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A structure-dynamic approach to cortical organization: Number of paths and accessibility

RODRIGUES, Francisco A.; COSTA, Luciano da Fontoura
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.65%
A structure-dynamic approach to cortical systems is reported which is based on the number of paths and the accessibility of each node. The latter measurement is obtained by performing self-avoiding random walks in the respective networks, so as to simulate dynamics, and then calculating the entropies of the transition probabilities for walks starting from each node. Cortical networks of three species, namely cat, macaque and humans, are studied considering structural and dynamical aspects. It is verified that the human cortical network presents the highest accessibility and number of paths (in terms of z-scores). The correlation between the number of paths and accessibility is also investigated as a mean to quantify the level of independence between paths connecting pairs of nodes in cortical networks. By comparing the cortical networks of cat, macaque and humans, it is verified that the human cortical network tends to present the largest number of independent paths of length larger than four. These results suggest that the human cortical network is potentially the most resilient to brain injures. (C) 2009 Elsevier B.V. All rights reserved.; CNPq[301303/06-1]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq[573583/2008-0]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); FAPESP[05/00587-5]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[07/50633-9]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Comparação de tecnicas de analise de caminhos de transferencia vibroacusticos; Comparison of techniques for vibro-acoustic transfer path analysis

Paulo Eduardo França Padilha
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/02/2006 PT
Relevância na Pesquisa
26.65%
Neste trabalho é feita uma comparação de técnicas analíticas e experimentais de Análise de Caminhos de Transferência Vibroacústicos. A Análise de Caminhos de Transferência, ou TPA como é conhecida pela abreviatura em inglês, é uma ferramenta para se avaliar a contribuição de diferentes caminhos de propagação de energia vibroacústica entre uma fonte e um receptor ligados entre si por várias conexões. Uma aplicação típica de TPA é quantificar e determinar a importância relativa desses caminhos numa dada banda de freqüência, verificando-se a contribuição mais significativa para o receptor. Nessa análise, basicamente duas quantidades devem ser obtidas: as forças operacionais em cada caminho de transferência e a Função de Resposta em Freqüência desses caminhos. Essas funções podem ser obtidas tanto experimentalmente quanto analiticamente, considerando-se ou não a impedância mecânica da fonte vibroacústica. As forças operacionais podem ser diretamente obtidas de medições, usando um transdutor de forças, ou indiretamente estimadas a partir de medições auxiliares. Neste trabalho são apresentados dois métodos de obtenção indireta das forças operacionais ? o Método da Rigidez Complexa e o Método da Inversão de Matrizes ? associados com as duas possíveis configurações para determinação das Funções de Resposta em Freqüência ? incluindo e excluindo a impedância da fonte. Essas técnicas são aplicadas a dois modelos: um analítico e um experimental. avaliadas com esse modelo analítico...

Trajetos escolares no ensino secundário: efeitos das origens sociais e expectativas dos estudantes

Nóvoas, David Samuel Assis
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2012 POR
Relevância na Pesquisa
26.65%
Mestrado em Sociologia e Planeamento; O presente trabalho tem como objeto de estudo os trajetos sociais e escolares de uma amostra de 6836 jovens de 568 escolas que foram inquiridos pelo Observatório de Trajetos dos Estudantes do Ensino Secundário (OTES) ao longo de cinco anos, através da aplicação de três inquéritos por questionários distintos, em momentos considerados chave no seu trajeto escolar e profissional. Pretende-se compreender de que modo as origens sociais influenciam os trajetos vividos e projetados dos jovens inquiridos, bem como as suas expectativas, respondendo a algumas questões consideradas fundamentais: que elementos contribuem mais para a definição dos trajetos escolares e profissionais, e se as representações e expectativas face ao mesmo variam ao longo do tempo. Ao longo do presente trabalho os trajetos serão reconstituídos e analisados, desde o período de entrada no sistema educativo, até ao pós-secundário, sendo abrangidos os casos de inserção profissional, e/ou no ensino superior.; This work’s main objective is to study school paths from a sample of 6836 youths from 568 schools, which participated in the first cohort of the Observatory of the Paths of Secondary Education Students (OTES) thought five years...

