Showing papers in "Or Spektrum in 2001"

Vehicle routing and reverse logistics: The vehicle routing problem with simultaneous delivery and pick-up

Abstract: Recently, the increasing focus on environmental protection has led to significant changes in logistics processes In addition to the distribution process to the customers, re-usable packaging and goods to be recycled or remanufactured have to be transported in the reverse direction If both tasks have to be performed simultaneously at the customers' locations which are serviced by a fleet of vehicles stationed in a depot or distribution/redistribution center, the vehicle routing problem with simultaneous delivery and pick-up arises In this paper, the relation between this problem and other vehicle routing problems is investigated A heuristic construction procedure is suggested The proposed algorithm is successfully applied to a real-life problem as well as test instances introduced in the literature earlier In addition, randomly generated instances are tackled in order to try to determine favorable settings for the parameters used in the solution approach

Models for recycling electronics end-of-life products

Abstract: Increasing environmental concerns about the disposal of mass produced products have resulted in efforts to take back end-of-life consumer products. Legislation aimed at forcing manufacturers to take back electronics products at the end of their useful lives has either been adopted or is impending in many countries. This, along with shrinking landfill capacity and the reluctance of communities to open new waste sinks underscores the importance of developing methods and models for the management of end-of-life materials and products. This paper reports a study of the reverse channels for recycling of electronics products. The economics of electronics recycling are modeled from the viewpoints of the generators, recyclers, and material processors separately. A variety of mathematical programming models, representative of the many ways in which the recycling industry currently operates, have been proposed along with numerical illustrations. Models integrating disassembly and material recovery decisions are also presented. These models can be used by recyclers and processors for optimizing recycling operations and thus contribute towards the economic sustainability of electronics recycling.

Optimal control of production and remanufacturing in a simple recovery model with linear cost functions

Abstract: One aspect in reverse logistics concerns returns of used products and recovery for another life cycle. Remanufactured parts can be used for assembly of new products or the entire (upgraded) product can be sold again. Limitations and enormous waste disposal cost, the duty for manufacturers to take back used products from customers, and the fact that returned products can be regarded as a resource for material requirements are reasons for a consideration of product recovery. In this paper, we present an optimal control approach to optimize the production, remanufacturing, and disposal strategy with respect to dynamic demand and returns.

Truncated branch-and-bound, schedule-construction, and schedule-improvement procedures for resource-constrained project scheduling

Abstract: We present heuristic procedures for approximately solving large project scheduling problems with general temporal and resource constraints. In particular, we propose several truncated branch-and-bound techniques, priority-rule methods, and schedule-improvement procedures of types tabu search and genetic algorithm. A detailed experimental performance analysis compares the different heuristics devised and shows that large problem instances with up to 1000 activities and several resources can efficiently be solved with sufficient accuracy.

Integrated technique assessment with imprecise information as a support for the identification of best available techniques (BAT)

Abstract: The determination of Best Available Techniques (BAT) plays an essential role in the realisation of the IPPC-Directive 96/61/EC (concerning integrated pollution prevention and control) in all Member States of the European Union From a methodological point of view, the BAT determination is based on a comprehensive cross-media assessment of the impacts on the environment in general and therefore forms a multi criteria decision situation However, exact data for the description of the investigated techniques and their potential environmental impact are rarely obtainable Therefore, a decision support tool for the identification of BAT should also take into account imprecise information In this paper, the Outranking method PROMETHEE has been chosen as a multi criteria decision support Enhancements towards the consideration of imprecise information are discussed, such as fuzzy intervals and incomplete data sets The application of the conceived multi criteria decision support tool as well as a graphical sensitivity analysis is presented with the help of a case study from the iron and steel making industry

Resource---constrained project scheduling: a heuristic for the multi---mode case

Abstract: This paper presents a heuristic solution procedure for a very general resource---constrained project scheduling problem. Here, multiple execution modes are available for the individual activities of the project. In addition, minimum as well as maximum time lags between different activities may be given. The objective is to determine a mode and a start time for each activity such that the temporal and resource constraints are met and the project duration is minimized. Project scheduling problems of this type occur e.g. in process industries. The heuristic is a multi---pass priority---rule method with backplanning which is based on an integration approach and embedded in random sampling. Its performance is evaluated within an experimental performance analysis for problem instances of real---life size with 100 activities and up to 5 modes per activity.

