4,659 research outputs found
The puzzling interpretation of NIR indices: The case of NaI2.21
We present a detailed study of the Na I line strength index centered in the
-band at , {\AA} (NaI2.21 hereafter) relying on different samples of
early-type galaxies. Consistent with previous studies, we find that the
observed line strength indices cannot be fit by state-of-art scaled-solar
stellar population models, even using our newly developed models in the NIR.
The models clearly underestimate the large NaI2.21 values measured for most
early-type galaxies. However, we develop a Na-enhanced version of our newly
developed models in the NIR, which - together with the effect of a bottom-heavy
initial mass function - yield NaI2.21 indices in the range of the observations.
Therefore, we suggest a scenario in which the combined effect of [Na/Fe]
enhancement and a bottom-heavy initial mass function are mainly responsible for
the large NaI2.21 indices observed for most early-type galaxies. To a smaller
extent, also [C/Fe] enhancement might contribute to the large observed NaI2.21
values.Comment: 13 pages, 4 figures, accepted for publication in MNRA
Shale oil : potential economies of large-scale production, preliminary phase
Producing shale oil on a large scale is one of the possible
alternatives for reducing dependence of the United States on imported
petroleum. Industry is not producing shale oil on a commercial scale now
because costs are too high even though industry dissatisfaction is most
frequently expressed about "non-economic" barriers: innumerable permits,
changing environmental regulations, lease limitations, water rights
conflicts, legal challenges, and so on. The overall purpose of this
study is to estimate whether improved technology might significantly
reduce unit costs for production of shale oil in a planned large-scale
industry as contrasted to the case usually contemplated: a small
industry evolving slowly on a project-by-project basis.
In this preliminary phase of the study, we collected published data
on the costs of present shale oil technology and adjusted them to common
conditions; these data were assembled to help identify the best targets
for cost reduction through improved large-scale technology They show
that the total cost of producing upgraded shale oil (i.e. shale oil
accpetable as a feed to a petroleum refinery) by surface retorting ranges
from about 28/barrel in late '78 dollars with a 20% chance that
the costs would be lower than and 20% higher than that range. The
probability distribution reflects our assumptions about ranges of shale
richness, process performance, rate of return, and other factors that
seem likely in a total industry portfolio of projects.
About 40% of the total median cost is attributable to retorting, 20%
to upgrading, and the remaining 40% to resource acquisition, mining,
crushing, and spent shale disposal and revegetation. Capital charges account for about 70% of the median total cost and operating costs for
the other 30%.
There is a reasonable chance that modified in-situ processes (like
Occidental's) may be able to produce shale oil more cheaply than surface
retorting, but no reliable cost data have been published; in 1978, DOE
estimated a saving of roughly $5/B for in-situ.
Because the total costs of shale oil are spread over many steps in
the production process, improvements in most or all of those steps are
required if we seek a significant reduction in total cost. A June 1979
workshop of industry experts was held to help us identify possible
cost-reduction technologies. Examples of the improved large-scale
technologies proposed (for further evaluation) to the workshop were:
- Instead of hydrotreating raw shale oil to make syncrude capable of
being refined conventionally, rebalance all of a refinery's
processes (or develop new catalysts/processes less sensitive to
feed nitrogen) to accommodate shale oil feed -- a change analogous
to a shift from sweet crude to sour crude.
- Instead of refining at or near the retort site, use heated
pipelines to move raw shale oil to existing major refining areas.
- Instead of operating individual mines, open-pit mine all or much
of the Piceance Creek Basin.
