20,159 research outputs found
VRPPO
No full textThis data sets are used in the computational section of the paper: Baller, A. C., Dabia, S., Dullaert, W. E. H., & Vigo, D. (2020). The vehicle routing problem with partial outsourcing. Transportation Science, 54(4), 1034-1052. https://doi.org/10.1287/TRSC.2019.094
VRPPO
No full textThis data sets are used in the computational section of the paper: Baller, A. C., Dabia, S., Dullaert, W. E. H., & Vigo, D. (2020). The vehicle routing problem with partial outsourcing. Transportation Science, 54(4), 1034-1052. https://doi.org/10.1287/TRSC.2019.094
An exact algorithm for a rich vehicle routing problem with private fleet and common carrier
No full textThe vehicle routing problem with private fleet and common carrier (VRPPC) is a generalization of the classical vehicle routing problem in which the owner of a private fleet can either visit a customer with one of the owner's vehicles or assign the customer to a common carrier. The latter case occurs if the demand exceeds the total capacity of the private fleet or if it is more economically convenient to do so. The owner's objective is to minimize the variable and fixed costs for operating the owner's fleet plus the total cost charged by the common carrier. This family of problems has many practical applications, particularly in the design of last-mile distribution services and has received some attention in the literature, in which some heuristics were proposed. We extend here the VRPPC by considering more realistic cost structures that account for quantity discounts on outsourcing costs and by considering time windows resulting in a rich VRPPC (RVRPPC). We present an exact approach based on a branch-and-cut-and-price algorithm for the RVRPPC and test the algorithm on instances from the literature.</p
An exact algorithm for a rich vehicle routing problem with private fleet and common carrier
Full text linkThe vehicle routing problem with private fleet and common carrier (VRPPC) is a generalization of the classical vehicle routing problem in which the owner of a private fleet can either visit a customer with one of the owner's vehicles or assign the customer to a common carrier. The latter case occurs if the demand exceeds the total capacity of the private fleet or if it is more economically convenient to do so. The owner's objective is to minimize the variable and fixed costs for operating the owner's fleet plus the total cost charged by the common carrier. This family of problems has many practical applications, particularly in the design of last-mile distribution services and has received some attention in the literature, in which some heuristics were proposed. We extend here the VRPPC by considering more realistic cost structures that account for quantity discounts on outsourcing costs and by considering time windows resulting in a rich VRPPC (RVRPPC). We present an exact approach based on a branch-and-cut-and-price algorithm for the RVRPPC and test the algorithm on instances from the literature
Erratum:Branch and Price for the Time-Dependent Vehicle Routing Problem with Time Windows (Transportation Science (2024) 58:5 (919-924) DOI: 10.1287/trsc.11200445)
Full text linkThe aim of this erratum is to correct an error in the computer implementation of the algorithm proposed by Dabia, Ropke, and van Woensel [Dabia S, Ropke S, van Woensel T (2013) Branch and price for the time-dependent vehicle routing problem with time windows. Transportation Sci. 47(3):295–454]. Section 6, “Computational Results,” from the original paper is rewritten to reflect the corrected implementation, the new computational setup, and the updated results.The aim of this erratum is to correct an error in the computer implementation of the algorithm proposed by Dabia, Ropke, and van Woensel [Dabia S, Ropke S, van Woensel T (2013) Branch and price for the time-dependent vehicle routing problem with time windows. Transportation Sci. 47(3):295–454]. Section 6, “Computational Results,” from the original paper is rewritten to reflect the corrected implementation, the new computational setup, and the updated results
The Dynamic-Demand Joint Replenishment Problem with Approximated Transportation Costs
Full text linkIn a vendor-managed inventory setting, a supplier determines the timing and size of replenishments for its customers. In the Dynamic-Demand Joint Replenishment Problem (DJRP), one assumes that the supplier pays a fixed fee for replenishing a customer which often occurs if the supplier outsources transportation. Hence, there is no incentive for the supplier to schedule replenishments for nearby customers in the same period. This results in higher transportation costs for the carrier, decreased vehicle utilization and increased future fees for the supplier. To lower costs for both parties, this paper extends the traditional DJRP to the DJRP with Approximated Transportation Costs (DJRP-AT) by taking transportation considerations into account. Since routing problems are difficult to solve and it is not necessary to know the sequence of the deliveries to the customers as these are outsourced, the transportation costs for a given set of customers are approximated using classical schemes. A solution approach for the DJRP-AT based on Branch-and-Cut-and-Price is validated using test instances from the literature. Results show improvements of 4% on average and up to 14.4% for individual instances compared with the DJRP. Moreover, when the DJRP-AT is compared with the DJRP on instances derived from a real-life case, similar savings are obtained. Comparing the DJRP-AT to an equivalent problem with actual routing costs, the solution values of the DJRP-AT are on average only 0.77% higher showing the value of the approximation
Writing from the shadowlands: how cross-cultural literature negotiates the legacy of Edward Said
Full text linkThis thesis examines the impact of Edward Said's influential work Orientalism and its legacy in respect of contemporary reading and writing across cultures. It also questions the legitimacy of Said's retrospective stereotyping of early examples of cross-cultural representation in literature as uncompromisingly 'orientalist'.
