• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 27
  • 23
  • 8
  • 5
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 86
  • 16
  • 11
  • 10
  • 10
  • 9
  • 9
  • 9
  • 9
  • 9
  • 9
  • 9
  • 9
  • 9
  • 8
  • 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.
51

Fractions primaire et secondaire de l'aérosol organique : Méthodologies et application à un environnement urbain méditerranéen, Marseille.

El Haddad, Imad 17 January 2011 (has links) (PDF)
La mise en place de politiques efficaces visant à la réduction des niveaux de concentrations en PM exige la connaissance préalable des sources primaires et secondaires de l'aérosol organique, une fraction majoritaire des PM demeurant encore mal appréhendée. Les travaux réalisés au cours de cette thèse s'inscrivent dans le cadre du projet FORMES qui avait pour principal objectif d'évaluer et de contraindre les principales méthodes de quantification de l'influence des différentes sources de la fraction organique de l'aérosol en milieu récepteur et d'en optimiser les procédures. La caractérisation physico-chimique de l'aérosol s'est articulée autour de deux campagnes de mesures intensives de 15 jours chacune dans deux environnements urbains très contrastés : Marseille en été, et Grenoble en hiver. Ce travail de thèse s'est concentré sur le cas de Marseille, un environnement très complexe, combinant une activité photo oxydante très intense à un ensemble d'émissions primaires qui incluent les sources industrielles et les émissions par les bateaux. L'analyse CMB appliquée sur le cas de Marseille a montré que les sources primaires sont dominées par les émissions véhiculaires contribuant à 17 % du carbone organique (OC). Bien que les sources industrielles contribuent faiblement à la masse de l'aérosol (2.5 % de l'OC), ces émissions contrôlent les concentrations des HAP et de certains métaux lourds. Ces sources contribuent également, en moyenne sur la période, à environ 30% du nombre des particules ultrafines (Dp<50 nm), ce qui augmente probablement leurs effets sanitaires. Contrairement à Grenoble, où la combustion de bois est une source prépondérante (environ 70 % de l'OC), à Marseille ces émissions ne constituent qu'une source minoritaire, contribuant à 0.8 % de l'OC. Toutefois, la principale information révélée par la déconvolution de sources par CMB est que les sources primaires considérées ne permettent d'expliquer, que 22 % de l'OC mesuré ; 78 % du carbone restant non expliqué. Cette fraction est associée majoritairement à l'aérosol organique secondaire (SOA). En combinant les résultats CMB aux mesures 14C, il a été montré que plus que 70% de cet aérosol est très vraisemblablement d'origine biogénique. En conséquence, les contributions du SOA formé à partir de l'isoprène, l'α- pinène et le β-caryophyllène ont été examinées moyennant une approche basée sur les marqueurs de cet aérosol. Le SOA issu de ces précurseurs a été estimé comme contribuant uniquement à 4.3 % de l'OC, laissant une grande fraction de ce carbone non-attribuée. Cette sous-estimation est la conséquence de trois causes : (i) les incertitudes associées à l'approche utilisée, (ii) des précurseurs biogéniques non-considérés et (iii) le vieillissement de l'aérosol secondaire au cours de son transport dans l'atmosphère, comme suggéré par les mesures d'organosulfates et de la fraction polycarboxylique de type HULIS. Cette dernière fraction peut contribuer à près de 40% de l'OC nonattribué
52

Factors Affecting the Corrosivity of Pulping Liquors

Hazlewood, Patrick Evan 11 April 2006 (has links)
Increased equipment failures and the resultant increase in unplanned downtime as the result of process optimization programs continue to plague pulp mills. The failures are a result of a lack of understanding of corrosion in the different pulping liquors, specifically the parameters responsible for its adjustment such as the role and identification of inorganic and organic species. The current work investigates the role of inorganic species, namely sodium hydroxide and sodium sulfide, on liquor corrosivity at a range of process conditions beyond those currently experienced in literature. The role of sulfur species, in the activation of corrosion and the ability of hydroxide to passivate carbon steel A516-Gr70, is evaluated with gravimetric and electrochemical methods. The impact of wood chip weathering on process corrosion was also evaluated. Results were used to identify black liquor components, depending on the wood species, which play a significant role in the activation and inhibition of corrosion for carbon steel A516-Gr70 process equipment. Further, the effect of black liquor oxidation on liquor corrosivity was evaluated. Corrosion and stress corrosion cracking performance of selected materials provided information on classes of materials that may be reliably used in aggressive pulping environments.
53

