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## Percolation in a network with long-range connections: Implications for cytoskeletal structure and function

Fonte: ELSEVIER SCIENCE BV
Publicador: ELSEVIER SCIENCE BV

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

25.99%

#Cell connectivity#F-actin#Mechanics#Model#Simulation#AIRWAY SMOOTH-MUSCLE#LENGTH ADAPTATION#BOND-PERCOLATION#MODEL#DYNAMICS#LATTICE

Cell shape, signaling, and integrity depend on cytoskeletal organization. In this study we describe the cytoskeleton as a simple network of filamentary proteins (links) anchored by complex protein structures (nodes). The structure of this network is regulated by a distance-dependent probability of link formation as P = p/d(s), where p regulates the network density and s controls how fast the probability for link formation decays with node distance (d). It was previously shown that the regulation of the link lengths is crucial for the mechanical behavior of the cells. Here we examined the ability of the two-dimensional network to percolate (i.e. to have end-to-end connectivity), and found that the percolation threshold depends strongly on s. The system undergoes a transition around s = 2. The percolation threshold of networks with s < 2 decreases with increasing system size L, while the percolation threshold for networks with s > 2 converges to a finite value. We speculate that s < 2 may represent a condition in which cells can accommodate deformation while still preserving their mechanical integrity. Additionally, we measured the length distribution of F-actin filaments from publicly available images of a variety of cell types. In agreement with model predictions...

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## Statistical analysis and modeling of optical transport networks; Análise estatística e modelação de redes óticas de transporte

Fonte: Universidade de Aveiro
Publicador: Universidade de Aveiro

Tipo: Tese de Doutorado

ENG

Relevância na Pesquisa

46.51%

#Engenharia electrotécnica#Redes de comunicação óptica#Análise estatística#Optical transport networks#statistical analysis#statistical modeling#link lengths#link length related parameters#shortest path lengths

Statistical analysis and modeling of networks is now an integral
part of network science and engineering. In case of optical
transport networks (OTNs), it can be used for the planning and
dimensioning when the complete information is not available or
is difficult to process. The core networks around the world today
are almost optical and they form the backbone of the Internet.
Therefore, the statistical characteristics of these networks must be
studied to understand their nature and to estimate their parameters.
In science and technology, network analysis and modeling
are used for several purposes such as the analysis of their stability,
reliability and long term evolution. Knowledge of the statistical
models helps in the estimation of several critical parameters of
the networks.
The work presented in this thesis is focused on the analysis and
modeling of link lengths and shortest path lengths in OTNs. The
parameters used in the models presented in this thesis can be
estimated from the very basic information of the networks such
as the coverage area and the number of nodes, both of which
can be found from the node locations. These models can be
applied to estimate key parameters of the networks.
In this thesis, we have shown that the link lengths of the OTNs follow
general extreme value distribution. The parameters of the
proposed distribution can be estimated from the average link
lengths of the networks. We develop expressions for the average
link lengths of OTNs which can be estimated with an average error
of just 11%. We apply the developed model to estimate link
length dependent parameters in OTNs. We show that the shortest
path lengths of the OTNs follow Johnson SB distribution. We estimate
the parameters of the developed model from the convex
area and the number of nodes of the network. We also apply this
model to estimate several shortest path-dependent parameters
in OTNs.; A análise estatística e modelação de redes é atualmente uma
parte integrante da ciência e engenharia de redes. No caso das
redes óticas de transporte (OTN)...

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## The measurement and dynamic implications of thin filament lengths in heart muscle.

Fonte: PubMed
Publicador: PubMed

Tipo: Artigo de Revista Científica

Publicado em /01/1979
EN

Relevância na Pesquisa

26.13%

1. The lengths of the thin filaments in amphibian and mammalian cardiac muscle have been determined from electron micrographs of serial transverse sections. Thin filament lengths in frog atrial trabeculae range from 0.8 to greater than 1.3 micrometers, with a maximum possible error of 0.14--0.15 micrometer. In rat atrial tissue the span is from 0.6 to more than 1.1 micrometer, whereas in rat papillary muscle the breadth of the distribution is much narrower, from 0.9 to greater than 1.1 micrometer. Double overlap of thin filaments should, therefore, exist over a wide range of sarcomere lenghts. Thin filaments from opposite halves of a sarcomere accommodate each other by flexing up to an angle of about 2 degrees and moving from the trigonal position among the thick filaments to the centre of the region between two thick filaments. Such rearrangement probably contributes to the internal resistance to shortening in the muscle. 2. Except for the variation in thin filament lengths, the over-all morphology of the cardiac sarcomere is generally similar to that found in skeletal muscle. Thick filaments in heart muscle are uniform in length, and their profiles change along their lengths. They are generally round in the M band, triangular adjacent to the M band...

