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.

Transcutaneous sampling of gaseous biomarkers

The development of wearable medical devices is a fundamental and essential in order to promote ambulatory medicine. Exhaled gases as transcutaneous gases (gases that diffuse through the skin) are known to carry molecules ("biomarkers") representative of pathologies or degradation of the physiological state, the ambulatory monitoring of which would be a real diagnostic and monitoring tool. However, the personal equipment associated to the continuous monitoring of exhaled gases is inappropriate for intensive sports activities, unlike the transcutaneous gases monitoring which could be carried out without losing mobility and discreetly (social impact), for example with a device placed on the forearm. Apart from oxygen and carbon dioxide, most of the biomarkers present are in very low concentrations and are therefore difficult to detect. One way of getting around this low concentration is to carry out a pre-concentration step, i.e. to accumulate over time, and therefore to concentrate enough molecules so that they are more easily detectable and measurable.
The objective of this thesis is therefore to develop and optimise a transcutaneous gas collector and pre-concentrator. The work will consist in particular in modelling the gas exchanges between the skin and the device in order to optimize the efficiency of the pre-concentration. The model will be compared with experimental results on a gas test bench for validation with two biomarkers of interest.
This subject requires a highly motivated person with skills in modelling and instrumentation. Skills in mechanical design of medical devices would be a plus.

Study and optimization of a blast wave generated by a pulsed electric generator

Distributed Passive Radar

Our objective is to detect and locate drones entering an urban area to be protected by observing the signals emitted by cellular stations. Studies have shown that it is possible to locate a drone if it is close to the listening system and the cellular station (i.e. the base station). When the situation is more complex (i.e. there is no direct path between the cellular station and the radar or in the presence of several transmitting cellular stations causing a high level of interference), a single listening system called passive radar cannot correctly detect and locate the drone. To overcome these difficult conditions, we wish to distribute or deploy in the area to be protected a set of low-complexity passive radars which optimally exploit the signals emitted by these cellular stations. A distribution and deployment strategy for passive radars must then be considered by taking into account the positions of the transmitting cellular stations. The possibility of exchanging information between passive radars must also be considered in order to better manage interference linked to cellular stations.

Pre-requisite: Master 2 level with a focus on digital signal processing. Good knowledge of telecommunications, radar and propagation is recommended.

At CEA Grenoble the doctoral student will work with experts in signal processing for télécommunications (http://www.leti-cea.fr/cea-tech/leti/english/Pages/Applied-Research/Facilities/telecommunications-platform.aspx)

Hyperpolarised, continuous-mode NMR based on parahydrogen and grafted catalysts

Nuclear Nuclear magnetic resonance (NMR) is a robust, non-invasive technique of analysis. It provides valuable information about chemical reactions, which can then be better characterised and optimised. However, NMR is poorly sensitive, and low-concentrated solutes, such as intermediates of reaction, may be unobservable by conventional NMR. One method known to drastically but temporarily increase the sensitivity of NMR is to create a hyperpolarised state in the system of nuclear spins, i.e. a polarisation much greater than that accessible with available magnetic fields. One hyperpolarisation method uses the specific properties of parahydrogen. A catalyst is required to add parahydrogen to a multiple bond or a metal.

The present thesis will investigate the combined contribution of (i) parahydrogen-based hyperpolarisation [1], (ii) the grafting of the appropriate catalyst onto nanoparticles [2], and (iii) a continuous analysis method [3] to detect and identify chemical intermediates, areas in which the laboratory has acquired experience. This subject involves a major investment in instrumentation, as well as skills in synthetic chemistry and NMR.

The thesis will be carried out at NIMBE, a joint CEA/CNRS unit at CEA Saclay. The hyperpolarised NMR and the synthesis will take place under the respective responsibility of Gaspard HUBER, from LSDRM, and Stéphane CAMPIDELLI, from LICSEN. These two NIMBE laboratories are located in nearby buildings.

References:
[1] Barskiy et al, Prog. Nucl. Magn. Reson. Spectrosc. 2019, 33, 114-115,.
[2] Hijazi et al., Org. Biomol. Chem., 2018, 16, 6767-6772.
[3] Carret et al., Anal. Chem. 2018, 90, 11169-11173.

