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Showing papers by "Delft University of Technology published in 1983"


Journal ArticleDOI
TL;DR: A fuzzy version of Saaty's pairwise comparison method (1980) extended by de Graan and Lootsma (1981), adapted in such a way, that decision-makers are asked to express their opinions in fuzzy numbers with triangular membership functions.

2,631 citations


Journal ArticleDOI
01 Sep 1983
TL;DR: A hypothesis is put forward which explains that ethanol production from xylose by yeast under anaerobic conditions is negligible, and it is suggested that the failure to fermentxylose anaerobically is due to a discrepancy between production and consumption of NADH in the overall conversion of xylOSE to ethanol.
Abstract: The kinetics of glucose and xylose utilization by batch cultures of Candida utilis were studied under aerobic and anaerobic conditions during growth in complex media. Rapid ethanol formation occurred during growth on glucose when aerobic cultures were shifted to anaerobic conditions. However, with xylose as a substrate, transfer to anaerobiosis resulted in an immediate cessation of metabolic activity, as evidenced by the absence of both ethanol formation and xylose utilization. The inability of the yeast to ferment xylose anaerobically was not due to the absence of key enzymes of the fermentation pathway, since the addition of glucose to such cultures resulted in the immediate conversion of glucose to ethanol. Furthermore, when the enzyme xylose isomerase was added to an anaerobic xylose culture, immediate conversion of xylose to ethanol was observed. This indicates that the inability of the yeast to form ethanol from xylose under anaerobic conditions is caused by metabolic events associated with the conversion of xylose to xylulose. A hypothesis is put forward which explains that ethanol production from xylose by yeast under anaerobic conditions is negligible. It is suggested that the failure to ferment xylose anaerobically is due to a discrepancy between production and consumption of NADH in the overall conversion of xylose to ethanol. When a hydrogen acceptor (i.e. acetoin) was added to anaerobic cultures of C. utilis, xylose utilization resumed, and ethanol and acetate were produced with the concomitant stoicheiometric reduction of acetoin to 2,3-butanediol.

270 citations


Journal ArticleDOI
TL;DR: In this paper, experimental results of the formation of methane hydrate in dependence of temperature and pressure in unsaturated solutions of NaCl in water were presented in a temperature range from 261.85 to 285.98 K and pressure up to 11.0 MPa.
Abstract: Experimental results of the formation of methane hydrate in dependence of temperature and pressure in unsaturated solutions of NaCl in water will be presented in a temperature range from 261.85 to 285.98 K and pressure up to 11.0 MPa. Furthermore the four-phase equilibrium NaCl X 2H/sub 2/O /SUB s/ -CH/sub 4/ X nH/sub 2/O /SUB s/ -L-G has been calculated from the experimental results. Also the heats of transformation of several other equilibria in the ternary system CH/sub 4/-H/sub 2/O-NaCl are obtained.

269 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of 0−5 mol % lanthanum oxide on the thermal stability of gamma alumina catalyst supports was investigated, and the phase transformation to alpha alumina was investigated by differential thermal analysis.

255 citations


Book ChapterDOI
TL;DR: The information on various aspects of the role of peroxisomes in the metabolism of one-carbon compounds in yeasts clearly shows that these unicellular organisms offer an almost ideal model system for the study of function, morphogenesis, and turnover of these intriguing organelles.
Abstract: Publisher Summary This chapter reviews the role of peroxisomes in the metabolism of methanol and methylated amines in yeasts. It provides information regarding their biogenesis and turnover. The studies on the physiology and biochemistry of methanol oxidation by methylotrophic yeasts exhibit that adaptation of these organisms to growth on methanol is associated with the proliferation of large microbodies in the cells. To evaluate the unique function and structure of the microbodies during methylotrophic growth in yeasts it is necessary to consider pertinent biochemical and physiological aspects of methanol metabolism in these organisms. Microbodies of methanol-grown yeasts show a number of characteristic properties.They appear in clusters in the cell and exist in close association with strands of endoplasmic reticulum. Evidence that the microbodies of methanol-grown yeasts contain alcohol oxidase and catalase is obtained via cell fractionation and cytochemical studies. The information on various aspects of the role of peroxisomes in the metabolism of one-carbon compounds in yeasts clearly shows that these unicellular organisms offer an almost ideal model system for the study of function, morphogenesis, and turnover of these intriguing organelles.

