Digital and analytical functions performed by today’s semiconductor devices are governed by the electronic transport across an engineered material system with a well-defined electronic structure. Even if a multitude of electrons are concerned in the device operation, the device fundamental characteristics arise from properties inherent to single electrons. For instance, photon emission is related to transitions between electronic states of the system and for optoelectronic devices operating in the mid and far infrared wavelength range is characterized by an extremely long spontaneous emission time (>100ns), which hinders the realization of efficient light emitting diodes. In this project we plan to realize novel optoelectronic devices, whose performances do not belong to single electron properties, but rather depend on the ensemble of the interacting carriers. We recently demonstrated that the optical properties of a dense electron gas do not reflect the energy spectrum, but depend on the Coulomb interaction between electrons. The absorption spectrum of a semiconductor quantum well with several occupied energy levels presents a single absorption peak at an energy completely different from the single particle transition energies. This unique optical resonance, concentrating the whole interaction with light, corresponds to a many-body excitation of the system, the “multisubband plasmon”, in which the dipole-dipole Coulomb interaction locks in phase the optically allowed transitions between confined states. In this project, the peculiar properties of multi-subband plasmons will be exploited for mid and far infrared optoelectronics. The first property is the fact that, as the permittivity of multisubband plasmons depends on the doping level and on the size of the quantum well, semiconductor layers with ad hoc dielectric properties (hence metamaterials) can be realized. As a first application we will design all-dielectric waveguides in the mid and far infrared for quantum cascade lasers. A second application will be the design of engineered infrared absorbers. The second part of the project is based on another fundamental property of collective electronic excitations: their superradiant nature. Indeed the multisubband plasmon is the bright state issued from the coherent superposition of several intersubband excitations. As a superradiant state can be visualized as one in which a macroscopic polarization is established over a region of space, a very interesting way to characterize this state will be its observation by using Electron Energy Loss Spectroscopy. The superradiant nature of multisubband plasmons results in a radiative lifetime of the order of few hundreds fs, thus much shorter than the typical intersubband spontaneous emission lifetime. We will exploit this property to conceive and realize two different classes of optoelectronic infrared emitters based on many-body excitations: - Quasi-monochromatic fast and tunable incandescent sources - Quantum engineered superradiant emitters The first kind of devices is based on the same geometry as a field effect transistor: the electron gas is excited by a source – drain current, while the electronic density can be controlled by a gate voltage. This point will be also studied in collaboration with STMicroelectronics, which will provide FDSOI and CMOS devices, in order to observe far-infrared optical signals in state-of-the-art electronic devices. In order to fully take advantage of the superradiant character of multisubband plasmons, another generation of devices will also be conceived, realized and characterized, using quantum engineering for resonant excitation. We will design a device based on vertical transport through the electron gas, a plasmon assisted tunnelling device. More selective injection mechanisms will also be investigated, by exploiting the dipole-dipole interaction in systems of tunnel coupled quantum wells.

The reduction of noise in aeronautics and car industry is currently driving an intensive research in aeroacoustics. In particular, numerical tools of simulation are developed, which should provide a better understanding of the complex phenomena resulting from the interaction between acoustics and flow. Besides the simulation of noise generation by turbulent flows which has been significantly improved in the past few years ' in particular with the progress of the Direct Numerical Simulation - the seemingly simpler problem (linear equations) of acoustic propagation in a known mean flow has been less investigated. Our objective is the design of a general finite element method, able to solve the time harmonic problem in the realistic cases that arise in industry. Such a tool would be very useful for the engineer by providing him intrinsic quantitative data (radiation pattern, resonance frequencies...) helpful for the optimum design of the industrial setup. The absence of such a useful code can be explained by several difficulties inherent in the problem. In particular, the choice of a finite element scheme is not straightforward in this context, the treatment of artificial boundaries of the computational domain is particularly intricate because of the coexistence of acoustic waves and hydrodynamic vortices and the modelization of realistic boundary conditions raise difficult open questions. Recent work of several teams give some possible strategies to build this tool: ' The team Innovation Works of EADS has developed a complete solution for the axisymetric potential case, using a coupling between finite elements and integral equations. ' POEMS and CERFACS teams, in partnership with EADS, have developed an alternative approach to handle with the non potential case: this method relies on a finite elements discretization of a so-called regularized formulation of Galbrun's equation. ' The team Guided Waves of the LAUM applies a multimodal strategy to solve the problem in a non-uniform duct. ' The LAUM and POEMS have studied and compared different numerical models for impedance discontinuities on the walls. Developing a general and efficient method is a challenge that requires both to overcome some limitations of the present methods and to build coupling strategies between them. We will build on the CERFACS experience in the field of high performance computing and in computational fluid dynamics. The EADS links with the aeroacoustic Airbus team will be leveraged to define representative test cases of industrial difficulties in the aeronautic industry. The four teams already have experience collaborating together. They belong to the working group « Modélisation physique et outils numériques : Comprendre et modéliser » of IROQUA (http://www.iroqua.net/). The project AEROSON has been approved by this working group during its meeting at ONERA.

