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Showing papers by "Delft University of Technology published in 1982"


Journal ArticleDOI
TL;DR: An algorithm “Fastsim” for the simplified theory of rolling contact is described which is 15-25 times as fast as the existing programs Simrol (Kalker), and 3 times asfast as Rolcon (Knothe).
Abstract: SUMMARY An algorithm “Fastsim” for the simplified theory of rolling contact is described which is 15-25 times as fast as the existing programs Simrol (Kalker), and 3 times as fast as Rolcon (Knothe). The relative total force computed with Fastsim differs at most 0.2 from that calculated with Simrol, Simcona (Goree & Law), Rolcon, and the “exact” program Duvorol (Kalker). Descriptions and lists of an Algol 60, and HP 67 program version are available upon request: the Fortran IV version is given in the paper.

821 citations


Journal ArticleDOI
TL;DR: In this article, three models, indicated as the refraction model, the parabolic refraction-diffraction model and the full refractiondiffraction models, are briefly described, together with a comparison of the computational results of these models with measurements in a hydraulic scale model.

325 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of line profiles in terms of Fourier coefficients is presented, and the subsequent steps of measurement, data correction and evaluation are elucidated; alternatives are indicated; and it is expected that line profile analysis will become an automated routine-like analytical method soon, since the tools are available: non-expensive computers, error calculations and commercially available software.
Abstract: Methods for the determination of crystallite size and lattice strain from X-ray diffraction line broadening are discussed. The subsequent steps of measurement, data correction and evaluation are elucidated; alternatives are indicated. Emphasis is laid on the rigorous analysis of line profiles in terms of Fourier coefficients. For the analysis in terms of integral breadth and full width at half maximum a powerful method exists which adopts a Voigt function for describing the shape of the profiles. Size broadening, strain broadening and single-line methods are commented. A practical example is given of the influence of a non-ideal standard line profile and of different background estimates when a Fourier deconvolution and a Warren-Averbach size-strain analysis are performed. It is expected that line profile analysis will become an automated routine-like analytical method soon, since the tools are available: non-expensive computers, error calculations and commercially available software.

316 citations


Book ChapterDOI
TL;DR: In this paper, the authors present solutions of the flow and deformation during the approach of two bubbles along their center line for the low Weber number case, and show that the thinning rate of the film between the bubbles tends to a constant high value.
Abstract: Solutions of the flow and deformation during the approach of two bubbles along their centre line are presented for the low Weber number case. When viscosity is absent, Weber number and radius ratio disappear from the equations under suitable transformations of the variables and a universal solution is obtained. This solution indicates the formation of a dimple, after which the thinning rate of the film between the bubbles tends to a constant high value. When liquid viscosity is included the Reynolds number, Re, enters the equations. A retardation of the coalescence process is found for Re <100, while for Re ≤1 dimple formation is suppressed. The influence of gas properties is considered briefly. An extrapolation of the inviscid results to Weber numbers of order unity suggests that the bubbles will bounce apart before coalescence is achieved.

251 citations


Journal ArticleDOI
TL;DR: A linear spatially distributed model of a chain of neurons and interneurons was investigated in relation to the generation of propagated alpha rhythmic activity and it was found that such a neuronal chain shows propagation properties for frequencies in the alpha band.

212 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the performance of sieve tray performance with reference to flow regimes and recently released commercial scale experimental data and found that flow regimes appeared to have a dominant effect on nearly all of the performance variables.

145 citations


Journal ArticleDOI
TL;DR: The infinite horizon optimal control problem is considered in the general case of linear discrete time systems and quadratic criteria, both with stochastic parameters which are independent with respect to time.

143 citations


Journal ArticleDOI
TL;DR: In this paper, the optical bandgap of glow-discharge and sputter-deposited a-Si was deduced from measurements of the absorption coefficient α using a linear extrapolation of (αhvn)1/3 as a function of the photon energy h v. The exponent 1/3 is used instead of 1/2, resulting in a much better fit to the data.
Abstract: The optical bandgap of glow-discharge and sputter-deposited a-Si has been deduced from measurements of the absorption coefficient α using a linear extrapolation of (αhvn)1/3 as a function of the photon energy h v. The exponent 1/3 is used instead of 1/2, resulting in a much better fit to the data. The influence of the method of extrapolation on the resulting value for the optical bandgap has been assessed.

