NEWSLETTER - 2011 bois-marie INSTITUT DES HAUTES ÉTUDES SCIENTIFIQUES

editorial Léon Motchane, the founder Institute’s identity; it also enjoys close proximity to a number of of IHÉS, was a visionary. In scientific institutions, their cooperation reinforced with the creating the Institute, he setting up of the Paris Saclay Campus. The Fondation wanted to give researchers mathématique Jacques Hadamard was created alongside the from all over the world a place of freedom and communication. Campus, under the aegis of the Paris Saclay Foundation for Keen to offer IHÉS scientists a suitable site for research, he Scientific Cooperation. Its aim is to reinforce research capacity made it possible for the Institute to acquire the Bois-Marie in fundamental mathematics and its interfaces. IHÉS is one of estate in 1962. Today, the campus is an integral part of the its founding members, together with Université Paris-Sud 11, the CNRS, École polytechnique and École Normale Supérieure de Cachan. The new organisation should make the area even more attractive to mathematicians on the international scene. As well as forging links with neighbouring research institutions, the Institute continues to reach out to the public in France and abroad. Encouraged by the success of the book, The Unravelers, Mathematical Snapshots , the Institute organised a day of conferences in the France Pavilion at the ShanghaiWorld Expo in October 2010. Following on from this event, The Unravelers photo exhibition is currently touring many Chinese towns, thanks to the Alliances Françaises network. Other projects are in hand, such as “The UnravelersTour in France”, which I hope will meet with great success.

Jean Pierre Bourguignon

table of contents

events ...... 2 - 3 professors ...... 4 awards ...... 5 publication ...... 7 the Schlumberger Chair ...... 7 - 10 the 50 th Anniversary Campaign ...... 11 - 15 point of view by ... / 2011 events ...... 16 l e r b e P n e i l u J ©

Institut des Hautes Études Scientifiques | Le Bois-Marie, 35 route de Chartres, F-91440 Bures-sur-Yvette, France Téléphone : +33 1 60 92 66 00 | Télécopie : +33 1 60 92 66 69 | Courrier électronique : [email protected] | Site internet : www.ihes.fr events

CARMIN inauguration of the The Institut Henri Poincaré (IHP), CIRM (Centre International de Rencontres Mathé - Hadamard Foundation matiques ), ICPAM (International Centre for Pure and Applied Mathematics) and IHÉS submitted a project, called The inauguration celebration of the CARMIN, for the reinforcement of their Fondation mathématique Jacques Hadamard cooperation, in response to the call for (FMJH) took place on 17 and 18 May 2011; “LabEx” (laboratories for excellence) in the morning of 17 May, it was held at proposals, which is one of the elements of Université Paris-Sud 11, in the presence of the “investments for the future” to be funded Valérie Pécresse, French Minister of Higher by the French State’s national loan. These Education and Research, and in the institutes represent collective tools which afternoon of 18 May it took place at École contribute to the French mathematical polytechnique, in the presence of around community’s international visibility. 200 students. Valérie Pécresse, Université Paris-Sud, 17 May The Foundation was created on 2 February 2011, following capital endowment from been taken, such as international scholarship graduate course ED107 the French State, as part of the national programmes at masters and postdoc levels and On Thursdays in February and March 2011 , Campus operation. The work of the Foundation support for conferences. Pierre Vanhov e gave a course on Perturbative will be to help the decompartmentalisation Partnership agreements are also being signed Calculation in Quantum Gravity to young of both institutions and research themes, with major science education and training doctoral students of the Paris region. and also to promote international activites. institutions in PR China. www.ihes.fr/~vanhove/cours-gravite.html Various practical measures have already

summer school 2010 kaleidoscopic view The second IHÉS French-Asian summer school, which took place from 19 to 30 July 2010, dealt of modern mathematics with Singularities in Partial Differential Equations . The next summer school will be organised at IHÉS in July 2012. Summer schools are entirely Claire Voisin and Sergiu Klainerman became They organised the first ever Publications funded by the Société Générale Fund at IHÉS. the managing editors of Les Publications Mathématiques meeting, Kaleidoscopic view of Mathématiques de l’IHÉS on 1 st January 2010. modern mathematics, from 8 to 10 January 2011. IHÉS hosted the event on 8 January. It was a great day of conferences given in turn nonlinear waves and by Horng-Tzer Yau, Gerhard Huisken, Alain Connes and Cédric Villani. The next two days dispersion of conferences on 9 and 10 January took One year after an IHP trimester on this topic, place at the Institut Henri Poincaré, and saw which had been very successful, Frank Merle presentations made by: Tom Mrowka, (Université de Cergy-Pontoise – IHÉS Chair) and Jean-Yves Welschinger, Jean-Pierre Demailly, Fabrice Planchon (Université Paris 13) organised Philippe Biane, Pierre Raphaël, Hiraku a meeting where young speakers featured Nakajima, Benjamin Enriquez and Gérard prominently, from 21 to 23 June 2010 at IHÉS. Laumon. Alain Connes

tribute to Lagrange and “The conference made it possible for the journal’s editors and some of its recent authors to Poisson meet. Presentations covered a wide range of topics, from mathematical physics to arithmetics. The conference was organised by Jean-Pierre Some presentations were made by the editors, others by authors who had recently had Bourguignon, Pierre Cartier and Yvette Kosmann - articles accepted by the journal; Gérard Laumon’s presentation on the “fundamental Schwarzbach (École Polytechnique), from 24 to lemma” belonged to both categories. This was an interesting experience and we hope that 26 March 2010 at IHÉS to commemorate the it helped to confirm and communicate the wish to broaden the thematic scope of the journal, 200 th anniversary of the publication of important which was behind the constitution of the new editorial team.” work by Joseph-Louis Lagrange and Siméon- Denis Poisson. Claire Voisin

2 events

three string generations at IHÉS “String theory is the interdisciplinary science, which combines methods and goals Conference organised at IHÉS from 16 to of physics and mathematics. One of the 20 May 2011 by Maxim Kontsevich, Nikita ambitious goals of string theory is to Nekrasov and Gabriele Veneziano, the aim of construct the fundamental theory of which was to celebrate the unity and diversity nature, combining quantum field theory of modern theoretical and mathematical and the theory of general relativity. Ideas physics. originating in string theory find unexpected applications in mathematics, the most The idea for this event was also to bring notable being the discovery of mirror together three generations of string theory symmetry, linking (complex) algebraic specialists. At the centre, the second generation, geometry and symplectic geometry. Mirror born in 1960-1962, represented in this symmetry provides the mechanism for the conference by Nathan Berkovits, Robbert geometric Langlands correspondence and Dijkgraaf, Michael Douglas, Igor Klebanov, gives the solution to the Schubert problem, Gregory Moore, Hirosi Ooguri, Samson the deformation quantization, the Shatashvili, Cumrun Vafa, Erik and Herman categorisation of the theory of knot Verlinde. With them, the two other invariants, the correspondence between two generations: their advisers, the string theory dimensional conformal field theories and pioneers, and their students. This international refined Donaldson theory, to name just a conference was supported by Foundation Cumrun Vafa few. ” Compositio Mathematica, the Richard Lounsbery Foundation, the Collège de France Nikita Nekrasov and the Fédération de Recherche Interactions Fondamentales (FRIF). Paris-Tokyo arithmetic geometry seminars

