Brane-World Inflation and the Transition to Standard Cosmology

In the context of a five-dimensional brane-world model motivated from heterotic M-theory, we develop a framework for potential-driven brane-world inflation. Specifically this involves a classification of the various background solutions of (A)dS_5 type, an analysis of five-dimensional slow-roll conditions and a study of how a transition to the flat vacuum state can be realized. It is shown that solutions with bulk potential and both bane potentials positive exist but are always non-separating and have a non-static orbifold. It turns out that, for this class of backgrounds, a transition to the flat vacuum state during inflation is effectively prevented by the rapidly expanding orbifold. We demonstrate that such a transition can be realized for solutions where one boundary potential is negative. For this case, we present two concrete inflationary models which exhibit the transition explicitly.Comment: 50 pages, 3 figures, minor typos correcte

Oxidative stress in endurance flight: an unconsidered factor in bird migration

Migrating birds perform extraordinary endurance flights, up to 200 h non-stop, at a very high metabolic rate and while fasting. Such an intense and prolonged physical activity is normally associated with an increased production of reactive oxygen and nitrogen species (RONS) and thus increased risk of oxidative stress. However, up to now it was unknown whether endurance flight evokes oxidative stress. We measured a marker of oxidative damage (protein carbonyls, PCs) and a marker of enzymatic antioxidant capacity (glutathione peroxidase, GPx) in the European robin (Erithacus rubecula), a nocturnal migrant, on its way to the non-breeding grounds. Both markers were significantly higher in European robins caught out of their nocturnal flight than in conspecifics caught during the day while resting. Independently of time of day, both markers showed higher concentrations in individuals with reduced flight muscles. Adults had higher GPx concentrations than first-year birds on their first migration. These results show for the first time that free-flying migrants experience oxidative stress during endurance flight and up-regulate one component of antioxidant capacity. We discuss that avoiding oxidative stress may be an overlooked factor shaping bird migration strategies, e.g. by disfavouring long non-stop flights and an extensive catabolism of the flight muscles

Origins of Extragalactic Cosmic Ray Nuclei by Contracting Alignment Patterns induced in the Galactic Magnetic Field

We present a novel approach to search for origins of ultra-high energy cosmic rays. These particles are likely nuclei that initiate extensive air showers in the Earth's atmosphere. In large-area observatories, the particle arrival directions are measured together with their energies and the atmospheric depth at which their showers maximize. The depths provide rough measures of the nuclear charges. In a simultaneous fit to all observed cosmic rays we use the galactic magnetic field as a mass spectrometer and adapt the nuclear charges such that their extragalactic arrival directions are concentrated in as few directions as possible. Using different simulated examples we show that, with the measurements on Earth, reconstruction of extragalactic source directions is possible. In particular, we show in an astrophysical scenario that source directions can be reconstructed even within a substantial isotropic background.Comment: 14 pages, 15 figure

Reactive membrane extraction in biorefineries

2011 Spring.Includes bibliographical references.Separations account for 60-80% of the processing costs of most mature chemical processes. Membrane based separations offer several advantages over conventional technology such as lower energy costs and easy scale up. Here we focus on membrane extraction for removal of acetic acid, sulfuric acid, furfural, HMF and other toxic compounds from biomass hydrolysates. As membrane extraction is non-dispersive it overcomes the disadvantages of conventional extraction. Experiments have been conducted using dilute sulfuric acid pretreated corn stover (hydrolysate). Acetic acid, in its protonated form, is extracted into an organic phase consisting of octanol/oleyl alcohol and Alamine 336, a tertiary amine, containing aliphatic chains of 8-10 carbon atoms. Co-extraction of sulfuric acid leads to an increase in hydrolyste pH. The effect of aqueous and organic phase flow rates and temperature, on the rate of extraction of acetic acid and sulfuric acid has been investigated. Changes in the rates of acetic and sulfuric acid extraction may be explained by considering the structure of the complexes formed in the organic phase. We conducted computational modeling to elucidate the extraction process of Alamine 336 in different solvents. Extraction of carboxylic acids, Furfural and HMF in water and octanol was simulated using the Gaussian 03 package. In the past the extraction process has been explained by the direct interaction of the carboxylic acid with the Alamine 336 to form an ion pair. More carboxylic acids could be extracted through hydrogen bonding forming a dimer or trimer complex form with the Alamine 336, stabilized by the organic solvent. Hydrolysates treated by membrane extraction and conventional conditioning technologies were fermented using a glucose-xylose fermenting bacteria to determine the viability of membrane technology to detoxify biomass hydrolysates. Membrane extraction could be a viable hydrolysate detoxification technology because the other conditioning technologies do not remove acetic acid