73 research outputs found
Mid-Infrared Variability of protostars in IC 1396A
We have used Spitzer/IRAC to conduct a photometric monitoring program of the
IC1396A dark globule in order to study the mid-IR (3.6 - 8 micron) variability
of the heavily embedded Young Stellar Objects (YSOs) present in that area. We
obtained light curves covering a 14 day timespan with a twice daily cadence for
69 YSOs, and continuous light curves with approximately 12 second cadence over
7 hours for 38 YSOs. Typical accuracies for our relative photometry were 1-2%
for the long timespan data and a few mmag, corresponding to less than 0.5%, for
the 7 hour continuous "staring-mode" data. More than half of the YSOs showed
detectable variability, with amplitudes from ~0.05 mag to ~0.2 mag. About
thirty percent of the YSOs showed quasi-sinusoidal light curve shapes with
apparent periods from 5-12 days and light curve amplitudes approximately
independent of wavelength over the IRAC bandpasses. We have constructed models
which simulate the time dependent spectral energy distributions of Class I and
I I YSOs in order to attempt to explain these light curves. Based on these
models, the apparently periodic light curves are best explained by YSO models
where one or two high latitude photospheric spots heat the inner wall of the
circumstellar disk, and where we view the disk at fairly large inclination
angle. Disk inhomogeneities, such as increasing the height where the accretion
funnel flows to the stellar hotspot, enhances the light curve modulations. The
other YSOs in our sample show a range of light curve shapes, some of which are
probably due to varying accretion rate or disk shadowing events. One star,
IC1396A-47, shows a 3.5 hour periodic light curve; this object may be a PMS
Delta Scuti star
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The integration of human resource and operation management practices and its link with performance: A longitudinal latent class study
This paper reviews the literature on the association between lean production and performance. From this, propositions on the integration and evolution of operation and human resource management practices associated with the lean production concept are developed. Using 24 years of data on the use of seven core OM and HRM practices in British manufacturing firms, the potential link between integration in the use of practices and productivity is tested. In each year, three latent clusters are identified via ordered restricted latent class models; the cluster that consistently makes a more integrated use of practices outperforms the others. Furthermore, the longitudinal nature of the data permits modeling the growth curves of each practice in the sample, recognizing any similarity in growth and investigating whether or not an early integration in adoption of practices is associated with higher final productivity. The results show that pioneers are more productive, thus suggesting that the head start in integrating core OM and HRM practices associated with the lean production concept has paid off. © 2010 Elsevier B.V. All rights reserved
The Rossiter-McLaughlin effect in Exoplanet Research
The Rossiter-McLaughlin effect occurs during a planet's transit. It provides
the main means of measuring the sky-projected spin-orbit angle between a
planet's orbital plane, and its host star's equatorial plane. Observing the
Rossiter-McLaughlin effect is now a near routine procedure. It is an important
element in the orbital characterisation of transiting exoplanets. Measurements
of the spin-orbit angle have revealed a surprising diversity, far from the
placid, Kantian and Laplacian ideals, whereby planets form, and remain, on
orbital planes coincident with their star's equator. This chapter will review a
short history of the Rossiter-McLaughlin effect, how it is modelled, and will
summarise the current state of the field before describing other uses for a
spectroscopic transit, and alternative methods of measuring the spin-orbit
angle.Comment: Review to appear as a chapter in the "Handbook of Exoplanets", ed. H.
Deeg & J.A. Belmont
Does Ownership Affect the Variability of the Production Process? Evidence from International Courier Services
The influence of non-isotropic scattering of thermal radiation on spectra of brown dwarfs and hot exoplanets
(abridged) We calculate near-infrared thermal emission spectra using a
doubling-adding radiative transfer code, which includes scattering by clouds
and haze. Initial temperature profiles and cloud optical depths are taken from
the drift-phoenix brown dwarf model. As is well known, cloud particles change
the spectrum compared to when clouds are ignored. The clouds reduce fluxes in
the near-infrared spectrum and make it redder than for the clear sky case. We
also confirm that not including scattering in the spectral calculations can
result in errors on the spectra of many tens of percent, both in magnitude and
in variations with wavelength. This is especially apparent for particles that
are larger than the wavelength and only have little iron in them. Scattering
particles will show deeper absorption features than absorbing (e.g. iron)
particles and particle size will also affect the calculated infrared colours.
Large particles also tend to be strongly forward-scattering, and we show that
assuming isotropic scattering in this case also leads to very large errors in
the spectrum. Thus, care must be taken in the choice of radiative transfer
method for heat balance or spectral calculations when clouds are present in the
atmosphere. Besides the choice of radiative transfer method, the type of
particles that are predicted by models will change conclusions about e.g.
infrared colours and trace gas abundances. As a result, knowledge of the
scattering properties of the clouds is essential when deriving temperature
profiles or gas abundances from direct infrared observations of exoplanets or
brown dwarfs and from secondary eclipse measurements of transiting exoplanets,
since scattering clouds will change the depth of gas absorption features, among
other things. Thus, ignoring the presence of clouds can yield retrieved
properties that differ significantly from the real atmospheric properties.Comment: Accepted for publication in Astronomy and Astrophysics. The abstract
and a part of the introduction have been re-worded compared to the accepted
version to avoid misinterpretation of the paper as much as possibl
Mouse models of cancers: opportunities to address heterogeneity of human cancer and evaluate therapeutic strategies
The heterogeneity of human breast cancer has been well described at the morphological, molecular, and genomic levels. This heterogeneity presents one of the greatest obstacles in the effective treatment of breast cancer since the distinct forms of breast cancer that reflect distinct mechanisms of disease will require distinct therapies. Although mouse models of cancer have traditionally been used to simplify the study of human disease, we suggest that there are opportunities to also model the complexity and heterogeneity of human cancer. Here, we illustrate the similarities of mouse models to the human condition in the heterogeneity of both pathologies and gene expression. We then provide an illustration of the potential of gene expression analysis methods when used in conjunction with current treatment options to model individualized therapeutic regimes
Análisis de programas de mejora continua. Un estudio longitudinal en una empresa industrial
Las empresas han utilizado diversas herramientas que permiten que los operarios contribuyan al proceso de mejora continua. Entre las herramientas más usadas podemos destacar los sistemas de sugerencias tanto individuales como en grupo. En esta comunicaciĂłn haremos un repaso de las principales caracterĂsticas de ambos sistemas y los modos habituales de implantaciĂłn. Nuestra ponencia pretende intentar responder a estas preguntas de investigaciĂłn. ÂżQuĂ© resultados se derivan de la implantaciĂłn de sistemas de sugerencias individuales o en grupo? ÂżCuál de los dos sistemas es más beneficioso para la empresa? ÂżQuĂ© problemas surgen durante el funcionamiento de estos programas? Para ello, analizaremos los datos de un caso de empresa industrial donde hemos recogido los datos histĂłricos de 5 años de aplicaciĂłn de un programa de mejora continua. Ambos programas han demostrado ser provechosos para la empresa, aunque las posibilidades de los sistemas de grupo parecen ser significativamente mayores
TMEM106B, a frontotemporal lobar dementia (FTLD) modifier, associates with FTD-3-linked CHMP2B, a complex of ESCRT-III
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