• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 280
  • 109
  • 32
  • 27
  • 13
  • 10
  • 8
  • 7
  • 4
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • Tagged with
  • 633
  • 115
  • 90
  • 52
  • 50
  • 48
  • 47
  • 46
  • 46
  • 45
  • 44
  • 44
  • 44
  • 44
  • 42
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Nature and dynamics of ice-stream beds : assessing their role in ice-sheet stability

Davies, Damon January 2018 (has links)
Ice streams are fast flowing outlet glaciers through which over 90% of the ice stored within the Antarctic Ice Sheet drains. The dynamic behaviour of ice streams is therefore crucial in controlling the mass balance of the ice sheet. Over the past few decades, Antarctica has been losing mass. Much of this mass loss has been focussed around coastal regions of the Antarctic Ice Sheet. Some of the most dramatic changes such as grounding-line retreat, acceleration and surface elevation change have been observed in Pine Island Glacier (PIG) and its neighbouring ice streams. This is of particular concern because these ice streams account for 10% of the discharge from the west Antarctic Ice Sheet and therefore have the potential to contribute significantly to global sea-level rise. One of the key challenges in accurately forecasting this future sea-level rise is improving understanding of processes occurring at the beds of ice streams. This requires detailed knowledge of the properties and dynamics of the bed. This thesis aims to address this knowledge gap by investigating the spatial and temporal characteristics of the bed of PIG using high-resolution geophysical data acquired in its trunk and tributaries and beneath the ice shelf. The thesis begins by analysing radar-derived high-resolution maps of subglacial topography. These data show a contrasting topography across the ice-bed interface. These diverse subglacial landscapes have an impact on ice flow through form drag, controlled by the size and orientation of bedrock undulations and protuberances. The next chapter provides a quantitative analysis of these landscapes using Fast Fourier analysis of subglacial roughness. This analysis investigates the roughness signature of subglacial bedforms and the how the orientation and wavelength of roughness elements determine their correlation with ice dynamic parameters. The slow-flowing inter-tributary site is found to have a distinct signature comparable to 'ribbed' patterns of modelled basal shear stress and transverse 'mega rib' bedforms. Roughness oriented parallel to ice flow with wavelengths approaching mean ice thickness are found to have the highest correlation with ice dynamic parameters. The temporal stability of PIG is analysed using repeat radar measurements. No significant change is observed over a period of 3-6 years with no evidence of rapid erosion or the evolution of subglacial bedforms as observed in previous repeat measurements of ice-stream beds elsewhere in Antarctica. This suggests that the widespread deforming till layer detected in extensive seismic reflection surveys is in steady state. Lastly, the thesis explores geomorphological evidence of twentieth-century grounding-line retreat beneath PIG Ice Shelf using high-resolution geophysical data acquired from autonomous underwater vehicle surveys. Evidence of erosion, deposition, meltwater flow and post-glacial modification is observed in fine detail. The observed distribution of sediment supported previous surveys indicating a geological transition coinciding with the ridge that acted as a former stable grounding-line location. Metre-scale resolution images of recently deglaciated ice stream beds were found to reveal bedforms that are not detectable with traditional offshore bathymetric surveys. Together these findings reveal the role of short wavelength topography as both an influence on, and product of fast ice stream flow. It also highlights the spatial diversity of subglacial environments and the need to focus future research on tying detailed observations of ice-stream beds with knowledge of basal properties over time.
192

Arbitration in international administrative contracts and administrative contracts with international dimensions in the UAE

