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

Sleep and Orofacial Pain: Physiological Interactions and Clinical Management

Sleep and pain are both vital functions on which wellbeing, health, and life itself depend. These two complex states interact in several ways serving homeostasis, but they are also regulated by a well-orchestrated, multi-oscillatory mechanism characterizing the Circadian Timing System. This interaction, which benefits critical physiological challenges, is also clinically crucial, as it mutually affects sleep and pain-related disturbances. It impacts pathophysiological pathways and relevant clinical aspects of many disorders. Furthermore, therapeutic success is frequently dependent on the adequate management of this cycle. The relationship of sleep and pain is undoubtedly of major relevance for diagnosis and successful management of various health conditions and disorders

Teachers’ motives for learning in networks:costs, rewards and community interest

Background: This paper discusses teachers’ perspectives on learning networks and their motives for participating in these networks. Although it is widely held that teachers’ learning may be developed through learning networks, not all teachers participate in such networks. Purpose: The theme of reciprocity, central to studies in the area of learning in networks, is often approached from a rational exchange perspective. This study attempts to extend this approach with reference to the concept of symbolic interactionism. The study was guided by the following research question: What is the relationship between teachers’ perceptions of learning networks and their motives for participation or non-participation in these networks? Design and methods: In order to address this research question, semi-structured interviews among 25 teachers in secondary education in the Netherlands were carried out. The semi-structured interviews consisted of three parts: background information, perspectives on learning networks and personal experiences with those networks. Data were analysed qualitatively and analyses consisted of within-case analysis, and cross-case analysis of interview fragments. Three themes were considered: (1) perspectives on learning networks, (2) motives for participation perceived as rational exchange, (3) motives for participation perceived as related to social order. Findings: The findings are presented around these three themes. Each theme is discussed in relation to relevant aspects from the literature. Findings indicated that teachers perceived learning networks to be organised both within-school and outside school, and mostly focused around specific content knowledge. Reasons for participation or non-participation were related to rational costs and rewards (such as time, technology, self-efficacy); in symbolic motives (such as joy, sharing and mutual understanding), and also in a sense of meaning that resulted from networking activities. Conclusions: We conclude that, in addition to social exchange motives, the data suggest that symbolic aspects of communication and interaction play an important role in considerations for participation in learning networks. This may be described in terms of four ‘types’ of networking teachers: the Community focused networking teacher, the Locally focused networking teacher, the Not-yet-networking teacher, and the Non-networking teacher. It is hoped that these exploratory findings could be helpful in supporting the development of learning networks for all teachers.</p

DNA structural elements required for ERCC1-XPF endonuclease activity

The heterodimeric complex ERCC1-XPF is a structure-specific endonuclease responsible for the 5' incision during mammalian nucleotide excision repair (NER). Additionally, ERCC1-XPF is thought to function in the repair of interstrand DNA cross-links and, by analogy to the homologous Rad1-Rad10 complex in Saccharomyces cerevisiae, in recombination between direct repeated DNA sequences. To gain insight into the role of ERCC1-XPF in such recombinational processes and in the NER reaction, we studied in detail the DNA structural elements required for ERCC1-XPF endonucleolytic activity. Recombinant ERCC1-XPF, purified from insect cells, was found to cleave stem-loop substrates at the DNA junction in the absence of other proteins like replication protein A, showing that the structure-specific endonuclease activity is intrinsic to the complex. Cleavage depended on the presence of divalent cations and was optimal in low Mn2+ concentrations (0.2 mM). A minimum of 4-8 unpaired nucleotides was required for incisions by ERCC1-XPF. Splayed arm and flap substrates were also cut by ERCC1-XPF, resulting in the removal of 3' protruding single-stranded arms. All incisions occurred in one strand of duplex DNA at the 5' side of a junction with single-stranded DNA. The exact cleavage position varied from 2 to 8 nucleotides away from the junction. One single-stranded arm, protruding either in the 3' or 5' direction, was necessary and sufficient for correct positioning of incisions by ERCC1-XPF. Our data specify the engagement of ERCC1-XPF in NER and allow a more direct search for its specific role in recombination

Engaging without over-powering: A case study of a FLOSS project

This is the post-print version of the published chapter. The original publication is available at the link below. Copyright @ 2010 IFIP International Federation for Information Processing.The role of Open Source Software (OSS) in the e-learning business has become more and more fundamental in the last 10 years, as long as corporate and government organizations have developed their educational and training programs based on OSS out-of-the-box tools. This paper qualitatively documents the decision of the largest UK e-learning provider, the Open University, to adopt the Moodle e-learning system, and how it has been successfully deployed in its site after a multi-million investment. A further quantitative study also provides evidence of how a commercial stakeholder has been engaged with, and produced outputs for, the Moodle community. Lessons learned from this experience by the stakeholders include the crucial factors of contributing to the OSS community, and adapting to an evolving technology. It also becomes evident how commercial partners helped this OSS system to achieve the transition from an “average” OSS system to a successful multi-site, collaborative and community-based OSS project

Unraveling the Role of Metal-Support Interactions on the Structure Sensitivity of Fischer-Tropsch Synthesis

Structure sensitivity plays a pivotal role in heterogeneous catalysis and the Fischer-Tropsch reaction is one of the prime examples of such a structure-sensitive reaction. The activity and selectivity of this reaction depend on the size of the nanoparticle and this trend is observed for a whole range of support materials. To understand why metal-support interactions do not affect this trend, a ReaxFF force field is developed that effectively mimics the broad variety of support materials and captures the metal-support interaction strength into a single structural parameter. Particles of 1-9 nm embedded on support materials are sampled using simulated annealing molecular dynamics and the effect of the metal-support interaction on the active site distribution is studied. It is found that although the size-dependency profile of various active site topologies depends on the interaction strength of the nanoparticle with the support, step-edge sites with an FCC(110) motif remain insensitive to the type of support. Based on microkinetic simulations, it is established that these sites are predominantly responsible for the observed atom-based FTS activity rationalizing why Fischer-Tropsch synthesis is structure-sensitive but support-insensitive.</p