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## Efficient Sparse Signal Transmission over a Lossy Link Using Compressive Sensing

Fonte: MDPI
Publicador: MDPI

Tipo: Artigo de Revista Científica

Publicado em 13/08/2015
EN

Relevância na Pesquisa

25.99%

Reliable data transmission over lossy communication link is expensive due to overheads for error protection. For signals that have inherent sparse structures, compressive sensing (CS) is applied to facilitate efficient sparse signal transmissions over lossy communication links without data compression or error protection. The natural packet loss in the lossy link is modeled as a random sampling process of the transmitted data, and the original signal will be reconstructed from the lossy transmission results using the CS-based reconstruction method at the receiving end. The impacts of packet lengths on transmission efficiency under different channel conditions have been discussed, and interleaving is incorporated to mitigate the impact of burst data loss. Extensive simulations and experiments have been conducted and compared to the traditional automatic repeat request (ARQ) interpolation technique, and very favorable results have been observed in terms of both accuracy of the reconstructed signals and the transmission energy consumption. Furthermore, the packet length effect provides useful insights for using compressed sensing for efficient sparse signal transmission via lossy links.

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## Multiple-antenna systems in ad-hoc wireless networks

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 229 leaves

ENG

Relevância na Pesquisa

25.99%

The increasing demand for wireless communication services has resulted in crowding of the electromagnetic spectrum. The "spectral-commons" model, where a portion of the electromagnetic spectrum is public and used on an ad-hoc basis, has been proposed to free up spectrum that has been allocated but underutilized. Ad-hoc wireless networks (networks with no central control) are also interesting in their own right as they do not require costly infrastructure, are robust to single-node failures, and can be deployed in environments where it is difficult to deploy infrastructure. The main contributions of this thesis are expressions for the mean and in some cases the variance of the spectral efficiency (bits/second/Hz) of single-hop links in random wireless networks as a function of the number of antennas per node, link-length, interferer density, and path-loss-exponent (an environmental parameter that determines signal decay with distance), under assumptions chosen for realistic implementability in the near future. These results improve our understanding of such systems as they indicate the data rates achievable as a function of tangible parameters like user density and environmental characteristics, and are useful for designers of wireless networks to trade-off hardware costs...

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## Distributed shortest path algorithms for computer networks

Fonte: Monterey, California. Naval Postgraduate School
Publicador: Monterey, California. Naval Postgraduate School

Tipo: Relatório
Formato: NA

EN_US

Relevância na Pesquisa

25.99%

This paper presents two distributed algorithms for finding shortest paths from a source node to all other nodes in an N-node network. These algorithms are executed at individual nodes using only local information. Algorithm 1 works in networks where there are no topological changes such as link failures, link recoveries or changes of link lengths. Algorithm 2 is a mofification of Algorithm 1 for networks where there are topological changes. Algorithm 1 determines the optimal shortest paths in at most N3/4 steps, which is only one-half of the computational upper bounds of Abram and Rhodes' and Segall, Merlin and Gallager's algorithms. After the last topological change, Algorithm 2 determines the optimal shortest paths in the same number of steps as Algorithm 1. There are many situations where the present algorithms will work up to N/2 times faster than the algorithms proposed by these authors; Prepared for: Chief of Naval Research
Arlington, VA; http://archive.org/details/distributedshort00yenj; N0001479WR90027; NA

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## Slope lengths and generalized augmented links

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

26.09%

In this paper, we determine geometric information on slope lengths of a large
class of knots in the 3-sphere, based only on diagrammatical properties of the
knots. In particular, we show such knots have meridian length strictly less
than 4, and we find infinitely many families with meridian length approaching 4
from below. Finally, we present an example to show that, in contrast to the
case of the regular augmented link, longitude lengths of these knots cannot be
determined by a function of the number of twist regions alone.; Comment: v2: 20 pages, 13 figures. Simplified proofs of main results and added
two sections, one giving examples of knots with meridian lengths approaching
the upper bound of 4, and one showing that there are no bounds on longitude
length in terms of twist number. Updated the title to reflect these changes.
To appear Comm. Anal. Geom

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## 2d quantum gravity with discrete edge lengths

