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Sample records for supercondutores ferromagneticos ruteno-cupratos

  1. Supercondutors

    International Nuclear Information System (INIS)

    Frota-Pessoa, S.

    1987-01-01

    The evolution of superconductors, since its discovery until the approach of ceramic superconductors is presented. A brief introduction of BCS theory is done, and some interesting properties under tecnological point of view are discussed. The ceramic superconductors, its tecnological powerful and the raised points with the approach of these new materials are emphasized. (M.C.K.) [pt

  2. Motor de histerese multifásico com polos variáveis de rotor cilíndrico supercondutor

    OpenAIRE

    Dionísio, Raúl Manuel Mendes

    2011-01-01

    Dissertação apresentada para obtenção do Grau de Doutor em Engenharia Electrotécnica e de Computadores, especialidade em Máquinas Eléctricas pela Universidade Nova de Lisboa, Faculdade de Ciências e Tecnologia Os materiais supercondutores de alta temperatura têm sido estudados e aplicados em conversores electromecânicos de energia onde se reconhecem oportunidades de melhoria das densidades volumétrica e gravimétrica de potência, por exemplo, face às máquinas de constru...

  3. Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples; Medidas de transporte em supercondutores: corrente critica de supercondutores granulares de alta temperatura critica

    Energy Technology Data Exchange (ETDEWEB)

    Passos, W.A.C., E-mail: wagner.passos@univasf.edu.br [Universidade Federal do Vale do Sao Francisco (IPCM/UNIVASF), Juazeiro do Norte, BA (Brazil). Instituto de Pesquisas em Ciencia dos Materiais; Silva, E.B. [Companhia Energetica do Sao Francisco (CHESF), Recife, PE (Brazil)

    2016-07-01

    This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa{sub 2}Cu{sub 3}O{sub 7-δ} sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T{sub c} of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

  4. Saltos classicos e quanticos de vortices intrinsicamente aprisionados em supercondutores de alta temperatura critica

    OpenAIRE

    Cristiane de Morais Smith

    1994-01-01

    Resumo: Uma generalização da teoria de tunelamento quântico macroscópico é obtida visando descrever o decaimento de sistemas com mais de um grau de liberdade aprisionados em estados meta-estáveis. Inicialmente nós estudamos um dc SQUID controlado por uma corrente externa, que constitui um sistema com dois graus de liberdade quânticos interagentes acoplados ao meio que os cerca. A probabilidade de decaimento é obtida na aproximação exponencial para o caso super-amortecido. Próximo à força crít...

  5. Study of the YBa{sub 2}Cu{sub 3}O-7{sub -{delta}} superconductor application as a low magnetic field sensor; Estudo da aplicacao do supercondutor YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} como sensor de baixo campo magnetico

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, G L; Shigue, C Y; Santos, C A.M. dos; Machado, A J [Faculdade de Engenharia Quimica de Lorena (Faenquil), SP (Brazil). Dept. de Engenharia de Materiais

    2000-07-01

    It has been proposed in the literature a new regime for high critical temperature superconductors labeled as thermally activated flux flow (TAFF). This regime presents a state in which vortex dynamic exhibit a ohmic behavior. The resistivity in this regime is proportional to the applied magnetic field for small current densities. Materials showing this behavior have high disordering and present semiconductor behavior in normal state with broad transition temperature. In this work is presented a systematic study of the magnetoresistance as a function of the applied magnetic field for polycrystalline samples with several thickness. Results of X ray diffraction, resistivity as a function of the temperature, I-V characteristic curves and magnetoresistance are showed. Finally is proposed a calibration curve of the magnetoresistance as a function of the magnetic field, that show the possibility of its use as magnetic field sensor. (author)

  6. Nano wire conductance experiments above and below the reservoirs Curie temperature

    Energy Technology Data Exchange (ETDEWEB)

    Costa-Kraemer, J. L.; Briones, F. [Instituto de Microelectronica de Madrid, Madrid (Spain); Serena, P. A. [Instituto de Ciencias de Materiales de Madrid, Madrid (Spain)

