Thèses : « Chemical clocks »

1

Lee, Ho-Hsin. « Gas-phase chemical models of interstellar molecular clouds / ». The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487948440824473.

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Wilkins, Anna Katharina. « Sensitivity analysis of oscillating dynamical systems with applications to the mammalian circadian clock ». Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/42944.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2008.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 227-234).
The work presented in this thesis consists of two major parts. In Chapter 2, the theory for sensitivity analysis of oscillatory systems is developed and discussed. Several contributions are made, in particular in the precise definition of phase sensitivities and in the generalization of the theory to all types of autonomous oscillators. All methods rely on the solution of a boundary value problem, which identifies the periodic orbit. The choice of initial condition on the limit cycle has important consequences for phase sensitivity analysis, and its influence is quantified and discussed in detail. The results are exact and efficient to compute compared to existing partial methods. The theory is then applied to different models of the mammalian circadian clock system in the following chapters. First, different types of sensitivities in a pair of smaller models are analyzed. The models have slightly different architectures, with one having an additional negative feedback loop compared to the other. The differences in their behavior with respect to phases, the period and amplitude are discussed in the context of their network architecture. It is found that, contrary to previous assumptions in the literature, the additional negative feedback loop makes the model less "flexible" in at least one sense that was studied here. The theory was also applied to larger, more detailed models of the mammalian circadian clock, based on the original model of Forger and Peskin. Between the original model's publication in 2003 and the present time, several key advances were made in understanding the mechanistic detail of the mammalian circadian clock, and at least one additional clock gene was identified. These advances are incorporated in an extended model, which is then studied using sensitivity analysis. Period sensitivity analysis is performed first and it was found that only one negative feedback loop dominates the setting of the period.
(cont.) This was an interesting one-to-one correlation between one topological feature of the network and a single metric of network performance. This led to the question of whether the network architecture is modular, in the sense that each of the several feedback loops might be responsible for a separate network function. A function of particular interest is the ability to separately track "dawn" and "dusk", which is reported to be present in the circadian clock. The ability of the mammalian circadian clock to modify different relative phases --defined by different molecular events -- independently of the period was analyzed. If the model can maintain a perceived day -- defined by the time difference between two phases -- of different lengths, it can be argued that the model can track dawn and dusk separately. This capability is found in all mammalian clock models that were studied in this work, and furthermore, that a network-wide effort is needed to do so. Unlike in the case of the period sensitivities, relative phase sensitivities are distributed throughout several feedback loops. Interestingly, a small number of "key parameters" could be identified in the detailed models that consistently play important roles in the setting of period, amplitude and phases. It appears that most circadian clock features are under shared control by local parameters and by the more global "key parameters". Lastly, it is shown that sensitivity analysis, in particular period sensitivity analysis, can be very useful in parameter estimation for oscillatory systems biology models. In an approach termed "feature-based parameter fitting", the model's parameter values are selected based on their impact on the "features" of an oscillation (period, phases, amplitudes) rather than concentration data points. It is discussed how this approach changes the cost function during the parameter estimation optimization, and when it can be beneficial.
(cont.) A minimal model system from circadian biology, the Goodwin oscillator, is taken as an example. Overall, in this thesis it is shown that the contributions made to the theoretical understanding of sensitivities in oscillatory systems are relevant and useful in trying to answer questions that are currently open in circadian biology. In some cases, the theory could indicate exactly which experiments or detailed mechanistic studies are needed in order to perform meaningful mathematical analysis of the system as a whole. It is shown that, provided the biologically relevant quantities are analyzed, a network-wide understanding of the interplay between network function and topology can be gained and differences in performance between models of different size or topology can be quantified.
by Anna Katharina Wilkins.
Ph.D.

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Munger, James William Hoffman Michael R. Hoffman Michael R. « The chemical composition of fogs and clouds in southern California / ». Diss., Pasadena, Calif. : California Institute of Technology, 1989. http://resolver.caltech.edu/CaltechETD:etd-02132007-152409.

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Nejad, Lida A. M. « Time-dependent chemical kinetic models of circumstellar envelopes and interstellar clouds ». Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702324.

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Minelli, Alice <1994&gt. « Chemical composition of Milky Way satellites : Magellanic Clouds and Sagittarius dwarf galaxy ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10313/1/PhDThesis_AliceMinelli.pdf.

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This PhD project is aimed at investigating the chemical composition of the stellar populations in the closest satellites of the Milky Way (MW), namely the Large and Small Magellanic Cloud (LMC and SMC, respectively) and the remnant of the Sagittarius (Sgr) dwarf spheroidal galaxy. Their proximity allows us to resolve their individual stars both with spectroscopy and photometry, studying in detail the characteristics of their stellar populations. All these objects are interacting galaxies: LMC and SMC are in an early stage of a minor merger event, and Sgr is being disrupted by the tidal field of the MW. There is a plenty of literature regarding the chemical composition of these systems, however, the extension of these galaxies prevents a complete and homogeneous analysis. Therefore, we homogeneously analysed stellar spectra belonging to MW and its satellites galaxies and we derived their chemical compositions. We highlighted the importance of a homogeneous analysis in the comparison among different galaxies or different samples, to avoid systematics due to different methods or physical assumptions.

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Szűcs, László [Verfasser], et Simon [Akademischer Betreuer] Glover. « Chemical evolution from diffuse clouds to dense cores / László Szűcs ; Betreuer : Simon Glover ». Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180301870/34.

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Morisawa, Yusuke. « Spectroscopic study of some chemically significant molecules in molecular clouds ». 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144599.

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Balakrishnan, Kaushik. « On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds ». Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34672.

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High explosive charges when detonated ensue in a flow field characterized by several physical phenomena that include blast wave propagation, hydrodynamic instabilities, real gas effects, fluid mixing and afterburn effects. Solid metal particles are often added to explosives to augment the total impulsive loading, either through direct bombardment if inert, or through afterburn energy release if reactive. These multiphase explosive charges, termed as heterogeneous explosives, are of interest from a scientific perspective as they involve the confluence and interplay of various additional physical phenomena such as shock-particle interaction, particle dispersion, ignition, and inter-phase mass, momentum and energy transfer. In the current research effort, chemical explosions in multiphase environments are investigated using a robust, state-of-the-art Eulerian-gas, Lagrangian-solid methodology that can handle both the dense and dilute particle regimes. Explosions into ambient air as well as into aluminum particle clouds are investigated, and hydrodynamic instabilities such as Rayleigh- Taylor and Richtmyer-Meshkov result in a mixing layer where the detonation products mix with the air and afterburn. The particles in the ambient cloud, when present, are observed to pick up significant amounts of momentum and heat from the gas, and thereafter disperse, ignite and burn. The amount of mixing and afterburn are observed to be independent of particle size, but dependent on the particle mass loading and cloud dimensions. Due to fast response times, small particles are observed to cluster as they interact with the vortex rings in the mixing layer, which leads to their preferential ignition/ combustion. The total deliverable impulsive loading from heterogeneous explosive charges containing inert steel particles is estimated for a suite of operating parameters and compared, and it is demonstrated that heterogeneous explosive charges deliver a higher near-field impulse than homogeneous explosive charges containing the same mass of the high explosive. Furthermore, particles are observed to introduce significant amounts of hydrodynamic instabilities in the mixing layer, resulting in augmented fluctuation intensities and fireball size, and different growth rates for heterogeneous explosions compared to homogeneous explosions. For aluminized explosions, the particles are observed to burn in two regimes, and the average particle velocities at late times are observed to be independent of the initial solid volume fraction in the explosive charge. Overall, this thesis provides useful insights on the role played by solid particles in chemical explosions.

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Ahlvind, Julia. « Isochrone and chemical ages of stars in the old open cluster M67 ». Thesis, Uppsala universitet, Observationell astrofysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-434634.

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The open cluster Messier 67 is known to have chemical composition, metallicity and age (~ 4 Gyr) close to the Sun. Therefore, it is advantageous for stellar physical studies and of stellar evolution, in particular for solar like stars within the cluster. This work considers three such stars, the formerly studied solar twin M67-1194 and two more recently suggested solar twins M67-1787 & 2018. Most solar twins show a ratio of volatile to refractory elements that systematically depart from the Sun’s. Our targets do not follow this trend as closely. Their composition is closer to the Sun and they are, therefore, exquisite targets for studies of stellar evolution within the cluster. However, their solar likeness also provides studies regarding the origin and evolution of the Solar system. The stellar ages of the solar twins are established through a chemical clock [Y/Mg] and via stellar isochrones from BaSTI. The latter age assessment of the solar twins is supplemented with the analysis of two subgiant stars M67-1442 & 1844. We approach the isochrone-based method using spectroscopically, astrometrically and photometrically derived parameters. The different ages of the stars and methods thus estimate the age of the cluster itself. The chemical ages of the stars suggest a cluster age of 4.56 ±0.44 Gyr and the isochrone-based estimates suggests a cluster age within the range 3.30-5.51 Gyr. Our results thus affirm and imply a near solar age of the cluster.

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Lin, Xing. « Model studies of rainout, washout and the impact of chemical inhomogeneity on SO₂ oxidation in warm stratiform clouds ». Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/25714.

