1,721,042 research outputs found
Mapping sub-pixel variation in land cover at the global scale using NOAA AVHRR imagery
No full textRemote sensing studies have tended to be conducted at local to regional scales. However, recently attention has increasingly been focused at regional to global scales. Remote sensing imagery with moderate and coarse spatial resolutions (for example, the National Oceanographic and Atmospheric Administration (NOAA) Advanced Visible High Resolution Radiometer (AVHRR) with a spatial resolution of (1.1 km by 1.1 km) are ideal for this since large contiguous regions are completely covered and data are provided synoptically. One problem which such imagery is that the intrinsic scale of spatial variation in much land cover (for example, New Forest area in the U.K.) is finer than the scale of sampling imposed by the image pixels. The result is that most pixels contain a mixture of land cover classes.Where the intrinsic scale of spatial variation at the ground is smaller than or equal to the scale of sampling imposed by the image pixels the objective should not be to assign a pixel to a single class (as with standard traditional spectral classification for example, maximum likelihood), but to several classes, where the sum of the proportions sum to one. There are, however, several alternatives. This thesis compares three possible techniques for classifying sub-pixel variation in land cover at the global scale: (i) artificial neural networks (ANN), (ii) mixture modelling (MM), and (iii) fuzzy c-means classification (FCM). The specific objective was to evaluate these techniques at the global scale, that is, for mapping sub-pixel variation in land cover over the entire globe for five text sites which involve drastically different land cover types.The major findings of the thesis are as follows: the ANN was consistently found to be more accurate than FCM classification (and MM) when trained with two-thirds of the available data. The ANN was found to be more accurate than (pilot project) and of similar accuracy to (main project) FCM (and more accurate than MM, pilot project only) when trained with an equivalent number of data. The ANN trained with data selected systematically from the available NOAA AVHRR imagery was of greater accuracy than the ANN trained with data representing the largest class proportions (obtained from the fine spatial resolution imagery). The FCM classifier trained with pixels selected from the NOAA AVHRR image using judgement was found to be sometimes more accurate and sometimes less accurate than the FCM classifier trained with the largest class proportions (obtained from the fine spatial resolution imagery).</p
Scaling law analysis of electrohydrodynamics and dielectrophoresis for isomotive dielectrophoresis microfluidic devices
No full textIsomotive dielectrophoresis (isoDEP) is a unique DEP geometrical configuration where the gradient of the field-squared (∇E2 rms) is constant. IsoDEP analyzes polarizable particles based on their magnitude and direction of translation. Particle translation is a function of the polarizability of both the particles and suspending medium, the particles’ size and shape, and the frequency of the electric field.However, other electrokinetics act on the particles simultaneously, including electrothermal hydrodynamics. Hence, to maximize the DEP force relative to over electrokinetic forces, design parameters such as microchannelgeometry, fabrication materials, and applied electric field must be properly tuned. In this work, scaling law analyses were developed to derive design rules, relative to particle diameter, to reduce unwanted electrothermal hydrodynamics relative to DEP-induced particle translation. For a particle suspended in 10 mS/m media, if the channel width and height are below ten particle diameters, the electrothermal-driven flow is reduced by ∼500 times compared to a channel that is 250 particles diameters in width and height. Replacing glasswith silicon as the device’s underlying substrate for an insulative-based isoDEP reduces the electrothermal induced flow approximately 20 times less
The European REFORM Project for Hydromorphological Quality in River Basin Management
No full textThe Water Framework Directive commits European Union member states to achieve good ecological and chemical status of all water bodies. As hydromorphology is a key factor for ecological status, a consortium of 26 partners from 15 countries studied the role of hydromorphological pressures and measures in the REFORM project. Its main objective was to answer the question: How to make river restoration successful? The project developed guidance for this by structuring the information along the different stages of restoration projects and river basin management plans, posing a logical sequence of questions: How does my river work? What’s wrong? How to improve? Things can be wrong for ecological status as a result of morphological alterations. These alterations form pressures that can be countered or mitigated by measures that improve sedimentological and morphological features. We present two specific results of REFORM that focus on river morphology. First, we provide an overview of methods to assess morphological quality and diagnose alteration. Second, we present systematic cause–effect relationships for restoration measures.Rivers, Ports, Waterways and Dredging Engineerin
Optimal advance angle for aided maximum-speed-node design of switched reluctance machines
Full text linkIn the design processes of Switched Reluctance Machines that operate in wide constant power speed ranges, the maximum power available at maximum speed must be evaluated for every machine candidate. This is critical to ensure compliance with the power requirement. Important parameters to include in the design routine are the duration of the energizing period and the advance of the turn-on instant, i.e. advance angle. The latter is highly related to the machine geometry and is usually evaluated through time-consuming finite-element-based iterative methods. In this paper, a simple, yet novel analytical model is proposed to cater for the torque maximising advance angle in a closed-form analytical expression, directly from the machine geometry. The goal is to provide a non-iterative design tool that speeds up the design process. Successful validations against finite element analyses and experimental results on an SR machine prototype are reported. The main outcome of this paper is shown by the improvement in computation time, without any significant loss of accuracy
Actual design space methodology for preliminary design analysis of switched reluctance machines
Full text linkIn the design of modern, high-performance switched reluctance machines, the highly restrictive sets of constraints and requirements severely limit the number of feasible solutions. In order to improve the chances of attaining a successful design, this work proposes a novel and fully analytical approach to the preliminary design analysis. Initially, the correct number of independent design variables is identified. Subsequently, constraints and requirements are introduced one by one, in order to progressively discard all of the unfeasible candidates. At the end of this process, the actual design space is attained, whose main characteristic is to be populated only by feasible candidates. A design case study shows how the proposed methodology allows: 1) to verify the design feasibility; 2) to reduce the number of candidates by orders of magnitude; and 3) to gain useful insight into the design problem and thus select the most convenient strategy to finalize it. As a result, a highly effective design process is attained, so that considerable computational resources can be saved
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
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