Normal mode paths for hydrogen exchange in the peptide ferrichrome

Sheridan, Robert P.; Levy, Ronald M.; Englander, S. W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1983 EN
Relevância na Pesquisa
26.65%
Possible paths for exposure to solvent and hydrogen exchange of the amide protons of ferrichrome, a cyclic hexapeptide, are examined. The paths are obtained from calculations of the vibrational normal modes of ferrichrome and correspond to low energy atomic displacements away from the local minimum in the multidimensional conformational space of the molecule. Exposure of exchangeable groups along the normal modes was determined by using the solvent accessible surface area algorithm of Lee and Richards. Three of the exchangeable protons (Gly1,2,3,) are largely exposed to solvent in the x-ray structure while the remaining three exchangeable protons of the ornithines are totally shielded from solvent. A very small number of normal mode displacements are found to expose the Orn2 and Orn3 amide groups while the Orn1 amide proton remains shielded from solvent for all the paths studied. The effective paths for exposure of Orn2 and Orn3 correspond to the lowest frequency (≈18 cm-1) motions. The paths are characterized in terms of the magnitude and energy of atomic displacements, correlated changes in dihedral angles, and the resulting changes in exposure and hydrogen bonding of exchangeable groups.

On Leveraging Partial Paths in Partially-Connected Networks

Heimlicher, Simon; Karaliopoulos, Merkouris; Levy, Hanoch; Spyropoulos, Thrasyvoulos
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/01/2009
Relevância na Pesquisa
26.69%
Mobile wireless network research focuses on scenarios at the extremes of the network connectivity continuum where the probability of all nodes being connected is either close to unity, assuming connected paths between all nodes (mobile ad hoc networks), or it is close to zero, assuming no multi-hop paths exist at all (delay-tolerant networks). In this paper, we argue that a sizable fraction of networks lies between these extremes and is characterized by the existence of partial paths, i.e. multi-hop path segments that allow forwarding data closer to the destination even when no end-to-end path is available. A fundamental issue in such networks is dealing with disruptions of end-to-end paths. Under a stochastic model, we compare the performance of the established end-to-end retransmission (ignoring partial paths), against a forwarding mechanism that leverages partial paths to forward data closer to the destination even during disruption periods. Perhaps surprisingly, the alternative mechanism is not necessarily superior. However, under a stochastic monotonicity condition between current v.s. future path length, which we demonstrate to hold in typical network models, we manage to prove superiority of the alternative mechanism in stochastic dominance terms. We believe that this study could serve as a foundation to design more efficient data transfer protocols for partially-connected networks...

On the Groupoid Model of Computational Paths

Ramos, Arthur F.; de Queiroz, Ruy J. G. B.; de Oliveira, Anjolina G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/06/2015
Relevância na Pesquisa
26.69%
The main objective of this work is to study mathematical properties of computational paths. Originally proposed by de Queiroz & Gabbay (1994) as `sequences or rewrites', computational paths are taken to be terms of the identity type of Martin L\"of's Intensional Type Theory, since these paths can be seen as the grounds on which the propositional equality between two computational objects stand. From this perspective, this work aims to show that one of the properties of the identity type is present on computational paths. We are refering to the fact that that the identity type induces a groupoid structure, as proposed by Hofmann & Streicher (1994). Using categorical semantics, we show that computational paths induce a groupoid structure. We also show that computational paths are capable of inducing higher categorical structures.; Comment: 16 pages, LSFA 2015 - Preliminary Acceptance

Closed Light Paths in Equiangular Spiral Disks

Hitzer, Eckhard
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/06/2013
Relevância na Pesquisa
26.69%
A new type of deformation for microscopic laser disks, the \textit{equiangular spiral deformation} is proposed. First a short review of the geometry of light paths in equiangular spirals in the language of real two-dimensional geometric calculus is given. Second, the constituting equations for \textit{closed paths} inside equiangular spirals are derived. Third, their numerical solution is performed and found to yield two generic types of closed light paths. \textit{Degenerate} closed paths that exist over large intervals of the deformation parameter, and \textit{nondegenerate} closed paths which only exist over relatively small deformation parameter intervals spanning less than 1% of the nondegenerate intervals. Fourth, amongst the nondegenerate paths a \textit{stable asymmetric bow-tie} shaped light trajectory was found.; Comment: 36 pages, 18 figures

