Study of the threshold line between macroscopic and bulk behaviors for homogeneous type II superconductors

In this work we solved the time dependent Ginzburg-Landau equations to simulate homogeneous superconducting samples with square geometry for several lateral sizes. As a result of such simulations we notice that in the Meissner state, when the vortices do not penetrate the superconductor, the response of small samples are not coincident with that expected for the bulk ones, i.e., $4\pi M=-H$. Thus, we focused our analyzes on the way which the $M(H)$ curves approximate from the characteristic curve of bulk superconductors. With such study, we built a diagram of the size of the sample as a function of the temperature which indicates a threshold line between macroscopic and bulk behaviors.Comment: 6 pages, 5 figure

Vortex-antivortex annihilation in mesoscopic superconductors with a central pinning center

In this work we solved the time-dependent Ginzburg-Landau equations, TDGL, to simulate two superconducting systems with different lateral sizes and with an antidot inserted in the center. Then, by cycling the external magnetic field, the creation and annihilation dynamics of a vortex-antivortex pair was studied as well as the range of temperatures for which such processes could occur. We verified that in the annihilation process both vortex and antivortex acquire an elongated format while an accelerated motion takes place.Comment: 4 pages, 5 figures, work presented in Vortex VII

Vortex-chain phases in layered superconductors

Layered superconductors in tilted magnetic field have a very rich spectrum of vortex lattice configurations. In the presence of in-plane magnetic field, a small c-axis field penetrates in the form of isolated vortex chains. The structure of a single chain is mainly determined by the ratio of the London [$\lambda$] and Josephson [$\lambda_{J}$] lengths, $\alpha= \lambda/\lambda_{J}$. At large $\alpha$ the chain is composed of tilted vortices [tilted chains] and at small $\alpha$ it consists of a crossing array of Josephson vortices and pancake stacks [crossing chains]. We studied the chain structures at intermediate $\alpha$'s and found two types of behavior. (I) In the range $0.4 < \alpha < 0.5$ a c-axis field first penetrates in the form of pancake-stack chains located on Josephson vortices. Due to attractive coupling between deformed stacks, their density jumps from zero to a finite value. With further increase of the c-axis field the chain structure smoothly evolves into modulated tilted vortices and then transforms via a second-order phase transition, into the tilted straight vortices. (II) In the range $0.5 < \alpha < 0.65$ a c-axis field first penetrates in the form of kinks creating kinked tilted vortices. With increasing the c-axis field this structure is replaced via a first-order phase transition by the strongly deformed crossing chain. This transition is accompanied by a large jump of pancake density. Further evolution of the chain structure is similar to the higher anisotropy scenario: it smoothly transforms back into the tilted straight vortices.Comment: Accepted to Phys. Rev. B, 20 pages 12 figures, animation of chain structure is available in http://mti.msd.anl.gov/movies/Chains/Nl8al06Im.gif (gif, 441 KB

Instabilities in the Flux Line Lattice of Anisotropic Superconductors

The stability of the flux line lattice has been investigated within anisotropic London theory. This is the first full-scale investigation of instabilities in the `chain' state. It has been found that the lattice is stable at large fields, but that instabilities occur as the field is reduced. The field at which these instabilities first arise, $b^*(\epsilon,\theta)$, depends on the anisotropy $\epsilon$ and the angle $\theta$ at which the lattice is tilted away from the $c$-axis. These instabilities initially occur at wavevector $k^*(\epsilon,\theta)$, and the component of $k^*$ along the average direction of the flux lines, $k_z$, is always finite. As the instability occurs at finite $k_z$ the dependence of the cutoff on $k_z$ is important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The instabilities only occur for values of the anisotropy $\epsilon$ appropriate to a material like BSCCO, and not for anisotropies more appropriate to YBCO. The lower critical field $H_{c_1}(\phi)$ is calculated as a function of the angle $\phi$ at which the applied field is tilted away from the crystal axis. The presence of kinks in $H_{c_1}(\phi)$ is seen to be related to instabilities in the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic instabilities. Calculation of the lower critical field is included, and the presence of kinks in $H_{c_1}$ is seen to be related to the elastic instabilities. 29 pages including 16 figures, LaTeX with epsf styl

