak position. PMID:24074113
Algebra and topology for applications to physics
NASA Technical Reports Server (NTRS)
Rozhkov, S. S.
1987-01-01
The principal concepts of algebra and topology are examined with emphasis on applications to physics. In particular, attention is given to sets and mapping; topological spaces and continuous mapping; manifolds; and topological groups and Lie groups. The discussion also covers the tangential spaces of the differential manifolds, including Lie algebras, vector fields, and differential forms, properties of differential forms, mapping of tangential spaces, and integration of differential forms.
Interface between topological and superconducting qubits.
Jiang, Liang; Kane, Charles L; Preskill, John
2011-04-01
We propose and analyze an interface between a topological qubit and a superconducting flux qubit. In our scheme, the interaction between Majorana fermions in a topological insulator is coherently controlled by a superconducting phase that depends on the quantum state of the flux qubit. A controlled-phase gate, achieved by pulsing this interaction on and off, can transfer quantum information between the topological qubit and the superconducting qubit. PMID:21517365
Emergence of magnetic topological states in topological insulators doped with magnetic impurities
NASA Astrophysics Data System (ADS)
Tran, Minh-Tien; Nguyen, Hong-Son; Le, Duc-Anh
2016-04-01
Emergence of the topological invariant and the magnetic moment in topological insulators doped with magnetic impurities is studied based on a mutual cooperation between the spin-orbit coupling of electrons and the spin exchange of these electrons with magnetic impurity moments. The mutual cooperation is realized based on the Kane-Mele model in the presence of magnetic impurities. The topological invariants and the spontaneous magnetization are self-consistently determined within the dynamical mean-field theory. We find different magnetic topological phase transitions, depending on the electron filling. At half filling an antiferromagnetic topological insulator, which exhibits the quantum spin Hall effect, exists in the phase region between the paramagnetic topological insulator and the trivially topological antiferromagnetic insulator. At quarter and three-quarter fillings, a ferromagnetic topological insulator, which exhibits the quantum anomalous Hall effect, occurs in the strong spin-exchange regime.
Blanco-Redondo, Andrea; Andonegui, Imanol; Collins, Matthew J; Harari, Gal; Lumer, Yaakov; Rechtsman, Mikael C; Eggleton, Benjamin J; Segev, Mordechai
2016-04-22
One-dimensional models with topological band structures represent a simple and versatile platform to demonstrate novel topological concepts. Here we experimentally study topologically protected states in silicon at the interface between two dimer chains with different Zak phases. Furthermore, we propose and demonstrate that, in a system where topological and trivial defect modes coexist, we can probe them independently. Tuning the configuration of the interface, we observe the transition between a single topological defect and a compound trivial defect state. These results provide a new paradigm for topologically protected waveguiding in a complementary metal-oxide-semiconductor compatible platform and highlight the novel concept of isolating topological and trivial defect modes in the same system that can have important implications in topological physics. PMID:27152805
Topological color code and symmetry-protected topological phases
NASA Astrophysics Data System (ADS)
Yoshida, Beni
2015-06-01
We study (d -1 ) -dimensional excitations in the d -dimensional color code that are created by transversal application of the Rd phase operators on connected subregions of qubits. We find that such excitations are the superpositions of electric charges and can be characterized by the fixed-point wave functions of (d -1 ) -dimensional bosonic symmetry-protected topological (SPT) phases with (Z2) ⊗d symmetry. While these SPT excitations are localized on (d -1 ) -dimensional boundaries, their creation requires operations acting on all qubits inside the boundaries, reflecting the nontriviality of emerging SPT wave functions. Moreover, these SPT excitations can be physically realized as transparent gapped domain walls which exchange excitations in the color code. Namely, in the three-dimensional color code, the domain wall, associated with the transversal R3 operator, exchanges a magnetic flux and a composite of a magnetic flux and the looplike SPT excitation, revealing rich possibilities of boundaries in higher-dimensional TQFTs. We also find that magnetic fluxes and the looplike SPT excitations exhibit nontrivial three-loop braiding statistics in three dimensions as a result of the fact that the R3 phase operator belongs to the third level of the Clifford hierarchy. We believe that the connection between SPT excitations, fault-tolerant logical gates and gapped domain walls, established in this paper, can be generalized to a large class of topological quantum codes and TQFTs.
Simulating Topological Defects in Twisted Fiber Bundles
NASA Astrophysics Data System (ADS)
Bruss, Isaac R.; Grason, Gregory M.
2012-02-01
Twisted bundles are a common motif found in naturally occurring structures of self-assembled fibers, such as collagen and fibrin. By understanding the general principles governing such organizations, new synthetic materials--from the nano to the macroscale--may also be realized. Recently, continuum elasticity theory has been applied to describe generic twisted fiber bundles. This has revealed a relation between a bundle's twist and the presence of topological defects in the cross-sectional packing of the fibers. Here we employ numerical simulations to examine this interdependence. We model a bundle's cross-section as beads confined to a plane. The interactions between beads is governed by a modified Lennard-Jones potential that accounts for the effects of twist. We observe configurations that range from perfect hexagonal packing for cases of no twist, to defect populated structures above a critical amount of twist. For small bundles of less than ˜100 beads, there exists a discrete spectrum of energy ground states corresponding to integer numbers of five-fold disclinations. For larger bundles, we hope to uncover what types of defect arrangements effectively screen the stresses caused by twist, and compare these to current predictions of the internal organization of collagen fibrils.
Phyllotaxis: a framework for foam topological evolution.
Rivier, Nicolas; Sadoc, Jean-François; Charvolin, Jean
2016-01-01
Phyllotaxis describes the arrangement of florets, scales or leaves in composite flowers or plants (daisy, aster, sunflower, pinecone, pineapple). As a structure, it is a geometrical foam, the most homogeneous and densest covering of a large disk by Voronoi cells (the florets), constructed by a simple algorithm: Points placed regularly on a generative spiral constitute a spiral lattice, and phyllotaxis is the tiling by the Voronoi cells of the spiral lattice. Locally, neighboring cells are organized as three whorls or parastichies, labelled with successive Fibonacci numbers. The structure is encoded as the sequence of the shapes (number of sides) of the successive Voronoi cells on the generative spiral. We show that sequence and organization are independent of the position of the initial point on the generative spiral, that is invariant under disappearance (T2 of the first Voronoi cell or, conversely, under creation of a first cell, that is under growth. This independence shows how a foam is able to respond to a shear stress, notably through grain boundaries that are layers of square cells slightly truncated into heptagons, pentagons and hexagons, meeting at four-corner vertices, critical points of T1 elementary topological transformations. PMID:26810397
Semen abnormalities with SSRI antidepressants.
2015-01-01
Despite decades of widespread use, the adverse effect profile of "selective" serotonin reuptake inhibitor (SSRI) antidepressants has still not been fully elucidated. Studies in male animals have shown delayed sexual development and reduced fertility. Three prospective cohort studies conducted in over one hundred patients exposed to an SSRI for periods ranging from 5 weeks to 24 months found altered semen param-eters after as little as 3 months of exposure: reduced sperm concentration, reduced sperm motility, a higher percentage of abnormal spermatozoa, and increased levels of sperm DNA fragmentation. One clinical trial showed growth retardation in children considered depressed who were exposed to SSRls. SSRls may have endocrine disrupting properties. Dapoxetine is a short-acting serotonin reuptake inhibitor that is chemically related to fluoxetine and marketed in the European Union for men complaining of premature ejaculation. But the corresponding European summary of product characteristics does not mention any effects on fertility. In practice, based on the data available as of mid-2014, the effects of SSRI exposure on male fertility are unclear. However, it is a risk that should be taken into account and pointed out to male patients who would like to father a child or who are experiencing fertility problems. PMID:25729824
The XXXXY Sex Chromosome Abnormality
Barr, M. L.; Carr, D. H.; Pozsonyi, J.; Wilson, R. A.; Dunn, H. G.; Jacobson, T. S.; Miller, J. R.; Chown, B.
1962-01-01
The most common sex chromosome complex in sex chromatin-positive males with Klinefelter's syndrome is XXY. When the complex is XXYY or XXXY, the clinical findings do not seem to differ materially from those seen in XXY subjects, although more patients with these intersexual chromosome complements need to be studied to establish possible phenotypical expressions of the chromosomal variants. Two male children with an XXXXY sex chromosome abnormality are described. The data obtained from the study of these cases and five others described in the literature suggest that the XXXXY patient is likely to have congenital defects not usually seen in the common form of the Klinefelter syndrome. These include a triad of (1) skeletal anomalies (including radioulnar synostosis), (2) hypogenitalism (hypoplasia of penis and scrotum, incomplete descent of testes and defective prepubertal development of seminiferous tubules), and (3) greater risk of severe mental deficiency. That the conclusions are based on data from a small number of patients is emphasized, together with the need for a cytogenetic survey of a large control or unselected population. ImagesFig. 1Fig. 2Fig. 3Fig. 4Fig. 5Fig. 6Fig. 7Fig. 8Fig. 9Fig. 10 PMID:13969480
Abnormal Mitochondrial Dynamics and Neurodegenerative Diseases
Su, Bo; Wang, Xinglong; Zheng, Ling; Perry, George; Smith, Mark A.; Zhu, Xiongwei
2009-01-01
Mitochondrial dysfunction is a prominent feature of various neurodegenerative diseases. A deeper understanding of the remarkably dynamic nature of mitochondria, characterized by a delicate balance of fission and fusion, has helped to fertilize a recent wave of new studies demonstrating abnormal mitochondrial dynamics in neurodegenerative diseases. This review highlights mitochondrial dysfunction and abnormal mitochondrial dynamics in Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and Huntington disease and discusses how these abnormal mitochondrial dynamics may contribute to mitochondrial and neuronal dysfunction. We propose that abnormal mitochondrial dynamics represents a key common pathway that mediates or amplifies mitochondrial dysfunction and neuronal dysfunction during the course of neurodegeneration. PMID:19799998
Chromosomal abnormalities in child psychiatric patients.
Hong, K E; Kim, J H; Moon, S Y; Oh, S K
1999-08-01
To determine the frequency of chromosomal abnormalities in a child psychiatric population, and to evaluate possible associations between types of abnormalities and patient's clinical characteristics, cytogenetic examination was performed on 604 patients. Demographic data, reasons for karyotyping, clinical signs, and other patient characteristics were assessed and correlated with the results from karyotyping. Chromosomal abnormalities were found in 69 patients (11.3%); these were structural in 49 cases and numerical in 20. Inversion of chromosome nine was found in 15 subjects, trisomy of chromosome 21 in 11, and fragile X in five patients. When karyotyping was performed because of intellectual impairment or multiple developmental delay, significantly more abnormalities were found than average; when performed because autistic disorder was suspected, the number of abnormalities was significantly fewer. There were no differences in clinical variables between structural and numerical abnormalities, nor among nine types of chromosomal abnormalities, except that numerical abnormalities and polymorphism were found at a later age, and that walking was more delayed and IQ was lower in patients with Down syndrome. Clinicians should be aware of the possible presence of chromosomal abnormalities in child psychiatric populations; the close collaboration with geneticists and the use of more defined guidelines for cytogenetic investigation are important. PMID:10485616
Radiologic atlas of pulmonary abnormalities in children
Singleton, E.B.; Wagner, M.L.; Dutton, R.V.
1988-01-01
This book is an atlas about thoracic abnormalities in infants and children. The authors include computed tomographic, digital subtraction angiographic, ultrasonographic, and a few magnetic resonance (MR) images. They recognize and discuss how changes in the medical treatment of premature infants and the management of infection and pediatric tumors have altered some of the appearances and considerations in these diseases. Oriented toward all aspects of pulmonary abnormalities, the book starts with radiographic techniques and then discusses the normal chest, the newborn, infections, tumors, and pulmonary vascular diseases. There is comprehensive treatment of mediastinal abnormalities and a discussion of airway abnormalities.
On the topology of flux transfer events
NASA Technical Reports Server (NTRS)
Hesse, Michael; Birn, Joachim; Schindler, Karl
1990-01-01
A topological analysis is made of a simple model magnetic field of a perturbation at the magnetopause that shares magnetic properties with flux transfer events. The aim is to clarify a number of topological aspects that arise in the case of fully three-dimensional magnetic fields. It is shown that a localized perturbation at the magnetopause can in principle open a closed magnetosphere by establishing magnetic connections across the magnetopause by the formation of a ropelike magnetic field structure. For this purpose a global topological model of a closed magnetosphere is considered as the unperturbed state. The topological substructure of the model flux rope is discussed in detail.
Topological spin and valley pumping in silicene
Luo, Wei; Sheng, L.; Wang, B. G.; Xing, D. Y.
2016-01-01
We propose to realize adiabatic topological spin and valley pumping by using silicene, subject to the modulation of an in-plane ac electric field with amplitude Ey and a vertical electric field consisting of an electrostatic component and an ac component with amplitudes and . By tuning and , topological valley pumping or spin-valley pumping can be achieved. The low-noise valley and spin currents generated can be useful in valleytronic and spintronic applications. Our work also demonstrates that bulk topological spin or valley pumping is a general characteristic effect of two-dimensional topological insulators, irrelevant to the edge state physics. PMID:27507592
Uranyl peroxide closed clusters containing topological squares
Unruh, Daniel K.; Burtner, Alicia; Pressprich, Laura; Sigmon, Ginger E.; Burns, Peter C
2010-01-01
Four self-assembling clusters of uranyl peroxide polyhedra have been formed in alkaline aqueous solutions and structurally characterized. These clusters consist of 28, 30, 36 and 44 uranyl polyhedra and exhibit complex new topologies. Each has a structure that contains topological squares, pentagons and hexagons. Analysis of possible topologies within boundary constraints indicates a tendency for adoption of higher symmetry topologies in these cases. Small angle X-ray scattering data demonstrated that crystals of one of these clusters can be dissolved in ultrapure water and that the clusters remain intact for at least several days.
Topological spin and valley pumping in silicene.