Natural language interactions for anomaly detection in mono and multi-variate time series using fondation models and retrieval augmented generation

Anomaly detection in mono and multi-variate time series highly depends on the context of the task. State-of-the-art approaches rely usually on two main approaches: first extensive data acquisition is sought to train artificial intelligence models such as auto-encoders, able to learn useful latent reprensations able to isolate abnormality from expected system behaviors; a second approach consists in careful features construction based on a combination of expert knowledge and artificial intelligence expert to isolate anomalies from normal behaviors using limited examples. An extensive analysis of the literature shows that anomaly detection refer to an ambiguous definition, because a given pattern in time series could appear as normal or abnormal depending on the application domain and the immediate context within the successive observed data points. Fondation models and retrieval-augmented generation has the potential to substantially modify anomaly detection approaches. The rationale is that domain expert, through natural language interactions, could be able to specify system behavior normality and/or abnormality, and a joint indexing of state-of-the-art literature and time series embedding could guide this domain expert to define a carefully crafted algorithm.

Design of a new light-sheet microscope for the temporal monitoring of organoids-on-chip

The subject of the thesis is the development of a fluorescence light-sheet microscope for the optical characterization of organoids-on-chips and 3D organoids. The thesis will focus on the conception of a compact multi-color 3D system, to allow time-lapse imaging of multi-scattering 3D samples directly in a cell culture incubator. The work will begin with a clear understanding of the miniaturization process on the quality of the images. The excitation will be correctly model to avoid optical artefacts and to allow the deepest penetration into the biological tissue. The candidate will be responsible to test different optical strategies as well as different excitation wavelengths. As a final step, the system will be characterized in a cell culture incubator for the morphological and functional monitoring of organs-on-a-chip and 3D organoids using specific fluorescent markers. If needed, novel modifications of the microfluidic chamber with integrated optical functions will be proposed. The research program will mainly focus on the morphological and functional monitoring of two samples: pancreatic organoids on a microfluidic chip and 3D brain organoids.

Taylor bubbles: experiments and modeling

This doctoral position focuses on the microscale phenomena that occur in the near-wall region at bubble motion in a capillary tube (also known as Taylor bubble). These are elongated bubbles of vapor having bullet-like shapes that are formed in compact heat exchangers used in a variety of industrial applications such as cooling of electronics and steam generators in nuclear reactors, for instance. The phenomena associated include dewetting dynamics, formation of micrometric thick liquid layers and heat transfer. The PhD candidate will conduct an experimental study at STMF/CEA and SPEC/CEA (Paris-Saclay, France) using advanced non-intrusive optical diagnostics to evaluate these phenomena, in particular the film profile. The student will use the experimental data to validate a numerical approach in the open-source software OpenFOAM that will be developed in partnership with the University of Nottingham (United Kingdom).

Experimental study and physical modelling for the characterization of the flow in an inclined pipe and of the exiting jet trajectory

The thermohydraulic circuits found in the nuclear industry consist of a complex network of horizontal, vertical, or inclined pipes. In particular, the Emergency Core Cooling (ECC) pipes are connected to the primary circuit and are intended to inject cold water into it in accidental situations. Different configurations and inclinations can be found depending on the reactor type. The flow in the ECC pipe, as well as the efficiency of the reactor cooling, are influenced by these different configurations. Therefore, characterizing the flow in these pipes is crucial.
The objective of this thesis is to acquire new experimental data to characterize the water-air flow in an inclined pipe and the trajectory of the exiting jet at atmospheric pressure. The experimental data obtained will be used to develop and/or improve the modeling of flows in inclined pipes.
This thesis should provide the following contributions:
• Set up the experimental facility and the measurement methodologies ;
• Acquisition of the experimental data for different test section geometries (round vs. square), pipe diameter, roughness, inclination, fluid density/viscosity, and flow rate;
• Development of physical models to characterize the flow in an inclined pipe, including liquid hold-up and detachment length;
• Development of a mathematical formulation to predict the trajectory of the exiting jet;
• Study of the impact of stratification in the ECC pipe on the Cocci et al. jet condensation model;
• Optionally, simulation of the experiment using a CFD code (e.g., NEPTUNE-CFD) to extend code validation and identify potential improvements.

Study of catalysis on stainless steels

The materials (mainly stainless steels) aging of the spent nuclear fuel reprocessing plant is the focus of an important R&D activity at CEA. The control of this aging will be achieved by a better understanding the corrosion mechanisms the stainless steels in nitric acid (the oxidizing agent used in the reprocessing steps).
The aim of the PhD is to develop a model of corrosion on a stainless steel in nitric acid as a function of temperature and the acid nitric concentration. This PhD represents a technological challenge because currently few studies exist on in situ electrochemical measurements in hot and concentrated nitric acid. The PhD student will carry out by coupling electrochemical measurements, chemical analyses (UV-visible-IR spectrometry...) and surfaces analyses (SEM, XPS,…). Based on these experimental results, a model will be developed, which will be incorporated in the future in a more global model of the industrial equipments aging of the plant.
The laboratory is specialized in the corrosion study in extreme conditions. It is composed of a very dynamic and motivated scientific team which has the habit to receive students.

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