10 research outputs found

    Loss compensation in microring-based Si photonics devices via Er3+doped claddings

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    FAPESP - FUNDA√á√ÉO DE AMPARO √Ä PESQUISA DO ESTADO DE S√ÉO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENT√ćFICO E TECNOL√ďGICOWe propose and demonstrate a method to compensate insertion losses in Si photonics devices based on ring resonators fabricated in SOI foundries, with no additional chip area used. It consists in the employment of Er:Al2O3 as the upper cladding layer on standard Si/SiO2 rings, requiring only one simple post-processing step. The method is modeled in detail, and simulation results for single-ring configurations and photonic molecules are discussed, where the potential for loss reduction is predicted for different design choices based on the quality factor. We experimentally verify the viability of the method, obtaining an output power increase of 1 dB when a single-ring resonator is pumped. This value is increased when the method is applied to devices based on photonic molecules, where a value of 2.6 dB has been measured. This is equivalent to a loss reduction potential higher than 3 dB for a photonic molecule designed to achieve a quality factor of 50000.104113FAPESP - FUNDA√á√ÉO DE AMPARO √Ä PESQUISA DO ESTADO DE S√ÉO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENT√ćFICO E TECNOL√ďGICOFAPESP - FUNDA√á√ÉO DE AMPARO √Ä PESQUISA DO ESTADO DE S√ÉO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENT√ćFICO E TECNOL√ďGICO08/57857-22014/04748-2574017/2008-

    Inhibitory Receptors Are Expressed by Trypanosoma cruzi-Specific Effector T Cells and in Hearts of Subjects with Chronic Chagas Disease

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    We had formerly demonstrated that subjects chronically infected with Trypanosoma cruzi show impaired T cell responses closely linked with a process of T cell exhaustion. Recently, the expression of several inhibitory receptors has been associated with T cell dysfunction and exhaustion. In this study, we have examined the expression of the cytotoxic T lymphocyte antigen 4 (CTLA-4) and the leukocyte immunoglobulin like receptor 1 (LIR-1) by peripheral T. cruzi antigen-responsive IFN-gamma (IFN-ő≥)-producing and total T cells from chronically T. cruzi-infected subjects with different clinical forms of the disease. CTAL-4 expression was also evaluated in heart tissue sections from subjects with severe myocarditis. The majority of IFN-ő≥-producing CD4+ T cells responsive to a parasite lysate preparation were found to express CTLA-4 but considerably lower frequencies express LIR-1, irrespective of the clinical status of the donor. Conversely, few IFN-ő≥-producing T cells responsive to tetanus and diphtheria toxoids expressed CTLA-4 and LIR-1. Polyclonal stimulation with anti-CD3 antibodies induced higher frequencies of CD4+CTAL-4+ T cells in patients with severe heart disease than in asymptomatic subjects. Ligation of CTLA-4 and LIR-1 with their agonistic antibodies, in vitro, reduces IFN-ő≥ production. Conversely, CTLA-4 blockade did not improved IFN-ő≥ production in response to T. cruzi antigens. Subjects with chronic T. cruzi infection had increased numbers of CD4+LIR-1+ among total peripheral blood mononuclear cells, relative to uninfected individuals and these numbers decreased after treatment with benznidazole. CTLA-4 was also expressed by CD3+ T lymphocytes infiltrating heart tissues from chronically infected subjects with severe myocarditis. These findings support the conclusion that persistent infection with T. cruzi leads to the upregulation of inhibitory receptors which could alter parasite specific T cell responses in the chronic phase of Chagas disease

    Superconductivity in the carbon-based materials

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    Orientador: Iakov Veniaminovitch KopelevitchDisserta√ß√£o (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Evid√™ncias experimentais e te√≥ricas recentes de que a supercondutividade nas v√°rias formas alotr√≥picas do carbono pode ocorrer em temperaturas pr√≥ximas ou at√© acima da temperatura ambiente, desencadearam um grande interesse cient√≠fico. Resultados do presente trabalho demonstraram a ocorr√™ncia de supercondutividade em comp√≥sitos de carbono v√≠treo-enxofre (CV-S) a T = 3 K. Nossas medidas revelaram que a supercondutividade ocorre em uma pequena fra√ß√£o da amostra, e que a grafitiza√ß√£o do carbono amorfo parece ser uma condi√ß√£o necess√°ria para disparar a supercondutividade. Apresentamos tamb√©m evid√™ncias de supercondutividade √† temperatura ambiente em sandu√≠ches de grafite/Si, e demonstramos que a supercondutividade est√° associada √† interface grafite/sil√≠cio. O comportamento encontrado √© semelhante ao conhecido para estruturas supercondutoras de baixadimensionalidade. Em particular, observamos oscila√ß√Ķes do tipo Josephson em curvas caracter√≠sticas de corrente-tens√£o (I-V), bem como sua supress√£o pela aplica√ß√£o de campo magn√©tico. Al√©m disso, o campo magn√©tico perpendicular transforma as curvas caracter√≠sticas I-V do tipo supercondutor para tipo isolante, assemelhando-se √† transi√ß√£o supercondutor-isolante induzida por campo magn√©tico em redes de jun√ß√Ķes Josephson. Todos estes resultados indicam que a interface grafite/sil√≠cio pode ser um material promissor para o desenvolvimento de dispositivos microeletr√īnicos sem dissipa√ß√£o √† temperatura ambienteAbstract: Recent both experimental and theoretical evidence that superconductivity in various allotropic forms of carbon can occur at temperatures near or even above room temperature, triggered a broad scientific interest. Results of the present work demonstrated the occurrence of superconductivity in carbon glassy-sulfur composites (CV-S) at T = 3 K. Our measurements revealed that the superconductivity occurs in a small fraction of the sample, and that the graphitization of the amorphous carbon seems to be a necessary condition to trigger the superconductivity. We also present evidence for the room temperature superconductivity in graphite/Si sandwiches and demonstrate that the superconductivity is associated with the graphite/silicon interface. The found behavior is similar to that known for low-dimensional superconducting structures. In particular, we have observed Josephson-type oscillations in current-voltage (I-V) characteristics as well as their suppression by applied magnetic field. Moreover, the perpendicular magnetic field transforms the superconducting-like to insulating-like I-V characteristics resembling the magnetic-field-driven superconductor-insulator transition in Josephsonjunction-arrays. All these results indicate that graphite-silicon interface can be a promising material for the development of microelectronic devices without dissipation at room temperatureMestradoSupercondutividadeMestre em F√≠sic

