2,003 research outputs found
Comparisons for Esta-Task3: Cles and Cesam
We present the results of comparing three different implementations of the
microscopic diffusion process in the stellar evolution codes CESAM and CLES.
For each of these implementations we computed models of 1.0, 1.2 and 1.3
M. We analyse the differences in their internal structure at three
selected evolutionary stages, as well as the variations of helium abundance and
depth of the stellar convective envelope. The origin of these differences and
their effects on the seismic properties of the models are also considered.Comment: 10 pages, 8 figures, Joint HELAS and CoRoT/ESTA Workshop on
Solar/Stellar Models and Seismic Analysis Tools, Novembre, Porto 2007 To be
published in EAS Publications Serie
Effect of local treatments of convection upon the solar p-mode excitation rates
We compute, for several solar models, the rates P at which the solar radial p
modes are expected to be excited. The solar models are computed with two
different local treatments of convection : the classical mixing-length theory
(MLT hereafter) and Canuto, Goldmann and Mazzitelli(1996, CGM hereafter)'s
formulation. For one set of solar models (EMLT and ECGM models), the atmosphere
is gray and assumes Eddington's approximation. For a second set of models (KMLT
and KCGM models), the atmosphere is built using a T(tau) law which has been
obtained from a Kurucz's model atmosphere computed with the same local
treatment of convection. The mixing-length parameter in the model atmosphere is
chosen so as to provide a good agreement between synthetic and observed Balmer
line profiles, while the mixing-length parameter in the interior model is
calibrated so that the model reproduces the solar radius at solar age. For the
MLT treatment, the rates P do depend significantly on the properties of the
atmosphere. On the other hand, for the CGM treatment, differences in P between
the ECGM and the KCGM models are very small compared to the error bars attached
to the seismic measurements. The excitation rates P for modes from the EMLT
model are significantly under-estimated compared with the solar seismic
constraints. The KMLT model results in intermediate values for P and shows also
an important discontinuity in the temperature gradient and the convective
velocity. On the other hand, the KCGM model and the ECGM model yield values for
P closer to the seismic data than the EMLT and KMLT models. We conclude that
the solar p-mode excitation rates provide valuable constraints and according to
the present investigation cleary favor the CGM treatment with respect to the
MLT.Comment: 4 pages, 3 figures, proceedings of the SOHO14/GONG 2004 workshop
"Helio- and Asteroseismology: Towards a Golden Future" from July 12-16 2004
at New Haven CT (USA
Seismic diagnostics for transport of angular momentum in stars 2. Interpreting observed rotational splittings of slowly-rotating red giant stars
Asteroseismology with the space-borne missions CoRoT and Kepler provides a
powerful mean of testing the modeling of transport processes in stars.
Rotational splittings are currently measured for a large number of red giant
stars and can provide stringent constraints on the rotation profiles. The aim
of this paper is to obtain a theoretical framework for understanding the
properties of the observed rotational splittings of red giant stars with slowly
rotating cores. This allows us to establish appropriate seismic diagnostics for
rotation of these evolved stars. Rotational splittings for stochastically
excited dipolar modes are computed adopting a first-order perturbative approach
for two benchmark models assuming slowly rotating cores. For red
giant stars with slowly rotating cores, we show that the variation of the
rotational splittings of modes with frequency depends only on the
large frequency separation, the g-mode period spacing, and the ratio of the
average envelope to core rotation rates (). This leds us to propose a
way to infer directly from the observations. This method is
validated using the Kepler red giant star KIC 5356201. Finally, we provide a
theoretical support for the use of a Lorentzian profile to measure the observed
splittings for red giant stars.Comment: 15 pages, 15 figures, accepted for publication in A&
Influence of local treatments of convection upon solar p mode excitation rates
We compute the rates P at which acoustic energy is injected into the solar
radial p modes for several solar models. The solar models are computed with two
different local treatments of convection: the classical mixing-length theory
(MLT hereafter) and Canuto et al (1996)'s formulation (CGM hereafter). Among
the models investigated here, our best models reproduce both the solar radius
and the solar luminosity at solar age and the observed Balmer line profiles.
