28,689 research outputs found
Impact of edge-removal on the centrality betweenness of the best spreaders
The control of epidemic spreading is essential to avoid potential fatal
consequences and also, to lessen unforeseen socio-economic impact. The need for
effective control is exemplified during the severe acute respiratory syndrome
(SARS) in 2003, which has inflicted near to a thousand deaths as well as
bankruptcies of airlines and related businesses. In this article, we examine
the efficacy of control strategies on the propagation of infectious diseases
based on removing connections within real world airline network with the
associated economic and social costs taken into account through defining
appropriate quantitative measures. We uncover the surprising results that
removing less busy connections can be far more effective in hindering the
spread of the disease than removing the more popular connections. Since
disconnecting the less popular routes tend to incur less socio-economic cost,
our finding suggests the possibility of trading minimal reduction in
connectivity of an important hub with efficiencies in epidemic control. In
particular, we demonstrate the performance of various local epidemic control
strategies, and show how our approach can predict their cost effectiveness
through the spreading control characteristics.Comment: 11 pages, 4 figure
Non-equilibrium spatial distribution of Rashba spin torque in ferromagnetic metal layer
We study the spatial distribution of spin torque induced by a strong Rashba
spin-orbit coupling (RSOC) in a ferromagnetic (FM) metal layer, using the
Keldysh non-equilibrium Green's function method. In the presence of the s-d
interaction between the non-equilibrium conduction electrons and the local
magnetic moments, the RSOC effect induces a torque on the moments, which we
term as the Rashba spin torque.
A correlation between the Rashba spin torque and the spatial spin current is
presented in this work, clearly mapping the spatial distribution of Rashba Spin
torque in a nano-sized ferromagnetic device. When local magnetism is turned on,
the out-of-plane (Sz) Spin Hall effect (SHE) is disrupted, but rather
unexpectedly an in-plane (Sy) SHE is detected. We also study the effect of
Rashba strength (\alpha_R) and splitting exchange (\Delta) on the
non-equilibrium Rashba spin torque averaged over the device. Rashba spin torque
allows an efficient transfer of spin momentum such that a typical switching
field of 20 mT can be attained with a low current density of less than 10^6
A/cm^2
Analytic Expression for the Joint x and Q^2 Dependences of the Structure Functions of Deep Inelastic Scattering
We obtain a good analytic fit to the joint Bjorken-x and Q^2 dependences of
ZEUS data on the deep inelastic structure function F_2(x, Q^2). At fixed
virtuality Q^2, as we showed previously, our expression is an expansion in
powers of log (1/x) that satisfies the Froissart bound. Here we show that for
each x, the Q^2 dependence of the data is well described by an expansion in
powers of log Q^2. The resulting analytic expression allows us to predict the
logarithmic derivatives {({\partial}^n F_2^p/{{(\partial\ln Q^2}})^n)}_x for n
= 1,2 and to compare the results successfully with other data. We extrapolate
the proton structure function F_2^p(x,Q^2) to the very large Q^2 and the very
small x regions that are inaccessible to present day experiments and contrast
our expectations with those of conventional global fits of parton distribution
functions.Comment: 4 pages, 3 figures, a few changes in the text. Version to be
published in Physical Review Letter
Ultra-high energy neutrino scattering
Estimates are made of the ultra-high energy neutrino cross sections based on
an extrapolation to very small Bjorken x of the logarithmic Froissart
dependence in x shown previously to provide an excellent fit to the measured
proton structure function F_2^p(x,Q^2) over a broad range of the virtuality
Q^2. Expressions are obtained for both the neutral current and the charged
current cross sections. Comparison with an extrapolation based on perturbative
QCD shows good agreement for energies where both fit data, but our rates are as
much as a factor of 10 smaller for neutrino energies above 10^9 GeV, with
important implications for experiments searching for extra-galactic neutrinos.Comment: 4 pages, 1 figure, 1 table; Title, abstract and text changed,
conclusions unchanged. Version accepted for publication in Physical Review
Surface segregation and the Al problem in GaAs quantum wells
Low-defect two-dimensional electron systems (2DESs) are essential for studies
of fragile many-body interactions that only emerge in nearly-ideal systems. As
a result, numerous efforts have been made to improve the quality of
modulation-doped AlGaAs/GaAs quantum wells (QWs), with an emphasis
on purifying the source material of the QW itself or achieving better vacuum in
the deposition chamber. However, this approach overlooks another crucial
component that comprises such QWs, the AlGaAs barrier. Here we show
that having a clean Al source and hence a clean barrier is instrumental to
obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the
2DES in GaAs QWs declines as the thickness or Al content of the
AlGaAs barrier beneath the QW is increased, which we attribute to
