Showing papers by "Delft University of Technology published in 1969"

Free convection at low Prandtl numbers

Abstract: In this paper it is shown that the free convection boundary layer approaches a singular character if the Prandtl number tends to zero. The method of matched asymptotic expansions is used to integrate the equations for this extreme case. An expression is derived for the Nusselt—Grashof relation and the results are compared with those of previous investigations which attack the problem in a different way.

Single server queues with restricted accessibility

Abstract: A queueing system has restricted accessibility if not every customer is admitted to the system. For such a system the admittance of a customer will in general depend on the state of the queueing system at the moment of his arrival. In this paper queueing models will be studied for which the accessibility depends on the actual waiting time of the arriving customer. Various queueing situations encountered in the allocation of memory equipment for information processing systems may be described as a single server queueing system with restricted accessibility; the mathematical models for the involved storage problems belong to queueing theory and are discussed in the present paper.

On ultrastructures in Rhodopseudomonas gelatinosa and Rhodospirillum tenue.

Abstract: Tile photosynthetic pigments in bacteria are associated with membranous structures, named chromatophores (Pardee, Schachmann and Stanier, 1952).The morphology ofchromatophores is diverse: in Athiorhodaceae the occurrence of vesicular and several types of lamellar structures are described (Cohen-Bazire and Sistrom, 1966). Another type of chromatophore structure has now been demonstrated by us in Rhodopseudomonas gelatinosa (Molisch) van Niel and Rhodo,~pirillum tenue (Pfennig, personal communication). Cells grown anaerobically (witb 95 ~ N,. and 5 ~/o CO,,,) in the light contain tubular intrusions

On the uniform distribution of sequences of random variables

Abstract: This paper deals with the almost sure uniform distribution (modulo 1) of sequences of random variables. In the case where the law of the increments Xn+h−Xnof the sequence X0, X1, ⋯ does not depend on n, sufficient conditions are given to assure the uniform distribution (modulo 1) with probability one. As an illustrative example the partial sums of a sequence of independent, identically distributed variables is considered.

Errors in cubic spline interpolation

Abstract: This paper deals with the problem of finding error bounds for cubic spline interpolation of functions of the classC 4[a, b], andC 5[a, b], by examining a relationship between cubic spline interpolation and piecewise cubic Hermitian interpolation. The method also gives an indication of what happens, in the case of almost uniform meshes, especially if the approximated function is in the classC 5[a, b]. Comparison is made with recent work carried out by K. E. Atkinson [3], in dealing with natural cubic spline interpolation.

Some transformation properties for the coefficients in a spherical harmonics expansion of the earth's external gravitational potential

Abstract: The earth's external gravitational potential may be mathematically expressed as an infinite series of spherical harmonics. The coefficients in such series depend numerically on the location and orientation of the adopted system of reference with respect to the body of the earth. The present subject is to derive general formulae for the numerical changes of the harmonic coefficients due to both a re-orientation and a re-location of the reference frame. Such formulae could be of value in critical studies of the impact of artificial satellites on dynamical geodesy, especially when combining the results with those from terrestrial geodesy. Use has been made of a transformation property of spherical harmonics which seems to be not a part of standard mathematics. Some simple numerical examples are given. DOI: 10.1111/j.2153-3490.1969.tb00464.x

Dissipative difference schemes for shallow water equations

Abstract: Three dissipative finite-difference schemes are discussed for the numerical calculation of discontinuous shallow water flow. The shallow water equations have been derived on assumptions which are not acceptable in the case of discontinuous flow. However, they may give satisfactory results if only weak jumps are present. It will be shown that a coarse network may affect the velocity of propagation of the computed bore.

Integral transforms for shock-shock interaction — Three dimensional planar wings

Abstract: Si une onde de choc de force arbitraire rencontre une aile pointue aplatie qui se deplace a une vitesse supersonique, une region de perturbations est generee. Une expression analytique explicite en termes de perturbations de pression est trouvee par l'application de transformations d'integrales au probleme des conditions initiales-limites. La theorie est appliquee au probleme de l'interaction d'une onde de choc plane et d'une aile delta plane (avec des bords d'attaque definiment supersoniques) en petite incidence. Les resultats numeriques pour la repartition des pressions sont presentes.

Paper 3: Recent Developments in Gear Tribology:

Abstract: The paper deals primarily with two theories which, in the last decade, have been increasingly incorporated in the theory of gear lubrication and enable both gear designers and lubricant technologis

Sucrose-gradient centrifugation of chromatophorous material from Athiorhodaceae

Abstract: Several investigators reported the occurrence of two bands when chromatophores were centrifuged in sucrose gradients. Cohen-Bazire and Kunisawa (1960) found that the light fraction of Rhodosph'illum rubrum chromatophores had a higher bacteriochlorophyll/protein ratio than the heavy fraction. Worden and Sistrom (1964) obtained similar results with Rhodopseudomonas spheroides chromatophores. They supposed that the heavy fraction might be derived from the cytoplasmic membrane since the relative anaount of heavy fraction was high when the bacteria were grown at a high light intensity (i.e. under conditions with few chromatophores). Electronmicroscopic observations of Holt and Marr (1965) showed that their heavy fraction consisted of chromatophores and cell envelopes, while the light fraction was not contaminated with larger structures. Gibson (1965) established that chromatophores aggregate readily in the presence of divalent metal ions at concentrations of 10-2M or in 0.1 M tris or 0.1 M phosphate buffer. He considered the lower band as a result of aggregation, since all the above mentioned investigators used buffers containing 10 -2 M magnesium sulphate. We studied the influence of 0.02 M potassium phosphate pH 7.0 with 0.01 M magnesium sulphate (PM buffer) and of 0.01 M tris pH 7.5 with and without 0.01 M magnesium sulphate (tris and TM buffer) on the results obtained in sucrose-gradient centrifugation experinaents with chromatophorous material from Rsp. rubrum, Rps. gelathmsa and Rps. pahtstris. Chromatophorous material was isolated by disintegration of cells by sonic oscillation followed by centrifugation at 20,000g for 30 rain and at 120,000g\" for one hr. Isolated chromatophorous material from Rps.gelatinosa (Fig. I) is more or less spherical as can be seen in thin sections (Fig. 2), although invaginations of the cytoplasmic membrane are the only internal membranous structures in this species. Lamellar structures dominate in the material from Rps. pahtstris (Figs. 3, 4). Some results are shown in Table 1. When PM or TM buffer were used during the isolation of chromatophorous material from Rsp. rubrum and Rps. gelatinosa, generally two bands, although with variable percentages of the total amount of bacteriochlorophyll, were obtained. With tris buffer only the upper band was present. No clear differences could be detected by electronmicroscopic observation of the material from both bands. Sucrose-gradient centrifugation of a 120,000g sedimented upper band of chromatophorous material of Rps. gelathtosa resulted again in two bands. The crude extract (the 20,000 g supernatant) however yielded only an upper band, independent of the buffer used. Our experiments do not support the supposition of Cusanovich and Kamen (1968) that lamellar structures (e.g. chromatophorous material from Rps. palustris) yield only a lower band. Neither could we confirm the results of Worden and Sistrom (1964) concerning the influence of the light intensity. These experiments show that the lower band is a result of strong aggregation of the chromatophorous material during the formation of the 120,000g pellet. Large aggregates remain present when the pellet is suspended in magnesium-containing buffers, unless drastic methods like sonic oscillation are used to clarify the suspension.