L’objectif de ce travail consiste à étudier, d’une part, les réactions des nitrates d’alkyles avec OH qui ont un intérêt atmosphérique, et d’autre part, les réactions des radicaux OH avec les alcanes et des atomes d’oxygène avec les oléfines qui ont un intérêt pour la combustion. Toutes les réactions ont été étudiées dans des réacteurs à écoulement à basse pression, y compris le réacteur à écoulement à haute température mis en place dans le cadre de la thèse, couplés à un spectromètre de masse quadripolaire à ionisation par impact électronique. Pour les réactions OH + nitrate d’alkyle, la dépendance en température de la constante de vitesse a été mesurée pour dix nitrates d'alkyles, dont pour huit nitrates pour la première fois, sur une large plage de température. Pour six nitrates, les produits de la voie réactionnelle menant au recyclage direct de NO₂, arrachement d’atome H de carbone α, ont été observés et leur rendements mesurés. La grande quantité de données obtenues dans ce travail a été utilisée pour une mise à jour de la relation structure-activité (SAR) pour les réactions d'alkyles nitrates avec OH et a permis d'améliorer les modèles atmosphériques actuels. Les études de réactions de radicaux OH avec les trois alcanes et de l'atome O avec l’éthylène et le propène ont permis de déterminer les constantes de vitesse respectives sur une large gamme de température allant de 220 à 900 K. De plus, la distribution des produits de réactions multivoies O + oléfine en fonction de la température a été déterminée pour la première fois. Ces résultats permettront d’améliorer les modèles de combustion actuellement utilisés. / The objective of this work was to study the reactions of alkyl nitrates with OH radicals relevant to atmosphere and reactions of OH radical with alkanes and oxygen atoms with olefins of interest for combustion chemistry. All reactions were studied in low pressure flow reactors (including high temperature flow reactor developed during the thesis) coupled to a quadrupole mass spectrometer with electron impact ionization. For OH reaction with nitrates, the temperature dependence of the rate constant was measured in an extended temperature range for ten alkyl nitrates, for eight of them for the first time. For six nitrates, the products of reaction pathway leading to direct recycling of NO₂ (H atom abstraction from α carbon) were observed and their yields were measured. The large amount of data obtained in this work has been used for an update of the structure-activity relation (SAR) for the reactions of alkyl nitrates with OH and will improve existing atmospheric models. For the reactions of OH radicals with three alkanes and O atoms with ethene and propene the rate constants were measured over a wide temperature range, 220-900 K. Moreover, the distribution of the products of the multichannel reactions O + olefin was determined as a function of temperature for the first time. These results are expected to improve current combustion models.

Poaceae (or Gramineae) belong to the grass family and is one of the largest families among flowering plants on land. They include some of the most important cereal crops such as rice (Oryza sativa), barley (Hordeum vulgare), wheat (Triticum aestivum), maize (Zea mays), and sorghum (Sorghum bicolor). The characteristic bushy appearance of grass plants, including cereal crops, is formed by the activities of axillary meristems (AMs) generated in the leaf axil. These give rise to tillers from the basal nodes which recapitulate secondary growth axis and AMs are formed during vegetative development. On transition to flowering the apical meristem transforming to an inflorescence meristem (IM) which produces branches from axillary meristem. These IM gives rise to branches that ultimately bear florets. Vegetative branching/tillering determines plant biomass and influences the number of inflorescences per plant. While inflorescence branching determines the number of florets and hence seeds. Thus the overall activity of axillary meristems plays a key role in determining plant architecture during both vegetative and reproductive stages. In Arabidopsis, research on the plant specific transcription factor LEAFY (LFY) has pioneered our understanding of its regulatory functions during transition from vegetative to reproductive development and its role in specifying a floral meristem (FM) identity to the newly arising lateral meristems. In the FM LFY activates other FM genes and genes for floral organ patterning transcription factors. LFY is strongly expressed throughout the young floral meristems from the earliest stages of specification but is completely absent from the IM (Weigel et al., 1992). LFY expression can also be detected at low levels in the newly emerging leaf primordia during the vegetative phase, and these levels gradually increase until the floral transition (Blazquez et al., 1997; Hempel et al., 1997). In rice, the LFY ortholog-RFL/APO2 is expressed predominantly in very young branching panicles/ inflorescence meristems (Kyozuka et al., 1998; Prasad et al., 2003) while in the vegetative phase RFL is expressed at axils of leaves (Rao et al., 2008). In rice FMs expression is restricted to primordia of lodicules, stamens, carpels and ovules (Ikeda-Kawakatsu et al., 2012). Knockdown of RFL activity or loss of function mutants show delayed flowering and poor panicle branching with reduced number of florets and lower fertility (Rao et al., 2008, Ikeda-Kawakatsu et al., 2012). In some genotypes reduced vegetative axillary branching is also compromised (Rao et al., 2008). On the other hand RFL overexpression leads to the early flowering, attributing a role as an activator for the transition of vegetative meristems to inflorescence meristems (Rao et al., 2008). Thus, RFL shows a distinct developmental expression profile, has unique mutant phenotypes as compared to Arabidopsis LFY thus indicating a divergence in functions. We have used various functional genomics approaches to investigate regulatory networks controlledby RFL in the vegetative axillary meristems and in branching panicles with florets. These regulatory