Dans ce travail, une méthode basée sur les éléments finis ondulatoires - Wave Finite Elements (WFE) - est proposée en vue de prédire le rayonnement acoustique de conduites axisyrnétriques de longueur finie, comportant un fluide interne, et immergées dans un fluide acoustique de dimensions infinies. La condition de rayonnement de Sommerfeld est prise en compte en entourant le fluide extérieur d'un perfectly matched layer (PML), c'est-à-dire une couche d'éléments absorbants dans laquelle les ondes acoustiques incidentes sont progressivement amorties. Dans le cadre de l'approche WFE, la conduite, le fluide qu'elle contient, le fluide extérieur et le PML constituent un guide d'ondes multiphysique qui est discrétisé par un maillage éléments finis périodique, et peut être ainsi modélisé comme un assemblage de sous-systèmes identiques de faible longueur. Une base d'ondes se propageant le long de la conduite, calculée à partir du modèle éléments finis d'un sous-système, est utilisée afin de prédire le comportement vibroacoustique de guides d'ondes de longueur finie à moindre coût. Des simulations numériques sont réalisées pour des cas de conduites de structure homogène ou multi-couches. La précision et l'efficacité de la méthode WFE sont clairement établies en comparaison avec la méthode des éléments finis conventionnelle. / In this work, a wave finite element (WFE) method is proposed to predict the sound radiation of finite axisymmetric fluid-filled pipes immersed in an external acoustic fluid of infinite extent, The Sommerfeld radiation condition is taken into account by means of a perfectly matched layer (PML) around the external fluid. Within the WFE framework, the fluid-filled pipe, the surrounding fluid and the PML constitute a multiphysics waveguide that is discretized by means of a periodic finite element mesh, and is treated as an assembly of identical subsystems of small length. Wave modes are computed from the FE model of a multi-physics subsystem and used as a representation basis to assess the vibroacoustic behavior of the finite waveguide at a low computational cost. Numerical experiments are carried out in the cases of axisymmetric pipes of either homogeneous or multi-layered crosssections, The accuracy and efficiency of the proposed approach are dearly highlighted in comparison with the conventional FE method.

Dans le cadre de l'étude des écoulements ouverts, deux types de dynamiques coexistent. Les écoulements de type oscillateur qui présentent une fréquence propre d'oscillation indépendante des perturbations extérieures (dynamique intrinsèque), ainsi que les écoulements de type amplificateur sélectif de bruit comme les écoulements de jets ou de couches limites décollées, caractérisés par une plus large gamme de fréquences dépendantes essentiellement de bruit extérieur (dynamique extrinsèque). Les études de couches limites décollées en régime incompressible ont montré un lien entre le phénomène auto-entretenu de basse fréquence qui apparaît et l'interaction non normale des modes globaux instables existants pour ce type de configuration. L'objectif de ce travail consiste à étendre cette interprétation lorsque l'écoulement est en régime subsonique. Dans ce but, un travail d'adaptation des conditions aux limites non-réfléchissantes aux problèmes de stabilité globale a été réalisé. Une méthode de zone absorbante de type Perfectly Matched Layer a été implémentée dans un code de simulation numérique utilisant des méthodes de collocation spectrale. Une méthode de décomposition de domaine adaptée aux calculs des solutions stationnaires ainsi qu'aux problèmes de stabilité globale a également été utilisée pour permettre la validation des conditions aux limites implémentées sur un cas d'écoulement rayonnant de cavité ouverte. Enfin, les études de stabilité d'un écoulement de couche limite décollée derrière une géométrie de type bosse ont été réalisées. L'étude des instabilités bidimensionnelles, responsables du phénomène basse fréquence (flapping), et réalisées en régime subsonique montre que le mécanisme observé en régime incompressible est aussi observé en régime subsonique. La stabilité de cet écoulement vis-à-vis de perturbations tri-dimensionnelles, et plus particulièrement les instabilités centrifuges ont aussi été étudiées en fonction du nombre de Mach. / In open flows context, there are generally two types of dynamic : oscillators, such as cylinder flow, exhibit a well defined frequency insensitive to external perturbations (intrinsic dynamics) and noise amplifiers, such as boundary layers, jets or in some cases the separated flows, which are characterized by wider spectrum bands that depend essentially on the external noise (dynamic extrinsic). Previous studies have shown that separated flows are subject to self-induced oscillations of low frequency in incompressible regime. These studies have revealed links between the interaction of non-normal modes and low oscillations in an incompressible boundary-layer separation and it will be to establish the validity of this interpretation in a compressible regime. In this regard, non-reflecting boundary conditions have been developed to solve the eigenvalue problem formed by linearised Navier-Stokes equations. An absorbing region known as Perfectly Matched Layer has been implemented in order to damp acoustic perturbations which are generated when the compressibility of the flow is considered. A multi-domain approach using spectral collocation discretisation has also been developed in order to study the influence of this absorbing region on the stability analysis of an open cavity flow which is known to generate acoustic perturbations. Finally, we focused on separated boundary layer induced by a bump geometry in order to understand what are the effects of compressibility on the bidimensional low frequency phenomenon and also on transverse instabilities which are known to be unstable for a lots of separated flows.

