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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Synthese der Bacteriocine Amylocyclicin A und Plantazolicin in Bacillus amyloliquefaciens FZB42

Scholz, Romy 21 February 2011 (has links)
Bacillus amyloliquefaciens FZB42 ist ein grampositives Bodenbakterium. Es kann in der Rhizosphäre das Wachstum von Pflanzen fördern und durch die Produktion von Sekundärmetaboliten phytopathogene Organismen hemmen. Aus der Genomanalyse und den dazugehörigen Arbeiten war bekannt, dass Bacillus amyloliquefaciens FZB42 nicht-ribosomal je drei antimikrobielle Polyketide und Lipopeptide herstellt, sowie zwei Siderophore und das Dipeptid Bacilysin. Für Bacillus typische Lantibiotika oder große Bacteriocine wurden nicht gefunden. In dieser Arbeit wird erstmalig gezeigt, dass Bacillus amyloliquefaciens FZB42 auf ribosomale Weise antibakterielle Peptide herstellt. Zwei bisher unbekannte Bacteriocine, Amylocyclicin A und Plantazolicin, und deren dazugehörigen Gencluster konnten identifiziert und charakterisiert werden. Amylocyclicin A ist ein unmodifiziertes Peptid, dessen N- und C-Terminus kovalent verbunden sind. Es wurde der Gruppe I der zirkulären Bacteriocine zugeordnet, dessen Mitglieder sich durch schwache Homologie untereinander, aber durch wahrscheinlich ähnliche 3D-Strukturen auszeichnen. Die Masse beträgt 6381 Da und die Substanz ist stark aktiv gegen grampositive Bakterien. Das Biosynthesecluster umfasst sechs Gene für die Synthese, den Export, die Zyklisierung und die Immunität. Plantazolicin ist ein hydrophobes, stark modifiziertes Peptid aus der TOMM-Gruppe, einer Gruppe aus Microcin B17-ähnlichen Peptiden, die nach neueren Erkenntnissen verbreiteter ist, als bisher bekannt. Plantazolicin ist schwach aktiv gegen grampositive Bakterien und besitzt die Masse 1335 Da. Das Biosynthesecluster umfasst zwölf Gene, mit allen nötigen Genen für Synthese, Modifikation, Regulation, Immunität und Export. / Bacillus amyloliquefaciens FZB42 is a Gram-positive, plant-associated bacterium, which stimulates plant growth and produces secondary metabolites that suppress soil-borne plant pathogens. Five gene clusters direct the non-ribosomal synthesis of the cyclic lipopeptides surfactin, bacillomycin, fengycin, an unknown peptide and the iron-siderophore bacillibactin. Three gene clusters direct the non-ribosomal synthesis of the antibacterial acting polyketides macrolactin, bacillaene and difficidin; in addition to the non-ribosomal synthesis of the antibacterial dipeptide bacilysin. Genes involved in ribosome-dependent synthesis of lantibiotics and other peptides are scarce. Only two incomplete gene clusters directing immunity against mersacidin and subtilin were found. In this work two ribosomally synthesized antibacterial peptides, amylocyclicin A and plantazolicin, and their corresponding gene clusters were identified. Amylocyclicin A is a circular peptide with a mass of 6381 Da and strong activity against Gram-positive bacteria. Six genes are responsible for the synthesis, maturation, export and immunity of this peptide belonging to group I of circular bacteriocins. Plantazolicin is a strongly modified hydrophobic peptide bearing a molecular mass of 1,335 Da and displaying antibacterial activity toward closely related Gram-positive bacteria. Essential modification contains the incorporation of azole heterocycles, which derive from Cys, Ser, and Thr residues of the precursor peptide and addition of two methyl groups. Twelve genes are responsible for synthesis, modification, export and immunity of this peptide belonging to the TOMM group of thiazol/oxazol modified microcins.
42

