Hyperpolarized Xenon NMR to probe the functionality of biological barriers
Optical pumping of xenon, giving rise to an intense NMR signal, is a specialty of the LSDRM team. Xenon, which is soluble in biological media, has a wide range of chemical shifts, which we use here to study the properties of cell barriers. Numerous pathologies stem from an alteration of these barriers.
In this thesis, we aim to develop a specific methodology using hyperpolarized xenon to study the functionality (integrity, permeability, selectivity) of biological barriers, using in vitro and in vivo spectroscopy and imaging. The thesis will be divided into two parts: in vitro, the aim will be to develop a device and NMR protocols for studying model cell assemblies; in vivo, studies on rodents will enable us to assess xenon's ability to reach organs more or less close to the lungs while maintaining its polarization, and to measure kinetics across barriers. This topic will enable major instrumental and methodological advances, as well as a deepening of our knowledge of selective transport processes at different biological barriers.
INVESTIGATION OF THE NUCLEAR TWO-PHOTON DECAY
The nuclear two-photon, or double-gamma decay is a rare decay mode in atomic nuclei whereby a nucleus in an excited state emits two gamma rays simultaneously. Even-even nuclei with a first excited 0+ state are favorable cases to search for a double-gamma decay branch, since the emission of a single gamma ray is strictly forbidden for 0+ to 0+ transitions by angular momentum conservation. The double-gamma decay still remains a very small decay branch (<1E-4) competing with the dominant (first-order) decay modes of atomic internal-conversion electrons (ICE) or internal positron-electron (e+-e-) pair creation (IPC).
The thesis project has two distinct experimental parts: First, we store bare (fully-stripped) ions in their excited 0+ state in the heavy-ion storage ring (ESR) at the GSI facility to search for the double-gamma decay in several nuclides. For neutral atoms the excited 0+ state is a rather short-lived isomeric state with a lifetime of the order of a few tens to hundreds of nanoseconds. At relativistic energies available at GSI, however, all ions are fully stripped of their atomic electrons and decay by ICE emission is hence not possible. If the state of interest is located below the pair creation threshold the IPC process is not possible either. Consequently, bare nuclei are trapped in a long-lived isomeric state, which can only decay by double-gamma emission to the ground state. The decay of the isomers is identified by so-called time-resolved Schottky Mass Spectroscopy. This method allows to distinguish the isomer and the ground state by their (very slightly) different revolution time in the ESR, and to observe the disappearance of the isomer peak in the mass spectrum with a characteristic decay time. Successful experiment establishing the double-gamma decay in several nuclides (72Ge, 98Mo, 98Zr) were already performed and a new experiment has been accepted by the GSI Programme Committee and its realization is planned for 2025.
The second part concerns the direct observation of the emitted photons using gamma-ray spectroscopy. While the storage ring experiments allow to measure the partial lifetime for the double gamma decay, further information on the nuclear properties can be only be achieved by measuring the photon themselves. A test experiment has been performed to study its feasibility and the plans a more detailed study should be developed with the PhD project.
All solid-state lithium batteries based on Pyrochlore solid electrolyte
Due to the increasing energy demand, developing efficient storage systems, both stationary and portable, is crucial. Among these, lithium-ion batteries stand out as the most advanced, capable of being manufactured using liquid or solid electrolytes. All-solid-state batteries have a bright future thanks to their non-flammable electrolytes and their ability to use metallic lithium to increase energy density. Although research on these batteries is dynamic, their commercialization is not yet a reality. Indeed, two significant obstacles to their development remain: the low intrinsic ionic conductivity of solids and the difficulty of obtaining good solid/solid interfaces within the composite electrodes and the complete system.
This thesis explores the potential of pyrochlore oxyfluoride as a new class of superionic material for all-solid-state batteries, which are more stable in air and have higher ionic conductivity than current solid oxide electrolytes. The electrochemical properties of all-solid-state batteries will be carefully examined using a combination of in situ and operando techniques, such as XRD, Raman, ion beam/synchrotron analysis, solid-state NMR, X-ray tomography, etc.
Keywords :
Solid electrolyte, All-solid battery, Nuclear magnetic resonance, Electrochemistry, Pyrochlore Oxyfluoride, in situ/operando, Spectroscopy, Synchrotron
Towards a high spatial resolution pixel detector for particle identification: new detectors contribution to physics
Future experiments on linear colliders (e+e-) with low hadronic background require improvements in the spatial resolution of pixel vertex detectors to the micron range, in order to determine precisely the primary and secondary vertices for particles with a high transverse momentum. This kind of detector is set closest to the interaction point. This will provide the opportunity to make precision lifetime measurements of short-lived charged particles. We need to develop pixels arrays with a pixel dimension below the micron squared. The proposed technologies (DOTPIX: Quantum Dot Pixels) should give a significant advance in particle tracking and vertexing. Although the principle of these new devices has been already been studied in IRFU (see reference), this doctoral work should focus on the study of real devices which should then be fabricated using nanotechnologies in collaboration with other Institutes. This should require the use of simulation codes and the fabrication of test structures. Applications outside basics physics are X ray imaging and optimum resolution sensors for visible light holographic cameras.
Synthesis and optical properties of quantum dots
Graphene as a constituent of graphite was close to us for almost 500 years. However, it is only in 2005 that A. Geim and K. Novoselov (Nobel Prize in 2010) reported for the first time the obtaining of a nanostructure composed by a single layer of carbon atom. The exceptional electronic properties of graphene make it a very promising material for applications in electronic and renewable energies.
