• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 92
  • 31
  • 11
  • 11
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 199
  • 35
  • 26
  • 25
  • 25
  • 20
  • 18
  • 17
  • 16
  • 14
  • 13
  • 11
  • 11
  • 10
  • 10
  • 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.
101

Idades de Soterramento \'ANTPOT.26 AI/\'\'ANTPOT.10 Be\' em grãos de quartzo e o assoreamento de sistemas de cavernas na região de Iraquara, (BA): 2 milhões de anos de registro sedimentar no Quaternário / not available

Laureano, Fernando Verassani 15 December 2014 (has links)
Idades de soterramento de grãos de quartzo pelos isótopos cosmogênicos \'ANTPOT.26 Al\' e \'ANTPOT.10 Be\' foram obtidas em depósitos sedimentares que assorearam os sistemas de cavernas associados aos vales cegos dos riachos das Almas e Água de Rega, região de Iraquara (BA). Os resultados também incluem a caracterização faciológica e uma abordagem preliminar sobre a arquitetura dos depósitos, além do mapeamento em campo do contexto geomórfico dos sistemas de condutos e seu preenchimento sedimentar. Coberturas terciárias assentadas sobre todas as unidades pré-cambrianas testemunham que a superfície cárstica e os sistemas de condutosfazem parte de uma longa história de evolução, envolvendo episódios de exposição, soterramento e exumação. Durante os dois últimos milhões de anos, a drenagem superficial e os sistemas de cavernas estavam plenamente articulados na condução de água e sedimentos, com rotas de fluxo subterrâneas que incluíam ainda trechos labirínticos pré-existentes, que serviam de repositório de sedimentos durante os eventos de inundação, proporcionando também, rotas alternativas ao canal,na medida em que o sistema agradava. A sucessiva migração do canal por estas redes labirínticas originou o padrão distributário observado na Lapa Doce e na Gruta da Torrinha. Os depósitos sedimentares estudados nas cavernas dividem-se em dois grupos: fluviais e de água estagnada. Osdepósitos fluviais ocorrem na base e são constituídos por fácies de canal e fácies de inundação. As idades de soterramento de grãos de quartzo destes sedimentos apontam para um período de assoreamento fluvial compreendido entre 1,91±0,12 e 0,36±0,08 milhões de anos para o sistema Lapa Doce-Torrinha (riacho Água de Rega) e 1,37±0,15 e 0,87±0,17 milhões de anos para o sistema Cão-Talhão (riacho das Almas). No sistema Lapa Doce-Torrinha as idades de soterramento concentram-se no intervalo compreendido por dois períodos úmidos (350-450 Ka e 900-1000 Ka), registrados em estudos anteriores através do crescimento de tufas calcárias no semiárido baiano.Tal fato sugere que a agradação fluvial verificada, tanto nos rios quanto nas cavernas, esteja associada a fatores climáticos, particularmente o aumento da carga dos rios derivado da diminuição na estabilidade dos grãos nas vertentes exercida por uma vegetação arbustiva esparsa ou ausente. No topo, os depósitos de água estagnada, preferencialmente compostos por lamas, não possuem estruturas trativas ou de corrente e são associados a uma sedimentação em ambiente freático,para o qual é necessário considerar a subida do nível de base. Gretas de contração, além de relações estratigráficas e erosivas destes depósitos com crostas calcíticas evidenciam que eles não foram depositados em um evento único. Idades U/Th obtidas nas crostas calcíticas apontam para uma deposição durante o Pleistoceno Tardio. Interpreta-se que as lamas foram depositadas durante períodos de elevação do nível de base devido aos eventos úmidos abruptos de escala milenar que ocorreram no nordeste brasileiro ao longo dos últimos 210 ka. / \'ANTPOT.26 Al\' and \'ANTPOT.10 Be\' burial ages have been obtained from quartz grains sampled in extensive sedimentary deposits that fill cave systems associated with Das Almas and Agua de Rega creeks blind valleys, Iraquara region, Bahia (Brazil). The geomorphic context of the caves and their sedimentary record is presented, as well a facies analyses and a preliminary architecture approach for subterranean deposits. Tertiary covers deposited over all Precambrian geological units give evidence that karstic surface and conduit systems are features of a long term evolving landscape, sculpted during episodes of exposure, burial and exhumation. In the last two million years, surface drainage and cave systems were full connected in terms of water and sediment transport.Conduit systems still connected with preexisting passage networks, working as sediment repositories during floods and offering alternative routes to the channels as the systems aggraded. Sucessive channel migration led to the distributary pattern observed in the caves Lapa Doce and Gruta da Torrinha. The cave sedimentary record can be divided into two major categories: alluvial and slackwater deposits. At the bottom of the sediments, channel and flood facies were recognized in alluvial deposits. Quartz simple burial ages point to fluvial aggradation between 1,91±0,12 and 0,36±0,08 My in Lapa Doce-Torrinha cave system (Água de Rega creek) and between 1,37±0,15 and 0,87±0,17 million years in Cão-Talhão cave system (Das Almas creek). Burial ages from Lapa Doce-Torrinha samples group in between two past humid periods (350-450 Ky and 900-1000 Ky) recorded in previous studies from travertines growth in arid regions of Bahia State. This fact suggests that valley and cave aggradation is associated with climate factors, particularly an increase in river load derived from decreased stabilization of hillslopes due to a sparse or absent forest vegetation. At the top of sedimentary pile slackwater deposits are ordinarily muddy without tractive or current sedimentary structures. They are assigned to be deposited in a phreatic environment which, in turn, necessarily requires the base level to rise longer than seasonal floods. Mud cracks, erosive surfaces and stratigraphic relations to calcite crusts and flowstones prove that they were not deposited in a single event. U/Th ages from interstratal calcite crusts point to mud deposition during the Late Pleistocene. Slackwater deposits are interpreted to be a result of sedimentation during successive abrupt wet events defined on millennial time scale for the Brazilian northeast during the last 210ky.
102

