1,130 research outputs found
Escape through a time-dependent hole in the doubling map
We investigate the escape dynamics of the doubling map with a time-periodic
hole. We use Ulam's method to calculate the escape rate as a function of the
control parameters. We consider two cases, oscillating or breathing holes,
where the sides of the hole are moving in or out of phase respectively. We find
out that the escape rate is well described by the overlap of the hole with its
images, for holes centred at periodic orbits.Comment: 9 pages, 7 figures. To appear in Physical Review E in 201
Crises in a dissipative Bouncing ball model
The dynamics of a bouncing ball model under the influence of dissipation is
investigated by using a two dimensional nonlinear mapping. When high
dissipation is considered, the dynamics evolves to different attractors. The
evolution of the basins of the attracting fixed points is characterized, as we
vary the control parameters. Crises between the attractors and their boundaries
are observed. We found that the multiple attractors are intertwined, and when
the boundary crisis between their stable and unstable manifolds occur, it
creates a successive mechanism of destruction for all attractors originated by
the sinks. Also, an impact physical crises is setup, and it may be useful as a
mechanism to reduce the number of attractors in the system
Separation of particles leading to decay and unlimited growth of energy in a driven stadium-like billiard
A competition between decay and growth of energy in a time-dependent stadium
billiard is discussed giving emphasis in the decay of energy mechanism. A
critical resonance velocity is identified for causing of separation between
ensembles of high and low energy and a statistical investigation is made using
ensembles of initial conditions both above and below the resonance velocity.
For high initial velocity, Fermi acceleration is inherent in the system.
However for low initial velocity, the resonance allies with stickiness hold the
particles in a regular or quasi-regular regime near the fixed points,
preventing them from exhibiting Fermi acceleration. Also, a transport analysis
along the velocity axis is discussed to quantify the competition of growth and
decay of energy and making use distributions of histograms of frequency, and we
set that the causes of the decay of energy are due to the capture of the orbits
by the resonant fixed points
Physical and numerical modeling of the role of hydrodynamic processes on adult-larval interactions of a suspension-feeding bivalve
The importance of hydrodynamic processes for adult-larval interactions in the cockle, Cerastoderma edule, was examined through physical and numerical modeling. A set of physical experiments in a flow-tank using adult cockles and larval mimics showed that the settlement of particles was affected by adult cockles. Settlement was reduced by 20% in an area of 2.5 cm2 surrounding the siphons, and the most marked decrease occurred near the inhalant siphon. On a larger spatial scale downstream of the siphons, settlement was more heterogeneous compared to surfaces without cockles. The experimental results near individual cockles were compared with numerical models of settlement dynamics in conditions with no horizontal flow. The models suggest that the vertical position of the siphon orifice determines whether any small-scale reduction in larval settlement should be expected near suspension-feeding benthic invertebrates. The results are compared qualitatively and quantitatively with previous observations of small-scale patterns (≈1 cm) around individual C. edule and with observations of larger-scale (1-10 m) differences among patches with varying densities of cockles. These comparisons indicate that passive hydrodynamic processes can explain patterns around individual cockles, whereas a combination of active and passive processes are necessary to explain differences among patches. Such hydrodynamic modification of larval behavior has previously been reported to greatly increase rates of mortality for settling bivalve larvae
On star edge colorings of bipartite and subcubic graphs
A star edge coloring of a graph is a proper edge coloring with no -colored
path or cycle of length four. The star chromatic index of
is the minimum number for which has a star edge coloring with
colors. We prove upper bounds for the star chromatic index of complete
bipartite graphs; in particular we obtain tight upper bounds for the case when
one part has size at most . We also consider bipartite graphs where all
vertices in one part have maximum degree and all vertices in the other part
has maximum degree . Let be an integer (), we prove that if
then ; and if , then ; both upper bounds are sharp.
Finally, we consider the well-known conjecture that subcubic graphs have star
chromatic index at most ; in particular we settle this conjecture for cubic
Halin graphs.Comment: 18 page
The Electromagnetic Self-Energy Contribution to M_p - M_n and the Isovector Nucleon Magnetic Polarizability
We update the determination of the isovector nucleon electromagnetic
self-energy, valid to leading order in QED. A technical oversight in the
literature concerning the elastic contribution to Cottingham's formula is
corrected and modern knowledge of the structure functions is used to precisely
determine the inelastic contribution. We find \delta M_{p-n}^\gamma =
1.30(03)(47) MeV. The largest uncertainty arises from a subtraction term
required in the dispersive analysis, which can be related to the isovector
magnetic polarizability. With plausible model assumptions, we can combine our
calculation with additional input from lattice QCD to constrain this
polarizability as: \beta_{p-n} = -0.87(85) x 10^{-4} fm^3.Comment: 5 pages, version accepted for publication in PR
A Lambda Calculus for Quantum Computation
The classical lambda calculus may be regarded both as a programming language
and as a formal algebraic system for reasoning about computation. It provides a
computational model equivalent to the Turing machine, and continues to be of
enormous benefit in the classical theory of computation. We propose that
quantum computation, like its classical counterpart, may benefit from a version
of the lambda calculus suitable for expressing and reasoning about quantum
algorithms. In this paper we develop a quantum lambda calculus as an
alternative model of quantum computation, which combines some of the benefits
of both the quantum Turing machine and the quantum circuit models. The calculus
turns out to be closely related to the linear lambda calculi used in the study
of Linear Logic. We set up a computational model and an equational proof system
for this calculus, and we argue that it is equivalent to the quantum Turing
machine.Comment: To appear in SIAM Journal on Computing. Minor corrections and
improvements. Simulator available at
http://www.het.brown.edu/people/andre/qlambda/index.htm
Reduced genetic diversity and increased structure in american mink on the swedish coast following invasive species control
Eradication and population reductions are often used to mitigate the negative impacts of nonnative invasive species on native biodiversity. However, monitoring the effectiveness of nonnative species control programmes is necessary to evaluate the efficacy of these measures. Genetic monitoring could provide valuable insights into temporal changes in demographic, ecological, and evolutionary processes in invasive populations being subject to control programmes. Such programmes should cause a decrease in effective population size and/or in genetic diversity of the targeted non-native species and an increase in population genetic structuring over time. We used microsatellite DNA data from Americanmink (Neovison vison) to determine whether the removal of this predator on the Koster Islands archipelago and the nearby Swedish mainland affected genetic variation over six consecutive years of mink culling by trappers as part of a population control programme. We found that on Koster Islands allelic richness decreased (from on average 4.53 to 3.55), genetic structuring increased, and effective population size did not change. In contrast, the mink population from the Swedish coast showed no changes in genetic diversity or structure, suggesting the stability of this population over 6 years of culling. Effective population size did not change over time but was higher on the coast than on the islands across all years. Migration rates from the islands to the coast were almost two times higher than from the coast to the islands. Most migrants leaving the coast were localised on the southern edge of the archipelago, as expected from the direction of the sea current between the two sites. Genetic monitoring provided valuable information on temporal changes in the population of American mink suggesting that this approach can be used to evaluate and improve control programmes of invasive vertebrates
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