Rock avalanches are a high magnitude, low frequency catastrophic mass movement involving the failure of over 1 x 106 m3 of mountainside. Rock avalanches are considered a major hazard of the high mountains due to the excessive run-out often associated with them. To date the mechanism that allows for such excessive travel distance is unproven although several dozen possibilities have been proposed. Rock-avalanche deposits exhibit characteristic features such as sharp lateral margins, confinement to local topography, super-elevation on valley sides, intensely fragmented interiors and preserved stratigraphy relative to the source. However, there are few detailed studies of the internal sedimentology of rock-avalanche deposits. Such studies are a vital piece of evidence in the search for the mechanisms of motion as rock avalanches are rarely witnessed. This thesis examines the detailed sedimentology of five rock avalanche deposits of varied lithology and morphology. A novel methodology is developed to sample deposits for their grainsize distributions (GSD). The GSD's prove similar for deposits, with significant variation due to preserved lithological banding in the interior. This finding refutes the commonly held view that rock-avalanche deposits are simply inversely graded. Instead, a facies model is developed of a coarse Carapace facies forming the surface and near surface that overlies a highly fragmented Body facies that is in turn underlain by the Basal facies that is free to interact with the substrate. The sedimentology of the Body facies is considered in fine detail and is shown to be fractal in nature, that is, self-similar at all scales of observation. A predictive sedimentological plot is presented that allows generation of the grain-size distribution and descriptive statistics from a simple estimation of weight percent gravel at a rock avalanche exposure. The morphology of rock-avalanche deposits are examined and a classification presented of 'spread' 'two-phase' and 'stalled'. The hazard and features of each morphology is described in relation to the observed deposits.

No description available.

The late Quaternary palaeoclimatic history of the lowland Southern Hemisphere Tropics of South America (SHTSA) has been little studied and analysis of key climatic events, such as the Last Glacial Maximum (centred ~ 21,000 years ago (21 cal. ka BP)) and the glacial-Holocene transition is limited. Studies from the SH tropical Andes and the Atlantic seaboard demonstrate a strengthening of the South American summer monsoon during the LGM, in tune with the ~ 20 kyr precession orbital cycle. However, palynological studies from SHTSA suggest a drier LGM. There are difficulties in interpreting different palaeoenvironmental proxy records and the extent to which they reflect changes in temperature, precipitation, and/or atmospheric CO2 concentrations. In particular, the palaeoenvironmental significance of palynological data is often unclear. Also, high frequency, millennial-scale events have not been captured in records from the lowland SHTSA due to a lack of high resolution temporal records. Diatoms have been used widely in other parts of the world to reconstruct lake level change and therefore provide an independent proxy for precipitation, and an understanding of the modern diatom ecology is essential for accurate palaeoreconstruction. The main rationale of this thesis is to address the uncertainty of the glacial-Holocene climate in South America. To this end, this thesis aims to: (a) investigate the distribution, ecology, and flora of diatom taxa at Laguna La Gaiba (17°45’S, 57°40’W) (LLG) in the heart of lowland tropical South America, where very few modern diatom studies exist; (b) determine whether modern diatom assemblages at LLG will provide a useful analogue for palaeoenvironmental reconstructions, in particular, lake depth reconstruction; (c) provide a detailed late Quaternary lake level reconstruction for the lowland interior of SHTSA, based upon fossil diatom analysis of a sedimentary core in LLG. Descriptive, quantitative and multivariate analyses were applied to modern diatom assemblages and environmental variables to ascertain the modern diatom environment of LLG. Diatom, pollen, and geochemical analyses, chronologically constrained by 18 AMS 14C dates, were performed on a sediment core extracted from LLG. Key findings indicate: (1) Aulacoseira ambigua, A. ambigua var. robusta. A. distans and A. granulata var. angustissima were the most abundant species. Shallowwater species, such as Staurosira and Eunotia spp., dominated the shallows and littoral zone, whilst deep-water species, such as Aulacoseira sp., dominated in open water; (2) The highest percent variance in the diatom data was explained by depth and pH; (3) Analysis of fossil diatom assemblages from the LLG core demonstrated that the Last Glacial Maximum (LGM) and late glacial period (prior to 12.5 kyr BP) was drier than present. This corroborates and significantly strengthens pollen-based palaeo-hydrological reconstructions from the same core; (4) An abrupt shift from 12.5 kyr BP from shallow water to deep water diatoms signals major flooding of LLG associated with the transition from relatively drier glacial conditions to wetter Holocene conditions and also highlights an anomalously wet period centred over 12.2 kyr BP that falls within the Younger Dryas chronozone; (5) Deep-water diatoms remain high throughout the Holocene, which means that the mid-Holocene aridity inferred from the pollen data (expansion of seasonally-dry tropical forest) is not captured by the diatom data. These results not only present the modern diatom ecology of a little studied area in lowland Bolivia, but also highlight the potential of diatoms as a proxy for past lake level fluctuations, improving the understanding of late Quaternary palaeoclimate of tropical South America. Used as part of a multiproxy reconstruction, this record has provided a more complete picture of the variation between regions of late Quaternary climate change in South America, as evidence of a dry LGM climate contrasts with the robust, well-dated climate archives of the central Andes and E Brazil. This suggests the climate in the continental interior of SHTSA was not driven by the precesionally-forced monsoon cycle but is in step with changes in glacialinterglacial cycle boundary conditions.

