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Showing papers by "Delft University of Technology published in 1990"


Journal ArticleDOI
TL;DR: This work proposes to compute distances based on very robust estimates of location and covariance, better suited to expose the outliers in a multivariate point cloud, to avoid the masking effect.
Abstract: Detecting outliers in a multivariate point cloud is not trivial, especially when there are several outliers. The classical identification method does not always find them, because it is based on the sample mean and covariance matrix, which are themselves affected by the outliers. That is how the outliers get masked. To avoid the masking effect, we propose to compute distances based on very robust estimates of location and covariance. These robust distances are better suited to expose the outliers. In the case of regression data, the classical least squares approach masks outliers in a similar way. Also here, the outliers may be unmasked by using a highly robust regression method. Finally, a new display is proposed in which the robust regression residuals are plotted versus the robust distances. This plot classifies the data into regular observations, vertical outliers, good leverage points, and bad leverage points. Several examples are discussed.

1,419 citations


Journal ArticleDOI
TL;DR: In this article, the quantum dynamics of tunnel junctions with very small capacitance, such that kBT is kBT, is studied. But the authors do not consider the case of tunnel junction with high capacitance.

565 citations


Journal ArticleDOI
01 May 1990
TL;DR: In this paper, the authors discuss the use of iterative restoration algorithms for the removal of linear blurs from photographic images that may also be degraded by pointwise nonlinearities such as film saturation and additive noise.
Abstract: The authors discuss the use of iterative restoration algorithms for the removal of linear blurs from photographic images that may also be assumed to be degraded by pointwise nonlinearities such as film saturation and additive noise. Iterative algorithms allow for the incorporation of various types of prior knowledge about the class of feasible solutions, can be used to remove nonstationary blurs, and are fairly robust with respect to errors in the approximation of the blurring operator. Special attention is given to the problem of convergence of the algorithms, and classical solutions such as inverse filters, Wiener filters, and constrained least-squares filters are shown to be limiting solutions of variations of the iterations. Regularization is introduced as a means for preventing the excessive noise magnification that is typically associated with ill-conditioned inverse problems such as the deblurring problem, and it is shown that noise effects can be minimized by terminating the algorithms after a finite number of iterations. The role and choice of constraints on the class of feasible solutions are also discussed. >

513 citations


Journal ArticleDOI
TL;DR: The physiology of Saccharomyces cerevisiae CBS 8066 was studied in anaerobic glucose-limited chemostat cultures in a mineral medium supplemented with ergosterol and Tween 80, suggesting that the observed difference in cell yield may be ascribed to an uncoupling effect of acetic acid.
Abstract: The physiology of Saccharomyces cerevisiae CBS 8066 was studied in anaerobic glucose-limited chemostat cultures in a mineral medium supplemented with ergosterol and Tween 80 The organism had a mu max of 031 h-1 and a Ks for glucose of 055 mM At a dilution rate of 010 h-1, a maximal yield of 010 g biomass (g glucose)-1 was observed The yield steadily declined with increasing dilution rates, so a maintenance coefficient for anaerobic growth could not be estimated At a dilution rate of 010 h-1, the yield of the S cerevisiae strain H1022 was considerably higher than for CBS 8066, despite a similar cell composition The major difference between the two yeast strains was that S cerevisiae H1022 did not produce acetate, suggesting that the observed difference in cell yield may be ascribed to an uncoupling effect of acetic acid The absence of acetate formation in H1022 correlated with a relatively high level of acetyl-CoA synthetase The uncoupling effect of weak acids on anaerobic growth was confirmed in experiments in which a weak acid (acetate or propionate) was added to the medium feed This resulted in a reduction in yield and an increase in specific ethanol production Both yeasts required approximately 35 mg oleic acid (g biomass)-1 for optimal growth Lower or higher concentrations of this fatty acid, supplied as Tween 80, resulted in uncoupling of dissimilatory and assimilatory processes

490 citations


Journal ArticleDOI
TL;DR: A review of the developments of the 1980s in the characterisation of organically-bound sulphur in the geosphere and summarises the geochemical significance of the results obtained by these studies can be found in this paper.

