2,295 research outputs found
Stability domains for time-delay feedback control with latency
We generalize a known analytical method for determining the stability of
periodic orbits controlled by time-delay feedback methods when latencies
associated with the generation and injection of the feedback signal cannot be
ignored. We discuss the case of extended time-delay autosynchronization (ETDAS)
and show that nontrivial qualitative features of the domain of control observed
in experiments can be explained by taking into account the effects of both the
unstable eigenmode and a single stable eigenmode in the Floquet theory.Comment: 9 pages, 6 figures; Submitted to Physical Review
On the Influence of Minor Mergers on the Radial Abundance Gradient in Disks of Milky Way-like Galaxies
We investigate the influence of stellar migration caused by minor mergers
(mass ratio from 1:70 to 1:8) on the radial distribution of chemical abundances
in the disks of Milky Way-like galaxies during the last four Gyr. A GPU-based
pure N-body tree-code model without hydrodynamics and star formation was used.
We computed a large set of mergers with different initial satellite masses,
positions, and orbital velocities. We find that there is no significant
metallicity change at any radius of the primary galaxy in the case of accretion
of a low-mass satellite of 10 M (mass ratio 1:70) except for the
special case of prograde satellite motion in the disk plane of the host galaxy.
The accretion of a satellite of a mass M (mass
ratio 1:23) results in an appreciable increase of the chemical abundances at
galactocentric distances larger than kpc. The radial abundance
gradient flattens in the range of galactocentric distances from 5 to 15 kpc in
the case of a merger with a satellite with a mass
M. There is no significant change in the abundance gradient slope in
the outer disk (from kpc up to 25 kpc) in any merger while the scatter
in metallicities at a given radius significantly increases for most of the
satellite's initial masses/positions compared to the case of an isolated
galaxy. This argues against attributing the break (flattening) of the abundance
gradient near the optical radius observed in the extended disks of Milky
Way-like galaxies only to merger-induced stellar migration.Comment: 17 pages, 15 figures, accepted for publication in Ap
Bifurcations in Globally Coupled Map Lattices
The dynamics of globally coupled map lattices can be described in terms of a
nonlinear Frobenius--Perron equation in the limit of large system size. This
approach allows for an analytical computation of stationary states and their
stability. The complete bifurcation behaviour of coupled tent maps near the
chaotic band merging point is presented. Furthermore the time independent
states of coupled logistic equations are analyzed. The bifurcation diagram of
the uncoupled map carries over to the map lattice. The analytical results are
supplemented with numerical simulations.Comment: 19 pages, .dvi and postscrip
Time--delay autosynchronization of the spatio-temporal dynamics in resonant tunneling diodes
The double barrier resonant tunneling diode exhibits complex spatio-temporal
patterns including low-dimensional chaos when operated in an active external
circuit. We demonstrate how autosynchronization by time--delayed feedback
control can be used to select and stabilize specific current density patterns
in a noninvasive way. We compare the efficiency of different control schemes
involving feedback in either local spatial or global degrees of freedom. The
numerically obtained Floquet exponents are explained by analytical results from
linear stability analysis.Comment: 10 pages, 16 figure
Towards predicting post-editing productivity
Machine translation (MT) quality is generally measured via automatic metrics, producing scores that have no meaning for translators who are required to post-edit MT output or for project managers who have to plan and budget for transla- tion projects. This paper investigates correlations between two such automatic metrics (general text matcher and translation edit rate) and post-editing productivity. For the purposes of this paper, productivity is measured via processing speed and cognitive measures of effort using eye tracking as a tool. Processing speed, average fixation time and count are found to correlate well with the scores for groups of segments. Segments with high GTM and TER scores require substantially less time and cognitive effort than medium or low-scoring segments. Future research involving score thresholds and confidence estimation is suggested
Collective motions in globally coupled tent maps with stochastic updating
We study a generalization of globally coupled maps, where the elements are
updated with probability . When is below a threshold , the
collective motion vanishes and the system is the stationary state in the large
size limit. We present the linear stability analysis.Comment: 6 pages including 5 figure
SDSS Absolute Magnitudes for Thin Disc Stars based on Trigonometric Parallaxes
We present a new luminosity-colour relation based on trigonometric parallaxes
for thin disc main-sequence stars in SDSS photometry. We matched stars from the
newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky
Catalogue of Point Sources, and applied a series of constraints, i.e. relative
parallax errors (), metallicity
( dex), age ( Gyr) and surface gravity
(), and obtained a sample of thin disc main-sequence stars. Then, we
used our previous transformation equations (Bilir et al. 2008a) between SDSS
and 2MASS photometries and calibrated the absolute magnitudes to the
and colours. The transformation formulae between 2MASS
and SDSS photometries along with the absolute magnitude calibration provide
space densities for bright stars which saturate the SDSS magnitudes.Comment: 7 pages, including 7 figures and 2 tables, accepted for publication
in MNRA
Precision Mass Measurements of 129-131Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process
Masses adjacent to the classical waiting-point nuclide 130Cd have been
measured by using the Penning- trap spectrometer ISOLTRAP at ISOLDE/CERN. We
find a significant deviation of over 400 keV from earlier values evaluated by
using nuclear beta-decay data. The new measurements show the reduction of the N
= 82 shell gap below the doubly magic 132Sn. The nucleosynthesis associated
with the ejected wind from type-II supernovae as well as from compact object
binary mergers is studied, by using state-of-the-art hydrodynamic simulations.
We find a consistent and direct impact of the newly measured masses on the
calculated abundances in the A = 128 - 132 region and a reduction of the
uncertainties from the precision mass input data
Periodicity Manifestations in the Turbulent Regime of Globally Coupled Map Lattice
We revisit the globally coupled map lattice (GCML). We show that in the so
called turbulent regime various periodic cluster attractor states are formed
even though the coupling between the maps are very small relative to the
non-linearity in the element maps.
Most outstanding is a maximally symmetric three cluster attractor in period
three motion (MSCA) due to the foliation of the period three window of the
element logistic maps. An analytic approach is proposed which explains
successfully the systematics of various periodicity manifestations in the
turbulent regime. The linear stability of the period three cluster attractors
is investigated.Comment: 34 pages, 8 Postscript figures, all in GCML-MSCA.Zi
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