10,291 research outputs found
Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse
The search for binarity in AGB stars is of critical importance for our
understanding of how planetary nebulae acquire the dazzling variety of
aspherical shapes which characterises this class. However, detecting binary
companions in such stars has been severely hampered due to their extreme
luminosities and pulsations. We have carried out a small imaging survey of AGB
stars in ultraviolet light (using GALEX) where these cool objects are very
faint, in order to search for hotter companions. We report the discovery of
significant far-ultraviolet excesses towards nine of these stars. The
far-ultraviolet excess most likely results either directly from the presence of
a hot binary companion, or indirectly from a hot accretion disk around the
companion.Comment: revised for Astrophysical Journa
Interpretation of runaway electron synchrotron and bremsstrahlung images
The crescent spot shape observed in DIII-D runaway electron synchrotron
radiation images is shown to result from the high degree of anisotropy in the
emitted radiation, the finite spectral range of the camera and the distribution
of runaways. The finite spectral camera range is found to be particularly
important, as the radiation from the high-field side can be stronger by a
factor than the radiation from the low-field side in DIII-D. By
combining a kinetic model of the runaway dynamics with a synthetic synchrotron
diagnostic we see that physical processes not described by the kinetic model
(such as radial transport) are likely to be limiting the energy of the
runaways. We show that a population of runaways with lower dominant energies
and larger pitch-angles than those predicted by the kinetic model provide a
better match to the synchrotron measurements. Using a new synthetic
bremsstrahlung diagnostic we also simulate the view of the Gamma Ray Imager
(GRI) diagnostic used at DIII-D to resolve the spatial distribution of
runaway-generated bremsstrahlung.Comment: 21 pages, 11 figure
Entomological characterization of malaria in northern Colombia through vector and parasite species identification, and analyses of spatial distribution and infection rates
Background: Malaria remains a worldwide public health concern and, in Colombia, despite the efforts to stop malaria transmission, the incidence of cases has increased over the last few years. In this context, it is necessary to evaluate vector diversity, infection rates, and spatial distribution, to better understand disease transmission dynamics. This information may contribute to the planning and development of vector control strategies. Results: A total of 778 Anopheles mosquitoes were collected in fifteen localities of Córdoba from August 2015 to October 2016. Six species were identified and overall, Anopheles albimanus was the most widespread and abundant species (83%). Other species of the Nyssorhynchus subgenus were collected, including Anopheles triannulatus (13%), Anopheles nuneztovari (1%), Anopheles argyritarsis (< 1%) and two species belonging to the Anopheles subgenus: Anopheles pseudopunctipennis (3%) and Anopheles neomaculipalpus (< 1%). Four species were found naturally infected with two Plasmodium species: Anopheles nuneztovari was detected naturally infected with Plasmodium falciparum and Anopheles pseudopunctipennis with Plasmodium vivax, whereas An. albimanus and An. triannulatus were found infected with both parasite species and confirmed by nested PCR. Conclusions: In general, the obtained results were contrasting with previous studies in terms of the most abundant and widespread collected species, and regarding infection rates, which were higher than those previously reported. A positive relationship between mosquito local abundance at the locality level and human infection at the municipality level was found. Mosquito local abundance and the number of houses with mosquitoes in each village are factors explaining malaria human cases in these villages. The obtained results suggest that other factors related to the apparent variation in malaria eco-epidemiology in northern Colombia, must be identified, to provide health authorities with better decision tools aiming to design control and prevention strategies
Characterization of complex quantum dynamics with a scalable NMR information processor
We present experimental results on the measurement of fidelity decay under
contrasting system dynamics using a nuclear magnetic resonance quantum
information processor. The measurements were performed by implementing a
scalable circuit in the model of deterministic quantum computation with only
one quantum bit. The results show measurable differences between regular and
complex behaviour and for complex dynamics are faithful to the expected
theoretical decay rate. Moreover, we illustrate how the experimental method can
be seen as an efficient way for either extracting coarse-grained information
about the dynamics of a large system, or measuring the decoherence rate from
engineered environments.Comment: 4pages, 3 figures, revtex4, updated with version closer to that
publishe
Algorithmic and Hardness Results for the Colorful Components Problems
In this paper we investigate the colorful components framework, motivated by
applications emerging from comparative genomics. The general goal is to remove
a collection of edges from an undirected vertex-colored graph such that in
the resulting graph all the connected components are colorful (i.e., any
two vertices of the same color belong to different connected components). We
want to optimize an objective function, the selection of this function
being specific to each problem in the framework.