    2001-03-01

    The transport properties of Ni nano wires are studied using a Scanning Tunneling Microscope (STM) under clean high vacuum conditions. A basically flat nano wire conductance histogram is found independently of the magnetic state of the electrodes. This agrees with our previous studies in air but disagrees with recently published results. The possible origin of these discrepancies, together with additional experiments trying to discern the existence of a spin-dependent conductance in ferromagnetic nano wires, are presented. [Spanish] Las propiedades de transporte de nanoalambres de Ni son estudiadas usando un microscopio de efecto tunel bajo condiciones limpias de alto vacio. Se encuentra un histograma esencialmente plano independiente del estado magnetico de los electrodos. Esto concuerda con nuestros estudios previos en aire pero contrasta con resultados publicados recientemente. Se presentara una discusion sobre el posible origen experimental de estas discrepancias, con el fin de discernir sobre la existencia de una conductancia dependiente del espin en nanoalambres ferromagneticos.

  7. Planning and production of a low cost cryostat for electrical characterization of materials

    OpenAIRE

    Torsoni, G.B. [UNESP; Carvalho, C.L. [UNESP

    2012-01-01

    Os supercondutores a base de BiSrCaCuO apresentam três fases principais, Bi2Sr2CuO, Bi2Sr2CaCu2O e Bi2Sr2Ca2Cu3O com temperaturas críticas de 20 K, 80 K e 110 K, respectivamente. Desta forma, torna-se fundamental a caracterização elétrica de tais materiais a baixas temperaturas. Com este objetivo confeccionou-se um criostato para medidas de caracterização elétrica. Utilizando-se nitrogênio líquido (77 K), e controlando a pressão sobre o refrigerante, atingiu-se uma temperatura da ordem de 64 ...

  8. Desenvolvimento e implantação de unidade piloto de precipitação de partículas usando antissolvente supercrítico (SAS)

    OpenAIRE

    Rossa, Guilherme Evaldt

    2015-01-01

    O interesse em micro e nanopartículas tem crescido nos últimos anos, uma vez que o avanço tecnológico ampliou as possibilidades de produção e manipulação dessas partículas. Por ter aplicações em diferentes setores, tais como os de pigmentos, explosivos, polímeros, fármacos e supercondutores, a nanotecnologia tem atraído cada vez mais o interesse de governos, pesquisadores acadêmicos e indústrias. Dentre as tecnologias para obtenção de micro e nanopartículas, destacam-se as que fazem uso de an...

  9. Studies on magnetocaloric and magnetic coupling effects =

    Science.gov (United States)

    Amaral, Joao Cunha de Sequeira

    O presente trabalho apresenta novas metodologias desenvolvidas para a analise das propriedades magneticas e magnetocaloricas de materiais, sustentadas em consideracoes teoricas a partir de modelos, nomeadamente a teoria de transicoes de fase de Landau, o modelo de campo medio molecular e a teoria de fenomeno critico. Sao propostos novos metodos de escala, permitindo a interpretacao de dados de magnetizacao de materiais numa perspectiva de campo medio molecular ou teoria de fenomeno critico. E apresentado um metodo de estimar a magnetizacao espontanea de um material ferromagnetico a partir de relacoes entropia/magnetizacao estabelecidas pelo modelo de campo medio molecular. A termodinamica das transicoes de fase magneticas de primeira ordem e estudada usando a teoria de Landau e de campo medio molecular (modelo de Bean-Rodbell), avaliando os efeitos de fenomenos fora de equilibrio e de condicoes de mistura de fase em estimativas do efeito magnetocalorico a partir de medidas magneticas. Efeitos de desordem, interpretados como uma distribuicao na interaccao magnetica entre ioes, estabelecem os efeitos de distribuicoes quimicas/estruturais nas propriedades magneticas e magnetocaloricas de materiais com transicoes de fase de segunda e de primeira ordem. O uso das metodologias apresentadas na interpretacao das propriedades magneticas de variados materiais ferromagneticos permitiu obter: 1) uma analise quantitativa da variacao de spin por iao Gadolinio devido a transicao estrutural do composto Gd5Si2Ge2, 2) a descricao da configuracao de cluster magnetico de ioes Mn na fase ferromagnetica em manganites da familia La-Sr e La-Ca, 3) a determinacao dos expoentes criticos β e δ do Niquel por metodos de escala, 4) a descricao do efeito da pressao nas propriedades magneticas e magnetocaloricas do composto LaFe11.5Si1.5 atraves do modelo de Bean-Rodbell, 5) uma estimativa da desordem em manganites ferromagneticas com transicoes de segunda e primeira ordem, 6) uma descricao de

