649 research outputs found

    A rolling horizon approach for the locomotive routing problem at the Canadian National Railway Company

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    Cette thèse étudie le problème du routage des locomotives qui se pose à la Compagnie des chemins de fer nationaux du Canada (CN) - le plus grand chemin de fer au Canada en termes de revenus et de taille physique de son réseau ferroviaire. Le problème vise à déterminer la séquence des activités de chaque locomotive sur un horizon de planification donné. Dans ce contexte, il faut prendre des décisions liées à l'affectation de locomotives aux trains planifiés en tenant compte des besoins d'entretien des locomotives. D’autres décisions traitant l'envoi de locomotives aux gares par mouvements à vide, les déplacements légers (sans tirer des wagons) et la location de locomotives tierces doivent également être prises en compte. Sur la base d'une formulation de programmation en nombres entiers et d'un réseau espace-temps présentés dans la littérature, nous introduisons une approche par horizon roulant pour trouver des solutions sous-optimales de ce problème dans un temps de calcul acceptable. Une formulation mathématique et un réseau espace-temps issus de la littérature sont adaptés à notre problème. Nous introduisons un nouveau type d'arcs pour le réseau et de nouvelles contraintes pour le modèle pour faire face aux problèmes qui se posent lors de la division de l'horizon de planification en plus petits morceaux. Les expériences numériques sur des instances réelles montrent les avantages et les inconvénients de notre algorithme par rapport à une approche exacte.This thesis addresses the locomotive routing problem arising at the Canadian National Railway Company (CN) - the largest railway in Canada in terms of both revenue and the physical size of its rail network. The problem aims to determine the sequence of activities for each locomotive over the planning horizon. Besides assigning locomotives to scheduled trains and considering scheduled locomotive maintenance requirements, the problem also includes other decisions, such as sending locomotives to stations by deadheading, light traveling, and leasing of third-party locomotives. Based on an Integer Programming formulation and a Time-Expanded Network presented in the literature, we introduce a Rolling Horizon Approach (RHA) as a method to find near-optimal solutions of this problem in acceptable computing time. We adapt a mathematical formulation and a space-time network from the literature. We introduce a new type of arcs for the network and new constraints for the model to cope with issues arising when dividing the planning horizon into smaller ones. Computational experiments on real-life instances show the pros and cons of our algorithm when compared to an exact solution approach

    Determinants of E-Cmmerce Adoption in SMEs

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    A deep insight of determinants of e-commerce adoption process is in needed to help small- and medium-sized enterprises (SMEs) to fasten up their e-commerce rush and overcome a great number of existed obstacles. This paper analyzed and classified factors taking effects on SMEs’ e-commerce adoption into four groups, specifically: (1) perceived benefits, (2) organizational readiness, (3) external environment, and (4) leadership attitudes and competences. Especially, the paper also gets an overview on the role of leadership in motivating the uptake of e-commerce within SMEs. Thorough analysis within the research contributes not only a general view about core determinants of e-commerce adoption, but also the engine toward the success of e-commerce distribution channel in SMEs

    CENPHER five year report 2009-2014: From a research project to a research center

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    Beginning in 2009 with a postdoc project working on environmental sanitation and health issues, the Hanoi School of Public Health (HSPH) research group gradually established other projects and activities that have been both nationally and internationally funded. This was the basis for the upgrade of the research group to a research center in 2012, Public Health and Ecosystem Research (CENPHER). The creation and the development of CENPHER reflects not only North- South partnership in research and public health action, but also how great issues in national public health and global health can be tackled through ecosystems/ecohealth approaches

    Effects of grain size distribution on the initial strain shear modulus of calcareous sand

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    The soil’s small strain shear modulus, Gmax or G0, is applied in dynamic behavior analyses and is correlated to other soil properties (density and void ratio) for predicting soil dynamic behavior under seismic loadings such as earthquakes, machinery or traffic vibrations. However, for calcareous sands, selecting representative samples for the field conditions is difficult; therefore, almost all measured soil parameters (post-seismic properties) do not reflect exactly the soil state before seismic loading. In some cases of dynamic loading, a change in grain size distribution (GSD) of soils, especially for calcareous sands might occur. Moreover, many of these sand types behave differently from silica sands owing to their mineralogy, particle characterization, soil skeleton, and the continuous changing of particle size. For this reason, a series of isotropic consolidation tests in ranges of confining pressure from 25 to 300 kPa as well as bender element measurements on a calcareous sand and on a reference silica sand were performed in this study. The effects of differences in gradation and in the type of material on the soil’s small strain shear modulus, Gmax, are discussed

    US financial crisis impact on Asian economies : does “decoupling” theory hold : the case of Singapore, Thailand and Vietnam

