14,542 research outputs found
Exponential Distributions in a Mechanical Model for Earthquakes
We study statistical distributions in a mechanical model for an earthquake
fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl
Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size
(moment), time duration and number of blocks involved in an event show that
exponential distributions are found in a given range of the paramenter space.
This occurs when the two kinds of springs present in the model have the same,
or approximately the same, value for the elastic constants. Exponential
distributions have also been seen recently in an experimental system to model
earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf
50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E
Love kills: Simulations in Penna Ageing Model
The standard Penna ageing model with sexual reproduction is enlarged by
adding additional bit-strings for love: Marriage happens only if the male love
strings are sufficiently different from the female ones. We simulate at what
level of required difference the population dies out.Comment: 14 pages, including numerous figure
From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio
The main goal of this work is to study element ratios that are important for
the formation of planets of different masses. We study potential correlations
between the existence of planetary companions and the relative elemental
abundances of their host stars. We use a large sample of FGK-type dwarf stars
for which precise Mg, Si, and Fe abundances have been derived using HARPS
high-resolution and high-quality data. A first analysis of the data suggests
that low-mass planet host stars show higher [Mg/Si] ratios, while giant planet
hosts present [Mg/Si] that is lower than field stars. However, we found that
the [Mg/Si] ratio significantly depends on metallicity through Galactic
chemical evolution. After removing the Galactic evolution trend only the
difference in the [Mg/Si] elemental ratio between low-mass planet hosts and
non-hosts was present in a significant way. These results suggests that
low-mass planets are more prevalent around stars with high [Mg/Si]. Our results
demonstrate the importance of Galactic chemical evolution and indicate that it
may play an important role in the planetary internal structure and composition.Comment: Accepted by A&A (Letter to the Editor
Reptilia, Squamata, Polychrotidae, <i>Anolis fuscoauratus</i> D'Orbigny, 1837: Distribution extension for the state of Rio Grande do Norte, Brazil
We provide the first record of Anolis fuscoauratus D’Orbigny, 1837 for the state of Rio Grande do Norte anda distribution map for the species in the Atlantic Rainforest of northeastern Brazil. The record of A. fuscoauratus in themunicipality of Tibau do Sul, state of Rio Grande do Norte, represents a distribution extension of 170 km northwesternfrom the municipality of Cabedelo, state of Paraíba. This is the northernmost record of this species in the Atlantic Rainforest
The first radial velocity measurements of a microlensing event: no evidence for the predicted binary
The gravitational microlensing technique allows the discovery of exoplanets
around stars distributed in the disk of the galaxy towards the bulge. However,
the alignment of two stars that led to the discovery is unique over the
timescale of a human life and cannot be re-observed. Moreover, the target host
is often very faint and located in a crowded region. These difficulties hamper
and often make impossible the follow-up of the target and study of its possible
companions. Gould et al. (2013) predicted the radial-velocity curve of a binary
system, OGLE-2011-BLG-0417, discovered and characterised from a microlensing
event by Shin et al. (2012). We used the UVES spectrograph mounted at the VLT,
ESO to derive precise radial-velocity measurements of OGLE-2011-BLG-0417. To
gather high-precision on faint targets of microlensing events, we proposed to
use the source star as a reference to measure the lens radial velocities. We
obtained ten radial velocities on the putative V=18 lens with a dispersion of
~100 m/s, spread over one year. Our measurements do not confirm the
microlensing prediction for this binary system. The most likely scenario is
that the assumed V=18 mag lens is actually a blend and not the primary lens
that is 2 magnitude fainter. Further observations and analyses are needed to
understand the microlensing observation and infer on the nature and
characteristics of the lens itself.Comment: submitted on 3rd June 2015 to A&ALette
Universal Programmable Quantum Circuit Schemes to Emulate an Operator
Unlike fixed designs, programmable circuit designs support an infinite number
of operators. The functionality of a programmable circuit can be altered by
simply changing the angle values of the rotation gates in the circuit. Here, we
