23,015 research outputs found
Citizens and Institutions as Information Prosumers. The Case Study of Italian Municipalities on Twitter
The aim of this paper is to address changes in public communication following the advent of Internet social networking tools and the emerging web 2.0 technologies which are providing new ways of sharing information and knowledge. In particular public administrations are called upon to reinvent the governance of public affairs and to update the means for interacting with their communities. The paper develops an analysis of the distribution, diffusion and performance of the official profiles on Twitter adopted by the Italian municipalities (comuni) up to November 2013. It aims to identify the patterns of spatial distribution and the drivers of the diffusion of Twitter profiles; the performance of the profiles through an aggregated index, called the Twitter performance index (Twiperindex), which evaluates the profiles' activity with reference to the gravitational areas of the municipalities in order to enable comparisons of the activity of municipalities with different demographic sizes and functional roles. The results show that only a small portion of innovative municipalities have adopted Twitter to enhance e-participation and e-governance and that the drivers of the diffusion seem to be related either to past experiences and existing conditions (i.e. civic networks, digital infrastructures) developed over time or to strong local community awareness. The better performances are achieved mainly by small and medium-sized municipalities. Of course, the phenomenon is very new and fluid, therefore this analysis should be considered as a first step in ongoing research which aims to grasp the dynamics of these new means of public communication
Phonon Bottleneck Identification in Disordered Nanoporous Materials
Nanoporous materials are a promising platform for thermoelectrics in that
they offer high thermal conductivity tunability while preserving good
electrical properties, a crucial requirement for high- effciency thermal energy
conversion. Understanding the impact of the pore arrangement on thermal
transport is pivotal to engineering realistic materials, where pore disorder is
unavoidable. Although there has been considerable progress in modeling thermal
size effects in nanostructures, it has remained a challenge to screen such
materials over a large phase space due to the slow simulation time required for
accurate results. We use density functional theory in connection with the
Boltzmann transport equation, to perform calculations of thermal conductivity
in disordered porous materials. By leveraging graph theory and regressive
analysis, we identify the set of pores representing the phonon bottleneck and
obtain a descriptor for thermal transport, based on the sum of the pore-pore
distances between such pores. This approach provides a simple tool to estimate
phonon suppression in realistic porous materials for thermoelectric
applications and enhance our understanding of heat transport in disordered
materials
Toward phonon-boundary engineering in nanoporous materials
Tuning thermal transport in nanostructured materials is a powerful approach
to develop high-efficiency thermoelectric materials. Using a recently developed
approach based on the phonon mean free path dependent Boltzmann transport
equation, we compute the effective thermal conductivity of nanoporous materials
with pores of various shapes and arrangements. We assess the importance of
pore-pore distance in suppressing thermal transport, and identify the pore
arrangement that minimizes the thermal conductivity, composed of a periodic
arrangement of two misaligned rows of triangular pores. Such a configuration
yields a reduction in the thermal conductivity of more than with
respect the simple circular aligned case with the same porosity.Comment: 4 pages, 4 figures, 1 tabl
Role of the particle's stepping cycle in an asymmetric exclusion process: A model of mRNA translation
Messenger RNA translation is often studied by means of statistical-mechanical
models based on the Asymmetric Simple Exclusion Process (ASEP), which considers
hopping particles (the ribosomes) on a lattice (the polynucleotide chain). In
this work we extend this class of models and consider the two fundamental steps
of the ribosome's biochemical cycle following a coarse-grained perspective. In
order to achieve a better understanding of the underlying biological processes
and compare the theoretical predictions with experimental results, we provide a
description lying between the minimal ASEP-like models and the more detailed
models, which are analytically hard to treat. We use a mean-field approach to
study the dynamics of particles associated with an internal stepping cycle. In
this framework it is possible to characterize analytically different phases of
the system (high density, low density or maximal current phase). Crucially, we
show that the transitions between these different phases occur at different
parameter values than the equivalent transitions in a standard ASEP, indicating
the importance of including the two fundamental steps of the ribosome's
biochemical cycle into the model.Comment: 9 pages, 9 figure
The boson-fermion model: An exact diagonalization study
The main features of a generic boson-fermion scenario for electron pairing in
a many-body correlated fermionic system are: i) a cross-over from a poor metal
to an insulator and finally a superconductor as the temperature decreases, ii)
the build-up of a finite amplitude of local electron pairing below a certain
temperature , followed by the onset of long-range phase correlations among
electron pairs below a second characteristic temperature , iii) the
opening of a pseudogap in the DOS of the electrons below , rendering these
electrons poorer and poorer quasi-particles as the temperature decreases, with
the electron transport becoming ensured by electron pairs rather than by
individual electrons. A number of these features have been so far obtained on
the basis of different many-body techniques, all of which have their built-in
shortcomings in the intermediate coupling regime, which is of interest here. In
order to substantiate these features, we investigate them on the basis of an
exact diagonalization study on rings up to eight sites. Particular emphasis has
been put on the possibility of having persistent currents in mesoscopic rings
tracking the change-over from single- to two-particle transport as the
temperature decreases and the superconducting state is approached.Comment: 7 pages, 8 figures; to be published in Phys. Rev.
Standard and Specialized Infant Formulas in Europe: Making, Marketing, and Health Outcomes
Infant formulas are the only suitable substitute for human milk. The most common infant formulas are standard formulas based on cow's milk. In addition, there are formulas for infants showing signs and symptoms of intolerance and for clinical conditions such as allergy, prematurity, and gastrointestinal diseases. A comprehensive review of the literature was made to review the composition of standard and specialized infant formulas and analyze indications for use, real or presumed nutrition differences and properties, and impact on infant growth. A brief consideration on costs is outlined for each formula. Over the past few years, industrial production and advertising of infant formulas have increased. Human milk still remains the most complete source of nutrition for infants and should be continued according to the current recommendations. Few differences exist between infant formulas, both for the nutrition action and the macronutrient/micronutrient composition. Specialized infant formulas have limited indications for use and high costs. The role of the pediatrician is crucial in the management of infant nutrition, promotion of breastfeeding, and prescribing of specialized formulas only in specific clinical conditions
A symmetry-adapted numerical scheme for SDEs
We propose a geometric numerical analysis of SDEs admitting Lie symmetries
which allows us to individuate a symmetry adapted coordinates system where the
given SDE has notable invariant properties. An approximation scheme preserving
the symmetry properties of the equation is introduced. Our algorithmic
procedure is applied to the family of general linear SDEs for which two
theoretical estimates of the numerical forward error are established.Comment: A numerical example adde
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