Letter to Sarah Leverette regarding a SEAALL Chapter Meeting, March 13, 1956

A letter from Stanley Bougas to Sarah Leverette regarding the SEAALL Chapter meeting, materials exchange, and membership dues payment

The development of a crystal modulator using a multipath reflection technique

An AOP lumped crystal transverse modulator has been developed, based upon a novel crystal cut, which operates at much lower driving voltages than presently available commercial state of the art modulators. With the latter, the modulation bandwidth is limited by the requirement for driving voltages in the range of 115V to 250V, which are difficult and expensive to produce using existing semiconductor technology. The reduction in driving voltage leads to an increased modulation bandwidth; low voltage wideband drivers are readily available. The modulator's novelty lies in a composite crystal scheme which allows a light beam to be reflected back and forth many times. The voltage requirement is reduced by a factor dependent on the number of times the light beam passes through the crystals. This modulator does not require a half wave plate and can therefore operate at any optical wavelength as is also the case with some of the existing designs. But in addition, unlike the existing designs, this novel modulator allows for multicolour multibeam operation. Using four AOP crystals (15.0mm length, 16.5mm width and 2.5mm thickness) a half wave voltage of 65V has been achieved after seven passes. The extinction ratios obtained were in the range of 50:1 to 100:1. A theory developed and supported by experimental results shows that the extinction ratio depends upon the angle of propagation of the light bean through the crystals. Improvements in this area are suggested. Finally, a technique for extending the operational bandwidth of any modulator is presented. The bandwidth of the multipath modulator was 70MHz

Letter to Kate Wallach regarding the SEAALL Chapter Meeting, October 21, 1958

A letter from Stanley Bougas to Kate Wallach regarding plans and ideas for the next SEAALL Chapter meeting

The Fabric of Time Myth

Back in the days of Ice and fog, on a cold and bitter morning, when the snow fell so high it blotted out the low rising sun, Time came down from the heavens as a naked lamb. “I am cold,” she said. “Who amongst you will weave me a garment strong enough to see me through these bitter days?

Letter to William Roalfe offering condolences upon the death of Mrs. Roalfe, November 17, 1959

A letter from Stanley Bougas to William Roalfe offering SEAALL\u27s sympathy upon learning of the death of Mrs. Roalfe

Letter to Sarah Leverette regarding SEAALL membership, September 29, 1954

A letter from Stanley Bougas to Sarah Leverette asking Leverette to add Bougas to the list of SEAALL affiliates

Forecasting air passenger traffic flows in Canada : an evaluation of time series models and combination methods

Ces quinze dernières années, le transport aérien a connu une expansion sans précédent au Canada. Cette étude fournit des prévisions de court et moyen terme du nombre de passagers embarqués\débarqués au Canada en utilisant divers modèles de séries chronologiques : la régression harmonique, le lissage exponentiel de Holt-Winters et les approches dynamiques ARIMA et SARIMA. De plus, elle examine si la combinaison des prévisions issues de ces modèles permet d’obtenir une meilleure performance prévisionnelle. Cette dernière partie de l’étude se fait à l’aide de deux techniques de combinaison : la moyenne simple et la méthode de variance-covariance. Nos résultats indiquent que les modèles étudiés offrent tous une bonne performance prévisionnelle, avec des indicateurs MAPE et RMSPE inférieurs à 10% en général. De plus, ils capturent adéquatement les principales caractéristiques statistiques des séries de passagers. Les prévisions issues de la combinaison des prévisions des modèles particuliers sont toujours plus précises que celles du modèle individuel le moins performant. Les prévisions combinées se révèlent parfois plus précises que les meilleures prévisions obtenues à partir d’un seul modèle. Ces résultats devraient inciter le gouvernement canadien, les autorités aéroportuaires et les compagnies aériennes opérant au Canada à utiliser des combinaisons de prévisions pour mieux anticiper l’évolution du traffic de passager à court et moyen terme. Mots-Clés : Passsagers aériens, Combinaisons de prévisions, Séries temporelles, ARIMA, SARIMA, Canada.This master’s thesis studies the Canadian air transportation sector, which has experienced significant growth over the past fifteen years. It provides short and medium term forecasts of the number of enplaned/ deplaned air passengers in Canada for three geographical subdivisions of the market: domestic, transborder (US) and international flights. It uses various time series forecasting models: harmonic regression, Holt-Winters exponential smoothing, autoregressive-integrated-moving average (ARIMA) and seasonal autoregressive-integrated-moving average (SARIMA) regressions. In addition, it examines whether or not combining forecasts from each single model helps to improve forecasting accuracy. This last part of the study is done by applying two forecasting combination techniques: simple averaging and a variety of variance-covariance methods. Our results indicate that all models provide accurate forecasts, with MAPE and RMSPE scores below 10% on average. All adequately capture the main statistical characteristics of the Canadian air passenger series. Furthermore, combined forecasts from the single models always outperform those obtained from the single worst model. In some instances, they even dominate the forecasts from the single best model. Finally, these results should encourage the Canadian government, air transport authorities, and the airlines operating in Canada to use combination techniques to improve their short and medium term forecasts of passenger flows. Key Words: Air passengers, Forecast combinations, Time Series, ARIMA, SARIMA, Canada