Visitor management in action: an analysis of the development and implementation of visitor management models at Jenolan Caves and Kangaroo Island

McArthur, Simon, n/a January 2000 (has links)
Many of the places that people value are the places they wish to visit and experience for themselves. However, each person that visits one of these places can cause impacts that reduce its value. A fimdamental aim of visitor management therefore is to ensure that each visitor's experience is a high quality one, and is sustainable. Various models have been designed to assist with this aim by linking visitor management planning, monitoring and decision making. However, there is a lack of published examples of how visitor management models have been implemented, what results they have yielded, and how well they have performed. There is also a lack of evidence of widespread application of such models. Without information and insight, there is only a theoretical case to argue for the greater use of visitor management models. The aim of this study was therefore to describe, analyse and explain the formulation and implementation of the most widely published visitor management models, with reference to case studies of Jenolan Caves (New South Wales) and Kangaroo Island (South Australia). The study involved: a literature review; personal observations by the author; in-depth interviews with those involved in developing and implementing the two case studies; and an objective analysis using a Goals Achievement Matrix. The thesis critically examined seven visitor management models with respect to their: evolution and definition; dimensions and planning and development approaches; documented applications in Australia and overseas; and limitations. This would appear to be the first time that these models have been critically examined in this way so that comparisons can be easily made between them. This would also appear to be the most comprehensive identification of examples of implemented visitor management models in Australia. The study identified five critical issues relating to development and implementation of visitor management models: 1. Poor planning hmeworks and poorly defined organisational culture, particularly in visitor and tourism management. 2. Lack of, or inconsistent human and financial resources. 3. Resistance to involving stakeholders in fimdamental decision-making. 4. Difficulty in choosing the right model for the situation. 5. Lack of strategic emphasis and technical ability. The study suggested that more effort needed to be made in the pre-development and implementation phases. Critical to such efforts is the development of an implementation plan, written as part of the development process. The implementation plan requires an individual(s) to take on a strategic coordination role that addresses marketing, staff development, budgeting, evaluation and areas for improvement. The study suggested that the conventional emphasis on technical expertise needs to be re-balanced with political skills to lobby for and protect the human and financial resources needed to implement a model long enough for it to prove its value. In the event where resourcing is too limited to fully operationalise an entire model at once, it was recommended to conservatively develop a portion of the chosen model all the way to the stage in which it delivers results that can be marketed to stakeholders. Finally, the study proposed a tool to assist visitor managers to clarify their need for a model, as well as their capability to develop and implement one. In the absence of sufficient information about the implementation of models, the tool empowers managers to consider the - merits of using a visitor management model further, and to select a model that best meets their needs.
103

