Does multifractal theory of turbulence have logarithms in the scaling relations?

The multifractal theory of turbulence uses a saddle-point evaluation in determining the power-law behaviour of structure functions. Without suitable precautions, this could lead to the presence of logarithmic corrections, thereby violating known exact relations such as the four-fifths law. Using the theory of large deviations applied to the random multiplicative model of turbulence and calculating subdominant terms, we explain here why such corrections cannot be present.Comment: 7 pages, 1 figur

Tearing instability and periodic density perturbations in the slow solar wind

In contrast with the fast solar wind, that originates in coronal holes, the source of the slow solar wind is still debated. Often intermittent and enriched with low FIP elements -- akin to what is observed in closed coronal loops -- the slow wind could form in bursty events nearby helmet streamers. Slow winds also exhibit density perturbations which have been shown to be periodic and could be associated with flux ropes ejected from the tip of helmet streamers, as shown recently by the WISPR white light imager onboard Parker Solar Probe (PSP). In this work, we propose that the main mechanism controlling the release of flux ropes is a flow-modified tearing mode at the heliospheric current sheet (HCS). We use MHD simulations of the solar wind and corona to reproduce realistic configurations and outflows surrounding the HCS. We find that this process is able to explain long ($\sim 10-20$h) and short ($\sim 1-2$h) timescales of density structures observed in the slow solar wind. This study also sheds new light on the structure, topology and composition of the slow solar wind, and could be, in the near future, compared with white light and in situ PSP observations.Comment: 8 pages, 5 figures, accepted for publication in ApJ

Making Distributed User Interfaces Interruption-Resistant : A Model-Based Approach

International audienceDistributed User Interfaces (DUIs) have gone beyond the fact that traditional user interfaces run on the same computing platform in the same environment. This new interaction paradigm affects the way these novel systems are designed and developed. New features need to be taken into account from the very beginning of the development process and new models and tools need to be considered for the correct development of interactive systems based on DUIs. The starting point of this paper is that DUI-based systems are susceptible of being interrupted in several ways as they are dependent on connectivity. In this proposal this issue is assessed from a conceptual point of view, asking the question of what new features should be considered and how should they be included within the development process? The model-based approach presented provides developers with means to make DUIs resilient or resistant to interruptions