<p>The astrophysical ³⁰P(<em>p</em>,<em>γ</em>)³¹S reaction rate is a key quantity used in both classical nova and type I X-ray burst models that predict isotopic abundances produced during nucleosynthesis in the outburst. Currently, uncertainties in ³¹S structure parameters lead to a variation in the reaction rate by a factor of 20 at nova temperatures causing predicted isotopic abundance ratios in the Si-Ar mass region to vary by factors of up to 4. The ³⁰P(<em>p</em>,<em>γ</em>)³¹S reaction rate can be determined indirectly by measuring transfer reactions populating excited states in ³¹S. Nuclear structure information for ³¹S resonant states above the proton threshold of 6131 keV and within the Gamow window that contribute most significantly to the reaction rate can be used to re-evaluate the rate for nova and type I X-ray burst temperatures and reduce current uncertainties. We have performed an experiment in order to study the level structure of ³¹S via the ³²S(<em>d</em>,<em>t</em>)³¹S single-nucleon transfer reaction using the MP tandem accelerator and Q3D magnetic spectrograph at MLL in Munich, Germany. Excited states of ³¹S in the 6-7 MeV region were observed and spin-parity constraints have been suggested. In this work we describe the experimental setup, data analysis and results for both experiments and provide recommendations for further investigation of the ³⁰P(<em>p</em>,<em>γ</em>)³¹S astrophysical reaction rate.</p> / Master of Science (MSc)

<p>Protostellar discs are generally thought to drive molecular outflows and jets observed in star forming regions, but there has been some debate as to how they form. The details of the driving and collimation of outflows help determine how much mass is cleared out and how much energy is fed back into the surroundings. Recently it has been argued that the magnetic brake is so strong that early protostellar disks cannot form.</p> <p>We have performed 3D ideal magnetohydrodynamic (MHD) simulations of collapsing Bonnor–Ebert spheres, employing sink particles within an AMR grid and using a cooling function to model radiative cooling of the gas. This allows us to follow the formation and early evolution of the accretion disc (2−8)×10⁴ years further into the Class 0 phase of its evolution. We form a rotationally dominated disc with a radius of 100 AU embedded inside a transient, unstable, flattened, rotating structure extending out to 2000 AU. The inner disc becomes unstable to a warping instability due to the magnetic structure of the outflow, warping 30 deg with respect to the rotation–axis by the end of the simulation. The disc is unstable to a Parker instability and sheds magnetic loops, degrading the orientation of the mean threading field. This reduces and locally reverses the magnetic braking torque of the large scale field back upon the disc. The reduction of magnetic braking allows a nearly Keplerian disc to form and may be the key way in which low mass stellar systems produce rotationally dominated discs. We discuss the relevance of our disc misalignment concerning the formation of mis–aligned hot Jupiters.</p> <p>Protostellar outflows are implicated in clearing mass from collapsing cores, and limiting the final mass of newly formed stars. The details of the driving and collimation of outflows help determine how much mass is cleared out and how much energy is fed back into the surroundings. The simulations generate outflows which are precessing, kinked, contain internal shocks and extend to a scale of 0.1 pc end–to–end. Our disc–wind theory describes magneto–centrifugal driving throughout the outflow bubble. The bulk properties of the outflow agree well with observations. The outflow has two components, a larger low speed wind (v_r < 1.5 km/s) dominated by a toroidal magnetic field Bφ, and an inner centrifugally driven jet dominated by Bp with speeds up to 20 km/s. The ratio of mass flux from the disk surface com- pared to accretion in the disk is measured to be M_out/M_in ∼ 0.1 from the inner component, whereas in the outer component M_out/M_in ∼ 1.0. The jet is misaligned and precesses as the disc warps by 30 deg with respect to the z–axis. We measure star formation efficiencies of ε_core = 0.63 (and growing), higher than theoretical predictions of ε_core = 0.29−0.39 and observations ε_core = 0.33.</p> <p>These new results reported in this thesis, show that disks can form in strongly magnetized media, in agreement with the observations - and that outflows are not as efficient in clearing away collapsing gas as has been assumed in various theoretical models. Both of these results have important implications for disk formation, and the origin of the IMF, as described in this work.</p> / Doctor of Philosophy (PhD)

