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Showing papers by "Technical University of Denmark published in 1971"


Journal ArticleDOI
TL;DR: In this paper, the relativistic augmented-plane-wave (RAPW) method was used to calculate the energy band structure of gold, and a comparison between this and the RAPW results demonstrates that the shifts and splittings due to relativism are of the same order of magnitude as the gaps (approximately 1 eV).
Abstract: The energy band structure of gold is calculated by the relativistic augmented-plane-wave (RAPW) method. A nonrelativistic calculation is also presented, and a comparison between this and the RAPW results demonstrates that the shifts and splittings due to relativistic effects are of the same order of magnitude as the gaps (approximately 1 eV). Various integrated functions, density of states, joint density of states, and energy distributions of joint density of states are derived from the RAPW calculation. These functions are used in an interpretation of photoemission and static reflectance measurements. It is shown that the photoemission results are extremely well described in terms of a model assuming all transitions to be direct whereas a nondirect model fails. The ${\ensuremath{\epsilon}}_{2}$ profile calculated in a crude model assuming constant matrix elements matches well the corresponding experimental results. The calculated interband edge ($\ensuremath{\hbar}{\ensuremath{\omega}}_{i}=2.38$ eV) agrees with experimental values, and the absorption tail below the interband edge which is found in experimental traces is also contained in the theoretical curve. By means of a calculation of the Fermi surface and the constant-energy-difference surfaces it has been possible to trace out the regions in $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space where the edge and tail transitions occur. It is demonstrated that structure in the static reflection curves are not related to critical points in the band structure. The arguments are supported by calculations of temperature shifts of the critical-point energies and comparison to the observed temperature shifts of the elements of structure in the experimental ${\ensuremath{\epsilon}}_{2}$ function. Such structure may originate in extended rather than localized regions of $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space. In contrast, critical-point transitions show up clearly in modulated reflectance spectra, and all elements of structure are fully accounted for by our band model. The temperature and strain responses in the band structure are determined by performing the RAPW calculation with two lattice constants and estimating the effects of the lattice vibrations by means of an OPW-LCAO (linear combination of atomic orbitals) scheme with pseudopotential Fourier constants reduced by the appropriate Debye-Waller factors. The phonon spectrum has been calculated for the latter purpose.

343 citations


Journal ArticleDOI
TL;DR: In this paper, the ion-sensitive surface of the new solid-state electrode consists of a very thin layer of an electroactive material adsorbed on the surface of hydrophobized graphite.

85 citations


Journal ArticleDOI
TL;DR: In this article, the binding energies, interparticle distances, oscillator strengths, and exchange corrections for the three-particle complex corresponding to an exciton bound to an ionized donor are calculated as functions of the mass ratio of the electron and hole.
Abstract: Binding energies, interparticle distances, oscillator strengths, and exchange corrections are calculated for the three-particle complex corresponding to an exciton bound to an ionized donor. The results are given as functions of the mass ratio of the electron and hole. Binding of the complex is obtained for mass ratios up to 0.426. The interparticle distances are up to 50 times larger than the corresponding exciton radius. The oscillator strengths are about ${10}^{4}$ times greater than those of free excitons, while the exchange corrections for the complex are comparable to those of free excitions. The results are applied to CdS and ZnO and compared with experimental results on these.

75 citations



Journal ArticleDOI
TL;DR: A nonparametric procedure used in a constant false alarm rate (CFAR) radar extractor for detecting targets in a background of noise with unknown statistical properties is described and a comparison is made with a detector based on the Mann-Whitney test, which usually is considered to be one of the betterNonparametric procedures for the two-sample case.
Abstract: A nonparametric procedure used in a constant false alarm rate (CFAR) radar extractor for detecting targets in a background of noise with unknown statistical properties is described. The detector is based on a generalization of the well-known two-sample sign test and thus requires a set of reference noise observations in addition to the set of observations being tested for signal presence. The detection performance against Gaussian noise is determined for a finite number of observations and asymptotically, for both nonfluctuating and pulse-to-pulse Rayleigh fluctuating target statistics. It is noted that the performance loss, as compared to the optimum parametric detector, depends critically on the number of reference noise observations available when the number of hits per target is not large. In the same case a much larger loss is also found for a pulse-to-pulse fluctuating target even though the asymptotic loss is the same as for a nonfluctuating target. A comparison is finally made with a detector based on the Mann-Whitney test, which usually is considered to be one of the better nonparametric procedures for the two-sample case.

45 citations



Journal ArticleDOI
TL;DR: In this article, numerical optimisation techniques have been used to find the maximum gain of specific parasitic arrays, such as an array of infinitely thin, equispaced dipoles loaded with arbitrary reactances.
Abstract: Numerical optimisation techniques have been used to find the maximum gain of some specific parasitic arrays. The gain of an array of infinitely thin, equispaced dipoles loaded with arbitrary reactances has been optimised. The results show that standard travelling-wave design methods are not optimum. Yagi--Uda arrays with equal and unequal spacing have also been optimised with experimental verification.

