5,055 research outputs found
Cosmic ray transport and radiative processes in nuclei of starburst galaxies
The high rate of star formation and supernova explosions of starburst
galaxies make them interesting sources of high energy radiation. Depending upon
the level of turbulence present in their interstellar medium, the bulk of
cosmic rays produced inside starburst galaxies may lose most of their energy
before escaping, thereby making these sources behave as calorimeters, at least
up to some maximum energy. Contrary to previous studies, here we investigate in
detail the conditions under which cosmic ray confinement may be effective for
electrons and nuclei and we study the implications of cosmic ray confinement in
terms of multifrequency emission from starburst nuclei and production of high
energy neutrinos. The general predictions are then specialized to three cases
of active starbursts, namely M82, NGC253 and Arp220. Both primary and secondary
electrons, as well as electron-positron pairs produced by gamma ray absorption
inside starburst galaxies are taken into account. Electrons and positrons
produced as secondary products of hadronic interactions are found to be
responsible for most of the emission of leptonic origin. In particular,
synchrotron emission of very high energy secondary electrons produces an
extended emission of hard X-rays that represent a very interesting signature of
hadronic process in starburst galaxies, potentially accessible to current and
future observations in the X-ray band. A careful understanding of both the
production and absorption of gamma rays in starburst galaxies is instrumental
to the assessment of the role of these astrophysical sources as sources of high
energy astrophysical neutrinos.Comment: Version accepted for publication in MNRA
Measuring Similarity in Large-Scale Folksonomies
Social (or folksonomic) tagging has become a very popular way to describe content within Web 2.0 websites. Unlike\ud
taxonomies, which overimpose a hierarchical categorisation of content, folksonomies enable end-users to freely create and choose the categories (in this case, tags) that best\ud
describe some content. However, as tags are informally de-\ud
fined, continually changing, and ungoverned, social tagging\ud
has often been criticised for lowering, rather than increasing, the efficiency of searching, due to the number of synonyms, homonyms, polysemy, as well as the heterogeneity of\ud
users and the noise they introduce. To address this issue, a\ud
variety of approaches have been proposed that recommend\ud
users what tags to use, both when labelling and when looking for resources. As we illustrate in this paper, real world\ud
folksonomies are characterized by power law distributions\ud
of tags, over which commonly used similarity metrics, including the Jaccard coefficient and the cosine similarity, fail\ud
to compute. We thus propose a novel metric, specifically\ud
developed to capture similarity in large-scale folksonomies,\ud
that is based on a mutual reinforcement principle: that is,\ud
two tags are deemed similar if they have been associated to\ud
similar resources, and vice-versa two resources are deemed\ud
similar if they have been labelled by similar tags. We offer an efficient realisation of this similarity metric, and assess its quality experimentally, by comparing it against cosine similarity, on three large-scale datasets, namely Bibsonomy, MovieLens and CiteULike
Effective Retrieval of Resources in Folksonomies Using a New Tag Similarity Measure
Social (or folksonomic) tagging has become a very popular way to describe
content within Web 2.0 websites. However, as tags are informally defined,
continually changing, and ungoverned, it has often been criticised for
lowering, rather than increasing, the efficiency of searching. To address this
issue, a variety of approaches have been proposed that recommend users what
tags to use, both when labeling and when looking for resources. These
techniques work well in dense folksonomies, but they fail to do so when tag
usage exhibits a power law distribution, as it often happens in real-life
folksonomies. To tackle this issue, we propose an approach that induces the
creation of a dense folksonomy, in a fully automatic and transparent way: when
users label resources, an innovative tag similarity metric is deployed, so to
enrich the chosen tag set with related tags already present in the folksonomy.
The proposed metric, which represents the core of our approach, is based on the
mutual reinforcement principle. Our experimental evaluation proves that the
accuracy and coverage of searches guaranteed by our metric are higher than
those achieved by applying classical metrics.Comment: 6 pages, 2 figures, CIKM 2011: 20th ACM Conference on Information and
Knowledge Managemen
User-Customizable Web Components for Building One-Page Sites
Most of online website builders work by combining and customizing reusable HTML modules. This approach could rise the risk of conflicts among modules. The World Wide Web Consortium (W3C) is writing the specification of
Web Components. This standard provides a browser-native solution in order to realize encapsulated Document Object Model (DOM) elements, in which the Cascading Style Sheets (CSS) and JavaScript scope is locally bound and the interaction with the document is strictly designed by the component author. Upon this standard, libraries have been built, Google’s Polymer being an example, which provide a declarative and easy way to realize Components. In this paper, we provide a solution to the module approach limit in website builders by using Web Components as modules that are customizable by the end user. Our approach uses standard web technologies that modern browsers are natively supporting. We describe how a customizable Web Component is designed and how to bind their options with the generator UI. Furthermore, we will show an application of this approach in a Landing Page generator. We demonstrate that the generator could import again the generated HyperText Markup Language (HTML) and edit it, without any intermediary data structure (i.e., eXtensible Markup
Language, XML or JavaScript Object Notation, Json). Finally, we outline further future development of this approach
The dentist who sat on her chair and lost a leg. N2O?
