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Offers : 23

Monitoring formation and repair of DNA damage by a non-invasive assay

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Start date : 1 October 2018

offer n° SL-DRF-18-0317

A wide variety of physical and chemical agents may damage the chemical structure of DNA, and in particular nucleic bases. As a consequence, mutations are produced that may trigger the cancerization of the damage cell. Fortunately, all cells have developed a series of enzymatic processes that can repair the damaged portion of DNA and limit the deleterious consequences of the damage. The effect of genotoxic agents results thus from the balance between the formation and the repair of DNA damage.

Monitoring the formation of DNA damage in Human requires collection of tissues, followed by extraction of DNA and analysis. Although internal organs may sometimes be studied when biopsies are taken in patients, samples available in the general population or at the working place are limited to skin biopsies and blood cells. Biopsies is a rather invasive procedure and the nature of the damage in blood cells does not represent the whole body exposure. Some limitations are also encountered in in vitro experiments. There is thus a need for less invasive procedures and more representative data.

In the present PhD project, we want to quantify the damages bases released from DNA by the repair enzymes. In particular, we want to quantify bulky adducts and photoproducts resulting from exposure to solar light. The work will first involve extensive analytical chemistry developments, using mostly solid phase extraction and HPLC associated to mass spectrometry. On-line HPLC preparation of the samples will also be investigated. The method will be then validated on cultured cells. Last, the protocol will be extended to the detection of repair products in biological fluids like urine for in vivo investigations. The technique will be applied to three main topics: the formation of photoproducts induced by solar UV in skin and its prevention by sunscreens (collaboration with the Pierre Fabre Dermo-Cosmétique company), the induction of adducts with pollutants like polycyclic aromatic hydrocarbons, and the formation of adducts between DNA and CEES, an analog of sulfur mustard (collaboration with the Military Biomedical Research Institute).

  • Keywords : Life Sciences, Analytic chemistry, Toxicology, INAC, SyMMES
  • Laboratory : INAC / SyMMES
  • CEA code : SL-DRF-18-0317
  • Contact : thierry.douki@cea.fr

Study of physical properties of magnetic skyrmions for sensing applications

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Start date : 1 September 2018

offer n° SL-DRF-18-0215

Skyrmions are chiral magnetic bubbles: magnetization follows a cycloid along a line across the skyrmion. They can appear in heavy metal/ferromagnet/oxide ultrathin trilayers. Such texture results from the presence of an interfacial interaction called Dzyaloskinskii-Moriya interaction. It makes the skyrmions stable, less sensitive to defects as compared to usual domain walls and easily moveable by electrical current. They are currently very popular as they could be used as dense storage nanoscale data bits, or for magnetic logic.

Their size may be modified by a magnetic field. Moreover, using magneto-optical microscopy, we have recently shown that a gate voltage can modulate the size and density of magnetic skyrmions in ultrathin films, ultimately leading to the realization of a skyrmion switch [1]. This new degree of freedom may thus allow to create multifunctional spintronic devices or to better control the skyrmion properties.

In order to develop skyrmion based spintronic devices, the objectives of this thesis would be:

-to better understand and control the different contributions in the Dzyaloshinskii-Moriya interaction by playing on the materials thanks to a support from theoreticians at Spintec.

– to optimize the tunability of skyrmion properties with the gate voltage by performing a material study. Skyrmion behavior with temperature will also be studied as a device should operate in the -40 to 100°C range for applications.

-to characterize the electrical signature of skyrmions by using magneto-optical microscopy coupled with magnetotransport. This electrical signal is necessary to read the state of a skyrmion-based device but is still a technological challenge, the signals being usually quite small.

– finally, to assess the potential for skyrmions to be used in spintronic devices.

[1] M. Schott et al. Nano Lett., 17, 3006 (2017)

  • Keywords : Solid state physics, surfaces and interfaces, INAC, SPINTEC
  • Laboratory : INAC / SPINTEC
  • CEA code : SL-DRF-18-0215
  • Contact : claire.baraduc@cea.fr

Bio-inspired vision chain for scene analysis.

