Showing papers by "Delft University of Technology published in 1977"
386 citations
TL;DR: In this article, the authors considered the problem of finding the root of λ which gives the most serious state of stress in the vertex region (the region r → 0) is the root closest to the limiting value Re λ > −3/2.
368 citations
300 citations
TL;DR: In this paper, the effect of a tangential force on the size of the contact area between elastic solids has been investigated and the relationship between the stress intensity factor of the normally loaded contact and the overall energy balance approach is discussed.
Abstract: This paper describes a study of adhesion between elastic solids and in particular the effect of a tangential force upon the size of the contact area In the first part of the paper, the relation between the stress intensity factor of the normally loaded contact and the overall energy balance approach is discussed In the second and main part of the paper, an analysis is given for the influence of a tangential force on the adhesive contact The equation derived to describe its effect on the contact size has been verified by experiments carried out on rubber hemispheres pressed against a glass flat The experimental results show qualitatively a clear reduction in contact area when a tangential force acts and quantitatively a reasonable agreement with theory within the limits of experimental error
259 citations
233 citations
TL;DR: In this paper, an experimental study on heat transfer of impinging circular jets shows the effect of turbulence for the stagnation zone, which relates to cases of small nozzle-to-plate distances.
183 citations
TL;DR: In this article, the authors investigated the stress distribution round a pin-loaded hole in an elastically ortho tropic or isotropic plate, where the hole is loaded frictionless on only a part of its edge by an infinitely rigid pin of the same diameter.
Abstract: The stress distribution round a pin-loaded hole in an elastically ortho tropic or isotropic plate is investigated. The hole is loaded frictionless on only a part of its edge by an infinitely rigid pin of the same diameter. The loading force is carried over on the edge by normal stresses, represented by a sine series. It is shown that these stresses depend strongly on the material properties. Infinite plate results are used to estimate the stresses in plates nite width. Numerical results are shown graphically for three laminates n fibre reinforced plastic and for three ratios of width of plate to mole diameter.
180 citations
TL;DR: In this article, the vertical distribution of the secondary flow in a shallow curved channel is derived from a logarithmic main velocity profile, and a numerical method for the computation of the depth-averaged flow field and the bed shear stress (magnitude and direction) is developed.
Abstract: Starting from a logarithmic main velocity profile, the vertical distribution of the secondary flow in a shallow curved channel is derived. The secondary circulation turns out to have one vertical and two horizontal components. The horizontal component in the main flow direction arises from the longitudinal acceleration of the main flow; the transverse horizontal component is due to the curvature of the main flow. In addition, a numerical method for the computation of the depth-averaged flow field and the bed shear stress (magnitude and direction) is developed. This model has great flexibility of allowable channel geometry. Its results agree better with experimental data if the bed is not flat than in case of a flat bed.
168 citations
166 citations
TL;DR: The use of h.r.v.c. measurement in both clinical applications and the neural cardiovascular research is discussed and it is shown that these signals are based on modifications of one model, namely the integral pulse frequency modulator.
Abstract: A definition of heart-rate variability (h.r.v.) is given. The use of h.r.v. measurement in both clinical applications and the neural cardiovascular research is discussed. For the latter applications, four different signals describing h.r.v. are reviewed. It is shown that these signals are based on modifications of one model, namely the integral pulse frequency modulator. In Part 2, a hardware device for measuring h.r.v. based on one of these modifications is described.
152 citations
TL;DR: In this article, the variational principles of contact elastostatics were developed in an engineering fashion without use of functional analysis, and the existence proofs of the French-Italian school are missing.
