523 research outputs found
Laboratory Studies of Hypervelocity Impacts on Solar System Analogues
No full textImpact cratering and asteroid collisions are major processes throughout the Solar System. Although previous collision-related impact investigations exist (Flynn et al. 2015, Holsapple et al. 2002 and Burchell et al. 1998 are good examples), in the works covering this broad range of investigation, the targets are non-rotating (for the purposes of catastrophic disruption) and different temperature conditions are not considered (for impact cratering). Accordingly, I present experimental processes and data, regarding hypervelocity impact experiments into analogues of (1) rotating asteroids and (2) temperature dependant terrestrial planetary rock.
During the course of this work, it was necessary to develop new apparatus and new experimental techniques such as three separate target holders to aid in both catastrophic disruption and heated impact projects, a 3-dimensional model analysis of craters and a completely new, statistically robust, technique to determine a complete crater profile called the KDM method where KDM is Kinnear-Deller-Morris.
The main result from this work showed that during an asteroid impact collision where the asteroid is not rotating, the impact energy density for catastrophic disruption is Q*static = 1442 ± 90 J kg-1. However, when the target asteroid was rotating, the condition Q*rotation = 1097 ± 296 J kg-1. The mean value of Q* had thus reduced, but the spread in the data on individual experiments was larger. This leads to two conclusions. The mean value for Q*, based on measurements of many impacts, falls, due to the internal forces acting in the body which are associated with the rotation. This energy term reduction means that the amount of energy to instigate catastrophic disruption is lower and that a rotating asteroid is effectively weaker upon impact than a stationary asteroid. However, the spread in the results indicates that this is not a uniform process, and an individual result for Q* for a rotating or spinning target may be spread over a large range. For the temperature related impacts, as the targets were heated to approximately 1000 K, the target rocks showed an impact dependence more similar to a plastic phase-state than to solidus, due to being held close to temperatures associated with semi-plastic phases. Basalt impact craters displayed this relationship greatest with crater sizes becoming smaller at the higher temperature ranges but larger in the colder brittle solidus temperatures, partly explained in experiments by increased spallation
Mapping and promoting South Africa : Barrow and Burchell\u27s rivalry
No full textBarrow\u27s six years at the Cape, with four long journeys, and Burchell\u27s close on five years ox-wagon travel gave Barrow\u27s Account of Travels pre-eminent authority status, with jealous attacks on rival travellers\u27 books and their maps. This criticism included those of Burchell, as scientist and mapmaker largely his superior. Burchell hit back with equal vituperation. Despite their enmity they advanced knowledge of the interior "least known to Europeans" (Barrow) and came together in promoting the Zuurveld as place of settlement for the 5 000 emigrants dispatched in 1820 by a government aiming to export potential radicals among the unemployed. Burchell depicted the Zuurveld as a demi-paradise to the Poor Law Commission of parliament and Barrow did the same to ministers. The anti-Xhosa \u27buffer\u27 was never an issue and the 1834 Rharhabe invasion unforeseen. Barrow, public figure and prolific author, outshone Burchell, the retired botanist and benefactor of Kew Gardens: the latter\u27s fame has come late. The long-term consequence of their case for Zuurveld settlement is still undecided
Pixelated flesh
No full textThe pixel and the technique of pixelating faces belong to a politics of fear and a digital aesthetics of truth which shapes public perceptions of criminality and the threat of otherness. This article will draw on Paul Virilio's account of the pixel in Lost Dimension in order to analyze its specific role and operation in relation to contemporary representations of incarceration. In particular, the article will consider the figure of the incarcerated informant. The incarcerated criminal or informant plays a complex role as both subversive other and purveyor of truth and as such constitutes an important example of the ways in which pixelation functions as a visible signifier of a dangerous truth whilst blurring, erasing and, ultimately, dehumanizing those "speaking" this truth. Our discussion forms part of a larger analysis of the production, framing and circulation of images of otherness, identifying Virilio as key to debates around the violence of the screen
A metodologia Great Place to Work – GPTW
No full textResenha do Livro: A melhor empresa para trabalhar: como construí-la, como mantê-la e por que isso é importanteAutores: Michael Burchell e Jennifer RobinResenha do Livro: A melhor empresa para trabalhar: como construí-la, como mantê-la e por que isso é importanteAutores: Michael Burchell e Jennifer Robi