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/09/1998

Relevância na Pesquisa

36.31%

An approximation of the Standard Regge Calculus (SRC) was proposed by the
$Z_2$-Regge Model ($Z_2$RM). There the edge lengths of the simplicial complexes
are restricted to only two possible values, both always compatible with the
triangle inequalities. To examine the effect of discrete edge lengths, we
define two models to describe the transition from the $Z_2$RM to the SRC. These
models allow to choose the number of possible link lengths to be $n =
{4,8,16,32,64,...}$ and differ mainly in the scaling of the quadratic link
lengths. The first extension, the $X^1_n$-Model, keeps the edge lengths limited
and still behaves rather similar to the "spin-like" $Z_2$RM. The vanishing
critical cosmological constant is reproduced by the second extension, the
$X^C_n$-Model, which allows for increasing edge lengths. In addition the area
expectation values are consistent with the scaling relation of the SRC.; Comment: 3 pages, 4 figures, contribution to LATTICE'98, to be published in
Nucl. Phys. B (Proc. Suppl.)

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## Ising-link Quantum Gravity

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/01/1994

Relevância na Pesquisa

36.16%

We define a simplified version of Regge quantum gravity where the link
lengths can take on only two possible values, both always compatible with the
triangle inequalities. This is therefore equivalent to a model of Ising spins
living on the links of a regular lattice with somewhat complicated, yet local
interactions. The measure corresponds to the natural sum over all 2^links
configurations, and numerical simulations can be efficiently implemented by
means of look-up tables. In three dimensions we find a peak in the ``curvature
susceptibility'' which grows with increasing system size. However, the value of
the corresponding critical exponent as well as the behavior of the curvature at
the transition differ from that found by Hamber and Williams for the Regge
theory with continuously varying link lengths.; Comment: 11 pages

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## The (n)-solvable filtration of the link concordance group and Milnor's invariants

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/11/2012

Relevância na Pesquisa

26.28%

We establish several new results about both the (n)-solvable filtration,
F_n^m, of the set of link concordance classes and the (n)-solvable filtration
of the string link concordance group. We first establish a relationship between
Milnor's invariants and links, L, with certain restrictions on the 4-manifold
bounded by M_L. Using this relationship, we can relate (n)-solvability of a
link (or string link) with its Milnor's invariants. Specifically, we show that
if a link is (n)-solvable, then its Milnor's invariants vanish for lengths up
to 2^{n+2}-1. Previously, there were no known results about the "other half" of
the filtration, namely F_{n.5}^m/F_{n+1}^m. We establish the effect of the Bing
doubling operator on (n)-solvability and using this, we show that
F_{n.5}^m/F_{n+1}^m is nontrivial for links (and string links) with
sufficiently many components. Moreover, we show that these quotients contain an
infinite cyclic subgroup. We also show that links and string links modulo
(1)-solvability is a nonabelian group. We show that we can relate other
filtrations with Milnor's invariants. We show that if a link is n-positive,
then its Milnor's invariants will also vanish for lengths up to 2^{n+2}-1.
Lastly, we prove that the Grope filtration...

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## Time evolution of link length distribution in PRL collaboration network

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

35.99%

An important aspect of a Euclidean network is its link length distribution,
studied in a few real networks so far. We compute the distribution of the link
lengths between collaborators whose papers appear in the PhysicalReview Letters
(PRL) in several years within a range of four decades. The distribution is
non-monotonic; there is a peak at nearest neighbour distances followed by a
sharp fall and a subsequent rise at larger distances. The behaviour of the
statistical properties of the distribution with time indicates that
collaborations might become distance independent in about thirty to forty
years.; Comment: References added, paper shortened and modified

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## On Wireless Link Scheduling and Flow Control

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 27/12/2008

Relevância na Pesquisa

26.04%

This thesis focuses on link scheduling in wireless mesh networks by taking
into account physical layer characteristics. The assumption made throughout is
that a packet is received successfully only if the Signal to Interference and
Noise Ratio (SINR) at the receiver exceeds the communication threshold. The
thesis also discusses the complementary problem of flow control. (1) We
consider various problems on centralized link scheduling in Spatial Time
Division Multiple Access (STDMA) wireless mesh networks. We motivate the use of
spatial reuse as performance metric and provide an explicit characterization of
spatial reuse. We propose link scheduling algorithms based on certain graph
models (communication graph, SINR graph) of the network. Our algorithms achieve
higher spatial reuse than that of existing algorithms, with only a slight
increase in computational complexity. (2) We investigate random access
algorithms in wireless networks. We assume that the receiver is capable of
power-based capture and propose a splitting algorithm that varies transmission
powers of users on the basis of quaternary channel feedback. We model the
algorithm dynamics by a Discrete Time Markov Chain and consequently show that
its maximum stable throughput is 0.5518. Our algorithm achieves higher maximum
stable throughput and significantly lower delay than the First Come First Serve
(FCFS) splitting algorithm with uniform transmission power. (3) We consider the
problem of flow control in packet networks from an information-theoretic
perspective. We derive the maximum entropy of a flow which conforms to traffic
constraints imposed by a generalized token bucket regulator (GTBR)...