Al Shamsi, Abdulla Rashid Obaid January 2017 (has links)
This is a study on some controversial legal aspects of resorting to arbitration in disputes concerning administrative contracts with an international dimension – i.e. contracts between public authorities in the United Arab State (UAE) and foreign companies, as well as contracts concluded between local parties but indirectly generate results of international dimensions. In this study, I have adopted a descriptive methodology, meticulously describing the legislative and judicial status in the UAE compared to those of both Egypt and France. In addition, I have also resorted to an analytical approach to provide a concise analysis of the essence of legal provisions guided by the established jurisprudence and judicial opinions. Finally, I used the comparative approach to draw parallels and difference within the legislature and the judiciary between three legal systems, with an eye at making use of relatively advanced legal systems. According to the above, and through utilizing the three research methods mentioned, (the descriptive, analytical and comparative), we attempted to analyze the various relevant jurisprudence and judicial opinions, together with court rulings and legislative provisions. The ultimate objective is to draw scientific results from the detailed evidences drawn from the selected rulings, as well as deciding on the position of both local and international jurisprudence and judiciary on this regard. This is to consolidate the theoretical positions with existing practice. At the outset of the thesis (chapter one) this study begins with a discussion of the main concepts of the constitutional system of the United Arab Emirates (UAE), with an explanation of the federal structure of the state and the nature of the UAE system of government. This is important because this study is mainly concerned with the UAE. This is followed by an illustration of the principles of administrative law within the UAE state. The study shows that the judicial system of the UAE state adopts a unitary judicial system whereby the same courts have jurisdiction on all sorts of disputes, both on disputes arising from administrative law and administrative contracts, as well as on disputes arising between private persons. This would unify the rules that apply to all disputes relating to the administration including administrative contracts with international dimensions. (Chapter two) attempts to define the concept of the administrative contract; the main focus of this study, and the criteria for distinguishing it from other types of contracts. It is concluded that the distinctive criteria for administrative contracts in the UAE are that: (i) one party to a contract shall be a public persona (such as the state, city authorities or municipalities); (ii) the contract shall be connected to the running or organization of a public facility (such as public institutions and authorities, security organizations and educational institutions) and (iii) it shall include exorbitant conditions which are unfamiliar in private law contracts. This distinction would help determining the nature of the legal rules to be applied on settlement of disputes, whether pertaining to the rules of administrative law or those of private law. (Chapter three) displays and critically reviews the main ideas related to arbitration in administrative contracts and shows the reservations and disadvantages that might arise from resorting to arbitration in this field. (Chapter four) This study comes to a number of conclusions in relation to these reservations and disadvantages. Despite the great importance of resorting to arbitration in administrative contracts as a speedy and distinctively confidential instrument for protecting the interests of the contractual parties, my opinion resorting to arbitration for settlement of disputes should be followed only if and to the extent it encourages investment in the UAE and it is respectful of higher administrative interests of the UAE state. The same limitation should apply to international administrative contracts and administrative contracts with international dimensions. Arbitration should be carried out without prejudice to the principle that a public authority in the UAE shall pursue a public interest without prejudice to private interests. This study argues that the legislator should intervene in an unambiguous manner to achieve the following results in relation to arbitration in administrative contracts with an international dimension and formulate proposals on how best to address these issues: 1. Determine the fields in which resorting to arbitration in administrative disputes should be admitted. 2. Specify the competent authority for approval of resorting to arbitration in this field (preferably the higher administrative authority within the state, such as the cabinet of ministers, the competent minister or authorized representative among public persona. No delegation is permissible, in this regard, for public persona assuming positions inferior to the above-mentioned ones because of their distinguished expertise which brought them to shoulder highly sensitive positions. Delegation in arbitration should be restricted to a very limited domain and only endowed upon those who assume the highest executive positions and qualified to shoulder high ranking positions and responsibilities. 3. The arbitration panel shall refrain from prejudicing the nature of the administrative contract, that is to refrain from prejudicing public interests, in order not to use resorting to arbitration as a means of evading application of the rules and regulations pertaining to the established administrative contract, which are stipulated to maintain public interest and public funds without prejudice to the rights and freedoms of private persons. Hence, it is pertinent to preserve the administrative nature and enforce the substantive regulations of the administrative contract. The contract should involve provisions for including arbitration, in addition to explicitly specify that the applicable law governing the contract should be the administrative law and the theory of administrative contract, which shall be applied in case of dispute. Arbitration should be restricted to administrative contracts with international dimensions, connected with public interest projects and leading to the encouragement of foreign investment and applying the principles of arbitration for conciliation in internal administrative contracts disputes only. The study concludes by arguing that legislative reform should be carried out to introduce legislative amendments, incorporating the above-mentioned arrangements, which are crucial to the settlement of administrative contracts disputes through arbitration. Resorting to arbitration should be restricted to certain types of contracts concluded by public authorities as an exception to the general principle of resorting to a judicial authority for looking into a legal disputes. These were put in place only to strike a balance between achieving public interests of the state and protecting the rights and freedoms of individuals.
193