487 citations


Journal ArticleDOI
TL;DR: In this paper, an array of ultrasmall tunnel junctions which acts like a turnstile for single electrons was fabricated, and when alternating voltage of frequency f is applied to a gate, one electron is transferred per cycle through the device.
Abstract: We have fabricated an array of ultrasmall tunnel junctions which acts like a turnstile for single electrons. When alternating voltage of frequency f is applied to a gate, one electron is transferred per cycle through the device. This results in a current plateau in the current-voltage characteristic at I=ef. The overall behavior of the device is well explained by the theory of Coulomb blockade of electron tunneling. We discuss the accuracy limitations of this device.

475 citations


Journal ArticleDOI
01 Apr 1990-Zeolites
TL;DR: The monoclinic framework structure of zeolite H-ZSM-5 (Si 95.68 Al 0.32 O 192 ) has been determined by single crystal X-ray diffraction as discussed by the authors.

467 citations


Journal ArticleDOI
TL;DR: In this article, the glass transition is caused by a rather sudden increase of free volume towards equilibrium near T g, which can be calculated by making use of the well known kinetics of freevolume annilation and production in some metallic glasses.
Abstract: The glass transition, observed in glasses during DSC experiments at a constant heating rate, is described as a kinetic phenomenon caused by the continuous approach of free volume towards equilibrium during the warming up. At a certain temperature below the glass temperature T g , the amount of free volume becomes smaller than the equilibrium value at that temperature. The glass transition is caused by a rather sudden increase of free volume towards equilibrium near T g . This can be calculated by making use of the well known kinetics of free volume annilation and production in some metallic glasses. Calculations performed on this basis are in good agreement with available experimental data, both on structural relaxation and the glass transition.

391 citations



Journal ArticleDOI
TL;DR: A very simple method to compute a rather close lower bound on the H ∞ - norm, based on the relation between the singular values of the transfer function matrix and the eigenvalues of a related Hamiltonian matrix.

290 citations


Journal ArticleDOI
TL;DR: In this article, an offset-reduction method for Hall plates has been developed which minimizes the influence of the stress and temperature on the offset by using only one single symmetrical Hall plate in which the direction of the current is made to spin by contact commutation with steps of π/6 radians or smaller.
Abstract: An offset-reduction method for Hall plates has been developed which minimizes the influence of the stress and the temperature on the offset. The new method uses only one single symmetrical Hall plate in which the direction of the current is made to spin by contact commutation with steps of π/6 radians or smaller. The consecutive Hall voltages are averaged over time and the offset cancels out. The residual offset is about a factor of 10 less than that specified for commercially available silicon Hall plates and is limited by inhomogeneities in the plate.

Journal ArticleDOI
TL;DR: Type species of 75 yeast genera examined for their ability to grow anaerobically in complex and mineral media revealed that Saccharomyces cerevisiae stands out as a yeast capable of rapid growth at low redox potentials.
Abstract: Type species of 75 yeast genera were examined for their ability to grow anaerobically in complex and mineral media. To define anaerobic conditions, we added a redox indicator, resazurin, to the media to determine low redox potentials. All strains tested were capable of fermenting glucose to ethanol in oxygen-limited shake-flask cultures, even those of species generally regarded as nonfermentative. However, only 23% of the yeast species tested grew under anaerobic conditions. A comparative study with a number of selected strains revealed that Saccharomyces cerevisiae stands out as a yeast capable of rapid growth at low redox potentials. Other yeasts, such as Torulaspora delbrueckii and Candida tropicalis, grew poorly mu max, 0.03 and 0.05 h-1, respectively) under anaerobic conditions in mineral medium supplemented with Tween 80 and ergosterol. The latter organisms grew rapidly under oxygen limitation and then displayed a high rate of alcoholic fermentation. It can be concluded that these yeasts have hitherto-unidentified oxygen requirements for growth.

