Search

The Volleyball Nations League is the elite annual international competition within volleyball, with the sixteen best nations per gender contesting the trophy in a tournament that spans over 6 weeks. The first five weeks contain a single round robin tournament, where matches are played in different venues across the globe. As a consequence, each team follows an intensive travel plan, where it happens quite often that there is a large discrepancy between travel burdens of opposing teams. This is considered a disadvantage for the team that travelled more. We analyse this problem, and find that it is closely related to the well-known Social Golfer Problem: we name the resulting problem the Traveling Social Golfer Problem (TSGP). We propose a decomposition approach for the TSGP, leading to the so-called Venue Assignment Problem and the Nation Assignment Problem. We prove that a solution to the Venue Assignment problem determines the amount of unfairness, and we also prove that any solution of the Venue Assignment problem can be extended to a solution to the Nation Assignment problem satisfying the so-called home-venue property. Using integer programming methods, we find, for real-life instances, the fairest schedules with respect to the difference in travel distance.

This paper focuses on revealed preference tests of the collective model of household consumption. We start by showing that the decision problems corresponding to testing collective rationality are NP-complete. This [...]

In the summer of 2020, Music Building Eindhoven (MBE) had to deal with the economic consequences of the COVID-19 pandemic for theater halls because governmental regulations were having a severe impact on the occupancy. In particular, MBE faced the challenge of determining how to maximize the number of guests in a theater hall while respecting social distancing rules. We have developed and implemented an optimization model based on trapezoid packings to address this challenge. The model showed that up to 40% of the normal capacity can be realized for a single show setting and up to 70% in cases where artists opt for two consecutive performances per evening without reusing seats. The solution was adopted by MBE with significant monetary and managerial benefits.History:This paper was refereed. This article has been selected for inclusion in the Special Issue on Analytics Remedies to COVID-19.Funding:The research of F. Spieksma is supported by Dutch Research Council (NWO) Gravitation Project NETWORKS [Grant 024.002.003].

Latency problems are characterized by their focus on minimizing the waiting time for all clients. We study periodic latency problems, a nontrivial extension of standard latency problems. In a periodic [...]

Classical measures of network connectivity are the number of disjoint paths between a pair of nodes and the size of a minimum cut. For standard graphs, these measures can be [...]

We consider a time-indexed formulation for the unrelated parallel machine scheduling problem. We show that all polyhedral knowledge known from the single machine problem (in particular, valid inequalities) is applicable to this formulation. We present new facet-inducing valid inequalities and a preprocessing technique involving fixing variables based on reduced costs. We combine both techniques in a basic cutting-plane algorithm and test the performance of the resulting algorithm by running it on randomly generated instances.

In this paper we describe a case study in the operational planning of the assembly of printed circuit boards. Given a line of placement machines and given a family of boards we develop a heuristic algorithm which focusses on the so-called feeder rack assignment problem. This problem addresses the question: where to attach the feeders alongside the feeder racks of the placement machines? Computational results on real-life instances indicate that the heuristic is superior to approaches currently used in practice.

AbstractThe Industrial and Applied Mathematics (IAM) master’s program at Eindhoven University of Technology received the INFORMS UPS George D. Smith Prize in 2022. This paper highlights the department’s history, the innovative aspects of the program, and its role in educating operations research practitioners. Eindhoven University of Technology emphasizes industry collaboration, societal involvement, and scientific excellence, principles that are integral to the IAM program.

