Ultra-High Energy Gamma Rays in Geomagnetic Field and Atmosphere

The nature and origin of ultra-high energy (UHE: reffering to > 10^19 eV) cosmic rays are great mysteries in modern astrophysics. The current theories for their explanation include the so-called "top-down" decay scenarios whose main signature is a large ratio of UHE gamma rays to protons. Important step in determining the primary composition at ultra-high energies is the study of air shower development. UHE gamma ray induced showers are affected by the Landau-Pomeranchuk-Migdal (LPM) effect and the geomagnetic cascading process. In this work extensive simulations have been carried out to study the characteristics of air showers from UHE gamma rays. At energies above several times 10^19 eV the shower is affected by geomagnetic cascading rather than by the LPM effect. The properties of the longitudinal development such as average depth of the shower maximum or its fluctuations depend strongly on both primary energy and incident direction. This feature may provide a possible evidence of the UHE gamma ray presence by fluorescence detectors.Comment: 27 pages, 12 figures, submitted to Phys.Rev.

Oxidative and nitrosative signaling in plants: Two branches in the same tree?

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) constitute key features underpinning the dynamic nature of cell signaling systems in plants. Despite their importance in many aspects of cell biology, our understanding of oxidative and especially of nitrosative signaling and their regulation remains poorly understood. Early reports have established that ROS and RNS coordinately regulate plant defense responses to biotic stress. In addition, evidence has accumulated demonstrating that there is a strong cross-talk between oxidative and nitrosative signaling upon abiotic stress conditions. The goal of this mini-review is to provide latest findings showing how both ROS and RNS comprise a coordinated oxidative and nitrosative signaling network that modulates cellular responses in response to environmental stimuli