A Computational Architecture Methodology For Design In Traditional Tissue: The Case Of Kalkan

Kutay, Karabag 01 September 2010 (has links) (PDF)
This study targets to address the problem of &#039 / new building in a traditional setting&#039 / , utilizing computational design tools. The intention is to provide a methodology for analysis of architectural features of a traditional tissue and moreover propose computational design strategies utilizing algorithms for processing analytical data serving new building design. In the introduction part, this goal is exposed as well as a critic discussion based on a conservationist perspective for contemporary examples of computational design. Contemporary digital tools and methods employed in the field of architecture are discussed with a focus on algorithmic approaches, followed by a brief history for utilization of computational tools and digital design philosophy in the following chapter. Moreover organic architecture is discussed as a complex entity composed of integral elements and their relations, as well as the designer
54

Aqueous Ammonia Treatment of Organic Material for Municipal Composting

MacIntyre, Stephen Eugene 13 September 2012 (has links)
Aqueous ammonia treatment of organic material to increase enzymatic digestibility is a growing area of research for animal fodder and biofuel production. The application of this treatment in the municipal composting process has not previously been investigated. Litterbags were used to investigate the effects of an aqueous ammonia treatment prior to composting on source-separated organic waste. The treatment consisted of soaking organic material in aqueous ammonia prior to introducing the material back into the composting process. Dry mass, ash content, ash-free dry mass, and water-solubility were measured. Three experiments were performed: one in the laboratory, one in an in-vessel system, and one in windrows. The aqueous ammonia treatment removed more dry mass compared to controls; however, the results indicate that the majority of the loss occurred during the soak. This treatment may be of interest for compost facilities if the leachate produced can be used in an economically beneficial way. / Ontario Centres of Excellence
55

Aqueous Phase Photo-oxidation of Water Soluble Organic Compounds (WSOC): Kinetics, Mechanisms and Method Characterization

Aljawhary, Dana 11 July 2013 (has links)
The aqueous phase photo-oxidation of water soluble organic compounds (WSOC) extracted from α-pinene ozonolysis secondary organic aerosol (SOA) was investigated using high resolution time-of-flight chemical ionization mass spectrometry (CI-ToFMS). The results have shown that WSOC get more functionalized and fragmented as the reaction proceeds. The capabilities of three reagent ions, were assessed; specifically, (H2O)nH+ ionizes organic compounds with carbon oxidation state (OSC) ≤ 1.3, whereas CH3C(O)O- and I(H2O)n- ionize highly oxygenated organics with OSC up to 4, with I(H2O)n- showing more selectivity. The aqueous phase OH oxidation of cis-pinonic acid and tricarballylic acid (a surrogate for 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), recognized as a tracer of α-pinene SOA) were also studied. The respective rate constants at 301 K were measured to be 3.4(±0.5)×10^9 M^-1s^-1 at pH=2 and 3.1(±0.3)×10^8 M^-1s^-1 at pH=4.6. This work also illustrates possible aqueous phase mechanism for MBTCA formation from cis-pinonic oxidation.
56

Aqueous Phase Photo-oxidation of Water Soluble Organic Compounds (WSOC): Kinetics, Mechanisms and Method Characterization