Le geyser d'Old Faithful dans le Parc National de Yellowstone, aux États-Unis, est l'undes geysers les plus connus au monde. La cyclicité de ses éruptions est étudiée depuis lesannées 60 a_n de comprendre sa dynamique. En e_et, le caractère bimodal de la fréquencede ses éruptions intriguent les scienti_ques qui cherchent à en connaître les causes.Les enregistrements sismiques réalisés à la surface du geyser démontrent des signauximpulsionnels dont l'origine fut identi_ée par Sharon Kedar. Ainsi, en 1992, S. Kedar etses collègues ont déployé plusieurs capteurs sismiques dans le but d'étudier la source dessignaux sismiques de type tremor enregistrés à la surface du dôme. Ils ont ainsi identi_éla source du signal sismique enregistré à la surface du geyser comme étant des signauxde cavitation de bulles. La cavitation se produisant à la surface du niveau de l'eau dansle conduit, les localisations des sources sismiques réalisées à partir des enregistrements desurface peuvent être reliées au niveau de l'eau dans le conduit.Dans un premier temps nous avons proposé de localiser les sources sismiques desenregistrements à partir de la méthode du Matched Field Processing (MFP) provenantde l'acoustique sous-marine. Plusieurs algorithmes du MFP ont été testés pour pouvoirlocaliser au mieux les sources sismiques. La bonne concordance des résultats obtenus avecchacun des algorithmes a permis d'obtenir un grand nombre de localisations des sourcesau cours du cycle. Les positions déterminées avec les di_érents algorithmes du MFP ontpermis de mettre en évidence deux zones d'activité hydrothermale du geyser associéesà di_érentes périodes du cycle éruptif, telles que le remplissage du conduit avant leséruptions et l'alimentation du geyser en eau une fois la vidange du conduit e_ectuée.Dans un second temps, l'analyse des variations de vitesse des signaux sismiques estproposée pour suivre des changements des propriétés du dôme du geyser, comme des variationsde pression avant l'éruption. Pour cela, une nouvelle méthode basée sur les mesuresde phases instantanées est suggérée. Les résultats obtenus montrent des faibles changementsde vitesse, pouvant être associés à la mise en pression du dôme ou à l'augmentationde la température du milieu avant l'éruption en surface. / The geyser of Old Faithful in the National Park of Yellowstone, in USA, is one of themost famous geysers in the world. The cyclic behavior of the geyser is studied since the60's with the aim to understand its dynamics. In fact, the bimodal nature of the frequencyof the eruptions raises questions and scientists want to know the causes of this behavior.The seismic signals recorded at the surface of the geyser present pulses whose origin wasidenti_ed by Sharon Kedar. Thus, in 1992, S. Kedar and his colleagues deployed severalseismic sensors in order to study the source of the seismic signals, which are tremor-like,recorded at the surface of the edi_ce. They identi_ed the source of the seismic signalrecorded at the surface of the geyser that they related to bubbles collapse. The bubblescollapse takes place at the surface of the water level in the conduit, thus the localizationsof the seismic sources determined with the records made at the surface would be relatedto the water level in the conduit.In a _rst time we proposed to locate the seismic sources of the records using theMatched Field Processing (MFP), a method used in ocean acoustics. Several algorithmsof the MFP were tested to better localize the seismic sources. The good agreement ofthe di_erent results obtained with each technique allowed to obtain a big number oflocalizations of the sources through the cycle. The locations determined with di_erentalgorithms of MFP allowed to highlight two areas of hydrothermal activities of the geyserlinked to di_erent periods of the eruption's cycle, as the _lling-up of the conduit beforeeruptions and the feeding of the geyser with water once the discharge of the conduitaccomplished.In a second time, the analysis of velocity's changes of the seismic records is proposedto follow changes in the properties of the edi_ce of the geyser, and pressure changes beforean eruption for example. To do that, a new technique based on the measurement of theinstantaneous phases is suggested. The results obtained show weak changes of velocity,that can be related to the pressure buildup of the edi_ce or to the increase of temperaturein the medium before an eruption.

