637 research outputs found
Linear spectro-polarimetry: a new diagnostic tool for the classification and characterisation of asteroids
We explore the use of spectro-polarimetry as a remote sensing tool for
asteroids in addition to traditional reflectance measurements. In particular we
are interested in possible relationships between the wavelength-dependent
variation of linear polarization and the properties of the surfaces, including
albedo and composition.
We have obtained optical spectro-polarimetric measurements of a dozen
asteroids of different albedo and taxonomic classes and of two small regions at
the limb of the Moon.
We found that objects with marginally different relative reflectance spectra
(in the optical) may have totally different polarization spectra. This suggests
that spectro-polarimetry may be used to refine the classification of asteroids.
We also found that in some cases the Umov law may be violated, that is, in
contrast to what is expected from basic physical considerations, the fraction
of linear polarization and the reflectance may be positively correlated. In
agreement with a few previous studies based on multi-colour broadband
polarimetry, we found that the variation of linear polarization with wavelength
and with phase-angle is correlated with the albedo and taxonomic class of the
objects. Finally, we have serendipitously discovered that spinel-rich asteroid
(599) Luisa, located very close to the Watsonia family, is a member of the rare
class of Barbarian asteroids.
We suggest that future modelling attempts of the surface structure of
asteroids should be aimed at explaining both reflectance and polarization
spectra.Comment: Accepted for publication in MNRAS Letter
Concepts, Mechanisms, and Algorithms to Measure the Potential of Container Sharing in Seaport Hinterland Transportation
This thesis analyzes how trucking companies of a hinterland region can improve their routes if shipping companies allow the mutual exchange of their containers. In this case, trucking companies that are assigned by shipping companies cooperate by sharing information regarding which locations empty containers are currently stacked. These containers can then be integrated into a vehicle's route of any operating trucking company in the hinterland. The investigation aims at measuring the quantitative potential of the container sharing idea by means of problem settings illustrating realistic hinterland regions of a seaport. As a first step, the impact of street turns on the transportation costs of a trucking company should be measured. By forbidding or allowing the use of street turns for a single trucking company, the potential of the container sharing idea can be indicated, and the interrelation of empty container movements and transportation costs can be shown. As a further step, the benefit of exchanging empty containers between several trucking companies needs to be analyzed. In doing so, it is possible to investigate the potential and realistic limits of container sharing
Carbachol increases intracellular free calcium concentrations in human granulosa-lutein cells
We investigated whether the stimulation of human granulosa-lutein cells with muscarinic and nicotinic receptor agonists can cause increases in intracellular free calcium (Ca2+), using Fura-2 microfluorimetry. The addition of carbachol (a non-selective muscarinic and nicotinic receptor agonist) to cultured human granulosa-lutein cells increased intracellular free Ca2+ levels. Concentrations as low as 10 nmol/l were effective. In contrast, nicotine did not evoke elevations of intracellular free Ca2+. Basal Ca2+ levels ranged around 70â140 nmol/l and maximal, carbacholinduced peaks reached 1·1 ”mol/l. The carbachol-induced Ca2+ signal was abolished after preincubation of the cells with the muscarinic receptor antagonists quinuclidinyl benzilate or atropine, but it was not affected by removal of extracellular Ca2+. Further evidence for the involvement of intracellular Ca2+ stores is provided by experiments in the absence of extracellular Ca2+. While thapsigargin (a blocker of ATP-driven Ca2+ uptake by intracellular stores) and ionomycin (an ionophore by which Ca2+ is released from intracellular stores) evoked small Ca2+ transients, cells pretreated with these agents did not respond to carbachol any more. These data suggest the presence of a functional muscarinic receptor on human granulosa-lutein cells and imply the involvement of intracellular Ca2+ stores during the cellular response. These results also suggest the participation of the nervous system, acting through muscarinic receptors, in the control of the function of human granulosa-lutein cells
Going Beyond the Text: The Inferencing Processes of Skilled Readers in L1 and L2 across Reading Tasks
