3,783 research outputs found
Swift observations of the 2015 outburst of AG Peg -- from slow nova to classical symbiotic outburst
Symbiotic stars often contain white dwarfs with quasi-steady shell burning on
their surfaces. However, in most symbiotics, the origin of this burning is
unclear. In symbiotic slow novae, however, it is linked to a past thermonuclear
runaway. In June 2015, the symbiotic slow nova AG Peg was seen in only its
second optical outburst since 1850. This recent outburst was of much shorter
duration and lower amplitude than the earlier eruption, and it contained
multiple peaks -- like outbursts in classical symbiotic stars such as Z And. We
report Swift X-ray and UV observations of AG Peg made between June 2015 and
January 2016. The X-ray flux was markedly variable on a time scale of days,
particularly during four days near optical maximum, when the X-rays became
bright and soft. This strong X-ray variability continued for another month,
after which the X-rays hardened as the optical flux declined. The UV flux was
high throughout the outburst, consistent with quasi-steady shell burning on the
white dwarf. Given that accretion disks around white dwarfs with shell burning
do not generally produce detectable X-rays (due to Compton-cooling of the
boundary layer), the X-rays probably originated via shocks in the ejecta. As
the X-ray photo-electric absorption did not vary significantly, the X-ray
variability may directly link to the properties of the shocked material. AG
Peg's transition from a slow symbiotic nova (which drove the 1850 outburst) to
a classical symbiotic star suggests that shell burning in at least some
symbiotic stars is residual burning from prior novae.Comment: Accepted by MNRAS 23 June 2016. Manuscript submitted in original form
5 April 201
Spherical harmonic decomposition applied to spatial-temporal analysis of human high-density EEG
We demonstrate an application of spherical harmonic decomposition to analysis
of the human electroencephalogram (EEG). We implement two methods and discuss
issues specific to analysis of hemispherical, irregularly sampled data.
Performance of the methods and spatial sampling requirements are quantified
using simulated data. The analysis is applied to experimental EEG data,
confirming earlier reports of an approximate frequency-wavenumber relationship
in some bands.Comment: 12 pages, 8 figures, submitted to Phys. Rev. E, uses APS RevTeX
style
The Reproductive Biology of Two Common Surfzone Associated Sciaenids, Yellowfin Croaker (Umbrina roncador) and Spotfin Croaker (Roncador stearnsii), from Southern California
Yellowfin croaker (Umbrina roncador) and spotfin croaker (Roncador stearnsii) were collected from San Clemente, California from May through September 2006. Both species were analyzed to determine batch fecundity. Yellowfin croaker ovaries were also histologically examined to describe their summer spawning activity. Batch fecundity in spotfin croaker (n 5 13) females ranged from 35,169 to 640,703 described by the equations BF 5 1.59E-07SL5.01 for length and BF 5 13.51W1.60 for total body weight. Yellowfin croaker (n 5 16) females batch fecundity ranged from 99,259 to 405,967 and was described by the equations BF 5 2.4E- 04SL2.02 for length or BF 5 0.33W0.68 for total body weight. Yellowfin croaker spawning was determined to begin by June and end by September
Magnon Polarons induced by a magnetic field gradient
In this work, we report the theoretical possibility of generating magnon
polaron excitations through a space-varying magnetic field. The spatial
dependence of the magnetic field in the Zeeman interaction gives rise to a
magnon-phonon coupling when a magnetic field gradient is applied, and such a
coupling depends directly on the strength of the gradient. It is also predicted
that the direction of the magnetic field gradient allows control over which
phonon polarization couples to the magnons in the material. Here we develop the
calculations of the magnon-phonon coupling for an arbitrary (anti)ferromagnet,
which are later used to numerically study its consequences. These results are
compared to the ones obtained with the phenomenological magnetoelastic coupling
in YIG, where we show that the magnon polaron bandgap seen in YIG can be also
obtained with a magnetic field gradient of T/m which can be achieved
with the current experimental techniques. Our results propose a new way of
controlling the magnetoelastic coupling in an arbitrary material and open a new
route to exploit the magnon-phonon interaction in magnonic and spintronic
devices
Extended Recurrence Plot Analysis and its Application to ERP Data
We present new measures of complexity and their application to event related
potential data. The new measures base on structures of recurrence plots and
makes the identification of chaos-chaos transitions possible. The application
of these measures to data from single-trials of the Oddball experiment can
identify laminar states therein. This offers a new way of analyzing
event-related activity on a single-trial basis.Comment: 21 pages, 8 figures; article for the workshop ''Analyzing and
Modelling Event-Related Brain Potentials: Cognitive and Neural Approaches``
at November 29 - December 01, 2001 in Potsdam, German
One dimensional Coulomb-like problem in deformed space with minimal length
Spectrum and eigenfunctions in the momentum representation for 1D Coulomb
potential with deformed Heisenberg algebra leading to minimal length are found
exactly. It is shown that correction due to the deformation is proportional to
square root of the deformation parameter. We obtain the same spectrum using
Bohr-Sommerfeld quantization condition.Comment: 11 pages, typos corrected, references adde
Discovering a junction tree behind a Markov network by a greedy algorithm
In an earlier paper we introduced a special kind of k-width junction tree,
called k-th order t-cherry junction tree in order to approximate a joint
probability distribution. The approximation is the best if the Kullback-Leibler
divergence between the true joint probability distribution and the
approximating one is minimal. Finding the best approximating k-width junction
tree is NP-complete if k>2. In our earlier paper we also proved that the best
approximating k-width junction tree can be embedded into a k-th order t-cherry
junction tree. We introduce a greedy algorithm resulting very good
approximations in reasonable computing time.
In this paper we prove that if the Markov network underlying fullfills some
requirements then our greedy algorithm is able to find the true probability
distribution or its best approximation in the family of the k-th order t-cherry
tree probability distributions. Our algorithm uses just the k-th order marginal
probability distributions as input.
We compare the results of the greedy algorithm proposed in this paper with
the greedy algorithm proposed by Malvestuto in 1991.Comment: The paper was presented at VOCAL 2010 in Veszprem, Hungar
Learned Garbage Collection
Several programming languages use garbage collectors (GCs) to automatically manage memory for the programmer. Such collectors must decide when to look for unreachable objects to free, which can have a large performance impact on some applications. In this preliminary work, we propose a design for a learned garbage collector that autonomously learns over time when to perform collections. By using reinforcement learning, our design can incorporate user-defined reward functions, allowing an autonomous garbage collector to learn to optimize the exact metric the user desires (e.g., request latency or queries per second). We conduct an initial experimental study on a prototype, demonstrating that an approach based on tabular Q learning may be promising
black hole at N=2 supergravity
In this paper, we consider the charged non-extremal black hole at five
dimensional N = 2 supergravity. We study thermodynamics of AdS_{5} black hole
with three equal charges (q_{1} = q_{2} = q_{3} = q). We obtain Schrodinger
like equation and discuss the effective potential. Then, we consider the case
of the perturbed dilaton field background and find presence of odd coefficients
of the wave function. Also we find that the higher derivative corrections have
no effect on the first and second even coefficients of the wave function.Comment: 17 pages, 4 figures. Published versio
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