1,720,955 research outputs found
Effects of internal structure and local stresses on fracture propagation, deflection, and arrest in fault zones
No full textThe way that faults transport crustal fluids is important in many fields of earth sciences such as petroleum geology, geothermal research, volcanology, seismology, and hydrogeology. For understanding the permeability evolution and maintenance in a fault zone, its internal structure and associated local stresses and mechanical properties must be known. This follows because the permeability is primarily related to fracture propagation and their linking up into interconnected clusters in the fault zone. Here we show that a fault zone can be regarded as an elastic inclusion with mechanical properties that differ from those of the host rock. As a consequence, the fault zone modifies the associated regional stress field and develops its own local stress field which normally differs significantly, both as regard magnitude and orientation of the principal stresses, from the regional field. The local stress field, together with fault-rock heterogeneities and interfaces (discontinuities; fractures, contacts), determine fracture propagation, deflection (along discontinuities/interfaces), and arrest in the fault zone and, thereby, its permeability development. We provide new data on the internal structure of fault zones, in particular the fracture frequency in the damage zone as a function of distance from the fault core. New numerical models show that the local stress field inside a fault zone, modelled as an inclusion, differ significantly from those of the host rock, both as regards the magnitude and the directions of the principal stresses. Also, when the mechanical layering of the damage zone, due to variation in its fracture frequency, is considered, the numerical models show abrupt changes in local stresses not only between the core and the damage zone but also within the damage zone itself. Abrupt changes in local stresses within the fault zone generate barriers to fracture propagation and contribute to fracture deflection and/or arrest. Also, analytical solutions of the effects of material toughness (the critical energy release rate) of layers and their interfaces show that propagating fractures commonly become deflected into, and often arrested at, the interfaces. Generally, fractures propagating from a compliant (soft) layer towards a stiffer one tend to become deflected and arrested at the contact between the layers, whereas fractures propagating from a stiff layer towards a softer one tend to penetrate the contact. Thus, it is normally easier for fractures to propagate from the host rock into the damage zone than vice versa. Similarly, it is easier for fractures to propagate from the outer, stiffer parts of the damage zone to the inner, softer parts, and from the stiff host rock to the outer damage zone, than in the opposite directions. These conclusions contribute to increased understanding as to how fractures propagate and become arrested within fault zones, and how the fault zone thickness is confined at any particular time during its evolution. (C) 2009 Elsevier Ltd. All rights reserved.Norwegian Research Council [163316/S30
Inverse modeling for estimating fluid-overpressure distributions and stress intensity factors from an arbitrary open-fracture geometry
No full textWe present a new solution for estimating the fluid overpressure (driving-pressure or net-pressure) acting on the walls of a fracture with an arbitrary opening displacement. In the paper, we first present a forward modeling solution, using Fourier cosine series, for the opening displacement of a fracture subject to an overpressure that varies irregularly along the length of a fracture. By changing the form of the solution, we provide a matrix equation for estimating the Fourier coefficients and thereby obtain the overpressure variation from the fracture geometry. As numerical tests of this inverse analysis, we estimated the overpressure variation from fracture-opening displacements given by well known analytical solutions, and found that this method can be used for overpressure estimates for a variety of fluid-driven fractures. We apply our solutions to a mineral vein hosted by gneiss (West Norway) and conclude from the aperture variation that, at the time of vein formation, the overpressure increased toward the vein tip. We also discuss the physical meaning of the Fourier coefficients by applying our results to man-made hydraulic wing fractures. The results indicate that the coefficients of n = 0 and n = 1 relate to the fluid overpressure and the critical stress intensity factor. (c) 2012 Elsevier Ltd. All rights reserved
Effects of overpressure variations on fracture apertures and fluid transport
No full textFor an isolated rock fracture in a homogeneous, isotropic rock subject to constant internal fluid overpressure or constant external driving stress, the ideal opening-displacement (aperture) profile or variation is that of a flat ellipse. For many mineral veins, dykes, tension fractures, normal faults, and other rock fractures, however, the opening-displacements show irregular aperture (thickness) variations very different from that of a flat ellipse. Here we present field data on typical fracture-aperture variations, as well as new numerical and analytical models to explain these data. We present the overpressure variation by Fourier cosine series, a very flexible method that can be used to model abrupt overpressure and driving-stress variations in vertical and lateral sections for fractures of various sizes and types. We calculate the opening-displacements of typical hydrofractures, and discuss the results with reference to mineral veins and dykes. We also present numerical models showing that when a fracture dissects layer, or parts of a single layer (such as a lava flow), with different stiffnesses (Young's moduli), the opening-displacement may show irregular variation even when the overpressure is constant. From the cubic law, the volumetric flow rates in the large-aperture segments of the mineral veins and dykes discussed in the paper may have been as much as 3-5-times the flow rates in the small-aperture segments. We propose that differences in volumetric flow rates are related to irregular opening-displacement variations in feeder-dykes is one principal reason for the development of crater cones, a universal feature of volcanic fissures. (C) 2012 Elsevier B.V. All rights reserved
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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