4,635 research outputs found

    On the probabilistic min spanning tree Problem

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    We study a probabilistic optimization model for min spanning tree, where any vertex vi of the input-graph G(V,E) has some presence probability pi in the final instance G′ ⊂ G that will effectively be optimized. Suppose that when this “real” instance G′ becomes known, a spanning tree T, called anticipatory or a priori spanning tree, has already been computed in G and one can run a quick algorithm (quicker than one that recomputes from scratch), called modification strategy, that modifies the anticipatory tree T in order to fit G ′. The goal is to compute an anticipatory spanning tree of G such that, its modification for any G ′ ⊆ G is optimal for G ′. This is what we call probabilistic min spanning tree problem. In this paper we study complexity and approximation of probabilistic min spanning tree in complete graphs under two distinct modification strategies leading to different complexity results for the problem. For the first of the strategies developed, we also study two natural subproblems of probabilistic min spanning tree, namely, the probabilistic metric min spanning tree and the probabilistic min spanning tree 1,2 that deal with metric complete graphs and complete graphs with edge-weights either 1, or 2, respectively

    A Binary-Ordered Probit Model of Cigarette Demand

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    This study analyzes the demand for cigarettes fitting observed zero outcomes with a trivariate model consisting of an equation for the starting smoking decision, an equation for the quitting decision, and an equation that models the level of cigarettes consumed. Five competing specifications are considered to explain level, with the ordered probit, which accommodates pile-ups of counts in the dependent variable, providing the best fit. Marginal effects of explanatory variables are calculated providing strong evidence of race and gender differences in consumption patterns. The estimated marginal effects are robust to alternative categorizations of the level of cigarettes.Demand and Price Analysis,

    New methods for digital halftoning and inverse halftoning

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    Halftoning is the rendition of continuous-tone pictures on bi-level displays. Here we first review some of the halftoning algorithms which have a direct bearing on our paper and then describe some of the more recent advances in the field. Dot diffusion halftoning has the advantage of pixel-level parallelism, unlike the popular error diffusion halftoning method. We first review the dot diffusion algorithm and describe a recent method to improve its image quality by taking advantage of the Human Visual System function. Then we discuss the inverse halftoning problem: The reconstruction of a continuous tone image from its halftone. We briefly review the methods for inverse halftoning, and discuss the advantages of a recent algorithm, namely, the Look Up Table (LUT)Method. This method is extremely fast and achieves image quality comparable to that of the best known methods. It can be applied to any halftoning scheme. We then introduce LUT based halftoning and tree-structured LUT (TLUT)halftoning. We demonstrate how halftone image quality in between that of error diffusion and Direct Binary Search (DBS)can be achieved depending on the size of tree structure in TLUT algorithm while keeping the complexity of the algorithm much lower than that of DBS

    The PRIMO FORTE framework for good governance in public, private and civic organisations : an analysis on small EU states

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    Purpose: In this article we lay out and discuss a framework proposed by the Public Risk Management Organisation (PRIMO) (https://www.primo-europe.eu/) of which the authors are board members and the results of a test on public and private entities of EU small jurisdictions, specifically Malta, Slovenia, Luxembourg, Lithuania, Latvia, Estonia and Cyprus. These are countries within the EU having less than 3 million people population. Design/methodology/approach: We collected our primary data by using a semi-structured questionnaire and administering it to participants who are working directly or indirectly with entities within these EU states. The questionnaire was structured using the FORTETM acronym as themes, ‘Financial and compliant design’, ‘Object orientation and delivery’, ‘Responsibility and stewardship’, ‘Tools and processes for creation’ and ‘Environmental awareness and interaction’, with 5 statements under each theme to which participants were required to answer using a 5-point Likert-scale ranging from “Strongly Disagree” to “Strongly Agree”. We, however, allowed the participants to open up and discuss each statement and recorded these comments. Some demographic data was also collected as to the type of entity the participants are working with, the level of expertise on governance of the participant and the size of the entity. The quantitative data was subjected to statistical analysis while the results from the open ended question was analysed using the Thematic approach. Findings: Factor analysis provided support for the FORTE Good Governance model for both the Private and Public entities, no-matter if they are small or large. Originality/value: The study provides a better understanding and supports the FORTE Model established by PRIMO-Europe, after approximately 15 years of collecting data on public risks and for the first time tests it on both Private and Public entities, in large and small firms in small EU Jurisdictions. Moreover, this model contributed to the vast literature on models of risk management within organisations, but was not validated empirically for reliability of the factors, and on small jurisdictions. Therefore, the significance and importance of such a study lies firstly on the premise that testing on small countries, can be deemed as small laboratories for more complex politics, regulations and policies of larger countries.peer-reviewe

    Immigrant students and educational systems. Cross-country evidence from PISA 2006

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    Using data from PISA 2006 on 29 countries, this paper analyses immigrant school gaps (difference in scores between immigrants and natives) and focuses on tracking and comprehensive educational systems. Results show that the wider negative gaps are present where tracking is sharp and less frequently in countries with comprehensive schooling. In both cases, negative gaps are concentrated in continental Western Europe, where they are also often related to immigrants and natives attending different schools, or are significant within schools