Der Elektromagnetische Aspekt der Magnetomechanischen Erscheinung in Gleich und im Monoalternant Pulsierenden Magnetfeld

The electromotive tension induced by Barkhausen discontinuities is studied. These Barkhausen discontinuities are excited by periodic mechanical stress in a d-c and a mono-alternating pulse magnetic field.     

Orientierung nematischer Phasen im Magnetfeld

Orientation of Nematic Phases in Magnetic Fields We discuss two methods to measure the reorientation times τ_0r of the director in nematic phases of liquid crystals in an external magnetic field. Both methods give the same results; advantages and disadvantages are considered. It appears that the relation resulting from continuum theory tan Φ ∞e^?t/τ0r is fulfilled (Φ twist angle). In the appendix we discuss optimum conditions for the pulse method.     

Die Hyperfeinstruktur des 32 P 1/2-Zustandes von Natrium im starken Magnetfeld

The hyperfine structure of the 3² P _1/2-state of²³Na has been measured by the optical double resonance technique in a magnetic field sufficiently strong to decoubleI andJ. The magnetic interaction constantA _1/2 and the Landég-factor were found to be:A _1/2=94.3(2) MHz,g=0.66581(12).     

Die Hyperfeinstruktur des 32P3/2-Zustands von Natrium im starken Magnetfeld

The hyperfine structure of the 3²P_3/2 State of Na²³has been measured by the optical double resonance technique in a magnetic field of 3.1 kG sufficiently strong to decouple completelyI andJ. In the case of π or (σ⁺+σ^?) excitation the double resonance signal represents the superposition curve of eight unresolved radio-frequency transitions. The dependence of the signal on the pressure of sodium vapour and the radio-frequency field strength has been studied. The analysis of the experimental curves yields for the hyperfine coupling constants the valuesa=(18.7±0.4) Mc/s andb=(3.4±0.4) Mc/s. The nuclear electric quadrupole moment derived from the ratio ofb/a isQ=(0.146±0.02) · 10^?24cm². The Lande factor and the lifetime for the 3²P_3/2state are g_J=1.3344±0.0004 and τ=(1.61±0.07) · 10^?8 sec.     

Messungen von Äquivalentbreiten im Homogenen Magnetfeld

The equivalent width of spectral lines with fine and hyperfine structure is not always increased by an external magnetic field, but can be reduced drastically. This prediction from theory has been checked by magnetooptical measurements for the Na-D₁-line and has been found to be correct in all essential details. Furthermore the experimental results demonstrate, that the formulae normally used to calculate the saturated vapour pressure of metals are valid only for a limited number of cases. Moreover the experiments furnish the basis for a more exact method for determinating particle densities in metal vapours.     

Dispersion und Absorption transversaler Schallwellen im Magnetfeld

The propagation velocity and absorption of transverse ultrasonic waves have bsen measured in a polycristalline metallic probe as functions of a magnetic field parallel to the direction of propagation. In agreement with the macroscopic theory, these measurements showed, that the propagation velocity was increased by the magnetic field for frequencies below a transition frequency characteristic for the medium. In case of high frequencies the magnetic field causes an absorption. In the dispersion region characterized by the transition frequency, the magnetohydrodynamic Reynolds number is of order one and the magnetically induced changes in propagation velocity and absorption are strongly frequency dependent.     

Zur Quantentheorie der Transportprozesse im Magnetfeld. III

In the presence of a transversal magnetic field the electric thermoelectric and thermal transportcoefficients are calculated, taking into account phonon drag. The calculations are based on the model of free electrons, phonons, and impurity scatterers. Starting from Kubo's formulae, and using truncation technique for Green's functions an integral equation (generalized transport equation) is developed. It is solved in the case of strong magnetic field. If phonon drag is neglected Titeica type formulae hold for all transportcoefficients. Phonon drag reduces the values in the sense that the electron-phonon-relaxation time is replaced by the sum of the electron-phonon- and phonon-scatterer-relaxation time.     

Zur Quantentheorie der Transportprozesse im Magnetfeld. I

A system of free electrons and fixed scatterers with spatially varying temperature and chemical potential in the presence of electric and magnetic fields is considered. Starting from the quantum-mechanical Liouville equation a simple derivation of the Kubo formulae for the transport coefficients is given. Their antisymmetric part has to be completed by the contribution of the local equilibrium density operator, similarly to the case of the steady diffusion considered by Nakajima. Using a damping theoretical expansion a generalized transport equation is obtained which takes account of the action of the external electric field and the gradient of the temperature and the chemical potential during the collisions (interference effect).     

Relativmessung der longitudinalen β-Polarisation des141Ce

We have measured the longitudinal polarization of the β-particles of¹⁴¹Ce. Whereas Lipnik and Sunier predicted a polarizationP approximate ?0.5v/c we get for an energyE=400 keV a valueP=?(0.91±0.09)v/c. The dependence ofP on the parameterY is discussed.     

Zur Quantentheorie der Transportprozesse im Magnetfeld. II

Applying Kubo's formulae and damping theoretical arguments the electric, thermoelectric and thermal transport coefficients for a system of free and independent electrons and fixed scatterers in the presence of an external magnetic field are calculated. Assumingδ-type scatterers it is shown that in the quantum regionkT?ω?ζ the Wiedemann-Franz law holds for the oscillating symmetric conductivities, whereas in the case of the antisymmetric ones quantum mechanical deviations from this law occur. For strong magnetic fields and arbitrary scattering potential the symmetric transversal transport coefficients can be expressed by Titeica type formulae.