This project aims at the control of wave properties through the control of disorder, an objective that can be achieved with waves that propagate in macroscopic media. It builds on a fruitful Chilean-French collaboration that goes back ten years, that has provided a solid theoretical backbone to our understanding of wave propagation in complex media. In addition, both sides have developed a close interaction with experimental groups in their respective countries. This proposal raises the ongoing collaboration to a new level of ambition, by bringing the experimental groups into a jointly articulated initiative. Research activities will be both of a theoretical and experimental nature, and carried out symmetrically in Chile and France. There will be significant cross-talk among the various participants in the different labs and countries, reflecting the existing culture of collaboration. Extensive use will be made of current communications technology to link the various groups, and face-to-face meetings will be organized to enable the type of communication that can only be achieved through personal, collective contact. The propagation of waves in complex media is a vast subject. Particularly, lack of quantitative understanding, much less control, of the role of disorder, hampers progress in many fields, from the technology of amorphous semiconductors, to the control of turbulence in fluids, to the characterization of granular materials in the mining, food, and pharmaceutical industries. In this proposal, two specific topics have been chosen for research: 1) Wave propagation in slightly disordered periodic media, and 2) Effect of nonlinearities on wave propagation through disordered media. Available theory will be revisited and expanded as needed and suggested by currently available numerical capabilities and experimental hardware. Specific experiments will be performed with centimetric microwaves in a metallo-dielectric metamaterial; with acoustic waves in a wave guide endowed with a chain of resonators; with surface waves on a fluid, and with ultrasonic waves in solid materials. The criteria that have been used to arrive at these topics are: A) Familiarity of proposers with one or several recently developed, and available, technologies that enable unique data-gathering capabilities. B) Ease of control of disorder in the propagating medium. C) Close relation between theoretical and experimental capabilities of proposers. D) Track record of successful collaboration among participants.

The flow of genetic information in all cells progresses from DNA to messenger RNA (mRNA) to protein. Many events must occur precisely to generate the protein product accurately and efficiently. As a consequence, eukaryotic cells have evolved a finely tuned “gene-expression factory” that encompasses the routing of a nascent transcript through multimeric mRNA–protein complexes that mediate its splicing, polyadenylation, nuclear export, translation and ultimate degradation. Traditionally, mRNA decay was considered a simple passive destruction step of mRNA but this view has been challenged in the recent years. Eukaryotic mRNA decay now appears as a highly regulated process that allows cells to rapidly modulate protein production in response to environmental factors. Regulation of mRNA decay rates is an important control point in determining the abundance of cellular transcripts. Decay rates of individual mRNAs differ extensively and the half-lives of certain mRNAs are known to change markedly throughout the cell cycle or in response to environmental cues. These differences in mRNA decay rates have notable effects on the expression of specific genes, and provide the cell with flexibility in effecting rapid change in transcript abundance as an essential step in the regulation of gene expression. To understand the control of gene expression, it is thus necessary to understand the regulation and mechanisms of mRNA degradation. Over the past years, most of the enzymes involved in mRNA decay have been identified, yielding to a well documented view of the general cytoplasmic mRNA decay. Although the proteins involved in mRNA decay are known, they are all part of dynamic and multifunctional protein assemblies. The importance of these protein-protein interactions is becoming increasingly evident. It is therefore essential to understand in molecular details the dynamics of these complexes, and the interactions involved, in order to unravel the mechanisms of mRNA decay and the logic of its regulation. Mature translatable eukaryotic mRNAs are protected from fast and uncontrolled degradation in the cytoplasm by two cis-acting stability determinants: a methylguanosine cap and a poly(A) tail at the 5’ and 3’ extremities, respectively. As a consequence, mRNA degradation necessitates a subsequent remodelling of the mRNP structure that is triggered by specific signals and leads to the recruitment of activators of decay and enzymes. Eukaryotic mRNA degradation typically initiates with deadenylation followed by the removal of the cap structure protecting the 5’ end of mRNAs. In yeast, this key step is accomplished by the recruitment of a decapping complex composed of the Dcp2 catalytic subunit and its activator Dcp1 that eliminate the cap structure protecting the 5’ end of mRNAs. The Dcp1-Dcp2 complex has a low intrinsic decapping activity. Several accessory factors activate this decapping enzyme by a mechanism that remains largely obscure. Once mRNAs are uncapped at their 5’ end, they are rapidly degraded in the 5’?3’ direction by the cytoplasmic exonuclease Xrn1 that interacts with the decapping machinery. Our goal is to unravel the mechanisms underlying the activation of the Dcp1-Dcp2 decapping enzyme by structural and functional approaches and using yeast S. cerevisiae as a model organism. We propose to focus on the various proteins known to influence decapping so as to determine their precise role on (1) Dcp1-Dcp2 activation; (2) mRNP remodelling and (3) relation between inhibition of translation initiation and mRNA degradation. To reach this goal, we have organized a highly complementary consortium with expertise in structural biology, biophysics, biochemistry, and molecular genetics.