The effect of enhanced ultraviolet-B radiation on the photosynthetic metabolism of terrestrial Antarctic plants

Smith, Andrew E. January 2009 (has links)
The potential effect of increased UV-B radiation on photosynthetic activity and related processes in a range of terrestrial Antarctic plant species was investigated; from a chlorophyte alga to a vascular plant (Deschampsia antartica). The relative contribution of the UV-B waveband to photosystem II (PSII) damage was used to construct an action spectrum for those species found to be sensitive to UV-B exposure. Investigation involved non-invasive measurements of photosynthesis using chlorophyll-a fluorescence emission coupled with polarographic measurement of oxygen and infra-red gas analysis of carbon dioxide. Compounds associated with UV-B protection were extracted, and analysed using high performance liquid chromatography. Different species exhibited differing sensitivity to UV-B exposure. Reduction in the efficiency of the light independent stage of photosynthesis and decrease in leaf length were found in D. antarctica. A decline in the potential activity of PSII (dark-adapted chlorophyll-a fluorescence) was found in some cryptogams, but no concurrent decrease in gas exchange parameters. Shorter wavelengths of UV-B were shown to be more effective in depression of PSII efficiency. The first action spectrum for terrestrial Antarctic plants would predict a higher weighted UV-B exposure under ambient ozone, but would expect less damage under stratospheric ozone depletion than the commonly used plant action spectrum. Some of the plants investigated contained increased amounts of UV absorbing flavonoids following UV-B exposure. The morphological changes found in D. antarctica should lower photosynthetic productivity, but are dependent on developmental stage. The action spectrum produced herein would still forecast increased damage to PSII due to early spring ozone depletion, but not as great as previously predicted. Moreover, current levels of UV-B radiation may be more damaging to some species than previously thought based on other plant action spectra.
194

Caracterização tafonômica das concentrações fossilíferas da Formação Cape Melville, Grupo Moby Dick (Mioceno Inferior), Ilha Rei George, Antártica / Taphonomic characterization of fossil concentrations from the Cape Melville Formation, Moby Dick Group (Early Miocene), King Georg Island, Antactica

