Showing papers by "Technical University of Denmark published in 1970"
TL;DR: In this paper, the stability of a sand bed in an alluvial channel is investigated by a two-dimensional mathematical model, based on the vorticity transport equation, which takes account of the internal friction and describes the non-uniform distribution of the suspended sediment.
Abstract: The stability of a sand bed in an alluvial channel is investigated by a two-dimensional mathematical model, based on the vorticity transport equation. The model takes account of the internal friction and describes the non-uniform distribution of the suspended sediment. It turns out that the inclusion of the friction and of a definite model of the sediment transport mechanism leads to results rather different from those obtained previously by potential-flow analysis.
302 citations
TL;DR: In this paper, a relativistic augmented plane-wave calculation of the band structures of the paramagnetic fcc transition metals Ir, Rh, Pt, and Pd was presented, and the agreement with de Haas-van Alphen Fermi-surface dimensions was very good.
Abstract: We give a complete description of a relativistic augmented-plane-wave calculation of the band structures of the paramagnetic fcc transition metals Ir, Rh, Pt, and Pd. The width and position of the $d$ band decrease in the sequence Ir, Pt, Rh, Pd; and $N({E}_{F})=13.8,23.2,18.7, \mathrm{and} 32.7$ (states/atom)/Ry, respectively. Spin-orbit coupling is important for all four metals and the coupling parameter varies by 30% over the $d$ bandwidth. Detailed comparisons with de Haas---van Alphen Fermi-surface dimensions have previously been presented and the agreement was very good. Comparison with measured electronic specific-heat coefficients $\ensuremath{\gamma}$ and cyclotron masses indicate that the average mass enhancements are 1.37, 1.44, 1.63, and 1.66 for Ir, Rh, Pt, and Pd, respectively; and that for both Pt and Pd the partial enhancements on the closed electron surface and on the open hole surface are 1.51 and 1.68, respectively. Saddle points in the fifth band are important for the large peak in $N(E)$ near the top of the $d$ band. The experimental $\ensuremath{\gamma}(x)$ for ${\mathrm{Rh}}_{x}{\mathrm{Pd}}_{1\ensuremath{-}x}$ is not uniformly enhanced over the calculated rigid-band $\ensuremath{\gamma}(x)$. The experimentally observed field and temperature dependences of the magnetic susceptibility for Pd are consistent with the calculated $N(E)$.
293 citations
TL;DR: In this article, a general procedure for evaluating the stiffness matrix of a cracked element is developed, and numerical results obtained by the simplest elements are compared with those provided by other methods.
Abstract: The calculation of stress intensity factors for complicated crack configurations in finite plates usually presents substantial difficulty. A version of the finite element method solves such problems approximately by means of special cracked elements. A general procedure for evaluating the stiffness matrix of a cracked element is developed, and numerical results obtained by the simplest elements are compared with those provided by other methods.
126 citations
TL;DR: The magnetic hyperfine (hf) fields in the Fe and Sn components are not, in general, proportional to the magnetic moments as discussed by the authors, and two simple relations containing the coordination numbers can be used within a wide range to describe the variations of these fields as a function of composition.
Abstract: Solid solutions $\mathrm{Fe}\mathrm{Sn}$ and the compounds ${\mathrm{Fe}}_{3}$Sn, ${\mathrm{Fe}}_{5}$${\mathrm{Sn}}_{3}$, ${\mathrm{Fe}}_{3}$${\mathrm{Sn}}_{2}$, FeSn, and Fe${\mathrm{Sn}}_{2}$ have been studied by the M\"ossabauer effect in both Fe and Sn nuclei. Also, standard x-ray diffraction and magnetization studies were performed. The magnetic hyperfine (hf) fields in the Fe and Sn components are not, in general, proportional to the magnetic moments. It is found that two simple relations containing the coordination numbers can be used within a wide range to describe the variations of these fields as a function of composition. The collected results indicate that the magnetic hf field at the iron nucleus is rather insensitive to the conduction-electron polarization in these alloys. The isomer shifts are linearly related to the number of Fe-Sn bonds in such a way that bonding reduces the electron densities at both nuclei. The bonding is covalentlike and predominantly unpolarized.
100 citations
TL;DR: In this paper, the shape of a rotationally symmetric plate is determined so that its first natural frequency of transverse vibrations becomes optimal, and the corresponding mathematical problem is shown to be an ordinary, fourth order, nonlinear and singular, but homogeneous eigenvalue problem.
78 citations
TL;DR: In this article, the imperfect pulse method was used to examine the mixing in the fluid phases of liquid and gas-liquid fluidised beds using radioactive isotopes as tracers, and a new method of data reduction possessing some advantages over the normally used method of moments was applied and discussed.
61 citations
29 Jan 1970
TL;DR: In this paper, the interaction between surface gravity waves and a steady current was studied and a simple graphical method for the computation of the wave length m a current field was presented, and a complete set of conservation equations for the case considered under point c was presented.
