233 research outputs found
SOFT X-RAY IRRADIATION OF PURE CARBON MONOXIDE INTERSTELLAR ICE ANALOGUES
There is an increasing evidence for the existence of large organic molecules
in the interstellar and circumstellar medium. Very few among such species are
readily formed in conventional gas-phase chemistry under typical conditions of
interstellar clouds. Attention has therefore focused on interstellar ices as a potential
source of these relatively complex species. Laboratory experiments show
that irradiation of interstellar ice analogues by fast particles or ultraviolet radiation
can induce significant chemical complexity. However, stars are sources of
intense X-rays at almost every stage of their formation and evolution. Such radiation
may thus provide chemical changes in regions where ultraviolet radiation
is severely inhibited.
After H2O, CO is often the most abundant component of icy grain mantles in
dense interstellar clouds and circumstellar disks. In this work we present irradiation
of a pure carbon monoxide ice using a soft X-ray spectrum peaked at 0.3 keV.
Analysis of irradiated samples shows formation of CO2, C2O, C3O2, C3, C4O and
CO3/C5. Comparison of X-rays and ultraviolet irradiation experiments, of the
same energy dose, show that X-rays are more efficient than ultraviolet radiation
in producing new species. With the exception of CO2, X-ray photolysis induces
formation of a larger number of products with higher abundances, e.g., C3O2
column density is about one order of magnitude higher in the X-ray experiment.
To our knowledge this is the first report on X-ray photolysis of CO ices. The
present results show that X-ray irradiation represents an efficient photo-chemical
way to convert simple ices to more complex species
Geochemistry of phosphatic nodules as a tool for understanding depositional and taphonomical settings in a paleolithic cave site (San teodoro, Sicily)
Interpreting depositional settings of cave sites is generally problematic, especially in absence of paleontological/archaeological evidence. This is the case of some deposits at San Teodoro Cave (Sicily), a key site for the Mediterranean Paleolithic. In a stratigraphic level interrupted by a carbonatic concretion, phosphatic nodules are present only in the part enclosed between the concretion and the cave wall. The discovery of these nodules combined with the punctual lack of fossils had initially suggested an erosion phenomenon and subsequent formation of nodules at a vadose level. Here we show the usefulness of an integrated, geochemical-paleoecological approach in defining stratigraphy and paleoenvironmental reconstructions. XRD, ICP-OES, ATR-FTIR and EDS analyses allowed the formulation of a new hypothesis regarding the origin of the nodules, the depositional dynamics, and the role played by the guano produced by an extensive colony of bats. The role of barium and rubidium in detecting taphonomical processes has been highlighted
QT Indexes in Cirrhotic Patients: Relationship with Clinical Variables and Potential Diagnostic Predictive Value.
BACKGROUND AND AIMS:
A wide spectrum of cardiovascular changes characterizes cirrhosis, ranging from subclinical alterations to hyperkinetic syndrome. We looked for ECG markers of ventricular repolarization in a population of patients with cirrhosis in comparison to patients without cirrhosis and we investigated the relationship between these and other clinical and laboratory variables.
METHODS:
In 149 patients with cirrhosis and 152 controls, we measured QT maximum interval (QTmax), QT corrected interval (QTc), QT minimum interval (QTmin), QT dispersion (QTdisp), QT peak and T peak-to-end (TpTe).
