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École doctorale physique (Grenoble)

Works: 1,027 works in 1,079 publications in 2 languages and 1,852 library holdings
Roles: Other, 996
Publication Timeline
Most widely held works by École doctorale physique (Grenoble)
Simulations numériques de collisions de vents dans les systèmes binaires by Astrid Lamberts-Marcade( )

2 editions published in 2012 in French and held by 3 WorldCat member libraries worldwide

The aim of this thesis is to understand the structure of colliding wind binaries composed of a massive star and a young pulsar, called gamma-ray binaries. They are expected to display a similar structure to colliding wind binaries composed of massive stars, with some particularities due to the relativistic nature of the pulsar wind. The interaction of the supersonic winds from massive stars creates a shocked structure with observational signatures from the radio domain to the X-rays. The structure is affected by various instabilities and by the orbital motion of the stars. To understand their impact, I carried out high resolution simulations of colliding wind binaries with the hydrodynamical code RAMSES. They are computationally demanding, especially when one of the winds strongly dominates the other one. Small scale simulations highlight the importance of the Non-linear Thin Shell Instability in isothermal collisions while the Kelvin-Helmholtz instability may strongly impact the dynamics of adiabatic collisions. I found that, at larger scales, this instability can destroy the expected large scale spiral structure when there is an important velocity gradient between the winds. WR 104 is a system that displays a spiral structure with important dust emission. The simulation of this system shows a good agreement with the observed structure and indicates cooling processes are necessary to enable dust formation. To model the pulsar wind in gamma-ray binaries, an extension of RAMSES has been developed, that incorporates relativistic hydrodynamics. I used this new relativistic code to perform preliminary simulations of gamma-ray binaries. They display a similar structure to colliding wind binaries with small relativistic corrections. We expect to use this code to perform large scale simulations of gamma-ray binaries. It will be part of the next public release of RAMSES and is suited for the study of many astrophysical problems such as relativistic jets, pulsar wind nebulae or gamma-ray bursts
La problématique de l'évolution des moments d'une densité de particules soumises à des forces non linéaires by Christophe Peaucelle( Book )

2 editions published in 2001 in French and held by 3 WorldCat member libraries worldwide

L'utilisation des accélérateurs linéaires de forte puissance dans différents projets (production de neutrons par spallation, réacteurs hybrides) nous a amené à se pencher sur les problèmes de la dynamique de faisceaux de haute intensité. Dans le cas de faisceaux intenses, les particules sont soumises à des forces non linéaires, principalement dues à l'effet de charge d'espace. Afin de disposer d'outils à la fois moins lourds et plus réalistes que les méthodes classiques de simulation (interaction particule-particule, modèle coeur-particule), la description de l'évolution d'une distribution de particules à partir de ses paramètres statistiques, ses moments, a donc été envisagée. Nous présentons donc dans une première partie une analyse détaillée de la problématique, menée dans un cadre simplifié mais non limitatif : tout d'abord, nous développons un formalisme original basé sur les propriétés fines des polygones orthogonaux permettant l'étude des moments d'une densité en une dimension. De cette analyse, nous voyons que l'on peut extraire, d'un nombre fini de moments, un certain nombre d'informations concernant la densité. En particulier, il en découle la notion fondamentale d'enveloppe convexe définissant le domaine d'existence de cette densité. Ceci permet de mieux comprendre la signification des moments. La généralisation de cette description en deux dimensions permet d'estimer avec une bonne précision où sont localisées les particules dans cet espace des phases. Enfin, nous abordons les difficultés rencontrées au cours de cette étude, fixant ainsi les limites de cette méthode. La deuxième partie de cette thèse, plus expérimentale, présente les mesures de faisceaulogie effectuées sur l'accélérateur GENEPI (GEnérateur de NEutrons Pulsé Intense) dans le cadre de l'étude des systèmes hybrides. Elles permettent, entre autres, la calibration du faisceau et la validation des codes de calculs nécessaires à la conception de la machine
Étude et optimisation de l'émission et de l'extraction de lumière des nanofils semiconducteurs grand gap : application à des dispositifs électroluminescents by Anne-Line Henneghien( Book )

3 editions published between 2010 and 2011 in French and held by 3 WorldCat member libraries worldwide