Contemporary Art and Transitional Justice in Northern Ireland: The Consolation of Form
No full textAbstract
Contemporary artworks in Northern Ireland are explored here as critical constellations, in Walter Benjamin’s sense, that engage the cultural processes of transition through their problematisation of it. It is argued that the artworks become sites in which the assumptions of transition are opened up for critical reflection, requesting attention to the foreclosing of the meanings of memory, of past-and-future, of community. A mode of critical questioning of the present renders the present problematic not in terms of exclusions nor with reference to a past that cannot or will not be erased, but in terms of the present’s inability to be conceived through a linear conception of time. That is, the past and its relation to both the present and to the future are set in oscillation as artworks explore the complex temporalities of a present self-consciously attempting to narrate itself away from the past. The artworks, ‘without the bigotry of conviction’ as Seamus Deane put it, suggest that the task of dealing with the past is flawed wherever the past is conceived as a history that can be rendered present to be judged by subjects who are thereby placed beyond it. That is the illusion of a present ‘no-time’ that dovetails with the desires of commercial enterprise and neo-liberal conceptions of freedom. If this suggests an unceasing restlessness, the consolation is that this questioning does take a form, not as judgement or political decision but as artworks which by definition, remain open to reinterpretation and new understandings. These issues are discussed with reference to the work of four artists in Northern Ireland: the paintings of Rita Duffy, the photography and installation work of Anthony Haughey, and the sculptural works of Philip Napier and Mike Hogg
Correction: Messer, T.L.; Burchell, M.R.; Birgand, F. Comparison of Four Nitrate Removal Kinetic Models in Two Distinct Wetland Restoration Mesocosm Systems. Water 2017, 9, 517
No full textThe authors wish to make the following corrections to this paper [1]:
(1): The author name “François Bírgand” should be François Birgand.
(2): Reference 38 should be the following:
Birgand, F.; Aveni-Deforge, K.; Smith, B.; Maxwell, B.M.; Horstman, M.; Gerling, A.B.; Carey, C.C. First report of a novel multiplexer pumping system coupled to a water quality probe to collect high temporal frequency in situ water chemistry measurements at multiple sites. Limnol. Oceanogr. Methods 2016, 14, 767–783, doi:10.1002/lom3.10122.
(3): Reference 49 should be the following:
Christensen, P.B.; Nielsen, L.P.; Sørensen, J.; Revsbech, N.P. Denitrification in Nitrate-Rich Streams: Diurnal and Seasonal Variation Related to Benthic Oxygen Metabolism. Limnol. Oceanogr. 1990, 35, 640–651
Philosophy of the imagination : time, immanence and the events that wound us in Wilson Harris’s Jonestown
No full textThis is a special issue of the Journal of Postcolonial Writing edited by Lorna Burns and Wendy KnepperIn his fictional recreation of the People’s Temple massacre, Jonestown, Harris presents us with a protagonist who counter-actualizes the trauma that wounds him, living creatively out of the event and constructing an alternative present-future. Drawing on Deleuzian philosophy, this essay argues for a re-conceptualization of Jonestown in terms that evoke not only Deleuze’s philosophy of time and immanence but also his distinction, via Nietzsche, between active and reactive forces. By means of a character (Francisco Bone) who embraces the power of transformation, creation and difference-in-itself, Harris demonstrates the value of active forces that do not depend on external recognition or dialectical negation in order to be for a postcolonial philosophy of the imagination.Peer reviewe
Hypervelocity impact in low earth orbit: finding subtle impactor signatures on the Hubble Space Telescope
No full textpublisher: Elsevier articletitle: Hypervelocity impact in low earth orbit: finding subtle impactor signatures on the Hubble Space Telescope journaltitle: Procedia Engineering articlelink: http://dx.doi.org/10.1016/j.proeng.2017.09.746 content_type: article copyright: © 2017 The Author(s). Published by Elsevier Ltd.© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 14th Hypervelocity Impact Symposium 2017. The file attached is the Published/publisher’s pdf version of the article.NHM Repositor
Measuring sprawl in the United States: a comparative analysis of procedures and results