RESULTS:
In subjects with cirrhosis, in comparison with controls, we observed a higher mean QTmax, mean QTc, mean QTmin, mean QTdisp and mean TpTe. At Cox regression analysis, diastolic blood pressure and beta-blocker treatment were significantly associated with mean QTmax, hypertension with mean QTmin and mean QTc, diastolic blood pressure, beta-blockers and ACE-inhibitors/ARBs with QT disp, and beta-blockers with TpTe. Analysis of ROC curves showed a significant area under curve towards cirrhosis diagnosis, respectively, for a cut-off value of >400 msec of QTmax, >360 msec of QTmin, >450 msec of QTc, >105 msec of TpTe and >55 msec of QTdisp
Lithium and age of pre-main sequence stars: The case of Parenago 1802
With the aim to test the present capability of the stellar surface lithium abundance in providing an estimation for the age of PMS stars, we analyze the case of the detached, double-lined, eclipsing binary system PAR 1802. For this system, the lithium age has been compared with the theoretical one, as estimated by applying a Bayesian analysis method on a large grid of stellar evolutionary models. The models have been computed for several values of chemical composition and mixing length, by means of the code FRANEC updated with the Trojan Horse reaction rates involving lithium burning
BeppoSAX observations of 3C 273
We present preliminary results of BeppoSAX AO1 observations of 3C 273
performed in January 1997. We also present a close comparison with data
obtained during the satellite SVP, in July 1996. On average, the AO1 flux is
about a factor 2 higher than the flux detected during the SVP, and roughly on
the middle of the historical X-ray flux range. Power law fits with galactic
absorption to all observations yield spectral indices in the range 1.53-1.6,
with the spectrum extending from 0.2 to at least up to 200 keV without any
significant slope change. The broad band spectrum appears basically
featureless, marking a clear difference from the SVP data, where an absorption
feature at low energy and a fluorescence iron emission line are present. The
lack of cold/warm matter signatures in our data may indicate that, at this
"high" level of luminosity, the featureless continuum produced in a
relativistic jet overwhelms any thermal and/or reprocessing component, while
the two components were at least comparable during the "low" state of July
1996.Comment: 1+4 pages, 3 ps inlined figures, espcrc2.sty. Proc. of the Conf. "The
Active X-Ray Sky: Results from BeppoSAX and Rossi-XTE", Rome 21-24 October
199
Progress on the development of the Stellar X-ray Polarimeter on board of the Spectrum-X-Gamma Satellite
We present the status of the Stellar X-ray Polarimeter at November’94 devoted to measure linear polarisation from cosmic X-ray sources between 2 keV and 15 keV which will be flown on the Spectrum-X-Gamma Satellite. In particular, we
focus on the performances of the engineering model after the calibrations at Lawrence Livermore Laboratories and on the improvements which have been introduced on the four flight model imaging proportional counters which are key
parts of the experiment
Extreme Energy Cosmic Rays (EECR) Observation Capabilities of an "Airwatch from Space'' Mission
The longitudinal development and other characteristics of the EECR induced
atmospheric showers can be studied from space by detecting the fluorescence
light induced in the atmospheric nitrogen. According to the Airwatch concept a
single fast detector can be used for measuring both intensity and time
development of the streak of fluorescence light produced by the atmospheric
shower induced by an EECR. In the present communication the detection
capabilities for the EECR observation from space are discussed.Comment: 3 pages (LaTeX). To appear in the Proceedings of TAUP'9
Expected performance of the ASTRI-SST-2M telescope prototype
ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is an
Italian flagship project pursued by INAF (Istituto Nazionale di Astrofisica)
strictly linked to the development of the Cherenkov Telescope Array, CTA.
Primary goal of the ASTRI program is the design and production of an end-to-end
prototype of a Small Size Telescope for the CTA sub-array devoted to the
highest gamma-ray energy region. The prototype, named ASTRI SST-2M, will be
tested on field in Italy during 2014. This telescope will be the first
Cherenkov telescope adopting the double reflection layout in a
Schwarzschild-Couder configuration with a tessellated primary mirror and a
monolithic secondary mirror. The collected light will be focused on a compact
and light-weight camera based on silicon photo-multipliers covering a 9.6 deg
full field of view. Detailed Monte Carlo simulations have been performed to
estimate the performance of the planned telescope. The results regarding its
energy threshold, sensitivity and angular resolution are shown and discussed.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at arXiv:1307.223
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