Open-system theory of photodetection

The transfer of the statistical properties of the electromagnetic field to the detector signal is reinvesti?ated in terms of the Dicke model with coupling of the photosensitive atoms to a reservoir. The interrelated dynamics of the atomic moments and the field moments as well as the photocounting rate for any initial field state are given in terms of not only the field-atom, but also the atom-reservoir, coupling constants.     

Pyrolyse-Gas-Chromatographie in der Lebensmittelchemie

Summary An overview is given on the application of pyrolytical methods in the GC of food samples. Curie point pyrolysis is employed in particular, as this technique assures reproducible heat treatment. The reproducibility was tested by pyrolizing several mono- and polysaccharides. The analysis of thickening agents and especially of couleurs and melanoidines is dealt with in detail.     

Investigations of model systems of the Maillard reaction: II. Pyrolysis—gas chromatography—mass spectrometry analysis of some non-volatile products of the reaction of d-glucose and 4-chloroaniline

Low molecular weight compounds resulting from the reaction of d-glucose with 4-chloroaniline were subjected to Curie-point pyrolysis, and the cleavage products were identified by gas chromatography—mass spectrometry. Based on their structures, some general features were detected which possibly are applicable to the structural analysis of higher molecular weight Maillard compounds of this type. It is shown in one example that pyrolysis and electron impact mass spectrometry obviously prefer similar fragmentation patterns. In addition to Curie-point pyrolysis, Pyrotest pyrolysis and dry distillation were also tested but yielded less reproducible results.     

Design and applications of a home-built in situ FT-Raman spectroscopic cell

In the field of heterogeneous catalysis, in situ spectroscopy is one of the topics with growing interest. The characterization of a catalyst under working conditions is essential to identify the catalytic active site and to study the relation between the surface structure of a catalyst and its catalytic performance. For the first time, the design of an in situ spectroscopic cell for FT-Raman is presented and its performance is demonstrated by monitoring the thermal conversion of as synthesized mesoporous titanium and by characterizing the molecular surface structure of the vanadium oxides grafted on MCM-48 after exposure to a probe molecule. The results in both cases indicate that the in situ FT-Raman cell is a promising technique for characterizing the molecular surface structure of catalyst materials.     

Subthreshold kaon production in Au on Au collisions at 1 GeV/u

Subthreshold kaon production in¹⁹⁷ Au+¹⁹⁷ Au collisions at 1.0 GeV/u has been investigated with the Kaon Spectrometer at SIS. At _lab =44±4 we found aK ⁺/p ratio of>3 · 10^–4 for the momentum range 650 MeV/c to 1150 MeV/c.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Imaging Local Proton Fluxes through a Polycarbonate Membrane by Using Scanning Electrochemical Microscopy and Functionalized Alkanethiols

A new application of scanning electrochemical microscopy (SECM) to probe the transport of protons through membranes is described. Herein, a probe ultramicroelectrode (UME) is modified with a self‐assembled monolayer (SAM) of 11‐mercaptoundecanoic acid to qualitatively image areas within different pH regions above a track‐etched membrane. The current response of the modified electrode in the presence of potassium hexacyanoferrate as electroactive component is different in acidic and alkaline solutions. Depending on the pH value of the solution, the SAM‐covered electrode exposes either a neutral or a negatively charged insulating monolayer at pH 3 or 7, respectively, which leads to an increase/decrease in the faradaic current due to electrostatic interactions between the neutral/charged surface and the charged redox mediator. Therefore, local pH changes in the close vicinity of a membrane‐like substrate lead to different current responses recorded at the tip electrode when scanning above the surface.