2,909 research outputs found
Note on the helicity decomposition of spin and orbital optical currents
In the helicity representation, the Poynting vector (current) for a
monochromatic optical field, when calculated using either the electric or the
magnetic field, separates into right-handed and left-handed contributions, with
no cross-helicity contributions. Cross-helicity terms do appear in the orbital
and spin contributions to the current. But when the electric and magnetic
formulas are averaged ('electric-magnetic democracy'), these terms cancel,
restoring the separation into right-handed and left-handed currents for orbital
and spin separately.Comment: 10 pages, no figure
Searching in Unstructured Overlays Using Local Knowledge and Gossip
This paper analyzes a class of dissemination algorithms for the discovery of
distributed contents in Peer-to-Peer unstructured overlay networks. The
algorithms are a mix of protocols employing local knowledge of peers'
neighborhood and gossip. By tuning the gossip probability and the depth k of
the k-neighborhood of which nodes have information, we obtain different
dissemination protocols employed in literature over unstructured P2P overlays.
The provided analysis and simulation results confirm that, when properly
configured, these schemes represent a viable approach to build effective P2P
resource discovery in large-scale, dynamic distributed systems.Comment: A revised version of the paper appears in Proc. of the 5th
International Workshop on Complex Networks (CompleNet 2014) - Studies in
Computational Intelligence Series, Springer-Verlag, Bologna (Italy), March
201
The Design of Effective Maintenance Outsourcing Contracts
Recent developments in maintenance planning and
management demonstrate that the establishment of optimized
maintenance policies may drastically improve the
performance and reduce the operating cost of facilities.
However maintenance activities are typically outside of the
core business of production facilities, hence enterprises often
fail to catch the opportunities that may originate by properly
optimized management strategies. A strategic maintenance
management should hence encompass the possibility of
outsourcing maintenance activities to ensure the necessary
perfomance of production systems, while allowing
enterprises to concentrate their resources on their core
activities. In order to be effectively undertaken an
outsourcing strategy must be supported by a proper
performance oriented contract. The present paper aims to
provide an adequate methodology to address such issues and
to define a framework for the definition of the relevant
contract variables such as availability levels, penalty
policies, rewards and service cost. The methodology here
proposed is based upon the evaluation of the expected profit
function of both the outsourcer and the provider, by
performing a trade-off analysis on the basis of the
transaction costs
Prevalence of Escherichia coli carriage in the oropharynx of ambulatory children and adults with and without upper respiratory symptoms
[No abstract available
Stakeholder engagement in green place branding:a focus on user-generated content
The purpose of this research is to investigate how the green image of a city can affect potential visitors' attitude toward the city in the context of userâgenerated content. The study adopts a 2 Ă 2 experimental design in which the greenness of the city image and the social distance between the users and the authors of social media content are examined. The results demonstrate that green image has a significant effect on attitudes toward cities. Moreover, the effects of social media content vary according to the perceived social distance between the author of the post and potential visitors. This study contributes to the literature by assessing the role that social media content plays in place branding and communication. Furthermore, it provides relevant insights on how institutions should enhance the sustainable resources of cities with their environmental policy and encourage the generation of content from various stakeholders to contribute to the development of a city's image
Service Orientation and the Smart Grid state and trends
The energy market is undergoing major changes, the most notable of which is the transition from a hierarchical closed system toward a more open one highly based on a âsmartâ information-rich infrastructure. This transition calls for new information and communication technologies infrastructures and standards to support it. In this paper, we review the current state of affairs and the actual technologies with respect to such transition. Additionally, we highlight the contact points between the needs of the future grid and the advantages brought by service-oriented architectures.
Exploring the randomness of Directed Acyclic Networks
The feed-forward relationship naturally observed in time-dependent processes
and in a diverse number of real systems -such as some food-webs and electronic
and neural wiring- can be described in terms of so-called directed acyclic
graphs (DAGs). An important ingredient of the analysis of such networks is a
proper comparison of their observed architecture against an ensemble of
randomized graphs, thereby quantifying the {\em randomness} of the real systems
with respect to suitable null models. This approximation is particularly
relevant when the finite size and/or large connectivity of real systems make
inadequate a comparison with the predictions obtained from the so-called {\em
configuration model}. In this paper we analyze four methods of DAG
randomization as defined by the desired combination of topological invariants
(directed and undirected degree sequence and component distributions) aimed to
be preserved. A highly ordered DAG, called \textit{snake}-graph and a
Erd\:os-R\'enyi DAG were used to validate the performance of the algorithms.