effects influence tillering and panicle branching, thus contributing to rice plant architecture. RFL functions in axillary meristem Vegetative AMs are secondary shoot meristems whose outgrowth determines plant architecture. In rice, AMs form tillers from basal nodes and mutants with altered tillering reveal that an interplay between transcription factors and the phytohormones - auxin, strigolactone underpins this process. We probed the relationship between RFL and other factors that control AM development. Our findings indicate that the derangements in AM development that occur on RFL knockdown arise from its early effects during specification of these meristems and also later effects during their outgrowth of AM as a tiller. Overall, the derailments of both steps of AM development lead to reduced tillering in plants with reduced RFL activity. Our studies on the gene expression status for key transcription factor genes, genes for strigolactone pathway and for auxin transporters gave an insight on the interplay between RFL, LAX1 and strigolactone signalling. Expression levels of LAX1 and CUC genes, that encode transcription factors with AM specification functions, were modulated upon RFL knockdown and on induction of RFL:ΔGR fusion protein. Thus our findings imply a likely, direct activating role for RFL in AM development that acts in part, through attaining appropriate LAX1 expression levels. Our data place meristem specification transcription factors LAX1 and CUC downstream to RFL. Arabidopsis LFY has a predominant role in conferring floral meristem (FM) identity (Weigel et al., 1992; Wagner, 2009; Irish, 2010; Moyroud et al., 2010). Its functions in axillary meristems were not known until recently. The latter functions were uncovered with the new LFYHARA allele with only partial defects in floral meristem identity (Chahtane et al., 2013). This mutant allele showed LFY can promote growth of vegetative AMs through its direct target REGULATOR OF AXILLARY MERISTEMS1 (RAX1), a R2R3 myb domain factor (Chahtane et al., 2013). These functions for Arabidopsis LFY and RAX1 in AMs development are parallel to and redundant with the pathway regulated by LATERAL SUPPRESSOR (LAS) and REGULATOR OF AXILLARY MERISTEM FORMATION1 (ROX1) (Yang et al., 2012; Greb et al., 2003). Interestingly, ROX1 is orthologous to rice LAX1 and our data show LAX1 expression levels in rice panicles and in culms with vegetative AMs is dependent on the expression status of RFL. Thus, we speculate that as compared to Arabidopsis AM development, in rice the LFY-dependent and LFY-independent regulatory pathways for AMs development are closely linked. In Arabidopsis, CUC2 and CUC3 genes in addition to their role in shoot meristem formation and organ separation play a role in AM development possibly by defining a boundary for the emerging AM. These functions for the Arabidopsis CUC genes are routed through their effects on LAS and also by mechanisms independent of LAS (Hibara et al., 2006; Raman et al., 2008). These data show modulation in RFL activity using the inducible RFL:∆GR protein leads to corresponding expression changes in CUC1/CUC2 and CUC3 genes expression in culm tissues. Thus, during rice AM development the meristem functions of RFL and CUC genes are related. Consequent to specification of AM the buds are kept dormant. Bud outgrowth is influenced by auxin and strigolactone signalling pathways. We investigated the transcript levels, in rice culms of genes involved in strigolactone biosynthesis and perception and found the strigolactone biosynthesis gene D10 and hormone perception gene are significantly upregulated in RFL knockdown plants. Further, bioassays were done for strigolactone levels, where we used arbuscular mycorrhiza colonization assay as an indicator for strigolactone levels in wild type plants and in RFL knockdown plants. These data validate higher strigolactone signalling in RFL knockdown plants. To probe the relationship between RFL and the strigolactone pathway we created plants knocked down for both RFL and D3. For comparison of the tillering phenotype of these double knockdown plants we created plants with D3 knockdown alone. We observed reduced tillering in plants with knockdown of both RFL and D3 as compared to the tiller number in plants with knockdown of D3 alone. These data suggest that RFL acts upstream to D3 of control bud outgrowth. As effects of strigolactones are influenced by auxin transport we studied expression of OsPIN1 and OsPIN3 in RFL knockdown plants. Their reduced expression was correlated with auxin deficiency phenotypes of the roots in RFL knockdown plants. These data in conjunction with observations on OsPIN3 the gene expression modulation by the induction of RFL:∆GR allow us to speculate on a relationship between RFL, auxin transport and strigolactones with regard to bud outgrowth. We propose that the low tillering phenotype of RFL knockdown plants arises from weakened PATS, consequent to low levels of PIN1 and PIN3, coupled with moderate increase in strigolactones. Taken together, our findings suggest functions for RFL during AM specification and tiller bud outgrowth. RFL functions in panicle branching Prior studies on phenotypes of RFL knockdown or loss of function mutants suggested roles for RFL in transition to flowering, inflorescence meristem development, emergence of lateral organs and floral organ development (Rao et al., 2008; Ikeda-Kawakatsu et al., 2012). It has been speculated that RFL acts to suppress the transition from inflorescence meristem to floral meristem through its interaction with APO1 (Ikeda-Kawakatsu et al., 2012). The downstream genes regulated by RFL in these processes have not yet been elucidated. To identify direct targets of RFL in developing panicles we adopted ChIP-seq coupled with studies on gene expression modulation on induction of RFL. For the former we raised polyclonal anti-sera and chromatin from branching panicles with few florets. For gene expression modulation studies, we created transgenics with a T-DNA construct where an artificial miRNA against 3’UTR specifically knocked endogenous RFL and the same