Turbulent Thermalization

We study, analytically and with lattice simulations, the decay of coherent field oscillations and the subsequent thermalization of the resulting stochastic classical wave-field. The problem of reheating of the Universe after inflation constitutes our prime motivation and application of the results. We identify three different stages of these processes. During the initial stage of ``parametric resonance'', only a small fraction of the initial inflaton energy is transferred to fluctuations in the physically relevant case of sufficiently large couplings. A major fraction is transfered in the prompt regime of driven turbulence. The subsequent long stage of thermalization classifies as free turbulence. During the turbulent stages, the evolution of particle distribution functions is self-similar. We show that wave kinetic theory successfully describes the late stages of our lattice calculation. Our analytical results are general and give estimates of reheating time and temperature in terms of coupling constants and initial inflaton amplitude.Comment: 27 pages, 13 figure

Energetic particle influence on the Earth's atmosphere

This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere

Species diversity and decomposition in laboratory aquatic systems: the role of species interactions

P>1. Interest in the effects of biodiversity on ecosystem processes is increasing, stimulated by the global species decline. Different hypotheses about the biodiversity-ecosystem functioning (BEF) relationship have been put forward and various underlying mechanisms proposed for different ecosystems. 2. We investigated BEF relationships and the role of species interactions in laboratory experiments focussing on aquatic decomposition. Species richness at three different trophic levels (leaf detritus, detritus-colonising fungi and invertebrate detritivores) was manipulated, and its effects on leaf mass loss and fungal growth were assessed in two experiments. In the first, monocultures and mixtures of reed (Phragmites australis), alder (Alnus glutinosa) and oak (Quercus cerris) leaf disks were incubated with zero, one or eight fungal species. Leaf mixtures were also incubated with combinations of three and five fungal species. In the second experiment, reed leaf disks were incubated with all eight fungal species and offered to combinations of one, two, three, four or five macroinvertebrate detritivores with different feeding modes. 3. Results from the first experiment showed that leaf mass loss was directly related to fungal mass and varied unimodally with the number of fungi, with a maximum rate attained at intermediate diversity in oak and reed and at maximum diversity in alder (the fastest decomposing leaf). 4. Mixing litter species stimulated fungal growth but interactions between species of fungi slowed down decomposition. In contrast, mixtures of macroinvertebrate detritivores reduced fungal mass and accelerated leaf decomposition. Possible explanations of the positive relationship between detritivore diversity and decomposition are a reduction in fungal dominance and a differentiation in the use of different resource patches promoted by higher fungal diversity. 5. In conclusion, the results show a general increase in decomposition rate with increasing biodiversity that is controlled by within- and between-trophic level interactions, and support the hypothesis of both bottom-up and top-down effects of diversity on this process