Survivable Paths in Multilayer Networks

Parandehgheibi, Marzieh; Lee, Hyang-Won; Modiano, Eytan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/04/2013
Relevância na Pesquisa
26.69%
We consider protection problems in multilayer networks. In single-layer networks, a pair of disjoint paths can be used to provide protection for a source-destination pair. However, this approach cannot be directly applied to layered networks where disjoint paths may not always exist. In this paper, we take a new approach which is based on finding a set of paths that may not be disjoint but together will survive any single physical link failure. First, we consider the problem of finding the minimum number of survivable paths. In particular, we focus on two versions of this problem: one where the length of a path is restricted, and the other where the number of paths sharing a fiber is restricted. We prove that in general, finding the minimum survivable path set is NP-hard, whereas both of the restricted versions of the problem can be solved in polynomial time. We formulate the problem as Integer Linear Programs (ILPs), and use these formulations to develop heuristics and approximation algorithms. Next, we consider the problem of finding a set of survivable paths that uses the minimum number of fibers. We show that this problem is NP-hard in general, and develop heuristics and approximation algorithms with provable approximation bounds. Finally...

Analytic Combinatorics of Planar Lattice Paths

Johnson, Samuel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/04/2013
Relevância na Pesquisa
26.69%
Lattice paths effectively model phenomena in chemistry, physics and probability theory. Asymptotic enumeration of lattice paths is linked with entropy in the physical systems being modeled. Lattice paths restricted to different regions of the plane are well suited to a functional equation approach for exact and asymptotic enumeration. This thesis surveys results on lattice paths under various restrictions, with an emphasis on lattice paths in the quarter plane. For these paths, we develop an original systematic combinatorial approach providing direct access to the exponential growth factors of the asymptotic expressions.; Comment: Master's thesis of the author, 97 pages

Symmetries of Analytic Paths

Fleischhack, Christian
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/03/2015
Relevância na Pesquisa
26.69%
The symmetries of paths in a manifold $M$ are classified with respect to a given pointwise proper action of a Lie group $G$ on $M$. Here, paths are embeddings of a compact interval into $M$. There are at least two types of symmetries: Firstly, paths that are parts of an integral curve of a fundamental vector field on $M$ (continuous symmetry). Secondly, paths that can be decomposed into finitely many pieces, each of which is the translate of some free segment, where possibly the translate is cut at the two ends of the paths (discrete symmetry). Here, a free segment is a path $e$ whose $G$-translates either equal $e$ or intersect it in at most finitely many points. Note that all the statements above are understood up to the parametrization of the paths. We will show, for the category of analytic manifolds, that each path is of exactly one of either types. For the proof, we use that the overlap of a path $\gamma$ with one of its translates is encoded uniquely in a mapping between subsets of $\dom\gamma$. Running over all translates, these mappings form the so-called reparametrization set to $\gamma$. It will turn out that, up to conjugation with a diffeomorphism, any such set is given by the action of a Lie subgroup of $O(2)$ on $S^1$...

Counting Humps in Motzkin paths

Ding, Yun; Du, Rosena R. X.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/09/2011
Relevância na Pesquisa
26.69%
In this paper we study the number of humps (peaks) in Dyck, Motzkin and Schr\"{o}der paths. Recently A. Regev noticed that the number of peaks in all Dyck paths of order $n$ is one half of the number of super Dyck paths of order $n$. He also computed the number of humps in Motzkin paths and found a similar relation, and asked for bijective proofs. We give a bijection and prove these results. Using this bijection we also give a new proof that the number of Dyck paths of order $n$ with $k$ peaks is the Narayana number. By double counting super Schr\"{o}der paths, we also get an identity involving products of binomial coefficients.; Comment: 8 pages, 2 Figures

Symmetries of statistics on lattice paths between two boundaries

Elizalde, Sergi; Rubey, Martin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.69%
We prove that on the set of lattice paths with steps N=(0,1) and E=(1,0) that lie between two fixed boundaries T and B (which are themselves lattice paths), the statistics `number of E steps shared with B' and `number of E steps shared with T' have a symmetric joint distribution. To do so, we give an involution that switches these statistics, preserves additional parameters, and generalizes to paths that contain steps S=(0,-1) at prescribed x-coordinates. We also show that a similar equidistribution result for path statistics follows from the fact that the Tutte polynomial of a matroid is independent of the order of its ground set. We extend the two theorems to k-tuples of paths between two boundaries, and we give some applications to Dyck paths, generalizing a result of Deutsch, to watermelon configurations, to pattern-avoiding permutations, and to the generalized Tamari lattice. Finally, we prove a conjecture of Nicol\'as about the distribution of degrees of k consecutive vertices in k-triangulations of a convex n-gon. To achieve this goal, we provide a new statistic-preserving bijection between certain k-tuples of non-crossing paths and k-flagged semistandard Young tableaux, which is based on local moves reminiscent of jeu de taquin.; Comment: Small typos corrected...