Luo, Wei; Sheng, L; Wang, B G; Xing, D Y
2016-01-01
We propose to realize adiabatic topological spin and valley pumping by using silicene, subject to the modulation of an in-plane ac electric field with amplitude Ey and a vertical electric field consisting of an electrostatic component and an ac component with amplitudes and . By tuning and , topological valley pumping or spin-valley pumping can be achieved. The low-noise valley and spin currents generated can be useful in valleytronic and spintronic applications. Our work also demonstrates that bulk topological spin or valley pumping is a general characteristic effect of two-dimensional topological insulators, irrelevant to the edge state physics. PMID:27507592
Magnetic topology of emerging flux regions
NASA Astrophysics Data System (ADS)
Pariat, Etienne
Coronal magnetic fields structure and governs the dynamics of the solar atmosphere. These magnetic fields are often complex, composed of multiples domains of magnetic-field-lines connectivity. The topology of the magnetic field allows a synthetic description of these complex magnetic field by highlighting the structural elements that are important for the dynamic and the activity of the corona. Topology identifies the key elements where magnetic reconnection will preferentially occurs, and allows to explain and predict the evolution of the coronal plasma. However the topological elements - such as null points, separatrices, separators - do not appear out of thin air. Along with energy, and helicity, the magnetic topology of an active region is build up as the consequence of flux emergence. Some topological elements, such as bald-patches, are even fully part of the mechanism of flux emergence mechanism and drive the evolution and the structuration of the coronal magnetic field as it crosses the lower layer of the solar atmosphere. In the present talk I will therefore review our current understanding of the formation of active region in terms of magnetic topology. I will speak on how the topological structures which are key to solar activity are formed. Meanwhile I'll also discus the topological properties of emerging active region and how topology influences the very process of flux emergence.
Inversion symmetry protected topological insulators and superconductors
NASA Astrophysics Data System (ADS)
Lee, Dung-Hai; Lu, Yuan-Ming
2015-03-01
Three dimensional topological insulator represents a class of novel quantum phases hosting robust gapless boundary excitations, which is protected by global symmetries such as time reversal, charge conservation and spin rotational symmetry. In this work we systematically study another class of topological phases of weakly interacting electrons protected by spatial inversion symmetry, which generally don't support stable gapless boundary states. We classify these inversion-symmetric topological insulators and superconductors in the framework of K-theory, and construct their lattice models. We also discuss quantized response functions of these inversion-protected topological phases, which serve as their experimental signatures.
Topology of nonsymmorphic crystalline insulators and superconductors
NASA Astrophysics Data System (ADS)
Shiozaki, Ken; Sato, Masatoshi; Gomi, Kiyonori
2016-05-01
Topological classification in our previous paper [K. Shiozaki and M. Sato, Phys. Rev. B 90, 165114 (2014), 10.1103/PhysRevB.90.165114] is extended to nonsymmorphic crystalline insulators and superconductors. Using the twisted equivariant K theory, we complete the classification of topological crystalline insulators and superconductors in the presence of additional order-two nonsymmorphic space-group symmetries. The order-two nonsymmorphic space groups include half-lattice translation with Z2 flip, glide, twofold screw, and their magnetic space groups. We find that the topological periodic table shows modulo-2 periodicity in the number of flipped coordinates under the order-two nonsymmorphic space group. It is pointed out that the nonsymmorphic space groups allow Z2 topological phases even in the absence of time-reversal and/or particle-hole symmetries. Furthermore, the coexistence of the nonsymmorphic space group with time-reversal and/or particle-hole symmetries provides novel Z4 topological phases, which have not been realized in ordinary topological insulators and superconductors. We present model Hamiltonians of these new topological phases and analytic expressions of the Z2 and Z4 topological invariants. The half-lattice translation with Z2 spin flip and glide symmetry are compatible with the existence of boundaries, leading to topological surface gapless modes protected by the order-two nonsymmorphic symmetries. We also discuss unique features of these gapless surface modes.
Copying and Evolution of Neuronal Topology
Fernando, Chrisantha; Karishma, K. K.; Szathmáry, Eörs
2008-01-01
We propose a mechanism for copying of neuronal networks that is of considerable interest for neuroscience for it suggests a neuronal basis for causal inference, function copying, and natural selection within the human brain. To date, no model of neuronal topology copying exists. We present three increasingly sophisticated mechanisms to demonstrate how topographic map formation coupled with Spike-Time Dependent Plasticity (STDP) can copy neuronal topology motifs. Fidelity is improved by error correction and activity-reverberation limitation. The high-fidelity topology-copying operator is used to evolve neuronal topologies. Possible roles for neuronal natural selection are discussed. PMID:19020662
Topological spin and valley pumping in silicene
NASA Astrophysics Data System (ADS)
Luo, Wei; Sheng, L.; Wang, B. G.; Xing, D. Y.
2016-08-01
We propose to realize adiabatic topological spin and valley pumping by using silicene, subject to the modulation of an in-plane ac electric field with amplitude Ey and a vertical electric field consisting of an electrostatic component and an ac component with amplitudes and . By tuning and , topological valley pumping or spin-valley pumping can be achieved. The low-noise valley and spin currents generated can be useful in valleytronic and spintronic applications. Our work also demonstrates that bulk topological spin or valley pumping is a general characteristic effect of two-dimensional topological insulators, irrelevant to the edge state physics.
Topological deformation of isolated horizons
Liko, Tomas
2008-03-15
We show that the Gauss-Bonnet term can have physical effects in four dimensions. Specifically, the entropy of a black hole acquires a correction term that is proportional to the Euler characteristic of the cross sections of the horizon. While this term is constant for a single black hole, it will be a nontrivial function for a system with dynamical topologies such as black-hole mergers: it is shown that for certain values of the Gauss-Bonnet parameter, the second law of black-hole mechanics can be violated.
Geometry, topology, and string theory
Varadarajan, Uday
2003-07-10
A variety of scenarios are considered which shed light upon the uses and limitations of classical geometric and topological notions in string theory. The primary focus is on situations in which D-brane or string probes of a given classical space-time see the geometry quite differently than one might naively expect. In particular, situations in which extra dimensions, non-commutative geometries as well as other non-local structures emerge are explored in detail. Further, a preliminary exploration of such issues in Lorentzian space-times with non-trivial causal structures within string theory is initiated.
Peptides that influence membrane topology
NASA Astrophysics Data System (ADS)
Wong, Gerard C. L.
2014-03-01
We examine the mechanism of a range of polypeptides that influence membrane topology, including antimicrobial peptides, cell penetrating peptides, viral fusion peptides, and apoptosis proteins, and show how a combination of geometry, coordination chemistry, and soft matter physics can be used to approach a unified understanding. We will also show how such peptides can impact biomedical problems such as auto-immune diseases (psoriasis, lupus), infectious diseases (viral and bacterial infections), and mitochondrial pathologies (under-regulated apoptosis leads to neurodegenerative diseases whereas over-regulated apoptosis leads to cancer.)
Mars: Noachian hydrology by its statistics and topology
NASA Technical Reports Server (NTRS)
Cabrol, N. A.; Grin, E. A.
1993-01-01
Discrimination between fluvial features generated by surface drainage and subsurface aquifer discharges will provide clues to the understanding of early Mars' climatic history. Our approach is to define the process of formation of the oldest fluvial valleys by statistical and topological analyses. Formation of fluvial valley systems reached its highest statistical concentration during the Noachian Period. Nevertheless, they are a scarce phenomenom in Martian history, localized on the craterized upland, and subject to latitudinal distribution. They occur sparsely on Noachian geological units with a weak distribution density, and appear in reduced isolated surface (around 5 x 10(exp 3)(sq km)), filled by short streams (100-300 km length). Topological analysis of the internal organization of 71 surveyed Noachian fluvial valley networks also provides information on the mechanisms of formation.
Charles Mielke
2009-02-27
Intense magnetic fields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magnetic fields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures~13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magnetic field induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magnetic fields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magnetic fields.
Thyroid abnormalities after therapeutic external radiation
Hancock, S.L.; McDougall, I.R.; Constine, L.S.
1995-03-30
The thyroid gland is the largest pure endocrine gland in the body and one of the organs most likely to produce clinically significant abnormalities after therapeutic external radiation. Radiation doses to the thyroid that exceed approximately 26 Gy frequently produce hypothyroidism, which may be clinically overt or subclinical, as manifested by increased serum thyrotropin and normal serum-free thyroxine concentrations. Pituitary or hypothalamic hypothyroidism may arise when the pituitary region receives doses exceeding 50 Gy with conventional, 1.8-2 Gy fractionation. Direct irradiation of the thyroid may increase the risk of Graves` disease or euthyroid Graves` ophthalmopathy. Silent thyroiditis, cystic degeneration, benign adenoma, and thyroid cancer have been observed after therapeutically relevant doses of external radiation. Direct or incidental thyroid irradiation increases the risk for well-differentiated, papillary, and follicular thyroid cancer from 15- to 53-fold. Thyroid cancer risk is highest following radiation at a young age, decreases with increasing age at treatment, and increases with follow-up duration. The potentially prolonged latent period between radiation exposure and the development of thyroid dysfunction, thyroid nodularity, and thyroid cancer means that individuals who have received neck or pituitary irradiation require careful, periodic clinical and laboratory evaluation to avoid excess morbidity. 39 refs.
Dislocations and other topological oddities
NASA Astrophysics Data System (ADS)
Pieranski, Pawel
2016-03-01
We will show that the book Dislocations by Jacques Friedel, published half a century ago, can still be recommended, in agreement with the author's intention, as a textbook "for research students at University and for students at engineering schools as well as for research engineers". Indeed, today dislocations are known to occur not only in solid crystals but also in many other systems discovered more recently such as colloidal crystals or liquid crystals having periodic structures. Moreover, the concept of dislocations is an excellent starting point for lectures on topological defects occurring in systems equipped with order parameters resulting from broken symmetries: disclinations in nematic or hexatic liquid crystals, dispirations in chiral smectics or disorientations in lyotropic liquid crystals. The discussion of dislocations in Blue Phases will give us an opportunity to call on mind Sir Charles Frank, friend of Jacques Friedel since his Bristol years, who called these ephemeral mesophases "topological oddities". Being made of networks of disclinations, Blue Phases are similar to Twist Grain Boundary (TGB) smectic phases, which are made of networks of screw dislocations and whose existence was predicted by de Gennes in 1972 on the basis of the analogy between smectics and superconductors. We will stress that the book by Jacques Friedel contains seeds of this analogy.
Quantum fields in toroidal topology
Khanna, F.C.; Malbouisson, A.P.C.; Santana, A.E.
2011-10-15
The standard representation of c*-algebra is used to describe fields in compactified space-time dimensions characterized by topologies of the type {Gamma}{sub D}{sup d}=(S{sup 1}){sup d}xM{sup D-d}. The modular operator is generalized to introduce representations of isometry groups. The Poincare symmetry is analyzed and then we construct the modular representation by using linear transformations in the field modes, similar to the Bogoliubov transformation. This provides a mechanism for compactification of the Minkowski space-time, which follows as a generalization of the Fourier integral representation of the propagator at finite temperature. An important result is that the 2x2 representation of the real-time formalism is not needed. The end result on calculating observables is described as a condensate in the ground state. We initially analyze the free Klein-Gordon and Dirac fields, and then formulate non-abelian gauge theories in {Gamma}{sub D}{sup d}. Using the S-matrix, the decay of particles is calculated in order to show the effect of the compactification. - Highlights: > C*-algebra is used to describe fields in compactified space-time dimensions. > The space-time is characterized by toroidal topologies. > Representations of the Poincare group are studied by using the modular operator. > We derive non-abelian gauge theories in compactified regions of space-time. > We show the compactification effect in the decay of particles using the S-matrix.
Acoustic design by topology optimization
NASA Astrophysics Data System (ADS)
Dühring, Maria B.; Jensen, Jakob S.; Sigmund, Ole
2008-11-01
To bring down noise levels in human surroundings is an important issue and a method to reduce noise by means of topology optimization is presented here. The acoustic field is modeled by Helmholtz equation and the topology optimization method is based on continuous material interpolation functions in the density and bulk modulus. The objective function is the squared sound pressure amplitude. First, room acoustic problems are considered and it is shown that the sound level can be reduced in a certain part of the room by an optimized distribution of reflecting material in a design domain along the ceiling or by distribution of absorbing and reflecting material along the walls. We obtain well defined optimized designs for a single frequency or a frequency interval for both 2D and 3D problems when considering low frequencies. Second, it is shown that the method can be applied to design outdoor sound barriers in order to reduce the sound level in the shadow zone behind the barrier. A reduction of up to 10 dB for a single barrier and almost 30 dB when using two barriers are achieved compared to utilizing conventional sound barriers.
Topological inflation with graceful exit
NASA Astrophysics Data System (ADS)
Marunović, Anja; Prokopec, Tomislav
2016-04-01
We investigate a class of models of topological inflation in which a super-Hubble-sized global monopole seeds inflation. These models are attractive since inflation starts from rather generic initial conditions, but their not so attractive feature is that, unless symmetry is again restored, inflation never ends. In this work we show that, in presence of another nonminimally coupled scalar field, that is both quadratically and quartically coupled to the Ricci scalar, inflation naturally ends, representing an elegant solution to the graceful exit problem of topological inflation. While the monopole core grows during inflation, the growth stops after inflation, such that the monopole eventually enters the Hubble radius, and shrinks to its Minkowski space size, rendering it immaterial for the subsequent Universe's dynamics. Furthermore, we find that our model can produce cosmological perturbations that source CMB temperature fluctuations and seed large scale structure statistically consistent (within one standard deviation) with all available data. In particular, for small and (in our convention) negative nonminimal couplings, the scalar spectral index can be as large as ns simeq 0.955, which is about one standard deviation lower than the central value quoted by the most recent Planck Collaboration.
