746 research outputs found
Environmental assessment of humic acid coated magnetic materials used as catalyst in photo-fenton processes
Persistent organic pollutants have been increasingly detected in natural waters, and this represents a real challenge to the quality of this resource. To remove these species, advanced treatment technologies are required. Among these technologies, Fenton-like and photo-Fenton-like processes have been investigated for the removal of pollutants from water. Delicate aspects of photo-Fenton processes are that light-driven processes are energy intensive and require a fair amount of chemical inputs, which strongly affects their overall environmental burdens. At present, aside from determining the efficiency of the processes to remove pollutants of a particular technology, it becomes fundamental to assess also the environmental sustainability of the overall process. In this work, the methodology of the life cycle assessment (LCA) was applied to identify the hotspots of using magnetite particles covered with humic acid (Fe3O4/HA) as a heterogeneous photo-Fenton catalyst for water remediation. The sustainability of the overall process was considered, and a comparative LCA study was performed between H2O2 and persulfate activation at different pH. The addition of humic substances to the particles allows the effectiveness of the catalyst to improve without increasing the environmental impacts; these processes are strongly correlated with energy consumption and therefore with the efficiency of the process. For this reason, working at acidic pH allows us to contain the impacts
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
New Improved Photometric Redshifts of Galaxies in the HDF
We report new improved photometric redshifts of 1048 galaxies in the Hubble
Deep Field (HDF). A standard chi^2 minimizing method is applied to seven-color
UBVIJHK photometry by Fernandez-Soto, Lanzetta, & Yahil (1999). We use 187
template SEDs representing a wide variety of morphology and age of observed
galaxies based on a population synthesis model by Kodama & Arimoto (1997). We
introduce two new recipes. First, the amount of the internal absorption is
changed as a free parameter in the range of E(B-V)=0.0 to 0.5 with an interval
of 0.1. Second, the absorption due to intergalactic HI clouds is also changed
by a factor of 0.5, 1.0, and 1.5 around the opacity given by Madau (1995). The
total number of template SEDs is thus 187x6x3=3,366, except for the redshift
grid. The dispersion sigma_z of our photometric redshifts with respect to
spectroscopic redshifts is sigma_z=0.08 and 0.24 for z2, respectively,
which are smaller than the corresponding values (sigma_z=0.09 and 0.45) by
Fernandez-Soto et al. Improvement is significant, especially in z>2. This is
due to smaller systematic errors which are largely reduced mainly by including
three opacities due to intergalactic HI clouds. We discuss redshift
distribution N(z) and cosmic star formation rate based on our new photometric
redshifts.Comment: 24 pages including 16 eps figures; accepted for publication in Ap
Gemini-South + FLAMINGOS Demonstration Science: Near-Infrared Spectroscopy of the z=5.77 Quasar SDSS J083643.85+005453.3
We report an infrared 1-1.8 micron (J+H-bands), low-resolution (R=450)
spectrogram of the highest-redshift radio-loud quasar currently known, SDSS
J083643.85+005453.3, obtained during the spectroscopic commissioning run of the
FLAMINGOS multi-object, near-infrared spectrograph at the 8m Gemini-South
Observatory. These data show broad emission from both CIV 1549 and CIII] 1909,
with strengths comparable to lower-redshift quasar composite spectra. The
implication is that there is substantial enrichment of the quasar environment,
even at times less than a billion years after the Big Bang. The redshift
derived from these features is z = 5.774 +/- 0.003, more accurate and slightly
lower than the z = 5.82 reported in the discovery paper based on the
partially-absorbed Lyman-alpha emission line. The infrared continuum is
significantly redder than lower-redshift quasar composites. Fitting the
spectrum from 1.0 to 1.7 microns with a power law f(nu) ~ nu^(-alpha), the
derived power law index is alpha = 1.55 compared to the average continuum
spectral index = 0.44 derived from the first SDSS composite quasar.
