Accueil > Séminaires
(7) Colloquium - Année 2024
Mer. 24/01/2024 09:45 Bâtiment 20, Amphi HEINER Zsuzsanna (Humboldt-Universität zu Berlin) Interfacial macromolecular folding and interactions from in situ nonlinear vibrational spectroscopy (Bio Nano Imagerie) Many important processes in chemistry and biology occur at interfaces where the molecular interactions and dynamics significantly differ from those observed in the bulk. Proper characterization of the behavior of peptides and proteins at macromolecular interfaces, including their reversible adsorption to surfaces and their folding into the membrane, is a prerequisite for understanding fundamental physiological processes stemming from intracellular reactions. A powerful noninvasive, optical, surface analytical tool is vibrational sum frequency generation (VSFG) spectroscopy, which often enables direct observation of the structural and dynamical properties of interfacial molecules. Nevertheless, the acquisition times and spectral resolution of traditional broadband VSFG spectrometers are far from ideal to follow the interaction of macromolecules at bio-interfaces in real-time and in situ. Pour plus d'informations, merci de contacter Finco A. |
Mer. 28/02/2024 09:45 Bâtiment 20, Amphi LACAZE Emmanuelle (Institut des NanoSciences de Paris, CNRS, Sorbonne Université) Impact of the ecological, energy and digital transitions on research in laboratories (sobriety) In 2022, the CNRS Institute of Physics (now CNRS-Physics) commissioned G. Debregeas and myself to write a text on the impact of the ecological, energy and digital transitions on research in the laboratories (sobriety). This text would then be used for the CNRS-Physics 2030 outlook. So we set up a bureau with, in addition to G. Debregeas and myself, Laëtitia Marty (I. Neel), Delphine Debarre (Liphy), Guillaume Roux (LPTMS), Sylvain Capponi (LPT Toulouse) and Christophe Arnold (Gemac - Versailles) for a group made up of researchers, teachers and research support staff. The idea was also to try to involve the community as much as possible in this work. Pour plus d'informations, merci de contacter Poy G. |
Mer. 06/03/2024 09:45 Bâtiment 20, Amphi CAMP Charles (NIST, US Department of Commerce) Imaging the Chemical Landscape within Cells and Tissues with Light (Bio Nano Imagerie) Distinguishing edited cells from non-edited/off-target edits would transform the manufacturing of cell editing products. Visualizing the separation of bacterial colony function would open up our fundamental understanding of microbiology. Identifying chemical cues in pap smear results before the appearance of cells with odd morphologies could lead to earlier identification of dysplasia, improving patient outcomes and treatment options. In short, imaging the dynamic chemical landscape within cells and tissues would revolutionize biological discovery and medicine. Pour plus d'informations, merci de contacter Finco A. |
Mer. 20/03/2024 09:45 Bâtiment 20, Amphi GANICHEV Sergey (University of Regensburg, Regensburg, Germany) Terahertz radiation-induced optoelectronic phenomena in graphene and graphene-based 2D materials (Spectroscopie Térahertz) The paper reviews experimental and theoretical studies on polarized terahertz radiation-induced photocurrents in graphene and graphene-based 2D materials. We consider the optoelectrical phenomena excited by THz radiation in graphene and twisted graphene and present the state of the art in this field, including both recent advances and well-established results, see e.g. [1-7]. Different physical mechanisms of the THz radiation excited dc currents proportional to the second powers of the radiation electric field are presented, including phenomenological description based on symmetry arguments, models visualizing the physics of nonlinear responses, and microscopic theory of several phenomena. The following effects yielding a dc current proportional to the square of the irradiation electric field are discussed: high-frequency Hall effect at zero magnetic field, edge photogalvanic effects, ratchet effects in graphene with lateral superlattices, cyclotron resonance (CR) assisted dc currents, terahertz induced magnetooscillations coupled to the CR harmonics, Bernstein modes, as well as multiple oscillations upon variation of the gate voltage in twisted bilayer graphene near the second magic angle. We show that nonlinear transport opens up new possibilities for probing Dirac electrons. Pour plus d'informations, merci de contacter Finco A. |
