一类两种群随机生态系统的稳定性

利用构造广义二次三项式作为随机李雅普诺夫函数的方法讨论了两种群随机Volterra生态系统的全局渐近稳定性，并对一类特殊情形给出了全局渐近稳定性的充分判据，推广了常微系统已有结果．     

基于关系契约视角的农户与农产品电子商务企业合作机制演化博弈分析

本文基于关系契约的视角,运用演化博弈理论,构建有限理性特性下的农户与农产品电子商务企业合作演化博弈模型,分析双方合作策略的演进过程、稳定策略及其影响因素,并通过Matlab仿真模拟分析影响双方合作策略选择的因素,验证博弈结果正确性。研究结果表明:农户和农产品电子商务企业选择合作策略与合作投入成本、实现的超额收益密切相关,博弈初始状态、再交易成本、单方不合作获得的收益及违约罚金等因素影响系统的演化稳定结果。因此完善农户与农产品电子商务企业的合作机制,需要构建合理的利益分配机制、良好的关系治理机制、有效的监督和惩罚机制和信息共享、沟通与协调机制。     

电商生态系统四方演化博弈研究

受启发于近些年频繁曝出的消费者权益保护问题,为探析消费者行为对电商生态系统中其他群体策略选择的影响,本文基于演化博弈理论,考虑消费者的投诉行为,构建由政府、电商平台、商家以及消费者组成的四方演化博弈模型;讨论各方主体的策略选择,分析策略组合稳定点,并应用MATLAB工具进行仿真模拟实验。经上述研究,本文得出结论：消费者的投诉行为有利于促进政府严格监管、电商平台严格管理、商家诚信经营。由此,建议政府和电商平台充分发挥监督管理作用,以更好地保障消费者的合法权益,并遏制消费者的恶意投诉行为,从而实现电商生态系统的稳定可持续发展。     

基于电商平台的混合销售渠道对供应链决策的影响研究

考虑到电商平台对消费者强大的吸引力,本文建立了由供应商和平台商构成的基于电商平台混合销售的供应链模型。混合销售渠道包含直销和分销,其中平台商拥有电商平台,供应商通过电商平台进行直销,平台商分享一定的收益;而分销是指平台商从供应商处批发产品进行销售。分别建立了集中式和分散式决策模型,研究发现:随着消费者对分销渠道接受程度的提高,两种情形下直销渠道的零售价不变,分销渠道的零售价提高;分散式情形下的批发价、供应商和平台商的利润均提高;随着供应商分享收益比例的提高,两种渠道的零售价都降低,但批发价提高,供应商的利润提高,而平台商的利润下降,但供应链的总利润提高;研究得到了保证博弈双方都能从直销渠道中获利的收益分享比例范围。     

Prospects and Limitations of an Isotope Tracer Technique for Understanding Sulfur Cycling in Forested and Agro-Ecosystems

Abstract

Applications of isotopically distinct sulfur compounds have recently been used for tracing the fate of added sulfur in whole catchments or sub-compartments therein. Basic principles, the analytical methodology, and data evaluation for this isotope tracer technique are briefly described. We recommend that δ³⁴S-values of applied and natural sulfur compounds in the investigated ecosystem should differ by more than 20‰ in order to successfully ascertain sulfur fluxes. Where possible, a high ratio of applied sulfur loads versus sulfur pool sizes in the ecosystem should also be realized in order to allow the assessment of sulfur transformations in the study area. Prospects and limitations of this isotope tracer technique are critically discussed by reviewing results from recently or currently conducted lysimeter and field experiments.     

GLOBAL ANALYSIS TO A KIND OF COMPETITION MODEL OF E-COMMERCE SITES

In this paper, we present a competition modei of e-commerce sites with the property of "better for better". Then we qualitatively analyze the special case of two dimensions. So we prove that there does not exist limit cycle, in the first quadrant of the phase plane and all trajectories tend to some singular points.     

Community Dynamics in a University Environment

Scholars have characterized academic communities of faculty, administration, and students in U.S. universities as organized anarchies. In contrast, we offer evidence that the community structures of two representative public university systems are notably systematic by applying empirical phase-diagram techniques from the nonlinear dynamics literature to reconstruct low-dimensional deterministic behavior from historic data on the coevolution of faculty, administration, and student populations in each system. Ecological community models, fit with population data for each university, reproduce the essence of this behavior. The models offer novel explanations of how university resources obtained from enrollments and other sources are systematically partitioned among faculty, administration, and student populations interacting in shifting and well-defined community roles. This work offers empirical evidence that ecological principles, typically reserved for characterizing nonhuman interactions in biological systems, can shed light on human interactions in social systems.     

考虑网络外部性的生鲜企业渠道选择策略研究

考虑到生鲜产品容易变质而且线上配送时间较长,并且线上销售可为消费者带来额外网络外部性,传统生鲜企业在电商冲击的背景下需要考虑是否入驻电商平台开拓线上业务。为解决此类企业所面临渠道选择问题,本文考虑一个传统生鲜企业和一个主导电商市场的电商平台,并通过构建理论模型研究企业最优生鲜产品定价和渠道选择策略。研究结果表明,若平台所收取年服务费较低,则企业应入驻平台;反之,企业不应入驻平台。此外,消费者网络外部性敏感程度对企业入驻平台行为具有正影响。在拓展模型,本文考虑分散式供应链情形下企业最优渠道选择,结果表明相较于集中式决策,分散式供应链情形下零售商更不愿意入驻平台。此外,本文通过设计收益共享契约以协调生鲜企业与电商平台,并发现通过契约协调,零售商更愿意入驻电商平台。     

Biomonitoring: an appealing tool for assessment of metal pollution in the aquatic ecosystem

Wide occurrence of aquatic metal pollution has caused much attention. Biomonitoring offers an appealing tool for the assessment of metal pollution in aquatic ecosystem. The bioindicators including algae, macrophyte, zooplankton, insect, bivalve mollusks, gastropod, fish, amphibian and others are enumerated and compared for their advantages and disadvantages in practical biomonitoring of aquatic metal pollution. The common biomonitoring techniques classified as bioaccumulation, biochemical alterations, morphological and behavior observation, population- and community-level approaches and modeling are discussed. The potential applications of biomonitoring are proposed to mainly include evaluation of actual aquatic metal pollution, bioremediation, toxicology prediction and researches on toxicological mechanism. Further perspectives are made for the biomonitoring of metal pollution in aquatic ecosystem.