The current blue or white light-emitting diodes (LEDs) are constituted by planar layers of GaN. The use of the nanowires as active layer is a hard and new concept which brings numerous potential advantages and revolutionizes the rules of LED design. This thesis deals with the light emission and extraction of nanowire structures made of wide band gap semi-conductors such as GaN or ZnO. The issue is to understand and to optimize the processes of extraction with the aim of a LED use. We were more particularly interested in three nanowire organizations attractive for the extraction. The first concept concerns nanowires which are enough separated to be considered as isolated. The emission properties of these structures are mainly controlled by the competition between localized resonance (whispering gallery modes) and guided modes which channel and propagate the spontaneous emission towards the nanowires ends. Our second contribution concerns the study of ensembles of small dense nanowires. Goniometry experiments on GaN nanowires made by MBE put in evidence the interest of a nanowires modelling by an effective anisotropic medium. The simulations of the extraction of these devices on silicon substrate are very promising for the creation of efficient and low cost LEDs. Perspectives on nanowires use in periodic organized array so as to realize a photonic crystal are the third part of the thesis. A numerical model allowed suggesting rules of arrays design
Contrôle de l'émission spontanée de boîtes quantiques semiconductrices insérées dans des micro-structures à confinement optique originales by Maela Bazin( Book )

3 editions published between 2010 and 2011 in French and held by 3 WorldCat member libraries worldwide

This study deals with the control of spontaneous emission, InAs quantum dot emitters, confined via original microstructures: GaAs photonic wires and micropillars with GaAs/AlAs Bragg mirrors. We present a higly efficient single-photon source based on a photonic wire. Correlation mesurements performed on a single quantum dot inserted in a photonic wire led to a pure and high broadband single-photon generation. The optimization of this geometry including an original mirror at the wire bottom and a taper at its top demonstrated a record efficiency of 70%. In addition, the systematic lifetime study of single quantum dots underlined the ability to observe a high inhibition of spontaneous emission in the leaky modes with this geometry. In the last part of this PhD Thesis, we show the laser effect in whispering gallery mode micropillars. Those modes have an almost stable behaviour in terms of wavelengh and a spectral narrowing maintained up to power corresponding to 7 times the laser threshold. This result confirms a better thermal stability of micropillars compared to microdisks, a geometry usually used to observe the whispering gallery modes
Préparation, détermination de la structure et des propriétés physiques de composés moléculaires basées sur le formiate by Lidia Mazzuca( )

1 edition published in 2018 in English and held by 2 WorldCat member libraries worldwide

The synthesis and the characterization of new materials are key challenges in chemistry and physics. In particular, metal-organic frameworks (MOFs) with two or more coupled functionalities are still rare and very attractive candidates because of their wide variety of properties, and promising applications interesting many disciplines. The impact of the development of new fascinating materials on our day life might be considerable. This is also one of the reason explaining the intense increasing of the research in material science and condensed matter.This thesis is focused on the synthesis and the physical characterization of magnetic metal formate frameworks using the combination of neutron and synchrotron X-Ray diffraction as well as other techniques. Metal-formate frameworks are a specific subgroup of metal-organic frameworks, where the metal centres are linked by the formate molecules to form an anionic framework. The negative charge of the framework is balanced by a counter-cation inside the frameworks' cavities, that can be for example protonated amines.Typically, these compounds are synthesized by reacting formate or formic acid with a metal salt under solvo-thermal conditions or by slow evaporation or diffusion techniques.In this work, I investigated the crystal structure, phase transitions and magnetic properties of two families of metal formate frameworks, which are represented by the hetero-metallic or mixed valance compounds adopting a niccolite-like structure, and the homo-metallic compounds adopting a perovskite-like (ABX3) structure.Altogether, the following compounds were synthesized and characterized: [(CH3)2NH3][FeIIIMII(HCOO)6] (M = Mg, Mn, Fe, Co, Ni), [(CH3)2NH3][FeIIIFeII(HCOO)6], [(CH3NH3)[M(HCOO)3] (M = Co, Mn, Fe, Ni, Cu), and [(NH4)[Mn(HCOO)3].The choice of using specific metal ions has been motivated by their different electronic configuration and therefore different physical behaviours, i.e. a large difference in the magnetic anisotropy is well known among the different divalent ions used in this study. Beside the effects on the properties when different divalent metal ions were introduced within the framework, the effects of the nature of the counterions was investigated.Even though there is not a clear correlation between the selected counterion and the change of magnetic behaviour, neutron diffraction allows elucidating the differences in the nuclear and in the magnetic structure when different counterions are used. Moreover, these works help us to compare our neutron results with the magnetometry measurements, which is a complementary technique.A variety of magnetic phenomena such as ferromagnetic behaviour, antiferromagnetic ordering, spin canting have been observed in the compounds studied. Furthermore, from the nuclear structure point of view many different kind of phase transitions were detected involving for instance, the order-disorder of the counter ion employed (in [(CH3)2NH3][FeIIIMII(HCOO)6] for example), or the transition from a commensurate to incommensurate phase giving rise to a modulation of the structure (in [(CH3NH3)[Co(HCOO)3] for example)
Etude de la structure partonique de l'hélium by Yohann Perrin( )