  10. Slowly rotating general relativistic superfluid neutron stars with relativistic entrainment

    International Nuclear Information System (INIS)

    Comer, G.L.

    2004-01-01

    Neutron stars that are cold enough should have two or more superfluids or supercondutors in their inner crusts and cores. The implication of superfluidity or superconductivity for equilibrium and dynamical neutron star states is that each individual particle species that forms a condensate must have its own, independent number density current and equation of motion that determines that current. An important consequence of the quasiparticle nature of each condensate is the so-called entrainment effect; i.e., the momentum of a condensate is a linear combination of its own current and those of the other condensates. We present here the first fully relativistic modeling of slowly rotating superfluid neutron stars with entrainment that is accurate to the second-order in the rotation rates. The stars consist of superfluid neutrons, superconducting protons, and a highly degenerate, relativistic gas of electrons. We use a relativistic σ-ω mean field model for the equation of state of the matter and the entrainment. We determine the effect of a relative rotation between the neutrons and protons on a star's total mass, shape, and Kepler, mass-shedding limit

  11. Results of the change of the lighting system in an institution of higher education; Resultados del cambio del sistema de iluminacion en una institucion de educacion superior

    Energy Technology Data Exchange (ETDEWEB)

    Torres P, Irene; Ambriz G, Juan Jose; Romero Paredes R, Hernando; Heras G, Francisco Javier [Universidad Autonoma Metropolitana. Iztapalapa (Mexico)

    2003-07-01

    In the Universidad Autonoma Metropolitana (UAM) actions have been made to diminish the energy consumption, one of them was the substitution and diminution of half of fluorescent lamps of 39W with ferromagnetic ballast for lamps of high electronic efficiency of 32W with electronic ballast. In this paper the results of the evaluation of the lighting level is presented after the indicated change, for which the measurement of the illumination level was made in the classrooms of 4 buildings of the UAM-1, as well as the calculation of the diminution of the electrical consumption for lighting taking into account previously measurements made of the consumption of electrical energy. The effect in the diminution of the electrical bill is significant, nevertheless, the lighting levels found are slightly insufficient. [Spanish] En la Universidad Autonoma Metropolitana se han realizado acciones enfocadas a disminuir el consumo de energia, una de ellas fue la sustitucion y disminucion a la mitad de lamparas fluorescentes de 39W con balastro ferromagnetico por lamparas de alta eficiencia de 32W con balastro electronico. En este trabajo se presentan los resultados de la evaluacion del nivel de iluminacion despues del cambio senalado, para lo cual se realizo la medicion del nivel de iluminacion en los salones de clase de 4 edificios de la UAM-I, asi como el calculo en la disminucion en el consumo electrico por iluminacion tomando en cuenta mediciones de consumo de energia electrica realizadas anteriormente. El efecto en la disminucion de la facturacion electrica es apreciable, sin embargo, los niveles de iluminacion encontrados son ligeramente insuficientes.

  12. Pesquisa e desenvolvimento em cerâmicas eletro-eletrônicas no IPEN

    Directory of Open Access Journals (Sweden)

    Muccillo R.

