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Dissertations / Theses on the topic 'Clumping'
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1
Bouret, J. C., T. Lanz, D. J. Hillier, and C. Foellmi. "Clumping in O-type Supergiants." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1766/.
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We have analyzed the spectra of seven Galactic O4 supergiants, with the NLTE wind code CMFGEN. For all stars, we have found that clumped wind models match well lines from different species spanning a wavelength range from FUV to optical, and remain consistent with Hα data. We have achieved an excellent match of the P V λλ1118, 1128 resonance doublet and N IV λ1718, as well as He II λ4686 suggesting that our physical description of clumping is adequate. We find very small volume filling factors and that clumping starts deep in the wind, near the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more compared to those obtained from smooth-wind models.
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Puls, Joachim, N. Markova, F. Najarro, and M. M. Hanson. "Clumping in O-star winds." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1768/.
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Gräfener, G. "Clumping in hydrodynamic atmosphere models." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1792/.
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We investigate the effect of wind clumping on the dynamics of Wolf-Rayet winds, by means of the Potsdam Wolf-Rayet (PoWR) hydrodynamic atmosphere models. In the limit of microclumping the radiative acceleration is generally enhanced. We examine the reasons for this effect and show that the resulting wind structure depends critically on the assumed radial dependence of the clumping factor D(r). The observed terminal wind velocities for WR stars imply that D(r) increases to very large values in the outer part of the wind, in agreement with the assumption of detached expanding shells.
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Blomme, R. "Corotating Interaction Regions and clumping." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1810/.
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We present hydrodynamical models for Corotating Interaction Regions, which were used by Lobel (2007) to model the Discrete Absorption Components in HD 64760. We also discuss our failure to model the rotational modulations seen in the same star.
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Runacres, M. C. "Hydrodynamical models of clumping beyond 50 R∗." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1803/.
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We present one-dimensional, time-dependent models of the clumps generated by the linedeshadowing instability. In order to follow the clumps out to distances of more than 1000 R∗, we use an efficient moving-box technique. We show that, within the approximations, the wind can remain clumped well into the formation region of the radio continuum.
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Moffat, Anthony F. J. "Observational overview of clumping in hot stellar winds." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1763/.
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In the old days (pre ∼1990) hot stellar winds were assumed to be smooth, which made life fairly easy and bothered no one. Then after suspicious behaviour had been revealed, e.g. stochastic temporal variability in broadband polarimetry of single hot stars, it took the emerging CCD technology developed in the preceding decades (∼1970-80’s) to reveal that these winds were far from smooth. It was mainly high-S/N, time-dependent spectroscopy of strong optical recombination emission lines in WR, and also a few OB and other stars with strong hot winds, that indicated all hot stellar winds likely to be pervaded by thousands of multiscale (compressible supersonic turbulent?) structures, whose driver is probably some kind of radiative instability. Quantitative estimates of clumping-independent mass-loss rates came from various fronts, mainly dependent directly on density (e.g. electron-scattering wings of emission lines, UV spectroscopy of weak resonance lines, and binary-star properties including orbital-period changes, electron-scattering, and X-ray fluxes from colliding winds) rather than the more common, easier-to-obtain but clumping-dependent density-squared diagnostics (e.g. free-free emission in the IR/radio and recombination lines, of which the favourite has always been Hα). Many big questions still remain, such as: What do the clumps really look like? Do clumping properties change as one recedes from the mother star? Is clumping universal? Does the relative clumping correction depend on $dot{M}$ itself?
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Urbaneja, M. A., R. P. Kudritzki, and Joachim Puls. "Clumping in the winds of O-type CSPNs." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1780/.
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Recent studies of massive O-type stars present clear evidences of inhomogeneous and clumped winds. O-type (H-rich) central stars of planetary nebulae (CSPNs) are in some ways the low mass–low luminosity analogous of those massive stars. In this contribution, we present preliminary results of our on-going multi-wavelength (FUV, UV and optical) study of the winds of Galactic CSPNs. Particular emphasis will be given to the clumping factors derived by means of optical lines (Hα and Heii 4686) and “classic” FUV (and UV) lines.
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Massa, D. L., R. K. Prinja, and A. W. Fullerton. "The effects of clumping on wind line variability." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1809/.
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We review the effects of clumping on the profiles of resonance doublets. By allowing the ratio of the doublet oscillator strenghts to be a free parameter, we demonstrate that doublet profiles contain more information than is normally utilized. In clumped (or porous) winds, this ratio can lies between unity and the ratio of the f-values, and can change as a function of velocity and time, depending on the fraction of the stellar disk that is covered by material moving at a particular velocity at a given moment. Using these insights, we present the results of SEI modeling of a sample of B supergiants, ζ Pup and a time series for a star whose terminal velocity is low enough to make the components of its Si VIλλ1400 independent. These results are interpreted within the framewrok of the Oskinova et al. (2007) model, and demonstrate how the doublet profiles can be used to extract infromation about wind structure.
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Kholtygin, A. F. "Modelling the induced clumping stochastic line profile variability." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1818/.
