4,263 research outputs found
Study of the stress intensity factors in the bulk of the material with synchrotron diffraction
Artículo de Proceedings de Congreso Internacional Fatigue2017In this work we present the results of a hybrid experimental and
analytical approach for estimating the stress intensity factor. It uses the
elastic strains within the bulk obtained by synchrotron X-ray diffraction
data. The stress intensity factor is calculated using a multi-point overdeterministic
method where the number of experimental data points is
higher than the number of unknowns describing the elastic field
surrounding the crack-tip. The tool is tested on X-ray strain
measurements collected on a bainitic steel. In contrast to surface
techniques the approach provides insights into the crack tip mechanics
deep within the sample.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The authors are grateful to the ESRF for ID15 beamtime awarded under MA-1483. Financial
support of Universidad de Malaga through Plan Propio, Junta de Andalucía through Proyectos de
Excelencia grant reference TEP-3244, Campus de Excelencia Internacional del Mar (CEIMAR)
and Ministerio de Economia y Competitividad through grant reference MAT2016-76951-C2-2-P is
also acknowledged. PJW acknowledges an ERC advanced grant
On the Correlation between the Magnetic Activity Levels, the Metallicities and the Radii of Low-Mass Stars
The recent burst in the number of radii measurements of very low-mass stars
from eclipsing binaries and interferometry of single stars has opened more
questions about what can be causing the discrepancy between the observed radii
and the ones predicted by the models. The two main explanations being proposed
are a correlation between the radius of the stars and their activity levels or
their metallicities. This paper presents a study of such correlations using all
the data published to date. The study also investigates correlations between
the radii deviation from the models and the masses of the stars. There is no
clear correlation between activity level and radii for the single stars in the
sample. Those single stars are slow rotators with typical velocities v_rot sini
< 3.0 km s^-1. A clear correlation however exists in the case of the faster
rotating members of binaries. This result is based on the of X-ray emission
levels of the stars. There also appears to be an increase in the deviation of
the radii of single stars from the models as a function of metallicity, as
previously indicated by Berger et al. (2006). The stars in binaries do not seem
to follow the same trend. Finally, the Baraffe et al. (1998) models reproduce
well the radius observations below 0.30-0.35Msun, where the stars become fully
convective, although this result is preliminary since almost all the sample
stars in that mass range are slow rotators and metallicities have not been
measured for most of them. The results in this paper indicate that stellar
activity and metallicity play an important role on the determination of the
radius of very low-mass stars, at least above 0.35Msun.Comment: 22 pages, 4 figures. Accepted for publication on Ap
Dynamic Model and Control of a New Underwater Three-Degree-of-Freedom Tidal Energy Converter
There is currently a growing interest in developing devices that can be used to exploit energy from oceans. In the recent past, the search for oil and gas at ever-greater depths has led to the evolution of devices with which these resources are extracted. These devices range from those that simply rest on the seabed to those that are fully floating and anchored to it. This trend can be considered as the basis needed to understand the future evolution of devices for harnessing depth renewable resources. This paper presents a simple dynamic modeling and a nonlinear multivariable control model-based system for a new three-degree-of-freedom underwater generator with which energy from depth marine currents is harnessed when reference trajectory tracking for the emersion maneuvers needed to carry out maintenance tasks is performed. The goodness of both the model and the proposed controller has been demonstrated through the development of various simulations in the MATLAB-Simulink environment. Additionally, the validation of the control algorithms was carried out by using the dynamic model offered by the simulation environment Orcina OrcaFlex (software for the dynamic analysis for offshore marine systems) through the MATLAB-OrcaFlex interface
Low Mass Companions for Five Solar-Type Stars from the Magellan Planet Search Program
We report low mass companions orbiting five Solar-type stars that have
emerged from the Magellan precision Doppler velocity survey, with minimum
(Msini) masses ranging from 1.2 to 25 Mjup. These nearby target stars range
from mildly metal-poor to metal-rich, and appear to have low chromospheric
activity. The companions to the brightest two of these stars have previously
been reported from the CORALIE survey. Four of these companions (HD 48265-b, HD
143361-b, HD 28185-b, HD 111232-b) are low-mass Jupiter-like planets in
eccentric intermediate and long-period orbits. On the other hand, the companion