This small exploratory study investigated the inferencing processes of skilled first language (L1) and second language (L2) readers for two academic tasks. The goal was to examine possible effects of language and task, or reading purpose, on the frequency and distribution of inferences. Participants (n = 10) were native speakers of German enrolled at a large university in Hessen, Germany in a B.Ed. program. Participants read two expository texts (one written in German and the other written in English) in two task conditions: summary and position-paper. Think-aloud protocols while reading and stimulated recall immediately after reading were recorded, transcribed, coded, and the results were compared quantitatively and qualitatively across tasks and languages. The statistical analyses indicated that there were task effects on inferencing processes, and that they were stronger in L2. When reading for a summary purpose, inferencing processes differed across languages which was not the case for the position-paper task. Readersâ inferencing processes differed significantly across tasks in L2, but not in L1. The results suggest that skilled readers strategically inference based on academic task demands, but that transfer of strategic inferencing skills from L1 to L2 is not complete even with advanced L2 readers. Findings raise questions about the explicit instruction of strategic inferencing for academic tasks in L2 reading classrooms
Influence of aerosols, clouds, and sunglint on polarization spectra of Earthshine
Ground-based observations of the Earthshine, i.e., the light scattered by
Earth to the Moon, and then reflected back to Earth, simulate space
observations of our planet and represent a powerful benchmark for the studies
of Earth-like planets. Earthshine spectra are strongly linearly polarized,
owing to scattering by molecules and small particles in the atmosphere of the
Earth and surface reflection, and may allow us to measure global atmospheric
and surface properties of planet Earth. Aims. We aim to interpret already
published spectropolarimetric observations of the Earthshine by comparing them
with new radiative transfer model simulations including a fully realistic
three-dimensional (3D) surface-atmosphere model for planet Earth. We used the
highly advanced Monte Carlo radiative transfer model MYSTIC to simulate
polarized radiative transfer in the atmosphere of the Earth without
approximations regarding the geometry, taking into account the polarization
from surface reflection and multiple scattering by molecules, aerosol
particles, cloud droplets, and ice crystals. We have shown that Earth
spectropolarimetry is highly sensitive to all these input parameters, and we
have presented simulations of a fully realistic Earth atmosphere-surface model
including 3D cloud fields and two-dimensional (2D) surface property maps. Our
modeling results show that scattering in high ice water clouds and reflection
from the ocean surface are crucial to explain the continuum polarization at
longer wavelengths as has been reported in Earthshine observations taken at the
Very Large Telescope in 2011 (3.8 % and 6.6 % at 800 nm, depending on which
part of Earth was visible from the Moon at the time of the observations). We
found that the relatively high degree of polarization of 6.6 % can be
attributed to light reflected by the ocean surface in the sunglint region
Effect of oxytocin on free intracellular Ca2+ levels and progesterone release by human granulosa-lutein cells
Oxytocin and its receptor are found in the corpus luteum in a variety of species, including the human. In the present study we used fura-2 microfluorimetry to investigate whether activation of the oxytocin receptor of cultured human granulosa-lutein cells causes intracellular calcium (Ca2+) signals and affects progesterone release. Although after 1 day in culture, cells were not responsive to oxytocin, the number of responsive cells increased steadily during the first 3 days in culture, reaching a maximum on days 4 and 5 (59-66%) and then declined again until day 8. Effective oxytocin concentrations were apparently independent of the culture day, and concentrations as low as 10 nmol/L increased intracellular free Ca2+ levels from 70-140 nmol/L (basal levels) to maximal peak levels of 800 nmol/L. The oxytocin-induced Ca2+ signal was not affected by removal of extracellular Ca2+ with EGTA. Moreover, depletion of intracellular Ca2+ stores by ionomycin treatment rendered the cells unresponsive to oxytocin, pointing also at the intracellular source of the oxytocin-inducible Ca2+ signal. Interestingly, after one single stimulation with oxytocin, cells became refractory to additional stimuli, and only extremely high concentrations of oxytocin induced a second increase in intracellular free Ca2+. To examine the possible effects of oxytocin on progesterone release by cultured cells, we incubated cells on culture day 2 (20% responsive cells in the fura measurements) and culture day 5 (66% responsive cells in the fura measurements) for 24 h with oxytocin (10 nmol/L) and hCG (10,000 IU/L). Although hCG significantly stimulated progesterone release, oxytocin alone was without a stimulatory effect on either day. However, a significant augmentation of the effect of hCG on progesterone release was found in incubations of cells on day 5. Interestingly, the effects of hCG also included stimulation of oxytocin release by cultured granulosa-lutein cells into the culture medium, as determined by RIA. In summary, our data indicate the presence of a functional oxytocin receptor on human granulosa-lutein cells that is linked to Ca2+ as a second messenger released from intracellular Ca2+ stores. The number of oxytocin-responsive cells increases during differentiation in culture. Moreover, oxytocin release induced by hCG and a stimulatory effect of oxytocin on the hCG-induced progesterone production during the period of maximal responsiveness of cultured cells were found. We, therefore, propose that oxytocin may have autocrine and/or paracrine functions in human granulosa-lutein cells, including fine-tuning of progesterone release
