1,720,964 research outputs found
Interdependent multi-objective sizing and control optimisation of a renewable energy hydrogen system
Full text linkThis paper presents a sizing and control optimisation architecture for the design
and evaluation of a small-scale stand-alone hybrid PV-wind-battery system for the production
of hydrogen (H2) using proton exchange membrane (PEM) technology. Three objectives are
considered simultaneously namely cost, efficiency and reliability. For this task an optimisation
approach is developed combining a single objective genetic algorithm (GA) with a multiobjective
GA (MOGA) to optimise nine system sizing variables and six power management
system control set-point variables. The nine sizing and six control variables are combined to
form a solution vector. The optimisation algorithm searches the search space, with user defined
boundaries, for non-dominated solution vectors. The result is a set of solution vectors which
are useful in the selection of components for the design and evaluation of these systems. The
optimisation approach developed sufficiently searches the bounded search space and provides
results in the form of a set of non-dominated solution vectors. These results are useful in
understanding how the different components of such a non-linear complex system affect each
other as well as the three objectives considered in this studyHySA Infrastructure
DST key program KP
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
Power management and sizing optimisation of renewable energy hydrogen systems
Full text linkPhD (Electrical and Electronic Engineering), North-West University, Potchefstroom Campus, 2016Solar and wind renewable energy (RE) sources are widely available and a viable alternative for generating cleaner energy. These RE sources are however intermittent and dependent on location, time of day and season. Adding to this, non-linear components make determining sizes for the components of these systems a complicated and difficult task. Optimisation techniques
are currently being used to perform the sizing of these systems, with system sizing and control optimisation performed separately. Objectives other than cost such as efficiency and reliability are not currently considered. The first objective of this study is to develop an integrated sizing and control optimisation strategy for a small-scale stand-alone RE system using multiple objectives while considering sizing and control simultaneously. A sizing and control optimisation algorithm is developed consisting of two optimisation algorithms simultaneously optimising sizing and control variables. A single objective genetic algorithm (GA) is implemented for control optimisation and a strength Pareto evolutionary algorithm (SPEA) is implemented for the sizing optimisation. The
developed strategy is referred to as SPEAGA in the rest of the document. Multiple objective functions fo cost, efficiency and reliability are used. An optimal control configuration is determined from the single objective GA which then determines an optimal sizing configuration for all three objective functions using the SPEA. Design, analysis and optimisation require a mathematical model of the system which is developed and validated. The SPEAGA is implemented on the system model. Results obtained from the optimisation process consist of non-dominated solution vectors known as Pareto optimal solutions. Each solution vector consist of six control variables, nine sizing variables and three objective function values. A second objective of this work is a genetic fuzzy system (GFS) developed to analyse the results and provide a reduced set of rules. A GA is implemented to train the fuzzy system which results in a rule-base for each objective of each site. Further a membership function reduction approach is followed to reduce the complexity of each rule-base by eliminating membership functions. A third objective is the insights derived from the fuzzy rule bases. Contributions made by this study include the multi-objective optimisation of sizing and control variables simultaneously through the development of the novel optimisation architecture, SPEAGA. Optimising sizing and control for multiple objectives presents an additional contribution in the sense that it analyses the information in a new way giving new insight. The developed GFS is successfully used to generate rules relating system inputs to outputs and is useful for system design. The SPEAGA successfully optimises a small-scale rural RE hydrogen (H2) system for three sites. Further results include a comparison between the standard SPEA and the developed SPEAGA. The SPEAGA provided improved values for both efficiency and
reliability. These results provide new insight into system design in terms of sizing and power management when considering multiple conflicting objectives. Efficiency and reliability are shown to be dependent on control parameters and are therefore improved using the SPEAGA through the additional control optimisation which is highlighted by the results. Insights are
obtained from the GFS which are considered useful for future system developments.Doctora
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
Model based predictive control for load following of a pressurised water reactor
Full text linkThesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.By September 2009 the International Atomic Energy Agency reported that the number of commercially operated nuclear reactors in 30 countries across the world is 436, around 50 reactors are currently being constructed, 137 reactors have been ordered or is already planned, and there are around 295 proposed reactors. Pressurised water reactors (PWRs) make up the majority of these numbers. The growing number of carbon emissions and the ongoing fight against fossil fuel power stations might see the number of planned nuclear reactors increase even more to be able to satisfy the world’s need for cleaner energy. To ensure that technology keeps pace with this growing demand, ongoing research is essential. Not only is the research of new reactor technologies (i.e. High Temperature Reactors) important, but improving the current technologies (i.e. PWRs) is critical. With the increased contribution of nuclear generated electricity to our grids, it is becoming more common for nuclear reactors to be operated as load following units, and not base load units as they are more commonly being operated. Therefore a need exists to study and develop new strategies and technologies to improve the automatic load following capabilities of reactors. PWR power plants are multivariable systems. In this study a multivariable, more specifically, a model predictive controller (MPC) is developed for controlling the load following of a nuclear power plant, more specifically a PWR plant. In developing this controller system identification is employed to develop a model of the PWR plant. For the identification of the model, measured data from a computer based PWR simulator is used as the input. The identified plant model is used to develop the MPC
controller. The controller is developed and tested on the plant model. The MPC controller is also evaluated against another set of measured data from the simulator. To compare the performance of the MPC controller to that of the conventional controller the ITAE performance index is employed. During the process Matlab®, the System Identification Toolbox™, the MPC Toolbox™ and Simulink® are used. The results reveal that MPC is practicable to be used in the control of non-linear systems such as PWR plants. The MPC controller showed good results for controlling the system and also outperformed the conventional controllers. A further result from the dissertation is that system identification can successfully be used to develop models for use in model based controllers like MPC controllers. The results of the research show that a need exists for future research to improve the methods to eventually have a controller that can be applied on a commercial plant.Master
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