1,721,047 research outputs found
Two-stage stochastic standard quadratic optimization
Get PDFTwo-stage stochastic decision problems are characterized by the property that in stage one part of the decision has to be made before relevant data are observed and the rest of the decision can be made in stage two after data are available. It is generally assumed that while the data missing in stage one are not known, their probability distribution is known. In this paper, we consider a special form of such problems where the objective function is quadratic in the first and second stage decisions and the goal is to minimize the expected quadratic cost function. We assume that the decisions must lie in a standard simplex, but do not require convexity of the uncertain objective. It is well known that such quadratic optimization programs are NP-complete and thus belong to the most complex optimization problems. A viable method to attack such problems is to find bounds for the original complicated problem by solving easier approximate problems. We describe such approximations and show that by exploiting their properties, good but not necessarily optimal solutions can be found. We also present possible applications, such as selecting invited speakers for conferences with the aim to generate a community with high coherence. Finally, systematic numerical results are provided
Optimal planning and economic evaluation of trigeneration districts
No full textTrigeneration, or combined cooling, heat and power (CCHP), is the process
by which electricity, heating and cooling are simultaneously generated from
the combustion of a fuel. Trigeneration systems for serving the electricity, thermal
and cooling loads in residential districts are a possible solution to enhance energy
efficiency, reduce fossil fuel consumption and increase the use of renewable energy
sources in the residential sector. Technical, economical and financial issues have to
be taken into account when planning a trigeneration system, or when expanding an
existing generation system. In this chapter a two-step decision support procedure is
presented for analysing alternative system configurations. The first step is based on
a mixed integer linear programming model that allows to describe the system components
in great detail and computes the annual optimal dispatch of the distributed
generation system with a hourly discretization, taking into account load profiles, fuel
costs and technical constraints. The optimal dispatch is then used for the economic
evaluation of the investment, taking into account prices of commodities, taxation,
incentives and financial aspects. The procedure allows to compare alternative plant
configurations and can be used as a simulation tool, for assessing the system sensitivity
to variations of model parameters (e.g. incentives, ratio debt/equity,...)
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
Pricing of energy contracts: From replication pricing to swing options
No full textThe principle of replication or superhedging is widely used for valuating financial contracts, in particular, derivatives. In the special situation of energy markets, this principle is not quite appropriate and might lead to unrealistic high prices, when complete hedging is not possible, or to unrealistic low prices, when own production is involved. Therefore we compare it to further valuation strategies: acceptability pricing weakens the requirement of almost sure replication and indifference pricing accounts for the opportunity costs of producing for a considered contract. Finally, we describe a game-theoretic approach for valuating flexible contracts (swing options), which is based on bi-level optimization
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