Polycyclic aromatic hydrocarbons (PAHs) are the most abundant large organic molecules in space. They are thought to be the main contributor to the unidentified infrared (UIR) emission bands from the interstellar medium (ISM) for several reasons: UIR intensities correspond to carbon abundance, indicating the presence of a carbon-based molecule; UIRs are found in extremely harsh environments which means the source must be a stable molecule. The most important evidence is if the bands in mid-infrared (MIR) or 'fingerprint' region match those of PAHs. Through the infrared spectroscopy of matrix-isolated polycyclic aromatic hydrocarbons a compound's unique neutral and ionized vibrational modes can be identified. In this work, the PAH anthracoronene (AntCor, C36H18) is suspended in a matrix of water-ice, irradiated with ultraviolet (UV) light, and then analyzed using Fourier Transform Infrared (FTIR) spectroscopy. AntCor has not been studied in water ice before, and therefore the vibrational transition data collected (i.e. band positions and intensities) has been compared to coronene and anthracene, the parent molecules, and with theoretical predictions made using density functional theory. The data from this work will be incorporated into the NASA Ames PAH IR Database, where it will be applied to astronomical observations of the unidentified infrared emissions of the ISM, as well as observations of infrared absorption features in dense molecular clouds.

The focus of this dissertation is to study the star-forming regions of the interstellar medium (ISM), using two very diverse environments: the Polaris Flare, high-galactic latitude, cirrus cloud complex consisting of several starless molecular cores with no nearby hot stars; and the Orion Nebula, which is the closest massive star forming region. The two environments provide a wide range of physical conditions. It is commonly assumed that the Herschel far-infrared (FIR) fluxes are a good measure of column density, hence, mass of interstellar clouds. We find that the FIR fluxes are insensitive to the column density if AV ≳ 2. The Polaris Flare has been previously observed with the Herschel Space Telescope. We use Cloudy to model the molecular cores in MCLD 123.5+24.9 of the Polaris Flare. The Polaris Flare, 150 pc distant, is well within the Galactic disc. There are no nearby hot stars. Therefore, the cloud is illuminated by an external far-ultraviolet (FUV) flux (6-13 eV) due to the galactic background interstellar radiation field (ISRF). The dust grains absorb the incident FUV flux and re-emit in the FIR continuum emission. We use detailed grain models that suggest that the grains in dense regions are coated with water and ammonia ices, increasing their sizes and opacities. In our models, dust temperatures decline rapidly into the cloud. Therefore, the cloud interiors contribute very little additional FIR flux, leading to an underestimate of inferred column density. Cloudy also predicts mm-wavelength molecular lines for comparison with published observations. Our models suggest that at low temperatures (≲ 20K), molecules freeze-out on grain surfaces, and desorption by cosmic rays becomes important. Our models of inter-core regions in MCLD 123.5+24.9 significantly under predict molecular line strengths unless the gas is clumped into high-density regions. We use Cloudy to construct a detailed model of the Orion H ii region. This study is an improvement over the work of Baldwin et al. 1991 with the new atomic data and stellar atmosphere models, and a wealth of archival observational data obtained over last two decades. We use collisionally excited lines to determine the elemental abundance of the region.

Nos estudos de populações pesqueiras é comum o uso de modelos hidrodinâmicos acoplados a modelos biológicos e, um tipo de modelo merece destaque: o baseado no indivíduo (IBM). A Plataforma Continental do Atlântico Sudoeste comporta uma importante atividade pesqueira e, a influência da circulação na distribuição de ovos/larvas nessa região é pouco entendida. Estudos anteriores sugerem que o transporte de Ekman em direção à costa e o deságue de água fluvial impedem a perda de ovos e larvas da área costeira. Este trabalho apresenta resultados de um estudo englobando os padrões de circulação e de transporte de larvas nessa área, realizado através do desenvolvimento de um IBM para os estágios iniciais da Engraulis anchoita e o acoplamento deste a dois campos de velocidade superficial: a de Ekman, e a saída de um modelo hidrodinâmico 3D. Os resultados mostram que somente a deriva de Ekman não é suficiente para explicar o padrão de retenção larval observado na região. Os valores de retenção encontrados com a utilização da saída do modelo estão próximos aos observados. Maiores concentrações larvais foram obtidas no outono/inverno e menores na primavera/verão. Estes resultados estão diretamente relacionados à combinação dos efeitos dos padrões de vento da área com a influência das Correntes do Brasil e das Malvinas e do deságue continental na circulação sobre a plataforma. / Recruitment of pelagic fishes is the net result a series of continuous events in their life cycle. Most of the variability in natural mortality is thought to occur during the early stages of development and is related to environmental factors. The use of coupled physical-biological modeling in the study of fisheries populations is very common and a particular type of model deserves special mention: the Individual Based Model (IBM). The Atlantic Southwestern Continental Shelf is one of the most productive fishing sites in the Western South Atlantic, but the processes involving the circulation in this area and its influence on eggs/larvae transport and retention are still poorly understood. Recent studies describe the spawning activity of anchovy and its relationship to oceanographic processes and suggest that predominant onshore Ekman transport, during the austral winter/spring, keeps the eggs and larvae in coastal areas. According to these studies, the river runoff contributes to the formation of a retention zone for planktonic organisms over the area. This work presents results of a study that considers both the circulation pattern and larval transport, throught the development of an IBM for the early stages of anchovy Engraulis anchoita. The model is coupled to two surface velocity fields: the Ekman drift, and the output of a 3D hydrographic model. The results show that just Ekman surface velocities are not able to explain the larval dispersion observed in this region. Retention values obtained with the model output are much closer to observed values. Autumn and winter seasons present the highest values of retention. These results are due to the combined effect of the wind patterns registered in the area with the influence of the river runoff and the Brazil-Malvinas shelf circulation.

