An estimated 1000 trillion cubic meters of gas in the unconventional hydrocarbon resource of gas hydrates in the world?s ocean floors far exceeds the known hydrocarbons in conventional reserves like coal, petroleum, and natural gas. These hydrate deposits also contain massive amounts of the greenhouse gases like methane and carbon dioxide. As relatively little is known about the oceanloor natural gas hydrates, mechanisms leading to the formation of these hydrates in ocean sediments need to be investigated before the significant technical challenges of recovery and environmental hazards are addressed. The subject research focuses on possible catalytic effects of biosurfactants on the formation of natural gas hydrates in oceanloor sediments. Sand/clay packs were saturated with seawater containing 1000 ppm of biosurfactant and pressurized with natural gas of 90 mole% methane, 6 mole% ethane and 4 mole% propane. The experimental results showed that gas hydrates formation in porous media is catalyzed by biosurfactants at very low concentrations. Commercially available representatives from the five biosurfactant classifications that microbes produce were purchased and evaluated in sand/clay packs at hydrateorming conditions. The rate of formation and induction time differed in the presence of bentonite and kaolin. The surface activities of biosurfactants were either specific to sand or clay surfaces. While in the presence of bentonite, Surfactin decreased hydrate induction time by 71% over a reference test with no biosurfactant in the seawater; Surfactin lowered induction time by 25% in the presence of kaolin. Rhamnolipid reduced the induction time by 58% in the presence of bentonite and by 66% in the presence of kaolin. Snomax and Emulsan, belonging to the classification of polysaccharide lipid complexes, reduced induction time by 30 to 40% in the presence of both kaolin and bentonite. Fatty acids reduced the induction time by 55% in the presence of bentonite and by 20% in the presence of kaolin. Surfactin enhanced the rate of formation by 400% in the presence of bentonite, but it had minimal effect in the presence of kaolin. Emulsan and Snomax increased the rate of formation by 250%, while rhamnolipid and phospholipids doubled formation rate in the presence of bentonite. Emulsan increased the rate of formation by 800%. In seawater, at hydrateorming conditions, rhamnolipid was found to have a critical micellar concentration of 12 ppm. This very low value of CMC suggests that minimal bacterial activity in ocean sediments could greatly catalyze hydrate formation. The recent analysis by Lanoil et al. (2001) of sediments from around gas hydrate mounds in the Gulf of Mexico gives a direct association between microbes and gas hydrates and supports the conclusions of the subject work.

In this paper, the effect of additives on COB2B hydrate formation is investigated in a high-pressure test cell surrounded by a thermostated coolant bath. An agitator is configured inside the cell. The characteristics of COB2B gas hydrate formation with additives SDS, THF and mixture of both were discussed. It was found that, in a quiescent system with single SDS，hydrate could form rapidly and the induction time of hydrates formation was reduced, while THF shows no improvement effect on COB2B hydrate formation. However, the mixture of SDS and THF can promote the hydrate formation rate considerably, and large amount of hydrates formed. In a stirring system with mixture additives, hydrates can form completely about 100 minutes early than that in the quiescent system.