Aljawhary, Dana 11 July 2013 (has links)
The aqueous phase photo-oxidation of water soluble organic compounds (WSOC) extracted from α-pinene ozonolysis secondary organic aerosol (SOA) was investigated using high resolution time-of-flight chemical ionization mass spectrometry (CI-ToFMS). The results have shown that WSOC get more functionalized and fragmented as the reaction proceeds. The capabilities of three reagent ions, were assessed; specifically, (H2O)nH+ ionizes organic compounds with carbon oxidation state (OSC) ≤ 1.3, whereas CH3C(O)O- and I(H2O)n- ionize highly oxygenated organics with OSC up to 4, with I(H2O)n- showing more selectivity. The aqueous phase OH oxidation of cis-pinonic acid and tricarballylic acid (a surrogate for 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), recognized as a tracer of α-pinene SOA) were also studied. The respective rate constants at 301 K were measured to be 3.4(±0.5)×10^9 M^-1s^-1 at pH=2 and 3.1(±0.3)×10^8 M^-1s^-1 at pH=4.6. This work also illustrates possible aqueous phase mechanism for MBTCA formation from cis-pinonic oxidation.
57

Aspectos físico-químicos de pernis suínos submetidos a tratamentos com ácidos orgânicos e vapor / Physico-chemical aspects of porks legs submitted to treatments with organics acids and steam

Machado, Andréa Rosa 20 June 2009 (has links)
Made available in DSpace on 2016-12-08T16:24:07Z (GMT). No. of bitstreams: 1 PGCA09MA054.pdf: 260243 bytes, checksum: 0f7b307401cecae66d2650af13dce4dd (MD5) Previous issue date: 2009-06-20 / The main objective of the slaughtering of animals for human consumption is to obtain meat in quantity and with quality. Thus, the meat needs to be within the standards required by current legislation. However, the agroindustry still faces serious problems due to microbiological contamination of carcasses during slaughter and/or processing. Alternatives proposed aiming to decontaminate carcasses during slaughter include treatment with the use of organic acids and/or steam. Such treatments aim to ensure the biological safety of foods and complement the autocontrol programs of industry on a prevention basis, such as hygiene care during the handling of foods and the sanitization of equipment to avoid any type of cross contamination. However, little research has provided conclusive information regarding whether these treatments lead to organoleptic and physico-chemical changes in the pork, which would be completely undesirable in terms of the quality parameters. Thus, this study aims to evaluate the possible physico-chemical changes in pork legs submitted to treatments with organics acids, steam and a combination of the two treatments. Visual and sensory analysis was carried out on the aspect, color, consistency and odor, before and after each treatment, together with physico-chemical analysis in order to determine the pH and the percentage of lipids, proteins, moisture and volatile compounds, also before and after each treatment. The results obtained revealed that the treatments used did not interfere in the attributes of aspect, color, odor and consistency and also did not lead to changes in the physico-chemical properties, with the exception that the treatment using organic acid combined with steam led to a decrease in the pH and increase in the moisture content and volatile compounds in the meat. However, this treatment did not denature the physicochemical quality of the pork, which remained within the standards, and therefore appropriate for human consumption / O abate de animais para o consumo humano tem por objetivo principal a obtenção de carne em quantidade e em qualidade. Para isso, é necessário que a carne esteja dentro dos padrões exigidos pela legislação vigente, porém, as agroindústrias ainda enfrentam sérios problemas com relação à contaminação microbiológica de carcaças durante o abate e/ou processamento. Entre as alternativas propostas visando descontaminar carcaças no abate, tem sido proposto o tratamento com uso de ácidos orgânicos e/ou vapor. Tais tratamentos têm o objetivo de garantir a segurança biológica dos alimentos e complementar os programas de autocontrole das indústrias de caráter preventivo, como os cuidados higiênicos na manipulação dos alimentos e na higienização dos equipamentos evitando todo e qualquer tipo de contaminação cruzada. Porém, poucas pesquisas trazem informações conclusivas sobre o fato desses tratamentos promoverem ou não alterações físico-químicas da carne suína, o que seria totalmente indesejável frente a seus parâmetros de qualidade. Assim sendo, o presente projeto se propôs a avaliar as possíveis alterações físico-químicas de pernis suínos submetidos a tratamentos com ácidos orgânicos, vapor e associação dos dois tratamentos. Sendo realizadas análises visuais e sensoriais de aspecto, coloração, consistência e odor, antes e após cada tratamento, bem como, análises físico-químicas visando determinação do percentual de lipídeos, proteínas, pH, umidade e voláteis, também, antes e após cada tratamento. Os resultados obtidos revelaram que os tratamentos utilizados não interferiram nos atributos aspecto, cor, odor e consistência e, também, não alteraram suas propriedades físico-químicas, sendo que, somente o tratamento de vapor associado aos ácidos orgânicos diminuiu o pH e aumentou o teor de umidade e voláteis da carne, porém, não descaracterizou a qualidade físico-química da carne suína, que permaneceu dentro de seus padrões ideais, apta ao consumo humano
58

