Showing papers by "Technical University of Denmark published in 1968"

Electron Correlation Models for Optical Activity

Abstract: A two‐system no‐overlap model for rotatory strength is developed for electric‐dipole forbidden as well as allowed transitions General equations which allow for full utilization of symmetry in the chromophore and in the environment are obtained The electron correlation terms are developed in full detail for an (1A2←1A1(C2υ) transition of a chromophore interacting with a nonpolar anisotropic perturber It ensues that perturber anisotropy of polarizability makes substantial contributions even in such zero‐order forbidden transitions The correlation terms for a strong electric‐dipole allowed transition (1A1←1A1) of the same chromophore gives sector rules that are decidedly different An additive calculational scheme for the n − π* transition rotatory strengths of ketones shows the anisotropy effect to substantially modify, indeed sometimes become larger than, the simple octant rule behavior which occurs for isotropic perturbers Since agreement with experimental rotatory strengths is correct in magnitude a

Low-Field Mobility and Galvanomagnetic Properties of Holes in Germanium with Phonon Scattering

Abstract: A theoretical calculation of the low-field galvanomagnetic properties of holes in Ge has been carried out incorporating all relevant details of the band structure. The scattering is limited to acoustic and optical phonons and is described by the deformation potentials $a$, $b$, $d$, and ${d}_{0}$. For pure acoustic scattering, no overall consistency is found between available galvanomagnetic data and deformation potentials derived directly from experiments on strained Ge. The discrepancies may be ascribed to ionized-impurity scattering, but at higher temperatures where optical phonon scattering is operative, the deviations are still appreciable. We are led to conclude that the deformation-potential theory of phonon scattering needs reconsideration, and a nontrivial correction is pointed out.

Gas-Liquid-Particle Operations in Chemical Reaction Engineering*

Abstract: Publisher Summary Gas–liquid-particle operations represent efficient tools or building blocks for the chemical engineer, and it seems likely that their application will spread. Definite and general conclusions can be reached at the present time regarding the comparable advantages and disadvantages of the five major types of gas–liquid-particle operation discussed in this chapter. The application of the theoretical models to the design of gas–liquid-particle operations must still, to some extent, be based on experimental investigations with specific, rather than general aims. The mass-transfer rates obtainable across the gas–liquid interface are of nearly the same magnitude in the different operations. Bubble-column slurries exhibit rather higher transfer rates than conventional packed columns with countercurrent trickle-flow, but the transfer rate in packed columns may be increased by concurrent-flow operation. Date for mass transfer across the liquid–solid interface is virtually nonexistent for packed-bed gas–liquid-particle operations. The smaller particle size that may be employed in suspended-bed operations should be an advantage in this respect, but the packed-bed operations have, on the other hand, the advantage of having higher possible relative velocities between liquid and solid.

Far field scattering at low frequencies

Abstract: An explicit formula is derived expressing the low frequency expansion of the far field coefficient for any radiating electromagnetic field in terms of the low frequency expansion of the near field. It is shown that a knowledge of a given number of near field terms suffices to determine the same number of far field terms, thus disproving the previously held contention that p+1 near field terms were needed to determine p far field terms.

Electronic Structure of Rare-Earth Metals. II. Positron Annihilation

Abstract: The angular correlation of the photons emitted when positrons annihilate with electrons has been studied in single crystals of the rare-earth metals Y, Gd, Tb, Dy, Ho, and Er, and in a single crystal of an equiatomic alloy of Ho and Er. A comparison of the results for Y with the calculations of Loucks shows that the independent-particle model gives a good first approximation to the angular distribution, although correlation effects probably smear out some of the structure. The angular distributions from the heavy rare-earth metals are very similar to that from Y and can be understood qualitatively in terms of the relativistic augmented-plane-wave calculations by Keeton and Loucks. The angular distributions in the $c$ direction in the paramagnetic phases are characterized by a rapid drop at low angles followed by a hump, and these features are associated with rather flat regions of Fermi surface normal to the $c$ axis. The same aspects of the Fermi surface are believed to be important in determining the stability of the periodic magnetic structures formed in some of the metals, and there is a strong correlation between the structure in the angular distribution and the magnetic properties. In the spiral phase of Ho, the structure in the $c$-axis distribution is much reduced, indicating that the Fermi surface is substantially modified by the magnetic ordering, as expected. The photon distribution from the equiatomic Ho-Er alloy is very similar to those from the constituent metals, although the structure is somewhat more pronounced.

Admittance of an infinite cylindrical antenna with realistic gap field

Abstract: A numerical comparison is made between the admittance of an infinite cylindrical antenna excited by a realistic electric field across a finite gap, and the admittance found by assuming a constant electric field in the same gap. A simple approximate relation between the two is derived, while a second simple expression shows how the admittance changes as the gap width is varied.