Abstract: This paper presents some theoretical results of a general study of the interaction between surface gravity waves and a steady current Assuming irrotational flow and a second order Stokes wave motion, the main objects of the paper have been a To present a simple graphical method for the computation of the wave length m a current field b To introduce the concept of the mean energy level for a periodic wave motion with a steady current superimposed c To utilize this for the calculation of the "current-wave set-down" for a two-dimensional motion with a constant discharge over a gently sloping bottom d To present a complete set of conservation equations for the case considered under point c e To present graphs and tables for the variation in length and height of wave for the case considered under point c No experimental results are presented.
58 citations
TL;DR: In this paper, the authors presented four convenient methods for determination of the mean residence time and axial dispersion coefficient of a flow system by analysis of data obtained by means of the imperfect tracer pulse method.
49 citations
37 citations
TL;DR: In this article, a series of ion-selective electrodes based on metal dithizonates is discussed and a theory to explain their behavior is proposed, where the higher the extraction constant of the metal Dithizonate, the greater is the selectivity of the electrode prepared from it for the particular metal involved in the extraction system.
36 citations
TL;DR: In this article, a relativistic band structure calculation for gold is presented, where the static spectrum cannot be interpreted in terms of critical points, but matches well the joint density-of-states function calculated on the basis of direct transitions with constant matrix elements.
TL;DR: In this article, the authors deal with a theoretical and experimental investigation of adsorption kinetics and derive the effective diffusion coefficient in the pore system and the gas film resistance as a function of gas velocity.
01 Jan 1970
TL;DR: A review of physical effects in piezoelectric semiconductors originating in the relative strong coupling between the electronic and sound wave systems is given in this paper, where sound amplification, non-electronic losses, effects of free carrier trapping, and a number of strong non-linear effects such as current saturation, current oscillations, and traveling high field and flux domains are discussed.
Abstract: A review is given of a variety of physical effects in piezoelectric semiconductors originating in the relative strong coupling between the electronic and sound wave systems. Among the topics discussed are sound amplification, non-electronic losses, effects of free carrier trapping, and a number of strong non-linear effects as current saturation, current oscillations, and traveling high field and flux domains. A short discussion of some recent non-linear theories is also included.
TL;DR: For a linear uniform array of n elements, an expression for the directivity as a function of the spacing and the phase constants was derived in this article for the cases of isotropic elements, collinear short dipoles, and parallel short dipole.
Abstract: For a linear uniform array of n elements, an expression is derived for the directivity as a function of the spacing and the phase constants. The cases of isotropic elements, collinear short dipoles, and parallel short dipoles are included. The formula obtained is discussed in some detail and contour diagrams of the directivity as a function of the spacing and the phase constants in the above-mentioned cases are exhibited.
TL;DR: Five species of the family Caricaceae were examined for glucosinolates and like Carica papaya L., they all contained benzylglucosinolate (I, R = C 6 H 5 CH 2 ) as the sole thioglucoside.
TL;DR: X-Ray Diffraction Investigation on the Effect of Experimental and in Situ Radiation on Mature Human Teeth a Preliminary Report.
Abstract: (1970). X-Ray Diffraction Investigation on the Effect of Experimental and in Situ Radiation on Mature Human Teeth a Preliminary Report. Acta Odontologica Scandinavica: Vol. 28, No. 5, pp. 623-631.
TL;DR: In this paper, the general properties of the exchange matrix element between hydrogenic exciton states in a cubic crystal are discussed and it is shown that the high frequency dielectric constant should be applied in the screening of the long range exchange interaction.
Abstract: The general properties of the exchange matrix element between hydrogenic exciton states in a cubic crystal are discussed. It is shown that the high frequency dielectric constant should be applied in the screening of the long range exchange interaction. The exchange effects are then incorporated in the quasi-cubic model of uniaxial crystals. Including also an external stress the energy levels and oscillator strengths of the exciton states are derived. The theoretical results are consistent with existing optical data on ZnO. By comparison values for the exchange integral and a valence band deformation potential are obtained.
Die allgemeinen Eigenschaften des Austausch-Matrixelements zwischen wasserstoffahnlichen Exzitonenzustanden in einem kubischen Kristall werden diskutiert. Es wird gezeigt, das man fur die Abschirmung der Fern-Austauschwechselwirkung die Hochfrequenz-Dielektrizitatskonstante benutzen mus. Diese Austausch-Effekte werden dann in das quasi-kubische Modell einachsiger Kristalle eingefuhrt. Die Energiezustande und die Oszillatorstarken der Exzitonenzustande werden fur den Fall einer auseren Spannung abgeleitet. Die theoretischen Ergebnisse stimmen mit entsprechend interpretierten optischen Messungen an ZnO uberein. Aus dem Vergleich werden Werte fur das Austauschintegral und ein Deformations-Potential des Valenzbandes erhalten.
TL;DR: In this paper, the Mossbauer spectrum of Fe at room temperature is an anomalously asymmetric quadrupole pattern, which is exceptionally sensitive to external magnetic fields and the asymmetry of the spectrum is diminished both when an external magnetic field is applied and when the temperature is decreased.