A 35-year-old female dentist laid on her
chair to test an N2O machine, and after
only a few minutes of inhaling the N2O,
she developed acute pyramidal syndrome.
The patient started walking again eight
months later, but still suffers from lower
limb motor deficit, in spite of intensive rehabilitation.
Genetic tests later showed that
the patient had Type 3 homocystinuria.
This is the first case report of acute neurological
toxicity after brief administration
of N2O. We suggest starting vitamin B12
and folic acid supplements promptly in patients
who experience neurological symptoms
after receiving N2O
Different spectra of cosmic ray H, He and heavier nuclei escaping compact star clusters
Cosmic ray acceleration at the termination shock of compact star clusters has
recently received much attention, mainly because of the detection of gamma ray
emission from some of such astrophysical sources. Here we focus on the
acceleration of nuclei at the termination shock and we investigate the role
played by proton energy losses and spallation reactions of nuclei, especially
downstream of the shock. We show that for a rather generic choice of the mean
gas density in the cavity excavated by the cluster wind, the spectrum of He
nuclei is systematically harder than the spectrum of hydrogen, in a manner that
appears to be qualitatively consistent with the observed and yet unexplained
phenomenon of discrepant hardening. We also find that the spallation reactions
of heavier nuclei are likely to be so severe that their spectra become very
hard and with a low normalization, meaning that it is unlikely that heavy
nuclei escaping star clusters can provide a sizeable contribution to the
spectrum of cosmic rays at the Earth.Comment: 9 Pages, Submitted to MNRA
Who Will Ever Kick Us Out? Italy, the Balanced Budget Rule and the Implementation of the Fiscal Compact
A Flexible Transport Service for Passengers
AbstractThe realization of innovative passengers transport services requires more and more often a greater flexibility and inexpensiveness of the service. To answer this request in many cases the physical solution is to realize a demand responsive transportation system (DRTS). A DRTS require the planning of travel paths (routing) and customers pick-up and drop-off times (scheduling) according to received requests, respecting the limited capacity of the fleet and time constraints (hard time windows) for each network's node, and the service time of the system. By the modelling point of view a DRTS can be effectively represented with a Dial-a-ride problem (DaRP). A DaRP derives from the Pick-up and Delivery Problem with Time Windows (PDPTW) and may operate according to a static or to a dynamic mode. In the static setting, all customers’ requests are known beforehand and the DaRP returns the vehicles routing and the passengers pick up and drop off time scheduling. The static setting may be representative of a phase of reservation occurred the day before the execution of the service. But, if the reservation requests must be processed on-line, even during the booking process there may be a certain level ad dynamism. In fact, if the algorithm works online, it manages each and every incoming request separately, and accepts or refuses it immediately, without knowing anything about the following. The operative program is constantly updated after each received request without refusal to carry out previous accepted services. In the dynamic mode, customers’ requests arrive when the service is already running and, consequently, the solution may change whilst the vehicle is already travelling. In this mode it is necessary that the schedule is updated when each new request arrives and that this is done in a short time to ensure that the potential customer will not leave the system before a possible answer. In this work, we describe a flexible people transport system capable of managing incoming transport demand in dynamic mode, using a solution architecture based on a two-stage algorithm to solve Dial-a-Ride Problem instances. In the first stage, a constructive heuristic algorithm quickly provides a feasible solution to accept the incoming demand. The algorithm in the second stage try to improve the solution evaluated at the first stage by using the time between two consecutive transportation events. The algorithm, unlike most of the works in the literature, use an objective function that optimizes the service punctuality
Metrological Characterization of an Improved DSP-Based On-line Integrator for Magnetic Measurements at CERN
An improved on-line version of the self-calibrating digital instrument for flux measurements on superconductive magnets for particle accelerators, prototyped at the European Organization for Nuclear Research (CERN) in cooperation with the University of Sannio, is proposed. The instrument acquires voltage arising from rotating coils transducers. Then, the samples are online integrated and suitably processed in order to achieve flux analysis time down to 2.0 ìs, with resolution of 50 ns. Details about hardware and firmware conception, on-line measurement principle, and preliminary results of metrological characterization of the prototype are provided
Metrics and Pairs of Left and Right Connections on Bimodules
Properties of metrics and pairs consisting of left and right connections are
studied on the bimodules of differential 1-forms. Those bimodules are obtained
from the derivation based calculus of an algebra of matrix valued functions,
and an SL\sb q(2,\IC)-covariant calculus of the quantum plane plane at a
generic and the cubic root of unity. It is shown that, in the
aforementioned examples, giving up the middle-linearity of metrics
significantly enlarges the space of metrics. A~metric compatibility condition
for the pairs of left and right connections is defined. Also, a compatibility
condition between a left and right connection is discussed. Consequences
entailed by reducing to the centre of a bimodule the domain of those conditions
are investigated in detail. Alternative ways of relating left and right
connections are considered.Comment: 16 pages, LaTeX, nofigure
- …