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Schulz, Christiane [Verfasser]. « Secondary organic aerosol in the pristine Amazonian atmosphere : chemical properties, formation pathways, and interactions with clouds / Christiane Schulz ». Mainz : Universitätsbibliothek Mainz, 2019. http://d-nb.info/1185711856/34.

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Blake, Geoffrey A. Phillips Thomas G. « On the chemical composition of interstellar molecular clouds : a millimeter and submillimeter spectral line survey of OMC-1 / ». Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-12092003-145807.

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Gómez, González Laura [Verfasser]. « Physical and Chemical Properties of Protocluster Clumps and Massive Young Stellar Objects Associated to Infrared Dark Clouds / Laura Gómez González ». Bonn : Universitäts- und Landesbibliothek Bonn, 2012. http://d-nb.info/1044081783/34.

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Yu, Elizabeth A. « Investigating Age-Dependent Arthropathy in a Circadian Mutant Mouse Model : A Dissertation ». eScholarship@UMMS, 2011. https://escholarship.umassmed.edu/gsbs_diss/544.

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Ectopic calcification can cause pain and limit mobility. Studies suggest that circadian genes may play a role in the calcification process. Core circadian genes Clock, Npas2, and Bmal1 are transcription factors that form CLOCK:BMAL1 or NPAS2:BMAL1 transactivator complexes that drive the rhythmic expression of circadian oscillator genes and output genes. Circadian oscillator genes Period1-3 and Cryptochrome1-2 encode proteins that form transcription repressor complexes that feedback to inhibit CLOCK/NPAS2:BMAL1 activity, thus completing the feedback loop that is the basis of the molecular circadian clockwork. Arrhythmic Bmal1-/- mice exhibit site-specific, age-dependent arthropathy. While studying the circadian phenotype of Clock-/-;Npas2m/m double mutant mice, we discovered that these double mutant mice develop site-specific arthropathy similar to the arthropathy described in Bmal1-/- mice. Based on the circadian clockwork mechanism, we hypothesized that CLOCK/NPAS2:BMAL1 transactivator complexes drive the expression of a gene (or genes) that prevents age-dependent arthropathy. To investigate Clock-/-;Npas2m/m double mutant mouse arthropathy, we evaluated mutant mice using X-ray, micro-computed tomography, and histology, and found that Clock-/-;Npas2m/m double mutant mice exhibit age-dependent, site-specific arthropathy that phenocopies that of Bmal1-/- mice. The costosternal junction and calcaneal tendon are most prominently affected, in that calcification of those tissues is detectable as early as 4-5 weeks and 11-12 weeks, respectively. The arthropathic lesions in these tissues consist of calcium phosphate vii deposits, and in Bmal1-/- costosternal junction calcifications, the deposits contain calcium pyrophosphate dihydrate crystals. Mechanical stress, disregulation of centrally-regulated circadian rhythms, and systemic serum mineral imbalances likely do not contribute to this pathology. In vitro micromass cultures generated from Clock-/-;Npas2m/m double mutant mouse embryonic fibroblasts do not exhibit irregular chondrocyte differentiation compared to wild-type cultures, suggesting that chondrocyte cell-autonomous mechanisms are insufficient to induce this arthropathy. Analysis of Clock-/-;Npas2m/m double mutant intersternebral tissue RNA did not reveal significant changes in chondrocyte or calcification-related gene expression. Histological stains showed an absence of osteoblasts and osteoclasts around costosternal junction calcifications, suggesting that these cell types are not contributing to this pathology. Instead, chondrocytes are localized to the costosternal junction but there were no significant changes in the distribution of chondrocyte markers in this tissue, as evaluated by immunohistochemistry. These findings suggest that Clock or Npas2, and Bmal1, regulate ectopic calcification through a combination of systemic and local factors, and that the cells affected by Clock and Npas2, or Bmal1, disruption are a subset of the cells distributed in specific tissues that develop age-dependent arthropathy. The significance of these findings is that “circadian genes” play a role in the regulation of ectopic calcification in a non-oscillator capacity. Understanding this new mechanism by which ectopic calcification is controlled could lead to novel approaches for the treatment of some human calcification diseases.

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Thiel, Vivien [Verfasser]. « Small-scale Physical and Chemical Structure of Diffuse and Translucent Molecular Clouds along the Line of Sight to the Galactic Center / Vivien Thiel ». Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1188731807/34.

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Vaupré, Solenn. « Ionisation des nuages moléculaires par les rayons cosmiques ». Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY049/document.

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Les rayons cosmiques (RC) ont un rôle fondamental sur la dynamique et l'évolution chimique des nuages moléculaires interstellaires, qui sont le lieu de formation stellaire et planétaire. Les RC sont probablement accélérés dans les enveloppes en expansion des rémanents de supernova (SNR), ainsi les nuages moléculaires situés à proximité peuvent être soumis à d'intenses flux de RC. Les protons relativistes ont principalement deux effets sur les nuages moléculaires : 1) en rencontrant le milieu dense, les protons de haute énergie (>280 MeV) induisent via la désintégration des pions l'émission de photons gamma. à cause de ce processus, les associations SNR-nuages moléculaires sont des sources intenses d'émission GeV et/ou TeV présentant des spectres similaires à celui des protons incidents. 2) à plus basse énergie, les RC pénètrent le nuage et ionisent le gaz, induisant la formation d'espèces moléculaires caractéristiques appelées traceurs de l'ionisation. L'étude de ces traceurs permet de déduire des informations sur les RC de basse énergie inaccessibles aux autres méthodes d'observation. J'ai étudié l'ionisation des nuages moléculaires par les RC près de trois SNR : W28, W51C et W44. Il existe des preuves observationnelles d'interaction avec le nuage voisin pour chaque SNR (présence de gaz choqué, masers OH, émission gamma). Mon travail repose sur la comparaison d'observations millimétriques des traceurs de l'ionisation à des modèles de chimie appliqués à ces nuages denses. Dans chaque région, nous avons déterminé un taux d'ionisation supérieur à la valeur standard, confortant l'hypothèse d'une origine des RC dans l'enveloppe du SNR voisin. L'existence d'un gradient d'ionisation en s'éloignant de l'onde de choc du SNR apporte des contraintes précieuses sur les propriétés de propagation des RC de basse énergie. La méthode utilisée repose sur l'observation des ions moléculaires HCO+ et DCO+, qui montre des limitations importantes à haute ionisation. C'est pourquoi j'ai également cherché à identifier des traceurs alternatifs de l'ionisation, par un effort croisé de modélisation et d'observation. En particulier, dans la région W44, les observations de N2H+ ont permis de mieux contraindre les conditions physiques, les abondances volatiles dans le nuage et l'état d'ionisation du gaz. Ce projet de recherche a amené une meilleure compréhension de la chimie induite par les RC dans les nuages moléculaires. Il a également ouvert de nouvelles perspectives de recherche interdisciplinaire vers la compréhension des RC, des observations millimétriques aux observations gamma
Cosmic rays (CR) are of tremendous importance in the dynamical and chemical evolution of interstellar molecular clouds, where stars and planets form. CRs are likely accelerated in the shells of supernova remnants (SNR), thus molecular clouds nearby can be irradiated by intense fluxes of CRs. CR protons have two major effects on dense molecular clouds: 1) when they encounter the dense medium, high-energy protons (>280 MeV) create pions that decay into gamma-rays. This process makes SNR-molecular cloud associations intense GeV and/or TeV sources whose spectra mimic the CR spectrum. 2) at lower energies, CRs penetrate the cloud and ionise the gas, leading to the formation of molecular species characteristic of the presence of CRs, called tracers of the ionisation. Studying these tracers gives information on low-energy CRs that are unaccessible to any other observations. I studied the CR ionisation of molecular clouds next to three SNRs: W28, W51C and W44. These SNRs are known to be interacting with the nearby clouds, from the presence of shocked gas, OH masers and pion-decay induced gamma-ray emission. My work includes millimeter observations and chemical modeling of tracers of the ionisation in these dense molecular clouds. In these three regions, we determined an enhanced CR ionisation rate, supporting the hypothesis of an origin of the CRs in the SNR nearby. The evolution of the CR ionisation rate with the distance to the SNR brings valuable constraints on the propagation properties of low-energy CRs. The method used relies on observations of the molecular ions HCO+ and DCO+, which shows crucial limitations at high ionisation. Therefore, I investigated, both through modeling and observations, the chemical abundances of several other species to try and identity alternative tracers of the ionisation. In particular, in the W44 region, observations of N2H+ bring additional constraints on the physical conditions, volatile abundances in the cloud, and the ionisation state. This research brought valuable insight into the CR induced chemistry in the interstellar medium. It also brought new perspectives of interdisciplinary research towards the understanding of CRs, from millimeter to gamma-ray observations

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Brosse, Fabien. « Influence de la couche limite convective sur la réactivité chimique en Afrique de l'Ouest ». Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30324/document.

