Showing papers by "Technical University of Denmark published in 1977"

Mode interaction in axially stiffened cylindrical shells

Abstract: Postbuckling behavior and imperfection sensitivity associated with mode interaction in axially stiffened cylindrical shells under axial compression are studied. The two modes considered are an overall mode with wavelengths that are long compared to stiffener spacing and a short-wavelength panel mode involving buckling between the stiffeners. A restricted optimization study is made where the number of stringers is treated as a design parameter, and the range of designs considered includes the optimum design for the perfect shell, where the two modes are simultaneous. The influence of a given level of imperfections on the optimum is explored. A general method for analyzing initial postbuckling behavior is proposed for structures with simultaneous or nearly simultaneous modes. Asymptotic expansions of all fields in the amplitudes of the competing modes provide a set of uniformly valid results.

Shunted-Josephson-junction model. II. The nonautonomous case

Abstract: The shunted-Josephson-junction model with a monochromatic ac current drive is discussed employing the qualitative methods of the theory of nonlinear oscillations. As in the preceding paper dealing with the autonomous junction, the model includes a phase-dependent conductance and a shunt capacitance. The mathematical discussion makes use of the phase-space representation of the solutions to the differential equation. The behavior of the trajectories in phase space is described for different characteristic regions in parameter space and the associated features of the junction $\mathrm{IV}$ curve to be expected are pointed out. The main objective is to provide a qualitative understanding of the junction behavior, to clarify which kinds of properties may be derived from the shunted-junction model, and to specify the relative arrangement of the important domains in the parameter-space decomposition.

The redox potential: Its use and control in biotechnology

Abstract: This review describes the theory for and the measurement of the redox potential and the use and control of redox potential in biotechnology.

Biological denitrification of sewage: a literature review

Abstract: Biological denitrification of sewage is a process which can be performed with a number of techniques. This paper reviews the literature reviews the literature on denitrification. The biochemistry and microbiology of the process is well-known whereas the impact of several of the important environment factors involved in denitrification are not fully understood yet. This is true for temperature and pH-dependence and the influence of toxic substances. Many technological alternatives can be used for denitrification and several of these are at present understood to such a degree that full-scale application is feasible, Examples are combined, suspended sludge processes with internal carbon sources, separate sludge processes with methanol as carbon source and filter denitrification with methanol as carbon source. The characteristics of sludge from denitrifying plants seem to be similar to those of other biological sludges.

Kinetics of phosphate limited algal growth

Abstract: The kinetics of phosphate limited growth of two green algae Chlorella pyrenoidosa and Selenastrum capricornutum have been studied in chemostats. Several kinetic models which express the specific growth rate as a function of the intracellular phosphorus content have been examined, and one of the models was found to be significantly better than the other models. The principles of this model were described in a recent paper by Nyholm. The kinetics of phosphate uptake have been investigated by adding pulses of phosphate to the chemostats, The uptake by phosphorus deficient cells could be described by Michaelis-Menten kinetics for phosphate concentrations below approximately 500 microng P/liter. Further, with the assumption of a discontinuous adjustment of the uptake rate at the onset of phosphorus deficiency, a complete kinetic model for growth and phosphate removal is proposed. The mean cell size and the contents of chlorophyll a and RNA per unit dry weight have been measured for C. pyrenoidosa as a function of the dilution rate.

Necking of biaxially stretched elastic-plastic circular plates

Abstract: T he necking of an elastic-plastic circular plate under uniform radial tensile loading is investigated both within the framework of the three-dimensional theory and within the context of the plane-stress approximation. Attention is restricted to axisymmetric deformations of the plate. The material behavior is described by two different constitutive laws. One is a finite-strain version of the simplest flow-theory of plasticity and the other is a finite-strain generalization of the simplest deformationtheory, which is employed as a simple model of a solid with a vertex on its yield surface. For an initially uniform plate made of an incompressible material, bifurcation from the uniformly stretched state is studied analytically. The regimes of stress and moduli where the governing axisymmetric three-dimensional equations are elliptic, parabolic or hyperbolic are identified. The plane-stress local-necking mode emerges as the appropriate limiting mode from the bifurcation modes available in the elliptic regime. In the elliptic regime, the main qualitative features of the bifurcation behavior are revealed by the plane-stress analysis, although three-dimensional effects delay the onset of necking somewhat. For the deformation theory employed here, the first bifurcation modes are encountered in the parabolic regime if the hardening-rate is sufficiently high. These bifurcations are not revealed by a plane-stress analysis. For a plate with an initial inhomogeneity, the growth of an imperfection is studied by a perturbation method, by a plane-stress analysis of localized necking, and by numerical computations within the framework of the three-dimensional theory. When bifurcation of the corresponding perfect plate takes place in the elliptic regime, the finite element results show that the plane-stress analysis gives reasonably good agreement with the numerical results. When bifurcation of the corresponding perfect plate first occurs in the parabolic regime, then a bifurcation of the imperfect plate is encountered, that is, the finite element stiffness matrix ceases to be positive definite.

Probe correction of spherical near-field measurements

Abstract: Probe correction has been implemented in a computer program which calculates antenna far fields from spherical nearfield measurements. The computer program has been applied to near-field measurements on a satellite model, and the accuracy of the computed far field is significantly improved, compared with the results obtained without probe correction.

Maximizing Higher Order Eigenfrequencies of Beams with Constraints on the Design Geometry

Abstract: With the cross-sectional area as the design variable, we seek the optimal design of a transversely vibrating beam of given volume that maximizes a natural frequency ω n of specified order, n. The beams considered are thin, elastic, and of geometrically similar cross-sections, and a minimum constraint is prescribed for the cross-sectional area. In addition, the length and the boundary conditions are assumed to be given, and the beams may carry specified nonstructural masses. Variational analysis is used for deriving the governing equations, which are strongly coupled and nonlinear. These equations are solved numerically by a successive iteration procedure based on a finite difference discretization. A number of optimal solutions are obtained, and significant features of the spectra of their eigenfrequencies are discussed.

