The management of parallel and series resonance conditions is important for ensuring that harmonic levels are managed on utility networks, and that shunt compensators are able to operate without constraints for various network conditions (states). For these and similar problems, harmonic impedance assessment of the ac network is required for the design of ac filter or shunt capacitor bank installations. This is particularly important for large installations connected to HV or EHV systems, because resonances at these voltage levels tend to be highly un-damped resulting in potentially damaging voltage and current amplification. The objective of this dissertation was to develop and demonstrate a design methodology which makes use of network impedance assessment methods to provide robust harmonic integration of large shunt compensators into a transmission and HVDC systems. The design methodology has two aspects. The first part considers network modeling, evaluation of different models and simulation of harmonic impedance. In the second part, methods of analyzing and assessing the simulated harmonic impedance are developed. A detailed step-by-step approach was taken in the development of the design methodology. The methodology was documented as a guideline and accompanied by the development of an Excel tool that can be used to assess the simulated harmonic impedance. The Excel tool permits a systematic assessment of the simulated network impedance where shunt compensators are integrated into transmission systems. The tool also ensures that the design of transmission and HVDC ac shunt compensation is optimally robust in terms of harmonic resonances. The theoretical and computational review has been tested and demonstrated on the existing Eskom Transmission system through several case studies. The results have shown the merits of the design methodology. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

Afin de réduire les vibrations d'une structure, on utilise des éléments piézoélectriques connectés à des circuits électriques passifs. L'objectif est de se rapprocher de l'efficacité du contrôle actif sans en supporter la complexité et la consommation. On considère d'abord l'association d'une résistance (qui a un effet similaire à un amortissement visqueux) et éventuellement d'une inductance (permettant de réaliser un oscillateur accordé) aux éléments piézoélectriques. Ces systèmes ont des propriétés intéressantes, mais sont peu efficaces à moins d'un accord très précis de l'inductance. Afin d'obtenir des performances élevées sans accord précis, on étudie un circuit à commutation, qui se ferme et s'ouvre à des instants bien précis. L'effet de la charge, qui freine la structure, s'apparente à un frottement sec. En synchronisant les commutations sur les vibrations, le système est auto-adaptatif et peut être auto-alimenté. Les fortes non-linéarités entraînent une excitation haute fréquence de la structure qui peut rendre la synchronisation problématique. Deux modèles électromécaniques (analytique et éléments finis) réduits sont proposés, permettant de décrire la dynamique du système complet de manière précise et de mettre en valeur le couplage entre un mode de vibration et le circuit électrique. Ce couplage est déterminant pour la réduction de vibrations. Une étude de l'influence de divers paramètres permet d'optimiser les éléments piézoélectriques, les circuits, et les instants de commutation. Ces résultats sont vérifiés expérimentalement. On constate un bon accord avec la théorie ; la difficulté de synchroniser correctement la commutation est aussi constatée.

L'étude présentée dans ce document a pour objet l'étude de différents modes de réduction de vibrations dans les structures avec liaisons. Le premier mode étudié se base sur la dissipation d'énergie apportée par la déformation d' éléments piézoélectriques connectés à un circuit électrique adapté. Le second mode proposé se base sur la propriété de la liaison boulonnée à changer les fréquences propres d'une structure en fonction du serrage appliqué. Cette propriété est utilisée avec plusieurs lois de contrôle du serrage afin d'éviter les plages de fréquences critiques. Ensuite une étude probabiliste est effectuée pour déterminer la robustesse de la réduction de vibrations par rapport à la variation de certains paramètres du modèle. Cette étude de robustesse est effectuée à travers des méthodes stochastiques non-intrusives, parmi lesquelles une méthode originale proposée. Elle permet une réduction de la taille du modèle stochastique à résoudre, ce qui réduit très considérablement le temps de calcul sans perte de qualité significative.