    1999-01-01

    Full Text Available O Grupo de Cerâmicas Eletro-eletrônicas do IPEN desenvolve trabalhos de pesquisa em materiais cerâmicos avançados para utilização em dispositivos sensores de espécies químicas e em células de combustíveis a eletrólitos sólidos. As principais áreas de atuação do grupo são em 1 síntese, processamento e caracterização elétrica de materiais cerâmicos, 2 estudo de correlação microestrutura-propriedades elétricas de materiais cerâmicos, 3 projeto, desenvolvimento, montagem e testes de sensores eletroquímicos de espécies químicas. Os principais materiais estudados são condutores iônicos (à base de ZrO2, ThO2 e outros, protônicos (à base de BaCeO3, varistores à base de SnO2, supercondutores cerâmicos de alta temperatura crítica (das famílias Y-Ba-Cu-O e Bi-Sr-Ca-Cu-O e compósitos de matriz cerâmica (dos tipos isolante em matriz condutora iônica e condutor iônico em matriz supercondutora. A infra-estrutura experimental dispõe de analisador de impedância, difratômetro de raios X, equipamento de análise térmica simultânea, fornos para sinterização e laboratório químico. O trabalho de pesquisa do Grupo é financiado por projetos FAPESP e PRONEX.

  13. Silica-gel structural characterization during the initial phases of gelation and drying; Caracterizacao estrutural de geis de silica durante as etapas iniciais de gelacao e secagem

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Max Passos

    1997-12-31

    For centuries, glasses and ceramics have been made via melting or solid state reactions at temperatures above 100 deg C. The sol-gel process offers new approaches to the synthesis of glasses and ceramics, combining control of composition and structure at the molecular level with the ability to shape materials in bulk, powder, fiber and thin-film forms. The growth of sol-gel technology research is due to the many unique features of that class of materials. Major applications include optical elements and integrated optical devices, ceramic filters, membranes, supercondutors, magnetic, catalytic and manostructured materials to antioxidant, anticorrosion coatings and composite and biomedical materials. In this work a variety of techniques like spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, light scattering nuclear magnetic resonance, X ray diffraction and nitrogen adsorption have been employed to investigate the initial phase of the sol-gel transition of gamma ray irradiated tetramethoxysilane (TMOS) solutions and non-irradiated TMOS solution and to get information about the structure of the silica gels obtained under different gelation conditions. Typically the tetramethoxysilane solutions were prepared using a molar ratio of TMOS to demineralized water of 1 to 16. Some experiments were made under catalysed conditions. The mixing was carried out at room temperature. The turbidity and light scattering experiments on the polycondensation of tetramethoxysilane show that exists no drastic difference in the gelling time of a gamma ray irradiated and a non-irradiated TMOS+H{sub 2}O (1+16 M) solution. In the absence of a catalyst, the gelling time for both reactions occurs in about 3.30 h. When HNO{sub 3} (o.03 M) was used, the gelling time observed was 3 days. Raman and ultraviolet-visible spectroscopy show no drastic difference during the initial phase at the sol-gel transition under ambient temperature/pressure and under gamma radiation. The gels

  14. Silica-gel structural characterization during the initial phases of gelation and drying

    International Nuclear Information System (INIS)

    Ferreira, Max Passos

    1996-01-01

    For centuries, glasses and ceramics have been made via melting or solid state reactions at temperatures above 100 deg C. The sol-gel process offers new approaches to the synthesis of glasses and ceramics, combining control of composition and structure at the molecular level with the ability to shape materials in bulk, powder, fiber and thin-film forms. The growth of sol-gel technology research is due to the many unique features of that class of materials. Major applications include optical elements and integrated optical devices, ceramic filters, membranes, supercondutors, magnetic, catalytic and manostructured materials to antioxidant, anticorrosion coatings and composite and biomedical materials. In this work a variety of techniques like spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, light scattering nuclear magnetic resonance, X ray diffraction and nitrogen adsorption have been employed to investigate the initial phase of the sol-gel transition of gamma ray irradiated tetramethoxysilane (TMOS) solutions and non-irradiated TMOS solution and to get information about the structure of the silica gels obtained under different gelation conditions. Typically the tetramethoxysilane solutions were prepared using a molar ratio of TMOS to demineralized water of 1 to 16. Some experiments were made under catalysed conditions. The mixing was carried out at room temperature. The turbidity and light scattering experiments on the polycondensation of tetramethoxysilane show that exists no drastic difference in the gelling time of a gamma ray irradiated and a non-irradiated TMOS+H 2 O (1+16 M) solution. In the absence of a catalyst, the gelling time for both reactions occurs in about 3.30 h. When HNO 3 (o.03 M) was used, the gelling time observed was 3 days. Raman and ultraviolet-visible spectroscopy show no drastic difference during the initial phase at the sol-gel transition under ambient temperature/pressure and under gamma radiation. The gels heated