T-DNA had a second expression cassette for generation of a chemically inducible RFL-ΔGR protein that is not targeted by amiR RFL. Our preliminary ChIP-seq data in the wild type panicle tissues hints that RFL binds to hundreds of loci across the genome thus providing first glimpse of direct targets of RFL in these tissues. These data, while preliminary, were manually curated to identify likely targets that function in flowering, we summarize here some key findings. Our study indicates a role of RFL in flowering transition by activating genes like OsSPL14 and OsPRMT6a. Recent studies indicate that OsSPL14 directly binds to the promoter of OsMADS56 or FTL1, the rice homologs of SOC1 and FT to promote flowering (Lu et al., 2013). As RFL knockdown plants show highly reduced expression of OsMADS50/SOC1 and for RFT1 (Rao et al., 2008), and we show here RFL can bind and induce OsSPL14 expression we suggest the RFL¬OsSPL14 module can contribute to the transition of the SAM to flowering. Further, OsSPL14 in the young panicles directly activates DENSE AND ERECT PANICLE1 (DEP1) to control panicle length (Lu et al., 2013). Thus RFL-OsSPL14-DEP1 module could explain the role of RFL in controlling panicle architecture (Rao et al., 2008; Ikeda-Kawakatsu et al., 2012). Thus RFL plays a role in floral transition and this function is conserved across several LFY homologs. Our data ChIP-seq in the wild type tissue and gene expression modulation studies in transgenics also give molecular evidences for the role of RFL in suppression of floral fate. The direct binding of RFL to OsMADS17, OsYABBY3, OsMADS58 and HD-ZIP-IV loci and the changes in their transcript levels on induction of RFL support this hypothesis. Once the transition from SAM to FM takes place, we speculate RFL represses the conversion of inflorescence branch meristems to floral fate by negatively regulating OsYABBY3, HD-ZIP class IV and OsMADS17 that can promote differentiation. These hypotheses indicate a diverged function for RFL in floral fate repression. Arabidopsis LFY is known to activate the expression of AGAMOUS (AG), whose orthologs in rice are OsMADS3 and OsMADS58. Our studies confirm conservation with regard to RFL binding to cis elements at OsMADS58 locus that is homologous to Arabidopsis AG. But importantly we show altered consequences of this binding on gene expression. We find RFL can suppress the expression of OsMADS58 which we speculate can promote a meristematic fate. Further, we also present the abnormal upregulation of floral organ fate genes on RFL downregulation. These data too indicate functions of RFL, are in part, distinct from the role of Arabidopsis LFY where it works in promoting floral meristem specification and development. These inferences are supported by our data that rice gene homologs for AP1, AP3 and SEP3 are not directly regulated by RFL, unlike their direct regulation by Arabidopsis LFY during flower development. We also report the expression levels of LAX1, FZP, OsIDS1 and OsMADS34 genes involved in meristem phase change and IM branching are RFL dependent. This is consistent with its role in the suppression of determinacy, thereby extending the IM activity for branch formation. But as yet we do not know if these effects are direct. Together, our data report direct targets of RFL that contribute to its functions in meristem regulation, flowering transition, and suppression of floral organ development. Overall, our preliminary data on RFL chromatin occupancy combined with our detailed studies on the modulation of gene expression provides evidence for targets and pathways unique to the rice RFL during inflorescence development. Comparative analysis of genes downstream to RFL in vegetative tillers Vs panicles Tillers and panicle branches arise from the axillary meristems at vegetative and reproductive stages, respectively, of a rice plant and overall contribute to the plant architecture. Some regulatory factors control branching in both these tissues - for example, MOC1 and LAX1. Mutants at these loci affect tillers and panicle branch development thus indicating common mechanisms control lateral branch primordia development (Li et al., 2003; Komatsu et al., 2003; Oikawa and Kyozuka, 2009). Knockdown of RFL activity or loss-of-function mutants cause significantly reduced panicle branching and in few instances, reduction in vegetative axillary branching (Rao et al., 2008; Ikeda- Kawakatsu et al., 2012). We took up the global expression profiling of RFL knockdown plants compared to wild type plants in the axillary meristem and branching panicle tissue. These data provide a useful list of potential targets of RFL in axillary meristem and branching panicle tissue. The comparative analysis of the genes affected in the two tissues indicates only a subset of genes is affected by RFL in both the vegetative axillary meristems and branching panicle. These genes include transcription factors (OsSPL14, Zn finger domain protein, and bHLH domain protein), hormone signalling molecules (GA2 ox9) and cell signalling (LRR protein) as a set of genes activated by RFL in both tissues. On the other hand, these comparative expression profiling studies also show distinct set of genes deregulated by RFL knockdown in these two tissues therefore implicating RFL functions have a tissue-specific context. The genes deregulated only in axillary meristem tissue only include D3- involved in the perception of strigolactone, OsMADS34 speculated to have a role in floral transition and RCN1 involved in transition to flowering. On the other hand, the genes – CUC1, OsMADS3, OsMADS58 involved in organ development and floral meristem determination were found to be deregulated only in panicle tissues of RFL knockdown plants. These data point towards presence of distinct mechanisms for the development of AMs as tillers versus the development of panicle axillary as rachis branches. Overall, these data implicate genes involved in transition to flowering, axillary meristem development and floral meristem development are controlled by RFL in different meristems to thereby control plant architecture and transition to flowering.

