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Showing papers by "Delft University of Technology published in 1999"


Journal ArticleDOI
TL;DR: In this article, the Activated Sludge Model No. 3 (ASM3) is proposed to predict oxygen consumption, sludge production, nitrification and denitrification of activated sludge systems.

2,108 citations


Journal ArticleDOI
TL;DR: This paper shows the use of a data domain description method, inspired by the support vector machine by Vapnik, called the support vectors domain description (SVDD), which can be used for novelty or outlier detection and is compared with other outlier Detection methods on real data.

1,581 citations


Journal ArticleDOI
18 Nov 1999-Nature
TL;DR: In this paper, electrical transport measurements on single-wall carbon nanotubes (SWNTs) with intramolecular junctions are reported, showing that a metal-semiconductor junction behaves like a rectifying diode with nonlinear transport characteristics that are strongly asymmetric with respect to bias polarity.
Abstract: The ultimate device miniaturization would be to use individual molecules as functional devices. Single-wall carbon nanotubes (SWNTs) are promising candidates for achieving this: depending on their diameter and chirality, they are either one-dimensional metals or semiconductors1,2. Single-electron transistors employing metallic nanotubes3,4 and field-effect transistors employing semiconducting nanotubes5 have been demonstrated. Intramolecular devices have also been proposed which should display a range of other device functions6,7,8,9,10,11. For example, by introducing a pentagon and a heptagon into the hexagonal carbon lattice, two tube segments with different atomic and electronic structures can be seamlessly fused together to create intramolecular metal–metal, metal–semiconductor, or semiconductor–semiconductor junctions. Here we report electrical transport measurements on SWNTs with intramolecular junctions. We find that a metal–semiconductor junction behaves like a rectifying diode with nonlinear transport characteristics that are strongly asymmetric with respect to bias polarity. In the case of a metal–metal junction, the conductance appears to be strongly suppressed and it displays a power-law dependence on temperatures and applied voltage, consistent with tunnelling between the ends of two Luttinger liquids. Our results emphasize the need to consider screening and electron interactions when designing and modelling molecular devices. Realization of carbon-based molecular electronics will require future efforts in the controlled production of these intramolecular nanotube junctions.

1,485 citations


Journal ArticleDOI
29 Jul 1999-Nature
TL;DR: The discovery of this missing lithotroph and its identification as a new, autotrophic member of the order Planctomycetales, one of the major distinct divisions of the Bacteria makes an important contribution to the problem of unculturability.
Abstract: With the increased use of chemical fertilizers in agriculture, many densely populated countries face environmental problems associated with high ammonia emissions. The process of anaerobic ammonia oxidation ('anammox') is one of the most innovative technological advances in the removal of ammonia nitrogen from waste water. This new process combines ammonia and nitrite directly into dinitrogen gas. Until now, bacteria capable of anaerobically oxidizing ammonia had never been found and were known as "lithotrophs missing from nature". Here we report the discovery of this missing lithotroph and its identification as a new, autotrophic member of the order Planctomycetales, one of the major distinct divisions of the Bacteria. The new planctomycete grows extremely slowly, dividing only once every two weeks. At present, it cannot be cultivated by conventional microbiological techniques. The identification of this bacterium as the one responsible for anaerobic oxidation of ammonia makes an important contribution to the problem of unculturability.

1,475 citations


Journal ArticleDOI
TL;DR: The physiology of anaerobic ammonium oxidizing (anammox) aggregates grown in a sequencing batch reactor was investigated quantitatively and the anammox process was completely inhibited by nitrite concentrations higher than 0.1 g of nitrogen per liter.
Abstract: The physiology of anaerobic ammonium oxidizing (anammox) aggregates grown in a sequencing batch reactor was investigated quantitatively. The physiological pH and temperature ranges were 6.7 to 8.3 and 20 to 43°C, respectively. The affinity constants for the substrates ammonium and nitrite were each less than 0.1 mg of nitrogen per liter. The anammox process was completely inhibited by nitrite concentrations higher than 0.1 g of nitrogen per liter. Addition of trace amounts of either of the anammox intermediates (1.4 mg of nitrogen per liter of hydrazine or 0.7 mg of nitrogen per liter of hydroxylamine) restored activity completely.