Nos estudos de populações pesqueiras é comum o uso de modelos hidrodinâmicos acoplados a modelos biológicos e, um tipo de modelo merece destaque: o baseado no indivíduo (IBM). A Plataforma Continental do Atlântico Sudoeste comporta uma importante atividade pesqueira e, a influência da circulação na distribuição de ovos/larvas nessa região é pouco entendida. Estudos anteriores sugerem que o transporte de Ekman em direção à costa e o deságue de água fluvial impedem a perda de ovos e larvas da área costeira. Este trabalho apresenta resultados de um estudo englobando os padrões de circulação e de transporte de larvas nessa área, realizado através do desenvolvimento de um IBM para os estágios iniciais da Engraulis anchoita e o acoplamento deste a dois campos de velocidade superficial: a de Ekman, e a saída de um modelo hidrodinâmico 3D. Os resultados mostram que somente a deriva de Ekman não é suficiente para explicar o padrão de retenção larval observado na região. Os valores de retenção encontrados com a utilização da saída do modelo estão próximos aos observados. Maiores concentrações larvais foram obtidas no outono/inverno e menores na primavera/verão. Estes resultados estão diretamente relacionados à combinação dos efeitos dos padrões de vento da área com a influência das Correntes do Brasil e das Malvinas e do deságue continental na circulação sobre a plataforma. / Recruitment of pelagic fishes is the net result a series of continuous events in their life cycle. Most of the variability in natural mortality is thought to occur during the early stages of development and is related to environmental factors. The use of coupled physical-biological modeling in the study of fisheries populations is very common and a particular type of model deserves special mention: the Individual Based Model (IBM). The Atlantic Southwestern Continental Shelf is one of the most productive fishing sites in the Western South Atlantic, but the processes involving the circulation in this area and its influence on eggs/larvae transport and retention are still poorly understood. Recent studies describe the spawning activity of anchovy and its relationship to oceanographic processes and suggest that predominant onshore Ekman transport, during the austral winter/spring, keeps the eggs and larvae in coastal areas. According to these studies, the river runoff contributes to the formation of a retention zone for planktonic organisms over the area. This work presents results of a study that considers both the circulation pattern and larval transport, throught the development of an IBM for the early stages of anchovy Engraulis anchoita. The model is coupled to two surface velocity fields: the Ekman drift, and the output of a 3D hydrographic model. The results show that just Ekman surface velocities are not able to explain the larval dispersion observed in this region. Retention values obtained with the model output are much closer to observed values. Autumn and winter seasons present the highest values of retention. These results are due to the combined effect of the wind patterns registered in the area with the influence of the river runoff and the Brazil-Malvinas shelf circulation.

