Folding dynamics of the helical structures in a minimal model

The folding of a polypeptide is an example of the cooperative effects of the amino-acid residues. Of recent interest is how a secondary structure, such as a helix, spontaneously forms during the collapse of a peptide from an initial denatured state. The Monte Carlo implementation of a recent helix-forming model enables us to study the entire folding process dynamically. As shown by the computer simulations, the foldability and helical propagation are both strongly correlated to the nucleation properties of the sequence.Comment: 3 figures Submitted to Europhys Lette

Modelling Chinese grassland systems to improve herder livelihoods and grassland sustainability

Recent degradation of Chinese grasslands has contributed to declining herder productivity and profitability, increased incidence of dust storms and regionally reduced air quality. Overgrazing due to a doubling of stocking rates since the mid-1980s has been identified as a key contributing factor. Several pathways and strategies exist to improve grassland management; however, there remains uncertainty around the long-term sustainability of alternative systems. Nineteen years of grasslands research in China has produced a suite of models designed to improve understanding of grassland systems and investigate options for change. The StageTHREE Sustainable Grasslands Model was used to evaluate the ability of selected strategies to meet economic, production and environmental objectives. Sets of strategies that focussed on flock size, lambing and selling times, supplementary feeding rules and grazing management were simulated for a typical herder located in the desert steppe of Siziwang Banner, in the Inner Mongolia Autonomous Region of China. The results from the risk efficiency analysis indicated that no single strategy set clearly dominates across all objectives. Although the current practice of herders was found to be risk-efficient, it did not achieve the highest rate of grassland recovery, minimise soil erosion or minimise the greenhouse gas (GHG) emission intensity for sheepmeat production. Targeting further improvements in these attributes could be at the detriment of herder livelihoods. The analysis indicated that if herders adopted biomass-based grazing management and improved supplementary feeding they would be able to improve grassland resilience and maintain positive long-term economic performance under reduced flock sizes. Individual decision-making units, however, would still need to trade off the importance of different attributes to identify the strategy set, or system, that best meets their objectives and attitude to risk

The radiation of cynodonts and the ground plan of mammalian morphological diversity

Cynodont therapsids diversified extensively after the Permo-Triassic mass extinction event, and gave rise to mammals in the Jurassic. We use an enlarged and revised dataset of discrete skeletal characters to build a new phylogeny for all main cynodont clades from the Late Permian to the Early Jurassic, and we analyse models of morphological diversification in the group. Basal taxa and epicynodonts are paraphyletic relative to eucynodonts, and the latter are divided into cynognathians and probainognathians, with tritylodonts and mammals forming sister groups. Disparity analyses reveal a heterogeneous distribution of cynodonts in a morphospace derived from cladistic characters. Pairwise morphological distances are weakly correlated with phylogenetic distances. Comparisons of disparity by groups and through time are non-significant, especially after the data are rarefied. A disparity peak occurs in the Early/Middle Triassic, after which period the mean disparity fluctuates little. Cynognathians were characterized by high evolutionary rates and high diversity early in their history, whereas probainognathian rates were low. Community structure may have been instrumental in imposing different rates on the two clades

Characterization of brain blood flow and the amplitude of low-frequency fluctuations in major depressive disorder: A multimodal meta-analysis.

Background In healthy subjects, there is an association between amplitude of low-frequency fluctuations (ALFF) and regional cerebral blood flow (rCBF). To date, no published meta-analysis has investigated changes in the regional ALFF in medication-free depressed patients. Methods In this study, we aimed to explore whether resting-state rCBF and ALFF changes co-occur in the depressed brain without the potential confound of medication. Using signed differential mapping (SDM), we conducted two meta-analyses, one of rCBF studies and one of ALFF studies, involving medication-free patients with major depressive disorder (MDD). In addition, we conducted a multimodal meta-analysis to identify brain regions that showed abnormalities in both rCBF and ALFF. Results A total of 16 studies were included in this series. We identified abnormalities in resting-state rCBF and ALFF in the left insula in medication-free MDD patients compared with healthy controls (HC). In addition, we observed altered resting-state rCBF in the limbic-subcortical-cortical circuit and altered ALFF in the default mode network (DMN) and some motor-related brain regions. Limitations The analysis techniques, patient characteristics and clinical variables of the included studies were heterogeneous. Conclusions The conjoint alterations in ALFF and rCBF in the left insula may represent core neuropathological changes in medication-free patients with MDD and merit further studying