Nichtstationäre Reflexion und Reemission von Wellen bei Herausbildung elektromagnetischer Strukturresonanzen im Plasma

The nonstationary resonant reflectivity of a density profile is studied which consists of two homogeneous overcritical layers, separated by a vacuum region whose width increases linearly in time. Analytical expressions are derived for the time dependence of both the reflexion coefficient and the cavity field in the case of normal incidence. If the configuration passes through a structure resonance, where the eigenfrequency of the density cavity coincides with the frequency of the external wave, the cavity field is strongly enhanced. The temporary formation and the subsequent decay of this resonant field leads to oscillations of the reflexion coefficient. In the case of a loss-less plasma it may reach the extreme values |R| = 0 |R| ≈ 3 and the moving plasma configuration temporarily acts as an energy storage (|R|² < 1) or an emitter (∣R∣² > 1).     

Streuung elektromagnetischer Wellen an rauhen Oberflächen mit anisotroper Autokorrelationsfunktion

Scattering of Electromagnetic Bulk Waves from Rough Surfaces with Anisotropic Autocorrelation Function Starting with the theory of light scattering given in [1]. a general theory of scattering of electromagnetic waves from a rough surface is deduced. In the general case of arbitrary anisotropic autocorrelation functions (acf) the spectral power densities for all different possibilities of polarisation variants of excitation and scattered light will be presented. In the special case of an elliptically anisotropic acf of surface roughness the measurement of the position of the acf-main axes will be described and the strategy of analyse of the measured indicatrix of scattered light for determining the acf will be given.     

Streuung elektromagnetischer Wellen an einer rauhen Oberfläche

Mar?elja's theory of a superconductor without long-range order is cast in a microscopic form. As a consequence, it is found that such a superconductor is gapless. Therefore, measurements of the tunneling density of states should provide a test of this theory.     

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.     

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.     

Zur Statistik neutraler Fermionen mit anomalem magnetischen Moment im äußeren Magnetfeld

In this paper we calculate the equation of state of a relativistic uncharged Fermi particle gas in a magnetic field, using the exact solutions of the Dirac-Pauli equation for an uncharged Fermi particle with an anomalous magnetic moment. We find that the stressenergy tensor is anisotropic. The anisotropy is introduced by the anisotropy of energy states.     

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.     

Plasmadiagnostik einer Azetylen-Sauerstoff-Flamme mit Mikrowellen und Magnetfeld

In order to determine the electron-molecule collision frequency in an acetylene-oxygen flame (burning within aX-band wave-guide) the decrease of microwave attenuation caused by an increasing magnetic field is being measured. It is shown that this decrease is equivalent to the wellknown high pass character of a plasma. The small attenuation is enlarged by using a Perot-Fabry type waveguide resonator. Nothing has to be known about its properties, since relative attenuation data are used for evaluation only. For the same reason no knowledge of electron concentration is necessary. The collision frequency value is exact within 4%, which is sufficient for excluding Coulomb collision interaction. The comparison with data in the literature is satisfying only, if the collision model of an electron induced dipol is accepted. With this and a flame temperature of about 3350 °K the collision frequency amounts to 179±7 GHz.