Zur Trennung von Gasgemischen

Ohne Zusammenfassung     

Mediated coadsorption at the liquid-solid interface: Stabilization through hydrogen bonds

Stable adsorption of 1,3,5-tris(4-pyridyl)-2,4,6-triazine (TPT) molecules from the liquid phase was only observed in binary solutions, that is, in the presence of a second (adsorptive) species. The process of mediated coadsorption of a molecular species at the liquid-solid interface was accomplished through complexation of TPT with a second type of molecule acting as a "molecular glue" via hydrogen bonds. Scanning tunneling microscopy (STM) was utilized to investigate the structure of the coadsorbed monolayers at the liquid-solid interface. Trimesic acid (TMA) and terephthalic acid (TPA)--both benzene rings with disposed carboxylic acid groups-were appropriate to precipitate the stable adsorption of TPT. According to the different symmetry and number of carboxylic acid groups, various networks were observed.     

Nucleic acid based biosensors: the desires of the user

The need for nucleic acid based diagnostic tests has increased enormously in the last few years. On the one hand, this has been stimulated by the discovery of new hereditary genetic disease loci following the completion of the Human Genome Project, but also by the presence of new rapidly spreading viral threats, such as that of the SARS epidemic, or even micro-organisms released for the purpose of biological warfare. As in many instances rapid diagnoses of specific target genetic loci is required, new strategies have to be developed, which will allow this to be achieved directly at the point-of-care setting. One of these avenues being explored is that of biosensors. In this review, we provide an overview of the current state of the art concerning the high-throughput analysis of nucleic acids, and address future requirements, which will hopefully be met by new biosensor-based developments.     

Distributed delays stabilize ecological feedback systems

We consider the effect of distributed delays in predator-prey models and ecological food webs. Whereas the occurrence of delays in population dynamics is usually regarded a destabilizing factor leading to the extinction of species, we here demonstrate complementarily that delay distributions yield larger stability regimes than single delays. Food webs with distributed delays closely resemble nondelayed systems in terms of ecological stability measures. Thus, we state that dependence of dynamics on multiple instances in the past is an important, but so far underestimated, factor for stability in dynamical systems.     

Determination of the orbital moment and crystal-field splitting in LaTiO3

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in LaTiO3 is strongly reduced from its ionic value, both below and above the Ne el temperature. Using Ti L2,3 x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the t2g subshell is about 0.12-0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.     

Influence of the dynamic ergodic divertor on the density limit in TEXTOR

A significant influence of the dynamic ergodic divertor (DED) on the density limit in TEXTOR has been found. In Ohmic discharges, where without DED detachment normally arises at the density limit, a MARFE (multifaceted asymmetric radiation from the edge) develops when the DED is operated in a static regime. The threshold of the MARFE onset in the neutral beam heated plasmas is increased by applying 1 kHz ac DED at the high-field side. The theoretical predictions based on the parallel energy balance taking poloidal asymmetries into account agree well with the experimental observation.     

Quantum-degenerate mixture of fermionic lithium and bosonic rubidium gases

We report on the observation of sympathetic cooling of a cloud of fermionic 6Li atoms which are thermally coupled to evaporatively cooled bosonic 87Rb. Using this technique we obtain a mixture of quantum-degenerate gases, where the Rb cloud is colder than the critical temperature for Bose-Einstein condensation and the Li cloud is colder than the Fermi temperature. From measurements of the thermalization velocity we estimate the interspecies s-wave triplet scattering length |amx|=20(+9)(-6)aB. We found that the presence of residual rubidium atoms in the |2, 1> and the |1, -1> Zeeman substates gives rise to important losses due to inelastic collisions.