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We model the line profile variability (lpv) in spectra of clumped stellar atmospheres using the Stochastic Clump Model (SCM) of the winds of early-type stars. In this model the formation of dense inhomogeneities (clumps) in the line driven winds is considered as being a stochastic process. It is supposed that the emission due to clumps mainly contributes to the intensities of emission lines in the stellar spectra. It is shown that in the framework of the SCM it is possible to reproduce both the mean line profiles and a common pattern of the lpv.
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St-Louis, N., and Anthony F. J. Moffat. "Do clumping corrections increase with decreasing mass-loss rates?" Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1769/.
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We report on new mass-loss rate estimates for O stars in six massive binaries using the amplitude of orbital-phase dependent, linear-polarimetric variability caused by electron scattering off free electrons in the winds. Our estimated mass-loss rates for luminous O stars are independent of clumping. They suggest similar clumping corrections as for WR stars and do not support the recently proposed reduction in mass-loss rates of O stars by one or two orders of magnitude.
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Najarro, F., Joachim Puls, A. Herrero, M. M. Hanson, J. Martín-Pintado, and D. J. Hillier. "Tracking the Clumping in OB Stars from UV to radio." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1770/.
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Kraus, M., J. Kubát, and J. Krtička. "Wind emission of OB supergiants and the influence of clumping." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1775/.
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The influence of the wind to the total continuum of OB supergiants is discussed. For wind velocity distributions with β > 1.0, the wind can have strong influence to the total continuum emission, even at optical wavelengths. Comparing the continuum emission of clumped and unclumped winds, especially for stars with high β values, delivers flux differences of up to 30% with maximum in the near-IR. Continuum observations at these wavelengths are therefore an ideal tool to discriminate between clumped and unclumped winds of OB supergiants.
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Krtička, J., Joachim Puls, and J. Kubát. "The influence of clumping on predicted O star wind parameters." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1796/.
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We study the influence of clumping on the predicted wind structure of O-type stars. For this purpose we artificially include clumping into our stationary wind models. When the clumps are assumed to be optically thin, the radiative line force increases compared to corresponding unclumped models, with a similar effect on either the mass-loss rate or the terminal velocity (depending on the onset of clumping). Optically thick clumps, alternatively, might be able to decrease the radiative force.
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Todt, Helge, Wolf-Rainer Hamann, and G. Gräfener. "Clumping in [WC]-type Central Stars from electron-scattering line wings." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1771/.
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While there is strong evidence for clumping in the winds of massive hot stars, very little is known about clumping in the winds from Central Stars. We have checked [WC]-type CSPN winds for clumping by inspecting the electron-scattering line wings. At least for three stars we found indications for wind inhomogeneities.
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Kholtygin, A. F. "Wavelets for looking for clumping in the wind of OB stars." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1779/.
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Hillier, D. J. "On the influence of clumping on O and Wolf-Rayet spectra." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1790/.
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Overwhelming observational and theoretical evidence suggests that the winds of massive stars are highly clumped. We briefly discuss the influence of clumping on model diagnostics and the difficulties of allowing for the influence of clumping on model spectra. Because of its simplicity, and because of computational ease, most spectroscopic analyses incorporate clumping using the volume filling factor. The biases introduced by this approach are uncertain. To investigate alternative clumping models, and to help determine the validity of parameters derived using the volume filling factor method, we discuss results derived using an alternative model in which we assume that the wind is composed of optically thick shells.
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Reimer, A. "Clumping effects on non-thermal particle spectra in massive star systems." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1824/.
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Observational evidence exists that winds of massive stars are clumped. Many massive star systems are known as non-thermal particle production sites, as indicated by their synchrotron emission in the radio band. As a consequence they are also considered as candidate sites for non-thermal high-energy photon production up to gamma-ray energies. The present work considers the effects of wind clumpiness expected on the emitting relativistic particle spectrum in colliding wind systems, built up from the pool of thermal wind particles through diffusive particle acceleration, and taking into account inverse Compton and synchrotron losses. In comparison to a homogeneous wind, a clumpy wind causes flux variations of the emitting particle spectrum when the clump enters the wind collision region. It is found that the spectral features associated with this variability moves temporally from low to high energy bands with the time shift between any two spectral bands being dependent on clump size, filling factor, and the energy-dependence of particle energy gains and losses.
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Onyambu, Frank Gekara. "Study of Platelet-mediated clumping adhesion phenotypes in Plasmodium falciparum malaria." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:2bc489a9-121e-41ab-8830-1cb07e5b01f2.
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Platelet-mediated clumping of Plasmodium falciparum-infected erythrocytes (IEs) is a common property of field isolates associated with severe disease (Pain, Ferguson et al. 2001). Platelet receptors CD36 (Pain, Ferguson et al. 2001), P-Selectin (Wassmer, Taylor et al. 2008) and gC1qR (Biswas, Hafiz et al. 2007) mediate clumping. To characterize the molecular specificities of the clumping phenotype, I cloned clumping parasite line IT/C10 by limiting dilution. I characterized var gene expression in the IT/C10 clones using generic primers for the DBL tag region (Bull, Berriman et al. 2005). Clumping assays were conducted in the presence of specific reagents to delineate host factors hypothesized to contribute to development of the clumping phenotype. Finally, I conducted a clinical study with isolates from children with malaria in Kilifi, Kenya. This study shows that in parasite line IT/C10, platelet-mediated clumping is associated with Itvar30 suggesting a prominent role for the PfEMP-1 encoded by this var gene in development of platelet-mediated clumping. For IT/C10 parasites, platelet activation appears to be involved in platelet-mediated clumping. Platelet P-Selectin appears to mediate clumping using lectin-dependent interactions. To further elucidate the mechanisms that mediate clumping by host platelets, I have used a panel of platelet antagonists to delineate specific platelet activation pathways. Our results show that platelet activation plays an important role in platelet-mediated clumping. Finally, in this study, platelet-mediated clumping was associated with parasitaemia, but not with disease severity.
