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

Protocols and indications for magnetic resonance (Stress) first-pass perfusion imaging of the myocardium

First-pass perfusion imaging with MRI under pharmacologically induced stress for the detection of myocardial ischemia has gained a lot of interest over the past years. With adenosine as the main pharmacological 'stressor'. Issues regarding the best contrast dose and injection speed have become clear. Several perfusion sequences have been studied over the past. Even some large multi-centre trail results have been published. Some issues are still extensively research, like interpretation strategies and patient population in regard to protocols. This review highlights the technique of adenosine perfusion MRI and other perfusion techniques. The short history and current important literature are reviewed. Furthermore building blocks for different stress perfusion examinations are discussed.</p

Protocols and indications for magnetic resonance (Stress) first-pass perfusion imaging of the myocardium

First-pass perfusion imaging with MRI under pharmacologically induced stress for the detection of myocardial ischemia has gained a lot of interest over the past years. With adenosine as the main pharmacological 'stressor'. Issues regarding the best contrast dose and injection speed have become clear. Several perfusion sequences have been studied over the past. Even some large multi-centre trail results have been published. Some issues are still extensively research, like interpretation strategies and patient population in regard to protocols. This review highlights the technique of adenosine perfusion MRI and other perfusion techniques. The short history and current important literature are reviewed. Furthermore building blocks for different stress perfusion examinations are discussed.</p

Testing the Within-State Distribution in Mixture Models for Responses and Response Times

Mixture models have been developed to enable detection of within-subject differences in responses and response times to psychometric test items. To enable mixture modeling of both responses and response times, a distributional assumption is needed for the within-state response time distribution. Since violations of the assumed response time distribution may bias the modeling results, choosing an appropriate within-state distribution is important. However, testing this distributional assumption is challenging as the latent within-state response time distribution is by definition different from the observed distribution. Therefore, existing tests on the observed distribution cannot be used. In this article, we propose statistical tests on the within-state response time distribution in a mixture modeling framework for responses and response times. We investigate the viability of the newly proposed tests in a simulation study, and we apply the test to a real data set

Spatially and Spectrally Resolved Observations of a Zebra Pattern in Solar Decimetric Radio Burst

We present the first interferometric observation of a zebra-pattern radio burst with simultaneous high spectral (~ 1 MHz) and high time (20 ms) resolution. The Frequency-Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe the X1.5 flare on 14 December 2006. By using OVSA to calibrate the FST the source position of the zebra pattern can be located on the solar disk. With the help of multi-wavelength observations and a nonlinear force-free field (NLFFF) extrapolation, the zebra source is explored in relation to the magnetic field configuration. New constraints are placed on the source size and position as a function of frequency and time. We conclude that the zebra burst is consistent with a double-plasma resonance (DPR) model in which the radio emission occurs in resonance layers where the upper hybrid frequency is harmonically related to the electron cyclotron frequency in a coronal magnetic loop.Comment: Accepted for publication in Ap