1,274 citations


Journal ArticleDOI
13 Aug 1999-Science
TL;DR: A qubit was designed that can be fabricated with conventional electron beam lithography and is suited for integration into a large quantum computer, allowing controlled transfer between qubits of the flux that is generated by the persistent currents, leading to entanglement of qubit information.
Abstract: A qubit was designed that can be fabricated with conventional electron beam lithography and is suited for integration into a large quantum computer. The qubit consists of a micrometer-sized loop with three or four Josephson junctions; the two qubit states have persistent currents of opposite direction. Quantum superpositions of these states are obtained by pulsed microwave modulation of the enclosed magnetic flux by currents in control lines. A superconducting flux transporter allows for controlled transfer between qubits of the flux that is generated by the persistent currents, leading to entanglement of qubit information.

1,189 citations


Book
01 Jan 1999

947 citations


Journal ArticleDOI
TL;DR: It is shown that granule formation in aerobic reactors is feasible and can be exploited to increase the volumetric conversion capacity of such reactors.

714 citations


Journal ArticleDOI
TL;DR: The proposed model can explain the unexpectedly small sizes of the variable errors in the localization of a seen hand that were reported earlier and implies that the CNS has knowledge about the direction-dependent precision of the proprioceptive and visual information.
Abstract: Integration of proprioceptive and visual position-information: an experimentally supported model. To localize one’s hand, i.e., to find out its position with respect to the body, humans may use pro...

689 citations


Journal ArticleDOI
TL;DR: ASM2d is based on ASM2 and is expanded to include the denitrifying activity of the phosphorus accumulating organisms (PAOs), which allows for improved modeling of the processes, especially with respect to the dynamics of nitrate and phosphate.

628 citations


Journal ArticleDOI
TL;DR: In this paper, a superconducting qubit that has circulating currents of opposite sign as its two states is presented. But the circuit consists of three nanoscale aluminum Josephson junctions connected in a super-conducting loop and controlled by magnetic fields.
Abstract: We present the design of a superconducting qubit that has circulating currents of opposite sign as its two states. The circuit consists of three nanoscale aluminum Josephson junctions connected in a superconducting loop and controlled by magnetic fields. The advantages of this qubit are that it can be made insensitive to background charges in the substrate, the flux in the two states can be detected with a superconducting quantum interference device, and the states can be manipulated with magnetic fields. Coupled systems of qubits are also discussed as well as sources of decoherence. @S0163-1829~99!00746-8#

Journal ArticleDOI
TL;DR: In this paper, the advantages and disadvantages of a multicarrier code-division multiple access (MC-CDMA) system are compared with those of a conventional direct-sequence (DS) CDMA system, and how to determine the number of subcarriers and the length of guard interval is discussed.
Abstract: This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.

Journal ArticleDOI
TL;DR: Two new techniques for the determination of building models from laser altimetry data are presented, both of which work on the original laser scanner data points without the requirement of an interpolation to a regular grid.
Abstract: Two new techniques for the determination of building models from laser altimetry data are presented. Both techniques work on the original laser scanner data points without the requirement of an interpolation to a regular grid. Available ground plan information may be used, but is not required. Closed solutions for the determination of the parameters of a standard gable roof type building model based on invariant moments of 2 1r2-D point clouds are shown. In addition, the analysis of deviations between point cloud and model does allow for modelling asymmetries such as dorms on a gable roof. By intersecting planar faces nonparametric buildings with more complex roof types can also be modelled. The techniques were applied to a FLI-MAP laser scanner dataset covering an area of 500= 250 m 2 with a density of more than 5 pointsrm 2 . Within this region, all but one building could be modelled. An analysis of the variance of the parameters within a group of buildings indicates a precision in the range of 0.1-0.2 m. q 1999 Elsevier Science B.V. All rights reserved.


