Unconventional magnetism in all-carbon nanofoam

We report production of nanostructured carbon foam by a high-repetition-rate, high-power laser ablation of glassy carbon in Ar atmosphere. A combination of characterization techniques revealed that the system contains both sp2 and sp3 bonded carbon atoms. The material is a novel form of carbon in which graphite-like sheets fill space at very low density due to strong hyperbolic curvature, as proposed for ?schwarzite?. The foam exhibits ferromagnetic-like behaviour up to 90 K, with a narrow hysteresis curve and a high saturation magnetization. Such magnetic properties are very unusual for a carbon allotrope. Detailed analysis excludes impurities as the origin of the magnetic signal. We postulate that localized unpaired spins occur because of topological and bonding defects associated with the sheet curvature, and that these spins are stabilized due to the steric protection offered by the convoluted sheets.Comment: 14 pages, including 2 tables and 7 figs. Submitted to Phys Rev B 10 September 200

Efficient IP-level network topology capture

International audienceLarge-scale distributed traceroute-based measurement sys- tems are used to obtain the topology of the internet at the IP-level and can be used to monitor and understand the behavior of the net- work. However, existing approaches to measuring the public IPv4 net- work space often require several days to obtain a full graph, which is too slow to capture much of the network's dynamics. This paper presents a new network topology capture algorithm, NTC, which aims to bet- ter capture network dynamics through accelerated probing, reducing the probing load while maintaining good coverage. There are two novel as- pects to our approach: it focuses on obtaining the network graph rather than a full set of individual traces, and it uses past probing results in a new, adaptive, way to guide future probing. We study the performance of our algorithm on real traces and demonstrate outstanding improved performance compared to existing work.Les systèmes de mesure distribué à grande échelle basés sur l'outil Traceroute sont utilisés pour obtenir la topologie de l'internet au niveau IP et peuvent être utilisés pour surveiller et comprendre le comportement du réseau sous-jascent. Cependant, les approches existantes pour mesurer l'espace public IPv4 du réseau Internet nécessitent souvent plusieurs jours pour obtenir un graphe complet, ce qui est trop lent pour capturer une grande partie de la dynamique du réseau. Cet article présente un nouvel algorithme pour la capture de la topologie du réseau, NTC, visant à cibler la dynamique du réseau à travers l'accélération de sondage, ce qui réduit la charge de la mesure, tout en maintenant une bonne couverture. Il ya deux nouveaux aspects à notre approche: l'algorithme se concentre sur l'obtention du graphe du réseau plutôt que d'effectuer un ensemble complet de traces individuelles, et il utilise les résultats de sondage précédentes de façon à adapter la mesure et de réduire les sondes envoyées. Nous étudions les performances de notre algorithme sur des traces réelles et démontrons la performance accrue de notre approche par rapport aux travaux existants

Quantifying the Effects of Circuitous Routes on the Latency of Intra-Africa Internet Traffic: A Study of Research and Education Networks

Despite an increase in the number of Internet eXchange Points (IXP) in Africa, as well as proliferation of submarine and terrestrial fibre optic cable systems, the level of peering among Africa’s Internet service providers remains low. Using active network measurements, this work characterizes the level of interconnectivity and peering among Africa’s National Research and Education Networks (NRENs),and examines the performance of traffic exchange in terms of latencies. This paper shows that over 75% of Africa’s inter-university traffic follows circuitous inter-continental routes, and is characterised by latencies that are more than double those of traffic exchanged within the continent

Router-level community structure of the Internet Autonomous Systems

The Internet is composed of routing devices connected between them and organized into independent administrative entities: the Autonomous Systems. The existence of different types of Autonomous Systems (like large connectivity providers, Internet Service Providers or universities) together with geographical and economical constraints, turns the Internet into a complex modular and hierarchical network. This organization is reflected in many properties of the Internet topology, like its high degree of clustering and its robustness. In this work, we study the modular structure of the Internet router-level graph in order to assess to what extent the Autonomous Systems satisfy some of the known notions of community structure. We show that the modular structure of the Internet is much richer than what can be captured by the current community detection methods, which are severely affected by resolution limits and by the heterogeneity of the Autonomous Systems. Here we overcome this issue by using a multiresolution detection algorithm combined with a small sample of nodes. We also discuss recent work on community structure in the light of our results