L'objectif de ce travail fut d'intensifier des procédés de polymérisation radicalaire par transfert d'atomes (ATRP) du méthacrylate de 2-(dimétylamino)éthyle (DMAEAMA) au moyen de technologies de microréaction (microréacteurs, micromélangeurs) et de paramètres de procédé (géométrie du réacteur, température, pression ... ).L'impact du prémélange sur les caractéristiques d'un copolymère statistique du DMAEMA et du méthacrylate de benzyle synthétisé dans des microréacteurs hélicoïdaux (CT) fut étudié en utilisant des principes différents de micromélange: bilamination, multilamination interdigitale (!MM) et jet d'impact. Des caractéristiques bien mieux contrôlées ont été obtenues avec !'IMM et l'intensification du procédé (Pl) a été clairement démontrée encomparaison d'un réacteur fermé ; en effet des masses molaires et conversions plus élevées ainsi que de plus faibles indices de polymolécularité (PDI) ont été obtenus pour des temps de passage inférieurs. Pour la production de PMADAME linéaire, le PI a également été réalisé par augmentation de la température et de la pression (jusqu'à 1 OO bars). Toutefois de trop hautes températures se sont avérées préjudiciables notamment pour de longs temps de passage. L'effet de l'augmentation du taux de cisaillement (via la longueur du réacteur) ne fut bénéfique qu'en régime dilué à un stade précoce de la réaction lorsque les masses molaires sont encore faibles. Comparés aux CT, un mélange interne favorisé par une technique d'inversion de flux s'est révélé être une stratégie très efficace pour réduire davantage le PDI et obtenir des masses molaires et conversions plus élevées. Des polymères branchés synthétisés en microréacteurs à inversion de flux (CFI) par ATRP en présence d'inimère présentèrent une structure plus ramifiée soulignant ainsi la supériorité des CFI sur les CT et réacteurs fermés en termes de PDI et d'efficacité de branchement. Considérant les caractéristiques des CFI, l'augmentation d'échelle des microréacteurs fut considérée par accroissement de leur diamètre. La productivité du procédé a été augmentée d'un facteur 4 tout en gardant un bon contrôle sur les caractéristiques macromoléculaires. Ainsi fut-il démontré que l'inversion de flux est un moyen très efficace pour contrebalancer l'effet négatif d'une augmentation du diamètre du microréacteur. / The aim of this work was to intensify Atom Transfer Radical polymerization (ATRP) processes for the production of DMAEMA-based (co)polymers by relying on microreaction technology tools (microreactor, micromixers) and process parameters (reactor geometry, temperature, pressure ... ). Impact of premixing on macromolecular characteristics of P(DMAEMA-co-BzMA) synthesized in coiled tube (CT) microreactors was studied using different micromixing principles: bilamination, interdigital multilamination (IMM) and impact jet.Better controlled characteristics were obtained with !MM and process intensification (PI) was clearly demonstrated in comparison with batch mode as higher molecular weights, increased monomer conversions and lower polydispersity indices (PDI) were obtained for lower residence times. For the production of linear PDAEMA, PI was also achieved by application of elevated temperature and pressure (up to 100 bars). However, high temperature was found to be detrimental for long residence times. Effect of increased shear rate (i.e. reactor length) was found only beneficial in dilute regime at the early stage of the polymerization reaction when molecular weights are low. ln comparison with CT reactors, internal mixing promoted by flow inversion technique was found to be quite an effective strategy to reduce further PDI and obtain higher molecular weights and monomer conversions. Branched polymers synthesized by self condensing vinyl copolymerization (SCVCP) adapted to ATRP in tubular coil flow inverter (CFI) microreactors exhibited higher branched structure highlighting the superiority of CFI microreactor over CT and batch reactors in terms of PD! and branching efficiency. Finally, considering such features of CFI, attempt was made to scale-up microreactors by increasing their diameter. lt was found that process throughput can be increased by more than a factor of 4 while keeping a good control over macromolecular characteristics. Thus itwas demonstrated that flow inversion is quite effective to counter balance the detrimental effect of an increase in microreactor diameter.