The Paris-Tokyo Arithmetic Geometry message of support and friendship to their Seminar is a video-seminar jointly Japanese colleagues. IHÉS joins them in organised between IHÉS and the expressing wholehearted solidarity with the University of Tokyo since 2010 by Ahmed Japanese people. Abbes (IHÉS-CNRS), Christophe Breuil The last session of the Paris-Tokyo (CNRS-Université Paris-Sud), Takeshi Arithmetic Geometry Seminar took place Saito (University of Tokyo), Atsushi Shiho on Wednesday 15 June 2011. The speaker (University of Tokyo) and Takeshi Tsuji was Tomoyuki Abe (IPMU, Tokyo), who (University of Tokyo). It takes place once a gave a presentation from Tokyo on month, with speakers alternately from Paris “Product formula for p-adic epsilon and Tokyo. factors” . Ahmed Abbes A session took place on Wednesday 11 May Other joint IHÉS and University of Tokyo 2011. The speaker was Michel Raynaud projects are planned for next year, including (Université Paris-Sud) who gave a the “Arithmetic Geometry Seminar in presentation from IHÉS on “Permanence Tokyo” conference, which will take place following Temkin” . On this occasion, the from 4 to 8 June 2012. organisers and participants in Paris expressed their sympathy to the victims of the recent devastation in Japan and sent a

3 professors awards

arrival of Ahmed Abbes

Ahmed Abbes joined Ahmed Abbes is a mathematician specialised in arithmetic and algebraic geometry. His joint IHÉS on 1 May 2011 arithmetic geometry. He studied at the École work with Takeshi Saito (University of Tokyo) as a long term CNRS Normale Supérieure in Paris from 1990 to 1994. enabled a significant breakthrough in the theory visitor. The Institute With a PhD in mathematics obtained in 1995 at of ramification . is very pleased Université Paris-Sud, he became a postdoc He is the author of a treatise presenting a to welcome this researcher at IHÉS in 1996. He was subsequently systematic development of rigid geometry talented and dynamic appointed CNRS research associate at Université following M. Raynaud’s approach, based on mathematician. Paris 13, then CNRS research director at formal schemes up to admissible blow-ups. A co-organiser of the IRMAR (Université de Rennes 1) from 2007. Ahmed Abbes received the CNRS bronze medal Paris-Tokyo arithmetic Ahmed Abbes mainly studies geometrical and in 2005. geometry seminars, he is behind the new cohomological properties of bundles on varieties “Arithmetics and Algebraic Geometry Course at on perfect fields of characteristic p>0 or on IHÉS” (see 2011 events page 16). p-adic fields designed for applications in departure of Dirk Kreimer

Dirk Kreimer received a von Humboldt Connes, with whom “Friendly Isolation Professorship in 2010. This award is given by he formed a sincere the Alexander von Humboldt Foundation, friendship. His work When I returned to following a nomination by a German research focuses today on Europe in the mid institution. It is the most prestigious scientific understanding the 90s from two postdoc award in Germany. analytical structure of years spent at the amplitudes in quantum University of Hobart, Following this award, Dirk Kreimer has joined field theory using Tasmania, I returned the Humboldt University of Berlin, where he mixed Hodge structures with many cherished leads the new Interdisciplinary Centre for and on the use of memories of loneliness Mathematical Physics and focuses on the matroids in spin field Dirk Kreimer, Alain Connes well spent: over there, solitude to think interactions between mathematics and theories. was provided in spades. theoretical physics. All those who have known him at the Institute When I arrived five years later at IHÉS, Dirk Kreimer came to France in 1991 will remember the 10 years he spent at IHÉS I found that cherished sense of isolation intending to enter into regular contact with as a long term CNRS visitor very fondly. We again, but in much gentler beautifully mathematicians interested in perturbative wish him every success in his new post. cultivated surroundings: the ability to quantum field theory. His approach to isolate yourself with your thoughts, in the renormalisation using Hopf algebras led him middle of an intellectual epicenter of to work from the end of the 1990s with Alain thoughtful reflection, is now the souvenir I will take with me from IHÉS. Thanks to Alain for his friendship, and thanks to all at IHÉS for a wonderful departure of Christophe Breuil decade in my scientific life. ”

Dirk Kreimer Christophe Breuil, who came to programme, which he started, with IHÉS in 2002 as a CNRS long several researchers now working on term visitor, moved to the it. With his students, he is looking to Mathematics Department at develop this programme for groups Université Paris-Sud in September other than GL 2(Q p), specifically 2010. GL 2(F) with [F:Q p] > 1 . He received A mathematician specialised in the Grand Prix Jacques Herbrand algebraic geometry and number from the Académie des Sciences de theory, his research is on all Paris in 2002. We also wish him aspects of the p-adic Langlands every success.

4 professors awards

Laurent Lafforgue honorary doctor The University of Notre Dame, Indiana, United States, awarded Laurent Lafforgue, Mikhail Gromov , ForMemRS IHÉS permanent professor, the title of honorary doctor on 22 May 2011. On that occasion, he made two scientific Mikhail Gromov was elected Foreign Member presentations on the Langlands programme, of the Royal Society (United Kingdom) on a topic he has been working on for many 20 May 2011. With this distinction, The Royal years, and gave a public conference entitled Society recognises Mikhail Gromov as one of “Does basic research have meaning? A few “the most deeply original mathematicians remarks by a catholic mathematician”. of our time” .

