Combined Intra- and Inter-domain Traffic Engineering using Hot-Potato Aware Link Weights Optimization

A well-known approach to intradomain traffic engineering consists in finding the set of link weights that minimizes a network-wide objective function for a given intradomain traffic matrix. This approach is inadequate because it ignores a potential impact on interdomain routing. Indeed, the resulting set of link weights may trigger BGP to change the BGP next hop for some destination prefixes, to enforce hot-potato routing policies. In turn, this results in changes in the intradomain traffic matrix that have not been anticipated by the link weights optimizer, possibly leading to degraded network performance. We propose a BGP-aware link weights optimization method that takes these effects into account, and even turns them into an advantage. This method uses the interdomain traffic matrix and other available BGP data, to extend the intradomain topology with external virtual nodes and links, on which all the well-tuned heuristics of a classical link weights optimizer can be applied. A key innovative asset of our method is its ability to also optimize the traffic on the interdomain peering links. We show, using an operational network as a case study, that our approach does so efficiently at almost no extra computational cost.Comment: 12 pages, Short version to be published in ACM SIGMETRICS 2008, International Conference on Measurement and Modeling of Computer Systems, June 2-6, 2008, Annapolis, Maryland, US

Heavy quark diffusion in perturbative QCD at next-to-leading order

We compute the momentum diffusion coefficient of a nonrelativistic heavy quark in a hot QCD plasma, to next-to-leading order in the weak coupling expansion. Corrections arise at O(g); physically they represent interference between overlapping scatterings, as well as soft, electric scale ($p\sim gT$) gauge field physics, which we treat using the hard thermal loop (HTL) effective theory. In 3-color, 3-flavor QCD, the momentum diffusion constant of a fundamental representation heavy quark at NLO is $\kappa = \frac{16\pi}{3} \alpha_s^2 T^3 (\ln \frac{1}{g} + 0.07428 + 1.8869 g)$. The convergence of the weak coupling expansion is poor.Comment: 4 pages, 3 figure

Fostering better engagement among male and female students in physics laboratory /

Publié comme vol. 24, no 3, spring 2011 de la revue Pédagogie collégiale.Bibliographie

Le vote des ouvriers, de l’alignement à gauche à une « droitisation » ?

Depuis un demi-siècle, les comportements électoraux et les attitudes politiques des ouvriers ont connu de profondes transformations. Les ouvriers constituent-ils un monde à part sur la scène politique ? Existe-t-il toujours une spécificité ouvrière ?Note publiée sur le site du Cevipof "Elections 2012" In "Le recueil des notes du Cevipof - Les électorats sociologiques

Pour un meilleur engagement des garçons et des filles au laboratoire de physique

Comprend des références bibliographiques

Fostering better engagement among male and female students in physics laboratory /

Publié comme vol. 24, no 3, spring 2011 de la revue Pédagogie collégiale.Bibliographie

John Cook Wilson on the indefinability of knowledge

Can knowledge be defined? We expound an argument of John Cook Wilson's that it cannot. Cook Wilson's argument connects knowing with having the power to inquire. We suggest that if he is right about that connection, then knowledge is, indeed, indefinable

Cook Wilson on knowledge and forms of thinking

John Cook Wilson is an important predecessor of contemporary knowledge first epistemologists: among other parallels, he claimed that knowledge is indefinable. We reconstruct four arguments for this claim discernible in his work, three of which find no clear analogues in contemporary discussions of knowledge first epistemology. We pay special attention to Cook Wilson’s view of the relation between knowledge and forms of thinking (like belief). Claims of Cook Wilson’s that support the indefinability of knowledge include: that knowledge, unlike belief, straddles an active/passive divide; that, rather than entailing belief, knowledge excludes belief; and that understanding forms of thinking other than knowledge (such as belief) depends on understanding knowledge. Reflecting on Cook Wilson’s framework highlights underappreciated concerns relevant to any attempt to define knowledge

Coherent Raman spectro-imaging with laser frequency combs

Optical spectroscopy and imaging of microscopic samples have opened up a wide range of applications throughout the physical, chemical, and biological sciences. High chemical specificity may be achieved by directly interrogating the fundamental or low-lying vibrational energy levels of the compound molecules. Amongst the available prevailing label-free techniques, coherent Raman scattering has the distinguishing features of high spatial resolution down to 200 nm and three-dimensional sectioning. However, combining fast imaging speed and identification of multiple - and possibly unexpected- compounds remains challenging: existing high spectral resolution schemes require long measurement times to achieve broad spectral spans. Here we overcome this difficulty and introduce a novel concept of coherent anti-Stokes Raman scattering (CARS) spectro-imaging with two laser frequency combs. We illustrate the power of our technique with high resolution (4 cm-1) Raman spectra spanning more than 1200 cm-1 recorded within less than 15 microseconds. Furthermore, hyperspectral images combining high spectral (10 cm-1) and spatial (2 micrometers) resolutions are acquired at a rate of 50 pixels per second. Real-time multiplex accessing of hyperspectral images may dramatically expand the range of applications of nonlinear microscopy.Comment: 8 pages, 3 figure