Avaliação de promotores de crescimento alternativos em substituição aos convencionais sobre o desempenho, características de carcaça e morfometria intestinal em frangos de corte / Evaluation of alternative growth promoters in order to substitute the conventionals on the performance, carcass yield and intestinal morphology of broilers

Corneli, Joaneis 28 December 2004 (has links)
The experiment was conducted at the Laboratory of Poultry (LAVIC) of the Department of Animal Science at Federal University of Santa Maria - RS, from November of 2003 to January of 2004 aiming to evaluate the use of prebiotics, organic acids (acidifiers), enzymes and garlic (phytotherapeutic) as alternative growth promoters, instead of the conventionals (antibiotics) commonly used in broilers feed. The amount of 480 males, day old, Cobb chicks were used, which were submitted to six experimental treatments: T1= Basic Diet (BD) without any growth promoters; T2= BD with 0.1% of garlic in powder; T3= BD with 0.2 % of garlic in powder; T4= BD with antibiotics (Zinc Bacitracina (10 g/ton) and Olaquindox (70 g/ton);T5= BD with prebiotic (mananoligossacarídeos(MOS)) and acidifier (fórmic acids (50%) + propionic acids (50%) and T6= BD whit prebiotic (mananoligossacarídeos(MOS)) and enzymes. The amount of prebiotic, acidifier and enzymes used were rated by the technical advise of the commercial products used. Twenty four experimental boxes of the 1.5 X1.5m, with 20 fowls each were used, with four replicates by treatment in a completely randomized design. The fowls were sheltered on reutilized bed wood shavings, in a mansory shed raised with animal feed based on corn and soy bean meal, ad libitum , isonutritives and divided in three phases: initial (1-21 days) bearing 22% Crude Protein (CP) and 3050 Kcal ME/Kg, growth (22-35 days) with 20% CP and 3100 Kcal ME/Kg, final (36- 43 days) with 18.5 % of CP and 3150 Kcal ME/Kg. The treatments did not show any statistic difference for the parameters: weigh gain (WG) and production factor (PF). There wasn t a significant effect on the feed intake (FI), in the phases of 1-21 and 22-35 days of live, but in the phase of 36-43 days there was a significant effect (P<005), with difference only between the treatments without growth promoters (T1) and the treatments with garlic (T2 and T3), but they did not diverge significantly from the others. Introductory the period of 1-43 days, to come different significant (P<0.05), at the feed intake (FI), of the fowls the treatments without growth promoters (T1) and with antibiotics (T4), but they did not diverge significantly from the others. The feed conversion (FC), did not differ statiscally (P>0.05) in the phases of 1-21 and 36-43 days of live the fowls. The phase of 22-35 days to come different significant (P<0.05), where the fowls submitted to treatment with antibiotics (T4) and with prebiotics + acidifier (T5), showed better feed conversion (FC) and it was statistically relevant (P<0.05), when compared with fowls of the treatment prebiotics + enzymes (T6), but the treatment with prebiotics + acidifier (T5), was not differences between them (P>0.05). In the period of 1-43 days, the fowls submitted to treatment with antibiotics (T4) showed better feed conversion (FC) and it was statistically relevant (P<0.05), when compared with fowls of the control treatments (T1) and prebiotics + enzymes (T6), but there were no differences between them (P>0.05). The feed conversion (FC) of the fowls submitted to the other treatments (T2, T3 and T5) did not differ statiscally (P>0.05). The results according to the intestinal morphology and carcass yield did not show significant effects (P>0.05) between the different growth promoters tested. Based on the results obtained, taking in to account the conditions of what the experiment was conducted, it was concluded that the alternative growth promoters tested did not affect negatively the characteristics of the intestinal morphology of the broilers validating them as substitutes to the conventional promoters. / O experimento