Integrated technique assessment with imprecise information as a support for the identification of best available techniques (BAT): Integrierte Technikbewertung bei unvollständigen Informationen als Unterstützung für die Bestimmung von Besten Verfügbaren Techniken (BVT)

Abstract: The determination of Best Available Techniques (BAT) plays an essential role in the realisation of the IPPC-Directive 96/61/EC (concerning integrated pollution prevention and control) in allMember States of the EuropeanUnion. From amethodological point of view, the BATdetermination is based on a comprehensive cross-media assessment of the impacts on the environment in general and therefore forms a multi criteria decision situation. However, exact data for the description of the investigated techniques and their potential environmental impact are rarely obtainable. Therefore, a decision support tool for the identification of BAT should also take into account imprecise information. In this paper, the Outranking method PROMETHEE has been chosen as a multi criteria decision support. Enhancements towards the consideration of imprecise information are discussed, such as fuzzy intervals and incomplete data sets. The application of the conceived multi criteria decision support tool as well as a graphical sensitivity analysis is presented with the help of a case study from the iron and steel making industry. Zusammenfassung. Die Identifikation von Besten Verfugbaren Techniken (BVT) spielt eine wesentliche Rolle bei der Umsetzung der IVU-Richtline (96/61/EG, EG-Richtlinie uber die integrierte Vermeidung und Verminderung der Umweltverschmutzung) in allen Mitgliedsstaaten. Aus methodischer Sicht stellt die Bestimmung von BVT eine Mehrzielentscheidung dar, die auf einer umfassenden medienubergreifenden Bewertung beruht. Allerdings konnen nur selten exakte Daten fur die Beschreibung samtlicher untersuchter Techniken und deren potentiellen Umweltauswirkungen erhobenwerden. Daher sollte eine EntscheidungsunterstutzCorrespondence to: J. Geldermann 138 J. Geldermann and O. Rentz ung auch die Auswertung unvollstandiger Informationen erlauben. In diesem Beitragwerden dasOutranking-Verfahren PROMETHEEund seineErweiterungsmoglichkeiten fur die Berucksichtigung ungenauer Informationen, wie etwa Fuzzy Intervalle und unvollstandige Datensatze, diskutiert. Anhand einer Fallstudie aus der EisenundStahlindustriewird dieAnwendungdesmultikriteriellenEntscheidungsunterstutzungssystems und einer graphischen Sensitivitatsanalyse vorgestellt.

Project scheduling with calendars

Abstract: For many applications of project scheduling to real-life problems, it is necessary to take into account calendars specifying time intervals during which some resources such as manpower or machines are not available. Whereas the execution of certain activities like packaging may be suspended during breaks, other activities cannot be interrupted due to technical reasons. Minimum and maximum time lags between activities may depend on calendars, too. In this paper, we address the problem of scheduling the activities of a project subject to calendar constraints. We devise efficient algorithms for computing earliest and latest start and completion times of activities. Moreover, we sketch how to use these algorithms for developing priority-rule methods coping with renewable-resource constraints and calendars.

OLAF - A general modeling system to evaluate and optimize the location of an air polluting facility

Abstract: We propose a general modeling and optimization system for the effects of a low toxic air pollutant on the inhabitants of different land-based ecosystems. The pollution load can be traced through different ecotrophic levels, while health effects are quantified on the basis of detailed cytodynamic effects in different organs and tissues. The software package OLAF (Optimal Locating Air Polluting Facilities) developed on the basis of this model does not only evaluate quantitatively the effects of a proposed decision, but uses an efficient optimization technique to optimize the location of a polluting facility with respect to the adverse effects of the total pollution load on the inhabitants of the region under consideration.

