Unoccupied electronic states of epitaxial iron layers on Cu(100)

Inverse photoemission spectra were taken for thin epitaxial iron films on Cu(100). For a film thickness of eight monolayers the observed electronic states are characteristic for a fcc(100) surface. Thed-bands of iron show a ferromagnetic exchange splitting of 1.1 eV, considerably smaller than the bulk value of 1.8 eV, which we observe for film thicknesses above 18 monolayers.     

Momentum-resolved bremsstrahlung isochromat spectroscopy of silver surfaces

Angle-resolved bremsstrahlung isochromat spectra of the Ag(100), Ag(110) and Ag(111) surfaces have been measured. Our work extends and complements several earlier investigations of other authors. The data are summarized in the form of final state dispersionsE(k ). Comparison is made to the available theoretical and experimental information. The results for the bulk as well as for the surface-specific features are in excellent to reasonable agreement among each others and with recent calculations.     

Ultraviolet Bremsstrahlung spectroscopy

Recent experimental progress has introduced Bremsstrahlung spectroscopy especially in the isochromat mode as a new surface analytical tool. Bremsstrahlung production may be regarded as radiative capture by solids and is therefore the inverse process to the well known photoemission. In contrast to photoemission which probes occupied electronic states at solid surfaces, Bremsstrahlung spectroscopy opens up the possibility to investigate unoccupied electronic states including the important region between Fermi- and vacuum energy. Measurements on polycrystalline materials will be discussed on the basis of an isotropic three step model for Bremsstrahlung emission. More recent experiments on single crystals with electrons of well defined energy and initial momentum $\text{k}\text{}$ have demostrated that $\text{k}\text{}$-resolved spectroscopy provides energy versus momentum dispersion relations for unoccupied bands. Application of spin polarized electron beams has advanced $\text{k}\text{}$-resolved Bremsstrahlung spectroscopy to a state of maturity comparable to spin polarized angle resolved photoemission. This paper attempts to review the development and summarize the present state of ultraviolet Bremsstrahlung isochromat spectroscopy.     

EFFECT OF U.V.-IRRADIATION ON SEDIMENTATION BEHAVIOR OF VARIOUS PROTEINS

Abstract— Moderate u.v.-doses (2537 Å) sufficient to reduce enzymatic activities of native enzymes up to about 90 per cent, in general do not produce measurable amounts of smaller dialyzable fragments.
The disappearance of the original boundary in sedimentation diagrams is mostly due to the formation of rapidly sedimenting polydispersed material. Generally the sedimentation constants of the native proteins are not significantly changed. The boundaries, however, often loose their symmetry. The quantum yields for the disappearance of the original boundaries are roughly inversely proportional to the molecular weights. The number of molecules disappearing from the main peak is smaller than the number of molecules inactivated by a given dose. The data indicate that ultracentrifugation provides no satisfactory method for separation of native molecules from the damaged and inactivated. Proteins with labile quaternary structures (e.g. thyroglobulin or hemocyanine) which tend to dissociate under very mild conditions show an enhanced dissociation after u. v.-irradiation.     

Signal broadening in potential modulation differentiation

A method is developed for handling the effect of a finite amplitude on the results of potential modulation differentiation. The procedure is applied to harmonic modulation and allows to extrapolate measured Fourier coefficients to zero modulation amplitude. It is therefore possible to use modulation amplitudes as dictated by signal-to-noise considerations avoiding dynamical broadening of the detected signal. The formalism can be easily extended to combine with dynamic background subtraction. Examples are given for soft x-ray appearance potential measurements.     

Unoccupied electronic states on Ni(100) induced by A c(2 × 2) oxygen overlayer

Bremsstrahlung isochromat spectra at hω₀ = 9.7 eV for electrons normally incident on a clean Ni(100) surface are compared to emission from Ni(100) with an ordered c(2 × 2) oxygen overlayer. We observe strong emission due to adsorbate induced antibonding electronic states near E_F and a simultaneous attenuation of previously identified direct bulk interband transitions. The results are in accord with theoretical predictions.     

Bestimmung von T-2-Toxin in pflanzlichen Nahrungsmitteln

Zusammenfassung Ein Verfahren zur quantitativen Bestimmung von T-2-Toxin in verschimmeltem Reis bzw. Mais durch Extraktion, dünnschicht-chromatographische Trennung und Fluorescenzintensitätsmessung der mit H₂SO₄ behandelten DC-Platte wird vorgestellt. Fluorescenzabsorptions- und Fluorescenzemissionsspektrum werden angegeben. Die Abhängigkeit der Mycotoxinkonzentration von der Fluorescenzintensität wird durch eine Gleichung beschrieben. Die analytische Detektion von T-2-Toxin läßt sich durch ein 4-(p-Nitrobenzyl)pyridin-Derivat und dessen Absorptionsspektrum bestätigen. Versuche mit zugesetztem T-2-Toxin zeigten einen Analysenfehler von weniger als 10%.

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Determination of T-2-toxin in vegetable foodstuffs1. T-2-toxin in mouldy rice and maize

Summary A procedure is described for the determination of T-2 toxin in extracts from mouldy rice and maize by thin-layer chromatography (TLC) and subsequent fluorescence intensity measurement of the H₂SO₄-treated TLC plates. The fluorescence absorption and emission spectra are presented. The dependence of the concentration of the mycotoxin on fluorescence intensity is described by an equation. The detection of T-2 toxin can be confirmed by colour reaction with 4-(p-nitrobenzyl)pyridine yielding a blue derivative. Experiments with added toxin revealed an analytical error smaller than 10%.