The majority of typically sized galaxies in the local Universe reside in a common dark matter halo with other similar galaxies known as a galaxy group. However, this was not always the case. Nine billion years ago, when the universe was one third its current age, these galaxies were almost exclusively the only massive galaxy in their dark matter haloes. In this thesis, I use both observational and theoretical methods to attempt to understand the effect these galaxy groups have on the evolution of galaxy properties. I examine the morphological and star formation properties of galaxies in redshift selected samples of galaxy groups at two redshift epochs, z=0 and z=0.4. Galaxy groups contain fewer disk galaxies, as determined by quantitative morphology measures, than similar luminosity field galaxies at both redshift epochs. Furthermore, the difference, at fixed luminosity, grows from 6% at z=0.4 to 19% at z=0. The fraction of passive galaxies, as determined from spectral energy distribution fitting of UV and optical photometry, shows similar behaviour. However, at neither redshift do we find that the disk dominated and star forming galaxies in groups have properties which are significantly different from those in the field. The disks in both environments show similar scaling relations and similar distributions of asymmetry. While both group and field star forming galaxies have similar average star formation rates at fixed stellar mass and redshift. These results argue in favor of a relatively gentle physical mechanism of transformation, like strangulation, which removes the hot halo of a galaxy as it falls into a more massive halo. I use a semi-analytic galaxy formation to understand the accretion histories of galaxies which reside in galaxy groups and clusters at different redshift epochs. The use of a simple model for environmental effects finds that the evolution seen in our observations of passive galaxies can be explained if a galaxy becomes passive 3 Gyrs after falling into a dark matter halo which has a mass of greater than 10E13 Msun. Finally, I use two novel methods for exploring how diffuse stellar mass and dust is distributed in and around galaxy groups. These are important probes of the environmental influence on galaxy evolution. By correlating the positions of hostless type Ia supernovae with galaxy groups, I find that as much as half of a galaxy's stellar mass is in a diffuse form outside of galaxies. These means that processes which shred or harass galaxies must be particularly strong in the group environment. I also find that dust is destroyed by the hot gas contained within groups and clusters. Dust is a necessary component of star formation, and its destruction could be an additional mechanism to suppress the production of stars in galaxy groups.

The performance of JSC “Interscalit” after recipience of sponsorship of European Union structural funds is investigated and strategy of further activities is framed in Master thesis; the review of scientific publications has been carried out, peculiarities of activities of the company have been highlighted, internal and external analysis of environment has been carried out, strategy of the company after recipience of sponsorship of EU structural funds has been prepared and strategy of the company in case of absence of sponsorship of EU structural funds has been forecasted, already present strategies inside the company have been identified, strong and weak angles of “Interscalit” have been set, the forecast of income and outlay has been carried out.

Cyanobacteria are prokaryotes that can grow photoautotrophically using oxygenic photosynthesis. Some filamentous cyanobacteria in media with insufficient fixed nitrogen develop a regular pattern of heterocyst cells that fix nitrogen for the remaining vegetative cells. We have built an integrated computational model of fixed nitrogen transport and cell growth for filamentous cyanobacteria. With our model, two qualitatively different experimentally observed nitrogen distributions between a pair of heterocysts are reconciled. By adding dynamic heterocyst placement into our model, we can optimize heterocyst frequency with respect to growth. Further introduction of modest leakage leads to distinct growth rates between different heterocyst placement strategies. A local placement strategy yields maximal growth and steady state heterocyst spacings similar to those observed experimentally. Adding more realistic fixed nitrogen storage based heterocyst commitment together with lateral inhibition to the model allows us to address initial heterocyst commitment and qualitatively reproduces many aspects of heterocyst differentiation. We also investigate patterns of starving cells and correlations of fixed nitrogen in filaments without heterocysts. We find percolation transitions in both spatial one dimensional patterns and space-time two dimensional patterns.

Simulations were performed to determine the effect of turbulence on protoplanets as they accrete inside of a planetary gas disk at the stage of planet formation that involves interactions between relatively large, similar sized bodies. The effect of turbulence was implemented into an existing N-Body code using a parameterization of magnetohydrodynamic (MHD) turbulence performed by Laughlin et. al. (2004). The investigation focussed on the effect of turbulent perturbations on planetary dynamics and accretion at various locations in the disk, particularly at large semimajor axis. At these distances, protoplanet collisions are generally less frequent due to the large induced eccentricities from close encounters and due to the trapping of protoplanets in mutual resonances. It is, however, essential that large protoplanets develop at these distances since some must eventually grow large enough to accrete the massive gas envelopes indicative of the giant planets. The interaction between a protoplanet and the surrounding gas disk creates a torque imbalance acting on the protoplanet, which is generally believed to result in the rapid inward spiraling of the protoplanet. In order to create a fixed region in the disk within which protoplanets may interact without migrating into the central star, two scenarios were considered that would inhibit the inward migration of the protoplanets. The first scenario involved a gas disk that had been truncated at the inner edge, referred to as a planet trap, and the second involved the existence of a stationary giant planet within a gap in the disk, referred to as a planet barrier. Each scenario was tested using different density profiles of the gas disk, different numbers and masses of initial protoplanets, various rates of gas disk decay and also four different levels of turbulence intensities. The results demonstrated that the addition of turbulence to the gas disk promotes planet mixing and results in an increased number of collisions between planets, even at large heliocentric distances. A turbulent disk has the tendency to create a final system where the planets are, on average, larger than those produced in a non-turbulent disk. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-17 14:41:52.607

