The Planck mission

These lecture from the 100th Les Houches summer school on "Post-planck cosmology" of July 2013 discuss some aspects of the Planck mission, whose prime objective was a very accurate measurement of the temperature anisotropies of the Cosmic Microwave Background (CMB). We announced our findings a few months ago, on March 21$^{st}$, 2013. I describe some of the relevant steps we took to obtain these results, sketching the measurement process, how we processed the data to obtain full sky maps at 9 different frequencies, and how we extracted the CMB temperature anisotropies map and angular power spectrum. I conclude by describing some of the main cosmological implications of the statistical characteristics of the CMB we found. Of course, this is a very much shortened and somewhat biased view of the \Planck\ 2013 results, written with the hope that it may lead some of the students to consult the original papers.Comment: 53 p.-34 fig; for spacetime consideration, the file here is not paying justice to the actual thing; a closer approximation of it can be found at https://www.researchgate.net/profile/Francois_Bouchet/publication/262004262_The_Planck_Mission/file/e0b495363b042e81dd.pd

Kurtosis in Large-Scale Structure as a Constraint on Non-Gaussian Initial Conditions

We calculate the kurtosis of a large-scale density field which has undergone weakly non-linear gravitational evolution from arbitrary non-Gaussian initial conditions. It is well known that the weakly evolved {\twelveit skewness} is equal to its initial value plus the term induced by gravity, which scales with the rms density fluctuation in precisely the same way as for Gaussian initial conditions. As in the case of skewness, the evolved {\twelveit kurtosis} is equal to its initial value plus the contribution induced by gravity. The scaling of this induced contribution, however, turns out to be qualitatively different for Gaussian versus non-Gaussian initial conditions. Therefore, measurements of the kurtosis can serve as a powerful discriminating test between the hypotheses of Gaussian and non-Gaussian nature of primordial density fluctuations.Comment: uuencoded compressed tar file including postscript text (17 pages) and 2 postscript figures, submitted to MNRA

The COBRAS/SAMBA CMB Project

COBRAS/SAMBA is a second generation satelitte dedicated to mapping at high resolution and sensitivity the anisotropies of the Cosmic Microwave Background (CMB). This mission is in the assessment study phase (A) at ESA, with a decision expected mid 1996, for a launch around 2003.Comment: PostScript, 4 pages, 4 figures in text, to appear in the Proceedings of the 1995 Moriond Meeting on ``Clustering in the Universe'

Fluctuation analysis of the far-infrared background — information from the confusion

We investigate the extent to which one can use a P(D) analysis to extract number counts of unclustered sources from maps of the far-infrared background. Such maps currently available, and those expected to emerge in the near future, are dominated by confusion noise resulting from poor resolution. We simulate background maps with an underlying two-slope model for N(S), and we find that, in an experiment of FIRBACK type, we can extract the high-flux slope with an error of a few per cent, whereas other parameters are not so well constrained. However, we find that, in a SIRTF-type experiment, all parameters of this N(S) model can be extracted with errors of only few per cen

Self-Regulated Learning: Comparing Online and Classroom Courses in Cognition, Metacognition, Motivation, Emotions, Contexts, and Behavior

International audienceThis research aims at evaluating the use of cognition, metacognition, motivational, emotional, contextual and behavioral processes in self-regulated learning in online and traditional classroom environments for two separate experiments with two groups each. We used a questionnaire developed based on the adaptation of six existing scales, with the addition of a general section about the course itself. By contrasting the two experiments, results were consistent for online courses suggesting a higher mastery of motivation and positive emotions after taking the course, although it was in many ways similar to a traditional course. Finally, online course might have been associated with higher scores in context control than traditional course but it could depend of the course content