Performance analysis of parallel identical machines with a generalized shortest queue arrival mechanism

Abstract: In this paper we study a production system consisting of a group of parallel machines producing multiple job types. Each machine has its own queue and it can process a restricted set of job types only. On arrival a job joins the shortest queue among all queues capable of serving that job. Under the assumption of Poisson arrivals and identical exponential processing times we derive upper and lower bounds for the mean waiting time. These bounds are obtained from so-called flexible bound models, and they provide a powerful tool to efficiently determine the mean waiting time. The bounds are used to study how the mean waiting time depends on the amount of overlap (i.e. common job types) between the machines.

Life cycle activity analysis: logistics and environmental policies for bottled water in Portugal

Abstract: An innovative mathematical programming decision support model –Life Cycle Activity Analysis (LCAA)– is presented, integrating considerations of optimal allocations of resources and impacts upon the environment during the life cycle of products. LCAA is based on the classical formulation of activity analysis and on the life cycle assessment framework. The concept of linear activities is extended to embrace mass and energy fluxes over the entire life cycle of products including their environmental impacts. Special attention is given to the presence of loops in the product chains, such as those occurring when materials/products are recovered (reused, recycled.). An application brought from the Portuguese bottled water industry is described. The model features alternative activities for production technologies and product recovery strategies and permits the joint consideration of monetary costs and environmental burdens. The results obtained under five scenarios, including distinct disposal strategies and environmental constraints, are discussed.

Environment-oriented project scheduling for the dismantling of buildings

Abstract: This paper presents a case study for the environment-friendly dismantling and recycling of buildings. Based on material-flow management it is shown how the dismantling on the construction site can be improved using resource-constrained project scheduling. Computational results show that strict environmental requirements like high recycling quotas and the reduction of harmful substances in recycling materials can be satisfied. Moreover, a comparison with results in practice indicates that project scheduling helps to achieve economic advantages for environment-friendly dismantling and recycling strategies.

Resource allocation with project management software

Abstract: We present results of a benchmark test evaluating the resource allocation capabilities of the project management software packages Acos Plus.1 8.2, CA SuperProject 5.0a, CS Project Professional 3.0, MS Project 2000, and Scitor Project Scheduler 8.0.1. The tests are based on 1560 instances of precedence--- and resource---constrained project scheduling problems. For different complexity scenarios, we analyze the deviation of the makespan obtained by the software packages from the best feasible makespan known. Among the tested software packages, Acos Plus.1 and Project Scheduler show the best resource allocation performance. Moreover, our numerical analysis reveals a considerable performance gap between the implemented methods and state---of---the---art project scheduling algorithms, especially for large---sized problems. Thus, there is still a significant potential for improving solutions to resource allocation problems in practice.

Efficient optimization of cyclic labor days-off scheduling Effizientes Optimierungsverfahren zur zyklischen Einsatzplanung

Abstract: An efficient method is presented for the optimum solution of the cyclic manpower days-off scheduling problem. This method, which is based on linear programming, allows unequal costs to be considered for different days-off patterns. First, the solution of the dual linear programming model is used to determine the minimum workforce size. Then, a procedure based on the dual solution is introduced to assign the workforce to days-off patterns in order to minimize the total labor cost. The new method offers an alternative to specialized linear or integer programming software, since it requires only few and simple calculations.

Planning stability in a product recovery system

Abstract: Recovery of used products is an issue of growing importance due to customer expectations and environmental regulation. As a consequence, companies need to adapt their material management taking into account inbound flows of used products. Corresponding inventory control models have been proposed in literature. In this paper we address the issue of planning stability in a product recovery context. To this end, we consider rolling horizon planning for a stock point facing stochastic demand and product returns. We analyze the impact of the return flow on planning stability and compare the system behaviour with a traditional production environment. We show that structural results derived for traditional inventory models remain valid in a product recovery context. Moreover we discuss counterintuitive effects resulting from interaction between planning stability and stock levels.