Modeling Stormwater Pollutant Transport in a Karst Region--Bowling Green, Kentucky

Ross, Allison H. 01 July 2009 (has links)
The management of stormwater runoff is a particular challenge for communities in karst regions. Most guidelines for compliance with regulations for stormwater monitoring and mapping pertain to non-karst environments. It can be argued that effective stormwater management is even more essential to karst regions because stormwater receives little or no natural filtration as it is transferred through conduits in the subsurface and the buildup of pollutants underneath can be detrimental to community and environmental health if not effectively mitigated. Because of the limited resources available to determine how stormwater runoff carries potential pollutants across the surface before being transferred to the karst subsurface and then reentering back on the surface across the landscape, this study aims to use geographic information systems (GIS) to investigate this problem. The objectives of this study are twofold. The first objective is to understand the transport mechanisms for stormwater runoff and how the movement through karst systems differs from non-karst systems, especially in regards to the surface and subsurface interactions. The second objective is to develop a general procedure for predicting stormwater runoff pathways in karst regions using GIS technologies and spatial analysis techniques – including identifying which data and techniques are essential to analyze surface and subsurface processes - to improve stormwater monitoring effectiveness. The premise of this study is broken down into a conceptual model with three significant components: Surface Input (stormwater runoff on surface), Subsurface Transport (stormwater transport through subsurface), and Output to Surface (output of stormwater to the surface via springs). The first component utilizes Hydrological Analysis and Network Analysis techniques to determine stormwater runoff pathways from potential point-source pollutant sites across surface to injection points where runoff enters subsurface. The second component uses Spatial Interpolation Techniques and Hydrological Analysis to predict subsurface accumulation areas that collect runoff from injection points and subsurface conduit pathways to output locations. The third and final component examines the output of the runoff back to the surface and identifies the locations where stormwater runoff can be sampled. The analyses of the Surface Input component proved to be effective in predicting the behavior of stormwater runoff between pollutant sites and their corresponding injection points. The analyses of the Subsurface Transport captured the overall patterns in the inferred dye tracing pathways that were used as the control dataset. The Output to Surface established the linkages among RCRA sites, their corresponding injection points and ultimately their output springs. These findings are very useful in developing informed stormwater sampling strategies and plans. In future investigations, these results could be verified with stormwater sampling and additional dye tracings and can be improved in two ways: more complete datasets of all stormwater features in the area – especially springs and drywells, and a more extensive and equally distributed dataset for groundwater depths across the study area to create a more accurate interpolated potentiometric surface.
104

Novel Bacterial Diversity in an Anchialine Blue Hole on Abaco Island, Bahamas

Gonzalez, Brett Christopher 2010 December 1900 (has links)
Anchialine blue holes found in the interior of the Bahama Islands have distinct fresh and salt water layers, with vertical mixing, and dysoxic to anoxic conditions below the halocline. Scientific cave diving exploration and microbiological investigations of Cherokee Road Extension Blue Hole on Abaco Island have provided detailed information about the water chemistry of the vertically stratified water column. Hydrologic parameters measured suggest that circulation of seawater is occurring deep within the platform. Dense microbial assemblages which occurred as mats on the cave walls below the halocline were investigated through construction of 16S rRNA clone libraries, finding representatives across several bacterial lineages including Chlorobium and OP8. In many blue holes, microbial metabolism of organic matter in the presence of seawater sulfate leads to anoxic and sulfidic conditions at or below halocline. Sunlight penetrating this sulfidic layer allows for in situ primary production to be dominated by bacterial anoxygenic phototrophs. Although water column chemistry and molecular genetic diversity of microbial mats in Cherokee Road Extension Blue Hole were investigated in this study, the full scope of the biogeochemistry of inland blue holes throughout the Bahamas Archipelago is complex and poorly understood. However, these microbial communities are clearly influenced by several factors including solar insolation, terrestrial and marine inputs of oxygen, carbon, and nutrients, water residence times, depth to the halo/chemocline, and cave passage geometry. The biogeochemistry of inland blue holes throughout the Bahamas is so distinctive which makes Abaco Island and the rest of the archipelago valuable as natural experiments, repositories of microbial diversity, and analogs for stratified and sulfidic oceans present early in Earth's history.
105

