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FACULTÉ DE PHYSIQUE
UFR 925

Année 2015

  1. Yuri DOKSHITZER - "Classical tunes of quantum field theory"
  2. Lyderic BOQUET - "Fluidics at the nanoscale"
  3. Emmanuelle DELEPORTE - "Propriétés optiques des pérovskites hybrides pour la photonique et le photovoltaïque"
  4. Yves COUDER - "Divers aspects d’une dynamique dominée par des effets de mémoire"
  5. Joachim ULRICH - "Physical units based on fundamental constants changing with time ?"
  6. A. Marco SAITTA - "From fundamental physics to the origins of life: ab initio Miller experiments"
  7. Christoph MORDASINI - "How the characterization of extrasolar planets allows to better understand the physics of planet formation"

 

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1er DÉCEMBRE 2015 :

Yuri DOKSHITZER - "Classical tunes of quantum field theory"

 

Yuri DOKSHITZER

LPTHE (Laboratoire de Physique Théorique et Hautes Energies), UPMC, Paris.

 

RÉSUMÉ :

Relativistic dynamics of quantum fields (Quantum Field Theory) looks intrinsically complicated. And so it is indeed. However, now and then QFT permits, all of a sudden, to use a simple classical language in order to describe certain important observables. This is markedly the case of momentum distributions of quarks and gluons inside a proton parton distribution functions, a key instrument of LHC searches for new physics. 

We will discuss how and why this happens, expose hidden beauty of QCD parton dynamics and glance at bright manifestations of quantum coherence in multiparticle production ("QCD radiophysics"). 

A deeper insight into the nature of "classicality" based on resurrection of well forgotten 60-years-old ideas may result in full analytic solvability of a supersymmetric QFT (N=4 SUSY) a close relative of Quantum ChromoDynamics. 

 

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 3 NOVEMBRE 2015 :

Lyderic BOQUET - "Fluidics at the nanoscale"

 

Lyderic BOQUET

Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris.

 

RÉSUMÉ :

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.

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.

 

        

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6 OCTOBRE 2015 :

Emmanuelle DELEPORTE - "Propriétés optiques des pérovskites hybrides pour la photonique et le photovoltaïque"

 

Emmanmuelle DELEPORTE

Professeur des Universités, Directrice du Département de Physique Laboratoire Aimé Cotton, École normale supérieure de Cachan.

 

RÉSUMÉ :

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.

 

        

 

 Retour au sommaire (année 2015)

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5 MAI 2015 :

Yves COUDER - "Divers aspects d’une dynamique dominée par des effets de mémoire"

 

Yves COUDER

Laboratoire Matière et Systèmes Complexes, Université Paris Diderot, Paris.

 

RÉSUMÉ :

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.

 

        

 

 

 Retour au sommaire (année 2015)

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7 AVRIL 2015 :

Joachim ULRICH - "Physical units based on fundamental constants changing with time ?"

 

Joachim ULLRICH

Président du Physikalisch-Technische Budesanstalt.

 

RÉSUMÉ :

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.

 

        

 

 Retour au sommaire (année 2015)

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10 MARS 2015 :

A. Marco SAITTA - "From fundamental physics to the origins of life: ab initio Miller experiments"

 

A. Marco SAITTA

IMPMC (Institut de Minéralogie, de physique des Matériaux et de Cosmochimie), UPMC, Paris

 

RÉSUMÉ :

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.

 

         

 

Retour au sommaire (année 2015)

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6 JANVIER 2015 :

Christoph MORDASINI - "How the characterization of extrasolar planets allows to better understand the physics of planet formation"

 

Christoph MORDASINI

Postdoctoral researcher at the planet and star formation department of the Max Planck institute for astronomy, Heidelberg, Germany.

 

RÉSUMÉ :

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.

 

         

 

 Retour au sommaire (année 2015)

02/06/17

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