264 research outputs found
CO excitation in the Seyfert galaxy NGC7130
We present a coherent multi-band modelling of the CO Spectral Energy
Distribution of the local Seyfert Galaxy NGC7130 to assess the impact of the
AGN activity on the molecular gas. We take advantage of all the available data
from X-ray to the sub-mm, including ALMA data. The high-resolution (~0.2") ALMA
CO(6-5) data constrain the spatial extension of the CO emission down to ~70 pc
scale. From the analysis of the archival CHANDRA and NuSTAR data, we infer the
presence of a buried, Compton-thick AGN of moderate luminosity, L_2-10keV ~
1.6x10^{43} ergs-1. We explore photodissociation and X-ray-dominated regions
(PDRs and XDRs) models to reproduce the CO emission. We find that PDRs can
reproduce the CO lines up to J~6, however, the higher rotational ladder
requires the presence of a separate source of excitation. We consider X-ray
heating by the AGN as a source of excitation, and find that it can reproduce
the observed CO Spectral Energy Distribution. By adopting a composite PDR+XDR
model, we derive molecular cloud properties. Our study clearly indicates the
capabilities offered by current-generation of instruments to shed light on the
properties of nearby galaxies adopting state-of-the art physical modelling.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Sismabeton: a new frontier for ductile concrete
The high ductility of Fiber Reinforced Self-consolidating concrete (called Sismabeton) can be developed not only in tension but also in compression. This aspect is evidenced in the present paper by measuring the mechanical response of normal concrete (NC), plain self-compacting concrete (SC) and Sismabeton cylindrical specimens under uniaxial and triaxial compression. The post-peak behaviour of these specimens is defined by a non-dimensional function that relates the inelastic displacement and the relative stress during softening. Both for NC and SC, the increase of the fracture toughness with the confinement stress is observed. Conversely, Sismabeton shows, even in absence of confinement, practically the same ductility measured in normal and self-compacting concretes with a confining pressure. Thus, the presence of Sismabeton in compressed columns is itself sufficient to create a sort of active distributed confinement
Mesocosm‐based simulations to optimize a bioremediation strategy for the effective restoration of wildfire‐impacted soils contaminated with high‐molecular‐weight hydrocarbons
Aims: We obtained four microbial isolates from soil exposed to forest fire and evaluated their potential bioremediation activity when combined with a biosurfactant-producing bacterial strain for the decontamination of wildfire-impacted soil polluted with high-molecular-weight (HMW) hydrocarbons. Methods and Results: We established mesocosm trials to compare three bioremediation strategies: natural attenuation, bioaugmentation and biostimulation. Chemical analysis, culture-dependent and culture-independent methods were used to evaluate the bioremediation efficiency and speciation of the microbial cenoses based on these approaches. After treatment for 90 days, bioaugmentation removed 75·2–75·9% of the HMW hydrocarbons, biostimulation removed 63·2–69·5% and natural attenuation removed ~22·5%. Hydrocarbon degradation was significantly enhanced in the mesocosm supplemented with the biosurfactant-producing bacterial strain after 20 and 50 days of treatment compared to the other bioremediation strategies. Conclusions: We found that the bioaugmentation approach was more effective than biostimulation and natural attenuation for the removal of HMW hydrocarbons from fire-impacted soil. Significance and Impact of the Study: Our study showed that micro-organisms from wildfire-impacted soil show significant potential for bioremediation, and that biosurfactant-producing bacterial strains can be combined with them as part of an effective bioremediation strategy
The assembly of "normal" galaxies at z=7 probed by ALMA
We report new deep ALMA observations aimed at investigating the [CII]158um
line and continuum emission in three spectroscopically confirmed Lyman Break
Galaxies at 6.8<z<7.1, i.e. well within the re-ionization epoch. With Star
Formation Rates of SFR ~ 5-15 Msun/yr these systems are much more
representative of the high-z galaxy population than other systems targeted in
the past by millimeter observations. For the galaxy with the deepest
observation we detect [CII] emission at redshift z=7.107, fully consistent with
the Lyalpha redshift, but spatially offset by 0.7" (4 kpc) from the optical
emission. At the location of the optical emission, tracing both the Lyalpha
line and the far-UV continuum, no [CII] emission is detected in any of the
three galaxies, with 3sigma upper limits significantly lower than the [CII]
emission observed in lower reshift galaxies. These results suggest that
molecular clouds in the central parts of primordial galaxies are rapidly
disrupted by stellar feedback. As a result, [CII] emission mostly arises from