Casati, Rafael 01 November 2007 (has links)
Trabalhos objetivando a tafonomia de concentrações fossilíferas geradas em ambiente glacial ou periglacial são raros. Neste contexto, a presente dissertação realizou a caracterização tafonômica das concentrações fossilíferas da Formação Cape Melville, Grupo Moby Dick (Mioceno Inferior), Ilha Rei George, Antártica, tendo em vista a elucidação da gênese destes depósitos. Para tanto, dados relativos a um total de 534 espécimes foram obtidos nas camadas ricamente fossilíferas das quatro seções, denominadas Pingüineira (PRS), Hard Ground (HGS), Chaminé (CS) e Lava Crag (LCS), levantadas no topo da Península Melville entre Janeiro e Fevereiro de 2003. Destas, apenas a Seção PRS apresenta duas camadas fossilíferas distintas (PRS-C1 e PRS-C2). A fauna estudada é composta predominantemente por restos de moluscos bivalves. Restos menos abundantes de corais, caranguejos, gastrópodes e braquiópodes, além de icnofósseis, também estão presentes. A análise da composição taxonômica, ecológica e tafonômica permitiu identificar semelhanças entre as Seções PRS e HGS e entre as Seções CS e LCS. As seções PRS e HGS são compostas dominantemente por bivalves depositívoros da infauna rasa (Ennucula frigida, Enncula musculosa e Yoldia peninsularis), preservados preferencialmente com as valvas articuladas fechadas, porém fora da posição de vida, indicando remobilização da fauna pré-soterramento; a ausência de sinais de fragmentação, abrasão e incrustação indica que os bioclastos não foram afetados por processos bioestratinômicos químicos, físicos ou biológicos intensos. A ocorrência de bioclastos piritizados na Seção HGS é interpretada como resultante da decomposição dos organismos soterrados, ainda vivos, em ambiente anóxico. As assembléias das seções CS e LCS são constituídas dominantemente por bivalves suspensívoros da infauna profunda (Neilo (N.) rongelii), preservados preferencialmente com as valvas desarticuladas, indicando que os processos bioestratinômicos físicos foram mais atuantes, sendo, no entanto, raros os sinais de fragmentação e de outras assinaturas tafonômicas como incrustação e bioerosão. As valvas desarticuladas estão preservadas preferencialmente com a convexidade voltada para baixo indicando que os bioclastos foram colocados em suspensão e redepositados fora da posição de maior estabilidade hidrodinâmica; a orientação em planta destes bioclastos exibe direção preferencial, indicando atuação de correntes fracas e um maior tempo de exposição na interface água/sedimento; a ocorrência de raros restos de bivalves suspensívoros escavadores da infauna profunda (Panopea (P.) cf. P. regularis) e de caranguejos (Antarctidromia inflata) preservados em posição de vida é indicativa de que esta comunidade foi soterrada in situ por sedimentos em suspensão que trouxeram a tanatocenose de valvas desarticuladas. Os resultados obtidos no presente estudo reiteram a importância dos estudos tafonômicos e paleoecológicos no entendimento da dinâmica deposicional do passado, contribuindo com um grande conjunto de dados úteis na caracterização de ambientes glaciais e periglaciais. / Works focusing on the taphonomy of fossil concentrations generated in glacial or periglacial environment are rare. In this context, the present dissertation carried out the taphonomic characterization of the fossil concentrations of the Cape Melville Formation, Moby Dick Group (Lower Miocene), King George Island, Antarctica, in order to elucidate the genesis of these deposits. To this end, data relative to a total of 534 specimens were obtained in the richly fossil layers of the four sections, called Pingüineira (PRS), Hard Ground (HGS), Chaminé (CS) and Lava Crag (LCS), investigated at the top of the Melville Peninsula between January and February of 2003. Of these, only the PRS Section presents two distinct fossil layers (PRS-C1 and PRS-C2). The studied fauna is mainly composed of remains of bivalve clams. Less abundant remains of corals, crabs, gastropods and brachiopods, as well as trace fossils, also are present. Taxonomic, ecological and taphonomic analyses allowed similarities to be identified between PRS and HGS and CS and LCS. PRS and HGS Sections are dominantly composed by shallow infaunal deposit-feeding bivalves (Ennucula frigida, Enncula musculosa Yoldia peninsularis), preserved preferentially with closed articulated valves, however out of life position, indicating remobilized fauna; the absence of signs of spalling, abrasion and incrustation indicates that the bioclasts were not affected by intense chemical, physical or biological bioestratinomic processes. The occurrence of pyritized bioclasts in HGS is interpreted as the result of decomposition of the entombed organisms, still alive, in an anoxic environment. The assemblages of CS and LCS Sections are dominantly constituted by deep infaunal suspension-feeding bivalves (Neilo (N.) rongelii), preserved preferentially with disarticulated valves, indicating that the physical biostratinomic processes were more operative; however there are few signs of spalling or other taphonomic signatures such as incrustation and bioerosion. Disarticulated valves are preferentially preserved convex down indicating that bioclasts were placed in suspension and redeposited in a position other than that of greatest hydrodynamic stability; the orientation of these bioclasts in plan view shows a preferential direction, indicating weak currents and a longer time of exposition at the water/sediment interface; the occurrence of rare remains of deep infaunal suspension-feeding bivalves (Panopea (P.) cf. P. regularis) and crabs (Antarctidromia inflata) preserved in life position is indicative that this community was entombed in situ by sediments in suspension that brought the thanatocenosis of disarticulated valves. The results obtained in the present study reiterate the importance of taphonomic and paleoecological studies for the understanding of the depositional dynamics of the past and contribute a great number of data useful in the characterization of glacial and periglacial environments.
195

