38,705 research outputs found
Diffusion on Complex Networks : A way to probe their large scale topological structures
A diffusion process on complex networks is introduced in order to uncover
their large scale topological structures. This is achieved by focusing on the
slowest decaying diffusive modes of the network. The proposed procedure is
applied to real-world networks like a friendship network of known modular
structure, and an Internet routing network. For the friendship network, its
known structure is well reproduced. In case of the Internet, where the
structure is far less well-known, one indeed finds a modular structure, and
modules can roughly be associated with individual countries. Quantitatively the
modular structure of the Internet manifests itself in an approximately 10 times
larger participation ratio of its slowest decaying modes as compared to the
null model -- a random scale-free network. The extreme edges of the Internet
are found to correspond to Russian and US military sites.Comment: Latex, 13 pages, 4 figures (To appear Physica A
The Architecture of a Novel Weighted Network: Knowledge Network
Networked structure emerged from a wide range of fields such as biological
systems, World Wide Web and technological infrastructure. A deeply insight into
the topological complexity of these networks has been gained. Some works start
to pay attention to the weighted network, like the world-wide airport network
and the collaboration network, where links are not binary, but have
intensities. Here, we construct a novel knowledge network, through which we
take the first step to uncover the topological structure of the knowledge
system. Furthermore, the network is extended to the weighted one by assigning
weights to the edges. Thus, we also investigate the relationship between the
intensity of edges and the topological structure. These results provide a novel
description to understand the hierarchies and organizational principles in
knowledge system, and the interaction between the intensity of edges and
topological structure. This system also provides a good paradigm to study
weighted networks.Comment: 5 figures 11 page
Topological Defects and the Formation of Structure in the Universe
Topological defects, in particular cosmic strings, give rise to an
interesting mechanism for generating the primordial perturbations in the early
Universe which are required to explain the present structure. An overview of
the cosmic string model will be given, focusing on the predictions of the
theory for the large-scale structure of the Universe and for cosmic microwave
background anisotropies.Comment: 12 pages, 4 figures, uses LATEX and eps
The structure of Inter-Urban traffic: A weighted network analysis
We study the structure of the network representing the interurban commuting
traffic of the Sardinia region, Italy, which amounts to 375 municipalities and
1,600,000 inhabitants. We use a weighted network representation where vertices
correspond to towns and the edges to the actual commuting flows among those. We
characterize quantitatively both the topological and weighted properties of the
resulting network. Interestingly, the statistical properties of commuting
traffic exhibit complex features and non-trivial relations with the underlying
topology. We characterize quantitatively the traffic backbone among large
cities and we give evidences for a very high heterogeneity of the commuter
flows around large cities. We also discuss the interplay between the
topological and dynamical properties of the network as well as their relation
with socio-demographic variables such as population and monthly income. This
analysis may be useful at various stages in environmental planning and provides
analytical tools for a wide spectrum of applications ranging from impact
evaluation to decision-making and planning support.Comment: 12 pages, 12 figures, 4 tables; 1 missing ref added and minor
revision
On-surface Assembly of Au-Dicyanoanthracene Coordination Structures on Au(111)
On-surface metal-organic coordination provides a promising way for
synthesizing different two-dimensional lattice structures that have been
predicted to possess exotic electronic properties. Using scanning tunneling
microscopy (STM) and spectroscopy (STS), we studied the supramolecular
self-assembly of 9,10-dicyanoanthracene (DCA) molecules on the Au(111) surface.
Close-packed islands of DCA molecules and Au-DCA metal-organic coordination
structures coexist on the Au(111) surface. Ordered DCAAu
metal-organic networks have a structure combining a honeycomb lattice of Au
atoms with a kagome lattice of DCA molecules. Low-temperature STS experiments
demonstrate the presence of a delocalized electronic state containing
contributions from both the gold atom states and the lowest unoccupied
molecular orbital of the DCA molecules. These findings are important for the
future search of topological phases in metal-organic networks combining
honeycomb and kagome lattices with strong spin-orbit coupling in heavy metal
atoms
The Revival of Cosmic Strings
Cosmic strings are one-dimensional topological defects which could have been
formed in the early stages of our Universe. They triggered a lot of interest,
mainly for their cosmological implications: they could offer an alternative to
inflation for the generation of density perturbations. It was shown however
that cosmic strings lead to inconsistencies with the measurements of the cosmic
microwave background temperature anisotropies. The picture is changed recently.
It was shown that, on the one hand, cosmic strings can be generically formed in
the framework of supersymmetric grand unified theories and that, on the other
hand, cosmic superstrings could play the r\^ole of cosmic strings. There is
also some possible observational support. All this lead to a revival of cosmic
strings research and this is the topic of my lecture.Comment: 13 pages, Invited Lecture in " Pomeranian Workshop in Fundamental
Cosmology" (Poland 2005), to be published in Annalen der Physi
Synchronization processes in complex networks
We present an extended analysis, based on the dynamics towards
synchronization of a system of coupled oscillators, of the hierarchy of
communities in complex networks. In the synchronization process, different
structures corresponding to well defined communities of nodes appear in a
hierarchical way. The analysis also provides a useful connection between
synchronization dynamics, complex networks topology and spectral graph
analysis.Comment: 16 pages, 4 figures. To appear in Physica D "Special Issue on
dynamics on complex networks
Topological kink states at a tilt boundary in gated multi-layer graphene
The search for new realization of topologically protected edge states is an
active area of research. We show that a tilt boundary in gated multi-layer
graphene supports topologically protected gapless kink states, associated with
quantum valley Hall insulator (QVH). We investigate such kink states from two
perspectives: the microscopic perspective of a tight-binding model and an
ab-initio calculation on bilayer, and the perspective of symmetry protected
topological (SPT) states for general multi-layer. We show that a AB-BA bilayer
tilt boundary supports gapless kink states that are undeterred by strain
concentrated at the boundary. Further, we establish the kink states as concrete
examples of edge states of {\it time-reversal symmetric} -type
SPT, protected by no valley mixing, electron number conservation, and time
reversal symmetries. This allows us to discuss possible phase transitions
upon symmetry changes from the SPT perspective. Recent experimental
observations of a network of such tilt boundaries suggest that transport
through these novel topological kink states might explain the long standing
puzzle of sub-gap conductance. Further, recent observation of gap closing and
re-opening in gated bi-layer might be the first example of a transition between
two distinct SPT's: QVH and LAF.Comment: Improved a discussion of the structural aspects of the tilt boundary.
Included a discussion of boundary condition dependence. Added new section on
connection to experiment
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