La poétique des éléments dans "La Pharsale" de Lucain

Loupiac, Annie January 1998 (has links)
Édition de : Thèse 3e cycle : Etudes latines : Paris 4 : 1986. / Bibliogr. p. [225]-228 Notes bibliogr. Index.
43

MONTE SIÃO EXTREMIDADE DO SAFON: Estudo da influência da mitologia cananéia na Teologia de Sião a partir da análise exegética do Salmo 48 / Mount of Zion, Extreme Parts of Saphon : Study of the Influence of the Canaanite Mythology in the Theology of Zion from the Exegetical

Mendonça, élcio Valmiro Sales de 29 February 2012 (has links)
Made available in DSpace on 2016-08-03T12:18:59Z (GMT). No. of bitstreams: 1 Elcio V S Mendonca.pdf: 938537 bytes, checksum: 5c2862b0c25ee6bf58d1c47c44fb8074 (MD5) Previous issue date: 2012-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Theology of Zion by the tradition of sons of Korah is somewhat curious. Tease is entertaining the idea of a canaanite influence in the Theology of Zion. There isn t denying that fact, because Psalm 48 seems to really have this influence. It is a canaanite influence and also the traditions of South Judahite. This research aims analyze the existing Theology of Zion in Jerusalem and presented in Psalm 48. This is to arrive at an answer about the influence that the sons of Korah may been the canaanite religion, using elements of canaanite myths in the composition of Psalm 48 and other psalms of this collection. Terms like Saphon, sea, death and Mount Zion, and concepts like mythology, sacred mountain, end of the world, Olympus, etc., make us think that really wanted to override the canaanite myths presenting a new reading from the faith in Yahweh. The sons of Korah had were North Israelite traditions, the cities where they lived were located in Ephraim, Manasseh and Dã. Some cities of Manasseh and Ephraim were canaanites cities. The kings of North were mostly promoter of the canaanite Religion. This was the environment where the sons of Korah lived and served your levitical minitstry. / A Teologia de Sião expressa pela tradição dos filhos de Corá é de certa forma curiosa. É implicante admitir a idéia de uma influência cananeia na Teologia de Sião. Não há como negar esse fato, pois o Salmo 48 parece realmente possuir esta influência. É uma influência cananeia e também das tradições do Sul judaíta. Esta pesquisa tem por objetivo analisar tal teologia de Sião existente em Jerusalém e apresentada no Salmo 48. Isto para chegar a uma resposta acerca da influência que os filhos de Corá podem ter sofrido da religião cananeia, ao utilizar elementos dos mitos cananeus na composição do Salmo 48 e de outros salmos de sua coleção. Termos como Safon, mar, morte, Monte Sião e outros, e conceitos como mitologia, montanha sagrada, extremidade do mundo, Olimpo, etc, fazem pensar que eles de fato queriam sobrepor os mitos cananeus apresentando uma nova leitura, a partir da fé em Javé. Os filhos de Corá possuíam tradição do Norte israelita. As cidades onde eles habitaram estavam situadas em Efraim, Manassés e Dã. Algumas cidades de Manassés e Efraim eram cananeias. Os reis do Norte eram em sua maioria promotores da religião cananeia. Este era o ambiente onde os filhos de Corá habitaram e cumpriram seu ministério levítico.
44

