类具有急慢性阶段和垂直传染的非线性SACS传染病模型(英文)

研究一类具有非线性接触率和垂直传染且在急慢性阶段均传染的非线性SACS传染病传播数学模型动力学性质,确定了各类平衡点存在的条件阈值,讨论了各平衡点的稳定性,并将会在临界值处出现Hopf分支,揭示了急慢性阶段传染对疾病发展趋势的共同影响.     

细胞内免疫滞后的病毒感染模型的稳定性和Hopf分支分析

在假设细胞内免疫反应有时间延迟的情况下对一个病毒感染模型的动力学形态进行了分析.研究了非负平衡点的稳定性和Hopf分支的存在性,并利用规范型和中心流形理论得出了分支方向、周期解的稳定性及周期的公式.

Abstract：

The dynamics of a viral infection model is analyzed under the assumption that the intracellular immune response is retarded. Stability of nonnegative equilibria and existence of Hopf bifurcation are studied. Using normal form theory and center manifold argument, we calculate the explicit formulas to determine the direction, stability and period of the bifurcating periodic solutions.     

具有竞争的Leslie型捕食者-食饵模型的定性分析

考虑了具有竞争的Leslie型模型.证明了解的最终有界性,和系统在一定条件下的一致持续生存性.研究了平衡点的局部稳定性.通过构建适当的Lyapunov函数,获得了正平衡点全局渐进稳定的充分条件.

Abstract：

In this paper, a competitive Leslie model is proposed. It is proved that the system's solution is ultimately bounded and the system is consistent and sustained under appropriate conditions. The local stability of the equilibria is investigated. By constructing a suitable Lyapunov functional, sufficient conditions are derived for the global stability of the positive equilibrium of the model.     

Correlation Analysis of Rice Seed Setting Rate and Weight of 1 000-Grain and Agro-Meteorology over the Middle and Lower Reaches of the Yangtze River, China

The purpose of this study is to reveal the effects of historic climate change on rice yield over the middle and lower reaches of the Yangtze River, China, and to better adapt to climate change in the future. This study presents the relation of temperature and precipitation and rice components from 1981 to 2003 at 48 early rice stations and 30 middle rice stations. It focuses on an analysis of three stages： flowering, pre-milk, and late milk. The results show that mean maximum temperature and mean daily precipitation at the stages of flowering and pre-milk are most related to early rice yield. Yield change of middle rice is mainly because of mean precipitation change at the flowering stage. Furthermore, percentage of undeveloped grain increases as mean maximum temperature rises at the flowering stage. Over-precipitation in the reproductive stage is a major reason for reduction in yield of early rice. Consecutive rainfall and continuous high temperature can have negative effects on middle rice yield. Global warming would affect middle rice more seriously than early rice.     

一类具有非线性发生率的SIS传染病模型的定性分析

应用微分方程定性理论,研究了一类具有非线性发生率的SIS传染病模型.给出了该系统极限环的存在性、唯一性以及无病平衡点和地方病平衡点的全局渐近稳定性的充分条件.

Abstract：

An epidemiological model with nonlinear incidence is studied. By using the qualitative theory of ordinary differential equations, sufficient conditions are obtained for the existence and uniqueness of the limit cycles and the global asymptotic stability of the disease-free equilibrium and the endemic equilibrium to the system.     

水生生态系统中有竞争和捕食效应的一类简单食物网模型的稳定性分析

提出了水生生态系统中有竞争和捕食的一类简单食物网模型.首先讨论了平衡点的存在条件,利用Hurwitz判据分析了局部渐近稳定性;通过构造Lyapunov函数得到了系统全局渐近稳定的条件,并具体解释了其生物含义.从以上讨论中得到了控制3类物种存活、灭绝或共存的4个阈值.生物分析表明,水草和鱼在控制富营养化问题中起着极其重要的作用.

Abstract：

In this paper, a simple food web model with competition and predation in aquatic ecosystems is proposed.The existence conditions of equilibria are discussed and the local asymptotic stability is analyzed.By means of Lya-punov functions, the global asymptotic stability of the model is obtained.Four thresholds, which indicate the coex-istence, survival or extinction of 3 species, are obtained from the above discussions.Bio-analysis shows that aquatic weeds and fish play an important role in the control of eutrophication.     