A high burnup model developed for the DIONISIO code

A group of subroutines, designed to extend the application range of the fuel performance code DIONISIO to high burn up, has recently been included in the code. The new calculation tools, which are tuned for UO2 fuels in LWR conditions, predict the radial distribution of power density, burnup, and concentration of diverse nuclides within the pellet. The balance equations of all the isotopes involved in the fission process are solved in a simplified manner, and the one-group effective cross sections of all of them are obtained as functions of the radial position in the pellet, burnup, and enrichment in 235U. In this work, the subroutines are described and the results of the simulations performed with DIONISIO are presented. The good agreement with the data provided in the FUMEX II/III NEA data bank can be easily recognized.Fil: Soba, Alejandro. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Denis, A.. Comisión Nacional de Energía Atómica; ArgentinaFil: Romero, L.. Comisión Nacional de Energía Atómica; ArgentinaFil: Villarino, E.. No especifíca;Fil: Sardella, F.. No especifíca

The Monumental UNESCO Site of Panamá Viejo: Investigation of the Masonry Mortars

The presented study illustrates the characterisation of several artificial materials (bedding, joint mortars, and plasters) belonging to the masonries of the UNESCO site of Panamá Viejo, located in Panama City (Panama). This monumental site represents the first Spanish settlement on the Pacific Coast, founded 500 years ago, in 1519. Through mineralogical and petrographic analyses of the collected samples, as stereomicroscope and polarized light microscopy (PLM) observations of bulk and thin sections, respectively, environmental scanning electron microscopy and micro-chemical investigations (ESEM-EDX) and X-Ray Powder diffraction (XRPD) analysis, it was possible to identify the composition of the materials utilized for the production of mortars and plasters, in addition to the determination of their state of conservation. Therefore, this work represents a substantial step for the preservation of the Panamá Viejo site, in order to support the selection of the most suitable restoration products, such as consolidants, protectives, etc., but also for choosing the most compatible materials for possible replacements/integrations in the masonries

Plasma Modification of PCL Porous Scaffolds Fabricated by Solvent Casting/Particulate Leaching for Tissue Engineering

This study points out how the plasma modification of PCL porous scaffolds, produced by Solvent Casting/Particulate Leaching, may enhance their biocompatibility. A C2H4/N2 plasma deposition followed by a H2 plasma treatment was used to increase the hydrophilicity of the whole scaffold to support osteoblast cell proliferation, both outside and inside the scaffold. A better cell growth was obtained on plasma modified scaffolds.JRC.I.4-Nanobioscience

Characterization of hydraulic mortars from archaeological complexes in Petra

In the sixth century B.C. Petra was conquered by the Nabataeans, who built an elaborated water system and turned a desert city into an artificial oasis and a prosperous centre controlling the main commercial routes of the region (100 B.C. - 100 A.D.). In 2007, it was added to UNESCO's prestigious list of World Heritage Sites, as one of the seven wonders of the world. The aim of this research is to characterize samples of mortars lining cisterns, reservoirs and pipelines collected from the archeological site of Petra, focusing in general on the identification of the possible raw materials employed and in particular on those components conferring hydraulicity. Specifically the specimens were sampled from different structures of the Great Temple (cistern and pipelines) and of the Garden and Pool Complex (cisterns and reservoir floor). A mineralogical and petrographic characterization was carried out by polarized light microscopy (PLM) observations to identify the texture and to highlight the hydraulic reaction areas, which underwent subsequently to a more detailed morphological and elemental analysis by Scanning Electron Microscopy (SEM-EDX). X-Ray Powder Diffraction analyses (XRPD) were also performed to complete the petrographic characterization, while Thermal Analyses (DTA-TGA) were carried out to classify the level of hydraulicity of each sample. The data obtained allowed us to achieve for the first time a mineralogical and petrographic characterization of the lining hydraulic mortars present in the two archaeological complexes under study and to provide preliminary hypotheses on the provenance of the raw materials employed for their production