The endocrine heart synthesises and secretes two polypeptide hormones: the natriuretic peptides (NP) atrial natriuretic factor (ANF) and B-type natriuretic peptide (BNP). The biological actions of these hormones serve both acutely and chronically to reduce systemic blood pressure and hemodynamic load to the heart, thus contributing to the maintenance of cardiorenal homeostasis. Considerable effort has been focused on the elucidation of the mechanistic underlying ANF and BNP gene expression and secretion but much remains to be determined regarding specific molecular events involved in the cardiocyte secretory function. These hormones are produced by the atrial muscle cells (cardiocytes), which display a dual secretory/muscle phenotype. In contrast, ventricular cardiocytes display mainly a muscle phenotype. Comparatively little information is available regarding the genetic background for this important phenotypic difference with particular reference to the endocrine function of the heart. We postulated that comparison of gene expression profiles between atrial and ventricular muscles would help identify transcripts that underlie the phenotypic differences associated with the endocrine function of the heart as well as identify signaling pathways involved in its regulation. The cardiac atrial and ventricular transcriptomes were analyzed using oligonucleotide microarrays under normal or chronically induced aortocaval shunt volume-overload conditions. Transcriptional differences were validated by RT-PCR and transcripts of interest were knocked-down by RNAi. Comparison of gene expression profiles in the rat heart revealed a total of 1415 differentially expressed genes between normal atrial and ventricular tissues. Functional classification and pathway analysis identified numerous transcripts involved in mechanosensing, vesicle trafficking, hormone secretion, and G protein signaling. Volume-overloaded animals exhibited a progressive increase in cardiac mass over the four-week time course, an increase in expression of known hypertrophic genes, as well as the differential expression of 700 genes within the atria. Volume-overload specifically downregulated the accessory protein for heterotrimeric G protein signaling RASD1 in the atria. In vitro, knockdown of RASD1 in the atrial-derived HL-1 cells, significantly increased ANF secretion, demonstrating a previously unknown negative modulator role for RASD1. The data developed in this investigation provides insight into the expression profiles of genes particularly centered on the secretory function of the heart under normal and chronic hemodynamic overload conditions. Genome-wide expression profile analysis identified RASD1 as being differentially expressed between cardiac tissues as well as being modulated by chronic volume overload. RASD1 emerges as a tonic inhibitor of ANF secretion. The novel function identified herein for RASD1 in the atria is of considerable interest given the fact that secretory impairment of the cardiac natriuretic hormones can negatively impact cardiovascular homeostasis.

The issue of chronic renal failure and cannulation of permanent venous accesses in patients treated at haemodialysis centres is a topical and widespread problem of these days. According to generally accessible resources the incidence of terminal stage of renal failure, and thus the necessity to treat a patient by means of elimination methods, is very high, it reaches four individuals per thousand inhabitants according to the statistics. It is obviously a widespread nursing problem. The theoretical part of the thesis is divided into a summary and description of the present situation in chronic renal failure, particularly a brief insight into the chronic renal failure and its causes and syndromes. It also deals with the topic of the present treatment possibilities with stress on patient treatment at nephrologic outpatient clinics and in haemodialysis centres. The next chapter of the thesis describes the development from haemodialysis history up to the present advanced elimination methods. The present elimination methods bring the necessity of functional provision of venous access, particularly cannulation of AV fistulas, it is a very frequent nursing operation provided by nurses treating chronically affected patients at haemodialysis centres. This chapter is concluded by general knowledge of the techniques of cannulation of permanent venous accesses, possible occurrence of complications during the cannula penetration itself in relation to the physical phase of nursing treatment about patients with chronic renal failure. The practical part of the thesis was aimed at discovering or possible confirmation of the hypotheses discussed in the theoretical part. The practical research was based on searching for problems among dialyzed patients related to the permanent venous access, on finding the approach of nurses working at dialysis centres to cannulation of permanent accesses and on mapping the access of patients with permanent venous access to nurses with short time experience at a dialysis centre. Research questions were determined for this purpose and were processed within qualitative research into case reports upon depth interviews with nurses working at the dialysis centres of České Budějovice Hospital, Český Krumlov Hospital and Písek Hospital and their patients. The research data were processed into charts, where responses from patients and those from nurses were assessed separately. Occurrence frequency of the individual answers was particularly monitored in the individual output tables, however the responses were not processed by means of standard statistic methods because of the chosen methodology and thus a low number of respondents, but the output data served for drawing conclusions and preparing recommendations for application of nursing methods. The thesis conclusion summarizes the obtained knowledge and recommends possible procedures of solving the problems of cannulation of permanent venous accesses in patients with chronic renal failure treated at haemodialysis centres.