Cu2ZnSnS4 (CZTS) is a promising absorber material for thin-film solar cells since it contains no rare or toxic elements, has a high absorption coefficient and a near ideal bandgap energy. It does, however, present some challenges due to the limited single-phase region of the desired kesterite phase and its instability towards decomposition. Sputtering of CZTS from quaternary, compound targets using RF magnetron sputtering is known. In this thesis work CZTS absorbers were made using pulsed DC magnetron sputtering on stainless steel substrates. The effects of varying substrate temperature and adding seed layers to promote grain growth were investigated, as well as the effects of a rapid thermal anneal in a S-rich atmosphere. Film compositions determined by X-ray fluorescence were found to be inside or close to the kesterite single-phase region in the phase diagram, but were generally too Cu-rich and Zn-poor to yield good results. The kesterite phase was confirmed with X-ray crystallography and Raman spectroscopy, indicating that it is possible to sputter CZTS from a single target with a high deposition rate. It was found that Cu2S seed layers could induce a significant increase in grain size, and preliminary experiments showed no evidence of the seed layer remaining after deposition of the absorber. Higher substrate temperatures also lead to increased grain size, but excessive heating caused the decomposition of the CZTS. Annealing induced grain growth, relaxed internal stress in the material and improved the electrical properties of the CZTS films, primarily by the removal of shunts.

This study aims to determine the late-Quaternary evolution of an ephemeral, transverse river system developed in southeast Spain, with particular reference to sediment provenance variation. The Rio Alias drains two inter-montane east-west orientated Neogene sedimentary basins; the Sorbas and Almeria basins. Pliocene to present transpressional tectonics has led to inversion of the sedimentary basins and incision of the developing fluvial system. Fluvial incision has led to the preservation of a suite of alluvial terraces recording the late-Quaternary development of the Rio Alias. Fluvial system inauguration began in the Plio-Pleistocene epoch. The primary fluvial system developed as a consequent river later becoming superimposed and transverse to structure. The drainage basin of the Rio Alias has been sub-divided into 4 sub-basins; The Lucainena, Polopos, Argamason and El Saltador sub-basins. Each basin is structurally controlled. The impact of climate, tectonics, river-capture and eustatic sea-level variation on the fluvial system evolution varies both spatially and temporally across the sub-basins of the Rio Alias. Across the region alluvial aggradation is thought to relate to global glacial periods and incision to interglacial periods. The Lucainena sub-basin is largely controlled by climatic variation related to glacial interglacial cycles with slight modification due to local small scale river-capture and regional epeirogenic uplift. The Polopos sub-basin is also largely controlled by climatic variation, however a major river-capture event c.70ka beheaded the Rio Alias of c.70% of its drainage area. Following the loss of drainage the beheaded Rio Alias system lost stream power, this is reflected in the decrease in size of bedform geometry and the reduced incisional capacity of the fluvial system of the post-capture terrace sequence. In the Argamason sub-basin the Rio Alias crosses the Carboneras Fault Zone, a left-lateral strike slip fault. Late-Quaternary tectonic activity has significantly modified the climatically generated signal. Large tortuous meanders developed in response to normal tectonic activity and continued tectonically driven base-level lowering led to abandonment of terraces and local incision. The El Saltador sub-basin is located at the seaward end of the system and the climate generated phases of aggradation and incision have been greatly complicated by eustatic sea-level variation related to glacial/interglacial cycles. The lowering of base-level due to sea-level regression initially led to pronounced incision along steep gradients and to the development of meander loops in the seaward end of the Rio Alias, during what regionally was a climate driven phase of aggradation. Analysis of the alluvial sediment using a combination of field based clast analysis and laboratory analysis (petrology, SEM, magnetic analysis) allows a detailed picture of sediment provenance variation to be established throughout the evolution of the Rio Alias. Provenance analysis provides information on the timing and extent of river-capture related loss of drainage area, the relative timing of local tectonic activity and also provides new information regarding sediment source area variation throughout the development of the fluvial system. Detailed analysis of the terrace sediments and the modern channel indicates that as the fluvial system incises, local input of sediment from the steepening valley sides grows increasingly dominant. The coupling between the hillslopes and the channel thus changes through time. Sediment provenance analysis has increased our understanding of the long-term fluvial evolution of the Rio Alias, identifying not only sediment provenance variation due to river-capture and changing geology but to fluvial system development.

