106 research outputs found
MOSE': A grid-enabled software platform to solve geoprocessing problems
Grid computing has emerged as an important new field in the distributed computing arena. It focus on intensive resource sharing, innovative applications, and in some cases,
high-performance orientation. This paper describes how
grids technologies can be used to develop an infrastructure for developing geoprocessing applications. We present the MOS`E system, a grid-enabled problem solving environment (PSE) able to support the activities that concern the modelling and simulation of spatio-temporal phenomena for analyzing and managing the identification and the mitigation of natural disasters like floods, wildfires, landslides, etc. MOSE' takes advantages of the standardized resource access and workflow support for loosely coupled software components provided by the web/grid services technologies
The complex organic molecular content in the L1498 starless Core
Interstellar matter and star formatio
The Complex Organic Molecular Content in the L1498 Starless Core
Observations carried out toward starless and prestellar cores have revealed that complex organic molecules are prevalent in these objects, but it is unclear what chemical processes are involved in their formation. Recently, it has been shown that complex organics are preferentially produced at an intermediate-density shell within the L1544 prestellar core at radial distances of ∼4000 au with respect to the core center. However, the spatial distribution of complex organics has only been inferred toward this core, and it remains unknown whether these species present a similar behavior in other cores. We report high-sensitivity observations carried out toward two positions in the L1498 starless core, the dust peak and a position located at a distance of ∼11,000 au from the center of the core where the emission of CH3OH peaks. Similarly to L1544, our observations reveal that small O-bearing molecules and N-bearing species are enhanced by factors of ∼4-14 toward the outer shell of L1498. However, unlike L1544, large O-bearing organics such as CH3CHO, CH3OCH3, or CH3OCHO are not detected within our sensitivity limits. For N-bearing organics, these species are more abundant toward the outer shell of the L1498 starless core than toward the one in L1544. We propose that the differences observed between O-bearing and N-bearing species in L1498 and L1544 are due to the different physical structure of these cores, which in turn is a consequence of their evolutionary stage, with L1498 being younger than L1544. © 2021. The American Astronomical Society. All rights reserved
Evolution of Chemistry in the envelope of Hot Corinos (ECHOS). I. Extremely young sulphur chemistry in the isolated Class 0 object B335
Within the project Evolution of Chemistry in the envelope of HOt corinoS
(ECHOS), we present a study of sulphur chemistry in the envelope of the Class 0
source B335 through observations in the spectral range 7, 3, and 2 mm. We have
modelled observations assuming LTE and LVG approximation. We have also used the
code Nautilus to study the time evolution of sulphur species. We have detected
20 sulphur species with a total gas-phase S abundance similar to that found in
the envelopes of other Class 0 objects, but with significant differences in the
abundances between sulphur carbon chains and sulphur molecules containing
oxygen and nitrogen. Our results highlight the nature of B335 as a source
especially rich in sulphur carbon chains unlike other Class 0 sources. The low
presence or absence of some molecules, such as SO and SO+, suggests a chemistry
not particularly influenced by shocks. We, however, detect a large presence of
HCS+ that, together with the low rotational temperatures obtained for all the S
species (<15 K), reveals the moderate or low density of the envelope of B335.
We also find that observations are better reproduced by models with a sulphur
depletion factor of 10 with respect to the sulphur cosmic elemental abundance.
The comparison between our model and observational results for B335 reveals an
age of 10t10 yr, which highlights the particularly early
evolutionary stage of this source. B335 presents a different chemistry compared
to other young protostars that have formed in dense molecular clouds, which
could be the result of accretion of surrounding material from the diffuse cloud
onto the protostellar envelope of B335. In addition, the analysis of the
SO2/C2S, SO/CS, and HCS+/CS ratios within a sample of prestellar cores and
Class 0 objects show that they could be used as good chemical evolutionary
indicators of the prestellar to protostellar transition
Gas phase Elemental abundances in Molecular cloudS (GEMS) VI. A sulphur journey across star-forming regions: study of thioformaldehyde emission
In the context of the IRAM 30m Large Program GEMS, we present a study of
thioformaldehyde in several starless cores located in star-forming filaments of
Taurus, Perseus, and Orion. We investigate the influence of the environmental
conditions on the abundances of these molecules in the cores, and the effect of
time evolution. We have modelled the observed lines of H2CS, HDCS, and D2CS
using the radiative transfer code RADEX. We have also used the chemical code
Nautilus to model the evolution of these species depending on the
characteristics of the starless cores. We derive column densities and
abundances for all the cores. We also derive deuterium fractionation ratios,
Dfrac, to determine and compare the evolutionary stage between different parts
of each star-forming region. Our results indicate that the north region of the
B213 filament in Taurus is more evolved than the south, while the north-eastern
part of Perseus presents an earlier evolutionary stage than the south-western
zone. Model results also show that Dfrac decreases with the cosmic-ray
ionisation rate, while it increases with density and with the degree of sulphur
depletion. In particular, we only reproduce the observations when the initial
sulphur abundance in the starless cores is at least one order of magnitude
lower than the solar elemental sulphur abundance. The progressive increase in
HDCS/H2CS and D2CS/H2CS with time makes these ratios powerful tools for
deriving the chemical evolutionary stage of starless cores. However, they
cannot be used to derive the temperature of these regions, since both ratios
present a similar evolution at two different temperature ranges (7-11 K and
15-19 K). Regarding chemistry, (deuterated) thioformaldehyde is mainly formed
through gas-phase reactions (double-replacement and neutral-neutral
displacement reactions), while surface chemistry plays an important role as a
destruction mechanism.Comment: 31 pages, 26 figure
Proceedings of the Merck & Elsevier Young Chemists Symposium (MEYCS 2018)
Dear participants,
welcome to the 18th edition of the Merck & Elsevier Young Chemists Symposium, formerly SAYCS and MYCS.