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Schnurr, O., and P. A. Crowther. "Mid-IR observations of WC stars, and the connection to wind clumping." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1788/.
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We present preliminary results of a tailored atmosphere analysis of six Galactic WC stars using UV, optical, and mid-infrared Spitzer IRS data. With these data, we are able to sample regions from 10 to 10³ stellar radii, thus to determine wind clumping in different parts of the wind. Ultimately, derived wind parameters will be used to accuratelymeasure neon abundances, and to so test predicted nuclear-reaction rates.
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Groh, J. H., D. J. Hillier, and A. Damineli. "Mass-loss rate and clumping in LBV stars : the impact of time-dependent effects." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1777/.
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This paper outlines a newly-developed method to include the effects of time variability in the radiative transfer code CMFGEN. It is shown that the flow timescale is often large compared to the variability timescale of LBVs. Thus, time-dependent effects significantly change the velocity law and density structure of the wind, affecting the derivation of the mass-loss rate, volume filling factor, wind terminal velocity, and luminosity. The results of this work are directly applicable to all active LBVs in the Galaxy and in the LMC, such as AG Car, HR Car, S Dor and R 127, and could result in a revision of stellar and wind parameters. The massloss rate evolution of AG Car during the last 20 years is presented, highlighting the need for time-dependent models to correctly interpret the evolution of LBVs.
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de, Koter A., J. S. Vink, and L. Muijres. "Constraints on wind clumping from the empirical mass-loss vs. metallicity relation for early-type stars." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1773/.
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We present the latest results on the observational dependence of the mass-loss rate in stellar winds of O and early-B stars on the metal content of their atmospheres, and compare these with predictions. Absolute empirical rates for the mass loss of stars brighter than 10$^{5.2} L_{odot}$, based on H$alpha$ and ultraviolet (UV) wind lines, are found to be about a factor of two higher than predictions. If this difference is attributed to inhomogeneities in the wind this would imply that luminous O and early-B stars have clumping factors in their H$alpha$ and UV line forming regime of about a factor of 3--5. The investigated stars cover a metallicity range $Z$ from 0.2 to 1 $Z_{odot}$. We find a hint towards smaller clumping factors for lower $Z$. The derived clumping factors, however, presuppose that clumping does not impact the predictions of the mass-loss rate. We discuss this assumption and explain how we intend to investigate its validity in more detail.
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Negrón, Oscar A. "Fibrin(ogen)-pathogen Interactions Support Antimicrobial Host Defense following Staphylococcus Aureus Peritonitis Infection." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin150488059846864.
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Liermann, A., and Wolf-Rainer Hamann. "Clumping in Galactic WN stars : a comparison of mass loss rates from UV/optical & radio diagnostics." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1781/.
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The mass loss rates and other parameters for a large sample of Galactic WN stars have been revised by Hamann et al. (2006), using the most up-to date Potsdam Wolf-Rayet (PoWR) model atmospheres. For a sub-sample of these stars exist measurements of their radio free-free emission. After harmonizing the adopted distance and terminal wind velocities, we compare the mass loss rates obtained from the two diagnostics. The differences are discussed as a possible consequence of different clumping contrast in the line-forming and radio-emitting regions.
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Robb, Stacey E. "Aggression, monopolization and growth depensation within groups of Japanese medaka, Oryzias latipes, interactions between the temporal and spatial clumping of food." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq25980.pdf.
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Abraham, Nabil Mathew. "Characterization of the Effect of Serum and Chelating Agents on Staphylococcus aureus Biofilm Formation; Chelating Agents Augment Biofilm Formation through Clumping Factor B." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2596.
