Univesité Pierre et Marie CURIE COLLOQUIUM 2015http://video.upmc.fr//differe.php?collec=S_C_colloquium2015Le colloquium Pierre et Marie Curie présente des exposés consacrés à la physique contemporaine et aux disciplines connexes. Ces exposés sont destinés à tous les étudiants et à tous les enseignants et chercheurs mais plus particulièrement aux étudiants de master et aux étudiants en thèse. Les exposés ont lieu soit en français soit en anglais.http://vodcast.upmc.fr/images/vignette_colloquium_15.jpgCOLLOQUIUM 2015http://video.upmc.fr//differe.php?collec=S_C_colloquium2015Fluidics at the nanoscalehttp://video.upmc.fr//differe.php?collec=S_C_colloquium2015&video=6 Fluid transport at the nanoscales is one of the remaining virgin territory in uid dynamics, in spite of hydrodynamics being a very old and established domain. Over the last years, a number of striking phenomena have been unveiled, such as superfast ows in carbon nanotubes or graphene oxides membranes, and manyof them are still waiting an explanation. A major challenge to adress the fundamental properties at the nanoscales lies in building distinct and well-controlled nanosystems, amenable to the systematic exploration of their properties. To this end, we have developed new methods based on the manipulation of nanoobjects, displacing, cutting, and gluing these elementary building blocks. This allows us to fabricate original fluidic and mechanical systems involving single nanotubes.<br/> <br/> I will first discuss fluidic transport inside single nanotubes, made of both carbon and boron-nitride materials. Putting osmotic transport and its fundamental origins into perspective, I will show how to harvest this powerful mechanism beyond the classical vant Ho_ law. Experiments of osmotic transport across boron-nitride nanotubes show unprecedented electric energy conversion from salt concentration gradients, thereby unveiling new perspectives in the field of osmotic energy harvesting from salinity gradient. I will then show that nanoscale confinement allows building more advanced uid transport functionalities, such as ionic or osmotic diodes. This opens new avenues in membrane science for energy harvesting and desalination questions. Thu, 26 Nov 2015 10:00:00 +0100S_C_colloquium2015_6Propriétés optiques des pérovskites hybrides pour la photonique et le photovoltaïquehttp://video.upmc.fr//differe.php?collec=S_C_colloquium2015&video=5 Les pérovskites hybrides organiques–inorganiques sont actuellement sur le devant de la scène pour leur utilisation dans les cellules solaires: un rendement de 20% vient d'être homologué, ce qui propulse ce matériau dans la cour des grands pour l’utilisation photovoltaïque. On parle même de "rupture technologique". Les pérovskites hybrides présentent aussi des propriétés optiques intéressantes pour des utilisations liées à leur émission: diodes électroluminescentes, lasers. Un grand avantage de ces cristaux moléculaires réside dans la simplicité de leur synthèse et dans leur versatilité : en effet, on peut imaginer de l'ingénierie moléculaire sur chaque partie de la molécule de facon à optimiser le matériau pour chaque application visée. Les propriétés optiques remarquables des pérovskites hybrides seront présentées. L’interaction lumière–matière sera étudiée dans des cavités de type Pérot–Fabry contenant ces cristaux moléculaires. Fri, 16 Oct 2015 10:00:00 +0200S_C_colloquium2015_5Divers aspects d’une dynamique dominée par des effets de mémoirehttp://video.upmc.fr//differe.php?collec=S_C_colloquium2015&video=4 On pense habituellement que les effets de mémoire sont une caractéristique des systemes complexes. Nous discuterons un cas où ils dominent la dynamique d’un objet élémentaire. Les expériences décrites concernent le mouvement d’une gouttelette, rebondissant sur une surface liquide et auto-propulsée par son couplage aux ondes qu’elle émet. Il y a entre les deux composantes de cette entité composite un échange itératif d’information. C’est la goutte qui génèere l’onde et c’est cette dernière qui détermine où la goutte va aller. Il ne s’agit pas d’une écho-localisation classique car le champ d’onde est formé d’ondes stationnaires et qu’il contient une mémoire de la trajectoire antérieure. Les résultats récents obtenus lorsque cette entité est confinée dans un puits de potentiel démontrent que cette mémoire de chemin conduit, dans ce système classique, à une double quantification des orbites stables possibles ainsi qu’à des