Journal ArticleDOI
TL;DR: In this article, a firm's propensity to patent is significantly higher among R&D collaborators, and it varies across sectors and by firm size, and the results have obvious consequences for the interpretation of patenting figures as an indicator of innovation.

Journal ArticleDOI
TL;DR: In this article, experimental results on the turbulent, strongly swirling flow field in a reverse flow gas cyclone separator are presented, and used to evaluate the performance of three turbulence closure models.

Journal ArticleDOI
TL;DR: In this article, a probabilistic justification for using the integer least squares estimator is given for global positioning system ambiguity resolution, which implies that the success rate of any other integer estimator of the carrier phase ambiguities will be smaller than or at the most equal to the ambiguity success rate.
Abstract: A probabilistic justification is given for using the integer least-squares (LS) estimator. The class of admissible integer estimators is introduced and classical adjustment theory is extended by proving that the integer LS estimator is best in the sense of maximizing the probability of correct integer estimation. For global positioning system ambiguity resolution, this implies that the success rate of any other integer estimator of the carrier phase ambiguities will be smaller than or at the most equal to the ambiguity success rate of the integer LS estimator. The success rates of any one of these estimators may therefore be used to provide lower bounds for the LS success rate. This is particularly useful in case of the bootstrapped estimator.

Journal ArticleDOI
TL;DR: A novel method for generating key frames and previews for an arbitrary video sequence by first applying multiple partitional clustering to all frames of a video sequence and then selecting the most suitable clustering option(s) using an unsupervised procedure for cluster-validity analysis.
Abstract: Key frames and previews are two forms of a video abstract, widely used for various applications in video browsing and retrieval systems. We propose in this paper a novel method for generating these two abstract forms for an arbitrary video sequence. The underlying principle of the proposed method is the removal of the visual-content redundancy among video frames. This is done by first applying multiple partitional clustering to all frames of a video sequence and then selecting the most suitable clustering option(s) using an unsupervised procedure for cluster-validity analysis. In the last step, key frames are selected as centroids of obtained optimal clusters. Video shots, to which key frames belong, are concatenated to form the preview sequence.

Journal ArticleDOI
01 Jan 1999-Carbon
TL;DR: In this paper, the development of the nitrogen functionality of model chars as a function of burn-off for gasification in CO2 or in O2 has been studied by X-ray photoelectron spectroscopy (XPS).

Journal ArticleDOI
TL;DR: In this article, the authors presented first principles charge and spin-consistent electronic structure computations on the Heusler-type disordered alloys for three different metalloids.
Abstract: We present first-principles charge- and spin-self-consistent electronic structure computations on the Heusler-type disordered alloys ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ for three different metalloids $X=(\mathrm{Si},\mathrm{Ga},$ and Al). In these calculations we use the methodology based on the Korringa-Kohn-Rostoker formalism and the coherent-potential approximation generalized to treat disorder in multicomponent complex alloys. Exchange correlation effects are incorporated within the local spin density approximation. Total energy calculations for ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Si}$ show that V substitutes preferentially on the $\mathrm{Fe}(B)$ site, not on the $\mathrm{Fe}(A,C)$ site, in agreement with experiment. Furthermore, calculations have been carried out for ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ alloys (with $x=0.25,$ $0.50,$ and $0.75),$ together with the end compounds ${\mathrm{Fe}}_{3}X$ and ${\mathrm{Fe}}_{2}\mathrm{V}X,$ and the limiting cases of a single V impurity in ${\mathrm{Fe}}_{3}X$ and a single $\mathrm{Fe}(B)$ impurity in ${\mathrm{Fe}}_{2}\mathrm{V}X.$ We delineate clearly how the electronic states and magnetic moments at various sites in ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ evolve as a function of the V content and the metalloid valence. Notably, the spectrum of ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ $(X=\mathrm{Al}$ and Ga) develops a pseudogap for the majority as well as minority spin states around the Fermi energy in the V-rich regime, which, together with local moments of $\mathrm{Fe}(B)$ impurities, may play a role in the anomalous behavior of the transport properties. The total magnetic moment in ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Si}$ is found to decrease nonlinearly, and the $\mathrm{Fe}(B)$ moment to increase with increasing x; this is in contrast to expectations of the ``local environment'' model, which holds that the total moment should vary linearly while the $\mathrm{Fe}(B)$ moment should remain constant. The common-band model, which describes the formation of bonding and antibonding states with different weights on the different atoms, however, provides insight into the electronic structure of this class of compounds.

