276 research outputs found
On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg II k
line at 2796.34 A. The work is based on a selection of 230 stars observed by
both the IUE and HIPPARCOS satellites, covering a wide range of spectral type
and absolute visual magnitudes. The Wilson-Bappu relationship here provided is
considered to represent an improvement over previous recent results for the
considerably larger data sample used as well as for a proper consideration of
the measurement errors. No evidence has been found for a possible dependence of
the WB effect on stellar metallicity and effective temperature.Comment: 8 pages, 8 figures Accepted for publication on A&
A study of the Mg II 2796.34 A emission line in late--type normal, and RS CVn stars
We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars
and make a comparison with the normal stars studied in a previous paper (Paper
I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS
parallaxes and observed at high resolution with IUE. We confirm that RS CVn
stars tend to possess wider Mg II lines than normal stars having the same
absolute visual magnitude. However, we could not find any correlation between
the logarithmic line width log Wo and the absolute visual magnitude Mv (the
Wilson--Bappu relationship) for these active stars, contrary to the case of
normal stars addressed in Paper I. On the contrary, we find that a strong
correlation exists in the (Mv, log L) plane (L is the absolute flux in the
line). In this plane, normal and RS CVn stars are distributed along two nearly
parallel straight lines with RS CVn stars being systematically brighter by
about 1 dex. Such a diagram provides an interesting tool to discriminate active
from normal stars. We finally analyse the distribution of RS CVn and of normal
stars in the (log L, log Wo) plane, and find a strong linear correlation for
normal stars, which can be used for distance determinations.Comment: 10 pages, 7 figures, latex, to be published in A&
Stochastic simulation of destruction processes in self-irradiated materials
Self-irradiation damages resulting from fission processes are common
phenomena observed in nuclear fuel containing (NFC) materials. Numerous
-decays lead to local structure transformations in NFC materials. The
damages appearing due to the impacts of heavy nuclear recoils in the subsurface
layer can cause detachments of material particles. Such a behaviour is similar
to sputtering processes observed during a bombardment of the material surface
by a flux of energetic particles. However, in the NFC material, the impacts are
initiated from the bulk. In this work we propose a two-dimensional mesoscopic
model to perform a stochastic simulation of the destruction processes occurring
in a subsurface region of NFC material. We describe the erosion of the material
surface, the evolution of its roughness and predict the detachment of the
material particles. Size distributions of the emitted particles are obtained in
this study. The simulation results of the model are in a qualitative agreement
with the size histogram of particles produced from the material containing
lava-like fuel formed during the Chernobyl nuclear power plant disaster.Comment: 11 pages, 8 figure
Entropy: From Black Holes to Ordinary Systems
Several results of black holes thermodynamics can be considered as firmly
founded and formulated in a very general manner. From this starting point we
analyse in which way these results may give us the opportunity to gain a better
understanding in the thermodynamics of ordinary systems for which a
pre-relativistic description is sufficient. First, we investigated the
possibility to introduce an alternative definition of the entropy basically
related to a local definition of the order in a spacetime model rather than a
counting of microstates. We show that such an alternative approach exists and
leads to the traditional results provided an equilibrium condition is assumed.
This condition introduces a relation between a time interval and the reverse of
the temperature. We show that such a relation extensively used in the black
hole theory, mainly as a mathematical trick, has a very general and physical
meaning here; in particular its derivation is not related to the existence of a
canonical density matrix. Our dynamical approach of thermodynamic equilibrium
allows us to establish a relation between action and entropy and we show that
an identical relation exists in the case of black holes. The derivation of such
a relation seems impossible in the Gibbs ensemble approach of statistical
thermodynamics. From these results we suggest that the definition of entropy in
terms of order in spacetime should be more general that the Boltzmann one based
on a counting of microstates. Finally we point out that these results are
obtained by reversing the traditional route going from the Schr\"{o}dinger
equation to statistical thermodynamics
The real-time earthquake monitoring system in Italy
As regards the transmission vectors – one of the most
critical points of a seismic network – we adopted a
mixed strategy: half of the stations are connected
through satellite links, and half through cable links.