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Staphylococcus aureus is the causative agent of a diverse array of acute and chronic infections, and some these infections, including infective endocarditis, joint infections, and medical device-associated bloodstream infections, depend upon its capacity to form tenacious biofilms on surfaces. Inserted medical devices such as intravenous catheters, pacemakers, and artificial heart valves save lives, but unfortunately, they can also serve as a substrate on which S. aureus can form a biofilm, attributing S. aureus as a leading cause of medical device-related infections. The major aim of this work was take compounds to which S. aureus would be exposed during infection and to investigate their effects on its capacity to form a biofilm. More specifically, the project investigated the effects of serum, and thereafter of catheter lock solutions on biofilm formation by S. aureus. Pre-coating polystyrene with serum is frequently used as a method to augment biofilm formation. The effect of pre-coating with serum is due to the deposition of extracellular matrix components onto the polystyrene, which are then recognized by MSCRAMMs. We therefore hypothesized that the major component of blood, serum, would induce biofilm formation. Surprisingly, serum actually inhibited biofilm formation. The inhibitory activity was due to a small molecular weight, heat-stable, non-proteinaceous component/s of serum. Serum-mediated inhibition of biofilm formation may represent a previously uncharacterized aspect of host innate immunity that targets the expression of a key bacterial virulence factor: the ability to establish a resistant biofilm. Metal ion chelators like sodium citrate are frequently chosen to lock intravenous catheters because they are regarded as potent inhibitors of bacterial biofilm formation and viability. We found that, while chelating compounds abolished biofilm formation in most strains of S. aureus, they actually augmented the phenotype in a subset of strains. We investigated the molecular basis of this phenomenon. Deletion and complementation analysis and thereafter antibody based inhibition assays confirmed a functional role for the surface adhesin clumping factor B as the causative determinant associated with the increased biofilm phenotype. Finally, we investigated the regulation of clumping factor B-mediated biofilm formation and the basis for the strain dependence. Regulation was determined to occur via two novel post-translational networks- one affecting ClfB activity, mediated by Ca2+ binding to the EF-Hand domain, and the other affecting protein stability, mediated by the enzymatic activity of the metalloprotease-aureolysin. Polymorphisms within the aureolysin gene sequence, between strains, was identified as the basis for some strains forming robust biofilms within chelated media versus other than do not exhibit this phenotype.
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Privé, Florian. "Genetic risk score based on statistical learning Efficient analysis of large-scale genome-wide data with two R packages: bigstatsr and bigsnpr Efficient implementation of penalized regression for genetic risk prediction Making the most of Clumping and Thresholding for polygenic scores." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAS024.
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Le génotypage devient de moins en moins cher, rendant les données de génotypes disponibles pour des millions d’individus. Par ailleurs, l’imputation permet d’obtenir l’information génotypique pour des millions de positions de l’ADN, capturant l’essentiel de la variation génétique du génome humain. Compte tenu de la richesse des données et du fait que de nombreux traits et maladies sont héréditaires (par exemple, la génétique peut expliquer 80% de la variation de la taille dans la population), il est envisagé d’utiliser des modèles prédictifs basés sur l’information génétique dans le cadre d’une médecine personnalisée.Au cours de ma thèse, je me suis concentré sur l’amélioration de la capacité prédictive des modèles polygéniques. Les modèles prédictifs faisant partie d’une analyse statistique plus large des jeux de données, j’ai développé des outils permettant l’analyse exploratoire de grands jeux de données, constitués de deux packages R/C++ décrits dans la première partie de ma thèse. Ensuite, j’ai développé une implémentation efficace de larégression pénalisée pour construire des modèles polygéniques basés sur des centaines de milliers d’individus génotypés. Enfin, j’ai amélioré la méthode appelée “clumpingand thresholding”, qui est la méthode polygénique la plus largement utilisée et qui estbasée sur des statistiques résumées plus largement accessibles par rapport aux données individuelles.Dans l’ensemble, j’ai appliqué de nombreux concepts d’apprentissage statistique aux données génétiques. J’ai utilisé du “extreme gradient boosting” pour imputer des variants génotypés, du “feature engineering” pour capturer des effets récessifs et dominants dans une régression pénalisée, et du “parameter tuning” et des “stacked regres-sions” pour améliorer les modèles polygéniques prédictifs. L’apprentissage statistique n’est pour l’instant pas très utilisé en génétique humaine et ma thèse est une tentative pour changer celaGenotyping is becoming cheaper, making genotype data available for millions of indi-viduals. Moreover, imputation enables to get genotype information at millions of locicapturing most of the genetic variation in the human genome. Given such large data andthe fact that many traits and diseases are heritable (e.g. 80% of the variation of heightin the population can be explained by genetics), it is envisioned that predictive modelsbased on genetic information will be part of a personalized medicine.In my thesis work, I focused on improving predictive ability of polygenic models.Because prediction modeling is part of a larger statistical analysis of datasets, I de-veloped tools to allow flexible exploratory analyses of large datasets, which consist intwo R/C++ packages described in the first part of my thesis. Then, I developed someefficient implementation of penalized regression to build polygenic models based onhundreds of thousands of genotyped individuals. Finally, I improved the “clumping andthresholding” method, which is the most widely used polygenic method and is based onsummary statistics that are widely available as compared to individual-level data.Overall, I applied many concepts of statistical learning to genetic data. I used ex-treme gradient boosting for imputing genotyped variants, feature engineering to cap-ture recessive and dominant effects in penalized regression, and parameter tuning andstacked regressions to improve polygenic prediction. Statistical learning is not widelyused in human genetics and my thesis is an attempt to change that
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Escolano, Cyril. "Analyse spectroscopique détaillée d'atmosphères stellaires : structure des vents et composition chimique de surface des étoiles O." Aix-Marseille 1, 2010. http://www.theses.fr/2010AIX10150.