A systematic numerical error in APW calculations

Abstract: A recalculation of the final stage of two self-consistent APW band structure calculations for Cu and Al shows the stated energies to be in error up to 0.08 Ry. It is also shown that a probable source of the error is an incorrect starting of the radial integrations. Eine Kontrollberechnung der resultierenden Eigenwerte von zwei selbstkonsistenten APW Bandstrukturberechnungen fur Cu und Al zeigt, das die angegebenen Energien mit Fehlern bis 0,08 Ry behaftet sind. Es wird gezeigt, das der Grund der Fehler wahrscheinlich falsche Anfangswerte der Radialintegrationen sind.

A Sequential Logic for Improving Signal Detectability in Frequency-Agile Search Radars

Abstract: Certain fading models have in the past become standard for taking into account the effects of fluctuations in target echoing area in the theoretical prediction of radar range performance. In the application of these models, fading has always been treated as an entirely random phenomenon. In this paper it is noted that this is not necessarily true for radars which have the transmission frequency as a controlled variable, since in that case the fading characteristics of the target may be modified by properly controlling the transmission frequency. A strategy for taking advantage of this possibility is developed and theoretical results obtained by Monte Carlo simulation for a specific logic indicate that gains in detectability of several decibels (relative to what is usually considered optimum) may be obtained when certain realistic assumptions are made for the target fading characteristics.

Cyclotron Resonance of Holes in Si

Abstract: Hole resonances are studied in 3900 Ωcm p-type Si samples at temperatures from 1.2 to 5.0 °K. Measurements are performed at 45 GHz using magnetic inductions B up to 10 kG corresponding to a maximum value of m*/m0 = 0.62, and a few resonances not reported previously are observed. The experimental data are in reasonably good agreement with the Luttinger theory [1] of Landau levels in the valence band of semiconductors when a suitable set of band parameters are chosen. Numerical calculations of the levels and the matrix elements for transitions between the levels are carried out for B pointing in the crystallographic directions [001], [111] and [110]. The variation of the level positions and of the matrix elements as a function of the band parameters is examined in order to find the parameters providing the best fit to the experimental data. Locher-Resonanzen in p-leitendem 3900 Ωcm Si sind bei Temperaturen von 1.2 bis 5.0 °K untersucht worden. Die Messungen wurden bei 45 GHz bei magnetischen Induktionen B bis zu 10 kG entsprechend einem Maximalwert von m*/m0 = 0.62 durchgefuhrt. Einige Resonanzen, von denen bisher nicht berichtet worden ist, sind beobachtet worden. Die experimentellen Daten stimmen recht gut mit der Luttinger-Theorie [1] der Landau-Niveaus im Valenzband von Halbleitern uberein, wenn ein passender Satz Band-Parameter gewahlt wird. Numerische Berechnungen der Niveaus und der Matrixelemente fur Ubergange zwischen den Niveaus sind fur B in den kristallographischen Richtungen [001], [111] und [110] durchgefuhrt worden. Die Anderungen der Niveaus und der Matrix-elemente als Funktion der Bandparameter sind untersucht worden, um die Parameter zu ermitteln, die mit den experimentellen Daten die beste Ubereinstimmung ergeben.

Spin tickling in nuclear magnetic resonance involving single and double quantum transitions

Abstract: (1968). Spin tickling in nuclear magnetic resonance involving single and double quantum transitions. Molecular Physics: Vol. 15, No. 4, pp. 423-424.

Neuristor waveform stability analysis by Lyapunov's second method

Abstract: Lyapunov's second method gives a sufficient condition for the asymptotic stability of a dynamic steady-state waveform on a nonlinear active transmission line. The result is consistent with that of an eigenfunction expansion technique.

Electroluminescence of Current Carrying ZnO Single Crystals

Abstract: Experimental results of electroluminescence originating from current carrying contacts on ZnO single crystals are presented. The measurements were carried out with high voltage pulses applied to either rectifying contacts (silverpaste) or non-rectifying contacts (indium). Spectral distributions and time variations were recorded. A yellow emission which was delayed relatively to the exciting voltage pulse was found, and the luminescence from current oscillating crystals was measured. Light emission correlated with travelling high field domains was detected.

The titration curve of insulin in the presence of various bivalent metal ions.

Abstract: 1. Titration curves of insulin in the presence and absence of various metal ions are reported. 2. The difference in base consumption with and without the metal ions is compared with calculated curves. 3. These experiments suggest that in dilute solutions Zn2+ and Cu2+ ions are bound to α-amino groups.