Topological structure of dictionary graphs
NASA Astrophysics Data System (ADS)
Fukś, Henryk; Krzemiński, Mark
2009-09-01
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 103 and 104. 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 Superconductivity with Magnetic Atoms
NASA Astrophysics Data System (ADS)
Glazman, Leonid
2015-03-01
Chains of magnetic impurities embedded in a conventional s-wave superconductor may induce the formation of a topologically non-trivial superconducting phase. If such a phase is formed along a chain, then its ends carry Majorana fermions. We investigate this possibility theoretically by developing a tight-binding Bogoliubov-de Gennes description, starting from the Shiba bound states induced by the individual magnetic impurities. While the resulting Hamiltonian has similarities with the Kitaev model for one-dimensional spinless p-wave superconductors, there are also important differences, most notably the long-range (power-law) nature of hopping and pairing as well as the complex hopping amplitudes. We develop an analytical theory, complemented by numerical approaches, which accounts for the electron long-range pairing and hopping along the chain, inhomogeneous magnetic order in the chain of embedded impurities or spin-orbit coupling in the host superconductor, and the possibility of direct electron hopping between the impurity atoms. This allows us to elucidate the domain of parameters favoring the formation of a topological phase and to find the spatial structure of Majorana states appearing in that phase. This talk is based on joint work with F. von Oppen, Falko Pientka, and Yang Peng.
Topological Behavior of Plasmid DNA
Higgins, N. Patrick; Vologodskii, Alexander V.
2015-01-01
The discovery of the B-form structure of DNA by Watson and Crick led to an explosion of research on nucleic acids in the fields of biochemistry, biophysics, and genetics. Powerful techniques were developed to reveal a myriad of different structural conformations that change B-DNA as it is transcribed, replicated, and recombined and as sister chromosomes are moved into new daughter cell compartments during cell division. This article links the original discoveries of superhelical structure and molecular topology to non-B form DNA structure and contemporary biochemical and biophysical techniques. The emphasis is on the power of plasmids for studying DNA structure and function. The conditions that trigger the formation of alternative DNA structures such as left-handed Z-DNA, inter- and intra-molecular triplexes, triple-stranded DNA, and linked catenanes and hemicatenanes are explained. The DNA dynamics and topological issues are detailed for stalled replication forks and for torsional and structural changes on DNA in front of and behind a transcription complex and a replisome. The complex and interconnected roles of topoisomerases and abundant small nucleoid association proteins are explained. And methods are described for comparing in vivo and in vitro reactions to probe and understand the temporal pathways of DNA and chromosome chemistry that occur inside living cells. PMID:26104708
Abnormalities of vascular structure and function in pediatric hypertension.
Urbina, Elaine M
2016-07-01
Hypertension is associated with adverse cardiovascular (CV) events in adults. Measures of vascular structure and function, including increased carotid intima-media thickness (cIMT) and elevated arterial stiffness predict hard CV events in adulthood. Newer data suggest that abnormalities in target organ damage are occurring in adolescents and young adults with high blood pressure. In this review, we discuss the techniques for measuring vascular dysfunction in young people and the evidence linking blood pressure levels to this type of target organ damage. PMID:26275663
Wang, Erjing; He, Zikai; Zhao, Engui; Meng, Luming; Schütt, Christian; Lam, Jacky W Y; Sung, Herman H Y; Williams, Ian D; Huang, Xuhui; Herges, Rainer; Tang, Ben Zhong
2015-08-10
Molecules with Möbius topology have drawn increasing attention from scientists in a variety of fields, such as organic chemistry, inorganic chemistry, and material science. However, synthetic difficulties and the lack of functionality impede their fundamental understanding and practical applications. Here, we report the facile synthesis of an aggregation-induced-emission (AIE)-active macrocycle (TPE-ET) and investigate its analogous triply and singly twisted Möbius topologies. Because of the twisted and flexible nature of the tetraphenylethene units, the macrocycle adjusts its conformations so as to accommodate different guest molecules in its crystals. Moreover, theoretical studies including topological and electronic calculations reveal the energetically favorable interconversion process between triply and singly twisted topologies. PMID:26177730
Topological defects in liquid crystals as templates for molecular self-assembly
NASA Astrophysics Data System (ADS)
Wang, Xiaoguang; Miller, Daniel S.; Bukusoglu, Emre; de Pablo, Juan J.; Abbott, Nicholas L.
2016-01-01
Topological defects in liquid crystals (LCs) have been widely used to organize colloidal dispersions and template polymerization, leading to a range of assemblies, elastomers and gels. However, little is understood about molecular-level assembly processes within defects. Here, we report that nanoscopic environments defined by LC topological defects can selectively trigger processes of molecular self-assembly. By using fluorescence microscopy, cryogenic transmission electron microscopy and super-resolution optical microscopy, we observed signatures of molecular self-assembly of amphiphilic molecules in topological defects, including cooperativity, reversibility and controlled growth. We also show that nanoscopic o-rings synthesized from Saturn-ring disclinations and other molecular assemblies templated by defects can be preserved by using photocrosslinkable amphiphiles. Our results reveal that, in analogy to other classes of macromolecular templates such as polymer-surfactant complexes, topological defects in LCs are a versatile class of three-dimensional, dynamic and reconfigurable templates that can direct processes of molecular self-assembly.
NASA Astrophysics Data System (ADS)
He, Yuan-Yao; Wu, Han-Qing; Meng, Zi Yang; Lu, Zhong-Yi
2016-05-01
Topological phase transitions in free fermion systems can be characterized by the closing of single-particle gap and the change in topological invariants. However, in the presence of electronic interactions, topological phase transitions can be more complicated. In paper I of this series [Phys. Rev. B 93, 195163 (2016), 10.1103/PhysRevB.93.195163], we have proposed an efficient scheme to evaluate the topological invariants based on the single-particle Green's function formalism. Here, in paper II, we demonstrate several interaction-driven topological phase transitions (TPTs) in two-dimensional (2D) interacting topological insulators (TIs) via large-scale quantum Monte Carlo (QMC) simulations, based on the scheme of evaluating topological invariants presented in paper I. Across these transitions, the defining symmetries of the TIs have been neither explicitly nor spontaneously broken. In the first two models, the topological invariants calculated from the Green's function formalism succeed in characterizing the topologically distinct phases and identifying interaction-driven TPTs. However, in the other two models, we find that the single-particle gap does not close and the topological invariants constructed from the single-particle Green's function acquire no change across the TPTs. Unexpected breakdown of the Green's function formalism in constructing the topological invariants is thus discovered. We thence classify the topological phase transitions in interacting TIs into two categories in practical computation: Those that have noninteracting correspondence can be characterized successfully by the topological invariants constructed from the Green's functions, while for the others that do not have noninteracting correspondence, the Green's function formalism experiences a breakdown, but more interesting and exciting phenomena, such as emergent collective critical modes at the transition, arise. Discussion on the success and breakdown of topological invariants
An Abnormal Psychology Community Based Interview Assignment
ERIC Educational Resources Information Center
White, Geoffry D.
1977-01-01
A course option in abnormal psychology involves students in interviewing and observing the activities of individuals in the off-campus community who are concerned with some aspect of abnormal psychology. The technique generates student interest in the field when they interview people about topics such as drug abuse, transsexualism, and abuse of…
Detection of Structural Abnormalities Using Neural Nets
NASA Technical Reports Server (NTRS)
Zak, M.; Maccalla, A.; Daggumati, V.; Gulati, S.; Toomarian, N.
1996-01-01
This paper describes a feed-forward neural net approach for detection of abnormal system behavior based upon sensor data analyses. A new dynamical invariant representing structural parameters of the system is introduced in such a way that any structural abnormalities in the system behavior are detected from the corresponding changes to the invariant.
Immune Abnormalities in Patients with Autism.
ERIC Educational Resources Information Center
Warren, Reed P.; And Others
1986-01-01
A study of 31 autistic patients (3-28 years old) has revealed several immune-system abnormalities, including decreased numbers of T lymphocytes and an altered ratio of helper-to-suppressor T cells. Immune-system abnormalities may be directly related to underlying biologic processes of autism or an indirect reflection of the actual pathologic…
Nail abnormalities in patients with vitiligo*
Topal, Ilteris Oguz; Gungor, Sule; Kocaturk, Ozgur Emek; Duman, Hatice; Durmuscan, Mustafa
2016-01-01
Background Vitiligo is an acquired pigmentary skin disorder affecting 0.1-4% of the general population. The nails may be affected in patients with an autoimmune disease such as psoriasis, and in those with alopecia areata. It has been suggested that nail abnormalities should be apparent in vitiligo patients. Objective We sought to document the frequency and clinical presentation of nail abnormalities in vitiligo patients compared to healthy volunteers. We also examined the correlations between nail abnormalities and various clinical parameters. Methods This study included 100 vitiligo patients and 100 healthy subjects. Full medical histories were collected from the subjects, who underwent thorough general and nail examinations. All nail changes were noted. In the event of clinical suspicion of a fungal infection, additional mycological investigations were performed. Results Nail abnormalities were more prevalent in the patients (78%) than in the controls (55%) (p=0.001). Longitudinal ridging was the most common finding (42%), followed by (in descending order): leukonychia, an absent lunula, onycholysis, nail bed pallor, onychomycosis, splinter hemorrhage and nail plate thinning. The frequency of longitudinal ridging was significantly higher in patients than in controls (p<0.001). Conclusions Nail abnormalities were more prevalent in vitiligo patients than in controls. Systematic examination of the nails in such patients is useful because nail abnormalities are frequent. However, the causes of such abnormalities require further study. Longitudinal ridging and leukonychia were the most common abnormalities observed in this study. PMID:27579738
[Abnormality in bone metabolism after burn].
Gong, X; Xie, W G
2016-08-20
Burn causes bone metabolic abnormality in most cases, including the changes in osteoblasts and osteoclasts, bone mass loss, and bone absorption, which results in decreased bone mineral density. These changes are sustainable for many years after burn and even cause growth retardation in burned children. The mechanisms of bone metabolic abnormality after burn include the increasing glucocorticoids due to stress response, a variety of cytokines and inflammatory medium due to inflammatory response, vitamin D deficiency, hypoparathyroidism, and bone loss due to long-term lying in bed. This article reviews the pathogenesis and regularity of bone metabolic abnormality after burn, the relationship between bone metabolic abnormality and burn area/depth, and the treatment of bone metabolic abnormality, etc. and discusses the research directions in the future. PMID:27562160
Insulator function and topological domain border strength scale with architectural protein occupancy
2014-01-01
Background Chromosome conformation capture studies suggest that eukaryotic genomes are organized into structures called topologically associating domains. The borders of these domains are highly enriched for architectural proteins with characterized roles in insulator function. However, a majority of architectural protein binding sites localize within topological domains, suggesting sites associated with domain borders represent a functionally different subclass of these regulatory elements. How topologically associating domains are established and what differentiates border-associated from non-border architectural protein binding sites remain unanswered questions. Results By mapping the genome-wide target sites for several Drosophila architectural proteins, including previously uncharacterized profiles for TFIIIC and SMC-containing condensin complexes, we uncover an extensive pattern of colocalization in which architectural proteins establish dense clusters at the borders of topological domains. Reporter-based enhancer-blocking insulator activity as well as endogenous domain border strength scale with the occupancy level of architectural protein binding sites, suggesting co-binding by architectural proteins underlies the functional potential of these loci. Analyses in mouse and human stem cells suggest that clustering of architectural proteins is a general feature of genome organization, and conserved architectural protein binding sites may underlie the tissue-invariant nature of topologically associating domains observed in mammals. Conclusions We identify a spectrum of architectural protein occupancy that scales with the topological structure of chromosomes and the regulatory potential of these elements. Whereas high occupancy architectural protein binding sites associate with robust partitioning of topologically associating domains and robust insulator function, low occupancy sites appear reserved for gene-specific regulation within topological domains. PMID
Topological insulators: A romance with many dimensions
NASA Astrophysics Data System (ADS)
Manoharan, Hari C.
2010-07-01
Electric charges on the boundaries of certain insulators are programmed by topology to keep moving forward when they encounter an obstacle, rather than scattering backwards and increasing the resistance of the system. This is just one reason why topological insulators are one of the hottest topics in physics right now.
Topology dictionary for 3D video understanding.
Tung, Tony; Matsuyama, Takashi
2012-08-01
This paper presents a novel approach that achieves 3D video understanding. 3D video consists of a stream of 3D models of subjects in motion. The acquisition of long sequences requires large storage space (2 GB for 1 min). Moreover, it is tedious to browse data sets and extract meaningful information. We propose the topology dictionary to encode and describe 3D video content. The model consists of a topology-based shape descriptor dictionary which can be generated from either extracted patterns or training sequences. The model relies on 1) topology description and classification using Reeb graphs, and 2) a Markov motion graph to represent topology change states. We show that the use of Reeb graphs as the high-level topology descriptor is relevant. It allows the dictionary to automatically model complex sequences, whereas other strategies would require prior knowledge on the shape and topology of the captured subjects. Our approach serves to encode 3D video sequences, and can be applied for content-based description and summarization of 3D video sequences. Furthermore, topology class labeling during a learning process enables the system to perform content-based event recognition. Experiments were carried out on various 3D videos. We showcase an application for 3D video progressive summarization using the topology dictionary. PMID:22745004
The topological description of coronal magnetic fields
NASA Technical Reports Server (NTRS)
Berger, Mitchell A.
1986-01-01
Determining the structure and behavior of solar coronal magnetic fields is a central problem in solar physics. At the photosphere, the field is believed to be strongly localized into discrete flux tubes. After providing a rigorous definition of field topology, how the topology of a finite collection of flux tubes may be classified is discussed.
Finite Topological Spaces as a Pedagogical Tool
ERIC Educational Resources Information Center
Helmstutler, Randall D.; Higginbottom, Ryan S.
