Showing papers by "Tilburg University published in 1986"
TL;DR: It is shown that the Chvátal rank of a polyhedron can be bounded above by a function of the matrixA, independent of the vectorb, a result which, as Blair observed, is equivalent to Blair and Jeroslow's theorem that ‘each integer programming value function is a Gomory function.’
Abstract: We consider integer linear programming problems with a fixed coefficient matrix and varying objective function and right-hand-side vector. Among our results, we show that, for any optimal solution to a linear program max{wx: Ax≤b}, the distance to the nearest optimal solution to the corresponding integer program is at most the dimension of the problem multiplied by the largest subdeterminant of the integral matrixA. Using this, we strengthen several integer programming ‘proximity’ results of Blair and Jeroslow; Graver; and Wolsey. We also show that the Chvatal rank of a polyhedron {x: Ax≤b} can be bounded above by a function of the matrixA, independent of the vectorb, a result which, as Blair observed, is equivalent to Blair and Jeroslow's theorem that ‘each integer programming value function is a Gomory function.’
197 citations
TL;DR: It is shown that the maximum weight independent set of an h -perfect graph can be found in polynomial time.
127 citations
TL;DR: In this article, an easy interpretation is given: kurtosis is a measure of dispersion around the two values μ ± σ, and there seems to be no universal agreement about the meaning and interpretation of Kurtosis.
Abstract: There seems to be no universal agreement about the meaning and interpretation of kurtosis. An easy interpretation is given here: kurtosis is a measure of dispersion around the two values μ ± σ.
123 citations
TL;DR: In this article, an extension of Lastovicka's four-mode components analysis is developed using a convenient notation, both a canonical and a least squares solution are derived The relation between both solutions and their computational aspects are discussed
Abstract: As an extension of Lastovicka's four-mode components analysis ann-mode components analysis is developed Using a convenient notation, both a canonical and a least squares solution are derived The relation between both solutions and their computational aspects are discussed
120 citations
TL;DR: Information and support by professionals, partners and/or fellow patients are related to positive rehabilitation outcomes such as the acquisition of speech, increases in constructive social functioning and decreases in depression.
Abstract: This study is a systematic analysis of the literature on psychosocial aspects in head and neck cancer patients. Patients with head and neck cancer experience a variety of physical as well as psychosocial problems. Physical problems include swallowing or chewing, speech and physical appearance. Psychosocial problems include anxiety, depression, loss of self-esteem and uncertainty about the future. Because of these problems, isolation from friends typically occurs, re-employment is difficult, and there are social and sexual tensions within families. Information and support by professionals, partners and/or fellow patients are related to positive rehabilitation outcomes such as the acquisition of speech, increases in constructive social functioning and decreases in depression.
106 citations
TL;DR: If G is an undirected graph which does not contain any homeomorph of K4 in which all triangles ofK4 have become odd circuits, then G ist-perfect, and this extends results of Boulala, Fonlupt, Sbihi and Uhry.
Abstract: A matrixA=(a
ij
) has theEdmonds—Johnson property if, for each choice of integral vectorsd
1,d
2,b
1,b
2, the convex hull of the integral solutions ofd
1≦x≦d
2,b
1≦Ax≦b
2 is obtained by adding the inequalitiescx≦|δ|, wherec is an integral vector andcx≦δ holds for each solution ofd
1≦x≦d
2,b
1≦Ax≦b
2. We characterize the Edmonds—Johnson property for integral matricesA which satisfy
$$\mathop \Sigma \limits_j |a_{ij} | \leqq 2$$
for each (row index)i. A corollary is that ifG is an undirected graph which does not contain any homeomorph ofK
4 in which all triangles ofK
4 have become odd circuits, thenG ist-perfect. This extends results of Boulala, Fonlupt, Sbihi and Uhry.
97 citations
TL;DR: The general bounds are improved to show that if G is a perfect graph with n nodes and w is a vector of integral node weights, then there exists a minimum w -covering of the nodes that uses at most n distinct cliques.
86 citations
79 citations
TL;DR: In this paper, the authors tried to provide information about the question whether people do not contribute to a public good because of greed or a desire to free ride or because of a fear of being gypped.
55 citations
TL;DR: In this article, pseudorandom procedures are used to compute factor similarity indices that come close in numerical values to those taken by H. J. Eysenck and associates as sufficient evidence for metric identity of EPQ scales across cultures.
Abstract: By means of pseudorandom procedures factor similarity indices are computed that come close in numerical values to those taken by H. J. Eysenck and associates as sufficient evidence for metric identity of EPQ scales across cultures. It is argued that considerable bias in the results by no means can be ruled out and that intercultural comparison of mean scores obtained on EPQ scales is unwarranted.
54 citations
TL;DR: In this paper, the relationship between personal values and vacation behavior has been studied for a Dutch sample of 713 families, using canonical correlation analysis useful and stable vacation segments have been found on the basis of relationships between domain specific (vacation) value and vacation attributes.
TL;DR: Among headache Subparameters, the duration and frequency of pain periods were mainly affected, with the exception of the tension-headache PR condition, in which decreases in duration and intensity of pain occurred jointly.
