The formation of planetary disks and winds: an ultraviolet view

Planetary systems are angular momentum reservoirs generated during star formation. This accretion process produces very powerful engines able to drive the optical jets and the molecular outflows. A fraction of the engine energy is released into heating thus the temperature of the engine ranges from the 3000K of the inner disk material to the 10MK in the areas where magnetic reconnection occurs. There are important unsolved problems concerning the nature of the engine, its evolution and the impact of the engine in the chemical evolution of the inner disk. Of special relevance is the understanding of the shear layer between the stellar photosphere and the disk; this layer controls a significant fraction of the magnetic field building up and the subsequent dissipative processes ougth to be studied in the UV. This contribution focus on describing the connections between 1 Myr old suns and the Sun and the requirements for new UV instrumentation to address their evolution during this period. Two types of observations are shown to be needed: monitoring programmes and high resolution imaging down to, at least, milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure

Copper and Barium Abundances in the Ursa Major Moving Group

We present Cu and Ba abundances for 7 G-K dwarf stars, members of the solar-metallicity, 0.3 Gyr old Ursa Major Moving Group. All analyzed member stars show [Ba/Fe] excesses of +0.3-plus, associated with [Cu/Fe] deficiencies of up to -0.23 dex. The present results suggest that there is an anti-correlation between the abundances of Cu and the heavy elements produced by the main component of the neutron capture s-process. Other possible anomalies are Na and C deficiencies with respect to normal solar-metallicity stars. The new data do not confirm the recent claim that the group member HR6094 is a Ba dwarf star.Comment: 8 pages, 6 figures, accepted to MNRA

The influence of statistical properties of Fourier coefficients on random surfaces

Many examples of natural systems can be described by random Gaussian surfaces. Much can be learned by analyzing the Fourier expansion of the surfaces, from which it is possible to determine the corresponding Hurst exponent and consequently establish the presence of scale invariance. We show that this symmetry is not affected by the distribution of the modulus of the Fourier coefficients. Furthermore, we investigate the role of the Fourier phases of random surfaces. In particular, we show how the surface is affected by a non-uniform distribution of phases

Topologically Protected Zero Modes in Twisted Bilayer Graphene

We show that the twisted graphene bilayer can reveal unusual topological properties at low energies, as a consequence of a Dirac-point splitting. These features rely on a symmetry analysis of the electron hopping between the two layers of graphene and we derive a simplified effective low-energy Hamiltonian which captures the essential topological properties of twisted bilayer graphene. The corresponding Landau levels peculiarly reveal a degenerate zero-energy mode which cannot be lifted by strong magnetic fields.Comment: 5 pages, 3 figures; published versio

Farm Knowledge Co-Production at an Old Amazonian Frontier: Case of the Agroforestry System in Tomé-Açu, Brazil

This paper addresses how co-producing knowledge can assist local farmers in reshaping their territories into sustainable farming systems. We describe the emergence and consolidation of an agroforestry system in an Eastern Amazon forest frontier, unpacking the co-production of a new farming system over recent decades. Instead of assuming pre-defined categories (e.g., traditional/technical, local/external), the analysis focuses on interactions among knowledge holders and how multiple knowledge sources are intercalated. The analysis is based on long-term ethnographic research, comprising of over 70 interviews, visits to 40 farm fields, and participation in several local meetings and four annual seminars. The agroforestry system locally called SAFTA has emerged from a farming crisis experienced by mid-scale farmers of Japanese descent. Grounded in traditional Amazonian farming practices, SAFTA has been enriched by scientific and organizational knowledge from various sources to become a local solution that reconciles economic, social and environmental demands. Built on a few basic principles, this new farm system enables flexibility in crop field designs according to each farmers preferences and available resources. SAFTA knowledge has spilled over to other farmer groups and has helped develop an innovative agroforestry system for oil-palm cultivation. The SAFTA model has been consolidated, legitimized by a range of national and international actors, and gradually institutionalized in policy and commercial circles. This case sheds light on the potential of knowledge co-production to transform complex rural landscapes featuring cultural diversity, asymmetrical relationships and history of land-use change. Analysis of social interactions and knowledge integration mechanisms give insight into how co-production under local cultural diversity and asymmetrical relations may yield mutual benefits among local farmer groups