Mikhail Gromov joins the ten or so great Royal Irish Academy French scientists who have also been elected gold medal Royal Society Foreign Members, among Samson Shatashvili, theoretical physicist, whom are Jean-Pierre Serre, Jacques Friedel, professor at Trinity College, Dublin and Louis Edouard Brézin and, more recently, Pascale Michel Visiting Chair holder at IHÉS since 2000, Cossart. received the Royal Irish Academy Gold Medal The Royal Society has around 140 Foreign on 24 November 2010, in recognition of his Members across all disciplines out of a total of several groundbreaking discoveries in the fields around 1450 Fellows. They are elected for life of theoretical and particle physics. through a peer review process; eight new Foreign Members are elected each year. Mikhail Gromov Peano prize David Ruelle, honorary professor at IHÉS, received the 2010 Peano Prize on 18 November Thibault Damour , 2010 in Turin, for his book La mente matematica (Ed. Dedalo), translated from the original French knight of the Legion of Honour version, which was published in 2008, L’étrange beauté des mathématiques (Ed. Odile Jacob). Thibault Damour received the insignia of knight of the Legion of Honour on 6 December 2010 during a ceremony organised at IHÉS. Amaldi medal Thibault Damour was awarded the Amaldi Medal His friend Philippe Starck came to confer the during the 19 th SIGRAV conference (Italian Society distinction, as the two men have known each for General Relativity and Gravitation) which other for ten years and each holds the other in took place in Pisa (Italia) from 27 September to great admiration. Here is an extract from the 1st October 2010. coulourful speech given by Philippe Starck on this occasion: Compositio Mathematica “We tried to meet regularly over the course of Thibault Damour, Philippe Starck a few years so that he could teach me things. prize It was extraordinary! poetry of science and that poetry is transposable The Compositio Mathematica Foundation has He talked about quantum ..., strings (…) I in real life. And I live much better today chosen to award the first Compositio Mathe - didn’t understand anything. But actually, the thanks to the little I have understood by matica Prize to Nikita Nekrasov, Davesh Maulik, point wasn’t that I understood or not, because osmosis, in a very varied way, in a very very Andrei Okounkov and Rahul Pandharipande what was important for me was to hear the personal way and I thank him for that.” for their article Gromov-Witten Theory and music, because I think there is a music to Donaldson -Thomas Theory II (Compositio Math. science. (...) 142 (2006), 1286-1304). I also think that, if we’re sensitive, there This prize was awarded during the Compositio is obviously poetry, a poetry of mathematics, a Prize Festivity at Amsterdam University on 2 July 2010.

5 publication the Schlumberger Chair

description of the last orbits of binary neutron star systems

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The relativistic gravity theorists, Thibault This article focuses on the description of the The paper also shows that this detection will Damour and Alessandro Nagar, with a team last few orbits before coalescence of binary allow the measurement of the ratio between from the Albert Eintein Institute, Germany, neutron star systems and their experimental the mass and radius of neutron stars. This have greatly advanced the description of the observation (which hopefully will happen measure is potentially very important because final orbits of binary systems of neutron stars. soon) by the network of gravitational wave it will give access to new information on the detectors LIGO / VIRGO - LIGO is in the equation of state of ultra-dense nuclear matter, An article describing this discovery was United States and VIRGO is the French- of which neutron stars are made. The results of published by Physical Review Letters (PRL): Italian gravitational wave detector installed in this article were obtained by comparing the Analytic Modelling of Tidal Effects in the Cascina, near Pisa. predictions of the IHÉS analytical method Relativistic Inspiral of Binary Neutron Stars , The main result of the article is to have shown with the best (and to date longest) numerical Phys. Rev. Lett 105 , 261101 (2010). that the new analytical description (called simulations (on supercomputers) of the This article is the result of a collaboration “effective one body” or EOB) of the dynamics gravitational wave signal emitted by binary between a team of relativistic gravity theorists, of binary systems, invented at IHÉS a few years neutron star systems. These numerical results Thibault Damour, permanent professor at ago (by Alessandra Buonanno and Thibault have been obtained recently thanks to the IHÉS, and Alessandro Nagar, visiting Damour) and recently developed at IHÉS by numerical methods developed at the Albert researcher at IHÉS, and a team of “numerical Thibault Damour and Alessandro Nagar, can Einstein Institute. relativity” specialists (all formerly together at be used to describe the gravitational signal the Albert Einstein Institute, a Max-Planck emitted by the last orbits of a system of two institute located in Golm, Germany) currently neutron stars with a precision adequate for working in several institutions: Luca Baiotti detection by LIGO / VIRGO. (Osaka and Kyoto Universities, Japan), Bruno Giacomazzo (University of Maryland and NASA Goddard Space Flight Center, US) and Luciano Rezzolla, head of the numerical relativity group of the Albert Einstein Institute.

Illustrations: numerical simulation of the last orbits of a binary neutron star system. Credits: B. Giacomazzo (AEI), R. Kaheler (ZIB/AEI), L. Rezzolla (AEI)

6 the Schlumberger Chair inauguration

Josselin Garnier and George Papanicolaou The Schlumberger inaugural conference are the first holders of the Schlumberger was held on 17 and 18 November 2010 at Chair for Mathematical Sciences at IHÉS. IHÉS. The theme chosen and presented by Background to the From September 2010 to February 2011, Josselin Garnier, Habib Ammari, Patrick Schlumberger Chair they worked together on imaging projects. Joly, Felix Otto, Grégoire Allaire and More specifically, they worked on a new George Papanicolaou was “Multiscale The sources of inspiration for theoretical type of robust beamforming method in Methods and Imaging” . sciences are many: questions lying, complex media and on the improvement Inaugural lectures by the first two holders sometimes for centuries, at the very of resolution in imaging with indirect of the Chair were given in the evening of foundation of sciences (such as in the lighting resulting from the heterogeneities 18 November. George Papanicolaou and creation of non-Euclidean geometries), of the medium. Josselin Garnier presented with great clarity problems arising from the development They have developed and analysed the work they have undertaken as part of of high technology (such as seismic mathematical models to estimate the the Schlumberger Chair, demonstrating the studies leading to the definition of systemic risk of a large number of validity of creating this Chair at IHÉS. The wavelets), or concepts originating in interacting agents each trying to spread resulting collaboration will be of benefit neighbouring sciences (such as the their individual risk. They have also both to the scientific community and the systematic consideration of non- initiated a study of propagation of world of industry. commutativity in mathematics stimulated uncertainty for a classic problem in by the success of quantum mechanics). geophysics, which consists in estimating the In the past few years, IHÉS has started to speed of surface waves from the explore new sources of inspiration, such measurement of travel times (see article as high technology and biology, while p. 8). maintaining its fundamental values: freedom of research, quest for excellence, interdisciplinarity, and also human and scientific diversity. Schlumberger Ltd. was a natural partner for a project on issues at the interface with applied “The proposal of a six-month term to hold research and of more direct interest to the Schlumberger Chair was perfect for me: companies. Schlumberger Ltd. is a high it came at a time when I was highly Philippe Lacour-Gayet technology company, whose products motivated and intrigued by innovative and services draw extensively from many types of research around imaging. The belief scientific domains: physics, chemistry, that IHÉS would provide the environment geology, geophysics and mathematics. In to develop these tracks was immediately many of these fields, the rigor necessary attractive. Finally the idea of working with “Joining the Schlumberger Chair was for to innovate requires the knowledge George Papanicolaou on these issues only me a unique opportunity to build a created at the frontiers of fundamental strengthened this conviction. So I could sustainable and productive relationship of research. Schlumberger has a tradition of only accept the proposal with enthusiasm. high-level research between my university deep interaction with the scientific The first few months, with many results on in Stanford and IHÉS. Our current and community by locating its laboratories in imaging and other issues that have emerged past students and our close collaborators in close proximity to strong academic over the course of my discussions with France and the United States will benefit institutions, while maintaining a large George Papanicolaou, fully satisfy me. greatly from working with us, Josselin internal research effort. They encourage me to believe that this Garnier and me, on research projects that semester is the beginning of an active and are both innovative and interdisciplinary. prolific period between IHÉS, Stanford We are already engaged on work on University, the Université Paris Diderot imaging, propagation of uncertainty and and École Normale Supérieure, where I systemic risk. I am very satisfied with the will be giving courses in the second semester progress on these issues in such a short and hosting a working group.” period. ”