Made available in DSpace on 2014-12-17T14:55:44Z (GMT). No. of bitstreams: 1 PauloVS_DISSERT.pdf: 1338370 bytes, checksum: 7f4728ef2faffa30200a5b0daf963f20 (MD5) Previous issue date: 2010-06-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work describes the experimental implementation of a shunt active power filter applied to a three-phase induction generator. The control strategy of active filter turned to the excitation control of the machine and to decrease the harmonics in the generator output current. Involved the implementation of a digital PWM switching, and was made a comparison of two techniques for obtaining the reference currents. The first technique is based on the synchronous dq reference method and the second on the theory of instantaneous power. The comparison is performed via simulation and experimental results. To obtain the experimental results, was mounted a bench trial and the control and communications needed were implemented using DSP - MS320F2812. The simulation results and experimental data proved the efficiency of the filter to apply, highlighting the technique of instantaneous power / Este trabalho descreve a implementa??o experimental de um filtro ativo paralelo de pot?ncia aplicado a um gerador de indu??o trif?sico. A estrat?gia de controle do filtro ativo voltou-se para o controle de excita??o da m?quina e para a minimiza??o dos harm?nicos na corrente de sa?da do gerador. Envolveu a implementa??o de um chaveamento PWM digital, tendo sido realizada a compara??o de duas t?cnicas para obten??o das correntes de refer?ncia. A primeira t?cnica se baseia no m?todo referencial s?ncrono dq e a segunda na teoria das pot?ncias instant?neas. A compara??o ? realizada via simula??o e resultados experimentais. Para obten??o dos resultados experimentais, foi montada uma bancada experimental e o controle e comunica??es necess?rias foram implementados utilizando-se um DSP - TMS320F2812. Os resultados de simula??o e experimentais obtidos comprovaram a efici?ncia do filtro para a aplica??o, com destaque para a t?cnica das pot?ncias instant?neas

Orientador: Maria Cristina Dias Tavares / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-10T09:15:34Z (GMT). No. of bitstreams: 1 ZevallosAlcahuaman_MiltonElvis_M.pdf: 2029693 bytes, checksum: 59155e98cbc8a1da85069d7cec8f451e (MD5) Previous issue date: 2007 / Resumo: O arco secundário surge na manobra de abertura monofásica durante a eliminação de faltas monofásicas não permanentes para terra. O problema se apresenta especialmente nas linhas de EAT, no isolamento aéreo, em faltas que têm características não permanentes. Neste trabalho analisamos diferentes linhas de transmissão com níveis de tensão de 345 kV até 765 kV e com comprimentos de 150 km até 900 km, variando seu nível de compensação reativa em derivação de 40 % até 100 % e para as linhas mais longas compensando também 50 % da sua impedância longitudinal. Em linhas de EAT com compensação reativa em derivação é possível aproveitar a associação dos reatores adicionando um reator de neutro para minimizar o acoplamento mútuo entre as fases das linhas de transmissão, sendo este acoplamento a causa principal da manutenção da corrente de arco secundário. Com valores de reatores de neutro ótimos minimizamos a corrente de arco secundário e avaliamos a viabilidade da aplicação do religamento monofásico nos sistemas em estudo, aumentando o desempenho e confiabilidade dos sistemas elétricos / Abstract: The secondary arc appears in single-phase switching during clearing of non-permanent ground single-phase to ground faults. The problem happens especially on EHV lines, on aerial isolation, in faults with non permanent characteristics. In this work different transmission lines with voltage levels of 345 kV up to 765 kV and with 150 km up to 900 km length are analyzed, varying its level of reactive shunt compensation from 40 % up to 100 % and for the longest lines compensating 50 % of its longitudinal impedance. In EHV lines with have reactive shunt compensation, it is possible to add a neutral reactor in order to minimize the phase coupling of the transmission lines, being this coupling the main cause for the maintenance of the secondary arc current. With optimal values of neutral reactors it was possible to minimize the secondary arc current and evaluate the viability of the application of the single-phase reclosure in the systems under study, increasing the performance and reliability of the electrical systems / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2016-08-05T13:21:33Z No. of bitstreams: 1 