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Start date : 1 October 2018

offer n° SL-DRT-18-0309

Artificial vision systems (camera(s) and processor(s)) have recognition capabilities well below those achieved by biological systems (eye – cortex). Moreover, biological systems are able to process information within a few milliseconds, which is still out of range of electronic systems, even though their electronic image sensors are far from achieving the resolution of human eyes (few dozen megapixel against more than one hundred million). This thesis aims at addressing the challenge posed by the biology by designing integrated bio-inspired sensor architectures. Our approach is based three assumptions: first, resolution biological imaging sensors is not uniform, the best resolved zone (the fovea) is dedicated to the acquisition of the areas of interest of the scene; secondly, pre-processing from the sensor are used to compress the information; finally, the processing of information is context and prior knowledge dependent. This exploratory thesis, aims to devise, within the frame of these hypothesis, breakthrough solutions with respect to the state of the art, to endow autonomous artificial systems (drones of all kinds (UAV, UGV, …), machine tools, smart camera) of ability to perception of their complex environment, while using only limited resources, i.e. those of embedded systems. The candidate should have strong tastes or skills in image processing and digital architectures.

  • Keywords : Engineering science, Automatics, Remote handling, Computer science and software, DACLE, Leti
  • Laboratory : DACLE / Leti
  • CEA code : SL-DRT-18-0309
  • Contact : laurent.soulier@cea.fr

SiNW composites in high energy density lithium-ion batteries

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Start date : 1 October 2018

offer n° SL-DRF-18-0291

The lithium-ion battery (LiB) technology, used for portable electronics as well as electrical vehicles, is based on continuously changing materials to improve their energy storage capacity, life span and safety. Silicon is interesting as an active material because it can absorb up to 10 times more lithium than carbon, the usual material in the negative electrode of commercial LiB. Besides silicon can be mixed with carbon in the electrode. Only silicon in the form of nanosized particles or wires can make long-standing battery electrodes, because mechanical constraints during the charge/discharge cycles induce silicon fracturing into disconnected powder. But on the other hand, nanosized silicon offers a large surface area to surface side-reactions, leading to lithium immobilization and performance loss.

In the present PhD project, two recent CEA technologies will be associated: a method for silicon nanowire growth at large scale (patents 2014-2016), and a process for making silicon-carbon composites in which nanosized silicon is embedded in carbon microparticles. The student will be in charge of material synthesis, characterization and performance tests in LiB. In order to optimize synthesis processes and LiB life span, he/she will try to understand the reactivity of all components of the composite during LiB cycling by electronic microscopy, spectroscopy and electrochemistry.

  • Keywords : Engineering science, Materials and applications, Ultra-divided matter, Physical sciences for materials, INAC, SyMMES
  • Laboratory : INAC / SyMMES
  • CEA code : SL-DRF-18-0291
  • Contact : cedric.haon@cea.fr

Antiferromagnetic spintronics

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Start date : 1 October 2018

offer n° SL-DRF-18-0274

Antiferromagnetic materials (antiparallel alignment of the atomic magnetic moments) could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics and are capable of generating large magneto-transport effects. Intense research efforts are being invested in unraveling spin-dependent transport properties in antiferromagnetic materials. Whether spin-dependent transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges to address.

The nature of the elements constituting the antiferromagnetic material and the quality of the interfaces will be the adjustable parameters. We will consider mainly the efficiency of spin injection and the interfacial filtering, the absorption of spins in the core of the material and the absorption characteristics lengths, the order temperatures and the magnetic susceptibility, and the efficiency of the spin-orbit coupling via the spin Hall effect.

This PhD thesis work is experimental. It will build on the many techniques of fabrication (sputtering, molecular beam epitaxy, clean room nanofabrication) and characterization (magnetometry, ferromagnetic resonance, transport) at SPINTEC and benefit from the collaboration with our partner laboratories for experiments with a resonant cavity and for access to complementary materials.

  • Keywords : Solid state physics, surfaces and interfaces, INAC, SPINTEC
  • Laboratory : INAC / SPINTEC
  • CEA code : SL-DRF-18-0274
  • Contact : vincent.baltz@cea.fr
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