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## Critical Points of Correlated Percolation in a Gravitational Link-adding Network Model

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/04/2012

Relevância na Pesquisa

26.29%

Motivated by the importance of geometric information in real systems, a new
model for long-range correlated percolation in link-adding networks is proposed
with the connecting probability decaying with a power-law of the distance on
the two-dimensional(2D) plane. By overlapping it with Achlioptas process, it
serves as a gravity model which can be tuned to facilitate or inhibit the
network percolation in a generic view, cover a broad range of thresholds.
Moreover, it yields a set of new scaling relations. In the present work, we
develop an approach to determine critical points for them by simulating the
temporal evolutions of type-I, type-II and type-III links(chosen from both
inter-cluster links, an intra-cluster link compared with an inter-cluster one,
and both intra-cluster ones, respectively) and corresponding average lengths.
Numerical results have revealed objective competition between fractions,
average lengths of three types of links, verified the balance happened at
critical points. The variation of decay exponents $a$ or transmission radius
$R$ always shifts the temporal pace of the evolution, while the steady average
lengths and the fractions of links always keep unchanged just as the values in
Achlioptas process. Strategy with maximum gravity can keep steady average
length...

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## The random link approximation for the Euclidean traveling salesman problem

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

26.04%

The traveling salesman problem (TSP) consists of finding the length of the
shortest closed tour visiting N ``cities''. We consider the Euclidean TSP where
the cities are distributed randomly and independently in a d-dimensional unit
hypercube. Working with periodic boundary conditions and inspired by a
remarkable universality in the kth nearest neighbor distribution, we find for
the average optimum tour length = beta_E(d) N^{1-1/d} [1+O(1/N)] with
beta_E(2) = 0.7120 +- 0.0002 and beta_E(3) = 0.6979 +- 0.0002. We then derive
analytical predictions for these quantities using the random link
approximation, where the lengths between cities are taken as independent random
variables. From the ``cavity'' equations developed by Krauth, Mezard and
Parisi, we calculate the associated random link values beta_RL(d). For d=1,2,3,
numerical results show that the random link approximation is a good one, with a
discrepancy of less than 2.1% between beta_E(d) and beta_RL(d). For large d, we
argue that the approximation is exact up to O(1/d^2) and give a conjecture for
beta_E(d), in terms of a power series in 1/d, specifying both leading and
subleading coefficients.; Comment: 29 pages, 6 figures; formatting and typos corrected

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## Comparing Mean Field and Euclidean Matching Problems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

26.2%

Combinatorial optimization is a fertile testing ground for statistical
physics methods developed in the context of disordered systems, allowing one to
confront theoretical mean field predictions with actual properties of finite
dimensional systems. Our focus here is on minimum matching problems, because
they are computationally tractable while both frustrated and disordered. We
first study a mean field model taking the link lengths between points to be
independent random variables. For this model we find perfect agreement with the
results of a replica calculation. Then we study the case where the points to be
matched are placed at random in a d-dimensional Euclidean space. Using the mean
field model as an approximation to the Euclidean case, we show numerically that
the mean field predictions are very accurate even at low dimension, and that
the error due to the approximation is O(1/d^2). Furthermore, it is possible to
improve upon this approximation by including the effects of Euclidean
correlations among k link lengths. Using k=3 (3-link correlations such as the
triangle inequality), the resulting errors in the energy density are already
less than 0.5% at d>=2. However, we argue that the Euclidean model's 1/d series
expansion is beyond all orders in k of the expansion in k-link correlations.; Comment: 11 pages...