38 citations



Journal ArticleDOI
TL;DR: In this article, it is shown that the current/potential curve of iron exhibits two anodic maxima, which can be explained by assuming an adsorption of a layer on the metal surface.

37 citations


Journal ArticleDOI
TL;DR: In this article, the performance and construction of a liquid-state electrode with solutions of iodine in carbon tetrachloride, benzene and mesitylene as the organic phase is described.

34 citations



Journal ArticleDOI
01 Dec 1971
TL;DR: In this article, measurements of pre-breakdown ionisation currents in SF6 at pressures of up to 400 torr have been carried out over a range of E/p (E being electric field strength, and p the gas pressure referred to 20°C) for 115 ⩽ E /p ⊽ 200 V/cm torr and values of the primary ionisation α, secondary ionisation γ and attachment η coefficients obtained within the acccuracy with which the values are known.
Abstract: Measurements of prebreakdown ionisation currents in SF6 at pressures of up to 400 torr have been carried out over a range of E/p (E being electric-field strength, and p the gas pressure referred to 20°C) for 115 ⩽ E/p ⩽ 200 V/cm torr and values of the primary ionisation α, secondary ionisation γ and attachment η coefficients obtained Within the acccuracy with which the values are known, ᾱ/p (where ⩽ = α - η), α/p, η/p and γ are functions of E/p only, and thus similarity is obeyed The experimental limitations are fully surveyed and the effect of field nonuniformity on the current growth is discussed

Journal ArticleDOI
TL;DR: In this article, a simple analysis is developed which defines the inductive and capacitive time constants controlling the voltage waveshape and explains the frequency tuning with bias voltage and the effective space charge control.
Abstract: Oversized n-GaAs diodes operating in the LSA mode with doping-to-frequency ratios in the 1-5×105s/cm3range are investigated in circuits that contain a short-circuited high impedance transmission line foreshortened to resonate the electronic parallel capacitance of the diode. By comparing computer simulations with experiments, such diodes are shown to operate in a nonsinusoidal LSA relaxation mode which offers good efficiency, effective space-charge control, and a fast buildup of the oscillations; details of the computer program are also given. A simple analysis is developed which defines the inductive and capacitive time constants controlling the voltage waveshape and explains the frequency tuning with bias voltage and the effective space-charge control. The analysis is shown to be suitable for oscillator design purposes.

Journal ArticleDOI
TL;DR: Dietary long‐chain alcohols and alkyl glycerols, including polyunsaturated compounds, are incorporated into theAlkyl and alk‐1‐enyl moieties of the ionic alkoxylipids of rat liver, whereas polyuns saturated fatty acids are not.

Journal ArticleDOI
TL;DR: In this paper, a simple model accounting for the influence of a surface on polariton waves is introduced, and the extra boundary condition needed in case of a dispersive resonance is derived.
Abstract: A simple model accounting for the influence of a surface on polariton waves is introduced. From this the extra boundary condition needed in case of a dispersive resonance is derived. The general result is discussed in relation to actual resonances in crystals. The theory of bulk waves and their boundary conditions is extended to include two or more dispersive resonances. The behavior of the measured exciton lines in ZnO agrees well with the computed spectra.

Journal ArticleDOI
TL;DR: In this article, an integral equation whose kernel is equal to the logarithm of the distance between two points on a plane, closed, smooth, and simple curve is replaced by a system of linear algebraic equations which can be solved numerically.
Abstract: When formulating boundary value problems within different branches of mathematical physics, one encounters an integral equation whose kernel is equal to the logarithm of the distance between two points on a plane, closed, smooth, and simple curve. This equation can be replaced by a system of linear algebraic equations which can be solved numerically.


Journal ArticleDOI
TL;DR: The glucosinolates in dried leaves of Capparis flexuosa (L.)L.

Journal ArticleDOI
TL;DR: In this article, the anodic and cathodic behavior of tin in alkaline solution has been investigated in order to determine the conditions for electrolytic detining of tinplate, and the diffusion-controlled limiting cds for deposition of tin are ig = 160.

Journal ArticleDOI
TL;DR: In this article, the errors inherent in Love's uncoupled strain energy expression were estimated on the basis of general considerations regarding physical dimensions and properties of invariance, especially with respect to inversion of the normal to the middle surface.

Journal ArticleDOI
TL;DR: In this article, the forced convection laminar boundary layer involving a two component gas with dispersed liquid particles over a dry isothermal surface is studied analytically and experimentally.