2012-01-01
We propose the use of finite topological spaces as examples in a point-set topology class especially suited to help students transition into abstract mathematics. We describe how carefully chosen examples involving finite spaces may be used to reinforce concepts, highlight pathologies, and develop students' non-Euclidean intuition. We end with a…
Topological insulators and superconductors from string theory
Ryu, Shinsei; Takayanagi, Tadashi
2010-10-15
Topological insulators and superconductors in different spatial dimensions and with different discrete symmetries have been fully classified recently, revealing a periodic structure for the pattern of possible types of topological insulators and superconductors, both in terms of spatial dimensions and in terms of symmetry classes. It was proposed that K theory is behind the periodicity. On the other hand, D-branes, a solitonic object in string theory, are also known to be classified by K theory. In this paper, by inspecting low-energy effective field theories realized by two parallel D-branes, we establish a one-to-one correspondence between the K-theory classification of topological insulators/superconductors and D-brane charges. In addition, the string theory realization of topological insulators and superconductors comes naturally with gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a gauge field theory of topological nature, such as ones with the Chern-Simons term or the {theta} term in various dimensions. This sheds light on topological insulators and superconductors beyond noninteracting systems, and the underlying topological field theory description thereof. In particular, our string theory realization includes the honeycomb lattice Kitaev model in two spatial dimensions, and its higher-dimensional extensions. Increasing the number of D-branes naturally leads to a realization of topological insulators and superconductors in terms of holography (AdS/CFT).
Topological insulators and superconductors from string theory
NASA Astrophysics Data System (ADS)
Ryu, Shinsei; Takayanagi, Tadashi
2010-10-01
Topological insulators and superconductors in different spatial dimensions and with different discrete symmetries have been fully classified recently, revealing a periodic structure for the pattern of possible types of topological insulators and superconductors, both in terms of spatial dimensions and in terms of symmetry classes. It was proposed that K theory is behind the periodicity. On the other hand, D-branes, a solitonic object in string theory, are also known to be classified by K theory. In this paper, by inspecting low-energy effective field theories realized by two parallel D-branes, we establish a one-to-one correspondence between the K-theory classification of topological insulators/superconductors and D-brane charges. In addition, the string theory realization of topological insulators and superconductors comes naturally with gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a gauge field theory of topological nature, such as ones with the Chern-Simons term or the θ term in various dimensions. This sheds light on topological insulators and superconductors beyond noninteracting systems, and the underlying topological field theory description thereof. In particular, our string theory realization includes the honeycomb lattice Kitaev model in two spatial dimensions, and its higher-dimensional extensions. Increasing the number of D-branes naturally leads to a realization of topological insulators and superconductors in terms of holography (AdS/CFT).
Nonlocal edge state transport in topological insulators
NASA Astrophysics Data System (ADS)
Protogenov, Alexander P.; Verbus, Valery A.; Chulkov, Evgueni V.
2013-11-01
We use the N-terminal scheme for studying the edge-state transport in two-dimensional topological insulators. We find the universal nonlocal response in the ballistic transport approach. This macroscopic exhibition of the topological order offers different areas for applications.
Search for Majorana fermions in topological superconductors.
Pan, Wei; Shi, Xiaoyan; Hawkins, Samuel D.; Klem, John Frederick
2014-10-01
The goal of this project is to search for Majorana fermions (a new quantum particle) in a topological superconductor (a new quantum matter achieved in a topological insulator proximitized by an s-wave superconductor). Majorana fermions (MFs) are electron-like particles that are their own anti-particles. MFs are shown to obey non-Abelian statistics and, thus, can be harnessed to make a fault-resistant topological quantum computer. With the arrival of topological insulators, novel schemes to create MFs have been proposed in hybrid systems by combining a topological insulator with a conventional superconductor. In this LDRD project, we will follow the theoretical proposals to search for MFs in one-dimensional (1D) topological superconductors. 1D topological superconductor will be created inside of a quantum point contact (with the metal pinch-off gates made of conventional s-wave superconductors such as niobium) in a two-dimensional topological insulator (such as inverted type-II InAs/GaSb heterostructure).
New supersymmetric localizations from topological gravity
NASA Astrophysics Data System (ADS)
Bae, Jinbeom; Imbimbo, Camillo; Rey, Soo-Jong; Rosa, Dario
2016-03-01
Supersymmetric field theories can be studied exactly on off-shell "localizing" supergravity backgrounds. We show that these supergravity configurations can be identified with BRST invariant configurations of background topological gravity coupled to background topological gauge multiplets. We apply this topological point of view to two-dimensional {N}=left(2,2right) supersymmetric matter theories to obtain, in a simple and straightforward way, a complete classification of localizing supersymmetric backgrounds in two dimensions. We recover all known localizing backgrounds and (infinitely) many more that have not been explored so far. The newly found localizing backgrounds are characterized by quantized fluxes for both graviphotons of the {N}=left(2,2right) supergravity multiplet. The BRST invariant topological backgrounds are parametrized by both Killing vectors and {{S}}^1 -equivariant cohomology of the two-dimensional spacetime. We completely reconstruct the supergravity backgrounds from the topological data: some of the supergravity fields are twisted versions of the topological backgrounds, but others are composite, in that they are nonlinear functionals of topological fields. Moreover, we show that the supersymmetric Ω-deformation is nothing but the background value of the ghost-for-ghost of topological gravity, a result which holds for higher dimensions too.
Topological Mechanics of Origami and Kirigami.
Chen, Bryan Gin-Ge; Liu, Bin; Evans, Arthur A; Paulose, Jayson; Cohen, Itai; Vitelli, Vincenzo; Santangelo, C D
2016-04-01
Origami and kirigami have emerged as potential tools for the design of mechanical metamaterials whose properties such as curvature, Poisson ratio, and existence of metastable states can be tuned using purely geometric criteria. A major obstacle to exploiting this property is the scarcity of tools to identify and program the flexibility of fold patterns. We exploit a recent connection between spring networks and quantum topological states to design origami with localized folding motions at boundaries and study them both experimentally and theoretically. These folding motions exist due to an underlying topological invariant rather than a local imbalance between constraints and degrees of freedom. We give a simple example of a quasi-1D folding pattern that realizes such topological states. We also demonstrate how to generalize these topological design principles to two dimensions. A striking consequence is that a domain wall between two topologically distinct, mechanically rigid structures is deformable even when constraints locally match the degrees of freedom. PMID:27081987
Topological Mechanics of Origami and Kirigami
NASA Astrophysics Data System (ADS)
Chen, Bryan Gin-ge; Liu, Bin; Evans, Arthur A.; Paulose, Jayson; Cohen, Itai; Vitelli, Vincenzo; Santangelo, C. D.
2016-04-01
Origami and kirigami have emerged as potential tools for the design of mechanical metamaterials whose properties such as curvature, Poisson ratio, and existence of metastable states can be tuned using purely geometric criteria. A major obstacle to exploiting this property is the scarcity of tools to identify and program the flexibility of fold patterns. We exploit a recent connection between spring networks and quantum topological states to design origami with localized folding motions at boundaries and study them both experimentally and theoretically. These folding motions exist due to an underlying topological invariant rather than a local imbalance between constraints and degrees of freedom. We give a simple example of a quasi-1D folding pattern that realizes such topological states. We also demonstrate how to generalize these topological design principles to two dimensions. A striking consequence is that a domain wall between two topologically distinct, mechanically rigid structures is deformable even when constraints locally match the degrees of freedom.
Topological nonsymmorphic ribbons out of symmorphic bulk
NASA Astrophysics Data System (ADS)
Araújo, Augusto L.; Wrasse, Ernesto O.; Ferreira, Gerson J.; Schmidt, Tome M.
2016-04-01
States of matter with nontrivial topology have been classified by their bulk symmetry properties. However, by cutting the topological insulator into ribbons, the symmetry of the system is reduced. By constructing effective Hamiltonians containing the proper symmetry of the ribbon, we find that the nature of topological states is dependent on the reduced symmetry of the ribbon and the appropriate boundary conditions. We apply our model to the recently discovered two-dimensional topological crystalline insulators composed by IV-VI monolayers, where we verify that the edge terminations play a major role on the Dirac crossings. Particularly, we find that some bulk cuts lead to nonsymmorphic ribbons, even though the bulk material is symmorphic. The nonsymmorphism yields a new topological protection, where the Dirac cone is preserved for arbitrary ribbon width. The effective Hamiltonians are in good agreement with ab initio calculations.
Constraints on topological order in mott insulators.
Zaletel, Michael P; Vishwanath, Ashvin
2015-02-20
We point out certain symmetry induced constraints on topological order in Mott insulators (quantum magnets with an odd number of spin 1/2 moments per unit cell). We show, for example, that the double-semion topological order is incompatible with time reversal and translation symmetry in Mott insulators. This sharpens the Hastings-Oshikawa-Lieb-Schultz-Mattis theorem for 2D quantum magnets, which guarantees that a fully symmetric gapped Mott insulator must be topologically ordered, but is silent about which topological order is permitted. Our result applies to the kagome lattice quantum antiferromagnet, where recent numerical calculations of the entanglement entropy indicate a ground state compatible with either toric code or double-semion topological order. Our result rules out the latter possibility. PMID:25763971
Topological Crystalline Insulator Phase in Graphene Multilayers
NASA Astrophysics Data System (ADS)
Kindermann, M.
2015-06-01
While the experimental progress on three dimensional topological insulators is rapid, the development of their 2D counterparts has been comparatively slow, despite their technological promise. The main reason is materials challenges of the to date only realizations of 2D topological insulators, in semiconductor quantum wells. Here we identify a 2D topological insulator in a material which does not face similar challenges and which is by now most widely available and well charaterized: graphene. For certain commensurate interlayer twists, graphene multilayers are insulators with sizable band gaps. We show that they are moreover in a topological phase protected by crystal symmetry. As its fundamental signature, this topological state supports one-dimensional boundary modes. They form low-dissipation quantum wires that can be defined purely electrostatically.
Measuring the topology of the universe
Cornish, Neil J.; Spergel, David N.; Starkman, Glenn D.
1998-01-01
Observations of microwave background fluctuations can yield information not only about the geometry of the universe but potentially about the topology of the universe. If the universe is negatively curved, then the characteristic scale for the topology of the universe is the curvature radius. Thus, if we are seeing the effects of the geometry of the universe, we can hope to soon see signatures of the topology of the universe. The cleanest signature of the topology of the universe is written on the microwave sky: There should be thousands of pairs of matched circles. These circles can be used to determine the precise topology and volume of the universe. Because we see hundreds of slices through the fundamental domain of the universe, we can use the microwave observations to reconstruct the initial conditions of the entire universe on the scale of a few megaparsecs. PMID:9419329
Topological Phases of Sound and Light
NASA Astrophysics Data System (ADS)
Peano, V.; Brendel, C.; Schmidt, M.; Marquardt, F.
2015-07-01
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.
Intrinsic topological superfluidity - fluctuations and response
NASA Astrophysics Data System (ADS)
Levin, K.; Wu, Chien-Te; Anderson, Brandon; Boyack, Rufus
Recent interest in topological superconductivity is based primarily on exploiting proximity effects to obtain this important phase. However, in cold gases it is possible to contemplate ``intrinsic'' topological superfluidity produced with a synthetic spin-orbit coupling and Zeeman field. It is important for such future experiments to establish how low in temperature one needs to go to reach the ordered phase. Similarly, it will be helpful to have a probe of the normal (pseudogap) phase to determine if the ultimate superfluid order will be topological or trivial. In this talk, we address these issues by considering fluctuation effects in such a superfluid, and calculate the critical transition temperature and response functions. We see qualitative signatures of topological superfluidity in spin and charge response functions. We also explore the suppression of superfluidity due to fluctuations, and importantly find that the temperature scales necessary to reach topological superfluidity are reasonably accessible
Topological superradiance in a degenerate Fermi gas
NASA Astrophysics Data System (ADS)
Pan, Jian-Song; Liu, Xiong-Jun; Zhang, Wei; Yi, Wei; Guo, Guang-Can; Yi's Group Team; Liu's Group Team; Zhang's Group Team
2015-05-01
We predict the existence of a topological superradiant state in a two-component degenerate Fermi gas in a cavity. The superradiant light generation in the transversely driven cavity mode induces a cavity-assisted spin-orbit coupling in the system and opens a bulk gap at half filling. This mechanism can simultaneously drive a topological phase transition in the system, yielding a topological superradiant state. We map out the steady-state phase diagram of the system in the presence of an effective Zeeman field, and identify a critical tetracritical point beyond which the topological and the conventional superraidiant phase boundaries separate. We propose to detect the topological phase transition based on its signatures in either the momentum distribution of the atoms or in the cavity photon occupation.
DETECTION OF TOPOLOGICAL PATTERNS IN PROTEIN NETWORKS.
MASLOV,S.SNEPPEN,K.
2003-11-17
Complex networks appear in biology on many different levels: (1) All biochemical reactions taking place in a single cell constitute its metabolic network, where nodes are individual metabolites, and edges are metabolic reactions converting them to each other. (2) Virtually every one of these reactions is catalyzed by an enzyme and the specificity of this catalytic function is ensured by the key and lock principle of its physical interaction with the substrate. Often the functional enzyme is formed by several mutually interacting proteins. Thus the structure of the metabolic network is shaped by the network of physical interactions of cell's proteins with their substrates and each other. (3) The abundance and the level of activity of each of the proteins in the physical interaction network in turn is controlled by the regulatory network of the cell. Such regulatory network includes all of the multiple mechanisms in which proteins in the cell control each other including transcriptional and translational regulation, regulation of mRNA editing and its transport out of the nucleus, specific targeting of individual proteins for degradation, modification of their activity e.g. by phosphorylation/dephosphorylation or allosteric regulation, etc. To get some idea about the complexity and interconnectedness of protein-protein regulations in baker's yeast Saccharomyces Cerevisiae in Fig. 1 we show a part of the regulatory network corresponding to positive or negative regulations that regulatory proteins exert on each other. (4) On yet higher level individual cells of a multicellular organism exchange signals with each other. This gives rise to several new networks such as e.g. nervous, hormonal, and immune systems of animals. The intercellular signaling network stages the development of a multicellular organism from the fertilized egg. (5) Finally, on the grandest scale, the interactions between individual species in ecosystems determine their food webs. An interesting
NASA Astrophysics Data System (ADS)
Liu, Jie; Wen, Guilin; Zhi Zuo, Hao; Qing, Qixiang
2016-07-01
The structural configuration obtained by deterministic topology optimization may represent a low reliability level and lead to a high failure rate. Therefore, it is necessary to take reliability into account for topology optimization. By integrating reliability analysis into topology optimization problems, a simple reliability-based topology optimization (RBTO) methodology for continuum structures is investigated in this article. The two-layer nesting involved in RBTO, which is time consuming, is decoupled by the use of a particular optimization procedure. A topology description function approach (TOTDF) and a first order reliability method are employed for topology optimization and reliability calculation, respectively. The problem of the non-smoothness inherent in TOTDF is dealt with using two different smoothed Heaviside functions and the corresponding topologies are compared. Numerical examples demonstrate the validity and efficiency of the proposed improved method. In-depth discussions are also presented on the influence of different structural reliability indices on the final layout.
