食品安全问题细分及其治理的新思考

为了统一食品安全问题的相关细分概念,依据行为实施者的行为和动机,将食品安全问题细分为食品质量问题、食品欺诈问题、食品风险问题和食品防护问题,进一步提出了对各个细分食品安全问题的治理对策。最后,对我国食品安全问题的治理提出了对策建议。     

推进城镇化进程中的问题和对策

随着城镇化步伐的加快,城镇化过程中出现了许多问题,如失地农民问题、生态环境问题、粮食安全问题、人口迁移问题等等,这些问题如果得不到有效的解决,将成为我国经济社会发展的严重障碍。本文试就相关问题进行探讨,并试图找出可能的解决方法。     

大学生微生物学实验技能培养的研究

针对我国高校目前比较普遍地存在的应届大学毕业生微生物学实验技能不够强、解决实际问题能力差的突出问题,分析了问题产生的主要原因和解决该问题的重要意义,提出了解决此问题的多方面的具体措施和多年实践的初步结果。     

通过创设问题情境提高生物课堂学习效率——“神经调节的基本方式”一课的教学设计与体会

总结了利用创设问题情景在＂神经调节的基本方式＂一课的教学设计和体会。初一学生生活阅历较少,思维较简单,课堂上提出的问题范围不要过大,不要过于抽象,使学生不知从何思考,最好把问题分解成几个小问题,使问题具体化,符合学生的认知规律,利于学生思维的发展;学生的思维发展是有层次性的,教师作为学生学习活动的组织者、促进者,面对不同的学生同一问题需要教师具备灵活多变的问题策略,循序渐进的引导学生分析问题、解决问题;一节课创设问题情景形式要多种多样,不能就问题解决问题,要注意新旧知识的联系或者区别,知识的承上启下的作用等方面。     

创设问题情境 提高学习效率

<正>爱因斯坦说过:"提出一个问题往往比解决一个问题更重要"。现代教育论研究指出:产生学习的根本原因是问题。因为有问题人们才会有学习的欲望,才会去深入思考。现代教育思想特别强调问题在学习活动中的重要性。在教学中,一方面强调通过问题来学习,把问题看作是学习的动力、起点和贯穿于学习过程的     

鸭稻共作生态系统的实践与理论问题探讨

鸭稻共作技术作为一项环保性生态农业技术,现已在亚洲许多国家和我国多个省份得到应用和推广。为了使鸭稻共作技术模式更好地、更科学地推广应用,还有很多实践和理论问题需要加以研究探索和解决,主要包括:(1)水稻品种和鸭子品种的筛选问题;(2)鸭稻共作模式系统的结构优化问题;(3)鸭子的生态学功能过程及其内在机理有关的科学问题;(4)水稻病虫害的综合防治问题;(5)稻田土壤肥力维持问题;(6)田间日常管理问题;(7)鸭子饲料来源问题;(8)稻田鸭子的疫病综合防治问题;(9)鸭稻共作技术模式的标准化问题;(10)鸭稻共作技术模式的经济效益问题。     

基于逻辑的问题体系构建及其在思维生成教学中的运用

在思维生成教学中,问题是思维运行的重要驱动力。因孤立的问题在运用中无法提供思维生成教学所要求的持续而连贯的过程性驱动力,也无法使问题的整个推进过程可调可控,所以在思维生成教学中,将核心问题进行"分解式"构建,把点状的问题分解为线,并进行"构筑式"构建,使得问题的线拓展成面,最终形成具有严整逻辑的问题体系,显得尤为重要。基于逻辑的问题体系为思维的运行提供连贯而具有纵深的思维平台,使教师能对问题的整个推进过程与课堂的思维生成的目标进行有效调控。     

微生物生态修复技术

生物修复技术本身是一项复杂的系统工程。生物修复技术成功运用的前提是尽可能解决其中涉及的科学问题。其中包括微生物的生存生长条件,生物修复过程中微生物的适应性机制与环境影响因素等问题,污染物的浓度与生物修复之间的关系问题,不同污染环境形成的不同污染土壤的修复问题,生物修复的现场放大技术问题,生物修复过程中污染物的淋溶过程问题,对生物修复技术的生态毒理诊断与评价问题等。     