Síntese de materiais compósitos micro-mesoporosos visando a captura de CO2

Silva, Silvia Caroline Gomes dos Santos 29 July 2015 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / factor responsible for climate change worldwide. In recent years, several research are intended to developing new methods and technologies to capture and separation CO2. The use of the adsorption method for separating CO2 is a promising alternative in view of the potential to reduce energy costs by eliminating aqueous solutions and providing capture and regeneration rates adequate. In this context, this paper presents the synthesis of composite type materials ZSM-12 / MCM-41 and ZSM-12 / MCM-48, seeking to combining the properties of the zeolitic material to the structural advantages of mesoporous materials, resulting in obtaining materials with high CO2 adsorption capacity. For this, the materials were synthesized by hydrothermal method and mechanosynthesis. The materials were characterized by XRD, absorption spectroscopy in the infrared, thermal analysis, adsorption-desorption analysis of N2 A 77 K, SEM and TEM. The CO2 adsorption capacity of these materials were investigated by gravimetric analysis. The results obtained from the characterization techniques showed that the synthesis methodology, used for desilication phase of ZSM-12, was efficient in obtaining a composite material with integrated micro and mesoporous phases. On the other hand, the results showed that by mechanosynthesis was possible to obtain materials formed by mixing between the micro and mesoporous phases. Also, comparing the results of adsorption CO2 the obtained composite materials by hydrothermal method with those obtained by mechanosynthesis it was concluded that the adsorption capacity is influenced by crystallinity and amount of the phase ZSM-12. The results showed from adsorption, in general, ZM48-75 samples, ZM41 A/MH R3 and ZM41-50 showed higher adsorption capacity than pure zeolitic and mesoporous materials, respectively. Thus, the composite materials of the type ZSM-12/ZSM-41 and MCM-12/MCM-48 are promising adsorbents for CO2 separation. / O aumento da concentração de dióxido de carbono na atmosfera é apontado como o principal fator responsável pelas mudanças climáticas em escala mundial. Nos últimos anos, várias pesquisas têm por finalidade o desenvolvimento de novos métodos e tecnologias para captura e separação de CO2. A utilização do método de adsorção para separação de CO2 é uma alternativa promissora, tendo em vista o potencial para reduzir os custos energéticos, eliminando soluções aquosas e proporcionando captura e taxa de regeneração adequadas. Nesse contexto, neste trabalho apresenta-se a síntese de materiais compósitos do tipo ZSM-12/MCM-41 e ZSM-12/MCM-48, visando combinar as propriedades do material zeolítico com as vantagens estruturais dos materiais mesoporosos, resultando na obtenção de materiais com elevadas capacidades de adsorção de CO2. Para isto, os materiais foram sintetizados pelo método hidrotérmico e por mecanosíntese. Os materiais obtidos foram caracterizados por DRX, espectroscopia de absorção na região do infravermelho, análise térmica, analise de adsorção-desorção de N2 A 77 K, MEV e TEM. A capacidade de adsorção de CO2 destes materiais foi investigadas através da análise gravimétrica. As técnicas de caracterização mostraram que a metodologia de síntese adotada via dessilicalização da fase ZSM-12 foi satisfatória na obtenção de um material compósito com as fases micro e mesoporosas integradas. Por outro lado, os resultados evidenciaram que através da mecanosíntese foi possível obter materiais formados pela mistura entre as fases micro e mesoporosas. Além disso, comparando-se os resultados de adsorção de CO2 dos materiais compósitos obtidos via método hidrotérmico com os obtidos via mecanosíntese foi possível concluir que a capacidade de adsorção é influenciada pela cristalinidade ou teor da fase ZSM-12. Considerando-se os resultados de adsorção apresentados, de maneira geral, as amostras ZM48-75, ZM41-A/R3-MH e ZM41-50, apresentaram maior capacidade de adsorção que os materiais zeolíticos e mesoporosos puros, respectivamente. Sendo assim, os materiais compósitos do tipo ZSM-12/MCM-41e ZSM-12/MCM-48 são promissores adsorventes para separação de CO2.
45

