SoS : School of Statistics

Une annonce peut-être un peu prématurée, mais en 2012 devrait avoir lieu l'école de statistiques de l'IN2P3:
http://sos.in2p3.fr/modeles/une.htm
J'y ai participé en 2010, et en suis revenue très enthousiaste.
Je conseille vivement cette école aux nouveaux arrivants, l'évènement et son contenu sont très enrichissants.

IDRIS

Suite du tour d'horizon des centres de calcul utlisés par le groupe, avec l'IDRIS.

L'IDRIS (Institut du développement et des ressources en informatique scientifique) est une unité de service de l'INS2I (Institut des sciences informatiques et de leurs interactions), fondée en 1993, dont l'objectif est d'accélérer les découvertes scientifiques nécessitant de très gros moyens de calcul. Pour se faire, le centre propose à la fois un accès à des ressources importantes et un service d'aide au passage à l'échelle et à l'optimisation des codes de simulation numérique. Les ressources sont utilisées par près de 420 projets scientifiques pour un total de 1000 utilisateurs environ.

Printer room readers ...

I reckon we all are. At least to some extent, from time to time. How at the end of the day could one avoid that while flipping through a stack of very important printouts spat out from a common room printer and which have not been ever collected ?!

A head in the cloud(s) ?!

Always wanted to outsource your needs for intensive, time,- memory-, and disc- wise, computations ... to somebody, somewhere, "out there" ... ? Dreamed about forgetting about operating systems, compilers, quotas, queues, architectures, etc ?!

Still dark but maybe somewhat more real ... [arXiv:1105.2862, 1105:2948]

Between two competing potential mechanisms behind the observed acceleration of the expansion of the Universe, this is the mysterious, negative-pressure component, which seems to be in favor these days. And this is thanks to a work by Australian researchers from the Wiggle-z team.

First detection of the power spectrum of the convergence field of gravitational lensing using ACT telescope data [1103.2124].

Gravitational lensing imprints distinctive non-gaussianities on the total intensity CMB map. Computation of the four-point correlation function over the map provides estimation of the integrated mass distribution along given lines of sight.
Moreover, it is remarkable to notice that measurements of CMB lensing are complementary to optical ones because they probe bigger volumes and have the advantage of a precisely known source redshift.

ACT, operating in Atacama desert

NERSC

Dans la continuité des précédents posts sur le calcul, je vous propose un petit tour d'horizon des différents centres, dont nous entendons parler régulièrement, ou dont nous nous servons (nous, Adamis).
L'idée est de synthétiser l'essentiel, le "bon à savoir", mais aussi de s'intéresser aux originalités propres à chaque centre. Ceci afin d'alimenter notre réflexion sur ce que nous pouvons mettre en place, à notre échelle, sur le cluster Adamis, ou future machine de calcul du FACe. Les commentaires sont donc les bienvenus !

First Planck science papers are out ... but CMB-free ... [arXiv:1101.2048, ..., arXiv:1101.1721]

First science results from Planck are finally available. At last ... Well they have been out since January, 11, but let's not be picky about these few weeks ... What is that after all, when compared to more than 15 years of sweating and toiling it took to get the instrument designed, built, tested, launched, and operating ... And moreover so well, as these recent results seem to demonstrate so convincingly.

New evidence for sterile neutrinos ... [arXiv1101.2755]

It looks like new evidence is slowly mounting in favor of some extra, 'sterile' families of neutrinos, coming from some hitherto uninvolved in the issue corners, and supporting some earlier results, which were also commented on in this blog.

Testing inflation ...

Inflation is no doubt a leading theory of the very early Universe. It provides a satisfactory explanation to such diverse observations as that of flatness of the Universe or a scale-invariance of the density fluctuations. Its predictions have been found consistent with a range of observables probing the Universe from the largest, e.g., Cosmic Microwave Background anisotropies, to the very small ones, say, Lyman-alpha forest. However, when looked upon in more detail, inflation is not what one might have wished for, i.e., a consistent well-defined model, but rather a bundle of diverse, specific implementation of the inflation's generic ideas. This has led some to refer to inflation more as a paradigm, i.e., a framework within which to think of the early Universe, rather than a scientific model.

A first step to reconstruct lensing potential [arXiv:1012.1600]

Somebody has already mentioned on this blog post the importance of gravitational lensing effect on CMB and the necessity somehow to get rid of its signature in a, hopefully soon, measured B-mode spectum to estimate signal due to inflationary processes.

