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339 results on '"Barba-Ortega, J."'

101. Induced Anisotropy by the Inclusion of Defects of Variable $$T_\mathrm{c}$$ in a Superconducting Disk.

Author

González, J. D., Joya, Miryam R., and Barba-Ortega, J.

Subjects
SUPERCONDUCTORS, ANISOTROPY, CRYSTAL defects, MIXED state (Superconductors), FREE energy (Thermodynamics)
Abstract

Static and non-static properties of the superconducting vortex state in a splice of weak and strong superconducting regions were studied. We considered a superconducting disk with triangular and circular defects, which lead to the appearance of anisotropy in the sample. This anisotropy is included in the time-dependent Ginzburg-Landau equations through a varied $$T_\mathrm{c}$$ , which leads to distinct differences in the magnetization, supercurrent, vorticity, and free energy curves. Several unconventional vortex states were found, some comprising vortex clusters or exhibiting asymmetry, which are formed owing to the competing interactions of vortices with different Meissner currents that can be found in the sample due to anisotropy. [ABSTRACT FROM AUTHOR]

Published
2018
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143. Superconducting State in two band MgB2 simple Ceramic.

Author

Sjogreen-Blanco, C., Joya, Miryam R., and Barba-Ortega, J.

Subjects
MAGNESIUM diboride, SUPERCONDUCTORS, ENERGY bands, CERAMIC materials, CONDENSATION, LANDAU theory
Abstract

Many phenomena of current physical interest are directly related to the difference in the healing lengths of the band condensates, such as the non-monotonic interaction between vortices, being a possible explanation for highly debated unusual vortex configurations observed in a simple ceramic MgB2. Effects due to the difference in the spatial profiles of different band condensates can be accounted for within the full microscopic numerical treatment with an enormous computational effort. These difficulties have stimulated a search for a general Ginzburg-Landau formalism with a coexistence of two band condensates with different healing lengths. In this work, we derive the free-energy functional for the extended formalism and the corresponding expression for the current density; also, using the time dependent Ginzburg-Landau theory, we calculate the vortex state in a superconducting simple ceramic exposed to a homogeneous magnetic field. [ABSTRACT FROM AUTHOR]

Published
2014
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144. 2D Barrier in a Superconducting Niobium Square.

Author

Joya, Miryam R., Sardella, Edson, and Barba-ortega, J.

Subjects
NIOBIUM, SUPERCONDUCTORS, TWO-dimensional models, FLUX-line lattice, MAGNETIC fields
Abstract

The presence of barriers changes the vortex structure in superconducting Nb square in presence of a uniform applied magnetic field. The Cooper pair configurations in a mesoscopics superconducting square of Nb with a barrier are calculated within the nonlinear Ginzburg Landau equations. We predict the nucleation of multi-vortex states into the sample and a soft entry of the magnetic field inside and around into the barrier. A novel and non-conventional vortex configurations occurs at determined magnetic field. [ABSTRACT FROM AUTHOR]

Published
2014
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149. The effect of the preparation method of NbO oxide influences the performance of the photocatalytic activity.

Author

Raba, A., Barba-Ortega, J., and Joya, M.

Subjects
*NIOBIUM compounds, *PHOTOCATALYSIS, *RAMAN spectroscopy, *CRYSTALLIZATION, *X-ray diffraction, *CALCINATION (Heat treatment), *TRANSMISSION electron microscopy
Abstract

In this paper, we present the experimental results of the photocatalytic properties evaluation of the niobium pentoxide $$\text {Nb}_{2}\text {O}_{5}$$ semiconductor oxide and its performance in processes photoinduced of Rhodamine B and Atrazine degradation, under visible light irradiation. The sample $$\text {Nb}_{2}\text {O}_{5}$$ photocatalysts were synthesized via pechini method. The nanoparticles structure of the samples was studied by X-ray diffraction, Brunauer-Emmett-Teller, Raman spectroscopy, UV-Vis and scanning and transmission electron microscopy. The increase in the calcination temperature during the synthesis resulted in enhanced crystallization, but decreased mesoporosity of the samples. [ABSTRACT FROM AUTHOR]

Published
2015
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150. Anharmonicity Study of Semiconductors and Metallic Nanotubes by Inelastic Spectroscopy.

Author

Joya, M. R., Gonzalez, J. D., and Barba-Ortega, J.

Subjects
CARBON nanotubes, SEMICONDUCTORS, SPECTRUM analysis, SCANNING electron microscopy, TEMPERATURE effect, THERMAL expansion, DECAY rates (Radioactivity)
Abstract

In this work, we have studied the temperature dependence from 83 to 1300 K in the change of position of Raman modes in single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The effects of synthesis on the quality and quantity of carbon nanotubes (CNTs) were analyzed with high-resolution scanning electron microscopy (SEM) and micro-Raman spectroscopy. The behavior of the modes G for CNTs with the application of temperatures was studied, and we find that the (G)-peak position shifts to low frequency with increasing temperature. When reducing the ambient temperature to 83 K, there is displacement of the G-mode but not many changes were observed in the other modes. At high temperatures, there are changes in the position and intensity of the different modes. This behavior cannot be understood by purely thermal effects, it may also be due to uniaxial tension. The analysis of the experimental data showed the temperature dependencies of frequencies (w) and linewidths (FWHM). As a result of FWHM and the thermal expansion theoretical data, we calculated the Grüneisen parameter and the phonon decay rate, which are well described, taking into account the contributions from thermal expansion and anharmonicity. [ABSTRACT FROM AUTHOR]

Published
2015
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