610 research outputs found
Lagrangian Statistics and Temporal Intermittency in a Shell Model of Turbulence
We study the statistics of single particle Lagrangian velocity in a shell
model of turbulence. We show that the small scale velocity fluctuations are
intermittent, with scaling exponents connected to the Eulerian structure
function scaling exponents. The observed reduced scaling range is interpreted
as a manifestation of the intermediate dissipative range, as it disappears in a
Gaussian model of turbulence.Comment: 4 pages, 5 figure
Unconventional Charge Ordering in Na0.70CoO2 below 300 K
We present the results of measurements of the dc-magnetic susceptibility
chi(T) and the 23Na-NMR response of Na_{0.70}CoO_{2} at temperatures between 50
and 340 K. The chi(T) data suggest that for T > 75 K, the Co ions adopt an
effective configuration of Co^{3.4+}. The 23Na-NMR response reveals pronounced
anomalies near 250 and 295 K, but no evidence for magnetic phase transitions is
found in chi(T). Our data suggest the onset of a dramatic change in the Co
3d-electron spin dynamics at 295 K. This process is completed at 230 K. Our
results maybe interpreted as evidence for either a tendency to electron
localization or an unconventional charge-density wave phenomenon within the
cobalt oxide layer, CoO_2, 3d electron system near room temperature.Comment: 4 pages, 4 figures, re-submitted to Physical Review Letters. The
manuscript has been revised following the recommendations of the referees.
The discussion section contains substantial change
Use of control to maintain period-1 motions during wind-up or wind-down operations of an impacting driven beam
We consider the dynamical response of a thin beam held fixed at one end while excited by an external driving force. A motion limiting constraint, or stop, causes the beam to impact. During wind-up or wind-down operations, in which the driving frequency is continuously altered, the system can undergo complicated motions close to the value of frequency at which impacts may first occur, the grazing bifurcation. In this region, the beam may experience several impacts within a long period-repeating solution or even chaotic behavior which, in practical terms, may be undesirable to the long-term integrity of the system. The first task is to identify the zones in the space of parameters (forcing amplitude or, alternatively, the gap between the beam and the stop) in which period-1 motions can be guaranteed. In this paper, in the areas in which complicated or chaotic motion occurs, a control strategy is proposed which stabilises unstable period-1 motions. As a consequence, numerical simulations indicate that, for any choice of parameter in the range, simple period-1 motions can be maintained, limiting the number of impacts (together with their velocity)
Mutual synchronization and clustering in randomly coupled chaotic dynamical networks
We introduce and study systems of randomly coupled maps (RCM) where the
relevant parameter is the degree of connectivity in the system. Global
(almost-) synchronized states are found (equivalent to the synchronization
observed in globally coupled maps) until a certain critical threshold for the
connectivity is reached. We further show that not only the average
connectivity, but also the architecture of the couplings is responsible for the
cluster structure observed. We analyse the different phases of the system and
use various correlation measures in order to detect ordered non-synchronized
states. Finally, it is shown that the system displays a dynamical hierarchical
clustering which allows the definition of emerging graphs.Comment: 13 pages, to appear in Phys. Rev.
The rp-process and new measurements of beta-delayed proton decay of light Ag and Cd isotopes
Recent network calculations suggest that a high temperature rp-process could
explain the abundances of light Mo and Ru isotopes, which have long challenged
models of p-process nuclide production. Important ingredients to network
calculations involving unstable nuclei near and at the proton drip line are
-halflives and decay modes, i.e., whether or not -delayed proton
decay takes place. Of particular importance to these network calculation are
the proton-rich isotopes Ag, Ag, Cd and Cd. We
report on recent measurements of -delayed proton branching ratios for
Ag, Ag, and Cd at the on-line mass separator at GSI.Comment: 4 pages, uses espcrc1.sty. Proceedings of the 4th International
Symposium Nuclei in the Cosmos, June 1996, Notre Dame/IN, USA, Ed. M.
Wiescher, to be published in Nucl.Phys.A. Also available at
ftp://ftp.physics.ohio-state.edu/pub/nucex/nic96-gs
Sub-Poissonian statistics in order-to-chaos transition
We study the phenomena at the overlap of quantum chaos and nonclassical
statistics for the time-dependent model of nonlinear oscillator. It is shown in
the framework of Mandel Q-parameter and Wigner function that the statistics of
oscillatory excitation number is drastically changed in order-to chaos
transition. The essential improvement of sub-Poissonian statistics in
comparison with an analogous one for the standard model of driven anharmonic
oscillator is observed for the regular operational regime. It is shown that in
the chaotic regime the system exhibits the range of sub- and super-Poissonian
statistics which alternate one to other depending on time intervals. Unusual
dependence of the variance of oscillatory number on the external noise level
for the chaotic dynamics is observed.Comment: 9 pages, RevTeX, 14 figure
Dynamics of trapped bright solitons in the presence of localized inhomogeneities
We examine the dynamics of a bright solitary wave in the presence of a
repulsive or attractive localized ``impurity'' in Bose-Einstein condensates
(BECs). We study the generation and stability of a pair of steady states in the
vicinity of the impurity as the impurity strength is varied. These two new
steady states, one stable and one unstable, disappear through a saddle-node
bifurcation as the strength of the impurity is decreased. The dynamics of the
soliton is also examined in all the cases (including cases where the soliton is
offset from one of the relevant fixed points). The numerical results are
corroborated by theoretical calculations which are in very good agreement with
the numerical findings.Comment: 8 pages, 5 composite figures with low res (for high res pics please
go to http://www.rohan.sdsu.edu/~rcarrete/ [Publications] [Publication#41
High Magnetic Field NMR Studies of LiVGeO, a quasi 1-D Spin System
We report Li pulsed NMR measurements in polycrystalline and single
crystal samples of the quasi one-dimensional S=1 antiferromagnet
LiVGeO, whose AF transition temperature is K.
The field () and temperature () ranges covered were 9-44.5 T and
1.7-300 K respectively. The measurements included NMR spectra, the spin-lattice
relaxation rate (), and the spin-phase relaxation rate (),
often as a function of the orientation of the field relative to the crystal
axes. The spectra indicate an AF magnetic structure consistent with that
obtained from neutron diffraction measurements, but with the moments aligned
parallel to the c-axis. The spectra also provide the -dependence of the AF
order parameter and show that the transition is either second order or weakly
first order. Both the spectra and the data show that has at
most a small effect on the alignment of the AF moment. There is no spin-flop
transition up to 44.5 T. These features indicate a very large magnetic
anisotropy energy in LiVGeO with orbital degrees of freedom playing an
important role. Below 8 K, varies substantially with the orientation
of in the plane perpendicular to the c-axis, suggesting a small energy
gap for magnetic fluctuations that is very anisotropic.Comment: submitted to Phys. Rev.
General Stability Analysis of Synchronized Dynamics in Coupled Systems
We consider the stability of synchronized states (including equilibrium
point, periodic orbit or chaotic attractor) in arbitrarily coupled dynamical
systems (maps or ordinary differential equations). We develop a general
approach, based on the master stability function and Gershgorin disc theory, to
yield constraints on the coupling strengths to ensure the stability of
synchronized dynamics. Systems with specific coupling schemes are used as
examples to illustrate our general method.Comment: 8 pages, 1 figur
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