Digitization of the masters theses and Ph.D. dissertations of El Centro Interdisciplinario de Ciencias Marinas (CICMAR).

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Direct observation of melting in a 2-D superconducting vortex lattice

Topological defects such as dislocations and disclinations are predicted to determine the twodimensional (2-D) melting transition. In 2-D superconducting vortex lattices, macroscopic measurements evidence melting close to the transition to the normal state. However, the direct observation at the scale of individual vortices of the melting sequence has never been performed. Here we provide step by step imaging through scanning tunneling spectroscopy of a 2-D system of vortices up to the melting transition in a focused-ion-beam nanodeposited W-based superconducting thin film. We show directly the transition into an isotropic liquid below the superconducting critical temperature. Before that, we find a hexatic phase, characterized by the appearance of free dislocations, and a smectic-like phase, possibly originated through partial disclination unbinding. These results represent a significant step in the understanding of melting of 2-D systems, with impact across several research fields, such as liquid crystal molecules, or lipids in membranes.Comment: Submitted to Nature Physic

A reconfigurable FPGA-based architecture for modular nodes in wireless sensor networks

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. J. Portilla, T. Riesgo, and Á. de Castro, "A reconfigurable FPGA-based architecture for modular nodes in wireless sensor networks", 3rd Southern Conference on Programmable Logic, SPL 2007, Mar del Plata (Argentina), pp. 203 - 206A reconfigurable platform for sensor networks is presented. This platform has features that allow easy reuse of the node in several applications avoiding redesigning the system from scratch. The node includes an FPGA which is the core of the reconfiguration capabilities of the node. Several hardware interfaces for sensor standard protocols like I2C or PWM have been developed and implemented in the FPGA. Remote reconfiguration is an important feature and sensor networks can take advantage of it in order to improve the global performance

Uniqueness for the inverse fixed angle scattering problem

We present a uniqueness result in dimensions $2$ and $3$ for the inverse fixed angle scattering problem associated to the Schr\"odinger operator $-\Delta+q$, where $q$ is a small real valued potential with compact support in the Sobolev space $W^{\beta,2}$ with $\beta>0.$ This result improves the known result, due to Stefanov, in the sense that almost no regularity is required for the potential. The uniqueness result still holds in dimension $4$, but for more regular potentials in $W^{\beta,2}$ with $\beta>2/3$