1,721,069 research outputs found
An overview of the eruption of Soufriere Hills Volcano, Montserrat from 2000 to 2010
No full textThe 1995–present eruption of Soufrière Hills Volcano on Montserrat has produced over a cubic kilometre of andesitic magma, creating a series of lava domes that were successively destroyed, with much of their mass deposited in the sea. There have been five phases of lava extrusion to form these lava domes: November 1995–March 1998; November 1999–July 2003; August 2005–April 2007; July 2008–January 2009; and October 2009–February 2010. It has been one of the most intensively studied volcanoes in the world during this time, and there are long instrumental and observational datasets. From these have sprung major new insights concerning: the cyclicity of magma transport; low-frequency earthquakes associated with conduit magma flow; the dynamics of lateral blasts and Vulcanian explosions; the role that basalt–andesite magma mingling in the mid-crust has in powering the eruption; identification using seismic tomography of the uppermost magma reservoir at a depth of 5.5 > 7.5 km; and many others. Parallel to the research effort, there has been a consistent programme of quantitative risk assessment since 1997 that has both pioneered new methods and provided a solid evidential source for the civil authority to use in mitigating the risks to the people of Montserrat
Inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs: an example from the Ocean Drilling Program
Full text linkIn boreholes with partial or no core recovery, interpretations of lithology in the remainder of the hole are routinely attempted using data from downhole geophysical sensors. We present a practical neural net-based technique that greatly enhances lithological interpretation in holes with partial core recovery by using downhole data to train classifiers to give a global classification scheme for those parts of the borehole for which no core was retrieved. We describe the system and its underlying methods of data exploration, selection and classification, and present a typical example of the system in use. Although the technique is equally applicable to oil industry boreholes, we apply it here to an Ocean Drilling Program (ODP) borehole (Hole 792E, Izu-Bonin forearc, a mixture of volcaniclastic sandstones, conglomerates and claystones). The quantitative benefits of quality-control measures and different subsampling strategies are shown. Direct comparisons between a number of discriminant analysis methods and the use of neural networks with back-propagation of error are presented. The neural networks perform better than the discriminant analysis techniques both in terms of performance rates with test data sets (2–3 per cent better) and in qualitative correlation with non-depth-matched core. We illustrate with the Hole 792E data how vital it is to have a system that permits the number and membership of training classes to be changed as analysis proceeds. The initial classification for Hole 792E evolved from a five-class to a three-class and then to a four-class scheme with resultant classification performance rates for the back-propagation neural network method of 83, 84 and 93 per cent respectively
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Use of a portable topographic mapping millimetre wave radar at an active lava flow.
Full text linkA ground-based millimetre wave radar, AVTIS (All-weather Volcano Topography Imaging Sensor), has been developed for topographic monitoring. The instrument is portable and capable of measurements over ranges up to ∼7 km through cloud and at night. In April and May 2005, AVTIS was deployed at Arenal Volcano, Costa Rica, in order to determine topographic changes associated with the advance of a lava flow. This is the first reported application of mm-wave radar technology to the measurement of lava flux rates. Three topographic data sets of the flow were acquired from observation distances of ∼3 km over an eight day period, during which the flow front was detected to have advanced ∼200 m. Topographic differences between the data sets indicated a flow thickness of ∼10 m, and a dense rock equivalent lava flux of ∼0.20 ± 0.08 m3s−1
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
AVTIS observations of lava dome growth at Soufrière Hills Volcano, Montserrat : 2004-2011
No full textTo solve the problem of lava dome growth at Soufrière Hills Volcano (SHV) being invisible and unmeasured owing to cloud, we have designed, built and deployed a ground-based millimetre-wave radar/radiometer: the All-weather Volcano Topography Imaging Sensor (AVTIS). In this chapter, after an outline technical sketch of the instruments, we describe the campaigns between 2004 and 2011 used to test their capabilities. We then present results from the campaigns to illustrate how signals of volcanological interest can be retrieved. The primary measurements of AVTIS are range (to within, at best, about 1 m), and, from that, topography, topographical change and effusion rates, and surface temperature (to within a few degrees Celsius). Changes in radar reflectivity can indicate surface processes (e.g. mass wasting). Surface motion within the instantaneous field of view produces a Doppler signal that allows detection of rockfall. Attenuation of the signal by rain along the path can, when stacked temporally, give an image of rain cloud structure and, by calibration, a rate of rainfall. We regard a strategy of two radars – one permanantly mounted (at Windy Hill) autonomous instrument, and the other used as a rover – as being best for capturing dome growth
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
Lithological classification within ODP holes using neural networks trained from integrated core-log data
No full textNeural networks offer an attractive way of using downhole logging data to infer the lithologies of those sections of ODP holes from which there is no core recovery. This is best done within a computer program that enables the user to explore the dimensionality of the log data, design the structure for the neural network appropriate to the particular problem and select and prepare the log- and core-derived data for training, testing and using the neural network as a lithological classifier. Data quality control and the ability to modify lithological classification schemes to particular circumstances are particularly important. We illustrate these issues with reference to a 250 m section of ODP Hole 792E drilled through a sequence of island arc turbidites of early Oligocene age. Applying a threshold of > 90% recovery per 9.7 m core section, we have available about 50% of the cored interval that is sufficiently well depth-matched for use as training data for the neural network classifier. The most useful logs available are from resistivity, natural gamma, sonic and geochemistry tools, a total of 15. In general, the more logs available to the neural network the better its performance, but the optimum number of nodes on a single ‘hidden’ layer in the network has to be determined by experimentation. A classification scheme, with 3 classes (claystone, sandstone and conglomerate) derived from shipboard observation of core, gives a success rate of about 76% when tested with independent data. This improves to about 90% when the conglomerate class is split into two, based on the relative abundance of claystone versus volcanic clasts
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