Síntese de materiais compósitos micro-mesoporosos visando a captura de CO2

Silva, Silvia Caroline Gomes dos Santos 29 July 2015 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / factor responsible for climate change worldwide. In recent years, several research are intended to developing new methods and technologies to capture and separation CO2. The use of the adsorption method for separating CO2 is a promising alternative in view of the potential to reduce energy costs by eliminating aqueous solutions and providing capture and regeneration rates adequate. In this context, this paper presents the synthesis of composite type materials ZSM-12 / MCM-41 and ZSM-12 / MCM-48, seeking to combining the properties of the zeolitic material to the structural advantages of mesoporous materials, resulting in obtaining materials with high CO2 adsorption capacity. For this, the materials were synthesized by hydrothermal method and mechanosynthesis. The materials were characterized by XRD, absorption spectroscopy in the infrared, thermal analysis, adsorption-desorption analysis of N2 A 77 K, SEM and TEM. The CO2 adsorption capacity of these materials were investigated by gravimetric analysis. The results obtained from the characterization techniques showed that the synthesis methodology, used for desilication phase of ZSM-12, was efficient in obtaining a composite material with integrated micro and mesoporous phases. On the other hand, the results showed that by mechanosynthesis was possible to obtain materials formed by mixing between the micro and mesoporous phases. Also, comparing the results of adsorption CO2 the obtained composite materials by hydrothermal method with those obtained by mechanosynthesis it was concluded that the adsorption capacity is influenced by crystallinity and amount of the phase ZSM-12. The results showed from adsorption, in general, ZM48-75 samples, ZM41 A/MH R3 and ZM41-50 showed higher adsorption capacity than pure zeolitic and mesoporous materials, respectively. Thus, the composite materials of the type ZSM-12/ZSM-41 and MCM-12/MCM-48 are promising adsorbents for CO2 separation. / O aumento da concentração de dióxido de carbono na atmosfera é apontado como o principal fator responsável pelas mudanças climáticas em escala mundial. Nos últimos anos, várias pesquisas têm por finalidade o desenvolvimento de novos métodos e tecnologias para captura e separação de CO2. A utilização do método de adsorção para separação de CO2 é uma alternativa promissora, tendo em vista o potencial para reduzir os custos energéticos, eliminando soluções aquosas e proporcionando captura e taxa de regeneração adequadas. Nesse contexto, neste trabalho apresenta-se a síntese de materiais compósitos do tipo ZSM-12/MCM-41 e ZSM-12/MCM-48, visando combinar as propriedades do material zeolítico com as vantagens estruturais dos materiais mesoporosos, resultando na obtenção de materiais com elevadas capacidades de adsorção de CO2. Para isto, os materiais foram sintetizados pelo método hidrotérmico e por mecanosíntese. Os materiais obtidos foram caracterizados por DRX, espectroscopia de absorção na região do infravermelho, análise térmica, analise de adsorção-desorção de N2 A 77 K, MEV e TEM. A capacidade de adsorção de CO2 destes materiais foi investigadas através da análise gravimétrica. As técnicas de caracterização mostraram que a metodologia de síntese adotada via dessilicalização da fase ZSM-12 foi satisfatória na obtenção de um material compósito com as fases micro e mesoporosas integradas. Por outro lado, os resultados evidenciaram que através da mecanosíntese foi possível obter materiais formados pela mistura entre as fases micro e mesoporosas. Além disso, comparando-se os resultados de adsorção de CO2 dos materiais compósitos obtidos via método hidrotérmico com os obtidos via mecanosíntese foi possível concluir que a capacidade de adsorção é influenciada pela cristalinidade ou teor da fase ZSM-12. Considerando-se os resultados de adsorção apresentados, de maneira geral, as amostras ZM48-75, ZM41-A/R3-MH e ZM41-50, apresentaram maior capacidade de adsorção que os materiais zeolíticos e mesoporosos puros, respectivamente. Sendo assim, os materiais compósitos do tipo ZSM-12/MCM-41e ZSM-12/MCM-48 são promissores adsorventes para separação de CO2.
46

The Impact of a Part 48 Training Program on the Health and Safety Knowledge Level of Newly Employed Inexperienced Miners