foi conduzido no Laboratório de Avicultura (LAVIC) do Departamento de Zootecnia da Universidade Federal de Santa Maria - RS, no período de novembro de 2003 a janeiro de 2004, com o objetivo de avaliar o uso de prebióticos, ácidos orgânicos (acidificantes), enzimas e alho (fitoterápico) como promotores de crescimento alternativos, em substituição aos convencionais (antibióticos), usualmente utilizados nas dietas para frangos de corte. Foram usados 480 pintos de corte, machos, com um dia de vida, da linhagem Cobb 500, os quais foram submetidos a seis tratamentos experimentais: T1= Dieta Base (DB) sem adição de promotor de crescimento; T2= DB com 0,1% de alho em pó; T3= DB com 0,2% de alho em pó; T4= DB com Bacitracina de Zinco (10g/ton) e Olaquindox (70g/ton); T5= DB com prebiótico (mananoligossacarídeos (MOS)) e acidificante orgânico (ácido fórmico (50%) + ácido propiônico (50%)) e T6= DB com prebiótico (mananoligossacarídeos (MOS)) e complexo enzimático (proteases, amilases e celulases). Os níveis utilizados de prebióticos, acidificantes e enzimas foram obtidos através das recomendações técnicas dos produtos comerciais usados. Foram usados 24 boxes experimentais de 1,5 X 1,5 m, contendo 20 aves cada, com quatro repetições por tratamento, distribuídos num delineamento experimental inteiramente casualizado. As aves foram alojadas em cama de maravalha reutilizada, num galpão de alvenaria, alimentadas com ração isonutritiva , à base de milho e farelo de soja, fornecida à vontade e dividida em três fases: inicial (1-21 dias), contendo 22% PB e 3050 Kcal de EM/Kg, crescimento (22-35 dias) com 20% PB e 3100 Kcal EM/Kg e final (36-43 dias) com 18,5% de PB e 3150 Kcal EM/Kg. Os tratamentos não apresentaram diferença estatística nos parâmetros de: ganho de peso (GP) e fator de produção (FP). Para o consumo de ração (CR), não se observaram diferenças significativas nas fases de 1-21 e 22-35 dias, mas na fase de 36-43 dias verificou-se efeito significativo (P<0,05), com diferença apenas entre os tratamentos sem adição de promotores de crescimento (T1) e os tratamentos com adição de alho (T2 e T3), estes com a adição de alho não diferiram significativamente dos demais tratamentos (T4,T5 e T6). Considerando o período total (1-43 dias), ocorreu diferença significativa (P<0,05), no consumo de ração entre as aves dos tratamentos sem adição de promotores de crescimento (T1) e com a adição de antibióticos (T4), nos demais tratamentos não houve efeito significativo em relação ao consumo de ração. A conversão alimentar (CA) não foi afetada nas fases de 1-21 e 36-43 dias de idade das aves. Na fase de 22-35 dias verificou-se efeito significativo, onde as aves com antibióticos convencionais (T4) e com MOS + Acidificantes (T5) obtiveram a melhor conversão alimentar, porém sem diferir significativamente entre ambas. Entretanto, as aves do tratamento T5 foram mais eficientes, diferindo significativamente (P<0,05) em relação as aves do T6 (MOS + enzimas), mas não diferiram significativamente das aves dos tratamentos ( T1, T2 e T3 ). Sendo que no período de 1-43 dias, as aves submetidas ao tratamento com antibióticos (T4) apresentaram melhor conversão alimentar (CA) estatisticamente significativa (P<0,05), quando comparadas as aves dos tratamentos sem adição de promotores de crescimento (T1) e prebiótico + complexo enzimático (T6), sendo que estes não diferiram entre si (P>0,05). A conversão alimentar das aves submetidas aos demais tratamentos (T2, T3 e T5) não diferiram entre si (P>0,05). Os resultados referentes à altura de vilos intestinais e rendimento de carcaça não apresentaram efeitos significativos (P>0,05) entre os diferentes promotores de crescimento avaliados. Com base nos resultados obtidos, levando em consideração as condições em que o experimento foi conduzido, conclui-se que os promotores de crescimento alternativos testados são uma opção aos antibióticos. Os promotores de crescimento alternativos testados não afetaram negativamente as características de carcaça e morfometria intestinal dos frangos de corte.
59

