Using HINODE/Extreme-Ultraviolet Imaging Spectrometer to confirm a seismologically inferred coronal temperature

The Extreme-Ultraviolet Imaging Spectrometer on board the HINODE satellite is used to examine the loop system described in Marsh et al. (2009) by applying spectroscopic diagnostic methods. A simple isothermal mapping algorithm is applied to determine where the assumption of isothermal plasma may be valid, and the emission measure locii technique is used to determine the temperature profile along the base of the loop system. It is found that, along the base, the loop has a uniform temperature profile with a mean temperature of 0.89 +- 0.09 MK which is in agreement with the temperature determined seismologically in Marsh et al. (2009), using observations interpreted as the slow magnetoacoustic mode. The results further strengthen the slow mode interpretation, propagation at a uniform sound speed, and the analysis method applied in Marsh et al. (2009). It is found that it is not possible to discriminate between the slow mode phase speed and the sound speed within the precision of the present observations

Acceleration of weakly collisional solar-type winds

One of the basic properties of the solar wind, that is the high speed of the fast wind, is still not satisfactorily explained. This is mainly due to the theoretical difficulty of treating weakly collisional plasmas. The fluid approach implies that the medium is collision dominated and that the particle velocity distributions are close to Maxwellians. However the electron velocity distributions observed in the solar wind depart significantly from Maxwellians. Recent kinetic collisionless models (called exospheric) using velocity distributions with a suprathermal tail have been able to reproduce the high speeds of the fast solar wind. In this letter we present new developments of these models by generalizing them over a large range of corona conditions. We also present new results obtained by numerical simulations that include collisions. Both approaches calculate the heat flux self-consistently without any assumption on the energy transport. We show that both approaches - the exospheric and the collisional one - yield a similar variation of the wind speed with the basic parameters of the problem; both produce a fast wind speed if the coronal electron distribution has a suprathermal tail. This suggests that exospheric models contain the necessary ingredients for the powering of a transonic stellar wind, including the fast solar one.Comment: Accepted for publication in The Astrophysical Journal Letters (accepted: 13 May 2005

Line intensity enhancements in stellar coronal X-ray spectra due to opacity effects

Context. The I(15.01 A)/I(16.78 A) emission line intensity ratio in Fe XVII has been reported to deviate from its theoretical value in solar and stellar X-ray spectra. This is attributed to opacity in the 15.01 A line, leading to a reduction in its intensity, and was interpreted in terms of a geometry in which the emitters and absorbers are spatially distinct. Aims. We study the I(15.01 A)/I(16.78 A) intensity ratio for the active cool dwarf EV Lac, in both flare and quiescent spectra. Methods. The observations were obtained with the Reflection Grating Spectrometer on the XMM-Newton satellite. The emission measure distribution versus temperature reconstruction technique is used for our analysis. Results. We find that the 15.01 A line exhibits a significant enhancement in intensity over the optically thin value. To our knowledge, this is the first time that such an enhancement has been detected on such a sound statistical basis. We interpret this enhancement in terms of a geometry in which the emitters and absorbers are not spatially distinct, and where the geometry is such that resonant pumping of the upper level has a greater effect on the observed line intensity than resonant absorption in the line-of-sight.Comment: accepted for publication in A&

Protocol for soil functionality assessment in vineyards

Protocols used by Resolve partners during the project, to assess soil functionality on degraded aeras and evaluate soil restoration after applying recovering practices

Wild and traditional barley genomic resources as a tool for abiotic stress tolerance and biotic relations

Barley (Hordeum vulgare L.) is one of the main crops cultivated all over the world. As for other cereals, throughout the centuries barley was subjected by human breeding to genetic erosion phenomena, which guaranteed improved yields in organized (and then mechanized) agriculture; on the other hand, this selection weakened the ability of barley to survive under adverse environments. Currently, it is clear that climate change requires an urgent availability of crop varieties able to grow under stress conditions, namely limited irrigation, salinity, high temperatures, and other stresses. In this context, an important role could be played by wild relatives and landraces selected by farmers, particularly in specific field areas and/or climatic conditions. In this review, we investigated the origin of barley and the potentialities of wild varieties and landraces in different contexts, and their resilience to abiotic stress. The data obtained from Next Generation Sequencing technologies were examined to highlight the critical aspects of barley evolution and the most important features for abiotic stress tolerance. Furthermore, the potential of appropriate mycorrhiza is discussed under the view of the essential role played by these symbioses in field crops. The abilities of specific barley wild varieties and landraces may represent novel opportunities and suggest innovative strategies for the improvement of abiotic tolerance in crops and particularly in barley

Precise Null Pointer Analysis Through Global Value Numbering

Precise analysis of pointer information plays an important role in many static analysis techniques and tools today. The precision, however, must be balanced against the scalability of the analysis. This paper focusses on improving the precision of standard context and flow insensitive alias analysis algorithms at a low scalability cost. In particular, we present a semantics-preserving program transformation that drastically improves the precision of existing analyses when deciding if a pointer can alias NULL. Our program transformation is based on Global Value Numbering, a scheme inspired from compiler optimizations literature. It allows even a flow-insensitive analysis to make use of branch conditions such as checking if a pointer is NULL and gain precision. We perform experiments on real-world code to measure the overhead in performing the transformation and the improvement in the precision of the analysis. We show that the precision improves from 86.56% to 98.05%, while the overhead is insignificant.Comment: 17 pages, 1 section in Appendi

Three-dimensional magnetic reconnection simulations using the Eulerian Conservative High Order (ECHO) code

Magnetic reconnection and shear driven instabilities are pervasive phenomena in the heliosphere and in astrophysical plasmas in general. Magnetic reconnection and Kelvin-Helmholtz-like instabilities require the use of high-order numerical approximations to study their linear and non-linear evolution. At the same time, in compressible MHD the dynamical activity following reconnection processes leads to formation of discontinuous modes which should be treated by shock-capturing numerical schemes. For this purpose we have designed an Eulerian Conservative High Order (ECHO) code in which, i) explicit diffusivity is taken into account, ii) high-order numerical approximations of flux derivatives are included and iii) shock-capturing algorithms are employed in managing flux discontinuities. This code has been applied successfully in studying the linear and non-linear 3D evolution of the tearing instability and in following the 3D evolution of a current sheet embedded in a sheared flow

Differential algebras on kappa-Minkowski space and action of the Lorentz algebra

We propose two families of differential algebras of classical dimension on kappa-Minkowski space. The algebras are constructed using realizations of the generators as formal power series in a Weyl super-algebra. We also propose a novel realization of the Lorentz algebra so(1,n-1) in terms of Grassmann-type variables. Using this realization we construct an action of so(1,n-1) on the two families of algebras. Restriction of the action to kappa-Minkowski space is covariant. In contrast to the standard approach the action is not Lorentz covariant except on constant one-forms, but it does not require an extra cotangent direction.Comment: 16 page