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Low frequency mechanical vibrations (<100 Hz) are naturally generated by skeletal muscles during voluntary contractions. Recording of these vibrations at the muscle surface are called surface mechanomyograms (S-MMGs). In this study, S-MMGs were recorded over a 3 x 5 grid of skin mounted accelerometers on the biceps brachii muscle during submaximal voluntary isometric contractions with the arm in a pronated position for ten healthy and young male subjects with no overt sign of neuromuscular diseases. For a given pair of accelerometers, the spatial coherence of S-MMG is a measure of the similarity of the S-MMG signals propagating between those two sensors. Two common techniques to estimate the spatial coherence for narrowband S-MMG signals, namely the magnitude squared coherence function and the maximum of the time-domain cross-correlation function, were found to yield similar results. In particular, high spatial coherence values were measured for sensor pairs aligned along the proximal to distal ends of the biceps, i.e. the longitudinal direction. On the other hand, the spatial coherence values for sensor pairs oriented perpendicular to the muscle fiber, i.e. along the transverse direction, were found to be significantly lower. This finding indicates that coherent S-MMGs were mainly propagating along the muscle fibers direction (longitudinal) of the biceps brachii within a frequency band varying between 10Hz to 50Hz. Additionally, the spatial coherence of S-MMGs along the longitudinal direction was found to decrease with increasing frequency and increasing sensor separation distance and to increase with contraction level varying between 20% to 60% of the maximum contraction level.

Noninvasive viscoelasticity imaging, or “dynamic elastography”, methods have recently been developed to objectively quantify the local viscoelastic properties of soft tissues by measuring the local propagation velocity of mechanical shear vibrations (e.g. faster velocity indicates stiffer material). But, the existing elastography technologies require a potentially uncomfortable external mechanical stimulation (e.g. vibrations probe) to induce muscle vibrations; and sophisticated and expensive imaging equipments (such as MRI and ultrafast ultrasound elastography), involving complex signal processing, to record and analyze these muscle vibrations. The work in this dissertation lays the foundation for the development of a low cost, passive, non-invasive elastography by analyzing and processing Surface Mechanomyograms (S-MMGs) measured with one dimensional accelerometers from the biceps brachii muscle. Aim 1 of this dissertation focused on the 3-dimensional aspect of vibrations measured by accelerometers on the skin surface above the biceps brachii. While Aim 2 focused on using one-dimensional accelerometers to determine the propagation direction of the propagating S-MMG waves. Using this newly developed knowledge on S-MMG Aim 3 was accomplished, a method to analyze the propagating wave and develop a metric that can track the changes in the muscle was developed, namely, the coherence length. The coherence length was found to significantly increase with increased contraction levels for all seven of the subjects. Overall the results of this study show that the propagation features of S-MMG vibrations reflect the architecture and contraction level of the biceps brachii muscle. Hence S-MMG could potentially be used for monitoring physiological changes of skeletal muscles.

隨著全球資訊網的發展，人們享受了資訊快速流通的便利，也造就了搜尋引擎的發展。針對學術文獻，ACM, IEEE等學術組織也將學術文獻數位化，並提供關鍵字查詢文獻的功能。此外，Google也發展了Google Scholar搜尋全球資訊網上的學術文獻。Google在回傳查詢結果時，除了考慮文獻內容與查詢關鍵字的相似度之外，也利用PageRank技術來考量文獻間的引用關係。但是，有時後使用者想查詢的是與查詢相關的重要參考文獻。這些文獻的內容與查詢未必有很高的相似度。 因此本論文的研究目的在研究並發展推薦重要參考文獻的技術。我們先利用蜘蛛程式( spider)與剖析程式( parser)擷取分析ACM Digital Library上所收錄的論文後設資料，並解析出論文篇名、作者、摘要、關鍵字、分類、參考文獻等論文的重要組成要素。接著利用Mixed Media Graph（MMG）以描述關鍵字與參考文獻間關係的MMG 模型。當使用者輸入關鍵字，利用MMG做random walk因此可以找出與輸入關鍵字相關性最高的參考文獻。 / The rapid development of the Internet, people enjoy the rapid flow of information to facilitate, but also created a search engine of development. ACM and IEEE have developed the digital libraries to provide literature search. Moreover, there exist some search engines for academic literature, such as Google Scholar. Google Scholar collects academic literatures from WWW and provides users the capability to query literatures by keywords. However, sometimes what users need is to search for important citations specified by authors, such as seminal survey papers or books. The aim of this thesis is to investigate and develop the mechanism for search for important citations. In the developed mechanism, first the spider crawls and collects the literature from ACM Digital Library. Then the parser parse and extract the meta information for each literature. The Mixed Media Graph is employed to capture the relationships between keywords and citations. Given a set of query keywords, the important citations are generated by random walk over the constructed Mixed Media Graph. Performance analysis shows that the proposed mechanism performs well.