For the MLT treatment, the rates P do depend significantly on the properties of
the atmosphere whereas for the CGM's treatment the dependence of P on the
properties of the atmosphere is found smaller than the error bars attached to
the seismic measurements. The excitation rates P for modes associated with the
MLT models are significantly underestimated compared with the solar seismic
constraints. The CGM models yield values for P closer to the seismic data than
the MLT models. We conclude that the solar p-mode excitation rates provide
valuable constraints and according to the present investigation clearly favor
the CGM treatment with respect to the MLT, although neither of them yields
values of P as close to the observations as recently found for 3D numerical
simulations.Comment: 11 pages, 7 figures, accepted for publication in Astronomy &
Astrophysic
Estudio comparativo entre la hipĂłtesis de la mortalidad aditiva y la hipĂłtesis de la mortalidad compensatoria mediante el empleo de un modelo de efectos aleatorios basado en datos de recuperaciĂłn de anillas
The interaction of an additional source of mortality with the underlying "natural" one strongly affects population dynamics. We propose an alternative way to test between two forms of interaction, total additivity and compensation. In contrast to existing approaches, only ring–recovery data where the cause of death of each recovered individual is known are needed. Cause–specific mortality proportions are estimated based on a multistate capture–recapture model. The hypotheses are tested by inspecting the correlation between the cause–specific mortality proportions. A variance decomposition is performed to obtain a proper estimate of the true process correlation. The estimation of the cause–specific mortality proportions is the most critical part of the approach. It works well if at least one of the two mortality rates varies across time and the two recovery rates are constant across time. We illustrate this methodology by a case study of White Storks Ciconia ciconia where we tested whether mortality induced by power line collision is additive to other forms of mortality.La interacciĂłn de una fuente adicional de mortalidad con la fuente subyacente "natural" incide de forma considerable en la dinámica poblacional. Proponemos un mĂ©todo alternativo para comprobar los dos tipos de interacciĂłn: la aditividad total y la compensaciĂłn. A diferencia de lo que sucede con los modelos empleados actualmente, en este caso sĂłlo se precisan datos de recuperaciĂłn de anillas de cada uno de los individuos recuperados cuando se conoce la causa que ha provocado su muerte. Los porcentajes de mortalidad inducida por una causa especĂfica se estiman a partir de un modelo de captura–recaptura multiestado. Las hipĂłtesis se comprueban examinando la correlaciĂłn existente entre los porcentajes de mortalidad inducida por una causa especĂfica. Posteriormente, se efectĂşa una descomposiciĂłn de varianza a fin de obtener una estimaciĂłn apropiada de la verdadera correlaciĂłn del proceso. La estimaciĂłn de los porcentajes de mortalidad provocada por una causa especĂfica representa el punto más crĂtico de este planteamiento. Funciona adecuadamente si por lo menos una de las dos tasas de mortalidad varĂa con el tiempo y las dos tasas de recuperaciĂłn se mantienen constantes en el tiempo. Para ilustrar esta metodologĂa, presentamos un estudio de la cigĂĽeña blanca Ciconia ciconia, en el que verificamos si la mortalidad inducida por colisiones con los tendidos elĂ©ctricos se suma a otras formas de mortalidad
Three boundary conditions for computing the fixed-point property in binary mixture data
The notion of “mixtures” has become pervasive in behavioral and cognitive sciences, due to the success of dual-process theories of cognition. However, providing support for such dual-process theories is not trivial, as it crucially requires properties in the data that are specific to mixture of cognitive processes. In theory, one such property could be the fixed-point property of binary mixture data, applied–for instance- to response times. In that case, the fixed-point property entails that response time distributions obtained in an experiment in which the mixture proportion is manipulated would have a common density point. In the current article, we discuss the application of the fixed-point property and identify three boundary conditions under which the fixed-point property will not be interpretable. In Boundary condition 1, a finding in support of the fixed-point will be mute because of a lack of difference between conditions. Boundary condition 2 refers to the case in which the extreme conditions are so different that a mixture may display bimodality. In this case, a mixture hypothesis is clearly supported, yet the fixed-point may not be found. In Boundary condition 3 the fixed-point may also not be present, yet a mixture might still exist but is occluded due to additional changes in behavior. Finding the fixed-property provides strong support for a dual-process account, yet the boundary conditions that we identify should be considered before making inferences about underlying psychological processes
Measuring the extent of convective cores in low-mass stars using Kepler data: towards a calibration of core overshooting
Our poor understanding of the boundaries of convective cores generates large
uncertainties on the extent of these cores and thus on stellar ages. Our aim is
to use asteroseismology to consistently measure the extent of convective cores
in a sample of main-sequence stars whose masses lie around the mass-limit for
having a convective core. We first test and validate a seismic diagnostic that
was proposed to probe in a model-dependent way the extent of convective cores
using the so-called ratios, which are built with and
modes. We apply this procedure to 24 low-mass stars chosen among Kepler targets
to optimize the efficiency of this diagnostic. For this purpose, we compute
grids of stellar models with both the CESAM2k and MESA evolution codes, where
the extensions of convective cores are modeled either by an instantaneous
mixing or as a diffusion process. Among the selected targets, we are able to
unambiguously detect convective cores in eight stars and we obtain seismic
measurements of the extent of the mixed core in these targets with a good
agreement between the CESAM2k and MESA codes. By performing optimizations using
the Levenberg-Marquardt algorithm, we then obtain estimates of the amount of
extra-mixing beyond the core that is required in CESAM2k to reproduce seismic
observations for these eight stars and we show that this can be used to propose
a calibration of this quantity. This calibration depends on the prescription
chosen for the extra-mixing, but we find that it should be valid also for the
code MESA, provided the same prescription is used. This study constitutes a
first step towards the calibration of the extension of convective cores in
low-mass stars, which will help reduce the uncertainties on the ages of these
stars.Comment: 27 pages, 15 figures, accepted in A&
Integrating organizational research–Individual, team, organizational and multilevel perspectives
Organizations are multilevel social systems (Hedberg, Nystrom, & Starbuck, 1976; Kesler & Kates, 2015) where (1) diverse employees are assigned to various jobs, embedded in multiple dyadic relationships, and expected to play diverse team roles; (2) functional and/or cross-functional teams integrate individual efforts and develop intra- and inter-group dynamics; and (3) multiple departments and business processes nested within or spanning across organizational boundaries deliver value through mutual interaction. Whereas the managerial priority in the globally digitalized world is to execute competitive strategic initiatives and achieve challenging business goals by vigilantly managing and continuously improving dynamic interactions between organizational system levels, the majority of scholars still populate disciplinary, specialized micro- (social psychology, organizational behavior, and organizational psychology), meso- (business process management and project management) or macro- (strategic management, organizational theory and design, and engineering/systems management) research camps (e.g., Hitt, Beamish, Jackson, & Mathieu, 2007; Molloy, Ployhart, & Wright, 2011)..
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