While worker flow analysis has grown in importance in many countries, Austria still lacks a specific longitudinal dataset as a prerequisite to perform similar analyses. For this reason, this article provides a coherent procedure to construct a longitudinal dataset based on the rotational panel structure of the Austrian quarterly LFS from 2004 to 2014. The procedure, which is available for researcher, is grounded on the discussion of several related and important issues inherent in constructing this sort of longitudinal data: First, it deals with the construction of the quarterly-matched dataset and the quality-of-measurement of several labour market variables. Second, the paper analyses non-response as a sample selection process, and shows that the selected (quarterly-matched) dataset causes biased estimates of worker flows. Third, the article proposes an iterative raking procedure to obtain survey weights as a bias-correcting device for any future analysis. Based on these adjustments, we present unbiased time-series of worker flows and transition rates, and conclude that the employment-unemployment margin is highly sensitive to economic shocks and that the Austrian labour market is additionally shaped by large movements within the participation margin. (authors' abstract) / Series: Department of Economics Working Paper Series

Abstract : In the contemporary world, English has become the international language in which most intercultural communication is conducted (Seidlhofer, 2011). The number of speakers using English as a foreign or second language (L2) outnumbers the number of native speakers of the language six times (Crystal, 2003) and, accordingly, English is used more commonly as a Lingua Franca in the international context than to communicate with its native speakers (Jenkins, 2007). Because of the global spread of English, there are more people who speak English with a non-native accent. Such accents often trigger a set of stereotypes insofar as it could have negative consequences for the speaker in terms of academic success and employability (Lippi-Green, 1994). From decades of research in social psychology and sociolinguistics, it has been established that accent plays a significant role in how native speakers perceive non-native speakers of English (Garrett, 2010). However, little has been done in exploring how non-native speakers of English view their own accent and judge acceptability of other non-native English accents. Therefore, this study addressed the need for further research focusing on non-native students’ attitudes towards Arabic- and Chinese-accented English in an English Intensive Program at an English-speaking university in Montreal. This study employed the verbal guise technique from the field of social psychology to elicit spontaneous reactions to L2 accented speech with two levels of first language (L1) influence. Unlike other verbal guise studies, this study did not include a native speaker sample for comparison. We believed our participants’ potential negative attitudes to L2-accented speech would be attenuated by the reference frame effect. To explain and clarify verbal guise test results, we also conducted semi-structured interviews. The results show that the respondents displayed a relatively low level of solidarity with Chinese and Arabic accents in English. Notwithstanding relatively low solidarity ratings given to the accented voices, they were still higher than the evaluations documented in the literature. In addition, high status ratings were found for non-native speakers despite the fact that they were recognized as such. This suggests that in addition to the positive effect triggered by the lack of inclusion of native speaker accents, there might be some contextual factors at play. We found that the participants were harsher in their ratings when the voices represented the more formal domain of higher education but more lenient when they referred to informal settings. From our data, it is also evident that non-segmentals play an important role in language attitudes. The female speakers who approximated their rhythm patterns and intonation contours to those of a native speaker received higher ratings on all the traits in our data. We believe that, if we want them to serve the needs of international students, these often ambivalent attitudes should be considered in the choice of a classroom pronunciation model, and in the development of pronunciation materials. / Résumé : Dans le monde contemporain, l’anglais est devenu la langue internationale utilisée pour la plupart des communications interculturelles (Seidlhofer, 2011). Le nombre de locuteurs utilisant l’anglais comme langue étrangère ou langue seconde est six fois plus important que le nombre de locuteurs natifs (Crystal, 2003). L’anglais est plus souvent utilisé comme Lingua Franca dans un contexte international que pour communiquer avec des locuteurs natifs (Jenkins, 2007). A cause de cette diffusion globale de l’anglais, la plupart des gens qui parlent anglais ont un accent non-natif. Ces accents déclenchent souvent une panoplie de stéréotypes qui peuvent avoir des conséquences négatives sur l’employabilité ou la réussite professionnelle des locuteurs (Lippi-Green, 1994). Des décennies de recherche en psychologie sociale et sociolinguistique ont reconnu que l’accent joue un rôle significatif sur la perception des locuteurs non-natifs par les locuteurs natifs (Garrett, 2010). Cependant, peu d’études se sont penchées sur la façon dont les locuteurs non-natifs perçoivent leur propre accent et jugent l’acceptabilité des autres accents non-natifs. Par conséquent, la présente étude se concentre sur les attitudes des étudiants internationaux du programme d’anglais intensif d’une université anglophone montréalaise envers les accents arabes et chinois en anglais. Cette étude utilise la technique de locuteur masqué employée dans le domaine de la psychologie sociale pour déclencher des réactions spontanées à un discours de langue seconde accentué par deux niveaux d’influence de la langue maternelle. Contrairement aux autres études utilisant la technique de locuteur masqué, cette étude n’inclus pas de discours de locuteurs natifs à des fins de comparaison. Nous pensons que les attitudes négatives potentielles pourraient être atténuées par l’effet de cadre de référence. Pour expliquer et clarifier les résultats de la technique de locuteur masqué, nous avons également mené des entrevues semi-dirigées. Les résultats montrent que les participants expriment un niveau de solidarité relativement faible envers les accents arabes et chinois en anglais. Pourtant, ce niveau de solidarité est tout de même plus haut que les études reportées dans la littérature. D’autre part, le statut social des locuteurs non-natifs a été évalué positivement malgré que les locuteurs aient été reconnus comme non-natifs. Ceci suggère qu’en plus d’un effet positif déclenché par l’exclusion des accents natifs, certains facteurs contextuels peuvent avoir influencé les résultats. Nous avons trouvé que les personnes interrogées notaient plus sévèrement les voix suggérant un niveau d’éducation élevé, mais étaient plus clémentes envers les voix faisant référence à un contexte informel. De l’analyse des données, il apparait que les non-segmentals jouent un rôle important dans les attitudes langagières. De plus, les locutrices se rapprochant du rythme et de l’intonation des natifs ont reçu des évaluations supérieures sur tous les traits. Nous pensons que ces attitudes souvent ambivalentes devraient être considérées dans le choix du modèle d’enseignement et dans le développement de nouveaux supports d’apprentissage de la prononciation pour les étudiants internationaux.