1 edition published in 2012 in French and held by 2 WorldCat member libraries worldwide

The structure of the nucleons and of the nuclei was actively studied during the twentiethcentury through electron elastic scattering (measuring the electromagnetic formfactors) and deep inelastic electron scattering (measuring the parton distributions). Theformalism of generalized parton distributions (GPD) achieved the unification of the formfactors and the parton distributions. This link gives a source of information about partondynamics, such as the distribution of nuclear forces and orbital momentum insidehadrons. The easiest experimental access to the GPD is the deeply virtual Comptonscattering (DVCS), which corresponds to the hard electroproduction of a real photon.While several experiments focussed on DVCS off the nucleon, only a few experimentsstudied DVCS off a nuclear target. This thesis is dealing with the study of the coherentchannel of DVCS off helium 4, with the aim to extract the real and imaginary parts ofthe Compton form factor thanks to the beam spin asymetry
Propriétés optiques des couches minces de dichalcogénures de métaux de transition by Maciej Koperski( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

The research reported in the thesis entitled 'Optical properties of thin layers of transition metal dichalcogenides' focuses on physical phenomena which emerge in the limit of two-dimensional (2D) miniaturisation when the thickness of fabricated films reaches an atomic scale. The importance of such man-made structures has been revealed by the dynamic research on graphene: a single atomic plane of carbon atoms arranged in honeycomb lattice. Graphene is intrinsically gapless and therefore mainly explored with respect to its electric properties. The investigation of semiconducting materials which can also display the hexagonal crustal structure and which can be thinned down to individual layers, bridges the concepts characteristic of graphene-like systems (K-valley physics) with more conventional properties of semiconductors. This has been indeed demonstrated in a number of recent studies of ultra-thin films of semiconducting transition metal dichalcogenides (sc-TMD). Particularly appealing, from the point of view of optical studies, is a transformation of the bandgap alignment of sc-TMD films, from the indirect bandgap bulk crystals to the direct bandgap system in single layers. The presented thesis work provides a comprehensive optical characterisation of thin structures of sc-TMD crystals. The manuscript is divided into five parts: three main chapters with a preceding introduction and the appendix reporting the supplementary studies of another layered material: hexagonal boron nitride.Introduction. The fundamental properties of the investigated crystals are presented, especially those which are important from the point of view of optical studies. The discussion includes information on the crystal structure, Brillouin zone and electronic band structure. Also, the general description of the samples' preparation process and experimental set-up is provided.Chapter 1. Basic optical characterisation of excitonic resonances in mono- and multi-layers of sc-TMDs. The optical response, as seen in the reflectance and luminescence spectra of thin sc-TMDs is analysed (mostly for MoSe2 and WSe2 materials). The impact of the number of layers and temperature on the optical resonances is studied and interpreted in details. The complementary time-resolved study is also presented.Chapter 2. Zeeman spectroscopy of excitonic resonances in magnetic fields. The evolution of the optical resonances in an external magnetic field, applied perpendicularly to the layers of sc-TMD materials is investigated. Based on these results, a phenomenological model is developed aiming to describe the linear with magnetic field contributions to the energy of individual electronic states in fundamental sub-bands of sc-TMD monolayers. Furthermore, the effects of optical pumping are investigated in WSe2 monolayers, which can be tuned by tiny magnetic fields.Chapter 3. Single photon sources in thin sc-TMD flakes. The discovery of localised narrow lines emitting centres has been in thin sc-TMD flakes is presented. An investigation of their fundamental properties is discussed. This includes the measurements of temperature and magnetic field evolution of the photoluminescence lines, and the analysis of the polarisation properties and the excitation spectra as well as photon correlation measurements.Appendix A. Single photon emitters in boron nitride crystals. Hexagonal boron nitride also belongs to the family of layered materials, but it exhibits much larger band gap than semiconducting transition metal dichalcogenides. A narrow lines emitting centres has been observed in boron nitride structures, which reveal multiple similarities to defect centres in wide gap materials. They are characterised in a similar manner as the emitting centres in WSe2
Nanostructures Al (Ga) N/GaN pour l'optoéléctronique intersousbande dans l'infrarouge proche et moyen by Prem Kumar Kandaswamy( Book )