Pesticide food safety standards as companions to tolerances and maximum residue limits

Allowable levels for pesticide residues in foods,known as tolerances in the US and as maximum residue limits(MRLs) in much of the world,are widely yet inappropriately perceived as levels of safety concern. A novel approach to develop scientifically defensible levels of safety concern is presented and an example to determine acute and chronic pesticide food safety standard(PFSS) levels for the fungicide captan on strawberries is provided. Using this approach,the chronic PFSS level for captan on strawberries was determined to be 2 000 mg kg–1 and the acute PFSS level was determined to be 250 mg kg–1. Both levels are far above the existing tolerance and MRLs that commonly range from 3 to 20 mg kg–1,and provide evidence that captan residues detected at levels greater than the tolerance or MRLs are not of acute or chronic health concern even though they represent violative residues. The benefits of developing the PFSS approach to serve as a companion to existing tolerances/MRLs include a greater understanding concerning the health significance,if any,from exposure to violative pesticide residues. In addition,the PFSS approach can be universally applied to all potential pesticide residues on all food commodities,can be modified by specific jurisdictions to take into account differences in food consumption practices,and can help prioritize food residue monitoring by identifying the pesticide/commodity combinations of the greatest potential food safety concern and guiding development of field level analytical methods to detect pesticide residues on prioritized pesticide/commodity combinations.     

Effects of lead stress on Vg expression in the beet armyworm over five successive generations

Heavy metals have been found to be endocrine disruptors in invertebrates.Lead is one of the most widespread elements of contamination,but there has been no research about the effects of lead stress on vitellogenin(Vg) gene expression in insects exposed to lead over multiple generations.In this paper,the effects of different concentrations of lead(0,0.3,4.8 and 76.8 mg kg~(–1)) on the expression of Vg in the beet armyworm over five successive generations were studied.The results showed that lead stress had significant effects on Vg expression in a dose-dependent manner.For females at the larval and adult stages,as lead concentration increased,Vg expression was significantly inhibited; for males at these two developmental stages,Vg expression was induced and increased as lead concentration increased.In addition,with the increase over stressed generations,inhibited effects for females and induced effects for males at the larval and adult stages became increasingly more obvious.However,at the pupal stage,Vg expression in the two genders was different from that at the larval and adult stages.The results indicate that lead stress can upregulate Vg expression in males which should be a useful indicator for environmental risk assessment.     

Unconditional and Conditional QTL Mapping for Tiller Numbers at Various Stages with Single Segment Substitution Lines in Rice （Oryza sativa L.）

Tiller is one of the most important agronomic traits which influences quantity and quality of effective panicles and finally influences yield in rice. It is important to understand ＂static＂ and ＂dynamic＂ information of the QTLs for tillers in rice. This work was the first time to simultaneously map unconditional and conditional QTLs for tiller numbers at various stages by using single segment substitution lines in rice. Fourteen QTLs for tiller number, distributing on the corresponding substitution segments of chromosomes 1, 2, 3, 4, 6, 7 and 8 were detected. Both the number and the effect of the QTLs for tiller number were various at different stages, from 6 to 9 in the number and from 1.49 to 3.49 in the effect, respectively. Tiller number QTLs expressed in a time order, mainly detected at three stages of 0-7 d, 14-21 d and 35-42 d after transplanting with 6 positive, 9 random and 6 negative expressing QTLs, respectively. Each of the QTLs expressed one time at least during the whole duration of rice. The tiller number at a specific stage was determined by sum of QTL effects estimated by the unconditional method, while the increasing or decreasing number in a given time interval was controlled by the total of QTL effects estimated by the conditional method. These results demonstrated that it is highly effective and accurate for mapping of the QTLs by using single segment substitution lines and the conditional analysis methodology.     