Proposed designs for Very Large Floating Structures motivate us to understand water-wave propagation through arrays of hundreds, or possibly thousands, of floating structures. The water-wave problems we study are each formulated under the usual conditions of linear wave theory. We study the frequency-domain problem of water-wave propagation through a periodically arranged array of structures, which are solved using a variety of methods. In the first instance we solve the problem for a periodically arranged infinite array using the method of matched asymptotic expansions for both shallow and deep water; the structures are assumed to be small relative to the wavelength and the array periodicity, and may be fixed or float freely. We then solve the same infinite array problem using a numerical approach, namely the Rayleigh-Ritz method, for fixed cylinders in water of finite depth and deep water. No limiting assumptions on the size of the structures relative to other length scales need to be made using this method. Whilst we aren t afforded the luxury of explicit approximations to the solutions, we are able to compute diagrams that can be used to aid an investigation into negative refraction. Finally we solve the water-wave problem for a so-called strip array (that is, an array that extends to infinity in one horizontal direction, but is finite in the other), which allows us to consider the transmission and reflection properties of a water-wave incident on the structures. The problem is solved using the method of multiple scales, under the assumption that the evolution of waves in a horizontal direction occurs on a slower scale than the other time scales that are present, and the method of matched asymptotic expansions using the same assumptions as for the infinite array case.

In this thesis, we use asymptotic methods to solve problems of wave propagation through infinite and finite (only consider those that are finite in one direction) arrays of scatterers. Both two- and three-dimensional arrays are considered. We always assume the scatterer size is much smaller than both the wavelength and array periodicity. Therefore a small parameter is involved and then the method of matched asymptotic expansions is applicable. When the array is infinite, the elastic wave scattering in doubly-periodic arrays of cavity cylinders and acoustic wave scattering in triply-periodic arrays of arbitrary shape rigid scatterers are considered. In both cases, eigenvalue problems are obtained to give perturbed dispersion approximations explicitly. With the help of the computer-algebra package Mathematica, examples of explicit approximations to the dispersion relation for perturbed waves are given. In the case of finite arrays, we consider the multiple resonant wave scattering problems for both acoustic and elastic waves. We use the methods of multiple scales and matched asymptotic expansions to obtain envelope equations for infinite arrays and then apply them to a strip of doubly or triply periodic arrays of scatterers. Numerical results are given to compare the transmission wave intensity for different shape scatterers for acoustic case. For elastic case, where the strip is an elastic medium with arrays of cavity cylinders bounded by acoustic media on both sides, we first give numerical results when there is one dilatational and one shear wave in the array and then compare the transmission coefficients when one dilatational wave is resonated in the array for normal incidence. Key words: matched asymptotic expansions, multiple scales, acoustic scattering, elastic scattering, periodic structures, dispersion relation.

