Selektion eines Pikosekundenimpulses aus einem lmpulszug mit Hilfe von sättigbaren Absorbern und Absorption in angeregten Zuständen

Selection of a Picosecond Pulse out of a Pulse Train by Saturable Absorbers and Absorption in Excited Levels The absorption of pulses out of a pulse train under the combined action of a saturable one-photon-absorber (in the ground level) and an one-photon-absorber (after two-photon-absorption) in an excited level is calculated. For several absorber arrangements the system of rate equations is solved and their suitability for pulse selection is studied.     

Bereichsgrösse von FeSi-Néel-kristallen in abhängigkeit von magnetfeld-behandlung und temperatur

The domain structure of prismatic 2.5%-silicon-iron single crystals with 110-axes is investigated using the magneto-optic Kerr effect. The effective field is systematically varied in the temperature range from 20°C to the Curie-temperature. The main domains, consisting of plates and wedges, are stable up to 745°C. In “idealized” samples, the mobility of the Bloch-walls and the width of the plates as a function of the effective field strongly depend on the preceding temperature and field treatments. This dependence vanishes only above 500°C. The measurements can be explained by a thermally activated interaction between Bloch-walls and atomic “complexes”.     

Über die Existenz von Entropiefunktionen in Nichtgleichgewichtszuständen chemischer Reaktionssysteme II

On the Existence of Entropy-Functions for Chemical Reaction-Systems in Non-Equilibrium-States. II. Closed chemical reactions-systems tend to equilibrium or, in mathematical terms, are asymptotically stable. Thus Lyapunov-functions exist and can be used to define nonequilibriumentropy-functions in non-equilibrium-states, even far from equilibrium states. The qualities of these functions are discussed, a comparison with the linear thermodynamics is carried out.     

Über die Existenz von Entropiefunktionen in Nichtgleichgewichtszuständen chemischer Reaktionssysteme I

On the Existence of Entropy-Functions for Chemical Reaction-Systems in Non-Equilibrium-States. I. Closed chemical reactions-systems tend to equilibrium or, in mathematical terms, are asymptotically stable. Thus Lyapunov-functions exist and can be used to define non-equilibrium-entropy-functions in non-equilibrium-states, even far from equilibrium states. The qualities of these functions are discussed, a comparison with the linear thermodynamics is carried out.     

Analogien zwischen außerordentlichen und ordentlichen Wellen nach nichtorthogonaler Koordinatentransformation und die parabolischen Näherungsgleichungen

Within the limits of Linear Optics we treat analogies between ordinary and extraordinary waves in uniaxial media which become conspicuous through a nonorthogonal transformation of coordinates. To any ordinary wave solution in unbounded uniaxial media we can construct a corresponding extraordinary wave solution by interchanging electrical and magnetical field components. Boundary conditions for instance for ideal conducting plane surfaces approximately preserve their original form, if the optical axis or the middle wave vector are normal to the surface. The parabolic approximative equations for slowly varying amplitudes are derived, the polarisation of these waves being considered as a slowly varying quantity. Further these approximative equations are expanded to include frequency dispersion. Through the specified transformation we can simplify problems with extraordinary waves.     

Dynamische Äquivalenz,GAUSSsche Konstante und Zeit-Skala für die nach-NEWTONschen Näherungen klassischer und relativistischer Gravitationstheorien

The post-NEWTON ian approximation of the gravo-dynamics of planetary motions is given by a LAGRANG ian . For ε = 1/8, β = 3/2 und γ = ?1/2 this LAGRANG ian is the well-know function for EINSTEIN 's geodesic motion in an isotropic SCHWARZSCHILD metric. The perihel motion is given by TISSERAND 's formula      

Das gravische Wechselwirkungspotential und die Korrekturen der GAUSSschen Gravitationskonstanten in der nach-NEWTONschen Näherung klassischer und relativistischer Gravitationstheorien

We are giving the LAGRANG ians and the interaction potentials for the post-NEWTON ian approximation of the one-body problem according to the classical and the relativistic theories of gravitation. From these interaction potentials we are finding the general formulas for the post-NEWTON ian corrections to KEPLER 's laws and to the GAUSS ian gravitation constant with corresponding corrections for the astronomical distances. These corrections give an absolute measure of the differences between “dynamically equivalent” gravitation theories.     

Anisotropic spin correlations in CuO above the Néel temperature

A single-crystal neutron scattering study of the spin correlations in the a-c plane of cupric oxide above its Néel temperature of 229 K has shown them to be anisotropic: at 230 K the correlation length parallel to (1, 0, -1) is estimated to be at least 300 Å, which is much larger than the correlation length of 50–60 Å in the approximately perpendicular direction parallel to (1, 0, 1). This correlation length falls approximately linearly with increasing temperature in the interval 230 to 234 K, being reduced by a factor of two at the latter temperature. The full-width at half-maximum of Q-scans along (1, 0, -1) is resolution-limited close to T_N, so the corresponding correlation lengths could not be determined accurately. However, no significant reduction is seen until the temperature is higher than 237 K. These observations, together with the results of susceptibility and specific heat measurements, clearly establish that CuO behaves as a low, probably quasi-one-dimensional antiferromagnet.     

