18,560 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
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.
Feedback from massive stars and gas expulsion from proto-globular clusters
© 2015. The American Astronomical Society. All rights reserved. Globular clusters (GCs) are considerably more complex structures than previously thought, harboring at least two stellar generations that present clearly distinct chemical abundances. Scenarios explaining the abundance patterns in GCs mostly assume that originally the clusters had to be much more massive than today, and that the second generation of stars originates from the gas shed by stars of the first generation (FG). The lack of metallicity spread in most GCs further requires that the supernova-enriched gas ejected by the FG is completely lost within ∼30 Myr, a hypothesis never tested by means of three-dimensional hydrodynamic simulations. In this paper, we use 3D hydrodynamic simulations including stellar feedback from winds and supernovae, radiative cooling and self-gravity to study whether a realistic distribution of OB associations in a massive proto-GC of initial mass M tot ∼ 10 7 M o is sufficient to expel its entire gas content. Our numerical experiment shows that the coherence of different associations plays a fundamental role: as the bubbles interact, distort, and merge, they carve narrow tunnels that reach deeper and deeper toward the innermost cluster regions, and through which the gas is able to escape. Our results indicate that after 3 Myr, the feedback from stellar winds is responsible for the removal of ∼40% of the pristine gas, and that after 14 Myr, 99% of the initial gas mass has been removed
Comment on the paper by Y.Komura and Y.Okabe [arXiv:1011.3321]
We point out that the claim of strong universality in the paper J.Phys. A 44,
015002, arXiv:1011.3321 is incorrect, as it contradicts known rigorous results.Comment: submitted to J.Phys.
Teleportation is necessary for faithful quantum state transfer through noisy channels of maximal rank
Quantum teleportation enables deterministic and faithful transmission of
quantum states, provided a maximally entangled state is pre-shared between
sender and receiver, and a one-way classical channel is available. Here, we
prove that these resources are not only sufficient, but also necessary, for
deterministically and faithfully sending quantum states through any fixed noisy
channel of maximal rank, when a single use of the cannel is admitted. In other
words, for this family of channels, there are no other protocols, based on
different (and possibly cheaper) sets of resources, capable of replacing
quantum teleportation.Comment: 4 pages, comments are welcom
Swift J1734.5-3027: a new long type-I X-ray bursting source
Swift J1734.5-3027 is a hard X-ray transient discovered by Swift while
undergoing an outburst in September 2013. Archival observations showed that
this source underwent a previous episode of enhanced X-ray activity in May-June
2013. In this paper we report on the analysis of all X-ray data collected
during the outburst in September 2013, the first that could be intensively
followed-up by several X-ray facilities. Our data-set includes INTEGRAL, Swift,
and XMM-Newton observations. From the timing and spectral analysis of these
observations, we show that a long type-I X-ray burst took place during the
source outburst, making Swift J1734.5-3027 a new member of the class of
bursting neutron star low-mass X-ray binaries. The burst lasted for about 1.9
ks and reached a peak flux of (6.01.8)10 erg cm
s in the 0.5-100 keV energy range. The estimated burst fluence in the
same energy range is (1.100.10)10 erg cm. By
assuming that a photospheric radius expansion took place during the first
200 s of the burst and that the accreted material was predominantly
composed by He, we derived a distance to the source of 7.21.5 kpc.Comment: Accepted for publication on A&
Two years of monitoring Supergiant Fast X-ray Transients with Swift
We present two years of intense Swift monitoring of three SFXTs, IGR
J16479-4514, XTE J1739-302, and IGR J17544-2619 (since October 2007).
Out-of-outburst intensity-based X-ray (0.3-10keV) spectroscopy yields absorbed
power laws with by hard photon indices (G~1-2). Their outburst broad-band
(0.3-150 keV) spectra can be fit well with models typically used to describe
the X-ray emission from accreting NSs in HMXBs. We assess how long each source
spends in each state using a systematic monitoring with a sensitive instrument.
These sources spend 3-5% of the total in bright outbursts. The most probable
flux is 1-2E-11 erg cm^{-2} s^{-1} (2-10 keV, unabsorbed), corresponding to
luminosities in the order of a few 10^{33} to 10^{34} erg s^{-1} (two orders of
magnitude lower than the bright outbursts). The duty-cycle of inactivity is 19,
39, 55%, for IGR J16479-4514, XTE J1739-302, and IGR J17544-2619, respectively.
We present a complete list of BAT on-board detections further confirming the
continued activity of these sources. This demonstrates that true quiescence is
a rare state, and that these transients accrete matter throughout their life at
different rates. X-ray variability is observed at all timescales and
intensities we can probe. Superimposed on the day-to-day variability is
intra-day flaring which involves variations up to one order of magnitude that
can occur down to timescales as short as ~1ks, and whichcan be explained by the
accretion of single clumps composing the donor wind with masses
M_cl~0.3-2x10^{19} g. (Abridged)Comment: Accepted for publication in MNRAS. 17 pages, 11 figures, 8 table
How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging
We present the results of applying new object classification techniques to
difference images in the context of the Nearby Supernova Factory supernova
search. Most current supernova searches subtract reference images from new
images, identify objects in these difference images, and apply simple threshold
cuts on parameters such as statistical significance, shape, and motion to
reject objects such as cosmic rays, asteroids, and subtraction artifacts.
Although most static objects subtract cleanly, even a very low false positive
detection rate can lead to hundreds of non-supernova candidates which must be
vetted by human inspection before triggering additional followup. In comparison
to simple threshold cuts, more sophisticated methods such as Boosted Decision
Trees, Random Forests, and Support Vector Machines provide dramatically better
object discrimination. At the Nearby Supernova Factory, we reduced the number
of non-supernova candidates by a factor of 10 while increasing our supernova
identification efficiency. Methods such as these will be crucial for
maintaining a reasonable false positive rate in the automated transient alert
pipelines of upcoming projects such as PanSTARRS and LSST.Comment: 25 pages; 6 figures; submitted to Ap
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