Josselin Garnier, George Papanicolaou, professor at Université Paris Diderot professor at Stanford University

7 article

Josselin Garnier George Papanicolaou Educated at the École Normale Supérieure in Paris, he is professor of Robert Grimmett Professor in Mathematics, Department of mathematics at Université Paris Diderot where he conducts his research Mathematics, Stanford University, since 1993, after spending much of in the Laboratoire de Probabilités et Modèles Aléatoires and in the his career at the Courant Institute for Mathematical Sciences at New Laboratoire Jacques-Louis Lions, Université Pierre-et-Marie-Curie. York University, he has received numerous prizes and awards, the two His main research interest is related to waves in random media. He most recent being: William Benter Prize in Applied Mathematics 2010 received the Felix Klein Prize in 2008. and Josiah Willard Gibbs Lecture, 2011. imaging with noise

In sensor array imaging waves are used to step of a typical time-reversal experiment, a randomly heterogeneous than when it is probe an unknown medium. Different wave point source emits a short pulse that propagates homogeneous. The mathematical analysis of transmission and reception modalities can be in a homogeneous or heterogeneous medium enhanced time-reversal refocusing in random implemented depending on the applications: (see Figure 1). The time-reversal mirror is used media has revealed that the time-reversal non destructive testing, medical imaging, as an array of receivers that record the wave experiment can be interpreted as a correlation seismology. Travel time tomography, signals. In the second step of the experiment, machine [1]: in the second step of the time- backpropagation or migration are well-known the time-reversal mirror is used as an array of reversal experiment, the time-reversed wave techniques to extract information from the emitters that re-emit the time-reversed revisits the same medium as the one that was array data. Recently new ideas have emerged recorded signals. The waves then propagate probed during the first step of the experiment, from experimental observations such as super- back into the medium. Due to the time and this is a key point. If the medium during resolution effects in time-reversal experiments reversibility of the wave equation it is expected the second step is exactly the same as the one or from theoretical concepts such as coherent that the wave refocuses on its original source during the first step, then the scattering with interferometry or cross correlation methods. In location. What was not so expected is that the the heterogeneities of the medium can particular the possibility to use uncontrolled refocusing is better when the medium is produce multi-pathing that builds up in a ambient noise sources instead of controlled coherent way to produce a sharp focusing at

active sources has attracted a lot of attention TRM TRM the original source location. If the medium especially in seismology. In this article we give during the second step is not exactly similar to y a brief overview that explains the connection y the original medium, then refocusing becomes between these different ideas and we give the poor and unstable. recent results obtained during our semester at In practice, the enhanced spatial focusing and IHÉS. time compression of signals in time reversal in random media (see Figure 2) have many Time-reversal Experiments. Time reversal FIG. 1: Ideal time-reversal experiment, with a diverse applications in detection and in focused experiments were first carried out by Mathias time-reversal mirror (TRM) that completely energy delivery on small targets as, for example, Fink and his group in Paris. They were done surrounds the region of interest. The left picture in the destruction of kidney stones. Enhanced with ultrasonic waves and have attracted plots the first step of the experiment. A point source spatial focusing is also useful in sonar and considerable attention because of the at y emits a short pulse that propagates through the wireless communications for reducing surprising effects of enhanced spatial focusing medium and is recorded by the time-reversal mirror. interference. Finally time reversal ideas have and time compression in random media [Fink, The right picture plots the second step of the time- played an important role in the development Scientific American 281 (1999), 91]. A time- reversal experiment. The time-reversal mirror of new methods for imaging in random media reversal experiment is based on the use of a re-emits the time-reversed recorded signals that as described below. very special device: the time-reversal mirror. It propagate back into the medium and refocus at the is a collection of transducers that can be used original source location. Coherent Interferometric Imaging. The either as emitters or as receivers. In the first mathematical analysis of time-reversal

8 article

experiments has shown that the cross backpropagating numerically the recorded time information. The main observation is that correlation of partially coherent waves is an signals, that are supposed to refocus on the the cross correlation of the noise signals important object. A new imaging method was locations of the main reflectors present in the recorded at two sensors is related to the travel then proposed in the context of sensor array medium, as is observed in time-reversal times between the sensors. As a consequence, imaging in random media. experiments. the background speed of propagation can then When imaging with waves the unknown This imaging method is very efficient when be obtained from the estimated travel times medium is probed with waves emitted from a the medium is homogeneous or perfectly between sensors in a network covering the set of sources and then the echoes are recorded known, since it is then strictly equivalent to a region of interest, as was done in the Southern time-reversal experiment in which the California region [Sabra et al., Geophys. Res. Reflected Signal Transmitted Signal 160 backpropagation is carried out numerically Lett. 32 (2005), L14311]. In fact the idea of 140 instead of physically. However, when the exploiting the ambient noise and using the 120 medium is heterogeneous and not perfectly 100 known one has to backpropagate the recorded 80 t 60 signals in a fictitious medium that is not the

40 real one, and poor refocusing is observed.