In Eurotransplant, relatively more females than males die while waiting for liver transplantation, and relatively fewer females undergo transplantation. With adult liver transplantation candidates listed between 2007 and 2019 (n = 21 170), we study whether sex disparity is inherent to the model for end-stage liver disease (MELD) scoring system, or the indirect result of a small candidate body size limiting access to transplantation. Cox proportional hazard models are used to quantify the direct effect of sex on waitlist mortality, independent of the effect of sex through MELD scores, and the direct effect of sex on the transplantation rate, independent of the effect of sex through MELD and candidate body size. Adjusted waitlist mortality hazard ratios (HRs) for female sex are insignificant (HR: 1.03, 95% CI: 0.88-1.20). We thus lack evidence that MELD systematically underestimates waitlist mortality rates for females. Transplantation rates are 25% lower for females than males in unadjusted analyses (HR: 0.74, 95% CI: 0.71-0.77), but HRs become insignificant with adjustment for mediators (HR: 0.98, 95% CI: 0.93-1.04), most importantly candidate body size. Sex disparity in Eurotransplant thus appears to be largely a consequence of lower transplantation rates for females, which are explained by sex differences in body size.

In this contribution, we study whether fatigue resulting from the previous match affects a player’s chances of winning his (or her) next match in Grand Slam tennis. We measure relative fatigue levels of two opponents by looking at the difference in number of sets played in their previous match. We develop two approaches to answer this question: the so-called carry-over method and the more common logit model. Both methods differ in the assumptions they make and the type of results they offer. Our results are based on data collected from the 4 Grand Slam tournaments (men and women) from 1992 till 2011, covering 20,320 matches. We find that there is indeed an impact of the relative effort invested in winning a match on the probability of winning the next match in a Grand Slam tournament. For women, having played one set more in the previous match than the opponent in her previous match, leads to a decreased winning probability. For men, this is the case only for a set difference of two. Our results show that this effect is present in each of the grand slam tournaments and does not vary with the surface type.

The classical result of Rose (Rev Econ Stud, 25:124–125, 1958) shows that, for single-member households, the Weak Axiom of Revealed Preferences(warp) and the Strong Axiom of Revealed Preferences(sarp) are equivalent when there are only two goods. Because sarpextends warpby requiring transitive preferences in addition, this means that transitivity of preferences need not be tested in the case of two goods. We consider the extension of this result towards $$L$$ L -member households, for which we introduce the concepts $$L$$ L -warpand $$L$$ L -sarp. For a general setting, we demonstrate that $$L$$ L -warpand $$L$$ L -sarpare not equivalent if there are at least $$L+1$$ L+1 goods, which means that transitivity of individual preferences is testable. However, we can also show that $$L$$ L -warpand $$L$$ L -sarpdo become equivalent for the restricted “labor supply” setting where we exclusively assign a single good to each different household member, i.e., $$L$$ L (out of $$L+1$$ L+1 ) goods are exclusive.

We provide results on the computational complexity of goodness-of-fit measures (i.e., Afriat’s efficiency index, Varian’s efficiency vector-index, and the Houtman-Maks index) associated with several revealed preference axioms (i.e., WARP, SARP, GARP, and HARP). These results explain the computational difficulties that have been observed in literature when computing these indices. Our NP-hardness results are obtained by reductions from the independent set problem. We also show that this reduction can be used to prove that no approximation algorithm achieving a ratio of O(n1 − δ), δ;> 0 exists for Varian’s index, nor for Houtman-Maks’ index (unless P = NP). Finally, we give an exact polynomial-time algorithm for finding Afriat’s efficiency index.

We describe a real-life problem arising at a crane rental company. This problem is a generalization of the basic crew scheduling problem given in Mingozzi et al. [18] and Beasley and Cao [6]. We formulate the problem as an integer programming problem and establish ties with the integer multicommodity flow problem and the hierarchical interval scheduling problem. After establishing the complexity of the problem we propose a branch-and-price algorithm to solve it. We test this algorithm on a limited number of real-life instances. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 723–742, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10044

We consider a special packing-covering pair of problems. The packing problem is a natural generalization of finding a (weighted) maximum independent set in an interval graph, the covering problem generalizes the problem of finding a (weighted) minimum clique cover in an interval graph. The problem pair involves weights and capacities; we consider the case of unit weights and the case of unit capacities. In each case we describe a simple algorithm that outputs a solution to the packing problem and to the covering problem that are within a factor of 2 of each other. Each of these results implies an approximative min-max result. For the general case of arbitrary weights and capacities we describe an LP-based (2 + ε)-approximation algorithm for the covering problem. Finally, we show that, unless P = NP, the covering problem cannot be approximated in polynomial time within arbitrarily good precision.

