416 research outputs found
Early star formation traced by the highest redshift quasars
The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page
Learning-by-mediating. Reflexive mediation in action
This paper aims at sharing some reflections and results concerning some experiences carried out within a European interdisciplinary Erasmus+ project. The main themes are community and peer mediation, considered from the perspective of educational innovation and experimentation. Two on-line videorecorded meetings of the project are analysed to show that the process of the project and this article-writing was consistent with mediation, that emerges as a topic within a discipline, but also as a cross- disciplinary methodology. The collective construction of meaning becomes a way to acquire knowledge, skills and attitudes while the participants are involved within interactive and constructive educational dynamics
satellite data analysis for identification of groundwater salinization effects on coastal forest for monitoring purposes
Abstract. In the phreatic aquifer below the San Vitale pinewood (Ravenna, Italy), natural and anthropogenic land subsidence, the low topography and the artificial drainage system have led to widespread saltwater intrusion. Since changes in the groundwater concentration induce variations in the vegetation properties, recognizable by different spectral bands, a comparison between satellite images, ASTER and Worldview-2, was made using the NDVI. The aim was to identify the portions of pinewood affected by salinization through a procedure that could reduce the expensive and time consuming ground monitoring campaigns. Moreover, the Worldview-2 high resolutions were used to investigate the Thermophilic Deciduous Forest (TDF) spectral behaviour without the influence of the allochthonous Pinus pinea species that is scattered throughout the pinewood. The NDVI, calculated with traditional bands, identified the same stressed areas using both satellite data. Instead, the new Red-Edge band of the Worldview-2 image allowed a greater correlation between NDVI and groundwater salinity
Geochemical Characterization of Groundwater in the Confined and Unconfined Aquifers of the Northern Italy
Having an accurate and easily accessible geochemical database is crucial for a correct groundwater management. Here, for the first time in Italy, chemico-physical data of groundwater collected by different Environmental Protection Agencies during the 2018 were integrated into a single database to assess the geochemical status of a wide and complex aquifer system. Data were assembled, reformatted, corrected, homogenized, and then grouped according to the aquifer type (phreatic, semi-confined, and confined) and the sampling seasons. A total of 3671 validated samples were classified into hydrochemical facies; inorganic N compounds and trace elements were also evaluated. The water were classified mainly as Ca-HCO3 and Ca-Mg-HCO3 (90%); locally, Na-HCO3, Mg-HCO3, Ca-SO4, Na-Cl, and Ca-Cl types were detected. In the phreatic aquifers, NO3 contamination and high concentrations of Na+, K+, and NH4+ were found and linked to anthropogenic sources, such as agricultural and livestock activities. Along the Adriatic coast, Na-Cl water confirmed saltwater intrusion phenomena. Landward, evaporitic rocks dissolution, and the upconing of relict marine water explained high EC, Na+, K+, Cl-, and SO42- concentrations. The dissolution of Fe-Mn oxide-hydroxides coupled with organic carbon oxidation under reducing environment justified high NH4+, Fe, Mn, and As recorded in the semi-confined and confined aquifers
SATELLITE AND UNMANNED AERIAL VEHICLE DATA FOR THE CLASSIFICATION OF SAND DUNE VEGETATION
Within coastal systems, sand dunes are the only natural barriers able to counteract erosive processes. Since their equilibrium is often threatened by human activities and high vulnerability of the coastal environment, dunes require increasing attention and specific monitoring. Located between the mainland and the sea, dunes are unique residue habitats for some plant and animal species. In particular, their vegetation is important because it has a consolidation function and promotes the vertical dune accretion. A georeferenced vegetation classification can be useful to define the advancements or erosion stage of the dune, usually based only on the geometric reconstruction. The proposed study aims to compare the classifications performed with some combinations of two of the last generation sensors and traditional image processing techniques. High spectral resolution satellite image (WorldView-2) and a multispectral orthophoto, obtained from data acquired by an unmanned aerial vehicle, were used. Objects and pixel algorithms were applied and the results were compared by a statistical test. Using the same bands, the findings show that both data are suitable for monitoring the evolutionary dune status. Specifically, the WorldView-2 pixel-based classification and UAV object-based classification provide the same accurate results
The Long-Term Experiment Platform for the Study of Agronomical and Environmental Effects of the Biochar: Methodological Framework
In this communication, a wide overview of historical Long-Term Experimental Platforms (LTEP) regarding changes in soil organic matter is presented for the purpose of networking, data sharing, experience sharing and the coordinated design of experiments in the area of Earth system science. This serves to introduce a specific platform of experiments regarding biochar application to soil (LTEP-BIOCHAR) and its use for agronomic and environmental purposes (e.g., carbon sequestration, soil erosion, soil biodiversity) in real conditions and over a significative timeframe for pedosphere dynamics. The methodological framework, including the goals, geographical scope and eligibility rules of such a new platform, is discussed. Currently, the LTEP-BIOCHAR is the first of its kind, a community-driven resource dedicated to biochar, and displays around 20 long-term experiments from Europe, the Middle East and Africa. The selected field experiments take place under dynamically, meteorologically and biologically different conditions. The purposes of the platform are (1) listing the field experiments that are currently active, (2) uncovering methodological gaps in the current experiments and allowing specific metadata analysis, (3) suggesting the testing of new hypotheses without unnecessary duplications while establishing a minimum standard of analysis and methods to make experiments comparable, (4) creating a network of expert researchers working on the agronomical and environmental effects of biochar, (5) supporting the design of coordinated experiments and (6) promoting the platform at a wider international level
