627 research outputs found
Global stellar variability study in the field-of-view of the Kepler satellite
We present the results of an automated variability analysis of the Kepler
public data measured in the first quarter (Q1) of the mission. In total, about
150 000 light curves have been analysed to detect stellar variability, and to
identify new members of known variability classes. We also focus on the
detection of variables present in eclipsing binary systems, given the important
constraints on stellar fundamental parameters they can provide. The methodology
we use here is based on the automated variability classification pipeline which
was previously developed for and applied successfully to the CoRoT exofield
database and to the limited subset of a few thousand Kepler asteroseismology
light curves. We use a Fourier decomposition of the light curves to describe
their variability behaviour and use the resulting parameters to perform a
supervised classification. Several improvements have been made, including a
separate extractor method to detect the presence of eclipses when other
variability is present in the light curves. We also included two new
variability classes compared to previous work: variables showing signs of
rotational modulation and of activity. Statistics are given on the number of
variables and the number of good candidates per class. A comparison is made
with results obtained for the CoRoT exoplanet data. We present some special
discoveries, including variable stars in eclipsing binary systems. Many new
candidate non-radial pulsators are found, mainly Delta Sct and Gamma Dor stars.
We have studied those samples in more detail by using 2MASS colours. The full
classification results are made available as an online catalogue.Comment: 15 pages, 5 figures, Accepted for publication in Astronomy and
Astrophysics on 09/02/201
Leading innovation in an interorganizational team together : the moderating role of shared leadership behavior in the transitioning between different phases of the open innovation process
Purpose – This study aims to contribute to the open innovation (OI) literature by investigating the transitions
between three phases in the OI process (i.e. idea generation, idea promotion and idea realization) and how these
are moderated by different forms of shared leadership (i.e. transactional, and transformational) as perceived by
participants in the OI process.
Design/methodology/approach – The authors tested a set of hypotheses using moderated mediation PLSSEM
models on a bootstrapped sample of OI participants (N 5 173).
Findings – The authors found a direct relationship between idea generation and realization, as well as
indirectly through idea promotion. This study implies that the promotion of ideas by participants can be
beneficial in inter-organizational OI teams, as promotion of ideas provides a linkage between the generation of
ideas and the idea realization phase. However, while shared leadership has been shown to be beneficial in
conventional teams, the authors found evidence that this may not be the case in inter-organizational OI teams.
Higher levels of shared transformational leadership from colleagues with whom employees do not share the
same organizational background may hamper the promotion of ideas.
Originality/value – In contrast to the mainstream view, the authors found significant evidence that
transformational shared leadership negatively moderates the direct relationship between idea generation and
the promotion of ideas and the indirect relationship between idea generation and realization via idea promotion.info:eu-repo/semantics/publishedVersio
Leadership, Complex Adaptive Systems, and Equivocality: The Role of Managers in Emergent Change
When managers are confronted with the necessity to change their organization owing to a turbulent and unpredictable environment, their change efforts are often not very successful. As managers are part of the change context itself, they have to act in a way that is different from the traditional role of the administrative leader to become successful change leaders. This article attempts to redefine organizational change using complexity theory and the work of Karl Weick and Ralph Stacey as a basis. Organizational change can be defined as emergent change in complex adaptive systems and is based on self-organizational principles. One important attractor that guides the process of emergence is equivocality. This article expounds the concept of equivocality as a main attractor for emergent change and how managers can make use of this attractor to make change successful. Research directions are also discussed
Modeling Ultraviolet Wind Line Variability in Massive Hot Stars
We model the detailed time-evolution of Discrete Absorption Components (DACs)
observed in P Cygni profiles of the Si IV lam1400 resonance doublet lines of
the fast-rotating supergiant HD 64760 (B0.5 Ib). We adopt the common assumption
that the DACs are caused by Co-rotating Interaction Regions (CIRs) in the
stellar wind. We perform 3D radiative transfer calculations with hydrodynamic
models of the stellar wind that incorporate these large-scale density- and
velocity-structures. We develop the 3D transfer code Wind3D to investigate the
physical properties of CIRs with detailed fits to the DAC shape and morphology.