Journal ArticleDOI
TL;DR: The expectation-maximization algorithm is proposed to optimize the nonlinear likelihood function in an efficient way and low-order parametric image and blur models are incorporated into the identification method.
Abstract: A maximum-likelihood approach to the blur identification problem is presented. The expectation-maximization algorithm is proposed to optimize the nonlinear likelihood function in an efficient way. In order to improve the performance of the identification algorithm, low-order parametric image and blur models are incorporated into the identification method. The resulting iterative technique simultaneously identifies and restores noisy blurred images. >

Journal ArticleDOI
TL;DR: The energetics of Saccharomyces cerevisiae were studied in anaerobic glucose-limited chemostat cultures via an analysis of biomass and metabolite production and a linear correlation was found between the energy required to compensate for import of protons and the amount of acid added.
Abstract: The energetics of Saccharomyces cerevisiae were studied in anaerobic glucose-limited chemostat cultures via an analysis of biomass and metabolite production. The observed YATP was dependent on the composition of the biomass, the production of acetate, the extracellular pH, and the provision of an adequate amount of fatty acid in the medium. Under optimal growth conditions, the YATP was approximately 16 g biomass (mol ATP formed)-1. This is much higher than previously reported for batch cultures. Addition of acetic acid or propionic acid lowered the YATP. A linear correlation was found between the energy required to compensate for import of protons and the amount of acid added. This energy requirement may be regarded as a maintenance energy, since it was independent of the dilution rate at a given acid concentration.

Journal ArticleDOI
TL;DR: This paper presents a preliminary model which, if verified, will provide at least a partial explanation for the simultaneous occurrence of nitrification and denitrification in some bacteria.
Abstract: Reports of the simultaneous use of oxygen and denitrification by different species of bacteria have become more common over the past few years. Research with some strains (e.g. Thiosphaera pantotropha) has indicated that there might be a link between this 'aerobic denitrification' and a form of nitrification which requires rather than generates energy and is therefore known as heterotrophic nitrification. This paper reviews recent research into heterotrophic nitrification and aerobic denitrification, and presents a preliminary model which, if verified, will provide at least a partial explanation for the simultaneous occurrence of nitrification and denitrification in some bacteria.

Journal ArticleDOI
TL;DR: In this paper, the chemical composition of a fossil resin from a Miocene outcrop in Brunei, South East Asia, is compared with its extant counterpart dammar, obtained from trees of the family Dipterocarpaceae, to establish the nature of the precursor of bicadinanes.

Journal ArticleDOI
TL;DR: In this article, the angle-dependent reflection coefficients from seismic data were obtained by means of prestack migration (multisource, multioffset) by downward extrapolation of source and reflected wave fields to one depth level.
Abstract: Most present day seismic migration schemes determine only the zero‐offset reflection coefficient for each grid point (depth point) in the subsurface. In matrix notation, the zero‐offset reflection coefficient is found on the diagonal of a reflectivity matrix operator that transforms the illuminating source‐wave field into a reflected‐wave field. However, angle dependent reflectivity information is contained in the full reflectivity matrix. Our objective is to obtain angle‐dependent reflection coefficients from seismic data by means of prestack migration (multisource, multioffset). After downward extrapolation of source and reflected wave fields to one depth level, the rows of the reflectivity matrix (representing angle‐dependent reflectivity information for each grid point at that depth level) are recovered by deconvolving the reflected wave fields with the related source wave fields. This process is carried out in the space‐frequency domain. In order to preserve the angle‐dependent reflectivity in the im...

Book
31 Dec 1990
TL;DR: The blur identification problem is formulated as a constrained maximum-likelihood problem, which directly incorporate a priori known relations between the blur (and image model) coefficients, such as symmetry properties, into the identification procedure.
Abstract: The blur identification problem is formulated as a constrained maximum-likelihood problem. The constraints directly incorporate a priori known relations between the blur (and image model) coefficients, such as symmetry properties, into the identification procedure. The resulting nonlinear minimization problem is solved iteratively, yielding a very general identification algorithm. An example of blur identification using synthetic data is given. >