Assuming an SMC-like extinction curve, we infer a color excess of E(B-V) = 0.09
+/- 0.01 at the quasar redshift. Only approximately 6% of quasars in the
optically-selected Sloan Digital Sky Survey show comparable levels of dust
reddening.Comment: 10 pages, 1 figure; to appear in the Astrophysical Journal Letter
XSHOOTER spectroscopy of the enigmatic planetary nebula Lin49 in the Small Magellanic Cloud
We performed a detailed spectroscopic analysis of the fullerene C60-containing planetary nebula (PN) Lin49 in the Small Magellanic Cloud (SMC) using XSHOOTER at the European Southern Observatory Very Large Telescope and the Spitzer/Infrared Spectrograph instruments. We derived nebular abundances for nine elements. We used TLUSTY to derive photospheric parameters for the central star. Lin49 is C-rich and metal-deficient PN (Z ⌠0.0006). The nebular abundances are in good agreement with asymptotic giant branch nucleosynthesis models for stars with initial mass 1.25 Mâ and metallicity Z = 0.001. Using the TLUSTY synthetic spectrum of the central star to define the heating and ionizing source, we constructed the photoionization model with CLOUDY that matches the observed spectral energy distribution (SED) and the line fluxes in the UV to far-IR wavelength ranges simultaneously. We could not fit the âŒ1â5 ÎŒm SED using a model with 0.005â0.1-ÎŒm-sized graphite grains and a constant hydrogen density shell owing to the prominent near-IR excess, while at other wavelengths the model fits the observed values reasonably well. We argue that the near-IR excess might indicate either (1) the presence of very small particles in the form of small carbon clusters, small graphite sheets, or fullerene precursors, or (2) the presence of a high-density structure surrounding the central star. We found that SMC C60 PNe show a near-IR excess component to lesser or greater degree. This suggests that these C60 PNe might maintain a structure nearby their central star
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
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
Photo-fenton degradation of pentachlorophenol l: competition between additives and photolysis
[EN] In the present work, the photo-Fenton degradation of pentachlorophenol (PCP, 1 mg/L) has been studied under simulated and natural solar irradiation; moreover, the effect on the process efficiency of urban waste-derived soluble bio-based substances (SBO), structurally comparable to humic acids, has been investigated. Experiments showed a crucial role of PCP photolysis, present in the solar pilot plant and hindered by the Pyrex (R) filter present in the solar simulator. Indeed, the SBO screen negatively affects PCP degradation when working under natural solar light, where the photolysis of PCP is relevant. In contrast, in the absence of PCP photolysis, a significant improvement of the photo-Fenton process was observed when added to SBO. Furthermore, SBO were able to extend the application of the photo-Fenton process at circumneutral pH values, due to their ability to complex iron, avoiding its precipitation as oxides or hydroxides. This positive effect has been observed at higher concentration of Fe(II) (4 mg/L), whereas at 1 mg/L, the degradation rates of PCP were comparable in the presence and absence of SBO.This work was realized with the financial support of the academic interchange from the Marie Sklodowska-Curie Research and Innovation Staff Exchange project, funded by the European Commission H2020-MSCA-RISE-2014 within the framework of the research project Mat4treaT (Project number: 645551).Vergura, EP.; GarcĂa-Ballesteros, S.; Vercher PĂ©rez, RF.; Santos-Juanes JordĂĄ, L.; Bianco Prevot, A.; ArquĂ©s Sanz, A. (2019). Photo-Fenton Degradation of Pentachlorophenol: Competition between Additives and Photolysis. Nanomaterials. 9(8):1-8. https://doi.org/10.3390/nano9081157S189
Heavy element abundances in blue compact galaxies
We present high-quality ground-based spectroscopic observations of 54
supergiant H II regions in 50 low-metallicity blue compact galaxies with oxygen
abundances 12 + log O/H between 7.1 and 8.3. We use the data to determine
abundances for the elements N, O, Ne, S, Ar and Fe. We also analyze Hubble
Space Telescope (HST) Faint Object Spectrograph archival spectra of 10
supergiant H II regions to derive C and Si abundances in a subsample of 7 BCGs.
The main result of the present study is that none of the heavy
element-to-oxygen abundance ratios studied here (C/O, N/O, Ne/O, Si/O, S/O,
Ar/O, Fe/O) depend on oxygen abundance for BCGs with 12 + log O/H < 7.6 (Z <
Zsun/20). This constancy implies that all these heavy elements have a primary
origin and are produced by the same massive (M > 10Msun) stars responsible for
O production. The dispersion of the C/O and N/O ratios in these galaxies is
found to be remarkably small, being only +/-0.03 dex and +/-0.02 dex
respectively. This very small dispersion is strong evidence against any
time-delayed production of C and primary N in the lowest-metallicity BCGs
(secondary N production is negligible at these low metallicities). The absence
of a time-delayed production of C and N is consistent with the scenario that
galaxies with 12 + log O/H < 7.6 are undergoing now their first burst of star
formation, and that they are therefore young, with ages not exceeding 40 Myr.
If very low metallicities BCGs are indeed young, this would argue against the
commonly held belief that C and N are produced by intermediate-mass (3Msun < M
< 9Msun) stars at very low metallicities, as these stars would not have yet
completed their evolution in these lowest metallicity galaxies.Comment: 37 pages, 5 EPS figures, to appear in ApJ, February 199
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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