TL;DR: A conceptual framework for studying the impact of childhood cancer on the psychological and social functioning of the patient and the family is presented in this article, where a model based on the literature about coping with stress, especially with respect to cancer, and on two psychosocial theories of human behavior (the attribution theory and the social comparison theory) is used as a starting point.
Abstract: This article presents a conceptual framework for studying the impact of childhood cancer on the psychological and social functioning of the patient and the family. A model based on the literature about coping with stress, especially with respect to cancer, and on two psychosocial theories of human behavior (the attribution theory and the social comparison theory) is used as a starting point. The model (1) describes the problems people experience when confronted with a threatening situation, (2) provides a classification of problems that has a manageable number of categories to which problems can be assigned, and (3) gives insight into some important coping strategies that children and their parents use to lessen the impact of those problems. The problem categories and coping strategies of the model are illustrated mainly from findings described in the literature and from information the authors obtained during interviews with patients and parents.
TL;DR: A review of studies on the effects of contacts between cancer-patients shows that most of these studies do not satisfy the methodological conditions necessary to draw firm conclusions as mentioned in this paper, which leads, among other difficulties, to the generation of conflicting hypotheses.
TL;DR: In this article, the authors provide a systematic treatment of the problem of identification in systems of linear structural equations where some of the disturbances are uncorrelated. But they do not consider the case where some disturbances are correlated.
TL;DR: In this paper, a linguistic description is given of the process of first language acquisition of Turkish children aged 4 to 8 in a Dutch submersion environment in the Netherlands, and the longitudinal data are compared with cross-sectional language data of five and seven-year-old children in Turkey.
Abstract: In the present paper a linguistic description is given of the process of first language acquisition of Turkish children aged 4 to 8 in a Dutch submersion environment in the Netherlands. On the basis of the assumption that language development involves the acquisition of distinct subskills in differential patternings, the development of lexical, morphosyntactic, and pragmatic abilities have been investigated separately. Furthermore, these longitudinal data are compared with cross-sectional language data of five- and seven-year-old children in Turkey. This comparison was made in order to be able to interpret whether the Turkish language skills of native Turkish-speaking children in the Netherlands were showing delay, stagnation, or attrition of skills. The overall results suggest that in the age range of 4 to 8 years the acquisition of first language skills by Turkish children in the Netherlands can best be characterized as stagnated.
TL;DR: In this paper, the authors present data from a longitudinal mail survey among participants of a source separation project in the Netherlands, where the costs and benefits that participants perceive are analyzed over time.
TL;DR: The eye-movements of nine aphasic and nine nonaphasic control patients were recorded while they were looking at slides, containing eight words, selected from four different linguistic categories (nouns, verbs, adjectives, and adverbs).
Abstract: The eye-movements of nine aphasic and nine nonaphasic control patients were recorded while they were looking at slides, containing eight words, selected from four different linguistic categories (nouns, verbs, adjectives, and adverbs). The task was to construct a 4-word sentence. The aphasic patients produced fewer syntactically and semantically correct sentences. Both aphasics and controls used more nouns than adverbs in their sentences. The eye-movement patterns revealed no statistically significant differences between the two groups in terms of fixation time per word category or in terms of fixation time per visual hemispace. Implications for a linguistic theory of sentence processing are discussed.
TL;DR: In this article, a small scale applicability of the Rasch estimates was investigated under simulated conditions of guess ing and heterogeneity in item discrimination, and the results showed that robustness could only be demonstrated for the correlational criterion.
Abstract: The small scale applicability of Rasch estimates was investigated under simulated conditions of guess ing and heterogeneity in item discrimination. The ac curacy of the Rasch estimates was evaluated by means of the correlation between the item/person parameters and their estimates, the standard deviations of the esti mates, and the difference as well as the root mean squared difference between parameters and estimates. Within the range of the present investigation (from 10 to 50 items and from 25 to 500 persons) these criteria yielded favorable results under conditions of heteroge neous item discrimination. Under conditions of guess ing, robustness could only be demonstrated for the correlational criterion. Guessing affects the difference measures between the parameter values and estimates quite strongly in a systematic way. It is argued that, notwithstanding these estimation errors, the Rasch model is to be preferred over nonstandard estimation procedures, from which the validity is unclear, or the use o...
01 Mar 1986
TL;DR: It is demonstrated that the skewness of the lead time demand distribution in the inventory model is also an important measure, which should be taken into account, as the cost differences with regard to the case where this skewnness measure is not used, can be considerable.
Abstract: In this paper the influence of the shape of the lead time demand distribution is studied for a specific inventory model which is described in a preceding paper by Heuts and van Lieshout [4]. This continuous review inventory model uses as lead time demand distribution a Schmeiser-Deutsch distribution (S-D distribution) [9]. In a previous paper [4] an algorithm was given to solve the decision problem.
TL;DR: In this article, it was shown that problems of rotational equivalence of restricted factor loading matrices in orthogonal factor analysis are equivalent to problems of identification in simultaneous equations systems with covariance restrictions.
