On radiation-zone dynamos

It is shown that the magnetic current-driven (`kink-type') instability produces flow and field patterns with helicity and even with \alpha-effect but only if the magnetic background field possesses non-vanishing current helicity \bar{\vec{B}}\cdot curl \bar{\vec{B}} by itself. Fields with positive large-scale current helicity lead to negative small-scale kinetic helicity. The resulting \alpha-effect is positive. These results are very strict for cylindric setups without z/I>-dependence of the background fields. The sign rules also hold for the more complicated cases in spheres where the toroidal fields are the result of the action of differential rotation (induced from fossil poloidal fields) at least for the case that the global rotation is switched off after the onset of the instability.Comment: 6 pages, 6 figures, submitted to Proceedings of IAU Symp. 274: Advances in Plasma Astrophysic

Low power memory allocation and mapping for area-constrained systems-on-chips

Large fractions of today’s embedded systems’ power consumption can be attributed to the memory subsystem. In order to reduce this fraction, we propose a mathematical model to optimize on-chip memory configurations for minimal power. We exploit the power reduction effect of splitting memory into subunits with frequently accessed addresses mapped to small memories. The definition of an integer linear programming model enables us to solve the twofold problem of allocating an optimal set of memory instances with varying size on the one hand and finding an optimal mapping of application segments to allocated memories on the other hand. Experimental results yield power reductions of up to 82 % for instruction memory and 73 % for data memory. Area usage, at the same time, deteriorates by only 2.1 %, respectively, 1.2 % on average and even improves in some cases. Flexibility and performance of our model make it a valuable tool for low power system-on-chip design, either for efficient design space exploration or as part of a HW/SW codesign synthesis flow

Eddy viscosity and turbulent Schmidt number by kink-type instability of strong toroidal magnetic fields

The potential of the nonaxisymmetric magnetic instability to transport angular momentum and to mix chemicals is probed considering the stability of a nearly uniform toroidal field between conducting cylinders with different rotation rates. The fluid between the cylinders is assumed as incompressible and to be of uniform density. With a linear theory the neutral-stability maps for m=1 are computed. Rigid rotation must be subAlfvenic to allow instability while for differential rotation with negative shear also an unstable domain with superAlfvenic rotation exists. The rotational quenching of the magnetic instability is strongest for magnetic Prandtl number Pm=1 and becomes much weaker for Pm unequal 1. The effective angular momentum transport by the instability is directed outwards(inwards) for subrotation(superrotation). The resulting magnetic-induced eddy viscosities exceed the microscopic values by factors of 10-100. This is only true for superAlfvenic flows; in the strong-field limit the values remain much smaller. The same instability also quenches concentration gradients of chemicals by its nonmagnetic fluctuations. The corresponding diffusion coefficient remains always smaller than the magnetic-generated eddy viscosity. A Schmidt number of order 30 is found as the ratio of the effective viscosity and the diffusion coefficient. The magnetic instability transports much more angular momentum than that it mixes chemicals.Comment: 9 pages, 12 figures, submitte

Positive-strand RNA viruses-a Keystone Symposia report

Positive-strand RNA viruses have been the cause of several recent outbreaks and epidemics, including the Zika virus epidemic in 2015, the SARS outbreak in 2003, and the ongoing SARS-CoV-2 pandemic. On June 18-22, 2022, researchers focusing on positive-strand RNA viruses met for the Keystone Symposium "Positive-Strand RNA Viruses" to share the latest research in molecular and cell biology, virology, immunology, vaccinology, and antiviral drug development. This report presents concise summaries of the scientific discussions at the symposium

The Twannberg iron meteorite strewn field in the Swiss Jura mountains: insights for Quaternary environmental conditions

The ~ 10 km 2 strewn field of the Twannberg type IIG iron meteorite is located in the Swiss Jura Mountains, 30 km northwest of Bern. The strewn field has been mapped by a group of citizen scientists since 2006, yielding more than 2000 meteorite fragments with a total mass of 152.7 kg until the end of 2022. With a terrestrial age of 176 ± 19 ka and a minimum pre-atmospheric mass of ~ 250 t, the Twannberg meteorite is a local time marker in an area with a poorly-known paleoenvironmental history. The Twannberg strewn field is located just outside of the maximum extent of ice during the Last Glacial Maximum (LGM). On the Mont Sujet, meteorites are size-sorted in a 6-km long section of the primary strewn field (altitude 945-1370 m a.s.l.), indicating a fall direction from east-northeast to west-southwest (azimuth approximately 250°). On the Twannberg plateau and in the Twannbach gorge, meteorites are not size-sorted and occur in a ~ 5.7-km long area associated with till and recent stream sediments (altitude 430-1075 m a.s.l.). The mass distribution of meteorites on the Twannberg plateau demonstrate that these meteorites were not found where they fell but that they must have been transported up to several km by glacier ice flow after the fall. The distribution of meteorites and of glacially transported Alpine clasts on the Mont Sujet and on the Chasseral chain indicates the presence of local ice caps and of an approximately 200-m higher Alpine ice surface with respect to the LGM at the time of fall. This high ice level during MIS 6 (Marine Isotopic Stage 6, 191-130 ka) indicated by the meteorite distribution is consistent with surface exposure ages of 50-144 ka from nearby resting erratic boulders at altitudes of up to 1290 m a.s.l., including the newly dated Jobert boulder (63 ka). These boulders indicate an ice level ~ 400 m higher than during LGM at a time not later than MIS 6. Post-LGM luminescence ages of loesscontaining meteorites on the Mont Sujet and 14 C ages of materials associated with meteorite finds indicate relatively young pedoturbation and increased oxidation of meteorites since ~ 7300 cal BP, possibly correlated with deforestation and enhanced erosion resulting from increased human activities since the Neolithic. This study shows that Twannberg meteorites in their palaeoenvironmental context provide valuable information about ice levels and transport directions during MIS 6 and about their interaction with the post-LGM environmental conditions. The unique Twannberg strewn field has the potential to reveal more valuable information