具有无限时滞离散的Predator-Prey系统周期正解的存在性

研究了具有三个物种周期的Predator-Prey差分模型,用拓扑度理论讨论了具有无限时滞差分系统的周期正解的存在性,证明了具有无限时滞差分系统的正周期解存在的充分条件为:(ⅰ) r1 a32- r3 a12exp(2 r2ω)>0;(ⅱ) r1 a32- r3 a12exp(2 r2ω)- r2 a11 a32exp(2 r1ω)<0;(ⅲ)- a32 a12 r1+ a32 a11 r2+ a21 a12 r3<0.

A generic methodological framework for accurately quantifying greenhouse gas footprints of crop cultivation systems

The greenhouse gas （GHG） footprint of an agricultural system is a measure of the climate change impact potential （CCIP） exerted by the formation of its product（s）, its accurate quantification is essential for determining the green value added tax of agricultural products for food markets, which in turn may drastically change the current patterns of food consumption and production towards a product life cycle oriented economy. This paper reviews the literature regarding GHG footprints of crop cultivation systems.The review concludes that few studies have fully considered the categories/ items of net GHG emissions from an investigated crop cultivation system, and thus probably led to biases in footprint estimation. Most studies to date have even neglected changes in the soil organic carbon stocks of ecosystems with annual crops, while process-oriented biogeochemical models so far have seldom been involved in GHG footprint quantification.To help with solving these problems or drawbacks, the authors propose a generic methodological framework for quantifying GHG footprints of crop cultivation systems free from grazing, which takes into account all direct/indirect GHG contributors within a ＇cradle-to-gate＇ life cycle. The authors then provide example values of some GHG emission factors, such as those from machinery operations and other agricultural inputs, extracted from the literature. In addition, direct measurements or model simulations of other major on-farm emission factors are emphasized. The need to further update this methodological framework in future studies, especially by adapting it to mixed crop-livestock production systems, is also indicated.

Economic Competition for High Profits from Antarctic Living Resources in Their Protection Area

Since 1790, Antarctic living resources were becoming subjects of competition among the exploiters to be first in obtaining the maximum profit from them. This led to subsequent extinction of valuable species from fur seals and next penguins, large through small whales, industrial demersal fish, further to pelagic species and now toothfish, crabs and krill. Catch proportions of their numerous and biomass decrease. The biomass of South Georgia Icefish estimated for 40 years in spide of decreasing trend has one of the largest components-the oscillations with periods of 3 years or 4 years. Their models explain large biomass fluctuations in the years 1975 to 1981 with amplitudes ±15 × 10^3 tonnes around average 20 ×10^3 tonnes and further decline up to 2005 season with oscillation ±4 ×10^3 tonnes around average 5 × 10^3 tonnes. For future season, 2016 model predicts a little increase of the biomass oscillation at level of 8 × 10^3 tonnes with reduced amplitude 2 × 10^3 tonnes. Slowly increase density of adult fish was also reported for target similar and close related mackerel icefish. Additional references for biomass levels help reduce the risk of further depletion biomass of Pseudochaenichthys georgianus which already declined to 75%. As global warming promote phytoplankton growth, replacing krill fishery by algae farms can save unique Antarctic heritages.

A Review on the Identification Indicators of Tea Germplasm

Tea plant is cross pollinated plant, it forms a variety of the tea Germplasm constantly in the long-term breeding process. Tea Germplasm resources are the material foundation for improving varieties and also the basic research which is good for developing and expanding tea well-bred varieties in tea field, especially in quality selection and biotechnology research. Furthermore, excellent tea germplasm is primary condition for tea breeding and quality. Therefore, identification and screening excellent tea germplasm become particularly important. We need accelerate develop high-quality tea varieties, and it need to base on exploring and studying tea germplasm. This paper reviews the research progress of tea germplasm on identification from morphological characteristic, biological characteristic, quality characteristic, resistance and heredity. However, there are still some problems on identification and screening of tea germplasm, no effective methods have been found so far which apply on early identification and genetic engineering, so we should make intensive and long lasting study tea germplasm and analyze systematically various identification, which are benefit for breeding high-quality seeds, shortening the breeding period and summing the new way of breeding. We expect them to play the key roles and provide the theory basis for genetic improvement, classification and breeding in tea plant.

稀土发挥生物效应的机制及其作用物种探讨

稀土在工业、医药领域、基础研究以及在我国的广泛农用引起了人们对其生物效应机理以及可能毒性的关注.在稀土生物学效应机理及毒性的研究中,无论是在动物水平还是细胞层次,引起生物学效应的稀土物种都是一个关键问题,一直存在争议.本文对以动物、细胞为模型的生物效应研究中的实验条件进行分析,对生理条件下引起稀土生物学效应的可能物种提出"稀土离子池"(rare earth ion pool)模型,并对其引起生物学效应的活性物种以及与细胞膜相互作用的方式进行了探讨,以期为阐明复杂生物学体系中稀土化合物的作用机制提供思路.

The role of miR156 in developmental transitions in Nicotiana tabacum

Plants undergo a series of developmental transitions during their life cycle. After seed germination, plants pass through two distinct phases: the vegetative phase in which leaves are produced and the reproductive phase in which flowering occurs. Based on the reproductive competence and morphological changes, the vegetative phase can be further divided into juvenile and adult phases. Here, we demonstrate that the difference between juvenile and adult phase of Nicotiana tabacum is characterized by the changes in leaf size, leaf shape as well as the number of leaf epidermal hairs(trichomes). We further show that miR156, an age-regulated microR NA, regulates juvenile-to-adult phase transition in N. tabacum. Overexpression of miR156 results in delayed juvenile-to-adult transition and flowering. Together, our results support an evolutionarily conserved role of miR156 in plant developmental transitions.

Time Delay Induced Stochastic Resonance in One Species Competition Ecosystem without a Periodic Signal

One-species competition ecosystem with noise and time delay was investigated as not driven by a periodic force.The results show that the time delay is responsible for stochastic resonance of the system as delay time is smaller than critical point of the Hopf bifurcation.

Role of reactive oxygen species in the antiproliferative effects of metavanadate on human prostate cancer DU145 cells

In the present study, the effects of metavanadate on the human prostate cancer cell line DU145 and the underlying mechanism were investigated. The results showed that metavanadate can cause cell cycle arrest at G2/M phase which was evidenced by cell cycle analysis and the increased phosphorylation of Cdc2 at its inactive Tyr-15 site. In addition, the results showed that metavanadate can induce reactive oxygen species （ROS） elevation and decrease the level of Cdc25C. This process can be rescued by an antioxidant, N-acetyl cysteine. In conclusion, the results demonstrate that metavanadate can inhibit cell proliferation via cell cycle arrest at G2/M phase in DU145 ceils. Metavanadate-induced ROS formation may play an important role in this process by mediating the degradation of Cdc25C.