Journal ArticleDOI
TL;DR: In this paper, the trend from non-catalytic to catalytic processes is discussed and examples from the areas of acid/base and redox catalysis are chosen to illustrate the trend.
Abstract: Progress towards environmentally responsible processing is marked by the elimination of waste and by-product generation and reduced dependence on hazardous chemicals. The key to both is often provided by catalytic as alternatives to stoichiometric processes. Heterogeneous catalysis, long established in bulk-chemicals processing, is beginning to make inroads into the fine-chemicals industry also. This tendency is helped by the availability of novel catalytic materials and modern techniques of creating and investigating specific active sites on catalyst surfaces. In this overview, examples from the areas of acid/base and redox catalysis are chosen to illustrate the trend from non-catalytic to catalytic processes.

Journal ArticleDOI
TL;DR: In this paper, large eddy simulations were performed on the flow in a baffled stirred tank, drien by a Rushton turbine at Res 29,000, using a lattice Boltzmann scheme for discretizing the Naier ) Stokes equations, and a force-field technique for representing the action of the impeller on the fluid.
Abstract: Large eddy simulations were performed on the flow in a baffled stirred tank, drien by a Rushton turbine at Res 29,000. The simulation procedure consisted of a lattice ) Boltzmann scheme for discretizing the Naier ) Stokes equations, and a force- field technique for representing the action of the impeller on the fluid. The subgrid-scale model was a conentional Smagorinsky model with a Smagorinsky constant c s 0.12. s The uniform, cubic computational grid had a size of about 6 = 10 6 nodes. The com- puter code was implemented on a parallel, shared-memory computer platform. The results on the phase-resoled aerage flow, as well as on the turbulence characteristics, are compared with phase-resoled experimental data. The trailingortex structure in the ¤icinity of the impeller was well represented by the simulations.

Journal ArticleDOI
TL;DR: This work presents a preconditioned conjugate gradient method to update the contrast, which introduces hardly any additional computation time, but achieves the same or even better results than the original CSI method.
Abstract: We discuss the problem of the reconstruction of the profile of a bounded object from scattered field data. Inspired by the successful implementation of the minimization of total variation (TV) in the modified gradient method, we have explored the possibilities of this image-enhancement technique in the contrast source inversion (CSI) method. In order to be able to implement the additional regularizer in the CSI method, the updating of the contrast has been modified. We present a preconditioned conjugate gradient method to update the contrast, which introduces hardly any additional computation time, but achieves the same or even better results than the original CSI method. The addition of the minimization of the total variation to the cost functional has a very positive effect on the quality of the reconstructions for both `blocky' and smooth profiles, but a drawback is the presence of an artificial weighting parameter in the cost functional, which can only be determined through considerable numerical experimentation. Therefore, we have introduced the TV as a multiplicative constraint. Numerical experiments demonstrate that the algorithm, based on this multiplicative regularization, seems to be robust, handling noisy as well as limited data very well, without the necessity of artificial parameters.

