1,720,989 research outputs found
Covering cubic graphs with matchings of large size
No full textLet m be a positive integer and let G be a cubic graph of order 2n. Weconsider the problem of covering the edge-set of G with the minimumnumber of matchings of size m. This number is called excessive [m]-indexof G in the literature. The case m = n, that is a covering with perfectmatchings, is known to be strictly related to an outstanding conjectureof Berge and Fulkerson. In this paper we study in some details the casem = n-1. We show how this parameter can be large for cubic graphswith low connectivity and we furnish some evidence that each cyclically4-connected cubic graph of order 2n has excessive [n-1]-index at most 4.Finally, we discuss the relation between excessive [n-1]-index and someother graph parameters such as oddness and circumference
Even Cycle Decompositions of index 3 by a novel coloring technique
Full text linkAn even cycle decomposition of an Eulerian graph is a partition of the edge set into even cycles. We color the even cycles so as two cycles sharing at least one vertex receive distinct colors. If k is the minimum number of required colors in such a coloring, then the even cycle decomposition has index k. We prove that the line graph of every bridgeless cubic graph of oddness 2 has an even cycle decomposition of index 3. The same property holds for the line graphs of some infinite families of class 2 cubic graphs with arbitrary large oddness. The construction of even cycle decompositions of index 3 in the line graph of a class 2 cubic graph is alternative to the constructions that are known in the literature; that one for the line graph of a cubic graph with arbitrary large oddness is also a new contribution to the more general problem on the existence of even cycle decompositions in the line graph of a bridgeless cubic graph. The constructions are obtained by applying a novel coloring technique on the edges of the line graph
On the minimum number of bond-edge types and tile types: An approach by edge-colorings of graphs
Full text linkThe purpose of this paper is twofold. On one hand, we want to describe from a new graph theory perspective the self-assembly of DNA structures with branched junction molecules having flexible arms. On the other hand, we employ edge-colorings and graph decompositions to study the well-known problem of determining the minimum number of bond-edge types and tile types, which are graph invariants appearing in this context. We provide a strategy that can be applied to arbitrary graphs for obtaining upper bounds for these graph invariants
Risk-based Vulnerability Analysis of Chemical Facilities Affected by Flooding
Full text linkFlooding may affect chemical facilities leading to major accidents (fires, explosions, contamination), following damages to structures and equipment. This type of accident is indicated as a “natural-technological” (Natech) event and occurred in the past, often leading to severe accidental scenarios. Recent studies allowed developing a specific methodology aimed at including Natech scenarios triggered by flooding into Quantitative Risk Assessment (QRA) analyses for chemical facilities. The methodology relies on the use of specific fragility models for the evaluation of failure probability of process units affected by flooding. Despite these models consider different types of equipment geometries and flooding conditions, they do not account for the presence of safety barriers (e.g., fire-protection systems, bunds, blanketing system). In the present work, the previously developed QRA methodology is improved in order to provide a risk-based vulnerability analysis of Natech scenarios induced by severe flooding taking into account the presence of safety barriers. The methodology is improved by including the availability assessment of safety barriers based on the possibility the systems have been impacted by the flood. A tailored Failure Mode and Effect and Criticality Analysis (FMECA) is presented for assessing the damages to safety barriers resulting from flooding events. As an example, the analysis of an important safety barrier through the FMECA approach is presented. The study shows an example of both risk informed decision-making concerning protection systems and development of new criteria for the assessment of safety barrier failure in case of natural hazards
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
Multi-target Inherent Safety Indices for the Early Design of Offshore Oil&Gas Facilities
No full textImproved tools are needed to manage major accident hazard of progressively more complex offshore oil&gas systems in environmentally sensitive areas. Inherent safety principles provide a strategic opportunity to reduce major accident hazards since the early design phase, but a suitable metric to orient safer design choices is needed to apply such principles intro practice. This study aims at providing a systematic approach to the assessment of the hazard profile of alternative process designs in offshore oil & gas production facilities. A novel methodology providing a ranking of inherently safer solutions in conceptual design is described. The methodology is able to highlight the different contributors to the safety profile of the offshore oil & gas production system, linking them to the specific features of the design. The proposed approach, based on multi-criteria Key Performance Indicators (KPIs), addresses different targets (people, assets, environment) and provides a quantitative assessment of the safety score, accounting for both the possible accident consequences and their credibility. An application to a case study concerning an offshore facility for gas production is discussed to demonstrate the potential of the methodology
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