Fungal Diversity and Cellulytic Activity in the Historic Huts, Ross Island, Antarctica

Duncan, Shona Margaret January 2007 (has links)
The goal of this study was to undertake a microbial investigation of the Historic Huts areas on Ross Island, to gain knowledge of the fungal biodiversity and biochemical framework, focusing on the wood degrading potential of these fungi at both psychrophilic (cold) and mesophilic (moderate) temperatures. Eight hundred and forty nine samples were collected from three Heroic Era Historic Huts of Antarctica, from a variety of substrates but predominantly structural wood. The huts, Discovery Hut at Hut Point, Terra Nova Hut at Cape Evans and Nimrod Hut at Cape Royds, are located on Ross Island and were all assembled in the early 20th century by the Heroic Era explorers to house the expeditions, stores and animals. These wooden huts were abandoned when the expeditions left. The introduction of wood and other organic material to a pristine environment along with the creation of a microclimate within the harsh Antarctica environment created interesting sites for studying fungal diversity, wood decay and fungal cellulase enzymes in an extreme environment. Each hut can be classified as offering different conditions and circumstances for fungal propagules. Of the three huts, Terra Nova Hut is the only hut where there are visible fungal blooms within the hut and it, with Discovery Hut, had the greatest number of samples that contained fungi compared to Nimrod Hut which had the least. Discovery Hut, at less than 500 metres from the United States McMurdo Station, is the most visited by scientist and base staff and has been the most demonstrably affected by human impact of the three huts due to its closeness to the research stations on Ross Island To ensure a full understanding of the fungal diversity of the Historic Hut sites, a variety of sampling techniques were used along with a variety of culture media. Two thousand and seventy six isolates consisting of 1177 filamentous fungi and 899 single celled microorganisms (yeast and bacteria) were isolated; all these cultures were frozen and now form the University of Waikato Antarctic Culture Collection. Five genera dominated the fungal isolates that were identified and these were Cladosporium, Geomyces, Cadophora, Penicillium and Thelebolus. The fungal diversity of these Historic Huts' communities is low but the members present are metabolically active, consistent with other microbial communities in the Antarctic. The Historic Huts and surroundings contain a diverse array of provision in the way of wood and supplies, which provide nutrient sources for fungal growth. Endemic organisms present in the soil could have been enriched by using the introduced nutrient sources as primary and/or second metabolic substrates. In addition, fungi could have been introduced with the wooden huts and supplies when they were brought to Antarctica by the Heroic Era explorers, or introduced in the subsequent years with visitors and conservation work conducted at the sites. These introduced organisms, though, would have had to adapt to the change in climate and conditions posed by the Antarctic in order to survive and be subsequently isolated in this study. A screen for carboxymethylcellulase (CMCase) activity was done on a selection of the fungal isolates as the first step to understand the cellulytic potential of the Antarctica fungal community inhabiting the huts. One hundred and six fungal isolates from a total of 404, that were screened were deemed to be CMCase positive, 27 fungal isolates were chosen for further study including quantifying the activity of extracellular endo-1,4-β-glucanase at psychrophilic and mesophilic incubation temperatures. All but one isolate could produce endo-1,4-β-glucanase activity at 4 C and many produced more endo-1,4-β-glucanase activity at 4 C than at 15 C. Cadophora malorum 182, Cadophora malorum 242, Penicillium roquefortii 405, Penicillium roquefortii 408, Geomyces sp. 711, Geomyces sp. 824 and Cladosporium oxysporium 805 were selected for in-depth study of growth characteristics including growth temperature preferences, growth on a variety of cellulose substrates, water activity, and carbon sources, the latter done by using a commercially available microtitre plate containing 95 carbon sources. All seven of the fungal isolates were classified as psychrotolerant and produced, when cultured at either 4 C or at 15 C, cellulase, protease, amylase, xylanase, and pectinase and mannanase enzyme activities. The range of water activity that the Antarctic Penicillium roquefortii isolates could grow at was distinctive when compared with food Penicillium roquefortii isolates. The utilisation of different carbon sources showed that like many studies of Antarctica organism they have a diverse range of enzymatic activity, but interestingly the activity does not differ greatly with incubation temperature with most carbon sources being used or not used at both incubation temperatures tested. Although it took longer for the fungi to grow at the psychrophilic temperatures, the range of carbon sources they utilised was not reduced. The protein composition of the extracellular supernatants was visualised using various electrophoretic and staining techniques. The cellulase activity of the protein bands was visualised by cellulose-containing zymograms, which illustrated that the cellulase complex in all fungi tested was multi-enzyme and differed between species, isolates and temperatures of culturing. The cellulase activity of Cadophora malorum 182 was enriched by purification techniques including ion exchange chromatography and native preparative electrophoresis. The protein complex was not purified to homogeneity, but enriched for a mixture of proteins and the mixture was described as having the following properties; a temperature range of β-1,4-glucan cellobiohydrolase activity from 20 C to 80 C with the optimum activity seen at 60 C, β-1,4-glucan cellobiohydrolase activity that is stable at 4, 25 and 40 C for at least 24 hrs, lost at 50 C and 80 C within 24 hrs and 2 minutes respectively. Along with β-1,4-glucan cellobiohydrolase activity, the protein mixture contained Avicelase, CMCase, xylanase and mannanase activity. The thesis research showed that there was limited fungal diversity in the Historic Huts and artefacts (a total of five dominant genera were identified) but the fungi are actively growing and producing viable spores in the cold of Antarctica and producing the necessary enzymes for degradation of wood. Although the metabolism and growth rate is slower at psychrophilic temperatures, the fungal isolates studied as part of this thesis research could still function enzymatically at cold temperatures and this includes the degradation of wood as evidenced by in vitro wood decay studies examined by scanning electron microscopy where two isolates of one species demonstrated the ability to degrade wood. The cellulase complex of the investigated fungal isolate was multi-enzymed and although the components were not purified to homogeneity, an enriched mixture of proteins had enzyme activity and stability in a broad temperature range, and activity to a variety of cellulosic substrates. This thesis research adds to the knowledge of the fungal biodiversity in the Antarctic and increases the understanding of the biochemical framework, participating in relation to wood decay potential of these Antarctic fungal isolates.
196

