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Search Results: 1 - 10 of 149903 matches for " H. Mariette "
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Geometrical effects on the optical properties of quantum dots doped with a single magnetic atom
Y. Leger,L. Besombes,L. Maingault,D. Ferrand,H. Mariette
Physics , 2005, DOI: 10.1103/PhysRevLett.95.047403
Abstract: The emission spectra of individual self-assembled quantum dots containing a single magnetic Mn atom differ strongly from dot to dot. The differences are explained by the influence of the system geometry, specifically the in-plane asymmetry of the quantum dot and the position of the Mn atom. Depending on both these parameters, one has different characteristic emission features which either reveal or hide the spin state of the magnetic atom. The observed behavior in both zero field and under magnetic field can be explained quantitatively by the interplay between the exciton-manganese exchange interaction (dependent on the Mn position) and the anisotropic part of the electron-hole exchange interaction (related to the asymmetry of the quantum dot).
Intrinsic limits governing MBE growth of Ga-assisted GaAs nanowires on Si(111)
Le Thuy Thanh Giang,C. Bougerol,H. Mariette,R. Songmuang
Physics , 2012,
Abstract: Diffusion-enhanced and desorption-limited growth regimes of Ga-assisted GaAs nanowires were identified. In the latter regime, the number of vertical NWs with a narrow length distribution was increased by raising the growth temperature. The maximum axial growth rate; which can be quantified by the supplied rate of As atoms, is achieved when a dynamical equilibrium state is maintained in Ga droplets i.e. the number of impinging As atoms on the droplet surface is equivalent to that of direct deposited Ga atoms combining with the diffusing ones. The contribution of Ga diffusion to the wire growth was evidenced by the diameter-dependent NW axial growth rate.
How does BAFF activate B cells in patients with autoimmune diseases?
Xavier Mariette
Arthritis Research & Therapy , 2012, DOI: 10.1186/ar3729
Abstract: In a study in a recent issue of Arthritis Research & Therapy, Yoshimoto and colleagues [1] demonstrate that peripheral monocytes from patients with Sj?gren's syndrome (SS) produce significantly higher amounts of the cytokines B cell-activating factor (BAFF) (also called B-lymphocyte stimulator, or BlyS) and interleukin-6 (IL-6) in comparison with normal monocytes. Increased expression of BAFF might explain pathogenic B-cell activation in several systemic autoimmune diseases (reviewed in [2]). Interestingly, autoreactive B cells depend more on BAFF for survival than do alloreactive B cells. BAFF involvement in the pathogenesis of autoimmune diseases is well illustrated in BAFF-transgenic mice, which exhibit an autoimmune disease mimicking systemic lupus erythematosus (SLE) and primary Sj?gren's syndrome (pSS) as well as a twofold increase in frequency of B-cell lymphoma [3]. In humans, an increased serum level of BAFF was reported in different autoimmune diseases, and findings concerning SLE and pSS were more consistent (reviewed in [2]).Recent findings showed that BAFF could be expressed and secreted by resident cell targets of autoimmunity after stimulation with different cytokines: synoviocytes in rheumatoid arthritis, astrocytes in multiple sclerosis, and epithelial cells in pSS [4]. Moreover, in the context of autoimmunity, BAFF could be secreted by T [5] and B [6] lymphocytes. However, the main sources of BAFF are myeloid cells and, especially, blood monocytes, myeloid dendritic cells, and macrophages [7].It has been suggested that monocytes from patients with autoimmune diseases were more susceptible to BAFF expression and secretion after stimulation with type 1 interferon (IFN) than those from healthy controls [8]. Yoshimoto and colleagues [1] add an important point to this discussion by emphasizing the role of monocytes in the overproduction of BAFF in autoimmunity. The authors demonstrate that peripheral pSS monocytes produce significantly higher amounts of
Room temperature Optical Orientation of Exciton Spin in cubic GaN/AlN quantum dots
D. Lagarde,A. Balocchi,H. Carrere,P. Renucci,T. Amand,X. Marie,S. Founta,H. Mariette
Physics , 2007, DOI: 10.1103/PhysRevB.77.041304
Abstract: The optical orientation of the exciton spin in an ensemble of self-organized cubic GaN/AlN quantum dots is studied by time-resolved photoluminescence. Under a polarized quasi-resonant excitation, the luminescence linear polarization exhibits no temporal decay, even at room temperature. This demonstrates the robustness of the exciton spin polarization in these cubic nitride nanostructures, with characteristic decay times longer than 10 ns.
Optical probing of spin fluctuations of a single magnetic atom
L. Besombes,Y. Leger,J. Bernos,H. Boukari,H. Mariette,J. Fernandez-Rossier,R. Aguado
Physics , 2008, DOI: 10.1103/PhysRevB.78.125324
Abstract: We analyzed the photoluminescence intermittency generated by a single paramagnetic spin localized in an individual semiconductor quantum dot. The statistics of the photons emitted by the quantum dot reflect the quantum fluctuations of the localized spin interacting with the injected carriers. Photon correlation measurements which are reported here reveal unique signatures of these fluctuations. A phenomenological model is proposed to quantitatively describe these observations, allowing a measurement of the spin dynamics of an individual magnetic atom at zero magnetic field. These results demonstrate the existence of an efficient spin relaxation channel arising from a spin-exchange with individual carriers surrounding the quantum dot. A theoretical description of a spin-flip mechanism involving spin exchange with surrounding carriers gives relaxation times in good agreement with the measured dynamics.
