2,084 research outputs found
Stellar Scattering and the Formation of Hot-Jupiters in Binary Systems
Hot Jupiters (HJs) are usually defined as giant Jovian-size planets with
orbital periods days. Although they lie close to the star, several
have finite eccentricities and significant misalignment angle with respect to
the stellar equator.
Two mechanisms have been proposed to explain the excited and misaligned
sub-population of HJs: Lidov-Kozai migration and planet-planet scattering.
Although both are based on completely different dynamical phenomena, they
appear to be equally effective in generating hot planets. Nevertheless, there
has been no detailed analysis comparing the predictions of both mechanisms.
In this paper we present numerical simulations of Lidov-Kozai trapping of
single planets in compact binary systems. Both the planet and the binary are
initially placed in coplanar orbits, although the inclination of the impactor
is assumed random. After the passage of the third star, we follow the orbital
and spin evolution of the planet using analytical models based on the octupole
expansion of the secular Hamiltonian.
The present work aims at the comparison of the two mechanisms, as an
explanation for the excited and inclined HJs in binary systems. We compare the
results obtained through this paper with results in Beaug\'e & Nesvorn\'y 2012,
where the authors analyze how the planet-planet scattering mechanisms works.
Several of the orbital characteristics of the simulated HJs are caused by
tidal trapping from quasi-parabolic orbits, independent of the driving
mechanism. These include both the 3-day pile-up and the distribution in the
eccentricity vs semimajor axis plane. However, the distribution of the
inclinations shows significant differences. While Lidov-Kozai trapping favors a
more random distribution, planet-planet scattering shows a large portion of
bodies nearly aligned with the equator of the central star.Comment: 12 pages, 6 figures. Accepted for publication at IJAB (internation
journal of astrobiology
Chaotic Diffusion in the Gliese-876 Planetary System
Chaotic diffusion is supposed to be responsible for orbital instabilities in
planetary systems after the dissipation of the protoplanetary disk, and a
natural consequence of irregular motion. In this paper we show that resonant
multi-planetary systems, despite being highly chaotic, not necessarily exhibit
significant diffusion in phase space, and may still survive virtually unchanged
over timescales comparable to their age.Using the GJ-876 system as an example,
we analyze the chaotic diffusion of the outermost (and less massive) planet. We
construct a set of stability maps in the surrounding regions of the Laplace
resonance. We numerically integrate ensembles of close initial conditions,
compute Poincar\'e maps and estimate the chaotic diffusion present in this
system. Our results show that, the Laplace resonance contains two different
regions: an inner domain characterized by low chaoticity and slow diffusion,
and an outer one displaying larger values of dynamical indicators. In the outer
resonant domain, the stochastic borders of the Laplace resonance seem to
prevent the complete destruction of the system. We characterize the diffusion
for small ensembles along the parameters of the outermost planet. Finally, we
perform a stability analysis of the inherent chaotic, albeit stable Laplace
resonance, by linking the behavior of the resonant variables of the
configurations to the different sub-structures inside the three-body resonance.Comment: 13 pages, 7 figures, 2 tables. Accepted for publication in MNRA
La vegetación de zonas erosionadas en la depresión media del Ebro y en el Prepirineo: influencia de factores climáticos, topográficos y geomorfológicos en la composición florÃstica de las comunidades vegetales
[Resumen] Se han analizado 732 inventarios de vegetación en zonas sometidas a procesos erosivo-sedimentarios de un área del NE de la PenÃnsula Ibérica, muy diversa climática y litológicamente (yesos, arcillas, margas y flysch). El objetivo del estudio es determinar cómo afectan dichos procesos a la composición florÃstica de las comunidades vegetales de los diferentes sustratos. El tipo de sustrato ejerció una gran influencia sobre los procesos estudiados, siendo la cobertura de las fanerógamas el parámetro que mejor se asoció con el grado de erosión. En las zonas más secas con bajas tasas de erosión (yesos), las caracterÃsticas topográficas controlaron la distribución de las comunidades vegetales, mientras que en las zonas más húmedas, sometidas a procesos erosivos más dinámicos (margas), la composición florÃstica fué más homogénea y menos dependiente de la topografÃa y del grado de erosión. Los procesos erosivosedimentarios explicaron mejor la composición florÃstica cuanto menor era la escala espacial de análisis.[Abstract] We have analysed 732 releves of plant communities taken from eroded lands in the NE Iberian Peninsula. This diverse area has very different climates and substrata: gypsum, clays, marls and flysch. The aim of the study was to explore how erosion and sedimentation processes affect floristic composition of plant communities in such different substrata. Substratum had a high influence on the studied processes, the cover of fanerogams being the best correlated parameter with erosion grade. In the driest lands, with low erosion rates (gypsum), plant community distribution was mostly affected by topography, but in the wettest areas, with strong and more dynamic erosional processes (marls), the floristic composition was more homogeneus and depended less on the topography and the erosion grade. The erosionsedimentation processes better explained the floristic composition when the scale of analysis was reduced
Optical spectroscopy and X-ray observations of the D-type symbiotic star EF Aql
We performed high-resolution optical spectroscopy and X-ray observations of
the recently identified Mira-type symbiotic star EF Aql. Based on
high-resolution optical spectroscopy obtained with SALT, we determine the
temperature (55 000 K) and the luminosity ( 5.3 ) of the
hot component in the system. The heliocentric radial velocities of the emission
lines in the spectra reveal possible stratification of the chemical elements.
