Showing papers by "University of Twente published in 1989"
TL;DR: A simple and reliable histogram-based method to estimate mutual information and the accuracies of this mutual information estimator and of a similar entropy estimator are discussed.
360 citations
TL;DR: In this article, a method for the selective diametrical functionalization of calix[4]arenes at the upper rim by transfer of functionality and selective substitutions at the para positions of the phenol rings is described.
245 citations
TL;DR: In this paper, the mechanical properties of impact modifiers were tested with both a torsion pendulum test and a tensile test and the notched impact strength of the blends was measured as a function of temperature.
188 citations
TL;DR: In this article, two methods were tested: a method using the osmotic pressure difference during an ultrafiltration experiment, and a method based on the variation in observed retention when cross-flow velocities are changed.
165 citations
TL;DR: In this article, the effect of maleic anhydride (MA) concentration on the blending process and the impact behavior of EPDM rubber was investigated using infra-red spectroscopy and elemental analysis.
164 citations
TL;DR: Magnesia was introduced into the γ-alumina membrane to enhance the adsorption and mobility of CO2 in this article, but the contribution of surface diffusion to the total transport decreases with the introduction of magnesia, as is shown by counterdiffusion.
162 citations
TL;DR: In this paper, a toughening mechanism is proposed in which the cavitation stress of the rubber and the interparticle spacing play crucial roles, and a correlation exists between the stress at which the rubber particles cavitate in the tensile test and the impact behaviour of the blend.
160 citations
TL;DR: In this paper, the theoretical status of existing school effectiveness models is analyzed by using perspectives from organizational theory and models of classroom effectiveness, which leads to the formulation of a basic framework for conceptualizing school effectiveness that includes variables at the levels of the school, the context of a school and the classroom, while background variables of pupils are also taken into account.
158 citations
TL;DR: A maximin model for IRT-based test design is proposed that serves as a constraint subject to which a linear programming algorithm maximizes the information in the test.
Abstract: A maximin model for IRT-based test design is proposed. In the model only the relative shape of the target test information function is specified. It serves as a constraint subject to which a linear programming algorithm maximizes the information in the test. In the practice of test construction, several demands as linear constraints in the model. A worked example of a text construction problem with practical constraints is presented. The paper concludes with a discussion of some alternative models of test construction.
155 citations
TL;DR: In this article, a general method for the explicit determination of all solutions of any Thue equation is presented, using a combination of Baker's theory of linear forms in logarithms and recent computational diophantine approximation techniques.
155 citations
TL;DR: In a secondary analysis of the data base of the IEA second mathematics study, the association of school and instructional characteristics with mathematics achievement within and across 17 countries at the school and student level was investigated as mentioned in this paper.
TL;DR: A new type of actuator for a microminiature pump that deflects a thin silicon membrane through the pressure of air in a cavity, raised by resistive heating, is presented.
01 Nov 1989
TL;DR: This work discusses general convex games, which Edmonds and Giles (1977) have shown to be of particular importance also in combinatorial optimization, and derives the corresponding core theorems from a sandwich theorem for set functions within the setting of linear programming.
Abstract: Games with restricted cooperation are cooperativeN-person games with sidepayments, where the collection of feasible coalitions need not comprise all subsets of players and thus is restricted. We study balanced and completely balanced games in this context and derive the corresponding core theorems from a sandwich theorem for set functions within the setting of linear programming. In particular, we discuss general convex games, which Edmonds and Giles (1977) have shown to be of particular importance also in combinatorial optimization.
TL;DR: The in vivo and in vitro degradation behavior of the polymers was comparable and the decrease of molecular weight of the copolymers and poly(DL-lactic acid) in time was similar, while the tissue reaction was more severe for polymers having a higher rate of degradation.
Abstract: A series of copolymers of glycine and DL-lactic acid with various compositions was synthesized and their in vivo and in vitro degradation behavior was studied. For the in vivo examination, discs of the copolymer films were subcutaneously implanted in rats. The in vitro studies were carried out in phosphate buffer at pH = 7.4 and 37°C. The decrease in molecular weight, the loss of weight, and the tissue reactions of the different copolymers were determined after 2, 5, and 10 weeks. Poly(DL-lactic acid) was used as reference material. The in vivo and in vitro degradation behavior of the polymers was comparable. The decrease of molecular weight of the copolymers and poly(DL-lactic acid) in time was similar. The weight loss for copolymers with a higher mole fraction of glycine units started earlier. The copolymer with the highest content of glycine units disappeared completely within 10 weeks both in vivo and in vitro. The poly(DL-lactic acid) implant lost only 25% weight over the same period. Tissue reactions against all materials started with an acute inflammatory reaction caused by the trauma of implantation, followed by wound-healing processes, ending in a very mild foreign body reaction for the poly(DL-lactic acid) and a more excessive macrophage mediated foreign body reaction for the glycine/DL-lactic acid copolymers. The tissue reaction was more severe for polymers having a higher rate of degradation.
TL;DR: In this paper, the authors compared models published in the two-phase flow literature for the added mass coefficient of a dilute bubbly dispersion and showed that the differences between the models are mainly due to the different ways in which the added masses are defined.
TL;DR: In this article, the authors describe the development of a this articleET concept that is based on the chemical attachment of a non-blocking polymeric layer, and the experimental results of an acrylate/polyHEMA-this articleET are shown in a differential ISFET/this articleET system.
TL;DR: The rate of reaction of methane with oxygen in the presence of a Li-doped MgO catalyst has been studied as a function of the partial pressures of CH4, O2 and CO2 in a well-mixed reaction system which is practically gradientless with respect to gas-phase concentrations.