Palaeoclimatic Significance of Perennial Ice Accumulations in Caves: an Example from Scarisoara Ice Cave, Romania

Persoiu Tiritu, Aurel 01 January 2011 (has links)
Stable isotopes in ice cores drilled in the polar and high-mountain region have been used intensively to reconstruct past climatic changes and atmospheric dynamics. However, no similar studies have been conducted on perennial ice accumulations in caves due to a limited understanding of the links between the external and cave environments, and the way in which the climatic signal can be recorded by the cave ice. In this thesis, we successfully designed and build a research methodology for the reconstruction of past climatic changes based on perennial ice accumulation in caves, using as example the Scarisoara Ice Cave, Romania. The ice block in this cave preserves a large variety of candidate proxies for both past climate and environmental changes, the most significant ones being the stable isotopic composition of the ice (a proxy for air temperature) and pollen remains. The ice block has formed by the successive accumulation of layers formed by the freezing of water accumulated from late summer through mid-autumn precipitation. An original method has been developed for the reconstruction of the stable isotopic composition of water before freezing, and further, of the late summer air temperature. Pollen in the ice has been found to reflect changes in surface vegetation at both local and regional scale. A 22 m long ice core has been extracted from the ice block, and stable isotope analyses were performed at high resolution on its entire length. Twenty-sex radiocarbon ages have been used to derive a precise depth-age model for this core. The stable isotope data covers almost the entire Holocene, between 0.09 and 9.75 ka BP. The first order fluctuation broadly follows the orbitally induced Northern Hemisphere September insolation, with a minimum in the early Holocene, a slow climb towards a maximum at ~5.0 ka, followed by a very slow cooling towards the present, accentuated after ~0.5 ka. Superimposed on the long-term variations a series of rapid cooling events (RCE) are recorde, the most notable ones being at 9.5 ka, 8.2 ka, 7.9 ka, 6 ka, 4.2 ka, 3.2 ka and 0.9 ka. The timing of these RCEs agrees remarkably well with the Holocene rapid climatic changes and the ice rafted debris (IRD) events in the North Atlantic (NA). Our data suggests that the general trends of temperature changes in mainland Europe during the Holocene were governed by changes in solar output. RCEs were synchronous with NA IRD events, the NA climatic signal originating from sea surface temperature changes and being amplified by atmospheric dynamics. The stable isotope data spanning the past 2000 years clearly shows four climatic events over this interval, attributed to the Roman Warm period (RWP), the Dark Ages Cold Period (DACP), Medieval Warm Period (MWP) and the Little Ice Age (LIA). Our data suggests that air temperature was highly variable during the LIA and more stable during the warm MWP and RWP. As ice caves were described in many parts of the world otherwise poorly represented in ice-based paleoclimatology, the results of this study could open a new direction in paleoclimatic research, so that an array of significant paleoclimate data can be developed based on their study.
106

Digital Dunhuang: the use of new technology for off-site interpretation of a fragile heritage site

Chan, Fung-lin., 陳鳳蓮. January 2012 (has links)
 The group cave-temples in Dunguang, Gansu Province of north-western China offer an unparalleled display of grotto art of over a thousand years from the fourth century to the fourteenth century. They represent a microcosm of ancient and medieval civilizations, providing us with enormous opportunities of heritage experience and understanding. However, these grotto treasures are extremely fragile. Over the centuries they have been suffering from serious deterioration and damage due to human and natural causes, and in recent decades the ever-increasing visitor load has posed even greater threat to the murals. The emerging trend of using advanced technology in the preservation and the interpretation of the grotto art offers new possibilities of remote access and interpretation which shall enhance understanding and enjoyment of the cultural treasures. This dissertation sets out to examine such trend of digital interpretation of heritage in off-site scenarios. The research includes a background of the study, the significance of the Dunhuang Caves, the application of new technology, followed by a case study of re-presenting and interpreting one of the Dunhuang caves in Hong Kong. / published_or_final_version / Conservation / Master / Master of Science in Conservation
107