present a new quantum circuit design technique resulting in two general
programmable circuit schemes. The circuit schemes can be used to simulate any
given operator by setting the angle values in the circuit. This provides a
fixed circuit design whose angles are determined from the elements of the given
matrix-which can be non-unitary-in an efficient way. We also give both the
classical and quantum complexity analysis for these circuits and show that the
circuits require a few classical computations. They have almost the same
quantum complexities as non-general circuits. Since the presented circuit
designs are independent from the matrix decomposition techniques and the global
optimization processes used to find quantum circuits for a given operator, high
accuracy simulations can be done for the unitary propagators of molecular
Hamiltonians on quantum computers. As an example, we show how to build the
circuit design for the hydrogen molecule.Comment: combined with former arXiv:1207.174
Abundance trend with condensation temperature for stars with different Galactic birth places
During the past decade, several studies reported a correlation between
chemical abundances of stars and condensation temperature (also known as Tc
trend). However, the real astrophysical nature of this correlation is still
debated. The main goal of this work is to explore the possible dependence of
the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality
spectra of about 40 stars observed with the HARPS and UVES spectrographs to
derive precise stellar parameters, chemical abundances, and stellar ages. A
differential line-by-line analysis was applied to achieve the highest possible
precision in the chemical abundances. We confirm previous results that [X/Fe]
abundance ratios depend on stellar age and that for a given age, some elements
also show a dependence on Rmean. When using the whole sample of stars, we
observe a weak hint that the Tc trend depends on Rmean. The observed dependence
is very complex and disappears when only stars with similar ages are
considered. To conclude on the possible dependence of the Tc trend on the
formation place of stars, a larger sample of stars with very similar
atmospheric parameters and stellar ages observed at different Galactocentric
distances is neededComment: Accepted by A&
Enhanced SnS phase purity of films produced by rapid thermal processing of SnS2 precursors
In this work, we present a procedure to grow single phase SnS thin films consisting on the annealing of RF magnetron sputtered SnS2 precursors . A series of samples was produced by rapid thermal processing of precursors deposited both on bare and Mo coated glass. For those samples the time at maximum temperature and heating rate were variedN/
The AMBRE Project: searching for the closest solar siblings
Finding solar siblings, that is, stars that formed in the same cluster as the
Sun, will yield information about the conditions at the Sun's birthplace. We
search for solar sibling candidates in AMBRE, the very large spectra database
of solar vicinity stars. Since the ages and chemical abundances of solar
siblings are very similar to those of the Sun, we carried out a chemistry- and
age-based search for solar sibling candidates. We used high-resolution spectra
to derive precise stellar parameters and chemical abundances of the stars. We
used these spectroscopic parameters together with Gaia DR2 astrometric data to
derive stellar isochronal ages. Gaia data were also used to study the
kinematics of the sibling candidates. From the about 17000 stars that are
characterized within the AMBRE project, we first selected 55 stars whose
metallicities are closest to the solar value (-0.1 < [Fe/H] < 0.1 dex). For
these stars we derived precise chemical abundances of several iron-peak, alpha-
and neutron-capture elements, based on which we selected 12 solar sibling
candidates with average abundances and metallicities between -0.03 to 0.03 dex.
Our further selection left us with 4 candidates with stellar ages that are
compatible with the solar age within observational uncertainties. For the 2 of
the hottest candidates, we derived the carbon isotopic ratios, which are
compatible with the solar value. HD186302 is the most precisely characterized
and probably the most probable candidate of our 4 best candidates. Very precise
chemical characterization and age estimation is necessary to identify solar
siblings. We propose that in addition to typical chemical tagging, the study of
isotopic ratios can give further important information about the relation of
sibling candidates with the Sun. Ideally, asteroseismic age determinations of
the candidates could solve the problem of imprecise isochronal ages.Comment: Accepted for publication in A&
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