20 Coherent interferometric imaging is based on

0 Incoming Pulse the backpropagation of local space-time cross −20 Random Medium correlations of array data and was introduced FIG. 3: Coherent interferometric imaging. In the left −160 −120 −80Refo −40cused 0Signal 40 80 120 160 z 160 in order to improve images when the medium picture a sensor array is used to probe an unknown

140 between the array and the object to be imaged medium in which reflectors are buried (one of the 120 is inhomogeneous and unknown [Borcea et al., transducer is used as a source, the other transducers 100 Inverse Problems 21 (2005), 1419]. During our are used as receivers and record the echoes, which 80 t semester at IHÉS we have shown that the form one column of the array response matrix). In 60 coherent interferometric imaging is in fact the right picture local cross correlations of recorded 40

20 equivalent to a windowed beamformer energy signals are backpropagated numerically and focus

0 function, that is, a quadratic function that more or less on the locations of the reflectors. Re−emitted Signal −20 Random Medium involves only time gating and time delaying −160 −120 −80 −40 0 40 80 120 160 FIG. 2: Time compression zof signals in time reversal signals in emission and in reception. In this cross correlation of noise signals to retrieve in random media (numerical simulations). The top form coherent interferometric imaging can be information about travel times was first picture plots the first step of the experiment. Each implemented efficiently both in hardware and proposed in helioseismology [Rickett et al., line is a snapshot of the wave profile at different software, at a computational cost that is, ideally, The Leading Edge 18 (1999), 957]. It has been times. The bottom blue line is the initial condition: comparable to the usual beamforming and applied to background velocity estimation a left-going wave is incoming from the left migration imaging methods. We have also from regional to local scales, volcano homogeneous half-space and enters the revisited the trade-off between image stability monitoring, and petroleum prospecting hetererogeneous region. The black lines plot the enhancement and loss of resolution from the [Larose et al., Geophysics 71 (2006), SI11]. wave profile as it propagates in the heterogeneous point of view of its equivalence to a windowed These observations have motivated novel ideas region. The top red line plots the reflected wave that beamformer energy imaging function [3]. for imaging. First of all one can explain is recorded by the time-reversal mirror. The bottom mathematically the relation between cross picture plots the second step of the time-reversal Ambient Noise Imaging. The geological correlations of noise signals and the travel time experiment. The bottom blue line is the initial structure of the Earth can be explored by between the two points. This is motivated by condition: it is the signal recorded at the end of the observing the propagation of elastic waves in the analogy between the cross correlation of first step that is time-reversed and re-emitted by the the Earth crust. In classical seismology only the the noise signals and a virtual time-reversal time-reversal mirror. The top red line plots the waves generated by earthquakes or by artificial experiment in which one of the points is the reflected wave, which shows that a time-compressed explosions and recorded by a network of original source, the other point is the receiver, signal emerges from the medium. sensors (geophones) are used. Time-reversal and the noise source locations play the role of experiments or active array imaging (using the virtual time-reversal mirror. This analogy at a set of receivers. In classical array imaging arrays of sources) are not possible in (together with the Helmholtz-Kirchhoff the data are collected in the form of the array seismology since controlled sources of seismic identity, a variant of Green’s identity) shows response matrix (see Figure 3). The array waves are difficult to construct. However, even that, when the support of the random noise response matrix is obtained column by column without any earthquake or explosion, a weak sources completely surrounds the region of by emitting a pulse from each source location incoherent signal is recorded by seismographs: interest, then the cross correlation of the at a time and then recording the echoes at all the seismic noise, whose frequency recorded signals has a peak at the travel time the receiver locations. Then the recorded components around 0.1Hz consist mostly of between the sensors (see Figure 4). In many signals are processed to generate an image at surface waves produced by the interaction of applications, however, the noise source search points (pixels) in the image domain of the ocean swell with the coast. It turns out that distribution is spatially limited and the waves interest. This processing consists in these noise signals can be used to obtain travel recorded by the sensors are dominated by the

9 flux coming from the direction of the noise sources. The cross correlations of the recorded piece of signal recorded at x

t signals then depend on the orientation of these 0 100 200 300 400 500 600 700 800 900 1000 piece of signal recorded at y sensors relative to the direction of the energy xy

t flux. This affects significantly the quality of the 0 100 200 300 400 500 600 700 800 900 1000 cross correlation x − y estimate for the travel time. As can be τ explained by stationary phase arguments, it is −500 −400 −300 −200 −100 0 100 200 300 400 500 good when the line between the sensors is

along the direction of the energy flux and bad FIG. 4: Ambient noise imaging (numerical 50 when it is perpendicular to it. simulations). When the spatial support of the noise x When there is multiple scattering in the sources (circles) extends over all space then the cross N

x 0 z medium, as in an ergodic cavity or as in a correlation of the signals recorded at x and y is r x randomly inhomogeneous medium, symmetric and exhibits two peaks that are centered 1

−50 directional diversity of the recorded signals is at plus and minus the travel time between the two 0 50 100 150 200 z enhanced by multi-pathing. This was studied points. in the context of time-reversal experiments and it has been shown that time-reversal cross correlations and therefore blurs the refocusing can be enhanced in a randomly image. During our semester at IHÉS we have scattering medium. It turns out that it is studied the trade-off between resolution possible to exploit the enhanced directional enhancement and signal-to-noise ratio diversity of the multiply scattered waves for reduction due to scattering [4] and we have travel time tomography using cross shown that it requires a deep understanding of correlations of ambient noise signals. Indeed wave propagation in random media and scaling the travel time between two sensors can be issues. Following the coherent interferometric FIG. 5: Reflector imaging using signals generated estimated even in unfavorable situations imaging ideas developed for broadband by ambient noise sources (numerical simulations). provided that special fourthorder correlation deterministic pulses, it is possible to form The configuration is plotted in the top picture: the functions with auxiliary sensors are used space-time local cross correlations of the cross circles are the noise sources, the squares are the [Stehly et al., J. Geophys. Res. 113 (2008), correlations and migrate them. The use of scatterers, the triangles are the sensors, and the B11306]. By unfavorable we mean that the iterated cross correlation can enhance diamond is a small reflector. The image obtained by main component of the energy flux from the dramatically the quality of the images (see migrating the matrix of cross correlations of the noise sources is roughly perpendicular to the Figure 5). These techniques are new and could recorded noise signals is plotted in the left bottom ray connecting the two sensors. The fourth- certainly be improved and extended to other picture. The image obtained by migrating special order correlations can be used effectively for areas, such as microwave imaging, and they can fourth-order cross correlations is plotted in the right enhancing travel time estimation between the in turn trigger new ideas in active array bottom picture. two sensors by exploiting the scatterers as imaging. secondary sources and by reducing the contribution of the primary flux. For further reading: Ambient noise signals can also be used for passive sensor imaging of reflectors embedded [1] L. Borcea, J. Garnier, G. Papanicolaou, and in the medium. Indeed, in the presence of C. Tsogka, Coherent interferometric imaging, reflectors, the cross correlations between any time gating, and beamforming , to appear in In - two sensors have, in addition to the main peaks verse Problems. at the travel times between them, other peaks [2] J.-P. Fouque, J. Garnier, G. Papanicolaou, and at lag times related to travel times from the K. Sølna, Wave propagation and time reversal in sensors to the reflectors. The analysis of the randomly layered media , Springer, New York, relation between the secondary peaks in the 2007. cross correlations and travel times between [3] J. Garnier and G. Papanicolaou, Passive sen - sensors and reflectors shows how to image the sor imaging using cross correlations of noisy si - reflectors by suitably migrating the correlations gnals in a scattering medium , SIAM J. Imaging [3]. The resolution of the image depends on Sciences 2 (2009), 396-437. the directional diversity of the noise signals [4] J. Garnier and G. Papanicolaou, Fluctuation relative to the sensor array and on the reflector theory of ambient noise imaging , to appear in location. When directional diversity is limited Compte Rrendu Acad. Sci. Paris Geosciences. it is possible to enhance it by exploiting the scattering properties of the medium. However, scattering increases the fluctuation level of the

