26,992 research outputs found
Perfect simulation of autoregressive models with infinite memory
In this paper we consider the problem of determining the law of binary
stochastic processes from transition kernels depending on the whole past. These
kernels are linear in the past values of the process. They are allowed to
assume values close to both 0 and 1, preventing the application of usual
results on uniqueness. More precisely we give sufficient conditions for
uniqueness and non-uniqueness. In the former case a perfect simulation
algorithm is also given.Comment: 12 page
One-dimensional infinite memory imitation models with noise
In this paper we study stochastic process indexed by
constructed from certain transition kernels depending on the whole past. These
kernels prescribe that, at any time, the current state is selected by looking
only at a previous random instant. We characterize uniqueness in terms of
simple concepts concerning families of stochastic matrices, generalizing the
results previously obtained in De Santis and Piccioni (J. Stat. Phys.,
150(6):1017--1029, 2013).Comment: 22 pages, 3 figure
Complex Networks from Classical to Quantum
Recent progress in applying complex network theory to problems in quantum
information has resulted in a beneficial crossover. Complex network methods
have successfully been applied to transport and entanglement models while
information physics is setting the stage for a theory of complex systems with
quantum information-inspired methods. Novel quantum induced effects have been
predicted in random graphs---where edges represent entangled links---and
quantum computer algorithms have been proposed to offer enhancement for several
network problems. Here we review the results at the cutting edge, pinpointing
the similarities and the differences found at the intersection of these two
fields.Comment: 12 pages, 4 figures, REVTeX 4-1, accepted versio
Equilibration and nonclassicality of a double-well potential
A double well loaded with bosonic atoms represents an ideal candidate to
simulate some of the most interesting aspects in the phenomenology of
thermalisation and equilibration. Here we report an exhaustive analysis of the
dynamics and steady state properties of such a system locally in contact with
different temperature reservoirs. We show that thermalisation only occurs
'accidentally'. We further examine the nonclassical features and energy fluxes
implied by the dynamics of the double-well system, thus exploring its
finite-time thermodynamics in relation to the settlement of nonclassical
correlations between the wells.Comment: 10 pages, 7 figures, Close to published versio
Know Your Enemy: Stealth Configuration-Information Gathering in SDN
Software Defined Networking (SDN) is a network architecture that aims at
providing high flexibility through the separation of the network logic from the
forwarding functions. The industry has already widely adopted SDN and
researchers thoroughly analyzed its vulnerabilities, proposing solutions to
improve its security. However, we believe important security aspects of SDN are
still left uninvestigated. In this paper, we raise the concern of the
possibility for an attacker to obtain knowledge about an SDN network. In
particular, we introduce a novel attack, named Know Your Enemy (KYE), by means
of which an attacker can gather vital information about the configuration of
the network. This information ranges from the configuration of security tools,
such as attack detection thresholds for network scanning, to general network
policies like QoS and network virtualization. Additionally, we show that an
attacker can perform a KYE attack in a stealthy fashion, i.e., without the risk
of being detected. We underline that the vulnerability exploited by the KYE
attack is proper of SDN and is not present in legacy networks. To address the
KYE attack, we also propose an active defense countermeasure based on network
flows obfuscation, which considerably increases the complexity for a successful
attack. Our solution offers provable security guarantees that can be tailored
to the needs of the specific network under consideratio
Cosmic Star Formation: a simple model of the SFRD(z)
We investigate the evolution of the cosmic star formation rate density (SFRD)
from redshift z=20 to z=0 and compare it with the observational one by Madau
and Dickinson derived from recent compilations of UV and IR data. The
theoretical SFRD(z) and its evolution are obtained using a simple model which
folds together the star formation histories of prototype galaxies designed to
represent real objects of different morphological type along the Hubble
sequence and the hierarchical growing of structures under the action of gravity
from small perturbations to large scale objects in \Lambda-CDM cosmogony, i.e.
the number density of dark matter halos N(M,z). Although the overall model is
very simple and easy to set up, it provides results that well mimic those
obtained from large scale N-body simulations of great complexity. The
simplicity of our approach allows us to test different assumptions for the star
formation law in galaxies, the effects of energy feedback from stars to
interstellar gas and the efficiency of galactic winds, and also the effect of
N(M,z). The result of our analysis is that in the framework of the hierarchical
assembly of galaxies the so-called time-delayed star formation under plain
assumptions mainly for the energy feedback and galactic winds can reproduce the
observational SFRD(z).Comment: ApJ (accepted for publication
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