Made available in DSpace on 2014-07-29T15:18:22Z (GMT). No. of bitstreams: 1 Dissertacao do Victor Emmanuel dos Reis -Volume01.pdf: 1187197 bytes, checksum: fe5b338cbf9dc68edcca13a88944ea39 (MD5) Previous issue date: 2010-10-18 / This work presents an evaluation of the processes of the physical environment in road construction, materialized in two case studies and thereby aims to contribute to a proposal for monitoring of these processes trigged or intensified by road constructions. In the first case study addressed the highway GO-309 located near the capital of Goiás. The applied methodology includes monitoring the construction phases of the highway, from the completion of field survey form to record information gathered over the years 2005, 2007, 2009 and 2010. We observed the processes of the physical environment and impacts and made relevant correlations and analysis. Were highlighted the erosion and landslides induced by construction of road works, causing degradation of the most diverse, compromising the body road practicability and safety of the user traffic. The survey also allowed, besides the qualification, the quantification of the recovery costs of degradation processes, observed compared to the physical environment that needed reconstruction and recovery of a great part of the road segment. The second case study is a stretch of the highway GO- 236 located in the northwestern state. The methodology used two geophysical researches: Non-invasive and non-destructive; The method of resistivity or electrical profiling, which allowed the analysis of the susceptibility to mass movements related to the location of karst cavities and structures of depth, and the method of Ground Penetrating Radar or Ground Penetrating Soil- GPR in locating natural or artificial structures and the assessment of stratigraphy, thickness and condition of the pavement layers. It has been shown in addition, the importance and relevance, the use of geophysical prospecting methods of investigation, with the use of the GPR and resistivity in road works. Mainly in the recognition of the area of interest, allowing a better foundation in decision making, mitigating potential future risks. The aim is to it, provide subsidies to road agencies in the preparation of technical specifications and terms of reference for controlling and monitoring the dynamics of the processes of the physical environment. / O presente trabalho apresenta uma avaliação dos processos do meio físico em construções rodoviárias, materializada em dois estudos de caso e com isso visa contribuir com uma proposta de monitoramento desses processos, intensificados ou deflagrados pelas construções viárias. No primeiro estudo de caso abordou-se a rodovia GO-309, localizada próximo à capital de Goiás. A metodologia empregada compreende o monitoramento das fases construtivas da rodovia, a partir do preenchimento de uma ficha de levantamento de campo para registro das informações coletadas durante os anos de 2005, 2007, 2009 e 2010. Foram observados os processos do meio físico e os impactos decorrentes e feitas correlações e análises pertinentes. Destacaram-se os processos erosivos e os escorregamentos induzidos pela construção das obras viárias, causando degradações as mais diversas, comprometendo o corpo estradal e a segurança do tráfego usuário. A pesquisa também permitiu, além da qualificação, a quantificação dos custos de recuperação das degradações observadas frente aos processos do meio físico, que ensejaram reconstruções e recuperação de grande parte do segmento rodoviário. O segundo estudo de caso tratou-se de um trecho da rodovia GO-236, localizada no noroeste do estado. A metodologia empregada neste segundo caso utilizou dois ensaios geofísicos, não-invasivos e não-destrutivos: o método da eletrorresistividade ou caminhamento elétrico, o que possibilitou a analise da suscetibilidade a movimentos de massa relacionados à localização de cavidades e estruturas cársticas em profundidade; e o método do Ground Penetrating Radar ou Radar de Penetração de Solo GPR na localização de estruturas naturais ou artificiais e para a avaliação da estratigrafia, espessura e condições das camadas do pavimento. Mostrou-se por acréscimo, a importância e pertinência ao emprego de métodos de prospecção geofísicos de investigação, com a utilização do GPR e da Eletrorresistividade, em obras viárias, principalmente na fase de reconhecimento da área de interesse, permitindo melhor embasamento na tomada de decisões, mitigando possíveis riscos futuros. Pretende-se com isso gerar subsídios a órgãos rodoviários, na elaboração de especificações técnicas e termos de referência para controle e monitoramento da dinâmica dos processos do meio físico.

Screen level temperature is measured at 2 meters above the ground. It is one of the most used atmospheric characteristics in various applications in meteorology and other fields related to weather prediction. Essential is not only the knowledge of its current state, but also its prediction. It is forecasted by numerical weather prediction (NWP) models from the atmospheric current state. Its long-term characteristics can be obtained from the integration of climate models. This text discusses fundamental parametriza- tions, mostly related to temperature forecast, used in the NWP model ALADIN and the regional climate model RegCM. Physical processes which influence temperature are studied using ALADIN in several cases which include the presence of low cloudiness, gravity waves and inappropriate thermic coefficient. A detailed description of the most relevant parametrization schemes is given and the results are studied in a form of indi- vidual feedback loops. Most dominant processes are also found. However, the level of 2 meters above the ground is not the model level, so temperature at 2 meters is obtained by interpolation from the surface temperature and the lowest model level temperature. Using RegCM, two differently complex interpolation schemes are compared to each other. 1