We also estimate the mass-loss rate of the Mira donor star. Our Swift
observation did not detect EF Aql in X-rays. The upper limit of the X-ray
observations is 10 erg cm s, which means that EF Aql is
consistent with the faintest X-ray systems detected so far. Otherwise we
detected it with the UVOT instrument with an average UVM2 magnitude of 14.05.
During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter.
The periodogram analysis of the V-band data reveals an improved period of
320.40.3 d caused by the pulsations of the Mira-type donor star. The
spectra are available upon request from the authors.Comment: Accepted for publication in MNRA
Experimental demonstration of a graph state quantum error-correction code
Scalable quantum computing and communication requires the protection of
quantum information from the detrimental effects of decoherence and noise.
Previous work tackling this problem has relied on the original circuit model
for quantum computing. However, recently a family of entangled resources known
as graph states has emerged as a versatile alternative for protecting quantum
information. Depending on the graph's structure, errors can be detected and
corrected in an efficient way using measurement-based techniques. In this
article we report an experimental demonstration of error correction using a
graph state code. We have used an all-optical setup to encode quantum
information into photons representing a four-qubit graph state. We are able to
reliably detect errors and correct against qubit loss. The graph we have
realized is setup independent, thus it could be employed in other physical
settings. Our results show that graph state codes are a promising approach for
achieving scalable quantum information processing
Growth of graph states in quantum networks
We propose a scheme to distribute graph states over quantum networks in the
presence of noise in the channels and in the operations. The protocol can be
implemented efficiently for large graph sates of arbitrary (complex) topology.
We benchmark our scheme with two protocols where each connected component is
prepared in a node belonging to the component and subsequently distributed via
quantum repeaters to the remaining connected nodes. We show that the fidelity
of the generated graphs can be written as the partition function of a classical
Ising-type Hamiltonian. We give exact expressions of the fidelity of the linear
cluster and results for its decay rate in random graphs with arbitrary
(uncorrelated) degree distributions.Comment: 16 pages, 7 figure
Relativistic Jets from Collapsars
We have studied the relativistic beamed outflow proposed to occur in the
collapsar model of gamma-ray bursts. A jet forms as a consequence of an assumed
energy deposition of erg/s within a cone
around the rotation axis of the progenitor star. The generated jet flow is
strongly beamed (\la few degrees) and reaches the surface of the stellar
progenitor (r cm) intact. At break-out the maximum Lorentz
factor of the jet flow is about 33. Simulations have been performed with the
GENESIS multi-dimensional relativistic hydrodynamic code.Comment: 6 pages, 2 figures, to appear in the proceedings of the conference
"Godunov methods: theory and applications", Oxford, October 199
New Relativistic Effects in the Dynamics of Nonlinear Hydrodynamical Waves
In Newtonian and relativistic hydrodynamics the Riemann problem consists of
calculating the evolution of a fluid which is initially characterized by two
states having different values of uniform rest-mass density, pressure and
velocity. When the fluid is allowed to relax, one of three possible
wave-patterns is produced, corresponding to the propagation in opposite
directions of two nonlinear hydrodynamical waves. New effects emerge in a
special relativistic Riemann problem when velocities tangential to the initial
discontinuity surface are present. We show that a smooth transition from one
wave-pattern to another can be produced by varying the initial tangential
velocities while otherwise maintaining the initial states unmodified. These
special relativistic effects are produced by the coupling through the
relativistic Lorentz factors and do not have a Newtonian counterpart.Comment: 4 pages, 5 figure
Matroids and Quantum Secret Sharing Schemes
A secret sharing scheme is a cryptographic protocol to distribute a secret
state in an encoded form among a group of players such that only authorized
subsets of the players can reconstruct the secret. Classically, efficient
secret sharing schemes have been shown to be induced by matroids. Furthermore,
access structures of such schemes can be characterized by an excluded minor
relation. No such relations are known for quantum secret sharing schemes. In
this paper we take the first steps toward a matroidal characterization of
quantum secret sharing schemes. In addition to providing a new perspective on
quantum secret sharing schemes, this characterization has important benefits.
While previous work has shown how to construct quantum secret sharing schemes
for general access structures, these schemes are not claimed to be efficient.
In this context the present results prove to be useful; they enable us to
construct efficient quantum secret sharing schemes for many general access
structures. More precisely, we show that an identically self-dual matroid that
is representable over a finite field induces a pure state quantum secret
sharing scheme with information rate one
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