1,720,968 research outputs found
Efficient probabilistic inversion of geophysical data
Get PDFEstimation of uncertainties is critical for subsequent decision making in all applications
of geosciences such as geological hazard analysis and risk mitigation, management and
exploitation of subsurface resources, and environmental waste disposal. More efficient
probabilistic inversion methods in geosciences are vital to making rapid and improved
predictions of geological hazards and estimation of subsurface resources from geophysical
data, and estimation of associated uncertainties. While this thesis focuses on seismic data
inversion for the estimation of geological properties, the methods developed may find a wide
variety of applications in all fields of research that involve spatial data analysis.
New concepts, models and methods are developed to perform more efficient
probabilistic inversion by making use of the latest developments in machine learning and
Bayesian inverse theory to solve geophysical inverse problems. The major contribution of this
thesis is the development of efficient geostatistical inversion methods for approximate
inference for structured inverse problems where probabilistic dependence between unknown
model parameters may be expressed as a Markov random field (MRF). These methods are
many orders of magnitude faster than the corresponding sampling based methods in such
types of inverse problems. Further, some of the commonly used but avoidable assumptions in
conventional geostatistical inversion methods are progressively relaxed and finally removed in
this research. The faster inversion methods allow more complex models to be evaluated for
more accurate predictions and improved estimation of uncertainty for given compute power
and time.
Most existing geostatistical inversion methods are based on the localized likelihoods
assumption, whereby the seismic data at a location are assumed to depend on the geology
only at that location. Such an assumption is unrealistic because of imperfect seismic data
acquisition and processing, and fundamental limitations of seismic imaging methods. It is also
assumed in most such previous research that the data are completely free of any correlated
noise or errors. Although these requirements are almost never met in reality, existing methods
use these assumptions to make solutions computationally tractable. Both of these
assumptions are progressively removed in this thesis while still allowing computationally
tractable solutions to be found for suitably structured problems. The class of problems
considered here spans a broad range of spatial data analysis and geosciences, where geology at a location is assumed to depend directly only on the geology within some pre-specified
neighbourhood of that location – the so called Markovian assumption – which is the core
assumption across the entire literature of geostatistics and has been proven to be valid for all
practical purposes.
Exact Bayesian inference is intractable in most models of practical interest because it
requires normalization of the posterior distribution by integrating model parameters over a
very high dimensional space. Therefore, approximate inference is used in practice. Stochastic
sampling (e.g., by using Markov-chain Monte Carlo – McMC) is the most commonly used
approximate inference method but is computationally expensive and detection of its
convergence is often based on subjective criteria and hence is unreliable. New Bayesian
inversion methods are introduced that estimate the spatial distribution of geological
properties from attributes of seismic data, by showing how the usual probabilistic inverse
problem can be solved using an optimization framework while still providing full probabilistic
results – the so called variational inference approach. The intractable posterior distribution is
replaced by a tractable approximation in the variational approach. Inference can then be
performed using the approximate distribution in an optimization framework, thus
circumventing the need for sampling, while still providing probabilistic results.
The methods developed in this thesis infer the post-inversion (posterior) probability
density of the unknown model parameters from seismic data and geological prior information.
These methods are shown to be robust against weak prior information and correlated noise in
the data. The methods are computationally efficient, and are expected to be applicable to 3D
models of realistic size on modern computers without incurring any significant computational
limitations
Public investment, private investment, governance and tourism growth in five South Asian Association for Regional Cooperation countries
Get PDFThe present research investigates the effects of public and private investment in Travel and Tourism (T&T), and their interaction effect on tourism growth in five South Asian
Association for Regional Cooperation (SAARC) countries. It also examines the interaction effect of public and private investment with governance on tourism growth in the region. The panel data for the five SAARC countries, from 1996 to 2015, is analyzed using Fully Modified Ordinary Least Squares and Pooled Mean Group methods. The study findings reveal that public investment, private investments, and their interaction positively affect tourism growth. The interaction effects of governance with public and private investments produce mixed results for the three indicators of governance. The interaction of political stability and absence of violence with private investment shows positive effect, however, its interaction with public investment illustrates negative effect on tourism growth. In addition, the interaction effect of control of corruption and public investment on tourism growth is positive, while there is an evidence of negative effect of the interaction of control of corruption and private investment. Similarly, the interaction effect of rule of law and public investment on tourism growth is positive, whereas, it is negative in case of the interaction of rule of law and private investment. Therefore, it is recommended that public investment needs to be increased in T&T, in addition to ensure conducive environment for private sector participation in order to reap its full potential. The study also suggests improving the governance, as it enhances the efficiency and productivity of public and private investments in T&T
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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