3,094 research outputs found
Mathematical Model of Easter Island Society Collapse
In this paper we consider a mathematical model for the evolution and collapse
of the Easter Island society, starting from the fifth century until the last
period of the society collapse (fifteen century). Based on historical reports,
the available primary sources consisted almost exclusively on the trees. We
describe the inhabitants and the resources as an isolated system and both
considered as dynamic variables. A mathematical analysis about why the
structure of the Easter Island community collapse is performed. In particular,
we analyze the critical values of the fundamental parameters driving the
interaction humans-environment and consequently leading to the collapse. The
technological parameter, quantifying the exploitation of the resources, is
calculated and applied to the case of other extinguished civilization (Cop\'an
Maya) confirming, with a sufficiently precise estimation, the consistency of
the adopted model.Comment: 9 pages, 1 figure, final version published on EuroPhysics Letter
Aging and Rejuvenation with Fractional Derivatives
We discuss a dynamic procedure that makes the fractional derivatives emerge
in the time asymptotic limit of non-Poisson processes. We find that two-state
fluctuations, with an inverse power-law distribution of waiting times, finite
first moment and divergent second moment, namely with the power index mu in the
interval 2<mu <3, yields a generalized master equation equivalent to the sum of
an ordinary Markov contribution and of a fractional derivative term. We show
that the order of the fractional derivative depends on the age of the process
under study. If the system is infinitely old, the order of the fractional
derivative, ord, is given by ord=3-mu . A brand new system is characterized by
the degree ord=mu -2. If the system is prepared at time -ta<0$ and the
observation begins at time t=0, we derive the following scenario. For times
0<t<<ta the system is satisfactorily described by the fractional derivative
with ord=3-mu . Upon time increase the system undergoes a rejuvenation process
that in the time limit t>>ta yields ord=mu -2. The intermediate time regime is
probably incompatible with a picture based on fractional derivatives, or, at
least, with a mono-order fractional derivative.Comment: 11 pages, 4 figure
The low-frequency radio catalog of flat spectrum sources
A well known property of the gamma-ray sources detected by COS-B in the
1970s, by the Compton Gamma-ray Observatory in the 1990s and recently by the
Fermi observations is the presence of radio counterparts, in particular for
those associated to extragalactic objects. This observational evidence is the
basis of the radio-gamma-ray connection established for the class of active
galactic nuclei known as blazars. In particular, the main spectral property of
the radio counterparts associated with gamma-ray blazars is that they show a
flat spectrum in the GHz frequency range. Our recent analysis dedicated to
search blazar-like candidates as potential counterparts for the unidentified
gamma-ray sources (UGSs) allowed us to extend the radio-gamma-ray connection in
the MHz regime. We also showed that below 1 GHz blazars maintain flat radio
spectra. Thus on the basis of these new results, we assembled a low-frequency
radio catalog of flat spectrum sources built by combining the radio
observations of the Westerbork Northern Sky Survey (WENSS) and of the
Westerbork in the southern hemisphere (WISH) catalog with those of the NRAO
Very Large Array Sky survey (NVSS). This could be used in the future to search
for new, unknown blazar-like counterparts of the gamma-ray sources. First we
found NVSS counterparts of WSRT radio sources and then we selected flat
spectrum radio sources according to a new spectral criterion specifically
defined for radio observations performed below 1 GHz. We also described the
main properties of the catalog listing 28358 radio sources and their logN-logS
distributions. Finally a comparison with with the Green Bank 6-cm radio source
catalog has been performed to investigate the spectral shape of the
low-frequency flat spectrum radio sources at higher frequencies.Comment: 10 pages, 10 figures, 1 table, ApJS published in 2014 (pre-proof
version uploaded
Integrating Dynamics and Wear Modelling to Predict Railway Wheel Profile Evolution
The aim of the work described was to predict wheel
profile evolution by integrating multi-body dynamics
simulations of a wheelset with a wear model.
The wear modelling approach is based on a wear
index commonly used in rail wear predictions. This
assumes wear is proportional to TÎł, where T is tractive
force and Îł is slip at the wheel/rail interface. Twin disc
testing of rail and wheel materials was carried out to
generate wear coefficients for use in the model.
The modelling code is interfaced with
ADAMS/Rail, which produces multi-body dynamics
simulations of a railway wheelset and contact conditions
at the wheel/rail interface. Simplified theory of rolling
contact is used to discretise the contact patches
produced by ADAMS/Rail and calculate traction and
slip within each.