2 editions published in 2010 in English and held by 2 WorldCat member libraries worldwide

This work reports on the design, epitaxial growth and characterization of AI(Ga)N/GaN quantum wells (QWs) and quantum dots (QDs) which constitute the active region of intersubband (ISB) devices operating in the near-inftared (NIR) and mid-infrared (MIR) spectral regions. Growth of these structures was performed using molecular beam epitaxy. The deposition process required fine tuning due to the large lattice mismatch. Infrared optical characterization demonstrates that the polarization-induced internaI electric fields introduces a blue shift of the transitions and can critically modify the absorption magnitude. Three-dimensionally confined GaN/AIN QDs introduces many novel properties for application as active region in ISB devices. The growth of QDs was performed under both Ga-rich and N-rich conditions. Dilution of QDs with required size was achieved using the enhanced-mobility condition of the Ga-rich method. Spectroscopic studies reveal absence ofnon-radiative recombination even in long lived QDs. Photodetectors fabricated on GaN/AIN QD superlattices present photocurrent at NIR and MIR, assigned to S-Pz and S-Pxy transitions, respectively. The dark current depends on the QD density due to hopping transport. Foreseeing the importance of ISB devices in MIR and far-inftared regions of the spectrum, we have achieved ISB wavelength extension up to - 10 f.lm. This was performed basically by decreasing the internai electric- field and reducing the quantum confinement in GaN/AiGaN QW superlattices. Doping can induce a blue shift of more than 50% of the ISB transition energy, due to many-body effects
Evolution microstructurale et comportement mécanique des composites à base de MgH₂ au cours des cycles d'hydruration by Simeon Nachev( )

1 edition published in 2015 in French and held by 2 WorldCat member libraries worldwide

The last decade the magnesium hydride stood out as the most attractive candidatefor solid storage of hydrogen at large scale. The main subject of this study is thephenomenon of irreversible swelling of the composites based on magnesium hydride, duringthe hydriding/dehydriding cycles as well as the evolution of their mechanical properties.In-situ dilatometry measurements and the microstructural characterizations (SEM,granulometry) were performed on magnesium hydride samples co-milled with vanadium orTi-V-Cr additive. The results reveal that the coalescence of nanometric particles tends tocreate large agglomerates, which induce an increase in porosity, and explain the progressiveswelling of composites.The nanoindentation tests performed on compacted pellets show an enhancement ofabout 30 % of the Young modulus after 10 cycles. From the Vickers hardness measured oncompacted powders, the hardness of a highly densified magnesium hydride wasextrapolated to 0.58 GPa, which shows that the magnesium hydride is harder thanmagnesium
Etude de structures avancées pour la détection IR quantique à haute température by Wala Hassis( )

1 edition published in 2014 in French and held by 2 WorldCat member libraries worldwide

The IR sensor makes quantum conventionally involves the absorption of photons in the semiconductor CdHgTe II -VI material . This alloy has a feature to allow an adjustment of the gap of the semiconductor at wavelengths covering the whole IR range by simply varying the composition of the alloy, which makes it a material of choice . However, small gaps at stake here impose a focal cooling to cryogenic temperatures generally planes ( typically hundred Kelvins ) . This cooling naturally represents an important limitation in the operation , the size and cost of such detectors .One of the great challenges ahead in the field of quantum IR detection is the detection at higher temperatures . A figure of merit for popular review the operation of these sensors is the dark current , which reflects its sound , in the case of a noise-limited current ( shot noise) detector. However, because the electrical properties of the semiconductor material used , the dark current increases sharply with the heating of the detector and makes it impossible to use at high temperature . In addition, another phenomenon also appears to limit the functionality of our photo-detectors: high temperature appears on the 1 / f noise whose origin is not fully understood today ( or bulk material interfaces , the debate remains open ... ) .To understand the physical phenomena governing the 1 / f noise in HgCdTe photodiodes through the variation this thesis aims to lots of physical and geometrical parameters in order to highlight the correlations or noise with these variants
Spectroscopies locales sur des nanostructures hybrides hors équilibre by Thomas Quaglio( )

1 edition published in 2012 in French and held by 2 WorldCat member libraries worldwide