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## Influence of the Measure on Simplicial Quantum Gravity in Four Dimensions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 22/04/1992

Relevância na Pesquisa

26.09%

We investigate the influence of the measure in the path integral for
Euclidean quantum gravity in four dimensions within the Regge calculus. The
action is bounded without additional terms by fixing the average lattice
spacing. We set the length scale by a parameter $\beta$ and consider a scale
invariant and a uniform measure. In the low $\beta$ region we observe a phase
with negative curvature and a homogeneous distribution of the link lengths
independent of the measure. The large $\beta$ region is characterized by
inhomogeneous link lengths distributions with spikes and positive curvature
depending on the measure.; Comment: 12pgs

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## The Link Prediction Problem in Bipartite Networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/06/2010

Relevância na Pesquisa

26.09%

We define and study the link prediction problem in bipartite networks,
specializing general link prediction algorithms to the bipartite case. In a
graph, a link prediction function of two vertices denotes the similarity or
proximity of the vertices. Common link prediction functions for general graphs
are defined using paths of length two between two nodes. Since in a bipartite
graph adjacency vertices can only be connected by paths of odd lengths, these
functions do not apply to bipartite graphs. Instead, a certain class of graph
kernels (spectral transformation kernels) can be generalized to bipartite
graphs when the positive-semidefinite kernel constraint is relaxed. This
generalization is realized by the odd component of the underlying spectral
transformation. This construction leads to several new link prediction
pseudokernels such as the matrix hyperbolic sine, which we examine for rating
graphs, authorship graphs, folksonomies, document--feature networks and other
types of bipartite networks.; Comment: 10 pages

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## Scaling of optimal-path-lengths distribution in complex networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 01/08/2005

Relevância na Pesquisa

26.18%

We study the distribution of optimal path lengths in random graphs with
random weights associated with each link (``disorder''). With each link $i$ we
associate a weight $\tau_i = \exp(ar_i)$ where $r_i$ is a random number taken
from a uniform distribution between 0 and 1, and the parameter $a$ controls the
strength of the disorder. We suggest, in analogy with the average length of the
optimal path, that the distribution of optimal path lengths has a universal
form which is controlled by the expression
$\frac{1}{p_c}\frac{\ell_{\infty}}{a}$, where $\ell_{\infty}$ is the optimal
path length in strong disorder ($a \to \infty$) and $p_c$ is the percolation
threshold. This relation is supported by numerical simulations for
Erd\H{o}s-R\'enyi and scale-free graphs. We explain this phenomenon by showing
explicitly the transition between strong disorder and weak disorder at
different length scales in a single network.

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## On the Maximum Span of Fixed-Angle Chains

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

26.09%

Soss proved that it is NP-hard to find the maximum 2D span of a fixed-angle
polygonal chain: the largest distance achievable between the endpoints in a
planar embedding. These fixed-angle chains can serve as models of protein
backbones. The corresponding problem in 3D is open. We show that three special
cases of particular relevance to the protein model are solvable in polynomial
time. When all link lengths and all angles are equal, the maximum 3D span is
achieved in a flat configuration and can be computed in constant time. When all
angles are equal and the chain is simple (non-self-crossing), the maximum flat
span can be found in linear time. In 3D, when all angles are equal to 90 deg
(but the link lengths arbitrary), the maximum 3D span is in general nonplanar
but can be found in quadratic time.; Comment: 28 pages, 21 figures. Preliminary version appeared in Proc. 18th
Canad. Conf. Comput. Geom., pages 93-96, 2006. This paper has been withdrawn
by the authors. Lemma 15 as stated is incorrect, and although we believe the
main theorems following (Thms. 17 & 18) are true, the proofs relying on
Lem.15 are not valid

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## Measuring the dimension of partially embedded networks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/08/2013

Relevância na Pesquisa

26.04%

#Physics - Physics and Society#Computer Science - Social and Information Networks#Physics - Data Analysis, Statistics and Probability

Scaling phenomena have been intensively studied during the past decade in the
context of complex networks. As part of these works, recently novel methods
have appeared to measure the dimension of abstract and spatially embedded
networks. In this paper we propose a new dimension measurement method for
networks, which does not require global knowledge on the embedding of the
nodes, instead it exploits link-wise information (link lengths, link delays or
other physical quantities). Our method can be regarded as a generalization of
the spectral dimension, that grasps the network's large-scale structure through
local observations made by a random walker while traversing the links. We apply
the presented method to synthetic and real-world networks, including road maps,
the Internet infrastructure and the Gowalla geosocial network. We analyze the
theoretically and empirically designated case when the length distribution of
the links has the form P(r) ~ 1/r. We show that while previous dimension
concepts are not applicable in this case, the new dimension measure still
exhibits scaling with two distinct scaling regimes. Our observations suggest
that the link length distribution is not sufficient in itself to entirely
control the dimensionality of complex networks...

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