394 research outputs found
Divergence of the Chaotic Layer Width and Strong Acceleration of the Spatial Chaotic Transport in Periodic Systems Driven by an Adiabatic ac Force
We show for the first time that a {\it weak} perturbation in a Hamiltonian
system may lead to an arbitrarily {\it wide} chaotic layer and {\it fast}
chaotic transport. This {\it generic} effect occurs in any spatially periodic
Hamiltonian system subject to a sufficiently slow ac force. We explain it and
develop an explicit theory for the layer width, verified in simulations.
Chaotic spatial transport as well as applications to the diffusion of particles
on surfaces, threshold devices and others are discussed.Comment: 4 pages including 3 EPS figures, this is an improved version of the
paper (accepted to PRL, 2005
Nano dust impacts on spacecraft and boom antenna charging
High rate sampling detectors measuring the potential difference between the
main body and boom antennas of interplanetary spacecraft have been shown to be
efficient means to measure the voltage pulses induced by nano dust impacts on
the spacecraft body itself (see Meyer-Vernet et al, Solar Phys. 256, 463
(2009)). However, rough estimates of the free charge liberated in post impact
expanding plasma cloud indicate that the cloud's own internal electrostatic
field is too weak to account for measured pulses as the ones from the TDS
instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper
we argue that the detected pulses are not a direct measure of the potential
structure of the plasma cloud, but are rather the consequence of a transitional
interruption of the photoelectron return current towards the portion of the
antenna located within the expanding cloud
Drastic facilitation of the onset of global chaos in a periodically driven Hamiltonian system due to an extremum in the dependence of eigenfrequency on energy
The Chirikov resonance-overlap criterion predicts the onset of global chaos
if nonlinear resonances overlap in energy, which is conventionally assumed to
require a non-small magnitude of perturbation. We show that, for a
time-periodic perturbation, the onset of global chaos may occur at unusually
{\it small} magnitudes of perturbation if the unperturbed system possesses more
than one separatrix. The relevant scenario is the combination of the overlap in
the phase space between resonances of the same order and their overlap in
energy with chaotic layers associated with separatrices of the unperturbed
system. One of the most important manifestations of this effect is a drastic
increase of the energy range involved into the unbounded chaotic transport in
spatially periodic system driven by a rather {\it weak} time-periodic force,
provided the driving frequency approaches the extremal eigenfrequency or its
harmonics. We develop the asymptotic theory and verify it in simulations.Comment: 5 pages, 4 figures, LaTeX, to appear PR
Self-similar motion for modeling anomalous diffusion and nonextensive statistical distributions
We introduce a new universality class of one-dimensional iteration model
giving rise to self-similar motion, in which the Feigenbaum constants are
generalized as self-similar rates and can be predetermined. The curves of the
mean-square displacement versus time generated here show that the motion is a
kind of anomalous diffusion with the diffusion coefficient depending on the
self-similar rates. In addition, it is found that the distribution of
displacement agrees to a reliable precision with the q-Gaussian type
distribution in some cases and bimodal distribution in some other cases. The
results obtained show that the self-similar motion may be used to describe the
anomalous diffusion and nonextensive statistical distributions.Comment: 15pages, 5figure
Chaotic and pseudochaotic attractors of perturbed fractional oscillator
We consider a nonlinear oscillator with fractional derivative of the order
alpha. Perturbed by a periodic force, the system exhibits chaotic motion called
fractional chaotic attractor (FCA). The FCA is compared to the ``regular''
chaotic attractor. The properties of the FCA are discussed and the
``pseudochaotic'' case is demonstrated.Comment: 20 pages, 7 figure
Using tasks to explore teacher knowledge in situation-specific contexts
This article was published in the journal, Journal of Mathematics Teacher Education [© Springer] and the original publication is available at www.springerlink.comResearch often reports an overt discrepancy between theoretically/out-of context expressed teacher beliefs about mathematics and pedagogy and actual practice. In order to explore teacher knowledge in situation-specific contexts we have engaged mathematics teachers with classroom scenarios (Tasks) which: are hypothetical but grounded on learning and teaching issues that previous research and experience have highlighted as seminal; are likely to occur in actual practice; have purpose and utility; and, can be used both in (pre- and in-service) teacher education and research through generating access to teachers’ views and intended practices. The Tasks have the following structure: reflecting upon the learning objectives within a mathematical problem (and solving it); examining a flawed (fictional) student solution; and, describing, in writing, feedback to the student. Here we draw on the written responses to one Task (which involved reflecting on solutions of x+x−1=0 of 53 Greek in-service mathematics teachers in order to demonstrate the range of teacher knowledge (mathematical, didactical and pedagogical) that engagement with these tasks allows us to explore
Ehrenfest times for classically chaotic systems
We describe the quantum mechanical spreading of a Gaussian wave packet by
means of the semiclassical WKB approximation of Berry and Balazs. We find that
the time scale on which this approximation breaks down in a chaotic
system is larger than the Ehrenfest times considered previously. In one
dimension \tau=\fr{7}{6}\lambda^{-1}\ln(A/\hbar), with the Lyapunov
exponent and a typical classical action.Comment: 4 page
Supersymmetric Method for Constructing Quasi-Exactly and Conditionally-Exactly Solvable Potentials
Using supersymmetric quantum mechanics we develop a new method for
constructing quasi-exactly solvable (QES) potentials with two known
eigenstates. This method is extended for constructing conditionally-exactly
solvable potentials (CES). The considered QES potentials at certain values of
parameters become exactly solvable and can be treated as CES ones.Comment: 17 pages, latex, no figure
Return interval distribution of extreme events and long term memory
The distribution of recurrence times or return intervals between extreme
events is important to characterize and understand the behavior of physical
systems and phenomena in many disciplines. It is well known that many physical
processes in nature and society display long range correlations. Hence, in the
last few years, considerable research effort has been directed towards studying
the distribution of return intervals for long range correlated time series.
Based on numerical simulations, it was shown that the return interval
distributions are of stretched exponential type. In this paper, we obtain an
analytical expression for the distribution of return intervals in long range
correlated time series which holds good when the average return intervals are
large. We show that the distribution is actually a product of power law and a
stretched exponential form. We also discuss the regimes of validity and perform
detailed studies on how the return interval distribution depends on the
threshold used to define extreme events.Comment: 8 pages, 6 figure
Cohort of Birth Modifies the Association between FTO Genotype and BMI
A substantial body of research has explored the relative roles of genetic and environmental factors on phenotype expression in humans. Recent research has also sought to identify gene-environment (or g-by-e) interactions, with mixed success. One potential reason for these mixed results may relate to the fact that genetic effects might be modified by changes in the environment over time. For example, the noted rise of obesity in the United States in the latter part of the 20th century might reflect an interaction between genetic variation and changing environmental conditions that together affect the penetrance of genetic influences. To evaluate this hypothesis, we use longitudinal data from the Framingham Heart Study collected over 30 y from a geographically relatively localized sample to test whether the well-documented association between the rs993609 variant of the FTO (fat mass and obesity associated) gene and body mass index (BMI) varies across birth cohorts, time period, and the lifecycle. Such cohort and period effects integrate many potential environmental factors, and this gene-by-environment analysis examines interactions with both time-varying contemporaneous and historical environmental influences. Using constrained linear age-period-cohort models that include family controls, we find that there is a robust relationship between birth cohort and the genotype-phenotype correlation between the FTO risk allele and BMI, with an observed inflection point for those born after 1942. These results suggest genetic influences on complex traits like obesity can vary over time, presumably because of global environmental changes that modify allelic penetrance
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