238 research outputs found
Dust as interstellar catalyst I. Quantifying the chemical desorption process
Context. The presence of dust in the interstellar medium has profound
consequences on the chemical composition of regions where stars are forming.
Recent observations show that many species formed onto dust are populating the
gas phase, especially in cold environments where UV and CR induced photons do
not account for such processes. Aims. The aim of this paper is to understand
and quantify the process that releases solid species into the gas phase, the
so-called chemical desorption process, so that an explicit formula can be
derived that can be included into astrochemical models. Methods. We present a
collection of experimental results of more than 10 reactive systems. For each
reaction, different substrates such as oxidized graphite and compact amorphous
water ice are used. We derive a formula to reproduce the efficiencies of the
chemical desorption process, which considers the equipartition of the energy of
newly formed products, followed by classical bounce on the surface. In part II
we extend these results to astrophysical conditions. Results. The equipartition
of energy describes correctly the chemical desorption process on bare surfaces.
On icy surfaces, the chemical desorption process is much less efficient and a
better description of the interaction with the surface is still needed.
Conclusions. We show that the mechanism that directly transforms solid species
to gas phase species is efficient for many reactions.Comment: Accepted for publication in A&
Composite pulses in Hyper-Ramsey spectroscopy for the next generation of atomic clocks
The next generation of atomic frequency standards based on an ensemble of
neutral atoms or a single-ion will provide very stringent tests in metrology,
applied and fundamental physics requiring a new step in very precise control of
external systematic corrections. In the proceedings of the 8th Symposium on
Frequency Standards and Metrology, we present a generalization of the recent
Hyper-Ramsey spectroscopy with separated oscillating fields using composites
pulses in order to suppress field frequency shifts induced by the interrogation
laser itself. Sequences of laser pulses including specific selection of phases,
frequency detunings and durations are elaborated to generate spectroscopic
signals with a strong reduction of the light-shift perturbation by off resonant
states. New optical clocks based on weakly allowed or completely forbidden
transitions in atoms, ions, molecules and nuclei will benefit from these
generalized Ramsey schemes to reach relative accuracies well below the
10 level.Comment: accepted as proceedings of the 8th Symposium on Frequency Standards
and Metrology (Potsdam Germany, 12-16 october 2015
Oxygen diffusion and reactivity at low temperature on bare amorphous olivine-type silicate
The mobility of O atoms at very low temperatures is not generally taken into
account, despite O diffusion would add to a series of processes leading to the
observed rich molecular diversity in space. We present a study of the mobility
and reactivity of O atoms on an amorphous silicate surface. Our results are in
the form of RAIRS and temperature-programmed desorption spectra of O2 and O3
produced via two pathways: O + O and O2 + O, investigated in a submonolayer
regime and in the range of temperature between 6.5 and 30 K. All the
experiments show that ozone is formed efficiently on silicate at any surface
temperature between 6.5 and 30 K. The derived upper limit for the activation
barriers of O + O and O2 + O reactions is 150 K/kb. Ozone formation at low
temperatures indicates that fast diffusion of O atoms is at play even at 6.5 K.
Through a series of rate equations included in our model, we also address the
reaction mechanisms and show that neither the Eley Rideal nor the Hot atom
mechanisms alone can explain the experimental values. The rate of diffusion of
O atoms, based on modeling results, is much higher than the one generally
expected, and the diffusive process proceeds via the Langmuir-Hinshelwood
mechanism enhanced by tunnelling. In fact, quantum effects turn out to be a key
factor that cannot be neglected in our simulations. Astrophysically, efficient
O3 formation on interstellar dust grains would imply the presence of huge
reservoirs of oxygen atoms. Since O3 is a reservoir of elementary oxygen, and
also of OH via its hydrogenation, it could explain the observed concomitance of
CO2 and H2O in the ices.Comment: 28 pages, 14 figure
Propagation of heavy baryons in heavy-ion collisions
The drag and diffusion coefficients of heavy baryons ( and
) in the hadronic phase created in the latter stage of the heavy-ion
collisions at RHIC and LHC energies have been evaluated recently. In this work
we compute some experimental observables, such as the nuclear suppression
factor and the elliptic flow of heavy baryons at RHIC and LHC
energies, highlighting the role of the hadronic phase contribution to these
observables, which are going to be measured at Run 3 of LHC. For the time
evolution of the heavy quarks in the QGP and heavy baryons in the hadronic
phase we use the Langevin dynamics. For the hadronization of the heavy quarks
to heavy baryons we employ Peterson fragmentation functions. We observe a
