1,363 research outputs found
Geometrical Description of Quantum Mechanics - Transformations and Dynamics
In this paper we review a proposed geometrical formulation of quantum
mechanics. We argue that this geometrization makes available mathematical
methods from classical mechanics to the quantum frame work. We apply this
formulation to the study of separability and entanglement for states of
composite quantum systems.Comment: 22 pages, to be published in Physica Script
Modification of magnetic and transport properties of manganite layers in Au/La_0.67Sr_0.33MnO_3/SrTiO_3 interfaces
The effect of gold capping on magnetic and transport properties of optimally
doped manganite thin films is studied. An extraordinary suppression of
conductivity and magnetic properties occurs in epitaxial (001)
La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of
Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity
increases by four orders of magnitude while the Curie temperature decreases by
180 K. Zero-field 55Mn nuclear magnetic resonance reveals a significant
reduction of ferromagnetic double-exchange mechanism in manganite films upon
the gold capping. We find evidence for the formation of a 1.9-nm thick magnetic
"dead-layer" at the Au/LSMO interface, associated with the creation of
interfacial non double-exchange insulating phases.Comment: 4 figure
Cu_{2}O as nonmagnetic semiconductor for spin transport in crystalline oxide electronics
We probe spin transport in Cu_{2}O by measuring spin valve effect in
La_{0.7}Sr_{0.3}MnO_{3}/Cu_{2}O/Co and
La_{0.7}Sr_{0.3}MnO_{3}/Cu_{2}O/La_{0.7}Sr_{0.3}MnO_{3} epitaxial
heterostructures. In La_{0.7}Sr_{0.3}MnO_{3}/Cu_{2}O/Co systems we find that a
fraction of out-of-equilibrium spin polarized carrier actually travel across
the Cu_{2}O layer up to distances of almost 100 nm at low temperature. The
corresponding spin diffusion length dspin is estimated around 40 nm.
Furthermore, we find that the insertion of a SrTiO_{3} tunneling barrier does
not improve spin injection, likely due to the matching of resistances at the
interfaces. Our result on dspin may be likely improved, both in terms of
Cu_{2}O crystalline quality and sub-micrometric morphology and in terms of
device geometry, indicating that Cu_{2}O is a potential material for efficient
spin transport in devices based on crystalline oxides.Comment: 15 pages, 10 figure
Using photo-elicitation to explore social representations of community multimedia centers in Mozambique.
Ten Mozambican Community Multimedia Centers (CMCs) were investigated by analyzing Social Representations of users and staff members. Photo-elicitation, an underexplored methodological approach in the domain of Information and Communication Technologies for Development (ICT4D), was employed to conduct the study, and a three-step qualitative content analysis was performed on both visual and textual data. Results tend to confirm and build upon outcomes from the existing literature on Public Access Venues (PAVs). Local communities value these centers because they bring social recognition to people working or learning there. The venues are associated with a symbolism that extends from the social recognition of the individual to the development and social inclusion of the whole community, which, because of the presence of the venue, does not feel left behind. In this vein, the study also shows that the importance of CMCs is often not related to the newest technology available, but to the technology that reaches the most of the community. The study also highlights neglected dimensions of CMCs, such as the importance of the exterior appearance of the venue, and the perception of a switch in their nature from static centers funded by third parties towards more entrepreneurial-driven ones. The presented research also contributes to the ICT4D field by proposing a promising research protocol, which is able to elicit representations otherwise difficult to obtain
Exploring the meanings of community multimedia centers in Mozambique : a social representations perspective
This article presents extensive research conducted in Mozambique that aims to deeply understand how different social groups understand community multimedia centers (CMCs), which are structures combining a community radio and a telecenter. The social representations theory was adopted to interpret narratives of 231 interviewees from 10 Mozambican provinces. Interviewees included representatives of initiating agencies, local staff members, CMC users (both the radio and telecenter components), users of only the community radio, and community members not using the CMCs. Following the analysis of transcribed interviews, six main clusters were identified, each of them shedding light on a specific understanding of a CMC. These are discussed according to a set of sociodemographic variables. This study suggests that the social representations theory is a valuable framework to provide an integrated view of ICT4D interventions by giving a voice to local perspectives without overlooking the initiating agencies’ expectations
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Exploring the meanings of community multimedia centers in Mozambique: a social representation perspective
This article presents extensive research conducted in Mozambique that aims to deeply understand how different social groups understand community multimedia centers (CMCs), which are structures combining a community radio and a telecenter. The social representations theory was adopted to interpret narratives of 231 interviewees from 10 Mozambican provinces. Interviewees included representatives of initiating agencies, local staff members, CMC users (both the radio and telecenter components), users of only the community radio, and community members not using the CMCs. Following the analysis of transcribed interviews, six main clusters were identified, each of them shedding light on a specific understanding of a CMC. These are discussed according to a set of sociodemographic variables. This study suggests that the social representations theory is a valuable framework to provide an integrated view of ICT4D interventions by giving a voice to local perspectives without overlooking the initiating agencies' expectations
Blind signal separation using steepest descent method
A method that significantly improves the convergence rate of the gradient-based blind signal separation (BSS) algorithm for convolutive mixtures is proposed. The proposed approach is based on the steepest descent algorithm suitable for constrained BSS problems, where the constraints are included to ease the permutation effects associated with the convolutive mixtures. In addition, the method is realized using a modified golden search method plus parabolic interpolation, and this allows the optimum step size to be determined with only a few calculations of the cost function. Evaluation of the proposed procedure in simulated environments and in a real room environment shows that the proposed method results in significantly faster convergence for the BSS when compared with a fixed step-size gradient-based algorithm. In addition, for blind signal extraction where only a main speech source is desired, a combined scheme consisting of the proposed BSS and a postprocessor, such as an adaptive noise canceller, offers impressive noise suppression levels while maintaining low-target signal distortion level
Nanoscale Analysis by EFTEM and FIB-Tomography for Optimization of Thin-Film Silicon Solar Cells
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 - August 5, 201
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