Matrixunabh?ngige kontinuierliche Dampfraum-Gas-Chromatographie

Zusammenfassung Ausgehend von systematischen Untersuchungen des Matrixeinflusses bei der gas-chromatischen Dampfraum-Analyse und aufgrund prinzipieller Überlegungen wird ein neues Arbeitsverfahren vorgestellt, das es erlaubt, sehr viele Stoffe matrixunabhängig zu bestimmen. Dieses wird durch eine fast quantitative Überführung der flüchtigen Komponenten in das Strip-Gas durch Zusatz von Salzlösungen und durch eine kontinuierliche multiple Gegenstromextraktion über einem strömenden Flüssigkeitsfilm erreicht. Die daraus erwachsenden Vorteile dieses Verfahrens gegenüber der herkömmlichen Technik werden anhand von Beispielen erläutert und aufgezeigt.

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Matrix-independent continuous Head-Space gas-chromatography

Summary A new Head-Space gas-chromatography is presented by means of which it is possible to perform a continuous and selective measurement of numerous organic components dissolved in water. By addition of salt solutions to the sample and a continuous multiple distribution between a thin film of the fluid sample and an inert strip-gas, organic components are nearly quantitatively transferred from the water sample to the strip-gas. The transfer is widely unaffected by the matrix components. The strip-gas, containing more then 95% of the organic components, is analyzed by gas-chromatography. The advantages of the new method as against the hitherto used techniques are demonstrated by means of several examples.

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Die vorliegende Arbeit wurde mit Mitteln des Ministers für Wissenschaft und Forschung des Landes Nordrhein-Westfalen gefördert. Dafür sei an dieser Stelle herzlich gedankt.     

Charge screening and mass spectrum in abelian gauge theories

We give a rigorous proof confiriming a statement of Swieca on a connection between the charge and the mass spectrum in Abelian gauge theories. Our argument is based on a detailed analysis of the momentum-space behavior of form factors in the absence of local charge-carrying fields.     

The role of shape and relative submergence on the structure of wakes of low-aspect-ratio wall-mounted bodies

The effects of shape and relative submergence (the ratio of flow depth to obstacle height, d/H) are investigated on the wakes around four different low-aspect-ratio wall-mounted obstacles at Re _H  = 17,800: semi-ellipsoids with the major axes of the base ellipses aligned in the streamwise and transverse directions, and two cylinders with aspect ratios matching the ellipsoids (H/D = 0.89 and 0.67, where D is the maximum transverse dimension). Particle Image Velocimetry was used to interrogate the flow. Streamwise features observed in the mean wake include counter-rotating distributions of vorticity inducing downwash (tip structures), upwash (base structures), and horseshoe vortices. In particular, the relatively subtle change in geometry produced by the rotation of the ellipsoid from the streamwise to the transverse orientation results in a striking modification of the mean streamwise vorticity distribution in the wake. Tip structures are dominant in the former case, while base structures are dominant in the latter. A vortex skeleton model of the wake is proposed in which arch vortex structures, shed from the obstacle, are deformed by the competing mechanisms of Biot-Savart self-induction and the external shear flow. The selection of tip or base structures in the ellipsoid wakes is caused by tilting of the arch structures either upstream or downstream, respectively, which is governed by ellipsoid curvature. An inverse relationship was observed between the relative submergence and the strength of the base structures for the ellipsoids, with a dominant base structure observed for d/H = 1 in both cases. These results demonstrate a means by which to achieve significant modifications to flow structure and thereby also to transport mechanisms in the flow. Therefore, this work provides insight into the modeling and control of flow over wall-mounted bodies.     

Identification of sulfoglycolipids from the alga Porphyridium purpureum by matrix-assisted laser desorption/ionisation quadrupole ion trap time-of-flight mass spectrometry

Sulfoglycolipids, isolated from different phototrophic organisms, particularly plants and algae, have already been identified as bioactive compounds. In addition to their antiviral activity their influence on the immune response in mammalian cells is the focus of many studies. For the first time it has been possible to investigate purified sulfoquinovosyldiacylglycerols (SQDGs) from the microalga Porphyridium purpureum by matrix-assisted laser desorption/ionisation (MALDI) in the negative ion reflectron mode. Thereby, different solid and ionic liquid matrices have been tested to improve signal intensity during the laser ionisation. By using the MALDI Trap time-of-flight (ToF) multiple-stage (MS(n)) hybrid mass spectrometer the fatty acid compositions of the SQDGs were analysed by MS, and confirmed by MS(2) and MS(3) experiments. Thereby, hexadecanoic acid (C16:0), octadecadienoic acid (C18:2), eicosatetraenoic acid (C20:4), and eicosapentaenoic acid (C20:5) were detected in the purified fraction of SQDGs. The localisation of hexadecanoic acid (C16:0) at the sn-2 position, and unsaturated fatty acids at the sn-1 position of the SQDGs, determined by specific enzymatic hydrolysis, marks a procaryotic biosynthesis of SQDGs in the eucaryotic alga cells.     

Ventral and dorsal streams processing visual motion perception (FDG-PET study)

ABSTRACT: BACKGROUND: Earlier functional imaging studies on visually induced self-motion perception (vection) disclosed a bilateral network of activations within primary and secondary visual cortex areas which was combined with signal decreases, i.e., deactivations, in multisensory vestibular cortex areas. This finding led to the concept of a reciprocal inhibitory interaction between the visual and vestibular systems. In order to define areas involved in special aspects of selfmotion perception such as intensity and duration of the perceived circular vection (CV) or the amount of head tilt, correlation analyses of the regional cerebral glucose metabolism, rCGM (measured by fluorodeoxyglucose positron-emission tomography, FDG-PET) and these perceptual covariates were performed in 14 healthy volunteers. For analyses of the visualvestibular interaction, the CV data were compared to a random dot motion stimulation condition (not inducing vection) and a control group at rest (no stimulation at all). RESULTS: Group subtraction analyses showed that the visual-vestibular interaction was modified during CV, i.e., the activations within the cerebellar vermis and parieto-occipital areas were enhanced. The correlation analysis between the rCGM and the intensity of visually induced vection, experienced as body tilt, showed a relationship for areas of the multisensory vestibular cortical network (inferior parietal lobule bilaterally, anterior cingulate gyrus), the medial parieto-occipital cortex, the frontal eye fields and the cerebellar vermis. The "earlier" multisensory vestibular areas like the parieto-insular vestibular cortex and the superior temporal gyrus did not appear in the latter analysis. The duration of perceived vection after stimulus stop was positively correlated with rCGM in medial temporal lobe areas bilaterally, which included the (para-)hippocampus, known to be involved in various aspects of memory processing. The amount of head tilt was found to be positively correlated with the rCGM of bilateral basal ganglia regions responsible for the control of motor function of the head. CONCLUSIONS: Our data gave further insights into subfunctions within the complex cortical network involved in the processing of visual-vestibular interaction during CV. Specific areas of this cortical network could be attributed to the ventral stream ("what" pathway) responsible for the duration after stimulus stop and to the dorsal stream ("where/how" pathway) responsible for intensity aspects.     

Cyclic polygons with rational sides and area

We generalise the notion of Heron triangles to rational-sided, cyclic n-gons with rational area using Brahmagupta's formula for the area of a cyclic quadrilateral and Robbins' formulæ for the area of cyclic pentagons and hexagons. We use approximate techniques to explore rational area n-gons for n greater than six. Finally, we produce a method of generating non-Eulerian rational area cyclic n-gons for even n and conjecturally classify all rational area cyclic n-gons.