Pulse advancement and delay in an integrated-optical two-port ring-resonator circuit: direct experimental observations

We report experimental observations of the negative-group-velocity (v(g)) phenomenon in an integrated-optical two-port ring-resonator circuit. We demonstrate that when the v(g) is negative, the (main) peak of output pulse appears earlier than the peak of a reference pulse, while for a positive v(g), the situation is the other way around. We observed that a pulse splitting phenomenon occurs in the neighborhood of the critical-coupling point. This pulse splitting limits the maximum achievable delay and advancement of a single device as well as facilitating a smooth transition from highly advanced to highly delayed pulse, and vice versa, across the critical-coupling point.     

Chiral Modification of Platinum by Co‐Adsorbed Cinchonidine and Trifluoroacetic Acid: Origin of Enhanced Stereocontrol in the Hydrogenation of Trifluoroacetophenone

Cinchonidine (CD) adsorbed onto a platinum metal catalyst leads to rate acceleration and induces strong stereocontrol in the asymmetric hydrogenation of trifluoroacetophenone. Addition of catalytic amounts of trifluoroacetic acid (TFA) significantly enhances the enantiomeric excess from 50 to 92 %. The origin of the enantioselectivity bestowed by co‐adsorbed CD and TFA is investigated by using in situ attenuated total reflection infrared spectroscopy and modulation excitation spectroscopy. Molecular interactions between the chiral modifier (CD), acid additive (TFA) and the trifluoro‐activated substrate at the solid–liquid interface are elucidated under conditions relevant to catalytic hydrogenations, that is, on a technical Pt/Al₂O₃ catalyst in the presence of H₂ and solvent. Monitoring of the unmodified and modified surface during the hydrogenation provides an insight into the phenomenon of rate enhancement and the crucial interactions of CD with the ketone, corresponding product alcohol, and TFA. Comparison of the diastereomeric interactions occurring on the modified surface and in the liquid solution shows a striking difference for the chiral preferences of CD. The spectroscopic data, in combination with calculations of molecular structures and energies, sheds light on the reaction mechanism of the heterogeneous asymmetric hydrogenation of trifluoromethyl ketones and the involvement of TFA in the diastereomeric intermediate surface complex: the quinuclidine N atom of the adsorbed CD forms an N?H?O‐type hydrogen‐bonding interaction not only with the trifluoro‐activated ketone but also with the corresponding alcohol and the acid additive. Strong evidence is provided that it is a monodentate acid/base adduct in which the carboxylate of TFA resides at the quinuclidine N‐atom of CD, which imparts a better stereochemical control.     

Hydroxylionen-Katalyse sowie pH- und H2O2-Konzentrations-Abhängigkeit dieser peroxidatischen Reaktion

Ohne Zusammenfassung     

Über amphotere Eigenschaften der Metalle und die donator-und defektelektronischen Zentren ihrer inhomogenen Oberfläche

Zusammenfassung Es wird eine Theorie über Metalle entwickelt, die in ihrem Grundgedanken dualistisch ist und sich in physikalischer und chemischer Beziehung an die vom Verf. früher angegebene Radikaltheorie aktiver Oxide in logischer Folge angliedert. Im einzelnen werden behandelt: Die Auflösung von Metallen in Säuren, ihre Passivierung sowie Oxidbildung und Rostverhütung, ferner elektrochemische Vorgänge, wie z. B. die NaCl-Elektrolyse. Katalytische Umsetzungen mitsamt Mechanismen wurden am Beispiel des SO₃-Kontaktverfahrens, der Ammoniaksynthese und-oxidation sowie von Dehydratisierungsreaktionen an Metallen besprochen. Auch das geschmolzene Metall fand in diesem Zusammenhang seine Berücksichtigung.

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A theory about metals is developed, which is basically of a dualistic nature, and physically and chemically is connected to a radical theory of active oxides, previously developed by the same author. Especially treated are: the dissolution of metals in acids, their passivation and formation of oxides, and the inhibition of rust formation, as well as electrochemical reactions, for instance the NaCl-electrolysis. Catalytic reactions and their mechanism, the catalytic SO₃-process, the NH₃-synthesis and-oxidation, as well as the dehydration reactions on metals are discussed. Molten metals are also considered in this connection.

     

Aktivierungsenergie des H2O2-Zerfalls im mikroheterogenen System in Gegenwart von Hydrosolen röntgenamorpher Eisen (III)-hydroxide

Zusammenfassung Die Hydrosole des röntgenamorphen Eisen (III)-hydroxids und seines Polymerysationsprodukts katalysieren in einer Reaktion I. Ordnung mit verschiedener Geschwindigkeit den H₂O₂-Zerfall, der bei 27° und 37° untersucht wurde. Auch die daraus berechneten Aktivierungsenergien ergaben differente Werte.     

Über amorphe Festkörper

Zusammenfassung Röntgenamorphe mechanische Gemenge oder Gemeinschaftsfällungen von Beryllium-Chrom(III)-Mischhydroxiden zeigen ein unterschiedliches Verhalten im H₂O₂-Zerfall, dessen Geschwindigkeit einer Reaktion I. Ordnung entspricht.

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X-ray amorphous mechanical mixtures and co-precipitations of mixed beryllium-chromium(III) hydroxides show activities differing in the rate of decomposition of H₂O₂, which corresponds to a first order reaction.

     

Zum Mechanismus der Blausäuresynthese aus Ammoniak,Methan und Luftsauerstoff am Platinkontakt

Ohne Zusammenfassung