121 citations


Journal ArticleDOI
TL;DR: In this article, the intrinsic limit on the current carrying capacity of the superconductor was measured outside the Ginzburg-Landau regime and an approximate method of solving their equations is given, the results of which agree with the exact solution to within 1%.
Abstract: Critical currents of narrow, thin aluminum strips have been measured as a function of temperature. For the smallest samples uniformity of the current density is obtained over a large temperature range. Hence the intrinsic limit on the current-carrying capacity of the superconductor was measured outside the Ginzburg-Landau regime. The experimental values are compared with recent theoretical predictions by Kupriyanov and Lukichev. An approximate method of solving their equations is given, the results of which agree with the exact solution to within 1%. Experimental data are in excellent agreement with theoretical predictions. The absolute values agree if one assumes a $\ensuremath{\rho}l$ value of 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ \ensuremath{\Omega}${\mathrm{m}}^{2}$ with ${v}_{F}=1.3\ifmmode\times\else\texttimes\fi{}{10}^{6}$ m/s. This value for $\ensuremath{\rho}l$ is the same as that found from measurements of the anomalous skin effect but differs from values extracted from size-effect-limited resistivity.

116 citations


Journal ArticleDOI
TL;DR: Competition experiments carried out between specialized and versatile Thiobacilli strongly indicate that the ecological advantage of the versatile thiobACilli may lie not so much in their short-term flexibility, but rather in their ability to grow mixotrophically.
Abstract: Recent studies on the ecophysiology of the obligate chemolithotroph Thiobacillus neapolitanus have given better insight into its specialization for an autotrophic mode of life. This appears not only from its high constitutive levels of autotrophic enzymes, but also from its possession of carboxysomes, which seem to be specialized organelles for CO2 fixation and concentrating reducing power. At the same time, these organisms are metabolically versatile with respect to nitrogen assimilation pathways, and during starvation are able to utilize endogenous resources such as polyglucose for carbon and energy. Studies on the facultative chemolithotrophs such as Thiobacillus novellus and Thiobacillus A2 have shown that they can grow mixotrophically on mixtures of inorganic and organic substrates, i.e. they can utilize these compounds simultaneously provided that they are growth limiting. Thiobacillus A2 displays a remarkable flexibility not only with respect to the organic substrates that it can utilize but, for example, also in the choice of various pathways for glucose metabolism. Competition experiments carried out between specialized and versatile thiobacilli strongly indicate that the ecological advantage of the versatile thiobacilli may lie not so much in their short-term flexibility, but rather in their ability to grow mixotrophically. Studies on most heterotrophic chemolithotrophs are still in their infancy. Promising progress has been made in the study of the physiology of Beggiatoa species. Renewed interest in the sulphur-oxidizing bacteria stems from recent findings about their role in food chains, and their possible application in industry.

105 citations


Journal ArticleDOI
TL;DR: In this article, a study has been made of the factors which determine the choice of parking places of visitors to a city center, including walking time, parking charges, occupation rates of different parking alternatives, possible parking-time restriction, and some accessibility factors connected with parking alternatives from which a visitor could make a choice.

Journal ArticleDOI
TL;DR: A minimum cost capacitated network flow algorithm is discussed, which yields the optimal solution with respect to the priori information, and is shown that this method can also be used in the presence of observation noise.

Journal ArticleDOI
TL;DR: In this article, the catalytic conversion of ethanol over zeolite H-ZSM-5 in the presence of water has been studied as a model system for converting ethanol-containing aqueous fermentation mixtures.

Journal ArticleDOI
TL;DR: In this article, the growth rate of calcium sulphate dihydrate crystals, gypsum, in aqueous suspension has been shown to be screw dislocation controlled in the supersaturation range 1.03 C C s.

Journal ArticleDOI
TL;DR: A method for the computation of HRV spectra directly from the heart beat event series as derived from the electrocardiogram has been developed and because of the computational efficiency achieved, this method is implemented on a personal computer.
Abstract: The analysis of fluctuations in heart rate or heart rate variability (HRV) has found applications in, among others, the study of the neural cardiovascular system and ergonomic psychology. In particular, the study of the frequency components of HRV is becoming increasingly important. A method for the computation of HRV spectra directly from the heart beat event series as derived from the electrocardiogram has been developed. Because of the computational efficiency achieved, this method is implemented on a personal computer. Apart from an external QRS detector, a completely stand-alone system is realized. User interaction takes place on a menu card display basis. The system can operate at both real time and up to eightfold increased speed. The resultant spectra are displayed as histograms. Different ways of smoothing and segment averaging are possible.

