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Showing papers by "Delft University of Technology published in 1994"


Journal ArticleDOI
TL;DR: Two algorithms to identify a linear, time-invariant, finite dimensional state space model from input-output data and a special case of the recently developed Multivariable Output-Error State Space (MOESP) class of algorithms based on instrumental variables are described.

848 citations


Journal ArticleDOI
TL;DR: A structured metabolic model, based on glycogen as the source of the reduction equivalents in the anaerobic phase and the effect of the pH on the energy requirement of the uptake of acetate, is developed and explains the experimental results satisfactorily.
Abstract: In the anaerobic phase of a biological phosphorus removal process, acetate is taken up and converted to PHB utilizing both energy generated in the degradation of polyphosphate to phosphate, which is released, and energy generated in the conversion of glycogen to poly-beta-hydroxy butyrate (PHB). The phosphate/acetate ratio cannot be considered a metabolic constant, because the energy requirement for the uptake of acetate is strongly influenced by the pH value. The observed phosphate/acetate ratio shows a variation of 0.25 to 0.75 P-mol/C-mol in a pH range of 5.5 to 8.5. It is shown that stored glycogen takes part in the metabolism to provide reduction equivalents and energy for the conversion of acetate to PHB. A structured metabolic model, based on glycogen as the source of the reduction equivalents in the anaerobic phase and the effect of the pH on the energy requirement of the uptake of acetate, is developed. The model explains the experimental results satisfactorily. (c) 1994 John Wiley & Sons, Inc.

763 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the differences between fully developed turbulent flow in an axisymmetric pipe and a plane channel geometry, and compared the results obtained from a channel flow simulation.
Abstract: Direct numerical simulations (DNS) and experiments are carried out to study fully developed turbulent pipe flow at Reynolds number Rec ≈ 7000 based on centreline velocity and pipe diameter The agreement between numerical and experimental results is excellent for the lower-order statistics (mean flow and turbulence intensities) and reasonably good for the higher-order statistics (skewness and flatness factors) To investigate the differences between fully developed turbulent flow in an axisymmetric pipe and a plane channel geometry, the present DNS results are compared to those obtained from a channel flow simulation Beside the mean flow properties and turbulence statistics up to fourth order, the energy budgets of the Reynolds-stress components are computed and compared The present results show that the mean velocity profile in the pipe fails to conform to the accepted law of the wall, in contrast to the channel flow This confirms earlier observations reported in the literature The statistics on fluctuating velocities, including the energy budgets of the Reynolds stresses, appear to be less affected by the axisymmetric pipe geometry Only the skewness factor of the normal-to-the-wall velocity fluctuations differs in the pipe flow compared to the channel flow The energy budgets illustrate that the normal-to-the-wall velocity fluctuations in the pipe are altered owing to a different ‘impingement’ or ‘splatting’ mechanism close to the curved wall

732 citations


Journal ArticleDOI
TL;DR: Manganese oxides of different crystallinity, oxidation state and specific surface area have been used in the selective catalytic reduction (SCR) of nitric oxide with ammonia, indicating a relation between the SCR process and active surface oxygen.
Abstract: Manganese oxides of different crystallinity, oxidation state and specific surface area have been used in the selective catalytic reduction (SCR) of nitric oxide with ammonia between 385 and 575 K. MnO2 appears to exhibit the highest activity per unit surface area, followed by Mn5O8, Mn2O3, Mn3O4 and MnO, in that order. This SCR activity correlates with the onset of reduction in temperature-programmed reduction (TPR) experiments, indicating a relation between the SCR process and active surface oxygen. Mn2O3 is preferred in SCR since its selectivity towards nitrogen formation during this process is the highest. In all cases the selectivity decreases with increasing temperature. The oxidation state of the manganese, the crystallinity and the specific surface area are decisive for the performance of the oxides. The specific surface area correlates well with the nitric oxide reduction activity. The nitrous oxide originates from a reaction between nitric oxide and ammonia below 475 K and from oxidation of ammonia at higher temperatures, proven by using 15NH3. Participation of the bulk oxygen of the manganese oxides can be excluded, since TPR reveals that the bulk oxidation state remains unchanged during SCR, except for MnO, which is transformed into Mn3O4 under the applied conditions. In the oxidation of ammonia the degree of oxidation of the nitrogen containing products (N2, N2O, NO) increases with increasing temperature and with increasing oxidation state of the manganese. A reaction model is proposed to account for the observed phenomena.