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Les étoiles massives sont au centre de nombreux processus astrophysiques : elles participent a l’évolution chimique et dynamique de leur environnement, en y injectant la matière enrichie synthétisée en leur coeur, et de l’énergie mécanique via leur vent stellaire, et sont à l’origine de la formation des régions HII. En outre, elles sont supposées étre les progéniteurs des événements les plus lumineux et les plus énergétiques observés à l’heure actuelle, à savoir les supernovæ (de type core-collapse) et les sursauts gamma. Bien loin des rnilieux homogènes décrits initialement par la théorie des vents radiatifs, on a pu se rendre compte ces dernières années que les atmosphères des étoiles massives étaient en fait très structurées (clumping) et regorgeaient d’ activité (émissivité dans le domaine des X, champs magnétiques). Au cours de ma thèse, je me suis particulièrement intéressé aux propriétés des étoiles de type O, qui sont des étoiles massives, chaudes et lumineuses. J ’ai réalisé l’analyse spectroscopique détaillée d’un échantillon de ces objets (dont certains magnétiques), avec le code de transfert radiatif CMFGEN (l’un des plus complets à l’heure actuelle). De cette analyse, j ’ai pu déterminer leurs paramètres fondamentaux (température effective, abondances chimiques de surface, taux de perte de masse,. . . ) et les confronter aux modèles théoriques les plus récents. Mes résultats confirment l’existence de forts contrastes entre les paramètres observationnels et ceux attendus par les modèles théoriques, tant pour ce qui concerne leurs vents que pour ce qui conceme leur évolution chimiqueMassive stars are the central engines of various astrophysical processes : they ionize the surrounding hydrogen, giving birth to HII regions and, through their stellar winds, they yield the processed material synthetized in their core and inject mechanical energy to the surrounding medium. In addition, they are suspected to be the progenitors of the most luminous and energetic events observed at the time, namely (core-collapse) supernovae and gamma ray bursts. Far from being the homogeneous outflows of material described initially by the radiatively driven winds theory, the massive stars’ atmospheres are highly structured (wind clumping) and exhibit an intense activity (X-rays emissivity and magnetic fields for instance). During my thesis, I was particularly interested in the properties of the massive, hot and luminous O type stars. I realized the detailed spectroscopic analysis of a sample of these objects (some of them hosting a magnetic field), with the state-of-art radiative transfer code CMFGEN. From this analysis, I determined their fundamental parameters (effective temperature, surface chemical abundances, mass loss rates,. . . ) and confronted them to the most recent theoretical models. My results confrm that strong contrasts exist between the observational parameters and those expected by both theoretical wind models and stellar evolution models
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Peral, Marion. "Calibration of the clumped-isotope thermometer in foraminifera and its application to paleoclimatic reconstructions of the mid-Pleistocene in the Gulf of Taranto." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS382/document.
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Quantifier les variations de température océanique du passé est nécessaire pour comprendre les mécanismes qui régissent l’évolution climatique. Les méthodes de paléo-thermométrie classiques peuvent souffrir de limitation inhérente à l’écologie des organismes et/ou à cause de l’influence d'effets physico-chimiques (salinité, acidité de l’eau de mer…). Ce travail se focalise sur la technique de paléothermométrie Δ47, qui repose sur la mesure du « clumping isotopique » dans les carbonates. Il vise d’abord à établir une calibration appliquée aux foraminifères et ensuite à mettre en œuvre cette calibration pour l’étude des variations climatiques au cours de la transition du Pléistocène moyen (MPT). Notre calibration Δ47-température des foraminifères planctoniques et benthiques, prélevés dans des sédiments modernes, couvre une gamme de température de -2 à 25°C. Les valeurs de Δ47 sur 9 espèces de foraminifères présentent une excellente corrélation avec la température de calcification des organismes, estimée à partir des mesures isotopiques de l’oxygène. Les résultats obtenus confirment l’absence d’effets liés à l’écologie des foraminifères (effets vitaux et de taille des organismes) et démontrent que la salinité n’affecte pas les mesures de Δ47. Cette étude constitue une avancée méthodologique importante pour les futures études paléocéanographiques sur les foraminifères. La MPT correspond à une transition climatique marquée par un changement de fréquence des cycles glaciaires-interglaciaires (de 41 000 à 100 000 ans). La compréhension de cette période est un enjeu scientifique majeur pour appréhender la mise en place du climat actuel. Notre calibration Δ47-température a permis de quantifier les variations de températures au cours de la MPT en mer méditerranée (Section de Montalbano Jonico, sud de l’Italie) et particulièrement des stades isotopiques marins 31 et 19, considérés comme des analogues à l’Holocène. Les résultats indiquent que (i) les températures (Δ47) obtenues sont en adéquation avec les températures obtenues par d’autres paléothermomètres, (2) les températures permettent de retracer les changements de régime océanographique et hydrologique, et (3) la mesure du Δ47 est complément prometteur pour les études multi-méthodes en paléocéanographieThe quantification of past oceanic temperature changes is a critical requirement for understanding the mechanisms which regulate climate variations. Classical methods of paleothermometry could suffer from well-known limitations related to ecology and/or to physico-chemical biases (sea water salinity, acidity…). This work focuses on clumped-isotope carbonate thermometry (Δ47). It aims to establish a calibration of Δ47 foraminifera and use it to study past climatic variations through the Mid-Pleistocene Transition (MPT). Our Δ47 calibration in planktonic and benthic foraminifera collected from modern marine sediment covers a temperature range of -2 to 25 °C. The clumped-isotope compositions of 9 species of foraminifera show a robust correlation with the calcification temperature, estimated from the measurements of oxygen-18. These results confirm the absence of bias linked to foraminifer ecology (species-specific and foraminifer size effects) and provide evidence that salinity does not affect the Δ47 thermometer. This study constitutes significant methodological progress for future paleoceanographic applications in foraminifera.The MPT is a climatic transition characterized by a shift in the frequencies of glacial-interglacial cycles (from 41 000 to 100 000 years). Understanding the MPT is a major scientific objective, which underlies our effort to study the establishment of our present climate. Our Δ47 calibration was used to quantify temperature changes through the MPT in the Mediterranea Sea (Montalbano Jonico section, south of Italy), and in particular the marine isotopic stages 31 and 19, which may be described as Holocene analogues. We find that (1) Δ47 temperatures are in good agreement with temperatures reconstructed from other paleothermometers, (2) these results allow reconstructing changes in past oceanographic and hydrologic regime, and (3) Δ47 measurement are a promising component of multi-proxy paleoceanographic studies
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Hu, Ronghai. "Estimation cohérente de l'indice de surface foliaire en utilisant des données terrestres et aéroportées." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD021/document.