more external accreting/satellite clumps of neutral gas. These findings are in
agreement with recent models of galaxy formation. Thermal far-infrared
continuum is not detected in any of the three galaxies. However, the upper
limits on the infrared-to-UV emission ratio do not exceed those derived in
metal- and dust-poor galaxies.Comment: 15 pages, 9 figures, MNRAS in press, replaced with accepted versio
Organic residues as immobilizing agents in aided phytostabilization: (I) Effects on soil chemical characteristics
A greenhouse experiment was conducted to evaluate the effect of three different organic residues, sewage
sludge (SS), municipal solid waste compost (MSWC), and garden waste compost (GWC), as immobilizing
agents in aided phytostabilization of a highly acidic metal-contaminated soil, affected by mining
activities, using perennial ryegrass (Lolium perenne L.). The organic residues were applied at 25, 50 and
100 Mg ha 1 (dry weight basis), and their effects on soil chemical characteristics and on relative plant
growth and metal concentrations were assessed. All the organic residues tested immobilized Cu, Pb
and Zn, decreasing their mobile fractions. This was corroborated by negative correlations obtained
between mobile Cu, Pb and Zn and other soil chemical characteristics, which rose as a consequence of
the amendments applied (i.e., pH, electrical conductivity, organic matter, nitrogen content, available P
and available K), and by the multivariate exploratory techniques performed that showed an inverse correlation
between these groups of variables. The greatest increase in ryegrass relative growth (more than
three times) was obtained in the presence of 50 Mg MSWC ha 1, followed by SS at the same application
dosage. GWC did not contribute to an increase in shoot growth, due to its small capacity to correct soil
acidity and to supply essential macronutrients (N, P, K). No extractant was able of demonstrating by a
linear correlation the uptake of Cu, Pb and Zn by ryegrass. This plant was therefore not a good ‘‘indicator”
of Cu, Pb and Zn availability in the soil. The results obtained in this study suggest that ryegrass can be
used in aided phytostabilization for this type of mine contaminated soils and that MSWC, and to a minor
extent SS, applied at 50 Mg ha 1, were effective in the in situ immobilization of metals, improving soil
chemical properties and leading to a large increase in plant biomas
Evaluation of tests to assess the quality of mine-contaminated soils
An acid metal-contaminated soil from the
Aljustrel mining area (a pyrite mine located in SW
Portugal in the Iberian Pyrite Belt) was subjected to
chemical characterisation and total metal quantiWcation
(Cd, Cr, Cu, Ni, Pb and Zn). Water-soluble metals
were determined and a sequential extraction
procedure was used to investigate metal speciation.
Two bioavailable metal fractions were determined: a
mobile fraction and a mobilisable fraction. Soil ecotoxicity
was studied using a battery of bioassays:
plant growth test and seed germination with cress
(Lepidium sativum L.), earthworm (Eisenia fetida)
mortality, E. fetida avoidance behaviour, luminescent
inhibition of Vibrio Wscheri and Daphnia magna
immobilisation. Although the total content of Cu, Zn and Pb in the soil was large (362, 245 and 1,250 mg/
kg dry matter, respectively), these metals were mostly
structurally bound (87% for Cu, 81% for Zn and 89%
for Pb) and, therefore, scarcely bioavailable. Nonetheless,
the D. magna immobilization test using soil
leachate showed an EC50 (48 h) of 36.3% (v/v), and
the luminescent inhibition of V. Wscheri presented an
EC20 (15 min) of 45.2% and an EC20 (30 min) of
10.7% (v/v), suggesting a considerable toxic eVect. In
the direct exposure bioassays, E. fetida avoided the
mine soil at the highest concentrations (50%, 75%
and 100% v/v). At the same soil concentrations, cress
showed negligible growth. The results suggest the
need to use a battery of toxicity tests, in conjunction
with chemical methods, in order to assess the quality
of mine-contaminated soils correctly
Evaluation of composts and liming materials in the phytostabilization of a mine soil using perennial ryegrass
A microcosm experiment was carried out to evaluate the effects of municipal solid waste
compost (MSWC) or garden waste compost (GWC), and liming materials in the rehabilitation
of a soil affected by mining activities, and to study the use of perennial ryegrass (Lolium
perenne L.) for phystostabilization. The performance of the amendments was assessed by
soil chemical parameters, total and bioavailable metals (Cu, Pb and Zn), soil enzymatic
activities, and plant relative growth and mineral composition. In general, both composts
corrected soil acidity and increased the total organic matter content of the soil, although
with a better performance in the case of MSWC, especially when considering total N and
available P and K levels in the amended soil. The application of both composts and liming
materials led to a decrease in the mobile fractions of Cu, Pb and Zn, but mobilisable fractions