to HD 43848 appears to be a long period brown dwarf in a very eccentric orbit.Comment: Accepted for publication on ApJ, 26 pages, 10 figures, 7 table
A low-mass planet candidate orbiting Proxima Centauri at a distance of 1.5 AU
Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).Our nearest neighbor, Proxima Centauri, hosts a temperate terrestrial planet. We detected in radial velocities evidence of a possible second planet with minimum mass m c sin i c = 5.8 ± 1.9 M ⊕ and orbital period P c = 5.21 - 0.22 + 0.26 years. The analysis of photometric data and spectro-scopic activity diagnostics does not explain the signal in terms of a stellar activity cycle, but follow-up is required in the coming years for confirming its planetary origin. We show that the existence of the planet can be ascertained, and its true mass can be determined with high accuracy, by combining Gaia astrometry and radial velocities. Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution.Peer reviewedFinal Published versio
Fundamental Properties of Cool Stars with Interferometry
We present measurements of fundamental astrophysical properties of nearby,
low-mass, K- and M-dwarfs from our DISCOS survey (DIameterS of COol Stars). The
principal goal of our study is the determination of linear radii and effective
temperatures for these stars. We calculate their radii from angular diameter
measurements using the CHARA Array and Hipparcos distances. Combined with
bolometric flux measurements based on literature photometry, we use our angular
diameter results to calculate their effective surface temperatures. We present
preliminary results established on an assortment of empirical relations to the
stellar effective temperature and radius that are based upon these
measurements. We elaborate on the discrepancy seen between theoretical and
observed stellar radii, previously claimed to be related to stellar activity
and/or metallicity. Our preliminary conclusion, however, is that convection
plays a larger role in the determination of radii of these late-type stars.
Understanding the source of the radius disagreement is likely to impact other
areas of study for low-mass stars, such as the detection and characterization
of extrasolar planets in the habitable zones.Comment: Contribution to Proceedings of Cool Stars 16 Workshop; 8 pages in ASP
format; 9 figure
The EBLM project. II. A very hot, low-mass M dwarf in an eccentric and long period eclipsing binary system from SuperWASP
In this paper, we derive the fundamental properties of
1SWASPJ011351.29+314909.7 (J0113+31), a metal-poor (-0.40 +/- 0.04 dex),
eclipsing binary in an eccentric orbit (~0.3) with an orbital period of ~14.277
d. Eclipsing M dwarfs orbiting solar-type stars (EBLMs), like J0113+31, have
been identified from WASP light curves and follow-up spectroscopy in the course
of the transiting planet search. We present the first binary of the EBLM sample
to be fully analysed, and thus, define here the methodology. The primary
component with a mass of 0.945 +/- 0.045 Msun has a large radius (1.378 +/-
0.058 Rsun) indicating that the system is quite old, ~9.5 Gyr. The M-dwarf
secondary mass of 0.186 +/- 0.010 Msun and radius of 0.209 +/- 0.011 Rsun are
fully consistent with stellar evolutionary models. However, from the
near-infrared secondary eclipse light curve, the M dwarf is found to have an
effective temperature of 3922 +/- 42 K, which is ~600 K hotter than predicted
by theoretical models. We discuss different scenarios to explain this
temperature discrepancy. The case of J0113+31 for which we can measure mass,
radius, temperature and metallicity, highlights the importance of deriving
mass, radius and temperature as a function of metallicity for M dwarfs to
better understand the lowest mass stars. The EBLM Project will define the
relationship between mass, radius, temperature and metallicity for M dwarfs
providing important empirical constraints at the bottom of the main sequence.Comment: 13 pages, 7 figures. Accepted for publication in A&
GIADA performance during Rosetta mission scientific operations at comet 67P
The Grain Impact Analyser and Dust Accumulator (GIADA) instrument onboard Rosetta studied the dust environment of comet 67P/Churyumov–Gerasimenko from 3.7 au inbound, through perihelion, to 3.8 au outbound, measuring the dust flow and the dynamic properties of individual particles. GIADA is composed of three subsystems: 1) Grain Detection System (GDS); 2) Impact Sensor (IS); and 3) Micro-Balances System (MBS). Monitoring the subsystems’ performance during operations is an important element for the correct calibration of scientific measurements. In this paper, we analyse the GIADA inflight calibration data obtained by internal calibration devices for the three subsystems during the period from 1 August 2014 to 31 October 2015. The calibration data testify a nominal behaviour of the instrument during these fifteen months of mission; the only exception is a minor loss of sensitivity for one of the two GDS receivers, attributed to dust contamination
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