Showing papers by "Delft University of Technology published in 1974"
TL;DR: Spatial contrast measurements have been carried out with sine wave modulated fields, varying the aperture and the luminance and the modulation threshold turns out to depend upon the number of cycles in the stimulus for numbers of cycles below a critical number ofcycles.
198 citations
TL;DR: In this paper, an integrated silicon sensor for the measurement of gas flow is introduced, which allows one to construct very sophisticated integrated circuits for the processing of electronic signals, such as transducers and transducers.
Abstract: At present, planar silicon technology allows one to construct very sophisticated integrated circuits for the processing of electronic signals. In the letter, an integrated silicon sensor for the measurement of gas flow is introduced.
148 citations
01 Aug 1974
TL;DR: In this article, the growth of the layers, formed in these couples, has been studied in the temperature range between 550 and 940°C, and all phases which, on the basis of the equilibrium diagram, could be expected under the circumstances, were found in the diffusion zone.
Abstract: Various types of diffusion couples have been prepared and the growth of the layers, formed in these couples, has been studied in the temperature range between 550 and 940°C. All phases which, on the basis of the equilibrium diagram, could be expected under the circumstances, were found in the diffusion zone. The layer growth of β-Ti(Ni), Ti2Ni and TiNi in all types of couples obeyed the parabolic law; the TiNi layer was the only exception. It is supposed that in this case grain boundary diffusion is responsible for the observed abnormal growth. The shape of the β-Ti/β-Ti + Ti2Ni boundary in the equilibrium diagram was constructed using data, both from recorded penetration curves and from equilibrated two-phase alloys. Excellent agreement between the results of these two methods was obtained. The eutectoid composition at 77Q°C has been placed at about 7 at. pct Ni, in contrast with earlier results. Furthermore, the composition range of TiNi has been determined from penetration curves.
143 citations
TL;DR: This paper describes the construction of strings representing straight lines in an arbitrary direction on a grid and compares some grammatical systems that generate these strings and compares them to Lindenmayer grammars, which are quite useless but still very convenient.
96 citations
TL;DR: In this paper, three aspects of these vibrations have been analyzed: the frequency, the critical bed height and the damping, which is the ratio of the fluid-to-solids-density.
96 citations
01 Aug 1974
TL;DR: In this paper, it was shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface and that Ni is by far the fastest moving component in β-Ti(Ni), Ti2Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni).
Abstract: Diffusion coefficients in the Ti-Ni system have been calculated by the aid of equations given by Sauer and Freise, and Wagner. Values for the TiNi (50 at. pct Ni) phase were found to be:Du (cm2/s) = 0.0020 exp - 142,000/R for the temperature range between 650 and 940°C. The heat of activation, expressed in J/mol, has an accuracy of ±6000. For the β-Ti(Ni) phase containing 6 at. pct Ni the temperature dependence of the diffusion coefficient is expressed by:Du (cm2/s) = 0.0688 exp - 141,000/RT. The uncertainty in the energy of activation is ±12000 J/mol. No clear variation of the diffusion coefficient with concentration could be detected. It was found that Ni is by far the fastest moving component in β-Ti(Ni), Ti2Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni). Values ofDNi/DTi have been calculated with an equation derived by van Loo. The significance of the calculated values is critically examined. By means of a practical example it is shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface.Diffusion coefficients in the Ti-Ni system have been calculated by the aid of equations given by Sauer and Freise, and Wagner. Values for the TiNi (50 at. pct Ni) phase were found to be:Du (cm2/s) = 0.0020 exp - 142,000/R for the temperature range between 650 and 940°C. The heat of activation, expressed in J/mol, has an accuracy of ±6000. For the β-Ti(Ni) phase containing 6 at. pct Ni the temperature dependence of the diffusion coefficient is expressed by:Du (cm2/s) = 0.0688 exp - 141,000/RT. The uncertainty in the energy of activation is ±12000 J/mol. No clear variation of the diffusion coefficient with concentration could be detected. It was found that Ni is by far the fastest moving component in β-Ti(Ni), Ti2Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni). Values ofDNi/DTi have been calculated with an equation derived by van Loo. The significance of the calculated values is critically examined. By means of a practical example it is shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface.