L’étude précise des transitions ß de Fermi super-permises 0+ ? 0+ offre un outil précieux pour explorer les propriétés de l’interaction faible dans le cadre du Modèle Standard (SM). Collectivement, les forces (ft) mesurées pour ces transitions permettent de vérifier l’hypothèse CVC et contribuent au test le plus rigoureux de l’unitarité de la première ligne de la matrice de mélange des quarks CKM en fournissant l’évaluation la plus précise de l’élément dominant (Vud). Jusqu’à récemment, un apparent défaut d’unitarité a semé le doute sur la validité du SM minimal et a mobilisé un effort considérable afin d’élargir le champ d’étude à d’autres émetteurs de Fermi. Le 62Ga et 38Ca sont parmi des noyaux clés pour mener ces tests de précision au travers de la vérification de la fiabilité des corrections imposées aux valeurs ft expérimentales. La décroissance ß de 62Ga a été étudiée auprès du séparateur IGISOL à Jyväskylä, avec un dispositif composé de 3 Clovers EUROBALL pour la détection du rayonnement ?. La mise en évidence de raies ? de très faible intensité (<1‰), au travers de corrélations ß-? et ß-?-?, a permis de reconstruire partiellement le schéma de niveaux excités dans le 62Zn. Le rapport d’embranchement analogue déduit (B.R.A = 99.893(24) %) est utilisé pour extraire la valeur Ft(62Ga) universelle. Celle-ci s’avère en bon accord avec les 12 valeurs précises connues de la littérature. La compatibilité constatée entre la limite supérieure dressée ici sur le terme (d1IM) et la prédiction théorique confirme l’importance des corrections de brisure de symétrie d'isospin dans les émetteurs ß (A = 62). L’étude de la décroissance de 38Ca a été réalisée auprès de l’installation ISOLDE du CERN. L’utilisation de la fluoration des fragments de réaction, pour isoler chimiquement les isotopes d’intérêt, alliée au piégeage d’ions assisté par REXTRAP et l’analyse TOF, ont permis de s’affranchir totalement du contaminant contraignant 38mK. Pour la première fois, la durée de vie de 38Ca est mesurée avec un échantillon de haute pureté. Le résultat préliminaire établi T1/2(38Ca) = 445.8(10) ms améliore la précision par rapport à l’ancienne valeur d’un facteur proche de 10. / Precise measurements of Fermi superallowed 0+? 0+ ß decays provide a powerful tool to study the weak interaction properties in the framework of the Standard Model (SM). Collectively, the comparative half-lives (ƒt) of these transitions allow a sensitive probe of the CVC hypothesis and contribute to the most demanding test of the unitarity of the quarks-mixing CKM matrix top-row, by providing, so far, the most accurate determination of its dominant element (Vud). Until recently, an apparent departure from unity enhanced a doubt on the validity of the minimal SM and thus stimulated a considerable effort in order to extend the study to other Fermi emitters available. The 62Ga and 38Ca are among key nuclei to achieve these precision tests and verify the reliability of the corrections applied to the experimental ƒt-values. The 62Ga ß-decay was investigated at the IGISOL separator in Jyväskylä, with an experimental setup composed of 3 EUROBALL Clovers for ?-ray detection. Very weak intensity (<1‰) ?-rays were identified, via ß-? and ß-?-? correlations, and allowed a partial decay scheme reconstruction in 62Zn. The newly established analog branching-ratio (B.R.A = 99.893(24) %) was used to compute the universal Ft-value (62Ga). The latter turned out to be in good agreement with the 12 well-known cases. Compatibility between the upper limit set here on the term (d1IM) and the theoretical prediction suggests that the isospin-symmetry-breaking correction is indeed large for the heavy (A = 62) ß-emitters. The study of the 38a decay was performed at the CERN- ISOLDE facility. Injection of fluorine into the ion source, in order to chemically select the isotopes of interest, assisted by the REXTRAP Penning trap facility and a TOF analysis, enabled us to eliminate efficiently the troublesome 38mK. For the first time, the 38Ca half-life is measured with a highly purified radioactive sample. The preliminary result obtained, T1/2(38Ca) = 445.8(10) ms, improves the precision on the half-life as determined from previous measurements by a factor close to 10.