634 citations


Journal ArticleDOI
TL;DR: It is demonstrated that the “detectability” as the conventional measure for the reliability of a measured displacement vector is very inefficient, compared to the three tests described here.
Abstract: A statistical model is introduced that describes the occurence of spurious vectors in PIV data. This model is used to investigate the performance of three different post-interrogation procedures: the global-mean, the local-mean and the local-median test. The model is also used to optimize the performance of these procedures. Predicted performances agree very well with those obtained from an artificially generated PIV record. It is demonstrated that the “detectability” as the conventional measure for the reliability of a measured displacement vector is very inefficient, compared to the three tests described here. The local-median test has the highest efficiency.

516 citations


Journal ArticleDOI
01 Jan 1994
TL;DR: In this article, a two-stage, compact, power-efficient 3 V CMOS operational amplifier with rail-to-rail input and output ranges is presented, which is very suitable as a VLSI library cell.
Abstract: This paper presents a two-stage, compact, power-efficient 3 V CMOS operational amplifier with rail-to-rail input and output ranges. Because of its small die area of 0.04 mm/sup 2/, it is very suitable as a VLSI library cell. The floating class-AB control is shifted into the summing circuit, which results in a noise and offset of the amplifier which are comparable to that of a three stage amplifier. A floating current source biases the combined summing circuit and the class-AB control. This current source has the same structure as the class-AB control which provides a power-supply-independent quiescent current. Using the compact architecture, a 2.6 MHz amplifier with Miller compensation and a 6.4 MHz amplifier with cascoded-Miller compensation have been realized. The opamps have, respectively, a bandwidth-to-supply-power ratio of 4 MHz/mW and 11 MHz/mW for a capacitive load of 10 pF. >

485 citations


Journal ArticleDOI
TL;DR: A detailed model of the shoulder mechanism has been developed which provides good insight into the function of morphological structures and is concluded that the optimum muscle length and force-length relationship are unknown.

481 citations


Journal ArticleDOI
TL;DR: Structured catalysts are promising as far as elimination of these setbacks is concerned as discussed by the authors, however, conventional fixed-bed reactors have some obvious disadvantages such as maldistributions of various kinds (including a nonuniform access of reactants to the catalytic surface), high pressure drop in the bed, etc.
Abstract: The use of structured catalysts in the chemical industry has been considered for years. Conventional fixed-bed reactors have some obvious disadvantages such as maldistributions of various kinds (including a nonuniform access of reactants to the catalytic surface), high pressure drop in the bed, etc. Structured catalysts are promising as far as elimination of these setbacks is concerned. Two basic kinds of structured catalysts can be distinguished: Structural packings covered with catalytically active material, similar in design to those used in distillation and absorption columns and/or static mixers. Good examples of catalysts of this kind are those offered by Sulzer, clearly developed by Sulzer column packings and static mixers. As in packed beds, there is an intensive radial convective mass transport over the entire cross-section of these packings. Structural packing catalysts and the reactors containing them are, however, not within the scope of this review. Monolithic catalysts are continuou...

448 citations


Proceedings ArticleDOI
26 Oct 1994
TL;DR: In this paper, the scattering of pure water is recalculated using the Einstein-Smoluchowski equation and the input for this equation is evaluated and the temperature dependency is included.
Abstract: The optical properties of pure water are basic input data for many geophysical investigations such as remote sensing of surface water and underwater radiative transfer calculations. Knowledge of the spectral properties of components in surface water is required for accurate interpretation of measured reflection and attenuation spectra in terms of their concentrations. Also the sources and sizes of errors in the basic data must be known. Absorption measurements were done with a submersible absorption meter in the temperature range 2.5 till 40.5 degree(s)C. The scattering of pure water is recalculated using the Einstein-Smoluchowski equation. The input for this equation is evaluated and the temperature dependency is included. New values for the absorption coefficient are given based on these results and analysis of data from the literature. Absorption in the wavelength range 300 - 550 nm is lower than presently used values. In the wavelength range about 700 nm the spectrum has a different shape. A formulation of the effect of temperature on the absorption spectrum is given.