245 citations


Journal ArticleDOI
TL;DR: In this paper, a model was proposed to describe the simultaneous changes in topological and chemical short range order during structural relaxation of metallic glasses, and the free volume and order parameter during isothermal and isochronal annealing were calculated.

213 citations


Journal ArticleDOI
TL;DR: The mild-slope equation is a vertically integrated refraction-diffraction equation, used to predict wave propagation in a region with uneven bottom slopes as mentioned in this paper, which is based on the assumption of a mild bottom slope.

198 citations


Journal ArticleDOI
TL;DR: In this paper, compositional data for the sterols isolated from a surface, Unit I, sediment from the Black Sea are reported and a procedure based on digitonin precipitation has been used to separate the more abundant free sterols from those occurring in esterified forms.

170 citations


Journal ArticleDOI
TL;DR: In this article, the zero structure, the polar structure, and the left and right null space structure of a polynomial matrix P(λ) have been computed using a new numerical method.

144 citations


Journal ArticleDOI
TL;DR: The idea of fuzzy relational equation with generalized connectives is introduced and algorithms of resolution of this class equations are presented in details, showing some types of well-known fuzzy relational equations can be treated as special cases of a wise class of equations under discussion.

134 citations


Journal ArticleDOI
TL;DR: A fast Kalman filter is derived for the nearly optimal recursive restoration of images degraded in a deterministic way by blur and in a stochastic way by additive white noise.
Abstract: In this paper a fast Kalman filter is derived for the nearly optimal recursive restoration of images degraded in a deterministic way by blur and in a stochastic way by additive white noise. Straightforwardly implemented optimal restoration schemes for two-dimensional images degraded by both blur and noise create dimensionality problems which, in turn, lead to large storage and computational requirements. When the band-Toeplitz structure of the model matrices and of the distortion matrices in the matrix-vector formulations of the original image and of the noisy blurred observation are approximated by circulant matrices, these matrices can be diagonalized by means of the FFT. Consequently, a parallel set of N dynamical models suitable for the derivation of N low-order vector Kalman filters in the transform domain is obtained. In this way, the number of computations is reduced from the order of O(N4) to that of O(N^{2} \log_{2} N) for N × N images.

Journal ArticleDOI
TL;DR: In this paper, the pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) was used to determine the ratios of amylose compounds, acids, furans, pyranones anhydrosugars and aromatic substances.

Journal ArticleDOI
TL;DR: To investigate the potentialities of hyperthermia as a cancer therapy, computer simulations have been performed and numerical results pertaining to the temperature distribution in a model of the human pelvis are presented.
Abstract: To investigate the potentialities of hyperthermia as a cancer therapy, computer simulations have been performed. This simulation consists of two tuccessive steps. First, the heat generated in a distribution of biological tissue when irradiated by a source of electromagnetic radiation is computed. The mathematical tool for determining the disbution of generated heat is the domain-integral-equation technique. This technique enables us to determine in a body with arbitrary distribution of permittivity and conductivity the electromagnetic field due to prescribed sources. The integral equation is solved numerically by an iterative minimization of the integrated square error. From the computed distribution of generated heat, the temperature distribution follows by solving numerically the pertaining heat transfer problem. The relevant differential equation together with initial and boundary conditions is solved numerically using a finite-element technique in space and a finite-difference technique in time. Numerical results pertaining to the temperature distribution in a model of the human pelvis are presented.

Journal ArticleDOI
TL;DR: In this article, a theoretical model for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe was developed, where the core is assumed to be solid and the interface to be a solid/liquid interface.

Journal ArticleDOI
TL;DR: It is concluded that the art of unstructured model building has already reached its maturity and that now much effort should be channelled into the development and verification of structured models.
Abstract: Microbial kinetics and energetics are discussed in connection with the formulation of unstructured growth models. The development of microbial energetics and the use of macroscopic methods in the study of microbial growth are briefly evaluated. The general approach to the modelling of microbial growth has been critically discussed and a strategy for the formulation of unstructured models is presented. A simple unstructured model based on Monod kinetics and the linear relation for substrate consumption is evaluated with reference to extensive experimental and simulation data obtained in batch, fed-batch, and continuous cultivation modes. Choice for a kinetic expression is discussed and has been shown not to be critical in most situations. It is shown that during growth in batch mode, the behavior of the system is rigidly fixed by the kinetic parameter: the maximum specific growth rate. The energetic parameters have minimal influence. In continuous cultivation the behavior is fixed by the energetic parameters: the maximum yield and the coefficient of maintenance. Implications of these observations have also been discussed. The linear relation for substrate consumption is tested with continuous culture data. It is shown that significant deviations at low growth rates cannot be fully accounted by the loss of viability. The situations where unstructured models will be adequate or not for system description, are evaluated and checked experimentally. Influence of an environmental factor, the temperature, on the unstructured model parameters is also quantitatively described. It is concluded that the art of unstructured model building has already reached its maturity and that now much effort should be channelled into the development and verification of structured models.