Prematurity, especially if extreme, is one of the leading causes of problems and/or death after delivery. Among all the problems encountered by premature infants, feeding difficulties are very common. Many premature infants are fed intravenously at first, and they progress to milk feedings provided by a tube passed into the stomach. At around 34 weeks of gestation, premature infants should be able to breastfeed or take a bottle. At the same time such premature infants are usually faced with difficulty making the transition from tube-feeding to full oral feeding. In this study three physiological measurements of premature infants including sucking, swallowing and breathing were measured. The objective of this work was to detect, identify and classify these three signals independently and in relation to each other. The goal was to look at the specification of sucking, swallowing and breathing signals to extract the ratio of suck swallow-breath coordination. The results of this study were used to predict the readiness of a premature infant for introduction to oral feeding.To accomplish this, three different methods were examined. In the first method, the integration of the wavelet packet transform and a neural network was investigated. According to results of the first approach, integration of the wavelet packet transform and the neural network failed due to the inefficiency of the feature extraction method. Thus, the wavelet packet energy nodes did not provide a good feature extraction tool in this specific application.In the second approach, the frequency content of each signal was investigated to study the relationship between the shape of each waveform and the frequency content of that specific signal. Spectral analysis for suck, swallow and breathing signals showed that the shape of the signal was not tightly related to the frequency content of that specific waveform. Therefore, the frequency content could not be used as a method of feature extraction in this specific application.In the third method, the integration of correlation and matched filtering techniques was investigated and demonstrated promising result for the detection of suck and breathing signal but not for the swallowing waveform. Based on the results for sucking and breathing signals, this method should also work for good quality swallowing signal. To understand the relationship between the suck, swallow and breathing signals a matrix containing information on the time of occurrence of each event was developed.

In this thesis, we derive, extend and generalise various aspects of impact theory and splash dynamics. Our methods throughout will involve isolating small parameters in our models, which we can utilise using the language of matched asymptotics. In Chapter 1 we briefly motivate the field of impact theory and outline the structure of the thesis. In Chapter 2, we give a detailed review of classical small-deadrise water entry, Wagner theory, in both two and three dimensions, highlighting the key results that we will use in our extensions of the theory. We study oblique water entry in Chapter 3, in which we use a novel transformation to relate an oblique impact with its normal-impact counterpart. This allows us to derive a wide range of solutions to both two- and three-dimensional oblique impacts, as well as discuss the limitations and breakdown of Wagner theory. We return to vertical water-entry in Chapter 4, but introduce the air layer trapped between the impacting body and the liquid it is entering. We extend the classical theory to include this air layer and in the limit in which the density ratio between the air and liquid is sufficiently small, we derive the first-order correction to the Wagner solution due to the presence of the surrounding air. The model is presented in both two dimensions and axisymmetric geometries. In Chapter 5 we move away from Wagner theory and systematically derive a series of splash jet models in order to find possible mechanisms for phenomena seen in droplet impact and droplet spreading experiments. Our canonical model is a thin jet of liquid shot over a substrate with a thin air layer trapped between the jet and the substrate. We consider a variety of parameter regimes and investigate the stability of the jet in each regime. We then use this model as part of a growing-jet problem, in which we attempt to include effects due to the jet tip. In the final chapter we summarise the main results of the thesis and outline directions for future work.

Approved for public release, distribution is unlimited / Linear sound sweeps from a towed J15-3 sound source were collected at a moored VLA hydrophone array in the South China Sea during the ASIAEX experiment in May 2001. Measured signals were filtered and pulse compressed. The processed data showed a high signal to noise ratio. Given an a priori chirp sonar survey, a two layer bottom "first guess" model was constructed. A broadband coupled-mode model was used to perform an exhaustive frequency variant sensitivity study of VLA pressures to changes in bottom properties as a basis for the geoacoustic inverse problem. Study results provided information on the observability of the various geoacoustic parameters and a procedure for the inversion. Matched field processing of the VLA data, using the same coupledmode model, was then performed to calculate ambiguity diagrams from which geoacoustic parameter estimates were obtained. Since VLA pressure fields were not sensitive to changes in the sediment attenuation coefficient, a matched field technique that correlated the slope of modeled transmission loss to the negative slope of 10log of the observed energy was performed in order to obtain estimates of the attenuation. These estimates showed a frequency dependent attenuation coefficient in the 50-600Hz frequency band. / Lieutenant, United States Navy