Generating Transition Paths by Langevin Bridges

Orland, Henri
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.69%
We propose a novel stochastic method to generate paths conditioned to start in an initial state and end in a given final state during a certain time $t_{f}$. These paths are weighted with a probability given by the overdamped Langevin dynamics. We show that these paths can be exactly generated by a non-local stochastic differential equation. In the limit of short times, we show that this complicated non-solvable equation can be simplified into an approximate stochastic differential equation. For longer times, the paths generated by this approximate equation can be reweighted to generate the correct statistics. In all cases, the paths generated by this equation are statistically independent and provide a representative sample of transition paths. In case the reaction takes place in a solvent (e.g. protein folding in water), the explicit solvent can be treated. The method is illustrated on the one-dimensional quartic oscillator.

The Complexity of Rerouting Shortest Paths

Bonsma, Paul
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.69%
The Shortest Path Reconfiguration problem has as input a graph G (with unit edge lengths) with vertices s and t, and two shortest st-paths P and Q. The question is whether there exists a sequence of shortest st-paths that starts with P and ends with Q, such that subsequent paths differ in only one vertex. This is called a rerouting sequence. This problem is shown to be PSPACE-complete. For claw-free graphs and chordal graphs, it is shown that the problem can be solved in polynomial time, and that shortest rerouting sequences have linear length. For these classes, it is also shown that deciding whether a rerouting sequence exists between all pairs of shortest st-paths can be done in polynomial time. Finally, a polynomial time algorithm for counting the number of isolated paths is given.; Comment: The results on claw-free graphs, chordal graphs and isolated paths have been added in version 2 (april 2012). Version 1 (September 2010) only contained the PSPACE-hardness result. (Version 2 has been submitted.)

A bag-of-paths framework for network data analysis

Françoisse, Kevin; Kivimäki, Ilkka; Mantrach, Amin; Rossi, Fabrice; Saerens, Marco
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/02/2013
Relevância na Pesquisa
26.69%
This work introduces a generic framework, called the bag-of-paths (BoP), that can be used for link and network data analysis. The primary application of this framework, investigated in this paper, is the definition of distance measures between nodes enjoying some nice properties. More precisely, let us assume a weighted directed graph G where a cost is associated to each arc. Within this context, consider a bag containing all the possible paths between pairs of nodes in G. Then, following, a probability distribution on this countable set of paths through the graph is defined by minimizing the total expected cost between all pairs of nodes while fixing the total relative entropy spread in the graph. This results in a Boltzmann distribution on the set of paths such that long (high-cost) paths have a low probability of being sampled from the bag, while short (low-cost) paths have a high probability of being sampled. Within this probabilistic framework, the BoP probabilities, P(s=i,e=j), of drawing a path starting from node i (s=i) and ending in node j (e=j) can easily be computed in closed form by a simple matrix inversion. Various applications of this framework are currently investigated, e.g., the definition of distance measures between the nodes of G...

Most probable paths in temporal weighted networks: An application to ocean transport

Ser-Giacomi, Enrico; Vasile, Ruggero; Hernandez-Garcia, Emilio; Lopez, Cristobal
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.69%
We consider paths in weighted and directed temporal networks, introducing tools to compute sets of paths of high probability. We quantify the relative importance of the most probable path between two nodes with respect to the whole set of paths, and to a subset of highly probable paths which incorporate most of the connection probability. These concepts are used to provide alternative definitions of betweenness centrality. We apply our formalism to a transport network describing surface flow in the Mediterranean sea. Despite the full transport dynamics is described by a very large number of paths we find that, for realistic time scales, only a very small subset of high probability paths (or even a single most probable one) is enough to characterize global connectivity properties of the network.