423 citations


Journal ArticleDOI
TL;DR: The uptake of phosphate and storage as polyphosphate is shown to have a direct effect on the observed oxygen consumption in the aerobic phase of the biological phosphorus removal process.
Abstract: In the aerobic phase of the biological phosphorus removal process, poly-beta-hydroxybutyrate, produced during anaerobic conditions, is used for cell growth, phosphate uptake, and glycogen formation. A metabolic model of this process has been developed. The yields for growth, polyphosphate and glycogen formation are quantified using the coupling of all these conversions to the oxygen consumption. The uptake of phosphate and storage as polyphosphate is shown to have a direct effect on the observed oxygen consumption in the aerobic phase. The overall energy requirements for the P-metabolism are substantial: 25% of the acetate consumed during anaerobic conditions and 60% of the oxygen consumptions is used for the synthesis of polyphosphate and glycogen. (c) 1994 John Wiley & Sons, Inc.

408 citations


Journal ArticleDOI
TL;DR: In this article, a comparative analysis of the vibrational and structural properties of carbon nanotubes is presented, where the first-order Raman spectrum exhibits two lines at 1582 cm −1 and at 1350 cm−1.

Journal ArticleDOI
TL;DR: In this paper, a mesoporous pure-silica molecular sieve MCM-41 was used for the synthesis of solid acid catalysts for the acid-type conversion and formation of organic compounds of large molecular size.
Abstract: New solid acid catalysts, consisting of heteropoly acid (HPA) H3PW12O40 (PW) supported on a mesoporous pure-silica molecular sieve MCM-41, have been prepared and characterized by nitrogen physisorption, X-ray diffraction, FT-IR, and31P magic angle spinning NMR. The PW/MCM-41 compositions with PW loadings from 10 to 50 wt% have ∼ 30 A uniformly-sized mesopores. HPA retains the Keggin structure on the MCM-41 surface and forms finely dispersed HPA species. No HPA crystal phase is developed even at HPA loadings as high as 50 wt%. PW/MCM-41 exhibits higher catalytic activity than H2SO4 or bulk PW in liquid-phase alkylation of 4-t-butylphenol (TBP) by isobutene and styrene. In the alkylation of TBP by styrene, PW/MCM-41 shows a size selectivity compared to bulk PW and PW/SiO2, providing higher yields of a 2-(1-phenylethyl)-4-t-butylphenol, at the expense of the more bulky 2,6-bis-(1-phenylethyl)-4-t-butylphenol. The PW/MCM-41 compositions, having strong acid sites and a regular mesoporous system, are promising catalysts for the acid-type conversion and formation of organic compounds of large molecular size.

Journal ArticleDOI
TL;DR: In this paper, the overall defects in LaMnO3+δ have been studied by powder neutron diffraction, electron diffraction and high resolution transmission electron microscopy on a sample with the formal composition LaO3.

Proceedings ArticleDOI
11 Apr 1994
TL;DR: In this paper, the authors used an ambiguity reparametrization that allows one to reformulate the original ambiguity estimation problem into a new problem that becomes much easier to solve, and demonstrated that a significant reduction in both the correlation between the ambiguities and in the elongation of the corresponding confidence ellipsoid can be reached.
Abstract: The Global Positioning System (GPS) double-difference carrier phase data are biased by an integer number of cycles. A new and successful method has been developed and demonstrated that enables very fast integer ambiguity estimation. The method makes use of an ambiguity reparametrization that allows one to reformulate the original ambiguity estimation problem into a new problem that becomes much easier to solve. The theoretical concepts of the method are presented, and some representative numerical results are given and discussed. In particular, it is demonstrated that a very significant reduction in both the correlation between the ambiguities and in the elongation of the corresponding confidence ellipsoid can be reached. Typically a reduction by a factor of between 10/sup 2/ and 10/sup 3/ of the square-root of the condition number of the confidence ellipsoid can be obtained. Also the gain in time, which is needed to follow through the various computational steps, is demonstrated. >

