192 research outputs found
Academic authorship: who, why and in what order?
No full textWe are frequently asked by our colleagues and students for advice on authorship for scientific articles. This short paper outlines some of the issues that we have experienced and the advice we usually provide. This editorial follows on from our work on submitting a paper1 and also on writing an academic paper for publication.2 We should like to start by noting that, in our view, there exist two separate, but related issues: (a) authorship and (b) order of authors. The issue of authorship centres on the notion of who can be an author, who should be an author and who definitely should not be an author, and this is partly discipline specific. The second issue, the order of authors, is usually dictated by the academic tradition from which the work comes. One can immediately envisage disagreements within a multi-disciplinary team of researchers where members of the team may have different approaches to authorship order
Modeling and Inversion Methods for the Interpretation of Resistivity Logging Tool Response
No full textThe electrical resistivity measured by well logging tools is one of the most important rock parameters for indicating the amount of hydrocarbons present in a reservoir. The main interpretation challenge is to invert the measured data, solving for the true resistivity values in each zone of a reservoir. Inversion is not always an easy task because logging tools measure a bulk average resistivity. Thus reservoir heterogeneity can have a considerable effect on inversion accuracy. Two of the most significant problems are effects caused by regions adjacent to zones of interest and resistivity anisotropy (variation of resistivity with direction). The growing use of directional drilling has recently focused attention on the magnitude of anisotropy effect. Therefore this thesis concentrates on the new area of inversion in anisotropic reservoirs. The geologic origins of anisotropy are examined, and a parametric inversion method is introduced for obtaining directional resistivity values in layered media. Background is also provided on practical modeling methods for use in inversion, and on the physics of various resistivity loggingtools.Information Systems and Technolog
Расчет фокусировки ионов с помощью плазменных электростатических линз в магнитном поле, созданном токами кольца счетчиков
No full textThe author would like to thank B.I. Ivanov for the proposition of the work subject, help in the work, and fruitful discussions
Coupling of eN transition prediction method with Reynolds-Averaged Navier-Stokes solver ENFLOW
No full textAerospace EngineeringAerodynamics, Wind Energy & Propulsio
Current Status Censoring Models: Smooth estimators and their asymptotic properties
No full textStatistics deals with answering questions based on collected data. In medical applications, the quantity of interest can often not be observed directly. They are censored. It is a challenge to answer the question as precisely as possible based on the incomplete data. The quantity of interest can be censored in many different ways. In HIV vaccine trials, censoring results in “current status continuous mark” data. This is a very specific type of censoring and the method of maximum likelihood that usually works very well does not work in this case. Hence, alternative methods are needed. In this thesis, different alternative methods are introduced and studied from different perspectives.Statistics and ProbabilityElectrical Engineering, Mathematics and Computer Scienc
Расчет фокусировки ионов с помощью плазменных электростатических линз в магнитном поле, созданном токами кольца счетчиков
No full textThe author would like to thank B.I. Ivanov for the proposition of the work subject, help in the work, and fruitful discussions
Optimizing the Performance of Data Analytics Frameworks
No full textData analytics frameworks enable users to process large datasets while hiding the complexity of scaling out their computations on large clusters of thousands of machines. Such frameworks parallelize the computations, distribute the data, and tolerate server failures by deploying their own runtime systems and distributed filesystems on subsets of the datacenter resources. Most of the computations required by data analytics applications are conceptually straight-forward and can be performed through massive parallelization of jobs into many fine-grained tasks. Providing efficient and fault-tolerant execution of these tasks in datacenters is ever more challenging and a variety of opportunities for performance optimization still exist. In this thesis we optimize the job performance of data analytics frameworks by addressing several fundamental challenges that arise in datacenters. The first challenge is multi-tenancy: having a large number of users may require isolating their workloads across multiple frameworks. Nevertheless, achieving performance isolation is difficult, because different frameworks may deliver very unbalanced service levels to their users. Second, users have become very demanding from these frameworks, thus expecting timely results for jobs that require only limited resources. However, even with a few long jobs that consume large fractions of the datacenter resources, short jobs may be delayed significantly. Third, improving the job performance in the face of failures is harder still, as we need to allocate extra resources to recompute work which was already done. In order to address these challenges we design, implement, and test several scheduling policies for the evolving usage trends that are derived from the analysis of basic theoretical models. We take an experimental approach and we evaluate the performance of our policies with real-world experiments in a datacenter, using representative workloads and standard benchmarks. Furthermore, we bridge the gap between those experiments and prior theoretical work by performing large-scale simulations of scheduling policies
Fraccability determination of a Posidonia Shale Formation analogue through geomechanical experiments and micro-CT fracture propagation analysis
No full textGas resources in The Netherlands are steadily running scarce, therefore alternative gas resources are necessary. One of those alternatives present in the Dutch subsurface is shale gas, present in among others the Posidonia Shale Formation (PSF). Little is known about this formation and drilled cores are rare. This study therefore focuses on a time and depositional equivalent in the U.K.: the Whitby Mudstone Formation (WMF). Stimulating the production of a reservoir by hydraulic fracturing (fraccing) is necessary in order to produce the gas economically viable. To determine the prospectivity of this fraccing (fraccability), several concepts are assessed, e.g. Brittleness Index (B.I.) (Rickman et al. 2008), Fracture Toughness (KIC) (Lawn & Wilshaw 1975) and Fraccability Index (F.I.) (Jin et al. 2014). The fraccability of the WMF is determined through geomechanical experiments and X-ray micro-computed tomography fracture propagation analysis. Samples were taken along an exhumed outcrop 8 meter in height. To account for anisotropy, experiments were conducted at different angles to the bedding. The applied unconfined stress to create new fractures in repetitive tests, depends on the interplay of the already present fractures. Fractures that do not reach the sample’s edges, simulate a triaxial ellipsoid shape and follow a sublinear aperture-length ratio. The WMF results show low KIC-values, which is favorable, but scattered B.I. and F.I. values, which do not provide a clear view on the prospectivity of the WMF. In general, the B.I. and F.I. provide important insights in fraccability, though its significance is relative. Values can be compared with other datasets or intervals under the condition that the same limits of experimentally measured Young’s Modulus, Poisson’s Ratio and Fracture Toughness in these concepts are applied. The WMF thus exhibits a questionable fraccability. Near the formation’ top and bottom, fraccing is preferred opposed to the middle. But weathering and exhumation of the WMF samples has certainly had its effect on the quality and uncertainty of the results.Petroleum EngineeringGeoscience & EngineeringCivil Engineering and Geoscience
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