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Cette thèse porte sur l'influence de la couche limite convective et nuageuse sur la réactivité chimique en Afrique de l'Ouest. Pour répondre à cette question, des simulations à haute résolution (50m) sont réalisées sur le modèle atmosphérique Méso-NH couplé à un mécanisme chimique détaillé représentant la chimie gazeuse et aqueuse. Cette échelle spatiale permet de représenter explicitement les caractéristiques spatiales et temporelles des structures turbulentes. Les thermiques en couche limite sont identifiés à l'aide d'un échantillonnage conditionnel basé sur l'utilisation d'un traceur passif à décroissance radioactive. L'impact du transport turbulent sur la redistribution d'espèces chimiques dépend du temps de vie chimique de ces espèces. La ségrégation spatiale créée au sein de la couche limite augmente ou réduit les taux de réaction moyens entre composés. La campagne de terrain AMMA, et plus récemment DACCIWA, sont utilisées pour définir des forçages dynamiques et chimiques pour des environnements simulés. Le premier est représentatif d'un environnement biogénique dominé par des émissions naturelles de COV. Le second reproduit un environnement urbain modérément pollué typique du Golfe de Guinée (Cotonou au Bénin). Pour simplifier, l'analyse des simulations est limitée aux réactions chimiques entre OH et l'isoprène dans le cas biogénique, entre les aldéhydes C>2 et OH dans le cas urbain. L'influence de la couche limite convective est étudiée à l'échelle du thermique et du domaine. Cela permet une connexion avec les modèles à résolution plus lâche qui adoptent une hypothèse de mélange parfait et immédiat, négligeant de fait les variabilités spatiales de composés chimiques au sein d'une maille. Les premiers résultats, basés sur la phase gazeuse uniquement, montrent que les nuages en couche limite convective affectent le transport vertical d'espèces chimiques. Les thermiques sont des zones de réactions privilégiées où la réactivité chimique est maximale. La plus grande intensité de ségrégation est calculée au sommet de la couche limite, toutefois de signes opposés entre les deux environnements. En environnement biogénique, le mélange non-homogène de l'isoprène et de OH dans cette zone induit une diminution maximale de 30% du taux de réaction moyen. Dans le cas urbain, la constante de réaction effective entre OH et les aldéhydes est supérieure de 16% à la constante moyenne. La réactivité de OH est supérieure de 15 à 40% dans les thermiques comparé au reste du domaine, dépendant de l'environnement chimique et de l'heure. Comme les thermiques occupent une faible portion du domaine, l'impact des structures turbulentes sur la réactivité totale de OH est une diminution de 9% pour le cas biogénique et une augmentation maximale de 5% dans le cas anthropique. Des simulations LES incluant la réactivité aqueuse révèlent une baisse importante des rapports de mélange de OH associée à la présence de nuages
This thesis focuses on the influence of the convective and cloudy boundary layer on the chemical reactivity in West Africa. To answer this question, high resolution simulations (50m) are performed on the atmospheric model Meso-NH coupled to a detailed chemical scheme representing the gaseous and aqueous phases. This spatial scale allow to explicitly represent the spatial and temporal characteristics of turbulent structures. Thermals in the boundary layer are identified by a conditional sampling based on a radioactive-decay passive scalar. The turbulent transport influence on the redistribution of chemical species depends on the chemical lifetimes of these species. Spatial segregation is created within the convective boundary layer that increases or decreases the mean reaction rates between compounds. AMMA campaign field study, and more recently DACCIWA, are used to define dynamical and chemical forcing of two simulated environments. The first one is representative of a biogenic environment dominated by natural emissions of VOC. The second reproduces a moderately polluted typical urban area of the Guinean Gulf (Cotonou in Benin). For the sake of simplicity, simulations analysis are limited to the chemical reaction between isoprene and OH in the biogenic case, and the reaction between C>2 aldehydes and OH in the anthropogenic case. The convective boundary layer influence is studied at thermal and domain scale. This makes the connection with coarse resolution models for which a hypothesis of perfect and immediate mixing is made, neglecting the spatial variability of chemical species within a grid cell. The first results are based on the gaseous phase only. Cloudy development in the convective boundary layer only affects the vertical transport of chemical species. The simulations show that thermals are preferential reaction zones where the chemical reactivity is the highest. The top of the boundary layer is the region characterized by the highest calculated segregation intensities but of the opposite sign in both environments. In the biogenic environment, the inhomogeneous mixing of isoprene and OH in this zone leads to a maximum decrease of 30% of the mean reaction rate. In the anthropogenic case, the effective rate constant for OH reacting with aldehydes is 16% higher at maximum than the averaged value. The OH reactivity is higher by 15 to 40% inside thermals compared to the surroundings depending on the chemical environment and time of the day. Because thermals occupy a small fraction of the simulated domain, the impact of turbulent motions on the domain-averaged OH total reactivity reaches a maximum 9% decrease for the biogenic case and a maximum of 5% increase for the anthropogenic case. LES simulations including the aqueous reactivity reveal a significant decrease in OH mixing ratios associated to the presence of clouds. Consequently, isoprene and C>2 aldehydes mixing ratios increase at these altitudes

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MORENZ, Danilo Antonio. « Caracter?sticas de crescimento e valor nutritivo de clones de capim-elefante (Pennisetum purpureum Schum.) manejados sob lota??o rotacionada na esta??o seca ». Universidade Federal Rural do Rio de Janeiro, 2011. https://tede.ufrrj.br/jspui/handle/jspui/2130.

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CNPq
The objective of this study was to evaluate the variables related to the heights in the pre and post grazing sward, the production of dry biomass of green forage, morphological composition, leaf:stem ratio and nutritive value of two clones of elephant grass managed under rotational stocking. Was adopted a completely randomized design with repeated measures in time (grazing cycles) and three replications (paddocks). The sward heights, in pre and post grazing were influenced by the clones and grazing cycles, being the highest values observed for clone CNPGL 03-01-00. The production of dry mass of green forage was influenced by clone and grazing cycle, with higher mean value observed for CNPGL 03-01- 00, which was 17% higher than that observed for CNPGL 92-198-7, and there was decreased of dry mass of green forage with the advance of grazing cycles. The production of dry matter of leaves was influenced only by grazing cycle, with gradual reduction from the first to the third cycle. However, in fourth cycle was increase in biomass of leaves, which did not differ from that observed in the second cycle. There was interaction clone x cycle for the production of dry matter of stem, being observed differences in the first and third cycles for the clones. There was no effect of the factors studied for the production of senescent material. The leaf: stem ratio was influenced by grazing cycles, with interaction of the factors. The clone CNPGL 91-198-7 kept the leaf:stem ratio stable over the cycles, while clone CNPGL 1-3-00 presented a decrease in leaf:stem ratio from first until to third cycle. The number of aerial tillers was influenced by grazing cycles, increasing from the first until to third cycle, while the fourth cycle was observed decreased in the number of these tillers. The basal tillers were only effect of clones, where CNPGL 91-198-7 showed a higher number of these tillers. Crude protein (CP) and lignin (LIG) content were not affected by clones or by grazing cycles. Neutral detergent fiber (NDF) and the in vitro dry matter digestibility (IVDMD) were affected only by grazing cycles. The highest values of NDF were observed at the firsts three grazing cycles and, in the fourth grazing cycle the NDF was reduced. The IVDMD decreased until the third cycle; however, in the fourth cycle the values obtained were similar to those of the first cycle. According to results obtained the clone CNPGL 92-198-7 showed higher production of dry matter of the leaves, lower production of dry matter of stem and higher density of basal tillers, which may indicate its greatest potential for use under grazing, when compared to CNPGL 01-03-00.
Objetivou-se estudar as alturas no pr? e p?s-pastejo do dossel forrageiro, a produ??o de biomassa seca de forragem verde, a composi??o morfol?gica, a rela??o folha:colmo, a densidade de perfilhos e o valor nutritivo de dois clones de capim-elefante manejados sob lota??o rotacionada. Foi utilizado delineamento inteiramente casualizado com medidas repetidas no tempo (quatro ciclos de pastejo) e tr?s repeti??es (piquetes). As alturas do dossel pr? e p?s pastejo foram influenciadas pelos clones e pelos ciclos de pastejo. Os valores mais elevados foram observados para o clone CNPGL 00-1-3. Para massa seca de forragem verde houve apenas efeito do clone e do ciclo de pastejo. O valor m?dio da massa seca de forragem verde do CNPGL 00-1-3 foi 17% maior do que a do CNPGL 92-198-7. Com o avan?ar dos ciclos de pastejo houve redu??o da massa seca de forragem verde. A produ??o de biomassa seca de folha foi influenciada apenas pelo ciclo de pastejo, com redu??o gradual do primeiro at? o terceiro ciclo. No quarto ciclo houve aumento na massa seca de folha, que n?o diferenciou daquela obtida no segundo ciclo. Houve intera??o clone x ciclo para a massa de colmo, sendo observadas diferen?as entre clones apenas no primeiro e terceiro ciclos. N?o foi observado efeito dos fatores estudados ou intera??o para a massa seca de material morto. A rela??o folha:colmo foi influenciada pelos ciclos de pastejo, havendo intera??o dos fatores estudados. O CNPGL 92-198-7 manteve a rela??o folha:colmo est?vel ao longo dos ciclos, enquanto que o CNPGL 00-1-3 apresentou decr?scimo na rela??o folha:colmo do primeiro at? o terceiro ciclo, com maior valor obtido no quarto ciclo. Quanto ao n?mero de perfilhos a?reos foi observado efeito dos ciclos de pastejo, com aumento do primeiro ao terceiro ciclo, enquanto que no quarto ciclo houve redu??o do n?mero desses perfilhos. Para os perfilhos basais houve efeito dos clones, onde o CNPGL 92-198-7 apresentou maior n?mero de perfilhos que o CNPGL 00-1-3. Os teores de prote?na bruta (PB) n?o foram influenciados pelos clones ou pelos ciclos de pastejo. Os teores de fibra em detergente neutro (FDN) e o coeficiente da digestibilidade in vitro da mat?ria seca (DIVMS) foram influenciados apenas pelos ciclos de pastejo. Os maiores valores de FDN foram observados nos tr?s primeiros ciclos de pastejo, j? no quarto ciclo de pastejo o teor de FDN reduziu. Quanto ? DIVMS houve queda at? o terceiro ciclo, enquanto que no quarto ciclo os valores obtidos foram semelhantes aos do primeiro ciclo. Para lignina n?o foi observada diferen?a dos fatores estudados. De acordo com os resultados obtidos, o clone CNPGL 92-198-7 apresentou maior produ??o de biomassa seca de folhas, menor produ??o de biomassa seca de colmo e maior densidade populacional de perfilhos basais, o que pode indicar seu maior potencial para uso sob pastejo, quando comparado ao CNPGL 00-1-3.

