1,721,256 research outputs found
Growth of borehole breakouts with time after drilling: Implications for state of stress, NanTroSEIZE transect, SW Japan
Get PDFResistivity at the bit tools typically provide images of wellbore breakouts only a few minutes after the hole is drilled. In certain cases images are taken tens of minutes to days after drilling of the borehole. The sonic caliper can also image borehole geometry. We present four examples comparing imaging a few minutes after drilling to imaging from about 30 min to 3 days after drilling. In all cases the borehole breakouts widen with time. The tendency to widen with time is most pronounced within a few hundred meters below the seafloor (mbsf), but may occur at depths greater than 600 mbsf. In one example the widening may be due to reduced borehole fluid pressure that would enhance borehole failure. In the three other cases, significant decreases in fluid pressure during temporal evolution of breakouts are unlikely. The latter examples may be explained by time-dependent failure of porous sediments that are in an overconsolidated state due to drilling of the borehole. This time-dependent failure could be a consequence of dilational deformation, decrease of pore fluid pressure, and maintenance of sediment strength until migrating pore fluids weaken shear surfaces and allow spallation into the borehole. Breakout orientations, and thus estimates of stress orientations, remain consistent during widening in all four cases. In vertical boreholes, breakouts wider than those initially estimated by resistivity imaging would result in higher estimates of horizontal stress magnitudes. Because the vertical overburden stress is fixed, higher estimated horizontal stresses would favor strike-slip or thrust faulting over normal faulting
Structural styles across the Nankai accretionary prism revealed from LWD borehole images and their correlation with seismic profile and core data: Results from NanTroSEIZE Stage 1 expeditions
Get PDFFour drill sites of IODP NanTroSEIZE Stage 1 Expedition transected the Nankai Trough, offshore SW Japan, from the deformation front to the Kumano fore-arc basin. Borehole resistivity images from the logging-while-drilling (LWD) data were analyzed to extract orientations of faults, fractures, and bedding planes to examine the structural styles. On the basis of these features, drilling intervals were classified into fore-arc basin deposits, surface slope sediments, and deformed accretionary wedge, and these can be compared with characteristics from seismic profiles and core structural data. Bedding orientations identified in these three data sets are generally comparable, but the difference in resolution between the data sets produces different results in interpretation where geology is highly deformed or includes finer internal structures. Faults can also be correlated between these three data sets, but the differences in their appearance require special attention for accurate correlation. Many faults imaged in seismic profiles actually consist of microfracture systems, as shown in cores, that can also be identified in borehole images. Some clear faults in seismic profiles cannot be identified in borehole images, probably because of their minimal resistivity contrast with the surrounding rocks or a more complex fault zone at the borehole scale. These results suggest that these three data sets can be used to extract not only the general structure but also different styles of deformation at different scales from core samples (mm to cm), to LWD (mm to 10 m), to seismic (10 m to tens of km). This correlation requires a deep understanding of the resolution and shortcomings of each methodology
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
<Research Report>Photoinduced conductive domains in quantum paraelectric SrTiO[3] and ferroelectric Sr[1-x]Ca[x]TiO[3]
No full textDielectric responses of quantum paraelectric SrTiO[3] and ferroelectric Sr[1-x]a[x]TiO[3] under photoexcitation have been investigated. In Sr[1-x]Ca[x]TiO[3], we observed the photoinduced reduction of ferroelectric transition temperature Tc, in addition to photoinduced Debye dispersion reported in nominally pure SrTiO[3]. The photoinduced Tc-reduction is attributed to the screening effect by Coulomb interaction between Ca-induced dipoles in Sr[1-x]Ca[x]TiO[3]. This implies that the mobile photocarriers are also involved in the photoinduced Debye dispersion. We supposed the conductive domains with mobile carriers should be partly created by photoexcitation and the photoinduced Debye dispersion was well reproduced by Maxwell-Wagner model
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