The clique partitioning problem (CPP) can be formulated as follows: Given is a complete graph G = (V, E), with edge weights wij ∈ ℝ for all {i, j} ∈ E. A subset A ⊆ E is called a clique partition if there is a partition of V into nonempty, disjoint sets V1,…, Vk, such that each Vp (p = 1,…, k) induces a clique (i.e., a complete subgraph), and A = ∪p=1^k {{i, j}|i, j ∈ Vp, i ≠ j}. The weight of such a clique partition A is defined as Σ{i,j}∈A wij. The problem is now to find a clique partition of maximum weight. The clique partitioning polytope P is the convex hull of the incidence vectors of all clique partitions of G. In this paper, we introduce several new classes of facet-defining inequalities of P. These suffice to characterize all facet-defining inequalities with right-hand side 1 or 2. Also, we present a procedure, called patching, which is able to construct new facets by making use of already-known facet-defining inequalities. A variant of this procedure is shown to run in polynomial time. Finally, we give limited empirical evidence that the facet-defining inequalities presented here can be of use in a cutting-plane approach for the clique partitioning problem. © 2001 John Wiley & Sons, Inc.

Geographical and temporal variations in the start dates of grass pollen seasons are described for selected sites of the European Pollen Information Service. Daily average grass pollen counts are derived from Network sites in Finland, the Netherlands, Denmark, United Kingdom, Austria, Italy and Spain, giving a broad longitudinal transect over Western Europe. The study is part of a larger project that also examines annual and regional variations in the severity, timing of the peak and duration of the grass pollen seasons. For several sites, data are available for over twenty years enabling long term trends to be discerned. The analyses show notable contrasts in the progression of the seasons annually with differing lag times occurring between southern and northern sites in various years depending on the weather conditions. The patterns identified provide some insight into geographical differences and temporal trends in the incidence of pollinosis. The paper discusses the main difficulties involved in this type of analysis and notes possibilities for using data from the European Pollen Information service to construct pan European predictive models for pollen seasons.

Among aerobiologists it is commonly accepted that forlong-term monitoring of atmospheric pollen quantities,observations at roof-top level (15–30 m) areappropriate. Yet, possible differences in airbornepollen concentrations at different heights are hardlyinvestigated, particularly in relation to nearbypollen sources. In a six-year survey with twovolumetric pollen traps, airborne concentrations ofpollen from eight selected taxa at roof-top level arecompared with those at street level. For pollen fromplants further away than 1000 m from the street-leveltrap, no difference between quantities of pollen atroof-top and street level is found. Concentrations ofairborne pollen from sources closer than 20 m to thestreet-level trap are 1.2 to 6.8 times higher atstreet level than those at roof-top level,particularly for mugwort (Artemisia). Aftercutting mugwort plants in an area of 100 m around thestreet-level trap, the ratio dropped from 4.8 to 2.7,averagely for the season. It seems that, also in theabsence of nearby sources, airborne mugwort pollenquantities of street level are higher than those atroof-top level but, at least in Leiden, not as much ashas been reported earlier by others.

In this paper we consider a general interval scheduling problem. The problem is a natural generalization of finding a maximum independent set in an interval graph. We show that, unless P=NP, this maximization problem cannot be approximated in polynomial time within arbitrarily good precision. On the other hand, we present a simple greedy algorithm that delivers a solution with a value of at least 1/2 times the value of an optimal solution. Finally, we investigate the quality of an LP-relaxation of a formulation for the problem, by establishing an upper bound on the ratio between the value of the LP-relaxation and the value of an optimal solution. Copyright © 1999 John Wiley & Sons, Ltd.