TL;DR: Etude de la permeabilite et de la selectivite des membranes composites constituees d'alumine-γ modifiee par de la silice.
Abstract: Etude de la permeabilite et de la selectivite des membranes composites constituees d'alumine-γ modifiee par de la silice
TL;DR: In this paper, it has been found that it is possible to improve the activity and stability for the oxidative coupling of methane of a Li/MgO catalyst by the addition of small amounts of the oxides of various transition and rare earth metals.
TL;DR: In this paper, a simple relationship between some properties of the parent coal particles, and the fragmentation and swelling during devolatilization was found, and experiments reported in this paper were aimed at finding the simple relationship.
TL;DR: FIXES as mentioned in this paper is a computer aided system for the automatic generation of set-ups and for fixture design for prismatic parts, to be used in an integrated process planning environment, in particular the automatic selection of the faces for the positioning, clamping and support of workpieces.
TL;DR: In this paper, the authors disentangle the constraints between traditional lines of political polarization (left-right placement) and newer distinctions (materialist/postmaterialist values) among mass publics.
Abstract: In this article we try to disentangle the constraints between traditional lines of political polarization (left-right placement) and newer distinctions (materialist/postmaterialist values) among mass publics. It is shown that voting or party preference is most clearly related to the left-right placement of the respondents. However, this placement is directly and strongly dependent on the materialist/postmaterialist orientation, while background variables like education, income and age are linked to voting via this value orientation. The materialist/postmaterialist orientation appears to be the present-day interpretation of the dominant political conflict in advanced industrial society. Although alignments and orientations count for a substantive part of the variance in voting, the power of these models to predict the actual vote of people turns out to be rather poor.
TL;DR: In this article, a method for the detection of item bias with respect to observed or unobserved subgroups is proposed, which uses quasi-loglinear models for the incomplete subgroup × test score × item 1 ×... × itemk contingency table.
Abstract: A method is proposed for the detection of item bias with respect to observed or unobserved subgroups. The method uses quasi-loglinear models for the incomplete subgroup × test score × Item 1 × ... × itemk contingency table. If subgroup membership is unknown the models are Haberman's incomplete-latent-class models. The (conditional) Rasch model is formulated as a quasi-loglinear model. The parameters in this loglinear model, that correspond to the main effects of the item responses, are the conditional estimates of the parameters in the Rasch model. Item bias can then be tested by comparing the quasi-loglinear-Rasch model with models that contain parameters for the interaction of item responses and the subgroups.
TL;DR: In this article, a two-dimensional (15 × 200 × 400 × 400 mm) high-temperature fluidized bed, devolatilization ignition and combustion phenomena of single coal particles have been studied.
TL;DR: The results of these studies show that mitosenes have a more limited range of activities than mitomycin C and Surprisingly, the in vivo activities of mitosene diol 8b and mitosenes diacetate 10b against the gastric human tumor xenograft GXF 97 were very high and comparable with that of mitomycycin C.
Abstract: Mitosenes of both the pyrrolo- and pyrido[1,2-a]indole type have been prepared via modification of these heterotricyclic compounds. Several mitosenes have been studied for their reactions with nucleophiles under reductive conditions. The results of these experiments show that the biological activity of mitosenes is based on the mechanism of bioreductive activation. When both leaving groups at C-1 and C-10 in the mitosene are the same, the nucleophile preferably adds to C-10 under reductive conditions. All mitosenes were studied for their biological activities in vitro against L1210, WiDr, and A204. On the basis of these results a selection of three mitosenes was made for a more detailed biological evaluation. Several tumor model systems were used, viz. P388, human tumor xenografts, MAC 13, and MAC 16. The results of these studies show that mitosenes have a more limited range of activities than mitomycin C. Surprisingly, the in vivo activities of mitosene diol 8b and mitosene diacetate 10b against the gastric human tumor xenograft GXF 97 were very high and comparable with that of mitomycin C.
TL;DR: In this article, an algorithm is presented for transforming a nonlinear state space system into a threefold set of equations; the first subset describing the dynamics of the unobservable part of the system, the second subset representing the remaining state variables as functions of inputs and outputs and their derivatives, and the last subset defining the external behaviour of a system.
TL;DR: The relationship between nerve stimulation, pulse amplitude and isometric muscle force was measured to investigate recruitment of motor units and indicated that small overlap of recruited motor unit groups occurred more often for intrafascicular than for extraneural electrodes.
Abstract: The relationship between nerve stimulation, pulse amplitude and isometric muscle force was measured to investigate recruitment of motor units. Force addition experiments were performed to obtain insight in the intersection of motor unit groups recruited by different electrodes. Intrafascicular and extraneural multielectrode configurations were used for nerve stimulation. Experiments were performed on rats. The common peroneal nerve was stimulated and the forces of the tibial anterior and extensor digitorum longus muscles were measured isometrically. Recruitment was more stable for intrafascicular electrodes than for extraneural electrodes. Especially for intrafascicular electrodes no strict inverse recruitment was observed. Force addition experiments indicated that small overlap of recruited motor unit groups occurred more often for intrafascicular than for extraneural electrodes.
TL;DR: In this article, a new version of the cake filtration model was proposed, which uses the unsteady state equation for solute mass transport to predict flux data by computer simulations, without assumptions concerning the concentration at the membrane, the concentration profile or the specific resistance of the boundary layer.
TL;DR: In this paper, three issues in the interpretation of the results of school effectiveness research are discussed: criterion choice, effect size and stability of effects, and various suggestions as to the improvement of future school research are offered, notably more refined research designs and more elaborate theory development.