838 research outputs found
Étude comparée des communautés benthiques et ripicoles endogées d'un réseau méditerranéen perturbé : l'Arc (Bouches-du-Rhône, France)
L'utilisation des méthodes biologiques et plus particulièrement l'étude des communautés benthiques pour l'appréciation de la qualité des eaux est actuellement d'un usage général. L'impact des perturbations des milieux peut être déduit de la composition et de la structure des peuplements qu'ils hébergent. En est-il de même pour les peuplements d'invertébrés ripicoles endogés humides, soumis moins directement à t'influence du milieu aquatique? Pour répondre à cette question une étude comparée (par analyse factorielle des correspondances) a été entreprise sur le réseau hydrographique d'une rivière de la région méditerranéenne, l'Arc, présentant des situations hydrochimiques variées.L'A.F.C., à partir de l'axe I, sépare les prélèvements d'invertébrés benthiques des prélèvements d'invertébrés ripicoles. Sur l'axe II les couples, prélèvement benthique - prélèvement ripicole de chaque station, possèdent sensiblement la même valeur sur l'axe et s'ordonnent selon un gradient de trophie croissant de l'amont vers l'aval. Les communautés ripicoles endogées humides peuvent donc être considérées comme des bio-indicateurs de la chimie de l'eau de la même manière que les communautés benthiques. Par contre le facteur temporarité (axe III) a une influence plus importante sur les communautés benthiques que sur les communautés ripicoles.L'examen de la répartition des taxons sur les axes factoriels a permis de déterminer un certain nombre d'espèces qui, tout en étant représentées dans les 2 milieux, sont caractéristiques de l'habitat rivulaire endogé humide. La prise en compte des peuplements ripicoles, malgré des difficultés d'ordre taxonomique, pourrait être envisagée lors de la détermination de la qualité des eaux.Utilization of biological methods and particularly through the study of benthic communities in order to estimate the quality of the water is for the present time very common. The impact of the disturbances of the medium may be deducted from the composition and the structure of the populations living there. But is it altogether the same for endogenous riparian wet invertebrate populations less directly submitted to the influence of the aquatic medium?To answer to this question, a comparative study (Factorial Analysis of Correspondences) has been carried out on the hydrographic network of the Arc River (Mediterranean region) which exhibits diversified hydrochemical situations. From and after axis I, the F.A.C. separates the benthic invertebrate samples from the riparian invertebrate ones. On axis II, the couples "benthic samples-riparian samples" of each station appreciably posses the same value on the axis and are arranged according to a trophic gradient ascending from upstream to downstream. The wet endogenous riparian communities can therefore be considered as bioindicators of the chemistry of the water in the same way as benthic communities. In contrast, the temporality factor (axis III) has a more important influence on the benthic communities than on the riparian ones.Examination of the distribution of the taxons on the factorial axis leads to identify a certain number of species which, although present in both mediums are characteristic of the wet endogenous riverside habitat. Taking into account of the riparian populations, in spite of taxonomic difficulties, should be considered as a valuable method for the determination of the quality of the waters
The Reddest DR3 SDSS/XMM Quasars
We have cross-correlated the SDSS DR3 Schneider et al. (2005) quasar catalog
with the XMM-Newton archive. Color and redshift selections (g - r > 0.5 and 0.9
z < 2.1) result in a sample of 17 red, moderate redshift quasars. The redshift
selection minimizes possible contamination due to host galaxy emission and
Lyalpha forest absorption. Both optical and X-ray information are required to
distinguish between the two likely remaining causes of the red colors: 1)
dust-reddening and 2) an intrinsically red continuum. We find that 7 of 17
quasars can be classified as probable `intrinsically red' objects. These 7
quasars have unusually broad MgII emission lines (=10,500 km s^{-1}),
moderately flat, but unabsorbed X-ray spectra =1.66+/-0.08), and low
accretion rates (mdot/mdot_{Edd}} ~ 0.01). We suggest low accretion rates as a
possible physical explanation for quasars with intrinsically red optical
continua. We find that 8 of 17 quasars can be classified as dust-reddened.
