Institutskolloquium des IPP 2016

Ort: Garching und Greifswald

En route to electron/positron pair plasmas

Institutskolloquium
The large mass imbalance between ions andelectrons — and the resulting separation of the two species’ length and timescales — is a cornerstone of traditional plasma physics.  Therefore, to consider the novel behavior ofa “pair plasma”, comprising particles with opposite charge but equal mass, isto revisit much of plasma physics from the ground up.  To date, over a thousand journal articleshave been devoted to this topic, describing a variety of analytical andcomputational treatments, but the experimental side of the investigation isstill in its nascence.  Laboratorycreation and confinement of electron/positron plasmas would enable the firsttests of many theory and simulation predictions (e.g., the stabilization ofanomalous transport mechanisms), with implications for our understanding notonly of pair plasmas (and astrophysical phenomena in which they play a role)but also of traditional electron/ion plasmas. This is the goal of the APEX/PAX (APositron-Electron eXperiment/PositronAccumulation eXperiment) project, in which a world-class positron beam(NEPOMUC, at FRM-II) is being combined with state-of-the-art techniques fromnon-neutral plasma physics.  This talkwill give an overview of milestones achieved in the past several years,including the demonstration of efficient ExB injection and subsequentconfinement (τ = 3-5 ms) of cold positrons in a dipole magnetic field, as wellas the upcoming upgrade from a supported permanent magnet to a supported HTSC(high-temperature superconductor) coil, then to a levitated HTSC coil suitablefor the simultaneous confinement of electrons and positrons. [mehr]

Transition to Darwinian evolution - towards the origin of the very first species

Institutskolloquium
The concept of Darwinian evolution relies on vertical gene transfer from one generation to the next. Such evolution brings about ever more species that originated from a universal common ancestor, the very first species. In contrast, it is hypothesized that in the era just before that species existed, life was fundamentally collective with genetic material freely shared through massive horizontal gene transfer (HGT). How did the era of collective evolution come to an end and start the Darwinian era we live in today? Here we propose a stochastic model dynamics that offers a fundamental mechanism for such a way out of collective evolution. The model suggests that HGT-dominated dynamics may have been intermittently interrupted by selection-driven processes during which genotypes became fitter and decreased their inclination towards HGT. Stochastic switching in the population dynamics with three-point (hypernetwork) interactions may have destabilized the HGT-dominated collective state and essentially contributed to the emergence of vertical descent and the first well-defined species in early evolution. A systematic nonlinear analysis of the stochastic model dynamics supports this view. Our findings thus suggest a viable direction out of early collective evolution, potentially enabling the start of individuality and vertical Darwinian evolution. [mehr]
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