We use a microscope combining atomic force microscopy (AFM) and scanning tunneling microscopy (STM) at very low temperature (~100 mK) to study mesoscopic nanocircuits. To perform AFM measurements, we use quartz tuning forks covered with metallic electrodes on which we glue the tip. By using the tuning fork as a dynamic force sensor, we can localize the sample. Then, switching off the oscillation, we can perform local spectroscopies along the conductive part. We use platinum-iridium coated tips to measure the local density of states. This work is focused on hybrid Josephson junctions composed of a normal metal (copper) island of approximately 1 µm separating two superconductors (aluminium). These samples are made by electronic lithography and shadow evaporation.The current-voltage characteristics of these junctions become hysteretic at very low temperature because of thermal dissipation in the normal part. We achieved the localization of a unique sample and performed simultaneously transport measurements and local spectroscopies. We observed that the density of states of the superconductor varies continuously close to the normal metal. We also observed heating in the superconductor when the junction is current biased. The measure of the density of states of the superconductors gives an estimation of the electronic temperature in the sample. The comparison with our thermal model shows that the energy produced in the normal metal seems to be evacuated better than expected
Etude théorique et expérimentale de la génération et des corrélations quantiques de photons triplets générés par interaction non linéaire d'ordre trois by Audrey Dot( )

1 edition published in 2011 in French and held by 2 WorldCat member libraries worldwide

This work deals about the study of coherence between triple photon beams generated by a third order non linear interaction. A protocol, based on the study of the field arising from sum-frequency of the triplet fields in a non linear crystal, was proposed. A theoretical model, in the quantum formalism, was developed, leading to an exhaustive research of the potential signature of the correlations. All the possible schemes were studied : triple fields generation from parametric fluorescence or from stimulated interaction, and recombination of two or three of the triple fields. The experiments we led, i.e. the bi-stimulated non linear generation and the recombination of the so-born fields, agree with our theoretical model and put into light the correlations hiding in this highly stimulated regime, since these correlations lie in the quantum fluctuations of the fields operators. The theoretical calculations predicts a strong correlations signature when the fields are generated from parametric fluorescence, and a weaker one in the case of a generation mono-stimulated
Gravitational and electromagnetic signatures of massive relics in Cosmology by Vivian Poulin( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

Beside their great successes, Cosmology and Particle Physics are facing deep issues that have been puzzling physicists for a long time. In particular, 85% of the matter content in our Universe is in the form a cold, non-interacting component, whose only impacts have been probed through gravity. On the other hand, the discovery of neutrino oscillations point towards the existence of tiny but non-vanishing neutrino masses, a phenomenon that cannot be successfully explained within the Standard Model of Particle Physics. This work tries to tackle the Dark Matter and neutrino masses canondrums, by looking for electromagnetic and gravitational signatures of peculiar massive relics onto Cosmological probesthat have been developed over the years. In particular, we study the impact on i) CMB temperature and polarization anisotropies; ii) Large Scale Structure surveys; iii) Spectral distortions of the CMB blackbody spectrum; iv) and Big Bang Nucleosynthesis.After a thorough review of all necessary tools to compute those observables, we make use of the latest data from present experiments, and forecast the potential for detection of future ones. We firstly focus on the purely gravitational effects of a decaying massive relics, deriving the strongest constraints to date from the pure gravitational effects of the decay and extending the phenomenology to multicomponent models with very high decay rate. Those constraints represent robust, vastly model independent bounds that any massive relic has to satisfy.In a second step, we switch on electromagnetic channels and compare the relative constraining power of non-thermal Big Bang nucleosynthesis, CMB spectral distortions and statistics of CMB anisotropies. As an example, we apply our results to specific models taken from the literature, and show that a loophole to the standard theory of e.m. cascade allow to solve the cosmological Lithium problem thanks to photon injection. We then study the impact of annihilating relics, with a special emphasis on annihilations in halos and its synergy with stars in reionizing our Universe.The last part of this work is devoted to the cosmological determination of neutrino properties with current and future data. We assess that: i) it is possible to make a robust statement about the detection of the cosmic neutrino background by CMB experiments; ii) the joint analysis of future CMB and Large Scale Structure data should allow the first Cosmological detection of neutrino masses. Our results emphasize the complementarity of the different probes, and the need for combined analyses when looking for new physics, especially in the era of precision Cosmology
Vérification de la reconstruction du signal d'onde gravitationnelle de Virgo à l'aide d'un dispositif d'étalonnage utilisant la pression de radiation laser by Timothée Accadia( )

1 edition published in 2012 in French and held by 2 WorldCat member libraries worldwide