A Carbon Nanofilament-Bead Necklace

Carbon nanofilaments with carbon beads grown on their surfaces were successfully synthesized reproducibly by a floating catalyst CVD method. The nanofilaments hosting the pearl-like structures typically show an average diameter of about 60 nm, which mostly consists of low-ordered graphite layers. The beads with diameter range 150−450 nm are composed of hundreds of crumpled and random graphite layers. The mechanism for the formation of these beaded nanofilaments is ascribed to two nucleation processes of the pyrolytic carbon deposition, arising from a temperature gradient between different parts of the reaction chamber. Furthermore, the Raman scattering properties of the beaded nanofilaments have been measured, as well as their confocal Raman G-line images. The Raman spectra reveal that that the trunks of the nanofilaments have better graphitic properties than the beads, which is consistent with the HRTEM analysis. The beaded nanofilaments are expected to have high potential applications in composites, which should exhibit both particle- and fiber-reinforcing functions for the host matrixes

Electrical conductivity of natural rubber cellulose II nanocomposites

[EN] Nanocomposite materials obtained from natural rubber (NR) reinforced with different amounts of cellulose II (cell) nanoparticles (in the range of 0 to 30 phr) are studied by dielectric spectroscopy (DS) in a broad temperature range (¿150 to 150 °C). For comparative purposes, the pure materials, NR and cell, are also investigated. An analysis of the cell content effect on the conductive properties of the nanocomposites was carried out. The dielectric spectra exhibit conductivity phenomena at low frequencies and high temperatures: Maxwell¿Wagner¿ Sillars (MWS) and electrode polarization (EP) conductive processes were observed in the nanocomposite samples.We thank Professor Regina Nunes of the Instituto de Macromoleculas Eloisa Mano (Universidade Federal do Rio de Janeiro) for providing us the NR and NR-cell samples. This work was financially supported by DGCYT through grant MAT2012-33483.Ortiz Serna, MP.; Carsí Rosique, M.; Redondo Foj, MB.; Sanchis Sánchez, MJ. (2014). Electrical conductivity of natural rubber cellulose II nanocomposites. Journal of Non-Crystalline Solids. 405:180-187. https://doi.org/10.1016/j.jnoncrysol.2014.09.026S18018740

Innate recognition of bacteria in human milk is mediated by a milk-derived highly expressed pattern recognition receptor, soluble CD14.

Published versio

Emission time scale of light particles in the system Xe+Sn at 50 AMeV. A probe for dynamical emission ?

Proton and deuteron correlation functions have been investigated with both impact parameter and emission source selections. The correlations of the system (129Xe + natSn) at 50 AMeV have been measured with the 4 pi INDRA which provides a complete kinematical description of each event. The emission time scale analyzed with a quantum model reveals the time sequence of the light particles emitted by the projectile-like fragment. The short and constant emission time of the proton, independent of the impact parameter, can be attributed to a preequilibrium process.Comment: 20 pages, with 11 included figures; Accepted by European Physics Journal

A review of friction models in interacting joints for durability design.

This paper presents a comprehensive review of friction modelling to provide an understanding of design for durability within interacting systems. Friction is a complex phenomenon and occurs at the interface of two components in relative motion. Over the last several decades, the effects of friction and its modelling techniques have been of significant interests in terms of industrial applications. There is however a need to develop a unified mathematical model for friction to inform design for durability within the context of varying operational conditions. Classical dynamic mechanisms model for the design of control systems has not incorporated friction phenomena due to non-linearity behaviour. Therefore, the tribological performance concurrently with the joint dynamics of a manipulator joint applied in hazardous environments needs to be fully analysed. Previously the dynamics and impact models used in mechanical joints with clearance have also been examined. The inclusion of reliability and durability during the design phase is very important for manipulators which are deployed in harsh environmental and operational conditions. The revolute joint is susceptible to failures such as in heavy manipulators these revolute joints can be represented by lubricated conformal sliding surfaces. The presence of pollutants such as debris and corrosive constituents has the potential to alter the contacting surfaces, would in turn affect the performance of revolute joints, and puts both reliability and durability of the systems at greater risks of failure. Key literature is identified and a review on the latest developments of the science of friction modelling is presented here. This review is based on a large volume of knowledge. Gaps in the relevant field have been identified to capitalise on for future developments. Therefore, this review will bring significant benefits to researchers, academics and industrial professionals