delianevileladeoliveira.pdf: 2301067 bytes, checksum: f01e829116b34f9daf190e8d706de303 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-08-05T13:22:25Z (GMT) No. of bitstreams: 1 delianevileladeoliveira.pdf: 2301067 bytes, checksum: f01e829116b34f9daf190e8d706de303 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-08-05T13:22:35Z (GMT) No. of bitstreams: 1 delianevileladeoliveira.pdf: 2301067 bytes, checksum: f01e829116b34f9daf190e8d706de303 (MD5) / Made available in DSpace on 2016-08-05T13:22:35Z (GMT). No. of bitstreams: 1 delianevileladeoliveira.pdf: 2301067 bytes, checksum: f01e829116b34f9daf190e8d706de303 (MD5) Previous issue date: 2013-07-11 / Resumo: Pesquisa quantiqualitativa cuja trajetória metodológica visou analisar as representações sociais da punção venosa entre indivíduos adultos que vivenciaram a experiência com o processo de punção de vasos periféricos. Adotou-se múltiplos métodos e técnicas. Na abordagem quantitativa foi realizado um survey e no delineamento qualitativo foram utilizadas entrevistas individuais com aplicação das técnicas de “recorte e colagem de gibi” e “evocação livre”. A aplicação destas técnicas visou captar as variáveis intervenientes sobre o processo de punção de vasos periféricos e subsidiar a identificação dos elementos e caracterizar a relevância da representação social sobre tal processo. Dados obtidos no período de outubro/2012 a fevereiro/2013, por meio de entrevistas individuais gravadas e registro cursivo em diário de campo, realizados numa instituição hospitalar (setor de internação convencional) e num serviço de terapia renal substitutiva. Amostra de seleção completa. Após a aplicação dos critérios de elegibilidade e exclusão, foram realizadas 365 abordagens de coleta de dados, tendo participado 235 pessoas na fase do survey, das quais 120 estavam internadas, 75 estavam em hemodiálise e 40 coletaram sangue. Houve abordagem individualizada do questionário com auxílio para preenchimento. Técnica de evocação aplicada a partir de entrevista com participação de 90 pessoas, sendo 30 delas internadas, em coleta de sangue ou em tratamento hemodialítico. Foram obtidas 444 palavras/expressões evocadas para cinco das solicitadas. Na aplicação da técnica de “recorte e colagem de gibi” e gravação do discurso explicativo participaram 60 pessoas, sendo 20 em cada situação abordada. Foi oferecido o mesmo material de figuras para os participantes desta etapa. Um mesmo participante integrou uma ou mais técnicas. Os dados do survey foram tratados em software Statistical Package for the Social Sciences (SPSS) versão 20 com análise descritiva. Os dados provenientes da evocação formaram o corpus, sendo consolidados no software EVOC versão 2000 com análise pela técnica do quadro de quatro casas. E os conteúdos obtidos pela técnica de recorte e colagem de gibi foram consolidados no software NVivo versão 10 e analisados segundo similitude de expressões. Todas as informações foram abordadas com padrões de anonimato, utilizando nomes de flores, pedras ou cores. Foram atendidos todos os requisitos éticos e legais de pesquisa envolvendo seres humanos. No perfil dos participantes da fase survey predominou a participação de mulheres na coleta de sangue e de homens internados ou em tratamento hemodialítico; com idade mais nova entre mulheres que coletavam sangue; predomínio de pele declarada como branca (40%), menos de nove anos de escolaridade (65%), união estável (55%) e filhos. Sendo o processo de punção de vasos um procedimento técnico/científico, os usuários, porém, se apropriam do mesmo de forma particular, havendo destaque de algumas etapas em detrimento de outras. Foi possível identificar as variáveis intervenientes (exposição às diferentes situações e ocasiões de ocorrência do processo de punção de vasos) comparando-as com as variáveis de desfecho, ou seja, com os sentimentos, percepções e comportamentos dos participantes diante do processo de punção de vasos sanguíneos. Houve modificação de percepções, de sentimentos e de comportamentos ao longo das etapas do processo de punção dos vasos. No período que antecedeu a introdução da agulha no interior do vaso houve predomínio de sentimentos de medo, desconforto, ansiedade, indiferença e normalidade e foram adotados comportamentos de silêncio, colaboração, normalidade e de "acostumado", embora xx acompanhados pelo nervosismo das pessoas que fizeram hemodiálise. O período de introdução da agulha foi vivenciado com sentimentos de dor e desconforto e comportamentos de colaboração, silêncio e nervosismo, com ocasional desvio do olhar para