comportements probabilistes qui seront discutés. Mon, 18 May 2015 10:00:00 +0200S_C_colloquium2015_4Physical units based on fundamental constants changing with time ?http://video.upmc.fr//differe.php?collec=S_C_colloquium2015&video=3 In 2018, on the occasion of the 25th meeting of the General Conference on Weights and Measures, CGPM, of the Metre Convention founded in 1875, it is envisaged to redefine the International System of Units (SI). In the future, as outlined by Max-Planck in his famous paper of 1900 postulating the Planck constant, it shall be based on fixing the numerical values of fundamental constants of nature, the defining constants: the velocity of light, the charge of the electron, the Boltzmann, Avogadro and the Planck constants, the Cs hyperfine clock transition and the luminous efficacy. In the talk an overview will be provided on the progress, challenges and future perspectives of the new Quantum SI. Moreover, the question will be discussed whether or not the fundamental constants are indeed constant in time. New experiments are presently being devised; one of them is based on next–generation optical clocks using transitions in highly charged ions that are read out via quantum–logic schemes. They bear the potential to trace potential changes in the fine structure constant α on the level of ∆α/α ≈ 10 ^ -20 per year.Thu, 16 Apr 152015 10:00:00 +0100S_C_colloquium2015_3From fundamental physics to the origins of life: ab initio Miller experimentshttp://video.upmc.fr//differe.php?collec=S_C_colloquium2015&video=2 Origins of life studies represent an exciting and highly multidisciplinary research field that incorporates contributions from geologists, physicists, biologists, mathematicians, chemists and computer scientists, inter alia. It was Charles Darwin who first hypothesized that life may have begun “in a warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity”, effectively giving birth to the “primordial soup hypothesis”. In 1953, Miller reported the stunning results of an electric discharge on a model atmosphere for the primitive Earth. The surprising result of this experiment was a substantial yield of a mixture of amino acids, thus providing support for the primitive soup theory. However, the chemical reactions involved in those experiments have never been studied at the fundamental atomic and electronic level. Here we present the first ab initio theoretical simulations of Miller experiments. This study, based on state-of-the-art ab initio metadynamics analysis of free-energy landscapes, shows that glycine spontaneously forms from mixtures of simple molecules once an electric field is switched on and identifies formic acid and formamide as key intermediate products of the early steps of the Miller reactions, and the crucible of formation of complex biological molecules. These results, which have had a large resonance in the scientific and large public press, pave the way to novel computational approaches in the research of the chemical origins of life. Tue, 10 Mar 2015 10:00:00 +0100S_C_colloquium2015_2How the characterization of extrasolar planets allows to better understand the physics of planet formationhttp://video.upmc.fr//differe.php?collec=S_C_colloquium2015&video=1 In the past few years, the research on extrasolar planets has shifted from the discovery of these objects to their physical characterization. This means that for the first time, the intrinsic luminosity, the internal structure, and the atmospheric composition of planets outside of the Solar System were measured. In my talk I will show how these observations can be used to better understand the physics of planet formation. I will address two different aspects: first, it is shown how observations of the intrinsic luminosity emitted by young giant planets constrains the physics of the accretion shock which occurs when a forming gas giant planet rapidly accretes gas from the protoplanetary nebula. Second, it is discussed how the amount of hydrogen/helium contained in an exoplanet (that can be derived from the combined measurement of the mass and radius) is an indicator of magnitude of the opacity in the atmosphere of forming protoplanet. This opacity is mainly due to micrometer sized grains that are suspended in the gas. Therefore, this observation allows to understand the dynamics of the grains like their growth and settling, which can be described with an analytical model. Wed, 21 Jan 2015 12:41:20 +0100S_C_colloquium2015_1