A unique K-band selected high-redshift spectroscopic dataset (UDSz) is exploited to gain further understanding of galaxy evolution at z > 1. Acquired as part of an ESO Large Programme, this thesis presents the reduction and analysis of a sample of ∼ 450 deep optical spectra of a random 1 in 6 sample of the KAB < 23, z > 1 galaxy population. Based on the final reduced dataset, spectrophotometric modelling of the optical spectra and multi-wavelength photometry available for each galaxy is performed using a combination of single and dual component stellar population models. The stellarmass and age estimates provided by the spectrophotometric modelling are exploited throughout the rest of the thesis to investigate the evolution of massive galaxies at z > 1. Focusing on a K-band bright (K < 21.5) sub-sample in the redshift range 1.3 < z < 1.5 the galaxy size-mass relation has been studied in detailed. In agreement with some previous studies it is found that massive, old, early-type galaxies (ETGs) have characteristic radii a factor ~- 1.5 − 3.0 smaller than their local counterparts at a given stellar-mass. Due to the potential errors in spectrophotometric estimates of the stellarmasses at high redshift velocity dispersion measurements are derived for a sub-sample of massive ETGs at z > 1.3 in order to calculate dynamical mass estimates. To date, only a handful of objects at z > 1.3 have individual velocity dispersion estimates in the literature. Here the largest single sample (13 objects) of velocity dispersion measurements at high redshift is presented. The results for the sub-sample of objects with dynamical mass estimates confirm the results based on stellar mass estimates that high redshift massive systems are more compact than their local counterparts. The fraction of K-band bright objects at high redshift that are passively evolving is calculated with specific star-formation rates from the UV rest-frame continuum, [OII] emission and 24μm data. It is concluded that ∼ 58 ± 10% of the K < 21.5, 1.3 < z < 1.5 galaxy population is passively evolving. Various photometric techniques for separating star-forming and passively evolving galaxies are assessed by exploiting the accurate spectral types derived for the UDSz spectroscopic sample. Popular highredshift selection techniques are shown to fail to effectively select complete samples of passive objects with low levels of contamination. Using detailed information available for the UDSz dataset, various techniques are optimised and then used to estimate the passive fraction from the full UDS photometric catalog. The passive fraction results from the full photometric catalog are found to agree well with the results derived from the UDSz sample. With the Visible and Infrared Survey Telescope for Astronomy (VISTA) now starting to produce data, the opportunity has been taken to develop high-redshift galaxy population dividers based on the VISTA filters. Using the first data release from the VISTA Deep Extragalactic Observations (VIDEO) survey (VVDS D1 field), the passive fractions of K-band limited samples have been estimated to compare with results derived in the UDS. Within the errors the passive fraction estimates in the UDS and VISTA VVDS D1 field are found to agree reasonably well. Finally, composite spectra are used to study the evolution of various different galaxy sub-samples as a function of redshift, age, stellar-mass and specific star-formation rate. This work produces an remarkably clean result, showing that the massive, absolute Kband bright, passively evolving ETGs are always the oldest population, with ages close to the age of the Universe at z ∼ 1.4. In contrast, the late-type, low-mass, star-forming galaxies are always found to be much younger systems. This result strongly supports the downsizing scenario, in which more massive systems complete their stellar-mass assembly before lower-mass counterparts.

Gas hydrate formation generally involves gas dissolution, formation of nuclei and growth of new nucleus. On condition of synthesizing experiments without agitation, the formation of hydrate nuclei is comparatively difficult and needs an induction period which is considerably uncertain and random. Some additives such as surfactant sodium dodecyl sulfate (SDS) can increase the formation rate and reduce the induction time. A hydrate formation and mini drilling experimental system was used to carry on methane hydrate formation experiments with small quantity of SDS and SDS- tetrahydrofuran(THF) in deionized water. The reactor is a high pressure cell (40Mpa) made of titanium alloy with 4 transparent windows and an inner volume of about 2.8 liters. The effect of SDS and THF hydrate on the formation rate and amount of methane hydrate was studied by comparative testing and analyzing the collected data of temperature and pressure. According to the results of the tests, the formation rate of methane hydrate in the SDS-THF solution was faster than that in the SDS solution. As a water-soluble hydrate former, THF hydrate nucleation may be benefit of methane hydrate nucleation. A small amount of SDS and THF could dramatically promote the formation of methane hydrate in the pure water, and rapidly increase the amount of methane hydrate too. Therefore, a great deal of time for experiment was saved, which established a good basis for the coming mini drilling and drilling fluid experiments.

<p>The effect of stellar feedback on the interstellar medium is investigated using numerical simulation. In particular, the roles of supernova feedback and ionization feedback on the star formation rate and structure of the interstellar medium are compared. We use Enzo, an adaptive mesh code, and employ the MUSCL-Hancock hydrodynamics scheme to run simulations of a section of a stratified galactic disk. A turbulent velocity field is imposed in the central region of the disk and self-gravity is applied. Star clusters are formed when density and temperature conditions are met, which, in turn, provide ionization and supernova feedback into the interstellar medium. Simulations were run with and without supernova and ionization feedback and the runs are compared. Ionization feedback is found to dominate over supernova feedback in regulating star formation rates. With no feedback, all the gas is converted to stars by 200 Myr. When supernova feedback is added, 98% of the gas is used to create stars by 300 Myr. With ionization feedback instead, at 1 Gyr into the run, only 30% of the gas is in stars. Even with supernova feedback added to ionization feedback, the gas converted to stars is just 29% at 1 Gyr. Very strong supernovae take this fraction down to 25%. The star formation rates in the runs with supernova feedback are consistent with the low end of the Kennicutt-Schmidt relation, while the runs without ionization feedback have star formation rates that are an order of magnitude larger. Gas phase masses and volumes produced in the ionization runs are broadly consistent with observations.</p> / Master of Science (MSc)

