378 research outputs found
Resonance and frequency-locking phenomena in spatially extended phytoplankton-zooplankton system with additive noise and periodic forces
In this paper, we present a spatial version of phytoplankton-zooplankton
model that includes some important factors such as external periodic forces,
noise, and diffusion processes. The spatially extended
phytoplankton-zooplankton system is from the original study by Scheffer [M
Scheffer, Fish and nutrients interplay determines algal biomass: a minimal
model, Oikos \textbf{62} (1991) 271-282]. Our results show that the spatially
extended system exhibit a resonant patterns and frequency-locking phenomena.
The system also shows that the noise and the external periodic forces play a
constructive role in the Scheffer's model: first, the noise can enhance the
oscillation of phytoplankton species' density and format a large clusters in
the space when the noise intensity is within certain interval. Second, the
external periodic forces can induce 4:1 and 1:1 frequency-locking and spatially
homogeneous oscillation phenomena to appear. Finally, the resonant patterns are
observed in the system when the spatial noises and external periodic forces are
both turned on. Moreover, we found that the 4:1 frequency-locking transform
into 1:1 frequency-locking when the noise intensity increased. In addition to
elucidating our results outside the domain of Turing instability, we provide
further analysis of Turing linear stability with the help of the numerical
calculation by using the Maple software. Significantly, oscillations are
enhanced in the system when the noise term presents. These results indicate
that the oceanic plankton bloom may partly due to interplay between the
stochastic factors and external forces instead of deterministic factors. These
results also may help us to understand the effects arising from undeniable
subject to random fluctuations in oceanic plankton bloom.Comment: Some typos errors are proof, and some strong relate references are
adde
Vortex studies in superconducting Ba(Fe0.93Co0.07)2As2
We present small-angle neutron scattering (SANS) and Bitter decoration
studies of the superconducting vortices in
Ba(FeCo)As}. A highly disordered vortex configuration
is observed at all measured fields, and is attributed to strong pinning. This
conclusion is supported by the absence of a Meissner rim in decoration images
obtained close to the sample edge. The field dependence of the magnitude of the
SANS scattering vector indicates vortex lattice domains of (distorted)
hexagonal symmetry, consistent with the decoration images which show primarily
6-fold coordinated vortex domains. An analysis of the scattered intensity shows
that this decreases much more rapidly than expected from estimates of the upper
critical field, consistent with the large degree of disorder.Comment: 5 pages, 4 figure
Generalized Phase Synchronization in unidirectionally coupled chaotic oscillators
We investigate phase synchronization between two identical or detuned
response oscillators coupled to a slightly different drive oscillator. Our
result is that phase synchronization can occur between response oscillators
when they are driven by correlated (but not identical) inputs from the drive
oscillator. We call this phenomenon Generalized Phase Synchronization (GPS) and
clarify its characteristics using Lyapunov exponents and phase difference
plots.Comment: 4 pages, 5 figure
Anomalous peak in the superconducting condensate density of cuprate high T_{c} superconductors at a unique critical doping state
The doping dependence of the superconducting condensate density, n_{s}^{o},
has been studied by muon-spin-rotation for
Y_{0.8}Ca_{0.2}Ba_{2}(Cu_{1-z}Zn_{z})_{3}O_{7-\delta} and
Tl_{0.5-y}Pb_{0.5+y}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{7}. We find that n_{s}^{o}
exhibits a pronounced peak at a unique doping state in the slightly overdoped
regime. Its position coincides with the critical doping state where the normal
state pseudogap first appears depleting the electronic density of states. A
surprising correlation between n_{s}^{o} and the condensation energy U_{o} is
observed which suggests unconventional behavior even in the overdoped region.Comment: 10 pages, 3 figure
Hydraulic resistance to overland flow on surfaces with partially submerged vegetation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96239/1/wrcr13661.pd
Elliptic Curves over Real Quadratic Fields are Modular
We prove that all elliptic curves defined over real quadratic fields are
modular.Comment: 38 pages. Magma scripts available as ancillary files with this arXiv
versio
Small-angle neutron scattering study of the vortex lattice in superconducting LuNi2B2C
We present studies of the magnetic field distribution around the vortices in
LuNi2B2C. Small-angle neutron scattering measurements of the vortex lattice
(VL) in this material were extended to unprecedentedly large values of the
scattering vector q, obtained both by using high magnetic fields to decrease
the VL spacing and by using higher order reflections. A square VL, oriented
with the nearest neighbor direction along the crystalline [110] direction, was
observed up to the highest measured field. The first-order VL form factor,
|F(q10)|, was found to decrease exponentially with increasing magnetic field.
Measurements of the higher order form factors, |F(qhk)|, reveal a significant
in-plane anisotropy and also allow for a real-space reconstruction of the VL
field distribution.Comment: 8 pages, 7 figure
Variational Principle underlying Scale Invariant Social Systems
MaxEnt's variational principle, in conjunction with Shannon's logarithmic
information measure, yields only exponential functional forms in
straightforward fashion. In this communication we show how to overcome this
limitation via the incorporation, into the variational process, of suitable
dynamical information. As a consequence, we are able to formulate a somewhat
generalized Shannonian Maximum Entropy approach which provides a unifying
"thermodynamic-like" explanation for the scale-invariant phenomena observed in
social contexts, as city-population distributions. We confirm the MaxEnt
predictions by means of numerical experiments with random walkers, and compare
them with some empirical data
- …