ORIGIN OF A DOMINANT BEER PROTEIN IMMUNOCHEMICAL IDENTITY WITH A β-AMYLASE-ASSOCIATED PROTEIN FROM BARLEY

Abstract: Two-dimensional immunoelectrophoretic techniques were used to elucidate the origin of a dominant beer antigen 1. Immunochemical identity was found between a protein Z associated with β-amylase in extracts of barley and one form of the beer antigen 1a. Immunochemical identity was also found between a papain-modified form of protein Z and the antigen form 1b from beer. The results indicate that protein Z is very resistant to degradation and denaturation during malting and brewing.

Analysis of bolted connections subject to prying

Abstract: High-strength bolted connections in steel structures in which the bolts are loaded in tension are studied. On the basis of the theory previously developed by the writer, the influence of the different variables affecting the magnitude of the prying forces in the connection has been examined. In the investigation a large number of connections have been analyzed on computer, and as a result of this analysis a diagram for direct use in the design has been established. The application of the design diagram in the analysis of connections is illustrated in examples covering the three basic cases of the theory. A comparison between the diagram resulting from the present investigation and those obtained on the basis of the formulas given in the current (7th ed.) AISC Manual of Steel Construction is included.

Cape York: The extraordinary mineralogy of an ordinary iron meteorite and its implication for the genesis of III AB irons.

Abstract: A study of accessory minerals in the Cape York iron meteorite has been carried out with the electron microprobe. Phases analyzed include chromite, sphalerite, two closely related potassium-bearing sulfides, silica, and native copper. In addition, four phosphate minerals were found: One chemically similar to buchwaldite, but rather rich in iron, one corresponding to terrestrial maricite, and two more, which seem to be new minerals on the basis of microprobe analysis. Evidence from the composition of accessory minerals as well as texture elucidates some details of the fractional crystallization of the group III AB parent melt. A modification of the fractional crystallization model is therefore proposed. We suggest that sulfide nodules have originated as droplets of an immiscible sulfur-rich liquid that continuously segregated from the parent melt during crystallization of the metal. The modified model also explains the Ni/Cr anticorrelation and the high abundance of sulfur in group III AB irons which could not be satisfactorily explained by previous models.

Low temperature vibrational spectroscopy. I. Hexachlorotellurates

Abstract: Far infrared and Raman spectra of six hexachlorotellurate (IV) salts have been obtained at ∼100 K for the first time. In the rubidium, cesium, ammonium, and tetramethylammonium salts the Raman active T2g cation lattice translatory mode was found. In the monoclinic K2[TeCl6] a number of low frequency lattice modes were observed and interpreted in terms of a phase transition near 165 K, similar to transitions in other K2[MX6] salts. The cubic tetramethylammonium hexachlorotellurate salt undergoes a phase transition of supposed first order at a temperature near 110 K, corresponding to transitions known in analogous uranium and tin compounds. Possible reasons for the transitions are discussed. In the low temperature phases the ν4 and ν6 bendings of [TeCl6]2− have been identified with bands near ∼130 and ∼110 cm−1. No evidence seemed to favor any stereochemical distortion due to the lone pair of electrons present in hexachlorotellurates.

A theory of electron transfer reactions at film-covered metal electrodes

Abstract: Various charge transfer mechanism through oxide films on metal electrodes in contact with a redox electrolyte are reviewed. A theory is presented for elastic coherent electron tunnelling through the film. The calculations are based on linear response theory and transfer hamiltonian formalism. The following models are employed for the subsystems: The electronic states in the metal and in the oxide are treated in the effective mass approximation, the electronic terms in the redox electrolyte in the harmonic approximation. The potential energy barrier in the oxide is assumed to be of trapezoidal shape; its dimensions depend on the applied potential. The properties of the barrier influence the electronic matrix element, which here, in contrast to metal electrodes, depends strongly on the applied potential, the energy of the transferring electron, the film thickness, and the barrier height. The numerical calculations exhibit a number of effects which are characteristics for oxide covered electrodes: the current distribution on the electronic levels is much broader than at metal electrodes; the energy of activation increases with the oxide thickness; similarly the cathodic transfer coefficient increases from 0.5 towards 1. The exchange current i 0 decreases with the oxide thickness a ; for high barriers a plot of log i 0 versus a is approximately linear, while for lower barriers a marked curvature is predicted. These results are discussed with respect to recent experimental work on oxide covered electrodes.

Low molecular weight sulphur-containing compounds in nature: a survey

Abstract: Sulphur, besides being an integral element of several macromolecular cell constituents, appears in a series of low-molecular weight, partly ubiquitously distributed compounds, e . g . S -containing protein amino acids, coenzyme A, S -adenosyl methionine, thiamine, and biotin, without which a steady state of living cells cannot be maintained. These, however, are not included in the present discussion. Rather, an attempt is being made to illustrate, by way of examples, the vast structural variation in other organic sulphur compounds with, as far as we know, a discontinuous distribution within the plant and animal kingdom. The chemical characteristics of these compounds are variegated, encompassing, inter alia , mercaptans, thiolesters, disulphides, sulphides (linear, cyclic, aromatic, and heterocyclic), amino acids, thioglycosides, terpenoids, sulphoxides, sulphones, and sulphates, the origin, transformations, and biological importance of which are mostly unknown. A bird's-eye view of the area is presented in the hope that this, however incomplete and blurred, may reveal some less obvious relationships and thus serve to invigorate further activity within the field.