The karst of west-central Florida

Florea, Lee John 01 June 2006 (has links)
Caves, the cornerstone feature of karst aquifers, are little understood in Florida. This dissertation, which analyzes the morphology, elevation, lithologic setting, and hydrology of caves in west-central Florida, demonstrates that the karst of the unconfined Floridan aquifer differs from the paradigm view of karst presented in modern geology textbooks. The differences reflect setting: eogenetic (west-central Florida) vs. telogenetic (conventional). Interpretations about the architecture of cavernous porosity in this dissertation come from detailed surveys (497 stations) of seven air-filled caves.The surveys reveal that solution cavities within the unconfined Floridan aquifer align along NE-SW and NW-SE fractures. The surveys further identify tabular zones of cavernous porosity that extend for tens of meters. Characteristic "plus-sign" passages occur at the intersection of solution-enlarged fractures and the tabular horizons. The caves, as surveyed, do not connect points of discrete aquifer input to springs. Rather, they are separated by intact bocks of aquifer matrix, ever- narrowing fissures, sediment fills, and breakdown. With an additional 574 spot elevations from 63 previously surveyed air-filled and submerged caves and 526 foot-length cavities encountered in 26 drilled wells, the assembled data reveal that cave passages above and below the watertable of the unconfined Floridan aquifer cluster at similar elevations throughout west-central Florida. At the largest scale, the levels of cavities cut across geologic structure, thus suggesting a water-table origin. The close linkage of the water table and sea level this coastal setting suggests the levels reflect positions of paleosea level. Given that the air-filled caves in west-central Florida reflect higher sea levels,the coastline would have been close when the air-filled caves formed. The levels organize according to a sea-level datum at elevations of 30 m, 20-22 m, 12-15 m,and 3-5 m. The levels are similar in elevation to nearby terraces evident in GIS and LIDAR topographic data. The terraces correspond to the classic, Quaternary marine terraces of the coastal plain of the southeastern U.S.A. Given that the now-submerged caves reflect lower sea levels, the coastline was far from the caves when they formed. They organize according to a watertable datum at depths of 15 m, 30-40 m, 60-70 m, and > 100 m with some correspondence to marine terrace and paleoshoreline features identified on the sea floor of the west florida shelf using GIS and multibeam bathymetry. The multigenerational origin of these deeper caves masks the correspondence. Although past water tables are seen to be the first-order control of cave passages regionally, lithology appears to play a significant role at the scale of an individual cave. Approximately 2,000 measurements of matrix permeability from more than 228 m of continuous core from the unconfined Floridan aquifer of west-central Florida reveal a wide-ranging facies-dependent matrix permeability[log k(m2)= -12.9 +/- 1.6, total range]. Solution passages tend to be wider where the matrix permeability is greater. Time-series analysis on measurements of spring discharge from 31 springs and published time series from 28 additional sites reveal key differences between eogenetic and telogenetic karst aquifers, reflecting the difference in matrix permeability of the eogenetic [log k(m2) from -14 to -11] and telogenetic[log k(m2) from -15 to -20] limestones. For instance, log Q/Qmin flow-duration curves have greater slopes at eogenetic karst springs, a manifestation of lowerratios between the maximum and mean discharge (Qmax/Qmean). Additionally,aquifer inertia as defined on auto correlograms is greater in eogenetic karst than telogenetic karst.Hydrographs of spring flow and water level vary on a seasonal or longertime scale. The localized, convective-style storm events typical of the Florida summer rainy season are not realized as individual peaks in these hydrographs.Apparently, large, widespread, storm events, such as hurricanes in the late summer and fall and frontal systems in the winter and spring, are necessary to produce significant changes in storage. Data from nine pressure transducers in caves and in the aquifer matrix across the unconfined Floridan aquifer all record immediate increases in the water level due to Hurricanes Frances and Jeanne in September of 2004. The increases are simultaneous over large regions. These changes do not propagate through the aquifer as a pulse like the classic scenario of conduit flow in telogenetic karst aquifers.
108