Faire Gruppenentscheidungen in der Investitionsplanung

Abstract: An der Planung eines Investitionsprogramms sind regelmasig mehrere Entscheidungstrager beteiligt. Dieser Beitrag beschreibt ein Verfahren zur Unterstutzung der zugehorigen kooperativen Gruppenentscheidung. Die Teilnehmer einigen sich darin zunachst auf gemeinsame Ziele und ermitteln jeder fur sich ein individuell “bestes” Programm von Investitionsprojekten. Dann werden daraus Zielgewichtungen abgeleitet und schlieslich Kompromisvorschlage generiert, die akzeptiert oder als Ausgangspunkt fur weitere Verhandlungen genutzt werden konnen. Das Verfahren zeichnet sich neben dem Verzicht auf a priori Informationen uber die Praferenzen der Entscheidungstrager vor allem durch die explizite Berucksichtigung von Fairnes als wesentliche Eigenschaft tragfahiger Gruppenentscheidungen aus.

Cooperation in capital deposits

Abstract: The rate of return earned on a deposit can depend on its term, the amount of money invested in it, or both. Most banks, for example, offer a higher interest rate for longer term deposits. This implies that if one individual has capital available for investment now, but needs it in the next period, whereas the opposite holds for another individual, then they can both benefit from cooperation since it allows them to invest in a longer term deposit. A similar situation arises when the rate of return on a deposit depends on the amount of capital invested in it. Although the benefits of such cooperative behavior may seem obvious to all individuals, the actual participation of an individual depends on what part of the revenues he eventually receives. The allocation of the jointly earned benefits to the investors thus plays an important part in the stability of the cooperation. This paper provides a game theoretical analysis of this allocation problem. Several classes of corresponding deposit games are introduced. For each class, necessary conditions for a nonempty core are provided, and allocation rules that yield core-allocations are examined.

Vollständigkeit, Konsistenz und Kompatibilität von Präferenzrelationen

Abstract: Praferenzen werden ublicherweise mittels Relationen formalisiert. Berucksichtigt man neben strikter Praferenz und Indifferenz auch Unvergleichbarkeit, dann sind Praferenzrelationen im allgemeinen nicht vollstandig. Verschiedene Praferenzrelationen sind auserdem nicht zwangslaufig widerspruchsfrei zueinander. In dieser Arbeit wird ein geeigneter Rahmen zur Systematisierung dieser Beziehungen zwischen Praferenzrelationen entwickelt. Dazu wird insbesondere definiert und analysiert, wann eine Praferenzrelation bezuglich einer anderen vollstandiger, konsistent und kompatibel ist. Mit Hilfe des begrifflichen Rahmens konnen beispielsweise die durch den Dominanzbegriff und durch PROMETHEE induzierten Praferenzrelationen zueinander in Beziehung gesetzt sowie nicht zwingend vollstandige, aus der Nutzentheorie herruhrende Praferenzrelationen untersucht werden.

Data Envelopment Analysis aus entscheidungstheoretischer Sicht

Abstract: Die Frage nach der „Effizienz” einer Handlung oder einer Organisation stellt eine der zentralen Problemstellungen okonomischer Analysen dar. Im Rahmen der betriebswirtschaftlichen Entscheidungstheorie unterstutzt das Multiobjective Decision Making das Management einer Organisation bei der Losung von Zielkonflikten. Zur Beurteilung der Effizienz bzw. Ineffizienz von Organisationen stellt die Data Envelopment Analysis unterschiedliche Kennzahlen bereit. Ein Vergleich beider Ansatze zeigt, das das zugrundeliegende vektorielle Entscheidungsproblem bei der Messung der Ineffizienz von Organisationen durch Abstandsfunktionen gelost wird. Bei einer Interpretation dieser Effizienzkennzahlen sollte aus entscheidungstheoretischer Sicht sowohl das verwendete Abstandsmas als auch die unterstellte Alternativenmenge jeweils kritisch hinterfragt werden.