Águas modais são formações oceânicas caracterizadas por camadas de propriedades praticamente homogêneas. Isso pode ser observada tanto através de baixos gradientes verticais de temperatura e salinidade, quanto de baixos valores de vorticidade potencial (VP). Portanto, para avaliarmos a formação da Água Modal Subtropical do Atlântico Sul (AMSTAS) foi utilizado o conjunto de dados In Situ Analysis System (ISAS - IFREMER) entre 2002 e 2014 para a região de 20&#186;S a 45&#186;S. Em conjunto aos critérios de Sato e Polito (2014) para a identificação da AMSTAS foram aplicados um novo intervalo de temperatura (13&#186;C a 16&#186;C) e a utilização de um gradiente vertical de temperatura (dT/dz = 0,02&#186;C m-1), tanto em superfície, de julho a novembro, quanto em subsuperfície durante todo o ano. Desse modo, os perfis selecionados foram utilizados para avaliar a variação do volume das camadas de AMSTAS. Na camada de superfície, buscou-se identificar os perfis que haviam sido recentemente afetados pela convecção local, que representa o principal mecanismo para a formação das águas modais, apenas entre julho e outubro. Para tanto, reduziu-se o valor máximo de VP dos perfis para 1,2 × 10-11 m-1 s-1. A partir da aplicação desse critério mais restritivo, calculou-se a taxa de formação de AMSTAS (&#916; f) mensal, entre 2002 e 2009, para compararmos com a taxa de formação estimada (&#916;F) pela teoria de Walin (1982), utilizando os dados do projeto Objectively Analyzed air-sea Fluxes (OAFlux). O &#916; f apresentou média inferior a &#916;F, indicando assim a necessidade de avaliarmos o conjunto de processos que afetam a formação da AMSTAS, em adição ao balanço de calor pela superfície. / Mode waters are oceanic formations characterized by layers of nearly homogeneous properties. This feature can be observed both at low temperature and salinity vertical gradients, as in low potential vorticity (PV) values. Therefore, to evaluate the formation of South Atlantic Subtropical Mode Water (SASTMW) the In Situ Analysis System (ISAS - IFREMER) data set was used for the period between 2002 and 2014 for the 20&#186;S to 45&#186;S region. Jointly with the criteria set by Sato e Polito (2014) for the identification of the SASTMW were applied a new temperature range (13&#186;C a 16&#186;C) and the use of a vertical temperature gradient (dT/dz = 0.02&#186;Cm-1 both in surface, between June and November, as in the subsurface throughout the year. Thus, the selected profiles were used to evaluate changes in the volume of the layers of SASTMW. Within the surface layer data, we sought to identify profiles that had been recently affected by the local convection, which is the main mechanism for the formation of mode water, only between July to October. Thereby, we reduced the maximum PV value of the profiles to 1.2 × 10-11 m-1 s-1. From the application of this more restrictive criteria, we calculated the SASTMW monthly formation rate (&#916;f) between 2002 and 2009 to compare with the estimated formation rate (&#916;F) from the Walin (1982) theory, using the data from the project Objectively Analyzed air-sea Fluxes (OAFlux). The &#916; f showed a mean value lower than the &#916;F rate, indicating the need to evaluate a broader set of processes that affect the SASTMW formation, in addition to the heat balance through the surface.