This conference is an international scientific event organized by the Young Group of the Italian Chemical Society (SCI Giovani) with the financial support of Merck and Elsevier.
This symposium is fully devoted to young researchers, such as MSc and PhD students, post-doc fellows and young researchers in companies. All the disciplines of Chemistry are covered: analytical, physical, industrial, organic, inorganic, theoretical, pharmaceutical, biological, environmental, macromolecular and electrochemistry. This year, a special emphasis will be given to chemistry from knowledge to innovation: how chemistry is increasingly present in all of the fields that are essential for human life, and how chemical fundamentals are pushing novel technologies?
This year we have the exceptional number of 212 participants; we thank you for the great trust shown towards SCI Giovani, Merck and Elsevier.
Enjoy the conference
Seeds of Life in Space (SOLIS): XI. First measurement of nitrogen fractionation in shocked clumps of the L1157 protostellar outflow
Context. The isotopic ratio of nitrogen presents a wide range of values in the Solar System: from 140 in meteorites and comets to 441 in the solar wind. In star-forming systems, we observe evena higher spread of ~150-1000. The origin of these differences is still unclear. Aims. Chemical reactions in the gas phase are one of the possible processes that could modify the 14N/15N ratio. We aim to investigate if and how the passage of a shock wave in the interstellar medium, which activates a rich chemistry, can affect the relative fraction of nitrogen isotopes. Theideal place for such a study is the chemically rich outflow powered by the L1157-mm protostar, where several shocked clumps are present. Methods. We present the first measurement of the 14N/15N ratio in the two shocked clumps, B1 and B0, of the protostellar outflow L1157. The measurement is derived from the interferometeric maps of the H13CN (1-0) and the HC15N (1-0) lines obtained with the NOrthern Extended Millimeter Array (NOEMA) interferometeras part of the Seeds of Life in Space (SOLIS) programme. Results. In B1, we find that the H13CN (1-0) and HC15N (1-0) emission traces the front of the clump, that is the apex of the shocked region, where the fast jet impacts the lower velocity medium with an averaged column density of N(H13CN) ~ 7 × 1012 cm-2 and N(HC15N) 2 × 1012 cm-2. In this region, the ratio H13CN (1-0)/HC15N (1-0) is almost uniform with an average value of ~5 ± 1. The same average value isalso measured in the smaller clump B0e. Assuming the standard 12C/13C = 68, we obtain 14N/15N = 340 ± 70. This ratio is similar to those usually found with the same species in prestellar cores and protostars. We analysed the prediction of a chemical shock model for several shock conditions and we found that the nitrogen and carbon fractionations do not vary much for the first period after the shock. The observed H13CN/HC15N can be reproduced by a non-dissociative, C-type shock with pre-shock density n(H) = 105 cm-3, shock velocity Vs between 20 and 40 km s-1, and cosmic-ray ionization rate of 3 × 10-16 s-1; this agrees with previous modelling of other chemical species in L1157-B1. Conclusions. Both observations and chemical models indicate that the rich chemistry activated by the shock propagation does not affect the nitrogen isotopic ratio, which remains similar to that measured in lower temperature gas in prestellar cores and protostellar envelopes
The complex organic molecular content in the L1517B starless core
Laboratory astrophysics and astrochemistr
Gas phase Elemental abundances in Molecular cloudS (GEMS) VII. Sulfur elemental abundance
Gas phase Elemental abundances in molecular CloudS (GEMS) is an IRAM 30m
large program aimed at determining the elemental abundances of carbon (C),
oxygen (O), nitrogen (N), and sulfur (S) in a selected set of prototypical
star-forming filaments. In particular, the elemental abundance of S remains
uncertain by several orders of magnitude and its determination is one of the
most challenging goals of this program. We have carried out an extensive
chemical modeling of the fractional abundances of CO, HCO, HCN, HNC, CS,
SO, HS, OCS, and HCS to determine the sulfur depletion toward the 244
positions in the GEMS database. These positions sample visual extinctions from
A 3 mag to 50 mag, molecular hydrogen densities ranging from a
few 10~cm to 310~cm, and T 1035 K.
Most of the positions in Taurus and Perseus are best fitted assuming early-time
chemistry, t=0.1 Myr, (0.51)10 s,
and [S/H]1.510. On the contrary, most of the positions in
Orion are fitted with t=1~Myr and 10 s.
Moreover, 40% of the positions in Orion are best fitted assuming the
undepleted sulfur abundance, [S/H]1.510. Our results
suggest that sulfur depletion depends on the environment. While the abundances
of sulfur-bearing species are consistent with undepleted sulfur in Orion, a
depletion factor of 20 is required to explain those observed in Taurus
and Perseus. We propose that differences in the grain charge distribution in
the envelopes of the studied clouds might explain these variations. The shocks
associated with past and ongoing star formation could also contribute to
enhance [S/H] in Orion.Comment: 22 pages, 15 figures, Astronomy and Astrophysics, in pres
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