10 cthhea i5re0 sth Anniversary Campaign

final year for the campaign

In March 2008, IHÉS officially launched its enable the organisation to engage in sustained It nevertheless remains important for IHÉS to second international fundraising campaign, fundraising efforts, especially through the have new institutions supporting it: strategic carried out in France, the United States, Japan organisation of events, which are key to objectives are yet to be met, such as recruiting and China. promoting the work of “Friends”. a sixth permanent professor or consolidating Efforts made towards China led to a few the Institute’s attractiveness at the international This major donor campaign will close at encouraging results. The Institute’s visibility has level. the end of the year ; the Institute intends increased there, but progress in the search for to make use of these last few months to Chinese donors to the Chern Fund is slow. maintain its level of commitment and attract Fundraising in France has been very successful, new donors. with a large increase, since the previous Looking to the United States, the campaign, in the number of French consolidation of the Friends of IHES, Inc. organisations among the Institute’s major organisation bodes well in that respect. In donors: several large companies supported the 2010, the organisation’s Board changed with Institute with very significant contributions. the election of its new President, in the person of Renaud Dutreil. This appointment enabled new elected members to join the “Friends” Board, all very enthusiastic about IHÉS and keen to increase the organisation’s visibility within New York business circles. The recruitment of an Executive Director will also “On 19 May 2011, the Institute organised a ceremony in honour of Jean-Paul Gimon who played a key role at a difficult time for IHÉS. The Institute wanted to express its profound gratitude to Jean-Paul him through the creation of a Chair. He was in fact the person who Gimon encouraged the Institute to undertake Chair its first fundraising campaign and provided the resources to make that Created in 2005 campaign a reality. That was back in 2000, and IHÉS was experiencing in memory of a worrying financial situation. Since then, over 30 million euros has been Jean-Paul Gimon, former member of the raised in France and worldwide. This is thanks also to new key figures who IHÉS Board of Directors, and a highly have rallied to the IHÉS cause. In this regard, I would like to thank valued adviser for the Institute as it Renaud Dutreil, Chairman of LVMH Inc., who has agreed to take over launched its first ever fundraising in representing Friends of IHES, Inc. in the United States, setting up an campaign in 2001, this Chair will provide effective team and making “Friends” a very dynamic organisation, which permanent funding for two months of plays an important role in the Institute’s international influence. research visits at the Institute each year. As Chairman of the Board of Directors of IHÉS, I also welcome the Jean-Paul Gimon was always mindful of commitment of new institutions to the Institute, and particularly Huawei making a place like IHÉS accessible to Technologies France, who recently made a significant gift to IHÉS. young people and in particular to those Other sources of satisfaction are the numerous awards received by IHÉS from developing countries; for this professors, but also efforts made in recent past years to improve the Institute’s reason, the Chair bearing his name is visibility through creative initiatives such as the public conference held intended for young people, with the at the World Expo in Shanghai or the book, The Unravelers, Mathematical priority given to researchers from Africa. Snapshots . Without this enhanced visibility, the 50 th Anniversary Campaign would not have been so successful.”

Philippe Lagayette

11 ccaomnfpéariegnnc eins tehte c éUlnébitreadt iSotnas tes chaires

renewal of the Board of Support from CIC Friends of IHES, Inc. The New York subsidiary of CIC has long been a supporter of the work carried out by Friends of IHES, Inc. thanks to 11 years into its existence, the Since its inception, “Friends” has helped Serge Bellanger, who was a fervent organisation has elected a new President IHÉS considerably in terms of visibility, admirer of IHÉS and of the excellence of and three new members. and also in terms of funds raised French mathematics. Friends of IHES, and transferred to the Institute. The Inc. is very happy to see the partnership Friends of IHES Inc. was set up in 1999 organisation is now a real asset for the continue in 2010 and 2011 and warmly mainly to help IHÉS increase its visibility Institute. thanks CIC for its support. in the United States. There are historical In May 2010, Renaud Dutreil, Chairman links between IHÉS and the United States, of LVMH Inc. was elected President of the going right back to the very early days, Board of Directors of Friends of IHES, Inc. when Léon Motchane convinced Robert Following this election, new members, Oppenheimer to join the Institute’s Board who come from the corporate world in of Directors and to help guide its first steps. New York, joined the organisation. These Since then, hundreds of American new arrivals will hopefully lead to researchers have been invited to the an increase in the activity of “Friends” Institute. Many IHÉS permanent professors and improvements in identifying and have also contributed to the vitality of convincing new donors. “Like many exchanges between the Institute and the others, I have American scientific community. always placed mathematics at the forefront of key disciplines and I am proud and pleased to see France – and IHÉS in particular – taking such a prominent role in their development, for the furtherance of science and intelligence. IHÉS created a unique community of international scientists with significant achievements in mathematics and theoretical physics, in an environment of extraordinary Reception at the Ambassador, Permanent Representative of France to the United Nations, Gérard Araud, at the French intellectual freedom and independence. Residence, New York, on 12 May 2010 The campaign launched in 2011 in the United States aims to provide American researchers with new opportunities to work at IHÉS. It is crucial for Friends of IHES, 2011 - 2012 US campaign Inc., making a fresh start in 2011, to organise scientific events to reach out to new US supporters, corporations and A new campaign has been launched by Friends of IHES, Inc. will be reaching out to foundations willing to support fundamental Friends of IHES, Inc, with a financial target of foundations, with a view to entering into new research in mathematics. 3 million dollars to be raised in 2011 and partnerships aimed at providing multi-annual Developing exchanges between the United 2012. grants for the support of American visitors. States and France will contribute to the In a new departure, “Friends” is creating a expansion of academic excellence of both Priority is to be given to securing funding for “Corporate club”, to bring it into closer nations and to the benefit of the world’s American visitors, who represent around 30% contact with new American companies, with scientific community. Supporting this cause of the visitor programme at IHÉS. a number of high profile events, which we means taking one step closer towards An endowed United States Fund will be set hope will soon become well known in New understanding the world.” up to provide permanent funding for some of York business circles. the American visiting researchers. In addition, Renaud Dutreil