From Student Questions to Student Profiles in a Blended Learning Environment

International audienceThe analysis of student questions can be used to improve the learning experience for both students and teachers. We investigated questions (N = 6457) asked before the class by first-year medicine/pharmacy students on an online platform, used by professors to prepare for Q&A sessions. Our long-term objectives are to help professors in categorizing those questions, and to provide students with feedback on the quality of their questions. To do so, we developed a coding scheme and then used it for automatic annotation of the whole corpus. We identified student characteristics from the typology of questions they asked using the k-means algorithm over four courses. Students were clustered based on question dimensions only. Then, we characterized the clusters by attributes not used for clustering, such as student grade, attendance, and number and popularity of questions asked. Two similar clusters always appeared (lower than average students with popular questions, and higher than average students with unpopular questions). We replicated these analyses on the same courses across different years to show the possibility of predicting student profiles online. This work shows the usefulness and validity of our coding scheme and the relevance of this approach to identify different student profiles. Notes for Practice • Questions provide important insights into students' level of knowledge, but coding schemes are lacking to study this phenomenon. • After providing a bottom-up coding scheme of student questions in a blended environment, we analyzed the relationship between the questions asked and the student profiles. • Profiling students based on their questions over a year allows us to predict the profiles of future students to help the teacher understand who asks what. • These results provide both a coding scheme that can be reused in various contexts involving questions, and a methodology that can be replicated in any context where students ask many questions, in particular to help the teacher in prioritizing them according to their own criteria. • Teachers need to focus on the nature of questions asked by their students, because they can reveal information about their profile (attendance, activity, etc.)

All sky CMB map from cosmic strings integrated Sachs-Wolfe effect

By actively distorting the Cosmic Microwave Background (CMB) over our past light cone, cosmic strings are unavoidable sources of non-Gaussianity. Developing optimal estimators able to disambiguate a string signal from the primordial type of non-Gaussianity requires calibration over synthetic full sky CMB maps, which till now had been numerically unachievable at the resolution of modern experiments. In this paper, we provide the first high resolution full sky CMB map of the temperature anisotropies induced by a network of cosmic strings since the recombination. The map has about 200 million sub-arcminute pixels in the healpix format which is the standard in use for CMB analyses (Nside=4096). This premiere required about 800,000 cpu hours; it has been generated by using a massively parallel ray tracing method piercing through a thousands of state of art Nambu-Goto cosmic string numerical simulations which pave the comoving volume between the observer and the last scattering surface. We explicitly show how this map corrects previous results derived in the flat sky approximation, while remaining completely compatible at the smallest scales.Comment: 8 pages, 4 figures, uses RevTeX. References added, matches published versio

Does a Peer Recommender Foster Students' Engagement in MOOCs?

International audienceOverall the social capital of MOOCs is under-exploited. For most students in MOOCs, autonomous learning often means learning alone. Students interested in adding a social dimension to their learning can browse discussion threads, join social medias and may decide to message other students… but usually in a random way. This common isolation might be a contributing factor on student attrition rate and on their general learning experience. To foster learners' persistence in MOOCs, we propose to enhance the MOOC experience with a recommender which provides each student with an individual list of rich-potential contacts, created in real-time on the basis of their own profile and activities. This paper describes a controlled study conducted from Sept. to Nov. 2015 during a MOOC on Project Management. A recommender panel was integrated to the users' interface and allowed to manage contacts, send them an instant message or consult their profile. The population (N = 8,673) was randomly split into 2 parts: a control group, without any recommendations, and an experimental group in which students could choose to activate and use the recommender. After having demonstrated that these populations were similar up to the activation of the recommender, we evaluate the effect of the recommender on the basis of four pillars of learners' persistence: attendance, completion, success and participation. Results suggest that the recommender improved all these four factors: students were much more likely to persist and engage in the MOOC if they received recommendations than if they did not

Increasing MOOC completion rates through social interactions: a recommendation system

International audienceE-learning research shows students who interact with their peers are less likely to drop out from a course, but is this applicable to MOOCs? This paper examines MOOC attrition issues and how encouraging social interactions can address them: using data from 4 sessions of the GdP MOOC, a popular Project Management MOOC, we confirm that students displaying a high level of social interaction succeed more than those who don't. We successively explore two approaches fostering social interactions: 1) in MOOC GdP5, we give access to private group forums, testing various group types and sizes, 2) in MOOC GdP6, we implement a recommendation system, suggesting relevant chat contacts using demographic and progression criteria. This papers presents our preliminary findings