Revel, Layton 12 1900 (has links)
The impact of a mandatory Part 48 training program on the health and safety knowledge level of newly employed inexperienced miners in Texas was studied. Part 48 training was defined by compliance with Mine Safety and Health Administration's (MSHA) mandatory health and safety training requirements. A two-group pretest, posttest research design was utilized. Group one individuals were newly employed inexperienced persons who received mandatory Part 48 training in accordance with MSHA guidelines. Group two subjects were newly employed inexperienced persons who worked for companies that were exempt from conducting a Part 48 training program. MSHA's health and safety knowledge inventory was utilized. A significant difference was found in the health and safety training program when compared with individuals who did not receive the training . A significant difference was also found in the posttest scores for eight of the ten subject areas of the MSHA health and safety knowledge inventory for persons who completed a Part 48 training program when compared to persons who did not receive the training . Analysis of gain scores resulted in significant differences in the same subject areas indicated by posttest scores. It was concluded that MSHA Part 48 did have a significant impact on the health and safety knowledge level of newly employed inexperienced miners. Additional implications noted relate to the impact of a Part 48 training program on accidents, productivity, absenteeism, turnover, job satisfaction and management styles; role of MSHA in miner training; development of new training materials; methods of training; and the evaluation of health and safety training programs.
47

Listening to the domestic music machine

Lockhart, William 19 December 2012 (has links)
Klavierbearbeitungen waren für die Aufführungs- sowie Hörgewohnheiten des nichtprofessionellen Musikers des neunzehnten Jahrhunderts entscheidend. Nicht nur deckten sie den dringenden Bedarf an einer kosteneffektiven musikalischen Verbreitungstechnologie sondern ihre immense Popularität verursachte eine mit großen Umfang kommerzielle musikalische Verlagsindustrie. Diese Dissertation stellt zum ersten Mal die viele Seiten des Klavierarrangements wieder her, indem es als musikalisches Schaffen, als Konsumware und als Objekt vieler kritischen Diskurse analysiert wird. Es wird gezeigt, dass Arrangement---als musikalisches Schaffen---eine Methodensammlung statt einer in sich geschlossenen Technik ist. Walter Benjamins Übersetzungstheorie wird mit einer Analyse der ersten, in dem Robertsbridge Codex aus 1360 sich befindenden, Klavierbearbeitung verbunden, um vorzuschlagen, dass Arrangements als eine Auferstehung ihrer Originale gesehen werden sollen. Die wirtschaftliche Wichtigkeit der Klavierbearbeitung wird durch einer vom Computer errechneten statistischen Analyse dargestellt, indem es gezeigt wird, dass Arrangementmethoden in 30 Prozent der in deutschsprachigen Ländern zwischen 1829 und 1900 publizierten Klaviermusik vorkommt. Die kritischen Diskurse mit denen den Wert eines Arrangements geschätzt wurde werden auch rekonstruiert: Musikalische Lexika werden benutzt, um eine Begriffsgeschichte mehrerer Schlüsselbegriffe zu schreiben. Letztlich werden die Ähnlichkeiten des Hörgewohnheiten der Hörer des neunzehnten und des einundzwanzigsten Jahrhunderts betont, damit neue Forschungsperspektiven eröffnet werden können. / Keyboard arrangement was central to both the performing and the listening habits of the nineteenth-century non-professional musician. Not only did it respond to the desperate need for a cheap technology of musical circulation, but its immense popularity helped create a commercial musical publishing industry of an unprecedented scale. This thesis reconstructs for the first time the many faces of the keyboard arrangement by analysing it simultaneously as a musical work, an economic commodity and the object of a number of critical discourses. As a musical work, arrangement is shown to be a collection of practices, rather than, and as has been previously assumed, a self-contained product. Walter Benjamin''s theory of translation is combined with an analysis of the first extant keyboard arrangement in the Robertsbridge Codex of 1360 to construct a model which suggests that arrangements should be understood as resurrections of the material of their originals. The economic significance of keyboard arrangement is demonstrated through a computer-aided statistical analysis which shows that on average practices of arrangement appeared in 30 percent of the keyboard music published in German-speaking countries from 1829 to 1900. Significant attention is given to an attempt to reconstruct the critical discourses by which arrangements were assessed: in particular, musical dictionaries are used to produce a Begriffsgeschichte of several key terms relating to the production of arrangements. Finally, throughout the thesis, emphasis is placed on the extent to which the kinds of listening experience that arrangement engendered show similarities with those offered by popular musical styles of today, thereby opening up new avenues for research.
48