Abstract: In this paper, the variational principles of contact elastostatics, which were proposed and proved by Fichera (1964) and Duvaut & Lions (1972) are developed in an engineering fashion without use of functional analysis. The theory contains a number of new elements, but the elegant existence proofs of the French-Italian school are missing. A start is made by extending the principle of virtual work to normal and frictional contact in such a manner that it needs no longer be known beforehand whether—in the case of normal contact—actual contact is or is not established, or—in the case of frictional contact—slip does or does not occur. Then the principle of minimal potential energy is set up for a non-linear elastic body in contact with a rigid base. Uniqueness and minimality of the solution are proved under certain conditions, the Reissner principle is established, and the principle of minimal complementary energy is derived. Finally the principles are cast hi what is termed surface mechanical form, and two examples are given: the variational principle for normal half-space contact problems, and a new principle for time-dependent frictional half-space contact. Upon discretization, these principles provide a quadratic object function to be minimized under linear or quadratic inequality constraints. The positions of the contact area and of the regions of slip and adhesion appear as by-products of the calculation.
TL;DR: In this paper, the literature on manual control will be reviewed briefly with attention focused on the use of the internal model concept, and an application is given in the human control of large ships.
Abstract: Many human operator studies have used successfully the concept that the human operator performs his task on the basis of certain knowledge about the system to be controlled, called the internal mod...
TL;DR: The theory of layer growth of crystals is generalized to describe the growth kinetics of interfaces free of screw dislocations when the initial surface is either of the deposited material or it is a foreign substrate as mentioned in this paper.
TL;DR: In this article, the pendant-drop profile of the maximum volume fitting a given small vertical tube intersects the exit plane at very nearly 90°, and the results agree with numerical solutions.
Abstract: A solution for the profile of a small drop or bubble symmetrical about a vertical axis and at rest in a second fluid is obtained as a first-order perturbation of a circle. At the end of the drop opposite the apex, the perturbation approach breaks down and a matching zero-gravity solution is used. The results agree with numerical solutions and indicate that the pendant-drop profile of maximum volume fitting a given small vertical tube intersects the exit plane at very nearly 90°. This enables the maximum volume to be determined accurately from a force balance.
TL;DR: In this article, a combination of three programs for computer assisted stage scanning cytophotometry and cytofluorometry of isolated, close-lying, or touching objects in different types of microscopical preparations is described.
Abstract: A description is given of a combination of three programs developed for computer-assisted stage scanning cytophotometry and cytofluorometry of isolated, close-lying, or touching objects in different types of microscopical preparations. The advantages and limitations of the individual programs are discussed, as well as the local specimen conditions determining the optimal application range of each of the programs. The applicability of these programs was investigated by determination of the integrated absorbance values of Feulgen or gallocyanin-chrome alum stained chicken erythrocytes, human leucocytes, and skin biopsy cells in imprint preparations, as well as of guinea pig peritoneal granulocytes which had been submitted to a simultaneous coupling azo dye incubation for alkaline phosphatase activity.
TL;DR: The cell wall of the blue-green alga Spirulina platensis was studied with the electron microscope using ultra-thin sectioning, shadowing, carbon-replication or freeze-etching techniques for specimen preparation to find certain structural properties of the septum seem to allow tangential stretching.
Abstract: The cell wall of the blue-green alga Spirulina platensis was studied with the electron microscope using ultra-thin sectioning, shadowing, carbon-replication or freeze-etching techniques for specimen preparation. The cell wall could be resolved into four layers, L-I through L-IV. The L-I and L-III layers contain fibrillar material. The septum is a three-layered wall: an L-II layer sandwiched between L-I layers. The shape in vitro of isolated septa might be an artifact due to the preparation technique used. Certain structural properties of the septum seem to allow tangential stretching; they might be reflected in the flexible gliding mobility of Spirulina species. The outer, L-IV layer contains material longitudinally arranged along the trichome axis.
TL;DR: In this article, the rubber-like stress-optical behavior of polymer melts is advocated as a powerful means in finding the thickness of the so-called freeze-off layer and in tracing back the development of shear stresses in the vicinity of the wall during injection.