For many applications, one should be able to modify and control precisely the electronic properties of graphene. In this context, we propose to synthesize chemically graphene nanoparticles and study their absorption and photoluminescence properties. We will focus on families of elongated nanoparticles, with the aim of studying how size can enable us to observe and control multiexcitonic processes in these materials. This project will be developed in collaboration with Physicists so the candidate will work in a multidisciplinary environment.
Condensates and Chromatin: How Phase Separation Shapes Plant Temperature Responses
Plants must adapt their development to environmental conditions, including rising temperatures due to climate change. Heat stress significantly impacts plant physiology, and to mitigate these effects, plants have evolved heat shock responses (HSR), with Heat Shock Factor A1a (HSFA1a) serving as a master regulator in Arabidopsis thaliana. Under nonstress conditions, HSFA1a remains cytosolic and inactive, bound to heat shock proteins (HSPs). Heat stress triggers HSP dissociation, enabling HSFA1a nuclear translocation, trimerization, chromatin binding, and activation of stress-responsive genes. Recent studies reveal that HSFA1a might act as a pioneer transcription factor to access closed chromatin regions and initiate HSR. Additionally, preliminary findings also suggest that HSFA1a undergoes liquid-liquid phase separation (LLPS) to form nuclear condensates that regulate gene expression. This project aims to 1) explore how temperature affects HSFA1a structure and oligomerization, 2) investigate LLPS of HSFA1a with and without DNA, 3) characterize HSFA1a pioneer activity, and 4) determine the physiological importance of LLPS in HSR.
Characterization of the molecular mechanism involved in the detection of rare earth elements in Pseudomonas putida and associated biosensors development.
Rare earths (REE) are widely used in high technology, and demand for REE is set to double over the next 30 years. The selective extraction and recycling of REE has a triple challenge: economic, technological and ecological. Currently, less than 1% of REEs are recycled. What's more, extraction methods are tedious and polluting. They require several stages with acids or solvents. The discovery in 2011 of enzymes that naturally use light REE has opened up new prospects. The development of biosourced methods could be a key element in unlocking current selectivity and extraction barriers. This thesis is part of the biotechnologies of tomorrow theme. The aim of this thesis is to acquire fundamental data on the molecular mechanism of a biological system for the selective perception of REE through a robust screening, in order to take advantage of it for the development of biosensors responding to certain specific REE. Cell biology, biochemistry and in silico analysis techniques based on artificial intelligence will be used to accomplish this project. The results obtained will enable us to identify: 1) the molecular mechanism of REE detection and the factors influencing its selectivity, 2) the binding sites of the regulator and the genes involved in this response, and 3) the development from 1) and 2) of robust and selective biosensors.
Plasma Mirrors: towards extreme intensity light sources and high-quality compact electron
Research objectives:
expand the capabilities of the WarpX Partice-In-Cell code for lower cost-to-convergence using mesh refinement.
Devise a high-charge high quality injector for laser-plasma accelerators.
Determine feasibility of the proposed scheme on a 100-TW-class laser system.
The researcher will benefit from a large variety of training available at CEA on HPC and computer programming as well as training at our industrial partners (ARM, Eviden) and Université Paris Saclay. The activities will be carried out in the framework of the Marie Sklodowska Curie Action Doctoral Network EPACE (European compact accelerators, their applications, and entrepreneurship)
The galaxy clusters in the XMM-Euclid FornaX deep field
The XMM Heritage project on the DEEP Euclid Fornax field aims to characterize distant galaxy clusters by comparing X-ray and optical/IR detections. The two methods call on very different cluster properties; ultimately, their combination will make it possible to set the free parameters of the Euclid cluster selection function over the entire WIDE survey, and thus constitute a fundamental ingredient for Euclid cosmological analysis.
The targeted redshift range ([1-2]) has never been systematically explored, despite being a critical area for the use of clusters in cosmology.
With FornaX, for the first time we'll have access to a large volume at these redshifts, enabling us to statistically quantify the evolution of clusters: role of AGNs in the properties of intracluster gas? Are there massive gas-deficient clusters? What are the respective biases of X-ray and optical detection?
The thesis work will involve (1) building and validating the X-ray cluster catalog; (2) correlating it with the optical/IR catalogs obtained by Euclid; and (3) studying the combined X-ray and optical evolution of the clusters.
All the algorithms for detecting and characterizing clusters in XMM images already exist, but we'll be pushing detection even further by using artificial intelligence techniques (combining spatial and spectral information on sources).
The complex problem of spatial correlation between XMM and Euclid cluster catalogs will also involve AI.
Project website: https://fornax.cosmostat.org/
Electrocatalyzed Reductive Couplings of Olefins and Carbonyls for the synthesis of sustainable molecules.
The LCMCE aims to develop a sustainable method for the reductive functionalization of carbonyl derivatives with olefins via electrochemistry. Traditional redox processes in organic synthesis often rely on thermochemical methods using stoichiometric oxidants or reductants and produce waste products. The electrification of these processes will improve their atom- and energy economy. The novelty of this project lies in the generation of "metal-hydride" catalytic species by cathodic reduction of organometallic complexes in the presence of protons rather than by adding chemical reductants, as described in the literature. Inserting an alkene function into the metal-hydride bond will lead to the formation of reactive intermediates for coupling with electrophilic carbonyls. The substrates for this project have been selected to provide rapid proof of concept and allow the study of more ambitious reactivities, including carboxylation reactions in which CO2 is the electrophile. Particular attention will be paid to the design of homogeneous catalysts and their synergy with electrochemical conditions to lead to active and selective species. The project will also focus on deciphering the mechanisms involved in these reactions.