Dual-topology insertion of a dual-topology membrane protein
Woodall, Nicholas B.; Yin, Ying; Bowie, James U.
2015-01-01
Some membrane transporters are dual-topology dimers in which the subunits have inverted transmembrane topology. How a cell manages to generate equal populations of two opposite topologies from the same polypeptide chain remains unclear. For the dual-topology transporter EmrE, the evidence to date remains consistent with two extreme models. A post-translational model posits that topology remains malleable after synthesis and becomes fixed once the dimer forms. A second, co-translational model, posits that the protein inserts in both topologies in equal proportions. Here we show that while there is at least some limited topological malleability, the co-translational model likely dominates under normal circumstances. PMID:26306475
Respiratory and psychiatric abnormalities in chronic symptomatic hyperventilation.
Bass, C; Gardner, W N
1985-01-01
Many physicians believe that the hyperventilation syndrome is invariably associated with anxiety or undiagnosed organic disease such as asthma and pulmonary embolus, or both. Twenty one patients referred by specialist physicians with unexplained somatic symptoms and unequivocal chronic hypocapnia (resting end tidal Pco2 less than or equal to 4 kPa (30 mm Hg) on repeated occasions during prolonged measurement) were investigated. All but one complained of inability to take a satisfying breath. Standard lung function test results and chest radiographs were normal in all patients, but histamine challenge showed bronchial hyper-reactivity in two of 20 patients tested, and skin tests to common allergens were positive in three of 18. Ventilation-perfusion scanning was abnormal in a further three of 15 patients studied, with unmatched perfusion defects in two and isolated ventilation defects in one. None of the 21 had thyrotoxicosis, severe coronary heart disease, or other relevant cardiovascular abnormalities. Ten of the 21 patients were neurotic and suffered from chronic psychiatric disturbance characterised by anxiety, panic, and phobic symptoms. The remainder had no detectable psychiatric disorders but reported proportionately more somatic than anxiety symptoms. Severe hyperventilation can occur in the absence of formal psychiatric or detectable respiratory or other organic abnormalities. Asthma and pulmonary embolus must be specifically excluded. PMID:3922504
QCD as a topologically ordered system
Zhitnitsky, Ariel R.
2013-09-15
We argue that QCD belongs to a topologically ordered phase similar to many well-known condensed matter systems with a gap such as topological insulators or superconductors. Our arguments are based on an analysis of the so-called “deformed QCD” which is a weakly coupled gauge theory, but nevertheless preserves all the crucial elements of strongly interacting QCD, including confinement, nontrivial θ dependence, degeneracy of the topological sectors, etc. Specifically, we construct the so-called topological “BF” action which reproduces the well known infrared features of the theory such as non-dispersive contribution to the topological susceptibility which cannot be associated with any propagating degrees of freedom. Furthermore, we interpret the well known resolution of the celebrated U(1){sub A} problem where the would be η{sup ′} Goldstone boson generates its mass as a result of mixing of the Goldstone field with a topological auxiliary field characterizing the system. We then identify the non-propagating auxiliary topological field of the BF formulation in deformed QCD with the Veneziano ghost (which plays the crucial role in resolution of the U(1){sub A} problem). Finally, we elaborate on relation between “string-net” condensation in topologically ordered condensed matter systems and long range coherent configurations, the “skeletons”, studied in QCD lattice simulations. -- Highlights: •QCD may belong to a topologically ordered phase similar to condensed matter (CM) systems. •We identify the non-propagating topological field in deformed QCD with the Veneziano ghost. •Relation between “string-net” condensates in CM systems and the “skeletons” in QCD lattice simulations is studied.
Babichev, E.
2006-10-15
We consider global topological defects in symmetry-breaking models with a noncanonical kinetic term. Apart from a mass parameter entering the potential, one additional dimensional parameter arises in such models - a kinetic mass. The properties of defects in these models are quite different from standard global domain walls, vortices, and monopoles, if their kinetic mass scale is smaller than their symmetry-breaking scale. In particular, depending on the concrete form of the kinetic term, the typical size of such a defect can be either much larger or much smaller than the size of a standard defect with the same potential term. The characteristic mass of a nonstandard defect, which might have been formed during a phase transition in the early universe, depends on both the temperature of a phase transition and the kinetic mass.
Topological classification of Brownian orbits.
Tanaka, Fumihiko
2012-09-14
This paper presents the exact formula for the bivariate probability distribution function of a Brownian particle as a function of its position and velocity, whose orbit makes a specified number of turns around an infinite straight line. In the limit of large friction constant, the solution reduces to the well-known results for random Wiener paths. Topological entanglements of stiff polymers are discussed on the basis of this solution. The method to find the solution is applied to the velocity space of a Brownian motion, and the probability to find a closed path with a specified winding number is obtained. Hence, closed two-dimensional Brownian orbits are classified into regular homotopy classes, whose statistical weight is derived as a function of the total length and the friction constant. PMID:22979890
Topological approach of Jungian psychology.
Viret, Jacques
2010-09-01
In this work, we compare two global approaches which are usually considered as completely unconnected one with the other. The former is Thom's topology and the latter is Jung's psychology. More precisely, it seemed to us interesting to adapt some morphologies of Thom's catastrophe theory to some Jung's notions. Thus, we showed that the swallowtail, which is one of these morphologies, was able to describe geometrically the structural organisation of the psyche according to Jung, with its collective unconscious, personal unconscious and conscious. Moreover, we have correlated this morphology with Jung's evolutive processes like individualization and individuation. These comparisons incited us to think that some morphologies of Thom's catastrophe theory are the geometrical dealing of Jung's archetypes. PMID:20658172
Homotopy theory in toric topology
NASA Astrophysics Data System (ADS)
Grbić, J.; Theriault, S.
2016-04-01
In toric topology one associates with each simplicial complex K on m vertices two key spaces, the Davis-Januszkiewicz space DJK and the moment-angle complex \\mathscr{Z}K, which are related by a homotopy fibration \\mathscr{Z}K\\xrightarrow{\\tilde{w}}DJ_K\\to \\prodi=1m{C}P∞. A great deal of work has been done to study the properties of DJK and \\mathscr{Z}K, their generalizations to polyhedral products, and applications to algebra, combinatorics, and geometry. Chap. 1 surveys some of the main results in the homotopy theory of these spaces. Chap. 2 breaks new ground by initiating a study of the map \\tilde{w}. It is shown that, for a certain family of simplicial complexes K, the map \\tilde{w} is a sum of higher and iterated Whitehead products. Bibliography: 49 titles.
Abnormal gephyrin immunoreactivity associated with Alzheimer disease pathologic changes.
Hales, Chadwick M; Rees, Howard; Seyfried, Nicholas T; Dammer, Eric B; Duong, Duc M; Gearing, Marla; Montine, Thomas J; Troncoso, Juan C; Thambisetty, Madhav; Levey, Allan I; Lah, James J; Wingo, Thomas S
2013-11-01
Many neurodegenerative disorders involve the abnormal accumulation of proteins. In addition to the pathologic hallmarks of neurofibrillary tangles and β-amyloid plaques in Alzheimer disease (AD), here we show that abnormal accumulations of gephyrin, an inhibitory receptor-anchoring protein, are highly correlated with the neuropathologic diagnosis of AD in 17 AD versus 14 control cases. Furthermore, gephyrin accumulations were specific for AD and not seen in normal controls or other neurodegenerative diseases including Parkinson disease, corticobasal degeneration, and frontotemporal degeneration. Gephyrin accumulations in AD overlapped with β-amyloid plaques and, more rarely, neurofibrillary tangles. Biochemical and proteomic studies of AD and control brain samples suggested alterations in gephyrin solubility and reveal elevated levels of gephyrin lower-molecular-weight species in the AD insoluble fraction. Because gephyrin is involved in synaptic organization and synaptic dysfunction is an early event in AD, these findings point to its possible role in the pathogenesis of AD. PMID:24128675
Sweating in Systemic Abnormalities: Uremia and Diabetes Mellitus.
Murota, Hiroyuki
2016-01-01
Sweating disorders are sometimes observed in various systemic diseases that include genetic disorders, organ damage, metabolic impairment, autoimmune diseases, and neuropathic disorders. In these diseases, various symptoms such as autonomic failures, psychopathic disorders, abnormal skin innervation, and sweat gland dysfunction can interact with one another in diverse ways, resulting in impaired sweating. This review focuses on the influence of uremia (with or without hemodialysis) and diabetes mellitus on impaired sweating. Dialysis patients perspire less, but their sweat contains higher levels of uremic toxins than do healthy subjects. Neuropathic disorders in diabetes patients develop in relation to disease severity and can impair sweating. Physicians should consider the development of various problems, such as increased body temperature, dry skin, and increased susceptibility to infection, due to decreased sweating, as they are often found in these systemic abnormalities. PMID:27584963
Phenotypic abnormalities in long-term surviving cystic fibrosis mice.
Kent, G; Oliver, M; Foskett, J K; Frndova, H; Durie, P; Forstner, J; Forstner, G G; Riordan, J R; Percy, D; Buchwald, M
1996-08-01
Mouse models for cystic fibrosis (CF) with no CFTR function (Cftr-/-) have the disadvantage that most animals die of intestinal obstruction shortly after weaning. The objective of this research was to extend the lifespan of CF mice and characterize their phenotype. Weanlings were placed on a nutrient liquid diet, and histologic and functional aspects of organs implicated in the disease were subsequently examined. Approximately 90% of Cftr-/- mice survived to 60 d, the majority beyond 100 d. Cftr-/- mice were underweight and had markedly abnormal intestinal histology. The intestinal epithelia did not respond to challenges with agents that raised intracellular cAMP, consistent with the absence of functional CFTR. No lesions or functional abnormalities were evident in the lungs. Liquid-fed Cftr-/- mice were infertile, although some males weaned to a solid diet were fertile before they died. Thus, we have succeeded in using dietary means to prolong the lives of Cftr-/- mice. PMID:8827771
Sleep physiology, abnormal States, and therapeutic interventions.
Wickboldt, Alvah T; Bowen, Alex F; Kaye, Aaron J; Kaye, Adam M; Rivera Bueno, Franklin; Kaye, Alan D
2012-01-01
Sleep is essential. Unfortunately, a significant portion of the population experiences altered sleep states that often result in a multitude of health-related issues. The regulation of sleep and sleep-wake cycles is an area of intense research, and many options for treatment are available. The following review summarizes the current understanding of normal and abnormal sleep-related conditions and the available treatment options. All clinicians managing patients must recommend appropriate therapeutic interventions for abnormal sleep states. Clinicians' solid understanding of sleep physiology, abnormal sleep states, and treatments will greatly benefit patients regardless of their disease process. PMID:22778676
Sleep Physiology, Abnormal States, and Therapeutic Interventions
Wickboldt, Alvah T.; Bowen, Alex F.; Kaye, Aaron J.; Kaye, Adam M.; Rivera Bueno, Franklin; Kaye, Alan D.
2012-01-01
Sleep is essential. Unfortunately, a significant portion of the population experiences altered sleep states that often result in a multitude of health-related issues. The regulation of sleep and sleep-wake cycles is an area of intense research, and many options for treatment are available. The following review summarizes the current understanding of normal and abnormal sleep-related conditions and the available treatment options. All clinicians managing patients must recommend appropriate therapeutic interventions for abnormal sleep states. Clinicians' solid understanding of sleep physiology, abnormal sleep states, and treatments will greatly benefit patients regardless of their disease process. PMID:22778676
Right Liver Lobe Hypoplasia and Related Abnormalities
Alicioglu, Banu
2015-01-01
Summary Background Hypoplasia and agenesis of the liver lobe is a rare abnormality. It is associated with biliary system abnormalities, high location of the right kidney, and right colon interposition. These patients are prone to gallstones, portal hypertension and possible surgical complications because of anatomical disturbance. Case Report Magnetic resonance imaging features of a rare case of hypoplasia of the right lobe of the liver in a sigmoid cancer patient are presented. Conclusions Hypoplasia of the right liver should not be confused with liver atrophy; indeed, associations with other coexistent abnormalities are also possible. Awareness and familiarity with these anomalies are necessary to avoid fatal surgical and interventional complications. PMID:26634012
Numerically abnormal chromosome constitutions in humans
1993-12-31
Chapter 24, discusses numerically abnormal chromosome constitutions in humans. This involves abnormalities of human chromosome number, including polyploidy (when the number of sets of chromosomes increases) and aneuploidy (when the number of individual normal chromosomes changes). Chapter sections discuss the following chromosomal abnormalities: human triploids, imprinting and uniparental disomy, human tetraploids, hydatidiform moles, anomalies caused by chromosomal imbalance, 13 trisomy (D{sub 1} trisomy, Patau syndrome), 21 trisomy (Down syndrome), 18 trisomy syndrome (Edwards syndrome), other autosomal aneuploidy syndromes, and spontaneous abortions. The chapter concludes with remarks on the nonrandom participation of chromosomes in trisomy. 69 refs., 3 figs., 4 tabs.