L’un des principaux objectifs de la physique des réacteurs nucléaires est de caractériser la répartition aléatoire de la population de neutrons au sein d’un réacteur. Les fluctuations de cette population sont liées à la nature stochastique des interactions des neutrons avec les noyaux fissiles du milieu : diffusion, capture stérile, ou encore émission de plusieurs neutrons lors de la fission d’un noyau. L’ensemble de ces mécanismes physiques confère une structure aléatoire branchante à la trajectoire des neutrons, alors modélisée par des marches aléatoires. Avec environs 10⁸ neutrons par centimètre cube dans un réacteur de type REP à pleine puissance en conditions stationnaires, les grandeurs physiques du système (flux, taux de réaction, énergie déposée) sont, en première approximation, bien représentées par leurs valeurs moyennes respectives. Ces observables physiques moyennes obéissent alors à l’équation de transport linéaire de Boltzmann. Au cours de ma thèse, je me suis penchée sur deux aspects du transport qui ne sont pas décrits par cette équation, et pour lesquels je me suis appuyée sur des outils issus de la théorie des marches aléatoires. Tout d’abord, grâce au formalisme de Feynman-Kac, j’ai étudié les fluctuations statistiques de la population de neutrons, et plus particulièrement le phénomène de « clustering neutronique », qui a été mis en évidence numériquement pour de faibles densités de neutrons (typiquement un réacteur au démarrage). Je me suis ensuite intéressée à différentes propriétés de la statistique d’occupation des neutrons effectuant un transport anormal (càd non-exponentiel). Ce type de transport permet de modéliser le transport dans des matériaux fortement hétérogènes et désordonnés, tel que les réacteurs à lit de boulets. L’un des aspects novateurs de ce travail est la prise en compte de la présence de bords. En effet, bien que les systèmes réels soient de taille finie, la plupart des résultats théoriques pré-existants sur ces thématiques ont été obtenus sur des systèmes de taille infinie. / One of the key goals of nuclear reactor physics is to determine the distribution of the neutron population within a reactor core. This population indeed fluctuates due to the stochastic nature of the interactions of the neutrons with the nuclei of the surrounding medium: scattering, emission of neutrons from fission events and capture by nuclear absorption. Due to these physical mechanisms, the stochastic process performed by neutrons is a branching random walk. For most applications, the neutron population considered is very large, and all physical observables related to its behaviour, such as the heat production due to fissions, are well characterised by their average values. Generally, these mean quantities are governed by the classical neutron transport equation, called linear Boltzmann equation. During my PhD, using tools from branching random walks and anomalous diffusion, I have tackled two aspects of neutron transport that cannot be approached by the linear Boltzmann equation. First, thanks to the Feynman-Kac backward formalism, I have characterised the phenomenon of “neutron clustering” that has been highlighted for low-density configuration of neutrons and results from strong fluctuations in space and time of the neutron population. Then, I focused on several properties of anomalous (non-exponential) transport, that can model neutron transport in strongly heterogeneous and disordered media, such as pebble-bed reactors. One of the novel aspects of this work is that problems are treated in the presence of boundaries. Indeed, even though real systems are finite (confined geometries), most of previously existing results were obtained for infinite systems.

Eine der stärksten Erweiterungen der klassischen Theorie formaler Sprachen und Automaten ist die Einbeziehung von Gewichten oder Vielfachheiten aus einem Halbring. Diese Dissertation untersucht gewichtete Automaten über Strukturen mit Nebenläufigkeit. Wir erweitern die Arbeit von Lodaya und Weil und erhalten so ein Modell gewichteter verzweigender Automaten, in dem die Berechnung des Gewichts einer parallelen Komposition anders als die einer sequentiellen Komposition gehandhabt wird. Die von Lodaya und Weil eingeführten Automaten modellieren Nebenläufigkeit durch Verzweigen. Ein verzweigender Automat ist ein endlicher Automat mit drei verschiedenen Typen von Transitionen. Sequentielle Transitionen überführen durch Ausführen eines Ereignisses einen Zustand in einen anderen. Dagegen sind Gabel- und Binde-Transitionen für das Verzweigen verantwortlich. Läufe dieser Automaten werden beschrieben durch sequentiell-parallele posets, kurz sp-posets. Alle Transitionen des Automaten werden in unserem Modell mit Gewichten versehen. Neben dem Nichtdeterminismus und der sequentiellen Komposition wollen wir nun auch die parallele Komposition quantitativ behandeln. Dafür benötigen wir eine Gewichtsstruktur mit einer Addition, einer sequentiellen und einer parallelen Multiplikation. Solch eine Struktur, genannt Bihalbring, besteht damit de facto aus zwei Halbringen mit derselben additiven Struktur. Weiterhin muss die parallele Multiplikation kommutativ sein. Das Verhalten eines gewichteten verzweigenden Automaten ist dann eine Funktion, die jeder sp-poset ein Element eines Bihalbrings zuordnet. Das Hauptresultat charakterisiert das Verhalten dieser Automaten im Sinne von Kleenes und Schützenbergers Sätzen über das Zusammenfallen der Klassen der erkennbaren und der rationalen Sprachen bzw. formalen Potenzreihen. Darüber hinaus untersuchen wir den Abschluss dieser Verhalten unter allen rationalen Operationen und unter dem Hadamard-Produkt. Letztlich diskutieren wir Zusammenhänge zwischen Reihen und Sprachen im Rahmen verzweigender Automaten. / One of the most powerful extensions of classical formal language and automata theory is the consideration of weights or multiplicities from a semiring. This thesis investigates weighted automata over structures incorporating concurrency. Extending work by Lodaya and Weil, we propose a model of weighted branching automata in which the calculation of the weight of a parallel composition is handled differently from the calculation of the weight of a sequential composition. The automata as proposed by Lodaya and Weil model concurrency by branching. A branching automaton is a finite-state device with three different types of transitions. Sequential transitions transform a state into another one by executing an action. In contrast, fork and join transitions are responsible for branching. Executions of such systems can be described by sequential-parallel posets, or sp-posets for short. In the model considered here all kinds of transitions are equipped with weights. Beside non-determinism and sequential composition we would like to deal with the parallel composition in a quantitative way. Therefore, we are in need of a weight structure equipped with addition, a sequential, and, moreover, a parallel multiplication. Such a structure, called a bisemiring, is actually composed of two semirings with the same additive structure. Moreover, the parallel multiplication has to be commutative. Now, the behavior of a weighted branching automaton is a function that associates with every sp-poset an element from the bisemiring. The main result characterizes the behavior of these automata in the spirit of Kleene's and Schützenberger's theorems about the coincidence of recognizable and rational languages, and formal power series, respectively. Moreover, we investigate the closure of behaviors under all rational operations and under Hadamard-product. Finally, we discuss connections between series and languages within our setting.

