Browsing by Author "Ramalho, M."
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- 2D PCA-Based localization for mobile robots in unstructured environmentsPublication . Carreira, Fernando; Christo, C.; Valerio, D.; Ramalho, M.; Cardeira, C.; Calado, João Manuel Ferreira; Oliveira, P.In this paper a new PCA-based positioning sensor and localization system for mobile robots to operate in unstructured environments (e. g. industry, services, domestic ...) is proposed and experimentally validated. The inexpensive positioning system resorts to principal component analysis (PCA) of images acquired by a video camera installed onboard, looking upwards to the ceiling. This solution has the advantage of avoiding the need of selecting and extracting features. The principal components of the acquired images are compared with previously registered images, stored in a reduced onboard image database, and the position measured is fused with odometry data. The optimal estimates of position and slippage are provided by Kalman filters, with global stable error dynamics. The experimental validation reported in this work focuses on the results of a set of experiments carried out in a real environment, where the robot travels along a lawn-mower trajectory. A small position error estimate with bounded co-variance was always observed, for arbitrarily long experiments, and slippage was estimated accurately in real time.
- Failure modes and effects analysis (FMEA) applied to two modern radiotherapy centresPublication . Teixeira, Nuno; Cunha, Gilda; Moreno, L.; Pontes, M.; Rosa, M.; Jacob, K.; Cardoso, I.; Ferreiras, P.; Ramalho, M.; Carvoeiras, P.; Galhós, R.FMEA is a quality improvement technique, generally applied to industry, that can provide an efficient, structured approach to assessing interconnected system failures. It is a bottom up analytical process, which identifies process hazards. According to this technique, each potential failure mode in the system is analysed to determine its effect and to classify it according to its severity. The objective is to identify reliability-critical areas in the system for which modifications to the design or maintenance procedures are required to eliminate single point failures and any catastrophic or critical consequences of such failures. Each individual component of the system is considered separately for each of its failure modes. The procedure involves the following steps: 1.Define the system and its required reliability performance. 2.Construct functional block diagrams to define and illustrate how the different sub-systems are interconnected. 3.List the components, identify their failure modes and where available their modal failure rates. 4.Complete a set of FMEA worksheets analysing the effect of each sub-assembly or component failure mode on overall system performance. Severity rankings are then assigned to each failure mode. 5.Review the worksheets to identify the reliability-critical components and make recommendations for design improvements or amendments to maintenance schedules In this work authors are presenting a FMEA study of two recent radiotherapy centres in Lisbon (Centro Oncológico Dra. Natália Chaves and Hospital CUF-Descobertas), where there are two very different radiotherapy equipments: Varian accelerator, VarisVision network and Eclipse TPS (in the first centre) and Elekta accelerator, Impac network and Xio TPS (in the second centre). This study covers a time-period of one year (all the 2004 year), and allows some very interesting conclusions related to the way the equipment behaves and how one may prevent some problems.
- Ionometric and fricke electron and gamma dosimetry for the implementation of waste water treatment by radiation in PortugalPublication . Ferreira, P.; Jacob, K.; Rosat, M.; Galhós, R.; Serrai, F.; Oliveira, S.; Teixeira, Nuno; Ramalho, M.Application of radiation as an efficient process to reduce the microbial levels in materials (food, environmental, health care products). Irradiation of organic and inorganic compounds with electron and gamma rays can modify the micro organisms, depending on the energy, dose rate, and others variables related to the irradiation conditions. Anthropogenic sources have been responsible for introducing high levels of chemical elements and compounds into the environment, many of this through the industrial waste waters. This is an issue of global concern, with potential impact on human health and the environment. IAEA recognizes the potentiality of radiation technology to clean up waste discharges, and since 2003 IAEA participate in this project. Although this is a multidisciplinary project, by the physical point of view the main objective is to characterize the most efficient electron (by intercomparison with gamma) beam, obtaining the better irradiation geometry, to implement waste water (originated in hospitals, food industry ...) treatments. Until now, we've characterized electron beams with Ionometric and fricke dosimetry at non-standard irradiation conditions, in commercial Linacs for radiotherapy purposes. We used a Varian Clinac 2100 CD, with the special TBI ETRAY conditions and nominal dose rate of 1000 UM/min, and an Elekta Digital Precise with nominal dose rate of 400 UM/min. The better dose rates obtained in water were approximately equal to 1.4 kGy/h and 0.7 kGy/h, respectively. The impact of the radiation has been studied microbiologically, toxicologically and chemically, and the evaluation between this kind of radiation and cobalt gamma radiation is also carried out at the same time. The results obtained until know and the continuous support of the IAEA experts in the project, indicates that this project will contribute to a better quality of the Portuguese industrial or hospital complexes, minimising the impact of pollutants on the environment.