12 ccaomnfpéariegnnc eins tehte c éUlnébitreadt iSotnas tes chaires

finance breakfast meeting at the Consulate General of France in New York

“Some New Directions at the Interface track record. A change of paradigm is clearly between Finance and Mathematics: Bottom - needed and the beginnings of it are already Up Finance” was the theme explored during emerging. This new approach is multi-faceted the “Finance breakfast meeting” organised by and is primarily based on the investigation of the Friends of IHES, Inc., on 12 May 2011. market as a complex system where large scale patterns emerge from elementary interactions The event, which took place in the elegant of reasonably simple agents. It should allow setting of the Consulate General of France in a unified framework to study the various New York, represented an phenomenological opportunity for scientists features (such as the and finance specialists, asymmetric behaviour of together with leading agents or non-linearities business people, to in macro-economics) interact and exchange that are central to the views on the topical design of efficient Yuri Tschinkel, Eugene Durenard subject of financial and profitable survival mathematics, which was strategies in the global heavily criticised after marketplace. the severe financial crisis Eugène Durenard in 2008. Véronique Carpentier, Thierry Simon, Jim Simons concluded his talk by Two scientists, whose explaining that the new work covers both mathematics and finance, made direction in mathematical finance should come brief presentations on this topic: Eugène from the confluence of recent research in Durenard, Partner, Orion Investment complex systems, control theory, autonomous Management Ltd., and Petter Kolm, Director of adaptive agents and some aspects of mathematical the Mathematics in Finance M.S. Program at the biology. Courant Institute of Mathematical Sciences, The event was also an opportunity to New York University. demonstrate the high quality of events now Eugène Durenard made the first of the offered by Friends of IHES, Inc.. We hope that presentations, during which he shared his many other events of this level will be organised thinking on current developments in financial soon. Luc Hardy, David Goldman mathematics. In his view, financial theory has long been based on a “top-down” approach, which is seen today as having had a disappointing

“... Links between the Insitute and the United States are very strong. They were so from the start, with the famous Institute for Advanced Study (IAS) in Princeton providing a sort of blueprint for the Institute. These links are just as strong today: the Institute has no fewer than 30% American mathematicians, physicists, biologists and computer scientists within its ranks. Further reinforcing the links between the Institute and the United States is a key objective for Friends of IHES. This morning, we wanted to bring together the worlds of finance and mathematics. French mathematicians represent a valued talent pool on Wall Street, and sometimes a controversial one (mathematicians are admittedly easy targets for criticism!). For my part, I am pleased to see that French training and expertise are so appreciated here ...”

Extract from Philippe Lalliot’s speech, Consul General of France in New York

13 campaign in the People’s Republic of China

world expo in Shanghai

For more than 10 years, IHÉS has been Diderot), Li Ta-Tsien (Institut Sino-Français undertaking projects aimed at increasing its de Mathématiques Appliquées), George visibility within the Chinese scientific Papanicolaou (IHÉS-Stanford University). community and attracting more Chinese They touched on a wider range of themes, researchers. including flexible polyhedra, imaging in seismology, mathematics in finance and the The Shanghai World Expo was a great golden ratio. opportunity to get in touch with the Chinese IHÉS thanks the Consulate General of France public, and also with students and researchers. in Shanghai, Yao Yi-Jun and his wife, Which was why IHÉS applied to organise a Xu Mingyu, for their invaluable help and conference in the France Pavilion, “meeting active contribution to the success of the the Unravelers” , a scientific conference for the Li Ta-Tsien day, together with the event sponsors: general public, consisting in a series of short EADS, Saint-Gobain, Société Générale and presentations. The conference, which was for the geometry of the universe . Cédric Villani LCL Banque privée initially planned over a half-day, had to be (Université de Lyon I - Institut Henri extended to a full day, to satisfy the many Poincaré) spoke of how galaxies evolve, using registration requests received. In the end, over an analogy from gas kinetics. Other speakers 200 people came to listen to leading scientists were: Jean-Pierre Bourguignon (CNRS- who were there to share some of their current IHÉS), Josselin Garnier (IHÉS-Université Paris research work or certain aspects of mathematics that they find particularly interesting. Four of the eight presentations dealt with mathematical physics and how geometry contributes to our understanding of the Universe: Liu Kefeng (Zhejiang University) Mathematics born of physics , Long Yiming (Chern Institute of Mathematics, Nankai University) The solar system seen by a mathematician and Hu Sen (University of Science and Technology of China) Searching Hu Sen , Liu Kefeng, George Papanicolaou, Josselin Garnier, Cédric Villani The Unravelers exhibition

The Paris - Île-de-France Pavilion at the World Expo, where the travelling exhibition The Unravelers was shown from 16 to 23 October 2010, was the starting point for the exhibition’s long tour across China, via the Alliances Françaises network. Nine major cities have chosen to show it between November 2010 and September 2011: Nankin, Canton, Jinan, Xi’an, Beijing, Hangzhou, Chongqing, Macao and Tianjin. The publication by Higher Education Press of the Chinese version of the book, The Unravelers , complements the exhibition, with Exhibition in Xi’an texts by Chinese scientists added to the original version. This book, edited in France by Éditions Inauguration of the exhibition in Beijing by Jean-Pierre Bourguignon Belin, is the work of J.-F. Dars, A. Lesne and A. Papillault.

14 campaign in the People’s Republic of China

donations for the Chern Fund

The Chern Fund is a fund set up to finance passed away, the Chern family has Chinese scientists invited to the Institute. maintained its full support to the project. In providing this support, it In November 2010, the helps meet three broader Chern Foundation made a objectives: intensifying new additional donation. scientific exchanges between IHÉS would like to express China and France, warmest thanks for her trust promoting scientific research to May Chu, Shiing Shen without any programme Chern’s daughter and the constraints and increasing Foundation’s President. the visibility of IHÉS Another major gift came to within Chinese scientific the Institute recently for the communities (in mathematics, Chern Fund, from the theoretical physics and at “Fondation d’entreprise the interface between EADS”. EADS is also one of mathematics and biology). the Institute’s long-standing partners. Over Many French companies have become the past ten years, various projects have partners of this project; the Institute hopes been set up at the Institute thanks to its Chern Shiing-Shen to also attract Chinese donors and is support. Chern Shiing-Shen is one of the greatest working actively to that end. geometers of the 20 th Century. His Since its creation in 2002, the Chern Fund contribution to differential geometry in has received the support of Professor particular was major, and had multiple Shiing-Shen Chern who was personally applications. Professor Chern would have involved in the development of the Chern celebrated his 100 th birthday in 2011. Fund, by making a financial contribution The Chern Institute of Mathematics, to it, through his own foundation. Since he Nankai University (Tianjin, China) and MSRI (Berkeley, United States), two institutes that owe their creation to him, will be organising celebrations from 24 to 28 October 2011 (at the CIM) and from 30 October to 5 November 2011 Louis Nirenberg (first receipient of the Chern medal) and (at MSRI). IHÉS will be organising a May Chu during the International Congress of Mathematicians day of conferences in his memory on at Hyderabad, August 2010 17 November 2011. Huawei Technologies Fund