    Study of nitrogen ion doping of titanium dioxide films

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    FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOThis study reports on the properties of nitrogen doped titanium dioxide (TiO2) thin films considering the application as a transparent conducting oxide (TCO). Sets of thin films were prepared by sputtering a titanium target under oxygen atmosphere on a quartz substrate at 400 or 500 degrees C. Films were then doped at the same temperature by 150 eV nitrogen ions. The films were prepared in Anatase phase which was maintained after doping. Up to 30 at% nitrogen concentration was obtained at the surface, as determined by in situ X-ray photoelectron spectroscopy (XPS). Such high nitrogen concentration at the surface lead to nitrogen diffusion into the bulk which reached about 25 nm. Hall measurements indicate that average carrier density reached over 10(19) cm(-3) with mobility in the range of 0.1-1 cm(2) V-1 s(-1). Resistivity about 3 . 10(-1) Omega cm could be obtained with 85% light transmission at 550 nm. These results indicate that low energy implantation is an effective technique for TiO2 doping that allows an accurate control of the doping process independently from the TiO2 preparation. Moreover, this doping route seems promising to attain high doping levels without significantly affecting the film structure. Such approach could be relevant for preparation of N:TiO2 transparent conducting electrodes (TCE).443619627FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2012/10127-52014/23399-

    The DUNE Far Detector Vertical Drift Technology, Technical Design Report

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    DUNE is an international experiment dedicated to addressing some of the questions at the forefront of particle physics and astrophysics, including the mystifying preponderance of matter over antimatter in the early universe. The dual-site experiment will employ an intense neutrino beam focused on a near and a far detector as it aims to determine the neutrino mass hierarchy and to make high-precision measurements of the PMNS matrix parameters, including the CP-violating phase. It will also stand ready to observe supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. The DUNE far detector implements liquid argon time-projection chamber (LArTPC) technology, and combines the many tens-of-kiloton fiducial mass necessary for rare event searches with the sub-centimeter spatial resolution required to image those events with high precision. The addition of a photon detection system enhances physics capabilities for all DUNE physics drivers and opens prospects for further physics explorations. Given its size, the far detector will be implemented as a set of modules, with LArTPC designs that differ from one another as newer technologies arise. In the vertical drift LArTPC design, a horizontal cathode bisects the detector, creating two stacked drift volumes in which ionization charges drift towards anodes at either the top or bottom. The anodes are composed of perforated PCB layers with conductive strips, enabling reconstruction in 3D. Light-trap-style photon detection modules are placed both on the cryostat's side walls and on the central cathode where they are optically powered. This Technical Design Report describes in detail the technical implementations of each subsystem of this LArTPC that, together with the other far detector modules and the near detector, will enable DUNE to achieve its physics goals

    The DUNE Far Detector Vertical Drift Technology, Technical Design Report

    No full text
    International audienceDUNE is an international experiment dedicated to addressing some of the questions at the forefront of particle physics and astrophysics, including the mystifying preponderance of matter over antimatter in the early universe. The dual-site experiment will employ an intense neutrino beam focused on a near and a far detector as it aims to determine the neutrino mass hierarchy and to make high-precision measurements of the PMNS matrix parameters, including the CP-violating phase. It will also stand ready to observe supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. The DUNE far detector implements liquid argon time-projection chamber (LArTPC) technology, and combines the many tens-of-kiloton fiducial mass necessary for rare event searches with the sub-centimeter spatial resolution required to image those events with high precision. The addition of a photon detection system enhances physics capabilities for all DUNE physics drivers and opens prospects for further physics explorations. Given its size, the far detector will be implemented as a set of modules, with LArTPC designs that differ from one another as newer technologies arise. In the vertical drift LArTPC design, a horizontal cathode bisects the detector, creating two stacked drift volumes in which ionization charges drift towards anodes at either the top or bottom. The anodes are composed of perforated PCB layers with conductive strips, enabling reconstruction in 3D. Light-trap-style photon detection modules are placed both on the cryostat's side walls and on the central cathode where they are optically powered. This Technical Design Report describes in detail the technical implementations of each subsystem of this LArTPC that, together with the other far detector modules and the near detector, will enable DUNE to achieve its physics goals

    The DUNE Far Detector Vertical Drift Technology, Technical Design Report