1,721,164 research outputs found
An exact approach for the bilevel knapsack problem with interdiction constraints and extensions
Full text linkWe consider the bilevel knapsack problem with interdiction constraints, an extension of the classic 0–1 knapsack problem formulated as a Stackelberg game with two agents, a leader and a follower, that choose items from a common set and hold their own private knapsacks. First, the leader selects some items to be interdicted for the follower while satisfying a capacity constraint. Then the follower packs a set of the remaining items according to his knapsack constraint in order to maximize the profits. The goal of the leader is to minimize the follower’s total profit. We derive effective lower bounds for the bilevel knapsack problem and present an exact method that exploits the structure of the induced follower’s problem. The approach strongly outperforms the current state-of-the-art algorithms designed for the problem. We extend the same algorithmic framework to the interval min–max regret knapsack problem after providing a novel bilevel programming reformulation. Also for this problem, the proposed approach outperforms the exact algorithms available in the literature
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
On fairness and diversification in WTA and ATP tennis tournaments generation
Full text linkSingle-elimination (knockout) tournaments are the standard paradigm for both main tennis professional associations, WTA and ATP. Schedules are generated by allocating first seeded and then unseeded players with seeds prevented from encountering each other early in the competition. Besides, the distribution of pairings in the first round between unseeded players and seeds for a yearly season may be strongly unbalanced. This provides often a great disadvantage to some “unlucky” unseeded players in terms of money prizes. Also, a fair distribution of matches during a season would benefit from limiting in first rounds the presence of Head-to-Head (H2H) matches between players that met in the recent past. We propose a tournament generation approach in order to reduce in the first round unlucky pairings and also replays of H2H matches. The approach consists in a clustering optimization problem inducing a consequent draw within each cluster. A Non-Linear Mathematical Programming (NLMP) model is proposed for the clustering problem so as to reach a fair schedule. The solution reached by a commercial NLMP solver on the model is compared to the one reached by a faster hybrid algorithm based on multi-start local search. The approach is successfully tested on historical records from the recent Grand Slams tournaments
Electrochemical and spectroscopic study of the transport-properties of composite polymer electrolytes
No full textThe addition of inert filler are known to increase the mechanical
properties of polymer electrolytes in their conductive
amorphous phase. So the addition of a-A1203 to PEO-LiC104 complexes produced a significant improvement
in the mechanical stability of the material at temperatures
in excess of 100 "C. This improvement was
explained assuming that the ceramic dispersoid act as a
filler providing a supporting matrix for the conductive
amorphous polymer complex, so as to retain an overall
solid structure even at high temperature. In this paper, thermal, electrical and spectroscopic characterization results all support a structural model which accounts for the effects exerted by finely dispersed ceramic additives on the trasnport properties of PEO-based polymer electrolytes. The addition of the dispersoid prevents the agglomeration of the polymer chain to form extended coiled crystalline clusters. While maintaining an overall rigid structure, these electrolytes assume structural and transport properties comparable to those of systems based on ow-molecular weight poly(ethy1ene glycol)-lithium salt solutions,
which are currently used to mimic low-crystallinity polymer
electrolytes
On approximating the Incremental Knapsack Problem
No full textWe consider the 0-1 Incremental Knapsack Problem (IKP) where the capacity grows over time periods and if an item is placed in the knapsack in a certain period, it cannot be removed afterwards. The contribution of a packed item in each time period depends on its profit as well as on a time factor which reflects the importance of the period in the objective function. The problem calls for maximizing the weighted sum of the profits over the whole time horizon. In this work, we provide approximation results for IKP and its restricted variants. In some results, we rely on Linear Programming (LP) to derive approximation bounds and show how the proposed LP-based analysis can be seen as a valid alternative to more formal proof systems. We first manage to prove the tightness of some approximation ratios of a general purpose algorithm currently available in the literature and originally applied to a time-invariant version of the problem. We also devise a Polynomial Time Approximation Scheme (PTAS) when the input value indicating the number of periods is considered as a constant. Then, we add the mild and natural assumption that each item can be packed in the first time period. For this variant, we discuss different approximation algorithms suited for any number of time periods and for the special case with two periods
Heuristic solution methods for the selective disassembly sequencing problem under sequence-dependent costs
No full textThe first Waste Framework Directive issued by the European Union dates back to the seventies but was drastically amended in the last decade to reduce environmental impacts of waste by encouraging reuse, recycling and remanufacturing. Product recovery starts with disassembly which results in high labor costs. Disassembly supports environmentally conscious choices like replacement of defective parts to extend the life span of products, removal of suitable components for reuse and extraction of hazardous substances to decontaminate materials for reprocessing. Besides, selective disassembly also accommodates maintenance and repairs. Optimizing the cost of disassembly is crucial to make this process an economically viable option. Due to change tools and parts reorientation, disassembly costs are sequence-dependent. Therefore minimizing the disassembly cost involves the search for an adequate sequence of disassembly tasks. Consequently, this paper addresses the disassembly sequencing problem for selective and sequential disassembly under sequence-dependent costs. As optimal formulations fail to handle real-world cases, we develop a randomized greedy algorithm (needing a very few number of parameters to be set and proving to be robust with respect to their value) and a matheuristic to solve efficiently medium to large-sized instances
The experience to be mother of a preterm infant]. L’esperienza di essere madre di un bambino pre-termine
No full textVariations 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
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