Journal ArticleDOI
Jack T. Pronk1, R. Meulenberg1, W. Hazeu1, P. Bos1, J.G. Kuenen1 
TL;DR: Thiobacillus ferrooxidans is widely used as a model organism to study the biological oxidation of pyrite and is an obligately chemolithoautotrophic, aerobic bacterium.
Abstract: Acidophilic sulphur-oxidizing bacteria were first isolated from acidic mine effluents [1], where they are the causative agents of the environmental problem acid mine drainage. Furthermore, acidophilic thiobacilli are at least partially responsible for the development of acid sulphate soils [2]. Over the past decades there has been a growing interest in the application of this type of organisms in the biological leaching of metal ores [3] and the biological dcsulphuriz~tion of coal [4,5]. The key reaction in the processes mentioned above is the biological oxidation of pyrite (Fe:S2) to ferric sulphate and sulphuric acid. Thiobacillus ferrooxidans is widely used as a model organism to study the biological oxidation of pyrite. T. ferrooxidans is an obligately chemolithoautotrophic, aerobic. Gram-negative bacterium. Energy sources for autotrophic growth include ferrous iron and a number of reduced inorganic sulphur compounds [6]. Most studies into the physiology and bio-en-

Journal ArticleDOI
TL;DR: A simple model demonstrates that the oscillations arise from the formation of a miniband structure in the periodic crystal, including energy gaps and minibands which contain fifteen discrete states.
Abstract: We have studied the magnetotransport properties of an artificial one-dimensional crystal. The crystal consists of a sequence of fifteen quantum dots, defined in the two-dimensional electron gas of a GaAs/AlGaAs heterostructure by means of a split-gate technique. At a fixed magnetic field of 2 T, two types of oscillations with different amplitude and period are observed in the conductance as a function of gate voltage. A simple model demonstrates that the oscillations arise from the formation of a miniband structure in the periodic crystal, including energy gaps and minibands which contain fifteen discrete states.

Journal ArticleDOI
TL;DR: In this paper, the Mossbauer ligand-field spectra and magnetic behaviour of both the hydrated and non-hydrated compounds are discussed, and the spin transition has been followed by EPR measurements with the aid of traces of Cu2+ ions which could be substituted for Fe2+ in the tetragonal structure.

Journal ArticleDOI
TL;DR: A number of different algorithms have recently been proposed to identify the image and blur model parameters from an image that is black-and-white.
Abstract: A number of different algorithms have recently been proposed to identify the image and blur model parameters from an image that is degraded by blur and noise. This paper gives an overview of the developments in image and blur identification under a unifying maximum likelihood framework. In fact, we show that various recently published image and blur identification algorithms are different implementations of the same maximum likelihood estimator resulting from different modeling assumptions and/or considerations about the computational complexity. The use of the maximum likelihood estimation in image and blur identification is illustrated by numerical examples.

Proceedings ArticleDOI
TL;DR: A real-time recursive testing procedure than can be used in conjunction with the Kalman filter algorithm is presented, along with diagnostic tools for inferring the detectability of particular model errors.
Abstract: A recursive testing procedure for use in integrated navigation systems is introduced. It can be used in conjunction with the Kalman filter algorithm. Diagnostic tools for inferring the detectability of particular model errors are given. The testing procedure consists of three steps: detection, identification, and adaptation. It can accommodate model errors in both the measurement model and the dynamic model of the integrated navigation system. The tests proposed are optimal in the uniformly-most-powerful-invariant sense. The procedure can accommodate slippages in the mean of the predicted residuals caused by outliers in the data, sensor failures, or switches in the dynamic model. The method is therefore also applicable to the important problem of GPS (Global Positioning System) failure detection and integrity checking. >

