Unilateral Fin Line Directional Coupler

Photonic band gap (PBG) crystals have been used as a perfectly reflecting substrate for many millimeter wave applications. In this work the fin line directional coupler with substrate PBG was analyzed using the TTL - Transverse Transmission Line - method. Compared to other full wave methods the TTL is an efficient tool to determine the coupler characteristics, making possible a significant algebraic simplification of the equations involved in the process. In order to analyze this structure the effective dielectric constant, the attenuation constant and the coupling were determined. The results obtained for this application and the conclusions are presented. This work was partially financed by CNPQ.     

High-Q-preserving coupling between a spiral and a semicircle micro-cavity

We present an efficient design for direct coupling between a spiral-shaped and a semicircle-shaped microcavity (micro-cavity) as an alternative to traditional evanescent wave coupling for planar integrated photonic technology. We observe the preservation of the high Q-value of the spiral oscillator when coupled to a semicircle under current injection using an AlGaAs single-quantum-well heterostructure. With slight alterations to the directly coupled micro-cavity configuration, such as coupling shape and overlap distance, the number of observed modes and output intensity are changed. AlGaAs and InGaN spiral-shaped microcavities have unidirectional emission normal to the spiral notch.     

Bound-states and polarized charged zero modes in three-dimensional topological insulators induced by a magnetic vortex

By coating a three-dimensional topological insulator (TI) with a ferromagnetic filmsupporting an in-plane magnetic vortex, one breaks the time-reversal symmetry (TRS)without generating a mass gap. It rather yields electronic states bound to the vortexcenter which have different probabilities associated with each spin mode. In addition, itsassociate current (around the vortex center) is partially polarized with an energy gapseparating the most excited bound state from the scattered ones. Charged zero-modes alsoappear as fully polarized modes localized near the vortex center. From the magnetic pointof view, the observation of such a special current in a TI-magnet sandwich comes about asan alternative technique for detecting magnetic vortices in magnetic thin films.     

Ba0.8Sr0.2TiO3 films crystallized on glass and platinized substrates by laser-assisted annealing at room temperature

In this work, Ba_0.8Sr_0.2TiO₃ (BST) films were grown by pulse laser ablation on bare glass and platinized substrates. The crystalline phase was obtained with the help of laser-assisted annealing (LAA) at room temperature, in air environment. By adjusting LAA conditions, like frequency of the laser and number of shots, we were able to grow crack-free BST thin films with pure perovskite phase on bare glass and platinized substrates. The crystalline layer was found to be the same irrespective of the substrate used, c.a. 250 nm thick. The electric characteristics of the amorphous and LAA crystalline BST films deposited on platinized substrate were further studied and analyzed. While in amorphous films it was found that the oxygen defects are responsible for conduction, in LAA films the amorphous/crystalline interface layer plays an important role in current leakage.     

Lentivirus-mediated transgene delivery to the hippocampus reveals sub-field specific differences in expression

Background  

In the adult hippocampus, the granule cell layer of the dentate gyrus is a heterogeneous structure formed by neurons of different ages, morphologies and electrophysiological properties. Retroviral vectors have been extensively used to transduce cells of the granule cell layer and study their inherent properties in an intact brain environment. In addition, lentivirus-based vectors have been used to deliver transgenes to replicative and non-replicative cells as well, such as post mitotic neurons of the CNS. However, only few studies have been dedicated to address the applicability of these widespread used vectors to hippocampal cells in vivo. Therefore, the aim of this study was to extensively characterize the cell types that are effectively transduced in vivo by VSVg-pseudotyped lentivirus-based vectors in the hippocampus dentate gyrus.