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Munier, Laurent. « Simulations expérimentale et numérique des effets retardés d'une explosion en milieu clos et en présence de produits liquides ». Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10091/document.

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Peut-on modéliser de manière fiable les effets collatéraux (en termes de quantité ou concentration de produits éjectés) et les conséquences d’une explosion en milieu clos, et en présence de produits chimiques liquides ? Pour répondre à cette vaste question, qui soulève spontanément de nombreux sous-problèmes, les travaux de thèse se sont déroulés en trois temps : 1/une étude qualitative et semi-quantitative du scénario général, afin de comprendre le déroulement chronologique des évènements, et d’émettre les hypothèses nécessaires à une modélisation, 2 /L’étude systématique des effets d’une explosion en milieu clos, en présence ou non de produits liquides. Avant de modéliser la dégradation du produit liquide soumis à une température et à une pression élevées, les expérimentations préliminaires ont en effet fait apparaître la nécessité de quantifier dans le temps et dans l’espace, les effets thermiques et mécaniques d’une explosion à volume constant, 3/L’élaboration de modèles 0D(t) à partir des conclusions précédentes afin, d’une part, d’estimer la durée de vie d’une phase liquide dans un environnement thermodynamique contraint et, d’autre part, de démontrer la possibilité de modéliser le problème global de manière réduite. En effet, le terme source d’un tel évènement ne peut être modélisé par une libération ponctuelle de produit : il s’agit d’une libération étendue dans le temps, par le biais d’un écoulement chaud a priori diphasique et de débit variable. Les couplages des phénomènes, observés expérimentalement, rendent nécessaires : 1 - Une modélisation instationnaire de l’évolution de la pression et une estimation du niveau de température atteint dans le volume d’étude, après détonation d’une charge explosive, 2 - Une modélisation de la libération de la phase liquide dans l’enceinte, sous forme de gouttes millimétriques ou de gouttelettes microniques 3 - Une modélisation instationnaire des transferts couplés de masse et d’énergie entre la phase liquide et la phase gazeuse en présence et prise en compte d’éventuelles réactions chimiques à haute pression et haute température 4 - Et enfin, une modélisation instationnaire des rejets à la brèche. L’étude d’une explosion à volume constant a montré qu’il est possible de modéliser de manière simple la montée continue en pression de l’enceinte par une fonction exponentielle croissante. Pour une configuration de référence donnée – explosion d’une sphère d’explosif dans un parallélépipède – la valeur maximale de pression est directement proportionnelle au taux de chargement en explosif, sur l’intervalle [0,01 – 0,6] kg/m3. Le passage à une géométrie différente ou plus complexe demande l’introduction d’un coefficient correctif pour traduire l’amplification (ou l’atténuation) de la combustion turbulente des produits de détonation avec l’air ambiant. En ce qui concerne le champ de température par contre, notre analyse a montré qu’il coexiste des zones chaudes et des zones dites « froides » et que la valeur de température homogène finale calculée à partir d’un code thermochimique ne peut constituer qu’une simple indication. Seule une estimation du volume respectif de ces zones a été proposée ici. Nous avons établi que les propriétés physico-chimiques des produits stockés sont un point clef du problème et on suppose ces données connues pour une gamme de produits chimiques liquides à pression ambiante, communément utilisés dans l’industrie. Seul le phénomène d’évaporation a été développé dans ce mémoire. L’introduction de réactions chimiques entre constituants se traduirait dans les modèles par des termes sources supplémentaires liés à l’apparition ou la disparition d’espèces
Is it possible to model collateral effects due to an explosion (on a chemical facility for instance) occuring in a closed volume containing liquid chemical products storage units ?This thesis deals with a zerodimensionnal modelisation of such a 3D complex problem to asses the final thermodynamic state of chemical products released in the atmosphere. Developped sub-models take into account:- the unsteady time histories of the internal overpressure and temperature,- the unsteady liquid ejection (droplets sizes)- the unsteady modelisation of the local heat and mass transfers between the gas phase and the liquid phase- the unsteady ejection process of the resulting multiphase mixture in the environment.Models and sub-models are validated thanks to many experimental results

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Santos, Deborah Rodrigues de Souza. « Avaliação tecnológica de clones-elite de Eucalyptus spp., crescendo no Estado de Goiás : qualidade do lenho para produção de polpa celulósica Kraft ». Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-10102018-121537/.

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O setor florestal brasileiro prevê forte expansão das florestas plantadas de eucalipto, o que torna essencial estudos que indiquem materiais genéticos superiores e adaptados a novas fronteiras regionais. O estado de Goiás tem se destacado como um território com grande potencial ao estabelecimento e expansão de novos plantios. Nesse sentido, o presente trabalho tem como objetivo a avaliação tecnológica de clones-elite de Eucalyptus spp., oriundos de um teste clonal instalado no município de Luziânia- GO, com foco na qualidade do lenho para produção de polpa celulósica Kraft. Do total de materiais genéticos do teste clonal, foram selecionados 6 clones híbridos de Eucalyptus spp, na idade de 4 anos, e cortadas 5 árvores de cada clone, obtendo-se discos de madeira em 6 posições longitudinais (0% (base), DAP, 25%, 50%, 75% e 100% da altura comercial) e 4 toretes (±50 cm de comprimento) em posições intermediárias. Os discos de madeira foram utilizados na determinação das características físicas, químicas e anatômicas dos clones e os toretes, transformados em cavacos, submetidos à polpação Kraft e avaliadas as características do cozimento. Os resultados indicam grande variabilidade entre os clones nas características avaliadas. Os seis clones diferiram quanto ao crescimento e volume, com destaque para os clones A, B, C e F, de melhores desempenho. Os valores médios de densidade básica ponderada observados para os clones de estudo (0,46-0,50 g/cm3), se encontram dentro da faixa considerada ideal para a produção de celulose. Foram observados valores médios de densidade aparente entre 0,56 e 0,65 g/cm3, sendo o maior valor verificado para o clone E. Em geral, foi observado efeito significativo apenas na variação radial das propriedades físico-anatômicas. A caracterização química do lenho dos seis clones indica potencialidade tecnológica para produção de celulose Kraft, com destaque ao clone E. Os melhores desempenhos na polpação kraft para Kappa ± 18, foram alcançados com os clones E e F. Os clones de Eucalyptus spp. do estudo, em sua maioria, apresentaram excelente adaptabilidade local e satisfatórias propriedades do lenho quanto à transformação tecnológica em polpa celulósica Kraft. O clone E, que apresentou menor teor de extrativos e maior teor de holocelulose em sua constituição, além de bom desempenho no processo de polpação Kraft, bem como o clone F, que obteve os melhores índices de crescimento e produvidade e satisfatórias características físicas, anatômicas e tecnológicas, foram indicados como os de maior potencial para a produção de celulose. Ressalta-se a importância de se desenvolver pesquisas futuras nos materiais em idade mais avançada, visando melhor qualificar a adaptação local, bem como a qualidade do lenho, em busca de maior alcance no desempenho e eficiência produtiva do processo de polpação celulósica.
The Brazilian forestry sector foresees a strong expansion of Eucalyptus forests, which makes essential studies indicating superior genetic material and adapted to new borders. Goiás state has stood out as a territory with great potential for the establishment and expansion of new forest plantations areas. In this sense, the aim of the present work was to evaluate the technological performance of Eucalyptus wood elite clones from a clonal test installed in the municipality of Luziânia-GO, focusing on the wood quality for kraft pulping. From the total genetic material of the clonal test, 6 Eucalyptus wood hybrid clones, at 4 years-old, were selected and 5 trees of each clone were cut, obtaining wooden discs in 6 longitudinal positions (0% (base), DBH, 25%, 50% , 75% and 100% of commercial height) of trunck. Also, 4 logs of 50 cm in length between the base and 100% of the commercial height. The wood discs were used for determining the physical, chemical and anatomical wood characteristics and the short logs were transformed into wood chips for kraft pulping that whose characteristics were evaluated. The results indicate a high variability among the clones. All clones differed in volume growth, especially clones A, B, C and F, with the best performances. The average values of weighted basic density observed in Eucalyptus spp. clones (0.46-0.50 g/cm3) are within the range considered ideal for the kraft pulping production. Average values of apparent density were observed between 0.56 and 0.65 g / cm3, being the highest value verified for clone E. In general, a significant effect of radial position of the trunk was observed only for physical-anatomical properties. The wood chemical characterization indicates, for all clones, technological potential for kraft pulp production, especially for clone E, with lower content of extractives and higher content of holocellulose,. The best performances of kappa number 18 of kraft pulping were observed in clones E and F. Eucalyptus wood clones, presented excellent adaptability and great wood technological properties. The clone E, which presented besides good performance in the kraft pulping process, as well as clone F, which obtained the best rates of growth and productivity and satisfactory physical, anatomical characteristics, were the ones with the best kraft pulping potencial. Future researches with the same Eucalyptus spp. trees at advanced ages are recommended, in order to provide a better information of local adaptation as well wood quality, in search of greater reach in the performance and productive efficiency of the kraft pulping process.

