Browsing by Issue Date, starting with "2015-10-01"
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- Optical processor based on a-SiC technology for spectral data error controlPublication . Vieira, Manuel; Vieira, Manuela; Vaz da Silva, V; Louro, PaulaThe SiC optical processor for error detection and correction is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Data shows that the background act as selector that pick one or more states by splitting portions of the input multi optical signals across the front and back photodiodes. Boolean operations such as exclusive OR (EXOR) and three bit addition are demonstrated optically with a combination of such switching devices, showing that when one or all of the inputs are present the output will be amplified, the system will behave as an XOR gate representing the SUM. When two or three inputs are on, the system acts as AND gate indicating the present of the CARRY bit. Additional parity logic operations are performed by use of the four incoming pulsed communication channels that are transmitted and checked for errors together. As a simple example of this approach, we describe an all optical processor for error detection and correction and then, provide an experimental demonstration of this fault tolerant reversible system, in emerging nanotechnology.
- Light memory function in a double pin SiC devicePublication . Vaz da Silva, V; Vieira, Manuela; Vieira, Manuel; Louro, Paula; Barata, ManuelA double pi'npin heterostructure based on amorphous SiC has a non linear spectral gain which is a function of the signal wavelength that impinges on its front or back surface. An impulse of a configurable length and amplitude is applied to a 390 nm LED which illuminates one of the sensor surfaces, followed by a time period without any illumination after which an input signal with a different wavelength is impinged upon the front surface. Results show that the intensity and duration of the impulse illumination of the surfaces influences the sensor's response with different output for the same input signal. This paper studies this effect and proposes an application as a short term light memory. (C) 2015 Elsevier B.V. All rights reserved.
- Música como comunicação e ritualPublication . Subtil, Filipa Mónica de Brito GonçalvesAs palavras que irei proferir exploram a relação que considero simbiótica entre comunicação e música. Uma primeira exploração de tal relação sustenta que, num sentido amplo, a música é evidentemente uma das expressões da comunicação humana. Ainda numa acepção ampla, podemos também afirmar que a comunicação humana é instituinte e constituinte das sociedades humanas, isto porque a comunicação humana é o meio através do qual, nas suas muito diversas expressões, é gerada a cultura no sentido antropológico do termo. Compreendendo aqui a cultura humana, as formas de sentido, o mundo dos símbolos, as artes, os saberes, a ciência e a religião. É verdade que a sociedade não é só cultura, pelo menos no sentido da cultura imaterial, simbólica, porque, para além desta, há que considerar também as corporizações em termos materiais, as tecnologias, os objectos, as instituições e as relações sociais. Mas é a cultura, gerada pela comunicação, que constitui o ambiente por excelência especificamente humano, a realidade humana suis generis, e é pois neste campo da comunicação e da cultura que a música se situa plenamente.
- Spectral invariants of periodic nonautonomous discrete dynamical systemsPublication . Alves, João Ferreira; Málek, Michal; Silva, LuísFor an interval map, the poles of the Artin-Mazur zeta function provide topological invariants which are closely connected to topological entropy. It is known that for a time-periodic nonautonomous dynamical system F with period p, the p-th power [zeta(F) (z)](p) of its zeta function is meromorphic in the unit disk. Unlike in the autonomous case, where the zeta function zeta(f)(z) only has poles in the unit disk, in the p-periodic nonautonomous case [zeta(F)(z)](p) may have zeros. In this paper we introduce the concept of spectral invariants of p-periodic nonautonomous discrete dynamical systems and study the role played by the zeros of [zeta(F)(z)](p) in this context. As we will see, these zeros play an important role in the spectral classification of these systems.