não acompanhar o procedimento técnico realizado. Manter a agulha no interior do vaso gerou predomínio de sentimentos de limitação de movimento e desconforto quando o período foi prolongado e houve comportamento de colaboração. O sentimento de alívio e a sensação de ardência foram aqueles que predominantemente emergiram por ocasião da remoção do cateter do interior do vaso e os participantes mencionaram adotar comportamentos de colaboração e de indiferença frente à remoção. No período pós-remoção predominaram os sentimentos de indiferença, alívio, normalidade e nada e comportamentos de silêncio e colaboração, caracterizando a não percepção deste momento como uma etapa do processo, exceção feita às pessoas que realizaram hemodiálise. Os resultados evidenciaram que a estrutura das representações sociais do processo de punção de vasos foi composta pelos elementos centrais de dor e medo. Como elementos periféricos apareceram a insegurança, quem punciona, habilidade profissional, resultado, repuncionar e sangrar, configurando uma abordagem negativa ou neutra expressa em diferentes situações de punções que se apoiaram em experiências, informações, julgamento de valores, concepção de sua finalidade e percepção sensorial, o que foi reafirmado pela técnica de recorte e colagem. Captar as representações sociais através dos sentimentos e comportamentos, bem como, conhecimentos, valores e experiências das pessoas que possuem seus vasos puncionados para fins de coleta de sangue, terapêutica farmacológica ou hemodialítica durante o processo de punção possibilitou fazer uma releitura da punção de vasos. Enquanto atividade processual, evidenciaram-se demandas de cuidado para as quais o enfermeiro dispõe de oportunidades para imprimir ao cuidado orientações educacionais, ações terapêuticas e gerenciais e captar/utilizar evidências a partir da investigação. Foram caracterizadas respostas dos indivíduos para as quais o enfermeiro é capaz de minimizar sentimentos e comportamentos negativos e favorecer formas positivas de enfrentamento. Ao propor-se uma abordagem quantiqualitativa, utilizando múltiplos métodos e técnicas a partir de um recorte conceitual e metodológico, a presente investigação mostrou-se enriquecedora e criativa e trouxe como limite a não comparação entre os participantes enquanto grupos que possuem vivências peculiares no processo de punção de vasos sanguíneos. / Abstract: Quanti-qualitative research whose methodological route intended to analyze the social representations of venipuncture among adults who have experienced the peripheral vessels puncture. Multiple methods and techniques were adopted. During the quantitative approach a survey research was conducted, while in the qualitative approach individual interviews were taken, applying the techniques of "cutting and pasting of comics" and "free recall". The application of these techniques aimed to capture intervening variables on the process of puncturing peripheral vessels and support the identification of elements and characterize the relevance of the social representation of this process. Data obtained from October 2012 to February 2013 through individually recorded interviews and field diary, both conducted in a hospital (regular hospitalization area) and in a program of renal replacement therapy. Sample selection complete. After applying the eligibility and exclusion criteria, there were 365 approaches for data collection, 235 people participated in the phase of the survey, of whom 120 were hospitalized, 75 were on hemodialysis and 40 collected blood samples. There was individualized approach and help to fill the questionnaire. Evocation technique applied in the interviews, with participation of 90 people, 30 of them hospitalized for blood collection or hemodialysis. With the inductive term appointed (process of vessel puncture). We obtained 444 words/expressions evoked to five of the requested. In applying the technique of "cutting and pasting of comics" and recording the explanatory discourse 60 people participated, 20 in each situation addressed. The same comics were shown to the participants of this step. A participant joined one or more techniques. For the treatment of the survey data, with descriptive analysis, was used the Statistical Package for Social Sciences (SPSS) version 20. Evocation data formed the corpus, consolidated in EVOC 2000 version, and were analyzed through the fourhouse board technique. The contents obtained by the technique of cutting and pasting the comics were consolidated into NVivo software version 10 and analyzed according to