The results of five years (1977-1981) of continuous monitoring of airborne pollen concentrations with a volumetric trap in Leiden, indicate that usually about 37% of the total pollen count comes from a group of 24 taxa, trees and shrubs flowering in the spring, from January to June. The main taxa in this group, representing over 90% of this pollen count, are: Alnus, Betula, Cupressaceae (including Taxaceae), Fraxinus, Pinaceae, Populus, Quercus, Salix, and Ulmus; almost 50% belongs to Alnus, Betula, and Salix. Comparison of the counts for the various years reveals that both the total number and the time of airborne presence of the different pollen types show great and irregular variations. Cases of pollinosis with clinical significance are rare, and have been ascribed to allergy to pollen from Betula and Alnus, although allergic sensitization to other pollen types without severe clinical manifestations do occur.

Four-hourly volumetric measurements of airborne grass-pollen concentrations at Leiden, near the west coast of the Netherlands, were analyzed according to wet-versus-dry meteorological conditions in the pollen source area, and according to the distance of the over-land advection to the pollen sampler. Airborne pollen concentrations appear to be low when the source surface is wet by past or present rain, fog, or dew; and high when the source area is dry. Air adverted over long over-land distances from dry source areas contains much pollen, especially in the afternoon, due to pollen release and decreasing air turbulence. High nightly pollen concentrations are observed after a warm and dry day with much pollen release in distant source areas when the nocturnal meteorological conditions stimulate concentration of pollen grains into the lower layers of the atmosphere.

The idea has been generally accepted that accumulative properties of the lower atmosphere during stable non-turbulent air conditions by night (inversion) would lead to relatively high concentrations of airborne particles including those of biological origin like pollen grains originating from wind pollinating plants. Using temperature gradient, air pollution potential, and urban grass-pollen counts as criteria in a meteorologically homogenous region in the western part of the Netherlands, this relation between inversion and airborne grass-pollen concentration appears to be very weak and of no significance for the causation of nightly peaks in the grass-pollen counts.

Summary: Aerobiology, in the strict sense, is the science which is studying the transportation of biological particles through the air. This process includes the release, the staying airborne, and deposition of particles of biological origin. Until recently, most of the allergological research has been done on the processes before and after the strict aerobiological pathway. The allergological studies were primarily dealing with the allergenic properties of the particles, irrespective of their aerobiological characteristics. Also, many studies have been done about the effects of allergens in sensitized people, after deposition in the respiratory organs. But for a more complete knowledge of the allergic process, allergological aerobiology in the strict sense is indispensable. The understanding of symptoms of respiratory allergy requires knowledge of the aerodynamic properties of airborne allergen carrying particles.

Summary: We collected the daily pollen samples during a 3-year period (Febr '87–Dec '89), using a Burkard volumetric trap, located on a high level area in the center of the city.Parietaria officinalis pollen was not differentiated under microscope from the other Urticaceae but through phenological criteria. The patients included in the detection of the sensitivity toP. officinalis pollen came from the Out-patient Clinic of Bronchial Asthma of the General Hospital «G. Papanikolaou». They had a seasonal pollinosis and they were submitted to Pricktest using a battery of 22 groups and aP. officinalis pollen extract. The Urticaceae pollen appears first in the atmosphere of Thessaloniki in the end of March, shows a peak in the beginning of May and continues to be present till the end of August. We detectedP. officinalis pollen sensitivity combined with other allergens in 24.1% of the patients and in 1.4% a monosensitivity toP. officinalis.

