3,800 research outputs found
Optimal paths on the road network as directed polymers
We analyze the statistics of the shortest and fastest paths on the road
network between randomly sampled end points. To a good approximation, these
optimal paths are found to be directed in that their lengths (at large scales)
are linearly proportional to the absolute distance between them. This motivates
comparisons to universal features of directed polymers in random media. There
are similarities in scalings of fluctuations in length/time and transverse
wanderings, but also important distinctions in the scaling exponents, likely
due to long-range correlations in geographic and man-made features. At short
scales the optimal paths are not directed due to circuitous excursions governed
by a fat-tailed (power-law) probability distribution.Comment: 5 pages, 7 figure
The self-organizing radio networks and ultra wide band signals
The paper proposes to use impulse radio ultra wide band signals in self-organizing ad hoc and MANET networks to solve multiple access and widen networks coverage area problems. New methods of signals reception and information capacity increasing are proposed
Increase of informative capacity of ultra wide band impulse signals
It is common to think that impulse radio ultra band signals (IR-UWB) in communication systems can carry the information at very high rates. But each impulse of the signal can carry just one bit of information. In radio networks it is necessary to add destination address to every information unit. The best way for each subscriber is use series of impulses mutually orthogonal to the rest of series in the network. But the orthogonality means long multi impulse series with low density of impulses to make time domain space transparent. As a result, data transmission rates become much less than expected. To increase data rates in radio networks modulation of each impulse by amplitude, duration and polarity in the series is proposed. Examples of transmitter and receiver are presented. As a result, informative loading on signals increases manifold, compensating or neutralizing losses, related to the transmission of symbols by impulse sequences
Large deviations in boundary-driven systems: Numerical evaluation and effective large-scale behavior
We study rare events in systems of diffusive fields driven out of equilibrium
by the boundaries. We present a numerical technique and use it to calculate the
probabilities of rare events in one and two dimensions. Using this technique,
we show that the probability density of a slowly varying configuration can be
captured with a small number of long wave-length modes. For a configuration
which varies rapidly in space this description can be complemented by a local
equilibrium assumption
Numerical implementation of dynamical mean field theory for disordered systems: Application to the Lotka-Volterra model of ecosystems
Dynamical mean field theory (DMFT) is a tool that allows one to analyze the stochastic dynamics of N interacting degrees of freedom in terms of a self-consistent 1-body problem. In this work, focusing on models of ecosystems, we present the derivation of DMFT through the dynamical cavity method, and we develop a method for solving it numerically. Our numerical procedure can be applied to a large variety of systems for which DMFT holds. We implement and test it for the generalized random Lotka-Volterra model, and show that complex dynamical regimes characterized by chaos and aging can be captured and studied by this framework
Impulse ultra-wideband signal relaying in ad hoc radio networks
A method of impulse ultra-wideband signals relaying in ad hoc radio networks is described. As the relaying signals a group of chipsets is used to represent various minimal information units. A system of markers is introduced to unambiguous determine the relaying routes. The chipset representation of transmitted signals reduces the delays coursed by multistep relaying and increases the data transfer rate
Statistics of the dissipated energy in driven single-electron transitions
We analyze the distribution of heat generated in driven single-electron
transitions and discuss the related non-equilibrium work theorems. In the
adiabatic limit, the heat distribution is shown to become Gaussian, with the
heat noise that, in spite of thermal fluctuations, vanishes together with the
average dissipated energy. We show that the transitions satisfy Jarzynski
equality for arbitrary drive and calculate the probability of the negative heat
values. We also derive a general condition on the heat distribution that
generalizes the Bochkov-Kuzovlev equality and connects it to the Jarzynski
equality.Comment: 5 pages, 2 figure
Non differentiable large-deviation functionals in boundary-driven diffusive systems
We study the probability of arbitrary density profiles in conserving
diffusive fields which are driven by the boundaries. We demonstrate the
existence of singularities in the large-deviation functional, the direct analog
of the free-energy in non-equilibrium systems. These singularities are unique
to non-equilibrium systems and are a direct consequence of the breaking of
time-reversal symmetry. This is demonstrated in an exactly-solvable model and
also in numerical simulations on a boundary-driven Ising model. We argue that
this singular behavior is expected to occur in models where the compressibility
has a deep enough minimum. The mechanism is explained using a simple model.Comment: 5 pages, 3 figure
A note on the violation of the Einstein relation in a driven moderately dense granular gas
The Einstein relation for a driven moderately dense granular gas in
-dimensions is analyzed in the context of the Enskog kinetic equation. The
Enskog equation neglects velocity correlations but retains spatial correlations
arising from volume exclusion effects. As expected, there is a breakdown of the
Einstein relation relating diffusion and
mobility , being the temperature of the impurity. The kinetic theory
results also show that the violation of the Einstein relation is only due to
the strong non-Maxwellian behavior of the reference state of the impurity
particles. The deviation of from unity becomes more significant as
the solid volume fraction and the inelasticity increase, especially when the
system is driven by the action of a Gaussian thermostat. This conclusion
qualitatively agrees with some recent simulations of dense gases [Puglisi {\em
et al.}, 2007 {\em J. Stat. Mech.} P08016], although the deviations observed in
computer simulations are more important than those obtained here from the
Enskog kinetic theory. Possible reasons for the quantitative discrepancies
between theory and simulations are discussed.Comment: 6 figure
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