Reflections on ice : scattering of flexural gravity waves by irregularities in Arctic and Antarctic ice sheets

Williams, Timothy D. C., n/a January 2006 (has links)
This thesis studies the scattering properties of different types of imperfections in large Arctic and Antarctic ice sheets. Such irregularities include cracks, pressure ridges and both open and refrozen leads. The scattering by a transition region between sea ice and a very thick ice shelf, for example as is found in the Ross Sea in Antarctica, is also treated. Methods of solution are based on applications of Green�s theorem to the appropriate situation, which leads to either a single integral equation or a pair of coupled integral equations to be solved at the boundary between the ice and the sea water. Those equations over a finite interval are solved using numerical quadrature, while those over semi-infinite ranges are solved using the Wiener-Hopf method. Results calculated using different techniques are able to be checked against each other, giving us great confidence in their accuracy. In particular, the scattering by three ice sheets of different thicknesses is confirmed analytically by mode-matching coupled with the residue calculus technique. The scattering by the single irregularities is investigated partly for its own sake, and partly with the aim of using it to treat the scattering when large numbers of features are included in a single ice sheet. The principal objective of doing this is to observe the change in the general amounts of reflection and transmission as the background ice thickness is changed. There is enough variation in our results for us to conclude that there is definite potential for using the change in an incident wave spectrum after passing through a given ice field to estimate the background ice thickness.
197