Es wird die Axiomatisierbarkeit einer Klasse von temporalen Prädikatenlogiken über verzweigenden Strukturen gezeigt. Entscheidbarkeitsresultate folgen für diverse Fragmente dieser Logiken. Anwendungen werden diskutiert.

Phylogenetic trees capture the relationships between species and can be investigated by morphological and/or molecular data. When focusing on macroevolution, one considers the large-scale history of life with evolutionary changes affecting a single species of the entire clade leading to the enormous diversity of species obtained today. One major problem of biology is the explanation of this biodiversity. Therefore, one may ask which kind of macroevolutionary processes have given rise to observable tree shapes or patterns of species distribution which refers to the appearance of branching orders and time periods. Thus, with an increasing number of known species in the context of phylogenetic studies, testing hypotheses about evolution by analyzing the tree shape of the resulting phylogenetic trees became matter of particular interest. The attention of using those reconstructed phylogenies for studying evolutionary processes increased during the last decades. Many paleontologists (Raup et al., 1973; Gould et al., 1977; Gilinsky and Good, 1989; Nee, 2004) tried to describe such patterns of macroevolution by using models for growing trees. Those models describe stochastic processes to generate phylogenetic trees. Yule (1925) was the first who introduced such a model, the Equal Rate Markov (ERM) model, in the context of biological branching based on a continuous-time, uneven branching process. In the last decades, further dynamical models were proposed (Yule, 1925; Aldous, 1996; Nee, 2006; Rosen, 1978; Ford, 2005; Hernández-García et al., 2010) to address the investigation of tree shapes and hence, capture the rules of macroevolutionary forces. A common model, is the Aldous\\\'' Branching (AB) model, which is known for generating trees with a similar structure of \\\"real\\\" trees. To infer those macroevolutionary forces structures, estimated trees are analyzed and compared to simulated trees generated by models. There are a few drawbacks on recent models such as a missing biological motivation or the generated tree shape does not fit well to one observed in empirical trees. The central aim of this thesis is the development and study of new biologically motivated approaches which might help to better understand or even discover biological forces which lead to the huge diversity of organisms. The first approach, called age model, can be defined as a stochastic procedure which describes the growth of binary trees by an iterative stochastic attachment of leaves, similar to the ERM model. At difference with the latter, the branching rate at each clade is no longer constant, but decreasing in time, i.e., with the age. Thus, species involved in recent speciation events have a tendency to speciate again. The second introduced model, is a branching process which mimics the evolution of species driven by innovations. The process involves a separation of time scales. Rare innovation events trigger rapid cascades of diversification where a feature combines with previously existing features. The model is called innovation model. Three data sets of estimated phylogenetic trees are used to analyze and compare the produced tree shape of the new growth models. A tree shape statistic considering a variety of imbalance measurements is performed. Results show that simulated trees of both growth models fit well to the tree shape observed in real trees. In a further study, a likelihood analysis is performed in order to rank models with respect to their ability to explain observed tree shapes. Results show that the likelihoods of the age model and the AB model are clearly correlated under the trees in the databases when considering small and medium-sized trees with up to 19 leaves. For a data set, representing of phylogenetic trees of protein families, the age model outperforms the AB model. But for another data set, representing phylogenetic trees of species, the AB model performs slightly better. To support this observation a further analysis using larger trees is necessary. But an exact computation of likelihoods for large trees implies a huge computational effort. Therefore, an efficient method for likelihood estimation is proposed and compared to the estimation using a naive sampling strategy. Nevertheless, both models describe the tree generation process in a way which is easy to interpret biologically. Another interesting field of research in biology is the coevolution between species. This is the interaction of species across groups such that the evolution of a species from one group can be triggered by a species from another group. Most prominent examples are systems of host species and their associated parasites. One problem is the reconciliation of the common history of both groups of species and to predict the associations between ancestral hosts and their parasites. To solve this problem some algorithmic methods have been developed in recent years. But only a few host parasite systems have been analyzed in sufficient detail which makes an evaluation of these methods complex. Within the scope of coevolution, the proposed age model is applied to the generation of cophylogenies to evaluate such host parasite reconciliation methods. The presented age model as well as the innovation model produce tree shapes which are similar to obtained tree structures of estimated trees. Both models describe an evolutionary dynamics and might provide a further opportunity to infer macroevolutionary processes which lead to the biodiversity which can be obtained today. Furthermore with the application of the age model in the context of coevolution by generating a useful benchmark set of cophylogenies is a first step towards systematic studies on evaluating reconciliation methods.