Les ondes gravitationnelles sont des solutions aux équations gourvenant la dynamique de la gravitation prédite en 1918 à partir de la théorie de la Relativité Générale d'Einstein. Elles représentent la propagation d'une oscillation de l'espace-temps induisant d'infimes variations de distance sur leur passage entre des masses libres. Depuis deux décennies, un réseau d'interféromètres de Michelson kilométriques a été développé et mis en opération à travers le monde afin de prouver l'existence des ondes gravitationnelles en détectant leur passage sur Terre. Leur signature est recherchée dans un canal de détection étalonné, obtenu à partir des mesures fournies par le détecteur et reconstruisant le signal absolu d'une onde gravitationnelle le traversant. La vérification de la procédure est nécessaire pour déceler d'éventuelles erreurs systématiques d'étalonnage biaisant l'exploitation du canal par les analyses des données. Depuis plusieurs années, une nouvelle technique d'étalonnage est développée à cette fin dans les différents interféromètres du réseau et repose sur la pression de radiation d'un laser modulé en puissance afin d'induire un déplacement étalonné de l'un de ses miroirs. Le dispositif, appelé étalonneur laser, permet de reproduire le passage d'une onde gravitationnelle connue et d'en vérifier la reconstruction dans le canal de détection. Le travail de cette thèse a concerné la mise en \oe uvre de cette technique pour l'interféromètre franco-italien Virgo afin de vérifier la reconstruction de son signal d'onde gravitationnelle. Le principe de fonctionnement de l'étalonneur laser installé sur le site est d'abord détaillé et son étalonnage est ensuite décrit avec les campagnes de mesures réalisées. Enfin, les vérifications faites durant les deux périodes de prises de données de Virgo qui se sont déroulées entre 2010 et 2011 seront présentées. Les résultats ont permis de valider la reconstruction du signal d'onde gravitationnelle de Virgo et ses incertitudes confirmant leur impact négligeable sur l'analyse des données
Détection indirecte de matière noire : des galaxies naines sphéroïdes en photons gamma à la recherche d'anti-hélium avec l'expérience AMS-02 by Vincent Bonnivard( )

1 edition published in 2016 in French and held by 2 WorldCat member libraries worldwide

Many astrophysical observations suggest the existence of large amounts of missing mass in the Universe, from the galactic to the cosmological scale. Discovering the nature of this invisible mass forms the dark matter problem, which appears as one of the major challenges of modern physics. This thesis is established in the context of indirect detection of dark matter. The latter could consist of new elementary particles, whose annihilation products may be observed in cosmic rays. We study in this work two of the most promising research channels!: gamma-rays and anti-nuclei.The best constraints on dark matter properties from gamma-ray observations come from the dwarf spheroidal galaxies (dSphs) of the Milky Way. The first part of our work was devoted to computing the annihilation J-factors of these objects, which quantify the magnitude of the expected gamma-ray flux. We have developed an optimized Jeans analysis setup in order to reconstruct the dark matter density profiles of these objects and their associated uncertainties, using stellar kinematic data. Our optimized setup was obtained using systematic tests on numerous simulated dSphs, and we applied it to twenty-three dSphs of the Milky Way. The second part of our work was dedicated to the search for anti-helium nuclei in the cosmic ray data collected by the AMS-02 experiment on the International Space Station. We have developed a classification method using boosted decision trees, and our preliminary analysis has led to the best constraints to date on the anti-helium to helium ratio
Effets de basse dimensionnalité et de la frustration magnétique dans les composés du type AB₂O₆ by Marlon Luiz Hneda( )

1 edition published in 2016 in French and held by 2 WorldCat member libraries worldwide

This thesis comprises a study of the compounds of AB₂O₆ type that have attracted wide interest in recent years due to their low-dimensional magnetism properties. To better understand their magnetic properties and the parameters that influence it, we have relied on a good knowledge of the crystal structure. All samples were studied by X-ray diffraction (ambient pressure or under high pressure) and neutron diffraction (low and/or high temperature). We also performed other characterisations, such as magnetic susceptibility, specific heat and Mössbauer spectroscopy measurements. We have produced the MnNb2-xVx O6 serie in order to vary the distances between magnetic interchains and thus the nature of the exchange interactions. These compounds are interesting due to the presence of low anisotropy and a coupling of magnetic moments in zigzag chains along the c-axis, which gives them a one-dimensional character, and an antiferromagnetic coupling between chains. We made a comparison with the theoretical model of the classical Heisenberg chain and obtained the exchange constants intra- and interchain, J and J', and its dependency on the content x. Then we made a study of MnxA1-xNb2O6 compounds with A = Fe, Co and Ni. Our aim was to check how the nature and the difference in atomic radii can influence the structural and magnetic properties of these compounds. For compounds which showed no magnetic ordering at 1.5 K we made a study of correlations at short distances using Bertaut's model. Thanks to the use of HP and HT synthesis we manage to stabilized MnV2O6 in orthorhombic symetry and determine its physical properties. We then perfomed a comparison with the monoclinic MnV2O6 and with the orthorhombic MnNb2O6 compound as well. Macroscopic magnetic behaviour of isostructural compounds are very similar but in the case of MnNb2O6, the magnetic moments form + - + - type chains while the MnV2O6 presents chains of + + - - type, a structure never observed before in this family of compounds
Modélisation et simulation du mouvement d'interfaces déformables dans une géométrie confinée : application à l'étude de l'écoulement des globules rouges dans la microcirculation by Othmane Aouane( )