Dynamic membrane protein topological switching upon changes in phospholipid environment
Vitrac, Heidi; MacLean, David M.; Jayaraman, Vasanthi; Bogdanov, Mikhail; Dowhan, William
2015-01-01
A fundamental objective in membrane biology is to understand and predict how a protein sequence folds and orients in a lipid bilayer. Establishing the principles governing membrane protein folding is central to understanding the molecular basis for membrane proteins that display multiple topologies, the intrinsic dynamic organization of membrane proteins, and membrane protein conformational disorders resulting in disease. We previously established that lactose permease of Escherichia coli displays a mixture of topological conformations and undergoes postassembly bidirectional changes in orientation within the lipid bilayer triggered by a change in membrane phosphatidylethanolamine content, both in vivo and in vitro. However, the physiological implications and mechanism of dynamic structural reorganization of membrane proteins due to changes in lipid environment are limited by the lack of approaches addressing the kinetic parameters of transmembrane protein flipping. In this study, real-time fluorescence spectroscopy was used to determine the rates of protein flipping in the lipid bilayer in both directions and transbilayer flipping of lipids triggered by a change in proteoliposome lipid composition. Our results provide, for the first time to our knowledge, a dynamic picture of these events and demonstrate that membrane protein topological rearrangements in response to lipid modulations occur rapidly following a threshold change in proteoliposome lipid composition. Protein flipping was not accompanied by extensive lipid-dependent unfolding of transmembrane domains. Establishment of lipid bilayer asymmetry was not required but may accelerate the rate of protein flipping. Membrane protein flipping was found to accelerate the rate of transbilayer flipping of lipids. PMID:26512118
Topology of transmembrane channel-like gene 1 protein.
Labay, Valentina; Weichert, Rachel M; Makishima, Tomoko; Griffith, Andrew J
2010-10-01
Mutations of transmembrane channel-like gene 1 (TMC1) cause hearing loss in humans and mice. TMC1 is the founding member of a family of genes encoding proteins of unknown function that are predicted to contain multiple transmembrane domains. The goal of our study was to define the topology of mouse TMC1 expressed heterologously in tissue culture cells. TMC1 was retained in the endoplasmic reticulum (ER) membrane of five tissue culture cell lines that we tested. We used anti-TMC1 and anti-HA antibodies to probe the topologic orientation of three native epitopes and seven HA epitope tags along full-length TMC1 after selective or complete permeabilization of transfected cells with digitonin or Triton X-100, respectively. TMC1 was present within the ER as an integral membrane protein containing six transmembrane domains and cytosolic N- and C-termini. There is a large cytoplasmic loop, between the fourth and fifth transmembrane domains, with two highly conserved hydrophobic regions that might associate with or penetrate, but do not span, the plasma membrane. Our study is the first to demonstrate that TMC1 is a transmembrane protein. The topologic organization revealed by this study shares some features with that of the shaker-TRP superfamily of ion channels. PMID:20672865
NASA Astrophysics Data System (ADS)
Furusaki, Akira; Nagaosa, Naoto; Nomura, Kentaro; Ryu, Shinsei; Takayanagi, Tadashi
2013-11-01
We discuss the thermal (or gravitational) responses in topological superconductors and in topological phases in general. Such thermal responses (as well as electromagnetic responses for conserved charge) provide a definition of topological insulators and superconductors beyond the single-particle picture. In two-dimensional topological phases, the Strěda formula for the electric Hall conductivity is generalized to the thermal Hall conductivity. Applying this formula to the Majorana surface states of three-dimensional topological superconductors predicts cross-correlated responses between the angular momentum and thermal polarization (entropy polarization). We also discuss a use of D-branes in string theory as a systematic tool to derive all such topological terms and topological responses. In particular, we relate the Z2 index of topological insulators introduced by Kane and Mele (and its generalization to other symmetry classes and to arbitrary dimensions) to the K-theory charge of non-BPS D-branes, and vice versa. We thus establish a link between the stability of non-BPS D-branes and the topological stability of topological insulators.
Topological lasing in resonant photonic structures
NASA Astrophysics Data System (ADS)
Pilozzi, Laura; Conti, Claudio
2016-05-01
We exploit topological edge states in resonant photonic crystals to attain strongly localized resonances and demonstrate lasing in these modes upon optical excitation. The use of virtually lossless topologically isolated edge states may lead to a class of thresholdless lasers operating without inversion. One needs, however, to understand whether topological states may be coupled to external radiation and act as active cavities. We study a two-level topological insulator and show that self-induced transparency pulses can directly excite edge states. We simulate laser emission by a suitably designed topological cavity and show that it can emit tunable radiation. For a configuration of sites following the off-diagonal Aubry-André-Harper model, we solve the Maxwell-Bloch equations in the time domain and provide a first-principles confirmation of topological lasers. Our results open the road to a class of light emitters with topological protection for applications ranging from low-cost energetically effective integrated laser sources, also including silicon photonics, to strong-coupling devices for studying ultrafast quantum processes with engineered vacuum.
Holographic entanglement renormalization of topological insulators
NASA Astrophysics Data System (ADS)
Wen, Xueda; Cho, Gil Young; Lopes, Pedro L. S.; Gu, Yingfei; Qi, Xiao-Liang; Ryu, Shinsei
2016-08-01
We study the real-space entanglement renormalization group flows of topological band insulators in (2+1) dimensions by using the continuum multiscale entanglement renormalization ansatz (cMERA). Given the ground state of a Chern insulator, we construct and study its cMERA by paying attention, in particular, to how the bulk holographic geometry and the Berry curvature depend on the topological properties of the ground state. It is found that each state defined at different energy scale of cMERA carries a nonzero Berry flux, which is emanated from the UV layer of cMERA, and flows towards the IR. Hence, a topologically nontrivial UV state flows under the renormalization group to an IR state, which is also topologically nontrivial. On the other hand, we found that there is an obstruction to construct the exact ground state of a topological insulator with a topologically trivial IR state. That is, if we try to construct a cMERA for the ground state of a Chern insulator by taking a topologically trivial IR state, the resulting cMERA does not faithfully reproduce the exact ground state at all length scales.
Robust interface between flying and topological qubits
Xue, Zheng-Yuan; Gong, Ming; Liu, Jia; Hu, Yong; Zhu, Shi-Liang; Wang, Z. D.
2015-01-01
Hybrid architectures, consisting of conventional and topological qubits, have recently attracted much attention due to their capability in consolidating robustness of topological qubits and universality of conventional qubits. However, these two kinds of qubits are normally constructed in significantly different energy scales, and thus the energy mismatch is a major obstacle for their coupling, which can support the exchange of quantum information between them. Here we propose a microwave photonic quantum bus for a strong direct coupling between the topological and conventional qubits, where the energy mismatch is compensated by an external driving field. In the framework of tight-binding simulation and perturbation approach, we show that the energy splitting of Majorana fermions in a finite length nanowire, which we use to define topological qubits, is still robust against local perturbations due to the topology of the system. Therefore, the present scheme realizes a rather robust interface between the flying and topological qubits. Finally, we demonstrate that this quantum bus can also be used to generate multipartitie entangled states with the topological qubits. PMID:26216201
Experimental realization of microwave photonic topological insulators
NASA Astrophysics Data System (ADS)
Dong, Jianwen
2015-03-01
Topological properties play a fundamental role in many physical phenomena. While topology focus on electronic systems, there has been a recent emergence of interest in exploring topological orders with photons. Recent experiments have demonstrated substantial progress towards the implementation of Hamiltonians with topological robustness, from microwave to visible frequency domains. Here, we will show the demonstration on nontrivial photonic bandgaps, as well as the topologically protected edge states. We designed and fabricated a metacrystal comprising non-resonant meta-atoms sandwiched between two metallic plates. Spin Chern number of photonic crystals is calculated based on group theory and accurately predicts topological characters of edge states in different gaps. Topologically nontrivial gaps are achieved by mode exchange at high symmetric k-points. Nontrivial bandgap was confirmed by experimentally measured transmission spectra and calculated nonzero spin Chern number. Gapless spin-filtered edge states were demonstrated experimentally by measuring Ez fields and Hz fields, as well as their phase differences. Robustness of the edge states were also observed when an obstacle is introduced near the edge.
How to model wireless mesh networks topology
NASA Astrophysics Data System (ADS)
Sanni, M. L.; Hashim, A. A.; Anwar, F.; Ahmed, G. S. M.; Ali, S.
2013-12-01
The specification of network connectivity model or topology is the beginning of design and analysis in Computer Network researches. Wireless Mesh Networks is an autonomic network that is dynamically self-organised, self-configured while the mesh nodes establish automatic connectivity with the adjacent nodes in the relay network of wireless backbone routers. Researches in Wireless Mesh Networks range from node deployment to internetworking issues with sensor, Internet and cellular networks. These researches require modelling of relationships and interactions among nodes including technical characteristics of the links while satisfying the architectural requirements of the physical network. However, the existing topology generators model geographic topologies which constitute different architectures, thus may not be suitable in Wireless Mesh Networks scenarios. The existing methods of topology generation are explored, analysed and parameters for their characterisation are identified. Furthermore, an algorithm for the design of Wireless Mesh Networks topology based on square grid model is proposed in this paper. The performance of the topology generated is also evaluated. This research is particularly important in the generation of a close-to-real topology for ensuring relevance of design to the intended network and validity of results obtained in Wireless Mesh Networks researches.
Topological phases: An expedition off lattice
Freedman, Michael H.; Gamper, Lukas; Gils, Charlotte; Isakov, Sergei V.; Trebst, Simon; Troyer, Matthias
2011-08-15
Highlights: > Models of topological phases where the lattice topology is a dynamical variable. > We discuss off-lattice hazards that destroy topological protection. > The Cheeger constant yields upper bound to the energy of excited states. > Baby universes meet condensed matter physics. > We study the graph Laplacian of loop gases and string nets on fluctuating lattices. - Abstract: Motivated by the goal to give the simplest possible microscopic foundation for a broad class of topological phases, we study quantum mechanical lattice models where the topology of the lattice is one of the dynamical variables. However, a fluctuating geometry can remove the separation between the system size and the range of local interactions, which is important for topological protection and ultimately the stability of a topological phase. In particular, it can open the door to a pathology, which has been studied in the context of quantum gravity and goes by the name of 'baby universe', here we discuss three distinct approaches to suppressing these pathological fluctuations. We complement this discussion by applying Cheeger's theory relating the geometry of manifolds to their vibrational modes to study the spectra of Hamiltonians. In particular, we present a detailed study of the statistical properties of loop gas and string net models on fluctuating lattices, both analytically and numerically.
Strain-Induced Ferroelectric Topological Insulator.
Liu, Shi; Kim, Youngkuk; Tan, Liang Z; Rappe, Andrew M
2016-03-01
Ferroelectricity and band topology are two extensively studied yet distinct properties of insulators. Nonetheless, their coexistence has never been observed in a single material. Using first-principles calculations, we demonstrate that a noncentrosymmetric perovskite structure of CsPbI3 allows for the simultaneous presence of ferroelectric and topological orders with appropriate strain engineering. Metallic topological surface states create an intrinsic short-circuit condition, helping stabilize bulk polarization. Exploring diverse structural phases of CsPbI3 under pressure, we identify that the key structural feature for achieving a ferroelectric topological insulator is to suppress PbI6 cage rotation in the perovskite structure, which could be obtained via strain engineering. Ferroelectric control over the density of topological surface states provides a new paradigm for device engineering, such as perfect-focusing Veselago lens and spin-selective electron collimator. Our results suggest that CsPbI3 is a simple model system for ferroelectric topological insulators, enabling future studies exploring the interplay between conventional symmetry-breaking and topological orders and their novel applications in electronics and spintronics. PMID:26814668
Topological photonic phase in chiral hyperbolic metamaterials.
Gao, Wenlong; Lawrence, Mark; Yang, Biao; Liu, Fu; Fang, Fengzhou; Béri, Benjamin; Li, Jensen; Zhang, Shuang
2015-01-23
Recently, the possibility of achieving one-way backscatter immune transportation of light by mimicking the topological properties of certain solid state systems, such as topological insulators, has received much attention. Thus far, however, demonstrations of nontrivial topology in photonics have relied on photonic crystals with precisely engineered lattice structures, periodic on the scale of the operational wavelength and composed of finely tuned, complex materials. Here we propose a novel effective medium approach towards achieving topologically protected photonic surface states robust against disorder on all length scales and for a wide range of material parameters. Remarkably, the nontrivial topology of our metamaterial design results from the Berry curvature arising from the transversality of electromagnetic waves in a homogeneous medium. Our investigation therefore acts to bridge the gap between the advancing field of topological band theory and classical optical phenomena such as the spin Hall effect of light. The effective medium route to topological phases will pave the way for highly compact one-way transportation of electromagnetic waves in integrated photonic circuits. PMID:25659022
Topological Z2 Gapless Photonic Crystals
NASA Astrophysics Data System (ADS)
Xie, Biye; Wang, Zidan
Topological properties of electronic materials with gapless band structure such as Topological Semimetals(TSMs) and Topological Metals(TMs) have drew lots of attention to both theoretical and experimental physicists recently. Although theoretical prediction of TSMs and TMs have been done well, experimental study of them is quite difficult to perform due to the fact that it is very difficult to control and design certain electronic materials. However, since the topological properties stem from the geometric feature, we can study them in Photonic Crystals(PhCs) which are much easy to be controlled and designed. Here we study 2-dimension PhCs consisting of gyrotropic materials with hexagonal structure. In the Brillouin corner, the dispersion relation has gapless points which are similar to Dirac Cones in electronic materials. We firstly derive the effective Hamiltonian of this system and show that if certain perturbation is added to this effective Hamiltonian, this system belongs to AII class according to Altland and Zirbauer topological classification and is described by a Z2 topological charge. Finally we also propose a way to detect this Z2 topological charge using momentum space Aharonov-Bohm interferometer which is firstly proposed by L.Duca and T.Li,etc.
Persistent topological features of dynamical systems
NASA Astrophysics Data System (ADS)
Maletić, Slobodan; Zhao, Yi; Rajković, Milan
2016-05-01
Inspired by an early work of Muldoon et al., Physica D 65, 1-16 (1993), we present a general method for constructing simplicial complex from observed time series of dynamical systems based on the delay coordinate reconstruction procedure. The obtained simplicial complex preserves all pertinent topological features of the reconstructed phase space, and it may be analyzed from topological, combinatorial, and algebraic aspects. In focus of this study is the computation of homology of the invariant set of some well known dynamical systems that display chaotic behavior. Persistent homology of simplicial complex and its relationship with the embedding dimensions are examined by studying the lifetime of topological features and topological noise. The consistency of topological properties for different dynamic regimes and embedding dimensions is examined. The obtained results shed new light on the topological properties of the reconstructed phase space and open up new possibilities for application of advanced topological methods. The method presented here may be used as a generic method for constructing simplicial complex from a scalar time series that has a number of advantages compared to the mapping of the same time series to a complex network.