We analyze three objective functions, and thus, three different problems,
which are believed to be relevant for the biological applications: minimizing
the number of singleton vertices, maximizing the number of edges in the
transitive closure, and minimizing the number of connected components.
Our main result is a polynomial time algorithm for the first problem. This
result disproves the conjecture of Zheng et al. that the problem is -hard
(assuming ). Then, we show that the second problem is -hard,
thus proving and strengthening the conjecture of Zheng et al. that the problem
is -hard. Finally, we show that the third problem does not admit
polynomial time approximation within a factor of for
any , assuming (or within a factor of , assuming ).Comment: 18 pages, 3 figure
Quantum finite automata and linear context-free languages: a decidable problem
We consider the so-called measure once finite quantum automata model introduced by Moore and Crutchfield in 2000. We show that given a language recognized by such a device and a linear context-free language, it is recursively decidable whether or not they have a nonempty intersection. This extends a result of Blondel et al. which can be interpreted as solving the problem with the free monoid in place of the family of linear context-free languages. © 2013 Springer-Verlag
Dimension minimization of a quantum automaton
A new model of a Quantum Automaton (QA), working with qubits is proposed. The
quantum states of the automaton can be pure or mixed and are represented by
density operators. This is the appropriated approach to deal with measurements
and dechorence. The linearity of a QA and of the partial trace super-operator,
combined with the properties of invariant subspaces under unitary
transformations, are used to minimize the dimension of the automaton and,
consequently, the number of its working qubits. The results here developed are
valid wether the state set of the QA is finite or not. There are two main
results in this paper: 1) We show that the dimension reduction is possible
whenever the unitary transformations, associated to each letter of the input
alphabet, obey a set of conditions. 2) We develop an algorithm to find out the
equivalent minimal QA and prove that its complexity is polynomial in its
dimension and in the size of the input alphabet.Comment: 26 page
The non-self-adjointness of the radial momentum operator in n dimensions
The non self-adjointness of the radial momentum operator has been noted
before by several authors, but the various proofs are incorrect. We give a
rigorous proof that the -dimensional radial momentum operator is not self-
adjoint and has no self-adjoint extensions. The main idea of the proof is to
show that this operator is unitarily equivalent to the momentum operator on
which is not self-adjoint and has no self-adjoint
extensions.Comment: Some text and a reference adde
Luminous Compact Blue Galaxies up to z~1 in the HST Ultra Deep Field: I. Small galaxies, or blue centers of massive disks?
We analyze 26 Luminous Compact Blue Galaxies (LCBGs) in the HST/ACS Ultra
Deep Field (UDF) at z ~ 0.2-1.3, to determine whether these are truly small
galaxies, or rather bright central starbursts within existing or forming large
disk galaxies. Surface brightness profiles from UDF images reach fainter than
rest-frame 26.5 B mag/arcsec^2 even for compact objects at z~1. Most LCBGs show
a smaller, brighter component that is likely star-forming, and an extended,
roughly exponential component with colors suggesting stellar ages >~ 100 Myr to
few Gyr. Scale lengths of the extended components are mostly >~ 2 kpc, >1.5-2
times smaller than those of nearby large disk galaxies like the Milky Way.
Larger, very low surface brightness disks can be excluded down to faint
rest-frame surface brightnesses (>~ 26 B mag/arcsec^2). However, 1 or 2 of the
LCBGs are large, disk-like galaxies that meet LCBG selection criteria due to a
bright central nucleus, possibly a forming bulge. These results indicate that
>~ 90% of high-z LCBGs are small galaxies that will evolve into small disk
galaxies, and low mass spheroidal or irregular galaxies in the local Universe,
assuming passive evolution and no significant disk growth. The data do not
reveal signs of disk formation around small, HII-galaxy-like LCBGs, and do not
suggest a simple inside-out growth scenario for larger LCBGs with a disk-like
morphology. Irregular blue emission in distant LCBGs is relatively extended,
suggesting that nebular emission lines from star-forming regions sample a major
fraction of an LCBG's velocity field.Comment: 11 pages, 2 figures, AASTeX; accepted for publication in
Astrophysical Journal Letter
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