10,567 research outputs found
Bottom changes in coastal areas with complex shorelines
A model for the sea-bottom change simulations in coastal areas with complex shorelines is proposed. In deep and intermediate water depths, the hydrodynamic quantities are calculated by numerically integrating the contravariant Boussinesq equations, devoid of Christoffel symbols. In the surf zone, the propagation of the breaking waves is simulated by the nonlinear shallow water equations. The momentum equation is solved inside the turbulent boundary layer in order to calculate intrawave hydrodynamic quantities. An integral formulation for the contravariant suspended sediment advection-diffusion equation is proposed and used for the sea-bottom dynamic simulations. The proposed model is applied to the real case study of Pescara harbor (in Italy)
Dynamically correlated regions and configurational entropy in supercooled liquids
When a liquid is cooled below its melting temperature, if crystallization is
avoided, it forms a glass. This phenomenon, called glass transition, is
characterized by a marked increase of viscosity, about 14 orders of magnitude,
in a narrow temperature interval. The microscopic mechanism behind the glass
transition is still poorly understood. However, recently, great advances have
been made in the identification of cooperative rearranging regions, or
dynamical heterogeneities, i.e. domains of the liquid whose relaxation is
highly correlated. The growth of the size of these domains is now believed to
be the driving mechanism for the increase of the viscosity. Recently a tool to
quantify the size of these domains has been proposed. We apply this tool to a
wide class of materials to investigate the correlation between the size of the
heterogeneities and their configurational entropy, i.e. the number of states
accessible to a correlated domain. We find that the relaxation time of a given
system, apart from a material dependent pre-factor, is a universal function of
the configurational entropy of a correlated domain. As a consequence, we find
that at the glass transition temperature, the size of the domains and the
configurational entropy per unit volume are anti-correlated, as originally
predicted by the Adam-Gibbs theory. Finally, we use our data to extract some
exponents defined in the framework of the Random First Order Theory, a recent
quantitative theory of the glass transition.Comment: 8 pages, 4 figures, 3 table
Socially Constrained Structural Learning for Groups Detection in Crowd
Modern crowd theories agree that collective behavior is the result of the
underlying interactions among small groups of individuals. In this work, we
propose a novel algorithm for detecting social groups in crowds by means of a
Correlation Clustering procedure on people trajectories. The affinity between
crowd members is learned through an online formulation of the Structural SVM
framework and a set of specifically designed features characterizing both their
physical and social identity, inspired by Proxemic theory, Granger causality,
DTW and Heat-maps. To adhere to sociological observations, we introduce a loss
function (G-MITRE) able to deal with the complexity of evaluating group
detection performances. We show our algorithm achieves state-of-the-art results
when relying on both ground truth trajectories and tracklets previously
extracted by available detector/tracker systems
Testing creation of matter with neutrinoless double beta decay
In this brief review, the importance of the so called neutrinoless double
beta decay transition in the search for physics beyond the Standard Model is
emphasized. The expectations for the transition rate are examined in the
assumption that ordinary neutrinos have Majorana masses. We stress the
relevance of cosmological measurements and discuss the uncertainties implied by
nuclear physics.Comment: 9 pages. Based on the review paper Neutrinoless double beta decay:
2015 review, Adv.High Energy Phys. 2016 (2016) 2162659. To appear in the
proceedings of the XVII International Workshop on Neutrino Telescopes 13-17
March 2017, Venice, Ital
VINCI-VLTI measurements of HR 4049: the physical size of the circumbinary envelope
We present the first detection of the envelope which surrounds the post-AGB
binary source HR 4049. VINCI-VLTI K-band interferometric observations of this
source imply the existence of a large structure with a Gaussian angular FWHM
22.4 +/- 1.4 mas or uniform disk diameter of 34.9 +/- 1.9 mas. With the
Hipparcos parallax of 1.50 +/- 0.64 mas these values correspond to a physical
size of 14.9 (+11.1,-4.4) AU and 23.3 (+17.3,-7.0) AU, respectively. Our
measurements, covering an azimuth range of about 60 degrees, for the
sky-projected baseline, provide information on the geometry of the emitting
region and show that there is only a slight variation of the measured angular
values along the different directions sampled. Thus, our results are consistent
with a spherical geometry of the envelope. However, we cannot completely rule
out the existence of an asymmetric envelope (like the circumbinary disk
envisaged by some recent models) because of the limited spatial frequency and
azimuth range covered by the observations.Comment: 4 pages, 4 postscript figures, accepted letter for A&
Learning to Divide and Conquer for Online Multi-Target Tracking
Online Multiple Target Tracking (MTT) is often addressed within the
tracking-by-detection paradigm. Detections are previously extracted
independently in each frame and then objects trajectories are built by
maximizing specifically designed coherence functions. Nevertheless, ambiguities
arise in presence of occlusions or detection errors. In this paper we claim
that the ambiguities in tracking could be solved by a selective use of the
features, by working with more reliable features if possible and exploiting a
deeper representation of the target only if necessary. To this end, we propose
an online divide and conquer tracker for static camera scenes, which partitions
the assignment problem in local subproblems and solves them by selectively
choosing and combining the best features. The complete framework is cast as a
structural learning task that unifies these phases and learns tracker
parameters from examples. Experiments on two different datasets highlights a
significant improvement of tracking performances (MOTA +10%) over the state of
the art
Dynamics of vitrimers: defects as a highway to stress relaxation
We propose a coarse-grained model to investigate stress relaxation in
star-polymer networks induced by dynamic bond exchange processes. We show how
the swapping mechanism, once activated, allows the network to reconfigure,
exploring distinct topological configurations, all of them characterised by
complete extent of reaction. Our results reveal the important role played by
topological defects in mediating the exchange reaction and speeding up stress
relaxation. The model provides a representation of the dynamics in vitrimers, a
new class of polymers characterized by bond swap mechanisms which preserve the
total number of bonds, as well as in other bond-exchange materials.Comment: 5 pages, 5 figures, with 6 pages SI appende
Computing Strong and Weak Permissions in Defeasible Logic
In this paper we propose an extension of Defeasible Logic to represent and
compute three concepts of defeasible permission. In particular, we discuss
different types of explicit permissive norms that work as exceptions to
opposite obligations. Moreover, we show how strong permissions can be
represented both with, and without introducing a new consequence relation for
inferring conclusions from explicit permissive norms. Finally, we illustrate
how a preference operator applicable to contrary-to-duty obligations can be
combined with a new operator representing ordered sequences of strong
permissions which derogate from prohibitions. The logical system is studied
from a computational standpoint and is shown to have liner computational
complexity
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