4,123 research outputs found
Gamma Ray Burst origin and their afterglow: story of a discovery and more
In this paper we review the story of the BeppoSAX discovery of the Gamma Ray
Burst afterglow and their cosmological distance, starting from their first
detection with Vela satellites and from the efforts done before BeppoSAX. We
also discuss the consequences of the BeppoSAX discovery, the issues left open
by BeppoSAX, the progress done up to now and its perspectives.Comment: 31 pages, 14 figures, published in 2011 in the international refereed
journal "La Rivista del Nuovo Cimento" of the Italian Physical Society, vol.
34. The occasion of this review paper was the award of the Fermi Prize 2010
to their authors "For the discovery of the X-ray afterglow of Gamma-Ray Burst
with the BeppoSAX satellite"
(http://www.sif.it/SIF/en/portal/activities/fermi_award
General History of X-Ray Polarimetry in Astrophysics
Soon after the discovery of the first extrasolar X-Ray sources it was
suggested that polarimetry could play a major role as a diagnostic tool.
Attempts to measure polarization of X-Ray sources was performed by the team of
Columbia University lead by Robert Novick. The technique of Bragg diffraction
at 45{\deg} was successful to detect the polarization of the Crab with rockets
and with OSO-8 satellite. In the following evolution of X-Ray Astronomy,
Polarimetry was too mismatched with the improved sensitivity of imaging and
spectroscopy, based on the use of optics. As a consequence no polarimeter was
flown any more. At the beginning of the century a new class of instruments
based on the photoelectric effect were developed. In the focus of an X-Ray
telescope they can perform angular, energy and time resolved polarimetry and
benefit of the large increase of sensitivity due to the optics. The Imaging
X-Ray Polarimetry Explorer, exploiting this technique, was launched at the end
of 2021.Comment: 19 pages, no figure, Invited Chapter for the "Handbook of X-Ray and
Gamma-Ray Astrophysics" (Eds. C.Bambi and A.Santangelo, Springer Singapore,
expected in 2022
Correlation methods for the analysis of X-ray polarimetric signals
X-ray polarimetric measurements are based on studying the distribution of the
directions of scattered photons or photoelectrons and on the search of a
sinusoidal modulation with a period of {\pi}. We developed two tools for
investigating these angular distributions based on the correlations between
counts in phase bins separated by fixed phase distances. In one case we use the
correlation between data separated by half of the bin number (one period) which
is expected to give a linear pattern. In the other case, the scatter plot
obtained by shifting by 1/8 of the bin number (1/4 of period) transforms the
sinusoid in a circular pattern whose radius is equal to the amplitude of the
modulation. For unpolarized radiation these plots are reduced to a random point
distribution centred at the mean count level. This new methods provide direct
visual and simple statistical tools for evaluating the quality of polarization
measurements and for estimating the polarization parameters. Furthermore they
are useful for investigating distortions due to systematic effects
Automating the Generation of Cyber Range Virtual Scenarios with VSDL
A cyber range is an environment used for training security experts and
testing attack and defence tools and procedures. Usually, a cyber range
simulates one or more critical infrastructures that attacking (red) and
defending (blue) teams must compromise and protect, respectively. The
infrastructure can be physically assembled, but much more convenient is to rely
on the Infrastructure as a Service (IaaS) paradigm. Although some modern
technologies support the IaaS, the design and deployment of scenarios of
interest is mostly a manual operation. As a consequence, it is a common
practice to have a cyber range hosting few (sometimes only one), consolidated
scenarios. However, reusing the same scenario may significantly reduce the
effectiveness of the training and testing sessions. In this paper, we propose a
framework for automating the definition and deployment of arbitrarily complex
cyber range scenarios. The framework relies on the virtual scenario description
language (VSDL), i.e., a domain-specific language for defining high-level
features of the desired infrastructure while hiding low-level details. The
semantics of VSDL is given in terms of constraints that must be satisfied by
the virtual infrastructure. These constraints are then submitted to an SMT
solver for checking the satisfiability of the specification. If satisfiable,
the specification gives rise to a model that is automatically converted to a
set of deployment scripts to be submitted to the IaaS provider
Molecular dynamics study on the Apo- and Holo-forms of 5-lipoxygenase