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L’indice de surface foliaire (Leaf Area Index, LAI), défini comme la moitié de la surface foliaire par unité de surface de sol, est un paramètre clé du cycle écologique de la Terre, et sa précision d'acquisition a toujours la nécessité et la possibilité d'amélioration. La technologie du scanner laser actif offre une possibilité d'obtention cohérente du LAI à plusieurs échelles, car le scanner laser terrestre et le scanner laser aéroporté fonctionnent sur le même mécanisme physique. Cependant, les informations tridimensionnelles du scanner laser ne sont pas complètement explorées dans les méthodes actuelles et les théories traditionnelles ont besoin d'adaptation. Dans cette thèse, le modèle de distribution de longueur de trajet est introduit pour corriger l'effet d’agrégation, et il est appliqué aux données du scanner laser terrestre et du scanner laser aéroporté. La méthode d'obtention de la distribution de longueur de trajet de différentes plates-formes est étudiée et le modèle de récupération cohérent est établi. Cette méthode permet d’améliorer la mesure du LAI des arbres individuels dans les zones urbaines et la cartographie LAI dans les forêts naturelles, et ses résultats sont cohérents à différentes échelles. Le modèle devrait faciliter la détermination cohérente de l'indice de surface foliaire des forêts à l'aide de données au sol et aéroportéesLeaf Area Index (LAI), defined as one half of the total leaf area per unit ground surface area, is a key parameter of vegetation structure for modeling Earth's ecological cycle and its acquisition accuracy always has the need and opportunity for improvement. Active laser scanning provides an opportunity for consistent LAI retrieval at multiple scales because terrestrial laser scanning (TLS) and airborne laser scanning (ALS) have the similar physical mechanism. However, the three-dimensional information of laser scanning is not fully explored in current methods and the traditional theories require adaptation. In this thesis, the path length distribution model is proposed to model the clumping effect, and it is applied to the TLS and ALS data. The method of obtaining the path length distribution of different platforms is studied, and the consistent retrieval model is established. This method is found to improve the individual tree measurement in urban areas and LAI mapping in natural forest, and its results at consistent at different scales. The model is expected to facilitate the consistent retrieval of the forest leaf area index using ground and airborne data
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Timerman, David. "Pollen Clumping and Release Mechanisms in Wind Pollinated Plants." Thesis, 2013. http://spectrum.library.concordia.ca/977471/1/MSc_Thesis_%2D_David_Timerman_5738520.pdf.
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Wind pollinated (anemophilous) angiosperm lineages have often converged independently on floral traits; the syndrome of traits presumably reflecting adaptation to more efficient pollen transport by wind and capture by receptive surfaces. One often-cited trait differentiating anemophiles from zoophiles is the cohesion of pollen grains into clumps, with greater clumping expected among the latter. Further, the mechanism by which grains are released remains underexplored. This thesis examines (1) whether pollen clumping can be used diagnostically to determine the vector, and (2) the hypothesis that resonance vibration of stamens in wind gusts is a mechanism of pollen release. Pollen clumping was studied intraspecifically in the wind pollinated Plantago lanceolata and interspecifically across 23 anemophilous and zoophilous species. Mean clump size was found to be well-distinguished species by vector, and the lognormal distribution was a reasonable characterization of clump size for the majority of the species examined. The stamens of P. lanceolata were manipulated in the laboratory and observed in the field to characterize their dynamic response to vibration. Stamens had elastic properties corresponding to modeling as underdamped cantilever beams and to theoretical ranges predicted to initiate resonance vibration in wind gusts. Pollen was released in multiple discrete bursts from resonating stamens with successively greater energy requirements. In the field, pollen release was observed from a resonating stamen. Understanding the function of stamen properties is crucial for developing an evolutionary theory of anemophily and modeling the wind pollination process. This study demonstrates that anemophilous stamens have distinct, quantifiable physical properties differentiating from stamens evolved for other mating systems.
