On dispersive stability of Hamiltonian systems on lattices

We study the long-time dynamics of oscillations in lattices of infinitely many particles interacting via certain non-linear potentials. The aim is to proof dispersive stability of such Hamiltonian systems analogously to results known for PDEs. To do so we first recapitulate the dynamics of linear Hamiltonian systems on an infinite chain and give optimal decay rates based on the dispersion relation. Based on this we proof that if the non-linearity is weak enough, the non-linear system shows a similar behaviour like its linearization. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Probing porous media with gas diffusion NMR.

We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for probing the structure of porous media. In random packs of glass beads, using both laser-polarized and thermally polarized xenon gas, we find that GD-NMR can accurately measure the pore space surface-area-to-volume ratio, S/V rho, and the tortuosity, alpha (the latter quantity being directly related to the system's transport properties). We also show that GD-NMR provides a good measure of the tortuosity of sandstone and complex carbonate rocks.     

On the coupling of compressible and incompressible regions

This contribution deals with the coupling of compressible to incompressible flow regions in one space dimension. Iterative coupling procedures based on jump conditions across the interface have been derived. They couple the solution of a half Riemann problem on the compressible side to the analytical solution of the incompressible side. For the incompressible equations, the pressure is split into a thermodynamic background and a hydrodynamic part. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Birth and growth of cavitation bubbles within water under tension confined in a simple synthetic tree

Water under tension, as can be found in several systems including tree vessels, is metastable. Cavitation can spontaneously occur, nucleating a bubble. We investigate the dynamics of spontaneous or triggered cavitation inside water filled microcavities of a hydrogel. Results show that a stable bubble is created in only a microsecond time scale, after transient oscillations. Then, a diffusion driven expansion leads to filling of the cavity. Analysis reveals that the nucleation of a bubble releases a tension of several tens of MPa, and a simple model captures the different time scales of the expansion process.     

On-site airborne pheromone sensing

Pheromones and other semiochemicals play an important role in the natural world by influencing the behavior of plants, mammals, and insects. In the latter case, species-dependent pheromone communication has numerous applications, including the detection, trapping, monitoring and guiding of insects, as well as pest management in agriculture. On-site sensors are desirable when volatile organic compounds (VOCs) are used as semiochemicals. Insects have evolved highly selective sensors for such compounds, so biosensors comprising complete insects, isolated organs or individual proteins can be highly effective. However, isolated insect organs have a limited lifetime as biosensor, so biomimetic approaches are needed for prolonged monitoring, novel applications, or measurements in challenging environments. We discuss the development of on-site biosensors and biomimetic approaches for airborne-pheromone sensing, together with biomimetic VOC sensor systems. Furthermore, the infochemical effect describing the anthropogenic contamination of the ecosystem through semiochemicals, will be considered in the context of novel on-site pheromone sensing-systems.     

The Application of a Sol-Gel Technique to Preparation of a Heavy Metal Biosorbent from Yeast Cells

In this work we compared biosorbents obtained by encapsulation of polysaccharides, isolated from waste brewing biomass, in sol-gel derived silicates and an organic polymer. Biosorbents were prepared by mixing cross-linking-agents—organic or siliceous—with dried cells envelopes. Siliceous prepolymers were synthezised via transesterification and hydrolysis from tetraethoxysilane (TEOS) and methanol. Sorption of Cd2+, Cu2+ and Ag+ by biosorbent granules (0.25–0.6 mm) was examined in batch and in a packed column. The biosorbent prepared by interesterification of TEOS showed a 2–3 times higher intensity of sorption than the biosorbent cross-linked with epichlorohydrin (the most effective cross-linking organic agent) while the sorption capacity of both biosorbents was equal. The specific surface area of the silica matrix was 597 m2/g but only traces of metals were sequestered from solution with a concentration of Cd2+ of 50 mg/l. The biosorbent with a silica matrix is a heterogeneous material containing microporous matrix inclusions of thin cell walls. Its high sorption intensity and good mechanical strength will be useful in continuous metal uptake of low concentrations of metals.