similarity of expressions. All information has been addressed with patterns of anonymity, using names of flowers, stones or colors. We met all ethical and legal requirements for research involving humans. In the survey phase participants profile predominated the participation of women in blood sample collection and men hospitalized or undergoing hemodialysis, with younger age among women who collected blood; predominance of skin declared as white (40%), less than nine years of education (65%), marital stability (55%) and children. As the process of vessel puncture is a technical/scientific procedure, users, however, interpret it in a particular way, featuring some steps over others. It was possible to identify the intervening variables (exposure to different situations and times of occurrence of vessels puncture processes) compared with the outcome variables, i.e., the feelings, perceptions and behaviors of the participants before the process of puncturing blood vessels. There was a modification of perceptions, feelings and behaviors throughout the stages of the process of vessels puncturing. In the period preceding the introduction of the needle inside the vessel there was a predominance of feelings of fear, discomfort, anxiety, indifference and normality and behaviors of xxii silence, collaboration, normality and "being used to" were adopted, although accompanied by the nervousness of those people in hemodialysis. The length of the needle insertion was experienced with feelings of pain and discomfort and behaviors of collaboration, silence and nervousness, with occasional gaze deviation, not to follow the technical procedure performed. Maintaining the needle in the vessel predominantly generated feelings of limitation of movement and discomfort when the period was extended. There was also the behavior of collaboration. The feeling of relief and burning sensation were predominantly those who emerged during the removal of the catheter inside the vessel and the participants mentioned to adopt behaviors of collaboration and indifference to the removal. In the post-removal time predominated feelings of indifference, relief, normality and nothing and behaviors of silence and collaboration, showing the non-perception of this moment as a step of the process, except to people who underwent hemodialysis. The results showed that the structure of social representations of vessel puncture was composed by the central elements of pain and fear. The peripheral elements appeared insecurity, who punctures, professional skill, result, repuncturing and bleed, setting a neutral or negative approach expressed in different puncture situations that relied on experience, information, value judgment, conception of its purpose and sensory perception, what was reaffirmed by the technique of cutting and pasting. To capture the social representations through the feelings and behaviors, as well as knowledge, values, experiences of people own their vessels punctured for the purpose of blood collection, drug therapy or hemodialysis during puncture, allowed to reread the puncture of vessels. While a procedural activity, care demands showed up for which the nurse has opportunities to print educational guidelines, therapeutic and management actions and to capture/use evidences from the investigation. Answers of individuals were characterized for which the nurse is able to minimize negative feelings and behaviors and to encourage positive ways of coping. In proposing a quanti-qualitative approach, using multiple methods and techniques from a conceptual and methodological framework, this research proved to be enriching and creative and brought as its limitation the not comparison of the participants while groups that have peculiar experiences in the process of blood vessels puncturing.

Ce travail porte sur l’étude d’amortissement piézoélectrique shunté pour les roues aubagées désaccordées de turbomachines. Les problèmes vibratoires sont de première importance pour les motoristes aéronautiques et, parmi ceux-ci, les vibrations causées par le désaccordage des aubes tiennent une place importante puisqu’elles sont à l’origine des phénomènes de fatigue oligocyclique et des risques de défaillance associés. L’usage de technologies d’amortissement est donc assez répandu pour réduire l’amplitude vibratoire. Ici, on s’intéresse à l’étude de l’amortissement piézoélectrique shunté appliqué aux roues aubagées désaccordées. Dans notre stratégie, des patchs piézoélectriques shuntés sont attachés sur la surface de la roue entre les aubes adjacentes afin de dissiper