Role of different system delays on ecological food chain dynamics: Mathematical modelling and analysis

<正> This paper studies a three tier ecological food chain model consisting of nutrient,autotroph,and herbivore populations.Regeneration of nutrient from dead autotroph and herbivore biomass bydecomposers present in the soil is included.The time required for maturation of the herbivore populationis incorporated as a distributed time delay.Next,the authors introduce the time lag requiredfor regeneration of nutrient from the dead herbivore as a discrete time delay.Stability and bifurcationbehavior of the one-and two-delay models are carried out and a comparative study of the significanceof these delays in controlling the system dynamics is performed.Numerical simulations are done tojustify analytical results.     

A whole-genome admixture scan finds a candidate locus for multiple sclerosis susceptibility

Multiple sclerosis is a common disease with proven heritability, but, despite large-scale attempts, no underlying risk genes have been identified. Traditional linkage scans have so far identified only one risk haplotype for multiple sclerosis (at HLA on chromosome 6), which explains only a fraction of the increased risk to siblings. Association scans such as admixture mapping have much more power, in principle, to find the weak factors that must explain most of the disease risk. We describe here the first high-powered admixture scan, focusing on 605 African American cases and 1,043 African American controls, and report a locus on chromosome 1 that is significantly associated with multiple sclerosis.     

Environmental and rock magnetic studies of rapid fluctuations of Asian summer monsoon during the last interglacial maximum (MIS 5e)

A systematic environmental rock magnetic study of a century-millennial scale loesspaleosol sequence of the last interglacial in the Jiuzhoutai well section, Lanzhou, on the western Loess Plateau demonstrates that Asian summer nonsoon experienced fast and large oscillations manifesting as three peaks and two valleys lasing about 1–2 ka. Valley 4 with a central age of 120.5 ka is the most evident, suggesting that summer monsoon was weakened nearly to a level in glaciations. This indicates that summer monsoon has a nature of instability in centurymillennial scale change in the last interglacial.     

Self-organization of supramolecular helical dendrimers into complex electronic materials

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. Here we show that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic materials. We find that attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometre-scale columns that contain in their cores pi-stacks of donors, acceptors or donor-acceptor complexes exhibiting high charge carrier mobilities. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble so that the polymer is incorporated in the centre of the columns through donor-acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive pi-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications.     

Tree barks as a natural trap for airborne spores and pollen grains from China

The present article deals with the use of tree barks as a natural trap for airborne spores and pollen grains in China. The study carried out at the southern part of Beijing Botanical Garden, Institute of Botany, Chinese Academy of Sciences has yielded a variety of palynomorphs mostly belonging to tree taxa. New methodologies for extraction of palynomorphs from tree barks have been suggested. Bark samples were collected from three taxa, i.e., Paulownia fortunei Hemsl. （Scrophulariaceae）, Quercus dentata Thunb. （Fagaceae）, and Picea meyeri Rehder ＆ E.H. Wilson （Pinaceae） having different bark morphologies. P. fortunei with a comparatively soft and fissured bark is believed to have a greater potential for trapping airborne spores and pollen grains compared to the stiff and less fissured barks of Q. dentata and the scaly bark of P. meyeri. Old barks yield better data in terms of quantity and quality of trapped pollen and spores. The present study throws new light on the modern pollen rain, spore-pollen dispersal, and their deposition in and aroundBeijing Botanical Garden, and other different parts of China.     

Enhanced elevated temperature wear resistance of Al-17Si-5Cu alloy after a novel short duration heat treatment

The goal of the present study is to improve the elevated temperature wear resistance of an Al-17 wt%Si-5 wt%Cu alloy(AR alloy) by a novel short duration heat treatment process. The elevated temperature(100°C) dry sliding wear behavior of an AR alloy was studied after microstructural modification using the proposed heat treatment. The study revealed considerable microstructural modifications after the heat treatment and the heat treated alloy was designated as HT(heat treatment) alloy. A higher hardness value was obtained for the HT alloy compared to the AR alloy. Accordingly, the wear rate for the HT alloy was found to be significantly lower compared to the as-cast AR alloy at all applied loads. Accelerated particle pull-out for the AR alloy at elevated temperatures resulted in poor wear behavior for it compared to the HT alloy. On the other hand, the Si particles remained intact on the worn surface of the HT alloy due to the good particle/matrix bonding that resulted from the isothermal heat treatment. Furthermore, the age hardening that occurred in the HT alloy during wear provided additional wear resistance. Thus, the HT alloy at 100°C exhibited a lower wear rate compared to the AR alloy even at room temperature for all applied loads. This improvement was attributed to microstructural modification upon isothermal heat treatment along with the age hardening effect.