of Cu and Zn increased with MSWC application. Plant biomass increased more than three
times in the presence of 50 Mg MSWC ha−1 and with the combined use of 25 or 50 Mg MSWC
ha−1 and CaO, but no significant differences were observed when GWC was applied. Plant
tissue analysis showed that the treatments did not significantly reduce Cu, Pb and Zn
uptake by the plant. Dehydrogenase, and the enzymes related to the N-cycle, urease and
protease, had increased activities with increasing MSWC application rate. Conversely, the
enzymatic activities of both enzymes related to the C-cycle, cellulase and β-glucosidase,
were only positively affected by GWC application, a compost obtained from raw materials
rich in C. Principal component analyses evidenced this clear separation between the effect
of MSWC on soil enzymes related to the N-cycle and of GWC on soil enzymes related to the
C-cycle. This study indicates that MSWC (50 Mg ha−1, limed or unlimed) can be used
successfully in the remediation of a highly acidic metal-contaminated soil, allowing the
establishment of perennial ryegrass
Sismabeton: a new frontier for ductile concrete
The high ductility of Fiber Reinforced Self-consolidating concrete (called Sismabeton) can be developed not only in tension but also in compression. This aspect is evidenced in the present paper by measuring the mechanical response of normal concrete (NC), plain self-compacting concrete (SC) and Sismabeton cylindrical specimens under uniaxial and triaxial compression. The post-peak behaviour of these specimens is defined by a non-dimensional function that relates the inelastic displacement and the relative stress during softening. Both for NC and SC, the increase of the fracture toughness with the confinement stress is observed. Conversely, Sismabeton shows, even in absence of confinement, practically the same ductility measured in normal and self-compacting concretes with a confining pressure. Thus, the presence of Sismabeton in compressed columns is itself sufficient to create a sort of active distributed confinement
CO excitation in the Seyfert galaxy NGC 7130
We present a coherent multiband modelling of the carbon monoxide (CO) spectral energy distribution of the local Seyfert galaxy NGC 7130 to assess the impact of the active galactic nucleus (AGN) activity on the molecular gas. We take advantage of all the available data from X-ray to the submillimetre, including ALMA data. The high-resolution (~0.2 arcsec) ALMA CO(6-5) data constrain the spatial extension of the CO emission down to an ~70 pc scale. From the analysis of the archival Chandra and NuSTAR data, we infer the presence of a buried, Compton-thick AGN of moderate luminosity, L2-10 keV ~1.6 × 1043 erg s-1. We explore photodissociation and X-ray-dominated-region (PDR and XDR) models to reproduce the CO emission. We find that PDRs can reproduce the CO lines up to J ~ 6; however, the higher rotational ladder requires the presence of a separate source of excitation. We consider X-ray heating by the AGNs as a source of excitation, and find that it can reproduce the observed CO spectral energy distribution. By adopting a composite PDR+XDR model, we derivemolecular cloud properties. Our study clearly indicates the capabilities offered by the current generation of instruments to shed light on the properties of nearby galaxies by adopting state-of-the-art physical modelling
ALMA constraints on the faint millimetre source number counts and their contribution to the cosmic infrared background
We have analysed 18 ALMA continuum maps in Bands 6 and 7, with rms down to
7.8Jy, to derive differential number counts down to 60Jy and
100Jy at 1.3 mm and 1.1 mm, respectively. The area
covered by the combined fields is at 1.1mm and at 1.3mm. We improved the source extraction method by
requiring that the dimension of the detected sources be consistent with the
beam size. This method enabled us to remove spurious detections that have
plagued the purity of the catalogues in previous studies. We detected 50 faint
sources with S/N3.5 down to 60Jy, hence improving the statistics by a
factor of four relative to previous studies. The inferred differential number
counts are at a 1.1 mm flux Jy, and at a 1.3
mm flux Jy. At the faintest flux limits,
i.e. 30Jy and 40Jy, we obtain upper limits on the differential number
counts of and , respectively. Our results provide a new
lower limit to CIB intensity of 17.2 at 1.1mm and of
12.9 at 1.3mm. Moreover, the flattening of the integrated
number counts at faint fluxes strongly suggests that we are probably close to
the CIB intensity. Our data imply that galaxies with SFR
certainly contribute less than 50% to the CIB while more than 50% of the CIB
must be produced by galaxies with . The differential
number counts are in nice agreement with recent semi-analytical models of
galaxy formation even as low as our faint fluxes. Consequently, this supports
the galaxy evolutionary scenarios and assumptions made in these models.Comment: 11 pages, 9 figures, A&A accepte
- …