Degradation of Chlorpyrifos and Fipronil in Rice from Farm to Fork and Risk Assessment

Degradation of pesticide residues （chlorpyrifos and fipronil） in rice from farm to fork and risk assessment for human health were studied to reveal the magnitude of risks faced by different populations of interest, so that appropriate measures can be taken to control the risks, and to refine and update the human health risk assessment data while helping to determine the maximum residue level （MRL） value and harvest interval. Different dosages and treatments were used in field trials for the harvest residue test. Residue levels of postharvest-applied chlorpyrifos and fipronil during storage, exposure to sunlight, washing and boiling processes （boiled rice） were investigated for brown rice. The dietary exposure evaluation model （DEEM） was employed to estimate acute and chronic risks faced by different populations of interest. Percent of reference dose （POR） and margin of exposure （MOE） were calculated. A positive correlation between pesticide residues and the dosage and application frequency of pesticide was found in the field trials. Risk quotients indicate that multiple applications and double dosages of chlorpyrifos increase the risks to the entire population and prolong exposures to toxic concentrations. The concentration of pesticide residues decreased as a function of time, after sunlight exposure, storage, washing, and boiling processes. 91.6 and 96.16% degradations were achieved at the end of the experimental period for fipronil and chlorpyrifos, respectively. The boiling process played an important role in the degradation of these pesticides. The result of risk assessment to human health showed that harvest residues of chlorpyrifos in rice and acute dietary risks of chlopyrifos were of concern. The acute dietary （food only） risk estimated for chlorpyrifos as percent of acute population adjusted dose （aPAD） was frequently over 100%. The risk faced by boys under the age of 14 was higher than that for girls of the same age. For the subpopulation above age 14, the risk reversed. The chronic dietary risk from food alone showed that dietary exposures with fipronil were below the level of concern for the entire population, including children. The risk faced by rural residents was more serious than that for urbanite residents with the most sensitive populations being children and male residents who faced higher acute dietary risk than the other subpopulation groups. The harvest interval was found to be the critical measure to mitigate risk for all populations for safe rice eating. All risk levels decreased to acceptable levels when the harvest interval was extended to 14 d. To address these risks, a number of measures including reduced application rates （should not be doubled at single application）, increased retreatment intervals （longer than 7 d） and extended interval of harvest （at least 14 d） will be needed. The MRL for fipronil in rice is recommended to be 0.01 mg kg 1 in accordance with Codex （ref）.     

加拿大的农业科技及其组织管理

本文详细介绍了加拿大农业科技体制改革及其组织,其总的研究发展方向由加拿大政府掌握.把科技政策、研究发展方向和国家需要结合起来通盘考虑,自上而下提出科研项目.     

保护地蔬菜病虫害发生特点及其综合防治

根据保护地蔬菜病虫害发生特点,掌握综合防治方法,把病虫为害损失控制在经济允许水平之下,达到优质、高产、低成本和农产品无污染的目的。     

秦汉时期的中印交通与农业科技文化交流

对秦汉时期中国与印度的交流进行考证,在丰富的史料基础上,研究了当时中印的交通状况与农业科技文化交流。     

矿难与科学技术

煤矿事故时有发生．分析认为发生事故的本质原因是工作人员缺乏有关的科学技术知识．发展、掌握、运用科学技术。提高人员的科学技术素质。不仅能促进经济发展，而且能保障人身安全，战胜灾害(包括煤矿灾害)．     

网络文化与高校思想政治工作研究

近年来,在社会经济的不断推动之下,互联网技术得到了飞速发展,随之而来的则是网络文化的兴起,这对于高校思想政治工作带来了较大的冲击,但同时也是一种新的挑战;因而各高校要对网络文化树立正确的认知,将其与高校思想政治工作相互结合,因势利导,才能推动高校思想政治工作的不断深入。本文针对当前网络文化与高校的思想政治工作展开进一步的研究与分析。     

池州市农业科技创新与转化存在问题及对策

本文对当地农业科技创新与转化情况及存在问题进行了分析,并结合实际提出了相应对策.     

Effects of fish and plankton and lake temperature and mixing depth

A comparative study of small temperate lakes (<20 square kilometers) indicates that the mixing depth or epilimnion is directly related to light penetration measured as Secchi depth. Clearer lakes have deeper mixing depths. This relation is the result of greater penetration of incident solar radiation in lakes and enclosures with high water clarity. Data show that light penetration is largely a function of size distribution and biomass of algae as indicated by a relation between the index of plankton size distribution (slope) and Secchi depth. Larger or steeper slopes (indicative of communities dominated by small plankton) are associated with shallower Secchi depth. In lakes with high abundances of planktivorous fish, water clarity or light penetration is reduced because large zooplankton, which feed on small algae, are reduced by fish predation. The net effect is a shallower mixing depth, lower metalimnetic temperature and lower heat content in the water column. Consequently, the biomass and size distribution of plankton can change the thermal structure and heat content of small lakes by modifying light penetration.