Journal ArticleDOI
TL;DR: All 31P NMR spectra of the yeasts studied indicated the presence of two major intracellular inorganic phosphate pools at different pH environments, which suggested that the in organic phosphate fraction at the lower pH and the polyphosphates originated from the same intrACEllular compartment, most probably the vacuole.
Abstract: 31P NMR spectra were obtained from suspensions of Candida utilis, Saccharomyces cerevisiae and Zygosaccharomyces bailii grown aerobically on glucose Direct introduction of substrate into the cell suspension, without interruption of the measurements, revealed rapid changes in pH upon addition of the energy source All 31P NMR spectra of the yeasts studied indicated the presence of two major intracellular inorganic phosphate pools at different pH environments The pool at the higher pH was assigned to cytoplasmic phosphate from its response to glucose addition and iodoacetate inhibition of glycolysis After addition of substrate the pH in the compartment containing the second phosphate pool decreased A parallel response was observed for a significant fraction of the terminal and penultimate phosphates of the polyphosphate observed by 31P NMR This suggested that the inorganic phosphate fraction at the lower pH and the polyphosphates originated from the same intracellular compartment, most probably the vacuole In this vacuolar compartment, pH is sensitive to metabolic conditions In the presence of energy source a pH gradient as large as 08 to 15 units could be generated across the vacuolar membrane Under certain conditions net transport of inorganic phosphate across the vacuolar membrane was observed during glycolysis: to the cytoplasm when the cytoplasmic phosphate concentration had become very low due to sugar phosphorylation, and into the vacuole when the former concentration had become high again after glucose exhaustion

Book ChapterDOI
01 Jan 1982
TL;DR: In this article, the Monte Carlo method is used to derive reliability functions based on measured initial imperfection distributions that are characteristic of the different fabrication processes, which can finally provide the practicing structural engineers with a design procedure that incorporates the concept of imperfection sensitivity in a rational manner.
Abstract: Despite decades of intensive research work most shells continue to be designed by the so-called Lower Bound Design Philosophy which has been in use since the turn of the century. It is shown that by collecting the data of extensive initial imperfection surveys on full scale structures in Initial Imperfection Data Banks improved design criteria can be developed. Especially the use of the Monte Carlo Method to derive reliability functions (based on measured initial imperfection distributions that are characteristic of the different fabrication processes), may finally provide the practicing structural engineers with a design procedure that incorporates the concept of imperfection sensitivity in a rational manner.

Journal ArticleDOI
TL;DR: In this paper, the thermodynamic stabilities of thirteen cholestane isomers have been computed using molecular mechanics, and the calculated composition of a mixture of these isomers at thermodynamic equilibrium is in agreement with the composition of an isomerate.

Journal ArticleDOI
TL;DR: In this paper, it was shown that K-values calculated with this equation are an accurate approximation for the stress intensity factor of small cracks at notches, and available data on calculated K values was analyzed, which confirmed the similarity concept.
Abstract: — It was found in a previous publication that stress fields around notches are quantitatively very similar, if the peak stress at the notch root (σpeak) and the notch root radius (ρ) are the same. As a consequence, small cracks (length l) should have the same stress intensity factor, if σpeak and ρ are similar. This implies that the geometry factor C in should primarily depend on l/ρ only, and not on other dimensions. Available data on calculated K values was analysed, which confirmed the similarity concept. An equation for C as a function of l/ρ was obtained. It was shown that K-values calculated with this equation are an accurate approximation for the stress intensity factor of small cracks at notches.

