272 research outputs found
Environmental effects on star formation in dwarf galaxies and star clusters
We develop a simple analytical criterion to investigate the role of the
environment on the onset of star formation. We will consider the main external
agents that influence the star formation (i.e. ram pressure, tidal interaction,
Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy
moving through an external environment. The theoretical framework developed
here has direct applications to the cases of dwarf galaxies in galaxy clusters
and dwarf galaxies orbiting our Milky Way system, as well as any primordial
gas-rich cluster of stars orbiting within its host galaxy. We develop an
analytic formalism to solve the fluid dynamics equations in a non-inertial
reference frame mapped with spherical coordinates. The two-fluids instability
at the interface between a stellar system and its surrounding hotter and less
dense environment is related to the star formation processes through a set of
differential equations. The solution presented here is quite general, allowing
us to investigate most kinds of orbits allowed in a gravitationally bound
system of stars in interaction with a major massive companion. We present an
analytical criterion to elucidate the dependence of star formation in a
spherical stellar system (as a dwarf galaxy or a globular cluster) on its
surrounding environment useful in theoretical interpretations of numerical
results as well as observational applications. We show how spherical
coordinates naturally enlighten the interpretation of the two-fluids
instability in a geometry that directly applies to astrophysical case. This
criterion predicts the threshold value for the onset of star formation in a
mass vs. size space for any orbit of interest. Moreover, we show for the first
time the theoretical dependencies of the different instability phenomena acting
on a system in a fully analytical way.Comment: ACCEPTED in A&A the 09/09/2014. Changes from ver 1: the non-inertial
linear-response theory for gas instabilities in spherical coordinates is
moved to the Appenidx and will be available only on-lin
A knowledge-intensive methodology for explainable sales prediction
Sales prediction in food market is a complex issue that has been addressed in the recent past with machine learning techniques. Although some promising results, an experimental work that we describe in this paper shows some drawbacks of the above mentioned data-driven method and habilitates the definition of a novel methodology, strongly involving a piori knowledg
Protecting the environment: A multi-agent approach to environmental monitoring
In this paper we discuss a transition model from commonly adopted models of data gathering, transfer and management for environmental monitoring towards more sophisticated ones based on Artificial Intelligence and IoT. The transition model is based on the paradigm of multiple agent systems. The adoption of this transition model is motivated by the need to improve effectiveness, efficiency and interoperability of environmental monitoring by simultaneously guaranteeing its sustainability in economic term
Range of reproduction number estimates for COVID-19 spread
To monitor local and global COVID-19 outbreaks, and to plan containment measures, accessible and comprehensible decision-making tools need to be based on the growth rates of new confirmed infections, hospitalization or case fatality rates. Growth rates of new cases form the empirical basis for estimates of a variety of reproduction numbers, dimensionless numbers whose value, when larger than unity, describes surging infections and generally worsening epidemiological conditions. Typically, these determinations rely on noisy or incomplete data gained over limited periods of time, and on many parameters to estimate. This paper examines how estimates from data and models of time-evolving reproduction numbers of national COVID-19 infection spread change by using different techniques and assumptions. Given the importance acquired by reproduction numbers as diagnostic tools, assessing their range of possible variations obtainable from the same epidemiological data is relevant. We compute control reproduction numbers from Swiss and Italian COVID-19 time series adopting both data convolution (renewal equation) and a SEIR-type model. Within these two paradigms we run a comparative analysis of the possible inferences obtained through approximations of the distributions typically used to describe serial intervals, generation, latency and incubation times, and the delays between onset of symptoms and notification. Our results suggest that estimates of reproduction numbers under these different assumptions may show significant temporal differences, while the actual variability range of computed values is rather small
New theory of stellar convection without the mixing-length parameter: New stellar atmosphere model
Stellar convection is usually described by the mixing-length theory, which makes use of the mixing-length scale factor to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is proportional to the local pressure scale height of the star, and the proportionality factor (i.e. mixing-length parameter) is determined by comparing the stellar models to some calibrator, i.e. the Sun. No strong arguments exist to suggest that the mixing-length parameter is the same in all stars and all evolutionary phases and because of this, all stellar models in the literature are hampered by this basic uncertainty. In a recent paper [1] we presented a new theory that does not require the mixing length parameter. Our self-consistent analytical formulation of stellar convection determines all the properties of stellar convection as a function of the physical behavior of the convective elements themselves and the surrounding medium. The new theory of stellar convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations expressed in a non-inertial reference frame co-moving with the convective elements. The motion of stellar convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time-dependent formalism. The predictions of the new theory are compared with those from the standard mixing-length paradigm with positive results for atmosphere models of the Sun and all the stars in the Hertzsprung-Russell diagram
Thin disk kinematics from RAVE and the solar motion
Aims. We study the Milky Way thin disk with the Radial Velocity Experiment
(RAVE) survey. We consider the thin and thick disks as different Galactic
components and present a technique to statistically disentangle the two
populations. Then we focus our attention on the thin disk component. Methods.
We disentangle the thin disk component from amixture of the thin and thick
disks using a data set providing radial velocities, proper motions, and
photometrically determined distances. Results. We present the trend of the
velocity dispersions in the thin disk component of the Milky Way (MW) in the
radial direction above and below the Galactic plane using data from the RAdial
Velocity Experiment (RAVE). The selected sample is a limited subsample from the
entire RAVE catalogue, roughly mapping up to 500 pc above and below the
Galactic plane, a few degrees in azimuthal direction and covering a radial
extension of 2.0 kpc around the solar position. The solar motion relative to
the local standard of rest is also re-determined with the isolated thin disk
component. Major results are the trend of the velocity mean and dispersion in
the radial and vertical direction. In addition the azimuthal components of the
solar motion relative to the local standard of rest and the velocity dispersion
are discussed.Comment: accepted on A&A, please see companion paper "THICK disk kinem...
Cancer incidence in Italian contaminated sites
INTRODUCTION: The incidence of cancer among residents in sites contaminated by
pollutants with a possible health impact is not adequately studied. In Italy,
SENTIERI Project (Epidemiological study of residents in National Priority
Contaminated Sites, NPCSs) was implemented to study major health outcomes for
residents in 44 NPCSs.
METHODS: The Italian Association of Cancer Registries (AIRTUM) records cancer
incidence in 23 NPCSs. For each NPCSs, the incidence of all malignant cancers
combined and 35 cancer sites (coded according to ICD-10), was analysed
(1996-2005). The observed cases were compared to the expected based on age
(5-year period,18 classes), gender, calendar period (1996-2000; 2001-2005),
geographical area (North-Centre and Centre-South) and cancer sites specific
rates. Standardized Incidence Ratios (SIR) with 90% Confidence Intervals were
computed.
RESULTS: In both genders an excess was observed for overall cancer incidence (9%
in men and 7% in women) as well as for specific cancer sites (colon and rectum,
liver, gallblad-der, pancreas, lung, skin melanoma, bladder and Non Hodgkin
lymphoma). Deficits were observed for gastric cancer in both genders, chronic
lymphoid leukemia (men), malignant thyroid neoplasms, corpus uteri and connective
and soft-tissue tumours and sarcomas (women).
DISCUSSION: This report is, to our knowledge, the first one on cancer risk of
residents in NPCSs. The study, although not aiming to estimate the cancer burden
attributable to the environment as compared to occupation or life-style, supports
the credibility of an etiologic role of environmental exposures in contaminated
sites. Ongoing analyses focus on the interpretation of risk factors for excesses
of specific cancer types overall and in specific NPCSs in relation to the
presence of carcinogenic pollutants
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