1,720,970 research outputs found
Ricerca di strutture speciali in problemi di programmazione lineare intera
No full textI problemi di Programmazione Lineare Intera sono in generale notoriamente
difficili da trattare sotto l’aspetto computazionale. La progettazione di algoritmi
efficienti per problemi di tale natura, quindi, spesso trae grande vantaggio
dallo studio della struttura matematica soggiacente. Prendendo come spunto
il problema di determinare una sottomatrice massima di tipo network di una
matrice a valori in {0,−1, 1}, nel lavoro di tesi si analizza il problema equivalente
di bilanciamento di un grafo signed (mbs, Max Balanced Subgraph)
e quindi si generalizzano alcuni dei risultati ottenuti a problemi combinatorici
di più ampia portata.
In particolare, lo studio ha portato all’ideazione e implementazione dell’euristica
CCH (Cycle-Contraction Heuristic) per il problema mbs che è risultata
più efficace delle euristiche esistenti in letteratura. L’algoritmo CCH è basato
su una regola originale di trasformazione e semplificazione dei grafi che ne riduce
progressivamente la lunghezza dei cicli senza per questo compromettere
l’ammissibilità delle soluzioni determinate sul grafo modificato.
Successivamente sono state ideate delle regole originali di data reduction che
hanno lo scopo di semplificare le istanze e/o ridurne la dimensione, pur conservando
su esse la soluzione ottima del problema. Con queste regole, le performance
dell’euristica CCH sono migliorate sia in termini di efficienza che di
efficacia.
Nella tesi viene poi proposto un nuovo modello esatto per il problema mbs
basato sulla trasformazione di un grafo signed in un grafo semplice detto 2-
layer, stabilendo una stretta connessione tra il problema mbs e il più comune
problema di massimo insieme stabile (mis). Il grafo 2-layer fornisce nuovi
strumenti per progettare algoritmi per il problema mbs, basati sui numerosi
metodi di soluzione (esatti o euristici) adottati per il problema mis.
Infine, è stato affrontato il tema della generalizzazione di alcuni problemi
combinatorici su grafi signed ed è stato esteso il modello 2-layer al modello
k-layer. In particolare è stato provato che il problema di k-coloring di un grafo
signed - che generalizza il problema di bilanciamento di un grafo signed e quello
di bipartizione di un grafo semplice - equivale al problema mis sul grafo k-layer
A heuristic based on negative chordless cycles for the maximum balanced induced subgraph problem
No full textA signed graph, i.e., an undirected graph whose edges have labels in {-1,+1}, is balanced if it has no negative cycles. Given a signed graph, we are interested in a balanced induced subgraph of maximum order (the MBIS problem). In the present work, we propose a greedy approach for the MBIS problem that is based on the progressive shortening of negative cycles, and that generalizes the well-known minimum-degree greedy heuristic for the maximum independent set problem. An extensive computational study on three classes of instances shows that the new algorithm outperforms the reference heuristics proposed in the literature
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
Soilless cultivation systems to produce tailored microgreens for specific nutritional needs
Get PDFBACKGROUNDThe awareness of the importance of following dietary recommendations that meet specific biological requirements related to an individual's health status has significantly increased interest in personalized nutrition. The aim of this research was to test agronomic protocols based on soilless cultivation for providing consumers with new dietary sources of iodine (I), as well as alternative vegetable products to limit dietary potassium (K) intake; proposed cultivation techniques were evaluated according to their suitability to obtain such products without compromising agronomic performance.RESULTSTwo independent experiments, focused on I and K respectively, were conducted in a commercial greenhouse specializing in soilless production. Four different species were cultivated using three distinct concentrations of I (0, 1.5 and 3 mg L-1) and K (0, 60 and 120 mg L-1). Microgreens grown in I-rich nutrient solution accumulate more I, and the increase is dose-dependent. Compared to unbiofortified microgreens, the treatments with 1.5 and 3 mg L-1 of I resulted in 4.5 and 14 times higher I levels, respectively. Swiss chard has the highest levels of K (14 096 mg kg-1 of FW), followed by rocket, pea and radish. In radish, rocket and Swiss chard, a total reduction of K content in the nutrient solution (0 mg L-1) resulted in an average reduction of 45% in K content.CONCLUSIONIt is possible to produce I-biofortified microgreens to address I deficiency, and K-reduced microgreens for chronic kidney disease-affected people. Species selection is crucial to customize nutritional profiles according to specific dietary requirements due to substantial mineral content variations across different species. (c) 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry
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