Mer. 10/04/2024 09:45 Bâtiment 20, Amphi BAIGL Damien (PASTEUR, Ecole Normale Superieure, PSL University, Sorbonne Université, CNRS) Synthetic self-assembly with life-like properties Self-assembly is both an advantageously spontaneous process to organize molecular or colloidal entities into functional superstructures and a key-feature of how life builds its components. However, compared to their living counterparts, synthetic materials made by self-assembly usually lack some of the interesting properties of living systems such as multicomponent character or capability to adapt, transform and evolve. In this presentation, I will describe different systems where life-like properties can emerge from self-assembled synthetic materials. First, I will show that user-defined and elaborate nanostructures (e.g., DNA origamis, nanogrids, SST assemblies) can be obtained by the isothermal self-assembly of hundreds of different DNA bricks and proteins with a unique capability to optimize, adapt, evolve and even completely transform their morphology, either spontaneously or under command [1-2]. I will also present a new DNA self-assembly principle that does not rely on base-pairing principles, showing in particular that photosensitive DNA intercalating molecules can co-assemble with DNA bases to form new extended supramolecular materials with intriguing dynamic properties. I will describe in particular the formation of photoswitchable 3D crystals with unique photoreversible growth and light-gated fluorescence [3]. Finally, I will present different colloidal self-assembly processes at air-water or liquid-liquid interfaces and explore how dynamic properties can emerge from such systems. Starting from the familiar situation of drying drop containing a colloidal suspensions, we have been interested in controlling/cancelling the so-called “coffee-ring effect” [4-7] or turning it into a low-cost yet powerful medical diagnostic tool [8]. In such systems, however, particles adsorb at the interface to form amorphous structures. This led us to invent a simple method in which bulk particles adsorb at the water-interface and directly crystallize there. Based on the use of ultralow amounts of surfactant, 2D colloidal crystals spontaneously form without any other applied force than their own weight [9]. This method allows us to crystallize a broad variety of nanometric and micrometric particles, including those made of polymers, metals or inorganic materials, and tune the characteristics of the colloidal crystals [10] that can be further deposited on solid substrates [11]. These colloidal crystals display intense structural colors as well as, under some conditions, some remarkable dynamic properties at the air/water interface. For instance, using light, we can reversibly melt/crystallize these colloidal assemblies on command, evidencing other life-like properties, such as dissipative character or living crystallization [12-13]. Pour plus d'informations, merci de contacter Poy G. |
Mer. 15/05/2024 09:45 Bâtiment 20, Amphi LELLOUCH Laurent (Centre de Physique Théorique, CNRS, Aix Marseille Univ, IPhU) The mysterious magnetism of the muon (Théorie des Interactions Fondamentales) Nearly twenty years ago in an experiment at Brookhaven National Laboratory, physicists measured the muon's anomalous magnetic moment, a_mu, with a remarkable precision of 0.54 parts per million. Since that time, the reference Standard Model prediction for a_mu has exhibited a discrepancy with experiment of over 3 standard deviations, raising the tantalizing possibility of elementary particles or fundamental forces as yet undiscovered. On April 7, 2021 the physicists of an ongoing experiment at Fermilab presented first results of a new measurement of a_mu, brilliantly confirming Brookhaven's measurement and bringing the discrepancy with the reference prediction to a near discovery level of 4.2 sigma. This discrepancy was further enhanced to 5.1 sigma this past with the publication of Fermilab’s new result that reduces the measurement uncertainty by a factor of 2. According to usual particle physics standards, such a discrepancy would mean that new fundamental physics has been uncovered. Pour plus d'informations, merci de contacter Finco A. |
Mer. 26/06/2024 09:45 Bâtiment 20, Amphi SADHU Tridib (Department of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai, India) Large deviations: a road to non-equilibrium statistical Physics A remarkable success of 20th-century Physics is the framework of statistical Physics that bridges the atomistic and macroscopic worlds. However, this framework is only limited to systems in thermal equilibrium. In reality, most systems in nature are outside equilibrium. A cup of coffee left on a table, reaches thermal equilibrium in an hour or so by releasing heat, but over longer periods it evaporates. Living matter, like bacteria, generates energy currents from burning ATP to self-organize at large scales. Such non-zero currents break time-reversal symmetry, thus constantly generating entropy. As a result, the statistics of these systems do not follow the principals of statistical Physics. In fact, at present, there is no general conceptual framework à la Gibbs-Boltzmann to describe non-equilibrium Physics from first principles. It is not even clear how to generalize the basic ideas of state variables like pressure and temperature, or thermodynamic potentials like the free energy. Pour plus d'informations, merci de contacter Poy G. |