Journal ArticleDOI
TL;DR: It is shown that the fuzzy model is not only more accurate but as opposed to other black-box approaches (such as neural networks), it also provides some insight into the nonlinear relationship represented by the model.

Journal ArticleDOI
TL;DR: The processes grouped under endogenous respiration in activated sludge models, such as maintenance, lysis, internal and external decay, predation and death-regeneration are discussed and organised in order to create a working platform for discussing more detailed activatedSludge models.

Journal ArticleDOI
TL;DR: A newly developed strategy for automatically segmenting movies into logical story units, designed to work on MPEG-DC sequences, where it is taken into account that at least a partial decoding is required for performing content-based operations on MPEG compressed video streams.
Abstract: We present a newly developed strategy for automatically segmenting movies into logical story units. A logical story unit can be understood as an approximation of a movie episode, which is a high-level temporal movie segment, characterized either by a single event (dialog, action scene, etc.) or by several events taking place in parallel. Since we consider a whole event and not a single shot to be the most natural retrieval unit for the movie category of video programs, the proposed segmentation is the crucial first step toward a concise and comprehensive content-based movie representation for browsing and retrieval purposes. The automation aspect is becoming increasingly important with the rising amount of information to be processed in video archives of the future. The segmentation process is designed to work on MPEG-DC sequences, where we have taken into account that at least a partial decoding is required for performing content-based operations on MPEG compressed video streams. The proposed technique allows for carrying out the segmentation procedure in a single pass through a video sequence.

Journal ArticleDOI
TL;DR: An electrostatically deformable, gold-coated, silicon nitride membrane mirror was used as a phase modulator to compress pulses from 92 to 15 fs to test the range of the deformable-mirror-based compressor.
Abstract: An electrostatically deformable, gold-coated, silicon nitride membrane mirror was used as a phase modulator to compress pulses from 92 to 15 fs. Both an iterative genetic algorithm and single-step dispersion compensation based on frequency-resolved optical gating calibration of the mirror were used to compress pulses to within 10% of the transform limit. Frequency-resolved optical gating was used to characterize the pulses and to test the range of the deformable-mirror-based compressor.

Journal ArticleDOI
TL;DR: The yeast Saccharomyces cerevisiae is unique among eukaryotes in exhibiting fast growth in both the presence and the complete absence of oxygen, and genome-wide transcriptional adaptation to aerobiosis and anaerobiosis was studied using DNA microarrays.
Abstract: The yeast Saccharomyces cerevisiae is unique among eukaryotes in exhibiting fast growth in both the presence and the complete absence of oxygen. Genome-wide transcriptional adaptation to aerobiosis and anaerobiosis was studied in assays using DNA microarrays. This technique was combined with chemostat cultivation, which allows controlled variation of a single growth parameter under defined conditions and at a fixed specific growth rate. Of the 6,171 open reading frames investigated, 5,738 (93%) yielded detectable transcript levels under either aerobic or anaerobic conditions; 140 genes showed a >3-fold-higher transcription level under anaerobic conditions. Under aerobic conditions, transcript levels of 219 genes were >3-fold higher than under anaerobic conditions.

Journal ArticleDOI
TL;DR: The network was trained to predict the UCS based on the hardness, porosity, density, grain size and rock type information of a rock sample, and the results are compared to predictions obtained by conventional statistical relations.

Journal ArticleDOI
TL;DR: Various approaches are studied to increase yields, these encompass screening and selection of high producing cell lines, media optimization, elicitation, culturing of differentiated cells (organ cultures), immobilization.
Abstract: The technology of large-scale plant cell culture is feasible for the industrial production of plant-derived fine chemicals. Due to low or no productivity of the desired compounds the economy is only in a few cases favorable. Various approaches are studied to increase yields, these encompass screening and selection of high producing cell lines, media optimization, elicitation, culturing of differentiated cells (organ cultures), immobilization. In recent years metabolic engineering has opened a new promising perspectives for improved production in a plant or plant cell culture.