Práce je zaměřena na šíření únavových trhlin v módech II, III a II + III v prahové oblasti v kovových materiálech. Byly provedeny experimenty pro ARMCO železo, titan, nikl a austenitickou ocel na třech druzích vzorků pro zatěžování trhliny ve smykových módech. Byl použit zvláštní způsob vytváření iniciační trhliny, který eliminoval efekt zavírání trhliny na začátku smykového zatěžování. Ve všech zkoumaných materiálech byly efektivní prahové hodnoty v módu II přibližně 1,7 krát nižší než v módu III. Měřením úhlů lokálních odklonů a natočení lomových faset s použitím stereofotogrammetrie v SEM bylo usuzováno na tendenci trhliny k vyhýbání do lokálního módu I. Nejmenší úhly byly zjištěny u ARMCO železa pro trhliny v módech II i III, středně velké úhly u titanu a niklu a největší úhly (vyhnutí do čistého módu I) byly pozorovány u austenitické oceli. Tyto rozdíly lze vysvětlit různým počtem dostupných skluzových systémů v krystalových mřížkách daných materiálů. Poměry mezi naměřenými prahovými hodnotami v módu I, II a III byly srovnány s předpověďmi teoretických modelů. Byl navržen analytický vztah pro efektivní prahové hodnoty v módu II, který byl v dobré shodě s experimentálními výsledky. Pomocí efektivních prahových hodnot bylo vyčísleno kritérium pro vyhýbání do módu I, které vedlo ke kritickému úhlu odklonu 40° souvisejícímu s přechodem z lokálního smykového módu do otevíracího módu.

Ein Algorithmus zur Identifizierung von Elektronen mit dem BABAR Detektor wird entwickelt. Basierend auf Spuren, deren Teilchenidentität aus rein kinematischen Überlegungen gefolgert werden kann, wird für Impulse zwischen 0.5 und 2.5 GeV/c die Selektionseffizienz für Elektronen zu 90% bestimmt. Im gleichen Impulsbereich liegt die Wahrscheinlichkeit, Pionen als Elektronen zu identifizieren, zwischen 0.05% und 0.1%. Auf diesem Algorithmus basiert die Messung des inklusiven Elektronen Impulsspektrums aus B-Meson Zerfällen anhand der Daten, die mit dem BABAR Detector am asymmetrischen Speicherring PEP-II (&amp;quot;B-Factory&amp;quot;) aufgezeichnet wurden. Das Volumen der analysierten Daten entspricht einer integrierten Luminosität von 4.13 1/fb auf der Y(4S) Resonanz und 0.97 1/fb bei einer um 40 MeV verringerten Schwerpunktsenergie. B - Anti-B Ereignisse werden anhand hochenergetischer Elektronen identifiziert. Elektronen von einem semileptonischen Zerfall des zweiten B-Mesons werden durch die relative Ladung und Impulsrichtung zum hochenergetischen Elektron vom Untergrund aus semileptonischen Charm Zerfällen isoliert. Das inklusive Verzweigungsverhältnis für den semileptonischen Zerfall des B-Mesons wird zu (10.85 +-0.22(stat.) +-0.34(sys))% gemessen. Zusammen mit der Lebenszeit von B-Mesonen lässt sich daraus |V_cb| bestimmen: |V_{cb}| = 0.0406 +-0.0009(exp) +-0.0019(theory). / An algorithm for identification of electrons with the BABAR detector is developed. Based on pure samples of electrons and hadrons obtained from data, we determine the electron identification efficiency to be above 90% for momenta above 0.5 GeV/c in the laboratory frame, while the pion fake rate lies between 0.05% and 0.1%. Based on this algorithm, a measurement of the inclusive lepton momentum spectrum in B meson decays is performed. We analyze 4.13 fb^-1 and 0.97 fb^-1 of data recorded at and slightly below the Upsilon(4S) resonance with the BABAR detector at the PEP-II a symmetric B-Factory. B-Bbar events are tagged by a high momentum electron. Using charge and angular correlations, leptons from a second semileptonic $B$ decay are separated from secondary charm semileptonic decays. The inclusive branching ratio is measured to be (10.85 +-0.22(stat.) +-0.34(sys))% . Combined with the B lifetime we determine |V_cb| = 0.0406 +-0.0009(exp) +-0.0019(theory).