Abstract: It is shown that problems of rotational equivalence of restricted factor loading matrices in orthogonal factor analysis are equivalent to problems of identification in simultaneous equations systems with covariance restrictions. A necessary (under a regularity assumption) and sufficient condition for local uniqueness is given and a counterexample is provided to a theorem by J. Algina concerning necessary and sufficient conditions for global uniqueness.
TL;DR: The fully distributed input—output model is applied to analyse the dynamic structure of the Polish economy and the effects of investment distributions are expressed by comparison with conventional, non-distributed input-output results.
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TL;DR: In this paper, the authors examined the incidence of several taxes in a macroeconomic model and showed that in the long run the system tends towards a Walrasian equilibrium, where price inertia leads to rationing in the market for goods and for labour.
Abstract: This paper examines the incidence of several taxes in a macroeconomic model. Producers and consumers optimize with perfect foresight. Price inertia leads to rationing in the market for goods and for labour. In the long run the system tends towards Walrasian equilibrium. Meanwhile there may be Keynesian Unemployment, Classical Unemployment or Repressed Inflation, with possible switches of regimes. Balanced budget policies are analysed by working through numerical examples.
TL;DR: In this article, the authors investigated the influence of some task variables on the effectiveness of precuing, in order to determine the locus of differential precuing effects, in either central decisional processing or in motor programming.
TL;DR: In this paper, two groups of 6 pigeons were exposed to either a fixed-time or a variable-time schedule of response-independent food presentation, and the duration of stimulus presentation (stimulus-food [SF] interval) was varied relative to the FF interval.
Abstract: Two groups of 6 pigeons were exposed to either a fixed-time (FT) or a variable-time (VT) schedule of response-independent food presentation. The interval between two successive food presentations (food-food [FF] interval) was either 20 or 40 sec. The duration of stimulus presentation (stimulus-food [SF] interval) was varied relative to the FF interval. All subjects were exposed to different information ratios (IRs; IR = SF/FF; IR = 1.00, 0.50, 0.15). To study the relative contribution of sign- and goal-tracking behavior to keypecking observed in standard autoshaping procedures, pigeons were autoshaped in a long-box. In the long-box, the stimulus key and the feeder are located 60 cm apart. Stimuli were always presented at one end of the box, and food was presented at the other end. Locomotor behavior and keypecks were recorded. Pigeons engaged in sign-tracking behavior when IR = 0.15, but only when presentation of the food was unpredictable on the basis of other variables (e.g., the passage of time since the last food presentation, as in FT schedules). In the case of FT schedules, subjects engaged in feeder-directed activities. No effects of varying the FF interval were found. Keypecking was observed only when the SF interval was short (IR = 0.15) and food was presented on a VT schedule.
TL;DR: The search for an efficient alternative medicine or a source for codeine other than opium poppy other than heroin is discussed with regards to the natural occurrence of morphinan derivatives and the biosynthetic pathways in available plants.
Abstract: Codeine, medically the most widely used opiate, is mostly derived from morphine, isolated from opium and poppy straw (Papaver somniferum, opium poppy). Morphine, however, is greatly misused by illegal conversion into its diacetyl-derivative: heroin. The discovery of an efficient alternative medicine or a source for codeine other than opium poppy may contribute to a curtailment of the heroin market. No major adverse properties should be present in such a new medicine or codeine source. In this paper the search for the latter is discussed with regards to the natural occurrence of morphinan derivatives and the biosynthetic pathways in available plants. Economic and social problems connected with the introduction of a new biological source for opiates are reviewed.
TL;DR: In this paper, the authors examined the incidence of several taxes in a macroeconomic model and showed that in the long run the system tends towards a Walrasian equilibrium, where price inertia leads to rationing in the market for goods and for labour.
TL;DR: Conception d'algorithmes efficaces pour des problemes d'optimisation combinatoire durs a partir d'une etude approfondie de la relation entre enveloppes convexes des ensembles realisables and realisations lineaires.
TL;DR: The data indicate that the effects of aging on lap rate were of two kinds: producing randomized shifts in the lapping rate of individual rats over long periods, with conservation of the stable mean rate, and accentuating the tendency for reduction in theLapping rate for the last 50 laps compared with that of the first 50.
TL;DR: The authors found that between ages 8 and 11 there are no changes in the tendency to configurationally encode unfamiliar faces; psychological concomitants of puberty onset are responsible for decreases in face recognition at age 1.
Abstract: Eight-to 12-year-old primary school children and 13-year-old secondary school children were given a live and a photographed face recognition task and several other figural tasks, all representing factors from Guilford's 'Structure of Intellect' model. While the scores on most tasks showed a more or less regular increase with age, the face recognition scores showed a different pattern. In the live face recognition task they did not change between ages 8 and 11, decreased at age 12 and returned to their former level at age 13. In the photographed face recognition task the scores did not change between 8 and 12 but significantly increased at age 13. There was no correlation between the recognition scores for live and photographed faces. The main conclusions drawn were: (1) between ages 8 and 11 there are, in face recognition tasks, no changes in the tendency to configurationally encode unfamiliar faces; (2) psychological concomitants of puberty onset are responsible for decreases in face recognition at age 1...