1,379 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
A numerical study of rigidity of hyperbolic splittings in simple two-dimensional maps
Chaotic hyperbolic dynamical systems enjoy a surprising degree of rigidity, a fact which is well known in the mathematics community but perhaps less so in theoretical physics circles. Low-dimensional hyperbolic systems are either conjugate to linear automorphisms, that is, dynamically equivalent to the Arnold cat map and its variants, or their hyperbolic structure is not smooth. We illustrate this dichotomy using a family of analytic maps, for which we show by means of numerical simulations that the corresponding hyperbolic structure is not smooth, thereby providing an example for a global mechanism which produces non-smooth phase space structures in an otherwise smooth dynamical system
Islam, Religiosity, and Immigrant Political Action in Western Europe
Cataloged from PDF version of article.The issues of migration and immigrant political integration in western democracies have
become increasingly intertwined with debates on religion, particularly Islam. To date, however,
we have surprisingly little systematic research on how religious beliefs are related to
immigrants’ political engagement. In this study, we argue that religion has a capacity to
mobilize immigrants politically but the strength of this relationship depends on immigrant
generation, religiosity, and the type of religion. Using survey data collected as part of the
European Social Survey (ESS) 2002–2010 in 18 West European democracies, our analyses
reveal that religion is indeed linked to political engagement of immigrants in a complex
way: while belonging to a religion is generally associated with less political participation,
exposure to religious institutions appears to have the opposite effect. Moreover, we find
that, compared to foreign-born Muslims, second-generation Muslim immigrants are not
only more religious and more politically dissatisfied with their host countries, but also that
religiosity is more strongly linked to their political engagement. This relationship, however,
is limited to uninstitutionalized political action
The X-ray Properties of the Most-Luminous Quasars from the Sloan Digital Sky Survey
Utilizing 21 new Chandra observations as well as archival Chandra, ROSAT, and
XMM-Newton data, we study the X-ray properties of a representative sample of 59
of the most optically luminous quasars in the Universe (M_i~~-29.3 to -30.2)
spanning a redshift range of z~~1.5-4.5. Our full sample consists of 32 quasars
from the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3) quasar catalog,
two additional objects in the DR3 area that were missed by the SDSS selection
criteria, and 25 comparably luminous quasars at z>~4. This is the largest X-ray
study of such luminous quasars to date. By jointly fitting the X-ray spectra of
our sample quasars, excluding radio-loud and broad absorption line (BAL)
objects, we find a mean X-ray power-law photon index of
Gamma=1.92^{+0.09}_{-0.08} and constrain any neutral intrinsic absorbing
material to have a mean column density of N_H<~2x10^{21} cm^{-2}. We find,
consistent with other studies, that Gamma does not change with redshift, and we
constrain the amount of allowed Gamma evolution for the most-luminous quasars.
Our sample, excluding radio-loud and BAL quasars, has a mean X-ray-to-optical
spectral slope of a_ox=-1.80+/-0.02, as well as no significant evolution of
a_ox with redshift. We also comment upon the X-ray properties of a number of
notable quasars, including an X-ray weak quasar with several strong narrow
absorption-line systems, a mildly radio-loud BAL quasar, and a well-studied
gravitationally lensed quasar.Comment: 18 pages (emulateapj), 11 figures. Accepted for publication in The
Astrophysical Journa
Anomalous dynamics in symmetric triangular irrational billiards
We identify a symmetry induced mechanism which dominates the long time behaviour in symmetric triangular billiards. We rigorously prove the existence of invariant sets in symmetric irrational billiards on which the dynamics is governed by an interval exchange transformation. Counterintuitively, this property of symmetric irrational billiards is analogous to the case of general rational billiards, and it highlights the non-trivial impact of symmetries in non-hyperbolic dynamical systems. Our findings provide an explanation for the logarithmic subdiffusive relaxation processes observed in certain triangular billiards. In addition we are able to settle a long standing conjecture about the existence of non-periodic and not everywhere dense trajectories in triangular billiards
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
Extensive study of nuclear uncertainties and their impact on the r-process nucleosynthesis in neutron star mergers
Theoretically predicted yields of elements created by the rapid neutron
capture (r-) process carry potentially large uncertainties associated with
incomplete knowledge of nuclear properties as well as approximative
hydrodynamical modelling of the matter ejection processes. We present an
in-depth study of the nuclear uncertainties by systematically varying
theoretical nuclear input models that describe the experimentally unknown
neutron-rich nuclei. This includes two frameworks for calculating the radiative
neutron capture rates and six, four and four models for the nuclear masses,
-decay rates and fission properties, respectively. Our r-process nuclear
network calculations are based on detailed hydrodynamical simulations of
dynamically ejected material from NS-NS or NS-BH binary mergers plus the
secular ejecta from BH-torus systems. The impact of nuclear uncertainties on
the r-process abundance distribution and early radioactive heating rate is
found to be modest (within a factor for individual nuclei and
a factor 2 for the heating rate), however the impact on the late-time heating
rate is more significant and depends strongly on the contribution from fission.
We witness significantly larger sensitivity to the nuclear physics input if
only a single trajectory is used compared to considering ensembles of
200-300 trajectories, and the quantitative effects of the nuclear
uncertainties strongly depend on the adopted conditions for the individual
trajectory. We use the predicted Th/U ratio to estimate the cosmochronometric
age of six metal-poor stars to set a lower limit of the age of the Galaxy and
find the impact of the nuclear uncertainties to be up to 2 Gyr.Comment: 26 pages, 22 figures, submitted to MNRA
Memory difference control of unknown unstable fixed points: Drifting parameter conditions and delayed measurement
Difference control schemes for controlling unstable fixed points become
important if the exact position of the fixed point is unavailable or moving due
to drifting parameters. We propose a memory difference control method for
stabilization of a priori unknown unstable fixed points by introducing a memory
term. If the amplitude of the control applied in the previous time step is
added to the present control signal, fixed points with arbitrary Lyapunov
numbers can be controlled. This method is also extended to compensate arbitrary
time steps of measurement delay. We show that our method stabilizes orbits of
the Chua circuit where ordinary difference control fails.Comment: 5 pages, 8 figures. See also chao-dyn/9810029 (Phys. Rev. E 70,
056225) and nlin.CD/0204031 (Phys. Rev. E 70, 046205
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