1,720,999 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Karst Hydrogeology and Geomorphology of the Sierra de El Abra and the Valles-San Luis Potosí Region, México
No full textThe general objective of this work was to develop a basic understanding of the karst hydrology, the nature and origin of the caves, the water chemistry, the surface geomorphology, and relationships among these aspects for a high relief tropical karst region having a thick section of limestone. The Valles-San Luis Potosí region of northeastern México, and in particular, the Sierra de El Abra, was selected for the study. A Cretaceous Platform approximately 200 km wide and 300 km long (N-S) delimits the region of interest. A thick Lower Cretaceous deposit of gypsum and anydrite, and probably surrounded by Lower Cretaceous limestone facies, is overlain by more than 1000 m of the thick-bedded middle Cretaceous El Abra limestone, which has a thick platform-margin reef. The Sierra de El Abra is a greatly elongated range along the eastern margin of the Platform. During the late Cretaceous, the region was covered by thick deposits of impermeable rocks. During the early Tertiary, the area was folded, uplifted, and subjected to erosion. A high relief karst having a wide variety of geomorphic forms controlled by climate and structure has developed. Rainfall in the region varies from 250-2500 mm and is strongly concentrated in the months June-October, when very large rainfalls often occur. A number of specific investigations were made to meet the general objective given above, with special emphasis on those that provide information concerning the nature of ground-water flow systems in the region. Most of the runoff from the region passes through the karstic subsurface. Large portions of the region have no surface runoff whatsoever. The El Abra Formation is continuous over nearly the whole Platform, and it defines a region of very active ground-water circulation. Discharge from the aquifer occurs at a number of large and many small springs. Two of them, the Coy and the Frío springs group, are among the largest springs in the world with average discharges of approximately 24 m³/sec and 28 m³/sec respectively. Most of the dry season regional discharge is from a few large springs at low elevations along the eastern margin of the Platform. The flow systems give extremely dynamic responses to large precipitation events; floods at springs usually crest roughly one day after the causal rainfall and most springs have discharge variations (0max/0min) of 25-100 times. These facts indicate well-developed conduit flow systems. The hydrochemical and hydrologic evidence in combination with the hydrogeologic setting demonstrate the existence of regional ground-water flow to several of the large eastern springs. Hydrochemical mixing-model calculations show that the amount of regional flow is at least 12 m³/sec, that it has an approximately constant flux, and that the local flow systems provide the extremely variable component of spring discharge. The chemical and physical properties of the springs are explained in terms of local and regional flow systems. Local studies carried out in the Sierra de El Abra show that large conduits have developed, and that large fluctuations of the water table occur. The large fossil caves in the range were part of great deep phreatic flow systems which circulated at least 300 m below ancient water tables and which discharged onto ancient coastal plains much higher than the present one. The western margin swallet caves are of the floodwater type. The cave are structurally controlled. Knowledge gained in this study should provide a basis for planning future research, and in particular for water resource development. The aquifer has great potential for water supply, but little of that potential is presently used.Doctor of Philosophy (PhD
Cavern Development in the Dimensions of Length and Breadth
Full text linkThree conceptual models are proposed for the integration of the large systems of conduits responsible for groundwater flow in soluble rocks. These models are supported by laboratory experiments with scaled solution models, flow-field analogues, and evidence from existing caves. The three models reflect different boundary conditions imposed by geologic structure and stratigraphy. They have three characteristics in common. First, the smaller elements of the larger systems propagate separately from points of groundwater input toward points of discharge as distributary networks. Second, the integration of the smaller networks proceeds headward from the resurgence, in a stepwise fashion. Third, the result of the integration process in each case is a tributary system with many inputs discharging through a single discharge point. The potential for growth of each of the smaller networks, within a common pressure field, is related to its distance from the discharge boundary and the distribution of other inputs. The first input to establish a low-resistance link to the discharge boundary will effect a localized depression within the potential field, thus attracting the flow and redirecting the growth of nearby networks until they eventually link with it. As additional orders of links develop, the system takes on a tributary pattern. The first model applies to steeply dipping rocks. Inputs occur where bedding planes are truncated by erosion, and discharge takes place to the strike. Conduits in this case evolve as a roughly rectangular grid of strike and dip oriented elements. Dip elements are the initial form, with subsequent integration along the strike. The type example is the Holloch in Switzerland. The second model applies to flat-lying rocks. Inputs occur over a broad area, and discharge takes place along a linear boundary. Conduits in this case evolve in a trellised array with elements normal to the discharge boundary predating those parallel to it. These latter conduits integrate the flow. The type example is the Mammoth Cave Region, Kentucky. The third model applies to simple systems which occur beneath an impermeable cap rock. Inputs occur where erosion has breached the capping beds. The type example is Cave Creek, Kentucky.Doctor of Philosophy (PhD
Hydrochemistry, etc. of the Caves Branch Karst, Belize
