5,093 research outputs found
On the Paramagnetic Impurity Concentration of Silicate Glasses from Low-Temperature Physics
The concentration of paramagnetic trace impurities in glasses can be
determined via precise SQUID measurements of the sample's magnetization in a
magnetic field. However the existence of quasi-ordered structural
inhomogeneities in the disordered solid causes correlated tunneling currents
that can contribute to the magnetization, surprisingly, also at the higher
temperatures. We show that taking into account such tunneling systems gives
rise to a good agreement between the concentrations extracted from SQUID
magnetization and those extracted from low-temperature heat capacity
measurements. Without suitable inclusion of such magnetization contribution
from the tunneling currents we find that the concentration of paramagnetic
impurities gets considerably over-estimated. This analysis represents a further
positive test for the structural inhomogeneity theory of the magnetic effects
in the cold glasses.Comment: 27 pages, 11 figures, 10 tables, 41 references: submitted to Journal
of Low Temperature Physic
Global existence for a nonlocal model for adhesive contact
In this paper we address the analytical investigation of a model for adhesive
contact, which includes nonlocal sources of damage on the contact surface, such
as the elongation. The resulting PDE system features various nonlinearities
rendering the unilateral contact conditions, the physical constraints on the
internal variables, as well as the integral contributions related to the
nonlocal forces. For the associated initial-boundary value problem we obtain a
global-in-time existence result by proving the existence of a local solution
via a suitable approximation procedure and then by extending the local solution
to a global one by a nonstandard prolongation argument
Humans and dolphins: Decline and fall of adult neurogenesis
Pre-clinical research is carried out on animal models, mostly laboratory rodents, with the ultimate aim of translating the acquired knowledge to humans. In the last decades, adult neurogenesis (AN) has been intensively studied since it is viewed as a tool for fostering brain plasticity, possibly repair. Yet, occurrence, location, and rate of AN vary among mammals: the capability for constitutive neuronal production is substantially reduced when comparing small-brained, short living (laboratory rodents) and large-brained, long-living species (humans, dolphins). Several difficulties concerning scarce availability of fresh tissues, technical limits and ethical concerns did contribute in delaying and diverting the achievement of the picture of neurogenic plasticity in large-brained mammals. Some reports appeared in the last few years, starting to shed more light on this issue. Despite technical limits, data from recent studies mostly converge to indicate that neurogenesis is vestigial, or possibly absent, in regions of the adult human brain where in rodents neuronal addition continues into adult life. Analyses carried out in dolphins, mammals devoid of olfaction, but descendant of ancestors provided with olfaction, has shown disappearance of neurogenesis in both neonatal and adult individuals. Heterogeneity in mammalian structural plasticity remains largely underestimated by scientists focusing their research in rodents. Comparative studies are the key to understand the function of AN and the possible translational significance of neuronal replacement in humans. Here, we summarize comparative studies on AN and discuss the evolutionary implications of variations on the recruitment of new neurons in different regions and different species
Age consistency between exoplanet hosts and field stars
Transiting planets around stars are discovered mostly through photometric
surveys. Unlike radial velocity surveys, photometric surveys do not tend to
target slow rotators, inactive or metal-rich stars. Nevertheless, we suspect
that observational biases could also impact transiting-planet hosts. This paper
aims to evaluate how selection effects reflect on the evolutionary stage of
both a limited sample of transiting-planet host stars (TPH) and a wider sample
of planet-hosting stars detected through radial velocity analysis. Then, thanks
to uniform derivation of stellar ages, a homogeneous comparison between
exoplanet hosts and field star age distributions is developed. Stellar
parameters have been computed through our custom-developed isochrone placement
algorithm, according to PARSEC models. The notable aspects of our algorithm
include the treatment of element diffusion, activity checks in terms of
and , and the evaluation of the stellar evolutionary
speed in the Hertzsprung-Russel diagram in order to better constrain age.
