162,058 research outputs found
The Pyramidal Capacitated Vehicle Routing Problem
No full textThis paper introduces the Pyramidal Capacitated Vehicle Routing Problem (PCVRP) as a restricted version of the Capacitated Vehicle Routing Problem (CVRP). In the PCVRP each route is required to be pyramidal in a sense generalized from the Pyramidal Traveling Salesman Problem (PTSP). A pyramidal route is de ned as a route on which the vehicle rst visits customers in increasing order of customer index, and on the remaining part of the route visits customers in decreasing order of customer index. Provided that customers are indexed in nondecreasing order of distance from the depot, the shape of a pyramidal route is such that its traversal can be divided in two parts, where on the rst part of the route, customers are visited in nondecreasing distance from the depot, and on the remaining part of the route, customers are visited in nonincreasing distance from the depot. Such a route shape is indeed found in many optimal solutions to CVRP instances. An optimal solution to the PCVRP may therefore be useful in itself as a heuristic solution to the CVRP. Further, an attempt can be made to nd an even better CVRP solution by solving a TSP, possibly leading to a non-pyramidal route, for each of the routes in the PCVRP solution. This paper develops an exact branch-and-cut-and-price (BCP) algorithm for the PCVRP. At the pricing stage, elementary routes can be computed in pseudo-polynomial time in the PCVRP, unlike in the CVRP. We have therefore implemented pricing algorithms that generate only elementary routes. Computational results suggest that PCVRP solutions are highly useful for obtaining near-optimal solutions to the CVRP. Moreover, pricing of pyramidal routes may due to its eciency prove to be very useful in column generation for the CVRP.vehicle routing; pyramidal traveling salesman; branch-and-cut-and-price
Scheduling participants of Assessment Centres
No full textAssessment Centres are used as a tool for psychologists and coaches to ob- serve a number of dimensions in a person's behaviour and test his/her potential within a number of chosen focus areas. This is done in an intense course, with a number of dierent exercises which expose each participant's ability level in the chosen focus areas. The participants are observed by assessors with the purpose of gathering material for reaching a conclusion on each participant's personal pro le. We consider the particular case that arises at the company Human Equity (www.humanequity.dk), where Assessment Centres usually last two days and involve 3-6 psychologists or trained coaches as assessors. An entire course is composed of a number of rounds, with each round having its individual duration. In each round, the participants are divided into a number of groups with prespeci ed pairing of group sizes and assessors. The scheduling problem amounts to determining the allocation of participants to groups in each round. We have developed a model and solution approach for this particular scheduling problem, which may be viewed as a rather extensive generalization of the Social Golfer Problem.No keywords;
Column generation approaches to ship scheduling with flexible cargo sizes
No full textWe present a Dantzig-Wolfe procedure for the ship scheduling problem with flexible cargo sizes. This problem is similar to the well-known pickup and delivery problem with time windows, but the cargo sizes are defined by an interval instead of a fixed value. We show that the introduction of flexible cargo sizes to the column generation framework is not straightforward, and we handle the flexible cargo sizes heuristically when solving the subproblems. This leads to convergence issues in the branch-and-price search tree, and the optimal solution cannot be guaranteed. Hence we have introduced a method that generates an upper bound on the optimal objective. We have compared our method with an a priori column generation approach, and our computational experiments on real world cases show that the Dantzig-Wolfe approach is faster than the a priori generation of columns, and we are able to deal with larger or more loosely constrained instances. By using the techniques introduced in this paper, a more extensive set of real world cases can be solved either to optimality or within a small deviation from optimalityTransportation; integer programming; dynamic programming
Optimal vehicle routing with lower and upper bounds on route durations
No full textThis article is concerned with the problem of finding optimal vehicle routes to minimize the overall travel time, with constraints on the minimum and maximum amount of time spent on each route. The problem extends previous work on the distance-constrained vehicle routing problem by introducing lower bounds on route durations to ensure that the resulting routes are balanced. The article also explicitly addresses the situation where a solution is artificially balanced as a result of inoptimal orders of visits. The article describes alternative ways in which the restrictions on route connectivity, duration, and artificial balancing can be formulated, and introduces an exact algorithm based on cutting planes and mixed-integer linear programming. To the best of our knowledge, this is the first exact algorithm proposed for such a problem that explicitly addresses artificially balanced routes. Computational results are presented for three versions of the exact algorithm using TSPLIB instance
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
Murder on the mountain: author talk with Peter J. Wosh
No full textAuthor talk by Peter J. Wosh on May 5th, 2022, on his book, "Murder on the Mountain: crime, passion, and punishment in gilded age New Jersey.