Abstract: Under practical mould filling conditions one always observes an interaction between polymer flow and heat transfer. A rather rough description of this process is given in the form of a dynamic model for the growth of the solidifying layer. A consideration is added concerning the usefulness of the birefringence pattern, which is observed in the moulded sample, as a source of information about previous melt flow during mould filling. The rubberlike stress-optical behaviour of polymer melts is advocated as a powerful means in finding the thickness of the so-called freeze-off layer and in tracing back the development of shear stresses in the vicinity of the wall during injection.
TL;DR: In this article, the influence of fiber misalignment on the tensile strength and Poisson's ratio of carbon fiber reinforced plastic has been investigated and an empirical relation between Young's modulus and tensile stress is derived.
Abstract: In the literature the tensile behaviour in the fibre direction of unidirec tional carbon fibre reinforced plastic (c.f.r.p.) is assumed to be linearly elastic up to failure.Some authors distinguish a primary and a secondary part in the stress- strain curve each showing Hookean behaviour.The experimental results of this paper show that Young's modulus of laminates increases proportionally with the tensile stress, as found in Ref. [1] for single non-impregnated fibres.An empirical relation between Young's modulus and the tensile stress is derived and the influence of fibre misalignment on this relation is exam ined.In addition, the influence of fibre misalignment on the tensile strength and Poisson's ratio is discussed.
TL;DR: An autopilot for ships designed with the aid of fuzzy sets is investigated, and a comparison is made between the fuzzy and a conventional PID controller which is most commonly used in autopilots.
TL;DR: In this article, the authors reported measurements of the critical current of long, narrow, superconducting thin-film strips of aluminum subjected to high-frequency radiation (10 MHz-10 GHz).
Abstract: Eliashberg has predicted that absorption of microwaves in a superconducting film leads to an increase of the energy gap by creating a nonequilibrium quasiparticle distribution. The frequency has to exceed the inverse relaxation time for inelastic scattering. In the present paper measurements are reported of the critical current of long, narrow, superconducting thin-film strips of aluminum subjected to high-frequency radiation (10 MHz–10 GHz). Above a critical frequency of about 200 MHz considerable enhancement of critical current and critical temperature is observed. Analysis of the results is performed by taking the critical current for a measure of the energy gap. The results are in reasonable agreement with Eliashberg's theory. As predicted, the transition between the superconducting and the normal states becomes of first order. The experimental results on critical current enhancement of micro-bridges (Dayem-Wyatt effect) can be explained consistently with gap enhancement.
TL;DR: In this paper, a mathematical analysis of second-order temperature-programmed desorption (TPD) spectra in the case of freely occurring readsorption is presented, and critical remarks are made about the use of equations relating the temperature of the peak maxima to the enthalpies of adsorption, both for first- and secondorder Desorption kinetics.
TL;DR: The results of a Monte Carlo simulation of the process of thin film deposition on to a face of Kossel crystal as a substrate are presented in this article, where the island and the layer modes of film growth are illustrated by morphological observations at different supersaturations β.
TL;DR: In this article, the authors present another partition in the phenomenological description of capillary rise for systems which have θ>0, showing that small variations in vapour pressure may induce discontinuous film thickness jumps, which may display itself macroscopically as a changing contact angle.
Abstract: THE mechanism of capillary rise in a random sphere packing is such that, depending on the absolute value of the wetting- or contact-angle, θ, at equilibrium either a saturation gradient, widest for θ = 0, is observed, or a sharp front between the saturated and the dry part of the porous medium, above some critical value of θ (ref. 1). We present here another partition in the phenomenological description of capillary rise for systems which have θ>0. There are systems in which θ remains constant and others in which θ decreases during capillary rise. In particular, attention is drawn to an uncommon hypothesis that can explain a decrease in θ. Given the nature of the absorption isotherm in the neighbourhood of saturation, small variations in vapour pressure may induce discontinuous film thickness jumps on a microscopic scale, which may display itself macroscopically as a changing contact angle.