Journal ArticleDOI
TL;DR: In this article, the infrared spectra of hydrogen halides of ethylenediamine were measured in the range of 4000-10 cm−1 for normal, C-, N-, and perdeuterated EDM chlorides and bromides.
Abstract: We wish to report on some hitherto partly unnoticed and unexplained features in the infrared spectra of hydrogen halides of ethylenediamine. We have prepared normal, C-, N-, and perdeuterated ethylenediammonium chlorides and bromides and measured their infrared spectra in the range 4000–10 cm−1.

Journal ArticleDOI
TL;DR: Treatment of 3,4-di-O-benzoyl-1,2-dideoxy-d-threo-pent-1-enopyranose, or the corresponding d-erythro compound, with methanol in the presence of boron trifluoride gives methyl 4- oedipine-2,3-didoxy- d-glycero-enthusiastside (3) as the main

Journal ArticleDOI
TL;DR: In this article, relaxation-broadened Mossbauer spectra of ferric alum have been obtained in the temperature range 85-250 K, with 0-5kG applied magnetic field.
Abstract: Relaxation-broadened M\"ossbauer spectra of ferric alum have been obtained in the temperature range 85-250 K, with 0-5-kG applied magnetic field. In fields above a few kG the spectra are only influenced by hyperfine fields fluctuating parallel to the applied-field direction. In low applied fields the spectra are also influenced by components of the hyperfine field fluctuating perpendicular to the applied-field direction, thereby inducing transitions between the nuclear sublevels. In the case of high applied fields, a simple model permits the determination of the spin-correlation time. In 5-kG applied fields, the spin-correlation time was found to decrease from 1.6\ifmmode\pm\else\textpm\fi{}0.15 nsec at 85 K to 0.50\ifmmode\pm\else\textpm\fi{}0.05 nsec at 245 K due to spin-lattice interactions. It is shown that these results cannot be compared with the values obtained by high-frequency susceptibility measurements.

Journal ArticleDOI
TL;DR: In this article, the Brillouin scattering technique was used to measure non-electronic losses with acoustoelectric domains in ZnO and CdS, which can be converted into domains of non-coupling sound waves by reflection.
Abstract: Acoustoelectric domains in ZnO and CdS can be converted into domains of non-coupling sound waves by reflection. These acoustoelectrically inactive waves have been used to measure non-electronic losses with the Brillouin scattering technique. Akustoelektrische Domanen in ZnO und CdS wurden durch Reflexion in Domanen aus inaktiven Schallwellen verwandelt. Diese konnen dazu benutzt werden, nichtelektronische Verluste mit Hilfe der Brillouinstreuung zu messen.

Journal ArticleDOI
TL;DR: The average electron-phonon renormalization is small in Au, 〈λ〉 ≈ 10%, but λ( k ) exhibits large variations over the Fermi surface as mentioned in this paper.

01 Jan 1971
TL;DR: In this article, 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.
Abstract: In linear slit measurements of the angular correlation of annihilation photons the use of finite slit lengths gives rise to an error in themeasured curves. It is shown that the point sample approximation, which is usually used in calculations of this error, always will give a far too large error under typical experimental conditions. The numerical values of the error for the free electron case are presented. The correct error is about 3–7 times smaller than the error calculated in the point sample approximation.

Journal ArticleDOI
TL;DR: In this paper, it was shown that a number of previously observed oscillations in the surface impedance of a semi-infinite silver specimen arise from points of zero-group velocity on the dispersion relation.
Abstract: Azbel'-Kaner cyclotron resonance in metals is accompanied by electromagnetic waves propagating in a direction perpendicular to the magnetic field. Taking into account the anisotropy of the silver Fermi surface, the dispersion relation for these waves is calculated in the limit where the wavelength is much smaller than the orbit diameter of the electrons. Thus it is shown that a number of previously observed oscillations in the surface impedance of a semiinfinite silver specimen arise from points of zero-group velocity on the dispersion relation. Physically, the oscillations reflect a matching of the electron-orbit diameter with an integer number of wavelengths. They may, therefore, be looked upon as geometric resonances in the surface impedance, complementary to the temporal cyclotron resonances. The surface impedance is calculated under the assumption of specular surface scattering. Satisfactory agreement with experiments is obtained by using an independent-particle model for the electron gas and band parameters based on APW calculations. The influence of the Fermi-surface geometry is demonstrated by comparing with calculations for a cylindrical and a spherical Fermi surface. The electric field in the metal is calculated for selected magnetic fields, and the expected result of a transmission experiment is presented. Finally, the absence of Fermi liquid effects in the experiments is briefly discussed.

Journal ArticleDOI
TL;DR: In this paper, a delta modulator with a second-order network in the feedback path is considered and the possible modes of oscillation are determined as a function of the zero of the linear network.
Abstract: A delta modulator with a second-order network in the feedback path is considered. For zero input signal the possible modes of oscillation are determined as a function of the zero of the linear network. The method could be employed with other types of feedback networks. A comparison is made with experimental results.