2,504 research outputs found
Super-hydrodynamic limit in interacting particle systems
This paper is a follow-up of the work initiated in [3], where it has been
investigated the hydrodynamic limit of symmetric independent random walkers
with birth at the origin and death at the rightmost occupied site. Here we
obtain two further results: first we characterize the stationary states on the
hydrodynamic time scale and show that they are given by a family of linear
macroscopic profiles whose parameters are determined by the current reservoirs
and the system mass. Then we prove the existence of a super-hyrdrodynamic time
scale, beyond the hydrodynamic one. On this larger time scale the system mass
fluctuates and correspondingly the macroscopic profile of the system randomly
moves within the family of linear profiles, with the randomness of a Brownian
motion.Comment: 22 page
Large Radio Telescopes for Anomalous Microwave Emission Observations
We discuss in this paper the problem of the Anomalous Microwave Emission
(AME) in the light of ongoing or future observations to be performed with the
largest fully steerable radio telescope in the world. High angular resolution
observations of the AME will enable astronomers to drastically improve the
knowledge of the AME mechanisms as well as the interplay between the different
constituents of the interstellar medium in our galaxy. Extragalactic
observations of the AME have started as well, and high resolution is even more
important in this kind of observations. When cross-correlating with IR-dust
emission, high angular resolution is also of fundamental importance in order to
obtain unbiased results. The choice of the observational frequency is also of
key importance in continuum observation. We calculate a merit function that
accounts for the signal-to-noise ratio (SNR) in AME observation given the
current state-of-the-art knowledge and technology. We also include in our merit
functions the frequency dependence in the case of multifrequency observations.
We briefly mention and compare the performance of four of the largest
radiotelescopes in the world and hope the observational programs in each of
them will be as intense as possible.Comment: Review accepted for publication in Advances in Astronom
Collective decision making in dynamic environments
Abstract: Collective decision making is the ability of individuals to jointly make a decision without any centralized leadership, but only relying on local interactions. A special case is represented by the best-of-n problem, whereby the swarm has to select the best option among a set of n discrete alternatives. In this paper, we perform a thorough study of the best-of-n problem in dynamic environments, in the presence of two options (n=2). Site qualities can be directly measured by agents, and we introduce abrupt changes to these qualities. We introduce two adaptation mechanisms to deal with dynamic site qualities: stubborn agents and spontaneous opinion switching. Using both computer simulations and ordinary differential equation models, we show that: (i) The mere presence of the stubborn agents is enough to achieve adaptability, but increasing its number has detrimental effects on the performance; (ii) the system adaptation increases with increasing swarm size, while it does not depend on agents’ density, unless this is below a critical threshold; (iii) the spontaneous switching mechanism can also be used to achieve adaptability to dynamic environments, and its key parameter, the probability of switching, can be used to regulate the trade-off between accuracy and speed of adaptation
Tunnelling in nonlocal evolution equations
We study "tunnelling" in a one-dimensional, nonlocal evolution equation by assigning a penalty functional to orbits which deviate from solutions of the evolution equation. We discuss the variational problem of computing the minimal penalty for orbits which connect two stable, stationary solutions
A fitness model for the Italian Interbank Money Market
We use the theory of complex networks in order to quantitatively characterize
the formation of communities in a particular financial market. The system is
composed by different banks exchanging on a daily basis loans and debts of
liquidity. Through topological analysis and by means of a model of network
growth we can determine the formation of different group of banks characterized
by different business strategy. The model based on Pareto's Law makes no use of
growth or preferential attachment and it reproduces correctly all the various
statistical properties of the system. We believe that this network modeling of
the market could be an efficient way to evaluate the impact of different
policies in the market of liquidity.Comment: 5 pages 5 figure
Large deviations for the macroscopic motion of an interface
We study the most probable way an interface moves on a macroscopic scale from an initial to a final position within a fixed time in the context of large deviations for a stochastic microscopic lattice system of Ising spins with Kac interaction evolving in time according to Glauber (non-conservative) dynamics. Such interfaces separate two stable phases of a ferromagnetic system and in the macroscopic scale are represented by sharp transitions. We derive quantitative estimates for the upper and the lower bound of the cost functional that penalizes all possible deviations and obtain explicit error terms which are valid also in the macroscopic scale. Furthermore, using the result of a companion paper about the minimizers of this cost functional for the macroscopic motion of the interface in a fixed time, we prove that the probability of such events can concentrate on nucleations should the transition happen fast enough
Current reservoirs in the simple exclusion process
We consider the symmetric simple exclusion process in the interval
with additional birth and death processes respectively on , , and
. The exclusion is speeded up by a factor , births and deaths
by a factor . Assuming propagation of chaos (a property proved in a
companion paper "Truncated correlations in the stirring process with births and
deaths") we prove convergence in the limit to the linear heat
equation with Dirichlet condition on the boundaries; the boundary conditions
however are not known a priori, they are obtained by solving a non linear
equation. The model simulates mass transport with current reservoirs at the
boundaries and the Fourier law is proved to hold
Multi-mode TES bolometer optimization for the LSPE-SWIPE instrument
In this paper we explore the possibility of using transition edge sensor
(TES) detectors in multi-mode configuration in the focal plane of the Short
Wavelength Instrument for the Polarization Explorer (SWIPE) of the
balloon-borne polarimeter Large Scale Polarization Explorer (LSPE) for the
Cosmic Microwave Background (CMB) polarization. This study is motivated by the
fact that maximizing the sensitivity of TES bolometers, under the augmented
background due to the multi-mode design, requires a non trivial choice of
detector parameters. We evaluate the best parameter combination taking into
account scanning strategy, noise constraints, saturation power and operating
temperature of the cryostat during the flight.Comment: in Journal of Low Temperature Physics, 05 January 201
Stability of planar fronts for a non--local phase kinetics equation with a conservation law in
We consider, in a dimensional cylinder, a non--local evolution equation
that describes the evolution of the local magnetization in a continuum limit of
an Ising spin system with Kawasaki dynamics and Kac potentials.
We consider sub--critical temperatures, for which there are two local
spatially homogeneous equilibria, and show a local nonlinear stability result
for the minimum free energy profiles for the magnetization at the interface
between regions of these two different local equilibrium; i.e., the planar
fronts: We show that an initial perturbation of a front that is sufficiently
small in norm, and sufficiently localized yields a solution that relaxes
to another front, selected by a conservation law, in the norm at an
algebraic rate that we explicitly estimate. We also obtain rates for the
relaxation in the norm and the rate of decrease of the excess free
energy
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