Journal ArticleDOI
TL;DR: In this article, a numerical method for the calculation of such concentration profiles was developed, and the results calculated were compared with experimental data, and it was found that during nitriding the nitrogen surface concentration approached relatively slowly the equilibrium value.
Abstract: On nitriding iron specimens nitrogen concentration profiles within the specimens are built up. A numerical method for the calculation of such concentration profiles was developed. The results calculated were compared with experimental data. It was found that during nitriding the nitrogen surface concentration approached relatively slowly the equilibrium value. This effect strongly influenced the development of the nitrogen concentration profile. The model predicted correctly the incubation time for compound(i. e., iron nitride) layer formation at the surface. If the fatigue resistance is strongly dependent on the (compressive) residual surface stress, the present treatment allows calculation of anoptimum nitriding time by determining when the maximum (compressive) residual surface stress occurs.

Journal ArticleDOI
TL;DR: A post-clinical investigation has been carried out among 42 unilateral amputees who lost their hand due to an accident, directed at the amputee, the problems he has to cope with, and the role the prosthesis plays in his life.
Abstract: A postclinical investigation has been carried out among 42 unilateral amputees who lost their hand due to an accident. The investigation was directed at two main topics of interest. Firstly the amputee, the problems he has to cope with, and the role the prosthesis plays in his life; and secondly the prosthesis, its use and its potential benefits and burdens. The group of amputees consisted of above-elbow and belowelbow amputees. Body powered as well as myoelectric prostheses were represented in the group. Most of the information was obtained during a twoday home visit where a semi-structured interview was conducted, and where a number of daily life activities were observed. The information thus obtained has led to a number of conclusions and recommendations with respect to the rehabilitation of this category of amputees, and with respect to the design criteria of protheses for unilateral amputees.

Journal ArticleDOI
TL;DR: In this paper, the authors observed the directional energy distributions of wind-generated waves with a relatively high directional resolution in fairly homogeneous and stationary wind fields in fetch-limited conditions using stereophotography of the sea surface.
Abstract: Directional energy distributions of wind-generated waves were observed with a relatively high directional resolution in fairly homogeneous and stationary wind fields in fetch-limited conditions using stereophotography of the sea surface In a situation that is traditionally considered as the ideal fetch-limited wave-generation situation, the shapes of the observed distributions were found to agree well with the cos2s(θ/2) model proposed by Longuet-Higgins et al (1963) In non-ideal situations in which the wind slanted across the upwind coastline or in which the upwind coastline was irregular, the shapes of the directional distributions were strongly influenced by the geometry of the upwind coastline This suggests that the process of wave generation is directionally decoupled

Journal ArticleDOI
TL;DR: In this article, the microwave part of the experimental setup is described as well as two probes in which DNP can be combined with 13C FID or 13C1H cross polarization experiments.

Journal ArticleDOI
TL;DR: In this article, the 13 C NMR spectra of three natural and two synthetic diamonds were obtained in this manner in 10-30 min, using the solid-state effect.

Journal ArticleDOI
TL;DR: In this article, a special-purpose computer for the study of static and dynamic properties of stochastic Ising-like systems of up to 4 × 106 spins is described.

Journal ArticleDOI
TL;DR: In this paper, the precipitation of silicon in rapidly solidified AlSi alloys was studied and the lattice parameters of the Alrich and of the Si-rich phases were measured after ageing at 397,425 and 448 K.
Abstract: The precipitation of silicon in rapidly solidified AlSi alloys was studied. For alloys with 2.4 and 11.0 wt % Si (2.3 and 10.3 at % Si, respectively) the lattice parameters of the Alrich and of the Si-rich phases were measured after ageing at 397,425 and 448 K. For alloys with 2.6 and 13.0 wt % Si crystallite sizes and lattice strains were determined by analysis of the X-ray diffraction line broadening. After ageing the lattice parameters of the Al-rich and the Si-rich phases were influenced by the difference in thermal expansion between both phases. After correction for this effect the amount of silicon dissolved in the Al-rich phase was estimated as a function of ageing time. Quenched-in (excess) vacancies influenced the precipitation kinetics. Activation energies for precipitation appeared to depend on the extent of transformation. Further, quenched-in vacancies caused anomalous maxima in the lattice parameter curves. The behaviour of the lattice microstrains on ageing was explained as a result of the disappearance of stresses due to quenching and the introduction and subsequent dissipation of stresses due to precipitation. After completed precipitation stresses due to the difference in thermal expansion between both phases still exist at room temperature.