Persistent topological features of dynamical systems.
Maletić, Slobodan; Zhao, Yi; Rajković, Milan
2016-05-01
Inspired by an early work of Muldoon et al., Physica D 65, 1-16 (1993), we present a general method for constructing simplicial complex from observed time series of dynamical systems based on the delay coordinate reconstruction procedure. The obtained simplicial complex preserves all pertinent topological features of the reconstructed phase space, and it may be analyzed from topological, combinatorial, and algebraic aspects. In focus of this study is the computation of homology of the invariant set of some well known dynamical systems that display chaotic behavior. Persistent homology of simplicial complex and its relationship with the embedding dimensions are examined by studying the lifetime of topological features and topological noise. The consistency of topological properties for different dynamic regimes and embedding dimensions is examined. The obtained results shed new light on the topological properties of the reconstructed phase space and open up new possibilities for application of advanced topological methods. The method presented here may be used as a generic method for constructing simplicial complex from a scalar time series that has a number of advantages compared to the mapping of the same time series to a complex network. PMID:27249945
Vootla, Vamshidhar R.; Daniel, Myrta
2015-01-01
Refeeding syndrome is defined as electrolyte and fluid abnormalities that occur in significantly malnourished patients when they are refed orally, enterally, or parenterally. The principal manifestations include hypophosphatemia, hypokalemia, vitamin deficiencies, volume overload and edema. This can affect multiple organ systems, such as the cardiovascular, pulmonary, or neurological systems, secondary to the above-mentioned abnormalities. Rarely, patients may develop gastrointestinal symptoms and show abnormal liver function test results. We report the case of a 52-year-old woman with anorexia nervosa who developed refeeding syndrome and simultaneous elevations of liver function test results, which normalized upon the resolution of the refeeding syndrome. PMID:26351414
Frequency Dependent Topological Patterns of Resting-State Brain Networks
Qian, Long; Zhang, Yi; Zheng, Li; Shang, Yuqing; Gao, Jia-Hong; Liu, Yijun
2015-01-01
The topological organization underlying brain networks has been extensively investigated using resting-state fMRI, focusing on the low frequency band from 0.01 to 0.1 Hz. However, the frequency specificities regarding the corresponding brain networks remain largely unclear. In the current study, a data-driven method named complementary ensemble empirical mode decomposition (CEEMD) was introduced to separate the time series of each voxel into several intrinsic oscillation rhythms with distinct frequency bands. Our data indicated that the whole brain BOLD signals could be automatically divided into five specific frequency bands. After applying the CEEMD method, the topological patterns of these five temporally correlated networks were analyzed. The results showed that global topological properties, including the network weighted degree, network efficiency, mean characteristic path length and clustering coefficient, were observed to be most prominent in the ultra-low frequency bands from 0 to 0.015 Hz. Moreover, the saliency of small-world architecture demonstrated frequency-density dependency. Compared to the empirical mode decomposition method (EMD), CEEMD could effectively eliminate the mode-mixing effects. Additionally, the robustness of CEEMD was validated by the similar results derived from a split-half analysis and a conventional frequency division method using the rectangular window band-pass filter. Our findings suggest that CEEMD is a more effective method for extracting the intrinsic oscillation rhythms embedded in the BOLD signals than EMD. The application of CEEMD in fMRI data analysis will provide in-depth insight in investigations of frequency specific topological patterns of the dynamic brain networks. PMID:25927525
Li, Yingzi; Naveed, Hammad; Kachalo, Sema; Xu, Lisa X.; Liang, Jie
2012-01-01
Regulation of cell growth and cell division has a fundamental role in tissue formation, organ development, and cancer progression. Remarkable similarities in the topological distributions were found in a variety of proliferating epithelia in both animals and plants. At the same time, there are species with significantly varied frequency of hexagonal cells. Moreover, local topology has been shown to be disturbed on the boundary between proliferating and quiescent cells, where cells have fewer sides than natural proliferating epithelia. The mechanisms of regulating these topological changes remain poorly understood. In this study, we use a mechanical model to examine the effects of orientation of division plane, differential proliferation, and mechanical forces on animal epithelial cells. We find that regardless of orientation of division plane, our model can reproduce the commonly observed topological distributions of cells in natural proliferating animal epithelia with the consideration of cell rearrangements. In addition, with different schemes of division plane, we are able to generate different frequency of hexagonal cells, which is consistent with experimental observations. In proliferating cells interfacing quiescent cells, our results show that differential proliferation alone is insufficient to reproduce the local changes in cell topology. Rather, increased tension on the boundary, in conjunction with differential proliferation, can reproduce the observed topological changes. We conclude that both division plane orientation and mechanical forces play important roles in cell topology in animal proliferating epithelia. Moreover, cell memory is also essential for generating specific topological distributions. PMID:22912800
Low-set ears and pinna abnormalities
Low-set ears; Microtia; "Lop" ear; Pinna abnormalities; Genetic defect-pinna; Congenital defect-pinna ... The outer ear or "pinna" forms when the baby is growing in the mother's womb. The growth of this ear part ...
Pinna abnormalities and low-set ears
... because they do not affect hearing. However, sometimes cosmetic surgery is recommended. Skin tags may be tied off, ... 5 years old. More severe abnormalities may require surgery for cosmetic reasons as well as for function. Surgery to ...
Spontaneous occurrence of chromosome abnormality in cats.
THULINE, H C; NORBY, D W
1961-08-25
A syndrome in male cats analogous to chromatin-positive Klinefelter's syndrome in human males has been demonstrated. The physical characteristics which suggested an abnormality of chromosome number in cats were "calico" or "tortoise-shell" coat colors in a male. Buccal mucosal smears were found to have "female-type" patterns in two out of 12 such male cats screened, and these two were found to have a diploid chromosome number of 39 rather than the normal 38. Testicular biopsy performed on one revealed an abnormal pattern; no gonadal tissue was found in the other cat with an abnormal chromosome number. These findings indicate that the cat, in addition to the mouse, is available for experimental study of chromosome number abnormalities. PMID:13776765
Scaling theory of {{{Z}}_{2}} topological invariants
NASA Astrophysics Data System (ADS)
Chen, Wei; Sigrist, Manfred; Schnyder, Andreas P.
2016-09-01
For inversion-symmetric topological insulators and superconductors characterized by {{{Z}}2} topological invariants, two scaling schemes are proposed to judge topological phase transitions driven by an energy parameter. The scaling schemes renormalize either the phase gradient or the second derivative of the Pfaffian of the time-reversal operator, through which the renormalization group flow of the driving energy parameter can be obtained. The Pfaffian near the time-reversal invariant momentum is revealed to display a universal critical behavior for a great variety of models examined.
Phonon analogue of topological nodal semimetals
NASA Astrophysics Data System (ADS)
Po, Hoi Chun; Bahri, Yasaman; Vishwanath, Ashvin
2015-03-01
Recently, Kane and Lubensky proposed a mapping between bosonic phonon problems on isostatic lattices to chiral fermion systems based on factorization of the dynamical matrix [Nat. Phys. 10, 39 (2014)]. The existence of topologically protected zero modes in such mechanical problems is related to their presence in the fermionic system and is dictated by a local index theorem. Here we adopt the proposed mapping to construct a two-dimensional mechanical analogue of a fermionic topological nodal semimetal that hosts a robust bulk node in its linearized phonon spectrum. Such topologically protected soft modes with tunable wavevector may be useful in designing mechanical structures with fault-tolerant properties.
Gapless topological superconductors: Model Hamiltonian and realization
NASA Astrophysics Data System (ADS)
Baum, Yuval; Posske, Thore; Fulga, Ion Cosma; Trauzettel, Björn; Stern, Ady
2015-07-01
The existence of an excitation gap in the bulk spectrum is one of the most prominent fingerprints of topological phases of matter. In this paper, we propose a family of two-dimensional Hamiltonians that yield an unusual class D topological superconductor with a gapless bulk spectrum but well-localized Majorana edge states. We perform a numerical analysis for a representative model of this phase and suggest a concrete physical realization by analyzing the effect of magnetic impurities on the surface of a strong topological insulator.
Interface between Topological and Superconducting Qubits
NASA Astrophysics Data System (ADS)
Jiang, Liang; Kane, Charles; Preskill, John
2011-03-01
We propose and analyze an interface between a topological qubit and a superconducting flux qubit. In our scheme, the interaction between Majorana fermions in a topological insulator is coherently controlled by a superconducting phase that depends on the quantum state of the flux qubit. A controlled phase gate, achieved by pulsing this interaction on and off, can transfer quantum information between the topological qubit and the superconducting qubit. This work was supported by the Sherman Fairchild Foundation, by NSF grants DMR-0906175 and PHY-0803371, by DOE grant DE-FG03-92-ER40701, and by NSA/ARO grant W911NF-09-1-0442.
Effective theory of Floquet topological transitions.
Kundu, Arijit; Fertig, H A; Seradjeh, Babak
2014-12-01
We develop a theory of topological transitions in a Floquet topological insulator, using graphene irradiated by circularly polarized light as a concrete realization. We demonstrate that a hallmark signature of such transitions in a static system, i.e., metallic bulk transport with conductivity of order e^{2}/h, is substantially suppressed at some Floquet topological transitions in the clean system. We determine the conditions for this suppression analytically and confirm our results in numerical simulations. Remarkably, introducing disorder dramatically enhances this transport by several orders of magnitude. PMID:25526148
Fibonacci topological order from quantum nets.
Fendley, Paul; Isakov, Sergei V; Troyer, Matthias
2013-06-28
We analyze a model of quantum nets and show it has a non-Abelian topological order of doubled-Fibonacci type. The ground state has the same topological behavior as that of the corresponding string-net model, but our Hamiltonian can be defined on any lattice, has less complicated interactions, and its excitations are dynamical, not fixed. This Hamiltonian includes terms acting on the spins around a face, around a vertex, and special "Jones-Wenzl" terms that serve to couple long loops together. We provide strong evidence for a gap by exact diagonalization, completing the list of ingredients necessary for topological order. PMID:23848854
Corner states in three dimensional topological insulators
NASA Astrophysics Data System (ADS)
Medhi, Amal; Banerjee, Abhimanyu; Shenoy, Vijay B.
2013-03-01
Localized electronic states appear at the corner formed by the intersection of two surfaces of a topological insulator. By constructing a 3D cubic lattice tight binding model that captures both topological and trivial phases, we study how the corner state evolve as the system changes from trivial to topological. We report the dispersion of the corner states and comment on novel physics and applications. AM acknowledges support from CPDF programme at IISc, Bangalore. VBS thanks DST (Ramanujan grant) and DAE (SRC grant) for generous support.
Global monopoles can change Universe's topology
NASA Astrophysics Data System (ADS)
Marunović, Anja; Prokopec, Tomislav
2016-05-01
If the Universe undergoes a phase transition, at which global monopoles are created or destroyed, topology of its spatial sections can change. More specifically, by making use of Myers' theorem, we show that, after a transition in which global monopoles form, spatial sections of a spatially flat, infinite Universe becomes finite and closed. This implies that global monopoles can change the topology of Universe's spatial sections (from infinite and open to finite and closed). Global monopoles cannot alter the topology of the space-time manifold.
Fermion path integrals and topological phases
NASA Astrophysics Data System (ADS)
Witten, Edward
2016-07-01
Symmetry-protected topological (SPT) phases of matter have been interpreted in terms of anomalies, and it has been expected that a similar picture should hold for SPT phases with fermions. Here a description is given in detail of what this picture means for phases of quantum matter that can be understood via band theory and free fermions. The main examples considered are time-reversal invariant topological insulators and superconductors in two or three space dimensions. Along the way, the precise meaning of the statement that in the bulk of a 3D topological insulator, the electromagnetic θ angle is equal to π , is clarified.
Chern-Simons theory and topological strings
Marino, Marcos
2005-04-01
A review of the relation between Chern-Simons gauge theory and topological string theory on noncompact Calabi-Yau spaces is given. This relation has made it possible to give an exact solution of topological string theory on these spaces to all orders in the string coupling constant. Here the focus is on the construction of this solution, which is encoded in the topological vertex, and the implications of the physics of string/gauge theory duality for knot theory and for the geometry of Calabi-Yau manifolds.
Designing topological bands in reciprocal space.
Cooper, N R; Moessner, R
2012-11-21
Motivated by new capabilities to realize artificial gauge fields in ultracold atomic systems, and by their potential to access correlated topological phases in lattice systems, we present a new strategy for designing topologically nontrivial band structures. Our approach is simple and direct: it amounts to considering tight-binding models directly in reciprocal space. These models naturally cause atoms to experience highly uniform magnetic flux density and lead to topological bands with very narrow dispersion, without fine-tuning of parameters. Further, our construction immediately yields instances of optical Chern lattices, as well as band structures with Chern numbers of magnitude larger than one. PMID:23215598
Effective Theory of Floquet Topological Transitions
NASA Astrophysics Data System (ADS)
Kundu, Arijit; Fertig, H. A.; Seradjeh, Babak
2014-12-01
We develop a theory of topological transitions in a Floquet topological insulator, using graphene irradiated by circularly polarized light as a concrete realization. We demonstrate that a hallmark signature of such transitions in a static system, i.e., metallic bulk transport with conductivity of order e2/h , is substantially suppressed at some Floquet topological transitions in the clean system. We determine the conditions for this suppression analytically and confirm our results in numerical simulations. Remarkably, introducing disorder dramatically enhances this transport by several orders of magnitude.
Weak side of strong topological insulators
NASA Astrophysics Data System (ADS)
Sbierski, Björn; Schneider, Martin; Brouwer, Piet W.