The very short-term resistance training (VST) model, utilizing only 2-3 training sessions, has been used to examine early phase skeletal muscle, neural, and performance adaptations. The VST model has previously been used to examine these early phase adaptations in bilateral and unilateral, isometric, isokinetic, and dynamic muscle actions in the limbs of the upper- and lower-body. The bilateral deficit (BLD) is a phenomenon in which the sum of the forces produced unilaterally is greater than the force produced bilaterally during maximal contraction of the limbs. The appearance of a bilateral deficit has been be related to various factors; including training status and mode of training (bilateral versus reciprocal muscle actions). No previous study, however, has examined the effects of VST on the BLD. The VST model has potential implications for examining acute changes in strength and neuromuscular responses of the trained muscles. These adaptations, however, may be specific to unilateral or bilateral training. Therefore, the purposes of this study were to: 1) examine one repetition maximum (1RM) strength and neuromuscular responses (EMG AMP, EMG MPF, MMG AMP, MMG MPF) during the measurement of bilateral and unilateral leg extension exercise before and after dynamic constant external resistance (DCER) VST; 2) examine the magnitude of the BLD; 3) examine the effect of bilateral versus unilateral training on the BLD; and 4) use the neuromuscular responses measured bilaterally and unilaterally to infer about the motor unit activation strategies that may underlie the BLD and changes in 1RM strength. Twenty-four (14 males, 10 females) subjects (mean ± SD age: 23.0 ± 3.2 yr; height: 174.7 ± 8.5 cm; body mass: 75.4 ± 14.1 kg) with no resistance training experience within the last three months were randomly assigned to either the bilateral (BL) training group or the unilateral (UL) training group. The subjects completed a total of seven visits, consisting of a familiarization, pre-test visit, three training visits, and one post-test visit. The pre-test visit was used to record the subject’s electromyographic (EMG) and mechanomyographic (MMG) responses from the right and left vastus lateralis (VL) during bilateral and unilateral seated maximum isometric voluntary contractions (MVIC) and 1RM. Visits four through six were the training sessions, with each subject preforming 5 sets of 6 repetitions utilizing 65% of the 1RM for resistance where the BL group trained both limbs (right and left) at the same time and the UL group trained both limbs separately. Visit seven was the post-test and the same testing procedures as the pre-test visit were followed. Statistical analyses consisted of four-way and three-way mixed model ANOVAs, with follow up three-, two- and one-way repeated measures and/or mixed model ANOVAs, Bonferroni corrected paired, and independent samples t-tests when appropriate. An alpha level of P ≤ 0.05 was considered statistically significant for all ANOVAs. The BL group demonstrated a significant increase (p = 0.006; 6.8%) in BL1RM pre- to post-test, but no change in unilateral summed (US1RM = right + left limb; p = 0.726) 1RM strength. The UL group demonstrated an 8.7% increase in BL strength collapsed across testing mode (BL1RM and US1RM) (p = 0.0001) and UL strength (p = 0.0001) collapsed across limb (UL left + UL right/2) from pre- to post-test. The BL group had a significant (p = 0.001) increase in the BI (indicating a decrease in the BLD) from pre- to post-test, but there was no significant change for the UL group. The BL group demonstrated a significant (p = 0.029) decrease in the EMG mean power frequency (MPF) measurement pre- to post-test, however the UL group showed no change. The unilateral movement, collapsed across limbs (unilateral left and unilateral right) also showed a significant (p = 0.022) decrease in the MMG MPF measurement pre- to post-test, whereas the BL movement showed no change. These findings indicated that BL and UL DCER training increased strength after 3 training sessions. The bilateral DCER training resulted in bilateral, but not unilateral strength increases and unilateral DCER training resulting in both bilateral and unilateral strength increases. However, bilateral training was the only mode of training that significantly decreased the BLD.

