8,723 research outputs found
Intermittent Synchronization in a Pair of Coupled Chaotic Pendula
Numerical simulations have been carried out for a pair of unidirectionally coupled identical pendula under the action of a common external ac torque. Both the master pendulum and the slave pendulum were in chaotic states. The only form of persistent locking appeared to be a computational artifact; otherwise the synchronization of slave to master was found to be intermittent
Intermittent Synchronization of Resistively Coupled Chaotic Josephson Junctions
Numerical simulations have been used to investigate the dynamics of a pair of resistively linked Josephson junctions with ac bias. For suitable choices of parameters, the chaotic states of the two junctions become intermittently synchronized. Intervals of synchronization are interleaved between bursts of desynchronized activity. The distributions of these laminar times and their dependence on the coupling strength are determined. The role of phase winding in the definition of synchronization intervals is considered
Inverting Chaos: Extracting System Parameters from Experimental Data
Given a set of experimental or numerical chaotic data and a set of model differential equations with several parameters, is it possible to determine the numerical values for these parameters using a least-squares approach, and thereby to test the model against the data? We explore this question (a) with simulated data from model equations for the Rossler, Lorenz, and pendulum attractors, and (b) with experimental data produced by a physical chaotic pendulum. For the systems considered in this paper, the least-squares approach provides values of model parameters that agree well with values obtained in other ways, even in the presence of modest amounts of added noise. For experimental data, the “fitted” and experimental attractors are found to have the same correlation dimension and the same positive Lyapunov exponent
3,000 Post-its: Minute Papers as Formative Assessment in Business Writing Courses
This presentation focuses on the implementation of this assessment method in the business classroom, data analysis of over 3,000 responses, and emergent themes such as student preparedness for business report writing and use of library resources. Changes to curriculum and ways instructors might use this in their own classrooms will also be shared
Unexpected phase locking of magnetic fluctuations in the multi-k magnet USb
The spin waves in the multi-k antiferromagnet USb soften and become quasielastic well below the antiferromagnetic ordering temperature TN. This occurs without a magnetic or structural transition. It has been suggested that this change is in fact due to dephasing of the different multi-k components: a switch from 3-k to 1-k behavior. In this work, we use inelastic neutron scattering with tridirectional polarization analysis to probe the quasielastic magnetic excitations and reveal that the 3-k structure does not dephase. More surprisingly, the paramagnetic correlations also maintain the same clear phase correlations well above TN (up to at least 1.4TN)
A First Comparison of SLOPE and Other LIGO Burst Event Trigger Generators
A number of different methods have been proposed to identify unanticipated
burst sources of gravitational waves in data arising from LIGO and other
gravitational wave detectors. When confronted with such a wide variety of
methods one is moved to ask if they are all necessary, i.e. given detector data
that is assumed to have no gravitational wave signals present, do they
generally identify the same events with the same efficiency, or do they each
'see' different things in the detector? Here we consider three different
methods, which have been used within the LIGO Scientific Collaboration as part
of its search for unanticipated gravitational wave bursts. We find that each of
these three different methods developed for identifying candidate gravitational
wave burst sources are, in fact, attuned to significantly different features in
detector data, suggesting that they may provide largely independent lists of
candidate gravitational wave burst events.Comment: 10 Pages, 5 Figures, Presented at the 10th Gravitational Wave Data
Analysis Workshop (GWDAW-10), 14-17 December 2005 at the University of Texas,
Brownsvill
Raman study of the Verwey transition in Magnetite at high-pressure and low-temperature; effect of Al doping
We report high-pressure low-temperature Raman studies of the Verwey
transition in pure and Al-doped magnetite (Fe_3O_4). The low temperature phase
of magnetite displays a number of additional Raman modes that serve as
transition markers. These transition markers allow one to investigate the
effect of hydrostatic pressure on the Verwey transition temperature. Al-doped
magnetite Fe_2.8Al_0.2O_4 (TV=116.5K) displays a nearly linear decrease of the
transition temperature with an increase of pressure yielding dP/dT_V = -0.096
GPa/K. In contrast pure magnetite displays a significantly steeper slope of the
PT equilibrium line with dP/dT_V = -0.18 GPa/K. The slope of the PT equilibrium
lines is related to the changes of the molar entropy and molar volume at the
transition. We compare our spectroscopic data with that obtained from the
ambient pressure specific heat measurements and find a good agreement in the
optimally doped magnetite. Our data indicates that Al doping leads to a smaller
entropy change and larger volume expansion at the transition. Our data displays
the trends that are consistent with the mean field model of the transition that
assumes charge ordering in magnetite.Comment: 17 pages, 3 figure
Dynamical Imaging with Interferometry
By linking widely separated radio dishes, the technique of very long baseline
interferometry (VLBI) can greatly enhance angular resolution in radio
astronomy. However, at any given moment, a VLBI array only sparsely samples the
information necessary to form an image. Conventional imaging techniques
partially overcome this limitation by making the assumption that the observed
cosmic source structure does not evolve over the duration of an observation,
which enables VLBI networks to accumulate information as the Earth rotates and
changes the projected array geometry. Although this assumption is appropriate
for nearly all VLBI, it is almost certainly violated for submillimeter
observations of the Galactic Center supermassive black hole, Sagittarius A*
(Sgr A*), which has a gravitational timescale of only ~20 seconds and exhibits
intra-hour variability. To address this challenge, we develop several
techniques to reconstruct dynamical images ("movies") from interferometric
data. Our techniques are applicable to both single-epoch and multi-epoch
variability studies, and they are suitable for exploring many different
physical processes including flaring regions, stable images with small
time-dependent perturbations, steady accretion dynamics, or kinematics of
relativistic jets. Moreover, dynamical imaging can be used to estimate
time-averaged images from time-variable data, eliminating many spurious image
artifacts that arise when using standard imaging methods. We demonstrate the
effectiveness of our techniques using synthetic observations of simulated black
hole systems and 7mm Very Long Baseline Array observations of M87, and we show
that dynamical imaging is feasible for Event Horizon Telescope observations of
Sgr A*.Comment: 16 Pages, 12 Figures, Accepted for publication in Ap
Search for Gravitational Waves from Intermediate Mass Binary Black Holes
We present the results of a weakly modeled burst search for gravitational waves from mergers of non-spinning intermediate mass black holes (IMBH) in the total mass range 100-450 solar Mass and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the IMBH mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 solar Mass , for non-spinning sources, the rate density upper limit is 0.13 per Mpc(exp 3) per Myr at the 90% confidence level
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