Three of these have upper-limits on the absorption column from X-ray spectral
fits of N_H = 3-13 x 10^{22} cm^2, while the other five quasars must be
absorbed by at least N_H = 10^{23} cm^2 in order to be consistent with a
comparably selected alpha_{ox}-l_{uv} distribution. Two objects in the sample
are unclassified.Comment: 20 pages, 12 figures, Accepted for publication in Ap
Continuum and Emission-Line Properties of Broad Absorption Line Quasars
We investigate the continuum and emission-line properties of 224 broad
absorption line quasars (BALQSOs) with 0.9<z<4.4 drawn from the Sloan Digital
Sky Survey (SDSS) Early Data Release (EDR), which contains 3814 bona fide
quasars. We find that low-ionization BALQSOs (LoBALs) are significantly
reddened as compared to normal quasars, in agreement with previous work.
High-ionization BALQSOs (HiBALs) are also more reddened than the average
nonBALQSO. Assuming SMC-like dust reddening at the quasar redshift, the amount
of reddening needed to explain HiBALs is E(B-V)~0.023 and LoBALs is
E(B-V)~0.077 (compared to the ensemble average of the entire quasar sample). We
find that there are differences in the emission-line properties between the
average HiBAL, LoBAL, and nonBAL quasar. These differences, along with
differences in the absorption line troughs, may be related to intrinsic quasar
properties such as the slope of the intrinsic (unreddened) continuum; more
extreme absorption properties are correlated with bluer intrinsic continua.
Despite the differences among BALQSO sub-types and nonBALQSOs, BALQSOs appear
to be drawn from the same parent population as nonBALQSOs when both are
selected by their UV/optical properties. We find that the overall fraction of
traditionally defined BALQSOs, after correcting for color-dependent selection
effects due to different SEDs of BALQSO and nonBALQSOs, is 13.4+/-1.2% and
shows no significant redshift dependence for 1.7<z<3.45. After a rough
completeness correction for the effects of dust extinction, we find that
approximately one in every six quasars is a BALQSO.Comment: 35 pages, 11 figures (1 color), 1 table; accepted by A
Initial Investigations of Controller Tools and Procedures for Schedule-Based Arrival Operations with Mixed Flight-Deck Interval Management Equipage
NASA's Air Traffic Management Demonstration-1 (ATD-1) is a multi-year effort to demonstrate high-throughput, fuel-efficient arrivals at a major U.S. airport using NASA-developed scheduling automation, controller decision-support tools, and ADS-B-enabled Flight-Deck Interval Management (FIM) avionics. First-year accomplishments include the development of a concept of operations for managing scheduled arrivals flying Optimized Profile Descents with equipped aircraft conducting FIM operations, and the integration of laboratory prototypes of the core ATD-1 technologies. Following each integration phase, a human-in-the-loop simulation was conducted to evaluate and refine controller tools, procedures, and clearance phraseology. From a ground-side perspective, the results indicate the concept is viable and the operations are safe and acceptable. Additional training is required for smooth operations that yield notable benefits, particularly in the areas of FIM operations and clearance phraseology
Probing the ISM Near Star Forming Regions with GRB Afterglow Spectroscopy: Gas, Metals, and Dust
We study the chemical abundances of the interstellar medium surrounding high
z gamma-ray bursts (GRBs) through analysis of the damped Lya systems (DLAs)
identified in afterglow spectra. These GRB-DLAs are characterized by large HI
column densities N(HI) and metallicities [M/H] spanning 1/100 to nearly solar,
with median [M/H]>-1. The majority of GRB-DLAs have [M/H] values exceeding the
cosmic mean metallicity of atomic gas at z>2, i.e. if anything, the GRB-DLAs
are biased to larger metallicity. We also observe (i) large [Zn/Fe] values
(>+0.6) and sub-solar Ti/Fe ratios which imply substantial differential
depletion, (ii) large a/Fe ratios suggesting nucleosynthetic enrichment by
massive stars, and (iii) low C^0/C^+ ratios (<10^{-4}). Quantitatively, the
observed depletion levels and C^0/C^+ ratios of the gas are not characteristic
of cold, dense HI clouds in the Galactic ISM. We argue that the GRB-DLAs
represent the ISM near the GRB but not gas directly local to the GRB (e.g. its
