Archive for Gaia

Nature highlights

Posted in Books, Kids, pictures, Statistics with tags , , , , , , , , , , , , , on October 16, 2016 by xi'an

Among several interesting (general public) entries and the fascinating article reconstituting the death of Lucy by a fall from a tree, I spotted in the current Sept. 22 issue of Nature two short summaries involving statistical significance, one in linguistics about repeated (and significant) links between some sounds and some concepts (like ‘n’ and ‘nose’) shared between independent languages, another about the (significant) discovery of a π meson and a K meson. The first anonymous editorial, entitled “Algorithm and blues“, was rather gloomy about the impact of proprietary algorithms on our daily life and on our democracies (or what is left of them), like the reliance on such algorithms to grant loan or determining the length of a sentence (based on the estimated probability of re-offending). The article called for more accountability of such tools, from going completely open-source to allowing for some form of strong auditing. This reminded me of the current (regional) debate about the algorithm allocating Greater Paris high school students to local universities and colleges based on their grades, wishes, and available positions. The apparent randomness and arbitrariness of those allocations prompted many (parents) to complain about the algorithm and ask for its move to the open. (Besides the pun in the title, the paper also contained a line about “affirmative algorithmic action”!) There was also a perfectly irrelevant tribune from a representative of the Church of England about its desire to give a higher profile to science in the/their church. Whatever. And I also was bemused by a news article on the difficulty to build a genetic map of Australia Aboriginals due to cultural reticence of Aboriginals to the use of body parts from their communities in genetic research. While I understand and agree with the concept of data privacy, so that to restrain to expose personal information, it is much less clear [to me] why data collected a century ago should come under such protections if it does not create a risk of exposing living individuals. It reminded me of this earlier Nature news article about North-America Aboriginals claiming right to a 8,000 year old skeleton. On a more positive side, this news part also mentioned the first catalogue produced by the Gaia European Space Agency project, from the publication of more than a billion star positions to the open access nature of the database, in that the Gaia team had hardly any prior access to such wealth of data. A special issue part of the journal was dedicated to the impact of social inequalities in the production of (future) scientists, but this sounds rather shallow, at least at the level of the few pages produced on the topic and it did not mention a comparison with other areas of society, where they are also most obviously at work!

trip to Besançon (and the stars)

Posted in Mountains, pictures, Statistics, Travel, University life with tags , , , , , , , , , on November 26, 2012 by xi'an

Today, I made a quick TGV trip to Besançon, in French Jura, to give a seminar to astronomers and physicists, in connection with the Gaia project I had mentioned earlier. I gave my talk straight out of the train and then we started discussing MCMC and ABC for the astronomy problems my guests face. To my surprise, I discovered that they do run some local form of ABC, using their own statistics and distances to validate simulation from the (uniform) prior on their parameter space. The discussion went far enough to take a peek under the hood, namely to look at some Fortran programs they are running (and make suggestions for acceleration and adaptation). It is quite interesting to see that ABC is actually a natural approach when people face complex likelihoods and that, while they construct appropriate tools, they feel somehow uncertain about the validation of those methods and are unaware of very similar tools in other fields. In addition to this great day of exchange, I had several hours of freedom in the train (and a plug) to work on the bayess package for Bayesian Essentials (not dead yet!). Here are my slides, pot-pourri of earlier talks. (Including the one on cosmology model choice in Vancouver.)

Gaia

Posted in Statistics, University life with tags , , , , , , , , on September 19, 2012 by xi'an

Today, I attended a meeting at the Paris observatory about the incoming launch of the Gaia satellite and the associated data (mega-)challenges. To borrow from the webpage, “To create the largest and most precise three dimensional chart of our Galaxy by providing unprecedented positional and radial velocity measurements for about one billion stars in our Galaxy and throughout the Local Group.” The amount of data that will be produced by this satellite is staggering: Gaia will take pictures of roughly 1Giga pixels that will be processed both on-board and on Earth, transmitting over five years a pentabyte of data that need to be processed fairly efficiently to be at all useful! The European consortium operating this satellite has planned for specific tasks dedicated to data handling and processing, which is a fabulous opportunity for would-be astrostatisticians! (Unsurprisingly, at least half of the tasks are statistics related, either at the noise reduction stage or at the estimation stage.) Another amazing feature of the project is that it will result in open data, the outcome of the observations being open to everyone for analyse… I am clearly looking forward the next meeting to understand better the structure of the data and the challenges simulation methods could help to solve!