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Vidal, Thomas. « Revisiting the chemistry of star formation ». Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0151/document.

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Les études astrochimiques de la formation stellaire sont particulièrement importantes pour la compréhension de l'évolution de l'Univers, du milieu interstellaire diffus à la formation des systèmes stellaires. Les récentes avancées en matière de modélisation chimique permettent d'apporter de nouveaux résultats sur le processus de formation stellaire et les structures mises en jeu. L'objectif de ma thèse était donc d'apporter un regard neuf sur la chimie de la formation stellaire en utilisant les récentes avancées sur le modèle chimique Nautilus. J'ai pour cela étudié l'évolution de la chimie du soufre durant la formation stellaire pour tenter d'apporter de nouvelles réponses au problème de déplétion du soufre. J'ai d'abord effectué une révision du réseau chimique soufré et étudié son effet sur la modélisation du soufre dans les nuages denses. En comparant aux observations, j'ai montré que le modèle textsc{Nautilus} était capable de reproduire les abondances des espèces soufrées dans les nuages denses en utilisant comme abondance élémentaire de soufre son abondance cosmique. Ce résultat m'a permis d'apporter de nouveaux indices sur les reservoirs de soufre dans ces objets. Puis j'ai effectué une étude complète de la chimie du souffre dans les coeurs chauds en me concentrant sur les effets sur la chimie de la composition pre-effondrement. J'ai également étudié les conséquences des différentes simplifications couramment faites pour la modélisation des coeurs chauds. Mes résultats montrent que la composition pre-effondrement est un paramètre majeur de l'évolution chimique des coeurs chauds, fournissant de nouveaux indices pour expliquer la variété de compositions en espèces soufrées observée dans ces objets. De plus, ma recherche a mis en évidence la nécessité d'uniformiser les modèles de chimie utilisés pour les coeurs chauds. Enfin, j'ai développé une méthode efficace pour inverser les paramètres initiaux d'effondrement de nuages denses en me basant sur une base de données de modèles physico-chimiques d'effondrement, ainsi que sur l'observation d'enveloppes de protoétoiles de Classe 0. A partir d'un échantillon de 12 sources, j'ai pu en déduire des probabilités concernant les possibles paramètres initiaux d'effondrement de la formation d'étoiles de faible masse
Astrochemical studies of star formation are of particular interest because they provide a better understanding of how the chemical composition of the Universe has evolved, from the diffuse interstellar medium to the formation of stellar systems and the life they can shelter. Recent advances in chemical modeling, and particularly a better understanding of grains chemistry, now allow to bring new hints on the chemistry of the star formation process, as well as the structures it involves. In that context, the objective of my thesis was to give a new look at the chemistry of star formation using the recent enhancements of the Nautilus chemical model. To that aim, I focused on the sulphur chemistry throughout star formation, from its evolution in dark clouds to hot cores and corinos, attempting to tackle the sulphur depletion problem. I first carried out a review of the sulphur chemical network before studying its effects on the modeling of sulphur in dark clouds. By comparison with observations, I showed that the textsc{Nautilus} chemical model was the first able to reproduce the abundances of S-bearing species in dark clouds using as elemental abundance of sulphur its cosmic one. This result allowed me to bring new insights on the reservoirs of sulphur in dark clouds. I then conducted an extensive study of sulphur chemistry in hot cores and corinos, focusing on the effects of their pre-collapse compositions on the evolution of their chemistries. I also studied the consequences of the use of the common simplifications made on hot core models. My results show that the pre-collapse composition is a key parameter for the evolution of hot cores which could explain the variety of sulphur composition observed in such objects. Moreover, I highlighted the importance of standardizing the chemical modeling of hot cores in astrochemical studies. For my last study, I developed an efficient method for the derivation of the initial parameters of collapse of dark clouds via the use of a physico-chemical database of collapse models, and comparison with observations of Class 0 protostars. From this method, and based on a sample of 12 sources, I was able to derive probabilities on the possible initial parameters of collapse of low-mass star formation

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Herrmann, Anders. « Structure and Activity of Circular Plant Proteins : Cytotoxic Effects of Viola Cyclotides ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8283.

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Joblin, Yaël. « Elaboration d’un microsystème d’analyse de l’air destiné à la détection rapide d’un développement fongique dans les espaces clos ». Thesis, Paris Est, 2011. http://www.theses.fr/2011PEST1027/document.

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Les champignons sont des biocontaminants courants des environnements intérieurs. De nombreuses études ont démontré leur rôle dans la dégradation des supports que ces microorganismes colonisent tels que les matériaux de construction, les ouvrages ou les œuvres d'art. De plus, ces biocontaminants sont susceptibles d'induire des allergies, des infections, des toxi-infections ou encore des irritations. Depuis 2005, une technique de détection de la croissance fongique, basée sur la recherche de traceurs chimiques spécifiques dans l'air, et un indice de contamination fongique (ICF), ont été développés et validés au cours de différentes campagnes de mesures dans l'habitat, les bureaux, les écoles, les crèches… L'objectivation d'une croissance fongique dans un environnement s'appuie sur des prélèvements par adsorption, une analyse chromatographique au laboratoire (GC/MS) et le calcul de l'ICF. Dans le cadre de la surveillance de la qualité microbiologique de l'air des environnements intérieurs, cette thèse a pour ambition de prolonger ces travaux en développant notamment un système de microcapteurs chimiques adapté à la mesure in situ. Cette recherche repose à la fois sur la méthode de détection fongique développée au CSTB et sur l'expertise scientifique et technique de l'ESIEE en matière de miniaturisation d'instruments de mesure, grâce à l'apport des microtechnologies. Le premier axe de cette étude a consisté à identifier expérimentalement les COV du métabolisme fongique spécifiques d'un développement sur des matériaux du patrimoine. Ces molécules ont permis de consolider l'ICF et de définir deux indices spécifiques à la problématique des sites patrimoniaux, validés dans des châteaux, musées, bibliothèques, grottes ornées… Le second axe porte, d'une part, sur la conception la réalisation et la caractérisation des briques élémentaires du microsystème d'analyse, à savoir un module de préconcentration (adsorption TENAX), un module de séparation (microGC) et un module de détection (capteurs polymères) et d'autre part sur les intégrations et pilotage de ces briques
Fungi are common microbial contaminants of indoor environments. Many studies have demonstrated their role in the partial or total degradation of materials they colonize such as building materials, or works of art. Moreover, those microbial contaminants are likely to lead to allergies, infections, poisoning or irritation. Since 2005, a new technique based on researching specific chemical tracers in the air, was developed and validated during different measurement campaigns. This approach is now applied to various indoor environments (houses, offices, schools, child care centers…) and allows the detection of recent and/or hidden contamination. The purpose of this work is to study and characterize a rapid and continuous air analysing microsystem for detection of fungal contamination in closed spaces. This study falls within the field of monitoring air microbiological quality in indoor environments. In addition to the time saved by the absence of any laboratory analysis, this system must provide a permanent monitoring of environments frequented by people, such as museums, schools, hospitals... This research is based both on the fungal detection method developed by CSTB and on scientific and technical expertise of ESIEE : specialised in design and manufacturing of miniaturized analysis systems obtained using microtechnology. The first step of this study was to define the compounds' nature to be detected for different cases of contamination along with the sampling strategy for the system. The second step focuses on the microstructures design and fabrication to be used in microanalytical system based on gas chromatography and the development of a miniaturised analysis system. So the first part of the study consisted in defining specific fungal contamination tracers for heritage conservation sites. This list allowed to reinforce a fungal contamination index for indoor environments and to define two specific indexes designed for heritage conservation sites. The validation of these different indexes allowed checking their compliance with those types of environments (castles, museums, libraries, decorated caves...) by detecting all cases of contamination, along with the control remediation of former contaminated environments. The second part of the study enabled the design and validation of three main modules constitutive of the microanalytical system based on gas chromatography. A miniaturised analysis system based on three modules has been developed

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Xie, Zhi. « Modelling genetic regulatory networks : a new model for circadian rhythms in Drosophila and investigation of genetic noise in a viral infection process ». Phd thesis, Lincoln University. Agriculture and Life Sciences Division, 2007. http://theses.lincoln.ac.nz/public/adt-NZLIU20070712.144258/.