Visual images of Vimalakīrti in the Mogao caves (581-1036)

Lin, Fan, 1972- January 2005 (has links)
This thesis examines the visual images of Vimalakirti, an ancient Indian lay Buddhist, painted on the walls of the Buddhist cave complex at Dunhuang, Gansu province, between 581 and 1036. The sixty-nine Vimalakirti, paintings preserved at Dunhuang are a valuable source for the exploration of historical, religious, and artistic dimensions of wall paintings and sutras. These visual images, together with other textual sources such as sutras, commentaries, and inscriptions, suggest a variety of interesting questions: Why was this theme repeatedly represented? Do the images all have the same prototype? Is there a spiritual function contained in the layout of the caves and composition of the wall paintings? Did the meaning of these images change according to historical context? Did the patrons have a political scheme in mind when commissioning these devotional artworks? While it is difficult to provide definitive answers to all these questions, this thesis will attempt to clarify them and offer preliminary answers on the basis of available visual and textual sources. / The introduction of this thesis includes an overview of basic concepts related to wall paintings, a short history of the transmission of the Vimalakirti,-nirdesa Sutra, and a review of past scholarship on Vimalakirti, paintings and related subjects. The body of the thesis is divided into three main chapters. The first chapter describes the important visual representations of Vimalakirti, before the Sui dynasty. The second chapter of the thesis will provide an introduction to representations of Vimalakirti, at Dunhuang from the late sixth to the early eleventh centuries. The third chapter examines the social functions and symbolic meanings of the Vimalakirti, paintings at Dunhuang.
109

Phylogeography of Darlingtonea Kentuckensis and Molecular Systematics of Kentucky Cave Trechines

Boyd, Olivia Frances 01 May 2015 (has links)
The monotypic cave carabid genus Darlingtonea is widely distributed along the eastern band of the Mississippian/Pennyroyal plateau in Kentucky and northern Tennessee. DNA sequence data from the mitochondrial gene cytochrome oxidase subunit I (COI) was collected from one to four individuals from 27 populations, and patterns of phylogeography and population structure were inferred from COI haplotypes. A hierarchical analysis of molecular variance found low nucleotide diversity within populations and statistically significant variation among geographically-defined groups tested based on two a priori hypotheses of structure. Population structure among five distinct genetic clusters identifies approximate locations of barriers to gene flow among closely grouped caves in the upper Rockcastle River drainage. Partial sequences of one mitochondrial (COI) and one nuclear (wingless) gene were gathered from 60 to 106 terminal taxa, including representatives of all five genera of cave trechines from Kentucky and Tennessee. Alignments were analyzed using maximum parsimony, Bayesian, and maximum likelihood methods of phylogenetic inference. Comparison of analyses demonstrates conflicting tree topologies among individual markers and different reconstruction methods. Despite a lack of consensus regarding genus-level relationships, most analyses supported each genus as natural (monophyletic) with the exception of Pseudanophthalmus
110

Rockshelters as unique cultural resources and distinct archaeological sites : a study of two rockshelters in Perry County, Indiana / Rock shelters as unique cultural resources and distinct archaeological sites

Nagle, Kimberly Jean January 2002 (has links)
Rockshelters are unique cultural resources whose diversity has been studied worldwide. In Indiana, this diversity has been overlooked and rockshelters have been classified as temporary habitation sites (Sieber et al. 1989). This characterization obscures a true understanding of what rockshelters were used for and has recently been shown as an inadequate means of interpretation of rockshelter utilization (Martin 2000, Water 2002). Through an examination of the depositional environments, preservation, artifacts, and various components found within rockshelters, this thesis will show the diversity found in these sites. An analysis of two rockshelters, 12-Pe-319 and 12-Pe-320, that have not been previously reported on will be used in this evaluation. / Department of Anthropology

Page generated in 0.0266 seconds