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981.
The different influence of functional groups on fragmentation reactions is demonstrated by the example of 17β-hydroxy-5α-androstanes. In 17β-hydroxy-5α-androstane the tendency of steroids to be cleaved by rupture of the C-13/C-17 bond under production of a charged centre at C-13 is only enhanced by the hydroxyl group. This influence of the hydroxyl group only predominates as long as substituents are absent which need less energy for ionization than is necessary to ionize the C-13/C-17 bond. Even the presence of a double bond may change the fragmentation pattern completely. If, however, an additional alkyl group is located at C-17, ionization occurs with high probability by elimination of an electron from the OH group connected to C-17. Therefore, other main degradation reactions occur than in molecular ions, having the charge located at C-13. In such compounds even the dominant influence of a conjugated system on the fragmentation reactions is considerably reduced. By etherfication of the hydroxyl group this effect is still very much increased. In the course of this investigation some not yet known degradation reactions, rather typical for the presence of certain groups in the steroid skeleton, were found. These are discussed briefly. 相似文献
982.
G. Großkopf R. Ludwig R. Molt H. G. Weber S. B. Zhang 《Applied physics. B, Lasers and optics》1988,45(3):171-174
The application of a semiconductor-laser amplifier with reduced facet reflectivity as all-optical switch is described. An optical data signal is switched on and off with an extinction ratio of 10 dB when an optical control signal is turned on and off. The two optical signals are polarized perpendicularly to each other. The device was operated up to 100 MHz.Nanjing Institute of Posts and Telecommunication Nanjing, PR China 相似文献
983.
Gerhard Lehmann 《Angewandte Chemie (International ed. in English)》1978,17(2):89-97
High-energy radiation can give rise to pairs of complementary defects in nonmetallic solids by the transfer of electrons between various types of atoms. These “color centers” which are generally paramagnetic, can usually be described as unusual valence states of an element. They are destroyed by heating and in most cases regenerated by renewed irradiation. In a heteropolar solid the formation of color centers usually leads to cancellation of point charges due to foreign ions of other valence or to vacancies. This is shown by the examples of kunzite, brazilianite, smoky quartz, and citrine; the most important methods for the structural elucidation of color centers are also described. Application of the principle of charge balance opens up possibilities for the production of unusual valence states, e.g. Al2+, F2?, Fe4+, and O?. Moreover, the type of the color center often permits far-reaching conclusions to be drawn about the defect structure of real crystals, which could hardly be clarified in other ways. 相似文献
984.
985.
Gerhard Kowol 《Archiv der Mathematik》1977,29(1):55-66
Ohne Zusammenfassung 相似文献
986.
987.
988.
Gerhard Goetze 《Zeitschrift für Physik A Hadrons and Nuclei》1960,158(3):347-358
Theβ-spectrum of MsTh1 (Ra228) has been measured in a proportional counter in 2π — and in 4π-geometry. Comparison of these measurements shows that there are no conversion electrons. Theβ-decay of MsTh 1 therefore leads in all cases to the ground level of MsTh2. The Kurie plot is straight from 15 keV up to the upper energy limit ofE 0=55±3 keV (logft=5·6). The result has been checked by a search for photons emitted by the MsTh1. Noγ-rays and no X-rays have been found. The measurements had to be made with a relatively large amount of natural Ra226 in the sources. — The results do not agree with those ofLecoin, Perey, Teillac andRiou, who proposed a complex decay sheme for MsTh1. 相似文献
989.
990.