40,002 research outputs found
Magnetism in the Square Kilometre Array Era
The unprecedented sensitivity, angular resolution and broad bandwidth
coverage of Square Kilometre Array (SKA) radio polarimetric observations will
allow us to address many long-standing mysteries in cosmic magnetism science. I
will highlight the unique capabilities of the SKA to map the warm hot
intergalactic medium, reveal detailed 3-dimensional structures of magnetic
fields in local galaxies and trace the redshift evolution of galactic magnetic
fields.Comment: 4 pages, Invited paper, Proceedings of FM8 "New Insights in
Extragalactic Magnetic Fields", XXXth General Assembly of the IAU, Vienna,
August 20-31, 201
Almost sure exponential stability of numerical solutions for stochastic delay differential equations
Using techniques based on the continuous and discrete semimartingale convergence theorems, this paper investigates if numerical methods may reproduce the almost sure exponential stability of the exact solutions to stochastic delay differential equations (SDDEs). The important feature of this technique is that it enables us to study the almost sure exponential stability of numerical solutions of SDDEs directly. This is significantly different from most traditional methods by which the almost sure exponential stability is derived from the moment stability by the Chebyshev inequality and the Borel–Cantelli lemma
Empirical Study of Simulated Two-planet Microlensing Event
We undertake the first study of two-planet microlensing models recovered from
simulations of microlensing events generated by realistic multi-planet systems
in which 292 planetary events including 16 two-planet events were detected from
6690 simulated light curves. We find that when two planets are recovered, their
parameters are usually close to those of the two planets in the system most
responsible for the perturbations. However, in one of the 16 examples, the
apparent mass of both detected planets was more than doubled by the unmodeled
influence of a third, massive planet. This fraction is larger than, but
statistically consistent with, the roughly 1.5% rate of serious mass errors due
to unmodeled planetary companions for the 274 cases from the same simulation in
which a single planet is recovered. We conjecture that an analogous effect due
to unmodeled stellar companions may occur more frequently. For seven out of 23
cases in which two planets in the system would have been detected separately,
only one planet was recovered because the perturbations due to the two planets
had similar forms. This is a small fraction (7/274) of all recovered
single-planet models, but almost a third of all events that might plausibly
have led to two-planet models. Still, in these cases, the recovered planet
tends to have parameters similar to one of the two real planets most
responsible for the anomaly.Comment: 21 pages, 9 figures, 2 tables; submitted to ApJ; for a short video
introducing the key results, see https://www.youtube.com/watch?v=qhK4a6sbfO
A New Photometric Model of the Galactic Bar using Red Clump Giants
We present a study of the luminosity density distribution of the Galactic bar
using number counts of red clump giants (RCGs) from the OGLE-III survey. The
data were recently published by Nataf et al. (2013) for 9019 fields towards the
bulge and have RC stars over a viewing area of . The data include the number counts, mean distance modulus
(), dispersion in and full error matrix, from which we fit the data
with several tri-axial parametric models. We use the Markov Chain Monte Carlo
(MCMC) method to explore the parameter space and find that the best-fit model
is the model, with the distance to the GC is 8.13 kpc, the ratio of
semi-major and semi-minor bar axis scale lengths in the Galactic plane
, and vertical bar scale length , is (close to being prolate). The scale length of the stellar
density profile along the bar's major axis is 0.67 kpc and has an angle
of , slightly larger than the value obtained from a similar study
based on OGLE-II data. The number of estimated RC stars within the field of
view is , which is systematically lower than the observed
value. We subtract the smooth parametric model from the observed counts and
find that the residuals are consistent with the presence of an X-shaped
structure in the Galactic centre, the excess to the estimated mass content is
. We estimate the total mass of the bar is . Our results can be used as a key ingredient to construct new density
models of the Milky Way and will have implications on the predictions of the
optical depth to gravitational microlensing and the patterns of hydrodynamical
gas flow in the Milky Way.Comment: 15 pages, 6 figures, 4 tables. MNRAS accepte
Approximate solutions of stochastic differential delay equations with Markovian switching
Our main aim is to develop the existence theory for the solutions to stochastic differential delay equations with Markovian switching (SDDEwMSs) and to establish the convergence theory for the Euler-Maruyama approximate solutions under the local Lipschitz condition. As an application, our results are used to discuss a stochastic delay population system with Markovian switching
Robustness of Majorana Modes and Minigaps in a Spin-Orbit-Coupled Semiconductor-Superconductor Heterostructure
We study the robustness of Majorana zero energy modes and minigaps of
quasiparticle excitations in a vortex by numerically solving
Bogoliubov-deGennes equations in a heterostructure composed of an \textit{s}
-wave superconductor, a spin-orbit-coupled semiconductor thin film, and a
magnetic insulator. This heterostructure was proposed recently as a platform
for observing non-Abelian statistics and performing topological quantum
computation. The dependence of the Majorana zero energy states and the minigaps
on various physics parameters (Zeeman field, chemical potential, spin-orbit
coupling strength) is characterized. We find the minigaps depend strongly on
the spin-orbit coupling strength. In certain parameter region, the minigaps are
linearly proportional to the \textit{s}-wave superconducting pairing gap
, which is very different from the dependence in a
regular \textit{s-} or \textit{\p}-wave superconductor. We characterize the
zero energy chiral edge state at the boundary and calculate the STM signal in
the vortex core that shows a pronounced zero energy peak. We show that the
Majorana zero energy states are robust in the presence of various types of
impurities. We find the existence of impurity potential may increase the
minigaps and thus benefit topological quantum computation.Comment: 11 pages, 15 figure
The Effect of Buying versus Leasing on Entry Deterrence
Monopoly; Entry Deterrence
Site evaluation for laser satellite-tracking stations
Twenty-six locations for potential laser satellite-tracking stations, four of them actually already occupied in this role, are reviewed in terms of their known local and regional geology and geophysics. The sites are also considered briefly in terms of weather and operational factors. Fifteen of the sites qualify as suitable for a stable station whose motions are likely to reflect only gross plate motion. The others, including two of the present laser station sites (Arequipa and Athens), fail to qualify unless extra monitoring schemes can be included, such as precise geodetic surveying of ground deformation
Stabilisation and destabilisation of nonlinear differential equations by noise
This paper considers the stabilisation and destabilisa- tion by a Brownian noise perturbation which preserves the equilibrium of the ordinary dierential equation x0(t) = f(x(t)). In an extension of earlier work, we lift the restriction that f obeys a global linear bound, and show that when f is locally Lipschitz, a function g can always be found so that the noise perturbation g(X(t)) dB(t) either stabilises an unstable equilibrium, or destabilises a stable equilibrium. When the equilibrium of the deterministic equation is non{hyperbolic, we show that a non{hyperbolic perturbation suffices to change the stability properties of the solution.
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