Browsing by Subject "gas"

Now showing 1 - 4 of 4
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    Accurate Recovery of H i Velocity Dispersion from Radio Interferometers
    (2017) Ianjamasimanana, R; Blok, W J G de; Heald, George H
    Gas velocity dispersion measures the amount of disordered motion of a rotating disk. Accurate estimates of this parameter are of the utmost importance because the parameter is directly linked to disk stability and star formation. A global measure of the gas velocity dispersion can be inferred from the width of the atomic hydrogen (H I) 21 cm line. We explore how several systematic effects involved in the production of H I cubes affect the estimate of H I velocity dispersion. We do so by comparing the H I velocity dispersion derived from different types of data cubes provided by The H I Nearby Galaxy Survey. We find that residual-scaled cubes best recover the H I velocity dispersion, independent of the weighting scheme used and for a large range of signal-to-noise ratio. For H I observations, where the dirty beam is substantially different from a Gaussian, the velocity dispersion values are overestimated unless the cubes are cleaned close to (e.g., ˜1.5 times) the noise level.
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    H i kinematics, mass distribution and star formation threshold in NGC 6822, using the SKA pathfinder KAT-7
    (2017) Namumba, B; Carignan, C; Passmoor, S; de Blok, W J G
    We present high sensitivity H I observations of NGC 6822, obtained with the Karoo Array Telescope (KAT-7). We study the kinematics, the mass distribution and the star formation thresholds. The KAT-7 short baselines and low system temperature make it sensitive to large-scale, low surface brightness emission. The observations detected ∼ 23 per cent more flux than previous Australian Telescope Compact Array observations. We fit a tilted ring model to the H I velocity field to derive the rotation curve (RC). The KAT-7 observations allow the measurement of the rotation curve of NGC 6822 out to 5.8 kpc, ∼1 kpc further than existing measurements. NGC 6822 is seen to be dark matter dominated at all radii. The observationally motivated pseudo-isothermal dark matter (DM) halo model reproduces well the observed RC while the Navarro Frank-White DM model gives a poor fit to the data. We find the best-fitting mass-to-light ratio (M/L) of 0.12 ± 0.01 which is consistent with the literature. The modified Newtonian dynamics gives a poor fit to our data. We derive the star formation threshold in NGC 6822 using the H I and H α data. The critical gas densities were calculated for gravitational instabilities using the Toomre-Q criterion and the cloud-growth criterion. We found that in regions of star formation, the cloud-growth criterion explains star formation better than the Toomre-Q criterion. This shows that the local shear rate could be a key player in cloud formation for irregular galaxies such as NGC 6822.
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    Open Access
    The impact of offshore and gas exploitation on the marine environment and its regulations under selected national regimes
    (2013) Fombang, Humphrey; Hare, John
    Despite the numerous advantages accrued from the exploitation of oil and gas worldwide, the repercussion of its activities on the marine environment has put the entire world under panic about the future of our beloved planet. Political leaders from both developed and developing countries through Conventions, Conferences, national policies and legislation, have been seeking various ways to regulate the exploitation of oil and gas on the continental shelf and Exclusive Economic Zone in order to protect the marine environment that is at the brink of losing its socio-economic values. With the present trend of events threatening the planet such as climate change and the call for sustainable development, the regulation of oil and gas exploitation on the marine environment remains a dilemma. It is now crystal clear that the principle of 'Common but Differentiated Responsibilities' as advocated by both the Rio and Johannesburg world summits on sustainable development, with regard to the regulations of oil and gas exploitation, which have already been put in place, must be strengthened.
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    The role of law in promoting public participation, transparency and accountability, and access to justice in the oil and gas extractive sector of Tanzania mainland
    (2026) Karia, Pooja Mahendra; Paterson, Alexander
    This thesis examines the extent to which Tanzania's legislation governing the extractive oil and gas sector adequately incorporates the procedural components of good governance; namely, public participation, transparency and accountability, and access to justice within permitting stage of the process. The study adopts a two-tiered methodological approach. Firstly, it explores procedural components of good governance and constructs a theoretical framework on the role of law in promoting each of them. This theoretical framework is founded upon an analysis of academic literature. Secondly, it uses this theoretical framework to critically review the relevant components of Tanzania's legislation governing the extractive oil and gas sector. This second component begins by explaining Tanzania's relevant legislation that spans the constitutional dispensation, relevant framework legislation, and sector-specific laws. It then critically assesses this domestic legislation against the theoretical framework developed in the first part of the thesis to determine the extent to which it adequately promotes these procedural components of good governance. Through this analysis, it identifies strengths and weaknesses of the existing legislation and proposes opportunities for legal reform to enhance the procedural aspects of good governance in the extractive oil and gas permitting stage of the process. In relation to public participation, it highlights how Tanzania's relevant legislation lacks clarity on who may participate, at which stages, and in what manner, particularly in project approvals and contract negotiations. Mechanisms for early, continuous participation and institutional representation remain weak. In relation to access to information, the analysis highlights relative strength of the overarching constitutional dispensation, but illustrates how framework environmental and sectoral petroleum legislation lack clear definitions of accessible information and procedural safeguards for disclosure. Finally, concerning, access to justice, the analysis identifies the prevalence of judicial remedies, but identifies several anomalies in the ability of these to realise administrative justice in the absence of dedicated legislation to facilitate administrative redress. These findings highlight the need for legal reforms that have been recommended to clarify procedural participatory rights, access to information, and establish a framework for administrative justice to promote the procedural governance in the oil and gas extractive sector of Tanzania.