Vertical Organic Field-Effect Transistors / Vertikale Organische Feld-Effekt-Transistoren

Günther, Alrun Aline 09 August 2016 (has links) (PDF)
Diese Arbeit stellt eine eingehende Studie des sogenannten Vertikalen Organischen Feld-Effekt-Transistors (VOFET) dar, einer neuen Transistor-Geometrie, welche dem stetig wachsenden Bereich der organischen Elektronik entspringt. Dieses neuartige Bauteil hat bereits bewiesen, dass es in der Lage ist, eine der fundamentalen Einschränkungen herkömmlicher organischer Feld-Effekt-Transistoren (OFETs) zu überwinden: Die für Schaltfrequenz und An-Strom wichtige Kanallänge des Transistors kann im VOFET stark reduziert werden, ohne dass teure und komplexe Strukturierungsmethoden genutzt werden müssen. Das genaue Funktionsprinzip des VOFET ist bisher jedoch weitgehend unerforscht. Durch den Vergleich von experimentellen Daten mit Simulationsdaten des erwarteten Bauteil-Verhaltens wird hier ein erstes, grundlegendes Verständnis des VOFETs erarbeitet. Die so gewonnenen Erkenntnisse werden im Folgenden genutzt, um bestimmte Parameter des VOFETs kontrolliert zu manipulieren. So wird beispielsweise gezeigt, dass die Morphologie des organischen Halbleiters, und damit seine Abscheidungsparameter, sowohl für die VOFET-Herstellung als auch für den Ladungsträgertransport im fertigen Bauteil eine wichtige Rolle spielen. Weiterhin wird gezeigt, dass der VOFET, genau wie der konventionelle OFET, durch das Einbringen von Kontaktdotierung deutlich verbessert werden kann. Mit Hilfe dieser Ergebnisse kann gezeigt werden, dass das Funktionsprinzip des VOFETs mit dem eines konventionellen OFETs nahezu identisch ist, wenn man von geringen Abweichungen aufgrund der unterschiedlichen Geometrien absieht. Basierend auf dieser Erkenntnis wird schließlich ein VOFET präsentiert, welcher im Inversionsmodus betrieben werden kann und so die Lücke zur konventionellen MOSFET-Technologie schließt. Dieser Inversions-VOFET stellt folglich einen vielversprechenden Ansatz für leistungsfähige organische Transistoren dar, welche als Grundbausteine für komplexe Elektronikanwendungen auf flexiblen Substraten genutzt werden können. / This work represents a comprehensive study of the so-called vertical organic field-effect transistor (VOFET), a novel transistor geometry originating from the fast-growing field of organic electronics. This device has already demonstrated its potential to overcome one of the fundamental limitations met in conventional organic transistor architectures (OFETs): In the VOFET, it is possible to reduce the channel length and thus increase On-state current and switching frequency without using expensive and complex structuring methods. Yet the VOFET's operational principles are presently not understood in full detail. By simulating the expected device behaviour and correlating it with experimental findings, a basic understanding of the charge transport in VOFETs is established and this knowledge is subsequently applied in order to manipulate certain parameters and materials in the VOFET. In particular, it is found that the morphology, and thus the deposition parameters, of the organic semiconductor play an important role, both for a successful VOFET fabrication and for the charge transport in the finished device. Furthermore, it is shown that VOFETs, just like their conventional counterparts, are greatly improved by the application of contact doping. This result, in turn, is used to demonstrate that the VOFET essentially works in almost exactly the same way as a conventional OFET, with only minor changes due to the altered contact arrangement. Working from this realisation, a vertical organic transistor is developed which operates in the inversion regime, thus closing the gap to conventional MOSFET technology and providing a truly promising candidate for high-performance organic transistors as the building blocks for advanced, flexible electronics applications.
60