Can we unpack the global in ESE? An introduction
No full textIn seeking co-provocateurs for this roundtable, the initial outreach was fuelled by anger regarding the devaluing of social sciences compared to natural sciences and economics (Mendel, 2014) as well as the frustration of seeing poorly designed research by natural scientists studying human behaviour and education without being informed by protocols and best practices developed for such work by the social sciences (Pooley, Mendelsohn & Milner-Gulland, 2014), and ignorance of deep critical explorations of educational and other social processes by sociologists, anthropologists amongst others (Sund & Lysgaard, 2013). However, the initial response provoked an offer to discuss the role of love in environmental and sustainability education research, ESER. While this reply was clearly housed in the same concerns and critique initially expressed, the use of the word “love”, a powerful concept simultaneously simple and complex, drew us to seek a circle of renewal and remembering of life and lives that may have been forgotten at times within ESER.The phrase “all our/my relations” comes from indigenous worldviews and practices of honouring all the people who have come before you as well as the other living beings with whom we share this planet (Kulnieks, Longboat & Young, 2013). This round table discussion will honour all our relations by remembering the current and past practices which take on issues related to motivation rooted in social and cultural patterns, as well as politics of knowledge with complex histories and inequities (Glass, Scott & Price, 2012; Sund & Öhman, 2014). We will respect people and scholarship via three main currents of discussion:The role of love in ESER“Ignored concepts” - Research and extensive discourse that gets ignored when defining questions that assume people are selfish and have never cooperated to protect the commons, or are not politically active (Gaiser, Rijke & Spanning, 2010) uncritical acceptance of people/nature dichotomy, uncritical use of education as transferring information from expert to ignorant.Political dimensions of ESER (postcolonial lens, global inequities, poverty in the “south”)The discussions will flow at the level of and through individuals, but also at infrastructural and conceptual spaces and places. Creative methodologies provide powerful avenues to disrupt imbalances and injustices and take into account issues of representation, legitimation and politics in research as well as communications about research (McKenzie, 2005). Philip Payne (2005) challenges the limitations of textual discourse as a way of knowing; he focuses on “being, doing and becoming a relational, social and ecological ‘self’” (p. 415) and suggests that strong cultural production constrains these qualities. Framing, metaphors and narratives are important for meaning making (Lakoff, 2010) and are particularly important to deconstruct when challenging dominant views that may have been taken as common sense (Stone-Mediatore, 2003), as well as inviting critical reflection on the very story being told. We will use creative juxtapositioning of the currents of discussion in order to evoke deeper insights than may arise from sequential presentations of the three discussion themes (Neilson, 2009). Additionally, the format of the round table will include multiple forms of communications to involve all who attend, and, the participants along with the provocateurs will physically be seated within a circle.ReferencesGaiser, W., Rijke, J.D., & Spanning, R. (2010). Youth and political participation – empirical results for Germany within a European context. Youth 18(4), 427-450. Glass, J. H., Scott, A., & Price, M. F. (2012). Getting active at the interface: How can sustainability researchers stimulate social learning? In A. Wals & P. Blaze Concoran (Eds.) Learning for sustainability in times of accelerating change. pp. 167-183. Wageningen University Press, NL. Kronlid, D.O., & Öhman, J. (2012). An environmental ethical conceptual framework for research on sustainability and environmental education. Environmental Education Research, ifirst article, 1-24. Kulnieks, A., Longboat, D. R. & Young, K. (2013). Contemporary Studies in Environmental and Indigenous Pedagogies. A Curricula of Stories and Place. Rotterdam: Sense Publishers. Lakoff, G. (2010). Praxis forum. Why it matters how we frame the environment. Environmental Communication, 4(1), 70-81. McKenzie, M. (2005). The ‘post-post period’ and environmental education research. Environmental Education Research, 11(4), 401-412. Mendel, J. (2014). Bad Research and High Impact: The Science: So What Campaign and Social Media Criticism. ACME: An International E-Journal for Critical Geographies, 13(1), 56-61. Neilson, A. L. (2009). The power of nature and the nature of power. Special Issue: Inquiries into practice. Canadian Journal of Environmental Education, 14, 136-148. Payne, P. (2005). Lifeworld and textualism: Reassembling the researcher/ed and ‘others’. Environmental Education Research, 11(4), 413-431. Pooley, S. P., Mendelsohn, J. A., & Milner‐Gulland, E. J. (2014). Hunting Down the Chimera of Multiple Disciplinarity in Conservation Science. Conservation Biology, 28(1), 22-32. Stone-Mediatore, S. (2003). Reading across border: Storytelling and knowledges of resistance. New York, NY: Palgrave. Sund, L., & Öhman, J. (2014). On the need to repoliticise environmental and sustainability education: Rethinking the postpolitical consensus. Environmental Education Research, 20(5), 639-659. Sund, P., & Lysgaard, J. (2013). Reclaim “Education” in Environmental and Sustainability Education Research. Sustainability, 5(4), 1598–1616.</p
Mr. Melvin J. Collier, RWWL AUC, June 2011
No full textThis video is a conversation with Mr. Melvin J. Collier. Mr. Collier talks about his book, "From Mississippi to Africa: A Journey of Discovery". Daniel Le, AUC Woodruff Library, is the interviewer
Reachability cuts for the vehicle routing problem with time windows
No full textThis paper introduces a class of cuts, called reachability cuts, for the Vehicle Routing Problem with Time Windows (VRPTW). Reachability cuts are closely related to cuts derived from precedence constraints in the Asymmetric Traveling Salesman Problem with Time Windows and to k-path cuts for the VRPTW. In particular, any reachability cut dominates one or more k-path cuts. The paper presents separation procedures for reachability cuts and reports computational experiments on well-known VRPTW instances. The computational results suggest that reachability cuts can be highly useful as cutting planes for certain VRPTW instances.Routing; time windows; precedence constraints
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