Spectral and Temporal Variability of Earth Observed in Polarization
We present a comprehensive set of spectropolarimetric observations of
Earthshine as obtained by FORS2 at the VLT for phase angles from 50degree to
135degree (Sun-Earth-Moon angle), covering a spectral range from 430nm to
920nm. The degree of polarization in BVRI passbands, the differential
polarization vegetation index, and the equivalent width of the O2A polarization
band around 760nm are determined with absolute errors around 0.1 percent in the
degree of polarization. Earthshine polarization spectra are corrected for the
effect of depolarization introduced by backscattering on the lunar surface,
introducing systematic errors of the order of 1 percent in the degree of
polarization. Distinct viewing sceneries such as observing the Atlantic or
Pacific side in Earthshine yield statistically different phase curves. The
equivalent width defined for the O2A band polarization is found to vary from
-5nm to +2nm. A differential polarized vegetation index is introduced and
reveals a larger vegetation signal for those viewing sceneries that contain
larger fractions of vegetated surface areas. We corroborate the observed
correlations with theoretical models from the literature, and conclude that the
Vegetation Red Edge(VRE) is a robust and sensitive signature in polarization
spectra of planet Earth. The overall behaviour of polarization of planet Earth
in the continuum and in the O2A band can be explained by existing models.
Biosignatures such as the O2A band and the VRE are detectable in Earthshine
polarization with a high degree of significance and sensitivity. An in-depth
understanding of Earthshines temporal and spectral variability requires
improved models of Earths biosphere, as a prerequisite to interpret possible
detections of polarised biosignatures in earthlike exoplanets in the future.Comment: 19 pages, 14 figures, 3 table
How do we teach them all? A needs analysis for a pre-sessional EGAP curricular review
Making EAP course outcomes congruent with post-secondary demands requires a needs analysis, in which a target situation analysis is imperative (Bocanegra-Valle, 2016; Hyland, 2016; Cabinda, 2013; Rosenfeld, Leung, & Oltman, 2001; Upton, 2012). This article details the theoretical considerations for a needs analysis, and reports the quantitative findings of a target situation analysis completed for a pre-sessional EGAP program at a Canadian College. 51 Professors from the college and a university completed questionnaires ranking academic tasks necessary for postsecondary success in all four language skill areas (reading, writing, listening, and speaking). 25 of the 43 language tasks were identified as âapproaching very importantâ and âvery importantâ to academic success at the tertiary level in Canada. The results indicated that major curricular changes were warranted, especially at the two most advanced levels, and examples are explicated
Orphaned Protostars
We explore the origin of a population of distant companions (~1000 - 5000 AU)
to Class I protostellar sources recently found by Connelley and co-workers, who
noted that the companion fraction diminished as the sources evolved. Here we
present N-body simulations of unstable triple systems embedded in dense cloud
cores. Many companions are ejected into unbound orbits and quickly escape, but
others are ejected with insufficient momentum to climb out of the potential
well of the cloud core and associated binary. These loosely bound companions
reach distances of many thousands of AU before falling back and eventually
being ejected into escapes as the cloud cores gradually disappear. We use the
term orphans to denote protostellar objects that are dynamically ejected from
their placental cloud cores, either escaping or for a time being tenuously
bound at large separations. Half of all triple systems are found to
disintegrate during the protostellar stage, so if multiple systems are a
frequent outcome of the collapse of a cloud core, then orphans should be
common. Bound orphans are associated with embedded close protostellar binaries,
but escaping orphans can travel as far as ~0.2 pc during the protostellar
phase. The steep climb out of a potential well ensures that orphans are not
kinematically distinct from young stars born with a less violent pre-history.
The identification of orphans outside their heavily extincted cloud cores will
allow the detailed study of protostars high up on their Hayashi tracks at
near-infrared and in some cases even at optical wavelengths.Comment: 16 pages, 5 figure
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