The bulk Lorentz factor crisis of TeV blazars : evidence for an inhomogeneous pileup energy distribution ?

There is growing evidence that the estimations of the beaming Doppler factor in TeV BL Lac object based on the Self Synchrotron Compton (SSC) models are in strong disagreement with those deduced from the unification models between blazars and radio galaxies. When corrected from extragalactic absorption by the diffuse infrared background (DIrB), the SSC one-zone models require very high Lorentz factor (around 50) to avoid strong gamma-gamma absorption. However, the statistics on beamed vs. unbeamed objects, as well as the luminosity contrast, favors much lower Lorentz factor of the order of 3. In this paper, we show that for the special case of Markarian 501, the need for very high Lorentz factor is unavoidable for all one-zone models where all photons are assumed to be produced at the same location at the same time. Models assuming a double structure with two different beaming patterns can partially solve the problem of luminosity contrast, but we point out that they are inconsistent with the statistics on the number of detected TeV sources. The only way to solve the issue is to consider inhomogeneous models, where low energy and high energy photons are not produced at the same place, allowing for much smaller Lorentz factors. It implies that the jet is stratified, but also that the particle energy distribution is close to a monoenergetic one, and that pair production is likely to be significant. The implications on relativistic jet physics and particle acceleration mechanism are discussed.Comment: 31 pages, 5 figures. Accepted for publication in Ap

Automated characterization of single-photon avalanche photodiode

We report an automated characterization of a single-photon detector based on commercial silicon avalanche photodiode (PerkinElmer C30902SH). The photodiode is characterized by I-V curves at different illumination levels (darkness, 10 pW and 10 uW), dark count rate and photon detection efficiency at different bias voltages. The automated characterization routine is implemented in C++ running on a Linux computer.Comment: Have permission to post journal-formatted version on arXi

A multi-flow model for microquasars

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/gamma-rays, by varying the transition radius r_J and disc accretion rate independently. Large values of r_J and low accretion rate correspond to Quiescent and Hard states. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expect to form at the jet basis. When r_J becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large accretion rate, an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions.Comment: 12 pages, 3 figures. Proceedings of ``High Energies in the Highlands'', Fort-William, 27 June-1 July 200

A single-crystal source of path-polarization entangled photons at non-degenerate wavelengths

We demonstrate a bright, narrowband, compact, quasi-phase-matched single-crystal source generating path-polarization-entangled photon pairs at 810 nm and 1550 nm at a maximum rate of 3 Mcounts/(s THz mW) after coupling to single-mode fiber, and with two-photon interference visibility above 90%. While the source can already be used to implement quantum communication protocols such as quantum key distribution, this work is also instrumental for narrowband applications such as entanglement transfer from photonic to atomic qubits, or entanglement of photons from independent sources.Comment: 7 pages, 3 figures, published in Optics Express (2008

Le renforcement du plancher pelvien combiné aux exercices généraux versus exercices généraux seuls chez les lombalgiques chroniques non-spécifiques: travail de Bachelor

Introduction: Environ 80% de la population des pays industrialisés va connaître un jour un épisode de lombalgie. Parmi ceux-ci, 10% vont évoluer vers une chronicisation des symptômes, engendrant des coûts socio-économiques importants. Dans le cadre de la lombalgie chronique non-spécifique, il existe toutes sortes de prises en charge, dont les exercices généraux, qui sont souvent appliqués et recommandés. Toutefois, aucune littérature ne s’est exprimée quant au renforcement du plancher pelvien, alors que ce dernier est fortement lié à la stabilité du tronc. Objectif: Évaluer si le renforcement du plancher pelvien a un impact sur la douleur et l’incapacité fonctionnelle chez les lombalgiques chroniques non-spécifiques. Méthode: Nous avons consulté les bases de données, Pubmed, Cinahl, The Cochrane Library, PEDro, Kinédoc. Les mots clés sont réunis autour de trois axes: la lombalgie chronique, le plancher pelvien et les exercices généraux. Les outcomes choisis sont l'Echelle Visuelle Analogique et l’Oswestry Disability Index. Finalement, deux études randomisées controlées (RCT) ont été retenues. Leur qualité a été évaluée avec l’échelle PEDro. Résultats: Les résultats concernant l’EVA et l’ODI diffèrent en fonction des études. L’étude durant 8 semaines n’a pas montré de différence significative alors que celle durant 24 semaines a démontré une amélioration significative des deux outcomes pour le groupe intervention. Conclusion: Il n’est pas possible d’être unanime quant à l’efficacité du renforcement du plancher pelvien combiné aux exercices généraux sur la douleur et l’incapacité fonctionnelle. D’autres études menées sur le long terme, incluant un échantillon de participants plus grand et mettant en place un follow-up seraient nécessaires pour obtenir des résultats plus précis

