Singletons and twistors

Singletons and twistors are unified from a group-theoretic point of view. In particular, singletons are described as the de Sitter analogue of twistors.     

Core-exciton spectra of AlxGa1−xAs studied with synchrotron radiation

Core-exciton spectra of Al_xGa_1?xAs have been measured in the photon-energy region from 19 to 27 eV by use of synchrotron radiation. The core-excitons associated with the Ga 3d core-hole and the conduction electron around the lowest L₆ and X₆ symmetry points are found to be coupled with each other through intervalley electron-hole interactions. Quantitative analyses have elucidated that intervalley Coulomb term is playing a dominant role for this coupling. Another higher energy doublet structure is interpreted as due to the transition from the Ga 3d core-levels to the rather flat region in the second lowest conduction band around the L₆ and L_{4, 5} symmetry points.     

Determination of trace metals in seawater by graphite furnace atomic absorption spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline in a flow-system

Summary A flow-system utilizing a miniature column packed with silica-immobilized 8-hydroxyquinoline (I-8-HOQ) was used for the preconcentration of Cd, Pb, Zn, Cu, Fe, Mn, Ni, and Co from seawater prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS). Enrichment factors sufficient to permit the analysis of an open ocean seawater reference material using 50 ml sample volumes (100 ml for Co determinations) were obtained. Recoveries of the above elements from seawater averaged 93% (range 87–97%) with absolute blanks ranging between 0.04 ng (Ni) and 4.0 ng (Fe). Estimated detection limits for these elements vary from 0.2 ng l^–1 (Co) to 40 ng l^–1 (Fe) based on a 50 ml sample volume (100 ml for Co).

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Bestimmung von Spurenmetallen in Meereswasser durch Graphitofen-AAS mit Anreicherung an Kieselgel-immobilisiertem 8-Hydroxychinolin in einem Durchflu\system

     

Raman scattering from plasmon-LO phonon coupled modes in ZnTe

Raman scattering spectra of LO phonon-plasmon coupled modes were observed at various temperatures below 400 K. The contributions of plasmon damping and phonon damping were analyzed by the use of the theoretical expression of the cross section and of Hall data. The temperature dependence of the calculated LO-phonon damping was discussed.     

Radiative recombination of donor-acceptor pairs in ZnTe

Lifetime of the first excited state of donor-acceptor pairs has been measured in ZnTe as a function of the donor-acceptor distance. The measured lifetime for the radiative recombinations of donor-acceptor pairs agrees well with the calculated one in which the central cell correction for the 1s state of the acceptors is taken into account. It has been found that the lifetime depends on the impurity concentration. The concentration dependence is discussed in connection with the non-exponential decay of the luminescence observed for more distant donor-acceptor pairs.     

Syntheses of azo dyes containing 4,5-diphenylimidazole and their evaluation as analytical reagents

Eight azo dyes containing the 4,5-diphenylimidazole group have been synthesized, and their potential for determinations of metals has been studied spectrophotometrically. Of these reagents, the pyridylazo and quinolylazo derivatives are suitable as chromogenic reagents, the best being 2-(quinolylazo)-4,5-diphenylimidazole (QAI), which reacts with several metal ions. The copper and mercury complexes of QAI show molar absorptivities of the order of 80 000 l mol^?1 cm^?1.     

Determination of nitrate in natural waters by flow-injection analysis

Summary Nitrate was determined in natural water samples by flow-injection spectrophotometry. It was reduced to nitrite with copperized cadmium and the nitrite thus produced reacted with p-aminoacetophenone and m-phenylenediamine. The limit of detection was about 1.5 g l^–1 for sample injections of 650 l. The sampling rate was about 40 samples h^–1 and the relative standard deviation was above 1% for 0.1–0.3 mg l^–1 nitratenitrogen. Nitrite present in the sample was determined separately and subtracted.

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Nitratbestimmung in natürlichen Wässern mit Hilfe der Fließinjektions-Analyse

Zusammenfassung Nitrat wird bei dieser Methode mit Hilfe einer Cu/Cd-Reduktionssäule zu Nitrit reduziert, das mit p-Aminoacetophenon und m-Phenylendiamin zur Reaktion gebracht wird. Die gebildete Verbindung wird spektral-photometrisch gemessen. Die Nachweisgrenze beträgt etwa 1,5 g/l bei injizierten Probevolumina von 650 l. Der Probendurchsatz beträgt 40/h. Die relative Standardabweichung liegt über 1% bei 0,1–0,3 mg/l Nitrat-Stickstoff. Vorhandenes Nitrit wird gesondert bestimmt und abgezogen.

     

Light scattering study of ferroelastics Hg2Br2

Brillouin and Raman scattering spectra of the soft modes in Hg₂Br₂ have been measured using triple pass Fabry-Perot interferometers. The temperature dependence of the coupled soft optical and acoustic modes are analyzed by use of the thermodynamic potential and the equations of motion for the coupled oscillators. These two methods have given the same result for explaining the elastic anomaly of Hg₂Br₂ crystals below the transition temperature.