molecular cloud or circumstellar material). We compare these observations with
DLAs intervening background quasars (QSO-DLAs). The GRB-DLAs exhibit larger
N(HI) values, higher a/Fe and Zn/Fe ratios, and have higher metallicity than
the QSO-DLAs. We argue that the differences primarily result from
galactocentric radius-dependent differences in the ISM: GRB-DLAs preferentially
probe denser, more depleted, higher metallicity gaslocated in the inner few kpc
whereas QSO-DLAs are more likely to intersect the less dense, less enriched,
outer regions of the galaxy. Finally, we investigate whether dust obscuration
may exclude GRB-DLA sightlines from QSO-DLA samples; we find that the majority
of GRB-DLAs would be recovered which implies little observational bias against
large N(HI) systems.Comment: 16 pages, 9 figures. Submitted to Ap
Environmental Assessment of Solar Photo-Fenton Processes at Mild Condition in the Presence of Waste-Derived Bio-Based Substances
[EN] The assessment of environmental sustainability has assumed great importance during the study and implementation of a new process, including those aimed to waste valorization and reuse. In this research, the environmental performance of the photo-Fenton processes was evaluated using the life cycle assessment (LCA) methodology. In particular, photo-Fenton conducted in mild conditions (almost neutral pH), using soluble bio-organic substances as auxiliary agents were compared with the "classic" photo-Fenton run at pH 2.8. The evaluation was carried out both, at the laboratory level and at pilot plant scale. LCA analysis shows that working in mild conditions reduces the environmental burden associated with the use of chemicals. On the other hand, the occurring drop in effectiveness significantly increases the overall impact, thus evidencing the need of considering the process as a whole.Costamagna, M.; Arqués Sanz, A.; Lo-Iacono-Ferreira, VG.; Bianco Prevot, A. (2022). Environmental Assessment of Solar Photo-Fenton Processes at Mild Condition in the Presence of Waste-Derived Bio-Based Substances. Nanomaterials. 12(16):1-13. https://doi.org/10.3390/nano12162781113121
Metallicities of 0.3<z<1.0 Galaxies in the GOODS-North Field
We measure nebular oxygen abundances for 204 emission-line galaxies with
redshifts 0.3<z<1.0 in the Great Observatories Origins Deep Survey North
(GOODS-N) field using spectra from the Team Keck Redshift Survey (TKRS). We
also provide an updated analytic prescription for estimating oxygen abundances
using the traditional strong emission line ratio, R_{23}, based on the
photoionization models of Kewley & Dopita (2003). We include an analytic
formula for very crude metallicity estimates using the [NII]6584/Halpha ratio.
Oxygen abundances for GOODS-N galaxies range from 8.2< 12+log(O/H)< 9.1
corresponding to metallicities between 0.3 and 2.5 times the solar value. This
sample of galaxies exhibits a correlation between rest-frame blue luminosity
and gas-phase metallicity (i.e., an L-Z relation), consistent with L-Z
correlations of previously-studied intermediate-redshift samples. The zero
point of the L-Z relation evolves with redshift in the sense that galaxies of a
given luminosity become more metal poor at higher redshift. Galaxies in
luminosity bins -18.5<M_B<-21.5 exhibit a decrease in average oxygen abundance
by 0.14\pm0.05 dex from z=0 to z=1. This rate of metal enrichment means that
28\pm0.07% of metals in local galaxies have been synthesized since z=1, in
reasonable agreement with the predictions based on published star formation
rate densities which show that ~38% of stars in the universe have formed during
the same interval. (Abridged)Comment: AASTeX, 49 pages, 16 figures, accepted for publication in The
Astrophysical Journa
The UCSD HIRES/KeckI Damped Lya Abundance Database: II. The Implications
We present a comprehensive analysis of the damped Lya abundance database
presented in the first paper of this series. This database provides a
homogeneous set of abundance measurements for many elements including Si, Cr,
Ni, Zn, Fe, Al, S, Co, O, and Ar from 38 damped Lya systems with z > 1.5. With
little exception, these damped Llya systems exhibit very similar relative
abundances. There is no significant correlation in X/Fe with [Fe/H] metallicity
and the dispersion in X/Fe is small at all metallicity.
