Dispersive anisotropic ballistic phonon propagation in [100] GaAs

We report experimental observations of the phonon focusing pattern in [100] GaAs using low temperature electron beam scanning for phonon generation. The typical dispersive effects for high-frequency phonons expected from the calculations by Tamura have clearly been observed using PbIn tunnel junctions for phonon detection. The quantitative comparison of our experimental results with the frequency dependent calculations by Tamura allowed to determine the dominant phonon frequencies contributing to the detector signal in our different experiments. Above the temperature of the -point the dominant phonon frequencies appear to be shifted considerably to lower values, which could be explained by a heating effect in the liquid-He layer adjacent to the tunnel junction detector. By comparing the observed magnitude of the detector signal with different theoretical treatments of the detector response, we have found satisfactory agreement for a model where the perturbation due to the high-frequency phonons is restricted to the base electrode of the detector reached first by the phonons following their passage through the crystal.     

Effect of methanol dilution on H-ZSM-5 zeolite deactivation in the process of light olefin formation

Conversion of methanol in the presence of H₂O, O₂, H₂, CO, CO₂ and He was studied at 733 K on H-ZSM-5 zeolite. The effect of diluent on the selectivity to light olefins and resistance to coking of H-ZSM-5 were observed. Among the diluents studied only water exerts a promoting effect on prolonged activity of the catalyst. Some explanations of the deactivation process are given.

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H₂O, O₂, H₂, CO, CO₂ He H-ZSM-5 733K. H-ZSM-5. . .

     

The synthesis of 1,4-diazacycl[3,2,2]azine

The diazaanalog of “cycl[3,2,2]azine”, “1,4-diazacycl[3,2,2]azine” (1,4,7b-triazacyclopent-[cd]indene) and its 2-methyl derivative were prepared. These compounds are subject to facile acid-catalyzed hydrolysis affording substituted imidazo[1,2-a]pyridines.