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https://openspace.dmacc.edu/banner_news/1432/thumbnail.jp

Impact of atmospheric CO₂ and galactic cosmic radiation on Phanerozoic climate change and the marine d18O record

[1] A new model is developed and applied to simulate the Phanerozoic evolution of seawater composition (dissolved Ca, Sr, dissolved inorganic carbon, alkalinity, pH, δ18O), marine carbonates (Sr/Ca, 87Sr/86Sr, δ13C, δ18O), atmospheric CO2 and surface temperature. The marine carbonate records (Sr/Ca, 87Sr/86Sr, δ13C) are used to reconstruct changes in volcanic/tectonic activity and organic carbon burial over the Phanerozoic. Seawater pH is calculated assuming saturation with respect to calcite and considering the changing concentration of dissolved Ca documented by brine inclusion data. The depth of calcite saturation is allowed to vary through time and the effects of changing temperature and pressure on the stability constants of the carbonate system are considered. Surface temperatures are calculated using the GEOCARB III approach considering also the changing flux of galactic cosmic radiation (GCR). It is assumed that GCR cools the surface of the Earth via enhanced cloud formation at low altitudes. The δ18O of marine carbonates is calculated considering the changing isotopic composition of seawater, the prevailing surface temperatures and seawater pH. Repeated model runs showed that the trends observed in the marine δ18O record can only be reproduced by the model if GCR is allowed to have a strong effect on surface temperature. The climate evolution predicted by the model is consistent with the geological record. Warm periods (Cambrian, Devonian, Triassic, Cretaceous) are characterized by low GCR levels. Cold periods during the late Carboniferous to early Permian and the late Cenozoic are marked by high GCR fluxes and low pCO2 values. The major glaciations occurring during these periods are the result of carbon cycling processes causing a draw-down of atmospheric CO2 and a coevally prevailing dense cloud cover at low-altitudes induced by strong GCR fluxes. The two moderately cool periods during the Ordovician - Silurian and Jurassic - early Cretaceous are characterized by both high pCO2 and GCR levels so that greenhouse warming compensated for the cooling effect of low-altitude clouds. The very high Jurassic δ18O values observed in the geological record are caused by low pH values in surface waters rather than cold surface conditions

Plasmodium falciparum antigenic variation. Mapping mosaic var gene sequences onto a network of shared, highly polymorphic sequence blocks

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a potentially important family of immune targets, encoded by an extremely diverse gene family called var. Understanding of the genetic organization of var genes is hampered by sequence mosaicism that results from a long history of non-homologous recombination. Here we have used software designed to analyse social networks to visualize the relationships between large collections of short var sequences tags sampled from clinical parasite isolates. In this approach, two sequences are connected if they share one or more highly polymorphic sequence blocks. The results show that the majority of analysed sequences including several var-like sequences from the chimpanzee parasite Plasmodium reichenowi can be either directly or indirectly linked together in a single unbroken network. However, the network is highly structured and contains putative subgroups of recombining sequences. The major subgroup contains the previously described group A var genes, previously proposed to be genetically distinct. Another subgroup contains sequences found to be associated with rosetting, a parasite virulence phenotype. The mosaic structure of the sequences and their division into subgroups may reflect the conflicting problems of maximizing antigenic diversity and minimizing epitope sharing between variants while maintaining their host cell binding functions

Association with pathogenic bacteria affects life-history traits and population growth in Caenorhabditis elegans.

Determining the relationship between individual life-history traits and population dynamics is an essential step to understand and predict natural selection. Model organisms that can be conveniently studied experimentally at both levels are invaluable to test the rich body of theoretical literature in this area. The nematode Caenorhabditis elegans, despite being a well-established workhorse in genetics, has only recently received attention from ecologists and evolutionary biologists, especially with respect to its association with pathogenic bacteria. In order to start filling the gap between the two areas, we conducted a series of experiments aiming at measuring life-history traits as well as population growth of C. elegans in response to three different bacterial strains: Escherichia coli OP50, Salmonella enterica Typhimurium, and Pseudomonas aeruginosa PAO1. Whereas previous studies had established that the latter two reduced the survival of nematodes feeding on them compared to E. coli OP50, we report for the first time an enhancement in reproductive success and population growth for worms feeding on S. enterica Typhimurium. Furthermore, we used an age-specific population dynamic model, parameterized using individual life-history assays, to successfully predict the growth of populations over three generations. This study paves the way for more detailed and quantitative experimental investigation of the ecology and evolution of C. elegans and the bacteria it interacts with, which could improve our understanding of the fate of opportunistic pathogens in the environment.We thank Andrew Grant and Craig Winstanley for providing strains and reagents. Some C. elegans and bacterial strains were provided by the Caenorhabditis Genetics Centre, which is funded by NIH’s Office of Research Infrastructure Programs (P40 OD010440). This research was funded by a grant from the Biotechnology and Biological Sciences Research Council (grant number BB/I012222/1) to O.R. O.R. also acknowledges funding from the Royal Society (University Research Fellowship). EQM was supported by a scholarship from the Winston Churchill Foundation of the United States, and EGR by an EUfunded Erasmus bursary (Lifelong Learning Programme). We also thank two anonymous referees for their valuable comments.This is the final published version. It first appeared at http://onlinelibrary.wiley.com/doi/10.1002/ece3.1461/abstract

Capturing egocentric biases in reference reuse during collaborative dialogue

Words that are produced aloud—and especially self-produced ones—are remembered better than words that are not, a phenomenon labeled the production effect in the field of memory research. Two experiments were conducted to determine whether this effect can be generalized to dialogue, and how it might affect dialogue management. Triads (Exp. 1) or dyads (Exp. 2) of participants interacted to perform a collaborative task. Analyzing reference reuse during the interaction revealed that the participants were more likely to reuse the references that they had presented themselves, on the one hand, and those that had been accepted through verbatim repetition, on the other. Analyzing reference recall suggested that the greater accessibility of self-presented references was only transient. Moreover, among partner-presented references, those discussed while the participant had actively taken part in the conversation were more likely to be recalled than those discussed while the participant had been inactive. These results contribute to a better understanding of how individual memory processes might contribute to collaborative dialogue

Facilitating student engagement and collaboration in a large postgraduate course using wiki-based activities

This paper investigates the impact of wiki-based activities on student participation and collaborative learning in a large postgraduate international management course. The wiki was used in this study as a facilitator for engagement and collaboration rather than a means of online discussions. Based on both qualitative and quantitative data, we find strong evidence that the use of the wiki facilitated student engagement and collaboration, both inside and outside the classroom. Moreover, student learning had significantly improved as a result of the enhanced learning environment

A review of the academic and psychological impact of the transition to secondary education

The transition from primary to secondary education is one of the most stressful events in a young person’s life (Zeedyk et al., 2003) and can have a negative impact on psychological wellbeing and academic achievement. One explanation for these negative impacts is that the transition coincides with early adolescence, a period during which certain psychological disorders (i.e., anxiety disorders) become more salient (Kessler et al., 2005) and marked social, biological, and psychological development occurs (Anderson, Jacobs, Schramm, & Splittgerber, 2000). This review evaluates the existing literature on the psychological and academic impacts of the transition to secondary education on young adolescents. We examine the factors that plausibly increase or mitigate the risk of developing mental health issues and/or a decline in academic performance during the transition to secondary education. We also review the interplay between psychological health and academic achievement across and beyond the transition. We conclude with a summary of what schools and parents can learn from these findings to support children in a successful transition into secondary education

Susceptibilities of Nonhuman Primates to Chronic Wasting Disease

A species barrier may protect humans from this disease