23,903 research outputs found
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
Lattice dynamics and electron-phonon coupling in Sr2RuO4
The lattice dynamics in SrRuO has been studied by inelastic neutron
scattering combined with shell-model calculations. The in-plane bond-stretching
modes in SrRuO exhibit a normal dispersion in contrast to all
electronically doped perovskites studied so far. Evidence for strong electron
phonon coupling is found for c-polarized phonons suggesting a close connection
with the anomalous c-axis charge transport in SrRuO.Comment: 11 pages, 8 figures 2 table
Quantum Reciprocity Conjecture for the Non-Equilibrium Steady State
By considering the lack of history dependence in the non-equilibrium steady
state of a quantum system we are led to conjecture that in such a system, there
is a set of quantum mechanical observables whose retarded response functions
are insensitive to the arrow of time, and which consequently satisfy a quantum
analog of the Onsager reciprocity relations. Systems which satisfy this
conjecture can be described by an effective Free energy functional. We
demonstrate that the conjecture holds in a resonant level model of a multi-lead
quantum dot.Comment: References revised to take account of related work on Onsager
reciprocity in mesoscopics by Christen, and in hydrodynamics by Mclennan,
Dufty and Rub
Vacuum discharge as a possible source of gamma-ray bursts
We propose that spontaneous particle--anti-particle pair creations from the
discharged vacuum caused by the strong interactions in dense matter are major
sources of -ray bursts. Two neutron star collisions or black
hole-neutron star mergers at cosmological distance could produce a compact
object with its density exceeding the critical density for pair creations. The
emitted anti-particles annihilate with corresponding particles at the ambient
medium. This releases a large amount of energy. We discuss the spontaneous
pair creations within two neutron star collision and estimate the
exploded energy from annihilation processes. The total energy could
be around erg depending on the impact parameter of
colliding neutron stars. This value fits well into the range of the initial
energy of the most energetic -ray bursts.Comment: 12 pages, Latex, 2 figures included; replaced by the revised version,
Int. J. Mod. Phys. E in pres
A morphometric analysis of vegetation patterns in dryland ecosystems
Vegetation in dryland ecosystems often forms remarkable spatial patterns. These range from regular bands of vegetation alternating with bare ground, to vegetated spots and labyrinths, to regular gaps of bare ground within an otherwise continuous expanse of vegetation. It has been suggested that spotted vegetation patterns could indicate that collapse into a bare ground state is imminent, and the morphology of spatial vegetation patterns, therefore, represents a potentially valuable source of information on the proximity of regime shifts in dryland ecosystems. In this paper, we have developed quantitative methods to characterize the morphology of spatial patterns in dryland vegetation. Our approach is based on algorithmic techniques that have been used to classify pollen grains on the basis of textural patterning, and involves constructing feature vectors to quantify the shapes formed by vegetation patterns. We have analysed images of patterned vegetation produced by a computational model and a small set of satellite images from South Kordofan (South Sudan), which illustrates that our methods are applicable to both simulated and real-world data. Our approach provides a means of quantifying patterns that are frequently described using qualitative terminology, and could be used to classify vegetation patterns in large-scale satellite surveys of dryland ecosystems
Metallic state in La-doped YBaCuO thin films with -type charge carriers
We report hole and electron doping in La-doped YBaCuO(YBCO) thin
films synthesized by pulsed laser deposition technique and subsequent
\emph{in-situ} postannealing in oxygen ambient and vaccum. The -type samples
show a metallic behavior below the Mott limit and a high carrier density of
10 cm at room temperature (\emph{T}) at the
optimally reduced condition. The in-plane resistivity () of the
-type samples exhibits a quadratic \emph{T} dependence in the
moderate-\emph{T} range and shows an anomaly at a relatively higher \emph{T}
probably related to pseudogap formation analogous to underdoped
NdCeCuO (NCCO). Furthermore, (T), \emph{T} and
\emph{T} with minimum resistivity (\emph{T}) were investigated in both
- and -side. The present results reveal the - asymmetry (symmetry)
within the metallic-state region in an underdoped cuprate and suggest the
potential toward ambipolar superconductivity in a single YBCO system.Comment: 4 pages, 5 figure
The Luminosity Function of high-redshift QSOs - A combined analysis of GOODS and SDSS
Aims: In this work the luminosity function of QSOs is measured in the
redshift range 3.5<z<5.2 for the absolute magnitude interval -21<M_{145}<-28.
The determination of the faint end of the luminosity function at these
redshifts provides important constraints on models of joint evolution of
galaxies and AGNs. Methods: We have defined suitable criteria to select faint
QSOs in the GOODS fields, checking in detail their effectiveness and
completeness. Spectroscopic follow-up of the resulting QSO candidates has been
carried out. The confirmed sample of faint QSOs is compared with a brighter one
derived from the SDSS. We have used a Monte-Carlo technique to estimate the
properties of the luminosity function, checking various parameterizations for
its shape and evolution. Results: Models based on Pure Density Evolution show
better agreement with observation than models based on Pure Luminosity
Evolution. However a different break magnitude with respect to z~2.1 is
required at 3.5<z<5.2. Models with a steeper faint end score a higher
probability. We do not find any evidence for a flattening of the bright end at
redshift z>3.5. Conclusions: The estimated space density evolution of QSOs
indicates a suppression of the formation and/or feeding of Supermassive Black
Holes at these redshifts. The QSO contribution to the UV background is
insufficient to ionize the IGM at 3.5<z<5.2.Comment: 17 pages, 13 ps figures, A&A accepted. Updated to journal versio
Spin-spin correlators in Majorana representation
In the Majorana representation of a spin 1/2 we find an identity which
relates spin-spin correlators to one-particle fermionic correlators. This
should be contrasted with the straightforward approach in which two-particle
(four-fermion) correlators need to be calculated. We discuss applications to
the analysis of the dynamics of a spin coupled to a dissipative environment and
of a quantum detector performing a continuous measurement of a qubit's state
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