Optical spin orientation of a single manganese atom in a quantum dot
C. Le Gall,L. Besombes,H. Boukari,R. Kolodka,H. Mariette,J. Cibert
Physics , 2008, DOI: 10.1103/PhysRevLett.102.127402
Abstract: A hight degree of spin polarization is achieved for a Mn atom localized in a semiconductor quantum dot using quasi-resonant optical excitation at zero magnetic field. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots.
Neurite outgrowth on a fibronectin isoform expressed during peripheral nerve regeneration is mediated by the interaction of paxillin with α4β1 integrins
Mariette Vogelezang, Ulrike B Forster, Jaewon Han, Mark H Ginsberg, Charles ffrench-Constant
BMC Neuroscience , 2007, DOI: 10.1186/1471-2202-8-44
Abstract: Expression of α4 with mutations in the paxillin-binding domain reduced neurite outgrowth on recombinant embryonic fibronectin fragments relative to wild type α4. Over-expression of paxillin promoted neurite outgrowth while a mutant isoform lacking the LD4 domain implicated in the regulation of ARF and Rac GTPases was less effective. Optimal α4-mediated migration in leucocytes requires spatial regulation of α4 phosphorylation at Ser988, a post-translational modification that blocks paxillin binding to the integrin cytoplasmic domain. In keeping with this α4(S988D), which mimics phosphorylated α4, did not promote neurite outgrowth. However, α4 was not phosphorylated in the PC12 cells, and a non-phosphorylatable α4(S988A) mutant promoted neurite outgrowth indistinguishably from the wild type integrin.We establish the importance of the α4 integrin-paxillin interaction in a model of axonal regeneration and highlight differing dependence on phosphorylation of α4 for extension of neuronal growth cones and migration of non-neural cells.Regrowth of the peripheral nervous system (PNS) after injuries such as axotomy is associated with changes in the expression of extracellular matrix (ECM) molecules in the environment traversed by the regenerating growth cones [1]. These changes may promote regeneration in at least two different ways. First, by generating increased levels of molecules such as laminin (Ln) and fibronectin (Fn) that can promote neurite outgrowth in cell culture and are therefore likely to promote regeneration in vivo [2,3]. Second, by altering the pattern of alternative splicing so as to switch from isoforms of ECM proteins expressed in adult nerve to those expressed earlier during a time of axon growth in development. An example of the second mechanism is provided by Fn, whose primary gene transcript is alternatively spliced in three regions [4-9]. Two of these include or exclude single Fn type III repeats (EIIIA and EIIIB) while the third partially or complete
Rui M. B. Carrilho,Artur R. Abreu,Mariette M. Pereira,V. H. Rodrigues
Acta Crystallographica Section E , 2011, DOI: 10.1107/s1600536811031722
Abstract: The title compound, C25H24O4, a methoxymethyl (MOM) bis-protected BINOL derivative containing a methyl substituent in position 3, is a key intermediate for the synthesis of a great variety of chiral auxiliaries. The planes of the naphthyl aromatic rings are at an angle of 70.74 (3)°. There are no conventional hydrogen bonds binding the molecules.
Fine structure of exciton excited levels in a quantum dot with a magnetic ion
M. M. Glazov,E. L. Ivchenko,L. Besombes,Y. Leger,L. Maingault,H. Mariette
Physics , 2006, DOI: 10.1103/PhysRevB.75.205313
Abstract: The fine structure of excited excitonic states in a quantum dot with an embedded magnetic ion is studied theoretically and experimentally. The developed theory takes into account the Coulomb interaction between charged carriers, the anisotropic long-range electron-hole exchange interaction in the zero-dimensional exciton, and the exchange interaction of the electron and the hole with the $d$-electrons of a Mn ion inserted inside the dot. Depending on the relation between the quantum dot anisotropy and the exciton-Mn coupling the photoluminescence excitation spectrum has a qualitatively different behavior. It provides a deep insight into the spin structure of the excited excitonic states.
Remote optical addressing of single nano-objects
M. Brun,A. Drezet,H. Mariette,J. C. Woehl,S. Huant
Physics , 2006, DOI: 10.1209/epl/i2003-00275-y
Abstract: We present a scheme for remotely addressing single nano-objects by means of near-field optical microscopy that makes only use of one of the most fundamental properties of electromagnetic radiation: its polarization. A medium containing optically active nano-objects is covered with a thin metallic film presenting sub-wavelength holes. When the optical tip is positioned some distance away from a hole, surface plasmons in the metal coating are generated which, by turning the polarization plane of the excitation light, transfer the excitation towards a chosen hole and induce emission from the underlying nano-objects. The method, easily applicable to other systems, is demonstrated for single quantum dots (QDs) at low temperature. It may become a valuable tool for future optical applications in the nanoworld.
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