First season QUIET observations [1012.3191]

L'expérience QUIET a observé le fond diffus cosmologique entre octobre 2008 et décembre 2010, utilisant un télescope dédié et des récepteurs à 43 et 95 GHz, depuis le désert d'Atacama au Chili (cf. photo ci-contre).
L'article que vous trouverez ici présente les résultats obtenus avec les 19 détecteurs fonctionnant à 43 GHz, d'une sensibilité de 69 uK/sqrt(Hz) pour l'ensemble du plan focal (durée d'observation : 3458 heures).
Le but scientifique de QUIET est la détection des modes B primordiaux, entre l=25 et l=475.

LSND - or on the virtues of being old

I meant  just older of course ...  just older ... As for the virtues ... well there are some. And no I do not think of gradual loss of short term memory though I can see that that could be sometimes a benefit. Instead I think for instance of the fact that one has been around for some time. And in the case of LSND (Liquid Scintillator Neutrino Detector) that actually matters.

... and around the world ...

Just piggybacking on the post by Maude below ... The supercomputing landscape as in Europe as worldwide is definitely not something engraved in a stone as some may think. In the contrary at least at its cutting edge it is by far a very dynamic system with a cut-throat competition be it a race to either putting on the floor first ever Tera (not so long time ago) and, more recently, Peta flop computer, or just for an over all leadership at any given time. In a recent change two Chinese supercomputers have reached for the very first time the 1st and 3rd spot on the so-called Top500 list, which aims at ranking all the most powerful computers of the world.

Le paysage du calcul en Europe

Ce post ne va peut-être rien vous apprendre, mais il m'aura au moins appris à moi :)

Au départ, je me suis agacée sur un article annonçant l'inauguration d'un second centre tier 0 en Europe, qui n'est autre que le 'Très Grand Centre de Calcul' (TGCC) du CEA. Tier 0, tier 0, c'est quoi ça tier 0 ? C'est annoncé dans le titre, pas plus d'explication dans le corps de l'article. Bref l'arrivée d'un tier 0 est un scoop, et je ne sais même pas ce que c'est. Donc je me suis mise en recherche de quelques informations sur le sujet, et je vous en retranscris ici l'essentiel.

Evidence for dark energy from geometrical test

The analysis of the Sloan Digital  and DEEP2 sky surveys data has uncovered a redshift-dependent anisotropy in the distribution of apparent (i.e, redshift-space) relative angles of galaxy pairs with respect to the line of sight. Such a dependence could have been predicted and can be considered as an example of the Alcock-Paczynski effect, where the redshift-space anisotropy of an otherwise spherically symmetric distribution is due to the cosmological expansion. Therefore at least in principle such observations could be used to set constraints on the energy content of the Universe in general and on the dark energy in particular.

The forgotten V

Anybody who ever read a book or some canonical introductory references on CMB polarization has found a small paragraph about the formal definition of the Stokes parameter Q, U, and V. From the combination of the Q and U parameters of the CMB signal it is straightforward to define the well known polarization field P=Q + iU which is now probably the most desired observable in cosmology. The poor V has always been left in the corner and in most of the paper I have ever read up to now is always neglected or claimed to be simply zero. As a (maybe) good student I always found myself thinking “Why is V damped so directly?”.

In the last year a few papers were published providing some further detail about the circular polarization of the CMB i.e. about the so-called V modes.

Sborinous(*) - seriously boring or boringly serious ?! ...

Have we got too serious, or plainly too boring ? Or maybe we, as a scientific community but also each of us individually, have just become responsible, tax-payers money minded, general public power aware members of the society ? (Ouch!)

Possible evidence of violent pre-Big-Bang activity [1011.3706]

Conformal Cyclic Cosmology (CCC) posits the existence of a cyclic history for our Universe.
Clusters and massive black holes from the previous aeon encounter, collapse, and the corresponding gravitational energy released is translated in our current aeon into a scalar field, an initial form of dark matter.

Une nouvelle physique accessible grâce à la nucléosynthèse ? [1011.1054]

La nucléosynthèse (BBN pour Big Bang Nucleosynthesis) correspond à l'époque de création des éléments légers dans notre Univers en expansion. L'observation précise des quantités respectives d'hydrogène, de deutérium, de l'hélium, de berilium et de lithium permet de contraindre et de sonder différents scénarios d'évolution de l'Univers : c'est le sujet de cette revue écrite par deux chercheurs du Perimeter institute for Theoretical Physics.