76 citations
TL;DR: In this article, it was shown that thermal treatment of a copper/zinc oxide CO-shift catalyst in a reducing gas causes a decrease in the BET surface area as well as partial reduction of zinc oxide followed by the formation of α-brass.
60 citations
TL;DR: In this article, a mathematical model for column separation and cavitation in extensive parts of the pipeline, referred to as cavitating flow, is presented, where a smoothing procedure is adopted in order to suppress nonlinear instability.
Abstract: Some applications are presented of a mathematical model concerning water hammer and release of dissolved gas in pipelines in the case where the pressure drops to the vapor pressure of the liquid transported. Column separation and cavitation in extensive parts of the pipeline, referred to as cavitating flow, are dealt with. A smoothing procedure is adopted in order to suppress nonlinear instability. Gas release is found to cause some damping of pressure waves in cases where only cavitating flow occurs. Gas release at a column separation cavity tends to increase the duration of column separation, whereas gas release in a possible cavitating flow region adjacent to the separation diminishes this duration, thus causing considerable damping of pressure peaks following subsequent column separations. Good agreement is obtained with experimental results available in the literature. Further experimentation is required as regards the parameters on which gas release depends.
57 citations
TL;DR: Both the details of the dissolution behaviour as well as the surface morphology observed indicate the presence of screw dislocations in the single crystals with the dislocation line parallel to the c-axis.
Abstract: The dissolution of hydroxyapatite single crystals is highly anisotropic. Parallel to the c-axis the dissolution is fast, while perpendicular to the c-axis dissolution is negligible. In 5 M citric acid solutions at 37°, the acid penetrates into the single crystals parallel to the c-axis with a velocity of approximately 60 nM/sec. Scanning electron microscopy shows that the single crystals are twisted along the c-axis. Both the details of the dissolution behaviour as well as the surface morphology observed indicate the presence of screw dislocations in the single crystals with the dislocation line parallel to the c-axis.
53 citations
TL;DR: Using this special purpose computer, many more and more precise simulations could be carried out which enabled us to check the validity of the two-dimensional nucleation theories in more detail.
53 citations
TL;DR: In this article, a rigorous solution is obtained for the problem of radiation from an electric line charge that moves, at a constant speed, parallel to an electrically perfectly conducting grating with a rectangular profile.
Abstract: A rigorous solution is obtained for the problem of radiation from an electric line charge that moves, at a constant speed, parallel to an electrically perfectly conducting grating with a rectangular profile. Through the method of separation of variables, which is performed separately in the region containing the grooves and the half-space above the grating, the solution of the wave equation is obtained. By imposing the continuity condition at the open end of the grooves, and the boundary condition at the remaining part of the interface, an infinite system of linear algebraic equations for either the amplitudes of the scattered waves or the amplitudes of the groove modes are derived. Numerical results pertaining to the radiation intensities are presented.
29 Jan 1974
TL;DR: In this paper, a numerical model is described concerning the velocity distribution in an oscillatory flow, respectively without and with resultant current, from the momentaneous velocity gradients eddy viscosities are derived.
Abstract: In this paper first a numerical model is described concerning the velocity distribution in an oscillatory flow, respectively without and with resultant current . From the momentaneous velocity gradients eddy viscosities are derived . Using the approach of VANONI [13 , a numerical model is given for the calculation of sediment concentration and suspended sediment transport. In order to give reliable results, the bed-load concentration should be known This will be investigated in the future; at the moment the model only provides qualitative results.
TL;DR: In this paper, an extension of the wave-digital filter structures introduced by Fettweis is introduced, viz, the digital translation of the Jaumann structure, which is a well-known canonical realization of analogue, symmetric, grounded lossless two-port networks.
Abstract: This paper deals with an extension of the wave-digital filter structures introduced by Fettweis.