Assessment of seasonal changes in water chemistry of the ridracoli water reservoir (Italy): Implications for water management
The Ridracoli artificial basin is the main water reservoir of the Emilia-Romagna region (Northeast Italy). The reservoir was made by construction of a dam on the Bidente River in 1982. It is used as the main drinking water supply of the region and for hydropower production. The physical and chemical parameterseters (temperature, pH, electrical conductivity, and dissolved oxygen) of shallow water are continuously monitored whereas vertical depth profiles of water chemical data (major anions and cations, as well as heavy metals) are available on a bimonthly base. The dataset used in this research is related to the years 2015 and 2016. Data show that the reservoir is affected by an alternation of water stratification and mixing processes due to seasonal change in water temperature, density, and the reservoir water level. In late summer and winter months, the water column is stratified with anoxic conditions at the bottom. During the spring, on the other hand, when storage is at its maximum, water recirculation and mixing occur. The reservoir is characterized by a dynamic system in which precipitation, dissolution, and adsorption processes at the bottom affect water quality along the reservoir depth column. The temperature stratification and anoxic conditions at the reservoir bottom influence the concentration and mobility of some heavy metals (i.e., Fe and Mn) and, consequently, the quality of water that reaches the treatment and purification plant. This study is relevant for water resource management of the reservoir. Assessing the seasonal changes in water quality along the reservoir water column depth is fundamental to plan water treatment operations and optimize their costs. The reservoir assessment allows one to identify countermeasures to avoid or overcome the high concentrations of heavy metals and the stratification problem (i.e., artificial mixing of the water column, new water intakes at different depths operating at different times of the year, blowers, etc.)
Origin of Two Distinct Populations in Dwarf Spheroidal Galaxies
We study the chemical and kinematic properties of the first galaxies which
formed at a high redshift, using high resolution cosmological numerical
simulations, and compared them with the recent observational results for the
Sculptor dwarf spheroidal galaxy by Tolstoy et al., who found two distinct
stellar populations: the lower metallicity stars are more spatially extended
and possess a higher velocity dispersion than the higher metallicity stars. Our
calculations reproduce these observations as the result of a steep metallicity
gradient, within a single populations, induced by dissipative collapse of the
gas component. We also predict strong [N/O] enhancements in the lowest
metallicity stars in dwarf spheroidals, due to the preferential retention of
ejected gas from intermediate mass stars, compared to Type II supernovae.Comment: 11 pages, 10 figures, accepted for publication in Ap
DNA HLA-DRB1 analysis in children of positive mothers and estimated risk of vertical HIV transmission.
RFLP HLA-DRB I analysis was performed on a total of 83 children born from HIV -infected mothers, 35 of whom were shown to be HIV -infected, while 48 reverted from seropositivity to seronegativity, indicating that they were not infected. Moreover, 89 healthy children were used as controls. It has been found that DRBI-14a and DRBI-13a.4 alleles were not present in the HIV-infected children, but were found in the sero-reverted (HIV-uninfected) children (in the proportion of 9·6 per cent and 5·3 per cent, respectively), and in the controls (5·6 per cent and 3·9 per cent, respectively). The possible correlation between DR and risk of HIV transmission from mother to baby was analysed considering every single allele, estimated by the ratio between the number of infected children and the number of all children born from seropositive mothers. There was also introduced a statisticGfor the control of 'statistical validity' of data
Iron as a tracer in galaxy clusters and groups
Available X-ray data are collected and organized concerning the iron and gas
content of galaxy clusters and groups, together with the optical luminosity,
mass and iron abundance of cluster galaxies. Several astrophysical inferences
are then drawn, including the evidence for rich clusters having evolved without
much baryon exchange with their surrondings, and having experienced very
similar star formation histories. Groups are much gas-poor compared to
clusters, and appear instead to have shed a major fraction of their original
cosmic share of baryons, which indicates that galaxy clusters cannot have
formed by assembling groups similar to the present day ones. It is argued that
this favors low- universes, in which the growth of rich clusters is
virtually complete at high redshifts. It is also argued that elemental
abundance ratios in clusters are nearly solar, which is consistent with a
similar proportion of supernovae of Type Ia and Type II having enriched both
the solar neghborhood as well clusters as a whole. Much of the iron in clusters
appears to reside in the intracluster medium rather than inside galaxies. It
appears that the baryon to star conversion in clusters has been nearly as
efficient as currently adopted for the universe as a whole. Yet the metallicity
of the clusters is times higher than the global metallicity adopted
for the nearby universe. It is concluded that the intergalactic medium should
have a metallicity solar if stellar nucleosynthesis has proceeded in
stars within field galaxies with the same efficiency as in stars within
clusters of galaxies.Comment: AASTex Latex, 29 pages, 6 figure
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