1,594 research outputs found
Effects of internal fluctuations on the spreading of Hantavirus
We study the spread of Hantavirus over a host population of deer mice using a
population dynamics model. We show that taking into account the internal
fluctuations in the mouse population due to its discrete character strongly
alters the behaviour of the system. In addition to the familiar transition
present in the deterministic model, the inclusion of internal fluctuations
leads to the emergence of an additional deterministically hidden transition. We
determine parameter values that lead to maximal propagation of the disease, and
discuss some implications for disease prevention policies
Velocity Distribution in a Viscous Granular Gas
We investigate the velocity relaxation of a viscous one-dimensional granular
gas, that is, one in which neither energy nor momentum is conserved in a
collision. Of interest is the distribution of velocities in the gas as it
cools, and the time dependence of the relaxation behavior. A Boltzmann equation
of instantaneous binary collisions leads to a two-peaked distribution with each
peak relaxing to zero velocity as 1/t while each peak also narrows as 1/t.
Numerical simulations of grains on a line also lead to a double-peaked
distribution that narrows as 1/t. A Maxwell approximation leads to a
single-peaked distribution about zero velocity with power-law wings. This
distribution narrows exponentially. In either case, the relaxing distribution
is not of Maxwell-Boltzmann form
Bullying and Victimization in Elementary Schools: A Comparison of Bullies, Victims, Bully/Victims, and Uninvolved Preadolescents
Research on bullying and victimization largely rests on univariate analyses and on reports from a single informant. Researchers may thus know too little about the simultaneous effects of various independent and dependent variables, and their research may be biased by shared method variance. The database for
this Dutch study was large (N = 1,065) and rich enough to allow multivariate analysis and multisource information. In addition, the effect of familial vulnerability for internalizing and externalizing disorders was studied. Gender, aggressiveness, isolation, and dislikability were most strongly related to bullying and victimization. Among the many findings that deviated from or enhanced the univariate knowledge
base were that not only victims and bully/victims but bullies as well were disliked and that parenting was unrelated to bullying and victimization once other factors were controlled.
Pulse propagation in decorated granular chains: An analytical approach
We study pulse propagation in one-dimensional chains of spherical granules
decorated with small grains placed between large granules. The effect of the
small granules can be captured by replacing the decorated chains by undecorated
chains of large granules of appropriately renormalized mass and effective
interaction between the large granules. This allows us to obtain simple
analytic expressions for the pulse propagation properties using a
generalization of the binary collision approximation introduced in our earlier
work [Phys. Rev. E in print (2009); Phys. Rev. E {\bf 69}, 037601 (2004)]Comment: 10 pages and 12 figure
Observation of two-wave structure in strongly nonlinear dissipative granular chains
In a strongly nonlinear viscous granular chain under conditions of loading
that exclude stationary waves (e.g., impact by a single grain) we observe a
pulse that consists of two interconnected but distinct parts. One is a leading
narrow "primary pulse" with properties similar to a solitary wave in a "sonic
vacuum." It arises from strong nonlinearity and discreteness in the absence of
dissipation, but now decays due to viscosity. The other is a broad, much more
persistent shock-like "secondary pulse" trailing the primary pulse and caused
by viscous dissipation. The medium behind the primary pulse is transformed from
a "sonic vacuum" to a medium with finite sound speed. When the rapidly decaying
primary pulse dies, the secondary pulse continues to propagate in the "sonic
vacuum," with an oscillatory front if the viscosity is relatively small, until
its eventual (but very slow) disintegration. Beyond a critical viscosity there
is no separation of the two pulses, and the dissipation and nonlinearity
dominate the shock-like attenuating pulse which now exhibits a nonoscillatory
front
Thermoelectric efficiency at maximum power in a quantum dot
We identify the operational conditions for maximum power of a
nanothermoelectric engine consisting of a single quantum level embedded between
two leads at different temperatures and chemical potentials. The corresponding
thermodynamic efficiency agrees with the Curzon-Ahlborn expression up to
quadratic terms in the gradients, supporting the thesis of universality beyond
linear response.Comment: 4 pages, 3 figure
Continuous and discontinuous phase transitions and partial synchronization in stochastic three-state oscillators
We investigate both continuous (second-order) and discontinuous (first-order)
transitions to macroscopic synchronization within a single class of discrete,
stochastic (globally) phase-coupled oscillators. We provide analytical and
numerical evidence that the continuity of the transition depends on the
coupling coefficients and, in some nonuniform populations, on the degree of
quenched disorder. Hence, in a relatively simple setting this class of models
exhibits the qualitative behaviors characteristic of a variety of considerably
more complicated models. In addition, we study the microscopic basis of
synchronization above threshold and detail the counterintuitive subtleties
relating measurements of time averaged frequencies and mean field oscillations.
Most notably, we observe a state of suprathreshold partial synchronization in
which time-averaged frequency measurements from individual oscillators do not
correspond to the frequency of macroscopic oscillations observed in the
population
Geotechnical Prediction and Performance of Eastern Scheldt Storm Surge Barrier
The construction of the Eastern Scheldt storm surge barrier was completed in 1986. The monitoring system meant to verify the functioning of the barrier during storm conditions became operational in 1988. Data concerning the geotechnical response was collected during the 4 days storm period between February 26 and March 2, 1990. In the paper some results are described. Conclusions with respect to the expected behaviour of the barrier during more extreme storms in future will be drawn in near future
Survival probability of a particle in a sea of mobile traps: A tale of tails
We study the long-time tails of the survival probability of an
particle diffusing in -dimensional media in the presence of a concentration
of traps that move sub-diffusively, such that the mean square
displacement of each trap grows as with .
Starting from a continuous time random walk (CTRW) description of the motion of
the particle and of the traps, we derive lower and upper bounds for and
show that for these bounds coincide asymptotically, thus
determining asymptotically exact results. The asymptotic decay law in this
regime is exactly that obtained for immobile traps. This means that for
sufficiently subdiffusive traps, the moving particle sees the traps as
essentially immobile, and Lifshitz or trapping tails remain unchanged. For
and the upper and lower bounds again coincide,
leading to a decay law equal to that of a stationary particle. Thus, in this
regime the moving traps see the particle as essentially immobile. For ,
however, the upper and lower bounds in this regime no longer coincide
and the decay law for the survival probability of the particle remains
ambiguous
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