2016-04-01
Strong topological insulators may have nonzero weak indices. The nonzero weak indices allow for the existence of topologically protected helical states along line defects of the lattice. If the lattice admits line defects that connect opposite surfaces of a slab of such a "weak-and-strong" topological insulator, these states effectively connect the surface states at opposite surfaces. Depending on the phases accumulated along the dislocation lines, this connection results in a suppression of in-plane transport and the opening of a spectral gap or in an enhanced density of states and an increased conductivity.
On the topological stability of magnetostatic equilibria
NASA Technical Reports Server (NTRS)
Tsinganos, K. C.; Rosner, R.; Distler, J.
1984-01-01
The topological stability of MHD equilibria is investigated by exploring the formal analogy, in the ideal MHD limit, between the topology of magnetic lines of force in coordinate space and the topology of integral surfaces of one- and two-dimensional Hamiltonian systems in phase space. It is demonstrated that in an astrophysical setting, symmetric magnetostatic equilibria satisfying the ideal MHD equations are exceptional. The principal result of the study is that previous infinitesimal perturbation theory calculations can be generalized to include finite-amplitude and symmetry-breaking effects. The effect of the ergodicity of perturbed symmetric equilibria on heat dispersal in magnetically dominated plasmas is discussed.
Topology and bistability in liquid crystal devices
Majumdar, A.; Newton, C. J. P.; Robbins, J. M.; Zyskin, M.
2007-05-15
We study nematic liquid crystal configurations in a prototype bistable device--the post aligned bistable nematic (PABN) cell. Working within the Oseen-Frank continuum model, we describe the liquid crystal configuration by a unit-vector field n, in a model version of the PABN cell. First, we identify four distinct topologies in this geometry. We explicitly construct trial configurations with these topologies which are used as initial conditions for a numerical solver, based on the finite-element method. The morphologies and energetics of the corresponding numerical solutions qualitatively agree with experimental observations and suggest a topological mechanism for bistability in the PABN cell geometry.
Learning topological maps: An alternative approach
Buecken, A.; Thrun, S.
1996-12-31
Our goal is autonomous real-time control of a mobile robot. In this paper we want to show a possibility to learn topological maps of a large-scale indoor environment autonomously. In the literature there are two paradigms how to store information on the environment of a robot: as a grid-based (geometric) or as a topological map. While grid-based maps are considerably easy to learn and maintain, topological maps are quite compact and facilitate fast motion-planning.
Abnormal brain scan with subacute extradural haematomas
Morley, J. Barrie; Langford, Keith H.
1970-01-01
Four patients are described with proven subacute extradural haematomas, each with an abnormal cerebral scan of diagnostic assistance. A possible mechanism of production of the subacute extradural haematoma is discussed, and appears to be similar to the mechanism involved in the subacute subdural haematoma. The means by which the abnormal scan results in such cases is also examined, from which it appears that non-specific meningeal membrane inflammatory reaction surrounding the haematoma is significant. Images PMID:5478950
Prevalence of asymptomatic urinary abnormalities among adolescents.
Fouad, Mohamed; Boraie, Maher
2016-05-01
To determine the prevalence of asymptomatic urinary abnormalities in adolescents, first morning clean mid-stream urine specimens were obtained from 2500 individuals and examined by dipstick and light microscopy. Adolescents with abnormal screening results were reexamined after two weeks and those who had abnormal results twice were subjected to systemic clinical examination and further clinical and laboratory investigations. Eight hundred and three (32.1%) individuals had urinary abnormalities at the first screening, which significantly decreased to 345 (13.8%) at the second screening, (P <0.001). Hematuria was the most common urinary abnormalities detected in 245 (9.8%) adolescents who had persistent urine abnormalities; 228 (9.1%) individuals had non glomerular hematuria. The hematuria was isolated in 150 (6%) individuals, combined with leukocyturia in 83 (3.3%) individuals, and combined with proteinuria in 12 (0.5%) individuals. Leukocyturia was detected in 150 (6%) of all studied adolescents; it was isolated in 39 (1.6%) individuals and combined with proteinuria in 28 (1.1%) of them. Asymptomatic bacteriuria was detected in 23 (0.9%) of all studied adolescents; all the cases were females. Proteinuria was detected in 65 (2.6%) of all the studied adolescents; 45 (1.8%) individuals had <0.5 g/day and twenty (0.8%) individuals had 0.5-3 g/day. Asymptomatic urinary abnormalities were more common in males than females and adolescents from rural than urban areas (P <0.01) and (P <0.001), respectively. The present study found a high prevalence of asymptomatic urinary abnormalities among adolescents in our population. PMID:27215241
Topological Modeling of Metamict Zircon
NASA Astrophysics Data System (ADS)
Hobbs, L. W.; Zhang, Y.; Yuan, X.
2006-05-01
Zircon (ZrSiO4) is the most studied metamict mineral and a leading model for candidate ceramic hosts designed to encapsulate highly radioactive nuclear waste and excess plutonium. It is also emblematic of compound oxide ceramics with a potential to phase separate in the amorphized state. Several groups have carried out ab initio or molecular dynamics (MD) simulations of melt-quenched or radiation-disordered zircon. A tendency for silica tetrahedra to polymerize, implying incipient phase separation, has been noted, but adequate descriptors of the amorphous state capable of distinguishing between different disordered arrangements have not been available. This contribution details critical modifications made to empirical potentials used in MD simulations and useful improvements in modeling efficiency that have facilitated constant pressure simulations of quenched and displacement cascade-amorphized zircon. The simulated end- states have been subjected to topological assessment algorithms for enumerating coordinations, bond lengths and bond angles; counting primitive rings and identifying structure-defining local primitive-ring clusters; and assessing degree of coordination-unit polymerization. The topologies of simulated melt, melt-quenched and cascade-amorphized disordered arrangements have been found to be different and distinguishable. A two-body Born-Mayer empirical potential with ZBL short-range repulsive term was fit to major structural, elastic, thermal and dielectric properties of crystalline zircon, but it was noted that the best crystalline fit, with non-stoichiometric partial ion charges, led to unrealistic coordinations in amorphized arrangements and uncontrolled expansions in constant pressure simulations because of silica polymerization. Therefore, stoichiometrically charge-balanced partial charges were instead chosen and optimized; the optimal choice of O-1.2, Si+2.4, Zr+2.4 led to realistic coordinations (Zr 7, Si 4) and well-behaved constant
A method for interactive specification of multiple-block topologies
NASA Technical Reports Server (NTRS)
Sorenson, Reese L.; Mccann, Karen M.
1991-01-01
A method is presented for dealing with the vast amount of topological and other data which must be specified to generate a multiple-block computational grid. Specific uses of the graphical capabilities of a powerful scientific workstation are described which reduce the burden on the user of collecting and formatting such large amounts of data. A program to implement this method, 3DPREP, is described. A plotting transformation algorithm, some useful software tools, notes on programming, and a database organization are also presented. Example grids developed using the method are shown.
Abnormal ferrite in hyper-eutectoid steels
Chairuangsri, T.; Edmonds, D.V.
2000-04-19
The microstructural characteristics of ultra-high carbon hyper-eutectoid Fe-C and Fe-C-Cu experimental steels have been examined after isothermal transformation in a range just beneath the eutectoid temperature. Particular attention was paid to the formation of so-called abnormal ferrite, which refers to coarse ferrite grains which can form, in hyper-eutectoid compositions, on the pro-eutectoid cementite before the pearlite reaction occurs. Thus it is confirmed that the abnormal ferrite is not a result of pearlite coarsening, but of austenite decomposition before the conditions for coupled growth of pearlite are established. The abnormal ferrite formed on both allotriomorphic and Widmanstaetten forms of pro-eutectoid cementite, and significantly, it was observed that the pro-eutectoid cementite continued to grow, despite being enclosed by the abnormal ferrite. Under certain conditions this could lead to the eventual formation of substantially reduced amounts of pearlite. Thus, a model for carbon redistribution that allows the proeutectoid cementite to thicken concurrently with the abnormal ferrite is presented. The orientation relationships between the abnormal ferrite and pro-eutectoid cementite were also determined and found to be close to those which have been reported between pearlitic ferrite and pearlitic cementite.
NASA Astrophysics Data System (ADS)
Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu
We employ two complementary theoretical approaches to explore the feasibility of altering the topological properties of two-dimensional Rashba spin-orbit coupled superconductors by proper introduction of magnetic disorders. First, using the self-consistent Born approximation, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorders, which gradually narrow, close, and reopen the quasi-particle gap of the paired electrons in a nontrivial manner. Such a topological phase transition is further characterized by the change in the corresponding topological invariant. The central predictions made here are then confirmed using the complementary numerical approach by solving the Bogoliubov-de Gennes equations self-consistently within a tight-binding model. We also discuss the validity of the present model studies in connection with existing experimental findings. Collectively, the present study offers appealing new schemes for potential experimental realization of topological superconductors. Supported by NSF of China.
Caputo, Marco; Panighel, Mirko; Lisi, Simone; Khalil, Lama; Santo, Giovanni Di; Papalazarou, Evangelos; Hruban, Andrzej; Konczykowski, Marcin; Krusin-Elbaum, Lia; Aliev, Ziya S; Babanly, Mahammad B; Otrokov, Mikhail M; Politano, Antonio; Chulkov, Evgueni V; Arnau, Andrés; Marinova, Vera; Das, Pranab K; Fujii, Jun; Vobornik, Ivana; Perfetti, Luca; Mugarza, Aitor; Goldoni, Andrea; Marsi, Marino
2016-06-01
Topological insulators are a promising class of materials for applications in the field of spintronics. New perspectives in this field can arise from interfacing metal-organic molecules with the topological insulator spin-momentum locked surface states, which can be perturbed enhancing or suppressing spintronics-relevant properties such as spin coherence. Here we show results from an angle-resolved photemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM) study of the prototypical cobalt phthalocyanine (CoPc)/Bi2Se3 interface. We demonstrate that that the hybrid interface can act on the topological protection of the surface and bury the Dirac cone below the first quintuple layer. PMID:27010705
Hosseini, S.M. Hadi; Black, Jessica M.; Soriano, Teresa; Bugescu, Nicolle; Martinez, Rociel; Raman, Mira M.; Kesler, Shelli R.; Hoeft, Fumiko
2013-01-01
Developmental dyslexia is a neurobiological deficit characterized by persistent difficulty in learning to read in children and adults who otherwise possess normal intelligence. Functional and structural connectivity data suggest that developmental dyslexia could be a disconnection syndrome. However, whether abnormalities in connectivity exist in beginning readers at-risk for reading difficulties is unknown. Using graphtheoretical analysis, we investigated differences in global and regional topological properties of structural brain networks in 42 beginning readers with (FH+) and without (FH−) familial risk for reading difficulties. We constructed separate structural correlation networks based on measures of surface area and cortical thickness. Results revealed changes in topological properties in brain regions known to be abnormal in dyslexia (left supramarginal gyrus, left inferior frontal gyrus) in the FH+ group mainly in the network constructed from measures of cortical surface area. We also found alterations in topological properties in regions that are not often advertised as dyslexia but nonetheless play important role in reading (left posterior cingulate, hippocampus, and left precentral gyrus). To our knowledge, this is the first report of altered topological properties of structural correlation networks in children at risk for reading difficulty, and motivates future studies that examine the mechanisms underlying how these brain networks may mediate the influences of family history on reading outcome. PMID:23333415
Topologically protected elastic waves in phononic metamaterials
Mousavi, S. Hossein; Khanikaev, Alexander B.; Wang, Zheng
2015-01-01
Surface waves in topological states of quantum matter exhibit unique protection from backscattering induced by disorders, making them ideal carriers for both classical and quantum information. Topological matters for electrons and photons are largely limited by the range of bulk properties, and the associated performance trade-offs. In contrast, phononic metamaterials provide access to a much wider range of material properties. Here we demonstrate numerically a phononic topological metamaterial in an elastic-wave analogue of the quantum spin Hall effect. A dual-scale phononic crystal slab is used to support two effective spins for phonons over a broad bandwidth, and strong spin–orbit coupling is realized by breaking spatial mirror symmetry. By preserving the spin polarization with an external load or spatial symmetry, phononic edge states are shown to be robust against scattering from discrete defects as well as disorders in the continuum, demonstrating topological protection for phonons in both static and time-dependent regimes. PMID:26530426
Spintronics device made of topological materials
NASA Astrophysics Data System (ADS)
Wu, Jiansheng; Shi, Zhangsheng; Wang, Maoji
Topological Materials is a new state of matter of which the bulk states are gapped insulator or superconductor while the surface states are gapless metallic states. Such surface states are robust against local disorder and impurities due to its nontrivial topology. It induces unusual transport properties and shows nontrivial topological spin texture in real space. We have made use of these two exotic properties to make application in spintronics. For example, we propose to make spin-filter transistor using of 1D or 2D quantum anomalous Hall insulator or 2D topological Weyl semimetal, we also propose a device to measure the spin-polarization of current, a device to generate entangled entangled electron pairs. Startup funds of SUSTC, Shenzhen Peacock Plan, Shenzhen Free Exploration Plan with Grant Number JCYJ20150630145302225.
Topological protection of multiparticle dissipative transport
NASA Astrophysics Data System (ADS)
Loehr, Johannes; Loenne, Michael; Ernst, Adrian; de Las Heras, Daniel; Fischer, Thomas M.
2016-06-01
Topological protection allows robust transport of localized phenomena such as quantum information, solitons and dislocations. The transport can be either dissipative or non-dissipative. Here, we experimentally demonstrate and theoretically explain the topologically protected dissipative motion of colloidal particles above a periodic hexagonal magnetic pattern. By driving the system with periodic modulation loops of an external and spatially homogeneous magnetic field, we achieve total control over the motion of diamagnetic and paramagnetic colloids. We can transport simultaneously and independently each type of colloid along any of the six crystallographic directions of the pattern via adiabatic or deterministic ratchet motion. Both types of motion are topologically protected. As an application, we implement an automatic topologically protected quality control of a chemical reaction between functionalized colloids. Our results are relevant to other systems with the same symmetry.