2,455 research outputs found
Containing epidemic outbreaks by message-passing techniques
The problem of targeted network immunization can be defined as the one of
finding a subset of nodes in a network to immunize or vaccinate in order to
minimize a tradeoff between the cost of vaccination and the final (stationary)
expected infection under a given epidemic model. Although computing the
expected infection is a hard computational problem, simple and efficient
mean-field approximations have been put forward in the literature in recent
years. The optimization problem can be recast into a constrained one in which
the constraints enforce local mean-field equations describing the average
stationary state of the epidemic process. For a wide class of epidemic models,
including the susceptible-infected-removed and the
susceptible-infected-susceptible models, we define a message-passing approach
to network immunization that allows us to study the statistical properties of
epidemic outbreaks in the presence of immunized nodes as well as to find
(nearly) optimal immunization sets for a given choice of parameters and costs.
The algorithm scales linearly with the size of the graph and it can be made
efficient even on large networks. We compare its performance with topologically
based heuristics, greedy methods, and simulated annealing
Entropy inequalities and Bell inequalities for two-qubit systems
Sufficient conditions for (the non-violation of) the Bell-CHSH inequalities
in a mixed state of a two-qubit system are: 1) The linear entropy of the state
is not smaller than 0.5, 2) The sum of the conditional linear entropies is
non-negative, 3) The von Neumann entropy is not smaller than 0.833, 4) The sum
of the conditional von Neumann entropies is not smaller than 0.280.Comment: Errors corrected. See L. Jakobcyk, quant-ph/040908
Non-Gaussian two-mode squeezing and continuous variable entanglement of linearly and circularly polarized light beams interacting with cold atoms
We investigate how entangled coherent states and superpositions of low
intensity coherent states of non-Gaussian nature can be generated via
non-resonant interaction between either two linearly or circularly polarized
field modes and an ensemble of X-like four-level atoms placed in an optical
cavity. We compare our results to recent experimental observations and argue
that the non-Gaussian structure of the field states may be present in those
systems.Comment: 10 pages, 7 figures, replaced with final published versio
Gene-network inference by message passing
The inference of gene-regulatory processes from gene-expression data belongs
to the major challenges of computational systems biology. Here we address the
problem from a statistical-physics perspective and develop a message-passing
algorithm which is able to infer sparse, directed and combinatorial regulatory
mechanisms. Using the replica technique, the algorithmic performance can be
characterized analytically for artificially generated data. The algorithm is
applied to genome-wide expression data of baker's yeast under various
environmental conditions. We find clear cases of combinatorial control, and
enrichment in common functional annotations of regulated genes and their
regulators.Comment: Proc. of International Workshop on Statistical-Mechanical Informatics
2007, Kyot
Gene-network inference by message passing
The inference of gene-regulatory processes from gene-expression data belongs
to the major challenges of computational systems biology. Here we address the
problem from a statistical-physics perspective and develop a message-passing
algorithm which is able to infer sparse, directed and combinatorial regulatory
mechanisms. Using the replica technique, the algorithmic performance can be
characterized analytically for artificially generated data. The algorithm is
applied to genome-wide expression data of baker's yeast under various
environmental conditions. We find clear cases of combinatorial control, and
enrichment in common functional annotations of regulated genes and their
regulators.Comment: Proc. of International Workshop on Statistical-Mechanical Informatics
2007, Kyot
Gene-network inference by message passing
The inference of gene-regulatory processes from gene-expression data belongs
to the major challenges of computational systems biology. Here we address the
problem from a statistical-physics perspective and develop a message-passing
algorithm which is able to infer sparse, directed and combinatorial regulatory
mechanisms. Using the replica technique, the algorithmic performance can be
characterized analytically for artificially generated data. The algorithm is
applied to genome-wide expression data of baker's yeast under various
environmental conditions. We find clear cases of combinatorial control, and
enrichment in common functional annotations of regulated genes and their
regulators.Comment: Proc. of International Workshop on Statistical-Mechanical Informatics
2007, Kyot
Directed percolation depinning models: Evolution equations
We present the microscopic equation for the growing interface with quenched
noise for the model first presented by Buldyrev et al. [Phys. Rev. A 45, R8313
(1992)]. The evolution equation for the height, the mean height, and the
roughness are reached in a simple way. The microscopic equation allows us to
express these equations in two contributions: the contact and the local one. We
compare this two contributions with the ones obtained for the Tang and
Leschhorn model [Phys. Rev A 45, R8309 (1992)] by Braunstein et al. [Physica A
266, 308 (1999)]. Even when the microscopic mechanisms are quiet different in
both model, the two contribution are qualitatively similar. An interesting
result is that the diffusion contribution, in the Tang and Leschhorn model, and
the contact one, in the Buldyrev model, leads to an increase of the roughness
near the criticality.Comment: 10 pages and 4 figures. To be published in Phys. Rev.
Bicoloring Random Hypergraphs
We study the problem of bicoloring random hypergraphs, both numerically and
analytically. We apply the zero-temperature cavity method to find analytical
results for the phase transitions (dynamic and static) in the 1RSB
approximation. These points appear to be in agreement with the results of the
numerical algorithm. In the second part, we implement and test the Survey
Propagation algorithm for specific bicoloring instances in the so called
HARD-SAT phase.Comment: 14 pages, 10 figure
Phase-Covariant Quantum Benchmarks
We give a quantum benchmark for teleportation and quantum storage experiments
suited for pure and mixed test states. The benchmark is based on the average
fidelity over a family of phase-covariant states and certifies that an
experiment can not be emulated by a classical setup, i.e., by a
measure-and-prepare scheme. We give an analytical solution for qubits, which
shows important differences with standard state estimation approach, and
compute the value of the benchmark for coherent and squeezed states, both pure
and mixed.Comment: 4 pages, 2 figure
Optical implementation and entanglement distribution in Gaussian valence bond states
We study Gaussian valence bond states of continuous variable systems,
obtained as the outputs of projection operations from an ancillary space of M
infinitely entangled bonds connecting neighboring sites, applied at each of
sites of an harmonic chain. The entanglement distribution in Gaussian valence
bond states can be controlled by varying the input amount of entanglement
engineered in a (2M+1)-mode Gaussian state known as the building block, which
is isomorphic to the projector applied at a given site. We show how this
mechanism can be interpreted in terms of multiple entanglement swapping from
the chain of ancillary bonds, through the building blocks. We provide optical
schemes to produce bisymmetric three-mode Gaussian building blocks (which
correspond to a single bond, M=1), and study the entanglement structure in the
output Gaussian valence bond states. The usefulness of such states for quantum
communication protocols with continuous variables, like telecloning and
teleportation networks, is finally discussed.Comment: 15 pages, 6 figures. To appear in Optics and Spectroscopy, special
issue for ICQO'2006 (Minsk). This preprint contains extra material with
respect to the journal versio
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