351 research outputs found
On the Tomography of Networks and Multicast Trees
In this paper we model the tomography of scale free networks by studying the
structure of layers around an arbitrary network node. We find, both
analytically and empirically, that the distance distribution of all nodes from
a specific network node consists of two regimes. The first is characterized by
rapid growth, and the second decays exponentially. We also show that the nodes
degree distribution at each layer is a power law with an exponential cut-off.
We obtain similar results for the layers surrounding the root of multicast
trees cut from such networks, as well as the Internet. All of our results were
obtained both analytically and on empirical Interenet data
Localization transition on complex networks via spectral statistics
The spectral statistics of complex networks are numerically studied.
The features of the Anderson metal-insulator transition are found to be
similar for a wide range of different networks. A metal-insulator transition as
a function of the disorder can be observed for different classes of complex
networks for which the average connectivity is small. The critical index of the
transition corresponds to the mean field expectation. When the connectivity is
higher, the amount of disorder needed to reach a certain degree of localization
is proportional to the average connectivity, though a precise transition cannot
be identified. The absence of a clear transition at high connectivity is
probably due to the very compact structure of the highly connected networks,
resulting in a small diameter even for a large number of sites.Comment: 6 pages, expanded introduction and referencess (to appear in PRE
Volatility of Linear and Nonlinear Time Series
Previous studies indicate that nonlinear properties of Gaussian time series
with long-range correlations, , can be detected and quantified by studying
the correlations in the magnitude series , i.e., the ``volatility''.
However, the origin for this empirical observation still remains unclear, and
the exact relation between the correlations in and the correlations in
is still unknown. Here we find analytical relations between the scaling
exponent of linear series and its magnitude series . Moreover, we
find that nonlinear time series exhibit stronger (or the same) correlations in
the magnitude time series compared to linear time series with the same
two-point correlations. Based on these results we propose a simple model that
generates multifractal time series by explicitly inserting long range
correlations in the magnitude series; the nonlinear multifractal time series is
generated by multiplying a long-range correlated time series (that represents
the magnitude series) with uncorrelated time series [that represents the sign
series ]. Our results of magnitude series correlations may help to
identify linear and nonlinear processes in experimental records.Comment: 7 pages, 5 figure
Width of percolation transition in complex networks
It is known that the critical probability for the percolation transition is
not a sharp threshold, actually it is a region of non-zero width
for systems of finite size. Here we present evidence that for complex networks
, where is the average
length of the percolation cluster, and is the number of nodes in the
network. For Erd\H{o}s-R\'enyi (ER) graphs , while for
scale-free (SF) networks with a degree distribution
and , . We show analytically
and numerically that the \textit{survivability} , which is the
probability of a cluster to survive chemical shells at probability ,
behaves near criticality as . Thus
for probabilities inside the region the behavior of the
system is indistinguishable from that of the critical point
Scale-Free Networks Emerging from Weighted Random Graphs
We study Erd\"{o}s-R\'enyi random graphs with random weights associated with
each link. We generate a new ``Supernode network'' by merging all nodes
connected by links having weights below the percolation threshold (percolation
clusters) into a single node. We show that this network is scale-free, i.e.,
the degree distribution is with . Our
results imply that the minimum spanning tree (MST) in random graphs is composed
of percolation clusters, which are interconnected by a set of links that create
a scale-free tree with . We show that optimization causes the
percolation threshold to emerge spontaneously, thus creating naturally a
scale-free ``supernode network''. We discuss the possibility that this
phenomenon is related to the evolution of several real world scale-free
networks
Stromal Gli2 activity coordinates a niche signaling program for mammary epithelial stem cells
The stem cell niche is a complex local signaling microenvironment that sustains stem cell activity during organ maintenance and regeneration. The mammary gland niche must support its associated stem cells while also responding to systemic hormonal regulation that triggers pubertal changes. We find that Gli2, the major Hedgehog pathway transcriptional effector, acts within mouse mammary stromal cells to direct a hormoneresponsive niche signaling program by activating expression of factors that regulate epithelial stem cells as well as receptors for the mammatrophic hormones estrogen and growth hormone.Whereas prior studies implicate stem cell defects in human disease, this work shows that niche dysfunction may also cause disease, with possible relevance for human disorders and in particular the breast growth pathogenesis associated with combined pituitary hormone deficiency. Copyright 2016 by the American Association for the Advancement of Science, all rights reserved.116Ysciescopu
Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling
We present a \u27top-down\u27 patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors
Effect of Disorder Strength on Optimal Paths in Complex Networks
We study the transition between the strong and weak disorder regimes in the
scaling properties of the average optimal path in a disordered
Erd\H{o}s-R\'enyi (ER) random network and scale-free (SF) network. Each link
is associated with a weight , where is a
random number taken from a uniform distribution between 0 and 1 and the
parameter controls the strength of the disorder. We find that for any
finite , there is a crossover network size at which the transition
occurs. For the scaling behavior of is in the
strong disorder regime, with for ER networks and
for SF networks with , and for SF networks with . For the scaling behavior is in the weak disorder regime, with for ER networks and SF networks with . In order to
study the transition we propose a measure which indicates how close or far the
disordered network is from the limit of strong disorder. We propose a scaling
ansatz for this measure and demonstrate its validity. We proceed to derive the
scaling relation between and . We find that for ER
networks and for SF networks with , and for SF networks with .Comment: 6 pages, 6 figures. submitted to Phys. Rev.
Critical points in the Bragg glass phase of a weakly pinned crystal of CaRhSn
New experimental data are presented on the scan rate dependence of the
magnetization hysteresis width ( critical current
density ) in isothermal scans in a weakly pinned single crystal
of CaRhSn, which displays second magnetization peak (SMP)
anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the
dynamical annealing of the disordered bundles of vortices injected through the
sample edges towards the destined equilibrium vortex state at a given .
These data, in conjunction with the earlier observations made while studying
the thermomagnetic history dependence in in the tracing of the minor
hysteresis loops, imply that the partially disordered state heals towards the
more ordered state between the peak field of the SMP anomaly and the onset
field of the PE. The vortex phase diagram in the given crystal of
CaRhSn has been updated in the context of the notion of the
phase coexistence of the ordered and disordered regions between the onset field
of the SMP anomaly and the spinodal line located just prior to the
irreversibility line. A multi-critical point and a critical point in the
() region of the Bragg glass phase have been marked in this phase diagram
and the observed behaviour is discussed in the light of recent data on
multi-critical point in the vortex phase diagram in a single crystal of Nb.Comment: To appear in Current trends in Vortex State Studies - Pramana J.
Physic
Surface superconductivity in multilayered rhombohedral graphene: Supercurrent
The supercurrent for the surface superconductivity of a flat-band
multilayered rhombohedral graphene is calculated. Despite the absence of
dispersion of the excitation spectrum, the supercurrent is finite. The critical
current is proportional to the zero-temperature superconducting gap, i.e., to
the superconducting critical temperature and to the size of the flat band in
the momentum space
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