strong suppression of both the and . We find that the
hadronic medium has a sizable impact on the heavy-baryon elliptic flow whereas
the impact of hadronic medium rescattering is almost unnoticeable on the
nuclear suppression factor. We evaluate the ratio at RHIC and
LHC. We find that ratio remain unaffected due to the hadronic
phase rescattering which enable it as a nobel probe of QGP phase dynamics along
with its hadronization.Comment: 22 pages, 15 figure
First record of Sphaeralcea bonariensis (Cav.) Griseb. (Malvaceae) as a casual alien species in the Mediterranean area
Sphaeralcea bonariensis (Cav.) Griseb. is here reported for the first time as alien species in Italy and in the Mediterranean area. It is a perennial shrub native to Southern America, where it is often considered a ruderal species frequent in cultivated areas. It was found in a population of a few individuals within Opuntia ficus-indica groves of Rocca Palumba territory (Western Sicily). Actually, due to short-term observational period and the low number of plants, Sphaeralcea bonariensis should be considered as a casual species in Italy. The ecological characteristics of the growing stand and the consistency of the population, as well as the possible causes of its introduction, are briefly discussed
On optical activity of Er⁺³ ions in Si-rich SiO₂ waveguides
Photoluminescence spectroscopy was used to explore the optical activity of Er³⁺ ions in Si-rich SiO₂waveguides prepared by ion implantation. Measurements were performed for a series of materials characterized by different Si excess levels, Er concentrations, and annealing temperatures. The highest fraction of optically active Er³⁺ ions which can be efficiently activated by nonresonant pumping was found to be 2.6%. This was realized in a waveguide with an Er concentration of [Er]=10¹⁸cm⁻³ and Si excess of 20%, annealed at 900°C. This optical activity level is insufficient to realize optical gain. It is therefore clear that further material improvement is needed before optical amplification in SiO₂:Er matrices sensitized by Si nanocrystals/nanoclusters can be achieved
The Geochemistry of the melilite-bearing lavas of the Nyiragongo volcanic complex (D.R. Congo)
A phenobarbital overdose: a case report
Background: Phenobarbital is a long-acting barbiturate,
responsible for many cases of poisoning, from unintentional
overdose or attempted suicide. We report a case of phenobarbital
overdose in a patient with history of depression.
Patients and Methods: A 60 year old woman was admitted to
our Internal Medicine Unit for drowsiness, irritability, difficulties in
the maintenance of an upright position, dysphasia and weakness.
She was suffering from depression and epilepsy and treated with
phenobarbital 150 mg/die.
Results: At the admittance, she had high fever and neck stiffness;
phenobarbital serum levels were 71.2 mcg/ml (3 times u.n.l.);
aminotransferases were 12-17u.n.l. Arterial blood pressure was
80/50 mmHg. An inflammatory meningeal process was excluded
by lumbar puncture; a brain and spinal cord CT scan excluded
spine bone lesions and ischemic stroke. In the suspect of an
overdose, a protocol of urine alkalinization was applied resulting
in a reduction of phenobarbital levels below the therapeutic range
in about 6 days, with state of consciousness, cognitive and
behavioral functions improvement. A rapid normalization in
aminotransferases levels was noted and serology for hepatitis
viruses (HAV, HBV, CMV, EBV, HSV) resulted negative.
Conclusions: In our patient phenobarbital was responsible for
stupor, hypotension, hypertonicity and aminotransferases
elevation, whereas fever was due to a concomitant pulmonary
inflammatory process resolved after antibiotic therapy. Despite the
use of these drugs has been progressively reduced, the number
overdose reports remains still hig
Geothermal resources within carbonate reservoirs in western Sicily (Italy): A review
Low-to-medium temperature fluid reservoirs hosted in carbonate rocks are some of the most promising and unknown geothermal systems. Western Sicily is considered a key exploration area. This paper illustrate a multidisciplinary and integrated review of the existing geological, geochemical and geophysical data, mainly acquired during oil and gas explorations since the 1950s, specifically re-analyzed for geothermal purposes, has led to understanding the western Sicily geothermal system as a whole, and to reconstructing the modalities and particular features of the deep fluid circulation within the regional reservoir. The data review suggests the presence of wide groundwater flow systems in the reservoir beneath impervious cap rocks. We identified the main recharge areas, reconstructed the temperature distribution at depth, recognized zones of convective geothermal flow, and depicted the main geothermal fluid flow paths within the reservoir.
We believe that our reconstruction of geothermal fluid circulation is an example of the general behavior of low-to-medium enthalpy geothermal systems hosted in carbonate units on a regional scale. Due to the recent technological developments of binary plants, these systems have become more profitable, not only for geothermal direct uses but also for power production
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