No description available.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

In many robotics tasks, it is advantageous for robots to assemble into formations. In many of these applications, it is useful for the robots to have differing capabilities (i.e., be heterogeneous). These differences are task specific, but the most obvious differences lie in sensing and locomotion capabilities. Groups of robots may also have only imperfect or partially-known information about one another as well. One key piece of information that robots lack is how many other robots are in the environment. This thesis describes a method for formation control that allows heterogeneous robots with limited information to dynamically assemble into formations, merge smaller formations together, and correct errors that may arise in the formation. The approach is shown to be scalable and robust against robot failure, and is evaluated in multiple simulated environments.

Despite considerable progress in recent years, a complete description of the physical drivers of galaxy formation and evolution remains elusive, in part because of our poor understanding of star formation, and how star formation in galaxies is regulated by feedback from supernovae and massive stellar winds. Insight into the star formation histories of galaxies, and the interplay between star formation and feedback, can be gained by measuring their chemical abundances, which until recently has only been possible for galaxies in the nearby universe. However, reliable star formation and abundance calibrations have been hampered by various systematic uncertainties, and the lack of a suitable spectrophotometric sample with which to develop better calibrations. To address the limitations of existing surveys, we have obtained integrated optical spectra for a diverse sample of more than four hundred nearby star-forming galaxies. Using these data, in conjunction with observations from the Sloan Digital Sky Survey, we conduct a detailed analysis of optical star formation indicators, and develop empirical calibrations for the [O II] 3727 and H-beta 4861 nebular emission lines. Next, we investigate whether integrated spectroscopy of star forming galaxies can be used to infer their gas-phase oxygen abundances in the presence of radial abundance gradients, diffuse-ionized gas emission, and dust attenuation. We conclude that the integrated R23 parameter is generally insensitive to these systematic effects, enabling the gas-phase metallicity to be measured with a precision of +/-0.1 dex. We apply these methods to study the evolution in the luminosity-metallicity relation at 0<z<1 based on an analysis of more than 3500 I-band selected galaxies observed as part of the AGN and Galaxy Evolution Survey, and data culled from the literature. Our principal results are that, at fixed luminosity, the mean gas-phase metallicity of luminous (MB<-19 mag), star-forming galaxies at z=1 is a factor of two lower than the gas-phase metallicity in comparably luminous galaxies at z=0. However, after accounting for the effects of luminosity evolution, we find that the amount of chemical evolution for luminous galaxies corresponds to an increase of only 10%-20% since z1⁺ё, assuming a direct evolutionary connection between nearby and distant star-forming galaxies.

No description available.

This thesis examines the social and biological reproduction of households in the sectores populares, ie low income groups, both rural and urban, in the Meseta Central, yields specific outcomes at household level: the social formation based, originally, on smallholder coffee also depends on unusually successful domestic labour. Only multidisciplinary team work could adequately evaluate reproduction at the household level and establish the crucial role of the household in the wider economic system, as well as the role of women in maintaining diverse forms of subordination. The standard of living of the groups studied was estimated from the nutritional status of the children as a basic indicator of wellbeing; explanations of this status were sought in multivariate analysis of biological, economic, and social factors. Unexpectedly, the explanatory power of such variables such as income proved weak, the explanation appearing rather to lie with the less quantifiable social factors which rendered domestic labour more or less effective. Surveys and analysis, 1981-1984, sought to establish household survival strategies; diversified household enterprise proved of great importance in a survival constantly endangered by the insecurity of temporary, part-time and seasonal work so familiar in the Costa Rican economy as a whole. The household itself, as a flexible social organisation, seems one of the best resources for livelihood in the sectores populares, along with the ‘peasant' tradition of unpaid female and child labour. Proletarianisation remains incomplete. The economic categories of traditional Marxism prove inadequate to explain the gender subordination which characterises male female relations in countries of markedly uneven development, such as Costa Rica.