Browsing by Issue Date, starting with "2011-08"
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- Visualizing fractional control system approximations by means of multidimensional scalingPublication . Tenreiro Machado, J. A.This paper addresses the use of multidimensional scaling in the evaluation of fractional system approximations. Algorithms are analysed based on the time response of the closed loop system under the action of a reference step input signal. Two alternative performance indices, based on the time and frequency domains, are tested. The numerical experiments demonstrate the feasibility of the proposed methodology.
- Online trigger processing for a small-animal RPC-PET cameraPublication . Clemêncio, Filomena M. C.; Loureiro, Custódio F. M.; Landeck, JorgeA complex task for positron emission tomography (PET) cameras is the design of an appropriate coincidence-detec tion trigger system as it usually encompasses coincidences in a large number of channels and requires tight time specifications. Those requirements are even greater for a resistive plate chamber (RPC)-based detector technology since the time window specifica tion is quite small (in the order of a few hundred picoseconds) and the number of coincidence-channels can be quite large. Previous work showed that the time resolution for gamma photon pairs of a detector based on resistive plate chamber technology is under 300 ps full width at half maximum. This allows for a very tight time window for coincidence detection, with the corresponding benefits in reducing the number of random coincidences observed and, hence, the overall noise on the acquired image. In this paper, we first show experimental results of a coincidence-detection algo rithm implemented inside a Xilinx Virtex-5 field-programmable gate array for a small-animal RPC-PET camera being built.
- Visualizing non-linear control system performance by means of multidimensional scalingPublication . Tenreiro Machado, J. A.This paper addresses the use of multidimensional scaling in the evaluation of control system performance. Both linear and non-linear systems are analysed based on the closed loop time response under the action of a reference step input signal. Two alternative performance indices, based on the time and frequency domains, are tested. The numerical experiments demonstrate the feasibility of the proposed methodology and motivate its extension for other performance measures and a broader classes of non-linearities.
- Fractional variable structure controlPublication . Tenreiro Machado, J. A.This paper studies fractional order variable structure control algorithms. For that purpose the fractional order of the sliding mode is varied and its effect upon the system performance is evaluated. The test bed is constituted by a simple mechanical manipulator. Both the system response and the control effort are analysed. The results show that the fractional order provides an extra method for adjusting the closed loop system response.