The trade-off between costs and carbon emissions from lot-sizing decisions

Logistics decisions can have a significant impact on carbon emissions, a driver of global warming. One possible way to reduce emissions is by adapting a lower delivery frequency, which enables better vehicle utilization or the usage of relatively effcient large vehicles. We study the situation in which a decision maker decides on the amount to be shipped in each period, where he/she can order items in each period and keep items on inventory. If the shipped quantity is large, vehicle capacity is well utilized, but many products have to be stored. Existing studies in this field of research, called lot-sizing, have introduced models for incorporating carbon emissions in the decision making, but do not focus on realistic values of the emission parameters. Therefore, we conduct a survey of empirical studies in order to establish the possible marginal emissions from holding inventory and performing a shipment with a truck.

The effect of pyramiding Phytophthora infestans resistance genes RPi-mcd1 and RPi-ber in potato

Despite efforts to control late blight in potatoes by introducing Rpi-genes from wild species into cultivated potato, there are still concerns regarding the durability and level of resistance. Pyramiding Rpi-genes can be a solution to increase both durability and level of resistance. In this study, two resistance genes, RPi-mcd1 and RPi-ber, introgressed from the wild tuber-bearing potato species Solanum microdontum and S. berthaultii were combined in a diploid S. tuberosum population. Individual genotypes from this population were classified after four groups, carrying no Rpi-gene, with only RPi-mcd1, with only RPi-ber, and a group with the pyramided RPi-mcd1 and RPi-ber by means of tightly linked molecular markers. The levels of resistance between the groups were compared in a field experiment in 2007. The group with RPi-mcd1 showed a significant delay to reach 50% infection of the leaf area of 3 days. The group with RPi-ber showed a delay of 3 weeks. The resistance level in the pyramid group suggested an additive effect of RPi-mcd1 with RPi-ber. This suggests that potato breeding can benefit from combining individual Rpi-genes, irrespective of the weak effect of RPi-mcd1 or the strong effect of RPi-ber

Sterkte-Zwakte analyse van e-therapieen

Deze scriptie is opgezet in de vorm van een literatuurstudie, ter afronding van de opleiding Psychologie aan de Rijksuniversiteit te Groningen. In deze scriptie wordt er een sterkte-zwakte analyse gemaakt van e-therapieën; een innovatief en nieuw aanbod in de geestelijke gezondheidszorg. De wachtlijsten in de Nederlandse geestelijke gezondheidszorg zijn al jaren een moeilijk oplosbaar probleem. Juist in het huidige technologische tijdperk kunnen e-therapieën een mooie aanvulling zijn op het bestaande aanbod in de geestelijke gezondheidszorg. E-therapieën zijn therapeutische behandelingen aangeboden via het internet, met of zonder contact met een behandelaar dat synchroon of asynchroon in de tijd kan lopen. De sterkte-analyse laat zien dat e-therapieën op grote schaal gebruikt kunnen worden en gelijktijdig de kosten van psychische zorg, jaarlijks zo’n acht miljard euro (www.cbs.nl) en bijkomend arbeidsverzuim aanzienlijk omlaag kunnen brengen. Afgaand op resultaten uit wetenschappelijke onderzoeken blijken e-therapieën een (kosten)effectieve en efficiënte innovatie om het huidige zorgaanbod te kunnen ondersteunen door de kortdurende, geprotocolleerde en ‘evidence based’ vorm van behandelen, gebaseerd op de ‘stepped care’ procedure. De zwakke kanten lijken grotendeels veroorzaakt door de relatieve nieuwheid van e-therapieën. Wet- en regelgevingen, beroepsrichtlijnen, privacybeveiligingen en de financiële infrastructuur zijn nog onvoldoende geregeld. Daarnaast zijn de behandelmogelijkheden en de kosteneffectiviteit van e-therapieën onvoldoende bekend. Mits deze knelpunten de nodige aandacht krijgen kunnen deze tijdig ondervangen worden.

Balancing the fit and logistics costs of market segmentations

Segments are typically formed to serve distinct groups of consumers with differentiated marketing mixes, that better fit their specific needs and wants. However, buyers in a segment are not necessarily geographically closely located. Serving a geographically dispersed segment with one marketing mix can increase the logistics costs in the form of high transportation costs and long lead times. This study proposes a segmentation method that balances the fit of a segmentation strategy against the corresponding logistics costs. An application to the problem of segmenting a set of European regions, using consumers' store attribute preferences as a segmentation basis, suggests segment-specific retail positioning strategies that reflect different decisions about store image attributes such as price, assortment, and atmosphere. This approach designates transnational segments that require acceptable logistics costs and offer the highest possible level of within segment homogeneity. (C) 2011 Elsevier B.V. All rights reserved

Lower tolerance-based Branch and Bound algorithms for the ATSP

In this paper, we develop a new tolerance-based Branch and Bound algorithm for solving NP-hard problems. In particular, we consider the asymmetric traveling salesman problem (ATSP), an NP-hard problem with large practical relevance. The main algorithmic contribution is our lower bounding strategy that uses the expected costs of including arcs in the solution to the assignment problem relaxation of the ATSP, the so-called lower tolerance values. The computation of the lower bound requires the calculation of a large set of lower tolerances. We apply and adapt a finding from [23] that makes it possible to compute all lower tolerance values efficiently. Computational results show that our Branch and Bound algorithm exhibits very good performance in comparison with state-of-the-art algorithms, in particular for difficult clustered ATSP instance