Dépistage en IRM mammaire / Breast MRI screening

Oldrini, Guillaume 19 December 2017 (has links)
L’IRM mammaire a une place prépondérante dans l’imagerie mammaire. Son utilisation plus large est limitée notamment par son coût et le nombre limité de machines. Nous avons travaillé sur plusieurs aspects de cette problématique. Dans un premier temps, nous avons modifié le positionnement en passant du procubitus au décubitus. Ceci a permis de montrer que le décubitus permettait une meilleure corrélation topographique des lésions avec l’échographie et était mieux toléré par les patientes. Dans un deuxième temps, nous avons étudié les facteurs de réduction du temps d’acquisition par l’intermédiaire des séquences à haute résolution temporelle et d’un protocole abrégé. Ces changements devraient permettre de faciliter l’accessibilité de l’IRM aux patientes, de réduire son coût tout en conservant les mêmes valeurs de sensibilité et spécificité que le protocole standard / Breast MRI has a prominent place in breast imaging. Its wider use is limited in particular by its cost and the limited number of machines. We have worked on several aspects of this problem. In a first step, we changed the positioning from procubitus to decubitus. This showed that the decubitus allowed a better topographic correlation of the lesions with the ultrasound and was better tolerated by the patients. In a second step, we studied the factors of reduction of the acquisition time via the sequences with high temporal resolution and an abbreviated protocol. These changes should make it easier for patients to access MRI, reduce costs while maintaining the same sensitivity and specificity values as the standard protocol
49

Étude des interactions par radiofréquence entre multiples dispositifs médicaux pour la compatibilité IRM / A study of radiofrequency interactions between multiple medical devices for MRI compatibility