We search the database for trends indicative of dust depletion and in a few
cases find strong evidence. Specifically, we identify a correlation between
[Si/Ti] and [Zn/Fe] which is unambiguous evidence for depletion.
We present a discussion on the nucleosynthetic history of the damped Lya
systems by focusing on abundance patterns which are minimally affected by dust
depletion. We find [Si/Fe] -> +0.25 dex as [Zn/Fe] -> 0 and that the [Si/Fe]
values exhibit a plateau of ~+0.3 dex at [Si/H] < -1.5 dex. Together these
trends indicate significant alpha-enrichment in the damped Lya systems at low
metallicity, an interpretation further supported by the observed O/Fe, S/Fe and
Ar/Fe ratios. We also discuss Fe-peak nucleosynthesis and the odd-even effect.
To assess the impact of dust obscuration, we present estimates of the
dust-to-gas ratios for the damped Lya sightlines and crudely calculate dust
extinction corrections. The distribution of extinction corrections suggests the
effects of dust obscuration are minimal and that the population of 'missing'
damped systems has physical characteristics similar to the observed sample.
We update our investigation on the chemical evolution of the early universe
in neutral gas. [significantly abridged]Comment: 29 pages, 26 figures. Uses emulateapj.sty. Accepted to ApJ: Oct 15,
200
The young age of the extremely metal-deficient blue compact dwarf galaxy SBS 1415+437
We use Multiple Mirror Telescope (MMT) spectrophotometry and Hubble Space
Telescope (HST) Faint Object Spectrograph (FOS) spectra and Wide Field and
Planetary Camera 2 (WFPC2) V and I images to study the properties and
evolutionary status of the nearby (D = 11.4 Mpc) extremely metal-deficient blue
compact dwarf (BCD) galaxy SBS 1415+437=CG 389. The oxygen abundance in the
galaxy is 12+log(O/H)=7.60+/-0.01 or Zsun/21. The helium mass fraction in SBS
1415+437 is Y=0.246+/-0.004 which agrees with the primordial helium abundance
determined by Izotov & Thuan using a much larger sample of BCDs. The
alpha-elements-to-oxygen abundance ratios (Ne/O, S/O, Ar/O) are in very good
agreement with the mean values for other metal-deficient BCDs and are
consistent with the scenario that these elements are made in massive stars. The
Fe/O abundance ratio is ~2 times smaller than the solar ratio. The Si/O ratio
is close to the solar value, implying that silicon is not significantly
depleted into dust grains. The values of the N/O and C/O ratios imply that
intermediate-mass stars have not had time to evolve in SBS 1415+437 and release
their nucleosynthesis products and that both N and C in the BCD have been made
by massive stars only. This sets an upper limit of ~100 Myr on the age of SBS
1415+437. The (V-I) color of the low-surface-brightness component of the galaxy
is blue (<0.4 mag) indicative of a very young underlying stellar population.
The (V-I) - I color-magnitude diagrams of the resolved stellar populations in
different regions of SBS 1415+437 suggest propagating star formation from the
NE side of the galaxy to the SW. All regions in SBS 1415+437 possess very blue
spectral energy distributions (SED). We find that the ages of the stellar
populations in SBS 1415+437 to range from a few Myr to 100 Myr.Comment: 25 pages, 12 PS and 5 JPG figures, to appear in Ap
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