Águas modais são formações oceânicas caracterizadas por camadas de propriedades praticamente homogêneas. Isso pode ser observada tanto através de baixos gradientes verticais de temperatura e salinidade, quanto de baixos valores de vorticidade potencial (VP). Portanto, para avaliarmos a formação da Água Modal Subtropical do Atlântico Sul (AMSTAS) foi utilizado o conjunto de dados In Situ Analysis System (ISAS - IFREMER) entre 2002 e 2014 para a região de 20&#186;S a 45&#186;S. Em conjunto aos critérios de Sato e Polito (2014) para a identificação da AMSTAS foram aplicados um novo intervalo de temperatura (13&#186;C a 16&#186;C) e a utilização de um gradiente vertical de temperatura (dT/dz = 0,02&#186;C m-1), tanto em superfície, de julho a novembro, quanto em subsuperfície durante todo o ano. Desse modo, os perfis selecionados foram utilizados para avaliar a variação do volume das camadas de AMSTAS. Na camada de superfície, buscou-se identificar os perfis que haviam sido recentemente afetados pela convecção local, que representa o principal mecanismo para a formação das águas modais, apenas entre julho e outubro. Para tanto, reduziu-se o valor máximo de VP dos perfis para 1,2 × 10-11 m-1 s-1. A partir da aplicação desse critério mais restritivo, calculou-se a taxa de formação de AMSTAS (&#916; f) mensal, entre 2002 e 2009, para compararmos com a taxa de formação estimada (&#916;F) pela teoria de Walin (1982), utilizando os dados do projeto Objectively Analyzed air-sea Fluxes (OAFlux). O &#916; f apresentou média inferior a &#916;F, indicando assim a necessidade de avaliarmos o conjunto de processos que afetam a formação da AMSTAS, em adição ao balanço de calor pela superfície. / Mode waters are oceanic formations characterized by layers of nearly homogeneous properties. This feature can be observed both at low temperature and salinity vertical gradients, as in low potential vorticity (PV) values. Therefore, to evaluate the formation of South Atlantic Subtropical Mode Water (SASTMW) the In Situ Analysis System (ISAS - IFREMER) data set was used for the period between 2002 and 2014 for the 20&#186;S to 45&#186;S region. Jointly with the criteria set by Sato e Polito (2014) for the identification of the SASTMW were applied a new temperature range (13&#186;C a 16&#186;C) and the use of a vertical temperature gradient (dT/dz = 0.02&#186;Cm-1 both in surface, between June and November, as in the subsurface throughout the year. Thus, the selected profiles were used to evaluate changes in the volume of the layers of SASTMW. Within the surface layer data, we sought to identify profiles that had been recently affected by the local convection, which is the main mechanism for the formation of mode water, only between July to October. Thereby, we reduced the maximum PV value of the profiles to 1.2 × 10-11 m-1 s-1. From the application of this more restrictive criteria, we calculated the SASTMW monthly formation rate (&#916;f) between 2002 and 2009 to compare with the estimated formation rate (&#916;F) from the Walin (1982) theory, using the data from the project Objectively Analyzed air-sea Fluxes (OAFlux). The &#916; f showed a mean value lower than the &#916;F rate, indicating the need to evaluate a broader set of processes that affect the SASTMW formation, in addition to the heat balance through the surface.

The rate at which stars have formed throughout the history of theuniverse is not constant, it started out slow, increased until around redshift ∼ 2 when it reversed and became slower again. The reason for this behaviour is still being investigated with various models and simulations usually based upon dark matter halos. The aim of this study is to instead investigate whether there is a correlation between the cosmic star formation rate and the evolution of cosmic voids. This is achieved by comparing the total mass flow from voids with the amount of matter forming stars. A simple model of void mass flow is created and compared with observational data of star formation. The model is shown to exhibit the same behaviour as the star formation rate indicating that there is indeed a correlation between void evolution and star formation. This suggests it to be fruitful to create a more involved, alternative model of star formation based upon void evolution as opposed to the common halo evolution / Hur snabbt stjärnor bildas har genom universums historia förändrats över tid, det började långsamt och ökade sedan fram till rödförskutning ∼ 2 då trenden vände och saktade ner igen. Förklaringen till detta beteende utforskas fortfarande genom diverse modeller och simularingar som vanligtvis bygger på mörk materia halos. Syftet med detta arbete är att istället undersöka ifall det finns en korrelation mellan tomrumsutveckling och den kosmiska stjärnbildningen. Detta åstadkoms genom att jämföra det totala massflödet från tomrum med den massa som bildar stjärnorna. En simpel model för tomrumsutveckling skapas och jämförs med observationell data för stjärnbildningshastighet. Denna modell visar samma beteende som stjärnbildningen och tyder på att det finns en korrelation mellan denna och tommrumsutveckling. Som slutsats pekar denna studie på att det kan vara fruktbart att utveckla en mer anancerad modell för den kosmiska stjärnbildningen som bygger på tomrumsutveckling istället för mörk materia halos.