3,144 research outputs found
Opinion modeling on social media and marketing aspects
We introduce and discuss kinetic models of opinion formation on social
networks in which the distribution function depends on both the opinion and the
connectivity of the agents. The opinion formation model is subsequently coupled
with a kinetic model describing the spreading of popularity of a product on the
web through a social network. Numerical experiments on the underlying kinetic
models show a good qualitative agreement with some measured trends of hashtags
on social media websites and illustrate how companies can take advantage of the
network structure to obtain at best the advertisement of their products
Particle based gPC methods for mean-field models of swarming with uncertainty
In this work we focus on the construction of numerical schemes for the
approximation of stochastic mean--field equations which preserve the
nonnegativity of the solution. The method here developed makes use of a
mean-field Monte Carlo method in the physical variables combined with a
generalized Polynomial Chaos (gPC) expansion in the random space. In contrast
to a direct application of stochastic-Galerkin methods, which are highly
accurate but lead to the loss of positivity, the proposed schemes are capable
to achieve high accuracy in the random space without loosing nonnegativity of
the solution. Several applications of the schemes to mean-field models of
collective behavior are reported.Comment: Communications in Computational Physics, to appea
The role of quenching time in the evolution of the mass-size relation of passive galaxies from the WISP survey
We analyze how passive galaxies at z 1.5 populate the mass-size plane
as a function of their stellar age, to understand if the observed size growth
with time can be explained with the appearance of larger quenched galaxies at
lower redshift. We use a sample of 32 passive galaxies extracted from the Wide
Field Camera 3 Infrared Spectroscopic Parallel (WISP) survey with spectroscopic
redshift 1.3 z 2.05, specific star-formation rates lower
than 0.01 Gyr, and stellar masses above 4.5 10
M. All galaxies have spectrally determined stellar ages from fitting of
their rest-frame optical spectra and photometry with stellar population models.
When dividing our sample into young (age 2.1 Gyr) and old (age 2.1
Gyr) galaxies we do not find a significant trend in the distributions of the
difference between the observed radius and the one predicted by the mass-size
relation. This result indicates that the relation between the galaxy age and
its distance from the mass-size relation, if it exists, is rather shallow, with
a slope alpha -0.6. At face value, this finding suggests that
multiple dry and/or wet minor mergers, rather than the appearance of newly
quenched galaxies, are mainly responsible for the observed time evolution of
the mass-size relation in passive galaxies.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figures, 1 tabl
Laparoscopic totally extraperitoneal inguinal hernia repair in the elderly: A prospective control study
Inguinal hernia (IH) repair can be obtained with both open and laparoscopic techniques, which are usually performed using a transabdominal preperitoneal (TAPP) or a totally extraperitoneal (TEP) approach. The aim of the study was to evaluate whether the results of laparoscopic TEP IH repair in the elderly ( 6565 years old) are different with respect to results obtained in younger patients. One hundred and four consecutive patients (four women and 100 men, median age of 57 years, range=21-85 years) with unilateral (N=21, 20.2%) or bilateral (N=83, 79.8%) IH were prospectively enrolled in the study. Patients were divided into two groups according to their age: group A (N=68, 65.4%) aged <65 years and group B (N=36, 34.6%) aged 6565 years. The mean operative time was not significantly different between groups (48\ub120 vs. 52\ub120 min, p=0.33). One case of increased PaCO2 was observed in each group (p=0.72) and two and one case of pneumoperitoneum (p=0.57) in groups A and B, respectively. Two (1.9%) patients (one in each group; p=0.55) required TEP conversion. Mild postoperative complications developed in four patients of each group (p=0.44). After one-year follow-up, three (2.9%) recurrences occurred (group 1=1, group 2=2, p=0.55), both in patients who had undergone direct IH repair. The overall postoperative relative risk of complications related to age was 1.08 (95% confidence interval=0.91-1.27, p=0.53). In conclusion, our results suggest that in patients with IH scheduled for TEP repair, age does not represent a contraindication to surgery in terms of complication rate and postoperative results
