424 research outputs found
Nonlinear Relaxation in Population Dynamics
We analyze the nonlinear relaxation of a complex ecosystem composed of many
interacting species. The ecological system is described by generalized
Lotka-Volterra equations with a multiplicative noise. The transient dynamics is
studied in the framework of the mean field theory and with random interaction
between the species. We focus on the statistical properties of the asymptotic
behaviour of the time integral of the i-th population and on the distribution
of the population and of the local field.Comment: 11 pages, 4 figures, in press in Int. Journal of Fractals (2001
Bridging the Gap: Lottery-based Procedures in Early Parliamentarization
How is the use of political lotteries related to party development? This article discusses the effects of a lottery-based procedure used to distribute committee appointments that was once common across legislatures in nineteenth-century Europe. The authors analyze the effects of a political lottery in budget committee selection in the French Third Republic using a microlevel data set of French deputies from 1877 to 1914. They argue that the adoption and benefit of lottery-based procedures were to prevent the capture of early institutions by party factions or groups of self-interested political elites. The authors find that partial randomization of selection resulted in the appointment of young, skilled, middle-class deputies at the expense of influential elites. When parties gained control of committee assignments in 1910, selection once again favored elites and loyal party members. The authors link lottery-based procedures to party development by showing that cohesive parties were behind the institutional reform that ultimately dismantled this selection process. Lottery-based procedures thus played a sanitizing role during the transformation of emerging parliamentary groups into unified, cohesive political parties.The Institutions of Politics; Design, Workings, and implications ( do not use, ended 1-1-2020
Stochastic resonance and noise delayed extinction in a model of two competing species
We study the role of the noise in the dynamics of two competing species. We
consider generalized Lotka-Volterra equations in the presence of a
multiplicative noise, which models the interaction between the species and the
environment. The interaction parameter between the species is a random process
which obeys a stochastic differential equation with a generalized bistable
potential in the presence of a periodic driving term, which accounts for the
environment temperature variation. We find noise-induced periodic oscillations
of the species concentrations and stochastic resonance phenomenon. We find also
a nonmonotonic behavior of the mean extinction time of one of the two competing
species as a function of the additive noise intensity.Comment: 11 pages, 6 figures, 17 panels. To appear in Physica
Nonlocal field correlations and dynamical Casimir-Polder forces between one excited- and two ground-state atoms
The problem of nonlocality in the dynamical three-body Casimir-Polder
interaction between an initially excited and two ground-state atoms is
considered. It is shown that the nonlocal spatial correlations of the field
emitted by the excited atom during the initial part of its spontaneous decay
may become manifest in the three-body interaction. The observability of this
new phenomenon is discussed.Comment: 17 pages, 1 figure, sub. to Phys. Rev.
Factors affecting the development of Bovine Respiratory Disease: a cross-sectional study in beef steers shipped from France to Italy
Bovine respiratory disease (BRD) is a complex, multifactorial syndrome and one of the major welfare and economical concerns for the cattle industry. This 1-year cross-sectional study was aimed at documenting the prevalence of BRD-related pathogens and clinical signs before and after a long journey and at identifying possible predisposition factors. Male Limousine beef steers (n = 169) traveling from France to Italy were health checked and sampled with Deep Nasopharyngeal Swabs (DNS) at loading (T0) and 4 days after arrival (T1). Real-time quantitative PCR was used to quantify the presence of bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), bovine alphaherpesvirus 1 (BoHV-1), bovine coronavirus (BCoV), bovine adenovirus (BAdV), bovine parainfluenza virus 3 (BPIV-3), Histophilus somni, Mannheimia haemolytica, Mycoplasma bovis, and Pasteurella multocida. Weather conditions at departure and arrival were recorded, and the travel conditions were taken from the travel documentation. At T0, even if no animals displayed clinical signs, some of them were already positive for one or more pathogens. At T1, the number of animals displaying clinical signs and positive for BCoV, BAdV, BRSV, H. somni, M. haemolytica, M. bovis, and P. multocida increased dramatically (p < 0.001). Transport also significantly increased co-infection passing from 16.0% at T0 to 82.8% at T1 (p < 0.001). An extra stop during the journey seemed to favor BRSV, M. haemolytica, and P. multocida (p < 0.05). Weather conditions, in particular sudden climate changes from departure to arrival and daily temperature variance, were found to be predisposing factors for many of the pathogens. The farm of arrival also played a role for BRSV, BAdV, and H. somni (p < 0.05). BCoV increased dramatically, but no associations were found confirming that it spreads easily during transport phases. Our findings increased our understanding of factors increasing the likelihood of BRD-related pathogens shedding and can be useful to minimize the incidence of BRD and to implement animal transport regulations
The Localization of -Wave and Quantum Effective Potential of a Quasi-Free Particle with Position-Dependent Mass
The properties of the s-wave for a quasi-free particle with
position-dependent mass(PDM) have been discussed in details. Differed from the
system with constant mass in which the localization of the s-wave for the free
quantum particle around the origin only occurs in two dimensions, the
quasi-free particle with PDM can experience attractive forces in dimensions
except D=1 when its mass function satisfies some conditions. The effective mass
of a particle varying with its position can induce effective interaction which
may be attractive in some cases. The analytical expressions of the
eigenfunctions and the corresponding probability densities for the s-waves of
the two- and three-dimensional systems with a special PDM are given, and the
existences of localization around the origin for these systems are shown.Comment: 12pages, 8 figure
Magnetic coupling to the Advanced Virgo payloads and its impact on the low frequency sensitivity
We study the electromagnetic coupling of the Advanced Virgo (AdV) Input
Mirror Payload (IMP) in response to a slowly time-varying magnetic field. As
the problem is not amenable to analytical solution, we employ and validate a
finite element (FE) analysis approach. The FE model is built to represent as
faithfully as possible the real object and it has been validated by comparison
with experimental measurements. The intent is to estimate the induced currents
and the magnetic field in the neighbourhood of the payload. The procedure found
21 equivalent electrical configurations that are compatible with the
measurements. These have been used to compute the magnetic noise contribution
to the total AdV strain noise. At the current stage of development AdV seems to
be unaffected by magnetic noise, but we foresee a non-negligible coupling once
AdV reaches the design sensitivity.Comment: 8 pages, 8 figures, 2 table
Robust non-Markovianity in ultracold gases
We study the effect of thermal fluctuations on a probe qubit interacting with
a Bose-Einstein condensed (BEC) reservoir. The zero-temperature case was
studied in [Haikka P et al 2011 Phys. Rev. A 84 031602], where we proposed a
method to probe the effects of dimensionality and scattering length of a BEC
based on its behavior as an environment. Here we show that the sensitivity of
the probe qubit is remarkably robust against thermal noise. We give an
intuitive explanation for the thermal resilience, showing that it is due to the
unique choice of the probe qubit architecture of our model.Comment: Submitted to FQMT11 topical issue of the Physica Script
Frozen and Invariant Quantum Discord under Local Dephasing Noise
In this chapter, we intend to explore and review some remarkable dynamical
properties of quantum discord under various different open quantum system
models. Specifically, our discussion will include several concepts connected to
the phenomena of time invariant and frozen quantum discord. Furthermore, we
will elaborate on the relation of these two phenomena to the non-Markovian
features of the open system dynamics and to the usage of dynamical decoupling
protocols.Comment: 29 pages, 8 figure
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