Theorie der parametrischen Vier-Photonen-Wechselwirkung. II., Verstärkung und Oszillation in der Näherung des vorgegebenen Pumpfeldes)

The processes of parametric amplification and oscillation in a medium with cubic polarization is investigated in parametric approximation. For the case of amplification the threshold power of the pump wave is calculated. The influence of a finite phase mismatching and of the initial phases on the amplification process is discussed. For larger values of mismatching a periodical change between amplification and depletion may appear. For the cases of a single resonant oscillator (for the signal wave only), a double resonant oscillator (for both signal and idler wave) and a double resonant oscillator with the pump wave reflected at the second mirror the threshold power of the pump wave and the rise time are calculated. Characteristic differences between four-photon and three-photon parametric oscillators are discussed. A numerical estimation of the threshold power for some media with nonlinear susceptibilities known from literature leads to the conclusion that the realization of a four-photon parametric oscillator should be possible. In the appendix we discuss the influence of diffraction, focussing, birefrigence, nonstationarity and depletion of the pump wave on the studied process as well as the conditions under which these effects can be neglected.     

Ionisierungs- und Umladequerschnitte von Wasserstoff-Atomen und Ionen von 9 bis 60 keV in Wasserstoff

This paper describes the measurement of ionization and charge exchange cross-sections for hydrogen atoms (H⁰), Protons (H⁺) and molecular hydrogen ions H ₂ ⁺ and H ₃ ⁺ in hydrogen gas in the energy range 9 to 60 keV. Further, the emission of secondary electrons from copper-beryllium by impact of these particles was measured. A beam of monoenergetic neutral hydrogen atoms was produced by charge exchange of a beam of protons in a gas chamber. Separation of the charged and uncharged components was accomplished by a magnetic field. The pressure in the chamber in which the cross-sections were measured was so low, that only a few particles of the incident beam suffered an effective collision. The positive and negative charges, which were produced by ionization and charge exchange along the path of the beam, were extracted by a transverse electric field and the saturation current was measured. The intensity of the neutral beam was determined at the same time by repeated charge exchange in an 80 mμ thick foil of aluminiumoxide.     

Phänomenologie und Energiebilanz von Lichtbogenkatoden bei niedrigen Drücken und hohen Stromstärken

The behaviour of an arc cathode in a coaxial gas stream is investigated experimentally in a pressure and current range of 15 to 120 mms Hg and 400 to 1000 A, respectively. Argon and hydrogen are used as ambient test gases. Particular phenomena occurring during the short instationary ignition period are described. Stationary operation characterized by a diffused cathode attachment covering a relatively large area is more closely studied. Measurements of the extension of the arc attachment and the distribution of the cathode temperature are made and evaluated quantitatively. Average current densities in the attachment are presented, as functions of pressure and current, by empirical expressions. Using a quasi-onedimensional approach, an interior energy balance of the cathode is set up and heat entering the cathode in the attachment region is calculated. Finally, under further simplifying assumptions, the cathode drop voltage and the fraction of current carried by ions are estimated and the so-called Richardson constant is determined assuming electron emission according to the Richardson-Schottky-equation. All data discussed depends — in general, strongly — on ambient pressure and current, and the type of gas has a substantial qualitative and quantitative influence.     

Verzweigungsverhältnisse und Konversionskoeffizienten von angeregten Zuständen des208Tl

The branching ratios of theγ rays of the second and fourth excited states of²⁰⁸Tl have been investigated by coincidence measurements between the α rays of²¹²Bi and subsequent 40keVγ ray. The detectors employed were a silicon surface barrier counter for α particles, and a 1.5 in ×2 mm NaJ (Tl) crystal forγ rays. It has been found that (75.6±3.7)% of all transitions of the 328 keV state and (94±7)% of all transitions of the (492 keV+473 keV) states populate the first excited state of²⁰⁸Tl. The 40 keV state is excited to (3.4±0.3)% by transitions of higher excited states relative to the direct excitation by α particles. The number of α particles with energyE _α = 6.047 MeV and the number of subsequent 40keVγ rays resulted in a conversion coefficient α(40keV)=22.55± 0.46. Similarly coincidence measurements between Tl-x rays and α particles have been used to determine theK- conversion coefficients α_K(328 keV)=0.31±0.03 and α_K(492 keV+ 473keV)=0.100±0.015. The experimental results are in good agreement with the theoretical values ofSliv.