l’énergie mécanique de la roue. Par conséquent, l’amplitude des aubes peut être réduite du fait du couplage entre les aubes et la roue. Cette stratégie est d’intérêt pour l’ingénieur car les transducteurs piézoélectriques sont placés en dehors du flux principal des turbomachines. Un modèle numérique a été développé intégrant des circuits piézoélectriques shuntés résonnants. L’amortissement piézoélectrique shunté et un motif optimisé de désaccordage piézoélectrique sont tous les deux introduits afin de minimiser l’effet du désaccordage des aubes. En pratique, le désaccordage des aubes change au cours de la vie du moteur. Les raisons peuvent être multiples comme l’usure, des endommagements par impacts qui vont conduire inévitablement à une évolution du motif du désaccordage. En s’appuyant sur la stratégie de contrôle adaptatif, nous avons proposé un shunt piézoélectrique résonant capable de suivre l’évolution de la structure au cours du temps. Les simulations numériques montrent qu’une bonne efficacité est obtenue en termes de réduction des vibrations de roues aubagées désaccordées. Dans cette thèse, une dernière stratégie est proposée qui correspond à la mise en place d’un système de pompage énergétique nonlinéaire basé sur les éléments piézoélectriques. Une fois intégrées dans une structure mécanique, il est donc en mesure d’agir en tant qu’amortisseur de vibrations, adaptatif et large bande. Une méthode numérique, à coefficient variables de balance harmonique, a été développée afin de calculer les réponses quasi-périodiques associés à ce type de problème. Ce dispositif de pompage énergétique piézoélectrique semble particulièrement intéressant dans le cadre des roues aubagées désaccordées, car il est capable d’interagir de façon adaptative avec chaque secteur de la roue désaccordé. Des résultats prometteurs ont été obtenus et illustrent démontrent ce point de vue. / This study deals with piezoelectric shunt damping in the mistuned bladed disks. Bladed disks are rich dynamical systems that are known to suffer from severe vibration problems. Blade mistuning is an issue of major concern since it is responsible for high cycle fatigue and failure risks. In the mitigation practice, additional damping is usually introduced into the structure to reduce vibration amplitudes. Here, we are interested in piezoelectric shunt damping applied into mistuned bladed disks. In our proposed damping strategy, shunted piezoelectrics are attached onto the disk surface between adjacent blades in order to dissipate the disk mechanical energy. Consequently the blade vibration can be reduced due to the blade-disk coupling. This strategy is of engineering interest since piezoelectric transducers are placed outside other main stream in turbomachinery. This idea is developed based on a lumped-parameter bladed disk model. Resonant shunt circuits are adopted. Both piezoelectric shunt damping and optimized piezoelectric mistuning are introduced to minimize the blade mistuning effect. Piezoelectric mistuning can be seen as a kind of damping mistuning; it is modeled as a small variation of the inductance value of each shunt circuit. In reality the blade mistuning pattern is not constant in the long run. Due to various complexities, a perturbation of the blade mistuning pattern might result. In benefitting from the manageability and controllability of piezoelectric shunt circuits, an adaptive control strategy is developed to adjust the optimal piezoelectric mistuning pattern according to the perturbation. Numerical simulations reveal that a fine performance is achieved in terms of reducing the blade vibration of slowly time-variant, mistuned bladed disks. An essentially nonlinear piezoelectric shunt circuit is proposed as practical realization of nonlinear energy sink (NES). This piezoelectricbased NES is featured by nonexistence of preferential resonant frequency. It is therefore able to act in essence, as a passive, adaptive, broadband vibration absorber, when integrated into a mechanical structure. A variable-coefficient harmonic balance method for quasiperiodic responses is devised. It helps gain insights into the complex dynamics of forced response when the coupled electromechanical system is under harmonic external forcing. The appealing property of the piezoelectric-based NES enables it especially suitable for applications in mistuned bladed disks since it is capable of adaptively interacting with each sector of mistuned bladed disks in a broadband fashion. Promising results obtained in the numerical studies further demonstrate this viewpoint.

