Improving file distribution performance by grouping in peer-to-peer networks

It has been shown that the peer-to-peer paradigm is more efficient than the traditional client-server model for file sharing among a large number of users. Given a group of leechers who wants to download a single file and a group of seeds who possesses the whole file, the minimum time needed for distributing the file to all users can be calculated based on their bandwidth availabilities. A scheduling algorithm has been developed so that every leecher can obtain the file within this minimum time. Unfortunately, this mechanism is not optimal with regard to the average download time among the peers. In this paper, we study how to reduce the average download time without prolonging the time needed for all leechers to obtain the file from a theoretical perspective. Based on the bandwidth capacities, the seeds and leechers are divided into different groups. We identify the necessary conditions for grouping to bring about benefits. We also study the impact on performance when leechers leave the system before the downloading process is complete. To evaluate our mechanism, we conduct extensive simulations and compare the performance with a BitTorrentlike file sharing algorithm. The results show that our grouping protocol successfully reduces the average download time over a wide range of system configurations. © 2009 IEEE.published_or_final_versio

Super-Yang-Mills and M5-branes

We uplift 5-dimensional super-Yang-Mills theory to a 6-dimensional gauge theory with the help of a space-like constant vector $\eta^M$, whose norm determines the Yang-Mills coupling constant. After the localization of $\eta^M$ the 6D gauge theory acquires Lorentzian invariance as well as scale invariance. We discuss KK states, instantons and the flux quantization. The 6D theory admits extended solutions like 1/2 BPS `strings' and monopoles.Comment: 15 pages; minor changes, to appear in JHE

Location and associated carbon storage of erosional escarpments of seagrass Posidonia mats

Seagrasses of the genus Posidonia can form an irregular seascape due to erosional processes exposing thick walls of organic matter-rich soils. However, little is known about the location and characteristics of these particular formations. Here we provide comprehensive estimates of organic carbon (Corg) storage in Posidonia oceanica and Posidonia australis meadows, while providing insight into their location and mechanisms of formation, and highlighting future research directions. Erosional reef escarpments are restricted to shallow highly productive P. oceanica meadows from the Mediterranean Sea and P. australis meadows from the Indian Ocean, and sustain the existence of Corg-rich deposits in surrounding meadows. The thickness of the mat escarpments can reach up to 3 m and their length can vary from few to hundreds of meters. Mechanisms of formation appear to differ among sites, from naturally-induced escarpments by wave action and/or tidal flow to human-induced escarpments by dredging activities. The inter-twined remains of seagrass shoots within the sediment matrix consolidate the sandy substrate and hold the exposed Posidonia mat escarpments together, maintaining a semi-rigid structure. This phenomenon is unusual but of exceptional importance in marine biogeochemical cycles, revealing the largest Corg sinks among seagrasses worldwide (ranging from 15 to 176 kg Corg m−2 in 2 m-thick mats accumulated at 2–249 g Corg m−2 yr−1 over 300–3000 yr)

Time resolved imaging of magnetization dynamics in hard disk writer yokes excited by bipolar current pulses

This is the final version of the article. Available from the American Institute of Physics via the DOI in this record.A partially built hard disk writer structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied by time and vector resolved scanning Kerr microscopy. All three time dependent components of the magnetization were recorded simultaneously as a bipolar current pulse with 1 MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously.The authors acknowledge the financial support of Seagate Pla

Uso de fontes em aulas de História e conciência histórica: encaminhamentos e discussões teóricas

Anais do XVII Congresso Internacional das Jornadas de Educaão História - teoria, pesquisa e prática - I Encontro da AIPEDH - Associação Iber-Americana de Pesquisadores em Educação História, realizado pela Universidade Federal da Integração Latino-Americana, entre 02, 03 e 04 de agosto de 2017.Este trabalho apresenta os encaminhamentos de uma pesquisa iniciada no curso de graduação em História na Universidade Estadual de Londrina, e prossegue como parte das discussões que estão sendo realizadas no Mestrado do Programa de Pós-Graduação em Educação da mesma universidade, sob orientação da Professora Dra. Marlene Rosa Cainelli. A investigação realizada tem como objetivo principal o estudo do uso de fontes no ensino de história, mais especificamente sobre a literatura em aulas de história na perspectiva da Educação Histórica, tendo como tema adaptações do clássico “Os Miseráveis”, de Victor Hugo. A pesquisa atual trata do uso de uma versão em História em Quadrinhos (HQ) da obra, buscando verificar como HQs podem contribuir para o desenvolvimento da consciência histórica dos alunos. Para tanto, utilizamo-nos, entre outros, dos escritos de Rüsen (2011) sobre a consciência histórica e Fronza (2007, 2012) sobre o uso de quadrinhos relacionados a temáticas históricasCAPE

Pseudomonas aeruginosa biofilm disruption using microbial surfactants.

AIMS: To establish the ability of the rhamnolipids biosurfactants from Pseudomonas aeruginosa, in the presence and absence of caprylic acid and ascorbic acid, to disrupt bacterial biofilms, compared with the anionic alkyl sulphate surfactant Sodium dodecyl sulphate (SDS). METHODS AND RESULTS: Pseudomonas aeruginosa ATCC 15442 biofilms were disrupted by rhamnolipids at concentrations between 0·5 and 0·4 g l(-1) and with SDS at 0·8 g l(-1) . The combination of rhamnolipids 0·4 g l(-1) and caprylic acid at 0·1 g l(-1) showed a remarkable effect on biofilm disruption and cell killing. After 30 min of treatment most of the biofilm was disrupted and cell viability was significantly reduced. Neither caprylic acid nor ascorbic acid has any effect on biofilm disruption at 0·1 g l(-1) . SDS is an effective antimicrobial agent; however, in the presence of caprylic acid its effect was neutralized. CONCLUSIONS: The results show that rhamnolipids at low concentration in the presence of caprylic acid are promising molecules for inhibition/disruption of biofilms formed by Ps. aeruginosa ATCC 15442. SIGNIFICANCE AND IMPACT OF THE STUDY: The disruption of biofilms has major significance in many industrial and domestic cleaning applications and in medical situations