No full textSprawl is significant, low-density development taking place at the periphery wherein there exists limited infrastructure and public services. It has been the subject of much research, due to its widespread occurrence. Previous empirical studies of sprawl measurement had three significant weaknesses: 1) incomplete coverage of the geography being measured; 2) an absence of regional differences in the density variable, and 3) a lack of exclusion of undevelopable lands when calculating the density of an area. In an effort to overcome these shortcomings, this study: 1) measures sprawl for all 3091 counties in the US using economic areas (EA) to group counties; 2) uses variable densities (locally-determined cultural densities) in the sprawl calculation; and 3) calculates “refined densities” for all states and counties in the US by excluding undevelopable lands from the density calculation. Further, the research results included here are compared with those of Rolf Pendall (1999), Robert W. Burchell (2002), and Reid Ewing (2003b), in order to ascertain the impact of their more comprehensive measurement methods on sprawl measurement results. Based upon accurate variable densities, one of six county land use types (urban center, urban, suburban, rural center, rural, undeveloped) is assigned to each US county; a sprawl/non-sprawl is then determined for each county. As a result, out of all 3091 US counties, 492 experience sprawl development during the 2000 to 2020 time period. Over 80 percent (or 396 counties) of these 492 sprawling counties are rural or undeveloped counties; the remaining one-fifth are developing suburban and rural center counties. With no exception, the “refined density” of an individual state is greater than its “gross density.” About 65 percent (or 32) of US states have “refined densities” that are at least 1.2 times their original gross densities. Several conclusions can be drawn using the comparative analyses included here. First, sprawl research must focus on the nation as a whole, or on select component regions. Second, variable density is crucial to the accurate calculation urban versus rural counties nationally. Third, developable land must be employed when calculating variable density (i.e. undevelopable lands must be excluded from the density calculation).Ph. D.Includes bibliographical referencesby Yue W
Constructed Wetlands as Remediation Tools for Shallow Groundwater Contaminated by Swine Lagoon Seepage
No full textSwine waste is typically flushed from beneath confinement houses into anaerobic lagoons for temporary storage and partial treatment. When improperly constructed, studies have shown that there is potential for the high strength wastewater to leak from the lagoon into the surrounding groundwater.
Constructed wetlands have been implemented as treatment systems for wastewater. Biogeochemical reactions in wetlands make them viable options for wastewater treatment. Wetlands may remove pollutants such as nutrients through adsorption, nitrification, denitrification, and plant uptake. Studies have shown that constructed wetlands are able to attenuate substantial amounts of nitrogen and phosphorous from wastewater. Denitrification is the primary mechanism by which nitrogen is removed from wastewater in constructed wetlands. Research has shown that nitrification of ammonium nitrogen to nitrate may indirectly limit denitrification.
One practice that may increase the nitrogen assimilation in a constructed wetland is the use of a nitrification pretreatment system such as a trickling filter. A trickling filter contains media on which nitrifying bacteria can attach, and provides an aerobic environment in which the nitrification process can take place.
This study evaluated a site where a swine lagoon had leaked into the surrounding groundwater. The swine lagoon was eventually closed-out and a plan to pump out the contaminated groundwater was initiated. The goal was to pump at a rate that would change the subsurface gradient causing the contaminated water to stop flowing towards a nearby stream. The water was pumped into a constructed wetland where nutrients could be removed. After three years of pumping the contaminated groundwater, a trickling filter was implemented to nitrify the wastewater before it was discharged into the wetland.
Over the course of the study, the average NH4-N concentration in wells located down gradient of the former lagoon decreased by more than 60%, and the hydraulic gradient between the former lagoon and the nearby stream was reduced by greater than 65%. The constructed wetland assimilated greater than 76% of the total nitrogen and more than 22% of the total phosphorous that it received, resulting in the assimilation greater than 915 kg of total nitrogen and more than 145 kg of total phosphorous.
The nitrification pretreatment system converted 20% of the NH4-N it received to NO3-N on a mass basis. In the samples taken from the trickling filter, the arithmetic average amount of NH4-N that was converted to NO3-N was 37%. Although the nitrification pretreatment system was functional, there was no identified increase in total nitrogen assimilation within the constructed wetland. This may have been due to influent ammonium nitrogen concentrations becoming too low for the trickling filter to function at maximum efficiency by the time it was incorporated into the system
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