Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Tearing Instability

The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive MHD for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters this model yields results consistent with observations.Comment: 5 pages, no figures; accepted for publication in Physical Review Letter

FDI, income inequality and poverty : a time series analysis of Portugal, 1973–2016

Using time series data for Portugal between 1973 and 2016, this paper examines to what extent, inward FDI contributes to income inequality and poverty in the long-run. It was found that increased flows of inward FDI are associated with a less unequal income distribution and lower poverty rates. The results further suggest that, in the Portuguese case there is mutual causality between inward FDI and poverty in the long run, i.e., FDI significantly reduces poverty, and lower levels of poverty lead to higher inward FDI flows. In the case of inequality, the evidence shows that FDI does not contribute to higher (or lower) income inequality. Instead, more unequal income distributions significantly and negatively impact on inward FDI in the long run. Finally, human capital emerged as a key determinant to mitigate income inequality and circumvent poverty, contributing, indirectly, to fostering additional FDI inflows. Such results call for integrated public policy interventions that emphasize social and institu- tional dimensions.info:eu-repo/semantics/publishedVersio

Turbulent Magnetic Reconnection in Two Dimensions

Two-dimensional numerical simulations of the effect of background turbulence on 2D resistive magnetic reconnection are presented. For sufficiently small values of the resistivity ($\eta$) and moderate values of the turbulent power ($\epsilon$), the reconnection rate is found to have a much weaker dependence on $\eta$ than the Sweet-Parker scaling of $\eta^{1/2}$ and is even consistent with an $\eta-$independent value. For a given value of $\eta$, the dependence of the reconnection rate on the turbulent power exhibits a critical threshold in $\epsilon$ above which the reconnection rate is significantly enhanced.Comment: Accepted to MNRA

Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas

A numerical study of magnetic reconnection in the large-Lundquist-number ($S$), plasmoid-dominated regime is carried out for $S$ up to $10^7$. The theoretical model of Uzdensky {\it et al.} [Phys. Rev. Lett. {\bf 105}, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is \normEeff\sim 0.02 independently of $S$ for $S\gg10^4$. The plasmoid flux ($\Psi$) and half-width ($w_x$) distribution functions scale as $f(\Psi)\sim \Psi^{-2}$ and $f(w_x)\sim w_x^{-2}$. The joint distribution of $\Psi$ and $w_x$ shows that plasmoids populate a triangular region $w_x\gtrsim\Psi/B_0$, where $B_0$ is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic "monster" plasmoids with $w_x\sim 10$% of the system size are shown to emerge in just a few Alfv\'en times, independently of $S$, suggesting that large disruptive events are an inevitable feature of large-$S$ reconnection.Comment: 5 pages, 6 figures, submitted for publicatio

Magnetic island merger as a mechanism for inverse magnetic energy transfer

Magnetic energy transfer from small to large scales due to successive magnetic island coalescence is investigated. A solvable analytical model is introduced and shown to correctly capture the evolution of the main quantities of interest, as borne out by numerical simulations. Magnetic reconnection is identified as the key mechanism enabling the inverse transfer, and setting its properties: magnetic energy decays as $\tilde t^{-1}$, where $\tilde t$ is time normalized to the (appropriately defined) reconnection timescale; and the correlation length of the field grows as $\tilde t^{1/2}$. The magnetic energy spectrum is self-similar, and evolves as $\propto \tilde t ^{-3/2}k^{-2}$, where the $k$-dependence is imparted by the formation of thin current sheets.Comment: 6 pages, 5 figures, submitted for publicatio

Polyploid lineages in the genus Porphyra

Whole genome duplication is now accepted as an important evolutionary force, but the genetic factors and the life history implications affecting the existence and abundance of polyploid lineages within species are still poorly known. Polyploidy has been mainly studied in plant model species in which the sporophyte is the dominant phase in their life history. In this study, we address such questions in a novel system (Porphyra, red algae) where the gametophyte is the dominant phase in the life history. Three Porphyra species (P. dioica, P. umbilicalis, and P. linearis) were used in comparisons of ploidy levels, genome sizes and genetic differentiation using flow cytometry and 11 microsatellite markers among putative polyploid lineages. Multiple ploidy levels and genome sizes were found in Porphyra species, representing different cell lines and comprising several cytotype combinations among the same and different individuals. In P. linearis, genetic differentiation was found among three polyploid lineages: triploid, tetraploid and mixoploids, representing different evolutionary units. We conclude that the gametophytic phase (n) in Porphyra species is not haploid, contradicting previous theories. New hypotheses for the life histories of Porphyra species are discussed.FCT (Fundacao para a Ciencia e a Tecnologia, Portugal) [SFRH/BPD/109452/2015, NORIGENOMICS - PTDC/MAR/099698/2008, UID/Multi/04326/2013, BIODIVERSA/004/2015-MARFOR