Journal ArticleDOI
TL;DR: The model provides good insight into the mechanics of the shoulder mechanism and enables an analysis of the function of morphological structures and it is concluded that EMG amplitude cannot be used for validation of complex musculoskeletal models.

Journal ArticleDOI
TL;DR: In this paper, the authors suggest variants of GMRES, in which a preconditioner is constructed per it<:ration st<:p by a suitable approximation process, e.g., by GMRES itself.
Abstract: Recently Eirola and Nevanlinna have proposed an iterativ<: solution method for unsymmetric linear systems, in which the preconditioner is updated from step to step. Following their ideas we suggest variants of GMRES, in which a preconditioner is constructed per it<:ration st<:p by a suitable approximation process, e.g., by GMRES itself. Our numerical experimenb indicate that this may lead to considerable savings in CPU-timc and memory requirements in typical CFD applications.

Journal ArticleDOI
TL;DR: In this paper, the principles underlying the observed effects of applied pressure on biological systems, and the current and potential application of pressure in biotechnological processes are discussed. But the authors focus on applying pressure to biological systems and processes to modify the properties of biological materials to preserve or improve their qualities.

Journal ArticleDOI
01 Jan 1994-Carbon
TL;DR: In this article, a gas-activated carbon and a chemically activated carbon were chemically modified by oxidation with nitric acid or hypochlorite, and the parent and modified carbons and chars were characterized by different techniques, such as acid/base adsorption, TGA/MS, FT-IR, and porosimetry.

Journal ArticleDOI
TL;DR: In this article, the Dirac-Fock-CI method is reviewed and the MOLFDIR program suite that was developed for calculations of this type on molecular systems is described in detail.

Journal ArticleDOI
TL;DR: The research discipline concerning liquid atomization by electrical means is a broad discipline with a long history as mentioned in this paper, however, from author to author, terminology and basic experimental techniques become incongruous and easy comparisons obviated.

Proceedings ArticleDOI
11 Apr 1994
TL;DR: This paper demonstrates that it is possible to largely reduce GPS code and carrier multipath errors by using a specific receiver structure which simultaneously estimates the parameters of line-of-sight plus multipath signals.
Abstract: This paper demonstrates that it is possible to largely reduce GPS code and carrier multipath errors by using a specific receiver structure which simultaneously estimates the parameters of line-of-sight plus multipath signals. Test results in various environments show an error reduction up to a factor of ten, as compared to a receiver with a small early-late spacing. >

Journal ArticleDOI
TL;DR: In this article, a self-similar fractal geometry is adopted to model the complex and much variable structure of cohesive sediment aggregates, which has been applied to aggregation in colloidal suspensions over more than a decade.
Abstract: The forces between particles and the structure of cohesive sediment aggregates to a large extent determine various mechanical and rheological properties of mud flocs and mud beds. The unifying concept of self-similar fractal geometry is adopted to model the complex and much variable structure of cohesive sediment aggregates. The fractal aggregate model, which has been applied to aggregation in colloidal suspensions over more than a decade, is related to Krone's (1963) notion or orders of aggregation. However, self-similarity on all scales implies that a unique relationship exists between aggregate size and number of primary particles that form the aggregate. The consequences of self-similar fractal structure concerning density and strength of flocs, and permeability, yield strength and viscosity of mud beds are analysed in some detail. Comparison of the results obtained with experimental data from the literature supports the fractal model.

