Initial simulation study on high-precision radio measurements of the depth of shower maximum with SKA1-low

As LOFAR has shown, using a dense array of radio antennas for detecting extensive air showers initiated by cosmic rays in the Earth's atmosphere makes it possible to measure the depth of shower maximum for individual showers with a statistical uncertainty less than $20\,g/cm^2$. This allows detailed studies of the mass composition in the energy region around $10^{17}\,eV$ where the transition from a Galactic to an Extragalactic origin could occur. Since SKA1-low will provide a much denser and very homogeneous antenna array with a large bandwidth of $50-350\,MHz$ it is expected to reach an uncertainty on the $X_{\max}$ reconstruction of less than $10\,g/cm^2$. We present first results of a simulation study with focus on the potential to reconstruct the depth of shower maximum for individual showers to be measured with SKA1-low. In addition, possible influences of various parameters such as the numbers of antennas included in the analysis or the considered frequency bandwidth will be discussed.Comment: To appear as part of the proceedings of the ARENA2016 meeting (Groningen, The Netherlands), published by EPJ-Wo

Simulation of radio emission from air showers in atmospheric electric fields

We study the effect of atmospheric electric fields on the radio pulse emitted by cosmic ray air showers. Under fair weather conditions the dominant part of the radio emission is driven by the geomagnetic field. When the shower charges are accelerated and deflected in an electric field additional radiation is emitted. We simulate this effect with the Monte Carlo code REAS2, using CORSIKA-simulated showers as input. In both codes a routine has been implemented that treats the effect of the electric field on the shower particles. We find that the radio pulse is significantly altered in background fields of the order of ~100 V/cm and higher. Practically, this means that air showers passing through thunderstorms emit radio pulses that are not a reliable measure for the shower energy. Under other weather circumstances significant electric field effects are expected to occur rarely, but nimbostratus clouds can harbor fields that are large enough. In general, the contribution of the electric field to the radio pulse has polarization properties that are different from the geomagnetic pulse. In order to filter out radio pulses that have been affected by electric field effects, radio air shower experiments should keep weather information and perform full polarization measurements of the radio signal.Comment: 26 pages, 12 figures, accepted for publication in Astroparticle Physic

From seed longevity to passive defense against pathogens: co-evolution of two traits to remain alive in the dry state?

In orthodox seeds, longevity is gradually acquired at the later stages of seed maturation. In our laboratory, we use seeds of Medicago truncatula, a model species for legumes, to unravel the mechanisms and regulatory pathways implicated in the acquisition of longevity. In this species, longevity increases progressively over 30-fold after seed filling is terminated and desiccation tolerance is acquired, allowing the separation of genes related to the different developmental  processes. In order to further discriminate other developmental programs from those related to longevity, an extensive physiological and molecular analysis was undertaken in developing seeds from  plants that were grown under different environmental conditions after seed set. This way, the timing and extent to which longevity is acquired was modulated. Using 104 transcriptomes acquired at different time points during seed maturation for five different parental environments, a network-based approach was applied to isolate a co-expression module related to longevity. Functional analysis in Arabidopsis confirmed the predictability and the conserved nature of this module. Interestingly, the longevity module is enriched with genes playing a crucial role in defense against biotic stress. Here, we will present evidence supporting a link between mechanisms implicated in defense against pathogens and survival in the dry state. We will discuss how seeds activate a developmentally regulated defense response during maturation that is also beneficial to long-term survival in the dry state

Monte Carlo simulations of air showers in atmospheric electric fields

The development of cosmic ray air showers can be influenced by atmospheric electric fields. Under fair weather conditions these fields are small, but the strong fields inside thunderstorms can have a significant effect on the electromagnetic component of a shower. Understanding this effect is particularly important for radio detection of air showers, since the radio emission is produced by the shower electrons and positrons. We perform Monte Carlo simulations to calculate the effects of different electric field configurations on the shower development. We find that the electric field becomes important for values of the order of 1 kV/cm. Not only can the energy distribution of electrons and positrons change significantly for such field strengths, it is also possible that runaway electron breakdown occurs at high altitudes, which is an important effect in lightning initiation.Comment: 24 pages, 19 figures, accepted for publication in Astroparticle Physic

Desiccation tolerance: From genomics to the field

Desiccation tolerance is defined as the ability to survive the removal of all, or almost all the cellular water without irreversible damage. It confers to dried organisms the ability to survive extreme conditions of the environment and to stay alive in a suspended animation for long periods of time. The biotechnological potential of anhydrous biology has been recognized for more than 60 years. With the fast development of “omics” technologies, it is now possible to better appreciate the biotechnological promises that can be made from the understanding of desiccation tolerance. This review will discuss the impact of post-genomics tools on identifying genes or gene products, and will give a comprehensive overview of the agronomical and biotechnological applications. We propose the term desiccomics to define the approach consisting of combining “omics” approaches to address the specific issues associated with the dry state