L’imagerie fonctionnelle cérébrale détecte les changements hémodynamiques induits par un stimulus pour déterminer les zones d’activation neuronale. Plus particulièrement, l’imagerie BOLD en IRMf détecte les changements d’oxygénation du sang grâce aux propriétés paramagnétiques de la déoxyhémoglobine. L’oxygène n’est donc pas uniquement un substrat énergétique pour le tissu neuronal, il joue également un rôle majeur dans l’imagerie noninvasive du cerveau humain. Au cours de ma thèse, j’ai tout d’abord participé à la mise au point d’une nouvelle technique non-invasive d’imagerie de l’oxygène dans le cerveau d’animaux anesthésiés. Couplant un nouveau senseur phosphorescent de l’oxygène (Finikova et al., 2008) et la microscopie biphotonique, cette approche permet à la fois de cartographier l’oxygène en 3D avec une résolution spatiale et temporelle jusqu’alors inégalée, mais aussi de suivre simultanément l’oxygène et le flux sanguin dans les capillaires cérébraux au repos ou lors d’une activation neuronale (Lecoq et al., 2011). Tirant profit des nouvelles possibilités de cette technique, nous avons alors démontré: • la présence d’un shunt artério-veineux uniquement basé sur la diffusion de l’oxygène. Ce résultat, obtenu chez le rat dans la couche la plus superficielle du bulbe olfactif: la couche du nerf (ONL), confirme que l’oxygène ne diffuse pas uniquement à partir des capillaires et démontre que les artérioles contribuent significativement à l’oxygénation du tissu cérébral. Il démontre également qu’il n’est pas possible de déterminer ni la Po2 capillaire ni la Po2 tissulaire à partir de la Po2 veineuse. • l’existence de transitoires de Po2 associés à chaque globule rouge dans le compartiment capillaire, appelés EATs (erythrocyte-associated transients) (Hellums, 1977; Cabrales and Intaglietta, 2007). En bref, de part leur diamètre supérieur à celui de la lumière d’un capillaire, les globules rouges passent un à un dans la lumière des capillaires, laissant entre eux un espace de plasma. Cependant, la faible solubilité de l’oxygène dans le plasma crée une barrière à la diffusion, ce qui se traduit par une inhomogénéité de la Po2 capillaire: celle-ci est élevée au bord du globule rouge et décroit avec la distance pour atteindre un minimum à mi-distance entre deux globule rouges. Poursuivant l’étude des EATs (Parpaleix et al., 2013), nous avons observé les points suivants: • La Po2 tissulaire dans l’environnement immédiat d’un capillaire peut être déterminée à partir de la Po2 vasculaire à mi-distance entre deux érythrocytes. Ce résultat est intéressant en ce qu’il permettra d’effectuer des mesures non invasives de Po2 tissulaire, utile notamment chez l’animal éveillé. • L’amplitude des EATs est si large (35 mmHg en moyenne) que la Po2 capillaire moyenne ne reflète en rien la saturation en oxygène de l’hémoglobine. • Une empreinte filtrée des EATs vasculaires est détectable dans le tissu (_5 mmHg d’amplitude). • Au cours d’une stimulation neuronale, une diminution de la Po2 capillaire moyenne peut être détectée avant l’hyperémie fonctionnelle, un résultat jusqu’à présent controversé dans le domaine de l’imagerie BOLD en IRMf, mais important en ce que ce dip pourrait être un rapporteur très résolutif de l’activation neuronale. Parmi les questions restant en suspens et pouvant être étudiées finement avec notre approche, j’en citerai une principale: quel est le poids des différents facteurs (métaboliques, présynaptiques ou post-synaptiques) et du flux sanguin dans l’établissement de la Po2 cérébrale au repos? / In humans, functional mapping of brain activity mainly relies on the increase of cerebral blood flow (CBF) triggered by neuronal activation. This neurovascular coupling provides energy substrates such as oxygen and glucose to the activated area. The steady state concentration of oxygen, as well as its dynamics upon neuronal activation, have been investigated with numerous methods, however, none of them provided highly resolute measurements in depth. During my PhD, we combined a phosphorescence quenching approach with two-photon microscopy to detect, in depth and with a micrometer spatial resolution scale, the emission of phosphorescence by PtP-C343, a new oxygen nano-sensor designed for two-photon excitation. We first characterized the technique and then reported two biological results, using the olfactory bulb (OB) glomerulus as a model to study oxygen concentration, at rest and upon odor stimulation. We found an arterio-venous shunt, purely based on diffusion, in the superficial nerve layer of the OB, confirming the role of arterioles in brain oxygenation. Simultaneous measurements of Po2 and blood flow allowed us to reveal the presence of erythrocyte-associated transients (EATs), i.e. Po2 fluctuations that are associated with individual erythrocytes. Pursuing the investigation of EAT characteristics, we found that in capillaries, Po2 at mid-distance between two erythrocytes is at equilibrium with, and thus reports Po2 in the nearby neuropil. Finally, we could observe that even in capillaries, a small oxygen initial dip can be detected prior to functional hyperemia, upon odor activation.