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In spite of remarkable progress in molecular biology, our understanding of the dynamics and functions of intra- and inter-cellular biological networks has been hampered by their complexity. Kinetics modelling, an important type of mathematical modelling, provides a rigorous and reliable way to reveal the complexity of biological networks. In this thesis, two genetic regulatory networks have been investigated via kinetic models. In the first part of the study, a model is developed to represent the transcriptional regulatory network essential for the circadian rhythms in Drosophila. The model incorporates the transcriptional feedback loops revealed so far in the network of the circadian clock (PER/TIM and VRI/PDP1 loops). Conventional Hill functions are not used to describe the regulation of genes, instead the explicit reactions of binding and unbinding processes of transcription factors to promoters are modelled. The model is described by a set of ordinary differential equations and the parameters are estimated from the in vitro experimental data of the clocks components. The simulation results show that the model reproduces sustained circadian oscillations in mRNA and protein concentrations that are in agreement with experimental observations. It also simulates the entrainment by light-dark cycles, the disappearance of the rhythmicity in constant light and the shape of phase response curves resembling that of experimental results. The model is robust over a wide range of parameter variations. In addition, the simulated E-box mutation, perS and perL mutants are similar to that observed in the experiments. The deficiency between the simulated mRNA levels and experimental observations in per01, tim01 and clkJrk mutants suggests some differences in the model from reality. Finally, a possible function of VRI/PDP1 loops is proposed to increase the robustness of the clock. In the second part of the study, the sources of intrinsic noise and the influence of extrinsic noise are investigated on an intracellular viral infection system. The contribution of the intrinsic noise from each reaction is measured by means of a special form of stochastic differential equation, the chemical Langevin equation. The intrinsic noise of the system is the linear sum of the noise in each of the reactions. The intrinsic noise arises mainly from the degradation of mRNA and the transcription processes. Then, the effects of extrinsic noise are studied by means of a general form of stochastic differential equation. It is found that the noise of the viral components grows logarithmically with increasing noise intensities. The system is most susceptible to noise in the virus assembly process. A high level of noise in this process can even inhibit the replication of the viruses. In summary, the success of this thesis demonstrates the usefulness of models for interpreting experimental data, developing hypotheses, as well as for understanding the design principles of genetic regulatory networks.

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Casali, Giada. « Galactic archaeology with ages based on chemical clocks ». Doctoral thesis, 2021. http://hdl.handle.net/2158/1228473.

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In the era of large spectroscopic surveys, high-quality spectra can contribute to our understanding of the Galactic chemical evolution, not only providing high-precision abundances of elements belonging to the different nucleosynthesis channels, but also giving constraints to one of the most elusive quantity in astrophysics, i.e. stellar age. Some abundance ratios, called chemical clocks, have proved to be excellent indicators of the stellar age. We can distinguish them in two families: ratios composed by elements whose surface abundances vary during the stellar evolution, such as [C/N], or ratios that are modified by the Galactic chemical evolution, such as [Y/Mg], [Y/Al] etc. In this PhD thesis, I described a method to calibrate empirical relations between abundance ratios, metallicity and stellar ages, using open clusters and solar-like stars as calibrators.

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Brock, Ivan Heinz. « Chemical acoustic emission analysis of the Briggs-Rauscher iodine clock ». Thesis, 1995. http://hdl.handle.net/2429/7203.

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The oscillations observed in the Briggs-Rauscher Iodine Clock were studied using chemical acoustic emission (CAE) analysis. The experimental system evolved through three separate designs. The first early design employed a batch delivery system and utilized a piezoelectric transducer as the CAE sensor. The second design employed a flow delivery system and the oscillating reaction was monitored simultaneously by CAE, ultraviolet-visible spectrophotometry, and an ion-selective electrode. Sampling periods of 4.0 seconds made this a “low resolution” system. The third design was an optimized version of the second, with shorter sampling periods (1.0 seconds), which led to higher resolution data. The concentrations of the reagents used in the first system were those recommended by Briggs and Rauscher. Four unique phases of the oscillator were observed. The peak slopes during the positive slope phase increased according to second order kinetics, and the decreasing peak slopes during the negative slope phase were found to be independent of reagent concentration. Analysis of the averaged power spectra revealed two distinct frequency regions. Chemometric analysis successfully identified signals due to noise. A series of experiments were conducted in which [iodate] varied over a range of ca. 0.004 to 0.037 M at three different temperatures: 25, 30 and 35°C. It was discovered that the number of oscillations (both CAE and iodine oscillations) was independent of temperature. The CAB peak rates (increase and decrease) were also found to be independent of temperature while the iodine production and consumption rates were found to ca. triple with each five degree rise in temperature. Integrated CAE d.c. rates followed second order kinetics. Another series of experiments were conducted in which H₂O₂ was varied over the range of ca. 0.078 to 0.78 M at 35°C, The number of observed CAE oscillations was found to be independent of initial [H₂O₂] while the number of iodine oscillations increased as initial [H₂O₂] increased. Integrated CAE d.c. rates followed no simple trend. Under the conditions examined, a minimum [iodate] of 0.0 19 M, and [H₂O₂] of 0.16 M was required for oscillations to commence. Periodicity in the CAE data was noted in those experiments which did not strongly oscillate and attributed to a dissolved oxygen model. A refinement of the currently accepted mechanism is proposed and the utility of CAE as a tool to investigate oscillatory kinetics is discussed.

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Dickens, James E. « Probing chemical evolution in molecular clouds with millimeter-wave observations ». 1999. https://scholarworks.umass.edu/dissertations/AAI9920595.

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We present results for a study of gas-phase and grain chemical processes in the dense interstellar medium (ISM) using millimeter-wavelength observations of the pure rotational transitions of molecules. We mapped emission from a large number of molecules over a 8.5' x 10' region in the quiescent dark cloud core L134N. Statistical equilibrium calculations were performed to determine the kinetic temperature from observations of NH 3, the molecular hydrogen density from measurements of HC3N, N2H+, and CS, and the chemical abundances. We determined that the cloud can be described by a single kinetic temperature of [special characters omitted]10 K, and that the average density toward all lines of sight is [special characters omitted]. The determinations of these physical conditions were then used to derive abundances relative to HCO+ and CO for the remaining molecular species. Significant abundance variations were observed and are discussed in relation to current gas-phase chemistry models. We investigated grain processes using the ortho/para ratio of formaldehyde (H2CO). We find modification of this ratio from that expected for gas-phase formation (i.e., ortho/para [special characters omitted] 3) for dark clouds in the earliest stages of star formation. This indicates formation on and subsequent removal of formaldehyde from grain mantles, related to the increased energetics of the forming star. Due to activation barriers in the gas-phase formation of molecules by the addition of hydrogen atoms, highly saturated molecules are not expected to be abundant in molecular clouds unless molecules are released from grain surfaces, where the hydrogen atom has sufficient time to tunnel through the barrier. We determined that the abundance of methylenimine (CH2NH), the hydrogenated cousin to CN and HCN, is well matched by gas-phase chemistry models in quiescent cores but greatly enhanced in massive star forming regions, suggesting direct evidence for grain formation of CH2NH in star forming cores. We also report the first interstellar detection of the cyclic molecule ethylene oxide (c-C2H4O), a precursor to the formation of the sugar phosphates which comprise the backbone of our molecular genetic structure. Its formation pathways are thought to be from molecules whose formation is related to grains, and its large abundance is indicative of such processing.

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Munger, James William. « The chemical composition of fogs and clouds in southern California ». Thesis, 1989. https://thesis.library.caltech.edu/629/1/Munger_jw_1989.pdf.

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Fogs and clouds are frequent occurrences in Southern California. Their chemical composition is of interest due to their potential role in the transformation of sulfur and nitrogen oxides to sulfuric and nitric acid and in the subsequent deposition of those acids. In addition, cloud and fog droplets may be involved in the chemistry of low-molecular-weight carboxylic acids and carbonyl compounds.

The major inorganic species in cloud and fogwater samples were NH[4]+, H+, NO[3]-, and SO[4][2-]. Concentrations in fogwater samples were 1-10 x 10[-3] M; pH values ranged from [~]2 to 6. Nitrate usually exceeded sulfate. Acidity depended on the availability of NH[3] from agricultural operations. Stratus cloudwater had somewhat lower concentrations; pH values were in the range 3 - 4. The major factors accounting for variation in fog- or cloudwater composition were the preexisting aerosol and gas concentrations and variations in liquid water content. Deposition and entrainment or advection of different air masses were also important during extended cloud or fog episodes.

