Magnetical Response and Mechanical Properties of High Temperature Superconductors, YBaCu3O7-X Materials

Since the discovery of the second generation High Superconductor Materials (2G-HTSC) in 1986, their magnetic properties have been widely studied by different research groups around the world. During the last years, the mechanical properties at micro-/ and nanometric scale are starting to be studied in order to know and improve the durability of conventional devices. In this book chapter, we would like to focus our attention on the magnetical response and also the mechanical properties of 2G-HTSC. In relation to the magnetic response, the Meissner effect is one important signature of the superconductivity. In this case, a diamagnetic response is observed due to exclusion of the magnetic flux of the interior of the superconducting material when the temperature is below the critical temperature. This important property allows to distinguish a superconducting material from a conducting one. But in several cases the superconducting materials exhibit a paramagnetic response instead of the conventional diamagnetism. This effect is frequently called paramagnetic Meissner effect (PME). In this case, the magnetic flux is not expelled, and a paramagnetic state can be originated. This effect is observed in several magnetic field regimes, and in some cases the paramagnetic response increases with the applied magnetic field, but in others the paramagnetic response decreases when the magnetic field increases..

Análise de Transiçao Resistiva e da irreversibilidade magnètica no superconductor YBACUO texturizado

Os supercondutores de alta temperatura crítica, em especial os granulares, apresentam uma transição resistiva que ocorre em duas etapas: a uma temperatura acima da temperatura crítica de transição Tc0, chamada de supercondutividade intragranular e a uma temperatura mais baixa onde ocorre a supercondutividade em toda a amostra, chamada de supercondutividade intergranular. Em Tc0 ocorre à ativação das ligações fracas e uma ordem de longo alcance é obtida, neste momento, a resistência elétrica é nula em toda amostra. Nos supercondutores de alta temperatura crítica, a linha de irreversibilidade magnética divide o estado misto do plano H-T em duas regiões: reversível e irreversível. Na região reversível todo o transporte elétrico sofre dissipação devido aos efeitos da dinâmica de fluxo magnético no supercondutor. Na região irreversível todo transporte de corrente elétrica é permitido. Em supercondutores granulares, as medidas de irreversibilidade magnética e resistividade nula não dependem das mesmas partes da amostra. Enquanto, a resistência elétrica depende de um arranjo de grãos que atravessam toda a amostra a irreversibilidade depende de clusters de grãos bem acoplados. Devido a isso, as medidas de resistência nula devem estar em pontos abaixo da linha de irreversibilidade magnética. O objetivo deste trabalho é analisar as medidas de transporte elétrico e magnetização e correlacionar às linhas de resistência nula e as linhas de irreversibilidade magnética, em diferentes orientações de campo-corrente, para uma amostra com a adição de 30% da fase Y211 (Y2BaCuO5) e comparar os dados obtidos com uma amostra na qual foram adicionados 17% desta mesma fase.Postprint (published version

Cross-generational trans fat intake exacerbates UV radiation-induced damage in rat skin

AbstractWe evaluated the influence of dietary fats on ultraviolet radiation (UVR)-induced oxidative damage in skin of rats. Animals from two consecutive generations born of dams supplemented with fats during pregnancy and breastfeeding were maintained in the same supplementation: soybean-oil (SO, rich in n-6 FA, control group), fish-oil (FO, rich in n-3 FA) or hydrogenated-vegetable-fat (HVF, rich in TFA). At 90days of age, half the animals from the 2nd generation were exposed to UVR (0.25J/cm2) 3×/week for 12weeks. The FO group presented higher incorporation of n-3 FA in dorsal skin, while the HVF group incorporated TFA. Biochemical changes per se were observed in skin of the HVF group: greater generation of reactive oxygen species (ROS), lower mitochondrial integrity and increased Na+K+-ATPase activity. UVR exposure increased skin wrinkles scores and ROS generation and decreased mitochondrial integrity and reduced-glutathione levels in the HVF group. In FO, UVR exposure was associated with smaller skin thickness and reduced levels of protein–carbonyl, together with increased catalase activity and preserved Na+K+-ATPase function. In conclusion, while FO may be protective, trans fat may be harmful to skin health by making it more vulnerable to UVR injury and thus more prone to develop photoaging and skin cancer

Caracterización mecánica a escala picométrica de YBa1.75Sr0.25Cu3O7-d monocristalino mediante la técnica de autoflujo

Se implementa un método para indentar superficies rígidas a niveles nanométricos utilizando un microscopio de fuerzas atómicas (Atomic Force Microscopy-AFM), empleando el modo de espectroscopia de fuerzas (Force Spectroscopy-FS), el cual nos permite generar un movimiento vertical de la punta sin producir fuerzas laterales. Uno de los factores más críticos durante este estudio ha sido caracterizar la máxima fuerza aplicada por el AFM la cual no produce deformación remanente, esto se ha obtenido a partir del factor de sensitividad de la palanca del AFM, así como de la correcta determinación del radio de curvatura (r) de la punta antes y después de la indentación. A partir de las curvas de fuerzapenetración (F vs. he) obtenidas a 200 nN de carga aplicada, y utilizando un modelo de contacto Hertziano, se ha podido determinar el módulo de Young (E) del material cuando se encuentra sometido a un campo de deformación totalmente elástico.Postprint (published version

The origin of paramagnetic magnetization in field-cooled YBa2Cu3O7 films

Temperature dependences of the magnetic moment have been measured in YBa_2Cu_3O_{7-\delta} thin films over a wide magnetic field range (5 <= H <= 10^4 Oe). In these films a paramagnetic signal known as the paramagnetic Meissner effect has been observed. The experimental data in the films, which have strong pinning and high critical current densities (J_c ~ 2 \times 10^6 A/cm^2 at 77 K), are quantitatively shown to be highly consistent with the theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13559 (1995)]. This finding indicates that the origin of the paramagnetic effect is ultimately associated with nucleation and inhomogeneous spatial redistribution of magnetic vortices in a sample which is cooled down in a magnetic field. It is also shown that the distribution of vortices is extremely sensitive to the interplay of film properties and the real experimental conditions of the measurements.Comment: RevTex, 8 figure

From mesoscale to nanoscale mechanics in single-wall carbon nanotubes

The experimental work was carried out in collaboration with W. Wenseleers and S. Cambré at the University of Antwerp, Belgium. The computational results presented have been achieved in part using the Vienna Scientific Cluster (VSC). DJD is grateful for support from the Region Rhône-Alpes through the programme “Accueil-PRO 2014” and from the iMUST Labex programme “Mobility in 2015”. ACTD, TFTC, WC, MALM, SB, DM and ASM acknowledge support from the French Agence Nationale de la Recherche through contract ANR-11-NANO-025 “TRI-CO”. ACTD acknowledges postdoctoral grant from Brazilian Ministry of Education (CAPES)

Pressure-induced radial collapse in few-wall carbon nanotubes: A combined theoretical and experimental study

Brazilian authors acknowledge funding from CNPq (grant 307317/2010-2, INCT NanoBioSimes) and Central Analítica-UFC/CT-INFRA-FINEP/Pró-Equipamentos-CAPES/CNPq-SisNano-MCTI (grant 402284/2013-5). R. S. Alencar is also in debt to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior under the grant No. 99999.004227/2014-00 for financial support. Alexander Soldatov (University of Lulea, Sweden) is warmly acknowledged for discussions on the RBM Raman spectra interpretation at the collapse region