Journal ArticleDOI
TL;DR: The mechanism of short-term Crabtree effect was investigated via a comparative enzymic analysis of eight yeast species as mentioned in this paper, and it was established that the fermentation rate of the organisms upon transition from glucose limitation to glucose excess is positively correlated with the level of pyruvate decarboxylase.
Abstract: In bakers9 yeast, an immediate alcoholic fermentation begins when a glucose pulse is added to glucose-limited, aerobically grown cells. The mechanism of this short-term Crabtree effect was investigated via a comparative enzymic analysis of eight yeast species. It was established that the fermentation rate of the organisms upon transition from glucose limitation to glucose excess is positively correlated with the level of pyruvate decarboxylase (EC 4.1.1.1). In the Crabtree-negative yeasts, the pyruvate decarboxylase activity was low and did not increase when excess glucose was added. In contrast, in the Crabtree-positive yeasts, the activity of this enzyme was on the average sixfold higher and increased after exposure to glucose excess. In Crabtree-negative species, relatively high activities of acetaldehyde dehydrogenases (EC 1.2.1.4 and EC 1.2.1.5) and acetyl coenzyme A synthetase (EC 6.2.1.1), in addition to low pyruvate decarboxylase activities, were present. Thus, in these yeasts, acetaldehyde can be effectively oxidized via a bypass that circumvents the reduction of acetaldehyde to ethanol. Growth rates of most Crabtree-positive yeasts did not increase upon transition from glucose limitation to glucose excess. In contrast, the Crabtree-negative yeasts exhibited enhanced rates of biomass production which in most cases could be ascribed to the intracellular accumulation of reserve carbohydrates. Generally, the glucose consumption rate after a glucose pulse was higher in the Crabtree-positive yeasts than in the Crabtree-negative yeasts. However, the respiratory capacities of steady-state cultures of Crabtree-positive yeasts were not significantly different from those of Crabtree-negative yeasts. Thus, a limited respiratory capacity is not the primary cause of the Crabtree effect in yeasts. Instead, the difference between Crabtree-positive and Crabtree-negative yeasts is attributed to differences in the kinetics of glucose uptake, synthesis of reserve carbohydrates, and pyruvate metabolism.

Journal ArticleDOI
01 Nov 1990-Fuel
TL;DR: A pyrolysis-gas chromatographic (py-g.c.) method for estimation of the S org C ratio in kerogens and other forms of sedimentary macromolecular organic matter is described in this paper.

Journal ArticleDOI
TL;DR: Photoreactivating enzyme, which specifically monomerizes pyrimidine dimers in UV-irradiated DNA, was purified 21,000-fold from the cyanobacterium Anacystis nidulans to apparent homogeneity with 41% overall yield.

Journal ArticleDOI
TL;DR: The behaviour of silica fume in cement systems, particularly, the pozzolanic reaction was investigated by monitoring the chemistry of the pore solution of a mixture of fume-blended cement pastes as discussed by the authors.

Journal ArticleDOI
TL;DR: A tangent operator that is consistent with the developed integration algorithm is formulated and its efficiency is assessed compared with the classical continuum tangent operators as discussed by the authors, and the relative accuracy of two algorithms is assessed by means of iso-error maps.
Abstract: Algorithms based upon the notion of return mapping have been developed for the Hill yield function of anisotropic plasticity. The relative accuracy of two algorithms is assessed by means of iso-error maps. The choice of the algorithm turns out to be much more critical for the orthotropic Hill criterion than for the underlying isotropic von Mises plasticity model. A tangent operator that is consistent with the developed integration algorithm is formulated and its efficiency is assessed compared with the classical continuum tangent operator. The model has been applied to three shell/plate structures.

Book ChapterDOI
01 Jan 1990
TL;DR: The theoretical background of the computer program SPACAR, based on the finite element formulation for multi-degree of freedom mechanisms, is presented and three examples, the mechanism and the robot in this handbook and a cantilever beam vibrating with large amplitude, are included to illustrate the capabilities of the program.
Abstract: In this contribution the theoretical background of the computer program SPACAR is presented. The program is based on the finite element formulation for multi-degree of freedom mechanisms. A brief survey of the program and its major modules is given. Three examples, the mechanism and the robot in this handbook and a cantilever beam vibrating with large amplitude, are included to illustrate the capabilities of the program.

Journal ArticleDOI
TL;DR: In this paper, a number of C25 and C30 highly branched isoprenoid (HBI) sulphur compounds (E.g., thiolanes, 1-oxo-thiolane, thiophenes, and benzo[ b ]thiophenses) were identified in sediments, ranging from Holocene to Upper Cretaceous.