Resazurin

Ohne Zusammenfassung     

Ueber die Wirkung des Magnesiums auf Salzl?sungen

Ohne Zusammenfassung     

Carbon nanostructures grown with electron and ion beam methods

We present a comparative study where carbon nanostructures were prepared by electron and ion beam methods. Thin films of 10×10 μm² area were prepared and analysed by Raman analysis, nanoindentation, energy dispersive X-ray analysis (EDX) and atomic force microscopy (AFM). The material formed is not soft and graphitic, but of intermediate hardness (6–13 GPa) and with Raman spectral features similar to those of hydrogenated amorphous carbon, although it contains a significant Ga content (up to 25 at. %). This study was used to form sharp AFM supertip structures which were used to image sintered ceramic samples and films of aligned carbon nanotubes. Compared to traditional Si tips, this gave an improved rendering of the sample’s aspect ratio although the resolution is limited by the diameter of the C supertips. PACS 81.05.Uw; 81.07.-b; 78.30.-j     

Intrinsic mechanical properties of ultra-thin amorphous carbon layers

In this work, we extracted the film's hardness (H_F) of ultra-thin diamond-like carbon layers by simultaneously taking into account the tip blunting and the substrate effect. As compared to previous approaches, which did not consider tip blunting, this resulted in marked differences (30-100%) for the H_F value of the thinner carbon coatings. We find that the nature of the substrate influences this intrinsic film parameter and hence the growth mechanisms. Moreover, the H_F values generally increase with film thickness. The 10 nm and 50 nm thick hydrogenated amorphous carbon (a-C:H) films deposited onto Si have H_F values of, respectively, ∼26 GPa and ∼31 GPa whereas the 10 nm and 50 nm thick tetrahedral amorphous carbon (t-aC) films deposited onto Si have H_F values of, respectively, ∼29 GPa and ∼38 GPa. Both the a-C:H and t-aC materials also show higher density and refractive index values for the thicker coatings, as measured, respectively by X-ray reflectometry and optical profilometry analysis. However, the Raman analysis of the a-C:H samples show bonding characteristics which are independent of the film thickness. This indicates that in these ultra-thin hydrogenated carbon films, the arrangement of sp² clusters does not relate directly to the hardness of the film.     

Improved liquid chromatographic method for the analysis of photosynthetic pigments of higher plants

The paper presents an improved reversed-phase LC method for the separation of the pigments from green leaves. A good separation of carotenoids and of their cis- and trans-isomers was achieved, especially for the separation of trans-lutein, zeaxanthin, cis-lutein, which are usually not well separated. No perfect separation of alpha-carotene, beta-carotene and pheophytin a was possible, but conditions for a perfect coelution of pheophytin a with either beta-carotene or alpha-carotene were established. Simultaneous equations allowing the determination of pheophytin a and alpha-carotene or pheophytin a and beta-carotene are also given.     

Use of cw-CRDS for studying the atmospheric oxidation of acetic acid in a simulation chamber

The coupling between cavity ring-down spectroscopy (CRDS) and an environmental chamber in the investigation of photo-induced reaction mechanisms is demonstrated for the first time. The development of the CRDS device and the corresponding analytical performances are presented. The first application is devoted to the investigation of the branching ratio of the ^?OH radical reaction of CH₃C(O)OH and CH₃C(O)OD under tropospheric conditions. An environmental chamber coupled to two complementary detection systems is used:

gas chromatography with FTIR spectroscopy for quantitative detection of acetic acid;

CRDS for quantitative detection of CO₂.

Investigation of the reaction kinetics of ^?OH+CH₃C(O)OH gives a rate constant of (6.5±0.5)×10^-13 cm³?molecule^-1?s^-1 (296 K) and shows good agreement with literature data. The product study indicates that the H-abstraction channel from the acid group is the dominant pathway with a branching ratio of (78±13)%, whereas the corresponding D-abstraction channel in the ^?OH+CH₃C(O)OD reaction represents only (36±7)%. This result could be attributed to a strong kinetic isotope effect. Glyoxylic acid has also been detected for the first time as by-product. These results illustrate the high interest of the CRDS technique in the investigation of atmospheric relevant problems.     

Evaluation of temperature gradients within combusting droplets in linear stream using two colors laser-induced fluorescence

The scope of this paper concerns the heating process of fuel droplets injected in a hot gaseous environment. The two colors laser-induced fluorescence technique allows measuring the temperature distribution within a droplet by scanning the droplet volume by a sufficiently small probe volume compared to the droplet volume itself. The temperature field is reconstructed using two approaches which have been compared. One is based on a geometrical optics model and the other is based on the 3D calculation of the internal excitation field within the droplet, using the generalized Lorenz-Mie theory. Experimental results have been obtained on a combusting monodisperse ethanol droplet stream (diameter around 200 m).