Kabil, Julie 11 January 2018 (has links)
Avec une population mondiale vieillissante, de plus en plus de personnes sont à risque de présenter des pathologies pour lesquelles l’Imagerie par Résonance Magnétique (IRM) est une modalité de choix : ainsi, le nombre d’examens IRM est en constante augmentation. Les patients âgés étant par ailleurs une population davantage susceptible de recevoir une implantation de dispositifs médicaux (tels qu’un pacemaker ou une prothèse de hanche), la sécurité des patients implantés en IRM est primordiale. En effet, cet appareil d’imagerie médicale fait intervenir différents champs électromagnétiques pouvant interagir avec un implant métallique et donner lieu à des risques potentiels pour le patient. Si des normes de compatibilité existent aujourd’hui pour soumettre individuellement les dispositifs médicaux à des tests standardisés et assurer leur innocuité en environnement IRM, les interactions entre multiples dispositifs médicaux vis-à-vis des ondes électromagnétiques radiofréquence (et des dangers qui peuvent en résulter) sont un domaine complexe qu’il est nécessaire de comprendre. L’objet de cette thèse est d’étudier ces interactions sur plusieurs niveaux : interactions intra-dispositif, interactions inter-dispositifs et interactions entre dispositif et plusieurs antennes. Une méthode de prédiction d’échauffement a été proposée pour simplifier l’étude de larges gammes d’implants, suivant les variations de paramètres caractérisant les différentes parties au sein d’une prothèse. Des simulations électromagnétiques et thermiques, associées à des mesures expérimentales dans un environnement IRM clinique, ont permis de mettre en évidence des phénomènes de couplages entre deux implants simplifiés et d’introduire une nouvelle métrique pour les quantifier. Enfin, une étude multi-antennes a fourni des éléments de réponse à la question de la sécurité d’un patient implanté en présence de plusieurs antennes, dans une configuration semblable à celle des examens en routine clinique. Les travaux présentés dans cette thèse ont ainsi permis d’évaluer les interactions vis-à-vis de la radiofréquence de l’IRM en présence d’un ou plusieurs dispositifs médicaux et antennes, ouvrant plusieurs perspectives pour aller vers une IRM sûre pour tous / With an aging population worldwide, more and more persons are at risk of suffering from pathologies which are best diagnosed or monitored with Magnetic Resonance Imaging (MRI): thus, the number of MRI exams is constantly increasing. Moreover, elderly patients being likely to undergo a medical device implantation (such as a pacemaker or a hip prosthesis) the safety of implanted patient in MRI is crucial. The medical imaging technique involves indeed different electromagnetic fields which can interact with a metallic implant and lead to potential hazard for the patient. Even though compatibility guidelines exist today to subject individually medical devices to standardized tests and ensure their harmlessness in an MRI environment, the interactions between multiple medical devices with respect to radiofrequency electromagnetic waves (and to the hazards that may follow) are a complex research area that has to be understood. The aim of this thesis is to study these interactions on different levels: intra-device interactions, inter-devices interactions and interactions between a device and several antennas. A prediction method has been proposed to simplify the study of large range of implants, according to the variations of parameters characterizing the different parts of a prosthesis. Electromagnetic and thermal simulations, associated with experimental measurements in a clinical MRI environment, allowed to highlight a coupling phenomenon between two simplified implants and to introduce a new metric to quantify them. Finally, a multi-antenna study led to some insights to answer the question of the safety of an implanted patient with several antennas, in a configuration similar to a clinical routine exam. Thus, the research work presented in this thesis allowed to assess the interactions with respect to MRI radiofrequency in presence of one or several medical devices and antennas, opening new prospects towards a safe MRI for everyone
50

Chemistry in the Final Stages of Stellar Evolution: Millimeter and Submillimeter Observations of Supergiants and Planetary Nebulae

Edwards, Jessica Louise January 2015 (has links)
High mass loss rates in evolved stars make them the major contributors to recycling processed material back into the interstellar medium. This mass loss creates large circumstellar shells, rich in molecular material. This dissertation presents millimeter and submillimeter studies of the end stages of low mass and high mass stars in order to probe their molecular content in more detail. In low mass stars, the molecular material is carried on into the planetary nebula (PN) stage. Observations of CS, HCO⁺, and CO in planetary nebulae (PNe) of various post-asymptotic giant branch ages have shown that molecular abundances in these objects do not significantly vary with age, as previously thought. More detailed observations of the slightly oxygen-rich PN NGC 6537 resulted in the detection of CN, HCN, HNC, CCH, CS, SO, H₂CO, HCO⁺ and N₂H⁺, as well as numerous ¹³C isotopologues. Observations of the middle-aged PN M2-48 showed the presence of CN, HCN, HNC, CS, SO, SO₂, SiO, HCO⁺, N₂H⁺, and several ¹³C isotopologues. These observations represent the first detections of CS, SO, SO₂, and SiO in any planetary nebula. The implications of these observations are discussed. A 1 mm spectral survey of the supergiant star NML Cygni has been carried out with the Arizona Radio Observatory Submillimeter Telescope resulting in the observation of 102 emission features arising from 17 different molecules and 4 unidentified features. The line profiles observed in this circumstellar shell are asymmetric and vary between different molecules, akin to what has been seen in another supergiant, VY Canis Majoris. The non-LTE radiative transfer code ESCAPADE has been used to model molecular abundances in the various asymmetric outflows of VY Canis Majoris, showing just how chemically and kinematically complex these supergiant circumstellar envelopes really are.

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