Drilling during ODP Leg 133 offshore Cairns, northeast Queensland, provided a unique opportunity to document carbonate production and facies development on a mixed carbonate-siliciclastic margin. Recent studies have shown that variations in the sedimentology of Late Quaternary and Pliocene periplatform sediments (Schlager and James, 1978), deposited on continental slopes and in deep basins surrounding shallow carbonate platforms, are linked to changes in sea-level (Droxler et al., 1993; Schlager et al., 1994). However, considerable debate has arisen to the timing of the production and export of shallow water carbonate material, with respect to sea level change. Two main hypotheses have been proposed to explain the response of shallow water carbonate platforms to variation in Late Quaternary sea level: I) 'highstand shedding' and 2) 'lowstand shedding'. Proponents of highstand shedding argue that depositional systems shed most of its carbonate sediments onto the platform slopes during highstands of sea level. Conversely, during lowstands of sea level bank top production and export of carbonate material is restricted, and platform slopes are largely starved of bank derived carbonate (Schlager, 1992; Schlager et al., 1994 ). Supporters of lowstand shedding maintain that significant carbonate production and export of shallow water carbonate material occurs during lowstands (and highstands) of sea level (Bosellini, 1989; Goldhammer and Harris. 1989; Grammer and Ginsburg. 1992). In order to investigate the response of mixed carbonate-siliciclastic systems to variations in Late Quaternary sea level and climate change, core material was collected from Ocean Drilling Program (ODP) Leg 133, Sites 819 and 823 (northeast Australian margin). These two sites form part of an eastward extending transect of drill localities, offshore Cairns, Queensland, from the outershelf/upper-slope of the Great Barrier Reef (Sites 821 /820/819), into the Queensland Trough (Site 823) and ultimately onto the flanks of the Queensland Plateau (Sites 824 and 811 /825). Pelagic to hemipelagic sediments collected from these two sites were examined for the downcore distribution of grain size, magnetic susceptibility, carbonate content, variations in carbonate mineralogy (XRD), and major and minor element (XRF) geochemistry. Using high resolution foraminiferal stable oxygen isotopes, coupled with biostratigraphic and magnetostratigraphic datums, well defined age models for Hole 819A and Hole 823A have been constructed, although it was not an easy task as hiatuses occur in these records. Age models for the sequences recovered from Hole 819A and Hole 823A have been further refined using correlation with existing isotopic stratigraphies in the Pacific Ocean (ODP Hole 677, Raymo et al., 1989), and comparison with high resolution sedimentologic records from other ODP Leg 133 marine sequences. Analysis of the mineralogical, sedimentological and geochemical records from Holes 819A and 823A indicate that, over the last 1.1 million years, highstands of sea level (and during the early regression) are characterized by increased shallow water carbonate production, and deposition on the upper slope. This pattern of carbonate deposition is consistent with the highstand carbonate shedding scenario outlined by Schlager et al. (1992), and Schlager et al. ( 1994 ). Lowstands of sea level (and particularly the early transgression) are characterized by increased deposition of non-carbonate (mainly terrigenous) material and/or were not diluted by shallow water carbonate platform material. During the lowstands of sea level the shallow water carbonate factories were switched off. Therefore, the sediments deposited during lowstands of sea level tend to record the greater influence of pelagic driven carbonate. Although the above mentioned scenario of highstand shedding applies to the entire record of 1.1 million years. mineralogical and geochemical data indicate that shallow burial diagenesis, and dissolution of solution sensitive carbonate, occurred in the lower part of the records. The diagenesis and dissolution, however, have played only a minor role in determining the composition of the Queensland margin sediments. Variations in the terrigenous input (Cr/Al and Ti/AI ratios) in Queensland margin sediments indicate that interglacial periods were generally wetter than corresponding glacials or lowstands of sea level, during the Late Quaternary.