Abstract: The M\"ossbauer spectrum of Fe${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}6 ${\mathrm{H}}_{2}$O at room temperature is an anomalously asymmetric quadrupole pattern, which is exceptionally sensitive to external magnetic fields. The asymmetry of the spectrum is diminished both when an external magnetic field is applied and when the temperature is decreased. Qualitatively, the experimental results can be explained by a combination of a temperature-and magnetic-field-dependent spin-spin relaxation and the Karyagin-Gol'danskii effect. This implies that the zero-field splitting is about 20\ifmmode^\circ\else\textdegree\fi{}K between the lowest-lying Kramers doublet, found to be the $|\ifmmode\pm\else\textpm\fi{}\frac{1}{2}〉$, and the other doublets. The fluctuating magnetic field at the Fe sites is found to be directed along the axis of crystal-field symmetry.
TL;DR: In this article, a strong seasonal variation in periodically-structured Pc 1 reception is found at Kanak and is attributed to a seasonal variation of propagation conditions in the polar cap F -layer horizontal waveguide.
TL;DR: In this paper, Brillouin scattering methods of the frequency spectrum for growing acousto-electric domains in CdS support the importance of parametric subharmonic frequency conversion effects.
TL;DR: Leaves of four South-American species of the genus Capparis (Capparidaceae) have been examined for their content of glucosinolates and it appears that C. baducca, C. hastata Jacq.
TL;DR: In this paper, the lifetimes of magnons propagating in the c-direction have been measured in the ferromagnetic phase of Tb, and are found to decrease with increasing temperature and wavevector, probably principally due to magnon-magnon interactions.
Abstract: Magnon energies and lifetimes have been studied in Tb and Tb‐10% Ho single crystals by inelastic neutron scattering. The lifetimes of magnons propagating in the c‐direction have been measured in the ferromagnetic phase of Tb, and are found to decrease with increasing temperature and wave‐vector, probably principally due to magnon‐magnon interactions. The interaction of magnons with phonons has also been observed and the effect of Ho impurities on this interaction studied. In addition, excitations which are ascribed to local modes associated with the Ho ions have been observed. The dependence of the indirect exchange interaction on temperature in the alloy gives information on the mechanisms responsible for the transition from the helical to ferromagnetic structures. The dependence of the magnon energies on magnetic field at low temperatures gives detailed information on the role of magnetoelastic effects in the magnetic anisotropy. It is found that the cylindrically symmetric magnetoelastic effect gives a...
TL;DR: It has been found that the lifetime τ 2 and the intensity I 2 of triplet positronium in light and heavy water show a sudden transition at the respective melting points for the two substances as mentioned in this paper.
TL;DR: In this paper, the mutual impedance between the dipole elements of the antenna is taken into account, and the field radiated due to a surface wave reflector of finite extent is determined by calculating the surface current distribution on the reflector plate.
Abstract: A method is set up for a theoretical investigation of arbitrary backfire antennas based upon dipole structures. The mutual impedance between the dipole elements of the antenna is taken into account, and the field radiated due to a surface wave reflector of finite extent is determined by calculating the surface current distribution on the reflector plate. Numerical results obtained for Yagi backfire antennas and short-backfire antennas using this theory are compared with experimental results.
TL;DR: In this article, the positron annihilation curves of Donaghy and Stewart for lithium have been reinterpreted using Mijnarends' method, and evidence is found for the possible existence of a neck in the Fermi surface in the (110) direction with a radius of the order of 13% of the free electron sphere radius.
Abstract: The positron annihilation curves of Donaghy and Stewart for lithium have been reinterpreted using Mijnarends' method. In this way it has been possible to split the total number of counts into two parts, one corresponding to electron momenta inside the main Fermi surface, the other arising from higher momentum components of the conduction electron wave functions and core annihilation. Evidence is found for the possible existence of a neck in the Fermi surface in the (110) direction with a radius of the order of 13% of the free electron sphere radius. The need for more detailed experimental investigations of positron annihilation in lithium is emphasized.
[Russian Text Ignored].
TL;DR: A fluorescent cation in seed extracts of the crucifer Sibara virginica (L). Rollins has been isolated, combined with thiocyanate ion and identified as (I), the choline ester of isoferulic acid (3-hydroxy-4methyoxycinnamic acid).
TL;DR: In this paper, it was shown that the point sample approximation always gives a far too large error under typical experimental conditions, and that the correct error is about 3-7 times smaller than the error calculated in the point sampling approximation.
TL;DR: Seeds of Reseda alba L. (Resedaceae) contain one glucosinolate, identified as 2-hydroxy-2-methylpropylglucosInolate (II), new to the family, but previously encountered in a few species of the family Cruciferae.
TL;DR: A large number of auxiliary lines may be generated in the frequency spectrum of an acousto-electric oscillator, if a small r.f. field of a frequency close to the fundamental frequency of the oscillator cavity is superposed on the d.c. field as mentioned in this paper.