关于医疗纠纷诉讼中的后续治疗费用问题的讨论

医疗纠纷诉讼涉及多项赔偿,其中后续治疗费用的赔偿问题,在司法实践操作中存在一些争议。就争议问题展开讨论,提出对后续治疗费用的司法鉴定问题及后续治疗费用相关问题的处理建议。     

2005年第16届国际生物学奥林匹克竞赛实验考试答案

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Expansion or extinction: deterministic and stochastic two-patch models with Allee effects

We investigate the impact of Allee effect and dispersal on the long-term evolution of a population in a patchy environment. Our main focus is on whether a population already established in one patch either successfully invades an adjacent empty patch or undergoes a global extinction. Our study is based on the combination of analytical and numerical results for both a deterministic two-patch model and a stochastic counterpart. The deterministic model has either two, three or four attractors. The existence of a regime with exactly three attractors only appears when patches have distinct Allee thresholds. In the presence of weak dispersal, the analysis of the deterministic model shows that a high-density and a low-density populations can coexist at equilibrium in nearby patches, whereas the analysis of the stochastic model indicates that this equilibrium is metastable, thus leading after a large random time to either a global expansion or a global extinction. Up to some critical dispersal, increasing the intensity of the interactions leads to an increase of both the basin of attraction of the global extinction and the basin of attraction of the global expansion. Above this threshold, for both the deterministic and the stochastic models, the patches tend to synchronize as the intensity of the dispersal increases. This results in either a global expansion or a global extinction. For the deterministic model, there are only two attractors, while the stochastic model no longer exhibits a metastable behavior. In the presence of strong dispersal, the limiting behavior is entirely determined by the value of the Allee thresholds as the global population size in the deterministic and the stochastic models evolves as dictated by their single-patch counterparts. For all values of the dispersal parameter, Allee effects promote global extinction in terms of an expansion of the basin of attraction of the extinction equilibrium for the deterministic model and an increase of the probability of extinction for the stochastic model.     

非线性种群反应扩散系统奇摄动ROBIN问题

研究了一类具有非线性种群反应扩散系统奇摄动Robin初始边值问题.在适当的条件下,利用微分不等式理论,讨论了问题解的存在性和渐近性态.     

Alternative attractors in an ecological-genetic model of populations with non-overlapping generations

This study classifies and analyzes various bifurcations of fixed points of the simple model of population dynamics with its number described by Ricker’s model and intrapopulation parameters determined by a single di-allelic locus. The model considered shows such nonlinear phenomena as multistability and coexistence of alternative attractors, which can violate the simple combination of the action of evolutionary-genetic and density-dependent ecological-dynamic processes, where gene elimination is determined by the genotypes’ resource parameters and the population number stability depends on their Malthusian parameters. The most interesting pattern in this regard is existence of polymorphic attractors, when the resource parameter of heterozygotes is not maximal. It presents a clear violation of the principle of natural selection optimality, which is caused precisely by the multistable phenomena of nonlinear dynamics. By which of the alternative attractors the dynamics is characterized by depends sensitively on the initial conditions, even small external influences can became significant, as they can shift the system from one attraction basin to another, and thus fundamentally change the dynamic mode and nature of the evolutionary process.     

Searching for Spatial Patterns in a Pollinator–Plant–Herbivore Mathematical Model

This paper deals with the spatio-temporal dynamics of a pollinator–plant–herbivore mathematical model. The full model consists of three nonlinear reaction–diffusion–advection equations defined on a rectangular region. In view of analyzing the full model, we firstly consider the temporal dynamics of three homogeneous cases. The first one is a model for a mutualistic interaction (pollinator–plant), later on a sort of predator–prey (plant–herbivore) interaction model is studied. In both cases, the interaction term is described by a Holling response of type II. Finally, by considering that the plant population is the unique feeding source for the herbivores, a mathematical model for the three interacting populations is considered. By incorporating a constant diffusion term into the equations for the pollinators and herbivores, we numerically study the spatiotemporal dynamics of the first two mentioned models. For the full model, a constant diffusion and advection terms are included in the equation for the pollinators. For the resulting model, we sketch the proof of the existence, positiveness, and boundedness of solution for an initial and boundary values problem. In order to see the separated effect of the diffusion and advection terms on the final population distributions, a set of numerical simulations are included. We used homogeneous Dirichlet and Neumann boundary conditions.     

