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Salem-Sugui Jr. S.,Federal University of Rio de Janeiro | Alvarenga A.D.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | Mosqueira J.,University of Santiago de Compostela | Dancausa J.D.,University of Santiago de Compostela | And 4 more authors.
Superconductor Science and Technology | Year: 2012

We report on magnetization measurements performed on a single crystal of Bi 2+xSr 2xCuO 6+δ with T c ≈ 7 K for H ∥ c-axis. The isofield M(T) curves show a large reversible region, with a pronounced rounding effect as M approaches zero which prevents the determination of T c(H). Deviations from the linear behavior of magnetization near T c(H) are studied through the asymptotic behavior of √-M(T) ∝ (T-T a) m, where m is an exponent and T a an apparent temperature transition. Values of m deviate from the expected mean field value, 1/2, suggesting the importance of phase fluctuations. Resulting values of T a, interpreted as the onset of phase correlations, decrease as field increases, showing an upward curvature. Values of T c(H) are obtained through a two-dimensional critical scaling analysis obeyed by many M(T) curves. The resulting phase diagrams do not show upward curvature and lie below the T a(H) line. The value of H c2(0) estimated from the initial slope dH c2/dT is twice the value suggested by the phase diagram. Amplitude fluctuations above T a(H) are explained in terms of a Ginzburg-Landau approach extended to high reduced temperatures and magnetic fields by the introduction of a total-energy cutoff in the fluctuation spectrum. © 2012 IOP Publishing Ltd.


Rey R.I.,University of Santiago de Compostela | Ramos-Alvarez A.,University of Santiago de Compostela | Carballeira C.,University of Santiago de Compostela | Mosqueira J.,University of Santiago de Compostela | And 5 more authors.
Superconductor Science and Technology | Year: 2014

The superconducting fluctuations well inside the normal state of Fe-based superconductors were experimentally studied through the in-plane paraconductivity in several high-quality, optimally doped BaFe 2-xNixAs2 crystals. These measurements were performed in magnetic fields with amplitudes up to 14 T, and different orientations relative to the c-axis of the crystals (, 53, and 90). The results allowed a stringent check of the applicability of a recently proposed Ginzburg-Landau approach for the fluctuating electrical conductivity of three-dimensional (3D) anisotropic materials in the presence of finite applied magnetic fields. © 2014 IOP Publishing Ltd.


Rey R.I.,University of Santiago de Compostela | Ramos-Alvarez A.,University of Santiago de Compostela | Mosqueira J.,University of Santiago de Compostela | Salem-Sugui Jr S.,Federal University of Rio de Janeiro | And 5 more authors.
Superconductor Science and Technology | Year: 2014

The temperature dependence of the in-plane magnetic penetration depth λab of Ba(Fe1-xNix)2As 2 single crystals is determined directly from the shielding magnetic susceptibility, measured in the Meissner region with the field parallel to the ab layers. The doping levels studied cover the underdoped, optimally doped and overdoped regimes. At temperatures below 0.5Tc a well-defined power-law behavior λab (T) - λab (0) = ATn (with n ≈ 2.5) is observed. At lower temperatures (T < 0.3Tc) the data are still consistent with n = 2 and , as predicted by the strong pair-breaking scenario proposed by Gordon et al (2010 Phys. Rev. B 81, 180501(R)). The temperature dependence of the superfluid density presents a marked positive curvature just below Tc, which is a sign of two-gap superconductivity. The analysis of ρs (T) in terms of a two-gap model allowed estimation of parameters like the in-band and inter-band couplings, the relative weight of each band, and their dependence on the doping level. A comparison with ρs (T) data obtained by using other techniques in compounds with a similar composition is also presented. © 2014 IOP Publishing Ltd.


