6,654 research outputs found
Correlated multiplexity and connectivity of multiplex random networks
Nodes in a complex networked system often engage in more than one type of
interactions among them; they form a multiplex network with multiple types of
links. In real-world complex systems, a node's degree for one type of links and
that for the other are not randomly distributed but correlated, which we term
correlated multiplexity. In this paper we study a simple model of multiplex
random networks and demonstrate that the correlated multiplexity can
drastically affect the properties of giant component in the network.
Specifically, when the degrees of a node for different interactions in a duplex
Erdos-Renyi network are maximally correlated, the network contains the giant
component for any nonzero link densities. In contrast, when the degrees of a
node are maximally anti-correlated, the emergence of giant component is
significantly delayed, yet the entire network becomes connected into a single
component at a finite link density. We also discuss the mixing patterns and the
cases with imperfect correlated multiplexity.Comment: Revised version, 12 pages, 6 figure
Search for Magnetic Order in Superconducting RuSr2Eu1.2Ce0.8Cu2O10
Neutron diffraction, polarized neutron transmission, and small angle neutron
scattering have been used to investigate the crystal structure and nature of
the magnetic order in a polycrystalline sample of RuSr2Eu1.2Ce0.8Cu2O10. The
sample was made with the Eu-153 (98.8%) isotope to reduce the high neutron
absorption for the naturally occurring element. Full refinements of the crystal
structure, space group I4/mmm, are reported. At low temperatures only a single
magnetic peak is clearly observed in a relatively wide angular range. A sharp
spin reorientation transition (SRT) is observed around 35 K, close to the
superconducting transition temperature (Tc~40 K). Between the spin
reorientation temperature and the Neel temperature of 59 K, additional magnetic
reflections are observed. However, none of these can be simply indexed on the
chemical unit cell, either as commensurate peaks or simple incommensurate
magnetism, and the paucity of reflections at low T compels the conclusion that
these magnetic Bragg peaks arise from an impurity phase. X-ray and neutron
diffraction on the pressed pellet both show that the sample does not appear to
contain substantial impurity phases, but it turns out that the magnetic
impurity peaks exhibit strong preferred orientation with respect to the pellet
orientation, while the primary phase does not. We have been unable to observe
any magnetic order that can be identified with the ruthenate-cuprate system.Comment: 7 figures. Submitted to Phys. Rev.
Supergravity loop contributions to brane world supersymmetry breaking
We compute the supergravity loop contributions to the visible sector scalar
masses in the simplest 5D `brane-world' model. Supersymmetry is assumed to be
broken away from the visible brane and the contributions are UV finite due to
5D locality. We perform the calculation with N = 1 supergraphs, using a
formulation of 5D supergravity in terms of N = 1 superfields. We compute
contributions to the 4D effective action that determine the visible scalar
masses, and we find that the mass-squared terms are negative.Comment: 12 pages, LaTeX 2
Cascade-based attacks on complex networks
We live in a modern world supported by large, complex networks. Examples
range from financial markets to communication and transportation systems. In
many realistic situations the flow of physical quantities in the network, as
characterized by the loads on nodes, is important. We show that for such
networks where loads can redistribute among the nodes, intentional attacks can
lead to a cascade of overload failures, which can in turn cause the entire or a
substantial part of the network to collapse. This is relevant for real-world
networks that possess a highly heterogeneous distribution of loads, such as the
Internet and power grids. We demonstrate that the heterogeneity of these
networks makes them particularly vulnerable to attacks in that a large-scale
cascade may be triggered by disabling a single key node. This brings obvious
concerns on the security of such systems.Comment: 4 pages, 4 figures, Revte
An SO(10) Grand Unified Theory of Flavor
We present a supersymmetric SO(10) grand unified theory (GUT) of flavor based
on an family symmetry. It makes use of our recent proposal to use SO(10)
with type II seesaw mechanism for neutrino masses combined with a simple ansatz
that the dominant Yukawa matrix (the {\bf 10}-Higgs coupling to matter) has
rank one. In this paper, we show how the rank one model can arise within some
plausible assumptions as an effective field theory from vectorlike {\bf 16}
dimensional matter fields with masses above the GUT scale. In order to obtain
the desired fermion flavor texture we use flavon multiplets which acquire
vevs in the ground state of the theory. By supplementing the theory with
an additional discrete symmetry, we find that the flavon vacuum field
alignments take a discrete set of values provided some of the higher
dimensional couplings are small. Choosing a particular set of these vacuum
alignments appears to lead to an unified understanding of observed quark-lepton
flavor:
(i) the lepton mixing matrix that is dominantly tri-bi-maximal with small
corrections related to quark mixings; (ii) quark lepton mass relations at GUT
scale: and and (iii) the solar to
atmospheric neutrino mass ratio in agreement with observations. The model predicts the neutrino
mixing parameter, ,
which should be observable in planned long baseline experiments.Comment: Final version of the paper as it will appear in JHEP
Self-similar disk packings as model spatial scale-free networks
The network of contacts in space-filling disk packings, such as the
Apollonian packing, are examined. These networks provide an interesting example
of spatial scale-free networks, where the topology reflects the broad
distribution of disk areas. A wide variety of topological and spatial
properties of these systems are characterized. Their potential as models for
networks of connected minima on energy landscapes is discussed.Comment: 13 pages, 12 figures; some bugs fixed and further discussion of
higher-dimensional packing
Fluctuation-driven dynamics of the Internet topology
We study the dynamics of the Internet topology based on the empirical data on
the level of the autonomous systems. It is found that the fluctuations
occurring in the stochastic process of connecting and disconnecting edges are
important features of the Internet dynamics. The network's overall growth can
be described approximately by a single characteristic degree growth rate
and the fluctuation strength , together with the vertex growth rate . A
stochastic model which incorporate these values and an adaptation rule newly
introduced reproduces several features of the real Internet topology such as
the correlations between the degrees of different vertices.Comment: Final version appeared in Phys. Rev. Let
Distributed flow optimization and cascading effects in weighted complex networks
We investigate the effect of a specific edge weighting scheme on distributed flow efficiency and robustness to cascading
failures in scale-free networks. In particular, we analyze a simple, yet
fundamental distributed flow model: current flow in random resistor networks.
By the tuning of control parameter and by considering two general cases
of relative node processing capabilities as well as the effect of bandwidth, we
show the dependence of transport efficiency upon the correlations between the
topology and weights. By studying the severity of cascades for different
control parameter , we find that network resilience to cascading
overloads and network throughput is optimal for the same value of over
the range of node capacities and available bandwidth
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