State-dependent impulsive models of integrated pest management (IPM) strategies and their dynamic consequences

A state-dependent impulsive model is proposed for integrated pest management (IPM). IPM involves combining biological, mechanical, and chemical tactics to reduce pest numbers to tolerable levels after a pest population has reached its economic threshold (ET). The complete expression of an orbitally asymptotically stable periodic solution to the model with a maximum value no larger than the given ET is presented, the existence of which implies that pests can be controlled at or below their ET levels. We also prove that there is no periodic solution with order larger than or equal to three, except for one special case, by using the properties of the LambertW function and Poincare map. Moreover, we show that the existence of an order two periodic solution implies the existence of an order one periodic solution. Various positive invariant sets and attractors of this impulsive semi-dynamical system are described and discussed. In particular, several horseshoe-like attractors, whose interiors can simultaneously contain stable order 1 periodic solutions and order 2 periodic solutions, are found and the interior structure of the horseshoe-like attractors is discussed. Finally, the largest invariant set and the sufficient conditions which guarantee the global orbital and asymptotic stability of the order 1 periodic solution in the meaningful domain for the system are given using the Lyapunov function. Our results show that, in theory, a pest can be controlled such that its population size is no larger than its ET by applying effects impulsively once, twice, or at most, a finite number of times, or according to a periodic regime. Moreover, our theoretical work suggests how IPM strategies could be used to alter the levels of the ET in the farmers' favour.     

A reaction-diffusion system of a predator-prey-mutualist model

Mutualism is part of many significant processes in nature. Mutualistic benefits arising from modification of predator-prey interactions involve interactions of at least three species. In this paper we investigate the Homogeneous Neumann problem and Dirichlet problem for a reaction-diffusion system of three species—a predator, a mutualist-prey, and a mutualist. The existence, uniqueness, and boundedness of the solution are established by means of the comparison principle and the monotonicity method. For the Neumann problem, we analyze the constant equilibrium solutions and their stability. For the Dirichlet problem, we prove the global asymptotic stability of the trivial equilibrium solution. Specifically, we study the existence and the asymptotic behavior of two nonconstant equilibrium solutions. The main method used in studying of the stability is the spectral analysis to the linearized operators. The O.D.E. problem for the same model was proposed and studied in [13]. Through our results, we can see the influences of the diffusion mechanism and the different boundary value conditions upon the asymptotic behavior of the populations.     

生态学中一类n维反应扩散方程组解的性质

本文讨论一类不满足所谓的拟单调条件的反应扩散方程组的初边值问题．应用谱论和单调性方法证明了问题解的存在唯一性和平衡解的渐近稳定性．并进一步讨论了生态学中n种群单食物链模型的第二初值问题,得到了问题的非负平衡解的存在性和渐近性以及相应的吸引区域．     

Multiple attractors in a discrete competition model

The existence of multiple attractors in a competition model implies that the question of coexistence vs. extinction can depend on initial conditions. A discrete stage-structured model of two competing species is derived from a well-tested single-species model of insect populations, and is shown to exhibit multiple attractors for parameter values similar to those used in laboratory experiments which demonstrated chaos in population dynamics. The corresponding basins of attraction are investigated and shown to have very complex structures, and the initial stage structure of the populations is shown to have a significant impact on final outcomes.     

具势能衰减的非线性拟抛物方程整体解的不存在性

利用Laplace算子的特征函数法研究了一类具势能衰减的非线性拟抛物方程的初边值问题整体解的不存在性与有限时间爆破．     

非线性种群反应扩散系统的奇摄动

研究了一类具有非线性种群反应扩散系统奇摄动问题,在适当的条件下,利用微分不等式理论,讨论了问题解的存在性和渐近性态．