The CIRs are caused by irregularities on the stellar surface that change the
radiative force in the stellar wind. In our hydrodynamic model we approximate
these irregularities by circular symmetric spots on the stellar surface. We use
the Zeus3D code to model the stellar wind and the CIRs, limited to the
equatorial plane. We constrain the properties of large-scale wind structures
with detailed fits to DACs observed in HD 64760. A model with two spots of
unequal brightness and size on opposite sides of the equator, with opening
angles of 20 +/- 5 degr and 30 +/- 5 degr diameter, and that are 20 +/- 5 % and
8 +/- 5 % brighter than the stellar surface, respectively, provides the best
fit to the observed DACs. The recurrence time of the DACs compared to the
estimated rotational period corresponds to spot velocities that are 5 times
slower than the rotational velocity. The mass-loss rate of the structured wind
model for HD 64760 does not exceed the rate of the spherically symmetric smooth
wind model by more than 1 %. The fact that DACs are observed in a large number
of hot stars constrains the clumping that can be present in their winds, as
substantial amounts of clumping would tend to destroy the CIRs.Comment: 58 pages, 16 figures, 1 animation. Accepted for publication in The
Astrophysical Journal, Main Journal. More information and animations are
available at http://alobel.freeshell.org/hotstars.htm
Line formation in solar granulation VI. [C I], C I, CH and C2 lines and the photospheric C abundance
The solar photospheric carbon abundance has been determined from [C I], C I,
CH vibration-rotation, CH A-X electronic and C2 Swan electronic lines by means
of a time-dependent, 3D, hydrodynamical model of the solar atmosphere.
Departures from LTE have been considered for the C I lines. These turned out to
be of increasing importance for stronger lines and are crucial to remove a
trend in LTE abundances with the strengths of the lines. Very gratifying
agreement is found among all the atomic and molecular abundance diagnostics in
spite of their widely different line formation sensitivities. The mean of the
solar carbon abundance based on the four primary abundance indicators ([C I], C
I, CH vibration-rotation, C_2 Swan) is log C = 8.39 +/- 0.05, including our
best estimate of possible systematic errors. Consistent results also come from
the CH electronic lines, which we have relegated to a supporting role due to
their sensitivity to the line broadening. The new 3D based solar C abundance is
significantly lower than previously estimated in studies using 1D model
atmospheres.Comment: Accepted for A&A, 13 page
The long period eccentric orbit of the particle accelerator HD167971 revealed by long baseline interferometry
Using optical long baseline interferometry, we resolved for the first time
the two wide components of HD167971, a candidate hierarchical triple system
known to efficiently accelerate particles. Our multi-epoch VLTI observations
provide direct evidence for a gravitational link between the O8 supergiant and
the close eclipsing O + O binary. The separation varies from 8 to 15 mas over
the three-year baseline of our observations, suggesting that the components
evolve on a wide and very eccentric orbit (most probably e>0.5). These results
provide evidence that the wide orbit revealed by our study is not coplanar with
the orbit of the inner eclipsing binary. From our measurements of the
near-infrared luminosity ratio, we constrain the spectral classification of the
components in the close binary to be O6-O7, and confirm that these stars are
likely main-sequence objects. Our results are discussed in the context of the
bright non-thermal radio emission already reported for this system, and we
provide arguments in favour of a maximum radio emission coincident with
periastron passage. HD167971 turns out to be an efficient O-type particle
accelerator that constitutes a valuable target for future high angular
resolution radio imaging using VLBI facilities.Comment: 8 pages, including 4 figures, accepted by Monthly Notices of the
Royal Astronomical Societ
ALMA observations of the supergiant B[e] star Wd1-9
Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible – radiatively driven winds, impulsive ejection and/or binary interaction – remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (∼100 km s-1 ) ionized wind, with an extreme mass-loss rate ≳6.4 × 105(d/5 kpc)1.5 Mȯyr-1. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they – and by extension the wider class of supergiant B[e] stars – may provide a unique window into the physics of a process that shapes the life-cycle of ∼70 per cent of massive stars found in binary systems
Content and changes in Provitamin A carotenoids during ripening of fruit from four popular Musa cultivars consumed in Eastern Democratic Republic of Congo
Poster presented at Nutrition Congress Africa 2012. Transforming the Nutrition Landscape in Africa. Bloemfontein (South Africa), 1-4 Oct 201
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