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Joshi, Gandhali. "Substructure and Gas Clumping in the Outskirts of Abell 133." Thesis, 2013. http://hdl.handle.net/10012/7837.
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Galaxy clusters are powerful tools for studying various astrophysical principles. Gas accreting onto the cluster is heated to 10^7-10^8 K through adiabatic compression and shocks, making clusters highly luminous in X-ray imaging. Measurements of the gas density and temperature profiles can be used to calculate the gas mass fraction f_gas, which is expected to closely match the cosmic baryon fraction Ω_b/Ω_m. Recent observations have found entropy profiles in cluster outskirts that are shallower than predicted and values of f_gas that are higher than the Universal baryon fraction inferred from the Cosmic Microwave Background (CMB). Abell 133 was an ideal candidate for studying this phenomenon, since it had recently been observed in a wide (R≈30') Chandra mosaic with an exposure time of ∼2 Ms. The X-ray imaging was combined with existing optical imaging from the Canada-France-Hawaii Telescope (CFHT) and spectroscopy obtained from the Magellan telescope, to search for any possible gas clumps and to study their properties.
The photometric analysis yielded over 3200 red sequence galaxies to a depth of r'=22.5, which were used to create a Gaussian smoothed intensity map and a significance map of the cluster (compared to CFHT Legacy Survey data). About 6 significant overdensities were detected in the significance map, although these did not fully correspond to contours obtained from the X-ray image. Spectroscopy obtained on the cluster yielded ∼700 secure redshifts, of which about 180 were cluster members. This included data from the NOAO Fundamental Plane Survey (NFPS) and the 6 Degree Field Galaxy Survey (6dFGS). We found a cluster redshift of z=0.0561±0.0002 and a velocity dispersion of σ=743±43 km/s. The dynamical analysis gave a virial radius of r_v=1.44±0.03 Mpc and a virial mass of M_v=(5.9±0.8)×10^14 M_sun. We also found values of R_500=1.21±0.07 Mpc and M_500=(5.3±0.9)×10^14 M_sun for γ=1/3 and R_500=0.99±0.05 Mpc and M_500=(2.9±0.5)×10^14 M_sun for γ=1/2, where γ is a parameter related to the assumed density profile and the velocity anisotropy.
About 30 overdensities with a radius R_c≥30" were detected as gas clumps on the X-ray image. The galaxy distribution in these clumps was analyzed, both for the stacked signal as well as the individual clumps, in ten parallel colour-magnitude bands to find any significant red sequences associated with them. Most of these clumps appeared to be background systems, some consisting of 1-2 galaxies, others being small groups or clusters. Only 2-3 clumps appeared to be associated with the cluster itself. This suggests that the cluster density profile is actually quite smooth, which may not agree with recent numerical simulations. Further studies are required to determine if the cluster density distribution is consistent with what is predicted and the nature of the background systems.
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Chang, Yu-Chen, and 張妤真. "A simulation study on estimation of the clumping parameter of a negative binomial distribution." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/40123732756803862450.
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"Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1398/.
Full textAbstract:
Stellar winds play an important role for the evolution of massive stars and their cosmic environment. Multiple lines of evidence, coming from spectroscopy, polarimetry, variability, stellar ejecta, and hydrodynamic modeling, suggest that stellar winds are non-stationary and inhomogeneous. This is referred to as 'wind clumping'.
The urgent need to understand this phenomenon is boosted by its far-reaching implications. Most importantly, all techniques to derive empirical mass-loss rates are more or less corrupted by wind clumping. Consequently, mass-loss rates are extremely uncertain. Within their range of uncertainty, completely different scenarios for the evolution of massive stars are obtained. Settling these questions for Galactic OB, LBV and Wolf-Rayet stars is prerequisite to understanding stellar clusters and galaxies, or predicting the properties of first-generation stars.
In order to develop a consistent picture and understanding of clumped stellar winds, an international workshop on 'Clumping in Hot Star Winds' was held in Potsdam, Germany, from 18. - 22. June 2007. About 60 participants, comprising almost all leading experts in the field, gathered for one week of extensive exchange and discussion. The Scientific Organizing Committee (SOC) included John Brown (Glasgow), Joseph Cassinelli (Madison), Paul Crowther (Sheffield), Alex Fullerton (Baltimore), Wolf-Rainer Hamann (Potsdam, chair), Anthony Moffat (Montreal), Stan Owocki (Newark), and Joachim Puls (Munich). These proceedings contain the invited and contributed talks presented at the workshop, and document the extensive discussions.
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Simic, Anita. "Refining the Concept of Combining Hyperspectral and Multi-angle Sensors for Land Surface Applications." Thesis, 2009. http://hdl.handle.net/1807/26477.