1 edition published in 2015 in English and held by 2 WorldCat member libraries worldwide

Vesicles are extensively used as a model for understanding dynamicsand deformation of red blood cells at the individual level but also regarding collective phenomena and rheology. Vesicles' membranes withstand to bending butdo not have a shear resistance, unlike red blood cells, but they still share several dynamical properties with red blood cells, like tank-treading and tumbling under linear shear flow, or parachute and slipper shapes under Poiseuille flow. The red blood cells are known to form train of cells in the microcirculation attributed to attractive hydrodynamic interactions. We investigate numerically several kind of problems such as: (i) the dynamics of isolated cells; (ii) the hydrodynamic coupling between the red blood cells (by using vesicles as a model) subject to a Poiseuille flow under different confinements; (iii) the aggregation of red blood cells and formation of rouleaux; and (iv) the contribution of macromolecules in the formation of clusters under flow condition. The obtained results give a new insight into thephysics of deformable objects under confinement that are transposable to the flow of red blood cells in the microcirculation
Réalisation de diodes électroluminescentes à base de nanofils GaN by Anne-Laure Bavencove( )

1 edition published in 2012 in French and held by 2 WorldCat member libraries worldwide

This thesis aims at studying the intrinsic properties of InGaN/GaN nanowires (NWs) in order to fabricate efficient light emitting diodes (LEDs). Two active region designs, obtained through different growth techniques, have been extensively investigated. Axial NW-based LEDs emitting from the blue to the red spectral range have been grown by MBE. In this case, single emitters present diameters typically smaller than 100 nm. MOCVD allowed the fabrication of LEDs emitting shorter wavelengths from Core/Shell heterostructures with typical dimensions in the micrometre range. In both cases, the spontaneous growth has been conducted on Silicon (111) highly conductive substrates in order to inject the current vertically into macroscopically contacted devices. Technological building blocks needed to fabricate LEDs have been investigated using a wide range of characterization techniques adapted for high aspect ratio structures. Thus, n-type (Silicon) and p-type (Magnesium) dopings have been assessed thanks to optical spectroscopy techniques, and these results have been confirmed by electrical measurements carried out on single wires. Furthermore, low temperature cathodoluminescence has been widely used to study the optical properties of InGaN-based active regions. After technological integration, electro-optical characterizations with spatial resolution down to the single wire level have revealed that device performances are mainly limited by the fluctuation of electrical and optical properties between single emitters
Pompage de spin et absorption de spin dans des hétérostructures magnétiques by Abhijit Ghosh( )

1 edition published in 2012 in French and held by 2 WorldCat member libraries worldwide