Summary: The term house-dust mite usually refers to those species of the mite family Pyroglyphidae, that are known to commonly occur, although sometimes regionally, in the dust of human dwellings. These species belong to five genera:Dermatophagoides, Euroglyphus, Hirstia, andMalayoglyphus. Related species ofDermatophagoides have the most world-wide occurrence, the commonest being:D. farinae, D. microceras, andD. pteronyssinus. A correct taxonomic identification of house-dust mites is very important, not only from a biological stand point, but also regarding the consequences of their respective allergenical properties. Several immuno-chemical studies revealed differences between the products of two hard to distinguish sibling species. A preliminary practical taxonomic key for the most common and important house-dust mites is presented.

Summary: On the basis of the results of seven years (1982–1988) of pollen and meteorological monitoring in the atmosphere of Perugia and Ascoli Piceno (central Italy) beginning of pollen season forecasts for Gramineae and Olea europaea L. are reported. The beginning of the pollen season for grass varied between May 2 nd and May 27th while for Olea it varied between May 26 th and June 23rd. By a statistical analysis of these data several significant correlations were found between the onset of the principal period of pollination and the air temperature in the preceding months and the number of heat units required to flower. Utilizing multiple regressions a predictive method of the beginning of pollen season for both the taxa is reported.

Summary: Airborne grass-pollen concentrations in six cities in the EEC are compared, based on observations from five years, 1982–1986. Results show that there are quantitative differences both between the monitoring stations and between the years. Very provisionally, the average seasonal total of the European urban airborne grass-pollen concentration can be put at 4 to 5000 per m3 of air. Also qualitatively, regarding the seasonal fluctuations, there are differences between the stations, and between the years. Generally, the results confirm that June is the most typical grass-pollen month in northwestern Europe, whereas in mediterranean Europe May is the more prominent grass-pollen period. There seems to be little coherence between the starting dates of the grass-pollen season even at relatively nearby stations in northwestern Europe, suggestive for a great influence of the actual weather situation.

The observations of airborne pollen ofOlea europeaand the incidence of clinical manifestations in patients allergic to this pollen type have not been registered so far in the city of Thessaloniki.

Results of five years of continuous monitoring of airborne pollen concentrations with a volumetric trap in Leiden indicate that almost 36% of the total pollen count originates from a group of 23 taxa, herbs and weeds flowering in the summer, between May and October. More than 95 % of the airborne summer-weed pollen are from Urtica, Rumex, Artemisia, Plantago, and Chenopodiaceae, Urtica predominating with over 85%. Of the three most frequent summer-weed pollen types, both Rumex and Urtica show variable seasonal patterns, whereas Artemisia is more constant. Although large concentrations of Urtica pollen are often found, allergic sensitization is infrequent. The converse is true of Artemisia pollen, which could be a cause of pollinosis in August in spite of the relatively low concentrations in the air.

The results of five years' (1977-1981) continuous monitoring of airborne pollen concentrations with a volumetric trap in Leiden indicate that almost 25% of the total pollen count derives from wild grasses. June is by far the most important month for airborne grass-pollen, generally taking more than 50% of the total seasonal count, July accounting for on average 30%. In spite of the consistency of this general seasonal pattern, the fluctuations from day to day and from hour to hour can be very large and highly irregular, and there is no consistent diurnal pattern in the grass-pollen count. Long-term prediction of the start of the grass-pollen season and of the intensity and course of the grass-pollen concentration is not (yet) possible. However, a short-term and relative prognosis for hay fever, intended for at least 200 000 sufferers in The Netherlands, has reached an accuracy of more than 80%.

