Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing, and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared local thermodynamic equilibrium line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find that the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line emission from the disk and subsequently improving agreement with observations. We find that NH3, CH3OH, C2H2, and sulfur-containing species are greatly enhanced by the inclusion of turbulent mixing. We demonstrate that disk winds potentially affect the disk chemistry and the resulting molecular line emission in a manner similar to that found when mixing is included.

Combination of CFD and DOE to analyse solid particle erosion in elbows

Solid particle erosion is a major concern in the engineering industry, particularly where transport of slurry flow is involved. Such flow regimes are characteristic of those in alumina refinement plants. The entrainment of particulate matter, for example sand, in the Bayer liquor can cause severe erosion in pipe fittings, especially in those which redirect the flow. The considerable costs involved in the maintenance and replacement of these eroded components led to an interest in research into erosion prediction by numerical methods at Rusal Aughinish alumina refinery, Limerick, Ireland, and the University of Limerick. The first stage of this study focused on the use of computational fluid dynamics (CFD) to simulate solid particle erosion in elbows. Subsequently an analysis of the factors that affect erosion of elbows was performed using design of experiments (DOE) techniques. Combining CFD with DOE harnesses the computational power of CFD in the most efficient manner for prediction of elbow erosion. An analysis of the factors that affect the erosion of elbows was undertaken with the intention of producing an erosion prediction model. © 2009 Taylor & Francis.

Complex organic molecules along the accretion flow in isolated and externally irradiated protoplanetary disks

(Abridged) The birth environment of the Sun will have influenced the conditions in the pre-solar nebula, including the attainable chemical complexity, important for prebiotic chemistry. The formation and distribution of complex organic molecules (COMs) in a disk around a T Tauri star is investigated for two scenarios: (i) an isolated disk, and (ii) a disk irradiated externally by a nearby massive star. The chemistry is calculated along the accretion flow from the outer disk inwards using a comprehensive network. Two simulations are performed, one beginning with complex ices and one with simple ices only. For the isolated disk, COMs are transported without major alteration into the inner disk where they thermally desorb into the gas reaching an abundance representative of the initial assumed ice abundance. For simple ices, COMs efficiently form on grain surfaces under the conditions in the outer disk. Gas-phase COMs are released into the molecular layer via photodesorption. For the irradiated disk, complex ices are also transported inwards; however, they undergo thermal processing caused by the warmer conditions in the irradiated disk which tends to reduce their abundance along the accretion flow. For simple ices, grain-surface chemistry cannot synthesise COMs in the outer disk because the necessary grain-surface radicals, which tend to be particularly volatile, are not sufficiently abundant on the grain surfaces. Gas-phase COMs are formed in the inner region of the irradiated disk via gas-phase chemistry induced by the desorption of strongly bound molecules such as methanol; hence, the abundances are not representative of the initial molecular abundances injected into the outer disk. These results suggest that the composition of comets formed in isolated disks may differ from those formed in externally irradiated disks with the latter composed of more simple ices.

Beach quality assessment and management in the Sotavento (Eastern) Algarve, Portugal

The purpose of this study on beach quality assessment and management was to evaluate the quality of five beaches in the Algarve Sotavento region of Portugal and to identify beach users’ preferences and priorities regarding their visit to a beach. The Algarve is one of the country’s most internationally known regions and it is generally perceived as a major tourist destination. Because of the increasing level of tourists, there is a specific need to address beach quality, as overcrowding can result in excessive litter, reduce water quality and consequently reduce the socio-economic value of the area. The main methodology for the evaluation of the beach quality in this pilot project was the Bathing Area Registration and Evaluation framework (BARE), which recognizes five beach types (rural, remote, resort, urban and village) through five main priority issues of concern to beach users (water quality, scenery, litter, safety, facilities) and evaluates the beach quality, ranging from one (low) to five (high) stars. After overall bathing area classification, Quarteira-Vilamoura, Ilha do Farol, Ilha Deserta and Ilha da Armona received three-star rating and Quinta do Lago site obtained a one-star rating. The quantitative research data on beach users’ preferences and priorities was obtained through administration of 50 questionnaires per beach and showed that beach users at all sites expressed the need for improved cleanliness, safety and facilities on the beach. The BARE framework, together with the questionnaire surveys, allowed the identification of management priorities required to improve the quality of individual beaches and therefore increase income from tourism.

The effect of shore armoring on beach slope in mixed sand-and-gravel beaches

Senior thesis written for Oceanography 445

Rethinking crises and the accretion of executive power: the “War on Terror” and conditionality evidence from seven political systems

External shocks to democratic systems are likely to threaten the stability of relations between the executive and the representative assembly. This article investigates the impact of the so-called “war on terror” on executive-assembly relations in comparative perspective. We analyze data from seven countries, which varied in terms of form of government, level of democracy, culture, social structure, and geographic location, to evaluate its effects. We find that whereas in some systems the “war on terror” altered the balance of power between the executive and the assembly, in other cases the extant balance of power was preserved. We postulate various conditions under which the constitutionally sanctioned balance of power is most likely to be preserved in times of crisis.

Quantification of the relation between surface morphodynamics and subsurface sedimentological product in sandy braided rivers

This study uses digital elevation models and ground-penetrating radar to quantify the relation between the surface morphodynamics and subsurface sedimentology in the sandy braided South Saskatchewan River, Canada. A unique aspect of the methodology is that both digital elevation model and ground-penetrating radar data were collected from the same locations in 2004, 2005, 2006 and 2007, thus enabling the surface morphodynamics to be tied explicitly to the associated evolving depositional product. The occurrence of a large flood in 2005 also allowed the influence of discharge to be assessed with respect to the processproduct relationship. The data demonstrate that the morphology of the study reach evolved even during modest discharges, but more extensive erosion was caused by the large flood. In addition, the study reach was dominated by compound bars before the flood, but switched to being dominated by unit bars during and after the flood. The extent to which the subsurface deposits (the product') were modified by the surface morphodynamics (the process') was quantified using the changes in radar-facies recorded in sequential ground-penetrating radar surveys. These surveys reveal that during the large flood there was an increase in the proportion of facies associated with bar margin accretion and larger dunes. In subsequent years, these facies became truncated and replaced with facies associated with smaller dune sets. This analysis shows that unit bars generally become truncated more laterally than vertically and, thus, they lose the high-angle bar margin deposits and smaller scale bar-top deposits. In general, the only fragments that remain of the unit bars are dune sets, thus making identification of the original unit barform problematic. This novel data set has implications for what may ultimately become preserved in the rock record.

A New guide to Niagara Falls and vicinity : giving a full and complete description of Niagara Falls, suspension bridge, Buffalo, Rochester, Ontario beach, Toronto, Lockport, Tonawanda, Lewiston, Niagara-on-the-Lake, Chautauqua, and other places of interest. --

Cover title: Illustrated guide to Niagara Falls and vicinity.