La présente thèse contribue à la littérature sur trois principaux axes de recherche relatifs à la structure du capital: les déterminants de la structure du capital, la profitabilité et la demande de travail. (i) Le fondement théorique des déterminants de la structure du capital montre qu'il existe trois modèles qui peuvent expliquer la structure du capital: la théorie de ratio optimal d'endettement, la théorie hiérarchique de financement et récemment la théorie de market timing. De plus, l'évaluation empirique montre un effet positif des coûts d'ajustement et de la garantie. Par contre, l'opportunité de croissance, l'impôt non lié à la dette et la rentabilité sont corrélés de façon négative avec l'endettement. (ii) L'impact de la structure du capital sur la profitabilité peut être expliqué par trois théories essentielles: la théorie du signal, l'influence de la fiscalité et la théorie de l'agence. L'analyse empirique a permis de distinguer trois groupes différents de secteurs: pour le premier groupe, la structure du capital n'a aucune incidence sur la profitabilité. Le deuxième, c'est le groupe où l'endettement affecte négativement la profitabilité de manière linéaire. Le dernier groupe se caractérise par la présence d'un effet négatif de façon linéaire et non linéaire (iii) Théoriquement, un impact négatif de la structure du capital sur la demande de travail est prévu. L'application empirique montre une hétérogénéité des comportements entre les secteurs en ce qui concerne l'effet de l'endettement sur la demande de travail, donc, il existe aussi trois groupes différents de secteurs (pas d'effet, effet négatif linéaire et effet négatif linéaire et non linéaire). De plus, la magnitude de l'effet de l'endettement sur la demande de travail et sur la profitabilité dépend, non seulement du secteur, mais aussi de la taille d'entreprise.

La présente thèse contribue à la littérature sur trois principaux axes de recherche relatifs à la structure du capital: les déterminants de la structure du capital, la profitabilité et la demande de travail. (i) Le fondement théorique des déterminants de la structure du capital montre qu’il existe trois modèles qui peuvent expliquer la structure du capital: la théorie de ratio optimal d’endettement, la théorie hiérarchique de financement et récemment la théorie de market timing. De plus, l’évaluation empirique montre un effet positif des coûts d’ajustement et de la garantie. Par contre, l’opportunité de croissance, l’impôt non lié à la dette et la rentabilité sont corrélés de façon négative avec l’endettement. (ii) L’impact de la structure du capital sur la profitabilité peut être expliqué par trois théories essentielles: la théorie du signal, l’influence de la fiscalité et la théorie de l’agence. L’analyse empirique a permis de distinguer trois groupes différents de secteurs: pour le premier groupe, la structure du capital n’a aucune incidence sur la profitabilité. Le deuxième, c’est le groupe où l’endettement affecte négativement la profitabilité de manière linéaire. Le dernier groupe se caractérise par la présence d’un effet négatif de façon linéaire et non linéaire (iii) Théoriquement, un impact négatif de la structure du capital sur la demande de travail est prévu. L’application empirique montre une hétérogénéité des comportements entre les secteurs en ce qui concerne l’effet de l’endettement sur la demande de travail, donc, il existe aussi trois groupes différents de secteurs (pas d’effet, effet négatif linéaire et effet négatif linéaire et non linéaire). De plus, la magnitude de l’effet de l’endettement sur la demande de travail et sur la profitabilité dépend, non seulement du secteur, mais aussi de la taille d’entreprise. / This thesis contributes to the literature in three main areas of research about capital structure: the determinants of capital structure, the profitability and the labour demand. (i) The theoretical basis of the determinants of capital structure shows that there are three models that explains the capital structure: Trade-Off theory, Pecking Order theory and Market Timing theory. Further, the empirical evaluation shows a positive effect of the adjustment costs and the tangibility. On the other hand, growth opportunity, non-debt tax shield and profitability are negatively correlated with debt. (ii) The impact of capital structure on profitability can be explained by three essential theories: signal theory, tax theory and the agency costs theory. The empirical analysis allowed to distinguish three different groups of sectors: for the first group, the capital structure has no impact on profitability. The second, it is the group where the debt affects negatively the profitability in a linear way. The last group is characterized by the presence of a negative effect in a linear and nonlinear way. (iii) Theoretically, a negative impact of the capital structure on labour demand is expected. The empirical application shows heterogeneity of behavior between sectors regarding the impact of debt on the demand for labor; therefore, there are three different groups of sectors (i.e. no effect, negative linear effect, and linear and non linear negative effect). Furthermore, the magnitude of the effect of debt on the labour demand and on the profitability depends not only of the sector, but also of the size of company.

