4,253 research outputs found
Assessing architectural evolution: A case study
This is the post-print version of the Article. The official published can be accessed from the link below - Copyright @ 2011 SpringerThis paper proposes to use a historical perspective on generic laws, principles,
and guidelines, like Lehman’s software evolution laws and Martin’s design principles, in order to achieve a multi-faceted process and structural assessment of a system’s architectural evolution. We present a simple structural model with associated historical metrics and
visualizations that could form part of an architect’s dashboard. We perform such an assessment for the Eclipse SDK, as a case study of a large, complex, and long-lived system for which sustained effective architectural evolution is paramount. The twofold aim of checking generic principles on a well-know system is, on the one hand,
to see whether there are certain lessons that could be learned for best practice of architectural evolution, and on the other hand to get more insights about the applicability of such principles. We find that while the Eclipse SDK does follow several of the laws and principles, there are some deviations, and we discuss areas of architectural improvement and limitations of the assessment approach
Helium Atmospheres on Warm Neptune- and Sub-Neptune-Sized Exoplanets and Applications to GJ 436 b
Warm Neptune- and sub-Neptune-sized exoplanets in orbits smaller than
Mercury's are thought to have experienced extensive atmospheric evolution. Here
we propose that a potential outcome of this atmospheric evolution is the
formation of helium-dominated atmospheres. The hydrodynamic escape rates of
Neptune- and sub-Neptune-sized exoplanets are comparable to the
diffusion-limited escape rate of hydrogen, and therefore the escape is heavily
affected by diffusive separation between hydrogen and helium. A helium
atmosphere can thus be formed -- from a primordial hydrogen-helium atmosphere
-- via atmospheric hydrodynamic escape from the planet. The helium atmosphere
has very different abundances of major carbon and oxygen species from those of
a hydrogen atmosphere, leading to distinctive transmission and thermal emission
spectral features. In particular, the hypothesis of a helium-dominated
atmosphere can explain the thermal emission spectrum of GJ 436 b, a warm
Neptune-sized exoplanet, while also consistent with the transmission spectrum.
This model atmosphere contains trace amounts of hydrogen, carbon, and oxygen,
with the predominance of CO over CH4 as the main form of carbon. With our
atmospheric evolution model, we find that if the mass of the initial atmosphere
envelope is 1E-3 planetary mass, hydrodynamic escape can reduce the hydrogen
abundance in the atmosphere by several orders of magnitude in ~10 billion
years. Observations of exoplanet transits may thus detect signatures of helium
atmospheres and probe the evolutionary history of small exoplanets.Comment: ApJ, accepte
A modern study of HD166734: a massive supergiant system
Aims. HD166734 is an eccentric eclipsing binary system composed of two
supergiant O-type stars, orbiting with a 34.5-day period. In this rare
configuration for such stars, the two objects mainly evolve independently,
following single-star evolution so far. This system provides a chance to study
the individual parameters of two supergiant massive stars and to derive their
real masses. Methods. An intensive monitoring was dedicated to HD166734.We
analyzed mid- and high-resolution optical spectra to constrain the orbital
parameters of this system. We also studied its light curve for the first time,
obtained in the VRI filters. Finally, we disentangled the spectra of the two
stars and modeled them with the CMFGEN atmosphere code in order to determine
the individual physical parameters. Results. HD166734 is a O7.5If+O9I(f)
binary. We confirm its orbital period but we revise the other orbital
parameters. In comparison to what we found in the literature, the system is
more eccentric and, now, the hottest and the most luminous component is also
the most massive one. The light curve exhibits only one eclipse and its
analysis indicates an inclination of 63.0{\deg} 2.7{\deg}. The
photometric analysis provides us with a good estimation of the luminosities of
the stars, and therefore their exact positions in the Hertzsprung-Russell
diagram. The evolutionary and the spectroscopic masses show good agreement with
the dynamical masses of 39.5 Msun for the primary and 33.5 Msun for the
secondary, within the uncertainties. The two components are both enriched in
helium and in nitrogen and depleted in carbon. In addition, the primary also
shows a depletion in oxygen. Their surface abundances are however not different
from those derived from single supergiant stars, yielding, for both components,
an evolution similar to that of single stars.Comment: 13 pages, 13 figures, A&A accepte
Searching for sub-stellar companion into the LkCa15 proto-planetary disk
Recent sub-millimetric observations at the Plateau de Bure interferometer
evidenced a cavity at ~ 46 AU in radius into the proto-planetary disk around
the T Tauri star LkCa15 (V1079 Tau), located in the Taurus molecular cloud.
