1,721,049 research outputs found
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
Multiplicities of temperature wave trains in periodically forced networks of catalytic reactors for reversible exothermic reactions
No full textNetworks of catalytic reactors with periodically switched inlet and outlet sections offer a competitive technological solution to the operation of reversible exothermic reactions. Traditionally, this operation mode is implemented by periodically shifting inlet and outlet sections so as to jump a single reactor unit in the flow direction. Here, a network of four catalytic reactors carrying on the methanol synthesis process is considered and the effect of varying the number (n s) of reactor units jumped by inlet and outlet sections on network stability and performance is investigated. Increasing n s, a greater variety of periodic regimes giving rise to trains of temperature waves characterized by spatial periodicity are detected as the switching velocity varies. These regimes well reproduce the inter-stage cooling effect of multistage fixed bed reactors and, hence, guarantee in general large conversion values. Moreover, an intriguing coexistence between T-periodic and multi-periodic temperature wave trains is revealed, T being the period needed for the system to recover its initial configuration. A T-periodic symmetric wave train characterized by k waves always coexists with a number of k-1 stable symmetric kT-periodic regimes, except when symmetry breaking is encountered. The k-1 coexisting regimes correspond to wave trains with a number of waves ranging between 1 and k-1. Bifurcational analysis is performed to characterize the stability range of periodic regimes and to systematically analyze multiplicities and bifurcations as the switching velocity is varied and at different n s. © 2011 Elsevier B.V
Temperature and conversion patterns in a network of catalytic reactors for methanol synthesis with different switch strategies
No full textA network of connected catalytic reactors with periodically switched inlet and outlet sections is numerically studied for reversible exothermic reactions. The methanol synthesis is selected as representative process example and two different switch strategies are compared with the objective of overcoming the conversion limits imposed by thermodynamic equilibrium. The first strategy, which is the most considered in literature, consists of periodically switching the feed to the second reactor of the current reactor sequence while the second strategy is implemented by periodically switching the feed to the last reactor of the current sequence. Periodic regimes corresponding to single square-like temperature waves travelling over the catalytic bed and characterized by comparable methanol conversion values are detected for both the considered strategies. These regimes exhibit, however, a significantly larger domain of existence for the second strategy. Moreover, the second strategy gives rise to other periodic regimes corresponding to spatiotemporal temperature patterns characterized by different spatial and temporal periodicity. These patterns arise in the form of temperature wave trains and ensure methanol conversion values significantly larger than those found under periodic regimes characterized by single temperature waves. © 2010 Elsevier Ltd
Nonlinear analysis of a network of three continuous stirred tank reactors with periodic feed switching: Symmetry and symmetry-breaking
No full textThe spatiotemporal symmetry properties of a periodically forced network of three continuous stirred tank reactors are assessed. The symmetry is induced to the system by a cyclic switching of the feed and discharge positions. The symmetry properties imply that the Poincare map is the third iterate of another non-stroboscopic map. This feature is here used to characterize the symmetry of the regime solns., and to carry out bifurcation anal. Possible bifurcation scenarios and, in particular, symmetry-breaking bifurcations are discussed. As the switch time is varied, different transitions were identified: among the others, an important role in the birth of asym. regimes is played by frequency-locking phenomena. In addn., different routes to chaotic regimes (both sym. and asym.) are reported
Detecting weak points of wildland fire spread: A cellular automata model risk assessment simulation approach
No full textIn this work, we propose a risk-assessment approach based on Cellular Automata (CA) simulations which incorporate both theoretical/ first principles and (semi)empirical fire behavioural models. The proposed approach can deal with spatial heterogeneity in both the fuel and landscape characteristics, can be coupled with Geographical Information Systems (GIS) and can take as input local meteorological data (even in real time). Using the CA model we are able to construct the topographic map of hazard intensity defined in terms of the expected burned area resulting from an ignition in a particular point of the region under surveillance. For our illustrations we used the case of Spetses Island whose a major part of its forest burned in 1990. Using the proposed framework, we revealed the weak points of fire spread risk, i.e. potential ignitions points which result to maximum likelihood of burned area. © Copyright 2014, AIDIC Servizi S.r.l.In this work, we propose a risk-assessment approach based on Cellular Automata (CA) simulations which
incorporate both theoretical/ first principles and (semi)empirical fire behavioural models. The proposed
approach can deal with spatial heterogeneity in both the fuel and landscape characteristics, can be
coupled with Geographical Information Systems (GIS) and can take as input local meteorological data
(even in real time). Using the CA model we are able to construct the topographic map of hazard intensity
defined in terms of the expected burned area resulting from an ignition in a particular point of the region
under surveillance. For our illustrations we used the case of Spetses Island whose a major part of its forest
burned in 1990. Using the proposed framework, we revealed the weak points of fire spread risk, i.e.
potential ignitions points which result to maximum likelihood of burned area
Effect of the switch strategy on the performance and stability of reactor networks for methanol synthesis
No full textA network of catalytic reactors with a periodic switching of the feed and discharge position (also called loop reactor) is studied for reversible exothermic reactions like methanol synthesis. The aim of the study is the comparison of two different switching strategies in overcoming the conversion limits imposed by the thermodynamic equilibrium. The first strategy, that is the only considered in previous works, consists of changing at each switch time the feed/discharge positions, so that the first reactor of the NTW is moved to the last place. The second strategy consists in moving the last reactor in the first place each switch time. We show through numerical simulations that the second forcing strategy is more convenient in terms of yield and methanol conversion, because it is able to create a conversion/temperature path closer to the optimal one. © 2010 Elsevier B.V
A nonlinear approach to the design of gain-scheduled controllers
No full textGain scheduling is a method widely applied in industrial practice to control processes where large changes of the operating conditions can occur. In its standard implementation, this technique requires to compute a family of steady states covering the operating region of interest and then to design a family of linear feedback controllers ensuring stability and desired output behavior about the selected steady states. In this contribution, a novel approach to design gain-scheduled controllers of nonlinear processes is presented. Parametric continuation and optimization techniques are implemented to compute a parameterized family of steady states covering the output range of interest and, at the same time, fulfilling a prescribed set of control requirements. Then, bifurcation analysis is performed to design a family of linear feedback controllers guaranteeing desired output behavior around the selected steady states and preventing the occurrence of state multiplicity. The method is validated on the problem of controlling a continuous exothermic reactor exhibiting state and input multiplicity. © 2010 Elsevier B.V. All rights reserved
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