Kinematics of galaxies from [CII] line emission
We study the kinematical properties of galaxies in the Epoch of Reionization
via the [CII] 158m line emission. The line profile provides information on
the kinematics as well as structural properties such as the presence of a disk
and satellites. To understand how these properties are encoded in the line
profile, first we develop analytical models from which we identify disk
inclination and gas turbulent motions as the key parameters affecting the line
profile. To gain further insights, we use "Althaea", a highly-resolved () simulated prototypical Lyman Break Galaxy, in the redshift range , when the galaxy is in a very active assembling phase. Based on
morphology, we select three main dynamical stages: I) Merger , II) Spiral Disk,
and III) Disturbed Disk. We identify spectral signatures of merger events,
spiral arms, and extra-planar flows in I), II), and III), respectively. We
derive a generalised dynamical mass vs. [CII]-line FWHM relation. If precise
information on the galaxy inclination is (not) available, the returned mass
estimate is accurate within a factor (). A Tully-Fisher relation is
found for the observed high- galaxies, i.e. for which we provide a simple, physically-based
interpretation. Finally, we perform mock ALMA simulations to check the
detectability of [CII]. When seen face-on, Althaea is always detected at ; in the edge-on case it remains undetected because the larger
intrinsic FWHM pushes the line peak flux below detection limit. This suggests
that some of the reported non-detections might be due to inclination effects.Comment: 14 pages, 12 figures, accepted for publication in MNRA
The Purple Haze of Eta Carinae: Binary-Induced Variability?
Asymmetric variability in ultraviolet images of the Homunculus obtained with
the Advanced Camera for Surveys/High Resolution Camera on the Hubble Space
Telescope suggests that Eta Carinae is indeed a binary system. Images obtained
before, during, and after the recent ``spectroscopic event'' in 2003.5 show
alternating patterns of bright spots and shadows on opposite sides of the star
before and after the event, providing a strong geometric argument for an
azimuthally-evolving, asymmetric UV radiation field as one might predict in
some binary models. The simplest interpretation of these UV images, where
excess UV escapes from the secondary star in the direction away from the
primary, places the major axis of the eccentric orbit roughly perpendicular to
our line of sight, sharing the same equatorial plane as the Homunculus, and
with apastron for the hot secondary star oriented toward the southwest of the
primary. However, other orbital orientations may be allowed with more
complicated geometries. Selective UV illumination of the wind and ejecta may be
partly responsible for line profile variations seen in spectra. The brightness
asymmetries cannot be explained plausibly with delays due to light travel time
alone, so a single-star model would require a seriously asymmetric shell
ejection.Comment: 8 pages, fig 1 in color, accepted by ApJ Letter
Soil quality and fertility in sustainable agriculture, with a contribution to the biological classification of agricultural soils
Soils and crops are particularly vulnerable to climate change and environmental stresses. In many agrosystems, soil biodiversity and ecosystem services provided by soils are under threat from a range of natural and human drivers. Agricultural soils are often subject to agronomic practices that disrupt soil trophic networks and make soils less productive in the long term. In this scenario, sustainable soil use aimed at improving plant/root status, growth and development plays a crucial role for enhancing the biological capacity of agricultural soils. This commentary paper is divided into the following four main sections: (i) the contentious nature of soil organic matter; (ii) soil biological quality/fertility; (iii) soil classification; and, (iv) which agricultural practices can be defined as sustainable? The published literature was analyzed within a holistic framework, with agrosystems considered as living systems where soil, vegetation, fauna and microorganisms co-evolve and are reciprocally influenced. Ultimately, this article will suggest a better stewardship of agricultural soils as a natural capital
Mumificaçao fetal em suínos associada à toxoplasmose.
bitstream/item/58346/1/CUsersPiazzonDocuments271.pd
- …