This thesis describes experiments made to test the corrosion inhibition of quaternary amines on steel.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science, 2011 / A multifactor ecological integrity index, focusing on freshwater ecosystems on a quaternary catchment scale, can be of great benefit to conservation planning. No ecological integrity index has previously been developed for South African quaternary catchments. In this study an index was developed based on three environmental surrogates: land cover, river integrity and fish species conservation status, with the intention of identifying quaternary catchments of highest conservation concern. By developing such an index, the aim was to provide a general indication of the degree to which catchments have been transformed from a natural environment to a human altered environment, thereby identifying catchments most in need of conservation. For the three available datasets, indices were developed using a five category point-scoring system. A score of one indicates a completely degraded environment and a score of five indicates a pristine environment. The original land cover data consisted of 49 different land cover types which were reduced to five land cover transformation scores. Available river integrity data already existed in five categories and a numerical score of one to five was applied to each category. Fish species conservation status was scored according to the IUCN red data list classifications on a similar basis. Subsequently, a weighted mean score expressed as a percentage was calculated for the three indices for each quaternary catchment. These indices indicate the degree of change/transformation from a natural system (100%) to a largely degraded system (20%). Ultimately, an ecological integrity index was calculated as a mean value of the three related but independent indices. However, the results of the developed ecological integrity index were not representative of real world conditions. This is largely attributed to the lack of complete data found in two out of the three datasets used in the study. Some of the main limitations encountered were the lack of river segment definitions within each catchment and the incomplete and un-systematic collected fish species data records. The land cover data, on the contrary, was of high definition and high standard. It is recommended that in the interim, the developed land transformation index, based on a detailed analysis of land cover, be used as an indicator index of ecological integrity of catchments

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Whether a species will flourish or face extinction under a new climate regime is largely determined by its dispersal ability, its adaptive capacity or some combination of these processes. These processes have also played important roles in the evolutionary histories of species, ultimately shaping their contemporary distributions. In terrestrial studies, a landscape genetics approach is often used to explain how geographic, ecological and evolutionary processes interact to structure spatial genetic variation across populations, but these approaches have only begun to be used in marine ecosystems. This dissertation fills an emerging niche in marine ecology by taking an interdisciplinary seascape genetics approach to investigating the interplay of climate, dispersal and adaptation as shallow-water marine fishes respond to environmental heterogeneity over space and climatological shifts over time. [TRUNCATED] / 2031-01-02

Proper folding of a protein to its native state is critical for the protein to be fully functional under biological conditions. Understanding protein folding and protein folding evolution within the same structural family are key to understand which processes assist or hinder protein folding and how to prevent misfolding. Tm0979 from Thermotoga maritima, Mth1491 from Methanobacterium thermoautotrophicum and YchN from Escherichia coli belong to the homologous superfamily of YchN-like proteins (SCOP and CATH: 3.40.1260.10). The structures of these proteins have been solved as part of structural proteomics projects, which consist of solving protein structures on a genome wide scale. In solution, Tm0979 forms a homodimer whereas Mth1491 folds as a trimer and YchN is a homohexamer. The structures of the individual monomeric subunits of these three proteins have high structural similarity, despite very low sequence similarity. The biological roles of these proteins are not yet well defined, but seem to be involved in catalysis of sulphur redox reactions. This thesis focuses on characterisation of the Tm0979 homodimer and the Mth1491 homotrimer, as well as the determination of the folding mechanisms of these two proteins. The folding mechanisms of the proteins are compared to each other and to the mechanisms of other dimeric and trimeric proteins. The evolution and basis of oligomeric structure within the YchN family are analyzed. Mutations of Tm0979 and Mth1491 are designed as a basis for future work to investigate processes responsible for switches in oligomeric protein quaternary.structure.