Lipoxygenases (LOXs) are nonheme iron-containing enzymes catalyzing the dioxygenation of polyunsaturated fatty acids. LOX catalytic activity depends on the presence of iron in the active site and the iron removal is also able to affect the membrane binding properties of the enzyme. Leukotrienes biosynthesis is initiated by the action of 5-LOX at the level of nuclear membrane and the mechanism of enzyme-membrane interaction is thought to involve structural flexibility and conformational changes at the level of the protein tertiary structure. In this study, we have analyzed by molecular dynamics simulations the conformational changes induced by iron removal in 5-LOX. The data indicate that the degree of enzyme flexibility is related to the presence of iron into the active site that is able to stabilize the protein increasing its rigidity. These findings provide further evidence that the conformation and the functional activity of LOXs is tuned by the presence of iron at the active site, suggesting new approaches for the design of enzyme inhibitors.Peer ReviewedPostprint (author's final draft
FORS2/VLT survey of Milky Way globular clusters I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8
(abridged) We have observed almost 1/3 of the globular clusters in the Milky
Way, targeting distant and/or highly reddened objects, besides a few reference
clusters. A large sample of red giant stars was observed with FORS2@VLT/ESO at
R ~ 2,000. The method for derivation of stellar parameters is presented with
application to six reference clusters. We aim at deriving the stellar
parameters effective temperature, gravity, metallicity and alpha-element
enhancement, as well as radial velocity, for membership confirmation of
individual stars in each cluster. We analyse the spectra collected for the
reference globular clusters NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and
Terzan 8. They cover the full range of globular cluster metallicities, and are
located in the bulge, disc and halo. Full spectrum fitting techniques are
applied, by comparing each target spectrum with a stellar library in the
optical region at 4560-5860 A. We employed the library of observed spectra
MILES, and the synthetic library by Coelho et al. (2005). Validation of the
method is achieved through recovery of the known atmospheric parameters for 49
well-studied stars that cover a wide range in the parameter space. We adopted
as final stellar parameters (effective temperatures, gravities, metallicities)
the average of results using MILES and Coelho et al. libraries. We identified 4
member stars in NGC 6528, 13 in NGC 6553, 10 in M 71, 5 in NGC 6558, 5 in NGC
6426 and 12 in Terzan 8. Radial velocities, Teff, log(g), [Fe/H] and
alpha-element enhancements were derived. We derived abundances for NGC 6426
from spectroscopy for the first time. The method proved to be reliable for red
giant stars observed with resolution R ~ 2,000, yielding results compatible
with high-resolution spectroscopy. The derived alpha-element abundances show
[A/Fe] vs. [Fe/H] consistent with that of field stars at the same
metallicities.Comment: 22 pages, 21 figures, accepted for publication in A&
Heterogeneous Photocatalysis Remediation of Wastewater Polluted by Indigoid Dyes
Organic dyes constitute one of the largest groups of wastewater’s pollutants. In general, they are released into the environment by textile industries. Approximately 100,000 dyes are widely used in the textile industry, and a large wastewater of dyestuff is generated annually. Among these, indigoid class is commercial dyes used mostly for cotton cloth dyeing. Indigo carmine (IC) is also one of the oldest dyes and still one of the most used in textile industry and is considered as a very toxic indigoid dye. Most toxic dyes are recalcitrant to biodegradation, causing a decrease in the efficiency of biological wastewater treatment plants. Titanium dioxide is a well-known photocatalyst mostly used in suspensions in photoreactions for wastewater treatment. The use of TiO2 has some advantages such as ease of handling, low cost, low toxicity, high photochemical reactivity, and non-specific oxidative attack ability. In this way, it can promote the degradation of different target organic compounds with little change of operational parameters. The aim of this chapter is to present the different approaches already used in our team for the remediation of waters containing IC mainly through heterogeneous photocatalysis with TiO2. Adsorption over activated carbon (AC) and photocatalytic degradation of IC mediated by titanium dioxide will be revised as well as some studies on the phototoxicity of the photoproducts with aquatic and terrestrial organisms. This chapter makes a comprehensive approach to the different results on the remediation of model effluents containing IC undertaken by this team of researchers
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