A new fund set up to finance invited researchers but also provide highly innovative technical of all nationalities was created by the French tools. Which is why this leading Chinese group subsidiary of Huawei Technologies at the decided to support fundamental research in beginning of the year. mathematics and chose IHÉS for that purpose, both because of the freedom This Chinese high technology company offered to its researchers and the has opened two research centres in excellence of the work carried out there. France, one in Lannion (Brittany) and The Huawei Technologies Fund at IHÉS one in Cergy-Pontoise (near Paris). will support 2 months of research visits Since its inception, Huawei Technologies has each year in perpetuity. always viewed research as an essential means to Leo Sun (Huawei France Managing Director), Jean-Pierre improve its ability to meet market requirements Bourguignon, François Quentin (Huawei France President), Philippe Lagayette

15 point of view by ...

Shelly Garion and Sefi Ladkani

The European Post-Doctoral Institute for problem, before formulating claims and assertions courses in the winter. The surrounding landscape Mathematical Sciences (EPDI), formed of ten which are then proved in full generality using around the Rhine is particularly pleasant. institutes spread throughout Europe, exists rigorous methods. In 2010 we moved to IHÉS at Bures-sur-Yvette, since 1995 to encourage the mobility of young We started our stay in Europe in 2008 by visiting a small town south of Paris. This quiet and scientists at the European level. IHÉS for two months and then we moved to tranquil place has inspiring surroundings allowing Testimony collected in March 2011. Bonn. Later, we were both selected as European one to concentrate on research and think of Postdoctoral Institute (EPDI) laureates for the mathematical problems in the relaxed atmosphere We are a married couple of mathematicians years 2009-11. This is a two-year postdoctoral among the woods of the Bois-Marie forest. One currently staying at IHÉS as EPDI laureates. We fellowship allowing one to carry out research at does not have to worry too much about everyday both graduated at the Hebrew University of prestigious institutes in Europe. This has several life here, as the staff of IHÉS takes care of many Jerusalem, Israel. Sefi’s research is in representation advantages at this early stage of the career; it aspects. Accommodation is provided at the well theory and homological algebra and Shelly works allows to focus on research without many external equipped Ormaille residence, and lunch is served in group theory. Both areas of research are in the disturbances as well as to establish contacts and at the cafeteria allowing also informal general field of algebra, so although each of us discuss ideas with researchers at these institutes, interaction among researchers. carries out his/her research independently, we try which differ from ordinary universities by the Nevertheless, IHÉS is close enough to Paris with to assist and support each other in general fact that there are relatively few, but very well all the possibilities this metropolis has to offer. questions and issues that arise during our work. known, permanent members, and most other Professionally, there are many universities so that In his research, Sefi focuses on the theme of scientists are visitors from all around the world. seminars, conferences and other activities are derived equivalence and its combinatorial aspects, We were very happy that we were both selected being held regularly. During leisure time, one can especially concerning categories arising from for this fellowship, as this enabled us to continue enjoy the cultural and historical gems that Paris n combinatorial data appearing naturally in living together while developing our careers, is full of. o s n i

algebraic, combinatorial and topological contexts. which is not at all trivial but was extremely Our stay in Europe provided us with many k l Derived categories, and more generally triangulated important to us. professional opportunities. We could conveniently i W

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categories, have found applications in diverse We started our EPDI itinerary in 2009 by travel in order to participate in scientific meetings H

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areas of mathematics and mathematical physics, staying one year at the Max-Planck-Institute for and give talks at various institutions. Easy travel o i t a l

forming also bridges between various domains of Mathematics (MPIM) in Bonn, located at the also facilitated collaboration with other scientists s n a algebra and geometry. heart of this pleasant city on the river Rhine. In as personal contact is still important even in our r T

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Shelly investigates finite simple groups. Finite Bonn there is a lot of mathematical activity, both current digital era. s i a

groups naturally occur when considering at the MPIM itself in the form of weekly seminars We will always have pleasant memories from d n the symmetry of mathematical and physical and various workshops as well as at the University the time during our EPDI fellowship. It gave us a a L - t

objects, the finite simple groups can be seen as of Bonn and the Hausdorff Institute. unique cultural experience as well as the n a h their building blocks. She focuses on the study of Bonn is also well known as the city of Beethoven opportunity to practice new foreign languages. c u the combinatorial and probabilistic aspects of and indeed there are many classical music events o T

. V these groups, utilizing techniques from number around the year, from Schloss concerts in the , s e

theory and algebraic geometry. summer to piano competitions and conducting m m a

A common aspect of our work is the quite J

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201 1 events e V

. C “The Unravelers Tour in France” 12 September, IHÉS . M

, s 26 September - 6 October: École Normale Supérieure Lyon Afternoon on Arithmetical Geometry on the occasion i a

th d 7 - 8 October: CIRM, Luminy of Takeshi Saito’s 50 birthday . n a L

10 - 21 October: Université de Montpellier From 17 to 21 October, IHÉS - t n 31 October - 1 1 November: Université de Strasbourg Differential Equations and Galois Theory Conference a h c

14 - 30 November: Université 1, Nancy as part of the celebration marking Evariste Galois’s u o T

st 1 December 2011 - 6 April 2012: Nord-Pas de Calais region bicentennial, co-organised by Y. André, A. Buium, . V

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Dates to be set for Rennes, Orléans and Grenoble. P. Cartier, J.-P. Ramis and H. Umemura . r a D

Details of this event can be found on the Institute’s website. 17 November, IHÉS . F . J

“The Unravelers Tour in China” Celebration of Chern Shiing-Shen’s centenary . : s o June : Alliance Française in Chongqing October, November 2011 - January, February 2012 t o h

July : Alliance Française in Macao on Thursdays, IHÉS P August - September : Alliance Française in Tianjin Arithmetics and Algebraic Geometry Course , From 7 to 9 September , IHÉS organised by A. Abbes, C. Breuil and L. Lafforgue . For more information: www.ihes.fr Joint master opening for students of Hadamard July 2012 (dates to be confirmed), IHÉS Foundation founding institutions. French-Asian Summer School