No full textAn extensive karst developed on Cretaceous limestones in Belize, Central America, was the site of a hydrochemical, hydrologic, and morphologic study. This thesis describes the results of analysis of several hundred water samples from this humid tropical environment (mean annual rainfall - 2376 mm; temperature - 24.5°C). An unusual positively correlated discharge/total hardness loading curve in a major cavern conduit is explained as due to a two-component mixing model. Hydrologic modelling, soil CO₂ sampling, and discriminant analysis were used to infer the interior structure of a karst aquifer. Minimum effective porosity was determined to be 0.7%. Mean areal hardness of 187 mg/L (as CaCO₃) was found for springs draining the aquifer, indicating a denudation rate of about 90 m³/Km²/year. Aqueous Pco₂ of these springs was 1.1%, significantly higher than the 0.7% of mean karst soil CO₂ levels. This implies open system calcite solution evolution and/or internal CO₂ production within the aquifer. Various morphologic analyses suggest the cockpit-type surfaces of numerous karsts in the tropics may be significant due to disaggregation of existing topographic lows originally formed by creation of a fluvial topography. These fluvial valleys acted as favorable sites for concentration of aggressive water and consequent cockpit formation. Over 40 km of cavern passage were explored in the Caves Branch, including one of the largest tropical cavern systems known. Cavern development appeared to have been chiefly influenced by regional fracture patterns and topographic dip. The present development was completed by at least 140,000-215,000 years B.P., according to results of speleothems dated by the uranium/thorium disequilibrium method.Doctor of Philosophy (PhD
The Littoral Karren of Neroutsos Inlet Northern Vancouver Island
Full text link Limestones exposed in the intertidal zone display numerous pits and basins which form where bodies of water are isolated during tidal retreat. These harbour both macro- and microscopic organisms whose metabolites enhance aggressivity and cause solution; grazing and boring activities further aid rock removal. In this area the basins are similar in shape throughout the littoral zone but they vary in size, the maximum relief being at mid tide level. Unlike the exposed west coast of Ireland, zonation is not well defined: the clearly
identifiable morphologies associated with the biological zones in Ireland are not displayed here. Instead it resembles the karren of the more sheltered Bristol channel area but with less mechanical erosion. In both of these areas variations in lithology affect the details of the
geomorphology, some beds being significantly more fractured and less pitted than others.ThesisCandidate in Philosoph
Karren On Quatsino Fm. Dip Slopes Recently Exposed By Deforestation Northern Vancouver Island
No full text This study reports on karren forms on limestone dip slopes, which were recently exposed by deforestation on the Quatsino Formation and observable relationships of the karren features of a specific sl~pe are represented as a detailed map. Also, many relationships of gravitomorphic runnel characteristics are analyzed for significance. Runnel types being considered are Hortonian, decantation and composite forms. Solution runnel width, depth and width/depth ratio are studied in association with length. These relationships determine whether the runnel types conform to a theoretical model. Typical aeas·ares of the karren in this area were also recorded. Composite forms are the most abundant because Hortonian and decantation runnels amalgamate beyond about 3m to form composites. All the runnel types, excluding the decanters, illustrate the perfect minimum friction open-channel cross-section. ThesisBachelor of Arts (BA
Investigations into the fluorescence of calcitic speleothems
No full textVariations in fluorescence in calcite speleothems may record environmental changes above a cave. It is established that many display annual banding of colour or fluorescence or both, but it is not known what produces the bands or what is the environmental significance of the variability in their fluorescence or thicknesses. Analysis of speleothem feed waters at Marengo Cave, Indiana, found that peak fluorescence values are highest in the spring when soil organics are flushed into the cave or during the early Fall drought. These seasonal characteristics permit annual sequences of fluorescence intensity to be recognized in many speleothems. A comparison of seasonal variability in quantity and types of organic substances in sod and cave waters found that the former display little seasonality in organic concentrations compared to cave waters' peak yields in the spring and fall. Fluorescence studies revealed shorter peak excitation and emission wavelengths in the cave waters, due to differences in concentration and significant changes in the proportional organic assemblages. Precipitation affects the fluorescence in both waters, with the dry fall producing the highest fulvic acid and particulate organic matter yields. Molecular size fractionation determined that larger hydrophobic compounds are preferentially removed from the percolation water and the smaller hydrophilic compounds become the dominant fluorophore in cave drips. Fluorescence of twelve sample speleothems (and extracts) from a wide range of geographical environments gave similar spectra, with broad emission maxima centred around 410-430 nm and two excitation maxima at approximately 255 nm and 330 nm. Trace elements are not responsible for these spectra. Organic acids, particularly fulvic acid, were the dominant fluorophore in the calcite, confirming the Marengo Cave results that show low molecular weight (Doctor of Philosophy (PhD
The Generation of Small Scale Relief Features of Eroded Limestone: A Study of Erosional Scallops
No full text Proposed theories concerning the nature and mode of formation of limestone scallops are examined. Some progress is made toward a purely theoretical understanding. Scallop formation is simulated by generation on blocks of Plaster of Paris in a laboratory flume under known and controlled conditions and the relationships between the resulting features, the generating conditions and the base material examined. Field Evidence both confirms these relationships and reveals other unsuspected factors. The similarity between these features and others found on ablating snow surfaces is investigated and the same laws found to apply. ThesisDoctor of Philosophy (PhD
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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