A new structure is introduced, viz, the digital translation of the Jaumann structure. The Jaumann structure is a well-known canonical realization of analogue, symmetric, grounded lossless two-port networks. With this structure, transfer functions with complex transmission zeros can be obtained in a wave-digital realization, which is not possible by means of a wave-digital ladder filter. Two examples are given, one of which has been implemented using TTL digital integrated circuits showing excellent properties.
TL;DR: In this paper, the mutual interaction between steps of a step train on a crystal surface in contact with a vapour phase has been investigated and the data obtained by Monte Carlo computer simulation experiments have been compared with recent numerical results, based on a description of these phenomena by Burton, Cabrera and Frank, including the Schwoebel effect.
TL;DR: In this paper, a survey is given of a set of five theories which can be applied to crystal growth from solution, including the morphological theory of Hartman and Perdok, statistical mechanical surface theories, computer simulation models, in conjuction with two dimensional nucleation theories and BCF step models.
01 Jan 1974
TL;DR: In this paper, the stability and postbuckling analysis for structures with an initially linear behavior is developed on the basis of the general theory founded by Koiter, where the location of the nodal points is defined in terms of the displacement vector and the orientation of an orthogonal triad attached to each nodal point is described by means of modified angular coordinates of Euler.
01 Jun 1974-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the transformation to austenite in a fine grained tool steel has been investigated quantitatively until the disappearance of the ferrite, and a constant growth rate was found up to 30 pct transformation.
Abstract: The transformation to austenite in a fine grained tool steel has been investigated quantitatively until the disappearance of the ferrite. The initial structure of the steel consisted of ferrite and globular carbides. The nucleation starts at carbides which lie at the ferrite grain boundaries. The kinetics are in good agreement with Cahn's theory of grain boundary nucleated transformation. A constant growth rate was found up to 30 pct transformation. Site saturation occurs early in the reaction; this was confirmed by metallographic examination. The rate law is controlled by growth and is independent of the nucleation rate. The mechanism which is controlling this growth is the advancing ferrite-austenite interface reaction. The alloying elements influence the atomic mobilities, increasing the necessary activation energy to about 110 kcal/mol.
01 Jan 1974
TL;DR: In this paper, the reflection of a monochromatic plane electromagnetic wave by a grating consisting of grooves in the surface of a semiconductor plasma (InSb) is investigated theoretically, in particular in that region of frequencies where the complex permittivity of the semiconductor plasmons has a negative real part.
Abstract: The reflection of a monochromatic plane electromagnetic wave by a grating consisting of grooves in the surface of a semiconductor plasma (InSb) is investigated theoretically, in particular in that region of frequencies where the complex permittivity of the semiconductor plasma has a negative real part. From the numerically obtained reflection factor pertaining to anH-polarized incident wave, the excitation and the dispersion of surface plasmons at the boundary of the medium is discussed. The grating problem is rigorously formulated as a boundary value problem employing a Green's function technique. Numerical results pertaining to the reflection factor are presented for different grating parameters.
01 Oct 1974
TL;DR: In this paper, a rigorous derivation of the power-reciprocity theorem in antenna theory is presented, which relates the absorption cross-section of the load in the receiving situation to the power gain of the antenna in the transmitting situation.
Abstract: A rigorous derivation of the power-reciprocity theorem in antenna theory is presented. It relates the absorption cross-section of the load in the receiving situation to the power gain of the antenna in the transmitting situation. The most general case is considered, namely (a) the materialof which the antenna is made may be lossy, anisotropic and inhomogeneous, if only linear in its electromagnetic behaviour, (b) the vectorial amplitude radiation characteristic of the antenna in the transmitting situation and the incident plane wave in the receiving situation may be arbitrarily elliptically polarised, and (c) the impedance of the load in the receiving situation may be arbitrarily mismatched to the input impedance of the antenna in the transmitting situation. Therefore the known, restricted form of the theorem is generalised; also some notions are made more precise. As a corollary, a generalised theorem is presented as to the average value of the absorption cross-section of the load taken over all directions of incidence.