Mosqueira J.,University of Santiago de Compostela | Dancausa J.D.,University of Santiago de Compostela | Carballeira C.,University of Santiago de Compostela | Salem-Sugui S.,Federal University of Rio de Janeiro | And 6 more authors.
Journal of Superconductivity and Novel Magnetism | Year: 2013

The magnetization around the superconducting transition was recently measured in a high-quality Ba1-x Kx Fe2As 2 single crystal with magnetic fields applied along and transverse to the crystal Fe-layers [J. Mosqueira et al. in Phys. Rev. B 83:094519, 2011]. Here we extend this study to the finite-field (or Prange) regime, in which the magnetic susceptibility is expected to be strongly dependent on the applied magnetic field. These measurements are analyzed in the framework of the three-dimensional anisotropic Ginzburg-Landau (3D-aGL) approach generalized to the short-wavelength regime through the introduction of a total-energy cutoff in the fluctuation spectrum. The results further confirm the adequacy of GL approaches to describe the fluctuation effects close to the superconducting transition of these materials. © 2012 Springer Science+Business Media New York.


Rey R.I.,University of Santiago de Compostela | Carballeira C.,University of Santiago de Compostela | Mosqueira J.,University of Santiago de Compostela | Salem-Sugui S.,Federal University of Rio de Janeiro | And 5 more authors.
Superconductor Science and Technology | Year: 2013

The superconducting fluctuations well inside the normal state of Fe-based superconductors were studied through measurements of the in-plane paraconductivity and magnetoconductivity in high quality BaFe 2-xNixAs2 crystals with doping levels from the optimal level (x = 0.10) up to highly overdoped (x = 0.20). These measurements, performed in magnetic fields up to 9 T perpendicular to the ab (Fe) layers, allowed a reliable check of the applicability to iron-based superconductors of Ginzburg-Landau approaches for 3D anisotropic compounds, even at high reduced temperatures and magnetic fields. Our results also allowed us to gain valuable insight into the dependence on the doping level of some central superconducting parameters (coherence lengths and anisotropy factor). © 2013 IOP Publishing Ltd.


Salem-Sugui Jr. S.,Federal University of Rio de Janeiro | Alvarenga A.D.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | Rey R.I.,University of Santiago de Compostela | Mosqueira J.,University of Santiago de Compostela | And 2 more authors.
Superconductor Science and Technology | Year: 2013

We study fluctuation conductivity in a single crystal of BaFe 1.9Ni0.1As2 superconductor (Tc = 20 K) as a function of temperature and applied magnetic field. Magneto-conductivity curves, Δσ versus T, were analyzed in terms of -1/ (dln(Δσ)/dT) versus T plots, which allow us to study different fluctuation regimes and to estimate exponent values and temperature widths of each regime. The analysis of magneto-conductivity curves evidences the existence of only two fluctuation regimes, a possible critical one (of glass-like type) going from the irreversible temperature to above Tc(H), followed by Aslamazov-Larkin fluctuations in the Gaussian regime. © 2013 IOP Publishing Ltd.


Neitzke-Montinelli V.,Federal University of Rio de Janeiro | Urmenyi T.P.,Federal University of Rio de Janeiro | Rondinelli E.,Federal University of Rio de Janeiro | Rondinelli E.,Instituto Nacional para Pesquisa Translacional em Saude e Ambiente na Regiao Amazonica | And 5 more authors.
American Journal of Human Biology | Year: 2012

Objective: We describe an association of two SNPs, rs3212345:C>T and rs3212346:G>A, located approximately 2.5 kb upstream of the melanocortin-1 receptor (MC1R) translation initiation codon, with pigmentation phenotype variation in a Southeast Brazilian miscegenated population. Methods: One hundred thirty-eight genetically unrelated subjects, with multicolor phenotype, were selected from the southeast region of Brazil. Skin, hair and eye color, and tanning ability were rated. Genotypes for each SNP (rs3212345:C>T and rs3212346:G>A) were determined. A logistic regression analysis was performed with the additive model to determine which of the polymorphisms contributed to a specific phenotype. Results: We found that the rs3212345:C>T is associated with light skin, red hair, and poor tanning ability, while the rs3212346:G>A is associated with dark skin, black hair, and strong tanning ability. The presence of rs3212345-C and rs3212346-A alleles in human, chimpanzee, gorilla, orangutan, and marmoset genomes suggests that they are the ancestral alleles. Conclusion: These data suggest that the rs3212345-T and rs3212346-G alleles may have contributed to lighter pigmentation phenotypes in modern humans. Genotyping for these SNPs may prove useful to the fields of molecular anthropology and forensic genetics. © 2012 Wiley Periodicals, Inc.