Even if they represent only a small proportion of the airborne particles present in the atmosphere, pollen grains can be causative agents of allergic responses in susceptible humans, and pollinosis (oculorhinitis and/or asthma) is now a public health problem. A characteristic feature of pollen sensitivity is its seasonal pattern of occurrence usually at the time when the pollen or other allergenic plant debris show a heavier atmospheric concentration.The air presence of allergenic pollen varies according to the climate, geography and vegetation. Europe, extending from the Atlantic to the Urals, offers a great diversity of climate and vegetation and consequently of the pollen seasons with different pollen calendars from one area to another. As a result of free mobility among citizens, people who travel for work or for leisure need to have reliable information about the likelihood of seasonal allergies when they visit another country. For this reason, knowledge of the atmospheric pollen concentration encountered in the different regions is of great interest for clinicians and allergic patients to establish a correlation between the concentration of pollen in the air and the symptoms of hay fever, in order to achieve better management of pollinosis symptoms. The most important airborne pollen types for all of Europe are of grasses followed by Urticaceae pollen. In Northern Europe, pollen of Betulaceae (birch, alder, hazel) is a significant contributor to the incidence of pollinosis, whereas Parietaria and olive (Olea) pollen is responsible for many cases of pollinosis in the Mediterranean regions.

Minimization of the makespan of a printed circuit board assembly process is a complex problem. Decisions involved in this problem concern the specification of the order in which components are to be placed on the board and the assignment of component types to the feeder slots of the placement machine. If some component types are assigned to multiple feeder slots, an additional problem emerges: for each placement on the board, one must select the feeder slot from which the required component is to be retrieved. In this paper, we consider this component retrieval problem for placement machines of the Fuji CP type. We explain why simple forward dynamic programming schemes cannot provide a solution to this problem, invalidating the correctness of an algorithm proposed by Bard, Clayton, and Feo (1994). We then present a polynomial algorithm that solves the problem to optimality.

This article analyzes a tool switching problem arising in certain flexible manufacturing environments. A batch of jobs have to be successively processed on a single flexible machine. Each job requires a subset of tools, which have to be placed in the tool magazine of the machine before the job can be processed. The tool magazine has a limited capacity, and, in general, the number of tools needed to produce all the jobs exceeds this capacity. Hence, it is sometimes necessary to change tools between two jobs in a sequence. The problem is then to determine a job sequence and an associated sequence of loadings for the tool magazine, such that the total number of tool switches is minimized. This problem has been previously considered by several authors; it is here revisited, both from a theoretical and from a computational viewpoint. Basic results concerning the computational complexity of the problem are established. Several heuristics are proposed for its solution, and their performance is computationally assessed.

Abstract: The following problem was originally motivated by a question arising in the automated assembly of printed circuit boards. Given aren jobs, which have to be performed on a single machine within a fixed timespan [0,T], subdivided intoT unit-length subperiods. The processing time (or length) of each job equalsp,p ∈ ℕ. The processing cost of each job is an arbitrary function of its start-time. The problem is to schedule all jobs so as to minimize the sum of the processing costs. This problem is proved to be NP-hard, already forp=2 and 0–1 processing costs. On the other hand, whenT=np+c, withc constant, the problem can be solved in polynomial time. A partial polyhedral description of the set of feasible solutions is presented. In particular, two classes of facet-defining inequalities are described, for which the separation problem is polynomially solvable. Also, we exhibit a class of objective functions for which the inequalities in the LP-relaxation guarantee integral solutions. Finally, we present a simple cutting plane algorithm and report on its performance on randomly generated problem instances.

In the reconstruction of past or recent vegetation the study of deposited pollen plays an important role. As reference value, very often the pollen content of moss polsters (“moss cushions”) is assessed to estimate the pollen depositions (“influx”) from the air. Recently, the data from moss-polster sampling and from sedimentation-trap sampling have been compared, showing both similarities and inconsistencies in the two sets of data. Whether the relative pollen presence in moss polsters is in accordance with airborne pollen concentrations as assessed by continuous volumetric air sampling has been studied rather scarcely.

In this survey, the most important aspects concerning information on airborne pollen concentrations in relation to hay fever are reported. Six of these aspects are briefly discussed. They are: target group, “spectivity”, subject exactness, routes, frequency. These aspects of information system can concern airborne pollen and/or pollinosis. The “Leiden” system has two flows of information: daily hay-fever forecast and weekly pollen bulletin.