Importance de la réactivité thermique au sein d'analogues de glaces interstellaires pour la formation de molécules complexes. / Importance of thermal reactivity in interstellar ice analogue for the formation of complex organics molecules

Vinogradoff, Vassilissa 27 September 2013 (has links)
Dans le milieu interstellaire (MIS) les grains de poussière jouent un rôle très important pour la chimie au sein des nuages moléculaires offrant une surface froide sur laquelle les atomes et molécules de la phase gazeuse vont s'accréter, formant un manteau de glace. Les nuages moléculaires sont caractérisés par des basses températures (10-50 K) et sont le lieu de formation des étoiles. Après effondrement gravitationnel du nuage suite à une trop forte densité en son sein, celui-ci devient le lieu de formation d'une nouvelle étoile. L'enveloppe autour de l'étoile évolue en disque dans lequel pourra se former des planètes, astéroïdes, comètes et autres objets d'un système planétaire. Durant cette formation stellaire, les glaces interstellaires (et les molécules qu'elles contiennent) sont alors soumises à plusieurs processus énergétiques (cycle de réchauffement, irradiations par des photons UV ou des particules chargées) qui vont affecter leurs compositions chimiques et finalement augmenter la complexité moléculaire avant leur incorporation dans les différentes objets du futur système planétaire. En laboratoire, afin de mieux comprendre l'évolution des molécules, composantes des glaces, nous avons développé une nouvelle approche qui consiste à réaliser des analogues "spécifiques" auxquels un seul processus énergétique à la fois est appliqué. Nous avons alors montré l'importance de l'effet thermique longtemps négligé pour la formation de molécules organiques complexes, montrant plusieurs implications astrophysiques et exobiologiques. Nos études permettent une meilleure compréhension des processus chimiques qui ont lieu dans la phase solide du MIS. / Dust grains in the interstellar medium (ISM) play an important role in dense molecular clouds chemistry in providing a surface (catalyst) upon which atoms and molecules can freeze out, forming icy mantles. Dense molecular clouds are characterized by low temperature (10-50 K) and represent the birth sites of stars. After a gravitational breakdown, a part of the dense molecular cloud collapses toward the formation of star and subsequently a protoplanetary disk from which planets, asteroids and comets will appear. During this evolution, interstellar organic material inside ices undergoes different range of chemical alterations (thermal cycling process, ultraviolet photons, cosmic rays irradiation) hence increasing the molecular complexity before their incorporation inside precometary ices. In laboratory, in order to better understand the evolution of molecules in interstellar ices, we developed a new approach by making "specifics" interstellar ices analogues submitted to one energetic process at time. Consequently we showed the importance of thermal reactivity (neglected effect for long time) for the formation of complexes organics molecules (HMT, trimers, aminoalcools) which are more refractory compounds than water. Our works have many implications in astrophysics since we gave crucial informations on the chemical processes that are happening in solid phase chemistry of the ISM, and on the formation of news molecules which could be incorporated in parent's body of meteorites/comets. We also show some Exobiological implications particularly for the formations of amino acids in the ISM.

Page generated in 0.0401 seconds