[pt] Este trabalho propõe um gráfico de controle EWMA para observações individuais ou médias amostrais, com a constante de amortecimento variando entre dois valores de acordo com o valor mais recente da estatística EWMA, para obter detecção mais rápida de alterações pequenas a moderadas na média do processo, e sem a complexidade operacional apresentada por outros esquemas adaptativos, pois o tamanho da amostra e o intervalo de amostragem são mantidos fixos. Já existe um outro trabalho propondo a variação da constante de amortecimento dos gráficos EWMA, mas com base em outro critério: Capizzi e Masarotto (2003). O esquema EWMA adaptativo foi combinado com limites de Shewhart para os valores individuais (ou médias amostrais), para acelerar a detecção de grandes deslocamentos da média do processo, também sem aumento da complexidade operacional. Os NMA1´s - números esperados de amostras até um sinal verdadeiro - foram calculados por um método de aproximação numérica usando um modelo matemático por cadeias de Markov, e comparados com os do esquema EWMA tradicional (com parâmetros fixos) e com os do esquema adaptativo de Capizzi e Masarotto (2003). O esquema proposto tende a fornecer NMA1´s menores para alterações na média acima de 1,0 desvio-padrão, e o esquema de Capizzi e Masarotto (2003) tende a fornecer NMA1´s menores para pequenas alterações. Ambos os esquemas possuem melhor desempenho que o gráfico EWMA com parâmetros fixos. Uma vantagem que pode se tornar decisiva para a adoção do esquema proposto é a simplicidade dos cálculos requeridos para o monitoramento. / [en] This work proposes an EWMA process control chart for individual observations or subgroup averages, in which the smoothing constant varies between two values according to the most recent value of the EWMA statistic, in order to achieve faster detection of small to moderate shifts in the process mean, and without the operational complexities presented by other adaptive schemes, since its sample size and sampling interval do not vary. There is one other work proposing the adaptive variation of the smoothing constant of EWMA charts, but based on a different criterion: Capizzi and Masarotto (2003). The adaptive EWMA scheme was combined with Shewhart limits for the individual values (or subgroup averages), to enhance its sensitivity to large shifts, again with no extra operational burden. The out-of-control average run lengths (ARL1´s) were calculated through a numerical approximation method based on a Markov chain model. The ARL1´s were compared of the proposed scheme, of the traditional (fixed parameter) EWMA chart and of Capizzi and Masarottos´s adaptive EWMA scheme. The proposed scheme generally provides the shortest ARL1´s for shifts in the mean above one standard deviation, and Capizzi and Masarotto´s scheme tends to outperform it for smaller shifts. Both schemes perform better than the fixed parameter EWMA. An advantage that can become decisive for the adoption of the proposed scheme is the simplicity of the calculations required for the monitoring.

We correlate in the first part of this study the specific heat and thermal expansivity to the temperature-and pressure-dependent frequency shifts, respectively, in ammonia solid I, solid II, hexagonal ice and ice close to their melting points. This is carried out for some fixed pressures for the two translational and one librational modes in ammonia solid I. By obtaining linear plots of specific heat and thermal expansivity against temperature-and pressure-dependent frequency shifts, the values of slope were deduced and compared with experimental values. The correlation between the thermal expansivity and frequency shifts was constructed in the ammonia solid II by calculating the Raman frequencies of the translational and the librational modes for some fixed pressures. Calculated values of slope were compared with experimental values. Temperature and pressure dependent frequency shifts of the translational modes in hexagonal and ice are correlated to the specific heat and the thermal expansivity, respectively. When the mode Gr&uuml / neisen parameter depends on temperature and pressure, correlations among the specific heat, thermal expansivity and, temperature-and pressure-dependent frequency shifts, respectively, are reexamined in hexagonal ice. When the mode Gr&uuml / neisen parameter depends on temperature, correlation between the specific heat and the frequency shifts is reexamined using translational modes in NH4Cl. In the second part of this study, we predict the damping constant for ammonium halides (NH4Cl and NH4Br) for zero pressure, and for the tricritical and second order phase transitions for a lattice mode of NH4Cl. Also, the observed Raman intensities of this mode are analyzed at those two pressures.