TL;DR: In this paper, the authors used more realistic linear models taking into account the unsprung mass, and the gain in comfort obtained by lowering the natural frequency of the sprung mass is calculated for various two-and three-mass models along with other characteristics such as the dynamic tyre load, spring and damper forces and relative motion of the masses.
Abstract: SUMMARY In a previous paper, [3] the random vibrations of simple linear models of automobile suspension were solved with respect to seat elasticity and human sensitivity to vibrations. The present study uses more realistic linear models taking into account the unsprung mass. Two configurations of masses are investigated: a two-mass system consisting of a sprung mass and an unsprung mass, and a three-mass system having an additional mass which acts as a vibration absorber. The gain in comfort obtained by lowering the natural frequency of the sprung mass is calculated for various two-mass and three-mass models along with other characteristics such as the dynamic tyre load, spring and damper forces and relative motion of the masses.
TL;DR: In this article, Boussinesq's concept from the lateral gradient of the mean velocity and the turbulence shear-stress was used to compute the eddy-viscosity in a turbulent boundary layer downstream of a hemi-spherical cap attached onto the plane rigid wall.
Abstract: Measurements have been made of the distributions of mean velocity, turbulence intensities and turbulence shear-stress in a turbulent boundary-layer downstream of a hemi-spherical cap attached onto the plane rigid wall. The eddy-viscosity, when computed in the classical way according to Boussinesq's concept from the lateral gradient of the mean velocity and the turbulence shear-stress, showed a very strong non-uniform lateral distribution, also across the outer region of the boundary-layer. More over , the non-dimensional values of the eddy viscosity, using the wall-friction velocity and the boundary-layer thickness as the velocity scale and length scale respectively, were higher than those for the boundary-layer when not disturbed by the wake of the spherical cap. However, when account is taken of an axial memory effect of the streamwise variation of the lateral gradient of the mean-velocity, the values of the non-dimensional eddy viscosity are close to those for the undisturbed boundary-layer.
TL;DR: In this article, the concept of statistical linearization is extended to an approximation with a series of functions and the parameters of these functions describing the non-linearity are estimated in the presence of noise by using correlation techniques.
Abstract: A method is proposed to describe non-linear systems without memory, forced by random excitation. The concept of statistical linearization is extended to an approximation with a series of functions. The parameters of these functions describing the non-linearity are estimated in the presence of noise by using correlation techniques. The results apply also if the non-linearity cannot be separated from a linear dynamic model.
TL;DR: In this article, a dihydroalloxazine system was used to generate one-electron reductions of A R -OOH or H 2 O 2, in which either a semiquinone or dihydroxyphenylalanine was used as reducing agent.
TL;DR: The processes preceding the development of asci and the ornamentation of the ascospore wall of several strains of Lipomyces were studied by light and by electron microscopy.
Abstract: The processes preceding the development of asci and the ornamentation of the ascospore wall of several strains of Lipomyces were studied by light and by electron microscopy. The polysaccharides excreted by living cells were analyzed by paperchromatography. Standard descriptions and latin diagnoses of L. kononenkoae and L. tetrasporus are presented. A key is given for the identification of the species.
TL;DR: The object of this paper is to present a uniform procedure to take over the plotting-and- position-estimating-part of the job, and to prevent it from being seen by the navigating ship's officers as "another black magic box."
Abstract: Astro-fixes have the advantages of being extremely cheap. However, the tedious work connected to the computation of altitudes and azimuths and the plotting of the position lines, has been a severe objection to this position fixing method. Moreover, the comparatively long time, needed to carry out these manipulations without the aid of a computer, is a severe potential disadvantage, especially for modern, fast going container carriers. Using a small, i.e. pocket size transistorized computer, the computing objections can be practically overruled. It is the object of this paper to present a uniform procedure to take over the plotting-and- position-estimating-part of the job. The procedure is fully explained, in order to prevent it from being seen by the navigating ship's officers as "another black magic box." In addition to that, the observer's skill in estimating standard deviations can be used as a highly valuable input.