The droplet size dependence of cloudwater composition was investigated on one occasion in an intercepted coastal stratus clouds. The observations were consistent with the hypothesis that small droplets form on small secondary aerosol composed of H[2]SO[4], HNO[3] and their NH[4+] salts, while large droplets form on large sea-salt and soil-dust aerosol. Species that can exist in the gas phase, such as HCl and HNO[3], may be found in either droplet-size fraction.

Concentrations of S(IV) and CH[2]O in the range 100 - 1000 µM were observed in fogwater from urban sites in Southern California. Lower concentrations were observed in stratus clouds. The high levels of S(IV) and CH[2]O were attributed to the formation of hydroxymethanesulfonate (HMSA), the S(IV) adduct of CH[2]O. Direct measurement of HMSA in fogwater samples from Bakersfield, CA were made by ion-pairing chromatography. Glyoxal and methyiglyoxal were observed at concentrations comparable to CH[2]O in fogwater samples from Riverside, CA and in stratus cloudwater samples from sites along the Santa Barbara Channel.

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Knez, Claudia. « Chemical evolution of ice and gas from molecular clouds to protostars ». Thesis, 2006. http://hdl.handle.net/2152/2741.

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Jaruga, Anna. « Chemical aspects of cloud - aerosol interactions ». Doctoral thesis, 2017. https://depotuw.ceon.pl/handle/item/2038.

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In the atmosphere cloud droplets form and grow on aerosol particles - tiny solid or liquid particles suspended in the air. When trapped inside water drops aerosol particles are affected by the processes happening in clouds such as collisions between water drops or aqueous phase chemical reactions inside water drops. It can be said that clouds and aerosol particles coexist, continuously changing each others properties. This dissertation studies the interactions between aerosol particles and water drops in warm (i.e. ice free) boundary layer clouds. The main focus is on the collisions between water drops and the aqueous phase oxidation of sulfur to sulfate occurring inside cloud droplets and the impact of those processes on the size distribution of aerosol particles.The study is carried out using numerical simulations employing a Lagrangian representation of cloud microphysics and aqueous phase chemical reactions. The Lagrangian methods, also called particle tracking or particle based, allow to represent cloud microphysical and chemical processes as if from a point of view of an aerosol particle or a water drop. They are computationally expensive but allow to resolve numerically the changes to both aerosol particle and water drop size distribution.This study uses the Lagrangian microphysics scheme developed at the Faculty of Physics at the University of Warsaw. For the purpose of this study the Lagrangian scheme was extended to cover also the aqueous phase processes in cloud droplets. The list of chemical processes includes the dissolving of trace gases into water drops their dissociation and the oxidation reaction of sulfur to sulfate by ozone and hydrogen peroxide.Six trace gases are included in the scheme: sulfur dioxide, ozone, hydrogen peroxide, carbon dioxide, ammonia and nitric acid. The scientific software created during this study is available for further use as a part of an open source library of schemes. Parts of this dissertation may serve as the first documentation of the design, performance and the user interface of the created Lagrangian microphysics and aqueous phase chemistry scheme.The dissertation contains a short theoretical introduction to the microphysical and chemical processes occurring in warm clouds. It presents the details of the Lagrangian representation of microphysics in a numerical scheme.The new module of the Lagrangian scheme responsible for aqueous phase chemical reactions is described and tested in an adiabatic parcel model framework. Next, the created Lagrangian microphysics and aqueous phase chemistry scheme is used in a 2-dimensional kinematic setup representing a vertical slice through a boundary layer topped with a stratocumulus deck. The discussion focuses on the impact of collisions between water drops and the in-cloud oxidation of sulfur to sulfate on the size distribution on aerosol particles. The sensitivity of the obtained results to different microphysical and chemical conditions is also investigated.
Kropelki chmurowe tworzą się na cząstkach aerozolu czyli drobinach zanieczyszczeń w fazie stałej lub ciekłej zawieszonych w powietrzu. Cząstki aerozolu znajdujące się w kropelkach chmurowych są poddane działaniom procesów chmurowych takich jak zderzenia między kropelkami wody lub reakcje chemiczne zachodzące w kropelkach wody. Chmury i cząstki aerozolu wzajemnie ze sobą oddziałują i wzajemnie wpływają na swoje własności. Przedstawiona rozprawa doktorska bada interakcje pomiędzy drobinami aerozolu atmosferycznego i kropelkami wody w płytkich chmurach warstwy granicznej (t.j. w chmurach bez lodu). Przedstawione wyniki skupiają się na zderzeniach miedzy kropelkami wody i reakcji utlenienia dwutlenku siarki do kwasu siarkowego VI zachodzącej w kropelkach chmurowych oraz ich wpływie na widmo rozmiarów drobin aerozolu.Badania przedstawione w rozprawie doktorskiej są prowadzone przy użyciu symulacji numerycznych wykorzystujących lagranżowski sposób opisu mikrofizyki chmur i reakcji chemicznych w kropelkach chmurowych. Metody te są kosztowne numerycznie, ale pozwalają na dokładną reprezentację w modelu numerycznym ewolucji widma rozmiarów zarówno kropel wody jak i cząstek aerozolu.W trakcie przeprowadzonych badań użyty został lagranżowski schemat mikrofizyczny tworzony na Wydziale Fizyki Uniwersytetu Warszawskiego. Na potrzeby przeprowadzonych badań schemat ten został rozszerzony o opis procesów chemicznych zachodzących w kropelkach chmurowych. Do schematu dodany został opis rozpuszczania gazów śladowych w kropelkach chmurowych, dysocjacji rozpuszczonych związków na jony i reakcji utlenienia rozpuszczonego dwutlenku siarki do kwasu siarkowego przez ozon i nadtlenek wodoru. Do schematu zostało dodanych sześć gazów śladowych: dwutlenek siarki, ozon, nadtlenek wodoru, dwutlenek węgla, amoniak i kwas azotowy. Stworzone oprogramowanie jest dostępne jako część otwartej biblioteki schematów numerycznych. Część przedstawionej rozprawy doktorskiej może służyć jako opis struktury i sposobu działania stworzonego oprogramowania oraz dokumentacja interfejsu użytkownika.Rozprawa doktorska zawiera krótki wstęp przedstawiający teoretyczne podstawy opisu procesów mikrofizycznych i chemicznych zachodzących w płytkich chmurach warstwy granicznej. Następnie zaprezentowany jest opis zasady działania mikrofizycznego schematu lagranżowskiego. W rozprawie opisany jest również nowy moduł odpowiedzialny za reakcje chemiczne zachodzące w kropelkach chmurowych. Poprawność stworzonego opisu reakcji chemicznych w kropelkach jest przetestowana przy użyciu adiabatycznego modelu cząstki. W ostatniej części rozprawy lagranżowski opis mikrofizyki i reakcji chemicznych w chmurach jest zastosowany w 2-wymiarowym modelu reprezentującym przekrój przez warstwę graniczną przykrytą chmurą stratocumulus. Dyskusja wyników skupia się na przedstawieniu wpływu zderzeń między kropelkami oraz reakcji chemicznych zachodzących w kropelkach chmurowych na widmo rozmiarów drobin aerozolu. Dyskutowane są również symulacje testujące czułość otrzymanych wyników na początkowe warunki mikrofizyczne i chemiczne panujące w modelu.

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Blake, Geoffrey A. « On the Chemical Composition of Interstellar Molecular Clouds : A Millimeter and Submillimeter Spectral Line Survey of OMC-1 ». Thesis, 1986. https://thesis.library.caltech.edu/4890/1/Blake_ga_1986.pdf.

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The same basic principles govern the chemical and physical evolution of systems throughout the universe. However, the dissimilar conditions on the Earth and in the interstellar medium lead to remarkably different chemical compositions for these two environments. While less familiar than terrestrial chemistry, the study of the chemical composition of the interstellar medium is important because it bears directly on the understanding of phenomena as diverse as star formation, galactic structure and dynamics, and the cosmological origin of the universe, in addition to providing a unique opportunity to investigate a number of fundamental chemical and physical processes.

We present here results from a millimeter and submillimeter spectral line survey of the core of the Orion molecular cloud (OMC-1). The millimeter-wave survey, conducted at the Owens Valley Radio Observatory (OVRO), covers a 55 GHz interval in the 1.3 mm (230 GHz) atmospheric window and contains emission from 29 molecules. Together with the frequency selective submillimeter observations of H₂D⁺ (372.4 GHz), Cl (492.2 GHz), NH₃ (572.5 GHz), and HCl (625.9 GHz) performed aboard NASA's Kuiper Airborne Observatory, over 800 emission lines have been detected from 33 chemically distinct species during the course of this work. The uniformly calibrated results from the unique and extensive OVRO spectral line survey place significant constraints on models of interstellar chemistry, and have allowed the chemical composition of the various regions in OMC-1 to be definitively characterized.

A global analysis of the observed abundances has shown that the markedly different chemical compositions of the kinematically distinct Orion subsources may be simply interpreted in the framework of an evolving, initially quiescent, gas-phase chemistry influenced by the process of massive star formation. The chemical composition of the extended Orion cloud complex is similar to that found in a number of other objects, but the central regions of OMC-1 have had their chemistry selectively altered by the high velocity outflow from the young star(s) embedded deep within the interior of the molecular cloud. Detailed arguments are presented in this thesis which relate the seemingly disparate chemical compositions of the individual regions to each other and to the expected physical manifestations of the circumstellar mass loss, and which suggest that similar mechanisms may operate in other molecular clouds as well.