Finally, three real case studies, namely, the \textit{C. elegans} cell lineage
network, a PhD student-advisor network and the Milgram's citation network were
analyzed using each randomization method. Results show how the interpretation
of degree-degree relations in DAGs respect to their randomized ensembles depend
on the topological invariants imposed. In general, real DAGs provide disordered
values, lower than the expected by chance when the directedness of the links is
not preserved in the randomization process. Conversely, if the direction of the
links is conserved throughout the randomization process, disorder indicators
are close to the obtained from the null-model ensemble, although some
deviations are observed.Comment: 13 pages, 5 figures and 5 table
Manometric evaluation of internal anal sphincter after fissurectomy and anoplasty for chronic anal fissure: a prospective study
Chronic anal fissure (CAF) is a common painful clinical disease and its pathogenesis remains poorly understood. After failure of pharmacological therapy, that is the first-line treatment, sur- gical sphincterotomy remains the treatment of choice although it is followed by a high rate of anal incontinence resulting from the sphincter damage; therefore, the research of a sphincter-saving surgical option has become an important goal. The aim of this study was to evaluate the mano- metric modifications and the incidence of anal incontinence after fissurectomy and anoplasty with advancement skin flap in patients affected by CAF with hypertonia of the internal anal sphincter (IAS). Fifteen patients affected by CAF with hypertonia of IAS, unresponsive to medical therapy, were enrolled. All subjects underwent fissurectomy and anoplasty with advancement skin flap. Anorectal manometry was performed preoperatively and after 6 and 12 months from surgery. Maximum resting pressure (MRP), maximum squeeze pressure (MSP), ultraslow wave activity (USWA), fissure healing, anal continence, and postoperative complications were recorded. All patients healed within 30 days from surgery. No intra- or postoperative complications were recorded except for a case of partial donor site break. No significant modifications of MSP were detected. Six months after surgery, MRP was higher with respect to healthy subjects but signif- icantly reduced in comparison to baseline levels. At 12 months, it was higher have versus 6-month values but significantly lower versus preoperative values. USWA was significantly represented in patients with CAF versus healthy subject. Both at 6 and 12 months, they decreased significantly with respect to preoperative values without significant differences versus healthy subjects. Both at 6 and 12 months, anal continence did not differ with respect to preoperative time. The fissurectomy with anoplasty resulted in a high healing rate without surgical sequelae or anal incontinence. Also, it was able to reduce IAS pressure in the same manner as surgical sphincterotomy or forceful dilatation
Residual Strength and Durability of Glass fiber FRCM and CRM Systems Aged in Alkaline Environments
Fabric Reinforced Cementitious Matrix (FRCM) and Composite Reinforced Mortar (CRM) systems are used as Externally Bonded Reinforcements (EBR) in civil and historical construction. These materials are made by fibrous reinforcement, in forms of dry (FRCM) or cured (CRM) meshes embedded in a cementitious/hydraulic lime matrix. At present, this technology is considered very promising in the field of structural strengthening, retrofitting and repair existing structures. This is true especially in those cases of masonry and historical buildings, due to the specific criteria of conservation and compatibility with the substrate that need to be fulfilled. These materials, in fact, results more compatible with masonry substrate because of the inorganic matrix, instead of polymeric resin used for the well-known FRP systems (Fiber Reinforced Polymers). The recent use of these new materials in civil engineering needs appropriate and complete guidelines, that regard not only the design aspects but also the durability features. This paper presents the results of a large experimental program focused on the durability of FRCM and CRM systems and their single components, in different alkaline environments. For the whole experimental campaign, the samples have been immersed into three different alkaline solutions, for four exposure times (500, 1000, 2000 and 3000 hrs). In addition, in order to study the different accelerating effects due to temperature, three different temperatures were maintained during the ageing periods: 23°C, 40°C and 70°C. The results about the mechanical characterization of residual properties are discussed in order to highlight the influence of alkaline environments on the mechanical properties of single elements and the whole strengthening systems that were tested herein
Electroexcitation of the P33(1232), P11(1440), D13(1520), S11(1535) at Q^2=0.4 and 0.65(GeV/c)^2
Using two approaches: dispersion relations and isobar model, we have analyzed
recent high precision CLAS data on cross sections of \pi^0, \pi^+, and \eta
electroproduction on protons, and the longitudinally polarized electron beam
asymmetry for p(\vec{e},e'p)\pi^0 and p(\vec{e},e'n)\pi^+. The contributions of
the resonances P33(1232), P11(1440), D13(1520), S11(1535) to \pi
electroproduction and S11(1535) to \eta electroproduction are found. The
results obtained in the two approaches are in good agreement with each other.
There is also good agreement between amplitudes of the \gamma^* N \to S11(1535)
transition found in \pi and \eta electroproduction. For the first time accurate
results are obtained for the longitudinal amplitudes of the P11(1440),
D13(1520) and S11(1535) electroexcitation on protons.Comment: 9 pages, 9 figure
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