Investigating self-similarity and heavy-tailed distributions on a large scale experimental facility

International audienceAfter the seminal work by Taqqu et al. relating selfsimilarity to heavy-tailed distributions, a number of research articles verified that aggregated Internet traffic time series show self-similarity and that Internet attributes, like Web file sizes and flow lengths, were heavy-tailed. However, the validation of the theoretical prediction relating self-similarity and heavy tails remains unsatisfactorily addressed, being investigated either using numerical or network simulations, or from uncontrolled Web traffic data. Notably, this prediction has never been conclusively verified on real networks using controlled and stationary scenarii, prescribing specific heavy-tailed distributions, and estimating confidence intervals. With this goal in mind, we use the potential and facilities offered by the large-scale, deeply reconfigurable and fully controllable experimental Grid5000 instrument, to investigate the prediction observability on real networks. To this end we organize a large number of controlled traffic circulation sessions on a nation-wide real network involving two hundred independent hosts. We use a FPGA-based measurement system, to collect the corresponding traffic at packet level. We then estimate both the self-similarity exponent of the aggregated time series and the heavy-tail index of flow size distributions, independently. On the one hand, our results complement and validate with a striking accuracy some conclusions drawn from a series of pioneer studies. On the other hand, they bring in new insights on the controversial role of certain components of real networks

Ovine serum biomarkers of early and late phase scrapie

<p>Abstract</p> <p>Background</p> <p>Transmissible spongiform encephalopathies are fatal neurodegenerative disease occurring in animals and humans for which no <it>ante-mortem </it>diagnostic test in biological fluids is available. In such pathologies, detection of the pathological form of the prion protein (i.e., the causative factor) in blood is difficult and therefore identification of new biomarkers implicated in the pathway of prion infection is relevant.</p> <p>Methods</p> <p>In this study we used the SELDI-TOF MS technology to analyze a large number of serum samples from control sheep and animals with early phase or late phase scrapie. A few potential low molecular weight biomarkers were selected by statistical methods and, after a training analysis, a protein signature pattern, which discriminates between early phase scrapie samples and control sera was identified.</p> <p>Results</p> <p>The combination of early phase biomarkers showed a sensitivity of 87% and specificity of 90% for all studied sheep in the early stage of the disease. One of these potential biomarkers was identified and validated in a SELDI-TOF MS kinetic study of sera from Syrian hamsters infected by scrapie, by western blot analysis and ELISA quantitation.</p> <p>Conclusions</p> <p>Differential protein expression profiling allows establishing a TSE diagnostic in scrapie sheep, in the early phase of the disease. Some proteic differences observed in scrapie sheep exist in infected hamsters. Further studies are being performed to identify all the discriminant biomarkers of interest and to test our potential markers in a new cohort of animals.</p

A dipicolinate lanthanide complex for solving protein structures using anomalous diffraction

International audienceTris-dipicolinate lanthanide complexes were used to prepare derivative crystals of six proteins: hen egg-white lysozyme, turkey egg-white lysozyme, thaumatin from Thaumatococcus daniellii, urate oxidase from Aspergillus flavus, porcine pancreatic elastase and xylanase from Trichoderma reesei. Diffraction data were collected using either synchrotron radiation or X-rays from a laboratory source. In all cases, the complex turned out to be bound to the protein and the phases determined using the anomalous scattering of the lanthanide led to high-quality electron-density maps. The binding mode of the complex was characterized from the refined structures. The lanthanide tris-dipicolinate was found to bind through interactions between carboxylate groups of the dipicolinate ligands and hydrogen-bond donor groups of the protein. In each binding site, one enantiomeric form of the complex is selected from the racemic solution according to the specific site topology. For hen egg-white lysozyme and xylanase, derivative crystals obtained by cocrystallization belonged to a new monoclinic C2 crystal form that diffracted to high resolution

Vérification du lien entre auto-similarité et distributions à queues lourdes sur un dispositif grande échelle

National audienc

Exploration of the supramolecular interactions involving tris-dipicolinate lanthanide complexes in protein crystals by a combined biostructural, computational and NMR study.

International audienceIncorporating in a non-covalent manner lanthanide derivatives into protein crystals has shown to be of prime interest for X-ray crystallography, insofar as these versatile compounds can co-crystallize with proteins through supramolecular interactions, in addition to being strong anomalous scatterers for anomalous-based diffraction techniques. In this paper, the selective affinity of tris-dipicolinate lanthanide complexes for cationic amino-acid residues is explored, using a panel of experimental (X-ray diffraction, NMR titration) and theoretical methods that provides access to an accurate description of the interaction process

Two-Photon Microscopy and Spectroscopy of Lanthanide Bioprobes

International audienceThe linear and non-linear photophysical properties of tris-dipicolinate europium and terbium complexes (absorption, emission, lifetime, luminescence induced by two-photon absorption) are studied in the crystalline state as well as in protein derivative crystals and compared to those in solution. Upon laser irradiation at 532 nm, luminescence of terbium is induced by a two-photon antenna effect, whereas luminescence of europium results from one-photon absorption in forbidden f–f transitions. Finally, linear and two-photon microscopy imaging experiments on biological and bio-inspired crystals are performed. These first proof-of-concept experiments open the way for the development of time-resolved non-linear microscopy that should combine the advantages of lanthanide luminescence (long lifetime, sharp emission bands, insensitivity to oxygen) with those of confocal biphotonic excitation (near-IR excitation, 3D resolution and reduced photodamage)