Additional Spitzer observations have corroborated this result possibly
explained by the presence of a massive (>= 5 MJup) planetary mass, a brown
dwarf or a low mass star companion at about 30 AU from the star. We used the
most recent developments of high angular resolution and high contrast imaging
to search directly for the existence of this putative companion, and to bring
new constraints on its physical and orbital properties. The NACO adaptive
optics instrument at VLT was used to observe LkCa15 using a four quadrant phase
mask coronagraph to access small angular separations at relatively high
contrast. A reference star at the same parallactic angle was carefully observed
to optimize the quasi-static speckles subtraction (limiting our sensitivity at
less than 1.0). Although we do not report any positive detection of a faint
companion that would be responsible for the observed gap in LkCa15's disk
(25-30 AU), our detection limits start constraining its probable mass,
semi-major axis and eccentricity. Using evolutionary model predictions, Monte
Carlo simulations exclude the presence of low eccentric companions with masses
M >= 6 M Jup and orbiting at a >= 100 AU with significant level of confidence.
For closer orbits, brown dwarf companions can be rejected with a detection
probability of 90% down to 80 AU (at 80% down to 60 AU). Our detection limits
do not access the star environment close enough to fully exclude the presence
of a brown dwarf or a massive planet within the disk inner activity (i.e at
less than 30 AU). Only, further and higher contrast observations should unveil
the existence of this putative companion inside the LkCa15 disk.Comment: 6 pages, 4 figures, accepted for publication in A&
Luminosity Discrepancy in the Equal-Mass, Pre--Main Sequence Eclipsing Binary Par 1802: Non-Coevality or Tidal Heating?
Parenago 1802, a member of the ~1 Myr Orion Nebula Cluster, is a
double-lined, detached eclipsing binary in a 4.674 d orbit, with equal-mass
components (M_2/M_1 = 0.985 \pm 0.029). Here we present extensive VIcJHKs light
curves spanning ~15 yr, as well as a Keck/HIRES optical spectrum. The light
curves evince a third light source that is variable with a period of 0.73 d,
and is also manifested in the high-resolution spectrum, strongly indicating the
presence of a third star in the system, probably a rapidly rotating classical T
Tauri star. We incorporate this third light into our radial velocity and light
curve modeling of the eclipsing pair, measuring accurate masses (M_1 = 0.391
\pm 0.032, M_2 = 0.385 \pm 0.032 M\odot), radii (R_1 = 1.73 \pm 0.02, R_2 =
1.62 \pm 0.02 R\odot), and temperature ratio (T_1/T_2 = 1.0924 \pm 0.0017).
Thus the radii of the eclipsing stars differ by 6.9 \pm 0.8%, the temperatures
differ by 9.2 \pm 0.2%, and consequently the luminosities differ by 62 \pm 3%,
despite having masses equal to within 3%. This could be indicative of an age
difference of ~3x10^5 yr between the two eclipsing stars, perhaps a vestige of
the binary formation history. We find that the eclipsing pair is in an orbit
that has not yet fully circularized, e = 0.0166 \pm 0.003. In addition, we
measure the rotation rate of the eclipsing stars to be 4.629 \pm 0.006 d; they
rotate slightly faster than their 4.674 d orbit. The non-zero eccentricity and
super-synchronous rotation suggest that the eclipsing pair should be tidally
interacting, so we calculate the tidal history of the system according to
different tidal evolution theories. We find that tidal heating effects can
explain the observed luminosity difference of the eclipsing pair, providing an
alternative to the previously suggested age difference.Comment: 49 pages, 16 figures, 11 tables. Accepted for publication to Ap
How Evolutionary Visual Software Analytics Supports Knowledge Discovery
[EN] Evolutionary visual software analytics is a specialization of visual analytics. It is aimed at supporting software maintenance processes by aiding the understanding and
comprehension of software evolution with the active participation of users. Therefore, it
deals with the analysis of software projects that have been under development and maintenance for several years and which are usually formed by thousands of software artifacts,which are also associated to logs from communications, defect-tracking and software configuration management systems. Accordingly, evolutionary visual software analytics aims to assist software developers and software project managers by means of an
integral approach that takes into account knowledge extraction techniques as well as
visual representations that make use of interaction techniques and linked views. Consequently,this paper discusses the implementation of an architecture based on the evolutionary visual software analytics process and how it supports knowledge discovery during software maintenance tasks.[ES] Analítica de software visual evolutivos es una especialización de la analítica visual. Está dirigido a apoyar los procesos de mantenimiento de software, ayudando al entendimiento y la comprensión de la evolución del software, con la participación activa de los usuarios. Por lo tanto, tiene que ver con el análisis de los proyectos de software que han estado bajo desarrollo y mantenimiento por varios años y que por lo general están formados por miles de artefactos de software, que también están asociadas a los registros de las comunicaciones, seguimiento de defectos y sistemas de gestión de configuración de software. En consecuencia, la analítica de software visual evolutivos tiene como objetivo ayudar a los desarrolladores de software y administradores de proyectos de software a través de un enfoque integral que tenga en cuenta las técnicas de extracción de conocimiento, así como representaciones visuales que hacen uso de técnicas de interacción y vistas enlazadas. En consecuencia, en este documento se analiza la implementación de una arquitectura basada en el proceso de analítica de software visual evolutivos y la forma en que apoya el descubrimiento de conocimiento durante las tareas de mantenimiento de softwar
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