True, false, paranormal, and 'designated'? : a reply to Jenkins

PostprintPeer reviewe

Effects of Neutral Hydrogen on Cosmic Ray Precursors in Supernova Remnant Shock Waves

Many fast supernova remnant shocks show spectra dominated by Balmer lines. The H$\alpha$ profiles have a narrow component explained by direct excitations and a thermally Doppler broadened component due to atoms that undergo charge exchange in the post-shock region. However, the standard model does not take into account the cosmic-ray shock precursor, which compresses and accelerates plasma ahead of the shock. In strong precursors with sufficiently high densities, the processes of charge exchange, excitation and ionization will affect the widths of both narrow and broad line components. Moreover, the difference in velocity between the neutrals and the precursor plasma gives rise to frictional heating due to charge exchange and ionization in the precursor. In extreme cases, all neutrals can be ionized by the precursor. In this paper we compute the ion and electron heating for a wide range of shock parameters, along with the velocity distribution of the neutrals that reach the shock. Our calculations predict very large narrow component widths for some shocks with efficient acceleration, along with changes in the broad- to-narrow intensity ratio used as a diagnostic for the electron-ion temperature ratio. Balmer lines may therefore provide a unique diagnostic of precursor properties. We show that heating by neutrals in the precursor can account for the observed H$\alpha$ narrow component widths, and that the acceleration efficiency is modest in most Balmer line shocks observed thus far.Comment: 9 pages, 3 figure

40 Gigabit ethernet: prototyping transparent end-to-end connectivity

The ever increasing demands of data intensive eScience applications have pushed the limits of computer networks. With the launch of the new 40 Gigabit Ethernet (40GE) standard, 802.3ba, applications can go beyond the common 10 Gigabit/s per data stream barrier for both local area, and as demonstrated in the GLIF 2010 and Supercomputing 2010 demos [3], wide area setups. In this article we profile the performance of state-of-the-art server hardware combined with 40GE technology. We give an insight on the issues involved with ultra high performance network adapters and suggest optimization approaches

A user-centric execution environment for <em>CineGrid</em> workloads

The abundance and heterogeneity of IT resources available, together with the ability to dynamically scale applications poses significant usability issues to users. Without understanding the performance profile of available resources users are unable to efficiently scale their applications in order to meet performance objectives. High quality media collaborations, like CineGrid, are one example of such diverse environments where users can leverage dynamic infrastructures to move and process large amounts of data. This paper describes our user-centric approach to executing high quality media processing workloads over dynamic infrastructures. Our main contribution is the CGtoolkit environment, an integrated system which aids users cope with the infrastructure complexity and large data sets specific to the digital cinema domain