By performing supporting laboratory spectroscopy to supplement existing millimeter-wave catalogues only 33 of the over 800 lines remain unidentified, in contradiction to earlier expectations which had predicted that the near millimeter-wave spectrum of molecular clouds would contain hundreds of strong, unidentifiable emission features. It is probable that a number of the unidentified lines left in the OVRO survey are due to transitions between states of either isotopically substituted or highly excited abundant and complex molecules such as CH₃OH, CH₃OCH₃, and HCOOCH₃ whose rotational spectra are poorly known at present. The very small percentage and weak strength of the unidentified lines implies that the dominant chemical constituents visible at millimeter wavelengths have been identified in the Orion molecular cloud.

Also presented are high resolution laboratory millimeter, submillimeter, and far-infrared absorption spectra of the transient molecular species OH, CN, HOC⁺, and HCO, The zero-field pure rotational spectrum of the OH radical was observed, for the first time, with a frequency agile far-infrared laser sideband spectrometer which promises to revolutionize high resolution spectroscopy at submillimeter and far-infrared wavelengths, while the HOC⁺ molecular ion was synthesized in a novel glow discharge cell that increases ion abundances by roughly two orders of magnitude as compared with those produced by previously reported methods. Studies of several ions produced in the new discharge cell have provided a theory of the mechanism responsible for the ion enhancement. Sixty-five transitions of CN in its first four vibrational states have been observed, allowing a detailed examination of vibrational and electronic effects in this astrophysically important free radical. The investigation of HCO is the first extensive zero-field analysis of the formyl radical, and is one of the very few millimeter and submillimeter laboratory studies of a non-linear free radical performed to date.

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Syed, Rehana Naz. « Chemical and Genetic Diversity in Sesame (Sesamum indicum L.) ». Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-000D-EF3B-E.

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Biologische Diversität existiert sowohl zwischen mehreren Arten als auch innerhalb einer Art, innerhalb von Populationen und Individuen einer Population. Die intraspezifische Diversität wurde bislang ausgiebig auf der Ebene des Genoms untersucht. Sie ist im Kontext metabolischer Zusammenhänge in Pflanzen bisher kaum untersucht und es existieren nur wenige Veröffentlichungen zu diesem Thema. Uns sind bisher keine Publikationen zu Phytohormonen in Sesam bekannt. Neben dem wissenschaftlichen Interesse an der metabolischen Diversität in Sesam, spielen Stresshormone eine wichtige Rolle in der pflanzlichen Abwehr. Der Phytohormonspiegel im Samen ist unter agronomischen Gesichtspunkten relevant, da es vorkommen kann, dass Sesamsamen spontan auskeimen, während sie sich noch an der grünen Pflanze befinden. Diese Eigenschaft ist unerwünscht, da der wertvolle Samen auf diese Weise verloren geht. Im Rahmen dieser Arbeit wurde die Variation im Phytohormonniveau in 16 Akzessionen mit unterschiedlicher geographischer Herkunft untersucht. In Blättern und Wurzeln konnten ABA, JA, SA und SAG nachgewiesen werden, während GA4 lediglich in Blättern vorkam. Eine der Akzessionen aus Japan („Japan 2“) produzierte JA, SA und SAG in hohem Ausmaß. Hier konnten außerdem hohe Gehalte an Chitinasen festgestellt werden. Chitinasen sind für den Abbau von Chitin, dem Hauptbestandteil der pilzlichen Zellwand, verantwortlich. Eine Charakterisierung der Akzessionen mittels AFLP-Analyse zeigte, dass sich „Japan 2“ genetisch nicht mehr von anderen Akzessionen unterschied, als das Mittel der Unterschiede innerhalb aller gesammelten Proben. Bereits in früheren Untersuchungen unserer Arbeitsgruppe im Rahmen einer ungerichteten Metabolitenanalyse, konnte eine hohe Variabilität bei Sesamakzessionen gezeigt werden (Laurentin et al. 2006). Darüber hinaus, stimmen die Unterschiede im metabolischen Profil der Akzessionen nicht mit dem Grad ihrer genetischen Verwandtschaft überein. Es ist bekannt, dass tageszeitliche Unterschiede viele biologische Prozesse kontrollieren. Wir haben die tageszeitlichen Effekte auf den Phytohormonstatus untersucht und dabei die Unterschiede in Pflanzenorganen berücksichtigt. Tageszeitliche Konzentrationen von ABA, JA, IAA, SA und SAG wurden zu 8 unterschiedlichen Tageszeitpunkten in 3 unabhängigen Replikaten mittels HPLC untersucht. Wir konnten keine statistisch signifikanten Unterschiede erkennen. Die Untersuchungen zeigten jedoch eine Variation in den Phytohormonkonzentrationen in unterschiedlichen pflanzlichen Organen. Sekundäre pflanzliche Metabolite spielen als Resistenzfaktoren gegen Mikroorganismen eine wichtige Rolle. Sesamakzessionen, die diese Substanzen im hohen Ausmaß produzieren, stellen eine wichtige züchterische Ressource da. Um die Variation innerhalb der Akzessionen zu untersuchen, die ein hohes Niveau an sekundären Inhaltsstoffen aufweisen, haben wir die Effekte von 32 Pflanzenextrakten aus Sesamakzessionen gegen phytopathogene Pilze untersucht. Darunter befand sich ein Wurzelpathogen mit Spezialisierung auf Sesam (Macrophomina phaseolina), ein Blattpathogen mit breitem Wirtspflanzenkreis (Alternaria alternata) und Gefäßpathogen (Fusarium oxysporum). Die Diversität der Effekte, die für die unterschiedlichen Akzessionen beobachtet werden konnten, führt zu der Annahme, dass die Resistenzeigenschaften der Pflanzen durch gezielte züchterische Beeinflussung der metabolischen Aktivität verbessert werden können. In weiterführenden Untersuchungen zur Aufreinigung der Substanzen mit inhibitorischer Wirkung wurden Pflanzenextrakte in 80% Ethanol mit verschiedenen organischen Lösungsmitteln fraktioniert. Die meisten inhibitorischen Effekte konnten der Diethylether-Fraktion zugeschrieben werden. Im ersten Schritt wurden 4L des Extraktes hergestellt. Zwei aufgereinigte Lignane aus Sesam wurden gegen M. phaseolina, A. alternata und F. oxysporum getestet. Sesamin zeigte keinen Effekt bis zu einer Konzentration von 5mg/ml, während Sesamol (und 2,4-Dinitrophenol als Kontrolle) einen starken inhibitorischen Effekt aufwies. Für diese Substanzen wurden IC50 Werte ermittelt. Man kann festhalten, dass Sesamol dazu dienen kann, das Wachstum invasiver Pathogene einzuschränken. Durch die Kreuzung von zwei Elternlinien, die in der AFLP-Analyse einen signifikanten Polymorphismus aufwiesen, wurden Inzuchtlinien erzeugt. Die Nachkommen dieser Kreuzung wurden in 5 Generationen selbstbefruchtet. Das so entstandene Set aus RILs wurde mittels AFLP charakterisiert. Alle untersuchten RILs waren Hybride. Dies zeigt, dass während der ersten Kreuzung der Elternlinien keine Selbstung erfolgte. Wie erwartet, spalteten polymorphe AFLP-Marker der Elternlinien in den RILs zufällig auf. Monomorphe Marker fehlten in einigen RILs. Des Weiteren traten neue Marker auf, die zuvor nicht in den Elternlinien festgestellt werden konnten. Das Auftreten neuer Marker kann durch Rekombination zwischen Restriktionsfragmenten erklärt werden, welche die AFLP-Marker begrenzen. Die RILs werden nun von unseren Kooperationspartnern zum Aufbau einer genetischen Karte verwendet (Prof. Sami Doganlar und seine Arbeitsgruppe, Universität Antalya, Türkei).

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Parisi, María Celeste. « Propiedades astrofísicas de cúmulos estelares y estrellas del campo de la Nube Menor de Magallanes / ». Doctoral thesis, 2011. http://hdl.handle.net/11086/156.

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Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2011.
En esta tesis se han determinado las metalicidades y velocidades radiales de 15 cúmulos estelares de la Nube Menor de Magallanes y de los campos estelares circundantes a los mismos, haciendo uso de espectros en la región del CaII obtenidos con el 'Very Large Telescope' (Paranal - Chile). Por otra parte las edades de los cúmulos han sido derivadas a partir de fotometría PSF realizada sobre imágenes en los filtros V e I obtenidas con el mismo telescopio. Esta información ha sido utilizada para analizar la distribución de metalicidades, la existencia de una gradiente de metalicidad, la relación edad-metalicidad y la cinemática de esta galaxia.
María Celeste Parisi.
Posiciones y valores medidos para las estrellas miembros de los cúmulos -- Posiciones y valores medidos para las estrellas del campo -- Método de Máxima Probabilidad.

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