the surface segregation of Oxygen atoms that originate from the Al source. This
conjecture is supported by the improved mobility in the GaAs QWs as the Al cell
is cleaned out by baking
An Optimal Algorithm for the Maximum-Density Segment Problem
We address a fundamental problem arising from analysis of biomolecular
sequences. The input consists of two numbers and and a
sequence of number pairs with . Let {\em segment}
of be the consecutive subsequence of between indices and
. The {\em density} of is
. The {\em maximum-density
segment problem} is to find a maximum-density segment over all segments
with . The best
previously known algorithm for the problem, due to Goldwasser, Kao, and Lu,
runs in time. In the present paper, we solve
the problem in O(n) time. Our approach bypasses the complicated {\em right-skew
decomposition}, introduced by Lin, Jiang, and Chao. As a result, our algorithm
has the capability to process the input sequence in an online manner, which is
an important feature for dealing with genome-scale sequences. Moreover, for a
type of input sequences representable in space, we show how to
exploit the sparsity of and solve the maximum-density segment problem for
in time.Comment: 15 pages, 12 figures, an early version of this paper was presented at
11th Annual European Symposium on Algorithms (ESA 2003), Budapest, Hungary,
September 15-20, 200
The effect of network structure on phase transitions in queuing networks
Recently, De Martino et al have presented a general framework for the study
of transportation phenomena on complex networks. One of their most significant
achievements was a deeper understanding of the phase transition from the
uncongested to the congested phase at a critical traffic load. In this paper,
we also study phase transition in transportation networks using a discrete time
random walk model. Our aim is to establish a direct connection between the
structure of the graph and the value of the critical traffic load. Applying
spectral graph theory, we show that the original results of De Martino et al
showing that the critical loading depends only on the degree sequence of the
graph -- suggesting that different graphs with the same degree sequence have
the same critical loading if all other circumstances are fixed -- is valid only
if the graph is dense enough. For sparse graphs, higher order corrections,
related to the local structure of the network, appear.Comment: 12 pages, 7 figure
Interference measurements of non-Abelian e/4 & Abelian e/2 quasiparticle braiding
The quantum Hall states at filling factors and are expected
to have Abelian charge quasiparticles and non-Abelian charge
quasiparticles. For the first time we report experimental evidence for the
non-Abelian nature of excitations at and examine the fermion parity,
a topological quantum number of an even number of non-Abelian quasiparticles,
by measuring resistance oscillations as a function of magnetic field in
Fabry-P\'erot interferometers using new high purity heterostructures. The phase
of observed oscillations is reproducible and stable over long times
(hours) near and , indicating stability of the fermion parity.
When phase fluctuations are observed, they are predominantly phase flips,
consistent with fermion parity change. We also examine lower-frequency
oscillations attributable to Abelian interference processes in both states.
Taken together, these results constitute new evidence for the non-Abelian
nature of quasiparticles; the observed life-time of their combined
fermion parity further strengthens the case for their utility for topological
quantum computation.Comment: A significantly revised version; 54 double-column pages containing 14
pages of main text + Supplementary Materials. The figures, which include a
number of new figures, are now incorporated into the tex
Nagy-Soper subtraction scheme for multiparton final states
In this work, we present the extension of an alternative subtraction scheme
for next-to-leading order QCD calculations to the case of an arbitrary number
of massless final-state partons. The scheme is based on the splitting kernels
of an improved parton shower and comes with a reduced number of final state
momentum mappings. While a previous publication including the setup of the
scheme has been restricted to cases with maximally two massless partons in the
final state, we here provide the final state real emission and integrated
subtraction terms for processes with any number of massless partons. We apply
our scheme to three jet production at lepton colliders at next-to-leading order
and present results for the differential C parameter distribution.Comment: 45 pages, 5 figures v2: several references added; v3: title changed,
references and a discussion of further scaling improvement added. Corresponds
to published journal versio
Some Exact Results for Spanning Trees on Lattices
For -vertex, -dimensional lattices with , the number
of spanning trees grows asymptotically as
in the thermodynamic limit. We present an exact closed-form result for the
asymptotic growth constant for spanning trees on the
-dimensional body-centered cubic lattice. We also give an exact integral
expression for on the face-centered cubic lattice and an exact
closed-form expression for on the lattice.Comment: 7 pages, 1 tabl
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