The wear model combines the simplified theory of
rolling contact, ADAMS/Rail output and the wear
coefficients to predict the wear and hence the change of
wheel profile for given track layouts
Optical spectroscopic observations of blazars and gamma-ray blazar candidates in the Sloan Digital Sky Survey Data Release Nine
We present an analysis of the optical spectra available in the Sloan Digital
Sky survey data release nine (SDSS DR9) for the blazars listed in the
ROMA-BZCAT and for the gamma-ray blazar candidates selected according to their
IR colors. First, we adopt a statistical approach based on MonteCarlo
simulations to find the optical counterparts of the blazarslisted in the
ROMA-BZCAT catalog. Then we crossmatched the SDSS spectroscopic catalog with
our selected samples of blazars and gamma-ray blazar candidates searching for
those with optical spectra available to classify our blazar-like sources and,
whenever possible, to confirm their redshifts. Our main objectives are
determining the classification of uncertain blazars listed in the ROMA-BZCAT
and discovering new gamma-ray blazars. For the ROMA-BZCAT sources we
investigated a sample of 84 blazars confirming the classification for 20 of
them and obtaining 18 new redshift estimates. For the gamma-ray blazars,
indicated as potential counterparts of unassociated Fermi sources or with
uncertain nature, we established the blazar-like nature of 8 out the 27 sources
analyzed and confirmed 14 classifications.Comment: 7 pages, 2 figures, 4 tables, AJ published in 2014 (pre-proof
version
A first assessment of genetic variability in the longhorn beetle Rosalia alpina (Coleoptera: Cerambycidae) from the Italian Apennines
The Rosalia longicorn (Rosalia alpina) is a strictly protected saproxylic beetle, widely distributed in Central and Southern Europe and mainly associated with ancient beech forests. To improve knowledge about the conservation status of R. alpina in Italy, available molecular markers (microsatellites and mitochondrial cytochrome c oxidase I(COI)) were tested for the first time on Italian populations. The study was performed in four sampling sites distributed in two areas placed in Northern (“Foreste Casentinesi” National Park) and Central Apennines (“Abruzzo, Lazio and Molise” National Park) where populational data about Rosalia longicorn were collected in the framework of the European LIFE MIPP Project. The genetic relationship among Apennine and Central/South-eastern European populations was explored by a comparison with mitochondrial DNA (mtDNA) data from literature. Microsatellite markers were only partially informative when applied to R. alpina Italian individuals, although providing some preliminary indication on an extensive gene flow among populations from the Apennines and local ongoing processes of genetic erosion. Genetic data are consistent with previous ecological data suggesting that the maintenance of variability in this species could be related to both habitat continuity and preservation of large senescent or standing dead trees in forests. Finally, a peculiar origin of the Apennine populations of R. alpina from a putative “Glacial Refugium” in Italy was inferred through COI data. The high genetic distance scored among the analysed populations and those from Central and South-eastern Europe indicates that the R. alpina deme from Apennine Mountains might represent a relevant conservation unit in Europe. Further genetic analyses will allow assessing other possible conservation units of R. alpina and, thus, defining large-scale conservation strategies to protect this endangered longhorn beetle in Europe
Results of low energy background measurements with the Liquid Scintillation Detector (LSD) of the Mont Blanc Laboratory
The 90 tons liquid scintillation detector (LSD) is fully running since October 1984, at a depth of 5,200 hg/sq cm of standard rock underground. The main goal is to search for neutrino bursts from collapsing stars. The experiment is very sensitive to detect low energy particles and has a very good signature to gamma-rays from (n,p) reaction which follows the upsilon e + p yields n + e sup + neutrino capture. The analysis of data is presented and the preliminary results on low energy measurements are discussed
Il background glottologico e orientalistico di un latinista dell’Accademia scientifico-letteraria: note sull’opera di Carlo Giussani
This paper analyses the figure and the work of the XIX century scholar Carlo Giussani, focusing on his earlier formation as a linguist and orientalist. Although he later became a Latin scholar (he is mostly known for his comment on Lucrece\u2019s De rerum natura), he started his studies at the Accademia Scientifico-Letteraria of Milan under the supervision of G. I. Ascoli, who addressed him to the study of the Indo-Iranian languages. The paper outlines Giussani\u2019s linguistic thought taking into account his first works, professedly devoted to Indo-Iranian topics, as well as other traces of his interest in linguistic matters, which are found in later works. The aim of the paper is to highlight the relevant role played by Giussani\u2019s formation as a linguist throughout his entire scholarly career
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