Cooperation Among Members of Online Communities

Today some of the most popular and successful applications over the Internet are based on Peer-to-Peer (P2P) solutions. Online Social Networks (OSN) represent a stunning phenomenon too, involving communities of unprecedented size, whose members organize their relationships on the basis of social or professional friendship. This work deals with a P2P video streaming platform and focuses on the performance improvements that can be granted to those P2P nodes that are also members of a social network. The underpinning idea is that OSN friends (and friends of friends) might be more willing to help their mates than complete strangers in fetching the desired content within the P2P overlay. Hence, an approach is devised to guarantee that P2P users belonging to an OSN are guaranteed a better service when critical conditions build up, i.e., when bandwidth availability is scarce. Different help strategies are proposed, and their improvements are numerically assessed, showing that the help of direct friends, two-hops away friends and, in the limit, of the entire OSN community brings in considerable advantages. The obtained results demonstrate that the amount of delivered video increases and the delay notably decreases, for those privileged peers that leverage their OSN membership within the P2P overlay.</jats:p

Taking Advantage of Social Network Relationships in P2P Streaming Overlays

Abstract-In recent years, classical Internet applications have been accompanied by the surging of a great variety of new services and exciting possibilities. Among such broad range, two particular phenomena are highly successful: Online Social Networks (OSNs) and Peer-to-Peer (P2P) services. This paper merges these distinct worlds, via the proposal of a P2P streaming system that takes advantage of the friendship relationships of an underlying OSN, to better distribute videos among the overlay peers that are also friends within the OSN. A category of privileged users is therefore created, that is guaranteed a satisfying viewing experience when the P2P overlay operates in critical conditions, i.e, when bandwidth availability is scarce. We show that the help of direct friends, two-hops away friends and, in the limit, of the entire OSN community brings in considerable advantages to the peers that are OSN members. In particular: the number of those among them that are able to download the entire video significantly increases; the number of video portions they can obtain consistently raises; as desired, when the P2P system is operating in underloaded conditions, a proper functioning is guaranteed to all of its nodes, regardless of their being members of the OSN or plain P2P users

Sur la d\ue9couverte de Characidae (Pisces, Cypriniformes) dans l\u27Eoc\ue8ne Inf\ue9rieur fran\ue7ais

Volume: 88Start Page: 175End Page: 17

Numerical Evaluation of Fatigue Strength on Mechanical Notched Components under Multiaxial Loadings

This paper deals with the fatigue behaviour of complex, three-dimensional, stress concentrations under multiaxial loadings. Starting from the stress field obtained by means of a linear elastic analysis and taking advantage of the so-called implicit gradient approach, a safety factor is calculated for high-cycle fatigue. In this first attempt, attention has been focused on the stress-invariant based approaches in the highcycle fatigue regime. The multiaxial damage evaluation is obtained by analysing the full loading path of the Crossland five-dimensional invariant deviatoric stress in Euclidean space by means of the variance reference frame. Explicit analytical solutions of the proposed criterion are given in the case of biaxial sinusoidal loads. The method was validated by comparison with experimental data involving multiaxial in-phase and out-of-phase loading of specimens which contained three-dimensional stress concentrations. These types of stress concentrations are known to present problems for other predictive methods

Linee guida per la prevenzione delle esposizioni al gas radon in ambienti indoor

La problematica del radon indoor è da anni ampiamente studiata e discussa a livello mondiale e, nel tempo, le strategie per la tutela della salute pubblica dalle esposizioni a gas radon sono state modulate in relazione alle conoscenze scientifiche all’epoca note. Nel passato, infatti, l’attenzione era posta sulla riduzione delle esposizioni a concentrazione di gas radon elevati. In effetti le stime di rischio di contrarre un tumore polmonare erano basate, fino a pochi anni fa, principalmente su studi epidemiologici che coinvolgevano gruppi di lavoratori di miniere sotterranee di uranio caratterizzate da valori molto alti di concentrazione di gas radon. L’Agenzia Internazionale per la Ricerca sul Cancro (IARC), organizzazione tecnico scientifica dell’Organizzazione Mondiale della Sanità (OMS), già dagli anni 90’, ha classificato il gas radon tra i cancerogeni accertati del gruppo I, per i quali vi è massima evidenza di cancerogenicità, fornendo indicazioni circa la necessità di intervenire sulle concentrazioni elevate di gas radon. Queste linee guida intendono rappresentare uno strumento operativo per i Comuni, per i progettisti e per i costruttori di edifici e mirano a fornire indicazioni e suggerimenti riguardanti la realizzazione di nuovi edifici radon-resistenti e le azioni per ridurre l’esposizione al gas radon nel caso di edifici esistenti, anche in sinergia con gli interventi finalizzati al risparmio energetico. Le evidenze scientifiche rilevano l’opportunità di intervenire sin dalla progettazione dell’edificio, attraverso sistemi che prevedano la riduzione sia dell’ingresso del gas radon nell’abitazione che la sua concentrazione negli ambienti chiusi al fine di contenere l’esposizione dei suoi abitanti al gas. Tali interventi possono essere anche realizzati durante interventi di manutenzione straordinaria che prevedano il coinvolgimento dell’interfaccia suolo-edificio

RISANAMENTI DA RADON IN EDIFICI SCOLASTICI IN PROVINCIA DI BERGAMO

Nell’ambito del Piano Nazionale Radon, coordinato dall’ISS, la Regione Lombardia ha affidato all’ASL di Bergamo un progetto finalizzato alla realizzazione di azioni di risanamento per la riduzione dell'inquinamento da Radon in alcuni edifici scolastici

THE PHYLOGENETIC RELATIONSHIPS AMONG REQUIEM AND HAMMERHEAD SHARKS: INFERRING PHYLOGENY WHEN THOUSANDS OF EQUALLY MOST PARSIMONIOUS TREES RESULT

Protein variation among 37 species of carcharhiniform sharks was examined at 17 presumed loci. Evolutionary trees were inferred from these data using both cladistic character and a distance Wagner analysis. Initial cladistic character analysis resulted in more than 30 000 equally parsimonious tree arrangements. Randomization tests designed to evaluate the phylogenetic information content of the data suggest the data are highly significantly different from random in spite of the large number of parsimonious trees produced. Different starting seed trees were found to influence the kind of tree topologies discovered by the heuristic branch swapping algorithm used. The trees generated during the early phases of branch swapping on a single seed tree were found to be topologically similar to those generated throughout the course of branch swapping. Successive weighting increased the frequency and the consistency with which certain clades were found during the course of branch swapping, causing the semi-strict consensus to be more resolved. Successive weighting also appeared resilient to the bias associated with the choice of initial seed tree causing analyses seeded with different trees to converge on identical final character weights and the same semi-strict consensus tree. The summary cladistic character analysis and the distance Wagner analysis both support the monophyly of two major clades, the genus Rhizoprionodon and the genus Sphyrna. . The distance Wagner analysis also supports the monophyly of the genus Carcharhinus . However, the cladistic analysis suggests that Carcharhinus is a paraphyletic group that includes the blue shark Prionace glauca .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73088/1/j.1096-0031.1992.tb00073.x.pd