Chapter 5 Imagining, designing and exhibiting architecture in the digital landscape

Designs for Experimentation and Inquiry examines how digital media is reconfiguring the established worlds of research, education, and professional practice. It reflects on the theoretical, methodological, and ethical issues shaping contemporary engagements with digital learning and offers insights for both analysing and intervening in digital learning practices. This insightful volume fills a gap in the current literature by bringing together experiences from Sociocultural Studies of Learning, Science and Technology Studies, and Design Studies. Each chapter is an innovative case study, examining a different aspect of digital media’s role in research, education and professional practice

Collisional Effects on HFS Transitions of Antiprotonic Helium

Collisions of metastable antiprotonic helium with medium atoms induce transitions between hyperfine structure sublevels as well as shift and broadening of the microwave M1 spectral lines. We consider these effects in the framework of a simple model with scalar and tensor interactions between $(\bar{p}\mathrm{He}^+)_{nL}$ and $\mathrm{He}$ atoms. $S$-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels $(F=L\pm 1/2, J=F\pm 1/2)$ of the $nL$ level and relative angular momenta up to $l=5$ at the kinetic energy $E\lesssim 10$ K. The calculated spin-flip cross sections are less than elastic ones by 4 orders of value. At the density $N=3\times 10^{20}$ cm$^{-3}$ and T=6 K we obtain the relaxation times $\tau(FJ\to F'J')\gtrsim 160$ ns, the frequency shifts of M1 spectral lines $\Delta\nu\lesssim 66$ KHz for the favored transitions ($\Delta F=\pm 1, \Delta J=\pm 1$) and frequency broadening of the M1 spectral lines $\gamma/2\lesssim 5.8$ MHz. The results are compatible with the recent experimental data obtained by a laser-microwave-laser resonance method.Comment: 4 pages, 3 figure, report on LEAP03, Japan, March 200

En finir avec la sacralité du sacrifice en Grèce ancienne

Examen, à l’intérieur du grec ancien, d’un « Étymon » : *jr- / *jer- Ou bien L’acte sacrificiel n’est pas d’abord un meurtre mais le geste fondateur d’une solidarité Étymologie Je développerai l’hypothèse que grec *hier- et latin *ri-t- ont la même origine, et que la racine est celle de *har-m- (le char, en grec ; *ar-m- le bras en latin ; l’assemblage fait de pièces « articulées » entre elles et solidarisées) ; que *h- est en vérité la trace de *j-, d’où, en grec, les alternances vocaliques ..

Three-color Sagnac source of polarization-entangled photon pairs

We demonstrate a compact and stable source of polarization-entangled pairs of photons, one at 810 nm wavelength for high detection efficiency and the other at 1550 nm for long-distance fiber communication networks. Due to a novel Sagnac-based design of the interferometer no active stabilization is needed. Using only one 30 mm ppKTP bulk crystal the source produces photons with a spectral brightness of 1.13x10^6 pairs/s/mW/THz with an entanglement fidelity of 98.2%. Both photons are single-mode fiber coupled and ready to be used in quantum key distribution (QKD) or transmission of photonic quantum states over large distances.Comment: 7 pages, 4 figure