On the origin of the cosmic elements and the nuclear history of the universe

The quest for the energy source of stars, capable of maintaining their long-lasting brightness, has puzzled physicists during centuries. Early suggestions, due to Julius R. von Mayer, John James Waterson, Hermann von Helmholtz, and William Thomson (Lord Kelvin), among others, relied on the conversion of gravitational potential energy into heat. However, the age of the Sun inferred in this framework was only a few million years, a value clearly at odds with estimates based on geological records

Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries: II. Systems with a giant component

By reanalyzing the Hipparcos Intermediate Astrometric Data of a large sample of spectroscopic binaries containing a giant, we obtain a sample of 29 systems fulfilling a carefully derived set of constraints and hence for which we can derive an accurate orbital solution. Of these, one is a double-lined spectroscopic binary and six were not listed in the DMSA/O section of the catalogue. Using our solutions, we derive the masses of the components in these systems and statistically analyze them. We also briefly discuss each system individually.Comment: 15 pages, 25 figures, Accepted in A&

Parallel action of AtDRB2 and RdDM in the control of transposable element expression.

International audienceIn plants and animals, a large number of double-stranded RNA binding proteins (DRBs) have been shown to act as non-catalytic cofactors of DICERs and to participate in the biogenesis of small RNAs involved in RNA silencing. We have previously shown that the loss of Arabidopsis thaliana's DRB2 protein results in a significant increase in the population of RNA polymerase IV (p4) dependent siRNAs, which are involved in the RNA-directed DNA methylation (RdDM) process. Surprisingly, despite this observation, we show in this work that DRB2 is part of a high molecular weight complex that does not involve RdDM actors but several chromatin regulator proteins, such as MSI4, PRMT4B and HDA19. We show that DRB2 can bind transposable element (TE) transcripts in vivo but that drb2 mutants do not have a significant variation in TE DNA methylation. We propose that DRB2 is part of a repressive epigenetic regulator complex involved in a negative feedback loop, adjusting epigenetic state to transcription level at TE loci, in parallel of the RdDM pathway. Loss of DRB2 would mainly result in an increased production of TE transcripts, readily converted in p4-siRNAs by the RdDM machinery