448 research outputs found
Evidence for a Two-stage Melting Transition of the Vortex Matter in Bi2Sr2Ca1Cu2O8+d Single Crystals obtained by Muon Spin Rotation
From muon spin rotation measurements on under- to overdoped Bi-2212 crystals
we obtain evidence for a two-stage transition of the vortex matter as a
function of temperature. The first transition is well known and related to the
irreversibility line (IL). The second one is located below the IL and has not
been previously observed. It occurs for all three sets of crystals and is
unrelated to the vortex mobility. Our data are consistent with a two-stage
melting scenario where the intra-planar melting of the vortex lattice and the
inter-planar decoupling of the vortex lines occur independently.Comment: 9 pages and 3 figure
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
Detecting local synchronization in coupled chaotic systems
We introduce a technique to detect and quantify local functional dependencies
between coupled chaotic systems. The method estimates the fraction of locally
syncronized configurations, in a pair of signals with an arbitrary state of
global syncronization. Application to a pair of interacting Rossler oscillators
shows that our method is capable to quantify the number of dynamical
configurations where a local prediction task is possible, also in absence of
global synchronization features
Effects of point defects on the phase diagram of vortex states in high-Tc superconductors in B//c axis
The phase diagram for the vortex states of high- superconductors
with point defects in axis is drawn by large-scale Monte
Carlo simulations. The vortex slush (VS) phase is found between the vortex
glass (VG) and vortex liquid (VL) phases. The first-order transition between
this novel normal phase and the VL phase is characterized by a sharp jump of
the density of dislocations. The first-order transition between the Bragg glass
(BG) and VG or VS phases is also clarified. These two transitions are compared
with the melting transition between the BG and VL phases.Comment: 4 pages, 9 eps figures (included in text), uses revtex.sty, overall
changes with several additional data points, though conclusion is unchange
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
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