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    Until recently, many investors believed in decoupling theory which says that emerging countries can be resilient from the weakening of US economy and keep stable growths. In 2007, international investors observed a rise on stock markets of some emerging countries when stock price on developed markets in the US or the UK dropped dramatically. Meanwhile, they also observed prosperous economic growth in these emerging markets. This trend supported decoupling theory’s proponents who argue that when emerging stock markets move against a slump on developed markets as US or UK, the economy of these countries will also grow healthily. Since this argument is on discussion, the paper plans to find out a plausible answer for the question: if decoupling theory holds for stock market of emerging countries, will it also hold for their economies. The paper made data research on US market in relation with three other export-dependent Asian markets – Singapore, Thailand and Vietnam and will discuss two problems: (1) how is co-movement of Asian and the US stock markets from 2007 to 2009, and (2) how the economy of these markets responds in the according year. The paper expects to find that stock markets in emerging Asian countries are decoupled from US stock market and their economies also move independently. Data showed that in 2007, there was decoupling effect between Singapore, Thailand and the US. However, from October 2008 until March 2009, stock markets of these countries tracked the movement of US market quite closely. At the same time, their macro economic indicators were on downward trend. In these Southeast Asian countries, decoupling theory just holds for a short period when world economy is in good condition and we could not find certain sign whether it will hold again in the future

    Interactive visual data query & exploration : techniques for visual data analytics through visual query modelling and multidimensional data interaction

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    University of Technology Sydney. Faculty of Engineering and Information Technology.The direct data manipulation through visualization and associated navigation techniques has been implemented for many years. However, these methods are not uniformly discussed in the context of user interface design. During the history of user interface development, the interaction between humans and computers is almost to be done through software widgets. Since in the last decade, many advanced data visualization and interaction techniques have been developed, now it is the time to bring them into the formal discussion about the context of user interface design, data queries, and data manipulation. The dissertation attempts to fulfill the gap between visual user interface design and interactive data visualization. In relational data queries, many visualization techniques have featured advanced interactive operation; however, a majority of those would concentrate on the traditional style, instead of a modern approach. This is the reason why today in visual analytics truly direct manipulation is highly encouraged, instead of the conventional methods. This dissertation focuses on the investigation of modern data query approaches. It attempts to model the new data query methods that apply those advanced visualization and interaction techniques to facilitate the data analysis procedures. The second contribution of the dissertation is the design of new interaction methods for multi-dimensional data visualization. We first introduce a new framework which includes straightforward manipulation techniques for relational data discovery. These novel techniques, named MCquery, SumUp, and FigAxis, are exclusively developed for the key characteristics of relational data such as data models and data dimensions. The core methodology is about interactive visual query design based upon node-link graphics, parallel coordinate geometries, and scatterplot visualization, where the direct interaction is performed by friendly action such as clicks and brushes. The tools materialized from these techniques can help to reduce users’ cognitive and behavioral effort efficiently in dealing with the issues of information search-retrieval, quantitative data analysis, and correlation examination

    Sustainability: Reusing Data Center Waste Heat

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    Data Centers are facilities used to house a large number of computer systems and their associated components, such as telecommunications and data storage systems. Nowadays many organizations depend on the reliable operation of their data centers for their day to day business operations. Data centers are designed with redundant and backup power supplies, redundant data communications connections, robust cybersecurity protocols and very strict environmental controls. The many computer systems held in a typical data center generate large heat loads that need to be continuously removed with high grade air conditioning systems. Anthem currently owns a large corporate data center in Richmond that generates a large amount of waste heat that is currently dissipated into the environment. The objective of this project is to design a system that will help Anthem reuse some or most of the waste heat generated by the data center, possibly using it to heat the adjoining office building. The proposed system would not only reduce Anthem’s energy costs to heat the office building but it would decrease Anthem’s overall environmental footprint. The solution that the team decided upon is to add a second condenser bundle to an already existing centrifugal chiller. This would allow for a higher-grade heat to be produced. This hot water would then be piped to a coil within the make-up air handler units and the outside air that would normally be heated by natural gas will now be heated by the hot water. The air passing through the coil would now be hot usable air and thus able to be distributed throughout the building.https://scholarscompass.vcu.edu/capstone/1128/thumbnail.jp

    Remote Working Burnout: Empirical Study from TOE and Technostress Model

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    Work stress and burnout negatively impact the individual and companies. Remote working exacerbates these issues due to the lack of company support and social interactions. Yet, research on identifying factors contributing to stress and burnout in remote workspaces and differentiating the components of stress and burnout in this context is limited. This work presents and empirically evaluates a conceptual framework, based on the Technology – Organization – Environment framework and the technostress theory, which aims to address these gaps. In particular, the model proposed here distinguishes between technostress, work stress, and burnout. Future work to examine the model will use a survey instrument for data gathering, as well as confirmatory factor analysis and partial least squares for analysis
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