Mechanomyography (MMG) has been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness. To investigate the question of preferred geometry, transducers with varying chamber shapes were designed, manufactured and tested. The best performance was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4 micron thick aluminized mylar membrane and a rigid conical chamber 7 mm in diameter and 5 mm in height. Furthermore, microphone-derived MMG spectra were found to be less influenced by motion artifact than corresponding accelerometer-derived spectra. However, artifact harmonics were present in both spectra, suggesting that bandpass filtering may not remove artifact influences permeating into MMG frequency bands.

Mechanomyography (MMG) has been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness. To investigate the question of preferred geometry, transducers with varying chamber shapes were designed, manufactured and tested. The best performance was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4 micron thick aluminized mylar membrane and a rigid conical chamber 7 mm in diameter and 5 mm in height. Furthermore, microphone-derived MMG spectra were found to be less influenced by motion artifact than corresponding accelerometer-derived spectra. However, artifact harmonics were present in both spectra, suggesting that bandpass filtering may not remove artifact influences permeating into MMG frequency bands.

Depuis 1990, bon nombres de pays industrialisés et émergents ont adopté la politique de ciblage d’inflation. Ce régime monétaire a été adopté sans théorie adjacente dans la mesure où il a démarré comme une solution alternative à la recherche sans fin d’un système d’ancrage nominal suite aux échecs répétés des politiques antérieurs. Ce retard théorique fait naître de nombreux débats économiques sur la conduite de ce régime monétaire dont les plus importants feront l’objet d’une discussion approfondie au sein de cette thèse. Dans un premier chapitre, nous définissons la politique de ciblage d’inflation. Dans un second chapitre nous abordons la question de la conduite optimale de ce régime d’un point de vue théorique et empirique. Nous montrons que la règle optimale est une règle à la Taylor de type Forward-Looking dont elle peut avoir un comportement asymétrique. Dans un troisième chapitre, nous abordons la question de l’efficacité de la politique de ciblage d’inflation. Pour ce faire, nous avons étudié l’effet d’intervention de ce régime sur la dynamique d’inflation. Nous avons recours à la théorie spectrale évolutive afin de modéliser la série de l’inflation dans le but de tester son évolution. Les résultats sont en faveur de l’efficacité de ciblage d’inflation. Le dernier axe de cette thèse s’intéresse à la question de la performance économique de ce régime monétaire. Pour ce faire nous développons une méthodologie originale évaluée selon une approche économétrique originale. En effet, nous qualifions le ciblage d’inflation comme économiquement performant s’il génère une stabilité de l’environnement de la politique monétaire. Le fondement de cette idée fera l’objet du quatrième chapitre. Quant au chapitre cinq, il développera l’approche économétrique basée sur la théorie co-spectrale pour mesure le degré de stabilité de cet environnement. Les résultats montrent que le ciblage d’inflation est économiquement performant. / The inflation targeting policy (ITP) was born after the failure of many monetary policies. However, the ITP was adopted without inherent theory which raised many discussions. In this dissertation, we study the most important debates. In the first chapter, we defined the ITP. Then, we treat the question of the optimal rule conduct. We show that the optimal monetary rule is a type Taylor rule under a Forward-Looking version and which can be linear or nonlinear. In the third chapter, we focus on the discussion about the relevance of the inflation targeting policy. To study this point we use the evolutionary spectral analysis to model the inflation series and we test then, if the ITP cause a structural break. Our results show the relevance of the ITP. The last discussion in this work is to check the macroeconomic performance of the ITP. The main idea is to consider the ITP as economically efficient when it generates a stable monetary environment. The latter is considered as stable when a long-run equilibrium exists to which the paths of economic variables (inflation rate, interest rate and GDP growth) converge. The convergence of the variables’ paths implies that these variables are more predictable and implies a less uncertainty in the economic environment. To measure the degree of convergence between economic variables, we propose, in this paper, a dynamic time-varying variable presented in the frequency approach named cohesion. This variable is estimated from the evolutionary co-spectral theory. The results show that the ITP is a relevance policy and generate a good performance.