Journal ArticleDOI
TL;DR: In this article, the dependence of output signals on bias conditions, which influence the emitter and collector-current distribution, is analyzed theoretically for both two-and four-collector structures.
Abstract: A recently introduced type of magnetic-field-sensitive silicon microtransducer is described. These devices consist of a multicollector n-p-n transistor fabricated with standard integration techniques. The dependence of output signals on bias conditions, which influence the emitter and collector-current distribution, is analyzed theoretically for both two- and four-collector structures. These one- and two-dimensional vector sensors have been fabricated and tested. The experimental results are compared qualitatively with the theory. Theory and measurements indicate that the two-collector structure gives a differential collector-output current, which is linearly proportional to a magnetic induction, applied along one axis only. Theory and measurements also indicate that the vector sensor gives output signals, which are a linear function of the two components of an in-plane magnetic-induction vector. Consequently, this device is capable of measuring the magnitude and direction of such a vector.

Journal ArticleDOI
TL;DR: Romberg's method gives fast convergence to an answer containing more significant digits than usual methods provide and is applied to improve the accuracy in the computation of the first and second derivatives of a real function.

Journal ArticleDOI
TL;DR: In this paper, a manolithic integrated direction-sensitive flow sensor for measuring the velocity of gas or liquid flow is described, which is based on the transfer of heat from a heated chip to a flowing fluid.
Abstract: A manolithic integrated direction-sensitive flow sensor for measuring the velocity of gas or liquid flow is described. Its operation is based on the transfer of heat from a heated chip to a flowing fluid. Temperature differences on the chip are a measure for the flow velocity and flow direction in a plane parallel with the chip's surface. The sensor can be embedded in a wall, for example, in a wall of a tube conducting a fluid flow, and can be shielded from a direct contact with the fluid. Measurements are stated for velocities in a range below 3 m/s for air at room temperature.


Journal ArticleDOI
TL;DR: Due to a numerical error, the computed noise energy of a dc SQUID, neglecting capacitance, as given by Tesche and Clarke is too small by a factor of about two.
Abstract: Due to a numerical error, the computed noise energy of a dc SQUID, neglecting capacitance, as given by Tesche and Clarke is too small by a factor of about two.

Journal ArticleDOI
TL;DR: In this article, the Split-Hopkinson-Bar technique was used in the investigation on tensile stress-strain behaviour of concrete and mortar at high stress rates (5-30 N/mm 2 ms).

Journal ArticleDOI
TL;DR: In this paper, the effect of random axisymmetric imperfections on the buckling of circular cylindrical shells under axial compression is investigated, where the initial imperfections are considered as random functions of the axial coordinate and the mean vector and variance-covariance matrix of the Fourier coefficients are calculated from experimental measurements of the shell profiles.

Journal ArticleDOI
TL;DR: In this paper, an expression for the segregating particle velocities has been derived, starting from two-phase flow momentum equations, and with this expression the non-equilibrium behaviour of a binary particle mixture has been analyzed.


Journal ArticleDOI
TL;DR: The general formal approach to structured modeling is developed in matrix notation and a simple two‐compartmental model, i.e., a structured model describing the activity of the biomass with two variables, is described.
Abstract: Models which consider changes in the composition of biomass in response to environmental changes are called Structured models. They provide a more comprehensive description of microbial behavior than unstructured models. Compared with the unstructured modeling efforts, very little has so far been done on the theory and practice of structured model building. In most of the works reported so far, no experimental data were provided, and hence no means of testing the proposed models were offered. Others only reported macroscopic response data and not the cellular composition. In an attempt to fill some of the gaps in this field, in this work, first the general formal approach to structured modeling is developed in matrix notation. Then, a simple two-compartmental model, i.e., a structured model describing the activity of the biomass with two variables, is described. The cell is divided into two fractions, one of which relates to the RNA fraction. The proposed model was then critically evaluated with experimental data, including the RNA data, obtained from fed-batch and continuous-culture experiments. The importance of using cellular structure data for model verification, i.e., RNA data in this case, is shown. Shortcomings and capabilities of the developed model are discussed.

Proceedings ArticleDOI
01 Nov 1982
TL;DR: A densitometric method is described to transform the brightness values in the digital image into cali-brated X-ray absorption profiles, thus creating the possibility to assess percentage area reduction of obstructions from single views.
Abstract: The computer-aided quantitative analysis of co-ronary obstructions from digitized coronary cineangiograms is described. First, the assessment of the percentage diameter reduction from single view angiograms is discussed. This method requires the delineation of the contours of the artery and the analysis of the diameter function. Next, a densitometric method is described to transform the brightness values in the digital image into cali-brated X-ray absorption profiles, thus creating the possibility to assess percentage area reduction of obstructions from single views.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.