L'interaction entre électrons de conduction itinérants et électrons localisés dans les hétérostructures magnétiques est à l'origine d'effets tels que le transfert de moment de spin, le pompage de spin ou l'effet Hall de spin. Cette thèse est centrée sur le phénomène de pompage de spin : une couche ferromagnétique (FM) en précession injecte un courant de spin pur dans les couches adjacentes. Ce courant de spin peut être partiellement ou totalement absorbé par une couche, dite réservoir de spin, placée directement en contact avec le matériau ferromagnétique ou séparée par une couche d'espacement. L'absorption de la composante transverse du courant de spin induit une augmentation de l'amortissement de la précession ferromagnétique de la couche libre. Cet effet à été mesuré par des expériences de résonance ferromagnétique avec, pour la couche en précession FM, trois matériaux ferromagnétiques différents (NiFe, CoFeB et Co), et pour la couche de réservoir de spin, différents matériaux paramagnétiques (Pt, Pd, Ru), ferromagnétiques et antiferromagnétiques. Dans un premier temps, nous avons vérifié que le facteur d'amortissement non-local généré est de type amortissement de Gilbert, et qu'il est inversement proportionnel à l'épaisseur de la couche en précession FM. L'analyse de l'augmentation de l'amortissement a été réalisée dans le cadre du modèle de pompage de spin adiabatique proposé par Tserkovnyak et al.. Dans un second temps et suivant ce modèle, nous avons extrait les paramètres de conductance avec mélange de spin à l'interface g↑↓ pour différentes interfaces, ces paramètres déterminent le transport du courant de spin à travers des interfaces ferromagnétique/métal non-magnétique. Un troisième résultat important de cette thèse porte sur la longueur d'absorption du courant de spin dans des matériaux ferromagnétiques et paramagnétiques. Celle-ci varie considérablement d'un matériau à l'autre. Pour les matériaux ferromagnétiques, la longueur d'absorption du courant de spin est linéaire par rapport à l'épaisseur de la couche réservoir de spin, avec pour longueur caractéristique ~ 1 nm. Ce résultat est en cohérence avec les théories antérieures et avec les valeurs de longueur de déphasage de spin pour le transfert de moment de spin dans les matériaux ferromagnétiques. Dans les paramagnétiques tels que Pt, Pd, Ru, la longueur d'absorption est soit linéaire soit exponentielle selon que le réservoir paramagnétique est directement en contact avec la couche en précession ou bien séparé par une couche mince d'espacement en Cu. La longueur caractéristique correspondante est inférieure à la longueur de diffusion de spin. Des mesures complémentaires de dichroïsme circulaire magnétique par rayons X ont révélé une induction de moments magnétiques dans les matériaux paramagnétiques comme Pd, Pt, lorsque couplé directement ou indirectement avec une couche FM. Ce résultat fournit une explication de la dépendance en épaisseur linéaire observée dans les hétérostructures en contact direct. Etant donné que le pompage de spin et le couple de transfert de spin (STT) sont des processus réciproques, les résultats de cette thèse sur la conductance avec mélange de spin, la longueur d'absorption de spin et les moments de spin induits sont également d'un grand intérêt pour les études de transfert de moment de spin, ainsi que d'effet Hall de spin, direct et inverse. L'avantage des études présentées ici réside dans le fait qu'elles sont effectuées sur des couches minces continues, sans aucune étape de nanofabrication
Coupled electrokinetic fluxes in a single nanochannel for energy conversion by Preeti Sharma( )

1 edition published in 2017 in English and held by 2 WorldCat member libraries worldwide

Les phénomènes électrocinétiques couplés au sein d'un nanocanal sont d'intérêt pour la conversion d'énergie et la production d'électricité reposant sur le mélange contrôlé d'eau douce et d'eau salée aussi appelée "énergie bleue". L'origine des phénomènes est lié à l'interaction avec des parois chargées et au transport d'ions au sein de ce qu'on nomme les couches de Debye. Ce travail vise à une meilleure compréhension de la physique et des phénomènes de transport dans ces couches dans le cadre de solutions confinées dans des nanocanaux.Une instrumentation spécifique a été développée pendant la thèse pour étudier les mécanismes qui gouvernent ces flux couplés. L'idée est de caractériser simultanément le transport de masse et le courant électrique au sein d'un nanocanal soumis à une différence de salinité de pression ou de tension électrique. Ce travail est divisé en trois parties.Dans la première partie, est décrite une cellule conçue pour la mesure et le contrôle de courant et tension électrique en présence de différence de pression ou de salinité au bornes d'un nanopores. L'utilisation de la cellule est illustrer dans le cas d'une membrane nanoporeuse de nafion.La seconde partie est focalisée sur une méthode simple de préparation d'un nanocanal directement connectable à un dispositif macroscopique. Le nanocanal, d'un micromètre de long, présente une géométrie conique, d'angle ajustable, et des extrémités équipées d'électrode déposées par pulvérisation cathodique.La troisième partie, concerne le développement d'une méthode pour la mesure directe de débit jusqu'à 10 pL/min s'écoulant au sein d'un nanocanal. Cette méthode combinée à une caractérisation électrique, pourra être utilisée, en présence de gradient de pression, de tension ou de salinité pour mesurer le débit et le courant électrique au sein d'un nanocanal de manière simultanée et indépendante
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Alternative Names
École doctorale 47

École doctorale de physique de Grenoble

ED 047

ED 47


ED PHYS (Grenoble)

ED Physique

ED physique (Grenoble)




French (20)

English (7)