On extreme values of orbit lengths in M/G/1 queues with constant retrial rate

Abstract: In the design of waiting facilities for the units in a retrial queue, it is of interest to know probability distributions of extreme values of the orbit length. The purpose of this paper is to investigate the asymptotic behavior of the maximum orbit length in the $M/G/1$ queue with constant retrial rate, as the time interval increases. From the classical extreme value theory, we observe that, under standard linear normalizations, the maximum orbit length up to the nth time the positive recurrent queue becomes empty does not have a limit distribution. However, by allowing the parameters to vary with n, we prove the convergence of maximum orbit lengths to three possible limit distributions when the traffic intensity $\rho_n$ approaches 1 from below and n approaches infinity.

Innerbetriebliche Transportoptimierung für ein Paketzentrum der Deutschen Post World Net

Abstract: Effiziente Warenverteilung ist auf den gegenwartigen Markten von wesentlicher Bedeutung. Fur die Konkurrenzfahigkeit eines Logistikdienstleisters ist neben der Planung der externen Transporte auch eine effiziente Gestaltung der innerbetrieblichen Transportleistungen unerlasslich. Der vorliegende Beitrag untersucht in einem Paketzentrum der Deutschen Post World Net die Transporte der Sendungen von den Endstellen, das sind Rutschen, uber welche die Sendungen die Sortier- und Verteilanlage in einem Paketzentrum verlassen, zu den Fahrzeugen an den Beladetoren. Dieser Transport erfolgt manuell oder durch Elektroschlepper in Rollbehaltern. Eine optimale Gestaltung der innerbetrieblichen Transporte hat verschiedene Besonderheiten zu berucksichtigen, wie beispielsweise unterschiedliche Ausstattungen der Beladetore, aus Zustellungsanforderungen abgeleitete Bedingungen oder eine moglichst gleichmasige Auslastung der Sort Verteilanlage. In diesem Beitrag wird die vorliegende Problemstruktur analysiert und ein modifiziertes dreidimensionales Zuordnungsmodell zur Problemreprasentation entwickelt. Zur Losung wird nach einer heuristischen Dekomposition Standardsoftware zur gemischt-ganzzahligen linearen Optimierung eingesetzt. Die erzielten Ergebnisse erlauben eine Reduktion des Transportaufwands um mehr als 40%.

Ressourcenallokation und Zeitpräferenz in der Gesundheitsdistriktplanung von Entwicklungsländern

Abstract: Die intertemporale Allokation knapper offentlicher Res- sourcen auf die verschiedenen Leistungserbringer hangt von der Zeitpraferenzrate der Entscheidungstrager ab. Die vorliegende Arbeit entwickelt ein Modell der Nicht-Linearen Programmierung, um im Rahmen der Gesundheitsdistriktplanung das Gesundheitsbudget eines fiktiven Distriktes in einem Entwicklungsland auf verschiedene Ebenen des kurativen und praventiven Gesundheitswesens zu verteilen. Dabei zeigt es sich, das eine hohe Gegenwartsorientierung vermehrt kurative Dienste bevorzugt, wahrend eine geringe Zeitpraferenzrate starker die Pravention forciert. Die optimale Allokation von Gesundheitsressourcen erfordert folglich eine detaillierte Analyse der Zeitpraferenz einer Bevolkerung. Es ist jedoch fraglich, ob dies in der Entwicklungshilfe, aber auch in der deutschen Gesundheitspolitik bislang ausreichend beachtet wurde.