Journal ArticleDOI
TL;DR: In Nocardia sp.
Abstract: A study was made of the enzymology of methanol metabolism by a Nocardia sp. The organism, previously known as Streptomyces sp. 239 is a facultative methylotroph, which assimilates methanol via the ribulose monophosphate (RuMP) pathway of formaldehyde fixation. This was evident from the high levels of hexulose phosphate synthase in methanol-grown cells and from the high apparent growth yields of methanol-limited chemostat cultures (0.51–0.55 g cells/g methanol). Methanol is probably oxidized by a quinoprotein type of dehydrogenase as was indicated by the excretion of pyrrolo-quinoline quinone (PQQ) by methanol-grown cells. However, the enzyme is not a normal classical methanol dehydrogenase (EC 1.1.99.8). The fate of formaldehyde in the dissimilation of methanol by the organism is obscure. A cyclic oxidation of formaldehyde as found in all other methanol utilizers with the RuMP pathway, appears unlikely since the activities of glucose-6-phosphate dehydrogenase and of 6-phosphogluconate dehydrogenase were rather low. Furthermore cells grown in carbon-limited chemostat cultures on mixtures of ethanol and formaldehyde did not contain hexulose phosphate synthase activity. Although methanol-grown cells showed a low formate-oxidizing capacity, neither dye-linked nor NAD-linked formate dehydrogenase could be detected in cell-free extracts. During growth of Nocardia sp. 239 in batch culture on a mixture of methanol and ethanol diauxic growth was observed. Oxidation of methanol and excretion of PQQ preceeded the synthesis of hexulose phosphate synthase indicating that the synthesis of dissimilatory and assimilatory enzymes is not coordinately controlled. It is concluded that in Nocardia sp. 239 the oxidation of methanol proceeds via a mechanism which must be different from those encountered so far in Gram-negative methylotrophs.

Journal ArticleDOI
TL;DR: The use of a packed bed reactor containing Ca-alginate immobilized Clostridium beijerinckii cells for continuous IBE (isopropanol-butanol-ethanol)-fermentation has been studied as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, phase equilibria of the second type are found in fluid (n-alkane + water) mixtures (gas + gas) of the first type.

Journal ArticleDOI
TL;DR: A solid basis for further technological developement of the process has been laid after it appeared to be possible to use the biocatalyst particles repeatedly for successive fermentations in a steady‐state reactor.
Abstract: The potential of continuous isopropanol-butanol-ethanol (IBE) fermentation by Ca-alginate-immobilized Clostridium beijerinckii cells in a continuous stirred-tank reactor is investigated. A mathematical model is presented to describe steady-state reactor performance. It appeared to be possible to use the biocatalyst particles repeatedly for successive fermentations (at least three times for a total duration of two months). Reactor productivity was 6-16 times higher than that of a batch fermentation (free cells), while the solvents yield was also increased. Measurements of substrate, product, and biomass concentrations were only partially in agreement with the model; however, a solid basis for further technological developement of the process has been laid.

Journal ArticleDOI
TL;DR: A convenient determination of pyrroloquinoline quinone (PQQ) in extracts of purified enzymes is possible with ion-pair chromatography on a HPLC reverse-phase column and with uv detection, but when culture supernatants have to be analyzed, a fluorescence detection system is more appropriate.

Journal ArticleDOI
TL;DR: It is proved that rather tight upper bounds can be given for the number of non-unique assignments that are achieved after solving the linear programming relaxation of some types of mixed integer linear assignment problems.

Journal ArticleDOI
TL;DR: It is demonstrated that, based mainly on the measured confusions between symbols, proposals for the redesign of symbols can be formulated.

Journal ArticleDOI
TL;DR: In this paper, the coordination chemistry of neutral benzotriazole towards several transition metal compounds has been studied, and the general formula M(BTAH) n X m, with M = 1, 2, 3, 4, X = Cl, Br and m = 2 or 4.