Search results for "RAV"
showing 10 items of 5866 documents
‘Each flight is different’ : Carbon emissions of selected flights in three geographical markets
2017
Abstract Air travel is considered the biggest individual climate sin. Avoiding flying, however, seems impossible. In this paper we argue that the flight a passenger chooses can be significant. For this purpose we compared the carbon emissions of selected flights in three geographical markets. We found tremendous differences in the environmental performance of individual flights. Furthermore, we also found that flying with the most modern aircraft or flying non-stop represents, in many cases, the least polluting option. Nevertheless, we were able to show that there are exceptions to this rule. Based on our results, we provide recommendations to the industry and for further research.
A New Branch-and-Cut Algorithm for the Generalized Directed Rural Postman Problem
2016
The generalized directed rural postman problem, also known as the close-enough arc routing problem, is an arc routing problem with some interesting real-life applications, such as routing for meter reading. In this article we introduce two new formulations for this problem as well as various families of new valid inequalities that are used to design and implement a branch-and-cut algorithm. The computational results obtained on test bed instances from the literature show that this algorithm outperforms the existing exact methods
Branch-price-and-cut algorithms for the pickup and delivery problem with time windows and multiple stacks
2016
Abstract This paper proposes models and algorithms for the pickup and delivery vehicle routing problem with time windows and multiple stacks. Each stack is rear-loaded and is operated in a last-in-first-out (LIFO) fashion, meaning that when an item is picked up, it is positioned at the rear of a stack. An item can only be delivered if it is in that position. This problem arises in the transportation of heavy or dangerous material where unnecessary handling should be avoided, such as in the transportation of cars between car dealers and the transportation of livestock from farms to slaughterhouses. To solve this problem, we propose two different branch-price-and-cut algorithms. The first sol…
The Chinese Postman Problem with Load-Dependent Costs
2018
[EN] We introduce an interesting variant of the well-known Chinese postman problem (CPP). While in the CPP the cost of traversing an edge is a constant (equal to its length), in the variant we present here the cost of traversing an edge depends on its length and on the weight of the vehicle at the moment it is traversed. This problem is inspired by the perspective of minimizing pollution in transportation, since the amount of pollution emitted by a vehicle not only depends on the travel distance but also on its load, among other factors. We define the problem, study its computational complexity, provide two mathematical programming formulations, and propose two metaheuristics for its soluti…
Using a hazard-independent approach to understand road-network robustness to multiple disruption scenarios
2021
Abstract A range of predictable and unpredictable events can cause road perturbations, disrupting traffic flows and more generally the functioning of society. To manage this threat, stakeholders need to understand the potential impact of a multitude of predictable and unpredictable events. The present paper adopts a hazard-independent approach to assess the robustness (ability to maintain functionality despite disturbances) of the Sioux Falls network to all possible disruptions. This approach allows understanding the impact of a wide range of disruptive events, including random, localised, and targeted link failures. The paper also investigates the predictability of the link combinations wh…
Web based survey to measuring social interactions, values, attitudes and travel behavior
2018
Abstract This paper presents the data collection methodology developed for Minerva research project. The aim of Minerva is to study the influence of values, attitudes and social interactions on travel behavior. For this purpose, a web based survey has been developed, which consists of several questionnaires to collect respondents’ values and attitudes; a two-day activity-travel diary; information about social interactions; and socio-demographic characteristics. To identify the social contacts, it is being used a contact diary methodology together with the activity-travel diary.
Flexible work arrangements and household-related journeys. Who takes the lead in dual-earner heterosexual couples?
2022
International audience; This research provides an exploration of the relationship between flexible work arrangements (FWA), CO2 emissions, and household travel allocation among dual-earner couples. Using data from the United Kingdom National Travel Survey for the period between 2002 and 2017, we develop a path analysis approach based on SEM that allows for a comprehensive study of travel behavior and trade-off effects. Results suggest that, although the partner who benefits from FWAs tends to carry out domestic provision and maintenance activities, the allocation of tasks within the household is still asymmetrical. Results also outline that the presence of children will intensely affect the…
Études scientifiques et marché du travail : éléments de réflexion sur la crise des formations en sciences
2007
Student disaffection towards sciences, most evident in pure science undergraduates, is causing increasing concern for the future of scientific training in France. If access to employment deteriorates more for science graduates than for graduates in other disciplines, science graduates will have a distinct advantage in terms of earnings and employment status, when the economic situation becomes less favourable. Within sciences, graduates of pure sciences have a more difficult transition from education to employment than those from applied sciences. Yet graduates from both disciplines compete for the same job in the private sector with pure science graduates receiving lower wages. The “crisis…
Housekeepers and the Siren Call of Hotel Chains
2009
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Practices of Writing in Ethnographic Work
2020
Although the practice of writing is key to the production of ethnographic knowledge, the topic remains understudied. Using material from our own ethnographic research in the fields of air travel and cultural heritage as data, we develop a reflexive account of ethnographic writing. We examine in detail the practices of jotting down observations, writing field notes, analytic annotating, ordering and rearranging, and drafting and revising papers. The article takes a praxeological stance, conceptualizing writing as a practice that is simultaneously cognitive, embodied, and material. Our analysis finds that writing influences and shapes all stages of ethnographic work, from orienting perception…