Kundenzuordnung und Rundreiseplanung im Außendienst

Abstract: In der neueren Literatur wird empfohlen, eine Zuordnung von (potenziellen) Kunden zu Ausendienstmitarbeitern durch eine Verkaufsgebietseinteilung durchzufuhren. Dabei werden kleine geographische Gebietseinheiten zu Verkaufsgebieten gruppiert, die jeweils genau einem Ausendienstmitarbeiter zugeordnet werden, wobei dann ein Ausendienstmitarbeiter ausschlieslich fur die Kunden seines Verkaufsgebietes zustandig ist. Eine wichtige Zielsetzung dabei ist die Maximierung des erwarteten Deckungsbeitrages. Hierzu wird ublicherweise eine konkave Deckungsbeitragsfunktion herangezogen, die fur die einzelnen Gebietseinheiten den Zusammenhang zwischen der aufgewendeten Verkaufszeit (= Fahrtzeit + Besuchszeit) und dem erwarteten Deckungsbeitrag abbildet. Inwieweit die Deckungsbeitragsfunktion die tatsachlichen Gegebenheiten widerspiegelt, zeigt sich in der nachgelagerten Rundreiseplanung. Stimmt die bei der Deckungsbeitragsfunktion unterstellte Proportionalitat der Besuchszeit zur Verkaufszeit nicht mit den Ergebnissen der Rundreiseplanung uberein, so kann eine nichtoptimale Zuordnung der Kunden zu den Ausendienstmitarbeitern durchgefuhrt worden sein. Zur Vermeidung dieser Problematik betrachten wir einen die Rundreiseplanung integrierenden Ansatz, der eine detaillierte Abbildung der Fahrt- und Besuchszeiten der einzelnen Ausendienstmitarbeiter gewahrleistet. Dabei handelt es sich um einen Set-Packing-Ansatz, in dem die Spalten zulassige Rundreisen reprasentieren. Wir zeigen, dass der Ansatz mit der Methode der Spaltengenerierung mit hoher Losungsgute losbar ist. Anhand eines Beispiels verdeutlichen wir die Vorgehensweise. In recent literature it is proposed to assign (potential) customers to salespersons via sales territory alignment such that the total expected profit margin will be maximized. By this approach sales coverage units (SCUs) will be clustered into larger geographic areas called sales territories where the number of designed sales territories is equal the number of salespersons, i.e. each sales territory will be unequivocally assigned to a salesperson. Usually, a concave objective function is considered measuring for each SCU the expected profit margin in dependence of the selling time (= driving time + visiting time) a salesperson is allocating to a SCU. One critical point of using such a function is that a known constant relation between driving time and selling time is assumed. How suitable the profit margin function is can only be seen afterwards in a second step when constructing tours for each salesperson. In the case that we observe that the proportionality between driving time and selling time is not as assumed the sales territory alignment results may be non-optimal. To avoid this problem we propose to consider an integrated approach in which the driving times and visiting times of the salespersons are explicitely taken into account, i.e. customer assignment is done by solving a multi period traveling salespersons problem with time windows. For the solution we propose a set packing approach in which the columns are representing feasible tours. We show that the problem can be solved with column generations with a high solution quality.

Der Einfluß der Benchmarkwahl auf das Ergebnis langfristiger Ereignisstudien

Abstract: Die Durchfuhrung langfristiger Ereignisstudien setzt ein geeignetes Benchmarkmodell voraus, welches die erwartete Rendite der Untersuchungswertpapiere liefert. In den meisten bisherigen Studien wird diese durch die Anderungsrate eines Aktienindexes approximiert. Nach unseren Simulationsergebnissen entstehen bei einer solchen Vorgehensweise jedoch erhebliche Verzerrungen der Mittelwerte und der dazugehorigen Teststatistiken.

Effects and relationships of parameters in a rule–based fuzzy system

Abstract: Hierarchies of criteria and fuzzy rule systems represent an approach which effectively portrays the problem of multiple objectives found in classic decision–making scenarios such as order sequencing or the evaluation of various corporate strategies They further help the decision–maker to select a concrete course of action The relevant decision criteria are formalized with the help of linguistic variables A hierarchy of criteria is then used to relate them to one another and to combine them by rule–bases Evaluation using fuzzy sets leads to an aggregated rating of the individual alternatives A problem of such fuzzy systems is the large number of required parameters and their influence on the evaluation results This article will use the example of a simple criteria hierarchy for a sequencing problem to analyze the effects of individual parameters and their relationships amongst one another in a fuzzy system