Chagas L.H.,Federal University of Juiz de fora | Chagas L.H.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | De Carvalho G.S.G.,Federal University of Juiz de fora | Do Carmo W.R.,Federal University of Juiz de fora | And 6 more authors.
Materials Research Bulletin | Year: 2015

Layered double hydroxides (LDHs) with Mg/Co/Al and Ni/Co/Al were synthesized for the first time by the urea hydrolysis method. The experimental conditions promoted aluminum rich and crystalline materials. The formation of LDHs was investigated by powder X-ray diffraction (XRD), chemical analysis, solid state nuclear magnetic resonance with magic angle spinning (27Al-MAS-NMR), simultaneous thermogravimetric/differential thermal analysis (TGA/DTA), FTIR spectroscopy, scanning electron microscopy (SEM), and N2 adsorption-desorption experiments. A single phase corresponding to LDH could be obtained in all the investigated compositions. Thermal calcination of these LDHs at 500 °C resulted in the formation of solid solutions in which Al3+ was dissolved. All the calcined materials have rock-salt like structures and high surface areas. © 2014 Elsevier Ltd. All rights reserved.


Guerra C.R.,Federal University of Rio de Janeiro | Seabra S.H.,Centro Universitario Estadual da Zona Oeste | De Souza W.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | De Souza W.,Federal University of Rio de Janeiro | Rozental S.,Federal University of Rio de Janeiro
PLoS ONE | Year: 2014

Cryptococcosis by the encapsulated yeast Cryptococcus neoformans affects mostly immunocompromised individuals and is a frequent neurological complication in AIDS patients. Recent studies support the idea that intracellular survival of Cryptococcus yeast cells is important for the pathogenesis of cryptococcosis. However, the initial steps of Cryptococcus internalization by host cells remain poorly understood. Here, we investigate the mechanism of Cryptococcus neoformans phagocytosis by peritoneal macrophages using confocal and electron microscopy techniques, as well as flow cytometry quantification, evaluating the importance of fungal capsule production and of host cell cytoskeletal elements for fungal phagocytosis. Electron microscopy analyses revealed that capsular and acapsular strains of C. neoformans are internalized by macrophages via both 'zipper' (receptor-mediated) and 'trigger' (membrane ruffle-dependent) phagocytosis mechanisms. Actin filaments surrounded phagosomes of capsular and acapsular yeasts, and the actin depolymerizing drugs cytochalasin D and latrunculin B inhibited yeast internalization and actin recruitment to the phagosome area. In contrast, nocodazole and paclitaxel, inhibitors of microtubule dynamics decreased internalization but did not prevent actin recruitment to the site of phagocytosis. Our results show that different uptake mechanisms, dependent on both actin and tubulin dynamics occur during yeast internalization by macrophages, and that capsule production does not affect the mode of Cryptococcus uptake by host cells. © 2014 Guerra et al.


Cacais F.L.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | Loayza V.M.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | Beatrici A.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | Quintao D.L.,Instituto Nacional Of Metrologia Qualidade E Tecnologia | Rebelo A.S.,Instituto Nacional Of Metrologia Qualidade E Tecnologia
CPEM Digest (Conference on Precision Electromagnetic Measurements) | Year: 2014

This paper describes the procedure to validate the uncertainty calculation of the method for traceability for susceptibility measurements provided by the BIPM Susceptometer. © 2014 IEEE.

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