BPS States on M5-brane in Large C-field Background

We extensively study BPS solutions of the low energy effective theory of M5-brane in large C-field background. This provides us an opportunity to explore the interactions turned on by C-field background through the Nambu-Poisson structure. The BPS states considered in this paper include the M-waves, the self-dual string (M2 ending on M5), tilted M5-brane, holomorphic embedding of M5-brane and the intersection of two M5-branes along a 3-brane.Comment: 25 pages, reference adde

Time resolved scanning Kerr microscopy of hard disk writer structures with a multilayered yoke

The erratum is available in ORE at http://hdl.handle.net/10871/21966Partially built hard disk writer structures with a multilayered yoke formed from 4 repeats of a NiFe(∼1 nm)/CoFe(50 nm) bilayer were studied by time and vector resolved scanning Kerr microscopy. Dynamic images of the in-plane magnetization suggest an underlying closure domain equilibrium state. This state is found to be modified by application of a bias magnetic field and also during pulse cycling, leading to different magnetization rotation and relaxation behavior within the tip region. © 2013 AIP Publishing LLC.The authors gratefully acknowledge financial support from the Seagate Plan

Star Formation in Nearby Clouds (SFiNCs): X-Ray and Infrared Source Catalogs and Membership

This is the final version of the article. Available from American Astronomical Society via the DOI in this record.The Star Formation in Nearby Clouds (SFiNCs) project is aimed at providing a detailed study of the young stellar populations and of star cluster formation in the nearby 22 star-forming regions (SFRs) for comparison with our earlier MYStIX survey of richer, more distant clusters. As a foundation for the SFiNCs science studies, here, homogeneous data analyses of the Chandra X-ray and Spitzer mid-infrared archival SFiNCs data are described, and the resulting catalogs of over 15,300 X-ray and over 1,630,000 mid-infrared point sources are presented. On the basis of their X-ray/infrared properties and spatial distributions, nearly 8500 point sources have been identified as probable young stellar members of the SFiNCs regions. Compared to the existing X-ray/mid-infrared publications, the SFiNCs member list increases the census of YSO members by 6%-200% for individual SFRs and by 40% for the merged sample of all 22 SFiNCs SFRs.The SFiNCs project is supported at Penn State by NASA grant NNX15AF42G, Chandra GO grant SAO AR5-16001X, Chandra GO grant GO2-13012X, Chandra GO grant GO3-14004X, Chandra GO grant GO4-15013X, Spitzer GO program 90179, and the Chandra-ACIS Team contract SV474018 (G. Garmire & L. Townsley, Principal Investigators), issued by the Chandra X-Ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. he Guaranteed Time Observations (GTO) included here were selected by the ACIS Instrument Principal Investigator, Gordon P. Garmire, of the Huntingdon Institute for X-Ray Astronomy, LLC, which is under contract to the Smithsonian Astrophysical Observatory; Contract SV2-82024. This research made use of data products from the Chandra Data Archive and the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (California Institute of Technology) under a contract with NASA. This research used data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has also made use of NASA's Astrophysics Data System Bibliographic Services and SAOImage DS9 software developed by Smithsonian Astrophysical Observatory, and the SIMBAD database (operated at CDS, Strasbourg, France)

Intracluster age gradients in numerous young stellar clusters

This is the final version of the article.Available from Oxford University Press via the DOI in this record.The pace and pattern of star formation leading to rich young stellar clusters is quite uncertain. In this context, we analyse the spatial distribution of ages within 19 young (median t ≲ 3 Myr on the Siess et al. time-scale), morphologically simple, isolated, and relatively rich stellar clusters. Our analysis is based on young stellar object (YSO) samples from the Massive Young Star-Forming Complex Study in Infrared and X-ray and Star Formation in Nearby Clouds surveys, and a new estimator of pre-main sequence (PMS) stellar ages, AgeJX, derived from X-ray and near-infrared photometric data. Median cluster ages are computed within four annular subregions of the clusters. We confirm and extend the earlier result of Getman et al. (2014): 80 per cent of the clusters show age trends where stars in cluster cores are younger than in outer regions. Our cluster stacking analyses establish the existence of an age gradient to high statistical significance in several ways. Time-scales vary with the choice of PMS evolutionary model; the inferred median age gradient across the studied clusters ranges from 0.75 to 1.5 Myr pc−1. The empirical finding reported in the present study – late or continuing formation of stars in the cores of star clusters with older stars dispersed in the outer regions – has a strong foundation with other observational studies and with the astrophysical models like the global hierarchical collapse model of Vázquez-Semadeni et al.The MYStIX project is now supported by the Chandra archive grant AR7-18002X. The SFiNCs project is supported at Penn State by NASA grant NNX15AF42G, Chandra GO grant SAO AR5-16001X, Chandra GO grant GO2-13012X, Chandra GO grant GO3-14004X, Chandra GO grant GO4-15013X, and the Chandra ACIS Team contract SV474018 (G. Garmire & L. Townsley, Principal Investigators), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. The Guaranteed Time Observations (GTO) data used here were selected by the ACIS Instrument Principal Investigator, Gordon P. Garmire, of the Huntingdon Institute for X-ray Astronomy, LLC, which is under contract to the Smithsonian Astrophysical Observatory; Contract SV2-82024. This research has made use of NASA's Astrophysics Data System Bibliographic Services and SAOImage DS9 software developed by Smithsonian Astrophysical Observatory