Working with TPH, the observational stellar mean density allows
us to compute stellar luminosity even if the distance is not available, by
combining with the spectroscopic . The median value of
the TPH ages is Gyr. Even if this sample is not very large, however,
the result is very similar to what we found for the sample of spectroscopic
hosts, whose modal and median values are [3, 3.5) Gyr and Gyr,
respectively. Thus, these stellar samples suffer almost the same selection
effects. We also conclude that the age of our Sun is consistent with the age
distribution of solar neighbourhood MS stars with spectral types from late F to
early K, regardless of whether they harbour planets or not. We considered the
possibility that our selected samples are older than the average disc
population.Comment: 13 pages, 1 longtable, 9 figures. Accepted by A&
Star formation and dust extinction in nearby star forming and starburst galaxies
We study the star formation rate and dust extinction properties of a sample
of nearby star forming galaxies as derived from Halpha and UV (2000 A)
observations and we compare them to those of a sample of starburst galaxies.
The dust extinction in Halpha is estimated from the Balmer decrement and the
extinction in UV using the FIR to UV flux ratio or the attenuation law for
starburst galaxies of Calzetti et al. The Halpha and UV emissions are strongly
correlated with a very low scatter for the star forming objects and with a much
higher scatter for the starburst galaxies. The Halpha to UV flux ratio is found
larger by a factor ~ 2 for the starburst galaxies. We compare both samples with
a purely UV selected sample of galaxies and we conclude that the mean Halpha
and UV properties of nearby star forming galaxies are more representative of UV
selected galaxies than starburst galaxies.
We emphasize that the Halpha to UV flux ratio is strongly dependent on the
dust extinction: the positive correlation found between F{Halpha}/F{UV}$ and
F{FIR}/F{UV} vanishes when the Halpha and UV flux are corrected for dust
extinction. The Halpha to UV flux ratios converted into star formation rate and
combined with the Balmer decrement measurements are tentatively used to
estimate the dust extinction in UV.Comment: accepted for publication in Astronomy & Astrophysic
Revising the ages of planet-hosting stars
This article aims to measure the age of planet-hosting stars (SWP) through
stellar tracks and isochrones computed with the \textsl{PA}dova \&
T\textsl{R}ieste \textsl{S}tellar \textsl{E}volutionary \textsl{C}ode (PARSEC).
We developed algorithms based on two different techniques for determining the
ages of field stars: \emph{isochrone placement} and \emph{Bayesian estimation}.
Their application to a synthetic sample of coeval stars shows the intrinsic
limits of each method. For instance, the Bayesian computation of the modal age
tends to select the extreme age values in the isochrones grid. Therefore, we
used the isochrone placement technique to measure the ages of 317 SWP. We found
that of SWP have ages lower than 0.5 Gyr. The age distribution peaks
in the interval [1.5, 2) Gyr, then it decreases. However, of the
stars are older than 11 Gyr. The Sun turns out to be a common star that hosts
planets, when considering its evolutionary stage. Our SWP age distribution is
less peaked and slightly shifted towards lower ages if compared with ages in
the literature and based on the isochrone fit. In particular, there are no ages
below 0.5 Gyr in the literature.Comment: 16 pages, 18 figures. Accepted by A&
Gestione di una flotta di veicoli di un sistema car-sharing: applicazione al centro urbano di Genova
Storia del car-sharing
Descrizione del sistema di trasporto in modalità car-sharing proposto
Descrizione del centro storico di Genova: territorio, trasporto pubblico, sosta
Modellazione del sistema PICAV applicato al centro storico di Genova
Simulazione del sistema PICAV tramite programma ad oggetti: Python
Conclusion
'From Zionism to Communism': Emilio Sereni and the Consiglio di Gestione in postwar Italy
This essay demonstrates that it is impossible to appreciate the actions of the Italian communist Emilio Sereni without considering his Zionist background. Anyone who is interested in understanding the complexities of communism in the past century and to avoid simplistic conclusions about this ideology will benefit from the study. The problem at stake is that researchers often approach communism in a monolithic manner, which does not adequately explain the multiform manifestations (practical and theoretical) of that phenomenon. This ought to change and to this extent this essay hopes to contribute to that recent strand of historical research that challenges simplistic views on communism. More specifically, by analysing the Management Councils that Sereni created in postwar Italy, we can see that many of their features in fact derived from, or found their deepest origins in, his previous experience as a committed socialist Zionist. The study, then, also relates Sereni to and looks at the broader experiences of early twentieth-century Zionism and Italian communism in the early postwar years
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