- Instead of building individual retorts, develop new methods for
mass production of hundreds of retorts
The Faber-Jackson relation for early-type galaxies: Dependence on the magnitude range
We take a sample of early-type galaxies from the Sloan Digital Sky Survey
(SDSS-DR7, 90 000 galaxies) spanning a range of approximately 7 in
both and filters and analyse the behaviour of the Faber-Jackson
relation parameters as functions of the magnitude range. We calculate the
parameters in two ways: i) We consider the faintest (brightest) galaxies in
each sample and we progressively increase the width of the magnitude interval
by inclusion of the brighter (fainter) galaxies
(increasing-magnitude-intervals), and ii) we consider narrow-magnitude
intervals of the same width ( ) over the whole magnitude
range available (narrow-magnitude-intervals). Our main results are that: i) in
both increasing and narrow-magnitude-intervals the Faber-Jackson relation
parameters change systematically, ii) non-parametric tests show that the
fluctuations in the values of the slope of the Faber-Jackson relation are not
products of chance variations. We conclude that the values of the Faber-Jackson
relation parameters depend on the width of the magnitude range and the
luminosity of galaxies within the magnitude range. This dependence is caused,
to a great extent by the selection effects and because the geometrical shape of
the distribution of galaxies on the plane depends on
luminosity. We therefore emphasize that if the luminosity of galaxies or the
width of the magnitude range or both are not taken into consideration when
comparing the structural relations of galaxy samples for different wavelengths,
environments, redshifts and luminosities, any differences found may be
misinterpreted.Comment: 15 pages, 5 figures. A&A. Accepte
The SAMI Galaxy Survey: Stellar population radial gradients in early-type galaxies
We study the internal radial gradients of the stellar populations in a sample
comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney- AAO
Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra
of individual spaxels in radial bins, and derive basic stellar population
properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial
gradient () and central value of the fits (evaluated at R/4) are
compared against a set of six possible drivers of the trends. We find that
velocity dispersion () - or, equivalently gravitational potential - is
the dominant driver of the chemical composition gradients. Surface mass density
is also correlated with the trends, especially with stellar age. The decrease
of [Mg/Fe] with increasing is contrasted by a rather shallow
dependence of [Z/H] with (although this radial gradient is
overall rather steep). This result, along with a shallow age slope at the
massive end, imposes stringent constraints on the progenitors of the
populations that contribute to the formation of the outer envelopes of ETGs.
The SAMI sample is split between a 'field' sample and a cluster sample. Only
weak environment-related differences are found, most notably a stronger
dependence of central total metallicity ([Z/H]) with , along
with a marginal trend of [Z/H] to steepen in cluster galaxies, a result
that is not followed by [Mg/Fe]. The results presented here serve as
constraints on numerical models of the formation and evolution of ETGs.Comment: 14 pages, 9 figures, 3 tables. Submitted to MNRA
Estudio histológico, histoquímico y microextractivo de sustancias alcaloídicas y grasas de la semilla de Annona cherimolia Mill
We have estudied the bistology and histocbemistry of A. cherimolia Mill. seed. In order to determine tbe most suitable conditions to extract, by means of solvents, substances Dragendorff positive and Sudan III positive, tbe appropiate histologic techniques were studied and tben applied.Hemos estudiado la histología e histoquímica de la semilla de A. cherimolia Mill. y se han puesto a punto y aplicado las técnicas histológicas adecuadas para determinar las condiciones idóneas de una posible extracción mediante disolventes, de principios que dan positivas las reacciones babituales de alcaloides y materias grasas
Age, Metallicity and Star Formation History of Cluster Galaxies at z~0.3 F
We investigate the color-magnitude distribution in the rich cluster AC 118 at
z=0.31. The sample is selected by the photometric redshift technique, allowing
to study a wide range of properties of stellar populations, and is complete in
the K-band, allowing to study these properties up to a given galaxy mass. We
use galaxy templates based on population synthesis models to translate the
physical properties of the stellar populations - formation epoch, time-scale of
star formation, and metallicity - into observed magnitudes and colors. In this
way we show that a sharp luminosity-metallicity relation is inferred without
any assumption on the galaxy formation scenario (either monolithic or
hierarchical). Our data exclude significant differences in star formation
histories along the color-magnitude relation, and therefore confirm a pure
metallicity interpretation for its origin, with an early (z~5) formation epoch
for the bulk of stellar populations. The dispersion in the color-magnitude
diagram implies that fainter galaxies in our sample (K~18) ceased to form stars
as late as z~0.5, in agreement with the picture that these galaxies were
recently accreted into the cluster environment. The trend with redshift of the
total stellar mass shows that half of the luminous mass in AC 118 was already
formed at $z~2, but also that 20% of the stars formed at z<1.Comment: 16 pages, 10 figures. ApJ in pres
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