Growth, structure, and desalination of refreezing cracks in sea ice

Petrich, Christian, n/a January 2005 (has links)
The aim of this study is to characterise the structure of refrozen cracks, and to deduce the details of their formation. Surveys and experiments are conducted on straight-sided, linear, refrozen cracks of width 80 mm to 340 mm in land-fast first-year sea ice in McMurdo Sound, Antarctica. Refreezing of cracks is simulated analytically, and with a numerical fluid dynamics model of brine movement in the porous sea ice and in the ocean. Systematic arch-shaped patterns of inclusions, upstream-growing crystals, and two-dimensional variations in salinity are identified in completely and partially refrozen, natural cracks, and in artificial cracks. Using a two-dimensional thermistor array, a relationship between the development of the sea ice structure and the temperature records is found, which identifies the transition from the porous, skeletal layer to consolidated ice in artificial cracks. A two-dimensional analytical model is developed that predicts the measured thickness of consolidated ice in refreezing cracks for this study and for the studies of others. From a heat balance within the refreezing cracks, it is concluded that some of the experiments were conducted in the presence of a negative ocean heat flux. A two-dimensional thermistor array beneath the ice-water interface of a refreezing crack provides evidence for sporadic, cold temperature, advective events at night. A two-dimensional, numerical fluid dynamics model based on the finite volume method is developed to simulate desalination and fluid flow in refreezing cracks. This requires a permeability-porosity relationship for sea ice, which is deduced from data of other groups, combined with the numerical model. To make comparisons among data sets, an analytical approximation is derived for the relationship between connected pore space and total pore space of a random porous medium, based on a Monte Carlo model that is adapted to the crystal structure of sea ice. The permeability-porosity relationship derived in this study is in good agreement with permeability functions published recently. The refreezing of cracks simulated with the numerical fluid dynamics model is consistent with experiments and with the analytical model. In addition, the numerical model simulates the high porosity, arch-shaped freezing front and inclusion structure. Supercooling of the liquid is found to cause excessive heat loss in the simulation. Since a large oceanic heat flux was not observed in the experimental heat balance of refreezing slots, it is suggested that this indicates platelet ice formation or frazil ice formation at the vertical crack interface in Antarctic experiments.
198

The influence of ocean waves on the distribution of sea ice in an MIZ

Downer, Joshua, n/a January 2005 (has links)
A marginal ice zone (MIZ) is characterised by distinct ice floes and its direct exposure to the open ocean. Sea ice is typically described as a continuous material but this description can be inappropriate in an MIZ due to the granular nature of the ice cover and the scale of processes acting on the ice floes. In this thesis, the kinematic behaviour of sea ice in an MIZ modelled as a granular material is investigated with an emphasis on the influence of ocean waves. The kinematic behaviour of a set of ice floes subject to ocean wave forcing was recorded in an experiment conducted in the Ross Sea. Kinematic data were recorded from each ice floe using a GPS receiver, tri-axial accelerometer, and compass. The data show (1) the influence of wave forcing and (2) collisions between neighbouring ice floes. It was also discovered that the GPS receivers were able to resolve the effects of ocean wave forcing despite their poor absolute accuracy. The number density and normalised structure factor (NSF) are introduced to describe the spatial structure of a set of ice floes. Four idealised distributions (in 1D and 2D) are analysed to gain insight into the way that different factors determine the shape of the NSF. It is shown that (1) a significant sinusoidal deviation causes a peak in the NSF, (2) ordered structure dominates low spatial frequencies, and (3) disorder dominates high spatial frequencies. A comparison of the contributions from these different factors is used to estimate the significance of a sinusoidal deviation in the positions of the ice floes. A granular model of an MIZ is developed using a novel set of equations of motion to examine the effect of ocean wave forcing. The equations of motion are derived for small ice floes and allows forcing by multiple waves. These equations predict a transient, wave-induced torque, which can be sustained by the application of a second force to the ice floe. Torque induced by the interaction of two forces on an ice floe may be a general feature of sea ice motion. The number density and NSF are used to analyse the distribution of ice floes in the granular model. At low solids-fractions the number density is correlated at the frequency of the wave forcing. As the solids-fraction is increased this correlation is destroyed by collisions between the ice floes and new correlations are created that are related to the packing structure of the ice floes. When the number density is weighted by the velocity of the ice floes, the correlations between floes are related to the convolution of the wave velocity field and the number density. These correlations may be incorporated into the thickness distribution of large-scale models using the maximum entropy method. The granular model was also examined as a percolating network of contacts and it was found that percolation was more likely to occur along the crest of a wave than in the direction of propagation.
199

The White Distance: a novel.