  15. Silica-gel structural characterization during the initial phases of gelation and drying; Caracterizacao estrutural de geis de silica durante as etapas iniciais de gelacao e secagem

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Max Passos

    1996-12-31

    For centuries, glasses and ceramics have been made via melting or solid state reactions at temperatures above 100 deg C. The sol-gel process offers new approaches to the synthesis of glasses and ceramics, combining control of composition and structure at the molecular level with the ability to shape materials in bulk, powder, fiber and thin-film forms. The growth of sol-gel technology research is due to the many unique features of that class of materials. Major applications include optical elements and integrated optical devices, ceramic filters, membranes, supercondutors, magnetic, catalytic and manostructured materials to antioxidant, anticorrosion coatings and composite and biomedical materials. In this work a variety of techniques like spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, light scattering nuclear magnetic resonance, X ray diffraction and nitrogen adsorption have been employed to investigate the initial phase of the sol-gel transition of gamma ray irradiated tetramethoxysilane (TMOS) solutions and non-irradiated TMOS solution and to get information about the structure of the silica gels obtained under different gelation conditions. Typically the tetramethoxysilane solutions were prepared using a molar ratio of TMOS to demineralized water of 1 to 16. Some experiments were made under catalysed conditions. The mixing was carried out at room temperature. The turbidity and light scattering experiments on the polycondensation of tetramethoxysilane show that exists no drastic difference in the gelling time of a gamma ray irradiated and a non-irradiated TMOS+H{sub 2}O (1+16 M) solution. In the absence of a catalyst, the gelling time for both reactions occurs in about 3.30 h. When HNO{sub 3} (o.03 M) was used, the gelling time observed was 3 days. Raman and ultraviolet-visible spectroscopy show no drastic difference during the initial phase at the sol-gel transition under ambient temperature/pressure and under gamma radiation. The gels

  16. Nuclear magnetic resonance in the evaluation of the disk luxation in the temporomandibular articulation conditioned for degenerative osseous changes; Resonancia magnetica nuclear en la valoracion de la luxacion discal en la articulacion temporomandibular condicionada por cambios degenerativos oseos

    Energy Technology Data Exchange (ETDEWEB)

    Marchegiani, Silvio; Guzman Urquhart, Romel; Marangoni, Alberto; Alvarez, Federico; Surur, Alberto [Sanatorio Allende, Cordoba (Argentina). Servicio de Diagnostico por Imagenes

    2006-07-01

    incidencia de la patologia de acuerdo al sexo, relacionar las luxaciones del disco interarticular con los cambios degenerativos oseos, relacionar la falta de reduccion del disco luxado en la apertura bucal, con los cambios degenerativos oseos, y evaluar la utilidad de la RM en el estudio de la articulacion temporo-mandibular. Material y metodo: Se evaluaron 215 pacientes, estudiados desde enero de 1999 a agosto de 2004. Se excluyeron a pacientes portadores de material ferromagnetico o que presentaron sindrome de claustrofobia. Se utilizo un equipo Elscint de 2 tesla de campo magnetico, con bobina especifica y secuencias T1 y T2 con supresion grasa. Se evaluaron: luxaciones (reductibles y no reductibles), cambios degenerativos oseos, osteocondritis, cambios degenerativos discales, perforaciones discales, y lesiones retrodiscales. Resultados: De los 215 pacientes, se analizaron 175 pacientes que presentaron anormalidades en el estudio por IRM. Los 40 pacientes restantes fueron excluidos por presentar un estudio de (IRM) normal. De estos 175 pacientes, 146 fueron mujeres y 29 hombres. La luxacion mas comun fue la anterior y la demostracion de las lesiones articulares y la artrosis por IRM fue satisfactoria en todos los casos. Discusion: en nuestro trabajo la disfuncion de la ATM mas comun fue la luxacion anterior, concordando con otros autores. Se encontro una relacion exacta entre las luxaciones no reductibles, con cambios degenerativos oseos. Conclusion: Se demuestra que la IRM es el examen de eleccion para evaluar la ATM. El sexo femenino es el mas afectado por este tipo de patologia. La luxacion del disco es la alteracion mas frecuente encontrada en la disfuncion de la ATM, demostrando que en pacientes con osteofitosis marginales del condilo no fue posible la reduccion del disco. (autor)