Journal ArticleDOI
TL;DR: The authors examined the effects of four conditions of product availability on consumers' preferences for recipe books, and the corresponding uniqueness judgments and cost evaluations for the same products, and found that books of limited availability due to market circumstances were perceived as more costly and more nearly unique than books that were accidentally unavailable or abundantly available.

Journal ArticleDOI
01 Jan 1994-Carbon
TL;DR: In this article, four commercially available carbons were subjected to ammonia and ammonia/oxygen gas mixtures at temperatures between 200 and 420°C. The pore structure of the carbons, as determined by nitrogen porosimetry, was virtually unchanged after the treatments.

Journal ArticleDOI
TL;DR: In the fine chemicals industry, the domain of synthetic organic chemists who, generally speaking, clung to the use of stoichiometric quantities of classical inorganic oxidants such as potassium dichromate and potassium permanganate as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, it was shown that the thickness of the degraded layer is of the order of magnitude of D/k, where D is the diffusion coefficient and k the pseudo-first-order rate constant for reactant consumption.
Abstract: For an ageing process involving the consumption of a small molecule (typically O2 or H2O) by reaction with the polymer, there are critical conditions of reaction rate and/or thickness above which the process becomes kinetically controlled by the diffusion of the small molecule in the polymer. Suitable lifetime prediction models must then involve the thickness distribution of reaction products. This latter can be predicted from Fick's law, modified by a term relative to the rate of consumption of the diffusing species by the chemical reaction. Some problems related to the use of this approach are examined here. It appears that, in the most frequent case, the thickness of the degraded layer is of the order of magnitude of D/k, where D is the diffusion coefficient and k the pseudo-first-order rate constant for reactant consumption. Some examples of application related to photochemical, radiochemical and thermochemical ageing are examined. It can, for instance, be shown that in photochemical or radiochemical ageing, the thickness of the oxidized layer (TOL) is proportional to the reciprocal of lβ, where l is the radiation intensity and Β an exponent depending essentially on the radical chain mechanism. It is generally expected that in the case of thermal ageing, the TOL is a decreasing function of the temperature. Some consequences of diffusion control on accelerated and natural ageing methods are briefly examined. The consequences of the ageing-induced “skin-core” structure due to the diffusion control are examined. The main features of the observed polymer embrittlement can be explained in terms of fracture mechanics.


Journal ArticleDOI
TL;DR: In this article, a surface micromachining process, using an oxide sacrificial layer and poly/nitride/poly membranes, has been developed for light modulators integrated on the same chip as the signal processing.
Abstract: The development of compact light modulators integrated on the same chip as the signal processing opens many opportunities for combining inter-chip optical communications with standard silicon circuitry. The use of surface micromachining allows high speed of operation and small size integration with other circuitry. The optical and mechanical requirements for the devices also have to be considered, to ensure compatability with standard silicon processing. A surface micromachining process, using an oxide sacrificial layer and poly/nitride/poly membranes, has been developed. This paper presents the optical and mechanical considerations in the development of a compact micromachined silicon Fabry-Perot interferometer. Initial tests have shown that these micromachined membranes represent a compact and effective light modulating method.

Journal ArticleDOI
TL;DR: In this paper, the water uptake of epoxy coatings is discussed and it is shown that the water taken up in the coating affects the coating polymer and results in swelling, which is reflected by a change of the dielectrical properties.

Journal ArticleDOI
01 Dec 1994
TL;DR: The results presented are an extension of a result by Brandwood (1983) concerning a complex gradient and are related by simple linear transformations.
Abstract: The gradient and Hessian are often used in analytical and numerical function optimisation complex valued parameter estimation problems. In a number of signal processing applications the function is a real function of complex variables. Then the optimisation is usually carried out with respect to the real and imaginary part of these variables; therefore, the gradient and Hessian concerned are real. The reason for this approach is to avoid difficulties with the definition and interpretation of the gradient and Hessian with respect to the complex variables. Definitions of a complex gradient and Hessian are proposed to solve these difficulties. The proposed and the real gradient and Hessian are fully compatible and are related by simple linear transformations. The results presented are an extension of a result by Brandwood (1983) concerning a complex gradient.