Diffraction errors in micromirror-array based wavefront generation

Using Laser-based Speckle-Interferometers, the shape of optically rough surfaces can be measured precisely and contactlessly from variable measuring distances even in regions of difficult access. This work is concerned with the integration of a micromirror array (MMA) into an electronic Speckle-Pattern-Interferometer. With the adaptive optics, it is intended to adapt the phasefront of a reference wave to critical surface areas of the measurement object. Yet, due to the topography of the MMA, diffraction effects occur which affect the phase and intensity of the generated wavefront. We demonstrate how these diffraction effects can be efficiently modelled by a Fraunhofer diffraction method. We compare the results of this model to theoretical data obtained by a numerical Fresnel diffraction model and to measurement data obtained from a measurement setup incorporating a multi mirror array.     

Surface cyclotron resonance in Si under uniaxial stress

The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m¹_c with stress S along the [001] direction. The effect is most strongly observed at low electron densities n_s. For $\text{S～1.5 × 10}{}^9\text{dyne}\text{cm}{}^2$ and n_s～2 × 10¹¹cm^-2 we obtain $\text{m}{}^1{}_{\mathrm{c}}\text{～0.4 m}{}_0$ instead of the expected 0.2m₀. Along with this change of $\text{m}{}^1{}_{\mathrm{c}}$ a strong narrowing of the resonance is noted. Raising the temperature gives an additional n_s- dependent increase of $\text{m}{}^1{}_{\mathrm{c}}$.     

Study of the level structure of239U using the thermal neutron capture reaction

For the investigation of vibrational states in odd A nuclei we have studied the level structure of²³⁹U by the²³⁸U (n _thermal,γ) reaction. Various complementary measurement techniques as curved-crystal-, anti-Compton-,γ-γ coincidence- and conversion electron spectroscopy have been applied. The resulting data have been used to establish the deexcitation scheme of²³⁹U up to ～1.3 MeV and to make spin assignments. Most of the levels are interpreted in terms of the Nilsson model. The data also indicate the presence of the Nilsson states ¦501?¦ and ¦750¦. Three members of theΒ-vibrational band built on the ¦631?¦ state and one member of theΒ-vibration built on the ¦622↑¦ ground state have been identified through transitions with strongE0 admixtures. The octupole vibrational state built on the ¦631?¦ band is proposed at 815 keV.     

Beiträge zur Spurenanalyse

Zusammenfassung Zur Spurenanalyse von Reinstselen werden die Spurenelemente aus 1 g Probematerial mit Oxin/Dithizon (in Chloroform) extraktiv angereichert und spektralanalytisch bestimmt. Mit diesem Verfahren sind 30 Elemente mit einem mittleren Fehler von ± 10% erfaßbar. Die Bestimmungsgrenze der Methode liegt bei 0,00001% und kann durch geeignete Maßnahmen noch um etwa zwei Zehnerpotenzen herabgesetzt werden.

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Summary In the trace analysis of the purest selenium the trace elements from 1 g of the sample are accumulated with oxine/dithizone (in chloroform) and determined spectrometrically. This procedure makes it possible to deal with 30 elements with a mean error of ±10%. The limit of determination of the method lies at 0.00001%, and can be lowered by about 2 powers of 10 if suitable precautions are taken.

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Résumé Pour le dosage de traces dans le sélénium pur, les éléments analysés sont enrichis par extraction par le réactif oxine/dithizone (dans le chloroforme) sur une prise d'essai de 1 g. Ils sont ensuite dosés par analyse spectrale. Cette méthode permet de déterminer trente éléments avec une erreur moyenne de ± 10%. La limite inférieure de sensibilité de la méthode est voisine de 0,00001% et peut encore être divisée par dix à la puissance deux par la mise en uvre de mesures appropriées.

     

On the number of conjugacy classes of a finite solvable group II

We prove that a finite solvable group G has at least (49p+1)/60 conjugacy classes whenever p is a prime such that p² divides the order of G. We also construct an infinite family of finite solvable groups, where this bound is attained.     

Quadrupole interactions in pionic and kaonic atoms

We discuss the quadrupole hyperfine structure in mesonic atoms for nuclei with spin I 1. The optical potential is expanded in terms of the non-spherical density contributions. Examples are given for the hyperfine splitting of peripheral and deeper-lying states in pionic and kaonic atoms.     

Results on the measurement ofK-series X-rays from antiprotonic hydrogen

The X-ray spectrum emerging from a liquid-hydrogen target when stopping antiprotons was measured with high resolution in order to determine the strong interaction shift and width of the atomic 1s level. Owing to strong Stark quenching only weak structures could be observed. The upper limit of the yield of any one of theK-series transitions is 3.5×10^?4 (95% C.L.) per stopped antiproton, assuming no broadening of the 1s level. Possible identifications of the weak lines with theK-series transitions are discussed.