1,720,969 research outputs found
Universal approximators for multi-objective direct policy search in water reservoir management problems: a comparative analysis
No full textThe optimal operation of water resources systems is a wide and challenging problem due to non-linearities in the model and the objectives, high dimensional state-control space, and strong uncertainties in the hydroclimatic regimes. The application of classical optimization techniques (e.g., SDP, Q-learning, gradient descent-based algorithms) is strongly limited by the dimensionality of the system and by the presence of multiple, conflicting objectives. This study presents a novel approach which combines Direct Policy Search (DPS) and Multi-Objective Evolutionary Algorithms (MOEAs) to solve high-dimensional state and control space problems involving multiple objectives. DPS, also known as parameterization-simulation-optimization in the water resources literature, is a simulation-based approach where the reservoir operating policy is first parameterized within a given family of functions and, then, the parameters optimized with respect to the objectives of the management problem. The selection of a suitable class of functions to which the operating policy belong to is a key step, as it might restrict the search for the optimal policy to a subspace of the decision space that does not include the optimal solution. In the water reservoir literature, a number of classes have been proposed. However, many of these rules are based largely on empirical or experimental successes and they were designed mostly via simulation and for single-purpose reservoirs. In a multi-objective context similar rules can not easily inferred from the experience and the use of universal function approximators is generally preferred. In this work, we comparatively analyze two among the most common universal approximators: artificial neural networks (ANN) and radial basis functions (RBF) under different problem settings to estimate their scalability and flexibility in dealing with more and more complex problems. The multi-purpose HoaBinh water reservoir in Vietnam, accounting for hydropower production and flood control, is used as a case study. Preliminary results show that the RBF policy parametrization is more effective than the ANN one. In particular, the approximated Pareto front obtained with RBF control policies successfully explores the full tradeoff space between the two conflicting objectives, while most of the ANN solutions results to be Pareto-dominated by the RBF ones
Analyzing tradeoffs between hydropower production and hydrological alteration to support water resources planning in large river systems
No full textIn many countries water is a key renewable resource to complement carbon-emitting energy production in the face of demand pressure from fast-growing industrial production and urbanization. In this study, we analyze the case of the Red River Vietnam, a large basin of 169.000 kmq where the storing capacity, mainly targeted at hydropower production, has steadily increased since from the Eighties through the construction of a number of reservoirs (Hoa Binh completed in 1994, Tuyen Quang in 2008, Son La in 2012), which nowadays account for the 15% of the national electric power production. On the other hand, reservoir operation dramatically alters downstream river hydrology, geomorphological processes and riverine ecosystems.
In this work, we focus in particular on the alteration of the hydrological regime downstream of the Hoa Binh reservoir and explore re-operation options to mitigate the hydrological alteration while guaranteeing reasonable hydropower production. To reach this goal we (i) define an index of hydrological alteration starting from the well established set of Indicators of Hydrological Alteration and applying a novel selection and aggregation procedure; (ii) embed such an index into a multi-objective optimization process, to design reservoir operating policies that represent Pareto-optimal solutions between maximization of hydropower production and minimization of hydrological alteration.
This work demonstrates the potential of multi-objective optimization and simulation tools to analyze tradeoffs between conflicting needs and thus support the evaluation and planning of sustainable energy production programs
Modelling water operators' time varying risk aversion by an agent-based multi lateral negotiation protocol
No full textMultipurpose water reservoirs are operated on a tradeoff point of multiple, often conflicting, operating objectives. Generally, this tradeoff has been selected to ensure efficient and balanced performance given the observed system boundary conditions. Extreme variability in the inputs might induce change in the operator’s risk aversion and a shift of tradeoff. In this work, we explore how the selection of different optimal tradeoffs among conflicting operating objectives is linked to the variations of the boundary conditions, such as, for example, drifting rainfall season or remarkable changes in crop prices. In particular, we argue that tradeoff dynamics is driven by recent, extreme variations in system performance: underperforming on one of the objectives should push the tradeoff toward disadvantaged objectives. To test this assumption, we develop an agent-based model to simulate the operators’ tradeoff selection process. We map the selection onto a multi lateral negotiation protocol, where different virtual agents optimize different operating objectives. The agents periodically negotiate a compromise on the operating policy. The agent’s rigidity in each negotiation round is determined by the recent system performance according to the specific objective it represents. The negotiation follows a set-based egocentric monotonic concession protocol: at each step an agent incrementally adds some options to the set of its acceptable compromises and (possibly) accepts lower and lower satisfying policies until an agreement is achieved. We apply this reiterated negotiation framework on the regulated Lake Como, Italy, simulating the lake dam operation and its recurrent updates over the last 50 years
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
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
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