TL;DR: Capillary rise experiments have been performed with homogeneous packings of coarse rotund particles, yielding a capillary rise at equilibrium of the order of 10 cm as discussed by the authors, where water, toluene and other organic liquids have been used as the wetting liquid, and glass beads, polystyrene beads, and sand to make the packings.
TL;DR: In this article, variable-thickness aluminum microbridges that are small with respect to coherence length and penetration depth were investigated, and it was shown that the voltage-carrying state shows an excess current of about 0.5Ic over a large range of currents.
Abstract: We have investigated variable-thickness aluminum microbridges that are small with respect to coherence length and penetration depth. The critical current depends linearly on temperature and is proportional to the normal-state conductance, in agreement with theory. The voltage-carrying state shows an excess current of about 0.5Ic over a large range of currents. Subharmonic energy gap structure is clearly present. The differential resistance observed corresponds with an effective length of about 2 µm, a value which is in agreement with three-dimensional diffusion for a diffusion length of 100 µm (this diffusion length is determined in experiments with long aluminum microstrips). An intrinsic upper frequency limit for the Josephson oscillation is not found. It is argued that the known relaxation times of the order parameter are not limiting. The results are in disagreement with the RSJπ model, introduced by Jensen and Lindelof. We also investigated tin microbridges and have found that at low temperatures, flux flow determines the voltage. The differences between the results on tin and aluminum microbridges seem to be due to the fact that in tin the bridge sizes are still too large with respect to coherence length and penetration depth.
01 Jan 1977
01 Jan 1977
TL;DR: In this article, the authors present a period in which the traditional methods coexist with new methods, many of which will also be based on biotechnology, and knowledge of the ecology of the traditional systems is important for improving the existing methods as well as for guiding their change into more profitable waste utilization.
Abstract: Biological waste treatment is now changing from a technology for defensive disposal of waste materials towards a technology for utilizing waste. This change will not happen overnight, so we shall be faced with a period in which the traditional methods coexist with new methods, many of which will also be based on biotechnology. As a result, knowledge of the ecology of the traditional systems is important for improving the existing methods as well as for guiding their change into more profitable waste utilization.
TL;DR: In this article, a complete framework, based on geometrical probability theory, is presented to obtain three-dimensional information from two-dimensional images produced by X-ray radiography, which can also serve to characterize the spatial properties of the fibre structure in the designed mix.
Abstract: SUMMARY
Different spacing factors and various orientation efficiency factors, applied to characterize the spatial distribution of the (steel) fibres in fibre reinforced cementitious materials, cannot constitute a sound basis for a mutual comparison of experiments or for an evaluation of experiments in a fracture mechanical sense.
This paper therefore presents a complete framework, based on geometrical probability theory, providing the investigator with methods to obtain three-dimensional information from two-dimensional images produced by X-ray radiography. In this approach the fibres are assumed to be disposed in such a way that on the average a partially planar-oriented structure is obtained. In addition, because of their high aspect ratio, the fibres are considered to be lineal features.
Two methods are elaborated, i.e. the feature counting technique and the method of directed secants. These operations have to be performed in the projection plane. Both methods yield data on the degree of inhomogeneity (segregation) and the degree of orientation (anisometry), as well as on spacing and orientation efficiency. By substituting design data in the presented formulae, this framework can also serve to characterize the spatial properties of the fibre structure in the designed mix.
The application of the theory is illustrated with the help of data that confirm the occurrence of segregation and preferred orientation effects due to vibration of the specimens.
TL;DR: Eccentric growth spirals were observed on the (0001) face of SiC crystals synthesized by the Lely method at the Toshiba Central Research Laboratories as mentioned in this paper, and they were interpreted as due to a supersaturation gradient over the surface.
TL;DR: In this paper, the authors simulated the growth of a (001) Kossel crystal surface under nucleation growth conditions using the Monte Carlo technique and obtained data for the nucleation rate, the spreading rate of super critical clusters and the size of the clusters at the initial moment of spreading.