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Assessment of leaf and canopy chlorophyll content provides information on plant physiological status; it is related to nitrogen content and hence, photosynthesis process, net primary productivity and carbon budget. In this study, a method is developed for the retrieval of total chlorophyll content (Chlorophyll a+b) per unit leaf and per unit ground area based on improved vegetation structural parameters which are derived using multispectral multi-angle remote sensing data. Structural characteristics such as clumping and gaps within a canopy affect its solar radiation absorption and distribution and impact its reflected radiance acquired by a sensor. One of the main challenges for the remote sensing community is to accurately estimate vegetation structural parameters, which inevitably influence the retrieval of leaf chlorophyll content. Multi-angle optical measurements provide a means to characterize the anisotropy of surface reflectance, which has been shown to contain information on vegetation structural characteristics. Hyperspectral optical measurements, on the other hand, provide a fine spectral resolution at the red-edge, a narrow spectral range between the red and near infra-red spectra, which is particularly useful for retrieving chlorophyll content.
This study explores a new refined measurement concept of combining multi-angle and hyperspectral remote sensing that employs hyperspectral signals only in the vertical (nadir) direction and multispectral measurements in two additional (off-nadir) directions within two spectral bands, red and near infra-red (NIR). The refinement has been proposed in order to reduce the redundancy of hyperspectral data at more than one angle and to better retrieve the three-dimensional vegetation structural information by choosing the two most useful angles of measurements.
To illustrate that hyperspectral data acquired at multiple angles exhibit redundancy, a radiative transfer model was used to generate off-nadir hyperspectral reflectances. It has been successfully demonstrated that the off-nadir hyperspectral simulations could be closely reconstructed based on the nadir hyperspectral reflectance and off-nadir multi-spectral reflectance in the red and NIR bands. This is shown using the Compact High-resolution Imaging Spectrometer (CHRIS) and Compact Airborne Spectrographic Imager (CASI) data acquired over a forested area in the Sudbury region (Ontario, Canada).
Through intensive validation using field data, it is demonstrated that the combination of reflectances at two angles, the hotspot and darkspot, through the Normalized Difference between Hotspot and Darkspot (NDHD) index has the strongest response to changes in vegetation clumping, an important structural component of canopy. Clumping index (Ω) and Leaf Area Index (LAI) maps are generated based on previous algorithms as well as empirical relationships developed in this study.
To retrieve chlorophyll content, inversion of the 5-Scale model is performed by developing Look-Up Tables (LUTs) that are based on the improved structural characteristics developed using multi-angle data. The generated clumping index and LAI maps are used in the LUTs to estimate leaf reflectance. Inversion of the leaf reflectance model, PROSPECT, is further employed to estimate chlorophyll content per unit leaf area. The estimated leaf chlorophyll contents are in good agreement with field-measured values. The refined measurement concept of combining hyperspectral with multispectral multi-angle data provides the opportunity for simultaneous retrieval of vegetation structural and biochemical parameters.
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Robb, Stacey E. "Aggression, monopolization and growth depensation within groups of Japanese medaka (Oryzias latipes) : interactions between the temporal and spatial clumping of food." Thesis, 1996. http://spectrum.library.concordia.ca/244/1/MQ25980.pdf.
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Resource defence theory predicts that defence and monopolization increase as the spatial clumping, spatial predictability, and temporal predictability of resources increase and as temporal clumping of resources decrease. Previous tests of resource defence theory have manipulated only one aspect of resource distribution at a time. I tested whether there was an interaction between the effects of the spatial and temporal clumping of food by allowing groups of ten Japanese medaka (Oryzias latipes) to compete, over a 4 week period, for food in a 2 x 2 factorial design. As expected, the intensity of aggression increased as the spatial clumping of food increased and as the temporal clumping of food decreased. However, there was also a significant interaction between the effects of the spatial and temporal clumping of food on the intensity of aggression and total aggression. The number of fish in the feeding patch, a measure of monopolization, decreased as the spatial clumping of food increased, but was not affected by the temporal clumping of food. Although measures of aggression were high in the economically defendable trials, there was no apparent cost to resource defence, since mean growth rates did not differ significantly among treatments. Growth depensation increased over time, but was not influenced by the temporal or spatial distribution of food. The power of my experiment to detect a significant effect of food distribution on growth depensation was low. Therefore, although I failed to reject the null hypothesis, I cannot confidently conclude that the spatial and temporal clumping of food have no effect on the magnitude of growth depensation. My results suggest that care must be taken when extrapolating the results of single factor experiments to multi-factor or field situations.
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Šurlan, Brankica. "Záření v hvězdných větrech." Doctoral thesis, 2012. http://www.nusl.cz/ntk/nusl-328660.
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Title: Radiation in stellar winds. Resonance line formation in inhomogeneous hot star winds Author: M.Sc. Brankica Šurlan Department: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor: RNDr. Jiří Kubát, CSc., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: To incorporate the three-dimensional (3-D) nature of stellar wind clump- ing into radiative transfer calculations, in this thesis a newly developed full 3-D Monte Carlo radiative transfer code for inhomogeneous expanding stellar winds is presented and used to investigate how different model parameters influence reso- nance line formation. Realistic 3-D models that describe the dense as well as the rarefied wind components are used to model the formation of resonance lines in a clumped stellar wind. Non-monotonic velocity fields are accounted for as well. It is shown that the 3-D density and velocity wind inhomogeneities have very strong impact on the resonance line formation. The models show that the line opacity is lower for a larger clump separation and shallower velocity gradients within the clumps. They also demonstrate that to obtain empirically correct mass-loss rates from UV resonance lines, wind clumping and its 3-D nature must be taken into account. 1