Particles in RSOS paths

Jacob, P.; Mathieu, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.69%
We introduce a new representation of the paths of the Forrester-Baxter RSOS models which represents the states of the irreducible modules of the minimal models M(p',p). This representation is obtained by transforming the RSOS paths, for the cases p> 2p'-2, to new paths for which horizontal edges are allowed at certain heights. These new paths are much simpler in that their weight is nothing but the sum of the position of the peaks. This description paves the way for the interpretation of the RSOS paths in terms of fermi-type charged particles out of which the fermionic characters could be obtained constructively. The derivation of the fermionic character for p'=2 and p=kp'+/- 1 is outlined. Finally, the particles of the RSOS paths are put in relation with the kinks and the breathers of the restricted sine-Gordon model.; Comment: 15 pages, few typos corrected, version published

Minimum-Link Paths Revisited

Mitchell, Joseph S. B.; Polishchuk, Valentin; Sysikaski, Mikko
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/02/2013
Relevância na Pesquisa
26.69%
A path or a polygonal domain is C-oriented if the orientations of its edges belong to a set of C given orientations; this is a generalization of the notable rectilinear case (C = 2). We study exact and approximation algorithms for minimum-link C-oriented paths and paths with unrestricted orientations, both in C-oriented and in general domains. Our two main algorithms are as follows: A subquadratic-time algorithm with a non-trivial approximation guarantee for general (unrestricted-orientation) minimum-link paths in general domains. An algorithm to find a minimum-link C-oriented path in a C-oriented domain. Our algorithm is simpler and more time-space efficient than the prior algorithm. We also obtain several related results: - 3SUM-hardness of determining the link distance with unrestricted orientations (even in a rectilinear domain). - An optimal algorithm for finding a minimum-link rectilinear path in a rectilinear domain. The algorithm and its analysis are simpler than the existing ones. - An extension of our methods to find a C-oriented minimum-link path in a general (not necessarily C-oriented) domain. - A more efficient algorithm to compute a 2-approximate C-oriented minimum-link path. - A notion of "robust" paths. We show how minimum-link C-oriented paths approximate the robust paths with unrestricted orientations to within an additive error of 1.; Comment: 29 pages...

Natural selection of paths in networks

Fernando, Chrisantha; Vasas, Vera; Szathmáry, Eörs; Husbands, Philip
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/submittedVersion Formato: application/pdf
Publicado em //2011 ENG
Relevância na Pesquisa
26.69%
We present a novel algorithm that exhibits natural selection of paths in a network. If each node and weighted directed edge has a unique identifier, a path in the network is defined as an ordered list of these unique identifiers. We take a population perspective and view each path as a genotype. If each node has a node phenotype then a path phenotype is defined as the list of node phenotypes in order of traversal. We show that given appropriate path traversal, weight change and structural plasticity rules, a path is a unit of evolution because it can exhibit multiplicative growth (i.e. change it’s probability of being traversed), and have variation and heredity. Thus, a unit of evolution need not be a spatially distinct physical individual. The total set of paths in a network consists of all possible paths from the start node to a finish node. Each path phenotype is associated with a reward that determines whether the edges of that path will be multiplicatively strengthened (or weakened). A pair-wise tournament selection algorithm is implemented which compares the reward obtained by two paths. The directed edges of the winning path are strengthened, whilst the directed edges of the losing path are weakened. Edges shared by both paths are not changed (or weakened if diversity is desired). Each time a node is activated there is a probability that the path will mutate...

Natural Selection of Paths in Networks

Chrisantha Fernando; Vera Vasas; Eörs Szathmáry; Philip Husbands
Fonte: Nature Preceedings Publicador: Nature Preceedings
Tipo: Manuscript
Relevância na Pesquisa
26.69%
We present a novel algorithm that exhibits natural selection of paths in a network. If each node and weighted directed edge has a unique identifier, a path in the network is defined as an ordered list of these unique identifiers. We take a population perspective and view each path as a genotype. If each node has a node phenotype then a path phenotype is defined as the list of node phenotypes in order of traversal. We show that given appropriate path traversal, weight change and structural plasticity rules, a path is a unit of evolution because it can exhibit multiplicative growth (i.e. change it’s probability of being traversed), and have variation and heredity. Thus, a unit of evolution need not be a spatially distinct physical individual. The total set of paths in a network consists of all possible paths from the start node to a finish node. Each path phenotype is associated with a reward that determines whether the edges of that path will be multiplicatively strengthened (or weakened). A pair-wise tournament selection algorithm is implemented which compares the reward obtained by two paths. The directed edges of the winning path are strengthened, whilst the directed edges of the losing path are weakened. Edges shared by both paths are not changed (or weakened if diversity is desired). Each time a node is activated there is a probability that the path will mutate...