5 resultados para Error analysis (Mathematics)


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O estudo sobre os textos escritos produzidos por alunos da 7ª classe em Angola foi estabelecido por nós com base na hipótese da existência de dificuldades de escrita. Há bastantes dúvidas entre os docentes angolanos sobre a capacidade dos alunos na elaboração de textos espontâneos. Desta forma, com o objectivo de conhecermos as capacidades de produção de textos escritos pelos alunos do ensino geral no Lubango, de elaborarmos uma tipologia de análise dos erros encontrados e de propormos estratégias de superação das dificuldades apresentadas nos textos dos alunos, fomos à Escola do I Ciclo do Ensino Secundário 27 de Março do Lubango – Huíla recolher as composições da Prova Trimestral para verificar as dificuldades de escrita apresentadas nos textos dos alunos. Partimos de 314 textos, dos quais foi extraída a amostra de 10%, correspondendo a 32 textos seleccionados através da tabela de números aleatórios. Os textos foram analisados com base na tipologia de erros de Sousa (1996). Desta forma, foram detectados erros de substituição, de omissão, de divisão/aglutinação, os quais foram muito significativos e ocorreram em 66,856% dos casos no total. Os erros de substituição maiúsculas/minúsculas, os de adição, de grafias homófonas constituem 30.856% dos casos. Confirmam-se as dificuldades apresentadas pelos alunos que devem merecer tratamento através das propostas de remediação apresentadas. As dificuldades encontradas nos textos destes alunos devem servir de base para a planificação da disciplina de Língua Portuguesa no Ensino Primário de forma a dotar o aluno de competências para a melhoria da comunicação escrita na sala de aula.

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Proceedings of the Information Technology Applications in Biomedicine, Ioannina - Epirus, Greece, October 26-28, 2006

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Dissertation submitted in the fufillment of the requirements for the Degree of Master in Biomedical Engineering

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Modern telecommunication equipment requires components that operate in many different frequency bands and support multiple communication standards, to cope with the growing demand for higher data rate. Also, a growing number of standards are adopting the use of spectrum efficient digital modulations, such as quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM). These modulation schemes require accurate quadrature oscillators, which makes the quadrature oscillator a key block in modern radio frequency (RF) transceivers. The wide tuning range characteristics of inductorless quadrature oscillators make them natural candidates, despite their higher phase noise, in comparison with LC-oscillators. This thesis presents a detailed study of inductorless sinusoidal quadrature oscillators. Three quadrature oscillators are investigated: the active coupling RC-oscillator, the novel capacitive coupling RCoscillator, and the two-integrator oscillator. The thesis includes a detailed analysis of the Van der Pol oscillator (VDPO). This is used as a base model oscillator for the analysis of the coupled oscillators. Hence, the three oscillators are approximated by the VDPO. From the nonlinear Van der Pol equations, the oscillators’ key parameters are obtained. It is analysed first the case without component mismatches and then the case with mismatches. The research is focused on determining the impact of the components’ mismatches on the oscillator key parameters: frequency, amplitude-, and quadrature-errors. Furthermore, the minimization of the errors by adjusting the circuit parameters is addressed. A novel quadrature RC-oscillator using capacitive coupling is proposed. The advantages of using the capacitive coupling are that it is noiseless, requires a small area, and has low power dissipation. The equations of the oscillation amplitude, frequency, quadrature-error, and amplitude mismatch are derived. The theoretical results are confirmed by simulation and by measurement of two prototypes fabricated in 130 nm standard complementary metal-oxide-semiconductor (CMOS) technology. The measurements reveal that the power increase due to the coupling is marginal, leading to a figure-of-merit of -154.8 dBc/Hz. These results are consistent with the noiseless feature of this coupling and are comparable to those of the best state-of-the-art RC-oscillators, in the GHz range, but with the lowest power consumption (about 9 mW). The results for the three oscillators show that the amplitude- and the quadrature-errors are proportional to the component mismatches and inversely proportional to the coupling strength. Thus, increasing the coupling strength decreases both the amplitude- and quadrature-errors. With proper coupling strength, a quadrature error below 1° and amplitude imbalance below 1% are obtained. Furthermore, the simulations show that increasing the coupling strength reduces the phase noise. Hence, there is no trade-off between phase noise and quadrature error. In the twointegrator oscillator study, it was found that the quadrature error can be eliminated by adjusting the transconductances to compensate the capacitance mismatch. However, to obtain outputs in perfect quadrature one must allow some amplitude error.