It is well known that the release of Edward Said's Orientalism in 1978 was responsible for the rise of a range of cultural and critical theories from multiculturalism to postcolonialism. It was a study that not only polarized critics and forced scholars to re-examine orientalist archives, but persuaded creative writers to re-think their ethnographic positions when it came to the literary representations of cultures other than their own. Without detracting from the enormous impact of Said, this thesis isolates gaps and silences in Said that need correcting. Furthermore, there is an element of intransigence, an uncompromising refusal to fine-tune what is essentially a binary discourse of the West and its other in Said's work, that encourages the continued interrogation of power relations but which, because of its very boldness, paradoxically disallows the extent to which the conflict of cultures indeed produced new, hybrid social and cultural formations.
In an attempt to challenge the severity of Said's claim that 'every European, in what he could say about the Orient, was consequently a racist, an imperialist, and almost totally ethnocentric', the thesis examines a number of different discursive contexts in which such a presumption is challenged. Thus while the second chapter discusses the 'traditional' profession-based orientalism of nineteenth-century E. G. Browne, the third considers the anti-imperialism of colonial administrator Leonard Woolf. The fourth chapter provides a reflection on the difficulties of diasporic 'orientalism' through the works of Michael Ondaatje while chapter five demonstrates the effects of the dialogism used by Amitav Ghosh as a defence against 'orientalism'. The thesis concludes with an examination of contemporary writing by Andrea Levy that appositely illustrates the legacy of Said's influence.
While the restrictive parameters of Said's work make it difficult to mount a thorough-going critique of Said, this thesis shows that, indeed, it is within the restraints of these parameters and in the very discourse that Said employs that he traps himself. This study claims that even Said is susceptible to 'orientalist' criticism in that he is as much an 'orientalist' as those at whom he directs his polemic
Time and multiple objectives in scheduling and routing problems
Full text linkMany optimization problems encountered in practice are multi-objective by nature, i.e., different objectives are conflicting and equally important. Many times, it is not desirable to drop some of them or to optimize them in a composite single objective or hierarchical manner. Furthermore, cost parameters change over time which makes optimization problems harder. For instance, in the transport sector, travel costs are a function of travel time which changes depending on the time of the day a vehicle is travelling (e.g., due to road congestion). Road congestion results in tremendous delays which lead to a decrease in the service quality and the responsiveness of logistic service providers. In Chapter 2, we develop a generic approach to deal with Multi-Objective Scheduling Problems (MOSPs) with State-Dependent Cost Parameters. The aim is to determine the set of Pareto solutions that capture the trade offs between the different conflicting objectives. Due to the complexity of MOSPs, an efficient approximation based on dynamic programming is developed. The approximation has a provable worse case performance guarantee. Even though the generated approximate Pareto front consist of fewer solutions, it still represents a good coverage of the true Pareto front. Furthermore, considerable gains in computation times are achieved. In Chapter 3, the developed methodology is validated on the multi-objective timedependent knapsack problem. In the classical knapsack problem, the input consists of a knapsack with a finite capacity and a set of items, each with a certain weight and a cost. A feasible solution to the knapsack problem is a selection of items such that their total weight does not exceed the knapsack capacity. The goal is to maximize the single objective function consisting of the total pro t of the selected items. We extend the classical knapsack problem in two ways. First, we consider time-dependent profits (e.g., in a retail environment profit depends on whether it is Christmas or not)
What said the economic theory about Portugal. Another approach
Full text linkWith this work we try to analyse the agglomeration process in the Portuguese regions, using the New Economic Geography models. This work aims to test, also, the Verdoorn Law, with the alternative specifications of (1)Kaldor (1966), for the 28 NUTS III Portuguese in the period 1995 to 1999. It is intended to test the alternative interpretation of (2)Rowthorn (1975). With this study we want, also, to test the Verdoorn´s Law at a regional and a sectoral levels (NUTs II) for the period 1995-1999. The importance of some additional variables in the original specification of Verdoorn´s Law is yet tested, such as, trade flows, capital accumulation and labour concentration. This study analyses, also, through cross-section estimation methods, the influence of spatial effects in productivity in the NUTs III economic sectors of mainland Portugal from 1995 to 1999, considering the Verdoorn relationship. The aim of this paper is, yet, to present a contribution, with panel data, to the analysis of absolute convergence and conditional of the sectoral productivity at regional level (from 1995 to 1999). The structural variables used in the analysis of conditional convergence is the ratio of capital/output, the flow of goods/output and location ratio.new economic geography; Verdoorn law; convergence; cross-section and panel data; Portuguese regions
What said the new economic geography about Portugal? An alternative approach
Full text linkWith this work we try to analyse the agglomeration process in Portugal, using the New Economic Geography models, in a linear and in a non linear way. In a non linear way, of referring, as summary conclusion, that with this work the existence of increasing returns to scale and low transport cost, in the Portuguese regions, was proven and, because this, the existence of agglomeration in Portugal. We pretend, also, in a linear way to explain the complementarily of clustering models, associated with the New Economic Geography, and polarization associated with the Keynesian tradition. As a summary conclusion, we can say which the agglomeration process shows some signs of concentration in Lisboa e Vale do Tejo and the productivity factor significantly improves the results that explain the regional clustering in Portugal. The aim of this paper is to analyze, yet, the relationship between the regional industry clustering and the demand for labor by companies in Portugal. Again, the results are consistent with the theoretical developments of the New Economic Geography, namely the demand for labor is greater where transport costs are lower and where there is a strong links "backward and forward" and strong economies of agglomeration.new economic geography; linear and non linear models; Portuguese regions
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