The use of satellite transmission presents several
advantages: the link is very robust, the constraints
for site selection are weak, and the cost is lower
than telephone lines. As regards the terrestrial cable
links, we use INGV digitizers (named GAIA), protected
IP connections of the Italian Public Administration
Network (RUPA): site selection is more delicate, and a
compromise must be found between low environmental
noise and availability of network infrastructures
Brafv600e and Ctbn1 Mutational Study in Rathke's Cleft Cysts
Aim: Rathke's cleft cysts and craniopharyngiomas tipically involve sellar region and their histogenetic relationship
is still matter of debate. Clinical and histopathologic differentiation of cystic lesions from the sellar region, that is,
craniopharyngiomas (CPs) and Rathke cleft cysts (RCCs), is challenging and has great importance with respect to
variable clinical manifestation and adapted surgical treatment strategies in both entities. The recent acquisition that
adamantinomatous and papillary craniopharyngiomas bear distinct molecular alterations i.e., β-catenin (CTNNB1)
and BRAFv600 mutations respectively, has suggest to screen for such alteration a series of Rathke cyst to seek a
possible relation with one of the two craniopharyngioma type.
Methods: Seven Rathke's cleft cysts were analyzed for BRAF and CTNNB1 mutational status by sequencing and
immunohistochemistry. Radiological, clinical and histological features were performed.
Results: None of the 7 Rathke's cleft cysts harbor BRAFV600E mutation. No CTNNB1 mutation was found.
Radiological, clinical and histological re-evaluation of the cases confirmed the diagnosis of Rathke's cleft cysts.
Conclusion: BRAFV600E and CTNNB1 mutations appeared, as most reliable factor for the differentiation
between purely cystic CPs and RCCs, whereas tumor location, tumor size, and radiological parameter of the tumor
were less consistent parameters. This study again confirms that craniopharyngiomas (CPs) and Rathke cleft cysts
(RCCs), are associated with distinct pathogenic pathways
Clinical Management of Acinic Cell Carcinoma of the Lacrimal Gland
To report a case of acinic cell carcinoma occurred in the lacrimal gland. A 59-year-old man was admitted because of sudden blurring of vision, progressive proptosis of the left eye, and mild double vision in left and down directions of the gaze (Hess-Lancaster test). His medical history detailed controlled bilateral keratoconus and open angle glaucoma. On examination, the best corrected visual acuity decreased from 8/20 till 1/50 in one week. There was a swelling of the left upper eyelid. A hard and tender mass was palpated in the superior temporal left orbit. Ultrasound scan showed an extraconal solid mass, situated in the superior lateral corner of the orbit. Computed tomography and magnetic resonance imaging (MRI) revealed a mass of two centimeters in diameter, with round well-defined outline, within the lacrimal gland. We per-formed an enucleoresection of the mass, via a coronal approach and a lateral orbitotomy by a piezosurgical device. The lesion appeared nodular, brownish, measuring about 2
7 1.5 cm. Histopathological findings were consistent with acinic cell carcinoma with a microcystic, focally papillary-cystic growth of pattern. Follow-up MRI outcomes led to removal of the residual lacrimal gland for suspicion of recurrence. No tumor recurrences where detected at 7-year follow-up
AEducaAR, Anatomical Education in Augmented Reality: A Pilot Experience of an Innovative Educational Tool Combining AR Technology and 3D Printing
Gross anatomy knowledge is an essential element for medical students in their education, and nowadays, cadaver-based instruction represents the main instructional tool able to provide three-dimensional (3D) and topographical comprehensions. The aim of the study was to develop and test a prototype of an innovative tool for medical education in human anatomy based on the combination of augmented reality (AR) technology and a tangible 3D printed model that can be explored and manipulated by trainees, thus favoring a three-dimensional and topographical learning approach. After development of the tool, called AEducaAR (Anatomical Education with Augmented Reality), it was tested and evaluated by 62 second-year degree medical students attending the human anatomy course at the International School of Medicine and Surgery of the University of Bologna. Students were divided into two groups: AEducaAR-based learning (“AEducaAR group”) was compared to standard learning using human anatomy atlas (“Control group”). Both groups performed an objective test and an anonymous questionnaire. In the objective test, the results showed no significant difference between the two learning methods; instead, in the questionnaire, students showed enthusiasm and interest for the new tool and highlighted its training potentiality in open-ended comments. Therefore, the presented AEducaAR tool, once implemented, may contribute to enhancing students’ motivation for learning, increasing long-term memory retention and 3D comprehension of anatomical structures. Moreover, this new tool might help medical students to approach to innovative medical devices and technologies useful in their future careers
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