  17. Recent Developments in the Chemical Thermodynamics of the Uranium Chalcogenides; Progres Accomplis Recemment dans la Thermodynamique Chimique des Chalcogenures d'Uranium; Poslednie dostizheniya v khimicheskoj termodinamike khal'kogenidov Urana; Recientes Progresos en la Termodinamica Quimica de los Calcogenidos de Uranio

    Energy Technology Data Exchange (ETDEWEB)

    Westrum, Jr., E. F. [University of Michigan, Ann Arbor, MI (United States)

    1966-02-15

    estado ferromagnetico y contrastan con la anomalia antiferro- magnetica hallada en el mononitruro isoestructural a 52 Degree-Sign K. Los nuevos datos termodinamicos concuerdan satisfactoriamente con los obtenidos mediante el procedimiento de evaluacion de entropia de Gronvold y Westrum. (author) [Russian] Rasprostranenie kriotermicheskih dannyh no U{sub 4}O{sub 9} na bolee vysokie temperatury pokazalo termofizicheskie aspekty (predpolagaemogo) postepennogo strukturnogo prevrashhenija tipa-A. pri temperature 348 Degree-Sign K s sootvetstvujushhim prirashheniem jentropii v razmere 1,84 kalorij/gramm-mol' OK, svjazannogo so smeshheniem vnedrennyh atomov kisloroda. Izmerenija kak teploemkosti, tak i magnitnoj vospriimchivosti na spechennoj dvuokisi urana Mol- linkrodta podtverdili, chto antiferromagnitnyj-paramagnitnyj perehod proishodit pri 30,4 Degree-Sign K so skachkom teploemkosti v 400 kalorij/gramm-mol' Degree-Sign K, a ne pri 28,7 Degree-Sign K s povysheniem teploemkosti na devjat' kalorij/gramm-mol' Degree-Sign K, kak soobshhalos' v literature. Jeto pozvoljaet teper' ob{sup j}asnit' termicheskuju anomaliju, obnaruzhennuju v {beta} -U{sub 3}O{sub 7}. Kriogennye teploemkosti, poluchennye na harakternyh obrazcah {alpha}-, {beta}-, i {gamma} utriokisi urana, podgotovlennyh doktorom E.G.P.Kordfunke iz Niderlandskogo reaktornogo centra, kombinirujutsja s teploemkostjami pri bolee vysokoj temperature, jental'pijami obrazovanija i drugimi termodinamicheskimi dannymi dlja poluchenija dannyh ob otnositel'noj stabil'nosti jetih vazhnyh jadernyh materialov. Obnaruzheno, chto kak monoselenid urana, tak i diselenid urana imejut anomalii tipa ljambda, svjazannye s magnitnym razuporjadocheniem. V diselenide urana jeto proishodit pri 13,1 Degree-Sign K s prirashheniem jentropii v 0,16 kalorij/gramm-mol' Degree-Sign K. Prirashhenie jentropii v monoselenide pri anomalii pri 160 Degree-Sign K sostavljaet velichinu 1,0 kalorij/gramm- mol' Degree-Sign K, chto mozhno sravnit' s velichinoj