Errington, Susan January 2008 (has links)
The White Distance’ is a work of fiction set in Australia and Antarctica at the time of World War I. The story focuses on two lovers, Dora and Daniel, who are part of Australia’s vigorous anti-war movement. Each of the lovers comes to the movement for different reasons. Dora’s beloved brother has been killed in France; Daniel is a printer interested in the new left-wing ideas emerging in Europe, especially Russia. Wanting to escape public pressure to join up and fight, Daniel takes a position with an Antarctic expedition and travels there with a small team from the Commonwealth Bureau of Meteorology to collect weather data. This was a time of major Antarctic exploration, with the Australian expedition led by Douglas Mawson taking place in 1913. In Antarctica, in the novel, the leader of Daniel’s expedition suffers a nervous breakdown and becomes dangerously violent, believing his men are German spies. Daniel and his colleagues have to consider the possibility that the only way to stop their leader might be to kill him. After Daniel leaves, Dora joins a more radical anti-war group led by the charismatic Malachy Mara. She is forced to reconsider what she believes when the group decides to place a pipe bomb in a railway station, which will kill many civilians. Worse for her, she is likely to be the one selected to put the bomb into position. ‘The White Distance’ is also a love story about two lovers who, after being very close, are separated by a great and unfathomable distance. Dora and Daniel struggle to keep their love alive by writing letters to one another, even though they cannot be posted, and keeping journals that will not be read until Daniel returns. Each confronts a deep personal crisis without the other there for support. They use their words to one another to draw the strength to hold on. Although set in the past, the novel raises issues which are relevant to current international and national concerns such as the clash of ideals and personal morality, terrorism, public violence, war and pacifism, love and separation. Exegesis The accompanying exegesis, ‘Reframing the Past for the Present: Writing ‘The White Distance’’, examines the research material and creative influences behind the development of the novel, ‘The White Distance’. It considers the issues which I confronted in writing an historical work of fiction, and concludes by placing the novel in the wider context of current debates about Australian historical fiction. / Thesis (Ph.D.) -- University of Adelaide, School of Humanities, 2008
200

Ein kleiner, schwarzer Punkt am weisslichen Himmel: Antarctica & Ice in German Expressionism

Essigmann, Joy M. 01 August 2010 (has links)
This work explores a fascinating and disturbing literary trope found in select German Expressionist prose in the years 1910-1920. Key Expressionist-era authors, including Georg Heym, Robert Musil, Egmont Colerus and Franz Kafka employed Antarctic and ice metaphors in their poetry and prose to exemplify inner feelings of displacement resulting from modernity. Expressionist discontent, as well as the “Heroic Age of Antarctic Exploration” that occurred from 1895 to 1922, led to the creation of polar dystopias in some literature. These dystopias explored abstract interpretations of the South Pole, not as a place of excitement and adventure, but rather as a journey into philosophical inner ice in the era of Modernism. Heym, Musil and Colerus did not invent the disturbing Antarctic allegory, but rather returned to an established literary tradition in a time of polar “pulp” fiction. This thesis first examines the South Pole as a place of emptying, shown in Georg Heym's 1911 fragment “Das Tagebuch Shakletons” (“Shakleton's Diaries”). In other works, such as Heym's 1911 novella “Die Südpolfahrer” (“Travelers to the South Pole”), the South Pole is portrayed as a blank slate. Two Austrian works show the idea of the South Pole as a refuge: Robert Musil’s 1911 Das Land über den Südpol (“The Land over the South Pole”) and Egmont Colerus’ 1915 novel Antarktis. These works exemplify and interpret the modern soul’s tepid “temperature,” something sharply criticized by Expressionists. These authors and poets longed to see an improved world and expressed discontent by portraying imperialist “heroes” of their time as mere specks lost in the sea of modernity. In the literature of Heym, Musil, Colerus and Kafka, a bleak Antarctic world mirrors the authors’ views on their “dying” society and the European “symptom” that resulted in suffocating mediocrity. Self-fulfillment becomes a static or moving point on the horizon that will never be realized by either the explorer or the freezing bourgeois soul.

Page generated in 0.055 seconds